JPH07252531A - Production of grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To stably produce a grain oriented silicon steel sheet having high magnetic flux density at a low cost by executing, in order, a hot-rolling, cold- rolling, heating-decarburization, nitriding treatment and finish annealing under the specific conditions to a silicon steel slab having a specific composition. CONSTITUTION:Rougher-rolling is executed in the starting temp. range of 1000-1200 deg.C to the silicon steel slab containing, by wt, 0.025-0.060% C, 2.0-4.5% Si, 0.010-0.080% acid soluble Al, 0.001-0.020% N, 0.0020-0.030% S and the balance Fe with inevitable impurities, and successively, the finish-rolling is executed. After heating the hot-rolled steel sheet obtd. by this hot-rolling in the range of 700-900 deg.C for 1-300sec, immediately, this steel sheet is cooled at quicker cooling velocity than the air-cooling and, thereafter, the steel sheet is made to be a prescribed thickness by single time cold-rolling. Successively, after heating-decarburizing in the range of 800-950 deg.C for 200-300sec, the nitriding treatment is executed while running the steel sheet, and further, anneal- separating agent is coated to apply the finish-annealing. By this method, the electrical steel sheet having excellent magnetic characteristic is obtd. by the simple annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet (hereinafter referred to as grain-oriented electrical steel sheet).

[0002]

2. Description of the Related Art In a method for manufacturing a grain-oriented electrical steel sheet (hereinafter referred to as TS method) in which a single cold rolling is performed to a product thickness, hot-rolled sheet annealing is performed by Japanese Patent Publication No. 46-23820.
As disclosed in JP-A-50-15727,
After heating to a high temperature at which the γ phase is considered to be most formed, secondary soaking is performed or controlled cooling is performed without secondary soaking. The present invention relates to a method (hereinafter referred to as SL method) for manufacturing by a method of continuously nitriding after primary recrystallization, among the manufacturing techniques of grain-oriented electrical steel sheet having a product thickness by this one cold rolling. However, even in this technique, Japanese Unexamined Patent Publication No. 259090/1990 and Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent No. 25446, the hot-rolled sheet annealing is controlled cooling after being subjected to primary soaking at 900 ° C. or 950 ° C. or higher and secondary soaking at a temperature lower than the primary soaking. The present invention provides a technique for stably and inexpensively manufacturing a grain-oriented electrical steel sheet having a remarkably high magnetic flux density by performing hot rolled sheet annealing in which the controlled cooling is performed immediately after the low temperature primary soaking in the SL method. .

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a method for stably manufacturing a grain-oriented electrical steel sheet at a low cost by simplifying the hot-rolled sheet annealing step.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is C:
0.025-0.060% by weight, Si: 2.0-4.5
% By weight, acid-soluble Al: 0.010 to 0.080% by weight, N: 0.001 to 0.020% by weight, S: 0.00
A silicon steel slab containing 20 to 0.030% by weight of components and the balance of Fe and unavoidable impurities is rough-rolled in a temperature range of 1000 ° C to 1200 ° C, and then finish-rolled, preferably 500 ° C. After winding at the following temperature, the hot-rolled steel strip is heated at a temperature of 700 ° C. or more and 900 ° C. or less for 1 second or more and 300 seconds or less, cooled at a cooling rate faster than air cooling, and then predetermined by one cold rolling. Thickness of 800 ℃
After heating and decarburizing in a temperature range of from 950 ° C. to 950 ° C. for 20 seconds to 300 seconds, a nitriding treatment is performed while the steel sheet is allowed to travel, an annealing separator is applied, and a final annealing is performed.

