JPH0489111A - Method for joining billets in hot rolling - Google Patents

Abstract

PURPOSE:To join billets so quickly and securely that the joined part of billets is not broken and separated in rolling time by reducing the thickness of the billet to uniformize the thickness to an abutting area for one side or both sides of each billet. CONSTITUTION:At a hot rough rolling stage or at the preceding stage of this induction heating treatment, the thickness of the billet is reduced by rolling or forging at the abutting area (the rear end area in the preceding sheet bar 2, the leading end area in the succeeding sheet bar 3) of one side or both sides. Though the sheet bars to be joined differ in thickness, the plate thickness can be equalized only at that area. In this way, heating time can be reduced, shock in rolling can be avoided and further the followup ability of AGC is improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a steel billet (sheet bar, slab, billet, or plume) that is conveyed in advance, and a subsequent steel billet that is conveyed subsequently. This invention relates to a method of joining steel billets which is particularly useful when butt joining is performed at the entry side of a finishing mill group in a hot rolling facility, and the joined steel billet is continuously rolled.

(Prior art) Conventionally, in a hot rolling line, after heating the steel billet to be rolled to a target temperature, the billet is passed one by one through a rough rolling process and a finishing rolling process to finish it into a hot rolled plate with a desired thickness. was, but
With such rolling methods, troubles such as line stoppages due to poor biting of the rolled material are likely to occur, especially during finish rolling, and yields are greatly reduced due to poor shapes at the leading and trailing ends of the rolled material. Therefore, early resolution of such problems was desired.

Eliminate the above troubles in hot rolling lines,
As an attempt to further improve productivity, a rolling technique as disclosed in Japanese Unexamined Patent Publication No. 60-244401 is known.

(Problems to be Solved by the Invention) The technology disclosed in each of the above-mentioned publications joins the rear end of the preceding rolled material and the leading end of the subsequent material on the entry side of the finishing rolling line, and several to This rolling method aims to continuously feed several dozen pieces of rolled material to the finish rolling process, and if this rolling method is followed, it will eliminate the biting defects that would occur when feeding steel pieces one by one to the rolling line. We were able to significantly improve productivity without causing any problems.

However, especially when induction heating is applied as a heating method for steel billets, it is necessary to adjust the strength of the magnetic field according to changes in the thickness of the steel billet, so it is difficult to join steel billets of maximum thickness. large-capacity heating equipment is required.

In addition, when the thickness of the preceding steel billet and the following steel billet are different, the magnetic field concentrates preferentially on the thicker steel billet, and as a result, only the thicker steel billet is heated. It is necessary to apply a magnetic field to suit the thin steel slabs, which requires a large amount of electric power, and it is difficult to uniformly heat the edges of each steel slab.

Furthermore, when the steel slabs have different thicknesses, even if the steel slabs can be joined to each other, the joined parts of the steel slabs may break and separate during the subsequent finish rolling process due to insufficient bonding. Even if there is no breakage and separation, automatic plate thickness control (AGC) cannot follow this, so there is a risk that off-gauge portions may occur and reduce product yield.

The purpose of this invention is to propose a new joining method that can quickly join steel billets without consuming wasted energy, and moreover, can reliably join steel billets so that the joints do not break and separate during rolling. It's there.

(Means for Solving the Problems) The present invention is directed to a trailing end of a preceding steel bill that is conveyed through hot rough rolling at the entry side of a hot finishing rolling mill, and a trailing end of a preceding steel bill that is conveyed following this. When the tips of the steel pieces are abutted in close proximity or in contact, the abutted area is heated by induction, and at least one of the steel pieces is pressed toward the other to bring the pieces of steel into close contact with each other and join them. of steel billets in hot rolling, characterized in that, at the hot rough rolling stage or before the heat treatment, a thinning process is applied to the butt region of one or both of the billets to make the plate thickness uniform. This is a joining method.

Now, FIG. 1 shows an example of rolling equipment suitable for carrying out the present invention. In the figure, number 1 is a hot finishing rolling mill group, and 2 is the entrance side of hot finishing rolling mill 1. The rough-rolled steel billet (hereinafter referred to as the preceding sheet bar) that is conveyed in advance at 3 is the subsequent steel billet that follows this steel billet 2 (hereinafter referred to as "preceding sheet bar").
4a and 4b are seat bars 2.
Pinch rolls 3 apply pressure during the conveyance and joining of these sheets, and 5 an induction roller that heats the abutting area when the rear end of the preceding sheet bar 2 and the leading end of the following sheet bar 3 are brought into close proximity or in contact with each other. A heating coil (such as an alternating magnetic field ordering coil), and a looper 6 for absorbing the joining time of the sheet bar. It is omitted in the case of .

