Hot-rolled Al-added medium Mn steel (Fe-8Mn-2.85Al-1Si-0.2C): Microstructural evolution and tensile behavior

Abstract

In this study, a low Al (<3%) added medium manganese steel has been developed through melting casting route in an open-air induction furnace. The cast steel ingot has been intercritical annealed at 720 °C after hot deformation, that includes hot forging and hot rolling treatment, respectively. Microstructure characterization coupled with X-ray diffraction (XRD) has been performed after each processing step to understand the extent of austenite formation and its subsequent transformation to ferrite/martensite. The processed steel possesses the ultimate tensile strength, yield strength and ductility of 1000±20 MPa,700±10 MPa and 18.5 ± 0.5, respectively. To understand the possible cause of enhanced strength and deformation mode rietveld analysis has been carried out. It reveals that developed (final processed) steel possesses ∼18% (volume%) of austenite that subsequently reduced to ∼6.139% after tensile testing, indicating significant transformation of austenite to martensite (continuous and enhanced TRIP effect). The morphological characteristic of martensite in developed steel has been investigated using transmission electron microscopy (TEM). It reveals lath morphology of martensite due to low carbon content. The TEM and 3D atom probe analysis reveals the precipitation of intergranular type kappa (k) carbide in intercritically annealed specimens due to probable segregation of C and Al. However, volume fraction of the same is low. The SFE of the steel has been found to be ∼16 mJ m− 2, calculated by the modified Olson and Cohen method that also concludes TRIP is the preferred deformation mechanism in the developed steel.