Thixoforming : Semi-solid Metal Processing

Figure 5.14 The density of 100Cr6. The dashed curve shows
the density in the case when austenite is retained metastably
below its stable range.
X210CrW12, thus relieving the situation somewhat. The melting behaviour can be
expected to be different from that of X210CrW12. It is unclear which sites are more
preferred for nucleation of the liquid. The more probable are grain boundaries and
non-metallic inclusions. The coarseness of the microstructure is probably controlled
by the (austenite) grain size, which can be rather coarse, leading to large globules.
Further nucleation of liquid droplets within the globules, in particular when they are
large, may be possible by self-blocking remelting as described in Chapter 2 and by
Kleiner et al. [22]. Reducing the austenite grain size appears to be an effective way to
reach an acceptably small globule size with no or limited internal droplets [23].
5.4
Calculations for the High-speed Steel HS6-5-2
5.4 Calculations for the High-speed Steel HS6-5-2j163
So far, only a relatively small amount of work has concerned the high-speed steel
HS6-5-2 (or any other high-speed steel). The physical metallurgy of this steel, as for
other high-speed steels, is very complex, involving several different carbides. It also
shows very strong microsegregation, making it difficult to produce using conventional
casting. Here, semi-solid processing could open up new possibilities. A
calculated temperature versus mass% C phase diagram is shown in Figure 5.15.
The interesting phase field here is the one marked g þ MC þ M 6C. This shows the