Properties of thermally embrittled cast duplex stainless steel

Abstract

Cast duplex stainless steel, grade CF-3, used in nuclear pump applications, was thermally aged at 400° C to induce an embrittling phase transformation, thereby simulating long term exposures at 280° C (536° F). The mechanical properties of as-cast material and the thermally aged materials were subsequently investigated. Fracture toughness, Charpy VNotch (CVN), tensile, precracked CVN, nil-ductility transition temperature, and hardness tests were performed on these materials. Tests were run as a function of temperature and loading rate. The as-cast structure of this duplex stainless steel is extremely tough, but thermal aging causes a decrease in upper shelf fracture toughness parameters and absorbed Charpy energy, and a marked increase in transition temperature. However, even the most severely aged material (14406 hr/400° C) appears to possess excellent upper shelf values, although the transition temperature shift is to a relatively high temperature. A conclusion is that cast duplex stainless steel is sufficiently tough, even in the aged condition, to resist crack initiation and propagation under expected nuclear pump service conditions.