FEATURE ADVANCED MATERIALS & PROCESSES | APRIL 2025 54 transformation for three scenarios: (a) fast quenching of a 5-mm cylinder, (b) slow quench of a 5-mm cylinder, and (c) slow quench of a 10-mm cylinder. The slow quenching rate model uses a 200 W/(m2K) HTC and 20°C nitrogen quenching gas, and it is confirmed that this cooling rate is fast enough to avoid any diffusive phase transformation for both cylinder sizes. The comparison between the temperature distributions in Figs. 6a and b shows that a slower quench rate improves temperature uniformity in the sample. The comparison between Figs. 6b and c shows that a smaller sample size improves temperature uniformity in the sample. The dilatometry sample size and the quenching rate affect the measured dilatometry curve and the final sample dimension. With a fast quench rate, the simulated dilatometry curve using the 10-mm diameter sample has a larger axial growth as shown in Fig. 7, which is mainly caused by the plastic deformation caused by the thermal stress at the beginning of the quenching step. With the 5-mm diameter sample, the thermal stress is below the yield strength of the material, which proves to be true by the matching dilatometry curves between the ideal and fast quench curves in the temperature range from 400° to 700°C, as shown in Fig. 7. The simulated sample shapes are different between the 5- and 10-mm samples, and the 10-mm sample shows a more significant OD barrel shape and a crown shape in the end faces. CONCLUSIONS The root causes of the inaccuracy in the measured dilatometry displacement data using a quench dilatometer are investigated using computer modeling. Temperature nonuniformity in the sample leads to inaccurate dilatometry data for the characterization of phase transformations. To improve the accuracy of the measured dilatometry data, the following recommendations should be considered: 1) Select a proper sample size, and use a smaller diameter cylinder if possible. 2) Use slow quenching rates to reduce the temperature gradient and eliminate possible plastic strain caused by the thermal stress. 3) Use customized cylinder samples with crown end face to make sure that the staring gauge measures displacement from point to point instead of from surface to surface. ~HTPro For more information: Charlie Li, president, DANTE Solutions Inc., 7261 Engle Rd., Suite 105, Cleveland, OH 44130, 440.876.7578, charlie.li@dante-solutions.com, dante-solutions.com. References 1. S. Papaefthymiou, M. Bouzouni, and R. Petrov, Study of Carbide Dissolution and Austenite Formation during Ultra-Fast Heating in Medium Carbon Chromium Molybdenum Steel, Metals, 8, p 646, 2018. 2. A.J. Clarke, et al., Perspectives on Quenching and Tempering 4340 Steel, Metallurgical and Materials Transactions A, Volume 51A, p 4984-5004, October 2020. Fig. 6 — Comparison of simulated temperature distributions when the core reaches Ms during quenching: (a) fast quenching with 5-mm diameter cylinder, (b) slow quenching with 5-mm diameter cylinder, and (c) slow quenching with 10-mm diameter cylinder. (a) (b) (c) Fig. 7 — Effect of sample size on the accuracy of the collected displacement data under high quenching rate. 10
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