RU2784933C1 - Method for producing a sheet of electrotechnical steel with oriented grain structure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely, to a method for manufacturing a sheet of electrotechnical steel with an oriented grain structure, used as the material of iron cores of transformers. Method involves the production of a silicon steel material containing, wt.%: Si: 0.8 to 7.0, C: 0.085 or less, acid-soluble Al: 0.010 to 0.065, N: 0.004 to 0.012, Mn: 1.00 or less, S: 0.050 or less, one or both from Sn and Sb: in total 0.01 to 0.20; if necessary, at least one element from the group consisting of the following: Cr: 0.02 to 0.50, Cu: 0.4 or less, P: 0.5 or less, Ni: 1.0 or less, B: 0.008 or less, V: 0.15 or less, Nb: 0.20 or less, Mo: 0.10 or less, Ti: 0.015 or less, Bi: 0.010 or less, the rest Fe and impurities. The resulting material is subjected to hot rolling in order to create a hot-rolled sheet. Cold rolling is performed in order to create a steel sheet of end thickness by single-stage or multi-stage cold rolling with intermediate stages of annealing. Decarbonising annealing is performed using a decarbonising annealing furnace containing a heating area and a sustaining area, wherein the degree of oxidation P1 of the gas atmosphere in the heating area and the degree of oxidation P2 of the gas atmosphere in the sustaining area satisfy the following ratios: 0.01<P1≤0.15, 0.01≤ P2<0.15, and P1>P2. An annealing separator containing aluminium oxide as the base component is applied to the steel sheet, and then the sheet is subjected to final annealing.

EFFECT: created sheet exhibits high magnetic properties.

3 cl, 1 dwg, 6 tbl, 6 ex

Description

The field of technology to which the invention belongs

[0001] The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.

Priority is claimed from Japanese Patent Application No. 2019-005060, filed January 16, 2019, the contents of which are hereby incorporated by reference.

Prior Art

[0002] Grain-oriented electrical steel sheets are soft magnetic materials and are mainly used as a material for iron cores of transformers. For this reason, grain-oriented electrical steel sheets must have magnetic properties such as high magnetization performance and low steel loss. The magnetization characteristics include the magnetic flux densities induced by excitation of the iron core. With an increase in the magnetic flux density, it is possible to reduce the size of the iron cores, which is advisable both from the point of view of the design of transformers and from the point of view of the cost of manufacturing transformers.

[0003] In order to improve the magnetization performance, it is necessary to adjust the texture to achieve a crystal orientation (Goss orientation) in which the {110} plane is oriented parallel to the surface of the steel sheet and the <100> axis is oriented in the rolling direction. To accumulate crystals in the Goss orientation, inhibitors such as AlN, MnS and MnSe are commonly used in steel, forming fine precipitates that allow control of secondary recrystallization.

[0004] In addition, the required magnetic properties are high magnetic flux density (expressed by the magnetic flux density value B8 when applying a magnetic field of 800 A/m) and low steel loss (expressed by the energy loss W _17/50 (W/kg) with density magnetic flux of 1.7 tesla (T) at a frequency of 50 hertz (Hz)).

[0005] Steel loss is the loss of energy expended in the form of thermal energy when the iron cores are excited by AC magnetic fields. To save energy, steel losses should be as low as possible. The level of loss in steel is affected by magnetic susceptibility, sheet thickness, film tension, amount of impurities, electrical resistivity, grain size, magnetic domain size, etc. At present, with the development of various technologies for the production of electrical steel sheets, research and development is constantly being carried out to reduce steel losses in order to improve energy efficiency.

[0006] Patent Document 1 (Japanese Examined Patent Application Second Publication No. S58-26405) discloses a method for reducing steel loss by irradiating a finish annealed steel sheet with a laser beam to cause the steel sheet to be slightly deformed so that magnetic domains are separated when using a sheet of electrical steel as a lamellar iron core.

[0007] In addition, Patent Document 2 (Japanese Unexamined Patent Application, First Publication No. S62-86175) describes a method in which the magnetic domain reduction effect does not disappear even if an electrical steel sheet is processed to obtain an iron core and then stress relief annealing, where electrical steel sheet is used for a stranded iron core. When dividing magnetic domains with the help of these technical means, losses in steel are significantly reduced.

[0008] However, the inventors of the present invention, while observing the movement of the magnetic domain as it was separated as described above, found that some of the magnetic domains did not move. Therefore, the inventors of the present invention have come to the conclusion that, in order to further reduce the amount of loss in the steel of the grain-oriented electrical steel sheet, it is as important as separating the magnetic domains to eliminate the pinning effect that prevents the movement of the magnetic domain, which is caused by the glass film on the surface. steel sheet.

[0009] In order to facilitate the movement of the magnetic domain as described above, it is expedient that no glass film is formed on the surface of the steel sheet. To solve this problem, Patent Document 3 (US Patent Specification No. 3,785,882) proposes a method for preventing the formation of a glass film on the surface of a steel sheet using high purity coarse alumina as an annealing separator. However, this method is not able to eliminate inclusions directly below the surface, and the limit of improvement in the steel loss index is no more than 2% at W _15/60 .

[0010] Patent Document 4 (Japanese Unexamined Patent Application, First Publication No. S64-83620) discloses a method for performing chemical polishing or electrolytic polishing after finishing annealing as a method for controlling inclusions just below the surface and providing a mirror-like surface finish. However, although this method allows chemical polishing and electropolishing of a material sample to be carried out at the laboratory level, problems regarding the control of the concentration and temperature of the chemical solution and the installation of pollution control equipment or the like must be solved in order to be carried out on an industrial scale. In addition, in terms of performance, this method is very difficult to implement in practice.

[0011] As a method for solving this problem, Patent Document 5 (Japanese Unexamined Patent Application First Publication No. H07-118750) discloses a method in which decarburization annealing is performed in a gas atmosphere having an oxidation state in which oxides based on iron (Fe ₂ SiO ₄ , FeO, etc.), and aluminum oxide is used as an annealing separator between sheets. However, it is clear that even if this process is carried out on an industrial scale, it would be difficult to obtain good magnetic properties with stable decarburization.

List of cited documents

Patent Documents

[0012] Patent Document 1 - Examined Japanese Patent Application Second Publication No. S58-026405

Patent Document 2 - Japanese Unexamined Patent Application First Publication No. S62-86175

Patent Document 3 - Description of US Patent No. 3,785,882.

Patent Document 4 - Japanese Unexamined Patent Application First Publication No. S64-083620.

Patent Document 5 - Japanese Unexamined Patent Application, First Publication No. H07-118750.

The essence of the invention

Technical task

[0013] The present invention has been made in view of the above problems, and its object is to provide a method for manufacturing a grain-oriented electrical steel sheet having good magnetic properties while satisfactorily performing decarburization in a decarburization annealing process.

