JPS621458B2 - - Google Patents

Description

[Detailed description of the invention] In the production of high magnetic flux density unidirectional electrical steel sheets, the present invention makes it possible to industrially and stably produce products with good properties and uniform magnetic properties in the longitudinal direction of the product. It is about the method.

As is well known, unidirectional electrical steel sheets are composed of crystal grains with an orientation represented by (110) [001] in the Miller index, and the <100> axis, which is the axis of easy magnetization, lies in the rolling direction. They are arranged in parallel.
In this way, the grain-oriented electrical steel sheet has particularly excellent magnetic properties in the rolling direction, since the crystal grains constituting it have a specific direction in the rolling direction. Such a specific orientation is achieved by high-temperature annealing of a steel plate that has reached its final thickness through hot rolling and cold rolling.
This is achieved by the so-called secondary recrystallization phenomenon in which primary recrystallized grains with the (110)[001] orientation selectively grow.

Unidirectional electrical steel sheets are soft magnetic materials that are mainly used in cores for transformers and generators. and iron loss) must be good. The quality of magnetization characteristics is determined by the magnitude of the magnetic flux density (generally expressed as the value of B ₁₀ (Tesla)) induced within the iron core in response to a constant applied magnetic field. Iron loss (W〓
It is generally displayed as a value of 〓〓. watt／
Kg) is the power loss consumed as thermal energy within the iron core when a predetermined alternating current magnetic field is applied to the iron core, and it is desirable that its value be small. Iron loss (W〓
The quality of 〓〓) is influenced by the thickness, amount of impurities, specific resistance, and residual strain of the unidirectional electrical steel sheet constituting the iron core, but the magnetization characteristics (B ₁₀ ) also have a large influence.

From the above, improving the magnetization properties (B ₁₀ ) of unidirectional electrical steel sheets makes it possible to downsize electrical equipment and save energy by reducing iron loss. As a method for manufacturing a high magnetic flux density unidirectional electrical steel sheet, a method by Satoru Taguchi et al. is disclosed in Japanese Patent Publication No. 15644/1972. In order to obtain a stable product using this method, Akira Sakakura et al. invented JP-A-48-51852.
The hot rolling conditions shown in the publication are important. In other words, in order to stably perform secondary recrystallization, based on the idea that Al should not be precipitated to an excessively large size, it is necessary to "shorten the residence time of the material in the AlN precipitation region during hot rolling." It is necessary to rapidly cool the temperature below the AlN precipitation temperature. If this condition is not satisfied, abnormal areas called fine grains that do not undergo secondary recrystallization will occur. A specific method for implementing hot rolling conditions based on this concept using a generally used continuous hot rolling mill is as follows.

150~300 manufactured by continuous casting or blooming rolling
After heating the mm slab, it is hot rolled to an intermediate thickness of 30 to 60 mm using a rough hot rolling mill, and then hot rolled to a final thickness hot rolled sheet using a continuous finishing hot rolling mill. Recently, continuous finishing hot rolling has been developed by directly casting thin slabs of 30 to 60 mm without rough rolling, and then heating them to high temperatures, or using the sensible heat of the slabs without heating. It may also be hot-rolled to the final thickness using a machine.

In accordance with the actual hot rolling method,
Considering the temperature history of the steel sheet during hot rolling to achieve the AlN precipitation state, it is as follows. At the intermediate thickness stage (usually 30 to 60 mm) before entering the continuous finishing hot rolling mill.
Attempting to cool the material below the precipitation temperature range of AlN will not only result in poor cooling efficiency, but also because the plate thickness will increase the temperature difference between the surface and the center, which is not appropriate since the state of AlN will vary in the thickness direction. Moreover, if the steel sheet is cooled at an intermediate thickness stage, the deformation resistance of the steel material will increase due to a decrease in the temperature of the steel sheet, and the processing power required for a continuous finishing hot rolling mill will increase, which is not economical. On the other hand, a method that maintains a relatively high temperature above the precipitation temperature range of AlN until the intermediate thickness stage and rapidly cools the steel material when it enters the continuous finishing hot rolling mill and becomes thinner is a method that improves the cooling efficiency of the steel material. This is desirable because it makes the AlN uniform in the thickness direction of the steel plate and reduces the power required for a continuous finishing hot rolling mill.

