JP2012188733A - Manufacturing method for grain-oriented electrical steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for advantageously manufacturing a grain-oriented electrical steel sheet excellent in magnetic characteristic at favorable productivity.SOLUTION: The manufacturing method for the grain-oriented electrical steel sheet hot-rolls a steel slab which contains, by mass, 0.020 to 0.15% of C, 2.5 to 7.0% of Si, 0.005 to 0.3% of Mn, 0.01 to 0.05% of sol.Al, 0.002 to 0.012% of N, 0.05% or lower in the total of one or two of S and Se, 0.01 to 0.20% of Sn, (0.2×Sn)% or higher and 0.10% or lower of Sb, and {0.7×(Sn+Sb)}% or higher and 1.0% or lower of Ni, cold-rolls the steel slab more than twice with intermediate annealing sandwiched between, primarily re-crystallization anneals the steel slab, and finish-anneals the steel slab. The manufacturing method for the grain-oriented electrical steel sheet is also characterized by controlling a pressure-lowering rate R at a temperature of 1,150°C at hot rolling and the highest arrival temperature T (°C) at the intermediate annealing in proper ranges according to contents of Sn, Sb and Ni of the steel slab.

Description

  The present invention relates to a method for producing a so-called grain-oriented electrical steel sheet in which crystal grains are highly accumulated in a Miller index of {110} on a plate surface and <001> in a rolling direction.

The grain-oriented electrical steel sheet, which is a soft magnetic material, is obtained by highly accumulating crystal grains in {110} <001> (hereinafter also referred to as “Goss orientation”) by performing secondary recrystallization annealing. Because of its excellent magnetic properties, it is widely used as an iron core material for electric devices such as transformers and rotating machines used in the commercial frequency range. As an evaluation index of magnetic properties, generally, the magnetic flux density B _{8 at} a magnetic field strength of 800 A / m and the iron loss W _17/50 per kg of steel sheet when magnetized to 1.7 T with an alternating magnetic field with an excitation frequency of 50 Hz. Used. The _grain- oriented electrical steel sheet is strongly required to have particularly low iron loss W _17/50 . This is because iron loss of a generator, a transformer, or the like is greatly reduced by using a material having a low W _17/50 . In particular, in recent years, demands for reducing the iron loss of grain-oriented electrical steel sheets have become stronger due to the increasing demand for energy saving.

  As a technique for reducing the iron loss of grain-oriented electrical steel sheets, for example, Patent Document 1 discloses a cold rolling containing 0.003 to 0.3 mass% of these elements in a combination of Sb and Mo or Sn and Cu. Low iron loss is achieved by heating the steel sheet at a rate of 100 ° C / s or higher and decarburizing and annealing, and by irradiating with laser in the middle of the manufacturing process or controlling the magnetic domain by grooving by etching. A technique for achieving this is disclosed. Although this technique can obtain relatively good magnetic properties due to the grain boundary segregation effect of Sn and Cu, the problem of embrittlement due to the addition of Sn and Cu, and the equipment cost for high-speed heating by decarburization annealing. There is a problem of an increase in manufacturing cost due to. In addition, the magnetic domain control is essential, which is disadvantageous in terms of cost as compared with the grain-oriented electrical steel sheet without the magnetic domain control.

  Further, in Patent Document 2, it is possible to obtain an extremely strong suppression force against the growth of primary recrystallized grains by adding appropriate amounts of Sb and Ni in addition to AlN as an inhibitor, and as a result. It is disclosed that a primary recrystallized texture is improved more than ever and a grain-oriented electrical steel sheet having a low iron loss value is obtained. However, from the viewpoint of achieving both low iron loss and high magnetic flux density by refining secondary recrystallized grains, it cannot be said that it is sufficient, and further, the addition of Sb and Ni causes brittleness during hot rolling. As a result, edge cracking or the like occurs and productivity is poor (yield is low).

Japanese Patent No. 4377477 Japanese Patent No. 3357578

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to propose an advantageous method for producing a grain-oriented electrical steel sheet having excellent magnetic properties with high productivity.

