JP3314844B2 - Manufacturing method of unidirectional electrical steel sheet with excellent magnetic properties and coating properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is mainly used as a core material for transformers and other electric equipment, and is required to have excellent magnetic properties such as excitation properties and iron loss properties. Numerical values representing the excitation characteristics include a normal magnetic field strength of 8
A magnetic flux density B _{8 at} 00 A / m is used. As the numerical value representing the iron loss characteristic, the iron loss W _17/50 per kg when magnetized at a frequency of 50 Hz to 1.7 Tesla (T) is used.

[0003] The magnetic flux density is the largest controlling factor of iron loss characteristics. Generally, the higher the magnetic flux density, the better the iron loss characteristics. In general, when the magnetic flux density is increased, the secondary recrystallized grains become large, and the iron loss characteristics may become poor.
In contrast, by controlling the magnetic domain, the iron loss characteristics can be improved regardless of the particle size of the secondary recrystallized grains.

[0004] This grain-oriented electrical steel sheet is produced by causing secondary recrystallization in the final finish annealing step to develop a so-called goss structure having {110} on the steel sheet surface and a <001> axis in the rolling direction. Have been. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction. Typical examples of the manufacturing technique of such high magnetic flux density unidirectional magnetic steel sheet include Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-1346.
No. 9 discloses a method.

[0005] In the former, M is the main inhibitor.
nS and AlN are used, and the latter uses MnS, MnSe, Sb, and the like. Therefore, it is indispensable in the current technology to appropriately control the size, morphology, and dispersion state of the precipitates functioning as these inhibitors.

With regard to MnS, in the present process, after the MnS is completely dissolved once during slab heating before hot rolling,
A method of precipitation during hot rolling is employed. A temperature of about 1400 ° C. is required to completely dissolve the required amount of MnS for secondary recrystallization. This is more than 200 ° C. higher than the slab heating temperature of ordinary steel, and this high-temperature slab heating treatment has the following disadvantages. 1) A high-temperature slab heating furnace dedicated to directional magnetic steel is required. 2) The unit energy consumption of the heating furnace is high. 3) The amount of the molten scale increases, and the adverse effect on the operation is large as seen in so-called scraping.

In order to avoid such a problem, the slab heating temperature may be reduced to the level of ordinary steel. However, this is at the same time reducing the amount of MnS effective as an inhibitor or not using it at all. This means that secondary recrystallization is inevitably destabilized. Therefore, in order to realize low-temperature slab heating, MnS
It is necessary to strengthen the inhibitor with other precipitates and the like to sufficiently suppress the normal grain growth during the finish annealing.

[0008] Such inhibitors include nitrides, oxides, and intergranular precipitation elements in addition to sulfides.
Known techniques include, for example, the following.
In Japanese Patent Publication No. 54-24687, As, Bi, Sn,
A method is disclosed in which a slab heating temperature is controlled to be in a range of 1050 to 1350 ° C. by containing a grain boundary segregation element such as Sb in steel. Japanese Patent Application Laid-Open No. 52-24116 discloses a method in which Zr, Ti, A method is disclosed in which a slab heating temperature is set in a range of 1100 to 1260 ° C. by containing a nitride-forming element such as B, Nb, Ta, V, Cr, and Mo.

In Japanese Patent Application Laid-Open No. 57-158322, low-temperature slab heating is performed by lowering the Mn content and the Mn / S ratio to 2.5 or less, and secondary recrystallization is performed by adding Cu. Discloses a technique for stabilizing the

[0010] Techniques have also been disclosed in which improvements are made from the metallographic side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, S,
By adding elements such as Se, Sb, Bi, Pb, Sn, and B, and combining the columnar crystal ratio of the slab and the secondary cold rolling reduction, a low-temperature slab heating of 1100 to 1250 ° C. is realized.

Further, in Japanese Patent Application Laid-Open No. 59-1990324, an inhibitor is composed mainly of Al, B and nitrogen in addition to S or Se, and this is subjected to pulse annealing at the time of primary recrystallization annealing after cold rolling. The technology to stabilize the secondary recrystallization is disclosed.

[0012] As described above, great efforts have been made to achieve low-temperature slab heating in the production of grain-oriented electrical steel sheets. Further, JP-A-59-5652
No. 2 discloses a technology that enables low-temperature slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less. By this method, the problem of occurrence of defective linear secondary recrystallization of a product due to coarsening of slab crystal grains during heating of a high-temperature slab was solved.

In the technical development on the premise of this low-temperature slab heating, the present inventors have developed a technique to which Cu is added. JP-A-6-145803 discloses a technique in which the amounts of N and Mn in a slab are minimized, Cu and S are added, and Cu-S is used instead of AlN as an inhibitor for primary recrystallized grain growth. Was presented. In Japanese Patent Application Laid-Open No. Hei 6-145801, the amount of N in a slab is reduced as much as possible, and Mn, Cu, and S are added, and Cu is used as an inhibitor of primary recrystallized grain growth instead of AlN.
A technique using -S, MnS was presented.