(Function) When an alternating magnetic field is applied by the induction heating coil 5 while the rear end of the leading seat bar 2 and the leading end of the trailing seat bar 3 butt against each other or are in contact with each other, the seat bar 2,
Eddy currents begin to flow along the width direction at each end of 3, and the temperature in that area increases preferentially in a very short time due to the Joule heat generated at that time. When the bonding temperature is reached, the sheet bars are pressed together, or by performing the above-described heat treatment while being pressed in advance, they will be brought into close contact and bonded to each other in a relatively short period of time.

By the way, in such an induction heating method, as mentioned above, it is necessary to adjust the strength of the applied magnetic field according to the change in the thickness of the steel billet. (The thickness varies from 30 to 50 mm depending on the application) A heating device with the necessary capacity is required, and also when the thickness of the preceding billet and the following billet are different, In this case, the magnetic field concentrates preferentially on the thicker steel pieces, and as a result, only the thicker steel pieces are heated, so it is necessary to apply the magnetic field to match the thinner steel pieces. However, this requires a large amount of electricity, and it is difficult to uniformly heat the ends of each steel piece.Furthermore, when the steel pieces have different thicknesses, it is difficult to join them together. Even though
During the subsequent finish rolling process, the joined parts of the steel billets may break and separate, so even if such breakage does not occur, AGC control is necessary when joining and rolling steel billets with a large difference in thickness. This resulted in an unavoidable drop in product yield as off-gauge areas were generated due to the inability to follow this.

In the present invention, in the hot rough rolling stage and before the induction heating treatment described above, the abutment area of one or both of the sheet bars 23 (the trailing end area of the preceding sheet bar 2, the trailing end area of the succeeding sheet bar 3), Since the thinning process is applied to the tip area (the tip area) by rolling or forging, even if the thickness of the sheet bars to be joined differs, only that area can be made to have the same thickness. , problems such as those mentioned above are advantageously avoided. Here, as the thinning treatment, it is preferable to specifically perform a taper-like process in which the plate thickness gradually becomes thinner toward the end of the steel billet, thereby shortening the heating time and
Impact during rolling can be avoided, and AGC followability is further improved. The form of the thinning process is such that when the preceding sheet bar 2 and the succeeding sheet bar 3 have the same thickness and are joined and continuously rolled, the preceding sheet bar 2. It is sufficient to perform the same processing on both subsequent seat bars 3. If one seat bar is thick and the other seat bar is relatively thin, use a thicker sheet to match the thickness of the thinner seat bar. The bar may be subjected to a thinning process, or the thickness may be thinned until all sheet bars have the same thickness. The thickness of the plate at the end is empirically set to the minimum thickness of 1 in order to prevent breakage and separation during rolling.
It is preferable to set it as about 5-30 mm.

Fig. 2 shows the situation when sheet bars of different thicknesses are joined and subjected to continuous hot rolling.

In the case of thinning treatment before heat treatment, for example, when performing forging processing, suitable anvils to be used include:
As shown in FIG. 3, the seat bar is sandwiched in the thickness direction by an anvil 7 having an entrance slope 7a for processing the leading end of the succeeding seat bar 3 and an exit slope 7b for processing the rear end of the preceding seat bar. It is preferable to arrange the anvils 7 vertically so that the anvils 7 are reciprocated toward and away from each other so as to have an inclination equal to the inclination 7a or the inclination 7b on the exit side, thereby achieving thinning.

FIG. 4 shows the temperature difference at the joint surface due to the difference in plate thickness when steel pieces having different thicknesses are joined, and it can be seen that the larger the difference in plate thickness, the larger the temperature difference at the joint surface.

