Post on 29-Mar-2015
transcript
High temperature Oxidationof Si Containing Steel
Computational Metallurgy Lab.Graduate Institute of Ferrous Technology
Pohang University of Science and Technology
Song, Eun Ju
Contents
Introduction
Oxidation of Steel
Red-scale
Prediction of Oxide Formation and Growth
Oxidation Test and Characterization of Oxides
Conclusions
Introduction – Oxidation of Steel
• Oxide of iron
Fe1-yO - wüstite (0.04 <y<0.17) Fe3O4 - magnetite Fe2O3 - hematite
Fe1-yO : Fe3O4 : Fe2O3 = 95 : 4: 1
• Growth of oxides
FeO, Fe3O4 - controlled by outward diffusion
Fe2O3
- controlled by inward diffusion Wagner C. Z. Phys. Chem (1933)Paidassi J. Rev. Met (1957)
Introduction – Oxidation of Steel
• Oxide growth at high temperature - controlled by diffusion, with a parabolic behavior
Introduction – Red-scale
Fukagawa et al. ISIJ Int. (1994)
Introduction – Red-scale
• Effects of Ni
Oxides formed at 1250 ºC, for 1h (d) ; Fe – 0.1 Si – 0.001 Ni wt%(h) ; Fe – 0.1 Si – 0.1 Ni wt%
Fukagawa et al. Journal of ISIJ Tetsu to Hagane (1996)Asai et al. ISIJ international (1997)
Prediction of Oxides Formation
• Formation energy of oxides
2Fe + O2 = 2FeO,
Si + O2 = SiO2,
Fe + ½ Si + O2 = ½ Fe2SiO4,
Prediction of Oxides Formation
Fe - 1 Si wt% steel, P(O2)=0.2 Fe - 10 Si wt% steel, P(O2)=0.2
-200 0 200 400 600 800 1000 1200 1400
-800
-750
-700
-650
-600
-550
-500
-450
-400
-350
2FeO SiO
2
1/2 Fe2SiO
4
For
ma
tion
En
erg
y (k
J/m
ol)
Temperature (C)
-200 0 200 400 600 800 1000 1200 1400-850
-800
-750
-700
-650
-600
-550
-500
-450
-400
-350
2FeO SiO
2
1/2 Fe2SiO
4F
orm
atio
n E
ne
rgy
(kJ/
mo
l)
Temperature (C)
Prediction of Oxides Formation
Fe - 1 Si wt% steel, 1000 ˚ C Fe - 10 Si wt% steel, 1000 ˚ C
• Equilibrium phase
0.0 0.1 0.2 0.30.0
0.2
0.4
0.6
0.8
1.0
Mo
le F
ract
ion
w(o)
FCC SiO2 Fe2SiO4 FeO Fe3O4 Fe2O3
0.0 0.1 0.2 0.30.0
0.2
0.4
0.6
0.8
1.0
Mo
le F
ract
ion
w(o)
FCC SiO2 Fe2SiO4 FeO Fe3O4 Fe2O3
Prediction of Oxides Growth
• Growth of Fe2SiO4, SiO2
- controlled by outward diffusion of Si (∵ )
8.58 ×10-4 μm2 s-1 at 1000 °C
1.99 ×101 μm2 s-1 at 1000 °C
Prediction of Oxides Growth
Wagner C. Z. Phys. Chem (1933)
k(SiO2) k(Fe2SiO4) k(FeO)
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
1000
Gro
wth
Ra
te(
m2 s
-1)
1-Si 10-Si
1000 ˚ C 1250 ˚ C
k(SiO2) k(Fe2SiO4) k(FeO)
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
Gro
wth
Ra
te(
m2 s
-1)
1-Si 10-Si
Prediction of Oxides Growth
Bhadeshia H. Proceedings of Solid-Solid Phase Transformations (1999).
