All mechanical quality of the soul - heat treatment knowledge
A little knowledge of the mechanical person should know that heat treatment is to give the inherent quality of the soul of the machine, China's mechanical processing is not bad, but the heat treatment level yet to be improved, burning it, the robot when the self-
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but by changing the microstructure inside the workpiece or changing the chemical composition of the workpiece surface , To give or improve the use of the workpiece performance. Which is characterized by improving the intrinsic quality of the workpiece, which is generally not visible to the naked eye.
Heat treatment process generally includes heating, heat preservation, cooling three processes, sometimes only heating and cooling the two processes. These processes are interlinked and irreversible. Metal heat treatment process can be divided into the overall heat treatment, surface heat treatment, local heat treatment and chemical heat treatment.
Overall heat treatment
The overall heat treatment is a metal heat treatment process in which the overall workpiece is heated and then cooled at an appropriate rate to change its overall mechanical properties. Iron and steel as a whole heat treatment is generally annealed, normalizing, quenching and tempering four basic processes. Annealing, normalizing, quenching, tempering is the overall heat treatment of the "four fire", which quenching and tempering closely related, often with the use of missing.
annealing:
Is to heat the workpiece to the appropriate temperature, according to the material and the workpiece size using different holding time, and then slow cooling, the purpose is to make the internal organization of metal or close to equilibrium, to obtain good process performance and performance, or for further quenching Organization preparation.
Normalizing:
Is to heat the workpiece to the appropriate temperature after cooling in the air, the effect of normalizing with the same annealing, but the organization is finer, often used to improve the cutting performance of low-carbon materials, and sometimes for some less demanding parts As the final heat treatment.
Quenching:
Is the workpiece after heat insulation, in water, oil or other inorganic salts, organic aqueous solution and other quenching medium in the rapid cooling. After quenching steel parts hardened, but at the same time become brittle
Tempering:
In order to reduce the brittleness of the steel, the quenched steel is heated at a temperature higher than room temperature and lower than 650 ° C for a long period of time and then cooled.
"Four fire" with the heating temperature and cooling different, but also evolved a different heat treatment process. In order to obtain a certain strength and toughness, quenching and high temperature tempering combined with the process, known as quenched and tempered. Some alloys are quenched to form a supersaturated solid solution, which is left at room temperature or slightly higher for an extended period of time to increase the hardness, strength, or electrical properties of the alloy. Such a heat treatment process is called aging treatment.
The pressure processing and deformation of the heat treatment effectively and tightly combined to make the workpiece to obtain a good strength, toughness method known as the deformation heat treatment; vacuum atmosphere or vacuum in the heat treatment known as vacuum heat treatment, it can not only make The workpiece is not oxidized, not decarburization, to keep the workpiece surface smooth, improve the performance of the workpiece, but also through the infiltration agent for chemical heat treatment.
Surface heat treatment
Only heat the surface of the workpiece to change the surface mechanical properties of the metal heat treatment process. In order to heat only the surface of the workpiece without passing too much heat into the interior of the workpiece, the heat source used must have a high energy density, that is, to give greater heat energy to the workpiece per unit area so that the surface or part of the workpiece can be short or instantaneous To reach high temperature. Surface heat treatment of the main methods are flame quenching and induction heating heat treatment, commonly used heat source aerobic acetylene or propane and other flame, induced current, laser and electron beam and so on.
Chemical heat treatment
By changing the surface chemical composition of the workpiece, the organization and performance of the metal heat treatment process. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface of the workpiece. Chemical heat treatment is the workpiece on carbon, nitrogen or other alloying elements in the medium (gas, liquid, solid) heating, heat for a long time, so that the surface of the workpiece into the carbon, nitrogen, boron and chromium and other elements. After infiltration of elements, sometimes other heat treatment processes such as quenching and tempering. Chemical heat treatment of the main methods are carburizing, nitriding, infiltration of metal.
