JP3157701B2 - Manufacturing method of grain-oriented silicon 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 silicon steel sheet having excellent magnetic properties, and more particularly to a method advantageous for improving magnetic flux density.

[0002] Grain-oriented silicon steel sheets are used in transformers and generators.
Used as a core, magnetic properties include magnetic flux density
(Magnetic flux B at 800 A / m₈ (Indicated by the value)
High and iron loss (maximum magnetic flux density 1.7 T and frequency 50Hz
Loss W per kg in _17/50Is low)
Is required.

[0003]

2. Description of the Related Art In recent years, in order to reduce the magnetic properties of grain-oriented silicon steel sheets, particularly the reduction of iron loss, a technique has been developed in which magnetic domains are subdivided by locally introducing strain or forming grooves on the steel sheet surface. This has made it possible to significantly reduce iron loss. In particular, this technique is extremely effective when applied to a steel sheet having a high magnetic flux density, and a reduction in iron loss is achieved along with an increase in the magnetic flux density.

In order to improve the magnetic flux density of a grain-oriented silicon steel sheet, it is necessary to highly integrate the crystal orientation of the product in the (110) [001] orientation, that is, the so-called Goss orientation. In the final finish annealing, it is obtained by a secondary recrystallization phenomenon. Therefore, in the secondary recrystallization, it is necessary to preferentially grow only the crystal grains close to the (110) 001 orientation and to suppress the growth of the crystal grains in the other directions. Addition of an inhibitor that suppresses growth is essential. This inhibitor contributes to an improvement in magnetic flux density by forming a precipitate dispersed phase in the steel and suppressing the growth of primary recrystallized grains (normal grain growth) until immediately before secondary recrystallization. However, in the actual manufacturing process, there has been a problem that grains whose crystal orientation is shifted from the (110) 001 orientation are often subjected to secondary recrystallization, thereby producing a steel sheet having deteriorated magnetic flux density.

According to a study conducted by the inventors regarding this problem, during annealing for secondary recrystallization (final finish annealing), the surface of the steel sheet is oxidized, and the inhibitor on the surface layer of the steel sheet is decomposed and disappears. It was found that the ability to suppress normal grain growth in the surface layer of the steel sheet before the secondary recrystallization was insufficient.

In order to suppress the decomposition and disappearance of the inhibitor in the surface layer of the steel sheet during the final finish annealing, an oxide layer (sub-scale) formed on the steel sheet surface in the decarburization annealing which is a step before the final finish annealing is required. It can be used. That is, when an oxide layer is present on the steel sheet surface, if this oxide layer becomes an obstacle to the diffusion of elements such as O, Mn, and Al, the oxidation of these elements is suppressed, and as a result, the decomposition of the inhibitor And disappearance is also suppressed.

As a result of intensive studies on the composition of the oxide layer that can contribute to the suppression of oxidation based on this technical idea, the ratio of firelite and silica is controlled within a certain range as the composition of the oxide layer on the steel sheet surface. The technology was developed and proposed in Japanese Patent Application Laid-Open No. Hei 4-20271.

[0008]

However, even with this technique, stabilization of magnetic characteristics in industrial production is not sufficient, and particularly, it is necessary to stably produce oriented silicon steel sheets having a high magnetic flux density. Was difficult. Accordingly, an object of the present invention is to propose a novel method for manufacturing a grain-oriented silicon steel sheet that can stably obtain a product having a high magnetic flux density even in industrial production.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the inventors have found that the surface roughness of the steel sheet after the final cold rolling is adjusted to a specific range, Stable improvement of magnetic flux density is realized by performing a cleaning treatment by electrolytic degreasing method before annealing to deposit electrodeposits containing Si on a steel plate surface in a specified amount or more, and controlling the atmosphere of decarburizing annealing. Then came the knowledge.
The present invention is based on the above findings.

That is, according to the present invention, a silicon-containing steel slab is subjected to hot rolling, and then to a final thickness by cold rolling once or a plurality of times including intermediate annealing, followed by decarburizing annealing,
Then, in producing a grain-oriented silicon steel sheet through a series of steps of applying an annealing separator and performing a final finish annealing, the arithmetic average roughness of the steel sheet surface after the final cold rolling is adjusted to 0.40 μm or less, and then the steel sheet is removed. Prior to charcoal annealing, the steel sheet surface is subjected to a cleaning treatment by an electrolytic degreasing method in which an electrodeposit containing Si adheres at a concentration of 0.1 mg / m ² or more, and then a ratio of a partial pressure of water vapor to a partial pressure of hydrogen in the atmosphere (hereinafter, referred to as P (H ₂ O) / P (H ₂ )) is adjusted to 0.30 to 0.65, and the temperature in the atmosphere is 850 to 950 ° C. and the partial pressure of steam is 0.05 to 3.0%.
And performing a decarburizing anneal in a later stage of performing a decomposition / regeneration / densification treatment of oxides on the surface of the steel sheet.

Next, various experimental results on which the present invention is based will be described. The materials used in the experiment were
C, Si and Al were contained as essential components. This is because C is a component useful for improving the structure in hot rolling and cold rolling, Si is a component useful for increasing electric resistance to improve iron loss, and Al is 2% as an inhibitor component. This is because it is a component useful for improving the secondary recrystallized grain orientation, that is, improving the magnetic flux density.

Experiment 1 C: 0.065% by weight, Si: 3.25% by weight, Mn: 0.070% by weight,
Al: 0.025% by weight, Se: 0.020% by weight and Sb: 0.025% by weight
After hot-rolling each of the three steel slabs containing, a hot-rolled sheet was annealed at 1000 ° C for 1 minute, and the first cold-rolling was performed to obtain a sheet thickness of 1.50 mm. N ₂ atmosphere (
Intermediate annealing at 1100 ° C for 60 seconds in a dew point of 40 ° C), quenched to 350 ° C at a cooling rate of 40 ° C / s using mist water, kept at 350 ° C for 20 seconds, and then cooled to room temperature .

