(1) Expand the scope of application of GCr15 steel

Generally GCr15 bearing steel ferrule M Hardening Effective wall thickness of 12mm or less. But BL nitrate quenching due to the strong cooling capacity, the use of a stirring, string action, water and other measures, the effective wall thickness of the rings can be expanded to about 28mm.

(2) Hardness stability, good uniformity

Since BL change is a slow process, generally GCr15 steel required 4h, GCr18Mo steel demand 5h, ferrule nitrate isothermal long time, the surface of the heart tissue transformation unit almost simultaneously, thereby stabilizing bearing hardness, good uniformity, general GCr15 steel BL after quenching hardness 59 ~ 61HRC, uniformity ≤1HRC, unlike when the thickness slightly larger M quench rings appeared low hardness, soft spots, and poor uniformity.

(3) Reduce quenching, grinding cracks

Railway, rolling bearing production, since the ring size, heavy weight, when oil quenching M tissue brittleness, in order to obtain a high hardness after quenching cooling often take strong measures, resulting in quenching microcracks; while BL quenching, due BL M tissue toughness is much better than the organization, while the surface of up to -400 ~ -500MPa compressive stress, which greatly reduces the tendency of quenching cracks [19]; ​​when the grinding surface compressive stress offset some of the grinding stress that overall stress levels drop, greatly reducing the grinding cracks.

Improve (4) bearing life

To withstand large impact loads of railways, rolling bearings, the main failure after quenching using M form: sets of cracks within the assembly, the process of using the outer wall by the impact off the block, inner fragmentation, and isothermal quenching bearings due to the impact toughness, surface stress, regardless of when the inner sleeve assembly cracking, or use coat ribs off the block, inner sleeve fragmentation tendency is greatly reduced, and can reduce the roller edge stress concentration. Thus, after quenching temperature, etc. and reliability higher than the average life expectancy after M quenching.