JPH10272584A - Butt welding method of hot rolled billet - Google Patents

Abstract

(57) [Summary] [Problem] To prevent blow holes from occurring in a weld bead,
The penetration depth of the weld bead portion is made uniform, and a flat bottom is obtained without spiking or excessive penetration. A method for butt-welding a hot-rolled bar (S) with a laser beam (LB) is disclosed.
Titanium, one or more of manganese is 0.05 to 3
% While supplying a filler wire W of an iron-based base material containing% to the welded portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for butt welding hot rolled steel slabs such as sheet bars and slabs with a laser beam.

[0002]

2. Description of the Related Art A focused laser beam LB as shown in FIG.
Is irradiated to the material S to be welded, and the keyhole K, which is the region having the highest energy density, is used as a heat source, and scanning is performed by the laser beam LB which is a high energy beam. By scanning the keyhole K, which is a region where the metal has evaporated in a cylindrical shape, the peripheral molten region gradually solidifies with the passage of the laser beam LB, and a weld bead is formed.

[0003] In laser welding of steel materials, Al, S
Blowholes are less likely to occur in the case of a steel type containing a certain amount or more of a metal element having a deoxidizing effect such as i or Ti, but when the content of the deoxidizing agent is low, a blowhole is included in the welded portion. Sometimes. In particular, when welding a high-temperature material such as a hot-rolled line, an oxide scale adheres to the groove surface, and when this oxide scale is taken in and welded, a blowhole is generated in a weld bead. The mechanism of blowhole generation is that carbon monoxide, which is formed by combining oxygen contained in steel or in the scale attached to the steel surface with carbon in the steel, is generated in the melting process during welding, and is generated in the bead during solidification. It is captured. Blow hole B of this weld bead WB
Not only reduces the joining strength of hot rolled billet S,
As shown in FIG. 8, it is involved in increasing and decreasing the penetration depth d. When the carbon monoxide gas is generated, the molten portion is pushed in the depth direction, and the penetration depth d temporarily increases by Δd.

When welding is performed with a high-power laser of 25 kW or more, the size of the plasma becomes extremely large, and the variation rate of the penetration depth d is very large, 25 to 30%. Further, in laser welding of hot-rolled steel slabs in a hot-rolling line, since the hot-rolled steel slabs are originally at a high temperature of 900 ° C. or higher, the metal easily reaches the boiling point and becomes plasma by laser irradiation. The interaction between the laser beam and the laser-induced plasma is activated, and the plasma generation region becomes unstable by repeatedly increasing and contracting the plasma. As a result, spiking occurs frequently and the penetration depth variation increases. I do.

[0005] As described above, if the penetration depth increases or decreases, for example, when butt welding is performed after shear cutting in hot continuous rolling, it is extremely difficult to secure a joint area ratio aimed at not breaking during rolling. Have difficulty. In addition, in the case of groove butt welding, if the increase in the penetration depth due to spiking is too large, a so-called burn-through MD in which the molten metal flows downward as shown in FIG. May decrease. For this reason, a margin A is taken as shown in FIG. For example, when the thickness of the hot-rolled steel slab is 35 mm, the effective thickness of the butted portion is 25 mm, and when the penetration depth is 20 mm, the allowance A is 5 mm. Conventionally, the joint area ratio is not aimed at the edge of the effective butt thickness, but the laser power is reduced or the welding speed is reduced. To reduce the variation in

Assuming that the ratio of the penetration depth variation Bd and the average penetration depth d shown in FIG. 9 is a variation rate Bd / d,
In a normal laser welding method, the variation rate Bd / d
Is about 20%.

[0007]

SUMMARY OF THE INVENTION The present invention prevents the occurrence of blowholes in a weld bead, makes the penetration depth of the weld bead uniform, and has a flat weld bottom without spiking or excessive penetration. The task is to obtain a shape.

[0008]

SUMMARY OF THE INVENTION A butt-welding method for hot-rolled steel slabs according to the present invention is a method for butt-welding hot-rolled bars with a laser beam.
Titanium, one or more of manganese is 0.05 to 3
Laser welding is performed while supplying a filler wire of an iron-based base material containing% to the welded portion.

