JPH01230721A - Manufacture of grain-oriented silicon steel sheet having high saturation magnetic flux density - Google Patents

Abstract

PURPOSE:To manufacture a grain-oriented silicon steel sheet having high magnetic flux density by successively subjecting a hot rolled sheet contg. specified amts. of Si, Al, Ti, N, B and S and/or Se to cold rolling, decarburization annealing in wet hydrogen, coating with a protective coating material for annealing, finish annealing and nitriding. CONSTITUTION:A hot rolled sheet contg., by weight, 1.5-4.8% Si, 0.012-0.05% AC, 0.002-0.012% Ti, 0.001-0.012% N, 0.0005-0.008% B and <=0.012%, in total, of S and/or Se satisfying Mn/(S+Se)>=4 is cold rolled once or more, decarburization-annealed in wet hydrogen, coated with a protective coating material for annealing and finish-annealed. The sheet is further nitrided in a heating stage between the end of the final cold rolling and the beginning of secondary recrystallization during the finish annealing. A grain-oriented silicon steel sheet having high magnetic flux density can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes basic metallurgical phenomena in the production of unidirectional silicon steel sheets used in iron cores of electrical equipment.
We proposed a new combination of ingredients as a precipitate '+yJ (generally called an inhibitor) that is effective against the development of secondary recrystallization, making it possible to manufacture unidirectional silicon steel plates with high magnetic flux density. It is something to do.

[Conventional technology]

The unidirectional silicon steel plate is composed of crystal grains having the so-called Goss orientation (expressed as the (110) <001> orientation in Miller index), with the steel plate plane being the (110) plane and the rolling direction having the <100> axis. It is used as a soft magnetic material in the cores of transformers and generators.

This steel plate must have good magnetic properties such as magnetization properties and iron loss properties. The quality of magnetization characteristics is determined by the level of magnetic flux density induced within the iron core in a constant magnetic field.
For products with high magnetic flux density, the iron core can be made smaller. The height of the magnetic flux density is determined by the orientation of the steel plate grains < 110) < OO
This can be achieved by highly aligning with H.

Iron loss is the electric power [4 losses] consumed as thermal energy when a specified alternating magnetic field is applied to the iron core. Affect.

Steel plates with high magnetic flux density make the iron core of electrical equipment smaller.

This is desirable because it reduces the amount of magnetic flux that can be produced and requires less iron, and the challenge in this technical field is to develop a method for producing products with as high a magnetic flux density as possible at a low cost.

In particular, recently, magnetic domain refining technology has been developed, and it has become possible to obtain materials with high magnetic flux densities with very low iron I-member values.

By the way, unidirectional silicon steel sheet is produced by finishing annealing the hot-rolled sheet to the final thickness by a combination of appropriate cold rolling and annealing (primary recrystallized grains having the 1101<001> direction). It is obtained by so-called secondary recrystallization, which selectively grows .Secondary recrystallization involves the formation of fine precipitates, such as MnS, Δj!N9, in the steel plate before secondary recrystallization.
This is achieved by the presence of MnSe*CuzS+ (8j!, 5i)N, etc., or by the presence of grain boundary-existing elements such as Sn and Sb. These precipitates and grain boundary-existing elements are described in J, E, May and D.

Turnbull (Trans, tlet, soc, A
(1101<
The growth of primary recrystallized grains other than the 001> orientation is suppressed, and (1
10) Has the function of selectively growing <001> oriented grains. Such a grain growth suppressing effect is generally called an inhibitor effect.

Therefore, the key issue for research and development in this field is how to stabilize secondary recrystallization using any kind of precipitates or grain-boundary elements, and how to improve °ζ correction (1101<
The problem lies in how to achieve an appropriate state of existence of grains with a 001> orientation in order to increase their abundance. In particular, recently, in the method using one type of precipitate, (110) < 00
1> Since there is a limit to controlling the height of orientation, by deeply understanding the disadvantages and advantages of each precipitate, it is possible to organically combine several precipitates to produce products with higher magnetic flux density stably and Progress is being made in developing technologies that can be manufactured at low cost.

