JPH07150250A - Production of grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To extremely stably perform the decarburization of a steel sheet and the supply of oxygen to the surface of the steel sheet and to stabilize film properties and magnetism at high values. CONSTITUTION:A hot rolled plate of silicon steel, having a composition consisting of, by weight, 2.0-4.8% Si, inhibitor components, and the balance iron with inevitable impurities, is subjected, if necessary, to annealing and is then cold rolled once or cold rolled two or more times while process annealed between the cold rolling stages to prescribed sheet thickness. Subsequently, at the time of performing primary recrystallization annealing including decarburizing stage, this primary recrystallization annealing including decarburizing stage is performed while regulating the atmosphere in a furnace so that it consists of, as dry gas, >=25% H2, <2% COx, and the balance inert gas and has 50-70 deg.C dew point. In addition, the amount of atmospheric gas is controlled to [100X(H1+D)X(H1+H2)/H1] to [400X(H1+D)X(H1+H2)/H1]Nm<3>/hr, when, by meter, H1 represents the shorter one between the distances, in a direction perpendicular to sheet surface, from the steel sheet passed into the furnace to the interior furnace walls on both sides of the steel sheet and H2 represents the longer one and, further, D represents the width of the surface in a sheet surface interior direction. Further, a separation agent at annealing is applied and finish annealing is done.

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 (hereinafter referred to as grain-oriented electrical steel sheet) having extremely low iron loss. In particular, in the primary recrystallization annealing process including the decarburization process, decarburization of the steel sheet and oxygen addition to the steel sheet surface are performed extremely stably, and it is intended to stabilize the film and magnetism at a high level.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are frequently used as magnetic iron cores for electric equipment and have been repeatedly improved to reduce energy loss. Improvements have been repeated from the optimization of so-called pre-process steelmaking components, the optimization of hot rolling conditions, etc. to the optimization of post-processes such as finish annealing. The primary recrystallization annealing process including the decarburization process was no exception. The main purpose of the primary recrystallization annealing process including the decarburization process is to remove the carbon (usually up to 5 × 10 ^-2 %) contained in the steel sheet for the reason of securing the γ phase region in the hot rolling process,
Decarburize to the extent that magnetism does not deteriorate with age in the final product (~
(Less than 15 ppm), and then appropriate oxygen is applied to the surface of the steel sheet to form Fe and Si oxides, and then the surface-coated MgO is reacted with finish annealing in the next step to prepare for forming a glass film. That is, the primary recrystallization is performed to the optimum grain size for secondary recrystallization in the finish annealing in the next step.

Conventionally, the primary recrystallization annealing step including the decarburizing step of the grain-oriented electrical steel sheet is carried out in a continuous annealing furnace, but the steel sheet is continuously decarburized in the furnace and oxygen is added to the surface of the steel sheet. At the same time, the atmospheric gas is also continuously changed (reduced), and the reaction process in this furnace is extremely complicated, and an analysis device (analyzer) that sufficiently analyzes the reaction in the furnace
In addition, the quality (magnetism, coating, etc.)
In particular, the effect of the annealing process was large, and as a result, a sufficient theoretical analysis was not performed, and only a slight improvement was made based on past experience.

[0004]

The primary recrystallization annealing process including the decarburizing process of the grain-oriented electrical steel sheet has been attempted to be improved by using the steel sheet temperature and the atmospheric gas component analysis value. The value is extremely unstable, and it is difficult to find the value of the atmospheric gas component in the furnace that represents the reaction.For example, regarding the method of supplying the atmospheric gas, the batch supply from the rear of the furnace and the multiple supply from the furnace I was unable to make a satisfactory evaluation of the pros and cons of divided supply, so I had to rely on experience. As a result, it is difficult to perform primary recrystallization annealing including a stable decarburization step, and often decarburization failure,
Alternatively, it causes a film defect or a magnetic defect and requires a great deal of time and cost to improve these defects. In view of the problems of the primary recrystallization annealing process including the conventional decarburizing process described above, the present invention stabilizes (uniformizes) the atmospheric gas in the furnace and stably manufactures a magnetic steel sheet. An object of the present invention is to provide a manufacturing method of.

