JP2521586B2 - Method for producing 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.
A magnetic flux density B _{8 at} / m is usually used. In addition, as the numerical value showing the iron loss characteristic, the iron loss W _17/50 per 1 kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is used. 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 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. 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. . In the former, MnS and AlN are used; in the latter, MnS and MnS
e, Sb, etc. are used as the 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. As for MnS, the current process is to completely dissolve MnS during slab heating before hot rolling and then to precipitate during hot rolling. 1400 ℃ to completely dissolve the required amount of MnS for secondary recrystallization
A certain 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 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. To avoid such problems, the slab heating temperature can be lowered to the level of ordinary steel, but this also means that the amount of MnS effective as an inhibitor is reduced or not used at all. , Inevitably causes instability 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 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, B
A method for controlling the slab heating temperature in the range of 1050 to 1350 ° C. by including grain boundary segregation elements such as i, Sn, and Sb in steel has been disclosed. In JP-A-52-24116,
In addition to Al, a slab heating temperature of 1100 is obtained by containing a nitride forming element such as Zr, Ti, B, Nb, Ta, V, Cr and Mo.
Disclosed is a method in the range of ˜1260 ° C. Further, in JP-A-57-158322, the Mn content is reduced to
A technique has been disclosed in which the low-temperature slab heating is performed by setting the ratio of / S to 2.5 or less, and the secondary recrystallization is stabilized by adding Cu. 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, elements such as S, Se, Sb, Bi, Pb, Sn, and B are added to Mn, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined with this. A low temperature slab heating of 1100 to 1250 ° C is realized. Further, JP-A-59-190324
In the publication, a technique is disclosed in which, in addition to S or Se, an inhibitor is mainly composed of Al and B and nitrogen, and the secondary recrystallization is stabilized by performing pulse annealing during the primary recrystallization annealing after cold rolling. Was done. 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 Japanese Patent Laid-Open No. 59-56522, Mn is 0.08 to 0.45% and S is 0.007%.
A technique for enabling low temperature slab heating by the following has been disclosed. 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]

Although the method using low-temperature slab heating is originally aimed at reducing the manufacturing cost, it cannot be industrialized unless it is a technique for obtaining good magnetic characteristics stably. . On the other hand, if the temperature of the slab heating is lowered, the hot rolling temperature is naturally lowered, so that the hot rolling is changed. 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: fragmentation by recrystallization of coarse crystal grains, fine precipitation of MnS, AlN, etc. 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 invention, as disclosed by the present inventor in Japanese Patent Application No. 1-1778, the metallographic structure after decarburization annealing may be made appropriate, Precipitate control on hot-rolled sheet is not essential.
Therefore, it can be said that the restriction on the hot rolling in the conventional method is small in the case of low-temperature slab heating.

In the production of unidirectional electrical steel sheets, hot-rolled sheet annealing is usually carried out 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. 46-2382
As disclosed in Japanese Patent No. 0, the method of controlling the inhibitor by precipitating AlN 3 in hot-rolled sheet annealing is adopted.

Usually, the grain-oriented electrical steel sheet is manufactured through main steps such as casting-hot rolling-annealing-cold rolling-decarburization annealing-finish annealing, and requires a large amount of energy. The manufacturing cost is also higher than the above. In recent years, the review of such a manufacturing process which consumes a large amount of energy has been promoted, and a demand for simplification of the process and energy has been increased. In order to meet such a demand, in a production 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 usual method of winding in a coil of 20 tons, there is a local difference in thermal history in the coil during the cooling process, which inevitably causes uneven deposition of AlN and the final magnetic characteristics are It varies depending on the location, 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 the hot-rolled sheet annealing (Japanese Patent Application Nos. 1-85540 and 1-85541) was presented. These techniques are characterized in that the hot-rolled sheet has a fine recrystallized structure by applying high pressure in the final three passes of the finish hot rolling and holding at a high temperature after the completion of the hot rolling.
It has become possible to achieve both slab heating at a temperature lower than 80 ° C. and omission of hot-rolled sheet annealing.

On the other hand, with respect to hot rolling of unidirectional electrical steel sheets, secondary recrystallization defects caused by coarse growth of slab crystal grains during high temperature slab heating (for example, 1300 ° C. or higher) (lines continuous in the rolling direction). In order to prevent the formation of fine grains, a method is proposed in which coarse crystal grains are cut by recrystallization under high pressure rolling at a reduction rate of 30% or more per pass at a temperature of 960 to 1190 ° C during hot rolling. It has been done (Sho 60-
No. 37172). Although this method certainly reduces the generation of linear fine grains, it is premised on a manufacturing process in which hot-rolled sheet annealing is performed.