The present invention will be described in detail below. SL
Regarding the metallurgical reason for performing hot-rolled sheet annealing by heating in a two-step manner at a temperature of 900 ° C. or higher in the method, it is stated that the texture and texture of the primary recrystallized sheet are arranged so that secondary recrystallization is easily exhibited. Especially when the primary soaking temperature is lower than 900 ° C, the recrystallization of the hot-rolled sheet annealing is insufficient and the magnetic properties B of the final product B
₈ is 1.9 T or less, and it is said that grain-oriented electrical steel sheets with high magnetic flux density cannot be produced. However, the inventor
0) As a result of metallurgical studies on the metallurgical principle of [001] secondary recrystallization manifestation and each process condition in the SL method, in the hot-rolled sheet annealing step, the texture is almost independent of the hot-rolled sheet annealing temperature. It was found that there was no change, and that the crystal structure did not change when the surface phase was removed. It is considered that this is because recrystallization in the hot-rolled sheet process corresponds to what is called recrystallization in that case, and new nucleation and growth are hardly observed. In other words, it can be said that in the hot-rolled sheet annealing, the dislocation density mainly decreases from the crystal grains with high strain, only recovery occurs, and no remarkable grain boundary migration occurs.

By the way, the structure and texture of the primary recrystallized sheet are the morphology of the second phase existing after hot-rolled sheet annealing and the solid solution C, N.
It is well known that the amount of abundance changes significantly. In the case of the steel of the present invention, the gamma phase exists in equilibrium at about 700 ° C. or higher, so that the hot-rolled sheet annealing temperature is maintained within the range of 700 ° C. to 900 ° C. shown in the range of the present invention, and then controlled cooling is performed. If it is carried out, it is possible to make the solid solution C, N and the second phase into a primary recrystallized plate which is advantageous for the development of secondary recrystallization before cold rolling. Therefore, it can be said that the presence or absence of recrystallization in the hot-rolled sheet referred to in the prior invention is not directly related to the secondary recrystallization.

In the present invention, the hot rolling coiling temperature is 500
C. or less is preferable. When such low temperature winding is performed,
The second phase is likely to form when reheated to 700 ° C or higher and then rapidly cooled, whereas when wound at 500 ° C or higher, decomposition into α and carbide progresses sufficiently in the state of the hot rolled sheet, so comparison at high temperature It is difficult to form the second phase unless controlled cooling is performed after reheating for an extremely long time. Therefore, the lower the hot rolling temperature is, the more preferable.

The lower limit of the heating temperature is set to 700 ° C. because the primary recrystallized plate which meets the purpose cannot be obtained at a temperature lower than this. The upper limit of the heating temperature is set to 900 ° C or less, because when heating at a higher temperature than this, secondary soaking is necessary to develop highly integrated secondary recrystallization, which is not economical, so 900 ° C or less And Heating time 1 second or more 3
It is within this range that (00) [0]
01] It is because a primary recrystallized plate that is advantageous for developing secondary recrystallization can be obtained. It is effective even if the heating time exceeds 300 seconds,
Since it is thermally uneconomical, the upper limit of the heating time was set to 300 seconds. If the time is less than 1 second, the effect is insufficient.

If the hot-rolled sheet is annealed in the above range and cold-rolled and then primary recrystallization is performed, a primary recrystallized plate that meets the purpose is obtained. In this case, the reason why the primary recrystallization temperature is set to 800 ° C. or higher is that even if the primary recrystallization is performed at a temperature lower than this temperature, (110) [001] secondary recrystallization having a high degree of integration does not occur, and the temperature is 950 ° C. The reason for setting below is that if recrystallization is carried out at a temperature higher than this, secondary recrystallization often does not occur. If the heating time is less than 20 seconds, decarburization is insufficient and heating for more than 300 seconds has no effect. Therefore, the heating time was set to 20 seconds or more and 300 seconds or less.

In order to preferentially recrystallize only the (110) [001] orientation from the primary recrystallized plate thus formed, growth of other crystal grains is suppressed and (110)
An inhibitor for growing preferentially only [001] oriented grains is necessary, and for this purpose, nitriding treatment is continuously performed after primary recrystallization annealing. It is extremely important to control the nitriding amount at this time, and it is preferable to set the nitrogen analysis value to 300 ppm or more and 1500 ppm or less. When the nitrogen analysis value after the nitriding treatment is less than 300 ppm or more than 1500 ppm, even if the secondary recrystallization occurs, the magnetic flux density is low or the secondary recrystallization partially develops and becomes unstable.

