12th Tooling Conference & Exhibition - Tooling 2022

To predict the solidification and product properties of tool steels with complex chem-ical compositions, an understanding of the transformation behaviour during and after solidification, depending on the chemical composition, is crucial. Therefore, the qua-ternary Fe-C system with 10 w.t.-% Cr and 3% W (subsystem of cold work steels, with M7C3 and M23C6 carbides) and the Fe-C system with 6% W and 5% Mo (simplified high speed steel without vanadium, with M6C and MC carbides) were selected.
As common DSC (differential scanning calorimetry) measurements of as-cast materi-als may not allow the equilibrium transformation temperatures of carbides to be de-tected, a unique time-temperature DSC setup was developed. Regular diffusion an-nealing of as-cast carbidic steels is time-consuming, but with in-situ heat treatment during the DSC measurement in the semi-solid zone (30-50% liquid phase fraction), a status close to equilibrium can be achieved within minutes due to the high diffusion. To prove the potential of the in-situ high-temperature equilibration by partial pre-melting in the DSC, additional “equilibration and quenching” experiments were per-formed at selected temperatures in a Tammann-type furnace and investigated using SEM-EDS and XRD analysis. By combining these methods, carbide types and the transformation temperatures can be verified to evaluate and construct complete phase diagrams.