JPH08311552A - Method for producing unidirectional electrical steel sheet with excellent magnetic properties and coating properties - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to improve the magnetic properties and coating properties of unidirectional electrical steel sheets used for iron cores of electric equipment. [Structure] A slab containing C, Si, acid-soluble Al, N, and consisting of residual Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and finally cold-rolled at a rolling reduction of 80% or more. In the method of producing a unidirectional electrical steel sheet by performing cold rolling one or more times with intermediate annealing, if necessary, followed by decarburizing annealing and final finishing annealing, the solid solution N amount during slab heating is Based on slab C, Si, acid soluble A
Determine the amount of each of l and N, control the total amount of SiO ₂ in the oxide film of the steel sheet after decarburization annealing, and control the average grain size of primary recrystallized grains after the completion of decarburization annealing until the start of final annealing. However, the nitriding treatment is performed after the hot rolling and before the start of secondary recrystallization in the final finish annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional magnetic steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. The magnetic field strength is usually 80 as a value representing the excitation characteristic.
A magnetic flux density B _{8 at} 0 A / m is used. In addition, as a numerical value showing the iron loss characteristic, the iron loss per kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is W _17/50.
Are using.

The magnetic flux density is the most dominant factor of the iron loss characteristics. Generally speaking, the higher the magnetic flux density, the better the iron loss characteristics. Generally, when the magnetic flux density is increased, the secondary recrystallized grains become large, which may result in poor iron loss characteristics.
On the other hand, by controlling the magnetic domains, the iron loss characteristics can be improved regardless of the grain size of the secondary recrystallized grains.

This unidirectional electrical steel sheet is produced by causing secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} axis on the steel sheet surface and <001> axis in the rolling direction. Has been done. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction.

A typical technique for producing such a high magnetic flux density unidirectional electrical steel sheet is Japanese Patent Publication No. 40-1564.
4 and Japanese Patent Publication No. 51-13469. In the former, Mn as the main inhibitor
S and AlN are used, and the latter uses MnS, MnSe, Sb and the like. Therefore, in the current technology, it is essential to appropriately control the size, morphology and dispersion state of the precipitates that function as these inhibitors. As for MnS, in the present process, M is applied when the slab is heated before hot rolling.
A method is used in which nS is once completely solid-solved and then precipitated during hot rolling.

A temperature of about 1400 ° C. is necessary to completely form a solid solution of MnS required for secondary recrystallization. This is higher than the slab heating temperature of ordinary steel by 200 ° C. or more, and this high-temperature slab heating treatment has the following disadvantages. 1) A high-temperature slab heating furnace dedicated to directional magnetic steel is required. 2) The energy intensity of the heating furnace is high. 3)
The amount of molten scale increases, and the adverse effect on operation is large, as seen in so-called shaving.

In order to avoid such a problem, the slab heating temperature should be lowered to the level of that of ordinary steel. This means that at the same time, the amount of MnS effective as an inhibitor is reduced or not used at all. Means that the destabilization of the secondary recrystallization is inevitably brought about.

Therefore, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor in some form with precipitates other than MnS to sufficiently suppress normal grain growth during finish annealing. Such inhibitors include nitrides, oxides, and grain boundary precipitated elements in addition to sulfides. Known techniques include, for example, the following.

In Japanese Patent Publication No. 54-24685, As,
A method of controlling the slab heating temperature in the range of 1050 to 1350 ° C. by containing grain boundary segregation elements such as Bi, Sn, Sb in the steel is disclosed, and in JP-A-52-24116, in addition to Al, Zr, Ti, B, Nb, Ta, V, C
It discloses a method of controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride forming element such as r and Mo.

Further, in JP-A-57-158332, low-temperature slab heating is performed by lowering the Mn content and setting the Mn / S ratio to 2.5 or less, and further secondary recrystallization is performed by adding Cu. The technology for stabilizing the is disclosed.

Techniques have also been disclosed in which improvements are made from the metallographic side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, S, in addition to Mn,
By adding elements such as Se, Sb, Bi, Pb, Sn, and B, and combining this with the columnar crystal ratio of the slab and the secondary cooling reduction ratio, low temperature slab heating at 1100 to 1250 ° C is realized.

Further, in JP-A-59-190324, in addition to S or Se, Al and B and nitrogen are mainly used as an inhibitor, which is subjected to pulse annealing at the time of primary recrystallization annealing after cooling. The technology to stabilize the recrystallization is open to the public.

As described above, in order to realize the low temperature slab heating in the production of grain-oriented electrical steel sheet, great efforts have been made so far. Furthermore, JP-A-59-56522
In Japanese Patent Laid-Open Publication No. 2008-242242, a technique is disclosed which enables low temperature slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less. By this method, the problem of defective linear secondary recrystallization of the product due to coarsening of the slab crystal grains during heating of the high temperature slab was solved.