Further, in the production method using MnS, MnSe and Sb as inhibitors, hot rolling is continuously performed at a temperature of 950 to 1200 ° C. at the time of hot rolling at a rolling reduction of 10% or more, and then 3 ° C.
MnS, MnSe
Has been proposed (Japanese Patent Laid-Open No. 51-20716) to improve the magnetic properties by uniformly and finely depositing 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. (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 crystals peculiar to the ultra-low carbon material are obtained by recrystallization during subsequent hot-rolled sheet annealing. A method for dividing grains has been proposed (Japanese Patent Publication No. 59-34212). However, even in this method, production by a single cold rolling method without annealing of a hot-rolled sheet has not been studied.

Therefore, the significance of the above-described technology (Japanese Patent Application Nos. 1-85540 and 1-85541) that enables both the low temperature slab heating and the omission of hot-rolled sheet annealing to be achieved by the present inventors is significant. It turns out to be big. The present inventors proceeded with factory experiments to commercialize these technologies, and confirmed that in the process, fluctuations in magnetism occur in the longitudinal direction of the coil. Therefore,
As a result of detailed examination of the cause of this magnetic fluctuation, the present inventors have found that this phenomenon is due to a temperature difference in the slab during low temperature slab heating.

[0015]

The subject matter of the present invention is as follows. (1) C: 0.021 to 0.075% by weight, Si:
2.5-4.5%, acid-soluble Al: 0.010-0.06
0%, N: 0.0030 to 0.0130%, S + 0.4
05 Se: 0.014% or less, Mn: 0.05 to 0.8%
A slab containing Fe and the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and then finally cold-rolled at a rolling reduction of 80% or more, with intermediate annealing as necessary 1 In the method of producing a unidirectional electrical steel sheet by performing cold rolling more than once, followed by decarburization annealing and final finishing annealing, the content of acid-soluble Al, N, Si in the slab is expressed as% by weight.
When Al (%), N (%) and Si (%) are used as a unit, the temperature difference ΔST (° C) in the slab at the time of heating completion is controlled within the range of the following formula, and ΔST (° C) ≤ 32.8 + 46060 {Al (%)-27/14 N
(%)} ² + 4.25Si (%) A unidirectional electrical steel sheet with excellent magnetic properties characterized by nitriding the steel sheet after decarburization annealing and before the start of secondary recrystallization in final annealing. Manufacturing method.

(2) The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the above item 1, wherein a slab containing Sn: 0.01 to 0.15% by weight is used. (3) The unidirectional electrical steel sheet with excellent magnetic properties according to the above item 1 or 2, wherein the hot rolling end temperature is 850 to 1050 ° C., and the cumulative rolling reduction of the final three hot rolling passes is 40% or more. Manufacturing method.

(4) The excellent magnetic properties described in the above item 1 or 2 or 3 are characterized in that the average grain size of the primary recrystallized grains after the completion of decarburization annealing is set to 18 to 30 μm until the start of final finishing annealing. Manufacturing method of unidirectional electrical steel sheet. (5) The method for producing a unidirectional electrical steel sheet having excellent magnetic properties according to the above item 1 or 2 or 3 or 4, wherein the hot rolled sheet is annealed at a temperature equal to or lower than a slab heating temperature.

[0018]

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, and then reduction. A final cold rolling with a rate of 80% or more, and if necessary, one or more cold rollings with intermediate annealing, decarburization annealing, and final finishing annealing are sequentially performed.

The inventors of the present invention have studied in detail the cause of magnetic fluctuation and its solution when a low temperature slab heating material is manufactured by a single cold rolling method without hot-rolled sheet annealing. As a result, a new finding that this phenomenon is caused by variation in AlN precipitation based on the temperature difference in the slab during slab heating, and the degree of magnetic fluctuation varies depending on the Al content, N content, and Si content Obtained.

