METHOD FOR PRODUCING AN NO ELECTRIC STRIP OF INTERMEDIATE THICKNESS

Abstract

The present invention relates to a process for producing a non-oriented electrical steel strip, comprising at least the following process steps (A) provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip, (B) cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip, (C) intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip, (D) cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip and (E) final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip, a non-oriented electrical steel strip obtained in such a way and the use thereof.

Claims

1. A non-oriented electrical steel strip comprising the following composition and texture (all figures in % by weight) from 2.1 to 3.6 of Si, from 0.3 to 1.2 of Al, from 0.01 to 0.5 of Mn, up to 0.05 of Cr, up to 0.005 of Zr, up to 0.04 of Ni, up to 0.05 of Cu, up to 0.005 of Cu, up to 0.005 of at least one rare earth metal, up to 0.005 of Co, balance Fe and unavoidable impurities, with
I.sub.ϵ,{554}<225>−I.sub.ζ,{110}<001><3, where I.sub.ϵ,{554}<225> and I.sub.ζ,{110}<001> have the following meanings: I.sub.ϵ,{554}<225> intensity I in the ϵ-fiber of the orientation density f(g) in Euler space at φ.sub.1=90°, φ.sub.2=45° and ϕ=60° and orientation {554}<225> and I.sub.ζ,{110}<001> intensity I of the orientation density f(g) in Euler space in the ζ-fiber at φ.sub.1=0°, φ.sub.2=0° and ϕ=45° and orientation {110}<001>.

2. The non-oriented electrical steel strip as claimed in claim 1, wherein the non-oriented electrical steel strip has a final thickness of from 0.24 to 0.36 mm.

3. The non-oriented electrical steel strip as claimed in claim 2, wherein the polarization J.sub.2500/50 at 2500 A/m and 50 Hz and the magnetic loss P.sub.1.5/50 at 1.5 T and 50 Hz satisfy the following relationships after the final heat treatment: for hot-rolled strip material which has not been bell heat treated: J.sub.2500/50>−0.045*P.sub.15/50.sup.2+0.3*P.sub.15/50+1.085 (1) for hot-rolled strip material which has been bell heat treated: J.sub.2500/50>−0.045*P.sub.15/50.sup.2+0.28*P.sub.15/50+1.165 (2).

4. A process for producing a non-oriented electrical steel strip as claimed in claim 3 , comprising at least the following process steps: (A) provision of a hot-rolled, optionally separately heat-treated, non-oriented electrical steel strip, by a conventional manufacturing route via a continuous casting plant or by thin slab manufacture, in a thickness of from 1 to 4 mm, (B) cold rolling of the electrical steel strip from step (A) to a thickness of from 0.5 to 0.8 mm in order to obtain a first cold-rolled strip, (C) intermediate heat treatment of the first cold-rolled strip from step (B) at a temperature of from 700 to 1100° C. in order to obtain an intermediate-heat-treated, first cold-rolled strip, (D) cold rolling of the intermediate-heat-treated, first cold-rolled strip from step (C) to a thickness of from 0.24 to 0.36 mm in order to obtain a second cold-rolled strip; and (E) final heat treatment of the second cold-rolled strip from step (D) at a temperature of from 900 to 1100° C. in order to obtain the non-oriented electrical steel strip.

5. The process as claimed in claim 4, wherein step (C) is carried out in one of a continuous furnace and as bell heat treatment.

6. The process as claimed in claim 5, wherein the cold rolling in step (B) is carried out with a degree of cold rolling of from 30 to 90%.

7. The process as claimed in claim 6, wherein the cold rolling in step (D) is carried out with a degree of cold rolling of from 30 to 90%.

8. The process as claimed in claim 7, wherein a hot-rolled strip bell heat treatment is carried out at a maximum temperature of from 640 to 900° C. in step (A).

9. A non-oriented electrical steel strip produced by the process as claimed in claim 8.

10. An electric motor comprising: an iron core having the non-oriented electrical steel strip as claimed in claim 3.

Description

FIGURES

[0084] FIG. 1 shows the improvement according to the invention in the case of hot-rolled strip material which has not been bell heat treated from examples 1, 2, 5 and 6.

[0085] FIG. 2 shows the improvement according to the invention in the case of hot-rolled strip material which has been bell heat treated from examples 3, 4, 7, 8, 13, 14 and 15 to 18.

[0086] FIG. 3 shows the orientation densities of the ODF along the ϵ-fibers in Euler space at φ.sub.1 at 90°, φ.sub.2 at 45° and ϕ in the range from 0° to 90° for example 1.

[0087] FIG. 4 shows orientation densities of the ODFs along the ζ-fibers in Euler space at ζ.sub.1=0° to 90°, φ.sub.2 at 0° and ϕ at 45° for example 1.

[0088] FIG. 5 shows orientation densities of the ODF along the ϵ-fibers in Euler space at φ.sub.1=90°, ϕ.sub.2=45° and ϕ in the range from 0° to 90° for example 2.

[0089] FIG. 6 shows orientation densities of the ODFs along the ζ-fibers in Euler space at φ.sub.1 of from 0° to 90°, φ.sub.2 at 0° and ϕ at 45° for example 2.

