Effects of Temperature and Strain Rate on Stress-Strain Curves for Dual-Phase Steels and Their Calculations by Using the Kocks-Mecking Model

Effects of temperature and strain rate on stress-strain curves for two types of dual-phase (DP) steel with different carbon contents were investigated from the viewpoints of tensile tests and the Kocks-Mecking (KM) model based on thermal activation theory. In the tensile tests, flow stress increased but elongation decreased with decreasing temperature or increasing strain rate. Uniform elongation for each DP steel was almost independent of deformation temperature between 123 and 373 K. In the comparison of strain rate sensitivity exponent (m), the m-value increased with decreasing the volume fraction of martensite. The calculated true stress-true strain curves by using the KM model agreed with the measured ones at various temperatures and strain rates for the DP steels. In terms of the parameters for the KM model, the athermal stress and mechanical threshold stresses were different between the two types of DP steel. This seems to be associated with the difference of volume fractions of ferrite and martensite.