JPH0649905B2 - Manufacturing method of thin low iron loss unidirectional electrical steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high magnetic flux density unidirectional electrical steel sheet having excellent iron loss characteristics, which is used for an iron core of a transformer or the like.

[Conventional technology]

The unidirectional electrical steel sheet is mainly used for the core material of transformers and generators, and has the characteristics of low iron loss and high magnetic flux density.
Nowadays, there is a demand for energy saving, and there is a demand from the market for products with even lower iron loss.

In order to achieve low iron loss, a method of increasing the Si content as much as possible to raise the specific resistance of the material to reduce the eddy current loss and a method of reducing the eddy current loss by making the product plate thickness as thin as possible are generally used. Are known. However, if the Si content is increased and the product sheet thickness is reduced, secondary recrystallization during finish annealing becomes unstable, and it is difficult to industrially obtain a product with excellent magnetic properties of less than 0.25 mm. there were. In order to stably carry out the secondary recrystallization, the precipitation-dispersed phase is present in the steel uniformly and finely before the finish annealing, and further, the grain boundary segregating elements are segregated in the crystal grain boundaries, and It is important to suppress grain growth of recrystallization as much as possible and preferentially grow secondary recrystallized grains of (110) [001] orientation in the subsequent finish annealing. by the way,
MnS, MnSe, CuxS, AlN and the like are generally known as precipitation dispersed phases, and very fine particles having a size of about 100 to 1000Å must be uniformly dispersed. Further, Sn, Sb, P, Te, Mo, Se and the like are known as grain boundary segregation elements.

One of the causes that the secondary recrystallization becomes unstable when the product plate thickness becomes thin is that when a thinner product is obtained from the same hot-rolled plate, a larger cold rolling reduction is applied, which is a disadvantage in the texture. It happens. As a solution to this cause,
A method of reducing the thickness of the hot-rolled sheet according to the product sheet thickness can be considered. However, thinning the hot-rolled sheet inevitably lowers the hot-rolling end temperature, and promotes precipitation of AlN, MnS, etc., resulting in an excessive precipitation size, which causes a drawback that magnetic properties deteriorate. Has a limit.

As means for solving the above problems, US Pat.
In No. 456, the hot-rolled sheet is held at a temperature range of 1000 to 1200 ° C. for 30 seconds to 10 minutes, annealed to precipitate AlN, and then an intermediate annealing is performed, and the cold rolling is performed twice or more including the final strong cold rolling. A method of applying rolling has been proposed.

[Problems to be solved by the invention]

The iron loss obtained by the method of the above-mentioned U.S. Pat.No. 3,632,456 is not satisfactory, and the present invention solves the drawbacks of the above-mentioned conventional techniques and industrially produces a thin low iron loss unidirectional electrical steel sheet. A method for stable production is provided.

[Means for solving problems]

[C] 0.015 to 0.090%, [Si] 2.0 to 4.0%, [Mn]
0.03-0.12%, [S] 0.010-0.040%, [Sol.Al] 0.01
0-0.065%, [N] 0.0040-0.0100%, [Cu] 0.03-
0.5%, [Sn] 0.03 to 0.5% Hot-rolled silicon steel slab containing balance iron and unavoidable impurities, hot-rolled sheet annealing, pre-cold rolling, intermediate annealing and final reduction of 81% to 95% reduction In the method of producing a high magnetic flux density unidirectional electrical steel sheet by decarburization annealing and final finishing annealing to a final sheet thickness of 0.25 mm or less by cold rolling, hot rolled sheet annealing is a soaking temperature range of 1080 to 1200 ° C. In the cooling after keeping the temperature within 60 seconds, the residence time from the soaking temperature range to the temperature range of 900 to 980 ° C is 20 seconds or more.
It is done within 500 seconds and then rapidly cooled to room temperature at a rate of 10 ° C / sec or more.
It is characterized in that the subsequent intermediate annealing is an annealing performed in a temperature range of 800 to 1100 ° C, and 100 to 1000Å which is effective as an inhibitor for the size of AlN and other precipitates.
Moreover, it is possible to obtain a product with low iron loss by controlling at a higher ratio than before and obtaining an appropriate texture.