Then, as a solution to the problem, the temperature difference in the slab upon completion of heating the slab is kept within a predetermined range determined according to the amounts of Al, N and Si, addition of Sn,
We have obtained a new finding that it is effective to control the average grain size of primary recrystallized grains from the completion of decarburization annealing to the start of final finishing annealing under high pressure in the final three passes of hot rolling. This will be described in detail below. The present inventors have paid attention to solid solution and precipitation of AlN 3 when heating the slab. At the temperature lower than 1280 ° C., which is the premise of the present invention, the complete solid solution of AlN in the α phase is not guaranteed within the Al, N and Si component ranges of the present invention. On the other hand, there are various slab heating methods, but after charging the slab into the furnace, moving it with a pusher and letting it out from the outlet, or placing a slab on the skit and moving the skit to move the slab from the inlet to the outlet. Etc. are generally performed. The temperature of the part of the slab that comes into contact with the lower surface of the skit or furnace is often low. Therefore, it was considered that the difference in the precipitation amount of AlN and the amount of solute N due to the temperature difference in the slab occurred. In the process from hot rolling to decarburization annealing, it is considered that most of the solid solution N during slab heating is finely precipitated as AlN, and the degree thereof depends on the amount of solid solution N during slab heating. It was In fact, when conducting an experiment in a factory, the average grain size of the primary recrystallized grains after decarburization annealing of the coil in which the magnetic characteristics fluctuated was measured using an optical microscope and an image analyzer. It was found that the diameter fluctuated. And the degree of the variation was different depending on the amounts of Al, N, and Si.

Therefore, first, the amount of solid solution N in the α phase was measured. First, by weight, C = 0.022%, Si = 3.4-
4.5%, acid-soluble Al = 0.025 to 0.041%, N
= 0.0068 to 0.0101%, S = 0.007%,
An ingot containing Mn = 0.12% and the balance of Fe and inevitable impurities was prepared by vacuum melting. Then, a small sample was cut out from the ingot, annealed at 1000 ° C. for 60 minutes, then annealed in ice-salt water, and annealed at 1250 ° C. for 60 minutes, then annealed in ice water, and N as AlN was measured by chemical analysis. NN as AlN was taken as the amount of solid solution N. Then, the amount of solid solution N [N] (T ₁ ) at _two temperatures T ₁ and T ₂ ,
Assuming that [N] (T ₂ ) is proportional to the temperature difference, the following formula was obtained.

[0022]

[Equation 1]

Then, solid solution N at 1250 ° C. and 1000 ° C.
An empirical formula expressing the difference in amount as a function of the amount of acid-soluble Al, N, Si was determined. The result is shown in the following formula.

[0024]

[Equation 2]

Here, the acid-soluble Al,
The amounts of N and Si are Al = Al (%), N = N (%), Si = Si
It is written as (%). Next, the relationship between the difference in the amount of solute N in the α phase and the variation in the magnetic properties of the product was investigated. First, Fig. 1 shows the difference Δ in the amount of solute N in the α phase during slab heating.
[B] (N) (%) and product magnetic flux density B ₈ (T) difference ΔB
₈ shows the relationship with (T). In this case, C = 0.0 by weight
53%, Si = 2.8 to 3.6%, acid-soluble Al = 0.02
1 to 0.051%, N = 0.0048 to 0.0087
%, S = 0.007%, Mn = 0.14%, balance
A slab of 20 components having a thickness of 40 mm and made of Fe and inevitable impurities was prepared. Then, two levels of temperature between 1050 to 1150 ° C are arbitrarily selected for the slabs of the respective components, soaked for 60 minutes, hot-rolled in 6 passes, and water-cooled after about 2 seconds,
After cooling to 550 ° C., a coiling simulation was performed in which the furnace was cooled at 550 ° C. for 1 hour. In this case, 6
The distribution of pass reduction is 40 → 15 → 7 → 3.5 → 3 → 2.
6 → 2.3 mm. Hot rolling end temperature is 883-927 ° C
Met. Without subjecting such hot-rolled sheet to hot-rolled sheet annealing, strong reduction rolling of about 85% was carried out to obtain a cold-rolled sheet having a final sheet thickness of 0.335 mm, which was held at 840 ° C. for 150 seconds, and subsequently 875
Decarburization annealing is held for 20 seconds at ℃, then 750 ℃
At the time of annealing 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 was 0.0194 to 0.0218% 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 the difference ΔB ₈ of B _{8 under} the two slab soaking conditions taken for the slab of the same component was obtained.

