JP2008261033A - Method for producing grain-oriented silicon steel sheet and its continuous decarburizing / nitriding annealing equipment - Google Patents

Abstract

The present invention provides a method for producing a grain-oriented silicon steel sheet capable of supplying atmospheric gas at low cost and achieving high film stability and high magnetic stability, and a continuous decarburizing / nitriding annealing equipment thereof.
A direction in which a cold-rolled steel sheet having a predetermined thickness containing Si of 2.0 to 4.8% is subjected to primary recrystallization annealing and nitriding annealing including a decarburizing step, and an annealing separator is applied to perform finish annealing. In the manufacturing method and manufacturing equipment for the heat-resistant silicon steel sheet, the atmospheric gas is recovered and dehydrated from the nitriding zone where the nitridation annealing is performed or from the atmosphere partition before and after the nitriding zone, and the NH ₃ is mainly composed of H ₂ and inert gas. Regenerative atmosphere gas containing less than 1 vol% (in terms of dry gas) is produced, and the nitriding zone atmosphere after supply is H ₂ concentration: 25 vol% (in terms of dry gas) or more, NH ₃ : 0.1 to 10 vol% (in terms of dry gas) The dew point is 10 ° C. or less, and the inert gas, NH ₃ , H ₂ 0 are added to the regeneration atmosphere gas so as to be the inert gas, and the components are adjusted before being supplied to the nitriding zone.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet with extremely low iron loss and a continuous decarburization / nitriding annealing facility for grain-oriented silicon steel sheets.

  Oriented silicon steel plates are frequently used as magnetic iron cores in electrical equipment, and have been repeatedly studied not only for improving the steel plates themselves to reduce energy loss, but also for improving the stability of manufacturing steel plates and reducing manufacturing costs. The decarburization annealing process and the nitriding annealing process in which the primary recrystallization annealing including the decarburization process is performed were no exception.

The main purpose of the decarburizing / nitriding annealing process is to secure carbon (usually about 5 × 10 ⁻² mass%) contained in the steel sheet in the final product for reasons such as securing the γ-phase region in the hot rolling process. Is decarburized to a region where aging does not deteriorate (less than 15 ppm by mass), then, after applying appropriate oxygen to the steel sheet surface to form Fe and Si oxides, applying appropriate nitrogen to the steel sheet, In the next annealing process, MgO applied to the surface is reacted to form a glass film, and as a preparation for secondary recrystallization, primary recrystallization is performed to an optimum crystal grain size.

Conventionally, the decarburization annealing process of the grain-oriented silicon steel sheet is performed in a continuous annealing furnace, the steel sheet is continuously decarburized in the furnace, oxygen is given to the steel sheet surface, and the atmospheric gas is also continuously reduced. It was burned out of the furnace. Further, in the nitriding annealing process, the steel sheet was continuously nitrided in the furnace, nitrogen was imparted to the steel sheet, and the atmospheric gas was continuously decomposed and reduced with NH ₃ and diffused and burned out of the furnace. .

  FIG. 3 shows an example of conventional continuous decarburization / nitriding annealing equipment. The furnace 2 includes a heating / soaking zone 3, a reduction zone 4, a nitriding zone 5, a cooling zone 6, and atmosphere partitions 7 to 9 between these treatment zones.

  The atmosphere gas in the heating / soaking zone 3 is supplied from the atmosphere gas supply pipe 20A behind the heating / soaking zone 3, and most of the atmosphere gas flows to the front of the furnace 2 while facing the steel plate 1, and the atmosphere gas discharge pipe 11A. Although more dissipated and burned, a part of it is dissipated from the furnace inlet and flows out to the atmosphere partition 7.

  The atmosphere gas in the reduction zone 4 is supplied from the atmosphere gas supply pipe 20B, diffused and burned from the atmosphere gas discharge pipe 11B, and flows out to the front and rear atmosphere partitions 7 and 8. The atmosphere gas in the nitriding zone 5 is supplied from the atmosphere gas supply pipe 20C, diffused and combusted from the atmosphere gas discharge pipe 11C, and flows out to the front and rear atmosphere partitions 8 and 9.

