JPS6241298B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for cooling a steel strip in a continuous annealing furnace, and when cooling the steel strip in continuous annealing equipment or continuous galvanizing equipment, the steel strip is heated to an overaging treatment temperature. The purpose is to provide a cooling method that can accurately control temperature.

Methods for cooling steel strip from high temperatures in continuous annealing equipment and continuous galvanizing equipment include cooling the steel strip by blowing atmospheric gas onto it;
A method in which the steel strip is cooled by passing it through water at a temperature below ℃ and scattering the vapor film generated on the surface of the steel strip using a spray nozzle.A method in which the steel strip is cooled by spraying air water in the air.Aqueous refrigerant liquid with a boiling point of 100℃ or higher JP-A No. 52-93619 and JP-A No. 53-Sho.
146219 and JP-A-1989-55 using molten salt as a refrigerant
104433, etc., but each of these conventional methods has disadvantages, shortcomings, or unresolved problems, and none of them has been able to be used as an effective steel strip cooling method yet. In other words, the cooling rate of the gas blowing method is slow, at most 40°C/sec, and therefore, when cooling the steel strip from temperatures above the recrystallization temperature, it is difficult to promote the precipitation of solid solution carbon, which is necessary to produce soft materials. When the force is insufficient or when manufacturing high tensile strength steel plates (α+
There is a limit to the cooling rate in order to expect the precipitation of martensite in cooling from the γ) phase. Furthermore, this method requires a large amount of gas circulation cooling air, which inevitably increases equipment costs and running costs. On the other hand, the cooling rate of the opposite method is approximately
Since it is extremely fast at 1000℃/sec, it can overcome the disadvantages of the gas cooling method described above, but in this method, the cooling end point drops to water temperature, so the steel strip must be reheated before proceeding to overaging treatment. Therefore, it is disadvantageous in terms of man-hours and energy. The other method can avoid the disadvantages of the method using air-water spray, but the formation of a steam film on the steel strip surface is not uniform between both ends and the center in the width direction, and the steam film at both ends is not uniform. This has the disadvantage that the temperature of the steel strip tends to disappear rapidly, which causes non-uniformity of the steel strip temperature in the width direction, which impairs the shape of the steel strip and may also have an adverse effect on the material quality. Among these methods, those using aqueous liquids are subject to supercooling and require energy to be reheated. In addition, in the case of using molten salt, improving the control accuracy of the end point temperature, such as cooling rate or end point temperature management, has not yet been considered, and there are still problems as a cooling technology for continuous annealing furnaces. .

The present invention was established after repeated studies in view of the above-mentioned circumstances, and the present invention is based on the above-mentioned soaking process. In the subsequent cooling, multiple refrigerant liquids are passed through the refrigerant whose liquid temperature is higher than or equal to the overaging treatment temperature, or refrigerant liquids with different liquid temperatures are passed through, or the liquid level of the refrigerant liquid is changed. By adjusting the cooling conditions and cooling the steel strip to the overaging treatment temperature, the steel strip was successfully cooled uniformly and efficiently in the width direction. That is, in the present invention, when a steel strip is annealed and cooled in a continuous annealing furnace or the like, a refrigerant liquid that has a high boiling point and does not easily generate a vapor film is used, and the temperature of the liquid is controlled close to the desired cooling end point temperature. The steel strip is cooled uniformly to the cooling end point temperature by passing the steel strip through the refrigerant liquid. Furthermore, in the present invention, in addition to the case where the number of cooling tanks containing the refrigerant liquid as described above is only one unit, two units are used.
It can be installed in multiple units, three units, or more, and by installing cooling tanks in multiple stages, it is possible to improve the quality of the steel strip from the cooling start temperature to the end point temperature according to the required quality, such as improving the steel strip material. It becomes possible to arbitrarily control the cooling rate. The boiling point of the refrigerant liquid to be used is 100℃.
Higher monoethylene glycol (boiling point 197 °C),
Diethylene glycol (boiling point: 245°C), triethylene glycol (boiling point: 278°C), tetraethylene glycol (boiling point: 327°C), polyethylene glycol (boiling point: 330°C or higher), and the like are appropriately used.

