Influence of the different variants of the surface treatment on the durability of forging dies made of Unimax steel

The study performs an analysis as well as makes a comparison of the durability of forging tools used in the die forging process made of high-strength steel Unimax. For tool steel WCL (1.2343 according to DIN), which has been applied so far, the obtained average durability has been at the level of about 6000 forgings. Additionally, in order to increase the durability of the Unimax material, two surface treatment variants were applied: in the form of ion nitriding (for nitrides A) and gas nitriding together with a PVD-Alvin coating, which were compared with the results for an insert without surface treatment. For each variant, three tools were produced, in order to obtain repeatable and verified results. In the first place, an analysis of the working conditions of the tools was performed through thorough observations of the industrial forging process, particularly the tribological conditions, including the manner of lubrication as well as the temperature distributions, by means of, among others, thermovisual examinations. Additionally, numerical modeling of the process was carried out with the purpose of a more accurate analysis of the tool work in contact. Next, a detailed analysis of the exploitation of the worn tools was performed, including a macroscopic and geometrical analysis through 3D scanning, microscopic optical, and SEM tests as well as microhardness measurements. The obtained results demonstrated that only the application of the new material, Unimax, itself caused a durability increase by 2.5 times with regard to the WCL steel used so far. In turn, with the application of additional surface engineering techniques, Unimax tools characterized in better operational properties (high thermal and abrasive wear resistance at elevated temperatures), which made it possible to forge over four times more forgings, i.e., 26,000 items, after nitriding with a PVD-Alvin coating had been applied to the tool.