The development direction of bearing materials and heat treatment in China is as follows:
1. Improve smelting technology to improve the cleanliness and uniformity of steel
Compared with industrial developed countries, although the oxygen content of bearing steel in China is close to the foreign advanced level, there is still a big gap between the uniformity and composition uniformity of inclusions and carbide size and distribution, such as large size. The inclusions and carbides are more, the basic components are uneven, and the black and white area is formed, which causes the bearing parts to be innately deficient, which seriously affects the bearing life, reliability and consistency.
In addition, the presence of large-sized inclusions on the rolling contact surface severely reduces surface accuracy and increases bearing noise. To this end, the bearing industry should negotiate with the metallurgical industry to enable the metallurgical industry to carry out research on casting solidification technology, rolling technology, inclusion control and detection technology on the basis of further reducing oxygen content, such as improving electromagnetic stirring during continuous casting. Add the size of Dalian slab, strengthen high temperature diffusion annealing, etc., to improve the size and distribution uniformity of inclusions and carbides.
Second, the development and promotion of new steel grades to meet the requirements of different bearings
With the miniaturization, light weight and high speed of the mainframe, the use environment of the bearing is more and more diversified, and the requirements on the bearing are becoming more and more demanding. At present, the existing steel grades in China cannot meet or can not fully satisfy the bearing of the main engine. The requirements, for this, should actively carry out the development and promotion of new materials. Such as the development of high-hardenability steel for large-size bearings, heavy-duty and clean lubrication conditions, steel for bearings used under small and lightweight conditions, high-carbon steel and carburized steel for bearings used under polluted conditions, quasi-high temperature ( Steel for bearings (stainless steel, high temperature steel) used for bearing steel and special conditions under operating conditions of 200 ° C or less.
Third, research and promotion of new heat treatment processes
Bainite quenching
The bainite austempered bearing has a good impact toughness and a compressive stress on the surface. The tendency of the inner sleeve to be cracked during assembly or the tendency of the outer side of the casing to be broken and the inner sleeve to be broken is greatly reduced. Reduce the stress concentration at the edge of the roller. Therefore, the average life and reliability of the bearing after austempering is significantly higher than that after conventional quenching. This process is widely used in railway bearings, rolling mill bearings and bearings used under special conditions. Compared with other life extension measures, this process is simple in process and low in cost. In recent years, China has developed a new steel gcr18mo bainite quenching special steel to promote the application of bainite quenching in large-size bearing parts. In view of the many advantages of this process, it is recommended to promote the use of bearings with poor conditions (large impact load, poor lubrication, etc.) or high reliability, and further study the wear resistance and fatigue life after bainite treatment.
2. Surface carbonitriding
In the 1980s, Luoyang Bearing Research Institute carried out research on martensitic stress quenching of bearing steel. By special carbonitriding and quenching of high carbon chromium bearing steel parts, the content of surface retained austenite was improved and improved. The surface stress state greatly improves the carbonitriding of the gearbox, and improves the residual austenite content on the surface without reducing the surface hardness, so as to improve the fatigue life and reliability of the bearing under the contaminated lubrication condition.
Fourth, surface modification technology
Improve surface properties with proper surface treatment to meet bearing performance requirements under special conditions. Such as the use of vapor deposition technology on the bearing raceway coated with diamond coating can achieve the effect of friction reduction, wear resistance, greatly improve the bearing wear life and accuracy maintenance performance, can be promoted in household appliances bearings, computer hard drive bearings; The use of thermal coating technology to coat the outer cylindrical surface of the bearing outer ring of alumina ceramic material can improve the electrical insulation performance of the bearing, prevent electric shock, improve the life and reliability of the motor bearing; sulphur or deposit mos2 on the surface of the bearing parts Achieve friction reducing lubrication.
5. Heat treatment equipment and related technologies
1. Atmosphere and control
It is heated by a controlled atmosphere to control the carbon potential and nitrogen potential in a controlled atmosphere. The performance of the parts after heat treatment is improved, and heat treatment defects such as decarburization and cracking are greatly reduced. Combined with heat treatment quenching deformation control technology, it can reduce the finishing allowance after heat treatment, improve material utilization and machining efficiency, and improve the surface condition of bearing parts after finishing, such as carbon content, microstructure, hardness and stress state of the surface. Wait.
