JP2019127616A - Manufacturing method of grain-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a method for manufacturing a grain-oriented electromagnetic steel sheet which stably realizes a low iron loss at high magnetic flux density compared with the prior art.SOLUTION: In the method for manufacturing a grain-oriented electromagnetic steel sheet, a steel material containing C: 0.010-0.10 mass%, Si: 2.5-4.5 mass%, Mn: 0.01-0.50 mass% is hot rolled, subjected to hot-rolled sheet annealing as necessary, cold rolled, and decarburization-annealed, followed by application of an annealing separator and finish annealing. In the soaking annealing of the decarburization annealing, the soaking temperature in the entire region is controlled to be within a range of 750-950°C, and the average oxygen potential P/Pof the atmosphere in the entire region is controlled to a range of 0.25-0.50. In addition, the soaking process is divided into two or more stages, the soaking time from the start of soaking to a prior stage to the final stage is controlled to 70-200 seconds, the soaking time of the final stage is set to 5-40 seconds, and (the in-furnace pressure in the final stage to the in-furnace pressure in the prior stage to the final stage) is set to more than 0 mm HO and 7 mm HO or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet, and specifically relates to a method for stably producing a grain-oriented electrical steel sheet having excellent magnetic properties.

  Electrical steel sheets are soft magnetic materials widely used for transformers, motor iron cores, etc. Above all, directional electrical steel sheets are highly integrated in the {110} <001> orientation whose crystal orientation is called the Goss orientation. In order to show excellent magnetic properties, it is mainly used for iron core materials for large transformers. Therefore, the main development problem of the conventional grain-oriented electrical steel sheet has been to reduce the loss that occurs when the steel sheet is excited, that is, iron loss, in order to reduce no-load loss (energy loss) in the transformer.

  Conventional methods for reducing the iron loss of the grain-oriented electrical steel sheet include increasing the Si content, reducing the plate thickness, improving the orientation of the crystal orientation, imparting tension to the steel sheet, smoothing the steel sheet surface, It is known that refinement of the secondary recrystallized structure is effective. And in order to achieve the said objective, many techniques which optimize the decarburization annealing conditions in a manufacturing process are proposed.

  For example, in Patent Document 1, when decarburization annealing is performed in a plurality of zones having different compositions or dew points of the atmosphere gas and a continuous annealing furnace in which an atmosphere partition is provided between the zones, the furnace pressure is applied to the atmosphere partition portion of the annealing furnace. There has been disclosed a technique for stabilizing a reaction such as decarburization or oxidation by providing an atmosphere isolation chamber having an exhaust hole provided with a control device and controlling the pressure to a predetermined furnace pressure.

Further, in Patent Document 2, the heating process of decarburizing annealing, the oxidation degree of the atmosphere in the soaking process, specifically, the range of the oxygen potential P _H2O / P _H2 is specified, and the rear part of the decarburizing annealing furnace Magnetic flux density during production on an industrial scale by varying P _h2O / P _H2 so as to be higher, and by performing decarburization annealing for at least the time when the amount of residual C in the steel sheet is 30 ppm or less. A technique for preventing the deterioration of the battery is disclosed.

In addition, Patent Document 3 adds a short-term holding treatment during the heating of the primary recrystallization annealing, specifies the temperature and time of the soaking process, and the oxygen potential P _H2O / P _H2 of the atmosphere. The process is divided into N stages (N: integer of 2 or more), and the temperature, time and atmosphere P _H2O / P _H2 in the first N stage to the (N-1) stage and the final N stage are controlled to specific ranges, respectively. Thus, a technique for improving the internal oxide layer and suppressing variation in magnetic characteristics is disclosed.

In Patent Document 4, the surface roughness of the steel sheet after the final cold rolling is specified and degreased before decarburization annealing, and the soaking temperature in the decarburization annealing and the oxygen potential P _H2O / P _{H2 of the} atmosphere. Is a specific range, and a technique for stably producing a directional electrical steel sheet having a high magnetic flux density by suppressing the fluctuation amount of P _H2O / P _H2 in the furnace length direction of the annealing furnace is disclosed.

Japanese Patent Application Publication No. 07-207348 Unexamined-Japanese-Patent No. 11-199939 Unexamined-Japanese-Patent No. 2014-152392 JP 09-041042 A

  However, in the technique of Patent Document 1 described above, the apparatus becomes too complicated, and it costs a lot to construct and modify the furnace, and the steel plate comes into contact with the atmosphere isolation layer, causing the occurrence of ear cracks and scratches. Further, although the technique of Patent Document 2 improves the magnetic characteristics, the effect is not stable, and there is a problem that the magnetic characteristics are deteriorated at a certain frequency and the product yield is greatly deteriorated. In addition, there is a problem that the annealing is performed for a long time in order to reduce the residual C amount of the steel sheet, and the productivity is impaired. Further, in the technique of Patent Document 3, a slight amount of oxygen may be mixed during the holding process during the temperature rising process, and the steel sheet surface may be externally oxidized to deteriorate the subscale structure. In addition, there is a problem that it becomes difficult to decarburize by setting the temperature before the soaking process higher than the latter stage. Further, the technique of Patent Document 4 has a problem that the fluctuation of the oxygen potential cannot be sufficiently suppressed because the dew point of the atmosphere varies depending on the furnace condition at that time. Furthermore, the magnetic characteristics of unknown cause may be deteriorated at a certain frequency.

