JPS6261713A - Cooling method for hot rolling steel plate - Google Patents

Abstract

PURPOSE:To make a uniform temp. distribusion and to prevent a deterioration of a material by interposing a masking member at a transverse and part of a hot rolling steel plate to a cooling water injected zone, to interrupting a part of cooling water from spray nozzles and controlling the temp. distribution. CONSTITUTION:Above side guide 36, 38 guiding the conveying direction of the steel plate, the masking trays 40, 42 receiving a part of cooling water from spray header are equipped freely movably in the transverse direction of the steel plate. In the same way, under the guids 36, 38, the masking trays 44, 46 to receive the cooling water from a stand spray 26 are equipped. The masking trays 40, 42 and 44, 46 are connected to driving mechanisms 48, 50 respectively and settled on desired distances from the side guids. The driving mechanisms 48, 50 are driven by signals from control devices.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cooling a steel plate in a hot rolling process, and particularly to a method for cooling a steel plate between rolling stands by supplying cooling water to the steel plate.

[Prior Art] In hot rolling, the mechanical properties or material properties of a steel plate are controlled by adjusting the temperature of the steel plate. For example, in a finish rolling mill, if rolling is not completed in the austenite region, a so-called low-temperature finish structure will be formed, and workability will be significantly deteriorated. For this reason, it is necessary to ensure a temperature equal to or higher than the Ar3 transformation point, but since the temperature of the steel plate is not uniform, this temperature range may not be maintained in some cases. For example, in low carbon steel, finish rolling may be finished at a low temperature just above the Ar3 transformation point (low temperature heating) in order to obtain fine α grains. In such a case, if the temperature distribution of the steel plate is uneven, it is difficult to ensure a temperature equal to or higher than the Ar3 transformation point. In particular, when a steel plate is conveyed to a hot finishing rolling mill, the edges in the width direction are more likely to be cooled than the center of the steel plate during air cooling or water cooling during conveyance, so the temperature at the edge of the steel plate is lower than that of the center. lower than the temperature in the center.

In a finishing mill, a steel plate is cooled to a predetermined temperature by spraying cooling water from spray nozzles provided between finishing stands. This spray nozzle is installed across the conveyance path of the steel plate, that is, along the width direction of the steel plate, and cools the steel plate uniformly in the width direction by uniformly spraying cooling water in a curtain shape. ing.

[Problems with the Prior Art] However, after the cooling water injected onto the steel plate hits the surface of the steel plate, it flows down from the edge of the steel plate along the surface of the steel plate. In other words, the cooling water injected into the center of the steel plate is also injected onto the surface of the steel plate, and then flows along the surface of the steel plate to the edge of the steel plate. The central part of the steel plate is cooled more strongly than the central part of the steel plate. Therefore, there is a problem that the temperature at the edge is lower than that at the center of the steel plate. In other words, unevenness occurs in the temperature distribution of the steel plate,
For example, the temperature at the edge of the steel plate is reduced by about 60°C compared to the temperature at the center of the steel plate.

There is a problem in that the material quality of the steel plate deteriorates due to such uneven temperature distribution of the steel plate.

[Means for Solving the Problems] The present invention was made in view of the above circumstances, and it is possible to uniformize the temperature distribution in the width direction of the steel plate during hot rolling of the steel plate, thereby improving the quality of the material. An object of the present invention is to provide a method for cooling a hot rolled steel plate that can prevent deterioration.

A method for cooling a hot-rolled steel plate according to the present invention is a method for cooling a hot-rolled steel plate in which the hot-rolled steel plate is cooled by injecting cooling water from a spray nozzle. The spray nozzle is interposed in the cooling water injection area to block part of the cooling water from the spray nozzle and adjust the temperature distribution in the width direction of the steel plate.

[Embodiments] Examples of the present invention will be described in detail below with reference to FIGS. 1 to 5 of the accompanying drawings.

As shown in FIG. 2, a rough rolling mill 12 and a finishing rolling mill 14 are arranged in this order in a conveyance line 10 for steel plates in a hot rolling process. This finishing rolling mill 14 has seven rolling stands (only three rolling stands are shown and the other stands are omitted in FIG. 2) along the conveyance direction of the steel plate, namely, a first rolling stand 16, a first rolling stand 16, and a second rolling stand. Two rolling stands 18, . . . and a seventh rolling stand 20 are provided at predetermined intervals. A cooling device 22 that cools the steel plate by supplying cooling water to the steel plate is disposed between each rolling stand.

