JPH11256235A - Heating operation method for steel material for continuous hot rolling - Google Patents

Abstract

(57) [Problem] To provide a continuous hot-rolled steel material in a continuous walking beam type heating furnace having a heating zone and a soaking zone, on the premise of ensuring stable quality. Provided is a method for heating and operating a steel material for continuous hot rolling that can realize a cryogenic heating-continuous hot rolling process that can reduce the heat unit consumption in a furnace and improve productivity by shortening the furnace time. SOLUTION: The steel material is rapidly heated in a heating zone having a furnace temperature of 1200 ° C to 1350 ° C, and a state where the maximum value of the average temperature of the steel material becomes 1100 ° C or less in a soaking zone with a furnace temperature of 1100 ° C or less before extraction. Hold for at least 30 minutes and raise the steel extraction temperature to 900
The extraction is carried out at a temperature of not less than 1 ° C. and not more than 1100 ° C., and consideration is given to the compensation of the decrease in the extraction temperature by the fixed skid beam and the generation of the scale for securing the scale-off amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating steel material for continuous hot rolling, and more specifically, to a continuous walking beam type heating furnace,
Heating of steel material for continuous hot rolling that realizes a low-temperature heating-continuous hot rolling process, which is applied when a steel material having a thickness of 100 to 300 mm is continuously hot-rolled to produce a steel sheet having a thickness of 6 mm or less. It relates to the operation method.

[0002]

2. Description of the Related Art Conventionally, a steel material (slab) having a thickness of 100 to 300 mm for continuous hot rolling is continuously hot rolled to a thickness of 6 mm.
When manufacturing the following hot-rolled steel sheets, a continuous walking beam heating furnace having a pre-tropical zone, a heating zone, a solitary zone, and the like is used for heating the steel material. The heating pattern of the steel material in this heating furnace is, for example, in the case of a normal-temperature steel material having a thickness of 250 mm, as shown in FIG.
After heating the steel material to 00 ° C, the steel material is soaked in the soaking zone until the average temperature of the steel material becomes about 1200 ° C and extracted, and rough rolling is started at a temperature of 1050 to 1150 ° C in a continuous hot rolling mill. . In this case, in the heating furnace, the steel material is
Since the extraction is performed at a temperature around 00 ° C., the furnace time is 20 minutes.
It is as long as 0 hours, which makes it difficult to improve productivity.

[0003] The temperature at which the steel material is extracted from the heating furnace is 900 to 11
If the temperature can be reduced to 00 ° C, the furnace time can be shortened, the heat intensity in the heating furnace can be reduced, and the yield can be stably secured.
The controllability of precipitates during rolling, the stabilization of the material, and the like can be ensured, and the merit is large in terms of improving productivity and the like. Nevertheless, the steel extraction temperature has been set to 110
The reason why the temperature was not set to 0 ° C. or lower is as follows. (1) When the extraction temperature from the soaking zone is 1100 ° C. or less, the temperature deviation due to the skid mark in the soaking zone increases, and the temperature of the lowest temperature part is particularly reduced. Stability cannot be ensured, and uniform continuous rolling cannot be performed. (2) Less steel scale is produced in the heating furnace, the amount of scale-off is reduced, and surface defects remain at the time of steel casting, which causes surface defects during hot rolling. (Reference technology: technology described in JP-A-56-102517, etc.). At present, there is no effective method that can solve such a concern, and in a steel heating furnace for continuous hot rolling, the extraction temperature of steel is set to 1100 ° C.
I can't find the example below.

[0004]

SUMMARY OF THE INVENTION The present invention has a thickness of 10 mm.
0-300mm steel, 6mm thick by continuous hot rolling
In the case of the following steel sheet, the extraction temperature of the steel material from the heating furnace is set to 900, which is close to the lower limit of the continuous hot rolling possible area.
C. or higher and 1100 ° C. or lower to eliminate the concerns described in (1) and (2) above, and on the premise of ensuring stable quality, it is possible to sufficiently secure productivity and reduce heat intensity.
An object of the present invention is to provide a heating operation method of a steel material for continuous hot rolling to realize a low-temperature heating-continuous hot rolling process.

[0005]

Means for Solving the Problems The present invention provides the following (1):
To (16). (1) When a continuous hot-rolled steel material is heated in a continuous walking beam type heating furnace, the steel material is heated to a temperature of 1200 ° C or more.
After rapid heating in a 1350 ° C. rapid heating zone,
In a tropical zone below 0 ° C, the maximum average temperature of steel is 110
A method for heating a steel material for continuous hot rolling, characterized in that the temperature of 0 ° C. or less is maintained for at least 30 minutes before steel material extraction and the steel material extraction temperature is extracted at 900 ° C. to 1100 ° C. A reduction in heat intensity in a heating furnace, an improvement in yield, an improvement in controllability of inclusions precipitated during rolling, a stabilization of a material, and the like are realized, and at the same time, a furnace time is shortened to improve productivity. In this rapid heating zone, it is preferable to use a regenerative switching combustion burner in order to more efficiently heat the steel material. (2) In the above (1), the amount of combustion by the burner is controlled so that the average temperature of the steel material exceeds the target temperature for extracting the steel material at least once during the heating of the steel material by the burner. This is a heating operation method for steel for cold rolling, which stabilizes the continuous hot rolling operation by stabilizing the temperature of the steel in the soaking zone in a short time and reducing the deviation of the extraction temperature of the steel to stabilize the quality of the rolled product. Aim. (3) In the above (1) and (2), after introducing the flue gas from the rapid heating zone into the soaking zone, and functioning as a heat source that maintains a soaking zone furnace temperature of 900 ° C. to 1100 ° C. This is a method of heating steel for continuous hot rolling, characterized by discharging from the soot-extracting steel extraction side, using the combustion exhaust gas from the rapid heating zone as a heat source for ripening in the solitary tropics. To reduce (4) The method for heating steel material for continuous hot rolling according to (3), wherein the combustion exhaust gas discharged from the soot-extracting steel material extraction side is introduced into a recuperator for preheating a burner supporting agent. In the case where heat recovery is performed by using flue gas for preheating a burner as a combustion supporting agent, the temperature of the flue gas is reduced to a level in the tropics to more reliably protect the recuperator. Here, it is also effective to arrange a regenerative switching combustion burner in the lower zone of the solitary zone to reduce the amount of exhaust gas flowing out from the extraction side.

