EP1509627B1 - PROCESS FOR PRODUCING COLD-ROLLED STEEL STRIP HAVING A Si-CONTENT OF AT LEAST 3.2 WT.-% USED FOR ELECTROMAGNETIC PURPOSES - Google Patents

Abstract

The present invention relates to a cold-rolled steel strip or sheet in thicknesses of <=0.70 mm for electromagnetic applications, consisting of a steel containing (in % by weight) C: <0.01%, Si: 3.2-7%, Al: <2%, Mn: <=1%, the remainder being iron and usual impurities, which after smelting has been cast to form a base material, such as a slab, a thin slab, or a thin strip, which has then been heated through to temperature T<SUB>R</SUB>>1000° C. and has been final hot-rolled at a hot-rolling final temperature T<SUB>F</SUB>>800° C. to form a hot strip, which has then been cooled, starting from a temperature T<SUB>C </SUB>of the hot strip amounting to at least 750° C. but less than 850° C., at a cooling speed DeltaT/Deltat of at least 400° C./min. to a temperature of less than 300° C., subjected after cooling to a surface treatment such as mechanical descaling and/or pickling, after the surface treatment has been cold-rolled at a temperature amounting to maximum 500° C., and has finally been final-annealed.

Description

The invention relates to a method for producing a cold-rolled steel strip or sheet in thicknesses of ≤ 0.70 mm for electromagnetic Applications with Si contents of at least 3.2 wt .-% and Al contents of less than 2% by weight. Such based high-silicon FeSi steels produced cold strips or sheets are usually considered non-grain oriented Electric sheets used.

Under the term "non-grain oriented electrical sheet" are here under the DIN EN 10106 ("final annealed Electrical sheet ") and DIN EN 10165 (" not fully annealed Elektroblech ") falling products also more anisotropic varieties are included, as long as they are not considered as grain-oriented electrical sheets. In that regard, in the following the terms "steel strip for electromagnetic purposes "and" sheet steel for electromagnetic purposes "as well as" electrical tape "and "Electrical sheet" used synonymously.

Usually, for the production of non-grain oriented electrical steel FeSi steels used their Si contents are at most 3.5 wt .-%. so limited FeSi steel alloys containing Si allow trouble-free production on the usual Production route. In particular, by a restriction the Si content to contents ≤ 3.0 wt .-% ensured that in conventional procedure, the obtained sheet is free of cracks after cold rolling.

In the course of conventional manufacturing is after the The steel alloy melts the melt into a slab or thin slab potted. This material is then in Direct deployment without reheating or after one Cooling and reheating in one Descaling, a rough rolling and one in a rule multistage hot roll relay performed Finished hot rolling comprehensive hot rolling process to a Rolled hot strip. The hot strip is then one usually subjected to a pickling surface treatment, which can be combined with a glow. If necessary, in addition, a hot strip annealing performed before the hot strip is cold rolled to cold strip becomes. Finally, the tape is final annealed or one Subjected to annealing with subsequent post-deformation.

Already at Si contents of more than 3 wt .-% show up first difficulties with cold rolling in the form of high Rolling forces and an increasing susceptibility to cracking. So occur during cold rolling of FeSi alloys with FeSi contents with more than 3.5 wt .-% produced hot strips regularly cracks, which the generation of a qualitative high quality electrical steel product with thicknesses ≤ 0.75 mm Exclude using the conventional production route.

The difficulties in production that the increase of the Si content leads to an increase of the electrical resistance and thus to a humiliation the magnetic losses in use leads. For one Range of applications, especially for in the audio, video, Data processing and medical technology used and miniature machines, as well as for drives and for magnetic cores in electromagnetic applications with higher Frequencies are therefore made of FeSi alloys Si contents in the range of 3.5% by weight to 7.0% by weight produced electrical sheets of particular interest. These highly silicon-containing materials have over the other soft magnetic materials, such as amorphous Fe, FeNi, FeCo base alloys, nanocrystalline soft magnetic materials or soft magnetic ferrites, a high saturation magnetization. This higher Saturation magnetization is combined with compared to conventional electrotechnical steels higher values the electrical resistance and thus lower magnetic losses, resulting in an application at higher Frequencies is possible.

FeSi materials with an Si content of approximately 6.5% by weight are available on the market. The production These products are made by chemical means Deposition of a highly-silica FeSi layer on one conventional electrical steel and a subsequent Diffusion annealing.