As is apparent from FIG. 1, when the difference Δ [N] (%) in the amount of solute N in the α phase during heating of the slab is 0.0010% by weight or less, the difference in the magnetic flux density of the product is obtained. ΔB ₈ (T) is less than 0.02T. Here, the difference in the amount of solute N in the α phase during slab heating was calculated using an equation. From the result of FIG. 1, the difference in the amount of solid solution N in the α phase caused by the temperature difference in the slab during heating of the slab should be 0.0010% by weight or less to reduce the variation in the magnetic flux density of the product. It turned out to be effective. Therefore, the temperature difference ΔST (° C.) in the slab is expressed as T ₁ −T _{2 in the} equation, and ΔST = T ₁ −T ₂ …, and the difference in the amount of solid solution N between T ₁ and T ₂ is 0.0.
If it is 010% by weight or less, [N] (T ₁ )-[N] (T ₂ ) ≦ 0.0010 ...
Get. Then, from the formula, ΔST (℃) ≤ 32.8 + 46060 {Al (%)-27/14 N (%)} ² + as the condition of the temperature difference in the slab to reduce the variation of the magnetic flux density of the product
4.25Si (%) ... is obtained.

The inventors of the present invention have studied the mechanism by which the variation in the magnetic flux density of the product is reduced by adjusting the temperature difference in the slab during heating of the slab so that the amount of solid solution N in the α phase is 0.0010% by weight or less. Thinks in the following way. In this experiment, the phenomenon caused by the temperature difference in the slab in the heating furnace was simulated in the laboratory by changing the slab heating temperature. In the composition range of Al, N and Si of the present invention, 1280 ° C.
When the slab heating temperature condition is less than less than the above, a difference occurs in the amount of solid solution and precipitation of AlN between the high temperature part and the low temperature part of the slab. There is a large amount of solute N in the high temperature portion of the slab when the slab is heated, and during the subsequent hot rolling and decarburization annealing, this solute N is finely precipitated in the form of AlN. On the other hand, there is little solid solution N in the slab low temperature part during slab heating, and AlN finely precipitates during the subsequent hot rolling and decarburization annealing.
The quantity is small. The spatial non-uniformity of such AlN precipitation is
It causes local nonuniformity of grain growth of primary recrystallized grains during decarburization annealing. In other words, in the part corresponding to the high temperature part in the slab during slab heating, there are many fine AlN during decarburization annealing,
Grain growth of primary recrystallized grains is suppressed. On the other hand, in the part corresponding to the low temperature part in the slab during heating of the slab, the primary recrystallized grains are likely to grow because of the small amount of fine AlN during decarburization annealing. For this reason, when the decarburization annealing is completed, there is a spatial nonuniformity of the primary recrystallized grain size in the coil due to the temperature difference in the slab during slab heating. The present inventors have filed Japanese Patent Application No. 1-177.
As disclosed in No. 8, the primary recrystallized grain size at the completion of decarburization annealing has an extremely strong correlation with the magnetic flux density of the product. Therefore, the spatial nonuniformity of the primary recrystallized grain size causes the spatial nonuniformity of the magnetic flux density in the product. Therefore, if the variation in the amount of solute N in the slab during heating of the slab, which causes the variation in the magnetic flux density, is set within a predetermined range, it is considered that the variation in the magnetic flux density of the product is reduced.

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 referred to as%), the secondary recrystallization becomes unstable, and even if secondary recrystallization is performed, 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 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 a low iron loss required as a transformer core material cannot be obtained. Desirably, it is at least 3.2%. In order to secure AlN or (Al, Si) N necessary for stabilizing secondary recrystallization, Al needs to be 0.010% or more as acid-soluble Al. Acid soluble
If Al exceeds 0.060%, AlN of the hot rolled sheet becomes unsuitable and secondary recrystallization becomes unstable, so the content was made 0.060% or less.

N is 0.00 in a normal steelmaking operation.
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. MnS
Even if MnSe is present in the steel, it is possible to improve the magnetic properties by appropriately selecting the manufacturing process conditions. However, if S or Se is high, secondary recrystallization defects called linear fine grains tend to occur. To prevent the generation of secondary recrystallization defects, (S + 0.405Se)
It should be ≦ 0.014%. If S or Se exceeds the above value, the probability of secondary recrystallization failure is increased, no matter how the manufacturing conditions are changed, which is not preferable. In addition, 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 this viewpoint.

