JP6981441B2 - Steel piece joining device in continuous hot rolling, steel piece joining method using the joining device, and hot-rolled steel sheet manufacturing method using the joining method. - Google Patents

Description

The present invention is a steel piece joining device for joining a leading steel piece and a trailing steel piece on the entry side of a finishing rolling mill in a continuous hot rolling line, a method for joining steel pieces using the joining device, and the joining method. The present invention relates to a method for manufacturing a hot-rolled steel sheet using the above.

In the so-called batch type hot rolling line, each piece of steel is heated, roughly rolled, and finished rolled to finish a steel sheet having a desired thickness. However, in this batch type hot rolling line, there are problems such as poor biting of the tip of the steel piece, narrowing of the tail end of the steel piece, and dimensional defect at the tip and tail end of the steel piece, especially in the finish rolling process.
For this reason, recently, a continuous rolling method (endless rolling method) in which the tail end of the preceding steel piece and the tip of the following steel piece are sequentially joined in the entry-side transfer line of the finish rolling machine and then subjected to finish rolling. ) Has been proposed, and various methods have been developed for joining steel pieces.

Among them, the induction heating pressure welding method is known as a method that can complete the joining in a relatively short time. In the induction heating pressure welding method, the tail end of the leading steel piece and the tip of the trailing steel piece are rapidly heated by induction heating, and then the joints are abutted against each other and pressed to form both the leading and trailing steel pieces. It is to join steel pieces (this pressing and joining are also referred to as upset below).

However, in the conventional method for joining steel pieces in continuous hot rolling, an oxide having a melting point higher than the melting point of the steel (1400 to 1600 ° C.) such as Cr, Ti, Mn, Al, Si, etc. in the steel. When stainless steel or high-strength steel plate containing a component that produces (Cr oxide: melting point of about 2000 ° C.) is used, these oxides generated on the joint surface during induction heating are solidified on the joint even after upset. It remains as a phase and significantly reduces the joint strength, causing problems such as breakage of the joint in the finish rolling in the subsequent step.

As a method for solving such a problem, Patent Document 1 describes that the temperature of each joint surface of the leading steel piece and the trailing steel piece is heated to a temperature equal to or higher than the liquidus temperature of the steel piece in the heating step by induction heating. A method of discharging the oxide that has become a liquid phase together with the molten steel to avoid a decrease in bonding strength is disclosed.

Japanese Unexamined Patent Publication No. 2000-271605

In the method described in Patent Document 1 described above, by heating the joint surface to a temperature equal to or higher than the melting point of the steel piece, an oxide produced on the joint surface even when stainless steel or high-strength steel is used. Although it is possible to make it easier to discharge, the molten steel may scatter due to the pressure at the time of upset because of its good discharge (low viscosity). The problems in such a case will be described with reference to FIG.

FIG. 5 is a diagram showing a process of joining the leading steel piece 3a and the trailing steel piece 3b using the misalignment prevention plate 31 in the joining device. FIG. 5A shows a state in which the tail end of the leading steel piece 3a and the tip of the trailing steel piece 3b are heated, and FIG. 5B shows a state in which the steel pieces are abutted and pressed together (upset) after heating. FIG. 5C shows a state in which the misalignment prevention plate 31 is opened up and down after the upset.
The misalignment prevention plate 31 shown in the figure has a convex portion 31a on the side facing the steel piece to prevent the joint surface from shifting up and down, and a liquid phase during heating and upset. A recess 31b is formed in which the molten steel 33 containing the converted oxide (hereinafter, also referred to as Noro 33) is discharged.

The broken line in the figure of FIG. 5A indicates the position where the tail end of the leading steel piece 3a and the tip of the trailing steel piece 3b before heating were located. When this portion is heated to a temperature equal to or higher than the liquidus temperature, it becomes liquid phase including the oxide generated by the heating and flows out into the recess 31b of the misalignment prevention plate 31.

After heating, when pressure joining (upset) is performed as shown in FIG. 5 (b), the molten steel (Noro) 33, whose viscosity is lowered by heating above the liquidus temperature, is affected by the pressure acting during upset. , Scatter and flow out into the recess 31b of the misalignment prevention plate 31.

