Effect of Chemical Composition on Tensile Property in TRIP-assisted Multiphase Steel Composed of Fe-Mn-Si-C

The microstructural changes and the tensile properties of the TRIP-assisted steels resulting from the different chemical compositions were investigated by using SEM, TEM, XRD and UTM. As a result of microscopic observation, morphology of retained austenite could be identified into two types: a granular type in steel containing higher Si and a film type in steel having higher C. In the case of the steel containing higher C with a tensile strength of 860 MPa and a total elongation of 38 %, the film-typed retained austenite could be observed among the lath bainitic ferrites. Actually, the metastable retained austenite was the requisite for the good formability, which means that the chemical composition plays a significant role in the microstructure and the tensile property of a TRIP-assisted steel. Regarding the tensile property, each steel containing adequate amount of Si and Mn showed a typical TRIP effect on a stress-strain curve while the steel containing a higher Mn content exhibited the similar behaviors shown in the dual phase steels.