JP2905393B2 - Method of joining billets in hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel slabs in hot rolling, and more particularly, to a method for uniformly heating the entire width of a steel slab.

[0002]

2. Description of the Related Art In recent years, at the entry side of a hot rolling line, a rear end of a slab to be transported in advance (hereinafter, referred to as a preceding slab) and a slab to be transported subsequently to the slab (hereinafter, referred to as a slab). By heating and joining the leading end of the succeeding billet by induction heating, several to several tens of rolling materials are continuously supplied to the rolling line, thus avoiding troubles such as line stoppage and improving the yield. Attempts have been made. Such a joining method is proposed in Japanese Patent Application Laid-Open No. 62-234679. According to this technology, a pair of orthogonal magnetic flux type induction heating devices are provided in which abutting surfaces of two plate members are opposed to each other in a non-contact state with a small gap, and are opposed to upper and lower surfaces of the plate members in this region. AC power is supplied to the coil for application to apply a magnetic field that penetrates the plate material vertically to generate an induced current in the plate material. Is what you do.

[0003]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Sho 62-62
According to the method described in Japanese Patent No. 234679, if attention is paid to the induction current generated in the steel slab due to the alternating magnetic field between the induction heating coils that are arranged to vertically sandwich the steel slab to be joined, the steel slabs are opposed to each other. After the billet, near the tip,
The current flowing through the width direction end is smaller than the current near the width direction center. Therefore, in the butt joint surface, the rate of temperature rise at the end of the slab width direction is lower than the rate of temperature rise near the center in the width direction. However, since the temperature at the end in the width direction did not reach the temperature, even if the steel pieces in such a state were pressed against each other, the end in the width direction could not be joined with sufficient strength. Also, since the width direction end is lower than the center, it is not relatively softened, and the width direction end resists this pressing force at the time of pressing. It was difficult to apply sufficient pressing force to obtain the required bonding strength.

[0004] Due to these inconveniences, the strength of the slab at the end in the width direction and in the vicinity thereof is lower than that in the region other than this region, that is, the region near the center in the width direction.
At the time of hot rolling after joining, a crack is first formed at the end of the slab with low joining strength in the width direction, this crack propagates toward the center, and eventually breaks over the entire width of the joint. As a result, there is a problem that the line is stopped.

In order to raise the temperature of the end of the slab in the width direction to a temperature suitable for joining, induction heating may be performed for a long time. In such a case, however, the center of the slab in the width direction is overheated. In addition to the problem of melting down, there is also a problem that the input power is increased.

The present invention advantageously solves the above-mentioned problem, and enables heating such that the rate of temperature rise at the end of the billet in the width direction is substantially the same as that in the center in the width direction.
To propose a method of joining steel slabs in hot rolling that can stably perform continuous hot rolling while avoiding the joint being broken due to such poor joining at the width direction ends. With the goal.

[0007]

According to the present invention, a gap is formed between the rear end of a slab to be conveyed in advance and the front end of a slab to be conveyed subsequently to the slab on the entry side of a hot rolling facility. The steel slab is induced by an alternating current generated by applying an alternating magnetic field that penetrates the steel slab from at least one pair of induction heating coils that are arranged so as to sandwich the rear and front ends of the opposing steel slabs in the thickness direction. In the method of heating the rear and front ends and pressing and joining them toward each other, at the time of heating, on both sides of at least one of the rear and front ends of the opposed steel slab, a conductor is connected to the steel slab. This is a method for joining billets in hot rolling, wherein the billets are arranged with a gap therebetween.

In a preferred aspect of the present invention, when the widths of the rear end portion and the front end portion of the opposing steel slabs are substantially equal, a conductor straddling each end portion is disposed. In another preferred aspect of the present invention, the coil for induction heating is arranged so as to overlap the conductor during heating. In another preferred embodiment of the present invention, a current having substantially the same phase as the induced current is applied to the conductor from the outside.

