JPH086138B2 - Method for manufacturing thin unidirectional silicon steel sheet with low iron loss - 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 thin unidirectional silicon steel sheet used for an iron core of an electric machine,
This makes it possible to manufacture a thin unidirectional silicon steel sheet with low iron loss.

[0002]

2. Description of the Related Art A unidirectional silicon steel plate has a steel plate surface of {110}
In the plane, the rolling direction has a <100> axis, and it is composed of crystal grains having a so-called Goss orientation (representing {110} <001> orientation in Miller index), and is used as a soft magnetic material for transformers and generators. Used for iron cores. This steel sheet must have good magnetic properties and iron loss properties. The quality of the magnetization characteristics is determined by the level of the magnetic flux density induced in the iron core in the applied constant magnetic field, and the iron core can be downsized in products with high magnetic flux density. The high magnetic flux density can be achieved by aligning the orientation of the steel plate crystal grains to {110} <001>.

Iron loss is a power loss consumed as heat energy when a predetermined AC magnetic field is applied to the iron core, and magnetic flux density, plate thickness, amount of impurities, specific resistance, size of crystal grains are determined according to the quality. And so on. A steel sheet having a high magnetic flux density can reduce the iron core of an electric device and also reduce an iron loss, which is desirable. In the technical field, development of a method of manufacturing a product having a high magnetic flux density at a low cost is an issue.

By the way, a unidirectional silicon steel sheet has a primary re-orientation having a {110} <001> orientation by finishing annealing a hot rolled sheet having a final thickness obtained by a combination of appropriate cold rolling and annealing. It is obtained by so-called secondary recrystallization in which crystal grains are selectively grown. The secondary recrystallization is a fine precipitate such as MnS, AlN, MnS in the steel sheet before the secondary recrystallization.
This is achieved by the presence of e, BN, (Al, Si) N, etc., or the presence of grain boundary existence type elements such as Sn, Sb, etc.

These precipitates and grain boundary type elements are JBMa
y and D. Turnbull (Trans.Met.Soc.AIME212 (1958) p769 /
781), it has the function of suppressing the growth of primary recrystallized grains other than the {110} <001> orientation in the finish annealing step and selectively growing the {110} <001> oriented grains. Such a grain growth suppressing effect is generally called an inhibitor effect. Therefore, the priority issue of research and development in this field is to determine what kind of precipitates or grain boundary existence type elements are used to stabilize the secondary recrystallization, and to determine the exact proportion of {110} <001> oriented grains. It is how to achieve their proper presence to enhance.

In particular, recently, the method using one kind of precipitate has a limit in controlling the altitude of the {110} <001> orientation. Therefore, by clarifying the disadvantages and merits of each precipitate, some precipitates are formed. Technological development is underway to organically combine products to stably manufacture products with higher magnetic flux density and at lower cost. At present, there are three types of typical industrially produced unidirectional silicon steel sheet manufacturing methods, each of which has advantages and disadvantages. The first technique is
This is a two-time cold rolling process using MnS disclosed in Japanese Patent Publication No. 30-3651 by MF Littmann, and the obtained secondary recrystallized grains grow stably, but a high magnetic flux density cannot be obtained. The second technique is Japanese Patent Publication No. 40-1564 by Taguchi et al.
This is a process in which the final cold rolling using AlN + MnS disclosed in Japanese Patent Publication No. 4 is a strong rolling reduction of 80% or more, and a high magnetic flux density can be obtained, but strict control of manufacturing conditions is required in industrial production. . The third technique is a process for producing silicon steel containing MnS (and / or MnSe) + Sb, which is disclosed in Japanese Examined Patent Publication No. 51-13469, by a double cold rolling process, and has a relatively high magnetic flux density. Although it can be obtained, the double cold rolling method increases the manufacturing cost.

