HOT-ROLLED STEEL SHEET FOR NON-ORIENTED ELECTROMAGNETIC STEEL SHEETS

Abstract

A hot-rolled steel sheet for non-oriented electrical steel sheets includes, by mass %: C: 0.0010% to 0.0050%; Si: 1.90% to 3.50%; Al: 0.10% to 3.00%; Mn: 0.05% to 2.00%; P: 0.100% or less; S: 0.005% or less; N: 0.0040% or less; B: 0.0060% or less; Sn: 0% to 0.50%; Sb: 0% to 0.50%; Cu: 0% to 0.50%; REM: 0% to 0.0400%; Ca: 0% to 0.0400%; Mg: 0% to 0.0400%; and a remainder including Fe and impurities, in which a hardness H.sub.D of a deformed structure of a thickness middle portion (½t position) in a sheet width direction end portion of the hot-rolled steel sheet for non-oriented electrical steel sheets is Hv 220 or less.

Claims

1. A hot-rolled steel sheet for non-oriented electrical steel sheets, the hot-rolled steel sheet comprising, by mass %: C: 0.0010% to 0.0050%; Si: 1.90% to 3.50%; Al: 0.10% to 3.00%; Mn: 0.05% to 2.00%; P: 0.100% or less; S: 0.005% or less; N: 0.0040% or less; B: 0.0060% or less; Sn: 0% to 0.50%; Sb: 0% to 0.50%; Cu: 0% to 0.50%; REM: 0% to 0.0400%; Ca: 0% to 0.0400%; Mg: 0% to 0.0400%; and a remainder including Fe and impurities, wherein a hardness H.sub.D of a deformed structure of a thickness middle portion (½t position) in a sheet width direction end portion of the hot-rolled steel sheet for non-oriented electrical steel sheets is Hv 220 or less.

2. The hot-rolled steel sheet for non-oriented electrical steel sheets according to claim 1, wherein a hardness difference H.sub.S=H.sub.D−H.sub.U between the hardness H.sub.D of the deformed structure and a hardness H.sub.U of a recrystallized structure of a thickness surface layer portion (⅛t position) in the sheet width direction end portion of the hot-rolled steel sheet for non-oriented electrical steel sheets is less than Hv 20.

3. The hot-rolled steel sheet for non-oriented electrical steel sheets according to claim 1, further comprising, by mass %, one or more selected from: Sn: 0.01% or more and 0.50% or less; Sb: 0.01% or more and 0.50% or less; Cu: 0.01% or more and 0.50% or less; REM: 0.0005% or more and 0.0400% or less; Ca: 0.0005% or more and 0.0400% or less; and Mg: 0.0005% or more and 0.0400% or less.

4. The hot-rolled steel sheet for non-oriented electrical steel sheets according to claim 2, further comprising, by mass %, one or more selected from: Sn: 0.01% or more and 0.50% or less; Sb: 0.01% or more and 0.50% or less; Cu: 0.01% or more and 0.50% or less; REM: 0.0005% or more and 0.0400% or less; Ca: 0.0005% or more and 0.0400% or less; and Mg: 0.0005% or more and 0.0400% or less.

Description

EXAMPLES

[0091] Next, examples of the present invention will be described. However, conditions of the examples are merely exemplary to confirm the operability and the effects of the present invention, and the present invention is not limited to these condition examples. The present invention can adopt various conditions within a range not departing from the scope of the present invention as long as the object of the present invention can be achieved under the conditions.

Example 1

[0092] The steel including the components shown in Table 1 was cast and hot-rolled to prepare a hot-rolled sheet having a sheet thickness of 2.0 mm Next, under conditions shown in Table 2, it was coiled, heat-conservated, and cooled. Manufacturing No. BO is a reference example in which hot-rolled sheet annealing was performed in an atmosphere of nitrogen 100% after coiling and cooling. Table 3 shows the measurement result of a fracture appearance transition temperature in a Charpy test that was performed in order to evaluate the hardness and the toughness of the deformed structure in the end portion of the prepared hot-rolled sheet.

[0093] In order to obtain the hardness of the steel sheet end portion, in a cross section parallel to a rolling direction in a position (sheet width direction end portion) at a distance of 10 mm from a sheet width direction end surface of the steel sheet to a sheet width direction middle portion, the hardness H.sub.D of the deformed structure of the thickness middle portion (½t position) and the hardness H.sub.U of the recrystallized structure of the thickness surface layer portion (⅛t position) were measured at 10 positions at intervals of 10 μm in a direction parallel to the rolling direction. The Vickers hardness was measured as “HV 10” according to JIS Z 2244 (2009). Specific measurement conditions are as follows: Indenter=a Vickers square-based diamond pyramid indenter with a facing angle of 136°; Indentation load=10 gf; and Indentation time=20 sec.

