Effect of Y on the Solidification Microstructure, Warm Compression Behavior, and Softening Mechanism of Non-Oriented 6.5%Si Electrical Steel
LI Min1,2, WANG Jijie1, LI Haoze2,3(), XING Weiwei2, LIU Dezhuang2, LI Aodi2, MA Yingche2
1 College of Materials Science and Engineering, Shenyang Areospace University, Shenyang 110136, China 2 Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3 School of Mechanical Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China
Cite this article:
LI Min, WANG Jijie, LI Haoze, XING Weiwei, LIU Dezhuang, LI Aodi, MA Yingche. Effect of Y on the Solidification Microstructure, Warm Compression Behavior, and Softening Mechanism of Non-Oriented 6.5%Si Electrical Steel. Acta Metall Sin, 2023, 59(3): 399-412.
With the rapid development of electric, electronics, and military industries, there is an urgent demand for high-performance electrical steel. Non-oriented 6.5%Si electrical steel is an advanced soft magnetic material that exhibits excellent high-frequency soft magnetic properties, such as low iron loss, high magnetic permeability, and near-zero magnetostriction, which attracts considerable attention and has broad application prospects in the high-frequency field. Microalloying of rare earth elements, including Ce, La, and Y, is known to improve the ductility of 6.5%Si electrical steel. However, there are relatively few studies on the enhancement mechanism of medium-temperature plasticity of 6.5%Si electrical steel by addition of Y. In this study, the effect of Y on the solidification microstructure, ordered phase, warm compression behavior, and softening mechanism of non-oriented 6.5%Si electrical steel was investigated by EPMA, EBSD, XRD, TEM, and hot compressive test. The results indicated that the addition of 0.017% and 0.15% of Y led to the formation of high-melting-point Y2O3 + Y2O2S/Y2O2S-YP compounds in the melt which effectively promoted heterogeneous nucleation. At the end of the solidification process, the interdendritic rare-earth compounds were identified as Y2Fe14Si3 and the solidification microstructure was obviously refined. In addition, with the increasing Y content, the ordered degree of the matrix decreased. The compression test at 500oC indicated that the deformation mechanisms of all the specimens were dominated by a dislocation slip. The critical strain corresponding to the peak stress of the specimens doped with Y decreased. The advancement of the work softening stage and reduction in the following work hardening rate suggested that the dynamic softening effect was enhanced in the specimens doped with Y. After deformation, the matrix was in a disordered state, however, the dislocation density in the matrix was directly proportional to the Y content. Eventually, the primary reason for the enhancement of the dynamic softening effect was attributed to the low ordered degree and high deformation-induced disordering of the matrix by addition of Y.
Table 1 Chemical compositions of the ingots with various Y contents
Fig.1 Macrostructures (a-c) and high magnified SEM images (d-f) of the as-cast 0Y (a, d), 0.017Y (b, e), and 0.15Y (c, f) ingots (Insets in Figs.1e and f show the magnified images. GB—grain boundary, IGC—intragranular rare-earth compound, IDC—interdendritic rare-earth compound)
Fig.2 SEM images and the corresponding EPMA elemental maps of the intragranular rare-earth compounds in the as-cast 0.017Y (a) and 0.15Y (b) ingots
Sample
Fe
Si
Y
O
S
P
0.017Y
2.64
1.17
30.60
63.68
0.82
1.09
0.15Y
18.40
2.15
35.85
28.73
11.08
3.79
Table 2 EDS results of the intragranular rare-earth compounds
[]s
[]n
/ nm
/ nm
θ / (o)
·cosθ / nm
δ
[] δ - Fe
[001]YP
0.2845
0.2826
0
0.2845
0.67%
[] δ - Fe
[]YP
0.6969
0.6922
0
0.6969
[] δ - Fe
[]YP
0.4023
0.3997
0
0.4023
Table 3 Calculated results of the lattice misfit between YP and δ-Fe (Case: )
Fig.3 SEM image (a), the corresponding Kikuchi patterns (b, c), and EDS elemental maps (d-f) of the interdendritic rare-earth compounds in the as-cast 0.017Y ingot
Fig.4 SEM image (a), the corresponding Kikuchi patterns (b, c), and EDS elemental maps (d-f) of the interdendritic rare-earth compounds in the as-cast 0.15Y ingot
Sample
Position
Atomic fraction / %
Fe
Si
Y
0.017Y
Matrix
88.16
11.84
0
Rare-earth compound
77.01
15.33
7.66
0.15Y
Matrix
87.96
12.04
0
Rare-earth compound
75.64
16.27
8.09
Table 4 EDS analysis results of the interdendritic rare-earth compounds in Figs.3 and 4
