Thixoforming : Semi-solid Metal Processing

84j 3 Material Aspects of Steel Thixoforming
Figure 3.33 Primary structure of the examined 100Cr6 states.
The alloying of titanium results in a reduction in the austenite grain growth in the
solid state because of the formation of TiN particles. The experiments in the partial
liquid state at 1400 C showed that this effect disappeared because the cast alloyed
with titanium and the cast without titanium possess very similar grain sizes.
Therefore, TiN cannot be used for the reduction of the unwanted grain growth
during holding in the partial liquid state. Only the indirect effect of the reduction of
the austenite grain growth during heating can be used in the solid state. In this case,
the grain size of the titanium-alloyed cast is lower than that of the cast without
titanium, as the examinations of the third test series show. For short holding times in
the partial liquid state, the growth constraint of the TiN particles in the solid state still
has an influence on the microstructure in the partial liquid state.
The metallographic image parallel to the rolling direction in the third test series
shows that (bottom left) the carbide bands continue within the austenite grains and
Figure 3.34 Element distribution images (N, Ti, Cr, C) of titaniumdoped
100Cr6 specimens quenched from the partial liquid state.