Hydrogen-assisted Crack Propagation in Pre-strained Twinning-induced Plasticity Steel: from Initiation at a Small Defect to Failure

Abstract

Hydrogen-assisted crack growth of pre-strained twinning-induced plasticity (TWIP) steel was investigated using artificial defects (micro-drilled holes), which acted as artificial crack initiation sites. Hydrogen was introduced into the specimens by electrochemical hydrogen charging during slow strain rate tensile test. The quasi-cleavage crack propagation observed was due to repeated crack initiation near the crack tip and subsequent coalescence. Crack initiation near the crack tip occurred after plastic deformation of the crack tip, and pre-straining facilitated plasticity-driven crack initiation. The early stage of plasticity-driven crack growth was sensitive to the crack length and remote stress level. Accordingly, the crack growth rate in the early stage increased with the increase in the initial defect size. In the following stage of the crack growth, the crack growth rate exhibited a complicated trend with respect to the crack length, which is possibly due to the plastic-wake-altered stress field around the crack tip, which depends on the initial defect size.

Application of Molecular Dynamics Calculations to Elucidation of the Mechanism of Hydrogen-Induced Crack Initiation in Fracture Toughness Tests Using Tempered Martensitic Steels

“…In addition, it is also important to understand the plastic deformation behavior in the plastic region of the crack tip affected by hydrogen. 19) Figures 5 and 6 show OM and SEM images of the fracture surfaces of microcrack initiation obtained by forced fracture under a liquid nitrogen atmosphere for the specimens tested in the air and hydrogen gas environments, respectively. In the OM observation results in Figs.…”