To explain the specific embodiment of the present invention shown in the attached drawings, a low carbon steel plate (C: 0.01 to 0.07%, Mn: 0.15 to 0.3%) is heated to 700°C as shown in Figure 1. Take an appropriate soaking time from then on, cool down to 400℃ at a rate of 50 to 1500℃/sec, perform an overaging treatment for 1 to 3 minutes at around 300℃ from this temperature, and cool to below 100℃ in the final cooling zone. In order to obtain a soft steel plate with excellent drawability and drawability outside the furnace, continuous annealing equipment as shown in FIG. 2 was used. That is, the steel strip 10 charged into the payoff reel 1
While unwinding the coil, the plate is passed through the inlet looper 2 to the heating zone 3 and soaking zone 4, and as mentioned above, the temperature is around 700°C, or higher depending on metallurgical requirements up to 850°C. Or cooling tank 13 from temperatures below 700°C to around 450°C.
is inserted into the refrigerant liquid 12, and rapidly cooled to the desired end point temperature at the cooling rate as described above. This material passes through an overaging treatment zone 5, a final cooling zone 6, an exit looper 7, a temper rolling mill 8, and is wound onto a tension reel 9. Details of the specific structure of the parts are separately shown in FIG.

Cooling chamber 15 with the cooling tank 13 provided at the bottom
An inlet gas seal 23 is provided at the inlet provided on the soaking zone 4 side, and the steel strip 10 is passed through the gas seal 23 into the refrigerant liquid 12 of the cooling tank 13. A liquid thermometer 18 is provided in the refrigerant liquid 12, and a temperature signal obtained by the liquid thermometer 18 is sent to an automatic temperature controller 19, and a control signal switch 2
0, a switching operation is given to the automatic heating regulator 22 for the heater 17 in the case of an increase in liquid temperature;
In the case of cooling, a switching operation is given to the automatic cooling water amount control valve 21 for the cooler 16 to perform an automatic temperature control operation to control the refrigerant liquid to a predetermined liquid temperature. 14, and the spray is sprayed from the spray nozzle 11 onto the surface of the steel strip 10 at a flow rate of 1 m/sec or more, and the temperature of the steel strip 10 is automatically measured by a plate thermometer 30 installed at the top of the cooling chamber 10. A signal is sent to the temperature controller 19, and a corrective operation is performed depending on the difference from the target plate temperature. The steel strip 10 is sent to the overaging treatment zone through the outlet gas seal 24 on the exit side of the cooling chamber. Prior to the outlet gas seal 24, a refrigerant liquid wiping 31 is used to wipe the refrigerant liquid with _N2 gas or the like. wipe it off.
Note that a line speed meter 27 is installed on the transfer roll of the steel strip 10 on the exit side of the overaging treatment zone 5 to detect the line speed, and the detection result is sent to the liquid level controller 29 via the current indicating converter 28 to The liquid level adjustment motor 25 is operated by the liquid level controller 29, and the liquid level adjustment gate 26 is raised and lowered to cool the cooling tank 1.
The liquid level of the refrigerant in 3 can be adjusted as appropriate.

As a specific example of the present invention, a case will be described in which a steel strip 10 is cooled from a cooling start temperature of 700° C. with polyethylene glycol [HO(CH ₂ CH ₂ O) nH]. The steel strip has a thickness of 0.8
refrigerant liquid temperature 400℃A, 350℃B when cooling a low carbon steel plate with a width of 1000mm with a throughput of 40T/Hr,
The relationship between steel strip temperature and cooling time at 300°C and 180°C is summarized in FIG. 4.
That is, for example, if you want to cool from 700°C and stop cooling at the end point temperature of 400°C, if you adopt a liquid temperature of 350°C, then the steel strip 10 will cool at a cooling rate α from 700°C to 400°C.
₂ = cooling in 0.75 seconds at 400°C/sec, and control accuracy requires a holding accuracy of 0.75±0.12 seconds for the cooling time when an end point temperature of 400°C ± 10°C is required. In addition, by adopting D with a liquid temperature of 180℃, the cooling end point temperature
If you try to stop it at 400℃, the cooling rate α ₄ is
The speed is 830℃/sec, so 400℃±10 as above.
To maintain the temperature at ℃, the cooling time retention accuracy is 0.37±
Requires even stricter cooling time control of 0.03 seconds. On the other hand, when the liquid temperature is 400°C and the cooling time holding accuracy is the same, the cooling end point temperature accuracy is the best, and as the liquid temperature becomes lower, the cooling rate becomes faster but the accuracy becomes worse. In other words, when considering the cooling end point temperature accuracy as ±10℃ in the present invention, the refrigerant liquid temperature is 350℃B.
If the allowable value of variation in cooling time is ±0.12 seconds, industrially it is possible to fully control it within 0.1 seconds, and in practice, this liquid temperature is controlled at 350℃B and always maintained at an appropriate temperature. Cooling can be performed according to the cooling end point temperature. Of course, in each case, the refrigerant liquid temperature can be changed depending on the tolerance value of the end point plate temperature accuracy and the desired cooling rate.

