Forging of Extremely Finely Grained Microstructure Materials by Use of Thermomechanically Treated Base Material

The newly developed forging process chain is based on a thermomechanically treated base material with an optimum microstructure at the edge of the nano-scale. It is associated with maximum properties in terms of high strength and excellent toughness. This offers the possibility of a novel and extraordinarily energy-efficient process chain of manufacturing of highly loaded and safety relevant parts in all kinds of machinery. Therefore, it is necessary to shape the thermomechanically treated base material, with its superior properties, without a loss to the near net shape part. Hot and warm forging processes are known as appropriate and efficient for the forming of high strength materials while also ensuring the materials’ formability is not overstressed through strain hardening. Within this paper it could be shown that the original microstructures were maintained, and in some cases improved. Therefore, a targeted heating strategy and a warm forging process were designed. The characterisation and numerical modelling of the novel material is presented and the effects of heating and forming on the microstructure of the pre-treated base material are shown in microsections. The influence on the resulting mechanical properties such as the significant increase of roughly 150 J (+400 %) in the notch impact energy (compared with forged parts from untreated material) are detailed described. Additionally, the influence of forming parameters on the microstructure such as effective plastic strain and forming temperatures are discussed.