As a component of the filler metal, it is essential to generate an oxide that does not gasify, and it is necessary to include a metal having high reactivity with oxygen (high reducing power). For this reason, it is necessary that a simple substance of aluminum, silicon, titanium, or manganese having a high reducibility or a combination of two or more of these elements be contained in a certain amount or more. The lower limit of the content of these components is set to 0.05%,
If it is less than 5%, a sufficient reducing power cannot be obtained. Further, the upper limit is set to 3% because if it exceeds 3%, the brittleness in the welded portion becomes severe and the welded portion may be broken at the time of rolling in the subsequent process.

[0010] The filler metal supplied to the welded portion dissolves in the mixture of the molten work material, which is a component of the molten bead, and the scale. As a result, due to the reducing power of the metal element such as aluminum, the reaction between carbon and oxygen in the scale, which is the main cause of blowholes, is prevented, and the generation of carbon monoxide gas is eliminated. In addition, even if there is a gap due to the supply of the filler, for example, because the groove portion is uneven, filling the portion with metal does not cause poor penetration.

[0011] In the butt welding method of the hot rolled steel slab, the filler wire may be supplied into the laser-induced plasma in front of the laser beam irradiation part in the welding direction. The filler wire is continuously heated to the laser welding position by the laser beam and supplied to the weld in a molten state. In a usual laser welding, a laser beam is directly applied to a filler as a filler wire supply unit. However, if the filler wire is supplied not directly to the laser irradiation part but into the laser-induced plasma, the material to be welded can be melted with the energy of the plasma without losing the energy of the laser.

Further, in the butt welding method for hot-rolled steel slabs, the center of the laser-induced plasma may be shifted from the laser beam optical axis in the welding direction. When the generation region of the laser-induced plasma deviates from the irradiation position of the laser beam, the laser beam irradiates the welded portion out of a relatively high range of the electron density in the plasma. For this reason, the absorption amount of the laser beam to the plasma is reduced. Further, the energy density of the laser beam reaching the hot-rolled billet increases and becomes constant. As a result, the occurrence of extreme spiking is suppressed, the burn-through due to excessive penetration is eliminated, the penetration depth becomes uniform, and the molten bottom becomes flat. In addition, the laser energy efficiency is improved, the melting depth and the melting width are increased, and a stable joint can be formed. As a result, even if the joint area is increased and the butt line fluctuates, the tolerance of the gap is increased and a stable joint is formed, thereby increasing the joint accuracy and the pressure welding process after laser welding. Can be prevented from breaking.

[0013]

FIG. 1 shows an example of a laser butt welding apparatus embodying the present invention. FIG. 2 shows a welding head of the laser butt welding apparatus and its periphery.

The pail pack 11 includes a filler wire W
Are stored in a coil shape. Filler wire W
May be a solid type or a flux-containing type. The filler wire W is pulled out of the pail pack 11 by the wire feeder 21 and sent out to the wire supply nozzle 25 through the conduit 13. The leading end of the wire supply nozzle 25 has an entry-side straight portion 29 and a curved portion 30.
And the outlet side straight portion 31. Pale pack 1
1 between the first roller leveler 15 and the wire feeder 21.
And a second roller leveler 18. The laser beam LB is transmitted from the laser oscillator 35 to the welding head 39 via the transmission mirror 37. The lower end portion of the welding head has a center gas nozzle 41 for supplying a center gas G _C in the weld. A side gas nozzle 43 that supplies the side gas G _S to the welding portion is disposed to face the wire supply nozzle 25. Argon gas or helium gas is used as the center gas G _C and the side gas G _S.

In the apparatus constructed as described above, the roller shaft of the first roller leveler 15 and the second roller leveler 18
Is 90 °, the filler wire W sent from the wire feeder 21 is straightened so that the straightening directions are shifted from each other by 90 °. The filler wire W is plastically deformed when passing through the wire supply nozzle 25. The filler wire (wire protruding portion) W _E protruding from the wire supply nozzle 25 is removed from the curl and is in a state of being curved but almost linear. Wire protruding portion W _E is along the welding line towards the welding point, is substantially parallel to the supply to the surface of the hot rolled steel strip S.

As shown in FIG. 3, if the ratio between the penetration depth variation Bd and the average penetration depth d is defined as the variation Bd / d, the variation B
d / d is about 20%. Also, the variation rate Bd / d
Does not depend on the welding speed V as shown in FIG. As the welding speed V increases, the penetration depth decreases, and the variation Bd decreases at the same rate. When laser-induced plasma generated during welding is used as a secondary heat source for a laser beam, 20% of the variation rate Bd / d is reduced to about 15%.

