| Abstract: | Semi‐solid metallurgy (SSM), also known as “thixoforming” or “thixoprocessing”, is of special interest as a new potential manufacturing technology for components in the automobile, machine and electronic industries. The aim of this technology is to produce complex shapes which cannot be produced with conventional processing methods. An important process step of semi‐solid processing (SSP) is the reheating and isothermal holding of the billet within the solid‐liquid range in order to obtain the required fraction liquid content and the desired globular microstructure. Aside from the investigation of billet heating and the development of a suitable tool design, the development and evaluation of adequate microstructures over a wide temperature area is very important. The focus of this paper is to determine the semi‐solid area of different steels through Differential Thermal Analysis (DTA) measurements. To determine a process window for handling the alloys in the semi‐solid state, the DTA‐results can be combined with microstructure parameters. Subsequent quenching experiments show the development of the microstructure parameters (e.g. grain size, phase distribution, volume fraction, shape factor, matrix character, contiguity, and particle density of the primary solid and liquid phases). A comparison of the slopes of the determined solid‐liquid areas for different steels show the width of the melting or freezing intervals to evaluate the possible process windows. DTA‐experiments performed at different heating rates show the influence of faster heating and cooling rates on the solidus‐liquidus interval. To evaluate the suitability for the thixoforming processes, this paper describes, and then compares, the semi‐solid intervals of different steel grades, which have been investigated in the Department of Ferrous Metallurgy at the RWTH Aachen University. The tool steel HS 6‐5‐3 and the cold work tool steel X210CrW12 have a wide semi‐solid area, which can be explained due to the dissolution of different carbides. In contrast to this, the steels C45, 42CrMo4, 16MnCr5, 34CrNiMo4, 100Cr6, X220CrVMo13‐4 and the Alloy 33 show a much smaller semi‐solid area. |
