JP2003253335A - Method for manufacturing grain-oriented magnetic steel sheet superior in magnetic property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a yield and a magnetic property in a technology for manufacturing a grain-oriented magnetic steel sheet without using an inhibitor, by effectively preventing edge parts cracking of a steel sheet in a cold rolling step. <P>SOLUTION: When manufacturing the grain-oriented magnetic steel sheet by using a steel slab having a composition comprising 0.01-0.08% C, 2.0-8.0% Si, 0.005-3.0% Mn, and Al reduced to less than 100 ppm, and S and Se each reduced to 50 ppm or less, this method comprises controlling a thermal history of the steel sheet between points in time after coiling up after annealing before final cold rolling and just before last cold rolling, to such a range as to satisfy the following expression (1): (∫10<SP>(-4300/</SP>T<SP>(t)-2.1)</SP>dt)<SP>0.5</SP>≤2.0×10<SP>-5</SP>, (wherein t is a time (s) after coil rolling and T(t) is a temperature (K) of the steel sheet at the time t), and limiting the temperature of the steel sheet just before cold rolling to 30°C or higher but 300°C or lower. <P>COPYRIGHT: (C)2003,JPO

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 characteristics, which is suitable for use in an iron core of a transformer or other electric equipment.

[0002]

2. Description of the Related Art In the production of grain-oriented electrical steel sheets, precipitates called inhibitors are used to preferentially recrystallize {110} <001> oriented grains called Goth oriented grains during final finish annealing. It is used as a general technique. For example, JP-B-40-15644 discloses a method of using AlN and MnS as inhibitors.
In addition, Japanese Patent Publication No. 51-13469 discloses that an inhibitor
A method using MnS and MnSe has been disclosed, and both have been industrially put to practical use. Aside from these, a technique of adding CuSe and BN is disclosed in Japanese Patent Publication No. 58-42244, and Ti, Zr,
A method using a nitride such as V is disclosed in Japanese Patent Publication No. 46-40855.

The method using these inhibitors is a useful method for stably developing secondary recrystallized grains, but since the precipitate must be finely dispersed, slab heating before hot rolling is required. It is required to be performed at a high temperature of 1300 ° C or higher. However, heating the slab at a high temperature has a problem that not only the equipment cost increases, but also the amount of scale generated during hot rolling increases, so that the yield decreases, and the maintenance of the equipment becomes complicated.

On the other hand, a method for producing a grain-oriented electrical steel sheet without using an inhibitor is disclosed in JP-A-64-55339.
JP-A-2-57635, JP-A-7-76732 and JP-A-7-197126. What these technologies have in common is that the surface energy is used as a driving force to preferentially grow the {110} plane. In order to effectively utilize the surface energy, it is inevitably required to reduce the plate thickness in order to increase the contribution of the surface. For example, in the technique disclosed in JP-A-64-55339, the plate thickness is 0.2 mm or less, and
In the technology disclosed in −57635 publication, the plate thickness is 0.15 mm or less,
Each is restricted. However, since the grain thickness of the grain-oriented electrical steel sheet currently used is mostly 0.20 mm or more, it is difficult to manufacture a normal grain-oriented electrical steel sheet by the method utilizing surface energy as described above.

Further, in order to utilize the surface energy, it is necessary to perform high temperature final finishing annealing while suppressing the formation of surface oxides. For example, JP-A-64-5533
The technique disclosed in Japanese Patent No. 9 discloses that vacuum or an inert gas, or hydrogen gas or a mixed gas of hydrogen gas and nitrogen gas is used at a temperature of 1180 ° C. or higher and as an atmosphere for final annealing. There is. In addition, JP-A-2
In the technique disclosed in Japanese Patent Laid-Open No. -57635, it is recommended that the temperature is 950 to 1100 ° C., the atmosphere is an inert gas atmosphere or hydrogen gas or a mixed atmosphere of hydrogen gas and an inert gas, and the pressure is reduced. Further, in the technique disclosed in Japanese Patent Laid-Open No. 7-197126, the oxygen partial pressure is 1000 to 1300 ° C.
It is described that the final finish annealing is performed in a non-oxidizing atmosphere of 0.5 Pa or less or in a vacuum.

