HOT-ROLLED STEEL SHEET FOR NON-ORIENTED ELECTRICAL STEEL SHEET

Abstract

A hot-rolled steel sheet for a non-oriented electrical steel sheet containing, in mass %, components of 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: 0.10% or less, S: 0.005% or less, N: 0.0040% or less and B: 0.0060% or less with a remainder consisting of Fe and impurities, in which, in a sheet width-direction end portion of the hot-rolled steel sheet for a non-oriented electrical steel sheet, a C concentration [atom %] in a crystal grain boundary is 3.0 or more times a P concentration [atom %], and the C concentration [atom %] in the crystal grain boundary of the hot-rolled steel sheet for a non-oriented electrical steel sheet is 3.5 or more times a C concentration in a crystal grain.

Claims

1. A hot-rolled steel sheet for a non-oriented electrical steel sheet comprising, in 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: 0.10% 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 consisting of Fe and impurities, wherein, in a sheet width-direction end portion of the hot-rolled steel sheet for a non-oriented electrical steel sheet, a C concentration [atom %] in a crystal grain boundary is 3.0 or more times a P concentration [atom %], and the C concentration [atom %] in the crystal grain boundary of the hot-rolled steel sheet for a non-oriented electrical steel sheet is 3.5 or more times a C concentration in a crystal grain.

2. The hot-rolled steel sheet for a non-oriented electrical steel sheet according to claim 1, comprising, in mass %, one or more of: 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.

3. A hot-rolled steel sheet for a non-oriented electrical steel sheet comprising, in 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: 0.10% 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 comprising Fe and impurities, wherein, in a sheet width-direction end portion of the hot-rolled steel sheet for a non-oriented electrical steel sheet, a C concentration [atom %] in a crystal grain boundary is 3.0 or more times a P concentration [atom %], and the C concentration [atom %] in the crystal grain boundary of the hot-rolled steel sheet for a non-oriented electrical steel sheet is 3.5 or more times a C concentration in a crystal grain.

Description

EXAMPLES

[0057] Next, examples of the present invention will be described, but conditions in the examples are examples of conditions adopted to confirm the feasibility and effect of the present invention, and the present invention is not limited to these examples. The present invention is capable of adopting a variety of conditions within the scope of the gist of the present invention as long as the objective of the present invention is achieved.

Example 1

[0058] Steels having components shown in Table 1 were cast and hot-rolled, thereby producing hot-rolled sheets having a sheet thickness of 2.0 mm. After that, under conditions shown in Table 2, the hot-rolled sheets were coiled into coils, heat was retained, and the coils were cooled, thereby producing hot-rolled steel sheets for a non-oriented electrical steel sheet.

[0059] The cooling was carried out by spraying an air to the end portions. As the cooling rates, the cooling rates at the positions of the steel sheet end portions were measured using a radiation thermometer.

[0060] A manufacturing method sign BO is a reference example in which the hot-rolled steel sheet was coiled, cooled and then hot-band annealed in a nitrogen 100% atmosphere. The measurement results of the C and P concentrations in the grain boundaries at the end portions of the produced hot-rolled steel sheets for a non-oriented electrical steel sheet and the transition temperatures in a Charpy test carried out to evaluate the toughness are shown in Table 3.

[0061] The C and P concentrations in the grain boundaries were measured by cutting Charpy test pieces from the sheet width-direction end portions of the steel sheets, making notches on the steel sheet side surface sides, carrying out the Charpy test in an atmosphere of −50° C. or lower and analyzing the intergranular fractured surfaces by Auger electron spectroscopy (AES).

[0062] The fractured surface transition temperatures were measured by carrying out a Charpy test according to JIS Z 2242. In the present examples, in a case where the fractured surface transition temperature was lower than 0° C., the toughness was determined to be favorable.

