Influence of Heating Rates on Temperature Gradients in Short Time Dilatometry Testing

Dilatometry test systems are commonly used for characterizing the transformation behavior in steels and induction heating is commonly the heating source. In these systems, the steel test article is assumed to have a uniform temperature throughout the sample. This is a good assumption for slow heating rates with small samples, however, for induction hardening heating rates this may not be accurate. Using computer models, it is possible to predict the temperature dynamics of the sample, both radially and axially, during heating. O1 tool steel in the quenched condition was utilized to characterize and model heating temperature gradients. The case of 50°C/s heating rate was presented previously. In this study, specimens instrumented with multiple thermocouples were induction heated at rates up to 1000 oC/s. The test data and geometry were evaluated with 2-D models to characterize transient temperature gradients. The goal of the modeling is to better characterize temperature corrections required when rapid heating is used to determine transformation behavior during rapid induction heating. This paper presents the data for faster heating rates and quantifies the impact of the different heating rates on the dynamic temperature distributions in the sample.