JP3169490B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent magnetic 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 an iron 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. Further, as a numerical value representing the iron loss characteristic, an iron loss W _17/50 per kg when magnetized at a frequency of 50 Hz to 1.7 Tesla (T).
You are using The magnetic flux density is the largest controlling factor of the 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.

[0003] This unidirectional electrical steel sheet undergoes 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. Being manufactured. 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.

[0004] As a typical production technique of such a high magnetic flux density unidirectional magnetic steel sheet, Japanese Patent Publication No. 40-15644 is disclosed.
And JP-B-51-13469. In the former, MnS and AlN are used as main inhibitors, and in the latter, MnS, MnSe, Sb and the like are used. 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 current process, MnS is used during slab heating before hot rolling.
Is once dissolved completely and then precipitated during hot rolling. A temperature of about 1400 ° C. is required to completely dissolve the required amount of MnS for secondary recrystallization.

[0005] This is 2 times lower than the slab heating temperature of ordinary steel.
The temperature is higher than 00 ° C.
A high-temperature slab heating furnace dedicated to grain-oriented electrical 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 also requires reducing the amount of MnS effective as an inhibitor or not using it at all. And inevitably leads to instability of secondary recrystallization. For this reason, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor with a precipitate other than MnS in some form, and to sufficiently suppress normal grain growth during finish annealing.

As such inhibitors, nitrides, oxides, grain boundary precipitation elements and the like can be considered in addition to sulfides.
Known techniques include, for example, the following.
In Japanese Patent Publication No. 54-24687, As, Bi, Sn,
A method has been disclosed in which a slab heating temperature is set in the 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 further, the secondary recrystallization is stabilized by adding Cu. To disclose the technology.

[0008] 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 JP-A-59-190324, 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, thereby performing secondary recrystallization. The technology to stabilize is disclosed.

As described above, great efforts have been made so far to realize the 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 reducing 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.

[0010]

The method using the low-temperature slab heating originally aims at reducing the manufacturing cost, but it cannot be industrialized unless it is a technique to obtain good magnetic properties stably as a matter of course. 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 by this nitriding treatment is mainly AlN at the start of the secondary recrystallization. Al as an inhibitor that does not change easily at high temperatures
N is selected, and in that sense, it is an essential condition that Al is contained in the slab.

On the other hand, the fact that the slab contains N more than necessary has room for reconsideration in view of the present technical system.
In other words, if there is essential Al and a certain amount of N in the slab, in the process from slab heating to decarburizing annealing, Al
N is formed and affects the grain growth of primary recrystallized grains during decarburizing annealing. The purpose of the present invention is to examine a control method of AlN precipitation in the above process, and to perform low-temperature slab heating,
Another object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having excellent properties by omitting hot-rolled sheet annealing.

[0012]

The gist of the present invention is as follows. (1) C: 0.075% or less by weight ratio, Si: 2.2 to
4.5%, acid-soluble Al: 0.010 to 0.060%,
N: 0.0130% or less, S + 0.405Se: 0.0
A slab containing 14% or less, Mn: 0.05 to 0.8%, and the balance being Fe and inevitable impurities is 1280 ° C.
Heating at a temperature less than or equal to, hot-rolling, and subsequently performing cold rolling under final high-pressure reduction of 80% or more without performing hot-rolled sheet annealing, and then performing decarburizing annealing and final finishing annealing to achieve unidirectionality In the method for producing an electrical steel sheet, the cumulative draft of the rough hot rolling is set to 60% or more, the time between the rough hot rolling and the finish hot rolling is set to 1 second or more, and the starting temperature of the finish hot rolling is set to 800 to 1100 ° C. , The content (wt%) of acid-soluble Al and N in the slab, and the deviation ΔFoT (° C) in the coil of the starting temperature of the finishing hot rolling within the range of the following formula (1), and after the completion of the decarburizing annealing, the final finishing The average grain size of primary recrystallized grains before the start of annealing is 18 to 35 μm
The steel sheet is subjected to a nitriding treatment for absorbing at least 0.0010% by weight of nitrogen into the steel sheet after the decarburization annealing and before the start of the secondary recrystallization of the final finish annealing, and has excellent unidirectional magnetic properties. Manufacturing method of electrical steel sheet. ΔFoT (° C.) ≦ 15 + 2500 × {Al (%) − (27/14) × N (%)} (1) where Al: acid-soluble Al

(2) A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties as described in the preceding paragraph, further comprising 0.01 to 0.15% of Sn as a slab component.

