JP5760590B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and more particularly to an advantageous method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics over the entire length of a product coil.

  The electromagnetic steel sheet is roughly classified into a directional electromagnetic steel sheet and a non-oriented electromagnetic steel sheet, which are widely used as iron core materials for transformers and generators. In particular, the former grain-oriented electrical steel sheet is highly integrated in the {110} <001> orientation, which is called the Goss orientation, and is therefore effective in reducing energy loss in transformers and generators. have. Conventionally, techniques for reducing iron loss of grain-oriented electrical steel sheets include reduction of sheet thickness, increase of Si content, improvement of orientation of crystal orientation, application of tension to the steel sheet, smoothing of the surface of the steel sheet, secondary re-treatment. Crystal grain refinement is known.

Among the above iron loss reduction techniques, the secondary recrystallized grains can be refined by a method of rapid heating during decarburization annealing or rapid heat treatment immediately before decarburization annealing to improve the primary recrystallization texture. The method is known. For example, in Patent Document 1, before decarburizing and annealing a strip that has been rolled to the final plate thickness, a rapid heat treatment is performed at 800 to 950 ° C. at an atmospheric oxygen concentration of 500 ppm or less and a heating rate of 100 ° C./second or more. The temperature of the front region in the carbon annealing process is set to 775-840 ° C. which is lower than the ultimate temperature in the rapid heating, and the temperature of the subsequent rear region is lowered by performing decarburization annealing at 815-875 ° C. which is higher than the front region. A technique for obtaining a directional electrical steel sheet with iron loss is disclosed in Patent Document 2 in a non-oxidizing atmosphere in which PH ₂ O / PH ₂ is 0.2 or less immediately before decarburizing and annealing a strip rolled to a final thickness. In particular, a technique for obtaining a grain-oriented electrical steel sheet having a low iron loss by heat treatment at a heating rate of 100 ° C./second or more to a temperature of 700 ° C. or more is disclosed.

Patent Document 3 discloses that a temperature range of at least 600 ° C. in the temperature rising stage of the decarburization annealing process is heated to 800 ° C. or higher at a temperature rising rate of 95 ° C./s or more, and the atmosphere in this temperature range is It is composed of an inert gas containing oxygen at a volume fraction of 10 ⁻⁶ to 10 ⁻¹ , and the constituents of the atmosphere during soaking of decarburization annealing are H ₂ and H ₂ O or H ₂ and H ₂ O. An inert gas is used, and the ratio PH ₂ O / PH ₂ of the H ₂ O partial pressure to the H ₂ partial pressure is set to 0.05 to 0.75, and the atmospheric flow rate per unit area is set to 0.01 Nm ³ / min. A technique for obtaining an electromagnetic steel sheet having excellent coating properties and magnetic properties in the range of m ² to 1 Nm ³ / min · m ² is also disclosed in Patent Document 4, which is at least 650 ° C. or higher in the temperature raising stage of the decarburization annealing process. Temperature range of 800 ° C or higher at a rate of temperature increase of 100 ° C / s And an atmosphere in this temperature range is an inert gas containing oxygen of 10 ⁻⁶ to 10 ⁻² in volume fraction, while the constituent components of the atmosphere during soaking of decarburization annealing are H ₂ By using H ₂ O, or H ₂ and H ₂ O and an inert gas, and the ratio PH ₂ O / PH ₂ of the H ₂ O partial pressure to the H ₂ partial pressure is 0.15 to 0.65, the film characteristics And a technology for obtaining a grain-oriented electrical steel sheet having excellent magnetic properties.

Japanese Patent Laid-Open No. 10-298653 Japanese Patent Laid-Open No. 07-062436 JP 2003-027194 A JP 2000-204450 A

  By applying the techniques described in Patent Documents 1 to 4, secondary recrystallized grains are finely divided as such, and iron loss can be reduced. However, in the above-mentioned conventional technology, there is a variation in the fine graining effect in the product coil due to the influence of fluctuations in the raw material components and the production conditions in the process before the primary recrystallization annealing. There was a problem that it was difficult to stably obtain the iron loss reduction effect.