Heat treatment is one of the important processes in the manufacture of mechanical parts and molds. It can control the various properties of the workpiece, such as wear, corrosion resistance, magnetic properties. But also can improve the rough tissue and stress state, in order to facilitate a variety of cold and hot processing. For example, white cast iron can be used for a long time annealing to obtain malleable cast iron, improve the plasticity; gear with the correct heat treatment process, the service life can be compared with the heat treatment of the gear times or several times to improve; In addition, inexpensive carbon steel through the infiltration Some alloying elements have some properties of alloy steel, can replace some of the heat-resistant steel, stainless steel; molds are almost all need to be heat treatment before use.
The difference between annealing and tempering
The difference between annealing and tempering is: (Simply put, annealing is not hardness, tempering also retain a certain hardness).
Tempering:
The high temperature tempering organization is tempered sorbite. Tempering is generally not used alone, after quenching in the parts after quenching, the main purpose is to eliminate the quenching stress, get the required organization, tempering according to the tempering temperature is divided into low temperature, medium temperature and high temperature tempering. Respectively, to obtain tempered martensite, talc and sorbite. Which after quenching high temperature tempering combined heat treatment known as quenching and tempering treatment, its purpose is to obtain strength, hardness and plasticity, toughness are better comprehensive mechanical properties. Therefore, it is widely used in automobile, tractor, machine tool and other important structural parts, such as connecting rods, bolts, gears and shafts. After tempering hardness is generally HB200-330.
annealing:
During the annealing process, the pearlite transition occurs. The main purpose of the annealing is to make the internal structure of the metal reach or close to equilibrium and prepare for subsequent processing and final heat treatment. The stress relief annealing is intended to eliminate the annealing process due to the deformation caused by plastic deformation, welding, and the residual stress present in the casting. Forging, casting, welding and cutting the workpiece after the existence of internal stress, if not promptly eliminated, will make the workpiece in the processing and use of the process of deformation, affecting the accuracy of the workpiece. It is very important to use stress relief annealing to eliminate the internal stress generated during the machining process. The heating temperature of the stress relief annealing is lower than the phase transition temperature, so that no tissue transition occurs during the entire heat treatment. Internal stress is mainly through the workpiece in the insulation and slow cooling process naturally eliminated. In order to eliminate the stress in the workpiece more thoroughly, the heating temperature should be controlled during heating. Usually low temperature into the furnace, and then heated at about 100 ℃ / h heating rate to the specified temperature. The heating temperature of the welding parts should be slightly higher than 600 ℃. Insulation time, as the case may be, usually 2 ~ 4h. Casting stress relief annealing time to take the upper limit, the cooling rate control in the (20 ~ 50) ℃ / h, cold to 300 ℃ below the baked air cooled. Aging treatment can be divided into natural aging and artificial aging two kinds of natural aging is castings placed in the open field for more than six months, then slowly occurs, so that the residual stress to eliminate or reduce the artificial aging is the casting heated to 550 ~ 650 ℃ For stress relief annealing, it saves time by natural time, and the residual stress is removed more thoroughly.
What is the temper?
Tempering is the heat of the metal after heating or parts heated to a certain temperature, after a certain period of time, in a certain way to cool the heat treatment process, tempering is followed by an operation after quenching, usually the final heat treatment of the workpiece A process, so the quenching and tempering of the joint process known as the final heat treatment. The main purpose of quenching and tempering is:
1) to reduce the internal stress and reduce the brittleness, quenching parts there is a lot of stress and brittleness, if not timely tempering often produce deformation or even cracking.
2) to adjust the mechanical properties of the workpiece, the workpiece after quenching, high hardness, brittleness, in order to meet the different performance requirements of various parts can be adjusted by tempering, hardness, strength, plasticity and toughness.
3) Stable workpiece size. Through the tempering can make the metallurgical organization tends to be stable, to ensure that the use of the process in the future no longer deformation.
4) to improve the cutting performance of some alloy steel.
In production, often based on the requirements of the workpiece performance. According to the different heating temperature, the tempering is divided into low temperature tempering, tempering tempering, and high temperature tempering. Quenching and subsequent high temperature tempering combined with the heat treatment process known as quenching and tempering, that is, with a high degree of strength at the same time, there are good plastic toughness. Mainly used to deal with the larger load of the machine structure parts, such as machine tool spindle, rear axle axle, strong gear and so on.
