Semi-solid processing and its as yet unexplored potential

Thanks to the available advanced control technology, manufacturing processes which have been described in the past but their hidden potential remained untapped are now continuing to be developed. As a result, even conventional materials which have been around for years can be manipulated to obtain unusual microstructures with specific mechanical and physical properties. Semi-solid processing belongs to the above-described group: it had been studied in the past but, due to complicated process control, it gradually lost its appeal. However, advanced techniques of temperature field control enable engineers to control this complex process accurately. 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, when compared to conventional thixoforming. The capabilities of this process were tested on X210Cr12 ledeburitic tool steel. After the optimum processing conditions were found, additional materials were tried, ranging from low- carbon microalloyed steels through medium-alloy steels to high-alloy tool steels. The microstructure evolution upon the mini-thixoforming process is an issue of its own. The final microstructure of X210Cr12 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-alloy steel, martensitic microstructure was obtained.