JPH0525596B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention produces a wider galvanized steel sheet by butt-welding a plurality of galvanized steel sheets or steel strips, each of which is galvanized on at least one side, using a laser beam. or relating to a method of manufacturing steel strip.

[Conventional technology]

In the galvanized steel fabrication industry, the width of the steel sheets required for specific purposes, such as forming steel sheets by deep drawing, may be larger than can be processed in existing galvanizing plants. In that case, there is no choice but to butt weld two or more steel plates together. When such steel plates are manufactured by conventional butt welding, post-treatment of the weld seam (weld joint) is required. The reason for this is that the weld seam is not flush with the steel plate surface, making it unsuitable for secondary processing such as deep drawing, and the weld seam lacks corrosion resistance. Another problem with conventional methods is that the thickness of the weld seam is non-uniform. Direct deep drawing or press working of the steel sheet produced in this manner causes problems such as damage to the forming tool and inability to perform forming with the required precision.

In one known method for butt welding galvanized steel sheets, the weld seam is formed by electron beam welding with replenishment of filler metal (welding wire). In order to obtain quality suitable for secondary processing, it is necessary to level the thickness of the weld seam (to make it flat with the surrounding steel plate surface) by grinding. Furthermore, since the welding temperature of electron beam welding is high, the zinc that forms the corrosion-resistant film evaporates, impairing the corrosion resistance not only of the weld seam but also of a relatively wide area adjacent to the weld seam. Therefore, after welding is completed, it is necessary to apply a corrosion-resistant coating not only to the weld seam but also to the wide area where the galvanized film has been lost. Such measures are merely expedient and do not fully meet the needs of the fabrication industry for steel plates that are corrosion resistant over their entire surface (on one or both sides) and are suitable for deep drawing.

In addition, a method of butt welding galvanized steel plates or steel strips using a laser beam is known, and in this method, the cut surfaces that are approximately perpendicular to the plate surface are intentionally placed facing each other with a certain distance between them. As a result, the gap between the grooves into which the filler metal (welding wire) melts and enters is made equal (see European Patent Publications Nos. EP-A0098306 and EP-A0117, 751). This method has a feature that, compared to butt welding using an electron beam, the irradiation accuracy is higher due to the use of a laser beam. Taking advantage of this high irradiation accuracy, the laser beam is directly irradiated only on the welding wire (which may have a diameter larger or smaller than the welded joint). As a result, the steel plate serving as the base plate for welding is melted only by the welding heat of the molten welding wire. However, with this method, the weld seam that has lost its corrosion-resistant coating is formed as a relatively wide and raised weld seam, which must be machined to make it even with the steel plate surface, and ultimately requires corrosion-resistant treatment. The drawback was that it required additional treatment.

[Problem that the invention seeks to solve]

By butt welding two or more galvanized steel plates or steel strips, the present invention produces a galvanized steel plate or steel plate having a wider width, a flat surface, excellent deep drawability, and corrosion resistance at the weld seam. It is an object of the present invention to provide a method for manufacturing steel strip without a large increase in cost.

[Means for solving problems]

The above object, according to the present invention, is a method for producing a wider galvanized steel sheet or steel strip by butt welding a plurality of galvanized steel sheets or steel strips that are galvanized on at least one side using a laser beam. When cutting a galvanized steel sheet or steel strip as a starting material sheet to prepare a blank plate for welding, the height of the wave-like irregularities that inevitably exist on the cut surface is 0.04 mm or less, and the cut surfaces are cut together. The plates are cut so that only a very small hole remains when they are butted together, and almost perpendicular to the plate surfaces, and the blank plates are butted and held at the cut surfaces, and the gaps between the butted cut surfaces are cut. A laser beam having a focal spot with a diameter large enough to cover the welding zone but not exceeding 0.2 mm is applied to the welding zone consisting of the gap and the very narrow blank end zones on both sides. By irradiating, the galvanized film on the surface of the blank plate is evaporated and removed in the edge zone of the blank plate, and then the steel of the blank plate is melted to fill the gap, and a filler metal is used. This is achieved by a method for producing galvanized steel sheets or steel strips with excellent deep drawability, which is characterized by welding the blank sheets together without any process.

