JP2000096150A - Continuous heat treatment method for steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous heat treatment method for a steel strip capable of preventing the pickup which arises at the hearth rolls in the inlet of a cooling furnace. SOLUTION: When heat treating the steel strip 1 in a heat treatment furnace having a heating furnace 3, a soaking furnace 4 and the cooling furnace 5, the steel strip 1 is heat treated by setting the surface temperature of the hearth rolls 6b in the inlet of the cooling furnace 5 or the rolls from the hearth rolls 6a in the outlet of the heating furnace 4 to the hearth rolls 6b in the inlet of the cooling furnace 5 at >=600 deg.C or <=450 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hearth roll in a furnace for a continuous heat treatment furnace for a steel strip, particularly a hearth roll at the inlet of a cooling furnace, or a hearth roll at an outlet of a soaking furnace to a hearth roll at an inlet of a cooling furnace. The present invention relates to a method for preventing occurrence of roll pick-up during this time.

[0002]

2. Description of the Related Art A continuous heat treatment furnace for performing heat treatment by passing a steel strip at a predetermined line speed usually includes an open flame heating furnace, a reduction heating furnace, a soaking furnace, and a cooling furnace. Heat treatment is performed by sequentially passing through each furnace. A hearth roll for guiding and conveying the steel strip is provided in each of the furnaces.

When the steel strip is heated in the heat treatment process, an oxide film is formed on the surface of the steel strip, and this oxide film is transferred and grown on the hearth roll, and serves as a pick-up, thereby causing a flaw on the surface of the steel strip. .

[0004] As a measure to prevent the occurrence of pickup, it is common to apply a thermal spray treatment to the surface of the hearth roll. Also, Japanese Patent Application Laid-Open No. Sho 53-130221, Japanese Patent Publication No. Sho 58-3
JP-A-9939 and JP-A-60-141834 propose that a roll chamber for accommodating a hearth roll is formed to prevent occurrence of pickup.

[0005]

However, the above prior art has the following problems.

[0006] In the thermal spraying treatment on the surface of the hearth roll, the occurrence of pickup cannot be completely prevented due to the deterioration of the thermal spray material and the inappropriate thermal spray material.

[0007] Pickup is generated not only at the hearth roll at the outlet of the direct heating furnace to the inlet of the reduction heating furnace, but also at the hearth roll at the entrance of the cooling furnace. JP-A-53-130211
Gazette, Japanese Patent Publication No. Sho 58-30939,
Japanese Patent Application Laid-Open No. 141834 mainly aims to prevent the occurrence of pickup in the hearth roll from the outlet of the direct heating furnace to the entrance of the reduction heating furnace, and the present invention aims to pick up the hearth roll at the entrance of the cooling furnace. No consideration is given to preventing the generation of the hearth, and the provision of the roll chamber that accommodates the hearth roll at the entrance of the cooling furnace cannot prevent the occurrence of the pickup of the hearth roll at the entrance of the cooling furnace.

That is, in the above-mentioned prior art, no effective means has been found yet which can prevent pickup occurring at the hearth roll at the inlet of the cooling furnace.

The present invention has been made in view of the above circumstances, and has as its object to provide a continuous heat treatment method for a steel strip which can prevent pickup occurring at a hearth roll at the entrance of a cooling furnace.

[0010]

Means of the present invention for solving the above problems are as follows.

(1) When heat-treating a steel strip in a heat treatment furnace including a heating furnace, a soaking furnace, and a cooling furnace, a hearth roll at the inlet of the cooling furnace or a hearth roll at the outlet of the soaking furnace is used to enter the cooling furnace. A continuous heat treatment of the steel strip, wherein the surface temperature of the roll is set to 600 ° C. or more or 450 ° C. or less until the hearth roll.

(2) In the above (1), a partition wall is provided on an outlet side of a communicating portion between the soaking furnace and the cooling furnace to form a roll chamber for accommodating a hearth roll at an inlet of the cooling furnace, and the hearth roll is formed. And heat treating the steel strip while isolating the steel strip from the atmosphere gas on the cooling furnace side.

(3) In the above (2), further, a partition wall is provided on an entrance side of a communicating portion between the soaking furnace and the cooling furnace, and a roll chamber for accommodating a hearth roll at an outlet of the soaking furnace is formed. A continuous heat treatment method for a steel strip, wherein the heat treatment is performed by isolating the roll from an atmosphere gas of a soaking furnace.

