Texture and grain boundary study in high strength Fe–18Ni–Co steel related to hydrogen embrittlement

Abstract

Crystallographic texture and grain–boundary distribution are introduced as a new method of reducing susceptibility to crack formation and propagation. In this work, slow strain rate tests (SSRT) were performed on fully martensitic ultra-high strength Fe–18Ni–Co steel in 0.6M NaCl atmosphere at −1.2 VSCE to investigate hydrogen embrittlement (HE). Micro and meso-texture in both crack stricken and crack free regions were characterized using electron backscattering diffraction (EBSD) technique, to find a pattern between crystallographic orientation and HE susceptibility. The Taylor factor analysis was used to determine the grains with higher susceptibility to crack initiation and propagation. The results showed that cracks can initiate and propagate through <100>//ND oriented grains, while {111} and {110}//ND fibers indicate higher resistance path for crack propagation. Moreover, the high amount of deformed fraction with high stored energy acts as one of the main reasons for high susceptibility of this steel against SSRT. It is concluded that the susceptibility of high strength Fe–18Ni–Co steel to HE can be reduced through crystallographic texture control and grain boundary engineering.