JP2804352B2 - Method of joining billets in hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a steel slab (sheet bar,
Slab, billet, or bloom) and the subsequent slab that is subsequently conveyed are butt-joined at the hot rolling equipment, especially on the entry side of the finishing mill group, and the joined slab is continuously rolled. In particular, the present invention relates to a method of joining steel slabs, which is particularly useful in such a case.

(Prior art) Conventionally, in a hot rolling line, a billet to be rolled is heated to a target temperature and then passed one by one through a rough rolling process and a finish rolling process to finish a hot rolled sheet having a desired thickness. However, in such a rolling method, particularly in finish rolling, troubles such as line stoppage due to poor biting of the rolled material are likely to occur, and the yield of the rolled material due to poor shape at the leading and trailing end portions is reduced. Because of the large decrease, it was desired to solve such a problem early.

As an attempt to solve the above-mentioned troubles in the hot rolling line and to further improve the productivity, a rolling technique as disclosed in JP-A-60-244401 is known.

(Problems to be Solved by the Invention) The technology disclosed in each of the above publications joins a rear end of a preceding rolled material and a front end of a succeeding material succeeding this on the entry side of the finish rolling line, and It is intended to continuously supply dozens of rolled materials to the finish rolling process, and according to such a rolling method, a biting defect that occurs when the steel slabs are supplied one by one to the rolling line. The productivity was significantly improved without causing any problems.

However, especially when the induction heating method is applied as a heating method for the slab, it is necessary to adjust the strength of the magnetic field according to the change in the thickness of the slab. Large-capacity heating equipment required for

Also, when the thickness of the preceding and subsequent slabs is different, the magnetic field concentrates preferentially on the thick slab, and as a result only the thick slab is heated, It is necessary to apply a magnetic field in accordance with a thin slab, which requires a large amount of electric power, and it is difficult to uniformly heat the end of each slab.

Furthermore, when the thickness of the billet is different, even if each billet can be joined to each other, the joint portion of the billet may be broken and separated in the subsequent finish rolling process due to insufficient bonding, Even if there is no break-off, automatic thickness control (AGC) cannot follow, and an off-gauge portion is generated, which may lower the product yield.

SUMMARY OF THE INVENTION An object of the present invention is to propose a novel joining method capable of joining joints of a steel slab quickly and without wasteful energy, and reliably joining the joints of the slab without breaking and separating during rolling. There.

(Means for Solving the Problems) The present invention relates to a rear end portion of a preceding steel slab conveyed through hot rough rolling at an entrance side of a hot finishing rolling mill, and a subsequent end portion conveyed subsequently thereto. When the tip of the slab is brought into close proximity or in contact with the slab, a process of inductively heating the butted region and a process of pressing at least one of the slabs toward the other are performed to adhere and join the slabs to each other. In the hot rough rolling stage or the preceding stage of the heat treatment, in one or both butted regions of each steel slab, the slab of hot slab in hot rolling characterized by performing a thinning treatment to equalize the plate thickness It is a joining method.

FIG. 1 shows an example of rolling equipment suitable for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a group of hot finishing rolling mills, and reference numeral 2 denotes an inlet side of the hot finishing rolling mill 1. The steel strip after the rough rolling (hereinafter, referred to as a preceding sheet bar) conveyed in advance at 3 is a succeeding steel piece (hereinafter, referred to as a succeeding sheet bar) following this steel piece 2, and 4a, 4b are sheets Pinch rolls for transporting bars 2 and 3 and applying pressure during joining
Is an induction heating coil (such as an alternating magnetic field generating coil) for heating the butted area in a state where the rear end of the preceding sheet bar 2 and the front end of the succeeding sheet bar 3 are close to or in contact with each other; The looper 6 is omitted when the heating coil 5 is of a type that can move in synchronization with the conveyance of the sheet bar.

