Effect of diffusible hydrogen level on heat-affected zone hydrogen-induced cracking of high-strength steels

The implant test was used to investigate the heat-affected zone (HAZ) hydrogen-induced cracking (HIC) sensitivity of two high-strength naval steels, HY-100 and HSLA-100. Welding was performed using the gas-metal arc welding process, and a high and a low hydrogen level was introduced using an Ar-15%H-2 and an Ar-5%H-2 shielding gas, respectively. The lower critical stress for HIC at the two hydrogen levels was determined using the implant test. In both cases, failure occurred in the coarse-grained HAZ (CGHAZ). The microstructures of the CGHAZ of the two steels were characterized by means of both optical and transmission electron microscopy, and Vickers hardness measurements. The fracture behavior was studied using scanning electron microscopy. Both the implant test results and the fractographic analysis indicate that HSLA-100 has better resistance to HAZ cracking and better tolerance to higher hydrogen contents than HY-100. This is attributed to the presence of a mixed martensitic/bainitic microstructure in the HSLA-100 CGHAZ, relative to a fully martensitic CGHAZ with higher hardness in HY-100.