JPH04289121A - Production of thin grain-oriented silicon steel sheet having stable magnetic property - Google Patents

Abstract

PURPOSE:To stabilize the magnetic properties of a grain-oriented silicon steel sheet used mainly as iron core material for electrical equipment such as transformer, particularly a grain-oriented silicon steel sheet having a thickness as thin as 0.10-0.25mm. CONSTITUTION:In a series of stages where a steel slab is hot-rolled and the resulting hot rolled plate is cold-rolled twice or more, while process-annealed between the cold rolling stages, and is subjected to decarburizing annealing and then to final finish annealing, this hot rolled plate is rolled down, prior to the above cold rolling, at 0.5-15% reduction of area by means of a rolling mill, where (roll diameter)/(plate thickness)=50 is satisfied, and is then subjected to hot rolled plate annealing at 700-1100 deg.C. By this method, the occurrence of abnormal structure where secondary recrystallization is not developed can be prevented and stable magnetic properties free from variance can be provided over the whole length, e.g. of a coil.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] This invention relates to grain-oriented silicon steel sheets mainly used as core materials for transformers and other electrical equipment, particularly those having a thickness of 0.10 to This invention relates to a method for stabilizing the magnetic properties of a grain-oriented silicon steel sheet as thin as 0.25 mm. [Prior Art] Iron core materials for this type of electrical equipment must have excellent magnetic properties, specifically magnetic field strength of 800 A.
The magnetic flux density B8 (T) at /m is high and 50H
Iron loss characteristic W17/ at AC magnetic flux density 1.7 T of z
50 (W/kg) is required. For this reason, grain-oriented silicon steel sheets utilize secondary recrystallization to improve {110}
It has developed crystal grains with <001> orientation, the so-called Goss orientation. In order to obtain materials with excellent magnetic properties,
It is necessary to highly align the <001> axis, which is the axis of easy magnetization, in the rolling direction, and it is possible to stably develop secondary recrystallized grains in the Goss orientation through various processes that combine appropriate rolling and heat treatment. is important. In particular, it is already known that it is essential to uniformly and finely disperse precipitates such as MnS, MnSe, AlN, etc. called inhibitors, and to have a texture favorable to the above-mentioned secondary recrystallization. On the other hand, the product thickness is 0.10, which is advantageous for reducing iron loss.
The demand for ~0.25 mm grain-oriented silicon steel sheets is increasing, but as the sheet thickness becomes thinner, it becomes difficult to achieve stable secondary recrystallization, which causes variations in the magnetic properties of the product. This left problems with stabilization. [0004] Regarding stabilization of magnetic properties, methods include performing high-temperature treatment at the initial stage of secondary recrystallization annealing, followed by normal annealing (see Japanese Patent Publication No. 58-55212), and oxidation generated during decarburization annealing. Method of controlling quantity (Unexamined Japanese Patent Publication No. 1983
For materials containing AlN as an inhibitor, 0.0070 to 0.030% decarburization is performed in the step before decarburization annealing (see JP-A-61-117215). or Sn or Cu
A method of adding (see JP-A-2-209427) and the like have been proposed. [0005]However, although these methods improve the magnetic properties, it is difficult to provide constant magnetic properties over the entire length of the coil. In particular, it is more difficult to properly develop secondary recrystallized grains over the entire length of the coil during final finish annealing as the plate thickness becomes thinner. This is because as the plate thickness becomes thinner, the number of {110}<001> oriented grains that can become nuclei of secondary recrystallized grains decreases. Although the reason for this is not clear, it is thought that the shear strain distribution during cold rolling differs depending on the plate thickness. By the way, in Japanese Patent Application Laid-Open No. 61-238916, CBS (Contact BendStretch) is used as a texture improvement method.
tch: Special Different Circumferential Speed Rolling Method) Although a rolling method is disclosed, such a method has poor productivity and lacks feasibility. Therefore, an object of the present invention is to propose a method for manufacturing a grain-oriented silicon steel sheet having stable magnetic properties. [0006] This invention provides C: 0.02 to 0.10wt.
