Phase Transformation-Induced Strain-Rate Dependence Effect in Economical Transformation-Induced Plasticity-Aided Duplex Stainless Steel

In this paper, mechanical properties and microstructure evolution of an economical 19Cr-type TRIP-aided duplex stainless steel were investigated under varied uniaxial tensile strain rates at room temperature. Deformation mechanisms of ferrite and austenite phases exhibit obvious distinctions: ferrite phase deforms by dislocation slipping, whereas deformation mechanism of austenite phase is dominated by martensite transformation accompanied with a small amount of dislocations. The annealing-treated duplex stainless steel exhibits good comprehensive combination of mechanical properties orientated from transformation-induced plasticity of metastable austenite phase: ultimate tensile strength of 950 MPa with 60% elongation at strain rate of 1.67 × 10−4 s−1. Mechanical properties are sensitive to tensile strain rates and exhibit obvious strain-rate dependence effects at room temperature. The increased strain rate promoting suppressed martensite phase transformation results in decreased ultimate tensile strength as well as elongation. Heterogeneous deformation of austenite and ferrite phases increases with the increasing in strain rate, promoting initiative microcracks at the interphase boundaries. This deterioration in mechanical properties of TRIP-aided duplex stainless steel hinders its forming process application at high deformation rate conditions at room temperature.