Prediction model for weld hydrogen cracking in high strength steel weld

Abstract

A prediction model for a weld hydrogen cracking, so called cold cracking, in high strength steel welds was developed by a coupled thermo-elastic-plastic and hydrogen diffusion analysis in the y-groove weld joint. In the weld cracking tests, the critical preheat temperature to prevent cracking was increased with thicker plate thickness and higher hydrogen concentration in the weld metal. The cracks were initiated at the weld metal in the root region where exhibits significant tensile residual stress by the welding. The y-groove weld joints with different plate thickness were modeled by FEM with the actual weld configuration and material properties in the base metal, heat affected zone (HAZ) and weld metal. Hydrogen was put in the weld metal as an initial condition, then welding simulation was conducted by a coupled thermo-elastic-plastic and hydrogen diffusion analysis. In the hydrogen diffusion analysis, the α-multiplication method, which stress gradient term in the diffusion law was multiplied, was applied to express realistic hydrogen diffusion enhanced by a hydrostatic stress field. Hydrogen accumulation occurred in the root region which showed highest residual stress. The point showing highest hydrogen accumulation was well corresponded to the crack initiation site. It was found that cracking was enhanced with thicker plate and higher initial hydrogen concentration because of higher tensile residual stress and higher hydrogen accumulation in the root region, respectively. Based on the FE analysis and comparison with the experimental results, the local criterion for weld cold cracking was proposed that can be useful to estimate the critical preheating temperature in the y-groove weld tests with different welding conditions.