Regarding the types of precipitates, M, F, Littmann in Japanese Patent Publication No. 30-3651, J, E, May and D, T
urnbull is TransMet, Soc, AIME
212 (1958) p769/781 with MnS, Taguchi, sheet metal with ΔIN and MnS with Special Publication Publication No. 33-4710,
Fiedler is Trans, Me
t, Soc AIMB 221 (1961) p12
VN from 01 to 1205, Imanaka is special public service 1977-134
69 with MnSe, Sb, J, A, Salsgiver
In JP-A No. 57-45818, An and copper sulfide are
Komatsu et al. in patent application No. 179855 (Al, 5i)
N, and other TiS, CrS,
CrC, NbC, 5iOz, etc. are known. In addition, as a grain boundary existing element, “Journal of the Japan Institute of Metals J 27 (1963
) As to p186 Tatsuo Saito.

Although Sn, Sb, etc. have been mentioned, there are no examples of these elements being used alone in industrial production, and all of them are used in coexistence with precipitates to achieve a supplementary effect. As more characteristic inhibitors, II, gre
US Pat. No. 3,905,842 (1975) by Noble, US Pat. That is, the presence of appropriate amounts of solid solution S, B, and N makes it possible to manufacture a unidirectional silicon steel plate with a high magnetic flux density. The selection criteria for precipitates that are effective for secondary recrystallization are not necessarily clear, but a representative opinion is that they are based on the results of calibration, "Tetsu to Hagane J 53 (1967) p. 1007-1.
023. To summarize, (1) the size is about 0.1 p (2) the required volume is 0.1 vol 1% or more (3) it is not possible to completely melt or not melt at all in the secondary recrystallization temperature range, so it is appropriate It is a solid solution to a certain extent. Although some of the above-mentioned various precipitates meet these conditions, not all phenomena meet these conditions. It has been found that (1) above does not have any important meaning in the method of nitriding steel sheets after recent cold rolling. As described above, currently no guiding principles have been established for selecting precipitates, and new inhibitor control techniques are being searched for through trial and error. In any case, in order to obtain a high magnetic flux density (high degree of accumulation in +1101<001> orientation), it is necessary to rinse the precipitates, finish them uniformly and in large quantities with H, and make them exist in the steel sheet before high-temperature annealing. Therefore, it is important to control the precipitates and at the same time adjust the properties before secondary recrystallization by an appropriate combination of rolling and heat treatment to match the characteristics of the precipitates.

[Problem to be solved by the invention]

Currently, there are three typical methods for manufacturing unidirectional silicon steel sheets that are industrially produced, and each method has its advantages and disadvantages. The first technique is a two-time cold rolling process using MnS, which was disclosed in Japanese Patent Publication No. 30-3651 by M.F. Littmann, and the resulting secondary recrystallized grains develop stably, but the magnetic flux is high. Density cannot be obtained. The second technology is a process in which the final cold rolling using AAN + MnS has a strong reduction rate of 80% or more, which was disclosed in Japanese Patent Publication No. 40-15644 by Kawaguchi et al. During production, the appropriate range of manufacturing conditions is narrow and stable production of products with the highest magnetic properties is lacking. Is the third technique published by Imao et al. in Special Publication No. 13469/1983? [The MnS shown here
(and/or MnSe> This is a process of manufacturing silicon steel containing Sb through a double cold rolling process, and although a relatively high magnetic flux density can be obtained, harmful and expensive elements such as Sb and Se are used. However, since it is a double cold rolling method, the manufacturing cost is high.The above three types of techniques have the following problems in common.