The present inventor, as a method of obtaining a product having a significantly low iron loss,
Annealing the hot-rolled sheet, pre-cold rolling, intermediate annealing, and rolling reduction 81 ~
A hot-rolled sheet is annealed and pre-cooled on the premise of a method of producing a high magnetic flux density unidirectional electrical steel sheet by decarburization annealing and final finishing annealing with a final sheet thickness of 0.25 mm or less by final cold rolling with 95% heavy reduction. For elongation and intermediate annealing, the size of AlN and other precipitates is controlled at a high ratio of 100 to 1000Å which is effective as an inhibitor, and an appropriate texture is obtained, for example, a product sheet thickness of 0.17 mm iron loss W _17/50
A method for manufacturing a product of 0.80 W / kg or less was examined.

As a result of studying a hot rolled sheet annealing method for uniformly and finely precipitating AlN, the present inventor has a method of holding 1080 at a temperature range of 1000 to 1200 ° C. for 30 seconds to 10 minutes as shown in US Pat. No. 3,632,456. 900 ~ 9 from the soaking temperature range in the cooling after keeping the soaking temperature range of ~ 1200 ℃ for less than 60 seconds
A method in which the residence time to the temperature range of 80 ° C is set to 20 seconds or more and 500 seconds or less, and then to room temperature is rapidly cooled at a rate of 10 ° C / second or more, the AlN size is effective as an inhibitor at a high rate of 100 to 1000Å It turned out to be excellent in terms of control. However, even if this method is used, AlN having a size exceeding 1000 Å exists, and although the number thereof is small, it accounts for a considerable proportion in terms of the precipitate volume fraction. However, the residence time from the soaking temperature range to the temperature range of 900 to 980 ° C. is 20 in cooling after keeping the soaking temperature range of 1080 to 1200 ° C. for 60 seconds or less on the hot rolled sheet.
After precipitating AlN by the method of quenching at room temperature to 500 seconds and then rapidly cooling to room temperature at a rate of 10 ° C / sec or more, if cold rolling with a reduction rate of 10% or more is performed,
It was newly discovered that AlN and other precipitates with a size of more than 1000 Å are crushed and finely pulverized to have an effective size as an inhibitor.

The problem here is the intermediate annealing conditions. If the intermediate annealing is performed at a high temperature, AlN and other precipitates that have been refined by hot-rolled sheet annealing and preliminary cold rolling grow to Ostwald-grown and coarsen. Therefore, the condition of the intermediate annealing is that hot rolling sheet annealing and pre-cooling should be 800-1100 ° C where AlN and other precipitates do not coarsen and the rolling structure is recovered and recrystallized by pre-cold rolling. It has been found to be important in combination with Enbu. That is, recovery of the rolling structure by preliminary cold rolling,
From the viewpoint of recrystallization, 800 ° C or higher is required, but 110
If the temperature exceeds 0 ° C, the finely divided precipitates become coarse, and 1
The rate of occurrence of sizes of 100 to 1000Å is increased, and the object of the present invention cannot be achieved.

The idea of U.S. Pat. No. 3,632,456 is to control AlN having a preferable size only by annealing a hot rolled sheet. On the other hand, the present invention is the idea of controlling the size of AlN and other precipitates by all of hot-rolled sheet annealing, pre-cold rolling, and intermediate annealing. Iron loss W at a thickness of 0.17 mm
_We have found a new method to manufacture a product whose _17/50 is 0.80 W / kg or less.

Now, FIG. 1 is an example of the result of an experiment conducted by the present inventor. [C] 0.075% in the composition range according to the present invention,
[Si] 3.25%, [Mn] 0.080%, [S] 0.025%,
[Sol.Al] 0.025%, [N] 0.0085%, [Cu] 0.07
%, [Sn] 0.12% and a hot rolled sheet with a thickness of 0.3 mm
After holding at 0 ° C for 10 seconds, it was cooled to 900 ° C for 50 seconds, kept at 900 ° C for 50 seconds and then rapidly cooled to room temperature at 100 ° C / second, and sample A was cold rolled at a reduction rate of 30%. It is a result of observing the precipitates of the sample B and the sample C cold-rolled at a rolling reduction of 45% with an electron microscope. The photograph of sample A shows acicular AlN compositely deposited on the spherical MnS in the center. The photographs of Samples B and C show that needle-shaped AlN was compositely precipitated on the spherical MnS in the center, but when 30% and 45% cold rolling was added, AlN was crushed and refined by cold rolling. It shows how it was done.