(Operation) When an alternating magnetic field is applied by the induction heating coil 5 in a close or contact state in which the rear end of the preceding sheet bar 2 and the front end of the succeeding sheet bar 3 abut, the sheet bars 2,
An eddy current flows along the width direction at each end of (3), and the temperature in that region rises preferentially in a very short time due to Joule heat at that time, and the target is set here. By pressing the sheet bars at the time when the joining temperature is reached, or by performing the above-mentioned heat treatment in a state where the sheet bars are pressed in advance, the sheet bars are brought into close contact with each other and joined in a relatively short time.

By the way, in such an induction heating method, as described above, it is necessary to adjust the strength of the applied magnetic field according to the change in the thickness of the steel slab. (The thickness varies in the range of 30 to 50 mm depending on the application) A heating device with the necessary capacity to join is required,
When the thickness of the preceding and subsequent slabs is different, the magnetic field concentrates preferentially on the thicker slab, and as a result, only the thicker slab is heated, so It is necessary to apply a magnetic field according to the thickness of the slab, which requires a large amount of power, it is difficult to uniformly heat the end of each slab, and furthermore, the thickness of the slab is In different cases, even though the billets can be joined to each other, in the subsequent finish rolling process, the joints of the billets may break apart, even if such break separation does not occur. When a steel slab having a large thickness difference was joined and rolled, AGC control could not be followed and an off-gauge portion was generated, so that a reduction in product yield was inevitable.

In the present invention, in the hot rough rolling stage and before the induction heating treatment, one or both of the sheet bars 2 and 3 are brought into contact with each other (in the preceding sheet bar 2, the rear end region, the succeeding sheet bar). In FIG. 3, the leading end portion) is subjected to a thinning treatment by rolling or forging, so that even if the thickness of the sheet bar to be joined may be different, it is supposed that only that region has the same thickness. As a result, the above-mentioned problems can be advantageously avoided.
Here, as the thinning treatment, it is preferable to specifically perform a tapered processing such that the plate thickness gradually decreases toward the end of the slab, thereby shortening the heating time, Shock during rolling can be avoided, and AGC
Followability is improved. As a form of the thinning process, when the preceding sheet bar 2 and the succeeding sheet bar 3 are joined to each other and are continuously rolled, the preceding sheet bar 2 and the succeeding sheet bar 3 are processed in the same manner. If one sheet bar has a large thickness and the other sheet bar has a relatively small thickness, a thinning process is applied to the thicker sheet bar to match the smaller thickness. It may be applied or a thinning process may be applied to each of the sheet bars until they have the same thickness. The thickness at the end is empirically set to the minimum thickness to prevent fracture separation during rolling.
It is preferably about 30 mm.

FIG. 2 shows a situation where sheet bars having different sheet pressures are joined to perform continuous hot rolling.

In the case of performing forging, for example, in the case of performing thinning in the thinning process at the stage prior to the heating process, as shown in FIG. 3, as shown in FIG. An anvil 7 having an outgoing slope 7b for processing the rear end of the preceding sheet bar is arranged vertically so as to sandwich the sheet bar in the thickness direction. It is preferable to reduce the wall thickness by giving the same inclination as that of the exit side inclination 7a.

FIG. 4 shows the state of the temperature difference of the joining surfaces due to the difference in plate thickness when steel pieces having different plate thicknesses are joined. It can be seen that the larger the difference in plate thickness, the larger the temperature difference of the joining surfaces.

As a joining form when joining the billets, heating and heating to a target joining temperature and pressing after stopping the heating, or a state where heating and heating are continued (before reaching the target temperature, Including any of the later cases)
Heating the end of each billet and pressing the billet, or a bonding form in which the steel sheet is heated in a state where the steel sheet is pressed in advance can be considered variously. The temperature is about 1000 to 1100 ° C., and the joining of each steel slab proceeds somewhat even by mere pressing, and it is possible to shorten the joining time and reduce the input power required for heating and heating. Is preferably heated while pressing the steel slab.

As the induction heating coil 5 of the heating device suitable for use in practicing the present invention, such a material as to surround a billet can be used.
For example, a solenoid type as shown in FIG. 1 above can be applied, but it is also possible to apply a transverse type coil that applies an alternating magnetic field that penetrates the billet in the thickness direction. it can.

