JPS6244530A - Cooling method for rolling stock in continuous hot rolling of steel bar, wire rod - Google Patents

Abstract

PURPOSE:To shorten length of nonwater cooled part and inadequately cooled part at rolling stock top end and to improve yield of product, by controlling respectively and independently flow rates of cooling water supplied to plural cooling pipes provided parallelly along a pass line of rolling stock. CONSTITUTION:Billet extracted from a heating furnace 20 is continuously hot rolled to rolled stock such as steel bar, wire rod by rolling mills 1-16. Cooling zones 24, 25 having cooling zones 34, 35 between tandem rolling mills 22, 23 and behind the tandem finish rolling mill 23 respectively are arranged, and the zones 34, 35 have plural cooling pipes 36 provided parallelly along the pass line 33 of rolling stock. Rolling stock is cooled by supplying cooling water to the pipes while being transferred in the pipes 36. At this time, flow rates of cooling water supplied to respective pipes 36 are controlled by controller contg. a process control computer 29 to, respectively and independently, control respective pipes 36, so that cooling water is blown to rolling stock from cooling nozzle of respective pipes 36 just after passing of rolling stock top end part through the zones 34, 35.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for cooling rolled material during continuous hot rolling of steel bars and wire rods.

(Prior art) A hot rolling process in which billets extracted from a heating furnace are passed through a number of rolling mills, from a rough rolling mill row, through an intermediate rolling mill row, and then to a finishing rolling mill row, to continuously roll rolled materials such as steel bars and wire rods. In continuous rolling, controlled rolling is performed by forced water cooling of the rolled material in the pre-cooling zone between the intermediate rolling mill row and the finishing rolling mill row, and the rolled material is forced water cooled after the finishing rolling mill row. Controlled cooling, etc. is performed.

In continuous hot rolling, the forced water cooling is performed for (suppression of Al scale formation, fb) equalization and control of mechanical properties, (c) improvement of surface quality, fd) efficiency of handling, etc. be exposed.

Controlled rolling and controlled cooling are automatically controlled by a computer, and these forced water coolings improve mechanical properties such as fine and uniform microstructure and high toughness and strength.

In particular, controlled rolling does not require heat treatment such as normalizing (
In this controlled rolling, the temperature of the rolled material is lowered by a predetermined temperature, and then finish rolling is performed in the non-recrystallized region.

By the way, the cooling zones at the front and rear stages where the above-mentioned controlled rolling and controlled cooling are performed are generally composed of a plurality of cooling zones arranged in parallel along the bus line of the rolled material, and each cooling zone has a A plurality of cooling pipes are arranged in parallel along the bus line, and the rolled material is cooled by cooling water supplied to the cooling pipes while being conveyed through the cooling pipes.

During cooling in each cooling zone, generally multiple cooling zones are used, and the temperature control of the rolled material, that is, the control of the cooling water flow rate, is performed for each cooling zone, but the flow rate of the cooling water used is compared. If the target is small, only one cooling zone is used.

(Problems to be Solved by the Invention) By the way, when controlled rolling is performed using a pre-cooling zone, it is necessary to prevent damage to the roll surface when rolled material bites in the rolling mill after the pre-cooling zone. Therefore, the tip end of the rolled material is usually made into a non-water cooled part where forced water cooling is not performed.

Therefore, during conventional controlled rolling using a pre-cooling zone, in each cooling zone of the pre-cooling zone, immediately after the non-water-cooled part of the tip of the rolled material passes through each cooling zone, the The rolled material is cooled by, for example, injecting cooling water onto the rolled material.

However, in the above conventional method, by the time cooling starts in the cooling zone, the part of the rolled material that has entered the cooling zone following the non-water-cooled part can only be incompletely cooled, and the cooling control of the said part cannot be performed well. I can't go to

Therefore, a considerably long incompletely cooled part corresponding to the length of each cooling zone is generated in the part of the rolled material following the non-water cooled part, and the temperature of the incompletely cooled part cannot be lowered by a predetermined temperature.

The incompletely cooled section cannot be used as a product, but as described above, the incompletely cooled section is quite long, so there is a problem in that the yield of the product is poor.

