JPS5843446B2 - Manufacturing method of high magnetic flux density unidirectional electrical steel sheet - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing high-density unidirectional electrical steel sheets, and in a continuous casting method, the volume ratio of columnar crystals is increased by accompanying electromagnetic stirring or ultrasonic vibration during the solidification process. We propose a new method for appropriately and advantageously manufacturing products with particularly few surface defects and excellent electromagnetic properties for high magnetic flux density unidirectional electrical steel sheets using continuously cast slabs obtained by adding Fc torpedo as a starting material. This is what I am trying to do.

Unidirectional silicon steel sheets are used as core materials for electrical equipment such as transformers, and are custom-made with magnetization in the rolling direction (100OA/
It is represented by the magnetic flux density BIO when magnetized at m.

) and iron loss characteristics (core loss W17150 when magnetized at 17KG"! in 50 cycles).

) It is characterized by excellent K. These unidirectional silicon steel sheets have crystal grains that have a Miller index of (10
The main reason for the excellent magnetic properties is that the secondary recrystallized grains represented by the 0)(001) orientation have an axis of easy magnetization (001) in the rolling direction.

By the way, in order to produce secondary recrystallized grains with (xto) (oot) orientation, it is necessary to use Mn, which is called an inhibitor.
It is necessary to disperse and precipitate a fine secondary dispersed phase such as S, MnSe or AeN in the steel base, and to form an appropriate texture of primary recrystallized grains, which are well known. As it is.

Over the past ten years or so, grain-oriented silicon steel has developed significantly, with so-called high magnetic flux density directionality (here, high magnetic flux density directionality refers to B).

(meaning one having a characteristic of 1.89T or more).

One of the conditions that made this technological development possible is to heat the slab at high temperatures before hot rolling (hereinafter referred to as hot rolling) in order to optimize the dispersion and precipitation of the inhibitor, which dissociates the inhibitor. One example is the discovery of the need for solid solution.

When producing high magnetic flux density grain-oriented silicon steel sheets, it is usually necessary to heat the slab at a temperature of 1,300°C or higher, preferably 1,350°C or higher; lower temperatures are said to cause BIO deterioration. It has come.

Heating the slab at such high temperatures inevitably increases the generation of slag from the slab, resulting in a decrease in yield, an increase in surface defects, and
Problems such as a reduction in the life of the heating furnace bottom and an increase in the frequency of slag treatment arise, and it is clear that this is not favorable from the point of view of energy conservation.

The object of the present invention is to provide an advantageous method for producing grain-oriented silicon steel sheets which should still exhibit high magnetic flux density at lower slab heating temperatures in order to overcome these disadvantages.

At the same time, it is an object of the present invention to provide an advantageous method that uses a slab produced by a continuous casting method as a starting material and that can nevertheless stably produce a grain-oriented electrical steel sheet with high magnetic flux density. Slabs produced by the continuous casting method usually have a characteristic crystal structure formed by columnar crystals and equiaxed crystals, and this crystal structure is produced by blooming from an ingot when heating the slab. The crystal grains tend to become coarser at lower temperatures than the crystal structure of the slab.

The crystal grains coarsened by this heating of the slab form incomplete secondary recrystallization regions in the later process and cause deterioration of the LJ aging characteristics, so continuous casting slabs are not suitable as materials for high magnetic flux density grain-oriented silicon steel. It was originally inappropriate.

In recent years, as described below, several methods have been proposed for producing high magnetic flux density grain-oriented silicon steel sheets using continuous casting (hereinafter abbreviated as C0C) slabs. Although the goal is to prevent this from occurring, it has weaknesses such as complicating the manufacturing process and operational difficulties.

Among these methods, the method of casting with electromagnetic stirring is the most advantageous compared to other methods in terms of complicating the process and making operations difficult, but it is usually difficult to reduce the generation of columnar crystals. However, it cannot contribute to complete prevention.

That is, in order to completely prevent columnar crystals, the casting temperature must be lowered considerably, which causes operational difficulties.