  The atmosphere gas in the cooling zone 6 is supplied from the atmosphere gas supply pipe 20D, flows out to the atmosphere partition 9 at the front, and is dissipated from the furnace outlet.

  In addition, atmospheric gas is diffused and burned from the atmospheric partitions 7 to 9 through the atmospheric gas discharge pipes 11E to 11G. In addition, the furnace pressure of each atmosphere partition is set to be lower by a certain value than the preceding and following processing zones, and the atmosphere gas is diffused and burned from each atmosphere gas discharge pipe 11A to 11C, EG to maintain this. Yes.

Patent Document 1 discloses gas recovery from a continuous decarburization / nitridation annealing facility. In this case, the entire atmospheric gas recovered from the nitriding furnace and its front and rear furnaces is decomposed into residual NH ₃ through an NH ₃ decomposition device, and further refined with an atmospheric gas generator, and then returned to a continuous decarburization / nitriding annealing facility. Is done.

JP-A-10-212527

  In the conventional decarburization / nitridation annealing process of the directional silicon steel sheet shown in FIG. 3, the atmosphere gas used is diffused and burned out of the furnace, which necessitates a high atmosphere cost. In order to reduce the atmospheric cost, attempts have been made to reduce the amount of atmospheric gas. However, it often causes nitriding defects or magnetic defects, and much time and cost must be spent on improving these defects.

In the continuous decarburization / nitridation annealing facility disclosed in Patent Document 1, all of the atmospheric gas recovered from the nitriding furnace and its front and rear furnaces passes through the NH ₃ decomposition apparatus, and the residual NH ₃ is thermally decomposed. Furthermore, it is a large-scale facility that is refined by an atmospheric gas generator and the atmospheric gas is refluxed to a continuous decarburization / nitridation annealing facility.

  That is, the continuous decarburization / nitridation annealing facility disclosed in Patent Document 1 requires a large amount of equipment necessary for gas recovery and refining, and the equipment cost is very high, making it difficult to apply only to a large heat treatment equipment.

  Therefore, in view of the problems of the above-described conventional decarburization / nitridation annealing process, the present invention can supply atmospheric gas at a low price in both large and small heat treatment facilities and has a high quality stable product. It aims at providing the manufacturing method of the grain-oriented silicon steel plate which can supply, and the continuous decarburization and nitriding annealing equipment of a grain-oriented silicon steel plate.

  The gist of the present invention is as follows (1) to (4).

(1) Si: 2.0 to 4.8% by mass, including an inhibitor component, the hot-rolled steel strip of a silicon steel plate composed of the remaining iron and inevitable impurities is annealed or annealed once thereafter. Or, cold rolling at least twice including intermediate annealing is performed to a predetermined thickness, then primary recrystallization annealing and nitriding annealing including decarburization process are performed, and further, annealing separator is applied to finish annealing. In a method for producing a grain-oriented silicon steel sheet,
(I) When performing primary recrystallization annealing and nitriding annealing including the decarburization step, the atmosphere gas in the furnace is recovered from the nitriding zone where the nitriding annealing is performed or the atmosphere partition before and after the nitriding zone, and dehydrated, H ₂ , Producing a regenerative atmosphere gas containing an inert gas as a main component and containing NH ₃ in an amount of less than 1 vol% (in terms of dry gas),
(Ii) The atmosphere of the nitriding zone after supplying the regeneration atmosphere gas is H ₂ concentration: 25 vol% (in terms of dry gas) or more, NH ₃ : 0.1 to 10 vol% (in terms of dry gas), dew point: 10 ° C. Hereinafter, the directional silicon steel sheet is supplied to the nitriding zone after adjusting the components by adding an inert gas, NH ₃ , H ₂ 0 to the regeneration atmosphere gas so that the remaining inert gas becomes an inert gas. Production method.

(2) After the remaining regeneration atmosphere gas supplied to the nitriding zone is thermally decomposed and refined with NH ₃ , H ₂ -containing gas, inert gas and H ₂ O are added to adjust the components, The method for producing a grain-oriented silicon steel sheet according to the above (1), wherein the steel sheet is supplied to one or more treatment zones except for the above.

