JPH06158180A - Continuous annealing equipment of metallic strip - Google Patents

Abstract

PURPOSE:To provide a continuous anealing equipment of a metallic strip which is useful in adding a carburized zone in an existing continuous annealing furnace, and can pass any metallic strip which requires or does not require the carburizing treatment as a series of metallic strips by changing the atmosphere within the carburizing zone in a short time. CONSTITUTION:A space is formed to the upper part or the lower part of a continuous carburizing furnace consisting of a preheating zone 1, a heating zone, a soaking zone 3, and a first and second cooling zones 5, 6, and a carburizing zone 4 having a horizontal path is constructed within this space, a strip A is passed from the soaking zone 3 into this carburizing zone 4, and then, passed through the cooling zones 5, 6. The strip which is horizontally passed in the carburizing zone 4 is levitated with the atmospheric gas which is dynamically ejected from a floater, and supported in a non-contact manner, the atmosphere gas which is ejected from this floater is switched to the carburizing atmospheric gas and the soaking atmospheric gas, and the soaking effect of the metallic strip which requires no carburizing treatment is maintained immediately before the cooling zone without changing the strip passing path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous annealing equipment for annealing a continuously fed metal strip, and particularly to a heating zone and a soaking zone in an annealing furnace in a cold rolling steel sheet passing step. It is suitable for continuous annealing equipment in which a carburizing / nitriding zone for continuously carburizing or nitrifying the cold rolled steel sheet is interposed between the cooling zone and the cooling zone.

[0002]

2. Description of the Related Art In the metal secondary processing industry such as the automobile industry, it is required for a metal plate to be processed to have both high workability and strength. Specifically, in the automobile industry, it is necessary to reduce the weight of the vehicle body in order to pursue low fuel consumption due to the global environmental problems that have recently become a problem, so a steel plate with higher strength while maintaining the conventional deep drawability Is required.

As an evaluation index of such a metal plate, for example, ductility, deep drawability, aging property, strength, secondary work brittleness, bake hardenability, spot weldability and the like are considered. Therefore, when the deep drawability is evaluated with a Rankford value (r value: metal plate width strain / plate thickness strain) with particular emphasis on the deep drawability, carbon in steel (hereinafter simply referred to as C) is used. It is known that it is most advantageous to reduce the amount thereof, and in addition, the low carbonization also improves the ductility (Elongation: El) and the non-aging property. However, on the other hand, there is a material property that deteriorates as the amount of C in steel decreases. For example, tensile strength (Tensile Strengt
h: TS) deteriorates, the grain boundary strength decreases, secondary processing brittleness deteriorates, and the amount of solute C decreases, and bake hardenability deteriorates. Further, when the C content in the steel is 50 ppm or less, the grain growth rate is accelerated by heating by welding, and the heat-affected zone (Heat A
Spot weldability deteriorates due to coarsening of the ffected zone (HAZ).

[0004] Therefore, while obtaining the above-mentioned ductility, deep drawability and aging property by continuously re-annealing a metal band made of ultra-low carbon steel by recrystallization annealing to develop the crystal orientation, the steel is continuously carburized. In order to improve the tensile strength, secondary work embrittlement, BH property, spot weldability and the like by allowing solid solution C to exist therein, the present applicant has disclosed in Japanese Patent Laid-Open No. 4-88126 as shown in FIG. The continuous annealing equipment for the metal strips described has been developed.

According to this continuous annealing equipment, after the predetermined recrystallization is performed on the metal strip in the heating zone 2 or the soaking zone 3, the steel sheet temperature, atmosphere specifications, transfer speed (in-furnace time), and cooling are performed. By performing the carburizing treatment under controlled conditions, it is possible to continuously manufacture the metal strip having the desired values of the carburizing depth and concentration distribution while satisfying the material specifications of the metal strip.

[0006]

By the way, in order to secure the productivity especially in the continuous annealing furnace for general cold-rolled steel sheets,
Generally, the total furnace length (total strip length) is 1000 to 200
It should be 0 m or longer. Generally, a vertical furnace is widely used in order to solve the problems such as the layout of a heating device such as a radiant tube and the cooling device such as a cooling gas chamber, and the overall required floor area while ensuring the total path length. Has been adopted. Based on these achievements, it is desirable that the carburizing zone be formed of a vertical furnace in the continuous annealing equipment for metal strips described in JP-A-4-88126.

