Stress-strain curve prediction of steel HAZ based on hardness

The prediction of the stress-strain curve at each point in steel HAZ (heat-affected zone) is rather complicated since the HAZ microstructure consists of multiple phases and varies continuously, and hence a simpler prediction method is desired. In this work, thermal simulation tests were conducted for tensile tests and hardness measurements. And using the experimental data, empirical equations to predict the stress-strain curve based on hardness have been developed. The stress-strain curve is divided into three regions. In the first region, the curve is described as a straight line. The curve in the second and the third regions is described by the Swift law, but the constants of the Swift law are different in the second and the third regions. The hardness value is the only data needed for the present prediction. The comparisons of the predictions with the experiments show that the present model can predict the stress-strain curves within an error of 100 MPa for most cases as long as the steel strength is up to 980 MPa. Hence, the present model can provide useful information for the evaluation of weld joint qualities.