Further, Japanese Patent Application Nos. 5-115033 and 6-158033 disclose JP-A-6-145803 and 6-1458.
As means for further improving the technology of JP-A-01, Ti,
A technique for controlling the growth of primary recrystallized grains by adding Zr was also proposed. With these techniques, it was possible to stabilize the magnetic properties at a high level, but it was difficult to achieve both film properties and magnetic properties.

[0015]

In order to improve the quality of a grain-oriented electrical steel sheet, measures for increasing the magnetic flux density are usually attempted. The same applies to the process of performing low-temperature slab heating. The present inventors, for industrialization of low-temperature slab heating, control of the average grain size of primary recrystallization before final finish annealing, and nitriding treatment of steel sheet after hot rolling and before the start of secondary recrystallization of final finish annealing. Has been built as a pillar.

The nitride formed in this nitriding treatment contains a large amount of Si or Mn, and this nitride is decomposed in a temperature range of about 900 to 1000 ° C. in a temperature rise stage of final finish annealing. , AlN or (Al, Si) N is deposited. Since secondary recrystallization usually occurs at 1000 to 1150 ° C., the inhibitor at the time of secondary recrystallization is AlN or (Al, Si) N.

On the other hand, it is known that grains having a high corresponding grain boundary density in the primary recrystallized sheet undergo secondary recrystallization. The higher the inhibitor strength (Zener factor), the more necessary the secondary recrystallization is. The critical value of the grain boundary density is increased, and as a result, the degree of integration of the secondary recrystallization texture is improved.

In this sense, increasing the intensity (Zener factor) of the inhibitors AlN and (Al, Si) N at the time of secondary recrystallization in the present invention can be achieved by {110} <00
1) It has the effect of sharpening the secondary recrystallization texture. Ze
The ner factor is inversely proportional to the size of the precipitate and proportional to the volume fraction. As for the volume fraction, when a nitride is used for an inhibitor as in the present technology, increasing the volume fraction increases the amount of nitrogen in the steel (the sum of the amount of nitrogen added in steelmaking and the amount of nitrogen added in nitriding). Leads to things.

This nitrogen in the steel is released out of the steel during the final annealing. Since nitrogen passes through the surface oxide layer and the forsterite in the course of this release, as the amount of nitrogen in the steel increases, the oxide layer and the forsterite are more likely to have defects and missing parts. Therefore, there is a limit to increasing the volume fraction as a method for increasing the Zener factor. Therefore, the present inventors have studied a method for reducing the size of the precipitate.

[0020]

The gist of the present invention is as follows. (1) C: 0.025 to 0.075% by weight, S
i: 2.2 to 5.0%, acid-soluble Al: 0.010
0.060%, N: 0.0040 to 0.0130%, S
+ 0.405Se: 0.005 to 0.020%, Mn:
A slab composed of less than 0.01%, Cu: 0.05 to 0.50%, and the balance being Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot rolled, and subsequently, if necessary, a hot rolled sheet. A method for producing a grain-oriented electrical steel sheet by performing annealing, followed by one or more times of cold rolling including intermediate cold annealing including final cold rolling with a rolling reduction of 80% or more, followed by decarburizing annealing and final finishing annealing. Hot-rolling in a temperature range of 700 to 1100 ° C., after the completion of decarburizing annealing, the average particle size of primary recrystallized grains until the start of final finishing annealing is 18 to 35 μm. Before the start of the next recrystallization, the steel sheet is subjected to a nitriding treatment for absorbing at least 0.0010% by weight of nitrogen, and the total amount of SiO ₂ in the surface oxide film after decarburizing annealing (S
IO2 (g / m ² )) and Cu amount of slab (Cu (%))
Is controlled within the range of the following equation (1), and the temperature is raised at a rate of 20 ° C./hour or less in a temperature range of 1000 to 1150 ° C. in the final finish annealing. For producing unidirectional electrical steel sheets with excellent coating properties. 0.7−0.6 × Cu (%) ≦ SIO2 ≦ 1.6 + 0.3 × Cu (%) (1) (2) The slab contains 0.01 to 0.15% of Sn by weight. (1) The method for producing a grain-oriented electrical steel sheet according to (1).

[0021]

The grain-oriented electrical steel sheet to which the present invention is directed is:
Molten steel obtained by the conventional steelmaking method is cast by continuous casting method or ingot making method, if necessary, into a slab with a lumping step, and then hot-rolled into a hot-rolled sheet. Anneal the hot-rolled sheet accordingly, and then apply one or more cold-rolling steps including intermediate annealing as necessary, including final cold-rolling with a reduction ratio of 80% or more, then decarburizing annealing, final finish annealing Are sequentially performed.

The present inventors have studied in detail how to improve the film properties and improve the magnetic properties when a low-temperature slab heating material is manufactured. As a measure, adding Cu to extremely lower the amount of Mn, controlling the finishing hot rolling temperature, and controlling the average grain size of primary recrystallized grains from the completion of decarburizing annealing to the start of final finishing annealing. ,
Applying a predetermined amount of nitriding treatment to the steel sheet before the start of the secondary recrystallization of the final finish annealing after hot rolling, lowering the rate of temperature rise in a predetermined temperature range in the temperature rise process of the final finish annealing, The total amount of SiO ₂ in the surface oxide film after the decarburizing annealing was
Controlling according to the amount was found to be effective.

