A gear shaft cracked during static standing after carburizing,quenching and tempering.In order to find out the failure mechanism of the gear shaft,macro and micro morphologies were observed and local chemical composition of the fracture surface was analyzed.In addition,the microstructure of the shaft near the fracture was examined,and the hardness and hydrogen content were tested.The results show that the failure mode of the gear shaft is delayed brittle cracking induced by hydrogen embrittlement.The crack initiated from the inside of the shaft and there is a large-size nonmetallic inclusion at the source zone,leading to greater stress concentration,which is the main cause for the hydrogen embrittlement cracking.Therefore,the material quality of the gear shafts should be strictly controlled,and nondestructive detection should be carried out to detect the large-size nonmetallic inclusions in the gear shafts so to prevent such failure.
万方数据