Influence carbon and/or iron carbide on the structure and properties of dual-phase steels

Abstract A study has been directed towards the effect of C and/or Fe 3 C on processing, structure and properties of dual-phase (ferrite+martensite) steel. Such type of steel was produced from 0.11C–1.58Mn–0.4Si (ferrite+pearlite) steel. An intercritical holding in the α+γ field followed by different cooling rates so as to obtain various dual-phase microstructures was carried out. It has been found that the carbon (either free or combined with iron) of the individual phase of dual-phase steel plays a significant role in controlling the properties of each phase. A higher interstitial carbon in ferrite resulting from drastic quenching leads to its embrittlement. In contrast, a lower carbon brought about by moderate cooling rates is thought to largely account for the improved properties of dual-phase steels. The yielding behavior depends upon the relative interaction between C/Fe 3 C and the so-called “mobile” dislocations in ferrite. The strength of ferrite or martensite is carbon dependent and affects markedly the work hardening behavior of dual-phase steels. TEM study reveals spherodization of Fe 3 C particles prior to the austenitizing process.