From the above, in order to control the AlN in hot-rolled sheets to an appropriate state, it is necessary to maintain the temperature of the steel material before it enters the continuous finishing hot-rolling mill, the so-called hot-rolling front temperature, above a predetermined temperature. It is.

However, recently there has been a trend to increase the unit quantity of coils in order to increase production efficiency and improve yield.
Since the rolling time per coil is longer, the temperature of the tail part of the coil is lower than that of the head part of the coil, and in some cases, secondary recrystallization defects may occur in the tail part of the coil. Alternatively, secondary recrystallization failure does not occur, but since the AlN precipitation state differs in the longitudinal direction of the coil, the problem arises that the magnetic flux density of the obtained product is not uniform in the longitudinal direction of the coil. In order to prevent the occurrence of incomplete secondary recrystallization in the tail portion of the coil due to this decrease in the steel plate temperature, it is conceivable to increase the temperature of the entire coil. In order to raise the temperature of the entire coil, there are problems such as an increase in heating energy or the need for equipment measures to increase slab heating more than the current level. In addition, because the overall temperature of the coil was raised, there was a problem called wire mixing at the head of the coil where the continuous finish hot rolling temperature was high.
A secondary recrystallization imperfection that extends long in the rolling direction is generated. This wire mixing is noticeable when a continuously cast slab is used, but it also occurs when a steel material with low C and high Si is used even when a slab formed by the blooming method is used.

As shown in Japanese Unexamined Patent Publication No. 120214/1984, this line mixing tends to occur when recrystallization does not occur during hot rolling because the hot rolling temperature is too high. The hot rolling temperature at which recrystallization is most likely to occur is around 1100°C, which is almost the same as the AlN precipitation temperature range, and it is necessary to achieve recrystallization during continuous finishing hot rolling to prevent wire mixing. .

As can be seen from the above, the hot rolling conditions for stably producing high magnetic flux density unidirectional electrical steel sheets in large unit coils are to keep the finishing front temperature below the temperature at which wire mixing does not occur over the entire length of the coil. It is important to ensure that the temperature is higher than that at which fine particles do not occur. When the material is made of ordinary steel containing about 3% Si, the hot rolling finishing front temperature needs to be about 1220°C or less and about 1100°C or more. To ensure such a temperature range, a predetermined temperature ensuring means is required, but as the unit weight of the coil increases, it becomes more difficult to ensure the predetermined temperature. Further, even if a predetermined temperature can be secured, the magnetism becomes non-uniform due to temperature differences in the longitudinal direction of the coil.

The purpose of the present invention is to completely solve these problems, and thereby to obtain industrially and stably a high magnetic flux density unidirectional electrical steel sheet having good properties with uniform magnetism in the longitudinal direction of the finished product. We are trying to provide a manufacturing method that can.

That is, the gist of the present invention is that Si:
4.0% or less, C: 0.085% or less, acid-soluble Al:
Molten steel containing 0.010 to 0.065%, Total N: 0.003 to 0.0100% is made into a slab by continuous casting or blooming hot rolling, hot rolled sheet by continuous hot rolling, rapidly cooled after high temperature continuous annealing, and rolled in one cold rolling process. In a method for manufacturing a unidirectional electrical steel sheet with excellent magnetic properties in the rolling direction, the method comprises the steps of: obtaining a finished product sheet thickness, performing continuous decarburization annealing in a wet hydrogen atmosphere, and further performing final annealing at a temperature of at least 800°C or higher. , the cooling after high-temperature continuous annealing of the hot-rolled sheet is carried out in the longitudinal direction of the coil so that the areas where the finish hot-rolling temperature is high are at a rapid cooling rate, and the areas where the finish hot-rolling temperature is low are at a slow cooling rate. A method for producing a high magnetic flux density unidirectional electrical steel sheet characterized by variable cooling continuously or stepwise.

