JPH09308903A - Manufacture of hot rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for manufacturing hot rolled sheets by which the productivity of a hot rolling mill is improved and the latitude of operation is enhanced by making the set temp. of a heating furnace definite without varying the output of the heating furnace in accordance with product size, kinds of steel, surface properties or the like, and furthermore enabling securement of a prescribed finish temp. SOLUTION: This method for manufacturing the hot rolled steel sheet in a hot rolled sheet manufacturing line provided with a heating furnace 1, a rough rolling mill 2, a rough bar (sheet bar) heating device 3 between the final stand of the roughing mill and a finishing mill 4 consists of a stage for heating a slab at a constant temp. which is independent on the rolling stock, a stage for roughly rolling the heated slab to obtain the rough bar, a stage for heating the rough bar to a prescribed temp. which is dependent on the rolling stock and a stage for finish-rolling the heated rough bar. If is preferable to execute the heating of the rough bar by an induction heating device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention does not depend on product dimensions such as plate thickness and plate width or steel grades such as hardness and softness, and operates at a constant set temperature of a heating furnace to obtain a predetermined finishing temperature. It relates to a method for manufacturing a hot rolled steel sheet to be secured.

[0002]

2. Description of the Related Art A general hot-rolled steel sheet manufacturing line uses a slab heating step for heating a slab (steel piece) to a high temperature in a heating furnace, and a heating slab having a rough bar (sheet bar with a plate thickness of about 30 to 40 mm). ) And a finish rolling step of rolling a rough bar to a predetermined plate thickness. In the hot rolling line, work rolls are replaced due to wear of the work rolls of the finish rolling mill and rough surface, and this replacement cycle is called a normal cycle. This cycle is composed of various steel types and product dimensions, and when rolling, it is necessary to support the rolling load of various steel types and product dimensions, or to secure a finishing temperature that is predetermined by the rolling material. Adjusting the temperature is done.

For example, the slab at the time of exiting the heating furnace is usually at a high temperature of 1000 ° C. or higher, but as it progresses to rough rolling / finish rolling, heat input due to processing heat during rolling and radiative cooling depending on rolling time. , Water cooling required for scale removal, or heat removal by contact with rolling rolls,
The temperature of the rolled material gradually decreases. This temperature drop greatly depends on the size of the product. For example, a thin material having a thickness of about 1 mm causes a large temperature drop. Therefore, when rolling thin material,
In order to secure the finishing temperature within the predetermined temperature range necessary for obtaining a good material, the slab heating set temperature of the heating furnace must be raised to around the maximum temperature specified in the furnace.

Further, since a hard material such as high tensile strength steel and SUS has a high rolling load, the heating furnace temperature is set high in order to relax the load constraint of the rolling mill. On the other hand, for products with strict surface texture, the heating furnace temperature is set low to prevent scale formation and growth during heating and rolling.

[0005]

As described above, the temperature of the heating furnace is determined depending on various factors such as product dimensions, steel type, and surface properties. For this reason, the operation of the heating furnace has become a major factor limiting the operational flexibility, and in recent years, it has been an obstacle in meeting the needs for high-mix low-volume production. Further, the temperature control of the heating furnace has a great influence on the productivity of the hot rolling mill in terms of responsiveness. Moreover, since the output of the heating furnace is frequently changed, a considerable running cost is required for the maintenance of the furnace.

[0006] In the past, various technical developments have been carried out on the heating furnace, including the combustion system, from the viewpoint of obtaining high response of temperature control. However, a heating furnace that satisfies the high responsiveness and high productivity of the rolling mill has not yet been realized. Also, as a method of relaxing the restrictions of the heating furnace, one means is to increase the speed of the rough rolling mill / finishing rolling mill, or to relax the load constraints by increasing the rolling load resistance, etc. Requires a large amount of investment.

The present invention changes the operating method of the heating furnace which impedes the production efficiency and the operational flexibility of the hot rolling line, so that the heating depends on the product size, steel type, surface texture, etc. By setting the heating furnace at a constant temperature and ensuring a predetermined finishing temperature without changing the output of the furnace, it is possible to improve the productivity of the hot rolling mill and increase the flexibility of operation. An object is to provide a method for manufacturing a steel sheet.