(3) In a continuous decarburization / nitridation annealing facility for grain-oriented silicon steel sheets, used atmosphere gas recovered from the nitriding zone for nitriding annealing or the atmosphere partition before and after the nitriding zone is dehydrated, and NH ₃ is 1 vol% (dry gas In addition to a dehydration device that produces a regeneration atmosphere gas containing less than the equivalent), an atmosphere gas component adjustment device for the nitriding zone that adjusts the composition by adding NH ₃ , inert gas and H ₂ O to the regeneration atmosphere gas A continuous decarburization and nitridation annealing facility for grain oriented silicon steel sheets.

(4) An NH ₃ thermal decomposition / refining device for thermally decomposing / refining NH ₃ in the remaining regeneration atmosphere gas after being supplied to the nitriding zone is provided, and an H ₂ -containing gas after thermal decomposition / refining, The grain oriented silicon steel sheet according to (3) above, wherein an atmosphere gas component adjusting device for one or more treatment zones excluding the nitriding zone for adjusting the components by adding an inert gas and H ₂ O is provided. Continuous decarburization and nitriding annealing equipment.

  According to the present invention, an atmospheric gas can be supplied at a low cost, and a grain-oriented silicon steel sheet can be manufactured extremely stably.

When the gas concentration in the furnace of the atmospheric gas was investigated in detail, in the nitriding zone, NH ₃ was mainly decomposed and changed to H ₂ and N ₂ , and part of the H ₂ was oxidized of the steel plate. The product was reduced and H ₂ O was found to increase slightly. Note that the dew point of the reducing zone atmosphere is generally not lower than the dew point of the nitriding zone.

Of these H ₂ , N ₂ , H ₂ O, and NH ₃ , the only gas component that hinders use in the nitriding zone is residual H ₂ O. The gas component as a failure of use in heating and soaking zone is, NH ₃ is only, also a gas component as a failure of use in heating and soaking zone and treatment zone other than the nitride band, NH _3, Only H ₂ O. Other atmospheric gas components can be reused by analyzing the concentration of each composition of the used atmospheric gas and replenishing the shortage.

  FIG. 1 shows an example of the continuous decarburizing / nitriding annealing equipment of the present invention. The furnace 2 includes a heating / soaking zone 3, a reduction zone 4, a nitriding zone 5, a cooling zone 6, and atmosphere partitions 7 to 9 between these treatment zones.

The atmospheric gas supplied into the furnace from the atmospheric gas supply pipe 20A at the rear of the heating / soaking zone 3 proceeds in opposition to the steel plate 1, most of which reaches the front of the furnace and is supplied from the atmospheric gas discharge pipe 11A to the furnace. Although it is discharged outside, a part of it is diffused from the furnace inlet and flows out to the atmosphere partition 7. Note that as the atmospheric gas flows to the front of the furnace, H ₂ O is consumed and reduced, and CO _x increases.

  The atmosphere gas in the reduction zone 4 is supplied from the atmosphere gas supply pipe 20B, discharged from the atmosphere gas discharge pipe 11B, and flows out to the front and rear atmosphere partitions 7 and 8. The atmospheric gas supplied from the atmospheric gas supply pipe 20C to the nitriding zone 5 is discharged out of the furnace from the atmospheric gas discharge pipe 11C and flows out to the front and rear atmospheric partitions 8 and 9.

  The atmosphere gas in the cooling zone 6 is supplied from the atmosphere gas supply pipe 20D, flows out to the atmosphere partition 9 at the front, and is dissipated from the furnace outlet. Moreover, atmospheric gas is discharged | emitted from each atmospheric partition 7-9 through atmospheric gas discharge pipe 11E-G. The furnace pressure of each atmosphere partition is set to be lower than the front and rear treatment zones by a certain value, and the atmosphere gas is discharged from each atmosphere gas discharge pipe 11A-C, EG to maintain this.

In the nitriding zone, the surface of the steel strip is slightly reduced, and accordingly, the H ₂ concentration in the atmosphere is slightly reduced, but is very small, and the oxidation potential {P (H ₂ O) / P (H ₂ )}.

On the other hand, the atmospheric gas discharged from the discharge pipe 11F contains NH ₃ and its dew point is generally higher than the dew point of the nitriding zone. Further, the atmospheric gas discharged from the discharge pipe 11G contains NH ₃ , and its dew point is generally lower than the dew point of the nitriding zone.