After the upset, when the misalignment prevention plate 31 is released up and down as shown in FIG. 5C, a part of the slag 33 flowing out into the recess 31b adheres to the steel piece, but the misalignment prevention plate 31 on the lower side adheres to the steel piece. A part of the slag 33 scattered in the recess 31b is left behind in the recess 31b without adhering to the steel piece.
Since the slag 33 attached to the steel slab is conveyed from the joining device together with the steel slab, it is removed from the steel slab by the deburring process, but the slag 33 attached to the recess 31b of the lower misalignment prevention plate 31 is inside the joining device. Will remain in.

In particular, in the case of continuous hot rolling, the above-mentioned Noro 33 is deposited in the misalignment prevention plate 31, and finally the deposited Noro 33 is bitten into the joint surface. , The strength of the joint portion of the steel piece is remarkably lowered, and there arises a problem that the steel piece breaks during finish rolling.

The present invention has been made to solve such a problem, and is a joining device for steel pieces in continuous hot rolling to prevent molten steel from depositing on a joining clamp, and joining of steel pieces using the joining device. It is an object of the present invention to provide a method and a method for manufacturing a hot-rolled steel sheet using the joining method.

(1) The steel piece joining device in continuous hot rolling according to the present invention is installed on the entry side of the finishing rolling mill of the continuous hot rolling line to heat the tail end of the leading steel piece and the tip of the trailing steel piece. The upstream side clamp that sandwiches the leading steel piece and the downstream side clamp that sandwiches the trailing steel piece are provided, and the upstream side clamp or the downstream side clamp is the same as the leading steel piece. It has a pair of upper and lower misalignment prevention plates that prevent misalignment of the trailing steel pieces, and the misalignment prevention plate has a convex portion protruding toward the steel piece side and a concave portion having a height lower than the convex portion in the steel piece width direction. The misalignment prevention plate arranged below the steel piece among the misalignment prevention plates has a comb tooth shape alternately arranged in the above direction, and is upstream from the joint position between the leading steel piece and the trailing steel piece. It is characterized in that the difference in height between the convex portion and the concave portion is set to 10 mm or less in a range of at least 50 mm on the side and the downstream side.

(2) Further, in the above-mentioned item (1), the difference in height between the convex portion and the concave portion of the misalignment prevention plate arranged on the lower side of the steel piece is arranged on the upper side of the steel piece. It is characterized in that it is smaller than the difference in height between the convex portion and the concave portion of the misalignment prevention plate.

(3) The method for joining steel pieces in continuous hot rolling according to the present invention uses the steel piece joining device according to (1) or (2) above, and the preceding steel is used in the joining device. A heating step in which the tail end of the piece and the tip of the trailing steel piece are arranged so as to face each other in a non-contact manner and the tail end of the leading steel piece and the tip of the trailing steel piece are heated, and heating in the heating step. A joining step is provided in which the tail end of the preceding steel piece and the tip of the trailing steel piece are abutted and pressed and joined, and the molten steel discharged into the recess in the joining step is attached to the lower surface of the steel piece. It is characterized in that it is conveyed to the outside of the joining device.

(4) The method for manufacturing a hot-rolled steel sheet according to the present invention is characterized in that the hot-rolled steel sheet is manufactured by using the method for joining steel pieces in the continuous hot rolling described in (3) above.

In the present invention, the difference in height between the concave portion and the convex portion in the misalignment prevention plate arranged under the steel piece is set to 10 mm or less, so that the conventional joining device does not adhere to the steel piece and makes a misalignment. Since the glue that had accumulated on the prevention plate can also be attached to the steel pieces and transported, it is possible to prevent the molten steel from accumulating on the joining clamp.

It is a figure explaining the joining apparatus which concerns on embodiment of this invention, and a part of the misalignment prevention plate is enlarged and shown in the figure. It is a figure explaining the misunderstanding prevention plate which concerns on embodiment of this invention. It is a figure explaining a part of the equipment structure of the continuous hot rolling line which concerns on embodiment of this invention. It is a figure which shows the joining process of the steel piece using the joining apparatus which concerns on embodiment of this invention, and is the figure which explains the state of molten steel. It is a figure which shows the joining process of the steel piece using the conventional joining apparatus, and is the figure which explains the state of molten steel.

