EP0651061B1 - Process for producing grain-oriented electrical steel sheet and magnetic cores produced therefrom - Google Patents

Abstract

The invention relates to a process for producing grain-oriented magnetic steel strip which is readily magnetisable in four directions in the rolling plane and to magnet cores for rotary (rotating) and non-rotary (non-rotating) electrical machines (electric machinery). The process is characterised in that steel slabs having a C content of < 0.10% and an Si content of from 0 to 2% and contents of Al, Mn, S, N, O in the concentrations usual for magnetic steel strip are preheated to about 1250 DEG C, are roughed (cogged, bloomed) in from 5 to 9 passes with small reductions for each individual pass and are finish-rolled in a separate roll line, with an entrance temperature of from 930 DEG C to 1100 DEG C and a finishing temperature of from 800 DEG C to 950 DEG C, with reductions per pass of 35%, and the hot strip thus produced is reeled without forced cooling (controlled cooling, ducted cooling) at a temperature of > 700 DEG C and after cooling, while an amount of deformation (a degree of deformation) of > 86% is maintained, is subjected to cold working (cold forming) which is followed by an interannealing stage under a neutral gas at from 500 DEG C to 750 DEG C for from 0.5 h to 20 h and further cold working at from 2 to 15% and subsequent final annealing at temperatures around 800 DEG C in an at least intermittently decarburising atmosphere. <IMAGE>

Description

The invention relates to a method for producing grain-oriented electrical steel with easy magnetization in four directions in the roller plane and of magnetic cores made from it for rotating and non-rotating Electrical machines.

Process for the production of grain-oriented electrical tapes with so-called GOSS texture {011} <100> are known. According to these procedures, the Alignment of the elementary cubes such that a cube edge of a Elementary cube lies in the rolling direction and two parallel to each other Area diagonal are arranged in the roller plane. In this way The material produced has good magnetizability in the rolling direction. As disadvantageously, however, the poor magnetizability of the material occurs vertically to the rolling direction in appearance. For the production of grain-oriented Electrical steel with a texture other than GOSS is described in DE-AS 1212124 Process described with which using a raw material with 2-5 % Si content an electrical steel is generated, its structural orientation is characterized in that two surfaces of the elementary cubes parallel to Sheet surface and the cube edges lying in the sheet plane are accumulate by at least four excellent directions or a nearly random one Have distribution. According to the process, the material is annealed, pickled and then cold rolled in one or more steps, the Cold rolling step or the last cold rolling step with a degree of deformation of more than 90%. A cube surface texture with an almost random one Cube edge distribution in the roller plane can then be achieved if after cold rolling with> 90% degree of deformation and an intermediate annealing treatment the material again in one step or in several stages is cold worked by 30 to 80%. For the final annealing, 1100 ° C, several hours glow time and hydrogen atmosphere specified. The Intermediate annealing takes place according to the process at temperatures between 800 and 1100 ° C. This process for the production of grain-oriented electrical steel is due to the required technological steps, intermediate annealing 800 - 1100 ° C, several deformation levels and the specified Material composition very complex. Especially the glow of the bundles at temperatures up to 1100 ° C and an annealing time of 5 hours Measures to avoid glue, which also makes the process in its economy is negatively affected. Furthermore, attempts have been made under Application of the method showed that cold rolling degrees> 90% did not inevitably leads to a sharp four-fold orientation training in the material to lead.

The object of the invention is to find a method with which the generation of grain-oriented electrical steel with an enrichment of cube surfaces or close to them in the roller plane and an accumulation of the cube edges in Directions that are about 45 ° to the rolling direction is possible and the production magnetic cores produced therefrom for electrical machines can be improved.

