Differential cooling is widely used in the automotive industry to tailor the microstructure and the mechanical properties in thin-walled beams through tool or spray quenching. However, thicker steel plates, such as those used in soil-working agricultural tools, typically require high hardness and are conventionally quenched by immersion in water. While this ensures strength, it does not account for the spatial variation of mechanical loads that these tools experience in service. By implementing differential cooling, it is possible to engineer hardness gradients that optimize both wear resistance and structural integrity.

This study explores the use of Impinging Jet Quenching Technique (IJQT) to achieve differential cooling of 15 mm-thick carbon steel plates by employing different water and air jet flow rates. The cooling process was monitored using embedded thermocouples, generating spatial and temporal temperature evolution data, which was then utilized in finite element simulations to predict phase transformations and final hardness gradients. The simulation framework enables extrapolation to other steel grades, using their chemical composition as an input parameter to a machine learning tool for phase transformation data generation, making the methodology adaptable for various industrial applications.

The experimental trials produced a wide range of cooling rates (0–43 °C/s) along the steel plate, depending on the quenching strategy and cooling medium. The simulated phase transformations revealed distinct hardness distributions across three steel grades with different hardenability levels (0.26, 0.27, and 0.38 mass-% C). The results showed that higher-hardenability steels retained a greater proportion of martensite, whereas lower-hardenability steels exhibited increased bainite, ferrite, and pearlite fractions, particularly in the slower cooling regions. The results clearly show how different steels react on different cooling medium and flow rates in terms of hardness profile variations along a potential component. Furthermore, it was found that differential air cooling could, in some cases, replicate the effects of slower water quenching, providing an alternative method for controlled microstructure tailoring.

These findings highlight the potential of IJQT as a flexible and scalable approach for achieving site-specific material properties in thick steel components. The demonstrated simulative and experimental approach opens new possibilities for enhancing the durability of steel components exposed to variable mechanical loads, offering an efficient means to optimize hardness distributions through controlled cooling strategies.