Annealing of brass blanks. Heat treatment of non-ferrous metals
Annealing and hardening of duralumin
Annealing of duralumin is carried out to reduce its hardness. The part or workpiece is heated to approximately 360° C, as during hardening, held for some time, and then cooled in air. The hardness of annealed duralumin is almost half that of hardened duralumin. The approximate heating temperature of a duralumin part can be determined as follows. At a temperature of 350--360° C, a wooden splinter, which is passed along the hot surface of the part, becomes charred and leaves a dark mark. The temperature of the part can be determined quite accurately using a small (about the size of a match head) piece of copper foil, which is placed on its surface. At a temperature of 400° C, a small greenish flame appears above the foil. Annealed duralumin has low hardness; it can be stamped and bent twice without fear of cracks. Hardening. Duralumin can be hardened. When hardening, parts made of this metal are heated to 360-400 ° C, held for some time, then immersed in water at room temperature and left there until completely cooled. Immediately after this, duralumin becomes soft and flexible, easily bent and forged. It acquires increased hardness after three to four days. Its hardness (and at the same time fragility) increases so much that it cannot withstand bending at a small angle. Duralumin acquires its highest strength after aging. Aging at room temperatures is called natural, and at elevated temperatures--artificial. The strength and hardness of freshly quenched duralumin, left at room temperature, increases over time, reaching highest level in five to seven days. This process is called duralumin aging
Annealing of honey and brass
Annealing of copper. Copper is also subjected to heat treatment. In this case, copper can be made either softer or harder. However, unlike steel, copper is hardened by slow cooling in air, and copper becomes soft by rapid cooling in water. If a copper wire or tube is heated red hot (600°) over a fire and then quickly immersed in water, the copper will become very soft. After giving the desired shape the product can again be heated over a fire to 400 ° C and allowed to cool in air. The wire or tube will then become solid. If it is necessary to bend the tube, it is tightly filled with sand to avoid flattening and cracking. Annealing brass increases its ductility. After annealing, brass becomes soft, easily bends, knocks out and stretches well. For annealing, it is heated to 500 ° C and allowed to cool in air at room temperature.
Blueing and "blueing" of steel
Blueing. After bluing, steel parts acquire a black or dark blue color of various shades, they retain a metallic luster, and a persistent oxide film forms on their surface; protecting parts from corrosion. Before bluing, the product is carefully ground and polished. Its surface is degreased by washing in alkalis, after which the product is heated to 60-70° C. Then it is placed in an oven and heated to 320-325° C. An even coloring of the surface of the product is obtained only when it is heated evenly. The product treated in this way is quickly wiped with a cloth soaked in hemp oil. After lubrication, the product is slightly warmed up again and wiped dry. "Blueing" of steel. Steel parts can be given a beautiful blue color. For this, two solutions are made: 140 g of hyposulfite per 1 liter of water and 35 g of lead acetate (“lead sugar”) also per 1 liter of water. Before use, the solutions are mixed and heated to a boil. The products are pre-cleaned, polished to a shine, then immersed in boiling liquid and kept until the desired color is obtained. The part is then washed in hot water and dry, after which they are lightly wiped with a rag moistened with castor or clean machine oil. Parts treated in this way are less susceptible to corrosion.
Annealing and normalization of steel
Annealing is a metal heat treatment process that involves heating and then slowly cooling the metal. Transition of a structure from a nonequilibrium state to a more equilibrium one. Annealing of the first kind, its types: return (also called metal rest), recrystallization annealing (also called recrystallization), annealing to relieve internal stress, diffusion annealing (also called homogenization). Annealing of the second type is a change in the structure of the alloy through recrystallization near critical points in order to obtain equilibrium structures. Annealing of the second kind, its types: complete, incomplete, isothermal annealing.
Annealing and its types in relation to steel are discussed below.
Return (rest) of steel - heating to 200 - 400o, annealing to reduce or remove hardening. Based on the results of annealing, a decrease in the distortion of crystal lattices in crystallites and a partial restoration of the physicochemical properties of steel are observed.
Recrystallization annealing of steel (recrystallization) - heating to temperatures of 500 - 550o; annealing to relieve internal stress - heating to temperatures of 600 - 700o. These types of annealing relieve internal stresses in the metal of castings due to uneven cooling of their parts, also in workpieces processed by pressure (rolling, drawing, stamping) using temperatures below critical. As a result of recrystallization annealing, new crystals grow from the deformed grains, closer to equilibrium ones, therefore the hardness of the steel decreases, and the ductility and toughness increase. To completely remove internal stresses, steel needs a temperature of at least 600o.
Cooling after holding at a given temperature must be quite slow: due to the accelerated cooling of the metal, internal stresses arise again.
Diffusion annealing of steel (homogenization) is used when the steel has intracrystalline segregation. Leveling the composition in austenite grains is achieved by the diffusion of carbon and other impurities in the solid state, along with the self-diffusion of iron. According to the results of annealing, the steel becomes homogeneous in composition (homogeneous), therefore diffusion annealing is also called homogenization.
The homogenization temperature should be high enough, but overburning and melting of the grains should not be allowed. If the burnout is allowed to occur, the oxygen in the air oxidizes the iron, penetrating into its thickness, and crystallites are formed, separated by oxide shells. Overburning cannot be eliminated, therefore overburnt workpieces are a final defect.
Diffusion annealing of steel usually results in too much grain coarsening, which should be corrected by subsequent full annealing (to fine grains).
Complete annealing of steel is associated with phase recrystallization, grain refinement at temperatures of points AC1 and AC2. Its purpose is to improve the structure of steel to facilitate subsequent processing by cutting, stamping or hardening, as well as to obtain a fine-grained equilibrium pearlite structure of the finished part. For complete annealing, the steel is heated 30-50 o above the GSK line temperature and slowly cooled.
After annealing, excess cementite (in hypereutectoid steels) and eutectoid cementite have the form of platelets, which is why pearlite is called lamellar.
When annealing steel onto lamellar perlite, the workpieces are left in the furnace until cooled, most often with the furnace partially heated with fuel, so that the cooling rate is no more than 10-20o per hour.
Rice. 1.
Annealing also achieves grain refinement. The coarse-grained structure, for example, of hypoeutectoid steel (Fig. 1), is obtained during solidification due to the free growth of grains (if the cooling of the castings is slow), as well as as a result of overheating of the steel. This structure is called Widmanstätten (named after the Austrian astronomer A. Widmanstätten, who discovered such a structure on meteoric iron in 1808). This structure imparts low strength to the workpiece. The structure is characterized by the fact that inclusions of ferrite (light areas) and pearlite (dark areas) are arranged in the form of elongated plates at different angles to each other. In hypereutectoid steels, the Widmanstätten structure is characterized by a streak-like arrangement of excess cementite.
Rice. 2.
Grain refinement is associated with the recrystallization of alpha iron into gamma iron; Due to cooling and the reverse transition of gamma iron to alpha iron, the fine-grained structure is preserved.
Thus, one of the results of annealing on lamellar pearlite is a fine-grained structure.
Incomplete annealing of steel is associated with phase recrystallization only at point temperature A C1; partial annealing is used after hot pressure treatment, when the workpiece has a fine-grained structure.
Annealing steel into granular pearlite is usually used for eutectoid and hypereutectoid steels to increase the ductility and toughness of steel and reduce its hardness. To obtain granular pearlite, the steel is heated above the AC1 point, then held for a short time so that the cementite does not completely dissolve in the austenite. Then the steel is cooled to a temperature slightly below Ar1 and maintained at this temperature for several hours. In this case, the particles of the remaining cementite serve as crystallization nuclei for all the released cementite, which grows as rounded (globular) crystallites scattered in the ferrite (Fig. 2).
The properties of granular pearlite differ significantly from the properties of lamellar pearlite in the direction of lower hardness, but greater lamellarity and viscosity. This especially applies to hypereutectoid steel, where all cementite (both eutectoid and excess) is obtained in the form of globules.
Isothermal annealing - after heating and holding, the steel is quickly cooled to a temperature slightly below point A 1 (Fig. 3), then maintained at this temperature until the austenite completely decomposes into pearlite, after which it is cooled in air. The use of isothermal annealing significantly reduces time and also increases productivity. For example, ordinary annealing of alloy steel lasts 13-15 hours, and isothermal annealing - only 4-7 hours. The isothermal annealing diagram is shown in Fig. 7.
Rice. 3.
A type of complete annealing is normalization, which consists of heating the steel 30-50°C above the GSE line, holding it at these temperatures, and then cooling it in air. The purpose of normalization is to remove residual stresses in the metal and align its structure.
Heat treatment of non-ferrous metal means heating to a certain temperature, followed by cooling at a certain speed. Overall efficiency heat treatment non-ferrous metal depends on its previous processing, on the temperature and heating rate, the duration of exposure at this temperature and the cooling rate
The processes of heat treatment of non-ferrous metals can be divided into two main groups: heat treatment, the purpose of which is to obtain a structure that is as close as possible to the equilibrium state, and heat treatment, the purpose of which, on the contrary, is to achieve a nonequilibrium state. In some cases, both mentioned groups of processes overlap each other
The first group includes recrystallization annealing deformed material, then annealing to relieve internal stress and finally homogenization annealing castings To the second group, which is sometimes considered heat treatment in in the narrow sense words, refers to heat treatment to obtain a nonequilibrium state, i.e. the so-called dispersion curing
Soft or recrystallization annealing
Soft annealing is a heat treatment of workpieces that have been cold worked. It is produced by heating the product to a certain temperature, holding it at this temperature for a certain time and, as a rule, slowly then cooling. The temperature level, holding time, as well as the heating and cooling rates, depend both on the method of previous processing and on the required properties of the product. Consequently, the process of this annealing is characterized by the degree of previous reduction, the temperature and duration of annealing and the required structure of the product. This can be briefly illustrated with the following examples:
Metal that has been hardened as a result pressure treatment, undergoes several mutually overlapping changes during heating. First, the so-called “restoration” occurs, characterized by the removal of internal stress, i.e., the elimination of violations crystal lattice induced in the material by pressure treatment. In this area mechanical properties change very little, although changes are already observed in some physical properties. With further heating, they begin to form embryos new-forming structure, and the growth of these embryos occurs. Collectively, these two processes are called recrystallization. Mechanical and physical properties, acquired by the material as a result of pressure treatment, are lost during recrystallization, and the material acquires the properties that it had before work hardening. This is followed by a grain growth stage in which the crystals fuse; in this case, some crystals grow at the expense of neighboring crystals, and the crystal structure becomes larger
The process of changing the mechanical properties of oxygen-free copper during cold hardening and recrystallization annealing is explained in the graphs below.
