RU2442832C1 - Method for production of high-silicone isotropic electrotechnical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: The invention relates to metallurgy, in particular, to production of cold-rolled isotropic electrotechnical steel of the fourth doping group. In order to improve the magnetic properties steel slabs with 2,8-3,8 of silicone are heated, hot-rolled, cold-rolled, the slabs undergo a combined decarburizing and recrystallization annealing, or recrystallization annealing at the temperature of at least 900°C, furthermore, the temperature in the end of hot-rolling is kept in the range of 780-860°C, then the piece is cooled with water to 580-630°C, whereas the heating of cold-rolled piece is carried out at first at the temperature of 480-520°C at the rate of at least 500°C/minute, then to the temperature below 800°C at the rate of 400°C/minute, and the finishing heating is carried out at any rate.

EFFECT: improved magnetic properties of steel.

1 ex, 1 tbl

Description

The invention relates to metallurgy, specifically to the production of cold-rolled isotropic electrical steel of the fourth alloying group.

Known methods for the production of cold-rolled isotropic electrical steel (EIS), including smelting of silicon steel, casting, hot rolling of strips with regulated temperatures at the end of rolling, accelerated cooling with water, cold rolling of strips and their high-speed recrystallization or combined decarburization-recrystallization annealing in a continuous furnace [1 2].

The disadvantages of the known methods are that the cold-rolled IES has low magnetic properties.

The closest analogue to the present invention is a method for the production of isotropic electrical steel, including the manufacture of slabs, their heating, hot rolling, cold rolling, combined decarburization-recrystallization annealing or recrystallization annealing at a temperature of at least 900 ° C [3].

The disadvantage of this method is that in the production of high-silicon IES with a silicon content of 2.8-3.8%, unfavorable anisotropic microstructure and crystallographic texture are formed in the cold-rolled strips after decarburization-recrystallization or recrystallization annealing. This leads to a deterioration in their magnetic properties.

The technical problem solved by the invention is to increase the magnetic properties of high-silicon isotropic electrical steel.

To solve the technical problem in the known method for the production of high-silicon isotropic electrical steel with a silicon content of 2.8-3.8%, including the manufacture of slabs, their heating, hot rolling, cold rolling, combined decarburization-recrystallization annealing or recrystallization annealing at a temperature not lower than 900 ° C, according to the invention, the temperature of the end of hot rolling is maintained in the range of 780-860 ° C, after which the strip is cooled with water to a temperature of 580-630 ° C, heating the cold-rolled strip at tzhige carried out initially at a rate of at least 500 ° C / min to a temperature of 480-520 ° C, then at a rate not exceeding 400 ° C / min to a temperature no higher than 800 ° C and completed at an arbitrary rate.

The essence of the proposed invention is as follows. During hot rolling of a high-silicon IES, inherited structural and texture parameters are laid, which significantly affect the magnetic properties of the finished metal product. At the temperature of the end of hot rolling of the strips Т _кп = 780-860 ° С and their subsequent accelerated cooling with water to the temperature Т _cm = 580-630 ° С, the carbon-containing phase of plate perlite with equiaxed recrystallized grains of 6 numbers at the strip surface and 5 numbers in the middle its sections.

The microstructure and texture of high-silicon steel formed during hot rolling has a hereditary effect on the structure and texture formation during high-speed combined decarburization-recrystallization annealing or recrystallization annealing of cold-rolled strips.

Studies have shown that the nucleation mechanism during primary recrystallization during the annealing of a high-silicon IES largely depends on the heating rates in various temperature ranges during annealing.

At heating rates of at least 500 ° C / min to a temperature of 480-520 ° C, the process of polygonization of the nuclei of new microstructure grains is suppressed. The increased silicon content makes diffusion processes difficult. This stimulates the intensive formation and growth of nuclei of new grains from the metal matrix deformed during cold rolling.

Heating at a speed of no more than 400 ° C / min to a temperature of no higher than 800 ° C prevents the development of heterogeneity and an increase in the texture of the central layers of the strip of the fraction of the unfavorable texture component {222}. Subsequently, the heating rate to a temperature of recrystallization annealing (not lower than 900 ° C) does not affect the final magnetic and mechanical properties of cold-rolled strips. Therefore, heating can be carried out at the maximum possible (based on the design parameters of the continuous furnace) speed.

It was experimentally established that with a decrease in the silicon content in the IES of less than 2.8% by weight, an increase in the specific magnetic loss index takes place. An increase in the silicon content of more than 3.8% by mass leads to the formation of anisotropic magnetic properties, which is unacceptable.

At the temperature of the end of hot rolling below 780 ° C, the grains of the microstructure of the metal matrix are unequal, which impairs the isotropy of the magnetic properties (contributes to an increase in the magnetic induction difference ΔВ ₂₅₀₀ , measured in the longitudinal and transverse directions). An increase in the temperature of the end of rolling above 860 ° C leads to the formation of an inhomogeneous microstructure along the thickness of the strips, and to a deterioration in the magnetic properties of the cold-rolled IES.

A decrease in the temperature at which cooling of hot-rolled strips ends with water below 580 ° C leads to the formation of uneven grain structure over the cross section and to a deterioration in magnetic properties. An increase in this temperature of more than 630 ° C increases the decarburization of the surface of the strips, leading to the formation of large ferrite grains. It also degrades the magnetic properties of the IES.

Recrystallization annealing of cold-rolled steel strips with a silicon content of 2.8-3.8% in a continuous furnace at a temperature below 900 ° C does not ensure the complete recrystallization process, removal of anisotropy of properties, and suppression of the deformation texture formed during cold rolling. This negatively affects the magnetic properties of the IES.