(5) The method of any one of the above (1) to (4), wherein a non-combustion zone is provided on the steel material extraction side in the solitary tropical zone. In the tropics, the temperature of steel products is made uniform in a shorter time, and the deviation of the extraction temperature of steel products is reduced. (6) In any one of the above (1) to (5), the temperature drop of the steel material due to the fixed skid beam in the solitary tropics can be reduced without water-cooling the fixed skid beam arranged in the solitary tropics and supporting the steel material. This is a method of heating and operating a steel material for continuous hot rolling, which reduces a deviation in the extraction temperature of the steel material due to local cooling of a specific portion of the steel material by a fixed skid beam in a soaking zone. (7) In any one of the above (1) to (6), the fixed skid beam that is arranged in a uniform zone and supports a steel material is divided into a plurality of pieces in the furnace length direction, and the divided fixed skid beams are shifted in the width direction. A method for heating a steel material for continuous hot rolling, characterized by reducing the local temperature drop of the steel material due to the fixed skid beam in the solitary zone by arranging and changing the supporting portion of the steel material in each fixed skid beam unit. By changing the supporting portion of the steel material by the fixed skid beam in the solitary zone, the deviation of the extraction temperature of the steel material due to the local cooling of the specific portion of the steel material is reduced. (8) In any one of the above (1) to (7), a heating pipe is arranged along a fixed skid beam that is arranged in the solitary tropics to support a steel material, and the fixed skid beam is heated to thereby form the soot tropic. A method of heating steel material for continuous hot rolling, characterized by minimizing the temperature drop of the steel material due to the fixed skid beam. To reduce the deviation of the extraction temperature. (9) In any one of the above (1) to (8), the lower surface of the moving steel material supported and fixed by the fixed skid beam in the soaking zone may be heated to reduce the temperature drop of the steel material due to the soaking zone fixed skid beam. This is a method of heating and operating a steel material for continuous hot rolling, which reduces a deviation in the extraction temperature of the steel material due to local cooling of a specific portion of the steel material by a fixed skid beam in a soaking zone. (10) In any one of the above (1) to (9), a line in the furnace length direction of each fixed skid beam in the solitary zone and a line in the discharge direction of each axial flow burner installed in the solitary zone are the furnace. A method for heating steel material for continuous hot rolling, characterized by strengthening the heating of the steel support portion of the fixed skid beam by matching in the width direction to reduce the temperature drop of the steel material by the fixed skid beam in the uniform tropical zone. By compensating for the temperature drop in the part of the steel material supported by the fixed skid beam in the solitary zone, the deviation of the extraction temperature of the steel material is reduced. (11) In any one of the above (1) to (10), the installation line in the furnace length direction of each fixed skid beam in a soaking zone and the installation line in the furnace length direction of a roof burner installed in a soaking zone are furnace widths. It is a heating operation method for a steel material for continuous hot rolling, characterized by strengthening the heating of the steel material support portion of the fixed skid beam by matching the directions and reducing the temperature drop of the steel material by the fixed skid beam in the soaking zone. By compensating for the temperature drop in the part of the steel material supported by the isotropy fixed skid beam, the extraction temperature deviation of the steel material is reduced.

