激光焊接304不锈钢气体柜应力腐蚀失效分析

Stress Corrosion Failure Analysis of Laser Welded 304 Stainless Steel Gas Cabinet

为了探寻304不锈钢气体柜激光焊接结构失效的内在原因及机理,采用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)、电子背散射衍射(EBSD)及焊接接头的硬度测试等,研究了焊接接头的组织、化学成分、断口形貌、接头及裂纹附近相、裂纹扩展路径和裂纹形貌。结果表明,激光焊接头组织主要由奥氏体相、高温δ铁素体组成。熔合线附近热影响区的奥氏体与铁素体间析出少量的碳化物。S形激光焊缝的热影响区位置容易产生应力集中;周期性凝露和沿海大气环境中较高含量的氯离子,使柜体表面形成了含氯离子的水膜,阻止了不锈钢钝化膜的形成。服役过程中在应力和氯离子联合作用下产生应力腐蚀开裂,在焊接残余应力作用下裂纹快速扩展,最终导致漏气失效。

In order to explore the internal cause and mechanism of the failure of the laser welding structure of the 304stainless steel gas cabinet, OM, SEM, EDS, XRD, EBSD and the hardness test of the welded joint were adopted, and the microstructure, chemical composition, fracture morphology, phase of the joint and position near the crack, crack propagation path and crack morphology of the welded joint were studied. The results show that the structure of laser welded joint is mainly composed of austenite phase, high temperature δ ferrite, and a small amount of carbide is precipitated between austenite and ferrite in the heat affected zone near the fusion line. Stress concentration is easy to occur in the heat affected zone of S laser weld. The periodic condensation and the high content of chloride ions in the coastal atmosphere make the surface of the cabinet form a water film containing chlorine ions, which prevents the formation of stainless steel passivation film. During service, stress corrosion cracking occurs under the combined action of stress and chloride ion, and cracks expand rapidly under the action of welding residual stress, eventually leading to air leakage failure.