BJ212汽车轮壳螺栓低扭矩断裂分析

Falure analysis on the fracture of wheel hull boits of high strength of BJ212 automabile

借助金相、扫描电镜等手段对低扭矩脆断的ＢＪ２１２汽车轮壳螺栓的金相组织特征，宏观和微观断口形貌等进行了研究，结果表明：这种头部薄的螺栓，渗层和淬透层过深，使头部薄区脆断抗力降低，在头部与杆的根部，由于淬火应力不均匀导致根部产生拉应力，均是导致螺栓低扭矩断裂的原因。

By means of metallographical examination and SEM,the microstructure characteristics,macro and microfractographs of the brittle broken wheel hull bolt of BJ212 automobile have been studied The results show that the thin headed screw,with excessively deep carbonitriding layer and hardening layer,has less resistance to brittle fracture in the thin area of its head At the root of the head connecting the stem,a tensile stress may emerge owing to the non even quenching stress Those are the two reasons for low torque fracture of bolt