JPH04329832A - Production of grain-oriented silicon steel sheet excellent in surface characteristic - Google Patents

Abstract

PURPOSE:To provide a method advantageously suited for the improvement in the surface characteristics of a grain-oriented silicon steel sheet used mainly for iron core material for electrical equipment, such as transformer. CONSTITUTION:Prior to the execution of hot rolling for a continuously cast slab of a silicon-containing steel having a composition containing at least 0.01-0.06% sol.Al and 0.0030-0.0120% N as inhibitor forming components, the slab is heated up to 1000-1300 deg.C, rolled at <=2% reduction of area, and heated up to a temp. in a high temp. region of >=1300 deg.C, by which micropores formed in the vicinity of inclusions entrapped in the course of continuous casting can be effectively crushed and the nuclei of cracking can be removed. By this method, a product free from surface defects can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method advantageously suited for improving the surface properties of grain-oriented silicon steel sheets, which are mainly used as core materials for transformers and other electrical equipment.

[0002] 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 50Hz
Iron loss characteristics W17/5 at AC magnetic flux density 1.7 T
0 (W/kg) is required. For this reason, grain-oriented silicon steel sheets utilize secondary recrystallization to
001> orientation, the so-called Goss orientation, is developed. In order to obtain a material with excellent magnetic properties, it is necessary to highly align the <001> axis, which is the axis of easy magnetization, in the rolling direction. It is important to stably develop secondary recrystallized grains. In particular, AlN, which is called an inhibitor, or MnS, Mn
It is important to uniformly and finely disperse precipitates such as Se.

0003

[Prior Art] Slabs, which are the starting material in the production of grain-oriented silicon steel sheets for the above-mentioned uses, are obtained by continuous casting, similar to other low-grade steels, mainly to improve productivity. There is a tendency to use However, the continuous casting method
During casting Al2O3, SiO2, MgO, CaO
Since inclusions such as The gas collects in microcavities near the inclusions, and cracks are introduced into the slab, whose tensile strength has decreased at high temperatures, which further propagate, and eventually remain on the steel plate as surface defects such as burrs and blisters. Therefore, it is necessary to limit the content of Al and N, but a predetermined amount is required to function as an inhibitor.

On the other hand, in Japanese Patent Publication No. 50-37009,
A method of improving the magnetic properties of grain-oriented silicon steel sheets using AlN as an inhibitor by subjecting the slab to appropriate blooming has been shown. This method is aimed at suppressing grain growth during high-temperature heating of the slab, and does not mention anything about preventing surface defects.

[0005]

[Problems to be Solved by the Invention] The present invention aims to prevent cracks that occur during slab heating without reducing the amount of Al and N, which are effective as inhibitor-forming components, and to prevent surface defects such as baldness and blistering. The purpose of this study is to propose a method for manufacturing unidirectional silicon steel sheets with a surface texture of

[0006]

[Means for Solving the Problems] When the inventors investigated the cause of the above-mentioned surface defects, it was found that micro cavities near the inclusions (near the boundary between the columnar structure and the equiaxed structure) generated during continuous casting. We determined that the cause of surface defects is that N2 gas decomposed from AlN gathers during the high-temperature heating process of the slab, and cracks occur in the slab, which has been exposed to high temperatures and whose tensile strength has decreased, starting from this point. Furthermore, as a countermeasure, the slab is heated to a high temperature range of 1000 to 1300°C, then rolled at a reduction rate of 2% or more, and then
It has been found that heating at a high temperature of 0° C. or higher is effective in suppressing the occurrence of surface defects.

That is, the present invention provides at least sol. Al: 0.01~0.0
6wt% (hereinafter simply referred to as %) and N: 0.0030~
A continuously cast slab of silicon-containing steel containing 0.0120% is hot-rolled to form a hot-rolled plate, and then the hot-rolled plate is cold-rolled in one or two passes. In manufacturing grain-oriented silicon steel sheets through a series of steps including decarburization annealing and final finish annealing, the slab is heated to a temperature range of 1000°C to 1300°C, and then 2% or more of This is a method for manufacturing a unidirectional silicon steel sheet with excellent surface properties, which is characterized by rolling at a reduction rate and then heating to a high temperature range of 1300° C. or higher.

