EP0431502A2 - Non-oriented electrical strip and method of manufacturing - Google Patents

Abstract

The invention relates to a non-grain-oriented electrical strip with large fractions of cubic texture or cubic-surface texture and a polarisation J 2500 > 1.7 T and a low remagnetisation loss, and to a manufacturing method for this. A steel ingot containing, apart from iron, less than 0.025% C, less than 0.1% Mn, 0 to 0.15% of surface-active elements, Si and Al, in such a way that the relationships (% Si) + 2(% Al) > 1.6% and (%Si) + (% Al) < 4.5% are met, is hot-rolled to a thickness of not less than 3.5 mm. The hot strip thus obtained is then cold-rolled at a degree of deformation of at least 86% without recrystallising and interannealing and, if necessary, finally annealed.

Description

The invention relates to non-grain-oriented electrical steel with cube texture (100) [001] or with cube surface texture (100) [0vw] and a final thickness of about 0.35 to 0.65 mm and a method for its production. The term “non-grain-oriented electrical steel” is understood here, regardless of its crystallographic texture, to be one according to DIN 46 400 Part 1 or 4, the loss anisotropy of which does not exceed the maximum values specified in DIN 46 400 Part 1.

The terms "electrical steel" and "electrical sheet" are understood here as synonyms. Unless otherwise stated, all percentages are parts by mass in%.

In the following "J 2500" denotes the magnetic polarization at a magnetic field strength of 2500 A / m and "P 1.5" the magnetic loss at a polarization of 1.5 T and a frequency of 50 Hz.

The electrical steel according to the invention has excellent magnetic properties in the longitudinal and transverse directions in the case of the cube texture, e.g. B. J 2500> 1.7 T and P 1.5 <3.3 W / kg for a steel with an average alloy content of (% Si) + (% Al) = 1.8%, and is therefore particularly suitable for electromagnetic Suitable circles that are magnetized mainly in two perpendicular directions, z. B. for small transformers, ballasts and stator plates of large generators.

In the case of the cube surface texture, the electrical steel or electrical sheet according to the invention is largely isotropic in its plane and has good properties in all directions, e.g. B. J 2500> 1.66 T and P 1.5 <3.3 W / kg, and is therefore particularly suitable for electromagnetic circuits that are magnetized in all directions, for. B. for electric motors and generators.

Methods for the production of electrical sheets with cubic textures with (100) faces in the sheet plane, which have a high magnetic polarization, are known. However, their commercial production has not been successful due to the manufacturing difficulties and the high costs.

The production of electrical sheet with cube texture as a soft magnetic material was mainly investigated between 1950 and 1970 as the core material for electric motors and transformers.

In the process known from DE-C-1 923 581, a slab with the usual silicon and / or aluminum contents, but low C contents (<0.005%, preferably <0.003%), is used as the starting material to a thickness of 10 mm hot-rolled and cold-rolled in three stages to 0.35 mm with two intermediate anneals. This process is complex because of the intermediate annealing. According to DE-A-1 966 686, a slab with an additional limited S content (0.005%, preferably 0.003%) is hot-rolled to 5 mm, cold-rolled to approx. 1 mm, and annealed between 900 and 1050 ° C. in dry H₂ 0.35 mm cold rolled and finally annealed between 1000 and 1100 ° C in a non-oxidizing atmosphere. Using this process, it was not possible to produce electrical steel strips commercially that exceed the typical properties of a type of electrical steel according to DIN 46 400 Part 1, which has the same alloy content and the same thickness.

According to a further method for cold rolling a Si steel strip known from DE-A-3 028 147, a recovery annealing is interposed in order to achieve a large reduction in thickness by cold rolling in order to reduce residual stresses without changing the magnetic properties of the finished strip. Here, a hot strip with a thickness of 1.52 to 4.06 mm is cold rolled to an intermediate thickness of 0.51 to 1.01 mm and then cold rolled to 0.152 to 0.457 mm.

Apparently, a high total degree of forming during cold rolling of up to 90% cannot be achieved without a recovery anneal between the cold rolling steps. This method does not refer to special alloys, but is propagated for grain-oriented electrical sheets (Goss texture), as is clear from the examples. There is no indication that good magnetic properties can also be achieved in the transverse direction.

