JPH05295443A - Production of grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To omit hot rolled plate annealing and to stably obtain superior magnetic properties by limiting the amount of solid-solution N in a slab at the completion of slab heating and controlling the average grain size of primary recrystallized grains before the initiation of final finish annealing. CONSTITUTION:A slab of a steel having a composition consisting of, by weight ratio, 0.021-0.075% C, 2.5-4.5% Sr, 0.010-0.060% acid-soluble Al, <=0.0150 N, <=0.014% of (S+0.405Se), 0.05-0.8% Mn, and the balance Fe with inevitable impurities, is heated up to <1280 deg.C and hot-rolled. The amount of solid-solution N in the slab at the completion of slab heating is regulated to <=0.0045wt.%. Final cold rolling is done at 80% draft. Subsequently, decarburizing annealing is done and the average grain size of primary recrystallized grains before the initiation of final finish annealing is regulated to 18-30mum. Then, final finish annealing is performed. In the course between the completion of hot rolling and the initiation of secondary recrystallization at final finish annealing, nitriding treatment is applied to the steel sheet. Further, it is preferable to regulate the cumulative draft of final three passes at hot rolling to >=40%.

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 electrical 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 800A as a numerical value indicating the excitation characteristic.
A magnetic flux density B _{8 at} / m is usually 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, and 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 and the iron loss characteristics may become poor. 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 undergoes secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and <001> axis in the rolling direction. Being manufactured. In order to obtain good magnetic properties, it is necessary to highly align <001>, which is the easy magnetization axis, in the rolling direction.

As a representative technique for manufacturing such a high magnetic flux density unidirectional electrical steel sheet, Japanese Patent Publication No. 40-15644.
There is a method described in JP-B No. 51-13469. MnS and AlN in the former and Mn in the latter
S, MnSe, Sb, etc. are used as main inhibitors. Therefore, in the present technology, it is indispensable to appropriately control the size, morphology and dispersion state of precipitates that function as these inhibitors.

Regarding MnS, in the present process, a method is employed in which MnS is once completely solid-soluted during slab heating before hot rolling and then precipitated during hot rolling. 1400 ℃ to completely dissolve the required amount of MnS for secondary recrystallization
Some temperature is required. 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 exclusively for grain oriented electrical 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 can be seen in so-called shaving.

In order to avoid such problems, the slab heating temperature should be lowered to the level of ordinary steel.
At the same time, this means that the amount of MnS effective as an inhibitor is reduced or not used at all, and inevitably results in destabilization of secondary recrystallization.

Therefore, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor in some form with precipitates other than MnS and sufficiently control normal grain growth during finish annealing. As such inhibitors, sulfides, nitrides, oxides, grain boundary precipitation elements and the like are conceivable, and known techniques include, for example, the following.

In Japanese Patent Publication No. 54-24685, A
By containing grain boundary segregation elements such as s, Bi, Sn, and Sb in the steel, the slab heating temperature is set to 1050 to 1350 ° C.
The method of making into the range of was disclosed. JP-A-52-2411
No. 6, in addition to Al, Zr, Ti, B, Nb, Ta,
A method of controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride forming element such as V, Cr and Mo has been disclosed. Also, JP-A-57-158322
In the publication, the Mn content is reduced and the Mn / S ratio is set to 2.5.
A technique has been disclosed in which low-temperature slab heating is performed by the following, and further, secondary recrystallization is stabilized by adding Cu.

On the other hand, a technique has 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, Se. By adding elements such as Sb, Bi, Pb, Sn, and B, and combining them with the columnar crystal ratio of the slab and the secondary cold rolling reduction ratio, low temperature slab heating at 1100 to 1250 ° C is realized.

Further, in JP-A-59-190324, an inhibitor is mainly composed of Al and B and nitrogen in addition to S or Se, which is pulse-annealed during primary recrystallization annealing after cold rolling. A technique for stabilizing the secondary recrystallization has been published. Thus, in order to realize low temperature slab heating in the production of grain-oriented electrical steel sheets, great efforts have been made so far.