[0005]

The present invention advantageously solves the problems of the prior art, and in order to achieve the above object, the inventors of the present invention used a furnace for a primary recrystallization annealing process including a decarburization process. Focusing on the atmosphere gas flow inside, detailed analysis of the reaction was performed, and as a result of repeated ingenuity, by controlling the atmosphere gas amount within a certain range, it was possible to produce the product extremely stably. is there.

The gist of the present invention is as follows. (1) In the production of grain-oriented electrical steel, Si: 2.0-
After annealing the hot-rolled silicon steel strip consisting of 4.8% by weight, inhibitor component, balance iron and unavoidable impurities, if necessary,
When performing cold rolling once or twice or more including an intermediate annealing to a predetermined plate thickness, and then performing primary recrystallization annealing including a decarburizing step, the furnace atmosphere is H ₂ 25% (dry gas) or more,
CO _x less than 2% (dry gas), dew point 50 to 70 ° C, balance inert gas, and the distance between the steel plate to be passed through the furnace and the inner walls of the furnace on both sides (distance in the direction perpendicular to the plate surface) The shorter distance is H1 (m) and the longer distance is H2
(M) and the furnace internal width (width in the plate surface direction) is D (m), the atmospheric gas amount is [100 × (H1 + D) × (H1 +
H2) / H1] Nm ³ / hr or more, [400 × (H1 + D)
× (H1 + H2) / H1] Nm ³ / hr or less, a primary recrystallization annealing including a decarburizing step is performed, and an annealing separator is further applied to perform finish annealing, which is a method for producing a grain-oriented electrical steel sheet.

(2) The atmospheric gas supplied into the furnace is supplied all at once to the final portion in the traveling direction of the steel sheet, is collectively flowed in the direction opposite to the steel sheet, and is discharged from the initial portion in the traveling direction of the steel sheet. The method for producing a grain-oriented electrical steel sheet according to (1) above. (3) The directional electromagnetic field according to (2) above, characterized in that the atmospheric gas discharged from the initial portion of the traveling direction of the steel sheet is recovered, the necessary components are adjusted, and then supplied from the final portion of the traveling direction of the steel sheet. Steel plate manufacturing method.

[0008]

The present invention will be described in detail below. The present inventors have investigated in detail the behavior of the gas flow in the furnace of the supply atmosphere of the primary recrystallization annealing furnace including decarburization, and found that the gas flow behavior in the furnace, especially the distance between the steel plate and the furnace, It has been found that there is a strong relationship between the width and the amount of gas and the variations in atmospheric gas components between the steel plate and the inner wall of the furnace. The survey was conducted as follows. FIG. 1 shows an example of a primary recrystallization annealing furnace including decarburization in which atmospheric gas is collectively supplied from the rear of the furnace. The atmospheric gas is supplied all at once from the atmospheric gas supply pipe 3 at the rear of the furnace 1, flows toward the front of the furnace while facing the steel plate 2, and is exhausted from the atmospheric gas exhaust pipe 4. FIG. 2 shows an example of a primary recrystallization annealing furnace including decarburization in which atmospheric gas is dividedly supplied from plural points of the furnace. The atmosphere gas is dividedly supplied from the plurality of atmosphere gas supply pipes 31 to 35 of the furnace 1, and the steel plate 2
Flowing toward the front of the furnace while facing the
Is being discharged more.

