JP2004167592A - Manufacturing method of hot-dipped steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a resistance welded tube, a method that causes no scratches on a coating layer and that hardly generates fracture in a heat-affected zone, in forming a hot-dipped steel plate into an open tube shape as the material and then abutting both ends in the plate width direction for high frequency welding. <P>SOLUTION: In performing high frequency welding by forming a hot-dipped steel plate into an open tube shape and then abutting both ends in the width direction using squeeze rolls, the squeeze rolls are either three-way squeeze rolls consisting of a pair of side rolls and one top roll or four-way squeeze rolls consisting of a pair of side rolls and two top rolls. When the squeeze rolls are used whose top roll has a circumferential surface covering the area of 5-10% of the outer circumference of the tube including the weld zone, no scratches are caused on the coating layer and also a force of constraint can be taken to a great extent, thus suppressing generation of fracture due to molten metal brittleness in the heat-affected zone. <P>COPYRIGHT: (C)2004,JPO

Description

【００１９】
表１に示す結果からもわかるように、めっき鋼帯を素材として造管する際、疵を生じさせず、しかも溶接不良を発生させないためには、従来の４ロール法では、熱／冷延鋼帯を素材とする場合と同じアプセット量で行おうとすると造管速度を遅くしなければならず生産性が低下する。また熱／冷延鋼帯を素材とする場合と同じライン速度で造管しようとすると、従来よりもアプセット量を少なくしなければならず強度低下につながる。さらに２ロール法では疵が生じやすい。
これに対して、所定の幅を持つトップロールを使用した３方あるいは４方のスクイズロールを使用した本発明法では、熱／冷延鋼帯を素材とする場合と同程度のアプセット量及び同程度のライン速度で、疵を生じさせることなく、しかも溶接不良を発生させることなく造管することができた。
【００２０】
【発明の効果】
以上に説明したように、素材の溶融めっき鋼帯を高周波溶接法で造管する際に、スクイズロールとして、一対のサイドロールと１個のトップロールからなる３方スクイズロールまたは一対のサイドロールと２個のトップロールからなる４方スクイズロールであって、管の溶接部を含む外周の５〜１０％の範囲をトップロールの周面とするものを使用することにより、鋼帯エッジ部にサイドロールによってある程度の拘束長さを残すことができ、溶接不良を発生させることなく、しかもロール疵を付けずに造管することができたものである。
本発明により、生産性を低下させることなく良質のめっき鋼管を得ることができた。
【図面の簡単な説明】
【図１】造管ラインの概略図
【図２】従来のスクイズロールの断面形状を説明する図、（ａ）は２方ロールで（ｂ）は４方ロール
【図３】スクイズロールと被溶接材料との接触領域（図中の網部）と拘束力の大きさを模式的に説明する図で、（ａ）は２方ロールを、（ｂ）は従来の４方ロールを用いた場合
【図４】本発明で使用するスクイズロールの断面形状を説明する図、（ａ）は４方ロールで（ｂ）は３方ロール[0001]
[Industrial applications]
The present invention relates to a method for manufacturing an ERW pipe using a hot-dip coated steel sheet as a raw material.
[0002]
[Prior art]
The welded steel pipe is manufactured by sequentially bending a steel strip slit to a predetermined width in a plate width direction with a multi-stage forming stand, forming a roll into an open pipe, and welding both ends in the plate width direction.
The forming stand 1 is arranged in multiple stages with an upper roll 1U and a lower roll 1D as a pair, and bends the steel strip S paid out from the payoff reel 2 in the width direction (FIG. 1). At a stage where the bending shape of the steel strip S has advanced to some extent, the steel strip S is held by the left and right roll groups 3 from the left and right directions and further bent. The left and right roll group 3 includes a plurality of pairs of a right roll 3R and a left roll 3L provided with a concave crown having the same curvature. The steel strip S is regulated by the roll circumferential surface of the right roll 3R and the left roll 3L, they are sequentially formed on the open pipe P _0.
