JPS61119620A - Annealing method of silicon steel strip by vertical continuous annealing furnace - Google Patents

Abstract

PURPOSE:To make annealing treatment possible without deteriorating magnetic characteristic, by specifying the diameter of hearth roll, at annealing of a specified Si steel strip by vertical continuous annealing furnace. CONSTITUTION:Si steel cold rolled strip contg. 1-4wt% Si and having 0.15-0.6mm thickness is passed through vertical continuous annealing furnace, in which up-and-down revolution and shuttling are repeated by hearth roll, in reducing gas atmosphere of 760-950 deg.C, to perform decarbonization or recrystallization annealing. Thereat, hearth roll whose diameter DA(mm) satisfies a relation of DA>=1.6X10<3>.d according to thickness d(mm) of said steel strip, is used. By this method, disadvantageous deteriorating magnetism of products due to plastic deformation accompanying with bending along hearth roll can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The manufacture of silicon steel sheets used as core materials for transformers, electric motors, etc. requires a complex and precise combination of processes.

As is well known, silicon steel can be broadly divided into oriented silicon steel sheets and non-oriented silicon steel sheets, which are used depending on the purpose.

When producing grain-oriented silicon steel sheets, the Goss orientation formed on the steel sheet surface during hot rolling is eliminated during the cold rolling process in order to obtain secondary recrystallized grains with a strong accumulation of Goss orientation in the final product. Ideally, in the manufacturing process of non-oriented silicon steel sheets, (100)
Although in-plane non-direction represented by [:ovw] is desirable, it is harmful to develop Goss orientation to some extent (1
11) It is considered advantageous in reducing surface strength.

However, in recent years, there has been an increasingly strong demand for energy saving and cost reduction, and continuous annealing equipment for silicon steel sheets is required to be as fast as possible to increase productivity and at the same time to lower the equipment test object. .

On the other hand, however, in order to reduce the iron loss of products, the thickness of the product plates tends to become thinner, and as a result, productivity with conventional equipment has to be reduced.

In order to advantageously solve this problem, we investigated the use of a so-called vertical continuous annealing furnace in which the coil is rotated up and down from a hearth roll and repeatedly folded, and its suitability was achieved as described below. The application of vertical continuous annealing furnaces to general cold-rolled steel sheets has already been reported in Japanese Patent Publication No. 4B-32249 and Japanese Patent Application Laid-open No. 50
Several types have been reported, such as in Publication No. -43708.

However, in the case where this type of vertical continuous annealing furnace was applied to continuous annealing of silicon steel sheets containing up to 4% by weight of Si,
This has never happened before, and the reason for this is that silicon steel sheets have poor hot strength at high temperatures, and plastic deformation occurs at the hearth roll section for folding due to the steel sheet tension and its own weight, which deteriorates the magnetic properties of the final product. This is thought to be because if the tension applied to the surface layer of the steel sheet is too large during the temperature rising process in which crystal grains containing Goss-oriented crystal grains form and grow, this may have an adverse effect on magnetism. .

(Problems to be Solved by the Invention) The influence of the hearth roll diameter on the magnetic properties of silicon steel sheets was investigated under various annealing conditions, and silicon steel sheets that could be processed in a vertical continuous annealing furnace without impairing the magnetic properties were investigated. It is an object of the invention to enable a suitable annealing treatment of the strip.

(Means for solving problems) The above objects of the invention can be advantageously achieved by the following steps.

1, 0.15-0.6 containing 1-4% by weight of Si
Decarburization is carried out by passing a cold-rolled silicon steel strip with a thickness of 760 mm to 950 t in a reducing gas atmosphere through a vertical continuous annealing furnace that repeatedly rotates up and down with hearth rolls. A method for annealing a silicon steel strip using a vertical continuous annealing furnace, which is characterized in that during recrystallization annealing, a hearth roll that satisfies the following formula depending on the thickness of the silicon steel cold rolled steel strip is used.