[Effect]

FIG. 3a shows two blank welding plates 30A and 30B cut to the required dimensions from a galvanized steel plate or steel strip that has been galvanized on both sides (or one side).
are held against each other with their cut surfaces 31A and 31B (the figure is a plan view seen from the direction of the plate surface of the raw plate). These cut surfaces 31A and 31B are generally not smooth in the strict sense, and inevitably have some degree of wavy unevenness as shown in the figure.

In the present invention, the cut surfaces 31A and 31B
The height of the unevenness on the wave that inevitably exists (height difference between adjacent peaks and valleys) is 0.04 mm or less, and the cut surface is 31A.
When and 31B are butted together, an extremely small hole is formed between both cut surfaces 31A and 31B.
Cut so that nothing remains.

The reason why the cut surfaces are defined in this way is to make the width of the space 32 between the butted cut surfaces 31A and 31B sufficiently narrow so as to satisfy the following (1) and (2). .

(1) Without supplying filler metal (welding wire),
The butt zone is filled with molten steel from the end zones of the blank sheet on both sides, so that the steel sheet surface and the weld seam can be substantially flattened, and thin and weak parts that deteriorate deep drawability are not generated.

(2) The width of the weld seam where the galvanized film has been lost is
It has a narrow width that can be provided with corrosion resistance by long-range corrosion protection from the galvanized coating on both sides.

Further, the reason why the cut surfaces 31A and 31B are made substantially perpendicular to the plate surfaces of the welding blanks 30A and 30B (the surface corresponding to the plane of the paper in FIG. 3a) is as follows.

When the laser beam is irradiated as shown in FIG. 3B, the zinc coating 36P on the irradiated side surface in the blank end zones 33A and 33B is directly hit by the laser beam and rapidly evaporated and removed. In the meantime, the temperature of the steel portion 37, which is the bare metal of the blank plates 30A and 30B, increases rapidly, and when the boiling point of zinc is reached, the zinc coating 36Q on the blank plate surface on the opposite side to the irradiation side evaporates. removed. Steel 37 has a melting point (Fe: 1536℃)
is much higher than the boiling point of zinc (Zn: 906° C.), so at the time the zinc coating 36Q on the back side evaporates, the underlying steel portion is still maintained in a solid state. After the front and back zinc coatings 36P and 36Q are completely evaporated and removed in this manner, the steel portion 37 begins to melt. This results in
It is possible to form a weld seam without zinc contamination from the plating film.

This effect can be obtained by making the cut surface approximately perpendicular to the surface of the blank. By making the cut surface substantially inclined with respect to the blank surface and making the groove V-shaped, the peripheral edge of the low-energy laser beam hits the low-melting point zinc coating on the irradiated side blank surface. At the same time, the high-energy laser beam core directly hits the steel base metal and melts it, which causes zinc to be mixed into the weld seam, weakening the weld seam, and forming the weld, especially deep drawing. It cannot withstand internal tensile, compressive and bending stress, and good deep drawability cannot be obtained.

The size of the focal spot of the laser beam was limited for the following reasons.

In order to fill the gap 32 between the abutted cut surfaces 31A and 31B without using filler metal, the base metal 37 of the blank plate is melted and supplied from both sides of the gap 32. There is a need. Therefore, the focal spot S of the laser beam L is between 〓3
2 and the raw plate end zones 33A and 33B on both sides thereof
It is necessary to have a size large enough to include the bonding zone 34 consisting of. On the other hand, the width of the zone in which the zinc coating is evaporated and removed by laser beam irradiation needs to be suppressed within a range in which corrosion resistance can be ensured by long-range corrosion resistance from the regions on both sides of which the zinc coating remains. For this purpose, it is necessary to limit the diameter of the focal spot of the laser beam to a range that does not exceed 0.2 mm at most.