The solution of the problem

[0014] (1) A method for manufacturing a grain-oriented electrical steel sheet, including: a process for producing a silicon steel material to obtain a silicon steel material; a hot rolling process for producing a hot rolled sheet in which the silicon steel material is subjected to hot rolling; a cold rolling process for producing a steel sheet of a finite thickness, in which the hot-rolled sheet is subjected to one cold rolling process or several cold rolling processes with intermediate annealing performed between the cold rolling processes; a decarburization annealing process in which a steel sheet is subjected to a decarburization annealing process; and a finish annealing process in which an annealing separator containing alumina as a main component is applied to the steel sheet, and then the steel sheet is finish annealed, wherein the silicon steel material contains, by mass .%: Si: 0.8 to 7.0%; C: 0.085% or less; acid soluble Al: 0.010 to 0.065%; N: 0.004 to 0.012%; Mn: 1.00% or less; S: 0.050% or less; one or both of Sn and Sb: 0.01 to 0.20% in total, and the balance: Fe and impurities.

[0015] (2) In the method for manufacturing grain-oriented electrical steel sheet according to (1), the decarburization annealing process may include: performing decarburization annealing using a decarburization annealing furnace comprising a heating zone and a holding zone, an oxidation state P1 of the gaseous atmosphere in the heating zone satisfies the following expression 1, and the oxidation state P2 of the gas atmosphere in the holding zone satisfies the following expression 2:

0.01≤P1≤0.15 (expression 1) and

0.01≤P2≤0.15 (expression 2).

[0016] (3) In the method for manufacturing grain-oriented electrical steel sheet according to (1) or (2), the silicon steel material may further contain, in wt %, Cr: 0.02 to 0.50%.

[0017] (4) In the manufacturing method of grain-oriented electrical steel sheet according to (2) or (3), the above P1 and P2 may satisfy the following expression 3:

P1>P2 (expression 3).

[0018] (5) In the method for manufacturing grain-oriented electrical steel sheet according to any of (1) to (4), the silicon steel material may further contain, in wt %: Cu: 0% or more to 0, 4% or less; P: 0% or more to 0.5% or less; Ni: 0% or more to 1.0% or less; B: 0% or more to 0.008% or less; V: 0% or more to 0.15% or less; Nb: 0% or more to 0.20% or less; Mo: 0% or more to 0.10% or less; Ti: 0% or more to 0.015% or less; and Bi: 0% or more to 0.010% or less.

[0019] (6) In the method for manufacturing the grain-oriented electrical steel sheet according to any of (1) to (5), the method for manufacturing the grain-oriented electrical steel sheet may further include a nitriding treatment process conducted in the period starting before the process of decarburizing annealing and ending before the start of secondary recrystallization in the process of finishing annealing.

[0020] (7) In the manufacturing method of the grain-oriented electrical steel sheet according to any one of (1) to (6), the manufacturing method of the grain-oriented electrical steel sheet may further include: a hot annealing process ( hot strip annealing) in which the hot-rolled sheet obtained in the hot rolling process is subjected to annealing after the hot rolling process and before the cold rolling process.

Invention Effects

[0021] According to the above aspect of the present invention, it is possible to provide a method for producing a grain-oriented electrical steel sheet having good magnetic properties while satisfactorily performing decarburization in decarburization annealing.

Brief description of the drawings

[0022] FIG. 1 is a flowchart for explaining a manufacturing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Embodiments of the invention

[0023] Although the studies described above were carried out in order to improve the magnetic properties of the grain-oriented electrical steel sheet in the prior art, there still remain problems to be solved, such as those mentioned above.

In order to solve these problems, the inventors of the present invention carried out various experiments. As a result, it has been found that by including an appropriate amount of Sn and/or Sb in the steel composition, it is possible to produce a grain-oriented electrical steel sheet with good magnetic properties if the decarburization is performed satisfactorily. In addition, it has been found that this effect is improved by adjusting the oxidation state (P _H2O /P _H2 ) of the gas atmosphere in the heating region and the holding region in the decarburization annealing process.

[0024] Next, preferred embodiments of the present invention will be described. It is understood that the present invention is not limited to the chemical compositions disclosed in these embodiments, and various modifications are possible without departing from the spirit of the present invention.

It is also understood that the independent elements of the following embodiments may be combined with each other within the scope of the present invention.

[0025] In addition, in the following embodiments, the numerically limited range includes a lower limit value and an upper limit value. However, numerical values indicated using the term "superior" and the expression "less than" are not included in this numerical range.

In addition, unless otherwise indicated, "%" of a chemical component in the following embodiments means "wt.%".

[0026] Next, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described.

[0027] A method for manufacturing a grain-oriented electrical steel sheet according to the following embodiments includes: a silicon steel material manufacturing process to obtain a silicon steel material; a hot rolling process for producing a hot rolled sheet by hot rolling a silicon steel material; a cold rolling process for producing a steel sheet of a finite thickness, in which the hot-rolled sheet is subjected to one cold rolling process or several cold rolling processes with intermediate annealing performed between the cold rolling processes; a decarburization annealing process in which a steel sheet is subjected to decarburization annealing; and a finish annealing process in which an annealing separator containing alumina as a main component is applied to the steel sheet and subjected to finish annealing of the steel sheet, wherein the silicon steel material contains in wt % : Si: 0.8 to 7.0%; C: 0.085% or less; acid soluble Al: 0.010 to 0.065%; N: 0.004 to 0.012%; Mn: 1.00% or less; S: 0.050% or less; one or both Sn and Sb: total 0.01 to 0.20%; the rest: Fe and impurities. In addition, in the method for manufacturing grain-oriented electrical steel sheet according to the above-described embodiment, a hot strip annealing process can be further provided in which the hot-rolled sheet obtained in the hot rolling process can be further annealed after the hot rolling and before the cold rolling process. .

[0028] Chemical components of silicon steel material

With an increase in the Si content, the electrical resistance increases and the losses in the steel improve. However, if the Si content exceeds 7.0%, cold rolling becomes extremely difficult and the steel material may crack during rolling. For this reason, the upper limit of the Si content is 7.0%. Preferably, the upper limit of the Si content is 4.5% and more preferably 4.0%.

In addition, if the Si content is less than 0.8%, γ-transformation occurs during finish annealing and the crystal orientation of the steel sheet deteriorates. For this reason, the lower limit of the Si content is 0.8%. Preferably, the lower limit of the Si content is 2.0%, and more preferably 2.5%.

[0029] C is an element that effectively regulates the primary recrystallization structure, but adversely affects the magnetic properties. Therefore, before finishing annealing, it is necessary to remove C by performing a decarburization process.

If the content of C in the silicon steel material is more than 0.085%, the decarburization annealing time increases and the productivity of the industrial process decreases. For this reason, the upper limit of the C content is 0.085%. More preferably, the upper limit of the C content is 0.070%.

[0030] In the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, acid-soluble Al is an important element for acting as an inhibitor when binding to N in the form of (Al, Si)N. The content of acid-soluble Al, at which the secondary recrystallization is stable, is from 0.010 to 0.065%.

Preferably, the lower limit of the content of acid-soluble Al is 0.020% and more preferably 0.025%. Preferably, the upper limit of the content of acid-soluble Al is 0.040% and more preferably 0.030%.

