某教学楼阳台304奥氏体不锈钢护栏发生断裂失效。采用宏观检查、化学成分分析、金相检验、扫描电镜及能谱分析等对护栏断裂原因进行了分析。结果表明：304奥氏体不锈钢护栏母材显微组织中存在大量非金属夹杂物，焊接接头存在的未焊透现象降低了接头强度；母材碳含量较高，在焊接热循环作用下，活动能力强的碳原子与铬化合形成碳化物析出，使热影响区晶界贫铬，形成“敏化”，增加了材料的晶间腐蚀倾向，降低了焊接接头的强度，最终导致护栏断裂失效。

The 304 austenitic stainless steel guardrail on the balcony of a teaching building broke down. Macroscopic examination, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis were used to analyze the causes of the guardrail fracture. The results show that there were a large number of nonmetallic inclusions in the microstructure of 304 austenitic stainless steel guardrail base metal. The non-penetration of welded joint reduced the joint strength. The carbon content of base metal was higher, and under the action of welding thermal cycle, the carbon atoms with strong activity combined with chromium to form carbide precipitation, which made the grain boundary of heat affected zone chromium-depleted and formed "sensitization" which increased the tendency of intergranular corrosion of materials, reduced the strength of welded joints, and ultimately led to the failure of guardrail.