EXAMPLES

[0090] The following working examples serve to illustrate the invention. The compositions 1, 2 and 3 as per table 1 are used.

TABLE-US-00001 TABLE 1 No. Si Al Mn C Cr Ni N S Ti P Nb Mo 1 3.14 0.656 0.15 0.0023 0.028 0.013 0.002 0.006 0.001 0.009 0.002 0.15 2 3.17 0.639 0.163 0.0017 0.028 0.013 0.0017 0.0005 0.0045 0.012 0.001 0.0011 3 3.133 0.623 0.151 0.0031 0.033 0.012 0.0012 0.0005 0.0027 0.010 0.001 0.0012 All figures in % by weight, balance Fe

Example 1

[0091] Composition 1 as per table 1 is used in example 1.

[0092] Examples 5, 6, 7 and 8 according to the invention and comparative samples 1, 2, 3 and 4 were produced. For this purpose, the slab obtained after melting of a composition 1 from table 1 was in each case hot rolled, optionally subjected to a hot-rolled strip bell heat treatment at 740° C. and cold rolled to an intermediate thickness of 0.70 mm. The material was subsequently subjected to intermediate heat treatment at 1000° C., cold rolled to a final thickness of 0.34 mm and then subjected to final heat treatment in the range from 1000° C. to 1080° C. The comparative sample 4 was hot rolled after melting, subjected to hot-rolled strip heat treatment, directly cold rolled to a final thickness of 0.34 mm and subjected to final heat treatment at 1000° C. Comparative example 3 results from the standard process, i.e. single-stage cold rolling with hot-rolled strip bell heat treatment. For details, see table 2.

[0093] The characteristic magnetic values, i.e. J100, J5000, J2500, P1.5/50 and P1.0/400, were in each case determined for samples with and without intermediate thickness after final heat treatment. The values for the polarization J of the examples according to the invention over the field strength range up to saturation at both tested frequencies 50 Hz and 400 Hz are higher than the values of the comparable comparative examples with the same thickness of 0.35 mm.

TABLE-US-00002 TABLE 2 Experiments according to the invention and comparative experiments as per example 1 HG Intermediate ZG Final SG Temperature thickness Temperature thickness Temperature J100 μ.sub.r at J5000 J2500 P1.5/50 P1.0/400 No. [° C.] [mm] [° C.] [mm] [° C.] [T] 0.8 T μ.sub.max [T] [T] [W/kg] [W/kg] 1 Comparison — — — 0.34 1080 0.994 8747 8748 1.602 1.509 2.362 17.498 2 Comparison — — — 0.34 1000 0.819 6529 6529 1.598 1.508 2.781 18.043 3 Comparison 740 — — 0.34 1100 1.053 9816 9816 1.643 1.549 2.141 16.432 4 Comparison 740 — — 0.34 1000 0.823 6553 6553 1.642 1.551 2.694 18.127 5 According — 0.7 1000 0.34 1080 0.952 8108 8164 1.654 1.559 2.201 16.736 to the invention 6 According — 0.7 1000 0.34 1050 1.085 9546 9546 1.667 1.578 2.120 15.782 to the invention 7 According 740 0.7 1000 0.34 1080 1.103 10094 10094 1.675 1.584 2.027 15.750 to the invention 8 According 740 0.7 1000 0.34 1050 1.072 9828 9828 1.670 1.577 2.077 16.223 to the invention HG optional bell heat treatment of the hot-rolled strip ZG intermediate heat treatment SG final heat treatment — not carried out

Example 2

[0094] Examples 11, 12 and 13 according to the invention having the composition 2 as per table 1, example 14 having the composition 3 and comparative examples 9 and 10 having the composition 2 of table 1 were produced under the conditions shown in table 3.

TABLE-US-00003 TABLE 3 HG Intermediate ZG Final SG Temperature thickness Temperature thickness Temperature J2500 J5000 P1.5/50 P1.0/400 Example [° C.] [mm] [° C.] [mm] [° C.] [T] [T] [W/kg] [W/kg]  9 Comparison 740 — — 0.29 1060 1.543 1.639 2.23 15.09 10 Comparison 740 — — 0.29 1030 1.542 1.637 2.28 14.94 11 According to 740 0.64 980 0.29 1030 1.578 1.672 2.06 14.02 the invention 12 According to 740 0.64 980 0.29 1000 1.573 1.666 2.19 14.46 the invention 13 According to 740 0.64 980 0.29 1050 1.573 1.666 2.10 14.47 the invention 14 According to 740 0.64 980 0.29 1030 1.572 1.664 2.18 14.68 the invention HG optional bell heat treatment of the hot-rolled strip ZG intermediate heat treatment SG final heat treatment — not carried out

[0095] The improvement achieved both in the magnetization losses and also the magnetic polarization in the case of manufacture according to the invention can be described by the relationships shown in formula 1 and formula 2 and are depicted in FIGS. 1 (for hot-rolled strip which has not been bell heat treated) and 2 (for hot-rolled strip which has been bell heat treated).