The above three types of technology have the following problems in common. That is, in any of the above techniques, the slab heating temperature prior to hot rolling as a technique for finely and uniformly controlling precipitates is 1260 ° C. or higher in the first technique and JP-A-48-51852 in the second technique. Depending on the amount of Si as the material, 1350 ° C. in the case of 3% Si, and 1230 ° C. or higher in the third technique as shown in JP-A-51-20716. By making the temperature extremely high such as 1320 ° C., coarsely existing precipitates are once solid-dissolved and then precipitated during hot rolling or heat treatment. Increasing the slab heating temperature increases the energy used during slab heating, decreases the yield due to the generation of slag, increases the heating furnace repair cost, and lowers the facility operating rate due to the increased heating furnace repair frequency. There is a problem that the continuous casting slab cannot be used because linear secondary recrystallization failure occurs as disclosed in Japanese Patent Publication No. 41526-415. However, more important than such a problem in terms of cost, if measures such as increasing Si and increasing the product thickness to reduce iron loss are taken, the occurrence of this linear secondary recrystallization defect increases. However, the technology based on the high temperature slab heating method has no hope for improving iron loss in the future. On the other hand, in the technique disclosed in Japanese Examined Patent Publication No. 61-60896, by reducing the S in the steel, the secondary recrystallization is extremely stable and a high Si thin hand product is made possible. However, this technique has a problem in the stability of the magnetic flux density in factory production on a mass production scale.
Although an improved technique disclosed in Japanese Patent Publication No.-40315 has been proposed, it has not been solved completely until now.

[0008]

As described above, the manufacturing method currently industrialized is to incorporate the inhibitor required for secondary recrystallization in the step before cold rolling. On the other hand, the present invention is a manufacturing method based on the same technical idea as JP-A-62-40315. That is, the inhibitor required for secondary recrystallization is decarburization annealing (primary recrystallization).
It is built in after completion until before secondary recrystallization occurs in finish annealing. As a means of that, N is introduced into the steel to function as an inhibitor (Al,
Si) N is formed.

As a means for injecting N into the steel, there is a method of utilizing N invasion from the atmospheric gas in the finish annealing temperature rising process as proposed in the prior art, but in the present invention, The stripping after the decarburization annealing or the strip after the completion of the decarburization annealing is performed in a continuous line using an atmosphere gas such as NH ₃ which serves as a nitriding source. Even when such a process is adopted, it is still important to reduce the secondary recrystallized grains and form a good quality film in order to obtain low iron loss, but this point is not yet sufficient. . In addition, the development of secondary recrystallized grains tends to become unstable when the plate thickness of the steel plate becomes thin, and it is necessary to solve such a problem.

[0010]

As a result of a more detailed study of this technique, the inventors of the present invention have found that the oxygen content of oxides produced during decarburization annealing and continuous nitriding annealing on the surface of a steel sheet and the temperature of finish annealing are increased. It was confirmed that the amount and quality of the oxide film formed by the additional oxidation in the process had a great influence on the nitridation of the atmospheric gas and the removal of the inhibitor and the formation process of the glass film in the subsequent finish annealing process. In addition to the new finding that the magnetic properties and glass coating properties in the final product can be significantly improved by the addition of Sn, Sb which is a grain boundary segregation type,
It has been found that the addition of Al has the effect of controlling the primary recrystallized grain growth up to the high temperature range of the finish annealing (secondary recrystallization start temperature), and is particularly effective in stabilizing the magnetic properties of thin products.

The control of the amount of oxygen formed on the surface of the steel sheet is usually carried out by controlling the atmospheric gas dew point during decarburization annealing and the amount of water carried in by the annealing separator, but the components of the steel such as Mn, Si,
The variation is unavoidable depending on the contents of Al, Cr, etc. or the surface properties of the steel sheet. Further, the thinner the steel plate is, the more the influence of the fluctuation of the inhibitor in the surface layer of the steel plate becomes, and the magnetic characteristics fluctuate.

The present invention aims to reduce these fluctuations, and has confirmed that the above problems are solved and the object is achieved by the combined addition of a small amount of Sn and Sb in steel. As a method of adding Sn to silicon steel using AlN as a basic inhibitor, for example, the method described in JP-A-53-134722 can be mentioned. This is the idea of conventional high temperature slab heating as can be seen from the examples. It is based on.

Next, the present invention will be described based on experimental results. C: 0.054%, Si: 3.3%, Mn: 0.1
4%, S: 0.007%, acid-soluble Al: 0.028
%, N: 0.0075%, Cr: 0.10%, redissolving a slab consisting of the balance Fe and unavoidable impurities,
The steel ingot to which Sn and Sb were added was heated to 1150 ° C., and 1.
It was hot rolled to 8 mm.

