JPH0118974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling a strip during continuous annealing.

When producing soft materials by continuous annealing, in order to ensure sufficient precipitation of solid solution C, the strip is heated to the recrystallization temperature, soaked, and then rapidly cooled, and then over-aged in a temperature range of about 400°C. be exposed. Conventionally, water immersion cooling has been used as a typical rapid cooling means after heating in such processing. As shown in Figure 1, this method has a high cooling rate, so the overaging treatment time after quenching can be shortened, but because of this cooling rate, it is not possible to control the temperature after quenching, and the plate temperature does not reach nearly room temperature. It gets cooled down. For this reason, in the past, it was necessary to reheat the strip from room temperature in the overaging treatment after such rapid cooling;
There was a problem in that new thermal energy was required, as shown by diagonal lines in the figure. Furthermore, when the above-mentioned rapid cooling is performed, scale is formed on the surface of the strip, and therefore a separate pickling tank must be installed to remove the scale immediately after the rapid cooling or after the over-aging treatment. This resulted in an increase in line length.

The present invention was created to solve the problems of the conventional methods as described above, and proposes a method that can prevent supercooling while ensuring a predetermined quenching rate, and can also appropriately remove scale that has formed. is its purpose.

In the present invention, when rapidly cooling a strip that has been heated and soaked above the recrystallization temperature, the strip is first sprayed in the air with an aqueous solution containing an organic acid, then immediately immersed in the aqueous solution, and further during this immersion. , an aqueous solution is sprayed underwater while being heated with a plurality of heating rolls that utilize the combustion waste heat of a heating furnace, and then an over-aging treatment is performed. While ensuring the specified quenching rate,
By heating the strip with multiple heating rolls during dipping, it is possible to prevent the strip from overcooling and keep its temperature within a range extremely close to the overaging treatment temperature.Moreover, the heating rolls utilize combustion waste heat from the heating furnace. No new energy is wasted. In addition, since aerial spraying and dipping are carried out in an aqueous solution containing an organic acid, it is possible to remove scale produced by rapid cooling.Moreover, at this time, the strip is heated with a heating roll and the scale produced on the surface of the strip is removed by underwater spraying. Appropriate scale removal is achieved as the vapor film is removed.

Examples of the organic acids used in the present invention include malonic acid, and the concentration thereof is usually 0.5 to 1%.
The temperature is selected in the range of 60-70℃. In addition, heat is supplied to the heating roll by exchanging waste heat of combustion exhaust gas from a heating furnace in the line with a high-boiling heat medium using a heat exchange device, and passing this high-boiling heat medium through the heating roll, As a result, the surface of the heating roll reaches about 300 to 350°C, and this roll temperature prevents the strip from being overcooled.

FIG. 2 schematically shows the equipment used to carry out the present invention, in which 1 is a processing tank, 2 is an aerial spray nozzle provided above the processing tank 1,
3 is an aqueous solution circulation tank, 4 is a heat exchanger, 5a,
5b and 5c are heating rolls that are continuously provided in the processing tank 1, 6 is a cooler for controlling the temperature of the aqueous solution, 7 is an underwater spray nozzle, and 8 and 8 are nozzles for draining and purging. In such equipment, an aqueous solution is supplied from the circulation tank 3 to the aerial spray nozzles 2, 2 and the underwater spray nozzle 7 via piping 9 and 10, respectively.
The aqueous solution sprayed from 2 falls into the processing tank 1 below. Also, processing tank 1
An aqueous solution can be separately supplied to the processing tank 1 through a pipe 11, and the aqueous solution in the processing tank 1 is returned to the circulation tank 3 through an overflow pipe 12. The heat exchanger 4 includes piping 1 for combustion exhaust gas from the heating furnace.
3, and a pipe 1 configured to circulate a high boiling point heat medium sequentially through heating rolls 5a, 5b, and 5c.
4 are respectively connected to perform heat exchange between the two fluids. In order to make the heating medium flow through each of the heating rolls 5, the heating medium is made to flow inside the roll shell from one shaft end of the roll, and is discharged from the other shaft end to the outside of the roll, and the discharged heating medium is It is configured such that it is supplied to the next heating roll 5.

