Premature tool failures in powder pressing and other tooling applications, such as chipping of tool edges, plastic deformation and adhesive wear are of different origins. At Erasteel the possible failure mechanisms have been recognised and a substantial amount of grade development, process development and customer market support has been aimed at finding means to counter them.
A good example of this is Erasteel’s constant drive to improve the “cleanliness” of the powder-metallurgy-produced ASP-steels. ASP-steels are high performance powder metallurgy high-speed steels (PM-HSS) which are used in many different types of demanding tooling applications such as cutting tools, cold forming tools, hot work tools and powder pressing tools.
Thanks to the improved levels of cleanliness, ASP-grades have reached very high levels of strength, which implies a reduced risk for tool chipping and the possibility for tool users to put high stresses on the tool edges. The latest achievement from Erasteel in improvement of cleanliness comes from the introduction of the Dvalin process by which carbide agglomerate inclusions in steel are minimised.
Thanks to the Dvalin process, Erasteel has managed to reach an unprecedented level of cleanliness, which in turn also has implied a substantial improvement of strength at a given hardness. In addition to the improved strength, a high cleanliness implies additional advantages such as a better polishability, better fatigue resistance etc.
For high hardness materials, such as ASP-steels, it is the size of the largest defect in the part of the tool under high tensile stress that sets the maximum strength. The ASP-steels with refined microstructure and very high level of cleanliness implies materials of very high strength. However, the full potential of ASP-steel is sometimes not used due to limited surface quality. Often, for the latest generation of ASP-steels, the bulk material is free from imperfection, and surface defects such as scratches or structural changes owing to the manufacturing of the tool are instead the limiting factor for the strength of the tool edge.
Adhesive wear, or galling, is a tool failure mechanism that can be encountered in powder pressing of material such as stainless steel or aluminium. Adhesive wear appears if the work material sticks or bonds to the tool material, sometimes this bond between the work material and tool material is very strong and in such case parts of the tool material will be removed when tool and work material is separated. A traditional solution to adhesive wear is from the use of lubrication, nitriding or PVD-coating. However, these solutions have inherent drawbacks such as environmental issues when using lubrication, brittleness for nitrided material and the need for recoating when using PVD-coatings. To circumvent these problems, Erasteel has developed a new anti-galling steel ASP2040. ASP2040 is a grade of steel having a unique chemical composition with a very high nitrogen content. Thanks to the high nitrogen content, ASP2040 combines high hardness and high wear resistance with very good anti-galling properties. When using ASP2040 very good anti-galling properties can be expected without the use of lubrication, coating or nitriding.
• The Dvalin process takes its name from the dwarf of Norse legend who forged the magic sword Tyrfing with a golden hilt that would never miss a stroke, would never rust and would cut through stone and iron as easily as through clothing or armour.
• Erasteel says it is “dedicated 100 per cent to HSS” and as the world’s leading producer of high-speed steels offers the widest range of products and grades on the market. It is part of the Eramet Group, formed through the 1992 merger of Kloster Speedsteel AB of Sweden and the French company Commentryenne

The author
This article is drawn from PM Tool steels for improved performance in powder pressing tools, a paper by Stefan Sundin, who works for Erasteel Kloster AB, Sweden. It was given at PM Asia 2007 in Shanghai last month.