Heat treatment modes for brass L60. Heat treatment of metals
Heat treatment of non-ferrous metal means heating to a certain temperature, followed by cooling at a certain speed. The overall effectiveness of heat treatment of non-ferrous metal depends on its previous treatment, 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 for removal internal stresses 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 region, the 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 |
HEAT TREATMENT OF COPPER AND BRASS
Copper.
Copper is used to produce sheets, strips, and wires using the cold deformation method. During deformation, it loses plasticity and gains elasticity. Loss of ductility makes calcination, broaching and drawing difficult, and in some cases makes further processing of the metal impossible.
To remove hardening or hardening and restore the plastic properties of copper, recrystallization annealing is carried out according to the following regime: heating to a temperature of 450-500 ° C at a speed of 200-220 ° C/h, holding time depending on the configuration and weight of the product from 0.5 to 1 .5 hours, cooling in still air. The structure of the metal after annealing consists of equiaxed crystals, strength σв = 190 MPa, relative elongation δ = 22%.
Brass.
An alloy of copper and zinc is called brass. There are two-component (simple) brasses, consisting only of copper, zinc and some impurities, and multi-component (special) brasses, into which one or more alloying elements (lead, silicon, tin) are introduced to give the alloy certain properties.
Depending on the processing method, two-component brass is divided into wrought and cast brass.
deformable two-component brasses (L96, L90, L80, L63, etc.) have high ductility and can be easily processed by pressure; they are used for the manufacture of sheets, tape, strips, pipes, wire and rods of various profiles.
Foundry brass is used for casting shaped parts. In the process of cold working, two-component brass, like copper, receives hardening, as a result of which strength increases and ductility decreases. Therefore, such brasses are subjected to heat treatment - recrystallization annealing according to the regime: heating to 450-650 ° C, at a rate of 180-200 ° C / h, holding for 1.5-2.0 hours and cooling in still air. Strength of brass after annealing σ Β = 240-320 MPa, relative elongation δ = 49-52%
Brass products with high internal stress in the metal are susceptible to cracking. When stored in air for a long time, longitudinal and transverse cracks form on them. To avoid this, products before long-term storage subjected to low-temperature annealing at 250-300° C.
Availability in multicomponent(special)latuniah alloying elements (manganese, tin, nickel, lead and silicon) gives them increased strength, hardness and high corrosion resistance in atmospheric conditions and sea water. Brasses alloyed with tin have the highest stability in sea water, for example LO70-1, LA77-2 and LAN59-3-2, called marine brass; they are used mainly for the manufacture of parts for marine vessels.
According to the processing method, special brasses are divided into wrought and cast brasses. Deformable brass is used to produce semi-finished products (sheets, pipes, tape), springs, watch parts and instruments. Foundry multicomponent brasses are used for the manufacture of semi-finished products and shaped parts by casting (propellers, blades, fittings, etc.). The required mechanical properties of special brass are ensured by heat treatment, the modes of which are given in the table. To obtain fine grains, before deep drawing, deformable brass for sheets, strips, and strips is subjected to annealing at a temperature of 450-500 ° C.
Heat treatment modes for special brasses *
|
Alloy grade |
Purpose of processing |
Type of processing |
Heating temperature, °C |
Duration, h |
|
Deformable brass |
||||
|
Removing cold hardening |
Recrystallization annealing |
|||
|
Relieving stress |
Low annealing |
|||
|
Foundry brasses |
||||
|
Relieving stress |
Recrystallization hot annealing |
|||
* Cooling medium - air.
THERMAL HARDENING OF BRONZE
Bronze is an alloy of copper with tin, lead, silicon, aluminum, beryllium and other elements. According to the main alloying element, bronzes are divided into tin and tin-free (special), and according to mechanical properties - into wrought and cast.
Deformable tin bronze grades Br.OF8-0.3, Br.OTs4-3, Br.OTsS4-4-2.5 are produced in the form of rods, strips, and wire for springs. The structure of these bronzes consists of an α-solid solution. The main type of heat treatment of bronzes is high annealing according to the regime: heating to 600-650 ° C, holding at this temperature for 1-2 hours and rapid cooling. Strength after annealing σ c - 350-450 MPa, relative elongation b = 18-22%, hardness HB 70-90.
Foundry tin bronze brands Br.OTs5-5-5, Br.OSNZ-7-5-1, Br.OTsSZ,5-7-5 are used for the manufacture of anti-friction parts (bushings, bearings, liners, etc.). Cast tin bronzes are annealed at 540-550°C for 60-90 minutes.