As shown in FIG. 1, the cooling device 22 includes an upper stand sprayer 24 that sprays cooling water onto the upper surface of the transported steel plate.
is provided above the conveyance line 10, and a lower stand spray 26 for spraying cooling water onto the lower surface of the steel plate is provided below the conveyance line 10, respectively. Spray headers 28, 30 extend perpendicularly to the conveying direction of the steel plate from the upper and lower spray stands 24, 26, respectively. In the spray header 28, 30, a plurality of spray nozzles 32, each of which sprays cooling water toward the surface of the steel plate, are arranged in a line from one end to the other end in the width direction of the conveyance line 10. A cooling water pipe 34 for introducing cooling water is connected to the central portions of the upper and lower spray headers 28, 30.

On the other hand, side guides 36 and 38 are installed on both sides of the steel sheet conveyance line 10 to guide the conveyance direction of the steel sheet. Each of the side guides 36 and 38 is provided so as to be movable in the width direction of the conveying line depending on the width of the steel plate to be rolled.

Above each side guide 36.38, a mask tray 44.46, which receives a portion of the cooling water from the upper spray header at its tip, moves in the width direction of the steel plate with respect to the side guide 36.38. It is set freely. Similarly, below the side guides 36 and 38 is a mask tray 44 for receiving cooling water from the stand sprayer 26 below.
．． 46 are provided. Upper mask tray 40.4
2, the lower mask tray 44, 46 is connected to the drive mechanism 48.
is connected to the drive mechanism 50 and is connected to one side portion 4 of the side guide.
It is set to a desired distance from 0.42. Mask tray 4
4.46 is fitted with a discharge conduit 52.54 for discharging the cooling water stored here.

The drive mechanism 48,50 is connected to the control device 5 as shown in FIG.
6 and is driven according to a control signal from a control device 56. This control device 56 includes a first thermometer 58 provided on the exit side of the rough rolling mill 12 and a first thermometer 58 provided on the exit side of the rough rolling mill 12 and a
is connected to a first thermometer 60 provided on the outlet side of the thermometer, and is controlled based on the measured values of these thermometers. At each node 1 and the second thermometer, the temperature distribution in the width direction of the steel plate is set at 71-1 so as to measure the temperature profile of the steel plate.

Next, the operation of this embodiment will be explained. Rough rolling mill 1
The steel plate (low carbon steel) rolled in step 2 is then conveyed to a finishing mill 14. In the finish rolling mill 14, the steel plate is finished rolled to a predetermined thickness by passing the steel plate from the first rolling stand 16 to the seventh rolling stand 20 in sequence, and is also subjected to low-temperature heat treatment. In this case, the steel plate is sequentially cooled to a predetermined temperature by the cooling device 22 provided in each rolling stand. In the cooling device 22, cooling water is injected from an upper stand spray 24 and a lower stand spray 26 to cool the steel plate to a predetermined temperature. In this case, the injected cooling water crosses the steel sheet conveying line 10 and forms a curtain-like spray area.

On the other hand, on the exit side of the first rough rolling mill 12, a first thermometer 58 provided here measures the temperature profile of the steel plate before being conveyed to the finishing mill, and this temperature profile is sent to the control device 56. It is sent as data. Furthermore,
On the exit side of the finish rolling mill 14, a second thermometer 60 similarly measures the temperature profile of the steel plate that has undergone finish rolling. The temperature profile after this finish rolling is also sent to the control device 56. Based on these temperature profiles, the control device 56 determines the width of the edge of the steel plate to be shielded from the cooling water and issues a drive signal to the drive mechanism 48,50. In this case, how many of the cooling devices installed between each rolling stand should be shielded (utilization rate) and how much of the area from the edge of the steel plate should be shielded (transportation factor)? Determine. The relationship between this usage rate and temperature is expressed as
As shown in the figure.

In the graph of FIG. 4, the horizontal axis shows the width of the steel plate shielded by the mask tray (shielding width), and the vertical axis shows the temperature.

Furthermore, the graphs for each usage rate are arranged vertically for comparison. In this case, for example, a 60% usage rate means that mask trays are used for three of the five cooling devices to shield the steel plate from the cooling water jet, and a 100% usage rate means:
This means that in all cooling systems a mask tray is used to shield the steel plate from the cooling water jet. This third
As is clear from the graph in the figure, in order to adjust the temperature difference between the center and edge of the steel plate to within a range of approximately 30°C,
It is desirable that the usage rate be about 80% or more.