That is, all of the above-mentioned technologies are technologies for controlling precipitates finely and uniformly, with the first technology increasing the heating temperature of the slab prior to hot rolling to 1260°C or higher, and the second technology increasing the heating temperature of the slab to 1260°C or higher, while the second technology
As shown in Publication No. 51852, it depends on the amount of Si in the material.
1350°C in the case of %Si, and 1350°C in the case of the third technology
-1230℃ or higher as shown in Publication No. 20716,
In the examples in which a high magnetic flux density was obtained, the temperature was raised to an extremely high temperature of 1320° C., so that the coarsely existing precipitates were once solid-dissolved, and then precipitated during the subsequent hot rolling or heat treatment. Increasing the slab heating temperature increases the energy used when heating the slab, reduces yield due to the generation of slag, increases heating furnace repair costs, and increases the frequency of heating furnace repairs. 't) There is a problem that continuous casting slabs cannot be used because of a decrease in the + ratio and, as shown in Japanese Patent Publication No. 57-41526, linear secondary recrystallization defects occur. However, more important than these cost issues is the use of Si to improve iron loss.
If measures are taken to increase the thickness of the finished product and reduce the thickness of the finished product, the occurrence of linear secondary recrystallization defects will increase, and with technology based on high-temperature slab heating, there is no hope for future improvements in steel (4). On the other hand, the technology disclosed in Japanese Patent Publication No. 61-60896 made secondary recrystallization extremely stable by reducing the amount of S in the steel, making it possible to produce thin, high-Si products.However, this technology was not suitable for mass production. There is a problem with the stability of magnetic flux density when manufacturing on a large scale, for example, in JP-A-62-4031.
Although improved techniques as disclosed in Japanese Patent No. 5 have been proposed, the problem has not been completely solved until now.

Apart from the above-mentioned technology, there are U.S. Patent No. 3.905.842 by Il. Grenoble and U.S. Patent No. 3.905.843 by H. Fiedler, but these technologies are inherently contradictory and have not been industrially produced. do not have. That is, since this technology mainly uses solid solution S as an inhibitor, it is essential to lower Mn and prevent the formation of MnS in order to ensure solid solution S. Specifically, Mn/S ratio 2.1
is necessary. By the way, it is widely known that solid solution S and Se have an extremely adverse effect on the toughness of materials. Therefore, in industrial production, it is extremely difficult to cold-roll a unidirectional silicon steel sheet that has a large amount of Si and is easily cracked in the presence of solid solution S or Se. As detailed above, it is necessary to rebuild the inhibitor design in order to satisfy the needs of 31% thin products that have low costs, high magnetic flux density characteristics, and a high possibility of low iron loss in the future. be.

[Means to solve the problem]

The present inventors combined appropriate amounts of A1 and N, and B and Ti under the conditions of reducing the amount of S or Se or their combination in molten steel below a certain amount and also reducing the amount of solid solution S or S'e. The final plate thickness is obtained by one or two normal cold rolling processes, and the process includes decarburization annealing, application of an annealing separator, and final annealing. By performing nitriding during the temperature rising stage before the start of the next recrystallization, we succeeded in manufacturing a unidirectional silicon steel plate with extremely high magnetic flux density.

As a result, in combination with magnetic domain control technology, it has become possible to obtain a material with a lower iron loss value than ever before.

The structural conditions that characterize the present invention will be explained.

If the amount of S or Se is large, linear secondary recrystallization defects will increase in the longitudinal direction of the product, making stable production impossible.
It becomes noticeable in a high Si range where t exceeds 3.2% (hereinafter, all percentages are by weight), and in thin products of 0.23 mm (9 mil products) or less. The upper limit of the S+Se content at which such linear secondary recrystallization defects do not occur is 0.0.
Limited to 12%. Even within this limited range, in the present invention, if the amount of S or Se, which was conventionally considered to be effective, increases, the magnetic flux density actually deteriorates, and the smaller the amount, the better the magnetic flux density becomes.However, with the current melting technology, the cost increases. The range that can be lowered without causing damage is generally 0.0005% or more. Next, in order to reduce costs, the present invention aims to completely eliminate rolling cracks during hot rolling and cold rolling, and in order to prevent cracking due to solid solution S or Se, Mn /S + Se ≧ 4 is set so that Mn/S+Se≧4 exists in the steel. Fine ff1s, se as much as possible
It was decided to fix it as S, MnSe.

Figure 1 shows C: 0.053%, Si: 3.35%, P:
0.030%, Ae: 0.030%, N: 0.
0075%, B: 0.0039%, Ti: 0.0
13. A 50 kg ingot containing Mn 0.038% and s3B changed to molten steel containing Mn 0.04% and 0.12%.
This figure shows cracks at the end of a hot rolled sheet after hot rolling after heating to 60°C and 1150°C. Cracking decreases rapidly when Mn/S≧4, especially when MnS is not dissolved as a solid solution 115
Cracks hardly occur when heating slabs at a low temperature of 0°C.

