1 College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China 2 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 3 China Electric Power Research Institute, Beijing 100192, China
Cite this article:
Junke HAN,Hong YAN,Yao HUANG,Lujun ZHOU,Shanwu YANG. Structural Features of Oxide Scales on Weathering Steel and Their Influence on Atmospheric Corrosion. Acta Metall Sin, 2017, 53(2): 163-174.
Oxide scale on hot rolled strip steel has been successfully applied to decrease the corrosion loss of the steel during its transport and storage. In recent years, some efforts have been made to improve atmospheric corrosion resistance of weathering steel by oxide scale on its surfaces. However, the structure and electrochemical properties of oxide scale and their evolution during atmospheric corrosion still need to be characterized. In this work, XRD, electrochemical test and scanning electron microscopy have been carried out to investigate structures of oxide scales on surfaces of weathering steel samples and their influence on subsequent atmospheric corrosion of the samples. To produce oxide scales, the samples had been held isothermally at 400~700 ℃ in open or close spaces for different times. It has been found that oxide scales consist of Fe3O4 and Fe2O3. The electrical resistance of oxide scales is far higher than that of oxide film on sample which has not been subjected to oxidation treatment. Meanwhile, oxidation results in obviously raised free corrosion potential. Oxide scales are composed of loose outer layers and compact inner layers from which protective action is derived. The relatively compact oxide scales form at 500~600 ℃ while prolonged holding time promotes oxide scales to become compact. The limited oxygen providing inhibits oxide scales to become compact. The compact oxide scales slow down atmospheric corrosion in initial stage while they accelerate atmospheric corrosion after long time. These results indicate that compact oxide scales are difficult to transform into corrosion products and remain as inclusions and defects in the rust layers which accelerate corrosion.
Fund: Supported by National Natural Science Foundation of China (No.51571026) and State Grid Corporation Science and Technology Project (No.GCB17201400162)
Table 1 Oxidation preparation parameters of different samples
Fig.1 XRD spectra of oxide scales of different samples
Fig.2 SEM images of oxide scales of different samples(a) No.1 (b) No.2 (c) No.3 (d) No.4 (e) No.5 (f) No.6 (g) No.7 (h) No.8
Fig.3 Cross-sectional SEM images of oxide scales of different samples (CDG—crystal drops of glue, Sub—steel substrate) (a) No.1 (b) No.2 (c) No.3 (d) No.4 (e) No.5 (f) No.6 (g) No.7 (h) No.8
Fig.4 EIS of different samples prior to corrosion
Fig.5 EIS equivalent circuit model of Fig.4[19] (Rs—solution/electrolyte resistance, Qc—capacitance of oxide scale, Rc—resistance of oxide scale)
Fig.6 Polarization curves of different samples prior to corrosion (E—free corrosion potential, i—corrosion current density) (a) No.0~No.5 (b) No.6~No.8
Sample No.
E / V
i / (10-5 Acm-2)
0
-0.4610
9.4290
1
-0.3916
0.9224
2
-0.4232
1.0550
3
-0.3392
0.7734
4
-0.4296
1.4820
5
-0.4012
1.2500
6
-0.4633
0.9816
7
-0.3708
0.4504
8
-0.4272
0.5549
Table 2 E and i of different samples prior to corrosion
Sample No.
α-FeOOH
β-FeOOH
γ-FeOOH
Fe3O4
δ-FeOOH
α/γ*[20~22]
0
0.96
1.75
2.18
2.53
92.58
0.15
1
1.09
2.22
3.63
2.40
90.66
0.13
2
1.00
2.14
2.86
2.45
91.55
0.13
3
1.12
3.65
3.19
3.05
88.99
0.11
4
0.82
2.50
2.34
1.97
92.37
0.12
5
1.41
4.79
3.13
3.01
87.66
0.13
6
1.30
3.20
3.59
3.27
88.64
0.13
7
0.93
2.08
2.64
2.67
91.68
0.13
8
1.42
2.96
4.14
4.64
86.84
0.12
Table 3 Relative content of phases and α/γ * values[20~22] of rust layers of different samples corroded for 80 d
Fig.8 SEM images of rust layers of different samples corroded for 80 d(a) No.0 (b) No.1 (c) No.2 (d) No.3 (e) No.4 (f) No.5 (g) No.6 (h) No.7 (i) No.8
Fig.9 Cross-sectional SEM images of rust layers of different samples corroded for 80 d(a) No.0 (b) No.1 (c) No.2 (d) No.3 (e) No.4 (f) No.5 (g) No.6 (h) No.7 (i) No.8
Sample No.
0 d
5 d
15 d
30 d
45 d
60 d
80 d
0
-0.4610
-0.7362
-0.6642
-0.6207
-0.5898
-0.5786
-0.5707
1
-0.3916
-0.7066
-0.6459
-0.6390
-0.6246
-0.6114
-0.6111
2
-0.4232
-0.7170
-0.6387
-0.6406
-0.6167
-0.5931
-0.5915
3
-0.3392
-0.5467
-0.6570
-0.6047
-0.5810
-0.6062
-0.5914
4
-0.4296
-0.7689
-0.6802
-0.6087
-0.5951
-0.5627
-0.5550
5
-0.4012
-0.7370
-0.6531
-0.6427
-0.6230
-0.5826
-0.5890
6
-0.4633
-0.7753
-0.6177
-0.6627
-0.5882
-0.5667
-0.5451
7
-0.3708
-0.7030
-0.6994
-0.6507
-0.5802
-0.5611
-0.5475
8
-0.4272
-0.5771
-0.6691
-0.6329
-0.5691
-0.5547
-0.5507
Table 4 E of different samples corroded for different times
Sample No.
5 d
15 d
30 d
45 d
60 d
80 d
0
33.12
36.89
59.45
55.95
58.81
66.37
1
39.19
32.37
35.76
44.80
50.21
61.98
2
37.48
33.48
36.03
38.91
44.62
45.89
3
51.60
38.72
43.69
38.13
49.13
50.87
4
30.64
29.88
49.06
42.02
63.52
63.44
5
30.71
28.86
33.27
40.29
50.84
62.75
6
25.37
30.65
49.95
62.23
83.58
86.70
7
55.56
33.08
56.74
71.77
84.58
98.09
8
133.70
41.72
47.52
65.20
81.60
92.53
Table 5 Electric resistances of rust layers of different samples corroded for different times
Fig.10 EIS equivalent circuit model for different samples with rust layers[23,24] (Rr—rust layer resistance, Cr—rust layer capacitance, Rt—charge transfer resistance, Cd—double layer capacitance, RW—Warburg diffusion impedance)
Fig.11 Absorption-dehydration curves of rust layer of different samples corroded for 80 d
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