JPH02182829A - Production of non-oriented magnetic steel plate excellent in surface property and magnetic characteristic - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a non-oriented electrical steel sheet that eliminates glue zinc from a finished electrical steel sheet and has a high magnetic flux density.

(Conventional technology) Electrical steel sheets are often used as a laminated iron core for electric motors, transformers, etc., and not only do they have excellent electromagnetic properties, but other factors such as space factor and interlayer resistance have a large effect on their properties. Excellent surface properties are also required.

In recent years, continuous casting has been widely adopted in the production of non-oriented electrical steel sheets as a method for obtaining excellent magnetic properties and improving product yield. When this continuous casting method is used, segregation of C, St, etc. is reduced, and it is an excellent method for producing homogeneous slabs. Furthermore, it is a well-known fact that the yield is significantly improved compared to the conventional agglomeration method.

However, in high-silicon steel sheets containing 1.0% or more of Sl,
A wave-like defect called ridging occurs in the final product, and these not only deteriorate the appearance, but also reduce the space factor when laminated, and essentially impair the characteristics of motors and transformers made from the product. This is a problem because of this.

Various theories have been proposed regarding the mechanism of this ridging, including a theory that phases with different compositions form bands, and a theory that it is caused by the texture caused by rolling, but in recent years, the appearance of ridging has been The idea that this is caused by a factor other than the texture, that is, the coarse columnar crystals of the slab obtained by continuous casting, seems to be justified.

This point has been clarified through many years of research by the present inventors, and it has been found that if large amounts of coarse columnar crystals in the slab remain as drawn grains in the hot-rolled sheet, the ridging in the final product will be large. There is.

Various methods have been considered to prevent ridging, but the basic idea is to (1) reduce the columnar crystallinity of the slab (addition of grain refining elements such as Nb, low-temperature casting, electromagnetic stirring, etc.). (casting inside, etc.). (2) Finely recrystallizing the generated coarse columnar crystals (effective use of γ-α transformation, blooming, etc.). (3) Adding an annealing step to the manufacturing process to recrystallize the stretched grain structure into fine grains; a specific method is the method shown in Japanese Patent No. 1102479.

The contents are continuously cast slabs at 1000℃-1200℃.
After heating to ℃, when performing rough rolling and finish rolling to obtain a hot rolled sheet, the rough final pass is completed at 900 ℃ or higher and strong reduction rolling of 50% or higher, and the subsequent finish and top rolling is performed at 850 ℃ or higher. ℃～
By finishing in the low temperature region of 720°C, uniform strain energy is accumulated in the hot rolled sheet in the thickness direction, and this strain energy is recrystallized during subsequent hot rolled sheet annealing or intermediate annealing before final annealing. The idea is to use it as a driving force.

In general, Mid-5t grade non-oriented electrical steel sheets with a Sl content of 1.0% to 3.0% have a strict core loss level and require a material with a high magnetic flux density. Therefore, an annealing process is added once or twice before the final annealing to force the steel sheet to undergo recrystallization treatment, resulting in a non-oriented electrical steel sheet with no glue or zinc and a high magnetic flux density. It's being served.

(Problem to be solved by the invention) However, with recent improvements in peripheral technology, studies have begun on methods to bring out the magnetic properties of low iron loss and high magnetic flux density, in addition to relying only on the annealing process performed before final annealing. There is.

Against this background, there is a strong demand for lower costs, and there is no doubt that manufacturing processes that omit this annealing step will become mainstream in the future.

However, if this annealing step is omitted, the recrystallization of the structure in the steel sheet cannot be achieved to a certain extent, and problems such as frequent occurrence of adhesive zinc and a decrease in magnetic flux density have occurred in the finished product.

The present invention provides a manufacturing technology that eliminates the occurrence of glue zinc in the final product and makes it possible to obtain a good magnetic flux density in the manufacturing process that does not include an annealing process before the final annealing process. It is.

