Thixoforming : Semi-solid Metal Processing

160j 5 Thermochemical Simulation of Phase Formation
Figure 5.10 Molar liquid fraction as a function of temperature for
100Cr6 using equilibrium (solid), standard Scheil (dash-dotted),
modified Scheil (dotted) and DICTRA (dashed) calculation.
simulation. The standard Scheil calculation is completely different. The fact that the
equilibrium and DICTRA curve are very close suggests that there is very little
segregation, but both Mn and Cr do segregate appreciably. It is not possible to
determine the liquid fraction from quenched metallographic samples in this steel [5].
Figure 5.11 shows a DICTRA simulation of quenching from 50% liquid. There is only
a gradual change in the composition profiles and there is no possibility of distinguishing
the austenite present in the initial state from the austenite formed during
quenching. Further details are given in Chapter 3.
5.3.3
Compositional Variations
As for X210CrW12, the influence of compositional variations can be quantified in a
straightforward manner. In the following, the influence of the composition on a
number of key points for 100Cr6 is considered. These are linearized around the
standard composition (given in Table 5.1) and given in mass%. They are roughly valid
within the composition limits given by, for example, the DIN standard. The liquidus
is given by:
T L ¼ 1455 C 72D%C 16D%Si 4:0D%Mn 1:2D%Cr ð5:7Þ
The temperature at which there is 50% liquid is given by:
T 50 ¼ 1418 C 109D%C 26D%Si 5:3D%Mn 0D%Cr ð5:8Þ