(12) In any one of the above (1) to (11), oxygen-enriched air or pure oxygen is used as a burner of the burner in the rapid heating zone to increase the oxidizing ability of the steel material, so that a desired surface of the steel material can be obtained. A heating operation method for a steel material for continuous hot rolling characterized by generating a scale film capable of securing a scale-off amount, wherein the scale film is formed on a surface of the steel material in a temperature rising region capable of effectively securing a desired scale-off amount. Efficiently produced, scale-off amount is secured, and the occurrence of surface flaws on hot-rolled products is prevented. (13) In the above (12), the average temperature of the steel material is 10
Oxygen-enriched air or pure oxygen is used as a burner of the burner in the region where the temperature reaches 00 to 1100 ° C. to increase the oxidizing ability of the steel material to form a scale film capable of securing a desired scale-off amount on the steel material surface. It is a method of heating and operating a steel material for continuous hot rolling characterized by efficiently generating a scale film in a temperature-raising region that can effectively secure a desired scale-off amount on a steel material surface and securing a scale-off amount. Prevents the generation of surface flaws on hot-rolled products. (14) In the above (12), the oxygen-enriched air or pure oxygen is used as a burner of the burner in a region where the average temperature of the steel material exceeds the target for extracting the steel material and in a region closer to the steel material charging side than this region. A heating operation method for a steel material for continuous hot rolling characterized by generating a scale film capable of securing a desired amount of scale-off on the surface of a steel material by increasing oxidizing ability, and effecting a desired amount of scale-off on the surface of the steel material. A scale film is efficiently generated in a temperature-raising region that can be ensured in a reliable manner, and a scale-off amount is ensured to prevent generation of surface defects of a hot-rolled product. (15) In any one of the above (12) to (14),
By supplying fuel directly into the furnace along a fixed skid beam located in the area where oxygen-enriched air or pure oxygen is used as a burner as a burner, the temperature deviation of the steel material is reduced and the oxidizing ability to the steel material is increased. A method for heating a steel material for continuous hot rolling, wherein a scale film capable of securing a desired scale-off amount is formed on the surface of the steel material. A scale film is efficiently generated in a warm region, a scale-off amount is secured, and the generation of surface defects of a hot-rolled product is prevented. (16) In any one of the above (12) to (15),
By directly supplying oxygen into the furnace along a fixed skid beam placed in an area where oxygen-enriched air or pure oxygen is used as a burner burner, the temperature drop of the steel material due to the sotropic fixed skid beam is reduced and A method of heating steel for continuous hot rolling, characterized in that a scale film capable of securing a desired scale-off amount on the surface of the steel is produced by increasing the oxidizing ability of the steel, and a skid beam fixed in a rapid heating zone. This compensates for the temperature drop in the steel part supported by the above, and also ensures the formation of a scale film that can secure a desired scale-off amount on the steel surface at this part.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a thickness of 1
The thickness of a steel material of 00 to 300 mm is 6 by continuous hot rolling.
When a steel sheet having a thickness of not more than mm is used, a pre-tropical zone and / or a rapid heating zone (a heating zone in a broad sense, but in the present invention, since it is a heating zone that heats much more rapidly than in the past, is hereinafter referred to as a "rapid heating zone". ), A continuous walking beam heating furnace having a solitary tropic (in a broad sense, a solitary tropic, but in the present invention, it is a soototropically much more soothing than before, so hereinafter referred to as “sotropic”). The extraction temperature of the steel
900 ° C or higher, which is close to the lower limit of the region where continuous hot rolling is possible 11
By reducing the heating temperature and shortening the furnace time while keeping the temperature at not more than 00 ° C. and eliminating the concerns described in (1) and (2) above, it is possible to save heat unit consumption and sufficiently secure productivity. Another object of the present invention is to realize a heating operation method of a steel material for continuous hot rolling that can realize a low-temperature heating-continuous hot rolling process.

That is, in the heating operation method of the steel material for continuous hot rolling according to the present invention, the steel material for continuous hot rolling is
When heating in a rapid heating zone, a continuous walking beam heating furnace having a soaking zone, for example, as shown in FIG.
In the rapid heating zone where the furnace temperature is 1200 ° C to 1350 ° C,
For example, after rapid heating at an average heating rate of 20 ° C./min or more, the state where the maximum value of the cross-sectional average temperature of the steel material is 1100 ° C. or less is maintained for 30 minutes or more before extraction in a soaking zone with a furnace temperature of 1100 ° C. or less. And the steel material extraction temperature from 900 ° C or higher to 11
This is a heating operation method in which extraction is performed at a temperature of 00 ° C or less.

On the other hand, in the conventional heating furnace operation, as shown in FIG. 8, a steel material is heated in a pre-tropical heating zone at a furnace temperature of 600 to 1300 ° C. for 100 to 140 minutes (the average heating rate is 10 to 140 ° C.). ℃ / min), furnace temperature 1300 ℃ ～ 1200 ℃
And heat is extracted for 60-80 minutes at about 1200 ° C.
It is necessary to maintain the furnace temperature at 1200 ° C. or higher for up to 220 minutes, and the heating heat intensity increases.

In the heating operation method according to the present invention, the steel material is heated to a furnace temperature of 1.
In a rapid heating zone of 200 ° C to 1350 ° C, the steel material was rapidly heated (average heating rate of about 20 ° C / min) until the average surface temperature of the steel material reached 1100 ° C over 60 to 70 minutes, and then the furnace temperature was raised to 90 ° C.
In a soaking zone maintained at 0 to 1100 ° C, soak (ripening) for 30 to 80 minutes and extract from the soaking zone at 900 to 1100 ° C.

For 60 to 70 minutes from the start of heating, the furnace temperature is kept at 1
Since it is necessary to maintain the temperature in the range of 200 to 1350 ° C., it is necessary to heat it. However, in a solitary tropical zone, the furnace temperature is lowered to 900 to 1100 ° C., so that it is often possible to secure this temperature range without heating. Even when heating is required, only small heating is required, so that the heat intensity can be significantly improved.

In the soaking zone, in order to reduce the deviation of the extraction temperature of the steel material (here, the difference between the maximum temperature and the minimum temperature in the cross section of the steel material), the maximum value of the average temperature of the cross section of the steel material during the soaking is reduced. It is preferable to maintain the temperature of 1100 ° C. or lower for 30 to 80 minutes. In the case where the holding time is less than 30 minutes, the temperature is from 1200 to 1350 ° C. to 900 to 110
The ripening heat after lowering the furnace temperature to 0 ° C. becomes insufficient, and the deviation of the extraction temperature of the steel material cannot be reduced.

In order to shorten the soaking time and shorten the holding time for reducing the deviation of the extraction temperature of the steel material, for example, as shown in FIG. It is more preferable to control the heating in the combustion control zone so that the average temperature of the steel exceeds the target extraction temperature of the steel material.