Next, after the intermediate annealing, the plate was pickled with a 15% aqueous solution of HCl, and a final thickness of 0.22 mm was obtained using a Sendzimir mill equipped with a work roll having a diameter of 180 mm. Incidentally, the surface roughness of the coil after the final cold rolling is an arithmetic average roughness of 0.30
0.30.35 μm.

Then, as a pretreatment for decarburizing annealing,
Surface cleaning was performed. That is, the first coil is 15
After brushing by passing through an aqueous solution of NaOH
Rinse with water and dry. The second coil is also 15
After passing through an aqueous solution of NaOH and brushing,
% HCl aqueous solution, then rinse with pure water and dry
did. The third coil is divided into 10 into a to j
After passing the coil through the sodium orthosilicate bath,
Rinsed and dried. Here, passing through a sodium orthosilicate bath
In doing so, the alternating coils are applied to the divided coils other than the divided coil a.
Flow to clean the steel sheet surface by electrolytic degreasing.
Was. The split coil b has 1.0 A / dm ^Two-+ Alternation
An electric current is added, and 0.01,
0.1, 0.5, 1.0, 3.0, 5.0, 8.0, 15A / dm^Two+-Alternation of
Current was applied.

[0015] In all of these pretreatment results, the steel sheet surface was clean, but the second coil was damaged by 0.2 μm thick on the steel sheet surface. For c to j, the electrodeposit containing Si adheres to the surface of the steel sheet.
0.03 mg / m ^2, in the d is 0.06 mg / m ^2, in the e is 0.10 mg / m ^2, in the f is 0.34 mg / m ^2, in the g is 0.54 mg / m ^2, in the h is ^{1.36mg / m 2, 2.4 mg /} m 2 in the i, in the j was 4.0 mg / m ^2.

Further, each of the twelve types of coils is divided into two parts and divided into two sets.
H ₂ and N ₂ balance atmosphere (dew point 60 ° C, P (H ₂ O)
/ P (H ₂ ): 0.39) at 840 ° C. for 2 minutes. The remaining 12 coils are ₂ % at 840 ° C under 50% H ₂ and residual N ₂ balance atmosphere (dew point 60 ° C).
After a continuous decarburization annealing for 10 minutes, a heat treatment was performed at 880 ° C. for 10 seconds in a dry N ₂ atmosphere at a dew point of −10 to −4 ° C. (H ₂ O partial pressure: 0.25 to 0.43%).

Next, these coils were made of 5% TiO ₂ and 2%
Sr (OH) containing ₂ · 8H ₂ O was applied to the annealing separator to the steel sheet surface mainly containing MgO, wound into a coil, 1200
° C. until the temperature was raised under a mixed atmosphere at heating rate 25% N ₂ and 75% H ₂ for 15 ° C. / h, further 1200 ° C. under an atmosphere of H _2, after 10h holding the final annealing to cooling gave. Then, after removing the unreacted annealing separating agent in each coil, a tension coating serving also as a flattening treatment was applied to the steel sheet surface and baked to obtain a product. The magnetic properties of the product coil thus obtained are shown in FIG.

As shown in FIG. 1, as a pretreatment for decarburization annealing, an electrolytic degreasing method is employed, and an electrodeposit containing Si is attached to a steel sheet surface at a concentration of 0.1 mg / m ² or more. , A product having high magnetic flux density and excellent magnetic properties was obtained.

In order to clarify the reason why these excellent magnetic properties were obtained, each of the decarburized annealed sheets was made of 25% N ₂ and 75% N _2.
% Mixed atmosphere of H ₂ (dew point 20 ° C.) 900 ° C. under, subjected to a heat treatment of 30 minutes, were investigated oxidation behavior and nitriding behavior. As a result, as shown in FIG. 2, it was found that under the condition that a material having a high magnetic flux density was obtained, oxidation and nitriding of the steel sheet were suppressed. That is, when oxidation and nitridation in the steel sheet surface layer portion are suppressed, in the final finish annealing, the inhibitor of the steel sheet surface layer portion is maintained in a good state,
It is estimated that appropriate secondary recrystallization was obtained.

Further, as described later, the heat treatment performed after the decarburizing annealing decomposes oxides on the surface of the steel sheet and then regenerates fine oxide particles, thereby reducing the oxide particles on the steel sheet surface to a high density. Since it has a function of suppressing the diffusion of oxygen and nitrogen for dispersion generation, it is referred to as a decomposition / regeneration / densification treatment of oxides on the surface of the steel sheet.

Experiment 2 Twelve steel slabs having the same composition as in Experiment 1 were each subjected to hot rolling, then annealed at 1050 ° C. for 1 minute, and subjected to a first cold rolling. From the 1.40mm thickness,
1050 ° C in a mixed atmosphere of 25% N ₂ and 75% H ₂ (dew point 45 ° C)
The steel sheet was subjected to an intermediate annealing for 60 seconds, rapidly cooled to 250 ° C. at a cooling rate of 40 ° C./s using mist water, kept at 350 ° C. for 120 seconds, and then cooled to room temperature.

Next, when performing the final cold rolling to a final thickness of 0.19 mm after the intermediate annealing, the first, second, third and fourth coils are cooled as they are after the intermediate annealing. The fifth, sixth, seventh and eighth coils were passed through a 15% HCl aqueous solution to remove the scale surface layer, and then cold-rolled. Th, sixth, tenth, eleventh and
The twelfth coil was subjected to cold rolling after removing all the oxide layers on the surface of the steel sheet over a width of 1000 mm with a surface grinder at intervals of about 0.1 mm.

