Effect of solute copper on yield strength in dislocation-strengthened steels

The effect of solute Copper (Cu) on yield strength was investigated in dislocation-strengthened iron such as martensitic steels and cold-rolled steels having various dislocation densities. Yield strength of the Cu bearing martensitic steels increases with increasing the solute Cu content. However, the increment of yield strength by Cu solid solution is smaller in the martensitic steels than in the ferritic steels. Dislocation density of martensitic steels increases with increasing Cu content, and yield strength is also enhanced depending on the dislocation density. The increment of yield strength can be reasonably explained by dislocation strengthening mechanism based on Bailey-Hirsch relationship. In the cold-rolled Cu bearing ferritic steels, the strengthening by Cu solid solution is significant but it tends to disappear with increasing the dislocation density. These facts indicate that yield strength of the steels with high dislocation density is determined by dislocation strengthening and the contribution of Cu solid solution disappears due to the high density of dislocations.