[0009]

The present invention will be described more specifically with reference to the drawings. FIG. 1 schematically shows an example of a method for joining billets according to the present invention. In the figure, reference numeral 1 denotes a leading billet, and 2 denotes a trailing billet. The drawing shows a case where the width of the leading billet 1a is equal to the width of the trailing billet 2a. The preceding slab 1a is clamped by the clamps 3a and 3b, and the following slab 2a is similarly
The clamp is held between the clamps 4a and 4b so that the rear end of the preceding slab 1a and the front end of the subsequent slab 2a face each other with a small gap. A pair of induction heating coils 5 is arranged at a position where the rear end of the preceding slab 1a and the front end of the following slab 2a face each other so as to vertically sandwich the slab. By applying an alternating magnetic field penetrating in the thickness direction of the slab from the heating coil 5 to generate an induced current at both the rear end of the preceding slab 1a and the front end of the following slab 2a, the preceding slab 1a And the leading end of the succeeding billet 2a are heated. According to the present invention, at the time of the above-mentioned heating, the conductor 6a is disposed on both sides of at least one of the rear end of the preceding slab 1 and the front end of the succeeding slab 2 with a small gap from the slab. This is one of the features.

The reason why it is possible to uniformly heat the entire width of the butt surface of the billet by disposing the conductor close to the side of the billet as described above is considered as follows. First, in the case of the conventional billet joining method in which no conductor is provided, as shown in FIG. 2, a main part near the joint end is shown in FIG. Less,
Since the induced current e flows in a circular arc as shown in the figure, the induced current was difficult to flow even if there was a skin effect. This causes a rise in the temperature of the end in the width direction. As a result, even if the rear end of the preceding slab and the front end of the succeeding slab are butt-joined, the slab width end In the part, the joining strength was low, and as shown in FIG. 3, during the subsequent rolling, the crack 7 generated from this part propagated to the center in the width direction, and eventually broke.

On the other hand, according to the present invention, as shown in FIG. 1, conductors 6a are arranged in proximity to each other on both sides of at least one butted surface of preceding and succeeding billets 1 in a non-contact state. Since an alternating magnetic field generated between a pair of induction heating coils 5 arranged opposite to each other with a steel piece also penetrates the conductor 6a, the induction current e is also applied to the conductor 6a.
Occurs. As a result of the induced current generated in the conductor 6a and the induced current generated in the steel slab being attracted to each other, the induced current generated in the steel slab flows closer to the end in the width direction of the steel slab. Therefore, the heating rate at the end in the width direction is close to the heating rate at the center in the width direction,
At the time of joining, the widthwise end of the butted surface can be heated to a temperature that is sufficient for joining with sufficient joining strength, and that enough pressing force can be applied for joining Therefore, it is considered that it is possible to completely join the steel slabs over the entire width including the ends in the width direction.

As long as the conductor in the present invention generates an induced current of a predetermined strength, the object can be achieved. The type of the conductor is not particularly limited. This is suitable because heat generation by the induced current is small and inexpensive. Further, a high melting point material such as a tungsten plate or a graphite plate can be used because it has resistance to heat generation. Further, a steel plate or an Al plate can be used for a long time by providing a cooling means.

In FIG. 1, the conductor 6a is connected to the preceding billet 1
4 and the following slab 2, but the present invention is not limited to the example shown in FIG. 4. As shown in FIG. 4, another example is shown in FIG. The same effect can be obtained even if a separate conductor 6b is provided at each of the tips of the row slabs.

Further, if the width of the conductor is too small, it is difficult to generate an induced current even if the magnetic flux from the coil penetrates. Therefore, a width enough to generate the induced current is necessary. You can choose the width. The thickness and length of the conductor are not particularly limited. It is necessary that the conductor and the steel slab are arranged close to each other so that the induced current generated on the steel slab and the induced current generated on the conductor are attracted to each other. Specifically, it may be more than 10 mm, but more preferably about 3 to 5 mm.

FIG. 5 shows a case where the widths of the billets to be joined are different. This figure shows a case where the leading billet 1d is a wide material and the trailing billet 2d is a narrow material, and the center in the width direction of the leading billet and the center in the width direction of the succeeding billet are opposed to each other, In this example, conductors 6c are arranged close to each other on both sides of the narrow succeeding billet 2d with a small gap. Thus, at the time of heating, an alternating magnetic field penetrates through the conductor 6c from the coil 5, and an induced current is generated in the conductor 6c. Therefore, a narrow width is generated due to the interaction with the induced current generated in the conductor 6c. The induced current generated in the succeeding billet 2d flows in the vicinity of the widthwise end of the billet tip, thereby enabling a uniform temperature increase in the billet width direction. This conductor can achieve the intended purpose even if it is arranged only on both sides of the end of the narrow billet. However, as shown in FIG. This is advantageous because the effect can be improved by disposing the conductor.

