JPH09174116A - Production of continuous hot rolling steel plate and equipment therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a joining part from occurrence breaking or edge cracking by adding a specific amount of strain at the joining part of the rear end of an advance steel being rough-rolled and the top end of a following steel and finish-rolling them. SOLUTION: The breaking cause of a joining part is owing to the joining part and the neighborhood are made to the high temperature and these parts are weakened caused on the high temperature brittleness. The high temperature brittleness is caused by formation of the coarse particles and densely centralizing a material of brittle cause at a γ-particle boundary. If a strain >=1.5% is added on the joining part, the re-crystallization is generated in the high temperature, the particle boundary is changed, and the cause of brittleness is removed. The strain adding method is to roll reduction the joining part with a roll. Otherwise, the joining part is pressed by clamping both joining part ends with respective clam mechanisms and approaching the clamp mechanisms or the joining part is pulled by reversely separating the clamp mechanisms. Because the breaking does not occur during rolling, the yield in the production of the hot rolling steel plate is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining method for hot rolling, in which a plurality of steel materials after rough rolling (hereinafter referred to as rough bars) are joined together to perform continuous finish rolling without breakage, and a method thereof. Regarding equipment.

[0002]

2. Description of the Related Art In a conventional hot rolling line, slabs are heated, rough rolled, and finish rolled one by one. With this method, temperature control during hot rolling of the front and rear ends of the material to be rolled is performed. Since it is difficult to control cooling and cooling, defective materials and defects are likely to occur, resulting in a decrease in yield.

Therefore, in recent years, in order to solve this problem,
Before the finish continuous rolling, a method of joining the rough bars and collectively finishing rolling a plurality of bars has been adopted.

As a rough bar joining facility for this purpose, in Japanese Unexamined Patent Publication (Kokai) No. 6-170411, a steel piece after rough rolling is wound into a coil, the end portion is cut and removed, and the cut surfaces are butted. We propose a facility that heats, presses and bonds, and then finish rolling.

[0005]

An important point in the joining of the rough bars is that the joined portions do not break before being wound up.

However, in the above-mentioned Japanese Patent Laid-Open No. 6-170411, since the butt joints are joined and then finish-rolled as they are, some materials may break during the finish-rolling or both ends of the joints may be largely broken. Because of (ear cracking), it was not possible to stably manufacture a steel sheet without breaking.

It is an object of the present invention to avoid such breakage and ear cracking, manufacture a steel sheet stably without breaking, and provide a facility that enables it.

[0008]

Means (1) of the present invention for solving the above-mentioned problems is to join a rear end portion of a roughly rolled leading steel material and a leading end portion of a trailing steel material, and then continuously finish them. In the method for producing a hot-rolled steel sheet by rolling, 0.5% or more of strain is applied to the joint after the joining, that is, the joint heated to a high temperature due to heating during joining, and the finish is applied. Characterized by performing rolling, the means (2),
As its manufacturing equipment, the hot-rolled steel sheet roughly rolled by the rough rolling mill, after joining the trailing end portion of the preceding steel material and the leading end portion of the trailing steel material with the joining device, continuously the joined hot-rolled steel sheet with the finishing rolling machine. In a hot-rolled steel sheet manufacturing facility for performing finish rolling, a strain adding device for applying a strain of 0.5% or more to a joint portion of the joined hot-rolled steel materials is provided between the rough rolling mill and the finish rolling mill. Is.

The joining method may be either a laser welding method or a heating / pressing method.

In the process of continuously producing hot-rolled steel sheets after bar joining, it is the most important matter not to break the joint during finish rolling. For this reason, conventionally, a method of increasing the joining ratio and increasing the strength of the joining portion has been adopted.

However, even if the entire cross-sections are joined to increase the joining rate, breakage may occur during rolling after joining. It is presumed that this is because the joint portion that has become hot due to the heating during joining and the portion in the vicinity thereof become weak due to high temperature embrittlement. This embrittlement is caused by heating above 1300 ° C,
It occurs when rolling at 850 to 1100 ° C., and does not occur when rolling at a temperature lower than this temperature (when it is at the Ar ₃ transformation point or lower). Further, steel grades having a low Mn content are likely to break. As the cause of embrittlement, it is conceivable that the crystal grains are coarsened and that the substance causing embrittlement is concentrated in the γ grain boundary.

The present inventors have conducted extensive experiments and studies on a method of avoiding this high temperature embrittlement state. As a result, they have found that embrittlement can be avoided by applying an appropriate strain to the joint and its vicinity.