As the furnace temperature in the above-mentioned heating zone (including the pre-tropical zone), rapid heating, and solitary zone, the temperature obtained as follows is used. (1) (Average temperature of upper zone): Temperature measurement value from at least one or more thermocouples arranged in each combustion zone at the center of the furnace at the position of 100 mm ceiling, and (2) (Average temperature of lower zone) ): The average temperature obtained from temperature measurement values from thermocouples arranged at a position of 100 mm from both side walls is used.

[Rapid Heating Zone, Means of Heating in Uniform Tropics] In the present invention, as a heating device used in the rapid heating zone and solitary tropics (heating in the solitary tropics is not essential), various gas fuels are used. By using a known axial flow burner, roof burner, regenerative burner that can control combustion, and by arranging these burners singly or in combination, the furnace temperature can be ensured, and particularly rapid In a heating zone where heating is performed, it is effective to use a regenerative burner that has high thermal efficiency and is suitable for high-temperature heating.

In the present invention, heating in the solitary zone is not indispensable. However, when heating is required, the combustion exhaust gas from the burner in the rapid heating zone is used in addition to the above-described heating device. Introduced into soaking tropics, soaking furnace temperature 900 ℃
After functioning as a heat source that maintains a state of not less than 1100 ° C. or less, discharging from the steel material extraction side of the soaking zone is effective for heat recovery and saving of heat consumption unit.
Further, when the exhaust gas is discharged from the soot-extracting steel material extraction side and introduced into the recuperator to be used for preheating the burner supporting agent, this combustion exhaust gas has an appropriate temperature (800 to 800) which does not easily damage the recuperator. 900 ° C.).

As described above, even if the heating is omitted on the extraction side of the solitary tropics, the furnace temperature of the solitary tropics is 900 ° C. or higher to 1100 ° C.
° C or less can be secured in some cases, and when such a heating operation alone is performed, all or a part of the heating means on the extraction side in the solitary tropical zone can be omitted. In addition, in the present invention, the furnace temperature on the inlet side of the soaking zone is set to be 200 ° C. or lower than the furnace temperature (maximum furnace temperature) on the outlet side of the rapid heating zone. It is preferable to provide a wall so that this temperature difference can be easily obtained.

[Measures for Temperature Deviation by Fixed Skid Beam] In the present invention, the temperature at which the steel material is extracted from the heating furnace is 900 to 900.
Since the temperature is set to 1100 ° C., which is lower by 100 to 300 ° C. than in the conventional case, the deviation of the extraction temperature of the steel material tends to be large compared to the case where the temperature is set to around 1200 ° C. as in the conventional case. Although this may be caused by insufficient heating control, it is often caused by a fixed skid beam of a walking beam type transfer device which is disposed in a level tropic region and used for transferring steel materials.

As shown in FIG. 9 (a), for example, a walking beam type transfer device 1 arranged on a level tropic 1b having a roof burner 2 on a ceiling portion has a fixed skid for supporting a steel material 3 inserted therein. The beam 4a comprises a beam 4a and a walking beam 4b for transferring the steel material 1 on the fixed skid beam 4a to the extraction side. In particular, the skid beams 4a and 4b for supporting the high-temperature steel material 3 for a long time are constantly used for a long time. As shown in FIG. 9 (b), the water cooling structure 5 is often provided, and the steel material portion 3a supported by the fixed skid beam 4a has a large temperature drop. When the average temperature of the sample is extracted by equalizing the temperature to 1000 ° C., the heat capacity is small, the recuperation is insufficient, and the difference between the maximum temperature and the minimum temperature appears more conspicuously. Results that are introduced into not shown), can not ensure optimum temperature for hot rolling, leading to defects of the rolled products.

In order to prevent the occurrence of such inconveniences, reduce the deviation of the extraction temperature of the steel material from the soaking zone, and secure the optimum rolling temperature in hot rolling, a long soaking period is required. As the heat intensity increases and the productivity decreases, in particular, for the fixed skid beam 4a,
It is effective to take the following measures.

The fixed skid beam 4a which is disposed in the leveling zone 1a and supports the steel material is not cooled by water. In the present invention, since the temperature of the soaking zone is 900 to 1100 ° C., even if the fixed skid beam 4 a is air-cooled, the durability of the fixed skid beam 4 a does not cause a problem. The fixed skid beam 4a that supports the steel material 3 and is disposed in the leveling zone 1a is displaced in the width direction of the heating furnace 1, and the steel material portion 3a supported by the fixed skid beam 4a is shifted to be dispersed to a plurality of portions to lower the temperature. To relax. By heating the surface of the fixed skid beam 4a which is disposed in the leveling zone 1a and supports the steel material 3, the temperature drop of the steel part due to the heat transfer from the surface of the fixed skid beam 4a in the leveling zone 1a is reduced. The low-temperature section generated in the front stage of the lower surface of the steel material 3 supported by the fixed skid beam 4a and heated by the walking beam 4b is heated by the fixed skid beam 4a.
Compensate for temperature drop due to a. In the case of the lower zone, the low-temperature portion generated in the rapid heating zone after the shift of the fixed skid beam is heated. When an axial flow burner is used for the soaking zone 1a, the fixed skid beam 4a is set in the furnace width direction so that the installation line in the furnace length direction of the fixed skid beam 4a and the line in the discharge direction of the axial flow burner above the soaking zone 1a. The heating of the supporting portion of the steel material 3 by the beam 4a is enhanced to compensate for the temperature decrease by the fixed skid beam 4a. When a roof burner is used for the soaking zone 1a, the installation line in the furnace length direction of the fixed skid beam 4a and the installation line in the furnace length direction of each roof burner in the upper part of the soaking zone are matched in the furnace width direction, so that the fixed skid The heating of the supporting portion of the steel material 3 by the beam 4a is enhanced to compensate for the temperature decrease by the fixed skid beam 4a. The above-mentioned measures for lowering the temperature of the steel material by the fixed skid beam 4a are also effective in the heating zone.

