KR20040051793A - Method for Manufacturing Steel Sheet for Brushing of Hearth Roll and Method for Brushing Hearth Roll - Google Patents

Abstract

PURPOSE: A method is provided which manufactures strip for brushing hearth rolls to remove foreign materials adhered to the surface of the hearth rolls of high temperature annealing furnace used when manufacturing grain-oriented magnetic strip, and a method for brushing the hearth rolls using the strip for brushing the hearth rolls is provided. CONSTITUTION: The manufacturing method of strip for brushing hearth rolls comprises the process of nitriding a cold rolled strip for manufacturing grain-oriented magnetic strip comprising 0.04 to 0.07 wt.% of C, 2.5 to 4.0 wt.% of Si, 0.5 to 0.25 wt.% of Mn, 0.03 wt.% or less of P, 0.02 wt.% or less of S, 0.1 wt.% or less of Al, 0.01 wt.% or less of N and a balance of Fe and other inevitably contained impurities at a dew-point temperature of 53 to 70 deg.C and nitriding temperature of 800 to 900 deg.C for 1 to 5 minutes as injecting ammonia gas into an atmosphere during high temperature annealing of the grain-oriented magnetic strip in a flow rate of 2.00 to 5.5 Nm¬3/hr. In a method for brushing the surface of the hearth rolls(6) using frictional force between the strip for brushing the hearth rolls and the hearth rolls by connecting a strip(7) for brushing hearth rolls to grain-oriented magnetic strip annealed at high temperature in an annealing furnace including hearth rolls, thereby moving the strip for brushing the hearth rolls in the state that the strip for brushing the hearth rolls is contacted with the surface of the hearth rolls by rotation of the hearth rolls, the brushing method of the hearth rolls comprises the process of brushing the surface of the hearth rolls for 5 to 10 minutes by using the strip for brushing the hearth rolls and rotating the hearth rolls to a rotation speed of 10 to 20 m/min in a rotation direction opposite to a proceeding direction of the strip.

Description

Method for manufacturing steel sheet for brushing of hearth roll and method for brushing hearth roll}

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for iron cores of electrical equipment such as small transformer cores and ballasts, and more particularly, attached to the surface of the hearth roll of a high-temperature annealing furnace used in the manufacture of the grain-oriented electrical steel sheet. It relates to a method for producing a steel sheet for brushing to remove foreign matters and a method for brushing the hearth roll surface using the brushed steel sheet.

In general, directional electrical steel sheets used as iron cores of electric devices such as small transformer cores and ballasts are subjected to insulation coating after glass coating is removed to improve the punchability.

On the other hand, one of the important characteristics of oriented electrical steel sheet is the low iron loss.

Iron loss of electrical steel is composed of vortex loss and hysteresis loss. Therefore, to reduce iron loss, vortex loss and hysteresis loss must be reduced.

As a method of reducing the eddy current loss, a method of increasing Si and Al for increasing the specific resistance and a method of reducing the thickness can be given.

In addition, in all the directional electrical steel sheet to the base coating (base coating) to ensure the interlayer insulation and the insulating coating on it, the double base coating is a thin glass film on the surface of the steel sheet greatly contributes to securing the insulation.

In addition, in order to reduce hysteresis loss, a method of greatly increasing grain size, which is a material characteristic of a steel sheet, or improving cleanliness is used.

On the other hand, the manufacturing process of the grain-oriented electrical steel sheet requires a high temperature annealing process.

During the high temperature annealing of the electrical steel sheet, foreign matters are attached to the hearth roll surface of the annealing furnace such that surface contamination occurs.

As described above, when the hearth roll surface portion is contaminated, a convex foreign matter mark or the like is generated on the steel sheet which is processed under high temperature conditions.

If convex foreign matter marks such as above occurs on the steel sheet, a space portion is formed during the insulation coating applied to ensure insulation, and the adhesion of the coating solution is reduced, thereby preliminary annealing for stress relief and the insulation coating layer is easily removed when the core is punched out. It is difficult to achieve insulation and prevent eddy current loss due to peeling, and a plurality of laminates are formed by punching electrical steel sheets in the form of cores, resulting in a drop in eddy current loss due to a noticeable drop in space ratio (adhesion between cores).

Therefore, in order to solve the above-mentioned problem, as shown in FIG. 1, the brushed steel sheet 7 connected to the rear of the steel sheet is introduced into the high temperature annealing furnace 9 to be mounted in the high temperature annealing furnace 9 after the online stop. The steel sheet for brushing 7 which rotates the rotation direction of the roll 6 for 30-40 minutes at the low speed of 20-30mpm in a positive direction (same direction as the traveling direction of a steel plate), and is in contact with the surface part of the hearth roll 6 The foreign matter 8 attached to the surface of the hearth roll is separated and removed from the surface of the hearth roll by contact friction with

In Fig. 1, reference numeral 1 denotes a "variable motor", reference numerals 2 and 3 denote a "rotating force transmission chain", reference numeral 4 denotes a "drive side sprocket wheel", and reference numeral 5 denotes a "hurdle roll side sprocket wheel". Indicates.