[0003]
Open pipes P ₀ is then fed into the fin-pass rolls 4. Fin pass rolls 4, includes a plurality of pairs of lower roll 4D to back up roll 4U and open the pipe P ₀ on which finned (not shown) in the barrel length direction central portion of the roll peripheral surface with a concave crown I have. By sending a steel strip S by inserting the fins of the upper roll 4U between widthwise ends of the open pipe P ₀ formed into steel strip S, the edge surface is maintained at a predetermined position, open the pipe P ₀ is Centered.
Both ends in the width direction of the steel strip S are heated by the high-frequency induction heating coil 5, and a predetermined weld is formed by the compressive force of the squeeze roll 6. Welded pipe P ₁ is, after the inner surface bead is appropriately bead cut according to the outer surface beads and required, the product steel pipe through sizing (shaped) step, the straightening process.
[0004]
In forming a welded pipe by roll forming, forming rolls are prepared for each outer diameter of the welded pipe, and materials having different springbacks due to plate thickness, material, and the like are formed into a welded pipe having the same outer diameter. Therefore, since it is not economical to design an optimal roll for each material, some rolls are replaced depending on the sheet thickness, but basically the same forming roll is used even if the material changes, Due to different bending conditions and springbacks for each material condition, the shape before welding differs depending on the material.
In addition, squeeze rolls, which are important for ensuring welding quality, take into account only workability and scratch resistance, and two-way squeeze rolls (FIG. 2A) are used for welded pipes having a diameter of about 100 mm or less. For medium-diameter welded pipes exceeding 100 mm in diameter, where flaws are likely to occur near the weld due to the upper flange, approximately 30 to 40 degrees on each side of the weld to minimize the difference in peripheral speed of the roll. Alternatively, a three-sided or four-sided squeeze roll (FIG. 2B) which is pressed by two top rolls is used.
[0005]
[Problems to be solved by the invention]
The roll forming as described above is also performed when manufacturing an electric resistance welded steel pipe using a hot-dip coated steel sheet as a raw material, and welding is performed by a squeeze roll.
In a squeeze roll, both ends of a heated steel strip are pressed and joined by applying further pressure after filling the open pipe in the roll. After joining, the steel pipe exits the squeeze roll and is released from the restraint by the squeeze roll as it goes away from the squeeze roll. At that time, the steel pipe that has gone through the roll forming process as described above will generate springback that reduces the curvature in the circumferential direction. At this time, if the residual stress and strength conditions of each part in the circumferential direction of the steel pipe are quite uniform, the cross-sectional shape of the welded closed steel pipe cannot be deformed by springback.
[0006]
However, in the actual steel pipe, particularly, both edges are not sufficiently bent, and there is a possibility that a large springback may occur as compared with other portions. In addition, near the weld immediately after welding, a steep temperature distribution from the high-temperature joint surface to the base metal via the heat-affected zone, in other words, a steep strength distribution is generated. The effect of the aforementioned springback of the edge is superimposed on this steep strength distribution, and the bends on both sides of the weld are reduced, and the effect is such that the high-temperature, low-strength weld is bent out of the pipe. Deforms into a drop-shaped cross section.
Due to such deformation of the welded portion due to the springback, a circumferential tensile stress is applied to the welded portion and its vicinity on the outer surface of the pipe. In addition, there is a region in the weld heat affected zone where the plated metal is melted by the welding heat, and the aforementioned tensile stress promotes the penetration of the molten plated metal into the crystal grain boundaries, so that the sheet metal can be brought into close proximity to the weld bead. Molten metal embrittlement cracks tend to occur in the thickness center direction.