However, the vertical furnace is generally expensive to build. In addition, the continuous annealing equipment provided with the carburizing / nitriding zone can achieve the same effect by adding the carburizing / nitriding zone to the existing continuous annealing equipment. Therefore, it is necessary to intervene in the post-process of the heating zone or soaking zone and in the pre-process of the cooling zone. Therefore, it is not possible to construct a vertical carburizing / nitriding zone in the existing vertical continuous carburizing furnace afterwards. Or, it is necessary to move the entrance side equipment before soaking or the exit side equipment after the cooling zone, which not only increases the required floor space, but also makes the cost of building an originally expensive vertical furnace more expensive. The difficulty of becoming

Further, there is a metal plate which does not require carburizing or nitrifying treatment in the continuous annealing operation. However, as is known, in actual continuous annealing operations, both metal sheets that do not require carburizing or nitriding treatment and metal sheets that require such treatment are carburized / nitrided as a series of strips in the inlet welding machine. It is passed through a continuous annealing facility with a band added. Moreover, nowadays it is necessary to produce various kinds of metal plates with various required specifications in small quantities, and these various kinds of metal plates are passed through a series of strips in a continuous carburizing / nitriding zone. It is extremely difficult to change the strip passage such as not doing so. On the other hand, in order to prevent the carburizing / nitriding process from being performed in the carburizing / nitriding zone, the atmosphere in the carburizing / nitriding zone is changed from the carburizing / nitriding atmosphere to another, for example, a soaking atmosphere. Although it has to be switched, there is also a problem that a specific means for switching such an atmosphere in a short time is lacking.

The present invention was developed in view of these problems, and is particularly useful when adding a carburizing / nitriding zone to an existing continuous annealing furnace, and a metal requiring carburizing / nitriding treatment. We provide continuous annealing equipment for metal strips, which can pass both strips and metal strips that are not required as a series of strips, and can change the atmosphere in the carburizing / nitriding zone necessary for controlling them in a short time. The purpose is to do.

[0010]

Means for Solving the Problems The inventors of the present invention have earnestly studied in view of the above problems, and as a result, have obtained the following knowledge. In setting the various conditions of the continuous annealing equipment with the carburizing / nitriding zone as described above, the specifications of the metal strip after the carburizing treatment were calculated from the specifications required for the steel sheet as described above. Since the metal strip of is a very low carbon steel, that is, the amount of C in the material is extremely low, and a small amount of solid solution C is required to exist only in the ultrathin surface layer of the steel sheet, the carburizing time is It was found that the carburizing time is extremely short compared to the carburizing treatment of, for example, a carburizing time of several seconds to several tens of seconds is effective.

When the amount of C in the metal surface layer is high to some extent and the carburizing time is long as in general tempered steel, the carburizing rate is such that C diffuses into the metal structure after the C concentration in the surface layer reaches the equilibrium concentration. It is proportional to the speed of movement and is usually proportional to the square root of time. On the other hand, when the C content of the metal surface layer portion is extremely low and the carburizing time is extremely short, as in the continuous annealing equipment that is continuous from the continuous annealing step to the carburizing / nitriding step to be solved by the present invention, Since the C concentration does not reach the equilibrium concentration,
The carburization rate is proportional to the surface reaction rate at which the metal surface layer portion and carbon directly react, that is, it is proportional to the time itself. Therefore, in the case of continuously carburizing a strip made of ultra-low carbon steel as described above, the carburizing time can be extremely short because it is in the surface reaction rate-controlling region.

This means that even if the transport speed of the metal plate that is passed through the continuous annealing step furnace is high, the in-furnace time may be short, and the total path length required for carburizing is calculated to be the annealing. It is only a few tens of meters, specifically about 60 to 100 m, compared to the total path length required for. In this case, a horizontal furnace that horizontally passes a metal plate is more efficient, and one horizontal path length of 30 to 50 m in two horizontal paths requires a required furnace length of 50 to 60 m, resulting in lower construction costs. In addition, the additional cost to the existing continuous annealing furnace can be small.

Further, in a horizontal carburizing / nitriding furnace having a short total path length, the atmosphere can be easily switched, so that, for example, for a metal band which does not require carburizing / nitriding treatment, for example, it is the same as or similar to the soaking zone atmosphere. By setting the atmosphere, the soaking effect up to the subsequent cooling zone can be maintained. Furthermore, in order to switch the atmosphere in the carburizing / nitriding zone in an extremely short time, if a floater that supports the metal zone by directly injecting the atmospheric gas into the metal strip to be passed is adopted, the continuous carburizing treatment is particularly performed. As described above, since the surface reaction rate-determining region is used, the atmosphere can be switched in an extremely short time.

That is, the continuous annealing equipment for a metal strip according to claim 1 of the present invention heats the metal strip as an annealing process furnace in the step of passing the continuously fed metal strip. As a carburizing / nitriding process furnace for continuously carburizing or nitrifying the heated or soaked metal strip between a heating zone or a heating zone and a soaking zone and then a cooling zone for cooling the metal zone In continuous annealing equipment for metal strips with carburizing / nitriding zones,
The carburizing / nitriding process furnace has a horizontal carburizing path.
It is characterized in that the nitrification zone is provided in the upper part or the lower part of the annealing process furnace composed of the heating zone, the soaking zone and the like.