Furthermore, FIG. 4 shows the relationship between usage rate and temperature.

The horizontal axis represents the usage rate, the vertical axis represents the temperature difference between the edge and the center of the steel plate, and the ratio of the shielding portion to the width of the steel plate is shown as the transference number. The graph in FIG. 4 shows the relationship between the usage rate and temperature at this transference number. In this case, since it is desirable that the temperature difference is about 30° C. or less, the transference number to be shielded can be determined by setting this temperature difference. For example, if the transference number is 15%, 15% of the total mask tray
% or more should be used.

Note that the allowable temperature difference between the center and edge of the steel plate differs depending on the steel plate. FIG. 5 shows the temperature and the inclusion rate of the low-temperature finish structure in the case of a low-order aluminum guild, where the inclusion rate of the low-temperature finish structure is the ratio of the thickness of the low-temperature finish structure part to the thickness of the plate. In the graph of FIG. 5, when the center part of the steel plate is set at about 850°C, the mixing rate of the low-temperature finished structure is 10% or less up to about 810°C, which has almost no effect on the finished structure of the steel plate. Therefore, in this case, a steel plate of substantially uniform material can be obtained.

When the steel plate is shielded from cooling water, the cooling water that is injected onto the upper surface of the steel plate is directly injected onto the surface of the steel plate at the center of the steel plate. Cooling water in a portion corresponding to the edge of the steel plate is received by the mask tray. Therefore, cooling water is not directly supplied to the edge of the steel plate.

Cooling water is also injected from the lower spray nozzle from below the steel plate in the same way as the above-mentioned upper spray nozzle, but the cooling water that is injected corresponding to the edge of the steel plate is sprayed by the mask tray 44, 46. shielded. Therefore, since the temperature at the edge of the steel plate does not drop below a predetermined value, the temperature in the width direction of the steel plate can be set to be approximately equal. As a result, a steel plate having a substantially uniform structure (material) can be obtained.

This invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist of the invention.

For example, in this embodiment, the spray nozzles for injecting cooling water are not limited to being provided above and below the conveyance line, and only one spray nozzle may be provided.

Furthermore, in the above embodiment, a temperature profile meter was installed on the outlet side of the rough rolling mill and the finishing rolling mill to measure the temperature profile of the steel plate. Alternatively, the temperature may be controlled by cooling the steel plate based on a predicted value without actually measuring the temperature profile.

Although the mask tray has been attached to the side guide, the present invention is not limited thereto, and can also be attached to the spray head, for example.

Furthermore, the mask tray that blocks the cooling water is not limited to a tray provided below the spray head, but may be one that blocks part of a plurality of spray nozzles.

[Effects of the Invention] According to the present invention, the temperature distribution of the steel plate is controlled to be approximately uniform by shielding a portion of the steel plate from cooling water, so that a steel plate of uniform material can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a cooling device according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing the arrangement of the cooling device in the rolling process, and Fig. 3 is a diagram showing the relationship between the usage rate of the shielding mask and the temperature. FIG. 4 is a graph showing the mask usage rate and temperature difference for each transport number, and FIG. 5 is a graph showing the relationship between the temperature of the steel plate and the low-temperature finish layer mixing rate. 22... Cooling device, 24... Upper stand spray, 26... Lower stand spray, 40.42.
44.46...Mask tray, 56...Control device, 58.60...Thermometer. Applicant's representative Patent attorney Takehiko Suzue S1 Figure 2 Oi5 30 ・r 0 100 200 300mm Ren Kenichi Figure 3

Claims (2)

[Claims] (1) In a method of cooling a hot-rolled steel plate by spraying cooling water onto the hot-rolled steel plate from a spray nozzle, a mask member is interposed in the cooling water injection area at the widthwise end of the hot-rolled steel plate. A method for cooling a hot-rolled steel sheet, the method comprising: adjusting the temperature distribution in the width direction of the steel sheet by blocking a part of the cooling water from a spray nozzle. (2) A method for cooling a hot-rolled steel plate according to claim 1, characterized in that the temperature distribution in the width direction of the steel plate is measured, and the shielding position of the mask member is adjusted based on the measurement result. .