In addition, as mentioned above, controlled rolling usually aims to make the structure fine and uniform without heat treatment such as normalizing, so it creates a suitable cooling structure within the cross section of the rolled material. Therefore, in controlled rolling, it is necessary to finely control the temperature distribution within the cross section of the rolled material by controlling the flow rate of cooling water.

However, in the past, although the flow rate of cooling water in each cooling zone could be controlled, the flow rate of cooling water in each cooling pipe in the cooling zone could not be controlled independently, making it impossible to finely control the temperature distribution within the cross section of the rolled material. However, the quality of the rolled material could not meet the target quality.

゛An object of the present invention is to provide a method for cooling rolled material in continuous hot rolling of steel bars and wire rods, which can solve the above-mentioned problems.

(Means for Solving the Problems) In order to achieve the above object, the present invention is characterized in that the billet extracted from the heating furnace 20 is transferred to the rolling mills 1 to 16.
A cooling zone 24.25 having a cooling zone 34.35 is provided between the rolling mill rows 22.23 and after the finishing mill row 23 to continuously hot-roll rolling materials such as steel bars and wire rods. , the cooling zone 34,35 has a plurality of cooling pipes 36 arranged in parallel along the bus line 33 for the rolled material, and the rolled material is supplied to the cooling pipe 36 while being conveyed through the cooling pipe 36. In those that are cooled by cooling water, each cooling pipe 3
The point is that the flow rate of cooling water supplied to each of the cooling water pipes 6 and 6 is independently controlled.

(Function) According to the present invention, the fillet 7 extracted from the heating furnace 20 is passed through the rolling mills 1 to 16 and continuously hot-rolled into rolling materials such as steel bars and wire rods.

The rolled material is cooled in cooling zones 24 and 25, 34 and 35.
While being conveyed through the plurality of cooling pipes 36, the cooling water is cooled by the cooling water, and the flow rate of the cooling water supplied to each cooling pipe 36 is independently controlled.

(Example) Hereinafter, the present invention will be described in detail with reference to the illustrated example.
The figure shows a hot continuous rolling line, where 20 is a heating furnace for heating the billet, and a rough rolling mill row 21, an intermediate rolling mill row 22, and a finishing rolling mill row 23 are provided in series at the subsequent stage. These rolling mill rows 21, 22, 23 are the first to sixteenth rolling mill rows.
It is composed of rolling mills 1 to 16. 24 is a front cooling zone provided between the intermediate rolling mill row 22 and the finishing rolling mill row 23; 25 is a rear cooling zone provided between the finishing rolling mill row 23 and the cooling bed 26; Obi 24.25
The flow rate of cooling water supplied to the rolled material is controlled by a control device including a process control computer 29.

30 is a thermometer that measures the surface temperature of the rolled material on the entry side of the ninth rolling mill 9; 31 is a thermometer that measures the finished surface temperature of the rolled material after forced water cooling on the exit side of the finishing rolling mill row 23; 32; is a thermometer that measures the surface temperature of the rolled material after forced water cooling on the exit side of the rear cooling zone 25.

When rolling steel bars, wire rods, etc., under automatic control by the computer 29, controlled rolling is performed in which cooling water is supplied to the rolled material in the first cooling zone 24 to control the temperature, and after this controlled rolling, the rolled material is subjected to controlled rolling in the second cooling zone 25. Either or both of controlled cooling, which involves supplying cooling water for cooling, is performed.

In particular, the present invention is applied to a cooling method in the pre-cooling zone 24, which will be explained based on FIG.

In FIG. 1, the front-stage cooling zone 24 includes front-stage and rear-stage cooling zones 34.
It is composed of 35 mag.

In each cooling zone 34, 35, four cooling pipes 36 through which the rolled material is conveyed are arranged in parallel along the bus line 33 for the rolled material.

The cooling pipe 36 has cooling nozzles inside, and these cooling nozzles supply cooling water to the rolled material passing through the inside to cool the rolled material.

Reference numeral 37 denotes a first supply pipe, which has a flow control valve 38 in the middle thereof, and supplies cooling water to a second supply pipe 39.

A third supply pipe 40 connects the second supply pipe 39 and each cooling pipe 36.