• hohe magnetische Polarisationswerte von J 2500 > 1,7 T durch Ausbildung geeigneter Texturkomponenten und gleichzeitig
• einen niedrigen Ummagnetisierungsverlust von z. B. P 1,5 < 3,3 W/kg für einen Stahl mit einem mittleren Legierungsgehalt von (% Si) + (% Al) = 1,8 %.

The invention has for its object to provide a non-grain oriented electrical steel with the following properties:

• high magnetic polarization values of J 2500> 1.7 T due to the formation of suitable texture components and at the same time
• a low magnetic loss of z. B. P 1.5 <3.3 W / kg for a steel with an average alloy content of (% Si) + (% Al) = 1.8%.

This object is achieved according to the invention by a non-grain-oriented electrical steel with high proportions of cube or cube surface texture and with a polarization J 2500> 1.7 T and low magnetic loss, which consists of a steel that

The Si content is preferably in the range from 0.5 to 4.0%, in particular in the range from 0.5 to 2.0%. While with the choice of the steel composition provided according to the invention with (% Si) + 2 (% Al)> 1.6% a substantial α-γ conversion freedom of the steel is determined, it is advantageous that the steel slab Si and Al in one contains such an amount that the relationship (% Si) + 2 (% Al)> 2% is satisfied. The aluminum content is preferably in the range from 0.3 to 2.0%.

Surprisingly, it has been shown that low manganese contents <0.1%, preferably less than 0.08% Mn, are necessary to adjust the (100) texture components. A layer structure with a recrystallized structure in areas near the surface with orientations predominantly (110) [001] and (11 2nd ) [111] and inside the band a polygonized structure with elongated larger grains, predominantly the stable orientation (100) [011] and (11 1 ) [112].

The carbon content should expediently be limited to a maximum of 0.015% and should preferably be between 0.001 and 0.015%. This low initial carbon content is advantageous, inter alia, with regard to the duration of the decarburization annealing in order to achieve an aging-free electrical steel strip or sheet a C content of less than 0.002%. The additional advantageous addition of surface-active elements, such as, for example, antimony and / or tin, leads to a considerable delay in the decarburization reaction.

Furthermore, the limitation of the carbon content to a maximum of 0.015%, in particular in connection with the setting of the Si and Al content in accordance with (% Si) + 2 (% Al)> 2%, ensures complete freedom from transformation of the steel, which with regard to the desired properties of the electrical steel or sheet is particularly advantageous. The freedom from transformation of the steel is important for the final annealing, since the set texture is lost when the alpha-gamma phase boundary is exceeded, and for the hot forming, since the ferritic single-phase area is necessary for the targeted formation of cubic texture components during hot rolling.

The addition of surface-active elements, such as antimony and / or tin, in a total amount of 0.005 to 0.15%, preferably 0.02 to 0.06%, leads to the suppression of the growth of grains with unfavorable (111) Texture components. This is particularly advantageous for long-term annealing in the hood furnace or in the stamping furnace when processing electrical steel that has not been finally annealed.

ist dadurch gekennzeichnet, daß die Stahlbramme auf eine Dicke von nicht unter 3,5 mm warmgewalzt wird, worauf das so erhaltene Warmband ohne rekristallisierendes Zwischenglühen mit einem Verformungsgrad von mindestens 86 % kaltgewalzt und das Kaltband geglüht wird.The method according to the invention for producing a non-grain-oriented electrical steel with high proportions of cube or cube surface texture and with a polarization J 2500> 1.7 T and low magnetic loss, consisting of a steel with

is characterized in that the steel slab is hot rolled to a thickness of not less than 3.5 mm, whereupon the hot strip thus obtained is cold rolled without recrystallizing intermediate annealing with a degree of deformation of at least 86% and the cold strip is annealed.

As already explained, phase transformation largely does not occur as a result of the steel composition according to the invention, which is important because the texture generated would be lost if the alpha-gamma phase boundary were exceeded, and this is also important for hot forming because of the targeted formation cubic texture components during hot rolling the ferritic single phase area is necessary. In the context of primary recrystallization and normal grain growth, the cold forming provided according to the invention with a total degree of deformation of at least 86% while avoiding recrystallizing intermediate annealing also contributes significantly to the formation of cubic texture components.