In addition, FIG. 2 (aHb) is a photograph showing the metal structure at the edge of FIG. 1, and FIG.
The figure shows the state when the slab heating temperature is 1350°C at Mn/S=2, and (b) shows the state when the slab heating temperature is 1350°C (1150°C as well). (similar to)).

Next, the effect of B will be explained.

C: 0.053%, Si: 3.25%, Mn: 0.1
4%, S: 0.007%, Ti: 0.003
0%, P: 0.023%, Al: 0.028%
, N: 0.0085% and B 0.0002 to 0.0
50kg ingot containing 095% was heated to 1150°C.
After heating, it was made into a 2.0 fin hot-rolled plate. 1120° (Hx3
After hot-rolled plate annealing for 0.20 min, cold-rolled to 810°C,
830℃.

Decarburization annealing was performed at 850°C, 870°C, 1890°C, and 910'c, and after coating MgO containing ferromanganese nitride, secondary recrystallization annealing was performed at 1200°C. The results are shown in FIG. It can be seen from the figure that when the decarburization annealing temperature is increased, the magnetic flux density B8 increases, but when the B content is low, fine grains are likely to be generated and the maximum value of Ba is small.

On the other hand, if there is too much, high B8 cannot be obtained, and the appropriate range is 0.00.
05 to 0.0080%.

FIG. 4 shows the results when B and Ti were added in combination.

C: 0.048%, Si: 3.30%, Mn:
0.100%, S: 0.008%, P: 0.0
25%, Aβ: 0.032%, N: 0.0075
The basic component is ~0.0092%, and 0.00% Ti is added to this as a basic component.
10-0.0180%, B 0.0002-0.009
115 50 kg ingot with compound addition in the range of 0%
After heating to 0°C, a hot-rolled plate of 2.0 mm was used. This is 11
0.20mm after annealing a hot rolled plate of 20°c x 3m1n
The material was cold-rolled, decarburized annealed at 850°C, coated with MgO containing ferromanganese nitride, and then subjected to secondary recrystallization annealing at 1200°C.

According to FIG. 4, B (II): those with a high magnetic flux density of 1.93T or more are TiO,0020~0.012
It has become clear that this can be obtained when the compound is added in a range of 5% to 0.0080% (BO,0011).

This effect of B and Ti is significant when the steel plate is nitrided after cold rolling, and it is thought that fine N or TiN probably has an effect. N: If it is less than 0.0010%, secondary recrystallized grains will not develop well. If it exceeds 0.0120%, swelling of the rope plate called blister will occur.

Next, A1 combines with N to form AIN, but in the present invention, it is essential to form a compound containing Al by nitriding in a subsequent step, so a certain amount or more of free /l is required. For this purpose, the appropriate range of Al is 0.012~
0.050% is required.

In addition to the above components, C is 0.025 to 0.075
A range of % is preferred.

If the C content is less than 0.025%, secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, the magnetic flux density of the product is low. On the other hand, if the C content exceeds 0.075%, the decarburization annealing time becomes longer, which inhibits productivity.

In addition, the Mn content has the following relationship with the S content:
As mentioned above, Mn/S≧4.0 is sufficient from the viewpoint of preventing edge cracking of the hot rolled sheet, but the upper limit of the Mn content is preferably 0.45%. If it exceeds 0.45%, film defects will occur.

Regarding the slab heating temperature, secondary recrystallization can be carried out either by high-temperature slab heating to dissolve the inhibitor as in the past, or by low-temperature slab heating using an ordinary copper plate, which was considered almost impossible in the past. However, as shown in FIG. 1, the temperature is preferably 1200° C. or lower, where no slag occurs, because cracks in the hot rolling can be reduced, and low-temperature slab heating, which requires less thermal energy, is advantageous.

In the steps after hot rolling, in order to obtain the highest B8, it is desirable to perform short-time annealing and then cold rolling at a high rolling reduction of 80% or more to achieve the final thickness. However, the hot-rolled sheet annealing may be omitted in order to reduce the cost, although the properties are slightly inferior. It is also possible to use a process that includes intermediate annealing to reduce the grain size of the final product.

Next, decarburization annealing is performed in wet hydrogen or a mixed atmosphere of wet hydrogen and nitrogen. The temperature at this time is not particularly important, but it is 80
The preferred range is 0°C to 900°C.

