Relation between Intergranular Stress of Austenite and Martensitic Transformation in TRIP Steels Revealed by Neutron Diffraction
Stefanus Harjo, Takuro Kawasaki, Noriyuki Tsuchida, Satoshi Morooka, Wu Gong
Abstract
In situ neutron diffraction measurements of two low-alloy steels and a 304-type stainless steel during tensile and creep tests were performed at room temperature. Changes in the diffraction pattern, the integrated peak intensities of austenite (γ), and the peak positions of γ were analyzed and discussed to elucidate the relationship between intergranular stress in γ and the occurrence of martensitic transformation during deformation. Tensile loading experiments revealed that the susceptibility to martensitic transformation depended on the γ-(hkl) grains, where γ-(111) grains underwent martensitic transformation at the latest. The volume fractions of γ were found to decrease under an applied load but to remain almost unchanged under constant load in creep tests, where the lattice strains of γ-(hkl) grains were mostly unchanged. The γ-hkl dependence of the susceptibility to 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.