Transcript AVOIDING NOZZLE CLOGGING DURING CONTINUOUS CASTING …

GTT-Technologies
AVOIDING NOZZLE CLOGGING DURING
CASTING OF STEELS
Steels contain additions of Aluminium (grain refining)
and Sulphur (machinability). In both cases, nozzle
clogging can occur during continuous casting.
o At what temperatures, O- and Cacontents can a steel with a given Aland S- content be cast without nozzle
clogging?
GTT-Technologies
AVOIDING NOZZLE CLOGGING DURING
CONTINUOUS CASTING OF STEELS
The figures show:
• Figure 1: From the phase diagram one can find which phases can
coexist at 1600°C in the system Al2O3-CaO.
• Figure 2: Depending upon the O- and Ca- content of the steel, one
can find at a given temperature either, solid aluminates, aluminate +
liquid oxide, liquid oxide only, or liquid oxide + CaS precipitate in
equilibrium with the liquid steel. Experimental findings are also
shown in the diagram.
• Figures 3, 4 & 5 show the nozzle clogging behaviour in different
perspective, e.g. when adding CaSi to a steel bath.
The conclusion is, that by influencing thermochemical parameters, it is
possible to find a “Slag-window” in which nozzle clogging does not
occur.
GTT-Technologies
FIGURE 1:
The system CaO – Al2O3
D:\FSage55\Results\SlagWindow\Al2O3.CaO.TC.wt%.emf
24.01.2007
from FACT database
2200
2000
Slag
1800
T(C)
Slag + CaO
CaO.6Al2O3 + CaO.2Al2O3
1600
CaO.2Al2O3 + CaO.Al2O3
3CaO.Al2O3+ CaO
1400
CaO.6Al2O3+Al2O3
3CaO.Al2O3+ CaO.Al2O4
1200
0
20
40
60
CaO wt%
80
100
GTT-Technologies
FIGURE 2:
D:\FSage55\Results\SlagWindow\SlagWindow1600C.2.emf
24.01.2007
Fe - S - Al - Ca - O
[S] = 50 wt ppm, [Al]= 0.04 wt%, T=1600°C
50
CaS + Fe-liq
40
CaS + Slag + Fe-liq
Slag + Fe-liq
[Ca] wt ppm
30
CaO.2(Al,Fe)2O3 + Slag + Fe-liq
20
CaO.2(Al,Fe)2O3 + Fe-liq
10
CaO.6(Al,Fe)2O3 + CaO.2(Al,Fe)2O3 + Fe-liq
CaO.6(Al,Fe)2O3 + (Al,Fe)2O+3 Fe-liq
Fe-liq
Fe-liq
0
0
10
20
30
[O] wt ppm
40
50
60
GTT-Technologies
Figure 3:
Phase Fields for T=1600 C and various wt ppm Oxgen
0.0
o
T = 1600 C
CaO/Liquid slag
log [wt% total Ca]
-1.0
Liquid slag/CaAl2O4 or CaAl4O7
Schurmann et al.[84]
Kimura and Suito[87]
Suito et al.[85]
Suito et al.[85]
Kimura and Suito[87]
Lee and Suito[83]
Ichihashi and Ikeda[86]
-2.0
Lee and Suito[83]
5
CaO
8 10
-3.0
5
Liquid slag
CaAl2O4
Liquid slag
-4.0
wt ppm oxygen =
50
20
30
15
10
CaAl4O7
8
5
8
10
15 30
20 50
CaAl12O19
-5.0
-5.0
-4.0
-3.0
-2.0
-1.0
log [wt% total Al]
0.0
1.0
GTT-Technologies
Figure 4:
Precipitation phases as function of CaSi addition
Amount of inclusions and [S] and [Ca], wt ppm
250
Initial conditions
o
T = 1600 C
wt ppm [0] = 6
wt ppm [S] = 30
200
wt ppm [Al] = 500
wt ppm Al 2O 3 = 100
150
CaO
Liquid
Al 2O 3
CaAl4O7
100
CaAl12O19
CaS
50
[S]
0
0
10
20
30
40
50
60
70
Addition of CaSi(kg) to 100 tonne liquid steel
80
90
100
Figure 5:
Amount of inclusions and [S] and [Ca], wt ppm
GTT-Technologies
Precipitation phases as function of CaSi addition, higher initial Al2O3
700
Initial conditions
wt ppm [0] = 6
wt ppm [S] = 30
wt ppm [Al] = 500
wt ppm Al2O3 = 300
600
500
400
o
T = 1600 C
CaO
Liquid
Al2O3
300
CaAl4O7
200
CaAl12O19
100
]
[Ca
CaS
[S]
0
0
10
20
30
40
50
60
70
80
Addition of CaSi(kg) to 100 tonne liquid steel
90
100