Dependence of mechanical properties during cold hardening on the degree of compression 
Dependence of mechanical properties during recrystallization annealing on temperature 
Hardness curves depending on the previous degree of reduction and temperature, as well as grain growth depending on temperature after recrystallization
Annealing to relieve internal stress
This annealing is called stabilization, and in relation to deformed workpieces - vacation. Annealing consists of heating to high temperature and short-term exposure at this temperature until the product is completely warmed up, followed by slow cooling. For workpieces treated by pressure, this is the temperature from the recovery region, i.e. below the recrystallization temperature. This annealing eliminates internal stresses caused, for example, in castings by uneven cooling and heat treatment, and in forgings by cold pressure treatment, heat treatment or cutting with large chip sections. The previous crystallization is preserved during this heating. Mechanical properties also do not change significantly, even after long-term storage
For products, especially complex configurations, this process ensures dimensional stability. An example of tempering temperatures for some wrought aluminum and copper alloys is given in Table 1
Tempering temperatures for relieving internal stresses in some deformable metals and alloys
Homogenization annealing
Homogenization annealing is a heat treatment consisting of heating to a high temperature and holding at that temperature for a certain time until a uniform composition and uniform structure are achieved. This is usually followed by slow cooling. IN cast alloys meets unevenness (heterogeneity) of two kinds. This - segregation of impurities, accumulating in those parts of the casting that harden last, and delamination (layering) each individual crystal of the solid solution. Irregularities inside the crystal are easily leveled out diffusion, if it occurs at a high enough temperature and for a long enough time. On the contrary, impurities accumulated in individual places of the casting are dissipated by annealing much less well. They are capable of diffusion only if they dissolve in the base metal at high temperatures. But even in this case, the homogenization process is difficult due to long way, which individual particles must pass through
Deformed metals can also be subjected to homogenization annealing if it is necessary to improve some of their mechanical properties, especially viscosity And chemical resistance alloy By heating to a high temperature certain alloying elements are transferred into solid solution until the alloy becomes homogeneous, and then rapid cooling suppresses segregation. However, this process is already moving into the area of heat treatment to obtain nonequilibrium states
Dispersion curing
For dispersion hardening of the alloy prerequisite is that the main crystals contain a partially soluble phase, the solubility of which decreases with decreasing temperature. With slow cooling, segregation occurs, as a result of which, depending on the shape of the diagram, pure metal, a solid solution of compounds, or some other phase can be released. In many cases, rapid cooling from the solid solution region can suppress segregation, and the alloy thus quenched can be brought into a nonequilibrium state of a supersaturated solid solution. With further moderate heating or normal temperature, the alloy tends to reach a stable state. This complex process is not yet fully understood, although a number of hardenable alloys are already used in practical technology. The process proceeds differently for different alloys being cured, and in many cases, differently even for the same alloy. Therefore, we will limit ourselves only brief description this process
Curing consists mainly of three stages. First, the alloy is heated to the appropriate temperature. This temperature is between solidus line and solid solubility line as close as possible to the solidus temperature. It is best to maintain this temperature, given its narrow range, especially for aluminum alloys (490-535 ° C), in a saline solution, and therefore it is precisely these solutions that are used most often. The purpose of this type of annealing is to obtain a rich solid solution. Holding at this temperature depends on the type of alloy and the type of workpiece. This is followed by rapid cooling (quenching in oil or water). The alloy passes through different stages approaching an equilibrium state, and the atoms of the supersaturated solid solution are arranged differently each time. This process is carried out at normal or elevated temperatures; sometimes called aging. In some cases, cold working is performed between hardening and aging. Aging at normal temperatures is called natural, and at elevated temperatures - artificial
During curing, the mechanical properties change. After hardening, the strength decreases slightly with increasing viscosity, and with aging, the strength increases again, and the toughness and ductility decrease slightly. These changes during aging are subject to certain patterns, depending on temperature, duration of aging and type of alloy. Upon reaching the maximum, the strength of the alloy decreases again with further heating. As a result of this " overaging» the alloy passes from an unstable hardened state to an equilibrium one, and the material acquires its previous mechanical properties. Of course, the strength in the hardened state is always greater than that which can be obtained from the same alloy by cold hardening, and in general, hardenable alloys have the greatest strength compared to other metals in this group. During the curing process, some physical properties also change.
Figure 5 shows the effect of temperature and duration of artificial aging on the mechanical properties of a wrought AlMgSi alloy.
General diagram of the dependence of temperature and duration of annealing at in various ways heat treatment of a wrought AlMgSi alloy is shown in Fig. 6
In some alloys of non-ferrous metals, when heat treated to a nonequilibrium state, recrystallization processes occur in the same way as in steel. For example, in some aluminum bronzes the so-called phase transformations γ - α, in connection with which the entire process, consisting of hardening and tempering, can be called thermal improvement. The changes in mechanical properties during improvement differ from those that accompany hardening: after quenching, the strength increases with a simultaneous decrease in toughness, and during tempering, the strength decreases again, while the toughness increases slightly
Values of mechanical properties of deformable aluminum alloys subjected to various heat treatments
| Alloy grade | Semifinished | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ10, (%) |
|---|---|---|---|---|
| Al 99.5 | Sheet | 1,5 | 7 — 10 | 22 |
| Al-Cu4-Mg1 | Sheet | 18 — 24 | 11 | |
| Al-Zn6-Mg-Cu | Bar | 18 — 28 | 9 | |
| Al-Mg-Si | Sheet | 11 — 15 | 16 | |
| Al-Mg | Sheet | 18 — 23 | 16 | |
| Al-Mg5 | Bar | 25 — 28 | 16 | |
| Al-Mg-Mn | Sheet | 17 — 26 | 15 | |
| Al-Mn | Pipe | 11 — 17 | 16 |
In solid state
| Alloy grade | Semifinished | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ10, (%) |
|---|---|---|---|---|
| Al 99.5 | Sheet | 11 | 13 | 4 |
| Al-Mg-Si | Sheet | 15 | 17 | 4 |
| Al-Mg | Sheet | 27 | 3 | |
| Al-Mg5 | Bar | 28 | 32 | 3 |
| Al-Mg-Mn | Sheet | 20 | 24 | 3 |
| Al-Mn | Pipe | 19 | 3 |
In a cured state
| Alloy grade | Semifinished | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ10, (%) | Notes |
|---|---|---|---|---|---|
| Al-Cu4-Mg1 | Sheet | 28 | 43,5 | 10 | Cured at normal temperature; all sizes |
| Al-Cu-Ni-Mg-Fe | Forging | 26 | 38 | 4 | Small forgings and in grain direction |
| Al-Zn6-Mg-Cu | Bar | 38 | 50 | 6 | High temperature cured |
| Al-Mg-Si | Sheet | 10 | 20 | 12 |
Heat treatment modes and values of mechanical properties of cast aluminum alloys
| Alloy grade | Casting | Method of heat treatment of casting | Quenching temperature (°C) | Duration of exposure at this temperature (hours) | Aging temperature (°C) | Duration of aging (hours) | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ5, (%) | HB |
|---|---|---|---|---|---|---|---|---|---|---|
| Al-Si-Cu5 | Into the sand | 180±5 | 15 | 16 | 65 | |||||
| Al-Si-Cu5 | Into the sand | Hot cured | 525±5 | 4 | 180±5 | 5 | 20 | 70 | ||
| Al-Si-Cu5 | Into the sand | 525 +5 -10 | 4 | 230±5 | 5 | 18 | 1 | 65 | ||
| Al-Si-Cu5 | In the chill mold | Artificially aged | 180±5 | 15 | 16 | 65 | ||||
| Al-Cu-Si5 | In the chill mold | Hardened and stabilized | 525 +5 -10 | 4 | 230±5 | 5 | 18 | 1 | 65 | |
| Al-Cu-Ni-Mg | Into the sand | Hot cured | 515±5 | 4 — 10 | 235±5 | 4 — 6 | 18 | 22 | 0,3 | 90 |
| Al-Cu-Ni-Mg | In the chill mold | Hot cured | 515±5 | 4 — 10 | 235±5 | 4 — 6 | 20 | 24 | 0,3 | 90 |
| Al-Mg11 | Into the sand | Tempered | 435±5 | 15 — 20 | 28 | 9 | 60 | |||
| Al-Si13 | Into the sand | Thermally untreated | 8 | 17 | 4 | 50 | ||||
| Al-Si13 | In the chill mold | Annealed | 9 | 20 | 3 | 55 |
Note: Mechanical property values are minimum values and refer to specially cast test rods
Heat treatment modes for deformable aluminum alloys
Hot deformation
| Alloy grade | Optimal temperature (°C) | |
|---|---|---|
| Al 99.5 | 380 — 500 | 1 — 2 |
| Al-Cu4-Mg1 | 400 — 450 | 4 — 8 |
| Al-Cu-Ni-Mg-Fe | 420 — 470 | 4 — 8 |
| Al-Zn6-Mg-Cu | 440 — 460 | 4 — 8 |
| Al-Mg-Si | 480 — 520 | 2 — 4 |
| Al-Mg | 400 — 450 | 2 — 4 |
| Al-Mg5 | 330 — 400 | 3 — 6 |
| Al-Mg-Mn | 400 — 450 | 2 — 4 |
| Al-Mn | 450 — 500 | 1 — 2 |
Full annealing
| Alloy grade | Temperature (°C) | Duration of exposure at this temperature (hours) | Cooling method |
|---|---|---|---|
| Al 99.5 | 360 — 400 | 2 — 6 | On air |
| Al-Cu4-Mg1 | 330 — 420 | 1 — 6 | |
| Al-Cu-Ni-Mg-Fe | 340 — 400 | 1 — 6 | Slow in the oven; rapid cooling 40 - 60 degrees/h to a temperature of 200°C |
| Al-Zn6-Mg-Cu | 420 — 440 | 2 | Slow in the oven; rapid cooling 30 - 50 deg/h |
| Al-Mg-Si | 360 — 400 | 4 — 8 | Slow in the oven; rapid cooling 60 - 100 degrees/h to a temperature of 200°C |
| Al-Mg | 360 — 400 | 2 — 4 | On air |
| Al-Mg5 | 360 — 400 | 2 — 4 | Slow in the oven |
| Al-Mg-Mn | 360 — 400 | 1/2 — 3 | On air |
