JPH0716685B2 - Joining method of billets in hot rolling - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for joining steel slabs in hot rolling,
In particular, it aims for quick and easy joining work.

(Prior Art) Conventionally, during hot rolling of steel slabs, the steel slabs extracted from the heating furnace were rolled one by one, so that various troubles as described below occurred particularly in the finish rolling step. .

a) Bad biting of the tip of the steel piece.

b) Narrowing the rear end of the billet.

c) Trouble running on the runout table at the tip of the billet.

d) Dimensional defects at the front and rear ends of the steel piece.

As a solution to the above-mentioned problem, in the inlet side conveying line of the hot finish rolling mill, the continuous rolling in which the trailing end of the preceding billet and the leading end of the following billet are sequentially joined and then subjected to finish rolling A method has been proposed, and along with this, various methods have been developed as a method for joining steel pieces.

For example, Japanese Patent Laid-Open No. 60-244401 discloses an induction heating pressure welding method using a so-called solenoid type coil (see FIG. 9).
However, Japanese Patent Laid-Open No. 61-159285 discloses an electric heating pressure welding method using an electrode roll.

Further, in JP-A-61-144203, the rear end portion of the preceding steel piece and the tip portion of the trailing steel piece are butted, and at least both widthwise end regions of the butted portion are pre-joined,
A joining method is disclosed which comprises rolling at a rolling reduction of 20% or more.

(Problems to be Solved by the Invention) However, JP-A-60-244401 and JP-A-61-
In any of the methods disclosed in Japanese Patent No. 159285, the rear end surface of the preceding steel piece and the entire front end surface of the trailing steel piece are used as joint surfaces, and heating is applied over the entire joint surface, so that there are the following problems. .

i) A large amount of electric power is required for heating.

ii) The heating time required to reach the desired bonding temperature is long.

iii) For this reason, when heating is performed with the heating equipment stopped, a long loop is required, while when heating is performed between runs, a long running distance is required and the equipment length becomes long.

Further, in the method disclosed in JP-A-61-144203, since the rolling treatment is indispensable after pre-joining, the joining also requires a long time, and the problem iii) still remains, and iv) the joining work is complicated. There was a problem.

The present invention advantageously solves the above problems, and an object thereof is to propose a quick and simple joining method.

(Means for Solving the Problem) As a result of intensive studies to solve the above problems, the inventors have found that when joining steel pieces, the entire abutting surfaces of the preceding and following steel pieces are not necessarily joined. It was found that it is not necessary to do this, and at least both end regions should be joined at a predetermined ratio.

The present invention is based on the above findings.

That is, the present invention, on the inlet side of the hot finish rolling mill, butts the trailing end portion of the preceding steel piece and the leading end portion of the following steel piece in contact with or in close proximity to each other, and then when heating and joining, The rear end of the steel slab and the tip of the trailing steel slab are contacted at least in both widthwise end regions of each steel slab in the butt contact state of the two, while cutting into a shape having a gap between them. Then, it is a method for joining steel pieces in hot rolling, which comprises locally heating and pressing the joining planned portions of the leading and trailing steel pieces to gradually increase the joining area.

The present invention will be specifically described below.

FIG. 1 schematically shows an inlet side conveyance line of a finish rolling mill incorporating a joining device suitable for carrying out the present invention.

Numbers 1-a and 1-b in the figure are the leading and trailing billets, respectively.
2 is a coil box, 3-a, 3-b and 3-c are pinch rolls, 4 is a leveler, 5 is a cutting device, and 6 is a joining device. In the figure, the joining device 6 is illustrated as a case where heating and joining processes are performed during so-called running in which the running of the steel slab 1 is synchronized. When performing, the looper shown by the broken line 7 is used. Further, 8 is an FSB (descaler), and 9 is the first stand of the finish rolling mill.

In the present invention, as the cutting method of the leading end after each of the preceding and following steel slabs, any conventionally known method such as shear, gas fusing and laser fusing is suitable, but a drum having two curved blades Cutting with a shear is particularly advantageous.

2A to 2G show a preferred cutting shape of the tip portion after the leading and trailing steel pieces.

FIG. 2a shows a case where the tip is cut into a concave shape with the same curvature, and FIG. 2b shows a case where both the tips are concave but the curvatures are different, but in FIG. In the case of the concave shape, in the same figure d, one is convex and the other is concave,
This is a case where the concave curvature is made slightly larger than the convex curvature, and further, FIG. 6G shows a case where a joint margin is provided at both end areas in the width direction and the central area is cut out. In all of the above examples, only the widthwise both end regions of the steel slab are brought into contact with each other and a gap is provided in the central region, but the cutting shape in the present invention is not limited to this, and is shown in FIGS. As described above, contact may be made at three points in both end regions and the center, and a gap may be provided between them, but although not shown in the drawing, a shape may be such that four or more contact portions are provided and a gap is provided therebetween.

In the present invention, the heating means is not particularly limited, and any of gas burner, electric heating and induction heating can be used. Among them, an alternating magnetic field as shown in FIG. 3 is applied in the plate thickness direction of the steel piece. Induction heating, which is a method of penetrating and applying (hereinafter, such a magnetic field applying method is referred to as a transverse method), is particularly advantageous.