[0094] The fracture appearance transition temperature was measured by performing the Charpy test according to JIS Z 2242. In Examples, when the fracture appearance transition temperature was lower than 0° C., the toughness was determined to be excellent.

[0095] In addition, the magnetic characteristics of the obtained non-oriented electrical steel sheet was measured according to JIS C 2556.

[0096] The iron loss was evaluated by collecting a sample having a size of 55 square mm from the non-oriented electrical steel sheet and measuring W15/50 (iron loss when the steel sheet was magnetized at 50 Hz at a magnetic flux density of 1.5 T) using a single sheet tester (SST). The magnetic flux density was evaluated using B50 as a magnetic flux density at a field intensity of 5000 A/m. Table 3 also shows the measurement result. A sample where B50 was 1.60 or more and W15/50 was 2.6 W/kg or less was determined as “Pass” regarding electromagnetic characteristics.

TABLE-US-00001 TABLE 1 Chemical composition (mass %) Steel No. C Si Mn P S Al N B Sn Sb Cu REM Ca Mg A1 0.0011 3.00 0.31 0.011 0.004 0.31 0.0023 0.0045 — — — — — — A2 0.0048 2.64 0.23 0.013 0.003 0.82 0.0022 0.0024 — — — — — — A3 0.0015 1.90 0.19 0.016 0.003 1.76 0.0024 0.0034 — — — — — — A4 0.0016 3.29 0.06 0.018 0.004 0.12 0.0023 0.0051 — — — — — — A5 0.0024 3.12 0.05 0.022 0.002 0.34 0.0018 0.0044 — — — — — — A6 0.0034 2.16 1.99 0.019 0.004 0.25 0.0016 0.0028 — — — — — — A7 0.0034 2.23 1.56 0.095 0.002 0.45 0.0026 0.0031 — — — — — — A8 0.0025 2.72 0.98 0.045 0.005 0.22 0.0018 0.0023 — — — — — — A9 0.0043 3.09 0.45 0.056 0.004 0.11 0.0022 0.0031 — — — — — — A10 0.0026 1.91 0.06 0.028 0.002 2.95 0.0023 0.0032 — — — — — — A11 0.0037 3.02 0.23 0.033 0.004 0.34 0.0039 0.0025 — — — — — — A12 0.0023 1.98 0.67 0.023 0.004 1.34 0.0022 0.0058 — — — — — — A13 0.0019 2.95 0.20 0.019 0.001 0.45 0.0021 0.0035 — — — — — — A14 0.0022 2.21 0.24 0.028 0.002 1.34 0.0023 0.0028 — — — — — — A15 0.0023 2.31 0.23 0.012 0.004 1.22 0.0024 0.0034 0.02 — — — — — A16 0.0022 2.03 0.27 0.015 0.008 1.55 0.0017 0.0031 — 0.01 — — — — A17 0.0025 2.01 0.29 0.023 0.003 1.56 0.0019 0.0029 — — 0.02 — — — A18 0.0026 2.16 0.33 0.021 0.008 1.34 0.0026 0.0045 0.01 — 0.03 — — — A19 0.0021 2.10 0.61 0.026 0.005 1.23 0.0022 0.0037 — — — 0.0009 — — A20 0.0014 2.15 1.01 0.018 0.006 0.91 0.0031 0.0029 — — — — 0.0011 — A21 0.0031 2.01 0.81 0.019 0.004 1.21 0.0024 0.0022 — — — — — 0.0024 a1 0.0002 2.51 0.23 0.047 0.003 0.98 0.0023 0.0034 0.09 — — — — — a2 0.0087 2.52 0.67 0.048 0.002 0.67 0.0025 0.0038   0.17 — — — — a3 0.0034 1.24 0.45 0.019 0.002 2.41 0.0033 0.0024     0.07 — — — a4 0.0022 4.20 0.07 0.018 0.003 0.12 0.0022 0.0028 0.07 0.07 0.07 — — — a5 0.0028 2.63 0.01 0.026 0.002 0.97 0.0026 0.0026 — — — 0.0100 — — a6 0.0036 1.93 3.45 0.022 0.003 0.12 0.0031 0.0035 — — — — 0.0400 — a7 0.0021 2.19 0.12 0.232 0.002 1.45 0.0026 0.0031 — — — — — 0.0300 a8 0.0028 2.25 0.34 0.098 0.011 1.23 0.0028 0.0045 — — — — — — a9 0.0033 2.99 0.78 0.034 0.004 0.02 0.0021 0.0042 — — — — — — a10 0.0025 1.92 0.13 0.033 0.005 3.22 0.0031 0.0043 — — — — — — a11 0.0038 2.07 0.67 0.016 0.002 1.23 0.0053 0.0049 — — — — — — a12 0.0039 2.20 0.26 0.038 0.003 1.34 0.0011 0.0089 — — — — — —