[0063] Next, the produced hot-rolled steel sheets for a non-oriented electrical steel sheet were pickled by being immersed in hydrochloric acid (85° C., 7.5 mass %) for 30 seconds, then, cold-rolled up to a thickness of 0.5 mm at a rolling reduction of 75% and final-annealed at 1050° C. for 30 seconds, thereby obtaining non-oriented electrical steel sheets.

[0064] In addition, the magnetic characteristics of the obtained non-oriented electrical steel sheets were measured according to JIS C 2556.

[0065] 55 mm×55 mm specimens were collected from the non-oriented electrical steel sheets, W15/50's (the iron losses at the time of magnetizing the steel sheets to a magnetic flux density of 1.5 T at 50 Hz) were measured with a single sheet tester (SST), and the iron losses were evaluated. The magnetic flux densities were evaluated using B50's, which are magnetic flux densities at a magnetic field intensity of 5000 A/m. The measurement results are all shown in Table 3.

TABLE-US-00001 TABLE 1 Chemical components (mass %) (remainder is Fe and impurities) Steel No. C Si Mn P S Al N B Sn Sb Cu REM Ca Mg A1 0.0011 3.21 0.21 0.05 0.003 1.18 0.0012 0.0013 — — — — — — Invention A2 0.0049 2.92 0.25 0.01 0.002 1.51 0.0023 0.0021 — — — — — — Example A3 0.0013 1.91 0.16 0.02 0.004 2.83 0.0021 0.0035 — — — — — — A4 0.0024 3.48 0.23 0.01 0.005 0.83 0.0016 0.0024 — — — — — — A5 0.0035 3.12 0.06 0.04 0.002 1.39 0.0013 0.0042 — — — — — — A6 0.0024 2.56 1.95 0.02 0.003 0.84 0.0026 0.0027 — — — — — — A7 0.0026 1.94 0.56 0.09 0.002 2.52 0.0023 0.0031 — — — — — — A8 0.0021 2.41 0.78 0.03 0.005 1.80 0.0021 0.0042 — — — — — — A9 0.0015 3.43 1.41 0.05 0.002 0.12 0.0031 0.0033 — — — — — — A10 0.0042 1.92 0.06 0.09 0.003 2.88 0.0024 0.0051 — — — — — — A11 0.0013 2.38 1.52 0.03 0.002 1.35 0.0039 0.0024 — — — — — — A12 0.0032 2.87 0.28 0.04 0.003 1.56 0.0021 0.0058 — — — — — — A13 0.0045 2.95 0.37 0.03 0.001 1.40 0.0023 0.0023 — — — — — — A14 0.0036 3.11 0.26 0.05 0.003 1.27 0.0014 0.0034 — — — — — — A15 0.0021 3.21 0.23 0.01 0.002 1.17 0.0032 0.0023 — — — — 0.0010 — A16 0.0023 3.14 0.25 0.01 0.001 1.24 0.0015 0.0023 — — — — — 0.0020 A17 0.0012 3.02 0.33 0.04 0.002 1.34 0.0023 0.0021 — — 0.34 — — — A18 0.0013 2.95 0.66 0.02 0.001 1.21 0.0016 0.0034 — — — 0.0009 — — A19 0.0012 3.02 0.15 0.02 0.002 1.46 0.0017 0.0021 0.43 — — — — — A20 0.0015 2.56 0.23 0.03 0.001 1.97 0.0016 0.0025 — 0.41 — — — — A21 0.0018 2.68 0.25 0.02 0.002 1.81 0.0023 0.0032 0.04 — 0.05 — — — a1 0.0002 3.24 0.06 0.02 0.002 1.24 0.0013 0.0032 — — — — — — Comparative a2 0.0081 2.97 0.24 0.04 0.003 1.46 0.0024 0.0054 — — — — — — Example a3 0.0034 1.82 0.07 0.02 0.002 3.00 0.0031 0.0023 — — — — — — a4 0.0021 4.13 0.07 0.06 0.003 0.13 0.0025 0.0031 — — — — — — a5 0.0028 2.65 0.02 0.02 0.004 2.00 0.0025 0.0051 — — — — — — a6 0.0032 1.99 3.44 0.06 0.004 0.56 0.0031 0.0021 — — — — — — a7 0.0013 2.37 1.35 0.21 0.002 1.47 0.0034 0.0034 — 0.03 — — — — a8 0.0023 2.65 1.25 0.04 0.009 1.19 0.0032 0.0032 0.04 — — — — — a9 0.0016 2.88 0.45 0.07 0.003 0.08 0.0021 0.0021 — — 0.22 — — — a10 0.0036 1.92 0.06 0.01 0.002 3.59 0.0011 0.0044 — 0.13 0.26 — — — a11 0.0028 3.16 0.75 0.01 0.003 0.89 0.0081 0.0025 0.22 0.34 — — — — a12 0.0043 2.67 0.58 0.02 0.001 1.61 0.0034 0.0088 0.37 0.24 0.25 — — —

