This paper focusses on the development of materials for exhaust gas components. The present work will focus on a ferritic SiMo-cast iron to create an economic alternative to the austenitic D5S. Aluminum and silicon are essential for this material development because they increase the transformation temperature. They also improve the durability of the protective oxide layer. Additionally, aluminum improves the high temperature mechanical properties by precipitation of a kappa-phase. The ferritic SiMoAl cast iron shows very good oxidation resistance and also mechanical properties.
By a vibration treatment during the solidification process it is possible to change the structure. Model tests were accomplished in order to understand the procedures as deep as possible. On cylindrical samples the influence of a vibration treatment for the process of the solidification was examined. Pure aluminium and the eutectic alloy AlSi12 showed clear differences in the solidification course and in the casting structure.
The present study investigated existing and potential approaches for hot cracking analysis of cast alloys and showed a promising and very applicable new specimen for high alloyed steels. The reliability of this specimen has been demonstrated by adding niobium to alloy HH (ASTM A297), or alloy 1.4837 (ISO 11973). Niobium shows a very positive impact on hot cracking behavior and can thereby reduce scrap in steel foundries. Amounts above 0.6 wt% niobium can reduce the size and number of hot cracks significantly. The reduction of hot cracking tendency was quantified by the cracking factor CFNb2. The positive effect is associated with the reduction in solidification interval length that was measured by thermal analysis and the observed “healing” of cracks in the microsections. Both effects are promoted by niobium. The promotion of the ferritic solidification seems to have no positive impact on the hot cracking behavior.
Low pressure casting is a very well established process for the casting of aluminium alloys. In the field of ferrous materials, however, the process has so far only found a few applications. The crucial reasons for this are the low flexibility and poor economic efficiency of the existing technologies. Since 2016, a new technology has been developed at the Foundry Institute of the TU Bergakademie Freiberg, in which an induction crucible furnace can be used as a melting unit and, in combination with a cover including a casting pipe, as a casting unit. The new technology stands out from existing low-pressure casting technologies for ferrous materials, particularly in terms of its flexibility and cost-effectiveness. The main focus of the activities was the development of a casting pipe as well as the verification of its lifetime, the elaboration and verification of process parameters and sequences as well as the upscaling of the technology for an industrial application. In all considerations, the focus was on both the technical feasibility and the economic efficiency of the process. The result is extensive expertise that can be used in the future to offer a finished product for industrial applications as a plug-and-play solution together with an induction furnace construction company.
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