[0014]

The grain-oriented electrical steel sheet to which the present invention is directed is:
The molten steel obtained by the conventional steelmaking method is cast by the continuous casting method or ingot making method, and if necessary, the slab is sandwiched by the sizing process, and subsequently hot-rolled to form a hot-rolled sheet. It is manufactured by performing final cold rolling in which the rolling reduction is 80% or more without annealing the rolled sheet, and then sequentially performing decarburizing annealing and final finishing annealing.

The present inventors have studied in detail the causes of magnetic fluctuations when manufacturing a low-temperature slab heating material by one-time cold rolling without the hot-rolled sheet annealing, and the solution thereof. As a result, the in-coil deviation of the finish hot rolling start temperature is controlled according to the acid-soluble Al content and N content of the slab, the cumulative draft of the rough hot rolling, the time between the rough hot rolling and the finish hot rolling, and the finish. By controlling the hot rolling start temperature, it was found that the magnetic fluctuation can be drastically reduced. First, effects of the present invention will be described based on experimental results.

FIG. 1 shows that Al (%)-(27) in the slab.
/ 14) × N (%) amount (however, Al: acid-soluble Al),
The relationship between the maximum and minimum difference ΔFoT (° C.) of the finish hot rolling start temperature and the variation of the magnetic flux density of the product is shown. In this case, by weight ratio, C: 0.024 to 0.031%, Si: 2.5 to
3.0%, acid-soluble Al: 0.034 to 0.040%,
N: 0.0054 to 0.0068%, S: 0.005 to
0.007%, Mn: 0.10 to 0.14%,
250 mm thick 20 consisting of balance Fe and unavoidable impurities
created a ton slab. And 1,050-1200 ° C
After holding at a temperature of about 120 minutes, rough hot rolling is performed in 7 passes to obtain a thickness of 40 mm, and then finish hot rolling is performed in 6 passes.
A hot-rolled sheet having a thickness of 2.3 mm was obtained.

In this hot rolling, water cooling is performed between the passes in the rough hot rolling, the time between passes is changed, or the time between the rough hot rolling and the finish hot rolling is positively changed. The starting temperature was taken over a wide range. In each coil of the hot-rolled sheet, a sample is cut out from a portion where the finish hot-rolling start temperature is highest and a portion where the hot-rolling finish temperature is lowest, and is subjected to strong rolling at a rolling reduction of about 85% without performing hot rolling annealing. Use a cold rolled sheet with a thickness of 0.335 mm.
Decarburization annealing at 35 ° C. for about 150 seconds,
During annealing at 770 ° C. for 30 seconds, NH 3 was introduced in the annealing atmosphere.
_Three gases were mixed to cause the steel sheet to absorb nitrogen.

The N content after the nitriding treatment is 0.0206 to
0.0237% by weight, and the average particle size of primary recrystallized grains (average value of equivalent circle diameters) was 21 to 26 μm.
An annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed. Thereafter, by measuring the magnetic flux density of the product, the same components, the same hot rolled condition two taken against hot-rolled sheet of the sample at (a maximum temperature portion of the final hot rolling start temperature and the minimum temperature portion) of the B ₈ The difference ΔB ₈ was determined.

As is clear from FIG. 1, ΔFoT (° C.)
≦ 15 + 2500 × ｛Al (%) − (27/14) × N
(%)｝, ΔB ₈ ≦ 0.02T, and stable magnetic characteristics are obtained. Although the effect mechanism for controlling the deviation of the hot rolling start temperature in the finish in accordance with the amounts of the acid-soluble Al and N of the slab shown in FIG. 1 is not necessarily clear, the present inventors presume as follows. ing.