  The inventors have intensively studied to solve the above problems. As a result, by optimizing the amount of Sn, Sb and Ni added as auxiliary inhibitor components, and further controlling the reduction rate during hot rolling and the maximum temperature reached during intermediate annealing to an appropriate range, Not only can it solve brittleness problems such as edge cracking during rolling, but it can also build an excellent primary recrystallized plate texture, and thus it can exhibit excellent magnetic properties after secondary recrystallization. The present invention has been completed by finding out what can be done.

That is, the present invention relates to C: 0.020 to 0.15 mass%, Si: 2.5 to 7.0 mass%, Mn: 0.005 to 0.3 mass%, sol. Al: 0.01-0.05 mass%, N: 0.002-0.012 mass%, one or two of S and Se: 0.05 mass% or less in total, Sn: 0.01-0. 20 mass%, Sb: (0.2 × Sn) mass% or more and 0.10 mass% or less, Ni: {0.7 × (Sn + Sb)} mass% or more and 1.0 mass% or less, with the balance being Fe and inevitable A steel slab having a component composition consisting of impurities is heated to 1300 ° C or higher, then hot-rolled at 850 ° C or higher, and the final thickness is obtained by two or more cold rollings with intermediate annealing between them. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing the final annealing after the crystal annealing, depending on the contents of Sn, Sb and Ni in the steel slab, Reduction Rate R (%) is the following formula (1);
R ≦ 90− (4 × Ni + 2 × Sn) (1)
Further, the maximum attainable temperature T (° C.) in the intermediate annealing is the following formula (2):
500 × (Sn + Sb) + 1000 ≦ T ≦ 1500 × (Sn + Sb) +1000
... (2)
It is the manufacturing method of the grain-oriented electrical steel sheet characterized by controlling to satisfy | fill. Here, each element symbol in the above formula is the content (mass%) of each component.

  The method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that a temperature increase rate between 500 and 700 ° C. in the primary recrystallization annealing is 50 ° C./s or more.

  Moreover, in addition to said component composition, the steel slab in the manufacturing method of the grain-oriented electrical steel sheet of this invention is further from Cu: 0.005-1.5mass% and P: 0.0001-0.50mass%. It contains one or two kinds selected.

According to the present invention, by adding appropriate amounts of Sn, Sb, and Ni, edge cracking and the like in hot rolling can be prevented, and by improving the primary recrystallization texture, it is more than conventional. A grain-oriented electrical steel sheet having excellent magnetic properties can be produced. Therefore, according to the present invention, even when the plate thickness is 0.23 _mm, which is difficult to manufacture, the iron loss W _17/50 after secondary recrystallization annealing has excellent iron loss characteristics of 0.90 W / kg or less. This makes it possible to produce a highly magnetic steel sheet with high productivity.

First, the component composition of the steel raw material used for manufacture of the grain-oriented electrical steel sheet of the present invention will be described.
Steel materials used in the present invention are C: 0.020 to 0.15 mass%, Si: 2.5 to 7.0 mass%, Mn: 0.005 to 0.3 mass%, sol. Al: 0.01-0.05 mass%, N: 0.002-0.012 mass%, one or two of S and Se: 0.05 mass% or less in total, Sn: 0.01-0. 20 mass%, Sb: (0.2 × Sn) mass% or more and 0.10 mass% or less, Ni: {0.7 × (Sn + Sb)} mass% or more and 1.0 mass% or less are required. is there. This will be specifically described below.

C: 0.020-0.15 mass%
C is an element necessary for improving the hot-rolled sheet structure by utilizing the γ transformation during soaking of hot-rolled and hot-rolled sheet annealing, but if the content is less than 0.020 mass%, The effect of improving the plate structure is small, and it becomes difficult to obtain a desired primary recrystallization texture. On the other hand, if the content exceeds 0.15 mass%, not only the decarburization load is increased, but also the decarburization becomes incomplete and causes magnetic aging in the product plate. Therefore, C is set to a range of 0.020 to 0.15 mass%. Preferably it is the range of 0.030-0.090 mass%.

