EP1194599B1 - Method for producing non-grain oriented electric sheet steel - Google Patents

Abstract

The invention relates to a method for producing non-grain oriented electric sheet steel in which a hot rolled strip is produced from a feed material, such as cast slabs, strips, pre-strips, or thin slabs which are made of a steel containing (in weight %) C: 0.001 - 0.05 %, Si: </= 1.5 %, Al: </= 0.4 % with Si + 2Al </= 1.7 %, Mn: 0.1 - 1.2 %, optionally up to a total of 1.5 % of alloy supplements, such as P, Sn, Sb, Zr, V, Ti, N, Ni, Co, Nb and/or B, and, as a remainder, iron as well as common companion elements. The hot rolled strip is produced by hot rolling the feed material, in a plurality of deforming passes, directly from the molten state or after a preceding reheating to a reheating temperature ranging from at least 1000 DEG C to a maximum of 1180 DEG C and by subsequently coiling the same. During the hot rolling, at least the first deforming pass is carried out in the austenite range, and one or more deforming passes are subsequently carried out in the ferrite range with a total deformation epsilon h of at least 45 %.

Description

The invention relates to a method for producing not grain-oriented electrical sheet, in which from a made of a steel material, such as cast Slabs, bands, curtains or thin slabs, a Hot strip is made, the electric sheet a low core loss and high Polarization and good mechanical properties has. Such non-grain oriented electrical sheets are mainly used as nuclear material in electrical Machines, such as motors and generators, with rotating magnetic flux direction 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 final annealed Electrical sheet ") falling electric sheets understood In addition, more anisotropic varieties are included, as long as they are not grain-oriented electrical sheets be valid.

From the manufacturing industry is the demand provided, non-grain-oriented electrical sheets for To provide their magnetic properties raised compared to conventional sheets of this type are. So are the Ummagnetisierungsverluste lowered and the polarization in each used Induction range can be increased. At the same time result arising from the respective processing and processing steps, which the electrical sheets in connection with their Uses are subjected to special requirements to the mechanical and technological properties of the Electrical sheets. In this context, comes the Cuttability of the sheets, e.g. when punching, special Meaning too.

By increasing the magnetic polarization of the Reduced magnetization requirement. Go with it also the copper losses back, which is a significant Share in the operation of electrical machines have incurred losses. The economic value Non-grain oriented electrical sheets with increased Permeability is therefore significant.

The demand for higher-permeability non-grain oriented Electrical sheet metal not only affects Non-grain oriented electrical sheets with high losses (P1.5 ≥ 5 - 6 W / kg), but also sheets with medium (3.5 W / kg ≤ P1.5 ≤ 5.5 W / kg) and low losses (P1.5 ≤ 3.5). Therefore one strives, the entire spectrum the weak, medium and highly silicated Electrotechnical steels in terms of its to improve magnetic polarization values.

A way based on medium or weakly silicated Alloys a higher permeable electrical sheet manufacture, is in the course of production the Hot strip to undergo a hot strip annealing. So will For example, proposed in WO 96/00306, a for the production of an electric sheet certain hot strip in the Austenite area ready to roll and rewind at Temperatures above full conversion into Make ferrite. In addition, there is a glow of the coil provided directly from the casting heat. In this way becomes an end product with good magnetic properties receive. However, because of the high Energy expenditure for warming before and during the Hot rolling and because of the required Alloy additives increased costs can be accepted.

According to EP 0 469 980, there is an increased reel temperature in combination with an additional hot strip annealing to strive, even at low alloy levels to obtain useful magnetic properties. Also this can only be done at the expense of additional costs be accomplished.

In addition to the above-described prior art from EP 0 609 190 A1 a method for the production of not grain oriented electrical sheet known in which a starting material consisting of a steel with (in% by weight) < 0.03% C, <0.004% N, <0.010% S, <0.010% P, <0.2% Mn, <0.5 Si, <0.05% Al and remainder iron is, a hot strip is produced by the starting material after a previous reheating to one no more than 1100 ° C rewarming temperature hot rolled in several forming passes and then is reeled, wherein during hot rolling at least the first forming pass in the austenite area and then with a total conversion of at least 90% or several forming passes in the Ferri area become. The purpose of this specification is to do the Rollers in the two-phase mixed area as much as possible avoid being too indefinable, difficult to dominant rolling conditions can come.

