JP5332134B2 - Manufacturing method of high magnetic flux density grain-oriented electrical steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the rapid heating region in the heating step in decarburization/annealing to the temperature at which induction heating can be used in the production of a grain-oriented magnetic steel sheet. <P>SOLUTION: When a silicon steel stock is heated at a temperature of 1,350&deg;C or lower and is thereafter hot-rolled, the hot-rolled sheet is annealed and is then cold-rolled, so as to be a steel sheet with a final sheet thickness, and the steel sheet is subjected to decarburization/annealing, is thereafter nitrided, is coated with a separation agent for annealing and is subjected to finish annealing, so as to produce a grain-oriented magnetic steel sheet, the hot rolled sheet annealing is conducted in a process where the steel sheet is heated to a prescribed temperature of 1,000 to 1,150&deg;C, is recrystallized and is thereafter annealed at 850 to 1,100&deg;C lower than that temperature, and the heating in the heating step in the decarburization/annealing for the steel sheet is conducted under such conditions that the heating rate during the period when the temperature of the steel sheet is in the range of 550 to 720&deg;C is 40&deg;C/sec or higher, preferably 50 to 250&deg;C/sec. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet, which is used as an iron core of an electrical device such as a transformer, as a soft magnetic material by low-temperature slab heating.

  The grain-oriented electrical steel sheet is a steel sheet containing 7% or less of Si composed of crystal grains accumulated in the {110} <001> orientation. Control of crystal orientation in the production of such grain-oriented electrical steel sheets is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.

  As one method for controlling this secondary recrystallization, fine precipitates called inhibitors are completely dissolved during slab heating before hot rolling, and then finely precipitated in hot rolling and subsequent annealing processes. The method is practiced industrially. In this method, in order to completely dissolve the precipitate, it is necessary to heat at a high temperature of 1350 ° C. to 1400 ° C. or higher, which is about 200 ° C. higher than the slab heating temperature of ordinary steel. There are problems such as requiring a heating furnace and a large amount of melt scale.

Therefore, in order to avoid the above-mentioned problems, research and development have been conducted on the production of grain-oriented electrical steel sheets by low-temperature slab heating at 1350 ° C. or lower.
As a manufacturing method by low-temperature slab heating, for example, Komatsu et al. Discloses a method using (Al, Si) N formed by nitriding as an inhibitor. Moreover, Kobayashi et al. Disclosed a method of nitriding in strip form after decarburization annealing as a method of nitriding treatment in that case, and the present inventors also disclosed in non-patent document 1 in strip form. The behavior of nitride when nitriding is reported.

  In addition, the present inventors have reported a production method in which nitriding treatment is carried out after completely dissolving an inhibitor at a temperature of 1200 to 1350 ° C. in Patent Document 3.

  And in the manufacturing method of the grain-oriented electrical steel sheet by such low-temperature slab heating, the present inventors have not formed an inhibitor during decarburization annealing, and therefore, the adjustment of the primary recrystallized structure in the decarburization annealing is secondary. It is important to control recrystallization, and it is patented that the secondary recrystallization becomes unstable when the variation coefficient of the particle size distribution of the primary recrystallized grain structure is larger than 0.6 and the grain structure becomes non-uniform. Shown in Reference 4.

  Furthermore, as a result of advancing research on a primary recrystallization structure and an inhibitor which are control factors of secondary recrystallization, the present inventors have found that {411} oriented grains in the primary recrystallization structure are {110} <001> secondary. It has been found that it affects the preferential growth of recrystallized grains. In Patent Document 5, the ratio of {111} / {411} of the primary recrystallization texture after decarburization annealing is adjusted to 3.0 or less, and then nitriding As a method for controlling the grain structure after primary recrystallization, a grain-oriented electrical steel sheet having a high magnetic flux density can be produced industrially stably by strengthening the inhibitor by performing the treatment, for example, a decarburization annealing step It has been shown that there is a method of controlling the heating rate in the temperature rising process to 12 ° C./second or more.

Then, it turns out that the method of controlling the heating rate has a great effect as a method of controlling the grain structure after the primary recrystallization. In the grain structure after decarburization annealing by heating at a heating rate of 40 ° C./second or more from a region where the steel plate temperature is 600 ° C. or less to a predetermined temperature in the range of 750 to 900 ° C. The method of stabilizing secondary recrystallization by controlling the ratio of {411} to 3 or less and adjusting the oxygen content of the oxide layer of the steel sheet to 2.3 g / m ² or less by subsequent annealing was proposed.
Here, I {111} and I {411} are ratios of grains having {111} and {411} planes parallel to the plate surface, respectively, and were measured in the plate thickness 1/10 layer by X-ray diffraction measurement. Represents the diffraction intensity value.

  In the said method, it is necessary to heat to the predetermined temperature in the range of 750-900 degreeC with the heating rate of 40 degreeC / second or more. As for the heating means for that purpose, Patent Document 6 discloses a facility in which a conventional decarburization annealing facility such as a radiant tube using normal radiant heat is modified, a method using a high-energy heat source such as a laser, induction heating, an electric heating device, etc. Among these heating methods, in particular, induction heating has a high degree of freedom in heating rate, can be heated in a non-contact manner with a steel plate, and is relatively easy to install in a decarburization annealing furnace. It is advantageous from a certain point.

