Some values of interaction parameters are given below.
| Alloying elements i = |
C |
Cr |
Ti |
P |
Si |
|
0.045 |
+0.005 |
-0.22 |
0.011 |
0.027 |
|
0.13 |
- 0.045 |
- |
0.051 |
0.047 |
|
 |
(8) |
 |
(9) |
Let us calculate value of  when molten steel is degassed at 1850 K under vacuum. The pressure above the melt is reduced in one case to 1mm Hg and in other cases to 0.1 mm Hg and 10 mm Hg. Steel contains  rest iron. Assume  .
| Pressure (mmHg)
0.1
1.0
10 |
[ppm H]
0.218
1.092
3.450 |
We note that with the decreasing pressure above the melt dissolved hydrogen in steel decreases. At 10 mm Hg pressure above the melt, dissolved hydrogen is 3.450 ppm which decreases to 0.218 ppm at 0.1mm Hg pressure, which is 6% of hydrogen at 10mm Hg pressure. Higher degree of vacuum is beneficial with reference to degassing. But higher degree of vacuum requires proper selection of ladle refractory material to avoid decomposition of the refractory and vacuum equipment. Also side reactions may occur at higher degree of vacuum.
|