As will be understood from the above-described effects of the conductor, the present invention requires that a magnetic field generated between at least a pair of induction heating coils penetrates the conductor. That is, the conductor must be arranged in a range where the magnetic flux generated between the induction heating coils penetrates. Looking at this in terms of the relationship between the width of the slab and the width of the induction heating coil, in the present invention, the induction heating coil is arranged to overlap the slab, and the magnetic flux generated from this coil causes not only the slab but also the More preferably, the arrangement is such that it penetrates at least a part of the conductor. Specifically, by using an induction heating coil wider than the width of the steel slab to be joined, the induction heating coil protrudes laterally from the steel slab, and the induction heating coils face each other. It is preferred that the magnetic poles face not only the billet but also a conductor arranged on the side of the billet. This means that the steel slab is disposed inside the widthwise end of the induction heating coil where the amount of magnetic flux is likely to decrease, which is effective for uniform heating in the steel slab width direction.

Further, as another example, when the width of the steel slab to be joined is wider than the width of the induction heating coil,
Arrange a plurality of induction heating coils in the width direction of the billet, let the plurality of induction heating coils protrude laterally from the billet,
It is preferable that the mutually facing magnetic poles of the induction heating coil face not only the billet but also a part of the conductor arranged on the side of the billet.

Even if the width of the induction heating coil sandwiching the steel slab is the same as or smaller than the width of the steel slab to be joined, leakage occurs on the side of the width of the steel slab. Since the magnetic flux is formed, the leakage magnetic flux formed on the side of the steel slab penetrates the conductor disposed at that position, so that the predetermined value is provided as long as the conductor is in the region where the conductor penetrates. The effect of can be obtained.

Next, a more advantageous example of the present invention is one in which a current having substantially the same phase as the induced current flows from the outside to the conductor. FIG. 6 is a main part of the butting area of the rear end of the preceding billet to be joined and the front end of the succeeding billet.
6b is a plan view, FIG. 6b is a sectional view taken along line AA of FIG. 6c, and FIG. 6c is a sectional view taken along line BB of FIG. 6a. The induction heating coil 5 in FIG. 6 is formed by winding a conductive wire around an iron core connecting a pair of magnetic poles facing a steel piece to each other.
In addition, the width is larger than the width of the preceding slab 1e and the following slab 2e. The induction heating coil having such a shape is formed by passing an alternating current from a power supply 8
Since the steel slab is arranged at the position of the gap of the magnetic circuit formed in the above, the magnetic force generated in the induction heating coil can be effectively applied to the steel slab. Such an induction heating coil is disclosed in Japanese Patent Application Laid-Open No. 4-89109.

As shown in FIGS. 6A to 6C, a conductor 6e is arranged on the side of the region opposite to the rear end of the preceding steel slab 1e and the front end of the following steel slab 2e. Then, an AC having the same phase as the induced current is applied from the external power supply 9. Thus, a current superimposed on the induced current flowing through the conductor flows through the conductor 6e, and the induced current generated in the steel slab is required to approach the end in the width direction regardless of the magnetic flux density passing through the conductor. Since an induced current with a high strength flows, the steel slab can be stably heated uniformly.

As described above, the purpose of supplying an alternating current to the conductor from an external power supply is to supply a current superimposed on the induced current generated in the conductor. Therefore, the alternating current supplied from the external power supply has substantially the same phase as the induced current. You need to be. This is because, even if the frequency is the same as that of the induced current, if the alternating current having the opposite phase is applied, the induced current and the alternating current cancel each other, which is the same as the case where the conductor is not arranged.

Next, in FIGS. 7 and 8, similarly to FIG. 6, an external current is applied to the conductor so that an external current superimposed on the induced current is applied to the conductor to stably heat the steel slab uniformly. First, in FIG. 7, when heating and joining a steel slab wider than the induction heating coil used in FIG.
FIG. 7A shows an example in which two sets of the induction heating coils 5 shown in FIG. 6 are prepared and arranged side by side in the billet width direction and heated.
7b is a plan view, FIG. 7b is a sectional view taken along line AA of FIG. 7a, and FIG. 7c is a sectional view taken along line BB of FIG. 7a. 7, the induction heating coil 5 having a substantially C-shaped iron core as in FIG.
Is placed at the end of the steel piece to be joined, and on both sides of the end to be joined, a conductor 6f is arranged with a small gap from the steel piece, and the conductor 6f is An example is shown in which a current having the same phase as the induced current generated in the body flows from the external power supply 9. FIG. 8 shows an example in which induction heating coils 10, which are separate bodies, are arranged in the facing area of the steel slab to be joined. FIG. 8A is a plan view, and FIG. Each figure is shown.