Si: 2.5-7.0 mass%
Si is an extremely effective element for increasing the electrical resistance of steel and reducing eddy current loss that constitutes a part of iron loss. This electrical resistance increasing effect increases monotonously until the Si content reaches 11 mass%. However, if Si exceeds 7.0 mass%, the workability is remarkably lowered and the productivity is deteriorated. On the other hand, if the Si content is less than 2.5 mass%, secondary recrystallization in the final finish annealing is hindered by the presence of the γ-α transformation, leading to a decrease in magnetic properties. Therefore, Si is set to a range of 2.5 to 7.0 mass%. Preferably it is the range of 2.8-4.0 mass%.

Mn: 0.005 to 0.3 mass%,
Mn is an important element in grain-oriented electrical steel sheets because it forms inhibitors MnS and MnSe and suppresses the growth of normal grains in the temperature raising process of secondary recrystallization annealing. When the Mn content is less than 0.005 mass%, the absolute amount of the inhibitor is insufficient, and thus the inhibitory power is insufficient. On the other hand, if it exceeds 0.3 mass%, the slab heating before hot rolling causes the inhibitor to be precipitated in a large amount in addition to the heating temperature for completely dissolving MnS and MnSe, and also suppresses. Lack of power. Therefore, Mn is in the range of 0.005 to 0.3 mass%. Preferably it is the range of 0.008-0.25 mass%.

sol. Al: 0.01-0.05 mass%
Al is an important element in grain-oriented electrical steel sheets because it acts as an inhibitor that suppresses the growth of normal grains in the temperature rising process of secondary recrystallization annealing by precipitating as AlN. However, Al is sol. When the content as Al (acid-soluble Al) is less than 0.01 mass%, the absolute amount of the inhibitor is insufficient and the inhibitory power is insufficient. On the other hand, when it exceeds 0.05 mass%, AlN coarsely precipitates, and on the contrary, the suppressing power is insufficient. Therefore, Al is sol. The Al content is in the range of 0.01 to 0.05 mass%. Preferably it is the range of 0.015-0.035 mass%.

N: 0.002-0.012 mass%
N is a component that binds to Al to form an inhibitor AlN. If the content is less than 0.002 mass%, the absolute amount of the inhibitor is insufficient and the inhibitory power is insufficient. On the other hand, if it exceeds 0.012 mass%, surface defects caused by pores called blisters are generated during cold rolling, which is not preferable. Therefore, N is set to a range of 0.002 to 0.012 mass%. Preferably it is the range of 0.004-0.010 mass%.

One or two of S and Se: 0.05 mass% or less in total S and Se are elements that combine with Mn to form the inhibitors MnS and MnSe, and the total of one or two types is 0.2. It is preferable to contain 001 mass% or more. However, if the total content of one or two of S and Se exceeds 0.05 mass%, purification in finish annealing results in incomplete S removal and Se removal, which causes deterioration of iron loss characteristics. Is 0.05 mass%.

In addition to the above essential components, the grain-oriented electrical steel sheet of the present invention needs to add Sn, Sb and Ni in the following ranges in order to exhibit the effects of the present invention.
Sn: 0.01-0.20 mass%
Sn has the effect of segregating at the grain boundaries and the like, and has the effect of refining crystal grains after secondary recrystallization and improving magnetic properties. This effect is manifested by addition of 0.01 mass% or more. However, if it exceeds 0.20 mass%, the degree of orientation integration after secondary recrystallization is reduced, leading to a decrease in magnetic properties. Therefore, the Sn content is in the range of 0.01 to 0.20 mass%.
Furthermore, the addition of Sn promotes embrittlement, causes edge cracking during hot rolling, and may reduce productivity. Therefore, in order to achieve both magnetic properties and high productivity, it will be described later. In addition, the content of the three elements Sn, Sb and Ni needs to be within an appropriate range.

Sb: (0.2 × Sn) mass% or more and 0.10 mass% or less Sb segregates at the grain boundaries and has an effect of suppressing normal grain growth and strengthening of grain boundaries, that is, an effect of suppressing brittleness. The above grain boundary strengthening effect is manifested by addition of (0.2 × Sn) mass% or more, and prevents edge cracking during hot rolling. In addition, it is effective in increasing the size of secondary recrystallized grains in the final product and improving the degree of crystal orientation integration, that is, improving magnetic properties. On the other hand, when it exceeds 0.10 mass%, it is difficult to decarburize. Therefore, Sb is added in the range of (0.2 × Sn) mass% to 0.10 mass%.

