RU2701606C1 - Method for production of anisotropic electrical steel with high permeability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy, particularly, to production of electro-technical anisotropic steel used in making magnetic conductors of power and distribution transformers. Performing steel melting, casting, hot rolling, etching, double cold rolling with intermediate decarburizing annealing, in which the strip in a non-oxidising atmosphere is quickly heated to temperatures of 700–980 °C with speed of not less than 100 °C/s and decarburized, application on strip of magnesian coating, high-temperature and straightening annealing. After hot rolling hot-rolled strip annealing is performed with heating to temperatures of 900–1,000 °C with arbitrary speed, holding at this temperature of not more than 60 seconds, cooling to temperature below 500 °C with a speed of not less than 28 °C/s and further cooling to ambient temperature at arbitrary speed. Further, the strip is subjected to subsequent processing operations. Method is particularly applicable in the production of electrical anisotropic steel containing copper from 0.4 to 0.6 wt%.

EFFECT: high permeability and uniformity of magnetic properties.

1 cl, 1 dwg, 2 tbl, 2 ex

Description

The invention relates to ferrous metallurgy and can be used in the manufacture of sheet electrical anisotropic steel (EAS, GO, CGO, RGO, HGO, Hi-B) with a thickness of 0.18-0.50 mm with a texture of (110) [001] (Goss texture, rib texture). Cold-rolled electrical anisotropic steel is the main soft magnetic material used in modern electrical engineering for the manufacture of cores of various kinds of electrical energy-converting devices [1].

The unique coarse-grained oriented structure of the EAS is formed as a result of a complex technological cycle, including rolling and annealing, one of the final stages of which is high-temperature annealing, during which secondary recrystallization (abnormal grain growth) is realized in steel with the formation of Goss texture - (110) [001] . The main conditions for the realization of abnormal growth in a metal are the prevention of collective recrystallization due to the presence of dispersed particles of the second (inhibitory) phase.

Currently, EAS with a thickness of 0.18-0.50 mm is produced according to five technology options [2, 3], based on the Goss patent [4]. The main amount of EAS in Russia is produced according to the so-called nitride-copper (Russian) version, containing 0.4-0.6 wt. % copper [2, 5-7].

Traditionally, EAS largest magnetic induction ₈₀₀ are divided into two classes, normal quality steel with B ₈₀₀ <1.88 T (commercial grade, CGO, RGO) and high-permeability steel ₈₀₀ ≥1.88 T (HGO, HI-B) [2, 3 ].

при горячей прокатке, а вторая, внедренная в 90-х годах [10-12], основана на введении основного элемента -азота (для формирования ингибиторной фазы

) при химико-термической обработке в конечной толщине (азотировании).At present, high-permeability steel is produced according to two technological options developed by Nippon Steel. A common condition of these technologies is a single cold rolling with a high degree of deformation. The difference between the options lies in the methods of controlling the inhibitory phase. The first classical sulfonitride technology [7–9] provides for the formation of the required inhibitory phase

during hot rolling, and the second, introduced in the 90s [10-12], is based on the introduction of the main nitrogen element (to form the inhibitory phase

) during chemical-thermal treatment in the final thickness (nitriding).

The main disadvantage of the first direction is the need for high-temperature heating of slabs (up to 1400 ° C), which can be realized only on special expensive equipment (furnaces with liquid slag removal, induction slab heaters), which is absent on standard hot rolling mills.

The second direction, firstly, significantly limits the performance of decarburization annealing furnaces and, secondly, involves the use of an environmentally unfavorable ammonia atmosphere.

The disadvantages of both technologies include:

- the need to introduce into the technological cycle the operation of heat treatment of hot-rolled steel at high (up to 1150 ° C) temperatures.

Another method for the production of highly permeable anisotropic electrical steel, using a scheme with double cold rolling of metal containing 0.4-0.6 wt. % copper (nitride-copper version of the technology), and the closest set of essential features to the claimed object (prototype) is the production method [13] (RF Patent 2637848. Method for the production of highly permeable anisotropic electrical steel / Akulov SV, Redikultsev A. A., Karenina L.S., Parshakov B.V., Mikhailov N.V. Applicant and patent holder Limited Liability Company “VI3-Steel” (RU). Publish. 07.12.2017, Bull. No. 34. Priority dated 31.01 .2017).