[0031] If the N content exceeds 0.012%, voids called bubbles occur in the steel sheet during cold rolling. Therefore, it is desirable that the N content does not exceed 0.012%. In addition, in order to bind to Al and act as an inhibitor, the N content must be 0.004% or more. The lower limit of the N content is preferably 0.006%, more preferably 0.007%. The upper limit of the N content is preferably 0.010% and more preferably 0.009%.

[0032] Mn and S are desirably added in a range satisfying Mn/(S+Se)≥4 to prevent hot rolling cracks. As the Mn content increases, the saturation magnetic flux decreases. Therefore, the Mn content is preferably 1.00% or less. The S content is preferably 0.050% or less, more preferably 0.015% or less, even more preferably 0.010% or less, and even more preferably 0.007% or less.

In addition, the part S can be replaced by Se. For this reason, if Se is included, it is preferable to have S+Se: 0.050% or less, and it is desirable to set a range satisfying Mn/(S+Se)≥4.

[0033] In some cases, Mn and S can be used as inhibitors of secondary recrystallization. In these cases, the content of Mn, which ensures stable secondary recrystallization, is in the range from 0.02 to 0.30%. The lower limit of the Mn content is preferably 0.05%, more preferably 0.07%. The upper limit of the Mn content is preferably 0.15% and more preferably 0.10%. In addition, in this case, the preferred content of S is in the range of 0.010 to 0.050%. The S content is preferably 0.015% or more, more preferably 0.020% or more. Even more preferably, the S content is 0.040% or less. In addition, S can also be replaced by Se.

[0034] In the production method of Taguchi, Sakakura et al. (such as described in Examined Japanese Patent Application Second Publication No. S40-15644) Mn and S are used as secondary recrystallization inhibitors. On the other hand, in the production method of Komatsu et al. (such as described in Examined Japanese Patent Application , Second Publication No. S62-45285), Mn and S are not used as inhibitors for secondary recrystallization.

Sn and Sb are well known grain boundary segregation elements. Also, up to now, Sb and Sn in grain-oriented electrical steel sheet have been known to improve surface sealing properties and prevent oxidation in a high dew point atmosphere, but they have not been known to promote decarburization in a low dew point atmosphere.

[0036] In order to obtain the decarburizing effect of Sn and/or Sb, it is necessary that the total content of one or both of Sn and Sb be 0.01% or more. The lower limit of the total content of Sn and/or Sb is preferably 0.03%, and more preferably 0.05%. The upper limit of the total content of Sn and/or Sb is 0.20%. Even if the total content of Sn and/or Sb exceeds 0.20%, the decarburization promoting effect is substantially strong.

[0037] Cr is an element that affects the nature of the formation of the oxide layer during decarburization annealing, improves the properties of decarburization, and contributes to the subsequent smoothing of the surface. For this reason, Cr may be included. When Cr is included in the composition, its content is preferably 0.02 to 0.50%, and the effect of improving the decarburization properties is achieved. More preferably, the lower limit of the Cr content is 0.05%. In addition, more preferably, the upper limit of the Cr content is 0.39%.

[0038] Further, in this embodiment, the silicon steel material may contain an optional element in addition to the base elements and impurities described above. For example, instead of the part of iron (Fe) that makes up the rest described above, one or more optional elements from the group consisting of Cu, P, Ni, B, V, Nb, Mo, Ti and Bi.

The content of these optional elements may correspond to their purpose. Therefore, it is not necessary to limit the lower limits of the selectable elements, and the lower limits may be 0%. In addition, even if these optional elements are contained as impurities, the above effects are not impaired.

[0039] Cu: 0% or more to 0.4% or less

Copper (Cu) is an element that increases electrical resistance and reduces losses in steel. Therefore, the Cu content may be 0.4% or less. If the Cu content is higher than 0.4%, the steel loss reduction effect reaches a limit, and in some cases during hot rolling, it may cause a surface defect called "copper peel". The lower limit of the Cu content is preferably 0.05%, more preferably 0.1%. The upper limit of the Cu content is preferably 0.3%, more preferably 0.2%.

[0040] P: 0% or more and 0.5% or less

Phosphorus (P) is an element effective in increasing electrical resistance and reducing losses in steel. Therefore, the P content may be 0.5% or less. If the P content is higher than 0.5%, there may be a problem with the rollability of the silicon steel sheet in some cases. The lower limit of the P content is preferably 0.005% and more preferably 0.01%. The upper limit of the P content is preferably 0.2% and more preferably 0.15%.

[0041] Ni: 0% or more and 1.0% or less

Nickel (Ni) is an element that increases electrical resistance and reduces losses in steel. In addition, Ni is an effective element for adjusting the metallographic structure of the hot-rolled sheet and improving the magnetic properties. Therefore, the Ni content may be 1.0% or less. If the Ni content exceeds 1.0%, secondary recrystallization may be unstable in some cases. The lower limit of the Ni content is preferably 0.01%, more preferably 0.02%. The upper limit of the Ni content is preferably 0.2%, more preferably 0.1%.

[0042] B: 0% or more and 0.008% or less

Boron (B) is an element effective to exert an inhibitory effect in the form of BN. Therefore, the B content may be 0.008% or less. If the content of B exceeds 0.008%, there is a danger of deterioration of the magnetic properties. The lower limit of B content is preferably 0.0005%, more preferably 0.001%. The upper limit of the B content is preferably 0.005%, more preferably 0.003%.

[0043] V: 0% or more and 0.15% or less

Nb: 0% or more and 0.20% or less

Ti: 0% or more and 0.015% or less

Vanadium (V), niobium (Nb) and titanium (Ti) are elements effective to function as inhibitors when bound to N or C. Therefore, V, Nb and/or Ti may be contained in the ranges of 0.15% or less, 0, 20% or less and/or 0.015% or less, respectively. If these elements remain in the finished product, and the V content exceeds 0.15%, the Nb content exceeds 0.20%, or the Ti content exceeds 0.015%, there is a problem of deteriorating magnetic properties.

The lower limit of the V content is preferably 0.002% and more preferably 0.01%. The upper limit of the V content is preferably 0.10% and more preferably 0.05%.

The lower limit of the Nb content is preferably 0.005%, more preferably 0.02%. The upper limit of the Nb content is preferably 0.10% and more preferably 0.08%.

The lower limit of the Ti content is preferably 0.002%, more preferably 0.004%. The upper limit of the Ti content is preferably 0.010%, more preferably 0.008%.

[0044] Mo: 0% or more and 0.10% or less

Molybdenum (Mo) is also an effective element for increasing electrical resistance and reducing steel losses. Therefore, Mo may be contained in the range of 0.10% or less. If the Mo content exceeds 0.10%, there may be a problem with the rollability of the steel sheet in some cases. The lower limit of Mo content is preferably 0.005%, more preferably 0.01%. The upper limit of the Mo content is preferably 0.08%, more preferably 0.05%.

