What is the pur***e of bearing heat treatment?
(1) The application scope of GCr15 steel has been expanded. Generally, the effective wall thickness of the ferrule when GCr15 steel m is quenched is less than 12mm, but due to the strong cooling capacity of nitrate salt during BL quenching, if measures such as stirring, series action and adding water are adopted, the effective wall thickness of the ferrule can be expanded to about 28 mm.
(2) Stable hardness and good uniformity
Because BL transformation is a slow process, generally GCr15 steel takes 4h, GCr18Mo steel takes 5h, the ferrule is isothermal in nitrate for a long time, and the surface and core structure transformation is almost carried out at the same time, so the hardness is stable and uniformity is good. Generally, the hardness of GCr15 steel bl after quenching is 59~61hrc, and the uniformity is ≤ 1 HRC, unlike the problems of low hardness, soft spots, poor uniformity and so on when the ferrule wall thickness is slightly larger during quenching.
(3) Reduce quenching and grinding cracks
In the production of railway and rolling mill bearings, due to the large size and heavy weight of the ferrule, the M structure is brittle during oil quenching. In order to obtain high hardness after quenching, strong cooling measures are often taken, resulting in quenching microcracks; During BL quenching, the toughness of BL structure is much better than that of M structure, and the compressive stress of -400~-500mpa is formed on the surface, which greatly reduces the tendency of quenching cracks; During grinding, the surface compressive stress counteracts part of the grinding stress, reduces the overall stress level, and greatly reduces the grinding cracks.
(4) Increase the service life of bearings
For railway and rolling mill bearings that bear large impact loads, the main failure forms when used after M quenching are: inner sleeve cracking during assembly, outer ring flange falling off and inner ring cracking during use, while isothermal quenched bearings have good impact toughness and surface compressive stress, no matter whether the inner sleeve cracking during assembly or the tendency of outer sleeve flange falling off and inner sleeve cracking during use is greatly reduced, And it can reduce the edge stress concentration of the roller. Therefore, the average service life and reliability after isothermal quenching are higher than those after M quenching. Provided by Longma bearing