According to the invention the object is solved by the features of claims 1 and 8. Here a steel with a Carbon content of C <0.10% preferably with C = 0.02 - 0.07% a Si content of Si = 0 - 2% and contents of Al, Mn, S, N, O used in the concentrations customary for electrical steel. The 200 - 300 mm thick steel slabs of this composition are preheated to approx. 1250 ° C and then hot-rolled in 5 to 9 stitches with small single stitch decreases in a roughing mill, the stitch decreases <20% for the first two and <30% for the following Stitches. When entering the finishing line. the material has a temperature between 930 ° C and 1100 ° C, preferably <1000 ° C when using unalloyed steel and preferably between 1000 ° C and 1100 ° C when using Si-alloyed steel. According to the process, the final rolling temperature is between 800 ° C and 950 ° C, preferably between 840 ° C and 870 ° C for unalloyed material and preferably up to 920 ° C for alloyed materials, the stitch decreases during finish rolling not exceeding 35%. The finished strip produced in this way is then coiled at a reel temperature of> 700 ° C without forced cooling. Depending on the desired cold strip thickness in the range of 0.1 to 0.6 mm, the hot strip thickness should be selected so that degrees of deformation of> 86%, preferably> 90%, can be achieved in the following cold forming. Thinner slabs, in particular those produced using the thin slab casting technology, are hot-rolled in the same way, with the stitch decreases here being approximately 10% higher due to the lower deformation rates.
It was found that with a hot strip produced in this way, the desired microstructure formation can be made considerably more economical by the subsequent cold forming. According to the process, it is advantageous if the cold forming which takes place after the usual pickling in several passes begins at elevated temperatures in the range from 150 ° C. to 350 ° C., preferably between 200 ° C. and 300 ° C. The strip, which is cold-formed with a degree of deformation> 86%, is then annealed for 0.5 to 20 h at 500 ° C. to 750 ° C. under neutral gas, preferably 1 to 5 h around 550 ° C. for unalloyed and at 620 ° C. to 680 ° C. for Si-alloyed material. After this intermediate annealing, the material is subjected to a further cold working of 2 to 15%, preferably 6 to 12% (tempered) and then finally annealed at temperatures around 800 ° C., depending on the composition, at or slightly above AG 1 in an at least temporarily decarburizing atmosphere. It has proven to be advantageous if the strip produced in this way is treated a second time and finally annealed. The final annealing can be carried out on the belt (fully finished) as well as on the stamped part or after packaging (semifinished). The grain-oriented electrical steel produced in accordance with the method is characterized by four magnetic preferred directions, which are at 45 ° to the rolling direction in the sheet metal plane. This structure formation, avoiding high-temperature annealing, can be designated with a structure orientation (001) <110>. The tape is particularly suitable for applications in which the magnetic flux is conducted in two mutually perpendicular directions. This is the case, for example, in stand packages of rotating or non-rotating electrical machines. The punched parts required for this are punched out of the band-shaped material, taking into account the course of the four preferred directions of easy magnetization, and assembled into a package. The core sheets for magnetic cores for rotating electrical machines can be made from circular blanks, which are each assembled into a package in such a way that core sheets that follow each other in each case are rotated by 45 ° to one another. When using segments for magnetic cores for rotating electrical machines, the individual segments are punched out of the band-shaped electrical steel strip so that the directions of easy magnetizability are detected by them. Magnetic cores produced in this way have a significantly lower production and processing outlay and better magnetic properties than previously used stamped parts.

The method according to the invention is intended to be based on three exemplary embodiments are explained in more detail.

Example A

An unalloyed steel slab with a C content of 0.07% and a thickness of 250 mm is preheated to 1250 ° C and rolled in 7 passes to 32 mm. Finishing rolling is carried out in 5 passes at an inlet temperature of 965 ° C and a finish rolling temperature of 840 ° C, with a single pass decrease of <30% to 5.6 mm with subsequent air cooling and reeling at> 700 ° C. After pickling, the pickled strip is annealed to 0.55 mm (degree of deformation 90%) at 560 ° C for 2 hours and then treated with 6%. This material is then subjected to a final annealing at 780 ° C., one hour in moist and four hours in dry H ₂ . The grain-oriented electrical steel produced afterwards has the following values for J and 2500 (T):

2500 = 1,78 T.Angular dependence of the magnetic polarization at H and = 2500 Am ^-1 (ϕ = angle to the rolling direction) ϕ 0 ° 15 ° 30 ° 45 ° 60 ° 75 ° 90 ° J and 2500 / (T) 1.62 1.73 1.86 1.92 1.87 1.71 1.60 The mean J across all directions is

2500 = 1.78 T.

Example B

A Si-alloy steel slab with a Si content of 1.1% and a C content of 0.05% and a thickness of 250 mm is preheated to a temperature of 1250 ° C and heated in the same way with regard to the number of stitches and degree of and cold rolled as in Example A, but with the following parameters changed: Inlet temperature of finish rolls 1080 ° C Finish rolling temperature 895 ° C Intermediate annealing temperature 660 ° C (2h)

The angular dependence of the magnetic polarization results in ϕ 0 ° 15 ° 30 ° 45 ° 60 ° 75 ° 90 ° J 2500 / (T) 1.64 1,685 1.77 1,795 1.64 1,635 1.56 with an average J across all directions 2500 = 1.70 T.

Example C

However, an unalloyed steel slab as in Example A is hot-rolled at a slightly higher temperature, then cold-rolled and annealed, with the first tempering (10%) followed by another intermediate annealing at 780 ° C for 2 hours in dry H2 and then the band of another 10 % cold deformation is subjected. The final annealing is carried out at 780 ° C for 1 h in moist and 4 h in dry H2. The grain-oriented electrical steel produced afterwards has the following value for J 2500 (T): ϕ 0 ° 15 ° 30 ° 45 ° 60 ° 75 ° 90 ° 1 trained 1.69 1.71 1.77 1.79 1,735 1,675 1.63 2 times 1.63 1.71 1.83 1.87 1.805 1.67 1.58

The mean values J across all directions are in the 1st case 2500 = 1.72 T in the second 2500 = 1.75 T.