  The present invention has been made in view of the above-mentioned problems of the prior art, and the object thereof is to stably refine the secondary recrystallized grains over the entire length of the product coil, and thus over the entire length of the coil. The object is to propose a method of manufacturing a grain-oriented electrical steel sheet capable of reducing iron loss.

  In order to solve the above problems, the inventors have focused on the temperature rising process in the primary recrystallization annealing, and have pursued a technique for stably making secondary recrystallized grains over the entire length of the product coil. It was found that it is effective to divide the temperature rising process of annealing into a low temperature region and a high temperature region, to rapidly increase the temperature in the low temperature region, and conversely to slow the temperature increase rate in the high temperature region. That is, it has been conventionally known that the secondary recrystallized grains become finer by increasing the temperature increase rate of the primary recrystallization. In the process, the temperature rise rate in the low temperature region where recovery occurs is made higher than the temperature rise rate in normal decarburization annealing, and the temperature rise rate in the high temperature region where primary recrystallization occurs is Knowing that the secondary recrystallized grains can be refined stably over the entire length of the product coil even when there are fluctuations in the raw material components and the manufacturing conditions of the previous process, by making it 50% or less, the present invention Led to the development.

That is, this invention is 1 type chosen from C: 0.001-0.20mass%, Si: 1.0-5.0mass%, Mn: 0.03-1.0mass%, S and Se or Total of two types: 0.005 to 0.040 mass%, sol. A steel slab containing Al: 0.003-0.050 mass%, N: 0.0010-0.020 mass%, with the balance being composed of Fe and inevitable impurities, hot-rolled, and once or intermediate annealing The steel sheet is subjected to cold rolling twice or more to obtain a final thickness, and when the C content in the steel slab is 30 massppm or less, primary recrystallization annealing or decarburization annealing is also performed, In the method for producing a grain- oriented electrical steel sheet in which the primary recrystallization annealing that also serves as a decarburization annealing is applied when it exceeds 30 massppm , and then the final finishing annealing is performed by applying an annealing separator mainly composed of MgO. In the temperature raising process of recrystallization annealing, the temperature rising rate S ₁ between 300 to 600 ° C. is 100 ° C./s or more, and the temperature rising rate S ₂ between 600 to 700 ° C. is 30 to (0.5 × S ₁ ) ° C. / range of s A method for producing a grain-oriented electrical steel sheet characterized by.

The method for producing a grain-oriented electrical steel sheet according to the present invention is characterized in that the oxidation potential P _H2O / P _H2 of the atmosphere during the temperature raising process of the primary recrystallization annealing is between 300 and 700 ° C. is 0.05 or less.

  Moreover, in addition to the said component composition, the manufacturing method of the grain-oriented electrical steel sheet of this invention is further Cu: 0.01-0.2mass%, Ni: 0.01-0.5mass%, Cr: 0.01- Of 0.5 mass%, Sb: 0.01-0.1 mass%, Sn: 0.01-0.5 mass%, Mo: 0.01-0.5 mass% and Bi: 0.001-0.1 mass% It contains 1 type or 2 types or more chosen from these.

  Moreover, in addition to the said component composition, the manufacturing method of the grain-oriented electrical steel sheet of this invention is further B: 0.001-0.01mass%, Ge: 0.001-0.1mass%, As: 0.005-. 0.1 mass%, P: 0.005-0.1 mass%, Te: 0.005-0.1 mass%, Nb: 0.005-0.1 mass%, Ti: 0.005-0.1 mass%, and V : It contains 1 type, or 2 or more types chosen from 0.005-0.1 mass%, It is characterized by the above-mentioned.

  According to the present invention, since the secondary recrystallized grains can be refined over the entire length of the product coil of the grain-oriented electrical steel sheet and the iron loss can be reduced, the product yield can be greatly improved, This greatly contributes to the improvement of the iron loss characteristics of the vessel.

The component composition of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.001 to 0.10 mass%
C is a component useful for the generation of goth-oriented grains, and needs to be contained in an amount of 0.001 mass% or more in order to effectively exhibit such action. However, if C is added in excess of 0.10 mass%, decarburization is insufficient even after decarburization annealing, so C is set in the range of 0.001 to 0.10 mass%.

