JPH086139B2 - Method for manufacturing thick unidirectional electrical steel sheet with excellent magnetic properties - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for 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 800A as a numerical value showing the excitation characteristics.
The magnetic flux density B _{8 at} / m is usually used. In addition, as a numerical value representing the iron loss characteristic, the iron loss W per 1 kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz.
I am using _17/50 . 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, 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 to highly align the <001> axis that is the easy magnetization axis with the rolling direction. Typical methods for producing such a high magnetic flux density unidirectional electrical steel sheet are methods described in Japanese Patent Publication No. 40-15644 by Satoru Taguchi and Japanese Patent Publication No. 51-13469 by Takuichi Imanaka. . MnS and AlN are used in the former and Mn are used in the latter.
S, MnSe, Sb, etc. are used as main inhibitors. 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. Regarding MnS, in the present process, a method is used in which MnS is once completely solid-soluted during slab heating before hot rolling and then precipitated during hot rolling. A temperature of about 1400 ° C. is necessary to completely form a solid solution of the required amount of MnS 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 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 a problem, the slab heating temperature should be lowered to the level of ordinary steel, but this means that the amount of MnS effective as an inhibitor is reduced at the same time or not used at all. However, this inevitably causes 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 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 and Sb in steel has been disclosed. In JP-A-52-24116, Zr, Ti, B, Nb, Ta, V, and C are used in addition to Al.
A method has been disclosed in which a slab heating temperature is set to a range of 1100 to 1260 ° C. by containing a nitride forming element such as r or Mo. Further, in JP-A-57-158322, low-temperature slab heating is performed by lowering the Mn content and setting the Mn / S ratio to 2.5 or less, and further adding Cu to stabilize secondary recrystallization. Techniques for doing so have been disclosed. On the other hand, a technique was also disclosed in which improvement was made from the side of the metal structure in combination with reinforcement of these inhibitors. That is, in JP-A-57-89433, in addition to Mn, S, Se,
By adding elements such as Sb, Bi, Pb, Sn, and B, and combining the columnar crystal ratio of the slab and the secondary cold rolling reduction, a low-temperature slab heating of 1100 to 1250 ° C. is realized. Further, in JP-A-59-190324, S
Alternatively, a technique has been disclosed in which, in addition to Se, an inhibitor is mainly composed of Al and B and nitrogen, and pulse annealing is performed at the time of primary recrystallization annealing after cold rolling to stabilize secondary recrystallization. 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.

[0006] First, in JP-A-59-56522, Mn is 0.08 to 0.45% and S is 0.00.
A technique has been disclosed which enables low temperature slab heating by making the content 7% 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.

[0007]

By the way, in recent years, there has been an increasing need to use grain-oriented electrical steel sheets in place of the current high-grade non-oriented electrical steel sheets for applications such as iron core materials for turbine generators. With respect to the above applications, the unidirectional magnetic properties are more important than the applications of other non-oriented electrical steel sheets, and thus there is an increasing need for using grain-oriented electrical steel sheets. On the other hand, the main process of manufacturing the grain-oriented electrical steel sheet after hot rolling is hot-rolled sheet annealing-cold rolling-decarburization annealing-finish annealing, which is the main step after hot rolling of non-oriented electrical steel sheet. It is more complicated than cold rolling-annealing. Therefore, in terms of manufacturing cost, the grain-oriented electrical steel sheet is considerably higher than the non-oriented electrical steel sheet.

Further, in a normal pickling line and a tandem cold rolling line, there is a limit to the plate thickness that can be passed, and if a cold rolled material having a large plate thickness is passed, breakage may occur. Therefore, if a thick material having a thickness of 0.5 mm or the like is to be cold-rolled once, there is an upper limit to the thickness of the cold-rolled material, so that the cold-rolling rate needs to be low. Further, in the production of grain-oriented electrical steel sheet, 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. 46-2
As disclosed in Japanese Patent No. 3820, AlN is used in hot-rolled sheet annealing.
In order to control the inhibitor, the method of controlling the inhibitor has been adopted.

