KR100372169B1 - The cooling device for heat treatment of austenite stainless steel - Google Patents

Abstract

The present invention provides a cooling box made of pure copper in which a heat treatment object is placed therein, and the cooling box outside of the cooling box so as to obtain austenite stainless steel of a large size without undergoing a pollution-inducing process such as pickling. It is provided with a casing for cooling, and between the cooling box and the casing is provided with a water spray nozzle along the longitudinal direction of the cooling device to cool the upper and both side portions of the cooling box of the austenitic stainless steel It relates to a cooling device for heat treatment.

Description

Heat treatment chiller for austenitic stainless steel {THE COOLING DEVICE FOR HEAT TREATMENT OF AUSTENITE STAINLESS STEEL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling apparatus for heat treatment, and more particularly, to a rapid cooling apparatus for use in solid solution heat treatment of austenitic stainless steel.

In general, in order to obtain austenite-based stainless steel, which is commonly used, the material is heated to an austenizing temperature to maintain a predetermined time and then subjected to a solid solution heat treatment for quenching. In other words, the material is non-magnetic, or a heat treatment is performed to solidify carbides near grain boundaries.

In the heat treatment heat treatment of the austenitic stainless steel, the heat treatment furnace heats the material to 1050 to 1100 ° C. by using heat transfer, gas or light oil. The heated material is quenched after maintaining a certain time, the cooling method is a direct cooling method and an indirect cooling method.

The direct cooling method has an advantage of excellent quenching effect by directly cooling the heated material in water. However, in the case of such quenching, since the surface of the heated material reacts with oxygen in water or in the air, a primary oxidation scale (SCALE) is generated on the surface, and an additional pickling process is required to remove the oxidation scale. do. However, this pickling process is a major factor in environmental pollution due to the problem of addictive ACID HUME and disposal of acid which is disposed of after use, and the complexity of the process is a factor that hinders productivity, which is a major factor in the cost increase of materials. do. It may also be a factor that inhibits the surface gloss of stainless steel.

For this reason, the indirect cooling method was adopted in the heat treatment process of stainless steel, which has been developed to minimize the occurrence of surface oxidation scale by heating and cooling in the atmosphere of an inert gas.

This indirect cooling method inserts a stainless steel tube or a rectangular tube into a water jacket filled with cooling water so that the internal heat treatment material is cooled by water cooling of the tube or tube. That's the way it is. Inert gas is filled inside the tube or the tube.

At this time, the tube or tube inserted into the water jacket is usually made of stainless steel due to its corrosion resistance. The stainless tube is composed of carbon steel containing a large amount of alloying elements (usually SUS 310S). In general, the thermal conductivity is extremely poor. For this reason, it is very difficult to transfer the cooling effect to the inside of the tube during the heat treatment of medium and large sizes.As a result of the delay of the cooling rate, chromium carbide is precipitated at the grain boundary, resulting in magnetism. It is difficult to obtain nonmagnetic properties, which are characteristic of the river, and it is difficult to maintain corrosion resistance. For this reason, only small sized materials can be heat-treated, and the size of stainless steel that can be produced in this way has been limited to diameters up to 1/2 inch.

In addition, the current indirect cooling method is a structure in which a cooling tube is deposited in the water jacket, and the basic cooling principle is convection. This convection method is advantageous in terms of long-term efficiency for a large amount of carbon steel to be treated, but the cooling effect of rapid cooling for a certain amount of weight to be treated such as austenitic stainless steel is disadvantageous. .

The present invention has been made in order to solve the above problems, by increasing the quenching effect during the heat treatment of austenitic stainless steel has a unique characteristic of austenitic stainless steel, and also rapid to produce a large austenitic stainless steel The purpose is to provide a cooling device.

Still another object of the present invention is to provide a rapid cooling apparatus for heat treatment of austenitic stainless steel, which can produce high quality austenitic stainless steel without undergoing a pickling process accompanying heat treatment of medium and large austenitic stainless steel.

1 is a cross-sectional view showing a cooling apparatus for heat treatment of the present invention.

Figure 2 is a side cross-sectional view of the bright annealing furnace combined with the heat treatment cooling device of the present invention.

Figure 3a is a view showing a temperature change during heat treatment with a bright annealing furnace combined with a heat treatment cooling device of the present invention.

Figure 3b is a view showing the temperature change during heat treatment with the existing bright annealing furnace.