The present invention relates to a method disclosed by the present inventors in JP-A-2-182.
It belongs to a technical system disclosed in Japanese Patent Publication No. 866 which is based on making the crystal structure after decarburization annealing appropriate. on the other hand,
It is considered that N dissolved in solid solution at the time of completion of slab heating becomes fine nitride (mainly AlN) during hot rolling or during decarburizing annealing (especially during temperature rise). It is considered that the size and the amount of precipitation of this fine nitride fluctuate even with a slight temperature change during decarburization annealing.

However, the grain growth suppressing effect (Zener factor) of the precipitate is inversely proportional to the size of the precipitate.
It is proportional to its volume fraction. Therefore, even if the amount of solute N at the time of completion of slab heating is excessively reduced, the effect of suppressing grain growth of precipitates becomes too small, and as a result, the grain growth during decarburization annealing becomes too remarkable, and the control of the crystal structure is performed. Becomes difficult.

ΔFot (° C.) ≦ 15 + 25 in FIG.
00 × {Al (%) − (27/14) × N (%)} is
This means that the deviation of the finish hot rolling start temperature is defined according to the acid-soluble Al content and N content of the slab. Where Al
The larger the value of (%)-(27/14) × N (%) is, the smaller the deviation of the amount of solute N at the start of hot rolling at the same temperature difference is. In this case, it means that the allowable range of the temperature deviation at the start of the hot rolling is wide.

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 and the slab heating temperature will be described in detail. If C is excessively large, the decarburizing annealing time becomes long and it is not economical. A particularly preferable range in terms of magnetic properties is 0.020 to 0.070%. If the content of Si exceeds 4.5%, cracking at the time of cold rolling becomes remarkable. If it is less than 2.2%, the specific resistance of the material is too low, and a low iron loss required as a transformer core material cannot be obtained. Al is AlN or (Al, S) necessary for stabilizing the secondary recrystallization.
i) To secure N, 0.010 as acid-soluble Al
% Or more is required. If the acid-soluble Al content exceeds 0.060%, the AlN of the hot-rolled sheet becomes inappropriate and secondary recrystallization becomes unstable.

If N exceeds 0.0130%, blisters called "blisters" occur on the surface of the steel sheet. Therefore, N is set to 0.0130% or less. Even if MnS and MnSe are present in steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, when S or Se is high, a secondary recrystallization defective portion called linear fine grain tends to occur. To prevent the occurrence of the secondary recrystallization defective portion, (S + 0.405Se) ≦ 0.014
Should be%. If S or Se exceeds the above-mentioned value, the probability of occurrence of a secondary recrystallization defective portion increases, no matter how the manufacturing conditions are changed, which is not preferable. In addition, the time required for purification in the final finish annealing is too long, which is not preferable. From such a viewpoint, it is meaningless to increase S or Se unnecessarily.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, the shape (flatness) of the hot rolled sheet obtained by hot rolling, that is, the side edge portion of the strip becomes corrugated, which causes a problem of lowering the product yield. On the other hand, if the Mn content exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable. Therefore, the upper limit of the Mn content is set to 0.8%. Sn is
Known as a grain boundary segregation element, it is an element that suppresses grain growth. On the other hand, when the slab is heated, Sn is completely dissolved.
It is considered that even in the slab at the time of heating having a temperature difference of several tens degrees Celsius which is generally considered, the solid solution is uniformly formed. Therefore,
It is considered that Sn uniformly distributed in the slab at the time of heating, despite the temperature difference, also acts uniformly in place on the grain growth suppressing effect at the time of decarburizing annealing.

For this reason, it is considered that Sn has the effect of diluting the spatial nonuniformity of grain growth during decarburization annealing caused by the spatial nonuniformity of AlN. Therefore, the addition of Sn is effective in further reducing the variation in the magnetic properties of the product. The proper range of Sn is 0.01 to 0.15.
%. Below this lower limit, the effect of suppressing grain growth is undesirably too small. On the other hand, if the upper limit is exceeded, nitriding of the steel sheet becomes difficult, which causes secondary recrystallization failure, which is not preferable.

