JPH0890004A - Joining method of slabs in continuous hot rolling - Google Patents

Abstract

PURPOSE: To suppress the generation of excessive tension which is generated in the clamped parts of a slab and to eliminate breaking in the joined part in a process where butt joining of the slabs is executed in continuous hot rolling by preliminarily heating the surfaces of clamping parts of a clamping device before a joining stage. CONSTITUTION: Before butting and joining the rear end part of a preceding slab S1 to the tip part of the succeeding slab S2 , the end part of a slab S to be ordinarily rolled before executing continuous rolling stage and/or the tip part of a 1st slab S in the continuous rolling stage is preliminarily clamped with the clamping parts of the clamping devices 3a, 3b and the slab is preheated so that temp. difference between clamped contact surface and the noncontact surface of the slab S is within 70 deg.C. Consequently, restraint of tension variation at the time of rolling the slab with a finishing rolling mill group 5 is enabled and rolling is executed without breaking in the joined part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a billet material, a slab, and other steel pieces, which are joined together by abutting them at their front and rear ends, and continuously rolling several to several tens of steel pieces. With respect to the joining method in continuous hot rolling, the present invention prevents breakage of the joining portion due to excessive tension that occurs when the clamp portion of the steel slab is rolled, and realizes stable continuous hot rolling.

[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 to finish a hot-rolled sheet having a desired thickness. However, such a rolling method cannot avoid troubles such as line stoppage due to defective biting of the rolled material in finish rolling, and also has a significant disadvantage in terms of yield reduction due to defective front and rear end shapes of the rolled material. there were.

For this reason, recently, prior to finish rolling, a continuous hot rolling method is used in which the rear end and the front end of a steel piece to be rolled are joined and continuously fed to a hot rolling line for rolling. It came to be adopted. Many sheet bar joining methods for the purpose of continuous hot rolling have been proposed, for example, in Japanese Patent Laid-Open No. 42306/1993.

That is, a method of heating the trailing end portion of the preceding steel piece and the leading end portion of the trailing steel piece by induction heating and pressing them together to join them (see Japanese Patent Laid-Open No. 42306/1993) or welding. , A method of joining by pressing, fitting, etc. In any of these methods, in order to improve the positioning accuracy of the preceding steel piece and the following steel piece or to improve the joining property by sufficient pressing, each steel piece is clamped using a clamp device. This is very important.

FIGS. 4 (a) and 4 (b) show an example thereof. The preceding steel piece S ₁ and the following steel piece S ₂ are clamped from above and below by using clamp devices C ₁ and C ₂ , respectively. For example, it is effective to clamp with a force of tens to hundreds of tonf.

[0006]

However, in the above,
Clamping device C in the prior art₁, C₂Clans
While the slab is at room temperature, the preceding billet S₁And trailing steel
Piece S₂Is about 900-1000 ℃, and the temperature difference is
Since it is always large, the preceding billet S in Fig. 4 (b) ₁And
And trailing billet S₂The T part indicated by the diagonal lines on the
The temperature decreases due to heat conduction in the
The decrease is large. The temperature difference between this clamp and the billet is
Depends on the lamp time, but for example 900 ° C slab
On the other hand, when clamped at room temperature for 15 seconds
Is the average temperature drop of the clamp part of the billet is about -80 ℃
It also becomes.

As described above, the temperature of the clamped portion of the steel slab is lower than that of the stationary portion, which causes disturbance during finish rolling.
Since the low temperature part has a larger deformation resistance than the other steady parts, rolling of this low temperature part increases the rolling load and the strip thickness on the delivery side of the rolling mill. Therefore, the reduction ratio of the rolled material decreases due to the reduction of the rolling reduction, the mass flow balance is disturbed, and the tension between the stands before and after the rolling mill acts to break.

The temperature drop in the clamp portion of the steel slab is short and instantaneous (for example, about 100 to 200 msec) with respect to a normal rolling disturbance represented by skid marks, etc. It is difficult to follow the response of the plate thickness control and the tension control by the main machine, and it is difficult to suppress the excessive tension by the rolling control. The present invention has been made to solve the above problems of the prior art, and joins the trailing end portion of the preceding steel piece and the leading end portion of the following steel piece by butt-joining in continuous hot rolling. It is an object of the present invention to provide a method for joining steel pieces in a continuous continuous hot rolling that suppresses the occurrence of excessive tension that occurs in the clamp portion of the steel pieces in the process of doing so and that does not break at the joining portion.