* Explanation of symbols for main parts of the drawings

10: cooling device for heat treatment 11: cooling box

12 casing 13: coolant spray nozzle

14: cooling water supply pipe 15: cooling water discharge pipe

20: bright annealing furnace 21: preliminary atmosphere holding unit

22: preheating unit 23: heating unit

24: conveyor device

In order to achieve the above object, the present invention provides an austenitic stainless steel, characterized in that provided with a cooling box made of pure copper in which the heat treatment object is placed therein and a casing for cooling the cooling box from the outside of the cooling box. It provides a cooling device for heat treatment.

In order to achieve another object of the present invention, an austenitic stainless steel is provided between the cooling box and the casing with a water spray nozzle along a length direction of the cooling device to cool the upper side and both side portions of the cooling box. It provides a cooling device for heat treatment of steel.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The cooling apparatus of the present invention adopts an indirect cooling method, and does not directly cool the heat treatment object, but cools the cooling box in which the heat treatment object is placed. 1 is a view schematically showing a cooling apparatus of a bright annealing furnace for heat treatment of austenitic stainless steel according to the present invention.

The cooling device 10 according to the present invention is largely composed of a cooling box 11 and a casing 12 surrounding the cooling box 11. The cooling box 11 is attached to the conveyor equipment (not shown) so that the heat treatment object is placed inside the cooling box 11 continuously, and the inside of the cooling box 11 is filled with an inert gas to generate an oxidation scale when the heat treatment object is cooled. To suppress as much as possible. A casing 12 is formed to surround the outside of the cooling box 11, and cooling means are disposed between the casing 12 and the cooling box 11.

As described above, in the heat treatment cooling apparatus 10 of the present invention, in the heat treatment of austenitic stainless steel, it is possible to increase the quenching effect and prevent the scale of oxidation. In other words, in order to eliminate the pickling process in the structure of the cooling device 10 as described above, the heat treatment object is not directly cooled, but indirectly cooled. However, the indirect cooling method is a cooling box 11 that is directly cooled, and the heat treatment object is cooled by heat transfer inside the cooling box 11. Therefore, in order to effectively cool the heat treatment object, it was important that the heat transfer from the cooling box 11 that is directly cooled to the heat treatment object therein be performed efficiently. In addition, the cooling box 11 which is in direct contact with a cooling medium such as cooling water is also very important in corrosion resistance. In this regard, conventionally, stainless steel was used as the cooling box 11, but stainless steel is excellent in corrosion resistance, but thermal conductivity is significantly lowered to high alloy steel. Therefore, when the size of the internal heat treatment target is large, there is a problem in that the cooling effect cannot be effectively obtained. In other words, in the manufacture of austenitic stainless steels having excellent surface gloss and nonmagnetic properties, if the cooling rate is delayed during heat treatment, chromium carbides are precipitated at grain boundaries, and thus the austenitic stainless steels become magnetic. . In addition, it is difficult to maintain corrosion resistance.

For this reason, the indirect cooling method has a limitation that is limited to a very small size in the heat treatment object, the present invention significantly improved the cooling effect to the heat treatment object by using such a cooling box 11 as a pure copper material. . That is, pure copper is known to be about 20 times better at room temperature than SUS 310S, which is a stainless steel that has a high thermal conductivity at room temperature. It was also found that pure copper was about 13 times better than SUS 310S at around 1100 ℃, the actual temperature of the bright heat treatment furnace.

When the cooling box 11 made of pure copper is used, since the thermal conductivity is very excellent, the cooling effect from the cooling box 11 cooled by the cooling water to the heat treatment object placed therein becomes very excellent.

The cooling apparatus according to the present invention also cools the cooling box 11 by dipping the cooling box 11 into the water jacket as in the conventional cooling method of the cooling box 11, thereby deviating from the cooling method due to the heat transfer effect by the convection of the cooling water. In 11), a shower type cooling system in which cooling water is directly injected is adopted. In other words, in the case where the cooling box 11 is deposited on the water jacket filled with the cooling water, the cooling water and the cooling box 11 exchange heat by the convection of the cooling water in the water jacket. It is. Therefore, the convective cooling device was used to rapidly cool by spraying the cooling water directly to the cooling box (11). In other words, the cooling water injection nozzle 13 is installed to surround the cooling box 11 to continuously supply the cooling water. Such a shower cooling method is advantageous in terms of rapid cooling efficiency as a radiant structure for rapid cooling.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

2 is a cross-sectional view schematically showing the bright annealing furnace of the austenitic stainless steel to which the heat treatment cooling device of the present invention is applied. The heat treatment furnace to which the preferred embodiment of the present invention is applied is a continuous bright annealing furnace of austenitic stainless steel, and is an equipment using an indirect heating method.