First, in JP-A-59-56522, Mn is 0.08 to 0.45% and S is 0.007.
A technique has been disclosed that enables low temperature slab heating by controlling the content to be not more than%. 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.

[0013]

Although the method by low temperature slab heating is originally intended to reduce the manufacturing cost, it is needless to say that it cannot be industrialized unless it is a technique for stably obtaining good magnetic characteristics. . On the other hand, lowering the slab heating naturally causes changes in hot rolling such as a decrease in hot rolling temperature. However, until now, an integrated manufacturing method of low temperature slab heating incorporating a hot rolling method has hardly been studied.

Conventional high temperature slab heating (eg 1300 ° C.)
In the above case, the main roles of hot rolling are three points: division by recrystallization of coarse crystal grains, fine precipitation of MnS, AlN or the like or suppression of precipitation, and formation by shear deformation of {110} <001> oriented grains. However, it is not necessary in the case of low-temperature slab heating, and as for the present inventor, as disclosed in Japanese Patent Application No. 1-1778, the crystal structure after decarburization annealing may be made appropriate, Precipitate control on hot-rolled sheet is not essential. Therefore, it can be said that there are few restrictions on hot rolling in the conventional method in the case of low temperature slab heating.

Meanwhile, in the production of unidirectional electrical steel sheets, hot-rolled sheet annealing is usually performed for the purpose of making the structure non-uniform after hot rolling, precipitation treatment and the like. For example, in the production method using AlN as the main inhibitor, Japanese Patent Publication No. 46-238
As disclosed in Japanese Unexamined Patent Publication No. 20 (1994), a method of controlling the inhibitor by performing AlN precipitation treatment in hot-rolled sheet annealing is adopted.

Generally, the grain-oriented electrical steel sheet is manufactured through the main steps of casting-hot rolling-annealing-cold rolling-decarburization annealing-finish annealing, and requires a large amount of energy. The manufacturing cost is higher than the above. In recent years, a review has been made on such a manufacturing process that consumes a large amount of energy, and a demand for simplifying the process and energy has increased. In order to meet such a demand, in a production method using AlN as a main inhibitor,
A method (Japanese Patent Publication No. 59-45730) of replacing the precipitation treatment of AlN in hot-rolled sheet annealing with high-temperature winding after hot-rolling has been proposed.

Certainly, even if the hot-rolled sheet annealing is omitted by this method, the magnetic characteristics can be secured to some extent, but in the usual method of winding in a coil shape of 5 to 20 tons, the cooling process is performed. A difference in thermal history occurs locally in the coil, which inevitably causes non-uniform deposition of AlN, and the final magnetic characteristics fluctuate depending on the location in the coil, resulting in a decrease in yield.

Therefore, the present inventors have paid attention to the recrystallization phenomenon after the final pass of hot rolling for finishing, which has hardly been noticed in the past, and utilizing this phenomenon, a production method by single cold rolling under a high pressure of 80% or more. The method of omitting hot-rolled sheet annealing (Japanese Patent Application No. 1-85540 and Japanese Patent Application No. 1-85541) was presented. These techniques are characterized in that the hot-rolled sheet has a fine recrystallized structure by being strongly pressed in the final three passes of hot-rolling and held at high temperature after completion of hot-rolling.
It became possible to achieve both slab heating at a temperature of less than 80 ° C and omission of hot-rolled sheet annealing.

On the other hand, regarding hot rolling of unidirectional electrical steel sheets, secondary recrystallization defects (lines extending in the rolling direction) caused by coarse growth of slab crystal grains during high temperature slab heating (eg, 1300 ° C. or higher) In order to prevent the formation of fine grains, a method is proposed in which recrystallization under high pressure rolling is performed at a reduction ratio of 30% or more per pass at a temperature of 960 to 1190 ° C during hot rolling to divide coarse crystal grains. Has been done (Japanese Patent Sho 60-
37172 publication). Although this method surely reduces the generation of linear fine grains, it is premised on the manufacturing process of hot-rolled sheet annealing.

