JP2000212645A - Continuous heating method for steel - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress overheating of the end portion in the longitudinal direction of a steel material for hot rolling in a continuous heating furnace. SOLUTION: When a continuous hot-rolled steel material is heated by a multi-zone walking beam type continuous heating furnace, the steel material is heated to a furnace temperature of 1%.
After rapid heating in a pre-tropical zone and / or heating zone of 200 ° C to 1350 ° C, the maximum temperature of the average temperature of the steel product in a soaking zone where the furnace temperature is set to be higher than the target steel extraction temperature and lower than the target steel extraction temperature + 20 ° C Is maintained at least 1100 ° C. for at least 30 minutes before steel extraction, and the steel extraction temperature is maintained at 900 ° C. or higher 1
A continuous heating method for a steel material, wherein the extraction is performed at 100 or less.

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 a steel material for continuous hot rolling, and more specifically, to a continuous walking beam type heating furnace.
Longitudinal direction 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 plate having a thickness of 6 mm or less. The present invention relates to a continuous heating method in a multi-zone walking beam type continuous heating furnace for suppressing overheating at the end of the heating furnace.

[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 multi-zone walking beam type continuous 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 000 ° C to 1300 ° C, the steel material is soaked in the soaking zone until the average temperature of the steel material becomes about 1200 ° C and extracted. The rough rolling is performed at a temperature of 1050 ° C to 1150 ° C by a continuous hot rolling mill. Has started. In this case, in the heating furnace, since the steel material is soaked and extracted at a temperature of about 1200 ° C., the furnace time is as long as about 200 minutes, which makes it difficult to improve productivity.

Further, the temperature distribution of a steel material immediately after extraction from a heating furnace is high at both ends in the longitudinal direction of the steel material, and sometimes the temperature at both ends may be higher than the average temperature of the steel material by 50 ° C. or more. . It is considered that the reason is that the end portion of the steel material is heated on three sides and the furnace temperature distribution in the furnace width direction increases on the side wall side depending on the combustion conditions.
When continuous hot rolling of steel material with large temperature deviation is performed, the material may be different at the tip, middle, and tail of the hot rolled sheet, and the tip may be discarded as defective material, and the yield of the hot rolling process May cause decline. Further, in order to prevent the roughening of the rolling roll, the steel material may wait in front of the rolling mill until the temperature on the roll biting side of the steel material decreases to an appropriate temperature, which means that the production in the hot rolling process is performed. It hinders the improvement of sex.

In order to prevent the end of the steel material from being overheated in a heating furnace, which hinders the improvement of the yield and productivity of the continuous hot rolling process, for example, Japanese Patent Application Laid-Open No. Sho 60-11451.
As disclosed in Japanese Patent Application Publication No. 5 (1999) -1995, there is a technique for preventing an end portion from being overheated by attaching an ascending / descending water-cooled shielding plate for reducing the amount of radiant heat to the steel material end portion in a heating furnace. However, 1
In the furnace at 200 ° C level, the operation of the elevating device is not reliable, the heating unit is deteriorated due to water cooling, it cannot be applied to the side burner furnace, and the shielding plate cannot be installed in the lower zone, In the prior art, end overheating could not be effectively suppressed substantially.

[0005]

SUMMARY OF THE INVENTION According to the present invention, an extraction temperature of a steel material in a heating furnace is set to 1100 ° C. or less, and a thickness of 100
In the case where a steel material having a thickness of 6 mm to 300 mm is formed into a steel sheet having a thickness of 6 mm or less by continuous hot rolling, overheating of the steel material in the longitudinal direction at the end in the multi-zone walking beam type continuous heating furnace is prevented to achieve uniform quality. An object of the present invention is to provide a steel material for rolling, and to provide a continuous heating method for a steel material capable of simultaneously improving yield and productivity in a continuous hot rolling process.

[0006]

According to the present invention, when a continuous hot-rolled steel material is heated in a multi-zone walking beam type continuous heating furnace, the steel material is heated to a pre-tropical temperature of 1200 to 1350 ° C. and / or heated. After rapid heating in the heating zone, the maximum value of the average temperature of the steel material calculated by the PROCON becomes 1100 ° C or less in a soaking zone where the furnace temperature is set to the target steel material extraction temperature or more and the target steel material extraction temperature + 20 ° C or less. Condition before steel extraction 3
Hold for at least 0 minutes and increase the steel extraction temperature from 900 ° C to 1100
It is a continuous heating method for a steel material, wherein the extraction is performed at a temperature of not more than ° C.

