600 MPA GRADE NON-ORIENTED ELECTRICAL STEEL SHEET AND MANUFACTURING METHOD THEREOF

Abstract

Provided is a 600 MPa grade non-oriented electrical steel sheet with excellent magnetic properties, comprising the following chemical elements in mass percentage: 0<C≤0.0035%; Si: 2.0-3.5%; Mn: 0.4-1.2%; P: 0.03-0.2%; Al: 0.4-2.0%; and the balance being Fe and unavoidable impurities. Also provided is a manufacturing method for the 600 MPa grade non-oriented electrical steel as described above, including the following steps: (1) converter smelting, RH refining and casting; (2) hot rolling; (3) normalizing; (4) cold rolling; (5) continuous annealing; and (6) applying an insulation coating to obtain a finished non-oriented electrical steel sheet.

Claims

1. A 600 MPa grade non-oriented electrical steel sheet, comprising the following chemical elements in mass percentage: 0<C0.0035%; Si: 2.0-3.5%; Mn: 0.4-1.2%; P: 0.03-0.2%; Al: 0.4-2.0%; and the balance being Fe and unavoidable impurities.

2. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, further comprising at least one of Sb and Sn in a total content of 0.003-0.2% by mass.

3. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, further comprising at least one of Mg, Ca and REM in a total content of 0.0005-0.01% by mass.

4. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, characterized in that the unavoidable impurities include: S0.003%; Ti≤0.001%; O≤0.002%; and N≤0.002%.

5. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, characterized in that the 600 MPa grade non-oriented electrical steel sheet has a {100} plane texture in a proportion of ≥25% and a {111} plane texture in a proportion of ≤31%.

6. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, characterized in that the 600 MPa grade non-oriented electrical steel sheet contains inclusions with a size greater than 0.5 μm, wherein the inclusions are at least one of AlN, CaS, and composite inclusions of AlN and CaS.

7. The 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, characterized in that the 600 MPa grade non-oriented electrical steel sheet has an iron loss P.sub.15/50 of 2 W/kg, a magnetic induction B.sub.50 of 1.69 T and a tensile strength of 600 MPa.

8. A manufacturing method for the 600 MPa grade non-oriented electrical steel sheet as claimed in claim 1, including the following steps: converter smelting, RH refining and casting; hot rolling; normalizing; cold rolling; continuous annealing: rapidly heating a cold-rolled steel sheet from an initial temperature for rapid heating T.sub.rapid heating initial to a soaking temperature at a heating rate of 50-2000° C./s to perform rapid heating annealing, wherein a volume content of H.sub.2 in an annealing furnace is ≥55% and a dew point in the annealing furnace is ≤−30° C.; and after the rapid heating annealing, slowly cooling the steel sheet at a cooling rate ≤5° C./s; and applying an insulation coating to obtain a finished non-oriented electrical steel sheet.

9. The manufacturing method as claimed in claim 8, characterized in that in the step of continuous annealing, the heating rate is 100-600° C./s.

10. The manufacturing method as claimed in claim 8, characterized in that in the step of continuous annealing, the initial temperature for rapid heating T.sub.rapid heating ranges from room temperature to 750° C.

11. The manufacturing method as claimed in claim 8, characterized in that in the step of RH refining, a value of t/ΣAl is in the range of 0.30-0.65, wherein t represents a time interval in minutes between adding at least one of elements Mg, Ca and REM and adding the element Al, and ΣAl represents a total time in minutes from adding the element Al to the end of RH refining.

12. The manufacturing method as claimed in claim 8, characterized in that in the step of hot rolling, a finishing rolling temperature is controlled to be ≤850° C., and a coiling temperature is controlled to be 500-750° C.

13. The manufacturing method as claimed in claim 8, characterized in that a single cold rolling process or a double cold rolling process with an intermediate annealing is utilized in the step of cold rolling.

