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 wer e investigated. They were: TIN. CrN, (Ti,Cr)N and Ti(C,N). The composites i nvestigated were created by means of the surface 'duplex' treatment method in a two stage separable cycle (the nitriding process and the PVD coating d eposition were carried out with different devices). The nitriding process w as executed with the use of the regulated gas nitriding method, whereas the PVD coating was executed by means of the are-vacuum method. The tools test ed 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 . The paper presents the results of maintenance investigations, executed tind er 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%. T he smallest durability was noted for tools covered with the composite 'nitr ided layer/TiN coating'. The results obtained proved that a proper choice o f the composite 'nitrided layer/PVD coating' structure may increase the dur ability of tools considerably for hot plastic working. (C) 2000 Elsevier Sc ience S.A. All rights reserved.