JP6879320B2 - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet suitable for use as an iron core material such as a transformer or a generator.

The grain-oriented electrical steel sheet is a soft magnetic material widely used as an iron core material for transformers, generators, etc., and has a crystal structure in which the <001> orientation, which is the easy axis of iron magnetization, is highly aligned in the rolling direction of the steel sheet. It is a feature that it has. Such a crystal structure causes secondary recrystallization in the finish annealing of the manufacturing process, and preferentially causes huge growth of crystal grains in the {110} <001> orientation, which is the so-called Goth orientation. It is formed.

As a technique for causing the above-mentioned secondary recrystallization, a technique in which a precipitate called an inhibitor is used and grains having a Goss orientation are preferentially secondary recrystallized during finish annealing is generally used. For example, Patent Document 1 discloses a technique of using AlN or MnS as an inhibitor, and Patent Document 2 discloses a technique of using MnS or MnSe as an inhibitor. The method using these inhibitors requires heating the slab to a high temperature of 1300 ° C. or higher, but it is an extremely useful technique capable of stably expressing secondary recrystallization.

Further, as an auxiliary inhibitor for enhancing the action of these inhibitors, a technique using Pb, Sb, Nb, Te (Patent Document 3) and Zr, Ti, B, Nb, Ta, V, Cr, Mo are used. A technique (Patent Document 4) has been proposed.

Further, unlike the above technique, Patent Document 5 contains 0.010 to 0.060 mass% of acid-soluble Al (sol.Al), and the slab heating temperature is suppressed to a low temperature of 1200 ° C. or lower. A technique has also been proposed in which (Al, Si) N is precipitated during secondary recrystallization by performing an appropriate amount of nitriding in the decarburization annealing step and used as an inhibitor.

Further, in the above-mentioned technique of using an inhibitor for secondary recrystallization, a technique has been proposed in which the effect as an inhibitor is maximized by optimizing the finish annealing conditions. For example, Patent Document 6 describes a method in which the dew point of an atmosphere in the secondary recrystallization temperature range of 800 to 1150 ° C. in finish annealing is set in the range of -20 to + 30 ° C. and the temperature range is heated at 35 hr or less. No. 7 is heated at 20 ° C./hr to an arbitrary predetermined temperature between 700 and 850 ° C. in the finish annealing, and 5 ° C./hr or more and 15 ° C./hr from the above-mentioned predetermined temperature to the temperature range of 1100 to 1300 ° C. A method of heating below is proposed.

Tokukousho 40-0156444 Special Publication No. 51-013469 Special Publication No. 38-008214 Japanese Unexamined Patent Publication No. 52-024116 Japanese Unexamined Patent Publication No. 03-002324 Japanese Unexamined Patent Publication No. 50-134917 Japanese Unexamined Patent Publication No. 03-013527

However, according to the experience of the inventors, the above-mentioned Patent Documents 6 and 7 disclose a technique for producing a grain-oriented electrical steel sheet from a steel slab containing an inhibitor-forming component and further containing an segregation element as an auxiliary inhibitor. Even if the finished finish annealing conditions are applied, it is difficult to stably produce grain-oriented electrical steel sheets having good magnetic properties.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to use a steel material containing an inhibitor-forming element and a grain boundary segregation element as an auxiliary inhibitor. It is an object of the present invention to propose a method for stably producing a grain-oriented electrical steel sheet having various magnetic properties.

In order to solve the above problems, the inventors have made extensive studies focusing on the effect of the grain boundary segregation element, which functions as an auxiliary inhibitor, on the magnetic properties through finish annealing. As a result, the total amount of the grain boundary segregating elements Sb, Sn, Mo and P greatly affects the appropriate range of the temperature rising rate and the cooling rate in the finish annealing, and the finish annealing is performed according to the total amount of the grain boundary segregating elements. It has been found that a directional electromagnetic steel sheet having good magnetic characteristics can be stably produced by controlling the heating rate and the cooling rate, and the present invention has been developed.

That is, in the present invention, C: 0.02 to 0.10 mass%, Si: 2.0 to 5.0 mass%, Mn: 0.01 to 1.00 mass%, sol. Al: 0.01 to 0.04 mass%, N: 0.004 to 0.020 mass%, one or two selected from S and Se are contained in the range of 0.002 to 0.040 mass% in total. Then, select from Sn: 0.010 to 0.200 mass%, Sb: 0.010 to 0.200 mass%, Mo: 0.010 to 0.150 mass% and P: 0.010 to 0.150 mass%. A steel slab containing one or more of the following types and having a component composition in which the balance is Fe and unavoidable impurities is reheated to a temperature of 1250 ° C. or higher, and then hot-rolled to obtain a hot-rolled plate. After or without plate annealing, one cold rolling or two or more cold rolling with intermediate annealing sandwiched between them to obtain a cold-rolled plate with the final plate thickness, and decarburization annealing that also serves as primary recrystallization annealing. In the method for producing a directional electromagnetic steel sheet, which comprises a series of steps of applying an annealing separator to the surface of the steel sheet, finishing annealing, and then flattening and annealing, the steel slab is produced by a continuous casting method and is continuous. At the time of casting, electromagnetic stirring in the mold is applied to generate a swirling flow velocity of 0.1 m / s or more in the molten steel, and the average temperature rise rate from 750 ° C. to 1050 ° C. in the temperature raising process of the finish annealing is R _h (° C./ hr), when the average cooling rate from 1000 ° C. to 700 ° C. in the cooling process of finish annealing is R _c (° C./hr), the total content of Sn, Sb, Mo and P is X (mass%). R _h (° C./hr) and R _c (° C./hr) are given by the following equation (1);
1 / 6X ≤ R _h ≤ 1 / X ... (1)
And equation (2);
80X ≤ R _c ≤ 400X ... (2)
We propose a method for manufacturing grain-oriented electrical steel sheets, which is characterized by satisfying the above conditions.