% (hereinafter simply shown as %), Si: 2.5 to 4.0%
and Mn: 0.03 to 0.15%, and further contains Se and/or S by 0.01 to 0.04%. In manufacturing a grain-oriented silicon steel sheet through a series of steps in which a hot-rolled sheet is cold-rolled two or more times with intermediate annealing in between, followed by decarburization annealing and final finish annealing, prior to the cold rolling, After rolling down the hot-rolled plate with a rolling mill with (roll diameter)/(plate thickness)≧50 at a rolling reduction rate of 0.5 to 15%, 700
This is a method for producing a thin grain-oriented silicon steel sheet with stable magnetic properties, which is characterized by subjecting the hot-rolled sheet to annealing in a temperature range of ~1100°C. [0007] The experimental results that formed the basis of this invention will be explained in detail below. In the process of manufacturing grain-oriented silicon steel sheets with a thickness of 0.10 to 0.25 mm, the inventors performed two cold rollings with intermediate annealing in between, and the final cold rolling reduction rate was 65%.
First, an experiment was conducted to try to optimize the rolling reduction ratio in the primary cold rolling before intermediate annealing. Experiment: C: 0.045
%, Si: 3.35%, Mn: 0.080%, S: 0
．． 025%, plate thickness 1.8 including Sb: 0.027%
The starting material was a hot-rolled sheet of mm2. Hot-rolled sheets are subjected to preliminary cold rolling (hereinafter referred to as pre-rolling) at various rolling reduction ratios to variously change the sheet thickness, and then each sheet is rolled at 1000°C for 30°C.
A material subjected to homogenization annealing of s was used. All these materials with different thicknesses are cold rolled to 0.4mm.
Finished to a thickness of 0.14 after intermediate annealing at 950°C for 60s.
After cold rolling to a thickness of mm, decarburization annealing was performed at 850° C. for 2 minutes, and after applying a separation agent containing MgO as a main component, final annealing was performed. Table 1 shows the results of investigating the magnetic properties of the obtained product. [0009] The experimental results shown in the same table show that secondary recrystallization developed stably when the reduction ratio of the first cold rolling before intermediate annealing was 75 to 76.5%, and the plate thickness was further increased. A follow-up experiment was conducted using a hot-rolled sheet finished to a thickness of 1.7 mm and not pre-rolled as a starting material under the conditions shown in Table B, but good magnetic properties could not be obtained due to the occurrence of an abnormal structure. Therefore 1
There was no correlation between the subsequent cold rolling reduction and the incidence of abnormal structures, and it was inferred that the improvement in magnetic properties was due to other factors. [0010] Therefore, the inventors conducted further experiments in order to investigate the influence of preliminary cold rolling before hot-rolled sheet annealing. That is, the starting materials used were the above-mentioned hot-rolled sheet with a thickness of 1.7 mm and hot-rolled sheets that were pre-rolled to a thickness of 1.5 mm and 1.3 mm before annealing the hot-rolled sheet. After that, the results of measuring the magnetic properties of the products obtained by hot-rolled plate annealing, primary cold rolling, intermediate annealing, secondary cold rolling, decarburization annealing, and final finish annealing under the same conditions as Table 1 are shown. Shown in 2. [0012] From the results shown in Tables 1 and 2, the inventors diligently investigated the effects caused by pre-rolling before annealing hot rolled sheets, and found that homogenization annealing at 1000°C for 30 seconds after pre-rolling was performed. It was found that there was a large difference in the crystal structure between the sample subjected to the treatment and the sample not treated. [0013] Normally, the structure of hot rolled silicon steel sheets consists of a band-like unrecrystallized structure extending in the hot rolling direction. In samples A and F that were not pre-rolled, this band-like structure remained as it was even after hot-rolled sheet annealing. In addition, in pre-rolled samples D, E, and H, the entire plate thickness was made up of recrystallized grains, although there were band-like remnants. However, in samples B, C, and G, which had a small pre-rolling reduction, recrystallized grains formed from the surface to about 1/4 of the plate thickness, and the center layer had a layered structure called a band structure. Although the reason for this is not clear, it has been found that samples with such recrystallized and band-like structures have stable magnetic properties even if they are thin plate products. Furthermore, when we repeated reproduction experiments to determine the applicable range of preliminary rolling, it was newly discovered that the effect may not be obtained depending on the rolling mill used. Since these rolling mills have different roll diameters, we conducted an experiment in which the same rolling mill was used with different work roll diameters. The material is
The hot-rolled plate is 2.0 mm thick, and the roll diameters used for preliminary rolling are 80 mmφ, 150 mmφ, 300 mmφ, and 5 mm.
00 mmφ, and the pre-rolling reduction rate was 0.5.