The details will be described below based on the experimental results. FIG.
Next, the Cu content of the slab and the total S in the surface oxide film after decarburization annealing
The effect of the amount of iO ₂ (SIO2 (g / m ² )) on the magnetic properties and coating properties was shown. In this case, by weight, C = 0.
054%, Si = 3.40%, acid-soluble Al = 0.02
9%, N = 0.0079%, S = 0.008%, Mn <
0.01%, Cu = 0-0.67%, and the remaining Fe
A slab having a thickness of 250 mm made of unavoidable impurities was prepared.

After soaking at 1100 ° C. for 60 minutes, five passes of rough hot rolling and six passes of finish hot rolling were carried out to obtain a 2.3 mm thick hot rolled sheet. At this time, the finishing hot rolling temperature is 835 to 1013.
° C. The hot-rolled sheet was kept at 1100 ° C. for 30 seconds, kept at 900 ° C. for 30 seconds, and then subjected to rapid cooling annealing. Thereafter, a high rolling was performed at a rolling reduction of about 90% to obtain a cold-rolled sheet having a final sheet thickness of 0.22 mm.

The cold rolled sheet is kept at 820 to 860 ° C. for 90 seconds by decarburizing annealing (N ₂ : 25%, H ₂ : 75%, D.C.
P. = 55 to 72 ° C), and then, at the time of annealing at 750 ° C for 30 seconds, NH ₃ gas was mixed in the annealing atmosphere to allow the steel sheet to absorb nitrogen. The N amount after this nitriding treatment was 0.0186 to 0.0213% by weight. The average primary recrystallized grain size of these nitrided plates was 21 to 26 μm.

The steel sheet after the nitriding treatment was coated with an annealing separator containing MgO as a main component, and was subjected to final finish annealing. In this final finish annealing, the temperature is raised to 1200 ° C. at a rate of 10 ° C./hour in an atmosphere of N ₂ : 25% and H ₂ : 75%,
H ₂ : This was performed in a 100% annealing atmosphere under the condition of holding for 20 hours. FIG. 1 shows the relationship between the magnetic flux density and film properties of the product and the experimental conditions.

As is clear from FIG. 1, Cu = 0.05
~ 0.50%, and 0.7-0.6xCu (%) ≤S
When IO2 ≦ 1.6 + 0.3 × Cu (%), B ₈ ≧
1.93 T and good film properties were obtained. Although the mechanism of the phenomenon shown in FIG. 1 is not necessarily clear, the present inventors presume as follows.

For the industrialization of low-temperature slab heating, the present inventors controlled the average grain size of primary recrystallized grains before final annealing, and after hot rolling, formed steel sheets by the start of secondary recrystallization in final annealing. We have built a technology that makes nitriding a pillar. The nitride formed in this nitriding treatment contains a large amount of Si or Mn, and this nitride is decomposed in the temperature range of about 900 to 1000 ° C. in the temperature rise stage of the final finish annealing to form AlN or (Al, Si) N precipitates. Since secondary recrystallization usually occurs at 1000 to 1150 ° C,
The inhibitor during secondary recrystallization is AlN or (Al, S
i) N.

On the other hand, it is known that grains having a high corresponding grain boundary density in the primary recrystallized plate undergo secondary recrystallization. The higher the inhibitor strength (Zener factor), the more necessary the secondary recrystallization. The critical value of the grain boundary density is increased, and as a result, the degree of integration of the secondary recrystallization texture is improved.

In this sense, increasing the intensity (Zener factor) of the inhibitors AlN and (Al, Si) N at the time of secondary recrystallization in the present invention can be achieved by {110} <00
1) It has the effect of sharpening the secondary recrystallization texture. Ze
The ner factor is inversely proportional to the size of the precipitate and proportional to the volume fraction. As for the volume fraction, when a nitride is used for an inhibitor as in the present technology, increasing the volume fraction increases the amount of nitrogen in the steel (the sum of the amount of nitrogen added in steelmaking and the amount of nitrogen added in nitriding). Leads to things.

This nitrogen in the steel is released out of the steel during the final finish annealing. Since nitrogen passes through the surface oxide layer and the forsterite in the course of this release, as the amount of nitrogen in the steel increases, the oxide layer and the forsterite are more likely to have defects and missing parts. Therefore, there is a limit to increasing the volume fraction as a method for increasing the Zener factor. Therefore, the present inventors have studied a method for reducing the size of the precipitate. The core of the present invention is to reduce the size of the precipitate.

As this method, an attempt was made to use Cu-S (Cu ₂ S or Cu _1.6 S) as a precipitation nucleus of AlN or (Al, Si) N. Here, since MnS is a sulfide that is more stable than Cu-S and tends to be larger in size, an experiment was performed with the amount of Mn reduced so as not to cause precipitation of MnS. Since Cu-S has a precipitation nose at about 1000 ° C., in the case of this experiment, Cu—S
Precipitates.

On the other hand, in this experiment, M
A nitride of n-N, Si-N, (Mn, Si) N precipitates. This nitride has a final finish annealing temperature of about 900 to 1
Decomposes in the temperature range of 000 ° C. to form AlN or (Al, S
i) N precipitates.