  As described above, although the improvement of the magnetic characteristics is gradually advanced by the application of the above-described conventional technology, it is not yet sufficient. Moreover, even if the manufacturing conditions of the above-described prior art are satisfied, the magnetic characteristics may be deteriorated at a certain frequency, and the cause is not clear.

  The present invention has been made in view of the above problems of the prior art, and its object is to provide a grain-oriented electrical steel sheet capable of stably realizing high magnetic flux density and low core loss compared to the prior art. It is to propose a manufacturing method.

  In order to solve the above-mentioned problems, the inventors made extensive studies by paying attention to the influence of decarburization annealing conditions on magnetic properties. As a result, it has been found that a parameter which was not considered at all in the prior art, such as the pressure in the furnace atmosphere in the soaking process of decarburization annealing, has greatly influenced the magnetic characteristics, and has led to the development of the present invention.

That is, the present invention contains C: 0.010 to 0.10 mass%, Si: 2.5 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, and the balance is Fe and inevitable impurities. The steel material having the following composition is hot-rolled to form a hot-rolled sheet, and after the hot-rolled sheet is subjected to hot-rolled sheet annealing or without being subjected to hot-rolled sheet annealing, After cold rolling as described above to obtain a cold-rolled sheet of the final thickness, after applying decarburization annealing that combines primary recrystallization annealing consisting of heating process, soaking process and cooling process, an annealing separator is applied to the steel sheet surface In the method of manufacturing a grain-oriented electrical steel sheet comprising a series of steps of annealing and annealing, the soaking process of the decarburizing annealing is carried out so that the soaking temperature of the whole area is in the range of 780 to 950 ° C. and the atmosphere of the whole area. 0.25 the average oxygen potential _P H2O _{/ P H2} The soaking process is divided into two or more stages, the total soaking time from the start of soaking to the previous stage of the last stage is 80 to 200 seconds, and the soaking time of the last stage is 5 to 40. range of seconds, and the difference of the furnace pressure in the final stage and the furnace pressure of the immediately preceding stage - a (furnace pressure in the last stage the final stage reactor pressure immediately before the stage) 0 mm H 2 _O than 7mmH ₂ O The manufacturing method of the grain-oriented electrical steel sheet characterized by controlling to the following ranges is proposed.

The method for producing a grain-oriented electrical steel sheet according to the present invention maintains the temperature of 800 to 950 ° C. in an atmosphere having an oxygen potential P _H2O / P _H2 of 0.20 or less in the final stage of the soaking process of the decarburizing annealing. The reduction process is performed.

  In the method of manufacturing a grain-oriented electrical steel sheet according to the present invention, secondary recrystallization is performed by maintaining the temperature for 5 to 200 hours in the temperature range of 800 to 950 ° C. in the above-mentioned finish annealing, and then heating or temporary heating 700 It is characterized in that after the temperature is lowered to not more than 0 ° C., reheating is performed and a purification treatment is performed at a temperature of 1120 ° C. or more for 2 hours or more.

  The steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention further contains Al: 0.010 to 0.04 mass% and N: 0.003 to 0.015 mass% in addition to the above component composition. Or Se: 0.003-0.030 mass% and / or S: 0.002-0.030 mass%, or Al: 0.010-0.04 mass%, N: 0.003- 0.015 mass%, Se: 0.003-0.030 mass% and / or S: 0.002-0.030 mass% are contained.

  In addition to the above component composition, the steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention further includes Al: less than 0.010 mass%, N: less than 0.005 mass%, and S: less than 0.005 mass%. And Se: characterized by containing less than 0.005 mass%.

  Moreover, in addition to the said component composition, the said steel raw material used for the manufacturing method of the grain-oriented electrical steel sheet of this invention is further Ni: 0.010-0.5 mass%, Cr: 0.01-0.50 mass%, Cu : 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0 .50 mass%, Mo: 0.005-0.100 mass%, B: 0.0002-0.0025 mass%, Te: 0.0005-0.0100 mass%, Nb: 0.0010-0.0100 mass%, V: One or two selected from 0.001 to 0.010 mass%, Ti: 0.001 to 0.010 mass%, and Ta: 0.001 to 0.010 mass% Characterized by containing the above.

  According to the present invention, by appropriately controlling the pressure in the furnace atmosphere in the soaking process of decarburization annealing, it is possible to manufacture a grain-oriented electrical steel sheet having a low iron loss and high magnetic flux density more stably than in the prior art. It becomes possible.

It is a graph which shows the influence which the difference in the furnace pressure of the last stage in the soaking | uniform-heating process of decarburization annealing and the stage immediately before has on a magnetic characteristic.

