Change in Tensile Properties of Dual-Phase Steels by Cu Addition

The effect of Cu addition on the tensile properties of dual-phase steels with various volume fractions of martensite was investigated. An increase in the intercritical-annealing temperature resulted in an increase in the volume fraction of martensite and in the hardness of steel. The Cu addition increased the hardness of steel for all volume fractions of martensite. The tensile properties strongly depended on the Cu addition and on the volume fraction of martensite. The Cu addition significantly increased the ultimate tensile stress and elongation, but it showed a negligible influence on the 0.2% proof stress. The Cu addition improved strength-ductility stability, which referred to the multiplication of ultimate tensile stress and uniform elongation, for all volume fractions of martensite. Modified Crussard-Jaoul analysis on the true stress-true strain curve indicated that the work-hardening behavior of steel was improved by adding Cu. In pre-strained steels, the dislocation density was increased by adding Cu for all volume fractions of martensite. The improvement in work-hardening behavior was explained by the increase in dislocation density attributed to the addition of Cu. Therefore, it could be concluded that the Cu addition could increase dislocation density and work hardening, thereby increasing the ultimate tensile stress and improving the strength-ductility stability of steel.