[0007]
When manufacturing a medium-diameter welded pipe exceeding 3 inches in diameter, a three- or four-sided press of one or two top rolls at about 30 to 35 degrees each on both sides of the welded portion so as to reduce the peripheral speed difference of the rolls When using a squeeze roll of the type, the area where the pipe is constrained by the side rolls is extremely short, and the squeeze rolls are insufficiently constrained, causing large springback and cracking due to the embrittlement of the molten metal. Easy to get up. For this reason, in order to avoid this cracking, it was necessary to reduce the line speed to form a pipe.
If a two-way squeeze roll is used to sufficiently constrain the squeeze roll, the difference in peripheral speed becomes too large, and the plating layer is likely to be scratched.
The present invention has been devised to solve such a problem. After forming into an open pipe shape using a hot-dip coated steel sheet as a raw material, when the both ends in the sheet width direction are butt-bonded with each other and subjected to high-frequency welding, the plating layer is damaged. It is an object of the present invention to provide a method for manufacturing an electric resistance welded pipe in which a heat-affected zone is less likely to be cracked without adding a crack.
[0008]
[Means for Solving the Problems]
The method for producing a hot-dip coated steel pipe according to the present invention includes a pair of side rolls when forming a hot-dip coated steel sheet into an open pipe shape and then performing high-frequency welding by butt-pushing both ends in the width direction of the plate with a squeeze roll. And a three-way squeeze roll consisting of one top roll or a four-way squeeze roll consisting of a pair of side rolls and two top rolls. Characterized in that a squeeze roll having a peripheral surface of is used.
[0009]
[Action]
The present inventors have continued to study the causes of cracks occurring near the weld when manufacturing ERW pipes using hot-dip coated steel sheets, particularly steel sheets hot-dip coated with an alloy containing zinc as a main component. .
When a steel strip or steel sheet cut to a width suitable for the product steel pipe is formed into an open pipe shape, and when welding both ends in the width direction, foreign materials such as oxides are extruded from the welded part and heated to ensure welding strength. Upsets are added to both ends in the width direction. Therefore, when released from the squeeze roll immediately after welding, tensile stress due to springback is applied to the weld. When a zinc-based alloy plated steel sheet is welded, the zinc-based alloy melted by welding heat has a lower liquidus temperature than zinc (melting point 420 ° C.), and maintains a molten state for a relatively long time. If the tensile stress due to springback exceeds a certain limit while the plated metal is being melted, the molten metal penetrates the crystal grain boundaries, causing the molten metal to become embrittled. As a result, crystal grain boundary cracks appear from the vicinity of the weld bead toward the center of the sheet thickness.
[0010]
When using a three- or four-way squeeze roll that holds down about 30 to 35 degrees on both sides of the weld with one or two top rolls and the remaining part with one set of side rolls, the squeeze roll restraint Is insufficient, and the contact area of the roll flange with the material to be welded is narrow (see FIG. 3B), so that cracks due to the embrittlement of the molten metal are likely to occur. Therefore, in order to suppress grain boundary cracking, after welding, the restraining force of the squeeze roll is large, the contact area of the roll flange is widened, and the time required for release from the roll, that is, the tensile stress caused by springback, is reduced. If the time until this is extended and tensile stress is applied after solidifying the molten metal composed of the plated metal, the molten metal does not enter the crystal grain boundaries and the occurrence of cracks near the weld can be prevented. I guessed. However, if a two-way squeeze roll having a wide contact area with the roll flange is used to increase the restraining force of the squeeze roll (see FIG. 3A), the difference in peripheral speed becomes too large, so that both sides of the welded portion become large. It becomes easy to be scratched.
[0011]
In the present invention, by repeatedly examining various shapes of squeeze rolls, when manufacturing a medium-diameter welded pipe having a diameter exceeding 3 inch (φ76.2 mm) by hot-dip welding using a hot-dip coated steel sheet as a material, As the squeeze roll, a three-way squeeze roll composed of a pair of side rolls and one top roll ((b) in FIG. 4) or a four-way squeeze roll composed of a pair of side rolls and two top rolls (( a)), in which a range of 5 to 10% of the outer periphery including the welded portion of the pipe is used as the peripheral surface of the top roll, it is possible to prevent the occurrence of flaws in the pipe and to reduce the binding force and the roll flange. It has been achieved that an electric resistance welded pipe can be obtained in which a wide contact area with the steel to be welded can be secured and cracks do not occur near the welded portion.
