ThegrainrefiningmechanismofC-Mnsteelsheetoncompactstripproduction(CSP)linewasinvestigatedinthisstudy.Thegrainwasabout100μmafterF1passanddecreasedallthewayoftherollingprocess(F2-F6)to15μm.Repeatedphasetransformationexperimentwasconductedtothesteelforgrainrefinement.Thephasetransformationat860℃and920℃canrefinethegrainsizeto7.5μm.