4. The re-emergence of carburized automotive bearings
The high-quality comprehensive mechanical properties of the bearing after carburizing are irreplaceable by other bearing materials, so carburized steel becomes the material of choice for high-end automotive bearings. The use of carburized steel for automotive bearings was popular in the 1980s. At that time, some domestic enterprises began to import heat treatment and carburizing equipment for complete sets of bearings. Later, with the improvement of the quality of high-carbon chromium bearing steel smelting, the initial development of the domestic automotive industry, the domestic low-end models required a large number of low-cost high-carbon chrome bearing steel bearings, and carburized automotive bearings were temporarily put on hold. In recent years, with the large number of foreign auto giants in China, the overall level of the domestic auto industry has improved, carburizing automotive bearings have been re-proposed, carburizing automotive bearings in the future will be in the safety factor of military vehicles, passenger cars and other key A large number of parts are used. Automotive carburizing bearings commonly used materials 20CrMnTi, 20CrNiMoA, etc., carburizing temperature are 900 ~ 930 °C. The high heat treatment costs of carburized automotive bearings limit their widespread adoption. Domestic companies have also begun to experiment with new carburizing processes, such as high temperature carburizing, that is, carburizing at 1000 ° C or 1050 ° C, can greatly shorten the carburizing time and reduce costs. However, due to the restriction of carburizing equipment, it is only at the trial stage, and it will take time to promote it in large quantities.
In addition, the development of the carburizing process of GCr15 bearing steel also provides a new idea for the use of high carbon chromium bearing steel.
5. Effectively in line with international standards
The domestic bearing heat treatment uses the most extensive JB/T1255-2000 "High Carbon Chromium Bearing Steel Rolling Bearing Parts Heat Treatment Technical Conditions" standard, and has to undergo a ten-year revision. At the bearing heat treatment industry conference held in Xi'an in 2009, the bearing standard unit, Luoyang Bearing Research Institute, has clearly proposed the revision requirements of the JB/T1255-2000 standard, the mesh carbide grade, the amount of retained austenite, and the The depth of the carbon layer and the field of view of the quenched and tempered martensite structure are revised to meet international standards. This standard revision should be completed within the next year. The revised JB/T1255-2000 standard will have a huge impact on the entire bearing industry.
The clearness of the reticular carbide over-grade level of 2.5 will prompt the bearing manufacturers to impose stricter requirements on the bearing steel production enterprises. After the steel plant increases the normalizing process, it will increase the bearing steel manufacturing cost and ultimately increase the bearing manufacturing cost. .
The tightening of the decarburization layer depth control will increase the promotion of the protective atmosphere heat treatment equipment, which will be beneficial to the improvement of bearing quality in China for a long time. The survival of some small bearing manufacturers will now be challenged.
To reduce the residual austenite content, the easiest way to do this is to increase the secondary water cooling treatment below 10 °C after quenching. Since the amount of retained austenite is clearly defined in the standard, there are few secondary cooling devices for the continuous heat treatment equipment of each bearing manufacturer. For example, the equipment layout is too compact and the transformation is quite difficult.
The standard organization picture field is changed from 500 times to 1000 times, which can improve the accuracy of the organization judgment, and the implementation is not difficult.
Every revision of the standard is fundamentally reflected in the interests of domestic leading bearing manufacturers. It is conceivable that this standard will eventually contribute to the further integration of the bearing industry.
In addition, automotive bearings, as an important branch of bearings, should have independent standards that are suitable for the characteristics of the automotive industry. These are achievable through the tireless efforts of automotive bearing workers.
Third, heat treatment equipment
Quenching and tempering equipment
With the private enterprises in the 1990s, the imitation, technical digestion, and partial renewal of the protective atmosphere furnaces such as the Muffle-type (trailer) mesh belt furnace, the casting chain furnace and the pusher furnace. The domestic heat treatment equipment production technology has been rapidly improved. After 2000, the domestic heat treatment equipment production technology has been basically mature, basically meeting the bearing production needs. In recent years, a large number of protective atmosphere devices have been widely used. In addition, the pressure swing adsorption and membrane nitrogen production technologies have matured, and the production mode of heat treatment quenching and tempering of small and medium-sized automobile bearings with nitrogen-based protective atmosphere has been basically formed. Its main advantages are high production efficiency and low energy consumption. For large-scale automotive bearings, more roller furnaces, multi-purpose furnaces and rotary hearth furnaces are used. The original old-fashioned equipment such as box furnace, salt bath furnace, drum furnace and imitation type K air heating furnace have been basically eliminated.
2. Annealing equipment
The protective atmosphere has low energy consumption, and can achieve little or no oxidation after annealing, which has a significant guarantee for improving the material utilization rate of bearing parts. Since the domestic precision forging technology is rarely used in bearing production, the promotion of protective atmosphere annealing is limited. In the long run, the energy-saving material-saving process of precision forging technology + protective atmosphere annealing is the development direction of bearing annealing in the future.
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