As shown in FIG. 3, 10 is an alternating magnetic field generating coil that penetrates the steel piece 1 in the plate thickness direction to generate an alternating magnetic field. The alternating magnetic field generating coil 10 is installed by sandwiching the steel piece vertically. It comprises a pair of cores 10-a, a coil 10-b continuously wound around these cores, and a power supply 10-c.

By the transverse method as shown in FIG. 3, an alternating magnetic field d is formed in the central area of the abutting portion a of the leading and trailing steel pieces.
Is applied, an eddy current e as shown in FIG. 4a is induced in the abutting portion a, and as shown in FIG. 4b, the contact regions at both ends of the abutting portion are heated preferentially. The induction heating method is particularly advantageous when it is important to heat at least both widthwise end regions of each steel piece as in the present invention. If the contact areas are located in the center or other positions in addition to the end areas, a predetermined number of alternating magnetic field generating coils are placed at the predetermined positions to preferentially heat each contact area. You can Further, FIG. 3 shows a case where a so-called split type alternating magnetic field applying coil in which steel pieces are vertically sandwiched is used as a transverse type alternating magnetic field applying coil. It is also possible to use a so-called C-type alternating magnetic field applying coil that uses the C-shaped monolith 10-d as the core, and the C-type coil moves in synchronization with the movement of the steel piece. In the case of performing the joining process while performing the above, there are advantages in that the handling is easy and the magnetic poles can be aligned easily and accurately.

Here, the temperature at which the joining proceeds satisfactorily is 1250 ° C. or higher, but if the heating temperature is too high, the ends of the steel slabs may melt, so even if heated, it is preferably 1450 ° C. or lower.

Now, according to the present invention, first, the rear end portion of the preceding steel piece and the front end portion of the following steel piece are cut into a concave shape by the cutting device, for example, as shown in FIG. 6a. Disconnect.

Then, the concave joint surfaces are abutted against each other in a contact state or a close state, and then heated and pressed. The heating and pressing treatments include: i) a method of stopping the heating when the temperature of the planned joining portion reaches the target temperature and then pressing, ii) if the temperature of the planned joining portion reaches the joinable temperature,
Method of starting pressing while heating is continued (however, the melting temperature of the steel pieces does not exceed), iii) Method of pressing the steel pieces from the beginning and heating the contact parts at the same time iv) Predetermined joining margin ( It is preferable to use a method in which the joining margin in both end regions of the steel slab is pressed to 1/10 or more of the width of the slab and then heated, but the methods iii) and iv) are particularly effective. This is because the steel pieces are still in a high temperature state of about 1000 to 1100 ° C before the hot finish rolling, so the joining of the steel pieces will proceed to some extent by just pressing. This is because if the heat treatment is performed at the same time as the start of or immediately after that, the joining can be effectively promoted, and the shortening of the joining time and reduction of the amount of electric power input for heating can be expected.

By applying the heating and pressing treatments as described above, the deformation starts from both end regions which are high temperature parts, and the joint region gradually expands from both end regions to the central region, as shown in FIG. 6b.
The joining force is effectively strengthened.

Here, the joining margin W is preferably 0.1 times or more, and 0.2 times or more in total in at least both end regions with respect to the steel billet width B. This is because if the total joining allowance is less than 0.2 times the width of the steel sheet, the front and rear steel pieces may be separated and fractured during the subsequent finish rolling.

FIG. 7 shows the result of examination on the relationship between the joining margin and the presence or absence of breakage in finish rolling.

As is clear from the figure, if the joining margin W in both end regions is 0.1 times or more the width B of the billet, there is no possibility of fracture separation in the subsequent finish rolling.

The above-mentioned pressing process can be easily carried out with pinch rolls provided by sandwiching the abutting parts of the steel piece front and back, and a pressing force of about 3 to 5 kg / mm ² is sufficient.

(Operation) In the present invention, the heating is actually applied only to the joining scheduled portion, and it is not necessary to heat the entire area in the width direction of the billet as in the conventional case. Also, the heating time up to the bonding temperature can be shortened. Therefore, when heating is performed in a stopped state, the loop length is short, and when heating is performed between runs, a short running distance is sufficient. Further, after heating up to a predetermined joining temperature, a desired joining strength can be obtained only by lightly pressing with, for example, a pinch roll, so that no complicated joining work is required.

Further, if a transverse induction heating is adopted as the heating means, the heating time can be further shortened.

Furthermore, by adopting the heating and pressing treatments in which heating is performed while pressing, it is expected that the heating time will be further shortened and the amount of input electric power will be reduced.

(Example) Example 1 Steel pieces were joined in the following manner in the transfer line on the entry side of the finishing mill shown in FIG. 1 above.

The steel pieces used in the experiment were low carbon steel sheet bars with a thickness of 30 mm and a width of 1000 mm for both the preceding steel piece 1-a and the following steel piece 1-b, and the cutting device 5 had two curved blades. Was used.

