RU2427654C1 - Procedure for production of isotropic electro-technical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel is melted and tapped, slabs are heated and strips are hot rolled. If necessary, hot rolled strips are normalised. Further, strips are etched, cold rolled and subjected to combined decarbonisation-re-crystallisation or to re-crystallisation annealing. Also, strips are cold rolled at summary reduction of 60-80 %. Cold-rolled strip is heated at annealing at rate not less, than 500°C/min forming texture in strip with concentration of crystallographic orientation of type {200} not less, than 30 %.

EFFECT: reduced specific magnetic losses and increased output of accepted product.

2 cl, 1 ex, 1 tbl

Description

The invention relates to the field of metallurgy, in particular to the production of cold-rolled sheet isotropic electrical (dynamo) steel for magnetic circuits of electrical machines.

A known method for the production of sheet isotropic electrical steel, including smelting, continuous casting, hot rolling, normalization of hot rolled steel, cold rolling in several stages and recrystallization annealing of cold rolled strips, the penultimate stage of cold rolling is carried out with compression of 20-50% in rolls with a surface roughness Ra = 1.0-4.0 μm, and the latter with a compression of 12-35% in rolls with a surface roughness Ra = 0.16-0.63 μm (Auth. Certificate. USSR No. 1710587, IPC C21D 8/12, 1992 g.).

The disadvantages of this method are that the cold-rolled dynamo steel has a high specific magnetic loss with a low yield.

The closest analogue to the present invention is a method for the production of isotropic electrical steel sheet, including steel smelting, hot rolling, normalization annealing, pickling, cold rolling and decarburization-recrystallization annealing, according to which the temperature of decarburization-recrystallization annealing is determined based on the content of silicon and aluminum in the steel (RF patent No. 2186861, IPC C21D 8/12, 2002).

The disadvantages of this method are that the texture of the finished sheet steel formed during cold rolling and annealing contains a large proportion of the unfavorable texture component {222} <UVW>. As a result, the specific magnetic losses expressed by the value of P _{1.5 / 50} [W / kg] increase, and the yield decreases.

The technical result achieved by the invention is to reduce specific magnetic losses and increase yield.

To achieve this technical result in a known method for the production of isotropic electrical steel, including smelting, casting steel, heating slabs, hot rolling strips, normalizing hot rolled strips or without it, etching, cold rolling, combined decarburization-recrystallization annealing or recrystallization annealing, according to the invention, a texture is formed in the strip with a concentration of crystallographic orientation of type {200} of at least 30%. In addition, the total reduction during cold rolling is set to 60-80%, and the cold-rolled strip is heated during annealing at a speed of at least 500 ° C / min.

The invention consists in the following. To obtain high electromagnetic and mechanical properties, it is necessary to maximize the cubic component of the texture in sheet steel by optimizing the modes of cold rolling and recrystallization annealing. This is achieved by increasing to at least 30% the fraction of the texture component with a crystallographic orientation of the {200} type while reducing the fraction of the unfavorable component {222}.

The formation of a texture with a concentration of crystallographic orientation of the type {200} of at least 30% while maintaining high mechanical properties is ensured by technologically regulated modes of deformation-heat treatment of the strip.

The occurrence of primary recrystallization nuclei in the cold-rolled strip during heating during annealing occurs sequentially in two stages. At the first stage of heating in the low-temperature region, starting at the beginning of the recrystallization process, the formation of a polygonal structure takes place. The long-term presence of the strip in the low-temperature region of recrystallization leads to the unification of individual polygons, which is undesirable, because in annealed steel, the component composition of the {222} type of cold-rolled strip is inherited. In this case, nuclei formed at a lower temperature in the first stage, when heated to the temperature of the onset of primary recrystallization, gain an advantage in growth.

At the second stage of heating (in the high-temperature region), recrystallization proceeds due to the formation and growth of new grain nuclei in a deformed metal matrix. The implementation of this recrystallization mechanism, carried out at a higher temperature, leads to a change in the texture composition component with the formation of the {200} component.

Studies have shown that the nucleation mechanism at the first stage of recrystallization depends both on the degree of total reduction during cold rolling and on the heating rate during annealing. When the degree of total compression of the strip during cold rolling is 60-80% and the heating rate is at least 500 ° C / min, both high mechanical properties and complete suppression of the union of polygons during the recrystallization process, a decrease in the fraction of crystallographic orientation {222} and an increase in the fraction of favorable crystallographic orientation are achieved {200} to at least 30%.

This was confirmed by the results of experimental studies. Thus, an increase in the heating rate of cold-rolled metal from 300-450 ° C / min to 500-800 ° C / min led to an increase in the fraction of the {200} component in the strip rolled with a total relative compression of 60-80%, from 22% to 30- 40% In this case, the fraction of component {222} decreased from 40% to 20-23%. The grain size after annealing at different heating rates differed slightly.