As described above, in order to obtain good magnetic properties by utilizing the surface energy, the atmosphere for the final finishing annealing requires an inert gas or hydrogen gas, and the recommended condition is to make a vacuum. However, it is extremely difficult in terms of equipment to achieve both high temperature and vacuum, and the cost is high.

Further, when the surface energy is utilized, only the {110} plane can be selected in principle, and the growth of Goss grains aligned in the <001> direction in the rolling direction is selected. Not necessarily. In the grain-oriented electrical steel sheet, the magnetic properties are improved only by aligning the easy magnetization axis <001> in the rolling direction, so that theoretically good magnetic properties cannot be obtained only by selecting the {110} plane. Therefore, the rolling conditions and the annealing conditions that can obtain good magnetic properties by the method of utilizing surface energy are extremely limited, and as a result, the obtained magnetic properties must be unstable.

Furthermore, in the method utilizing surface energy, the final finish annealing must be carried out while suppressing the formation of the surface oxide layer, and the annealing separator such as MgO cannot be applied and annealed. After finish annealing, it is impossible to form an oxide film similar to that of a conventional grain-oriented electrical steel sheet. For example, a forsterite coating is a coating that is formed when MgO is used as the main component as an annealing separator, but this coating not only gives tension to the steel sheet surface, but also phosphates that are further applied and baked onto it. It is responsible for ensuring the adhesion of the insulation tension coating, which is mainly composed of Therefore, without such a forsterite coating, iron loss is significantly deteriorated.

As described above, the method using an inhibitor has a problem in terms of equipment cost and manufacturing cost associated with high temperature slab heating before hot rolling, while the method using surface energy without using an inhibitor. , The steel plate thickness is limited, the secondary recrystallization orientation is poorly accumulated,
Since there is no surface oxide film, there are problems such as poor iron loss.

By the way, the inventors previously developed a technique for developing Goss-oriented crystal grains by secondary recrystallization in a material containing no inhibitor as a solution to the above-mentioned problems. No. 129356. However, with this method, there is a problem that cracking occurs in the steel sheet edge portion during cold rolling and the yield decreases, and it has been necessary to improve this from the viewpoint of industrial production.

[0011]

DISCLOSURE OF THE INVENTION The present invention was developed in view of the above situation, and in the production technology of grain-oriented electrical steel sheet that does not use an inhibitor, effectively reduces the edge cracks of the steel sheet in the cold rolling process. It is an object of the present invention to propose an advantageous manufacturing method of a grain-oriented electrical steel sheet having excellent magnetic characteristics, which is achieved by preventing it and improving the yield as well as improving the magnetic characteristics.

[0012]

That is, the gist of the present invention is as follows. 1. % By mass, C: 0.01 to 0.08%, Si: 2.0 to 8.0% and Mn: 0.005 to 3.0%, Al less than 100 ppm, S,
A steel slab with a composition that reduces Se to 50 ppm or less is hot-rolled, hot-rolled and annealed, and then cold-rolled once to finish to the final thickness, followed by decarburization annealing and annealing separation. After applying the agent, in the method for producing a grain-oriented electrical steel sheet consisting of a series of steps for performing final finishing annealing, the thermal history of the steel sheet from coil winding after hot rolling sheet annealing to immediately before cold rolling, Formula (1) (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 ≤ 2.0 × 10 ^-5 --- (1) where, t: time from coil winding (s) T ( t): Directional electromagnetic wave with excellent magnetic properties, which is characterized by controlling the steel plate temperature (K) at time t within a range that satisfies it and limiting the steel plate temperature immediately before cold rolling to 30 ° C or higher and 300 ° C or lower. Steel plate manufacturing method.

2. % By mass, C: 0.01 to 0.08%, Si: 2.
0-8.0% and Mn: 0.005-3.0%, Al is 100 p
A steel slab having a composition of less than pm and S and Se reduced to 50 ppm or less is hot-rolled, hot-rolled sheet is annealed if necessary, and then cold-rolled twice or more with an intermediate annealing. In the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps of finishing the final plate thickness, then decarburizing annealing, then applying the annealing separator, and then performing the final finishing annealing, after the intermediate annealing before the final cold rolling. The thermal history of the steel sheet from coil winding to immediately before the final cold rolling is calculated by the following equation (1) (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 ≤ 2.0 × 10 ^-5 --- (1) where, t: time from coil winding (s) T (t): steel plate temperature (K) at time t is controlled within a range that satisfies the requirement, and the steel plate temperature immediately before cold rolling is 30 ° C or more. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by being limited to 300 ° C or less.

