JP3311968B2 - Method of manufacturing high magnetic flux density grain-oriented electrical steel sheet with excellent surface properties - Google Patents

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 electrical steel sheet, and aims to propose a method for stably obtaining high magnetic properties.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron cores in transformers and other electric equipment, and it is basically important to have excellent magnetic properties such as magnetic flux density and iron loss value in order to meet such applications. . Therefore, what is important in the production of grain-oriented electrical steel sheets is that the orientation of crystal grains that have undergone secondary recrystallization in the so-called finish annealing step is highly integrated in the {110} <001> orientation, the so-called Goss orientation. It is.

[0003] Further, if surface defects are present in the product, not only does the space factor decrease when the laminated product is used in a transformer or the like and the space efficiency is deteriorated, but also a short circuit occurs due to a decrease in insulation between the laminated products. It becomes a serious problem in using. For this reason, obtaining a product having good surface properties is of great interest to those skilled in the art as well as magnetic properties.

In order to effectively promote the accumulation of the secondary recrystallized grains, a dispersed phase called an inhibitor for selectively suppressing the growth of the primary recrystallized grains is formed in a uniform and appropriate size. It is important to. As such inhibitors, substances such as sulfides, selenium compounds and nitrides, such as MnS, MnSe and AlN, which have a low solubility in steel are mainly used. For this reason, conventionally, in slab heating before hot rolling, high-temperature heating is performed to completely dissolve the inhibitor, and a method of finely dispersing and depositing the inhibitor in the process from the hot rolling step to the second recrystallization. Has been taken. Note that Sb, Sn, As, Bi, B, Pb, S
Elements such as e, Cu, and Mo are additionally used as auxiliary inhibitors.

A method of achieving a particularly high magnetic flux density by using Bi among the auxiliary inhibitors is disclosed in, for example, Japanese Patent Laid-Open No. 6-88.
173 and 6-88173. Although extremely high product magnetic flux densities can be obtained by this method, irregular surface defects due to the addition of Bi are sporadic.

[0006]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problem relating to the occurrence of surface defects.
An object of the present invention is to propose a method for manufacturing a grain-oriented electrical steel sheet capable of achieving a high magnetic flux density without causing unevenness defects in a grain-oriented electrical steel sheet to which Bi is added.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted various experiments in view of the above problems. As a result, by adding a very small amount of boron (B) among the various additives, the above-mentioned irregularity defects were reduced. It can be effectively suppressed without deteriorating magnetism. At that time, it is necessary to limit the amount of hydrogen (H) in the steel, and the reduction in the diameter of the rolling roll on the high-temperature side of hot finish rolling is effective in suppressing defects. And that the relatively low frequency induction heating is suitable for slab heating, and that the effect of the present invention can be further enhanced by reducing the rolling load in the first pass of rough rolling. . The gist configuration of the present invention based on the above knowledge is as follows.

[0008] Si: 2.0-6.5 mass% and Bi: 0.0005-0.
A slab made of silicon steel containing 05 mass% is heated, then subjected to hot rough rolling, followed by hot finish rolling to form a hot-rolled steel strip, and further subjected to cold rolling with annealing and then to primary rolling. When producing a grain-oriented electrical steel sheet by performing recrystallization annealing and then secondary recrystallization annealing, the amount of boron in the slab was 0.2 mass
In the range of not less than ppm and not more than 20 mass ppm, and the hydrogen amount is 3 mass
Basically, each is controlled to be less than or equal to ppm, and when the surface temperature of the rolled material at the start of hot finish rolling is 1100 ° C. or higher, the surface temperature is 11
A high magnetic flux density grain-oriented electrical steel sheet having an excellent surface property, wherein a roll having a ratio of roll radius / rolled material sheet width of 0.4 or less is used as a roll work roll of a rolling stand through which a rolled material at a temperature of 00 ° C. or more is passed. Manufacturing method. Further, in the present invention, after performing the heating of the slab in the range of 1350 ° C. to 1450 ° C. using induction heating at a frequency of 50 Hz or more and 200 Hz or less, the hot rough rolling is performed at a linear pressure of the first pass of 1000 t / m. It is preferable to perform the following.

Japanese Patent Application Laid-Open No. 6-1364 discloses a grain-oriented electrical steel sheet in which Bi and B are added in combination as in the present invention.
No. 45 and JP-A-7-316657, C, Si
In addition to the basic components such as Sb, Sn, Cu, Mo, Ge,
One, two or more selected from B, Te, As and Bi
Although the addition of 3 to 0.3% is disclosed, the purpose of the additional addition of Bi and B in these publications is to improve magnetism by grain boundary segregation of the added component. In addition to the fact that there is no suggestion for the prevention of uneven surface defects due to the combined effect of B and B, there is no example of simultaneous addition. Moreover, the recommended range of the B content is 0.003 to 0.3%.
However, the effect of the present invention with the addition of a trace amount of 0.002% or less was not known at all. Furthermore,
As far as the inventor knows, nothing is disclosed about the effect of hydrogen at the time of adding Bi and B composites.

