JP2005095963A - Method for forming butt welding joint of band steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure sound shape/quality of band steel by preventing generation of weld zone damage (porosity D<SB>A</SB>, crack D<SB>C</SB>, etc.) that is prone to be caused at separation of a tab plate (melt-sticking to a butt welding zone) after welding, in a method of forming a butt joint for welding the end edges of a band steel by using a tab plate. <P>SOLUTION: Succeedingly to a butt welding execution using a tab plate, the butt weld zone (W) is temporarily annealed with the tab plate melt-sticking, and then, the tab plate is separated from the band steel by bending the tab plate while the melt-sticking part of the tab plate is held in a soft state. In the temporary annealing performed with the tab plate melt-sticking, irregularities are caused in the temperature distribution in the width direction of the butt welding zone. Accordingly, after the tab plate separation, a heat treatment (regular annealing) is newly carried out to impart homogenous annealing texture to the entirety of the butt welding zone. The temporary annealing and the regular annealing processing can be efficiently performed by using a resistance heating apparatus that energizes by clamping the band steel (1) between a conductive table (31) (31) and an electrode (32) (32) that is controllably driven vertically. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a butt weld joint in which end portions of a steel strip coil are welded and lengthened, and in particular, a tab plate welded to a welded portion following a butt welding operation using a tab plate. Handling from the steel strip can be performed efficiently without damaging the weld.

  In continuous processing lines that perform press forming while winding steel strips such as carbon steel and stainless steel from the steel strip coil, as a measure to improve line operation efficiency, lengthening the steel strip coil to shorten coil switching time Is desired. The length of the steel strip coil is increased by abutting the end edges of the steel strip and joining the butt portion by TIG arc welding or YAG laser beam welding. The formed butt weld is in a hard and brittle quenching state as it is, so that it is subjected to a heat treatment (tempering) for tempering and wound around a coil.

Tab plates are used for butt welding of steel strips. FIG. 2 shows a welding construction state using a tab plate. The end edges of the two strip steel strips (1) to be welded were butted together, and tab plates (2) (2 _A , 2 _B ) were placed on the left and right side edges across the butted section (L) In addition, with the plate surface of one tab plate (2 _A ) as the welding start point and the plate surface of the other tab plate (2 _B ) as the welding end point, the welding torch (21) is moved along the butt portion (L). To form a butt joint.
The tab plate (2) is used for butt welding because the output control at the start / end of welding (output ON / OFF) is unstable. This is because 1 mm × band width 30 mm) is likely to cause melting damage (burnout of the butt portion) due to excessive welding heat input. By setting the plate surface of the tab plate (2) (2 _A , 2 _B ) as the welding start point and end point, the above defects caused by output fluctuations at ON / OFF are avoided, and welding is performed under stable output conditions. A joint can be formed.
JP 51-018955 A JP 07-246495 A

The tab plate (2) is welded to the edge of the butt weld (W) as shown in FIG. 5 after welding, and this is obtained by bending the strip as shown in FIG. Disconnected. As shown in Fig. 7.1, the strip steel (1) after separating the tab plate (2) has fracture marks (D _A ) (D _B ) at the edge of the butt weld (W). Remain. The fracture mark (D _A ) is “defect” (the dent where the rim of the butt weld is attached to the tab plate 2 _A ), and the fracture mark (D _B ) is “burr” (tab plate 2 _B is a projection in which a part of the plate thickness of _B adheres and remains on the steel strip. In addition, as shown in FIG. 7.2, a crack (D _C ) may occur in the butt weld (W) due to the bending / separating operation of the tab plate (2) and the impact of handling.

Since the vicinity of the butt weld (W) is a portion scheduled to be cut off, even if the fracture marks (D _A ) and (D _B ) exist, it does not directly affect the strip steel quality. However, when the steel strip (1) is supplied to, for example, a continuous press processing line, if there are defects (dents) (D _A ) or burrs (D _B ), the steel strip is continuously fed, such as being caught in the press die. This may cause troubles such as line stoppage and die damage. In this case, the burrs (D _B ) can be removed in advance with a grinder or the like, but the defects (D _A ) cannot be repaired. Moreover, if a crack (D _C ) occurs in the butt weld (W), the welding work becomes meaningless.
As another method for separating the tab plate, a method other than bending (tensile, twisting, etc.) can be used (rather, the occurrence of fracture marks and cracks becomes remarkable). In addition, the method of cutting the boundary between the steel strip (1) and the tab plate (2) using a blade is difficult to put into practice because it complicates the apparatus configuration of the line and significantly lowers the operation efficiency.