The method for producing grain-oriented electrical steel sheets of the present invention is characterized in that the average heating rate between 1050 ° C. and 1150 ° C. in the heating process of finish annealing is in the range of 10 to 30 ° C./hr.

Further, the method for producing a grain-oriented electrical steel sheet of the present invention is characterized in that it is held for 5 hours or more at any temperature between 750 ° C. and 1050 ° C. in the temperature raising process of the finish annealing.

Further, the steel slab used in the method for producing a grain-oriented electrical steel sheet of the present invention has Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu in addition to the above component composition. : Contains one or more selected from 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Te: 0.005 to 0.050 mass% and Nb: 10 to 200 ppm. It is characterized by doing.

According to the present invention, it is preferable to optimize the heating rate and the cooling rate in the finish annealing based on the total contents of the grain boundary segregating elements Sb, Sn, Mo and P contained in the steel slab. It becomes possible to industrially stably manufacture grain-oriented electrical steel sheets having various magnetic properties.

It is a graph which shows the influence of the total amount X of the grain boundary segregating element on the _{heating rate R h} and the cooling rate R _c of finish annealing which can obtain excellent magnetic properties. It is a graph which shows the influence of the total amount X of grain boundary segregating elements and the average temperature rise rate R _h of finish annealing on the magnetic flux density B _8. It is a graph which shows the influence of the total amount X of grain boundary segregating elements and the average cooling rate R _c of finish annealing on the iron loss W _{17/50 of a product plate.} It is a graph which shows the influence on the magnetic flux density of the swirling flow velocity of molten steel at the time of continuous casting.

First, the experiments that led to the development of the present invention will be described.
<Experiment 1>
C: 0.074 mass%, Si: 3.51 mass%, Mn: 0.12 mass%, S: 0.002 mass%, sol. Steel slab A having a component composition of Al: 0.025 mass%, N: 0.0075 mass%, Se: 0.023 mass%, Sb: 0.025 mass% and Mo: 0.010 mass%, and C: 0.070 mass%. , Si: 3.45 mass%, Mn: 0.11 mass%, sol. Steel slab B having a component composition of Al: 0.024 mass%, N: 0.0071 mass%, S: 0.002 mass%, Se: 0.024 mass%, Sb: 0.120 mass% and Mo: 0.052 mass%. Manufactured by the continuous casting method, electromagnetic stirring in the mold was applied to generate a molten steel flow having a swirling flow velocity of 0.3 m / s. Next, the steel slab is reheated to a temperature of 1400 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.4 mm, annealed by hot-rolled plate at 1000 ° C. × 60 s, and then cold-rolled. The intermediate plate thickness was 1.5 mm, and after intermediate annealing at 1150 ° C. × 150 s, it was cold-rolled to finish a cold-rolled plate having a final plate thickness of 0.23 mm.

_Then, the steel sheet _{50vol% H 2 -50vol% N 2} , under an atmosphere of a dew point of 60 ° C., was subjected to decarburization annealing serving also as a primary recrystallization annealing of 840 ° C. × 150s, the annealing separator consisting mainly of MgO It was applied to the surface and subjected to finish annealing at 1200 ° C. × 5 hr. The atmosphere of finish annealing was a nitrogen atmosphere when the temperature was from room temperature to 900 ° C. in the temperature raising process and 900 ° C. or lower in the cooling process, and a hydrogen atmosphere was used otherwise. At this time, the average heating rate from normal temperature to 750 ° C. in the finishing annealing heating process is 30 ° C./hr, the average heating rate from 1050 ° C. to 1200 ° C. is 10 ° C./hr, and the average heating rate from 1200 ° C. to 1000 in the cooling process. ° C. / average cooling rate average cooling rate of 30 ° C. / hr, 700 ° C. or less up hr is set to 10 ° C. / hr, the average heating rate _{R h} to 1050 ° C. from 750 ° C. heating process, the cooling process _{The average cooling rate R c} from 1000 ° C to 700 ° C was varied.

After that, the steel sheet after finish annealing was subjected to flattening annealing at 840 ° C. × 30 s, and then a test piece was sampled, and the magnetic flux density B ₈ (magnetic flux density at a magnetization force of 800 A / m) was described in JIS C 2550. It was measured by the method of.

The results of the above measurements are shown in FIG. 1 (a) for the steel slab A and in FIG. 1 (b) for the steel slab B. From this result, the appropriate ranges of the _{average heating rate R h} and the average cooling rate R _c for obtaining a good magnetic flux density are significantly different between the steel slab A and the steel slab B in which the total amounts of the segregating elements Sb and Mo are different. You can see that.