The object of the invention is a inexpensive way to produce electrical sheets indicate with improved properties.

This object is achieved by a method for producing non-grain oriented electrical steel sheet comprising: a starting material, such as cast slab, strip or thin slab, made of a steel having% by weight 0.001-0.05% C, 0.7-1 , 5% Si, ≦ 0.4% Al, with Si + 2 Al ≦ 1.7%, 0.1-1.2% Mn, optionally up to a total of 1.5% of alloying additives from the group P, Sn, Sb , Zr, V, Ti, N, Ni, Co, Nb and / or B, and the remainder being iron and customary impurities, a hot strip is produced by directing the starting material directly from the casting heat or after a previous reheating to at least 1000 At least 1180 ° C reheating temperature hot rolled in several forming passes and then coiled, wherein during hot rolling at least the first forming pass in Austenitgebiet and then with a total change in shape ε _h of at least 45% one or more Umformstiche durchgefhrt in the ferrite be heard.

The invention is based on the recognition that Electrical sheets with optimized properties through the Selection of specific forming rates during hot rolling in the phase regions γ-phase (austenite), γ / α-phase (Two-phase mixed region) and α-phase (ferrite) at transforming alloy of the type in question here can be produced. It has been shown that by a suitable combination of the phase sequence in Hot rolling in conjunction with certain final rolling and Reel temperatures are a crucial boost to the can achieve magnetic polarization.

According to the invention, the magnetic Properties of an electrical sheet by deformation during the individual in the course of hot rolling durchformenen forming passes depending on the respective Microstructure influenced specifically. Decisive share has rolling in the austenite and ferrite regions, whereas the proportion of deformation in the two-phase mixed area should be as low as possible. The invention Procedure is therefore particularly for the processing of such Fe-Si alloys are suitable, which no pronounced two-phase mixed area between the austenite and have the ferrite region.

The coordination of the alloying additions to ferrite and austenite-forming elements is taken into account the inventively provided salary ranges of single elements starting from a Basic composition of (Si + 2Al) ≤ 1.7.

In the case of the use of cast slabs as Starting material, these are at a temperature ≥ 1000 ° C. so reheated that the material completely is in the austenitic state. From the same As a result, thin slabs or ribbons are also submerged Utilization of the casting heat used directly and if necessary, at rolling start temperature of more heated to 1000 ° C. The required grows Reheating temperature with increasing Si content, where an upper limit of 1180 ° C is not exceeded becomes.

The hot rolling according to the invention is usually in one formed of several rolling stands Finishing roll completed. There is the Purpose of one or more stitches Walzens Austenitgebiet on the one hand, the transition from austenite to ferrite controlled within the Finishing roll to be able to perform. On the other hand serve the austenitgebiet durchformenen Umformstiche in addition, the thickness of the hot strip before the start of rolling in the ferrite region so that during the Ferrite rolling desirable overall shape change safely is reached. Rolling in the ferrite area comprises also at least one forming pass. Preferably However, several Umformstiche in ferrite go through to the required overall shape change of At least 45% safe to reach and so the desired To obtain adjustment of the hot strip structure.

The term "total change in shape ε _h " is understood here to mean the ratio of the decrease in thickness during rolling in the respective phase region to the thickness of the strip when entering the relevant phase region. According to this definition, a hot strip produced according to the invention has, for example, a thickness h ₀ after rolling in the austenite region. In the course of the subsequent rolling in the ferrite region, the thickness of the hot strip is reduced to h ₁ . By definition, this yields, for example, the total change in shape ε _h achieved during ferrite rolling to (h ₀ -h ₁ ) / h ₀ with h ₀ = thickness when entering the first rolling stand in the ferrite state and h ₁ = thickness when leaving the rolling scale, the end rolling in the ferrite area.

