The role of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement of type 304L stainless steel

Abstract

The role 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 304 L stainless steel was quantitatively studied. The results indicated that hydrogen-induced martensites formed when hydrogen concentration C ₀ exceeded 30 ppm, and increased with an increase in C ₀, i.e. M(vol%)=62–82.5 exp (−C ₀/102). The relative plasticity loss caused by the martensites increased linearly with increasing amount of the martensites, i.e. l _δ(M), %=0.45 M (vol %)=27.9−37.1 exp(−C₀/102). The plasticity loss caused by atomic hydrogen l _δ(H) increased with an increase in C ₀ and reached a saturation value l _δ(H)max=40% when C ₀>100 ppm. l _δ(H) decreased with an increase in strain rate $\dot \varepsilon$, i.e. l _δ(H), $\% = - 21.9 - 9.9\dot \varepsilon$, and was zero when $\dot \varepsilon \geqslant \dot \varepsilon _c = 0.032/s$. HIC under sustained load was due to atomic hydrogen, and the threshold stress intensity for HIC decreased linearly with in C ₀, i.e. K _IH (Mpam^1/2)=91.7−10.1 In C ₀ (ppm). The fracture surface of HIC was dimple if K ₁ was high or/and C ₀ was low, otherwise it was quasi-cleavage. The boundary line between ductile and brittle fracture surface was K ₁-54+25exp(−C ₀/153)=0.