The inventors repeatedly investigated the properties of CC slabs obtained by applying electromagnetic stirring or ultrasonic vibration, and found that even if such slabs have a certain proportion of columnar crystals, low-humidity slab heating Temperature and specific cold rolling (hereinafter abbreviated as cold rolling)
We have discovered scales that can be advantageously used as rolling materials for high magnetic flux density grain-oriented silicon steel by applying a rolling reduction of

Therefore, in this invention, in order to advantageously realize hot rolling of a CC slab made of high magnetic flux density grain-oriented silicon steel at a lower heating temperature than before, the properties of the CC slab by electromagnetic stirring are utilized.
The key point is to perform cold rolling at a cold rolling reduction rate commensurate with the heating temperature.By the way, as mentioned above, the reason why heating the slab at high temperatures is considered unavoidable despite various disadvantages. This is because it was considered essential to completely dissociate and dissolve the inhibitor in the steel base prior to hot rolling.

In this regard, for example, in JP-A-50-86418, a silicon steel slab containing one or more of MnS, AeN, VN, and MnSe is heated to 130 °C by slab heating prior to hot rolling. It is stated that it is necessary to make the precipitated dispersed phase into a solid solution by using high mixed heating at 1450°C, and JP-A-51-20716 discloses that MnS';& or MnS';
1 for silicon steel materials containing type 1 or 2 of S e.
It is stated that it is necessary to heat the slab to 230°C or higher.

In this way, if the slab is not heated to a high temperature, the effect of the inhibitor cannot be fully utilized, and the BIO is 1.
Although it was not possible to obtain a grain-oriented silicon steel with a high magnetic flux density of 89T or higher, as mentioned above, there were problems such as a decrease in product yield and an increase in product surface defects due to the outflow of molten slag that occurs during high-temperature slab heating. increased energy consumption;
In addition, disadvantages such as shortened life of the heating furnace bottom and increased frequency of slag treatment operations can be overlooked, so several methods have been proposed to lower the heating temperature of high magnetic flux density grain-oriented silicon steel slabs. .

For example, Japanese Patent Publication No. 54-24685 discloses that when casting molten steel containing four elements other than Se, As, Bi, Pb, and Sb singly or in combination, the solidification cooling rate is increased, and the precipitation morphology before slab heating is The slab heating temperature is 1350~1 by making it fine and making solid solution easier when heating the slab.
It is stated that the temperature can be raised to 050°C, preferably 1300 to 1100°C.

However, if the precipitate becomes fine with this method, the time required for complete dissociation and solid solution may be shortened, but since the solubility product of the inhibitor at a certain temperature is considered to be constant,
There are doubts about the basis that the heating temperature can be lowered by 1 to the extent disclosed.

Further, the final cold rolling reduction ratio at that time is required to be at least 60φ or more, preferably 70 or more.

In JP-A-52-24116, Zr, Ti, B, and Nb are used in addition to acid-soluble aluminum.

It has been proposed to heat the slab to 1100 to 1260'C by containing nitride-forming elements such as Ta, V, Cr, and Mo singly or in combination.

However, in this method, when manufacturing high magnetic flux density grain-oriented silicon steel sheets, it is common practice to use an inhibitor that can be removed from the base steel during the manufacturing process, especially during final annealing. Since nitride-forming elements, which are difficult to remove, are used as inhibitors,
In particular, a final cold rolling reduction of 65 to 90% is required.

In contrast to the prior art of doffing, this invention does not necessarily require complete dissociation of precipitates to achieve solid solution in order to heat the slab at low temperatures, but it is possible to achieve optimal cold rolling according to the amount of inhibitor dissociated and dissolved in solid solution. The basis of the idea is different, stemming from the discovery that a rolling reduction exists and that its effect is influenced by the casting structure of the slab, especially the presence of columnar structure.

Therefore, the structure and heating temperature of this CC slab will be described.