The present inventors conducted various investigations by changing the size of the furnace, the position of the steel sheet in the furnace, the amount of atmospheric gas, and the position of supplying the atmospheric gas. As a result, it was found that there is a strong correlation between the atmosphere supply gas amount and the atmospheric concentration variation between the steel plate and the inner wall of the furnace, and further detailed analysis revealed that the steel plate passed through the furnace and the inner walls of the furnace on both sides Of the distances (distance in the direction perpendicular to the plate surface), the shorter distance is H1 (m), and the longer distance is H2 (m) (H1 + H2: distance between inner walls of the furnace on both sides of the steel plate that passes through the furnace). , Furnace width (width in the plate surface direction) D
(M) and α = (H1 + D) × (H1 + H2) / H1
Then, it was found that there is a strong correlation between the atmospheric gas supply amount with α as a variable and the atmospheric concentration variation between the steel plate and the inner wall of the furnace.

FIG. 3 shows variations in the atmospheric gas supply amount and the atmospheric gas concentration between the steel plate in the furnace and the inner wall of the furnace (point 5 near the steel plate).
And the measured value difference of the dew point between the steel plate and the center point 6 of the inner wall of the furnace). The supply atmosphere gas was such that H _{2 was} 75% (dry gas), CO _x (most of which was CO, and part of CO ₂ was included) was less than 1%, and the dew point was 64 ° C. Further, the thickness of the passed steel plate is 0.30 mm, the composition is Si: 3.0% by weight,
Acid-soluble Al: 0.029% by weight, N: 0.075% by weight, Mn: 0.12% by weight, S: 0.007% by weight,
C: 0.05% by weight, balance Fe and inevitable impurities. It has been clarified that when the atmospheric gas amount exceeds 100 × αNm ³ / hr, the variation in the atmospheric gas concentration between the steel plate and the inner wall of the furnace becomes extremely small. In addition, regarding the method of supplying atmospheric gas, it was clarified that batch supply from the rear of the furnace significantly reduces the variation in the concentration of the atmospheric gas between the steel plate and the inner wall of the furnace, compared to the split supply into the furnace. The inventors of the present invention have conducted similar studies on various component systems and have verified that the above relationship holds.

The implementation conditions will be described below. The steel component in the present invention comprises Si: 2.0 to 4.8% by weight, an inhibitor component necessary for the production of grain-oriented electrical steel, the balance Fe and inevitable impurities, and the other components are not specified. Si is important for increasing electric resistance and reducing iron loss, but if its content exceeds 4.8% by weight, it tends to crack during cold rolling. On the other hand, if it is less than 2.0% by weight, the electric resistance is low and there is a problem in reducing iron loss. Moreover, Mn, S, Al, N, Se, and
It is effective for all of Sn, B, Bi, Nb, Ti, P and the like.

When the H ₂ concentration (dry gas) of the atmosphere gas in the primary recrystallization annealing step including the decarburizing step is less than 25%,
It has a strong oxidation potential and hinders the selective oxidation of Si on the surface. If the CO _x concentration (dry gas) exceeds 2%, the oxidation potential is weak and the decarburizing property is reduced. When the dew point is less than 50 ° C, the oxidation potential is low and the decarburizing property is lowered. On the other hand, if it exceeds 70 ° C., the amount of water per 1 ° C. becomes too large, and the fluctuations in the components of the supply atmosphere are increased. The atmosphere gas amount in the primary recrystallization annealing step including the decarburization step is [100 × (H1
If less than + D) × (H1 + H2) / H1] Nm ³ / hr, the atmosphere gas flow in the furnace is unstable, and the variation of the atmosphere gas component in the vertical direction of the steel sheet is large. On the other hand, [400 ×
If (H1 + D) × (H1 + H2) / H1] Nm ³ / hr is exceeded, the amount of atmospheric gas is too large, which is uneconomical.

The method of supplying the atmospheric gas in the primary recrystallization annealing step including the decarburizing step is that the gas is supplied all at once to the final portion in the traveling direction of the steel sheet, and is collectively flowed in the direction opposite to the steel sheet. Compared to the split supply method, the method of discharging from the initial part has less variation in the atmosphere gas in the furnace, and
The equipment is simplified. It becomes more economical by collecting the atmospheric gas discharged from the initial portion of the traveling direction of the steel sheet, adjusting the necessary components and then supplying it from the final portion of the traveling direction of the steel sheet.