By the way, when an electromagnetic steel sheet is heated by induction heating, the current penetration depth of the eddy current becomes deep when the temperature near the Curie point is reached due to the thin plate thickness, and the vortex circulating around the surface layer of the cross section in the strip width direction. Since the currents are reversed and eddy currents do not flow, it is difficult to heat the electrical steel sheet to a temperature above the Curie point.
Since the Curie point of the grain-oriented electrical steel sheet is about 750 ° C., even if induction heating is used for heating up to that temperature, the heating to a temperature higher than that can be replaced with induction heating, for example, electric heating. It is necessary to use other means.
However, the combined use of other heating means loses the advantage of the equipment using induction heating, and for example, there is a problem that the steel plate needs to come into contact with the current heating and the steel plate is damaged.
For this reason, when the end of the rapid heating region is 750 to 900 ° C. as shown in Patent Document 3, there is a problem that the advantage of induction heating cannot be fully enjoyed.

Japanese Examined Patent Publication No. 62-45285 Japanese Patent Laid-Open No. 2-77525 JP 2001-152250 A Japanese Patent Publication No. 8-32929 Japanese Patent Laid-Open No. 9-256051 JP 2002-60842 A JP 2005-226111 A "Materials Science Forum" 204-206 (1996), pp593-598

  Therefore, when producing a grain-oriented electrical steel sheet by low-temperature slab heating of 1350 ° C. or less disclosed in Patent Document 3, the present invention provides a decarburization annealing in order to improve the grain structure after the primary recrystallization after the decarburization annealing. It is an object of the present invention to eliminate the above-mentioned drawbacks by setting the temperature range in which the heating rate is controlled in the temperature raising process to a range that can be heated only by induction heating.

In order to solve the above problems, the present invention is characterized as follows.
Invention of the grain-oriented electrical steel sheet according to claim 1 is mass%, Si: 0.8-7%, C: 0.085% or less, acid-soluble Al: 0.01-0.065%, N: 0.0075% or less, Mn: 0.02~0.20%, Seq = S + 0.406 × Se:. containing from 0.003 to 0.05%, silicon ing the balance Fe and unavoidable impurities The steel material is hot-rolled after heating at a temperature not lower than 1350 ° C. and any of temperatures T1, T2 and T3 (° C.) represented by the following formula, and the obtained hot-rolled sheet is annealed. Next, a plurality of cold rollings are performed through one cold rolling or annealing to obtain a steel plate having a final thickness, and after decarburizing and annealing the steel plate, an annealing separator is applied, finish annealing is performed, and the steel is removed. Processing to increase the amount of nitrogen in the steel plate from the start of secondary recrystallization of carbon annealing to finish annealing In the manufacturing method of the grain-oriented electrical steel sheet, the annealing of the hot-rolled sheet is heated to a predetermined temperature of 1000 to 1150 ° C. and recrystallized, and then annealed at a lower temperature of 850 to 1100 ° C. By performing in the process, the lamellar spacing is controlled to 20 μm or more in the grain structure after annealing, and the temperature of the steel sheet is increased from 550 ° C. to 720 ° C. in the temperature rising process when decarburizing and annealing the steel plate having the final thickness. Heating is performed at a heating rate of 40 ° C./second or more for a certain period.
T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273
Here, [Al], [N], [Mn], [S], and [Se] are contents (mass%) of acid-soluble Al, N, Mn, S, and Se, respectively.
The lamellar structure refers to a layered structure parallel to the rolling surface, and the lamellar interval is an average interval of the layered structure.

Invention of the grain-oriented electrical steel sheet according to claim 2 is the invention according to claim 1, wherein the silicon steel material further contains Cu: 0.01 to 0.30% by mass%. It is characterized by performing hot rolling after heating at a temperature equal to or higher than T4 (° C.) below.
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Cu] is the Cu content (% by mass).

  An invention of a method for producing a grain-oriented electrical steel sheet according to claim 3 is the invention according to claim 1 or 2, wherein the steel sheet temperature is changed from 550 ° C. to 720 ° C. in the temperature rising process when the steel plate is decarburized and annealed. Heating is performed at a heating rate of 50 to 250 ° C./second for a certain period.

  Invention of the grain-oriented electrical steel sheet which concerns on Claim 4 WHEREIN: In the invention which concerns on any one of the said Claims 1-3, the said steel plate temperature at the time of decarburizing annealing of a steel plate exists in 550 to 720 degreeC. Heating in between is performed by induction heating.

The invention of the method for producing a grain-oriented electrical steel sheet according to claim 5 is the invention according to any one of claims 1 to 4, wherein when the steel sheet is decarburized and annealed, it is heated at the heating rate in the temperature rising process. When the range is Ts (° C.) to 720 ° C., the following Ts (° C.) to 720 ° C. range is set according to the heating rate H (° C./second) from room temperature to 500 ° C. .
H ≦ 15: Ts ≦ 550
15 <H: Ts ≦ 600

  Invention of the grain-oriented electrical steel sheet according to claim 6 is the invention according to any one of claims 1 to 5, wherein the decarburization annealing has a primary recrystallized grain size of 7 μm or more and less than 18 μm after decarburization annealing. It is characterized by being carried out at such a temperature and time width as follows.