At the time of the precipitation of AlN and (Al, Si) N,
Cu-S acts as a precipitation nucleus, and when a proper amount of Cu was added, a fine and uniform precipitation-dispersed phase of AlN and (Al, Si) N was obtained. Then, in the condition range in which the fine and uniform precipitation-dispersed phase was obtained, a high magnetic flux density was obtained.

This is because the secondary recrystallization progressed in a state where the inhibitor strength (Zener factor) was high, so that the {9} corresponding grain boundary density was high {110} in the primary recrystallized plate.
It is considered that only orientation grains close to the <001> orientation were due to secondary recrystallization.

On the other hand, the amount of SiO ₂ in the surface oxide film
The reason why the appropriate range according to the amount exists is considered as follows. Cu is an element that concentrates on the surface,
Suppresses oxidation during decarburizing annealing and final finishing annealing. On the other hand, in the surface oxide layer and the internal oxide layer formed during the decarburization annealing, SiO ₂ and MgO which is a main component of the annealing separator are used.
Reacts at the time of raising the final finish annealing temperature (800 to 1100 ° C.) to form Mg ₂ SiO ₄ .

When Cu is added, this S
Since it is difficult to form iO _{2, in} order to secure the amount of SiO ₂ ,
It is necessary to increase the oxygen potential in the annealing atmosphere. Since it is necessary to secure a predetermined amount of SiO ₂ in order to make the coating good, the existence of the lower limit of the amount of SiO ₂ in FIG. 1 can be understood. On the other hand, the higher the Cu content, the more this SiO
We believe that the lower limit of the _two quantities will decrease as follows.

As a result of a detailed analysis of the reaction for forming Mg ₂ SiO ₄ at the time of raising the temperature of the final finish annealing, as the amount of Cu increases, the reaction for forming Mg ₂ SiO ₄ occurs from a lower temperature.
It was found that g ₂ SiO ₄ was easily formed. For this reason, Si for securing the required amount of Mg ₂ SiO ₄
It is considered that the lower limit of the O ₂ amount decreases as the Cu amount increases as shown in FIG.

On the other hand, SiO 2 for obtaining a good magnetic flux density
We consider the reason why there is an upper limit of _two quantities as follows. The main inhibitor for the secondary recrystallization in the present invention is AlN or (Al, Si) N. As the amount of SiO _{2 in} the surface oxide film increases, AlN, (Al, Decomposition of Si) N is likely to occur. On the other hand, there was a tendency that the larger the amount of Cu, the larger the Cu-S.

As a result, Cu—S + AlN or Cu—S + (Al, Si) after precipitation of AlN, (Al, Si) N
It was observed that the size of N tended to increase as the amount of Cu increased. Therefore, Cu-S + AlN or Cu-S +
The decomposition of (Al, Si) N during the final annealing temperature increase occurred at higher temperatures as the Cu content was higher. As a result, the temperature at which secondary recrystallization occurs increases as the amount of Cu increases.

In this case, as the amount of SiO _{2 in} the surface oxide film increases, AlN, (Al,
Since the decomposition of Si) N is likely to occur, it is considered that as the amount of SiO ₂ increases, the phenomenon that the precipitate is less likely to decompose when the amount of Cu is higher is eventually reduced. For this reason, it is considered that the larger the amount of Cu, the higher the range of the amount of SiO ₂ of the surface oxide film which is appropriate for obtaining a high magnetic flux density is shifted.

The conditions for obtaining these high magnetic flux densities can be understood from the viewpoint of proper secondary recrystallization and control of the decomposition behavior of precipitates at that time. In other words, secondary recrystallization
This phenomenon is considered to be caused by the dependence of grain boundary movement on the grain boundary character.
In the case of secondary recrystallization of {110} <001> oriented grains, when secondary recrystallization occurs in a temperature range where the difference in the grain boundary moving speed between the general grain boundary and the {9} grain boundary is large, {110} <001 It is considered that the degree of integration of the orientation is high.

When the amount of Cu is increased, the temperature at which secondary recrystallization occurs is increased. Therefore, in order to maintain the secondary recrystallization temperature in an appropriate range,
It is considered that it is necessary to increase the amount of SiO _{2 in the} surface oxide film.

Next, the reasons for limiting the constituent elements of the present invention will be described. First, the reasons for limiting the components of the slab will be described. C is 0.025% by weight (hereinafter simply referred to as%)
If it is less than 2, secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, it is difficult to obtain B ₈ > 1.80 (T), so the content was limited to 0.025% or more. On the other hand, if the C content is too large, the decarburization annealing time becomes long and it is not economical.
It was specified as 5% or less. If the content of Si exceeds 5.0%, cracks during cold rolling become remarkable, so the content was made 5.0% or less. Also, 2.
If it is less than 2%, the specific resistance of the material is too low, and a low iron loss required as a transformer core material cannot be obtained. Desirably, it is at least 3.2%.

Al is AlN necessary for stabilizing secondary recrystallization.
Alternatively, to secure (Al, Si) N, acid-soluble A
l needs to be 0.010% or more. If the acid-soluble Al content exceeds 0.060%, the AlN of the hot-rolled sheet becomes inappropriate and secondary recrystallization becomes unstable. Therefore, the content needs to be 0.060% or less.

