JP2001247913A - Heating furnace for steel material and method for heating steel material for hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating furnace and method, with which scale amount formed on a steel material surface is restrained and the yield of the steel material is improved. SOLUTION: One of partition wall near an ejecting hole door and further, one or more of the partition walls at a charging hole side from the ejecting hole door, are arranged, and a zone parted with the partition walls, is repeatedly subjected to combustion and suction with heat-storage type burners and heated with <1% oxygen concentration in the zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for heating a steel material for hot rolling in a continuous heating furnace, which suppresses the amount of scale generated on the surface of the steel material and improves the yield of the steel material, and a heating furnace for heating the steel material. It is about the method.

[0002]

2. Description of the Related Art When manufacturing steel products from billets such as slabs and billets, they are generally heated in a heating furnace and then shaped by hot rolling. When the steel slab is heated in the heating furnace, a thick oxide film, that is, scale is formed on the surface of the steel material because the inside of the heating furnace is in an oxidizing atmosphere. Since scale needs to be removed in a post-process in terms of product quality, formation of scale causes a reduction in steel product yield. To minimize the yield loss,
Development of a technique for suppressing the generation of scale is desired.

As a method of suppressing the formation of scale, a method of heating in an atmosphere having an oxygen concentration of 1% or less (Japanese Patent Application Laid-Open No. 6-4 / 1988)
No. 1753) has been proposed. However, in the continuous heating furnace, since the opening portions of the billet loading door and the extraction door are large and not a closed space, the oxygen concentration in the furnace is easily affected by outside air intrusion.

The following measures have been proposed to solve the above problems. For example, Japanese Unexamined Patent Publication No. 7-97617 discloses that incomplete combustion is performed in a high-temperature region on the extraction end side in a furnace so as to be in a non-oxidizing or reducing atmosphere, thereby suppressing scale generation. When one of the alternately burning burners is burning, it is recovered by the other burner, and the recovered unburned gas is supplied as a combustion gas in a low-temperature region on the inlet side of the furnace interior. Have been. Japanese Patent Application Laid-Open No. 9-20919 discloses a method of suppressing scale formation by blowing a high-temperature non-oxidizing gas around a steel material charged in a heating furnace and heating the steel material in a non-oxidizing atmosphere. I have.

[0005]

The problem to be solved by the invention
According to the technique described in Japanese Patent Application Laid-Open Publication No. H11-107, although the combustion efficiency can be improved, incomplete combustion is performed, so that the heating efficiency is reduced. Also,
When unburned gas is sucked, the cost of equipment increases, such as a need to take measures against heat generation due to combustion in the piping. Further, Japanese Unexamined Patent Publication No.
In the technology disclosed in Japanese Patent No. 20919, it is necessary to separately supply a high-temperature non-oxidizing gas in addition to the fuel and the combustion air, and the cost is high in terms of the complexity of the gas piping and the supply of extra non-oxidizing gas.

Further, in any of the methods, when the slab is extracted from the heating furnace, invasion of outside air due to opening and closing of the extraction port cannot be prevented, and the slab is exposed to an oxidizing atmosphere having a high oxygen potential in a high temperature region near the extraction port. , So that the effect of suppressing the scale in a non-oxidizing atmosphere was halved,
Scale production increases. In addition, since the outside air flows from the extraction port side to the charging port side in the same direction as the gas flow in the furnace, the furnace length of the oxidizing atmosphere from the heating furnace extraction port becomes longer, and a sufficient scale formation suppression effect cannot be obtained. .

The present invention has been made to solve the above-mentioned problems, and it is possible to suppress the generation of scale in a heating furnace of a steel material for hot rolling, to reduce the equipment cost, and to improve the yield of the steel material, and a heating method therefor. The purpose is to provide.

[0008]

Means for Solving the Problems The present invention for achieving the above object is as follows: (1) When a steel material for hot rolling is heated by a continuous heating furnace, one partition wall is provided near an extraction port door, and 1 on the loading side
A heating furnace comprising: at least one partition wall; and a regenerative burner that repeats combustion and suction in a zone divided by at least two partition walls from an extraction side. (2) The heating method according to (1), wherein the oxygen concentration in a zone separated by a partition wall not adjacent to the opening such as the extraction port door is heated to less than 1%. (3) In the heating furnace according to the above (1), the steel material has a surface temperature of 900 ° C. that is not adjacent to an opening such as an extraction door.
A heating method wherein the zone is heated at an oxygen concentration of less than 1%. (4) A method for heating a steel material for hot rolling, wherein the atmospheric pressure in the zone where the oxygen concentration is less than 1% and the atmospheric pressure is set higher than the other zones according to (1). (5) In the heating method according to (4), wherein the atmosphere pressure in the zone where the oxygen concentration is less than 1% is higher than that in the other zones, the regenerative burner in the zone where the oxygen concentration is less than 1%. A method for heating a steel material for hot rolling, wherein the pullback ratio of the steel material is lower than that of other zones. It is.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors considered the effect of the stay time in a high oxygen concentration zone due to the invasion of outside air near the door on the assumption that the entire heating time was constant and the oxygen content was initially less than 1%. Heating at a high oxygen concentration near the slab extraction port (4
%), The amount of scale formation was examined by changing the time of stay. As a result, it was confirmed that the amount of scale generation rapidly increased with the increase in the time spent in the high oxygen concentration. That is, it has been found that it is important to minimize the high oxygen concentration zone due to the invasion of the outside air to suppress the scale generation amount.