[0014]

Although the method using low temperature slab heating is originally intended to reduce the manufacturing cost, it cannot be industrialized unless it is a technique that can stably obtain good magnetic characteristics. The present inventors, for the industrialization of low-temperature slab heating, average grain size control of primary recrystallized grains before final finishing annealing, and after hot rolling, nitrided into steel sheet between the start of secondary recrystallization of final finishing annealing. We have constructed a technology centered on the treatment.

In this technical system, in order to make the iron loss of the product, to reduce the cost, to improve the cold rolling stripability, etc.,
It becomes necessary to change the components such as Si and C. in this case,
It has become difficult to achieve both magnetic property control and film property control by controlling the average grain size of primary recrystallized grains.

An object of the present invention is to provide a measure for achieving both magnetic property control by controlling the average grain size of primary recrystallized grains and control of the coating property when it is necessary to change the composition. Then, as a means thereof, solid solution N at the time of heating the slab is used.
The present invention has been completed based on the knowledge that it is effective to design the components based on the amount and control the total amount of SiO ₂ in the oxide film of the steel sheet after decarburization annealing.

[0017]

The gist of the present invention is as follows. (1) C: 0.025 to 0.075% by weight, Si:
2.5-4.5%, acid-soluble Al: 0.010-0.0
60%, containing N: 0.0010 to 0.0130%,
The slab consisting of the balance Fe and unavoidable impurities is 128
Heating at a temperature of less than 0 ° C, hot rolling, including final cold rolling with a rolling reduction of 80% or more, if necessary, one or more cold rollings with intermediate annealing sandwiched, then decarburization annealing, and final finish annealing In the method for producing a grain-oriented electrical steel sheet, the slab C, Si, acid-soluble A based on the amount of solid solution N at the time of heating the slab.
The amount of each of l and N is determined, and the total amount of SiO ₂ in the oxide film of the steel sheet after decarburization annealing is set to 0.7 to 1.6 g / m ^2, and the primary after the completion of decarburization annealing until the start of final finishing annealing The average grain size of the recrystallized grains is set to 18 to 35 μm, and the steel sheet is nitrided before the secondary recrystallization of the final finish annealing after hot rolling. Method for manufacturing grain-oriented electrical steel sheet.

(2) The amount of solid solution N during heating of the slab is calculated, and at the time of the calculation, acid-soluble Al of the slab is used.
The amount and the amount of N are Al (%) and N (%), respectively, and the amount (% by weight) of Al- (27/14) N in the α phase and the γ phase is the same value (1). A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties as described.

(3) The hot-rolled sheet is annealed in the range of 850 to 1250 ° C. after hot rolling (1) or (2).
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties as described. (4) In any one of (1) to (3), further
% By weight, Mn: 0.06-0.8%, S + 0.405
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, which comprises using a slab containing Se: 0.005 to 0.020%.

(5) In any one of (1) to (3), further, by weight%, Mn: less than 0.01%, Cu:
0.05-0.50%, S + 0.405Se: 0.00
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, which comprises using a slab containing 5 to 0.020%.

(6) In any one of (1) to (3), further, in% by weight, Mn: 0.06 to 0.8%, C
u: 0.05 to 0.50%, S + 0.405 Se: 0.
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, which comprises using a slab containing 005 to 0.020%.

(7) In any one of (1) to (6), a slab containing Sn: 0.01 to 0.15% by weight is further used, and the magnetic properties and the coating are provided. A method for producing a grain-oriented electrical steel sheet having excellent properties.

[0023]

The unidirectional electrical steel sheet targeted by the present invention is
The molten steel obtained by the conventional manufacturing method is cast by continuous casting method or ingot making method, and if necessary, the slab is separated by the slabbing process, and then hot rolled into hot rolled sheet. Annealing the hot-rolled sheet according to the above, and then including final cold rolling with a rolling reduction of 80% or more, if necessary, performing one or more cold rollings with intermediate annealing, followed by decarburizing annealing and final finishing. It is manufactured by sequentially performing annealing.

The inventor of the present invention has conducted various studies on measures for achieving both magnetic properties and film properties when it is necessary to change the composition of Si, C, etc. in a manufacturing process premised on low-temperature slab heating. As a result, we obtained new knowledge that it is effective to design the composition based on the amount of solute N during slab heating and control the total amount of SiO ₂ in the oxide film of the steel sheet after decarburization annealing. The details will be described below based on the experimental results.

FIG. 1 shows the influence of the amount of solute N and decarburization annealing temperature at the completion of slab heating on the magnetic properties and coating properties. In this case, by weight ratio, C: 0.028 to 0.070
%, Si; 2.5 to 3.4%, acid-soluble Al; 0.02
0-0.054%, N: 0.0048-0.0088%
250, containing the balance Fe and unavoidable impurities
A mm-thick slab was created. And 1000 to 1260 ° C
After soaking for 60 minutes, the product was hot-rolled to a thickness of 2.3 mm.

