Martensite tensile deformation and bulk texture evolution in austenite-martensite multilayered steel by neutron diffraction

Xu, P. G.   ; Ojima, Mayumi*; Inoue, Junya*; Shiro, Ayumi; Akita, Koichi; Nambu, Shoichi*; Suzuki, Hiroshi  ; Harjo, S.   ; Gong, W.; Tomota, Yo; Koseki, Toshihiko*

Monolithic low carbon martensite steel is rarely applied as an important structural sheet material because of its very low tensile ductility. Recently, some austenite-martensite multiphase steels with proper multilayer structure design have been found to possess a high uniform elongation similar to the commercial high strength steel sheets (such as DP590) even at a double tensile strength. It is valuable to clarify why the martensite in the multiphase multilayer condition may approach a much higher ductility than that in the monolithic condition through high statistical texture measurement. The monolithic martensite during uniform deformation shows similar deformation characteristic to the monolithic ferrite in IF steel. However, for the martensite in multiphase multilayered condition, it is found that the main crystallographic orientation of martensite layer from {111}112 component at 0% tensile strain rotated to {111}110 component at 15% tensile strain through the transition of {556}1-75+{221}01-2 split texture components. It suggested that the inter-layer constraint in multiphase multilayered steel induced such difference in martensite during tensile deformation, which finally resulted into much higher elongation than the monolithic martensite steel.