N is preferably set to 0.0040 to 0.0130%. By setting the content in this range, it is possible to achieve both the control of the primary recrystallization grain size, which will be described later, and the securing of a free Al amount during nitriding. Further, in addition, N is 0.013.
If it exceeds 0%, blisters called blisters are undesirably generated on the steel sheet.

The range of S + 0.405Se is 0.005
０．０0.020%. If it is less than 0.005%, the amount of Cu-S (or Cu-Se), which is the essence of the present invention, becomes insufficient, which is not preferable. On the other hand, if it exceeds 0.020%, a secondary recrystallization failure phenomenon that occurs in a row in the rolling direction occurs, which is not preferable.

The ranges of the Mn content and the Cu content are each 0.01%.
, Less than 0.05 to 0.50%. When the amount of Mn is 0.01% or more, MnS or MnSe is precipitated, and Cu—S or Cu—S which is the main object of the present invention is used.
The precipitation of e becomes insufficient, and as a result, the inhibitor during the final finish annealing is undesirably coarsened.

Regarding the amount of Cu, as shown in FIG.
Since good magnetic properties can be obtained in the range of 0.05 to 0.50%, this range is defined. If less than 0.05%, C
Undesirably, the precipitation of u-S becomes insufficient. 0.50%
If it is excessive, Cu-S is excessively coarsened, and as a result, the inhibitor during the final finish annealing is undesirably coarsened, which is not preferable.

More preferably, the range of Sn is 0.01 to 0.15%. Sn increases the {110} <001> orientation grain in the primary recrystallization texture, and as a result, has the effect of reducing the secondary recrystallization grain size and the effect of uniformizing the precipitation of sulfide. is there. Therefore, the effect of controlling sulfide precipitation as in the present invention is further promoted. If the amount of Sn is less than 0.01%, the above effect is insufficient, and if it exceeds 0.15%, it is not preferable because nitriding of the steel sheet becomes difficult and causes secondary recrystallization failure.
In addition, Sb, which is known as an inhibitor constituent element,
A small amount of Cr, Ni, B, Ti, Nb, etc. may be contained.

The heating temperature of the slab was limited to less than 1280 ° C. for the purpose of reducing the cost as compared with ordinary steel. Preferably it is 1200 ° C or lower. The heated slab is subsequently hot-rolled into a hot-rolled sheet.

This hot rolling includes rough rolling performed at low speed in reverse or tandem, and high-speed finishing hot rolling performed in tandem. The temperature of this finishing hot rolling is 700 to 1100 ° C.
It is preferable that This is because by performing the finish hot rolling in this temperature range, the precipitation of Cu-S with the dislocations introduced by the hot rolling as nuclei easily occurs, and a finely dispersed dispersed phase of Cu-S is easily obtained.

The hot-rolled sheet is then subjected to one or two or more cold-rolling steps with intermediate annealing. At this time, the rolling reduction of the final cold rolling is set to 80% or more. The reason why the rolling reduction of the final cold rolling is set to 80% or more is that the rolling reduction is within the above range,
Sharp {110} <001> orientation grains in the decarburized plate,
The corresponding orientation grains ({111} <11
2> orientation grains) can be obtained in an appropriate amount, which is preferable in increasing the magnetic flux density. Although not particularly limited, it is more preferable to perform hot-rolled sheet annealing at 800 to 1200 ° C. as necessary after the hot-rolling in order to stabilize magnetic properties to a high degree. Heat treatment in this temperature range is caused by A
This has the effect of reducing the spatial nonuniformity of the hot rolled 1N, Cu-S sheet.

The steel sheet after the final cold rolling is subjected to decarburizing annealing, application of an annealing separator, and final finishing annealing to become a final product. Here, after the decarburizing annealing is completed, controlling the average grain size of the primary recrystallized grains to 18 to 35 μm until the start of the final finish annealing,
More preferred. The reason is that a good magnetic flux density is easily obtained in the range of the average particle diameter, and the change of the magnetic flux density with respect to the fluctuation of the particle diameter is small.

The reason that the steel sheet is subjected to the nitriding treatment before the secondary recrystallization of the final finish annealing after the hot rolling is defined as follows:
This is because in the process based on low-temperature slab heating as in the present invention, the inhibitor strength required for secondary recrystallization tends to be insufficient. The method of nitriding is not particularly limited, but may be a method of nitriding by mixing NH ₃ gas in the annealing atmosphere after decarburizing annealing, a method using plasma, adding a nitride to the annealing separator, and increasing the final finish annealing. Any method may be used, such as a method of absorbing nitrogen formed by the decomposition of nitrides in a temperature into a steel sheet, or a method of nitriding the steel sheet by increasing the N ₂ partial pressure in an atmosphere of final finish annealing.

The amount of nitriding is 0.0010
% Or more is necessary. If the content is less than 0.0010%, the phenomenon of substitution of AlN or (Al, Si) N from a nitride containing a large amount of Si or Mn in the final finish annealing temperature raising process, which is the essence of the present invention, is not sufficient, which is not preferable. . The upper limit of the nitrogen increase amount is not particularly specified, but is preferably 0.1000% or less in order to reduce the defects of the forsterite film.

