Thixoforming : Semi-solid Metal Processing

372j 10 Thixoforging and Rheoforging of Steel and Aluminium Alloys
Figure 10.3 Selected thixoformed components made of different steel alloys [3].
Analogous to the thixocasting process, different routes for preparation of the
feedstock can be applied for forging in the semi-solid state (Figure 10.4).
The conventional route begins with the casting of the precursor material, which is
cooled to below the solidus temperature and indirectly reheated into the semi-solid
interval (thixoforming). The rheo-process is characterized by cooling of the melt into
the semi-solid interval so that it is directly utilized for the forming operation
(rheoforming) (Section 10.3.7). In both cases, the forming operation in the semisolid
state is dependent on precise heating and reproducible handling of the
preheated precursor material [25]. In comparison with the processing of aluminium,
small variations of the process duration lead to critical differences in the temperature
in the steel billets due to the higher billet temperature and increased radiation
losses [6, 25].
Figure 10.4 Temperature control of thixoforming and rheoforming route.