RU2476606C2 - Method for making isotropic electrical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: in order to obtain isotropic electrical steel in plates or coils, the following is performed: melting, vacuum processing (unnecessarily), hot rolling, normalisation (unnecessarily), single cold rolling of a strip to final thickness, decarburising annealing at 800-850°C and recrystallisation annealing at 800-1050°C; at that, heating to the decarburising annealing temperature is performed at the speed of 100-500°C/sec in wet protective nitrogen-hydrogen mixture. Heating up to recrystallisation annealing temperature is performed at the speed of 100-500°C/sec in dry protective nitrogen-hydrogen mixture.

EFFECT: increased magnetic properties of steel at minimum anisotropy.

2 cl, 2 ex, 2 tbl

Description

The invention relates to metallurgy, specifically to the production of isotropic electrical steel used for the manufacture of magnetic circuits of electrical equipment operating in a rotating magnetic field. This steel should have minimal specific magnetic losses during magnetization reversal and increased induction in medium and strong fields with minimal anisotropy of magnetic properties.

A known method (B.V. Molotilov "Sulfur in electrical steels", M., Metallurgy, 1973, p.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 ° C. In this case, due to the use of large reductions and the occurrence of the α↔λ transformation, the secondary recrystallization process is suppressed. Steel processed 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 isotropic electrical steel (according to US Pat. RU 2085598 C21D 8/12, 1994), including smelting, hot and single cold rolling to a final thickness, after cold rolling, electron beam annealing the strip in the temperature range 600-1200 ° С, then decarburizing annealing at 800-850 ° С and recrystallization annealing at 800-1050 ° С. However, the inclusion of additional electron-beam annealing complicates the production technology and significantly increases the cost of finished products, and is also difficult to achieve in large-scale production. In addition, although when conducting electron beam annealing, it is possible to achieve metal heating rates of the order of 100-500 ° C / s, however, the use of a beam of such power will cause surface melting and lead to marriage.

The proposed technical solution is aimed at solving the problem of intensifying the heat treatment processes and improving the magnetic properties of isotropic electrical steel. This is achieved by decarburization or recrystallization annealing using high-speed heating in longitudinal and transverse magnetic fields.

The specified result is achieved during processing by a method that includes the following technological operations.

Smelting, optionally evacuation, hot rolling, optionally normalizing, single cold rolling of a strip to a final thickness, decarburization annealing at 800-850 ° C in a wet nitrogen-hydrogen mixture and recrystallization annealing at 800-1050 ° C in a dry protective environment, while heating to a temperature decarburization annealing is carried out at a speed of 100-500 ° C / sec in a wet protective nitrogen-hydrogen mixture. Heating to a temperature of recrystallization annealing is carried out at a speed of 100-500 ° C / s in a dry protective nitrogen-hydrogen mixture.

The peculiarity of high-speed heating in longitudinal and transverse magnetic fields is that the material being processed is heated not from the surface, as with other heat treatment methods, but throughout the depth of penetration of the magnetic field and does not cause surface melting.

Smelting of isotropic electrical steel is carried out in an electric arc furnace or an oxygen converter. Next, hot rolling is carried out with or without normalization, and then cold rolling to a final thickness. Subsequently, the heating for decarburization or recrystallization annealing is carried out using longitudinal and transverse magnetic fields inductors at the furnace inlet. The heating atmosphere is determined on the basis of the tasks to be solved by subsequent exposure: for decarburization - moistened nitrogen-hydrogen mixture, for recrystallization - dry nitrogen-hydrogen mixture.

Inductors of longitudinal and transverse magnetic zeros provide fast through heating of the strip to the required temperature in the range of 800-1150 ° C at a speed of 100-500 ° C / s. The heating temperature depends on the chemical composition and alloying group of the steel. A change in the heating rate is provided by a change in the frequency and power of the induced field and depends on the thickness of the heated material.

Induction heating accelerates diffusion processes in steel, helps to accelerate structural transformations, and ensures the rapid production of recrystallized grain throughout the metal volume. In turn, this further contributes to obtaining a larger grain size than under normal conditions after aging and the development of texture components favorable from the point of view of magnetic properties.