The lower limit of Mn is 0.05%. 0.05
If it is less than%, 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 amount exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable, so the upper limit of the Mn amount 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, Sn is completely in solid solution during heating of the slab, and it is considered that Sn is evenly dissolved in the slab during heating having a temperature difference of several tens of degrees C. Therefore, Sn evenly distributed in the slab during heating despite the temperature difference, the grain growth suppression effect during decarburization annealing,
It is thought that it acts uniformly in place. Therefore, AlN
It is considered that Sn has the effect of diluting the non-uniformity of grain growth during decarburization annealing, which is caused by the non-uniformity of Al.
Therefore, in addition to the technique of the present invention for limiting the difference in the amount of solute N in the α phase, the addition of Sn is effective in further reducing the spatial variation in 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 acceptable to contain a small amount of Sb, Cu, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements. In particular, the constituent elements of the nitride such as B, Ti and Nb may be positively added in order to reduce the spatial difference in the amount of solute N due to the temperature difference in the slab. 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.

It was specified that the temperature difference ΔST in the slab at the time of completion of heating was set within the range of the following formula according to the contents of acid-soluble Al, N and Si in the slab. ΔST ≦ 32.8 + 46060 {Al-27 / 14N} ² + 4.25Si Within this condition range, the difference in the solid solution N of the α phase in the slab is 0.0.
It becomes 010% or less, and as a result, the local variation of the magnetic flux density of the product is reduced.

The heated slab is subsequently hot rolled to form a hot rolled plate. The end temperature of this hot rolling is set to 850 to 1050.
It is more preferable that the temperature is set to 0 ° C. and the cumulative rolling reduction of the final three hot rolling passes is set to 40% or more in order to reduce the local variation in the magnetic flux density of the product. The hot rolling process is usually 100 to 400
After heating a mm-thick slab, it consists of rough hot rolling and finish hot rolling, each of which is performed 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 3. The feature of the present invention is the finish hot rolling following the rough hot rolling. Finishing hot rolling is usually 4
It is performed by high-speed continuous rolling for 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 1
The time is between 0 and 3000 m / min, and the time between passes is between 0.01 and 100 seconds. What is limited in the present invention is only the hot rolling end temperature and the cumulative rolling reduction in 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 the work-induced precipitation to some extent. Also, in the last three passes, it is particularly effective to strongly reduce the pressure in the last pass. Normally, slabs with a thickness of 100 to 300 mm are 1 to 5
In the hot rolling process to be a hot rolled sheet with a thickness of mm, as the plate thickness during hot rolling becomes thinner, heat conduction in the plate thickness direction becomes easier,
The temperature difference in the slab gradually decreases. At this stage, in order to further promote the precipitation of AlN 2, it is effective to apply strain to increase the dislocations as AlN precipitation nuclei. Therefore, the work strain is applied in the latter stage of the finish hot rolling where the temperature difference in the steel sheet is most reduced to promote the precipitation of AlN, which is caused by the temperature difference in the slab during slab heating.
It is considered to be effective in suppressing as much as possible the spatial non-uniformity of the solid solution amount of Al and the precipitation amount of AlN from being inherited to the subsequent processes.

Next, the reasons for limiting the above hot rolling conditions will be described. The hot rolling end temperature was 850 to 1050 ° C. 10
When it exceeds 50 ° C, precipitation of AlN hardly occurs, and Al of the present invention
The effect of eliminating localized nonuniformity of N precipitation is not sufficient. on the other hand,
If the temperature is lower than 850 ° C, subsequent recrystallization is unlikely to occur after the hot rolling is completed, 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 hot rolling final three passes was set to 40% or more. Below this value, the effect of work-induced precipitation of AlN is insufficient, which is not preferable. The final 3
Although the upper limit of the cumulative rolling reduction of the pass is not particularly limited, 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 ~
After being air-cooled for about 100 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 it is preferable to perform air cooling for 1 second or more after hot rolling and keep the steel sheet in the AlN precipitation temperature range as long as possible in order to promote the precipitation of AlN. .

The hot-rolled sheet is then subjected to final cold rolling with a rolling reduction of 80% or more and, if necessary, one or more cold rollings with intermediate annealing. The reduction ratio of the final cold rolling is set to 80% or more, by setting the reduction ratio in the above range, 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 and the like can be obtained, which is preferable in increasing the magnetic flux density.

