The application range of GCr15 steel has been expanded. Generally, the effective wall thickness of the ring is below 12mm when GCr15 steel M is quenching.however, due to the strong cooling capacity of nitro salt in BL quenching, the effective wall thickness of the ring can be expanded to about 28mm if mixing, stringing and adding water are adopted.
Stable hardness, good uniformity: because BL transformation is a slow process, generally GCr15 steel needs 4h, GCr18Mo steel needs 5h, ferrules in nitro salt for a long time isothermal, surface core tissue transformation almost at the same time, so the hardness is stable, good uniformity, generally GCr15 steel BL quenching hardness in 59 ~ 61HRC, uniformity ≤1HRC.
Reducing quenching and grinding cracks in the production of railway and rolling mill bearings, due to the large size and heavy weight of the rings, the M structure is brittle when oil is quenched. In order to obtain high hardness after quenching, strong cooling measures are often taken, resulting in quenching micro-cracks.Since the surface of M is tensile stress after quenching, the superposition of grinding stress during grinding process makes the overall stress level increase, and it is easy to form grinding cracks, resulting in batch waste.However, when BL is quenched, the toughness of BL tissue is much better than that of M tissue. At the same time, the compressive stress on the surface is up to -400 ~ -500 mpa, which greatly reduces the quenching crack tendency.During grinding, the surface compressive stress offsets part of the grinding stress, which reduces the overall stress level and greatly reduces the grinding crack.
Improve the service life of bearing to bear large impact load of railroad, rolling mill bearings, etc., after M quenching when using main failure forms is: inner sleeve cracking when assembling, use in the process of impact outer ring, inner ring fracture, falling guard and isothermal quenching bearing with good impact toughness, surface compressive stress, whatever the assembly inner sleeve craze, or using Chinese and foreign set of guard metal shed and inner sleeve fracture tendency is greatly reduced, and can reduce the edge stress concentration of roller.Therefore, the average life and reliability are improved after isothermal quenching than after M quenching.
Carburizing, nitriding and carbonitriding
Low pressure carburizing process for carburizing, nitriding and co-carburizing acetylene of low carbon steel
Residual stress of carburizing or carbonitriding in high carbon chromium bearing steel
Surface modification technology
Surface coating physical vapor deposition (PVD) chemical vapor deposition (CVD), rf sputtering, ion spraying, electroless plating, etc
Heat treatment of large bearings with surface heating and quenching
The surface is hard and wear-resisting martensite, the heart is good toughness of sostenite, troostite
The quenching deformation and hardness inhomogeneity of large bearing rings are reduced