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

在考虑气固相互作用的预合金化粉末冶金钢和耐磨MMC的第一个资金周期框架内，研究了含氮气氛对烧结件的烧结行为和力学性能的影响。目的是了解粉末材料在气固相互作用过程中的基本过程。这些知识应用于优化工艺和/或材料。在此背景下，研究了两种不同的冷作工具钢，一种热作工具钢和一种CrMn奥氏体不锈钢的粉末颗粒表面和块状组织的过程。第二个资助期的一个主要议题是用两种新材料--双相不锈钢和粉末冶金生产的金属基复合材料(PM-MMC)来补充所取得的成果。粉末冶金MMC的母材是经过广泛分析的CrMn奥氏体不锈钢。一方面，PM-MMC结合了富碳化物冷作工具钢和单相奥氏体钢的知识。另一方面，氮作为合金元素在双相钢领域具有重要的技术意义。其目的是阐明大气对表面(还原)和本体(相变、相组成等)过程的影响。第二个主要主题是利用第一个资助期获得的基本结果来优化与技术相关的工艺：就奥氏体不锈钢而言，重点在于通过实现最佳的C/N比和完全致密化相结合来提高强度和耐腐蚀性。为此，应优化工艺路线(温度和大气控制)，包括致密化、体积氮浓度和还原工艺。如果是冷作工具钢，在含氮气氛下烧结会降低材料的固相线温度。这种效应可以通过富钒碳化物向碳氮化物的转变来解释，导致碳释放到金属基质中。该研究的目标是设计一种热处理(温度和大气控制)，结合氮气气氛的有益效果，同时优化所研究的钢的淬透性。该研究项目的目的是进一步建立氮合金化的气固相互作用，以优化不同高合金钢的机械、腐蚀和摩擦学性能以及工艺参数。

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.