[0008] As the silicon-containing steel which is the material of the present invention, any of the conventionally known compositions containing the above-mentioned inhibitor-forming components are suitable, but typical compositions are as follows. C: 0.01-0.12% C is an element that is useful not only for uniform refinement of the structure during hot rolling and cold rolling, but also for the development of Goss orientation. Containment is preferred. However, 0.1
If the content exceeds 2%, the Goss orientation will be disturbed, so the upper limit is preferably about 0.12%. Si: 2.0 to 4.5% Si increases the specific resistance of the steel sheet and effectively contributes to reducing iron loss, but if it exceeds 4.5%, cold rollability is impaired;
．． If it is less than 0%, not only the specific resistance will decrease, but also 2
During the final high temperature annealing for the next recrystallization and purification, α−
Since γ transformation causes randomization of crystal orientation and a sufficient iron loss improvement effect cannot be obtained, the amount of Si is 2.0 to 4.
It is preferable to set it to about 5%. Mn: 0.02-0.15% Mn is at least 0.02% to prevent hot embrittlement
It is preferable to set the upper limit at about 0.12%, since too much content deteriorates the magnetic properties.

[0009] As the inhibitor, the so-called A
In addition to the IN type, there are MnS and MnSe types. First A
In the case of lN system, sol. Al: 0.01-0.06% N: 0.0030-0.0120% Al and N are powerful elements as inhibitors that control secondary recrystallization of grain-oriented silicon steel sheets. From the viewpoint of securing suppressive force, Al and N should be at least 0.01% and 0.01%, respectively.
0.030% is required, but the effect is impaired if Al exceeds 0.060% and N exceeds 0.0120%, so the lower limits are Al: 0.01% and N: 0.01%, respectively.
0030%, upper limit is Al: 0.06% and N: 0.01
It shall be 20%. In addition, in the case of MnS and MnSe, Se
, at least one selected from S: 0.005
The range of ~0.060% Se, S was also set to the above range for the same reason as in the case of the AlN system described above. In addition, the above-mentioned MnS, MnSe system and A
Each of the IN systems can be used in combination.

[0010] As the inhibitor component, the above-mentioned S,
In addition to Se and Al, Cu, Ni, Sn, Cr, and G
e, Sb, Mo, Zn, Te, Bi and P
Since they are also advantageously compatible, they can also be contained together in small amounts. Here, the preferred addition ranges of the above components are Cu, Ni, Sn, and Cr: 0.01 to 0.0.
15%, Ge, Sb, Mo, Zn, Te, B
i: 0.005-0.1%, P: 0.01-0.2%, and each of these inhibitor components can be used alone or in combination.

[0011]

[Function] Now, the silicon steel slab with the above composition is
Manufactured by continuous casting from molten steel melted to a specified composition. And this silicon steel slab has 1000 to 130
After heating to a temperature range of 0 ° C., rolling with a reduction ratio of 2% or more,
Next, after heating to a high temperature range of 1300° C. or higher, hot rolling is performed.

[0012] Here, the first heating prior to hot rolling is
Since the strength of the slab material does not decrease below 1000℃,
Micro cavities generated near inclusions that are rolled up during continuous casting cannot be crushed by subsequent light rolling of 2% or more. On the other hand, if the first heating temperature exceeds 1300°C, the tensile strength of the slab material decreases, and cracks caused by N2 gas that have already collected in the cavity will develop, and these cracks will be caused by subsequent light rolling of 2% or more. Otherwise, the bond will not be crimped, resulting in surface defects such as blisters and flakes. Therefore, the first heating is
The temperature range is 1000-1300°C. The heating time is determined by the slab dimensions, especially the thickness, and is the time required to reach a predetermined temperature range up to the center of the wall thickness.

[0013] Further, the rolling reduction ratio in the subsequent rolling is required to be 2% or more, since the cavities cannot be crushed by rolling if it is less than 2%. Although the effect remains almost unchanged even if the reduction rate is increased beyond 30%,
As the thickness of the slab decreases, operational disadvantages arise, such as the need to reduce the unit weight of the slab due to the dimensional constraints of the next high-temperature heating furnace, so it is desirable that the upper limit is 30%.

Furthermore, the temperature when heating again after the above-mentioned rolling is set to 1300°C or higher, since secondary recrystallization becomes unstable if it is lower than 1300°C. In other words, AlN precipitates have an effect on secondary recrystallization in the Goss orientation, and in order to obtain AlN of a specific minute size, which is especially effective, AlN must be solid-dissolved in the steel base once during the slab heating stage during hot rolling. The minimum temperature required for solid solution of AlN is 130℃.
It is 0°C. The heating time is mainly determined by the thickness of the slab, and is the time required to reach a predetermined temperature range up to the center of the thickness. After the above-described treatment prior to hot rolling, a unidirectional silicon steel sheet without sagging or blistering can be obtained by hot rolling and cold rolling using known methods.

