小型試験片を用いた水素脆化試験法による電磁ステンレス鋼の耐水素脆化性に有効な添加元素の特定

摘要

On the basis of the test method of fatigue crack growth (FGR) under hydrogen charged condition using a small scale specimen which has been proposed from results of hydrogen concentration behaviors around a notch tip obtained by our proposed method of analysis on hydrogen diffusion, FGR tests were conducted for electro-magnetic stainless steels with various additive elements. From experimental results of acceleration ratio of FGR under hydrogen charged condition to that under atmospheric condition and the law of hydrogen concentration rate derived by our proposed hydrogen diffusion analysis, the algorithm on the specification of additive elements effective in the resistance to the hydrogen embrittlement was established and effective chemical elements in the hydrogen embrittlement for electro- magnetic stainless steels were specified. That is, more than 18% Cr and 0.1～0.2% Ti are found to be useful as additive chemical elements. From the metallurgical view point, previous literatures have predicted the former is considered to cause film on the surface of metal which interrupt enter of hydrogen from outer surface and the latter is considered to cause trap site of hydrogen. Results obtained by this research validated these metallurgical view point predictions.%水素環境下での鋼の疲労き裂成長速度の測定は,燃料電池車の水素脆化対策等,安全維持に関して重要である.特に,電磁ステンレス鋼は電磁弁などに使用されるため，材料開発を含めて,疲労き裂成長速度が,どの程度水素脆化敏感性を有するかを定量化する方法の確立が望まれている.また,水素脆化は，腐食反応から水素が算出する場合もあり，水素チャージ試験のみならず,腐食環境下での評価も必要である.