(Means for Solving the Problems) The present invention has a weight ratio of C: 0.02% or less, SI: 1.
0-3.0%, Mn: 0.1-1.0%, A, Q:
Continuously cast slabs obtained from molten steel consisting of 1.0% or less and the balance consisting of Fe and other unavoidable impurities,
In the method for producing a non-oriented electrical steel sheet in which the sheet is heated to a temperature of 1250°C, rough rolling and finish rolling are performed to obtain a hot rolled sheet, and thereafter cold rolling and final annealing are performed once according to a conventional method. The process time from the start to the start of finish rolling is longer than (1) X seconds, and the finish rolling is finished in a high temperature range of 750 to 900 °C. This is a method for manufacturing grain-oriented electrical steel sheets.

X (seconds) - [130 - Equiaxed crystallinity of slab (%)]... (1)
Furthermore, the present invention has C: 0.02% or less, Sl: 1.0~
3.0%, Mn: 0.1-1.0%, Afl: 1.0
% or less, and B: 0.0003 to 0.005
This method uses continuously cast slabs obtained from molten steel containing 0% Fe and the balance consisting of Fe and other unavoidable impurities to produce non-oriented electrical steel sheets with excellent surface properties and good magnetic properties.

The present invention will be explained in detail below.

FIG. 1 shows a method for calculating the equiaxed crystallinity of a slab.

Photos A and B in Figure 2 show metal phase photos (L cross section) of the bar before finish rolling after rough rolling.
% is used as the starting material, and the time from the start of rough rolling to the start of finish rolling is 80 seconds in Photo A and 105 seconds in Photo B.

As seen in photo A, when the time from the start of rough rolling to the start of finish rolling is as short as 80 seconds, there is a finely crystallized structure near the center of the bar thickness in an area of about 40% of the plate thickness. However, in most of the remaining parts, elongated grains are observed, which are thought to have remained after the columnar crystal structure seen in the slab structure was stretched as it was during rolling.

The fact that these drawn grains become the zinc that remains until the finished product is
This has already been explained in many documents and is a well-known fact.

On the other hand, as shown in Photo B, when the time from the start of rough rolling to the start of finish rolling was 105 seconds, it can be seen that a finely crystallized structure spreads over almost the entire thickness of the bar. .

It has been discovered that the remaining ratio of drawn grains can be controlled by increasing or decreasing the time from the start of rough rolling to the start of finish rolling with respect to such a constant equiaxed crystal ratio.

This phenomenon is thought to occur in the following metallurgy.

Ultra-low carbon steel containing 1.0% to 3.0% Sl is 9
It has a transformation point around 00℃. In order to increase the magnetic flux density, which is an important element of magnetic properties, these materials need to be finished rolled at a temperature between 750°C and 900°C. ~1
It is necessary to carry out the process in a temperature range of 100°C.

In other words, this rough rolling temperature region is a region entering the transformation region, and can be said to be a region where fine crystallization is likely to occur. However, by simply controlling the temperature within this range, it was impossible to eliminate the stretched grains from the entire bar thickness. Further, if the rough rolling temperature is lowered to a lower temperature than this, there is a problem that the finishing temperature cannot be maintained from 750°C to 900°C.

In other words, a large amount of reduction is applied from the slab to the bar thickness in the temperature range of 900°C to 1100°C, and during several times of bus rolling, the fracture of the drawn grains occurs due to the strain energy caused by the reduction during rough rolling. This phenomenon can be actively caused by making the time between each bath longer than the value, and this makes it possible to eliminate stretched grains over the entire thickness of the bar before finish rolling. .

Figure 3 shows the relationship between the time and the finished product ridging score over a wide range of times from the start of rough rolling to the start of finish rolling for a slab with an equiaxed grain ratio of 30%. .