Example 1 with decarburization annealing in a humid atmosphere

Isotropic electrical steel with a content of 0.65% Si, 0.18% Al, 0.155% P, 0.034% C, the rest - Fe and impurities were smelted in the converter, slabs were obtained by continuous casting. After hot rolling to a thickness of 2.2 mm, the metal was etched and cold rolled to a thickness of 0.5 mm. The cold-rolled metal was cut into samples with dimensions of 0.5 × 30 × 305 mm. The samples were subjected to high-speed heating at a rate of 250 ° C / s to a temperature of 830 ° C in a humidified protective atmosphere, the heating time of 3.3 seconds. After heating, the samples were kept for 2 min in a humidified atmosphere for decarburization of the metal. This was followed by exposure for 1 min to a dry protective nitrogen-hydrogen mixture to undergo recrystallization. For comparison, samples of the same batch of steel after cold rolling were heated to 830 ° C for 5 min and held for 2 min in a humidified protective atmosphere for decarburization and held for 1 min in a dry protective nitrogen-hydrogen mixture to undergo recrystallization. According to the results of processing, it was found that in the samples that underwent rapid heating, the passage of collective recrystallization up to 50% was found, whereas in the structure of the steel treated without high-speed heating only primary recrystallized grains were observed. The magnetic properties according to the annealing results are given in table 1.

Example 2 with recrystallization annealing in a dry atmosphere

Isotropic electrical steel with a content of 0.64% Si, 0.15% Al, 0.133% P, 0.005% C, the rest - Fe and impurities were smelted in the converter, evacuated, slabs were obtained by continuous casting. After hot rolling to a thickness of 2.2 mm, the metal was etched and cold rolled to a thickness of 0.65 mm. The cold-rolled metal was cut into samples with dimensions of 0.65 × 30 × 305 mm. The samples were subjected to high-speed heating at a rate of 220 ° C / sec to a temperature of 830 ° C in a dry protective nitrogen-hydrogen mixture, the heating time was 3.7 sec. Next, the samples were kept for 3 min to undergo recrystallization. Decarburization was not required, as the metal underwent preliminary non-furnace evacuation. For comparison, samples of the same batch of steel after cold rolling were subjected to heating to 830 ° C for 5 min and holding for 3 min in a dry protective nitrogen-hydrogen mixture to undergo recrystallization. According to the results of processing, it was revealed that in the samples that underwent high-speed heating, the passage of collective recrystallization to 50% was detected, while in the structure of steel treated without high-speed heating, only primary recrystallized grains are observed. Preliminary evacuation and annealing in a dry protective nitrogen-hydrogen mixture allowed us to get rid of the zone of internal oxidation. The magnetic properties according to the annealing are given in table 2.

Table 1 Magnetic characteristics of isotropic electrical steel treated in two modes, thickness 0.5 mm (Example 1) without speed heating with high-speed heating P _{1.5 / 50} , W / kg B ₂₅₀₀ , T P _{1,5 / 50} , W / kg B ₂₅₀₀ , T 7.13 1,663 5.32 1,671 7.5 1,679 5.41 1,693 7.46 1,681 5,4 1,691 7.18 1,684 5.1 1,695 7.03 1,679 5,6 1,681

table 2 The magnetic characteristics of isotropic electrical steel, machined in two modes, the thickness of 0.65 mm (Example 2) without speed heating with high-speed heating P _{1,5 / 50} , W / kg B ₂₅₀₀ , T P _{1.5 / 50} , W / kg B ₂₅₀₀ , T 8.11 1,672 6.24 1,684 8.32 1,683 6.27 1,695 8.4 1,667 6.38 1.68 8.27 1.68 6.35 1,694 8.0 1,681 6.09 1,693

The magnetic properties in table 2 are indicated for a thickness of 0.65 mm (Example 2). When converted to a thickness of 0.5 mm, they turn out to be higher than in table 1.

Thus, carrying out high-speed heating in the indicated parameters, ceteris paribus, provides a faster passage of recrystallization processes and provides an increase in the magnetic properties of isotropic electrical steel.

A study of scientific and technical literature showed the absence of similar technical solutions, i.e. the invention meets the criterion of "Novelty."

Claims (2)

1. A method of producing isotropic electrical steel, including smelting, optionally evacuating, hot rolling, optionally normalizing, single cold rolling of a strip to a final thickness, decarburization annealing at 800-850 ° C in a wet nitrogen-hydrogen mixture and recrystallization annealing at 800-1050 ° C in dry protective environment, characterized in that the heating to a temperature of decarburization annealing is carried out at a speed of 100-500 ° C / s in a wet protective nitrogen-hydrogen mixture. 2. The method according to claim 1, characterized in that the heating to a temperature of recrystallization annealing is carried out at a speed of 100-500 ° C / s in a dry protective nitrogen-hydrogen mixture.