First, an experiment that triggered the development of the present invention will be described.
C: 0.05% by mass, Si: 3.3% by mass, Mn: 0.07% by mass, with the balance being composed of Fe and unavoidable impurities, the steel was melted and made into a steel slab by continuous casting. Then, it is heated to a temperature of 1250 ° C and hot-rolled to form a hot-rolled sheet with a thickness of 2.2 mm, subjected to hot-rolled sheet annealing at 1000 ° C x 60 seconds, and then primary cold-rolled to an intermediate sheet thickness After the intermediate annealing at 1100 ° C. for 80 seconds, the secondary cold rolling (final cold rolling) was performed to obtain a cold rolled sheet having a final thickness of 0.23 mm.
Next, the cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing consisting of a heating process, a soaking process, and a cooling process. At this time, in the heating process up to the soaking temperature, after a holding treatment of heating from room temperature to 550 ° C. at 150 ° C./s and holding at a temperature of 550 ° C. for 1 s, between 550 to 700 ° C. at 100 ° C./s. The sample was heated and further heated to a soaking temperature (800 ° C.) at 8 ° C./s. The furnace atmosphere at this time was a wet hydrogen atmosphere having an oxygen potential P _H2O / _PH2 of 0.45. In the soaking process, the soaking time is set to 150 seconds, which is divided into two stages of 140 seconds in the former stage and 10 seconds in the latter stage, the former stage is the above-mentioned wet hydrogen atmosphere, and the latter stage has a P _H2O / _PH2 of 0. In addition to a dry hydrogen atmosphere of 2 or less, the difference between the pressure in the furnace atmosphere in the subsequent stage (final stage) (pressure in the furnace) and the pressure in the atmosphere in the previous stage (stage immediately before the final stage) (internal pressure) (In-furnace pressure in the final stage−in-furnace pressure in the stage immediately before the final stage) was variously changed.
Thereafter, an annealing separator mainly composed of MgO was applied to the surface of the steel sheet, dried, held at 850 ° C. for 50 hours to complete secondary recrystallization, and subsequently heated to 1200 ° C. under a hydrogen atmosphere. Finish annealing for 7 hours of purification treatment was performed.

Ten pieces of test pieces each having a width of 100 mm in the sheet width direction were collected from the steel sheet after finish annealing thus obtained under each condition, and the magnetic flux density B ₈ (T) and iron loss W ₁₇ were measured by the method described in JIS C2556. _{/ 50} (W / kg) was measured and the average value was determined. The results at this time are shown in FIG. 1 as the relationship between the pressure difference in the furnace and the magnetic characteristics.

From this figure, it was found that the magnetic characteristics greatly change depending on the pressure difference in the furnace between the latter stage (final stage) and the former stage (stage immediately before the final stage) in the soaking process of decarburization annealing. That is, when the pressure in the furnace at the rear stage is lower than that at the front stage, the magnetic properties are all deteriorated. Further, when the pressure at the rear stage is higher than that at the front stage, the magnetic characteristics are greatly improved, but the magnetic characteristics are deteriorated even if the pressure difference in the furnace becomes too large. Therefore, there is a proper range in the inner pressure difference between the subsequent and the preceding, specifically, it became clear that 0 mm H 2 _O than 7mmH 2 _O following ranges is appropriate.

Although the reason why such a result is obtained is not sufficiently clear, the inventors consider as follows.
In the previous stage of the soaking process of the decarburization annealing, the atmosphere gas and the steel plate react to generate a trace gas. These trace gases are mainly CO ₂ due to oxidation of C in steel, H ₂ S and NH ₃ due to reaction between S and N in steel and hydrogen in the atmosphere. By such desorption of inhibitor-forming components such as S and N in the steel, the inhibitory power of the inhibitor on the steel sheet surface layer portion during the secondary recrystallization of finish annealing is reduced. Therefore, at the time of finish annealing, the inhibitor's inhibitory power remains high in the central part of the steel plate thickness, and primary grain growth is suppressed, but the inhibitor's inhibitory power is reduced in the surface layer part, so primary grain growth is accelerated. Is done. As a result, in the steel sheet surface layer portion, the growth of crystal grains deviated from the Goss orientation is suppressed, and crystal grains aligned in the Goss orientation inside the steel plate can grow. Therefore, good magnetic properties can be obtained.

However, if the pressure in the furnace in the latter stage is lower than that in the former stage, the atmosphere gas in the former stage flows into the latter stage, so that trace gas components such as CO ₂ , H ₂ S, and NH ₃ generated in the former stage enter the steel sheet again. And the inhibitory power of the inhibitor in a surface layer part will be strengthened. Therefore, as described above, primary grain growth in the surface layer portion during secondary recrystallization is inhibited, so that crystal grains aligned with Goss orientation inside the steel plate can not grow, and the magnetic characteristics deteriorate.
On the other hand, if the pressure in the latter furnace is too high compared to the previous stage, the atmospheric gas does not flow from the previous stage, but conversely, the atmospheric gas flows from the latter stage to the previous stage, and the gas in the previous furnace The flow becomes uneven. As a result, changes occur in the flow rate and flow rate of the gas in the front and back surfaces and the plate width direction of the steel plate in the previous stage. Since decarburization reaction, denitrification reaction and desulfurization reaction in the decarburization annealing furnace are non-equilibrium reactions, even if the oxidizing property of the atmosphere is controlled to an appropriate value, the reaction rate is determined by the flow rate or flow rate of the atmosphere gas Changes significantly. When the flow rate or flow rate is large, the adsorption probability of H ₂ O or H _{2 in} the atmospheric gas to the steel sheet surface increases, and the reaction is promoted. Conversely, when the flow rate or flow rate is small, the reaction is delayed. Therefore, if the atmosphere gas flow becomes non-uniform, the above reaction becomes non-uniform, and the site where the reaction is suppressed has a large inhibitory suppressive force, and the site where the reaction is promoted has a small inhibitory suppressive force. As a result, the magnetic characteristics become uneven.

As described above, there is an appropriate range for the pressure difference in the furnace between the final stage of the soaking process and the stage immediately before it, and by controlling within that range, stable and excellent magnetic properties can be obtained. It is done.
Many technologies have been proposed to divide the soaking process of decarburization annealing into multiple stages, but there is no technology that focuses on the pressure difference in the furnace. Also, for example, a method for keeping the flow rate of the atmospheric gas within an appropriate range has been proposed, but since the furnace pressure is not taken into consideration, the obtained effect is not sufficient.