A high-speed response three-way valve 41 is interposed in the middle of each third cooling pipe 40, and a relief pipe 42 is connected to each three-way valve 41.

Although a simple on-off valve may be provided instead of the three-way valve 41, the three-way valve 41 is used here in order to improve responsiveness.

Further, the cooling water that has escaped through the relief pipe 42 may be simply discharged to the outside, but in order to eliminate wasted cooling water, the cooling water that has escaped from the relief pipe 42 may be discharged into the first and second pipes. It may also be returned to the supply pipes 37, 39.

Furthermore, the relief pipe 42 may be provided with an on-off valve.

According to the embodiment configured as described above, during continuous hot rolling work, the valve opening degrees of the cooling pipe 36 and the flow rate regulating valve 38 to be used are determined according to the required flow rate of cooling water in the pre-cooling zone 24. Ru.

Now, the situation during cooling will be explained assuming that all the cooling pipes 36 are used to cool the rolled material.

That is, the leading end of the rolled material is a non-water-cooled part where forced water cooling is not performed in order to prevent damage to the roll surface when the rolled material is bitten in the rolling mills 13 to 16 after the pre-cooling zone 24.

Therefore, when the rolled material is sent to the pre-cooling zone 24, it is necessary to control the cooling by the cooling water so as not to cool the leading end of the rolled material.

In the above case, immediately after the tip of the rolled material passes through the cooling zones 34 and 35 of the pre-cooling zone 24, each cooling pipe 36
Instead of spraying cooling water onto the rolled material using the cooling nozzle, the following operation is performed.

That is, first, each three-way valve 41 is switched to the relief pipe 42 side, and each time the tip of the rolled material passes through each cooling pipe 36,
The corresponding three-way valves 41 are sequentially switched so that the cooling pipe 36 immediately cools the portion of the rolled material following the tip.

In this way, by the time cooling is started in each cooling pipe 36, the portion of the rolled material that has entered each cooling pipe 36 following the non-water-cooled part is only incompletely cooled, and the part of the rolled material that has entered each cooling pipe 36 is only partially cooled. Since the temperature cannot be set to the target temperature, this incomplete cooling section cannot be used as a product from the viewpoint of quality.

However, the length of the incomplete cooling section is only slightly longer than the length of the cooling pipe 36, and compared to the conventional incomplete cooling section which is slightly longer than the length of each cooling zone 34, 35, the length of the incomplete cooling section is considerably longer. The length can be shortened and the product yield can be improved.

The part following the incomplete cooling part of the rolled material is the cooling pipe 3.
While being conveyed through the inside of the cooling pipe 36, the cooling water is sprayed from the cooling nozzle inside the cooling pipe 36 to cool it down to the target temperature.

Further, when the feeding interval of the rolled material is short and the rear end of the rolled material is within the cooling zone 34.35 of the front and rear cooling zones 24, the leading end of the next rolled material enters the cooling zone 34.35. When the rear end of the rolled material passes through the cooling pipe 36, the corresponding three-way valve 41 is sequentially switched to the relief pipe 42 side, and the above-mentioned By performing this operation, it is possible to prevent the rear end of the rolled material from being incompletely cooled and to prevent the next forced water cooling of the leading end of the rolled material from being performed.

Furthermore, the combination of cooling pipes 36 to be used is selected appropriately (for example, the combination of cooling pipes 36
(e.g., using the same method on every other roll), the temperature distribution within the cross section of the rolled material can be controlled more precisely than before, improving the temperature distribution and causing uneven cooling such as suitable cooling structures within the cross section of the rolled material. can be prevented from happening.

Next, a comparison experiment was conducted between the cooling of the rolled material by controlling each cooling pipe 36 in the above case of the present invention and the cooling of the rolled material by controlling each cooling zone 34, 35 in the conventional case.

During the above experiment, the length of the front cooling zone 24 was 10 m.
, the length of each cooling zone 34.35 was 5 m, the length of the cooling pipe 36 was 111, the diameter of the rolled material when passing through the front cooling zone 24 was 45 mm, and the rolling speed was 3 m/sec.

FIGS. 3 and 4 are graphs showing the experimental results, and the graphs show the temperature at each surface in the longitudinal direction of the rolled material after cooling.