After the NH ₃ -containing gas discharged from the three atmospheric gas discharge pipes 11C, F, and G is collected, the scattered matter from the furnace is removed by the filter 21 and guided to the dehydrating device 22, and H ₂ O is removed.

There is no particularly difficult condition for dehydration, and it is sufficient that H ₂ O is removed and the dew point of the nitriding zone atmosphere is lower, and an adsorption method or other methods may be used. For example, in the case of the adsorption method, the adsorbent is not particularly specified as long as it does not react with alkali. Also, a cooling type dehydrator may be used. The recovered atmosphere temperature may be cooled from the dew point of the nitriding zone atmosphere. Further, the cooling temperature of the recovered atmospheric gas can be reduced by taking a method of increasing the pressure.

The regeneration atmosphere gas dehydrated by the dehydrator 22 is analyzed for the concentration of gas components by the gas analyzer 26, and the lacking NH ₃ , H ₂ O and, if necessary, inert gas by the atmosphere gas component adjuster 19C. Is replenished and supplied to the nitriding zone 5. Excess regeneration gas is diffused and burned. In the circuit, an atmospheric gas circulation device 13 is provided to apply a driving force necessary for the circulation and dehydration of the atmospheric gas.

  The filter used in the present invention is made of a non-oxidizing metal such as stainless steel made of fine fibers, and a filter made by sintering a material made by sintering with a wrinkle is safe even at high temperatures. For this reason, it is preferable, but other structures can be used as long as they have heat resistance and filter ability.

  The grain-oriented silicon steel sheet according to the present invention comprises Si: 2.0 to 4.8% by mass, and further contains an inhibitor component necessary for producing the grain-oriented silicon steel sheet, and is composed of the remaining Fe and inevitable impurities. Other components are not particularly defined.

  Si is important for increasing electric resistance and lowering iron loss, but if its content exceeds 4.8% by mass, cracking is likely to occur during cold rolling. On the other hand, if it is less than 2.0% by mass, the electrical resistance is low, and there is a problem in reducing iron loss.

  Inhibitor components include Mn, S, Al, N, Se, Sn, B, Bi, Nb, Ti, and P.

  Si: 2.0 to 4.8% by mass, and a molten steel containing an inhibitor component necessary for the production of the grain-oriented silicon steel sheet, and the balance Fe and unavoidable impurities are continuously cast in a normal process, for example, , Hot-rolled steel sheet or hot-rolled steel strip. This hot-rolled steel sheet or hot-rolled steel strip is subjected to annealing for improving the magnetic flux density in a temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes or not, and then these hot-rolled steel sheet or hot-rolled steel strip Cold-roll the steel strip.

  The cold rolling is performed at a final cold rolling rate of 50% or more, desirably 80% or more as disclosed in Japanese Patent Application Laid-Open No. 2003-3215. The material after cold rolling is put into a continuous decarburizing / nitriding annealing facility.

First, decarburization annealing is performed at a steel plate temperature of 800 to 850 ° C. At this time, the composition of the atmospheric gas supplied to the furnace is H ₂ : 25 vol% (in terms of dry gas) or more, preferably 75 vol% (in terms of dry gas), dew point: 50 to 75 ° C., and the balance inert gas.

Next, reduction annealing is performed at a steel plate temperature of 800 to 850 ° C. The composition of the atmospheric gas supplied to the furnace is H ₂ : 25 vol% (in terms of dry gas) or more, preferably 75 vol% (in terms of dry gas), dew point: 45 ° C. or less, and the remaining inert gas.

Next, nitriding annealing is performed at a steel plate temperature of 700 to 800 ° C. The atmosphere of the nitriding zone is NH ₃ : 0.1 to 10 vol% (in terms of dry gas), H ₂ : 25 vol% (in terms of dry gas) or more, preferably over 65 vol% (in terms of dry gas), dew point: 10 ° C. or less The atmosphere of the remaining inert gas is used.

