矿车球形壳体的开裂失效分析

Cracking Failure Analysis of Pherical Shell for Tramcar

利用金相显微镜、硬度计及拉伸试验机对QT5007球黑铸铁球形壳体的力学性能进行了检测,利用扫描电镜对其断口形貌进行了分析。结果表明:球形壳体的力学性能符合GB/T 1348要求,断裂位置的金相组织为珠光体+铁素体+石墨+大量的渗碳体,断裂位置比较薄,冷却速度较快,导致渗碳体大量析出,局部硬度升高,超过了GB/T1348要求。材料脆性增加是开裂的主要原因。整个断口的微观形貌是解理断裂,呈现一次性开裂的脆性断裂特征。经过在断口处增加保温材料,降低冷却速度,抑制渗碳体的析出,彻底解决了壳体的开裂问题。

The mechanical properties of the QT500-7 ductile iron spherical shell were tested by metallographic microscope, hardness tester and tensile testing machine, and the fracture morphology was analyzed by SEM. The results show that the mechanical properties of the spherical shell meet GB/T1348 requirements. The metallographic structure of the fracture position is pearlite+ferrite+ graphite+a large number of cementite. The fracture position is relatively thin, and the cooling rate is faster, resulting in a large number of cementite precipitation, local hardness increases, exceeding the GB/T1348 requirements.The increase of material brittleness is the main cause of cracking. The micro-morphology of the whole fracture is cleavage fracture, showing the brittle fracture characteristics of one-time cracking. By adding thermal insulation material at the fracture,reducing the cooling rate and inhibiting the precipitation of cementite, the cracking problem of the shell is completely solved.