Tinless bronze Br.5, Br.7, Br.AMts9-2, Br.KN1-3 and other brands have high strength, good anti-corrosion and anti-friction properties. Gears, bushings, membranes and other parts are made from these bronzes. To facilitate pressure treatment, bronze is homogenized at 700-750° C, followed by rapid cooling. Castings that have internal stresses are annealed at 550° C with a holding time of 90-120 minutes.
Most often used in industry double - aluminum bronze grades Br.A5, Br.A7 and bronze, additionally alloyed with nickel, manganese, iron and other elements, for example Br.AZHN10-4-4. These bronzes are used for various bushings, flanges, guide seats, gears and other small parts that experience heavy loads.
Double aluminum bronzes are subjected to quenching and tempering according to the following regime: heating for quenching to 880–900° C at a rate of 180–200° C/h, holding at this temperature for 1.5–2 hours, cooling in water; tempering at 400-450°C for 90-120 minutes. The structure of the alloy after quenching consists of martensite, after tempering it consists of a thin mechanical mixture; bronze strength σв = 550MPa, δ = 5%, hardness HB 380–400.
Beryllium bronze Br.B2 is an alloy of copper and beryllium. Unique properties - high strength and elasticity with simultaneous chemical resistance, non-magneticity and the ability to be thermally hardened - all this makes beryllium bronze an indispensable material for the manufacture of watch and instrument springs, membranes, springy contacts and other parts. High hardness and non-magnetic properties make it possible to use bronze as a percussion tool (hammers, chisels) that does not produce sparks when hitting stone and metal. This tool is used when working in explosive environments. Bronze Br.B2 is hardened at 800–820° C with cooling in water, and then subjected to artificial aging at 300–350° C. In this case, the strength of the alloy σ Β = 1300 MPa, hardness HRC37–40.
THERMAL HARDENING OF ALUMINUM ALLOYS
Deformable aluminum alloys They are divided into those that cannot be strengthened by heat treatment and those that can be strengthened. TO non-hardening aluminum alloys include alloys of the AMts2, AMg2, AMgZ brands, which have low strength and high ductility; They are used for products obtained by deep drawing and are strengthened by cold pressure treatment (cold-pressing).
The most common alloys are hardenable heat treatment. These include duralumin grades D1, D16, D3P, which contain aluminum, copper, magnesium and manganese. The main types of thermal hardening of duralumin are hardening and aging. Quenching is carried out at 505-515° C with subsequent cooling in cold water. Aging is used both natural and artificial. With natural aging, the alloy is aged for 4-5 days, with artificial aging - 0.8-2.0 hours; aging temperature - not lower than 100-150°C; strength after processing σ Β = 490 MPa, 6 = 14%. Alloys D1 and D16 are used for the manufacture of parts and elements of building structures, as well as products for aircraft.
Avial (AV, AVT, AVT1) is a deformable alloy that has higher ductility, weldability and corrosion resistance than duralumin; subjected to hardening in water at 515-525 ° C and aging: AB and AVT alloys - natural, AVT1 alloy - artificial at 160 ° C with exposure for 12-18 hours. Aviation is used for the production of sheets, pipes, helicopter rotor blades and so on.
High-strength (σ = 550-700 MPa) aluminum alloys B95 and B96 have less ductility than duralumin. Thermal treatment of these alloys consists of quenching at 465-475 ° C with cooling in cold or hot water and artificial aging at 135-145° C for 14-16 hours. Alloys are used in aircraft construction for loaded structures operating long time at 100-200° C.
Forged aluminum alloys of grades AK1, AK6, AK8 are subjected to hardening at 500-575 ° C with cooling in running water and artificial aging at 150-165 ° C with exposure for 6-15 hours; alloy strength σ Β = 380-460 MPa, relative elongation δ = 7-10%.
Foundry aluminum alloys called silumi-nami. The most common thermally hardenable alloys are AL4, AL6 and AL20 grades. Castings from AL4 and AL6 alloys are hardened at 535-545 ° C with cooling in hot (60-80 ° C) water and subjected to artificial aging at 175 ° C for 2- 3 hours; after heat treatment σ = 260 MPa, δ = 4-6%, hardness HB 75-80. To relieve internal stresses, castings from these alloys are annealed at 300°C for 5–10 hours with cooling in air. Heat-resistant alloys of grades AL 11 and AL20, used for the manufacture of pistons, cylinder heads, boiler furnaces operating at 200-300 ° C, are subjected to hardening (heating to 535-545 ° C, holding at this temperature for 3-6 hours and cooling in running water), as well as stabilizing tempering at 175-180 ° C for 5-10 hours; after heat treatment σ =300-350 MPa, δ=3-5%.
