JPH0813042A - Method for controlling plate temperature in continuous annealing furnace - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a plate temperature control method for a continuous annealing furnace that does not cause heat buckle and has little hardness change in the same lot, and that can obtain a product of extremely high quality. is there. [Composition] The strip speed of the steel strip passing through the furnace is detected by a strip speed gauge, and based on the data of the proper annealing temperature range for the strip speed determined in advance from the past results of the combination of strip speed and annealing temperature. The appropriate annealing temperature corresponding to the strip passing speed detected by the strip speed meter is determined by the arithmetic processing means, and the heating device installed in the furnace is controlled to increase or decrease the in-furnace temperature to determine the strip temperature of the steel strip. Keep within temperature range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate temperature control method for a continuous annealing furnace for annealing a steel strip for drawing or for a soft tin plate.

[0002]

2. Description of the Related Art Steel strips for drawing and soft tin plate are produced by annealing a steel strip after cold rolling in a continuous annealing furnace. Since the annealing temperature of the annealing treatment is influenced by the manufacturing conditions in the hot rolling process, it is usually set to a high value within the allowable range. By the way, since the temper rolling mill is installed in the line in the recent process line, it is necessary to lower the strip running speed of the steel strip in the furnace when changing the roll of the temper rolling mill. The annealing time may be extended by about 3 times. If the annealing temperature is kept high even though the annealing time is extended in this way, defective products such as draw wrinkles called heat buckles occur in the length direction of the steel strip due to long-term high temperature annealing. There was a problem. Further, there is also a problem that the hardness change becomes large within the same lot due to fluctuations in the strip passing speed due to roll replacement of the temper rolling mill and the like, which causes troubles in the can making process.

[0003]

SUMMARY OF THE INVENTION The present invention solves the problems as described above, and it is possible to obtain a product of extremely high quality in which a heat buckle does not occur and hardness change in the same lot is small. An object of the present invention is to provide a plate temperature control method for an annealing furnace.

[0004]

A plate temperature control method for a continuous annealing furnace according to the present invention, which has solved the above problems, detects a plate passing speed of a steel strip passing through the furnace by a plate speed meter, The appropriate annealing temperature corresponding to the strip running speed detected by the strip speed meter is determined by the arithmetic processing means on the basis of the data of the proper annealing temperature range for the strip speed determined in advance from the past results of the combination of the strip speed and the annealing temperature. The heating device installed in the furnace is controlled to increase or decrease the temperature in the furnace to keep the plate temperature of the steel strip within a predetermined temperature range.

[0005]

The plate temperature control method of the continuous annealing furnace of the present invention detects, by means of the plate speed meter, that the plate passing speed in the furnace has decreased due to the roll change of the temper rolling mill being carried out during the annealing of the steel strip. Then, the data of the measured strip passing speed is input to the calculating means. The arithmetic processing means determines an appropriate annealing temperature range corresponding to the sheet passing speed detected by the plate speed gauge, using the appropriate annealing temperature range determined from the past results of the combination of the sheet passing speed and the annealing temperature as data.
Then, the heating device installed in the furnace is controlled so that the furnace has the proper annealing temperature obtained by the arithmetic processing means, and the annealing temperature is lowered until the plate temperature of the steel strip falls within the predetermined temperature range. Even if the strip running speed varies, the hardness of the steel strip varies little, and the hardness variation within the same lot is also extremely small. Moreover, as the annealing temperature becomes lower, the stripping speed becomes slower, so that the recrystallization of the steel strip is surely performed, the grain size is sufficiently grown, and the mechanical properties such as fluting resistance are good. Becomes

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the illustrated embodiments. 1 is an annealing furnace comprising a heating zone 2, a soaking zone 3, a primary cooling zone 4 and an overaging zone 5. Reference numeral 6 is a radiation type heating device provided in the heating zone 2, and this heating device 6 is composed of a radiant tube for burning COG. Reference numeral 7 is a heating device provided with an electric heater provided in the soaking zone 3. 8 is a plate speedometer for detecting the speed of the steel strip provided on the inlet side of the heating zone 2, 9 is a steel strip provided on the outlet side of the heating zone 2, the soaking zone 3, the primary cooling zone 4 and the overaging zone 5. It is a plate thermometer that detects the plate temperature of.

[0007] 10 is an appropriate annealing temperature corresponding to the strip running speed detected by the strip speed meter based on the data of the proper annealing temperature range for the strip running speed determined in advance from the past results of the combination of the strip running speed and the annealing temperature. It is an arithmetic processing means for determining the range, and the heating device 7 installed in the furnace composed of the heating device 6 of the radiant tube and the electric heater is controlled based on the proper annealing temperature range obtained by the arithmetic processing device 10. Is.

Next, the arithmetic expression of the arithmetic processing means 10 is shown as Equation 1.

[Equation 1] T = 0.1ν + 580 where T: annealing temperature (° C) ν: furnace running speed (m / min)

The heating devices 6 and 7 may be controlled manually based on the proper annealing temperature range determined by the arithmetic processing means 10, but the appropriate annealing temperature determined by the arithmetic processing means 10 may be used. Radiant heating device 6 consisting of a radiant tube provided in heating zone 2 based on range
Automatically controls the input amount of COG fuel, and turns on the heating device 7 which is an electric heater provided in the soaking zone 3.
It may be off controlled and automatically controlled so that the plate temperature of the steel strip falls within the set temperature range. Further, the arithmetic processing means 10 can control the heating devices 6 and 7 based on the temperature of the steel strip detected by the plate thermometer 9 in addition to the function as described above, so that the heating device 6 can be controlled according to the strip passing speed. If it is detected that the plate temperature has not reached the set temperature even after controlling the plate temperature, the heating devices 6 and 7 can be further controlled according to the plate temperature to set the annealing temperature within an appropriate range.

