Preliminary studies of increasing the durability of forging tools subjected to various variants of surface treatment used in the hot die forging process of producing valve forgings

Abstract

The paper discusses the durability of forging punches used in the industrial precision forging process of prducing valve forgings for truck engines. The tools are made of 1.2365 steel, and the forging material is high chromium-nickel steel -NCF3015. Due to the hard operational conditions in the forging process (cyclic thermal loads and high mechanical stresses, intensive abrasive wear), the tool life, in the case of forming these steels, is much shorter than in the case of producing forgings from typical carbon steel. In order to increase the durability of the punches, a surface engineering hybrid layer type: GI (ion nitride surface) and four PVD coatings (CrN, TiAlN, AlTiCrN and AlTiCrSiN) were used on a punch, whose working surface was divided into 4 quarters (one coating by one quarter). The tool wear was analysed and represented by the material destruction on the working surface of the punches, based on the 3D scanning and the change of the material volume of the periodically collected forgings (Indirect 3D scanning method). The punches were also subjected to a surface analysis with the use of SEM as well as a microstructure analysis (Light microscope) and hardness measurements. Based on the preliminary analysis, it was established that a few various destructive mechanisms are dominant (coating chipping and adhesive wear). The best results were obtained for the TiAlN coating and the worst for AlTiCrN. In order to confirm the final results, it is necessary to carry out further tests (one coating for one working surface of the punch) under industrial conditions.