Next, Fig. 2 shows the same hot-rolled sheet as in Fig. 1, which was held at 1130 ℃ for 10 seconds, cooled to 900 ℃ in 50 seconds, and kept at 900 ℃ for 50 seconds, and then at room temperature. Rapid cooling at 100 ℃ / sec, pre-cold rolling with 41% rolling reduction, intermediate annealing at various temperatures, final cold rolling with 87% rolling reduction to 0.170 mm thickness, It shows the relationship between iron loss W _17/50 and various intermediate annealing conditions by _forming a product by the steps of carbon annealing, final finishing annealing and final coating. From this, it can be seen that good magnetic characteristics can be obtained in the temperature range of 800 to 1100 ° C. As a result of observing the metallographic structure and precipitation-dispersed phase of the intermediate annealed sheet of this experiment, the present inventor found that when the temperature was lower than 800 ° C, the cold-rolled structure remained and the primary recrystallized structure was formed. However, when the temperature was higher than 1100 ° C, it was found that the precipitate was coarsened.

[Relationship with Conventionally Known Technology] In Japanese Examined Patent Publication No. 40-15644 and Japanese Unexamined Patent Publication No. 59-126722, Japanese Examined Patent Publication No. 40-15644, the thickness of the hot-rolled sheet is 1.5 mm to 7 mm, and the final cold rolling process Reduction rate at 81 ~ 95
%, The rolling reduction in the other cold rolling process is performed in the range of 5 to 40%. A method has been proposed in which so-called cold rolling of two or more steps and annealing of one or more times are performed. In addition, JP-A-59
No. 126722 proposes a method in which a hot-rolled sheet is pre-cold-rolled at a cold-rolling rate of 15 to 40%, annealed, and then finally cold-rolled at 80 to 90%. However, although these methods do not describe hot-rolled sheet annealing, hot-rolled sheet annealing is indispensable in the present invention, and is different from that of JP-B-40-15644 and JP-A-59-126722. To be done.

In JP-A-57-198214, JP-A-57-198214 discloses a precipitation annealing method immediately before final cold rolling, which is 2 to 10 degrees Celsius in the temperature rising process from 800 degrees Celsius to 1080 degrees Celsius to 1200 degrees Celsius. In the cooling after the temperature is raised at a heating rate of / sec and kept in the soaking temperature range for 60 seconds or less, the residence time from the soaking temperature range to the temperature range of 900 to 980 ° C is 20 seconds or more 50
A method has been proposed in which the temperature is set within 0 seconds, and then the temperature is rapidly cooled to room temperature at a rate of 10 ° C./second or more. The idea of this method is
By limiting the precipitation annealing method immediately before the final cold rolling, precipitates of a preferable size, particularly AlN, are precipitated. Even if a precipitate, particularly AlN, is deposited by the precipitation annealing method described immediately before the final cold rolling as in JP-A-57-198214, the final cold rolling makes AlN and other precipitates finer. To be done. However, in the present invention, the annealing method of hot-rolled sheet annealing is limited, and AlN is controlled to a size of 100 to 1000Å at a higher ratio than before, and then cold rolling is performed by 10% or more preliminary cold rolling and high-pressure final cold rolling. And the size of AlN and other precipitates is much higher than that of the method of JP-A-57-198214 by 100 to 10
The present invention has been successful in controlling the temperature to 00Å, and JP-A-57-198214 is a method proposed for a thick product having a product plate thickness of 0.30 mm.
-It is understood as a technology different from 198214.

Each step of the method of the present invention will be specifically described below.