%, 1%, 5%, 10%, 15%, 20%, 25%, and then hot-rolled plate annealing at 1000°C for 30 seconds, the finished thickness of the first cold rolling 0.4mm
Aligned to. After that, it was intermediately annealed at 950°C for 60s to give a final thickness of 0.14mm, and further annealed at 850°C x 2
Figure 1 and Table 3 show the results of investigating the magnetic flux density and abnormal structure occurrence rate of products obtained by decarburizing annealing for 1 minute, applying an annealing separator mainly composed of MgO, and final annealing. . [0015] From the results in the same table, it can be seen that when the rolling reduction ratio is 0.5 to 15
It has been found that the occurrence of abnormal structures can be avoided by performing preliminary rolling in the range of 1.5%. It is also believed that the roll diameter also affects the recrystallization behavior, that is, the stress state exerted on the plate changes depending on the size of the roll diameter, resulting in a difference in the recrystallization behavior of the plate surface layer. This is clear from other experimental results, and the ratio of roll diameter to hot rolled sheet thickness is 50.
It has also been found that good results can be obtained when the amount is more than twice as large. [Operation] The composition of the steel slab that is the starting material of this invention is C: 0.02 to 0.10%, Si: 2.5 to 4.0%.
%, Mn: 0.03-0.15%, Se and/or S:
0.01-0.04% is required. The reason for limiting the content of each component will be explained below. C: 0.
02 to 0.10% C is required to be 0.02% or more in order to utilize γ transformation during hot rolling, but if it exceeds 0.10%, decarburization annealing in the subsequent process becomes difficult. Si: 2.5 to 4.0% If Si is less than 2.5%, the electrical resistance is low and no improvement in iron loss characteristics can be expected, while if it exceeds 4.0%, cold rolling becomes extremely difficult. . Mn: 0.03-0.15%, Se and/or S: 0.
01-0.04% Mn and Se and S are MnSe, M
It is an element necessary to form nS, and the appropriate amount of Mn is 0.03 to 0.15%, and Se and/or S is 0.01%.
%, the amount of MnSe and MnS is insufficient, and 0.
．． If it exceeds 0.05%, it becomes difficult to disperse and precipitate to a uniform fine size. [0018] In addition to the above components, Sb, Cu,
There is no problem in containing one or a combination of known elements such as Sn, Cr, Ni, and Mo. The maximum allowable amount of these elements is 0.3 for Cu, Sn, Cr, and Ni.
%, Sb, and Mo are 0.05%. That is, Cu
, Sn, Cr, Ni, etc., if the content exceeds 0.3%, not only the magnetic properties deteriorate, but also pickling properties and decarburization properties are deteriorated, which is not preferable. Furthermore, if Sb or Mo exceeds 0.05%, decarburization is significantly inhibited, which is not preferable. [0019] The molten steel having the above-mentioned composition is formed into a slab through a steelmaking and casting process according to conventional methods, subjected to solution treatment for the inhibitor component at a high temperature of 1350°C or higher, and then hot-rolled into a hot-rolled plate. . Next, after hot-rolled sheet annealing, cold rolling is performed two or more times with intermediate annealing in between, and the appropriate rolling reduction ratio for each is 30 to 80%. Prior to annealing the hot-rolled sheet, a rolling mill in which the ratio of the work roll diameter (mm) of the rolling mill to the thickness (mm) of the hot-rolled sheet is 50 times or more is used to reduce the total rolling reduction to 0.5.
Applying ~15% rolling in one or multiple passes,
It is important that the hot-rolled sheet is then annealed for a short time at 700 to 1100°C to control the crystal structure in the thickness direction before cold rolling. Hot-rolled sheet annealing must be performed at a temperature of 700°C or higher in order to recrystallize the surface layer of the pre-rolled hot-rolled sheet.On the other hand, if the temperature exceeds 1100°C, MnSe, MnS
This is not preferable because the precipitates such as the like will grow coarsely and the inhibitor function will be impaired. Regarding the time, since the purpose is recrystallization, it is sufficient to reach the desired temperature, and there is no problem even if the time is short as long as the annealing can be performed stably. [Example] Example 1 Molten steel having the composition shown in Table 4 was made into a slab by continuous casting, and after high temperature reheating at 1430°C for 15 minutes, the plate thickness was 2.7 mm.
It was made into a hot rolled sheet. This hot rolled sheet has a work roll diameter of 900.
Rolling was performed by a total of 8% in two passes using a mmφ skin pass mill. In addition, for comparison, a Sendzimer mill with a work roll diameter of 85 mmφ was used for another coil of the same composition.