In this way, while the conventional Production of sheets containing high silicum contents Avoid occurring difficulties. There are, however Additional work steps required by the Complicate production and make it more expensive.

There are numerous in the scientific literature Working in which the forming behavior of FeSi alloys examined with Si contents of more than 3.2 wt .-% and the Possibilities of manufacturing such a steel on the usual metallurgical way have been considered. So have G. Schlatte, W. Pietsch in the journal for Metallkunde, Volume 66 (1975) Issue 11, page 661 et seq., And W. Pepperhoff, W. Pietsch in Archive Ironworks 47 (1976), No. 11, page 685 et seq., Mentions that a steel with up to about 6 wt .-% silicon still at around 400 ° C to 300 ° C can be formed (critical temperature: 300 ° C). Below a critical of the Si content Temperature imagine a brittle behavior and as a result, a cold brittleness that no Cold deformation permit. Above the critical temperature on the other hand, for FeSi alloys with more than 4% w / w Silicon forming possible, in addition to the each processed alloy of temperatures below 700 ° C to a temperature below 400 ° C cooled. Also found in the aforementioned articles Restriction of deformability to one Temperature range above the critical temperature limits the possibilities of production of highly silicated electrical steel products over the Thus, a strong conventional manufacturing process.

By G. Rassmann, P. Klemm is in Neue Hütte, Issue 7, 8th year, 1963, page 403 ff. Found that For alloys with 5 and 6 wt .-% Si, a cold rolling at 220 ° C or 350 ° C with a total conversion of up to 40% and further rolling at room temperature can be realized. Similar references can be found in US Patent 3,099,176. In this type of two-stage at different However, cold rolling takes place Prehistory of the material until cold rolling no Rainfall.

In practice, however, that shows how the above mentioned works by G. Schlatte and W. Pietsch do not confirm such a cold rolling in reality without further ado for an arbitrarily manufactured hot strip can be realized, the hot strip production so one significant impact on the processability of a highest Has silicon content hot strip to cold strip.

Besides the above-mentioned prior art, it is from EP 0 229 846 B1, during hot rolling reached Gesamtumformgrad depending on the Grain size before final rolling (finished hot rolling) adjust. However, this procedure is liable to the Disadvantage that the grain size before the final rolling of the Conditions of reheating and pre-rolling as well depends on the particular chemical composition. As a result, before entering the Finished hot rolling mill in pre-rolled steel precursor do not clearly specify existing grain sizes. In addition is the measurement of grain size in one in practice continuously running production process not with a technically and cost moderately reasonable effort feasible.

EP 0 377 734 B1 discloses a process for FeSi alloys been described in which after the Reheating the slab a transformation at temperatures of not less than 600 ° C and then one Direct use for another hot rolling or another Heating to temperatures of not less than 400 ° C with subsequent hot rolling is performed. Subsequently Cold rolling takes place to final thickness. These Process parameters are not specific for higher silicided alloys. In practice, that shows up when using the known from EP 0377 734 B1 Process steps for highly-silicided FeSi alloys of According to the invention processed kind no satisfactory Achieve work results.

According to EP 0 467 265 A2, a highly-silicated one can be used Cold-rolling FeSi steel by cold rolling Sheet temperatures in the range of 120 ° C to 350 ° C is carried out. However, it does not specify how the hot strip must be generated, which processes in this way can be. In the practical application of this known Procedure therefore poses the problem that, like the above mentioned articles and own investigations of Applicant prove the processing of highly semi- Electric steel just is not independent of the while of hot strip processing. So gave practical experiments that it is conventional Production method of hot strip with more than 3.5 wt .-% lying Si contents and then cold rolling among those in the EP 0 467 265 A2 conditions regularly already in first cold rolling pass came to cracking.

Based on the above-mentioned state of Technique was the object of the invention in a koslengünstiges and practical manufacturing process for cold rolled steel sheet or strip with thicknesses of not more than 0,70 mm and a Si content of 3.5 wt .-% and more, which is for electromagnetic Applications is suitable. ,

This object is achieved by a method according to claim 1.

