Research and Simulation of Heat Treatment of Steel Elements of Metal Molds for Semi-Dry Vibrocompression

Abstract

This work investigates the full cycle of heat treatment (carburizing and quenching) of steel elements of metal molds used in the production of concrete products manufactured by the semi-dry vibrocompression method.
Severe abrasive wear of the working surfaces of metal molds necessitates the optimization of chemical–heat treatment. Traditional methods do not allow accurate prediction of the final phase composition or hardness profile, particularly considering the complex influence of carbon concentration on quenching kinetics. Therefore, a numerical model for process prediction and quality control is required.
A coupled multiphysics 2D model (diffusion, heat transfer, and phase transformations) was developed and implemented for a steel specimen with dimensions 100 × 100 × 20 mm. Carburizing simulations were performed for two initial carbon concentrations (0.08 and 0.2 wt.%) achieving a final surface concentration of up to 0.9 wt.%. After water quenching (typical heat-transfer coefficient h ≈ 5000 W/(m²·K)), the simulations demonstrated the formation of 80–85% martensite in the carburized layer. However, an increased content of retained austenite (15–20 %) was observed in the near-surface region.
The presence of retained austenite in the carburized layer is explained by the significant reduction of the martensite-start temperature (MS) due to high local carbon enrichment. This confirms that even at high cooling rates (h ≈ 5000 W/(m²·K)), complete martensitic transformation does not occur, indicating the need for additional heat-treatment operations.
The use of the Koistinen–Marburger model with concentration-dependent MS(c) and a locally refined mesh enabled accurate determination of the boundaries of the carburized and quenched layers. This provided a quantitative evaluation of the final phase composition profile, which is essential for hardness prediction.
The simulation results can be applied by process engineers to optimize carburizing parameters (temperature and duration) and quenching conditions (cooling rate) to increase the service life of steel metal molds, as well as to justify the necessity of low-temperature tempering.