[0015]

[Example] Example 1 C: 0.06%, Si: 3.05%, sol. Al: 0
．． 023%, Mn: 0.075%, S: 0.025
%, N: 0.0085%, with the remainder essentially consisting of iron and unavoidable impurities, a number of silicon steel slabs obtained by continuous casting were heated at various temperatures in the range of 900 to 1300°C for 20 minutes. After that, it was rolled at various rolling reductions in the range of 0 to 30%, further heated at 1370°C for 30 minutes, and then hot rolled to a thickness of 1.8 mm. The hot rolled sheet was then continuously annealed at 1050°C, rapidly cooled to room temperature for 60 seconds, and then cold rolled at a rolling reduction of 88.9% to form a 0.20 m
m final plate thickness, followed by decarburization annealing, and H2:
A final annealing was performed at 1200°C in an atmosphere of 25% and N2:75%. The results of investigating the number of occurrences of blisters and blisters in the final product thus obtained are shown in FIG. 1 as the number of occurrences per 1000 m of product coil. From the figure, it can be seen that by performing the treatment according to the present invention prior to hot rolling, a unidirectional silicon steel sheet with fewer surface defects and excellent surface properties can be obtained.

Example 2 C: 0.06%, Si: 3.05%, sol. Al: 0
．． 028%, Mn: 0.070%, Se: 0.02
A large number of silicon steel slabs obtained by continuous casting, containing 0.0%, N: 0.0090%, and the remainder substantially consisting of iron and unavoidable impurities, were heated at various temperatures in the range of 900 to 1300°C for 20 minutes. After heating, rolling was performed at various reduction ratios in the range of 0 to 30%, further heated at 1400° C. for 30 minutes, and then hot rolled to a thickness of 1.8 mm. The hot rolled sheet was then continuously annealed at 1100°C, rapidly cooled to room temperature for 60 seconds, and then cold rolled at a rolling reduction of 87.2%.
mm final plate thickness, followed by decarburization annealing, and H2
Final annealing was performed at 1200° C. in an atmosphere of :25% and N2 :75%. The results of investigating the number of occurrences of blisters and blisters in the final product thus obtained are shown in FIG. 2 as the number of occurrences per 1000 m of product coil. From the figure, it can be seen that by performing the treatment according to the present invention prior to hot rolling, a unidirectional silicon steel sheet with fewer surface defects and excellent surface properties can be obtained. In addition, for a hot-rolled sheet whose first heating temperature was 1100°C and the subsequent rolling reduction ratio was 15%, the second heating was performed at 1250°C, 1300°C,
The results obtained at various heating temperatures of 1400° C. are shown in FIG. From the same figure, it was found that the appearance was improved at 1300°C or higher.

Example 3 C: 0.06%, Si: 3.05%, sol. Al: 0
．． A large number of silicon steel slabs obtained by continuous casting, containing 0.030%, N: 0.0095%, and the remainder substantially consisting of iron and unavoidable impurities, were heated at various temperatures in the range of 900 to 1300°C for 20 minutes. After heating, rolling was performed at various reduction rates in the range of 0 to 30%, and further at 1250 and 1350°C.
After heating for 50 minutes, it was hot rolled to a thickness of 1.8 mm. The hot-rolled sheet was then continuously annealed at 1050°C, then rapidly cooled to room temperature for 60 seconds, then cold rolled at a reduction rate of 88.9% to a final thickness of 0.20mm, followed by decarburization annealing, and H2: 1 in an atmosphere of 25% and N2:75%.
A final annealing was performed at 200°C. Table 1 shows the results of investigating the number of blisters and blisters in the final product thus obtained.

[0018]

[Table 1] From the same table, it can be seen that by performing the treatment according to the present invention prior to hot rolling, a unidirectional silicon steel sheet with fewer surface defects and excellent surface properties can be obtained.

[0019]

Effects of the Invention According to the present invention, cracks that occur during slab heating can be prevented without reducing the amount of Al and N, which are effective as inhibitor-forming components, and an excellent surface free from surface defects such as baldness and blistering can be achieved. It is possible to produce a unidirectional silicon steel sheet having the desired properties, and it is possible to provide a product that is particularly suitable for use as a material for laminated cores of electrical equipment.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between slab heating temperature and surface defect occurrence rate.

FIG. 2 is a graph showing the relationship between slab heating temperature and surface defect occurrence rate.

FIG. 3 is a graph showing the relationship between slab heating temperature and surface defect incidence rate.

Claims (1)

[Claims] 1. The inhibitor-forming component comprises at least sol. Al: 0.01-0.06wt% and N:
After hot rolling a continuously cast slab of silicon-containing steel containing 0.0030 to 0.0120 wt% to form a hot rolled sheet,
This hot-rolled sheet is subjected to one-step or two-step cold rolling, followed by decarburization annealing and final finish annealing to produce a grain-oriented silicon steel sheet. unidirectionality with excellent surface texture characterized by heating to a temperature range of 1000°C to 1300°C, rolling at a rolling reduction of 2% or more, and then heating to a high temperature range of 1300°C or more. Method of manufacturing silicon steel sheet.