In addition, trace amounts of Sb, Cu, Cr, Ni, B, Ti, Nb and the like, which are known as inhibitor constituent elements, may be contained. In particular, B, Ti,
Nitride constituent elements such as Nb may be positively added to reduce the amount of solute N in steel during slab heating.
When there is an element having a higher affinity for N than Al, when calculating an equation for defining a finish hot rolling start temperature deviation to be described later, it is formed for B, Ti, and Nb contained from the total N amount. Subtracting the N content of the nitride to be performed is preferable for improving the accuracy of the control effect in the present invention.

The slab heating temperature is limited to less than 1280 ° C. for the purpose of reducing the cost to the level of ordinary steel. Preferably it is 1200 ° C or lower. The heated slab is subsequently hot-rolled into a hot-rolled sheet. The hot rolling process
Usually, after heating a slab having a thickness of 100 to 400 mm, the slab consists of rough hot rolling and finish hot rolling performed in a plurality of passes. The cumulative rolling reduction of the rough hot rolling needs to be 60% or more. In the case of the AlN precipitation control technique as in the present invention, it is necessary to introduce many dislocations as precipitation nuclei of AlN. If the cumulative rolling reduction is less than 60%, the introduction of the dislocations is insufficient.
It was defined as 0% or more. The upper limit of the cumulative rolling reduction is not particularly limited, and is allowed up to about 99.9%.

The time between passes of the rough hot rolling and the finish hot rolling was specified to be 1 second or more. This is to cause the precipitation of AlN between the passes, and less than 1 second has little effect. The upper limit of the inter-pass time is not particularly limited, but taking an inter-pass time of 1 hour or more is not preferable in terms of productivity.

The finish hot rolling starting temperature was specified to be 800 to 1100 ° C. If it exceeds 1100 ° C., precipitation of AlN in hot rolling becomes insufficient, which is not preferable. On the other hand, if the temperature is lower than 800 ° C., recrystallization by hot rolling in the finish becomes insufficient, which is not preferable.

The final hot-rolling start temperature deviation ΔFoT (° C.)
FoT (° C.) ≦ 15 + 2500 × ΔAl (%) − (27
/ 14) × N (%｝) because it is necessary to stabilize the magnetic characteristics as shown in FIG. There is no particular limitation on the method of setting the range, a method of adjusting the slab temperature by a temperature gradient or the like, a method of changing the sheet thickness at the end of the rough hot rolling in the rolling direction position, an adjustment of the time between passes of the rough hot rolling, Adjustment of the time between passes of rough hot rolling and finish hot rolling, cooling control for each location in the coil between the rough hot rolling and the pass, and maintenance of the temperature between the rough hot rolling and the finish hot rolling or water cooling for each location in the coil Temperature control and the like can be performed.

The subsequent finishing hot rolling is usually performed by high-speed continuous rolling of 4 to 10 passes. Normally, the rolling distribution of hot rolled finish is
The rolling reduction is higher in the former stage and the rolling reduction is lower in the latter stage, so that the shape is good. Rolling speed is usually 100-30
0m / min and the time between passes is 0.01-10
0 seconds. In the present invention, the conditions for the finish hot rolling are not limited, but in order to perform AlN precipitation,
In addition to controlling the deviation of the finish hot rolling start temperature, which is one of the features of the present invention, it is necessary to actively adjust the finish hot rolling end temperature and adjust the rolling reduction.

The temperature range where AlN is easily deposited (800 to 9)
50 ° C) or around it, actively increase the draft,
Producing the work-induced precipitation is also an effective means for controlling the amount of AlN precipitation. After the final pass of hot rolling, the steel sheet is usually 0.1 mm.
Air-cooled for about 1-100 seconds, then water-cooled 300-700
It is wound at a temperature of ° C. and slowly cooled. The cooling process is not particularly limited, but a method of performing air cooling or the like for 1 second or more after hot rolling and keeping the steel sheet in the AlN precipitation temperature range as long as possible is used for controlling the amount of AlN precipitation. Is preferred.

