Ni- and Co-BASED SUPERALLOYS AS POTENTIAL TOOL MATERIALS FOR THIXOFORMING OF STEELS

Thixoforming of steel is very demanding on tool materials. With process temperatures often exceeding 1300 degrees C, the surface-to-interior temperature gradients and the thermal stresses thus generated across the die are much larger than with Al and Mg. The principle die failure mechanism is thus claimed to be thermal fatigue as the mechanical loading on the tooling is modest owing to a mushy feedstock. The erosive wear caused by abrasion and impact of the already solid particles in the slurry and high temperature oxidation of the die surface, cannot be overlooked either. The conventional hot work tool steels were shown to rapidly deteriorate under such severe conditions. Suitable die materials with extended service life are required to set up an appropriate process for the production of steel parts on an industrial scale. Ni- and Co-based superalloys were tested in the present work for their potential to withstand the steel thixoforming environment for an economically acceptable life.