Effect of Microstructure on Stress Corrosion Cracking Susceptibility of Ultra-High Strength Steel

Microstructural effect on stress corrosion cracking ( SCC) susceptibility of ultra-high strength steel (UHSS) has been investigated by slow strain rate test (SSRT) in a 3.5% NaCl solution under applied potentials (E-corr -0.1 V and +0.1 V) at a strain rate of 10(-6) s(-1). Tempered martensite appeared in all planes together with elongated grains in transverse-direction (T-D) and rolling-direction (R-D) plane. Microstructure consists of packet, block, and lath inside of prior austenite grain (PAG) boundary classified by its misorientation angle. Under applied potential of E-corr -0.1 V, tensile elongation was 30 similar to 40% less than in air. Under applied potential of E-corr +0.1 V, tensile strength and elongation decreased together, and the reduction in tensile elongation was 50 similar to 70% in both R-D and T-D specimens. In our study, hydrogen embrittlement and anodic dissolution mechanisms were suggested to explain the decrease in tensile properties in environment over in air employing fractographic analysis.