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In this study,effects of alloying elements and hot rolling conditions on the final microstructures and the related mechanical properties of the hot-rolled DP780Y steels were discussed.Controlled rolling patterns,especially step cooling temperature and duration time ( sheet traveling time on the runout table),were simulated by thermomechanical simulator for producing DP 780Y steels on a kind of low carbon steel containing higher amounts of Mn and P.Microstructures and quantitative analysis of the volume fractions of the phases and the fracture surface were characterized by the scanning electron microscopy ( SEM),transmission electron microscopy ( TEM) and the image analyzer,respectively.It was found that the alloy contents of Mn and P elements,not only affected the microstructure of ferrite and martensite phase morphologies,proportions and formations,but also affected the performance of the final steel.In addition,increase of the cooling temperature and duration time decreased the yield and tensile strength,but increased the total elongation.The results showed that with the appropriate proportion of the alloy addition and the cooling process control,an optimized combination of high strength and good elongation balance can be obtained.