As a method for smelting the steel of the present invention, a known steel-making method such as a converter, an electric furnace, an open hearth can be used.
Subsequent scouring can be used in combination. Subsequently, for the production of the slab, a continuous casting method is generally applied at present, but the conventional ingot-casting method is also applicable. The slab thus obtained is slab-heated and hot-rolled by a usual method. At this time, as shown in Japanese Examined Patent Publication No. 59-37330, while the center temperature of the slab continuously cast by the continuous casting method is between 1200 ℃ and 600 ℃, 1250 ℃ ~ 140
It is more preferable to adopt a method of heating the slab at a temperature of 0 ° C. Further, as the hot rolling conditions, as shown in JP-A-60-197819, the finishing front surface temperature is 1150 to 1250 ° C., and the finishing rear surface temperature is 950. It is more preferable to employ a method of controlling the temperature range to 1050 ° C and the winding temperature in the temperature range of 500 to 600 ° C. The plate thickness after hot rolling is determined according to the cold rolling ratio of the subsequent pre-cold rolling and final cold rolling under high pressure, but if it is too thin, the finish front surface temperature will be too low, so that it is usually 1.5 to 7 mm. It is advantageous. Now, hot-rolled sheet annealing, pre-cold rolling, and intermediate annealing are particularly important for obtaining a product with low iron loss as described above, and hot-rolled sheet annealing is performed in a soaking temperature range of 1080 to 1200 ° C for 60 seconds. In the cooling after keeping the temperature within the range, the residence time from the soaking temperature range to the temperature range of 900 to 980 ° C is set to 20 seconds or more and 500 seconds or less, and then room temperature is rapidly cooled at a rate of 10 ° C / second or more. Yes, the reduction rate of pre-cold rolling is 10 to 50%, the intermediate annealing is
It must be annealed in the temperature range of 800-1100 ° C. The cold reduction rate of the subsequent final cold rolling under strong reduction is 81%.
Must be ~ 95%. This rolling may be performed by an ordinary method, but as shown in Japanese Patent Publication No. 54-13866, 10 rolling is performed for each pass.
It is more preferable to adopt a method of giving a heat effect of about 0 to 300 ° C. The cold-rolled sheet having the final thickness is subjected to decarburization annealing, and a known method such as a normal method, for example, a method of annealing in wet hydrogen at 750 to 950 ° C. for about 2 to 15 minutes can be applied. After decarburization annealing, final finishing annealing is performed in order to develop secondary recrystallization. This annealing is usually a method of applying an annealing separating agent containing magnesia as a main component to a steel sheet, raising the temperature to about 1200 ° C. by box-type annealing, and holding at that temperature for 10 to 30 hours,
Any other known method may be used. An insulating coating is usually applied to the steel sheet after the final finish annealing, and any known coating can be applied to this coating. Of course, the coating need not be applied.

Hereinafter, various conditions and reasons for limitation of the present invention will be described.

If the lower limit of 0.015% is less than 0.015, the secondary recrystallization becomes unstable, and the upper limit of 0.090% is limited because if the amount of [C] is higher than this, the time required for decarburization becomes long and it is economically disadvantageous. did. If [Si] is less than the lower limit of 2%, good iron loss cannot be obtained, and if it exceeds the upper limit of 4%, cold rolling property is significantly deteriorated.
[Mn] is an element necessary for forming MnS. If the lower limit is less than 0.03%, the absolute amount of MnS is insufficient, and the upper limit is 0.
If it exceeds 12%, the slab heating temperature for solid solution of MnS becomes too high, which makes industrialization difficult.
[S] is an element necessary for forming MnS, CuxS, and if the lower limit is less than 0.010%, the absolute amount of MnS, CuxS is insufficient, and the upper limit is 0.0
If it exceeds 40%, hot cracking occurs, and desulfurization becomes difficult in the final finish annealing. [Sol.Al] is an element necessary for forming AlN. If the lower limit is less than 0.010%, the absolute amount of AlN is insufficient, and if it exceeds the upper limit of 0.065%, a proper dispersed state of AlN cannot be obtained. [N] is an element necessary for forming AlN. If the lower limit is less than 0.0040%, the absolute amount of AlN is insufficient, and if it exceeds the upper limit of 0.0100%, a proper dispersed state of AlN cannot be obtained. [Cu] is an element that forms CuxS. If the lower limit is less than 0.03%, the absolute amount of CuxS is insufficient, and the upper limit is
If it exceeds 0.5%, the pickling property and decarburizing property deteriorate. It is preferably less than 0.080%. [Sn] segregates at grain boundaries to stabilize secondary recrystallization, but if the lower limit is less than 0.03%, the amount of segregation is insufficient, and the upper limit of 0.5% is due to economic reasons and deterioration of decarburization.

