Steel strip for producing a non-grain-oriented electrical steel, and method for producing such a steel strip

Abstract

The invention relates to a steel strip for producing a non-oriented electrical steel. To achieve greatly improved frequency-independent magnetic properties, in particular greatly reduced hysteresis losses, in comparison with known electrical steels, the following alloy composition in wt % is proposed: C: ≤0.03, Al: 1 to 12, Si: 0.3 to 3.5, Mn: >0.25 to 10, Cu: >0.05 to 3.0, Ni: >0.01 to 5.0, total of N, S and P: at most 0.07, remainder iron and smelting-related impurities, with the optional addition of one or more elements from the group Cr, Mo, Zn and Sn, wherein the steel strip has an insulation layer substantially consisting of Al2O3 and/or SiO2 with a thickness in the range from 10 μm to 100 μm. The invention also relates to a method for producing such a steel strip.

Claims

1. A steel strip for producing a non-grain-oriented electrical steel sheet comprising a following alloy composition in wt. %: C: ≤0.03 Al: 1 to 12 Si: 0.3 to 3.5 Mn: >0.25 to 10 Cu: >0.05 to 3.0 Ni: >0.01 to 5.0, a total of N, S and P: at most 0.07, with the remainder being iron and melting-induced impurities, said steel strip comprising an insulation layer substantially including Al.sub.2O.sub.3 and/or SiO.sub.2 having a thickness in a range of 20 μm to 100 μm, wherein the alloy composition includes at least one element selected from the group consisting of Cr, Mo, Zn and Sn, wherein a total content of Cr and Mo is 0.01 to 0.5 wt. %.

2. The steel strip of claim 1, wherein the thickness of the insulation layer is in a range of 20 μm to 50 μm.

3. The steel strip of claim 1, wherein a total content of Zn and Sn is 0.01 to 0.05 wt. %.

4. The steel strip of claim 1, wherein a maximum Al content is 10 wt. %.

5. The steel strip of claim 1, wherein a maximum total content of Mn and Al is 20 wt. %.

6. The steel strip of claim 1, wherein an Si content is 1.0 to 3.0 wt %.

7. The steel strip of claim 1, wherein an Si content is 1.5 to 2.5 wt. %.

8. The steel strip of claim 1, wherein a maximum Ni content is 3 wt. %.

9. The steel strip of claim 1, wherein the alloy composition includes in wt. %: Al: 1 to 6 Si: 0.5 to 1 Mn: >1.0 to 7 Cu: >0.1 to 2.0 Ni: >0.1 to 3.0.

10. The steel strip of claim 1, wherein the alloy composition includes in wt. %: Al: >6 to 10 Si: 0.5 to 0.8 Mn: >0.5 to 3 Cu: >0.1 to 2.5 Ni: >0.1 to 2.5.

11. The steel strip of claim 10, wherein the alloy composition includes in wt. %: Si: 0.3 to 0.5 Mn: >0.5 to 2 Cu: >0.1 to 0.5.

12. The steel strip of claim 1, wherein the steel strip has a specific density of 6.40 to 7.3 g/cm.sup.3.

13. The steel strip of claim 1, wherein the steel strip has a strength Rm of 450 to 690 MPa, a yield strength Rp0.2 of 310 to 550 MPa and an elongation A80 of 5 to 30%.

14. A method for producing a steel strip for producing a non-grain-oriented electrical steel sheet, said method comprising: melting a steel melt made from a steel comprising a following ahoy composition in wt. %: C: ≤0.03 Al: 1 to 12 Si: 0.3 to 3.5 Mn: >0.25 to 10 Cu: >0.05 to 3.0 Ni: >0.01 to 5.0, a total of N, S and P: at most 0.07, with the remainder being iron and melting-induced impurities; casting the steel melt to form a pre-strip by means of a horizontal or vertical strip casting process approximating a final dimension or casting the steel melt to form a slab or thin slab by means of a horizontal or vertical slab or thin slab casting process; re-heating the slab or thin slab to 1050° C. to 1250° C. and then hot-rolling the slab or thin slab to form a hot strip, or re-heating the pre-strip, produced to approximately final dimension, to 1000° C. to 1100° C. and then hot-rolling the pre-strip to form a hot strip, or hot-rolling the pre-strip without re-heating from the casting heat to form a hot strip with optional intermediate heating between individual rolling passes of the hot-rolling; reeling the hot strip at a reeling temperature between 850° C. and room temperature, single or multi-stage finish-rolling of the hot strip or the pre-strip, produced to approximately final dimension, having a thickness of less than 3 mm to form a steel strip having a minimum final thickness of 0.10 mm; and subsequently annealing the steel strip with the following parameters: annealing temperature: 900 to 1080° C., annealing duration: 10 to 60 seconds with subsequent cooling in air to adjust an insulation layer substantially including Al.sub.2O.sub.3 and/or SiO.sub.2 on the steel strip having a thickness in a range of 20 μm to 100 μm, wherein the alloy composition includes at least one element selected from the group consisting of Cr, Mo, Zn and Sn, wherein a total content of Cr and Mo is 0.01 to 0.5 wt. %.

15. The method of claim 14, wherein the hot strip is annealed with the following parameters: annealing temperature: 550 to 800° C., annealing duration: 20 to 80 min, and subsequently cooled in air.

