Deformation behavior of thermal aged duplex stainless steels studied by nanoindentation, EBSD and TEM

The cast duplex stainless steels were investigated in order to understand the plastic deformation behaviors and fracture mechanisms after thermal aging at 400 degrees C for up to 10, 000 h. Tensile strength has an obvious improvement, but the yield strength has a slightly increase after long-term thermal aging. Microcracks initiate in the ferrite and extend to phase boundaries, leading to the fracture of ferrite before the tensile failure of specimen. Nanoindentation tests indicate that hardness in ferrite continuously increases with aging time, but not strongly affected by deformation degree. Electron backscattered diffraction observations reveales that high-stress concentration on the phase boundaries causes the phase boundary separating. The dislocations pile-up at spinodal decomposition precipitates in ferrite phases and along G-phase boundaries, leading to the reduction of mechanical property of the ferrite.