The hot-rolled sheet is annealed from the soaking temperature range of 900 to 980 ° C in the cooling after being kept in the soaking temperature range of 1080 to 1200 ° C for 60 seconds or less.
The residence time up to the temperature range of 20 seconds to 500 seconds,
Then, it must be rapidly cooled to room temperature at a rate of 10 ° C./second or more. If the soaking temperature is less than 1080 ° C, the effect of this annealing is weak, while if it exceeds 1200 ° C, A
In addition, the size change of 1N is likely to occur, and it is not preferable in terms of metal structure. The soaking time was set to less than 60 seconds for the same reason. Next, the residence time of primary cooling depends on the AlN in the cooling process.
The amount of precipitation is controlled, and the longer this time is, the more the amount of precipitation increases and the secondary recrystallization becomes stable. The reason for setting the upper limit to 500 seconds is that no improvement in magnetic properties is observed even if the time is longer than this, and it is also disadvantageous from the industrial viewpoint. On the other hand, the lower limit is set to 20 seconds, and if it is less than this, the amount of precipitation is small, so that secondary recrystallization becomes unstable and magnetic properties cannot be obtained. Next, the reason why the secondary cooling start temperature is set to 900 to 980 ° C is that if the temperature is higher than the upper limit of 980 ° C, coarsening of AlN is likely to occur, and if it is lower than the lower limit of 900 ° C, the amount of precipitation of AlN is small. Because it will be. From the temperature range of 900 to 980 ° C. to room temperature, it must be forcibly cooled with water or the like at a rate of 10 ° C./sec or more, and if it is less than 10 ° C./sec, an appropriate amount of solid solution [C], [ N] cannot be obtained and good magnetic properties cannot be obtained.

If the reduction ratio of the pre-cold rolling is less than 10%, crushing and refining of AlN and other precipitates by cold rolling cannot be achieved. If it exceeds 50%, the texture becomes unsuitable and the magnetic flux density is remarkably reduced. In the intermediate annealing, if the temperature is lower than 800 ° C, the cold-rolled structure by pre-cold rolling is recovered and recrystallization does not occur.
If it exceeds 1100 ° C, it is sufficient for recovery and recrystallization of the cold rolling structure, but AlN and other precipitates grow by Ostwald's growth and become coarse. The holding time also affects the recrystallization and the size of AlN and other precipitates, and is preferably 30 to 200 seconds.

The cold reduction ratio of the final cold rolling under strong reduction is 9 even if it is less than 81%.
Even if it exceeds 5%, the texture becomes unsuitable, and instability occurs in secondary recrystallization.

The reason for limiting the product sheet thickness to 0.25 mm or less is to obtain a low iron loss unidirectional electrical steel sheet in response to recent demand needs.

Further, the starting material may contain one or more of Mo, B, P, Ni, Bi, Sb and As to further reduce the iron loss.

〔Example〕

[Example 1] [C] 0.079%, [Si] 3.24%, [Mn] 0.081%,
[S] 0.025%, [Sol.Al] 0.027%, [N] 0.0080%,
13 slabs containing [Cu] 0.07% and [Sn] 0.12%
After heating at 50 ° C. for 2.5 hours, hot rolling was performed to obtain a hot coil having a thickness of 2.0 mm. Hot-rolled sheet annealing and intermediate annealing are performed under the conditions shown in Table 1, pre-cold rolling is performed at a reduction rate of 33% to 1.35 mm, and final cold rolling at a high reduction is performed at a reduction rate of 87%. The plate thickness was 0.170 mm. Then, the obtained cold-rolled sheet was subjected to 840 in an atmosphere of hydrogen 25%, nitrogen 75%, and dew point 43 ° C.
Decarburization annealing is performed by holding at 200 ° C. for 200 seconds, then an annealing separator is applied, and then final finishing annealing is performed at 1200 ° C. for 20 hours in a hydrogen stream. The coating liquid was applied to obtain a product. Table 1 shows the conditions of hot-rolled sheet annealing and intermediate annealing, and the magnetic properties (magnetic flux density B ₁₀ , iron loss W _17/50 ) of the obtained product.
From this, it is understood that the present invention example can obtain better magnetic characteristics than the comparative example.