Si: 1.0-5.0 mass%
Si is a component necessary to increase the electrical resistance of steel, reduce iron loss, stabilize the BCC structure (ferrite structure) of iron, and enable high-temperature heat treatment, and is at least 1.0 mass%. The above addition is required. However, if added over 5.0 mass%, it is difficult to cold-roll. Therefore, Si was limited to 1.0 to 5.0 mass%.

Mn: 0.01 to 1.0 mass%
Mn is an effective component for preventing hot brittleness of steel, and is a useful component that combines with S and Se to form precipitates such as MnS and MnSe, and acts as an inhibitor. is there. However, if the Mn content is less than 0.01 mass%, the above effect cannot be obtained. On the other hand, if it exceeds 1.0 mass%, precipitates such as MnSe are coarsened and the function as an inhibitor is lost. Therefore, Mn is in the range of 0.01 to 1.0 mass%.

sol. Al: 0.003 to 0.050 mass%
Al is a useful component that forms AlN in steel and acts as an inhibitor as a dispersed second phase. However, sol. If the addition amount as Al is less than 0.003 mass%, the above effect cannot be obtained because the precipitation amount of AlN cannot be sufficiently secured. On the other hand, if the addition amount exceeds 0.050 mass%, AlN becomes coarse and becomes an inhibitor. Will be lost. Therefore, Al is sol. The range of 0.003 to 0.050 mass% is made of Al.

N: 0.0010-0.020 mass%
N, like Al, is a component necessary for forming AlN. However, if the amount of N added is less than 0.0010 mass%, sufficient AlN is not formed, and thus the above effect cannot be obtained. On the other hand, if the amount added exceeds 0.020 mass%, blistering or the like occurs during slab heating. Causes defects. Therefore, N is set to a range of 0.001 to 0.020 mass%.

S and Se: 0.01-0.05 mass% in total of 1 type or 2 types
S and Se are useful components that combine with Mn and Cu to form MnSe, MnS, Cu _2-x Se, Cu _2-x S and precipitate as a dispersed second phase in the steel, exhibiting an inhibitory action. is there. However, if the total content of S and Se is less than 0.01 mass%, the above-described addition effect is poor. On the other hand, if it exceeds 0.05 mass%, solid solution during slab heating becomes incomplete, It can also cause surface defects. Therefore, the total addition amount is in the range of 0.01 to 0.05 mass% in both cases of single addition and composite addition.

In addition to the essential components, the grain-oriented electrical steel sheet of the present invention further includes Cu: 0.01 to 0.2 mass%, Ni: 0.01 to 0.5 mass%, Cr: 0.01 to 0.5 mass. %, Sb: 0.01 to 0.1 mass%, Sn: 0.01 to 0.5 mass%, Mo: 0.01 to 0.5 mass%, and Bi: 0.001 to 0.1 mass% 1 type (s) or 2 or more types can be added.
All of these elements are elements that are easily segregated at the grain boundaries and the surface, and act as auxiliary inhibitors, and are effective components for further improving the magnetic properties. If the addition amount of these elements is less than the above lower limit value, the effect of suppressing the coarsening of primary grains in the high temperature region of the secondary recrystallization process is insufficient, and a sufficient addition effect cannot be obtained. Addition exceeding the value tends to cause poor appearance of the film and poor secondary recrystallization. Therefore, when adding the said component, it is preferable to set it as the said range.

  In addition to the above components, the grain-oriented electrical steel sheet of the present invention further includes B: 0.001 to 0.01 mass%, Ge: 0.001 to 0.1 mass%, As: 0.005 to 0.1 mass%. , P: 0.005 to 0.1 mass%, Te: 0.005 to 0.1 mass%, Nb: 0.005 to 0.1 mass%, Ti: 0.005 to 0.1 mass%, and V: 0.005. One or more selected from ˜0.1 mass% can be added. By adding these elements in the above range, the inhibitor effect (suppression force) is further strengthened, the degree of integration in the Goth direction is further improved, and a high magnetic flux density can be stably obtained.