This ridging rating is the gap amount of the unevenness on the surface of the C section of the final product read in μ units, A: 4μ,
B: 4.0~5.4μ, C: 5.5~6.9μ, D=
>6.9μ, and based on many years of experience with customers, it is possible to ship products up to B.

It can be seen that in order to obtain passing grades A and B in this example, a time of 100 seconds is required from the start of rough rolling to the start of finish rolling.

Next, FIG. 4 shows how the effect of crushing the drawn grains depending on the time from the start of rough rolling to the start of finish rolling is influenced by the equiaxed crystallinity of the slab.

As seen in Figure 4, it can be seen that a slab with a high equiaxed crystallinity requires a short time, and a slab with a low equiaxed crystallinity requires a long time. This is because the drawn grains that cause product ridging are proportional to the degree of columnar crystals in the slab stage, and the smaller this portion is, the more the effect of crushing the drawn grains due to the time from the start of rough rolling to the start of finish rolling will be reduced. This means that less is required.

The present inventors have discovered that there is a certain relationship between the equiaxed crystallinity of the slab, the time from the start of rough rolling to the start of finish rolling, and the ridging of the finished product. Equation (1) is a mathematical expression of this relationship based on experimental results.

X (seconds) - (130 - Equiaxed crystallinity of slab (%))... (1)
In other words, when the equiaxed crystallinity of the slab is 0%, by setting the time from the start of rough rolling to the start of finish rolling to 130 seconds or more, the finished product has a good zinc rating of B or below. In addition, when the equiaxed product ratio of the slab is 70%, by setting the time from the start of rough rolling to the start of finish rolling to be 60 seconds or more, the zinc rating of the finished product can be lower than B. It is possible to make it good.

In this way, by ensuring the time from the start of rough rolling to the start of finish rolling of X seconds or more that satisfies formula (1), it is possible to prevent the occurrence of glue zinc in the finished product.

Due to the widespread use of electromagnetic stirrers and improvements in casting temperature control technology, the equiaxed product ratio of slabs actually obtained is currently possible from 0% to 100%, but due to the stability of casting and equipment costs, In reality, it is produced in a range of 0% to 70%.

Next, FIG. 5 shows the relationship between finishing temperature and magnetic flux density.

As shown in Figure 5, in processes that incorporate hot-rolled plate annealing, there is no effect on magnetic flux density due to finishing temperature, but in cases where hot-rolled plate annealing or no annealing is performed before final annealing, There is a correlation between the finishing temperature and the magnetic flux density, and the lower the finishing temperature, the worse the magnetic flux density becomes.

This material has a transformation point around 900℃,
In the low temperature range below 0°C, it is in the α phase. Within this α phase, by keeping the temperature as high as possible for as long as possible, orientations that improve the magnetic flux density increase in the steel sheet.

That is, by processing the hot-rolled sheet at a high finishing temperature of 750° C. to 900° C., the texture that controls the orientation of the hot-rolled sheet is improved, making it possible to omit hot-rolled sheet annealing.

Here, the upper limit of the finishing temperature was limited to 900° C., but it goes without saying that a temperature as high as possible within this range is good for magnetic flux density.

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

When the amount of C in silicon steel exceeds 0.602%, the amount of Ci in the finished product is
In order to reduce Cil, a long decarburization annealing process is required, which not only significantly deteriorates productivity but also deteriorates magnetic properties. Therefore, in the present invention, Cil in steel is set to 0.0.
It was limited to 2%.

For 5ljt, the target is <4.8W/kg at W15150, which is the required iron loss, and the lower limit of Sl is
The content was set to 1.0% or more. On the other hand, the upper limit was set at 3.0% in consideration of threadability.

Mn is added to increase the hardness of the steel sheet and improve punchability, but the upper limit of 1.0% is for economic reasons. Furthermore, the lower limit value was set at 0.1%, which would reduce its effectiveness.