<Experiment 2>
C: 0.050 to 0.055 mass%, Si: 3.27 to 3.45 mass%, Mn: 0.07 to 0.09 mass%, sol. Al: 0.022 to 0.025 mass%, N: 0.0069 to 0.0077 mass%, S: 0.002 to 0.003 mass%, and Se: 0.017 to 0.022 mass%, and further. Steel slabs containing various amounts of segregating elements Sb, Sn, Mo and P were produced by a continuous casting method. At that time, electromagnetic stirring in the mold was applied to generate a molten steel flow having a swirling flow velocity of 0.2 m / s. Next, the steel slab was reheated to a temperature of 1350 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.6 mm, annealed by hot-rolled plate at 1050 ° C. × 60 s, and then cold-rolled. The intermediate plate thickness was set to 1.8 mm, and after intermediate annealing at 1150 ° C. × 150 s, it was cold-rolled to finish a cold-rolled plate having a final plate thickness of 0.23 mm.

_{Then, 55vol% H 2 -45vol% N} 2, was subjected to decarburization annealing serving also as a primary recrystallization annealing of 840 ° C. × 150s under an atmosphere of a dew point of 62 ° C., the steel sheet surface with an annealing separator composed mainly of MgO Was applied to and subjected to finish annealing at 1220 ° C. × 15 hr. The atmosphere of finish annealing was a nitrogen atmosphere when the temperature was from room temperature to 900 ° C. in the temperature raising process and 900 ° C. or lower in the cooling process, and a hydrogen atmosphere in other cases. At this time, the average heating rate from normal temperature to 750 ° C. in the finishing annealing heating process is 40 ° C./hr, the average heating rate from 1050 ° C. to 1200 ° C. is 15 ° C./hr, and the average heating rate from 1200 ° C. to 1000 in the cooling process. ° C. / average cooling rate average cooling rate of 25 ° C. / hr, 700 ° C. or less up hr is set to 20 ° C. / hr, the average heating rate _{R h} to 1050 ° C. from 750 ° C. heating process, the cooling process _{The average cooling rate R c} from 1000 ° C to 700 ° C was varied.

After that, the steel sheet after finish annealing was subjected to flattening annealing at 820 ° C. × 20 s, and then a test piece was sampled to _{obtain a magnetic flux density B 8} (magnetic flux density at a magnetization force of 800 A / m) and an iron loss W _{17 /. 50} (iron loss when excited by 1.7 T at a frequency of 50 Hz) was measured by the method described in JIS C 2550.

Figure 2 is a measurement result of the magnetic flux density _{B 8,} segregation elements Sb, Sn, the total content of Mo and P (hereinafter, also referred to as "total") X and the average temperature from 750 ° C. to finish annealing to 1050 ° C. It is shown organized in relation to the temperature rate R _h. For each point shown in FIG. 2, there is a condition that the total amount X of the segregated elements and the average heating rate R _h are the same and the average cooling rate R _c is different, but the magnetic flux density shown in FIG. 2 is present. The evaluation of the above shows the evaluation result of the magnetic flux density B _{8 having the best value among them.} That is, FIG. 2 is an evaluation of the magnetic flux density when the _{average cooling rate R c is optimized.}

Then, from FIG. 2, the range of the average Atsushi Nobori rate R _h in finish annealing good magnetic flux density B ₈ is obtained, largely changed by the total amount X of segregating elements, specifically, the following equation (1);
1 / 6X ≤ R _h ≤ 1 / X ... (1)
It was found that a good magnetic flux density can be obtained within the range satisfying.

Further, FIG. 3 _shows the measurement results of the iron loss W 17/50, the total content (total amount) X of the segregating elements Sb, Sn, Mo and P, and the average cooling rate R of the finish annealing from 1000 ° C. to 700 ° C. It is shown organized in relation to _c. Similar to FIG. 2, for each point shown in FIG. 3, there is a condition that the total amount X of the segregated elements and the average cooling rate R _c are the same, but the average temperature rise rate R _h is different. The evaluation of the iron loss characteristics shown in (1) shows the evaluation result _{of the iron loss W 17/50, which is the best value among them.} That is, FIG. 3 is an evaluation of the iron loss characteristics when the _{average temperature rise rate R h is optimized.}

Then, from FIG. 3, _{the range of the average cooling rate R c} between 1000 ° C. and 700 ° C. in the cooling process in the finish annealing in which _{a good iron loss W 17/50} is obtained varies depending on the total amount X of the segregated elements, and is concrete. The following equation (2);
80X ≤ _RC ≤ 400X ... (2)
It was found that good iron loss characteristics can be obtained within the range satisfying.