Next, the component composition which the steel raw material (slab) used for manufacture of the method electrical steel sheet of the present invention should have will be described.
C: 0.010-0.10 mass%
If C is less than 0.010 mass%, the grain boundary strengthening effect due to C is lost, and defects such as cracks in the slab are produced. On the other hand, when it exceeds 0.10 mass%, it becomes difficult to reduce C to 0.004 mass% or less at which no magnetic aging occurs in decarburization annealing. Therefore, the C content is preferably in the range of 0.010 to 0.10 mass%. More preferably, it is the range of 0.02-0.08 mass%.

Si: 2.5-4.5 mass%
Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. If the effect is less than 2.5 mass%, it is not sufficient. On the other hand, if it exceeds 4.5 mass%, the workability deteriorates and it becomes difficult to roll and manufacture. Therefore, the Si content is preferably in the range of 2.5 to 4.5 mass%. More preferably, it is in the range of 2.8 to 3.7 mass%.

Mn: 0.01 to 0.50 mass%
Mn is an element necessary for improving the hot workability of steel. If the effect is less than 0.01 mass%, it is not sufficient. On the other hand, if it exceeds 0.50 mass%, the magnetic flux density of the product plate decreases. Therefore, the Mn content is preferably in the range of 0.01 to 0.50 mass%. More preferably, it is the range of 0.02-0.20 mass%.

About components other than the said C, Si, and Mn, in order to produce secondary recrystallization, it differs with the case where an inhibitor is utilized, and the case where it does not use.
First, in the case where an inhibitor is used to cause secondary recrystallization, for example, when an AlN-based inhibitor is used, Al and N are respectively added to Al: 0.01 to 0.04 mass%, N: 0. It is preferable to make it contain in the range of 003-0.015 mass%. Moreover, when utilizing a MnS * MnSe type | system | group inhibitor, it is preferable to contain 1 type or 2 types in S: 0.002-0.030 mass% and Se: 0.003-0.030 mass%. Moreover, as an inhibitor, you may use together an AlN type | system | group and a MnS * MnSe type | system | group, In that case, Al: 0.01-0.04mass%, N: 0.003-0.015mass%, S: 0.002 It is preferable to contain -0.030 mass% and / or Se: 0.003-0.030 mass%. When the content is less than the lower limit, the inhibitor effect cannot be sufficiently obtained. On the other hand, when the content exceeds the upper limit, the inhibitor-forming component remains undissolved during slab heating, resulting in a decrease in magnetic properties. .

  On the other hand, when an inhibitor is not used to cause secondary recrystallization, the content of Al, N, S and Se, which are the above-described inhibitor forming components, is reduced as much as possible, Al: less than 0.010 mass%, N : It is preferable to use a steel material reduced to less than 0.005 mass%, S: less than 0.005 mass%, and Se: less than 0.005 mass%.

  The balance other than the above components in the steel material used in the present invention is basically Fe and inevitable impurities. However, in addition to the above components, the steel material used in the present invention has Ni: 0.010 to 0.5 mass%, Cr: 0.01 to 0.50 mass%, and Cu: 0.01 for the purpose of improving magnetic properties. -0.50 mass%, P: 0.005-0.50 mass%, Sb: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, Mo: 0.005-0.100 mass%, B: 0.0002-0.0025 mass%, Te: 0.0005-0.0100 mass%, Nb: 0.0010-0.0100 mass%, V: 0.001- One or more selected from 0.010 mass%, Ti: 0.001 to 0.010 mass%, and Ta: 0.001 to 0.010 mass%, as appropriate It may have.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
After the steel having the above-described composition is melted by a conventional refining process, a steel material (slab) may be manufactured by a conventionally known ingot-lump rolling method or continuous casting method. Alternatively, a thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method. According to a conventional method, the slab is heated to a temperature of about 1400 ° C. when it contains an inhibitor-forming component, and is heated to a temperature of about 1250 ° C. when it does not contain an inhibitor-forming component. After that, hot rolling is performed to obtain a hot-rolled sheet having a predetermined thickness. In addition, when not containing an inhibitor formation component, you may use for a hot rolling immediately after casting, without heating. Further, in the case of a thin cast slab, hot rolling may be performed, or hot rolling may be omitted.

  Next, the hot-rolled sheet obtained by hot rolling is subjected to hot-rolled sheet annealing as necessary. The soaking temperature of this hot-rolled sheet annealing is preferably in the range of 800 to 1150 ° C. in order to obtain good magnetic properties. If the temperature is less than 800 ° C., the effect of hot-rolled sheet annealing becomes insufficient, the band structure formed by hot rolling remains, and it becomes difficult to obtain a primary recrystallization structure of sized grains, so the development of secondary recrystallization May be inhibited. On the other hand, if the temperature exceeds 1150 ° C., the crystal grains after hot-rolled sheet annealing become too coarse, and it is also difficult to obtain a primary recrystallized structure of sized grains.

  The hot-rolled sheet after the hot rolling or after the hot-rolled sheet annealing is cold-rolled twice or more across one cold rolling or intermediate annealing to obtain a cold-rolled sheet having a final thickness. The soaking temperature of the intermediate annealing is preferably in the range of 900 to 1200 ° C. If it is less than 900 ° C., the recrystallized grains after the intermediate annealing become fine and the Goss nuclei in the primary recrystallized structure decrease, so that the magnetic properties of the product plate tend to deteriorate. On the other hand, when it exceeds 1200 ° C., the crystal grains become too coarse as in the case of hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of grain size.