Al is also an element added to improve iron loss by increasing the specific resistance of silicon steel, but if added too much, it will impede the cold rollability of the plate, and for economic reasons, the upper limit has been set at 1. It was set to 0%.

In addition, Ag, which inhibits grain growth, acts as a precipitated dispersed phase.
For materials that prevent N precipitation and improve iron loss, A
Since the technology is applicable to both cases, the range is set to 0 and the range is 1.0% or less.

In order to produce iron loss, the primary grain growth in the annealing process is used to increase the crystal grain size of the finished product to 20 to 100μ to produce the specified iron loss, but the heating temperature is high. and MnS
, AffN, and the like become a solution, precipitate during the hot rolling process, inhibit primary grain growth during the annealing process, and result in poor magnetic properties.

Therefore, the upper limit of the heating furnace temperature was limited to 1250°C.

The lower limit was set at 1000° C. based on the rolling load capacity.

Although the present invention is limited to manufacturing processes that do not include an annealing process after the hot-rolled sheet is produced and before the final annealing process, a method that partially omits such an annealing process will not produce a predetermined magnetic flux density. Therefore, we limited the temperature range where magnetic flux density is likely to occur.

If the temperature is lower than 750°C, sufficient magnetic flux density cannot be obtained. 90 again
If it exceeds 0°C, rolling will occur in the two-layer region of a region and γ region in the finishing rolling mill, resulting in extremely poor rolling properties and saturated magnetic flux density, so the upper limit temperature was set at 900°C.

It is a well-known fact that AIN, which is a precipitated dispersed phase, significantly inhibits the grain growth of finished products, but in order to prevent this, N
By adding B, which has a strong affinity with
Remove N that reacts with

In the present invention, in order to exhibit the effects of B addition, the range of B is 0.0003% to 0.0050%. If it is less than the lower limit of 0.0003%, the effect of B addition will not be exhibited, and the upper limit of 0.0050% is due to economic reasons.

(Example 1) Weight ratio: C: 0.0025%, Si: 1.5%, M
n: 0.25%, P: 0.02%, s: o, oo
a%, 5o11. Molten steel with Afl: 0.33% and the balance consisting of iron and unavoidable impurities was cast using a curved continuous casting machine to cast a slab with a thickness of 250 m+*. After heating this slab as a starting material to a temperature of 1100° C., the time from the start of rough rolling to the start of finish rolling was changed as shown in Table 1.

In particular, for slabs, we used an electromagnetic stirrer to change the proportion of equiaxed parts inside the slab and evaluated the correlation with hot rolling conditions (for slabs of 10% or more, an electromagnetic stirrer was used). did).

Table 1 also shows the equiaxed crystallinity of the slab, hot rolling conditions, passing conditions after hot rolling, finished product paste zinc, magnetic property results, and overall evaluation.

In Comparative Example 1, the time from the start of rough rolling to the start of finish rolling was calculated using equation (1) as shown in Table 1 using a slab whose equiaxed crystallinity was changed from 0 to 70% as a starting material. As can be seen, all of the equiaxed products had adhesive zinc with a rating of C or higher, which is a problem in finished products.

As for the magnetic flux density, finish rolling was performed within the temperature range of the present invention, and good results were obtained.

(Example 2) fift ratio: C: 0.0025%, S: 1:1.5
%, Mn: 0.25%, P: 0.02%, S: 0
．． 003%, sol, Afl: 0.03%, B:
Molten steel with a concentration of 0.0020% and the remainder consisting of iron and unavoidable impurities was cast using a curved continuous casting machine to cast a slab with a thickness of 250 mm. Using this slab as a starting material, the internal equiaxed crystal ratio was varied and the correlation with hot rolling conditions was evaluated (for 10% or more, a slab electromagnetic stirrer was used).

Table 2 also shows the equiaxed crystallinity of the slab, hot rolling conditions, passing conditions after hot rolling, finished product paste zinc, magnetic property results, and overall evaluation.

