JP3393217B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent surface properties - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flattening annealing method for obtaining a grain-oriented electrical steel sheet having excellent surface properties. [0002] Grain-oriented electrical steel sheets are mainly used for transformers,
It is used as an iron core material for electric equipment such as power generation, and it is important that the excitation characteristics and iron loss characteristics of magnetic characteristics are good. 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 necessary, and performing one or two or more cold treatments with intermediate annealing. A cold-rolled sheet having a final thickness is obtained by rolling. Next, after decarburizing annealing, an annealing separating agent containing MgO as a main component is applied, finish annealing is performed to develop secondary recrystallized grains having a Goss orientation, and further impurities such as S and N are added. And a glass coating is produced. [0004] In the finish annealing, the coil is usually annealed in a high temperature region of 1150 ° C or higher for 20 hours, so that the coil is wound and the edge of the coil called a base plate is buckled and deformed. The amount of buckling deformation may be 30 to 80 mm in width and may span the entire length of the coil. [0005] After the finish annealing, flattening annealing is performed in the state of a strip (steel plate). This is applied with an insulating coating to increase the insulating property, and is also applied under 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 performed 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. At this time, when a leveler is applied while a foreign substance of 1 to 3 mm is on the steel sheet, not only is the steel sheet directly flawed, but also the foreign substance adheres to the leveler, is laminated, and the pressing flaw is transferred to the strip surface for shape correction. This impairs product value. Conventionally, in an annealing furnace which performs a flattening treatment, for example, a refractory having a high spalling property is used as a refractory on a ceiling of the annealing furnace so as to prevent foreign matter from falling on the upper surface of the steel sheet in order to prevent a pressing flaw on the steel sheet. Attempts have been made to put a metal plate such as stainless steel on the entire surface of the ceiling, but it has not been possible to take sufficient measures to eradicate the pressing flaw. Further, the oxygen potential (P H ₂ O /
P H ₂ ) is set to 0.4 or more and the upper limit is set to 3.0. In the atmosphere control in the annealing furnace, although the effect is obtained by suppressing the exfoliation due to the reduction of the Fe-based oxide, It was not enough. [0009] In the present invention, the oxygen potential in the flattening annealing furnace is set to 200 or more to form a Ni oxidized region and form a protective coating on the surface of the radiant tube. It is another object of the present invention to stably obtain a grain-oriented electrical steel sheet having excellent surface properties without pressing flaws by suppressing foreign matter drop accompanying oxidation suppression. The gist of the present invention is that a slab of an electromagnetic steel sheet is heated, then hot-rolled, hot-rolled or hot-rolled, and then decarburized. Thereafter, in a method for producing a grain-oriented electrical steel sheet that performs finish annealing and subsequent flattening annealing, the oxygen potential (P
It is characterized in that a grain-oriented electrical steel sheet having an excellent surface texture with H ₂ O / P H ₂ ) of 200 or more can be stably obtained. [0011] [Means for Solving the Problems] gist of the present invention, after heating the slab of magnetic steel sheets, hot rolled, remains hot rolled or hot-rolled sheet annealing, once or intermediate annealing At least twice
In the method for producing a grain- oriented electrical steel sheet in which the above cold rolling is performed, followed by decarburizing annealing, and then performing finish annealing and subsequent flattening annealing ,
Oxygen potential flattening annealing furnace used (P H ₂ O /
It is characterized in that a grain-oriented electrical steel sheet having excellent surface properties and having a PH ₂ ) of 200 or more can be stably obtained. [0012] Among these fallen foreign substances, a method of increasing the oxygen potential in the flattening annealing furnace to 200 or more and exposing Ni, which is the main component of the radiant tube, to an oxidizing atmosphere in order to reduce the peeling of the radiant tube is considered. .
Accordingly, it is considered that since a Ni oxide having a low diffusion coefficient is formed in the oxide on the outer surface of the radiant tube, the oxidation is suppressed, and thus, the fall of foreign matter is suppressed. By doing so, the conventional technique (Japanese Patent Laid-Open No. 6-25748) can be used.
Japanese Unexamined Patent Publication (Kokai) No. H11-205, the effect of suppressing foreign matter falling far outpacing the technique disclosed in Japanese Patent Application Laid-Open No. H10-216, was obtained. 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 thickness of 0.23 mm. The thickness was set. [Table 1] Next, a dew point of 65 ° C., H _{2 of} 75%, N _{2 of} 25
% For 155 seconds in an atmosphere consisting of MgO
Is applied, and finish annealing is performed by 118
This was performed at 0 ° C. × 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 baked on the steel sheet at a temperature of 850 ° C. in the atmosphere conditions shown in Table 1 in a flattening annealing furnace using a radiation tube as a heating source, and the shape of the steel sheet was corrected by a leveler. FIG. 2 and Table 2 show the surface properties of the obtained grain-oriented electrical steel sheet. [Table 2] According to the present invention, a grain-oriented electrical steel sheet having excellent surface properties can be obtained by adjusting the oxygen potential P H ₂ O / P H ₂ of the atmosphere of the flattening annealing furnace to 200 or more. Obtained stably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a flattening annealing furnace according to the present invention. FIG. 2 Oxygen potential P H in the atmosphere of a flattening annealing furnace
_{5 is} a graph showing the frequency of occurrence of press flaws when ₂ O / P H ₂ is changed. [Explanation of symbols] 2 brick 3 radiant tube 5 leveler 6 transport roll

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-25748 (JP, A) JP-A-6-93337 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/46 501 C21D 8/12 H01F 1/16

Claims (1)

(57) [Claims] [Claim 1] After heating a slab of an electromagnetic steel sheet, hot-rolling, hot-rolling or hot-rolled sheet annealing, and once or twice with intermediate annealing In the method for producing a grain-oriented electrical steel sheet in which the above cold rolling is performed, followed by decarburization annealing, and then, finish annealing and subsequent flattening annealing, the steel sheet contains Ni.
A method for producing a grain-oriented electrical steel sheet having excellent surface properties, wherein the oxygen potential (P H ₂ O / P H ₂ ) in the atmosphere of the flattening annealing using a radiant tube is 200 or more.