[0009]

SUMMARY OF THE INVENTION The present invention is a method of butt-joining a trailing edge of a preceding steel piece and a leading edge of a trailing steel piece that have undergone a rough rolling step in continuous hot rolling, while clamping them by a clamping device. 2. In the method for joining steel slabs in continuous hot rolling, the surface of the clamp part of the clamp device is heated in advance before the joining step.

It is desirable to heat the unsteady part so that the temperature difference between the clamped unsteady part of the steel slab and the unclamped steady part is within 70 ° C. Further, prior to the continuous rolling process, the unsteady part is continuously heated. Clamping the end of the billet that is normally rolled immediately before the rolling process and / or the tip of the first billet that is rolled in the continuous rolling process with a clamping device to heat the surface of the clamping part of the clamping device. It is better to

[0011]

[Operation] According to the present invention, before the rear end portion of the preceding steel piece and the front end portion of the trailing steel piece are butted and joined together, the clamp portion of the clamp device is subjected to the normal rolling before the continuous rolling step. By clamping the end of the rolled steel slab and / or the tip of the first steel slab in the continuous rolling process, the unsteady part (contact surface) and the steady part (non-contact surface) of the clamped part of the steel slab are clamped. By preheating so that the temperature difference between and is within 70 ° C, it becomes possible to suppress the tension fluctuation when rolling in the finishing rolling mill group, and it is possible to perform rolling without breaking at the joint part. .

The operation of the main requirements constituting the present invention will be individually described below. (1) Reason for reducing the temperature difference between the steady and unsteady parts of the steel slab; generally, when objects with different temperatures contact each other, the heat conduction per unit time is smaller when the temperature difference is smaller. It is known. Therefore, by preheating the clamp part of the clamp device using the method of the present invention to reduce the temperature difference between the clamp part and the steel piece, the clamp part of the steel piece (T portion in FIG. 4 (b) above). It is possible to suppress the amount of temperature drop of 2) and reduce the temperature difference between the steady portion and the unsteady portion of the steel slab.

FIG. 5 shows the relationship between the initial temperature of the clamp part of the clamp device and the average temperature of the clamp part of the steel slab after being clamped for 15 seconds. Since the difference in deformation resistance between the clamp portion and the stationary portion also becomes small, the above-mentioned excessive tension is reduced and it becomes possible to prevent breakage at the joint portion. (2) Reason for limiting the amount of temperature drop to -70 ° C or lower; as described above, the low temperature region, which is a non-steady part, has a larger deformation resistance than the high temperature regions of other steady parts. Then, the rolling load increases and the strip thickness on the delivery side of the rolling mill increases. Therefore, the reduction rate is reduced and the advanced rate of the rolled material is reduced, the mass flow balance is disturbed, and the tension between the stands before and after the rolling mill acts to break.

Therefore, the relationship between the temperature drop amount at the clamp portion of the steel slab and the tension between stands was investigated. Figure 6
Shows the relationship between the temperature drop at the clamp and the inter-stand tension generated at the joint when the steel bar with a sheet bar size of 30 mm thick and 1000 mm wide was continuously hot-rolled and the clamp was rolled. It is a thing. From this figure, it can be seen that if the temperature is within 70 ° C, the excessive tension generated at the joint is within the breaking limit, and that the plate can be passed stably without breaking.
Note that the temperature drop amount is an average value in the plate width direction, and when the entire width region is not clamped, it is necessary to consider the width direction average.

(3) The reason for clamping the leading and trailing ends of the hot rolled steel slab to be rolled; the material properties of the product depend on the finish rolling temperature, and the clamp portion of the steel slab has a temperature drop, so this finish rolling temperature Can not be secured and is often discarded because it does not become a product. Therefore, in consideration of this, by clamping the unsteady portions at the front and rear ends, which are highly likely to be cut off due to the plate thickness or the shape defect, for preheating, the cut-off allowance can be minimized.

Therefore, as the steel piece to be clamped in advance, for example, a steel piece which is normally rolled before the continuous rolling cycle may be used, or the tip of the first steel piece in the continuous rolling cycle is clamped. Alternatively, both may be combined. (4) The reason for clamping the tip of the first steel piece in the continuous rolling cycle; in this case as well, the unsteady part of the tip is clamped for preheating in order to improve the yield, similarly to the reason described above. Thus, it is possible to minimize the truncation allowance. Further, since there is no joint in the vicinity of the first tip portion, there is an advantage that the excessive tension generated when the clamp portion is rolled does not act on the joint.