TABLE-US-00002 TABLE 2 Hot rolling Hot-rolled Heat After heat process sheet annealing conservation process conservation process Slab From coiling process Heat Heat From 600° C. Manufacturing heating Finish Coiling 400° C. Average Annealing conservation conservation to 400° C. Average method temperature temperature temperature cooling rate CR1 temperature temperature time cooling rate CR2 symbol (° C.) (° C.) (° C.) (.sup.o C./h) (° C.) (° C.) (min) (° C./h) B0 1160  860 668 340 880 — — — B1 1082  934 810  72 — 750  15 45 B2 1190  923 820  69 — 740  18 63 B3 1138  853 720  87 — 680  19 34 B4 1179  998 738  84 — 740  67 67 B5 1123  913 740  83 — 740  1 82 B6 1123  897 729  92 — 710 117 81 B7 1090  880 723 103 — 720  78 34 B8 1120  915 740 105 — 730  72 118 B9 1134  950 840  57 — 780  50 93 B10 1123  940 820  51 — 780  74 81 b1  980  923 774  89 — 720  45 102 b2 1340  890 780  83 — 740  65 56 b3 1134  789 710 102 — 650  39 78 b4 1189 1090 736  98 — 720  57 74 b5 1164  910 811  91 — 740  0.4 102 b6 1138  923 802  97 — 755 140 98 b7 1142  915 788 130 — 770  82 130 b8 1142  915 788  20 — 770  82 20

TABLE-US-00003 TABLE 3 1/2t position0048 Hot-rolled sheet Manufacturing Hardness H.sub.D of toughness Charpy Magnetic flux Iron loss Steel method deformed Recrystallization test transition density B50 W15/50 Symbol No. symbol structure (Hv) ratio % temperature (° C.) (T) (W/kg) Reference C0 A6 B0 250 85 12 1.62 2.71 example Inventive C1 A1 B1 203 75 −3 1.66 2.52 Example C2 A2 B2 204 72 −6 1.66 2.53 C3 A3 B3 201 80 −4 1.67 2.52 C4 A4 B4 205 72 −5 1.68 2.54 C5 A5 B5 203 60 −6 1.68 2.51 C6 A6 B6 199 60 −1 1.67 2.57 C7 A7 B7 197 69 −9 1.65 2.51 C8 A8 B8 208 71 −8 1.68 2.49 C9 A9 B9 203 74 −9 1.67 2.53 C10 A10 B10 205 73 −9 1.66 2.53 C11 A11 B1 207 65 −6 1.66 2.54 C12 A12 B2 200 66 −8 1.66 2.57 C13 A13 B6 180 69 −7 1.68 2.48 C14 A14 B7 195 71 −8 1.68 2.48 Comparative c1 a1 b1 230 82 12 1.61 2.66 exaxmple c2 a2 b2 234 89 12 1.61 2.65 c3 a3 b3 235 91 11 1.62 2.61 c4 a4 b4 238 82 9 1.62 2.63 c5 a5 b5 236 84 8 1.59 2.62 c6 a6 b6 238 90 9 1.58 2.61 c7 a9 b1 231 82 10 1.58 2.69 c8 a10 b2 235 85 8 1.58 2.71 c9 a11 b3 235 84 12 1.62 2.69 c10 a12 b4 238 86 11 1.61 2.63 c11 A2 b1 229 82 6 1.62 2.62 c12 A4 b2 234 81 8 1.62 2.63 c13 A6 b3 238 81 9 1.61 2.65 c14 a1 B1 205 75 8 1.64 2.59 c15 a2 B2 206 72 −10 1.62 2.71 c16 A1 b7 230 58 −1 1.62 2.71 c17 A2 b8 230 90 10 1.63 2.72

[0097] It was verified that, by using the hot-rolled steel sheet for non-oriented electrical steel sheets according to the present invention, fracture does not occur in the steel sheet during pickling and a non-oriented electrical steel sheet having excellent characteristics can be obtained as in a non-oriented electrical steel sheet formed of a hot-rolled steel sheet for non-oriented electrical steel sheets on which hot-rolled sheet annealing in the related art is performed.