TABLE-US-00002 TABLE 2 Hot-band Heat conservation Hot rolling process annealing treatment process Average cooling rate Slab process Heat Heat Coiling 600° C. heating Finish Coil coiling Annealing conservation conservation temperature to Manufacturing temperature temperature temperature temperature temperature time to 600° C. 400° C. method sign (° C.) (° C.) (° C.) (° C.) (° C.) (min) (° C./min) (° C./hr) B0 1160 870 650 920 — — — — B1 1082 890 760 — 750 65 50 58 B2 1195 882 790 — 780 63 60 67 B3 1123 852 819 — 790 28 90 76 B4 1187 998 778 — 760 48 30 38 B5 1165 920 768 — 740 2 30 56 B6 1189 870 813 — 800 118 40 84 B7 1154 890 780 — 760 28 70 35 B8 1176 928 797 — 780 47 60 118 B9 1143 932 780 — 750 114 30 50 B10 1128 890 782 — 740 39 50 112 b1 970 904 778 — 790 45 30 45 b2 1423 936 739 — 780 109 90 79 b3 1165 801 728 — 750 46 30 86 b4 1187 1180 716 — 740 29 40 98 b5 1165 890 729 — 760 0.5 50 55 b6 1165 920 726 — 730 200 20 102 b7 1181 930 709 — 720 114 30 12 b8 1174 890 729 — 740 93 70 198 b9 1165 890 780 — 740 65 110 80 b10 1156 920 770 — 800 70 5 90 b11 1176 900 760 — 680 70 30 80 b12 1156 880 780 — 900 65 20 90 b13 1156 890 770 — 720 45 30 20

TABLE-US-00003 TABLE 3 Hot-rolled sheet toughness Magnetic Iron Charpy transition flux density loss Steel Manufacturing temperature B50 W15/50 Sign No. method No. TR = C/P (° C.) (T) (W/kg) C0 A1 B0 1.2 28 C1 A1 B1 4.2 −4 1.68 2.51 C2 A2 B2 4.5 −3 1.68 2.56 C3 A3 B3 5.3 −4 1.71 2.54 C4 A4 B4 5.6 −10 1.68 2.58 C5 A5 B5 4.2 −10 1.68 2.55 C6 A6 B6 3.7 −6 1.68 2.57 C7 A7 B7 5.5 −8 1.65 2.55 C8 A8 B8 3.7 −2 1.65 2.54 C9 A9 B9 3.5 −7 1.66 2.54 C10 A10 B10 4.8 −9 1.67 2.59 C11 A11 B1 4.2 −10 1.67 2.54 C12 A12 B2 5.1 −11 1.69 2.52 C13 A13 B7 5.6 −9 1.71 2.51 C14 A14 B8 6.3 −8 1.72 2.52 c1 a1 b1 2.8 13 1.61 2.63 c2 a2 b2 2.7 14 1.61 2.68 c3 a3 b3 1.3 13 1.58 2.65 c4 a4 b4 1.5 15 1.58 2.64 c5 a5 b5 1.6 17 1.59 2.67 c6 a6 b6 1.5 9 1.55 2.66 c7 a7 b7 1.4 8 1.54 2.65 c8 a8 b8 1.3 7 1.55 2.64 c9 a9 b1 1.8 9 1.54 2.65 c10 a10 b2 1.8 9 1.57 2.69 c11 a11 b3 2.1 8 1.56 2.69 c12 a12 b4 2.1 15 1.59 2.64 c13 A1 b5 2.8 9 1.62 2.62 c14 A2 b6 2.9 8 1.59 2.63 c15 A3 b7 2.7 7 1.59 2.64 c16 A4 b8 2.8 9 1.58 2.63 c17 A4 b9 2.5 5 1.56 2.62 c18 A5 b10 2.4 6 1.58 2.67 c19 A6 b11 2.4 7 1.57 2.64 c20 A7 b12 2.6 2 1.56 2.66 c21 A8 b13 2.1 8 1.59 2.67 c22 a1 B1 1.2 5 1.56 2.63 c23 a2 B2 1.6 3 1.57 2.64 c24 a3 B3 1.2 4 1.58 2.63 c25 a4 B4 2.5 6 1.58 2.64 c26 a5 B5 1.2 7 1.58 2.64

