This paper reviews the phenomenon of dynamic strain aging in carbon steels and considers its effects on the fracture behavior of carbon-steel pipes and pressure vessels in lightwater reactors operating at elevated temperatures near 290°C (550°F).
Dynamic strain aging is a phenomenon in which aging occurs simultaneously with plastic straining. It occurs over a range of temperatures that depends on strain rate. In tensile tests, it is manifested by increased tensile strength, increased strain-hardening rate, serrated stress-strain curves, and decreased ductility.
Evidence is presented to show that the occurrence of dynamic strain aging can significantly lower the fracture resistance of carbon steels. This lowering of fracture resistance may be manifested in several ways: (1) JIc is lower at light-water reactor (LWR) temperatures than at room temperature, (2) the tearing modulus is lower at LWR temperatures than at room temperature, and (3) stable ductile crack growth may be interrupted by unstable ductile fracture at LWR temperatures but not at room temperature.
The paper examines probable causes of dynamic strain aging and describes methods for identifying which steels are susceptible to it.