In recent years, the manufacturing process of such grain-oriented electrical steel sheet which consumes a large amount of energy has been reviewed, and there has been an increasing demand for simplification of the process and energy. In order to meet such a demand, in a manufacturing method using AlN as a main inhibitor, a method of substituting the precipitation treatment of AlN in hot-rolled sheet annealing by high temperature winding after hot rolling (Japanese Patent Publication No. 59-45730). Was 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 ordinary method of winding in a coil shape of 5 to 20 tons, in the coil during the cooling process, Difference in the thermal history due to the location occurs, inevitably the deposition of AlN becomes non-uniform, and the final magnetic characteristics vary 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 hot rolling final pass, which has received little attention in the past, and utilizing this phenomenon, a manufacturing method by single cold rolling under a high pressure of 80% or more. In the above, a 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 the hot-rolling is completed.
It became possible to achieve both slab heating at a temperature of less than 280 ° C and omission of hot-rolled sheet annealing.

Regarding hot rolling of unidirectional electrical steel sheet, secondary recrystallization failure (generation of linear fine grains continuous in the rolling direction occurs due to coarse growth of slab crystal grains during high temperature slab heating (eg, 1300 ° C. or higher). ) At the time of hot rolling to prevent
A method has been proposed in which coarse crystal grains are divided by performing recrystallization high-pressure rolling at a reduction rate of 30% or more per pass at a temperature of 1190 ° C. (Japanese Patent Publication No. 60-37172). Although this method certainly reduces the generation of linear fine grains, it is premised on the manufacturing process of hot-rolled sheet annealing.

In addition, in the manufacturing method using MnS, MnSe, and Sb as inhibitors, 950 to 1200 during hot rolling is 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 ℃, and subsequently cooling at a cooling rate of 3 ℃ / sec or more to improve magnetic properties. (Japanese Patent Laid-Open No. 51-2071
No. 6). Further, there is a method of improving magnetic properties by performing hot rolling at a low temperature to suppress the progress of recrystallization and prevent {110} <001> oriented grains formed by shear deformation from being reduced by the subsequent recrystallization. It has been proposed (Japanese Patent Publication No. 59-32526 and Japanese Patent Publication No. 59-35415). Even in these methods, production by the single cold rolling method without hot-rolled sheet annealing has not been studied. In the hot rolling of silicon steel slabs containing ultra-low carbon, hot rolling at low temperature and large pressure that causes strain to accumulate in the hot-rolled sheet is performed, and the coarse crystal grains peculiar to the ultra-low carbon material are obtained by recrystallization during subsequent hot-rolled sheet annealing. Has been proposed (Japanese Patent Publication No. 59-34212). However, even in this method, the production by the single cold rolling method without hot-rolled sheet annealing has not been studied.

[0013] Therefore, the present inventors have made it possible to achieve both the low temperature slab heating and the omission of hot-rolled sheet annealing (Japanese Patent Application No.
It is understood that the significance of -85540 and Japanese Patent Application No. 1-85541) is great.

[0014]

According to the present invention, C: 0.021-0.075% by weight, Si: 2.5-4.5 by weight.
%, Acid-soluble Al: 0.010 to 0.060%, N:
0.0030 to 0.0130%, S + 0.405Se:
A slab containing 0.014% or less, Mn: 0.05 to 0.8% and the balance Fe and unavoidable impurities
Heating at a temperature of less than 280 ° C., hot rolling, and cold rolling with a rolling reduction of 60 to 79% without annealing the hot rolled sheet,
Then, decarburization annealing and final finishing annealing are applied to 0.4 to 1.0.
In a method for producing a thick unidirectional electrical steel sheet having a thickness of mm, the hot rolling end temperature is set to 850 to 1100 ° C, the cumulative rolling reduction of the final three passes of hot rolling is set to 40% or more, and The temperature is set to 200 ° C. or less, the average particle size of the primary recrystallized grains is set to 18 to 30 μm after the completion of decarburization annealing and before the start of final finish annealing, and after hot rolling until the start of secondary recrystallization of final finish annealing. By nitriding the steel sheet in the meantime, it is possible to stably obtain a thick unidirectional magnetic steel sheet having excellent magnetic properties.

[0015]

The unidirectional electrical steel sheet targeted by 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 may be sandwiched between slabs, followed by hot rolling into a hot-rolled sheet, followed by heat treatment. Cold rolling with a rolling reduction of 60 to 79% without performing annealing of a rolled sheet,
It is manufactured by sequentially performing decarburization annealing and final finishing annealing.