| Al-Mn | 500 - 550 (fast heating) | 1 — 4 | On air |
Curing
| Alloy grade | Quenching temperature (°C) | Duration of exposure at this temperature (hours) | Aging temperature (°C) | Duration of aging (hours) |
|---|---|---|---|---|
| Al-Cu4-Mg1 | 490 — 505 | 1/4 - 1, bath | At normal temperature | 5 days |
| Al-Cu-Ni-Mg-Fe | 520 — 540 | 1/2 - 1, bath | 180 — 195 | 12 - 14 h |
| Al-Zn6-Mg-Cu | 465 — 475 | 5 - 15 min, bath; 10 - 30 min, air oven | 130 — 140 | 16 hours |
| Al-Mg-Si | 520 — 535 | 1/3 - 1, bath | 155 — 160 | 4 - 6 hours |
Values of mechanical properties of wrought copper alloys subjected to various heat treatments
In a soft state or after hot deformation
| Alloy grade | Semifinished | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ10, (%) |
|---|---|---|---|---|
| Cu 99.5 | Sheet | 20 | 30 | |
| Cu-Sn 6 | Bar | 15 | 35 | 40 |
| Ms (brass) 90 | Sheet | 8 | 25 | 40 |
| Ms (brass) 70 | Sheet | 13 | 28 | 47 |
| Ms (brass) 63 | Shaped profile | 12 | 31 | 40 |
| Cu-Ni2-Si | Bar | 10 | 25 | 30 |
| Cu-Al 10-Fe-Ni | Bar | 40 | 65 | 5 |
| Cu-Be (2.0%)-Co (0.3%) | Sheet and rod | 17 — 25 | 42 — 52 | 35 — 50 |
In solid state
| Alloy grade | Semifinished | σ t, (kg/mm 2) | σ vr, (kg/mm 2) | δ10, (%) |
|---|---|---|---|---|
| Cu 99.5 | Sheet | 16 | 30 | 4 |
| Cu-Sn 6 | Bar | 45 | 50 | 8 |
| Ms (brass) 90 | Sheet | 20 | 35 | 8 |
| Ms (brass) 70 | Sheet | 30 | 45 | 15 |
| Ms (brass) 63 | Shaped profile | 35 | 42 | 15 |
| Cu-Be (2.0%)-Co (0.3%) | Sheet and rod | 52 — 60 | 63 — 70 | 10 — 20 |
Annealing of steel parts
To facilitate mechanical or plastic processing of a steel part, its hardness is reduced by annealing. The so-called full annealing consists in the fact that the part or workpiece is heated to a temperature of 900 ° C, maintained at this temperature for some time necessary to warm it throughout its entire volume, and then slowly (usually together with the furnace) cooled to room temperature.
Internal stresses that arise in the part during machining, are removed by low-temperature annealing, in which the part is heated to a temperature of 500-600°C and then cooled along with the furnace. To relieve internal stresses and slightly reduce the hardness of steel, incomplete annealing is used - heating to 750-760 ° C and subsequent slow (also together with the furnace) cooling.
Annealing is also used when hardening is unsuccessful or when it is necessary to overheat a tool for processing another metal (for example, if a copper drill needs to be overheated to drill cast iron). During annealing, the part is heated to a temperature slightly below the temperature required for hardening, and then gradually cooled in air. As a result, the hardened part again becomes soft and amenable to machining.
Copper is also subjected to heat treatment. In this case, copper can be made either softer or harder. However, unlike steel, copper is hardened by slow cooling in air, and copper becomes soft by rapid cooling in water. If a copper wire or tube is heated red hot (600° C) over a fire and then quickly immersed in water, the copper will become very soft. After giving the desired shape, the product can again be heated over a fire to 400 ° C and allowed to cool in air. The wire or tube will then become solid. If it is necessary to bend the tube, it is tightly filled with sand to avoid flattening and cracking.
Annealing brass increases its ductility. After annealing, brass becomes soft, easily bends, knocks out and stretches well. For annealing, it is heated to 600 ° C and allowed to cool in air at room temperature.
Annealing and hardening of duralumin
Annealing of duralumin is carried out to reduce its hardness. The part or workpiece is heated to approximately 360°C, as during hardening, held for some time, and then cooled in air. The hardness of annealed duralumin is almost half that of hardened duralumin.
Approximately the heating temperature of a duralumin part can be determined as follows: At a temperature of 350-360°C, a wooden splinter, which is passed along the hot surface of the part, becomes charred and leaves a dark mark. The temperature of the part can be determined quite accurately using a small (about the size of a match head) piece of copper foil, which is placed on its surface. At a temperature of 400°C, a small greenish flame appears above the foil.
Annealed duralumin has low hardness; it can be stamped and bent twice without fear of cracks.
Hardening. Duralumin can be hardened. When hardening, parts made of this metal are heated to 360-400°C, held for some time, then immersed in water at room temperature and left there until completely cooled. Immediately after this, duralumin becomes soft and flexible, easily bent and forged. It acquires increased hardness after three to four days. Its hardness (and at the same time fragility) increases so much that it cannot withstand bending at a small angle.
Duralumin acquires its highest strength after aging. Aging at room temperatures is called natural, and at elevated temperatures it is called artificial. The strength and hardness of freshly hardened duralumin, left at room temperature, increases over time, reaching its highest level after five to seven days. This process is called duralumin aging.
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Soldering or welding aluminum? What's the difference and which is better?
First, let's look at the definitions. Welding is the process of producing all-in-one joints by establishing interatomic bonds. Soldering is the process of joining metals in a heated state by melting an alloy, melting solder, such as the metals being joined.
In other words, when welding, the edges of the welded parts are melted and then frozen. In soldering, ordinary metal is heated only to a certain temperature, and the joint is made by surface diffusion and chemical reaction of the solder and fused metals.
So, which is better, soldering or aluminum welding?
To answer this question, consider the main methods of soldering and welding aluminum alloys, their advantages and disadvantages.
Aluminum welding.
Four types of welding are most commonly used when welding aluminum:
1. Electrode or TIG welding. As an electrode that does not consume, tungsten is used with special alloying additives (lanthanum, cerium, etc.).
An electric arc occurs through this electrode, which melts the metal. The welding wire is manually fed by the welding pool. The whole process is very similar to conventional gas welding, only the metal is heated not by burning a torch, but by an electric arc in a protective environment. Such welding is carried out exclusively in argon or helium atmosphere or mixtures thereof.
Is there a difference between argon and helium welding? Eat. The bottom line is that helium provides a more compact combustion arc and therefore deeper and more efficient penetration of the base metals. Helium is more expensive and its consumption is much higher than that of argon. In addition, helium is very liquid, which creates additional problems during production, transportation and storage.
Therefore, it is recommended to use it as a shielding gas only when welding large parts where deep and effective fusion of the weld edges is required. In practice, helium is rarely used as an inert gas, since almost the same penetration effect can be achieved in argon, which only increases the welding current. TIG welding of aluminum generally results in alternating current.
Why with alternating current? It's all about aluminum oxide, a small amount of which is inevitably present in all types of welding. The fact is that the melting point of aluminum is about 660 degrees. The melting point of aluminum oxide is 2060. Therefore, aluminum oxide cannot melt in a weld - the temperature is not enough.
And there will be no manual for high quality welding oxide. What to do? The income comes from the feedback polarity, which has a very interesting feature for cleaning the seam from unnecessary impurities. This property is called "cathode dispersion". However, reverse polarity welding current has very low melting power. Therefore, the arc also contains straight-polarity current components, which are designed to be insensitive but melt metals.
And the exchange of forward and reverse polar currents is an alternating current, which combines both cleaning and melting properties.
2. Consumable electrode welding or semi-automatic welding (MIG welding). All this applies to this type of welding with the only difference that, as a rule, the only permanent "cleaning" is the replacement of the poles of the arc flows and does not pass through the tungsten electrode and directly through the welding wire melted during welding.
A regular semi-automatic machine is used for welding, but with higher wire feeding requirements. This type of welding is characterized by high productivity.
Manual arc welding with coated electrodes (MMA welding). It is used for welding hard parts with a thickness of 4 mm or more. It is applied to reverse polarity flow and has a poor quality seam.
4. Gas welding of aluminum. It can only be used on a limited number of aluminum alloys, which have poor weld quality. This is very difficult and not accessible to every mortal.
In practice this is almost never used.
Leaving exotic welding alone (friction welding, explosion welding and plasma), the quality of the welded joint and its prevalence are far ahead of the form, AC argon arc welding.
It allows welding of pure aluminum, duralumin, silane, etc., alloys from a few millimeters to several centimeters. In addition, it is the most economical and the only one possible for nuclear welding and some other aluminum alloys.
Soldering aluminum
Usually separates low temperature (soft-joint soldering) and high temperature (soldering) type of soldering.
Soldering of aluminum soft solder is usually done with a regular soldering iron and can be used as a special solder for high-zinc aluminum and regular lead-tin solder. The main problem with this type of soldering is the fight against light aluminum oxide. To neutralize it, it is necessary to use various types of fluxes, soldering fats and special types of soldering. In some cases, the surface of the aluminum is plated with a thin layer of copper, which is already soldered with traditional soldering.
