JPS6044122A - Method and apparatus for cooling hot rolled steel plate - Google Patents

Abstract

PURPOSE:To prevent lowering of strength and incorrect deformation of rear end part of a hot rolled thick steel plate by cooling preliminarily the rear end part of the hot rolled thick steel plate discharged and carried from a rolling mill over specified length and then cooling over the whole length thereof. CONSTITUTION:Specified length of rear end part, about 250-600mm. from the rear end, of the hot rolled thick steel plate 6 discharged from the rolling mill 1 and carried by a carrying device 2 is cooled preliminarily by a preliminary cooling device 4 to about 100 deg.C. The preliminary cooled hot rolled thick steel plate 6 is carried and then cooled over the whole length thereof. by a main cooling device by jetting cooling water from nozzles 30 from both sides. By this processing, the deficiency of strength in the rear end part due to insufficient cooling and in- correct deformation caused by unequal cooling can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling a hot thick steel plate that has been rolled and formed, and a cooling device for a hot thick steel plate that implements this method. The purpose of this is to prevent a decrease in strength due to insufficient cooling of the rear end portion of the steel plate during cooling, and to prevent improper deformation due to uneven cooling.

In recent years, many controlled cooling methods have been developed that aim to improve the mechanical properties of the steel plate, such as its strength or toughness, by water-cooling a hot thick steel plate immediately after rolling to a predetermined temperature at an arbitrary cooling rate. Steel plates can now be produced efficiently.

However, as a result of investigating the strength distribution of this type of heat-treated steel sheet in the longitudinal direction (the direction in which the steel sheet advances during cooling), it is clear that the strength of the rear end of the steel sheet is lower than that of the central portion due to insufficient cooling. It has become.

It is believed that the cause of insufficient cooling at the rear end of the hot thick steel plate is due to the type of nostle that sprays cooling water onto the hot thick steel plate, but at present, there is no explanation as to why the cooling is insufficient. It is not precisely 1'1 whether the shortage occurs.

In any case, the insufficient cooling that occurs at the rear end of the hot thick steel plate is a major cause of the quality deterioration and yield reduction of the heat-treated steel sheet as a product, so an effective countermeasure must be developed as soon as possible. That was what was hoped for.

The present invention was devised in order to solve the problems and inconveniences in the conventional examples described above, and the present invention is designed to solve the problems and inconveniences in the conventional example. The rear end portion of a predetermined length range where insufficient cooling of the steel plate occurs is pre-cooled in advance, and then the hot thick steel plate is uniformly cooled over its entire length.

The implementation of the present invention (flJ) will be described below with reference to the drawings.

The method for cooling a hot thick steel plate according to the present invention includes pre-cooling a rear end portion over a predetermined length range of a hot thick steel plate 6 discharged from a rolling mill 1 and sent 1All, and then pre-cooling this rear end portion. The heated thick steel plate 6 is uniformly cooled over its entire length.

That is, before uniformly cooling the entire hot thick steel plate 6 discharged from the rolling mill 1 and sent to the flJ.

When the entire hot thick steel plate 6 is uniformly cooled by cooling only the rear end portion of the hot thick steel plate 6 over a predetermined length range where insufficient cooling occurs.

This is to prevent insufficient cooling from occurring in the rear end portion of the hot thick steel plate 6 over a predetermined length range.

Based on many actual measurement results, the rear end portion of the hot thick steel plate 6 that needs to be pre-cooled over a predetermined length range is approximately 250 to 600 mm long from the rear end of the hot thick steel plate 6. And the degree of preliminary cooling for this 81S is:
Approximately 100°C (for example, heat the hot thick steel plate 6 from 800°C to 40°C)
When cooling to 0°C, after the hot thick steel plate 6 described above,
Good results were obtained by pre-cooling the 111 portion to 700°C.

Next, a configuration example of a cooling device that is considered to be most suitable for carrying out the method for cooling hot thick steel plates according to the present invention will be described with reference to the drawings.

