JPH06336610A - Method for producing grain-oriented silicon steel sheet with good magnetic properties and few surface defects - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a grain-oriented silicon steel sheet having a magnetic property of B ₈ of 1.92 T or more and not causing swelling as a surface defect. [Structure] A slab with an N content of 70 wtppm or more is used as a silicon-containing steel slab. As a slab heating condition prior to hot rolling, the holding time t (min) at 1400 ° C or more is 38 min or more and the N content is Depending on the above, the following formula [Formula 1] t ≦ − (2/3) × N (ppm) +320/3 is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet mainly used as a core material for transformers and other electric equipment, and particularly to a method for advantageously producing a steel sheet having excellent magnetic properties and few surface defects. Is to propose.

[0002]

2. Description of the Related Art As a core material for this kind of electric equipment,
It is required to have excellent magnetic properties, specifically, a high magnetic flux density B ₈ (T) at a magnetizing force of 800 A / m. This is because it can be expected to reduce the size and performance of devices. The grain-oriented silicon steel sheet used as such an iron core material utilizes secondary recrystallization to produce {11
0} <001> orientation A so-called Goth orientation crystal grain is developed. In order to obtain a product having excellent magnetic properties among the grain-oriented silicon steel sheets, it is necessary to highly align the <001> axis, which is the easy magnetization axis, in the rolling direction. It is important to stably develop the secondary recrystallized grains in the Goss orientation by the manufacturing process combined under the conditions. In this way, Goth bearing 2
In order to develop the secondary recrystallized grains, precipitates such as AlN and MnSe, MnS, which are called inhibitors, are dispersed uniformly and finely in the steel, and the grain growth of the other position is effectively performed during finish annealing. It is essential to suppress it.

To achieve this, the inhibitor is once dissociated and solid-dissolved during heating of the slab prior to hot rolling.
It is necessary to finely disperse and precipitate by subsequent hot rolling and subsequent cooling. However, when AlN is contained as an inhibitor, nitrogen generated by dissociation of AlN during slab heating becomes N ₂ gas and expands, and surface defects such as blisters often occur in the final product. That was a problem.

Japanese Patent Publication No. Sho 42-42208 discloses a technique for preventing the formation of blisters that can be considered to be this kind of blistering, according to which the nitrogen contained in the steel is It is said that the occurrence of blisters can be prevented by adjusting the content to [Al (%) × 10 ³ +40] ppm or less. However, this method is intended to limit the content of Al and N, and as a result, the required amount of the inhibitor is insufficient, resulting in a magnetic property, particularly B ₈ of 1.
It was not possible to obtain a product having a good magnetic property of 92T or more.

[0005]

SUMMARY OF THE INVENTION The present invention advantageously solves the above problems, and is particularly useful for producing a grain-oriented silicon steel sheet having good magnetic properties and free from blistering. The purpose is to propose a method that was made possible by devising a slab heating method.

[0006]

[Means for Solving the Problems] According to the research conducted by the inventors, in order to obtain good magnetic properties, slab heating is performed at 1400 ° C. or higher using a slab having a nitrogen content of 70 ppm or higher. Has proved to be particularly advantageous. Figure 2
Then, the nitrogen content of the steel ingot was variously changed within the range of 59 to 105 ppm, and after heating and holding at 1400 ° C or higher, hot rolling was performed, and then secondary recrystallization was performed through a predetermined process according to a conventional method. The results of measuring the magnetic properties of the silicon steel sheet are shown in the graph. The Al content was kept constant at 0.020%. Figure 2
As is clear from the above, in the range of 72 to 97 ppm of nitrogen, a silicon steel sheet having good magnetic properties was stably obtained.
However, even among the samples exhibiting such good magnetic properties, quite a few samples were found to blister during annealing after cold rolling.

From the results of this experiment, in order to further elucidate the degree of swelling, various production conditions were examined, and as a result, there was a clear relationship with the time of heating to 1400 ° C. or higher, and the nitrogen content. It has become clear that there is a relationship. Therefore, prepare multiple slabs with different nitrogen contents, and keep the slab heating time of 1400 ° C or higher at 35 ~
The magnetic properties and the presence or absence of blistering were checked under several conditions within a range of 65 minutes. The result is shown in FIG. As is clear from FIG. 1, B ₈ has good magnetic characteristics of 1.93 T or more when the holding time is 40 minutes or more and the nitrogen content is 70% or more.
It was found that the blistering, which is above ppm, has a long retention time. Moreover, the time changes depending on the amount of nitrogen,

## EQU00002 ## No blistering occurred if the condition of t.ltoreq.-2 / 3 [N (ppm)] + 320/3 was satisfied.

According to the present invention based on the above findings, a silicon-containing steel slab containing at least Al and N as inhibitor-forming components is heated to 1400 ° C. or higher for hot rolling, and then once or for intermediate annealing. In order to manufacture a grain-oriented silicon steel sheet by a series of steps of performing decarburization annealing, applying an annealing separating agent and then performing final annealing after carrying out cold rolling a plurality of times for sandwiching to obtain the final sheet thickness, the above-mentioned silicon is used. A slab having an N content of 70 wtppm or more is used as the raw steel slab, and the slab heating is performed for a holding time t (min) of 38 min or more and N
The following formula according to the content

[Equation 3] A method for producing a grain-oriented silicon steel sheet having good magnetic properties and few surface defects, which is characterized in that t ≦ − (2/3) × N (ppm) +320/3 is satisfied. is there.