  In view of the above, the present invention can efficiently separate the tab plate of the butt welding construction without causing defects, cracks, or the like in the butt welded portion, and can stably ensure the shape quality of the butt welded portion. A method of forming a steel strip butt weld joint is provided.

The butt-welding joint method of the steel strip according to the present invention is as follows:
The end edges of the steel strips are abutted on the steel strip transfer line, and the tab plate is brought into contact with the left and right side edges of the steel strip with the butted portion sandwiched between them. A method for forming a butt joint in which a butt portion is welded with the plate surface of the other tab plate as a welding end point, and after welding, the tab plate welded to the edge of the butt weld portion is separated from the strip steel The butt weld of the steel strip and the tab plate are pre-annealed by heating and air cooling, and the tab plate is removed from the steel strip while the welded portion of the tab plate is maintained in a soft state during the temperature lowering process. After the separation and the tab plate separation, the butt weld is annealed.

When the tab plate welded to the butt weld is cut off, it is easy to cause defects (D _A ), burrs (D _B ) [Fig. 7.1] and cracks (D _C ) [Fig. 7.2]. This is because the welded joint is in a hard and brittle quenched state as it is. In accordance with the present invention, the butt welds are annealed (temporary annealing), and the tab plate is cut off while the air-cooling process is hot or warm, that is, while the weld is held in a soft state. The occurrence of D _A ) and cracks (D _C ) is suppressed and prevented, and as shown in FIG. 8, the edge line (E) of the welded portion (W) after the tab plate separation has a substantially flat shape (E ). In addition, in the said annealing process (temporary annealing) performed in the state in which the tab board (2) was welded, the temperature in the width direction of the butt weld (W) is accompanied by partial heat due to the cooling action of the tab board. Unevenness is likely to occur. Therefore, in the present invention, the annealing for separating the tab plate is pre-annealed, and after the tab plate is separated, the final butt weld is subjected to the main annealing again. By performing this two-stage annealing, the width of the butt weld is obtained. A uniform annealing structure based on a uniform heating effect throughout the direction is ensured.

FIG. 1 shows a continuous butt joint forming line for practicing the present invention.
This butt joint forming line is composed of a pre-process part (10), a welding apparatus part (20), a heat treatment part (30), a post-process part (40), and the like. The welding apparatus section (20) is provided with an inert gas arc welding machine such as a TIG welding machine or a YAG laser beam welding machine. The heat treatment section (30) has a resistance heating device (described later) including an electrode and a conductive base plate, and clamps the strip steel between the electrode and the conductive base plate and anneals the strip steel by resistance heating ( (Temporary annealing and main annealing). The upstream process section (10) on the upstream side of the welding apparatus section is provided with, for example, a shear or the like that cuts and removes the tail and tail ends of the steel strip coil to form a butt groove. The downstream side post-process part (40) displays, for example, a banding-shaped straightening device such as an earsliding device (burr grinder grinding removal, etc.), a leveler (bending of the steel strip bending), and the position of the butt weld. A coloring device or the like is arranged, and predetermined processing is performed on each.

In the above-mentioned band steel butt joint forming line, the band steel (1) is unwound from the band coil (C ₁ ) on the line start end side and introduced into the welding apparatus part (20) via the pre-process part (10). Is done. In the welding device section (20), as shown in FIG. 2, butt welding of the end edges of the steel strip (1) (the tail end of the preceding coil strip and the tip of the subsequent coil strip) is performed. Is called. Operations such as butting the edges of the steel strip (1) and assembling the tab plate may be performed using the jig (22) as appropriate. The steel strip (1) and the tab plate (2) (2 _A , 2 _B ) is clamped, and a butt joint is formed by inert gas arc welding such as TIG arc or YAG laser beam using a filler (filler material) of the same type as that of the steel strip.