Although FIGS. 6 to 8 use an induction heating coil wider than the width of the steel slab to be joined as a preferred example, the present invention is limited to the illustrated example. Even if an induction heating coil having a width smaller than the width of the slab is used, the strength of the current applied from the external power source is few and the strength is sufficient to uniformly heat the ends of the slab. There is no problem because the current can flow through the conductor.

As described above, the rear end of the preceding slab and the front end of the succeeding slab are joined by the combination of the heating step of the slab according to the present invention and the step of pressing the slabs toward each other. I do. In this combination, after the rear end of the preceding slab and the front end of the following slab are placed close to each other in a non-contact state, power is applied until this joint area reaches the target temperature for joining, Stopping the power supply and pressing, and also placing the bonding area close to each other in a non-contact state, and if the temperature of this area reaches the target temperature, reduce the input power to the extent that spark does not occur and heat it There is a method of starting the pressing while keeping the operation.

[0025]

【Example】

Example 1 On the entry side of a hot rolling mill, as shown in FIG.
The slabs having the same width of the preceding slab and the width of the following slab were joined. Both the preceding and following billets are ultra-low carbon steels, and the billet size is 30 mm thick, 1000 mm wide and 6000 mm long. The two billets are opposed to each other in a state where a minute gap (5 mm) is formed between the preceding billet and the succeeding billet, and both ends of the width of the leading billet and the trailing billet are used as conductors. A copper plate was placed in close proximity with a small gap of 5 mm, and alternating current was applied to an induction heating coil as shown in the figure to apply an alternating magnetic field that vertically penetrated both steel pieces to perform heating. The billet temperature before this heating was 1000 ° C, the size of the copper plate passed over the leading billet and the trailing billet was 30 mm in thickness, 200 mm in width, and 600 mm in length, and the dimensions of the core of the induction heating coil were It has a length of 240 mm and a width of 1000 mm in cross-section parallel to the billet. The distance between the steel slab and the iron core was 90 mm on the upper side and 90 mm on the lower side, the frequency of the alternating magnetic field was 1000 Hz, and the input power was 980 kW. After such induction heating was performed for 10 seconds, the preceding steel slab and the following steel slab were pressed against each other with a pressing force of 50 t by a clamp to complete the joining. On the other hand, as a comparative example, the steel slabs were joined under the same conditions as in the above example, except that the copper plate was not disposed on the side of both the steel slabs.

With respect to these examples and comparative examples, the heating rate near the end to be joined was measured, and the heating rate ratio near the end in the width direction when the center in the width direction was set to 1 is shown in FIG. Show. This temperature measurement was performed two times from the longitudinal end of the billet.
This was performed by embedding a K-type sheath thermometer at the position of mm. As is apparent from the figure, according to the present invention, in the embodiment in which the conductor is disposed close to the side of the steel piece, the heating rate at the end in the width direction approaches the heating rate at the center. This is because the induced current generated immediately below the iron core of the induction heating coil flows to the widthwise end of the joining end, and thus the widthwise end of the joining end is sufficiently formed after the joining. It was possible to raise the temperature to a temperature sufficient for joining so as to have sufficient strength, and the width direction end at the joining end was sufficiently softened. As a result, it becomes possible to join over the entire width including the width direction end, and when subjected to rolling thereafter, cracks do not develop from the joint and do not lead to fracture, and a good threading plate can be secured. Was.

Example 2 As shown in FIG. 4, separate copper plates were arranged close to each side of the preceding steel slab and both sides of the following steel slab. The size of the copper plate was 30 mm in thickness, 200 mm in width, 300 mm in length, and the gap between the steel slab and the copper plate was 5 mm in all cases. Other joining conditions were the same as those in Example 1, such as the steel type and size of the preceding and following billets, the size of the induction heating coil, the input power and the frequency thereof. The heating rate in the vicinity of the joining end of the slab during heating was measured, and the ratio of the heating rate at the end in the width direction to the center in the width direction was examined. The same result as in Example 1 was obtained. Further, the joining portion was joined over the entire width including the width direction end, and even after rolling, no crack was generated or propagated, and good threading was possible.

