Thermal Softening Effects in Type 224 Carbon Steel

An extensive investigation has been carried out on the compressive mechanical behaviour of type 224-carbon steel (0.18 wt % C, 1.21 wt % Mn) over the temperature range -110°C to +300°C and strain-rate 10" to 5000s", making possible the determination of the thermal sensitivity of this material. In several tests, a thermocouple was mounted inside each small cylindrical specimen to observe any temperature variation during compression. For low strain-rates (<10~s) no appreciable temperature rise was observed, while at rates above 4s" temperature rises were measured which agree with predictions based on adiabatic behaviour. Combining the measured thermal sensitivity with the predicted temperature rise for particular tests has allowed the reduction in flow stress ascribable to adiabatic softening to be determined. This reduction can be as high as 20% of the flow stress in low ambient temperature compression, and can account for the convergence and overlapping of the stress/strain curves at high strain rates with those obtained under quasistatic conditions.