Abstract
Due to a strain-induced martensitic transformation (SIMT), TRIP (transformation-induced plasticity) steel possesses favorable mechanical properties such as high strength, ductility and toughness. However, since the SIMT depends on temperature, strain rate and stress state, the desired mechanical properties are obtained only in a fairly restricted working environment. On the other hand, a spatial distribution of geometrical characteristics of martensitic phase, including size, shape, and orientation against the loading axis, are heterogeneous at a microstructure of TRIP steel as observed in micrographs. It can be thought that the mechanical properties of TRIP steel manifest strong dependences on the geometrical inhomogeneity and spatial configuration of martensite. If these geometrical characteristics can be controlled, the enhancement of the mechanical properties of TRIP steel might be expected. Hence, it is necessary to evaluate the geometrical characteristics in TRIP steel to describe and control its deformation behavior. Here, in order to study the geometrical orientation from micrographs, the Fourier transformation image analysis (FTIA) is employed. After the suitable magnification of the micrographs for the FTIA and a spatial frequency are discussed, the dependences of plastic strain, temperature and stress states on the geometrical orientation are investigated by using the FTIA.