Mouth ≧1.6 A cold-rolled silicon steel strip of 6 city thickness is decarburized by passing it through a vertical continuous annealing furnace in which it is repeatedly turned up and down with hearth rolls in a reducing gas atmosphere at a temperature of 760 to 950 °C. or during recrystallization annealing, using a hearth roll that satisfies the relationship of the following formula (1) depending on the thickness of the silicon steel cold rolled steel strip,
During the temperature raising process prior to threading, the temperature was 500 to 750°C.
Silicon steel in a continuous annealing furnace characterized by using a hearth roll that satisfies the following formula (2) according to the Si content, thickness, and temperature of the silicon steel cold-rolled steel strip in the temperature range of Method of annealing raw steel strip.

DA ≧1.6 xto3 ・d -----(1
)0 crossing ≧(6XIO"-1,1XIO" -
1.1×102 [Si) +1,4 4)XdDA
Near 60-950℃ range hearth roll diameter (mm) D,
+500~750℃ range hearth diameter (mm)
d: Silicon steel cold-rolled steel strip thickness (mm) [Si]: Silicon gold collection amount (weight%
)T: Silicon steel cold rolled steel strip temperature (°C) The usefulness of determining the hearth roll diameters DA and D as described above was confirmed by the following experimental results.

Figure 1 shows 0,30. m1
When decarburizing cold-rolled steel strips for grain-oriented silicon steel with a thickness of 11 and 0.20 mm in a vertical continuous annealing furnace at 800 °C in wet hydrogen, the steel strips were rotated up and down in the furnace. The diameter DAmm of the hearth roll for repeated folding and the steel plate thickness d
The magnetic flux density of the final product (B, o
) changes are summarized. D/d ≧1.6
At XIO', the magnetic flux density 810 of the product is 1.
It can be seen that it shows a high value of 90 or more.

Next, as an experiment to investigate the influence of the diameter OR of the hearth roll in the temperature rising process,
When decarburizing and recrystallizing a 0 mm thick cold-rolled steel strip for grain-oriented silicon steel at 800 °C in a vertical continuous annealing furnace, the temperature range is 500 to 75 where primary recrystallization progresses during heating.
Stage annealing is performed by holding the temperature in the range of 0°C for 1 minute, during which time the diameter of the hearth roll is reduced to 0. We investigated the relationship between the magnetic properties of the latest product and the hearth roll diameter by changing a few things. The diameter DA of the hearth roll other than the step annealing area is 800 m.
It was m. Figure 2 shows this result.8. , l
The diameter D11 of the hearth roll exhibiting an amount of 90 or more corresponds to the shaded area, and it is clear that the critical radius at which magnetism is not deteriorated increases as the temperature increases.

Next, determine the appropriate hearth roll diameter during the temperature rising process,
An example of an experiment conducted to determine the relationship between

Si 2.51.2.90.3.20 and 3.44
When decarburizing cold-rolled steel strips for grain-oriented silicon steel containing OJOmm thickness at four levels of weight percent in a vertical continuous annealing furnace while repeating up and down turns with hearth rolls,
The temperature was maintained at 600° C. for 1 minute while the temperature was rising while recrystallization progressed, and the diameter of the hearth roll was varied at this time, followed by decarburization annealing at 800° C. for 3 ml. 600℃
The diameter DA of all hearth rolls other than those used for holding is 8.
00 mm.

Figure 3 shows the magnetic flux density (B,...
) (7) Hearth roll diameter 0. In order to see the tendency of deterioration due to the decrease of
i, a difference of 810 was shown for each amount of Si. The deterioration degree of B1° is expressed in consideration of the difference in saturation magnetic flux density depending on the amount of Si.

As seen in Figure 3, as the amount of Si increases, Lo
The critical roll diameter that indicates deterioration tends to become smaller, and Lo
0. The shaded area is given as a condition to prevent deterioration beyond OIT.

FIG. 4 shows how the relationship between /%-throttle diameter and electromagnetic properties during the temperature rising process changes depending on the steel plate thickness. Contains 3.20% Si, thickness 0.1? ,
When a 0.23.0.30.0.35 mm grain-oriented cold-rolled steel strip for silicon steel is decarburized and annealed in a vertical annealing furnace by repeatedly turning and turning up and down using hearth rolls, The temperature was held at 600 °C for 1 minute while the temperature was rising while crystallization progressed, and the diameter of the hearth roll at this time was varied.
Subsequently, decarburization annealing was performed at 800° C. for 3 ml.