  In addition, the rolling (final cold rolling) which makes the final sheet thickness in the cold rolling is a warm rolling in which the steel plate temperature during the cold rolling is increased to 100 to 300 ° C., or during the cold rolling. An aging treatment is preferably performed once or a plurality of times at a temperature of 100 to 300 ° C. This improves the primary recrystallization texture and further improves the magnetic properties.

Next, the cold-rolled sheet having a final thickness is subjected to decarburization annealing that also serves as primary recrystallization annealing including a heating process, a soaking process, and a cooling process. Here, the most important thing in the present invention is to divide the soaking process into two or more stages, and prevent the furnace atmosphere gas in the stage immediately before the final stage from flowing into the furnace of the final stage, and the steel sheet surface layer The pressure in the furnace atmosphere (in-furnace pressure) of each stage is controlled to satisfy a specific relationship in order to optimize the suppression power of the inhibitor. Specifically, the pressure in the last The difference from the in-furnace pressure in the second stage (the in-furnace pressure in the last stage−the in-furnace pressure in the stage immediately before the last stage) is controlled to be in the range of 0 mmH ₂ O to 7 mmH ₂ or less. If the above difference is less than 0 mmH ₂ O, the atmospheric gas in the furnace immediately before the final stage flows into the final stage furnace, which causes deterioration of magnetic characteristics. On the other hand, if it exceeds 7 mmH ₂ O, the atmospheric gas in the final stage flows into the furnace immediately before the final stage, the gas flow in the furnace becomes non-uniform, and this also causes variations in magnetic properties. . The pressure difference is preferably 0 mm H ₂ O than 5mmH ₂ O, and more preferably not more than 0 mm H ₂ O than 3mmH ₂ O. The pressure (absolute value) in the furnace of each stage of the soaking furnace is not particularly limited, but from the viewpoint of preventing the outside air from entering the furnace, each stage is about 1 to 50 mm H ₂ O. In general, the present invention has no problem within this range.

  In the present invention, in the heating process of the decarburization annealing, the secondary recrystallized grains are refined and the iron loss characteristics are further improved, so that the heating rate between 500 and 700 ° C. is 50 ° C./s or more. It is preferable to More preferably, it is 80 ° C./s or more.

  In addition, when performing the rapid heating of 50 degreeC / s or more in the said heating process, you may perform the retention process hold | maintained for 0.5 to 10 second at any temperature between 300-500 degreeC in the middle of the heating. . This retaining treatment has an effect that the texture is further improved and the secondary recrystallized grains are refined.

  The soaking temperature in the soaking process is in the range of 780 to 950 ° C. in all the soaking processes. If it is lower than 780 ° C., decarburization will be insufficient, and primary recrystallized grains will have insufficient grain growth. On the other hand, when the temperature exceeds 950 ° C., decarburization may be insufficient, or primary recrystallized grains may grow excessively, resulting in secondary recrystallization failure. More preferably, it is in the range of 800 to 930 ° C.

  Moreover, the soaking process of the said decarburization annealing sets the soaking time from soaking to the front | former stage of the last stage to the range of 80-200 s. If it is less than 80 seconds, decarburization may be insufficient, or primary recrystallized grains may be insufficiently grown. On the other hand, if it exceeds 200 s, the primary recrystallized grains may grow too much and cause secondary recrystallization failure. More preferably, it is in the range of 90 to 150 s.

  The soaking time at the final stage when the soaking process is divided into two or more stages is in the range of 5 to 40 s. If it is less than 5 s, the effect of the present invention is small. On the other hand, if it exceeds 40 s, the form of the internal oxide layer may change and the magnetic characteristics may become unstable. More preferably, it is in the range of 10 to 35 s.

  The soaking temperature in the final stage when the soaking process is divided into two or more stages is adjusted within the above range, but the inhibitory power of the inhibitor on the steel sheet surface layer is moderately reduced to achieve magnetic properties. From the viewpoint of further improving the temperature, it is preferable that the temperature is higher than the soaking temperature immediately before the final stage and is set to a higher temperature within the above temperature range, specifically in the range of 800 to 950 ° C. Conversely, from the viewpoint of preventing the picking up of the steel sheet by the pickup, the soaking temperature in the final stage is preferably lower than that in the preceding stage.

Further, the atmosphere in the furnace in the soaking process of the decarburizing annealing is a wet hydrogen atmosphere, and the average of the oxygen potentials P _H2O / P _H2 in all the soaking processes is controlled in the range of 0.25 to 0.50. preferable. If the average of P _H2O / _PH2 is less than 0.25, there is a risk of decarburization failure. On the other hand, if it exceeds 0.50, a peroxide film containing FeO is formed on the surface of the steel sheet, which causes a detrimental effect that the forsterite film deteriorates. More preferred _P H2O _{/ P H2,} is in the range of 0.30 to 0.48.

Note that the atmosphere when the soaking process is divided into two or more stages may be controlled separately if the average P _H2O / P _H2 of the entire soaking process is within the above range. However, in this case, P _H2O / P _H2 of each stage is 0.58 at the maximum. This is because if it exceeds 0.58, FeO is formed on the surface of the steel sheet, resulting in significant deterioration of the coating properties.