In the continuous annealing equipment for a metal strip according to claim 2 of the present invention, in the carburizing / nitriding zone, the atmosphere in the carburizing / nitriding zone is set to an atmosphere equivalent to or similar to the soaking zone. It is characterized in that an atmosphere switching device for switching between each other is added. In the continuous annealing equipment for metal strips according to claim 3 of the present invention, the carburizing / nitriding zone is provided with a metal strip that is passed through a horizontal path in the carburizing / nitriding zone by means of an atmospheric gas injected. It is characterized in that a supporting floater is provided.

[0016]

In the continuous annealing equipment for a metal strip according to claim 1 of the present invention, a heating zone for heating the metal strip as an annealing process furnace in the strip passing step of the continuously fed metal strip. Alternatively, as a carburizing / nitriding process furnace interposed between a heating zone and a soaking zone, and then a cooling zone for cooling the metal zone, a carburizing / nitriding zone having a horizontal path is used as the heating zone or the soaking zone. By providing the upper part or the lower part of the annealing process furnace composed of, especially when adding a carburizing / nitriding zone to an existing continuous annealing furnace, a space is formed by excavation in the lower part of the continuous annealing furnace, Alternatively, a carburizing / nitriding zone can be formed and added to these spaces by utilizing the extra space above.

In the continuous annealing equipment for a metal strip according to claim 2 of the present invention, the atmosphere in the carburizing / nitriding zone is set to be the same as or similar to the soaking zone in the carburizing / nitriding zone. By adding an atmosphere switching device to switch to
For example, the atmosphere in the carburizing / nitriding zone is carburized or changed without changing the passage path of a series of strips of metal plates that do not require carburizing / nitriding treatment or metal plates that require such treatment. A metal plate that requires carburizing / nitriding treatment as a nitrifying atmosphere is subjected to the same treatment, and the atmosphere in the carburizing / nitriding zone is soaked to a metal plate that does not require carburizing / nitriding treatment. The effect can be maintained until just before the cooling zone.

In the continuous annealing equipment for metal strips according to claim 3 of the present invention, the metal which is passed through the carburizing / nitriding zone by a horizontal path in the carburizing / nitriding zone with the atmospheric gas injected. Since the floater supporting the belt is provided, for example, by changing the atmosphere gas injected from the floater to carburizing or nitrifying atmosphere gas, the carburizing atmosphere is controlled in an extremely short time particularly in the carburizing treatment in the surface reaction rate-controlling region. By switching the atmosphere gas injected from the floater to the soaking atmosphere gas by the atmosphere switching device, a soaking atmosphere on the surface of the metal plate in the carburizing / nitriding zone can be obtained in a short time. It will be possible.

[0019]

EXAMPLE FIG. 1 shows an example of the continuous annealing equipment for metal strips according to the present invention, which shows an example of continuous annealing carburizing equipment for strips made of ultra-low carbon steel. In the figure, the ultra-low carbon steel strip A is an unillustrated inlet side equipment having a coil rewinding machine, a welding machine, a washing machine, etc., a preheating zone 1, a heating zone 2, a soaking zone 3, a carburizing zone 4, a first cooling zone 5 , The second cooling zone 6, the shearing machine, the winding machine, and the like, which are not shown, are passed through in this order on the outlet side equipment. In the present embodiment, the continuous annealing furnace including the pre-tropical zone 1, the heating zone 2, the soaking zone 3, the first and second cooling zones 5 and 6 other than the carburizing zone 4 passes the strip A through a vertical pass. It consists of a so-called vertical furnace. As described above, in the continuous annealing process, the stripping speed is set based on the required processing time, that is, the productivity, under the furnace temperature (furnace temperature) set by the calculation of the furnace capacity, etc. The total path length of is set. Since the length thereof reaches approximately 1000 m to 2000 m, it is most efficient to construct the continuous annealing equipment in the vertical furnace to effectively use the required floor area. The continuous annealing furnace of this embodiment is also constructed in advance according to such a technical idea.

The heating zone 2 is for heating the strip A, which is continuously fed from the inlet side equipment and preheated, to a recrystallization temperature or higher. Specifically, the temperature in the furnace is 850 to 1
The strip A is heated so that at 000 ° C the temperature of strip A is above the recrystallization temperature of 700-950 ° C.
Then, the heated strip A is maintained at the recrystallization temperature or higher for the required time in the soaking zone 3 to develop a {1,1,1} texture advantageous for deep drawability.

