JPH03146201A - Production and heat treatment device for hot rolled steel sheet - Google Patents

Abstract

PURPOSE:To enhance the efficiency of subsequent heat treatments and to improve the characteristics of a hot rolled steel sheet by continuously feeding a finish rolled stock from a finishing mill to a cooler to lower its temp., and then coiling the rolled stock after the rolled stock is heat treated in a nonoxidative atmosphere of a heat treating device. CONSTITUTION:The rolled stock rolled by a roughing mill 6 is once coiled by a coiler 9 of a coil box 8 and the coil 7 is un-coiled by the ensuing un-coiler 9' and is sent to the finishing mill 10. The rear end (a) of the preceding rolled stock 11 under finish rolling and the tip end (b) of the coil 12 of the succeeding rolled stock stored in the coiler 9 are joined by a joining machine 13 on the inlet side of the finishing mill. The rolled stock joined in such a manner is continuously passed in the finishing mill 10. The finished material is cooled by water spraying, etc., down to a prescribed temp. by a cooler 15 and is then cut to a prescribed length by a cutting machine 17 after the rolled stock is heat treated by the heat treating device 16. The cut sheets are alternately coiled by two units of coilers 18, 19.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a method for producing hot-rolled steel sheets, more specifically, an effective heat treatment process for producing hot-rolled steel sheets with excellent properties online. The present invention relates to a method for producing hot rolled steel sheets, and a heat treatment apparatus used therein.

(Prior art) In recent years, hot-rolled steel sheets have been replacing thick sheets with a temporary cold-rolled g thickness of 1.211+1 or more, and as a result, even hot-rolled steel sheets have become similar to cold-rolled steel sheets. Formability and processability are required, and today there is a strong desire to improve the hot rolling process in order to improve these properties. Furthermore, since it is necessary to manufacture in large quantities and at low cost, improvements in the manufacturing process are required from the viewpoint of production efficiency.

FIG. 1 shows an outline of a conventional rolling line. As can be seen from this, conventionally, the rolled material 1 is rolled to a predetermined size in a rough rolling mill 2, then rolled in a finishing mill 3 consisting of a plurality of stands, and then rolled in a cooling device 4 to a predetermined coiling temperature. It is water-cooled to 8.15 and wound up.

When the wound hot-rolled copper plate is used as a final product instead of the cold-rolled mesh plate, it is necessary to further perform a predetermined heat treatment such as annealing treatment.

On the other hand, hot rolling is performed by a combination of rough rolling and finish rolling, but since the speed of the rolled material on the entry side of the finishing mill is slower than the speed of the rolled material on the exit side of the rough rolling mill, the rolling material is continuously rolled. It is difficult to achieve this, and the process must be interrupted between the rough rolling mill and the finishing mill. Each rolled material is passed through a finishing mill. The efficiency of the manufacturing process will be greatly hindered.

Moreover, since the finishing entry rolling speed is slow, the temperature drop in the intermediate to rear end portions of the rolled material becomes large during finish rolling, which also causes deterioration in the quality of the hot rolled steel sheet.

In order to prevent such a temperature drop, a rolling line has been proposed in which a coil box is installed to temporarily wind the rolled material into a coil at the entry side of the finishing mill, but even in that case, each rolled material is The sheet is being passed through the finishing rolling mill.

As already mentioned, the demand for hot-rolled steel sheets is increasing today, and there is a need to improve their productivity.
To this end, it has become necessary to achieve continuity by preventing interruptions between the rough rolling mill and the finishing mill as described above, and to also improve the properties of the hot rolled steel sheet.

(Problems to be Solved by the Invention) Therefore, the inventor of the present invention has repeatedly studied various methods for manufacturing hot-rolled W4 sheets, and has found that in order to improve the properties of hot-rolled steel sheets compared to cold-rolled steel sheets, finishing rolling It has been found that heat treatment can be performed before post-rolling, but there are the following problems when heat treatment is performed on a hot rolling line.

■Since the finish rolling mill rolls the material every pitch for a certain period of time, it is difficult to pass it through the heat treatment furnace continuously.

■The rolling material speed at the exit side of the finishing mill is usually fast, and a very long line is required to raise the temperature and scorch the material.

In addition, hot-rolled steel sheets are sometimes pickled by users to remove scale called black scale after coil winding.
Another problem is that this pickling cost is high.

The present invention is a method for solving the above problems, and its specific purpose is to achieve 1! It is an object of the present invention to provide a method for manufacturing a hot rolled steel sheet that can improve the efficiency of the subsequent heat treatment process and improve the properties of the hot rolled steel sheet.