HEAT TREATMENT OF MAGNESIUM AND TITANIUM ALLOYS
Magnesium alloys.
The main elements in magnesium alloys (except magnesium) are aluminum, zinc, manganese and zirconium. Magnesium alloys are divided into wrought and cast alloys.
Deformable magnesium alloys grades MA1, MA8, MA14 are subjected to thermal hardening according to the following regime: heating for hardening to 410-415 ° C, holding for 15-18 hours, cooling in air and artificial aging at 175 ° C for 15-16 hours; after heat treatment σ Β = 320~430 MPa, δ = 6-14%. Alloys MA2, MAZ and MA5 are not subjected to heat treatment; they are used for the manufacture of sheets, plates, profiles and forgings.
Chemical composition foundries magnesium alloys (ML4, ML5, ML12, etc.) is close to the composition of wrought alloys, but the ductility and strength of cast alloys is much lower. This is due to the rough casting structure of the alloys. Heat treatment of castings followed by aging promotes the dissolution of excess phases concentrated along the grain boundaries and increases the ductility and strength of the alloy.
A feature of magnesium alloys is the low rate of diffusion processes (phase transformations occur slowly), which requires a long soaking time for hardening and aging. For this reason, hardening of alloys is only possible in air. Aging of cast magnesium alloys is carried out at 200-300° C; for hardening they are heated to 380-420 ° C; after hardening and aging σ in = 250-270 MPa.
Magnesium alloys can be used as heat-resistant, capable of operating at temperatures up to 400° C. Due to their high specific strength, magnesium alloys are widely used in aviation, rocketry, the automotive and electrical industries. A big disadvantage of magnesium alloys is their low resistance to corrosion in a humid atmosphere.
Titanium alloys.
Titanium is one of the most important modern structural materials; has high strength, high melting point (1665° C), low density (4500 kg/m 3) and high corrosion resistance even in sea water. High-strength alloys are formed on the basis of titanium, widely used in aviation and rocketry, power engineering, shipbuilding, chemical industry and other areas of industry. The main additives in titanium alloys are aluminum, molybdenum, vanadium, manganese, chromium, tin and iron.
Titanium alloys of grades VT5, VT6-S, VT9 and VT16 are subjected to annealing, hardening and aging. Semi-finished products (rods, forgings, pipes) from an alloy additionally alloyed with tin (VT5-1) undergo recrystallization annealing at 700-800° C in order to remove hardening. Sheet titanium alloys are annealed at 600-650° C. The duration of annealing for forgings, rods and pipes is 25-30 minutes, for sheets - 50-70 minutes.
Highly loaded parts made of VT14 alloy, operating at a temperature of 400°C, are hardened with subsequent aging according to the following regime: hardening temperature 820-840°C, cooling in water, aging at 480-500°C for 12-16 hours; after hardening and aging: σ in = 1150-1400 MPa, 6 = 6-10%, hardness HRC56-60.
When developing technology for heat treatment of copper and its alloys, it is necessary to take into account two of their features: high thermal conductivity and active interaction with gases during heating. When heating thin products and semi-finished products, thermal conductivity is of secondary importance. When heating massive products, the high thermal conductivity of copper is the reason for their faster and more uniform heating over the entire cross-section compared, for example, with titanium alloys.Due to the high thermal conductivity, the hardenability problem does not arise during the strengthening heat treatment of copper alloys. With the dimensions of semi-finished products and products used in practice, they are calcined through.
Copper and alloys based on it actively interact with oxygen and water vapor when elevated temperatures, at least more intensively than aluminum and its alloys. Due to this feature, protective atmospheres are often used during the heat treatment of semi-finished products and products made of copper and its alloys, while in the technology of heat treatment of aluminum, protective atmospheres are rare.
Annealing of copper and its alloys is carried out in order to eliminate those deviations from the equilibrium structure that arose during the solidification process or as a result of mechanical action or previous heat treatment.