Without subjecting the hot-rolled sheet to the hot-rolled sheet annealing, it was subjected to a strong reduction rolling of about 85% to obtain a cold-rolled sheet having a final sheet thickness of 0.335 mm, which was 820 ° C, 830 ° C, 840 ° C,
Decarburization annealing under 4 conditions of holding at 850 ° C. for 150 seconds (annealing atmosphere: N ₂ : 25%, H ₂ : 75%, dew point: 40 to 70).
° C.) alms, then during annealing to hold 30 seconds 750 ° C., is mixed NH ₃ gas into the annealing atmosphere, was allowed to absorb nitrogen steel.

The amount of N after this nitriding treatment is 0.0210.
It was 0.0224% by weight, and the average grain size of the primary recrystallized grains was 19 to 27 μm. After the nitriding treatment, the steel plate is
An annealing separator containing gO as a main component was applied, and final finish annealing was performed. Further, a slab having the same composition as that described above is prepared, and each slab is heated under the same slab heating conditions as described above and immediately water-cooled to obtain an N content and a nitride content (N as Nit).
ride) was measured, and the difference was defined as the amount of solute N at the time of completion of slab heating.

As is clear from FIG. 1, it was found that good magnetic characteristics and film properties can be obtained by combining the amount of solute N at the completion of slab heating and the decarburization annealing temperature. The present inventor examined the findings shown in FIG. 1 in more detail. Figure 2
1 shows the relationship between the film properties when good magnetic properties of B ₈ ≧ 1.90 T were obtained and the total amount of SiO ₂ in the oxide film of the steel sheet after nitriding in FIG. As is clear from FIG. 2, total SiO in the oxide film of the steel sheet after nitriding
_{When the} amount of ₂ was 0.7 to 1.6 g / m ² , good film properties were obtained.

The mechanism of development shown in FIGS. 1 and 2 is not necessarily clear, but the present inventors presume as follows. The present invention is made by the present inventors in Japanese Patent Application No.
-1778 belongs to the technical system based on making the crystal structure after decarburization annealing appropriate. on the other hand,
It is considered that the N that was in solid solution at the time of completion of heating the slab becomes fine nitrides (mainly AlN) during hot rolling or during decarburization annealing (especially during temperature increase).

The grain growth behavior during decarburization annealing is strongly influenced by the grain boundary migration suppressing force (Zener factor) of precipitates. The Zener factor is proportional to the volume fraction of the precipitate and inversely proportional to the size.

When low-temperature slab heating is performed and hot-rolled sheet annealing is omitted as in the present invention, N which is in solid solution during slab heating is finely precipitated as AlN during hot rolling and decarburizing annealing. .

The fine AlN had a strength ratio of 70 to 80% of the Zener factor during decarburization annealing. That is, the amount of solute N during heating of the slab governed the grain growth behavior during decarburization annealing.

Therefore, in the combination of the amount of solid solution N during slab heating and the decarburization annealing temperature in FIG. 1, there is a range in which good magnetic characteristics can be obtained. The larger the amount of solid solution N is (the higher the Zener factor is). It is considered that, since the appropriate decarburization annealing temperature is high, good magnetic properties can be obtained if an appropriate primary recrystallized grain size distribution is obtained.

In order to obtain this proper primary recrystallized grain size distribution, under the condition that the amount of solid solution N is large at the time of slab heating which is strong enough to suppress grain growth of primary recrystallized grains during decarburization annealing. It is considered necessary to raise the temperature of decarburization annealing to promote the grain growth of primary recrystallized grains.

On the other hand, in FIG. 2, the total SiO in the oxide film of the steel sheet after nitriding in order to improve the film properties of the product.
_The reason why there is an appropriate range for the _two quantities is estimated as follows. In the case of this experiment, after the nitriding treatment, an annealing separator containing MgO as a main component is applied to the steel sheet, and final finish annealing is performed.

When the temperature of this final finish annealing is increased, SiO ₂ in the steel sheet surface oxide film reacts with MgO in the annealing separator, and M
g ₂ SiO ₄ is formed. This difference in the amount of Mg ₂ SiO ₄ formed is observed as the film properties of the product.

When it is necessary to change the decarburization annealing temperature according to the amount of solute N during slab heating in order to obtain good magnetic properties as in the present invention, the steel sheet surface oxide film It is very important to secure an appropriate amount of SiO ₂ . This amount of SiO ₂ depends on the temperature and time of decarburization annealing and the oxygen potential in the annealing atmosphere, and this control requires a high level of technology, and therefore requires careful attention.

The present inventor further developed the knowledge shown in FIG. 1 and developed a component design method. The amount of solid solution N in the slab heating is the amount of solid solution N in the α phase, the amount of solid solution N in the γ phase, γ
Rate, but in the two phases α and γ, Si, A
Since the distribution of l and N occurs, it is not enough to calculate by considering independently.