The cold rolling is performed by a Sendzimir rolling mill.
1st, 2nd, 5th, 6th, 9th,
The tenth coil was performed using a work roll having a diameter of 250 mm, and the remaining coils were performed using a work roll having a diameter of 150 mm. Further, at the time of rolling the first, third, fifth, seventh, ninth and eleventh coils,
A high-viscosity rolling oil was used, and the remaining coils were rolled using a low-viscosity rolling oil.

The average roughness of the steel sheet surface after the final cold rolling is as follows:
The first coil is 0.74μmR_a, The second coil is 0.68
μmR_a, The third coil is 0.62μmR_a, Fourth
0.56μmR_aThe fifth coil is 0.39μm
R_aAnd the sixth coil is 0.35μmR_a, The seventh
0.31μmR_aThe eighth coil is 0.27μm
R _aThe ninth coil is 0.52μmR_a, The tenth
0.44μmR_aThe eleventh coil is 0.37μm
R_a, The twelfth coil is 0.33μmR_aMet.

These 12 types of coils were further divided into two and divided into two sets. As a pretreatment for decarburization annealing, one set of 16 types of coils was subjected to alkaline degreasing in a 15% aqueous NaOH solution followed by pure water. perform rinsing, the set 16 types of coils remains, when Tsuban through the ortho sodium silicate bath, - + - + for flowing alternating current subjected to electrolytic degreasing, 1.0 to 2.5 mg / m ² S
After depositing the electrodeposit containing i on the surface of the steel sheet, rinsing with pure water was performed.

Thereafter, each coil was subjected to decarburizing annealing at 850 ° C. for 2 minutes in an atmosphere (dew point: 60 ° C.) with a balance of 45% H ₂ and the balance of N ₂ , followed by 65% H ₂ in the same continuous annealing furnace. And the rest
N ₂ balance atmosphere (dew point -5~5 ℃, H ₂ O partial pressure: 0.46
(0.86%) at 860 ° C for 15 seconds.

Next, these coils are coated with an annealing separator containing 10% TiO ₂ and 3% Sr (OH) ₂ .8H ₂ O and containing MgO as a main component on the surface of the steel sheet, and then wound into a coil. ,
After holding in 35 hours N ₂ at 850 ° C., 2 at a heating rate of 15 ° C. / h
The temperature was raised to 1200 ° C. in a mixed atmosphere of 5% N ₂ and 75% H ₂ , further maintained at 1200 ° C. for 10 hours in an atmosphere of H ₂ , and then subjected to final finishing annealing in which the temperature was lowered. Then, after removing the unreacted annealing separating agent in each coil, a tension coating serving also as a flattening treatment was applied to the steel sheet surface and baked to obtain a product. FIG. 3 shows the magnetic characteristics of the product coil thus obtained.

FIG. 3 shows that the surface roughness of the steel sheet surface after the final cold rolling is set to 0.40 μm _Ra or less, the electrolytic degreasing method is used as a pretreatment for decarburization annealing, and the steel sheet surface contains Si. It can be seen that when the kimono was attached, a product having high magnetic flux density and excellent magnetic properties was obtained.

In order to clarify the reason why the excellent magnetic properties were obtained, each of the decarburized annealed sheets was heated at 900 ° C. and 30 ° C. in a mixed atmosphere of 25% N ₂ and 75% H ₂ (dew point: 20 ° C.). When the oxidation behavior and the nitridation behavior were examined by performing a heat treatment for 1 minute, the oxidation and nitridation of the steel sheet were suppressed under the condition that a material having a high magnetic flux density was obtained as in Experiment 1.

Experiment 3 A steel slab having the same composition as in Experiment 1 was hot-rolled, then annealed at 1050 ° C. for 1 minute, and the first cold-rolled 1.40 mm plate was subjected to cold rolling. 25% N ₂ and 75% H ₂
Intermediate annealing at 1050 ° C for 60 seconds in a mixed atmosphere (dew point 45 ° C) of 300 ° C at a cooling rate of 40 ° C / s using mist water
After rapidly cooling to 300 ° C., the mixture was kept at 300 ° C. for 60 seconds, and then cooled to room temperature. Then, by pickling with a 15% HCl aqueous solution,
The outer scale of the steel plate was removed. Thereafter, a final thickness of 0.19 mm was obtained using a Sendzimir rolling mill equipped with a roll having a diameter of 200 mm. Incidentally, final cold surface roughness of the steel sheet after rolling was 0.25~0.30μmR _a.

Next, as a pretreatment for decarburizing annealing, electrolytic degreasing in an aqueous solution of sodium orthosilicate was performed to deposit an electrodeposit containing Si of 0.4 to 1.0 mg / m ^2. The mixture was divided and subjected to decarburization annealing at 850 ° C. for 2 minutes while varying the atmosphere P (H ₂ O) / P (H ₂ ).

That is, by changing the mixing ratio of H ₂ and N ₂ and changing the dew point of the atmosphere, P (H ₂ O) / P (H ₂ )
To 0.05, 0.15, 0.20, 0.30, 0.45, 0.55, 0.65, 0.70
And 0.75 in an atmosphere of decarburization annealing, respectively. These eight coils have 60% H ₂ and residual N ₂
Balance atmosphere (dew point 6 to 8 ° C, H ₂ O partial pressure 0.92 to 1.06
%) At 870 ° C for 20 seconds.