Diameter DA of hearth rolls other than those used to maintain 600 °C
were all 800 mm. As seen in FIG. 4, the thinner the plate thickness, the smaller the hearth roll diameter at which the magnetic flux density becomes worse, and the B of 1.90 or more. The shaded area is required as a condition that is satisfied.

These magnetic deteriorations that occur when the hearth roll diameter is small are determined to be due to the development of the Goss orientation being impaired by the strain applied to the surface layer of the steel sheet during heating. The diameter is S
It is obtained as a function of i amount, plate temperature, and plate thickness as shown in the following equation.

0, ≧[6X102-1. I X102Si +1
．． 4T) xdThe material to which this invention is applied is Si1.
It is a silicon steel containing O~4.0%. The reason why the upper limit of Si is 4.0% is determined from the viewpoint of workability, and is because if Si is less than 1%, the influence of the hearth roll diameter on the formation of Goss orientation will not be a problem.

In the case of grain-oriented silicon steel, in addition to 81, elements such as S, Se, AR, B, Sb, and Bi, which are known as inhibitors, are present in the range of 0.002 to 0. Approximately 10% is included as necessary.

Also, in non-oriented silicon steel, Aj! , Mn is 0
．． It is contained in the range of 0.010 to 3%.

Silicon steel slabs containing these components are hot-rolled using a known method to form a hot-rolled steel strip with a thickness of 1.4 to 3.0 ml, and then cold-rolled once or twice with an intermediate annealing in between. , finished into a cold-rolled steel plate with a thickness of 15 to 0.60 mm.

After this, in non-oriented silicon steel, final annealing is performed for the purpose of recrystallization and decarburization if necessary, and in grain-oriented silicon steel, decarburization annealing is performed. The reason for this is that these annealing operations can be carried out efficiently using a vertical continuous annealing furnace without impairing the magnetism.

(Function) As stated in the introduction, it is important to develop the Goss orientation to some extent not only in grain-oriented silicon steel but also in non-grained silicon steel in order to improve the magnetic properties of the final product. For this purpose, it is important not to apply tension above a certain level in a vertical continuous annealing furnace, especially near the surface of the steel sheet where Goss orientation is likely to develop.

The regulation of the diameter of the hearth roll in this invention is due to the problem peculiar to silicon steel related to the development of Goss orientation, and since the annealing temperature range is generally 760 to 950 °C, Diameter opening to plate thickness d
In contrast, it was determined that ≧1.6 XIO'd.

In addition, in the temperature range of 500 to 750 °C during heating in which primary recrystallized grains with Goss orientation are formed, the diameter Dimm of the hex roll in this temperature range is equal to the plate thickness da +
m, Si (%), plate temperature T (t')
6XlO"-1, IX102Si +1.47)
It is necessary to satisfy the condition xd.

The tension applied to the silicon steel cold-rolled steel strip is particularly large at the turning rolls, so the roll diameter is regulated as described above, but the tension of the steel strip before and after entering the vertical furnace is also within the normal range. Line tension 1.0kg/mn+' or less,
Desirably, 0.2 to 0.6 kg/mm2 is appropriate.

The grain-oriented silicon steel cold-rolled steel strip decarburized and annealed in this way is then coated with an annealing separator such as MgO, subjected to high-temperature box annealing for secondary recrystallization and purification, and then top coated. Needless to say, coating is applied to achieve a finish of up to 1% of the product.

(Example) Example I C0,050%, Si 3JO%, Mn 0.080%
A grain-oriented silicon steel slab containing 1025% of SbO, 5eO and 30% of SbO was hot-rolled into a hot-rolled sheet of 2.5 mm thickness, and then first cold-rolled to 75% to 0.0.
The intermediate thickness was 63 mm, and after intermediate annealing at 1000° C. and 1 ml, the product was rolled between two methods to give a product thickness of 0.23 mm.

After that, 800 tons of decarburization annealing was performed using a vertical continuous annealing furnace.
5m1n, when conducting in a wet hydrogen atmosphere with a dew point of 50°C, the diameter of the hearth roll in the heating zone where the steel plate temperature is 500 to 750°C is DR1. Annealing was performed with the changes shown in Table 1. Decarburization annealing The steel plate coated with MgO as a separator was subjected to high-temperature box annealing at 1200°C for 5 hours in hydrogen, including secondary recrystallization retention treatment at 840°C for 30 hours, and then tension coated to obtain the final product. Ta.