• Erschmelzen eines (in Gew.-%) C: < 0,01 %, Si: 3,2 - 7 %, Al: < 2 %, Mn: < 1 %, Rest Eisen und übliche Verunreinigungen enthaltenden Stahls,
• Vergießen des Stahls zu einem Vormaterial, wie einer Bramme, einer Dünnbramme oder einem Dünnband,
• Durchwärmen des Vormaterials auf eine Temperatur T_R > 1000 °C,
• Fertigwarmwalzen des durchwärmten Vormaterials bei einer Warmwalzendtemperatur T_F von > 800 °C zu einem Warmband,
• Abkühlen des Warmbands im Anschluss an das Fertigwarmwalzen ausgehend von einer mindestens 750 °C jedoch weniger als 850 °C betragenden Temperatur T_C des Warmbands mit einer mindestens 400 °C/min betragenden Abkühlgeschwindigkeit ΔT/Δt auf eine weniger als 300 °C betragende Temperatur,
• Oberflächenbehandeln des abgekühlten Warmbands,
• Kaltwalzen des oberflächenbehandelten Warmbands bei einer höchstens 500 °C betragenden Temperatur T_CR und
• Schlussglühen des erhaltenen kaltgewalzten Stahlbands oder -blechs.

In the manufacture of a cold rolled steel strip or sheet for electromagnetic applications, the following steps are performed:

• Melting a (in wt .-%) C: <0.01%, Si: 3.2 to 7%, Al: <2%, Mn: <1%, remainder iron and conventional impurities containing steel,
• Casting the steel into a starting material, such as a slab, a thin slab or a thin strip,
• Heating the starting material to a temperature T _R > 1000 ° C,
• Finish hot rolling of the heat-treated starting material at a hot rolling end temperature T _F of> 800 ° C. into a hot strip,
• Cooling the hot strip following the finish hot rolling starting from a temperature T _{C of} the hot strip at least 750 ° C but less than 850 ° C with a cooling rate ΔT / Δt of at least 400 ° C / min to a temperature of less than 300 ° C,
• Surface treatment of the cooled hot strip,
• Cold rolling of the surface-treated hot strip at a maximum temperature of _TCR and 500 ° C
• Final annealing of the obtained cold rolled steel strip or sheet.

• die Wiederwärmungstemperatur,
• die Warmwalzendtemperatur,
• die von einer in einem bestimmten Temperaturbereich liegenden Temperatur ausgehende gezielte rasche Abkühlung des Warmbands nach dem Ende des Fertigwalzens
  und
• die Temperatur des Bandes beim Kaltwalzen

in der durch die Erfindung vorgegebenen Weise aufeinander abgestimmt werden.The invention is based on the finding that starting from a conventionally assembled, highest content of silicon of 3.2 wt .-% to 7 wt .-% and Al contents of up to 2 wt .-% containing steel alloy while maintaining the used in conventional cold strip production steps can produce a high quality, especially crack-free cold strip, if

• the reheating temperature,
• the hot rolling end temperature,
• the purposeful rapid cooling of the hot strip after the end of the finish rolling, starting from a temperature lying within a certain temperature range
  and
• the temperature of the strip during cold rolling

be coordinated with each other in the manner prescribed by the invention.

Surprisingly, it has been shown that only through compliance the combination according to the invention of the relevant Parameter an excessive brittleness of the processed Materials can be avoided and the hot-rolled one for proper cold rolling sufficient ductility owns which for the production of crack-free Electrical sheet with the desired final thickness of at most 0.70 mm, preferably at most 0.35 mm is required.

Here comes each of the relevant parameters one equivalent importance. So it has been found that in those cases where those for the beginning the cooling temperature specified over a Tolerance exceeding or falling below had received no crack-free product.

In cases where the hot rolling end temperature is more than 800 ° C, but less than 850 ° C, the Cooling of the hot strip in direct connection to the Hot rolling to be performed. Otherwise, with the Start the rapid cooling wait until the temperature of the hot strip in the predetermined by the invention Area has dropped, within which the rapid Refrigeration should begin.

Of course, the cooled according to the invention Hot strip at a suitable time of Production process to be coiled before it the further processing is fed to cold strip.

Of course, it is also possible to limit the production path according to the invention on panels.
With regard to the transition from the warm strip production to the production of the cold strip, the speed at which the rapid cooling of the hot strip is carried out following hot rolling is of particular importance. If the further processing of the hot strip to cold strip in a period within which there is not yet in the range to be observed according to the invention lower limit of the cooling rate for cold embrittlement, so it is possible to produce a crack-free cold-rolled steel product even at relatively low cooling rates. However, if a longer period of time, such as many days or weeks, passes between the hot strip production and the cold rolling, it is still possible to reliably produce a crack-free steel strip or sheet produced according to the invention for electromagnetic purposes in that the cooling rate ΔT / Δt is at least 2000 ° C / min.
By such a high cooling rate, the embrittlement effects to be expected with a longer storage time of the hot strip and a slower cooling can be safely avoided.