[Countermeasures for Scale Generation for Ensuring Scale-Off Amount] In the present invention, since the temperature of the steel material 3 in the soaking zone 1a of the heating furnace is as low as 900 to 1100 ° C., the generation of scale is small, and the scale-off amount is small. And surface cracks and surface layer inclusions generated during steel casting are introduced into the subsequent continuous hot rolling mill without being scaled off, which causes surface defects during hot rolling. Such a phenomenon occurs remarkably especially when the steel material 3 is an aluminum killed steel containing Al and Mn. In order to prevent the occurrence of such surface defects, it is necessary to generate a necessary minimum scale film.

[0024] In a temperature rising region such as a pre-tropical zone and / or a rapid heating zone in which steel is charged, oxygen-enriched air or pure oxygen is used as a fuel supporting agent for a heating burner (axial burner, side burner, regenerative burner, etc.). Therefore, it is effective to increase the oxidizing ability of the steel material to form a scale film that can secure a desired scale-off amount on the surface of the steel material. In this case, the oxygen-enriched air or pure oxygen has a good controllability of scale formation and has an average temperature of 1000 to 1 for steel.
It is effective to use it even in the so-tropic region reaching 100 ° C.

If there is a combustion control zone in which the average temperature of the steel product exceeds the target temperature for extraction of the steel product, the oxygen control is performed in this combustion control zone and all the combustion control zones on the steel material extraction side of the combustion control zone. It is effective to use enriched air or pure oxygen. In the meantime, the steel surface temperature is 1100 ° C. or less in the solitary tropics, and the scale generation effect is small even if oxygen-enriched air or pure oxygen is used. The use of oxygen-enriched air or pure oxygen as a combustion support agent is mainly in the rapid heating zone, but a fixed skid beam having a water-cooled structure that supports steel is also arranged in the rapid heating zone. If not, the temperature of the steel part supported by the fixed skid beam is lowered, which may cause a temperature deviation of the steel material extracted from the isotropy. Further, as described above, even if oxygen-enriched air or pure oxygen is used as a combustion support agent in the combustion control zone, the temperature of the steel material portion supported by the fixed skid beam is reduced, and therefore, the surface of the steel material portion is reduced. In this case, it is impossible to uniformly form a scale film capable of securing a desired scale-off amount.

If there is such a concern, a fixed skid beam is supplied by directly supplying fuel along a fixed skid beam arranged in a combustion control zone using oxygen-enriched air or pure oxygen as a combustion supporting agent to enhance combustion. It is effective to reduce the temperature drop of the steel part supported by the steel and to increase the oxidizing ability to the steel part to uniformly generate a scale film capable of securing a desired scale-off amount on the steel surface.

In addition, oxygen is directly supplied along a fixed skid beam disposed in a combustion control zone using oxygen-enriched air or pure oxygen as a combustion supporting agent to enhance combustion, thereby increasing the temperature of a steel material portion supported by the fixed skid beam. In addition to reducing the decrease, increase the oxidation capacity of this steel part,
It is similarly effective to uniformly form a scale film capable of securing a desired scale-off amount on the surface of a steel material.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below together with examples of a heating furnace for practicing the present invention shown in FIGS. FIG.
Is a walking beam type heating furnace for carrying out the present invention, which comprises a rapid heating zone 1a at the front stage and a soaking zone 1b at the rear stage.
a and 6b, and between the partition walls 6a and 6b,
A vertically narrow steel material 3 and a flue gas flow passage 7 are formed.

An axial flow burner 8 is disposed above the rapid heating zone 1a, and a regenerative switching combustion type side burner 9 is disposed on both lower sides. Oxygen O ₂ is supplied to the air supply pipe 10 which is a burner of each burner in the rapid heating zone 1a.
An oxygen supply pipe 11 for enriching the fuel gas is connected (a fuel gas supply system is not shown). In addition, a roof burner 12 having a small capacity is arranged on the upper part of the later leveling zone 1b, and side burners 13 are arranged on both lower sides. Each of the above burners has a combustion controllable structure using, for example, LNG as fuel and air (or oxygen-enriched air) as a combustion support.

A fixed skid beam for supporting the steel member 3 and the steel member 3 are provided below the rapid heating zone 1a and the soaking zone 1b.
A transfer device 4 composed of a walking beam for transferring the light beam is provided. The fixed skid beam 4a of the transfer device 4 of the rapid heating zone 1a has a water cooling structure 5 as shown in FIG. 4 (a), and a steel material 3 supported by the fixed skid beam is provided on the side. A fuel gas outlet 14 for compensating for a temperature drop in the part and generating scale.
A heating tube 14 having a is provided.

As shown in FIG. 4B, the fixed skid beam 4a of the transfer device 4 for the soaking zone 1b has a water cooling structure as shown in FIG. As shown in FIG. 5, each of the fixed skid beams 4a1, 4a2,
The steel 4a3 is shifted in the furnace width direction so that the steel support portion is changed for each divided fixed skid beam. A flue 15 for discharging the combustion exhaust gas 13 from each burner is disposed above the steel material extraction side of the solitary tropics 1b. In this flue, a combustion supporting agent (air) supplied to each burner is provided.
A recuperator 16 for preheating is provided.