As described above, in the case of the brushing steel sheet used to remove the foreign matter adhering to the surface of the hearth roll of the high temperature annealing furnace, it is repeatedly used at high temperature due to the characteristics of use, so that the softening of the material is easily generated and used again as the brushing steel sheet. It is difficult to control the tension in the annealing furnace at the time, so it is easily stretched during the brushing operation, and there are problems such as breaking of the plate in the annealing furnace and early scrap processing.

The present invention is to perform the research and experiment to solve the above problems of the prior art, based on the results of the present invention, the present invention is a nitriding treatment on the surface of the steel sheet for brushing in the high temperature annealing furnace surface It is to provide a steel sheet for brushing that is suppressed premature soft nitriding by strengthening, there is an object.

In addition, another object of the present invention is to provide a brushing method capable of removing foreign matter adhering to the surface of the hearth roll more efficiently in a shorter time.

1 is a schematic view showing a process of hot annealing a grain-oriented electrical steel sheet in a horizontal high temperature annealing furnace

Figure 2 is a schematic diagram showing a foreign matter removal process of the hearth surface surface in accordance with the present invention

Explanation of symbols on the main parts of the drawings

One . . Variable motors 2,3. . Chain for torque transmission 4. . Follower sprocket wheel 5. . Hearth roll side sprocket wheel 6. . Hearth roll

7. . Brushed Steel Sheet 8. . . Foreign object 9. . . Horizontal High Temperature Annealing Furnace

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, by weight%, C: 0.04 to 0.07%, Si: 2.5 to 4.0%, Mn: 0.5 to 0.25%, P: 0.03% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.01% or less, the balance, 53-70, while Fe and other unavoidable ammonia gas injected at a flow rate of 2.00~5.5 Nm ³ / hr-containing grain-oriented electrical steel sheet cold-rolled steel sheet for making a composition which impurities to atmosphere during high temperature annealing of the grain-oriented electrical steel sheet It relates to a method for producing a brushed steel sheet by nitriding for 1 to 5 minutes at a dew point temperature of ℃ and nitriding treatment temperature of 800 ~ 900 ℃.

In addition, the present invention by connecting the brushed steel sheet to the directional electrical steel sheet hot-annealed in the annealing furnace including the hearth roll to move the brushed steel sheet in contact with the surface of the hearth roll by the rotation of the hearth roll for brushing In the method of brushing the hearth roll surface by the friction between the steel plate and the hearth roll,

Using a brushed steel sheet manufactured according to the present invention as the brushed steel sheet; And a method of brushing the surface of the hearth roll for 5 to 10 minutes with the rotational speed of the hearth roll being 10 to 20 mpm and the rotational direction being the reverse direction of the steel sheet.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, by weight%, C: 0.04 to 0.07%, Si: 2.5 to 4.0%, Mn: 0.5 to 0.25%, P: 0.03% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.01% Hereinafter, the cold rolled steel sheet for producing a grain-oriented electrical steel sheet composed of the balance Fe and other unavoidable impurities is used as a starting material, and the cold rolled steel sheet has the same composition as that of the grain-oriented electrical steel sheet to which the present invention is applied.

In order to carry out nitriding treatment according to the present invention, ammonia gas should be injected at a flow rate of 2.00 to 5.5 Nm ³ / hr into the atmosphere at the time of high temperature annealing of a conventional grain-oriented electrical steel sheet.

When the input amount of the ammonia gas is less than 2.0 Nm ³ / hr, since the amount of active nitrogen decomposed from the ammonia gas is small, it is difficult to form a nitride layer having a sufficient thickness on the surface of the brushed steel sheet, and when it exceeds 5.5 Nm ³ / hr, This is because a too thick nitride layer is formed on the surface of the steel sheet for brushing so that the steel sheet can be easily broken.

In the present invention, while injecting ammonia gas into the atmosphere at the time of high temperature annealing of the grain-oriented electrical steel sheet, the nitriding treatment is performed at a dew point temperature of 53 to 70 ° C. and a nitriding treatment temperature of 800 to 900 ° C. for 1 to 5 minutes.

In the present invention, the nitriding treatment temperature is limited to 800 to 900 ° C. The reason is that when the nitriding treatment temperature is less than 800 ° C, sufficient nitriding does not occur and sufficient surface hardening cannot be obtained. It is coarse and the material is too soft.