The inventors of the present invention have extensively studied a method for improving the magnetic properties at a rolling reduction of less than 80% because of the necessity of lowering the rolling reduction due to the plate thickness limitation of the cold rolled material. As a result, they have found that it is effective not to unnecessarily increase the plate temperature between cold rolling passes to obtain good magnetic properties at a low cold rolling rate of less than 80%. The details will be described below based on the experimental results.

FIG. 1 is a graph showing the effect of the temperature of the steel sheet between the passes during cold rolling on the magnetic flux density of the product. Here, C: 0.040% by weight, Si: 3.01% by weight,
Acid-soluble Al: 0.030% by weight, N: 0.0068% by weight, S: 0.007% by weight, Mn: 0.14% by weight, with the balance being Fe and inevitable impurities 40 mm
The thick slab is heated to 1150 ° C and 2.0mm in 6 passes.
A thick hot rolled sheet was used. At this time, the pass schedule is 40 →
It was 22 → 13 → 8 → 5 → 3 → 2 (mm), and the hot rolling finish temperature was 953 ° C. In this case, the cumulative rolling reduction of the final 3 passes was 75%. After hot rolling for 2 seconds and after air cooling, 550 ℃
A water-cooling simulation was carried out in which water cooling was performed, the temperature was maintained at 550 ° C. for 1 hour, and then the furnace cooling was performed. Then, the hot rolled sheet was pickled, and then cold rolled at a rolling reduction of 75% to obtain a cold rolled sheet having a thickness of 0.50 mm. At this time, when the plate thickness is 1.5 mm and 1.0 mm, 50 ° C. × 5 minutes (soaking), 100 ° C. × 5 minutes (soaking), 150 ° C. × 5 minutes (soaking), 200 ° C. × 5 minutes ( Soaking), 250 ° C x 5 minutes (soaking), 300 ° C x 5
Eight types of cold-rolled sheets were prepared, which were subjected to eight types of aging treatments (minus heat soaking), 350 ° C. × 5 min (soaking), and no aging treatment. Then, hold at 840 ° C for 400 seconds, 870 ° C ×
Decarburization annealing was performed for 20 seconds. After that, 750 ℃
During the heat treatment of holding for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet was 0.0189 to 0.0220% by weight.
The average grain size of the primary recrystallized grains in the entire thickness of this steel plate was measured using an optical microscope and an image analyzer, and was 23 to 24.
μm. Then, an annealing separator containing MgO as a main component was applied to the plate after the nitriding treatment, and final finish annealing was performed.

As is apparent from FIG. 1, a good magnetic flux density is obtained when the steel sheet temperature between passes is 200 ° C. or less. FIG.
Although the reason why the relationship as shown in (1) is established is not always clear, the present inventors presume as follows. Conventionally, the cold rolling rate has been known as a controlling factor of the cold rolling recrystallization texture, and in particular, it is {110} <001>, {111} <1 as a controlling factor for the secondary recrystallization orientation.
12> The abundance of oriented grains is important. The {110} <001> oriented grains in the recrystallized texture become maximum when the rolling reduction is 60 to 70%, and decrease in the rolling reduction range of more than 70% as the rolling reduction increases. On the other hand, the {111} <112> oriented grains in the recrystallized texture tend to increase in the rolling reduction range up to about 90% as the rolling reduction increases. On the other hand, aging between passes in cold rolling promotes the formation of deformation zone during cold rolling, and nucleates from the deformation zone {110} <001.
> There is a tendency to increase oriented grains in the recrystallization texture.
On the other hand, the inter-pass aging is {1 in the recrystallized texture.
11} <112> tends to reduce the amount of oriented grains. Therefore, {110} <001> oriented grains and {111}
From the viewpoint of the abundance of <112> oriented grains in the recrystallized texture, performing inter-pass aging has the same effect as lowering the cold rolling rate. Therefore, usually 80%
It is effective to eliminate the influence of interpass aging as much as possible in the present invention in order to bring the recrystallized texture obtained at the above high cold rolling rate to the one having a low cold rolling rate of less than 80% as close as possible. Conceivable.

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
(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 is set to 0.021% or more. on the other hand,
If C becomes 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 of Si is set to 4.5% or less. 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. Desirably, it is 3.2 or more. Al is AlN or (Al, Si) nitride necessary for stabilizing secondary recrystallization.
In order to secure s, 0.010% or more is required as acid-soluble Al. If the acid-soluble Al exceeds 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.