Next, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention will be described.
The grain-oriented electrical steel sheet of the present invention is a steel material (steel slab) produced by melting steel having the above-described component composition by a conventionally known refining process and using a continuous casting method or an ingot-bundling rolling method. After that, the steel slab is hot-rolled to obtain a hot-rolled sheet, and if necessary, hot-rolled sheet annealing is performed, and then the final sheet is subjected to cold rolling twice or more sandwiching one or intermediate annealing. A thick cold-rolled sheet, primary recrystallized annealing, and after applying final finishing annealing by applying an annealing separator mainly composed of MgO, and also as required to apply and bake insulation coating Although it can manufacture with the manufacturing method which consists of a series of processes which pass flattening annealing, conventionally well-known conditions can be employ | adopted about manufacturing conditions other than the said primary recrystallization annealing process, and there is no restriction | limiting in particular.
Hereinafter, conditions for primary recrystallization annealing after the final cold rolling will be described.

The conditions for primary recrystallization annealing, particularly the rate of temperature increase in the temperature increasing process, have a great influence on the secondary recrystallized structure as described above, and therefore must be strictly controlled. Therefore, in the present invention, the secondary recrystallized grains are stably refined over the entire length of the product coil, and the above temperature rising process is recovered in order to increase the ratio of the region having excellent iron loss characteristics in the product coil. It is necessary to divide it into a low temperature region where the recrystallization occurs and a high temperature region where primary recrystallization occurs, and to appropriately control the temperature rising rate of each region. Specifically, the temperature increase rate S ₁ in the low temperature region (300 to 600 ° C.) where recovery, which is a precursor process of primary recrystallization, is set to 100 ° C./s or higher, which is higher than that of normal annealing, and the primary recrystallization is performed. and a high temperature range (600 to 700 ° C.) the heating rate _{S 2} 30 ℃ / s or more to occur there must be 50% or less of the low temperature range. Thereby, even when the steel component and the fluctuation material of the manufacturing conditions before the primary recrystallization annealing change, the iron loss reduction effect can be stably obtained.

Here, it is known that secondary recrystallized nuclei with Goss orientation {110} <001> exist in a deformation band generated in a {111} fiber structure in which strain energy is easily accumulated in a rolled structure. In addition, the said deformation | transformation zone means the area | region where strain energy was accumulate | stored especially among {111} fiber structures.
Low temperature region of the primary recrystallization annealing when (300 to 600 ° C.) heating rate S ₁ at is lower than 100 ° C. / s, in the very high deformation band strain energy, (relaxation of strain energy) preferentially recovered Therefore, recrystallization in the Goss direction {110} <001> cannot be promoted. On the contrary, when the S ₁ and 100 ° C. / s or more, since the strain energy deformed tissue can be held up to a high temperature remains high, the Goss orientation at a relatively low temperature (600 ° C. vicinity) {110} <001> recrystallization can be promoted.

In addition, in order to control the grain size of the Goss orientation {110} <001> that has been recrystallized secondarily, the amount of {111} texture that is phagocytosed in the Goss orientation {110} <001>. It is a demand to control the temperature within an appropriate range. That is, if there are too many {111} orientations, the growth of secondary recrystallized grains tends to proceed, and even if there are many Goss orientations {110} <001>, one structure becomes coarse before each grows. On the contrary, if the amount is too small, the growth of secondary recrystallized grains is difficult to proceed, which may result in secondary recrystallization failure.
{111} orientation, although not as much as deformation zone, to produce recrystallized from strain high energy {111} fiber structure than the surrounding, the heating rate S ₁ to 600 ° C. as 100 ° C. / s or higher In the heat cycle of the present invention to be heated, the crystal orientation is likely to cause recrystallization next to the Goth orientation {110} <001>.
Therefore, when heated to a high temperature (700 ° C. or higher) at which primary recrystallization occurs at a rate higher than the rate of temperature specified in S ₂ , Goss orientation {110} <001> and recrystallization is likely to proceed next { 111} orientation recrystallization remains suppressed, and the texture after primary recrystallization is randomized. As a result, the 600 to 700 ° C. as compared with the case of heating at a lower rate than heating rate specified in S _2, the Goss orientation {110} recrystallization texture of <001> is reduced, the secondary recrystallized grains of the fine Or the {111} orientation decreases, and secondary recrystallized grains do not grow sufficiently. Conversely, if the 600 to 700 ° C. and lower than the Atsushi Nobori rate specified in S ₂ is the crystallization easily in a temperature range {111} orientation is increased, the secondary recrystallized grains become coarse afraid There is.