Next, these coils are coated with MgO containing 10% TiO ₂ and 3% Sr (OH) ₂ .8H ₂ O as an annealing separator on the surface of the steel sheet, and then wound into a coil. 850
After holding in 15 hours N ₂ at ° C., 25% at a heating rate of 15 ° C. / h
In a mixed atmosphere of N ₂ and 75% H ₂ , the temperature was raised to 1200 ° C.
The sample was kept at 1200 ° C. for 10 hours in an atmosphere of H ₂ and then subjected to final finish annealing in which the temperature was lowered. Then, after removing the unreacted annealing separating agent in each coil, a tension coating serving also as a flattening treatment was applied to the steel sheet surface and baked to obtain a product. As shown in FIG. 4, the magnetic properties of the product coil thus obtained were such that P (H ₂ O) / P (H ₂ ) in the atmosphere of decarburizing annealing was 0.30.
By setting it to 0.65, excellent magnetic properties with high magnetic flux density were obtained.

In order to clarify the reason why these excellent magnetic properties were obtained, each of the decarburized annealed sheets was made of 25% N ₂ and 75% N _2.
% H mixed atmosphere of ₂ (dew point 20 ° C.) 900 ° C. under, subjected to a heat treatment of 30 minutes, were investigated oxidation behavior and nitriding behavior, under the condition that a material having high magnetic flux density in the same manner as in Experiment 1 were obtained In addition, oxidation and nitriding of the steel sheet were suppressed.

Experiment 4 Next, the optimum conditions for decomposing, regenerating and densifying the oxides on the steel sheet surface following the decarburizing annealing were investigated. Hot rolling a steel slab of the same composition as in Experiment 1 2.
Use a coil with a thickness of 0 mm, and place in a wet N ₂ atmosphere (dew point 35 ° C) 11
After subjecting the hot-rolled sheet to annealing at 50 ° C for 1 minute, it is cooled to room temperature using mist water at an average cooling rate of 40 ° C / s, and then 15%
The oxide surface layer of the steel sheet was removed by pickling with an aqueous HCl solution.

The coil was cold rolled to a final thickness of 0.26 mm by a Sendzimir mill having a work roll of 200 mm diameter. The surface roughness of the steel sheet after cold rolling is as follows:
It was 0.28 to 0.32 μm _Ra .

Next, as a pretreatment for decarburization annealing, electrolytic degreasing in an aqueous sodium orthosilicate solution was performed to deposit 0.5 to 0.8 mg / m ^{2 of} the electrodeposit containing Si, and then 55% H ₂ and atmosphere residual N ₂ (dew point 65 ° C.) 850 ° C. below, were subjected to decarburization annealing for 100 seconds. This coil was divided into 131, and each coil was subjected to various heat treatments described below.

[Conditions of heat treatment atmosphere] Forty of the divided coils were subjected to a heat treatment at 870 ° C. for 20 seconds, each containing 100% H ₂ gas containing H ₂ O, 75% H ₂ and 25% N ₂ gas containing H ₂ O, 50% H ₂ and
50% N ₂ gas containing H ₂ O, 25% H ₂ and 75% N ₂ gas containing H ₂ O, 100% N ₂ gas
The test was performed in an atmosphere containing H ₂ O. The amount of H ₂ O contained was 0.01%, 0.03%, 0.05% by gas partial pressure.
%, 0.1%, 0.5%, 3.0%, 5.2% and 12%.

[0039] After the heat treatment, the 41 coils including first coil is not subjected to this heat treatment, the MgO containing 10% TiO ₂ and _{4% Sr (OH) 2 ·} 8H 2 O with an annealing separator consisting mainly after coating the surface of the steel sheet, wound into a coil, 840 ° C. in N _2, after 40h maintained, 15 ℃ / h 1200 ℃ in a mixed atmosphere of 25% N ₂ and 75% H ₂ at a heating rate of The temperature was raised to 1,200 ° C. for 10 hours in an atmosphere of H ₂ , and then the temperature was lowered to perform final finish annealing.

Then, after removing the unreacted annealing separating agent in each coil, a tension coating serving also as a flattening treatment was applied to the steel sheet surface and baked to obtain a product. FIG. 5 shows the magnetic characteristics of the product coil thus obtained. Incidentally, the magnetic flux density of the product did not perform the heat treatment was 1 ₈ value B.
865 T. From FIG. 5, in order to obtain a product with a high magnetic flux density, the content of H ₂ O is determined regardless of the mixing ratio of N ₂ and H _2.
It is understood that the content needs to be 0.05 to 3.0%.

[Temperature and Time Conditions of Heat Treatment] Using the remaining 90 coils, heat treatment was performed in an atmosphere containing 1.8% of H ₂ O in a mixed atmosphere of 40% N ₂ and 60% H _2. went. Here, the heat treatment raises the temperature to 800, 825, 850, 875, 900,
9 levels of 925, 950, 975, 1000 ° C and time
5,10,15,20,30,40,50,60 levels as 10 levels
They were performed in combination.

After such heat treatment, these 90 types of split coils contain M containing 10% TiO ₂ and 4% Sr (OH) ₂ .8H ₂ O.
After coating an annealing separator consisting mainly on the surface of the steel sheet to gO, wound into a coil, 840 ° C. in N _2, after 40h holding, 25% N ₂ and at a heating rate of 15 ° C. / h 75 % H _{2 in} a mixed atmosphere to 1200 ° C., then H _{2 in} an atmosphere of 1200 ° C.
The temperature was raised to 1,200 ° C. and 110 hours in an atmosphere of H ₂ , and then the temperature was decreased, and a final finish annealing was performed.

Then, after removing the unreacted annealing separating agent in each coil, a tension coating serving also as a flattening treatment was applied to the steel sheet surface and baked to obtain a product. FIG. 6 shows the magnetic characteristics of the product coil obtained in this manner, and it can be seen that the optimum conditions of temperature and time are in the range of 850 to 950 ° C. for 5 to 40 seconds.

