Microstructure and Stress Corrosion Cracking Resistance of GMAW-Welded Ultra-High-Strength Steel

Abstract This work addressed the stress corrosion cracking (SCC) resistance of welded ultra-high-strength steel (UHSS) using gas metal arc welding (GMAW) with ER100 and ER120 filler metals. The microstructure of welds was characterized, and SCC resistance assessed using slow strain rate to compare the percentage of elongation at failure (pct EL) when testing in air and full immersion in 0.6 M NaCl solution. The analysis shows that UHSS base material is susceptible to SCC with a change in pct EL from 5.21 pct in air to 1.94 pct in 0.6 M NaCl. For all welded samples, the strain was localized within the weld metal (WM) due to the lower yield strength condition. All welded samples exhibited lower elongation and brittle fracture when loaded in 0.6 M NaCl compared to air, demonstrating that SCC occurs in welded UHSS with failure observed within the WM. The microstructure presented higher hardness in the ER120 WM, and a microstructure with acicular ferrite, martensite, and bainite was present. In areas that were not utilized for SCC testing, the ER120 material presented a crack in the as-welded condition, and fractography and EBSD maps indicated the presence of transgranular mode with some intergranular branches in cracks present within the as-welded material. Graphical Abstract