JPH0639406A - Method and equipment for continuously hot rolling billet - Google Patents

Abstract

PURPOSE:To achieve stable continuous hot rolling with high productivity by making the joint of mutual billets more rigid. CONSTITUTION:Cutting work is respectively executed in such a condition that at least both end parts in the breadthwise direction of billet are brought into contact in the butting state of the respective billets to the rear end part of a preceding billet A and the tip part of the successively following billet B. Next the respective billets are brought into contact with each other and also joined over the whole of the cut faces by pressurizing the mutual billets under heating. After this joining treatment, the billets are fed to a finishing mill group 5, at the time of continuously executing hot rolling, the descaling treatment with high pressure water is executed to the cut faces of the billets on the inlet side of a joining means 2 and the cut faces are held in an inert atmosphere or a reducing atmosphere until the joining of the mutual billets is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot rolling method suitable for continuously rolling several to several tens of steel pieces such as a sheet bar, a slab, a billet or a bloom, and its equipment. It is a thing.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line for billets, the billets to be rolled are individually heated, rough-rolled and finish-rolled into hot-rolled sheets having a desired thickness. In such a rolling method, stoppage of the line due to defective biting of the rolled material is unavoidable in finish rolling, and there is a significant disadvantage that the yield is reduced due to defective shape of the leading end and the trailing end of the rolled material.

For this reason, recently, a rolling system has been adopted in which the rear end portion and the front end portion of the steel pieces to be rolled are joined prior to the finish rolling, and this is continuously supplied to the hot rolling line for rolling. It's starting to happen. Reference is made to JP-A-61-144203 as prior art regarding this point.

The technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-144203 is such that a steel piece that is conveyed first (hereinafter referred to as a preceding steel piece) and a steel piece that is conveyed subsequently. (Less than,
The leading end portion of a trailing steel piece) is butted over its entire surface, both widthwise end portions thereof are pre-joined, and rolling is performed while maintaining this state. However, this technique requires a long joining time in order to give a sufficient joining strength to the pre-joint portion, which is disadvantageous in that the line is extended.

The inventors of the present invention have attempted to solve such a problem by alternating the rear end portion of the preceding steel piece and the front end portion of the following steel piece so that the steel piece penetrates in that region in the thickness direction of the steel piece. We have developed a joining method consisting of a combination of heating and pressing, in which a magnetic field is applied and the joint surface is heated and pressed by the induced current induced by this alternating magnetic field.
No. 109 and No. 4-89110. With the development of this joining method, the joining work has become quicker and easier than ever before.

[0006]

By the way, in the above joining method, since there is an unjoined gap between the pre-joined portions, it is desired to close this gap in the subsequent finish rolling to complete the joining. However, a secondary scale after cutting with a crop shear, etc., is generated on such unbonded surface. (It takes about 20 to 40 seconds for bonding and transportation time from crop cutting before pre-bonding to arrival at the finishing rolling mill, The thickness is about 30 to 50 μm), and depending on the thickness, the joining over the entire surface is not completed during finish rolling, and sufficient joining strength cannot be obtained, so there is room for improvement in this respect. It had been.

Although this point was attempted to be solved by the technique proposed in Japanese Patent Application No. 4-41247, the cut surface generated especially in the region from cutting to joining means. The effect of the secondary scale in (2) is unavoidable (scale of about 20 to 30 μm is generated during this period), and its reduction has been required.

The present invention advantageously responds to the above-mentioned requirements, and it is an object of the present invention to propose a method and equipment capable of realizing complete continuous welding in the strip width direction in finish rolling and realizing stable continuous hot rolling. It is what

[0009]

SUMMARY OF THE INVENTION According to the present invention, at least the width direction of a steel strip is abutted on each of the rear end portion of the preceding steel strip and the leading end portion of the succeeding steel strip that follows the steel strip. After performing a cutting process in which both ends contact each other and then performing a joining process of joining the steel pieces to each other by pressing them while heating and pressing each other, they are fed to the finishing rolling mill group. Then, during continuous hot rolling, the cut surface of the steel pieces is descaled with high pressure water at the entrance side of the joining means, and the cut surfaces are inactive until the joining of the steel pieces is completed. It is a continuous hot rolling method for a steel slab in hot rolling, which is characterized in that it is maintained in an atmosphere or a reducing atmosphere.

Further, according to the present invention, at least both ends in the width direction of the steel sheet are brought into contact with the rear end portion of the preceding steel sheet and the front end portion of the succeeding steel sheet following the steel sheet in the butted state. A cutting means for performing a cutting process, a joining means for joining the steel pieces to each other over the entire surface by bringing the steel pieces into contact with each other on the cut surface and pressing while heating, and a debonding method for the entire length of the joined steel pieces. An array of a scale breaker that performs scale treatment and a group of hot finish rolling mills that finish-rolls the joined steel pieces from which scale has been removed, and the atmosphere is an inert or reducing atmosphere while joining the steel pieces to the joining means. Atmosphere adjusting means for holding the same is provided, and descaling means for removing secondary scale generated on the cut surface of the steel piece is arranged on the inlet side of the joining means. A continuous hot rolling equipment pieces.