Further, in the production method using MnS, MnSe, and Sb as inhibitors, 950 to 120 during hot rolling are used.
A method is proposed in which MnS and MnSe are uniformly and finely precipitated by continuously hot rolling at a rolling reduction of 10% or more at a temperature of 0 ° C. and subsequently cooling at a cooling rate of 3 ° C./sec or more to improve magnetic properties. (JP-A-51-2071)
No. 6). Also proposed is a method of improving the magnetic properties by performing hot rolling at a low temperature to suppress the progress of recrystallization and prevent the {110} <001> oriented grains formed by shear deformation from being reduced by subsequent recrystallization. Has been done (Japanese Patent Publication Sho 5
9-32526, Japanese Patent Publication No. 59-35415).

Even in these methods, the production by the single cold rolling method without annealing the hot rolled sheet has not been studied. Also,
During hot rolling of silicon steel slabs containing ultra-low carbon, hot rolling at low temperature and large pressure that accumulates strain in the hot-rolled sheet is performed, and coarse crystal grains peculiar to the ultra-low carbon material are obtained by recrystallization during subsequent hot-rolled sheet annealing A method of dividing is proposed (Japanese Patent Publication No. 59-342).
No. 12). However, even in this method, the production by the single cold rolling method without hot-rolled sheet annealing has not been studied.

Therefore, the significance of the technique (Japanese Patent Application No. 1-85540, Japanese Patent Application No. 1-85541) which enables the present inventors to achieve both the low-temperature slab heating and the omission of hot-rolled sheet annealing described above is significant. It turns out to be big. The inventors of the present invention proceeded with factory experiments in order to industrialize these technologies, and in the process, magnetic fluctuations occurred, which became a problem. Therefore, the present inventors extensively investigated the cause of this, and found that this magnetic variation was due to solid solution N in the steel during slab heating.

[0023]

The subject matter of the present invention is as follows. (1) C: 0.021 to 0.075% by weight ratio, Si:
2.5-4.5%, acid-soluble Al: 0.010-0.0
60%, N: 0.0150% or less, S + 0.405S
e: 0.014% or less, Mn: 0.05 to 0.8%, and the balance is 1 slab consisting of Fe and unavoidable impurities.
Heating is performed at a temperature of less than 280 ° C., hot rolling is performed, and then final cold rolling with a rolling reduction of 80% or more is performed, and if necessary, one or more cold rollings with intermediate annealing sandwiched are performed, followed by decarburization annealing and final In the method for producing a grain-oriented electrical steel sheet by applying finish annealing, the solid solution N in the slab upon completion of heating the slab is 0.0
045% by weight or less, the average grain size of primary recrystallized grains after completion of decarburization annealing until the start of final finish annealing is 18 to 30 μm, and after hot rolling, until the start of secondary recrystallization of final finish annealing. A method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises subjecting a grain to a nitriding treatment.

The present invention also uses a slab containing Sn: 0.01 to 0.15% by weight, the cumulative rolling reduction of the final three hot rolling passes is 40% or more, and the hot rolled sheet is heated to the slab heating temperature. It can be annealed at the following temperatures.

[0025]

The function of the grain-oriented electrical steel sheet of the present invention is
Molten steel obtained by the conventional steelmaking method is cast by a continuous casting method or an ingot casting method, and if necessary, a slab is sandwiched between slabs, followed by hot rolling into a hot rolled sheet, and then reduction. A final cold rolling with a rate of 80% or more is included, and it is manufactured by sequentially performing one or more cold rollings with intermediate annealing interposed therebetween, decarburizing annealing, and final finishing annealing.

The present inventors have studied in detail the cause of variation in magnetism and its solution when a low temperature slab heating material is manufactured by the single cold rolling method without hot-rolled sheet annealing. As a result, this phenomenon is caused by the solid solution N at the time of heating the slab.
It was found that the variation was caused by the precipitation of 1N.