14. The manufacturing method as claimed in claim 13, characterized in that in the step of cold rolling, at least one pair of working rolls in each pass or stand has a surface roughness of ≤0.40 μm, and/or each pass or stand has an accumulative reduction ratio of 75-85%, and the final pass or stand has a reduction ratio of ≤20%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0051] FIG. 1 is a schematic diagram of annealing process curves using different annealing processes, i.e., the present technical solution and conventional process;

[0052] FIG. 2 is a SEM diagram of the conventional steel sheet in Comparative Example A2;

[0053] FIG. 3 is a SEM diagram of the high-strength non-oriented electrical steel sheet in Inventive Example A17;

[0054] FIG. 4 schematically shows the effect of different t/ΣAl values on iron loss;

[0055] FIG. 5 schematically shows the effect of different heating rates on the proportion of {100} plane texture; and

[0056] FIG. 6 schematically shows the effect of different heating rates on the proportion of {111} plane texture.

DETAILED DESCRIPTION

[0057] The high-strength non-oriented electrical steel sheet with excellent magnetic properties and manufacturing method thereof according to the present invention will be further explained and illustrated below in combination with the accompanying drawings and specific embodiments. However, the technical solutions of the present invention are not limited to the explanation and illustration.

Inventive Examples A9-A20 and Comparative Examples A1-A8

[0058] The high-strength non-oriented electrical steel sheets in Inventive Examples A9-A20 and conventional steel sheets in Comparative Examples A1-A8 were manufactured by the following steps.

(1) The molten iron and steel scrap were prepared according to the compositions as shown in Table 1. After converter smelting, RH refining which included decarbonization, deoxidation and alloying was carried out, and then the molten steel was cast by continuous casting to obtain a continuous casting billet.
(2) Hot rolling: the thickness of a hot-rolled steel sheet was controlled to be 0.8-2.0 mm, a finishing rolling temperature was controlled to be ≤850° C., and a coiling temperature was controlled to be 500-750° C.
(3) Normalizing: the hot-rolled steel sheet was normalized, wherein the soaking temperature for normalizing was set to be 800-1000° C. and the soaking time was set to be 1-180 s.
(4) Cold rolling: the steel sheet was rolled to a thickness of the finished product by using a single cold rolling process, wherein the thickness was 0.1-0.3 mm.
(5) Continuous annealing: a cold-rolled steel sheet was rapidly heated from an initial temperature T.sub.rapid heating initial to a soaking temperature at a heating rate of 50-2000° C./s to perform rapid heating annealing, wherein the volume content of H.sub.2 in an annealing furnace was ≥55% and a dew point in the annealing furnace was ≤−30° C.; and after the rapid heating annealing, the steel sheet was slowly cooled at a cooling rate ≤5° C./s. The initial temperature for rapid heating T.sub.rapid heating initial ranged from room temperature to 750° C.
(6) An insulation coating was applied to obtain a finished non-oriented electrical steel sheet.

[0059] In some preferred embodiments, in the step of RH refining, the t/ΣAl value is in the range of 0.30-0.65, wherein t represents a time interval in minutes between adding the at least one of elements Mg, Ca and REM and adding the element Al, and ΣAl represents a total time in minutes from adding the element Al to the end of RH refining.

[0060] In some preferred embodiments, a single cold rolling process or a double cold rolling process with an intermediate annealing is utilized in step (4). And/or, in step (4), at least one pair of working rolls in each pass or stand has a surface roughness of ≤0.40 μm; and/or each pass or stand has an accumulative reduction ratio of 75-85%, and the final pass or stand has a reduction ratio of ≤20%.

[0061] Table 1 lists the mass percentages of chemical elements of the high-strength non-oriented electrical steel sheets according to Inventive Examples A9-A20 and the conventional steel sheets according to Comparative Examples A1-A8.

[0062] Table 2 lists the specific process parameters of the high-strength non-oriented electrical steel sheets according to Inventive Examples A9-A21 and the conventional steel sheets according to Comparative Examples A1-A8. For Comparative Examples Al and A4, the initial temperature for rapid heating T.sub.rapid heating initial was “/”, which indicated that a rapid heating process was not utilized.

