Sintering of prealloyed PM-steels and wear resistant MMC under consideration of gas-solid interaction

• Applicant: Professor Dr.-Ing. Werner Theisen
• Subject Area: Glass, Ceramics and Derived Composites
• Term: from 2008 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 86463846

In the frame of the first funding period of the project Sintering of prealloyed PM-steels and wear resistant MMC under consideration of gas-solid interaction the influence of a nitrogen containing atmosphere on the sintering behavior and the mechanical properties of sintered parts was investigated. The objective was to gain knowledge about fundamental processes of the powder material during gas-solid interaction. This knowledge shall be used to optimize the process and/or the materials. In this context, the processes on the surface and in the bulk of the powder grain of two different cold work tool steels, one hot work tool steel and one CrMn austenitic stainless steel were investigated. One main topic of the second funding period is to complement the obtained results with two new materials, a duplex stainless steel and a powder metallurgically produced metal matrix composite material (PM-MMC). The matrix material for the PM-MMC is the extensively analyzed CrMn austenitic stainless steel. On the one hand, the PM-MMC combines the knowledge about the carbide-rich cold work tool steels and the single phase austenitic steel. On the other hand, nitrogen as alloying element is of great technical relevance in the field of duplex steels. The objective is to clarify the influence of the atmosphere on the processes on the surface (reduction) and in the bulk (phase transformation, phase composition, etc.) of the powder grains.The second main topic is to use the obtained fundamental results of the first funding period for optimization of processes with technical relevance:In the case of the austenitic stainless steel the focus lies on the enhancement of strength and corrosion resistance by realizing an optimal C/N-ratio combined with full densification. For this purpose the processing route (temperature and atmospheric control) shall be optimized regarding densification, bulk nitrogen concentration, and reduction processes.In case of the cold work tool steels sintering under nitrogen containing atmosphere decreases the solidus temperature of the material. This effect can be explained by the transformation of the vanadium-rich carbides to carbonitrides resulting in a release of carbon to the metallic matrix. The ambition is to design a thermal treatment (temperature and atmospheric control) which combines the beneficial effect of an N2 atmosphere while simultaneously optimizing the hardenability of the investigated steels.The research project is aimed to further establish gas-solid interaction for nitrogen alloying in order to optimize mechanical, corrosive, and tribological properties as well as processing parameters of different high alloyed steels.

• DFG Programme: Research Grants
• Participating Persons: Professor Dr.-Ing. Stephan Huth; Professor Dr.-Ing. Sebastian Weber