For example, when the height of the wave-like unevenness on the cut surface is 0.04 mm, which is the upper limit of the specified range of the present invention, the width of the gap 32 is the maximum, which is 0.08 mm (=0.04×2). In this case, if a laser beam with a focal spot diameter D of 0.2 mm is used, which is the upper limit of the specified range of the present invention, then
The raw plate end zones 33A and 33 on both sides of the gap 32
Assuming that the laser beam hits B equally, both end bands 33A and 33B will be 0.06 mm (=(0.2-
0.08)/2) are irradiated with the laser beam.

In the end zones 33A and 33B that have been irradiated with the laser beam, the zinc coatings 36P and 36Q on the surface of the blank are evaporated and removed as described above, and then the steel that is the base metal of the blank is melted and the gap 32 is removed. Fill.

The width of the band at the end of the blank plate, where the zinc coating is evaporated and removed by laser beam irradiation and the steel ingot is melted, is filled with molten steel to make the weld seam as flat as possible (less thickness reduction relative to the blank plate). The width of the weld seam without a zinc coating should be set depending on the individual case so that a long-range corrosion resistance is effective.

According to the present invention, the weld seam is not only already substantially flattened with the surface of the steel plate in the as-welded state, but also has corrosion resistance. Therefore, there is no need for a step of flattening the weld seam by reworking after welding, and there is no need for a subsequent step of imparting corrosion resistance to the weld seam.

The amount of steel necessary to fill the gap that remains as an extremely small hole when the cut surfaces according to the invention are butted together is supplied from the edge zone of the blank plate adjacent to the gap, but the steel is supplied from the edge zone of the blank plate adjacent to the gap. galvanized steel sheet (steel strip)
The thickness of the weld seam is usually at least 10 times that of the base plate, so there is almost no thickness reduction in the weld seam compared to the base plate, and the weld seam can be made almost flat with respect to the base plate. It is therefore possible to directly deep draw or press the weld seam without the mechanical reworking previously required to flatten the weld seam. In addition, since the weld seam without zinc coating is very narrow, long-range corrosion resistance from adjacent areas is effective, so there is no practical disadvantage in terms of corrosion resistance compared to a steel plate fully coated with zinc coating. Not at all.

The advantage of the galvanized steel plate (steel strip) manufacturing industry according to the present invention is that, while suppressing the increase in cost, it is possible to use the galvanized steel plate (steel strip) with the existing galvanizing equipment, which reduces the strength and corrosion resistance of the weld seam part. It is possible to manufacture steel plates (steel strips) that are several times as wide as the conventional method.

In one embodiment of the present invention, the welding blank is cooled on both sides of the weld line in order to minimize the thermal influence of the laser beam on the zinc coating in the edge zone of the blank. This cooling can be performed, for example, by blowing cooling gas. A particularly effective cooling method is to tighten the entire length of the blank plate to be welded using a tightening jig made of a material with good thermal conductivity, such as copper, and to tighten the inside of this jig as appropriate. The purpose is to circulate the cooling medium to cool the jig itself. In order to effectively cool the surface of the blank and at the same time ensure sufficient flatness of the blank, it is best to tighten the blank at a distance of about 5 to 10 mm from the weld using a tightening jig. As a result, the raw steel melts only within the range of the laser beam focus spot, and the molten steel solidifies as soon as it leaves the laser beam focus spot.

Since it is necessary to prevent molten steel from flowing out from the portion that will become the welded joint, it is particularly important to cool the bottom surface of the blank plate well. A method to effectively prevent leakage is to strongly cool the lower surface side of the blank plate of the tightening jig.

