Thixoforming : Semi-solid Metal Processing

Cr (mass%)
25
20
15
10
grain growth
1330ºC
Cr
C
2
5
1
solid phase eutectic phase
solid phase
0
0
120 130 140 150 160 170 180 190 200
Distance (µm)
Figure 3.24 Element contents at a former solid–liquid boundary
surface, where the grey underlaid areas show the fields in which
the former phase boundary surfaces could have been located.
existed, whereas in the areas of the eutectic with carbon and chromium contents
above 2% or 8% (peak), liquid phase was present. In the grey underlaid transition
area, the chromium content increases slowly, which fits well with the diffusion
calculations. However, no conclusion can be drawn about where the austenite–liquid
phase boundary was located within the transition area at the time of quenching. Due
to the shallow transition of the element concentrations, the grain growth cannot be
determined with this analysis method and the determination of the liquid-phase
content or the structural morphology in the partial liquid state is, therefore, also not
possible by means of a microprobe.
Table 3.3 shows the thermodynamically calculated and measured element contents
within the austenite. Whereas the carbon contents are in very good agreement, the
deviations are higher for tungsten. Also for chromium and silicon, slightly higher
element contents are calculated than measured experimentally. However, the tendency
concerning the depletion and the enhancement of the elements in the different
phases could not be confirmed.
In conclusion, it can be noted that an estimation of the former grain boundary
positions in the partial liquid state seems to be very difficult or even impossible due to
Table 3.3 Comparison of the calculated and measured element
contents (line-scan) within the austenite.
3.4 Structural Parameter Development and Material Selectionj75
C (%) Cr (%) Si (%) W (%)
1305 C (calculated) 1.13 8.95 0.31 0.31
1290 C (line-scan) 1.23–1.32 8.29–8.85 0.26–0.27 0.44
1285 C (calculated) 1.23 9.16 0.32 0.34
8
7
6
5
4
3
C (mass%)