18CrNiMo7⁃6钢齿轮轴开裂失效分析

Cracking failure analysis of 18CrNiMo7⁃6 steel gear s

某齿轮轴渗碳+淬火+回火热处理后在静置期间发生开裂。为了明确齿轮轴的失效性质和原因,对断口进行了宏、微观形貌观察和能谱成分分析,对断口附近材料微观组织进行了检查,并且测试了材料的硬度和氢含量。结果表明,齿轮轴开裂性质为氢致延迟脆性开裂。裂纹从齿轮轴内部起源,源区存在大尺度条状非金属夹杂,导致较大应力集中,是其发生氢脆开裂的主要原因。因此,应严格控制齿轮轴的材质。此外,可以采用无损检测方法对齿轮轴内部的大尺度非金属夹杂进行检测,以防止同类故障的发生。

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.