It was experimentally established that a decrease in the concentration of crystallographic orientation of the {200} type in the cold-rolled strip led to an increase in the increase in specific magnetic losses, deterioration of mechanical properties and a decrease in the yield for both hot-rolled strips subjected to normalization and without it, as well as for cases of decarburizing recrystallization annealing, and recrystallization annealing of cold-rolled strips with initially low carbon content.

A decrease in the total relative reduction of less than 60% slowed down the recrystallization process and led to a partial polygonization of the microstructure, which increased the specific magnetic losses and reduced the strength properties and yield. At the same time, a decrease in the heating rate during annealing of less than 500 ° C / min, as well as an increase in the total relative compression of more than 80%, increased the residence time of cold-rolled strips at low temperatures during heating. It also increased the specific magnetic loss, reduced the strength properties and yield.

The proposed method can be applied in the production of both a fully finished (fully-process) and semi-finished (isotropic) sheet of isotropic electrical steel, regardless of the presence in the technological scheme of normalized annealing of hot rolled strips, as well as when combined decarburization-recrystallization annealing of steel with increased carbon, and during recrystallization annealing of steel with a low carbon content.

Method implementation examples

In an oxygen converter, smelting of electrical isotropic (dynamo) steel of the 2nd alloying group was carried out with a carbon content of 0.03-0.06%, silicon 1.3-1.4%, aluminum 0.30-0.60%, manganese 0 , 2-0.3%, phosphorus 0.02%, sulfur 0.003%. Steel was poured into slabs, which were subjected to hot rolling on a continuous broadband mill 2000 in strips with a thickness of H = 2.5 mm. The temperature of the end of the rolling support in the range of T _KP = 990 ± 30 ° C. The rolled strips were rapidly cooled by water to a winding temperature T _cm = 650 ± 30 ° C. Those hot-rolled strips for which the actual values of T _cp and T _cm were beyond the specified limits were subjected to normalization in a continuous furnace at a temperature of 870 ° C.

Then the hot rolled strips were subjected to etching and cold rolling on a continuous 5-stand mill 1400 to a final thickness h = 0.6 mm with a total relative compression ε equal to:

Cold-rolled strips with a carbon content of more than 0.04% were subjected to high-speed decarburization-recrystallization annealing in a continuous furnace by heating at a speed of V = 600 ° C / min to a temperature of T = 910 ° C, and cold-rolled strips with a carbon content of 0.04% or less recrystallization annealing in a continuous furnace also by heating at a speed of V = 600 ° C / min to a temperature of T = 910 ° C.

The concentration of crystallographic orientations (the fraction of components {200} and {222}) and the specific magnetic loss P _{1.5 / 50} were determined on samples of finished electrical isotropic steel. According to the results of the sorting of metal products, the yield was estimated.

Implementation options for the production method of sheet isotropic electrical steel are given in the table.

Table Modes of production of isotropic electrical steel and indicators of their effectiveness Option No. ε,% V, ° C / min Share of component {200},% Share of component {222},% P _{1,5 / 50} , W / kg Yield,% one 58 495 22 40 4.72 80.1 2 60 500 thirty 23 3.92 99.5 3 76 600 33 22 3.91 99.6 four 80 700 40 twenty 3.90 99.7 5 82 800 twenty 42 5.20 77.6

From the data given in the table, it follows that when using the proposed method (options No. 2-4), the specific magnetic losses P _{1.5 / 50 are} reduced with a maximum yield of sheet isotropic electrical (dynamical) steel. In the case of transcendental values of the declared parameters (options No. 1 and No. 5), there is an increase in the specific magnetic loss and a decrease in the yield.

The technical and economic advantages of the proposed method consist in the fact that the formation of a texture strip with a concentration of favorable crystallographic orientation {200} of at least 30%, formed during cold rolling of strips with a total relative compression of at least 70% and heating to a temperature of recrystallization annealing at a rate of less than 500 ° C / min, allows to suppress the polygonization process and reduce the concentration of the unfavorable component {222}. Due to this, the specific magnetic losses are reduced, the yield of metal products increases.

As a basic object in determining the technical and economic advantages of the proposed method adopted the prototype method. Using the proposed technology will increase the profitability of the production of dynamo sheet by 20-26%.

Claims (2)

1. A method of manufacturing a strip of isotropic electrical steel, including smelting, casting steel, heating slabs, hot rolling of strips, if necessary, normalizing hot rolled strips, etching, cold rolling and annealing of a cold rolled strip, characterized in that cold rolling is carried out with a total reduction equal to 60-80%, and the cold-rolled strip is heated during annealing at a rate of at least 500 ° C / min with the formation in the strip of texture with a concentration of crystallographic orientation of type {200} of at least 30%. 2. The method according to claim 1, characterized in that decarburization-recrystallization or recrystallization annealing of the cold-rolled strip is carried out.