Identification of constitutive equation for TRIP steel and its application to improve mechanical properties

Due to the strain-induced martensitic transformation during plastic deformation, a transformation-induced plasticity (TRIP) steel possesses favorable mechanical properties such as high strength, ductility and toughness. Since its favorable mechanical properties are realized under restricted circumstances, the prediction and control of deformation processes are indispensable to determine the expected mechanical properties of TRIP steel. However, it is very difficult to obtain TRIP steel that only has the martensitic structure before deformation, and the stress-strain relationship of each phase at various temperatures cannot be measured experimentally. Therefore, the identification of the parameters in the constitutive equations for TRIP steel is necessary. Here, a method employing finite-element simulation and the nonlinear leasts-quares method under constraint conditions was proposed to identify the constitutive parameters of TRIP steel from the true stress-plastic strain and the volume fraction of martensite-plastic strain relations obtained by the uniaxial tensile test and computational simulations. Then, the application of this procedure employing virtual data of an ideal TRIP steel that possesses highly favorable mechanical properties is discussed to investigate the improvement of the mechanical properties of TRIP steel.