Therefore, the present inventor has (1) for the base component system and the design component system of the component design,
When there is no distribution of Si and N, (2) Al to the α and γ phases,
If there is no N distribution but Si distribution, (3) α,
When there is no distribution of Si to the γ phase, but there is distribution of Al and N, (4) Four cases where there is distribution of Al, Si and N to the α and γ phases, solid solution during slab heating Calculate the amount of N and design the amount of Al-27 / 14N when the amount of Al-27 / 14N is the maximum when the amount of dissolved N is the same in each case in the base component system and the design component system. The method adopted as an ingredient system was developed.

In this case, as a result, the amount of solid solution N at the time of heating the slab in the design component system is the same as or smaller than that in the base component system. That is, regarding the grain growth behavior during decarburization annealing, the design component system has the same grain growth as the base component system, or the grain growth is somewhat easier. Since the base component system is capable of satisfying both magnetic properties and coating properties, a proper primary recrystallized grain structure can be realized if the grain growth is the same as or slightly easier than that of the base component system.

This design method requires a database concerning the amount of solute N, the γ ratio, and the distribution of Si, Al, and N components into the α and γ phases, which the inventor has completed, but one Only the need to make bold assumptions arose. This point will be described. Examples of equations for obtaining the solid solution N amount ([N] (wt%)) of the α phase and the γ phase are shown in (1) and (2), respectively.

[0042]

[Equation 1]

[Si] is the amount of solid solution Si (% by weight),
T is temperature (° K), Al _R = Al-27 / 14N (% by weight). However, the amount of acid-soluble Al is shown as Al (%). Although the above formula is an example, the amount of Al _R is included in the formula [N] regardless of which formula is used.

Then, in the above component design, [N] of the α + γ phase
When calculating the amount, Al _R and γ-phase of the Al _R of α phase is coming in a single expression, variables in one equation is impossible to obtain the two and turned in solution. Therefore, "α
The equation can be solved by assuming that "Al _{R of the} phase and γ phase are the same".

Next, the reasons for limiting the constituent features of the present invention will be described. First, the reasons for limiting the components of the slab and the slab heating temperature will be described in detail. C is 0.025% by weight
(Hereinafter simply abbreviated as%), the secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, B ₈ > 1.80.
Since (T) is hard to obtain, it was set to 0.025% or more. on the other hand,
If C is too much, the decarburization annealing time becomes long and it is not economical, so the content was made 0.075% or less.

If Si exceeds 4.5%, cracking during cold rolling becomes significant, so the content of Si is set to 4.5% or less. On the other hand, if it is less than 2.5%, the specific resistance of the material is too low, and the low iron loss required for the transformer core material cannot be obtained.
It is preferably 3.2% or more.

Al is AlN necessary for stabilizing the secondary recrystallization.
Alternatively, to secure (Al, Si) N, acid-soluble A
l must be 0.010% or more. Acid soluble Al
Is more than 0.060%, the AlN of the hot-rolled sheet becomes unsuitable and the secondary recrystallization becomes unstable, so the content was made 0.060% or less.

When N exceeds 0.0130%, blisters on the surface of the steel sheet called blisters occur, so N is set to 0.0130% or less. If N is less than 0.0010%, the grain growth behavior of the primary recrystallized grains during decarburization annealing becomes unstable, so it is set to 0.0010% or more.

Even if MnS and MnSe are present in the steel, it is possible to improve the magnetic characteristics by properly selecting the conditions of the manufacturing process. However, when S and Se are high, secondary recrystallization defective portions called linear fine grains tend to be generated, and in order to prevent the generation of this secondary recrystallization defective portion, (S + 0.405Se) ≦ 0.020 It is more preferable to set it as%. In addition, S + 0.405Se ≧ 0.005
%, It becomes easier to control the grain growth of the primary recrystallized grains during decarburization annealing, which is more preferable.

It is more preferable that the amount of Mn is 0.06 to 0.8%. If it is less than 0.06%, the probability that the shape (flatness) of the hot-rolled sheet obtained by hot rolling, that is, the side edge portion of the strip becomes corrugated and the product yield is reduced, increases. On the other hand, by setting the Mn content to 0.8% or less, it becomes easy to maintain the magnetic flux density of the product at a high level.

When the amount of Mn is less than 0.01%, C
u: 0.05 to 0.50%, S + 0.405 Se: 0.
It is further preferable to contain 005 to 0.020% in the slab. By setting the range of Cu and S + 0.405Se to the above values, Cu-S, Cu- during decarburization annealing
It is more preferable because the effect of suppressing the growth of primary recrystallized grains by Se falls within an appropriate range. In addition, when the temperature of the final finish annealing is increased, Cu--S and Cu--Se are used as nuclei for AlN, (Al,
Fine precipitation of Si) N occurs, and it is easy to obtain a high magnetic flux density.

