Abstract: The preparation of laminated ultra-fine grain dual-phase microstructure by rolling DP590 steel at different temperatures in the dual-phase zone and its effect on mechanical properties were investigated. The results showed that the laminated ultra-fine grain ferrite and martensite dual-phase microstructure was obtained when the steel was rolled at 720， 760 and 800℃ in the dual-phase zone(corresponding to WR720， WR760 and WR800). The corresponding martensite volume fractions are 26.5%， 37.2% and 30.8%， respectively， and the average grain sizes of large angle grain boundary ferrite are (1.92±1.32)，(1.44±2.14) and (1.79±1.54)μm， respectively. It is worth noting that the microstructure characteristics and mechanical properties do not correspond linearly with the warm rolling temperature， but the intermediate temperature， i.e.， 760℃， rolled steel plate grain size is the smallest， martensite volume fraction is the highest， the corresponding yield strength and tensile strength is the highest. This nonlinear relationship between temperature and mechanical properties is discussed in terms of deformation-induced ferrite phase transformation and dynamic recrystallization of ferrite.

Key words: warm rolling; laminated ultra-fine grain; dual-phase steel; grain refinement; dynamic recrystallization