Influence of strain rate and strain at temperature on TRIP effect in a metastable austenitic stainless steel

Metastable TRIP (TRansformation-Induced Plasticity) steel strips with a microstructure comprising ferrite, retained austenite and martensite were subjected to tensile tests at different strain rates of 10(-5) s(-1), 10(-4) s(-1), 10(-5) s(-1) and temperatures 27 degrees C, 50 degrees C and 100 degrees C. The TRIP steel specimens exhibited very high tensile strengths (up to similar to 1700 MPa) in tests carried out at room temperature, which is attributed to the TRIP effect. Thermal stability of the phases present in the TRIP steel in the as-received condition was assessed by in-situ high temperature XRD and DSC (Differential Scanning Calorimetry) analysis to determine the retained austenite decomposition temperature. Microstructural analysis by XRD, optical microscopy and electron microscopy was used before and after the tensile tests to identify the features present at micro- and nano-scales, which are responsible for the observed mechanical properties. Macrographs taken from the surface of the specimens after the tensile tests showed the presence of Luders bands and their occurrence was concurrent with the TRIP effect. The effect of strain rate and temperature on the TRIP effect and the associated mechanical response are discussed in detail.