3. The steel slab, in mass%, also contains Ni: 0.
005 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50
%, Cu: 0.01 to 1.50%, P: 0.005 to 0.50% and Cr:
3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to 1 or 2 above, which contains one or more selected from 0.01 to 1.50%.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the experimental results that led to the present invention will be described. In addition, unless otherwise indicated, "%" display regarding components means mass% (mass%). C: 0.06%, Si:
3.3%, Mn: 0.03%, Al: 20 ppm, S: 10 ppm, Se: 0.
A steel slab with a composition containing 1 ppm and N: 20 ppm is heated to 1100 ° C and then hot-rolled to a plate thickness of 2.0.
A hot-rolled coil of mm was formed, and then the hot-rolled sheet was annealed at 1000 ° C. for 1 minute, cooled, and then wound into a coil to obtain a hot-rolled annealed sheet coil. Then, this hot rolled annealed plate coil,
After being heated to various temperatures of 15 to 200 ° C. and kept heat, it was immediately subjected to cold rolling to obtain a cold rolled plate having a plate thickness of 0.25 mm. Table 1 shows the thermal history from coil winding to rolling. In addition, Table 1 also shows the results of the examination of the steel sheet temperature immediately before cold rolling and the presence or absence of cracks in the edge portion of the cold rolled sheet after cold rolling.

After that, decarburization annealing was performed at 850 ° C. for 2 minutes, an annealing separating agent containing MgO as a main component was applied, and then final finishing annealing was performed at 1200 ° C. for 20 hours. Then,
A tension coating treatment liquid containing phosphate-colloidal silica as a main component was applied and baked to form a tension coating film to obtain a product. The results of examining the magnetic properties of the obtained products are also shown in Table 1.

[0017]

[Table 1]

As shown in the table, it became clear that when the steel sheet temperature immediately before cold rolling was set to 30 ° C. or higher, cracking did not occur in cold rolling. However, it was also clarified that the magnetic characteristics may be significantly deteriorated.

Therefore, the present inventors have investigated the cause of the deterioration of the magnetic characteristics, and have found that the cause is due to the precipitation of solute carbon. Table 1 shows the carbon diffusion distance L (cm) calculated from the heat history of the steel sheet until the cold rolling after the hot rolled steel sheet was annealed and wound into a coil.
The results of the survey are also shown.

Here, L is represented by the following equation (2) L = (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 (cm) --- (2), and t is a coil winding. Time since taking (s), T (t)
Is the steel plate temperature (absolute temperature K) at time t. This formula is based on the literature (RPSmith: Trans.Met.Soc.AIME., 224 (196
2) Based on the diffusion formula of carbon in steel obtained in P.105), and L represents the average diffusion distance of carbon. As shown in the table, it became clear that good magnetic characteristics can be obtained when the carbon diffusion distance L is 2.0 × 10 ⁻⁵ cm or less.

[0021]

In the present invention, the reason why secondary recrystallization occurs in steel containing no inhibitor component is not always clear, but is considered as follows. As a result of intensive studies on the reason why the Goth-oriented grains undergo secondary recrystallization, the inventors discovered that the grain boundary having a misorientation angle of 20 to 45 ° in the primary recrystallization structure plays an important role. And Ac
Ta Material 45 (1997) p. 1285.

The primary recrystallization structure of the grain-oriented electrical steel sheet immediately before the secondary recrystallization is analyzed, and the grain boundary misorientation angle is 20 to 45 for the grain boundaries around the respective crystal grains having various crystal orientations.
FIG. 1 shows the result of the investigation on the ratio (%) of the grain boundaries with respect to the whole. In the figure, the crystal orientation space is shown using a Φ ₂ = 45 ° cross section of Euler angles (Φ ₁ , Φ, Φ ₂ ), and the main directions such as the Goss orientation are schematically displayed. According to this figure, the Goss orientation has the highest frequency of existence of the grain boundaries of the grain boundaries having a misorientation angle of 20 to 45 °.