In the production of high magnetic flux density unidirectional electrical steel sheets,
Regarding the cooling rate after hot-rolled sheet annealing,
As disclosed in Japanese Patent No. 23820, the present invention can be applied even when the continuous finish hot rolling temperature is outside the above-mentioned temperature range of 1220 to 1100°C, or when the temperature difference in the longitudinal direction of the coil is uneven. However, by changing the cooling rate after hot-rolled sheet annealing continuously or stepwise in the longitudinal direction of the coil in accordance with the hot-rolling conditions, magnetic defects can be eliminated and uniform magnetic properties can be achieved in the longitudinal direction of the coil. This made it possible to obtain the following products.

The present invention will be described in more detail below.

The magnetism of the product obtained when the cooling rate after hot-rolled sheet annealing is changed will be explained for the coil head and tail portions having different hot-rolling temperatures.

Si: 3.05%, C: 0.045%, acid soluble Al: 0.032
%, T・N: Molten steel containing 0.0090% was continuously cast into a slab with a thickness of 250 mm and a weight of 10 tons, and was cast in a heating furnace.
After heating to 1400℃, it is hot rolled to a thickness of 40mm using a rough hot rolling mill.
It was made into a 2.3mm hot-rolled plate using a continuous finishing hot-rolling machine. At this time, the temperature at the front of the hot-rolled finish is approximately 1230℃ at the head and approximately 1230℃ at the tail.
It was 1070℃. The head and tail parts of this hot-rolled sheet were heated at 1120°C for 2 min.
Quenched in water at 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C, cold rolled to a thickness of 0.30 mm,
Decarburization annealing was performed in wet hydrogen at 840°C for 3 minutes, MgO was applied, and high temperature annealing was performed at 1200°C for 20 hours. The magnetism of the product obtained in this process is shown in FIG.

As can be seen from FIG. 1, the hot-rolling head, where the hot-rolling finishing front surface temperature is high, has good magnetism when the quenching water temperature is low, that is, by rapid cooling, so that no line mixing occurs in the product. On the other hand, the hot-rolled tail part, which has a low hot-rolled finish front temperature, has good magnetism when the quenching water temperature is high, that is, when it is slowly cooled, no fine grains are generated in the product. Therefore, over the entire length of this hot-rolled coil, there is no wire contamination or fine grains, and uniform magnetism is achieved by changing the cooling rate after annealing the hot-rolled sheet so that it gradually slows down from the hot-rolled head to the tail. It can be obtained by In the case of actual factory production, one way to change the cooling rate in the longitudinal direction of the coil after high-temperature continuous annealing of a hot-rolled sheet is to change the temperature of the cooling water, but the method of changing the amount of cooling water is It's actually easy.

This method will be described in more detail. First, for a hot-rolled sheet manufactured with predetermined components and hot-rolling equipment, the amount of cooling water that achieves the cooling rate that provides the best magnetism is determined for the head section at the highest point and the tail section at the lowest point of hot-rolling temperature. Next, record the hot-rolled finishing front temperature in the longitudinal direction of the coil as a value representative of the hot-rolling temperature, and use the cooling water amount that achieves the optimum cooling rate of the hot-rolling head and tail as a reference point, and hot-roll within this cooling water amount range. The pattern of change in the amount of cooling water in the longitudinal direction of the coil is determined in proportion to the finished front temperature. This change pattern in the amount of cooling water is set in the water meter in the cooling zone of the hot-rolled sheet annealing furnace. When the hot-rolled sheet after annealing enters the cooling zone, the amount of cooling water is controlled in accordance with this change pattern of the amount of cooling water. In addition, instead of the method of completely and continuously making the cooling rate after hot-rolled sheet annealing follow the fluctuation of the hot-rolling temperature as described above, it is also possible to adopt the following simple method. Divide the entire length of the coil into several parts, determine the average hot-rolling temperature of each part, determine the cooling rate that matches the average hot-rolling temperature, and set the amount of cooling water to achieve that cooling rate in a stepped manner in the longitudinal direction of the coil. This is a method of cooling.

Next, the constituent elements of the present invention will be described.