Further, in a multi-zone walking beam type continuous heating furnace using an axial flow burner in a soaking zone burner, the burning amount of the axial flow burner on one or both side walls is reduced by the amount of combustion of the other axial flow burners. A continuous heating method for a steel material, wherein the method is set to a combustion amount or less.

In a multi-zone walking beam type continuous heating furnace using a roof burner in a soaking zone combustion device, a roof burner group on the same line along the furnace length direction installed on one or both side walls is provided. A continuous heating method for a steel material, wherein a total combustion amount is set to be equal to or less than a total combustion amount of roof burner groups on other lines.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a thickness of 1
When a steel material of 00 mm to 300 mm is converted into a steel plate having a thickness of 6 mm or less by continuous hot rolling, the extraction temperature of the steel material from the multi-zone walking beam type continuous heating furnace is set to 900 ° C.
１1100 ° C. to suppress the end overheating in the longitudinal direction of the steel material to produce a homogeneous hot rolled sheet over the entire length of the steel sheet. This realizes a continuous heating method.

That is, in the method for continuously heating steel material for continuous hot rolling of the present invention, the steel material for continuous hot rolling is
When heating with a multi-zone walking beam type continuous heating furnace, for example, as shown in FIG.
After rapid heating in the pre-tropical zone and / or heating zone of ~ 1350 ° C, the maximum average steel temperature is 1100 ° C or lower in a solitary zone where the furnace temperature is set to the target steel extraction temperature or higher and the target steel extraction temperature + 20 ° C or lower. This is a continuous heating method in which the state is maintained for at least 30 minutes before steel material extraction, and the steel material extraction temperature is set to 900 ° C. or higher and 1100 or lower to perform extraction. Here, it is desirable that the time for maintaining the state where the maximum value of the average temperature of the steel material is 1100 ° C. or less in the solitary zone be 90 minutes or less. The reason is that the heating time for heating the average temperature of the steel material to about 1100 ° C. immediately before the soaking is approximately 80 minutes to 100 minutes.
This is because if the soaking time is 90 minutes or more, the in-furnace time becomes about 200 minutes, which hinders improvement in productivity. The average temperature of the steel material in the furnace is generally controlled by a value of a process control provided for combustion control and operation monitoring. The average temperature is determined, for example, by the calculation described in the document "Heat transfer experiment and calculation method in a continuous billet heating furnace (edited by the Heating Furnace Subcommittee of the Japan Iron and Steel Association Thermal Economics Technology Section, 1971)".

An important point of the continuous heating method of the present invention is that the difference between the soaking zone furnace temperature and the target steel extraction temperature is set to 20 ° C. or less. Since the heat transfer rate of the steel longitudinal direction end is faster than the central part of the steel longitudinal direction mainly due to three-sided heating, by making the furnace time of the steel material in the soaking zone 30 minutes or more,
The end of the steel material in the longitudinal direction at the time of the heating furnace extraction has a value close to the soaking zone furnace temperature. For this reason, the difference between the temperature at the end and the temperature at the center in the longitudinal direction of the steel material is suppressed to 20 ° C. or less by setting the soaking zone furnace temperature within the range of the target extraction temperature or more and the target extraction temperature + 20 ° C. or less. can do.

The reason for setting the lower limit of the set value of the soaking zone furnace temperature to be equal to or higher than the target steel material extraction temperature is to secure the steel material extraction temperature. Further, the reason why the upper limit is set to be equal to or lower than the target steel material extraction temperature + 20 ° C. is that the lower limit of the feasible temperature difference between the skid mark portion and other portions is about 20 ° C. In the low-temperature heating-continuous hot rolling process, it is important to realize uniform heating of the steel material in a continuous heating furnace in order to secure the rolling temperature of the steel material. For example, Japanese Patent Application No. Hei 10-
According to No. 55510, the skid marks are reduced by a multi-band walking beam type continuous heating furnace which has been subjected to proper skid arrangement, height increase of skid buttons, reinforcement of skid insulation, etc. On the premise, even if various measures are taken, the limit value of the skid mark at the time of extraction is about 20 ° C.

Therefore, for example, Japanese Patent Application No. Hei 10-5551.
No. 0, Japanese Patent Application Laid-Open No. 4-3047, and Japanese Patent Application Laid-Open No. 4-30
No. 1048, Japanese Patent Application Laid-Open No. Hei 4-31049, a continuous heating furnace employing a skid button, and Japanese Patent Application No. 10-10.
It is desirable to carry out the continuous heating method of the present invention in a continuous heating furnace employing a skid beam according to Japanese Patent Application No. 1247 and Japanese Patent Application No. 10-113363 or a continuous heating furnace combining these techniques.

