法兰密封螺栓断裂失效分析

Failure Analysis on Fracture of Flange Sealing Bolts

通过宏观检验、化学成分分析、拉伸试验、硬度试验、金相检验、断口分析等方法对某批20Cr13钢法兰密封螺栓断裂失效原因进行了分析。结果表明:由于淬火加热温度偏低造成该法兰密封螺栓显微组织中存在大量颗粒状碳化物,部分区域还存在大量带状未溶铁素体,致使该处产生应力集中,并造成螺栓的强度偏低、硬度分散度大,组织存在严重的不均匀性,当螺栓承受正常的工作载荷时,就会在应力集中的法兰密封螺栓螺纹根部沿着铁素体带产生裂纹并疲劳扩展,最终导致螺栓断裂失效。

Through macrographic examination, chemical composition analysis, tensile test, haedness test,metallographic examination,fracture analysis and other methods,the fracture failure reasons of a batch of 20Cr13 steel flange sealing bolts were analyzed. The results show due to the low quenching temperature,there were a lot of granular carbides in the microstructure of the flange sealing bolts and a lot of banded undissolved ferrite which led to local stress concentration in some areas. At the same time,it also resulted in lower strength,uneven hardness and inhomogeneous microstructure. When the bolts were under normal working lood,cracks would appear and propagate along the banded ferrite at the stressconcentrated thread root,and eventually fracture failure of the bolts happened.