[0045] Bi: 0% or more and 0.010% or less

Bismuth (Bi) is an element that is effective for stabilizing excretions such as sulfides and enhancing the function as an inhibitor. Therefore, Bi may be contained in the range of 0.010% or less. If the Bi content exceeds 0.010%, the magnetic properties may deteriorate in some cases. The lower limit of the Bi content is preferably 0.001%, more preferably 0.002%. The upper limit of the Bi content is preferably 0.008%, more preferably 0.006%.

[0046] A method for manufacturing a grain-oriented electrical steel sheet

To manufacture a grain-oriented electrical steel sheet having a texture developed in the {110} <001> orientation from a silicon steel material having the above-described chemical composition, the following steps are performed.

[0047] First, molten steel having the above-described chemical composition is cast (S100) to obtain a silicon steel material and a hot-rolled sheet made from this silicon steel material by a conventional hot rolling step (S102). Alternatively, instead of the hot rolling step (S102), the liquid steel can be continuously cast to form a thin strip.

[0048] The hot-rolled sheet or continuously cast thin strip is subjected to a cold rolling step (S106) immediately or after a hot annealing step (S104).

Annealing in the hot annealing step (S104) may be performed in a temperature range of 750 to 1200° C. for a period of 30 seconds to 30 minutes.

[0049] The hot annealing step is effective in improving the magnetic properties of the article. The presence or absence of the hot annealing step can be determined according to the properties and production cost required for the final production of the grain oriented electrical steel sheet, and the hot annealing step can be omitted.

[0050] Cold rolling in the cold rolling step (S106) is performed once or repeatedly with annealing between the cold rolling steps. In the single cold rolling step, the rolling reduction is preferably 80% or more. When performing multiple cold rolling with annealing between cold rolling steps, the final cold rolling reduction after the last annealing is preferably 80% or more. The cold rolled sheet obtained in this step is a steel sheet having a final sheet thickness.

[0051] The material that has been cold rolled is subjected to a decarburization annealing step (S108) to remove the carbon contained in the steel.

[0052] In the method for manufacturing grain-oriented electrical steel sheet according to this embodiment, in the decarburization annealing step (S108), decarburization annealing is performed in a humid hydrogen atmosphere. Annealing is performed by adjusting the gas atmosphere in the decarburization annealing step (S108) to an oxidation state such that iron-based oxide (Fe) is not formed.

[0053] In the decarburization annealing step (S108), when decarburization annealing is performed using a decarburization annealing furnace comprising a heating zone and a holding zone, it is desirable that the oxidation state P1 of the gaseous atmosphere in the heating zone satisfies Expression 1:

0.01≤P1≤0.15 (Expression 1).

[0054] It is desirable that the oxidation state of the gas atmosphere P2 in the holding zone in the decarburization annealing step (S108) satisfies expression 2:

0.01≤P2≤0.15 (Expression 2).

[0055] The oxidation state P1 and the oxidation state P2 are oxidation states expressed as the ratio "P _H2O /P _H2 " of the partial pressure of water vapor to the partial pressure of hydrogen in a gas atmosphere containing hydrogen, nitrogen and water vapor.

If the oxidation state P1 of the gas atmosphere in the heating zone and the oxidation state P2 in the decarburization annealing step (S108) are determined using the above expressions 1 and 2, it is considered that Sn and/or Sb segregate on the surface during heating, changing the original oxide film on the outer surface and improving decarburization properties.

[0056] In order to apply an annealing separator containing alumina as a main component in a subsequent process for laminating a steel sheet and smoothing the surface of a steel sheet that has been finish annealed, it is desirable to carry out annealing at an oxidation state at which no oxides based on Fe (Fe ₂ SiO ₄ , FeO, etc.). For example, in the temperature range of 800 to 850°C, in which decarburization annealing is usually carried out, it is possible to suppress the formation of Fe-based oxides by adjusting the oxidation state P1 of the gas atmosphere in the heating zone and the oxidation state P2 of the gas atmosphere in the holding zone to 0.15 or less.

[0057] If the oxidation state P1 or the oxidation state P2 is greater than 0.15, inclusions are formed under the surface of the product, which prevents the loss of steel from being reduced. Meanwhile, if any of the oxidation states is too much lowered, the decarburization rate is also lowered. When both are taken into account, in this temperature range, the P1 oxidation state and the P2 oxidation state (P _H2O /P _H2 ) are preferably within the range of 0.01 to 0.15.

[0058] In addition, in order to further reduce carbon and improve the steel loss rate in the decarburization annealing process, it is even more desirable that the oxidation state P1 of the gas atmosphere in the heating zone and the oxidation state P2 of the gas atmosphere in the holding zone satisfy the following expression 3:

P1>P2 (Expression 3).

[0059] In the decarburization process, the heating rate from room temperature to the holding zone temperature (heating zone heating rate) is preferably 7°C/sec or more on average, more preferably 9°C/sec or more. If the heating rate is too slow, the decarburization properties deteriorate. There is no need to specify an upper limit, but if the heating rate is too high, it will be difficult to control the holding temperature.

[0060] The temperature of the holding zone and the residence time in the holding zone are preferably 750 to 900°C and 10 to 600 seconds. If the temperature (annealing temperature) of the holding zone is lower than 750°C, the decarburization rate decreases and the productivity decreases. On the other hand, if the temperature of the holding zone is higher than 900° C., the primary recrystallization grain size exceeds the desired size, and therefore the magnetic properties deteriorate after the finish annealing. In addition, if the residence time is less than 10 seconds, decarburization cannot be performed sufficiently. On the other hand, if the residence time exceeds 600 seconds, the performance is degraded.

[0061] In the period starting before the decarburization annealing step (S108) and ending before the start of the secondary recrystallization in the finish annealing step (S112), a nitriding treatment step (S110) may be provided.

[0062] The nitriding treatment step is not particularly limited. A method is known in which a nitride capable of being nitrided, such as ammonia, is added to an annealing separator, and so on.

For example, in the nitriding treatment step (S110), it is desirable to apply the nitriding treatment according to the production method of Komatsu et al., which uses (Al, Si)N as the main inhibitor (Japanese Patent Application Examined , Second Publication No. S62-45285 or etc.).

[0063] In the finishing annealing step (S112), an annealing separator containing alumina as the main component (50 mass% or more of alumina) is used. Desirably, in addition to alumina, the annealing separator contains from 5 to 50% by weight of magnesium oxide. The presence of magnesium oxide suppresses the formation of inclusions such as mullite (3Al ₂ O ₃ .2SiO ₂ ) on the surface of the steel sheet and stably improves the steel loss index.

In the finish annealing, the above-described annealing separator containing alumina as a main component is applied to the surface of a steel sheet having an oxide layer and dried. After drying, the steel sheet is coiled and subjected to finishing annealing (secondary recrystallization annealing).

[0064] By using an annealing separator containing alumina (Al ₂ O ₃ ) as a main component, even if the steel sheet is finish annealed, it is possible to suppress the formation of a film of an inorganic mineral substance such as forsterite on the surface of the steel sheet.