In contrast to the above-described continuous heating method according to the present invention, in the conventional continuous heating method, as shown in FIG. 1, steel is heated at a furnace temperature of 600 ° C. to 1300 ° C. in a pre-tropical zone and a heating zone.
Heating is performed for 60 minutes to 190 minutes, soaking is performed in a soaking zone at a furnace temperature of about 1250 ° C. for 40 to 50 minutes, and extraction is performed from the soaking zone at about 1200 ° C. The furnace temperature in the soaking tropics is the target steel extraction temperature + 40 ° C to 70 ° C. At the end of the steel material with a relatively high heat transfer rate, the temperature is almost equal to the setting furnace temperature in the soaking tropics. The central portion in the longitudinal direction of the steel material has a temperature near the target steel material extraction temperature. For this reason, overheating of the end portion in the longitudinal direction of the steel material becomes remarkable.

When a continuous heating method according to the continuous heating method of the present invention is applied to a steel material extraction temperature of about 1200 ° C. in a conventional continuous heating furnace, the furnace temperature in the pre-tropical zone and the heating zone is 1300 ° C. to 1350 ° C. It needs to be about ℃. The upper limit of the furnace temperature is determined by the service temperature of the furnace wall refractory used, but the upper limit of the furnace temperature in a hot-rolled heating furnace is generally about 1350 ° C. Therefore, it is difficult to obtain a desired heat pattern for a steel material having an extraction temperature of about 1200 ° C. In addition, if a desired heat pattern is realized by using a refractory having a higher heat-resistant temperature, in addition to the economical disadvantage that expensive heat insulating material is required, an increase in exhaust gas heat loss leads to an increase in heat intensity. Greatly worsens.

In the continuous heating method according to the present invention, when an axial burner is used in a soot-tropical combustion device, the combustion amount of the axial burner on one or both side walls is set to be equal to or less than the combustion amount of the other axial burners. It is effective to do. When a roof burner is used in a soaking zone burner, the total combustion amount of the roof burners on the same line along the furnace length direction installed on one or both side walls is calculated as the roof burner group on the other lines. It is effective to set the combustion amount to be equal to or less than the total combustion amount.

Since the heat transfer rate at the end in the longitudinal direction of the steel material is higher than that at the center in the longitudinal direction of the steel material due to three-face heating, the furnace temperature distribution in the furnace width direction in the solitary zone is lower on the side wall side, and the vicinity of the furnace width center is lower. It is desirable to have a high distribution. By using the continuous heating method according to the present invention for realizing the furnace temperature distribution in the furnace width direction, overheating of the steel material in the longitudinal direction can be suppressed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the continuous heating method of the present invention will be described below with reference to FIGS. 3 to 9 together with a multi-zone walking beam continuous heating furnace for carrying out the present invention. FIG. 3 is a schematic diagram in the furnace length direction of a multi-zone walking beam type continuous heating furnace embodying the present invention. This continuous heating furnace is composed of a non-combustion zone 1, a pre-tropical zone 2, a heating zone 3 and an isotropy zone 4. Each zone is divided into an upper zone and a lower zone with a steel material S interposed therebetween. Each band is partitioned by an upper partition wall 5a and a lower partition wall 5b, and a steel material S is provided between the partition walls 5a and 5b.
And a flow passage for the combustion exhaust gas.

Side burners are arranged in the first half of the upper pre-tropical zone 2a, and the latter half of the upper pre-tropical zone 2a and the upper heating zone 3
An axial flow burner is arranged at a, and a roof burner is arranged at the upper leveling zone 4a. Side burners are arranged in the lower pre-tropical zone 2b, the lower heating zone 3b, and the lower level zone 4b.

Each of the above burners is, for example, LN as fuel.
It has a combustion controllable structure using G and air or oxygen-enriched air as a combustion supporting agent. The combustion supporting agent sent to each burner is preheated by the recuperator 6 to about 400 ° C. to 600 ° C. by heat recovered from sensible heat of the exhaust gas in the furnace.

The burners in each band are not limited to the type shown in this embodiment. The burners in each band including the upper band and the lower band may be any of side burners, axial burners, and roof burners. Further, a regenerative switching combustion burner may be used for all or a part of the burners. In this case, the recuperator 6 does not preheat the combustion supporting agent guided to the regenerative switching combustion burner.