First, the effect of the present invention will be described based on experimental results. FIG. 1 shows the relationship between the amount of solid solution N at the completion of slab heating and the fluctuation of the magnetic flux density of the product. In this case, by weight,
C: 0.035 to 0.070%, Si: 2.5 to 3.6
%, Acid-soluble Al; 0.017 to 0.055%, N;
0.0051-0.0097%, S; 0.005-0.
A slab of 20 kinds of components having a content of 007%, Mn; 0.10 to 0.16% and a balance of Fe and unavoidable impurities and having a thickness of 40 mm was prepared. And 1000 to 1260 ° C
After soaking for 60 minutes in 6 passes, hot rolling was performed in 6 passes, water cooling was performed after about 2 seconds, cooling to 550 ° C., and holding at 550 ° C. for 1 hour were performed to perform a coiling simulation. In this case, the reduction distribution of 6 passes is 40 → 15 → 7 → 3.5 → 3
→ 2.6 → 2.3 mm.

Without subjecting the hot-rolled sheet to annealing of the hot-rolled sheet, strong reduction rolling of about 85% was carried out to obtain a cold-rolled sheet having a final sheet thickness of 0.335 mm, and 810 ° C, 820 ° C, 830 ° C,
Decarburization annealing under 4 conditions of holding at 840 ° C for 150 seconds,
Next, during annealing at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere to allow the steel sheet to absorb nitrogen.

The amount of N after this nitriding treatment is 0.0214-
It was 0.0231% by weight. An annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed. After that, the magnetic flux density B _{8 of the} product was measured and taken for hot-rolled sheets under the same hot-rolling conditions with the same components 4
Difference between the highest and lowest B ₈ under two decarburization annealing conditions ΔB ₈
I asked.

Further, a slab having the same composition as the above slab is prepared, and each slab is heated under the same slab heating conditions as described above and immediately water-cooled to obtain an N amount and a nitride amount (N as Nit).
Ride) was measured, and the difference was taken as the amount of solute N at the completion of slab heating.

As is apparent from FIG. 1, when the amount of dissolved N at the completion of slab heating is 0.0045% or less, ΔB ₈ is 0.
The magnetic property is stable at or below 03T, which is stable.

The mechanism of the effect of controlling the amount of solid solution N at the completion of slab heating shown in FIG. 1 is not necessarily clear, but the present inventors presume as follows.

The present invention was made by the present inventors in Japanese Patent Application No. 1-177.
It belongs to the technical system disclosed in No. 8 that is 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 slab heating becomes fine nitrides (mainly AlN) during hot rolling or during decarburization annealing (especially at the time of temperature increase). It is considered that the size and precipitation amount of this fine nitride fluctuate even with a slight temperature change during decarburization annealing.

It is considered that the variation of the precipitate causes the variation of the crystal structure, which leads to the variation of the magnetic characteristics. Therefore, it is considered that reducing the amount of solute N at the time of completion of heating the slab, which causes the variation in the crystal structure, is effective in reducing the variation in magnetic characteristics.

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 0.021% by weight
If it is less than (hereinafter simply abbreviated as%), the secondary recrystallization becomes unstable, and even if secondary recrystallization is performed, B ₈ > 1.80.
Since (T) is difficult to obtain, it was set to 0.021% or more. on the other hand,
If C is too large, 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 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, in order to secure (Al, Si) N, acid-soluble A
0.01% or more is required as l. 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 0.0150%, blisters on the surface of the steel sheet called blister occur, so N is set to 0.0150% or less.

Even if MnS and MnSe are present in the steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, if S and Se are high, secondary recrystallization defects called linear fine grains tend to occur. To prevent the generation of secondary recrystallization defects, (S + 0.405Se) ≦ 0.014 Should be%.

