RU2422929C1 - Heat-resistant coating for anisotropic electro-technical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: coating includes following components, wt %: dispersed silica 75-89; magnesium oxide 10-20; colloid silica 1-3.

EFFECT: high electric resistance and maintaining magnetic properties of steel at acceptable level due to elimination of zone enriched with non-metallic inclusions in under-surface layers.

2 dwg, 2 tbl

Description

The invention relates to the production of electrical steel, more specifically to transformer steel and a heat-resistant coating on it.

The loss of electricity during magnetization reversal is determined by the degree of perfection of the crystal texture, the dispersion of the domain structure, and, not least, by the structure of the subsurface zone (1-3).

If the subsurface zone is saturated with non-metallic inclusions (such as shown in figure 1), magnetization reversal is difficult. Magnetic losses increase in proportion to the depth of the degraded zone and the development of the interface between the metal and the surface of the ceramic layer (soil layer). The main reason for the degradation of the subsurface layer is the uncontrolled interaction of the heat-resistant magnesia coating with metal, as evidenced by the composition of inclusions, represented mainly by fosterite (Mg ₂ SO ₄ ). Therefore, improving the structure of the subsurface zone is determined by the ability to control the interaction of metal and magnesia coating.

This problem was partially solved by introducing components passivating the metal surface (Sb, Cu) into steel. It is more efficient to remove fayalite (Fe ₂ SiO ₄ ) from the surface of steel formed during decarburization annealing and acting as a catalyst during the interaction of metal with a heat-resistant coating. However, the removal of fayalite is realized due to etching of the surface, which increases costs.

The closest analogue of the proposed invention is a heat-resistant coating for anisotropic electrical steel, obtained from a composition containing the following components, wt.%: Phosphoric acid 45.3-48.5, magnesium oxide 3.9-4.4, aluminum hydroxide 2.0 -2.6, boric acid 0.3-0.4, liquid complex fertilizers 5-10, water - the rest (4).

The main objective of the invention is the selection of a heat-resistant coating, in which the process of soil formation is realized only on the metal surface, which eliminates the degradation of the subsurface layer. The problem is achieved in that the heat-resistant coating for anisotropic electrical steel contains the following components, wt.%: Powdered silica 75-89, magnesium oxide 10-20, colloidal silica 1-3 in terms of SiO ₂ .

The technical result provided by the invention is to improve the quality of the heat-resistant coating by eliminating the zone enriched in non-metallic inclusions in the subsurface layers, which makes it possible to obtain a coating having high electrical resistance, which allows maintaining the magnetic properties of steel at an acceptable level.

The main component of the proposed coating composition is powdered silica, which is inert with respect to the metal, colloidal silica (silica sol) is added to stabilize the suspension, i.e. prevent its stratification, and magnesium oxide - to form a thin soil layer that does not penetrate into the metal.

The experimental results described below confirm the effectiveness of using the heat-resistant coating of the proposed composition.

For experiments, the metal was smelted in oxygen converters (composition, wt.%: Si 3.10-3.30; C 0.03-0.004; Mn 0.28-0.33; S 0.003-0.004; Cu 0.5- 0.55; Al 0.015-0.018; N ₂ 0.01-0.012; the rest is iron and inevitable impurities) and poured into slabs on continuous casting machines. Cast slabs were heated in methodological furnaces to a temperature of 1240-1260 ° C, rolled on a broadband mill into strips 2.5 mm thick. Hot rolled strips were processed according to the following scheme: etching, the first cold rolling to a thickness of 0.7 mm, decarburizing annealing, the second cold rolling to a thickness of 0.27 mm, degreasing, applying a heat-resistant coating, high-temperature annealing, straightening annealing with the application of a magnetically active insulating coating.

As a heat-resistant coating, compositions of the following composition were used (table 1).

Table 1 Cover option The content of components, wt.% magnesium oxide
MgO dispersed silica powder colloidal silica in terms of SiCO ₂ one one hundred - - 2 thirty 70 - 3 twenty 80 - 4 (corresponds to the claimed composition) twenty 77 3 5 (corresponds to the claimed composition) fifteen 83 2 6 (corresponds to the claimed composition) 10 89 one 7 5 93 2

Table 2 illustrates the differences in the level of magnetic properties and the quality of the coating when using various compositions of heat-resistant coatings.

table 2 Qualitative indicators of steel when using heat-resistant coatings of various compositions. Variant of coating composition (table 1) Magnetic properties Substrate quality characteristic B ₈₀₀ , T P _{1.7 / 50} , W / kg one 1.87 1,11 high quality soil layer 2 1.87 1.09 uneven soil 3 1.87 1,08 the suspension is stratified, the soil layer is unsatisfactory four 1.88 1,04 high quality soil layer 5 1.88 1,03 satisfactory soil layer 6 1.89 1,02 - ,, - 7 1.87 1,02 uneven soil

From the data (table 2) it follows that the use of a heat-resistant coating of the recommended composition (options 4-6) can reduce the specific magnetic loss P _{1.7 / 50} by 5-7% while maintaining the quality of the soil layer at an acceptable level, quite sufficient to obtain a high level of electrical resistance in the finished metal. A positive effect in improving the magnetic properties is achieved by eliminating the degraded layer in the subsurface zone of the strips (figure 2).

Thus, the introduction into the composition of the heat-resistant coating of silica in the form of a dispersed powder and colloid (sol) of silica allows to improve the quality of the finished metal at minimal cost.

Information sources

1. JP 2000-038615, IPC C21D 8/12, 08.02.2000.

2. US 6733599 B2, IPC C21D / 70, 10/09/2003.

3.JP 11-302731 A, 11/02/1999.

4. RU 2108634 C1, IPC H01B 3/02, 04/10/1998 (prototype).

Claims (1)

Heat-resistant coating for anisotropic electrical steel containing magnesium oxide, characterized in that it further comprises dispersed powdered silica and colloidal silica in the following ratio, wt.%:
dispersed silica powder 75 ÷ 89 magnesium oxide 10 ÷ 20 colloidal silica 1 ÷ 3

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