PLASTICITY OF DUAL-PHASE STEELS AND CLAD STEELS IN A TENSILE STATE OF STRESS

The paper describes non-homogeneous plastic strain during the hot forming of dual-phase steels and clad bimetallic materials It presents a hypothesis explaining the origin of unstable strain by the different hardening exponents and different strain rate sensitivities of the two phases of metals. Differing conditions for the onset of unstable strain then induce additional stresses at interphase boundaries, stresses that can attain the magnitude of the cohesive strength and cause crack formation. Strain instability is further accelerated by changes in the proportion of ferrite in the instability domain. changes brougth about by disruption of the thermodynamic equilibrium between the two phases.