As is well known, the adoption of continuous casting generally brings about major benefits such as eliminating the ingot blooming process and improving yield, but when it comes to high magnetic flux density grain-oriented silicon steel, CC slabs are usually used. , has a characteristic crystal structure consisting of equiaxed crystals and columnar crystals, and S and Se are present at the center of the thickness of the slab.
The problem lies in the presence of dense segregation bands such as

In other words, when heating this type of CC slab before hot rolling, in order to completely dissociate and dissolve the precipitates present in these dense segregation zones, it is necessary to heat it at a much higher temperature than in the case of slabs made from agglomerated materials. Where slab heating is required,
The crystal structure of this type of CC slab tends to become significantly coarser than that of agglomerated materials, and the grain size decreases by several degrees when the slab is heated to over 1,300°C, which is required for the production of high magnetic flux density grain-oriented silicon steel sheets. .

It also extends to

The coarse grains of the slab leave an impact as grains that are difficult to recrystallize in the post-hot rolling process, resulting in the formation of secondary recrystallization incomplete areas in the final product sheet, which affects the magnetic properties. This becomes a factor in deterioration.

The phenomenon of magnetic customization deterioration in CC slabs has been known for a long time, and for this reason, the industrial production of grain-oriented silicon steel sheets by continuous casting came to a halt.

Thereafter, in order to prevent the above-mentioned deterioration phenomenon, the slab is rolled before hot rolling and reheated (Japanese Patent Publication No. 50-3700).
No. 9, No. 54-27820, etc.), a method of applying pressure during slab casting (Japanese Patent Laid-Open No. 53-53522), and a method of lowering the temperature of molten metal during casting (Japanese Patent Laid-Open No. 52-191).
69), method of adding electromagnetic stirring (JP-A No. 53-19)
913) etc. were proposed.

However, all of these methods have disadvantages.

In other words, the method of rolling down and reheating the first slab requires an extra process in the manufacturing process, and the advantages of continuous casting are halved.

The method of applying rolling reduction during casting of the second slab encased involves operational regulations such as restrictions on slab thickness.

The third method of lowering the temperature of the molten metal has significant disadvantages in terms of quality and operation, such as inhibition of floating of inclusions and risk of breakout.

Finally, the fourth method of adding electromagnetic stirring has advantages such as reducing the degree of dense segregation at the center of the slab, but it is difficult to completely suppress the development of columnar crystals.
When heated at a high temperature of 300° C. or higher, the grains become coarse from the vicinity of the boundary between columnar crystals and equiaxed crystals, which may cause the generation of abnormal grains.

The method according to the present invention discovers and utilizes a correlation between the casting structure of a slab, the deepness of lump heating, and the cold rolling reduction.

This compensated for the drawbacks of the continuous casting slab application mentioned above.

In other words, the feature of this invention is that when the slab heating temperature is low, the optimal value of the final cold rolling reduction ratio shifts to the lower reduction side, and this phenomenon occurs when columnar crystals are used as the initial crystal structure. , I discovered that it appeared more effectively and used it.

By the way, in the conventional manufacturing method of high magnetic flux density grain-oriented silicon steel sheets, the rolling reduction during final cold rolling is, for example, the method using MnS or MnSe as an inhibitor (
55-80%, M
Other methods using nSe as an inhibitor (Japanese Patent Publication No. 51-2920) and methods using A6N (Japanese Patent Publication No. 46-23819) have a high cold rolling reduction ratio of 60 to 95, which is more than 55%. B
It is said that IO is necessary to obtain a high magnetic flux density grain-oriented electrical steel sheet of 1.89T or more.

According to the research conducted by the inventors, the optimum final cold rolling reduction ratio that shows the best magnetic customization depends on the heating temperature of the slab, that is, the amount of dissociated solid solution of the inhibitor.9 When the amount of inhibitor precipitation is small, It was discovered that the rolling reduction ratio was lower than the above-mentioned 55 or more.

By the way, in the case of normal ingot slabs, if the slab heating temperature is low, the magnetic properties at the optimum final cold rolling reduction will deteriorate;
When lower than 1300℃, BIO is almost 1.89T.
Become and become.

