Modeling of Short Time Dilatometry Testing of High Carbon Steels

Dilatometry test systems are commonly used for characterizing the transformation behavior in steels using induction heating for the heating source and gas flow for the cooling source. In these systems, the steel test article is assumed to have a uniform temperature throughout the sample. The accuracy of this assumption depends on the design of the induction heating and gas cooling systems, as well as the time scales for heating and cooling. Using computer models, it is possible to predict the temperature dynamics of the sample, both radially and axially, during the thermal processing cycle (heating and cooling). O1 tool steel was utilized to characterize and model heating and cooling temperature gradients. Specimens instrumented with multiple thermocouples were induction heated and gas quenched. The test data and geometry were evaluated using 2-D induction heating models along with 3-D CFD models to characterize transient temperature gradients. The 3-D CFD modeling was used to improve the design of the gas quenching system to provide more uniform cooling. The modeling results were also used to better characterize temperature corrections required when rapid heating and cooling processes are used to determine transformation behavior in induction hardenable steels.