  Invention of the grain-oriented electrical steel sheet which concerns on Claim 7 WHEREIN: In invention which concerns on any one of Claims 1-6, the nitrogen amount [N] of a steel plate is the acid-soluble property of a steel plate in the process which increases the amount of nitrogen. According to the amount of Al [Al], it is performed to satisfy the formula: [N] ≧ 14/27 [Al].

An invention of a method for producing a grain-oriented electrical steel sheet according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein the silicon steel material is further in mass%, and Sn: 0.3% or less. It contains the following:

  In the invention which concerns on Claim 1 or 2, in manufacture of the grain-oriented electrical steel sheet by low-temperature slab heating, hot-rolled sheet annealing is performed in a two-step temperature range as described in the said claim, thereby decarburizing annealing. In order to improve the grain structure after the subsequent primary recrystallization, the upper limit of the control temperature range of the heating rate in the temperature raising process of decarburization annealing should be set to a lower temperature range that can be heated only by induction heating. Therefore, heating can be performed more easily, and a grain-oriented electrical steel sheet having excellent magnetic properties can be obtained more easily.

  In the invention which concerns on Claim 3, the further magnetic flux density improvement effect can be acquired by performing control of the heating rate in the temperature rising process of decarburization annealing more strictly.

  For this reason, like the invention which concerns on Claim 4, by performing the said heating by induction heating, the freedom degree of a heating rate is high, it can heat in a non-contact with a steel plate, and also installation in a decarburization annealing furnace is possible. Effects such as being relatively easy can be obtained.

In the invention according to claim 5, in the temperature raising process of decarburization annealing, the starting temperature for controlling the heating rate is increased by adjusting the heating rate in the low temperature region up to the starting temperature, thereby controlling the heating rate. The required temperature range can be reduced.
By making it like the invention which concerns on Claim 6, 7, when raising the heating rate of decarburization annealing, secondary recrystallization is performed more stably and the product with high magnetic flux density is manufactured stably. Can do.
In addition, according to the eighth aspect of the present invention, a grain-oriented electrical steel sheet having further improved magnetic properties and the like according to the additive element can be produced.

  When manufacturing the grain-oriented electrical steel sheet by the low-temperature slab heating of 1350 degrees C or less disclosed in patent document 3, the present inventors have the lamella space | interval in the grain structure of the hot-rolled sheet after annealing to the grain after primary recrystallization. Even if the temperature at which rapid heating during decarburization annealing is interrupted is lowered (even before the temperature at which primary recrystallization occurs), the abundance ratio of {411} grains in the primary recrystallization texture The relationship between the lamellar spacing in the grain structure after annealing of the hot-rolled sheet to the magnetic flux density B8 of the steel sheet after secondary recrystallization and the magnetic flux density B8 The effect of heating rate at each temperature in the temperature raising process of decarburization annealing was investigated.

  As a result, in the step of annealing the hot-rolled sheet, after recrystallization by heating at a predetermined temperature, further annealing is performed at a lower temperature, and the lamellar spacing is controlled to 20 μm or more in the grain structure after annealing. In this case, the large temperature range of the structure change in the temperature rising process of the decarburization annealing process is 700 to 720 ° C, and the heating rate in the temperature range of 550 ° C to 720 ° C including the temperature range is 40 ° C / second or more, More preferably, by setting the temperature to 50 to 250 ° C./second, the primary recrystallization can be controlled so that the ratio of I {111} / I {411} of the texture after decarburization annealing is not more than a predetermined value. The present invention was completed by obtaining the knowledge that the crystal structure can be stably developed.

Below, the experiment for which the knowledge was obtained will be described.
First, the relationship between hot-rolled sheet annealing conditions and the magnetic flux density B8 of the sample after finish annealing was investigated.
FIG. 1 shows the relationship between the lamellar spacing of the grain structure in the sample before cold rolling and the magnetic flux density B8 of the sample after finish annealing.
The sample used here is mass%, Si: 3.2%, C: 0.045 to 0.065%, acid-soluble Al: 0.025%, N: 0.005%, Mn: 0.04. %, S: 0.015%, and a slab composed of Fe and unavoidable impurities is heated at a temperature of 1300 ° C. and then hot-rolled to a thickness of 2.3 mm (in the case of this component system, T1 = 1246) , T2 = 1206 ° C.) After that, after recrystallization by heating to 1120 ° C., two-stage hot-rolled sheet annealing is performed at a temperature of 800 to 1120 ° C. After cold rolling to a thickness of 3 mm, heat to 550 ° C. at a heating rate of 15 ° C./second, heat a temperature range of 550 to 720 ° C. at a heating rate of 40 ° C./second, and then heat at 15 ° C./second Further heating at a rate and decarburization annealing at a temperature of 830 ° C., followed by ammonia And annealed in closed atmosphere performs nitrogen nitriding treatment increases the in steel sheet, then, after applying an annealing separator mainly comprised of MgO, in which were finish annealing.
The adjustment of the lamella spacing was performed by changing the amount of C and the temperature of the second stage in the two-stage hot-rolled sheet annealing.

