Exists on the SKF bearing quenching different parts can cause stress concentration factors (including metallurgy, defects), the benefit of quenching crack, but only within the tensile stress field (particularly under the maximum tensile stress) will be displayed, if there is no crack in the compressive stress field.
Quench cooling rate is an important factor affecting the decision quality and residual stress in quenching, is also a capable of quenching crack gives important and decisive factors.
In order to achieve the purpose of quenching, typically need to accelerate parts for high-temperature cooling rates, and faster than the critical quenching of steel to get martensite organizations. Residual stress is concerned, doing so due to increased thermal stress value of offsetting organizations stress, so can reduce the tensile stresses on the workpiece surface and achieve the purpose of suppression of longitudinal crack. The effect will vary with the high temperature cooling the pace of increases. Moreover, in the case of through hardening, section size larger workpieces, while the actual cooling rate is more sustained, cracking the risks have become higher.
All this is because this type of SKF bearings steel heat stress increases the actual cooling slows with the dimension, heat stress decreases, stress increases with the size increase, resulting to stress the role of stress in workpiece surface characteristics. And smaller and cooled more slowly stress tradition varies widely. This type of steel, quenched high hardenability steels under normal conditions only in formation of longitudinal cracks. Avoid reliable principle is to minimize the cross section for quenching crack of martensite transformation of unequal both within and outside. Only implement slow cooling of Martensitic transformation is insufficient to prevention of longitudinal crack formation.
General situation Xia SKF bearing only produced in non-hardenability pieces in the of arc crack, although to overall fast cooling for necessary of formed conditions, but it of real formed causes, is is not fast cooling (including horse′s body changes area within) itself, but quenching pieces local location (by geometry structure decided), in high temperature critical temperature area within of cooling speed significantly slowed, thus no quenching hard due to. In a large non-hardenability of transverse and longitudinal splitting, thermal stress are the main components of the residual stress in quenched parts Center, and quench hardened at the end of the section at the Center, first forming cracks and caused by an extended outward. In order to avoid such cracks, tend to make the water-oil-quenching process of two-liquid.
SKF bearing in this process to implement rapid cooling of high temperature period, purpose is only to ensure that the outer layer of the metal is martensite organizations, and from the point of view of internal stress, rapid cooling counter-productive. Secondly, the cool late-slow cooling purposes, not primarily in order to reduce the bloat of Martensitic phase transformation and organizational stress, but reducing the temperature difference between sections and cross sections as far as possible the Center metal contraction velocity, which reduces stress and ultimately inhibit the purpose of quenching crack.