What is quenching?
Quenching is the metal into the material or parts heated to the phase transition temperature above, after insulation, to a greater than the critical cooling rate of the rapid cooling, in order to obtain martensite heat treatment process. Quenching is to get martensite, and then after tempering, the workpiece to obtain good performance, in order to give full play to the potential of the material. Its main purpose is:
1) improve the mechanical properties of metal or parts. For example: to improve the hardness of tools, bearings and wear resistance, improve the flexibility of the spring limit, improve the mechanical properties of shaft parts and so on.
2) to improve the performance of certain special steel material or chemical properties. Such as improving the corrosion resistance of stainless steel, increasing the permanent magnetism of the magnet.
Quenching and cooling, in addition to the need to choose a reasonable quenching medium, but also have the correct quenching method, commonly used quenching method, mainly single-liquid quenching, two-liquid quenching, grading quenching, isothermal quenching, local quenching and so on.
The difference and connection of "four fire"
Justification has the following purpose and use.
① Eutectoid steel, normalizing to eliminate casting, forging, welding overheating coarse grain structure and Wei's organization, rolling material in the ribbon; grain refinement; and can be used as pre-heat treatment before quenching.
② on the eutectoid steel, normalizing can eliminate reticular secondary cementite, and make pearlite refinement, not only to improve the mechanical properties, but also conducive to the subsequent ball annealing.
③ For low carbon deep drawing steel plate, normalizing can eliminate the free cementite in the grain boundary to improve its deep drawing performance.
④ low carbon steel and low carbon low alloy steel, the use of normalizing, can be more fine pearlite organization, so that the hardness increased to HB140-190, to avoid cutting the "stick knife" phenomenon, improve the machinability The Of medium carbon steel, in both the use of normalizing and annealing can be used, with Zhengrong more economical and convenient.
⑤ for ordinary carbon structural steel, in the mechanical performance requirements are not high occasions, can be used instead of quenching plus high temperature tempering tempering, not only easy to operate, but also the steel structure and size stability.
⑥ high temperature normalizing (Ac3 above 150 ~ 200 ℃) due to the high diffusion rate at high temperatures, can reduce the composition of castings and forging segregation. The coarse grains after high temperature normalizing can be refined by the subsequent second lower normalizing.
⑦ for some of the steam turbine and boiler low, medium carbon alloy steel, often used to obtain normal bainite bainite, and then by high temperature tempering, for 400 ~ 550 ℃ with good creep resistance.
⑧ In addition to steel and steel, normalizing is also widely used in ductile iron heat treatment, to obtain pearlite matrix, to improve the strength of ductile iron.
As the normalizing is characterized by air cooling, the ambient air temperature, stacking method, airflow and workpiece size have an effect on the organization and performance after normalizing. Normalizing the organization can also be used as a classification of alloy steel. Usually according to the diameter of 25 mm sample heated to 900 ℃, the air-cooled organization, the alloy steel is divided into pearlitic steel, bainitic steel, martensitic steel and austenitic steel.
Annealing is a metal heat treatment process in which the metal is slowly heated to a certain temperature, maintained for a sufficient time, and then cooled at a suitable speed. Annealing heat treatment is divided into complete annealing, incomplete annealing and stress relief annealing. The mechanical properties of the annealed material can be tested by tensile tests or by hardness tests. Many steel are annealed heat treatment state of supply, steel hardness testing can be used Rockwell hardness tester, test HRB hardness, for thin steel, steel and thin-walled steel pipe, you can use the surface Rockwell hardness tester, the detection of HRT hardness The
The purpose of annealing is:
① to improve or eliminate the steel in the casting, forging, rolling and welding process caused by a variety of tissue defects and residual stress, to prevent deformation of the workpiece, cracking.
② soften the workpiece for cutting.
③ fine grain, improve the organization to improve the mechanical properties of the workpiece.