The tightening jig on the bottom side of the blank plate for welding has a deep groove that straddles the part that will become the weld joint, and by blowing inert gas into this groove, the weld line can be made inert. It is advantageous to use a jig which can be maintained under an atmosphere of active gas. This not only prevents oxidation of the high-temperature parts of the blank plate for welding, but also assists in cooling the lower surface of the blank plate. Furthermore, if the inert gas supplied into the groove is pressurized, the effect of suppressing the outflow of molten steel as described above can be obtained.

The welding method of the present invention can be applied to welding blank plates of equal thickness and to welding blank plates of different thickness. When the thicknesses of the blank plates are different, especially when the thickness of the blank plates is 0.5 to 3.0 mm, the relative positions during welding should be as follows. In other words, the surface of the blank on the laser beam irradiation side (front surface) or the surface of the blank on the opposite side (back surface) is held so that it is almost flat, and/or the portion adjacent to the cut surface of the thicker blank sheet is held. The thickness is reduced by chamfering the excess material.

〔Example〕

In the typical embodiment shown in FIG. 1, galvanized steel sheets 1 and 2 are butt welded.
are held on the flat support surface 4 of the support base 3 which is fitted and fixed to the base 17, with the cut surfaces butted against each other. In the figure, both steel plates 1 and 2
The butted cut surfaces of the two are indicated by a common reference numeral 7. The cut surface 7 is substantially perpendicular to the plate surfaces of the steel plates 1 and 2. The support base 3 is provided with a groove 5 that is open on the support surface 4 side. The groove 5 has an elongated shape along the cut surface 7 extending perpendicularly to the plane of the drawing, and is shaped to straddle the cut surfaces 7 that are butted together. Steel plates 1 and 2 are pressed and fixed against support base 3 by tightening jigs 8 and 9, respectively. The support stand 3 and the tightening jigs 8 and 9 include
Holes 10-13 are provided for the flow of cooling medium. The inert gas introduced into the elongated groove 5 whose upper opening is closed by the steel plates 1 and 2 cools the jig and the steel plate and pressurizes the lower surface of the steel plate.

Next, referring also to FIG. 3, the butted cut surfaces 7 (31A and 31 in FIG. 3)
The laser gun 14 that irradiates the laser beam 15 (L in FIG. 3) onto the bonding zone (34 in FIG. 3) along the line B) is movable along the bonding zone 34. The laser beam 15 (or L) has a focal spot S with a maximum diameter D of 0.2 mm. The center of this focal spot S is aimed at the center of the width of the bonding zone 34, as shown in FIG.

The moving speed of the laser gun 14 when moving along the joining zone 34 including the cut surface 7 and the welding energy supplied from the laser beam 15 to the steel plate end zone (33A and 33B in FIG. 3) of the joining zone 34 must be set depending on the thickness of the steel plates 1 and 2. As an example, if galvanized steel plates 1 and 2 with a thickness of 0.8 mm are used and the distance from the water-cooled copper fastening jigs 8 and 9 to the center of the butt band 7 is 3 mm, the focal spot diameter of the laser beam is 0.2mm, which is the specified range of the present invention.
If it is below, the moving speed of the laser gun is 2m/
Setting it to min gives good results. The energy supplied to the steel plate end zones 33A and 33B in this case is approximately 375 J/cm.

The welded seam obtained in this way has no deterioration in terms of corrosion resistance and mechanical properties (elongation, strength), and the steel plate can be formed by deep drawing etc. without any problems at the welded seam. be able to.