Each of the decarburized annealed plates was made of 25% N ₂ and 75% H ₂
In a mixed atmosphere (dew point: 20 ° C), heat treatment was performed at 900 ° C for 30 minutes to investigate oxidation and nitridation behavior.
As in Experiments 1 and 2, under the condition that a material having a high magnetic flux density was obtained, oxidation and nitriding of the steel sheet were suppressed.

Further, 0.05 to 0.35% H ₂ O is added to the decarburized annealed plate.
In order to investigate in detail why oxidation and nitridation are suppressed when heat treatment is performed in a partial pressure atmosphere, SEM photographs of the cross section of the steel sheet were observed, and firelite (Fe ₂ SiO) present in the surface layer of the steel sheet due to this heat treatment was observed. ₄ ) was decomposed according to the reaction shown in the following equation (1), and it was found that fine particles of silica (SiO ₂ ) were generated at a high density.

## EQU1 ## Fe ₂ SiO ₄ + Si → 2SiO ₂ +2 Fe ----- (1)

That is, as shown in FIG. 7 (a), the oxides formed on the decarburized annealed plate generally generate firelite on the surface side and silica on the ground iron side. In particular, since firelite is generated on the surface side having a high oxygen partial pressure, it is formed as coarse particles as shown in FIG.

Here, when the heat treatment is performed in an atmosphere having a H ₂ O partial pressure of 0.05 to 3.0%, as shown in FIG. 7B, part of the firelite is decomposed into silica, iron and oxygen, and Combines with a trace amount of Si dissolved in iron to form further silica. Trace amounts of dissolved silica and iron formed by these decompositions
Silica formed by bonding with Si is an extremely fine particle and exists at a high density in the sub-scale. Therefore, the silica has a large effect of hindering diffusion of oxygen and nitrogen through the sub-scale. For this reason, the steel sheet is protected from oxidation and nitridation during the final finish annealing, and the initial state of the inhibitor is maintained until secondary recrystallization, and good magnetic properties are obtained. Therefore, such a heat treatment is referred to as an oxide decomposition / regeneration densification treatment of the steel sheet surface.

In order to generate fine silica particles in the oxide at a high density by the decomposition / regeneration / densification treatment of the oxide on the steel sheet surface, sufficient firelite particles must be present before the treatment. is necessary. That is, the surface roughness of the steel sheet after the final cold rolling is set to 0.40 μm _Ra or less, and the electrodeposits containing Si on the steel sheet surface is 0.1 mg / m ² or more by electrolytic degreasing as a pretreatment of decarburization annealing. P (H ₂ O)
It has been newly found that setting / P (H ₂ ) to 0.30 to 0.65 has the effect of increasing the amount of firelite in the oxide formed by decarburizing annealing.

If the temperature is too low or the time is too short as a condition for the decomposition and regeneration of oxides, the progress of the reaction of decomposition of firelite and regeneration of fine silica is slow. Conversely, if the temperature is too high, the particle size of the silica regenerated by the decomposition of the firelite becomes coarse, and the effect of suppressing oxidation and nitridation of the sub-scale does not function sufficiently. On the other hand, if the treatment time is too long, the firelite is completely decomposed and disappears.As a result, at the time of the final finish annealing, it reacts with MgO in the annealing separator to form the olivine forming reaction represented by the following formula (2). As a result, the magnetic properties are degraded.

2 x MgO + Fe ₂ SiO ₄ → (Mg _x Fe _1-x ) ₂ SiO ₄ + 2xFeO ----- (2)

It is to be noted that the decarburized annealed plate was 890
Regarding the technology of heat annealing at ~ 1050 ° C,
-24686, the atmosphere shown here is also non-oxidizing to Si, and the H ₂ O partial pressure is 0.01
% Or less. Also, the heat treatment temperature is as high as 890 ° C. or higher, and there is no description about the oxides in the subscale, such as firelite and silica. Therefore, this is a technique different from the present invention, which is a technique for dispersing and regenerating fine SiO _2. .

In Japanese Patent Publication No. 57-1575, the decarburizing annealing is divided into the first half and the second half, and P (H ₂ O) / P (H
₂ ) The decarburizing annealing technology for lowering the amount of P (H ₂ O) / P (H ₂ ) from the first half is disclosed, which changes the oxide generated by changing the level of P (H ₂ O) / P (H ₂ ). The ratio between the partial pressures of H ₂ and H ₂ O is problematic. That is, it is essentially different from the present invention in which the partial pressure of H ₂ O is controlled to a certain value or less to decompose the firelite and regenerate silica, and the difference between the two is, for example, 100% N _2. It will be clear if the suitability for the case where a small amount of H ₂ O is contained in the atmosphere is evaluated.
Further, the publication does not describe firelite or silica which is an oxide in the sub-scale, and does not suggest a treatment for increasing the firelite or a fine dispersion of silica.

As described above, the present invention provides a process for producing a grain-oriented silicon steel sheet in which the surface roughness of the steel sheet after the final cold rolling is appropriately adjusted, and then, as a pretreatment for decarburization annealing, an electrolytic degreasing method is used. the electrodeposit containing Si is subjected to a cleaning process to adhere at 0.1 mg / m ² or more on the surface of the steel sheet, before decarburization annealing, the late atmosphere _{P (H 2 O) / P} (H 2) a predetermined amount of By setting the H ₂ O partial pressure in the atmosphere in the latter period to a predetermined amount or less and setting the temperature to a predetermined temperature range, the decomposition of oxides on the steel sheet surface after decarburizing annealing promotes fine dispersion and regeneration. The purpose of the present invention is to suppress the oxidation and nitriding of the steel sheet during the final finish annealing, and finally improve the magnetic flux density of the product.