Further, by incorporating furnace passing speed prediction control into the arithmetic processing means 10 and controlling the heating devices 6 and 7 based on the prediction, the steel strip is annealed within a proper annealing temperature range without causing a time lag. Therefore, it is possible to obtain a higher quality product.

A specific example of a product obtained by subjecting a steel strip after cold rolling to an annealing treatment in a continuous annealing furnace using the apparatus as described above and temper rolling in a temper rolling machine is described below.
For example, plate thickness 0.17 to 0.40 mm, plate width 700 to 1
A 050 mm steel strip is passed through the annealing furnace 1 at a stripping speed of 300 to 900 m / min, annealed at 600 to 670 ° C. for 25 to 75 seconds in the heating zone 2 and the soaking zone 3, and then the primary cooling zone after annealing. In 4 the steel strip is cooled to 250-400 ° C,
After performing the overaging treatment in the overaging zone 5 at 250 to 400 ° C. for 70 to 250 seconds, 1.0 to 1.
An example is the case where temper rolling is performed at a reduction rate of 5%.

In the above-mentioned process, when the strip passing speed is lowered due to the roll replacement in the temper rolling mill or other reasons, the strip speed meter 8 provided at the start end of the heating zone 2 is used. When the detected strip running speed data is input to the arithmetic processing means 10, the arithmetic processing means 10 uses, as data, the appropriate annealing temperature range determined from the past results of the combination of the strip running speed and the annealing temperature. Since it is held or can be calculated based on an arithmetic expression, the proper annealing temperature range data held in the table based on the detected strip speed data or the proper annealing temperature calculated from the arithmetic expression of the above-mentioned equation 1 According to the range data, the CO of the radiant heating device 6 including the radiant tube provided in the heating zone 2
In addition to controlling the input amount of G fuel manually or automatically, the heating device 7 including an electric heater provided in the soaking zone 3 is manually or automatically controlled to be turned on and off, and the furnace temperature is set to an appropriate annealing temperature range. The plate temperature of the steel strip is set within the set range. As described above, when the fuel supply amount of the heating device 6 is reduced and the electric heater of the heating device 7 is turned off with the reduction of the strip running speed of the steel strip, the annealing temperature is lowered but the annealing time is lengthened, so that recrystallization is performed. Is certainly done,
Since it can grow sufficiently to the required crystal grain size,
Mechanical properties such as fluting resistance can be satisfied.

The steel strip component thus obtained is C:
0.08 to 0.13%, Si: to 0.034%, Mn:
0.3 to 0.4%, P: to 0.02%, S: to 0.02
3%, Al: 0.02 to 0.04%, N: to 0.009
% Hardness performance of products, be as shown in FIG. 3, the management of the conventional hardness results shown in Figure 4 the range H _R 30-T = 6
It was possible to make the actual hardness value H _R 30-T = 65 higher than that of 3 to 67.

As is apparent from the above description, the present invention controls the heating device by the arithmetic processing means according to the strip running speed to change the annealing temperature. Therefore, when the strip running speed decreases, the annealing is performed. The temperature can be lowered to prevent high-temperature annealing, the softening of the steel strip can be accurately prevented, and the hardness accuracy of the steel strip can be greatly improved, and the hardness variation due to the variation of the strip running speed within the same lot is extremely small. As a result, it is possible to reliably avoid the occurrence of troubles in the can making process, and the annealing temperature is lowered when the plate passing speed becomes slow, so that no heat buckle occurs. Moreover, since the annealing temperature is lowered, the plate passing speed is also slowed down, so that recrystallization can be reliably performed and the crystal grain size can be sufficiently grown. You can get quality products. Further, since the annealing temperature is lowered, there are various advantages such as the fuel consumption and electric power consumption in the heating device can be suppressed and the cost can be reduced.
Therefore, the present invention is extremely significant when it is brought to the industry as a plate temperature control method for a continuous annealing furnace which solves the problems in the conventional strip annealing process.

[Brief description of drawings]

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

FIG. 2 is a graph showing a relationship between an allowable annealing temperature range and a strip running speed.

FIG. 3 is a graph showing the actual results of hardness of a soft steel strip according to the method of the present invention.

FIG. 4 is a graph showing the actual results of hardness of a soft steel strip according to a conventional method.

[Explanation of symbols]

 6 heating device 7 heating device 8 plate speed meter 10 arithmetic processing means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryuji Okamoto 5-3 Tokai-cho, Tokai-shi, Aichi New Nippon Steel Co., Ltd. Nagoya Steel Works

Claims (1)

[Claims] 1. Data of an appropriate annealing temperature range for a strip speed preliminarily determined from a past result of a combination of the strip speed and the annealing temperature by detecting a strip speed of a steel strip passing through the furnace. Based on the above, the appropriate annealing temperature corresponding to the plate passing speed detected by the plate speed meter is determined by the arithmetic processing means, and the heating device installed in the furnace is controlled to increase or decrease the temperature in the furnace to thereby increase or decrease the plate temperature of the steel strip. Is maintained within a predetermined temperature range, a method for controlling the plate temperature of a continuous annealing furnace.