[0010] Minimizing the high oxygen concentration zone means
Minimization of the zone where the outside air enters directly and minimization of the influence on the zone adjacent to the high oxygen concentration zone. In the heating furnace of the present invention, one partition wall is provided at a position closest to the extraction port door, and one or more partition walls are further provided on the charging side, and combustion and suction are performed in a zone separated by the partition wall. A regenerative burner having a repeating function is provided.
Here, the zone divided by the partition wall means a space whose one end or both ends are partitioned by the partition wall.

Since the zone separated by the partition wall and the extraction port has a high oxygen concentration due to the invasion of the outside air, the independence of the atmosphere is increased by installing the partition wall, and the oxygen concentration in the adjacent zone is reduced. Further, the reason why one or more partition walls are required on the loading side is also to suppress the influence of the invasion of outside air from the loading door. The partition wall provided closest to the door is preferably installed as close as possible to the door in order to minimize the zone where the outside air enters directly.

Heating each zone by using a regenerative burner which repeats combustion and exhaust gas suction can be achieved by increasing the flow of high oxygen concentration gas in the furnace length direction accompanying the gas flow in the furnace from the extraction port side to the charging port side. And the effect of the atmosphere on the zone adjacent to the high oxygen concentration zone can be minimized.

The effect of reducing the oxygen concentration increases synergistically as the number of zones separated by the partition wall is increased in the furnace, but the cost for installing the partition wall made of refractory increases accordingly. I do. Therefore, the number of partition walls to be installed is determined by the trade-off between cost and effectiveness.

The more the number of zones in which the regenerative burners are installed, the greater the independence of the atmosphere in the furnace and the greater the effect of reducing the oxygen concentration.
Burner installation cost increases. Therefore, the installation zone of the regenerative burner is installed in at least two zones from the extraction side in order to prevent the outside air from entering from the extraction door, and the burner type is determined based on the balance between the cost and the effect.

In the heating furnace of the present invention, the oxygen concentration in a zone not adjacent to the opening such as the extraction port door is set to less than 1%.
There is almost no difference in the amount of scale production at 1% or more, and the amount of scale production decreases at less than 1%. As a result, the amount of scale removed in a subsequent step is also reduced, that is, the amount of iron lost by oxidation is reduced, so that the yield of steel materials is improved. Since the amount of scale generation decreases as the oxygen concentration decreases, the oxygen concentration is preferably as low as possible.

Further, if the oxygen concentration is less than 1% in all zones that are not adjacent to the opening such as the extraction door, the amount of scale generation is minimized. However, the scale is mainly 900
A large amount is generated above ℃. Therefore, steel surface temperature is 9
Even if the heating operation is performed so that the oxygen concentration is less than 1% only in the zone where the temperature is 00 ° C. or more, the effect of suppressing the scale can be sufficiently obtained. As a result, it is possible to minimize the installation cost of the partition wall and improve the yield of the steel material at low equipment cost.

In order to further increase the independence of the atmosphere, the atmospheric pressure in the zone where the oxygen concentration is less than 1% is set higher than in the other zones, so that the atmospheric gas in the high oxygen concentration zone reduces the oxygen concentration. If it is less than 1%, it becomes difficult to flow into the heating zone.

As a method for setting the atmospheric pressure in the zone where the oxygen concentration is lower than 1% to be higher than that in the other zones, the pull-back rate of the regenerative burner in the zone where the oxygen concentration is lower than 1% is set higher than the other zones. Also set it low. Here, the pullback ratio is a ratio of the amount of exhaust gas sucked by the regenerative burner. By relatively lowering the pull-back rate in the zone where the oxygen concentration is less than 1% as compared with the other zones, the amount of exhaust gas flowing from the zone to the adjacent zone is increased, that is, the atmospheric pressure is relatively increased, and It is less affected by the atmosphere from the zone.

