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某机车加工车间生产的空心轴锻件,经调质热处理后,探伤发现,21件产品中有7件开裂。开裂在端部中间部位呈环状开裂,开裂位置及形态较为特殊,与通常淬火开裂方式有所不同。对开裂空心轴试验分析,试验结果表明,化学成分符合空心轴材质要求;锻件致密度良好;显微组织属调质组织,但晶粒度粗大不合格;扫描电镜断口微观分析为典型沿晶断裂。综合试验分析认为,空心轴端面环形开裂系热处理淬火裂纹,形成原因系淬火工艺过程控制不当造成。
A locomotive processing workshop production of hollow shaft forgings, after quenching and tempering, flaw detection found that 21 out of 21 products in the crack. Cracking ring in the middle of the end of the crack, the location and form of cracking is more special, and usually quench cracking method is different. The experimental results show that the chemical composition conforms to the material requirements of the hollow shaft; the density of the forgings is good; the microstructure is quenched and tempered but the coarse grain size is unacceptable; the microscopic analysis of the fracture surface of the scanning electron microscope is a typical intergranular fracture . Comprehensive analysis shows that the hollow shaft end surface cracking ring heat treatment quench crack, the reason for quenching process caused by improper control.