Homogenization annealing involves heating the ingots to the highest possible temperature without causing melting of the structural components of the alloys. Liquation phenomena in copper and brasses develop insignificantly, and heating the ingots for hot pressure treatment is sufficient for their homogenization.
The main copper alloys that require homogenization annealing are tin bronzes, since the compositions of the liquid and solid phases in the Cu-Sn system are very different, and therefore intense dendritic liquation develops.
As a result of homogenization annealing, the homogeneity of the structure and chemical composition of the ingots increases. Homogenization annealing is one of the conditions for obtaining a high-quality final product.
Recrystallization annealing is one of the common technological stages in the production of semi-finished copper and alloys based on it.
The temperature of the onset of recrystallization of copper is intensively increased by Zr, Cd, Sn, Sb, Cr, while Ni, Zn, Fe, Co have a weak effect. The increase in the temperature of the onset of recrystallization in the simultaneous presence of several elements is non-additive, but slightly exceeds the contribution from the most effective impurity. In certain cases, for example, when lead and sulfur are introduced into copper, the total effect is higher than the individual effects. Copper deoxidized by phosphorus, in contrast to oxygen-containing copper, is prone to strong grain growth during annealing. The recrystallization threshold in the presence of phosphorus shifts to higher temperatures.
The critical degree of deformation for oxygen-free copper with a grain size of the order of 2*10v-2 cm after annealing at 800°C for 6 hours is approximately 1%. Impurities, such as iron, increase the critical degree of deformation, which for brass is 5-12% (Fig. 44).
The recrystallization temperature of brass is also influenced by previous processing, primarily the degree of cold deformation and the size of the grain formed during this processing. For example, the time before the start of recrystallization of L95 brass at temperatures of 440° C is 30 minutes at a degree of cold deformation of 30% and 1 minute at a degree of deformation of 80%.
The size of the initial grain affects the crystallization process in the opposite way to an increase in the degree of deformation. For example, in the L95 alloy with an initial grain size of 30 and 15 μm, annealing after 50% deformation at a temperature of 440°C leads to recrystallization after 5 and 1 min, respectively. At the same time, the size of the initial grain does not affect the recrystallization rate if the annealing temperature exceeds 140°C.
In Fig. Figure 45 shows data on the effect of the composition of α-brasses on the annealing temperature (degree of deformation 45%, annealing time 30 min), which ensures obtaining a given grain size. Under the same conditions of deformation and annealing, with increasing zinc content, the grain size decreases, reaches a minimum and then increases. So, for example, after annealing at 500°C for 30 minutes, the grain size is: in copper 0.025 mm; in brass with 15% Zn 0.015 mm, and in brass 35% Zn 0.035 mm. Figure 45 also shows that in α-brasses the grain begins to grow at relatively low temperatures and grows up to solidus temperatures. In two-phase (α+β)- and special brasses, grain growth, as a rule, occurs only at temperatures at which one β-phase remains. For example, for L59 brass, a significant increase in grain begins when annealing above a temperature of 750 ° C.
The annealing temperature of brass is chosen approximately 250-350° C above the temperature at which recrystallization begins (Table 16).
When copper alloys containing 32-39% Zn are annealed at temperatures above the α⇔α+β transition, the β phase is released, which causes uneven grain growth. It is advisable to anneal such alloys at temperatures not exceeding the α⇔α+β equilibrium line of the Cu-Zn system. In this regard, brass, whose composition is close to the point of maximum solubility of zinc in copper, should be annealed in furnaces with high accuracy of temperature control and high uniformity of its distribution throughout the volume of copper.
In Fig. 46 shows the optimal annealing modes for simple brasses based on the results of a generalization of technological recommendations accumulated in domestic and world practice. There is a tendency for the complete annealing temperature of brass to increase with increasing zinc content.
When choosing recrystallization annealing modes for brasses, it should be taken into account that alloys lying near the phase boundary α/α+β (Fig. 46) can be thermally strengthened due to the variable solubility of zinc in copper. Hardening of brasses containing more than 34% Zn makes them prone to aging (Fig. 47), and the ability to harden during aging increases with increasing zinc content up to 42%. Practical Application I have not found this type of thermal hardening of brass. Nevertheless, the cooling rate of L63 type brasses after recrystallization annealing affects their mechanical properties. The possibility of decomposition of supersaturated solutions in α-brasses containing more than 34% Zn and in α+β-brasses should also be taken into account when choosing annealing modes to reduce stress. Severe cold deformation can accelerate the decomposition of supersaturated α- and β-solutions upon annealing.
