JP3371820B2 - Continuous heat treatment method for steel strip - Google Patents

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 continuous heat treatment furnace for steel strips, particularly a hearth roll at an 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 roll pickup during the period.

[0002]

2. Description of the Related Art A continuous heat treatment furnace for carrying out heat treatment by passing a steel strip at a predetermined line speed is usually equipped with a direct-fired 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 that guides and conveys a steel strip is disposed in each furnace.

When the steel strip is heated during 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 becomes a pickup to cause flaws on the surface of the steel strip. .

As a measure for preventing the pickup from occurring, it is general to subject the hearth roll surface to a thermal spraying treatment. Further, JP-A-53-130211, JP-B-58-3
No. 0939, Japanese Patent Laid-Open No. 60-141834, etc., propose to form a roll chamber for accommodating a hearth roll to prevent pickup.

[0005]

However, the above-mentioned prior art has the following problems.

In the thermal spraying treatment on the surface of the hearth roll, the occurrence of pickup cannot be completely prevented due to deterioration of the thermal spraying material, inadequacy of the thermal spraying material and the like.

Pickup occurs not only in the hearth roll from the direct-fired heating furnace outlet to the reduction heating furnace inlet, but also in the cooling furnace inlet hearth roll. JP-A-53-13021
JP-B, JP-B-58-30939, JP-A-60-
Japanese Patent No. 141834 is aimed mainly at preventing the occurrence of pickup in the hearth roll from the direct-fired heating furnace outlet to the reduction heating furnace inlet, and the hearth roll pickup at the cooling furnace inlet intended by the present invention. No consideration is given to the point of preventing the occurrence of the hearth roll, and it is not possible to prevent the occurrence of the pick-up of the hearth roll at the inlet of the cooling furnace simply by providing the roll chamber for housing the hearth roll at the inlet of the cooling furnace.

That is, in the above-mentioned prior art, an effective means for preventing the pickup which occurs in the hearth roll at the inlet of the cooling furnace has not yet been found.

In view of the above circumstances, it is an object of the present invention to provide a continuous heat treatment method for a steel strip capable of preventing pickup occurring in the hearth roll at the inlet of the cooling furnace.

[0010]

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

[0011]

( 1 ) A heating furnace, a soaking furnace and a cooling furnace are passed through a steel strip.
For heat treatment of steel strip in a heat treatment furnace equipped in this order in the plate direction
Saishi and, on the outlet side of the communication portion of the soaking furnace and the cooling furnace is provided with a partition wall, isolate to form a roll chamber for accommodating the inlet of the hearth rolls of the cooling furnace the hearth rolls from the cooling furnace side atmospheric gas And the hearth roll table at the inlet of the cooling furnace.
A continuous heat treatment method for a steel strip, which comprises heat treating a steel strip at a surface temperature of 600 ° C. or higher or 450 ° C. or lower .

( 2 ) A heating furnace, a soaking furnace and a cooling furnace are passed through a steel strip.
For heat treatment of steel strip in a heat treatment furnace equipped in this order in the plate direction
Saishi and, by a partition wall provided in the entrance side of the communicating portion of the soaking furnace and cooling furnace, the hearth rolls of the outlet of the soaking furnace to form a roll chamber for accommodating the hearth rolls of the outlet of the soaking furnace Isolate it from the atmosphere gas of the soaking furnace, and make sure that the communication part between the soaking furnace and the cooling furnace is not exposed.
Side wall is installed to store the hearth roll at the inlet of the cooling furnace.
To form a roll chamber to accommodate the hearth roll on the cooling furnace side.
Isolate from atmospheric gas, and at the outlet of the soaking furnace
From the hearth roll to the hearth roll at the inlet of the cooling furnace
The surface temperature of the roll between 600 ℃ or more or 450 ℃ or less
Continuous heat treatment method of steel strip, which comprises heat-treating the steel strip in the.