Example 3 As shown in FIG. 5, joining was performed for a case where the width of the preceding steel slab was different from that of the succeeding steel slab. The width of the leading billet is 1150
mm and the width of the succeeding billet was 1000 mm. Separate copper plates were placed close to each side of the preceding slab and both sides of the following slab as conductors. The size of the copper plate was 30 mm in thickness, 200 mm in width, 300 mm in length, and the gap between the steel slab and the copper plate was 5 mm in all cases. Other joining conditions, i.e., the leading billet, the following billet steel type, the size of the induction heating coil,
The input power and its frequency were all the same as in Example 1.

The heating rate in the vicinity of the joining end of the subsequent slab during heating was measured, and the ratio of the heating rate at the end in the width direction to the center in the width direction was examined. The heating rate at the widthwise end was approaching the heating rate at the center. Thus, the widthwise end of the joining end of the succeeding billet could be heated to a temperature sufficient for joining so as to have sufficient strength after joining, and the corner portion was sufficiently softened. As a result, the narrow succeeding billet can be joined over the entire width including the width-direction end, and when subjected to rolling, cracks may develop from the joint and lead to fracture. It disappeared, and a good threading board could be secured.

Embodiment 4 In this embodiment, an example is shown in which a pair of magnetic poles of an induction heating coil facing each other are arranged to overlap a conductor. As a preceding and following billet, a billet having a width of 1900 mm was joined. In this case, as shown in FIG. 7, two sets of induction heating coils having a substantially C-shaped iron core (cross-sectional size parallel to the slab: 1000 mm in length and 240 mm in width) are used in the width direction of the slab. Heating was performed. The steel type of the leading and following billets is ultra-low carbon steel, the temperature before heating is 900 ° C, and the leading and trailing billets are passed over the leading and trailing ends of the billet. The conductors were arranged close to both sides of. This conductor was made of copper and had a size of 30 mm in thickness, 200 mm in width, and 600 mm in length. The frequency of the alternating magnetic field was 1000 Hz, and the input power was 1860 kW. Such induction heating was performed for 10 seconds. Thereafter, the preceding and subsequent slabs were pressed against each other by a clamp with a pressing force of 95 t to complete the joining.

The heating rate in the vicinity of the joining end of the subsequent slab during heating was measured, and the ratio of the heating rate at the end in the width direction to the center in the width direction was examined. The heating rate at the end was approaching the heating rate at the center.
Thus, the widthwise end of the joining end of the succeeding billet could be heated to a temperature sufficient for joining so as to have sufficient strength after joining, and the corner portion was sufficiently softened. As a result, the narrow succeeding billet can be joined over the entire width including the width-direction end, and when subjected to rolling, cracks may develop from the joint and lead to fracture. It disappeared, and a good threading board could be secured.

Embodiment 5 This embodiment shows an example in which a current having the same phase as an induced current is applied to a conductor from the outside. As shown in FIG. 6, a 800-mm-wide steel slab was joined as a leading slab and a following slab.
At the time of this heating, an induction heating coil having an iron core that is substantially C-shaped (cross-sectional size parallel to the steel slab: length 1000 mm, width 240
mm) and a pair of magnetic poles of a copper plate as a conductor and a coil for induction heating were arranged to overlap. The steel type of the leading and succeeding slabs is SUS 304, the temperature before heating is 900 ° C. The conductor was arranged closer to the other side. The size of this conductor is 30mm thick, 200mm wide, 600mm long
Met. The frequency of the alternating magnetic field is 500 Hz to 10 kHz.
500 Hz, 1 kHz and 10 kHz were used as the various frequencies, and the input power was 780 kW. Such induction heating
Performed for 10 seconds. Thereafter, the preceding and succeeding slabs were pressed against each other by a clamp with a pressing force of 40 t to complete the joining.

The heating rate at the vicinity of the joining end of the succeeding steel slab during heating at each frequency was measured, and the ratio of the heating rate at the end in the width direction to the center in the width direction was determined as an average value. The heating rate at the end in the width direction was closer to the heating rate at the center than in Example 1. Thus, the widthwise end of the joining end of the succeeding billet could be heated to a temperature sufficient for joining so as to have sufficient strength after joining, and the corner portion was sufficiently softened. As a result, the narrow succeeding billet can be joined over the entire width including the width-direction end, and when subjected to rolling, cracks may develop from the joint and lead to fracture. It disappeared, and a good threading board could be secured.