Note that the dew point of the atmosphere at this time is preferably +30°C or higher.

Next, an annealing separator is applied and a high IA (usually 1100℃~1
200°C) long-term final annealing. The most preferred embodiment of nitriding in the present application is to perform nitriding during the temperature raising process of the final annealing, thereby making it possible to create an inhibitor necessary for secondary recrystallization. To achieve this, an appropriate amount of a compound with nitriding ability, such as MnN, CrN, etc., is added to the annealing separator, or N
A gas capable of nitriding, such as H3, is added to the atmospheric gas.

In addition, as other embodiments of nitriding in the present invention, nitriding is performed in an atmosphere of a gas capable of nitriding after soaking during decarburization annealing, or heat treatment with an atmosphere of NH, etc. separately provided after decarburization annealing. It may be passed through a furnace for nitriding, or a combination of the above methods may be used.

After completion of secondary recrystallization, purification annealing is performed in a hydrogen atmosphere.

〔Example〕

(1) C: 0.055%, Si: 3.3%, Mn
: 0.14%, P: 0.030%, S:
0.007%, Ti: 0.0040%, Cr: 0
．． 12%, /l: 0.030%, N: 0.00
2. A slab of silicon steel consisting of 80% Fe and unavoidable impurities, with B added in the amount shown in the table below, was heated at 1150°C.2. We made Oam hot-rolled sheets. This is 1100”C
x 2 minutes of annealing and one cold rolling to 0.20u 85
Decarburization annealing was performed at 0°C for 90 seconds in a wet hydrogen-nitrogen mixed gas at 60°C. Next, annealing separator (a) containing 3% TiO□ and 5% by weight of ferromanganese nitride in MgO and Mg
It was coated with two types of annealing separator (b) containing only O and 0□3% Ti, heated to 1200°C at a temperature increase rate of 10°C/hr, and annealed for 20 hours.

At this time, the atmospheric gas is N during the heating process up to 1200℃.
Using a mixed gas of 225% and H275%, 1200℃
During soaking, the temperature was HzlOO%. All materials in which ferromanganese nitride, which serves as a nitriding source, was added to the annealing separator underwent secondary recrystallization, and all materials in which B was added obtained extremely high magnetic flux densities.

On the other hand, in all cases where ferromanganese nitride was not added, secondary recrystallization was defective. The results are shown in the table below.

(2) C: 0.048%, Si: 3.25%
, Mn: 0.12%, P: 0.025
%, Cr: 0.14%, Ti: 0.0030
%, Al: 0.028%, N: 0
．． 0070%, B: S content of silicon copper consisting of 0.0030% balance Fe and unavoidable impurities (a)
0.003%, (b) 0.009%, (c) 0.0
The 18% slab was heated at 1200°C to produce a hot-rolled sheet with a thickness of 1.8%. This was annealed at 1100°C for 2 minutes to obtain a 0.18 fin in one cold rolling, and decarburized at 830°C for 90 seconds in a wet hydrogen-nitrogen mixed gas at 55°C.
An annealing separator containing 7% by weight of ferromanganese nitride added to MgO was applied, and the temperature was heated to 1200°C at a heating rate of 15°C/hr.
℃ and annealed for 20 hours. The atmospheric gas at this time is the same as in Example 1.

The results are shown below.

If the S content is high, high magnetic flux density cannot be obtained.

(3) C: 0.045%, Si: 3.50%, Mn
: 0.16%, P: 0.035%, /10.028
%, N: 0.0080%, Ti: 0.004
0%, B: 0.0035%, Se added to molten steel consisting of the balance Fe and unavoidable impurities (a) 0.0050%
, (b) 0.0100%, (c) 0.0200%
The added slab was heated and hot-rolled at 1150°C.2. Oam
A hot-rolled sheet was manufactured.

This hot-rolled sheet was annealed at 1150° C. for 2 minutes + 900° C. for 2 minutes, then rapidly cooled, pickled, and cold rolled to 0.2 (ha).

After this, decarburization annealing was performed at 830°C for 90 seconds, an annealing separator containing 5% by weight of ferromanganese nitride added to MgO was applied, and the mixture was heated to 1200°C at a temperature increase rate of 10°C/hr. Annealing was performed for 20 hours.