( 3 ) In the above ( 1 ) or ( 2 ), the temperature measuring means for the hearth roll at the inlet of the cooling furnace and the atmospheric temperature adjusting means for the roll chamber accommodating the hearth roll are provided to measure the hearth roll temperature. The surface temperature of the hearth roll at the inlet of the cooling furnace detected by means is 600 ° C. or higher or 450
A continuous heat treatment method for a steel strip, characterized in that 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 ° C.

( 4 ) A continuous heat treatment method for a steel strip according to any one of (1) to ( 3 ) above, wherein the roll surface roughness of the hearth roll is Ra 1.0 μm or more.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION First, the function of the present invention and the reason for limitation will be described.

Pick-up is likely to occur on rolls between the hearth roll at the exit of the soaking furnace and the hearth roll at the inlet of the cooling furnace, particularly pick-up at the hearth roll at the inlet of the cooling furnace. Occur. The present inventors have made various studies on the cause of the pickup and its preventive measures. As a result, the main component of the pickup generated on the roll is a sintered body of a composite oxide of Si (silicon), Al (aluminum), and Mn (manganese),
It has been found that the occurrence of pickup can be reduced by defining the surface temperature of the roll at 600 ° C. or higher or 450 ° C. or lower.

The reason why the occurrence of pickup can be remarkably reduced by defining the mechanism of occurrence of pickup in the roll and the surface temperature of the roll as described above is considered to be as follows.

During the heat treatment process of the steel strip, the steel strip is heated to a temperature of about 800 ° C. at the exit of the soaking furnace, and is cooled in the cooling furnace at 45 ° C.
It is cooled to a temperature of about 0 ° C. In the heat treatment process, the surface of the steel strip is oxidized to form an oxide when passing through an open flame heating furnace,
This oxide remains even after passing through the reduction heating furnace. Especially silicon
Since aluminum oxide is hard to be reduced, it tends to remain on the surface of the steel strip 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 while the oxide remains.

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
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, the difference between the steel strip and the hearth roll surface temperature becomes large as shown in FIG.
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 surface of the roll and becomes 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, aluminum, etc. are easily oxidized, the growth of the pickup is promoted, and the grown pickup causes a flaw in the steel strip.

Further, the roll arranged at the inlet of the cooling furnace from the outlet of the soaking furnace such as the hearth roll at the outlet of the soaking furnace flows to the soaking furnace side through the communication part between the soaking furnace and the cooling furnace. Since it is affected by the low-temperature atmosphere gas of the cooling furnace, the temperature tends to be low, although not as high as the hearth roll at the inlet of the cooling furnace.
Therefore, pickup is likely to occur on the roll surface due to the same mechanism as the hearth roll at the inlet of the cooling furnace.

By defining the roll surface temperature at 600 ° C. or higher, the temperature difference between the plate temperature and the roll surface temperature becomes small, and the heat shrinkage of the steel strip becomes small. As a result, the oxide on the surface of the steel strip is less likely to be transferred to the roll, the occurrence of pickup can be reduced, and the steel strip is free from flaws.

Further, by limiting the roll surface temperature to 450 ° C. or lower, a temperature range in which an oxide is hard to form is set, so that the pickup does not grow on the roll surface.

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

Next, embodiments 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 a direct heating furnace (not shown) and a reduction heating furnace 2, a soaking furnace 4, and a cooling furnace 5. Figure 4
In the heat treatment furnace of FIG. 3, a partition wall 12b is provided on the exit side of the communication part 11 of the soaking furnace 4 and the cooling furnace 5 to form a roll chamber 13b for housing the hearth roll 6b at the inlet of the cooling furnace 5. It is a device. In FIG. 4, 14b is a roll chamber 13.
a temperature adjusting device for adjusting the atmospheric temperature in b, 15
b is a thermometer for detecting the surface temperature of the hearth roll 6b, 1
Reference numeral 6 denotes a cooling furnace 5 for blowing the cooled atmospheric gas onto the steel strip 1.
It is a cooling device.