However, the use of galvanic coatings is far from technologically feasible and economically feasible. In any case, soldering aluminum alloys at low temperatures is quite difficult, and the quality of solder joints is usually more than average. In addition, due to the heterogeneity of metals, the bonded joint is susceptible to corrosion and must always be coated with varnish or paint. Soft joint soldering cannot be used on loaded systems.
In particular, it should not be used to repair air conditioner radiators, but can be used to repair radiator motors.
High temperature soldering of aluminum. When soldering aluminum radiators in factories, soldering is used. Its characteristic is that the melting point of the solder is only 20-40 degrees below the melting point of the metal itself. This soldering typically involves a special high temperature paste (such as nylon) used for soldering and then sintered in special ovens under a protective gas environment.
This soldering process is characterized by high strength and low corrosion resistance of the resulting joints, since the solder is used as a composition close to the base metal. This type of solder is ideal for thin-walled products, but its technology is quite complex and completely useless for repairs.
The second type of high-temperature aluminum brazing is gas flame brazing. 
Special self-tapping rods are used as solder (for example, HTS 2000, Castolin 21 F, etc.).
Acetylene, propane and, preferably, a hydrogen flame (hydrolysis) are used for heating. The technology here is as follows. First, the torch flame heats the metal, and then the soldering iron is carefully filled into the soldering area. When the rod melts, the flame is removed. The melting point of the rod is not much lower than the temperature of the base plate, so it must be heated thoroughly to prevent it from being removed.
It should be noted that this type of solder is very, very expensive and can cost up to $300. for 1 kilogram. Typically it is used for local repairs.
So which is better?
Baker melts at home: step by step, video
Soldering or welding aluminum? Now we can answer this question. If the thickness of the metals is more than 0.2-0.3 mm, then use argon arc welding. In particular, argon welding of simple honeycomb balm emitters, trays, fenders, brackets, alloy wheels, steering gear, engine head, etc. The resulting weld. It is a monolithic, chemically resistant and strong bond.
If the thickness of the metals is less than 0.2-0.3 mm, it is better to use high-temperature soldering of aluminum. Firstly, it is used for soldering thin honeycomb wall radiators from the engine, which is very difficult to drink with argon. Lower temperature soft soldering is better, if not used at all, as these joints are much weaker and less chemically resistant.
In addition, the acidic fluxes used in low-temperature soldering can destroy both ordinary metals and solder joints in a relatively short time.
Most common metals cannot be strengthened by heat treatment. However, almost all metals are strengthened—to some degree—by forging, rolling, or bending. This is called cold hardening or hardening of metal.
Annealing is a type of heat treatment to soften metal that has become hardened so that it can continue to be cold worked.
Cold working: copper, lead and aluminum
Ordinary metals vary greatly in their degree and rate of strain hardening - cold hardening or cold hardening.
Copper is hardened quite quickly as a result of cold forging, and, therefore, quickly reduces its malleability and ductility. Therefore, copper requires frequent annealing so that it can be processed further without the risk of destruction.
On the other hand, lead can be hammered into almost any shape without annealing or risk of breaking it.
Lead has such a reserve of ductility that allows it to obtain large plastic deformations with a very low degree of strain hardening. However, although copper is harder than lead, it is generally more malleable.
Aluminum can withstand quite a large amount of plastic deformation through hammer forming or cold rolling before it needs to be annealed to restore its ductile properties.
Pure aluminum hardens much more slowly than copper, and some sheet aluminum alloys are too hard or brittle to allow much hardening.
Cold working of iron and steel
Industrial pure iron can be cold worked to large degrees of deformation before it becomes too hard for further processing.
Impurities in iron or steel impair the cold workability of the metal to such an extent that most steels cannot be cold worked, except of course special low carbon steels for the automotive industry. At the same time, almost all steel can be successfully processed plastically in a red-hot state.
Why is metal annealing necessary?
The exact nature of the annealing process to which the metal is subjected depends largely on the purpose of the annealed metal.
There is a significant difference in the method of annealing between annealing in factories where huge quantities of sheet steel are produced, and annealing in a small auto repair shop, where only one part requires such processing.
In short, cold working is plastic deformation by destruction or distortion of the grain structure of the metal.
During annealing, a metal or alloy is heated to a temperature at which recrystallization occurs - the formation of new grains - not deformed and round - instead of old - deformed and elongated - grains. Then the metal is cooled at a given speed. In other words, crystals or grains within the metal that have been displaced or deformed during cold plastic working are given the opportunity to realign and recover to their natural state, but at an elevated annealing temperature.
Annealing of iron and steel
Iron and mild steels must be heated to temperatures of around 900 degrees Celsius and then allowed to cool slowly to ensure they are as "soft" as possible.
At the same time, measures are taken to prevent contact of the metal with air in order to avoid oxidation of its surface. When this is done in a small auto repair shop, warm sand is used for this.
High carbon steels require similar processing except that the annealing temperature for them is lower and is about 800 degrees Celsius.
Annealing of copper
Copper is annealed at about 550 degrees Celsius, when the copper is heated to a deep red color.
Once heated, the copper is cooled in water or allowed to cool slowly in air. The cooling rate of copper after heating at the annealing temperature does not affect the degree of “softness” of this metal obtained. The advantage of rapid cooling is that it cleans the metal of scale and dirt.
Annealing aluminum
Aluminum is annealed at a temperature of 350 degrees Celsius.
Heat treatment of non-ferrous alloys
In factories this is done in suitable ovens or salt baths. In the workshop, aluminum is annealed with a gas torch. They say that in this case a wooden splinter is rubbed over the surface of heated metal.
When the wood begins to leave black marks, it means that the aluminum has received its annealing. Sometimes a bar of soap is used instead of wood: when the soap begins to leave brown marks, the heating should be stopped. The aluminum is then cooled in water or left to cool in air.
Annealing of zinc
Zinc becomes malleable again at temperatures between 100 and 150 degrees Celsius.
This means that it can be annealed in boiling water. Zinc must be processed while it is hot: when it cools, it loses much of its malleability.
Copper is widely used in the manufacture of products for various purposes: vessels, pipelines, electrical distribution devices, chemical equipment, etc. The variety of uses of copper is associated with its special physical properties.
Copper has high electrical and thermal conductivity and is resistant to corrosion. The density of copper is 8.93 N/cm3, the melting point is 1083°C, the boiling point is 2360°C.
The difficulties in welding copper are due to its physical and chemical properties4. Copper is prone to oxidation with the formation of refractory oxides, absorption of gases by the molten metal, has high thermal conductivity, and a significant coefficient of linear expansion when heated.
The tendency to oxidation necessitates the use of special fluxes during welding that protect the molten metal from oxidation and dissolve the resulting oxides, converting them into slag.
High thermal conductivity requires the use of a more powerful flame than when welding steel. The weldability of Cu depends on its purity; the weldability of Cu is especially impaired by the presence of B1, Pb, 3 and Oz in it. The content of rg, depending on the grade of Cu, ranges from 0.02 to 0.15%, III and Pb give copper brittleness and red brittleness. The presence of oxygen in Cu in the form of copper oxide Cu20 causes the formation of brittle layers of metal and cracks that appear in the thermal zone influence.
Copper oxide forms a low-melting eutectic with copper, which has a lower melting point. The eutectic settles around the copper grains and thus weakens the bond between the grains.
The copper welding process is influenced not only by oxygen dissolved in copper, but also by oxygen absorbed from the atmosphere. In this case, along with copper oxide CuO, copper oxide CuO is formed. When welding, both of these oxides make gas welding difficult and must be removed using flux.
Hydrogen and carbon monoxide also negatively affect the Cu welding process.
As a result of their interaction with copper oxide CuO, water vapor is formed and carbon dioxide, which form pores in the weld metal. To avoid this phenomenon, copper welding must be performed with a strictly normal flame. The purer the Si and the less 0-2 it contains, the better it welds.
According to GOST 859-78, the industry produces copper grades M1r, M2r MZr, which has a reduced content of Oa- (up to 0.01%), for the manufacture of welded structures.
In C gas welding, butt and corner joints are used; T-joints and lap joints do not give good results.
Before welding, the welded edges must be cleaned of dirt, oil, oxides and other contaminants in an area of at least 30 mm from the welding site. Welding areas are cleaned manually or mechanically with steel brushes. Welding of copper with a thickness of up to 8 mm is carried out without cutting the edges, and with a thickness over 3 mm, an X-shaped cutting of the edges at an angle of 45° is required on each side of the joint. The bluntness makes it equal to 0.2 of the thickness of the metal being welded. Due to the increased fluidity of copper in the molten state, thin sheets are butt welded without a gap, and sheets over 6 mm are welded on graphite and carbon backings.
The power of the welding flame when welding copper up to 4 mm thick is selected based on the acetylene consumption of 150-175 dm3/h per 1 mm thickness of the metal being welded; for a thickness of up to 8-10 mm, the power is increased to 175-225 dm8/h.
For large thicknesses, it is recommended to weld with two torches - one for heating and the other for welding. To reduce heat dissipation, welding is performed on an asbestos backing. To compensate for large heat losses due to removal to the heat-affected zone, preliminary and concomitant heating of the welded edges is used.
The edges are heated with one or more burners.
The flame for welding C is chosen strictly normal, since the oxidizing flame causes strong oxidation, and with a carburizing flame, pores and cracks appear. The flame should be soft and should be directed at a greater angle than when welding steel. Welding is carried out in a recovery zone, the distance from the end of the core to the metal being welded is 3-6 mm.
During the welding process, the heated metal must be protected by flame at all times. Welding is performed using both the left and right methods, however, the right method is most preferable when welding copper. Welding is carried out at maximum speed without interruptions.