The reason for this is that the secondary recrystallization temperature changes depending on the amount of nitrogen. When the amount of nitriding is small and secondary recrystallization occurs at low temperature, the magnetic flux density is low, and the amount of nitriding is too large to cause secondary recrystallization. This is because when the recrystallization temperature is too high, the magnetic flux density becomes low when the secondary recrystallization appears, or the secondary recrystallization only partially develops. In the case of performing the conventional two-stage uniform hot-rolled sheet annealing by the SL method, if the amount of nitrogen is set to about 200 ppm to 300 ppm, secondary recrystallization with a high magnetic flux density appears, but the hot-rolled sheet of the present invention method In the case of annealing, it is necessary to increase the amount of nitriding in order to develop secondary recrystallization having a high magnetic flux density. Increasing the nitriding amount in the nitriding process hardly affects the cost, so increasing the nitriding amount does not impair the merit of simplifying the hot-rolled sheet annealing process of the present invention.

The reason why the other conditions are limited will be briefly described below. When processed according to the method of the present invention, C is 0.025.
If it is less than 0.1%, secondary recrystallization with a high magnetic flux density can be obtained, but the secondary recrystallization grain size that develops becomes large, and as a result, iron loss may be poor, so it was made 0.025% or more. Also 0.0
Even if C exceeds 6%, secondary recrystallization with high magnetic flux density appears, but even if C is increased beyond this, improvement in magnetic properties is not seen and decarburization time becomes long, which is not preferable. Below.

Next, S is limited to the range of 0.002 to 0.030% because S in the material component of the present invention is 0.0
If it is less than 02%, secondary recrystallized grains deviating from (110) [001] are more likely to occur. The more S, the more effective the secondary recrystallization is. However, when S is large, cracking occurs in the hot rolling process. Therefore, the upper limit is set to 0.030% in the present invention. As the Si content increases, the specific resistance increases and the eddy current loss of the product decreases. Therefore, the more Si the better, in order to reduce the eddy current loss. The reason why Si is limited to 2% or more is that the lower limit is 2% because eddy current loss is large and it is not preferable if Si is less than this. However, Si becomes more likely to crack in the cold rolling process as the added amount increases. If the Si content exceeds 4.5%, the upper limit is set to 4.5% because the cold rolling requires a special device and the purpose of the present invention is to economically manufacture.

Al forms (Al, Si) N and acts as an inhibitor, but the effect is not exhibited unless the content of acid-soluble Al is 0.01% or more, so the lower limit was made 0.01%. The upper limit is set to 0.08% because if it exceeds this amount, it will not work effectively as an inhibitor. N forms (Al, Si) N and acts as an inhibitor, but the effect is not exhibited unless it is 0.001% or more at the slab stage, so the lower limit was made 0.001%. The upper limit is set to 0.02% because if it is contained more than this, surface scratches called blister occur.

If the hot rolling start temperature exceeds 1200 ° C., the secondary recrystallization becomes unstable with the components of the present invention, the secondary recrystallization becomes stable, and the probability that the magnetic flux density of the product will be 1.80 Tesla or less increases. Therefore, the temperature was set to 1200 ° C. or lower. Good magnetic properties can be obtained even when the crude hot rolling start temperature is less than 1000 ° C., but a lot of energy required for hot rolling is required and it is not economical because the surface of the steel sheet is easily scratched during hot rolling.
The crude hot rolling start temperature was set to 1000 ° C or higher.