The method involves steelmaking, casting, hot rolling, pickling, double cold rolling with intermediate decarburization annealing, applying a magnesia coating to the strip, high temperature and straightening annealing. Before the stage of decarburization of steel in the intermediate thickness, a heating is performed in which the strip in an oxidizing atmosphere quickly heats up to temperatures of 700-980 ° C at a speed of at least 100 ° C / s, as well as the cooling of the heated strip in an oxidizing atmosphere to temperatures of 600-840 ° C at a speed of at least 60 ° C / s immediately after reaching the maximum temperature in the heating phase. Further, the strip in the intermediate thickness is subjected to decarburization annealing and subsequent processing operations. The method is particularly applicable in the production of electrical anisotropic steel containing copper from 0.4 to 0.6 wt. %

The prototype involves rapid heating of a metal strip in an intermediate thickness before decarburization annealing to temperatures of 700-980 ° C. However, as shown, the authors of the application for the invention of a study of the properties of the metal by this technology can be improved.

The present invention is the development of an improved method for the production of sheet EAS with high permeability and low magnetic loss according to the nitride-copper version of the technology. A distinctive feature of the invention is the addition of the operation of low-temperature annealing of the hot-rolled strip, together with the subsequent rapid heating of the cold-rolled strip at a speed of at least 100 ° C / s in the intermediate thickness before decarburization annealing.

The proposed method for producing EAS containing copper includes:

1. The smelting of the metal of the following composition, wt. %: Cu 0.4-0.6, C 0.018-0.045, preferably 0.002-0.03, Mn 0.10-0.40, preferably 0.20-0.35, Si 3.0-3.50, preferably 3.15-3.40, Al 0.010-0.035, preferably 0.010-0.025, N ₂ 0.008-0.015, preferably 0.009-0.013, the rest is iron and unavoidable impurities;

2. Continuous casting into slabs, including thin slabs on casting and rolling modules;

3. Hot rolling to a thickness of 1.5-3.5 mm, with the completion of deformation at temperatures not lower than 900 ° C and winding into rolls at a temperature not higher than 580 ° C;

4. Annealing of the hot-rolled strip at a temperature of 900-1000 ° C with a holding time of not more than 60 seconds and cooling to a temperature below 500 ° C at a speed of at least 28 ° C / s;

5. Cold rolling to an intermediate thickness of 0.50-0.80 mm;

6. Decarburizing annealing of the strip in a humidified nitrogen-hydrogen mixture, comprising a heating step in which the strip in the intermediate thickness is quickly heated to temperatures of 700-980 ° C with a heating rate of at least 100 ° C / sec. In this case, rapid heating enters the heating phase of decarburization annealing and is performed in an oxidizing atmosphere [13];

7. Cold rolling to a thickness of 0.15-0.50 mm;

8. Application of heat-resistant coating;

9. High-temperature annealing with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / h;

10. Rectifier annealing with electrical insulating coating.

Hot rolling, cold rolling and other methods in the invention are traditional technical methods in this technical field.

The essence of the proposed technical solution is as follows. It was previously believed that a high degree of perfection and uniformity of the (110) [001] texture in an EAE can be achieved either by the formation of a large amount of a highly dispersed inhibitory phase during hot rolling and heat treatment of the tack, as well as a powerful force effect on the steel texture, which is a single cold rolling (degree of deformation of more than 80%, optimal - 88%). Either, when using double rolling, due to the use of high-speed heating before decarburizing annealing in the intermediate thickness [13], or to preserve the structure and texture of the hot-rolled steel, characteristic of the deformed state [14]. A study of the invention by the authors showed that high permeability and a particularly low level of magnetic losses in the EAS can be obtained by affecting the structure of the metal containing copper (0.4-0.6%), the parameters of heating and cooling the strip after hot rolling in combination with the parameters of heating and cooling the strip at the stage of decarburization annealing in the intermediate thickness.

Reducing magnetic losses and increasing the degree of perfection of the texture (110) [001] in the finished EAS containing copper 0.40-0.60 wt. % can be obtained by adding to the production technology using induction heating of the strip [13], the operation of annealing the hot rolled strip at a temperature of 900-1000 ° C with a holding time of not more than 60 seconds and cooling to a temperature below 500 ° C at a speed of at least 28 ° C / s

The application of the claimed technical solution allows you to:

1. Due to heating and holding the hot-rolled strip at a temperature of 900-1000 ° C:

1.1 Recrystallize the hot-rolled structure with an increase in the subsurface layer of the band of the share of sharp rib orientation (110) [001].