Welding is carried out upward. The angle of inclination of the torch mouthpiece to the product being welded is 40-50°, and the filler wire is 30-40°. When making vertical seams, the angle of inclination of the torch mouthpiece is 30° and welding is carried out from the bottom up. When welding copper, it is not recommended to fasten parts with tacks. Long seams are welded in a free state using a reverse-step method.
Gas welding of copper is performed in only one pass.
The composition of the filler wire has a great influence on the gas welding process. For welding, rods and wire in accordance with GOST 16130-72 of the following grades are used as an additive: M1, MSr1, MNZH5-1, MNZHKT5-1-0.2-0.2.
Error 503 Service Unavailable
Welding wire MSr1 contains 0.8-1.2% silver. The diameter of the filler wire is selected depending on the thickness of the metal being welded and is taken equal to 0.5-0.75 8, where 5 is the thickness of the metal, mm, but not more than 8 mm.
The welding wire should melt smoothly, without spattering. It is desirable that the melting temperature of the filler wire be lower than the melting temperature of the base metal. To protect Cu from oxidation, as well as to deoxidize and remove the resulting oxides into the slag, welding is carried out with flux. Fluxes are made from oxides and salts of boron and sodium. Fluxes for welding Cu are used in the form of powder, paste and in gaseous form. Fluxes No. 5 and 6, containing salts of phosphoric acid, must be used when welding with wire that does not contain phosphorus and silicon deoxidizers.
Si welding can also be performed using BM-1 gaseous flux; in this case, the torch tip must be increased by one number in order to reduce the heating rate and increase the power of the welding flame. When using gaseous flux, the KGF-2-66 installation is used. Powdered flux is sprinkled onto the welding site 40-50 mm on both sides of the weld axis. Flux in the form of a paste is applied to the edges of the metal being welded and to the filler rod. Remains of flux are removed by washing the seam with a 2% solution of nitric or sulfuric acid.
To improve the mechanical properties of the deposited metal and increase the density and.
To ensure the plasticity of the weld, it is recommended to forge the weld metal after welding. Parts up to 4 mm thick are forged in a cold state, and with greater thickness - when heated to a temperature of 550-600°C.
Additional improvement of the seam after forging is provided by heat treatment - heating to 550-600°C and cooling in water. The products to be welded are heated with a welding torch or in a furnace. After annealing, the weld metal becomes tough.
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Home>>Welding of non-ferrous metals>>Welding of copper and steel
Welding copper and its alloys with steel. How to weld copper and steel?
In practice, welding of copper and steel is most often carried out in butt joints. Depending on the nature of the structure, the seams in such a connection can be external or internal.
For welding brass to steel, gas welding is best suited, and for welding red copper to steel, electric arc welding with metal electrodes.
Good results are also obtained when welding with carbon electrodes under a layer of flux and gas welding under a submerged arc BM-1. Often in practice, gas welding of brass to steel is performed using copper as a filler material.
The preparation of welded edges with the same thickness of non-ferrous metal and steel is carried out in the same way as when welding ferrous metals.
Welding of sheets less than 3 mm thick is performed without cutting, and sheets starting from 3 mm are welded with beveled edges.
If the edges are insufficiently beveled, or if there is contamination at the ends of the parts being welded, good penetration cannot be achieved. Based on this, when welding parts of large thicknesses in which an X-shaped groove is made, blunting should not be done.
Welding copper with steel is a complex task, but quite feasible for surfacing and welding, for example, parts of chemical equipment, copper wire with a steel block.
The quality of welding of such joints meets the requirements for them. The strength of copper can be increased by introducing up to 2% iron into its composition. With more iron, strength begins to decrease.
When welding with a carbon electrode, it is necessary to use direct current of straight polarity.
The voltage of the electric arc is 40-55V, and its length is approximately 14-20mm. The welding current is selected in accordance with the diameter and quality of the electrode (carbon or graphite) and is in the range of 300-550A. The flux used is the same as for welding copper; the composition of these fluxes is given on this page.
Flux is introduced into the welding zone, pouring it into the groove.
The welding method is used "left".
The best results when welding copper busbars to steel are obtained when welding “in a boat”. The diagram of such welding is shown in the figure. First, the copper edges are heated with a carbon electrode, and then welded with a certain position of the electrode and filler rod (see figure). The welding speed is 0.25m/h. Welding copper with cast iron is carried out using the same technological techniques.
Welding of low-alloy bronze of small thickness (up to 1.5 mm) to steel with a thickness of up to 2.5 mm can be done overlapping with a non-consumable tungsten electrode in an argon environment on an automatic machine with a filler wire with a diameter of 1.8 mm supplied from the side.
In this case, it is very important to direct the arc towards the overlap from the copper side. Modes of such welding: current 190A, arc voltage 11.5V, welding speed 28.5m/h, wire feed speed 70m/h.
Copper and brass can be welded well to steel using flash butt welding.
With this welding method, steel edges melt quite strongly, and non-ferrous metal edges melt slightly. Taking into account this circumstance, and taking into account the difference in the resistivity of these metals, the overhang for steel is taken to be 3.5d, for brass 1.5d, for copper 1.0d, where d are the diameters of the rods being welded.
For butt welding of such rods using the resistance method, an overhang of 2.5d for steel, 1.0d for brass and 1.5d for copper is recommended. The specific resistance of the settlement is assumed to be in the range of 1.0-1.5 kg/mm2.
In practice, it often becomes necessary to weld studs with a diameter of 8-12 mm made of copper and its alloys to steel, or steel studs to copper products.
Such welding is carried out using direct current of reverse polarity under fine flux of the OSTS-45 brand without preheating.
Copper studs with a diameter of up to 12 mm or brass studs of grade L62, with a diameter of up to 10 mm, with a current strength of 400 A are well welded to steel or cast iron.
And studs made of brass grade LS 59-1 are not used for welding.
Steel studs are poorly welded to copper and brass products.
How to weld copper at home?
If you put a copper ring 4 mm high on the end of a pin with a diameter of up to 8 mm, then the process of welding metals proceeds satisfactorily. The same studs with a diameter of 12 mm for broze brand Br. OF 10-1 are welded well. For arc welding of copper and steel, the best results are provided by K-100 electrodes.
Graaver 04-03-2010 20:17
I'll start from far away...
I have been making sports medals for more than ten years, but there are questions that I constantly encounter, and I have never found out the final answers to them.. can anyone help? here is one of them..
To increase ductility, when pressing, the brass workpiece must be annealed... and this is where the fun begins...
At the moment I am using this recipe for annealing L63 brass (derived experimentally):
Heating in an oven to t=560 C, holding for 1.5-2 hours, cooling in air..
With the same parameters (brand of brass, maintenance mode), the output results are completely different.
In one case, all the “chicks and puffs” ... the brass becomes “soft”, is easily deformed and has an even, mirror-smooth surface (corresponding to the “mirror” of the stamp).
In another version, everything seems to be the same.. “soft” (plastic), only where there should be a “mirror”, a light, barely noticeable “orange peel cellulite” appears.. it seems like a trifle, but it’s terribly unpleasant
The question is...
Has anyone encountered a similar problem and how was it solved?
Interested in temperature, holding time when heating and cooling time (method) ..
Also, is it possible to “cure” brass blanks “infected with cellulite” (incorrect maintenance)?
With all respect, Andrew.
Ress75 04-03-2010 20:47
In jewelry techniques, there is such a technique: it’s called p.. (I don’t remember longer). The point is repeated annealing (6 times) of silver, etc. The metal begins to grind from the inside of the product and with each cycle locally the surface of the product swells - such a desert relief appears with orange peel. In general, it’s beautiful. Then there’s natural bleaching, etc. Maybe something similar will come out here?
YUZON 04-03-2010 21:45
Exactly the whole L 63? or maybe PM
Graaver 04-03-2010 22:08
quote: Is the brass from the same batch, or different supplies?
Exactly the whole L 63? or maybe PM
Party one..
Sometimes they cut three sheets (even if we assume that the sheets are different, all the blanks are brought in one bag, this is about 900 pieces, 300 pieces per sheet), I anneal... part is normal, part is “cellulite” (i.e. one batch after maintenance is all normal, other problem)..
True, I admit that the holding time in the oven is different..
Problems with temperature differences are excluded.. the oven allows you to keep the temperature "+"_"-" 1 degree C
Without annealing there is no “cellulite”, but it’s also oh so difficult to push through such a workpiece..
If anyone has encountered this, is there a guaranteed recipe?
To be “soft” and without “cellulite”...?
Graaver 04-03-2010 22:19
Does anyone know under what conditions (exceeding what parameters) this nasty thing happens?
sm special 04-03-2010 23:35
Perhaps “Googling” a query about annealing defects in brass might clarify something...
YUZON 05-03-2010 11:53
You can also try:
There is no need to make a long shutter speed, according to the process: loading at t=600 C, warming up at about 1 mm/min. Once the temperature has leveled off, cool it in air or with water.
IMHO: When exposed to an oxidizing atmosphere for a long time, zinc begins to oxidize and “scratch” the surface.
And sometimes the sheet rollers are to blame (they can’t handle their technical process)
Graaver 05-03-2010 14:41
When experimenting with t=600 C, I was guaranteed to get “cellulite”, although the exposure time was long..
There will be an opportunity to experiment again in the near future..
I'll try to reduce the time the pieces spend in the oven..
Nestor74 05-03-2010 16:39
2Graaver
After the holidays, I’ll check with my friends (the guys work a lot with brass - souvenirs, award paraphernalia), maybe they can tell me something, I’ll write back if by then this question is still relevant.
YUZON 05-03-2010 16:50
quote: I'll try to reduce the time the pieces spend in the oven..
In terms of time: the less, the better. as long as the oven gets back to normal.
Do not ship in a tight pack.
Boule 05-03-2010 17:28
you can, your 5 kopecks: straight into the water, without exposure to air
Boule 05-03-2010 17:29
simple hardening of copper alloys is exactly the opposite of hardening of steels - ductility increases
Graaver 05-03-2010 20:12
quote: after the holidays, I’ll check with my friends (the guys work a lot with brass - souvenirs, award paraphernalia), maybe they can tell me something, I’ll write back if by then this question is still relevant.
