48MnV钢曲轴裂纹分析

Analysis on 48MnV steel crankshaft crack

某曲轴轴颈经磁探伤发现有微裂纹,经裂纹形貌观察、能谱分析、轴颈表面残余应力测试及显微硬度分析等,确定失效曲轴轴颈裂纹为磨削裂纹。裂纹的产生主要是由于砂轮磨削量过大,磨削的瞬间温度过高而且集中在工件表面层的局部部位,造成工件表面层显微组织的局部转变为回火托氏体;组织的变化不但使轴颈表面产生二次收缩,而且还产生很大的组织应力;同时磨削烧伤让轴颈表面产生低温回火脆性,碳化物沿晶界析出,导致沿晶开裂。

Micro cracks were found on a crankshaft neck detected by magnetic flaw detection, crack reason was analyzed by means of crack morphology observation, energy spectrum analysis, residual stress measurement and microhardness analysis of journal surface. The results show that cracks on the failure crank journal are some grinding cracks mainly due to the excessive grinding of wheel. The instantaneous temperature of wheel grinding is too high and concentrated in the local part of surface layer of the workpiece, which results in the partial transformation of the microstructure of the surface layer of the workpiece to the tempered martensite. The change of microstructure not only causes the contraction of the neck surface, but also produces a great deal of transformation stress; At the same time, the grinding burn causes the low temperature temper brittleness, the carbides precipitated along grain boundaries which brings the intergranular crack.