Predicting the mechanical properties of a quenched and tempered steel thanks to a “tempering parameter”

The Hollomon-Jaffe parameter is commonly used to characterize thermal cycles and define time-temperature equivalences during tempering, but it can only be computed for simple thermal cycles defined by a couple of values [temperature; time]. Its use is not adapted for complex thermal cycles. Three tempering parameters which integrate the full thermal cycles were investigated: the Hollomon-Jaffe derivative parameter, and the Tsuchiyama and Arrhenius laws. Simple and complex thermal cycles were performed on a water-quenched carbon steel (i.e. different heating and cooling rates or two-step cycles, with temperature varying between 450 °C and 750 °C and times from 30 s to 3 days). All three tempering parameters show good correlation with the tensile properties of the material, even when complex cycles were performed, provided that the material constant is optimized. The sensitivity to the determination of this constant is low for the Tsuchiyama and Arrhenius laws: they can be considered as robust and reliable. On the contrary, the Hollomon-Jaffe derivative parameter proved unstable.