The Rolling Contact Fatigue Behavior of Nb and B Added Microalloyed Forging Steels

The possibility of applying two types of raw materials which have transition elements such as B and Nb was investigated to develop new bearings which have metallurgical characteristics and fatigue resistance enhanced for advanced automotive transmissions which are known to supply severe lubrication environments.

Those results were compared with the results of typical low carbon chromium steel which is widely used for the automotive transmission. Thrust type rolling contact fatigue testers were used for the evaluation of fatigue life of steel grades, and each specimen was tested under clean and contaminated lubrication environment. As a result, the microalloyed forging steels have shown the behavior of stabilized austenitic grain superior to comparative grade at high temperature regions.

On the other hand, the test steels have shown a large amount of non-metallic microscopic inclusion or carbide segregation on near surface below the flaking. Also, their rolling contact fatigue lives under lubricated environment containing foreign particles were worse than comparative grade. It thus appeared that distribution of non-metallic microscopic inclusions affected the rolling contact fatigue life of heat-treated products.