According to a preferred embodiment of the method, it is expedient that during hot rolling in the finishing train the deformation is a maximum of 30% per pass if the slab temperature is in the range between 1000 and 1060 ° C. The finish rolling temperature should preferably be between 900 and 960 ° C. This favors the aforementioned layer structure.

According to a further advantageous embodiment of the method, a first section of the cold forming is to be carried out up to a strip thickness of 1.3 to 1.9 mm at an elevated temperature of 180 to 300 ° C. In this way, together with the carbon content according to the invention of <0.025%, in particular <0.015%, and the dynamic deformation aging occurring in this temperature range as a result of the carbon-dislocation interaction, a blocking or anchoring of sliding dislocations and thus the activation of other sliding systems or a inhomogeneous deformation (shear bands) can be achieved, which particularly contributes to an increase in the magnetic polarization in the transverse direction.

A better isotropy of the magnetic properties in the strip plane in the case of electrical steel with a cube-surface texture can be achieved in a further embodiment of the process according to the invention in that the cold-rolled strip is non-recrystallizing at a strip thickness which is still 1.12 to 1.2 times the final thickness Recuperation annealing, in particular between 400 and 500 ° C for 1 to 10 h, subjected and then cold rolled and annealed. The sheet produced in this way is particularly suitable for rotating machines.

To produce a finally annealed strip, the strip rolled to its final thickness is preheated in a continuous furnace, optionally decarburizing in this furnace, and then finally annealed in the same furnace at temperatures between 900 and 1100 ° C. The final annealing temperature should not be below 900 ° C, because then the grain size of the material is not large enough to achieve a low loss of magnetization.

To produce a non-final annealed strip, the cold-rolled strip is placed in a hood furnace under a hydrogen atmosphere between 600 to 900 ° C or in a continuous furnace between 750 to 900 ° C for less than 5 min. annealed recrystallizing. in the In the case of bell annealing, the strip must then be straightened or re-rolled with a degree of deformation of less than 7%. Stamped parts are then produced in the usual manner from the strips which have not been finally annealed, and a stamped part annealing, e.g. B. according to DIN 46 400 Part 4. To achieve particularly good magnetic properties, however, the duration and temperature of the stamped part annealing should be reduced to e.g. B. 15 h and 950 ° C for steel compositions with surfactants.

The invention is illustrated by the following examples.

EXAMPLE 1

8 hot strips with different compositions and strip thicknesses were used as the starting material (Table 1). These were cold rolled to the final thickness of 0.5 mm, then decarburized at 840 ° C and annealed at 950 ° C for 1 h. The magnetic result is shown in Table 2.

Bands B, C and D are comparative examples not belonging to the invention. The Si and Al portions of bands B and C do not satisfy the relationship (% Si) + 2 (% Al)> 1.6. Bands C and D have too high a Mn content.

EXAMPLE 2

• a) Kaltwalzen auf eine Banddicke von 0,5 mm;
• b) Vorwärmen des Warmbandes auf 230 °C und Kaltwalzen bei dieser Temperatur auf 1,5 mm, dann Fertigwalzen auf 0,5 mm Enddicke;
• c) wie b), jedoch mit einer Erholungsglühung 480 °C/4 h bei einer Zwischendicke von 0,58 mm.

The hot strips A and E from Table 1 were rolled in three different variants:

• a) cold rolling to a strip thickness of 0.5 mm;
• b) preheating the hot strip to 230 ° C and cold rolling at this temperature to 1.5 mm, then finish rolling to 0.5 mm final thickness;
• c) as b), but with a recovery annealing 480 ° C / 4 h with an intermediate thickness of 0.58 mm.

The strips were then decarburized and annealed for 1 minute at 1050 ° C (hot strip E, Table 3) or 1 h at 950 ° C (hot strip A, Table 4).

In the case of short-time annealing (Table 3), variant b brings about a slight improvement in the polarization, which is even more clearly recognizable after long-term annealing (Table 4). The almost equally large values in the longitudinal direction (0 °) and transverse direction (90 °) indicate a particularly high proportion of grains with cube orientation.

A pronounced isotropy of the polarization in the sheet metal plane can be achieved by variant c.