Looking at Figures 3 and 4, in the conventional case, the target temperature T0°C is not reached unless the tip of the rolled material is at least 6.5m behind, and the length of the incompletely cooled part of the rolled material is approximately 6.5m. In contrast, in the case of the present invention, the length of the incompletely cooled part of the rolled material is reduced to about 2.5 m.

Next, the cooling pipe 36 is used as the cooling pipe 36 of the pre-cooling zone 24.
A case of using an immersion type in which the inside is filled with cooling water will be explained.

In this case, generally, in each cooling zone 34, 35, the number of cooling pipes 36 (minimum cooling water flow rate required to fill the cooling pipes 36 with cooling water) is equal to In the case of the invention, it is the number of cooling pipes 36 used in each cooling zone 34.35, and in the conventional case, since the use or non-use of the cooling pipes 36 cannot be selected, it is the number of cooling pipes 36 provided in each cooling zone 34.35. If the set cooling water flow rate for each cooling zone 34, 35 is greater than the limit cooling water flow rate obtained by multiplying the product by For example, each cooling zone 34.
35 can be used.

The reason for this is that if the set cooling water flow rate used is smaller than the limit cooling water flow rate, the rolled material will be cooled without cooling water filling the cooling pipe 36, and the rolled material will be significantly uneven. This is because it is cooled to

Therefore, in the present invention, since the cooling water flow rate can be controlled for each cooling pipe 36, the minimum immersion flow rate of one cooling pipe 36 can be controlled in each cooling zone 34,35. If the set cooling water flow rate is larger than the value obtained by adding the correction value during online temperature control, each cooling zone 34.35 can be used, but in the conventional case, each cooling zone 34.35 Since we are trying to control each
This cannot be done as in the present invention.

Then, the minimum immersion flow rate for each cooling pipe 36 is set to 2 On? /h, correction flow rate during online temperature control is 1O
n? /h, in the present invention, each cooling zone 3
Is the cooling water flow rate set for 4 and 35 3 On? /h, each cooling zone 34.35 can be used, whereas in the conventional case, the cooling water flow rate set for cooling zone 34.35 is 120 m/h (each cooling zone 34.35
If the number of cooling pipes 36 provided in 5 is 4) or more, each cooling zone 34.35 cannot be used, and the present invention has a lower cooling water flow rate in each cooling zone 34.35. The control range can be widened.

In addition, when online temperature control is not performed, in the above case,
Is the cooling water flow rate set for each cooling zone 34,35 in the present invention 2Or+? /h or more, each cooling zone 3
4, 35 can be used.

Even if the pre-cooling zone 24 has a plurality of (two in the embodiment) cooling zones 34,35, each cooling zone 34.
If the cooling water flow rate set in 4.35 is smaller than the limit cooling water flow rate, the cooling zone to be used 34.35 I&
For example, in the case of the example,
It is necessary to reduce the number of cooling zones 34, 35 used to one.

Even in such a case, in the embodiment, by appropriately selecting the cooling pipes 36 to be used (for example, using every other cooling pipe 36), the temperature of the rolled material can be controlled more precisely than before. The temperature distribution can be improved, and the occurrence of cooling unevenness such as moderately cooled Mi weave in the cross section of the rolled material can be prevented.

Next, the following experiment was conducted in the front cooling zone 24 where the cooling pipe 36 was of the immersion type.

That is, the cross section of the billet extracted from the heating furnace 20 is a square with a side length of 155 mm, and when this billet is rolled into a steel bar with a diameter of 30 mm, the flow rate of cooling water used in the front cooling zone 24 is set to 200 m / h, and when this used cooling water flow rate is used only in the front cooling zone 34, and when this used cooling water flow rate is used in both cooling zones 34 and 35 and every other cooling pipe 36 is used (i.e. A comparison experiment was conducted between the cooling pipe 36 and the corresponding three-way valve 41 (switched only to the cooling pipe 36 side).

In this case, the steel type of the rolled material is 548C1, the diameter of the rolled material when passing through the front cooling zone 24 is 45 mm, the cross-sectional circle average temperature of the rolled material at the start of cooling is 890°C, the cooling time is 2 seconds, and the cooling water temperature is 30 mm. ℃.