[0009]

The function of the silicon-containing steel slab used in the present invention is as follows.
Any of the conventionally known component compositions containing at least Al and N as the above-mentioned inhibitor-forming components are suitable, and the representative compositions are as follows. C: 0.04 to 0.12 wt% C is a component useful not only for the refinement of the structure during hot rolling and cold rolling but also for the development of Goss-oriented crystal grains, and the C content is less than 0.04 wt%. If it does not, the texture becomes inadequate due to its poor effect, while if it exceeds 0.12 wt%, decarburization becomes insufficient and the texture becomes insufficient.
Sufficient secondary recrystallization does not occur. Si: 2.0 to 4.5 wt% Si is a component that increases the resistivity of the steel sheet and effectively contributes to the reduction of iron loss, but if the Si content is less than 2.0 wt%, not only the resistivity decreases, During the finish annealing performed for secondary recrystallization / purification, the α-γ transformation causes randomization of the crystal orientation, which increases iron loss. On the other hand, if it exceeds 4.5 wt%, rolling will be hindered. Mn: 0.02 to 0.15 wt% Mn is not only a component effective for preventing hot embrittlement, but also useful as a component for forming MnS and MnSe inhibitors. If the Mn content is less than 0.02 wt%, the amount of the inhibitor formed is too small and not only the Goss orientation secondary recrystallization becomes insufficient but also the workability deteriorates, while 0.15 wt%
If it exceeds, magnetic properties will deteriorate.

As well known, AlN is an inhibitor.
System, MnS, and MnSe system, and since this invention is intended to suppress the blistering, which was a problem peculiar to the case of containing an AlN system inhibitor, at least the AlN system is essential. , MnS, MnSe system can be used together. First, in the case of AlN system, Al: 0.010 to 0.060 wt% Al needs to be at least 0.010 wt% in order to secure the inhibitory power as an inhibitor. If it is less than this, the inhibitor is insufficient and the magnetic properties are poor. become. Meanwhile 0.
Even if it exceeds 06 wt%, the magnetic properties will be poor. N: 70 wtppm or more The content of N is one of the main requirements constituting the present invention. If the N content is less than 70 ppm, the desired magnetic properties cannot be obtained.

Next, when MnS and MnSe inhibitors are used in combination, one or two selected from S and Se alone or in total 0.005 to 0.060 wt% S and Se must be less than 0.005 wt%. It is difficult to obtain sufficient magnetic properties because the amount as an inhibitor is insufficient, and if it exceeds 0.060 wt%, the dissociated solid solution of the inhibitor becomes insufficient during heating, and the magnetic properties also become poor.

As the inhibitor component, Sb or Sn is advantageously suited in addition to the above components, and further improvement of magnetic properties can be expected by incorporating one or two of these. The desirable content here is 0.01 or a total of 0.01
It is 0 to 0.030 wt%.

Further, Cu, Ni, Cr, Ge, Mo, Zn, Te, Bi
In addition to the above-mentioned components, P and P may be contained alone or in combination in a small amount in addition to the above components. The preferable addition amount of these components is Cu, Ni, Cr: 0.01 to 0.15 wt%
Degree, Ge, Mo, Zn, Te, Bi: about 0.005 to 0.1 wt%,
P: 0.01 to 0.2 wt% or so.

Next, the silicon-containing steel slab having the above-described composition is heated to 1400 ° C. or higher to dissociate the inhibitor to form a solid solution. The lower limit temperature is set as the lower limit value at which the inhibitor existing in the slab can be dissociated and solid-dissolved. Here, the slab heating time is one of the main requirements constituting the present invention, and the holding time at 1400 ° C. or higher is 38 minutes or longer and the slab has the following formula depending on the N content.

[Equation 4] It is important to carry out in a range satisfying t ≦ − (2/3) × N (ppm) +320/3. If this holding time is less than 38 minutes, the desired magnetic properties of B ₈ of 1.92 T or more cannot be obtained. Also, the holding time is related to the N content of the slab by the following formula

## EQU00005 ## If the time (minutes) calculated by-(2/3) .times.N (ppm) +320/3 is exceeded, blistering will occur. This blister is one in which the nitrogen solid-dissolved in the slab is locally aggregated and gasified to form a blister part, and good magnetic properties can be obtained only by heating the slab under the conditions according to the present invention. It is now possible to achieve both gain and suppression of blistering.