The reheating of the starting material preferably takes place at Temperatures ranging from 1000 ° C to 1190 ° C to the Formation of feyalite sure to avoid.

Particularly good electromagnetic properties of the cold-rolled electric sheet obtained, if the optionally pre-rolled starting material in maximum seven stitches with a total deformation of more than 90% to a hot strip thickness of not more than 1.5 mm is finish-rolled. It serves the same purpose when the degree of cold rolling is greater than 60% but less than 82% is.

Another essential feature of the invention is in that during cold rolling those of the invention given upper limit of the temperature of the processed Bandes in the context of manufacturing unavoidable Tolerance is maintained. Basically, therefore, is favorable when the hot strip is at room temperature at the beginning of cold rolling having. It should be in consequence of the entry to Deformation energy unavoidable heat generation during the cold rolling preferably be performed so that Temperatures of ≤ 200 ° C are not exceeded. Should Nevertheless, taking into account the above-explained Research findings elevated the cold rolling at Temperatures should be carried out so these should be in the Range of 200 ° C and 500 ° C lie. The for the Preheating the hot strip provided before cold rolling Time should be limited to less than 20 minutes be, to otherwise occurring structural changes avoid. These emasculate embrittlement phenomena yourself.

The invention is suitable for the production of the lower Area of high-silicon steels settled, 4.0-5.0% by weight Si-containing electric sheets for which Production of in the middle range of high-silicon steels settled, more than 5.0 wt .-% Si containing electrical sheets and to Production of in the upper region of the most silicon-containing Steels containing 6.0 to 6.8 wt .-% Si containing Electrical sheets. It can especially in the higher Si-containing alloys, the content of A1 limited the range of unavoidable impurities be.

The invention is based on Embodiments explained in more detail.

To demonstrate the effect of the invention, a steel HiSi and a steel LoSi were melted and cast into slabs. The alloys of HiSi and LoSi steels are given in Table 1. alloy Si al C Mn S rest LoSi 4.2 0,003 0.009 0.047 0,003 Fe, other impurities Hisi 6.3 0,002 0,006 0.088 0,002 Fe, other impurities Data in% by weight

The slabs are reheated to a reheating temperature T _R , pre-rolled and final hot rolled in a seven roll stand hot roll stand at a hot rolling end temperature T _F to a hot strip of WB _D thickness.

After leaving the hot rolling stand, the hot strip was cooled with a cooling rate ΔT / At at least 400 ° C / min as soon as its temperature T _{c was} in the range of 750 ° C to 850 ° C. The thus cooled to room temperature hot strip is then subjected to a mechanical pretreatment of its surfaces and then pickled.

In order to detect the influence of heating of the hot strip before cold rolling, a part of the hot strips produced in the manner described above within a time t _CR have been heated to a temperature T _CR .

In cold rolling itself Gesamtumformgrade Δ _{KW have been} achieved.

Table 2 shows the process parameters observed in the course of production for six cold strips E1 to E6 produced according to the invention. E1 E2 E3 E4 E5 E6 alloy Hisi Hisi Hisi LoSi LoSi LoSi T _R [° C] 1150 1150 1150 1150 1150 1150 T _F [° C] ≈940 ≈940 ≈940 ≈950 ≈950 ≈950 WB _D [Mm] 1, 8 1.8 1.8 1.7 1, 7 1.7 T _C [° C] ≈780 ≈780 ≈780 ≈820 ≈820 ≈820 .DELTA.T / .DELTA.t [° C / min] ≈2100 ≈2100 ≈2100 ≈2100 ≈2100 ≈2100 T _CR [° C] RT 300 500 RT *) 300 500 t _CR [Min] - ≈18 ≈18 ≈14 ≈18 Δ _KW [%] 67 68 68 72 72 72 cracking NO NO NO NO NO NO

With these examples is proven that despite the high Silicon content of both processed steel alloys HiSi or LoSi crack-free electrical sheets can be produced, as long as the reheating temperature, the Hot rolling end temperature, the temperature at which the Cooling begins, the cooling rate and the Temperature during hot rolling in the invention remain predetermined frame.

