The heat treatment process generally includes three processes of heating, heat preservation and cooling, and sometimes only heating and cooling processes. These processes are connected with each other and cannot be interrupted. Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. The earliest use of charcoal and coal as heat sources led to the use of liquid and gaseous fuels. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be used for direct heating, and can also be indirectly heated by molten salts or metals as well as floating particles.
When the metal is heated, the workpiece is exposed to air and oxidation and decarburization often occur (ie, the surface carbon content of the steel parts is reduced), which has a negative effect on the surface properties of the heat-treated parts. Thus metals should generally be heated in controlled atmospheres or protective atmospheres, in molten salts and in vacuum, and can also be protected by coating or packaging methods.
The heating temperature is one of the important process parameters of the heat treatment process. Selecting and controlling the heating temperature is a major issue in ensuring the quality of the heat treatment. The heating temperature varies depending on the metal material to be treated and the purpose of the heat treatment, but generally it is heated above the phase transition temperature to obtain a high temperature structure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain time, so that the temperature inside and outside the same, so that the complete transformation of the microstructure, this time is called the holding time. With high energy density heating and surface heat treatment, the heating rate is extremely fast, generally there is no holding time, and the heat treatment time of chemical heat treatment is often longer.
Cooling is also an indispensable step in the heat treatment process, and the cooling method differs depending on the process, mainly controlling the cooling rate. In general, the cooling rate of the annealing is the slowest, the normalized cooling rate is faster, and the quenching cooling rate is faster. However, there are different requirements depending on the type of steel. For example, hardened steel can be quenched with a normal cooling rate.
The metal heat treatment process can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each major category can be divided into several different heat treatment processes. Different heat treatment processes are used for the same metal to obtain different structures and thus have different properties. Steel is the most widely used metal in the industry, and the microstructure of steel is also the most complex. Therefore, there are many types of steel heat treatment processes.
The overall heat treatment is a metal heat treatment process that heats the entire workpiece and then cools at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel generally includes four basic processes of annealing, normalizing, quenching and tempering.
Annealing is to heat the workpiece to the appropriate temperature, according to the size of the material and the workpiece using different insulation time, and then slowly cooling, the purpose is to make the metal internal organization at or near equilibrium, to obtain good process performance and performance, or for further quenching Prepare for the organization. Normalizing is to heat the workpiece to a suitable temperature and then cool it in air. The effect of normalizing is similar to that of annealing, but the resulting structure is finer and is often used to improve the cutting performance of materials. It is also sometimes used for parts that do not require high quality. As a final heat treatment.
Quenching is the rapid heating of the workpiece after heating, in the water, oil or other inorganic salts, organic aqueous quenching medium such as rapid cooling. Hardened steel after hardening, but at the same time become brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept at a suitable temperature higher than room temperature and lower than 650°C for a long time and then cooled. This process is called tempering. Annealing, normalizing, quenching and tempering are the “four fires†in the overall heat treatment. Quenching and tempering are closely related to each other. They are often used together and are indispensable.
"Four fires" evolved with different heat treatment processes depending on the heating temperature and cooling method. In order to obtain a certain degree of strength and toughness, the process of combining quenching and high temperature tempering is called quenching and tempering. After some alloys are quenched to form supersaturated solid solutions, they are kept at a suitable temperature at room temperature or slightly higher for a longer period of time to increase the hardness, strength, or electrical magnetic properties of the alloy. This heat treatment process is called aging treatment.
Combining the pressure processing deformation with the heat treatment effectively and tightly, the method that the workpiece obtains good strength and toughness is called the deformation heat treatment; the heat treatment in the negative pressure atmosphere or the vacuum is called the vacuum heat treatment, it can not only make The workpiece is not oxidized, decarburization is not performed, the surface of the workpiece is kept clean after treatment, and the performance of the workpiece is improved, and the infiltration agent can also be used for chemical heat treatment.
Surface heat treatment is a metal heat treatment process that only heats the surface of the workpiece to change the mechanical properties of its surface. In order to heat only the surface of the workpiece without introducing excessive heat into the interior of the workpiece, the heat source used must have a high energy density, that is, a large amount of thermal energy is given to the workpiece per unit area, so that the surface or local area of ​​the workpiece can be short-time or instantaneous. Reach high temperatures. The main methods of surface heat treatment are flame quenching and induction heat treatment. Commonly used heat sources include oxyacetylene or oxygen propane flames, induced currents, lasers, and electron beams.
Chemical heat treatment is a metal heat treatment process that changes the chemical composition, texture, and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface layer of the workpiece. Chemical heat treatment is the workpiece placed in carbon, nitrogen or other alloying elements of the medium (gas, liquid, solid) heating, heat for a long time, so that the workpiece surface infiltration of carbon, nitrogen, boron and chromium and other elements. After infiltrating elements, other heat treatment processes such as quenching and tempering are sometimes performed. The main methods of chemical heat treatment are carburizing, nitriding, and infiltration of metals.
Heat treatment is one of the important processes in the manufacture of mechanical parts and tooling. In general, it can ensure and improve the various properties of the workpiece, such as wear and corrosion resistance. It can also improve the microstructure and stress state of the blank to facilitate various cold and hot processing.