In contrast, in slabs with controlled columnar crystals during continuous casting by electromagnetic stirring or ultrasonic vibration,
Contrary to the fact that the deterioration of magnetic properties at the optimum final cold rolling reduction occurs at a lower heating temperature than in the case of ingot slabs, in the case of slabs cast by the normal continuous casting method, the magnetic properties obtained are It is too low to meet the purpose of this invention.

The reason for this is that there is a dense segregation zone of inhibitor components in the center of the slab manufactured by the normal continuous casting method, which remains after the cold rolling process and has an adverse effect on the secondary recrystallization. It is thought that this is because of this.

Although the mechanism of this transition phenomenon of the final cold-rolling optimum normal rolling is not currently clear, the cold-rolling reduction is the most fundamental factor that determines the texture, and it is related to the dispersion state of the inhibitor during recrystallization. It can be inferred that this is strongly influenced by the orientation and grain size of the initial crystal grains in the slab before cold rolling.

Figure 1 shows a grain-oriented silicon steel slab (composition: C0,031%) that was continuously cast while applying electromagnetic stirring.

Si3.02%, Mn0.081%, So, 020'%
, and SbO, 025%) were heated to their respective predetermined temperatures and then hot-rolled to obtain various final cold-rolling reduction ratios. , o are shown by level.

The shaded area in the figure shows the relationship between the appropriate slab heating temperature and final cold rolling reduction ratio obtained by the present invention.

For each heating temperature, the optimal final cold rolling reduction ratio at which BIO reaches the highest value is 45 and 50%, respectively, at 1125°C and 1150°C, which are higher than 1100°C, and 40 to 55%.
, and 45-57.5% at 1200℃, further [123
At 0°C, it shifts to the lower side of high pressure by 45-65%.

By the way, in the case of FC1350℃, the optimal final cold rolling reduction ratio is 6.
Although it further moves to 0 or better, the characteristics deteriorate in some places leading to this and the manufacturing process becomes unstable.

This is because in the case of a CC slab containing columnar crystals, abnormal grains occur due to coarsened crystal grains.

In short, this type of abnormal grain has a random tendency to occur;
Although it does not always occur, the frequency increases as the heating temperature increases under heating conditions exceeding 1300°C.

Figure 2 shows 1100 pieces of slabs cut out using different casting methods.
These are the results of a half-process experiment in which hot rolling was carried out at various heating temperatures of 1380°C to 1380°C.

During continuous casting, we used three types of slabs: one with and without electromagnetic stirring, and one that was cast in old ingots and then bloomed into slabs of the same thickness, and the optimum cold rolling reduction ratio was determined at each heating temperature. This shows the BIO in the case of .

In the case of the CC slab subjected to electromagnetic stirring according to the present invention, the magnetic customization deteriorates when the heating temperature is 1350° C. and 1380° C., and this is due to the formation of coarse grains.

Moreover, as the heating temperature became lower, the optimum cold rolling reduction ratio shifted to the smaller side.

The deterioration of IO is rapid on the lower side and occurs at temperatures below 1100°C.

Note that when ingot material is used, it shows very good magnetic customization at temperatures above 1300°C, but when the temperature falls below 1275°C, the magnetic properties deteriorate rapidly.

The difference in the behavior of the two slabs is shown in the temperature at which deterioration begins.

We also showed the results of ordinary CC material without electromagnetic stirring, and the overall result was B.

is low. The features of this invention that enable low-temperature heating of slabs using continuous casting slabs have been described above.

Next, the reason for limiting the range of components of the starting materials in this invention will be described.

In this invention, it is necessary to contain 2 to 4.5% KSi in order to increase the specific electrical resistance value of the product and reduce iron loss. This is because if it exceeds 4 or 5, the processability deteriorates significantly, making it difficult to produce on an industrial scale.