The details of the experiment leading to the present invention will be described below.
First, FIG. 1 shows the results of an experiment on a laboratory scale that led to the definition of the limited range of the characteristic portion of the constituent elements of the present invention.
Shown in The result of component analysis of the vacuum steel ingot used was approximately C: 0.05.
mass% (hereinafter simply indicated as “%”), Si: 3.25%, M
n: 0.07%, Se: 0.02%, Al: 0.023%, N: 0.009
%, H: 0.4 mass ppm (hereinafter simply referred to as “ppm”)
In addition to the above, various amounts of Bi and B shown in the figure are included, and the balance is mainly composed of Fe. After heating this ingot to 1400 ° C in an electric heating furnace, it was made into a hot-rolled sheet of 2.5 mm in a total of 4 passes (surface temperature of the input side material at the time of finish rolling: 1100 ° C). After hot-rolled sheet annealing, it is primarily cold-rolled to 1.8 mm, subjected to intermediate annealing at 1000 ° C for 100 seconds, water-cooled, secondly cold-rolled to 0.23 mm, primary recrystallized at 830 ° C, and then attained the maximum temperature of 1200 After the secondary recrystallization annealing at ℃, the measurement of the magnetic characteristic value B _{8 and} the number of uneven defects per 1680 cm ^{2 of} surface area are performed. FIG. 1 shows that irregular defects can be suppressed by adding B: 0.2 ppm or more irrespective of the amount of Bi, however, when B is added in excess of 20 ppm at the time of adding Bi, magnetic deterioration is shown.

Next, a factory experiment was conducted. The composition of the test pieces used in this factory experiment was approximately C: 0.05%, Si:
3.25%, Mn: 0.07%, Se: 0.02%, Al: 0.023%, N:
0.009%, Sb: 0.05% plus Bi: 0.0045% and B: 1.
In addition to 5 ppm, contains various amounts of hydrogen (H),
The balance is mainly composed of Fe. After heating the steel having such a composition to 1400 ° C. in a gas combustion furnace or an induction heating furnace, hot rolling is performed, and then cold rolling is performed to 2.6 mm.
The primary cold-rolled from the hot-rolled sheet to 1.8 mm, and subjected to an intermediate annealing at 1000 ℃, 100 seconds, and then secondary cold-rolled to a sheet thickness of 0.23 mm,
Primary recrystallization annealing at 830 ° C and final finishing annealing at 1200 ° C were performed. The results are shown in FIG. In the same figure, the result of the component in which the amount of H exceeds 3 ppm is indicated by x. With this component, unevenness defects could not be suppressed under any of the rolling conditions.
FIG. 2 shows the appearance ratio of uneven defects with the coarse initial pass linear pressure described later on the horizontal axis. The result when the roll diameter was reduced is indicated by a black circle in FIG.

[0012] In the hot finish rolling, as a rolling work roll of a rolling stand in which the surface temperature of the rolling material on the entry side is 1100 ° C or higher, in other words, a rolling stand through which the rolling material having a surface temperature of 1100 ° C or higher passes. When a roll having a ratio of radius / rolled material sheet width of 0.4 or less was used, high magnetism in the product and particularly good surface properties were maintained. More preferably, as shown in FIG. 2, slab heating is performed using induction heating at a frequency of 50 Hz or more and 200 Hz or less, and heating is performed in the range of 1350 ° C. to 1450 ° C., and then the linear pressure of the first pass of hot rough rolling is 1000
When hot rolling at t / m or less was performed, the appearance of the defect was almost completely eliminated.

As a method for reducing the linear pressure, a method of rolling while keeping the material temperature high, a method of reducing the rolling speed, and a method of reducing the rolling reduction have all been effective. In the method of changing the load, the change in the load was small, and the effect of improving the surface properties was also small.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been mainly directed to a method for manufacturing a grain-oriented electrical steel sheet, but is applicable to a grain-oriented electrical steel sheet utilizing a similar secondary recrystallization phenomenon. In addition, the present invention can be applied to a method in which the primary recrystallization annealing and the secondary recrystallization annealing are performed during the same annealing, a low-temperature slab heating method, and products subjected to various magnetic domain refining treatments. For the cold rolling and annealing steps from the hot rolled sheet to the finished sheet, known methods such as a single cold rolling method and a double cold rolling method can be used.

