A Multivariate Experimental Design to Investigate the Effect of Different Heat Treatment Procedures and Parameters’ Interactions on the Hardness and Retained Austenite of K340 Cold-work Tool Steel

High-carbon, high-chromium cold work tool steels are a group of steels that are used in various industrial applications due to their exceptional properties such as high hardness and wear resistance. Heat treatment plays a critical role in tailoring these characteristics for each application to meet the required needs. This study investigates the effect of austenitizing and tempering temperatures and tempering steps on the hardness and retained austenite (RA) content and aims at providing a model which can estimate the resulting hardness of each heat treatment recipe. Fifteen heat treatment procedures were defined using a face-centered central composite design. The microstructure of the material was studied by scanning electron microscopy and energy-dispersive spectroscopy, and the RA was measured by x-ray diffraction. Vickers microhardness measurement was also used to characterize the mechanical properties of the material. The results showed that austenitizing at 1040 °C and 3-step tempering at 550 °C resulted in the minimum hardness value (732 HV). However, the maximum hardness (801HV) was achieved when the material was austenitized at 1055 °C and tempered at 525 °C for 3 steps. The data were analyzed by Chemometric Agile Tool software and the results showed that the interaction of austenitizing and tempering temperatures had the most significant effect on hardness. On the other side, the amount of RA was mainly affected by the tempering temperature. By increasing the austenitizing temperature from 1040 to 1070 °C, an increase in the peak hardness value was observed. Additionally, by increasing the tempering temperature the hardness increased followed by a decline after reaching a peak value. Given the generated model, this research contributes to a deeper understanding of intricate relationships between heat treatment parameters and material properties, facilitating the design of heat treatment procedures based on requirements of each specific application.