Influence of Residual Stress on Hydrogen Permeation and Mechanical Behavior in Shot-Peened Steel

This study aims to understand how residual stresses, introduced by shot peening and bending, affect hydrogen permeability in steel and influence hydrogen uptake. Previous studies have shown that shot-peened steel, after hydrogen charging, undergoes changes in both its compressive residual stress depth profile and dislocation density. Since the residual stress profile results from a combination of plastic strain introduced by peening and elastic bending to balance the internal stress within the specimen, it is important to determine how these factors independently affect hydrogen permeability in order to understand how the stress state influences hydrogen uptake. The influence of residual stress on hydrogen permeation and subsequent mechanical behavior was investigated. 1070 steel Almen strip samples were subjected to two treatments: (1) shot peening to induce biaxial compressive residual stress near the surface, and (2) bending to introduce geometric stress prior to hydrogen permeation testing. Hydrogen charging was performed electrochemically on one side in an H-type cell, with hydrogen permeation flux measured at quasi-steady state on the opposite side. Tests were conducted on both sides of the samples to assess hydrogen entry under residual stress, transitioning from tensile to compressive and from compressive to tensile in the bent specimens, and under the same setup for shot-peened specimens. A stress-free sample was used as a reference for comparison. Changes in surface residual stress caused by hydrogen uptake were examined using X-ray diffraction. Microhardness testing was performed to evaluate potential embrittlement after hydrogen charging and subsequent storage in ambient air. To minimize the influence of surface finish while preserving induced residual stresses, electropolishing was carried out before both microhardness testing and hydrogen charging.