JPH0649949B2 - Method for producing grain-oriented electrical steel sheet having punching properties and metallic luster with excellent magnetic properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having a metallic luster excellent in punchability and magnetic properties.

(Prior Art) A grain-oriented electrical steel sheet is generally manufactured as follows. Si
Magnetic steel slab containing 0.4% or less of aluminum is hot-rolled, and as-rolled or after hot-rolled sheet annealing, cold rolling is performed once or twice with intervening intermediate annealing to obtain the final sheet thickness and Charcoal annealing is performed to form an oxide film containing SiO ₂ on the surface of the steel sheet, then an annealing separator containing MgO as a main component is applied and dried, and then wound on a coil, and then finish annealing is performed to have a Goss orientation. In addition to developing secondary recrystallized grains, a glass film is formed by the reaction between the SiO ₂ and MgO in order to improve the insulating property and magnetic properties. Then, if necessary, an insulating coating solution is applied, and a baking heat treatment is performed to form an insulating coating film.

The grain-oriented electrical steel sheet is used as a core material for electric devices such as generators and transformers. The iron core is usually punched with a mold or sheared to produce a large number of laminated single iron core plates. For example, manufacturing an iron core of a turbine generator requires 100,000 to 200,000 single iron core plates, depending on its capacity. It is important that these core single plates have a small punch-back, for example, 30 μm or less, in order to prevent an abnormal increase in iron loss due to an end face short circuit of the core when the core single plates are laminated. Further, it is desired that the punching back be small in order to facilitate the iron core manufacturing process.

On the grain-oriented electrical steel sheet, a glass coating or a double insulating coating of the coating and an insulating coating is formed. These insulating coatings have the effect of applying tension to the steel sheet to reduce iron loss, but, on the other hand, the glass coating is hard and therefore wears the die during punching. So, for example, a few thousand
If punching is performed twice, the punching back will be over a predetermined value, and the mold must be re-polished or replaced with a new one. This significantly lowers the workability and raises the cost.

In order to improve the punching property, a method for producing a grain-oriented electrical steel sheet in which the formation of a glass coating is suppressed has been proposed. For example, in Japanese Unexamined Patent Publication No. 53-22113, a finish annealing is performed by using a fine particle alumina mixed with a hydrous silicate mineral powder as an annealing separator with an oxide film thickness of 3 μm or less formed by decarburizing annealing. ing. Thus, a glass coating which is easily peeled off is formed on the steel sheet by the thinning of the oxide film and the above-mentioned annealing separator containing alumina as a main component to improve the punchability.

Further, in JP-A-59-96278, the reaction with the oxide film on the surface of the steel sheet is made possible by using, as an annealing separator, fine particle alumina having a grain size of 10 μm or less and inert MgO which has been burned at a high temperature of 1300 ° C. It suppresses the formation of a glass film or makes it easy to peel off to improve the punchability.

(Problems to be Solved by the Invention) According to these, there is a certain effect, the formation of the glass film on the surface of the grain-oriented electrical steel sheet is suppressed, and the punching property is improved.

However, in a production line such as hot rolling, decarburization annealing or finish annealing, for example, in the grain-oriented electrical steel sheet, the front end portion or the rear end portion of the coil may have a temperature deviation from other portions. Due to the temperature deviation and the subtle difference in the annealing atmosphere, the oxide film formed on the steel sheet surface has a difference in thickness and composition within the steel sheet position. Such a difference appears even after decarburization annealing. By the way, conventional glass film formation prevention uses the fact that alumina, which is the main component of the annealing separator, has a weak reactivity with SiO ₂ in the oxide film, and attempts to suppress the film formation or peel it as a glass film that is easy to peel. However, the punchability may not always be good due to the partial difference in the composition and thickness of the oxide film.

The present invention, even if there is a difference in the oxide film on the surface of the steel sheet due to changes in decarburization annealing conditions, etc., no glass film is formed,
An object of the present invention is to industrially stably obtain a grain-oriented electrical steel sheet which has a metallic luster over the entire surface of the steel sheet, has extremely excellent punchability, and has excellent magnetic properties.

(Means for Solving the Problem) The gist of the present invention is that a grain-oriented electrical steel sheet cold-rolled to a final sheet thickness is decarburized and annealed, and an annealing separator is applied to finish-anneal the grain-oriented electrical steel sheet. In the method for producing, a magnesia having a hydration water content of 2% or less and sulfide, polysulfide, hydroxide, chloride, nitrate, phosphoric acid of an alkali metal or an alkaline earth metal with respect to 100 parts by weight of the magnesia. salt,
A grain-oriented electrical steel sheet having a metallic luster excellent in punchability and magnetic characteristics, characterized by applying an annealing separator containing 1 to 40 parts by weight of one or more carbonates to a steel sheet and finish annealing. There is a manufacturing method.

Next, the present invention will be described in detail.

In the present invention, it is not necessary to specify the steel components and the process conditions until the decarburization annealing and the annealing separating agent are applied, and it is optional.

After the decarburization annealing is annealed finish and coated with an annealing separating agent, but as the annealing separator, and prevents the reaction of MgO in the SiO ₂ and該焼blunt separating agent in the oxide film formed in decarburization annealing the steel sheet surface On the other hand, on the other hand, in order to completely remove the impurities in the steel sheet and improve the magnetic properties, the following constitution is adopted.