_{As described above, the reason why the optimum ranges of the temperature rising rate R h} and the cooling rate R _c of the finish annealing differ depending on the total amount X of the segregated elements has not been sufficiently clarified at this time, but the inventors have described the following. I'm thinking.
First, from FIG. 2, when the total amount X of segregated elements is large, the magnetic flux density tends to be good when _{the average temperature rise rate R h from 750 ° C. to 1050 ° C. in the finishing annealing temperature rise process is slow.} Be done. The temperature range of 750 ° C. to 1050 ° C. is the temperature at which secondary recrystallization starts, but when there are many segregating elements, a large amount of segregating elements segregate at the grain boundaries of the secondary recrystallized grains, so that the secondary recrystallization is secondary. Grain growth of recrystallized grains is inhibited. Further, when the grain growth of the secondary recrystallized grains is inhibited and the primary recrystallized grains that are not recrystallized by the secondary recrystallized grains are heated to a high temperature while remaining, the remaining primary recrystallized grains have an unfavorable orientation. It is considered that secondary recrystallized grains are generated, primary recrystallized grains grow normally and become coarse, and regions that are not eroded by the secondary recrystallized grains are generated, resulting in deterioration of magnetic properties. Therefore, when the total amount of segregating elements is large, it takes time to complete the secondary recrystallization, so that the decrease in the magnetic flux density is suppressed by slowing the temperature rise rate in the temperature range where the secondary recrystallization occurs.

Conversely, if the total amount X of segregating elements is small, the average heating rate R _h from 750 ° C. heating process of final annealing to 1050 ° C. is slow, is observed a tendency that rather flux density decreases. The reason for this is that if the rate of temperature rise is slow, the time until the start of secondary recrystallization is considered to be relatively long, but since there are few segregating elements, the normal grain growth of the primary recrystallization grains is small during that time. It is considered that this occurs without any problem and adversely affects the magnetic flux density.
If the above mechanism is correct, it is considered preferable to keep the temperature range in which secondary recrystallization occurs at a constant temperature for a certain period of time when the total amount of segregating elements is large.

Further, from FIG. 3, when the total amount X of the segregated elements is large, the iron loss characteristic tends to be _{improved as the average cooling rate R c of the finish annealing from 1000 ° C. to 700 ° C. is faster.} In the cooling process of finish annealing, secondary recrystallization has already been completed and grain boundary movement hardly occurs, but segregation of solute atoms to the grain boundaries occurs, and when the cooling rate is slow, grains of segregating elements Segregation to the world is promoted. Then, in the flattening annealing following the finish annealing, the steel sheet is annealed in a state where tension is applied, so that strain (transition) is introduced into the steel sheet. Normally, the strain introduced here disappears during annealing, but at grain boundaries where a large amount of segregating elements are present, the movement of dislocations is hindered, the strain is excessively accumulated, and the iron loss characteristics are adversely affected. .. Therefore, it is considered that the larger the total amount X of the segregating elements, the higher the cooling rate of the finish annealing and the suppression of the grain boundary segregation, thereby preventing the iron loss deterioration in the flattening annealing.

<Experiment 3>
C: 0.068 mass%, Si: 3.22 mass%, Mn: 0.15 mass%, sol. Steels having a component composition of Al: 0.025 mass%, N: 0.0075 mass%, Se: 0.017 mass%, Sb: 0.055 mass% and Mo: 0.040 mass% are melted and subjected to a continuous casting method. It was a steel slab. At that time, by applying electromagnetic agitation in the mold and adjusting the applied current, the swirling flow velocity of the molten steel in the mold can be changed in various ways. Next, the steel slab was reheated to a temperature of 1370 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.3 mm, annealed by hot-rolled plate at 1000 ° C. × 60 s, and then cold-rolled. The intermediate plate thickness was 1.8 mm, and after intermediate annealing at 1100 ° C. × 150 s, it was cold-rolled to finish a cold-rolled plate having a final plate thickness of 0.20 mm.

_{Then, 50vol% H 2 -50vol% N} 2, under an atmosphere of a dew point of 62 ° C., was subjected to decarburization annealing serving also as a primary recrystallization annealing of 840 ° C. × 100s, an annealing separator composed mainly of MgO It was applied to the surface of a steel sheet and subjected to finish annealing at 1200 ° C. × 5 hr. The atmosphere of finish annealing was a nitrogen atmosphere when the temperature was from room temperature to 900 ° C. in the temperature raising process and 900 ° C. or lower in the cooling process, and a hydrogen atmosphere was used otherwise. At this time, the average heating rate from normal temperature to 750 ° C. in the finishing annealing heating process is 25 ° C./hr, the average heating rate from 1050 ° C. to 1200 ° C. is 8 ° C./hr, and the average heating rate from 1200 ° C. to 1000 in the cooling process. ° C. / average cooling rate average cooling rate of 30 ° C. / hr, 700 ° C. or less up hr is set to 10 ° C. / hr, the average heating rate _{R h} to 1050 ° C. from 750 ° C. heating process is 8 ° C. / hr _{The average cooling rate R c} from 1000 ° C to 700 ° C in the cooling process was set to 20 ° C / hr.

After that, the steel sheet after finish annealing was subjected to flattening annealing at 840 ° C. × 30 s, and then a test piece was sampled, and the magnetic flux density B ₈ (magnetic flux density at a magnetization force of 800 A / m) was described in JIS C 2550. It was measured by the method of. The result is shown in FIG. From this result, it can be seen that good magnetic characteristics are obtained by setting the swirling flow velocity of the molten steel flow during continuous casting to 0.1 m / s or more.