1.2 To increase the content and uniformity of the distribution of carbon in solid solution (by increasing solubility and partial austenitization (formation of γ-iron)).

2. Due to the rapid cooling of the hot-rolled strip to a temperature below 500 ° C with a speed of at least 28 ° C / sec (quenching from the heating temperature), fix carbon in a solid solution and avoid the precipitation of large carbides.

3. During the first cold rolling, carbon stored in a solid solution of ferrite contributes (under conditions of increasing dislocation density and a noticeable increase in the temperature at the deformation zone), due to the release of atmospheres at the dislocations, to the difficulty of deformation due to slip and intensification of the process of formation of shear bands [15 ]. This, in turn, leads to an increase in the {111} <112> octahedral strain component in the strain structure and an increase in the stored strain energy in regions with (110) rib orientation [001].

4. Due to the rapid heating of the strip in the intermediate thickness to temperatures of 700-980 ° C, increase the temperature of the onset of primary recrystallization, which leads to an increase in the number of primary recrystallization nuclei with sharp rib orientation (110) [001] upon further annealing, enhanced by the effect of the stored carbon (increasing the sharpness of the texture (110) [001] compared with the use of induction heating only). The resulting texture differences increase the sharpness of the (110) [001] rib component in the subsurface layer of the metal strip at the final stages of annealing before secondary recrystallization in the final thickness, leading to the formation of a unique level of magnetic properties (high permeability and especially low magnetic losses).

In fig. 1 shows the production scheme of EAS in accordance with the prototype (a), the production of highly permeable EAS according to the classical sulfonitride technology (b) and the production of EAS containing copper, in accordance with the claimed technical solution (c). The key features of each production scheme are highlighted in bold.

The method can be carried out as follows.

After hot rolling to a thickness of 1.5-3.5 mm, the strip is annealed in a continuous industrial annealing unit (for example, a standard normalization unit). Annealing includes heating to temperatures of 900-1000 ° C at an arbitrary speed, holding at a given temperature for no more than 60 seconds, cooling to a temperature below 500 ° C at a speed of at least 28 ° C / s and further cooling to ambient temperature at an arbitrary speed . Next, the strip is subjected to subsequent processing operations.

Thus, the technical result of the claimed invention is the possibility of producing EAS containing 0.4-0.6 wt. % Cu, with high permeability and a particularly low level of magnetic loss.

The following is a description of the experiments conducted by the authors of the present invention. The conditions of the experiments and their results are examples used to confirm the feasibility of the results of the present invention, while the present invention is not limited to the examples.

Example 1. Smelted steel with a chemical composition, wt. %: C 0.018-0.035, Mn 0.1-0.4, Si 3.00-3.50, Al 0.01-0.035, N ₂ 0.08-0.015, Cu 0.4-0.6, the rest is iron and inevitable impurities. The resulting slabs were heated, followed by hot rolling, to obtain a hot-rolled strip 2.5 mm thick.

After hot rolling, the strips were annealed. Annealing parameters were varied to provide different holding temperatures and cooling rates. The strips were etched and then rolled to a thickness of 0.70 mm in a cold rolling mill. After rolling, the strips were heated in an induction furnace before decarburization at a rate of 100 ° C / sec. Then, each strip underwent decarburization annealing in a humid nitrogen-hydrogen atmosphere at a constant temperature of 840 ° С.

Further redistribution included a second cold rolling to a thickness of 0.27 mm, applying a magnesia coating, high-temperature annealing at a temperature of 1150 ° C with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / hour. Then, the magnesium oxide residues were washed off the strips and an insulating coating was applied to the previously formed forsterite layer. The corresponding processing modes and results are shown in table 1.

From the data of table 1 it follows that the application of the claimed technical solution allows to achieve the level of magnetic properties characteristic of high-permeability steel, which is explained by the processes of texture formation associated with the redistribution of carbon and the presence of copper.

The best magnetic properties were obtained by heating a hot-rolled strip to temperatures of 900-1000 ° C, holding for no more than 60 seconds and cooling to temperatures below 500 ° C at a speed of at least 28 ° C / s, and further cooling to ambient temperature at an arbitrary speed.

