Variation of Yield Stress With Strain Rate for Three Carbon Steels

Abstract

This paper presents an experimental study of the strain-rate and temperature dependence of the yield stress for three low carbon steels (percent c = 0.2, 0.3, and 0.4). Tension test results using notched specimens are reported for temperatures of −20°C, 0°C, and 25°C and strain rates from 10−4 s−1 to 200 s−1 . Two regions with different kinetics have been observed. The yield stress shows a low sensitivity to strain-rate at higher temperatures and lower strain rates (region I), but the rate sensitivity is high at lower temperatures and higher strain rates (region II). An approximately linear dependence of yield stress on log strain rate is displayed in both regions. The carbon content of the steel strongly affects strengthening in region I, but weakening appears as the strain rate increases in region II. Deformation in the two regions is analyzed according to standard formalisms. When the yield stress is separated into athermal and thermally activated components, the carbon concentration dependence is shown to isolate to the athermal stress component, which becomes rate controlling at high temperatures and low strain rates.