TABLE-US-00001 TABLE 1 (%, the balance being Fe and other impurities other than S, Ti, O and N) No. C Si Mn P S Al O N Ti A1 0.0011 1.68 0.57 0.18 0.0028 2.16 0.0022 0.0018 0.0020 A2 0.0007 1.94 1.37 0.13 0.0025 0.71 0.0018 0.0013 0.0009 A3 0.0024 2.07 0.84 0.08 0.0013 0.92 0.0027 0.0012 0.0011 A4 0.0006 2.11 0.41 0.06 0.0019 1.85 0.0011 0.0025 0.0007 A5 0.0018 2.83 1.00 0.06 0.0015 0.48 0.0009 0.0014 0.0005 A6 0.0021 2.84 0.49 0.05 0.0035 1.93 0.0017 0.0009 0.0007 A7 0.0007 3.17 0.21 0.02 0.0011 0.003 0.0008 0.0012 0.0005 A8 0.0018 3.65 0.87 0.06 0.0008 1.52 0.0006 0.0019 0.0012 A9 0.0022 2.15 1.16 0.18 0.0018 0.42 0.0007 0.0017 0.0005 A10 0.0027 2.18 0.94 0.03 0.0008 1.91 0.0006 0.0011 0.0005 A11 0.0012 3.05 0.40 0.20 0.0030 1.14 0.0011 0.0013 0.0007 A12 0.0035 2.00 0.77 0.08 0.0020 0.75 0.0020 0.0008 0.0004 A13 0.0017 2.85 0.48 0.15 0.0015 0.97 0.0007 0.0012 0.0010 A14 0.0032 2.91 0.82 0.07 0.0008 0.68 0.0006 0.0006 0.0008 A15 0.0024 2.90 0.48 0.13 0.0011 0.40 0.0011 0.0020 0.0006 A16 0.0014 3.14 0.81 0.08 0.0006 0.52 0.0007 0.0009 0.0006 A17 0.0023 2.88 0.67 0.05 0.0014 2.00 0.0014 0.0012 0.0004 A18 0.0012 3.21 0.83 0.05 0.0005 0.80 0.0005 0.0008 0.0005 A19 0.0016 3.50 1.20 0.04 0.0008 0.42 0.0006 0.0010 0.0005 A20 0.0028 3.48 0.41 0.04 0.0005 1.35 0.0008 0.0005 0.0008 No. Mg Ca REM Sn Sb Note A1 0.002 0.002 0.002 / / Comparative Example A2 / / / 0.03 0.03 Comparative Example A3 0.008 / / 0.03  0.007 Comparative Example A4 / 0.005 / 0.05 0.08 Comparative Example A5 / / 0.004 / 0.12 Comparative Example A6 0.005 0.003 0.002 0.18 / Comparative Example A7 0.001 0.003 0.006 0.01 0.16 Comparative Example A8 0.003 0.005 0.001  0.003 0.01 Comparative Example A9  0.0005 / / 0.05 / Inventive Example A10 0.005 / 0.005 / 0.04 Inventive Example A11 0.008  0.0011 / 0.03 0.05 Inventive Example A12 0.001  0.0005 0.003 0.10 0.10 Inventive Example A13 0.005 0.001  0.0005 0.01 0.01 Inventive Example A14 0.001 0.003 0.001  0.003 / Inventive Example A15 / /  0.0005 0.01 0.03 Inventive Example A16 / 0.002 0.007 0.18 / Inventive Example A17 0.001 / 0.008 / 0.11 Inventive Example A18 0.001 0.001 0.001 0.05 0.02 Inventive Example A19 / 0.008 0.002 0.04 0.08 Inventive Example A20 / 0.010 / 0.05  0.007 Inventive Example