When the heating rate is less than 500 ° C / min, carried out to a temperature below 480 ° C, an undesirable process of polygonization of microstructure grains is intensified in steel with a silicon content of 2.8-3.8%, the grains acquire an uneven shape. If this heating is completed at a temperature above 520 ° C / min, the amount of the unfavorable component {222} increases in the texture. All this worsens the magnetic properties of the IES.

When the reheating rate is more than 400 ° C / min or the temperature of the end of this heating is higher than 800 ° C, the grains of the recrystallized microstructure of steel with a silicon content of 2.8-3.8% have a large variation in size: from 5 to 9 numbers, the content of favorable crystallographic decreases orientation {200}, isotropy worsens and the level of magnetic properties of the IES decreases.

Method implementation examples

In an oxygen converter, an IVP of the 4th group of alloying of the following chemical composition is smelted, wt.%:

FROM Si Mn Al P S Cr Ni Cu N 0.04 3.3 0.3 0.40 0.012 0.003 0.08 0.10 0.15 0.006

The smelted steel is subjected to continuous casting into slabs with a cross section of 250 × 1200 mm and a length of 8 m, which are annealed at a temperature of 900 ° C.

The annealed slabs are heated in a methodical furnace of a continuous broadband mill 2000 to an austenitization temperature of 1190 ° C and hot rolled into strips 2.5 mm thick. The temperature of the end of the hot rolling is maintained equal to T _kn = 820 ° C. After leaving the last stand, the strips are rapidly cooled with water on the discharge roller table to a temperature of T _cm = 600 ° C and wound into rolls.

Hot rolled strips are subjected to hydrochloric acid etching, and then rolled on a continuous four-stand mill of cold rolling quarto into 0.50 mm thick strips.

Cold-rolled strips are subjected to high-speed decarburization-recrystallization (or recrystallization) annealing in a continuous annealing unit (ANO).

During annealing, the strip transported through the ANO is first heated at a speed of V ₁ = 550 ° C / min to a temperature of T ₁ = 500 ° C. Then the strip is subjected to heating at a speed of V ₂ = 380 ° C / min to a temperature of T ₂ = 790 ° C. The final heating is carried out at a speed of 900 ° C / min to the annealing temperature T _anne = 1050 ° C.

The annealed strip is cooled in ANO by jets of nitrogen, after which an insulating coating is applied to it and the mechanical and magnetic properties are measured.

Implementation options of the proposed method for the production of IES and indicators of their effectiveness are presented in the table.

From the data in the table it follows that when implementing the proposed method (options No. 2-4) provides an increase in the magnetic properties of high-silicon isotropic electrical steel:

- minimum magnetic induction B ₂₅₀₀ = 1.51-1.54 T;

- minimal anisotropy of magnetic properties ΔВ ₂₅₀₀ = 0.03-0.04 T;

- minimum specific magnetic losses P _{1.5 / 50} = 2.50-2.73 W / kg

With exorbitant values of the declared parameters (options No. 1 and No. 5), the magnetic properties of the IES decrease. Also, lower magnetic properties are achieved in the case of the implementation of the known method of obtaining the IES [3]: ₂₅₀₀ = 1.57 T; ΔB ₂₅₀₀ = 0.07 T; P _{1.5 / 50} = 2.96 W / kg.

Table Production modes of cold-rolled IES and magnetic properties No. p / p Si,% T _CP , ° C T _cm , ° C V ₁ , ° C / min T ₁ , ° C V ₂ ° C / min T ₂ ° C T _OT , ° C B ₂₅₀₀ , T ΔВ ₂₅₀₀ , T P _{1.5 / 50} , W / kg one 2.7 770 570 490 470 410 770 890 1,58 0.06 3.76 2 2,8 780 580 500 480 390 780 900 1,54 0.04 2.65 3 3.3 820 600 550 500 380 790 1050 1.51 0,03 2,50 four 3.8 860 630 700 520 370 800 1030 1,53 0.04 2.73 5 3.9 870 640 720 530 360 820 1020 1,56 0.05 2.90

The technical and economic advantages of the proposed method consist in the fact that it ensures the formation in a high-silicon IES of the predominance of the textural component of the cubic and rib orientation, the strip has a minimum pole density of the octahedral component. The concentration of the favorable texture component {200} is maximum. The grains of the microstructure are equiaxial and correspond to 6–7 number over the entire volume of the strip. As a result of this, both high isotropy of magnetic properties and minimum specific magnetic losses are achieved simultaneously.

As a basic object in determining the technical and economic efficiency of the proposed method, the closest analogue was adopted [3]. Using the proposed method provides an increase in the profitability of the production of high-silicon isotropic electrical steel by 10-15%.

Information sources

1. RF patent No. 2147616, IPC C21D 8/12, 2000;

2. RF patent No. 2149194, IPC C21D 8/12, 2000;

3. RF patent No. 2186861, IPC C21D 8/12, 2002

Claims (1)

A method for the production of high-silicon isotropic electrical steel with a silicon content of 2.8-3.8%, including the manufacture of slabs, their heating, hot rolling, cold rolling, combined decarburization-recrystallization annealing or recrystallization annealing at a temperature of at least 900 ° C, characterized in that the temperature of the end of hot rolling is maintained in the range of 780-860 ° C, after which the strip is cooled with water to a temperature of 580-630 ° C, while the cold-rolled strip is heated during annealing first to a temperature of 480-520 ° C from at least 500 ° C / min, then to a temperature of no higher than 800 ° C with a speed of not more than 400 ° C / min, and the final heating is carried out at an arbitrary speed.