Overview of Hydrogen Effects on <i>γ</i>−<i>ε</i> Martensitic Transformation in Steels
Motomichi Koyama, Satoshi Iikubo, Rama Srinivas Varanasi
Abstract
This paper presents an overview of our recent works on the effects of hydrogen on γ-ε martensitic transformations in steels. The study first discusses how hydrogen impacts these transformations. While hydrogen suppresses thermally-induced γ–ε martensitic transformation, it increases the fraction and number density of deformation-induced ε-martensite and decreases its thickness. Secondly, we discuss the effects of γ–ε martensitic transformations on hydrogen kinetics. The study also highlights the significance of low hydrogen diffusivity in the hexagonal-close-packed (HCP) lattice of pure iron, demonstrating the effectiveness of ε-martensite in resisting hydrogen. Moreover, the characteristic behavior of the HCP phase-related diffusionless transformation from a hydride is discussed. We believe that this overview will assist in developing hydrogen-resistant steels and in exploring new microstructural control concepts using hydrogen.