Example 2. Hot rolled strips with a thickness of 2.5 mm, manufactured by nitride-copper technology, were annealed at 900-1000 ° C, holding for 60 seconds and cooled to 450 ° C at different speeds. Then the strips were etched and were cold rolled to a thickness of 0.65 mm in a cold rolling mill. After rolling, the strips were heated in an induction furnace before decarburization at a rate of 100 ° C / sec. Then, each strip underwent decarburization annealing in a humid nitrogen-hydrogen atmosphere at a constant temperature of 840 ° С. Further redistribution included a second cold rolling to a thickness of 0.23, 0.27 and 0.30 mm, application of a magnesia coating, high-temperature annealing at a temperature of 1150 ° C with a limitation of the heating rate of the coils in the temperature range 400-700 ° C to 20-25 ° C / hour. Then, the magnesium oxide residues were washed off the strips and an insulating coating was applied to the previously formed forsterite layer. The corresponding processing modes and results are shown in table 2.

From the data of table 2 it follows that the application of the claimed technical solution allows to obtain an unambiguous stable improvement in electromagnetic induction B ₈ and specific losses P _{1.7 / 50} in the EAS containing 0.4-0.6 wt. % copper, for thicknesses of 0.23-0.30 mm.

LITERATURE

1. Kazadzhan LB Magnetic properties of electrical steel and alloys / L.B. Kazadzhan. Ed. V.D. Durneva. M .: LLC “Science and Technology. 2000.224 s.

2. Lobanov M.L., Rusakov G.M., Redikul'tsev A.A. Electrical anisotropic steel. Part I. History of development // MiTOM. 2011. No7. S. 18-25.

3. Lobanov M.L., Rusakov G.M., Redikul'tsev A.A. Electrical anisotropic steel. Part II Current state // MiTOM. 2011. No8. S. 3-7.

4. N.P. Goss, US Patent No. 1965559. 07/03/1934.

5. Baryatinsky V.P., Belyaeva G.D., Udovichenko N.V. et al. Study of the structural features of the Fe-3% Si alloy doped with copper // In Sb. Precision alloys in electrical engineering and instrument making. M .: Metallurgy. 1984. S. 33-37.

6. Frantsenyuk I.V., Kazadzhan VB, Baryatinsky V.P. Achievements in improving the quality of electrical steel at NLMK // Steel. 1994. No. 10. S. 35-38.

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10. Kobayashi H., Kuroki K, Minakuchi M., Yakashiro K. US Patent No. 4979996. Process for Preparation of Grain-Oriented electrical steel sheet containing a nitriding treatment. 12/25/1990.

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13. Akulov S.V. et al. Method for the production of highly permeable anisotropic electrical steel. RF patent 2637848, IPC51 C21D 8/12, H01F 1/16. / Akulov S.V., Redikul'tsev A.A., Karenina L.S., Parshakov B.V., Mikhailov N.V .; Applicant and patent holder VI3-Steel Limited Liability Company (RU); publ. 12/07/2017, Bull. No. 34 (Application 2017103282, priority January 31, 2017).

14. Tsyrlin M.B. Method for the production of highly permeable anisotropic electrical steel / RF Patent 2516323 C1. / Tsyrlin M.B. Applicant and patent holder Tsyrlin MB (RU); publ. 05/20/2014. Priority from 11/14/2012.

15. Lobanov M.L., Redikul'tsev A.A., Rusakov G.M., Belyaevskikh A.S. The effect of strain aging during cold rolling on the formation of the structure and properties of the technical alloy Fe-3% Si // Izvestiya VUZov. Ferrous metallurgy. 2015.V. 58. No. 7. S. 520-525.

Claims (1)

 A method of manufacturing a highly permeable electrical anisotropic steel containing copper 0.4-0.6 wt. %, including steel smelting, casting, hot rolling, pickling, double cold rolling with intermediate heating in a non-oxidizing atmosphere to temperatures of 700-980 ° C at a rate of at least 100 ° C / s and subsequent decarburization annealing, application of a high temperature coating to the strip of magnesia and rectifying annealing, characterized in that after hot rolling annealing of the hot-rolled strip is carried out by heating the strip to temperatures of 900-1000 ° C at an arbitrary speed, holding at a heating temperature of not more than 60 seconds, cooling temperature to below 500 ° C at a rate of at least 28 ° C / s and further cooling to ambient temperature at an arbitrary speed.

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