Microstructure Analysis of TRIP Fe-1.39Si-2.57Mn-0.17C Steel

Abstract

In this work, the phase transformations were studied during the intercritical treatment in TRIP steel with chemical composition of Fe-1.39Si-2.57Mn-0.17C. Steel specimens were heated in the intercritical region, ferrite and austenite, at 750° C for 30 min, austempered at 430 °C, quenched in water without agitation, and normalized by air cooling. Microstructural analysis was performed by optical microscopy and scanning electron microscopy, and by X-ray diffraction. All samples were mechanically characterized by uniaxial tension and Rockwell tests. Microstructural and phase analysis was also carried out with the Thermo-Calc software. The microstructural characterization results showed that the phases and microconstituents were ferrite, austenite, cementite, and austenite. Thermo-Calc results are consistent with the phases and microconstituents found for each heat treatment condition. On the other hand, the tension test results showed that the yield strength and ultimate tensile strength are between 763–818 MPa, and 1190–1255 MPa, respectively, for these heat-treated steels.