Further, as a result of studying the high temperature embrittlement avoiding method by adding the strain, 0.5% or more of strain is applied between the rough rolling machine and the finish rolling as shown in FIG. It was found that it is possible to avoid the occurrence of breakage and ear cracks from the joint and its vicinity, which is considered to be due to the avoidance of the embrittlement factor due to the change in grain boundaries due to recrystallization at high temperature. The mechanism is not clear.

The method of adding strain is to roll down the joint position and the joint portion in the vicinity thereof, or to clamp the ends of both coarse bars to be joined by a scissor mechanism to bring the scissor mechanism closer. By pressing the joint part of the both coarse bars by, or conversely to pull the joint part by avoiding the scissors mechanism away, the strain due to these may be, but after the joint is always the strain on the joint part It is important to add and then finish rolling.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(Examples) Next, examples of the present invention will be described together with comparative examples.

The slab S (component material which easily breaks) having the components shown in Table 1 is heated to 1000 to 1250 ° C. in the heating furnace A and taken out, and then rough rolling is performed by the rough rolling machine B to 20 to 20 ° C.
After forming a coarse bar having a thickness of 45 mm, it is wound up by a coil box C, rewound, and a shear D cuts the rear end portion of the preceding coarse bar and the front end portion of the following coarse bar. Then, the cut rear end portion of the preceding coarse bar and the rear end portion of the following coarse bar were abutted against each other and joined using a laser welding device E.

After that, 1 to 30 seconds after the completion of joining, 3
A position apart from the joint (a position separated by at least 10 mm or more from the joint) by the strain imparting device F capable of applying a load of 00 tons is scissored by the scissors mechanism of the strain imparting device F, and the joint (joint And a range of 10 mm from the joint)
A strain of 15% or less is applied to the sample by pressing or pulling.

5 to 120 seconds after that, finish rolling is sequentially performed by a finish rolling machine G to form a steel plate having a thickness of 0.8 mm to 10 mm, and then the joint portion is cut by a shear cutting machine H, and then a winding machine. The winding process was performed at 1.

Table 2 shows an example of this result. Nos. 4 to 9, which are examples of the present invention, were completed in a good winding state without breakage of the bar joint.

Comparative Examples Nos. 1 and 2 are examples in which no strain was applied after joining, and the fracture occurred at the initial stage of finish rolling, and continuous rolling stopped. Further, in No. 3, the strain application was 0.3%, which was out of the range of the present invention, so that a large edge crack occurred during finish rolling.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

As described above, 0.5% as in the present invention.
By adding the above strain amount, it is possible to finish-roll the rough bar joint material without breaking or causing edge cracks, and it is possible to improve the yield in the production of hot-rolled steel sheet, and the economic effect is very high. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between breakage or edge cracking and the amount of strain applied to a steel plate.

FIG. 2 is a simplified explanatory view showing an equipment arrangement of this embodiment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masamitsu Wakao 1st Nishinosu, Oita City Oita Steel Co., Ltd. (72) Inventor Junji Houji 1st Nishinosu Oita City Nippon Steel Co., Ltd. Oita (72) Inventor Junichi Wakita, 1st Nishinosu, Oita-shi, Oita City Shin-Nippon Steel Co., Ltd. Oita Steel (72) Inventor, Shinji Matsuo 1st Nishinosu, Oita-shi Oita Steel Co., Ltd. 72) Inventor Masahiro Ohara 1 Nishinosu, Oita-shi, Oita Steel Co., Ltd. (72) Inventor Katsuhiro Minanda 1 Nishinosu, Oita-shi, Nippon Steel Co., Ltd. Oita Steel (72) Inventor Hisashi Tsunefumi, Oita City, Nishi 1

Claims (2)

[Claims] 1. A method for producing a hot-rolled steel sheet by joining a rear end portion of a roughly rolled preceding steel material and a leading end portion of a trailing steel material and then continuously finishing rolling them to produce a hot rolled steel sheet with 0 A method for manufacturing a continuous hot-rolled steel sheet, characterized in that the finish rolling is performed by applying a strain of 5% or more. 2. A hot-rolled steel sheet roughly rolled by a rough rolling mill is joined by a joining device to a trailing end portion of a preceding steel material and a leading end portion of a trailing steel material, and then the joined hot-rolled steel sheet is continuously joined by a finishing rolling mill. In the hot-rolled steel sheet manufacturing facility for finish rolling, a strain adding device for applying a strain of 0.5% or more to the joint portion of the joined hot-rolled steel material is provided between the rough rolling mill and the finish rolling mill. Characteristic hot rolled steel sheet manufacturing equipment