EXAMPLE 3

• a) 1 Minute bei 1050 °C
• b) 1 Stunde bei 950 °C
• c) 15 Stunden bei 950 °C

The hot strips E and F3 from Table 1 were preheated to 230 ° C., rolled to 1.5 mm at this temperature, then finish-rolled to 0.5 mm. After decarburization at 840 ° C, annealing was carried out in three different ways:

• a) 1 minute at 1050 ° C
• b) 1 hour at 950 ° C
• c) 15 hours at 950 ° C

Variant a) is required to produce a final annealed electrical sheet; Variants b) and c) represent the stamped annealing of a sheet that is not finally annealed.

Table 5 shows the influence of the different annealing variants on the magnetic result.

In variant c), the addition of antimony results in a significantly higher polarization in hot strip F3 than in hot strip E without antimony.

EXAMPLE 4

A melt was processed into hot strip (composition in Table 6).

• a) Endwalztemperatur: 920 °C
• b) Endwalztemperatur: 850 °C

The hot strip was finished rolled to 4.8 mm strip thickness at two different final rolling temperatures:

• a) Final rolling temperature: 920 ° C
• b) Final rolling temperature: 850 ° C

The hot strips were then cold rolled to a final thickness of 0.5 mm, decarburized and annealed at 950 ° C for 1 h. The result is shown in Table 7.

The final rolling temperature of variant a is in the preferred range of 900 to 960 ° C and thus leads to a considerably higher polarization.

Claims (18)

Non-grain oriented electrical steel with high proportions of cube or cube surface texture and with a polarization J 2500> 1.7 T and low magnetic loss, consisting of a steel with

Electrical steel according to claim 1,
characterized in that it is alloyed with 0.5 to 4.0% Si. Electrical steel according to claim 2,
characterized in that it is alloyed with 0.5 to 2.0% Si. Electrical steel according to one of claims 1 to 3,
characterized in that it is alloyed with 0.3 to 2.0% Al. Electrical steel according to claim 1,
characterized in that it is alloyed with an amount of Si and Al such that the relationship (% Si) + 2 (% Al)> 2% is satisfied. Electrical steel according to one of claims 1 to 5,
characterized in that it is alloyed with less than 0.08% Mn. Electrical steel according to claim 5,
characterized in that it is alloyed with a maximum of 0.015% C. Electrical steel according to claim 1,
characterized in that it is alloyed with 0.001 to 0.015% C. Electrical steel according to one of claims 1 to 8,
characterized in that it is alloyed with a total of 0.005 to 0.15% Sn and / or Sb as surface-active elements. Process for the production of non-grain-oriented electrical steel with high proportions of cube or cube surface texture and with a polarization J 2500> 1.7 T and low magnetic loss from a steel with

including unavoidable impurities, which is hot rolled to a thickness not less than 3.5 mm, whereupon the hot strip thus obtained is cold rolled without recrystallizing intermediate annealing with a degree of deformation of at least 86% and the cold strip is annealed. A method according to claim 10,
characterized in that during hot rolling in the finishing train, if the slab temperature is in the range from 1000 to 1060 ° C, is deformed at most by 30% per pass. A method according to claim 10 or 11,
characterized in that hot rolling is carried out with a final rolling temperature in the range from 900 to 960 ° C. Method according to one of claims 10 to 12,
characterized in that a strip temperature of 180 to 300 ° C is maintained in cold rolling up to a thickness of 1.3 to 1.9 mm. Method according to one of claims 10 to 13,
characterized in that the cold rolled strip is subjected to a non-recrystallizing recovery annealing at a strip thickness which is still 1.12 to 1.20 times the final thickness, before it is subsequently cold rolled to final thickness. The method of claim 14
characterized in that the annealing is carried out in the temperature range of 400 to 500 ° C for 1 to 10 h. Method for producing a final annealed electrical steel strip according to one of Claims 10 to 15,
characterized in that the strip rolled to final thickness is preheated in a continuous furnace, optionally decarburizing and then finally annealed in the temperature range from 900 to 1100 ° C. Method for producing a non-final annealed electrical steel strip according to one of Claims 10 to 15,
characterized in that the cold-rolled strip is recrystallized in a bell annealing furnace under an H₂ atmosphere and then straightened or re-rolled with a degree of deformation of less than 7%. Method for producing a non-final annealed electrical steel strip according to one of Claims 10 to 15,
characterized in that the cold-rolled strip is annealed in a continuous furnace at a temperature in the range from 750 to 900 ° C for less than 5 minutes.