The present invention is constructed based on the process of omitting hot-rolled sheet annealing. However, when hot-rolled sheet annealing is performed at a temperature lower than the slab heating temperature, the temperature difference in the slab during slab heating is also the same. The magnetic flux density of the product is locally varied due to. Therefore, also in this case, the temperature difference limitation in the slab, the addition of Sn, the high pressure of the final three passes of hot rolling, and the control of the grain size after decarburization annealing described later can be used in this case, and the hot rolled sheet annealing can be performed. Better properties are obtained than the omission process.

The steel sheet after the 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 more preferable 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 a good magnetic flux density is easily obtained in the range of the average particle diameter, and the change of the magnetic flux density with respect to the fluctuation of the particle diameter is small.

It is defined that the steel sheet is subjected to the nitriding treatment after the decarburization annealing and before the start of the secondary recrystallization of the final finish annealing in the process which is premised on the low temperature slab heating as in the present invention. This is because the inhibitor strength required for secondary recrystallization tends to be insufficient. The nitriding method is not particularly limited, a method of nitriding by mixing NH ₃ gas into an annealing atmosphere after decarburization annealing, a method of using plasma, a method of adding a nitride to an annealing separator and adding a final finishing annealing step. Any method may be used, such as a method of absorbing nitrogen formed by decomposition of nitrides in the temperature into the steel sheet, a method of increasing the N ₂ partial pressure in the atmosphere of final finish annealing and nitriding the steel sheet. For the nitriding amount not particularly limited, 1 ppm or more is required.

[0041]

EXAMPLES Examples will be described below. Example 1 C: 0.049% by weight, Si: 3.21% by weight, Mn: 0.
14% by weight, S: 0.007% by weight as a basic component,
Acid-soluble Al: 0.032% by weight, N: 0.0068% by weight, acid-soluble Al: 0.020% by weight, N: 0.008
Two kinds of Al and N amounts of 7% by weight were added to prepare two kinds of 250 mm thick slabs consisting of balance Fe and unavoidable impurities. And the temperature difference at the time of slab heating that is within the allowable range of the variation of the magnetic flux density of the product,
Calculated by formula. The slab is then a 1150
After soaking for 60 minutes at 2 levels of 10 ° C and b 1095 ° C, hot rolling is started immediately, the thickness is 40 mm in 5 passes, and hot rolling is performed in 6 passes to a hot rolled plate of 2.3 mm. . At this time, the reduction distribution is 40 → 15 → 7 → 3.5 → 3 → 2.6 → 2.
It was set to 3 (mm).

Next, after the hot rolling is finished, air cooling is performed for 1 second and then 550.
A coiling simulation was performed in which the material was cooled to 0 ° C with water, held at 550 ° C for 1 hour, and then cooled in a furnace. This hot-rolled sheet is pickled to make a cold-rolled sheet of 0.335 mm with a reduction of about 85% at 830 ° C.
For 150 seconds and then at 870 ° C. for 20 seconds for decarburization annealing. After that, annealing was carried out at 750 ° C. for 30 seconds, and NH ₃ gas was mixed in the annealing atmosphere so that the steel sheet absorbed nitrogen. The N content of this steel sheet after nitriding is 0.0
It was 193 to 0.0220% by weight. Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and N ₂ 25
%, H ₂ 75% in an atmosphere gas at a rate of 10 ° C./hour for 12
The temperature was raised to 00 ° C., and then the final finishing annealing was carried out by keeping the temperature at 1200 ° C. for 20 hours in an atmosphere gas of H ₂ 100%.

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

[0044]

[Table 1]

Example 2 C: 0.051% by weight, Si: 3.01% by weight, Mn: 0.
15% by weight, S: 0.006% by weight, N: 0.0085
% As a basic component and acid-soluble Al as 0.019% by weight, 0.028% by weight, 0.037% by weight 3
Three types of 250 mm-thick slabs containing the balance Fe and unavoidable impurities were prepared by adding at the level of level. Then, the temperature difference during slab heating, which is within the allowable range of variations in the magnetic flux density of the product, was calculated by the formula for the component of.
Then, the slab is a 1150 ° C., b 109
After soaking at two levels of temperature of 5 ° C for 60 minutes, hot rolling was started at 1080 ° C to obtain a hot rolled sheet of 2.3 mm. The rolling distribution under hot rolling, the cooling conditions after hot rolling, and the process conditions up to final finishing annealing after hot rolling were performed under the conditions described in Example 1. N after nitriding
The amount was 0.0183-0.0211% by weight.