FIG. 1 shows the structure of a continuous hot rolling facility according to the present invention.

In FIG. 1, reference numeral 1 denotes a cutting means such as a drum shear, which cuts the rear end portion of the preceding steel piece A and the leading end portion of the following steel piece B as shown in FIG. In the butted state, the cutting process is performed in which at least both ends in the width direction of the billet are brought into contact with each other.

In FIG. 3, the steel pieces A and B are brought into contact with each other at the cut surface and pressed while being heated.
As shown in a and b, the joining area of the steel slabs is gradually increased to join the steel slabs to each other over the entire surface thereof. The joining means 2 is an alternating magnetic field generator 2a (shown in FIG. 4). A structure comprising a core a forming a magnetic pole, a coil b, and a power source c, and applying an alternating magnetic field penetrating in the thickness direction of the steel slab and heating with an induced current induced by the magnetic field, Japanese Patent Laid-Open No. 89120/1992. (See above) and a plurality of sets of pressing pinch rolls 2b for sandwiching the steel pieces A and B vertically. Further, 3 in the figure is an atmosphere adjusting means, and by supplying an inert gas or a reducing gas to the joint portion by this adjusting means 3, the generation of a secondary scale on the cut surface (scheduled surface) is generated. Try to suppress.

Further, 4 is a scale breaker for descaling the joined steel pieces A and B over their entire length, and 5 is a rolling mill group for performing hot finish rolling on the joined steel pieces after descaling,

Reference numeral 6 denotes a descaling means for removing the secondary scale formed on the cut surfaces of the steel pieces A and B at the entrance side of the joining means 2. The descaling means 6 is as shown in FIG. In addition, high-pressure water jet nozzles 6a, 6b capable of jetting high-pressure water of about 100 kgf / cm ² or more to the cut surfaces of the steel pieces A and B and having a rotatable head are applied.

[0016]

If the joining means 2 is used to join the steel strips A and B over the entire surface in the plate width direction (a state in which there is no gap in the center in the width direction), no scale is generated thereafter.
Therefore, it can be said that the method of completely closing the gap in the central portion in the width direction when joining steel pieces to each other is an extremely effective means.

However, between the cutting of the steel slab and the joining means 2, a secondary scale of about 20 to 30 μm has already formed on the cut surface of the steel slab, and depending on its thickness, sufficient joining may be desired. It wasn't.

In the present invention, the cutting means 1 to the joining means 2
The secondary scale on the newly-formed surfaces (planned surfaces to be joined) of the steel pieces A and B exposed by cutting, which are generated during the period up to, is removed by the descaling means 6 arranged on the inlet side of the joining means 2 to remove the inert atmosphere. Alternatively, the steel pieces are joined together in a reducing atmosphere (there is no gap in the widthwise center of the steel pieces), so it is possible to suppress scale growth at that portion, and In the finish rolling, the joined portion is metallically joined under the action of high compressive stress in the roll gap, and there is no fracture separation from the portion in the subsequent rolling.

The reason for carrying out the descaling treatment using high-pressure water is that when high-pressure water is jetted toward the cut surface of the steel slab, the surface temperature becomes 700 ° C. or lower. This is because the growth rate of the scale has a strong correlation with the temperature of the steel material, and the scale hardly grows at 600 ° C. or less, which is advantageous for removing the scale and suppressing the scale generation due to the temperature decrease.

The joining treatment of the preceding billet A and the following billet B and the subsequent hot finish rolling are carried out according to the following procedure.

Using the cutting means 1, each of the steel pieces A and B that have passed through the rough rolling mill group 7 is cut into a flat shape such that at least both ends in the width direction are in contact with each other in the abutting state of the steel pieces. After processing, when the leading end and the trailing end of the steel piece reach the descaling means 6 on the inlet side of the joining means 1, high-pressure water is jetted to the cut surface to restore the cut surface to a high temperature. It is conveyed to the joining means 2 before being heated.

Then, each of the steel pieces A,
B is brought into contact with each other and pressed while being heated, thereby gradually increasing the joining area of the steel pieces as shown in FIG. 3 and joining the steel pieces to each other over the entire width direction.
Next, scale breaker 4 for removing surface scale
After passing through, the sheet is fed to the rolling mill group 5 to perform hot finish rolling.

In the present invention, the heating method of the joining means 2 is not limited to the method of applying an alternating magnetic field, and as long as the joining time is not extended, a direct-fire gas burner (acetylene torch, etc.) or The direct current heating method can be applied, but especially for the type that applies an alternating magnetic field, it is considered that a very large electric capacity is required when completely joining steel strips over their entire width, so this type is used. In this case, the heating is continued until the end of the billet is connected to the center of the billet by about 100 to 300 mm, after that the heating is stopped and the pressing of the billets is continued and the widthwise center is continued. It is better to close the gap at the part, in which case the time required to join the steel pieces (the time required to join the area from the width end to 100 to 300 mm) is approximately 2 to 3 seconds. , Splicer 2 can be occupied easily perform these tasks if as a structure that can be moved towards the finishing mill group 5 using a truck or the like.

