Influence of bainite/martensite-content on the tensile properties of low carbon dual-phase steels

This investigation aims to examine structure–property relations of ferrite–bainite dual-phase (FBDP) steels and to compare these against that of ferrite–martensite dual-phase (FMDP) steels. For this purpose, a series of FBDP and FMDP steels containing wide variation (20–90%) of the harder constituents have been prepared from a low carbon Nb-micro-alloyed base material by suitable heat treatments. Hardness and tensile properties of the developed steels have been examined against the volume fraction of bainite or martensite. The nature of variation of the estimated mechanical properties such as hardness, yield and tensile strength, percentage elongation and strain-hardening exponent with the amount of the harder constituents of the FBDP and FMDP steels exhibits subtle to significant differences. These differences have been explained using the influence of the nature of the microstructural constituents and their mutual interactions. Low carbon FBDP steel with 60–70% bainite appears to possess excellent potential for structural applications.