Next, the typical composition ranges of grain-oriented electrical steel sheets to which the present invention is applied are as follows. Si: 2.0 to 6.5% Si is an effective component for increasing the specific resistance of steel sheets and reducing iron loss. However, if the content exceeds 6.5%, the cold rolling property is impaired, while the content is less than 2.0%. Not only does the amount decrease the specific resistance, but also randomization of the crystal orientation occurs due to α → γ transformation during the final finish annealing performed for secondary recrystallization and purification, and a sufficient iron loss reduction effect cannot be obtained So Si
The content is preferably in the range of 2.0 to 6.5%. Bi: 0.0005-0.05% Since Bi improves the magnetic properties of the product even in a small amount, the minimum is 0.00
It is desirable to have 05%. However, if an attempt is made to add more than 0.05%, the loss due to volatilization is large in a normal steelmaking process, so the upper limit is set to 0.05%.

B: 0.2 ppm to 20 ppm B has a remarkable effect of suppressing the irregularity defects due to the addition of bismuth even in a trace amount, and at least 0.2 ppm must be present. However, at the time of adding Bi, if the amount of B increases, the magnetism deteriorates, so it must be controlled to 20 ppm or less. H: 3 ppm or less Even a small amount of H promotes the generation of unevenness defects at the time of adding bismuth, so it is controlled to 3 ppm or less by a known method such as RH type vacuum degassing.

C: 0.10% or less C is a component useful not only for uniformly dispersing the composition during hot rolling and cold rolling, but also for developing Goss-oriented crystal grains, and it is desirable that C be present even in a trace amount. . However, 0.10%
If the content exceeds the range, decarburization becomes difficult, and the accumulation of Goss-oriented crystal grains is rather disturbed. Therefore, the upper limit is not necessarily limited, but is preferably 0.1% or less. Mn: 0.02 to 0.12% Mn is not necessarily limited, but at least about 0.02% is required to prevent hot embrittlement, and if the Mn content is too large, the magnetic properties deteriorate. Therefore, it is desirable to set the upper limit to about 0.12%.

When AlN is used as an inhibitor,
For Al and N, recommended upper and lower limits are determined for the following reasons. Al: 0.004 to 0.03% If the amount of Al is too small, the absolute amount of the inhibitor will decrease.
However, the above range is recommended, although not necessarily limited, since it is impossible to completely solid-dissolve this. N: 0.004 to 0.010% The amount of N in the hot-rolled sheet material is not necessarily limited for the same reason as Al, but the above range is recommended.

As a precipitation-type inhibitor, MnS, MnSe, CuS _X , CuSe _X, or the like can be used instead of AlN, and these can be used in combination with AlN. Further, it can be used in combination with a grain boundary segregation type inhibitor. As the inhibitor component, in addition to the above S, Se, Al, Sb, S
Since n, As, Pb, Ce, Ti, Cu, Mo, and the like also have an advantageous effect, these components can be added together in small amounts. The preferred range of these components is approximately 0.0003 to 0.
2%, and for each of these inhibitor components,
One or more combined uses are possible. in addition,
It is also effective to use a method in which nitriding is carried out after the end of the final cold rolling until the start of the secondary recrystallization to enhance the inhibitor. The steel sheet after the secondary recrystallization is coated with an insulating coating as necessary, and is flattened to obtain a product.

In the present invention, the reason why unevenness defects can be reduced by controlling the amounts of boron and hydrogen is not clear, but it is probable that both elements that diffuse quickly in the steel cause some interaction with Bi during hot rolling. It is likely that the effects of the invention were achieved.

In the present invention, hot finish rolling
The roll work roll diameter of the rolling stand in the temperature range of the entry side material surface temperature of 1100 ° C or higher, and the ratio of roll radius / material plate width
It is essential that the process be performed with a roll having a small diameter of 0.4 or less, but under these conditions, it is considered that internal defects that become buds of unevenness defects in the product can be effectively pressed.

In addition, slab heating is performed using induction heating at a frequency of 50 Hz or more and 200 Hz or less, and the temperature is increased from 1350 ° C. to 1450 ° C.
The above-mentioned effect is enhanced by heating while appropriately controlling the temperature difference inside the slab by performing heating in the range of, and hot rolling is performed so that the linear pressure of the first pass of the rough rolling becomes 1000 t / m or less. Thus, it is considered that the above effects are reinforced by causing a structural change such as recrystallization without producing defect buds by light rolling. Here, the linear pressure of the pass is obtained by dividing the roll load during the passing by the sheet width.