[0012]
By the way, when the squeeze rolls rotate integrally, the outermost side rotates at a fast speed and the inner side rotates at a slow speed. And its speed is proportional to the radius.
On the other hand, the material travels at a certain speed between the fastest and slowest portions of the roll while contacting the portions of the roll at different speeds. At this time, the portion of the roll that is rotating at a speed that matches the speed of the material is called a neutral point. Outside this neutral point, the roll advances faster than the material, and its direction is also different from the direction in which the material advances. In addition, since the corner of the roll is in particularly strong contact with the material at the edge of the roll, slipping occurs due to a difference in the direction in which the material and the roll travel, resulting in a flaw.
[0013]
The contact area between the roll and the material in the vicinity of the weld is the longest in the case of a two-way squeeze roll (see FIG. 3A), and the constraint distance of the edge portion is extremely large in a roll combining a top roll and a side roll. (See FIG. 3B). In other words, the larger the angle from the center to the neutral point in the above description, the larger the contact area becomes.However, when using a top roll, the neutral point can be made nearly horizontal, so the angle from the center to the neutral point is minimized. The contact area becomes very short.
If the contact area is long, a flaw is generated. Therefore, it is a conventional method to divide the squeeze roll to shorten the contact area of the roll at the edge where the flaw easily enters (see FIG. 2B). It is. However, since the contact area is, in other words, an area where the material is constrained by the rolls, when the constrained distance is short, the influence of the constraining by the rolls is eliminated immediately when the squeeze roll is released, and a shape change due to springback occurs.
[0014]
The present invention, in order to satisfy the conflicting requirements of strengthening the restraint for the prevention of flaws and welding defects, in order to satisfy the conflicting requirements, the area shared by the top roll is limited to the vicinity of the extreme edge where flaws are a problem, and to some extent by side rolls This is based on the development of a split roll with a narrow top roll angle (width) that combines both functions by leaving the constraint length.
When the conventional top roll angle of 30 to 40 degrees was changed to 9 to 18 degrees, the length restricted by the side rolls could be left to some extent, and the above conflicting requirements could be satisfied. Since the angle of 9 to 18 degrees is 5 to 10% when converted to the ratio of the outer circumference, the intended purpose can be achieved when the width of the top roll is set to 5 to 10% of the outer circumference of the pipe.
[0015]
【Example】
After cutting a 400 N class hot-dip coated steel sheet of various thicknesses on which a Zn-6% Al-3% Mg alloy plating layer is formed into a predetermined size, it is formed into an open pipe shape by a breakdown roll group, a side cluster and a fin pass stand group. Formed, high-frequency induction heating with seam guide rolls having fins that enter the opening of this open pipe while regulating the position of both edges, adding upsets with squeeze rolls, welding, and subsequently cutting off bead on the outer surface After that, the cut portion was coated by thermal spraying, and then the welded portion was cooled and shaped, straightened, and cut into a predetermined cross section to produce a structural square steel pipe having an outer dimension of 100 mm x 100 mm.
[0016]
Hereinafter, the 2.3 mm material will be described. As a comparative example, a squeeze roll in a four-way roll direction in which a range of approximately 35 degrees on both sides of a welded portion conventionally used is held by two top rolls and the remaining portion is held by a pair of side rolls. Indicates the case where If a material such as a hot / cold rolled steel strip is not concerned about the embrittlement of molten metal, use this squeeze roll to take an upset of about 1.5 mm necessary for reliable welding at a speed of 120 m / min and sound. It is possible to manufacture a simple welded steel pipe. However, in the case of using the above-mentioned plated steel strip having a concern of molten metal embrittlement, if a 1.5 mm upset is secured, cracking is avoided unless the pipe forming speed is reduced from the normal 120 m / min to 80 / min. Could not. In addition, when operated at 120 m / min, cracks occurred when the upset exceeded 1.0 mm.