In the present invention, the reason why the nitriding treatment time is limited to 1 to 5 minutes is that when the nitriding treatment time is less than 1 minute, the dense oxide layer on the surface of the steel sheet prevents the activated nitrogen from penetrating into the surface of the steel sheet, thereby providing sufficient nitriding. If it is difficult to form a layer and exceeds 5 minutes, a thick and coarse oxide layer composed mainly of FeO, which is a Fe oxide generated at high temperature, is formed on the surface of the steel sheet, and active nitrogen easily diffuses into the steel sheet, that is, the ammonia decomposition reaction takes place very actively. This thick and excessive nitriding occurs.

In addition, in the present invention, the dew point temperature is limited to 53 to 70 DEG C. The reason is that below 53 DEG C, the formation of the glass film formed on the surface of the steel sheet is suppressed and the oxide layer is thin. This is because the excessive formation of the oxide layer is so great that the glass film is too thick to be peeled off from the surface of the steel sheet during the brushing operation and thus to contaminate the hearth surface.

Hereinafter, the hearth roll brushing method of the present invention will be described.

In the hearth roll brushing method of the present invention, a brushed steel sheet is connected to a oriented electrical steel sheet annealed at a high temperature in an annealing furnace including a hearth roll to move the brushed steel sheet in contact with the surface of the hearth roll by rotation of the hearth roll. It is applied to the method of brushing the surface of the hearth roll by the frictional force between the steel sheet for brushing and the hearth roll.

In the present invention, a brushed steel sheet subjected to nitriding treatment according to the present invention is used.

When brushing the hearth roll using a brushed steel sheet subjected to nitriding according to the present invention, the rotational speed of the hearth roll is 10 to 20 mpm, and the rotational direction thereof is in the opposite direction to the traveling direction of the steel sheet.

The reason for limiting the rotational speed of the hearth roll to 10 to 20 mpm as described above is that when the rotational speed is less than 10 mpm, the frictional force with the brushed steel sheet is reduced and foreign matters on the surface of the hearth roll are impossible to remove. If it exceeds 20 mpm, the friction force between the hearth roll surface and the brushed steel sheet is excessively generated, which causes premature damage to the glass film and the nitride layer on the steel sheet surface, thereby facilitating soft nitriding and causing plate breakage during the brushing operation.

In addition, the reason for limiting the direction of rotation of the hearth roll to the reverse direction of the traveling direction of the steel sheet is to rotate in a direction opposite to the direction of the foreign matter formed on the hearth roll surface so that the foreign matter is easily separated from the hearth roll surface. This is because when the brushing operation is performed with the rotational direction in the same direction, foreign matter removal may not occur sufficiently.

In the present invention, when brushing the surface of the hearth roll, the brushing time is limited to 5 to 10 minutes. The reason for this is that when the brushing time is less than 5 minutes, foreign matters on the surface of the hearth roll do not completely fall and remain. This is because the friction between the roll surface and the brushing coil causes a problem that the glass film and the nitride layer of the steel sheet surface are peeled off and reattached to the hearth roll surface again.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

By weight%, C: 0.04 to 0.07%, Si: 2.5 to 4.0%, Mn: 0.5 to 0.25%, P: 0.03% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.01% or less, remainder The silicon steel slab composed of Fe and other unavoidable impurities is reheated to a temperature below 1,170 ~ 1,200 ℃, hot rolled, wound up at 560 ~ 640 ℃, and hot rolled at 1,000 ~ 1,150 ℃. After pickling, cold rolling was performed once with a thickness of 0.65 to 0.7 mm, and then ammonia gas was injected into the atmosphere gas consisting of H ₂ : 15-20% and N ₂ : 75-80% as shown in Table 1 below. Nitriding was carried out under the conditions of nitriding treatment temperature, nitriding treatment time and dew point temperature as shown in Table 1 to prepare a steel sheet for brushing, and then the surface roughness, thickness change degree and brushing repeatability after brushing were investigated. Shown in

Psalm No. Ammonia injection volume (Nm ³ / hr) Nitriding temperature (℃) Nitriding Treatment Time Dew point (℃) Steel plate surface roughness after brushing Thickness change Brushing Repeatability Comparative material 1 0.5 650 24 sec 20 × × × Comparative material 2 1.0 700 36 seconds 30 × × × Comparative material 3 1.5 750 48 seconds 40 △ × △ Invention 1 2.0 800 1 minute 30 seconds 53 ○ ○ ○ Invention Material 2 4.0 850 3 minutes 60 ○ ○ ○ Invention 3 5.5 900 4 minutes 70 ○ ○ ○ Comparative material 4 6.0 950 6 minutes 80 × × × Comparative material 5 7.0 1000 7 minutes 90 × × × Legend ○: Passed, △: Normal X: Failed

In Table 1, the surface roughness of the steel sheet after brushing is very rough when the surface of the steel sheet is touched four times after brushing. If the roughness is very weak, it was classified as pass (○).