Further, the Mn content is 0.06 to 0.8%, the Cu
Amount, S + 0.405Se amount of 0.05 to 0.50
%, 0.005 to 0.020% is more preferable. By setting the range of Mn, Cu, S + 0.405Se to the above values, MnS, MnSe,
The grain growth suppressing effect of the primary recrystallized grains due to Cu-S and Cu-Se falls within an appropriate range, which is more preferable.

In addition, when the temperature of the final finish annealing is increased (C
u, Mn) S, (Cu, Mn) Se, Cu-S, Cu-
Fine precipitation of AlN and (Al, Si) N with Se as the nucleus occurs, and high magnetic flux density is easily obtained.

Sn is known as a grain boundary biasing element and is an element that suppresses grain growth. On the other hand, when slab is heated S
n is completely dissolved, and is considered to be uniformly dissolved even in the slab at the time of heating having a temperature difference of several tens degrees Celsius which is normally considered. Therefore, it is considered that Sn which is uniformly distributed in the slab at the time of heating despite the temperature difference also acts on the grain growth suppressing effect at the time of decarburizing annealing uniformly in place.

Therefore, it is considered that Sn has the effect of diluting the spatial nonuniformity of grain growth during decarburization annealing due to the local nonuniformity of AlN. Therefore, the addition of Sn is effective in further reducing the fluctuation of the magnetic properties of the product.

The appropriate range of Sn is 0.01 to 0.15.
%. Below this lower limit, the grain growth suppressing effect is too small, which is not preferable. On the other hand, if the upper limit is exceeded, nitriding of the steel sheet becomes difficult, which causes secondary recrystallization failure, which is not preferable.

In addition, it is permissible to contain trace amounts of Sb, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements. In particular, nitride constituent elements such as B, Ti and Nb may be positively added in order to reduce the amount of solute N in the steel during slab heating. Further, in the case where there is the above-mentioned nitride constituent element, it is useful for improving the accuracy of the component design to consider the reduction amount of the solid solution N amount due to the presence of the nitride at the time of the component design described below.

The slab heating temperature was limited to less than 1280 ° C. for the purpose of cost reduction in the same manner as ordinary steel. It is preferably 1200 ° C or lower. C, Si, acid-soluble Al, N of the slab based on the amount of solid solution N when the slab is heated
Stipulated to determine each amount of. This is because, as shown in FIG. 1, the amount of solid solution N at the time of heating the slab is an important factor for controlling the magnetic characteristics, and the amounts of C, Si, acid-soluble Al and N and the slab heating temperature are fixed. This is because it is a factor influencing the amount of dissolved N.

This component can be designed by actually measuring the amount of solid solution N, or can be calculated by an empirical formula by creating a database. When calculating, calculate the amount of acid-soluble Al and the amount of N in the slab, respectively.
(%), N (%), α- and γ-phase Al-27 /
It is more preferable that the amount of 14N is the same.

The equation can be mathematically solved by setting the values of Al-27 / 14N to be the same for the α and γ phases. If this assumption is not made, the value of Al-27 / 14N needs to be stored in a database for each of the α and γ phases and each temperature, and a great deal of labor is required for the component design.

The heated slab is subsequently hot rolled to form a hot rolled plate. The hot-rolling process is usually performed by heating a slab having a thickness of 100 to 400 mm and then performing rough hot-rolling and finish hot-rolling in multiple passes. The method of rough hot rolling is not particularly limited, and a usual method is used. The time from the rough hot rolling to the start of the finish hot rolling is not particularly limited, but it is preferable to start the finish hot rolling over 1 second or more from the viewpoint of promoting precipitation of AlN.

Finishing hot rolling is usually performed by high speed continuous rolling for 4 to 10 passes. Normally, the rolling reduction of the finish hot rolling is such that the rolling reduction is higher in the former stage and the rolling reduction is lower in the latter stage so that the shape is good. The rolling speed is usually 100 to 3000 m / min, and the time between passes is 0.01 to 100 seconds.

Although not particularly limited, increasing the cumulative rolling reduction in the final three passes of hot rolling is effective for working-induced precipitation of AlN. It is also preferable to perform strong reduction in the stage before rough hot rolling and finish hot rolling, because it causes work-induced precipitation to some extent. Further, even in the final three passes, strong reduction in the final pass is particularly effective.

Normally, a slab with a thickness of 100 to 300 mm is
In the hot rolling step of forming a hot-rolled sheet having a thickness of 5 mm, as the sheet thickness during hot rolling becomes thinner, heat conduction in the sheet thickness direction becomes easier, so that the temperature difference existing in the slab gradually decreases. At this stage, in order to further promote the precipitation of AlN, it is effective to apply strain to increase the dislocations as AlN precipitation nuclei. Therefore, by applying a processing strain at the latter stage of the finish hot rolling in which the temperature difference in the steel sheet is most reduced, and by promoting the precipitation of AlN, it is possible to minimize the variation of the amount of AlN precipitated from being passed on to the subsequent process. It is considered effective.

