Influence of Different Plasma Nitriding Treatments and Coatings on the Wear Behaviour of Forging Tools for the Production of Automotive Diesel Injection Parts

摘要

Forging tools have a short lifetime compared to cold forming tools, e.g., for sheet metal forming. Tool life quantities are often limited to just a few thousand parts. High local surface temperatures alternately to spray cooling with water based lubricants fatigue the tool material. Crack initiation and crack growth due to thermal shock exposure often cause spalling of the tool steel and are starting points of extensive wear. Hard coatings like CrN or TiAIN have only a minor influence on this behaviour. That's why forging tools are mostly uncoated up to now. On the other hand plasma nitriding has a significant influence on the ductility and crack resistance of the tool surface especially under thermal shock conditions. Exemplary the main wear mechanism will be discussed for plasma nitrided and additionally coated forging tools, made from X38CrMoV5-3 (1.2367) hot forming tool steel. The influence of nitriding parameters like temperature, nitrogen flow and nitriding time on nitriding depth, hardness and crack sensitivity will be analysed. Different chromium based coatings like CrWN and CrVN were investigated. Comparative application tests in the production of automotive diesel injection parts showed the influence of the different surface treatments on the wear behaviour.