N is 0.00 in normal steelmaking work.
Since it is difficult to make it less than 30% and it is not economically preferable, it is set to 0.0030% or more, while 0.01
If it exceeds 30%, "blister on the steel plate surface" called blister occurs, so the content was made 0.0130% or less. Mn
Even if S 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 defective portions called linear fine grains tend to occur, and in order to prevent the generation of this secondary recrystallization defective portion, (S + 0.40
It is desirable that 5Se) ≦ 0.014%. If S or Se exceeds the above value, the probability of occurrence of defective secondary recrystallization is increased no matter how the manufacturing conditions are changed, which is not preferable. Further, the time required for purification in the final finish annealing is undesirably too long, and from this viewpoint, S
Alternatively, there is no point in unnecessarily increasing Se.

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, especially the side edge portion of the strip becomes corrugated, 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 lowered, which is not preferable, so the upper limit of the Mn content was set to 0.8%. In addition, Sn and S, which are known as inhibitor constituent elements,
It is permissible to contain a trace amount of b, Cr, Cu, Ni, B, Ti and the like.

The slab heating temperature is 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 subsequent hot-rolling step usually consists of rough hot-rolling and finish hot-rolling, which are performed by heating a slab having a thickness of 100 to 400 mm and then performing a plurality of passes. The method of rough hot rolling is not particularly limited and may be a normal method. 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. 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. Rolling speed is usually 100-3000
The time between passes is 0.01 to 1
It is 00 seconds. What is limited in the present invention is only the hot rolling end temperature and the cumulative rolling reduction of the final hot rolling three passes, and other conditions are not particularly limited, but in the pre-stage of rough hot rolling and finish hot rolling. Performing a strong reduction is also preferable because it causes recrystallization to some extent and improves the structure. Even in the final three passes, strong reduction in the final pass is particularly effective in promoting recrystallization after hot rolling.

Next, the reasons for limiting the above hot rolling conditions will be described. The hot rolling end temperature was 850 to 1100 ° C. 11
When the temperature exceeds 00 ° C, the strain is largely reduced due to the dynamic recovery during rolling, and recrystallization after hot rolling is less likely to occur. On the other hand, 850
If the temperature is lower than 0 ° C, the temperature is too low, and subsequent recrystallization is less likely to occur after completion of hot rolling, and the magnetic flux density of the product is lowered, which is not preferable.

On the other hand, the cumulative rolling reduction in the final three hot rolling passes was set to 40% or more. Below this value, the effect of recrystallization after hot rolling is insufficient, which is not preferable. The upper limit of the cumulative rolling reduction of the final three passes is not particularly limited, but it is industrially difficult to apply a cumulative rolling reduction of 99.9% or more. After the final pass of hot rolling, usually 0.1-10
After being air-cooled for about 0 seconds, it is water-cooled, wound at a temperature of 300 to 700 ° C., and gradually cooled. The cooling process is not particularly limited, but air cooling for 1 second or more after hot rolling is preferable for promoting recrystallization. This hot-rolled sheet is cold-rolled at a rolling reduction of 60 to 79% without annealing the hot-rolled sheet, and becomes a cold-rolled sheet of 0.4 to 1.0 mm.

The thickness of the cold rolled sheet is specified to be 0.4 to 1.0 mm for the purpose of the present invention to obtain a thick unidirectional electrical steel sheet. If it exceeds 1.0 mm, decarburization annealing takes too much time, which is not preferable. This reduction rate is 60 to 79
The reason for defining as% is that if the cold-rolled material is too thick, it is necessary to lower the cold-rolling rate because it is likely to cause breakage when passing through the pickling line or the cold-rolling line. This upper limit comes from the plate thickness limitation of the cold rolled material, while the lower limit is specified because it is necessary to keep the magnetic flux density high. The temperature of the steel sheet between the cold rolling passes was set to 200 ° C or lower. If this temperature is exceeded, the effect of inter-pass aging is exerted as shown in FIG. 1. Therefore, in the case of the low cold rolling reduction rate according to the present invention, the magnetic flux density is rather lowered, which is not preferable.

The cold rolling method is not particularly limited. Either the tandem method or the reverse method may be used. It is sufficient to keep the temperature between passes at 200 ° C or lower. Although the number of passes is not particularly limited,
It makes no sense to take more than 100 passes unnecessarily. The steel sheet after such cold rolling is subjected to decarburization annealing, applying an annealing separating agent, and finally finishing annealing by a usual method to obtain a final product.
Here, the average grain size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final finish annealing is set to 18 to 30 μm, B ₈ (T) ≧ 1.88 in this range of values. This is because the magnetic flux density can be obtained.

