JPH07278680A - Continuous annealing equipment for steel sheet - Google Patents

Abstract

PURPOSE:To enable small-quantity production of many kinds by suppressing extreme lengthening of continuous annealing equipment for steel sheets and decreasing thermal inertia. CONSTITUTION:Electrical heating is adopted for a heating zone 2 to intensity a heating ability and to decrease the thermal inertia. A coil box 6 is adopted for an overaging zone to avoid extreme lengthening of this overaging zone and to execute an overaging treatment by each coil. As a result, the equipment is made compact and simultaneously, the thermal inertia is decreased. Changing of conditions, such as heating rate and cooling rate, is facilitated. Since changing of the conditions for the averaging by each coil is possible, the small-quantity production of many kinds is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous annealing equipment for steel sheets.

[0002]

2. Description of the Related Art Cold rolled steel sheets have a fibrous structure and are poor in workability. Therefore, recovery by annealing,
It is necessary to recrystallize and grow grains to improve workability. In particular, compared with coil annealing, continuous annealing makes it possible to perform a uniform treatment on continuous steel sheets, obtain a homogeneous material, shorten the treatment time, and significantly reduce the number of process days, etc. Is excellent in terms of.

Generally, a continuous annealing equipment for steel sheets is provided with a heating zone 2, a soaking zone 3, a cooling zone 4, an overaging zone 12 and a secondary cooling zone 13 from the inlet side as shown in FIG. The steel sheet 1 is conveyed through the formed hearth roll 14 and continuously annealed.

Direct heating type non-oxidizing heating is used for heating the heating zone.
Radiant tube heating and the like are generally used in a soaking zone heating method, and radiant tube heating, indirect electric heating and the like, and roll contact cooling, gas jet cooling, mist cooling and the like are generally used in the cooling zone.
Further, the overaging zone is a furnace for holding the steel sheet at 300 to 400 ° C. for about 3 minutes, and an electric heater is provided in a long furnace shell. The equipment is configured so as to satisfy the annealing conditions according to the quality of the drawing steel plate, the high-tensile steel plate and the like.

[0005]

Although continuous annealing of steel sheets has the advantages as described above, it is inevitable that the equipment will be lengthened. For example, if the most common radiant tube heating method is used for the heating zone, 30% of the total steel plate length
Is a heating zone and 50% is an overaging zone, and as a result, there is a large-scale one in which the total length of the steel plate in the continuous annealing furnace exceeds 2000 m. Although it is possible to make the heating zone compact up to about half by using a direct-fire non-oxidizing heating method as a part of the heating method, it is still a long heating facility. On the other hand, the overaging zone can be omitted by designing a component that can render C and N harmless by adding expensive Ti, Nb, etc. to the steel sheet, but the time required for overaging treatment is determined in the ordinary component system. Therefore, it is extremely difficult to shorten the overaging zone in continuous annealing.

[0006] In this way, if the equipment is lengthened, the amount of equipment investment becomes enormous, not only a vast area is required for the location, but also the thermal inertia of the equipment becomes extremely large. And when the thermal inertia becomes large, it becomes difficult to change the condition settings such as heating temperature, and there is no problem in mass production under the same annealing conditions, but it is necessary to change the annealing conditions frequently for high-mix low-volume production. It will be impossible.

[0007] Therefore, an object of the present invention is to provide a continuous annealing equipment capable of avoiding the lengthening of the continuous annealing equipment and at the same time reducing the thermal inertia and capable of producing a wide variety of products in small quantities.

[0008]

According to the present invention, in a continuous annealing equipment for a steel sheet including a heating zone, a soaking zone, a cooling zone and an overaging zone, an electric heating is used for the heating zone and a coil box is used for the overaging zone. This is a continuous annealing equipment for steel plates, which is characterized in that Furthermore, it is preferable to apply electric heating to the soaking zone.

[0009]

In the present invention, electric heating is used for the heating zone. The energization heating is to pass an electric current through the steel sheet through an energizing roll and heat the steel sheet by Joule heat of the steel sheet itself.
As disclosed in Japanese Patent Publication No. 60-26818, a method of directly energizing a steel plate from an external power source, and JP-A-1-14
As described in JP-A-2032 and JP-A-1-187789, a steel plate is provided in front of and behind a steel plate penetrating the annular transformer, and the two conductive rolls are connected by a conductive member.
A closed circuit is configured by a current-carrying roll and a conductive member, and an induction current is generated by using the closed circuit as a secondary coil by passing an alternating current from an external power source to the annular transformer,
There is a transformer type electric heating method of heating a steel sheet by Joule heat by this induced current, but any of them can be adopted in the present invention.