④ for the final heat treatment (quenching, tempering) to prepare for the organization.
Commonly used annealing processes are:
① complete annealing. Used to refine the medium and low carbon steel after casting, forging and welding after the emergence of poor mechanical properties of the superheated tissue. The workpiece is heated to the total transformation of ferrite into austenite temperature above 30 ~ 50 ℃, holding for a period of time, and then slowly cooling with the furnace, the austenite in the cooling process changes again, you can make the steel tissue thinning The
Spherical annealing. To reduce the tool steel and bearing steel after forging high hardness. The workpiece heated to the beginning of the formation of austenite to the temperature above 20 ~ 40 ℃, slowly cooling after the insulation, in the process of pearlite in the lamellar cementite into a spherical shape, thereby reducing the hardness.
③ isothermal annealing. To reduce the high nickel, chromium content of high alloy steel structure of high hardness, for cutting. Generally first to a faster cooling to the most unstable temperature of austenite, holding the appropriate time, austenite into a twist or sorbite, hardness can be reduced.
④ recrystallization annealing. To eliminate the metal wire, thin plate in the cold drawing, cold rolling process of hardening (hardness, plastic decline). Heating temperature is generally the beginning of the formation of steel austenite temperature below 50 ~ 150 ℃, the only way to eliminate the hardening effect of the hardening of the metal.
⑤ Graphite annealing. Used to make a large number of cementite cast iron into a good plastic malleable cast iron. The process operation is to heat the casting to about 950 ℃, the insulation after a certain period of time appropriate cooling, so that the formation of cementite decomposition floc graphite.
⑥ diffusion annealing. To make the chemical composition of the alloy casting homogenization, improve its performance. The method is heated in the absence of melting under the premise of the casting heated to the highest possible temperature and long time to keep the alloy in the distribution of various elements tend to even after the distribution of slow cooling.
⑦ to stress annealing. To eliminate the internal stress of steel castings and weldments. For the steel products after heating began to form austenite temperature below 100 ~ 200 ℃, after cooling in the air cooling, you can eliminate the internal stress.
A little knowledge of the mechanical person should know that heat treatment is to give the inherent quality of the soul of the machine, China's mechanical processing is not bad, but the heat treatment level yet to be improved, burning it, the robot when the self-
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but by changing the microstructure inside the workpiece or changing the chemical composition of the workpiece surface , To give or improve the use of the workpiece performance. Which is characterized by improving the intrinsic quality of the workpiece, which is generally not visible to the naked eye.
Heat treatment process generally includes heating, heat preservation, cooling three processes, sometimes only heating and cooling the two processes. These processes are interlinked and irreversible. Metal heat treatment process can be divided into the overall heat treatment, surface heat treatment, local heat treatment and chemical heat treatment.
Overall heat treatment
The overall heat treatment is a metal heat treatment process in which the overall workpiece is heated and then cooled at an appropriate rate to change its overall mechanical properties. Iron and steel as a whole heat treatment is generally annealed, normalizing, quenching and tempering four basic processes. Annealing, normalizing, quenching, tempering is the overall heat treatment of the "four fire", which quenching and tempering closely related, often with the use of missing.
annealing:
Is to heat the workpiece to the appropriate temperature, according to the material and the workpiece size using different holding time, and then slow cooling, the purpose is to make the internal organization of metal or close to equilibrium, to obtain good process performance and performance, or for further quenching Organization preparation.
Normalizing:
Is to heat the workpiece to the appropriate temperature after cooling in the air, the effect of normalizing with the same annealing, but the organization is finer, often used to improve the cutting performance of low-carbon materials, and sometimes for some less demanding parts As the final heat treatment.
Quenching:
Is the workpiece after heat insulation, in water, oil or other inorganic salts, organic aqueous solution and other quenching medium in the rapid cooling. After quenching steel parts hardened, but at the same time become brittle
Tempering:
In order to reduce the brittleness of the steel, the quenched steel is heated at a temperature higher than room temperature and lower than 650 ° C for a long period of time and then cooled.