TABLE-US-00002 TABLE 2 Hot-rolled Finishing Elements steel sheet rolling Coiling Cold Surface Total used for t/ΣAl thickness temp. temp. rolling roughness of reduction No. deoxidation Value [mm] [° C.] [° C.] mode roll [μm] ratio [%] A1 Si / 2.0 820 750 Single 1.0 87.5 A2 Al 0.41 2.0 850 570 Single 0.4 90.0 A3 Si / 2.8 850 550 Single 0.2 91.1 A4 Al 0.17 1.6 835 600 Double 0.4 90.6 A5 Al 0.78 1.8 825 620 Single 2.0 86.1 A6 Si / 2.0 840 680 Double 0.2 85.0 A7 Al 0.52 2.0 850 570 Single 0.6 87.5 A8 Al 0.39 2.0 815 600 Single 0.1 87.5 A9 Si 0.52 1.6 850 750 Single 0.4 84.4 A10 Si 0.30 1.8 840 650 Single 0.1 83.3 A11 Si 0.65 1.2 840 620 Single 0.2 75 A12 Si 0.52 1.6 855 570 Double 0.4 84.4 A13 Si 0.40 0.8 815 500 Single 0.4 81.3 A14 Si 0.49 1.2 845 650 Single 0.2 79.2 A15 Si 0.60 2.0 820 550 Single 0.2 85.0 A16 Si 0.62 2.0 825 680 Single 0.1 85.0 A17 Si 0.52 2.0 840 570 Single 0.3 85.0 A18 Si 0.42 2.0 835 650 Double 0.3 85.0 A19 Si 0.63 1.2 815 530 Single 0.2 83.3 A20 Si 0.48 1.6 825 720 Double 0.3 84.4 Reduction ratio Heating Dew point H.sub.2 Cooling of final pass or T.sub.rapid heating initial rate in furnace Content rate No. stand [%] [° C.] [° C./s] [° C.] [%] [° C./s] Note* A1 5 / 75 −20 30% 1 CE A2 10  25 150 −38 40% 2 CE A3 15 300 350 −35 55% 2 CE A4 20 / 75 −30 60% 1 CE A5 5 600 600 −28 57% 2 CE A6 10 450 400 −32 60% 3 CE A7 15 100 1800 −37 62% 6 CE A8 20 200 200 −35 65% 4 CE A9 20 400 2000 −40 55 1 IE A10 5 500 50 −37 57 2 IE A11 15 200 200 −40 60 2 IE A12 10 300 300 −35 60 2 IE A13 15 750 500 −40 55 5 IE A14 8 200 100 −30 55 3 IE A15 12 350 400 −35 55 2 IE A16 15 600 350 −38 63 2 IE A17 20 400 300 −37 61 1 IE A18 5 550 550 −35 57 1 IE A19 15 650 600 −38 55 4 IE A20 5 750 300 −40 65 3 IE * CE= Comparative Example; IE= Inventive Example

[0063] Table 3 lists the performance values of the high-strength non-oriented electrical steel sheets according to Examples A9-A20 and conventional steel sheets according to Comparative Examples A1-A8.

TABLE-US-00003 TABLE 3 Tensile Iron loss Magnetic strength P.sub.15/50 induction No. [MPa] [W/kg] B.sub.50 [T] Note A1 484 2.47 1.65 Comparative Example A2 511 2.61 1.64 Comparative Example A3 524 2.70 1.63 Comparative Example A4 498 2.35 1.65 Comparative Example A5 537 2.18 1.67 Comparative Example A6 531 2.20 1.68 Comparative Example A7 510 2.11 1.62 Comparative Example A8 581 2.18 1.62 Comparative Example A9 611 1.94 1.70 Inventive Example A10 632 1.85 1.71 Inventive Example A11 618 1.90 1.70 Inventive Example A12 627 1.94 1.71 Inventive Example A13 635 1.91 1.71 Inventive Example A14 660 1.88 1.69 Inventive Example A15 704 1.79 1.70 Inventive Example A16 641 1.91 1.71 Inventive Example A17 665 1.89 1.70 Inventive Example A18 682 1.88 1.69 Inventive Example A19 739 1.86 1.70 Inventive Example A20 659 1.84 1.69 Inventive Example

[0064] As can be seen from FIGS. 1 to 3, the high-strength non-oriented electrical steel sheets in all Inventive Examples had high cleanliness, as well as a small quantity and a large size of inclusions; moreover, the finished steel sheets had good recrystallization effect, uniform and coarse grain size, a high proportion of favorable textures, and excellent electromagnetic properties, wherein the high-strength non-oriented electrical steel sheets according to each Inventive Example had an iron loss P.sub.15/50 of ≤2 W/kg, a magnetic induction B.sub.50 of ≥1.69 T and a tensile strength of ≥600 MPa.

[0065] FIG. 1 is a schematic diagram of annealing process curves using different annealing processes, i.e., the present technical solution and conventional process.

