Characterization of Plastic Deformation Behavior of a Thermally Aged Duplex Stainless Steel

Abstract

In situ tensile tests at room temperature have been conducted on a duplex stainless steel (DSS) thermally aged at 400 °C for 10,000 h to investigate both the plastic deformation mechanisms and the effect of long-term thermal aging on crack initiation. After thermal aging, the ultimate tensile strength of the DSS increases and the plasticity significantly decreases. The fracture morphology changes from ductile fracture with shallow dimples to a mixture of cleavages in ferrite and tearing in austenite. Electron backscattered diffraction (EBSD) technique has been used to determine the crystallographic orientations of austenite and ferrite grains on three areas deformed differently. The EBSD analysis results indicate that high strain occurs near grain boundaries and phase boundaries. The localized strain incompatibility is considered to be responsible for high stress concentration and crack initiation. The long-term thermal aging affect on the crack initiation and the cleavage cracks are found to be initiated in aged ferrite grains.