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Knowledge of carbon content in retained austenite (RA) with different neighbouring phases is essential to understand the chemical stability of RA, which is useful for microstructure tuning of transformation-induced plasticity (TRIP) steels. The present study investigates different morphologies and chemical compositions of RA by correlating electron backscattering diffraction, transmission electron microscopy and atom probe tomography. The effect of neighbouring phases, such as polygonal ferrite, bainitic ferrite lath, ferrite in granular bainite and carbides, on the carbon content in the RA is investigated. The results reveal that the film RA morphology does not always have a higher carbon content than the blocky RA; as coarse RA sometimes displays a higher carbon content than the fine RA films or islands depending on the neighbouring phases. The diffusion of carbon and manganese between austenite and ferrite in bainitic ferrite/granular bainite has been explained according to either diffusionless and/or diffusional mechanism of bainitic ferrite formation followed by tempering. Refereed/Peer-reviewed

The strip casting is a recently appeared technology with a potential to significantly reduce energy consumption in steel production, compared to hot rolling and cold rolling. However, the quantitative dependences of the steel microstructure and mechanical properties on strip casting parameters are unknown and require investigation. In the present work we studied the effects of strain and interrupted cooling temperature on microstructure and mechanical properties in conventional dual phase steel (0.08C-0.81Si-1.47Mn-0.03Al wt%). The strip casting process was simulated using a Gleeble 3500 thermo-mechanical simulator. The steel microstructures were studied using optical, scanning and transmission electron microscopy. Mechanical properties were measured using microhardness and tensile testing. Microstructures consisting of 40-80% polygonal ferrite with remaining martensite, bainite and very small amount of Widmanstatten ferrite were produced. Deformation to 0.17-0.46 strain at 1050 degrees C refined the prior austenite grain size via static recrystallisation, which led to the acceleration of ferrite formation and the ferrite grain refinement. The yield stress and ultimate tensile strength increased with a decrease in ferrite fraction, while the total elongation decreased. The improvement of mechanical properties via deformation was ascribed to dislocation strengthening and grain boundary strengthening. Refereed/Peer-reviewed

Conventional dual phase (DP) steel (0.08C–0.81Si–1.47Mn–0.03Al wt.%) was manufactured using simulated strip casting schedule in laboratory. The average grain size of prior austenite was 117 ± 44 μm. The continuous cooling transformation diagram was obtained. The microstructures having polygonal ferrite in the range of 40–90%, martensite with small amount of bainite and Widmanstätten ferrite were observed, leading to an ultimate tensile strength in the range of 461–623 MPa and a corresponding total elongation in the range of 0.31–0.10. All samples exhibited three strain hardening stages. The predominant fracture mode of the studied steel was ductile, with the presence of some isolated cleavage facets, the number of which increased with an increase in martensite fraction. Compared to those of hot rolled DP steels, yield strength and ultimate tensile strength are lower due to large ferrite grain size, coarse martensite area and Widmanstätten ferrite. Keywords: Strip casting, Dual phase steel, Continuous cooling transformation diagram, Mechanical properties, Crussard–Jaoul model, Electron microscopy