Thermal-sensing-assisted Process Monitoring of Surface Layer Development during Gas Carburizing

Continuous thermal sensing provides valuable process information for intelligent heattreatment systems.However, systematic investigations of the relationship between measurable thermal history and surface layer evolution during gas carburizing remain limited, restricting the application of thermal sensing to process monitoring and quality evaluation.In this study, a thermal-sensing-assisted evaluation framework was developed to investigate the relationship between measurable thermal history and surface layer development.Three K-type thermocouples were employed to continuously record furnace temperature histories during gas carburizing, providing time-resolved process information for comparison with the subsequent material response, while hardness characterization, diffusion-based estimation, and metallographic observations were integrated to evaluate surface layer evolution.The thermal sensing system exhibited stable and consistent temperature responses throughout the investigated temperature range, supporting its suitability for continuous process monitoring.Increasing the holding time promoted the progressive growth of the hardened layer, resulting in greater effective and metallographic case depths while maintaining nearly constant surface hardness.The metallographically determined case depths showed a growth trend similar to that of the Harris diffusion-based estimates.The proposed framework demonstrates that integrating thermal sensing with conventional materials characterization provides a practical approach for correlating measurable thermal history with surface layer evolution, offering an experimental basis for the future development of predictive virtual sensors in intelligent gas carburizing systems.