Vacuum quenching
2023-09-14 12:12:08
At present, some heat treatments are inseparable from the cleaning and drying process, especially the various types of heat treatments that require oil cooling. The task of cleaning and drying is more arduous and more difficult. The most effective cleaning agent in the world is a halogen-based cleaning agent. Vacuum heat treatment is a metal heat treatment process in which a metal workpiece is heated below 1 atmosphere (ie, under a negative pressure).
At the end of the 1920s, with the development of electric vacuum technology, a vacuum heat treatment process appeared, which was only used for annealing and degassing. Due to equipment limitations, this process has not made much progress for a long time. In the 1960s and 1970s, successively developed air-cooled vacuum heat treatment furnaces, cold-wall vacuum oil quenching furnaces and vacuum-heated high-pressure gas quenching furnaces, which made the vacuum heat treatment process a new development. Carburizing in a vacuum, the progress of carburizing, nitriding or infiltrating other elements under the action of a vacuum medium ion field, and further enhancing the application range by vacuum heat treatment.
Vacuum heat treatment can be used for annealing, degassing, solution heat treatment, quenching, tempering and precipitation hardening. It can also be used for chemical heat treatment after passing through a suitable medium.
Quenching in vacuum is both gas quenching and liquid quenching. Gas quenching is to cool the workpiece after heating in a vacuum to a high-purity neutral gas such as nitrogen. Suitable for gas quenching materials such as high-speed steel and high-carbon high-chromium steel with lower critical martensite cooling rate. The liquid quenching is to heat the workpiece in the heating chamber, then move it to the cooling chamber and fill it with high-purity nitrogen gas and immediately send it into the quenching oil tank for rapid cooling. If high surface quality is required, tempering and precipitation hardening of the workpiece after vacuum quenching and solution heat treatment should still be carried out in a vacuum furnace.
Vacuum high pressure gas quenching technology The current vacuum high pressure gas quenching technology has developed rapidly, and there have been negative pressure (<1×105Pa) high flow rate air cooling, pressure (1×105～4×105Pa) air cooling and high pressure ( 5×105～10×105Pa) Air-cooled, ultra-high pressure one (10×105～20×105Pa) air-cooling and other new technologies not only greatly improve the vacuum gas quenching ability, but also have good surface brightness and small deformation after quenching. It also has the advantages of high efficiency, energy saving and no pollution.
Vacuum high pressure gas quenching is used for quenching and tempering of materials, stainless steel "target=_blank> solid solution and aging of stainless steel and special alloys, ion carburizing and carbonitriding, as well as vacuum sintering, cooling after brazing and Quenching.
When quenching with 6×105Pa high pressure nitrogen, the cooled load can only be loose. The high speed steel (W6Mo5Cr4V2) can be hardened to 70-100mm, and the high alloy hot work die steel (such as 4Cr5MoSiV) can reach 25~100mm. Gold cold work die steel (such as Cr12) can reach 80 ~ 100mm.
When quenching with 10 x 105 Pa high pressure nitrogen, the cooled load can be dense, and the load density is increased by about 30% to 40% when cooled at 6 x 105 Pa.
When quenched by 20 x 105 Pa ultra-high pressure nitrogen or a mixture of helium and nitrogen, the cooled load is dense and can be bundled together. Its density is 80%~150% higher than that of 6×105Pa nitrogen cooling. It can cool all high speed steel, high alloy steel, hot work die steel and Cr13% chrome steel and more alloy oil quenched steel. Size 9Mn2V steel.
A dual chamber air-cooled quench furnace with a separate cooling chamber has a better cooling capacity than a single chamber furnace of the same type. The cooling effect of the 2 x 105 Pa nitrogen cooled dual chamber furnace is comparable to that of a 4 x 105 Pa single chamber furnace. However, operating costs and maintenance costs are low. As China's basic materials industry (graphite, molybdenum, etc.) and supporting components (motors) and other levels need to be improved. Therefore, while improving the quality of 6×105Pa single-chamber high-pressure vacuum protection, the development of dual-chamber pressurization and high-pressure gas-cooled quenching furnace is in line with China's national conditions.