  After the butt welding, the butt weld (W) is transferred to the heating device (30) with the tab plate (2) being welded, and the butt weld (W) is heat treated (temporary annealing treatment). ) This heat treatment is intended to soften the butt weld (hardened structure), and is performed by heating and holding in the austenite temperature range for an appropriate time and then air cooling. By the pre-annealing treatment, the quenched structure of the butt weld is eliminated and a fine pearlite structure (which may exhibit a mixed phase structure including pro-eutectoid ferrite or pro-eutectoid cementite depending on the composition of the strip steel).

FIG. 3 shows a specific example of the device configuration of the heating device section (30). In this heating device, a conductive base plate (31) and an electrode (32) arranged opposite to the conductive plate (31) are arranged opposite to each other at an appropriate interval on the upstream side and downstream side of the line. The electrode (32) is lifted and lowered by the lift drive device (33) so as to approach or separate from the conductive base plate (31). Further, as shown in FIG. 4, the conductive base plate (31) and the electrode (32) have a surface size that covers the steel strip (1) and the tab plate (2) (2 _A , 2 _B ). . This is for heating the steel strip (1) and the tab plate (2) (2 _A , 2 _B ) simultaneously. As shown in the drawing, the butt weld (W) of the steel strip (1) is stopped so as to be positioned substantially at the center of the conductive platform (31) (31), and each electrode (32). (32) is lowered and clamped by sandwiching the steel band (1) and tab plate _{(2) (2} a, _{2 B),} butt by resistance heating to heat weld the (W) to a predetermined temperature.

After the butt weld (W) is heated and held at a predetermined temperature, the energization is stopped and the left and right electrodes (32) and (32) are moved upward to be air-cooled so that the butt weld (W) is in a soft state. The tab plate (2) is cut off in a hot or warm state holding the. The tab plate separation can be handled by bending the tab plate (2) with respect to the steel strip (1) as shown in FIG. The butt weld (W) of the steel strip (1) from which the tab plate (2) (2 _A , 2 _B ) has been separated has a defect (D _A ) [Fig. 7.1] and cracks (D _C ) [Fig. 7.2] has a healthy shape (Figure 8).

After the tab plate (2) is cut off, the butt weld is subjected to a main annealing process. The reason why the annealing process is performed again after the separation of the tab plate is to form a uniform annealing structure over the entire width direction in the butt weld (W) as described above. This annealing is performed by lowering the electrodes (32) and (32) in the heating device section (30) [FIGS. 3 and 4], and the steel strip (1) between the conductive base plates (31) and (31). This is achieved by sandwiching and holding and heating to the austenite temperature range by resistance heating, and then performing controlled slow cooling. The cooling rate is controlled by adjusting the current.
After the main annealing process, the process is shifted to the post-process part (40), subjected to a predetermined process (shape correction, surface inspection, etc.) and then wound on a winder (C2).

In the above description, the tab plate of steel strip (1) and (2 _A) the separation of the (2 _B), although a be performed in the cooling process of the provisional annealing treatment, one of the tab plate (2 _{B) [welding} end point The tab plate] may be cut off before the preliminary annealing treatment. While the fracture mark of the steel strip that occurs when the tab plate (2 _A ) on the welding start side is separated is a defect (D _A ), the fracture trace that occurs when the tab plate (2 _B ) on the welding end side is separated is This is because it is a burr (D _B ), and the burr (D _B ) can be subjected to shape correction using a grinder or the like.

  In addition, although the grade of the steel strip in the present invention is not particularly limited, as a typical example, various polished special steel strips defined in JIS G3311 (strip steels such as carbon steel, carbon tool steel, alloy steel, and alloy tool steel) can be cited. It is done. Moreover, it is preferable to use the board | plate material which has the same thickness as the steel strip as the tab board (2) applied to the butt | matching part of a steel strip.

  The steel strip is supplied to the steel strip butt joint forming line (FIG. 1), butt welding using a tab plate is performed in the butt welding device section (20), and the butt weld portion is formed in the heating device section (30). The heat treatment is performed and the tab plate is separated and annealed.