This hot rolled sheet is then subjected to final cold rolling at a rolling reduction of 80% or more without performing hot rolled sheet annealing. The reason why the rolling reduction of the final cold rolling is set to 80% or more is that the sharpening {110} <0 in the decarburized plate is achieved by setting the rolling reduction within the above range.
This is because an appropriate amount of <01> orientation grains and corresponding orientation grains (e.g., {111} <112> orientation grains) easily susceptible to silkworm can be obtained, which is preferable in increasing the magnetic flux density. The steel sheet after such cold rolling is subjected to decarburizing annealing, application of an annealing separating agent, and final finish annealing by a usual method, and becomes a final product. Here, it is necessary to control the average particle size of the primary recrystallized grains from the completion of the decarburization annealing to the start of the final finish annealing to 18 to 35 μm. 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 after the decarburizing annealing and before the start of the secondary recrystallization of the final finishing annealing is that the process premised on the low-temperature slab heating as in the present invention is performed by the secondary heating. This is because the inhibitor strength required for 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 separating nitrides in a temperature into a steel sheet, or a method of nitriding a steel sheet by increasing the N ₂ partial pressure in an atmosphere of final finish annealing. The amount of nitriding is required to be 10 ppm or more in order to stably develop secondary recrystallization.

[0036]

【Example】

Example 1 By weight%, Si: 3.25%, C: 0.046%, acid-soluble Al: 0.034%, N: 0.0062%, Mn:
For a 250 mm thick 20 ton slab containing 0.14%, S: 0.007%, Z (° C) = 15 + 2500 ×
{Al (%) − (27/14) × N (%)} was calculated to be 70. From the equation (1), it was predicted that it is necessary to set the deviation in the coil of the hot-rolling start temperature in the coil to 70 ° C. or less in order to obtain good magnetic properties. After holding the slab at 1150 ° C. for about 90 minutes, it was roughly hot-rolled in 7 passes to a thickness of 40 mm (cumulative rolling reduction: 84%), and then finished hot-rolled in 6 passes to obtain a 2.3 mm thick hot roll. It was a rolled sheet. At this time, two types of hot rolling were performed: (A) a heat retaining cover was placed over the latter half of the rolling direction until the start of finish hot rolling, and air cooling for 15 seconds, and (B) air cooling for 15 seconds until the start of finish hot rolling. . In this case, the finish hot rolling start temperature is (A) 1054-10
90C and (B) 1010 to 1089C.

These hot-rolled coils were pickled, and about 85%
To a 0.335 mm thick cold-rolled coil, and kept at 845 ° C. for 150 seconds by decarburizing annealing (25% N ₂
+ 75% H ₂ , dew point 62 ° C) and then 770
Annealing at 30 ° C. for 30 seconds, and NH _{3 in} an annealing atmosphere.
Gas was mixed to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding was 0.0204 to 0.0230%, and the average particle size of the primary recrystallized grains of the steel sheet was 23 to 30 μm. Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and final finish annealing was performed by a known method. Table 1 shows the experimental conditions and the results of the magnetic characteristics.

[0038]

[Table 1]

Example 2 By weight%, Si: 3.07%, C: 0.031%, acid-soluble Al: 0.026%, N: 0.0070%, Mn:
For a 250 mm thick 10 ton slab containing 0.13%, S: 0.006%, Z (° C.) = 15 + 2500 ×
{Al (%) − (27/14) × N (%)} was calculated to be 46. From the equation (1), it could be predicted that it is necessary to make the deviation in the coil of the hot rolling start temperature in the coil equal to or less than 46 ° C. in order to obtain good magnetic properties. After holding this slab at 1180 ° C. for about 60 minutes, it was roughly hot-rolled in 30 passes to a thickness of 30 mm (cumulative rolling reduction: 88%), and then finished hot-rolled in 6 passes to obtain a 2.3 mm thick hot roll. It was a rolled sheet. At this time, (A) the first half of the rolling direction was 15
2 seconds water cooling, (B) 15 seconds air cooling until the start of finishing hot rolling
Hot rolling was performed as follows. In this case, the finish hot rolling start temperature is
(A) 1025-1052 ° C, (B) 1030
It was 1091 degreeC.