FIG. 2 shows another example of the continuous decarburizing / nitriding annealing equipment of the present invention. The difference from FIG. 1 is that residual NH ₃ supplied to the nitriding zone 5 is not diffused and burned, and the remaining NH ₃ is thermally decomposed and purified by the NH ₃ decomposition / refining device 23, and the atmospheric gas components are analyzed by the analyzer 27. The deficient H ₂ source gas, inert gas and H ₂ O are adjusted by the atmospheric component adjusting devices 19A and 19B and supplied to the heating / soaking zone 3 and the reduction zone 4.

In this example, all of the nitriding zone or the atmospheric gas containing NH ₃ flowing out from the atmosphere partition before and after the nitriding zone has been recovered and reused, thereby eliminating the fear of environmental pollution.

  The steel sheet or steel strip thus decarburized and further coated with an annealing separator mainly composed of MgO is put into a finish annealing furnace, and after reaching 920 to 1150 ° C., it is held for 5 hours or more and 2 Next, recrystallization is performed, and then the temperature is raised to 1200 ° C. for purification, and this temperature is maintained for 10 hours or more. After finish annealing, tension coating including magnetic domain refinement is performed as necessary.

  Si: 3.2% by mass, acid-soluble Al: 0.029% by mass, N: 0.065% by mass, Mn: 0.12% by mass, S: 0.008% by mass, C: 0.05% by mass In addition, the hot-rolled steel strip of the silicon steel plate including the remaining Fe and inevitable impurities was annealed at 1100 ° C. for 2 minutes and then cold-rolled to a thickness of 0.23 mm.

In Example 1 of the present invention, ammonia decomposing gas (H ₂ : 75 vol%, N ₂ : 25 vol%, both in terms of dry gas): 200 m ³ / hr, NH ₃ : 100 m ³ / hr at the beginning of the dew point in the nitrogen band The furnace was replenished from the gas supply pipe at 0 ° C. The atmosphere gas was recovered from the nitriding zone and the front and rear atmosphere partitions, and the recovered atmosphere gas was cooled and dehydrated with a dehydrator, dehydrated to 0 ° C., adjusted again with NH _3, and then circulated through the nitrogen zone.

Along with this, the supply of ammonia decomposition gas was gradually reduced to zero. For heating and soaking, ammonia decomposition gas (H ₂ : 75 vol%, N ₂ : 25 vol%, both in terms of dry gas) was supplied from a gas supply pipe with a dew point of 69 ° C. Further, ammonia decomposition gas (H ₂ : 75 vol%, N ₂ : 25 vol%, both in terms of dry gas) was supplied to the reduction zone from the gas supply pipe with a dew point of 35 ° C.

  In this process, a steel plate is passed through, annealed at a steel plate temperature of 830 ° C. for 2 minutes, treated with a reduction zone, and finally subjected to nitriding treatment in an ammonia atmosphere to stabilize secondary recrystallization. The target of the nitrogen amount of the steel sheet was set to 200 mass ppm, the inhibitor was strengthened, and then cooled in an ammonia decomposition gas atmosphere.

In Example 2 of the present invention, the remaining gas after supplying the recovered and dehydrated atmospheric gas to the nitriding zone was decomposed and purified by NH ₃ and reused. The atmospheric conditions are the same as those of Example 1 of the present invention.

In Comparative Examples 11 and 12, from the gas supply pipe to the nitriding zone, ammonia decomposition gas (H ₂ : 75 vol%, N ₂ : 25 vol%, both in terms of dry gas): 100, 150 m ³ / hr and NH ₃ : 70 and 60 m ³ / hr were supplied at a dew point of 0 ° C., and the target of the amount of nitrogen in the steel sheet was 200 mass ppm. Heating, soaking, and atmosphere supply to the reduction zone are the same as in the example of the present invention.

Thereafter, in both the inventive examples and the comparative examples, an annealing separator mainly composed of MgO was applied and subjected to high temperature annealing. In the high temperature annealing, the temperature was increased to 1100 ° C. in a 10 vol% N ₂ -90 vol% H ₂ atmosphere while maintaining a temperature increase rate of 150 ° C./hr, and after reaching 1100 ° C., the temperature was maintained for 10 hours.

Thereafter, the atmosphere was 100 vol% H ₂ , the temperature was further raised to 1200 ° C., and the temperature was maintained for 10 hours. After finishing annealing, phosphoric acid-chromic acid type tension coating treatment was performed. Table 1 shows the obtained characteristics and coating conditions.