Ni: {0.7 × (Sn + Sb)} mass% or more and 1.0 mass% or less Since Ni is an austenite generating element, the effect of improving magnetic properties by improving the hot-rolled sheet structure using transformation It is a useful element. However, if it is less than {0.7 × (Sn + Sb)} mass%, the effect of improving the hot-rolled sheet structure of Ni is suppressed due to the effect presumed to be caused by grain boundary segregation of Sn or Sb, and the magnetic properties Improvement effect cannot be obtained. On the other hand, if it exceeds 1.0 mass%, the secondary recrystallization becomes unstable and not only the magnetic properties are deteriorated, but also the workability is lowered and the yield is lowered due to edge cracking during hot rolling. Therefore, Ni is set to a range of {0.7 × (Sn + Sb)} mass% to 1.0 mass%.

  As described above, it is extremely important to balance the contents of the three elements of Sn, Sb and Ni in order to prevent deterioration of workability due to the addition of Ni and to obtain good magnetic properties. However, as will be described later, it is necessary to control the rolling reduction during hot rolling within an appropriate range.

The grain-oriented electrical steel sheet of the present invention is further selected from Cu: 0.005-1.5 mass% and P: 0.0001-0.50 mass%, in addition to the essential basic component and inhibitor component described above. Species or two can be contained.
Cu and P are effective elements for improving the magnetic properties. However, if the content of any element is less than the lower limit of the above range, the effect of improving the magnetic properties is small, while the content is within the above range. If the upper limit is exceeded, secondary recrystallization becomes unstable and magnetic properties deteriorate, so it is preferable to add in the above range.

  In the grain-oriented electrical steel sheet of the present invention, the balance other than the above components is composed of Fe and inevitable impurities. However, it is a matter of course that other components are not rejected as long as the effects of the present invention are not impaired.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The method for producing a grain-oriented electrical steel sheet according to the present invention involves melting steel that conforms to the above-described component composition into a steel slab, then hot rolling, and subjecting to hot rolling as necessary, intermediate It consists of a series of processes in which the final sheet thickness is obtained by two or more cold rollings that sandwich the annealing, the primary recrystallization annealing is also performed for decarburization, and then the final annealing is performed.
Steel melting may be performed by a generally known smelting process through a converter, vacuum degassing, and the like. Steel slabs are also generally known by continuous casting or ingot-bundling rolling. There is no particular limitation as long as it is manufactured by the above method.

The slab reheating temperature before hot rolling is preferably set to a temperature of 1300 ° C. or higher in order to sufficiently dissolve inhibitor components such as AlN, MnSe, and MnS.
In the subsequent hot rolling, the rolling reduction R at a temperature of 1150 ° C. or lower is expressed by the following formula (1):
R ≦ 90− (4 × Ni + 2 × Sn) (1)
(However, each element symbol indicates the content (mass%) of the component.)
It is necessary to perform control so as to satisfy the above. This is because if the rolling reduction R exceeds {90− (4 × Ni + 2 × Sn}), edge cracking during hot rolling becomes remarkable, resulting in a significant decrease in yield. However, the γ phase increases with the addition of Ni, the interface between the α phase and the γ phase, which is prone to cracking, increases, and the grain boundary strength decreases due to the addition of Sn that easily segregates at the grain boundaries. It is thought to have influenced.
Moreover, it is preferable that the rolling completion temperature in hot rolling shall be 850 degreeC or more. This is because if the hot rolling end temperature is less than 850 ° C., surface defects in hot rolling are increased due to embrittlement of the steel sheet.
Furthermore, in order to suppress the coarsening of the precipitated AlN, the hot-rolled coil is preferably cooled quickly after rolling and wound at a temperature of 650 ° C. or lower.

