Powder Metallurgy in Tooling - Theoretical Background, Material Production and Processing

The ledeburitic steels are long ago known as promising materials for tool applications. Their development over last two centuries led to the widening of the scale of manufactured materials and partly also to the quality improvement. Nevertheless, some of unwanted phenomena, the macrosegregation in particular, are immanent for the classical ingot metallurgy and can not be entirely suppressed by this production way. These consequences, caused by the heterogeneous nucleation and slow cooling, were overcame only by the use of the rapid solidification for the material production. Compared to the as-cast ingots, rapidly solidified powder exhibits a considerable refinement of the microstructure and is free of macrosegregations. These symptoms remain in existence also after the consolidation that results in an excellent structure and properties of steel billets. After the heat treatment, the tools made from the P/M ledeburitic steels have the hardness ranging between 700 and 800 HV and can directly be used in an industry. In several cases, however, further improvement of some surface properties is needed. Plasma nitriding, PVD-layering or their combination known as duplex - coating is successfully applied for the surface processing of P/M ledeburitic steels.