If S or Se exceeds the above value, the probability of occurrence of secondary recrystallization defects becomes high no matter how the manufacturing conditions are changed, which is not preferable. Further, the time required for purification in the final finish annealing is too long, which is not preferable, and it is meaningless to increase S or Se unnecessarily from such a viewpoint.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, the shape (flatness) of the hot-rolled sheet obtained by hot rolling, that is, the side edge portion of the strip becomes wavy, which causes a problem of lowering the product yield. On the other hand, if the Mn content exceeds 0.8%, the magnetic flux density of the product is reduced, which is not preferable, so the upper limit of the Mn content was set to 0.8%.

Sn is known as a grain boundary segregation element and is an element that suppresses grain growth. On the other hand, when heating the slab S
It is considered that n is completely in solid solution, and is uniformly dissolved even in the slab at the time of heating having a temperature difference of several tens of degrees Celsius which is usually considered. Therefore, it is considered that Sn, which is uniformly distributed in the slab during heating despite the temperature difference, also acts locally in terms of the grain growth suppressing effect during decarburization annealing.

Therefore, it is considered that Sn has the effect of diluting the non-uniformity of grain growth during decarburization annealing due to the non-uniformity of AlN. Therefore, in addition to the technique of the present invention for limiting the upper limit of the amount of solute N, addition of Sn is effective for further reducing the fluctuation of the magnetic properties of the product.

The suitable 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 possible to contain a small amount of Sb, Cu, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements. In particular, B, Ti,
Nb and other nitride constituent elements are solid solution N in steel during slab heating.
It may be added positively to reduce the amount.

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. The amount of solute N in the slab upon completion of heating the slab must be 0.0045% or less. If it exceeds 0.0045%, as shown in FIG. 1, the magnetic fluctuation becomes large, which is not preferable.

The heated slab is subsequently hot rolled to form a hot rolled plate. It is more preferable to set the cumulative rolling reduction of the final three passes of hot rolling to 40% or more in order to reduce the spatial variation in the magnetic flux density of the product.

The hot-rolling step usually comprises rough hot-rolling and finish hot-rolling, in which a slab having a thickness of 100 to 400 mm is heated and then each is subjected to a plurality of passes. The method of rough hot rolling is not particularly limited, and a usual method is used. The time from the start of rough hot rolling to the start of finish hot rolling is not particularly limited, but starting the finish hot rolling over 1 second or more
It is preferable in terms of promoting the precipitation of AlN.

The feature of the present invention is the finish hot rolling following the rough hot rolling. Finishing hot rolling is usually performed by high speed continuous rolling for 4 to 10 passes. In the rolling distribution of the normal hot rolling, the rolling ratio is high in the front stage and lower in the rear 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.

The present invention is limited only to the cumulative rolling reduction in the final three passes of hot rolling, and other conditions are not particularly limited, but a strong reduction is performed before rough hot rolling and finish hot rolling. It is also preferable to carry out the above 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.

Usually, a slab with a thickness of 100 to 300 mm is
In the hot rolling process for 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 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, adding work strain in the latter stage of finishing hot rolling where the temperature difference in the steel sheet is most reduced to promote the precipitation of AlN suppresses the variation of the precipitation amount of AlN to the succeeding process as much as possible. Considered to be effective.

Next, the reasons for limiting the above hot rolling conditions will be described. The cumulative rolling reduction in the final 3 passes of hot rolling was set to 40% or more. Below this value, the effect of processing-induced precipitation of AlN is insufficient, which is not preferable. Although the upper limit of the cumulative rolling reduction of the final 3 passes is not particularly limited,
Industrially, it is difficult to apply a cumulative reduction of 99.9% or more.

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 or the like for 1 second or more after hot rolling and keep the steel sheet in the AlN precipitation temperature region as long as possible for promoting 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 with intermediate annealing sandwiched as necessary. 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 {111} <112> oriented grains and the like) can be obtained in an appropriate amount, which is preferable in increasing the magnetic flux density.