Any advice is relevant!
And practical experience is especially important!
quote: load at 600 and switch the oven to t=560.
Do not ship in a tight pack.
I tried cooling in water.. but again, the exposure of the blanks in the oven was significant, and everything in the batch was as “tight” as possible..
This was probably the reason for the failure...
Graaver 12-03-2010 19:52
What I least expected happened...
The story in short is this...
I ordered two sheets of brass and sent them to production without checking..
It turned out that one sheet, as ordered, was brass (L63), and the second was bronze (brand unknown, has a pleasant pink tint)..
Bronze doesn't suit me technically. characteristics.
Therefore, the whole party, in order not to be wasted, moves to a flea market.
Maybe someone will need it?!!
Here is a photo of blanks and a “test” medal made from this material.
Graaver 13-03-2010 09:27
I conducted an experiment with a new batch... “minimum required” holding time in the oven + “loose” loading + cooling in water.”.
The experiment was a success... there is no “cellulite”!
Many thanks to the one-tent campers “Bul” and “YUZON” for their practical advice!!!
I apologize for being intrusive..
Is it possible to “restore” brass after improper maintenance?
With all respect, Andrew.
BRASS
Brasses are the most common copper-based alloys. A summary list of standard brasses according to GOST 15527 and their foreign analogues is given in table. 1.
The state diagram of the copper-zinc alloy is shown in Fig. 1
And changes in the temperature of evaporation, melting and casting of copper-zinc alloys depending on the zinc content - in Fig. 2.
Change in the normal elastic modulus of copper-zinc alloys depending on the zinc content - Fig. 3.
Basic parameters of intermetallic phases of system alloys Cu-Zn are given in table. 2.
During the transition from a disordered β-phase to an ordered one β ’-phase in the specified temperature range there is a decrease in the coefficient of mutual diffusion and the growth rate of the phase. The activation energy of mutual diffusion in the β’-phase increases, and in the β-phase it decreases with increasing zinc concentration, while itapproximately 1.5 times greater in the β' phase than in the β phase. Partial atomic diffusion coefficients Zn 2 times more than Cu atoms in the disordered β-phase, and almost coincide with the ordered β’-phase.
Simple brass having a phase composition have practical applications α, α + β, β and β + γ .
The chemical composition of brass processed by pressure, according to domestic standards, is given in the appendix. 1.
SIMPLE BRASS
Simple brass, depending on the phase composition, is divided into two types: single-phase α (up to 33% Zn) and two-phase α + β (over 33% Zn).
In single-phase brasses, in which the zinc content is close to the saturation limit, small amounts of the β-phase are sometimes present as a result of slow diffusion processes. However, inclusions of the /3-phase, observed in very small quantities, do not have a noticeable effect on the properties α - brass. Thus, although these brasses have a two-phase structure, in terms of their physical, mechanical and technological properties it is advisable to classify them as single-phase brasses.
Pressure processing of plain brasses
Single-phase (A)brass during hot deformation is very sensitive to the content of impurities, especially fusible ones ( Bi, Pb ). Bismuth in the alloy can segregate along the boundaries, so even a monatomic layer of it can cause red brittleness in single-phase brasses with a high zinc content. Machinability α - When brass is hot, it deteriorates with increasing zinc content. When cold, single-phase brass can be processed well.
Two-phaseα + β - brasses are processed in a hot state better than single-phase ones due to the presence of highly plastic at elevated temperatures β -phases and are less sensitive to impurities. However, they are sensitive to temperature and cooling speed conditions. For this reason, a non-uniform structure is often observed in hot-pressed semi-finished products. For example, the front end of a rod (strip or pipe) has a predominantly fine needle-like structure and high mechanical properties; at the rear end of the rod, as a result of cooling, the structure is granular and has reduced mechanical properties.
In the cold state, two-phase brass is processed worse than single-phase brass. Their plasticity in a cold state depends on the structure. If α -phase is located on the main background of crystals β -phases in the form of thin needles, then the workability of two-phase brass in the cold state improves.
The effect of zinc content in brasses on the temperature range of hot pressure treatment is shown in Fig. 4.
In brasses, in the temperature range of 200-600°C, depending on the phase composition and zinc content, a zone of reduced ductility is observed.
When cold rolling, drawing and deep stamping of brasses, regardless of their phase composition, a structure with a grain size of no more than 0.05 mm is preferred.
The total degree of cold deformation of simple brasses is determined by a certain limit, above which the ductility drops sharply. This limit of permissible total cold deformation, which decreases with increasing zinc content, is set for each brand of brass.
If we assume the highest hot ductility in a homogeneous region β -phase, and at room temperature in the region α -phase for 100%, then the workability of brass by pressure can be assessed quantitatively ( table. 3).
Such assessments of the workability of metals and alloys by pressure and other technological characteristics are often used in foreign practice.
Heat treatment of plain brasses. The main types of heat treatment of simple brass are recrystallization annealing and annealing to relieve internal stresses. The recrystallization process of brasses is determined by the zinc content and phase composition.
Recrystallization onset temperature α -brass decreases with increasing zinc content. Recrystallization α -phase in highly deformed two-phase brass begins at 300°C. Under these conditions, the β-phase remains unchanged and its recrystallization begins at a higher temperature. Therefore, when choosing the annealing temperature to obtain the optimal structure, it is necessary to take into account this feature of two-phase brasses.
The grain sizes of single-phase brasses are determined according to microstructure standards (GOST 5362).
When brass semi-finished products are annealed in an air or oxidizing atmosphere, spots form on their surface - oxidation products that are difficult to remove during etching. Reducing the oxygen partial pressure (vacuum annealing) prevents staining but poses the risk of dezincification. Therefore, it is recommended to carry out annealing at a minimum temperature and in a protective atmosphere. In production conditions, stains are most difficult to avoid in brasses containing 37-40% zinc.
Machinability of simple brass by cutting. The machinability of brass by cutting (turning, milling, planing, grinding) depends on the phase composition of the brass. When cutting single-phase brass, the chips are long. Two-phase ( A + β ) brasses are processed better than single-phase α - brass. As the /3-phase content increases, the chips become more brittle and shorter. A quantitative assessment of the machinability of simple brass by cutting is determined by comparison with brass LS63-3, the machinability of which is taken as 100%. Single-phase α -brasses are highly polished, two-phase ones are somewhat worse. The machinability of brass by cutting and polishability is given in table. 4.
Soldering and welding of simple l atuney. Plain brass is very easy to join with soft solders. Before soft soldering, the surface is cleaned either by grinding or acid etching. It is preferable to use alloys containing 60% tin as solder. The antimony content in solder due to its strong affinity for zinc should be no more than 0.25-0.5%. Soft soldering is preferably performed with chloride fluxes.
Single-phaseα -brasses can also be easily joined by soldering with hard solders, including silver, two-phase A + β - somewhat worse.
Copper-phosphorus solders are self-fluxing, so soldering of brass with these solders is carried out without fluxes. When soldering with other hard solders, appropriate fluxes must be used.
The lead content in hard solders is limited to 0.5%.
Quantitative assessment of the solderability of plain brasses,%: single phaseα - brass (soft solders) – 100%, single-phaseα - brass (hard solders) – 100%, two-phaseα+ β - brass (soft solders) – 100%, two-phaseα+ β - brass (hard solders) – 75%.
The weldability of simple brass is somewhat worse than the solderability. General quantitative assessment of the weldability of brass -75% compared to oxygen-free copper, taken as 100%. The following types of welding are used to join brass: arc with a carbon electrode, arc with a consumable electrode, arc with a tungsten (non-consumable) electrode in a protective (inert gas) environment, arc with a consumable electrode in an inert gas environment, oxygen-acetylene, electric contact (spot) , roller, butt).
Brass content 20% Zn does not lend itself well to electric contact welding, lighter - brass with 40% Zn . The high zinc content in dual-phase brasses makes arc welding difficult due to its evaporation. Therefore, filler materials used in arc welding must contain relatively small amounts of zinc. Brasses containing more than 0.5% Pb are usually difficult to weld. To improve the wettability of the metal during the welding process, preheating to a temperature of 260 ° C is necessary, especially for brass with a high copper content. Carbon electrode welding of brasses containing 15-30%, Zn , is best done using filler rods (wire) made of Cu alloy + 3% Si . For single-pass welds, copper rods (wire) alloyed with a small amount of tin can be used; for multi-pass welds it is better to use alloy rods Cu + 3% Si.
Brasses containing more than 30% Zn , can be welded with a carbon electrode with filler rods (wire) made of brass Cu + 40% Zn or Cu + 3% Si . To improve the quality of welding, it is necessary to preheat the metal to a temperature of 210°C. Wire or rods made of tin-phosphorus bronze or aluminum bronze are used as consumable electrodes.
Arc welding of brass with a tungsten electrode in an inert gas environment is complicated by the release of zinc oxide vapors, which suppress the action of the arc. Therefore, welding should be carried out at high speeds.
Oxy-acetylene welding gives good results. For welding brass with a content of 15-30% Zn it is necessary to use filler rods (wire) made of alloy Cu + 1.5% Si. Ifoperating conditions of finished products do not cause local corrosion (dezincification), you can use brass with 40% Zn (L60). For welding brasses containing more than 30% Zn an alloy is used as a filler material Cu + 3% Si.
The influence of impurities on the properties of simple brasses. Impurities do not have a significant effect on the mechanical, physical (with the exception of iron, which, with a content of > 3.0%, changes the magnetic properties of brasses) and Chemical properties simple brasses, but noticeably affect their technological characteristics. During hot pressure treatment, single-phase brasses are especially sensitive to low-melting impurities.
The quality of products obtained from brass by deep stamping depends on the purity of the alloy, therefore, in simple brasses intended for deep stamping, the impurity content should be minimal.