(1) Steel strip and tab plate Steel strip: Polished special steel strip “S55C” (JIS-G3311) wall thickness 1.0 × strip width 28 (mm)
Tab plate: Polished special steel strip “S55C” (JIS-G3311), plate thickness 1.0 mm, surface size 28 × 300 (mm)

(2) Butt welding YAG laser beam welding. Uses the same component filler as the strip steel. In the welding device section (20), as shown in FIG. 2, the edge portions of the steel strips (1) and (1) are butted together using an assembling jig (22), and tab plates (2) are formed on both side edges. (2 _A , 2 _B ) is abutted and clamped, one tab plate (2 _A ) is the welding start point, the other tab plate (2 _B ) is the welding end point, and the laser beam along the welding line (L) (Output: 550 W) was irradiated to weld the butt.

(3) Temporary annealing and separation of tab plate In the heating unit (30), the butt weld (W) is positioned at the approximate center of the conductive base plates (31) and (31), and then the electrode (32) ( 32) is lowered to be pinched steel strip (1) and on both sides of the tab plate ₍₂ a) _{(2 B),} the weld (W) is heated holding butted by resistance heating. Next, energization was stopped and the electrodes (32) and (32) were withdrawn upward, and the tab plates (2 _A ) and (2 _B ) were bent as shown in FIG. 6 and separated from the steel strip (1). The heat pattern in this temporary annealing is shown in FIG. The plate temperature of the butt weld (W) during tab plate separation handling is approximately 400 to 500 ° C.
Temperature rising rate (R _H ): about 20 ° C./second Heating temperature: 750 ° C. (≈A ₁ point + 30 ° C.)
Heating and holding time: 50 seconds Cooling after stopping energization: Air cooling

(4) after disconnecting the annealing treatment tab plate (2 _{A) (2 B),} electrode (32) is lowered to (32), is heated and kept at a predetermined temperature energized by clamping the steel strip (1). Then, by energization control (current adjustment), it was gradually cooled until it reached 550 ° C., and then energization was stopped and air cooling was performed to room temperature. FIG. 10 shows the heat pattern.
Temperature increase rate: Approx. 20 ° C / sec Heating temperature: 750 ° C (≒ A ₁ point + 30 ° C)
Heating and holding time: about 50 seconds Cooling speed of slow cooling process (750 → 550 ℃): about 4 ℃ / sec

(5) Butt weld quality
(5.1) Metal structure and hardness FIG. 11 shows the metal structure of the butt weld (W) as it is welded (without pre-annealing). 11a is an a portion of FIG. 11, FIG. 11.b is an enlarged view of the b ₁ and b ₂ portions, and FIG. 11.c is an enlarged view of the c ₁ and c ₂ portions (at the bottom of each figure, Each hardness _HV5 is added). A portion of the butt weld martensitic structure, its proximity _{(b 1, b 2)} exhibits a bainite structure is significantly hard _{(H V5} 739).
FIG. 12 shows the metal structure of the butt weld (W) of the strip steel subjected to temper welding (temporary annealing to room temperature) following the butt welding according to the present invention. 12a is an a part of FIG. 12, FIG. 12.b is an enlarged view of parts b ₁ and b ₂ , and FIG. 12.c is an enlarged view of each of c ₁ and c ₂ parts (at the bottom of each figure). , Each hardness _HV5 is added). In this butt weld, as shown in the figure, the quenching structure in FIG. 11 (FIGS. 11.a to 11.c) is eliminated, and the part a and its vicinity are changed to a mixed phase structure composed of fine pearlite and ferrite. And softened.

(5.2) Shape quality of butt weld (after tab plate separation)
As shown in FIG. 8, the edge of the butt weld (W) is broken (D _A ) in the steel strip that has been subjected to pre-annealing and separated the tab plate in the air cooling process (hot or warm) according to the present invention. [Figure 7.1] and cracks (D _{C) [Figure} 7.2] has a sound shape quality without the like. This is due to the above-described structural change of the butt weld due to temporary annealing and accompanying softening.

The table below shows the observation results of the shape quality of the butt joint. The effect of improving the shape quality due to the preliminary annealing is obvious.
Abnormality incidence (%) = D / M x 100
However, D ... Number of defects (D _A ) or cracks (D _C )
M ... Number of butt joints formed (= 20)

According to the present invention, it is easy to separate the tab plate welded to the strip steel butt weld, and the occurrence of defects (D _A ), cracks (D _C ), etc. in the butt weld is suppressed and the shape quality is reduced. Therefore, it is possible to cope with the demand for lengthening the steel strip coil (increase in the weight of a single coil) in a continuous press forming processing line. It guarantees a smooth and continuous supply of steel strip and enables line efficiency to be improved.