In the lower band of each band, there is provided a transfer device 7 comprising a fixed skid beam for supporting the steel S and a walking beam for transferring the steel S by shifting the steel S a plurality of times in the transfer direction. The fixed skid beam and the walking beam constituting these transfer devices 7 have a water-cooled structure as shown in FIG. The skid button 71 that comes into contact with the steel material S is a heat-resistant alloy. The skid button is supported by a metal member 72, and the metal member is welded to a water-cooled pipe 70. Further, a large number of studs 73 are welded to the water-cooled pipe to support a heat-insulating castable 74 in which ceramic fibers are mixed.

The laying line of the fixed skid beam in the lower non-combustion zone 1b, the lower pre-tropical zone 2b and the lower heating zone 3b and the laying line of the fixed skid beam in the lower level zone 4b are shifted by 600 mm in the furnace width direction. I have. Thereby, the supporting portion of the steel material S is shifted in the longitudinal direction of the steel material S during heating.

The steel material S is supplied to the non-combustion zone 1 by the charging pusher 8.
, And is rapidly heated in the pre-tropical zone 2 and the heating zone 3 while being intermittently transferred by the transfer device 7, and is soaked in the soaking zone 4. The furnace temperature of the soaking zone 4 is set to be equal to or higher than the target steel extraction temperature and equal to or lower than the target steel extraction temperature + 20 ° C. In addition, the highest value of the average temperature of the steel material S is 1100
° C or less is maintained for 30 minutes or more, and the steel material S is extracted at an extraction temperature of 900 ° C or more and 1100 ° C or less. Thereafter, the steel material S is extracted from the leveling zone 4 to the outside of the furnace by the extractor 9, conveyed to a continuous hot rolling mill (not shown) in a post-process by a conveying table, and hot-rolled to a predetermined thickness. The average temperature and the surface temperature of the steel material in the furnace are represented by values calculated by a process controller provided in the heating furnace.

In this embodiment, the furnace temperature of the pre-tropical zone 2 is set to 1250 ° C. by controlling the fuel flow rate and the flow rate of the combustion supporting agent of each burner of the pre-tropical zone 2. The steel material S charged into the furnace by the charging pusher 8 has a surface temperature of 1100 ° C.
It is rapidly heated for about 80 minutes at an average heating rate of about 15 ° C./min until it reaches 1150 ° C.

The surface temperature of the steel material S is 1100 ° C. to 1150
When the temperature reaches 0 ° C., the steel S is transferred to the heating zone 3 in which the furnace temperature is set to 1060 ° C. (in the present embodiment, the steel S is uniformly heated in the heating zone 3 and the soaking zone 4). 3
And soak in the tropical zone 4 for about 100 minutes, average temperature 105
It is extracted by the extractor 9 from the soaking zone 4 at 0 ° C. to the outside of the furnace.

In this embodiment, the steel S (target extraction temperature 1)
FIG. 2 shows the temperature history of the steel material surface and the average temperature of the steel material in the furnace at 050 ° C.). The surface temperature of the steel material S is heated to about 1135 ° C. 80 minutes after the heating, and then transferred to the heating zone 3 set to 1060 ° C. By the subsequent soaking for 70 minutes, the surface temperature of the steel material S becomes 10 which is the target extraction temperature.
It is slightly higher than 50 ° C. Further, it was heated for 30 minutes to bring the surface temperature close to the target extraction temperature, and was extracted at an extraction temperature of 1050 ° C. for 180 minutes in the furnace.

FIG. 5 shows the average temperature distribution in the cross section in the thickness direction of the steel S immediately after the extraction. In the continuous heating method according to the example of the present invention, overheating of the end portion temperature of the steel material S is suppressed (end temperature deviation 5 ° C.), and high uniformity is realized over the entire length of the steel material S (overall temperature deviation). 30 ° C).

The conventional continuous heating method for steel material is performed by a water-cooling method for suppressing overheating of the steel material in the longitudinal direction shown in FIG. A conventional continuous heating method for steel materials was carried out using a multi-zone walking beam type continuous heating furnace provided with a type shielding plate 10 (water cooling unit not shown). In such a heating furnace, the steel S was heated according to the heating pattern shown in FIG. At this time, the side burner in the first half of Pre-Tropical 2 is extinguished. The steel material S was intermittently transferred from the charging side to the extraction side by the transfer device 7, and was extracted at a steel material temperature of about 1190 ° C. in a furnace time of about 240 minutes. FIG. 7 shows the average temperature distribution in the cross section in the thickness direction of the steel material S immediately after the extraction. In the continuous heating method according to the prior art, overheating of the temperature of the end portion of the steel material S is remarkable (45 ° C. in the end portion).