[0023]

【Example】

(Example 1) C: 0.05%, Si: 3.25%, Mn: 0.07%, C
u: 0.10%, S: 0.02%, Al: 0.020%, N: 0.007%,
Bi: 0.006%, Sn: 0.12%, B: 12ppm, H: 1.2ppm
(The H amount is adjusted by performing a vacuum degassing process.)
The slab mainly composed of Fe is cast to a thickness of 220 mm by continuous casting, the slab is heated to 1380 ° C. in a gas-fired furnace, and then subjected to three-pass rough rolling. The work roll in the first pass was subjected to a total of 7 passes of finish hot rolling using a small-diameter roll having a whirl roll radius of 305 mm for a material width of 0.9 m to obtain a 2.0 mm thick silicon steel strip. This hot rolled sheet was annealed at 1080 ° C for 40s, cold rolled to 0.30mm, primary recrystallization annealing at 820 ° C, and then secondary recrystallization annealing at a maximum temperature of 1180 ° C. . The magnetic properties of the obtained product are B ₈ : 1.973 T,
A product with a surface defect count of 0.6 / 100m was obtained.

(Example 2) C: 0.05%, Si: 3.25%, M
n: 0.07%, Cu: 0.12%, S: 0.06%, Al: 0.023%,
N: 0.007%, Bi: 0.006%, Sn: 0.15%, B: 0.6 pp
m, H: 1.5 ppm (Adjustment of H amount is performed by performing vacuum degassing.) A slab mainly composed of Fe is cast to a thickness of 220 mm by continuous casting, and the slab is subjected to 1190 g in a gas combustion furnace. After heating to ℃, rough rolling was performed in four passes, and hot-rolling was finished so that the inlet temperature was 1010 ° C or higher to obtain a 2.0 mm thick silicon steel strip. 0.30 of this silicon steel strip
The steel sheet was cold-rolled to 850 mm, subjected to primary recrystallization annealing at 820 ° C., further subjected to nitriding treatment, and then subjected to secondary recrystallization annealing at a maximum temperature of 1180 ° C. The magnetic property value of the obtained product is B ₈ :
A product with 1.975 T and the number of generated surface defects 0.4 / 100m was obtained.

(Example 3) C: 0.05%, Si: 3.25%, M
n: 0.07%, Se: 0.02%, Bi: 0.02%, Sb: 0.04%,
B: 3.5 ppm, H: 6 ppm (The H amount is adjusted by performing vacuum degassing.) A slab mainly composed of Fe is cast to a thickness of 220 mm by continuous casting. After heating to 1430 ° C. in an induction heating furnace at 4 Hz, the coarse rolling in the first pass of the rough rolling has a linear pressure of 360 t / m in four passes (the linear pressure was controlled by controlling the rolling speed and the rolling reduction). Then, the work rolls up to the second pass where the surface temperature becomes 1100 ° C or more are hot-rolled in a total of 7 passes using a small-diameter roll with a radius of 315 mm for a material width of 1 m and a thickness of 2.5 mm. Silicon steel strip. This hot-rolled sheet was annealed at 900 ℃ for 40 s, then cold-rolled to 1.8 mm, subjected to intermediate annealing at 1000 ℃ for 100 s, water-cooled, and second-rolled to 2.3 mm. First recrystallization annealing at 830 ° C. was performed, and then the next recrystallization annealing at a maximum temperature of 1200 ° C. was performed. B ₈ : 1.978 T as the magnetic property value of the obtained product
Thus, a product having no surface defects was obtained.

[0026]

As is apparent from the above, according to the present invention, when manufacturing a grain-oriented electrical steel sheet, extremely high magnetic properties and surface properties are compatible.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of B addition on the magnetic properties and surface properties of a Bi additive.

FIG. 2 is a diagram showing the influence of a finished work roll diameter and a rough rolling initial pass linear pressure on unevenness defects.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-145799 (JP, A) JP-A-5-214445 (JP, A) Thin sheet manual “Hot rolled steel plate”, The Iron and Steel Institute of Japan, Showa 57 September 25, pp. 117-118 (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 B21B 3/02 C22C 38/00-38/60 H01F 1/16

Claims (2)

(57) [Claims] (1) Si: 2.0 to 6.5 mass% and Bi: 0.0005 to
A slab made of silicon steel containing 0.05 mass% is heated, and then subjected to hot rough rolling, followed by hot finish rolling to form a hot-rolled steel strip, and further cold-rolled with annealing. When producing grain-oriented electrical steel sheets by performing primary recrystallization annealing and then secondary recrystallization annealing, the amount of boron in the slab is controlled to be in the range of 0.2 mass ppm to 20 mass ppm, and the amount of hydrogen is controlled to 3 mass ppm or less. Basically, if the surface temperature of the rolled material at the start of hot finish rolling is 1100 ° C or more, in addition, in hot finish rolling, the rolling stand through which the rolled material having a surface temperature of 1100 ° C or more is passed. A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent surface properties, wherein a roll having a ratio of roll radius / rolled material sheet width of 0.4 or less is used as a rolled work roll. 2. The heating of the slab is performed in the range of 1350 ° C. to 1450 ° C. using induction heating at a frequency of 50 Hz or more and 200 Hz or less, and then the hot rough rolling is performed so that the linear pressure in the first pass is 1000 t / m or less. The method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent surface properties according to claim 1.