通过化学成分分析、力学性能测试、宏观及微观检验对C70S6钢在疲劳试验中发生早期开裂的原因进行了分析.结果表明：裂纹源位于螺栓孔下端螺纹V型槽底部.切削丝锥加工的螺纹存在细小的刀痕,化学成分中硫、铬、钒含量超标,材料局部出现疏松,这些因素共同作用使得连杆在疲劳试验中过早开裂.因此,建议改善螺纹加工工艺和锻件锻造工艺.

By means of chemical composition analysis,mechanical properties testing,macro and micro examination,the premature cracking reason of connecting rod of steel C70S6 in the fatigue test was analyzed.The results showed that the crack initiated at the bottom of V-shape screw thread around the lower end of bolt hole.There were tiny machining marks around thread manufactured by screw cutting tap;the content of S,Cr and V was unqualified;the porosity appeared in some parts of connecting rod,the premature cracking was caused by these factors together in fatigue test.Therefore,it was proposed that the processing technology of screw thread and the forging technology should be improved.