The partition wall 12b accommodates a heat insulating material inside and S
It is composed of a plurality of box structure members produced by molding a metal plate of US or the like, and in order to efficiently shut off the furnace atmosphere gas on the cooling furnace 5 side of the roll chamber 13b, each member or the above members. A heat-insulating sealing material is packed in the clearance of the furnace wall of the cooling furnace 5 for sealing. Further, at least one member of the partition wall 12b is openable / closable so that a worker can enter the furnace during work such as hearth roll inspection and steel strip breaking processing.

In FIG. 3, a steel strip 1 includes a heating furnace 3 comprising a direct heating furnace (not shown) and a reduction heating furnace 2, a soaking furnace 4, and a cooling furnace 5, and a hearth arranged in each furnace. Roll 6
And is subjected to the required heat treatment. At that time, in the apparatus shown in FIG.
By adjusting the ambient temperature in 3b, the surface temperature of the hearth roll 6b detected by the thermometer 15b is 600 ° C or higher or 45
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 pickup of the hearth roll 6b can be prevented, and the steel strip 1 can be prevented from being flawed.

The surface roughness of the hearth roll 6b is Ra1.0.
When the thickness is not less than μm, meandering and slipping of the steel strip 1 can be prevented, and the effect of preventing the 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 inlet side of the communication portion 11 of the roll chamber 1 for containing the hearth roll 6a at the outlet of the soaking furnace 4.
2a is a device formed. In the apparatus of FIG. 5, 6a
Is a hearth roll at the outlet of the soaking furnace 4, 14a is a roll chamber 1
A temperature adjusting device for adjusting the ambient temperature in 3a, 1
Reference numeral 5a is a thermometer for detecting the surface temperature of the hearth roll 6a. The partition walls 12a and 12b are the partition walls 12 of the device of FIG.
It has 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 of FIG. 5, the temperature of the thermometer 1 is adjusted by adjusting the atmosphere temperature in the roll chamber 13a by the temperature adjusting device 14a.
The surface temperature of the hearth roll 6a detected by 5a is adjusted to a predetermined temperature defined in the present invention, and the temperature adjusting device 14
The ambient temperature in the roll chamber 13b is adjusted by b, and the surface temperature of the hearth roll 6b detected by the thermometer 15b is adjusted to the predetermined temperature specified in the present invention.

In this apparatus, the hearth rolls 6a and 6b are
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 to reliably prevent the occurrence of pickup.

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 the lower position of the heat treatment furnace, and between them. Although the remaining rolls are not provided in FIG.
As exemplified in (c), in order to prevent meandering, slipping, etc. of the steel strip or to enhance the gas sealing effect in the communicating portion, a single or a plurality of rolls may be arranged between the both rolls, Further, as illustrated in FIGS. 7A to 7C, these rolls may be arranged at the upper position of the heat treatment furnace. Further, the surface roughness of the roll arranged between the both rolls is preferably Ra 1.0 μm or more.

[0034]

EXAMPLE When a steel strip was heat-treated using the apparatus shown in FIGS. 3 to 4 with the surface temperature of the hearth roll 6b being 600 ° C. or higher, the occurrence of steel plate flaws caused by the roll pickup investigated.

Regarding the occurrence of blemishes, the steel strip after the heat treatment is inspected with a grindstone, and the bleaching situation on the surface of the steel strip after the whetstone is inspected is observed. Evaluated to. A score of 1 indicates no occurrence of blemishes, and the larger the score is, the more pronounced blemishes occur. At a score of 5, it is necessary to load dummy coils or stop the line to remove the roll pickup. .

The survey results are shown in FIG. For comparison, FIG. 8 also shows the condition of occurrence of blemishes in the case of the conventional example heat-treated under the same conditions as those of the present invention example, except that a roll chamber for collecting the hearth roll 6b was not provided.