[0096] Formula 1 (for hot-rolled strip material which has not been bell heat treated): J.sub.2500/50>−0.045*P.sub.15/50.sup.2+0.3*P.sub.15/50+1.085

[0097] Formula 2 (for hot-rolled strip material which has been bell heat treated): J.sub.2500/50>−0.045*P.sub.15/50.sup.2+0.28*P.sub.15/50+1.165

[0098] X-ray texture determinations using CoKα radiation were carried out and the {100}, {200} and {211} pole figures of the finally heat treated samples 1, 3, 5, 7, 9, 11, 12 and 14 were determined. To obtain better measurement statistics, 5 X-ray samples were measured for each of the samples. The orientation distribution functions (OVF) were calculated from the average pole figures.

[0099] The orientation of the crystal coordinate system relative to the sample coordinate system can be depicted by the OVF by each point in a space spanned by the Euler angles φ.sub.1, φ.sub.2 and ϕ being assigned an orientation density f(g) or intensity I. For a pictorial representation, these orientation distribution functions can be depicted with the aid of the intensity of fibers in sectional areas of this space.

[0100] Here, the ϵ-fiber and the ζ-fiber are examined. In the ϵ-fiber, the <110> direction lies parallel to the transverse direction and runs at φ.sub.1=90°, φ.sub.2=45° and ϕ in the range from 0° to 90°. In the case of the ζ-fiber, the <110> direction lies parallel to the normal direction and runs at φ2=0°, ϕ=45° and φ1=0° to 90°.

[0101] For the section of the OVF relevant for the respective fiber, the orientation densities f(g) of the ζ-fiber and ϵ-fiber were plotted for the course of Euler angles of from 0 to 90°.

[0102] FIGS. 3 to 6 show the course of the OVF versus the angle ϕ for the ϵ-fiber and the angle φ.sub.1 for the ζ-fiber. The specific positions {554}<225>, {110}<001> and more are drawn in.

[0103] The samples 1, 3 and 9 of the single-stage manufacture have the main intensity of their texture in the vicinity of the magnetically poor γ-fiber or the γ-skeletal line (see {554}<225> in the ϵ-fiber).

[0104] Here, the ϵ-fiber at {554}<225> contributes to a worsened texture since the ideal γ-fiber can be shifted by the manufacture by some degrees, which is referred to as γ-skeletal line. A skeletal line refers to a connecting line of points of greatest intensity through Euler space and intensity fluctuations along this can be interpreted as fluctuations within the manufacturing tolerance. For this reason, the maximum intensity I of the γ-fiber shifts to the ϵ-fiber at φ.sub.1 at 90°, φ.sub.2 at 45° and ϕ at 60° and orientation {554}<225>. The process according to the invention of two-stage manufacture reduces the orientation density of this disadvantageous ϵ-fiber texture value at {554}<225> (see table 3 and FIGS. 3 to 6).

[0105] The ζ-fiber, which does not contain any magnetically difficult magnetization reversal direction, is occupied more strongly in the case of the two-stage manufacture according to the invention than in the case of the single-stage manufacture. The individual values are shown in table 4.

TABLE-US-00004 TABLE 4 Texture I.sub.ε,{554}<225> − I.sub.ε,{554}<225> − sample Example I.sub.ε,{554}<225> I.sub.ζ,{110}<001> I.sub.ζ,{110}<001> I.sub.ζ,{110}<001> ≤ 3 1  1 Comparison 6.8 0 6.8 No 3  3 Comparison 8.0 1.1 6.9 No 2  5 According to 1.5 1.8 −0.3 Yes the invention 4  7 According to 0.4 5.0 −4.6 Yes the invention 4  9 Comparison 7 0 7 No 1 11 According to 3.5 2.2 1.3 Yes the invention 2 12 According to 2 4.2 −2.2 Yes the invention 3 14 According to 2.9 2.5 0.4 Yes the invention I.sub.ε,{554}<225> Intensity I of the orientation density f(g) in Euler space in the ε-fiber at φ.sub.1 = 90°, φ.sub.2 = 45° and ϕ = 60° and orientation {554}<225> I.sub.ζ,{110}<001> Intensity I of the orientation density f(g) in Euler space in the ζ-fiber at φ.sub.1 = 0°, φ.sub.2 = 0° and ϕ = 45° and orientation {110}<001>

[0106] An improvement in the texture is achieved by the two-stage manufacture since the two-stage manufacture brings about the increase in the intensity of the orientation density at {110}<001> in the ζ-fiber and the lowering of the intensity of the orientation density at {554}<225>in the ϵ-fiber (see table 4). Non-oriented electrical steel strip which has been produced by manufacture according to the invention with intermediate thickness and which satisfies the condition

I.sub.ϵ,{554}<225>−I.sub.ζ,{110}<001><3

therefore has particularly good magnetic properties.

INDUSTRIAL APPLICABILITY

[0107] The process of the invention makes it possible to produce a non-oriented electrical steel strip which displays particularly low magnetic losses both at low frequencies and at high frequencies and displays good rollability so that it can be rolled particularly thin. It can therefore be used advantageously in rotating electric machines, in particular in electric motors and generators.