According to the invention, the total change in shape ε _h during ferrite rolling should reach at least 45% in order to set a state of hot-rolled strip favoring the desired magnetic and technological properties in terms of grain size, texture and precipitations or to prepare it for the subsequent processing steps. By taking place mainly in the ferrite with the greatest possible circumvention of the two-phase mixing area hot rolling can thus produce a hot strip, which can be used in the further for the production of an electrical steel and for the production of components with excellent magnetic properties. Costly additional processing steps or the maintenance of certain high temperatures during hot rolling are not required for this purpose. Instead, the method according to the invention makes it possible to inexpensively produce a high-quality electrical sheet material by means of a rolling strategy which is optimized both with regard to the temperature control and with regard to the staggering of the deformations in conjunction with a suitably selected coiling temperature.

It has been found that already by the Combination of the measures according to the invention electric sheets make their properties, the properties of the properties from those produced in a conventional manner Electrical sheets equal, the additional time and costly process steps, such as a supplementary Hot strip annealing, have gone through. Next is has been found that in the event that a Hot strip annealing in addition to the invention Approach is applied, the interaction of these Measures to electric sheets leads, which in their magnetic and mechanical properties conventional are superior to manufactured electrical sheets. Consequently causes the invention on the one hand a clear Reduction of costs in the production of high quality electric sheets. on the other hand can be based on the invention Process produce sheets whose properties conventionally produced electrical sheets are far superior.

A particular with respect to the resulting during the implementation of a method rolling forces and the technological properties of the produced hot strip particularly advantageous embodiment of the invention is characterized in that the hot strip is so strongly cooled after the Austenitgebiet in the transformation that the ferrite conversion before the subsequent performed Forming is essentially complete. In this variant of the method according to the invention, the two-phase mixed area austenite / ferrite is passed through the two shortest paths between two forming passes, so that the rolled strip is rolled in the austenite area only in the ferrite area after rolling. In this case, the total change in shape ε _h during rolling in the ferrite region should preferably be at least 50%. This rolling in the austenite and ferrite is carried out under exclusion of rolling in the mixed area austenite / ferrite.

A particularly suitable embodiment of the invention is characterized in that after the at least one forming pass in the austenite region, the hot strip undergoes at least one forming pass in the two-phase mixed region austenite / ferrite, during which a total degree of deformation ε _h of at most 30% is reached, during which process at least one subsequently in Ferritgebiet carried out Umformstichs a Gesamtumformgrad ε _h of at least 45% is achieved. In this variant of the invention, too, the extent of rolling in the two-phase mixing area is largely restricted and the center of gravity of the forming is placed on the rolling in the ferrite area.

Basically suitable for carrying out the According to the invention a reel temperature of at least 700 ° C. In compliance with this reel temperature can be an additional hot strip annealing whole or at least be saved to a substantial extent. The hot strip is already softened in the coil, with his Characteristics determining characteristics, such as grain size, Texture and excretions are positively affected. It is particularly advantageous in this context, if the coiled hot strip from the coil heat of a direct Annealing is subjected and when the annealing time at a Annealing temperature above 700 ° C for at least 15 minutes is. Such "in-line" annealing of the uncoiled at high temperature, not in the coil otherwise cooled hot-rolled strip may be otherwise possibly required hot strip annealing completely replace. This is how annealed hot strips can be with particularly good magnetic and technological Create properties. The required time and Energy expenditure is considerably lower than with the conventionally for improving the properties of Electric sheet performed hot strip annealing.

According to an alternative embodiment of the invention there are improvements in the material properties, if the reel temperature is less than 600 ° C, especially less than 550 ° C, is. The reeling in These temperatures leads to a solidified Hot strip state. In practice, it has been found that this approach, especially for steel too particularly good results, which is at least 0.7 Contain% by weight of Si.

Depending on the type of tape to be produced, it may be in this Context be favorable when the hot strip immediately is accelerated after being rewound.

At least one of the last in the ferrite area completed forming passes should be done with lubrication hot rolled. By hot rolling with lubrication on the one hand, lower shear deformations occur, so that the rolled strip resulted in a more homogeneous structure over the cross section receives. On the other hand, by the lubrication reduces the rolling forces, so that over the each rolling pass a higher reduction in thickness possible is. Therefore, it may, depending on the desired properties of the electric sheet to be produced, be advantageous if all rolled passes passed during hot rolling a rolling lubrication be performed.