After the final pass of hot rolling, it is usually air-cooled for about 0.1 to 100 seconds, water-cooled, wound at a temperature of 300 to 700 ° C., and gradually cooled. The cooling process is not particularly limited, but it is preferable to carry out air cooling for 1 second or more after hot rolling and keep the steel sheet in the precipitation temperature range of AlN as long as possible in order to promote the precipitation of AlN. .

This hot-rolled sheet is then subjected to one or more cold-rollings including a final cold-rolling with a rolling reduction of 80% or more, and if necessary, intermediate annealing. The reduction ratio of the final cold rolling is set to 80% or more because the reduction ratio is set in the above range because the sharpened {110} <001> oriented grains in the decarburized plate and the corresponding oriented grains ( This is because an appropriate amount of {111} <112> oriented grains, etc. can be obtained, which is preferable in increasing the magnetic flux density.

The present invention is based on the hot-rolled sheet annealing omission process. However, when hot-rolled sheet annealing is performed at a temperature of 850 to 1250 ° C., the local nonuniformity of AlN during slab heating is reduced. It has a reducing effect, and is more preferable. Also in this case, determining the respective amounts of C, Si, acid-soluble Al and N on the basis of the amount of solid solution N at the time of heating the slab is effective in stabilizing the magnetic characteristics at a high level.

The cold rolled steel sheet is subjected to decarburization annealing, application of an annealing separating agent, and final finishing annealing by a usual method to obtain a final product. Here, it is necessary to control the average grain size of the primary recrystallized grains to 18 to 35 μm after the completion of decarburization annealing and before the start of final finish annealing. The reason is that it is easy to obtain a good magnetic flux density in this range of the average particle size, and the change of the magnetic flux density due to the particle size variation is small. Furthermore, the total amount of SiO ₂ in the oxide film of the steel sheet after decarburization annealing is 0.7 to 1.
It was defined as 6 g / m ² . As shown in FIG. 2, a good coating property can be obtained by setting this range.

The means for satisfying the above conditions is not particularly limited. The above relationship can be satisfied by controlling the temperature and dew point during decarburization annealing. Oxidation behavior is affected by the elements added to the steel and their amounts. Therefore, in order to satisfy the above relationship, it is necessary to set conditions according to the material. Since Sn and Cu are elements that suppress oxidation,
Special attention is needed.

When the nitriding treatment is continuously performed after the decarburizing annealing or the nitriding treatment is separately performed, the SiO ₂ content of the steel sheet after the decarburizing annealing is specified for the steel sheet immediately before the final finish annealing. Is understood. Then, it is specified that the steel sheet is subjected to the nitriding treatment before the start of the secondary recrystallization of the final finish annealing after hot rolling, in the process that is premised on the low temperature slab heating as in the present invention, it is necessary for the secondary recrystallization. This is because the inhibitor strength tends to be insufficient.

The method of nitriding is not particularly limited, and after decarburizing and annealing, a method of nitriding by subsequently mixing NH ₃ gas in an annealing atmosphere, a method of using plasma, a method of adding a nitride to an annealing separator, and finally finishing Any method may be used, such as a method of absorbing nitrogen formed by the separation of nitrides in the steel sheet during the temperature rise of the annealing, a method of increasing the N ₂ partial pressure in the atmosphere of final finishing annealing and nitriding the steel sheet. The amount of nitriding is not particularly limited, but 1 ppm or more is required.

[0072]

【Example】

[Example 1] C: 0.046% by weight (hereinafter abbreviated as%),
Si: 3.0%, acid-soluble Al: 0.0333%, N:
Slab heating temperature of 1 using 0.0061% slab
When the temperature was set to 150 ° C. and hot-rolled sheet annealing was omitted and a 0.335 mm thick material was manufactured, a product having good magnetic properties and good coating properties was obtained. In order to shorten the decarburization annealing time, it was necessary to set the C content of the slab to 0.042%. At this time, the amount of solute N of the standard component material when the slab heating was completed was measured and found to be 0.0034%.

Therefore, Si: 3.0%, N: 0.0061
%, The amount of acid-soluble Al in the material having the same solid solution N content at 1150 ° C. was found to be 0.0296%.

Therefore, (A) C: 0.042%, Si:
3.0%, acid-soluble Al: 0.0296%, N: 0.0
061%, (B) C: 0.042%, Si: 3.0%,
Acid-soluble Al: 0.0333%, N: 0.0061% two kinds of 250 mm thick slabs were created, and then such slabs were soaked at a temperature of 1150 ° C. for 60 minutes and then hot rolling was started, A hot rolled sheet having a thickness of 2.3 mm was used.

This hot-rolled sheet was pickled to obtain a cold-rolled sheet having a thickness of 0.335 mm and a reduction rate of about 85%.
Decarburization annealing that holds for seconds is performed, and the annealing atmosphere at this time is
N ₂ : 25%, H ₂ : 75%, dew point 65 ° C, N ₂ : 2
5%, H ₂ : 75%, dew point 40 ° C.

