固定板断裂的失效分析

Failure Analysis on Fracture of Retaining Plate

为了找出40CrMn钢固定板开裂的真正原因,利用扫描电镜、直读光谱仪、拉力机试验机、硬度计和金相显微镜研究了固定板的断口形貌、化学成分、力学性能和微观组织。结果表明:固定板的化学成分、显微组织、力学性能符合技术要求;裂纹起源于沉孔的倒圆角位置,裂纹源处无夹杂物,断口属于疲劳断裂。经过工艺追溯,沉孔倒圆角为R0.5,而图纸要求R4,倒圆角过小产生了高度的应力集中效应,导致出现早期断裂失效。再次生产的固定板沉孔圆角按照R4加工,未出现早期断裂。

The fracture morphology,chemical composition,mechanical property and microstructure of 40 CrMn steel retaining plate were analyzed by SEM,direct reading spectrometer,tensile test machine and metallographic microscope. Results showed that the chemical composition,microstructure and mechanical properties met the technical requirements. The crack was originated from the chamfer position of the caisson,and there was no inclusion at the crack source. The fracture belonged to fatigue fracture. After the process tracing,the fillet of sinking hole was R0.5 while the drawing required R4. It was noted that the smaller fillet produced a high stress concentration effect,which led to early fracture failure. For re-produced retaining plate caisson roundness according to R4 processing,there was no early fracture.