24 Microalloyed Steels Crack Propagation Resistance Due to Hydrogen and Static Stress Level Effects in Notched MWOL Specimens

Two high strength Microalloyed Steels with different microstructures and similar yield strengths were evaluated under hydrogen charging conditions and different static stress levels. The bainitic steel shows significant resistance to crack incubation even at high stress levels, showing elapsed times above 10⁷ seconds (4 months) before a visible crack appears and twofold elapsed times to propagate very short cracks (less than 1 mm). The martensitic steel shows catastrophic failures with very fast crack growth rates. This shows that microstructure plays a significant role for crack initiation and propagation for steels with similar yield strengths under hydrogen charging conditions. The bainitic steel structure and the grain boundaries could effectively retard the hydrogen and stress level effects to prevent fast crack initialization and propagation.