采用宏观观察、化学成分分析、硬度测试、金相检验、扫描电镜及能谱分析等方法分析某大口径法兰开裂原因。结果表明:法兰热影响区基体组织敏化,截面变化处与热影响区重合导致应力叠加;法兰基体组织的晶粒粗大,且含有大量条状夹杂;法兰长期在敏化温度范围内运行,最终导致其发生应力腐蚀开裂。最后针对具体开裂原因,提出了相应的改进措施。

The cracking reason of a large diameter flange was analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the matrix structure of the flange heat affected zone was sensitized, and the overlap between the cross section changed and the heat affected zone led to the superposition stress. The grains of the flange matrix structure were coarse and contained a large number of strip inclusions. The flange ran within the sensitized temperature range for a long time, which eventually led to stress corrosion cracking of the flange. Finally, according to the specific cracking reasons, the corresponding improvement measures were put forward.