2. Automation and intelligence
On the one hand, according to the use requirements of the parts, materials, structural dimensions, the use of physical metallurgical knowledge and advanced computer simulation and detection technology, optimize the process parameters to achieve the required performance or maximize the potential of the material; on the other hand, improve The degree of automation and stability of the heat treatment fully guarantees the stability of the optimized process and achieves the goal of small (or zero) dispersion of the product quality, thereby meeting the performance requirements of the host under different conditions of use, improving the reliability and life of the bearing. .
Sixth, deformation and dimensional stability
During the martensite quenching process, due to the uneven cooling of the parts, inevitably, thermal stress and tissue stress appear to cause deformation of the parts. The deformation of the part after quenching and tempering (including dimensional changes and shape changes) is affected by many factors, such as the shape and size of the part, the uniformity of the original structure, and the roughing state before quenching. The size of the tool, the residual stress of machining, etc.), the heating rate and temperature during quenching, the way the workpiece is placed, the mode of oiling, the characteristics of the quenching medium and the circulation mode, and the temperature of the medium all affect the deformation of the part. The deformation should be studied in combination with specific equipment and products, and measures to control deformation, such as rotary quenching, die quenching, and control of part oiling, etc., can be used to reduce heat treatment deformation and improve processing efficiency and part performance.
After martensite quenching, the dimensional stability of the part is mainly affected by three different transformations: carbon migration from the martensite lattice to form ε-carbide, residual austenite decomposition and formation of fe3c. Superimposed. Between 50 and 120 ° C, due to the precipitation of ε-carbide, the volume of the part is reduced. The general part has completed this transformation after tempering at 150 ° C, which affects the dimensional stability of the part after use. It can be neglected; between 100 and 250 °C, the residual austenite decomposes and transforms into martensite or bainite, which will be accompanied by a volume increase; above 200 °C, ε-carbide transforms into cementite, resulting in The part size is reduced. Studies have shown that retained austenite decomposes at the external load or at a lower tempering temperature (even at room temperature), resulting in dimensional changes in the part. Therefore, in actual use, the firing temperature of all bearing parts should be higher than the operating temperature of 50 ° C. For parts with higher dimensional stability, the content of retained austenite should be reduced as much as possible, and the storage and use should be improved. Dimensional stability, accuracy, longevity and reliability.
1. Improve smelting technology to improve the cleanliness and uniformity of steel
Compared with industrial developed countries, although the oxygen content of bearing steel in China is close to the foreign advanced level, there is still a big gap between the uniformity and composition uniformity of inclusions and carbide size and distribution, such as large size. The inclusions and carbides are more, the basic components are uneven, and the black and white area is formed, which causes the bearing parts to be innately deficient, which seriously affects the bearing life, reliability and consistency.
In addition, the presence of large-sized inclusions on the rolling contact surface severely reduces surface accuracy and increases bearing noise. To this end, the bearing industry should negotiate with the metallurgical industry to enable the metallurgical industry to carry out research on casting solidification technology, rolling technology, inclusion control and detection technology on the basis of further reducing oxygen content, such as improving electromagnetic stirring during continuous casting. Add the size of Dalian slab, strengthen high temperature diffusion annealing, etc., to improve the size and distribution uniformity of inclusions and carbides.
Second, the development and promotion of new steel grades to meet the requirements of different bearings
With the miniaturization, light weight and high speed of the mainframe, the use environment of the bearing is more and more diversified, and the requirements on the bearing are becoming more and more demanding. At present, the existing steel grades in China cannot meet or can not fully satisfy the bearing of the main engine. The requirements, for this, should actively carry out the development and promotion of new materials. Such as the development of high-hardenability steel for large-size bearings, heavy-duty and clean lubrication conditions, steel for bearings used under small and lightweight conditions, high-carbon steel and carburized steel for bearings used under polluted conditions, quasi-high temperature ( Steel for bearings (stainless steel, high temperature steel) used for bearing steel and special conditions under operating conditions of 200 ° C or less.
Third, research and promotion of new heat treatment processes
Bainite quenching
The bainite austempered bearing has a good impact toughness and a compressive stress on the surface. The tendency of the inner sleeve to be cracked during assembly or the tendency of the outer side of the casing to be broken and the inner sleeve to be broken is greatly reduced. Reduce the stress concentration at the edge of the roller. Therefore, the average life and reliability of the bearing after austempering is significantly higher than that after conventional quenching. This process is widely used in railway bearings, rolling mill bearings and bearings used under special conditions. Compared with other life extension measures, this process is simple in process and low in cost. In recent years, China has developed a new steel gcr18mo bainite quenching special steel to promote the application of bainite quenching in large-size bearing parts. In view of the many advantages of this process, it is recommended to promote the use of bearings with poor conditions (large impact load, poor lubrication, etc.) or high reliability, and further study the wear resistance and fatigue life after bainite treatment.