Also, along with inhibitors, C is necessary to control the texture, which is an element to enable secondary recrystallization, and if it is less than 0.01%, the effect will be small;
% or more, the decarburization annealing time becomes longer and production efficiency decreases.

Also, Mn and S, Se, Sb, Bi, Pb, Sn and B
At least one of these is contained as an element constituting an inhibitor.

If these amounts are below the respective lower limits, the amount of the inhibitor dispersed and precipitated will be extremely small, making secondary recrystallization impossible.

The upper limit was determined because there are many undesirable aspects of containing more inhibitor than necessary, such as an increase in cost and a decrease in the inhibitory effect due to the coarsening rate of the inhibitor.

Note that S, Sb, Se, Bi, and Pb. Sn, B, etc. have the same effect as inhibitor components.

The next KCC slab has columnar crystals in a volume ratio of 30 to 70%.
If it is less than the lower limit of 30%, the effect of the final low reduction rolling on the columnar crystals will be weakened, and this will mean lowering the casting temperature, which means that the above-mentioned casting temperature of the molten metal is low. Defects that occur at the time of loading appear.

On the other hand, if it exceeds 70%, the structure becomes similar to that of a normal CC slab to which no ordinary electromagnetic stirring is applied, and the effect of the present invention is lost.

The CC slab obtained as described above is heated and then hot rolled.

The upper limit of the heating temperature is 1250° C. If this temperature is exceeded, the CC slab according to the present invention contains columnar crystals and equiaxed crystals, so coarse grains frequently occur and the magnetic properties become unstable.

In addition, the heating temperature must be higher than 1100°C, because below this temperature the amount of inhibitor dissolved in solid solution is extremely small, and therefore secondary recrystallization does not occur.
More preferably, the temperature is 1150°C or higher.

The material manufactured by hot rolling is finished to the product thickness by cold rolling twice including intermediate annealing, but the final cold rolling reduction is 40.
If the ratio is outside the range of ~65%, the characteristics deteriorate.

The optimum cold rolling reduction ratio shifts to the lower rolling reduction side as the slab heating temperature is lower, and the final cold rolling reduction ratio (R%) required here is T/15-38<R by the slab heating temperature (T°C) VC. <T/12-37.

This region is not affected by the amount of inhibitor contained, but unlike the case of complete dissociation and solid solution, the amount of inhibitor Q that dissolves and precipitates is determined because the solubility product is uniquely determined by temperature. , it is inferred that the slab heating temperature determines the amount of inhibitor precipitated.

The material that has been cold-rolled to the finished thickness undergoes a decarburization process that also serves as primary recrystallization.

This forms the texture required for secondary recrystallization, and after that, a normal separation agent is applied, followed by a highly mixed finish annealing, followed by secondary recrystallization, which can be carried out in the same way as in conventional methods. .

Next, the present invention will be explained by examples.

Example 1 C0,040%, Si3.05%, Mn0.07%, S
A slab was manufactured by continuous casting while electromagnetically stirring molten steel containing 0.025% eO and 0.030% Sb.

The columnar crystal portion accounted for 52% of the cross-sectional area. Slab thickness is 20
011t11L, and 10 of the same charges were heated at 1200°C for 2 hours and then rolled to a thickness of 3.011mm by a continuous finishing mill using a rough rolling mill and a tandem mill.
It was made into an LTILO hot rolled sheet.

Also, 4 slabs in the same charge are separately heated to 1350℃.
After heating for 2 hours, a hot rolled sheet of 3.0 order was prepared in the same manner.

After annealing these hot-rolled sheets by heating them at 950°C for 5 minutes, the entire amount of the 1350°C heating coil and the 1200°C heating coil are cold rolled.
0.891Wi for 3 of the °C heating coils! , 12 again
The remaining 7 coils heated at 00°C had an intermediate thickness of 0.621 ul.

Thereafter, after intermediate annealing at 950° C. for 5 minutes, it was finished to a plate thickness of 0.30 mat by secondary cold rolling, and then decarburized annealing was performed at 800° C. for 5 minutes in wet hydrogen.