In addition, when the soaking process is divided into two or more stages, the atmosphere of the final stage is a reducing atmosphere with an oxygen potential P _{H 2 O 2} / P _{H 2} of 0.20 or less, and in this atmosphere, 800 to 950 ° C. You may perform the reduction process hold | maintained for 5 to 40 seconds at temperature. By this reduction treatment, the form of the internal oxide layer formed on the surface layer portion of the steel sheet is densified, which is advantageous for improving magnetic characteristics and film characteristics. In this case, more preferable P _H2O / P _H2 is 0.15 or less.

The steel sheet subjected to the above decarburization annealing is then applied with an annealing separator mainly composed of MgO on the surface of the steel sheet, dried, then subjected to finish annealing, and a secondary recrystallized structure highly accumulated in the Goss orientation. The forsterite film is formed.
In addition, in order to improve a film characteristic and a magnetic characteristic, you may contain a well-known additive in the said annealing separation agent.
Further, in the present invention, chloride is added as an additive to the above-mentioned annealing separator mainly composed of MgO, or an annealing separator mainly composed of Al ₂ O ₃ is used instead of the annealing separator mainly composed of MgO. Or the forsterite film may not be formed.

  In addition, although the said finish annealing should just be performed according to a conventional method, in order to reduce the inhibitory power of the inhibitor of a steel plate surface layer moderately and to obtain a healthy secondary recrystallized grain, it is 5 to 800 to 950 degreeC temperature range. It is preferable to perform a holding process for holding for 200 hours. During the retention treatment, elements such as Mn, N, and S are discharged from the steel out of the system, and the amount of precipitates on the surface layer is reduced, so that the inhibitor's inhibitory power is moderately reduced, but the temperature is lower than 800 ° C. Then, since the diffusion rate of the above-mentioned elements in the steel is lowered, the discharge amount is small, and the inhibitor's inhibitory force reducing effect is small. On the other hand, if it exceeds 950 ° C., the effect of the retention treatment cannot be obtained because the secondary recrystallization has already been completed. More preferable holding treatment conditions are in the range of 820 to 930 ° C. × 10 to 150 hours.

  After the retention treatment for the secondary recrystallization, heating is performed following the retention treatment, or, after the retention treatment, the temperature is once lowered to a temperature of 700 ° C. or lower and then reheated at a temperature of 1120 to 1250 ° C. It is preferable to carry out a purification treatment for holding for 2 to 50 hours and for purifying the impurities in the steel and forming a forsterite film. When the temperature of the purification treatment is lower than 1120 ° C. or the holding time is shorter than 2 hours, the purification becomes insufficient. On the other hand, when the temperature of the purification treatment exceeds 1250 ° C. or the holding time is longer than 50 hours, the coil shape The steel sheet wound on the buckling buckles, causes a shape defect, and causes a decrease in yield. More preferable purification treatment conditions are in the range of 1150-1230 ° C. × 3-40 hr.

  In addition, although the temperature increase rate to the purification treatment temperature is not particularly limited, when performing the retention treatment, from the retention treatment temperature to the purification treatment temperature, regardless of the presence or absence of the temperature reduction after the retention treatment to secondary recrystallization, Moreover, when not performing a retention process, it is preferable to heat from 950 degreeC to the purification process temperature with the average temperature increase rate of 5-50 degreeC / hr. A more preferable temperature increase rate is in the range of 8 to 30 ° C / hr.

  It is preferable that the steel sheet after the finish annealing is subjected to flattening annealing and then straightened after performing water washing, brushing, pickling, etc. to remove the unreacted annealing separator adhering to the steel sheet surface. . This is because finish annealing is generally performed in a coiled state, and the steel sheet after finish annealing has coil curling flaws, so as to prevent significant deterioration in magnetic properties when used as a product plate. .

  Furthermore, when the steel plate (product plate) of the present invention is laminated and used, it is preferable to deposit an insulating coating on the surface of the steel plate in the above-described flattening annealing or in the process before or after. In particular, when emphasizing iron loss characteristics, it is preferable to apply a tension-imparting coating that imparts tension to the steel sheet as the insulating coating. In addition, when depositing a tension-imparting film, after depositing an inorganic layer on the steel sheet surface layer through a binder or by physical vapor deposition or chemical vapor deposition, depositing a tension-imparting film results in improved film adhesion. An insulating film that is excellent and has a large iron loss reduction effect can be formed.

  Moreover, in order to further reduce the iron loss, it is preferable to perform a magnetic domain fragmentation process. As a method of subdividing the magnetic domain, a method of forming a groove in a final product plate, a method of introducing linear or point-like thermal strain or impact strain by laser irradiation or plasma irradiation, and a final plate are generally used. In a step after cold rolling to a thickness, a method of forming a groove by etching the steel plate surface can be used.

C: 0.060 mass%, Si: 3.25 mass%, Mn: 0.07 mass%, Al: 0.026 mass%, N: 0.009 mass%, Se: 0.025 mass% and Sb: 0.05 mass% And a steel slab of the component composition of which the balance is Fe and unavoidable impurities is produced by continuous casting, heated to a temperature of 1410 ° C., and hot-rolled to form a hot-rolled sheet having a thickness of 2.5 mm, 1000 After hot-rolled sheet annealing at 50 ° C for 50 seconds, primary cold rolling to an intermediate thickness of 1.8 mm, intermediate annealing at 1100 ° C for 20 seconds, and secondary cold rolling to final A cold-rolled sheet having a thickness of 0.23 mm was used.
Next, the cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing. At this time, the heating process of the decarburization annealing is performed by heating from room temperature to a soaking temperature in a wet hydrogen atmosphere having an oxygen potential of P _H2O / P _H2 : 0.40 at a heating rate of 50 ° C./s. The process was divided into two stages, a front stage and a rear stage, and the soaking temperature, soaking time, and oxygen potential P _H2O / P _H2 of the atmosphere were variously changed as shown in Table 1.
Then, the steel sheet after decarburizing annealing applies an annealing separator mainly composed of MgO on the surface of the steel sheet and dries it, and then heats from room temperature to 1180 ° C. at an average temperature rising rate of 20 ° C./hr. Then, after the secondary recrystallization was completed by continuous heating without holding treatment in the heating, finishing annealing was performed to perform a purification treatment of 1180 ° C. × 10 hr. The atmosphere gas for the finish annealing was H _{2 at} the time of 1180 ° C. holding for the purification treatment, and Ar at the time of other temperature rise, at the time of the holding treatment and at the time of temperature drop.