For example, white cast iron can obtain malleable cast iron after long-time annealing to improve plasticity. The gears adopt the correct heat treatment process, and the service life can be increased by a factor of several times or several times compared to the heat-treated gears. In addition, the inexpensive carbon steel penetrates through.
When the metal is heated, the workpiece is exposed to air and oxidation and decarburization often occur (ie, the surface carbon content of the steel parts is reduced), which has a negative effect on the surface properties of the heat-treated parts. Thus metals should generally be heated in controlled atmospheres or protective atmospheres, in molten salts and in vacuum, and can also be protected by coating or packaging methods.
The heating temperature is one of the important process parameters of the heat treatment process. Selecting and controlling the heating temperature is a major issue in ensuring the quality of the heat treatment. The heating temperature varies depending on the metal material to be treated and the purpose of the heat treatment, but generally it is heated above the phase transition temperature to obtain a high temperature structure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain time, so that the temperature inside and outside the same, so that the complete transformation of the microstructure, this time is called the holding time. With high energy density heating and surface heat treatment, the heating rate is extremely fast, generally there is no holding time, and the heat treatment time of chemical heat treatment is often longer.
Cooling is also an indispensable step in the heat treatment process, and the cooling method differs depending on the process, mainly controlling the cooling rate. In general, the cooling rate of the annealing is the slowest, the normalized cooling rate is faster, and the quenching cooling rate is faster. However, there are different requirements depending on the type of steel. For example, hardened steel can be quenched with a normal cooling rate.
The metal heat treatment process can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each major category can be divided into several different heat treatment processes. Different heat treatment processes are used for the same metal to obtain different structures and thus have different properties. Steel is the most widely used metal in the industry, and the microstructure of steel is also the most complex. Therefore, there are many types of steel heat treatment processes.
The overall heat treatment is a metal heat treatment process that heats the entire workpiece and then cools at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel generally includes four basic processes of annealing, normalizing, quenching and tempering.
Annealing is to heat the workpiece to the appropriate temperature, according to the size of the material and the workpiece using different insulation time, and then slowly cooling, the purpose is to make the metal internal organization at or near equilibrium, to obtain good process performance and performance, or for further quenching Prepare for the organization. Normalizing is to heat the workpiece to a suitable temperature and then cool it in air. The effect of normalizing is similar to that of annealing, but the resulting structure is finer and is often used to improve the cutting performance of materials. It is also sometimes used for parts that do not require high quality. As a final heat treatment.
Quenching is the rapid heating of the workpiece after heating, in the water, oil or other inorganic salts, organic aqueous quenching medium such as rapid cooling. Hardened steel after hardening, but at the same time become brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept at a suitable temperature higher than room temperature and lower than 650°C for a long time and then cooled. This process is called tempering. Annealing, normalizing, quenching and tempering are the “four fires†in the overall heat treatment. Quenching and tempering are closely related to each other. They are often used together and are indispensable.
"Four fires" evolved with different heat treatment processes depending on the heating temperature and cooling method. In order to obtain a certain degree of strength and toughness, the process of combining quenching and high temperature tempering is called quenching and tempering. After some alloys are quenched to form supersaturated solid solutions, they are kept at a suitable temperature at room temperature or slightly higher for a longer period of time to increase the hardness, strength, or electrical magnetic properties of the alloy. This heat treatment process is called aging treatment.
Combining the pressure processing deformation with the heat treatment effectively and tightly, the method that the workpiece obtains good strength and toughness is called the deformation heat treatment; the heat treatment in the negative pressure atmosphere or the vacuum is called the vacuum heat treatment, it can not only make The workpiece is not oxidized, decarburization is not performed, the surface of the workpiece is kept clean after treatment, and the performance of the workpiece is improved, and the infiltration agent can also be used for chemical heat treatment.
Surface heat treatment is a metal heat treatment process that only heats the surface of the workpiece to change the mechanical properties of its surface. In order to heat only the surface of the workpiece without introducing excessive heat into the interior of the workpiece, the heat source used must have a high energy density, that is, a large amount of thermal energy is given to the workpiece per unit area, so that the surface or local area of ​​the workpiece can be short-time or instantaneous. Reach high temperatures. The main methods of surface heat treatment are flame quenching and induction heat treatment. Commonly used heat sources include oxyacetylene or oxygen propane flames, induced currents, lasers, and electron beams.
Chemical heat treatment is a metal heat treatment process that changes the chemical composition, texture, and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface layer of the workpiece. Chemical heat treatment is the workpiece placed in carbon, nitrogen or other alloying elements of the medium (gas, liquid, solid) heating, heat for a long time, so that the workpiece surface infiltration of carbon, nitrogen, boron and chromium and other elements. After infiltrating elements, other heat treatment processes such as quenching and tempering are sometimes performed. The main methods of chemical heat treatment are carburizing, nitriding, and infiltration of metals.
Heat treatment is one of the important processes in the manufacture of mechanical parts and tooling. In general, it can ensure and improve the various properties of the workpiece, such as wear and corrosion resistance. It can also improve the microstructure and stress state of the blank to facilitate various cold and hot processing.
For example, white cast iron can obtain malleable cast iron after long-time annealing to improve plasticity. The gears adopt the correct heat treatment process, and the service life can be increased by a factor of several times or several times compared to the heat-treated gears. In addition, the inexpensive carbon steel penetrates through.
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