[0066] As shown in FIG. 1, in the manufacturing method according to the present invention, the rapid heating annealing was utilized, which was different from a conventional heating annealing process. The heating rate in the present invention was controlled to be 50-2000° C./s due to the facts that: if the heating rate is too fast, the requirements for equipment capabilities will be too high, the cost will be expensive, and the residence time of the cold-rolled steel sheet in the high temperature stage will be too long, resulting in poor uniformity of the grain structure. Meanwhile, in view of the fact that (internal) oxidation and nitridation are prone to occur on the surface of the finished steel sheet under high temperature annealing conditions, it will result in grain refinement, the deterioration of iron loss of finished steel sheet and the decrease of the surface quality of finished steel sheet. Therefore, the volume content of H.sub.2 in the annealing furnace is controlled to be ≥55% and a dew point in the annealing furnace is controlled to be ≤−30° C. After the rapid heating annealing, the finished steel sheet is required to be slowly cooled, and a cooling rate is required to be limited to be ≤5° C./s, so as to control the shape of the finished steel sheet and to reduce the stress in the steel sheet, and thus, the finally obtained non-oriented electrical steel sheet has good surface condition and is characterized by high magnetic induction, low iron loss and high strength.

[0067] FIG. 2 is a SEM diagram of the conventional steel sheet in Comparative Example A2. FIG. 3 is a SEM diagram of the high-strength non-oriented electrical steel sheet in Inventive Example A17.

[0068] As can be seen from FIGS. 2 and 3, compared with Comparative Example A2, the high-strength non-oriented electrical steel sheet in Inventive Example A17 had high cleanliness, as well as a smaller quantity and a larger size of inclusions.

[0069] The inclusions in the specimens of finished products corresponding to Comparative Example A2 and Inventive Example A17 were observed with a HITACHI S4200 Scanning Electron Microscope. Each specimen was continuously observed for 10 fields of view. The distribution of the types, sizes and quantities of inclusions were counted and listed in Tables 4 and 5.

[0070] Table 4 lists the types, sizes and quantities of inclusions in the specimen of finished product according to Comparative Example A2.

TABLE-US-00004 TABLE 4 Inclusions AlN + MnS FeO FeO + SiO.sub.2 MnS + Cu.sub.2S CaO + Al.sub.2O.sub.3 + SiO.sub.2 Al.sub.2O.sub.3 Total 0-0.5 μm A large quantity of AlN, MnS and Cu.sub.2S inclusions 0.5-1.0 μm 44 0 0 20 3 0 67 1.0-1.5 μm 10 0 0 1 0 0 11 1.5-5.0 μm 18 6 1 2 2 4 33 5.0-10 μm 0 0 3 0 0 0 3

[0071] Table 5 lists the types, sizes and quantities of inclusions in the specimen of finished product according to Inventive Example A17.

TABLE-US-00005 TABLE 5 Al.sub.2O.sub.3 + AlN + Inclusions AlN CaS SiO.sub.2 MgO/SiO.sub.2 CaS FeO Total 0-0.5 μm Almost no 0.5-1.0 μm 14 0 0 0 0 0 14 1.0-1.5 μm 14 8 0 0 0 0 22 1.5-5.0 μm 101 19 0 4 4 0 128 5.0-10 μm 0 0 1 1 0 0 2

[0072] As can be seen from FIGS. 4 and 5, according to the statistic data of inclusions, for the specimen of finished product in Comparative Example A2, there were a large quantity of AlN, MnS and Cu.sub.2S inclusions with a size of 0.5 μm or less; the inclusions with a size of 0.5 μm or more were mainly AlN+MnS composite inclusions or MnS+Cu.sub.2S composite inclusions, which were larger in quantity and smaller in size; and further, the specimen also contained a small quantity of oxide inclusions. In contrast, for the specimen of finished product in the Inventive Example, there were almost no inclusions with a size of 0.5 μm or less; and the inclusions with a size of 0.5 μm or more were mainly AlN and CaS, accompanied by a small quantity of oxide inclusions and AlN+CaS composite inclusions which were relatively large in size.