[0034]

Thus, according to the present invention, the slab is induction-heated by applying an alternating magnetic field penetrating in the thickness direction of the slab from the induction heating coil, and the heating step and the pressing step are combined to combine the slabs. At the time of joining, at the rear end of the preceding billet to be joined, at least one of the leading ends of the succeeding billet, preferably on both sides of both sides, a conductor is placed in close proximity with a small gap. In addition, uniform heating and heating can be performed over the width direction of the end portion of the steel slab, and bonding can be performed with sufficient bonding strength over the entire width, thereby eliminating the trouble of breakage due to rolling.

Further, by arranging the induction heating coil so as to overlap the conductor, the magnetic flux penetrates the conductor directly, so that the induced current can be generated in the conductor reliably and stably. Further, more stable heating becomes possible.

Further, by flowing an alternating current having the same phase as the induced current generated in the conductor from the external power supply to the conductor, a current superimposed on the induced current flows through the conductor, thereby enabling further uniform heating.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a method for joining billets according to the present invention.

FIG. 2 is a schematic diagram illustrating a conventional method for joining billets.

FIG. 3 is a view for explaining the growth of cracks caused by rolling in a steel slab joined by a conventional steel slab joining method.

FIG. 4 is a schematic diagram illustrating another example of the method for joining billets according to the present invention.

FIG. 5 is a schematic diagram for explaining another example of the method for joining steel slabs according to the present invention in the case of joining steel slabs having different widths.

FIG. 6 is a view illustrating another example of the method of joining a slab according to the present invention, showing a main part of a butted region of a rear end of a preceding slab and a front end of a following slab.

FIG. 7 is a view for explaining another example of the method of joining a slab according to the present invention, showing a main part of an abutting region of a rear end of a preceding slab and a front end of a following slab.

FIG. 8 is a view illustrating another example of a method of joining a slab according to the present invention, showing a main part of a butted region of a rear end of a preceding slab and a front end of a following slab.

FIG. 9 is a graph showing a heating rate ratio of a width direction end portion to a width direction center portion with respect to a width direction center portion in Examples and Comparative Examples.

[Explanation of symbols]

 1a-1g Leading slab 2a-2g Trailing slab 3a, 3b Clamp 4a, 4b Clamp 5 Induction heating coil 6a-6g Conductor 7 Conductor 8 Power supply 9 External power supply 10 Induction heating coil

──────────────────────────────────────────────────の Continuing on the front page (72) Nozomi Tamura 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Hiromi Yamada 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Inside Steel Works, Chiba Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Works Inside Chiba Works, Chiba (72) Inventor Shigeru Isoyama 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Company Chiba Works (72) Inventor Toshiaki Amagasa 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd.Chiba Works (72) Inventor Kanji Hayashi 4-6-2-2 Kanon Shinmachi, Nishi-ku, Hiroshima Hiroshima Prefecture Mitsubishi Heavy Industries Hiroshima Manufacturing Co., Ltd. (72) Inventor Kazuo Morimoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture (72) Inventor Hideo Sakamoto 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Itami Works (56) References JP-A-4-89178 (JP, A) Kaihei 4-89115 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B21B 1/26 B21B 15/00 B23K 13/02

Claims (4)

(57) [Claims] At the entry side of a hot rolling facility, a rear end of a steel slab to be transported in advance and a front end of a steel slab to be transported subsequent to the steel slab are opposed to each other with a gap therebetween. The rear and front ends of the slab are heated by an induction current generated by applying an alternating magnetic field penetrating the slab from at least one pair of induction heating coils arranged with the rear and front ends of the slab sandwiched in the thickness direction. In the method of pressing and joining to each other, at the time of heating, it is preferable that a conductor is disposed on both sides of at least one of the rear and front ends of the opposed steel pieces with a gap from the steel pieces. A method of joining billets in hot rolling, which is a feature. 2. The method for joining steel slabs in hot rolling according to claim 1, wherein a conductor is disposed over the rear end and the front end of the opposing steel slabs. 3. The method for joining steel slabs in hot rolling according to claim 1, wherein the induction heating coil is arranged so as to overlap the conductor during heating. 4. The method according to claim 1, wherein a current having substantially the same phase as the induced current is applied to the conductor from the outside.