(4) In the above (2) or (3), a means for measuring the temperature of the hearth roll at the inlet of the cooling furnace and a means for adjusting the ambient temperature of the roll chamber for accommodating the hearth roll are provided. The surface temperature of the hearth roll at the inlet of the cooling furnace detected by the means is 600 ° C. or more or 450 ° C.
A continuous heat treatment method for a steel strip, wherein the temperature of the roll chamber is adjusted using an atmosphere temperature adjusting means of the roll chamber so as to be equal to or lower than 0 ° C.

(5) The continuous heat treatment method for a steel strip according to the above (1) to (4), wherein the roll surface roughness of the hearth roll is Ra 1.0 μm or more.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the operation of the present invention and the reasons for limitation will be described.

[0017] Pickup is likely to occur on the roll between the hearth roll at the outlet of the soaking furnace and the hearth roll at the inlet of the cooling furnace, particularly the hearth roll at the inlet of the cooling furnace. appear. The present inventors have studied various causes of the occurrence of the pickup and measures for preventing the pickup. As a result, the main component of the pickup generated in the roll is a sintered body of a composite oxide of Si (silicon), Al (aluminum), and Mn (manganese),
It was found that by setting the surface temperature of the roll at 600 ° C. or higher or 450 ° C. or lower, the occurrence of pickup could be reduced.

It is considered that the occurrence of pickup can be significantly reduced by defining the mechanism of occurrence of pickup in the roll and the surface temperature of the roll as described above for the following reasons.

During the heat treatment of the steel strip, the steel strip is heated to a temperature of about 800 ° C. at the outlet of the soaking furnace, and is cooled to 45 ° C. in the cooling furnace.
It is cooled to a temperature of about 0 ° C. In the heat treatment process, the steel strip surface is oxidized when passing through a direct-fired heating furnace to form an oxide,
This oxide remains after passing through the reduction heating furnace. Especially silicon
Since aluminum oxide is not easily reduced, it tends to remain on the steel strip surface even after reduction heating, as shown in FIG. The steel strip contacts the hearth roll located at the inlet of the cooling furnace from the outlet of the soaking furnace with the oxide remaining.

Since the hearth roll at the inlet of the cooling furnace is directly cooled by the cooling gas of the cooling furnace, its surface temperature is 5 ° C.
It is about 00 ° C. Therefore, when the steel strip comes into contact with the hearth roll arranged at the inlet of the cooling furnace, as shown in FIG. 2, the difference between the steel strip and the hearth roll surface temperature increases,
Large heat shrinkage occurs in the steel strip, and as shown in FIG. 1 (b), the oxide on the surface of the steel strip is transferred to the roll surface to become a pickup.

Further, silicon, aluminum and the like contained in the steel strip are easily oxidized at around 500 ° C. Since the surface temperature of the hearth roll at the inlet of the cooling furnace is about 500 ° C. and silicon and aluminum are easily oxidized, the growth of the pickup is promoted, and the grown pickup causes an indentation on the steel strip.

Further, a roll provided from the outlet of the soaking furnace such as a hearth roll at the outlet of the soaking furnace to the inlet of the cooling furnace flows toward the soaking furnace through a communicating portion between the soaking furnace and the cooling furnace. Because it is affected by the low-temperature atmosphere gas of the cooling furnace, the temperature tends to be low, though not as much as the hearth roll at the entrance of the cooling furnace.
Therefore, pickup is likely to occur on the roll surface by the same mechanism as the hearth roll at the entrance of the cooling furnace.

By defining the roll surface temperature at 600 ° C. or higher, the temperature difference between the sheet temperature and the roll surface temperature is reduced, and the heat contraction of the steel strip is reduced. As a result, the oxide on the surface of the steel strip is less likely to be transferred to the roll, the occurrence of pick-up can be reduced, and the steel strip does not suffer from dents.

By setting the surface temperature of the roll to 450 ° C. or lower, the temperature range is such that oxides are hardly formed, so that the pickup does not grow on the roll surface.

When the steel strip meanders or slips, the oxide on the steel strip surface is easily transferred to the roll surface. By regulating the surface roughness of the hearth roll to Ra 1.0 μm or more, the meandering and slipping of the steel strip can be prevented, and the effect of preventing the occurrence of pickup is further improved.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a view showing a main part of a heat treatment furnace including a heating furnace 3 including an open flame heating furnace (not shown) and a reduction heating furnace 2, a soaking furnace 4, and a cooling furnace 5. FIG.
In the heat treatment furnace of FIG. 3, a partition wall 12b is provided on the exit side of the communicating part 11 between the soaking furnace 4 and the cooling furnace 5, and a roll chamber 13b for accommodating the hearth roll 6b at the entrance of the cooling furnace 5 is formed. Device. In FIG. 4, 14b is the roll chamber 13
temperature adjusting device for adjusting the ambient temperature in b, 15
b is a thermometer for detecting the surface temperature of the hearth roll 6b, 1
6 is a cooling furnace for blowing a cooled atmosphere gas onto the steel strip 1
Cooling device.

