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Dual-phase steels, commonly employed in the automotive industry, are characterised by their ferrite and martensite microstructure. In many cases, the martensite can be seen to be banded in the rolling direction. This banded microstructure arises from micro-segregation during solidification, primarily of manganese followed by subsequent rolling. The martensite banding can degrade the uniform elongation and ductility. In this study, the concept of altering the morphology of martensite has been employed to enhance the uniform elongation of DP steel. In this context, the influence of manganese segregation on the distribution of the second phase has been neutralised by redesigning the steel composition compared to conventional DP grades. The new DP steel grade has been introduced as ‘segregation-neutralised (SN)’ DP steel. A combination of micromechanical finite element modelling and uniaxial tensile tests was utilised to study the effect of change in the distribution of martensite on strain distribution and uniform elongation in DP steel. The strain-field measurement from the finite element modelling revealed a more homogeneous shear band formation in SN-DP, resulting in a decrease in the frequency of the high-localised strain regions in SN-DP compared to a commercially benchmarked DP grade. Tensile results also showed an improvement in uniform elongation in SN-DP (+2.3 % absolute) compared to the benchmark DP grade with similar tensile strength.
Keywords: Dual-phase steel, martensite morphology, strain distribution, uniform elongation© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.