In particular, the finish rolling temperature is controlled at 700°C.
The temperature was varied between 1000°C and 1000°C.

For slabs, an electromagnetic stirring device was used, and slab comparison example 2 was prepared.
The equiaxed product ratio of the slab is scaled from 0 to 50%, and from the value of the equiaxed product ratio of each slab, the time from the start of rough rolling to the start of finish rolling that satisfies equation (1) is calculated. After ensuring this, the results of experiments were conducted with finishing rolling temperatures ranging from 750°C or lower to 900°C or higher.

As shown in Table 2, when the temperature is 750° C. or lower, the magnetic flux density decreases significantly. . Further, when the temperature was 900° C. or higher, although a magnetic flux density equivalent to that of the good material could be obtained, the passability in finish rolling became unstable due to rolling in a two-phase region.

It should be noted that the comparison material of the finished glue zinc also had a good rating of A.

Moreover, by adding B, 5aj2. A (Even if the l value is lowered, the harmful effects of A and QN can be prevented, and a better iron loss than in Example 1 is obtained.

(Effects of the Invention) As described above, according to the present invention, the time from the start of rough rolling to the start of finish rolling in the hot rolling process can be appropriately controlled in accordance with the equiaxed product ratio of the slab; By controlling the subsequent finish rolling temperature within the range of 750° C. to 9° C. (10° C.), it is possible to produce a non-oriented electrical steel sheet that does not produce glue zinc and has a good magnetic flux density.

[Brief explanation of the drawing]

Diagram m1 is a schematic diagram showing a method of observing the internal structure of a slab after puff-polishing the cross section of slab C and then macro-etching it, and calculating the equiaxed crystal ratio from the thickness ratio of equiaxed crystals and columnar crystals.
Figure 2 shows the finishing rolling of a slab with an equiaxed crystallinity of 30% as a starting material, varying the time to start rolling at two levels: 80 seconds (Photo A) and 105 seconds (Photo B). Figure 3 is a micrograph showing the macro-etching of the L cross section with the previous bar thickness, and shows the time from the start of rough rolling to the start of finish rolling using a cast slab with an equiaxed grain ratio of 30% as a starting material. Figure 4 is a scatter diagram of the glue zinc rating of the final product when the level was changed from 80 seconds to 115 seconds. In rolling and hot rolling, the time from the start of rough rolling to the start of finish rolling is 50 seconds to 1
Figure 5 is a scatter diagram of the adhesive and zinc ratings for the final product of each material, varying the level for up to 35 seconds. 2 is a chart showing the relationship between magnetic flux density and finish rolling temperature when hot-rolled sheets are passed through to final products with and without annealing. Figure 1 Figure 3

Claims (1)

[Claims] 1. C: 0.02% or less Si: 1.0 to 3.0% Mn: 0.1 to 1.0% Al: 1.0% or less The balance is Fe and others Continuously cast slabs obtained from molten steel containing unavoidable impurities are heated to a temperature of 1,000 to 1,250°C, then rough rolled and finish rolled to form hot rolled sheets, which are then cold rolled once according to conventional methods. In a method for manufacturing non-oriented electrical steel sheets that performs final annealing, the processing time from the start of rough rolling to the start of finish rolling is set to be at least X seconds according to formula (1), and the subsequent finish rolling is performed in a high temperature range of 750°C to 900°C. A method for producing a non-oriented electrical steel sheet having excellent surface properties and good magnetic properties. X (seconds) = [130 - Equiaxed crystallinity of slab (%)]...(1)
Formula 2, weight ratio: C: 0.02% or less Si: 1.0-3.0% Mn: 0.1-1.0% Al: 1.0% or less B: 0.0003-0.0050% 2. The method for producing a non-oriented electrical steel sheet with excellent surface texture and good magnetic properties according to claim 1, wherein a continuously cast slab obtained from molten steel with the balance being Fe and other unavoidable impurities is used.