JPS6050117A - Method for annealing hot rolled coil of nonoriented electrical steel - Google Patents

Abstract

PURPOSE:To homogenize the steel structures of the inside, outside and intermediate parts of a hot rolled coil and to stabilize the magnetic characteristics by preheating a heating furnace to a temp. which is above the desired annealing temp. by a specified temp. or below, putting the hot rolled coil in the furnace, and changing the set temp. of the furnace to the annealing temp. or below. CONSTITUTION:A nonoriented electrical steel slab is hot rolled and coiled at >=750 deg.C. This hot rolled coil is put in a heating furnace at one, and the hot rolled plate is annealed by making use of its potential heat. At this time, the heating furnace is preheated to a temp. which is above the desired annealing temp. by <=100 deg.C, and after putting the hot roller coil, the set temp. of the furnace is changed to the annealing temp. or below.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing non-oriented electrical steel sheets.

More specifically, the present invention relates to a method of annealing a non-oriented electrical steel hot-rolled coil after hot rolling.

Non-oriented electrical steel sheets are used for cores of electrical equipment such as electric motors, generators, and small transformers. Non-oriented electrical steel sheets are S9 to 860 according to JIS standards (C2552, 2554).
As shown in the classification, there is a wide range from high-grade to low-grade materials, and materials of 814 or lower are usually treated as high-grade materials.

By the way, it is necessary for non-oriented electrical steel sheets to have low iron loss values, and this demand has recently become stronger in the electrical industry, and steel sheet manufacturers are working to improve iron loss values for all grades, from high-end to low-grade products. .

(Prior art) As one means of achieving this, hot-rolled sheet annealing is performed according to the grade size or Si content.In hot-rolled sheet annealing, the hot-rolled and wound-up coil is left to cool, and then the coil is heated in an annealing furnace. The annealing process is performed by heating the coil at a predetermined temperature, but in recent years, where there is a strong demand for energy conservation, it is possible to heat the coil by winding it at a high temperature during hot rolling or by using the heat retained in the hot rolled coil. Attempts have been made to perform sheet rolling annealing.

For example, a slab of non-oriented electrical steel is hot-rolled at 850 to 1000°C, rolled up at a temperature of 750°C or higher, and self-annealed using the heat possessed by the non-oriented electrical steel hot-rolled film (hereinafter referred to as hot-rolled coil). Alternatively, a method has been proposed in which the hot-rolled coil is charged into a heat retention furnace or a heating furnace, and a slight amount of heat is added to the retained heat to anneal the coil.

These methods have advantages such as not only energy saving but also somewhat improved pickling properties compared to conventional hot rolled sheet annealing. However, on the other hand, hot-rolled carp/l'! Since the coil is wound up through the segments, heat is removed from the inside of the coil by the segments. Even after the first segment is removed, the temperature on the outside of the coil and the inside of the coil tends to drop more than in the middle of the coil, resulting in a temperature deviation. Although this temperature deviation can be considerably reduced by the action of the heat retention furnace and heating furnace, there are the following problems.

That is, when the hot-rolled sheet is annealed by applying additional heat while utilizing the heat retained in the hot-rolled coil.

Although the inner and outer portions of the coil are heated to reduce the temperature deviation, coarsening of crystal grains may occur locally in the middle portion of the coil. This causes variations in the magnetic properties of product sheets produced by subsequent cold rolling and annealing, and needs to be improved.

[Purpose of the invention]

The purpose of the present invention is to homogenize the steel structure in the inner, outer, and intermediate parts of the hot-rolled coil in hot-rolled plate annealing using the heat retained in the hot-rolled coil, thereby making the magnetic properties of the product plate more stable. There is.

(Structure and operation of the invention) The gist is that a non-oriented electromagnetic steel slab is hot rolled and
When the hot-rolled coil is coiled at a temperature of ℃ or higher and immediately charged into the heating furnace and the retained heat is used to annealing the hot-rolled sheet, the heating furnace is heated up to 100℃ higher than the desired hot-rolled sheet annealing temperature in advance. A method for annealing a hot-rolled coil of non-oriented electrical steel, which is characterized by preheating and changing the set temperature to a desired annealing temperature or lower after the hot-rolled coil is inserted.