Regardless of the chosen sequence of Rolling steps can further improve the Characteristics of the produced electrical strip thereby be achieved that the hot strip after reeling additionally at an annealing temperature of at least 740 ° C is annealed. This glowing can be done in the hood furnace or in the Continuous furnace be performed.

The hot strip produced in accordance with the invention is especially due to its mechanical properties suitable, in one or more stages in a conventional manner a final thickness to be cold rolled. If that Cold rolling is carried out in several stages, should be in Connect to at least one of the cold rolling stages Intermediate annealing done to the good mechanical Maintain properties of the band.

If a "fully-finished" -Elektroband be prepared This is followed by a final annealing at the cold rolling an annealing temperature, which preferably> 740 ° C. is.

On the other hand, if a "semi-finished" -Electromagnetic band is generated be followed, if necessary, in several stages performed cold rolling a recrystallizing annealing in a hood or continuous furnace at temperatures of at least 650 ° C. After that, that will cold rolled and annealed electrical steel straightened and re-rolled.

Cold-rolled electrical steel produced according to the invention is excellent cutting and punching and is suitable as such, especially to components, such as lamellae or blanks to be processed. In case of Processing of a "semi-finished" sheet suitably from this electrical sheet finished components at the user final annealing.

Regardless of whether a "semi-finished" or a "fullyfinished" Electrical sheet is produced, carried out according to a further embodiment of the invention, the final annealing of the cold-rolled electric sheet preferably in one decarburizing atmosphere.

The invention is based on Embodiments explained in more detail.

"J2500", "J5000" and "J10000" refer to the following the magnetic polarization at magnetic field strengths of 2500 A / m, 5000 A / m or 10000 A / m.

Under "P 1.0" or "P 1.5" is the Loss of magnetization at a polarization of 1.0 T. or 1.5 T and a frequency of 50 Hz understood.

The given in the following tables Magnetic properties are each on individual strips measured along the rolling direction.

In Table 1, for three steels used to make electrical steel sheets, the contents of the major alloying ingredients are shown in weight%. The steel C is a steel of the present invention having an Si content ranging from 0.7 to 1.5% by weight. stole C Si al Mn A 0,008 0.1 0.12 0.34 B 0,008 0.33 0.25 0.81 C 0,007 1.19 0.13 0.23

In Table 2, the magnetic properties J ₂₅₀₀ , J ₅₀₀₀ , J ₁₀₀₀₀ , P _1.0 and P _1.5 measured on individual strips along the rolling direction are for three electric sheets B1, B2, B3 made of the steels A, B, C specified. The slabs cast from the steels A, B and C, respectively, have been reheated as starting material to a temperature of more than 1000 ° C. in each case and passed into a rolling scale. At least the first forming pass has been carried out exclusively in the austenite area in the finishing hot rolling mill. Following rolling in the austenite region, the hot strips were cooled to such an extent that the two-phase mixed area austenite / ferrite passed in a very short time and the ferrite conversion was completed before the next rolling stand was reached. The subsequent forming passes in the finish rolling scale have accordingly been carried out exclusively in the ferrite area. In this case, the total deformation degree ε _h achieved in the ferrite region was 50%. The rolled hot strips were then rewound at a reel temperature of 750 ° C. The coiled coils were then held at reel temperature for a prolonged period of at least 15 minutes. sheet J ₂₅₀₀ [T] J ₅₀₀₀ [T] J ₁₀₀₀₀ [T] P _1.0 [W / kg] P _1.5 [W / kg] B1 1,732 1,806 1,904 3,480 7,045 B2 1,722 1,799 1,898 3,177 6,382 B3 1,724 1,799 1,893 2,609 5,243