[0065] Regarding the application of the annealing separator, if the decarburized annealed sheet is laminated (coiled), the surface that has been finish annealed can be mirror polished, and steel loss can be greatly reduced by using an annealing separator containing alumina as the main a component that hardly reacts with silica, in the form of an aqueous suspension by electrostatic coating, and the like.

[0066] This layered decarburized annealed sheet is finish annealed to cause secondary recrystallization and purification from nitrides, sulfides or the like. Performing secondary recrystallization in a given temperature range using means such as keeping the secondary recrystallization at a constant temperature is effective in increasing the magnetic flux density.

Although the finish annealing can be performed, for example, under conditions where the temperature is raised to 1150 to 1250°C and annealing is performed for 10 to 30 hours in a gas atmosphere containing hydrogen and nitrogen, when cleaning and the like is performed. from nitrides and sulfides or the like, after completion of the secondary recrystallization, it is desirable to perform annealing at a temperature of 1100° C. or higher in 100% hydrogen.

[0067] After the finish annealing step (S112), in the insulation coating forming step (S114), an insulation coating for applying tension to the steel sheet can be formed on the surface of the steel sheet.

[0068] In addition, if necessary, between the described processes, processing for grinding magnetic domains by a mechanical method using a tooth profile or the like, a chemical method using etching or the like, laser irradiation, electron beam irradiation, or the like can be performed. P.

[0069] As described above, in the decarburization annealing process in which decarburization annealing is performed in a humid hydrogen atmosphere to remove carbon contained in cold-rolled steel, the annealing performed under gas atmosphere control to obtain an oxidation state in which no iron-based oxide is formed is the main feature of the manufacturing method of grain-oriented electrical steel sheet according to an embodiment of the present invention.

[0070] In addition, in the method for manufacturing the grain-oriented electrical steel sheet according to the above embodiment, it is possible to further provide a nitriding treatment process conducted in a period starting before the decarburization annealing process and ending before the start of secondary recrystallization in the finish annealing process (for example, in the temperature range from 600 to 1000°C). In particular, the nitriding treatment process can be performed offline before the decarburization annealing process, performed in one or more of the heating step, the holding step and the cooling step in the decarburization annealing process, be performed offline after the decarburization annealing process, or be performed before the start of secondary recrystallization in the finish annealing process by adding a nitrogen compound to the annealing separator.

[0071] The grain-oriented electrical steel sheet obtained by the manufacturing method according to the above-described embodiment can be used mainly as the iron core of a transformer or other electrical devices.

Examples

[0072] Although examples of the present invention will be described below, it is understood that the conditions adopted in these examples are embodiments confirming the feasibility and technical result of the present invention, and the present invention is not limited to these embodiments.

[0073] The inventors of the present invention assumed that the oxide layer formed in the initial stage of decarburization annealing significantly affects the character of subsequent decarburization relative to the character of decarburization on the surface of the silicon steel sheet, and conducted various experiments related to this assumption.

[0074] The present inventors investigated the stability of the decarburization reaction in the decarburization annealing step in which the decarburization annealing is carried out in a humid hydrogen atmosphere to remove carbon contained in cold-rolled steel when Sn or Sb is contained as components of a silicon steel material and is further contained cr.

[0075] <Example 1>

Silicon steel slab obtained by casting and containing in wt.%: 3.3% Si,; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-soluble Al: 0.027%; N 0.008%; the rest: Fe and impurities, heated, and then subjected to hot rolling to obtain a sheet with a thickness of 2.0 mm. The hot-rolled sheet was heated to 1100°C, and after lowering the temperature of the hot-rolled sheet to 900°C, held for 30 seconds, and then subjected to one cold rolling to a final sheet thickness of 0.22 mm.

[0076] This cold-rolled sheet was subjected to decarburization annealing, in which the oxidation state (P _H2O /P _H2 ) was changed by changing the dew point in a gas atmosphere containing 75% hydrogen and 25% nitrogen, raising the temperature to 830°C at a heating rate of 7° C/sec and kept for 120 seconds. In example 1, the degree of oxidation in the heating zone is equal to the degree of oxidation in the exposure zone.

[0077] After that, the amount of nitrogen in the steel was increased to 0.02 wt.% in ammonia gas and strengthened inhibitor.

[0078] The decarburized annealed sheet was subjected to finish annealing, in which an annealing separator (80 wt.% alumina + 20 wt.% magnesium oxide) containing alumina as a main component in the form of an aqueous suspension was applied thereon, the temperature was raised to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, this gas atmosphere was replaced by a gas atmosphere of 100% hydrogen, and then annealing was carried out at 1200°C for 20 hours.

[0079] The samples prepared in the above steps were washed with water, cut, subjected to stress relief annealing, formed with an insulating coating to provide tension to the steel sheet (requires application of a tension coating), subjected to laser irradiation, and performed magnetic measurements by SST . Table 1 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained by said magnetic measurements.

[0080] Table 1

Sample No. Degree of oxidation during decarburization annealing Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Steel Loss Estimation Comprehensive assessment one 0.01 66 B 0.63 Ex B 2 0.04 57 B 0.64 Ex B 3 0.06 45 B 0.66 Ex B four 0.11 38 B 0.67 Ex B 5 0.15 31 B 0.67 Ex B 6 0.20 19 Ex 0.74 B G 7 0.25 7 Ex 0.81 B G

[0081] In Table 1, "Ex" means an excellent result, "G" a good range (allowable), and "B" a poor result.

[0082] It can be seen from Table 1 that when annealing was carried out in a humid gas atmosphere (a mixture of steam, hydrogen and nitrogen) with an oxidation state of 0.01 to 0.15, the amount of carbon decreased to 0.02% or less. Therefore, the orientation crystal was not broken by transformation during finish annealing, and good steel loss performance of 0.70 W/kg or less was obtained. However, since the amount of carbon in the steel exceeded 0.0030% (30 ppm), there is concern that magnetic aging (deterioration of magnetic properties due to aging) occurs.

In addition, when annealing was carried out in a humid gas atmosphere having an oxidation state of 0.20 or more, the amount of carbon in the steel was 0.0030% or less, but a good loss rate in the steel was not achieved.

[0083] It is believed that the reason why the amount of carbon did not decrease to 0.0030% or less was the dependence on the quality and morphology of the oxide formed on the surface of the steel sheet when heated in the process of decarburization annealing. On the surface subjected to the decarburization annealing, a decarburization reaction (oxidation of carbon in steel) and a reaction to form silicon dioxide (oxidation of silicon in steel) or the like. usually resisted moisture in the atmosphere.

From the results of Example 1, it was found that when annealing was carried out in a gas atmosphere with a low oxidation state that does not form iron-based oxides, silicon dioxide was generally formed on the surface of the steel sheet as a dense film preventing decarburization.

[0084] <Example 2>

The effect of surface segregation-forming elements and oxide-forming elements on the silica formation reaction was investigated. The results will be presented below in example 2.

