异种钢焊接中氢蚀剥离的产生机理研究

利用电子显微镜技术（ＴＥＭ、ＳＥＭ）分析了焊态和长期在高温、高压氢环境中服役后，Ｃｒ５Ｍｏ＋奥３０２（Ｃｒ２５Ｎｉ１３）异种钢焊接熔合区附近的显微组织变化。认为氢蚀剥离裂纹的产生机理为：工件在运行过程中，组织不均匀的熔合区周围，富集氢和碳（碳化物），并发生反应，在奥氏体（Ａ）／类马氏中（Ｍ－Ｌ）焊接边界处生成ＣＨ＿４气泡，不断的冷热疲劳使气泡不断长大，并逐渐连在一起。当工件停止运行冷却到室温后，由于母材和焊缝金属之间热膨胀系数以及导热系数的差异，使边界处的应力集中重新出现，导致接头沿气泡连接部位开裂。

STUDY OF HYDROGEN-INDUCED DISBONDING MECHANISM IN DISSIMILAR STEEL WELDS

The microstructures of the dissimilar Cr5Mo-Cr25Ni13 fusion bond,in as-welded state and after high-temperature and high-pressure hydrogen service,have been observed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The mechanism of the hydrogen attack disbonding process is reported as follows:during service,the reaction of hydrogen and carbon (or carbide) enriched around the heterogeneous transition zone forms the CH_4(methane) bubbles at the austenite (A)/martensite-like(M-L) weld interface,The continual heating-cooling fatigue process makes these bubbles grow and connect with each other along the interface,When the workpiece is shut down and cooled to ambient temperature,the tensile stress concentration at the fusion bond reappears due to the difference of thermal conductivity and expansion between the base metal and weld metal,This stress,consequently,leads to a disbonding.