The relationship between the total amount of SiO ₂ (SIO2 (g / m ² )) in the surface oxide film of the steel sheet after the decarburizing annealing and the Cu amount (Cu (%)) of the slab is 0.7-0. 6 × Cu (%) ≦ SIO2 ≦ 1.6 + 0.3 × Cu (%) As shown in FIG. 1, by setting the content in this range, good magnetic properties and good film properties can be obtained. If the SIO2 is less than the lower limit, film formation is poor, which is not preferable. If the upper limit of SIO2 is exceeded,
The magnetic flux density is undesirably reduced.

Means for satisfying the above conditions are not particularly limited. The above relationship can be satisfied by controlling the temperature and dew point during decarburization annealing. The oxidation behavior is affected by the elements added to the steel and their amounts. Therefore, in order to satisfy the above relation, it is necessary to set conditions according to the material. Since Sn and Cu are elements that suppress oxidation, special care must be taken.

When the nitriding treatment is continuously performed after the decarburizing annealing or the nitriding treatment is performed separately, the amount of SiO _{2 in} the steel sheet after the decarburizing annealing is defined for the steel sheet immediately before the final finish annealing. Is understood.

The dew point, atmosphere gas, and thermal cycle during decarburization annealing are not particularly limited. The dew point is 30-8
At 0 ° C., a mixed gas of N ₂ and H ₂ is usually used as an atmosphere gas. 800-900 ° C for thermal cycle
Until the steel sheet is heated. It is preferable to control the dew point, the atmosphere gas, and the thermal cycle according to Mn, Cu, and the like, in order to realize the effects of the present invention as shown in FIG.

Further, when the final finish annealing temperature was raised to 1000 to 1000
It was specified that heating was performed between 1150 ° C at a heating rate of 20 ° C / hour or less. This is not preferable when secondary recrystallization is caused by using a fine precipitate as an inhibitor as in the present invention, and when the secondary recrystallization temperature is too high, the precipitate is rapidly decomposed. For this reason, if the temperature rise rate is exceeded, the secondary recrystallization temperature becomes too high, which is not preferable. The lower limit of the heating rate is not particularly limited.
It is not preferable to set the temperature to 1 ° C./hour or less in terms of cost.

The atmosphere during the final finish annealing is not particularly limited. However, in terms of securing an oxidation potential, it is preferable to perform annealing in an atmosphere containing N ₂ gas at the time of raising the temperature. After the final finish annealing, annealing is performed for both shape correction and tension coating. This annealing is performed by heating the steel sheet to 800 to 900 ° C., and a coating containing phosphoric acid or the like is also applied.

[0063]

【Example】

[Example 1] C: 0.050% (% is% by weight, the same applies hereinafter), Si: 3.29%, Mn: 0.005%, S:
0.008%, acid-soluble Al: 0.029%, N: 0.
0080% as a basic component, and the Cu content is <0.001
%, 0.10%, 0.36%, 0.61% 4
Four 250 mm thick slabs were added at the standard level.

After the slab was soaked at 1100 ° C. for 60 minutes, hot rolling was started immediately. The thickness of the slab was increased to 40 mm by 5 passes of coarse hot rolling, and then 2.3 mm by hot finishing of 6 passes. Board. At this time, the temperature from the start of finishing hot rolling to the end temperature (finishing hot rolling temperature) was 850 to 1035 ° C.

Next, after the hot-rolling is completed, the air-cooling is performed for 550 seconds for 2 seconds.
A cooling simulation was performed in which water was cooled to 550 ° C., the temperature was maintained at 550 ° C. for 1 hour, and then the furnace was cooled. 1100
C. for 3 minutes, then a 0.285 mm cold-rolled sheet with a reduction of about 88%, and a 150.degree.
A decarburizing anneal for 2 seconds was performed. The annealing atmosphere at this time was (a) N ₂ : 25%, H ₂ : 75%, dew point 65 ° C.
(B) Two conditions were set: N ₂ : 25%, H ₂ : 75%, and dew point 40 ° C.

Thereafter, annealing was performed at 750 ° C. for 30 seconds, and NH ₃ gas was mixed into the annealing atmosphere to absorb nitrogen into the steel sheet. The N content of this steel sheet after nitriding is 0.0
185-0.0210%. The average grain size of the primary recrystallized grains of the steel sheet after the nitriding treatment was 22 to 26 μm.

Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and the temperature was increased to 1200 ° C. at a rate of 15 ° C./hour in an atmosphere gas of N ₂ : 25% and H ₂ : 75%. Followed by 1200 ° C. in a 100% atmosphere of H ₂ gas.
For 20 hours. Table 1 shows the results of the experimental conditions, magnetic properties, and film properties.

[0068]

[Table 1]

Example 2 C: 0.060%, Si:
3.47%, S: 0.012%, Cu: 0.20%, acid-soluble Al: 0.026%, N: 0.0060% as basic components, Mn is 0.006%, 0.019 %, 0.031%, and three levels, and three types of slabs having a thickness of 250 mm and comprising the balance of Fe and unavoidable impurities were prepared. After the slab was soaked at 1120 ° C. for 60 minutes, hot rolling was immediately started, and the hot-rolled sheet having a thickness of 40 mm was obtained by rough-rolling in five passes, and then a 2.3-mm thick sheet was formed by finishing hot-rolling in six passes. . At this time, the finishing hot rolling temperature was 905 to 1007 ° C.

