In-situ Neutron Diffraction Study on Work-hardening Behavior in a Ferrite-Martensite Dual Phase Steel

Abstract

Strength and work-hardening in steels are discussed from the viewpoint of heterogeneous deformation. In-situ neutron diffraction studies made it clear that misfit strains between grains accompanied grain-scaled internal stresses (intergranular stress). In a dual phase steel, the intergranular stress was superposed on the phase stress. These results show good agreement with the predictions of a simple dual-phase material model: the strong martensite phase yields higher stress than the macro-yield stress, resulting in high strengthening of (ferrite + martensite) dual phase steels. Both long-range internal stress and short-range ones such as forest dislocation hardening may cause resistance to dislocation motion in the steels. Therefore, work-hardening takes place more effectively with higher internal stress and larger volume fraction.