Roles of Microalloying Elements in Hydrogen Induced Cracking Resistant Property of HSLA Steels

The effects of alloying elements such as niobium, copper, chromium, molybdenum, and titanium in high-strength, low-alloy (HSLA) steels on hydrogen induced cracking (HIC) were investigated. The HIC test was performed to NACE TM-02-84 in BP (saturated H₂S synthetic sea water) and NACE solutions. The test data were analyzed with an optical microscope, scanning electron microscope, electron probe microanalyzer, Auger electron spectrometer, transmission electron microscope, and an image analyzer. Results showed the addition of Nb increased the aspect ratio of inclusions and decreased HIC resistance. In BP solution, Cu-bearing steel formed a protective film of γ-Fe₂O₃ enriched with Cu on the outside and FeS on the inside. Cr and Mo showed a synergistic effect on the formation of low-temperature transformation products and the increase of HIC sensitivity. The suitable parameter for these two elements on HIC sensitivity was $Cr15+Mo5$⁠, and the critical value of this parameter was 0.1%. Additionally, coarse TiN precipitates, as well as elongated MnS inclusions, were the initiation sites of HIC. Both cooperated to result in HIC.