Another object of the present invention is to improve the manufacturing process by providing continuity between the rough rolling mill and the finishing mill.

(Means for Solving the Problems) Therefore, the inventor of the present invention conducted various studies to achieve the above-mentioned object, and found that the steel sheet that had been cooled after finish rolling was reheated.
It has been found that the mechanical properties (for example, r value) of the hot rolled steel sheet are significantly improved by cooling and winding. Then, he learned that in order to realize this, it was necessary to install a heat treatment furnace in the rolling line, and completed the present invention.

I also learned that if heat treatment is performed continuously, finish rolling must also be continuous, and that continuous operation is more effective in improving the properties of hot-rolled steel sheets and making the manufacturing process more efficient. , completed the invention.

Here, the gist of the present invention is that finish rolled material from a finish rolling mill is continuously sent to a cooling device to lower its temperature, then sent to a heat treatment device to be heat treated in a non-oxidizing atmosphere, and then continuously This is a method for producing a hot rolled steel sheet, which is characterized by winding the steel sheet.

In addition, from another aspect of the present invention, the trailing end of the preceding rolled material and the leading end of the trailing rolling material are joined between a rough rolling mill and a finishing rolling mill, and then finish rolling is performed continuously. A method for producing a hot-rolled mesh board that is then wound using a winder, the method comprising passing the rolled material through a heat treatment device in a non-oxidizing atmosphere between the finishing rolling mill and the winding machine. This is a method for manufacturing hot-rolled steel sheet.

Here, it is preferable that the heat treatment apparatus used in the method for manufacturing a hot rolled steel sheet is an apparatus in which a direct-fired reduction heating furnace, an indirect heating furnace, and a cooling device are installed in series on-line. In that case, scale on the surface of the steel plate can be removed by direct reduction heating or indirect heating in a reducing atmosphere.

When finish rolling is performed continuously in the present invention, the sheet can be continuously passed through the heat treatment furnace.Furthermore, since the finish rolling is performed continuously, the conventional idle time for each rolled material is eliminated. The finish rolling speed can be lowered and the heat treatment space becomes smaller.

Note that the distance between the finishing mill and the winding machine is usually 200 m or less, and it is impossible to install a heat treatment device in this line, and it was previously unthinkable to install a heat treatment device as in the present invention. Ta. In a new line, it is possible to install a heat treatment line between the finishing mill and the winding engine, but the distance between these lines is several hundred meters, resulting in an enormous amount of space and equipment costs. On the other hand, if you use a vertical line that is used for continuous annealing instead of the horizontal line mentioned above, the space will be smaller, but in reality, the rolled material is not always continuous but comes out of the finishing mill one by one. Therefore, 1 on the vertical line
It is impossible to thread each sheet from the tip at high speed.

In addition, since the plates are passed one by one, it is difficult to seal the entrance and exit, making it impossible to maintain a non-oxidizing atmosphere.

In this regard, the present invention attempts to solve such a problem by making finish rolling continuous as described above.

(Function) Here, the structure and function of the present invention will be further explained in detail with reference to the accompanying drawings.

FIG. 2 shows a rolling line for carrying out the method for producing hot rolled steel sheets according to the present invention.

In FIG. 2, the rolled material rolled by the rough rolling mill 6 is once wound into a coil shape by the winder 9 of the coil box 8, and the wound coil 7 is unwound by the next unwinder 9. , and sent to the finishing mill 10. On the entry side of the finish rolling mill, the rear end a of the preceding rolled material 11 during finish rolling and the tip end of the coil 12, which is the trailing rolled material stored in the winding [9], are joined by a joining machine 13. . The rear end portion a of the pre-rolled material 11 can be stopped by appropriately moving the looper 14 up and down to facilitate joining. In addition, the joining machine 13
As for the looper 14, a known one may be used, and its operation will be easily understood by those skilled in the art from the above explanation.

In this way, the joined rolled materials are continuously passed through the finish rolling process [10]. After finishing rolling, the finishing material is sent to the cooling device 15
by water spray etc. to a predetermined temperature, usually 500 to 7
After being cooled down to about 00°C and then subjected to heat treatment in a heat treatment device 16, it is cut into a predetermined length by cutting [17] and wound up alternately by two winders 1a18 and 19.

