JP2500950B2 - Continuous annealing furnace with excellent atmosphere controllability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous annealing furnace having excellent controllability of the atmosphere inside the furnace.

[0002]

2. Description of the Related Art For example, continuous strip annealing furnaces include those in which a heating zone, a soaking zone, and a cooling zone are connected in series, and those in which a heating zone, a decarburizing zone, a reduction zone and a cooling zone are connected in series. .
Continuous annealing or continuous decarburizing annealing is performed with a desired atmosphere gas in each zone.

In the case of continuously annealing strips whose surface properties need to be controlled strictly, those which need to be decarburized, and strips whose oxide layer on the surface of the steel sheet needs to be controlled, for example, a heating zone. The atmosphere of each of the decarburization zone and the reduction zone needs to be maintained in a predetermined atmosphere, for example, the dew point in a specific range, and the specific component in the atmospheric gas composition must be constantly maintained at a constant concentration.

For this reason, it has been proposed to add a device such as a partition in the furnace to the boundary between the strips in the continuous annealing furnace to prevent mixing of atmospheric gas in the furnace. For example, JP
According to Japanese Patent Laid-Open No. 324038/1989, a seal box provided at a band boundary is provided with a seal body which can be moved up and down so as to face a transport roll, and the seal body is brought into contact with a strip plate surface to seal the zones.

[0005]

This is effective because it has the effect of suppressing the mixing of atmospheric gas, but the annealing conditions are changed depending on the material to be annealed to increase the dew point or the ratio of specific gas components in the furnace atmosphere. It takes a long time to achieve a predetermined atmosphere in the furnace when changing the above. For example,
Moisture partial pressure (dew point) of furnace atmosphere gas in the decarburization zone is 35% ~
When changing to 10%, even if the water partial pressure of the supply atmosphere gas is lowered and the gas is supplied into the decarburizing zone, it takes several hours or more to change to the above value in the zone.

[0006] This means that the effective use of the continuous annealing furnace is deteriorated and the productivity is deteriorated. In addition, if annealing is not performed in a predetermined atmosphere, it will be a cause of producing defective parts in quality in the non-annealed material. The present invention, when changing the atmosphere in the continuous annealing furnace zone for the purpose of annealing the material to be annealed,
The purpose of the present invention is to provide a continuous annealing furnace with excellent atmosphere controllability that can be quickly changed to a predetermined condition.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted experiments and studies in order to speed up the atmosphere change in the continuous annealing furnace. As a result, not only the atmosphere gas in the furnace exists in the furnace but also the furnace wall It was found that it became a kind of atmosphere gathering place that was absorbed and exhausted by. It has been found that this phenomenon is often present in conventional insulating bricks and ceramic fiber furnace walls as described in, for example, Japanese Utility Model Application Laid-Open No. 63-10399, and it is a multifunctional product having a decarburizing zone or a nitriding zone that requires a wet atmosphere. It was found that the continuous annealing furnace has a furnace wall that does not absorb gas.

The present invention has been made on the basis of this finding, and its gist is to provide a continuous annealing furnace having a partitioned decarburizing zone and / or a nitriding zone in the furnace. It is characterized in that the inner wall of the furnace is constructed by a dense castable formed by mixing a refractory aggregate containing 75% or more of mullite with SiO ₂ having a particle size of 10 μm or less and an Al ₂ O ₃ ratio of 0.2 to 0.4. It is in a continuous annealing furnace with excellent atmosphere controllability.

The present invention will be described below in detail with reference to the drawings based on an embodiment. In the drawing, 1 is a continuous annealing furnace, which is provided with a heating zone 2 and a decarburization zone 3 in this embodiment, and inside the decarburization zone is a humid atmosphere, for example, H ₂ and N ₂ whose dew point is adjusted to 40 ° C. It is made with gas. Reference numeral 4 denotes a reduction zone, which is a dry H ₂ and N ₂ atmosphere in order to reduce the oxide layer formed on the surface of the steel sheet in the decarburization zone 3. Reference numeral 5 denotes a nitriding zone, which is set in an atmosphere containing a nitridable gas such as NH ₃ . 6 is a cooling zone.

Reference numeral 7 denotes an atmosphere partition, which is provided between the decarburizing zone 3 and the reducing zone 4, between the reducing zone 4 and the nitriding zone 5, and between the nitriding zone 5 and the cooling zone 6 in this embodiment. It prevents the atmosphere from entering and exiting. Atmosphere gas is supplied to each of the zones from an atmosphere gas supply pipe (not shown).

