Carburized Layer Cracking Analysis of Counterweight Blocks of Speed Controller

Abstract

Trace and fracture analysis, metallographic examination, residual stress testing, and material analysis were carried out, coupled with examining the failure timeline, to analyze the cracking problem of 12CrNi3A steel counterweight blocks under multi-factor coupling. The results show that the cracks of the counterweight blocks are intergranular microcracks in the carburized layer and they are delayed cracks under the joint action of microstructure stress, grinding stress and hydrogen. The delayed cracking of the counterweight blocks is mainly related to abnormal hydrogen absorption during surface treatment and poor grinding quality. The obvious microstructure segregation in raw material and the thicker carburized layer promoted the cracking. The following measures should be comprehensively taken to prevent such failure: strictly controlling raw material quality, hydrogen absorption and stress, as well as increasing the processes to remove hydrogen, reduce stress and stabilize microstructure.