As described above, the reason why good magnetic properties can be obtained by applying electromagnetic agitation in the mold during continuous casting and generating a molten steel flow with a swirling flow velocity of 0.1 m / s or more is that the segregation element added in a large amount has a flow velocity. It is considered that the effect of the above was uniformly dispersed in the slab, and the effect of improving the magnetic characteristics was uniformly exhibited. In addition, when electromagnetic stirring is not performed, local concentration of segregated elements is promoted, and the main solidified structure becomes columnar crystals, which increases unfavorable crystal orientation and deteriorates the magnetic properties of the final product. Conceivable.

The inventors have described cooling by finish annealing as a technique for avoiding iron loss deterioration by flattening annealing due to excessive grain boundary segregation that occurs in the cooling process of finish annealing as described above. A technique for limiting the tension applied to a steel sheet by flattening annealing according to the speed has been developed and already disclosed in International Publication No. 2016/140373. However, the technique of the present invention is a method of preventing iron loss deterioration without controlling the tension of flattening annealing, and the technical idea is different from the above technique.

Next, the composition of the steel material (steel slab) used in the production of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.02 to 0.10 mass%
If C is less than 0.02 mass%, the structure becomes α single phase, and the material becomes brittle during casting or hot rolling, causing cracks in the slab, and cracks in the edges of the steel sheet after hot rolling. As a result, defects that interfere with manufacturing will occur. On the other hand, if the C content exceeds 0.10 mass%, it becomes difficult to reduce it to 0.005 mass% or less, which does not cause magnetic aging due to decarburization annealing. Therefore, C is in the range of 0.02 to 0.10 mass%. It is preferably in the range of 0.025 to 0.08 mass%.

Si: 2.0-5.0 mass%
Si is an element necessary to increase the specific resistance of steel and reduce iron loss. The above effect is not sufficient if it is less than 2.0 mass%, while if it exceeds 5.0 mass%, the workability is lowered and it becomes difficult to manufacture by rolling. Therefore, Si is in the range of 2.0 to 5.0 mass%. It is preferably in the range of 2.5 to 4.0 mass%.

Mn: 0.01 to 1.00 mass%
Mn is an element required to improve the hot workability of steel. The above effect is not sufficient if it is less than 0.01 mass%, while if it exceeds 1.00 mass%, the magnetic flux density of the product plate is lowered. Therefore, Mn is set in the range of 0.01 to 1.00 mass%. It is preferably in the range of 0.02 to 0.30 mass%.

sol. Al: 0.01 to 0.04 mass%
Al is an element that forms and precipitates AlN and functions as an inhibitor that suppresses normal grain growth in secondary recrystallization annealing. However, if the Al content is less than 0.01 mass% of acid-soluble Al (sol.Al), the absolute amount of the inhibitor is insufficient, and the ability to suppress normal grain growth is insufficient. On the other hand, when it exceeds 0.04 mass%, AlN grows Ostwald and becomes coarse, and the ability to suppress normal grain growth is also insufficient. Therefore, the Al content is sol. The range of Al is 0.01 to 0.04 mass%. It is preferably in the range of 0.012 to 0.030 mass%.

N: 0.004 to 0.020 mass%
N forms Al and AlN and precipitates to function as an inhibitor, but if the content is less than 0.004 mass%, the absolute amount of the inhibitor is insufficient and the ability to suppress normal grain growth is insufficient. On the other hand, if the N content exceeds 0.020 mass%, slab swelling may occur during hot rolling. Therefore, the content of N is set to 0.004 to 0.020 mass%. It is preferably in the range of 0.006 to 0.010 mass%.

One or two of S and Se: 0.002 to 0.040 mass% in total
S and Se combine with Mn to form MnS and MnSe as inhibitors. However, if it is less than 0.002 mass% alone or in total, the effect cannot be sufficiently obtained. On the other hand, if it exceeds 0.040 mass%, the inhibitor grows Ostwald and becomes coarse, and the inhibitory power of normal grain growth becomes insufficient. Therefore, the total contents of S and Se are in the range of 0.002 to 0.040 mass%. It is preferably in the range of 0.005 to 0.030 mass%.

Sn: 0.010 to 0.200 mass%, Sb: 0.010 to 0.200 mass%, Mo: 0.010 to 0.150 mass%, P: at least one of 0.010 to 0.150 mass% Sn, Sb, Mo and P are all elements having a strong tendency to segregate at grain boundaries, and are essential elements in the present invention from the viewpoint of improving magnetic properties. When the content of each of these elements is less than 0.010 mass%, the effect of improving magnetic properties cannot be sufficiently obtained, while when Sn and Sb exceed 0.200 mass% and Mo and P exceed 0.150 mass%, Segregation to the grain boundaries becomes excessive, which may cause problems such as cracks at the grain boundaries. Therefore, Sn, Sb, Mo and P are each within the above range. Preferably, Sn: 0.020 to 0.150 mass%, Sb: 0.020 to 0.100 mass%, Mo: 0.010 to 0.100 mass%, P: 0.02 to 0.08 mass%. ..

In the steel material used for manufacturing the grain-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and unavoidable impurities, but for the purpose of improving the magnetic flux density, Ni: 0.010 to 1.50 mass%, Cr. : 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Te: 0.005 to 0.050 mass% and Nb: 0.0010 to 0 It can contain one or more selected from 0.0200 mass. If the content of each is less than the lower limit of the above range, the effect of improving the magnetic flux density is small, and conversely, if the content exceeds the upper limit of the above range, the saturation magnetic flux density is lowered and the magnetic characteristics are lowered. Therefore, when any one or more of Ni, Cr, Cu, Bi, Te and Nb is added, it is preferably in the above range.

