(1) expand the application range of GCr15 steel, GCr15 steel M general quenching ring effective wall thickness below 12mm, but the BL quenching due to nitrate cooling ability, if the mixing, series, water and other measures, effective wall thickness of ring can be expanded to about 28mm.
(2) stable hardness, good uniformity due to BL change is a slow process, generally GCr15 to 4h steel, GCr18Mo steel 5h, ring isothermal long time in nitrate in surface, change heart tissue were almost at the same time, so the stable hardness, good uniformity, general BL GCr15 steel quenched hardness in 59~61HRC, uniformity ≤ 1HRC, unlike the quenching ring wall thickness slightly larger problems of low hardness, soft point, poor uniformity.
(3) reduce the quenching, grinding cracks in the production of railway, rolling mill bearing ferrule, because of large size, heavy weight, oil quenching M brittleness, in order to obtain high hardness after quenching often adopt strong cooling measures, resulting in the quenching crack quenching; while BL, because the BL tissue than in M tissue toughness much, also formed on the surface of up to -400~-500MPa compressive stress, which greatly reduces the quenching cracking tendency; the grinding surface compressive stress to offset a portion of the grinding stress, so that the overall stress levels down, greatly reducing the grinding crack.
(4) the service life of the bearing to bear large impact load of railway, rolling bearings, the M quenching when used after the main failure modes are: assembly sleeve cracking, affected by the impact of external flange off block, the inner ring fragmentation in the use process, and the isothermal quenching bearing due to the impact ductility, compressive surface stress both the assembly sleeve, cracking, or in the process of using the jacket rib off block, the inner sleeve fracture tendency is greatly reduced, and can reduce the roller edge stress concentration. Therefore, isothermal quenching ratio increase the average life and reliability of M after quenching.