Decrease in the brittle-to-ductile transition temperature in Cu added nickel-free austenitic stainless steels

Brittle-to-ductile transition (BDT) in Cu added Ni-free austenitic stainless steel was investigated. Temperature dependence of apparent fracture toughness was measured using four-point bending tests, indicating that the BDT temperature was decreased with the increase in the Cu content. The activation energy was obtained from the deformation rate dependence of BDT temperatures. It was found that the values of the activation energy was decreased with the increase in the Cu content, suggesting that the dislocation mobility in austenitic stainless steels was increased by Cu addition. The increase in the dislocation mobility induces the decrease in the BDT temperature. The values of the activation energy are deviated from the regression line drawn on the data which obtained from the materials with high Peierls potentials. Temperature dependence of 0.2% proof stress indicated that the effective stress was nearly independent from the Cu content while the values of activation volume were decreased with the increase in the Cu content. A model for dislocation glide was proposed to explain the both decrease in the activation energy and the activation volume with the increase in the Cu content.