Next, the method for manufacturing the grain-oriented electrical steel sheet of the present invention will be described.
First, the steel slab having the component composition described above needs to be produced by a continuous casting method and to generate a swirling flow velocity of 0.1 m / s or more in the molten steel by applying electromagnetic agitation in the mold. If the flow velocity is less than 0.1 m / s, the above-mentioned segregating elements segregate during solidification, and the magnetic properties of the final product cannot be improved. It is preferably 0.2 m / s or more. Further, as a similar technique, there is an electromagnetic agitation technique in a strand, and the case where a swirling flow velocity is generated by using this technique also falls under the present invention. The swirling flow velocity is a value obtained by electromagnetic field analysis calculation of the flow velocity of the molten steel in the vicinity of the solidified shell at the position 1/4 in the width direction of the solidifying slab facing the electromagnetic stirring coil.

Next, the steel slab is reheated to a temperature of 1250 ° C. or higher, and then hot-rolled. If the heating temperature of the slab is less than 1250 ° C., the added inhibitor-forming component does not sufficiently dissolve in the steel. The preferred slab heating temperature is 1300 ° C. or higher. As the means for heating the slab, known means such as a gas furnace, an induction heating furnace, and an energizing furnace can be used. The hot rolling following the reheating of the slab may be performed under conventionally known conditions, and is not particularly limited.

Next, the steel sheet (hot-rolled sheet) after the hot-rolling may be directly transferred to cold-rolling, but in order to obtain good magnetic properties, it is preferable to perform hot-rolled sheet annealing. The soaking temperature of the hot-rolled sheet annealing is preferably in the range of 800 to 1200 ° C. If it is less than 800 ° C., the effect of hot-rolled sheet annealing is not sufficient, while if it exceeds 1200 ° C., the particle size becomes too coarse and it becomes difficult to obtain a sized primary recrystallized structure.

Next, the hot-rolled plate after hot-rolling or after hot-rolling plate annealing is cold-rolled once or cold-rolled two or more times with intermediate annealing sandwiched between them to achieve the final plate thickness (product plate thickness). And. The soaking temperature of the intermediate annealing is preferably in the range of 900 to 1200 ° C. Below 900 ° C., the recrystallized grains become too fine, the Goss nuclei in the primary recrystallized structure decrease, and the magnetic properties deteriorate. On the other hand, if the temperature exceeds 1200 ° C., the particle size becomes too coarse as in the case of hot-rolled sheet annealing, and it becomes difficult to obtain a sized primary recrystallized structure. In cold rolling (final cold rolling), which is the final plate thickness, the temperature of the cold rolled steel sheet is heated to a temperature of 100 to 300 ° C. from the viewpoint of improving the recrystallization texture and improving the magnetic properties. It is preferable to employ warm rolling performed in the cold rolling, or to perform aging treatment (inter-pass aging) once or multiple times at a temperature of 100 to 300 ° C. in the middle of cold rolling.

Next, the cold-rolled plate having the final plate thickness is subjected to decarburization annealing that also serves as primary recrystallization annealing. From the viewpoint of promoting decarburization, decarburization annealing is preferably performed in a temperature range of 800 to 900 ° C. in a moist atmosphere with a dew point of 10 ° C. or higher.

Next, the steel sheet after the primary recrystallization is coated with an annealing separator mainly composed of MgO on the surface thereof, dried, and then subjected to finish annealing to develop a secondary recrystallization structure and to form a forsterite film. To form. This finish annealing step is the most important step in the present invention, and as described above, the finish annealing step is performed according to the total content X of the segregating elements Sn, Sb, Mo and P in the steel slab. _{The average temperature rise rate R h} between 750 ° C. and 1050 ° C. in the temperature rise process _{and the average cooling rate R c} between 1000 ° C. and 700 ° C. in the cooling process are defined by the above-mentioned equations (1) and (2). It is necessary to control within the appropriate range.

Here, the average speed between the temperatures of the two points is a value obtained by dividing the temperature difference between the two points by the time spent for the temperature change between the two points, and the temperature rise rate between the two points. It is not affected by changes in the cooling rate or even if there is a treatment to keep the temperature constant. This is because in finish annealing in industrial production, the rate of temperature rise and the rate of cooling change with time, and it is generally difficult to keep them constant.

Further, the average heating rate between 1050 ° C. and 1150 ° C. in the temperature raising process of the finish annealing is preferably in the range of 10 to 30 ° C./hr from the viewpoint of improving the film characteristics. If the rate of temperature rise during this period is less than 10 ° C./hr, the peeling resistance of the coating film tends to deteriorate, while if it exceeds 30 ° C./hr, there is a high possibility that the coating film formation will be insufficient. is there. More preferably, it is in the range of 15 to 25 ° C./hr.

Further, in the temperature range where the secondary recrystallization from 750 ° C. to 1050 ° C. in the temperature raising process of the finish annealing starts, as described above, from the viewpoint of obtaining good magnetic characteristics, any temperature between the above temperatures is obtained. It is preferable to hold 5 hr or more. A more preferred retention time is in the range of 20-75 hr. In this case as well, the average temperature rise rate R _h from 750 ° C. to 1050 ° C. is a value obtained by dividing the temperature difference of 300 ° C. by the time spent for raising the temperature from 750 ° C. to 1050 ° C. including the holding time. ..