As shown in FIG. 1, the steel piece joining device 1 in the continuous hot rolling according to the embodiment of the present invention follows the tail end of the preceding steel piece 3 (preceding steel piece 3a) and the preceding steel piece 3a. The tip of the trailing steel piece 3 (following steel piece 3b) to be transported is heated and pressure-bonded, and the joining surfaces of the leading steel piece 3a and the trailing steel piece 3b are arranged so as to face each other in a non-contact manner. A clamp 5 (upstream side clamp 5a and a downstream side clamp 5b) that holds the steel pieces so as to be held, an induction heating device 7 that heats the joint surface of the steel piece 3 held by the upstream side clamp 5a and the downstream side clamp 5b, and the upstream side. It is provided with a pressing cylinder 9 that pushes the clamp 5a toward the downstream side clamp 5b and presses and joins (upsets) the joint surfaces abutting against each other.
The upstream side clamp 5a and the downstream side clamp 5b having a characteristic portion of the present invention will be described in detail below.

<Upstream side clamp>
The upstream side clamp 5a is for sandwiching the leading steel piece 3a, and a pair of upper and lower steel piece supporting blocks 11 (leading steel piece support) for sandwiching and supporting and positioning the leading steel piece 3a in the steel piece thickness direction. It has a block 11a).

<Downstream side clamp>
The downstream side clamp 5b is for sandwiching the trailing steel piece 3b, and a pair of upper and lower steel piece supporting blocks 11 (posterior) for pinching and supporting and positioning the trailing steel piece 3b in the steel piece thickness direction. It has a steel piece support block 11b) and a pair of upper and lower misalignment prevention plates 13 that prevent the steel pieces 3 from shifting in the vertical direction during press joining.
Hereinafter, the misalignment prevention plate 13 will be described in detail.

《Mistaken prevention plate》
As shown in FIG. 1, the misalignment prevention plate 13 is fixed to the trailing steel piece support block 11b, and by arranging the misalignment prevention plate 13 on the upper side and the lower side of the steel piece joint portion, the steel piece 3 is moved in the vertical direction at the time of pressure joining. It is intended to prevent the shift to. The shape of the misalignment prevention plate 13 will be described with reference to FIGS. 1 and 2.

FIG. 1 shows an enlarged view of the misalignment prevention plate 13 in the vicinity of the joint position (broken line circle portion) of the steel pieces 3, and FIG. 2 shows a perspective view for explaining the shape of the misalignment prevention plate 13.
As shown in the enlarged view of FIG. 1 and FIG. 2, the misalignment prevention plate 13 has an upper misalignment prevention plate 15 arranged on the upper side of the steel piece 3 and a lower misalignment plate 13 arranged on the lower side of the steel piece 3. The upper misalignment prevention plate 15 and the lower misalignment prevention plate 17 are composed of a prevention plate 17, and a plurality of rod-shaped members are alternately arranged in the width direction of the steel piece. On the steel piece 3 side of the upper and lower misalignment prevention plates 15 and 17, convex portions 15a and 17a protruding toward the steel piece 3 and concave portions 15b and 17b having a height lower than the convex portion are formed to form a comb leaf shape. ing.
The convex portions 15a and 17a can be arranged at positions close to the upper surface and the lower surface of the steel piece 3 to prevent the joint surfaces of the leading steel piece 3a and the trailing steel piece 3b from shifting in the vertical direction during press joining. It is a part.
Further, the recesses 15b and 17b are arranged with respect to the upper surface and the lower surface of the steel piece 3 through a certain gap, and are portions into which the liquid-phased molten steel 33 flows in at the time of pressure joining.

The lower misalignment prevention plate 17 in the present embodiment is characterized in that the step h, which is the difference in height between the convex portion 17a and the concave portion 17b shown in the enlarged view of FIG. 1, is smaller than that of the conventional misalignment prevention plate. ..
By setting the step h small, the distance from the lower surface of the steel piece 3 to the recess 17b becomes shorter, and the slag 33 discharged thereby easily comes into contact with the lower surface of the steel piece 3.