As a gas for creating an inert atmosphere,
For example, nitrogen gas and nitrogen gas containing hydrogen in an amount of about 0.5% (weakly reducing) are suitable as the gas for creating the reducing atmosphere.

The atmosphere adjusting means 3 is shown as a cover system only on the upper surface of the steel slab as shown in FIG. 4 above, but it may be a system which is installed only on the lower surface or on the upper and lower surfaces. Ceramics are suitable for the material.

The injection timing of the high-pressure water by the descaling means 6 may be calculated and controlled from the conveying speed of the steel slab, and the detection of detecting the end of the steel slab at the nozzle portion of such means 6, for example. It is also possible to arrange a container and control based on the detection result.

[0027]

[Example] A low carbon steel slab having a width of 1200 mm and a thickness of 260 mm was roughly rolled by rough rolling to a thickness of 30 mm, and then sent to a continuous hot rolling facility having the configuration shown in FIG. 1 above. Feed and cut the steel piece with a crop shear (cut into a plane shape as shown in FIG. 2a: the trailing end of the preceding steel piece is linear, and the leading end of the following steel piece is recessed in the widthwise central part ( (Depression allowance: 20 mm) Circular), and then the descaling means placed on the inlet side of the joining means descales the cut surface with high-pressure water of approximately 150 kgf / cm ² (0.025 seconds), and then joins (alternating) Adopts a heating method in which a magnetic field is applied and both ends are 200 mm in the first 3 seconds.
After that, the heating is stopped for 3 seconds, and only the pressing is continued to close the gap), and then finish rolling is performed to finish the strip with a thickness of 3 mm, and it is checked whether the plate is broken during rolling. did.

In this embodiment, during the joining of steel slabs,
A mixed gas of H ₂ : 0.5% and N ₂ : 99.5% was supplied to suppress the generation of scale on the cut surface.

As a result, it was confirmed that when the steel pieces were joined and hot-rolled in accordance with the present invention, there was no fracture separation at the joints of the steel pieces and stable rolling could be performed.

On the other hand, under the same conditions except that the steel pieces were joined under the atmosphere, the plates were separated and fractured between the 6th and 7th stands of the finish rolling mill.
Under the same conditions except that the descaling process on the inlet side of the joining means was omitted, the third to fourth finish rolling mills were used.
Separation and breakage of the plate was observed between the stands.

[0031]

EFFECTS OF THE INVENTION According to the present invention, since the inclusion of oxide scale in the joint portion of the preceding steel piece and the following steel piece can be extremely reduced, the mutual joining of the steel pieces can be further strengthened, and the production Stable continuous hot rolling with high property can be carried out.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of equipment suitable for carrying out the present invention.

2A and 2B are views showing a cut shape of a steel slab.

3A and 3B are explanatory views of a joining state of steel pieces.

FIG. 4 is an explanatory diagram of a joining state of steel pieces.

FIG. 5 is a diagram showing a descaling situation.

[Explanation of symbols]

 1 cutting means 2 joining means 3 atmosphere adjusting means 4 scale breaker 5 finishing rolling mill group 6 descaling means 7 rough rolling mill A leading steel strip B trailing steel strip a core b coil c power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yusaku Fujii 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Division, Kawasaki Iron & Steel Co., Ltd. (72) Inventor Norio Takashima, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (2)

[Claims] 1. A cutting process in which at least both ends in the width direction of the steel piece are brought into contact with each other at the rear end portion of the preceding steel piece and the front end portion of the succeeding steel piece that follows the steel piece in a butted state. Then, the steel pieces are brought into contact with each other and pressed together with heating to join the steel pieces to each other over the entire surface, and then the steel pieces are fed to the finishing rolling mill group and continuously hot-rolled. In doing so, the cut surface of the steel piece is subjected to descaling treatment with high pressure water on the inlet side of the joining means, and the cut surface is kept in an inert atmosphere or a reducing atmosphere until the joining of the steel pieces is completed. A continuous hot rolling method for billets, which is characterized in that 2. A cutting process in which at least both ends in the width direction of the steel piece are brought into contact with each other at the rear end portion of the preceding steel piece and the leading end portion of the succeeding steel piece that follows the steel piece in a butted state. A cutting means, a joining means for joining the steel pieces to each other at their cut surfaces and pressing them while heating them together, and a descaling treatment on the joined steel pieces over their entire length. An atmosphere that consists of a scale breaker and a group of hot finish rolling mills that performs finish rolling on the joined steel pieces from which scale has been removed, and an atmosphere that maintains the atmosphere in an inert or reducing atmosphere while joining the steel pieces to the joining means. Continuous hot rolling of the steel slab characterized in that adjustment means is provided, and descaling means for removing the secondary scale generated on the cut surface of the steel slab is arranged on the inlet side of the joining means. Facility.