  The hot-rolled steel sheet (hot-rolled sheet) is then preferably subjected to hot-rolled sheet annealing as necessary to improve the hot-rolled sheet structure. The hot-rolled sheet annealing is preferably performed under conditions of soaking at a temperature of 800 to 1200 ° C. for 2 to 300 seconds. If the soaking temperature is less than 800 ° C. or the soaking time is less than 2 s, an unrecrystallized portion remains, so that the effect of improving the hot rolled sheet structure cannot be sufficiently obtained. On the other hand, when the soaking temperature is higher than 1200 ° C. or the soaking time exceeds 300 s, the dissolution of AlN, MnS, and MnSe proceeds, so that the inhibitor repressing power in the secondary recrystallization process is insufficient, and the secondary recrystallization. This is because the rate is drastically lowered and the magnetic properties are lowered.

Thereafter, the hot-rolled sheet after hot rolling or after hot-rolled sheet annealing is made into a cold-rolled sheet having a final thickness by cold rolling at least twice with intermediate annealing interposed therebetween.
In the intermediate annealing before the final cold rolling, the maximum attained temperature T (° C.) is the following formula (2):
500 × (Sn + Sb) + 1000 ≦ T ≦ 1500 × (Sn + Sb) +1000
... (2)
(However, each element symbol indicates the content (mass%) of the component.)
It is necessary to satisfy. If the maximum temperature reached is less than {500 × (Sn + Sb) +1000} ° C., a heterogeneous structure derived from an unrecrystallized structure at the time of hot rolling remains because of grain growth suppression effect due to grain boundary segregation of Sn or Sb. The recrystallized structure is not sized, the desired secondary recrystallized grain growth cannot be caused, and the magnetic properties are deteriorated. On the other hand, if the maximum temperature reached is higher than {1500 × (Sn + Sb) +1000} ° C., the crystal grains become coarse, and the orientation integration degree after the secondary recrystallization is lowered, leading to a decrease in magnetic properties.

  In addition, it is preferable that the soaking time at the highest attained temperature in the intermediate annealing is in the range of 2 to 300 s, and the cooling after the annealing is rapidly performed at a rate of 10 to 200 ° C./s between 800 to 400 ° C. If the soaking time is less than 2 s, a non-uniform structure derived from an unrecrystallized structure at the time of hot rolling remains, making it difficult to obtain a desired structure. On the other hand, if the soaking time is longer than 300 s, the crystal grains become coarse, leading to a decrease in the degree of orientation accumulation after secondary recrystallization, and the dissolution of AlN, MnS, and MnSe proceeds, and in the secondary recrystallization process Inhibitors have insufficient inhibitory power, and a desired secondary recrystallized structure cannot be obtained, which may cause deterioration of magnetic properties. Further, when the cooling rate between 800-400 ° C. in the intermediate annealing is less than 10 ° C./s, the coarsening of the carbide proceeds, and the texture improving effect in the subsequent cold rolling or primary recrystallization annealing is weakened, There is a risk of deteriorating magnetic properties. On the other hand, if the cooling rate exceeds 200 ° C./s, the fraction of hard retained austenite phase or martensite phase increases, and it becomes difficult to obtain a desired primary recrystallized structure, which may cause a decrease in magnetic properties. Because there is.

  The final cold rolling with the final sheet thickness is preferably performed with the rolling reduction in the range of 60 to 92%, and more preferably in the range of 60 to 85% on the light rolling side. The final cold rolling may be performed by known aging between passes or warm rolling for the purpose of improving magnetic properties.

The cold-rolled sheet with the final thickness is then subjected to primary recrystallization annealing that also serves as decarburization, but before that, it is also subjected to magnetic domain refinement treatment such as providing grooves on the surface of the steel sheet in order to reduce iron loss. May be.
The primary recrystallization annealing is preferably performed at a soaking temperature in the range of 700 to 1000 ° C. If the soaking temperature is less than 700 ° C., an unrecrystallized structure remains and it becomes difficult to obtain a desired structure. On the other hand, when it exceeds 1000 ° C., secondary recrystallization of Goss orientation grains may occur. In addition, when performing also decarburization, it is preferable to perform annealing in a wet hydrogen atmosphere.

  Furthermore, in this invention, it is preferable that the temperature increase rate between 500-700 degreeC in the said primary recrystallization annealing shall be 50 degrees C / s or more. The reason for this is that the rate of temperature increase between 500 and 700 ° C. is 50 ° C./s or more, so that the presence rate of Goss orientation grains in the steel sheet after primary recrystallization annealing is increased, and the crystal grains after secondary recrystallization are increased. This is because it can be effectively miniaturized to further improve the magnetic properties.