16. The method of claim 14, further comprising, prior to the finish-rolling, heating the hot strip to a temperature above room temperature, wherein the finish-rolling is executed at said temperature to the final thickness.

17. The method of claim 14, further comprising, prior to the finish-rolling, heating the hot strip to a temperature of 350 to 570° C., wherein the finish-rolling is executed at said temperature to the final thickness.

18. The method of claim 14, further comprising heating the hot strip, prior to the finish-rolling, to a temperature of 360 to 520° C., wherein the finish-rolling is executed at said temperature to the final thickness.

19. The method of claim 14, further comprising in a multi-stage finish-rolling procedure, between rolling steps, reheating to a temperature of 600 to 800° C. followed by cooling to rolling temperature.

20. A steel strip for producing a non-grain-oriented electrical steel sheet comprising a following alloy composition in wt. %: C: ≤0.03 Al: >6 to 10 Si: 0.5 to 0.8 Mn: >0.5 to 3 Cu: >0.1 to 2.5 Ni: >0.1 to 2.5, a total of N, S and P: at most 0.07, with the remainder being iron and melting-induced impurities, said steel strip comprising an insulation layer substantially including Al.sub.2O.sub.3 and/or SiO.sub.2 having a thickness in a range of 20 μm to 100 μm.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which the sole FIG. 1 shows various production routes for producing a steel strip in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) In dependence upon the specific alloy composition, a plurality of advantageous production routes have emerged for producing a steel strip in accordance with the invention, see FIG. 1. FIG. 1 illustrates three advantageous production routes.

(3) The abbreviations below denote the following:

(4) T.sub.HR: hot-rolling at temperatures between 1000 to 1150° C.,

(5) CR: cold-rolling,

(6) T.sub.1, T.sub.2C, T.sub.3C: final annealing for all routes (900 to 1080° C., 10-60 s, air cooling),

(7) T.sub.2A, T.sub.2B, T.sub.3A, T.sub.3B: intermediate annealing for routes 2 and 3 (550 to 800° C., 20 to 80 min.),

(8) T.sub.R: finish-rolling for route 3 at elevated temperatures of 350 to 570° C.

(9) According to route 1, the hot strip is finish-rolled to the required final thickness at room temperature.

(10) Should the alloy be too solid for classic cold-rolling at room temperature, a two-stage cold-rolling procedure according to route 2 can be used, in that rolling is performed initially at a thickness reduction degree of up to 60% to the desired final thickness at room temperature, then said alloy is rolled out at a temperature range of 550 to 650° C. for 40 to 60 min. and then the remaining 40% of the desired final thickness is achieved, in turn, by cold-rolling.

(11) A material in particular comprising an increased Al content greater than 6 wt. % or Al+Si in total greater than 6 wt. % which has edge cracks after the first cold-rolling procedure can be produced according to route 3 by finish-rolling at elevated temperature. After heating in a temperature range of 350 to 600° C., preferably 350 to 520° C., rolling is performed and then reheating is performed iteratively in the aforementioned temperature range for 2-5 min. in each case between the rolling steps and finish-rolling is performed until the desired final thickness is achieved.

(12) Some results relating to alloys in accordance with the invention are described hereinafter.

(13) Alloys were tested as per table 1, wherein only the essential elements were determined. The alloys 13, 17 and 22 are in accordance with the invention and were tested in comparison with the reference material Ref1 not in accordance with the invention.

(14) TABLE-US-00001 TABLE 1 Al Si Mn Cu Ni P S C Alloy wt. % 13 9.90 0.45 0.97 0.98 0.02 0.003 0.003 0.012 17 7.90 0.53 1.91 0.20 0.02 0.003 0.003 0.024 22 6.10 0.49 2.04 2.10 0.02 0.055 0.003 0.005 Ref1 1.90 1.93 — — — 0.004 0.003 0.001

(15) Table 2 shows the mechanical properties of the alloys and the ascertained specific density of the materials. In addition to different mechanical properties, materials having different specific densities can also be produced, so that various requirements of the materials in accordance with the invention can be met.

(16) TABLE-US-00002 TABLE 2 Mechanical properties; 0.7 mm thick Rp0.2 A80 Density Alloy [N/mm.sup.2] Rm [%] [kg/dm.sup.3] 13 679 688 2 6.8 17 570 635 6 6.9 22 560 600 1.6 7.1 Ref1 500 600 15.0 7.6

(17) Table 3 shows the results of the measurement of the frequency dependence of the magnetic flux density B.sub.max of steel sheets having a thickness of 0.7 mm of the tested alloys. The measurements were performed at frequencies f of 50, 200, 400, 750 and 1000 Hz. The results tellingly prove the extensive frequency independence of the magnetic flux density and thus the hysteresis losses in a periodic alternating field.

(18) TABLE-US-00003 TABLE 3 Frequency dependence (f = 50-1000 Hz); 0.7 mm thickness f [Hz] 50 200 400 750 1000 Alloy Bmax [T] 13 1.38 1.39 1.39 1.39 1.39 17 1.44 1.44 1.44 1.44 1.44 22 1.44 1.44 1.45 1.45 1.45