The energization heating is not heating by heat transfer but heating by applying an electric current to the steel sheet itself and utilizing its Joule heat, and the heating rate can be easily controlled by adjusting the current value. Also, the heating capacity is large, for example, 4
It is even possible to heat ultra-rapidly at 1000 ° C./sec to a high temperature of 700 to 900 ° C. by passing a current of 0 A / mm or more, and it is possible to avoid lengthening the equipment. Furthermore, since the steel plate itself generates heat, it is not necessary to use thick bricks for the furnace shell, and the thermal inertia of the furnace is reduced, and it becomes easy to change the conditions such as heating temperature and heating rate.

A coil box is used as the over-aging zone. This does not perform the entire annealing as a coil like the conventional coil annealing, but performs the overaging treatment only as a coil while taking advantage of the continuous annealing for heating, soaking, and cooling. As a result, the problem of lengthening the overaging zone does not occur even when long-term overaging treatment is required as in the case of drawing steel sheets.

When the mist cooling is used for the cooling device, the surface of the steel sheet is oxidized, so that it is not necessary to make the coil box a non-oxidizing atmosphere, and an air atmosphere may be used.
If necessary, a pickling treatment may be performed thereafter.

As described above, according to the present invention, the heating capacity of the heating zone is strengthened to make the equipment compact, the thermal inertia is reduced, and the overageing by the coil box is adopted to prevent the overaging zone from being lengthened. The coil is over-aged. That is, by suppressing the thermal inertia of the heating zone and the cooling zone to be small, it becomes easy to change the heating condition and the cooling condition, and the adoption of the coil box makes it possible to change the overaging condition for each coil. As a result, it becomes possible to meet the demand for high-mix low-volume production, which was not possible with conventional long continuous annealing equipment.

Further, if electric heating is adopted even in the soaking zone, soaking can be performed while controlling the atmosphere. Thereby, nitriding or carburizing can be performed simultaneously with the soaking.

[0015]

EXAMPLE FIG. 1 shows an example of the continuous annealing equipment for steel sheets of the present invention.

A steel sheet 1 wound into a coil through a cold rolling process is continuously fed out and charged into a heating zone 2. The heating zone 2 employs an energization heating device that applies current to the steel sheet 1 via the energization rolls 7 and 8 to heat it by Joule heat. The steel sheet 1 that has been rapidly heated to 900 ° C. at 200 ° C./sec in the heating zone 2 is subsequently subjected to soaking in the soaking zone 3. In this example, the energizing rolls 9 and 10 are also arranged in the soaking zone 3 to perform soaking by energization heating. Here, nitriding or carburizing treatment can be performed with NH ₃ gas or CO gas. Next, the steel sheet 1 is rapidly cooled in the cooling zone 4 by a mist cooling device 11 such as a water spray at, for example, 60 ° C./sec or more. Then, the steel sheet 1 is wound into a coil shape in the coil box 6 through the reheating zone 5 and is overaged at 400 ° C. for 3 minutes, for example. The steel sheet that has been subjected to these treatments is sent to a pickling step to remove the surface oxide film, if necessary.

[0017]

EFFECTS OF THE INVENTION The continuous annealing equipment of the present invention not only makes the equipment compact but also reduces the thermal inertia, making it easy to change the heating rate and cooling rate and changing the conditions for overaging treatment for each coil. Therefore, high-mix low-volume production is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of continuous annealing equipment for steel sheets of the present invention.

FIG. 2 is a diagram showing a conventional continuous annealing equipment for steel plates.

[Explanation of symbols]

 1 Steel Plate 2 Heating Zone 3 Soaking Zone 4 Cooling Zone 5 Reheating Zone 6 Coil Box 7 Energizing Roll 8 Energizing Roll 9 Energizing Roll 10 Energizing Roll 11 Mist Cooling Device 12 Overaging Zone 13 Secondary Cooling Zone 14 Hearth Roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Saito 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Works Hirohata Works Ltd.

Claims (2)

[Claims] 1. A continuous steel sheet annealing apparatus comprising a heating zone, a soaking zone, a cooling zone and an overaging zone, wherein the heating zone is electrically heated and the overaging zone is a coil box. Annealing equipment. 2. The method according to claim 1, wherein electric heating is applied to the soaking zone.
Continuous annealing equipment for the steel sheet described.