After that, annealing was carried out at 750 ° C. for 30 seconds, NH ₃ gas was mixed in the annealing atmosphere, and nitrogen absorption was caused in the steel sheet. The N content of this steel sheet after nitriding is
It was 0.0205 to 0.0223%. The average grain size of the primary recrystallized grains of this steel sheet was 24 to 27 μm. Then, an annealing separator having MgO as a main component was applied to this steel sheet, and final finish annealing was performed by a known method.
Table 1 shows the experimental conditions, the magnetic properties of the products, and the coating properties.

[0077]

[Table 1]

Example 2 C: 0.030%, Si:
2.8%, acid-soluble Al: 0.034%, N: 0.00
Slab heating temperature is 1100 ° C using 61% slab
However, when the hot rolled sheet annealing was omitted and a 0.285 mm thick material was manufactured, a product having good magnetic properties and good coating properties was obtained.

In order to improve the iron loss characteristics, the slab Si
The amount needed to be 3.25%. At this time, a component system in which the amount of solid solution N of the reference component material when the slab heating was completed was the same value was designed as follows. As a prerequisite, C =
It was decided to calculate the amount of acid-soluble Al at which the equilibrium solid solution N amount at 1100 ° C. is the same as that of the above-mentioned reference component system, with 0.054% and N = 0.0061%.

[Condition 1] (No distribution of Si, Al, and N into α and γ phases) The equilibrium solid solution N content at 1100 ° C. of the reference component system is expressed by the formula (1), (2) in the present text. When calculated using the formula, 0.
It was 0028%. At this time, the value obtained in the experiment was used as the γ ratio.

Then, using the expressions (1) and (2), Al _R (= Al- (2
7/14) N) leads to equation relating, as the γ ratio using the experimental values, and solving the equation numerically, Al _R
= 0.0158%.

[Condition 2] (No distribution of Si into α and γ phases, distribution of Al and N into α and γ phases) Equilibrium solid solution N content at 1100 ° C. of the standard component system in the present invention When calculated using the equations (1) and (2) of No.
It was 0031%. At this time, the value obtained by the experiment was used as the γ ratio.

Then, using the equations (1) and (2), Al _R (= Al- (2
7/14) N) leads to equation for, using the experimental values as γ ratio, alpha, the value of Al _R in γ phase assuming identical, and solving the equation numerically, Al _R = 0.01
It was 84%.

[Condition 3] (with distribution of Si into α and γ phases and without distribution of Al and N into α and γ phases) The equilibrium solid solution amount of N at 1100 ° C. in the standard component system according to the present invention. When calculated using the equations (1) and (2),
It was 0.0027%. At this time, the γ ratio and α
The values obtained by experiments were used for the amounts of Si in the phases and the γ phase.

Then, using the equations (1) and (2), Al _R (= Al- (2
7/14) N) is derived and the γ ratio and α phase,
For the amount of Si in the γ phase, use the one obtained by experiment,
Solving the equation by numerical calculation, Al _R = 0.0160
%Met.

[Condition 4] (with distribution of Si, Al and N into α and γ phases) The equilibrium solid solution N content at 1100 ° C. in the standard component system is expressed by the formula (1), (2) in the present text. ) Was calculated using
It was 0.0033%. At this time, the γ ratio and α
The values obtained by experiments were used for the amounts of Si in the phases and the γ phase.

Then, using the expressions (1) and (2), Al _R (= Al- (2
7/14) N) is derived and the γ ratio and α phase,
For the amount of Si in the γ phase, the value obtained by experiment is used, and α
Assuming that the values of Al _R in the phase and γ phase are the same, the equation was solved by numerical calculation to find that Al _R = 0.0187%.

[Summary] Among the conditions 1 to 4, in order to stabilize the grain growth of the primary recrystallized grains, the one having the highest Al _R was selected. Therefore, Al _R = 0.0187% and N =
Since it is 0.0061%, acid-soluble Al: 0.0305%
Became. Therefore, (A) C: 0.054%, Si:
3.25%, acid-soluble Al: 0.034%, N: 0.0
061%, (B) C: 0.054%, Si: 3.25
%, Acid-soluble Al: 0.0305%, N: 0.0061
%, (C) :( B) component, Mn: 0.14%,
S: 0.007% was added to the components (D): (B), and Mn: 0.005%, Cu: 0.10%, S: 0.
09% was added to the components (E) :( B), and Mn:
0.10%, Cu: 0.20%, S: 0.010% added, (F): (B) component further Sn: 0.06% added, (G): (B) component In addition, Mn: 0.14
%, Cu: 0.09%, Se: 0.0017%, Sn:
Seven 250 mm thick slabs with 0.10% addition were made.