(5) Relationship between Clamping Time and Surface Temperature of Clamping Part; FIG. 7 shows the relationship between clamping time and surface temperature of the clamping part, which changes in a hyperbolic shape and requires a long clamping time. Thus, it can be seen that the contact surface temperature of the clamp portion of the clamp device increases. By increasing the clamping time in this way, the contact surface temperature of the clamping device increases, but it is cooled after the clamp is opened. In addition, there is a limit to the time when one billet can be clamped according to the rolling time schedule. Therefore, when the clamping time required for preheating for one steel piece cannot be taken sufficiently, a method of preheating by repeatedly clamping a plurality of steel strips for normal rolling is effective.

(6) Regarding a method for clamping a steel slab by a clamp device; as a preheating heating method, a method of simultaneously clamping both the clamping device on the leading steel piece side and the clamping device on the trailing steel slab side is used. Alternatively, a method of clamping one by one may be used. In the former case, the time required for preheating the clamp portion for clamping at the same time becomes shorter, but the clamped portion of the steel slab becomes longer than in the latter case, so the off gauge length increases and the yield decreases. The latter, conversely, increases the time required for preheating but yields better. Therefore, each method may be selected as needed.

[0019]

EXAMPLES Examples of the present invention will be described below.
As shown in FIG. 1, a continuous hot rolling line for carrying out the present invention includes a rough rolling mill 1, a shear 2 for removing the crops at the leading and rear ends of the billet on the exit side of the rough rolling mill 1, and a preceding billet S _1. the rear end, the clamping device 3a that each clamping tip portion of the trailing steel strip S _2, comprises a 3b, bonding device 4 for butt joining the leading and trailing ends, the steel strip S ₁ joined, S ₂ of With a group of finish rolling machines 5 for continuously rolling and rolling to a predetermined thickness, a cutting machine 6 for cutting the steel slab S into a predetermined length, and two winding machines 7a, 7b for winding into a coil shape. Composed.

Then, the clamp surfaces of the clamp devices 3a and 3b are preheated in the following procedure. When a start command for continuous rolling is issued, first, it is determined whether or not there is a slab to be normally rolled before the step of carrying out the continuous rolling cycle. Then, if there is a normally rolled steel piece, the steel piece S
The front and / or rear end of the clamp device 3a, 3
Preheat by clamping at b. At this time, the leading end of the first steel piece in the continuous rolling cycle may be continuously clamped for further preheating. If there is no billet for normal rolling, the tip of the first billet in the continuous rolling cycle is clamped and preheated. Then, continuous rolling is started.

The size of the seat bar is both 30 mm thick and 1000
The results of preheating the clamp part using the method of the present invention when continuously rolling the preceding and following steel slabs each having a width of mm and a temperature of the steady portion of 900 ° C. will be described. For comparison, the results of the conventional method in which the clamp part is not preheated are also shown below. [Comparative Example] First, as in the conventional case, the clamp device 3 is used.
The clamp portions of a and 3b were clamped by a normal temperature clamp portion without preheating to join the trailing end portion of the preceding steel piece and the leading end portion of the following steel piece. At this time, the clamp time required for joining was 15 seconds, and the average temperature drop amount of the unsteady part in contact with the clamp part of the steel slab was −80 ° C. When this joint was subjected to finish rolling with the finish rolling mill group 5, FIG. 2 (a)
Tension fluctuations as shown in Fig. 3 occurred and an excessive tension of about 6 kgf / cm ² acted on the joint, leading to fracture. [Example 1] Before joining with the joining device 4, the tip of the first steel piece in the continuous rolling cycle was clamped for 15 seconds,
The surface of the clamp part was heated to 470 ° C. And
60 seconds after the clamp was opened, the front and rear end portions of the leading and trailing steel pieces were joined by the joining device 4 in 15 seconds. The surface temperature immediately before joining was 250 ° C, but the average temperature drop on the contact surface of the steel strip at the clamp was -60 ° C.

The transition of the surface temperature of the clamp part at this time is shown in FIG. 3 (a). As shown in the figure, the clamp was started at the 0 point and ended at the point A after 15 seconds. afterwards,
The temperature drops sharply when the clamp is opened, but B
Since the steel piece has passed under the clamp devices 3a and 3b for about 60 seconds until the time point, the temperature drop temporarily becomes gentle due to the radiation from the steel piece.