Thereafter, MgO was applied as an annealing separator, and box annealing was performed at 1200° C. for 15 hours.

The magnetic properties and abnormal grain generation block rate of the product thus obtained are shown.

Example 2 C0,043%, Si3.06%, Mn0.082%.

It was produced by continuous casting while applying electromagnetic stirring from molten steel containing SO, 03φ and SbO, 030%.

The cross-sectional area of the columnar crystal portion at that time was 55 pieces.

Slab heating 123 times for 8 slabs with a thickness of 2007nlft
After heating at 0°C for 2 hours, it was rolled to a thickness of 3.5 mm by rough rolling and continuous finish rolling using a tandem mill. A Q muO hot rolled sheet was used.

Also, 6 of the same charges were heated separately at 1370°C for 2 hours and then subjected to 3. It was made into a Q yratbO hot rolled sheet.

These hot-rolled sheets were heated at 950°C for 5 minutes and then cold rolled to give an intermediate thickness of 0.92 mal for all coils heated at 1370°C and two coils heated at 1230°C.

The remaining 6 coils heated at 1230°C were set to 0.69 mm.

Thereafter, after intermediate annealing at 950° C. for 5 minutes, the product was subjected to second cold rolling to have a product thickness of 0.30 mal, and a final product was obtained in the same manner as in Example 1.

Shows the magnetic properties and surface flaw incidence of the final product.

Example 3 Ten slabs were cast from molten steel containing 0.045% C, 3.01% Si, 0.070% Mn, and 0.24% SO while being electromagnetically stirred.

The cross-sectional area of the columnar crystal portion was 55%.

In addition, three slabs were cast with the same charge and were not subjected to electromagnetic stirring.

The cross-sectional area of the columnar crystal portion was 58%.

A slab with a thickness of 200m171 was heated at 1230℃ for all coils.
After heating for a period of time, continuous finish rolling is performed using a rough rolling mill and a tandem mill to a thickness of 3. Q mmO hot rolled sheet.

These hot-rolled sheets were subjected to a two-time cold rolling process including intermediate annealing at 950° C. for 5 minutes to give a finished thickness of o and aomm.

The rolling reduction of the second cold rolling was 56.5%, and the product was then manufactured in the same manner as in Example 1.

This shows the magnetic special order made at that time.

BIO(T) (Invention method) Coil with electromagnetic stirring 1.89 to 1.92
(Comparative method) No electromagnetic stirring 〃1.75-1.8
According to the present invention, a high magnetic flux density unidirectional electrical steel sheet is made of a CC material whose columnar crystals have been adjusted, and the heating temperature is lower than the relatively low heating temperature of the slab. Stable production is easily possible under a secondary cold rolling reduction ratio corresponding to the following.

[Brief explanation of the drawing]

Figure 1 shows that the heating temperature and final cold rolling reduction of the CC slab are B.
FIG. 2 is a graph showing the influence on the slab heating temperature B. It is a chart comparing the influence on the value between the presence and absence of electromagnetic stirring and the agglomerated slab.

Claims (1)

[Claims] I Si is 2.~4.5 weight φ weight 0.01~0.
08 weight and contains Mn in the range of 0.02 to 0.15 weight φ, and S, Se, Sb, Bi, Pb, Sn
and B, and in the case of two or more types, a total of 0.005 to 0.10 wt. Alternatively, a step of obtaining a slab in which the volume ratio of columnar crystals is adjusted to a range of 30 to 70% by applying ultrasonic vibration, and heating this slab to a temperature in the range of 1, higher than 1100°C and up to 1250°C. The steel strip obtained by hot rolling is subjected to two rounds of cold rolling with intermediate annealing in between to obtain the final product thickness, followed by decarburization and final finish annealing, and then left to dry within the above temperature range. Slab heating mixed layer T (℃
), the rolling reduction ratio R (%) of the second cold rolling satisfies the following conditions. Here KT ('c) is the nislab heating temperature, R (%) is the second cold rolling reduction ratio.