RU2085598C1 - Method of manufacturing isotropic electrical steel - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: invention relates to manufacturing steel in sheets or rolls with thickness 0.5 mm and elevated magnetic induction in strong fields with minimum anisotropy and low specific loss. Such result is achieved by intensification of heat treatment. To this end, prior to be submitted to decarbonizing baking, steel is subjected to radiation-thermal treatment with current of relativistic electrons allowing high-speed heating within temperature range 600-1200 C. This treatment is executed after cold rolling followed by decarbonizing- recrystallization baking. EFFECT: increased level of magnetic induction (by 40-60 mTl and stability of magnetic properties. 2 tbl

Description

 The invention relates to ferrous metallurgy, in particular to the production of cold-rolled isotropic electrical steel used for the manufacture of magnetic circuits of rotating machines: engines, generators, etc. Such steel should have increased magnetic induction in strong fields with its minimum anisotropy and low specific losses.

A known method of producing cold-rolled isotropic steel, where both treatments are combined by increasing the temperature of the final decarburization: first, the strip is heated to temperatures of 760-897 ^o C, and then to 940-1177 ^o C with a total duration of 3.5-8 minutes (U.S. Patent 3021237, NKI 148-111, 1962). The processing of steel by this method does not provide the required degree of decarburization and magnetic properties.

A known method (BV Molotilov "Sulfur in electrical steels", M. Metallurgy, 1973, S. 139-147) for the manufacture of cold-rolled isotropic steel, including a single cold rolling with a compression of 65-95% and subsequent recrystallization annealing at a temperature of 800- 1200 ^o C. In this case, due to the use of large reductions and the occurrence of α ⇄ γ transformation, the secondary recrystallization process is suppressed. Steel treated by this method is characterized by insufficient ductility and increased specific losses, which is associated with the presence of a high carbon content in steel.

The closest to the described invention in technical essence and the achieved result is a method for producing cold-rolled isotropic electrical steel (according to ed. Certificate of the USSR N 785367, C 21 D 1/78, 1980), including a single cold rolling to a final thickness and additional annealing before decarburizing annealing at a temperature T [800 + 100 (Si, + Al% 10% C)] ± 20 ^o C with a holding time of 20-60 s and cooling at a speed of 600-1300 ^o C / min.

 However, the inclusion of additional annealing complicates the production technology and significantly increases the cost of finished products. In addition, the proposed method of processing steel from 2.72 to 3.27% Si does not provide stable isotropic properties by induction.

The technical result of the invention is to improve the magnetic properties of isotropic electrical steel. The indicated result is achieved by carrying out a relativistic electron beam before decarburization annealing of the radiation-thermal treatment, which allows heating the strip in the temperature range 600-1200 ^o C. The peculiarity of this treatment is that the irradiated material is heated not from the surface, as with other heat treatment methods, but the entire depth of electron penetration.

Steel with a content of 0.8 to 3.2% Si is smelted in an electric arc furnace or an oxygen converter. After hot rolling to a thickness of 2.0 to 3.0 mm, normalizing or without it, a single cold rolling to a final thickness is carried out. Subsequently, the cold rolled metal is subjected to electron beam processing, as a result of which the strip is heated to a certain temperature. The power of the electron beam and the radiation dose (fluence) are selected taking into account the temperature of the heating strip. The duration of irradiation depends on the grain size in the steel before decarburization annealing. After radiation-thermal treatment, decarburization annealing of the strip is carried out in the temperature range 800 850 ^o C with a dew point of +20 +30 ^o C in a nitrogen-hydrogen atmosphere and the final recrystallization annealing at a temperature of 1000 1100 ^o C.

 Thermoradiation treatment accelerates diffusion processes, intensifies structural phase transformations, and leads to modification of the irradiated material. Heating a metal with an electron beam reduces the tendency of the metal to oxidize the surface in the secondary oxidation zone, reduces the heterogeneity, and promotes the development of texture components that are favorable in terms of magnetic properties and orientations.