When joining steel pieces, there are two joining methods: heating and raising the temperature to the target joining temperature and pressing after stopping the heating, or continuing heating and raising the temperature (before reaching the target temperature, Various joining methods can be considered, such as heating the ends of each steel piece and pressing the steel pieces, or heating the steel plates after pressing them in advance. However, the temperature of the steel slabs at the entry side of the finishing rolling mill is usually around 1000 to 1100°C, and the joining of the steel slabs progresses to some extent even with mere pressing, which reduces the joining time and increases heating and temperature. In the present invention, it is particularly preferable to heat the steel billet while pressing it, since the required input power can be reduced.

As the induction heating coil 5 of the heating device suitable for carrying out this invention, a solenoid type coil that surrounds a steel piece, for example as shown in FIG. 1 above, can be applied. It is also possible to apply a transverse coil that applies an alternating magnetic field that penetrates the steel piece in its thickness direction.

(Example) Using the equipment shown in Figure 1 above, which is equipped with a 7-stand tandem rolling mill, a sheet with a width of 1000 mm and a thickness of 40 m was manufactured.
The ends of the trailing sheet bar of 35 mm and the leading sheet bar of 35 mm in thickness were processed so that they had a planar shape as shown in FIG. And this low carbon steel sheet bar (ff
I: 3000 Peng, T: 28 Peng, thinning treatment by adjusting the interval between rolls during rough rolling) are continuously fed to a rolling mill while being joined according to the following conditions to produce a hot-rolled plate with a thickness of 3. Finished.

a. Alternating magnetic field: Insertion type crab 2000KW.

Heating time: 14 seconds, Frequency: 500 seconds, b, Heating temperature: 1420°C1 (joint end surface) C1 pressing force 2 Surface pressure of 2 kgf/mm'' Pressure time = 5 seconds, d, Joining form: Pre-pressed As a result, the joints of the sheet bars did not break during rolling, and stable rolling was possible.In addition, the sheet bars were heated under the same conditions and in the same shape as in the conventional high-frequency heating method (however, the sheet bars at the tip It was confirmed that the power consumption could be reduced by about 40%, and the bonding time could be reduced by about 5 seconds, compared to the bonding method (with no thinning treatment at the rear end).

In addition, as shown in Figure 2 above, we investigated the joining conditions when several types of sheet bars with different thicknesses were joined, but even in such joining, there was no possibility that the joint would break due to rolling. There was no breakage or separation of the joints that would have occurred if no thinning treatment was applied to the tip or rear end of the seat bar, and the off-gauge ratio was also higher than when no thinning treatment was applied. We were able to reduce this by approximately 90%.

Furthermore, products (thickness 3.0 mm,
A comparison of changes in plate thickness in the longitudinal direction of a width of 100100O is shown in FIGS. 6(a) and 6(b). In accordance with the present invention, it was confirmed that the thickness deviation of the thinned portion was improved from 300 μm to 35 μm due to improved tracking of AGC, and there was almost no difference from the normal portion.

(Effects of the Invention) Thus, according to the present invention, the rear end of the preceding steel billet and the leading end of the following steel billet can be quickly and quickly made to have the same thickness regardless of the change in the thickness of the steel billet. Since it can be reliably joined, continuous hot rolling with high productivity can be achieved. Further, according to the present invention, the capacity of the heating device can be reduced, the pressing force when joining the steel pieces can be relatively small, and off-gauge in the vicinity of the joint can be avoided as much as possible.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of a rolling equipment suitable for carrying out the present invention. Fig. 2 is an explanatory diagram of the procedure for joining several types of steel pieces according to the present invention. Fig. 3 is an explanatory diagram of an anvil. Figure 4 shows the installation situation, a graph shows the relationship between the plate thickness difference and temperature difference of the steel slabs, Figure 5 shows the joining status of the steel slabs in the example, and Figure 6 (a) b) is a diagram showing how the plate thickness changes in the longitudinal direction of the product. ■... Finish rolling mill group 2... Leading sheet bar 3
...Following seat bars 4a, 4b...Pinch roll

Claims (1)

[Claims] 1. At the entry side of the hot finishing rolling mill, the rear end of the preceding steel billet to be conveyed through hot rough rolling and the tip end of the succeeding billet to be conveyed subsequently are brought into close proximity or in contact. In order to bond and join each steel billet to each other by applying induction heating to the butted area and pressing at least one of the steel billets toward the other, the hot rough rolling step or the above heat treatment is performed. A method for joining steel billets in hot rolling, characterized in that, in the preceding step, a thinning process is applied to the butt region of one or both of the steel billets to make the plate thickness uniform.