In general, primary recrystallization annealing is often performed in combination with decarburization annealing, but in the present invention, primary recrystallization annealing can also be performed as decarburization annealing. In this case, rapid heating may be performed in a decarburizing atmosphere, but in that case, a low iron loss can be stably obtained when the atmosphere is less oxidizable. This is because if decarburization occurs in the temperature rising process, a primary recrystallized structure that is disadvantageous for the refinement of secondary recrystallized grains will result. Therefore, in the present invention, the oxygen potential P _H2O / P _{H2 in} the atmosphere between 300 and 700 ° C. in the temperature raising process is preferably controlled to 0.05 or less.

  In addition, about other conditions in primary recrystallization annealing, for example, conditions, such as soaking temperature, soaking time, the atmosphere at the time of soaking, and a cooling rate, it may carry out in accordance with a conventional method, and there is no restriction | limiting in particular. Moreover, when C content in steel slab is 30 massppm or less, it is not necessary to perform decarburization annealing in particular, and normal primary recrystallization annealing may be performed after the final cold rolling.

C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.08 mass%, S: 0.023 mass%, sol. A steel slab containing Al: 0.03 mass%, N: 0.007 mass%, Cu: 0.2 mass%, and Sb: 0.02 mass% is heated at 1430 ° C. for 30 minutes and then hot-rolled to obtain a sheet thickness of 2. 2 mm hot-rolled sheet, 1000 ° C. × 1 minute hot-rolled sheet annealed, then cold rolled to an intermediate sheet thickness of 1.5 mm, 1100 ° C. × 2 minute intermediate annealed, and finally cooled Cold rolling was performed by hot rolling to a sheet thickness of 0.23 mm. Then, the temperature rise conditions (temperature rise rate S ₁ between 300 to 600 ° C., temperature rise rate S ₂ between 600 to 700 ° C. and oxygen potential P _H2O / P _{H2 in} the atmosphere between 300 to 700 ° C.) are shown in Table 1. As shown in FIG. 1, after performing primary recrystallization annealing that also serves as decarburization annealing that is heated at 840 ° C. for 2 minutes, and then MgCl is the main component and TiO ₂ is contained at 10 mass%. The product coil is coated and dried, wound into a coil, and finally annealed, followed by flattening annealing that combines the application and baking of phosphate-based insulation tension coating and the flattening of the steel strip. It was.

Test pieces were continuously collected at regular intervals from the length direction of the product coil thus obtained, the iron loss over the entire length of the coil was measured, and the iron loss W _17/50 relative to the total length of the product coil was 0.80 W / kg. The ratio (%) of the following parts was obtained.
Table 1 shows the results of the above measurements. From this, in the steel sheets of the inventive examples subjected to primary recrystallization annealing suitable for the temperature rise rate according to the present invention, the ratio of the portions where W _17/50 ≦ 0.80 W / kg is 70% or more of the total coil length. Furthermore, when the oxygen potential P _H2O / P _H2 of the atmosphere between 300 and 700 ° C. in the temperature raising process is set to 0.05 or less, the ratio of the low iron loss part can be further increased. .