Grain boundaries having a misorientation angle of 20 to 45 ° are CG Dunn
Experimental data from AIME Transaction 188 (1949)
According to page 368), it is a high energy grain boundary. This high energy grain boundary has a large free space in the grain boundary and has a disordered structure. Grain boundary diffusion is a process in which atoms move through the grain boundaries, so grain boundary diffusion is faster in high-energy grain boundaries with a large free space in the grain boundaries. It is known that the secondary recrystallization is accompanied by the growth of a precipitate called an inhibitor due to diffusion control. The precipitation on the high-energy grain boundaries preferentially grows during finish annealing, so the pinning is preferentially disengaged to initiate grain boundary migration, and a mechanism for the growth of Goss grains was shown.

The inventors further developed this research, and the essential factor of the secondary recrystallization of Goss-oriented grains is the distribution state of high-energy grain boundaries in the primary recrystallization structure, and the role of the inhibitor is , It was found that there is a difference in the moving speed between the high energy grain boundary and other grain boundaries. Therefore, according to this theory,
If a difference in moving speed of grain boundaries can be generated, secondary recrystallization can be performed.

Impurity elements existing in steel are likely to segregate at grain boundaries, especially at high energy grain boundaries. Therefore, when a large amount of impurity elements are contained, there is a difference in moving speed between the high energy grain boundaries and other grain boundaries. Is considered to have disappeared. On the other hand, if the influence of the impurity element as described above can be eliminated by improving the purity of the material, the inherent difference in the moving speed depending on the structure of the high-energy grain boundary becomes apparent, and the difference in the Goss-oriented grain It is considered that next recrystallization will be possible.

Further, in order to enable stable secondary recrystallization by utilizing the difference in grain boundary migration speed, it is important to keep the primary recrystallization structure as uniform in grain size distribution as possible. This is because when the uniform grain size distribution is maintained, grain growth is suppressed because the frequency of low-energy grain boundaries with a low grain boundary migration velocity is high in crystal grains other than Goss-oriented grains. By exerting the so-called Texture Inhibition effect,
This is because the secondary recrystallization as the selective grain growth of the Goss-oriented grains in which the frequency of high-energy grain boundaries with a high grain boundary migration speed is maximum proceeds. On the other hand, if the grain size distribution is not uniform, normal grain growth occurs with the grain size difference between adjacent crystal grains as the driving force, so that crystal grains that grow due to factors different from the grain boundary migration velocity difference Texture Inhibi to be selected
The selective effect of Goss-oriented grains does not occur without exerting the tion effect.

In the secondary recrystallization of the material containing no inhibitor component as described above, in order to obtain good magnetic properties, the steel sheet before final cold rolling contains 0.01 to 0.08% of C.
It is extremely important that it is contained. I mean,
The carbon solid-solved or precipitated in the steel sheet before final cold rolling is
This is because the primary recrystallization structure is improved and the secondary recrystallization grain orientation is accumulated in the Goss orientation.

Further, the relationship between the thermal history and the magnetic properties from coil winding after hot-rolled sheet annealing to immediately before cold rolling is estimated as follows. It is presumed that part of C in the steel sheet during coil winding after hot-rolled sheet annealing is precipitated as carbide and the rest is in solid solution. In cold rolling, in order to prevent cracking of the steel sheet, the steel sheet temperature immediately before cold rolling should be set to
It is important to set the temperature to 30 ° C. or higher, preferably 50 ° C. or higher. At this time, it is considered that the solid solution C in the steel sheet precipitates as carbides. As a result, the diffusion distance L of C is 2 × the threshold value.
If it exceeds 10 ⁻⁵ cm, it is considered that the amount of solid solution C necessary for forming the desired primary recrystallized structure decreases and the magnetic properties deteriorate.