The starting steel in the present invention has Si: 4.0% or less and C:
0.085% or less, acid-soluble Al: 0.010-0.065%,
Contains T/N: 0.003 to 0.0100%, with the remainder consisting of iron and some impurities. Si is 4.0
%, the steel plate will break during cold rolling.
4.0% or less. If the amount of C is too large, the annealing time will be long in the decarburization annealing process, which will result in poor industrial productivity, so the content is set to 0.085% or less. The purpose of the present invention is to obtain a high magnetic flux density unidirectional electrical steel sheet by the action of AlN, and since it is necessary to secure an appropriate amount of AlN, the acid-soluble Al should be 0.010% or more, T.
The N content was set to 0.003% or more. and acid soluble
As the amount of Al increases, secondary recrystallization becomes incomplete.
The content was set to 0.065% or less, and since too much T/N causes blistering defects on the surface of the steel sheet, the content was set to 0.010% or less. The components of the starting steel material used in the present invention other than Si, C, acid-soluble Al, and T/N are not particularly limited.
In addition to these components, for example, Mn, S, Sb, and Se act effectively as precipitated dispersed phases and have the effect of improving magnetism.
Cu, Ni, P, and Sn are effective in stabilizing magnetism, and although it is desirable to include these components, they are not essential components of the material in the present invention.

Although the present invention is particularly effective when the starting material is a continuously cast slab that is susceptible to secondary recrystallization defects, it can of course also be applied to slabs obtained by the conventional agglomeration-blooming method. This slab is usually heated and then hot-rolled into a hot-rolled plate. The heating temperature of the slab may be high if the acid-soluble Al or T/N is large, or low if the acid-soluble Al or T/N is small, and may be within the range of approximately 1150°C to 1400°C as long as the ingredients are within the range of the present invention. For hot rolling, when the slab thickness is as thick as 150 to 300 mm,
Rough hot rolling is performed several times to achieve a specified thickness (30 to 60
Generally, it is made into an intermediate material (mm), and then made into a hot-rolled sheet by continuous finish hot rolling. Slab thickness is 30
When the thickness is ~100 mm, rough hot rolling is omitted and the hot rolled sheet is directly finished hot rolled. Hot rolled plate is 950~
Continuously annealed at a high temperature in the range of 1200℃, then rapidly cooled. If the annealing temperature is less than 950°C, high magnetic velocity density cannot be obtained, and if it exceeds 1200°C, secondary recrystallization will not occur.
This cooling after annealing is carried out continuously so that in the longitudinal direction of the coil, the areas where the finishing hot rolling temperature is high (usually the hot rolling head) have a rapid cooling rate, and the areas where the finish hot rolling temperature is low (usually the hot rolling tail) have a slow cooling rate. Do this step by step. In normal hot rolling, the temperature is lower near the hot rolling tail, but
When heating a slab, the temperature may not rise on the furnace skid or at both ends of the slab. In such a case, there may be a region with a low temperature at the center in the longitudinal direction of the coil. Thereafter, it is cold rolled once to the final thickness of the finished product, subjected to continuous decarburization annealing in a wet hydrogen atmosphere, and final annealed at a temperature of 800°C or higher to produce a finished product. The higher the final annealing temperature is, the lower the iron loss is desirable, but if there is a limit to the production of the γ phase due to transformation, the magnetic flux density will deteriorate, so depending on the amount of Si, the temperature at which the γ phase does not appear, that is, when the amount of Si is zero, is The limited range was 800°C (some γ phase appeared, but no problem).

In the present invention, the magnetic non-uniformity caused by the slab heating conditions during hot rolling and the temperature history of rolling differing in the longitudinal direction of the coil can be changed by adjusting the cooling conditions after annealing the hot rolled sheet in correspondence with the hot rolling temperature in the longitudinal direction of the coil. This can be resolved through control. In the future, there is a trend to increase the coil unit weight of grain-oriented electrical steel sheets for efficient production, and it is expected that the temperature history will expand from the hot-rolled head to the tail. The present invention, which can make magnetic properties uniform throughout, is extremely effective in obtaining electrical steel sheets having homogeneous magnetic properties.