Vacuum high pressure gas cooling austempering Large workpieces with complex shapes are prone to deformation or even cracks when continuously cooled from high temperature. In the past, it can be solved by austempering in a salt bath. Can air-cooled austempering in a single-chamber vacuum high-pressure gas-cooled quenching furnace? Fig. 1 is a comparison result of two sets of φ320mm×120mm two-piece stacked carbon structural steel quenched by different cooling methods in a single-chamber high-pressure gas-cooled quenching furnace with convection heating function. The set of curves in the figure is the result of continuous cooling with high purity nitrogen gas at a pressure of 6 x 105 Pa (the wind direction is alternating between upper and lower, and switching once in 40 s) after heating at 102 °C. The other group is controlled cooling at 370 ° C on the surface and core of the sample. It can be seen from the comparison of the two sets of curves that the temperature of the core passes through the time of 50 ° C (semi-cold time) only about 2 min. It takes 27 minutes from the time the surface is controlled to cool down until the heart temperature reaches 370 °C. It can be seen that isothermal gas quenching in a single chamber vacuum high pressure gas quenching furnace is feasible.
Vacuum nitriding technology vacuum nitriding is the use of a vacuum furnace to heat the steel parts as a whole, filling a small amount of gas, in the low pressure state, the active nitrogen atoms infiltrate and diffuse into the steel to achieve hardening; and ion nitriding is by the light The active N ions generated by the discharge bombard and heat only the surface of the steel parts, and a chemical reaction occurs to form a nucleation to achieve hardening.
During vacuum infiltration, after evacuating the vacuum furnace to a higher vacuum of 0.133 Pa (1×10-3 Torr), the workpiece is raised to 530-560 ° C, and is fed with ammonia-containing active material. A variety of composite gases, and precise control of the feed rate of various gases, the furnace pressure is controlled at 0.667Pa (5Torr), after 3 to 5 hours of heat preservation, rapid cooling is carried out with inert gas in the furnace. Different materials, after this treatment, can obtain a hardened layer having a depth of 20 to 80 μm and a hardness of 600 to 1500 HV.
Vacuum nitriding is known as vacuum venting nitrocarburizing, which is characterized by vacuum technology to activate and purify the metal surface. During the whole heat treatment process of heating, heat preservation and cooling, the impure trace gas is discharged, and the pure composite gas containing the active material is fed, which makes it possible to adjust and control the surface layer structure, improve the quality and improve the efficiency. . X-ray diffraction analysis confirmed that after vacuum nitriding treatment, the compound layer in the layer was ε single-phase structure, and no other brittle phases (such as Fe3C, Fe3O4) existed, so the hardness was high, the toughness was good, and the distribution was good. The hardness and material composition of the "white layer" single phase ε compound layer is related. The higher the amount of Cr in the material, the higher the hardness. When Cr13%, the hardness can reach 1200HV; when it contains Cr18% (mass fraction, the same), the hardness can reach 1500HV; when it contains 25% Cr, the hardness can reach 1700HV. The wear resistance of the single-phase ε compound layer without brittle phase is higher than that of the gas nitrocarburizing structure, and is excellent in anti-friction burn, heat-resistant, anti-welding and anti-melting properties. However, the existence of the "white layer" has disadvantages for some molds and parts, and it is easy to cause the forging die to cause cracking at the initial stage of forging, and it is easy to generate pinholes during welding repair. Vacuum nitriding also has the advantage that by controlling the type and amount of the composite gas containing the activating substance in the furnace, it is possible to obtain a structure having almost no compound layer (white layer) but only a diffusion layer. The reason may be that it is formed after the vacuum furnace is exhausted to 0.133 Pa (1 × 10 -3 Torr), and the other reason is that the composite gas with the active material diffuses into the formed structure in the steel in a short time. The advantage of this type of structure is that it is excellent in thermal shock resistance and crack resistance. Therefore, for high-temperature tempering hot work molds, such as high-speed steel or 4Cr4MoSiV (H13) steel mold can obtain high surface hardness, good wear resistance, good thermal shock resistance, crack resistance and toughness. However, when only the diffusion layer is organized, the mold's anti-seizure property, welding resistance, and melt loss performance are not good enough. Due to the different service conditions and performance requirements of the mold or mechanical parts, it is necessary to adjust the structure and properties of the surface layer during surface heat treatment. In addition to the application of vacuum nitriding, it has obvious effects on improving the performance of precision gears and mechanical parts and springs that require wear and corrosion resistance. The materials that can be treated are also widely used.
