制氢转化炉管与法兰异质焊接接头失效原因的研究

Analysis of Failure of Dissimilar Metal Wdding Joints between Furnace Tubes and Flanges in Hydrogen Manufacturing Unit

针对用奥407焊条焊接HK-40炉管和Cr5Mo法兰的异质焊接接头在高温运行期间开裂泄漏的情况,采用光学显微镜、扫描电镜等手段进行了失效分析。结果表明,在长期高温运行中碳从低铬材料向高铬材料扩散迁移,在熔合区邻近Cr5Mo钢母材一侧形成脱碳层,其基体因贫碳软化,强度降低。加上Cr5Mo钢和奥氏体焊缝金属的线膨胀系数有较大差异,高温下变形不协调,熔合线界面上应力集中,导致在熔合区邻近Cr5Mo钢母材侧脱碳层上萌生裂纹,并沿脱碳层扩展,穿透内外壁,造成泄漏。

In view of the cracking and leaking occured in high-temperature operation of dissimilar metal welding joints between HK-40 furnace tube and Cr5Mo flange using austenic 407 steel welding rods, the failure was analyzed with optical microscope and scanning electron microscope etc. The results indicated that dur- ing a long period of operating at high temperature, carbon diffused and moved from the lean chromium material into the rich one, forming a decarbonized layer at the CrSMo base metal side near the molten zone. Therefore, the matrix material softened and the strength decreased due to the lacking of carbon. In addition, owing to the great difference in linear expansion coefficients of the Cr5Mo steel and the austenic weld metal, the inconsistent deformation at high temperature and the concentration at the melting interface, cracks were induced on the decarbonized layer at the Cr5Mo base metal side near the molten zone and extended along with the decarbonized layer to penetrate both inter and external walls and re-sulted in leaking.