By the way, in this embodiment, the decarburizing zone 3, the reducing zone 4 and the nitriding zone 5 have the furnace wall 8 (the same applies hereafter) as shown in FIG. Reference numeral 9 is a heat-insulating brick, and a steel skin 10 is provided on the outer side thereof, and a dense castable is provided on the inner side, that is, the innermost furnace wall. The dense castable 11 contains 75% or more of mullite and has a particle size of 10 μm.
following the fine SiO ₂ m, the Al ₂ O ₃ SiO ₂ / Al
₂ O ₃ is added as 0.2 to 0.4, does not absorb H ₂ , N ₂ , H ₂ O, etc. in the annealing atmosphere, has high high temperature strength, and is repeatedly heated and cooled. Does not crack.

Mullite is 75% to increase high temperature strength
That is all. The particle diameter of SiO ₂ is set to 10 μm or less in order to reduce the porosity of the furnace inner wall and reduce the air permeability so that the annealing atmosphere is not absorbed. Si
If the ratio SiO ₂ / Al ₂ O _{3 of} O ₂ and Al ₂ O ₃ is small, the sinterability becomes insufficient and the strength increases, so it is set to 0.2 or more.
Further, if this ratio becomes large, cracking occurs due to high temperature shrinkage, so it is made 0.4 or less. In this embodiment, the dense castable 11 is provided only on the innermost furnace wall of the furnace wall 8. However, the present invention is not limited to this, and the dense castable 11 may be formed from the innermost furnace wall to the inside of the furnace wall 8 or the entire furnace wall.

Next, the operation will be described. When strips are continuously passed through a continuous annealing furnace for heating, decarburization and nitriding, the decarburization zone 3 has a high dew point, for example, a dew point of 60 ° C., and carbon in steel is removed in a short time. I am trying.
On the other hand, in the reduction zone 4 adjacent to the decarburization zone 3, H ₂ and N ₂ gas having a low dew point, for example, −40 ° C. is supplied to give a reducing action to the oxide layer formed on the plate surface. The strip is nitrided.

By the way, when the passing strip is changed and the atmosphere in the decarburizing zone 3 is to be changed to a dew point of 30 ° C., the decarburizing zone 3
Even if the dew point of the supply atmosphere gas is set to 30 ° C., the dew point of the atmosphere gas in the furnace has conventionally required several hours or more, but in the present invention, the innermost wall of the decarburizing zone 3 is the dense castable 11
Since it is constructed by, the furnace atmosphere is not sucked, that is, the furnace wall does not absorb H ₂ O. Therefore, when the dew point of the supply atmosphere gas was changed, the dew point of the atmosphere gas in the furnace was 30 ° C. in this embodiment in a short time, for example, 20 minutes. Further, when changing the NH ₃ concentration of the nitriding zone 5 from 600ppm to 100 ppm, the NH ₃ concentration 600ppm in the feed atmosphere 100
Although it was reduced to ppm, this change took 10 hours in the past, but since the furnace wall of the nitride zone 5 does not suck the atmosphere in the furnace,
NH ₃ concentration of readiness and furnace atmosphere changes NH ₃ concentration in the supply atmosphere is changed.

[0015]

According to the present invention, since the furnace inner wall of the zone such as the decarburizing zone and the nitriding zone which is partitioned by the atmosphere partition is constructed by the dense castable, the atmosphere gas in the furnace is not sucked in the furnace. The atmosphere is changed in a short time. This is because the continuous annealing furnace has a small atmospheric inertia, and the atmosphere in the furnace can be easily controlled, and the continuous annealing can be performed in an atmosphere according to the strip material at an early stage.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a continuous annealing furnace according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a furnace according to an embodiment of the present invention.

[Explanation of symbols] 1 continuous annealing furnace 2 heating zone 3 decarburization zone 4 reduction zone 5 nitriding zone 6 cooling zone 7 atmosphere partition 8 furnace wall 9 heat insulating brick 10 iron crust 11 dense castable

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayoshi Mizuguchi 1-1, Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Yasuko Kondo, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka Prefecture No. 1 No. 1 in the Yawata Works, Nippon Steel Co., Ltd. (72) Inventor Morifumi Yonemaru No. 1 in Hibatacho, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka In the Yawata Works, 72 Nippon Steel Co., Ltd. Fujita Katsuhiro 1-1 Hibahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside the Yawata Works (56) References JP-A-2-25686 (JP, A) JP-A-60-65770 (JP, A) Actual public Sho 63-4941 (JP, Y2)

Claims (1)

(57) [Claims] 1. In a continuous annealing furnace having a decarburization zone and / or a nitriding zone which are partitioned, a furnace inner wall of the zone partitioned by an atmosphere partition is made into a refractory aggregate containing 75% or more of mullite and has a particle size of 10 μm or less. SiO ₂ to Al ₂ O ₃ ratio of 0.
A continuous annealing furnace with excellent atmosphere controllability, characterized by being constructed with a dense castable compounded as 2 to 0.4.