The steel material 3 is loaded into the rapid heating zone 1a by the carry-in table 17, is rapidly heated while being intermittently transported by the transporting device 4, and then passes through the flow passage 7 between the partition walls 6a, 6b to the uniform tropical zone 1b. After being heated and equalized here, it is extracted and introduced into the subsequent continuous hot rolling mill by the unloading table 18 to be hot-rolled. Here, the combustion exhaust gas 13 that has contributed to the heating in the rapid heating zone a is divided into the partition wall 6a,
The fuel gas is circulated to the soaking zone 1a through the flow passage 7 between the boilers 6b, and the combustion exhaust gas is used for soaking in the soaking zone 1b. The fuel is exhausted from a flue 15 provided in the furnace, introduced into a recuperator 16, and a combustion support (air) supplied to each burner is used as a heat source for preheating. The flue gas 13 discharged from the steel material extraction side of the soaking tropic 1b is diluted as necessary so that the recuperator 16 is not damaged 90.
Use below 0 ° C.

In this embodiment, in the rapid heating zone 1a, the combustion of the fuel gas by each burner is controlled to reduce the furnace temperature to 12%.
The temperature is set to 100 to 1350 ° C., the charged steel material 3 is heated at a heating rate of about 20 ° C./min, and the surface temperature is set to 1100 to 1150 ° C.
Heat rapidly until At this time, the rapid heating zone 1 in the temperature range where the surface temperature of the steel material 3 becomes 1000 to 1100 ° C.
By enriching the combustion supporting agent (air) of each burner (air) with oxygen so as to be 5 to 10% of the theoretical oxygen amount required for complete combustion, a scale capable of securing a scale-off amount is uniformly generated.

The surface temperature of the steel material 3 is 1100-1150 ° C.
Then, the steel material 3 is passed through the narrowed flow passage 7 partitioned by the partition walls 6a and 6b, and the combustion exhaust gas 13 from the rapid heating zone 1a and the furnace temperature 1100 are controlled by the combustion control of the fuel gas.
~ 900 ° C and introduced into the soaking zone 1b with a furnace temperature 200 ° C or more lower than the furnace temperature of the rapid heating zone 1a, the steel material 3 surface temperature and the steel material average temperature were kept at 1100 to 900 ° C for 30 minutes or more, Extracted from the isotropy 1b, introduced into a subsequent continuous hot rolling mill, and hot-rolled.

In this embodiment, the flue gas 13 from the rapid heating zone 1a is introduced into the soaking zone 1b to be used as a heat source for soaking, and then introduced into the recuperator 16 to be used as a combustion support agent for each burner. Since it is used for preheating, the heat intensity can be further reduced. Further, the steel material 3 supported by the fixed skid beam 4a in the solitary zone 1b
By reducing the temperature drop in the part, the deviation of the extraction temperature of the steel material can be reduced to ± 15 ° C., and the optimum conditions for the continuous hot rolling operation can be stably ensured. Furthermore, a scale that includes three steel members supported by the fixed skid beam of the rapid heating zone 1a and that can secure a scale-off amount by enriching the burner of the rapid heating zone 1a with oxygen can be stably generated. Thus, a high-quality steel sheet having extremely few surface defects can be manufactured.

In this embodiment, the fixed skid beam 4a is not provided with a water-cooled structure in order to reduce the temperature drop of the three steel materials supported by the fixed skid beam 4a of the soaking zone 1b. Divided, each fixed skid beam divided and shifted in the furnace width direction,
Although the supporting portion of the steel material is changed in units of the divided fixed skid beam, for example, when the roof burner 12 is arranged on the level tropic 1b, the roof burner 12 is fixed as shown in FIG. It is also effective to arrange so as to coincide with the installation line of the skid beam 4a.

When the axial flow burner 8o is arranged, as shown in FIG.
It is also effective to arrange the installation line a so that the discharge direction line of the axial flow burner 8o in the upper band coincides. It is also effective to arrange a heating tube (not shown) for heating three portions of the steel material supported by the fixed skid beam 4a, and it is also effective to selectively combine and use these means.

On the other hand, in the rapid heating zone 1a, a fixed skid beam 4a having a water cooling structure 5 is used, and the temperature of three steel materials supported by the fixed skid beam 4a is reduced, and the scale is not sufficiently generated. For this reason, a heating pipe for supplying the fuel gas is arranged along the fixed skid beam 4a. However, it is also effective to supply a fuel gas and an oxygen-enriched combustion supporting agent to the heating pipe to use a burner equivalent means. is there.

In the above embodiment, the rapid heating zone 1a
The recuperator 16 is disposed on the extraction side of the steel material 3 of the solitary tropic 1b, but when the flue gas of the rapid heating zone 1a is not introduced into the solitary tropic 1b, It is also effective to dispose a recuperator on the side of the rapid heating zone 1a on which the steel material 3 is charged, and to use the recuperator for preheating the burner in each burner.

[0040]

[Experimental example] Room-temperature slab (C 0.1-0.5%, Al 250 mm thick, 1500 mm wide and 13 m long)
The heating operation of the present invention was carried out using a walking beam heating furnace as shown in FIG. 3 for low carbon steel containing 0.01 to 0.1% and Mn of 0.01 to 0.5%). ,
The heated slab was introduced into a continuous hot rolling mill to produce a hot-rolled steel sheet having a thickness of 3 mm. In order to evaluate the present invention, the existence time of the heating furnace, the heating unit, the extraction temperature deviation of the slab, the scale generation amount, and the occurrence of surface flaws on the steel sheet were examined. The experimental conditions and survey results are described below.

