Relation between Intergranular Stress in Austenite and Martensitic Transformation in TRIP Steels Revealed by Neutron Diffraction

Abstract

In situ neutron diffraction measurements of two low-alloy TRIP steels and a 304-type stainless steel during tensile and creep tests were performed at room temperature. Changes in the diffraction pattern, the peak integrated intensities of austenite (γ) and the peak positions of γ were analyzed and discussed to understand a relationship between intergranular stress in γ and the occurrence of martensitic transformation during deformation. From tensile loading, it was found that the susceptibility of martensitic transformation depended on γ-(hkl) grains, in which γ-(111) grains underwent martensitic transformation at the latest. The volume fractions of γ were found to decrease during applying load, but almost unchanged during holding the constant load in creep tests where the lattice strains of γ-(hkl) grains were mostly unchanged. The γ-hkl dependence in the susceptibility of martensitic transformation was found to be controlled by the shear stress levels in γ-(hkl) grains, which were affected by the intergranular stress partitioning during deformation.