The influence of impurities on the quality of semi-finished brass products:
aluminum deteriorates the quality of casting, causing foaming in castings; bismuth causes hot brittleness of brasses, especially single-phase ones; iron complicates the recrystallization process;
siliconimproves soldering and welding processes, increases corrosion resistance; nickel increases the temperature at which recrystallization begins;
leadcauses hot brittleness of brass, especially single-phase brasses containing zinc in the range of 30-33%;
antimonynegatively affects the workability of brass by pressure. Antimony microadditives (<0,1 %) к двухфазным латуням частично локализуют коррозию, связанную с обесцинкованием;
arsenicimpairs the ductility of brasses as a result of the release of brittle phases at concentrations above its solubility limit: in brasses in the solid state (>0.1%). Arsenic additives in small quantities (< 0,04%) предохраняют латуни от коррозионного растрескивания и обесцинкования при контакте с морской водой;
phosphorus refines the structure in the cast state and prevents cracking when heated, accelerates grain growth during recrystallization; reduces corrosion associated with dezincification; not recommended as a deoxidizing agent for copper-zinc alloys;
tinreduces the ductility of brasses and may cause heat cracking if the iron content is > 0.05%.
Modification of brasses carried out by introducing into the melt:
additions of elements that form refractory compounds, which, if structurally consistent, will serve as crystallization centers;
surface active metals, which, concentrating on the faces of nascent crystals, slow down their growth.
Elements such as iron, nickel, manganese, tin, yttrium, calcium, boron, and misch metal are used as modifiers in brasses.
Corrosion properties of brasses. Brasses have satisfactory resistance to industrial, marine and rural atmospheres. They fade in air. Corrosive effect on brasses containing >15% zinc, are caused by carbon dioxide and halogens.
Brasses containing <15% Zn , in terms of their corrosion resistance are close to industrial purity copper.
Under the influence of oxidizing acids, brass corrodes intensively. The limiting concentration of nitric acid at which no noticeable corrosion is observed is 0.1% (by weight). Sulfuric acid acts less aggressively on brass, however, in the presence of oxidizing salts K 2 SG 2 ABOUT 7 And Fe 2 (S0 4) 3the corrosion rate increases 200-250 times. Of the non-oxidizing acids, hydrochloric acid has the most corrosive effect.
The corrosion resistance of brass to most acids that do not have oxidizing ability is satisfactory. Brass is also resistant to dilute hot and cold alkaline solutions (with the exception of ammonia solutions) and cold concentrated neutral salt solutions. Brass is inert towards river and salt water. When in contact with river water containing small amounts of sulfuric acid, or in sea water, plain brass noticeably corrodes. The rate of corrosion depends on temperature, concentration, degree of contamination and flow rate around the metal surface. Brasses have good corrosion resistance to soil and are neutral to food products. The corrosion rate of brass in soil ranges from 0.0005 mm/year (in loamy soil with pH 5.7) to 0.075 mm/year (in ash soil with pH 7,6).
Dry gases - fluorine, bromine, chlorine, hydrogen chloride, hydrogen fluoride, carbon dioxide, carbon and nitrogen oxides at a temperature of 20 ° C and below have practically no effect on brass, however, in the presence of moisture, the effect of halogens on brass increases sharply; sulfur dioxide causes corrosion of brass when its concentration in the air is 1% and air humidity > 70%; Hydrogen sulfide has a significant effect on brass under all conditions, but brasses containing Zn > 30% more resistant than brass with low zinc content.
Fluorinated organic compounds, such as freon, have virtually no effect on brass.
In humid saturated steam at high speeds (about 1000 m 3 / c ) pitting corrosion is observed, so brass is not used for superheated steam.
Corrosion resistance of brasses in different environments given in table. 5.
In mine waters, especially if there is Fe2(SO4 ) 3 brass is highly corroded. Fluoride salts present in water have a weak effect on brass, chloride salts have a stronger effect, and iodide salts have a very strong effect.
Brass, in addition to general corrosion, is also subject to special types corrosion: zinc plating and “seasonal” cracking.
Dezincification is a special form of corrosion in which a solid solution of zinc is dissolved in copper and copper is electrochemically deposited at the cathode sites. Zinc corrosion products can be removed or retained in the form oxide film. The solution in which brass is dezincified typically contains more zinc than copper.
As a result of dezincification, brass becomes porous, reddish spots appear on the surface, and mechanical properties deteriorate. Dezincification is observed when brass comes into contact with electrically conductive media (acidic and alkaline solutions) and manifests itself in two forms: continuous and local. The dezincification process intensifies with increasing zinc content, as well as with increasing temperature and aeration. Single-phase brass containing >15% Zn , are subjected to dezincification in acidic solutions (nitrates, sulfates, chlorides, ammonium salts and cyanides). In two-phase brasses, the dezincification process is noticeably enhanced and can occur even in aqueous media. The most vulnerable isβ phase.
Small additions of arsenic, phosphorus and antimony partially localize the corrosion associated with dezincification. Arsenic and antimony protect against dezincification mainlyα -phase.
"Seasonal" or intergranular cracking is observed in brasses as a result of exposure to corrosive agents in the presence of tensile stresses. Corrosive agents include: ammonia vapors or solutions, condensates with sulfur dioxide gases, wet sulfuric anhydride, solutions of mercury salts, various amines, components of etching solutions, wet carbon dioxide. If the atmosphere contains traces of ammonia, wet carbon dioxide, sulfur dioxide and other corrosive agents, then “seasonal” cracking occurs when temperature fluctuations result in condensation of corrosive agents on the surface of parts.
Brasses containing up to 7% zinc are little sensitive to “seasonal” cracking. In brasses containing from 10 to 20% zinc, intergranular cracking is not observed if internal tensile stresses do not exceed 60 MPa. Brasses containing 20-30% Zn , are subject to corrosion cracking only in the cold-deformed state in aqueous solution ammonia. Single-phase brasses with a zinc concentration close to the saturation limit and two-phase brasses are most prone to corrosion cracking. They are resistant to seasonal cracking only in the presence of tensile stresses< 10 МПа.
The tendency to corrosion cracking of copper-zinc alloys in ammonia vapor is shown in Fig. 5.
To prevent corrosion cracking of brasses, it is necessary to use low-temperature annealing and protect them from oxidation during storage. To relieve internal stresses, pre-recrystallization annealing is performed.
To protect brass from oxidation, it is recommended to passivate them in the following environments: a slightly acidic aqueous solution containing about 6% chromic anhydride and 0.2% sulfuric acid; aqueous solution containing 5 % chromium and 2% chrome alum.
Brass is also protected using corrosion inhibitors, for example, benzotriazole or toluenetriazole. Benzotriazole forms a film on the surface (< 5 нм), которая предохраняет латуни от коррозии в водных средах, различных атмосферах и других агентах. Коррозионные ингибиторы могут быть введены в состав лаков и защитной оберточной бумаги.
In the case of electrochemical corrosion, brass, when in contact with various metals and alloys, manifests itself in two ways: in some cases as an anode, in others as a cathode ( table 6 ).
When brass comes into contact with silver, nickel, cupronickel, copper, aluminum bronze, tin and lead, electrochemical corrosion does not occur.
When heated, brass oxidizes. The rate of oxidation of brass increases exponentially with increasing temperature, doubling approximately every 360K. At temperatures above 770K, zinc evaporation is most intense if its concentration in the alloys exceeds 20 %.
The change in some physical and mechanical properties of brasses depending on the zinc content is shown in Fig. 6-9.
Typical physical, mechanical and technological properties brasses are given in P ril. 2, 3, 4.
Special brasses, pressure treated
Special or multi-component brasses are copper-zinc alloys of complex compositions in which the main alloying elements are aluminum, iron, manganese, nickel, manganese, nickel, silicon, tin and lead. These elements are usually introduced into brass in such quantities that they are completely dissolved inα andβ phases. In addition to the indicated elements, small additions of arsenic, antimony and other elements are introduced into brass.
The influence of alloying elements is manifested in two ways: phase properties change (Aand/3) and their relative quantities, i.e. boundary of phase transformations.
To determine the boundaries of phase transformations in the system or the “apparent” (“fictitious”) copper content when adding an alloying element, use the empirical equation:
A ’ = A *100/(100+ X *(K e-1)),
Where A'- apparent (fictitious) copper content, % (by weight); A -actual copper content, % (by weight); X- content of the third component, % (by weight); Ke- Guinier coefficient, characterizing the influence of the alloying element on the phase composition (at K e> 1, the number increasesβ '-phase).
Meaning Kefor various elements: for Ni K uh from -1.2 to -1.4, for Co K e=-1, for Mn K e=0.5, for Fe K e=0.9, for Pb K e=1, for Sn K e=2, for Al K e=6, for Si K e from 10 to 12.
Lead brasses
Lead brasses are copper-zinc alloys alloyed with lead. System State Diagram Cu - Zn - Pb presented on rice. 10.
The solubility of lead in alloys in the solid state is negligible. In two-phase copper-zinc alloys (containing Zn 40%) lead solubility at 750°C inβ -phase a little more than 0.2%; At room temperature, lead is practically insoluble. In two-phase brasses (in equilibrium), lead is located insideα Andβ -phases and partially at the boundaries of these phases. Lead, when released along phase or grain boundaries, noticeably worsens the deformability of brass in a hot state.
Lead in alloys A + β performs a dual role: on the one hand, it is used as a phase that promotes chip grinding, on the other - as a lubricant that reduces the coefficient of friction during cutting. The effectiveness of lead additives is determined by its quantity and the structure of the alloy, the size and nature of the distribution of lead particles, and the grain size a -phase, quantity and distributionβ phases.
By improving machinability, lead significantly reduces the impact strength of brass, impairs machinability, soldering and welding, polishability, and complicates galvanic surface treatment of products.
The strength characteristics of lead brasses decrease more rapidly with increasing temperature compared to simple brasses. The tensile strength of brasses containing about 2% lead at a temperature of 600°C is 10 MPa, at a temperature of 800°C - practically equal to zero.
Depending on the processing of finished deformed semi-finished products, lead brass is classified into three main types: for cold forming, for hot stamping, for processing on automatic lathes.