Example C: 0.060%, Si: 2.90%, acid soluble Al: 0.026
%, T・N: Molten steel containing 0.008% is continuously cast.
It was made into a 10 ton slab. After heating to 1380℃, it is rough hot-rolled in 3 passes to form an intermediate material with a thickness of 40mm, and then finished hot-rolled.
It was made into a hot-rolled plate with a thickness of 2.3 mm. At this time, the temperature of the hot rolling head before finishing hot rolling is 1250℃, the tail part is 1080℃,
The temperature in the center was 1170°C. Hot-rolled plate at 1100℃
After annealing for 2 minutes, it was cooled with water to room temperature using a nozzle. As cooling conditions at this time, the amount of water in the longitudinal direction of the coil was changed to the following two types.

Constant amount of cooling water over the entire length of the coil〓m2 ^/
hr (This amount of cooling water is the optimum amount of cooling water to obtain the optimum magnetism at a hot rolling temperature of 1170℃.) Amount of chilled water for a 1.5 ton coil head: 1.2 αm ³ /hr Amount of cooling water for a 7.0 ton coil central portion αm ³ / hr Cooling water volume for 1.5 tons of coil tail: 0.8αm ³ /hr (*Note) This water volume is not a fixed value, as it changes depending on the amount of steel plate passing through the cooling zone. For example, 10m/
If the sheet threading rate is min, it will be approximately 50m ³ /hr with water at 45℃.

This steel plate was cold rolled to a thickness of 0.30 mm, decarburized in wet hydrogen at 840°C for 3 minutes, coated with MgO, dried, and final annealed at 1200°C for 20 hours.

The magnetic properties of the obtained product were as follows.

Condition top: B ₁₀ = 1.87T,
W = 1.25w / Kg Center: B ₁₀ = 1.94T,
W〓〓〓=1.05w/Kg Tailmost part: B ₁₀ =1.82T,
W〓〓〓=1.40w/Kg Approximately 0.7ton of the head is W〓〓〓〓: 1.14w/Kg or more and it fails G7. Approximately 1.0ton of the tail is W〓〓〓: 1.14w/Kg or more and it fails _G7 . Passing condition topmost: B ₁₀ = 1.93T,
W = 1.08w / Kg Center: B ₁₀ = 1.94T,
W〓〓〓=1.05w/Kg Tailmost part: B ₁₀ =1.93T,
W〓〓〓=1.07w/Kg The total amount (10 tons) passed G7 As described above, according to the present invention, high magnetic flux density unidirectional electrical steel sheets with good characteristics with uniform magnetism in the longitudinal direction of the product can be industrially produced. Since it can be manufactured stably, it is extremely beneficial to industry.

[Brief explanation of the drawing]

Figure 1 shows the head and tail of a hot-rolled plate heated at 1120℃ for 2 minutes.
After heating, it is immersed in cooling water, cold rolled, decarburized annealed,
FIG. 3 is a diagram showing the relationship between the magnetic properties of a product obtained through high-temperature annealing and the temperature of immersion cooling water.

Claims (1)

[Claims] 1 Si: 4.0% or less, C: 0.085% or less, acid soluble
Al: 0.010~0.065%, Total N: 0.003~0.0100%
molten steel is made into a slab by continuous casting or blooming hot rolling, hot rolled plate is made by continuous hot rolling, rapidly cooled after high temperature continuous annealing, finished plate thickness is obtained by one cold rolling, and continuous desorption is carried out in a wet hydrogen atmosphere. A method for producing a grain-oriented electrical steel sheet with excellent magnetic properties in the rolling direction, which includes a step of charcoal annealing and final annealing at a temperature of at least 800°C, in which cooling after continuous high-temperature annealing of the hot-rolled sheet is performed. , the coil is variable-cooled continuously or stepwise in the longitudinal direction of the coil so that the parts with high finishing hot-rolling temperature are at a rapid cooling rate, and the parts with low finishing hot-rolling temperature are cooling at a slow cooling rate. A manufacturing method for unidirectional electrical steel sheets with a characteristic high magnetic flux density.