Causes Analysis on Grinding Cracks of 20CrMnMo Steel Carburized Gears

The forming reasons for grinding cracks of 20CrMnMo steel carburized gears were analyzed by means of chemical composition analysis, metallographic examination, microhardness test and residual stress test. The results show that the main reasons for the grinding cracks were secondary quenching burn and tempering burn on the gear surface during grinding. Grinding cracks were caused by the combined effects of serious decline in hardness and surface tensile stress at the subsurface of the secondary quenching burn area and the edge tempering burn area. Besides, the grinding cracking sensitivity was increased due to the acicular martensite and massive retained austenite existing in the carburized layer, which was also an important reason for the grinding cracks.