A Method to Determine the Mobile Dislocation Density in Low-Carbon Steels

Abstract

At the transition from the Lüders-band extension to the homogeneous plastic flow in a low-carbon steel the flow stress rises abruptly. It is shown that this increase of stress is a direct measure of the effective stress, σ*, at the Lüders strain. With the help of a power law v=B(σ*)ⁿ the average dislocation velocity v is determined. The remaining constants B and n are evaluated by making stress-relaxation tests during the Lüders-band propagation according to a technique proposed by Prewo et al. Once the velocity v is determined the mobile dislocation density ρm is obtained from the Orowan equation for plastic flow, ε = bρmv.