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

[0047]

[Table 2]

Example 3 C: 0.038% by weight, Si: 3.05% by weight, Mn: 0.
15% by weight, S: 0.006% by weight, acid-soluble Al: 0.
023% by weight as a basic component, N :: 0.0
087 wt%, Sn: 0.002 wt%, N: 0.00
87% by weight, Sn: 0.07% by weight, N: 0.0045
%, Sn: 0.002% by weight, N: 0.0045% by weight, Sn: 0.07% by weight, and the balance Fe.
And four types of 250 mm thick slabs consisting of unavoidable impurities were prepared. Then, the temperature difference during slab heating, which is within the allowable range of variations in magnetic flux density, was calculated by the equation for the components of and.

Then, the slab is a 1200
After soaking for 60 minutes at two levels of 1 ° C and b1150 ° C, hot rolling was started at 1100 ° C to obtain a 2.3 mm hot rolled sheet. The rolling distribution under hot rolling, the cooling conditions after hot rolling, and the process conditions up to cold rolling were performed under the conditions described in Example 1. Thereafter, the cold rolled sheet was held at 845 ° C. for 150 seconds, and then subjected to decarburization annealing at 875 ° C. for 20 seconds. After that, annealing is performed at 750 ° C. for 30 seconds, and then in an annealing atmosphere.
NH ₃ gas was mixed in to allow the steel sheet to absorb nitrogen. The amount of N after nitriding was 0.0213 to 0.0225% by weight. Then, an annealing separator containing MgO as a main component was applied to this steel sheet, and the temperature was kept at 15 ° C. in an atmosphere gas of N ₂ 25% and H ₂ 75%.
The temperature is increased to 1200 ° C at a speed of 1 / hour, and then H ₂ 100 is added.
% Final atmosphere annealing was carried out at 1200 ° C. for 20 hours in an atmosphere gas.

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

[0051]

[Table 3]

Example 4 C: 0.044% by weight, Si: 3.15% by weight, Mn: 0.
14% by weight, S: 0.007% by weight, N: 0.0080
It contains 0.1% by weight as a basic component and contains 0.1% of acid-soluble Al.
Two levels of 020% by weight and 0.034% by weight were added to prepare a 40 mm thick slab consisting of two kinds of components consisting of the balance Fe and inevitable impurities. Then, the temperature difference at the time of heating the slab, which is within the allowable range of the variation in the magnetic flux density of the product, was calculated by the formula. Then, the slab is a
After soaking at two levels of temperature of 1150 ° C. and b1095 ° C. for 30 minutes, hot rolling was immediately started to obtain a hot rolled sheet of 1.8 mm. At this time, the reduction distribution is A 40 → 16 → 7 → 2.
9 → 2.5 → 2.1 → 1.8 (mm), B 40 → 30 →
The two conditions were 20 → 10 → 5 → 2.5 → 1.8 (mm). After hot-rolling for 4 seconds, air-cool to 400 ℃, 400
A coiling simulation was carried out in which the furnace was held for 1 hour and then cooled in the furnace. In this case, the hot rolling finish temperature is 893 to 924 ° C.
Met. This hot-rolled sheet has a reduction rate of 86% and 0.260 mm.
Then, the process conditions until the final finish annealing were performed under the same conditions as in Example 3.

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

[0054]

[Table 4]

Example 5 C: 0.057% by weight, Si: 3.40% by weight, Mn: 0.
14% by weight, S: 0.007% by weight, N: 0.0083
The basic component is wt%, acid-soluble Al is added at two levels of 0.022 wt% and 0.038 wt%, and two types of 40 mm consisting of balance Fe and unavoidable impurities are added.
Created a thick slab. Then, the temperature difference during heating of the slab, which is within the allowable range of variations in the magnetic flux density of the product, was calculated by the formula for the component. Then, this slab
a at 1150 ° C, b at 1090 ° C at two levels of 60
Immediately after soaking, the hot rolling was started immediately to obtain a hot rolled sheet of 2.3 mm. The reduction distribution of hot rolling from 40 mm, the cooling conditions after hot rolling, and the process conditions until cold rolling were performed under the conditions described in Example 1. The cold-rolled sheet was subjected to decarburization annealing under three conditions of holding at 810 ° C for 150 seconds, holding at 840 ° C for 150 seconds, holding at 840 ° C for 150 seconds, and then holding at 870 ° C for 20 seconds. After that, annealing was performed 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 0.0187-
It was 0.0223% by weight. The average grain size of the primary recrystallized grains in the entire cross section of the steel sheet was measured using an optical microscope and image analysis. Then, 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.