The magnetic properties of the final product are shown in Table 1, and those that satisfied the conditions of this invention showed excellent magnetic properties.

Table 1 C0,003%, Si 3.02%, Aj'0.4%,
2. A non-oriented silicon steel slab containing 0.15% Mn was hot rolled. Hot-rolled plate with Om+n thickness, 900
°C, 5m1n no/L,? After the treatment, the product plate was cold rolled once to give a product thickness of 0.50+nm.

Then, recrystallization annealing was performed using a vertical continuous annealing furnace at 920°C.
℃ for 5 ml of dry water, OR the /'%-throll diameter of the heating zone when the steel plate temperature is between 500 and 750 ℃, and the second half of the heating zone and the soaking zone when the steel plate temperature is 750 ℃ or higher. The magnetic properties of the final product obtained by annealing with the nozzle roll diameter DA changed as shown in Table 2 and then applying an insulating coating to the surface are shown in Table 2, which satisfies the conditions of this invention. It showed excellent magnetic properties.

(Effects of the Invention) According to the first invention, silicon steel sheets do not lose product magnetism due to plastic deformation due to bending along the nozzle roll in a vertical continuous annealing furnace due to hot strength at high temperatures. In addition, in the second invention, the continuous annealing furnace described above has the advantage that the magnetism deteriorates due to excessive tension during the temperature rising process, which results in the formation and growth of primary recrystallized grains including Goss-oriented crystal grains. It becomes possible to realize the annealing treatment for decarburization or recrystallization at extremely high production efficiency.

[Brief explanation of drawings]

Figure 1 shows the hearth roll diameter DA (mm) and steel plate thickness d when grain-oriented silicon steel plate is decarburized and annealed in a vertical continuous annealing furnace.
The magnetic flux density B of the final product varies with the change in the ratio D/d of mm.
, Q (T). Figure 2 shows the hearth roll diameter when the steel plate temperature is 500 to 700 °C during the temperature increase process when decarburizing a grain-oriented silicon steel plate in a vertical piece continuous annealing furnace. DII (mm) and magnetic flux density B of the final product
, 0 (T), and FIG. 3 is a diagram showing a vertical continuous annealing furnace for grain-oriented silicon steel sheets. l 2 3 4 DA/d (XlO 1 degree (t) S, (%) Fig. 4015 0.20 0.25 0.30
0.35R thickness d9n)

Claims (1)

[Claims] 1.0.15 to 0.6 mm containing 1 to 4% by weight of Si
A thick cold-rolled silicon steel strip is passed through a vertical continuous annealing furnace in which it is repeatedly turned up and down with hearth rolls in a reducing gas atmosphere at a temperature of 760 to 950°C for decarburization or re-rolling. A method for annealing a silicon steel strip using a vertical continuous annealing furnace, which is characterized in that during crystal annealing, a hearth roll that satisfies the following formula depending on the thickness of the silicon steel cold rolled steel strip is used. D_A≧1.6×10^3・d D_A: Hearth roll diameter (mm) d: Thickness of silicon steel cold-rolled steel strip (mm) 2. Contains 1 to 4% by weight of Si, 0.15 ~0.6mm
A thick cold-rolled silicon steel strip is passed through a vertical continuous annealing furnace in which it is repeatedly turned up and down with hearth rolls in a reducing gas atmosphere at a temperature of 760 to 950°C for decarburization or re-rolling. During crystal annealing, a hearth roll that satisfies the following formula (1) according to the thickness of the silicon steel cold-rolled steel strip is used, and during the temperature raising process prior to threading, in the temperature range of 500 to 750 ° C. , characterized by using a hearth roll that satisfies the relationship of the following formula (2) depending on the Si amount, thickness and temperature of the silicon steel cold rolled steel strip,
Method for annealing silicon steel strip in a vertical continuous annealing furnace
6×10^2-1.1×10^2 [Si]+1.4・T
) × d---(2) D_A: Diameter of hearth roll in 760-950°C range (mm) D_R: Diameter of hearth roll in 500-750°C range (mm) d: Thickness of silicon steel cold-rolled steel strip (mm) [Si ]: Silicon content (weight%) T: Silicon steel cold-rolled steel strip temperature (°C)