对48MnV非调质钢汽车发动机曲轴探伤磁痕现象产生原因进行了分析,指出由于在锻造过程中原材料不均匀流变,造成原材料心部组织偏向连杆颈内侧部位,并在其后的机加工过程中心部组织外露,导致产生探伤磁痕现象。分析微观特征,结果证实其实质是心部碳偏析带在近表层的分布。分析了探伤磁痕现象对曲轴疲劳性能的影响,结果表明: 对于按技术条件检验合格的原材料,曲轴出现的偏析现象不会成为疲劳裂纹优先萌生的条件,即偏析区与正常区域在零件受力中的行为没有明显差别,没有降低曲轴疲劳强度。

The magnetic trace phenomenon in nondestructive detection of 48MnV micro-alloy metal automobile engine crank in manufacturing process was analyzed. It indicated that the magnetic trace was because of raw material ununiformity deformation in forging which caused raw centre segregations flowed to the inner subsurface of crankpin and uncovered after by machine process. The metallographic characteristic was described and it proved that the essential of the magnetic trace was raw carbon centre segregations distributed in subsurface of the part. The influence of magnetic trace on fatigue properties were researched. It indicated that raw centre segregations on the part which its raw material passed by received inspection had no influence to the fatigue strength of crank and had not become the prior initiation of fatigue crack, in other word, the centre segregations area had the same behavior with the normal area in the loading process.