Example 2

[0098] A hot-rolled steel sheet for non-oriented electrical steel sheets was prepared in the same manner as described above using the steel shown in Table 1 and the manufacturing method shown in Table 2. Using this hot-rolled steel sheet for non-oriented electrical steel sheets, a non-oriented electrical steel sheet was obtained.

[0099] Regarding the obtained hot-rolled steel sheet, in addition to the measurement result of Example 1, in the sheet width direction end portion of the hot-rolled steel sheet for non-oriented electrical steel sheets, the hardness difference H.sub.S=H.sub.D—H.sub.U between the hardness H.sub.D of the deformed structure of the thickness middle portion (½t position) and the hardness H.sub.U of the recrystallized structure of a thickness surface layer portion (⅛t position) was measured. In the non-oriented electrical steel sheet, magnetic characteristics were measured using the same method as that of Example 1. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 1/2t 1/8t Hot-rolled position position Hardness sheet Hardness Hardness difference toughness Magnetic H.sub.D of H.sub.U of HS = Charpy test flux Iron Manufacturing deformed recrystallized HD − transition density loss Steel method structure structure HU temperature B50 W15/50 Symbol No. symbol (Hv) (Hv) (Hv) (° C.) (T) (W/kg) D1 A1 B5 203 234 31  −3 1.66 2.52 D2 A2 B6 204 232 28  −6 1.66 2.53 D3 A13 B9 180 196 16 −10 1.68 2.48 D4 A14 B10 195 205 10 −12 1.68 2.48

[0100] It was verified that, by adjusting the hardness difference H.sub.S between the hardness H.sub.D of the deformed structure of the thickness middle portion (½t position) and th'e hardness H.sub.U of the recrystallized structure of the thickness surface layer portion (⅛t position) to be less than HV 20, higher toughness can be obtained.

Example 3

[0101] In Example C1 and Comparative Example c16 shown in Table 3, the rolling reduction as a cold rolling condition was set as 75%, soaking conditions as final annealing conditions were set as 1000° C.×30 seconds, and cold rolling and final annealing were performed to obtain a non-oriented electrical steel sheet. Regarding each of the non-oriented electrical steel sheets, the hardness of the thickness middle portion (½t position) in the sheet width direction end portion was measured.

[0102] The hardness of the end portion of the non-oriented electrical steel sheet was measured in the following procedure. The cross section parallel to the rolling direction in the position (sheet width direction end portion) at a distance of 10 mm from the sheet width direction end surface of the steel sheet to the sheet width direction middle portion was set as a measurement surface. In this measurement surface, the hardness of the thickness middle portion (½t position) was measured at 10 positions at intervals of 10 in a direction parallel to the rolling direction. The Vickers hardness was measured as “HV 10” according to JIS Z 2244 (2009). Specific measurement conditions are as follows: Indenter=a Vickers square-based diamond pyramid indenter with a facing angle of 136°; Indentation load=10 gf; and Indentation time=20 sec. The measurement results are shown in Table 5.

TABLE-US-00005 TABLE 5 l/2t position hardness HD Hardness at of deformed stage of structure non-oriented (Hot-rolled electrical Steel Manufacturing steel sheet) steel sheet Symbol No. method symbol (HV) (HV) C1 A1 B1 203 241 c16 A1 b7 230 238

[0103] In C1 and c16, the chemical compositions were the same, and the hardness values at the stage of the non-oriented electrical steel sheet were substantially at the same level. However, the hardness values of the deformed structure at the stage of the hot-rolled steel sheet were largely different from each other. In other words, it is difficult to estimate the hardness at the stage of the hot-rolled steel sheet from the hardness measured at the stage of the non-oriented electrical steel sheet.

INDUSTRIAL APPLICABILITY

[0104] According to the present invention, it is possible to provide a hot-rolled steel sheet for non-oriented electrical steel sheets in which sufficient hot-rolled sheet toughness can be obtained even when annealing in a hot rolling process is skipped and low iron loss and high magnetic flux density can be achieved when a non-oriented electrical steel sheet is obtained from the hot-rolled steel sheet for non-oriented electrical steel sheets. As a result, a non-oriented electrical steel sheet having low iron loss and high magnetic flux density can be stably produced and provided without fracture. Therefore, urgent demand for mass production in the fields of electrical equipment where the non-oriented electrical steel sheet is used as an iron core material can be sufficiently satisfied, and the industrial value thereof is extremely high.