AN EXPRESSION OF STRENGTH OF MARTENSITEFERRITE DUAL PHASE STEELS

Starting from certain similarities in the structural distribution and the deformation behaviour between the martensite-ferrite dual phase steels and the composite materials reinforced by discontinuous short fibers, a new expression is proposed for the tensile strength of the steels on the basis of the shear lag analysis, i. e. σ_(bDP)=(β/3~(1/2)+0.65)1/Kσ_(bM)V_M+σ_(bF)(1-V_M) where σ_(bDP), σ_(bM) or σ_(bF) is the tensile strength of the steel, the martensite or the ferrite phases respectively, β is the aspect ratio of martensite islands, K is the strength ratio of martensite to ferrite strength, V_M is the volume fraction of martensite and then (1-V_M) is the volume fraction of ferrite. It is in good agreement after quite a few examinations on a variety of dual phase steels with different composition and structure. The load transfer from ferrite to martensite and the utility of strength of martensite have been also discussed.