"Four fire" with the heating temperature and cooling different, but also evolved a different heat treatment process. In order to obtain a certain strength and toughness, quenching and high temperature tempering combined with the process, known as quenched and tempered. Some alloys are quenched to form a supersaturated solid solution, which is left at room temperature or slightly higher for an extended period of time to increase the hardness, strength, or electrical properties of the alloy. Such a heat treatment process is called aging treatment.
The pressure processing and deformation of the heat treatment effectively and tightly combined to make the workpiece to obtain a good strength, toughness method known as the deformation heat treatment; vacuum atmosphere or vacuum in the heat treatment known as vacuum heat treatment, it can not only make The workpiece is not oxidized, not decarburization, to keep the workpiece surface smooth, improve the performance of the workpiece, but also through the infiltration agent for chemical heat treatment.
Surface heat treatment
Only heat the surface of the workpiece to change the surface mechanical properties of the metal heat treatment process. In order to heat only the surface of the workpiece without passing too much heat into the interior of the workpiece, the heat source used must have a high energy density, that is, to give greater heat energy to the workpiece per unit area so that the surface or part of the workpiece can be short or instantaneous To reach high temperature. Surface heat treatment of the main methods are flame quenching and induction heating heat treatment, commonly used heat source aerobic acetylene or propane and other flame, induced current, laser and electron beam and so on.
Chemical heat treatment
By changing the surface chemical composition of the workpiece, the organization and performance of the metal heat treatment process. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface of the workpiece. Chemical heat treatment is the workpiece on carbon, nitrogen or other alloying elements in the medium (gas, liquid, solid) heating, heat for a long time, so that the surface of the workpiece into the carbon, nitrogen, boron and chromium and other elements. After infiltration of elements, sometimes other heat treatment processes such as quenching and tempering. Chemical heat treatment of the main methods are carburizing, nitriding, infiltration of metal.
Heat treatment is one of the important processes in the manufacture of mechanical parts and molds. It can control the various properties of the workpiece, such as wear, corrosion resistance, magnetic properties. But also can improve the rough tissue and stress state, in order to facilitate a variety of cold and hot processing. For example, white cast iron can be used for a long time annealing to obtain malleable cast iron, improve the plasticity; gear with the correct heat treatment process, the service life can be compared with the heat treatment of the gear times or several times to improve; In addition, inexpensive carbon steel through the infiltration Some alloying elements have some properties of alloy steel, can replace some of the heat-resistant steel, stainless steel; molds are almost all need to be heat treatment before use.
The difference between annealing and tempering
The difference between annealing and tempering is: (Simply put, annealing is not hardness, tempering also retain a certain hardness).
Tempering:
The high temperature tempering organization is tempered sorbite. Tempering is generally not used alone, after quenching in the parts after quenching, the main purpose is to eliminate the quenching stress, get the required organization, tempering according to the tempering temperature is divided into low temperature, medium temperature and high temperature tempering. Respectively, to obtain tempered martensite, talc and sorbite. Which after quenching high temperature tempering combined heat treatment known as quenching and tempering treatment, its purpose is to obtain strength, hardness and plasticity, toughness are better comprehensive mechanical properties. Therefore, it is widely used in automobile, tractor, machine tool and other important structural parts, such as connecting rods, bolts, gears and shafts. After tempering hardness is generally HB200-330.