Next, the filler supply speed will be described. FIG. 5 shows the relationship between the penetration rate of the penetration depth and the feed rate of the filler. As shown in FIG. 6, when the filler supply speed Vf is increased, the content of blowholes per unit length in the weld bead decreases. in this way,
The occurrence of blowholes in the weld bead is the variation rate Bd /
It can be seen that this is the cause of the increase in d. Therefore,
It is necessary to prevent the occurrence of blowholes in the weld bead in order to make the welding depth uniform. As is clear from FIG. 5, the variation rate Bd / d is such that the filler supply amount Vf is 2 m / mi.
n, the filler supply amount Vf is determined to be sufficient in the vicinity of the filler supply amount Vf. Therefore, the filler supply amount V
f is desirably 2 m / min or more.

When supplying the filler wire to the laser-induced plasma in front of the laser beam irradiation part in the welding direction, a curved nozzle may be used as shown in FIG. To weld the center of the laser induced plasma is shifted from the center of the laser beam in the welding direction, blowing side gas G _S from the side gas nozzle 43 shown in FIG. 2, to control the amount of displacement by the gas pressure. The displacement is about 0.5 to 1.5 times the reference plasma diameter determined by the laser output and beam diameter, and the type and flow rate of the shield gas.

According to the butt welding method of the present invention, in order to reduce the load of metal melting by laser, not all the necessary welding sections for hot billet welding are welded by laser, but only a part of the welding section. The present invention is also effective for tack welding by laser, which takes the form of pressure welding by subsequent rolling.

[0020]

EXAMPLE While a center gas (helium) was sprayed, a steel material at about 1000 ° C. was butt-welded with a 45 kW carbon dioxide laser. The welding speed V was 3 m / min. Ti
A filler wire containing 3% was used, and the filler supply speed was 4 m / min. At this time, the variation rate Bd / d was reduced from about 20% when no filler was supplied to about 10%. Also, there is no molten metal burnout at the butt weld,
There was no decrease in the bonding area ratio.

[0021]

According to the present invention, it is possible to prevent the occurrence of blowholes in a weld bead, to make the penetration depth of a weld bead uniform, and to obtain a flat bead shape without spiking or excessive penetration. Can be. As a result, a sound butt weld is obtained, and the joining strength is improved.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an example of a laser butt welding apparatus for performing a butt welding method of the present invention.

FIG. 2 is a drawing showing a welding head of the laser butt welding device and its periphery.

FIG. 3 is a drawing for explaining a definition of a variation rate of a penetration depth.

FIG. 4 is a graph showing an example of a relationship between a welding speed and a variation rate of a penetration depth.

FIG. 5 is a graph showing a relationship between a filler supply speed and a penetration depth variation rate.

FIG. 6 is a graph showing a relationship between a filler supply speed and the number of blowholes generated per unit length in a weld bead.

FIG. 7 is a diagram illustrating a general method of laser welding.

FIG. 8 is a view for explaining an increase in penetration depth due to a blow hole by a conventional laser welding method.

FIG. 9 is a view for explaining an increase and a decrease in penetration depth by a conventional laser welding method.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 Pail pack 13 Conduit 15 First roller leveler 18 Second roller leveler 21 Wire feeder 25 Wire supply nozzle 29 Incoming linear part 30 Curved part 31 Outgoing linear part 35 Laser oscillator 39 Welding head 41 Center gas supply nozzle 43 Side gas supply nozzle LB the laser beam G _C center gas G _S side gas P laser induced plasma W filler wire S hot rolled steel strip (workpieces)

Continued on front page (72) Inventor Kazuhiro Nishiyama 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (3)

[Claims] 1. A method for butt-welding hot rolled bars with a laser beam, wherein a filler wire of an iron base material containing 0.05 to 3% of one or more of aluminum, silicon, titanium and manganese is provided. A butt welding method for hot rolled steel slab that performs laser welding while supplying to the weld. 2. The method for butt welding hot-rolled steel slabs according to claim 1, wherein said filler wire is supplied into the laser-induced plasma in front of the laser beam irradiation part in the welding direction. 3. The butt welding method for a hot-rolled steel slab according to claim 1, wherein the welding is performed with the center of the laser-induced plasma shifted from the optical axis of the laser beam in the welding direction.