Here, the raw material component of the present invention generally follows that of oriented silicon steel, and for example, the following component composition is advantageously adapted. C: 0.020 to 0.10 wt% C is a component useful for improving the structure in hot rolling and cold rolling, and this effect cannot be obtained unless the content is less than 0.020 wt%. On the other hand, if the content exceeds 0.10% by weight, the decarburization becomes poor and the magnetic properties are deteriorated.
The range was limited to 0.10% by weight. Si: 1.0 to 5.0% by weight Si is a heavy component in increasing the electrical resistance of the product and reducing eddy current loss. For this purpose, 1.0% by weight or more is necessary, but it exceeds 5.0% by weight. , The cold rollability deteriorates, so the range is limited to 1.0 to 5.0% by weight. Mn: 0.05 to 2.5% by weight Mn is an inhibitor-forming component to be described later, and is also a component necessary for enhancing hot rolling property. For this purpose, 0.05% by weight or more is required, while 2.5% by weight is required. %, The decarburization becomes difficult, so the content was limited to the range of 0.05 to 2.5% by weight.

Next, as an inhibitor-forming component, in addition to the above-mentioned Mn, Al, S or Se is contained in the range of 0.005 to 0.04% by weight. That is, Al, S or Se is AlN, M
Necessary for fine precipitation in steel as nS or MnSe to form an inhibitor, and one or more of these must be contained. For this purpose, 0.005
However, if it exceeds 0.04% by weight, it becomes difficult to finely disperse and precipitate, and the function of the inhibitor deteriorates. Therefore, the content is in the range of 0.005 to 0.04% by weight. When two or more kinds are contained, it is preferable to limit each component to the range of 0.005 to 0.04% by weight.

In addition, if necessary, Ge, P, V, Sn, Sb, Bi, B, and N may be added as inhibitor components to 0.005.
0.040% by weight, 0.005 to 0.2% by weight of Sn and Sb, Bi
And B are preferably added in the range of 0.0003 to 0.0100% by weight. Note that N can be added by nitriding during the manufacturing process. Further, in order to improve hot rollability, Mo may be contained in a range of up to 0.05% by weight.

[0056]

Next, a manufacturing method according to the present invention will be described in detail. The steel slab having the above-mentioned preferred composition is obtained by casting steel obtained by a conventionally used steelmaking method, re-rolled if necessary, and then hot-rolled into a hot-rolled coil. Such a hot-rolled coil has a final thickness by cold rolling once or a plurality of times with intermediate annealing, but the surface roughness of the steel sheet after this final cold rolling is reduced to 0.
Adjustment to 40 μm _Ra or less is an essential requirement of the present invention. This can be achieved by changing the removal amount of the oxide layer on the steel sheet surface before the cold rolling, the work roll diameter of the rolling mill, the viscosity of the rolling oil, the rolling speed, and the like.

Here, the average roughness of the steel sheet surface is 0.40 μmR
_{If the value} exceeds _a , the content of firelite in the oxide formed in the first half of the decarburization annealing decreases, and the effect of the decomposition and regeneration of the oxide in the second half of the decarburization annealing cannot be obtained.

The oxides on the surface of the steel sheet after the final cold rolling are removed by changing the removal amount when removing the surface scale after annealing before the final cold rolling. Further, as a removing means, a conventionally known method such as pickling or grinding can be used. The coil after the final cold rolling is then subjected to decarburizing annealing, and it is necessary to perform a cleaning treatment by an electrolytic degreasing method as a pretreatment of the decarburizing annealing. That is, the electrolytic degreasing method is a technique in which a steel sheet is immersed in a bath and a positive or negative current flows from the steel sheet surface into the bath to clean the steel sheet surface. In such washing by electrolytic degreasing, it is important to finally deposit an electrodeposit containing Si on the steel sheet surface at a concentration of 0.1 mg / m ² or more. This is because the deposition amount of the electrodeposit containing Si is 0.1 mg /
When it is less than m ^2, followed by decreased content of fayalite in oxides of the steel sheet surface formed in the previous period of decarburization annealing, the effect of decomposition regeneration densification of the oxide in the decarburization annealing late Can not be obtained.

The adhesion amount of the electrodeposits containing Si can be detected by using the count number of the Si intensity per unit time by the fluorescent X-ray. That is, the attached electrodeposits are washed off with a very low concentration of HCl, and the weight change before and after the change is measured, and the weight change is associated with the change in the Si intensity count number due to the fluorescent X-ray, and a calibration curve is created in advance. By doing so, the measurement of the attached amount is easily performed.

The decarburizing annealing may be performed in the same continuous furnace in the first and second stages in terms of operability, or may be performed as separate annealing processes in the first and second stages. The first stage of the decarburization annealing is a normal decarburization annealing. However, in order to increase the composition ratio of firelite in the oxide formed on the surface of the steel sheet, P (H ₂ O) / P (H ₂ ) in the atmosphere is used. Must be in the range of 0.30 to 0.65. That is, P (H ₂ O) / P (H
_{If the value of 2} ) is less than 0.30, the generation of firelite becomes insufficient, and the generation of fine silica becomes insufficient in the decomposition and regeneration high-density treatment of oxides on the steel sheet surface in the latter stage of decarburization annealing. On the other hand, when P (H ₂ O) / P (H ₂ ) exceeds 0.65, wustite is generated, and similarly, it becomes difficult to generate fine silica in the decomposition / regeneration high-density treatment of the oxide. Therefore, the atmosphere P (H
₂ O) / P a (H ₂₎ and 0.30 to 0.65.