As shown in FIG. 2 (b), the fluctuation in tension when this joint is rolled by the finishing rolling mill group 5 is such that the excessive tension at the joint is reduced to 4 kgf / cm ² , and Rolling could be performed without breaking. The low temperature part at the tip of the first rolled material was a disturbance during rolling and over tension was generated. However, since there was no joint at the tip of the first rolled material, there was no great influence on the threadability. . [Example 2] Before joining with the joining device 4, the tips of six normally rolled steel pieces were clamped by the clamping devices 3a and 3b for 15 seconds each to be preheated, and then the first of the continuous rolling cycle was performed. The tip of the steel piece was clamped to preheat the surface of the clamp. The transition of the surface temperature of the clamp part at that time is as shown in FIG. 3 (b).

That is, the first steel piece was clamped to 0
From the time point to the time point B at which the billet has passed, FIG.
Following the same temperature transition as above, after the point B at which the steel piece passed, the clamp part was in the state of being air-cooled, and the temperature reached the minimum temperature by the time point C at the start of the next clamp. After that, the surface temperature of the clamp part rises every time when the second and subsequent steel pieces are clamped, and at 60 seconds (immediately before joining) 60 seconds after the clamp release at the tip of the first steel piece in the continuous rolling cycle. Its surface temperature was 560 ° C. After that, when the steel pieces were joined, the average temperature drop amount at the contact surface of the steel pieces at the clamp portion was −30 ° C., which was even lower than in the case of Example 1.

The fluctuation of tension when the contact surface of the steel slab with the clamp portion was rolled by the finishing rolling mill group 5 was further suppressed by the excessive tension of 3 kgf / cm ² at the joint portion and was stable without breaking at the joint portion. It could be rolled and rolled.

[0026]

As described in detail above, according to the present invention, the temperature drop of the clamped portion of the steel slab due to the clamping at the time of joining the steel slabs together is reduced, so that when the clamp part is rolled, Since it is possible to suppress the excessive tension generated at the joint, it is possible to perform stable strip passing at the joint of the steel slab, which can improve the operating rate of the rolling equipment and improve product quality. -It is possible to improve the yield.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of a continuous hot rolling line for carrying out the present invention.

FIG. 2 is a characteristic diagram showing (a) a conventional example and (b) a first example of the present invention, which shows tension fluctuations in a steel bill clamp part.

FIG. 3 is a characteristic diagram in (a) the first embodiment and (b) the second embodiment showing the transition of the surface temperature of the clamp part of the clamp device.

FIG. 4 is a plan view showing an outline of a conventional clamp device,
(b) It is a side view.

FIG. 5 is a characteristic diagram showing the relationship between the initial temperature of the clamp part and the average temperature of the clamp part of the steel slab.

FIG. 6 is a characteristic diagram showing a relationship between a temperature drop amount at a clamp portion of a steel slab and a tension between stands.

FIG. 7 is a characteristic diagram showing the relationship between the clamp time and the surface temperature of the clamp part.

[Explanation of symbols]

1 Rough rolling mill 2 Shear 3a, 3b Clamping device 4 Joining device 5 Finishing rolling mill group 6 Cutting machine 7a, 7b Winding machine S Steel billet S ₁ Leading billet S ₂ Trailing billet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Imae 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Iron & Steel Manufacturing Co., Ltd. Steel Research Laboratory (72) Inventor Kunio Isobe Central, Chiba-shi, Chiba Kawasaki-Cho, Kawasaki Steel Co., Ltd., Steel Research & Development Division, Steel Research Laboratory (72) Inventor Hideyuki Nikaido, Kawasaki-Cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Steel Development & Production Headquarters, Chiba Steel Works

Claims (4)

[Claims] 1. A method for joining a trailing end of a preceding steel piece and a leading end of a following steel piece, which have undergone a rough rolling process in continuous hot rolling, by butting with a clamping device while abutting and joining them together. A method for joining steel slabs in continuous hot rolling, characterized in that the surface of the steel is preheated before the joining step. 2. The method according to claim 1, wherein the non-steady-state portion is heated so that the temperature difference between the clamped non-steady-state portion and the non-clamped steady-state portion of the steel slab is within 70 ° C. 3. Prior to the continuous rolling process, the end of the steel strip that is normally rolled immediately before the continuous rolling process is clamped by a clamp device, and the surface of the clamp part of the clamp device is heated. The method according to Item 1 or 2. 4. The front end of the first steel strip rolled in the continuous rolling step is clamped by a clamp device to heat the surface of the clamp part of the clamp device. The method described.