Emir Subasic

Thixocasting combination spanners using stainless steel X39CrMo17

Forging is state-of-the-art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high-strength forging steels were used to provide cavity-free components with high mechanical load capacity. Moreover, forging is a cost-effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near-net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi-solid state. Cast parts were heat-treated to enhance the toughness of components, which was subsequently measured by a standardized torque test. Moreover, a hypothetical approach of a possible, industrial batch process was carried out using the simulation software MAGMAsoft.

A multi-phase micro-segregation model

Abstract A multi-component multi-phase micro-segregation model was developed to cope with eutectic transformations of ductile iron, assuming mixed dendritic–globular solidification morphology. Solute partitioning is calculated by an equilibrium assumption at the interfaces using commercial CALPHAD software. Time-sensitive micro-segregation patterns and phase fractions are solved by the micro-segregation model. The development of fraction liquid over temperature with time was compared to Gulliver–Scheil simulations for a model with and without cross-diffusion. The micro-segregation model was coupled to a commercial process simulations tool to deal with interaction effects between material and process scale during solidification of a benchmark test casting made of EN-GJSA-X NiCr 20–2. The precipitation kinetics of phases, especially of graphite, is of particular interest during solidification of ductile iron, due to feeding effects. The coupling procedure as well as important aspects during solidification of ductile iron will be explained.