As is apparent from FIG. 1, when the lamella spacing is controlled to 20 μm or more, the temperature is increased at a heating rate of 40 ° C./second in the temperature range of 550 to 720 ° C. for decarburization annealing, so that B8 is 1.92 T or more. It can be seen that a high magnetic flux density can be obtained.
Moreover, as a result of analyzing the primary recrystallization texture of the decarburized and annealed plate of the sample obtained with B8 of 1.92T or more, the value of I {111} / I {411} is 3 or less in all samples. It was confirmed that

Next, the heating conditions at the time of decarburization annealing in which a steel sheet with a high magnetic flux density (B8) was obtained under the condition that the lamella spacing of the grain structure in the sample before cold rolling was 20 μm or more were examined.
The sample used here was C: 0.055%, and the hot-rolled sheet annealing temperature was 1120 ° C. for the first stage, 920 ° C. for the second stage, and the lamellar spacing was 26 μm. For the cold-rolled sample prepared in the same manner as in the above, the heating rate in the temperature range of 550 to 720 ° C. during decarburization annealing was variously changed during the temperature increase, and the magnetic flux density B8 of the sample after finish annealing was measured. .
From FIG. 2, in the temperature range of 550 ° C. to 720 ° C. in the temperature raising process of decarburization annealing, when the heating rate at each temperature within this range is controlled to 40 ° C./second or more, a magnetic flux density of 1.92 T or more ( It can be seen that when the electrical steel sheet having B8) is controlled in the range of preferably 50 to 250 ° C./more preferably 75 to 125 ° C./second, an electrical steel sheet having a higher magnetic flux density (B8) can be obtained.

  From the above, in the step of annealing a hot-rolled sheet, after recrystallization by heating to a predetermined temperature of 1000 to 1150 ° C., annealing is performed at a lower temperature of 850 to 1100 ° C., and the grains after annealing By controlling the lamellar spacing to 20 μm or more in the structure, even if the temperature range for rapid heating in the temperature raising process of the decarburization annealing process is a range where the steel plate temperature is 550 ° C. to 720 ° C., the presence of grains in {411} orientation The ratio of I {111} / I {411} can be reduced to 3 or less as shown in Patent Document 3, and a grain-oriented electrical steel sheet having a high magnetic flux density can be manufactured stably. You can see that

  The reason why the texture of {411} and {111} changes by controlling the lamellar spacing in the grain structure after hot-rolled sheet annealing has not yet been clarified, but currently considers as follows. . In general, it is known that there are preferential sites where recrystallized grains are generated depending on the recrystallization orientation. In the cold rolling process, {411} is recrystallized inside the lamellar structure and {111} is recrystallized in the vicinity of the lamellar. To explain the phenomenon that the abundance ratio of {411} and {111} crystal orientations after primary recrystallization changes by controlling the lamellar spacing of the crystal structure before cold rolling, assuming that nuclei are formed Can do.

The present invention made on the basis of the above findings will be sequentially described below.
First, the reasons for limiting the components of the silicon steel material used in the present invention will be described.
In the present invention, at least by mass, Si: 0.8-7%, C: 0.085% or less, acid-soluble Al: 0.01-0.065%, N: 0.0075% or less, Mn: 0.02 to 0.20%, Seq. = S + 0.406 × Se: 0.003 to 0.05%, a component composition consisting of the balance Fe and inevitable impurities, or Cu to this component composition It is based on the component composition of 0.01 to 0.30% by mass, and uses silicon steel slabs for grain-oriented electrical steel sheets containing other components as necessary. The reasons for limitation are as follows.

  When Si is added in an increased amount, the electrical resistance increases and the iron loss characteristics are improved. However, if added over 7%, cold rolling becomes extremely difficult and cracks during rolling. More suitable for industrial production is 4.8% or less. On the other hand, if it is less than 0.8%, γ transformation occurs during finish annealing, and the crystal orientation of the steel sheet is impaired.

  C is an effective element for controlling the primary recrystallization structure, but it adversely affects the magnetic properties, so it is necessary to decarburize before finish annealing. When C is more than 0.085%, the decarburization annealing time becomes long, and the productivity in industrial production is impaired.

In the present invention, acid-soluble Al is an element essential for binding to N and acting as an inhibitor as (Al, Si) N. The limiting range is 0.01 to 0.065% at which secondary recrystallization is stabilized.
If N exceeds 0.012%, voids called blisters are formed in the steel sheet during cold rolling, so N should not exceed 0.012%. Moreover, in order to function as an inhibitor, it is necessary to set it as 0.0075 or less. If it exceeds 0.0075%, the dispersion state of the precipitates becomes non-uniform and secondary recrystallization becomes unstable.

  If Mn is less than 0.02%, cracks are likely to occur in hot rolling. In addition, MnS and MnSe function as an inhibitor. However, if it exceeds 0.20%, the dispersion of MnS and MnSe precipitates tends to be non-uniform and secondary recrystallization becomes unstable. Preferably, it is 0.03 to 0.09%.

  S and Se bind to Mn and function as an inhibitor. When Seq. = S + 0.406 × Se is less than 0.003%, the function as an inhibitor is reduced. On the other hand, if it exceeds 0.05%, the dispersion of precipitates tends to be non-uniform and secondary recrystallization becomes unstable.

  In the present invention, Cu can be further added as an inhibitor constituent element. Cu also functions as an inhibitor by forming precipitates with S and Se. If it is less than 0.01%, the function as an inhibitor is reduced. If the addition amount exceeds 0.3%, the dispersion of precipitates tends to be non-uniform and the iron loss reduction effect is saturated.