Rolling was performed by 8% in total in passes. Then 1 at 1000℃
After hot-rolled plate annealing and pickling for 5 seconds, the first cold rolling was performed to obtain a plate thickness of 0.78 mm. Furthermore, as intermediate annealing, light decarburization is performed when the temperature is raised to 1000
After soaking at ℃ for 60 seconds, the mixture was rapidly cooled to room temperature. After that, it was finished with a second cold rolling to a final plate thickness of 0.30 mm, and then subjected to decarburization annealing at 850 °C for 3 minutes in a wet hydrogen atmosphere, and then an annealing separator mainly composed of MgO was applied. Secondary recrystallization annealing and final annealing were performed. As shown in Table 5, the results of investigating the magnetic properties of the thus obtained product showed that good magnetic properties were obtained by applying the present invention. [0022] [0024] Example 2 C: 0.04%, Si: 3.35%, Mn: 0.07%
, Se: 0.021%, Sb: 0.027%, Cu
: A steel slab with a composition containing 0.06% was heated at 1430℃ for 20
After heating for 30 minutes, the coil was hot-rolled to a thickness of 1.8 mm and the hot-rolled sheet of the same composition was rolled into a work roll with a diameter of 850 m.
mφ skin pass rolling mill, work roll diameter 350 mm
Coils were prepared which were pre-rolled by a total of 10% using a tandem rolling mill with a diameter of φ and a Sendzimer rolling mill with a work roll diameter of 90 mm. Thereafter, the hot-rolled plate was annealed at 900°C for 100 seconds, and finished to a thickness of 0.5 mm by cold rolling. Next, it was subjected to intermediate annealing at 950 °C for 60 seconds, then rapidly cooled to room temperature, and then cold rolled for the second time to a thickness of 0.20 mm.
Finished thickly. After further decarburizing annealing at 850° C. for 2 minutes, an annealing separator containing MgO as a main component was applied, followed by secondary recrystallization annealing and final annealing. As shown in Table 6, the magnetic properties of the thus obtained product were investigated, and as shown in Table 6, good magnetic properties were obtained by applying the present invention. Example 3 The molten steel shown in Table 7 was made into a slab by continuous casting.
After high temperature reheating at ℃ for 20 minutes, the plate thickness was 1.8 mm and 1.4 mm.
It was made into a hot rolled sheet of mm. This hot-rolled plate has a work roll diameter of 6
Rolling was performed at a rolling reduction of 5% in one pass using a skin pass mill with a diameter of 0.00 mm. For comparison, another coil having the same composition was rolled at a reduction rate of 5% in one pass using a Sendzimer mill with a work roll diameter of 80 mm. then 100
After annealing the hot-rolled sheet for 30 seconds at 0°C, pickling was carried out, and then the first cold rolling was performed using a hot-rolled sheet with a thickness of 1.8 mm as a starting material (A) 0.6 mm thick. and (B) 0.
(C) A product using a 1.4 mm thick hot-rolled plate as a starting material was finished to a thickness of 0.3 mm. Subsequently, after intermediate annealing at 950 °C x 60 s, a second cold rolling was performed to (A) 0.23 mm, (B) 0.15 mm, (
C) After finishing the product thickness of 0.10 mm, 850
Decarburization annealing was performed at 1200° C. for 2 minutes, and an annealing separator containing MgO 2 as a main component was applied, followed by final finish annealing consisting of secondary recrystallization annealing at 850° C. followed by purification annealing at 1200° C. As shown in Table 8, the results of investigating the magnetic properties of the thus obtained product showed that good magnetic properties were obtained by applying the present invention. [0027] [0028] [0029] According to the present invention, in particular, the product thickness is 0.
It is possible to eliminate the abnormal structure due to undeveloped secondary recrystallization that tends to occur in grain-oriented silicon thin steel sheets of 10 to 0.25 mm, and for example, it is possible to impart stable magnetic properties without variations over the entire length of the coil.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of roll diameter on magnetic flux density.

Claims (1)

[Claims] [Claim 1] C: 0.02 to 0.10 wt%, Si
:2.5-4.0 wt% and Mn:0.03-0.
Contains 15 wt% and further contains 0.01 Se and/or S.
After hot rolling a steel slab with a composition containing ~0.04 wt% to make a hot rolled sheet, this hot rolled sheet is subjected to intermediate annealing.
In manufacturing grain-oriented silicon steel sheets through a series of steps of cold rolling several times, followed by decarburization annealing and final finish annealing, the hot rolled sheets (roll diameter)/ (Plate thickness) ≧ 50 rolling mill Reduction rate: 0
．． 1. A method for producing a thin grain-oriented silicon steel sheet with stable magnetic properties, which comprises rolling the steel sheet by 5 to 15% and then annealing the hot-rolled sheet in a temperature range of 700 to 1100°C.