Fig.5 Schematic of the solidification process of non-oriented 6.5%Si electrical steel doped with Y
Fig.6 XRD spectra of the ingots with various Y contents
Fig.7 SAED patterns along [001] zone axes of the as-cast 0Y (a), 0.017Y (b), and 0.15Y (c) samples
Fig.8 True stress-true strain curves of the as-cast 0Y (a), 0.017Y (b), and 0.15Y (c) samples at 500oC with constant strain rate of 1 s-1 and constant reduction of 40%
Fig.9 Comparisons of θ-ε curves (a), peak stress and the corresponding critical strain (b) of the as-cast samples with various Y contents compressed at 500oC (θ—work hardening rate, ε—true strain)
Fig.10 Macrographies of the as-cast samples with various Y contents after compression at 500oC
Fig.11 Longitudinal OM images showing the micro-structures of the as-cast 0Y (a), 0.017Y (b), and 0.15Y (c) samples after compression at 500oC, and statistical results of cracks in the surface regions (d) (CD—compression direction)
Fig.12 CD-inverse pole figures (IPFs) (a-c), Σ3-60°<111> special grain boundary distribution maps (d-f), and EDS elemental maps (g-i) of the as-cast 0Y (a, d, g), 0.017Y (b, e, h), and 0.15Y (c, f, i) samples after compression at 500oC
Fig.13 Longitudinal EBSD grain orientation maps (a, c, e) and local misorientation (LM) maps (b, d, f) of the as-cast 0Y (a, b), 0.017Y (c, d), and 0.15Y (e, f) samples after compression at 500oC
Fig.14 LM distribution histograms of the as-cast 0Y (a), 0.017Y (b), and 0.15Y (c) samples after compression at 500oC, and the corresponding geometrically necessary dislocation (GND) densities (ρGND) (d) (R2—coefficient of determination)
Fig.15 Dislocation configurations in bright-field TEM images (a-c) and the corresponding SAED patterns (d-f) along [001] zone axes of the as-cast 0Y (a, d), 0.017Y (b, e), and 0.15Y (c, f) samples after compression at 500oC
1
Ouyang G Y, Chen X, Liang Y F, et al. Review of Fe-6.5 wt%Si high silicon steel—A promising soft magnetic material for sub-kHz application [J]. J. Magn. Magn. Mater., 2019, 481: 234
doi: 10.1016/j.jmmm.2019.02.089
2
Li H Z, Liu H T, Liu Z Y, et al. Microstructure, texture evolution and magnetic properties of strip-casting non-oriented 6.5 wt. % Si electrical steel doped with cerium [J]. Mater. Charact., 2015, 103: 101
doi: 10.1016/j.matchar.2015.03.024
3
Li H Z, Liu H T, Wang X L, et al. Effect of cerium on the as-cast microstructure and tensile ductility of the twin-roll casting Fe-6.5wt. % Si alloy [J]. Mater. Lett., 2016, 165: 5
doi: 10.1016/j.matlet.2015.11.100
4
Yu X, Zhang Z H, Xie J X. Effects of rare earth elements doping on ordered structures and ductility improvement of Fe-6.5 wt%Si alloy [J]. Mater. Lett., 2016, 184: 294
doi: 10.1016/j.matlet.2016.08.074
5
Yu X, Zhang Z H, Xie J X. Microstructure, ordered structure and warm tensile ductility of Fe-6.5% Si alloy with various Ce content [J]. Acta Metall. Sin., 2017, 53: 927
Cai G J, Wang Y Z, Huang Y R, et al. Effect of Ce on bending properties and soft magnetic properties of Fe-6.9wt% Si steel [J]. Mater. Sci. Technol., 2020, 28(4): 16
Cai G J, Yang Y, Huang Y R, et al. The significance of Ce on hot compression deformation and mechanical behavior of Fe-6.9wt%Si alloy: Decrease of order degree and transformation of dislocations [J]. Mater. Charact., 2020, 163: 110220
doi: 10.1016/j.matchar.2020.110220
8
Liu D F, Qin J, Zhang Y H, et al. Effect of yttrium addition on the hot deformation behavior of Fe-6.5wt% Si alloy [J]. Mater. Sci. Eng., 2020, A797: 140238
9
Zhao H B, Qin J, Liu D F, et al. Effect of rare earth yttrium on the tensile properties of 6.5%Si steel [J]. Nonferrous Met. Sci. Eng., 2021, 12: 131
Zhou Q Y, Qin J, Liu D F, et al. Effects of rare earth Y on microstructure and texture evolution of 6.5 wt. % Si high-silicon steel during hot and warm rolling [J]. J. Iron Steel Res., 2021, 33: 600
Yu H Y, Ming K S, Wu H C, et al. Ordering suppression and excellent ductility in soft-magnetic Fe-6.5wt%Si sheet by Hf addition [J]. J. Alloys Compd., 2018, 766: 186
doi: 10.1016/j.jallcom.2018.06.343
12
Du T. Thermodynamics of rare earth elements in iron-base solutions [J]. J. Iron Steel Res., 1994, 6(3): 6
杜 挺. 稀土元素在铁基溶液中的热力学 [J]. 钢铁研究学报, 1994, 6(3): 6
13
Bramfitt B L. The effect of carbide and nitride additions on the heterogeneous nucleation behavior of liquid iron [J]. Metall. Trans., 1970, 1: 1987
14
Villars P, Okamoto H. Fe-Si-Y isothermal section of ternary phase diagram [DB/OL].
