Hydrogen embrittlement induced by atomic hydrogen and hydrogen-induced martensites in type 304L stainless steel

The roles of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement in slow strain rate tensile tests and hydrogen-induced delayed cracking (HIC) in sustained load tests for type 304L stainless steel were quantitatively studied. The results indicated that hydrogen-induced martensites formed when hydrogen concentration C0 exceeded 30 wppm, and increased with increasing C0. The relative plasticity loss caused by the martensites increased linearly with increasing volume fraction of matensite. The plasticity loss caused by atomic hydrogen Iδ(H) increased with increasing C0 and reached a saturation value Iδ(H)max=40% when C0>100 wppm. Iδ(H) decreased linearly with increasing logarithm of strain rate ε̇, i.e., Iδ(H), %=−21.9−4.3 ln ε̇. HIC at sustained load was due to atomic hydrogen, and the threshold stress intensity for HIC decreased linearly with increasing ln C0, i.e., KIH=91.7−10.1 ln C0. The fracture surface of HIC was dimpled if KI was high or/and C0 low; otherwise it was quasi-cleavage. The boundary line between ductile and brittle fractography was KI−54+25 exp(−C0/153)=0.