The carburizing zone 4 is, in this embodiment, the pretropical zone 1, the heating zone 2, the soaking zone 3, the first and second cooling zones 5, 5.
It is arranged below the continuous annealing furnace composed of 6,
Specifically, the carburizing furnace is embedded in the space formed by excavating the floor below the first to second cooling zones 5 and 6. As described above, the technical idea of improving the material property of the strip by interposing the carburizing step between the heating or soaking step and the cooling step in the continuous annealing step previously proposed by the applicant is industrially Although it is of high utility value, the idea itself was after the construction of continuous annealing equipment, so in many cases the existing continuous annealing equipment is added with a carburizing zone. On the other hand, if it is found that the required length of the furnace for the carburizing zone is approximately 50 to 60 m as described above, it is not necessary to purposely construct the carburizing zone with a vertical furnace, which is expensive to construct. In the example, a horizontal carburized zone was formed in the space obtained by excavating the floor. As a result, in order to install the vertical carburizing furnace between the soaking zone and the first cooling zone, the existing inlet side equipment before the soaking zone is moved to the inlet side or
It is not necessary to move the outlet side equipment after the cooling zone to the outlet side, and it is possible to reduce the space and the required floor area corresponding to the amount of movement.

In order to carburize the carburizing zone 4 from the strip surface, the carburizing furnace in the carburizing zone 4 is controlled to a furnace temperature of 700 to 950 ° C. by a host computer (not shown), and the strip moves in the carburizing furnace. The strip speed is controlled so that the strip passes in 10 to 120 seconds. Further, the temperature distribution in the carburizing zone is preferably controlled so that the temperature difference in the furnace is within 50 ° C. in order to prevent sooting on metal objects (for example, furnace wall) in the furnace.

The physical properties in the carburizing furnace, the carburizing temperature, the stripping speed, that is, the carburizing time are regarded as the physical quantities (control quantities) to be controlled in the actual continuous carburizing, and are required to be formed into strips by the host computer. In order to realize the carburizing amount, for example, set the carburizing amount from the usage specifications such as the carburizing concentration distribution of the carburizing layer and the carburizing depth, and appropriately select various basic equations related to these preset control amounts. The respective controlled variables are calculated, and the controlled variables are set in consideration of the capacity and process of other equipment.

The composition and supply / exhaust flow rate of the carburizing gas supplied into the carburizing furnace are determined by the host computer in consideration of the material balance in the furnace and the atmospheric composition model in which the free energy in the furnace is minimized. It is controlled according to various conditions calculated based on the formula. The composition of the carburizing gas and the supply / exhaust flow rate thereof are controlled so as to suppress the increase of CO ₂ and dew point and prevent the decrease of the carburizing reaction rate and the temper color.

Here, in the case of continuous carburizing according to the specifications of the steel sheet required for a series of strips by the continuous carburizing equipment as in the present embodiment, the actual carburizing condition of such continuous carburizing operation is the conventional one. The level of the carburizing treatment conditions and the items necessary for satisfying the carburizing treatment conditions will be described. Conventional carburizing technology is carried out for the purpose of surface hardening to improve wear resistance and impact resistance of discontinuous materials such as gears, shafts and bearings made of so-called heat-treated steel. Therefore, the amount of C in the material is 0.05% or more, the required carburizing amount is 0.1% or more, and the carburizing depth is 0.5 to 1.5 mm or more. Therefore, the carburizing time is 1 to 5 hours. Extends to Under such conditions, the C concentration in the surface layer of the steel sheet reaches the equilibrium concentration with respect to time, so the carburizing rate is in the steel diffusion-controlled region according to the diffusion rate into the steel, and the carburizing rate varies with time. Proportional to the square root. In this carburizing rate range, it is necessary to control the carbon potential (C potential) of the atmospheric gas so that the diffusion rate in steel becomes the surface reaction rate, and CO / CO ₂ control is important as an actual operation control index. .

On the other hand, in the continuous carburization of the strip as in this embodiment, the strip is a continuous product made of the above-mentioned ultra-low carbon steel, and the surface characteristics of this strip are improved and the material of the steel plate itself is improved. It is done for the purpose. Therefore, for example, the specifications required for the metal for improving the secondary processing brittleness resistance (Japanese Patent Laid-Open No. 19934/1993).
When the carburizing conditions for the metal strip are obtained from
In this embodiment, the amount of C in the material is 20 ppm, the required carburizing amount is 200 ppm or less, and the carburizing depth is 50 to 200 μm.
And the carburizing time depends on the strip running speed is 120
Less than a second Under such conditions, C of the steel plate surface layer portion
Since the concentration does not reach the equilibrium concentration with respect to time, the report by Ha et al. (Youn Ha, Shiro Haruyama et al .: Journal of Japan Institute of Metals 49 (1985))
7,529), the carburizing rate is a surface reaction rate-determining region according to the reaction rate of the steel surface, and the carburizing rate is proportional to the time itself. Since the carburizing amount and carburizing depth are in a non-equilibrium state in this surface reaction rate-determining region, CO / CO is controlled by C potential control so that the equilibrium C concentration in the surface layer of the steel is simply used as an actual operation control index. It is necessary to set the carburizing conditions so as to obtain the carburizing amount determined from the required specifications of the steel sheet, in addition to managing No. ₂ and taking into consideration a large number of control amounts in the furnace.