Then, if necessary, the steel sheet after the primary recrystallization is subjected to a finish annealing that causes secondary recrystallization after applying an annealing separator mainly composed of MgO to the steel sheet surface. In addition, if this finish annealing is performed in a hydrogen atmosphere, it can also serve as purification.
Then, the steel sheet after the finish annealing is a grain-oriented electrical steel sheet which is a product plate through an insulating coating application process and a planarization annealing process.

Steels A to G having the composition shown in Table 1 are melted by a generally known smelting process, continuously cast into a steel slab having a thickness of 240 mm, and then heated to a temperature of 1400 ° C. And hot rough rolled at a temperature of 1230 ° C. or higher to obtain a sheet bar having a thickness of 45 mm, hot finish-rolled with a rolling end temperature of 900 ° C., cooled and wound on a coil at a temperature of 580 ° C., A plate thickness of 2.2 mm was used for hot rolling. In the hot rolling, the rolling reduction R at 1150 ° C. or lower was controlled to be the value of R shown in Table 2. Next, the hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C. × 40 s, and then pickled, and the first cold rolling was performed to obtain an intermediate sheet thickness of 1.5 mm and wet hydrogen having a dew point of 50 ° C. In the atmosphere, after intermediate annealing was performed under the same conditions as shown in Table 2, the steel sheet temperature was 220 ° C. and warm rolling (second cold rolling) was performed to obtain a cold rolled sheet having a final thickness of 0.22 mm. .
In addition, about said hot-rolled sheet, the sample of length 1m is extract | collected from the length direction center part of each coil, and the maximum depth of the crack which generate | occur | produced in the steel plate edge part (maximum depth from a coil edge) is measured. And hot workability (brittleness) was evaluated. Incidentally, in this invention, if the maximum depth of the crack was within 10 mm, it evaluated that it was not a level which has a bad influence on productivity.

Thereafter, the cold-rolled sheet is degreased, heated to 850 ° C. at a heating rate of 500 to 700 ° C. at 30 ° C./s, and subjected to primary recrystallization annealing also serving as decarburization at 850 ° C. × 2 min. After that, an annealing separator containing MgO as a main component and 3 mass% of TiO ₂ was applied to the steel sheet surface, and finish annealing was performed. The finish annealing is performed by heating up to 900 ° C. in an N ₂ atmosphere, between 900 and 1050 ° C. in a mixed atmosphere of 25 vol% N ₂ +75 vol% H ₂ , and between 1050 and 1150 ° C. in an H ₂ atmosphere. after 1150 ° C. × 6hr maintained in an atmosphere of _{H 2} up to 600 ° C. in an atmosphere of _{H 2} was less temperature conditions cooling in _{N 2} atmosphere. The steel sheet after the finish annealing was then subjected to removal of the unreacted annealing separator, and then coated with magnesium phosphate containing 50 mass% of colloidal silica as a tension coating and baked at 800 ° C. to obtain a product plate.

A test piece was collected from each product plate obtained as described above, and the magnetic flux density B ₈ and the iron loss W _17/50 were measured. 2 together.
As shown in Table 2, a steel sheet that satisfies the component composition of the present invention and appropriately controls the reduction ratio in hot rolling and the maximum temperature reached in intermediate annealing not only has excellent magnetic properties, but also improves manufacturability. It turns out that it is excellent.