The slab is intended to be a continuously cast product or a slab that has been agglomerated from an ingot, but it goes without saying that a slab that has been abruptly re-pressed after being continuously cast is also included in the subject. Next, the slab after heating is hot-rolled and then finish-rolled to form a hot-rolled sheet. Then, if necessary, hot-rolled sheet annealing is performed, and then final rolling is performed by one or multiple cold-rolling steps with intermediate annealing. It is considered to be the plate thickness.
After that, decarburization and primary recrystallization annealing are applied, and an annealing separator is applied to the surface of the steel sheet, then secondary recrystallization and purification are performed by finish annealing at around 1200 ° C, and then an insulating coating is applied. And

[0016]

【Example】

Example 1 C: 0.081 wt%, Si: 3.2 wt%, Mn: 0.08 wt%, Se: 0.
A slab containing 016 wt%, Al: 0.023 wt% and N: 0.0080 wt% was prepared. Because of this slab

Calculating − (2/3) × N (ppm) +320/3 gives slab heating time t satisfying the present invention.
Is t ≦ 53.3 (min). This slab in an induction heating furnace
When heating above 1400 ° C, hold at this temperature for 30 ~
After being variously heated for 60 minutes, hot rolling was performed to obtain a hot-rolled sheet having a sheet thickness of 2.2 mm. This hot-rolled sheet was cold-rolled to a thickness of 1.5 mm, annealed at 1100 ° C. for 1 minute, and then cold-rolled to a final sheet thickness of 0.23 mm. After that, primary recrystallization annealing that also serves as decarburization annealing is performed at 830 ° C for 1 minute, an annealing separator containing MgO as a main component is applied to the steel sheet surface, and then secondary recrystallization annealing is performed at 1200 ° C for 5 hours. went. Table 1 shows the results of examining the magnetic properties and the swelling defect occurrence rate of the steel sheet thus obtained.

[0017]

[Table 1]

Example 2 C: 0.075 wt%, Si: 3.2 wt%, Mn: 0.075 wt%, Se:
0.016 wt%, Al: 0.022 wt%, N: 0.0090 wt% and Sb:
A slab containing 0.024 wt% was prepared. Because of this slab

[Formula 7]-(2/3) × N (ppm) +320/3 is calculated, and the slab heating time t satisfying the present invention is calculated.
Is t ≦ 46.7 (min). This slab in an induction heating furnace
When heating above 1400 ° C, hold at this temperature for 30 ~
After being variously heated for 60 minutes, hot rolling was performed to obtain a hot-rolled sheet having a sheet thickness of 2.2 mm. This hot-rolled sheet was cold-rolled to a thickness of 1.5 mm, annealed at 1100 ° C. for 1 minute, and then cold-rolled to a final sheet thickness of 0.23 mm. After that, primary recrystallization annealing that also serves as decarburization annealing is performed at 830 ° C for 1 minute, an annealing separator containing MgO as a main component is applied to the steel sheet surface, and then secondary recrystallization annealing is performed at 1200 ° C for 5 hours. went. Table 2 shows the results of examining the magnetic properties and the blistering defect occurrence rate of the steel sheet thus obtained.

[0019]

[Table 2]

[0020]

According to the method for producing a grain-oriented silicon steel sheet of the present invention, a slab having an N content of 70 wtppm or more is used as a silicon steel slab, and heating of this slab prior to hot rolling is performed for a holding time t (min. ) Is 38 min or more and is changed according to the N content, the blistering surface defect that was often inevitable when AlN was contained as an inhibitor, is advantageously eliminated without impairing the excellent magnetic properties. You can, and the effect is great.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the N content in a slab and the slab heating temperature on the magnetic properties of products and the swelling occurrence state.

FIG. 2 is a graph showing the effect of nitrogen content in steel on the magnetic properties of products.

Claims (1)

[Claims] 1. At least an inhibitor-forming component
A silicon-containing steel slab containing Al and N is heated to 1400 ° C. or higher and hot-rolled, and then cold-rolled once or a plurality of times with intermediate annealing to obtain a final plate thickness. In producing a grain-oriented silicon steel sheet by a series of steps of decarburization annealing, followed by application of an annealing separator and then final annealing, a slab having an N content of 70 wtppm or more is used in the above-mentioned silicon steel slab. Slab heating is performed within a range where the holding time t (min) is 38 min or more and the following formula is satisfied according to the N content: t ≦ − (2/3) × N (ppm) +320/3 A method for producing a grain-oriented silicon steel sheet having good magnetic properties and few surface defects, which is characterized by being performed.