High temperature stress relaxation behavior of high Si, Mo-doped austenitic stainless steels

Abstract

The resistance to stress relaxation at high temperatures is of importance to fasteners. In this study, the stress relaxation behavior of high Si, Mo-doped austenitic stainless steels at 450, 510, 550, 600 and 650 °C were investigated, taking the microstructure evolution at high-temperature long-term condition into account. It is found that Mo can effectively mitigate the plastic strain rate at high temperatures by impeding the extension of partial dislocations, thus leading to a noteworthy enhancement in the stress relaxation resistance. The first-principles calculations indicated that the addition of Mo can suppress the formation of a multi-phase composed of G phase and ferrite at high temperatures, by increasing the segregation energy of Si, Cr, and Ni at grain boundaries. This multi-phase induces the formation of stacking faults and twins, and therefore is responsible for an abnormal reduction in the residual stress.