The choice of temperature range for RTO cold rolled metal in the range of 600 to 1200 ^o C due to the following reasons. Lowering the temperature of the strip during electron beam processing (ELO) of less than 600 ^o C leads to the incomplete development of primary recrystallization processes, contributes to the formation of a heterogeneous structure, reinforces unfavorable orientations that contribute to the deterioration of the magnetic properties of steel. An increase in the strip temperature during ELO of more than 1200 ^° C leads to an intensive growth of ferrite grains and different grain sizes, which has a negative effect on the magnetic characteristics of steel. When a cold-rolled metal is heated by a beam of relativistic electrons in the range of 600–1200 ^° C, the average grain size, depending on the silicon content, is in the range of 70–400 microns. Moreover, the higher the silicon content in the steel, the larger the grain size. In addition, annealing the strip in the indicated temperature range eliminates the heterogeneity of the structure over the strip cross section, reduces microhardness, and contributes to the formation of blog-like orientations in terms of magnetic properties.

 Example 1

After hot rolling of steel with a content of 1.45 Si, 0.40% Al, 0.038% C, the rest is Fe and impurities according to the current factory technological instructions for a thickness of 2.20 mm, the metal was etched and cold rolled to a thickness of 0.50 mm. The cold-rolled metal with sample sizes of 0.5x30x305 mm was subjected to electron beam processing at an ELV-4 accelerator with a power of 2.0 • 10 ¹⁶ cm ^-2 to a temperature of 800 ^o C. After that, the samples were decarburized at 820 ^o C with a dew point of +25 ^o in an atmosphere containing 95% N ₂ + 5% H ₂ to a carbon content of 0.05% The final recrystallization annealing was carried out at a temperature of 1050 ^o C in a dry protective gas for 7 minutes As a result of this treatment, the grain size obtained 150-200 microns. Magnetic properties: P _{1.5 / 50} 4.2 W / kg; B ₂₅₀₀ 1.68 T; DB 0.13 T.

 Example 2

Steel containing 2.61% Si; 0.37% Al and 0.04% C, was hot rolled to a thickness of 2.25 mm, normalized at a temperature of 850 ^o C, followed by etching of the strip surface in a hydrochloric acid solution. Then, cold rolling to a thickness of 0.50 mm and radiation-thermal treatment with an electron beam with a power of 2.8 • 10 ¹⁶ cm _-2 to a temperature of 900 ^o C. were carried out. The decarburization and recrystallization annealing was performed according to the regimes indicated in example 1. As a result, processing obtained grain size in the range of 180-220 microns, and the level of magnetic properties was: P _{1.5 / 50} 3.85 W / kg; B ₂₅₀₀ 1.63 T; ΔB 0.12 T.

 Example 3

Steel of chemical composition containing 3.15% Si, 0.46% Al, 0.042% C, after hot rolling to a thickness of 2.2 mm, was subjected to normalized annealing at a temperature of 800 ^o C and etching. Cold rolling was carried out to a thickness of 0.50 mm. Samples of cold-rolled metal with a size of 0.5x30x305 mm were subjected to electron beam treatment with a dose rate of 3.0 • 10 ¹⁶ cm ^-2 to a temperature of 1100 ^o C. After this treatment, the grain size in the steel was 250-300 microns, and the level of magnetic properties P _{1 , 5/50} 3.04 W / kg, B ₂₅₀₀ 1.61 T; ΔB 0.12 T.

 In the table. 1 shows the magnetic properties of steels of various grades with a thickness of 0.50 mm, processed by a known and proposed method (table. 2).

 Comparison of the results given in table. 1 and 2, shows an increase in the stability of the isotropic properties of steel by induction.

Claims (1)

A method of producing isotopic electrical steel, including its smelting, hot and single cold rolling of a strip to a final thickness, decarburization annealing at 800 850 ^o С and recrystallization annealing at 800 1050 ^o С, characterized in that steel containing, by weight, is smelted. 0.3 3.2 silicon, 0.2 0.7 aluminum and 0.02 0.05 carbon, decarburization and recrystallization annealing is carried out in a protective atmosphere, and after cold rolling, additional electron-beam annealing of the strip is carried out in the temperature range 600 1200 ^o FROM.

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