JPS5812824Y2 - Austenitic stainless steel strip cooling system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooling device that can prevent carbide precipitation and suppress the occurrence of shape defects during the cooling process of an austenitic stainless steel strip from an annealing temperature.

Conventionally, cooling devices for stainless steel strips include cooling devices using only air jets, cooling devices using only air/water mixture injection, and cooling devices for cooling from 1100°C to 800°C in high temperature parts to 60°C.
There is a cooling device (Japanese Patent Publication No. 51-21368) which cools the temperature from 0°C to 400°C by air jet and cools the low temperature part below 500°C by continuous mixing injection.

That is, FIG. 1 shows a cooling device using only air jets, in which the stainless steel strip 2 of the material to be treated leaving the heating furnace 1 is cooled by air jets from the air jet nozzles 4 of the cooling device 3.

This air jet nozzle uniformly cools the surface of the strip, so the shape of the strip is good, but the cooling effect is small, so rapid cooling is not possible, and when an austenitic stainless steel strip is cooled, the carbon in the steel is It precipitated as bites, resulting in a decline in quality.

This tendency was particularly strong when the plate thickness was 1.5 mm or more.

In addition, a cooling system using only an air/water mixing nozzle consisting of an air nozzle 5 and a water nozzle 5 shown in Fig. 2 allows rapid cooling and prevents carbide precipitation, but cooling with water causes a sudden change in cooling capacity, which will be described later. At temperatures below 500°C, uneven cooling tends to occur, deteriorating the shape of the strip, and hindering threading after cooling, which necessitated shape correction in the process prior to production.

Furthermore, in the cooling device that performs air jet cooling and air/water mixed cooling, which combines the air jet nozzle 4 and the air/water mixing nozzle T shown in FIG. Rapid cooling between 900℃ and 600℃, which is the carbide precipitation temperature range (approximately 0℃)
/Sec or more) is not performed.

For this reason, especially when the plate thickness is 1.5 mm or more, carbide precipitates and the quality deteriorates, and at temperatures of 600° C. to 400° C. or less, air/water spray cooling is used, so the shape deteriorates as described above.

The present invention provides a cooling device that can prevent the precipitation of carbide and the occurrence of defective shapes during the cooling process of austenitic stainless steel strips, thereby producing excellent stainless steel strips.

Generally, austenitic stainless steel has a rating of 950 to 850.
Temperatures ranging from ℃ to below 650℃! Precipitation of carbides can be prevented by rapidly cooling the solution.

In addition, when cooling with cooling water such as air-water mixed injection, as shown in curve 8 shown in Figure 4, when the strip temperature drops below 400 to 500°C, the cooling heat transfer coefficient increases rapidly, resulting in poor strip shape and plate thickness. If there is a variation in the cooling rate, it becomes difficult to make the temperature distribution uniform across the width of the strip, and the shape of the strip becomes irregular.

Taking these points into consideration, the present invention uses a cooling device for austenitic stainless steel strips to slowly cool the strip with air jets until the temperature of the strip reaches 950-850℃, and then cools the strip slowly between 950-850℃ and 650-550℃. This device is characterized in that it is configured to perform rapid cooling by air-water mixed injection and gradual cooling from 650 to 550°C by air jet.

The apparatus of the present invention will be explained below with reference to the embodiment shown in FIG.

FIG. 5 shows the most preferred example of the device of the present invention, in which the cooling device fjr is divided into two zones.

That is, the front part of the first zone is cooled by the air jet from the air jet nozzle 4, and the rear part is cooled by the air-water mixture jet from the air-water mixing nozzle T consisting of the air nozzle 5 and the water nozzle 6. By configuring the air-water mixing cooling device with a complicated device configuration and a high equipment cost, it is possible to shorten the air-water mixing cooling device as much as possible, and at the same time, prevent the water from the air-water temperature mixing nozzle T from entering the annealing furnace 1. can.

Additionally, air blocking nozzles 9 and 10, for example, are provided as water blocking means between the air jet nozzle 4 and the air/water mixing nozzle T to prevent water from entering the air jet nozzle 4 due to air/water mixing injection. .