The present invention is based on the process of omitting hot-rolled sheet annealing. However, when hot-rolled sheet annealing is performed at a temperature equal to or lower than the slab heating temperature, it is similarly caused by the solid solution N during slab heating. Changes in the magnetic properties of the product. Therefore, also in this case, solid solution N limitation in the slab of the present invention, addition of Sn,
It is possible to use the control of the grain size after decarburization annealing, which will be described later, under the high pressure of the final three passes of hot rolling, and obtain better characteristics than the hot rolling sheet annealing skipping process.

The steel sheet after cold rolling 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 30 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.

It is defined that the steel sheet is nitrided after the hot rolling and before the secondary recrystallization of the final finish annealing.
This is because the inhibitor strength required for secondary recrystallization tends to be insufficient in the process that is premised on low temperature slab heating as in the present invention.

The method of nitriding is not particularly limited. After decarburization 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 in which the steel sheet absorbs nitrogen formed by the separation of nitrides during the temperature rise during annealing, a method in which the N ₂ partial pressure in the atmosphere of final finishing annealing is increased, and the steel sheet is nitrided. The nitriding amount is not particularly limited, but 1 ppm or more is necessary.

[0058]

【Example】

Example 1 C: 0.049% by weight, Si: 3.21% by weight, Mn:
0.14 wt%, S: 0.007 wt% as a basic component, acid-soluble Al: 0.027 wt%, N: 0.008
0 wt% was added to make a 40 mm thick slab consisting of the balance Fe and inevitable impurities.

Then, the slab is heated to 1250 ° C.
After soaking at two levels of temperature of 1080 ° C. for 60 minutes, hot rolling was immediately started, and hot rolling was performed for 6 passes to obtain a hot rolled sheet of 2.3 mm. At this time, the reduction distribution is 40 → 15 → 7 → 3.5 → 3
→ 2.6 → 2.3 (mm). In addition, the slab having the same composition as the above was water-quenched after completion of heating the slab under the conditions of, N and nitride were analyzed, and the amount of dissolved N was 0.0055% by weight, 0.0025% by weight. % By weight.

After completion of the hot rolling, a coiling simulation was conducted in which air cooling was performed for 1 second, water cooling was performed up to 550 ° C., holding at 550 ° C. for 1 hour, and then furnace cooling. This hot-rolled sheet was pickled to make a cold-rolled sheet of 0.335 mm with a reduction rate of about 85%, and a: 810
Decarburization annealing was performed for 150 seconds under four temperature conditions of ° C, b: 820 ° C, c: 830 ° C, and d: 840 ° C.

After that, annealing was carried out at 750 ° C. for 30 seconds, and NH ₃ gas was mixed in the annealing atmosphere to allow the steel sheet to absorb nitrogen. The N content of this steel sheet after nitriding is 0.02
It was 13 to 0.0232% by weight. The average grain size of the primary recrystallized grains in the entire cross-sectional thickness of this steel sheet was measured by using an optical microscope and an image analyzer, and it was 20 to 26 μm.

Next, an annealing separator containing MgO as a main component was applied to this steel sheet, and the temperature was raised to 1200 ° C. at a rate of 15 ° C./hour in an atmosphere gas of N ₂ 25% and H ₂ 75%, and then continued. 20 at 1200 ° C in H ₂ 100% atmosphere gas
A final finish annealing was carried out for holding for a time. Table 1 shows the experimental conditions and the magnetic properties of the products.

[0063]

[Table 1]

The present invention has less variation in magnetic properties due to decarburization annealing.

Example 2 C: 0.054% by weight, Si: 3.08% by weight, Mn:
0.16% by weight, S: 0.006% by weight, N: 0.00
85 wt% as a basic component, acid-soluble Al, 0.0
It was added at two levels of 19% by weight and 0.040% by weight, and two 250 mm thick slabs composed of the balance Fe and unavoidable impurities were prepared.

Then, the slab was soaked at a temperature of 1180 ° C. for 60 minutes, and then hot rolling was started at 1080 ° C. to obtain a hot rolled sheet of 2.3 mm. The reduction distribution of hot rolling, the cooling conditions after hot rolling, and the process conditions until final finishing annealing after hot rolling were performed under the conditions described in Example 1. Solid solution N when slab heating is completed
The amount was 0.0061% by weight and 0.0032% by weight. The amount of N after nitriding is 0.0203 to 0.0214% by weight, and the average grain size of the primary recrystallized grains after nitriding is 18 to
It was 26 μm. Table 2 shows the experimental conditions and the magnetic properties of the products.

