Prediction of tensile properties of intercritical heat affected zone

Abstract

The tensile properties of the intercritical heat affected zone of structural steels have been examined using the weld thermal simulation technique. The investigation includes one normalised C–Mn steel, one normalised and one rapidly cooled low carbon microalloyed steel, and two quenched and tempered high strength low alloy steels. Depending on the base plate strength, high strength values with corresponding low ductility may be obtained at rapid cooling rates (∆t_8/5 < 5 s, where ∆t_8/5 is the time to cool the weld from 800 to 500°C). With increasing cooling time, the yield strength was reduced to a level below that of the respective base plate, with an associated improvement in ductility. In contrast, the tensile strength was higher than the initial base metal strength, independent of weld cooling time and chemical composition of the steel. Both theoretical and empirical equations have been combined to predict the strength of the intercritical heat affected zone from the volume fraction of martensite–austenite islands, the Vickers hardness, the strain hardening exponent, the weld cooling time between 800 and 500°C, and the peak temperature. A comparison of measured and calculated values shows that both the yield strength and the tensile strength can be predicted with relatively high accuracy.

MST/1833