FLOW-STRESS AND PHASE-TRANSFORMATION ANALYSES IN THE AUSTENITIC STAINLESS-STEEL UNDER COLD-WORKING - (.1. PHASE-TRANSFORMATION CHARACTERISTICS AND CONSTITUTIVE FORMULATION BY ENERGETIC CRITERION)

A constitutive model for determining the flow stress of SUS 304 austenitic stainless steel has been formulated for cold forming conditions by using an energetic criterion which defines the energy consumed to deform the phases in the system as being equivalent to energy consumed to deform the aggregate. A general constitutive relationship is explicitly established by using the volume fraction of the strain-induced martensitic phase and the flow stress and strain ratio of both the austenitic and martensitic phases. The volume fraction of martensite is determined through a series of uniform compression tests under isothermal conditions. Flow stress of austenitic phase at several constant temperatures is determined by conducting differential compression tests. On the other hand, martensitic flow stress is determined by differential compression experiments aided by numerical simulations of aggregate deformation. Through several finite-element analyses, the strain ratio between each phase has been determined numerically. It has been demonstrated that the developed constitutive expression, successfully predicts the flow stress behavior.