A predictive method for hardness distribution in laser-quenched medium-carbon steel using an ultrafast non-equilibrium phase transformation model

Laser transformation hardening is a key surface technique for improving the wear resistance and fatigue life of medium-carbon steel parts. However, predicting the resulting hardness distribution is challenging. Traditional experiments are destructive, and common simulations, which rely on equilibrium-based empirical models, lack accuracy for ultrafast non-equilibrium phase transformations. This study overcomes these limitations by developing a novel kinetic framework that captures the non-equilibrium phase transformation behavior during laser quenching, and establishes a high-fidelity hardness prediction methodology. The framework innovatively adapts the classical JMAK model to analyze the dynamic evolution of transformation mechanisms under ultrafast thermal cycles, building a parameterized model informed by physical data from isothermal transformation curves. This kinetics model is integrated with a microstructure-hardness mapping to form a comprehensive computational model. Experimental validation on various medium-carbon steels confirms the model's effectiveness in predicting hardened layer depth, microstructural distribution, and hardness gradients. This work thus provides a non-destructive, precise analytical tool for optimizing laser quenching processes and performance assessment of medium-carbon steel components.