Then, the slab was soaked at a temperature of 1100 ° C. for 60 minutes and then hot rolling was started to obtain a hot rolled sheet having a thickness of 2.6 mm. Some of this hot-rolled sheet has 2
A hot-rolled sheet that is soaked for a minute is annealed, combined with a sample that does not have the hot-rolled sheet annealed, and pickled.
A cold rolled sheet having a thickness of mm was subjected to decarburization annealing in which the temperature was kept at 835 ° C. for 120 seconds.

At this time, the annealing atmosphere was set to N ₂ : 25%,
H ₂ : 75%, dew point: 70 ° C., N ₂ : 10%, H ₂ :
90%, dew point: 2 levels of 40 ° C. After that, 7
Annealing is performed by holding at 70 ° C for 30 seconds, and N
H ₃ gas is mixed, the steel sheet was caused to nitrogen absorption.
The N content of this steel sheet after nitriding is 0.0201 to 0.024.
It was 1%. The average grain size of the primary recrystallized grains of this steel sheet was 21 to 28 μm.

Then, an annealing separator containing MgO as a main component was applied to this steel sheet, and final finish annealing was performed by a known method. Table 2 shows the experimental conditions, the magnetic properties of the products, and the coating properties.

[0092]

[Table 2]

[0093]

INDUSTRIAL APPLICABILITY In the present invention, the amounts of C, Si, acid-soluble Al and N of the slab are determined based on the amount of solid solution N during heating of the slab, and the amount of C, Si and acid-soluble Al and N in the slab is determined in the oxide film of the steel sheet after decarburization annealing All of SiO ₂
The amount is controlled to control the average grain size of the primary recrystallized grains from the completion of decarburization annealing to the start of final finish annealing, and the nitriding treatment is performed after hot rolling and before the start of secondary recrystallization of final finish annealing.

Furthermore, the above component design was calculated based on the assumptions about the amount of acid-soluble Al and the amount of N, and Mn, S, Se and C were calculated.
By adding a predetermined amount of u and Sn, it is possible to stably obtain good magnetic properties and good film properties even if low-temperature slab heating is performed and hot-rolled sheet annealing is omitted. The effect is extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the amount of solid solution N and the decarburization annealing temperature at the completion of slab heating on magnetic properties and coating properties.

FIG. 2 is a graph showing the relationship between the film properties and the total amount of SiO ₂ in the oxide film of the steel sheet after nitriding when good magnetic characteristics were obtained in FIG.

Claims (7)

[Claims] 1. By weight%, C: 0.025 to 0.075%, Si: 2.5 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.0010 to 0. A slab containing 0.0130% of which the balance is Fe and inevitable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and finally cold-rolled at a reduction rate of 80% or more, and optionally subjected to an intermediate annealing. In a method of producing a grain-oriented electrical steel sheet by performing cold rolling at least once between sandwiching, followed by decarburizing annealing and final finishing annealing, based on the amount of solid solution N during slab heating, C, Si, Acid soluble Al, N
Of the total amount of Si in the oxide film of the steel sheet after decarburization annealing
The amount of O ₂ was 0.7 to 1.6 g / m ^2, and the average particle size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final finishing annealing was 1
A method for producing a unidirectional electrical steel sheet having excellent magnetic properties and coating properties, wherein the steel sheet has a thickness of 8 to 35 μm and is subjected to a nitriding treatment after hot rolling and before the start of secondary recrystallization in final annealing. 2. The amount of solute N dissolved during heating of the slab is calculated, and the amount of acid-soluble Al in the slab, N
2. The magnetic material according to claim 1, wherein the amounts are Al (%) and N (%), respectively, and the amounts (% by weight) of Al- (27/14) N in the α phase and the γ phase are the same. A method for producing a grain-oriented electrical steel sheet having excellent properties and coating properties. 3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to claim 1 or 2, wherein hot-rolled sheet annealing is performed in the range of 850 to 1250 ° C. after hot rolling. . 4. Further, Mn: 0.06 to 0.
8%, S + 0.404Se: 0.005-0.020%
A slab containing a slab is used.
3. The method for producing a grain-oriented electrical steel sheet according to any one of 3 above, which has excellent magnetic properties and coating properties. 5. Further, by weight%, Mn: less than 0.01%, Cu: 0.05 to 0.50%, S + 0.405S
The slab containing e: 0.005-0.020% is used, The manufacturing method of the grain-oriented electrical steel sheet excellent in the magnetic property and coating property in any one of Claims 1-3. 6. Further, in% by weight, Mn: 0.06 to 0.
8%, Cu: 0.05 to 0.50%, S + 0.405S
The slab containing e: 0.005-0.020% is used, The manufacturing method of the grain-oriented electrical steel sheet excellent in the magnetic property and coating property in any one of Claims 1-3. 7. Further, Sn: 0.01 to 0.
A slab containing 15% is used, and the method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to any one of claims 1 to 6.