Vacuum cleaning and drying technology At present, some heat treatments are inseparable from the cleaning and drying process, especially the various types of heat treatments that require oil cooling. The task of cleaning and drying is more arduous and more difficult. The most effective cleaning agent in the world is a halogen-based cleaning agent. The ratio of the halogen-based cleaning agent used in developed countries such as Japan is shown in Table 1. Among them, trichloroethane and Freon have been banned due to their destruction of atmospheric ozone. Other halogen-based substances are also restricted from being used in the ecological environment, humans and animals. Therefore, countries are studying various alternative cleaning and drying technologies.
Vacuum water cleaning and drying technology is the mainstream in the development of alternative technologies, the principle of which is steam distillation and vacuum distillation. The steam distillation is a method in which water vapor is blown onto a workpiece having a substance such as oil-insoluble oil, and the volatile component such as oil is distilled off together with water. When this method is applied, the vapor of the volatile component such as oil occurs simultaneously with the water vapor, so the boiling point of the oil component is lowered. This is the use of azeotropic methods to form oil and fillers into low boiling materials, making it possible to wash at lower temperatures below the tempering temperature. The vacuum distillation is because when the steam is distilled under normal pressure, the vapor pressure of the oil is low, and the amount of oil volatilized with the water vapor is small. If steam distillation is carried out under vacuum, the boiling point of the oil will be further lowered. At the same time, the high-boiling heat-treated quenching oil can be washed and dried at the tempering temperature by steam distillation and vacuum distillation. This method is suitable for use in large and medium-sized enterprises and high-volume production lines, and the efficiency is relatively high. The disadvantage is the high cost of recovery and handling of the cleaning fluid and recycling.
Vacuum oil cleaning and drying technology refers to the use of light solvent oil with relatively high vapor pressure to dissolve and clean the lower vapor pressure cutting oil, stamping oil and quenching oil attached to the workpiece; The oil is separated by evaporation to achieve the purpose of washing. The choice of the solvent oil should be as high as possible, the viscosity should be low, and the grease attached to the workpiece to be cleaned has a strong dissolving ability; the workpiece is non-corrosive and the cost is low. Solvent oils Nos. 190 and 20O introduced in China's national standards can be used as a reference for selection.
Simply put, it is quenched in the true state, the surface is very good after treatment, and there is no oxidation.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
At the end of the 1920s, with the development of electric vacuum technology, a vacuum heat treatment process appeared, which was only used for annealing and degassing. Due to equipment limitations, this process has not made much progress for a long time. In the 1960s and 1970s, successively developed air-cooled vacuum heat treatment furnaces, cold-wall vacuum oil quenching furnaces and vacuum-heated high-pressure gas quenching furnaces, which made the vacuum heat treatment process a new development. Carburizing in a vacuum, the progress of carburizing, nitriding or infiltrating other elements under the action of a vacuum medium ion field, and further enhancing the application range by vacuum heat treatment.
Vacuum heat treatment can be used for annealing, degassing, solution heat treatment, quenching, tempering and precipitation hardening. It can also be used for chemical heat treatment after passing through a suitable medium.
Quenching in vacuum is both gas quenching and liquid quenching. Gas quenching is to cool the workpiece after heating in a vacuum to a high-purity neutral gas such as nitrogen. Suitable for gas quenching materials such as high-speed steel and high-carbon high-chromium steel with lower critical martensite cooling rate. The liquid quenching is to heat the workpiece in the heating chamber, then move it to the cooling chamber and fill it with high-purity nitrogen gas and immediately send it into the quenching oil tank for rapid cooling. If high surface quality is required, tempering and precipitation hardening of the workpiece after vacuum quenching and solution heat treatment should still be carried out in a vacuum furnace.
Vacuum high pressure gas quenching technology The current vacuum high pressure gas quenching technology has developed rapidly, and there have been negative pressure (<1×105Pa) high flow rate air cooling, pressure (1×105～4×105Pa) air cooling and high pressure ( 5×105～10×105Pa) Air-cooled, ultra-high pressure one (10×105～20×105Pa) air-cooling and other new technologies not only greatly improve the vacuum gas quenching ability, but also have good surface brightness and small deformation after quenching. It also has the advantages of high efficiency, energy saving and no pollution.