Next, in controlling the composition of the atmospheric gas in the surface reaction rate-controlling region, it is necessary to prevent sooting and suppress the rise in dew point as described above. Reasoning like. Generally, the atmospheric gas composition under carburizing conditions can be determined by chemical equilibrium. In the conventional solution method, all possible reactions are listed, and the gas composition is obtained by solving the nonlinear simultaneous equations from the equilibrium of these reactions. However, it is extremely difficult to accurately determine the limit of sooting (sooting) only from the reaction formula of the gas phase system.

Therefore, in this example, the thermodynamic (atmosphere composition) model formula was considered as follows, and the atmosphere gas composition for preventing sooting was determined. In the case of an isothermal and isobaric system, the Gibbs free energy decreases naturally, and the Gibbs free energy of the system takes a minimum value at equilibrium. Therefore, in order to obtain the equilibrium state of the atmospheric gas, the Gibbs free energy of the whole system obtained by using the concentration of each component gas of the production system as a variable is used as the objective function, and the elemental component brought into the original system is constant. Each component should be at its minimum value under the constraint condition of the balance, specifically, under the constraint condition that the composition and supply amount of the atmospheric gas supplied into the furnace and the C amount taken out from the furnace into the metal band by carburization are constant. The gas concentration should be calculated. This component gas concentration is the equilibrium composition of the atmospheric gas at the given furnace temperature and furnace pressure.

The strip A fed from the soaking zone 3 into the carburizing furnace or delivered from the carburizing furnace to the first cooling zone 5 is horizontally (horizontally) passed through a deflector roll 20 shown in FIG. Passed). A chromium Cr alloy is used for these deflector rolls 20 in order to maintain the strength and wear resistance of the rolls themselves. Further, these deflector rolls 20 are cooled, for example, in the vicinity of bearings in order to maintain the rotatability and roll crown in a predetermined state. Therefore, when the carburizing atmosphere gas reaches the vicinity of the deflector roll 20, the carburizing atmosphere gas is cooled and the sooting progresses. Therefore, free C [C] adheres to the deflector roll 20 and then diffuses inside the roll. In this case, the Cr
And C combine to precipitate Cr carbide, which destroys or expands the crystal grains, while reducing the solid solution Cr, so that the deflector roll 20 is embrittled and oxidizes to cause pore-like corrosion. To do. When the rolls are exposed to the carburizing atmosphere gas as described above, it has been found from experiments by the present inventors that the rolls must be replaced within two years. Therefore, in this embodiment, the deflector roll chamber is separated from the carburizing atmosphere by a non-contact sealing device 21 to prevent the deflector roll 20 from deteriorating, and the deflector roll chamber is prevented from deteriorating to such an extent. By making the carburized state weak, it was possible to prevent decarburization while the strip A passed through the separated deflector roll chamber. When the strip passes through the deflector roll chamber for a very short time and the decarburization from the steel sheet surface layer portion during the time is not a problem, the deflector roll chamber may be set to a non-carburizing atmosphere.

The sealing device 21 includes, for example, as shown in FIG. 2, three layers of sealing layers 22a, 22b and 22c interposed between a deflector roll chamber and a carburizing furnace, of which a deflector roll chamber side seal is provided. The weak carburizing atmosphere gas is jetted to the layer 22a, the carburizing atmosphere gas is jetted to the seal layer 22c on the carburizing furnace side, and the middle seal layer 22b is exhausted. And controlling the injection flow rate so that the flow of each atmospheric gas is directed to the intermediate seal layer side, and the circulation flow generated by the plate laminar flow accompanying the strip passing plate is applied in the width direction of the strip of each seal layer. The exhaust was formed from the discharge port formed on the end face. Incidentally, the sealing device 21 between the soaking zone and the deflector roll chamber shown in FIG. 2 and the sealing device 21 between the first cooling zone and the deflector roll chamber have the same basic structure as described above, but each of them has a soaking zone seal. Layer 22
The gas injected from c and the first cooling zone side seal layer 22c is the soaking atmosphere gas and the first cooling zone atmosphere gas.