The hot rolled sheet was annealed at 1120 ° C., pickled and cold rolled to obtain a cold rolled sheet having a thickness of 0.20 mm. Then, decarburization annealing is performed at a temperature of 840 ° C., N ₂ : 25%, H ₂ : 7.
It was conducted in an atmosphere of 5% and a dew point of 65 ° C. Next, nitriding treatment is performed at 750 ° C. for 30 seconds, N ₂ : 25%, H ₂ : 75%,
It was performed in an atmosphere in which a slight amount of NH ₃ was mixed. The amount of [N] after nitriding was adjusted to about 200 ppm. Then MgO
After applying a slurry containing TiO ₂ and TiO ₂ as main components,
After finish annealing at 00 ° C. for 20 hours, tension coating was applied. The result is shown in FIG.

Sb is in the range of 0.00 to 0.10%, and
n was compounded in the range of 0.00 to 0.14%. The total amount of Sb and Sn that gives good iron loss is 0.03 to 0.
It is in the range of 15%. Especially Sb: 0.02-0.04
%, Sn: those added in the range of 0.04 to 0.08% are excellent. If Sb exceeds 0.08%, the decarburizing property becomes poor.

Next, the reasons for limitation of the present invention will be described. C
When the content of is less than 0.025%, the secondary recrystallization becomes unstable, and even when the secondary recrystallization is performed, the magnetic flux density (B ₈ value) of the product becomes lower than 1.80 T. On the other hand, when the content of C exceeds 0.075% and becomes too large, the decarburization annealing time becomes long and the productivity is remarkably impaired.

When the Si content is less than 2.5%, it is difficult to obtain a product with low iron loss, while when the Si content exceeds 4.5% and is too large, cracking occurs during cold rolling of the material. However, frequent fractures make stable cold rolling impossible. One of the characteristics of the component system of the starting material of the present invention is that S is 0.
It is at a point of 015% or less, preferably 0.010% or less.

Conventionally known techniques, for example, Japanese Patent Publication No. 40-1
In the technology disclosed in Japanese Patent No. 5644 or Japanese Patent Publication No. 47-25250, S is essential as an element for forming MnS, which is one of the precipitates necessary for causing secondary recrystallization. In the above-mentioned known technology, there is a content range in which S exerts the most effect, and it has been defined as an amount capable of forming a solid solution of MnS in the heating step of the slab performed prior to hot rolling.

However, as an inhibitor (A
In the present invention using l, Si) N, MnS is not particularly required. Rather, an increase in MnS is not preferable in terms of magnetic properties. Therefore, in the present invention, the S content is 0.015% or less, preferably 0.010% or less. Al combines with N to form AlN, but in the present invention, it is essential to form (Al, Si) N by nitriding the steel in a later step, that is, after completion of primary recrystallization. Al is required to have a certain amount or more. Therefore, sol. 0.010 as Al
Add 0.050%.

If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. Proper content is 0.050 to 0.45
%. If N is less than 0.0010%, the development of secondary recrystallized grains becomes poor. On the other hand, if it exceeds 0.0120%, swelling of the steel sheet called blister occurs.

When Sn and Sb are added in combination, it is particularly effective in improving the magnetic flux density, iron loss and stabilization of a thin material having a plate thickness of 0.23 mm or less. The proper range is 0.03 to 0.15% in total of these two. Cr is an element that greatly affects the oxidation behavior during decarburization annealing, but if it is added at the same time as Sn and Sb, the quality and amount of the oxide layer are reduced, and the film formation during finish annealing is stabilized. The addition amount is 0.0
If it is less than 4%, the effect is small, while if it exceeds 0.20%, it is not preferable in terms of magnetic properties. The appropriate range is 0.04 to 0.
20%.

Regarding the slab heating temperature, the secondary recrystallization is carried out by the conventional high temperature slab heating in which the inhibitor is solid-dissolved, and also by the low temperature slab heating which is considered to be almost impossible in the past, which is similar to that of ordinary steel. . However, it is desirable that the slab heating temperature is 1200 ° C. or less at which no slag is generated, because the number of cracks in hot rolling can be reduced and the low temperature slab heating with less heat energy is advantageous.

In the process after hot rolling, the highest B ₈
In order to obtain the above, it is desirable to employ a method in which after annealing for a short time, cold rolling with a high rolling rate of 80% or more is performed to obtain the final plate thickness. However, the hot-rolled sheet annealing may be omitted in order to reduce the cost although the characteristics are slightly inferior. It is also possible to perform the step including intermediate annealing in order to reduce the crystal grains of the final product. Next, decarburization annealing is performed in wet hydrogen or a mixed atmosphere gas of wet hydrogen and nitrogen. The temperature at this time is not particularly limited, but 800 to 900 ° C. is a preferable range.

