Hydrogen trapping in sub-stoichiometric niobium and vanadium carbide precipitates in high-strength steels

TL;DR

This study uses first-principles calculations to explore how sub-stoichiometric vanadium and niobium carbides trap hydrogen in high-strength steels, revealing composition-dependent trapping behaviors and diffusion barriers that influence hydrogen embrittlement resistance.

Contribution

It provides new insights into hydrogen trapping mechanisms in V/Nb carbides with varying vacancy contents, guiding alloy design for improved HE resistance.

Findings

Hydrogen trapping transitions from reversible to irreversible with increasing vacancies.

Diffusion energy barriers decrease as vacancy content increases.

Composition-dependent hydrogen dissolution energies influence trapping strength.

Abstract

High-strength steel is a structural metal crucial for load-bearing components yet is known to be highly susceptible to hydrogen embrittlement (HE). Vanadium (V) and niobium (Nb) containing precipitated carbides introduce strong hydrogen traps to immobilize hydrogen, thus mitigating HE. However, variations in intrinsic vacancy concentrations in these carbides affect hydrogen thermodynamics and kinetics but remain poorly understood. Employing first-principles calculations, hydrogen trapping and diffusion in V/Nb carbides were investigated. Hydrogen dissolution energies are composition-dependent, revealing a transition from reversible to irreversible trapping with increasing carbon vacancy content, prescribed by the strength of covalent bonds with neighboring V/Nb atoms. Meanwhile, the diffusion energy barrier decreases with increasing carbon vacancy content, attributed to changes in vacancy patterns within carbides. The findings contribute new and critical knowledge for understanding hydrogen trapping and diffusion in sub-stoichiometric V/Nb carbides, providing valuable guidance for process and composition innovation of high-strength alloy steels for better HE resistance.