Ten specimens each having a width of 100 mm in the width direction of the steel sheet were collected from the steel sheet after finish annealing obtained as described above under each condition, and the magnetic flux density B ₈ and iron loss W ₁₇ were measured by the method described in JIS C2556. _{/ 50} was measured and the average value was obtained. The results are also shown in Table 1. From the table, the pressure difference in the furnace of the latter stage (final stage) of the soaking process of the decarburization annealing and the stage immediately before it (the pressure in the furnace of the final stage-the pressure in the furnace of the stage just before the final stage) It can be seen that by controlling to (over 0 mmH ₂ O to 7 mmH ₂ O or less), the magnetic characteristics, particularly the iron loss characteristics are greatly improved. Furthermore, it can be seen that a grain-oriented electrical steel sheet with more excellent magnetic properties can be obtained by optimizing other soaking conditions for decarburization annealing.

C: 0.055 mass%, Si: 3.35 mass%, Mn: 0.07 mass%, Al: 0.021 mass%, N: 0.007 mass% and Cu: 0.05 mass%, the balance being Fe and unavoidable A steel slab of the component composition consisting of chemical impurities is manufactured by continuous casting, heated to a temperature of 1390 ° C., and then hot rolled to form a hot-rolled sheet with a thickness of 2.0 mm, hot-rolled at 1030 ° C. × 10 seconds After the plate annealing, it was cold-rolled to finish a cold-rolled sheet having a final sheet thickness of 0.23 mm.
Next, the cold-rolled sheet was subjected to decarburization annealing that also served as primary recrystallization annealing. Under the present circumstances, the heating process of decarburization annealing heated from room temperature to 700 degreeC with the temperature increase rate of 80 degreeC / s. In the soaking process, the soaking time is 120 seconds, which is divided into two stages of 90 seconds in the former stage and 30 seconds in the latter stage. The former stage has a soaking temperature of 850 ° C. and the atmosphere is an oxygen potential P _H2O / P. _H2 is a wet hydrogen atmosphere of 0.39, the latter stage is a soaking temperature of 890 ° C., the atmosphere is a dry atmosphere of oxygen potential P _H2O / P _H2 : 0.15, and the furnace pressure in the latter stage is higher than that in the previous stage. It adjusted so that it might become ₂ mmH2O high.
Next, the steel sheet after the decarburization annealing was subjected to finish annealing after applying an annealing separator mainly composed of MgO to the steel sheet surface. At this time, after the above-mentioned finish annealing is heated at an average temperature rising rate of 25 ° C./hr to the holding treatment temperature shown in Table 2, the holding treatment for holding holding treatment time also shown in Table 2 is performed to carry out secondary recrystallization. After completion, heating was continued at an average temperature increase rate of 25 ° C./hr up to a temperature of 1230 ° C., and the temperature was maintained for 3 hrs for purification treatment. The atmosphere gas is a mixed gas of N ₂ until the end of the holding process and 75 vol% H ₂ + 25 vol% N ₂ from the holding process to the purification process temperature (if not subjected to the holding process, N ₂ from room temperature to 880 ° C.) , At 880 ° C., the gas was switched to a mixed gas of 75 vol% H ₂ +25 vol% N ₂ ), H ₂ during the purification treatment, Ar up to 1100 ° C. during cooling, and N ₂ thereafter. In addition, about a part of steel plate, after holding treatment at a temperature of 900 ° C., the temperature is temporarily lowered to a temperature of 700 ° C. or less, and then heated at a temperature rising rate of 25 ° C./hr to a temperature of 1230 ° C. The purification treatment was performed while maintaining the temperature for 3 hours.

Ten specimens each having a width of 100 mm in the width direction of the steel sheet were collected from the steel sheet after finish annealing obtained as described above under each condition, and the magnetic flux density B ₈ and iron loss W ₁₇ were measured by the method described in JIS C2556. _{/ 50} was measured and the average value was obtained. The results are also shown in Table 2. From the table, after controlling the pressure difference in the furnace in the soaking process in the decarburizing annealing to an appropriate range, the temperature and time in the holding treatment of the finish annealing are controlled in an appropriate range, thereby achieving high magnetic flux density and low iron loss. It can be seen that a grain-oriented electrical steel sheet having excellent magnetic properties is obtained. Moreover, it turns out that the same outstanding effect as the above is acquired also on the conditions which temperature-reduced once after a retention process, and was reheated and refine | purified after that.

