1 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China 2 Beijing Key Laboratory of Special Melting and Preparation of High-End Metal Materials, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
Jing GUO,Hanjie GUO,Keming FANG,Shengchao DUAN,Xiao SHI,Wensheng YANG. Morphology Prediction Theory and Experimental Measurement for the Secondary Phase Particle in Steel. Acta Metall Sin, 2017, 53(7): 789-796.
It is significant to reduce the negative effects of non-metallic inclusion on steel and to improve steel mechanical properties through controlling the morphology of the secondary phase particle including non-metallic inclusion, nitride and carbide. Compared with particles with irregular shape, globular second phase particle could reduce the stress concentration during rolling and heat treatment process obviously and lower its harmfulness to steel toughness. A theoretical model to predict the morphology of the secondary phase particle in steel has been established by introducing a dimensionless Jackson α factor, and the morphology of the secondary phase particle is determined by its dissolved entropy, growth direction and temperature or undercooling. Non-aqueous solution electrolysis extraction and room temperature organic (RTO) technique were applied to detect the 3D morphology of the secondary phase particle and its inner morphology combining with SEM. The morphologies of particles observed in four different types of steels are in good agreement with the theoretical predictions. Theoretical predictions and experimental observation were both confirmed that the secondary phase particle is faceted in morphology when its Jackson α factor is more than 3 and non-faceted when its Jackson α factor less than 2.
Fund: Supported by National Natural Science Foundation of Steel Joint Research Funds of China (No.U1560203) and Fundamental Research Fund for the Central Universities (No.FRF-TP-16-079A1)
Fig.1 Relations between crystal/melt interface relative energy and fraction of crystal lattice atom (X) with different Jackson α factors (ΔF—crystal/melt interface free energy, N—the number of crystal lattice on the crystal/melt interface, k—Boltzman constant, T—temperature)
Fig.2 Schematic of apparatus for non-aqueous solution electrolysis (1—specimen, 2—stainless steel sheet, 3—thermometer, 4—solution, 5—beaker, 6—holder, DC—direct current)
Fig.3 Schematic of steps wrapping and cutting the extracted secondary phase particle by room temperature organic (RTO) technique
Steel grade
C
Si
Mn
P
S
Als
Ti
Cr
Ni
Mo
Co
A
0.04
0.02
0.15
0.01
0.005
0.04
0.06
-
-
-
-
B
0.05
0.50
1.10
0.01
0.008
-
-
18.22
8.10
-
-
C
0.03
0.29
0.13
0.014
0.002
5.20
0.12
24.20
0.12
-
-
D
1.14
0.50
0.60
0.03
0.007
-
0.0049
4.70
-
9.30
8.10
Table 1 Tested steel grades and compositions
Fig.4 Morphologies of the secondary phase particles in steel B after extration by non-aqueous solution electrolysis (a) and after cutting by RTO technique (b)
Particle type
Crystalline structure
ξ(hkl)
Tm/ K
ΔHm/ (kJmol-1)
α
Al2O3 (corundum)
hcp
0.5~1.0
2327
118.41
3.06~6.12
AlN (S-G)*
hcp
0.5~1.0
4349
189.61
2.62~5.24
SiO2 (quartz)
Tetragonal
0.5~1.0
1996
9.58
0.29~0.58
CaO (lime)
fcc
0.5~1.0
2845
28.50
1.18~3.36
CaF2
cubic
0.5~1.0
1691
29.71
1.06~2.11
FeO
fcc
0.5~1.0
1650
24.06
0.43~0.86
MgO
fcc
0.5~1.0
3098
77.40
1.51~3.01
MnO
fcc
0.5~1.0
2058
54.39
1.59~3.18
MnS
fcc
0.5~1.0
1803
26.11
0.44~0.87
NbO
fcc
0.5~1.0
2218
54.39
1.48~2.95
Nb2O3
0.5~1.0
1785
102.93
3.47~6.94
NiO
fcc
0.5~1.0
2230
50.68
1.37~2.73
TiC
fcc
0.5~1.0
3290
71.13
1.38~2.76
TiN
fcc
0.5~1.0
2023
54.39
3.15~6.29
TiO
0.5~1.0
2112
110.46
4.06~8.11
Ti2O3
0.5~1.0
2047
138.07
1.88~3.76
Ti3O5
0.5~1.0
2143
66.94
4.17~8.33
TiO2
0.5~1.0
943
66.27
1.78~3.55
V2O5
0.5~1.0
2950
87.03
3.15~6.29
ZrO2
0.5~1.0
2023
54.39
4.06~8.11
MgAl2O4
-
0.5~1.0
2381
160.65
4.06~8.12
CaSiO3
-
0.5~1.0
1813 (1817)
57.00 (56.07)
1.85~3.70
CaAl4O7
-
0.5~1.0
2038
128.4
3.79~7.57
CaAl2O4
0.5~1.0
1877
55.0
1.76~3.51
Ca12Al14O33
0.5~1.0
1709
432.0
15.19~30.38
Ca3Al2O6
0.5~1.0
1814
72.0
5.59~11.18
Table 2 Jackson α factor of some typical secondary phase particles in steel[22,23]
Fig.5 Typical morphologies of Al2O3 with α=3.06~6.12 (a, b), MgAl2O4 with α=4.06~8.12 (c, d) and TiN with α=3.15~6.29 (e, f) inclusions in steel A
Fig.6 Morphologies of typical inclusion after non-aqueous solution electrolysis
(a, b) faceted Al2O3 from steel A under different magnifications (c, d) spherical or spheroidal CaO-SiO2-MnO from steel B under different magnifications
Fig.7 Inner morphologies of the secondary phase particle after being cut using RTO technique
(a, b) polyhedral Al2O3 from steel A under different magnifications, no precipitates (c, d) spherical or spheroidal CaO-SiO2-MnO from steel B under different magnifications
Fig.8 Morphologies of typical nitrides in steel C (a~c) and carbides in steel D (d~f)
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