In this embodiment, the total combustion amount of the roof burner group on the same line along the furnace length direction installed in the upper isotropy 4a is set to be equal in each row.
When the furnace temperature distribution in the furnace width direction in the upper isotropy 4a is high on the side wall side and low at the center part in the furnace width direction as shown in FIG. It is effective to make the total combustion amount of the roof burner group 11 on the line smaller than the total combustion amount of each row of the roof burner group on the other line.

In the case where an axial burner is installed in the upper leveling zone 4a and the temperature distribution in the furnace width direction of the upper leveling zone 4a is high on the side wall side and low at the central portion in the furnace width direction, FIG.
As shown in (1), it is effective to make the combustion amount of the axial flow burner 12 installed on one or both outermost side walls smaller than the combustion amount of the other axial flow burners.

[0032]

According to the continuous heating method of the present invention, the overheating of the steel material for hot rolling extracted at 900 ° C. to 1100 ° C. in the longitudinal direction of the steel material is suppressed by the continuous heating method, and the heating furnace is uniformly heated over the entire length of the steel sheet. A hot rolled sheet can be manufactured, and the yield and productivity of the continuous hot rolling process can be simultaneously improved.

[Brief description of the drawings]

FIG. 1 is a view showing a heating pattern of a steel material by a conventional continuous heating method.

FIG. 2 is a view showing a heating pattern of a steel material in a continuous heating method according to the present invention.

FIG. 3 is a schematic view in the furnace length direction of a multi-zone walking beam heating furnace for performing a continuous heating method according to the present invention.

FIG. 4 is a view showing a heat insulating configuration of a skid beam of a multi-zone walking beam type heating furnace for implementing a continuous heating method according to the present invention.

FIG. 5 is a diagram showing a cross-sectional average temperature distribution at the time of extracting a steel material in an embodiment of the continuous heating method according to the present invention.

FIG. 6 is a diagram illustrating equipment for preventing overheating at the end of a multi-zone walking beam type heating furnace that implements a conventional continuous heating method.

FIG. 7 is a diagram showing a cross-sectional average temperature distribution at the time of extracting a steel material in an example of a conventional continuous heating method.

FIG. 8 is a diagram illustrating the total combustion amount in each row of the roof burner group on the same line along the furnace length direction installed in the soaking zone in the embodiment of the continuous heating method according to the present invention.

FIG. 9 is a diagram for explaining the combustion amount of an axial flow burner installed in a soaking zone in the embodiment of the continuous heating method according to the present invention.

[Explanation of symbols]

 1, 1a, 1b: Non-combustion zone 2, 2a, 2b: Pre-tropical zone 3, 3a, 3b: Heating zone 4, 4, a, 4b: Uniform tropical zone 5, 5a, 5b: Partition wall 6, Recuperator 7, Transfer device 8: Charge pusher 9 ... Extractor 10 ... Water-cooled shield plate 11 ... Roof burner 12 ... Axial flow burner 70 ... Water-cooled pipe 71 ... Skid button 72 ... Skid button pedestal 73 ... Stud 74 ... Insulated castable S ... Steel material

Claims (3)

[Claims] When a continuous hot-rolled steel material is heated in a multi-zone walking beam type continuous heating furnace, the steel material is heated to a furnace temperature of 1%.
After rapid heating in the pre-tropical zone and / or heating zone set at 200 ° C. to 1350 ° C., the average temperature of the steel product in the solitary zone where the furnace temperature is set above the target steel extraction temperature and below the target steel extraction temperature + 20 ° C. The state where the maximum value of the steel is 1100 ° C. or less is maintained for 30 minutes or more before steel extraction, and the steel extraction temperature is set to 90 °.
A method for continuously heating steel material, wherein the extraction is performed at a temperature of 0 ° C to 1100 ° C. 2. A method of continuously heating steel by a multi-zone walking beam type continuous heating furnace using an axial flow burner in a soaking zone burner, wherein the amount of combustion of the axial flow burner on one or both side walls is other than that. 2. The method for continuously heating steel material according to claim 1, wherein the combustion amount is set to be equal to or less than the combustion amount of the axial flow burner. 3. A continuous heating method for a steel material by a multi-zone walking beam type continuous heating furnace using a roof burner in a soaking zone burner, wherein the same line is installed along one side or both side walls along the furnace length direction. 2. The method for continuously heating steel materials according to claim 1, wherein the total combustion amount of the roof burner groups on the upper line is set to be equal to or less than the total combustion amount of the roof burner groups on the other lines.