Effects of strain rate and temperature on tensile behavior of hydrogen-charged SA508 Cl.3 pressure vessel steel

The tensile behavior of hydrogen-charged SA508 Cl.3 pressure vessel steel and the dependence of strain rate at both room and high temperatures (473–623 K) was investigated. It was found that charged hydrogen induced a slight hardening and a decrease in ductility at room temperature. There was an abrupt decrease in ductility at the low strain rate of 10−5 s−1. Distinct quasi-cleavage or cleavage features appeared near the inclusions. However, charged hydrogen induced a softening and a decrease in ductility at the high temperatures, especially in the dynamic strain aging (DSA) region. The presence of hydrogen shifted the temperature at which DSA happens to a higher level. The fracture mode of hydrogen-charged steel was microvoid coalescence at high temperatures, with flat, or brittle-like areas, on local fracture surfaces and the dimples being smaller and shallower. Observable hydrogen effects appeared at the strain rate of approximate 10−3 s−1 at the high temperatures compared with 10−5 s−1 at room temperature. The observed tensile behavior may be attributed to interactions between hydrogen and dislocations at room temperature and between hydrogen and DSA at the high temperatures.