When the squeeze roll was changed to a two-way roll type having a stronger binding force, it was possible to form a pipe without cracking even at a normal 120 m / min and 1.5 mm upset. However, flaws were generated on both sides of the weld due to friction between the roll and the flange.
[0017]
Therefore, the width of the top roll of the four-sided squeeze roll was reduced so as to maintain 15 degrees on both sides of the welded portion, and a squeeze roll in which the area of the side roll was enlarged by that amount was used. Cracking and flaws did not occur even when pipe was formed with a 5 mm upset.
It should be noted that either a four-way squeeze method using two top rolls with a weld bead interposed therebetween (FIG. 4A) or a three-way squeeze roll method integrating two top rolls (FIG. 4B). However, the effect of preventing the top roll from cracking is almost the same, but the roll position adjustment is easier with the three-way roll.
The results are shown in Table 1.
The same tube-forming test was performed on plated steel strips having plate thicknesses of 1.6 mm, 3.2 mm, 4.5 mm, and 6.0 mm. Table 1 also shows the results.
[0018]

[0019]
As can be seen from the results shown in Table 1, when forming a tube from a plated steel strip as a material, in order to prevent flaws and poor welding, the conventional four-roll method requires a hot / cold rolled steel. If an attempt is made to use the same upset amount as in the case of using a band as a material, the pipe-forming speed must be reduced, and the productivity is reduced. Further, if it is attempted to form a tube at the same line speed as when a hot / cold rolled steel strip is used as a material, the upset amount must be reduced as compared with the conventional case, leading to a reduction in strength. Further, the two-roll method tends to cause flaws.
On the other hand, in the method of the present invention using a three- or four-sided squeeze roll using a top roll having a predetermined width, the upset amount and the same amount as in the case of using a hot / cold rolled steel strip as a material are used. At about the line speed, the pipe could be formed without generating flaws and without causing welding defects.
[0020]
【The invention's effect】
As described above, when forming a hot-dip steel strip of a material by high-frequency welding, as a squeeze roll, a three-way squeeze roll including a pair of side rolls and one top roll or a pair of side rolls is used. By using a four-sided squeeze roll composed of two top rolls and having a range of 5 to 10% of the outer circumference including the welded portion of the pipe as the peripheral surface of the top roll, side edges are formed on the steel strip edge. The roll can leave a certain restrained length, and the pipe can be formed without causing welding defects and without forming roll flaws.
According to the present invention, a high-quality plated steel pipe can be obtained without lowering the productivity.
[Brief description of the drawings]
FIG. 1 is a schematic view of a pipe making line. FIG. 2 is a view for explaining a cross-sectional shape of a conventional squeeze roll. FIG. 3A is a two-way roll, and FIG. FIGS. 4A and 4B schematically illustrate a contact area with a material (a net portion in the figure) and a magnitude of a binding force. FIG. 4A illustrates a case where a two-way roll is used, and FIG. FIG. 4 is a view for explaining a cross-sectional shape of a squeeze roll used in the present invention, wherein (a) is a four-way roll and (b) is a three-way roll.

Claims (1)

After forming hot-dip coated steel sheet into an open pipe shape, when squeezing rolls are used to butt both ends in the width direction of the sheet and perform high-frequency welding, a three-way squeeze roll consisting of a pair of side rolls and one top roll or a pair of side rolls is used. A hot-dip galvanized steel pipe comprising a four-sided squeeze roll including two top rolls, wherein a squeeze roll having a range of 5 to 10% of an outer circumference including a welded portion of the pipe is used as a peripheral surface of the top roll. Manufacturing method.

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