Influence of the structure of the composite: ‘nitrided layer/PVD coating’ on the durability of tools for hot working

The paper presents research results of the influence of the ‘nitrided layer/PVD coating’ composite on the durability of tools for hot plastic working. Four structures of the composite differing in the PVD coating material were investigated. They were: TiN, CrN, (Ti,Cr)N and Ti(C,N). The composites investigated were created by means of the surface ‘duplex’ treatment method in a two stage separable cycle (the nitriding process and the PVD coating deposition were carried out with different devices). The nitriding process was executed with the use of the regulated gas nitriding method, whereas the PVD coating was executed by means of the arc-vacuum method. The tools tested were forge dies made of ISO steel 35CrMoV5 (0.4%C, 0.4%Mn, 1.0%Si, 5.0%Cr, 1.3%Mo, 0.3%V) designed for the plastic working of automotive half-shafts. per presents the results of maintenance investigations, executed under manufacturing conditions, obtained for tools used for hot forging which were covered with different composites. The investigations proved that the best durability was achieved for tools covered with the composite ‘nitrided layer/CrN coating’, for which the increase in durability was almost 90%. The smallest durability was noted for tools covered with the composite ‘nitrided layer/TiN coating’. The results obtained proved that a proper choice of the composite ‘nitrided layer/PVD coating’ structure may increase the durability of tools considerably for hot plastic working.