JPH08187560A - Heat treatment method of continuously cast slab - Google Patents

Abstract

PURPOSE: To provide a heat treatment method of a continuously cast slab which can be applied in on-line and does not give the effect to casting velocity of the cast slab and further, can accurately execute the heat treatment. CONSTITUTION: On the way of carrying the cast slab 10 produced by continuous casting and cut off into a prescribed length by laying on a carrying table D, water of >=0.3m<3> /min.m<2> flow rate is sprayed from sprays 13-16 arranged vertically and horizontally to the carried cast slab 10 to execute the rapid cooling treatment on the surface of the cast slab 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for improving the structure of the surface layer portion of a cast steel slab produced by continuous casting (hereinafter referred to simply as a slab).

[0002]

2. Description of the Related Art A slab produced by a continuous casting method is then conveyed to a heating furnace and heated to a predetermined temperature,
Although it is rolled by a rolling mill, when it is conveyed to a heating furnace immediately after casting, various cracks occur depending on the composition of the slab, the structure, the heating temperature, or the rolling conditions. For example, it is described in JP-A-63-168260. As described above, when the slab is cooled to a temperature whose surface temperature is 150 to 50 ° C. higher than the Ar ₃ transformation point, the inside of the slab is in a red hot state by the cooling medium, and the surface temperature is 100 to 100 ° C. from the Ar ₁ transformation point. 40
There has been proposed a hot working method for a continuously cast piece in which the structure is bainite-transformed by rapidly cooling it to a temperature lower by 0 ° C. Further, in JP-A-2-299701, a slab produced by a continuous casting machine is cut into a predetermined length by a cutting device, and a slab at 800 to 900 ° C. is arranged at a position different from the line by a tong crane. There has been proposed a hot working method for a base material in which a base material is heat-treated by immersing it in a water tank for a certain period of time.

[0003]

However, the hot working method for continuous cast pieces described in Japanese Patent Laid-Open No. 168260/1988 has the following problems. It is difficult to cool a slab that continuously flows at a changing casting speed for a predetermined time by spray cooling or the like, and as a result, it is difficult to perform accurate heat treatment. Since the cast slab is cooled by the cooling medium before it is gas cut, the temperature of the slab is lowered, which inevitably reduces the subsequent gas cutting speed, resulting in a decrease in casting speed and production. I have no choice but to reduce my ability. Further, the method of hot treating the base material disclosed in Japanese Patent Laid-Open No. 2-299701 has the following problems. It is necessary to once immerse the slabs being transported in the casting line in the offline water tank, a handling facility such as a crane is required, and the time to immerse the slabs in the water tank must be accurately controlled, so the operation is complicated. Becomes The water tank for immersing the slab requires water supply and drainage pipes, and it is necessary to install a jet water pipe on the lower surface of the slab during immersion, which complicates the equipment as a whole, including the handling device. Invites a sharp rise in prices. The present invention has been made in view of such circumstances, and a heat treatment method for continuously cast slabs that can be performed online, and that does not affect the casting speed of the slabs, and that can also accurately perform heat treatment. The purpose is to provide.

[0004]

A method according to the above-mentioned object.
According to the heat treatment method for continuously cast slabs described above, a slab, which is manufactured by continuous casting and cut into a predetermined length, is placed on a conveyor table and conveyed, and then sprayed from top, bottom, left, and right to a value of 0. Water of 3 m ³ / min · m ² or more is sprinkled on the moving slab to quench the surface of the slab. The heat treatment method for continuously cast slabs according to claim 2 is the method according to claim 1, wherein the heat treatment time of the slabs is controlled by adjusting the table moving speed of the transport table. .

[0005]

In the heat treatment method for continuously cast slabs according to claims 1 and 2, since the heat treatment is performed after the continuously cast slab is cut into a predetermined length, the heat treatment step by spray injection is performed. The speed of the slab can be freely set regardless of the casting speed, and therefore continuous casting can be performed in the best condition. On the other hand, since the temperature of the slab after cutting is lower than the temperature of the slab before cutting, if the heat transfer efficiency is also lowered and heat treatment is performed efficiently, cooling in a water tank that is more efficient than conventional spray cooling is performed. However, when cooling the water tank (so-called soaking the slab in the water tank), the above-mentioned problems occur. Of course, if it is done with conventional spray cooling for a long time, it has the same heat removal ability as water tank cooling, but it takes time, so the inside of the slab is cooled, and the heat retained inside the slab after the rapid cooling is retained. Heat treatment of heating the surface structure again becomes difficult.

Therefore, in the heat treatment method for continuously cast slabs according to the first and second aspects, the amount of cooling water by spray injection is set to 0.3 m ³ / min · m ² or more, which is sufficient for a short time. It was made possible to apply appropriate heat treatment to the slab by subjecting the slab to rapid cooling similar to water bath cooling, which cools the surface of the slab. Hereinafter, the reason will be described in more detail while comparing with the water tank cooling. FIG. 1 shows the temperature change on the surface of the slab when the slab after cutting was cooled in a water tank for a predetermined period of time and immediately pulled up by dividing it into static water and stirring with a fountain. It has been found that the surface of has a bainite structure and cracks and other defects are less likely to occur during the heating and rolling processes. Next, FIG.
3 shows the relationship between the heat transfer coefficient (h) in the water tank cooling and the surface temperature, and FIG. 3 shows the relationship between the water amount density and the heat transfer coefficient in the spray cooling for each surface temperature. Therefore, if the heat transfer coefficient is the same regardless of whether it is water tank cooling or spray cooling, it will have the same cooling ability for the slab. As shown. In FIG. 4, the lower line a indicates cooling of the water tank with still water. Therefore, when this is adapted to spray cooling, the amount of cooling water is 0.3 m ³ / mi.
It can be seen that there is enough if n / m ² or more. When the water tank is cooled, the upper line b in FIG. 4 is the upper limit, but the upper limit is about 2 m ³ / min · m ² ,
In the case of supporting water tank cooling, the amount of cooling water from the spray is suitable to be 0.3 to ² m ³ / min · m ² ,
If the cooling capacity is increased by further increasing the amount of cooling water from the spray, it is possible to further improve the transport speed of the slab during cooling. Particularly, in the heat treatment method for continuously cast slabs according to claim 2, the cooling time by spraying can be changed by adjusting the table moving speed of the slab conveying table, whereby the steel type and application It is possible to perform heat treatment according to.