It is well known that the grain-oriented electrical steel sheet containing an inhibitor deteriorates in magnetic properties due to coarsening of carbides (for example, Japanese Patent Laid-Open No. 9-1577).
45 publication). In the grain-oriented electrical steel sheet containing such an inhibitor, the deterioration of the magnetic properties due to the coarsening of the carbides occurs by holding at 150 ° C. or higher for a long time. Therefore, in order to prevent cracking of the steel sheet during cold rolling, the temperature of the steel sheet during coil winding after hot-rolled sheet annealing has been set to 100 to 150 ° C, and the coil is kept warm or charged in a heating box. In general, the coil is kept at 100 to 150 ° C. and the coil is taken out of the heat retaining or heating box immediately before rolling and rolled. However, in the grain-oriented electrical steel sheet containing no inhibitor, the magnetic properties are greatly deteriorated in the above steps.

The novel point of the present invention is that, in the production of grain-oriented electrical steel sheet containing no inhibitor, the primary recrystallization structure is deteriorated by the precipitation of solute carbon even at a low temperature where coarsening of carbide does not occur. However, it has been found that the magnetic characteristics are deteriorated thereby.

Next, in the present invention, the reason why the composition of the raw material slab is limited to the above range will be described. C: 0.01 to 0.08% If C is less than 0.01%, the effect of improving the primary recrystallization structure is small, and satisfactory magnetic properties cannot be obtained.
When it exceeds 08%, the C of the product does not cause magnetic aging 50pp
Since it becomes difficult to reduce it to m or less, the C content is 0.01-
It was limited to the range of 0.08%. Si: 2.0 to 8.0% Since Si is an element useful for increasing the electric resistance of steel and reducing iron loss, it is contained at 2.0% or more. However, if the content exceeds 8.0%, the workability is remarkably reduced and cold rolling becomes difficult. Therefore, the Si content is limited to the range of 2.0 to 8.0%. Mn: 0.005-3.0% Mn is an element useful for improving hot workability, but if the content is less than 0.005%, its addition effect is poor,
On the other hand, if it exceeds 3.0%, the magnetic flux density will decrease, so the Mn content should be in the range of 0.005 to 3.0%.

Al: less than 100 ppm, S and Se are 50 p each
Further, it is indispensable to reduce the impurity element Al to less than 100 ppm, and S and Se to 50 ppm or less, preferably 30 ppm or less, respectively, for good secondary recrystallization. In addition, nitride forming elements such as Ti, Nb, B, Ta, V
Regarding the above, it is effective to reduce the iron content to 50 ppm or less in order to prevent deterioration of iron loss and ensure good workability.

Although the essential component and the inhibitory component have been described above, other elements described below can be appropriately contained in the present invention. Ni: 0.005 to 1.50%, S
n: 0.01 to 0.50%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.5
At least one kind of Ni selected from 0%, P: 0.005 to 0.50%, and Cr: 0.01 to 1.50% is a useful element for improving the hot rolled sheet structure and magnetic properties. However, if the content is less than 0.005%, the amount of improvement in magnetic properties is small, while if it exceeds 1.50%, secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the Ni content was made 0.005 to 1.50%. Also,
Each of Sn, Sb, Cu, P, and Cr is an element useful for improving iron loss, but if the lower limit of each of the above ranges is not satisfied, the effect of improving iron loss is small, while if it exceeds the upper limit, Since the development of secondary recrystallized grains is inhibited, Sn: 0.01 to 0.50, respectively.
%, Sb: 0.005 to 0.50%, Cu: 0.01 to 1.50%, P: 0.00
5 to 0.50%, Cr: 0.01 to 1.5%.

Next, the manufacturing process of the present invention will be described. Molten steel adjusted to the above-mentioned preferred component composition is smelted by a known method using a converter, an electric furnace, etc., and if necessary subjected to vacuum treatment or the like, then using a usual ingot making method or continuous casting method. Manufacture slabs. Also, using direct casting method, 100
You may directly manufacture the thin slab with a thickness of less than mm. The slab is heated by a usual method and hot-rolled, but it may be directly subjected to hot rolling without heating after casting. Further, in the case of a thin cast piece, hot rolling may be performed, or hot rolling may be omitted and the process may be directly performed. It is particularly desirable to control the slab heating temperature before hot rolling to 1250 ° C. or lower in order to reduce the amount of scale generated during slab heating.
It is also desirable to lower the slab heating temperature in the sense that the crystal structure is made finer and the harmful effects of the inhibitor component mixed inevitably are made harmless to realize a uniform sized primary recrystallization structure.