( μm-2 , A=1 μm2)
Oxide,α
Prediction of Oxides Growth
Volume Fraction of Oxides
sio2 fe2sio4 feo1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
Vo
lum
e F
rac
tio
n
1-Si 10-Si
sio2 fe2sio4 feo1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
Vo
lum
e F
rac
tio
n
1-Si 10-Si
1000 ˚ C 1250 ˚ C
Oxidation Tests
1. Surface polish
2. Oxidation at 1250 ˚ C and 1000 ˚ C for 2h in the air
3. Microscopy analysis with the cross section of the sample
10mm7mm
5mm
Steel
Steel C / wt% Si / wt% Mn / wt% Ni / wt% Al / wt% Fe
Alloy 1 0.1 - 1.5 - - balance
Si Alloy 0.1 0.943 1.54 - - balance
Ni Alloy 0.1 1.0 1.50 0.197 - balance
Al Alloy 0.101 1.01 1.49 - 0.216 balance
Characterization of Oxides
Si Alloy, 1000 ˚C
• Volume fraction, FeOx / Fe2SiO4
= 92 / 8 ~ 86 / 14
Characterization of Oxides
Si Alloy, 1250 ˚C
Characterization of Oxides
W = FeOM = Fe3O4
F = Fe2SiO4
20 30 40 50 60
0
500
1000
1500
2000
WM W
F
M
M
W,M
Si Alloy_1250C
Inte
nsi
ty
2
F
(a)
Characterization of Oxides
(a)
(b)
Ni Alloy, 1000 ˚C(a)- BSE
(b)-O (c)-Fe
(d)-Si (e)-Ni
• Volume fraction of FeOx / Fe2SiO4
= 91 / 9 ~ 84 / 16
Characterization of Oxides
Ni Alloy, 1250 ˚C
Characterization of Oxides
Al Alloy, 1000 ˚C Al Alloy, 1250 ˚C
Conclusions
• FeO, SiO2, Fe2SiO4 can form spontaneously in the air. Fe2SiO4 is more favored than SiO2 at the Fe/FeO interface
• To form SiO2, silicon needs to diffuse more comparing with Fe2SiO4. The growth of Fe2SiO4 more favored than SiO2 with 0<x(si)<14 wt%.
• At 1000 ˚C, the mixture of FeO and Fe2SiO4 was observed. At 1250 ˚C, the eutectic compound of FeO /Fe2SiO4 was observed.
• Ni addition (> 0.05 wt%) makes the scale/steel interface uneven because of the noble property and low diffusivity.
• Al addition (< 0.2 wt%) has no significant effect on Fe2SiO4.
THANK YOU!!
Prediction of Oxides Formation
• Formation energy of oxides
2Fe + O2 = 2FeO,
Si + O2 = SiO2,
Fe + ½ Si + O2 = ½ Fe2SiO4,
Prediction of Oxides Formation
-50 -40 -30 -20 -10 0-600
-400
-200
0
200 2FeO SiO
2
1/2 Fe2SiO
4
For
mat
ion
Ene
rgy
(kJ/
mol
)
lnP(O2)
-40 -20 0-600
-400
-200
0
200 2FeO SiO
2
1/2 Fe2SiO
4
For
mat
ion
Ene
rgy
(kJ/
mol
)
ln P(O2)
-40 -20 0-600
-400
-200
0
200 2FeO SiO
2
1/2 Fe2SiO
4
For
mat
ion
Ene
rgy
(kJ/
mol
)
P(O2)
-40 -20 0-600
-400
-200
0
200 2FeO SiO
2
1/2 Fe2SiO
4
For
mat
ion
Ene
rgy
(kJ/
mol
)
ln P(O2)
Fe - 1 Si wt% steel, 1000 ˚ C Fe - 1 Si wt% steel, 1250 ˚ C
Fe - 10 Si wt% steel, 1000 ˚ C Fe - 10 Si wt% steel, 1250 ˚ C
Prediction of Oxides Growth
0 2000 4000 6000 8000
0
400
800
1200
1600
2000
Fe2SiO
4
SiO2
FeO
Thi
ckne
ss (m
)
time (s)
(a)
0 2000 4000 6000 8000-5
0
5
10
15
20
25
30
Fe2SiO
4
SiO2
Thi
ckne
ss (m
)
time (s)
(b)
0 2000 4000 6000 8000
0
200
400
600
800
Fe2SiO
4
SiO2
FeO
Thi
ckne
ss (m
)
time (s)
(a)
0 2000 4000 6000 8000
0
1
2
3
4
5
Fe2SiO
4
SiO2
Thi
ckne
ss (m
)
time (s)
(b)
Fe - 1 Si wt% steel, 1000 ˚ C
Fe - 1 Si wt% steel, 1250 ˚ C
Prediction of Oxides Growth
Steel / wt% Temp. / ˚C Fe2SiO4 SiO2FeO
Fe - 0.1 Si 1000 1.82×10-14 5.18×10-16 1.00
1250 3.33×10-13 9.49×10-15 1.00
Fe - 1 Si 1000 2.01×10-11 5.34×10-13 1.00
1250 3.68×10-10 9.77×10-12 1.00
Fe - 10 Si 1000 1.09×10-7 7.42×10-10 1.00
1250 2.00×10-6 1.36×10-8 1.00
Volume Fraction of Oxides
• Volume fraction of FeOx / Fe2SiO4
= 91 / 9 ~ 86 / 13
Characterization of Oxides
20 30 40 50 60 70 80
W
WH
M
HW
W
H
W,M,H
HMMM
F
H
M
M
W,M,H
MH
Alloy 1_1250C Si Alloy_1250C Si Alloy_1250C
Inte
nsi
ty
2
F
(a)
W = FeOM = Fe3O4
H = Fe2O3
F=Fe2SiO4