In the present invention, as a slab of material, in addition to the above components, if necessary, the Sn Furthermore, by mass%, 0. It can be contained in an amount below 3% or less.
Further, although not specifically defined in the claims, at least one of Cr, P, Sb, Ni, and Bi is 0.3% or less for Cr, 0.5% or less for P, and 0.3% for Sb. Hereinafter, Ni can be contained in a range of 1% or less, and Bi in a range of 0.01% or less.

Cr improves the decarburization annealing oxide layer and is an effective element for glass coating formation, and is added in the range of 0.3% or less.
P is an element effective for increasing the specific resistance and reducing the iron loss. If the addition amount exceeds 0.5%, a problem arises in rolling properties.

  Sn and Sb are well-known grain boundary segregation elements. Since the present invention contains Al, depending on the conditions of finish annealing, Al is oxidized by moisture released from the annealing separator, and the inhibitor strength varies at the coil position, and the magnetic characteristics may vary at the coil position. is there. As one of the countermeasures, there is a method of preventing oxidation by adding these grain boundary segregation elements. Therefore, each of them can be added in a range of 0.30% or less. On the other hand, if it exceeds 0.30%, it is difficult to be oxidized during the decarburization annealing, the formation of the glass film becomes insufficient, and the decarburization annealability is significantly inhibited.

Ni is an element effective for increasing the specific resistance and reducing the iron loss. Moreover, it is an element effective in improving the magnetic properties by controlling the metal structure of the hot-rolled sheet. However, when the addition amount exceeds 1%, secondary recrystallization becomes unstable.
Bi, when added in an amount of 0.01% or more, has the effect of stabilizing precipitates such as sulfides and strengthening the function as an inhibitor. However, addition of 0.01% or more adversely affects the formation of the glass film.

  Furthermore, the silicon steel material used in the present invention may contain elements other than those described above and / or other inevitable elements as long as the magnetic properties are not impaired.

Next, the manufacturing conditions of the present invention will be described.
A silicon steel slab having the above component composition is obtained by melting steel with a converter or electric furnace, etc., vacuum-degassing the molten steel as necessary, and then performing continuous casting or block rolling after ingot forming. It is done. Thereafter, slab heating is performed prior to hot rolling. In the present invention, the slab heating temperature is set to 1350 ° C. or less to avoid various problems of high-temperature slab heating (problems such as requiring a dedicated heating furnace and a large amount of melt scale).

Further, in the present invention, the lower limit temperature of slab heating requires that the inhibitor (AlN, MnS, MnSe, etc.) be completely in solution. For this purpose, it is necessary to set the slab heating temperature to be equal to or higher than any of the temperatures T1, T2, and T3 (° C.) represented by the following formula, and to control the amount of inhibitor constituent elements. Regarding the contents of Al and N, the following formula T1 needs to be 1350 ° C. or lower. Similarly, regarding the contents of Mn and S, the contents of Mn and Se, and the contents of Cu and S, T2, T3, and T4 in the following formulas must be 1350 ° C. or lower, respectively.
T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Al], [N], [Mn], [S], [Se], and [Cu] are the contents (mass%) of acid-soluble Al, N, Mn, S, Se, and Cu, respectively. is there.

  Silicon steel slabs are usually cast to a thickness of 150 to 350 mm, preferably 220 to 280 mm, but may be so-called thin slabs of 30 to 70 mm. In the case of a thin slab, there is an advantage that it is not necessary to perform roughing to an intermediate thickness when manufacturing a hot-rolled sheet.

  The slab heated at the above-mentioned temperature is subsequently hot-rolled to obtain a hot-rolled sheet having a required thickness. The hot-rolled sheet is heated to a predetermined temperature of 1000 to 1150 ° C. and recrystallized, and then annealed at a lower temperature of 850 to 1100 ° C. for a necessary time, and the lamellar spacing is 20 μm in the grain structure after annealing. Control above. The first stage annealing is performed at a heating rate of 5 ° C./second or more, preferably 10 ° C./second or more from the viewpoint of promoting recrystallization of the hot-rolled sheet, and at a high temperature of 1100 ° C. or more, 0 second, about 1000 ° C. At low temperatures, annealing for 30 seconds or more may be performed. The second annealing time may be 20 seconds or more from the viewpoint of controlling the lamella structure. After the second annealing, from the viewpoint of preserving the lamella structure, it may be cooled at an average cooling rate of 5 ° C / second or more, preferably 15 ° C / second or more.

  Note that performing the hot-rolled sheet annealing in two stages is also described in part in Patent Document 7, but the purpose of the annealing is to adjust the inhibitor state, as in the present invention, When manufacturing grain-oriented electrical steel sheets by the latter method, the rapid heating range in the temperature raising process of decarburization annealing is lower by controlling the lamellar spacing in the grain structure after annealing by two-stage hot-rolled sheet annealing. Even in the temperature range, there is no suggestion that it is possible to increase the ratio of grains having orientations that are easily recrystallized after primary recrystallization.

  Thereafter, the final thickness is obtained by cold rolling at least once or two or more times with annealing. The number of cold rolling operations is appropriately selected in consideration of the desired property level and cost of the product. In cold rolling, it is necessary to make the final cold rolling rate 80% or more in order to develop primary recrystallization orientations such as {411} and {111}.