2. Surface carbonitriding
In the 1980s, Luoyang Bearing Research Institute carried out research on martensitic stress quenching of bearing steel. By special carbonitriding and quenching of high carbon chromium bearing steel parts, the content of surface retained austenite was improved and improved. The surface stress state greatly improves the carbonitriding of the gearbox, and improves the residual austenite content on the surface without reducing the surface hardness, so as to improve the fatigue life and reliability of the bearing under the contaminated lubrication condition.
Fourth, surface modification technology
Improve surface properties with proper surface treatment to meet bearing performance requirements under special conditions. Such as the use of vapor deposition technology on the bearing raceway coated with diamond coating can achieve the effect of friction reduction, wear resistance, greatly improve the bearing wear life and accuracy maintenance performance, can be promoted in household appliances bearings, computer hard drive bearings; The use of thermal coating technology to coat the outer cylindrical surface of the bearing outer ring of alumina ceramic material can improve the electrical insulation performance of the bearing, prevent electric shock, improve the life and reliability of the motor bearing; sulphur or deposit mos2 on the surface of the bearing parts Achieve friction reducing lubrication.
5. Heat treatment equipment and related technologies
1. Atmosphere and control
It is heated by a controlled atmosphere to control the carbon potential and nitrogen potential in a controlled atmosphere. The performance of the parts after heat treatment is improved, and heat treatment defects such as decarburization and cracking are greatly reduced. Combined with heat treatment quenching deformation control technology, it can reduce the finishing allowance after heat treatment, improve material utilization and machining efficiency, and improve the surface condition of bearing parts after finishing, such as carbon content, microstructure, hardness and stress state of the surface. Wait.
2. Automation and intelligence
On the one hand, according to the use requirements of the parts, materials, structural dimensions, the use of physical metallurgical knowledge and advanced computer simulation and detection technology, optimize the process parameters to achieve the required performance or maximize the potential of the material; on the other hand, improve The degree of automation and stability of the heat treatment fully guarantees the stability of the optimized process and achieves the goal of small (or zero) dispersion of the product quality, thereby meeting the performance requirements of the host under different conditions of use, improving the reliability and life of the bearing. .
Sixth, deformation and dimensional stability
During the martensite quenching process, due to the uneven cooling of the parts, inevitably, thermal stress and tissue stress appear to cause deformation of the parts. The deformation of the part after quenching and tempering (including dimensional changes and shape changes) is affected by many factors, such as the shape and size of the part, the uniformity of the original structure, and the roughing state before quenching. The size of the tool, the residual stress of machining, etc.), the heating rate and temperature during quenching, the way the workpiece is placed, the mode of oiling, the characteristics of the quenching medium and the circulation mode, and the temperature of the medium all affect the deformation of the part. The deformation should be studied in combination with specific equipment and products, and measures to control deformation, such as rotary quenching, die quenching, and control of part oiling, etc., can be used to reduce heat treatment deformation and improve processing efficiency and part performance.
After martensite quenching, the dimensional stability of the part is mainly affected by three different transformations: carbon migration from the martensite lattice to form ε-carbide, residual austenite decomposition and formation of fe3c. Superimposed. Between 50 and 120 ° C, due to the precipitation of ε-carbide, the volume of the part is reduced. The general part has completed this transformation after tempering at 150 ° C, which affects the dimensional stability of the part after use. It can be neglected; between 100 and 250 °C, the residual austenite decomposes and transforms into martensite or bainite, which will be accompanied by a volume increase; above 200 °C, ε-carbide transforms into cementite, resulting in The part size is reduced. Studies have shown that retained austenite decomposes at the external load or at a lower tempering temperature (even at room temperature), resulting in dimensional changes in the part. Therefore, in actual use, the firing temperature of all bearing parts should be higher than the operating temperature of 50 ° C. For parts with higher dimensional stability, the content of retained austenite should be reduced as much as possible, and the storage and use should be improved. Dimensional stability, accuracy, longevity and reliability.
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