This cooling device includes a conveying device 2 that conveys the hot thick steel plate 6 rolled and discharged from the rolling mill 1, and a conveying device 2 that conveys the hot steel plate 6 that has been rolled and discharged from the rolling mill 1;
jul! A pre-cooling device 4 that pre-cools the rear end portion of the hot IV steel plate 6 over a predetermined length range, and a main cooling device 3 that uniformly cools the hot thick steel plate 6 over its entire length. The main cooling device 3 is arranged on the outlet side of the preliminary cooling device 4, and the cooling water flow opening/closing valve 3L41 and the cooling water N which are individually controlled to open and close in both cooling devices 3.4 are provided.
It is constructed by providing control valves 32 and 42.

The conveying device 2 carries a hot thick steel plate 6 rolled and formed by the rolling mill 1.
This is to set up a transport line to transport the material to the destination.
In the illustrated embodiment, a large number of conveyors and rollers are used.

The main cooling device 3 has a sufficiently long cooling zone,
By injecting cooling water from above and below onto the supplied hot thick steel plate 6, the hot thick steel plate 6 is uniformly cooled over its entire length. It is constructed by a combination of a pair of cooling function parts having the same configuration, which are disposed above and below the conveying device 2 that conveys the thick steel plate 6.

This pair of cooling function parts includes a large number of nozzles 30 that open their nozzles toward the hot thick steel plate 6 being conveyed by the conveying device 2, and a supply cutoff of the cooling water injected from these nozzles 30. It is composed of a combination of a cooling water supply valve 31 and a flow rate adjustment valve 32 that are controlled, and a cooling water supply pipe 33 that supplies cooling water from the main cooling water supply pipe 5 to each nozzle 30.

In the case of the illustrated embodiment 5 Cooling water supply valve 31 and flow N control valve 32
A plurality of combinations of cooling water supply valves 31 and flow rate adjustment valves 32 are connected in parallel, and two or three nozzles 30 are connected to each combination of cooling water supply valves 31 and flow rate adjustment valves 32. However, this is to enable more fine-grained setting of the cooling power and to freely set the length of the cooling zone of the main cooling device 3.

The pre-cooling device 4 has almost the same configuration as one of the cooling function parts of the main cooling device 3 described above, except that the size of the pre-cooling device C1 is reduced.

Zunawaji, nozzle 40 and 1 Cooling water supply valve 41 and flow control valve 4 that control the supply cutoff of cooling water to this nozzle 40
2 and the cooling water to the main cooling water supply pipe 5.
The cooling water supply pipe 43 is configured to supply cooling water to each nozzle 40 from the cooling water supply pipe 43 .

As described above, this preliminary cooling device 4 only needs to cool the rear end portion of the hot thick steel plate 6, so its cooling zone is limited to the length of the rear end portion of the hot thick steel plate 6. This may be a good thing, but it depends on how the hot thick steel plate 6 is cooled by the preliminary cooling device 4.

It goes without saying that the cooling zone of the preliminary cooling device 4 can be made shorter.

The hot thick steel plate cooling device shown in FIG. 1 has the structure as described above.First, an example of the cooling operation of the hot thick steel plate 6 by this cooling device will be explained in order.

The hot thick steel plate 6 rolled and discharged from the rolling mill 1 is conveyed by the conveying device 2, and as shown in FIG. At this point, cooling water is jetted from the nozzle 40 of the pre-cooling device 4 to the rear end portion of the hot Jy-1J plate 6 to pre-cool the rear end portion.

During this preliminary cooling, a part of the hot thick steel plate 6 may enter the cooling zone of the main cooling device 3 as shown in FIG. 3
must be kept in a stopped state.

Also, in some cases, during this pre-cooling.

The operation of the hot thick steel plate 6 by the conveying device 2 at j ship speed may be stopped.