Then, hot-rolled sheet annealing is performed. In order to highly develop the Goss structure in the product sheet, the hot rolled sheet annealing temperature is preferably in the range of 800 to 1100 ° C. This is because when the hot-rolled sheet annealing temperature is lower than 800 ° C, the band structure in hot rolling remains and it becomes difficult to realize the primary recrystallization structure of the grain size, which hinders the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C, the inhibitor components that are inevitably mixed are solid-dissolved and re-precipitate unevenly during cooling,
This is because it becomes difficult to realize sized primary recrystallized fiber, and the development of secondary recrystallization is also hindered. Further, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after the hot-rolled sheet annealing becomes excessively large, which is extremely disadvantageous in realizing the primary recrystallized structure of sized grains.

After annealing the hot rolled sheet, it is cooled and wound into a coil.
Then, the final thickness is finished by cold rolling, but it is important that the steel sheet temperature immediately before cold rolling is 30 ° C or higher and 300 ° C or lower, because the steel sheet temperature immediately before cold rolling is 30 ° C.
If the temperature is less than ℃, cold rolling will cause cracks in the edge of the steel sheet and the yield will be significantly deteriorated, while if it exceeds 300 ℃, the cold rolling rolls will thermally expand and become a drum shape called heat crown. This is because rolling becomes impossible.

Further, the thermal history of the steel sheet after coil winding after hot-rolled sheet annealing and immediately before cold rolling is calculated by the following equation (1) (∫10 ^{(-4300 / T (t) -2.1)} dt ) ^0.5 ≤ 2.0 × 10 ^-5 --- (1) where, t: time from coil winding (s) T (t): steel plate temperature (K) at time t can be controlled within a range satisfying. is important. This is because the diffusion distance L of C shown on the left side of the above equation (1) is 2.0.
This is because if it exceeds x 10 ^-5 (cm), the magnetic properties deteriorate due to the precipitation of solid solution C.

In order to make the heat history of the steel sheet from coil winding after hot-rolled sheet annealing to immediately before cold rolling a heat history satisfying the above formula (1), hot-rolled sheet annealing is performed. The temperature of the steel sheet during coil winding after that is lower than that of the conventional one, preferably 20 ° C. or less, and the steel sheet is quickly heated immediately before cold rolling,
Cold rolling is required. As a method of heating the steel sheet, a heating apparatus such as induction heating, infrared heating, or electric heating is arranged between the coil payout device (pay-off reel) on the entrance side of the rolling mill and the rolling mill to continuously heat the steel sheet. It is desirable to do. This is because this method can increase the heating rate of the steel sheet to about 1 to 100 ° C./s, and as a result, can reduce the carbon diffusion distance L until the desired temperature is reached. Is.

In addition to the above-described method in which the product thickness is obtained by one cold rolling after the hot-rolled sheet annealing, the hot-rolled sheet is optionally annealed, and then cold-rolled twice or more with intermediate annealing. A method of finishing to the final plate thickness by hot rolling can also be applied. In this case, the steel sheet temperature immediately before the final cold rolling is set to 30 ° C or higher and 300 ° C or lower, and the steel sheet temperature between the coil winding after the intermediate annealing before the final cold rolling and immediately before the final cold rolling is set. The thermal history may be controlled within a range that satisfies the following equation (1) (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 ≤ 2.0 × 10 ^-5 (cm) --- (1).

Then, the cold-rolled steel sheet having the final finished thickness is subjected to decarburization annealing so that C is not magnetically aged at 50 p.
pm or less, preferably 30ppm or less. Such decarburization annealing is preferably carried out in a humid atmosphere at a temperature of 700-1000 ° C. Also, a technique of increasing the Si content by a siliconizing method after decarburization annealing may be used together. After that, an annealing separator is applied and final finishing annealing is performed to develop a secondary recrystallization structure and form a forsterite coating. The final finish annealing needs to be performed at 800 ° C. or higher in order to develop the secondary recrystallization, but the heating rate up to 800 ° C. does not have a great influence on the magnetic properties, so any conditions may be used.