In order for the discharged slag 33 to come into contact with the lower surface of the steel piece 3 and to be more easily adhered, the step h must be 10 mm or less.
Further, the range s in which the step h is 10 mm or less is 50 mm or more on the upstream side and the downstream side from the joining position 19 shown in the enlarged view of FIG. 1, respectively. The joining position 19 in the figure is a position where the leading steel piece 3a and the trailing steel piece 3b are joined after the end portion of the steel piece 3 is liquefied and flows out by heating during the heating process by the induction heating device 7. be. As described above, the joining position in the present invention is the position where the leading steel piece 3a and the trailing steel piece 3b are scheduled to be joined.

In the present embodiment, an example is shown in which the step h is constant over the entire length of the lower misalignment prevention plate 17, but the present invention is not limited thereto, for example, 50 mm from the joint position 19 to the upstream / downstream side. If the step h is 10 mm or less in the range of, there may be a portion where the step h is larger than 10 mm in the other range.

As the step h of the lower misalignment prevention plate 17 is reduced, the molten steel (slag) 33 that cannot flow into the recess 17b of the lower misalignment prevention plate 17 moves upward at the joint to prevent the upper misalignment prevention plate 17. It is assumed that it will be discharged to the plate 15 side. In order not to hinder the discharge of the slag 33, it is preferable to provide a sufficient difference in height between the convex portion 15a and the concave portion 15b of the upper misalignment prevention plate 15. However, in the present invention, the difference in height between the convex portion 15a and the concave portion 15b of the upper misalignment prevention plate 15 is not limited.

In the above description, an example is shown in which the upstream side clamp 5a is pressed toward the downstream side clamp 5b side and the joining surfaces are abutted against each other for pressure joining, but the present invention is not limited thereto, for example, downstream. The side clamp 5b may be pressed toward the upstream side clamp 5a to be pressed and joined.
Further, in the above-mentioned example, the downstream side clamp 5b is provided with the misalignment prevention plate 13, but the present invention is not limited thereto, and either the upstream side clamp 5a or the downstream side clamp 5b has a misalignment prevention plate. 13 may be provided.

Next, FIG. 3 shows an example of a method of joining the steel pieces 3 using the joining device 1 according to the present embodiment configured as described above and a method of manufacturing a hot-rolled steel sheet using the joining method. , FIG. 4 will be described below.

FIG. 3 is a diagram illustrating a part of the equipment configuration of the continuous hot rolling line 21 in the present embodiment. It shows the equipment arrangement from the coil box 23 to the first stand of the finish rolling mill 25, and it is assumed that the steel piece 3 is conveyed in the direction of the arrow in the figure.
As shown in FIG. 3, the steel piece 3 coming out of the rough rolling mill (not shown) is wound around the coil box 23, and then the steel piece 3 unwound from the coil box 23 is tipped and tailed by the crop shear 27. The end is cut off. The tail end of the leading steel piece 3a cut by the crop shear 27 and the tip of the trailing steel piece 3b are joined by the joining device 1.
The method of joining the steel pieces 3 by the joining device 1 will be described in detail with reference to FIGS. 1 and 4.

The leading steel piece 3a with the tail end cut and the trailing steel piece 3b with the tip cut are the leading steel piece supporting block 11a and the downstream side clamp 5b of the upstream side clamp 5a in the joining device 1 shown in FIG. It is clamped and supported by the trailing steel piece support block 11b, and the cut surfaces are held so as to face each other in a non-contact manner.

After that, when the tail end of the leading steel piece 3a and the tip of the trailing steel piece 3b are heated to the liquidus temperature of the steel piece 3 or higher by the induction heating device 7, the leading steel piece 3a is shown in FIG. 4A. The tail end of 3a and the tip of the trailing steel piece 3b (the portion shown by the broken line in the figure) become liquid phase and flow out into the recess 17b of the lower misalignment prevention plate 17 (heating step).

