Comparison of hydrogen embrittlement in the coarse-grained heat-affected zone of X52 and X65 steels fabricated by GMAW, CMT and FCAW

Purpose The purpose of this study is to investigate the hydrogen embrittlement (HE) behavior of the coarse-grained heat-affected zone (CGHAZ) of X52 and X65 steels fabricated by gas metal arc welding (GMAW), cold metal transfer (CMT) and flux-cored arc welding (FCAW). Design/methodology/approach Gaseous hydrogen permeation tests, slow strain rate tensile (SSRT) tests and microstructure characterization were used to study the HE behavior of the CGHAZ of the two steels. Findings The CGHAZ of X52 weld joints primarily consisted of quasi-polygonal ferrite and granular bainite, whereas that of X65 weld joints was dominated by lath bainite and granular bainite. The hydrogen diffusion rate in the heat-affected zone of X52 and X65 steels followed the order CMT > GMAW > FCAW. The fraction of brittle area and HE index in the CGHAZ of X65 weld joints was higher than that of X52 weld joints. In addition, the CGHAZ of the FCAW weld joints had more hydrogen traps than other weld joints and showed dimpled fracture surfaces, indicating the best resistance to HE. Originality/value The results of the study provide crucial insights for selecting welding methods in hydrogen-blended gas pipelines.