It is a schematic diagram which shows the butt-welding joint formation line of a strip steel. It is a perspective explanatory view showing butt welding construction using a tab plate in a band steel butt joint forming line. It is front explanatory drawing which shows the heating apparatus in a strip steel butt joint formation line. FIG. 4 is an explanatory plan view of FIG. 3. It is plane explanatory drawing which shows the state which the tab board welded to the butt welding part of the strip steel. It is an isometric view explanatory view which shows a mode that the tab board welded to the butt welding part of a steel strip is cut | disconnected from a steel strip. It is plane explanatory drawing which shows the fracture | rupture trace of the butt-welding part after tab board cutting | disconnection in the conventional method. It is plane explanatory drawing which shows the state which the crack generate | occur | produced in the butt-welding part at the time of tab plate separation in the conventional method. It is plane explanatory drawing which shows the shape of the butt-welding part after tab board cutting | disconnection in this invention.

It is a graph which shows the example of the heat pattern of the temporary annealing process performed at the time of tab board cutting | disconnection of this invention. It is a graph which shows the example of the heat pattern of this annealing process performed after tab board cutting | disconnection of this invention. It is a drawing substitute micrograph which shows the metal structure (as-welded) of a strip butt weld. FIG. 12 is a drawing-substituting micrograph showing an enlarged view of a part of FIG. 11. FIG. 12 is a drawing-substituting micrograph showing an enlarged view of b ₁ and b ₂ parts of FIG. 11. FIG. 12 is a drawing-substituting micrograph showing an enlarged view of c ₁ and c _{2 in} FIG. 11. It is a drawing-substituting micrograph showing the metal structure of the steel strip butt weld (preliminary annealing treatment). FIG. 13 is a drawing-substituting micrograph showing an enlargement of part a in FIG. 12. FIG. 13 is a drawing-substituting micrograph showing an enlarged view of the b ₁ and b ₂ parts of FIG. 12. FIG. 13 is a drawing-substituting micrograph showing an enlarged view of the c ₁ and c ₂ parts of FIG. 12.

Explanation of symbols

1: Steel strip 2 (2 _A , 2 _B ): Tab plate 10: Pretreatment unit 20: Welding device unit 21: Welding torch 22: Jig 30 for assembling the steel strip and tab plate 30: Heating device unit 31: Conductivity Base 32: Electrode 33: Electrode lifting / lowering drive device 40: Post-process part C1: Strip steel coil C2: Strip steel winding coil D _A : Fracture mark (defect) of butt weld
D _B: butt weld fracture trace Bari
D _C: butt crack the weld L: Welding line (butt portion)
W: Butt weld

Claims (2)

  The end edges of the steel strips are abutted on the steel strip transfer line, and the tab plate is brought into contact with the left and right side edges of the steel strip with the butted portion sandwiched between them. A method for forming a butt joint in which a butt portion is welded with the plate surface of the other tab plate as a welding end point, and after welding, the tab plate welded to the edge of the butt weld portion is separated from the strip steel The butt weld of the steel strip and the tab plate are pre-annealed by heating and air cooling, and the tab plate is removed from the steel strip while the welded portion of the tab plate is maintained in a soft state during the temperature lowering process. A method for forming a butt-weld joint for strip steel, characterized in that the butt-welded portion is annealed after separating and separating the tab plate.   A steel strip butt welding apparatus, and a steel strip in which a resistance heating device including a conductive base plate for heat-treating a butt weld and an electrode controlled to be lifted and lowered with respect to the conductive base plate is disposed. The steel strip is fed from the steel strip coil to the butt joint forming line, butt welding of the steel strip is performed with a butt welding device, and the steel strip and tab plate are connected to the conductive base plate and electrode in the resistance heating device. The tab plate is separated from the steel strip in the temperature-decreasing process of the pre-annealing process in which the electrode is retracted and air-cooled with the electrode heated and heated, and after separation of the tab plate, the steel strip is again attached to the conductive base plate. The method for forming a butt weld joint for a steel strip according to claim 1, wherein the butt weld is annealed by clamping between the electrodes.

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