After that, the pressing cylinder 9 presses the upstream side clamp 5a in the downstream side clamp 5b direction (in the direction of the arrow in FIG. 4A), so that the tail end of the leading steel piece 3a is pressed against the tip of the trailing steel piece 3b. Then, as shown in FIG. 4B, the leading steel piece 3a and the trailing steel piece 3b are joined (joining step).
In the present invention, since the step h is set to 10 mm or less, the slag 33 discharged to the lower surface side of the steel piece 3 during the joining process also easily comes into contact with the steel piece 3. Therefore, as shown in FIG. 4C, even after the misalignment prevention plate 13 is released up and down, the slag 33 can be attached to the steel piece 3 and conveyed.

The steel pieces 3 pressed and joined by the joining step are then finished by a finishing rolling mill 25 and another stand (not shown) after the Noro 33 adhering to the steel pieces 3 is removed by the cutting device 29 and the Noro 33 is removed. Rolled to produce hot-rolled steel sheets.

As described above, in the present embodiment, by setting the step h of the lower misalignment prevention plate 17 of the joining device 1 to 10 mm or less, the Noro 33, which has conventionally been deposited on the joining clamp, is also made of steel. Since it is attached to the piece 3 and can be transported, it is possible to prevent the slag 33 from accumulating inside the joining device 1. As a result, it is possible to manufacture a hot-rolled steel sheet by continuous hot rolling without causing breakage of the steel sheet caused by the slag 33 deposited inside the joining device 1, which has occurred in the past.

The present invention is effective regardless of the steel type, but at least one of the leading steel piece 3a and the trailing steel piece 3b is an element that produces an oxide having a melting point higher than that of steel, for example, C, Cr, Ti, Mn, This method is particularly effective when the steel grade contains 1 wt% or more of Al, Si, etc. alone or in total. Specifically, C is 0.03% by mass to 2.0% by mass, Cr is 0.03% by mass to 35.0% by mass, and Ti is 0.001% by mass to 0.5. Mass%, Mn 0.03% by mass to 6.2% by mass, Al 0.01% by mass to 0.5% by mass, Si 0.03% by mass to 4.0% by mass It contains a degree, and the balance is a particularly effective technique when the steel grade has a composition consisting of Fe and unavoidable impurities.

Since a specific experiment was conducted to confirm the action and effect of the joining device 1 of the present invention, the results will be described below.
In this embodiment, continuous hot rolling is performed on the continuous hot rolling line 21 as shown in FIG. 3, and the steel piece 3 has a high tension with a plate width of 1200 mm and a thickness of 35 mm after rough rolling. Steel (Si 1.5% by mass, C0.12% by mass, Mn2.7% by mass, Cr 0.9% by mass, Ti0.015% by mass, Al0.03% by mass, P0.008% by mass, S0.0015% by mass) Was used.

Further, in the joining device 1 in the present embodiment, as shown in FIG. 1, the tail end of the leading steel piece 3a and the tip of the trailing steel piece 3b are arranged so as to face each other with a gap of 5 mm, and the induction heating device 7 is provided. The heating condition of the induction heating device 7 was an input power of 1000 kW, a frequency of 1000 Hz, and a heating time of 6.0 seconds. This heats the steel piece 3 in this embodiment to a temperature equal to or higher than the melting point. Further, the region to be heated to a temperature higher than the melting point was set to a range of 12 mm from the tail end of the leading steel piece 3a and the tip of the trailing steel piece 3b before heating.

After joining the steel pieces 3 with the joining device 1 as described above, the Noro 33 was removed by the cutting device 29, and rolling was performed by the finish rolling mill 25 so that the plate thickness was 2.0 mm.
In this embodiment, the step h between the convex portion 17a and the concave portion 17b of the lower misalignment prevention plate 17 of the joining device 1 as shown in FIG. 1 and the range s from the joining position 19 where the step h is 10 mm or less are defined. After changing and performing continuous hot rolling, the appearance of the joint after finish rolling is monitored with a surface inspection meter, and if there is a crack defect with a length of 50% or more with respect to the plate width, continuous rolling is performed. Was decided to be discontinued, and continuous hot rolling was performed up to a maximum of 10.