This hot rolled sheet was kept at 1100 ° C. for 30 seconds,
Subsequently, the sheet was held at 900 ° C. for 30 seconds and then subjected to quenched hot-rolled sheet annealing. Subsequently, a cold rolled sheet of 0.220 mm was formed at a rolling reduction of about 90%, and decarburizing annealing was performed at 845 ° C. for 90 seconds.

The annealing atmosphere during the decarburizing annealing is shown in FIG.
N ₂ : 25%, H ₂ : 75%, dew point 58 ° C, (b)
N ₂ : 75%, H ₂ : 25%, dew point 75 ° C. Two conditions were set. Thereafter, annealing was performed at 770 ° C. for 30 seconds, and NH ₃ gas was mixed during annealing to allow the steel sheet to absorb nitrogen. The N content of this steel sheet after nitriding is 0.0185 to
0.0210%.

Next, this steel sheet contains MgO as a main component,
An annealing separator containing 3% TiO ₂ was applied, and N ₂ : 5
The temperature was raised to 1200 ° C. at a rate of 15 ° C./hour in an atmosphere gas of 0% and H ₂ : 50%, and then a final finish annealing was performed at 1200 ° C. for 20 hours in a 100% H ₂ atmosphere gas. . Table 2 shows the relationship between the experimental conditions, magnetic properties, and film properties.
Shown in

[0073]

[Table 2]

Example 3 C: 0.057%, Si:
3.55%, Mn: 0.12%, S: 0.010%, acid-soluble Al: 0.030%, Cu: 0.23%, and further N is 0.0018%, 0.0079 %
Was added to produce two types of slabs each having a thickness of 250 mm and consisting of the balance of Fe and unavoidable impurities. Such a slab is a:
1250 ° C., b: After soaking for 60 minutes each at two levels of temperature of 1100 ° C., immediately start hot rolling, and perform 4 passes by rough hot rolling of 5 passes.
After the thickness was reduced to 0 mm, a hot-rolled sheet having a thickness of 1.8 mm was formed by finishing hot rolling in 6 passes. At this time, the finishing hot rolling temperature was a: 1008 to 1151 ° C. and b: 875 to 1 with respect to the heating conditions a and b, respectively.
016 ° C.

Then, the hot-rolled sheet was kept at 1100 ° C. for 30 seconds, immediately subjected to hot-rolled sheet annealing at 850 ° C. and rapidly cooled, and then formed into a cold-rolled sheet of 0.170 mm at a rolling reduction of about 91%. Decarburization annealing was performed at 830 ° C. for 90 seconds. The annealing atmosphere when the _{N 2: 30%, H 2} : 70%, and dew point 60 ° C.. Thereafter, annealing was performed at 750 ° C. for 30 seconds, and NH ₃ gas was mixed into the annealing atmosphere to cause nitrogen absorption in the steel sheet. The N content of this steel sheet after nitriding is 0.1.
0210 to 0.0241%, and the amount of SIO2 is 0.1%.
9 to 1.1 g / m ² . The average grain size of the primary recrystallized grains of the steel sheet after the nitriding treatment was 21 to 28 μm.

Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and A: 25 ° C./hour and B: 10 ° C./hour in an atmosphere gas of N ₂ : 50%, H ₂ : 50%. The temperature was raised to 1200 ° C. at two levels of speed, followed by H ₂ : 100
A final finish annealing was performed in an atmosphere gas at 1200 ° C. for 20 hours. Table 3 shows the experimental conditions and the results of the magnetic characteristics.

[0077]

[Table 3]

Example 4 C: 0.049%, Si:
3.26%, Mn: 0.008%, S: 0.014%,
Cu: 0.17%, acid-soluble Al: 0.027%, N:
A slab having a thickness of 250 mm was prepared by adding 0.0081% and the balance being Fe and unavoidable impurities. After the slabs were soaked at 1100 ° C. for 60 minutes each, hot rolling was started immediately, and after 5 passes of coarse hot rolling to a thickness of 40 mm, a hot rolled sheet of 6 passes finishing hot rolling and 2.6 mm thick was rolled. did. At this time, the finishing hot rolling temperature was 895 to 1044 ° C.

Next, the hot-rolled sheet was pickled to obtain a 0.335-mm cold-rolled sheet at a rolling reduction of about 87%, and subjected to decarburization annealing at 840 ° C. for 150 seconds. The annealing atmosphere when the _{N 2: 25%, H 2} : 75%, and dew point 64 ° C.. Thereafter, the steel sheet was annealed at 750 ° C. for 30 seconds, and NH ₃ gas was mixed into the annealing atmosphere to cause the steel sheet to absorb nitrogen. The N content of this steel sheet after nitriding is 0.021.
9%. The average crystal grain size of this steel sheet is 24
μm, and SIO2 was 1.1 g / m ² .