In addition, in Table 1, the degree of change in thickness is reduced to 0.005 to 0.01 mm compared to the thickness of the initial brushing steel sheet (0.65 to 0.7 mm), with no corrugated load as pass (○), and thickness (0.65 to 0.7 mm). If the corrugation is visible while decreasing to 0.01 ~ 0.03mm compared with the standard, it was divided into normal (△) and failed (×) when the corrugated plate could be identified while decreasing to 0.03 ~ 0.07mm from the thickness (0.65 ~ 0.7mm).

In addition, the brushing repeatability in Table 1 is the brushing operationofRepeat 8 times if there is no material softening or width change It was set as pass ((circle)), and it classified into normal ((triangle | delta)) when width change was 5-20 mm, and rejected (x) when width change was 20-40 mm.

As shown in Table 1, in the case of brushed steel sheet nitrided under the conditions of the present invention (Inventive material 1-3), the steel sheet surface roughness, thickness after brushing than the comparative material (1-5) outside the scope of the present invention The degree of change and brushing repeatability are all excellent.

(Example 2)

Using the invention material 2 of Example 1 as a steel sheet for brushing and brushing under the same conditions as in Table 2, the degree of foreign matter mark generation (touch), the presence of the hearth roll contamination (visual) and whether the product surface foreign matter mark generation It investigated and the results are shown in Table 2 below.

In the following Table 2, the degree of foreign material mark is determined after the brushing operation by inserting a separate foreign material check strip into the annealing furnace and idling the hearth roll for about 10 seconds to determine the degree of absorption generated in the strip. There was no pass (○) and no touch, but it was classified as normal (△) if severe scratches were observed with the naked eye, and failed (×) if touch and scratches were found.

In addition, in the following Table 2, the presence or absence of contaminated hearth rolls are visually confirmed by the naked eye, and if there is no foreign matter, pass (○), visually undiscovered but normal (△), and if foreign matters are classified as fail (×). It was.

In addition, in the following Table 2, the product surface foreign matter mark generation is raised to the temperature of the annealing condition, if the foreign material mark is not generated in the product passed through the product strip into the annealing furnace passed (○), there is a foreign material mark trace If there is no touch, it is classified as normal (△), and when a foreign material mark occurs, it fails (x).

Example No. Brushing time (minutes) Hearth roll speed (mpm) Hearth roll rotation direction Measurement result Foreign matter mark occurrence (touch) Hearth roll contamination (visual) Foreign mark on product surface Comparative Example 1 One 2 Forward direction × × × Comparative Example 2 3 5 Forward direction × × △ Inventive Example 1 5 10 Reverse ○ ○ ○ Inventive Example 2 10 20 Reverse ○ ○ ○ Comparative Example 3 15 25 Forward direction △ × △ Comparative Example 4 20 30 Forward direction × × × Legend ○: Passed, △: Normal, ×: Failed

As shown in Table 2, the invention examples (1 and 2) in accordance with the scope of the present invention compared to the comparative example (1-4) outside the scope of the present invention foreign matter mark occurrence degree, the presence of hearth roll contamination, and the product surface It can be seen that the foreign matter mark is excellent.

As described above, according to the present invention, the surface of the brushed steel sheet is nitrided to suppress premature soft nitriding of the brushed steel sheet (reduced strength of the tissue generated during repeated use), thereby extending the number of times of the brushed steel sheet to reduce raw units. It is also possible to remove foreign matters on the surface of the hearth roll in a short time.

Claims (2)

By weight%, C: 0.04 to 0.07%, Si: 2.5 to 4.0%, Mn: 0.5 to 0.25%, P: 0.03% or less, S: 0.02% or less, Al: 0.1% or less, N: 0.01% or less, remainder Dew point of 53-70 ° C., while injecting a cold rolled steel sheet for the production of grain-oriented electrical steel sheet composed of Fe and other unavoidable impurities into the atmosphere during the high temperature annealing of the grain-oriented electrical steel sheet at a flow rate of 2.00 to 5.5 Nm ³ / hr. Method for producing a steel roll brushing brush for nitrosing for 1 to 5 minutes at a temperature and a nitriding temperature of 800 to 900 ° C The brushed steel sheet is connected to the oriented electrical steel sheet subjected to high temperature annealing in the annealing furnace including the hearth roll to move the brushed steel sheet in contact with the surface of the hearth roll by the rotation of the hearth roll, In the method of brushing the hearth roll surface by the frictional force of, Using the brushed steel sheet manufactured according to claim 1 as the brushed steel sheet; And the hearth roll brushing method for brushing the surface of the hearth roll for 5 to 10 minutes with the rotational speed of the hearth roll being 10 to 20 mpm, and the rotational direction being the reverse direction of the steel sheet.