Steel slabs having various component compositions shown in Table 2 were heated at 1430 ° C. for 30 minutes, and then hot rolled to form a hot-rolled sheet having a thickness of 2.2 mm and subjected to hot-rolled sheet annealing at 1000 ° C. for 1 minute. After that, it is cold-rolled to a sheet thickness of 1.5 mm, subjected to intermediate annealing at 1100 ° C. × 2 minutes, and further cold-rolled to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm. For this purpose, a linear groove was formed. Then, the oxygen potential P _H2O / P _H2 of the atmosphere between 300 and 700 ° C. in the temperature rising process is set to 0.03, and the temperature rising rate S ₁ between 300 to 600 ° C. is set to 200 ° C./s. After the temperature was raised to 700 ° C. 600 to 700 of the heating rate _{S 2} between ° C. as 50 ° C. / s, the temperature was raised at an average heating rate of 10 ° C. / s between 700~840 _{℃, P} H2O _/ P _H2 After subjecting to primary recrystallization annealing that also serves as decarburization annealing at 840 ° C for 2 minutes in an atmosphere of 0.4, a water slurry annealing separator containing MgO as the main component and 10 mass% of TiO ₂ is applied. -Dried, wound around the coil, and subjected to final finish annealing, and then applied flattening annealing that combines application and baking of phosphate-based insulation tension coating and flattening of the steel strip to obtain a product coil.

After collecting Epstein test pieces continuously at regular intervals from the length direction of the product coil obtained in this way, after applying strain relief annealing at 800 ° C. × 3 h in a nitrogen atmosphere, the iron loss was measured by the Epstein test method. W _17/50 was measured, the ratio (%) of the portion where the iron loss W _17/50 with respect to the total length of the product coil was 0.80 W / kg or less was determined, and the results are also shown in Table 2. From these results, a cold-rolled sheet having a component composition suitable for the present invention is subjected to primary recrystallization annealing under conditions suitable for the present invention, thereby producing a low iron loss directional electrical steel sheet over the entire length of the product coil. I know you get. In particular, one, two or more selected from Cu, Ni, Cr, Sb, Sn, Mo and Bi having an inhibitor effect, or B, Ge, As, P, Te, Nb, Ti and V When one or more selected from among these are additionally added, a product coil having a high iron loss W _17/50 ratio of 0.80 W / kg can be stably produced.

Claims (4)

C: 0.001 to 0.20 mass%, Si: 1.0 to 5.0 mass%, Mn: 0.03 to 1.0 mass%, total of one or two selected from S and Se: 0 .005-0.040 mass%, sol. A steel slab containing Al: 0.003-0.050 mass%, N: 0.0010-0.020 mass%, with the balance being composed of Fe and inevitable impurities, hot-rolled, and once or intermediate annealing The steel sheet is subjected to cold rolling twice or more to obtain a final thickness, and when the C content in the steel slab is 30 massppm or less, primary recrystallization annealing or decarburization annealing is also performed, In the method for producing a grain- oriented electrical steel sheet in which the primary recrystallization annealing that also serves as a decarburization annealing is performed when it exceeds 30 massppm , and then the final finishing annealing is performed by applying an annealing separator mainly composed of MgO. In the temperature raising process of recrystallization annealing, the temperature rising rate S ₁ between 300 to 600 ° C. is 100 ° C./s or more, and the temperature rising rate S ₂ between 600 to 700 ° C. is 30 to (0.5 × S ₁ ) ° C. / range of s Method for producing a grain-oriented electrical steel sheet characterized by. Method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that a 0.05 to oxidation potential _P H2O _{/ P H2} atmosphere between 300 to 700 ° C. in the primary recrystallization annealing Atsushi Nobori process. In addition to the above component composition, Cu: 0.01 to 0.2 mass%, Ni: 0.01 to 0.5 mass%, Cr: 0.01 to 0.5 mass%, Sb: 0.01 to 0.1 mass %, Sn: 0.01 to 0.5 mass%, Mo: 0.01 to 0.5 mass%, and Bi: 0.001 to 0.1 mass%. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that In addition to the above component composition, B: 0.001-0.01 mass%, Ge: 0.001-0.1 mass%, As: 0.005-0.1 mass%, P: 0.005-0.1 mass %, Te: 0.005-0.1 mass%, Nb: 0.005-0.1 mass%, Ti: 0.005-0.1 mass%, and V: 0.005-0.1 mass%. It contains 1 type (s) or 2 or more types, The manufacturing method of the grain-oriented electrical steel sheet of any one of Claims 1-3 characterized by the above-mentioned.