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

[0029]

EXAMPLES Examples will be described below. Example 1 C: 0.035% by weight, Si: 3.00% by weight, Mn:
0.15% by weight, S: 0.007% by weight, acid-soluble A
1: 0.029% by weight, N: 0.0070% by weight, a 40 mm thick slab consisting of the balance Fe and unavoidable impurities was heated at a temperature of 1150 ° C., and then hot rolling was started at 1050 ° C., 40 → 23 → 14 → 9 → 6 → 3.5 → 2
A hot rolled sheet was obtained by hot rolling with a pass schedule of (mm). At this time, the hot rolling end temperature is 936 ° C., and in this case,
The cumulative rolling reduction in the final 3 passes was 78%. A coiling simulation was performed in which after hot rolling, air cooling was performed for 4 seconds, water cooling was performed to 550 ° C., holding at 550 ° C. for 1 hour, and furnace cooling. After a while
This hot rolled sheet is pickled, then cold rolled at a rolling reduction of 75%,
It was a cold-rolled sheet having a thickness of 0.50 mm. At this time, when the thickness is 1.2 mm, there is no aging treatment, 100 ° C. × 5 minutes (soaking),
Three types of cold-rolled sheets which were subjected to three types of aging treatment of 300 ° C. × 5 minutes (soaking) were prepared. Then, decarburization annealing was carried out by holding at 830 ° C. for 300 seconds and at 880 ° C. for 20 seconds.
Then, during the heat treatment of holding at 770 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet was 0.0194 to 0.021.
It was 1% by weight. The average grain size of the primary recrystallized grains in the entire thickness of this steel plate was measured with an optical microscope and an image analyzer, and it was 24 to 25 μm. Then, 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 by a known method.

Table 1 shows the experimental conditions and the magnetic properties of the products.

[0031]

[Table 1]

Example 2 C: 0.041% by weight, Si: 3.23% by weight, Mn:
0.14% by weight, S: 0.007% by weight, acid-soluble A
1. A slab of 40 mm thickness containing 1: 0.028% by weight and N: 0.0060% by weight and consisting of balance Fe and unavoidable impurities was heated at a temperature of 1150 ° C., and then hot-rolled by 6 passes to 2. It was a 3 mm hot rolled sheet. At this time, the reduction distribution is 40
→ 24 → 16 → 11 → 6.6 → 3.9 → 2.3 (mm)
And At this time, the hot rolling end temperature was 947 ° C., and in this case, the cumulative rolling reduction in the final 3 passes was 79%. After the hot rolling, air cooling was performed for 2 seconds, water cooling was performed up to 550 ° C., holding at 550 ° C. for 1 hour, and then furnace cooling was performed. After that, the hot rolled sheet was pickled, and then cold rolled in the same direction at a reduction rate of 78% to obtain a cold rolled sheet having a thickness of 0.50 mm. On this occasion,
When 1.5mm and 1.0mm thick, no aging treatment,
Two types of cold-rolled sheets that had been subjected to two types of aging treatment at 250 ° C. for 5 minutes (soaking) were prepared. Then 300 at 830 ° C
Decarburization annealing was performed by holding for 2 seconds and holding at 870 ° C. for 20 seconds. Then, during the heat treatment of holding at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet is 0.0201 to 0.0
It was 212% by weight. The average grain size of the primary recrystallized grains in the entire thickness of this steel sheet was 25 to 26 μm when measured using an optical microscope and an image analyzer. Then, 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 by a known method.

Table 2 shows the experimental conditions and the magnetic properties of the products.