[0067]

[Table 2]

The present invention has less variation in magnetic properties due to decarburization annealing.

Example 3 C: 0.038% by weight, Si: 3.05% by weight, Mn:
0.15% by weight, S: 0.006% by weight, acid-soluble A
1: 0.030 wt%, N: 0.0085 wt% as a basic component, Sn: 0.002 wt%, S
Two kinds of slabs having a thickness of 250 mm and made of balance Fe and unavoidable impurities were prepared with two kinds of components of n: 0.07% by weight.

Then, the slab was soaked at a temperature of 1150 ° C. for 60 minutes, and then hot rolling was started at 1100 ° C. to obtain a hot rolled sheet of 2.3 mm. The reduction distribution of hot rolling, the cooling conditions after hot rolling, and the process conditions until cold rolling were performed under the conditions described in Example 1. After that, the cold rolled sheet was a: 820 ° C,
Decarburization annealing was performed for 150 seconds under four temperature conditions of b: 830 ° C, c: 840 ° C and d: 850 ° C.

Thereafter, annealing was carried out at 750 ° C. for 30 seconds, NH ₃ gas was mixed in the annealing atmosphere, and the steel sheet was made to absorb nitrogen. The amount of N after nitriding is 0.0207-
It was 0.0228% by weight, and the average grain size of the primary recrystallized grains after nitriding was 20 to 26 μm.

Then, an annealing separator containing MgO as a main component was applied to this steel sheet, and the temperature was raised to 1200 ° C. at a rate of 10 ° C./hour in an atmosphere gas of N ₂ 50% and H ₂ 50%, and then continued. 20 at 1200 ° C in H ₂ 100% atmosphere gas
A final finish annealing was carried out for holding for a time. The measured values of the solid solution N of the above components when the slab heating was completed were 0.0040% by weight and 0.0039% by weight. Table 3 shows the experimental conditions and the magnetic properties of the products.

[0073]

[Table 3]

In the case of the present invention, the variation in magnetic characteristics was small, but it was even better when Sn was added.

Example 4 C: 0.054% by weight, Si: 3.45% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid-soluble A
A 40 mm thick slab containing 1: 0.049% by weight, N: 0.0108% by weight, and the balance Fe and inevitable impurities was prepared. Then, after soaking the slab at a temperature of 1150 ° C. for 30 minutes, hot rolling is immediately started,
It was a hot rolled sheet of 1.8 mm. At this time, the reduction distribution is 40 → 1
6 → 7 → 2.9 → 2.5 → 2.1 → 1.8 (mm), 4
0 → 30 → 20 → 10 → 5 → 2.5 → 1.8 (mm) 2
It was a condition. After the hot rolling, air cooling was performed for 4 seconds, followed by water cooling to 400 ° C., holding at 400 ° C. for 1 hour, and then furnace cooling.

This hot-rolled sheet was 0.260 at a rolling reduction of about 86%.
A cold-rolled sheet having a thickness of mm was used, and the process conditions until the final finish annealing were the same as in Example 1. The measured value of the amount of dissolved N at the time of completion of heating the slab was 0.0025% by weight. And, the amount of N after nitriding is 0.0213 to 0.0229% by weight.
The average grain size of the primary recrystallized grains after nitriding is 21 to 27.
was μm. Table 4 shows the experimental conditions and the magnetic properties of the product.

[0077]

[Table 4]

In the case of the present invention, there was little variation in the magnetic properties due to decarburization annealing. The larger cumulative rolling reduction in the final three passes of hot rolling was even smaller.