In the nitriding treatment in the present invention, after decarburization annealing, NH ₃ is mixed with a mixed gas containing hydrogen gas and nitrogen gas under the condition of running the strip, and the oxidation potential: PH ₂ O / PH ₂ ≦ 0. In the atmosphere of 04, 500 ~
It is preferable to perform it in the temperature range of 900 ° C. Then, an annealing separator is applied, and finish annealing is performed at high temperature (normally 1100 to 1200 ° C.) for a long time.

[0025]

EXAMPLES Examples will be described below. Example 1 C: 0.050%, Si: 3.30%, Mn: 0.10.
%. S: 0.007%, acid-soluble Al: 0.030%,
N: 0.0073% and Cr: 0.10% were used as basic components, and Sb and Sn were added thereto as shown in Table 1 below to produce an ingot.

This was heated at 1150 ° C., hot rolled, and 1.
A hot rolled plate having a thickness of 6 mm was obtained. This hot rolled sheet is cut to 110
Annealed at 0 ℃ for 2.5 minutes + 900 ℃ for 2 minutes, 100 ℃
After being cooled in hot water, pickled and cold rolled to a thickness of 0.17 mm
It was Next, decarburization annealing at 830 ° C for 90 seconds was performed at a dew point of 60 ° C.
It was performed in an atmosphere of wet hydrogen and nitrogen. Next, hydrogen 75%, nitrogen
Elementary 25%, 750 ° C x 3 in a small amount of ammonia mixed gas
Nitriding is performed for 0 seconds and the nitrogen content of the steel plate is adjusted to 180 ppm.
did. Then MgO and TiO₂5% and Na₂B _FourO
₇After applying the slurry obtained by adding 0.3%, 12
Finish annealing was performed at 00 ° C. for 20 hours. Then tension cord
Processing was performed. The magnetic properties are shown in Table 2.

[0027]

[Table 1]

[0028]

[Table 2]

Composite of Sn and Sb from Sn alone and Sb alone
The added one showed excellent magnetic properties. Example 2 C: 0.052%, Si: 3.45%, Mn: 0.12
%. S: 0.007%, acid-soluble Al: 0.028%,
N: 0.0075%, Cr: 0.08% included, balance Fe
And material A consisting of inevitable impurities and S in this component
n: 0.08%, of the material B with Sb 0.02% added
Annealing of 1.3 mm hot rolled sheets for 950 ° C x 5 minutes
And cooled in hot water at 100 ° C. Then, pickling,
It was cold rolled to a thickness of 13 mm. Next, decarburization at 830 ° C for 90 seconds
Annealing was performed in a wet hydrogen / nitrogen atmosphere with a dew point of 60 ° C. Next
Nitrogen treatment at 750 ° C for 30 seconds is performed with hydrogen, nitrogen, and ammonia.
Nitrogen mixed gas, nitrogen content after nitriding 180ppm
And Then MgO and TiO ₂5% and Sb₂(S
O_Four)₃A slurry prepared by adding 0.2% was applied.
Then, finish annealing was performed at 1200 ° C. for 20 hours.

Then, laser irradiation was performed to control magnetic domains, and then tension coating was applied. The magnetic properties were as follows. Sample B containing Sn and Sb showed very excellent magnetic properties. Sample A Sample B B ₈ (T) 1.89 1.92 W _13/50 (W / kg) 0.40 0.31

[0031]

According to the present invention, a thin unidirectional silicon steel sheet with low iron loss can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amounts of Sb and Sn in a product and iron loss.

Claims (1)

[Claims] 1. C: 0.025 to 0.075% by weight,
Si: 2.5-4.5%, S ≦ 0.015%, acid-soluble Al: 0.010-0.050%, N: 0.0010
0.012%, Mn: 0.050 to 0.45%, Cr:
0.04 to 0.20%, Sn and Sb combined to 0.03 to
After heating a silicon steel slab containing 0.15% and the balance Fe and unavoidable impurities to a temperature of 1200 ° C. or lower, hot rolling is performed and rolling is performed once or twice or more by intermediate annealing. A process for producing a unidirectional silicon steel sheet in which the final rolling rate is 80% or more, followed by decarburization annealing and finish annealing. After decarburizing annealing, hydrogen, nitrogen, and ammonia are mixed under the condition of running the strip. A method for manufacturing a thin unidirectional silicon steel sheet with low iron loss, which comprises nitriding in a gas.