In the examples of the present invention, the occurrence of flaws is not recognized. On the other hand, in the case of the conventional example, since the number of heat treatment coils was 3rd, a flaw was generated by the pickup, and the degree became severe as the number of heat treatment coils increased, and the score became 5 at the 9th heat treatment, requiring roll maintenance.

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

[0039]

As described above, according to the present invention, no pickup occurs 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. Further, it is not necessary to stop the line for removing the roll pickup or to insert the dummy coil, so that the productivity can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a state of thermal contraction 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 diagram of an apparatus in which a roll chamber that houses a hearth roll at an inlet of a cooling furnace is formed in the heat treatment furnace of FIG.

FIG. 5 is a view of an apparatus in which a roll chamber for accommodating the 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 view showing an example of the arrangement of rolls from the hearth roll at the exit of the soaking furnace to the hearth roll at the entrance of the cooling furnace.

FIG. 7 is a diagram showing another example of the arrangement of rolls from the hearth roll at the outlet of the soaking furnace to 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]

1 steel strip 2 Reduction heating furnace 3 heating furnace 4 Soaking furnace 5 cooling furnace 6, 6a-6e Hearth roll 11 Communication 12a, 12b Partition plate 13a, 13b Roll chamber 14a, 14b Temperature control device 15a, 15b Thermometer 16 Cooling system

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Okada 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Shinki Sumiyoshi 1-2-1 Marunouchi, Chiyoda-ku, Japan Japan Steel Pipe Co., Ltd. (72) Inventor Shinichi Kawakami 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (56) Reference JP-A-2-88722 (JP, A) JP-A-5-25550 ( JP, A) JP-A-9-241762 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 9/52 101 C21D 9/56 101

Claims (4)

(57) [Claims] 1. A steel strip passing method for a heating furnace, a soaking furnace and a cooling furnace.
When heat-treating a steel strip in a heat treatment furnace equipped in this order
A partition wall on the exit side of the communication part between the soaking furnace and the cooling furnace,
The roll chamber for accommodating the inlet of the hearth rolls of the cooling furnace formed to be isolating the hearth rolls from the cooling furnace side atmospheric gas
And the surface temperature of the hearth roll at the inlet of the cooling furnace.
A continuous heat treatment method for a steel strip, which comprises heat treating the steel strip at a temperature of 600 ° C. or higher or 450 ° C. or lower . 2. A steel strip passing method for a heating furnace, a soaking furnace and a cooling furnace.
When heat-treating a steel strip in a heat treatment furnace equipped in this order
A partition wall on the inlet side of the communication part between the soaking furnace and the cooling furnace,
To form a roll chamber for accommodating the hearth rolls of the outlet of the soaking furnace to isolate the hearth rolls of the outlet of the soaking furnace from the ambient gas of the soaking furnace and the exit side of the communicating portion of the soaking furnace and cooling furnace To
A partition wall is provided to accommodate the hearth roll at the entrance of the cooling furnace.
To form a roll chamber in which the hearth roll is placed in the atmosphere on the cooling furnace side.
Isolate it from air and gas, and remove it from the outlet of the soaking furnace.
Between the sroll and the hearth roll at the inlet of the cooling furnace
Keep the surface temperature of the roll above 600 ℃ or below 450 ℃
Continuous heat treatment method of steel strip, which comprises heat-treating the steel strip Te. 3. The method of claim 1 or claim 2, the ambient temperature adjusting means of the roll chamber for accommodating the temperature measuring means at the inlet of the hearth rolls in the cooling furnace and the hearth rolls disposed at hearth roll temperature measuring means 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, characterized in that the temperature of the roll chamber is adjusted using the atmosphere temperature adjusting means of the roll chamber as described below. 4. The method of claim 1 to claim 3, continuous heat treatment method of steel strip, wherein the surface roughness of the hearth rolls is not less than Ra1.0Myuemu.