Now, the trailing edge of the leading seat bar 1-a and the trailing seat bar 1
The tip of -b was cut into an arc shape as shown in FIG. The radius of curvature of each sheet bar cut surface was 20 m. Then, the rear end portion of the preceding seat bar 1-a and the rear end portion of the following seat bar 1-b are butted against each other in a contact state, and only the both end regions are solenoid-type induction coils (input power: 4000 kW, frequency: 500H
heated in z). When the heating temperature reaches 1400 ℃, the heating is stopped and the pinch rolls 3-b and 3
-c was used to press both with a force of 3 kg / mm ² . Due to this pressing force, the joining margin was expanded to W = 200 mm.

Here, the heating time for the planned joining portion was 10 s, and the required time was greatly shortened compared to 15 s for the conventional method of heating the entire area in the point width direction.

Further, in the subsequent finish rolling, the joining surface did not separate, and good continuous rolling could be continued.

Example 2 In the same manner as in Example 1, the rear end portions of the leading sheet bar 1-a and the trailing end sheet bar 1-b were brought into contact with each other at their both end regions, and then joined in the following manner. Was applied.

Alternating magnetic field (C-type magnetic pole) Input power: 2000Kw Frequency: 500Hz b. Heating temperature: 1400 ℃ c. Pressing force: Face pressure of 3kgf / mm ² d. Joining margin after heating and pressing W = 200mm (one side) 100mm) e. Joining form: Stop heating and press when heating reaches 1400 ° C. The time required to finish heating the planned joining part is 4 s, and the conventional method of heating the entire point width direction Compared to that of 15s, the time required was significantly shortened.
In addition, the power consumption was halved.

Further, in the subsequent finish rolling, the joining surface did not separate, and good continuous rolling could be continued.

Example 3 In the same manner as in Example 1, the rear end portions of the preceding sheet bar 1-a and the front end portions of the succeeding sheet bar 1-b were abutted against each other in a contact state, and then joined in the following manner. Was applied.

Alternating magnetic field (C-type magnetic pole) Input power: 2000Kw Frequency: 500Hz b. Heating temperature: 1400 ℃ c. Pressing force: Face pressure of 3kgf / mm ² d. Joining margin after heating and pressing W = 200mm (one side) 100 mm) e. Joining form: Pressing and heating in advance In this case, the heating time required for joining was 2.4 s, and the required heating time could be further shortened compared to the conventional method.

In the above examples, the case where the induction heating method was used as the heating means was mainly described, but it has been confirmed that the same effect can be obtained even when other means such as a gas burner is used.

(Effect of the Invention) Thus, according to the present invention, in joining the trailing end portion of the preceding billet and the leading end portion of the trailing billet in the entry side conveyance line of the finishing rolling mill, the time required is significantly longer than that in the conventional case. It is possible to reduce the size of heating equipment and shorten the equipment length.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an inlet side conveyance line of a finish rolling mill incorporating a joining device suitable for carrying out the present invention, and FIGS. 2A to 2G are respectively preceding and following billets according to the present invention. After that, a plan view showing a preferable cutting shape of the tip portion, FIG. 3 is a schematic view of a transverse induction heating device (divided type) according to the present invention, and FIG. 4a is induced by the transverse method. The figure which shows the flow of the eddy current, the figure b which shows the temperature distribution of the abutting region when heating with the same method, Figure 5 is the other transverse induction heating device (C
6), 6a and 6b are diagrams showing changes in the shape of the end of the steel piece before and after pressing according to the present invention, and FIG. 7 shows the relationship between the joining margin and the presence or absence of breakage in finish rolling. 8A and 8B are explanatory views of a procedure for cutting, heating and pressing a steel piece according to the present invention, and FIG. 9 is a schematic view of a conventional solenoid type coil. 1-a ... Leading billet, 1-b ... Trailing billet 2 ... Coil box 3-a, 3-b, 3-c ... Pinch roll 4 ... Leveler 5 ... Cutting device 6 ... Joining device, 7 ... Looper 8 ... FSB, 9 ... First stand 10 ... Alternating magnetic field generating coil 10-a ... Core, 10-b ... Coil 10-c ... Power supply, 10-d ... C-type core

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kunio Yoshida 1 Kawasaki-cho, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd. (72) Inventor Naoki Hadano 1 Kawasaki-machi, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Steel In-house (72) Hiroshi Sekiya 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (56) Reference JP-A-61-259804 (JP, A)

Claims (2)

[Claims] 1. On the entry side of a hot finish rolling mill, when the rear end of the preceding steel slab and the front end of the subsequent steel stake are brought into contact or in close contact with each other and then heated and joined, the preceding The rear end of the steel slab and the tip of the trailing steel slab are contacted at least in both widthwise end regions of each steel slab in the butt contact state of the two, while cutting into a shape having a gap between them. Then, the joining method of the steel slab in hot rolling is characterized in that the joining area of each of the leading and trailing steel slabs is locally heated and pressed to gradually increase the joining area. 2. The method for joining steel slabs in hot rolling according to claim 1, wherein the heating and pressing treatment is heating while pressing.