Connectivity of slip systems between different phases in ferrite–martensite dual-phase steels

Abstract

► The crystallographic study of ferrite and martensite in dual-phase was performed. ► Crystal orientation relationship was examined between martensite and ferrite. ► The parallel relationship depends on the heat-treatments of the specimens. ► They suggest the formation of martensite laths. Ferrite–martensite dual-phase high-strength steels exhibit good formability. This study focuses on the morphology and crystallography of martensite and ferrite in these steels by using quantitative analysis. Three kinds of ferrite–martensite dual-phase specimens subjected to three different heat treatments, step-quenched, hot-rolled–annealed–quenched and quenched–annealed–quenched, were used as specimens in the experiments. Martensite in hot-rolled–annealed–quenched specimens exhibits a parallel relationship between the common close-packed planes of martensite packets and the close-packed planes of adjacent ferrites. This is because these specimens contain fine film-like austenite regions. Fine grained austenite contains high elastic strain energy. Martensite laths, whose shear directions are parallel to their habit planes, are formed from fine austenite regions to accommodate martensitic transformation strain induced by emitting dislocations into adjacent ferrite grains.