In order to further verify this, three cold strips V1 to V3 are made from the alloy HiSi and a cold strip V4 from the alloy LoSi using the method steps used to produce the samples E1 to E6 according to the invention, but with process parameters outside the specifications of the invention , The relevant parameters are listed in Table 3 for the non-inventive cold strips V1 to V4 produced for comparison. V1 V2 V3 V4 alloy Hisi Hisi Hisi LoSi T _R [° C] 1150 1150 1250 1250 T _F [° C] ≈1000 ≈730 ≈850 ≈800 WB _D [Mm] 2.1 1.4 1.65 1.85 T _C [° C] ≈1000 ≈650 ≈800 ≈800 .DELTA.T / .DELTA.t [° C / min] ≈2100 ≈2100 ≈1 ≈1 T _CR [° C] RT RT *) RT *) RT *) t _CR [Min] - - - - Δ _KW [%] **) **) **) cracking YES YES YES YES

It turned out that even a deviation in only one process parameter leads to the result that no crack-free cold strip can be produced any longer. Thus, in the comparative sample V1 already leads to the high temperature T _c , from which the rapid cooling took place, in the rest with the inventive sample E1 substantially matching, within the invention lying parameters for cracking. The same effect was caused by the too low temperature T _c in the comparative sample V2 and the too low cooling rate ΔT / Δt in the comparative samples V3, V4.

Claims (16)

1. Method for the manufacture of a cold-rolled steel strip or sheet for electromagnetic applications, during which the following steps are run through:

   Smelting of a steel containing (in % by weight):
   C: < 0.01 %
   Si: 3.2 - 7 %
   A1: < 2 %
   Mn: ≤ 1 %,
   the remainder being iron and usual impurities,

   Casting of the steel to form a base material, such as slabs, thin slabs, or thin strip,

   Heating through the base material to a temperature T_R of > 1000 °C

   Heating the base material through at a hot-rolling final temperature T_F of > 800 °C to form a hot strip,

   Cooling the hot strip following the finish hot-rolling, starting from a temperature T_c of 750 °C as a minimum but less than 850 °C of the hot strip, at a cooling speed ΔT/Δt of at least 400 °C/min, to a temperature of less than 300 °C,

   Surface treatment of the cooled hot strip,

   Cold-rolling of the surface-treated hot strip at a temperature T_CR amounting to a maximum of 500 °C, and

   Final annealing of the cold-rolled steel strip or sheet obtained.
2. Method according to Claim 1, characterised in that the cooling speed ΔT/Δt is ≥ 2000 °C/min.
3. Method according to any one of the foregoing claims, characterised in that the reheating of the base material takes place at temperatures in the range from 1000 °C to 1190 °C.
4. Method according to any one of the foregoing claims, characterised in that the base material is finish hot-rolled in a maximum of seven passes at a total deformation rate of more than 90 % to a thickness of the hot strip of maximum 1.5 mm.
5. Method according to any one of the foregoing claims, characterised in that the degree of deformation during cold-rolling is greater than 60 % but less than 82 %.
6. Method according to any one of the foregoing claims, characterised in that the cold-rolled steel strip or sheet obtained has a thickness of maximum 0.35 mm.
7. Method according to any one of the foregoing claims, characterised in that the hot strip has room temperature at the beginning of the cold-rolling.
8. Method according to any one of the foregoing claims, characterised in that the cold-rolling is carried out at temperatures of ≤ 200 °C.
9. Method according to any one of the foregoing claims, characterised in that the hot strip is heated before the cold-rolling, within a period of less than 20 minutes, to a temperature from 200 °C to 500 °C, and is cold-rolled at temperatures lying within this range.
10. Method according to any one of the foregoing claims, characterised in that the final annealing takes place in a decarburizing atmosphere.
11. Method according to any one of the foregoing claims, characterised in that the final annealing takes place in a non-decarburizing atmosphere.
12. Method according to any one of the foregoing claims, characterised in that the steel contains 4.0 - 5.0 by weight Si.
13. Method according to any one of the foregoing claims, characterised in that the steel contains > 5.0 - 6.8 by weight Si.
14. Method according to any one of the foregoing claims, characterised in that the steel contains 6.0 - 6.8 by weight Si.
15. Method according to any one of the foregoing claims, characterised in that the content of Al is restricted to the range of unavoidable impurities.
16. Method according to any one of the foregoing claims, characterised in that the surface treatment comprises a mechanical descaling and/or pickling.