As shown in the figure, the continuous bright annealing furnace 20 to which the preferred embodiment of the present invention is applied comprises a preliminary atmosphere holder 21, a preheater 22, a heating device 23, and a cooling device 10. And, the heat treatment object is a structure to pass it continuously by the conveyor equipment (24).

The preliminary atmosphere holding unit 21 is a place where the hydrogen and nitrogen introduced into the heating device 23 and the cooling device 10 reach the heat treatment object introduced into the furnace. Hydrogen and nitrogen gas decomposed in the ammonia cracking furnace (not shown) are injected into the heating apparatus 23 and the cooling apparatus 10, and the excess gas used in these two places is discharged toward the inlet through which the heat treatment object is introduced. . At this time, by holding the discharged hydrogen and nitrogen gas in the inlet side to remove the oxygen and other impurities attached to the heat treatment object to be injected, and maintains the inert atmosphere in the preheater 22 of about 600 ℃. At the same time, it also serves to prevent external air from entering the preheater or heater.

The preheater 22 prevents rapid heating of the injected heat treatment object and reduces the heating rod in the heating device 23, and the preheater 23 allows the temperature to reach about 600 ° C. Thus, the temperature of the preheater 22 reaches 600 degreeC, and shortens the heating time to 1,100 degreeC in the subsequent heating apparatus 23. As shown in FIG. As a result, the retention time of the object can be lengthened, thereby ensuring sufficient time for intraoral dissolution of δ-ferrite mixed in the input material, and suppressing the generation of residual martensite that can occur during subsequent cold working. It can be done.

The heating device 23 maintains the temperature at 1,050 to 1,100 ° C., and it is possible to determine whether or not to solidify the δ-ferrite by heating conditions or cracking conditions in the heating device 23. In-mouth employment of the remaining carbides can be achieved.

The object heated in this way is quenched by the cooling apparatus 10, and obtains the stainless steel which has glossiness.

In the continuous process as described above, depending on the role of the cooling device 10, which is the final process, the quantity and quantity of the final product are determined. When the material heated to 1,100 ° C cannot be quenched, Chromium carbide is precipitated and thus becomes magnetic.

Figure 3a is a diagram showing the temperature change when using the cooling device 10 according to the present invention as described above, Figure 3b is a diagram showing the temperature change when using a conventional bright heat treatment furnace. In this test, a 60 mm square material was used as a heat treatment object. As shown in the figure, it takes about 5 minutes to cool from 1,100 ℃ to 80 ℃ when using the cooling apparatus according to the present invention, 7 minutes to cool from 1,100 ℃ to 150 ℃ in the conventional bright heat treatment furnace And much more time to cool to the same temperature. In other words, it can be seen that the cooling effect is significantly lowered for the heat treatment object having a large size, so that rapid cooling cannot be performed. In this case, it becomes difficult to maintain nonmagnetic properties, which are inherent to austenitic stainless steels.

As described above, when the cooling box is pure copper according to the present invention, the cooling effect can be greatly improved, and the quenching effect can be greatly improved. In addition, due to the high quenching effect, larger size austenitic stainless steel can be manufactured by indirect cooling method beyond the size range of 12.7mm, which is the limit of conventional indirect cooling bright heat treatment.

In addition, when using the shower cooling method of the present invention can further increase the rapid cooling effect, it can be more effective in the production of austenite stainless steel of a large size. Therefore, the pickling process, which is inevitably added when manufacturing a large size austenitic stainless steel, can be eliminated, thereby reducing manufacturing costs and preventing pollution.

What has been described above is just one embodiment of the cooling device for heat treatment of austenitic stainless steel of the present invention, and the present invention is not limited to the above embodiment, and as claimed in the following claims, Without departing from the gist of the present invention, one of ordinary skill in the art will have the technical spirit of the present invention to the extent that various modifications can be made.

Claims (3)

In the cooling apparatus for continuous bright heat treatment provided with a cooling box (11) in which a heat treatment object is placed inside and a casing (12) for cooling the cooling box (11) outside of the cooling box (11), The cooling box 11 is a cooling device for heat treatment of austenitic stainless steel, characterized in that made of pure copper. The method of claim 1, Between the cooling box 11 and the casing is provided with a water spray nozzle 13 along the longitudinal direction of the cooling device 10 to cool the upper side and both side portions of the cooling box (11). Cooling apparatus for heat treatment of austenitic stainless steel. The method according to claim 1 or 2, Cooling apparatus for heat treatment of austenitic stainless steel, characterized in that the inside of the cooling box 11 is filled with an inert gas.