The strip A horizontally passed by the deflector roll 20 passes through the bend floater 10 in the carburizing furnace for two passes. The strip A in each pass is supported by the floaters 11 and 12 in a non-contact manner so that the catenary does not cause slack between the bend portions. Of these floaters, the atmospheric gas in the carburizing furnace is dynamically injected from the floater 11 and the bend floater 10 in the carburizing furnace, and the floater 1 in the deflector roll chamber is injected.
From above, the weak carburizing atmosphere gas is injected under dynamic pressure, and the strip A is levitated by the kinetic energy of these atmosphere gases and supported in a non-contact manner.

A contact type hearth roll can be used in place of the bend floater 10 to pass the strip back, and a contact type support roll can be used in place of the floaters 11 and 12 to prevent loosening. Can also be used. However, as described above, in the carburizing atmosphere, the free C causes a material defect on the metal surface. Therefore, if the strip is supported by these contact rolls, the material defect may damage the strip side. In order to prevent this material loss, it is necessary to separate the carburizing atmosphere into individual chambers like the above-mentioned deflector roll, which would shorten the effective carburizing furnace length accordingly. There are disadvantages. Further, it is technically difficult to separate the support rolls into individual rooms.

On the other hand, the dynamic pressure injection type floaters 11, 1
Since 2 and the bend floater 10 float and support the strip A in a non-contact manner, even if a material defect due to the free C occurs on the surfaces of the floater and the bend floater, the strip may be directly damaged. small. Therefore, if it is determined that the life of these support materials is the time when the scratches are formed on the strip, the life of the floater or the bend floater is longer, and the man-hours for maintenance and inspection are reduced accordingly.

Since the atmospheric gas is jetted dynamically from these floaters and bend floaters to support the strip in a non-contact manner, the kinetic energy of the jetted atmospheric gas is larger than that of static pressure jet, and the flow velocity and flow rate are also higher. Is also big. Therefore, when these atmospheric gas compositions are changed by the atmospheric gas switching device described later, the surface atmospheric gas composition of the strip can be switched in a relatively short time. This means that in continuous annealing equipment that passes a small amount of various cold-rolled steel sheets as a series of strips by welding, it is possible to perform high response control of atmospheric gas according to the specifications of each cold-rolled steel sheet. .

The atmospheric gas switching device (not shown) switches the atmospheric gas supplied to each of the floaters and bend floaters to an atmospheric gas having predetermined specifications. As described above, in this type of continuous annealing equipment that passes a wide variety of cold-rolled steel sheets as a series of strips, it is extremely difficult to switch the passage path so as to avoid the carburizing zone that has started to be passed once. . Further, among the specifications of the various types of cold-rolled steel sheets, some require carburizing treatment and some do not. Therefore, it is necessary to switch the atmosphere in the carburizing furnace from the carburizing atmosphere to the non-carburizing atmosphere.

On the other hand, in a normal carburizing furnace, atmosphere control or atmosphere switching is performed by changing the composition of the atmosphere supplied to the entire furnace or a zone obtained by dividing the furnace into several zones. With the atmosphere switching method, the reaction speed is slow and it takes time to change the atmosphere. However, in the carburizing zone of the present embodiment, since the atmospheric gas is dynamically pressure-injected from the floater for non-contact support, it is possible to change the strip surface atmospheric composition in a relatively short time by switching the atmospheric gas. Is. Therefore, in the case of a cold-rolled steel sheet that does not require the carburizing treatment, the carburizing furnace is switched by switching the atmospheric gas injected from the floater to an atmospheric gas equivalent or similar to that in the soaking zone by the atmospheric gas switching device. Without carburizing inside,
Moreover, the recrystallization annealing efficiency can be improved by increasing the soaking time. A specific example of this atmospheric gas switching device is an electromagnetic valve for switching the supplied atmospheric gas flow path.

Strip A delivered from this carburizing zone 4
Is fed to the first cooling zone 5. In the first cooling zone 5, the solid solution C is fixed only in the extremely thin area of the surface of the carburized strip A, so that the carburized strip A has a steel plate temperature of 600 ° C. or lower, preferably 500 ° C.
It is rapidly cooled at a cooling rate of 20 ° C / sec. Or more until it reaches about 400 ° C. In the first cooling zone 5, the flow rate, flow rate, cooling roll temperature, wrapping angle, etc. of the cooling gas blown to the strip conveyed in the cooling zone are controlled so that this cooling condition can be achieved.