(Example) Applying the equipment as shown in FIG. 1 provided with a tandem rolling mill with 7 stands, a succeeding sheet bar having a width of 1000 mm and a thickness of 40 mm and a preceding sheet bar having a thickness of 35 mm can be formed. The ends were processed to have a planar shape as shown in FIG. And the sheet bar of low carbon steel with this end processed (l: 3000mm, t: 28mm,
Adjusting the distance between rolls in rough rolling to reduce the thickness)
Was continuously supplied to a rolling mill while being joined according to the following conditions to finish a hot-rolled sheet having a thickness of 3 mm.

a. Alternating magnetic field: input power: 2000 kw, heating time: 14 seconds, frequency: 500 Hz, b. heating temperature: 1420 ° C., (joining end face) c. pressing force: 2 kgf / mm ² as surface pressure, pressing time: 5 seconds, d. Joining form: Heating while pressing in advance As a result, the joining portion of the sheet bar did not break during rolling, and stable rolling was possible. In addition, the sheet bar of the same condition and the same shape as the conventional high-frequency heating method (however, the front and rear ends are not thinned)
It was confirmed that the power consumption can be reduced by about 40% and that the bonding time can be reduced by about 5 seconds, as compared with the case of the bonding of FIG.

In addition, as shown in Fig. 2 above, we also examined the bonding situation when several types of sheet bars having different plate thicknesses were bonded. But not the tip of the seat bar,
No break-off of the joints occurred when the rear end was not subjected to the thinning treatment, and the off-gauge ratio was reduced by about 90% as compared with the case where the thinning treatment was not performed. .

Further, the product (3.0 mm thick, 100 mm wide) obtained by joining and rolling according to the present invention and joining and rolling according to the conventional method
6 (a) and 6 (b) show how the thickness changes in the longitudinal direction (0 mm). In accordance with this invention, AG
Since the follow-up of C was improved, the thickness deviation of the portion subjected to the thinning treatment was also improved from 300 μm to 35 μm, and it was confirmed that there was almost no difference from the normal portion.

(Effects of the Invention) Thus, according to the present invention, the rear end portion of the slab conveyed in advance and the front end portion of the succeeding slab are made to have the same thickness regardless of the change in the thickness of the slab and quickly and quickly. Since joining can be performed reliably, continuous hot rolling with high productivity can be realized. Further, according to the present invention, there are advantages that the capacity of the heating device can be reduced, the pressing force at the time of joining the steel pieces can be relatively small, and the off gauge near the joint can be avoided as much as possible.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a configuration of a rolling equipment suitable for carrying out the present invention. FIG. 2 is an explanatory view of a procedure for joining several kinds of billets according to the present invention. FIG. FIG. 4 is a graph showing the relationship between the difference in plate thickness and the temperature difference of the billet. FIG. 5 is a diagram showing the joining state of the billet in the example. FIG. (B) is a figure which shows the change situation of the board thickness in the longitudinal direction of a product. 1 ... finishing rolling mill group 2 ... preceding sheet bar 3 ... subsequent sheet bar 4a, 4b ... pinch roll 5 ... induction heating coil (solenoid type) 6 ... looper, 7 ... anvil 7a ... Side inclination, 7b ... Outside inclination

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanori Ebihara 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (72) Inventor Hideo Takegawa 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. Inside Chiba Works (56) References JP-A-60-244401 (JP, A) JP-A-59-130603 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21B 1/26 B21B 15/00

Claims (1)

(57) [Claims] At the entry side of a hot finishing mill, a rear end of a preceding steel slab conveyed through hot rough rolling and a front end of a subsequent steel slab conveyed subsequently thereto are brought close to each other. Or butting in a contact state, a process of induction heating the butted area,
In performing the treatment of pressing at least one of the steel slabs toward the other and bringing the steel slabs into close contact with each other and joining them, in the hot rough rolling stage or the preceding stage of the heat treatment, either one of the steel slabs or A method for joining billets in hot rolling, characterized in that both butted regions are subjected to a thinning treatment for equalizing the plate thickness.