Effects of sub-zero and tempering heat treatments on microstructure, hardness, and wear mechanisms of Elmax powder metallurgy tool steel across a wide temperature range

Abstract

This study investigates the effects of different heat treatment conditions on the microstructure and hardness of Uddeholm Elmax SuperClean tool steel, a high-chromium powder metallurgy alloy known for its wear resistance, corrosion resistance, and dimensional stability. Six differently heat-treated samples (UDH-1 to UDH-6) were examined using optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and hardness testing. The microstructural analysis revealed a martensitic matrix with chromium- and vanadium-rich carbides distributed throughout the samples. The amount, size, and distribution of these carbides varied depending on the heat treatment applied. UDH-1 showed coarser carbide clusters, while UDH-6 displayed finer and more uniformly dispersed carbides, indicating better thermal stability and phase homogeneity. Hardness results supported these observations. UDH-4 exhibited the highest hardness (62.5 HRC), while UDH-6 showed the lowest (57.5 HRC), likely due to tempering effects and carbide coarsening. These findings highlight how heat treatment parameters affect the carbide structure and mechanical performance of Elmax steel. Overall, the results provide a clearer understanding of how controlled heat treatments can optimize the hardness and structural properties of Elmax tool steel for advanced engineering and tooling applications. The wear behavior of this steel showed significant differences depending on the ambient temperature. At -40 degrees C, wear mainly occurred as a result of brittle fracture, while wear resistance remained relatively high. At room temperature, increased ductility promoted micro-ploughing and surface flow, resulting in higher wear. At 250 degrees C, the formation of oxide tribofilms yielded the lowest wear rate. ANOVA results showed that heat treatment parameters significantly affected wear behavior, especially at room and high temperatures. Sub-zero treatment did not provide a consistent improvement in wear resistance. Microstructure, ambient temperature, and tribofilm stability were found to be influential in determining wear performance.