Vacuum high pressure gas quenching is used for quenching and tempering of materials, stainless steel "target=_blank> solid solution and aging of stainless steel and special alloys, ion carburizing and carbonitriding, as well as vacuum sintering, cooling after brazing and Quenching.
When quenching with 6×105Pa high pressure nitrogen, the cooled load can only be loose. The high speed steel (W6Mo5Cr4V2) can be hardened to 70-100mm, and the high alloy hot work die steel (such as 4Cr5MoSiV) can reach 25~100mm. Gold cold work die steel (such as Cr12) can reach 80 ~ 100mm.
When quenching with 10 x 105 Pa high pressure nitrogen, the cooled load can be dense, and the load density is increased by about 30% to 40% when cooled at 6 x 105 Pa.
When quenched by 20 x 105 Pa ultra-high pressure nitrogen or a mixture of helium and nitrogen, the cooled load is dense and can be bundled together. Its density is 80%~150% higher than that of 6×105Pa nitrogen cooling. It can cool all high speed steel, high alloy steel, hot work die steel and Cr13% chrome steel and more alloy oil quenched steel. Size 9Mn2V steel.
A dual chamber air-cooled quench furnace with a separate cooling chamber has a better cooling capacity than a single chamber furnace of the same type. The cooling effect of the 2 x 105 Pa nitrogen cooled dual chamber furnace is comparable to that of a 4 x 105 Pa single chamber furnace. However, operating costs and maintenance costs are low. As China's basic materials industry (graphite, molybdenum, etc.) and supporting components (motors) and other levels need to be improved. Therefore, while improving the quality of 6×105Pa single-chamber high-pressure vacuum protection, the development of dual-chamber pressurization and high-pressure gas-cooled quenching furnace is in line with China's national conditions.
Vacuum high pressure gas cooling austempering Large workpieces with complex shapes are prone to deformation or even cracks when continuously cooled from high temperature. In the past, it can be solved by austempering in a salt bath. Can air-cooled austempering in a single-chamber vacuum high-pressure gas-cooled quenching furnace? Fig. 1 is a comparison result of two sets of φ320mm×120mm two-piece stacked carbon structural steel quenched by different cooling methods in a single-chamber high-pressure gas-cooled quenching furnace with convection heating function. The set of curves in the figure is the result of continuous cooling with high purity nitrogen gas at a pressure of 6 x 105 Pa (the wind direction is alternating between upper and lower, and switching once in 40 s) after heating at 102 °C. The other group is controlled cooling at 370 ° C on the surface and core of the sample. It can be seen from the comparison of the two sets of curves that the temperature of the core passes through the time of 50 ° C (semi-cold time) only about 2 min. It takes 27 minutes from the time the surface is controlled to cool down until the heart temperature reaches 370 °C. It can be seen that isothermal gas quenching in a single chamber vacuum high pressure gas quenching furnace is feasible.
Vacuum nitriding technology vacuum nitriding is the use of a vacuum furnace to heat the steel parts as a whole, filling a small amount of gas, in the low pressure state, the active nitrogen atoms infiltrate and diffuse into the steel to achieve hardening; and ion nitriding is by the light The active N ions generated by the discharge bombard and heat only the surface of the steel parts, and a chemical reaction occurs to form a nucleation to achieve hardening.
During vacuum infiltration, after evacuating the vacuum furnace to a higher vacuum of 0.133 Pa (1×10-3 Torr), the workpiece is raised to 530-560 ° C, and is fed with ammonia-containing active material. A variety of composite gases, and precise control of the feed rate of various gases, the furnace pressure is controlled at 0.667Pa (5Torr), after 3 to 5 hours of heat preservation, rapid cooling is carried out with inert gas in the furnace. Different materials, after this treatment, can obtain a hardened layer having a depth of 20 to 80 μm and a hardness of 600 to 1500 HV.