[0019]

EXAMPLES Table 1 shows the components of steel materials used in Examples of the present invention. Table 1 (% by mass) C Si Mn PS 01166 0.128 0,700 0.015 0.009

FIG. 1 is a schematic view of a heating furnace to which an embodiment of the present invention is applied, as viewed from the side. The heating furnace 1 is a device for heating the slab 2 and charges the slab from the charging port 3 to heat it. At this time, burners 4 are provided above and below the slab for each zone, and pipes 5 for supplying combustion air and fuel are connected to the burners. Each zone is formed by the partition wall 7. The slab 2 is heated at a predetermined air ratio for each moving zone, so that the heating temperature and the scale generation amount are controlled, and the slab 2 is extracted from the extraction port 6.

In this embodiment, the length in the heating furnace is 40 m,
The inside was divided into four zones by three partition walls, and the oxygen concentration was controlled for each zone. Each zone was divided as follows. Zone 1: A furnace zone having a slab surface temperature of 900 ° C. or lower, which is partitioned by a partition wall closest to the charging port from the charging port. Zone 2: a furnace zone of 900 to 1250 ° C. in a heating area separated by a partition wall closest to the charging inlet and a partition wall in the middle of the heating furnace. Zone 3: Furnace zone divided by a partition wall in the middle of the heating furnace and a partition wall closest to the extraction port. Zone 4: Furnace zone partitioned by the extraction port door and the partition wall closest to the extraction port.

In a heating furnace having these zones, a slab having the composition shown in Table 1 was charged, and oxygen concentration was controlled under the conditions A to J shown in Table 2. In particular, in zone 3, the effect of zone 4 in which high oxygen concentration was caused by the invasion of outside air appears,
The oxygen concentration in the zone is slightly higher. Extraction temperature is 1250
C. and the heating time were 150 minutes. As a result, different scale amounts were generated for each oxygen concentration control condition.

In the case of the conditions A to C, the scale thickness is reduced as compared with the condition 1 which is a conventional heating furnace using a normal combustion burner. The scale thickness is the thinnest in the case of the condition B where the oxygen concentration in the zone is low. Condition D is zone 1
Although only the oxygen concentration is 1% or more, scale formation at 900 ° C. or less is small, so that the amount of scale formation is suppressed.
Condition E uses a regenerative burner but does not have a partition wall to prevent the flow of oxygen that enters from outside air from the extraction port side to the charging port side, and generates scale in zones 2 and 3 at 900 ° C. or higher. And the effect of suppression is not obtained. Similarly, under the conditions F and G, since the oxygen concentration at 900 ° C. or more is 1% or more, scale generation is not suppressed. In the condition H, there is a partition wall, but since the oxygen concentration is 1% or more, there is no suppression effect. Further, under the conventional heating furnace condition I without a partition wall and the condition J in which only the partition wall is provided, the oxygen concentration cannot be reduced to less than 1%, and the effect of suppressing the scale cannot be obtained.

[0024]

[Table 1]

[0025]

As described above, according to the present invention, it is possible to suppress the generation of scale of the steel material charged into the heating furnace and to improve the yield of the steel material at a low cost and at a high energy efficiency.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of the present invention.

[Explanation of Signs] 1: Heating furnace 1 2: Slab 2 3: Inlet 4: Burner 5: Pipe 5 6: Extraction port 7: Partition wall

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C21D 9/00 101 C21D 9/00 101T (72) Inventor Hideki Murakami 20-1 Shintomi, Futtsu-shi, Chiba New Japan (72) Inventor Shigeya Kubo 1 Chikuko-Hachimancho, Sakai-shi, Osaka Nippon Steel Corporation Sakai Works

Claims (5)

[Claims] 1. When a steel material for hot rolling is heated in a continuous heating furnace, one partition wall is provided near an extraction port door, and one or more partition walls are further provided on a charging side thereof. A heating furnace characterized in that a regenerative burner that repeats combustion and suction is provided in a zone separated by at least two or more partition walls. 2. A method for heating a steel material for hot rolling according to claim 1, wherein the zone not adjacent to the opening is heated at an oxygen concentration of less than 1%. 3. The heating furnace according to claim 1, wherein the oxygen concentration in a zone not adjacent to the opening and having a steel material surface temperature of 900 ° C. or more is heated at an oxygen concentration of less than 1%. Heating method for steel for rolling. 4. The method for heating a steel material for hot rolling according to claim 1, wherein the atmosphere pressure in the zone where the oxygen concentration is less than 1% is higher than that in the other zones. . 5. The steel material for hot rolling according to claim 4, wherein the full-back rate of the regenerative burner in the zone heated at an oxygen concentration of less than 1% is lower than that in the other zones. Heating method.