The partition wall 12b accommodates a heat insulating material inside,
Each of the members or the members described above is composed of a plurality of box-structured members manufactured by molding a metal plate such as a US, etc., in order to efficiently shut off the atmosphere gas in the furnace on the cooling furnace 5 side of the roll chamber 13b. The space between the furnace walls of the cooling furnace 5 is sealed with a heat insulating seal material. Also, at least one of the members of the partition wall 12b is openable and closable so that an operator can enter the furnace during operations such as hearth roll inspection and steel strip breaking processing.

In FIG. 3, a steel strip 1 includes a heating furnace 3, which includes an open flame heating furnace (not shown) and a reduction heating furnace 2, a soaking furnace 4, and a cooling furnace 5, each of which has a hearth arranged in each of the furnaces. Roll 6
And subjected to a required heat treatment. At this time, in the apparatus shown in FIG.
3b, and adjust the surface temperature of the hearth roll 6b detected by the thermometer 15b to 600 ° C. or more or 45 ° C.
Keep below 0 ° C. Since the cooling gas of the cooling furnace 5 is shut off by the partition wall 12b, the temperature adjustment can be accurately performed. As a result, the occurrence of pickup of the hearth roll 6b can be prevented, and the occurrence of a flaw on the steel strip 1 can be prevented.

The surface roughness of the hearth roll 6b is Ra1.0.
When the thickness is at least μm, meandering and slippage of the steel strip 1 can be prevented, and the effect of preventing occurrence of pickup can be further improved.

FIG. 5 shows a soaking furnace 4 and a cooling furnace 5 of the apparatus shown in FIG.
A partition wall 12a is further provided on the entrance side of the communicating portion 11 of the roll chamber 1 for accommodating the hearth roll 6a at the outlet of the soaking furnace 4.
This is an apparatus in which 2a is formed. In the apparatus of FIG.
Is a hearth roll at the outlet of the soaking furnace 4, and 14a is a roll chamber 1.
3a, a temperature adjusting device for adjusting the ambient temperature in the
5a is a thermometer for detecting the surface temperature of the hearth roll 6a. The partition walls 12a and 12b correspond to the partition walls 12 of the apparatus shown in FIG.
This is the same configuration as b. In this case, it is desirable that the surface roughness of the hearth roll 6b be Ra 1.0 μm or more.

In the apparatus shown in FIG. 5, the temperature of the atmosphere in the roll chamber 13a is adjusted by the temperature adjusting device 14a.
The surface temperature of the hearth roll 6a detected at 5a is adjusted to a predetermined temperature defined in the present invention, and the temperature adjusting device 14
The surface temperature of the hearth roll 6b detected by the thermometer 15b is adjusted to the predetermined temperature specified in the present invention by adjusting the ambient temperature in the roll chamber 13b by b.

In the present apparatus, the hearth rolls 6a and 6b
Is separated from the high-temperature gas of the soaking furnace 4 and the cooling gas of the cooling furnace 5, the roll temperature can be adjusted to the temperature specified in the present invention, and the occurrence of pickup can be reliably prevented.

In the apparatus shown in FIGS. 3 to 5, the hearth roll 6a at the outlet of the soaking furnace 4 and the hearth roll 6b at the inlet of the cooling furnace 5 are arranged at a lower position of the heat treatment furnace. The remaining rolls are not provided in FIG.
As exemplified in (c), one or more rolls may be disposed between the two rolls in order to prevent meandering, slipping, etc. of the steel strip or to enhance the gas sealing effect in the communicating portion. Further, as illustrated in FIGS. 7A to 7C, these rolls may be arranged at an upper position of the heat treatment furnace. Further, it is desirable that the surface roughness of the roll disposed between the two rolls is Ra 1.0 μm or more.

[0034]

EXAMPLE In the case where the steel strip was heat-treated by setting the surface temperature of the hearth roll 6b to 600 ° C. or higher using the apparatus shown in FIGS. investigated.

The state of occurrence of indentation is evaluated by performing a grinding test on the steel strip after the heat treatment, observing the state of occurrence of indentation on the surface of the steel strip after the grinding test, and according to the degree, there are five stages from 1 to 5. Was evaluated. In the case of the score 1, there is no occurrence of nicks, and as the score increases, the occurrence of the nicks becomes remarkable. When the score reaches 5, it is necessary to insert a dummy coil or stop the line, etc., and to remove the rolls. .