Example 2

[0066] Hot-rolled steel sheets for a non-oriented electrical steel sheet were produced in the same manner using steels shown in Table 1 and manufacturing methods shown in Table 2, and then non-oriented electrical steel sheets were obtained.

[0067] Regarding the obtained hot-rolled steel sheets for a non-oriented electrical steel sheet, in addition to the measurement results of Example 1, the ratios between the grain boundary C concentration and the intragranular C concentration were measured. Regarding the non-oriented electrical steel sheets, the magnetic characteristics were measured in the same manner as in Example 1. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Hot-rolled sheet toughness Magnetic Charpy transition flux density Iron loss Steel Manufacturing temperature B50 W15/50 Sign No. method No. TR = C/P CR = C.sub.GB/C.sub.IG (° C.) (T) (W/kg) D1 A1 B4 4.2 3.2 −4 1.68 2.51 Comparative Example D2 A2 B6 4.5 3.1 −3 1.68 2.56 Comparative Example D3 A13 B9 5.6 5.2 −19 1.71 2.51 Invention Example D4 A14 B2 6.3 6.1 −18 1.72 2.52 Invention Example D5 a1 b1 2.8 3.1 13 1.61 2.63 Comparative Example D6 A2 b6 2.9 3.2 8 1.59 2.63 Comparative Example D7 a1 B1 1.2 3.1 5 1.56 2.63 Comparative Example

[0068] It was possible to confirm that, when the ratio CR=C.sub.GB/C.sub.IG of the C concentration C.sub.GB [atom %] present in the grain boundaries to the C concentration C.sub.IG [atom %] present in the grains was set to 3.5 or more, superior characteristics were obtained. While not explicitly shown in Table 3, CR's were 3.5 or more in C1, C2, C3, C5, C9, C11 and C12.

[0069] It was possible to confirm that the use of the hot-rolled steel sheet for a non-oriented electrical steel sheet of the present invention makes it possible to obtain a non-oriented electrical steel sheet having as excellent characteristics as non-oriented electrical steel sheets for which a conventional hot-rolled steel sheet for a non-oriented electrical steel sheet that had undergone hot-band annealing was used without causing the fracturing of the steel sheet during pickling.

INDUSTRIAL APPLICABILITY

[0070] According to the present invention, it is possible to provide a hot-rolled steel sheet for a non-oriented electrical steel sheet having sufficient hot-rolled sheet toughness even in the case of skipping annealing in a hot rolling process and satisfying both a low iron loss and a high magnetic flux density when a non-oriented electrical steel sheet is produced. Therefore, it is possible to stably produce and provide a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density without causing fracturing, and thus the present invention is capable of sufficiently meeting an urgent demand for mass production in the field of electrical equipment for which the non-oriented electrical steel sheet is used as an iron core material and has an extremely high industrial value.