[0008]

[Means for Solving the Problems] The above-mentioned problem of operating a heating furnace at a constant set temperature and ensuring a predetermined finishing temperature is a new problem between a rough rolling mill and a finishing rolling mill. This is achieved by installing a bar heating device and heating the entire rough bar after rough rolling. That is, the present invention, the step of heating the slab to a constant temperature that does not depend on the rolling material, the step of roughly rolling the heated slab into a rough bar, and the rough bar at a predetermined temperature that depends on the rolling material. It is a manufacturing method of a hot-rolled steel sheet including a step of heating and a step of finish-rolling a heated rough bar.

The heating of the rough bar in the present invention means that the rough bar is positively heated over the entire width, and that the amount of temperature rise can be controlled by adjusting the output thereof.

The apparatus for heating the coarse bar according to the present invention is
It is necessary to have one that has the ability to actively heat, and not just to suppress radiative cooling from the end of rough rolling to the start of finish rolling, such as a heat insulating cover made of a reflector or heat insulating material. Absent. A rough bar edge heater is generally well known as a device for heating the rough bar. However, this edge heater is used for the purpose of compensating for the temperature decrease in the widthwise edge portion where the temperature decrease of the rough bar is the largest. Therefore, this edge heater only locally heats a part of the rough bar, and the effect of greatly simplifying the heating furnace operation cannot be expected as intended by the present invention. In the present invention, the auxiliary use of the edge heater does not cause any problem.

[0011]

FIG. 1 shows a hot rolling line for carrying out the present invention, wherein a heating furnace 1, a row of rough rolling mills 2, a row of rough bar heating devices 3, a row of finishing rolling mills 4, a runout cooling device 5 are shown.・
It consists of a coiler 6 and a thermometer 7. The slab heated in the heating furnace 1 to a constant temperature that does not depend on the rolling material is rolled by the rough rolling mill train 2 to form a rough bar. This coarse bar
While the actual temperature is measured by the thermometer 7 and controlled to the required temperature rise amount, the rough bar heating device 3 heats it to a predetermined temperature depending on the rolling material, and then the heated rough bar finishes the rolling mill. Rolled in row 4, then cooled in runout cooler 5 as usual and finally in coiler 6
Is wound into a coil.

(Slab heating step) FIG. 2 shows a flow of a heating furnace temperature setting method performed prior to rolling. Here, a low-temperature heating furnace operation performed for the purpose of energy saving of the heating furnace will be described as an example. First, set the initial value of the heating furnace temperature (arbitrarily low temperature), and sequentially set the heating furnace temperature in consideration of the load restrictions of the rough rolling mill based on all steel types and total rough bar dimensions (rough rolling schedule) that compose the cycle. Fix it. Next, based on all steel types that make up the cycle, product dimensions (finish rolling schedule), rough bar heating amount of the rough bar heating device, and target finishing temperature, the heating capacity of the rough bar heating device, load constraint of the finishing rolling mill, and runout. Revise the heating furnace temperature again considering the running property. By conducting these examinations in advance, it becomes possible to operate the heating furnace at a constant temperature. It should be noted that such calculation may be omitted if there is a record of past operations. Also, in the above example, the work roll replacement time is one unit,
In a finish rolling mill equipped with an RG (online roll grinder), wear and surface roughness of work rolls can be neglected, so there is no need to consider the restriction.

(Rough Rolling Step) The step of roughly rolling the heated slab into a rough bar may be carried out by an ordinary method.

(Rough bar heating step) In the rough bar heating apparatus according to the present invention, if necessary, the heating output in the longitudinal direction is changed according to the change in the temperature distribution of the rolled material or the rolling conditions, and the finishing temperature is kept in an appropriate range. You may adjust so that it may be controlled stably. So-called zooming, which accelerates the speed of finish rolling to adjust the finish rolling temperature, has been conventionally performed. However, for example, thin materials have limitations such as runout runnability, and there is a limit to the temperature adjusting ability for zooming.

As a rough bar heating device, a gas heating system
Although an electric heating method, an induction heating method, etc. can be considered, the induction heating method is the most preferable in terms of excellent control response. If such a heating method with excellent control response is adopted, it is easy to adjust the output in the longitudinal direction of the coarse bar. (Finishing Rolling Step) The step of finish rolling the heated rough bar may be carried out by an ordinary method.