These hot-rolled coils were pickled, and about 85%
To a 0.335 mm thick cold-rolled coil and decarburized annealing (25% N ₂₎ maintained at 840 ° C. for 150 seconds.
+ 75% H ₂ , dew point 64 ° C) and then 770
Annealing at 30 ° C. for 30 seconds, and NH _{3 in} an annealing atmosphere.
Gas was mixed to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding was 0.0221 to 0.0242%, and the average particle size of the primary recrystallized grains of the steel sheet was 20 to 26 μm. Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and final finish annealing was performed by a known method. Table 2 shows the experimental conditions and the results of the magnetic properties.

[0041]

[Table 2]

Example 3 Si: 2.85%, C: 0.029%, acid-soluble Al: 0.024%, N: 0.0065%, Mn:
For a 250 mm thick 20 ton slab containing 0.14%, S: 0.007%, Z (° C) = 15 + 2500 ×
{Al (%) − (27/14) × N (%)} was calculated to be 44. From the equation (1), it was predicted that it is necessary to set the deviation in the coil of the hot rolling start temperature in the coil to 44 ° C. or less in order to obtain good magnetic properties. This slab is subjected to (A) the leading portion 1100 ° C. in the rolling direction,
Maintain a temperature gradient for about 60 minutes to reach 0 ° C, (B) 1100
After performing two types of slab heating at about 60 ° C. for about 60 minutes,
Rough hot rolling to 40 mm thickness in 7 passes (cumulative rolling reduction: 84
%), And then air-cooled for 5 seconds and hot-rolled for finish in 6 passes to obtain a hot-rolled sheet having a thickness of 2.6 mm. In this case, the finish hot rolling start temperatures are (A) 1020 to 1057 ° C., and (B)
1001 to 1056 ° C.

These hot-rolled coils were pickled, and about 87%
To a 0.335 mm thick cold-rolled coil, and kept at 845 ° C. for 150 seconds by decarburizing annealing (25% N ₂
+ 75% H ₂ , dew point 60 ° C) and then 770
Annealing at 30 ° C. for 30 seconds, and NH _{3 in} an annealing atmosphere.
Gas was mixed to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding was 0.0215 to 0.0237%, and the average grain size of the primary recrystallized grains of the steel sheet was 25 to 30 μm. Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and final finish annealing was performed by a known method. Table 3 shows the experimental conditions and the results of the magnetic characteristics.

[0044]

[Table 3]

Example 4 By weight%, Si: 2.82%, C: 0.029%, acid-soluble Al: 0.034%, N: 0.0065%, Mn:
0.14%, S: 0.006%,
(2) Z (° C.) = 15 + 2500 × ΔAl (%) − (27) For two kinds of 150 mm thick 10 ton slabs containing Sn <0.005% and (2) Sn: 0.06%.
/ 14) × N (%)} was 69. From the equation (1), it was predicted that it is necessary to make the deviation of the finish hot rolling start temperature in the coil equal to or less than 69 ° C. in order to obtain good magnetic properties.