The heat treatment apparatus 16 at this time is comprised of a direct-fired reduction heating furnace 20, a radiant tube type indirect heating furnace 21, and a cooling device 22, as shown in detail in FIG. In the direct-fired reduction heating furnace 20, a reducing flame having an air ratio of 1.0 or less is applied directly to the surface of the rolled material 11 from a burner 23, and the rolled material 11 is rapidly heated to 700 to 950°C.

The rolled material 11 that has been rapidly heated in this way is scorched in the next indirect heating furnace 21. In this indirect heating furnace 21, the rolled material 11 is passed through multiple passes by hearth rolls 24, and a radiant tube 25 whose inside is heated by a burner is arranged between the rolled materials running adjacently. Due to the radiant heat of this radiant tube, the rolled material 1
1 is soaked. In this case, the atmosphere in the furnace is a mixed gas of hydrogen and nitrogen, and the hydrogen concentration is usually preferably 3 to 40%.

The scale of the rolled material 11 is reduced by these heating and soaking zones. In addition, in order to ensure scale reduction and removal, it is necessary to use a non-oxidizing atmosphere from the finish rolling mill to the winding machine.
For example, it is desirable to cover with an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere.

At the rear of the indirect heating furnace 21, there is a cooling device 22 for lowering the temperature of the rolled material to a predetermined coiling temperature, usually about 500 to 700°C. Cool by spraying with water.

The hot-rolled steel sheets produced in this way can be used as final products, for example, for forming purposes, and those with a thickness of 1.21 or more can be used as inexpensive products in place of conventional cold-rolled steel sheets. You can get excellent profits.

Next, the present invention will be explained in more detail with reference to Examples.

Example In this example, the rolling line and heat treatment equipment shown in Figs.
V+, low carbon steel sheets having a width of 600 to 2000 mm were successively joined by welding, and the sheets were continuously passed through a finishing mill and thereafter to produce hot rolled steel sheets. Here, the plate thickness at the exit side of the finish rolling mill was 1.2 to 4.51.

Next, the rolled material of this low carbon steel plate is cooled with water to 650°C on the exit side of the finishing rolling mill, and then heated to 85°C in a heat treatment equipment maintained in an inert atmosphere of hydrogen and nitrogen.
When heated from 0 to 950°C and wound at 650°C, the method of the present invention showed that the r value (Lankford value) was ) improved by about 0.5 on average.

In addition, according to the present invention, improvements in properties such as virtually no scale generation and improved elongation were observed compared to conventional methods. Furthermore, due to continuous rolling, the finish rolling speed was lowered and the power used by the rolling mill was reduced, resulting in the finish thickness being reduced to 0. It was made as thin as hm.

(Effects of the Invention) According to the present invention, heat treatment can be carried out in advance in a hot rolling line in which finish rolling is made continuous, and such a configuration itself is unique to the present invention, but The effects are also remarkable, such as the properties of the hot-rolled steel sheet being significantly improved without the need for additional heat treatment as in the past, and the hot-rolled steel sheet being able to be used for forming purposes as is.

Conventionally, the only ways to improve the properties are to change the finish rolling conditions of hot rolling, the coiling temperature, and the cooling temperature pattern from the finish mill to the coiler, and it has been found that the effects are small. If you think about it, the significance of the present invention is great.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of a conventional rolling line, and Figure 2 is a
FIG. 3 is a schematic explanatory diagram of a rolling line for carrying out the manufacturing method of the present invention, and a schematic explanatory diagram of a heat treatment apparatus of the present invention. 1.11: Rolled material 3.10: Finish rolling mill 5.18.19: Winding machine 13: Joining machine 16: Heat treatment equipment 21: Indirect heating furnace 2.6: 4.15: 8: 14: 20: Rough Rolling mill cooling equipment coil box root size Direct fire reduction heating furnace/llID Collection 2 Figure 3

Claims (2)

[Claims] (1) Finish rolling material from the finish rolling mill is continuously sent to a cooling device to lower the temperature, then sent to a heat treatment device to be heat treated in a non-oxidizing atmosphere, and then continuously rolled up. Method of manufacturing rolled steel plate. (2) The rear end of the leading rolled material and the leading end of the trailing rolled material are joined between the rough rolling mill and the finishing rolling mill, then finish rolling is performed continuously, and then the heat is applied to the winding machine. 1. A method for manufacturing a hot-rolled steel sheet, the method comprising passing the rolled material through a heat treatment device in a non-oxidizing atmosphere between the finishing mill and the winding machine. (2) Claim 1 or 2, characterized in that the direct-fired reduction heating furnace, the indirect heating furnace, and the cooling device are provided in succession.
A heat treatment apparatus for hot-rolled steel sheets used in the described method.