In the final annealing of the present invention, the total amount X of segregating elements increases, it is necessary to slow the average heating rate R _h of between 750 ° C. to 1050 ° C., since the productivity is lowered, from room temperature until 750 ° C., the rate R was raised at a faster rate than _h, it is to avoid deterioration in productivity preferred.

Next, the steel sheet after the finish annealing is washed with water, brushed, pickled, etc. to remove the unreacted annealing separator adhering to the surface of the steel sheet, and then the shape defects such as curl in the finish annealing are corrected to cause iron loss. It is preferable to perform flattening annealing in order to improve the characteristics.

When the grain-oriented electrical steel sheets are laminated and used, it is preferable to coat the surface of the steel sheets with an insulating film in the above-mentioned flattening annealing or before or after the flattening annealing in order to improve the iron loss. From the viewpoint of reducing iron loss, it is preferable to use a tension applying film that applies tension to the steel sheet. Further, in order to further improve the film adhesion and obtain a better iron loss reduction effect, a tension-applying film is formed via a binder, or an inorganic film is applied to the surface of the steel sheet by a physical vapor deposition method or a chemical vapor deposition method. After forming the above, it is preferable to cover the tension applying film.

Further, in order to further reduce the iron loss, magnetic domain subdivision treatment may be performed. As a method of subdividing the magnetic domain, a conventionally known method can be used. For example, the surface of a steel sheet as a final product is irradiated with a laser, plasma, or the like to introduce linear or dotted thermal strain or impact strain. A method of forming a groove on the surface of a steel plate having a final plate thickness in any of the steps can be used.

C: 0.055 mass%, Si: 3.45 mass%, Mn: 0.12 mass%, sol. Al: 0.020 mass%, S: 0.0020 mass%, Se: 0.020 mass%, N: 0.0072 mass%, Sn: 0.020 mass%, Sb: 0.036 mass%, Mo: 0.022 mass% and P : A steel slab containing 0.030 mass% and having a composition of the balance consisting of Fe and unavoidable impurities was produced by continuous casting. At this time, the swirling flow velocity of the molten steel was changed as shown in Table 1 by applying electromagnetic agitation in the mold and adjusting the applied current. The total content X of the segregating elements (Sn, Sb, Mo, P) of the steel slab is 0.108 mass%, and from this value, the parameter 1 in the above-mentioned equations (1) and (2) of the present invention. When / 6X, 1 / X, 80X and 400X are obtained, 1 / 6X = 1.54, 1 / X = 9.25, 80X = 8.64 and 400X = 43.2, respectively.

Next, the steel slab was reheated to a temperature of 1300 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.7 mm, annealed by hot-rolled plate at 1000 ° C. for 30 s, and then cold-rolled. The intermediate plate thickness was 1.8 mm, and after intermediate annealing at 1125 ° C. × 120 s, the final cold rolling was performed to obtain a cold-rolled plate having a plate thickness of 0.23 mm. _Then, the steel sheet _{55vol% H 2 -45vol% N 2} , under an atmosphere of a dew point of 60 ° C., was subjected to decarburization annealing serving also as a primary recrystallization annealing of 840 ° C. × 150s, the annealing separator consisting mainly of MgO It was applied to the surface and subjected to finish annealing at 1220 ° C. × 10 hr. The atmosphere of the finish annealing was a nitrogen atmosphere at room temperature to 900 ° C. in the temperature raising process and 900 ° C. or lower in the cooling process, and a hydrogen atmosphere at other times. _{At this time, the average temperature rise rate R h1} from normal temperature to 750 ° C. in the temperature rise process of the finish annealing is 25 ° C./hr, the average temperature rise rate from 1050 ° C. to 1220 ° C. is 20 ° C./hr, and 1220 in the cooling process. ° C. from 1000 ° C. / hr an average cooling rate of up to 30 ° C. / hr, 700 ° C. the average cooling rate below the 50 ° C. / hr, the average heating rate _{R h} to 1050 ° C. from 750 ° C. heating process, _{The average cooling temperature rate R c} from 1000 ° C. to 700 ° C. in the cooling process was variously changed as shown in Table 1 in consideration of the total amount X of segregated elements of the steel slab described above.

After that, the steel sheet after the finish annealing was subjected to flattening annealing at 850 ° C. × 100 s, and then a test piece was sampled to _{obtain a magnetic flux density B 8} (magnetic flux density at a magnetization force of 800 A / m) and an iron loss W _{17 /. 50} (iron loss when excited by 1.7 T at a frequency of 50 Hz) was measured by the method described in JIS C 2550.

The results obtained are also shown in Table 1.
From this result, electromagnetic stirring is applied to generate a swirling flow velocity within the range of the present invention in the molten steel, and the average heating rate R _h and the average cooling rate R _c of the present invention in consideration of the total amount X of segregated elements are satisfied. It can be seen that the steel sheets that have been finish-annealed under the conditions are all excellent in magnetic flux density and iron loss characteristics.