Table 5 shows the experimental conditions and the magnetic properties of the products.

[0057]

[Table 5]

Example 6 A slab of the four components described in Example 3 was used as a 1150
After soaking for 60 minutes at two levels of temperatures of 1 ° C. and 1100 ° C., hot rolling was started immediately and the thickness was 40 mm in 5 passes.
After that, A 40 → 15 → 7 → 3.5 → 3 → 2.6 →
2.3 (mm), B40 → 30 → 20 → 10 → 6 → 4 →
Hot rolling was performed under the two conditions of 2.3 (mm), the subsequent cooling conditions and the process conditions until the final finish annealing were performed under the conditions described in Example 1. In this case, the hot rolling end temperature was 925 to 947 ° C. Moreover, the amount of N after nitriding is 0.0193 to 0.0
It was 214% by weight.

Table 6 shows the experimental conditions and the magnetic properties of the products.

[0060]

[Table 6]

Example 7 The four kinds of hot-rolled sheets described in Example 1 were subjected to hot-rolled sheet annealing of 950 ° C. × 2 minutes (soaking) and then rapid cooling, and then 0.285 mm thick with a rolling reduction of about 88%. Cold rolled sheet, 150 at 830 ℃
Decarburization annealing was performed by holding for 2 seconds and then at 850 ° C. for 20 seconds. After that, annealing was performed 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 0.0198 to 0.02
It was 15% by weight. Then, 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.

Table 7 shows the experimental conditions and the magnetic properties of the products.

[0063]

[Table 7]

[0064]

As described above, in the present invention, fluctuation regulation of the amount of solute N in the α phase in the slab during slab heating, Sn addition, hot-rolling end temperature and hot-rolling final 3 pass By controlling the cumulative rolling reduction and controlling the average grain size of the primary recrystallized grains between the completion of decarburization annealing and the start of final finishing annealing, hot rolled sheet annealing can be omitted and good magnetic properties can be obtained. Since it can be obtained stably without spatial variation,
Its industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the difference in the amount of solute N in the α phase and the difference in the magnetic flux density of products during slab heating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hodaka Hodaka 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu, Fukuoka Prefecture Inside the 3rd Technical Research Laboratories, Nippon Steel Corporation (72) Kirei Ishibashi Kitakyushu, Fukuoka Prefecture No. 1-1 Tobata-cho, Tobata-ku, Shinagawa Nippon Steel Co., Ltd. Yawata Works (72) Inventor Hisawa Kitagawa No. 1-1 Tobita-cho, Tobata-ku, Kitakyushu, Kitakyushu Shin-Nippon Steel Co., Ltd. Yawata Works

Claims (5)

(57) [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 to
A slab containing 0.8% and the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C. to perform hot rolling,
Next, a method of producing a unidirectional electrical steel sheet by including final cold rolling with a rolling reduction of 80% or more, performing cold rolling once or more with intermediate annealing if necessary, and then performing decarburizing annealing and final finishing annealing. In, the content of the acid-soluble Al, N, Si of the slab in units of% by weight, Al (%), N (%), Si (%)
, The temperature difference in the slab when heating is completed ΔST (℃)
Is controlled within the range of the following formula, and ΔST (℃) ≦ 32.8 + 46060 {Al (%)-27/14 N
(%)} ² + 4.25Si (%) A unidirectional electrical steel sheet with excellent magnetic properties characterized by nitriding the steel sheet after decarburization annealing and before the start of secondary recrystallization in final annealing. Manufacturing method. 2. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein a slab containing Sn: 0.01 to 0.15% by weight is used. 3. A unidirectional method having excellent magnetic properties according to claim 1, wherein the hot rolling end temperature is 850 to 1050 ° C., and the cumulative rolling reduction in the final three hot rolling passes is 40% or more. For manufacturing high-performance electrical steel sheet. 4. The excellent magnetic properties according to claim 1, wherein the average grain size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final finish annealing is 18 to 30 μm. Manufacturing method of unidirectional electrical steel sheet. 5. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, 2 or 3 or 4, wherein the hot rolled sheet is annealed at a temperature equal to or lower than a slab heating temperature.