After steel A shown in Table 1 was continuously cast into a steel slab having a thickness of 240 mm, the steel slab was heated to a temperature of 1400 ° C. and hot rough rolled at a temperature of 1230 ° C. or higher to a thickness of 45 mm. A hot-rolled sheet having a thickness of 2.2 mm was prepared by hot finish rolling with a rolling end temperature of 900 ° C., cooled, and wound on a coil at a temperature of 580 ° C. In the above finish rolling, the rolling reduction R at 1150 ° C. or lower is No. in Table 2. Control was performed so that the R value was 1. Next, the hot-rolled sheet is subjected to hot-rolled sheet annealing at 1000 ° C. × 40 s, and then pickled, primary cold-rolled to an intermediate sheet thickness of 1.5 mm, and a wet hydrogen atmosphere with a dew point of 50 ° C. Inside, after performing the intermediate annealing on the conditions shown in Table 3, the steel sheet temperature was 220 ° C., and the steel sheet was warm-rolled (second cold rolling) to obtain a cold-rolled sheet having a final thickness of 0.22 mm.
In addition, about said hot-rolled sheet, the sample of length 1m is extract | collected from the length direction center part of each coil, and the maximum depth of the crack which generate | occur | produced in the steel plate edge part (maximum depth from a coil edge) is measured. And hot workability (brittleness) was evaluated. Incidentally, in this invention, if the maximum depth of the crack was within 10 mm, it evaluated that it was not a level which has a bad influence on productivity.

Next, after degreasing the cold-rolled sheet, heating between 500-700 ° C. to 850 ° C. at the rate of temperature increase shown in Table 3, followed by primary recrystallization annealing that also serves as decarburization at 850 ° C. × 2 min. After that, an annealing separator containing MgO as a main component and 3 mass% of TiO ₂ was applied to the steel sheet surface, and finish annealing was performed. The finish annealing is performed by heating up to 900 ° C. in an N ₂ atmosphere, between 900 and 1050 ° C. in a mixed atmosphere of 25 vol% N ₂ +75 vol% H ₂ , and between 1050 and 1150 ° C. in an H ₂ atmosphere. After holding at 1150 ° C. for 6 hours in _two atmospheres, finish annealing was performed to lower the temperature. The cooling atmosphere was an H ₂ atmosphere up to 600 ° C., and the temperature below that was an N ₂ atmosphere. The steel sheet after the finish annealing was then subjected to removal of the unreacted annealing separator, and then coated with magnesium phosphate containing 50 mass% of colloidal silica as a tension coating and baked at 800 ° C. to obtain a product plate.

A test piece was collected from each product plate obtained as described above, and the magnetic flux density B ₈ and the iron loss W _17/50 were measured. It was shown in 3.
As can be seen from Table 3, after satisfying the component composition of the present invention and appropriately controlling the reduction ratio in hot rolling and the highest temperature reached in intermediate annealing, further in primary recrystallization annealing (decarburization annealing). By increasing the heating rate, it is possible to manufacture a grain-oriented electrical steel sheet having excellent magnetic properties stably and with high productivity even with a material having a thickness of 0.23 mm or less, which is difficult to manufacture.

Claims (3)

C: 0.020-0.15 mass%, Si: 2.5-7.0 mass%, Mn: 0.005-0.3 mass%, sol. Al: 0.01-0.05 mass%, N: 0.002-0.012 mass%, one or two of S and Se: 0.05 mass% or less in total, Sn: 0.01-0. 20 mass%, Sb: (0.2 × Sn) mass% or more and 0.10 mass% or less, Ni: {0.7 × (Sn + Sb)} mass% or more and 1.0 mass% or less, with the balance being Fe and inevitable A steel slab having a component composition consisting of impurities is heated to 1300 ° C or higher, then hot-rolled at 850 ° C or higher, and the final thickness is obtained by two or more cold rollings with intermediate annealing between them. In the manufacturing method of grain-oriented electrical steel sheet consisting of a series of steps of performing finish annealing after crystal annealing,
Depending on the contents of Sn, Sb and Ni in the steel slab, the rolling reduction R (%) at 1150 ° C. or lower in hot rolling is controlled to satisfy the following formula (1),
A method for producing a grain-oriented electrical steel sheet, wherein the maximum attainable temperature T (° C.) in the intermediate annealing is controlled to satisfy the following expression (2).
R ≦ 90− (4 × Ni + 2 × Sn) (1)
500 × (Sn + Sb) + 1000 ≦ T ≦ 1500 × (Sn + Sb) +1000
... (2)
Here, each element symbol in the above formula is the content (mass%) of each component. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein a temperature increase rate between 500 to 700 ° C. in the primary recrystallization annealing is set to 50 ° C./s or more. In addition to the above component composition, the steel slab further contains one or two selected from Cu: 0.005-1.5 mass% and P: 0.0001-0.50 mass%. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that