Vacuum nitriding is known as vacuum venting nitrocarburizing, which is characterized by vacuum technology to activate and purify the metal surface. During the whole heat treatment process of heating, heat preservation and cooling, the impure trace gas is discharged, and the pure composite gas containing the active material is fed, which makes it possible to adjust and control the surface layer structure, improve the quality and improve the efficiency. . X-ray diffraction analysis confirmed that after vacuum nitriding treatment, the compound layer in the layer was ε single-phase structure, and no other brittle phases (such as Fe3C, Fe3O4) existed, so the hardness was high, the toughness was good, and the distribution was good. The hardness and material composition of the "white layer" single phase ε compound layer is related. The higher the amount of Cr in the material, the higher the hardness. When Cr13%, the hardness can reach 1200HV; when it contains Cr18% (mass fraction, the same), the hardness can reach 1500HV; when it contains 25% Cr, the hardness can reach 1700HV. The wear resistance of the single-phase ε compound layer without brittle phase is higher than that of the gas nitrocarburizing structure, and is excellent in anti-friction burn, heat-resistant, anti-welding and anti-melting properties. However, the existence of the "white layer" has disadvantages for some molds and parts, and it is easy to cause the forging die to cause cracking at the initial stage of forging, and it is easy to generate pinholes during welding repair. Vacuum nitriding also has the advantage that by controlling the type and amount of the composite gas containing the activating substance in the furnace, it is possible to obtain a structure having almost no compound layer (white layer) but only a diffusion layer. The reason may be that it is formed after the vacuum furnace is exhausted to 0.133 Pa (1 × 10 -3 Torr), and the other reason is that the composite gas with the active material diffuses into the formed structure in the steel in a short time. The advantage of this type of structure is that it is excellent in thermal shock resistance and crack resistance. Therefore, for high-temperature tempering hot work molds, such as high-speed steel or 4Cr4MoSiV (H13) steel mold can obtain high surface hardness, good wear resistance, good thermal shock resistance, crack resistance and toughness. However, when only the diffusion layer is organized, the mold's anti-seizure property, welding resistance, and melt loss performance are not good enough. Due to the different service conditions and performance requirements of the mold or mechanical parts, it is necessary to adjust the structure and properties of the surface layer during surface heat treatment. In addition to the application of vacuum nitriding, it has obvious effects on improving the performance of precision gears and mechanical parts and springs that require wear and corrosion resistance. The materials that can be treated are also widely used.
Vacuum cleaning and drying technology At present, some heat treatments are inseparable from the cleaning and drying process, especially the various types of heat treatments that require oil cooling. The task of cleaning and drying is more arduous and more difficult. The most effective cleaning agent in the world is a halogen-based cleaning agent. The ratio of the halogen-based cleaning agent used in developed countries such as Japan is shown in Table 1. Among them, trichloroethane and Freon have been banned due to their destruction of atmospheric ozone. Other halogen-based substances are also restricted from being used in the ecological environment, humans and animals. Therefore, countries are studying various alternative cleaning and drying technologies.
Vacuum water cleaning and drying technology is the mainstream in the development of alternative technologies, the principle of which is steam distillation and vacuum distillation. The steam distillation is a method in which water vapor is blown onto a workpiece having a substance such as oil-insoluble oil, and the volatile component such as oil is distilled off together with water. When this method is applied, the vapor of the volatile component such as oil occurs simultaneously with the water vapor, so the boiling point of the oil component is lowered. This is the use of azeotropic methods to form oil and fillers into low boiling materials, making it possible to wash at lower temperatures below the tempering temperature. The vacuum distillation is because when the steam is distilled under normal pressure, the vapor pressure of the oil is low, and the amount of oil volatilized with the water vapor is small. If steam distillation is carried out under vacuum, the boiling point of the oil will be further lowered. At the same time, the high-boiling heat-treated quenching oil can be washed and dried at the tempering temperature by steam distillation and vacuum distillation. This method is suitable for use in large and medium-sized enterprises and high-volume production lines, and the efficiency is relatively high. The disadvantage is the high cost of recovery and handling of the cleaning fluid and recycling.
Vacuum oil cleaning and drying technology refers to the use of light solvent oil with relatively high vapor pressure to dissolve and clean the lower vapor pressure cutting oil, stamping oil and quenching oil attached to the workpiece; The oil is separated by evaporation to achieve the purpose of washing. The choice of the solvent oil should be as high as possible, the viscosity should be low, and the grease attached to the workpiece to be cleaned has a strong dissolving ability; the workpiece is non-corrosive and the cost is low. Solvent oils Nos. 190 and 20O introduced in China's national standards can be used as a reference for selection.
Simply put, it is quenched in the true state, the surface is very good after treatment, and there is no oxidation.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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