Structure lead thick brass. processed by cold pressure condition, consists ofα -phase and lead, the content of which must be within such limits as to ensure high machinability. Such alloys include brass grades LS74-3, LS64-2, JIC 63-3 and LS63-2.
Svintsovs e lat un and hot pressure treated condition and intended for hot forging and stamping - two-phase (α +β). The zinc content in brasses must be such that the transformation α + β into the clearβ -phase occurred completely and at a relatively low temperature.
Estimated content β -phase is about 20%. Lead content from 1 to 3%. Such brasses include lead brasses of the LS60-1, LS59-1 and LS59-3 brands. Svintsovs e latu ni. used for processing on automatic lathes and in microtechnology (i.e. for the manufacture of parts that are very small in size, about 1 mm) - two-phase, with a high lead content; LS63-3 (low content/3-phase) and LS58-3 (high content β -phases).
Brasses used in microtechnology are subject to special requirements for uniformity of chemical composition, tolerances on the main components and microstructure (size and distribution of lead particles, quantity and distribution β -phases, grain size α -phases). Uniformity of the chemical composition (homogeneity of the alloy) must be ensured in small areas.
The limits for optimizing the microstructure of lead brasses for “micro parts” are determined by the content β -phase from 10 to 30%, grain size α -phase - from 10 to 50 microns with an average diameter of lead particles of 1-5 microns.
Processing of lead brasses. Oxides of various elements impair the machinability of lead brass by cutting, therefore, when melting and casting them, careful control over their content is necessary. Of the impurity elements, iron has the most negative effect on machinability, therefore special restrictions are set on its content. Casting is carried out in two ways: in molds and semi-continuous (continuous) method. To achieve stability of the chemical composition, it is preferable to cast lead brasses in a continuous (semi-continuous) manner.
Lead does not affect the temperature and crystallization process of copper-zinc alloys; it solidifies at 326°C and, in the case of precipitation along grain (phase) boundaries, impairs the hot deformability of two-phase alloys.
The composition ranges of standard hot and cold processed lead brasses are shown in Fig. eleven.
When hot stamping lead brasses containing 56-60% Cu (LS59-1), the tendency to crack formation is determined mainly by the deformation temperature. The optimal temperature range at which cracks do not form is quite narrow and is located in the temperature range that makes up the lines on the phase diagram Cu-Zn , delimiting the two-phase α + β Andsingle-phaseβ -regions
The content of lead, as well as low-melting impurities (bismuth, antimony and others) does not affect the tendency to crack formation during hot stamping of two-phase leaded brasses (α + β ).
The influence of the chemical composition on the cutting and pressure machinability of lead brasses is shown in Table. 7.
Leadα -brass is processed in a cold state, but under certain conditions hot pressing is also possible.
The main types of heat treatment for lead brasses are full recrystallization annealing and low-temperature annealing to relieve internal stresses.
Leaded brass is not as good as plain brass in joining with solders, welding and polishing. To join lead brass, it is not recommended to use oxygen-acetylene welding, gas-shielded arc welding, or arc welding with a consumable electrode.
Co. corrosion resistance of lead brasses . Lead brasses have: excellent resistance to the effects of pure bicarbonates, freon, fluorinated bicarbonate coolants and varnishes; good resistance to industrial, marine, rural atmospheres, alcohols, diesel fuel and dry carbon dioxide; moderate resistance to crude oil and hydrocarbon dioxide; poor resistance to ammonium hydroxide, hydrochloric and sulfuric acids.
Tin yannaya la t uni
Tin has little effect on changing the boundaries of phase transformations, but noticeably changes the nature β -phases. System State Diagram Cu - Zn - Sn shown on rice. 12.
Dual-phase tin brasses have high corrosion resistance in many environments. With an increased tin content in brasses, a new γ phase appears. The γ phase is a brittle component that significantly impairs the cold workability of brass. Appearance γ -phases in two-phase brass (a +/3) observed at tin contents above 0,5% (if the tin content exceeds this limit, then during the transformation β the δ-phase is released, enveloping α -phase. The appearance of brittle phases limits the alloying of brass with tin. Tin content more 2% in brasses, it impairs their hot workability. Standard tin brasses can be divided into two types: single phase (α - solid solution) and three-phase ( α + β + γ ).
Aluminum brass
Aluminum brasses are copper-zinc alloys in which the main alloying additive is aluminum.
Aluminum, due to its high Guinier coefficient (Ke = 6) and significant solubility in the solid state compared to other elements (except silicon), has even small quantities noticeable effect on the properties of brass. Aluminum additives increase the mechanical properties and corrosion resistance of brass, but somewhat impair their ductility. The amount of introduced aluminum is limited to the limits above which brittleness appears. γ -phase ( rice. 13).
With copper content,% (by weight): 70; >/ J 65; 60 limiting aluminum content, % (by weight): 6; 5 and 3 respectively. In pressure-processed brasses, the aluminum content does not exceed 4%, in cast high-strength brasses - 7%.
Alloying of brass is carried out with aluminum alone or in certain proportions with other elements (iron, nickel, manganese and etc.).
As a rule, single-phase brasses (LA85-0.5, LA77-2) are alloyed with aluminum alone. To localize dezincification and prevent corrosion cracking upon contact with sea water in single-phase aluminum brasses containing more than 15% Zn, introduce 0.02-0.04 As (LAMsh77-2-0.05).
Excess arsenic (> 0.062%) impairs the ductility of brasses. Aluminum together with iron (LAZH60-1-1) and nickel (LAN59-3-2) are introduced mainly into two-phase brasses.
Iron improves the ductility of brasses containing lead, when hot, it crushes the structure and increases their mechanical properties; Nickel increases corrosion resistance. Iron and nickel somewhat reduce the ductility of brass when cold.
Alloying brass with aluminum, nickel and small additions of manganese and silicon (LANKMts75-2-2.5-0.5-0.5) makes them dispersion-hardening and significantly improves mechanical properties, especially elastic characteristics.
Single-phase aluminum brasses are satisfactorily processed by pressure in a hot state and well in a cold state; two-phase - good when hot and satisfactory when cold. Cutting machinability ranges from 30 to 50% (compared to LS63-3 brass).
Aluminum brass, compared to lead, is less easily joined by solders, but is slightly better welded; in terms of polishability, they are close to two-phase simple brass ( tab l. 8).
Iron-containing brasses
Iron additives significantly refine the structure of brass, thereby improving mechanical properties and technological characteristics. However" alloys system Cu - Zn - Fe rarely used. Multi-component brasses have become widespread.
Manganese brass
Alloying brass with manganese significantly increases their corrosion resistance when in contact with sea water, chlorides and superheated steam.
Alloy System Diagram Cu - Zn - Mn shown in Fig. 14.
Manganese additions have a minor effect on the structure of brass. However, manganese reduces the stability of the ordered phase lattice β . When the Mn content is > 4.7% (at.), a partially disordered state is observed in the alloy at a quenching temperature of 520°C.
Manganese has the most favorable effect on the properties and technological characteristics of brass in combination with other alloying elements (aluminum, iron, tin, nickel).
Silicon brasses
Silicon in the solid state is soluble in brass in significant quantities, but its solubility decreases with increasing zinc content. Solid solution region Aunder the influence of silicon and zinc, it shifts sharply towards the copper angle (Fig. 15 ) .
With increasing silicon content in the alloy structure Cu - Zn - Si a new phase appears Tohexagonal syngyny, which is plastic at elevated temperatures and, unlike β -phase is polarized. As the temperature decreases (below 545°C), eutectoid decomposition of the k-phase occurs intoα + γ ".
Silicon brasses containing 20% Zn and 4% Si not suitable for pressure treatment due to low ductility. To obtain deformed semi-finished products, silicon brasses containing<4% Si.
Small additions of silicon improve the technological characteristics of brass during casting and hot forming, increase mechanical properties and anti-friction properties
Nickelbrass
Alloying brasses with nickel increases their mechanical properties and corrosion resistance. Nickel brasses are more resistant to dezincification and corrosion cracking than other brasses.
As can be seen from the phase diagram of the alloy system Cu - Zn - Ni (rice. 16), nickel has a noticeable effect on the structure of brasses, expanding the region of the solid solution α
When alloying with nickel, some two-phase brasses can be converted to single-phase.
Alloying L62 brass with nickel in an amount of 2-3% (by weight) makes it possible to obtain a single-phase alloy with fine grains, high and uniform mechanical properties and increased corrosion resistance. Thanks to the addition of nickel in the production of deformed semi-finished products, the appearance of such a negative phenomenon as a stitch structure is eliminated.
Recommendations for improving the properties of copper-zinc alloys taking into account foreign experience. The properties of brasses, along with the purity of the initial components of the alloys, methods and modes of melting and casting, are greatly influenced by the modes of their processing and the preparation of the charge.
To reduce the formation of porosity and bubbles in sheets (strips) and tapes made of brass grades L70, L68, L63 and L60: avoid contamination of the charge with phosphorus; waste in the form of chips containing oil, emulsion, etc. is subjected to oxidative firing before melting; add copper oxide to the melt in an amount of 0.1-1.0 kg per 100 kg of charge; pay special attention to optimal casting and hot rolling conditions; anneal hot-rolled strips before cold rolling.
To increase the resistance of brasses L68 and L70 to corrosion cracking, it is necessary to pay great attention to the selection of cold rolling and annealing conditions. The total reduction during the last cold rolling should be more than 50%, the optimal annealing temperature is 260-280°C.
To increase the resistance of two-phase brass to dezincification (and this is possible if the proportion β -phase in the structure of the alloy is about 30%) it is necessary to carry out heat treatment in the temperature range 400-700°C (depending on the composition of the alloy).
To prevent dezincification of L63 brasses and to obtain a high-quality surface during bright annealing (in bell-type and shaft furnaces), the recrystallization annealing temperature is maintained within 450-470°C. At this temperature, within 1-4 hours, a strip (tape) is obtained with a grain size of 0.035-0.045 mm, a tensile strength of 33-35 kgf/mm 2 and a relative elongation of 50%.