FIG. 8 shows the results of the investigation. For comparison, FIG. 8 also shows the state of occurrence of a flaw in the case of the conventional example heat-treated under the same conditions as the example of the present invention except that a roll chamber for accommodating the hearth roll 6b was not provided.

In the example of the present invention, generation of an impression is not recognized. On the other hand, in the case of the conventional example, the number of heat treatment coils increased from the third to cause the pressing flaw due to the pick-up, and the degree became severe with the increase in the number of heat treatment coils. The score became 5 at the ninth heat coil, and roll maintenance was required.

In the example of the present invention, the temperature of the hearth roll 6b was set to 600 ° C. or higher. However, when the temperature of the roll was set to 450 ° C. or lower, similarly to the example of the present invention, the occurrence of pick-up was prevented, and the indentation was prevented. can do.

[0039]

As described above, according to the present invention, pick-up does not occur on the roll between the hearth roll at the outlet of the soaking furnace and the hearth roll at the inlet of the cooling furnace. Can be prevented and the quality of the steel sheet can be improved. In addition, since it is not necessary to stop the line for removing the roll pickup or to insert the dummy coil, productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a mechanism of occurrence of a pickup.

FIG. 2 is a view for explaining a state of heat shrinkage of a steel strip in a hearth roll at an inlet of a cooling furnace.

FIG. 3 is a diagram showing a main part of a heat treatment furnace including a heating furnace, a soaking furnace, and a cooling furnace.

FIG. 4 is a view of an apparatus in which a roll chamber for accommodating a hearth roll at the inlet of the cooling furnace is formed in the heat treatment furnace of FIG.

5 is a view of an apparatus in which a roll chamber for accommodating a hearth roll at the outlet of the soaking furnace and a roll chamber for accommodating the hearth roll at the inlet of the cooling furnace are formed in the heat treatment furnace of FIG.

FIG. 6 is a diagram showing an example of the arrangement of rolls between a hearth roll at an outlet of a soaking furnace and a hearth roll at an inlet of a cooling furnace.

FIG. 7 is a diagram showing another example of the arrangement of rolls between the hearth roll at the outlet of the soaking furnace and the hearth roll at the inlet of the cooling furnace.

FIG. 8 is a diagram showing the effect of the present invention.

[Explanation of symbols]

 Reference Signs List 1 steel strip 2 reduction heating furnace 3 heating furnace 4 soaking furnace 5 cooling furnace 6, 6a to 6e hearth roll 11 communication part 12a, 12b partition plate 13a, 13b roll chamber 14a, 14b temperature control device 15a, 15b thermometer 16 cooling apparatus

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Nakamura 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Tetsuo Okada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor: Shinki Sumiyoshi 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Japan In-tube (72) Inventor: Shinichi Kawakami 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan 4K043 AA01 CA01 DA05 EA06 FA11 GA01 GA07 GA10

Claims (5)

[Claims] When a steel strip is heat-treated in a heat treatment furnace having a heating furnace, a soaking furnace, and a cooling furnace, a hearth roll at the inlet of the cooling furnace or a hearth roll at the outlet of the soaking furnace is connected to the inlet of the cooling furnace. The surface temperature of the roll until the hearth roll is 6
A continuous heat treatment method for a steel strip, wherein the steel strip is heat-treated at a temperature of not less than 00 ° C or not more than 450 ° C. 2. A partition wall is provided on an outlet side of a communicating portion between the soaking furnace and the cooling furnace to form a roll chamber for accommodating a hearth roll at the inlet of the cooling furnace, and the hearth roll is separated from the cooling furnace side atmospheric gas. 2. The method for continuous heat treatment of a steel strip according to claim 1, wherein the heat treatment is performed separately. 3. A roll chamber for receiving a hearth roll at an outlet of the soaking furnace is provided by providing a partition wall on an entrance side of a communicating portion between the soaking furnace and the cooling furnace. 3. The method according to claim 2, wherein the heat treatment is performed separately from the atmosphere gas. 4. A hearth roll temperature measuring means according to claim 2, further comprising a hearth roll temperature measuring means at an inlet of the cooling furnace and an atmosphere temperature adjusting means for a roll chamber for accommodating the hearth roll. The detected surface temperature of the hearth roll at the inlet of the cooling furnace is 600 ° C or higher or 450 ° C
A continuous heat treatment method for a steel strip, wherein the roll chamber temperature is adjusted by using an atmosphere temperature adjusting means of the roll chamber as described below. 5. The continuous heat treatment method for a steel strip according to claim 1, wherein the surface roughness of the hearth roll is Ra 1.0 μm or more.