70MPa水素ガス中における低合金鋼SCM435の疲労特性評価と疲労限度に及ぼす切欠き感度評価

摘要

Fossil fuels exhaustion and global warming are urging mankind to change its energy consumption. On this end, hydrogen energy attracts attention as clean energy to replace fossil fuels. Since many equipment will be expected to be used in the high-pressure hydrogen gas environment in the future, it is necessary to guarantee the safety and durability under hydrogen environment. In particular, reliability of the hydrogen tanks and accumulators, used in fuel cell vehicle as instance, have to be strictly ensured due to the huge hazards inherent to high-pressure hydrogen H_2. Thus, it is necessary to understand the influence of hydrogen on the metallic materials' strength to establish safety this type of mechanical parts. Lately, instead of the commonly used SUS316L steel in high-pressure hydrogen gas conditions, accumulators made of SCM435 low alloy steel with heat treatment are tested due to its cheapness. However, research equipment needed for this kind of experiments are very costly due to safety concerns, thus limiting the number of equipped facilities. Previous studies underline the heat treatment influence on the hydrogen sensitivity of SCM 435 properties. This leads to a lot of remaining investigations in the following years to assess the reliability of this kind of hydrogen accumulators. In this study, 4-point bending fatigue strength and evaluation of notch sensitivity on the fatigue limit of heat treated SCM435 low alloy steels are carried out under high-pressure hydrogen gas environment.%化石燃料の枯渴ゃ地球温暖化の進行が危惧される現代において、CO_2フリーで化石燃料に替わるクリーンェネルギーゃ化石燃料だけに頼らないエネルギーの多様性が求められることから，水素エネルギーが再び注目を集めている.具体例として2020年に開催される東京ォリンピックにおける水素サプライチエーン計画が挙げられる.これを皮切りに将来的には多くの機械部品が高圧水素ガス環境下での利用が予想されるため，水素利用機器の安全性と耐久性を保証する必要がある.また機器の設計に不可欠な切欠き，つまり応力集中部を有する材料の疲労限度に及ぼす水素の影響を調べることは必須であるが，切欠き材の疲労限度に及ぼす水素の影響評価は少ない.本研究では水素利用機器の候補材である低合金鋼SCM435を対象とした.SCM435は現在，35MPa級水素ステーションの蓄圧器に使われており，将来的には低コスト化の観点から燃料電池自動車の配管に使われる可能性がある.またSCM435は熱処理条件を変えると，水素感受性に影響があると報告されている.