Then, (A) the slab is heated to 1000 ° C. for about 6 hours.
After holding for 0 minutes, rough hot rolling was performed in 7 passes, and the top 4
The sheet thickness was inclined from 0 mm thickness to 50 mm thickness at the rear end in the rolling direction (cumulative rolling reduction: 73 to 67%). Thereafter, the sample was air-cooled for 15 seconds until the start of finishing hot rolling. .
It was a hot-rolled sheet having a thickness of 3 mm. The finish hot rolling start temperature at this time is
865-899 ° C. For comparison, (B) a slab of the same component was held at 1000 ° C. for 60 minutes, and then roughly hot-rolled to a thickness of 65 mm in five passes (cumulative rolling reduction: 57%). After air cooling for 15 seconds, finish hot rolling was performed in 6 passes to obtain a 2.3 mm thick hot rolled sheet. The hot rolling start temperature at this time was 875 to 920 ° C. Further, for comparison, a slab of the same component (C)
After holding at 60 ° C. for 60 minutes, the sheet was roughly hot-rolled to a thickness of 30 mm in 7 passes (cumulative rolling reduction: 80%). Thereafter, it was cooled with water for 25 seconds until the start of the finish hot rolling, followed by finishing hot rolling in 6 passes. 2.
It was a hot-rolled sheet having a thickness of 3 mm. The finish hot rolling start temperature at this time is
755-799 ° C.

The hot-rolled coils were pickled, and about 88%
To a cold rolled coil having a thickness of 0.285 mm, and kept at 840 ° C. for 150 seconds by decarburizing annealing (25% N ₂
+ 75% H ₂ , dew point 60 ° C) and then 750
Annealing at 30 ° C. for 30 seconds, and NH _{3 in} an annealing atmosphere.
Gas was mixed to absorb nitrogen into the steel sheet. The N content of the steel sheet after nitriding was 0.0225 to 0.0241%, and the average grain size of the primary recrystallized grains of the steel sheet was 20 to 31 μm. Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and final finish annealing was performed by a known method. Table 4 shows the experimental conditions and the results of the magnetic characteristics.

[0048]

[Table 4]

[0049]

In the present invention, the cumulative draft of the rough hot rolling, the time between the rough hot rolling and the finishing hot rolling are controlled, the starting temperature of the finishing hot rolling is controlled, and the amounts of the acid-soluble Al and N are reduced. Based on this, control the in-coil deviation of the start temperature of the finish hot rolling, control the average grain size of the primary recrystallized grains, and after decarburizing annealing , nitridize the steel sheet until the start of the secondary recrystallization in the final finish annealing. Processing, and then S
By adding n, even if the low-temperature slab heating is performed and the hot-rolled sheet annealing is omitted, good magnetic properties can be stably obtained, so that the industrial effect is large.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing a relationship between an in-coil deviation of an acid-soluble Al amount and an N amount and a finish hot rolling start temperature in a coil and a change in magnetic flux density.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Koji Yamazaki 1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi Nippon Steel Corporation Yawata Works (56) References JP-A-5-125445 (JP, A) JP-A-5-9580 (JP, A) JP-A-4-297525 (JP, A) JP-B 5-67683 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 H01F 1/16 C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. C: 0.075% or less by weight, Si: 2.2 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.0130% or less, S + 0. 405Se: 0.014% or less, Mn: 0.05 to 0.8% 128 slabs with the balance being Fe and unavoidable impurities
Heating is performed at a temperature of less than 0 ° C., hot rolling is performed, followed by final high-pressure cold rolling at a rolling reduction of 80% or more without performing hot-rolled sheet annealing, followed by decarburizing annealing and final finishing annealing. In the method for producing a grain-oriented electrical steel sheet, the cumulative draft of the rough hot rolling is set to 60% or more, the time between the rough hot rolling and the finish hot rolling is set to 1 second or more, and the starting temperature of the finish hot rolling is set to 800 to 1100.
℃, acid-soluble Al and N content (% by weight) of the slab, deviation in the coil ΔFoT of the starting temperature of the finish hot rolling
Controls (℃) in the following ranges (1), after completion of the decarburization annealing, the average particle size of the primary recrystallized grains to a final finish annealing started and 18～35Myuemu, the decarburization annealing after the final finish annealing two A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, comprising subjecting a steel sheet to a nitriding treatment for absorbing at least 0.0010% by weight of nitrogen before the start of the next recrystallization. ΔFoT (° C.) ≦ 15 + 2500 × {Al (%) − (27/14) × N (%)} (1) where Al: acid-soluble Al 2. Sn: 0.01 to as a component of the slab.
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein 0.15% is contained.