In the first cooling zone 5, the strip A is first moved up in the first cooling chamber 32a via the hearth roll 30 and is conveyed substantially horizontally in the hearth roll chamber 33, and then is passed through the hearth roll 30. The second cooling chamber 32b is passed through so as to descend. Each of the cooling chambers 32a, 32b
A cooling gas chamber chamber 31 including a gas jet chamber, a gas jet nozzle, and the like is internally provided inside. Further, the hearth roll chamber 33 includes the cooling chambers 32a,
32b is separated from each other and is connected only via the passage 34 through which the strip A passes. In each of the gas chambers 31 of the cooling chambers 32a and 32b, as in the conventional case, the cooling gas is fed into the gas jet chamber and is installed so as to face both surfaces of the strip A to be passed therethrough. Cooling is performed by blowing the heat of the strip A from the cooling gas by spraying on both surfaces from the gas jet nozzle. Further, in order to balance the cooling gas to be fed in the cooling chambers 12a and 12b, side exhaust is provided from the exhaust ports provided at the substantially central portions of the cooling gas chamber chambers 11 on both sides in the width direction of the strip A. Is going. In addition,
As with the conventional gas jet nozzle, a slit type nozzle is used in which the cooling gas is uniformly sprayed over the entire width direction of the strip. Further, by using this slit type gas jet nozzle, an air flow along the surface of the strip is generated from the opening of each cooling gas chamber 31 toward the outside in accordance with the basic equation of motion of the cooling gas.

On the other hand, in the hearth roll chamber 33, heating heaters using a heating gas inflow system or an electric heater in the heating zone 2 are installed so as to substantially oppose both ends of the hearth roll 30 in the longitudinal direction. There is. As is known, since the strip in the cooling zone has a higher temperature than the hearth roll, a temperature difference occurs in which the central portion of the strip in contact with the strip in the longitudinal direction has a higher temperature than the end portions in the longitudinal direction. As a result, a so-called thermal crown is generated in which the central portion of the roll in the longitudinal direction expands from the end portion in the longitudinal direction, which causes buckling called a cooling buckle. Therefore, the heater is used to heat the end portion of the hearth roll in the longitudinal direction to reduce the relative temperature difference and reduce the thermal crown amount. The heating capacity of the heater is set according to the inflow amount of the cooling gas from each of the cooling chambers 32a and 32b described later.

When the air flow of the cooling gas flows from each of the cooling chambers into the hearth roll chamber, a circulating flow of the cooling gas is generated between the cooling chamber and the hearth roll chamber, and the circulation of the cooling gas causes the amount of heat in the hearth roll chamber to increase. Since it is robbed, the heating efficiency of the heating heater is reduced, and as a result, the heating capacity of the heating heater must be increased, and the applied heating energy is wasted. From these points, the inflow of the cooling gas into the hearth roll chamber must be suppressed as much as possible.

Therefore, in this embodiment, the backflow gas jet nozzles are installed so as to face both surfaces of the strip A through which the backflow gas jet nozzle is passed. This backflow gas jet nozzle is specifically connected to the gas jet chamber, and the strip A
The cooling gas in the gas jet chamber is injected as a backflow gas toward the cooling gas jet nozzle side at the uppermost lower part of each cooling gas chamber chamber over substantially the entire width direction. The backflow gas jetted from the backflow gas jet nozzle is blown in the direction opposite to the air flow generated along the plate surface, so that the kinetic energy of the backflow gas causes the kinetic energy of the cooling gas. The generated air flow can be suppressed, and thus the circulating flow generated around the strip can be suppressed.

Further, in this embodiment, a space is formed in the cooling chamber above and below the backflow gas jet nozzle. This space is for exhausting the airflow, which cannot be avoided only by the kinetic energy of the backflow gas, by the side exhaust. Further, in this embodiment, the seal rolls are arranged so as to face both surfaces of the strip on the cooling chamber side in the hearth roll chamber and both surfaces of the strip on the hearth roll chamber side in each cooling chamber. By disposing the seal rolls in this way, the air flow of the cooling gas, which cannot be avoided even by the backflow gas, is separated from the strip surface, and the effect of exhausting by the side exhaust is assisted.

The strip A delivered from the first cooling zone 5 is then delivered to the second cooling zone 6. In the second cooling zone 6, gas cooling is performed up to a steel plate temperature of about 250 to 200 ° C. In this way, an extremely low carbon cold-rolled steel sheet for press forming can be finally obtained in which solid solution C exists only in the surface layer portion. FIG. 4 shows another embodiment of the continuous annealing equipment for metal strips of the present invention. In this embodiment, the carburizing zone 4 is composed of a horizontal carburizing furnace arranged above the cooling furnaces constituting the cooling zones 5 and 6. The specific structure is almost the same as that of FIG. 1, and the strip A fed from the soaking zone 3 is pulled up from below and the strip A fed to the cooling zone is pulled down from above. And

FIG. 5 shows still another embodiment of the continuous annealing equipment for metal strips according to the present invention, which is lateral to the main strip running direction in the continuous annealing equipment comprising heating, soaking and cooling zones. A carburizing zone 4 composed of a carburizing furnace is arranged in a direction orthogonal to the carburizing zone 4 and below the continuous annealing furnace. In order to convert the passage direction into the twisting direction in this way, it is possible to use, for example, a tapered bend float 13 alone or in combination as shown in FIG. By the way, when the taper type contact roll is rotated, the peripheral speed of the roll is different due to the difference in the bus bar contact position, so that the smooth passage cannot be performed.

