Relationship between hydrogen states present in the vicinity of the fracture surface and hydrogen embrittlement susceptibility for ferrite-martensitic dual-phase steels

Abstract

The relationship between hydrogen states present in the vicinity of the fracture surface and hydrogen embrittlement susceptibility was investigated for ferrite-martensitic dual-phase steels. Hydrogen embrittlement susceptibility was evaluated in tensile tests based on the ratio of the fracture strength of hydrogen charged and not-charged specimens. Tensile tests at strain rates of 8.33×10−6 s−1 and 1.67×10−6 s−1 were conducted on specimens containing different amounts of hydrogen. The hydrogen states present near the fracture surface were analyzed by thermal desorption analysis just after the specimens fractured. The results indicated that hydrogen embrittlement susceptibility markedly increased as the amount of hydrogen increased. Additionally, only the specimen that fractured at the highest amount of hydrogen showed not only a lower temperature peak but also a higher temperature peak. Hydrogen embrittlement susceptibility also increased at slower strain rates, and also showed the higher temperature peak. The relationship between hydrogen states present in the vicinity of the fracture surface and mechanical properties indicated that the defects corresponding to higher temperature peaks probably increased hydrogen embrittlement susceptibility. Since microvoids at the crack tips were observed by SEM only in specimens that fractured at lower strain rates, the defects corresponding to higher temperature peaks were probably voids.