Nondestructive evaluation of tempering treatment in a spray-formed 440C martensitic stainless steel using thermoelectric power measurements

Assessing mechanical properties during the fabrication process or in service is crucial in the tool steel manufacturing industry. Microstructural characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction, (XRD), and hardness measurements are widely used to track the effect of the heat treatment on the microstructure and material properties, which require laboratory conditions and specialized techniques. This study explores the potential of thermoelectric power (TEP) measurements as a nondestructive alternative for evaluating microstructural features in 440C martensitic stainless steel manufactured by spray forming technology. Microstructural properties including retained austenite volume fraction and martensite tetragonality were evaluated on heat-treated (HT) samples after quenching and tempering using microhardness measurements, SEM, and XRD analysis. The results were then compared to TEP measurements. The TEP coefficient demonstrates a strong correlation with microstructural features, such as phase fraction and tetragonality. This suggests TEP can be a valuable tool for in-field quality control.Graphical AbstractThe loss of tetragonality caused by the tempering treatment could be related to TEP coefficient