Measurement of local strain-induced martensitic phase transformation by micro-hardness

Abstract

By the duplex effect produced by two kinds of phases of austenite and martensite, the transformation-induced plasticity (TRIP) steel is improved in ductility and fracture toughness. The strain-induced martensitic phase transformation could be associated with the strain localization behavior. Accordingly, the measurement of the amount of local transformation is necessary in order to construct a more physical evolution model in the constitutive equation. In this study, a new measurement system using a micro-hardness tester is proposed to obtain a volume fraction map of the martensitic phase expanding in the neighbor of strain localization. Then the system is applied to investigate the inhomogenous transformation behavior around the notch root of SUS 304 stainless steel bar under uniaxial tension.