The steel sheet after cold rolling is subjected to decarburization annealing in a humid atmosphere in order to remove C contained in the steel. At that time, a product having a high magnetic flux density is obtained by performing a treatment in which the ratio of I {111} / I {411} is set to 3 or less in the grain structure after decarburization annealing and then nitrogen is increased before secondary recrystallization is exhibited. Can be manufactured stably.
The primary recrystallization after the decarburization annealing is controlled by adjusting the heating rate in the temperature rising process of the decarburization annealing process. The present invention is characterized in that heating is performed at a heating rate of 40 ° C./second, preferably 50 to 250 ° C./second, more preferably 75 to 125 ° C./second while the steel sheet temperature is between 550 ° C. and 720 ° C. .

  The heating rate has a great influence on the primary recrystallization texture I {111} / I {411}. In primary recrystallization, the recrystallization easiness varies depending on the crystal orientation. Therefore, in order to set I {111} / I {411} to 3 or less, the heating rate is controlled so that the {411} orientation grains are easily recrystallized. There is a need. Since {411} oriented grains are most easily recrystallized at a speed near 100 ° C./second, in order to stably produce a product having a high magnetic flux density (B8) with I {111} / I {411} being 3 or less. The heating rate is 40 ° C./second, preferably 50 to 250 ° C./second, more preferably 75 to 125 ° C./second.

The temperature range that needs to be heated at this heating rate is basically the temperature range from 550 ° C to 720 ° C. Of course, you may start the rapid heating in the said heating rate range from the temperature of 550 degrees C or less. The lower limit temperature of the temperature range where the heating rate should be maintained at a high heating rate is affected by the heating cycle in the low temperature range. Therefore, when the temperature range requiring rapid heating is 720 ° C. from the starting temperature Ts (° C.), the following Ts (° C.) to 720 ° C. according to the heating rate H (° C./second) from room temperature to 500 ° C. It is good to be in the range up to.
H ≦ 15: Ts ≦ 550
15 <H: Ts ≦ 600

  When the heating rate in the low temperature region is a standard heating rate of 15 ° C./second, it is necessary to rapidly heat the range of 550 ° C. to 720 ° C. at a heating rate of 40 ° C./second or more. When the heating rate in the low temperature region is slower than 15 ° C./second, it is necessary to rapidly heat the temperature from 550 ° C. or lower to 720 ° C. at a heating rate of 40 ° C./second or higher. On the other hand, when the heating rate in the low temperature range is faster than 15 ° C./second, rapid heating is performed at a temperature higher than 550 ° C. from 600 ° C. to 720 ° C. at a heating rate of 40 ° C./second or more. It is enough. For example, when heating from room temperature at 50 ° C./second, the temperature increase rate in the range of 600 ° C. to 720 ° C. may be 40 ° C./second or more.

  The method for controlling the heating rate of the decarburization annealing is not particularly limited. However, in the present invention, since the upper limit of the temperature range of the rapid heating is 720 ° C., induction heating can be effectively used. it can.

Further, in order to stably exhibit the effect of adjusting the heating rate, as shown in Patent Document 5, the degree of oxidation of the atmospheric gas (PH 2 O / P) in the temperature range of 770 to 900 ° C. after heating is performed. It is effective to adjust the amount of oxygen in the steel sheet to 2.3 g / m ² or less by setting PH2) to more than 0.15 and 1.1 or less. If the degree of oxidation of the atmospheric gas is less than 0.15, the adhesion of the glass coating formed on the steel sheet surface deteriorates, and if it exceeds 1.1, defects occur in the glass coating. Further, by setting the oxygen content of the steel sheet to 2.3 g / m ² or less, it is possible to stably produce a grain-oriented electrical steel sheet having a high magnetic flux density by suppressing decomposition of the (Al, Si) N inhibitor. .

  Further, as shown in Patent Document 3, the decarburization annealing is performed at a temperature and a time width such that the primary recrystallized grain size becomes 7 to 18 μm, thereby making secondary recrystallization more stable. And a more excellent grain-oriented electrical steel sheet can be produced.

As a nitriding treatment for increasing nitrogen, a method of annealing in an atmosphere containing a nitriding gas such as ammonia following decarburization annealing, and a nitriding powder such as MnN are added to the annealing separator. For example, there is a method to be performed during finish annealing.
In order to perform secondary recrystallization more stably when the heating rate of decarburization annealing is increased, it is desirable to adjust the composition ratio of (Al, Si) N, and the nitrogen after the increase As the amount, the ratio of nitrogen amount: [N] to Al amount in steel: [Al], that is, [N] / [Al] is set to 14/27 or more as a mass ratio.
Thereafter, after applying an annealing separator mainly composed of magnesia, finish annealing is performed to preferentially grow {110} <001> oriented grains by secondary recrystallization.