[0007]

Embodiments of the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. 5 is a side view of equipment to which the heat treatment method for continuously cast slabs according to an embodiment of the present invention is applied, and FIG. 6 is a front sectional view of the same.

As shown in FIG. 5, continuously cast slab 1
The transport table for transporting 0 is composed of a roller conveyor and is divided into a cutter table A, a cutter outlet table B, a pre-cooling table C, a slab cooling table D, an outlet table E, and a transport table F, each of which has its own table. It has a motor that can control the speed independently.

A gas cutting machine 11 is provided above the cutter table A, and continuously cast slabs (for example, 370 m).
m × 480 mm) 10 is gas-cut to a predetermined length (for example, 3 to 6 m). Further, the periphery of the slab cooling table D is covered by the chamber 12, and as shown in FIGS. 5 and 6, sprays (sprinklers) 13 to 16 are vertically and horizontally arranged in the slab traveling direction. A large amount of cooling water provided by a pump (not shown) is ejected from the sprayers 13 to 16 to form a slab 10.
Is cooled from four sides. As described above, by covering the periphery of the sprays 13 to 16 with the chamber 12, it is possible to prevent the splashed water from spouting out of the system.

A water collecting groove 17 is provided at the bottom of the slab cooling table D so as to collect the cooling water after being sprayed on the slab 10 by the sprays 13 to 16. The amount of water ejected from the sprays 13 to 16 is 0.3 to 2 m ³ / area of the slab area as described above.
It can be adjusted within the range of min · m ² . In this way, by controlling the flow rate of water and the transport speed of the slab cooling table D, it is possible to control the heat treatment according to the steel type.

Therefore, in this equipment, about 0.6 m
After cutting the slab 10 cast at a speed of / min to a predetermined length by the gas cutting machine 11, the slab 10 is placed on the slab cooling table D via the cutter delivery side table B and the pre-cooling table C for 2-3 m / Transport at a speed of min. by this,
The slab heated to about 50 to 150 ° C. from the Ar ₃ transformation point is rapidly cooled to a temperature 100 to 400 ° C. lower than the Ar ₁ transformation point, and the surface structure of the slab 10 becomes a bainite structure. In the two-phase region, precipitation of AlN at the γ grain boundary can be prevented, and since the bainite structure has a higher ductility than the ferrite + pearlite structure, it is possible to prevent thermal expansion and microstructural transformation during transportation and heating. It has the advantage of being hard to break. The cooling temperature of the slab 10 by the sprays 13 to 16 naturally varies depending on the steel type. The slab 10 that has been subjected to the above heat treatment is placed on the transport table F via the delivery table E and is transported at high speed.

In the above embodiments, the flow rate of the cooling water from the spray is set to 0.3 to ² m ³ / min · m ² , but it is also possible to further increase the water pressure and the water amount for cooling. In particular, in the air, unlike underwater, there is no resistance to the surrounding water, so the water speed can be significantly improved,
Efficient cooling can be expected.

[0013]

The heat treatment method for continuously cast slabs according to claims 1 and 2 is 0.3 m ³ / min · m ² by spraying while conveying the cut slabs on a transport table.
Since the above-described water is sprayed onto the slab for cooling, the slab can be heat-treated while exhibiting the same cooling effect as the water tank cooling online. And, in the cooling process, since the slab to be heat treated is separated from the slab being continuously cast, the continuous casting speed can be freely set, and the slab cooling control can also be freely performed, resulting in a more accurate The heat treatment can be controlled. Furthermore, it is necessary to put a slab in a water tank and spray water at high speed from the left and right, and from above and below at a very large scale and with a large amount of power.
Since there is no resistance of surrounding water in the air, it is extremely easy and the device can be made compact.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a cooling time in a water tank cooling and a slab surface temperature distribution.

FIG. 2 is a graph showing a relationship between a slab surface temperature and a heat transfer coefficient in cooling in a water tank.

FIG. 3 is a graph showing a relationship between a water amount density and a heat transfer coefficient in spray cooling.

FIG. 4 is a graph showing the relationship between the surface temperature of a slab and the amount of spray water.

FIG. 5 is a side view of equipment to which a heat treatment method for continuously cast slabs according to an embodiment of the present invention is applied.

FIG. 6 is a front sectional view of the same.

[Explanation of symbols]

 10 Slab 11 Gas cutting machine 12 Chamber 13 Spray 14 Spray 15 Spray 16 Spray 17 Water collecting groove A Cutter table B Cutter outlet table C Pre-cooling table D Slab cooling table E Ejection table F Transport table

Claims (2)

[Claims] 1. A slab, which is manufactured by continuous casting and cut into a predetermined length, is 0.3 m ³ / m from a spray provided on the upper, lower, left and right sides while being carried on a carrier table.
A heat treatment method for continuously cast slabs, characterized by sprinkling water of in · m ² or more onto the moving slabs to quench the surface of the slabs. 2. The heat treatment method for continuously cast slabs according to claim 1, wherein the heat treatment time of the slab is controlled by adjusting the table moving speed of the transport table.