JP3311026B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent surface properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent surface properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron core materials for electric equipment such as transformers and generators.

[0003] Normally, grain-oriented electrical steel sheets are obtained by hot-rolling a silicon steel slab containing 2 to 4% of Si, annealing the hot-rolled sheet as needed, and performing one or two or more intermediate annealing steps. A cold-rolled sheet having a final thickness is obtained by cold rolling. Next, after performing decarburization annealing, an annealing separator containing MgO as a main component is applied,
It is manufactured by performing a finish annealing to develop secondary recrystallized grains having a Goss orientation, removing impurities such as S and N, and forming a glass coating. Further, in the flattening annealing, the coil is wound and the shape defect is corrected at the same time as the insulating coating treatment is performed.

In the finish annealing, the coil is usually annealed in a high temperature range of 1150 ° C. or more for 20 hours, so that the coil is wound and the edge of the coil in contact with a coil mounting table called a base plate. Buckles and deforms. This amount of buckling deformation may span the entire length of the coil with a width of 30-80 mm.

[0005] After the finish annealing, flattening annealing is performed in the state of a strip (steel sheet). This is applied with an insulating coating to increase the insulating properties, and is also applied with tension to improve the iron loss of the electromagnetic steel sheet. . Another function of the flattening annealing is to correct the deformation of the coil caused by the finish annealing described above.

[0006] Deformation correction is carried out in a temperature range of 700 to 900 ° C at a plate temperature by applying pressure to a strip called a leveler by vertically sandwiching the strip. If a leveler is applied while foreign matter is on the steel sheet, not only will the steel sheet be directly scratched, but also the foreign matter will adhere to and stack on the leveler and transfer a few μm to several tens of μm pressing flaws to the strip surface for shape correction. , Impairing the product value.

[0007]

The annealing furnace for performing the flattening treatment is designed to prevent foreign matter from falling on the upper surface of the strip in order to prevent the strip (steel plate) from being flawed. Strong ones have been constructed. Attempts have been made to put a metal plate such as stainless steel over the entire ceiling, but this was not a sufficient measure and could not eliminate the pressing flaw.

In view of such a conventional problem, the present invention provides a flattening annealing in which the partial pressure ratio P of moisture and hydrogen in the atmosphere gas is increased.
By optimizing H ₂ O / P H ₂ , there is no pressing flaw,
It is another object of the present invention to stably obtain a grain-oriented electrical steel sheet having a good glass coating and excellent surface properties.

[0009]

The gist of the present invention is that a slab of electromagnetic steel is heated and then hot-rolled, and hot-rolled or hot-rolled sheet is annealed, and a single or intermediate annealing is performed. Cold rolling more than once, then decarburizing annealing, or forming an inhibitor by nitriding treatment subsequent to decarburizing annealing, then, in the method of manufacturing a grain-oriented electrical steel sheet performing finish annealing and subsequent flattening annealing, H in atmosphere of flattening annealing
_A grain-oriented electrical steel sheet having excellent surface properties, characterized in that the partial pressure ratio (P H ₂ O / P H ₂ ) between ₂ O and H ₂ is 0.78 or more and the upper limit is 3.0. In the manufacturing method.

Hereinafter, the present invention will be described in detail. Normally, flattening annealing is performed by using H ₂ to secure a weak reducing atmosphere.
Annealing is performed in an atmosphere gas condition consisting of 5% and the remainder of N ₂ .

In order to maintain this atmosphere, the heating source is as follows:
Indirect heating is performed by a radiation tube called a radiant tube. In order to investigate the source of press flaws in flattening annealing, after periodically stopping the furnace for inspection and repair of the annealing furnace equipment, the press flaws on the steel sheet immediately after restarting the annealing furnace Investigation of the frequency of occurrence showed that the frequency of occurrence of press flaws tended to increase over time as shown in FIG.

When the dew point in the furnace at that time was examined,
As shown in FIG. 1, it was found that the dew point in the furnace decreased. Next, in order to grasp the relationship between the dew point in the furnace and the occurrence of pressing flaws, the relationship between the surface properties (scratch and appearance) of the steel sheet was investigated by actively changing the atmosphere dew point in the furnace.

When P H ₂ O / P H ₂ was 0.78 or more, it was found that almost no pressing flaw was generated. Also P H ₂ O / P H
₂ is made when the steel plate is oxidized than 3.0, it was found that not be 3.0 operate in super to begin to discolor.

Next, P H ₂ O / P H ₂ is reduced to less than 0.78 ,
Pull the leveler out of the furnace with many pressing flaws,
When the substance attached to the leveler was examined, it was a substance containing Fe as a main component.

[0015] From these facts, the oxide of Fe, which is a part of the material of the radiant tube used as a heating source, is reduced and peels off, falls on a steel plate, and causes a pressing flaw at a leveler. It is possible that

When a laboratory experiment was performed based on this estimation,
It was confirmed that the Fe oxide was reduced and peeled off in the radiant tube where the PH ₂ O / P H ₂ was less than 0.78 .

By keeping the composition of the atmosphere gas in the range of 3.0 ≧ (P H ₂ O / P H ₂ ) ≧ 0.78 in such flattening annealing, no press flaws are generated and the coating film A grain-oriented electrical steel sheet with excellent appearance can be obtained.

[0018]

EXAMPLE A slab having the composition shown in Table 1 was heated under the conditions shown in the table, hot-rolled to a thickness of 1.6 mm, and the hot-rolled sheet was cold-rolled to a sheet thickness of 0.23 mm. did.

Next, dew point 65 ° C., H ₂ 75%, N ₂ 25%
For 155 seconds in an atmosphere consisting of Further, depending on the treatment, 750 ° C. × 30 seconds, H ₂ 75%, N ₂
Nitriding was performed with NH _{3 in} an atmosphere of 25% and a dew point of −15 ° C.

Then, an annealing separator containing MgO as a main component was applied and finish annealing was performed at 1180 ° C. for 20 hours.

Next, after unwinding the coil, an insulating coating solution containing chromium phosphate as a main component was applied in a strip state, and then dried in a drying oven. Subsequently, the coating was applied to the steel sheet by a flattening annealing furnace using a radiation tube as a heating source.
Baking was performed at a temperature of 0 ° C. under the atmospheric conditions shown in Table 1, and the shape of the steel sheet was corrected by a leveler. Table 2 shows the surface properties of the obtained grain-oriented electrical steel sheet.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

According to the present invention, by appropriately adjusting the partial pressure P H ₂ O / P H ₂ of the atmosphere of the flattening annealing furnace, a grain-oriented electrical steel sheet having excellent surface properties can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a table showing the frequency of occurrence of press flaws over time in a flattening annealing furnace and changes in the dew point in the furnace.

(56) References JP-A-62-36803 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/46 501 C21D 1/26 C21D 8/12

Claims (1)

(57) [Claims] 1. A slab of magnetic steel sheet is heated and then hot-rolled, hot-rolled or hot-rolled sheet is annealed, cold-rolled one or more times with intermediate annealing interposed, and then cold-rolled. In a method for producing a grain-oriented electrical steel sheet in which an inhibitor is formed by decarburizing annealing or nitriding treatment subsequent to decarburizing annealing, and then performing finish annealing and subsequent flattening annealing, H ₂ O in an atmosphere of flattening annealing is used. H ₂ partial pressure ratio (P H ₂ O / P
A method for producing a grain-oriented electrical steel sheet having excellent surface properties, wherein H ₂ ) is 0.78 or more and the upper limit is 3.0.