  As described above, in the present invention, silicon steel is heated at a temperature not lower than the temperature at which a predetermined precipitate is completely formed into a solution and not higher than 1350 ° C., and then hot-rolled, hot-rolled and annealed. After multiple cold rolling or annealing, multiple cold rolling is performed to obtain the final thickness, after decarburization annealing, an annealing separator is applied, finish annealing is performed, and secondary from decarburization annealing to final annealing In the process of annealing the hot-rolled sheet when the steel sheet is subjected to nitriding treatment before the start of recrystallization to produce a grain-oriented electrical steel sheet, it is recrystallized by heating to a predetermined temperature of 1000 to 1150 ° C. After that, by annealing at 850 to 1100 ° C. at a lower temperature than that, the lamellar spacing is controlled to 20 μm or more in the grain structure after hot-rolled sheet annealing, and in the temperature rising process when decarburizing and annealing the steel sheet, Steel plate temperature from 550 ° C While being at 20 ° C., heating at a heating rate of 40 ° C./second or more, preferably 50 to 250 ° C./second, more preferably 75 to 125 ° C./second, followed by decarburization annealing, A directional electrical steel sheet having a high magnetic flux density can be produced by performing the treatment over a temperature and time such that the range is 7 to 18 μm.

  Examples of the present invention will be described below, but the conditions adopted in the examples are one example of conditions for confirming the feasibility and effects of the present invention. The present invention is not limited to this example, and various conditions can be adopted as long as the object of the present invention is achieved without departing from the present invention.

In mass%, Si: 3.2%, C: 0.05%, acid-soluble Al: 0.024%, N: 0.005%, Mn: 0.04%, S: 0.01% are contained. Then, the slab composed of the remaining Fe and inevitable impurities is heated at a temperature of 1320 ° C. (in the case of this component system, T1 = 1242 ° C. and T2 = 11181 ° C.) and then hot-rolled to a thickness of 2.3 mm. Thereafter, some samples (A) were subjected to one-step annealing at 1130 ° C., and some samples (B) were subjected to two-step annealing at 1130 ° C. + 920 ° C. After these samples were cold rolled to a thickness of 0.3 mm, (1) heated to 720 ° C. at a heating rate of 15 ° C./second, (2) 40 ° C./second, and (3) 100 ° C./second, After that, decarburization annealing is performed by heating at 10 ° C./second to a temperature of 850 ° C., followed by annealing in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.02%, and then annealing with MgO as the main component After applying the separating agent, finish annealing was performed.
Table 1 shows the magnetic properties of the obtained sample after finish annealing. In addition, the symbol of a sample shows the combination of an annealing method and a heating rate. A high magnetic flux density is obtained when the conditions of the present invention are satisfied for both hot-rolled sheet annealing and decarburization annealing.

In mass%, Si: 3.2%, C: 0.055%, acid-soluble Al: 0.026%, N: 0.005%, Mn: 0.05%, Cu: 0.1%, S: The slab containing 0.012% and the balance Fe and inevitable impurities was heated at a temperature of 1330 ° C. (in this component system, T1 = 1250 ° C., T2 = 1206 ° C., T4 = 1212 ° C.). Thereafter, it was hot-rolled to a thickness of 2.3 mm, after which some samples (A) were subjected to one-step annealing at 1120 ° C., and some samples (B) were subjected to two-step annealing at 1120 ° C. + 900 ° C. After these samples were cold-rolled to a thickness of 0.3 mm, they were heated to 550 ° C. at a heating rate of 20 ° C./second, and (1) 15 ° C./second, (2) 40 ° C./second, (3) 100 The steel sheet is heated to 550 to 720 ° C. at a heating rate of ℃ / second, then further heated at a heating rate of 15 ° C./second, decarburized and annealed at a temperature of 840 ° C., and subsequently annealed in an ammonia-containing atmosphere. Nitrogen was increased to 0.02%, and then an annealing separator mainly composed of MgO was applied, followed by finish annealing.
Table 2 shows the magnetic properties of the obtained sample after finish annealing. A high magnetic flux density is obtained when the conditions of the present invention are satisfied for both hot-rolled sheet annealing and decarburization annealing.

In mass%, Si: 3.2%, C: 0.055%, acid-soluble Al: 0.026%, N: 0.005%, Mn: 0.05%, Cu: 0.1%, S: A slab containing 0.012% and the balance Fe and inevitable impurities is heated at a temperature of 1330 ° C., then hot-rolled to a thickness of 2.3 mm, and then subjected to a two-stage annealing at 1120 ° C. + 900 ° C. The lamella spacing was 24 μm. This sample was cold-rolled to a thickness of 0.3 mm, then heated to 550 ° C. at a heating rate of 20 ° C./second, further heated to 550-720 ° C. at a heating rate of 40 ° C./second, and then 15 ° C./second. Is further decarburized and annealed at a temperature of 840 ° C., followed by annealing in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.08 to 0.02%, and then MgO as the main component After applying the annealing separating agent, finish annealing was performed.
Table 3 shows the magnetic properties after finish annealing of the obtained samples having different amounts of nitrogen.

As a sample, the cold-rolled sheet used in Example 3 was heated to 720 ° C. at a heating rate of 40 ° C./second, then further heated at a heating rate of 15 ° C./second, and decarburized and annealed at a temperature of 800 to 900 ° C. Subsequently, annealing was performed in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.02%. Then, after applying an annealing separator mainly composed of MgO, finish annealing was performed.
Table 4 shows the magnetic properties after finish annealing of the obtained samples having different primary recrystallized grain sizes after decarburization annealing.