Then, an annealing separator containing MgO as a main component was applied to the steel sheet, and the steel sheet was heated at a rate of 15 ° C./hour and 30 ° C./hour in an atmosphere gas of N ₂ : 50% and H ₂ : 50%.
The temperature was raised to 00 ° C., followed by final finish annealing in which the temperature was kept at 1200 ° C. for 20 hours in a 100% atmosphere of H ₂ gas. Table 4 shows the relationship between the experimental conditions, magnetic properties, and film properties.

[0081]

[Table 4]

Example 5 C: 0.056%, Si:
3.45%, Mn: 0.09%, S: 0.007%, C
u: 0.20%, acid-soluble Al: 0.029%, N:
0.0075% as a basic component, without addition of Sn (<0.01%), 0.05%, 0.10% 3
Added at a level, the balance consisting of Fe and unavoidable impurities 3
250 mm thick slabs of various types were made. After soaking the slab at 1050 ° C. for 60 minutes, immediately start hot rolling,
After a rough hot rolling of 5 passes and a thickness of 40 mm, a hot rolled sheet of 2.3 mm thick was formed by finishing hot rolling of 6 passes. At this time, the finishing hot rolling temperature was 840 to 975 ° C.

Then, the hot-rolled sheet was held at 1100 ° C. for 30 seconds, immediately subjected to hot-rolled sheet annealing at 900 ° C. and rapidly cooled, and then a cold-rolled sheet having a rolling reduction of about 90% and a 0.220 mm thickness was obtained. Decarburization annealing was performed at 835 ° C. for 90 seconds. The annealing atmosphere when the _{N 2: 50%, H 2} : 50%, and a dew point of 50 ° C.. Thereafter, the steel sheet was annealed at 750 ° C. for 30 seconds, and NH ₃ gas was mixed into the annealing atmosphere to cause nitrogen absorption in the steel sheet. The N content of this steel sheet after nitriding is 0.0206-0.0230%,
2 weight was 0.9~1.2g / m ^2. The average grain size of the primary recrystallized grains of the steel sheet after the nitriding treatment is from 24 to 2
It was 7 μm.

[0084] Then, an annealing separator composed mainly of MgO was applied to this steel _{sheet, N 2: 25%, H} 2: 75% a in an atmospheric gas. Heat up to 1200 ° C at 10 ° C / hour,
b. The temperature is raised to 90 ° C at a rate of 10 ° C / hour, and from 900 ° C to 12 ° C.
After the temperature was raised to 200 ° C. at two levels of 50 ° C./hour, both a and b were heated at 1200 ° C. in 100% H ₂ at 1200 ° C.
A final finish annealing of 0 hours was performed. Table 5 shows the experimental conditions and the results of the magnetic properties.

[0085]

[Table 5]

[0086]

According to the present invention, Cu is added and Mn is added.
Controlling the hot rolling temperature,
Controlling the average grain size of the primary recrystallized grains from the completion of decarburizing annealing to the start of final finish annealing, and subjecting the steel sheet to a predetermined amount of nitriding before the start of secondary recrystallization of final finish annealing after hot rolling. Stable good magnetic properties by controlling the amount of SiO _{2 in} the steel sheet after decarburizing annealing according to the amount of Cu in the slab, and by lowering the heating rate in a specific temperature range during the final finishing annealing Therefore, the industrial effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the Cu content of a slab and the total SiO ₂ content in a surface oxide film after decarburizing annealing on magnetic properties and coating properties.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-158322 (JP, A) JP-A-6-145803 (JP, A) JP-A-6-145801 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/60 H01F 1/16

Claims (2)

(57) [Claims] 1. A weight ratio of C: 0.025 to 0.075%, Si: 2.2 to 5.0%, acid-soluble Al: 0.010 to 0.060%, N: 0.0040 to 0.0130%, S + 0.405Se: 0.005 to 0.020%, Mn: less than 0.01%, Cu: 0.05 to 0.50%, The balance is 128 slabs composed of Fe and unavoidable impurities.
Heating is performed at a temperature of less than 0 ° C., hot rolling is performed, and then, if necessary, hot-rolled sheet annealing is performed, and then, one or more times of cold rolling including intermediate annealing, including final rolling at a reduction of 80% or more, is performed. Then, in a method for producing a grain-oriented electrical steel sheet by performing decarburization annealing and final finish annealing, the finish hot rolling is performed at 700 to 1100.
° C., after the completion of decarburizing annealing, the average particle size of the primary recrystallized grains until the start of the final finish annealing is 18 to 35 μm, after hot rolling, until the start of the secondary recrystallization of the final finish annealing The steel sheet is subjected to a nitriding treatment for absorbing 0.0010% by weight or more of nitrogen, and the total SiO ₂ in the surface oxide film after the decarburizing annealing is performed.
Amount (SIO2 (g / m ² )) and the slab Cu amount (Cu
(%)) Is controlled within the range of the following expression (1), and the temperature of the steel sheet in the temperature rising process of the final finish annealing is 1000 to 1150 ° C.
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties, wherein the temperature is raised at a rate of 20 ° C./hour or less in the range of (1). 0.7−0.6 × Cu (%) ≦ SIO2 ≦ 1.6 + 0.3 × Cu (%) (1) 2. The method according to claim 1, wherein the slab contains 0.01 to 0.15% by weight of Sn in the slab.