Insight into hydrogen-induced cracking behavior in heat-affected zone of E690 steel

Abstract This study investigates the hydrogen-induced cracking (HIC) behavior and underlying mechanisms in the heat-affected zone (HAZ) of welded joints made from E690 high-strength low-alloy steel for marine engineering applications. An integrated experimental approach, including hydrogen permeation tests, electrochemical hydrogen charging, residual stress measurement, and comprehensive microstructural characterization via scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), was conducted. The results reveal significant differences in HIC susceptibility between the welded joint (WJ) and the base metal (BM), as well as among the various HAZ subzones: the coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and intercritical HAZ (ICHAZ). The WJ exhibits a hydrogen diffusion coefficient approximately three times higher than that of the BM, with diffusible hydrogen predominantly accumulating around weld defects, leading to its greater HIC susceptibility. Residual stress analysis showed that the CGHAZ as the region with the maximum tensile stress, reaching about 400 MPa. Fractographic analysis demonstrated distinct cracking modes: intergranular cracking along prior austenite grain boundaries in CGHAZ, transgranular propagation of long, thin cracks in FGHAZ, and a mixed intergranular-transgranular mode with a tortuous, discontinuous path in ICHAZ, where martensite-austenite (M-A) constituents act as barriers to crack advance. The overall HIC susceptibility, evaluated using crack susceptibility parameters (CSR, CTR, CLR), follows the order: CGHAZ > FGHAZ > ICHAZ.