At this time, the atmospheric gas is N during the heating process up to 1200℃.
Using a mixed gas of 250% and 8250%, 1200℃
(during soaking) (21oo%).

The magnetic properties were as follows.

If the Se content is too high, high magnetic flux density cannot be obtained.

(4) C: 0.0/15%, Si: 3.30%,
Mn: 0.150%, S: 0.009%, P
:0.030%1. An! : 0.031%, N:
Slab (a) consisting of 0.0070%, Ti: 0.0060%, balance Fe and unavoidable impurities, and slab (b) with further addition of 0.0035% B were prepared at 110%.
A hot-rolled plate with 2.3 fins was produced by heating and hot-rolling at 0°C.

(1) No hot rolled sheet annealing, (2) Hot rolled sheet annealing at 90%
0℃×5 minutes and then rapidly cooled, (3) 1150℃×
3 after rapid cooling after hot-rolled plate annealing for 2 minutes + 900℃ x 2 minutes
Prepared the standard.

This was cold rolled once to a 0.30 fin, and decarburized annealed at 830°C for 150 seconds in a wet hydrogen-nitrogen mixed gas at 650°C.
Apply an annealing separator containing TiO□ to hBo, and
It was heated to 1200°C at a temperature increase rate of °C/hr, and final annealing was performed for 20 hours.

The atmospheric gas during this heating process is 25% nitrogen and 75% hydrogen.
Nt13 gas was added to the mixed gas of 1,200° C. using a loppm Soenokawa gas filter, and during soaking at 1200° C., only hydrogen gas was used for purification.

The magnetic properties (B,) were as follows.

A high B value was obtained with or without hot-rolled sheet annealing in the case where B was added, compared to the case where B was not added.

(5) C: 0.056%, Si: 3.40%, M
n: 0.130%, S: 0.005%, P
: 0.030%, AZ: 0.027%, N:
0.0075%, Ti: 0.0030%, B:
A slab consisting of 0.0042%, balance Fe and unavoidable impurities was heated and hot rolled at 1150°C to form 2.5 fl and 1.6 fl.
I made a hot-rolled fin plate. 2.5 mm thick hot-rolled sheet is 1. after pickling.
Cold-rolled to 5 xyh, 1
After annealing at 120° C. for 2.5 minutes, a rapid cooling treatment was performed. Set this to 0
．． It was cold rolled to 150 +n, decarburized annealed at 830°C for 70 seconds, coated with an annealing separator containing MgO with TiO□ and MnN, and final annealed at 1200"C for 20 hours.

The atmospheric gas during this heating process is 25% nitrogen and 75% hydrogen.
A mixed gas was used, and during soaking at 1200° C., only hydrogen gas was used for purification. The magnetic properties were as follows.

〔Effect of the invention〕

As described above, the present invention is capable of obtaining an extremely high magnetic flux temperature with few rolling cracks by heating a plain copper pan at a low temperature, so its industrial value is extremely high.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between Mn/S and the crack depth at the end of the hot rolled sheet, Figure 2 (aHb) is a photograph showing the metallographic structure of the end of the hot rolled sheet in Figure 1, and Figure 3 is B FIG. 4 is a diagram showing the relationship between the temperature and the decarburization annealing temperature, and FIG. 4 is a diagram showing the state of magnetic flux density when Ti and B are added in combination.

Claims (1)

[Claims] (1) In weight%, Si: 1.5-4.8% Al: 0.012-0.050% Ti: 0.0020-0.0120% N: 0.0010-0.0120% B: 0 .0005 to 0.0080% A silicon steel containing one or two types of S or Se in a total of 0.012% or less, Mn/(S+Se): (weight ratio) ≧4.0, the balance being Fe and inevitable impurities. A hot rolled sheet is subjected to one or more cold rolling processes to achieve the final thickness, then decarburized annealed in wet hydrogen, coated with an annealing separator, and finished for the purpose of secondary recrystallization and purification. A method for producing a unidirectional silicon steel sheet having a high magnetic flux density, characterized in that annealing is performed and a nitriding treatment is performed during a temperature rising stage from the final cold rolling to the start of secondary recrystallization in finish annealing.