According to literature data, the temperature at which recrystallization of L63 brass begins ranges from 250 to 480° C. The finest-grained structure in the L63 alloy is formed after annealing at temperatures of 300-400° C. The higher the degree of previous cold deformation, the smaller the size of the recrystallized grain and the greater the hardness (Fig. 48) under the same annealing conditions.
The quality of the annealed material is determined not only by its mechanical properties, but also the size of the recrystallized grain. The grain size in a fully recrystallized structure is quite uniform. If the recrystallization annealing modes are incorrectly set, two groups of grains of different sizes are clearly detected in the structure. This so-called double structure is particularly undesirable during deep drawing, bending or polishing operations and etching of the product.
As the grain size increases to a certain limit, the stampability of brass improves, but the surface quality deteriorates. On the surface of the product, with a grain size of more than 40 microns, a characteristic “orange peel” roughness is observed.
The stages of evolution of the deformed structure are significantly extended in time, and therefore it seems possible to obtain a partially or completely recrystallized structure with fine grains by varying the annealing time. Semi-finished products with an incompletely recrystallized structure and a very small grain size are stamped without the formation of an “orange peel”.
Partial annealing, the duration of which is determined by the degree of preliminary deformation, is carried out in the range of 250-400 ° C. To maintain precise technological conditions, such annealing should be carried out in broaching furnaces, where it is strictly controlled working temperature and dwell time (propagation speed).
Partial annealing is used primarily to reduce residual stresses, which can lead to so-called “seasonal cracking.” This type of corrosion, inherent in brasses containing more than 15% Zn, consists of the gradual development of intergranular cracks under the simultaneous influence of stress (residual and applied) and specific chemical reagents (for example, solutions and vapors of ammonia, solutions of mercury salts, wet sulfuric anhydride, various amines etc.). It is believed that the sensitivity of brasses to seasonal cracking is due to stress inhomogeneity rather than to their absolute magnitude.
The effectiveness of annealing to reduce residual stresses is checked by a mercury test. The mercury test method provides a qualitative assessment of the presence of residual stresses. It is based on the different behavior of stressed and unstressed materials when exposed to mercury nitrate. During the test, longitudinal and transverse cracks appear on the stressed material, visible to the naked eye. They appear in places of tensile stress, which can cause destruction of the product in operation or during storage as a result of corrosion cracking.
Annealing modes for brass to reduce residual stress are given in Fig. 46 and in table. 16.
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Thanks to annealing, copper becomes softer and more ductile, after which it bends easily. This allows the metal to be forged and shaped into the desired shape without breaking it. You can anneal copper of any grade and thickness if you have a powerful enough torch. The easiest way to anneal copper is to heat it with an oxy-acetylene torch and then quickly cool it in water.
Steps
Part 1
Preparing for annealing- Safety glasses used for annealing, arc cutting and welding are rated on a scale of 2 to 14, with 2 being the least tinted and 14 being the darkest. An acetylene torch produces a much less bright flame than a welding torch, so slightly tinted glass is sufficient to protect your eyes.
- If you don't have safety glasses, purchase some from a hardware or welding supply store.
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Connect one hose to each cylinder to prepare the acetylene torch. The burner itself, which produces the flame, has two hoses coming out of it. Connect the red torch hose to the acetylene cylinder and the black hose to the oxygen cylinder. The acetylene will ignite the flame, after which oxygen will continue to feed it. By changing the amount of oxygen supplied from the cylinder, you can control the intensity of the flame.
Turn the acetylene valve a quarter turn clockwise. By doing this, you will open the acetylene cylinder and gas will begin to flow into the reducer. Turn the valve only a quarter turn - this will be enough for the acetylene to maintain the flame, but the flow of gas will not be too strong and you can control it. Watch the pressure gauge and adjust the valve so that the pressure is 0.5 atmospheres.
- The pressure gauge is located on top of the acetylene cylinder. It has a round scale with the inscriptions “pressure” and “atm”.
- Once the flame is established, you can adjust its intensity using the valve on the acetylene cylinder. The valve is located at the top of the cylinder. Typically, it is located next to the pressure gauge (or even connected to it).
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Turn the valve on the oxygen cylinder fully counterclockwise. Then adjust the pressure using the screw on the reducer (turn it clockwise). At the same time, keep an eye on the pressure gauge on the oxygen cylinder - make sure it shows 2.7 atmospheres.