The embodiments of the present invention will be described below. Si: 2.0 to 4.8 wt%, hot rolled steel sheet or hot rolled steel sheet, which is composed of an inhibitor component necessary for the production of grain-oriented electrical steel sheet, the balance Fe and unavoidable impurities, in a normal process or continuously cast. Use steel strip. This hot-rolled steel sheet or hot-rolled steel strip is, if necessary, annealed at a temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes to improve the magnetic flux density, and then these hot-rolled steel sheet or hot-rolled steel sheet is hot rolled. The steel strip is cold rolled. Cold rolling is a final cold rolling rate of 50% or more,
Desirably, it is 80% or more as disclosed in Japanese Examined Patent Publication No. 40-15644. The material after cold rolling is put into a primary recrystallization annealing furnace including decarburization annealing.

The primary recrystallization annealing including the decarburization annealing is performed at a steel plate temperature of 800 to 850 ° C. At this time, the atmosphere gas supplied to the furnace has a gas composition of 75% or more of H ₂ (dry gas), less than 2% of CO _x (dry gas), and a dew point of 5
0 to 70 ° C., the balance is inert gas, and the amount of atmospheric gas is [100 × (H1 + D) × (H1 + H2) / H
1] Nm ³ / hr or more, [400 × (H1 + D) × (H1 +
H2) / H1] Nm ³ / hr or less. In this way, the decarburized steel sheet or steel strip that has undergone primary recrystallization is coated with an annealing separator containing MgO as a main component, and enters a finishing annealing furnace.
After reaching 20 to 1150 ° C., secondary recrystallization is performed by holding for 5 hours or more, and thereafter, the temperature is raised to 1200 ° C. for purification,
This temperature is maintained for 10 hours or more. After finishing annealing,
If necessary, tension coating including magnetic domain subdivision processing is performed.

[0016]

【Example】

Example 1 Si: 3.0 wt%, acid-soluble Al: 0.026 wt%, N: 0.0090 wt%, Mn: 0.08 wt%,
S: 0.027% by weight, C: 0.05% by weight, balance Fe
And hot-rolled silicon steel strip consisting of unavoidable impurities at 1100 ° C
After annealing for 2 minutes, it was cold-rolled to 0.23 mm. These cold-rolled sheets were annealed at a steel sheet temperature of 830 ° C. for 2 minutes, with a supply atmosphere gas composition H _{2 of} 75% (dry gas), CO _{x of} less than 1% (dry gas), a dew point of 68 ° C., and a balance of inert gas. A primary recrystallization including decarburization was performed. Then MgO
Was annealed at a high temperature. In the high temperature annealing, the temperature was raised up to 1100 ° C. in a 10% N ₂ -90% H ₂ atmosphere while maintaining a temperature rising rate of 150 ° C./hr.
After reaching 00 ° C, the temperature was maintained for 10 hours. afterwards,
In a 100% H ₂ atmosphere, further raise the temperature to 1200 ° C.,
Hold at this temperature for 10 hours. After finishing annealing, phosphoric acid-chromic acid-based tension coating treatment was performed. The properties and film conditions obtained are shown in Table 1.

[0017]

[Table 1]

Example 2 Si: 3.2% by weight, acid-soluble Al: 0.030% by weight, N: 0.0060% by weight, Mn: 0.13% by weight,
S: 0.007 wt%, C: 0.05 wt%, balance Fe
And hot-rolled silicon steel strip consisting of inevitable impurities at 1120 ° C
After annealing for 2 minutes, it was cold-rolled to 0.23 mm. These cold-rolled sheets were made into a supply atmosphere gas composition H _{2 of} 75% (dry gas), CO _{x of} less than 1% (dry gas), a dew point of 65 ° C., and a balance inert gas, and were annealed at a steel plate temperature of 820 ° C. for 2 minutes, A primary recrystallization including decarburization was performed. Next, in order to stabilize the secondary recrystallization, nitriding treatment was performed in an ammonia atmosphere to adjust the amount of nitrogen to 190 ppm to strengthen the inhibitor. After that, an annealing separator containing MgO as a main component was applied, and high temperature annealing was performed.