[Experimental Conditions] Heating furnace Rapid heating zone: furnace length 20 m, furnace width 14 m, furnace height 5 m Furnace temperature: 1200-1350 ° C. Furnace time: 70 minutes Slab temperature Surface temperature: 20-1150 ° C. Average temperature: 20 ９950 ° C. Fuel gas: LNG Flame retardant: air (preheated to 600 ° C.) Oxygen enrichment: enriched with theoretical oxygen ratio + 5% in the latter stage of heating Furnace atmosphere: oxidizing atmosphere Uniform tropicalization: furnace length 20 m, furnace width 14 m, furnace height 3m Furnace temperature: 1050 to 970 ° C (temperature of flue gas introduced from rapid heating zone 1100 to 1000 ° C) Furnace time: 70 minutes (1000 ° C holding time before extraction: 45 minutes) Slab temperature Surface temperature: 970 to 1000 ° C average Temperature: 950-1000 ° C Average extraction temperature: 1000 ° C Continuous hot rolling Rolling temperature: 1000-820 ° C

In the experimental example of the present invention, the heating time in the heating furnace is 140 minutes, and the productivity at 1200 ° C. is about 3 times lower than that of the conventional extraction.
0% could be improved. The heat intensity is 243 kc
Al / t was able to save about 20% compared to the conventional extraction at 1200 ° C. Also, the extraction temperature deviation of the slab is as shown in FIG.
The temperature in the length direction of the slab was 1030 to 1000 ° C. and the temperature difference was 30 ° C., and a sufficiently satisfactory result was obtained.
On the other hand, the conventional method using a fixed skid beam having a water-cooled structure in a solitary tropical zone, the slab extraction temperature is 1000
The temperature in the length direction of the slab when set to 1050C is 1050
The temperature difference was 70 ° C. at ９980 ° C., and satisfactory results could not be obtained. The scale generation amount (one-sided average) in the experimental example of the present invention was 800 μm, and no surface defects were observed in the steel sheet obtained by continuous hot rolling.

The present invention is not limited to the conditions of the above-described examples and experimental examples. The heating furnace structure, heating operation conditions, and the like for carrying out the invention include the conditions of the slab to be heated and the rolling operation conditions of the steel sheet. It will be changed accordingly.

[0044]

According to the present invention, the temperature at which the steel material is extracted from the heating furnace is set to 900, which is close to the lower limit of the region where continuous hot rolling is possible.
C. or more and 1100 ° C. or less, it is possible to save heating unit consumption, shorten furnace time, and sufficiently secure productivity. In addition, since the flue gas from the rapid heating zone is introduced into the soaking zone and used as a heat source for soaking, it is introduced into a recuperator to be used for preheating the burner's burner. Further savings can be made. Furthermore, the temperature drop of the steel part supported by the fixed skid beam can be reduced, and the deviation of the extraction temperature of the steel can be reduced to ± 15 ° C. In addition, by enriching oxygen in the burner containing the steel part supported by the fixed skid beam, a scale film that can secure the scale-off amount can be generated stably, and a high-quality steel sheet with extremely few surface flaws can be produced. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a heating pattern in an example of a heating operation method according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a heating pattern in another example of the heating operation method of the present invention.

FIG. 3 is an explanatory side sectional view showing a structural example of a walking beam type heating furnace for implementing the heating operation method of the present invention.

4 (a) is a partially sectional three-dimensional explanatory view showing an example of a partial structure of a steel support portion of a fixed skid beam of a rapid heating zone of the walking beam type heating furnace of FIG. 3, and FIG. 3
FIG. 3 is a partially sectional three-dimensional explanatory view showing an example of a partial structure of a steel support portion of a fixed skid beam in a soaking zone in a walking beam type heating furnace.

5 is an explanatory plan view showing an example of the arrangement of fixed skid beams in the walking beam type heating furnace in FIG.

FIG. 6 (a) is a plan explanatory view showing an example of the arrangement of a fixed skid beam and a roof burner in a walking beam type heating furnace used in the present invention, and FIG. FIG. 2 is an explanatory plan view showing an example of the arrangement of a fixed skid beam and an axial flow burner.

FIG. 7 is an explanatory diagram showing an example of a longitudinal temperature distribution of an extracted steel material from a solitary zone in an experimental example of the present invention and a conventional example.

FIG. 8 is an explanatory view showing an example of a heating pattern in a conventional heating operation method of a heating furnace.

FIG. 9 is a front cross-sectional explanatory view showing an example of a state in which a steel material is supported by a fixed skid beam in a soaking zone of a conventional walking beam type heating furnace.

FIG. 10 is a partially sectional three-dimensional explanatory view showing an example of a partial structure of a steel material supporting portion of a soaking fixed skid beam and a walking beam in the walking beam type heating furnace of FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Walking beam type heating furnace 2 Roof burner 3 Steel material 3a Steel material part 4 Transfer device 4a, 4a1, 4a2, 4a3 Fixed skid beam 4b Walking beam 5 Water cooling structure 5a Air cooling structure 6a, 6b Partition wall 7 Flow path 8, 8o Axial flow burner REFERENCE SIGNS LIST 9 side burner 10 combustion support agent supply pipe 11 oxygen supply pipe 12 roof burner 13 combustion exhaust gas 14 heating pipe 14 a fuel gas outlet 15 flue 16 recuperator 17 carry-in table 18 carry-out table

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C21D 1/52 C21D 1/52 FR 1/76 1/76 NG 6/00 6/00 T

Claims (16)