[Example 2] [C] 0.081%, [Si] 3.30%, [Mn] 0.075%,
[S] 0.025%, [Sol.Al] 0.026%, [N] 0.0081%,
13 slabs containing [Cu] 0.07% and [Sn] 0.13%
After heating at 50 ° C. for 3 hours, hot rolling was performed to obtain hot coils having various plate thicknesses. Subsequently, hot-rolled sheet annealing was held at 1130 ° C for 10 seconds, then cooled to 900 ° C in 50 seconds, and kept at 900 ° C for 5
After keeping it for 0 seconds, it was rapidly cooled to room temperature at 100 ° C./second. In the pre-cold rolling, the reduction ratio was changed according to the sheet thickness of the hot coil, and the sheet thickness after the pre-cold rolling was 1.55 mm in all cases. Subsequently, the intermediate annealing was held at 950 ° C for 100 seconds, then rapidly cooled to room temperature at 100 ° C / second, and the final cold rolling under strong reduction was performed at a reduction rate of 86%.
The plate thickness was 0.220 mm. After that, the cold-rolled sheet obtained was subjected to 1% at 840 ° C in an atmosphere of 25% hydrogen, 75% nitrogen and 43 ° C dew point.
After holding for 80 seconds to carry out decarburizing annealing, and then applying an annealing separating agent, it was held at 1200 ° C. for 20 hours in a hydrogen stream for final finishing annealing, and a coating liquid was applied to obtain a product. Table 2 shows the plate thickness of the hot coil, the reduction ratio of the pre-cold rolling, and the magnetic properties (magnetic flux density B ₁₀ , iron loss W _17/50 ) of the obtained product. From this, it is understood that the material of the present invention having a reduction ratio of 10 to 50% in the pre-cold rolling has better magnetic properties than the comparative example.

[Effects of the Invention] As described in detail above, 0.25 mm is obtained by hot-rolled sheet annealing, preliminary cold rolling, intermediate annealing, and final cold rolling under strong reduction with a reduction rate of 81 to 95%.
The following final plate thickness, decarburization annealing, in the method of producing a high magnetic flux density unidirectional electrical steel sheet by final finishing annealing,
By specifying specific conditions for hot-rolled sheet annealing, pre-cold rolling and intermediate annealing, it is possible to obtain products with significantly low iron loss,
Its industrial effect is very large.

[Brief description of drawings]

Fig. 1 shows that the hot-rolled sheet was held at 1130 ℃ for 10 seconds and then
Sample A, which was cooled to 900 ° C for 2 seconds, kept at 900 ° C for 50 seconds, and then rapidly cooled to room temperature at 100 ° C / second, and 30%
2 is a metallographic micrograph showing the results of observing the precipitates of Sample B cold-rolled at a rolling reduction of No. 2 and Sample C cold-rolled at a rolling reduction of 45% with an electron microscope. Figure 2 shows
It is a relationship diagram of an intermediate annealing temperature and magnetic characteristics.

Claims (1)

[Claims] 1. [C] 0.015 to 0.090%, [Si] 2.0 to 4.0
%, [Mn] 0.03 to 0.12%, [S] 0.010 to 0.040%,
[Sol.Al] 0.010 to 0.065%, [N] 0.0040 to 0.0100%,
[Cu] 0.03-0.5%, [Sn] 0.03-0.5% Hot-rolled silicon steel slab containing balance iron and unavoidable impurities, hot-rolled sheet annealing, pre-cold rolling, intermediate annealing, and rolling reduction 81%- 95
In the method of producing a high magnetic flux density unidirectional electrical steel sheet by decarburization annealing and final finishing annealing, the final sheet thickness of 0.25 mm or less is obtained by final cold rolling under a strong reduction of 10%.
In the cooling after keeping the soaking temperature range of 80 to 1200 ° C. for 60 seconds or less, the residence time from the soaking temperature range to the temperature range of 900 to 980 ° C. is set to 20 seconds or more and 500 seconds or less, and then room temperature is set to 10 seconds. It is said that it is rapidly cooled at a rate of ℃ / sec or more, the reduction rate of pre-cold rolling is 10 to 50%, and the subsequent intermediate annealing is 80%.
A method for producing a thin low iron loss grain-oriented electrical steel sheet, which is characterized in that the annealing is performed in a temperature range of 0 to 1100 ° C.