[0085] Silicon steel slab obtained by casting and containing in wt.% Si: 3.3% Mn: 0.14%; C: 0.05%; S: 0.007%; acid-soluble Al: 0.027%; N 0.008%; Sn: 0.07%; the rest: Fe and impurities, heated, and then subjected to hot rolling to obtain a sheet with a thickness of 2.0 mm. The hot rolled sheet was heated to 1100°C, cooled to 900°C, held for 30 seconds, and then subjected to one cold rolling to a final sheet thickness of 0.22 mm.

[0086] The cold-rolled sheet was subjected to decarburization annealing, in which the oxidation state (P _H2O /P _H2 ) was changed by changing the dew point in a gas atmosphere containing 75% hydrogen and 25% nitrogen, raising the temperature to 830°C at a heating rate of 7°C /sec and kept for 120 seconds. In example 2, the degree of oxidation in the heating zone was equal to the degree of oxidation in the exposure zone.

[0087] After that, the amount of nitrogen in the steel was increased to 0.02 wt.% (nitriding treatment) in ammonia gas to enhance the inhibitor.

[0088] The decarburized annealed sheet was subjected to finishing annealing, in which an annealing separator (50 wt.% alumina + 50 wt.% magnesium oxide) containing alumina as the main component in the form of an aqueous suspension was applied thereon, the temperature was raised to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, this gas atmosphere was replaced by a gas atmosphere of 100% hydrogen, and then annealing was carried out at 1200°C for 20 hours. The samples prepared by the above steps were washed with water, cut, subjected to stress relief annealing, coated with an insulating coating to create a tension of the steel sheet (requires the application of a tension coating), subjected to laser irradiation, and carried out magnetic measurements by the SST method. Table 2 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained using the above magnetic measurements.

[0089] Table 2

Sample No. Oxidation degree in decarburizing annealing Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Steel Loss Estimation Comprehensive Assessment one 0.01 43 B 0.63 Ex G 2 0.04 26 Ex 0.63 Ex Ex 3 0.06 21 Ex 0.64 Ex Ex four 0.11 19 Ex 0.65 Ex Ex 5 0.15 16 Ex 0.65 Ex Ex 6 0.20 eighteen Ex 0.72 B G 7 0.25 9 Ex 0.77 B G

[0090] In Table 2, "Ex" means an excellent result, "G" a good range, and "B" a poor result.

It can be seen from Table 2 that when annealing was carried out in a humid gas atmosphere (a mixture of steam, hydrogen and nitrogen) with an oxidation state of 0.01 to 0.15, good steel loss performance was obtained and the amount of carbon in steel was 0. 0030% or less.

[0091] From the above experiment, it can be seen that when an appropriate amount of Sn is contained, the decarburization reaction is accelerated if the decarburization annealing is performed in a low oxidation gas atmosphere in which iron oxide is not generated. Even when Sb is contained, the same effect is achieved as with Sn, and this effect can be provided by the total amount of Sb and Sn. It is assumed that Sb and Sn are segregation elements, and they both segregate on the surface of the steel sheet, suppressing the diffusion of Si to the surface and suppressing the formation of a surface film of silicon dioxide.

[0092] <Example 3>

In Example 3, the stabilization of the decarburization reaction was studied when an appropriate amount of Cr was contained together with Sn and Sb (segregation elements) in Example 2.

[0093] Silicon steel slab obtained by casting and containing in wt .%: Si: 3.3%; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-soluble Al: 0.027%; N 0.008%; Sn: 0.05%; Sb: 0.01%, Cr: 0.12%; the rest: Fe and impurities, heated, and then subjected to hot rolling to obtain a sheet with a thickness of 2.0 mm. The hot rolled sheet was heated to 1100° C., held for 30 seconds, and then subjected to one cold rolling to a final sheet thickness of 0.22 mm.

[0094] The cold-rolled sheet was subjected to decarburization annealing, in which the oxidation state (P _H2O /P _H2 ) was changed by changing the dew point in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the temperature was raised to 830°C at a heating rate of 7°C /second and kept at 830°C for 120 seconds. In example 3, the degree of oxidation in the heating zone is equal to the degree of oxidation in the exposure zone.

[0095] After that, the amount of nitrogen in the steel was increased to 0.02 wt.% in ammonia gas to enhance the inhibitor.

[0096] The decarburized annealed sheet was subjected to finishing annealing, in which an annealing separator (70 wt.% alumina + 30 wt.% magnesium oxide) containing alumina as a main component in the form of an aqueous suspension was applied to it, the temperature was raised to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the gas atmosphere was replaced with a gas atmosphere of 100% hydrogen, and then annealing was carried out at 1200°C for 20 hours.

[0097] The samples prepared in the above steps were washed with water, cut, subjected to stress relief annealing, formed with an insulating coating to provide tension to the steel sheet (requires application of a tension coating), subjected to laser irradiation, and carried out magnetic measurements by the SST method .

[0098] Table 3 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained from the above magnetic measurements.

[0099] Table 3

Sample No. Degree of oxidation during decarburization annealing Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Estimation of steel losses Comprehensive assessment one 0.01 eighteen Ex 0.63 Ex Ex 2 0.04 13 Ex 0.63 Ex Ex 3 0.06 eight Ex 0.62 Ex Ex four 0.11 3 Ex 0.65 Ex Ex 5 0.15 2 Ex 0.65 Ex Ex 6 0.20 2 Ex 0.70 Ex Ex 7 0.25 2 Ex 0.74 B G

[0100] In Table 3, "Ex" means an excellent result, "G" a good range, and "B" a poor result.

It can be seen from Table 3 that when annealing was carried out in a humid gas atmosphere (a mixture of steam, hydrogen and nitrogen) with an oxidation state of 0.01 to 0.20, good steel loss indicators were obtained and the amount of carbon in the steel was 0.0030% or less. In the case of the presence of Cr, the upper limit of the oxidation state can be extended. In contrast to Sn and Sb, it is assumed that the contained Cr influences the formation of a silica film and promotes the decarburization reaction when an oxide is formed during the heating process of the decarburization annealing.

[0101] <Example 4>

In example 4, the stabilization of the decarburization reaction was investigated by changing the oxidation state in the heating region and the oxidation state in the holding region.

[0102] Silicon steel slab obtained by casting and containing in wt.%: Si: 3.3,; Mn: 0.14%; C: 0.05%; S: 0.007%; acid-soluble Al: 0.027%; N 0.008%; Sn: 0.05%; and Sb: 0.01%, balance: Fe and impurities, heated, and then subjected to hot rolling to obtain a sheet with a thickness of 2.0 mm. The hot-rolled sheet was subjected to annealing in which the hot-rolled sheet was heated to 1120°C, then cooled to 950°C and held for 30 seconds, and then subjected to one cold rolling to a final sheet thickness of 0.22 mm.

[0103] The cold-rolled sheet was subjected to decarburization annealing, in which the oxidation state (P _H2O/PH2 ) was changed by changing the dew point in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the temperature was raised to 830°C with a heating rate of 7°C/ sec and kept at 830°C for 120 seconds. In Example 4, the oxidation state in the holding zone was set to 0.08, and the oxidation state in the heating zone was changed.