Next, to explain the cooling end point plate temperature control, when the plate temperature end point is 400°C as described above, the refrigerant target set temperature is set to 350°C. In other words, if the liquid temperature is increased to 400℃, the cooling temperature accuracy will improve as shown in Figure 5, but in the case of the above-mentioned refrigerant liquid, the vapor film will enter the non-uniformity generation area F in the width direction of the steel strip and the shape will change. becomes worse. Therefore, considering both of these conditions, it is appropriate to set the temperature to about 350°C.

Once the target liquid temperature is determined as described above, it is constantly controlled by the automatic temperature controller 19 as shown in FIG.
Since the speed change changes the refrigerant passage time, a signal is given to the liquid level controller 29 to correct the amount of change, and the motor 25 adjusts the gate 26.

Further, in the present invention as described above, by arranging the cooling units as described above in multiple stages, the cooling rate can be arbitrarily selected and controlled during cooling depending on the material requirements of the steel strip 10. In other words, the cooling rate can be controlled in each cooling tank by changing the refrigerant liquid temperature as shown in Figure 4, and the cooling end point in the middle is determined by the steel plate passage time in each cooling tank (i.e., liquid level control). can be properly obtained by Therefore, for example, if the cooling tank is
700 as described above when arranged in stages.
For example, cooling from ℃ to 50℃ in the first tank.
It can be cooled to 650℃ at a cooling rate of about ℃/sec, cooled to 450℃ at a cooling rate of about 800℃/sec in the second tank, and then cooled to 400℃ at a cooling rate of 50℃/sec in the third tank. . In addition, the first and second tanks cool down to 600℃ at a cooling rate of about 50℃/sec, respectively.
Then, in the third tank, the cooling rate was 400°C/sec.
Such cooling to 0.degree. C. is achieved under preferred threading operating conditions.

According to the present invention as explained above, this type of steel strip can be cooled to the overaging treatment temperature under precise temperature control conditions in a continuous annealing facility, thereby achieving special characteristics that cannot be obtained with conventional cooling techniques. This invention is industrially highly effective because it can exhibit the following effects.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the invention,
Fig. 1 is a diagram showing a steel strip heating and cooling process as an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the general structural relationship of continuous annealing equipment that implements the method of the present invention, and Fig. 3 is an explanatory diagram showing details of the structural relationship of the cooling tank part, Figure 4 is a diagram showing the relationship between cooling time and steel strip temperature when the refrigerant liquid temperature is varied, and Figure 5 is a diagram showing the relationship between the cooling time and steel strip temperature when the refrigerant liquid temperature is variously changed. It is a chart showing the relationship between liquid temperature and cooling temperature accuracy. However, in these drawings, 4 is the soaking zone, and 5 is the soaking zone.
1 is an over-aging treatment zone, 10 is a steel strip, 12 is a refrigerant liquid, 1
3 is a cooling treatment tank, 14 is a circulation pump, 16 is a cooler, 17 is a heater, 19 is an automatic temperature controller, 20 is a control signal switch, 25 is a liquid level adjustment motor, 26 is a liquid level adjustment gate, 27 is a line speed 29 is a liquid level controller, 30 is a plate temperature gauge, and 31 is a refrigerant liquid wiping.
℃ and D indicate the case of 180℃, respectively.

Claims (1)

[Claims] 1. When heating a steel strip, soaking it, cooling it, then overaging it, and then finally cooling it, in a refrigerant whose liquid temperature is 180°C or more and below the overaging temperature during cooling after the soaking, Should multiple refrigerant liquids be passed through, or should refrigerant liquids with different liquid temperatures be passed through?
Or, a method for cooling a steel strip in a continuous annealing furnace, characterized in that the liquid level of the refrigerant is changed and the cooling condition is adjusted to cool the steel strip to the overaging treatment temperature.