[0034]

[Table 2]

Example 3 C: 0.030% by weight, Si: 3.10% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid-soluble A
1: 0.029% by weight, N: 0.0070% by weight, and a 30 mm thick slab containing the balance Fe and unavoidable impurities was heated at a temperature of 1150 ° C., and then hot rolling was started at 1050 ° C. Allocation 30 → 20 → 13 → 8 → 5 →
It was set to 3.0 → 2.3 (mm). At this time, the hot rolling finish temperature was 892 ° C., and in this case, the cumulative rolling reduction in the final three passes was 71%. A coiling simulation was performed in which after hot rolling, air cooling was performed for 1 second, water cooling was performed to 400 ° C., holding at 400 ° C. for 1 hour, and furnace cooling. Then, the hot rolled sheet was pickled, and then cold rolled at a rolling reduction of 78% to obtain a cold rolled sheet having a thickness of 0.50 mm. At this time, when the thickness is 1.8 mm, 1.2 mm, and 0.8 mm, two types of cold rolling subjected to two types of aging treatment of 50 ° C. × 5 minutes (soaking) and 300 ° C. × 5 minutes (soaking) I made a board. Then, decarburization annealing was carried out at 840 ° C. for 400 seconds. Then, during the heat treatment of holding at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel plate is 0.0195.
Was 0.0211% by weight. The average grain size of the primary recrystallized grains in the entire thickness of the steel sheet was measured with an optical microscope and an image analyzer, and it was 21 to 22 μm. Then, an annealing separator having MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed by a known method.

Table 3 shows the experimental conditions and the magnetic properties of the products.

[0037]

[Table 3]

Example 4 C: 0.045% by weight, Si: 3.35% by weight, Mn:
0.15% by weight, S: 0.007% by weight, acid-soluble A
1: 0.030% by weight, N: 0.0068% by weight, S
After heating a 40 mm-thick slab containing n: 0.050 wt% and the balance Fe and unavoidable impurities at a temperature of 1100 ° C., hot rolling is immediately started and the reduction distribution is 40 →
It was set to 23 → 16 → 10 → 7 → 4 → 2.3 (mm). At this time, the hot rolling end temperature is 873 ° C, and in this case, the final 3
The cumulative rolling reduction of the pass was 77%. A coiling simulation was performed in which after hot rolling, air cooling was performed for 4 seconds, water cooling was performed to 550 ° C., holding at 550 ° C. for 1 hour, and furnace cooling. Then, the hot-rolled sheet was pickled, and then cold-rolled at a reduction rate of 74% to obtain 0.60 m.
It was a cold-rolled sheet of m thickness. At this time, 1.5mm, 1.0mm
When the thickness was thick, two types of cold-rolled sheets were prepared without aging treatment and subjected to two types of aging treatment of 250 ° C. × 10 minutes (soaking). Then, decarburization annealing was carried out by holding at 830 ° C. for 350 seconds and then at 870 ° C. for 20 seconds. Then, during the heat treatment of holding at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet was 0.0197 to 0.0213.
% By weight. The average grain size of the primary recrystallized grains in the entire thickness of this steel plate was measured by using an optical microscope and an image analyzer, and it was 22 to 23 μm. Then, an annealing separator having MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed by a known method.

Table 4 shows the experimental conditions and the magnetic properties of the products.

[0040]

[Table 4]

[0041]

As described above, in the present invention,
The hot rolling end temperature, the cumulative rolling reduction of the final 3 passes of hot rolling, the temperature of the steel sheet between cold rolling passes, and the average grain size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final annealing. By controlling and nitriding the steel sheet, hot-rolled sheet annealing is omitted,
Since it is possible to obtain a thick unidirectional electrical steel sheet having a low cold rolling rate and good magnetic properties, its industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the temperature of a steel sheet between passes during cold rolling on the magnetic flux density of a product.

Claims (1)

[Claims] 1. C: 0.021 to 0.075% by weight,
Si: 2.5-4.5%, acid-soluble Al: 0.010
0.060%, N: 0.0030 to 0.0130%, S
+0.405 Se: 0.014% or less, Mn: 0.05
A slab containing 0.8% by weight and the balance Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot rolled, and continuously rolled without annealing a hot rolled sheet.
In the method of manufacturing a thick unidirectional electrical steel sheet having a thickness of 0.4 to 1.0 mm by performing 9% cold rolling, then decarburizing annealing and final finishing annealing, the hot rolling ending temperature is set to 850 to 1100.
C, the cumulative rolling reduction of the final 3 passes of hot rolling is 40% or more, the temperature of the steel sheet between passes of cold rolling is 200 ° C. or less, and the primary finish between the completion of decarburization annealing and the start of final finish annealing. An average grain size of recrystallized grains is set to 18 to 30 μm, and a nitriding treatment is performed on a steel sheet after hot rolling and before the start of secondary recrystallization of final annealing, which is one of thick plate thicknesses with excellent magnetic properties. Method for manufacturing grain-oriented electrical steel sheet.