Influence of the application of a PN+Cr/CrN hybrid layer on the improvement of the lifetime of hot forging tools

This article presents the results of field tests performed on forging tools in a selected lid hot forging process. The aim of the studies was to increase the durability of hot forging tools. Different coating types dedicated to hot forging tools were proposed and first tested in laboratory conditions. Based on the laboratory test results, the PN + Cr/CrN hybrid layer was selected to improve tool durability. Tools (upper punches used in second forging operation) with a PN + Cr/CrN layer applied on them were tested in comparison with gas-nitrided tools. The hybrid layer was produced on a plasma-nitrided substrate, onto which a PVD Cr/CrN coating was deposited. All the analyzed tools were tested in industrial conditions through the manufacturing of specific quantities of forgings. Next, the wear of each tool was analyzed by surface scanning and then compared to the CAD model. All the tools were checked for changes in the surface layer under an optical and a scanning electron microscope, as well as by way of a microhardness measurement. The results obtained in industrial conditions confirmed the effect of improvement of the forging tool lifetime owed to the application of the PN + Cr/CrN hybrid layer.