annealing:
During the annealing process, the pearlite transition occurs. The main purpose of the annealing is to make the internal structure of the metal reach or close to equilibrium and prepare for subsequent processing and final heat treatment. The stress relief annealing is intended to eliminate the annealing process due to the deformation caused by plastic deformation, welding, and the residual stress present in the casting. Forging, casting, welding and cutting the workpiece after the existence of internal stress, if not promptly eliminated, will make the workpiece in the processing and use of the process of deformation, affecting the accuracy of the workpiece. It is very important to use stress relief annealing to eliminate the internal stress generated during the machining process. The heating temperature of the stress relief annealing is lower than the phase transition temperature, so that no tissue transition occurs during the entire heat treatment. Internal stress is mainly through the workpiece in the insulation and slow cooling process naturally eliminated. In order to eliminate the stress in the workpiece more thoroughly, the heating temperature should be controlled during heating. Usually low temperature into the furnace, and then heated at about 100 ℃ / h heating rate to the specified temperature. The heating temperature of the welding parts should be slightly higher than 600 ℃. Insulation time, as the case may be, usually 2 ~ 4h. Casting stress relief annealing time to take the upper limit, the cooling rate control in the (20 ~ 50) ℃ / h, cold to 300 ℃ below the baked air cooled. Aging treatment can be divided into natural aging and artificial aging two kinds of natural aging is castings placed in the open field for more than six months, then slowly occurs, so that the residual stress to eliminate or reduce the artificial aging is the casting heated to 550 ~ 650 ℃ For stress relief annealing, it saves time by natural time, and the residual stress is removed more thoroughly.
What is the temper?
Tempering is the heat of the metal after heating or parts heated to a certain temperature, after a certain period of time, in a certain way to cool the heat treatment process, tempering is followed by an operation after quenching, usually the final heat treatment of the workpiece A process, so the quenching and tempering of the joint process known as the final heat treatment. The main purpose of quenching and tempering is:
1) to reduce the internal stress and reduce the brittleness, quenching parts there is a lot of stress and brittleness, if not timely tempering often produce deformation or even cracking.
2) to adjust the mechanical properties of the workpiece, the workpiece after quenching, high hardness, brittleness, in order to meet the different performance requirements of various parts can be adjusted by tempering, hardness, strength, plasticity and toughness.
3) Stable workpiece size. Through the tempering can make the metallurgical organization tends to be stable, to ensure that the use of the process in the future no longer deformation.
4) to improve the cutting performance of some alloy steel.
In production, often based on the requirements of the workpiece performance. According to the different heating temperature, the tempering is divided into low temperature tempering, tempering tempering, and high temperature tempering. Quenching and subsequent high temperature tempering combined with the heat treatment process known as quenching and tempering, that is, with a high degree of strength at the same time, there are good plastic toughness. Mainly used to deal with the larger load of the machine structure parts, such as machine tool spindle, rear axle axle, strong gear and so on.
What is quenching?
Quenching is the metal into the material or parts heated to the phase transition temperature above, after insulation, to a greater than the critical cooling rate of the rapid cooling, in order to obtain martensite heat treatment process. Quenching is to get martensite, and then after tempering, the workpiece to obtain good performance, in order to give full play to the potential of the material. Its main purpose is:
1) improve the mechanical properties of metal or parts. For example: to improve the hardness of tools, bearings and wear resistance, improve the flexibility of the spring limit, improve the mechanical properties of shaft parts and so on.
2) to improve the performance of certain special steel material or chemical properties. Such as improving the corrosion resistance of stainless steel, increasing the permanent magnetism of the magnet.
Quenching and cooling, in addition to the need to choose a reasonable quenching medium, but also have the correct quenching method, commonly used quenching method, mainly single-liquid quenching, two-liquid quenching, grading quenching, isothermal quenching, local quenching and so on.
The difference and connection of "four fire"
Justification has the following purpose and use.
① Eutectoid steel, normalizing to eliminate casting, forging, welding overheating coarse grain structure and Wei's organization, rolling material in the ribbon; grain refinement; and can be used as pre-heat treatment before quenching.
② on the eutectoid steel, normalizing can eliminate reticular secondary cementite, and make pearlite refinement, not only to improve the mechanical properties, but also conducive to the subsequent ball annealing.
③ For low carbon deep drawing steel plate, normalizing can eliminate the free cementite in the grain boundary to improve its deep drawing performance.
④ low carbon steel and low carbon low alloy steel, the use of normalizing, can be more fine pearlite organization, so that the hardness increased to HB140-190, to avoid cutting the "stick knife" phenomenon, improve the machinability The Of medium carbon steel, in both the use of normalizing and annealing can be used, with Zhengrong more economical and convenient.
