某S30408不锈钢U形螺栓使用约0.5 a（年）后就发生了断裂。通过化学成分分析、硬度测试、拉伸试验、金相检验、非金属夹杂物测试、断口分析及能谱测试等方法对该U形螺栓的断裂原因进行了分析。结果表明：该S30408不锈钢U形螺栓在冷加工硬化时产生了残余应力，后又叠加了工作应力，再加上在潮湿的腐蚀环境下工作，螺栓发生了应力腐蚀开裂，裂纹不断扩展最终导致该U形螺栓断裂。

A S30408 stainless steel U-bolt fractured after about 0.5 years of use. The fracture causes of the U-bolt were analyzed by means of chemical composition analysis, hardness test, tensile test, metallographic examination, non-metallic inclusion test, fracture analysis and energy spectrum test. The results show that the S30408 stainless steel U-bolt produced residual stress during cold work hardening, then superimposed the working stress. In addition, the stress corrosion cracking of the bolt occurred in humid corrosive environment, and the crack continued to expand, which eventually led to the fracture of the U-bolt.