The quality of stainless steel bearing depends on the quality of chrome steel, and the quality of chrome steel mainly consider its purity which is the surface quality, homogeneity, and the content of inclusions in steel of chrome steel, including dimensional accuracy and surface crack. The problem of dimensional accuracy mainly resolved at smelting stage. What’s more, the surface quality of chrome steel is closely related to heat treatment process. Heat treatment process is most important process to implement bearings’ performance and longevity. The quality of chrome steel’s heat treatment process directly affects the subsequent machining process and eventually, affecting stainless steel bearing’s precision and longevity.
The type of bearing’s heat treatment process
（1）Cleaning heat treatment
Cleaning heat treatment can solve the environmental pollution problems such as waste water, waste gas, waste salts, dust, noise, electromagnetic radiation pollution and others. It is also one of the heat treatment technology development directions in the developed countries. Currently, most of countries eliminate the use of coal as fuel, less and less of heavy oil, more and more in the use of light oil. Natural gas is most optimal fuel in cleaning heat treatment technology.
(2)Precision heat treatment
On one hand, precision heat treatment based on bearing’s operation requirements, materials, structure size, the use of physical metallurgy knowledge, advanced computer simulation and testing technology and then to reach the required performance or maximize the potential of materials. On the other hand, it refers to fully ensure the stability of the process optimization, ensure the product’s quality achieve minimal dispersion and minimal heat distortion zero.
(3)Energy saving heat treatment
Lily-bearing thinks scientific production and energy management are two basic elements of affecting the use of energy. Establishing professional heat treatment factory to ensure fully production, and putting good use of the equipment capacity is the choice of scientific management. In terms of heating treatment energy structure, choosing primary energy first, making full use of waste heat, after heat, use the low-energy, short cycle process to take place of energy consumption, long cycle technology.
(4)Less non-oxidation heat treatment
By the use of protective atmosphere heating instead of oxidizing atmosphere heating, it can accurately control carbon atmosphere and nitrogen potential to control atmosphere. After heat treatment, the performance of the parts are improved, heat treatment defects such as decarbonization and cracks decrease greatly, finishing allowance reduced, and it also improved the utilization rate of material and machining efficiency. Vacuum heating gas quenching, vacuum or low pressure carburizing , nitriding, nitrocarburizing and boriding can significantly improve quality, reduce distortion and improve longevity.
The effect of heat treatment technology
In the production of railway and rolling mill bearing, owing to ring’s large size, heavy weight, oil quenching, GCr15’s large steel organization brittleness, to obtain high hardness after quenching, we often take strong cooling measures, which result in quenching cracks. Because GCr18Mo’s steel organization tenacity is better than GCr15 steel, when GGR18Mo quenches,its surface up to 400~500Mpa simultaneously, and reducing the quenching crack tendency greatly. When grinding, its surface stress offset some of the grinding stress, which decrease the overall stress levels , greatly reducing the grinding cracks.
For railway and rolling mill bearin which need to bear heavy impact load, after GCr15 steel quenching, the main failure forms are as followed: the inner ring cracks when it assembling, the outer ring flange block out and inner ring cracks owing to stress in the using process. But for austempering bearings, because of its good toughness and without pressure of surface, it improves the inner ring’s cracking, outer ring’s block out , inner ring’s cracking tendency, and it will also reduce the roller edge stress concentration. Therefore, after austempering, GCr15 steel’s working life improved a lot.