The grain-oriented electrical steel produced according to the invention is particularly suitable for applications in which the magnetic flux is conducted in two directions perpendicular to one another. For this purpose, in non-rotating electrical machines, the stamped parts required for the assembly in the magnetic body are manufactured from the strip material in accordance with the arrangement of the sectional shapes shown in FIG. 1, the beams 1, 2, 3, 4 identifying the four directions of easier magnetization. The magnetic cores for rotating electrical machines are manufactured in such a way that either immediately successive core sheets are arranged at 45 ° to one another or that, according to FIG. 2, the magnetic core is made up of segments, the segments capturing the angles of easy magnetization. In the former alternating layering of the blanks, the following results were found for the angular dependence of the J 2500 values for blanks according to Example C: 0 ° 15 ° 30 ° 45 ° 60 ° 75 ° 90 ° Pr.1 1.72 1.76 1.85 1.89 1,835 1.72 1.57 Pr.2 1.68 1.73 1.81 1.84 1.79 1.67 1.60 0 ° stratification 1.70 1,745 1.83 1.87 1.81 1.705 1.63 45 ° stratification 1.79 1,795 1.79 1.77 1,775 1.77 1.75

The mean values J 2500 for all directions are obtained for Pr. 1 Pr. 2 0 ° stratification 45 ° stratification 1.79 T. 1.75 T. 1.77 T. 1.78 T.

The magnetic cores produced afterwards are characterized by better magnetic ones Properties.

Claims (10)

1. Process for producing grain-oriented magnetic steel strip which is readily magnetizable in four directions in the rolling plane, in which steel slabs having a C content of <0.10% and an Si content of from 0 to 2% and contents of Al, Mn, S, N, O in the concentrations which are usual for magnetic steel strip are preheated to approximately 1250°C, are roughed in from 5 to 9 passes with small reductions for each individual pass and are finish-rolled in a separate roll line, with an entry temperature of from 930°C to 1100°C and a finishing temperature of from 800°C to 950°C, with reductions for each pass of (35%, and the hot strip produced in this way is coiled without forced cooling at a temperature of >700°C and, after cooling, while a degree of deformation of >86% is maintained, is subjected to cold working which is followed by intermediate annealing under neutral gas at from 500°C to 750°C for from 0.5 h to 20 h and further cold working of from 2 to 15% with subsequent final annealing at temperatures of around 800°C in an at least intermittently decarburizing atmosphere.
2. Process according to Claim 1, characterized in that, in the case of unalloyed steel, the temperature on entry into the finishing roll line is <1000°C and on exit from the finishing roll line is from 840°C to 870°C.
3. Process according to Claim 1, characterized in that, in the case of steel, the temperature on entry into the finishing roll line is from 1000°C to 1100°C and on exit from the finishing roll line is up to 920°C.
4. Process according to Claims 1 to 3, characterized in that expediently, before cold working, the hot strip is preheated to a temperature of from 150°C to 350°C, preferably to 200°C to 300°C.
5. Process according to Claims 1 and 2, characterized in that the unalloyed magnetic steel strip, after cold rolling, is subjected to intermediate annealing, preferably at 520°C to 580°C for one to five hours under neutral gas.
6. Process according to Claims 1 and 3, characterized in that the alloyed magnetic steel strip, after cold rolling, is subjected to intermediate annealing, preferably at from 620°C to 680°C for one to five hours under neutral gas.
7. Process according to Claims 1 to 5, characterized in that the cold-rolled magnetic steel strip is skin-rolled at 2-15% and undergoes final annealing intermittently in a decarburizing atmosphere, the magnetic steel strip, if appropriate, being subjected to further rerolling and final annealing.
8. Process for producing magnet cores for electrical machines from grain-oriented magnetic steel strip which is produced according to one of Claims 1 to 7 and is readily magnetizable in four directions in the rolling plane, in which process the stamped parts which are to be produced for the magnet cores are stamped out taking into account the course of the four directions of ready magnetizability, which run at 45° to the direction of rolling, and are combined to form an assembly.
9. Process according to Claim 8, characterized in that the stamped parts for magnet cores for rotary electrical machines comprising discs which are combined to form an assembly in such a way that core plates which immediately follow one another are arranged rotated through 45° with respect to one another.
10. Process according to Claim 8, characterized in that the stamped parts for magnet cores for rotary electrical machines comprise segments which are combined to form an assembly in such a way that the individual segments each pick up the directions of ready magnetizability.

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