[0073] The reasons were as follows: during the solidification process of the molten steel of the Comparative Example, oxide inclusions of larger size were first precipitated, and then MnS inclusions began to precipitate as the temperature of the molten steel continued to drop, and finally the AlN and Cu.sub.2S inclusions were precipitated with the MnS inclusion as the core respectively. In contrast, during the solidification process of the molten steel of the Inventive Example, oxide inclusions of larger size had fully floated, and the binding capacity of Mg, Ca and REM with the element S was much greater than that of the elements Mn and S with the elements Cu and S, such that MgS, CaS and REM-S inclusions with a melting point as high as 2500° C. would be preferentially precipitated, thereby effectively inhibiting the precipitation of MnS and Cu.sub.2S inclusions. Then, AlN inclusions began to precipitate as the temperature of the molten steel continued to drop. Since most of the molten steel had solidified at this time, only a small quantity of AlN inclusions can be combined with CaS inclusions to form AlN+CaS composite inclusions of relatively larger size that were prone to float and remove.

[0074] FIG. 4 schematically shows the effect of different t/ΣAl values on iron loss.

[0075] As shown in FIG. 4, in the step of RH refining, when the t/ΣAl value was controlled to be 0.30-0.65, the magnetic properties of obtained non-oriented electrical steel sheets were better. The reasons were as follows: when performing deoxidation alloying after decarbonization, Si is utilized for deoxidation to avoid the direct use of aluminum for deoxidation and the formation of fine-sized inclusions. After ferro-silicon alloy is added, silicon oxide inclusions are easier to float up and remove. Afterwards, as the viscosity of the molten steel increases, the alumina inclusions are not easy to float up and remove; thus, the alumina inclusions are treated with Mg, Ca and REM to generate aluminate compounds with a lower melting point, and at the same time, to suppress fine and dispersed small particle inclusions. In order to ensure the treatment effect of Mg, Ca and REM, in addition to controlling the addition amount of Mg, Ca and REM, the value of t/ΣAl may be preferably controlled to be 0.30-0.65, so as to ensure the effective concentrations of Mg, Ca and REM in the molten steel, thereby ensuring that the inclusions can be fully denatured. By controlling the residence time of Mg, Ca and REM in the molten steel, the molten steel can fully react with Mg, Ca and REM, so as to achieve a good effect of improving inclusions.

[0076] It should be noted that t represents a time interval in minutes between adding the at least one of elements Mg, Ca and REM and adding the element Al, and ΣAl represents a total time in minutes from adding the element Al to the end of RH refining.

[0077] FIG. 5 schematically shows the effect of different heating rates on the proportion of {100} plane texture. FIG. 6 schematically shows the effect of different heating rates on the proportion of {111} plane texture.

[0078] As can be seen from FIGS. 5 and 6, when the heating rate was controlled to be 50-2000° C./s, the proportion of the {100} plane texture could be controlled to be ≥25%, and the proportion of the {111} plane texture could be controlled to be ≤31%. Therefore, it is proven that by utilizing the manufacturing method according to the present invention, the high-strength non-oriented electrical steel sheets had good recrystallization effect, uniform and coarse grain size, high proportion of favorable textures and excellent electromagnetic properties.

[0079] To conclude, by optimizing the design of the chemical composition of high-strength non-oriented electrical steel sheets, the cleanliness of steel was improved, and thus high-strength non-oriented electrical steel sheets with excellent magnetic properties were obtained in the present invention.

[0080] In addition, the manufacturing method according to the present invention also has the above advantages and beneficial effects.

[0081] It should be noted that for the prior art part of protection scope of the present disclosure, it is not limited to the examples given in this application document. All the prior arts that do not contradict with the present disclosure, including but not limited to prior patent documents, prior publications, prior public use, etc., can be included in the protection scope of the present disclosure.

[0082] In addition, the combination of various technical features in the present disclosure is not limited to the combination described in the claims or the combination described in specific embodiments. All the technical features described in the present disclosure can be freely combined or combined in any way unless there is a contradiction between them.

[0083] It should also be noted that the above-listed Examples are only specific embodiments of the present disclosure. Apparently, the present disclosure is not limited to the above embodiments, and similar variations or modifications that are directly derived or easily conceived from the present disclosure by those skilled in the art should fall within the scope of the present disclosure.