In the latter half of the decarburizing annealing, it is necessary to set the H ₂ O partial pressure in the annealing atmosphere at 0.05 to 3.0% and the annealing temperature at 850 to 950 ° C. That is, when the partial pressure of H ₂ O is 0.05% or less,
Fe, O, and SiO ₂ are produced, and fine and fine silica is not dispersed. On the other hand, if it exceeds 3.0%, decomposition of firelite is inhibited. Further, when the annealing temperature is lower than 850 ° C., the progress of the decomposition reaction of the firelite becomes insufficient. On the other hand, when the annealing temperature exceeds 950 ° C., the silica particles become coarse and the dense oxide particles cannot be dispersed. Thus, H ₂ O partial pressure in the annealing atmosphere is set to 0.05 to 3.0%, and to limit the annealing temperature in the range of 850 to 950 ° C..

[0062] The densification treatment for the decomposition and regeneration of the oxide is slightly insufficient for less than 5 seconds, and excessively long for more than 40 seconds, resulting in excessive decomposition of firelite and deterioration of magnetic properties. A range of 40 seconds is preferred.

After the decarburizing annealing, the annealing separator is applied, and the final finishing annealing is performed at a temperature of about 1200 ° C. to obtain a final product. Then, if necessary, an insulating coating is applied, and a flattening process is performed to obtain a product. It is also possible to provide a groove on the surface of the steel sheet, or to apply a plasma jet or a laser to locally impart distortion to perform a magnetic domain refining treatment.

[0064]

【Example】

Example 1 After hot rolling steel slabs A to P having compositions according to Table 1, 1000 ° C.
For 1 minute, and then the first cold rolling is performed to set the intermediate sheet thickness to 1.5 mm for A to L and 0.60 mm for M to P. ° C and M ~
P was annealed at 1000 ° C. for 40 seconds in a 25% wet N ₂ and 75% H ₂ atmosphere (dew point: 40 ° C.), and then was heated to 40 ° C./s using mist water.
Rapid cooling to 350 ° C at a cooling rate of 350 ° C
M and P were kept at 200 ° C. for 25 seconds, and then gradually cooled in the air to room temperature. The coil after the intermediate annealing was pickled with a 15% aqueous solution of HCl, and then the final sheet thickness was 0.22 mm by a Sendzimir mill having a work roll having a diameter of 180 mm. The surface roughness of these coils was 0.25 to 0.30 as shown in Table 2.
It was μmR _a.

Next, these coils are divided into two parts, one of which is
Passed through an alkaline degreasing bath as a pretreatment for decarburization annealing
Thereafter, it was rinsed with pure water and washed. The other is pre-treatment of decarburization annealing
And electrolytic degreasing using a sodium orthosilicate bath, containing Si
1.0 to 2.3 mg / mm ^TwoAttached. After that,
Il 50% H_TwoAnd the residual N_TwoBalance atmosphere (dew point 60
℃, P (H_TwoO) / P (H_Two): 0.39) at 840 ℃ for 2 minutes
Of decarburization annealing, and subsequently in the later stage of decarburization annealing,
50% H_TwoAnd the rest N_TwoBalance atmosphere (dew point 5 ℃, H_TwoO
Partial pressure: 0.9%) under 880 ° C for 20 seconds of oxide fraction
A solution regeneration densification process was performed.

[0066]

[Table 1]

These coils have 3% TiO ₂ and 2%
Of Sr (OH) containing ₂ · 8H ₂ O was applied to the annealing separator to the steel sheet surface mainly containing MgO, wound into a coil, after the holding of 840 ° C. 45h in N _2, 25 at a heating rate of 15 ° C / h
% Was heated to 1200 ° C. in an atmosphere of N ₂ and 75% H _2, in H ₂
After the temperature was kept at 1200 ° C. for 10 hours, the temperature was lowered and a final finish annealing was performed. Then, after removing the unreacted annealing separating agent, a tension coating was applied and baked to serve as a flattening treatment to obtain a product. The magnetic properties of the product thus obtained are also shown in Table 2.

[0068]

[Table 2]

Example 2 After hot-rolling steel slab A described in Table 1, subjecting it to hot-rolled sheet annealing at 1150 ° C. for 1 minute, it was cooled to room temperature using mist water at a cooling rate of 40 ° C./s. Cool. Then, after pickling with a 15% aqueous solution of HCl, a final thickness of 0.26 mm was obtained using a Sendzimir rolling mill having a work roll with a diameter of 180 mm. Here, the surface roughness of the coil was 0.28 to 0.32 μm _Ra .

Next, as a pretreatment for decarburizing annealing, electrolytic degreasing is performed using a sodium orthosilicate bath, and the electrodeposit containing Si is removed.
Deposited at 0.8 mg / m ² . In this coil, 45% H ₂ and residual N ₂ balance atmosphere (dew point 60 ° C, P (H ₂ O) / P
(H ₂ ): After decarburizing annealing at 850 ° C for 2 minutes at 0.44),
Divide into two, and place one in an N ₂ atmosphere (dew point -5 ° C, H ₂ O partial pressure: 0.
(4%) at 860 ° C. for 20 seconds. The remaining one was sent to the next step as it was.

These coils are made of 10% TiO ₂ and 2%
Sr (OH) containing ₂ · 8H ₂ O was applied to the annealing separator to the steel sheet surface mainly containing MgO, wound into a coil, 25% N ₂
And 30% / h from 850 ° C to 1200 ° C in a 75% H ₂ atmosphere
The temperature was raised to 15 ° C. at a rate of 15 ° C./h, and the temperature was maintained at 1200 ° C. for 10 hours in H ₂ , followed by final finishing annealing in which the temperature was lowered. Then, after removing the unreacted annealing separating agent, a tension coating was applied and baked to serve as a flattening treatment to obtain a product. Table 3 shows the magnetic properties of the product thus obtained.