[0104] After that, the amount of nitrogen in the steel was increased to 0.02 wt.% in ammonia gas to enhance the inhibitor.

[0105] The decarburized annealed sheet was subjected to finish annealing, in which an annealing separator (70 wt.% alumina + 30 wt.% magnesium oxide) containing alumina as a main component, in the form of an aqueous suspension, was applied to it, the temperature was increased to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the gas atmosphere was replaced with a gas atmosphere of 100% hydrogen, and then annealing was performed at 1200° C. for 20 hours.

[0106] The samples prepared in the above steps were washed with water, cut, subjected to stress relief annealing, formed with an insulating coating to provide tension to the steel sheet (requires application of a tension coating), subjected to laser irradiation, and carried out magnetic measurements by the SST method.

[0107] Table 4 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained by the above magnetic measurements.

[0108] Table 4

Sample No. Degree of oxidation during decarburization annealing Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Steel Loss Estimation Comprehensive assessment one 0.08 7 Ex 0.63 Ex Ex 2 0.10 2 Ex 0.62 Ex Ex 3 0.15 one Ex 0.62 Ex Ex

[0109] Table 4 shows that if the oxidation state of the wet gas (a mixture of steam, hydrogen and nitrogen) in the heating zone is higher than the oxidation state (0.08) in the holding zone, the amount of carbon is further reduced and even better performance is achieved. steel losses.

[0110] <Example 5>

The cold rolling process was also investigated. The results will be explained below with Example 5.

[0111] Silicon steel slab obtained by casting and containing in wt.%: Si: 3.2; Mn: 0.1%; C: 0.05%; S: 0.006%; acid-soluble Al: 0.028%; N 0.008%; Sn: 0.05%; Cr: 0.11%; the rest: Fe and impurities, heated, and then subjected to hot rolling to obtain a sheet with a thickness of 2.6 mm. A portion of the hot-rolled sheet was annealed (hot annealed) at 1100°C, subjected to annealing in which cold rolling to a sheet thickness of 2.0 mm and heating to 1120°C was performed, and then annealing was performed in which the temperature was reduced to 950°C. and holding for 30 seconds (intermediate annealing), and then performing cold rolling to a final sheet thickness of 0.22 mm (process A). The remaining hot-rolled sheet was subjected to annealing in which cold rolling was performed to obtain a sheet with a thickness of 2.0 mm without hot annealing, heated to 1120°C, and annealing was carried out in which the temperature was lowered to 950°C and held for 30 seconds. and then cold rolling to a final sheet thickness of 0.22 mm was performed (Process B). The reduction ratio during cold rolling after finishing annealing was 89% in each case.

[0112] The cold rolled sheet was subjected to a decarburization annealing in which the temperature was raised to 830°C at a heating rate of 30°C/sec at an oxidation state (P _H2O/PH2 ) of 0.06 in a gas atmosphere containing 75% hydrogen and 25% nitrogen, and held for 120 seconds. In example 5, the degree of oxidation in the heating zone is equal to the degree of oxidation in the exposure zone.

[0113] After that, the amount of nitrogen in the steel was increased to 0.025 wt.% in ammonia gas to enhance the inhibitor.

[0114] The decarburized annealed sheet was subjected to finish annealing, in which an annealing separator (90 wt.% alumina + 10 wt.% magnesium oxide) containing alumina as the main component, in the form of an aqueous suspension, was applied to it, the temperature was increased to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the gas atmosphere was replaced with a gas atmosphere of 100% hydrogen, and then annealing was carried out at 1200°C for 20 hours.

The samples prepared in the above steps were washed with water, cut, subjected to stress relief annealing, formed with an insulating coating to provide tension to the steel sheet (tension coating is required), subjected to laser irradiation, and magnetic measurements were taken by the SST method.

Table 5 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained by the above magnetic measurements.

[0115] Table 5

Process Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Steel Loss Estimation Comprehensive assessment A 13 Ex 0.66 Ex Ex B ten Ex 0.65 Ex Ex

[0116] In Table 5, "Ex" means an excellent result.

As can be seen from Table 5, no matter which step was carried out, if the amount of carbon in the steel that was subjected to decarburization was 0.0030% (30 ppm) or less, good steel loss performance was obtained.

[0117] <Example 6>

A silicon steel slab containing the components shown in Table 6 and the rest of Fe and impurities obtained by casting was heated and then hot rolled to a sheet thickness of 2.3 mm. The hot-rolled sheet was subjected to annealing in which the temperature was raised to 1100° C., held for 60 seconds, and then subjected to one cold rolling to a final sheet thickness of 0.22 mm.

[0118] The cold rolled sheet was subjected to a decarburization annealing in which the temperature was raised to 830°C at a heating rate of 30°C/sec at an oxidation state (P _H2O/PH2 ) of 0.10 in a gas atmosphere containing 75% hydrogen and 25% nitrogen, and change the oxidation state (P _H2O/PH2 ) to the oxidation state (P _H2O/PH2 ) 0.06, and hold for 120 seconds.

[0119] Thereafter, the amount of nitrogen in the steel was increased to 0.025 wt.% in ammonia gas to enhance the inhibitor.

[0120] The decarburized annealed sheet was subjected to finish annealing, in which an annealing separator (60 wt.% alumina + 40 wt.% magnesium oxide) containing alumina as a main component in the form of an aqueous suspension was applied to it, the temperature was raised to 1200 °C in a gas atmosphere containing 75% hydrogen and 25% nitrogen, the gas atmosphere was replaced with a gas atmosphere of 100% hydrogen, and then annealing was carried out at 1200°C for 20 hours. The samples prepared in the above steps were washed with water and then cut, stress relieved annealed, formed with an insulating coating to provide tension to the steel sheet (tension coating required), subjected to laser irradiation, and magnetic measurements were taken by SST. Table 6 shows the amounts of carbon after decarburization annealing and steel loss rates (W _17/50 ) obtained by the above magnetic measurements.

