Tribological Behavior of AlCrSiN-Coated Tool Steel K340 Versus Popular Tool Steel Grades

The tribological performance of metalwork steel tools is of vital importance in both cold and hot working processes. One solution for improving metal tool life is the application of coatings. This paper investigates the differences in quantitative wear behavior and wear mechanisms between AlCrSiN-coated and bare steel K340 and five reference tool steels: X155CrVMo12-1, X37CrMoV5-1, X40CrMoV5-1, 40CrMnMo7 and 90MnCrV8. The investigated tool steels were heat-treated, while K340 was subjected to thermochemical treatment and then coated with an AlCrSiN hard film (K340/AlCrSiN). The hardness, chemical composition, phase structure and microstructure of steels K340 and K340/AlCrSiN were examined. Tribological tests were conducted using the ball-on-disc tester in compliance with the ASTM G99 standard. The tests were performed under dry unidirectional sliding conditions, using an Al₂O₃ ball as a counterbody. The wear factor and coefficient of friction were estimated and analyzed with respect to hardness and alloying composition of the materials under study. Scanning electron microscopy (SEM) observations were made to identify the sliding wear mechanisms of the analyzed tool steels and physical vapor deposition (PVD)- coated K340 steel. In contrast to the harsh abrasive-adhesive wear mechanism observed for uncoated tool steels, the abrasive wear dominates in case of the AlCrSiN. The deposited thin film effectively prevents the K340 substrate from harsh wear severe degradation. Moreover, thanks to the deposited coating, the K340/AlCrSiN sample has a coefficient of friction (COF) of 0.529 and a wear factor of K = 5.68 × 10^-7 m³ N^-1 m^-1, while the COF of the reference tool steels ranges from 0.70 to 0.89 and their wear factor ranges from 1.68 × 10^-5 to 3.67 × 10^-5 m³ N^-1 m^-1. The AlCrSiN deposition reduces the wear of the K340 steel and improves its sliding properties, which makes it a promising method for prolonging the service life of metalwork tools.