[0072]

[Table 3]

Example 3 C: 0.040% by weight, Si: 3.25% by weight, Mn: 0.07% by weight,
P: 0.004% by weight, Al: 0.001% by weight, S: 0.002% by weight, Se: 0.018% by weight, Mo: 0.010% by weight and Sb: 0.
Two silicon steel slabs containing 25% by weight, the balance being Fe and unavoidable impurities were hot-rolled and subjected to hot-rolled sheet annealing at 1000 ° C. for 30 seconds to obtain a sheet thickness of 0.64 mm. Then 75
1000% in an atmosphere with a balance of% H ₂ and residual N ₂ (dew point 35 ° C)
Intermediate annealing at 30 ° C. for 30 seconds was performed, and after cooling, the surface was ground. After that, a final thickness of 0.20 mm was obtained using a low-viscosity oil in a tandem rolling mill. At this time, the surface roughness of the steel sheet is 0.35 to 0.38
It was μmR _a.

Next, as a pretreatment for decarburization annealing, electrolytic degreasing is performed using a sodium orthosilicate bath, and the electrodeposit containing Si is removed.
2.3 g / m ^{2 were} deposited. These coils were divided into two parts, one of which was in an atmosphere with a balance of 45% H ₂ and the balance of N ₂ (dew point 60 ° C, P
(H ₂ O) / P (H ₂ ): 0.44), decarburizing annealing at 820 ° C. for 2 minutes, followed by an atmosphere of 50% H ₂ and residual N ₂ balance (dew point 12 ° C., H ₂₀ Under a partial pressure of 1.4%), the oxides were subjected to a high-density decomposition / regeneration process at 860 ° C for 20 seconds. For comparison, the other coil was used in an atmosphere of 45% H ₂ and the balance of the remaining N ₂ (dew point 60 ° C., P (H ₂ O) / P (H ₂ ): 0.44).
Pre-decarburization annealing at 20 ° C for 2 minutes, followed by 100% H ₂
Under the atmosphere (dew point −40 ° C, H ₂ O partial pressure: 0.01%)
The oxides were decomposed, regenerated, and densified at 20 ° C for 20 seconds.

These two coils have 2% TiO ₂ and
After the coated surface of the steel sheet annealing separator composed mainly of MgO containing 1.2% of SrSO _4, wound into a coil, in N ₂
After holding at 850 ° C for 50 hours, 30 ° C in an atmosphere of 25% N ₂ and 75% H ₂
/ at a Atsushi Nobori rate was raised to 1200 ° C. for h, 1200 ° C. in H _2, 10h
After the temperature was maintained, the temperature was lowered and a final finish annealing was performed. afterwards,
After removing the unreacted annealing separator, a tension coating is also applied and baked to serve as a flattening process, and then a plasma jet is irradiated in the rolling direction at intervals of 5 mm in a direction perpendicular to the rolling direction to perform a magnetic domain refining process. , And the product. Table 4 shows the magnetic properties of the product thus obtained.

[0076]

[Table 4]

[0077]

According to the present invention, a grain-oriented silicon steel sheet having a high magnetic flux density can be stably manufactured, and the effect in the production of grain-oriented silicon steel sheet on an industrial scale is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a pretreatment method of decarburizing annealing and an amount of deposited Si-containing electrodeposits on a steel sheet surface and magnetic properties.

FIG. 2 is a diagram showing a relationship between pretreatment conditions for decarburizing annealing and oxidation resistance and nitriding resistance of a decarburized annealed sheet.

FIG. 3 is a diagram showing a relationship between an oxygen basis weight indicating an amount of oxide remaining on a steel sheet surface after final cold rolling and magnetic properties.

FIG. 4 is a diagram showing the relationship between magnetic properties and P (H ₂ O) / P (H ₂ ) in the atmosphere before decarburization annealing.

FIG. 5 is a diagram showing the relationship between the atmosphere in the latter stage of decarburizing annealing and magnetic properties.

FIG. 6 is a diagram showing a relationship between temperature and time of late treatment of decarburizing annealing and magnetic properties.

FIG. 7 is a schematic view showing a state in which the composition of the oxide and the distribution of the oxide particles are changed by the decomposition and regeneration of the oxide on the surface of the steel sheet to increase the density.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Yamaguchi 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works (56) References JP-A-7-180100 (JP, A JP-A-7-180099 (JP, A) JP-A-7-180098 (JP, A) JP-A-5-195071 (JP, A) JP-A-7-41861 (JP, A) JP-A-6-1994 336617 (JP, A) JP-A-6-336616 (JP, A) JP-A-6-336612 (JP, A) JP-A-1-119622 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C21D 9/46 501 C21D 8/12 H01F 1/16

Claims (2)

(57) [Claims] 1. A silicon steel slab is subjected to hot rolling, and then to a final thickness by one or a plurality of cold rollings sandwiching intermediate annealing, followed by decarburizing annealing and applying an annealing separating agent. In producing a grain-oriented silicon steel sheet by a series of steps of performing final finish annealing, the arithmetic average roughness of the steel sheet surface after final cold rolling is adjusted to 0.40 μm or less, and then, prior to decarburization annealing, electrolytic year performed electrodeposit containing Si in the steel sheet surface by degreasing method performs a cleaning process to be deposited at 0.1 mg / m ² or more, then, by adjusting the ratio of steam partial pressure to hydrogen partial pressure in the atmosphere from 0.30 to 0.65 And the atmosphere temperature is 850-950 ° C and the water vapor partial pressure is 0.05-3.0%
A method for producing a grain-oriented silicon steel sheet having excellent magnetic properties, comprising performing a decarburizing anneal in a later stage of decomposing and regenerating an oxide on the surface of a steel sheet by adjusting the temperature of the steel sheet. 2. The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein the decomposition / regeneration / densification treatment is performed for 5 to 40 seconds.