The high temperature annealing is performed at 10% N ₂ − up to 1100 ° C.
The temperature was raised in a 90% H ₂ atmosphere while maintaining the temperature rising rate of 150 ° C./hr, and after reaching 1100 ° C., the temperature was maintained for 10 hours. Then, the atmosphere is set to 100% H ₂ and further 1200
The temperature was raised to 0 ° C. and the temperature was maintained for 10 hours. After finishing annealing, phosphoric acid-chromic acid-based tension coating treatment was performed. Table 2 shows the obtained characteristics and film conditions. As is clear from Example 1 and Example 2, stable production of the product including the magnetism and the film was achieved by homogenizing the atmosphere gas in the furnace (reducing variation). It is also possible to recover the atmosphere in the furnace, adjust the gas component, and reuse. In this way, more economical manufacturing was made possible.

[0020]

[Table 2]

[0021]

According to the present invention, by controlling the gas amount of the atmosphere gas in the furnace in the primary recrystallization annealing process including the decarburization process within a certain range, it becomes possible to stabilize the film performance and magnetism at a high level. It becomes possible to produce products with extremely high stability, and its industrial value is enormous.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a primary recrystallization furnace including decarburization in which an atmospheric gas is collectively supplied from the rear of the furnace.

FIG. 2 is an explanatory diagram showing an example of a primary recrystallization furnace including decarburization in which atmospheric gas is dividedly supplied into the furnace.

FIG. 3 is a table showing the relationship between the amount of atmospheric gas and the concentration variation of the atmospheric gas between the steel plate in the furnace and the inner wall of the furnace.

[Explanation of symbols]

 1 furnace 2 steel plate 3 atmospheric gas supply pipe (second half batch supply) 4 atmospheric gas discharge pipe 5 steel plate vicinity point 6 steel plate to furnace inner wall center point 31 to 35 atmosphere gas supply pipe (divided supply inside furnace)

Claims (3)

[Claims] 1. In the production of a grain-oriented silicon steel sheet, Si:
A hot-rolled silicon steel strip composed of 2.0 to 4.8% by weight, an inhibitor component, the balance iron and unavoidable impurities is annealed if necessary, and then cold rolled once or twice or more including an intermediate annealing. When performing the primary recrystallization annealing including a predetermined plate thickness and then including a decarburizing step, the furnace atmosphere is H ₂ 25% or more (dry gas), CO _x 2% or less (dry gas), dew point 50 to
70 ° C., with the balance of the inert gas, the shorter distance of the distance between the steel plate to be passed through the furnace and the inner walls of the furnace on both sides (distance in the direction perpendicular to the plate surface) is H1 (m), and the longer one is When the distance is H2 (m) and the furnace width (width in the plate surface direction) is D (m), the amount of atmospheric gas is [100 × (H1 + D) ×
(H1 + H2) / H1] Nm ³ / hr or more, [400 × (H
1 + D) × (H1 + H2) / H1] Nm ³ / hr or less, a primary recrystallization annealing including a decarburization step is performed, and a finish separating annealing is further applied by applying an annealing separator to produce a grain-oriented silicon steel sheet. Method. 2. The atmosphere gas supplied into the furnace is collectively supplied to the final portion in the traveling direction of the steel sheet, and in a direction facing the steel sheet,
The method for manufacturing a grain-oriented silicon steel sheet according to claim 1, wherein the steel sheet is poured in a batch and discharged from an initial portion in the traveling direction of the steel sheet. 3. The directivity according to claim 2, wherein the atmospheric gas discharged from the initial portion of the steel sheet in the traveling direction is recovered, and after the necessary components are adjusted, the atmospheric gas is supplied from the final portion of the steel sheet in the traveling direction. Manufacturing method of silicon steel sheet.