After that, flattening annealing is performed to correct the shape. Then, after the above flattening annealing, it is advantageous to apply an insulating coating for imparting tension to the surface of the steel sheet for the purpose of improving iron loss. Further, it goes without saying that a known magnetic domain subdivision technique can be applied.

[0042]

EXAMPLES Example 1 C: 0.01%, Si: 3.8%, Mn: 0.15% are contained, and Al is 10%.
ppm, S to 20 ppm, Se to 0 ppm, N to 30 ppm,
The balance consists of molten steel with a composition of Fe and unavoidable impurities,
A slab was manufactured by continuous casting. This slab was hot-rolled into a 2.0 mm thick hot-rolled sheet without reheating, annealed at 1000 ° C for 1 minute, then cooled and formed into a coil at the temperature shown in Table 2. I wound up. Then, the heat history of the steel sheet until cold rolling was changed as shown in Table 2 and subjected to cold rolling. Table 2 shows the measurement results of the carbon diffusion distance L (cm) between the coil winding and the start of cold rolling and the steel sheet temperature immediately before the start of cold rolling.

Then, the final plate thickness is 0.25 mm by cold rolling.
Cold-rolled sheet was finished, decarburization annealed at 800 ° C for 2 minutes, MgO was applied, and then finish annealed at 1200 ° C for 5 hours. After that, an insulating coating treatment liquid containing phosphate and silica as a main component was applied, followed by annealing for also planarization.
The results of examining the magnetic properties of the products thus obtained are also shown in Table 2.

[0044]

[Table 2]

As is apparent from the table, the product obtained according to the present invention showed a high magnetic flux density without cracking during cold rolling.

Example 2 C: 0.07%, Si: 3.3%, Mn: 0.05%, Cr: 0.08%, C
u: 0.08%, Sb: 0.02% contained, Al 60 ppm, S 20
A slab was produced by continuous casting from molten steel in which ppm, Se were reduced to 10 ppm, N was reduced to 55 ppm, and the balance was Fe and inevitable impurities. After heating this slab to 1200 ° C,
A hot rolled sheet with a thickness of 2.5 mm was obtained by hot rolling. Then, the steel sheet was cold-rolled for the first time to an intermediate thickness of 1.8 mm, subjected to intermediate annealing at 900 ° C. for 1 minute, cooled, and then wound into a coil at a temperature shown in Table 3. After that, the heat history of the steel sheet until the second cold rolling was changed variously as shown in Table 3.
Table 3 shows the carbon diffusion distance L (cm) after the coil winding after the intermediate annealing until the start of the final cold rolling and the steel plate temperature immediately before the start of the second cold rolling.

Then, the final cold rolling was finished by the second cold rolling to a final thickness of 0.22 mm, followed by decarburization annealing at 850 ° C. for 5 minutes, and then 5%.
Of MgO containing TiO ₂ was applied, and then finish annealing was performed at 1200 ° C. for 5 hours. After that, an insulating coating treatment liquid containing phosphate and silica as a main component was applied, followed by annealing for also planarization. The results of examining the magnetic properties of the product thus obtained are also shown in Table 3.

[0048]

[Table 3]

As is clear from the table, the product obtained according to the present invention showed a high magnetic flux density without cracking during cold rolling.

Example 3 C: 0.05%, Si: 2.5%, Mn: 0.5% are contained, and Al is 90%.
ppm, S to 48 ppm, Se to 3 ppm, N to 15 ppm,
Further, a slab was produced by continuous casting from molten steel containing Ni, Sn, Sb, Cu, P, and Cr in the ranges shown in Table 4, with the balance being Fe and inevitable impurities. After heating this slab to 1100 ° C., it was hot-rolled into a hot-rolled sheet having a thickness of 2.5 mm. Then, after annealing the hot rolled sheet at 850 ° C for 1 minute,
After cooling and winding on a coil, the coil was heated to change the heat history of the steel sheet up to cold rolling into two conditions, and then subjected to cold rolling. The carbon diffusion distance L (cm) after coil winding until the start of cold rolling was 2.0 × 10 ⁻⁵ (condition I) and 8.2 × 10 ⁻⁴ (condition II). The steel sheet temperature immediately before the start of cold rolling was 40 ° C.

