Heat treatment technology application effect
(1) Expanding the range of GCr15 steel applications
Generally, the effective wall thickness of the ferrule of GCr15 steel M is 12mm or less when quenched, but due to the strong cooling capacity of the nitrate salt during the BL quenching, the effective wall thickness of the ferrule can be enlarged to about 28mm if measures such as stirring, stringing and watering are adopted.
Since the BL transformation is a slow process, generally GCr15 steel needs 4h, GCr18Mo steel needs 5h, ferrules in isothermal salt nitrate for a long time, the surface of the heart and heart tissue changes almost simultaneously, so hardness stability, good uniformity, the general GCr15 steel BL After quenching the hardness of 59 ~ 61HRC, uniformity ≤ 1HRC, unlike the ring when the ring is slightly larger than the quenching hardness, soft point, poor uniformity and other issues.
(3) reduce quenching,grinding cracks
In the railway, rolling mill bearing production, due to large ferrule size, heavy weight, M tissue brittle oil quenching, in order to obtain high hardness after quenching often take strong cooling measures, resulting in quenching micro-cracks; and BL quenching, due to The toughness of BL tissue is much better than that of M, and at the same time the compressive stress of up to -400 ~ -500MPa is formed on the surface, which greatly reduces the tendency of quenching crack. The surface compressive stress counteracts part of the grinding stress during the grinding and makes the overall stress level Fall, greatly reducing the grinding cracks.
Bearing life increase
For large load to withstand the railway, rolling mill bearings, quenched by M after the main failure mode is used: When the inner sheath cracking, the outer wall of the outer wall of the block during use, the inner ring fragmentation, and austempered bearings Due to good impact toughness and surface compressive stress, no matter whether the inner sleeve is cracked during assembling or the outer sleeve is blocked off during use, the propensity of the inner sleeve is greatly reduced and the stress concentration on the edge of the roller can be reduced. Therefore, after quenching after quenching than M, the average life expectancy and reliability increase.