[0121] Table 6

Sample No. Wt%: (balance: Fe and impurities) Si Mn C S Acid Soluble Al N sn Sb Cr Cu P Ni B V Nb Mo Ti Bi one 3.20 0.10 0.05 0.006 0.027 0.008 0.05 − − − − − − − − − − − 2 3.30 0.11 0.06 0.005 0.028 0.007 − 0.01 − − − − − − − − − − 3 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 − − − − − − − − − four 3.20 0.10 0.05 0.005 0.028 0.007 0.05 − 0.10 − − − − − − − − − 5 3.30 0.11 0.06 0.006 0.027 0.008 − 0.01 0.10 − − − − − − − − − 6 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.10 − − − − − − − − − 7 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.02 − − − − − − − − − eight 3.20 0.10 0.05 0.006 0.027 0.008 0.05 0.01 0.50 − − − − − − − − − 9 2.70 0.12 0.05 0.005 0.028 0.008 0.04 − 0.11 − − − − − − − − − ten 3.80 0.12 0.06 0.005 0.028 0.008 0.04 − 0.11 − − − − − − − − − eleven 3.20 0.14 0.05 0.007 0.027 0.007 0.06 − 0.12 − − − − − − − − − 12 3.20 0.45 0.05 0.007 0.027 0.007 0.06 − 0.12 − − − − − − − − − 13 3.30 0.11 0.04 0.006 0.026 0.008 0.05 − 0.09 − − − − − − − − − fourteen 3.20 0.11 0.07 0.006 0.026 0.008 0.05 − 0.09 − − − − − − − − − fifteen 3.30 0.13 0.06 0.004 0.027 0.007 − 0.02 0.12 − − − − − − − − − 16 3.20 0.13 0.05 0.015 0.027 0.007 − 0.02 0.12 − − − − − − − − − 17 3.30 0.10 0.06 0.005 0.025 0.008 0.03 0.01 0.13 − − − − − − − − − eighteen 3.30 0.10 0.06 0.005 0.035 0.008 0.03 0.01 0.13 − − − − − − − − − 19 3.20 0.11 0.05 0.006 0.027 0.004 0.07 0.12 − − − − − − − − − twenty 3.20 0.11 0.05 0.006 0.027 0.010 0.07 0.12 − − − − − − − − − 21 3.30 0.12 0.06 0.005 0.029 0.008 0.05 − 0.10 0.2 − − − − − − − − 22 3.20 0.11 0.05 0.006 0.027 0.008 0.05 − 0.11 − 0.2 − − − − − − − 23 3.20 0.14 0.06 0.006 0.026 0.008 − 0.02 0.12 − − 0.3 − − − − − − 24 3.30 0.11 0.05 0.005 0.027 0.008 − 0.01 0.11 − − − 0.003 − − − − − 25 3.20 0.10 0.05 0.006 0.025 0.009 0.03 0.01 0.12 − − − − 0.07 − − − − 26 3.30 0.11 0.06 0.006 0.026 0.009 0.02 0.01 0.13 − − − − − 0.05 − − − 27 3.30 0.11 0.05 0.006 0.027 0.008 0.04 − 0.11 − − − − − − 0.05 − − 28 3.20 0.14 0.06 0.008 0.027 0.007 − 0.02 0.12 − − − − − − − 0.005 − 29 3.20 0.10 0.05 0.006 0.028 0.008 0.05 − 0.12 − − − − − − − − 0.005

Table 6 continued

Sample No. Amount of carbon in decarburized steel (ppm) Estimating the amount of carbon Steel loss (W _17/50 ) (W/kg) Steel Loss Estimation Comprehensive assessment one 12 Ex 0.66 Ex Ex 2 fourteen Ex 0.66 Ex Ex 3 eleven Ex 0.65 Ex Ex four ten Ex 0.65 Ex Ex 5 eleven Ex 0.64 Ex Ex 6 eight Ex 0.64 Ex Ex 7 ten Ex 0.65 Ex Ex eight ten Ex 0.65 Ex Ex 9 eight Ex 0.64 Ex Ex ten 17 Ex 0.61 Ex Ex eleven 7 Ex 0.65 Ex Ex 12 eight Ex 0.67 Ex Ex 13 eight Ex 0.66 Ex Ex fourteen 12 Ex 0.69 Ex Ex fifteen 9 Ex 0.69 Ex Ex 16 eight Ex 0.68 Ex Ex 17 7 Ex 0.67 Ex Ex eighteen 9 Ex 0.63 Ex Ex 19 eight Ex 0.69 Ex Ex twenty 7 Ex 0.63 Ex Ex 21 eight Ex 0.63 Ex Ex 22 ten Ex 0.65 Ex Ex 23 9 Ex 0.64 Ex Ex 24 7 Ex 0.64 Ex Ex 25 ten Ex 0.65 Ex Ex 26 9 Ex 0.63 Ex Ex 27 eight Ex 0.65 Ex Ex 28 9 Ex 0.67 Ex Ex 29 eight Ex 0.64 Ex Ex

[0122] As can be seen from Table 6, regardless of the composition of the silicon steel slab to be used, if the amount of carbon in the steel subjected to decarburization was 0.0030% (30 ppm) or less, good loss performance was obtained. become.

[0123] The above results show that the decarburization reaction proceeds stably, and that a product with good steel loss performance can be obtained if the surface of the steel sheet is promoted to smooth when the silicon steel slab is contains in as components of Sn and Sb and contains a corresponding amount of Cr, in the decarburization annealing step of performing decarburization annealing in a humid hydrogen atmosphere to remove carbon contained in steel that has been cold rolled.

Industrial Applicability

[0124] The present invention provides a method for manufacturing a grain-oriented electrical steel sheet having good magnetic properties while satisfactorily performing decarburization in a decarburization annealing process. Therefore, the present invention has a high industrial applicability.

Claims (37)

1. A method for manufacturing a grain-oriented electrical steel sheet, comprising: a silicon steel material manufacturing process to obtain a silicon steel material; a hot rolling process for producing a hot rolled sheet in which the silicon steel material is subjected to hot rolling; a cold rolling process for producing a steel sheet of a finite thickness, in which the hot-rolled sheet is subjected to one cold rolling process or several cold rolling processes with intermediate annealing performed between the cold rolling processes; a decarburization annealing process in which the steel sheet is subjected to decarburization annealing, and a finishing annealing process in which an annealing separator containing alumina as a main component is applied to a steel sheet, and then the steel sheet is finished annealed, moreover, the silicon steel material contains, wt.%: Si: 0.8 to 7.0%; C: 0.085% or less; acid soluble Al: 0.010 to 0.065%; N: 0.004 to 0.012%; Mn: 1.00% or less; S: 0.050% or less; one or both of Sn and Sb: 0.01 to 0.20% in total, optionally, at least one element from the following group consisting of: Cr: 0.02 to 0.50%, Cu: 0.4% or less; P: 0.5% or less; Ni: 1.0% or less; B: 0.008% or less; V: 0.15% or less; Nb: 0.20% or less; Mo: 0.10% or less; Ti: 0.015% or less and Bi: 0.010% or less the rest: Fe and impurities, wherein in the decarburizing annealing process: decarburizing annealing is performed using a decarburizing annealing furnace comprising a heating zone and a holding zone, the oxidation state P1 of the gas atmosphere in the heating zone satisfies the following expression 1, and the degree of oxidation P2 of the gaseous atmosphere in the holding zone satisfies the following expression 2, and mentioned P1 and P2 satisfy the following expression 3: 0.01<P1≤0.15 (expression 1), 0.01≤P2<0.15 (expression 2), P1>P2 (expression 3). 2. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1, further comprising: a nitriding treatment process carried out in the period starting before the decarburization annealing process and ending before the start of secondary recrystallization in the finish annealing process. 3. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1 or 2, further comprising: a hot annealing process in which a hot rolled sheet obtained in the hot rolling process is annealed after the hot rolling process and before the cold rolling process.

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