Effect of martensite on the mechanical behavior of ferrite-bainite dual phase steels

Abstract

This paper reports study on correlations obtained between the microstructure and mechanical properties of four hot rolled ferrite-bainite dual phase steels containing 2-6% of martensite phase. It has been observed in these steels that a small amount of martensite (2 % and above) is adequate to produce the continuous yielding behavior, characteristic of conventional dual phase steels. These dual phase steel contain substantial amounts of bainite (47 to 74%) and can achieve high mechanical strength coupled with adequate ductility. The value of the strain hardening exponents of such steels is however rather low. The addition of substitutional alloying elements such as Cr, Mo or V has been found to increase significantly the strength levels of such steels over that of the C-Mn-Si base composition. © 2007 ISIJ.