(Reference example)
In mass%, Si: 3.2%, C: 0.055%, acid-soluble Al: 0.026%, N: 0.006%, Mn: 0.05%, S: 0.05%, Se: A slab containing 0.015%, Sn: 0.1%, and the balance Fe and inevitable impurities is heated to a temperature of 1330 ° C. (in the case of this component system, T1 = 1269 ° C., T2 = 11152 ° C., T3 = 1217 ° C. ) And then hot rolled to a thickness of 2.3 mm, after which some samples (A) are subjected to one-step annealing at 1130 ° C. and some samples (B) are two-step annealing at 1130 ° C. + 920 ° C. Was given. These samples were cold-rolled to a thickness of 0.3 mm, then heated to 550 ° C. at a heating rate of 20 ° C./second, and (550) at a heating rate of (1) 15 ° C./second and (2) 100 ° C./second. Heat to ~ 720 ° C, then further heat at a heating rate of 15 ° C / second and decarburize and anneal at a temperature of 840 ° C, then anneal in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.018% Then, after applying an annealing separator mainly composed of MgO, finish annealing was performed.
Magnetic properties after finish annealing of the obtained samples are shown in Table 5.

Using the cold-rolled plate of Example 3, at a heating rate of (A) 15 ° C./sec, (B) 50 ° C./sec, (1) 500 ° C., (2) 550 ° C. and (3) 600 ° C. After that, it was heated to 720 ° C. at a heating rate of 100 ° C./second, and further heated to 830 ° C. at 10 ° C./second to perform decarburization annealing. Subsequently, annealing was performed in an ammonia-containing atmosphere to increase the nitrogen in the steel sheet to 0.018%. Then, after applying an annealing separator mainly composed of MgO, finish annealing was performed.
Table 6 shows the magnetic properties of the samples after finish annealing. It can be seen that by increasing the heating rate in the low temperature region, good magnetic properties can be obtained even if the starting temperature of heating at 100 ° C./second is increased to 600 ° C.

It is a figure which shows the relationship between the lamella space | interval of the grain structure before cold rolling, and magnetic flux density B8. It is a figure which shows the relationship between the heating rate of the temperature range of 550-720 degreeC in the middle of temperature rising of decarburization annealing, and the magnetic flux density (B8) of a product.

Claims (8)

In mass%, Si: 0.8-7%, C: 0.085% or less, acid-soluble Al: 0.01-0.065%, N: 0.0075% or less, Mn: 0.02-0. 20%, Seq = S + 0.406 × Se:. containing from 0.003 to 0.05 percent, the silicon steel material ing the balance Fe and unavoidable impurities, the temperature T1, T2 represented by the following formula, and Hot rolling after heating at any temperature of T3 (° C.) or higher and 1350 ° C. or lower, annealing the obtained hot-rolled sheet, and then a plurality of cold through one cold rolling or annealing The steel sheet is rolled to the final thickness, and the steel sheet is decarburized and annealed, and then the annealing separator is applied, finish annealing is performed, and the steel sheet between decarburization annealing and the start of secondary recrystallization of finish annealing is applied. In a method for producing a grain-oriented electrical steel sheet, comprising applying a treatment to increase the amount of nitrogen
In the grain structure after annealing, the hot-rolled sheet is annealed at a temperature of 850 to 1100 ° C., which is lower than 850 to 1100 ° C., after being recrystallized by heating to a predetermined temperature of 1000 to 1150 ° C. While controlling the lamella spacing to 20 μm or more,
A grain-oriented electrical steel sheet, wherein the steel sheet is heated at a heating rate of 40 ° C./second or more while the steel sheet temperature is in the range of 550 ° C. to 720 ° C. in the temperature raising process when decarburizing and annealing the steel plate having the final thickness. Manufacturing method.
T1 = 10062 / (2.72−log ([Al] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273
Here, [Al], [N], [Mn], [S], and [Se] are the contents of acid-soluble Al, N, Mn, S, and Se, respectively.
The silicon steel material further contains, by mass%, Cu: 0.01 to 0.30%, and is hot-rolled after being heated at a temperature equal to or higher than T4 (° C) below. The manufacturing method of the grain-oriented electrical steel sheet described in 1.
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [Cu] is the Cu content.   The temperature rising process at the time of decarburizing annealing of the steel sheet is performed at a heating rate of 50 to 250 ° C / second while the steel sheet temperature is in the range of 550 ° C to 720 ° C. Method for producing a grain-oriented electrical steel sheet.   The directionality according to any one of claims 1 to 3, wherein the heating during the decarburization annealing of the steel plate is performed by induction heating while the steel plate temperature is between 550 ° C and 720 ° C. A method for producing electrical steel sheets. When the steel sheet is decarburized and annealed, the heating rate H (° C./sec) from room temperature to 500 ° C. when the temperature range heated at the heating rate in the temperature raising process is Ts (° C.) to 720 ° C. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the range is from the following Ts (° C) to 720 ° C.
H ≦ 15: Ts ≦ 550
15 <H: Ts ≦ 600   The direction according to any one of claims 1 to 5, wherein the decarburization annealing is performed at a temperature and a time width such that a primary recrystallization grain size after decarburization annealing is 7 µm or more and less than 18 µm. Method for producing an electrical steel sheet.   The treatment for increasing the nitrogen amount is performed so that the nitrogen amount [N] of the steel sheet satisfies the formula: [N] ≧ 14/27 [Al] according to the amount of acid-soluble Al [Al] of the steel plate. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 6. Said silicon steel material further contains, by mass%, S n: the manufacturing method of the grain-oriented electrical steel sheet according to claim 1, characterized in that it contains 0.3% or less.

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