[Claims] When a continuous hot-rolled steel material is heated in a continuous walking beam heating furnace, the steel material is heated to a furnace temperature of 12 ° C.
After rapid heating in a rapid heating zone of 00 ° C to 1350 ° C, the state where the maximum value of the average temperature of the steel material is 1100 ° C or less is maintained for 30 minutes or more before the extraction of the steel material in a soaking zone with a furnace temperature of 1100 ° C or less. A heating operation method for a steel material for continuous hot rolling, wherein the steel material is extracted at a temperature of 900 ° C or higher and 1100 ° C or lower. 2. The combustion amount of the burner is controlled such that the average temperature of the steel material exceeds the target temperature of extracting the steel material at least once during the heating of the steel material by the burner. Item 4. A heating operation method for a steel material for continuous hot rolling according to Item 1. 3. The combustion exhaust gas is introduced from the rapid heating zone into the soot-tropic zone, and after functioning as a heat source for maintaining a soother-trophic furnace temperature of 900 ° C. or more and 1100 ° C. or less, from the soot-extracting steel material extraction side. The method for heating a steel material for continuous hot rolling according to claim 1 or 2, wherein the steel material is discharged. 4. The continuous heat as claimed in claim 3, wherein the soot combustion exhaust gas is discharged from the steel material extraction side and introduced into the recuperator, and the burner supporting agent is preheated in the recuperator. Heating method for hot rolling steel. 5. The heating operation method for a steel material for continuous hot rolling according to claim 1, wherein a non-combustion zone is provided on a side of the soot-extracting steel material extraction side. 6. The method according to claim 1, wherein the fixed skid beam for supporting the steel material arranged in the solitary zone is not cooled with water, and the temperature drop of the steel material due to the fixed skid beam in the solitary zone is reduced. 2. The heating operation method for a steel material for continuous hot rolling according to claim 1. 7. A fixed skid beam for supporting a steel material which is arranged in a uniform zone and divided into a plurality of pieces in the furnace length direction, and the divided fixed skid beams are arranged so as to be shifted in the width direction. By changing the support site,
The heating operation method for a steel material for continuous hot rolling according to any one of claims 1 to 6, wherein a local decrease in temperature of the steel material due to the fixed skid beam in a soaking zone is reduced. 8. A heating pipe is arranged along a fixed skid beam that supports a steel material by disposing it in a solitary tropical zone, and heats the fixed skid beam, thereby reducing the temperature drop of the steel material due to the fixed skid beam in the solitary zone. The heating operation method for a steel material for continuous hot rolling according to any one of claims 1 to 7, characterized in that: 9. The method according to claim 1, wherein the lower surface of the moving steel material supported and fixed by the fixed skid beam is heated to reduce the temperature drop of the steel material due to the fixed skid beam. 2. The heating operation method for a steel material for continuous hot rolling according to claim 1. 10. A fixed skid beam steel material in which a line in a furnace length direction of each fixed skid beam in a soaking zone and a line in a discharge direction of each axial flow burner installed in the soaking zone are matched in a furnace width direction. The heating operation method for a steel material for continuous hot rolling according to any one of claims 1 to 9, wherein the heating of the support portion is strengthened to reduce a temperature drop of the steel material due to the fixed skid beam in the solitary zone. 11. A fixed skid beam steel material in which the installation line in the furnace length direction of each fixed skid beam in the soaking zone and the installation line in the furnace length direction of each roof burner installed in the soaking zone are matched in the furnace width direction. The heating operation method for a steel material for continuous hot rolling according to any one of claims 1 to 10, wherein heating of the support portion is strengthened to reduce a temperature drop of the steel material due to the fixed skid beam in the uniform tropical zone. 12. A scale film capable of securing a desired scale-off amount on the surface of a steel material by using oxygen-enriched air or pure oxygen as a burner of a burner in a rapid heating zone to enhance the oxidizing ability of the steel material. Claims 1 to 1
The heating operation method for a steel material for continuous hot rolling according to any one of the preceding claims. 13. The steel material has an average temperature of 1000 to 1100.
Using oxygen-enriched air or pure oxygen as a burner for the burner in the region where the temperature reaches ℃, the oxidation capacity for steel is increased,
The heating operation method for a steel material for continuous hot rolling according to claim 12, wherein a scale film capable of securing a desired scale-off amount is generated on the surface of the steel material. 14. An oxygen-enriched air or pure oxygen is used as a burner of a burner in a region where the average temperature of a steel material exceeds a target temperature for extracting the steel material and in a region on the side where the steel material is charged from this region, and the oxidizing power for the steel material is reduced. 13. The heating operation method for a steel material for continuous hot rolling according to claim 12, wherein a scale film capable of securing a desired scale-off amount on the surface of the steel material is generated by increasing the scale film. 15. Directly supplying fuel into the furnace along a fixed skid beam disposed in a region using oxygen-enriched air or pure oxygen as a burner as a burner, thereby reducing the temperature deviation of the steel material and reducing the temperature of the steel material. The oxidizing ability is enhanced to form a scale film capable of securing a desired scale-off amount on the surface of a steel material.
15. The heating operation method for a steel material for continuous hot rolling according to any one of 14 to 14. 16. The temperature of a steel material by a sotropic fixed skid beam by supplying oxygen directly into the furnace along a fixed skid beam located in a region using oxygen-enriched air or pure oxygen as a burner burner. 16. A scale film capable of securing a desired scale-off amount on the surface of a steel material by increasing the oxidizing ability with respect to the steel material while reducing the decrease, thereby producing a scale film.
The heating operation method for a steel material for continuous hot rolling according to the above item.