Table 1 shows the values of the range s from the joining position 19 where the height difference (step) h and h of the convex portion 17a and the concave portion 17b of the lower misalignment prevention plate 17 set in this embodiment are 10 mm or less. The number of lines that could be continuously rolled under each condition is shown.
For those who could perform continuous rolling for 4 or more, it was judged that the decrease in joint strength could be prevented, and the joint strength pass / fail was passed (○), cracks occurred and continuous rolling was canceled after 3 or less. Those that were rejected were marked as rejected (x).

Test No. 1 and No. As shown in 2, if the height difference (step) h between the convex portion 17a and the concave portion 17b of the lower misalignment prevention plate 17 corresponding to the conventional example is larger than 10 mm, the joint portion is formed within three continuous rolling lines. A crack has occurred. In addition, the test No. 8 and No. As shown in 9, even if the height difference (step) h is 10 mm or less, when the range s is smaller than 50 mm, cracks occur in the joint within three continuous rolling lines.
On the other hand, the test No. 3 to No. As shown in 7, when the height difference (step) h is 10 mm or less and the range s is 50 mm or more, four or more continuous rollings can be performed.

1 Joining device 3 Steel piece 3a Leading steel piece 3b Trailing steel piece 5 Clamp 5a Upstream side clamp 5b Downstream side clamp 7 Induction heating device 9 Pressing cylinder 11 Steel piece support block 11a Leading steel piece support block 11b Trailing steel piece Support block 13 Misalignment prevention plate 15 Upper misalignment prevention plate 15a Convex 15b Concave 17 Lower misalignment prevention plate 17a Convex 17b Recess 19 Joint position 21 Continuous hot rolling line 23 Coil box 25 Finishing rolling mill 27 Crop shear 29 Cutting device 31 Misalignment prevention plate (conventional example)
31a Convex part (conventional example)
31b recess (conventional example)
33 Molten steel (Noro)

Claims (3)

It is a joining device installed on the entrance side of the finishing rolling mill of the continuous hot rolling line to heat and press-join the tail end of the leading steel piece and the tip of the trailing steel piece.
The upstream side clamp for sandwiching the leading steel piece and the downstream side clamp for holding the trailing steel piece are provided, and the upstream side clamp or the downstream side clamp prevents the leading steel piece and the trailing steel piece from being misaligned. It has a pair of upper and lower misalignment prevention plates, and the misalignment prevention plate has a comb-teeth shape in which convex portions protruding toward the steel piece side and concave portions having a height lower than the convex portions are alternately arranged in the width direction of the steel piece. And
Among the misalignment prevention plates, the misalignment prevention plate arranged on the lower side of the steel piece is convex within a range of at least 50 mm upstream and downstream from the joint position between the leading steel piece and the trailing steel piece. The difference in height between the portion and the concave portion is set to 10 mm or less, and the difference in height between the convex portion and the concave portion in the misalignment prevention plate arranged on the upper side of the steel piece is arranged on the lower side. The continuous hot steel is provided so as not to prevent the molten steel that cannot flow into the recess of the misalignment prevention plate from moving upward through the joint and being discharged to the misalignment prevention plate side on the upper side. A device for joining steel pieces in rolling. A method for joining steel pieces in continuous hot rolling using the steel piece joining device according to claim 1.
A heating step in which the tail end of the leading steel piece and the tip of the trailing steel piece are placed facing each other in a non-contact manner in the joining device, and the tail end of the leading steel piece and the tip of the trailing steel piece are heated. And a joining step of pressing and joining the tail end of the leading steel piece and the tip of the trailing steel piece heated in the heating step, and in the joining step, the lower misalignment prevention plate is provided. The molten steel discharged into the recess is attached to the lower surface of the steel piece, and the molten steel that cannot flow into the recess of the misalignment prevention plate arranged on the lower side and is moved to the misalignment prevention plate side on the upper side is the steel piece. A method for joining steel pieces in continuous hot rolling, which comprises attaching the steel to the upper surface of the steel and transporting it to the outside of the joining device. A method for manufacturing a hot-rolled steel sheet, which comprises manufacturing a hot-rolled steel sheet by using the method for joining steel pieces in the continuous hot rolling according to claim 2.

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