The underwater spray nozzle 7 is divided into a plurality of parts in the axial direction of the heating roll 5, as shown in FIG. 3, and the nozzle is used properly depending on the strip width. That is, this prevents spraying onto the roll surface and prevents the aqueous solution 15 from being heated from the heating roll 5 as much as possible. In other drawings, 16 and 17 are pumps.

According to the above-described equipment, the strip S from the soaking furnace 18 is passed between the aerial spray nozzles 2 and 2, and is passed through the heating rolls 5a, 5b, and 5c of the processing tank 1, and then subjected to overaging treatment. At this time, the strip S is sprayed with an aqueous solution containing an organic acid by the aerial spray nozzles 2, 2, rapidly cooled, and immediately immersed in the aqueous solution 15 in the processing tank 1. Further cooling is suppressed by sequentially passing through heating rolls 5a, 5b, and 5c. That is, a high boiling point heating medium recovered from the combustion exhaust gas of the heating furnace in the heat exchanger 4 flows through the heating rolls 5a, 5b, and 5c, and the temperature of the roll surface is about 300 to 350°C. Further cooling of the strip S in contact with the heating roll 5c is suppressed, and the temperature is maintained within the above temperature range at the exit side of the final heating roll 5c. Figure 4 shows a thermal cycle including the cooling process of the present invention, where A is the heating/cooling process.
B shows the cycle of soaking, B shows the quenching by air spraying and partial immersion in an aqueous solution, C shows the heating with the heating roll 5, and D shows the overaging treatment cycle. As described above, according to the present invention, overcooling of the strip S can be prevented.

Further, in the above process, the scale generated during aerial spraying is reduced and removed by the organic acid used during the spraying and the organic acid in the aqueous solution immersed immediately after the spraying. Particularly in the processing tank 1, the removal reaction is promoted by the heating of the heating roll 5, and the spray from the underwater spray nozzle 7 wipes away the vapor film that adheres to the surface of the strip S and inhibits the removal reaction. Descaling is carried out appropriately.

The strip that has passed through the final heating roll 5c is drained and purged by nozzles 8, 8, and then led to an overaging treatment furnace 19.

According to the present invention described above, an aqueous solution containing an organic acid is sprayed onto the strip in the air, and then the strip is immediately immersed in the aqueous solution, and during this immersion, a plurality of heating rolls are installed using combustion waste heat from a heating furnace. Since the aqueous solution is sprayed underwater while being heated, the strip is heated by a heating roll using the combustion waste heat of the heating furnace, while ensuring a predetermined quenching rate by aerial spraying and immersion in the aqueous solution. Overcooling can be prevented, which not only reduces the overaging time as with conventional water immersion cooling, but also significantly reduces the supply of new thermal energy for strip heating in the overaging furnace. In addition, by performing aerial spraying and dipping with an aqueous solution containing an organic acid, and by applying a reaction accelerating effect to the heated roll and underwater spray, it is possible to appropriately remove the scale generated by rapid cooling. I can do it, etc.
It has various excellent effects.

[Brief explanation of drawings]

FIG. 1 shows a conventional continuous annealing thermal cycle. 2 and 3 schematically show the quenching equipment used for implementing the present invention, FIG. 2 is an overall explanatory diagram, and FIG. 3 is an explanatory diagram partially showing an underwater spray nozzle. . FIG. 4 shows a thermal cycle of continuous annealing using the cooling method of the present invention. In the figure, 1 is a processing tank, 2 is an aerial spray nozzle, 5a, 5b, 5c are heating rolls, and 7 is an underwater spray nozzle.

Claims (1)

[Claims] 1. When producing a soft cold-rolled steel sheet, when rapidly cooling a strip that has been heated and soaked above the recrystallization temperature, an aqueous solution containing an organic acid is sprayed onto the strip in the air, and then the strip is immediately immersed in the aqueous solution. A method for cooling a strip in continuous annealing, characterized in that during this immersion, an aqueous solution is sprayed underwater while heating with a plurality of heating rolls utilizing combustion waste heat of a heating furnace.