  As is apparent from Table 1, in the present invention example, the atmospheric gas can be supplied at a low cost, and the product quality including the magnetism and the film is stabilized at a high level.

It is a figure which shows an example of the continuous decarburization and nitridation annealing equipment of this invention. It is a figure which shows another example of the continuous decarburization and nitridation annealing equipment of this invention. It is a figure which shows an example of the conventional continuous decarburization and nitridation annealing equipment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Furnace 3 Heating and soaking zone 4 Reduction zone 5 Nitriding zone 6 Cooling zone 7-9 Atmosphere partition 11A-C, E-G Atmospheric gas exhaust pipe 12C, F Atmospheric gas exhaust pipe valve 13 Atmospheric gas circulation device 18A- B Recovery atmospheric gas supply pipe valve 19A to C Atmospheric gas component adjustment apparatus 20A to D Atmospheric gas supply pipe 21 Filter 22 Dehydration apparatus 23 NH ₃ pyrolysis and refining apparatus 26, 27 Gas analyzer 33 H ₂ source gas supply pipe 34A ˜DH ₂ source gas supply pipe valve 35 H ₂ O source gas supply pipe 36A, B H ₂ O source gas supply pipe valve 37 NH ₃ gas supply pipe 38 NH ₃ gas supply pipe valve X Steel plate soaking temperature reaching point

Claims (4)

Si: 2.0 to 4.8% by mass, including an inhibitor component, the hot-rolled steel strip of the silicon steel plate composed of the remaining iron and unavoidable impurities is annealed or annealed once or thereafter without annealing. The directionality which performs cold rolling of 2 times or more including, and makes it a predetermined plate thickness, then performs primary recrystallization annealing and nitriding annealing including a decarburization step, and further performs finish annealing by applying an annealing separator In the method for producing a silicon steel plate,
(I) When performing primary recrystallization annealing and nitriding annealing including the decarburization step, the atmosphere gas in the furnace is recovered from the nitriding zone where the nitriding annealing is performed or the atmosphere partition before and after the nitriding zone, and dehydrated, H ₂ , Producing a regenerative atmosphere gas containing an inert gas as a main component and containing NH ₃ in an amount of less than 1 vol% (in terms of dry gas),
(Ii) The atmosphere of the nitriding zone after supplying the regeneration atmosphere gas is H ₂ concentration: 25 vol% (in terms of dry gas) or more, NH ₃ : 0.1 to 10 vol% (in terms of dry gas), dew point: 10 ° C. In the following, a directionality is characterized in that an inert gas, NH ₃ , and H ₂ O are added to the regeneration atmosphere gas to adjust the components so that the remaining inert gas atmosphere is provided, and then supplied to the nitriding zone. A method for producing a silicon steel sheet. The remaining regeneration atmosphere gas supplied to the nitriding zone is thermally decomposed and refined with NH ₃ , then H ₂ -containing gas, inert gas and H ₂ O are added to adjust the components, and the nitriding zone is removed. The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein the steel sheet is supplied to the treatment zone. In continuous decarburization / nitridation annealing equipment for grain-oriented silicon steel sheets, used atmosphere gas recovered from the nitriding zone for nitriding annealing or the atmosphere partition before and after the nitriding zone is dehydrated, and NH ₃ is less than 1 vol% (in terms of dry gas) And a dehydrating device for producing a regenerating atmosphere gas including an atmosphere gas component adjusting device for a nitriding zone for adjusting components by adding NH ₃ , an inert gas and H ₂ O to the regenerating atmosphere gas. A feature of continuous decarburization and nitriding annealing equipment for directional silicon steel sheets. Wherein the NH ₃ in the residual regeneration atmospheric gas after supplying the nitriding zone disposed the NH ₃ Pyrolysis and finishing line equipment for thermal decomposition and finishing line, H ₂ containing gas after the pyrolysis and purification, an inert gas 4. The continuous decarburization of grain-oriented silicon steel sheet according to claim 3, further comprising an atmosphere gas component adjusting device for one or more treatment zones excluding a nitriding zone for adjusting components by adding H ₂ O. 5.・ Nitride annealing equipment.

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