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

Abstract

The tensile behavior of hydrogen-charged SA508 C1.3 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. (C) 2002 Elsevier Science B.V. All rights reserved.