- The oxygen valve is located at the top of the oxygen cylinder. There may be an arrow on it that indicates which direction the valve should be unscrewed.
- It is necessary to achieve the correct ratio of oxygen and acetylene to obtain a controlled hot flame.
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Light the acetylene torch using a silicon lighter. To light the flame, hold the torch in one hand and turn the valve at the top of the acetylene bottle half a turn clockwise with the other hand. As a result, gas will begin to flow into the burner. Bring the silicon lighter closer to the burner nozzle about 1.5 centimeters. Click it until an orange-red flame appears.
- Light the flame no later than 2-3 seconds after turning off the valve on the acetylene cylinder, as this gas is highly flammable.
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Adjust the valve on the burner until the flame turns blue. Once the burner begins to produce a light orange flame, turn the oxygen valve on the side of the burner clockwise to introduce oxygen into the burning acetylene. Continue turning the valve until the flame turns blue. The blue color of the flame indicates that its temperature is ideal for annealing copper.
- Turn the oxygen valve slowly to avoid a sudden flash of flame.
- A flame that is too hot will burn the metal, and a flame that is too cold will not heat the copper enough and its durability and ductility will not be affected.
Part 2
Heating copper-
When annealing, keep the flame at a distance of 7.5–10 centimeters from the surface of the copper. Point the flame directly at the copper plate or pipe. Don't get the torch too close to the metal or you will burn the surface. Hold the torch at least 10-13 centimeters from the surface of the copper and wait until the metal heats up.
Move the torch flame quickly across the metal surface. Move the torch along the entire surface to heat the copper evenly. It is necessary to distribute the heat evenly throughout the volume of the metal so that certain areas do not anneal faster than others. In this case, you will notice that in places where it is heated, the surface of the copper turns red or orange.
- When working with open flames, keep a dry chemical fire extinguisher handy. If anything catches fire, use a fire extinguisher immediately.
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Thicker and more massive pieces of copper should take longer to heat up. Annealing softens any piece of copper, regardless of its thickness or size. However, the thicker the metal, the longer it should be heated.
- For example, it is enough to heat a thin piece of jewelry copper for 20 seconds to anneal it. At the same time, a massive copper pipe or copper sheet 1.5 centimeters thick must be heated for at least 2–3 minutes.
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Keep the flame in one place until the copper turns red. When heated with an acetylene torch, the surface of the copper will first turn black. Don't worry, it will turn red after this. Continue moving the flame across the surface of the metal until the black color changes to a glowing bright red. This color indicates that the copper has been annealed.
Wear safety glasses before working with the burner. When handling open flames, safety glasses must be worn. Wear safety glasses with a shade rating of at least 4 to properly protect your eyes from the glare of an acetylene flame. Looking into an acetylene torch flame without safety glasses can cause serious eye damage.
Hardening a metal allows you to make some changes in its structure, making it softer or, conversely, harder. When hardening, a lot depends not only on the heating itself, but also on the cooling process and time. Manufacturers mainly harden steel, making the product more durable, however, copper can also be hardened if the need arises.
Copper hardening - production process
Copper is hardened using the annealing method. During heat treatment, copper can be made softer or harder, depending on what it will be used for in the future. However, it is important to remember that the method of hardening copper is significantly different from the way steel is hardened.
Copper is hardened by slow cooling in air. If it is necessary to obtain a softer structure, then hardening is carried out by rapidly cooling the metal in water immediately after heating. If you need to get a very soft metal, then you should heat the copper until red hot (this is about 600 °), and then lower it into water. After the product has gone through the deformation process and acquired the desired shape, it can be heated again to 400° and then allowed to cool in the air.
Copper hardening plant
Copper is hardened in special equipment designed for this purpose. There are several types of hardening installations, but the most popular today is induction equipment. The induction installation is excellent for hardening copper, allowing you to obtain a product High Quality. Thanks to automated software HDTV equipment, it is adjusted with high precision, where the heating time, temperature, and also the method of cooling the metal are indicated.
If the company constantly hardens metal products, then it would be best to pay attention to special complex equipment designed for comfortable, quick hardening. The ELSIT hardening complex has everything necessary equipment for hardening HDTV. The hardening complex includes: an induction installation, a hardening machine, a manipulator and a cooling module. If the customer needs to harden products of different shapes, then a set of inductors of various sizes can be included in the hardening complex.