Table 3 shows the magnetic properties J ₂₅₀₀ , J ₅₀₀₀₀ , J ₁₀₀₀₀ , P _1.0 and P _1.5 for an electric sheet B4 produced based on the steel C of the present invention. In contrast to the electrical steel sheets B1, B2, B3, this electrical steel strip B4 has been coiled after hot rolling in the finishing roll scale at a temperature of 600.degree. The coiled hot-rolled strip was immediately cooled before it was fed to the cold strip for further processing. sheet J ₂₅₀₀ [T] J ₅₀₀₀ [T] J ₁₀₀₀₀ [T] P _1.0 [W / kg] P _1.5 [W / kg] B4 1,671 1,748 1,845 2,660 5,413

Claims (17)

1. A method for producing non grain-oriented electric steel sheet in which hot strip is produced from an input stock such as cast slabs, strip, roughed strip, or thin slabs, made of steel comprising in weight %
      C: 0.001 - 0.05 %
      Si: 0.7 - 1.5 %
      Al: ≤ 0.4 %
      with Si + 2Al ≤ 1.7 %
      Mn: 0.1 - 1.2 %
      if necessary up to a total of 1.5 % of alloying additions from the group P, Sn, Sb, Zr, V, Ti, N, Ni, Co, Nb and/or B;
      with the remainder being iron as well as the usual impurities
   in that the input stock is hot-rolled directly from the casting heat or after preceding reheating to a reheating temperature between min. 1000 °C and max. 1180 °C in several deformation passes, and subsequently coiled, wherein during hot-rolling at least the first deformation pass is carried out in the austenitic region and subsequently, at a total deformation ε_h of at least 45 %, one or several deformation passes are carried out in the ferritic region.
2. The method according to claim 1, characterised in that the hot strip after deformation in the austenitic region is cooled to such an extent that ferrite transformation is essentially completed prior to the subsequently carried out deformation.
3. The method according to claim 2, characterised in that the total deformation ε_h achieved during rolling in the ferritic region is at least 50 %.
4. The method according to any one of the preceding claims, characterised in that the hot strip after the deformation pass in the austenitic region, of which deformation pass there is at least one, passes at least one deformation pass in the two-phase mixing region austenite / ferrite, during which deformation pass a total deformation ε_h of max. 30 % is achieved, and in that during the subsequent deformation pass which is carried out in the ferritic region, of which deformation pass there is at least one, a total deformation ε_h of at least 45 % is achieved.
5. The method according to any one of the preceding claims, characterised in that the coiling temperature is at least 700 °C.
6. The method according to claim 5, characterised in that the coiled hot strip from the coil heat is subjected to direct annealing and in that the annealing time at an annealing temperature exceeding 700 °C is at least 15 minutes.
7. The method according to one of claims 1 to 4, characterised in that the coiling temperature is less than 600 °C, in particular less than 550 °C.
8. The method according to claim 7, characterised in that immediately following coiling, the hot strip is subjected to accelerated cooling in the coil.
9. The method according to any one of the preceding claims, characterised in that during hot-rolling in the ferritic region, at least one deformation pass is carried out with the use of lubricant.
10. The method according to any one of the preceding claims, characterised in that after coiling, the hot strip is annealed at an annealing temperature of at least 740 °C.
11. The method according to claim 10, characterised in that annealing of the coiled hot strip is carried out in a hood-type furnace.
12. The method according to claim 10, characterised in that annealing is carried out in a continuous furnace.
13. The method according to any one of the preceding claims, characterised in that the hot strip is cold-rolled in single-stage or multi-stage rolling, to a final thickness.
14. The method according to claim 13, characterised in that cold-rolling is carried out in multi-stage rolling and in that at least one of the cold-rolling stages is followed by intermediate annealing.
15. The method according to one of claims 13 or 14, characterised in that following cold-rolling, the cold strip is subjected to final annealing at an annealing temperature of > 740 °C.
16. The method according to claims 14 and 15, characterised in that following cold-rolling, the cold strip is subjected to recrystallising annealing in a hood-type annealing furnace or in a continuous annealing furnace at annealing temperatures > 650 °C to form an electric steel strip not having been subjected to final annealing; with the cold strip subsequently being levelled and rerolled.
17. The method according to one of claims 15 or 16, characterised in that annealing is carried out in a decarburising atmosphere.