Phase transformation kinetics of high-carbon steel during continuous heating

Effects of heating temperature, heating rate, and holding time on the austenitization process of near-eutectoid high-carbon steel have been investigated. The dilatometric tests were carried out at different heating rates of 1-100 degrees C/Sec. The Ac1 and Ac3 critical temperatures, the volume fractions of the parent and produced austenite phases, and consequently, the coefficient of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation were obtained from dilatometric diagrams. The activation energy for the transformation was estimated using the Kissinger equation. The optical microscope was used for the micro structural characterization of samples austenitized at different temperatures and durations. The grain growth kinetics of austenite during processing was also characterized. Cellular Automata simulation was used to investigate the nucleation and growth of austenite from the initial full pearlitic structure. Based on the results, the activation energy of 242.6 kJ/mol at low heating rates (1 degrees C/Sec to 12 degrees C/Sec) and 436.94 kJ/mol at high heating rates (25 degrees C/Sec to 100 degrees C/Sec) were obtained, which indicated the different phase transformation mechanisms. This was attributed to the presence of boron, which postpones nucleation at grain boundaries and helps to activate the shear mechanism at high heating rates. Finally, a continuous heating transformation (CHT) diagram was drawn, which is an indispensable tool to consider the effect of heating rate on the austenitization process and austenite grain size.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The effects of heating temperature, heating rate, and holding time on the austenitization process of near-eutectoid high-carbon steel were investigated. Experimental tests and simulations were conducted to understand the variations of relevant parameters and the underlying reasons for different phase transformation mechanisms. A continuous heating transformation diagram was drawn to consider the influence of heating rate on the austenitization process and austenite grain size.