⑤ for ordinary carbon structural steel, in the mechanical performance requirements are not high occasions, can be used instead of quenching plus high temperature tempering tempering, not only easy to operate, but also the steel structure and size stability.
⑥ high temperature normalizing (Ac3 above 150 ~ 200 ℃) due to the high diffusion rate at high temperatures, can reduce the composition of castings and forging segregation. The coarse grains after high temperature normalizing can be refined by the subsequent second lower normalizing.
⑦ for some of the steam turbine and boiler low, medium carbon alloy steel, often used to obtain normal bainite bainite, and then by high temperature tempering, for 400 ~ 550 ℃ with good creep resistance.
⑧ In addition to steel and steel, normalizing is also widely used in ductile iron heat treatment, to obtain pearlite matrix, to improve the strength of ductile iron.
As the normalizing is characterized by air cooling, the ambient air temperature, stacking method, airflow and workpiece size have an effect on the organization and performance after normalizing. Normalizing the organization can also be used as a classification of alloy steel. Usually according to the diameter of 25 mm sample heated to 900 ℃, the air-cooled organization, the alloy steel is divided into pearlitic steel, bainitic steel, martensitic steel and austenitic steel.
Annealing is a metal heat treatment process in which the metal is slowly heated to a certain temperature, maintained for a sufficient time, and then cooled at a suitable speed. Annealing heat treatment is divided into complete annealing, incomplete annealing and stress relief annealing. The mechanical properties of the annealed material can be tested by tensile tests or by hardness tests. Many steel are annealed heat treatment state of supply, steel hardness testing can be used Rockwell hardness tester, test HRB hardness, for thin steel, steel and thin-walled steel pipe, you can use the surface Rockwell hardness tester, the detection of HRT hardness The
The purpose of annealing is:
① to improve or eliminate the steel in the casting, forging, rolling and welding process caused by a variety of tissue defects and residual stress, to prevent deformation of the workpiece, cracking.
② soften the workpiece for cutting.
③ fine grain, improve the organization to improve the mechanical properties of the workpiece.
④ for the final heat treatment (quenching, tempering) to prepare for the organization.
Commonly used annealing processes are:
① complete annealing. Used to refine the medium and low carbon steel after casting, forging and welding after the emergence of poor mechanical properties of the superheated tissue. The workpiece is heated to the total transformation of ferrite into austenite temperature above 30 ~ 50 ℃, holding for a period of time, and then slowly cooling with the furnace, the austenite in the cooling process changes again, you can make the steel tissue thinning The
Spherical annealing. To reduce the tool steel and bearing steel after forging high hardness. The workpiece heated to the beginning of the formation of austenite to the temperature above 20 ~ 40 ℃, slowly cooling after the insulation, in the process of pearlite in the lamellar cementite into a spherical shape, thereby reducing the hardness.
③ isothermal annealing. To reduce the high nickel, chromium content of high alloy steel structure of high hardness, for cutting. Generally first to a faster cooling to the most unstable temperature of austenite, holding the appropriate time, austenite into a twist or sorbite, hardness can be reduced.
④ recrystallization annealing. To eliminate the metal wire, thin plate in the cold drawing, cold rolling process of hardening (hardness, plastic decline). Heating temperature is generally the beginning of the formation of steel austenite temperature below 50 ~ 150 ℃, the only way to eliminate the hardening effect of the hardening of the metal.
⑤ Graphite annealing. Used to make a large number of cementite cast iron into a good plastic malleable cast iron. The process operation is to heat the casting to about 950 ℃, the insulation after a certain period of time appropriate cooling, so that the formation of cementite decomposition floc graphite.
⑥ diffusion annealing. To make the chemical composition of the alloy casting homogenization, improve its performance. The method is heated in the absence of melting under the premise of the casting heated to the highest possible temperature and long time to keep the alloy in the distribution of various elements tend to even after the distribution of slow cooling.
⑦ to stress annealing. To eliminate the internal stress of steel castings and weldments. For the steel products after heating began to form austenite temperature below 100 ~ 200 ℃, after cooling in the air cooling, you can eliminate the internal stress.
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