Steel slabs having various component compositions shown in Table 2 were produced by a continuous casting method. At this time, electromagnetic stirring in the mold was applied to set the swirling flow velocity of the molten steel to 0.25 m / s. Next, the steel slab was reheated to a temperature of 1410 ° C. and then hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.5 mm, annealed by hot-rolled plate at 950 ° C. × 30 s, and then cold-rolled. The intermediate plate thickness was 1.6 mm, and after intermediate annealing at 1165 ° C. × 20 s, the final cold rolling was performed to obtain a cold rolled plate having a plate thickness of 0.20 mm.

_Then, the steel sheet _{60vol% H 2 -40vol% N 2} , under an atmosphere of a dew point of 58 ° C., was subjected to decarburization annealing serving also as a primary recrystallization annealing of 835 ° C. × 100s, the annealing separator consisting mainly of MgO It was applied to the surface and held at a temperature of 900 ° C. for 50 hours to cause secondary recrystallization, and then finish annealing was performed at a temperature of 1200 ° C. for 5 hours. The atmosphere of the finish annealing was a nitrogen atmosphere at room temperature to 900 ° C. in the temperature raising process and 900 ° C. or lower in the cooling process, and a hydrogen atmosphere at other times.
At this time, the average heating rate from normal temperature to 750 ° C. in the process of raising the temperature of finish annealing is the average from 40 ° C./hr, 750 ° C. to 1050 ° C. after retention at 900 ° C. Temperature rise rate R _h is 5 ° C / hr, average temperature rise rate from 1050 ° C to 1200 ° C is 15 ° C / s, and average cooling rate from 1200 ° C to 1000 ° C in the cooling process is 40 ° C / hr, from 1000 ° C. The average cooling rate R _{c up} to 700 ° C. was 20 ° C./hr, and the average cooling rate below 700 ° C. was 40 ° C./hr. Incidentally, the average heating rate R _h and the average cooling rate R _c are defined by the total amount X of the segregating elements (Sn, Sb, Mo, P) contained in each slab shown in Table 2 (1). And Eq. (2) is expressed in No. Except for 8 and 9, it was satisfied.
After that, the steel sheet after the finish annealing was subjected to flattening annealing at 870 ° C. × 30 s, and then a test piece was sampled to _{obtain a magnetic flux density B 8} (magnetic flux density at a magnetization force of 800 A / m) and an iron loss W _{17 /. 50} (iron loss when excited by 1.7 T at a frequency of 50 Hz) was measured by the method described in JIS C 2550.

The results obtained are also shown in Table 2.
From this result, a steel sheet subjected to finish annealing under the conditions of satisfying the _{average heating rate R h} and the average cooling rate R _c of the present invention in consideration of the total amount X of segregated elements using a steel material satisfying the composition of the present invention. It can be seen that both have excellent magnetic flux density and iron loss characteristics.

Claims (3)

C: 0.02 to 0.10 mass%, Si: 2.0 to 5.0 mass%, Mn: 0.01 to 1.00 mass%, sol. Al: 0.01 to 0.04 mass%, N: 0.004 to 0.020 mass%, one or two selected from S and Se are contained in the range of 0.002 to 0.040 mass% in total. Then, select from Sn: 0.010 to 0.200 mass%, Sb: 0.010 to 0.200 mass%, Mo: 0.010 to 0.150 mass% and P: 0.010 to 0.150 mass%. A steel slab containing one or more of the following types and having a component composition in which the balance is Fe and unavoidable impurities is reheated to a temperature of 1250 ° C. or higher, and then hot-rolled to obtain a hot-rolled plate. After or without plate annealing, one cold rolling or two or more cold rolling with intermediate annealing sandwiched between them to obtain a cold-rolled plate with the final plate thickness, and decarburization annealing that also serves as primary recrystallization annealing. In the method for manufacturing a directional electromagnetic steel sheet, which consists of a series of steps of applying an annealing separator to the surface of the steel sheet, finishing annealing, and then flattening and annealing.
The steel slab is manufactured by a continuous casting method, and electromagnetic stirring in the mold is applied during continuous casting to generate a swirling flow velocity of 0.1 m / s or more in the molten steel.
The average heating rate from 750 ° C to 1050 ° C in the finishing annealing heating process is R _h (° C / hr), and the average cooling rate from 1000 ° C to 700 ° C in the finishing annealing cooling process is R _c (° C / hr). When hr), the total contents X (mass%), R _h (° C / hr) and R _c (° C / hr) of the Sn, Sb, Mo and P contents are the following equations (1) and (2). A method for producing a directional electromagnetic steel plate, which satisfies the formula and sets the average heating rate between 1050 ° C. and 1150 ° C. in the temperature raising process of the finish annealing in the range of 15 to 30 ° C./hr.
Note 1 / 6X ≤ R _h ≤ 1 / X ... (1)
80X ≤ R _c ≤ 400X ... (2) In any temperature until 1050 ° C. from 750 ° C. in the temperature elevation process of the final annealing method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that retaining least 5 hr. In addition to the above component composition, the steel slab further contains Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, and Bi: 0. The invention according to claim 1 or 2 , wherein one or more selected from 005 to 0.50 mass%, Te: 0.005 to 0.050 mass% and Nb: 10 to 200 ppm are contained. Manufacturing method of grain-oriented electrical steel sheet.

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