JPH07138651A - Method and device for quickly replacing atmospheric gas in continuous heat treatment furnace - Google Patents

Abstract

PURPOSE:To provide a continuous heat treatment furnace which can quickly replace atmospheric gas, and a method therefor. CONSTITUTION:In the continuous heat treatment furnace for using at least two kinds of atmospheric gas components or concns. in carburizing treatment, nitrogenizing treatment or general heat treatment, at least one of chamber 3 surrounding the periphery of a steel strip 1 between a hearth roll 2 and the other hearth roll 2 is arranged. Further, an atmospheric gas supplying means 4 into the chamber 3 is arranged, and at least one side of the end parts of the chamber 3 at an inlet side or an outlet side of the steel strip, is opened. Guide roll may be arranged at the end part or the inner part of the chamber 3. The atmospheric gas is supplied in this chamber 3 and the atmosphere in the chamber 3 can quickly be replaced. In the carburizing furnace, each different kind of the atmospheric gases are independently supplied into each chamber 3 arranging plural sets and the carburized rate on the steel strip can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atmosphere gas replacement technique such as carburizing / nitriding treatment in a continuous heat treatment furnace.

[0002]

2. Description of the Related Art In recent years,
As a method for producing a steel sheet requiring high formability such as an automobile steel sheet, a method of continuously annealing ultra-low carbon steel containing Ti and Nb is adopted. On the other hand, bake hardening type steel plate (hereinafter referred to as BH steel plate) to which bake hardenability (hereinafter referred to as BH), which is one method for increasing the strength of the steel plate, is used as an outer panel for automobiles. . However, the ultra low carbon steel as described above has insufficient bake hardenability because there is no solid solution C in the steel.

Therefore, as a technique for producing a BH steel sheet, a method has been proposed in which Ti is added in an amount less than the atomic equivalent of C with respect to the amount of C in the steel making stage to leave solid solution C in the steel (Japanese Patent Publication No. 61-2732). ing. However, in this method, in addition to the deterioration of the deep drawability, it is extremely difficult to control the amount of solid solution C to be left by the added amount of C and Ti, and it cannot be said that the productivity is necessarily good.

As a technique for achieving both deep drawability and bake hardenability, a technique for trace carburizing and nitriding during continuous annealing has been proposed, as disclosed in JP-A-3-72032. However, although the carburizing method using the continuous annealing furnace can achieve high bake hardenability and deep drawability, in order to actually manufacture in the continuous heat treating furnace, it is necessary to perform the treatment between the general treated steel sheet and the carburized steel sheet and vice versa. It was necessary to pass a dummy steel plate during the treatment of 1 to replace the carburizing atmosphere with the necessary reducing atmosphere. Usually, for gas replacement, it is necessary to insert a replacement gas of 5 times or more the furnace volume. As a method of replacing the gas in the furnace in a continuous heat treatment furnace, it has been proposed to have a plurality of carburizing / nitriding zones as in Japanese Patent Laid-Open No. 4-202650 to switch the atmosphere gas. In the method of substituting the atmosphere gas of the strip itself, it takes time to replace the gas or an apparatus for supplying a large volume of atmosphere gas is required, resulting in deterioration of productivity or cost performance.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a continuous heat treatment furnace and method capable of rapidly replacing atmospheric gas.

[0006]

As a means for solving the above-mentioned problems, the present invention provides a continuous heat treatment furnace using at least two kinds of atmospheric gas components or concentrations in carburizing treatment, nitrifying treatment or general heat treatment, A continuous heat treatment furnace is characterized in that at least one chamber surrounding a steel strip between the hearth roll and the hearth roll is provided, and an atmosphere gas supply unit is provided in the chamber.

Another aspect of the present invention is a continuous heat treatment method using at least two kinds of atmospheric gas components or concentrations in a carburizing treatment, a nitrifying treatment, or a general heat treatment. At least 1 to surround
The gist is a continuous heat treatment method characterized in that individual chambers are provided and an atmosphere gas is supplied into the chambers to rapidly replace the atmosphere in the chambers.

[0008]

The present invention will be described in more detail below.

According to the present invention, in essence, at least one chamber surrounding the steel strip in the furnace is provided, and the atmosphere gas having a desired component or concentration is supplied into the chamber to rapidly replace the inside of the chamber. It is intended to improve the atmosphere gas replacement rate.

[0010]

【Example】

FIG. 1 shows an example in which a chamber in a continuous annealing furnace is used as a carburizing furnace zone or a nitriding furnace zone. Hearth roll for transporting steel strip (1) in the furnace
A plurality of (2) are installed. At least one chamber (3) is installed between the hearth roll (2) and the hearth roll (2) so as to surround the steel strip (1) to be conveyed. Chamber
An atmosphere gas supply hole (4) is installed on the side surface of (3) to supply a gas having a necessary component or concentration (see FIG. 2). Normally, the end of the chamber is open, and the supplied gas flows along the steel plate in the chamber (3) from the end of the chamber (3) (outside the furnace) as shown in FIG. Spill to. Atmospheric gas suction hole (5) for sucking and discharging the outflowing gas
May be provided. (6) is a sealing device, and (7) is an atmosphere gas analyzer, which are provided as appropriate. The sealing device (6) has a shielding structure. Atmosphere gas analyzer (7) is a chamber
Outside of (3), for example, analyze that the atmospheric gas in the carburizing or nitriding furnace became the target atmospheric gas, and analyze the chamber (3)
It is provided for the purpose of reducing the gas supply amount to the.