FIG. 5 is a graph showing the above experimental results, showing the temperature at the internal position of the cross section of the rolled material. It can be seen that when every other cooling pipe is used, the temperature difference is smaller and the temperature distribution within the cross section of the rolled material is better, which shows the effectiveness of the present invention of controlling the cooling water flow rate for each cooling pipe 36.

The temperature distribution shown in FIG. 5 was calculated from an experimental formula for the cooling capacity of the cooling pipe 36 obtained through an actual cooling experiment.

Moreover, Fig. 6 and Fig. 7 show photographs (100x magnification) of the rolled material obtained by the latter method, with Fig. 6 showing the surface layer and Fig. 7 showing the central part. .

If you look at Figures 6 and 7, you can see that the center part is thermal, and even in the surface part, we were able to obtain a fine and uniform ferrite/pearlite structure without generating a proper cooling structure (uneven cooling). I understand.

In the embodiment, a three-way valve was installed in the third supply pipe, but a flow rate adjustment valve was installed in the third supply pipe so that the flow rate of cooling water supplied to the cooling pipe could be adjusted steplessly. It's okay.

Furthermore, the present invention is also applicable to a cooling method in the latter cooling zone, and also during cooling in this latter cooling zone, in order to prevent damage to the roller surface of the roller table after the latter cooling zone. , the tip of the rolled material is a non-water-cooled part that is not forcedly water-cooled, but even in this case, by applying the present invention, the length of the incompletely cooled part following the non-water-cooled part of the rolled material can be shortened. .

(Effects of the Invention) As described in detail above, the present invention independently controls the flow rate of cooling water supplied to each cooling pipe, so that non-conformity at the tip of the rolled material during controlled rolling and controlled cooling is reduced. The length of the incomplete cooling section following the water cooling section can be made shorter than before, and even when the interval between rolled materials is small, there is no need to create an incomplete cooling section at the rear end of the preceding rolled material. A non-water-cooled part can be created at the tip of the material, improving product yield.Also,
The temperature within the cross section of the rolled material can be controlled more precisely than before, and the temperature distribution within the cross section can be improved.
It is possible to prevent the occurrence of unevenness in cooling water such as a properly cooled structure, and improve the quality of rolled material subjected to controlled rolling and controlled cooling.

Furthermore, when the cooling pipe is of the immersion type, the control range of the flow rate of cooling water used in the cooling zone can be expanded. The present invention has the above advantages and is of great practical benefit.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, FIG. 1 is a schematic diagram of the main parts, FIG. 2 is a schematic diagram of a continuous hot rolling line, and each of FIGS. 3 to 5 is a graph showing experimental results. , FIG. 6, and FIG. 7 are photographs of the metallographic structure of the rolled material. 1 to 16-1st to 16th rolling mills, 20... heating furnace, 2
1゜22, 23--Roughing, intermediate and finishing rolling mill rows, 24.
25-front/back cooling zone, 26--cooling bed, 33--bus line, 34° 35-front/back cooling zone, 36-
・・Cooling pipe, 37, 39.40・-1st to 3rd supply pipe,
38...Flow M control valve, 41...3-way valve, 42...
Relief piping. Patent Applicant: Kobe Steel, Ltd. Kabuto 6 (Route Figure 7 t100≠Outside)

Claims (1)

[Claims] 1. The billet extracted from the heating furnace 20 is transferred to rolling mills 1 to 16
In addition to continuously hot rolling rolling materials such as steel bars and wire rods through the rolling stock, cooling zones 24 and 25 having cooling zones 34 and 35 are provided between the rolling mill rows 22 and 23 and after the finishing mill row 23. , the cooling zones 34 and 35 have a plurality of cooling pipes 36 arranged in parallel along the bus line 33 for the rolled material, and the rolled material is supplied to the cooling pipe 36 while being conveyed through the cooling pipe 36. In those that are cooled by cooling water, each cooling pipe 3
6. A method for cooling a rolled material in continuous hot rolling of steel bars and wire rods, characterized in that the flow rate of cooling water supplied to each step is independently controlled.