The atmosphere of finish annealing may be the same as that of the conventional finish annealing of grain-oriented electrical steel sheet. However, when annealing is performed in an atmosphere of nitrogen of 90% or more, preferably 95% or more in the finish annealing temperature rising process, stable and good magnetic characteristics can be obtained. In this case, it is preferable to set such an atmosphere in a region of 800 ° C. or higher in the temperature rising process of finish annealing. In this case, the reason for limiting the temperature to 800 ° C. or higher is that if the amount of nitrogen is remarkably increased at a temperature lower than this temperature, the steel sheet may be oxidized due to the influence of moisture in the annealing separator, and a good film may not be formed.

[0017]

【Example】

Example 1 C: 0.034%, Si: 3.27%, Mn: 0.09
8%, P: 0.026%, Al: 0.026%, S:
0.0070%, Cr: 0.118%, Cu: 0.01
A slab containing 1%, Sn: 0.052%, and N: 0.0070% as main components was heated at a temperature of 1100 ° C. for 2 hours, then rough-rolled, finish-rolled, rapidly cooled, and wound at room temperature ( Thickness 2.0 mm). Then, hot-rolled sheet annealing was performed at 875 ° C for 12
Conditions for heating for 0 seconds and quenching in saline at 5 ° C (condition A)
And the condition of quenching in boiling water (condition B). After pickling, cold rolling was performed to a thickness of 0.30 mm.
In this case, the plate thickness during cold rolling is 1.6mm, 1.2mm, 0.8
mm, 0.6 mm, and 0.4 mm were also cold-rolled under the condition of holding at 250 ° C. for 20 minutes (referred to as “Passing with Aging”, cold rolling without this treatment was performed with “Pass-by-Agi”).
Called cold rolling without ng).

Next, after heating at the temperature and time shown in Table 1, nitriding treatment was continuously performed in an atmosphere of N ₂ —H ₂ —NH _{3 in} the cooling process. Next, MgO is applied and heated to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 95% N ₂ —H ₂ and then 100
It was heated in a% H ₂ atmosphere for 20 hours and then cooled. Then, strain relief annealing was performed to measure the magnetic properties. The results are shown in Table 1.
For comparison, hot-rolled sheet annealing was heated at 1080 ° C. for 30 seconds and then 90
After holding at 0 ° C for 150 seconds, cooling in boiling water (condition C), heating at the temperature time shown in Table 1, and then N in the cooling process
Continuously in an atmosphere of ₂ -H ₂ -NH ₃ nitrided, treated specimen by the same process as the present invention is also produced, as shown in Table 1 together with the result. As shown in the table, the material of the present invention has good magnetic characteristics equivalent to or better than those of the comparative material despite the low annealing temperature of the hot rolled sheet.

[0019]

[Table 1]

[0020]

According to the present invention, a magnetic steel sheet having excellent magnetic properties can be manufactured at low cost by a simple hot-rolled sheet annealing.

Claims (2)

[Claims] 1. C: 0.025 to 0.060% by weight, Si: 2.0 to 4.5% by weight, acid-soluble Al: 0.010 to 0.080% by weight, N: 0.001 to 0. 0.020% by weight, S: 0.0020 to 0.030% by weight, 1 of a silicon steel slab containing the balance Fe and unavoidable impurities
After the rough rolling is started in the temperature range of 000 ° C to 1200 ° C and the finish rolling is subsequently performed, the hot rolled steel strip is heated to 700 ° C.
After heating at a temperature of 900 ° C or lower for 1 second or more and 300 seconds or less, immediately cool at a cooling rate faster than air cooling, and then perform one cold rolling to a predetermined plate thickness, and in a temperature range of 800 ° C to 950 ° C for 20 seconds. A method for producing a grain-oriented silicon steel sheet having a high magnetic flux density, which is decarburized by heating within 300 seconds, nitrided in a state in which the steel sheet is allowed to travel, and then applied with an annealing separation agent and subjected to finish annealing. 2. The amount of nitrogen after nitriding is 300 ppm or more 1
The method according to claim 1, wherein the range is 500 ppm or less.