Effect of deformation and charging conditions on crack and blister formation during electrochemical hydrogen charging

Abstract

Hydrogen induced cracks were introduced in an ultra-low carbon (ULC) steel by subjecting it to electrochemical hydrogen charging. The damage characteristics were investigated for three material conditions, i.e. cold deformed, recovered, and recrystallized state. The aim of the work was to understand the effect of deformation induced defects on the hydrogen induced cracking of this material. Additionally, the effect of the charging conditions, i.e. charging time and current density, on the cracking characteristics were verified. The blister surfaces and related hydrogen induced cracks were studied by optical microscopy, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Deformed samples were considerably more sensitive to hydrogen induced cracking, which demonstrates the important role of dislocations in hydrogen induced damage mechanisms. Permeation tests were performed in order to elucidate the role of hydrogen diffusion in the process. Charging conditions had a clear influence on the hydrogen induced cracking behavior of the material. This should be taken into account when designing experimental parameters in order to obtain results valid under real life conditions.