The second zone is configured to be cooled by an air jet from an air jet nozzle 4.

Note that the zone length of the air nozzle 4 of the first zone is determined in consideration of the thickness of the strip, etc. so that the strip after passing through the zone is cooled to 950 to 850°C.

The zone length of the air/water mixing nozzle 7 in the first zone is such that the strip can be cooled from 950 to 850 degrees Celsius to 650 to 550 degrees Celsius at a cooling rate of 10 degrees Celsius or more at which carbide does not precipitate. The belt is 650-5 mentioned above.
Take the length necessary to cool from 50°C to the final cooling temperature.

In such a device, the annealing temperature is increased from 950 to 850°C by means of an air jet from the air nozzle 4 in the first zone.
from 950 to 850 degrees Celsius to 650 to 55 degrees Celsius by spraying a mixture of steam and water from the steam and water mixing nozzle T in the first zone.
Rapid cooling to 0℃, air jet nozzle 4 in the second zone
The temperature is gradually cooled from 650 to 550°C using air jets from the inside.

The cooling characteristics of such a cooling device are shown in solid line 1 in Figure 6.
3, the temperature ranges from 950 to 850℃ to 650℃ in the first zone.
~550℃ by cooling by air/water temperature injection to 10℃
Precipitation of carbide can be prevented by rapid cooling at a cooling rate of 400° C./sec or more, and by performing slow cooling with an air jet from 650 to 550° C. in the second zone, the heat transfer coefficient rapidly increases. ~5
There was no unevenness in the temperature distribution of the strip in the temperature range of 00° C. or lower, and therefore no shape defects occurred.

The curve shown by the dotted line 14 in contrast to the curve shown by the solid line 13 obtained by the device of the present invention shows an example in which cooling is performed by air jet at 850°C or less, and in this case, from 950 to 850°C,
Carbide precipitated because cooling between 50°C and 10°C/sec or higher cooling rate was not possible.

Curve 15 shown by a dashed line in the box shows an example of cooling below 550°C using an air jet and a steam/water mixing nozzle. A defective shape occurred in the strip.

In the present invention, if no water blocking means is provided in the first zone, the water from the air-water mixture injection will enter the air jet side and the strip in this zone will be cooled to below 950-850°C. Since a cooling rate of ℃/see or higher cannot be obtained, carbide precipitates.

Note that it is desirable to install a water blocking means between the first partition and the second partition in order to obtain a water-draining effect from the strip.

Next, the results of cooling SUS 304 stainless steel strips from the annealing temperature to room temperature using the device of the present invention and the conventional device are shown in the following table.

[Brief explanation of the drawing]

Fig. 1 shows a conventional strip cooling device using an air jet nozzle, Fig. 2 shows a strip cooling device using a conventional air/water mixing nozzle, Fig. 3 shows a conventional strip cooling device using an air jet nozzle + air/water mixing nozzle, and Fig. 4 shows a strip cooling device using a conventional air jet nozzle + air/water mixing nozzle. The figure shows the relationship between the strip temperature and the heat transfer coefficient when the strip is cooled by an air/water mixing nozzle, Figure 5 is an explanatory diagram of the strip cooling device according to the present invention, and Figure 6 is the cooling zone length and strip A diagram showing the relationship between temperatures. 1... Annealing furnace, 2... Stainless steel strip, 3...
- Cooling zone, 4... Air jet nozzle, 5... Air nozzle, 6... Water nozzle, I... Air-water mixing nozzle,
8... Heat transfer coefficient curve due to cooling water, 9, 10... Water cutoff nozzle.

Claims (1)

[Scope of utility model registration request] The device for cooling the heated strip is divided into two sections, the first section is cooled to 950-850 degrees Celsius by air jets from air jet nozzles at the front, and the rear section is heated by a button. is from 950-850℃ to 650-550℃ by air-water mixing injection from the air-water temperature mixing nozzle.
each of which is configured to be cooled by a housing, a water blocking means is provided between the air jet nozzle and the air-water mixing nozzle of the first zone, and the second zone is cooled by the air jet from the air jet nozzle. Austenitic stainless steel strip cooling device each constructed as follows.