When the preliminary cooling is completed and the hot steel plate 6 conveyed by the first general conveying device 2 enters the cooling zone of the main cooling device 3 as shown in FIG. 3, the cooling water supply valve is closed. 31 is opened and a predetermined flow rate of cooling water is injected onto both the front and back surfaces of the hot thick steel plate 6 to cool the hot thick steel plate 6 to a predetermined temperature.

While the main cooling device is cooling the hot thick steel plate 6, the preliminary cooling device 4 may be operated.
In order to reduce energy costs, it is preferable to stop this preliminary cooling device 4.

In this way, the rear end portion of the hot thick steel plate 6, which is insufficiently cooled, is cooled in advance by the amount of insufficient cooling, and then the whole is uniformly cooled to a predetermined temperature, so that the hot thick steel plate 6
The rear end part will not be insufficiently cooled, and the hot thick steel plate 6
Since cooling can be performed uniformly over the entire length of the hot thick steel plate 6, it is possible to obtain a heat-treated steel plate having uniform mechanical properties over the entire hot thick steel plate 6.

Further, deformation of the rear end portion of the hot thick steel plate 6 due to uneven cooling can also be prevented.

Examples of experimental measurements showing the effects of the present invention are shown in Figures 4 and 5.
As shown in the figure.

FIG. 4 is a diagram showing the tensile strength distribution along the longitudinal direction of a hot thick steel plate after cooling according to a conventional example. It is clearly shown that there is a significant decrease in comparison.

On the other hand, FIG. 5 is a diagram showing the tensile strength distribution along the longitudinal direction of the hot thick steel plate 6 after cooling according to the present invention. It can be seen that the strength is almost the same as that of other parts, and that the entire cold-treated hot thick steel plate 6 is formed to exhibit uniform tensile strength.

As is clear from the above explanation, the present invention can cool the entire hot thick steel plate uniformly over its entire length, so it can effectively eliminate uneven cooling of the hot thick steel plate to be heat treated. In addition, it is possible to obtain a uniform mechanical strength distribution over the entire length of the hot-treated steel plate, which is very useful for improving the quality of the heat-treated steel plate, as well as increasing the strength of the rear end of the 2wJ plate. It exhibits many excellent effects, such as being able to prevent a decrease in yield due to cutting due to shortage, which greatly helps in reducing the price of high-quality heat-treated steel sheets.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a typical configuration example of a cooling device for carrying out the method of the present invention. FIG. 2 is an explanatory diagram showing a preliminary cooling operation state. FIG. 3 is an explanatory diagram showing the main cooling operation performed after the preliminary cooling shown in FIG. 2. FIG. 4 is a strength distribution diagram showing changes in tensile strength over the entire length of a hot thick steel plate cooled by a conventional cooling method. FIG. 5 is a strength distribution diagram showing changes in tensile strength over the entire length of hot thick steel plates cool-formed by the method of the present invention. Explanation of symbols 1: Rolling mill, 2: Conveying device, 3: Main cooling device. 4; Pre-cooling device, 6; Hot thick steel plate. Applicant Kawasaki Steel Nutan 7nozu Co., Ltd. ←z/77

Claims (2)

[Claims] (1) After pre-cooling the rear end portion over a predetermined length range of a hot thick steel plate discharged from a rolling mill and sent +M, the hot thick steel plate is obtained by pre-cooling the rear end portion. A method for cooling a hot thick steel plate, which cools the entire length of the hot thick steel plate. (2) A conveyance device that conveys hot thick steel plates rolled and discharged from the rolling mill, and a rear end portion over a predetermined length range of the hot thick steel plates discharged from the rolling mill and sent for tM is pre-cooled. It consists of a preliminary cooling device and a main cooling device that cools the hot thick steel plate along its entire length, and the main cooling device is disposed on the exit side of the preliminary cooling device, and each of the two cooling devices is individually controlled to open and close. A cooling device for hot thick steel plates, which is equipped with an on-off valve for cooling water flow and a cooling water flow control valve.