[0016]

[Example] An operation in which the set temperature of the heating furnace was kept constant in a hot rolling line composed of a heating furnace, a rough rolling mill (4 stands), a rough bar heating device, and a finishing rolling mill (7 stands) was examined. Here, two steel types (A: soft carbon steel, B: hard high-tensile steel) having greatly different materials and rolling schedules were used. Figure 3 shows the slab dimensions, rough bar thickness, and
The finish plate thickness and target finish temperature are shown. By the method shown in FIG. 2 described above, the heating temperature of the cycle in which this test was carried out was set to 1150 ° C. in consideration of the load constraint of the rough rolling mill and the finish rolling mill, the constraint of the rough bar heating capacity, and the like. A,
FIG. 4 shows the preliminary examination result of the temperature transition (slab / coil tip portion) from the heating furnace to the exit side of the finish rolling mill for each steel type B. Although the temperature transitions of the two steel types differ due to differences in the rough bar thickness, finished plate thickness, deformation resistance, and target finishing temperature, the coarse bar heating device is used to increase the temperature by 60 ° C for steel type A and 30 ° C for steel type B. The finishing temperature can be secured,
It was confirmed that the expected load was within the allowable range for both the rough rolling mill and the finish rolling mill.

FIG. 5 shows the output results of the finishing side rolling mill thermometer during the actual rolling of both steel types. The finish temperatures of both A and B steel types are 820 ° C. and 850 ° C., which are the target values over the entire rolling length. It was possible to secure above ℃. Also,
Both the rough rolling mill and the finishing rolling mill had no problems due to load restrictions, and satisfied the prescribed dimensional accuracy and surface texture.

[0018]

According to the present invention, the step of heating the slab to a constant temperature which does not depend on the rolled material, the step of roughly rolling the heated slab into a rough bar, and the predetermined step depending on the rolled material By carrying out the method for producing hot rolled steel sheet that includes the step of heating to the temperature of the above and the step of finish rolling the heated rolling material, the output of the heating furnace depends on the product dimensions, steel type, surface texture, etc. Even if the set temperature of the heating furnace is kept constant without changing, a predetermined finishing temperature can be secured. Therefore, the operation of the heating furnace can be greatly simplified, and the productivity of the hot rolling line and the degree of freedom of operation can be increased. In addition, it is possible to expect a reduction in running costs such as maintenance of the heating furnace. Furthermore, by adjusting the output of the rough bar heating device, it becomes easier to control the finishing temperature, which makes it possible to stabilize the material and make pinpoint production, which can be expected to achieve high-mix low-volume production with advantage. .

[Brief description of drawings]

FIG. 1 is an explanatory view showing a hot rolling line composed of a heating furnace, a rough rolling mill train, a rough bar heating device, a finish rolling mill train, a runout cooling device, and a coiler.

FIG. 2 is a flowchart showing a method of setting a heating furnace temperature.

FIG. 3 is a diagram showing specific examples of slab dimensions, rough bar thickness, finished plate thickness, and target finishing temperature of two steel types having different materials and rolling schedules. (A: soft carbon steel, B: hard high-tensile steel)

FIG. 4 is an explanatory diagram of a result of preliminary examination of temperature transition of the slab / coil tip portion from the heating furnace of the above two steel types to the exit side of the finish rolling mill.

FIG. 5 is a diagram showing an example of actual output results of the thermometer on the exit side of the finish rolling mill for the two steel types.

[Explanation of symbols]

 1 heating furnace 2 row of rough rolling mills 3 row of rough bar heating equipment 4 row of finishing rolling mills 5 runout cooling device 6 coiler (winder) 7 thermometer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadakazu Masuda 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masaaki Yamamoto 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside the Steel Pipe Co., Ltd. (72) Inventor Naoko Eda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Co., Ltd. (72) Takuma Terauchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. A step of heating a slab to a constant temperature that does not depend on a rolling material, a step of roughly rolling the heated slab into a rough bar, and heating the rough bar to a predetermined temperature that depends on the rolling material. And a step of finish-rolling the heated rough bar, the method for producing a hot-rolled steel sheet. 2. The method according to claim 1, wherein the rough bar heating is performed by an induction heating device.