A detailed description of the invention follows.

First, the raw material steel slab of the non-oriented electrical steel sheet applied to the present invention is Sl depending on the grade of the intended product.

Added At, etc., and Si content is 4.0% or less.

St is added in a range of 2.0% or less. Further, in order to improve the magnetic properties, Sn and B + M4 may be added. C is harmful to magnetic properties and is controlled to be 0.06% or less, for example, in order to shorten decarburization annealing after cold rolling. S, 0. It is preferable to have fewer unavoidable components such as N.

Slabs are melted in a converter, electric furnace, etc., and manufactured by continuous casting or ingot formation and blooming rolling. The slab is then heated and hot rolled. Although the finishing temperature does not need to be specified, it is 850 to 1000°C. Winding is performed at a temperature of 750° C. or higher.

The reason for this is that when the winding temperature becomes lower, the heat retained in the hot rolled coil after winding decreases, and its utilization becomes less effective, so winding is performed at a temperature of 750° C. or higher.

Although the upper limit does not have to be strictly defined, it is set at 950° C. from the viewpoint of preventing deterioration of pickling properties.

The hot-rolled coil is immediately charged into the heating furnace. At this time, the heating furnace is preheated to a temperature within 100° C. higher than the desired hot-rolled sheet annealing temperature, for example, 780° to 900°.

A hot-rolled coil is charged into the heating furnace. After charging, the set temperature is changed to a desired hot-rolled sheet annealing temperature or a temperature lower than that L.

The reason why the heating furnace is preheated to within 100°C above the desired hot-rolled sheet annealing temperature is to rapidly raise the temperature of the inside and outside of the hot-rolled coil in cooperation with the heat possessed by the hot-rolled coil itself. This is to make the steel structure of all the hot-rolled coils homogeneous. If preheating is performed at a temperature higher than this temperature, coarse grains will locally occur in the hot rolled coil, which is not desirable.

According to the present invention, there are further effects as described below. In other words, when hot-rolling, winding into a hot-rolled coil, and then charging it into a heating furnace, although it is said that the process is carried out directly, it actually takes about 5 to 5 hours for operations such as rolling and transportation.
It physically takes 15 minutes. During this time, the hot rolled coil is inside (
Since the heat dissipation in the outside part is much larger than that in the middle part, the temperature in these parts drops significantly, but this part is very quickly reheated due to the preheating temperature and the heat retained in the hot-rolled coil. , the heating furnace can then change the set temperature to the desired hot-rolled plate annealing temperature or lower.
No coarsening of crystal grains occurs in the middle part of the hot-rolled coil.

Therefore, hot-rolled sheet annealing is completed in a short time, and furthermore, when the product sheet is produced, the variation in magnetic properties is extremely reduced.

After hot-rolled sheet annealing, the sheet is descaled and then cold-rolled.

If necessary, it is cold rolled two or more times with annealing in between,
It is then annealed. The steps after this hot-rolled sheet annealing are as usual.

(Example〕 Next, an example will be described.

C: 0. O05 Section, 8i: 1.0%, AA: 0.020
blood.

Mn: 0.20%, S: O, 001%, 1': 0.
Hot rolling a continuously cast electromagnetic steel slab containing 0.020%
The thickness of the board was that of Qi. The finishing temperature at this time was 930°C, and the film was rolled up at 820°C. The hot-rolled coil was immediately charged into a heating furnace, which had been preheated to the temperatures shown in Table 1.

Note that the desired hot-rolled sheet annealing temperature is 800°C.

Those whose heating temperature was lower than the above-mentioned 800°C were annealed by heating to the above-mentioned temperature. After that, it is pickled and the plate thickness is 0.3
It was cold rolled to a thickness of 5+ nm, annealed at 1000° C. for about 1 minute, and its magnetic properties were measured. The results are also shown in Table 1.

Claims (1)

[Claims] A non-oriented electrical steel slab is hot-rolled and wound at a temperature of 750°C or higher, and the hot-rolled coil is immediately charged into a heating furnace and the retained heat is used to annealing the hot-rolled sheet. Preheating to a temperature within 100°C higher than the desired hot-rolled sheet annealing temperature,
Hot-rolled coil annealing method of electrical steel charged with hot-rolled coil.