Capabilities of Thixoforming of Steels

Abstract

Thanks to innovative processing routes, even conventional materials which have been around for years can be manipulated to obtain unconventional microstructures with specific mechanical and physical properties. This also holds for various semi-solid forming processes, which represent a dynamically developing field. Yet, these processes are still under development due to their technological complexity. One of the innovative methods of semi-solid processing is mini-thixoforming. As it focuses on very small-size products, it offers very steep heating curves and extremely high solidification and cooling rates, unlike conventional thixoforming. These features have profound impact on the evolution of microstructure and the resulting properties of the product. As in the conventional thixoforming process, complex-shaped products can be manufactured with high precision, using a single forming step. The potential and capabilities of the process were explored using the ledeburitic X210Cr12 steel as the experimental material. Once the optimum conditions were found, other tool steels were used for trials as well. Thanks to closely-controlled temperature field, mini-thixoforming was successfully used on a steel with a freezing range of a mere 15 °C. The microstructure evolution in the mini-thixoforming process is an issue of its own. The final microstructure of X210Cr12 after processing consisted of more than 90 % of austenite and chromium carbides. Semi-solid processing of a steel with a high vanadium content led to a microstructure comprising MA matrix and globular vanadium carbides. In a low-alloyed steel, martensitic microstructure was obtained.Keywords: thixoforming, mini-thixoforming, semi-solid processing, tool steels