In this embodiment, only the case where carburizing is performed in the continuous annealing furnace has been described, but a carburizing zone may be replaced with a carburizing zone for carburizing. Also, by changing the atmosphere, it is possible to use the same furnace for carburizing and nitrifying separately. As the nitriding atmosphere, it is sufficient to use (N ₂ + H ₂ ) gas containing NH ₃ gas or other mixed gas. The carburizing zone of the present invention may be not only carburized but also carbonitrided.

Further, in the above-mentioned embodiment, only continuous annealing of the cold rolled steel sheet of ultra low carbon steel was explained, but the present invention is not limited to this, and low carbon steel sheets such as low carbon-rimmed steel and low carbon-aluminum killed steel can be used. It can be applied to any metal belt. Furthermore, a plate temperature control zone is provided between the soaking zone and the carburizing zone, and the soaking zone and the plate temperature control zone are formed by the same furnace.
It is possible to abbreviate it as the soaking zone, provide a diffusion zone for adjusting the carburizing depth between the carburizing zone and the first cooling zone, and use two cooling zones as one cooling zone. is there.

[0047]

As described above, according to the continuous annealing equipment for metal strips of the present invention, the carburizing / nitriding zone having the horizontal path is provided at the upper part or the lower part of the continuous annealing process furnace. When adding a carburizing / nitriding zone to the continuous annealing furnace of
Space can be formed in the lower part of the continuous annealing furnace by excavation, or by utilizing the extra space in the upper part, carburizing / nitriding zones can be formed and added to those spaces, saving space and reducing construction costs. Allows for savings. In addition, by switching the atmosphere in the carburizing / nitriding zone to the same or similar atmosphere as the soaking zone by the atmosphere switching device, the carburizing / nitriding process can be performed without changing the strip passing path. The soaking effect can be maintained until just before the cooling zone in the unnecessary metal plate portion. Further, by supporting the metal strip through which the horizontal path in the carburizing / nitriding zone is passed by the atmospheric gas injected from the floater, the carburizing atmosphere in the carburizing process in the surface reaction rate-controlling zone is controlled in an extremely short time. It is possible to obtain a uniform heating atmosphere on the surface of the metal plate in a short time by the atmosphere switching device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a continuous annealing equipment for metal strips of the present invention.

FIG. 2 is a detailed view of a horizontal carburizing zone in the continuous annealing equipment of FIG.

3A and 3B are explanatory views of each floater in the carburizing zone of FIG. 2, FIG. 3A is a side view of the floater, and FIG. 3B is a side view of the bend floater.

FIG. 4 is a schematic configuration diagram showing another embodiment of the continuous annealing equipment for metal strips of the present invention.

FIG. 5 is a schematic configuration diagram showing still another embodiment of the continuous annealing equipment for metal strips of the present invention.

6 is an explanatory view of a tapered bend float for supplying a strip to a horizontal carburizing zone in the continuous annealing equipment of FIG.

FIG. 7 is a schematic configuration diagram showing an example of a conventional continuous annealing equipment for metal strips.

[Explanation of symbols]

 1 is pre-tropical zone 2 is heating zone 3 is soaking zone 4 is carburizing zone 5 is first cooling zone 6 is second cooling zone 10 is bend floater 11 is floater 12 is floater 13 is bend floater A is strip

Claims (3)

[Claims] 1. A heating zone or a heating zone and a soaking zone for heating the metal strip as an annealing process furnace in a striping process of a continuously fed metal strip, and then cooling the metal strip. Carburizing and carburizing as a furnace for carburizing or nitrifying the heated or soaked metal strip continuously with the cooling zone.
In a continuous annealing equipment for metal strips with an intervening nitrification zone, as the carburizing / nitriding step furnace, the carburizing / nitriding zone having a horizontal path is an upper part of the annealing step furnace composed of the heating zone and the soaking zone. Alternatively, the continuous annealing equipment for metal strips is provided at the bottom. 2. The carburizing / nitriding zone is provided with an atmosphere switching device for mutually switching the atmosphere in the carburizing / nitriding zone to an atmosphere equivalent to or similar to the soaking zone. The continuous annealing equipment for a metal strip according to claim 1. 3. The carburizing / nitriding zone is provided with a floater for supporting a metal strip through which a horizontal path in the carburizing / nitriding zone is passed by an injected atmospheric gas. The continuous annealing equipment for a metal strip according to claim 1 or 2.