Then, by cold rolling, the final plate thickness: 0.35 mm
After decarburization annealing at 800 ° C for 2 minutes, MgO was applied and then finish annealing at 1200 ° C for 5 hours. After that, an insulating coating treatment liquid containing phosphate and silica as a main component was applied, followed by annealing for also planarization. The results of examining the magnetic properties of the product thus obtained are also shown in Table 4.

[0052]

[Table 4]

As is clear from the table, no cracks were generated during cold rolling in any of the products, but a sufficient magnetic flux density was not obtained in the comparative example (condition II). A high magnetic flux density is obtained in the product obtained according to the invention (condition I).

[0054]

As described above, according to the present invention, when the grain-oriented electrical steel sheet is manufactured by the method of causing the secondary recrystallization without using the inhibitor, the coil winding after the annealing before the final cold rolling is performed. By controlling the heat history of the steel sheet during the period from to just before the final cold rolling, it is possible to effectively prevent the steel sheet edge cracks in the cold rolling process and improve the product yield. Can be improved.

[Brief description of drawings]

FIG. 1 shows the primary recrystallization structure of grain-oriented electrical steel,
For the grain boundaries around each crystal with various crystal orientations,
The ratio (%) to the entire grain boundaries having a grain boundary misorientation angle of 20 to 45 ° is shown.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsumasa Kurosawa             1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama             Shi) Kawasaki Steel Co., Ltd. Mizushima Steel Works F-term (reference) 4K033 AA02 CA01 CA02 CA03 CA07                       CA08 EA02 JA04 LA01 TA02                       TA03                 5E041 AA02 CA02 HB11 NN01 NN18

Claims (3)

[Claims] 1. By mass%, C: 0.01 to 0.08%, Si: 2.0
~ 8.0% and Mn: 0.005-3.0%, Al 100 ppm
Steel, and a steel slab having a composition in which S and Se are reduced to 50 ppm or less, respectively, after hot rolling and hot-rolled sheet annealing,
In a method for producing a grain-oriented electrical steel sheet, which comprises a series of steps in which a final thickness is finished by one cold rolling, a decarburization annealing is performed, an annealing separator is applied, and then a final finishing annealing is performed. The thermal history of the steel sheet from coil winding after annealing to immediately before cold rolling is calculated by the following equation (1) (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 ≤ 2.0 × 10 ^-5- -(1) where, t: time from coil winding (s) T (t): control within a range satisfying the steel plate temperature (K) at time t, and the steel plate temperature immediately before cold rolling is 30 A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by limiting the temperature to 300 ° C or higher. 2. C: 0.01 to 0.08%, Si: 2.0 by mass%
~ 8.0% and Mn: 0.005-3.0%, Al 100 ppm
Steel slabs with a composition of less than 50 ppm and less than 50 ppm of S and Se are hot-rolled, and if necessary hot-rolled sheet annealed, and then cold-rolled twice or more with an intermediate anneal. In the method for producing a grain-oriented electrical steel sheet, which comprises a series of steps of finishing the plate thickness, then decarburizing and annealing, then applying the annealing separator, and then performing the final finish annealing, the coil after the intermediate annealing before the final cold rolling. The thermal history of the steel sheet from winding to immediately before the final cold rolling is calculated by the following equation (1) (∫10 ^{(-4300 / T (t) -2.1)} dt) ^0.5 ≤ 2.0 × 10 ^-5 --- ( 1) where, t: time from coil winding (s) T (t): steel plate temperature (K) at time t is controlled in a range satisfying the condition, and the steel plate temperature immediately before cold rolling is 30 ° C. or higher 300 A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by being limited to ℃ or less. 3. The steel slab further comprises Ni: 0.00 by mass%.
5 to 1.50%, Sn: 0.01 to 0.50%, Sb: 0.005 to 0.50%,
Cu: 0.01 to 1.50%, P: 0.005 to 0.50% and Cr: 0.01
3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1 or 2, containing one or more selected from the range of 1.50%.