A novel method for experimentally assessing strength contribution of strain-induced martensitic transformation in a lean duplex stainless steel

The tensile behavior of a lean duplex stainless steel with strain-induced martensite transformation (SIMT) was studied in the deformation temperature range of 20 degrees C similar to 60 degrees C. The microstructure evolution referring to strain-hardening characteristics was analyzed by EBSD and TEM, and the variation of SIM content with tensile strain at 20 degrees C was quantified by XRD. Based on the deformation temperature-dependent mechanical behavior and transformation behavior, a novel method, i.e., conducting continuous tension and two-step tension, respectively, to induce plastic hardening plus transformation-hardening in the former, and plastic hardening itself in the latter, was proposed to assess the strength increment induced by SIMT Delta sigma(SIMT). The intrinsic strengthening mechanisms and influencing factors were also discussed here referring to the microstructure evolution. It shows that the Delta sigma(SIMT,) which was verified and further extended to larger strain levels using the modified Ludwik equation, increases as tensile deformation proceeds once SIMT is activated, possessing a closed association with SIM content. The Delta sigma(SIMT) consists of an indirect hardening term induced by strain partitioning and a direct strengthening term induced by substitution, both of which depend on the inherent properties of austenite phase.