Steel slabs having various component compositions shown in Table 3 were manufactured by a continuous casting method, heated to a temperature of 1420 ° C., and then hot-rolled to form a hot-rolled sheet having a thickness of 2.2 mm, 1050 ° C. × 20 After performing hot-rolled sheet annealing for 2 seconds, it was cold-rolled to finish a cold-rolled sheet having a final sheet thickness of 0.23 mm, and then subjected to decarburization annealing that also served as primary recrystallization annealing.
Here, in the decarburization annealing, the heating process was performed from room temperature to 600 ° C. at an average temperature increase rate of 200 ° C./s and from 600 to 700 ° C. at an average temperature increase rate of 60 ° C./s. In the soaking process, the soaking temperature is set to 800 ° C., the soaking time is set to 100 s, and the above soaking time is divided into 60 seconds of the former stage and 40 seconds of the latter stage. a wet hydrogen atmosphere of _{P H2O} / P _H2 0.36, subsequent to a dry atmosphere having an oxygen potential _P H2O _{/ P H2} of 0.10, and, 3mmH ₂ O is higher as than preceding the furnace pressure in the subsequent stage It was adjusted.
Next, the steel sheet after the decarburization annealing was subjected to finish annealing after applying an annealing separator mainly composed of MgO to the steel sheet surface. At this time, the above-mentioned finish annealing is carried out by heating from room temperature to 900 ° C. at a temperature rising rate of 30 ° C./hr in Ar atmosphere, and then holding for 70 hours at 900 ° C. in Ar atmosphere to perform secondary recrystallization. Is completed and then heated from 900 ° C. to 1150 ° C. under a H ₂ atmosphere at a temperature rising rate of 15 ° C./hr, and then maintained for 8 hours at a temperature of 1150 ° C. under a H ₂ atmosphere. After application, it was cooled in an Ar atmosphere.

Ten specimens each having a width of 100 mm in the width direction of the steel sheet were collected from the steel sheet after finish annealing obtained as described above under each condition, and the magnetic flux density B ₈ and iron loss W ₁₇ were measured by the method described in JIS C2556. _{/ 50} was measured and the average value was obtained. The results are also shown in Table 3. From the same table, using a slab with a composition suitable for the present invention as a raw material, optimizing the pressure in the furnace during the soaking process of decarburization annealing, and further optimizing the finish annealing conditions, high magnetic flux density and low iron loss It can be seen that a grain-oriented electrical steel sheet having excellent magnetic properties is obtained.

Claims (6)

C: steel containing 0.010 to 0.10 mass%, Si: 2.5 to 4.5 mass%, Mn: 0.01 to 0.50 mass%, with the balance being composed of Fe and inevitable impurities The material is hot-rolled to form a hot-rolled sheet, and after the hot-rolled sheet is subjected to hot-rolled sheet annealing or without being subjected to hot-rolled sheet annealing, it is cold-rolled at least once with intermediate annealing. A series of cold-rolled sheets with the final sheet thickness, and after decarburization annealing also serving as primary recrystallization annealing consisting of heating process, soaking process and cooling process, and then applying annealing separator to the steel sheet surface and finishing annealing In the method for producing a grain-oriented electrical steel sheet comprising the steps of:
The soaking process of the above decarburization annealing is carried out so that the soaking temperature of the whole area is in the range of 780 to 950 ° C., and the average oxygen potential PH _{2 O 2} / P _{H 2} of the atmosphere of the whole area is in the range of 0.25 to 0.50. As well as control
The soaking process is divided into two or more stages, the total soaking time from the start of soaking to the preceding stage of the last stage is 80 to 200 seconds, the soaking time of the last stage is in the range of 5 to 40 seconds, characterized by controlling the - (furnace pressure in the final stage immediately before the stage furnace pressure in the last stage) to 0 mm H 2 _O than 7mmH 2 _O the range difference furnace pressure and furnace pressure of the immediately preceding stage A method for producing a grain-oriented electrical steel sheet. The final stage of the soaking process of the decarburizing annealing is characterized in that a reduction treatment is performed at a temperature of 800 to 950 ° C. in an atmosphere under an oxygen potential P _{H 2 O} / P _{H 2} of 0.20 or less. A method for producing the grain-oriented electrical steel sheet according to 1. In the above-mentioned finish annealing, after holding for 5 to 200 hours in the temperature range of 800 to 950 ° C. and secondary recrystallization, it is continuously heated, or once cooled to 700 ° C. or less and then reheated, 1120 ° C. or more The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein a purification treatment is performed for 2 hours or more at a temperature of 3. In addition to the above component composition, the steel material further contains Al: 0.010 to 0.04 mass% and N: 0.003 to 0.015 mass%, or
Contains Se: 0.003-0.030 mass% and / or S: 0.002-0.030 mass%, or
Al: 0.010 to 0.04 mass%, N: 0.003 to 0.015 mass%, Se: 0.003 to 0.030 mass% and / or S: 0.002 to 0.030 mass% The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3. The steel material further contains Al: less than 0.010 mass%, N: less than 0.005 mass%, S: less than 0.005 mass%, and Se: less than 0.005 mass% in addition to the above component composition. The manufacturing method of the grain-oriented electrical steel sheet according to any one of claims 1 to 3. In addition to the above component composition, the steel material further includes Ni: 0.010 to 0.5 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.00. 005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0.005 to 0.100 mass% , B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.0100 mass%, Nb: 0.0010 to 0.0100 mass%, V: 0.001 to 0.010 mass%, Ti: 0.001 It contains 1 type or 2 types or more chosen from -0.010mass% and Ta: 0.001-0.010mass% of Claims 1-5 characterized by the above-mentioned. Method for producing a grain-oriented electrical steel sheet according to item 1 Zureka.

Images