15
Lin C N, Sun Y X, Liu Z X, et al. Magnetic properties of Si-substituted Y2Fe17 [J]. Solid State Commun., 1992, 81: 299
doi: 10.1016/0038-1098(92)90813-O
16
Cheng Z Y, Liu J, Xiang Z D, et al. Effect of Cu addition on microstructure, texture and magnetic properties of 6.5wt% Si electrical steel [J]. J. Magn. Magn. Mater., 2021, 519: 167471
doi: 10.1016/j.jmmm.2020.167471
17
Li L F, Xing Z S. Solubilities of Ce, Nd and Y in α-Fe [J]. Acta Metall. Sin. (Engl. Lett.), 1993, 6: 309
18
Ji Y P, Zhang M X, Ren H P. Roles of lanthanum and cerium in grain refinement of steels during solidification [J]. Metals, 2018, 8: 884
doi: 10.3390/met8110884
19
Qian M, Cao P, Easton M A, et al. An analytical model for constitutional supercooling-driven grain formation and grain size prediction [J]. Acta Mater., 2010, 58: 3262
doi: 10.1016/j.actamat.2010.01.052
20
Shi X J, Liang Y F, Liu B B, et al. Warm deformation behavior and work-softening mechanism of Fe-6.5wt. %Si alloy [J]. J. Iron Steel Res. Int., 2020, 27: 342
doi: 10.1007/s42243-019-00325-8
21
Cai G J, Li C S, Cai B, et al. Effect of rolling reduction on antiphase domains, grain boundary character distribution and plastic deformation of Fe-6.5wt%Si alloy [J]. Mater. Lett., 2019, 238: 249
doi: 10.1016/j.matlet.2018.11.167
22
Swann P R, Grånäs L, Lehtinen B. The B2 and D03 ordering reactions in iron-silicon alloys in the vicinity of the curie temperature [J]. Met. Sci., 1975, 9: 90
doi: 10.1179/030634575790445279
23
Wen S B, Han C Y, Zhang B, et al. Flow behavior characteristics and processing map of Fe-6.5wt. %Si alloys during hot compression [J]. Metals, 2018, 8: 186
doi: 10.3390/met8030186
24
Fu H D, Zhang Z H, Jiang Y B, et al. Applying the grain orientation dependence of deformation twinning to improve the deformation properties of an Fe-6.5wt%Si alloy [J]. J. Alloys Compd., 2016, 689: 307
doi: 10.1016/j.jallcom.2016.07.319
25
Xie J X, Fu H D, Zhang Z H, et al. Deformation twinning in an Fe-6.5 wt. % Si alloy with columnar grains during intermediate temperature compression [J]. Mater. Sci. Eng., 2012, A538: 315
26
Xie J X, Fu H D, Zhang Z H, et al. Deformation twinning feature and its effects on significant enhancement of tensile ductility in columnar-grained Fe-6.5wt. %Si alloy at intermediate temperatures [J]. Intermetallics, 2012, 23: 20
doi: 10.1016/j.intermet.2011.12.011
27
Ashby M F. The deformation of plastically non-homogeneous materials [J]. Philos. Mag., 1970, 21: 399
28
Gao H, Huang Y, Nix W D, et al. Mechanism-based strain gradient plasticity—I. Theory [J]. J. Mech. Phys. Solids, 1999, 47: 1239
doi: 10.1016/S0022-5096(98)00103-3
29
Kubin L P, Mortensen A. Geometrically necessary dislocations and strain-gradient plasticity: A few critical issues [J]. Scr. Mater., 2003, 48: 119
doi: 10.1016/S1359-6462(02)00335-4
30
Calcagnotto M, Ponge D, Demir E, et al. Orientation gradients and geometrically necessary dislocations in ultrafine grained dual-phase steels studied by 2D and 3D EBSD [J]. Mater. Sci. Eng., 2010, A527: 2738
31
Mo Y K, Zhang Z H, Fu H D, et al. Effects of deformation temperature on the microstructure, ordering and mechanical properties of Fe-6.5wt% Si alloy with columnar grains [J]. Mater. Sci. Eng., 2014, A594: 111
32
Li H, Liang Y F, Yang W, et al. Disordering induced work softening of Fe-6.5wt%Si alloy during warm deformation [J]. Mater. Sci. Eng., 2015, A628: 262
33
Wang X L, Li H Z, Zhang W N, et al. The work softening by deformation-induced disordering and cold rolling of 6.5 wt pct Si steel thin sheets [J]. Metall. Mater. Trans., 2016, 47A: 4659
34
Raviprasad K, Aoki K, Chattopadhyay K. The nature of dislocations and effect of order in rapidly solidified Fe-(5.5-7.5)wt. %Si alloys [J]. Mater. Sci. Eng., 1993, A172: 125
35
Mao W M, Yang P. Influence of structure transition on plastic behaviors of iron based ordered alloys [J]. Sci. China Technol. Sci., 2012, 55: 2920
doi: 10.1007/s11431-012-4947-x
