Influences of Composition on the Transformation-Controlled {100} Textures in High Silicon Electrical Steels Prepared by Mn-Removal Vacuum Annealing
YANG Ping1(), WANG Jinhua1, MA Dandan1, PANG Shufang2, CUI Feng'e3
1.School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 2.Iron and Steel Research Institute, Angang Group, Anshan 114000, China 3.Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
YANG Ping, WANG Jinhua, MA Dandan, PANG Shufang, CUI Feng'e. Influences of Composition on the Transformation-Controlled {100} Textures in High Silicon Electrical Steels Prepared by Mn-Removal Vacuum Annealing. Acta Metall Sin, 2022, 58(10): 1261-1270.
Laboratory experiments demonstrate that the magnetic-beneficial {100} texture can be strongly produced using the so-called surface effect transformation treatment either in low-grade electrical steels or in high-grade 3%Si steels. In the latter case, the solid-phase transformation is introduced into Si steels by adding carbon and manganese elements. In addition, vacuum annealing and subsequent wet hydrogen decarburization are needed. Although such treatment differs remarkably from conventional industry production facilities, its superiority of producing extremely sharp {100} texture, immensely high magnetic induction, and low core loss keeps the method attractive for environmental friendly and high-efficiency rotating machines. Our previous results indicated that the heavy rolling reduction favors the rotated cube texture {100}<011> formation; however, the cube texture {100}<001> is expected due to the easiness of sheet cutting for iron core production in the industry. In this study, the influences of compositions on the formation of the cube texture, 25°-rotated cube texture, and rotated cube texture were investigated. The phase diagram features of the alloy consisting of strong cube texture were also examined. The aim is to establish the theoretical bases for quantitative control of the alloy composition suitable for cube texture in 3%Si electrical steels. Four steel compositions are designed using different combinations of carbon and manganese contents. Thus, the transformation temperatures, ferrite grain sizes, and pearlite volume fractions will be different, leading to distinct growth rates of {100} oriented grains during vacuum annealing at a constant temperature. They were cold-rolled by 50% reduction, which is beneficial for the cube texture formation. The results of experimental determination and calculated phase diagrams indicate that the alloy with lower carbon and Mn contents in the investigated four steel compositions shows a faster and stronger cube texture in the Mn-removal surface layer. The area fraction of the {100} texture in the Mn-removal layer of the alloy after vacuum annealing at 1100oC for 30 min reaches 77.3%. In addition, the suitable decarburization temperature after the formation of the Mn-removal surface layer is discussed and suggested based on the calculated phase diagrams.
Table 1 Compositions, hot rolling parameters, equilibrium transformation temperatures, and equilibrium volume fractions of pearlite in four electrical steels
Fig.1 OM images of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d) after hot rolling (RD—rolling direction, ND—normal direction. White grains are ferrites, black regions are pearlites)
Fig.2 Constant φ2 = 45° sections of orientation distribution function (ODF) of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d) after cold rolling with 50% reduction (φ1, Φ, φ2—Euler angles)
Fig.3 OM images of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d) after cold rolling and quickly heating to 1100oC in vacuum for 30 min (White arrows in Fig.3c show Widmanstätten structures, and black arrows show equiaxed ferrites)
Fig.4 EBSD orientation maps and corresponding {100} pole figures of the surface region of alloy 1, {100}<011> texture (a), alloy 2, {100} texture (b), alloy 3, {100}<021> texture (c), and alloy 4, {100}<001> texture (d) after vacuum annealing at 1100oC for 30 min (TD—transverse direction)
Alloy
Area fraction of {100} grains (≤ 15°) / %
Average grain size
Average size of {100} grain / μm
Average size of {111} grain / μm
μm
1#
60.9
90
121
85
2#
55.0
57
75
52
3#
81.3
93
135
65
4#
77.3
120
155
61
Table 2 Surface grains information of 4 alloys after Mn-removal annealing in vacuum
Fig.5 Relationships of volume fractions of different phases and temperatures of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d)
Fig.6 Calculated phase diagrams (relation of temperature and manganese content) of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d)
Fig.7 Calculated phase diagrams showing the relation of temperature and carbon content of alloy 1 (a), alloy 2 (b), alloy 3 (c), and alloy 4 (d)
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