The above-mentioned chamber (3) may have a structure in which at least two or more parts are divided in each pass in the furnace zone or in one pass. In FIG. 1, the chamber on the left side is the case where one is provided in one pass, and the chamber on the right side is 1
This is a case where the path is divided into two parts. In addition, 1 pass means between the hearth rolls (2) and the hearth rolls (2) which are adjacent to each other.

In the case of a carburizing or nitriding furnace, at least two or more chambers (3) surrounding the steel strip in the furnace and having open ends are provided, and each chamber is individually controlled to a desired atmospheric gas, The required carburizing length can be quickly switched.

Next, the operation of the continuous heat treatment furnace will be described.
In order to switch the supply gas for replacing the atmosphere gas, the replacement gas is supplied from the atmosphere gas supply port (4) to the chamber (3).
Supply in. The supplied gas moves to the lower pressure side, that is, to the outside of the chamber (3), and therefore flows from the ambient gas supply hole (4) to both ends of the chamber (3),
To the outside of. Further, in order to make the gas flow in the chamber (3) smooth, the atmospheric gas according to the amount of supplied gas is discharged from the atmospheric gas suction hole. According to the results measured by the atmospheric gas analyzer (7), if the inside of the carburizing or nitrifying furnace zone is completely replaced with the target gas, the
The gas flow to the outside of (3) becomes unnecessary, so switch to the supply gas amount to maintain the furnace pressure.

When the atmospheric gas in each chamber is controlled individually, if the measurement result of the atmospheric gas analyzer (7) is the average value of the atmospheric gas supplied from the atmospheric gas supply hole (4), gas replacement is performed. May be considered complete.

FIG. 4 shows a modification. Chamber (3)
This is a modified example for stabilizing the atmospheric gas concentration in the chamber while reducing the gas supply amount to the chamber and preventing scratches caused by the contact between the chamber (3) and the steel strip (1).

That is, in order to rapidly replace the gas in the chamber (3), the volume of the chamber (3) may be reduced, but contact with the steel plate may occur. Further, in order to stabilize the gas concentration in the chamber (3), it is necessary to prevent convection from the outside of the chamber. For this purpose, the area of the chamber end surface may be reduced, but there is a possibility of contact with the steel plate as in the above case. As a measure for improving the above two points, a guide roll (9) that rotates at the same speed as the steel strip is installed on the end surface of the chamber (3). By installing the guide roll (9) closer to the steel strip than the end face of the chamber, it is possible to prevent contact between the steel strip and the chamber and to have a gap according to the gas supply amount and to release the atmospheric gas from the chamber. it can. A guide roll for preventing contact with the steel strip may be installed in the chamber.

[0018]

As described in detail above, according to the present invention,
Since the chamber can be made extremely small compared to the volume of the furnace zone, it is possible to rapidly replace the gas in the chamber with the target gas. In a realistic continuous heat treatment furnace, the path length between the hearth rolls (≒ chamber length) is sufficiently long compared to the length in contact with the hearth rolls. It is possible to secure 70% or more of the chamber passage time with respect to the passage time. That is, by rapidly replacing the gas in the chamber, substantially the same effect as when replacing the atmospheric gas in the carburizing or nitriding furnace can be obtained. Further, by reducing the chamber volume, the required gas flow rate can be suppressed to a low level, and the gas supply capacity can be reduced, which in turn can reduce the equipment cost.

Particularly, in carburizing and nitrifying, the processing speed,
The necessary carburizing and nitriding amount, that is, the necessary carburizing and nitriding time changes depending on the plate thickness, etc. Therefore, it is necessary to change the carburizing and nitriding length. It can be divided into multiple parts in one pass and controlled, and the carburizing / nitriding atmosphere chamber and the reducing atmosphere chamber can be individually controlled as needed, so carburizing / nitriding according to the processing speed and plate thickness. The length can be changed rapidly compared to the conventional carburizing / nitriding furnace.

[Brief description of drawings]

FIG. 1 is a side view when a continuous heat treatment furnace is applied to a carburizing or nitriding furnace.

FIG. 2 is a perspective view of a chamber.

FIG. 3 is a schematic diagram showing a gas flow in a chamber.

FIG. 4 is an explanatory diagram showing a modified example of the chamber.

[Explanation of symbols]

 1 Steel strip 2 Hearth roll 3 Chamber 4 Atmosphere gas supply port 5 Atmosphere gas suction port 6 Sealing device 7 Atmosphere gas analyzer 8 Supply gas flow 9 Guide roll

Claims (6)

[Claims] 1. A continuous heat treatment furnace which uses at least two kinds of atmospheric gas components or concentrations in a carburizing treatment, a nitrifying treatment or a general heat treatment, and at least a chamber surrounding a steel strip between the hearth rolls. One provided,
Further, a continuous heat treatment furnace characterized by being provided with an atmosphere gas supply means into the chamber. 2. The continuous heat treatment furnace according to claim 1, wherein at least one chamber surrounding the circumference of the steel strip is provided between the other hearth rolls and the hearth rolls. 3. The continuous heat treatment furnace according to claim 1 or 2, wherein at least one of the end portions of the chamber on the steel strip entrance side or the steel strip exit side is open. 4. The continuous heat treatment furnace according to claim 1, 2 or 3, wherein a guide roll is provided at an end or inside of the chamber. 5. In a continuous heat treatment method using at least two kinds of atmospheric gas components or concentrations in carburizing treatment, nitrifying treatment or general heat treatment, at least one surrounding the steel strip between the hearth rolls. The continuous heat treatment method is characterized in that the chamber is provided, and an atmosphere gas is supplied into the chamber to rapidly replace the atmosphere in the chamber. 6. The carburizing furnace according to claim 5, wherein different kinds of atmospheric gases are independently supplied to a plurality of chambers installed to control the carburizing amount of the steel strip. Method.