The thixoforming of metals is a new forming technology, which combines the advantages of casting and forging and focuses on the production of structural components with complex shapes. Various components made of aluminium and magnesium are already industrially produced. Apart from this, using steels in the thixoforming processes is still a matter of research. This paper summarises the state of the art of steel thixoforming. Besides relevant material and process parameters, different process routes, numerical modelling techniques, and tool requirements are discussed. In addition, thixoformed prototypes of different steel grades are presented and evaluated with defect index cards, which characterise occurring defects and give suggestions how to avoid them. The design of suitable tool materials and tool concepts, the development of heating strategies which provide a homogeneous temperature distribution, and the development of thixoformable steels are main topics of current research. This paper focuses on the technology of steel thixoforming with regard to the material requirements, the production processes, and the accompanying current technical problems.

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This paper describes the basic investigation on material behaviour of cold working steel X210CrW12 in semi-solid state concerning the semi-solid forging. It includes a study of flow behaviour and microstructure by means of a high temperature isothermal upsetting test applying a special cylinder sample with a shell, which is designed to avoid collapsing of samples during the compression. The flow curve of the semi-solid steel is determined by an inverse modelling via FEM using the obtained load curve of the samples and the separately obtained flow stress of the shell material. An extensive microstructure study of the compressed samples provides a comprehensive understanding on the flow mechanism of the semi-solid steel. At the end of the paper some general restrictions and remarks for the semi-solid forging process are given based on the gained results.

The experimental set-up and the results of high temperature compression tests for the characterization of tool materials for steel thixoforming are presented. The scope of this test is to reproduce the load profile of steel thixoforming processes consisting of mechanical, thermal, tribological, and chemical components on the forming mould. Tool materials were chosen following a concept within the Collaborative Research Center -SFB 289 -"Forming of metals in the semi-solid state and their properties". Three materials groups are distinguished: thin film deposited by physical vapor deposition (PVD) and plasma assisted chemical vapour deposition (PACVD), thick coatings (thermal spraying), and bulk ceramic materials. Samples were characterized using scanning electron microscopy (SEM), electron-dispersive spectroscopy (EDS) and X-Ray diffraction analysis (XRD). The results show varying resistance of the tool materials concerning the load profile. In order to provide an appropriate tool solution for the thixoforming of steels, different load profiles within the forming moulds are identified and the corresponding tool part is made from that material with the best performance.

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