In the typical embodiment shown in FIG. 2, the support base 3 is not integrated but is separated into two parts, left and right, and the cross section of the elongated groove 5 is in the shape of a funnel that is wide downward. This differs from the example shown in FIG. 1 in this respect. Groove 5
By having such a cross-sectional shape, it is possible to prevent splash from scattering toward the weld seam. The left and right support portions are each screwed to the base 17. The reason why the support base 3 is separated into left and right parts is to facilitate the manufacture of the support base 3 when the cross section of the groove 5 is shaped like a funnel with a wide bottom.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing a state in which butt welding is performed according to the method of the present invention, and FIG. A is a plan view seen from the board surface direction of the blank showing the vicinity and the focal spot of the laser beam in an enlarged manner, and b is a cross-sectional view taken along the line A-A including the diameter of the focal spot. 1, 2... Galvanized steel plate to be welded, 3...
Support stand, 4... Flat support surface of support stand 3, 5...
an elongated groove extending across and along the weld seam;
7... Each cut surface of the steel plates 1 and 2, 8, 9... Tightening jig, 10, 11... Holes provided in the support base 3 through which the cooling medium passes, 12, 13... Tightening jig 8 ,9
A hole through which a cooling medium passes, 14... Laser gun, 15... Laser beam, 17... Support stand 3
30A, 30B...Material plates for welding, 31A, 31B...Each cut surface of the raw plates 30A, 30B, 32...The space remaining between the cut surfaces 31A and 31B, 33A, 33B... End zones of the blank plates 30A and 30B that receive laser beam irradiation,
34... A bonding zone consisting of the gap 32 and the raw plate end zones on both sides thereof, 36P... Galvanized film on the raw plate surface on the side directly receiving laser beam irradiation, 3
6Q... Galvanized film on the surface of the raw plate opposite to 36P, 37... Steel base metal part of the blank plates 30A and 30B, L... Laser beam, S... Focus spot of laser beam L, D... Diameter of focal spot S.

Claims (1)

[Claims] 1. A method for producing a wider galvanized steel sheet or steel strip by butt welding a plurality of galvanized steel sheets or steel strips each having galvanized surfaces on at least one side using a laser beam, the starting material comprising: When cutting galvanized steel sheets or steel strips to prepare blank sheets 30A and 30B for welding, the height of wavy irregularities that inevitably exist on the cut surfaces 31A and 31B is 0.04 mm or less, and the cut surfaces 3
Cut the blank plates 30A, 30B so that only a very small hole (=32) remains when they are butted together, and approximately perpendicular to the plate surface, and then connect the raw plates 30A, 30B to the cut surfaces 31A,
31B, and a joining zone 34 consisting of the gap 32 between the butted cut surfaces 31A and 31B and very narrow blank end zones 33A and 33B on both sides thereof.
By irradiating the laser beam L having a focal spot S with a diameter D that is large enough to encompass the bonding zone 34 but not exceeding 0.2 mm, the element is bonded in the edge zones 33A and 33B of the blank. Board 30
Galvanized film 36P, 36 on the surface of A, 30B
After Q is evaporated and removed, the blank plates 30A, 30
Melt the steel 37 of B and fill the space 32,
A method for producing a galvanized steel sheet or steel strip with excellent deep drawability, characterized by welding the blank plates 30A and 30B together without using filler metal. 2. During welding by laser beam irradiation, the width of the zone affected by the heat of welding is 1 over the entire length of both sides of the welding line of the welding plates 30A and 30B.
The method according to claim 1, characterized in that the method is cooled to less than mm. 3. The method according to claim 1 or 2, wherein the welding blank plates 30A and 30B are cooled from both sides during welding by the laser beam irradiation. 4. A patent characterized in that during welding by the laser beam irradiation, the surface of the blank plates 30A, 30B on the opposite side to the side receiving the laser beam irradiation is maintained in a protective gas atmosphere in the area including the weld line. A method according to any one of claims 1 to 3. 5. Claims characterized in that during welding by the laser beam irradiation, the surface of the blank plates 30A, 30B on the side opposite to the side receiving the laser beam irradiation is pressurized with gas in a region including the weld line. The method according to any one of paragraphs 1 to 4. 6. Claims characterized in that during welding by the laser beam irradiation, the welding blank plates 30A, 30B are held in a predetermined position by a cooled tightening jig placed immediately near the welding line. The method according to any one of paragraphs 1 to 5.