The annealing separator, magnesia (MgO), has a hydration water content of 2% or less. If the amount of hydrated water is large, dew point unevenness occurs in the coil in the finish annealing atmosphere, creating gas mark-like surface unevenness and impairing the appearance. Further, grain boundary oxidation occurs and magnetic properties are deteriorated, so the content is limited to 2% or less.

MgO reacts with SiO ₂ in the oxide film and tries to form a glass film. To prevent this, Li, Na, K such as alkali metal or Ca, Ba, Mg, Sr such as alkaline earth metal sulfide, polysulfide, hydroxide, chloride, nitrate, phosphate,
One or more carbonates are blended with the annealing separator.

These compounding agents penetrate into the oxide film formed on the surface of the steel sheet and disable the reaction between SiO ₂ and MgO to prevent the formation of the glass film. In order to exert this effect,
1 part by weight or more of these compounding agents are mixed with 100 parts by weight of MgO. On the other hand, when the blending amount of these compounding agents increases,
The appearance, magnetic characteristics, or workability of the steel plate deteriorates due to the surface of the steel plate being roughened or entering the grain boundaries.
It should be less than or equal to parts by weight.

The compounding agent and the added annealing separator are applied to the decarburized and annealed steel sheet. For this application, a known method such as coating in a slurry state or electrostatic coating is adopted.

After the annealing separator is applied to the steel sheet, finish annealing is performed. On this occasion,
Partial difference in the oxide film on the surface of the steel plate Even if both sides of the steel plate are thicker than others, and even if the front and rear ends of the steel plate coil are thicker, the oxide film itself does not have the glass film forming function due to the compounding agent. Therefore, the glass coating does not occur, and the entire surface of the steel sheet becomes a metallic luster surface. Therefore, the punching property becomes extremely excellent.

When performing flattening annealing after finish annealing, an inorganic coating agent on the surface of the metallic luster steel sheet, for example, phosphoric acid, aluminum phosphate, phosphates such as magnesium phosphate, chromic acid, aluminum chromate, magnesium chromate and other chromium. 1 type of acid salt, dichromate, colloidal silica or 2
One or more seeds may be applied and flattening annealed.

After the flattening annealing, an organic coating agent such as acrylic, styrene, polyvinyl, melamine, phenol, vinyl acetate, epoxy coating agent or a semi-organic coating agent or an organic coating agent and an inorganic coating agent is applied. If a mixture of these materials is applied and baked, the punchability will be much better.

Examples will be described below.

<Example 1> C: 0.048%, Si: 3.08%, Mu: 0.062%, S: 0.024
%, The rest of the grain-oriented electrical steel sheet slab consisting of iron and unavoidable impurities was hot-rolled to a thickness of 2.3 mm, and then intermediate-annealed at 980 ° C. for 3 minutes, and then cold-rolled twice to obtain a final sheet thickness of 0.
It was 35 mm thick.

Next, 850 ° C. × 3 minutes, N ₂ + H ₂ atmosphere, PH ₂ O / PH ₂ = 0.4
After decarburization annealing under the conditions of 6, after applying the annealing separator having the composition shown in Table 1, final finishing annealing at 1200 ° C. for 20 hours was performed. This steel sheet was coated with a coating solution of Al phosphate + colloidal silica and was subjected to baking treatment also as flattening annealing. Table 2 shows the results of an examination of the appearance, punchability and magnetic properties of each of the obtained test materials.

<Example 2> The same as in Example 1, the final plate thickness was investigated by a known method.
A 30 mm cold-rolled sheet was decarburized and annealed under the conditions of N ₂ + H ₂ , PH ₂ O / PH ₂ = 0.42, and as an annealing separator, the primary layer (slurry (hydrated water content 1.5% ), A coating amount of 4 g / m ² ) and a secondary layer (non-hydrating; electrostatic coating, coating amount of 10 g / m ² ) are separately applied, and final annealing is performed at 1200 ° C. for 20 hours, and the same as in Example 1. An insulating film treatment was applied. Table 4 shows the results of an examination of the appearance, punchability and magnetic properties of each of the obtained test materials.

(Effect of the invention) As described above, according to the present invention, the grain coating is prevented, the entire surface exhibits a metallic luster, the punching property is remarkably excellent, and the grain-oriented electrical steel sheet having good magnetic properties is also subjected to decarburizing annealing conditions. It is obtained without being affected by the subtle fluctuations of.

Claims (1)

[Claims] 1. A method for producing a grain-oriented electrical steel sheet, comprising decarburizing and annealing a grain-oriented electrical steel sheet cold-rolled to a final thickness, applying an annealing separator, and finish annealing. 2% or less of magnesia and one kind of sulfide, polysulfide, hydroxide, chloride, nitrate, phosphate, carbonate of alkali metal or alkaline earth metal per 100 parts by weight of magnesia or A method for producing a grain-oriented electrical steel sheet having a punching property and a metallic luster excellent in magnetic properties, which comprises applying an annealing separator containing 1 to 40 parts by weight of two or more kinds and finishing annealing.