Example 5 C: 0.059% by weight, Si: 3.48% by weight, Mn:
0.14% by weight, S: 0.007% by weight, acid-soluble A
l: 0.035 wt% and N: 0.0080 wt% were added to prepare a 40 mm thick slab consisting of the balance Fe and unavoidable impurities. Then, after soaking the slab at a temperature of 1150 ° C. for 60 minutes, hot rolling is immediately started to 2.
A 3 mm hot rolled sheet was used. The reduction distribution of hot rolling from 40 mm, the cooling conditions after hot rolling, and the process conditions until cold rolling are the same as in Example 1.
The conditions were as described. This cold-rolled sheet is heated to 800 ° C for 1
Decarburization annealing was performed for 50 seconds, 840 ° C. for 150 seconds, and 880 ° C. for 150 seconds.

Thereafter, annealing was carried out at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere, and the steel sheet was made to absorb nitrogen. The amount of N after nitriding is 0.0207-
It was 0.0232% by weight. The average grain size of the primary recrystallized grains in the entire cross-section thickness of this steel sheet was measured using an optical microscope and image analysis.

Next, an annealing separator containing MgO as a main component was applied to this steel sheet, and final finish annealing was performed under the conditions described in Example 1. The measured value of solid solution N at the completion of slab heating is
It was 0.0035% by weight. Table 5 shows the experimental conditions and the magnetic properties of the products.

[0082]

[Table 5]

Example 6 The two kinds of hot-rolled sheets described in Example 1 were annealed at 980 ° C. for 2 minutes (soaking) and then rapidly cooled, and then rolled at a reduction ratio of about 88% to a thickness of 0.285 mm. As a cold-rolled sheet, decarburization annealing was performed under the conditions of Example 1. After that, annealing was carried out at 760 ° C. for 30 seconds, NH ₃ gas was mixed in the annealing atmosphere, and the steel sheet was made to absorb nitrogen.

The amount of N after nitriding is 0.0201 to 0.02.
It was 10% by weight, and the average grain size of the primary recrystallized grains after nitriding was 22 to 26 μm. Next, an annealing separator having MgO as a main component was applied to this steel sheet, and final finish annealing was performed under the conditions described in Example 1. Table 6 shows the experimental conditions and the magnetic properties of the products.

[0085]

[Table 6]

In the present invention, the difference in magnetic properties due to decarburization annealing was smaller than that in the comparative example.

[0087]

In the present invention, the amount of solute N in the slab at the time of heating the slab is completed, the addition of Sn and the control of the cumulative rolling reduction of the final three passes of hot rolling and the completion of decarburization annealing are completed. By controlling the average grain size of the primary recrystallized grains until the start of finish annealing, hot-rolled sheet annealing can be omitted and good magnetic properties can be stably obtained, so its industrial effect is It is extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of solid solution N at the completion of slab heating and the variation in magnetic flux density of a product.

Claims (4)

[Claims] 1. By weight ratio, C: 0.021 to 0.075%, Si: 2.5 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.0150% or less. , S + 0.405Se: 0.014% or less, Mn: 0.05 to 0.8%, and a balance of 1280 with a slab consisting of Fe and unavoidable impurities.
Heating at a temperature below ℃, hot rolling is performed, and then a rolling reduction of 80
% Or more final cold rolling, if necessary, one or more cold rollings with intermediate annealing sandwiched therebetween, followed by decarburizing annealing and final finishing annealing to produce a unidirectional electrical steel sheet. When the heating is completed, the solid solution N in the slab is 0.0045
After the deoxidizing annealing is completed, the average grain size of the primary recrystallized grains is 18 to 30 μm after the completion of deoxidation annealing, and after hot rolling, the steel sheet is formed before the secondary recrystallization of the final finish annealing. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by performing a nitriding treatment. 2. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the weight ratio of Sn is 0.01 to 0.15%. 3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the cumulative rolling reduction in the final three hot rolling passes is 40% or more. 4. The method for producing a grain-oriented electrical steel sheet with excellent magnetic properties according to claim 1, 2 or 3, wherein the hot rolled sheet is annealed at a temperature not higher than the slab heating temperature.