Powder Metallurgical Tool Steel with Excellent Galling Resistance

摘要

Galling and adhesive wear are failure mechanisms responsible for irregular production interruptions and/or regular maintenance of tool steel components in blanking, cold forming, powder pressing etc. This phenomenon is predominantly in focus when soft and adherent work materials as austenitic stainless steel, mild and high strength steel and/or aluminum are used. Often, galling is counteracted by surface coating via nitriding, PVD or CVD. However, severe stress conditions may result in wear, delamination or abrasive penetration of the coating layer and this will result in products with surface defects. The tool set has to be refurbished and recoated if this is possible or be replaced with new tool components. In some cases the geometry of the tooling may prevent it from being surface coated. Instead of utilizing various coating processes to counteract galling/adhesive wear the steel may be manufactured with a process resulting in an "internal nitride coating". This process includes powder manufacturing, nitriding of powder, HIP and hot working of the PM capsule to flat or round bars. Tool making and heat treatment are according to standard procedures. When the tool needs refurbishment this can rapidly be performed in-house by conventional procedures as machining, grinding, electro discharge machining and polishing. This paper presents the properties of the new tool steel and results from industrial field tests.