Effects of chemical compositions and microstructure on hydrogen embrittlement of austenitic stainless steel weld metal in high-pressure gaseous hydrogen environment

摘要

The effect of chemical compositions and microstructures on hydrogen embrittlement of austenitic stainless steel weld metals in high-pressure hydrogen gas was surveyed by using the slow strain rate test (SSRT). As a result, hydrogen embrittlement of the weld metal was hardly influenced by δ ferrite in the weld metal, but by stability of austenite phase, which was estimated by Md30 value or Ni equivalent. In the weld metal with poor stability of austenite, α'-martensite was formed near a crack induced by SSRT. In addition, although the crystal structure of α'-martensite is as same as δ ferrite, susceptibility of hydrogen embrittlement became higher with the increase in α'-martensite. The mechanism to explain the difference between δ ferrite and a'-martensite was considered as following. The hardness, which increases the hydrogen embrittlement susceptibility in bcc structure, is higher in α'-martensite than in 8 ferrite. In addition, α'-martensite might be formed continuously with propagation of a crack. Therefore, the effect of a'-martensite on hydrogen embrittlement could be larger compared with δ ferrite.