JPH08281479A - Production of flux cored wire for welding - Google Patents

Abstract

PURPOSE: To obtain a flux cored wire for welding which has high productivity without disconnection even if high-speed drawing is executed in the stage of a small diameter. CONSTITUTION: A flux composed of ferromagnetic raw material powder and weakly magnetic raw material powder at a specific compounding ratio is used as the basic prescription for the flux in this process for producing the flux cored wire for welding by supplying the flux to a tubular body during the course of forming metallic band steel to the tubular shape and joining the butt parts of the tubular body by high-frequency welding, then reducing the diameter. The flux is the plural divided prescription fluxes formed by at least bisecting this basic prescription to the first kind divided prescription flux 5 compounded with the weakly magnetic raw material powder and the second kind divided prescription flux 6 compounded with the ferromagnetic raw material powder. The first kind divided prescription flux 5 is supplied to the upper layer side of the tubular body 3 and the second kind divided prescription flux 6 to the lower layer side of the tubular body 3. At least the second kind divided prescription flux 6 is pellets. In addition, iron oxide in the form of superfine powder of a grain size of <=1.0μm is incorporated into the second kind divided prescription flux 6 at 0.2 to 2.0% of the total weight of the filled flux.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flux-cored wire for welding, which is widely used in welded structures such as ships, steel frames and bridges.

[0002]

2. Description of the Related Art In recent years, gas shielded arc welding using a flux-cored wire for the construction of various welded structures has been remarkably popular. This is because of the effect of the flux filled in the steel outer shell, the arc is stable, there is little spatter, the metal does not sag even in the vertical, upward, horizontal, etc. welding positions, and it is easy to weld and the bead appearance is good. This is because the melting speed of the wire is high and highly efficient welding can be performed.

Recently, with the spread of flux-cored wires, various proposals have been made to improve the productivity of the manufacturing method. For example, JP-A-60-2347
Japanese Patent Laid-Open No. 95 proposes the following manufacturing method. First, the strip steel is slitted with a required width, and the strip steel after slit is gradually formed from a U-shape to an O-shape by a forming roll. During this forming, the flux is supplied from the opening along the longitudinal direction of the U-shaped strip steel to the strip steel valley portion by the feeder. Then, at the same time as forming the O-shape, the opposite edge surfaces of the opening are joined by welding, and subsequently the diameter is reduced.
Further, after annealing if necessary, the tube filled with the flux is drawn to a predetermined wire diameter and then wound up to obtain a product.

As the welding method for the edge surface, high frequency welding such as high frequency induction welding method and high frequency resistance welding method is widely used. In all of these welding methods, when formed into a substantially O-shape, the edge surface of the opening is heated to the melting temperature by Joule heat generated by a high frequency current, and the opposing edge surfaces are pressed against each other by a pair of squeeze rolls.

By the way, when the pipe filled with the flux containing a large amount of metal powder and welded is rolled or reduced in diameter by wire drawing or the like, cracks may occur in the outer skin portion. The cause of this cracking is considered as follows. During welding, some of the flux particles are adsorbed on the opening edge surface of the tubular body.
That is, at the welding position, the opening edge of the tubular body becomes a magnetic pole due to the magnetic field generated by the welding current. Therefore, a part of the flux particles is adsorbed to the opening edge portion along with the ferromagnetic component of the flux particles. The flux particles adsorbed on these opening edge portions become inclusions in the welded joints and cause welding defects. Then, due to this welding defect, a crack is generated in the outer skin portion at the time of the diameter reduction, causing a wire breakage at the time of the subsequent diameter reduction, and lowering the productivity. Further, if a crack is generated in the outer skin portion when the diameter is reduced, the crack is directly carried to the product, that is, the flux-cored wire for welding even if the wire is not broken, and the welding workability is deteriorated.

To solve such a problem, Japanese Patent Laid-Open No. 60-23
Japanese Patent No. 4792 proposes that the upper layer is filled with only a non-magnetic material and the lower layer is filled with only a ferromagnetic material so that the powder of the ferromagnetic material in the lower layer does not fly up to reach the opening edge portion.

[0007]

However, when the flux as proposed above is divided into two layers and filled, even if cracking of the outer skin can be prevented, it is often the case in high-speed wire drawing in the small diameter stage. The disconnection becomes a problem.

Therefore, it is an object of the present invention to provide a method for manufacturing a flux-cored wire for welding which is free from disconnection and has high productivity even when high-speed wire drawing is performed in a small diameter stage.

[0009]

That is, the gist of the present invention is as follows.
In the method of manufacturing a flux-cored wire for welding, which comprises supplying a flux to a tubular body in the course of forming a metal strip into a tubular body, joining the abutting portions of the tubular body by high-frequency welding, and then reducing the diameter, the flux is a ferromagnetic raw material. The basic prescription is a flux composed of powder and weak magnetic raw material powder in a predetermined mixing ratio,
A plurality of divided prescription fluxes which are constituted by dividing the basic prescription into at least two types: a first type divided prescription flux mixed with a weak magnetic raw material powder and a second type divided prescription flux mixed with a ferromagnetic raw material powder, The second-type split prescription flux is supplied to the lower layer side of the tubular body, and the first-type split prescription flux is supplied to the upper layer side of the tubular body, and at least the second-type split prescription flux is a granulated product, and the second type split A method for producing a flux-cored wire for welding, characterized in that the prescription flux contains 0.2 to 2.0% of ultrafine powdery iron oxide having a particle size of 1.0 μm or less based on the total weight of the filling flux. .

[0010]

The present invention will be described in detail below. The present inventors investigated the cause of wire breakage of the flux-cored wire manufactured by the two-layer filling method. FIG. 2 schematically shows an observation result of a cross section in the longitudinal direction of the wire in the vicinity of a disconnection portion generated by high-speed wire drawing in a small diameter stage. In the outer skin portion near the disconnection portion, there was a portion with a small cross-sectional area (arrow in the figure), that is, a portion with a thin outer skin thickness, and in the flux portion 6, lumped flux 4 was observed. From the results of this investigation, the cause of the wire breakage that occurs in the small diameter stage is that the metal powder filled in the lower layer due to the progress of wire drawing is pressure-molded as the diameter is reduced by wire drawing and becomes a lump, and it bites in the outer skin. Put in. As a result, when the diameter is reduced thereafter, the outer skin portion is locally thinned to cause a wire breakage. The reason why the metal powder becomes agglomerate by pressure molding is that the powder particles have a force to bond with each other, and the oxide film is locally broken at the deformation interface between the particles, and the metal atoms between the metal atoms are broken. This is because binding occurs.

As a measure for preventing wire breakage in the small diameter stage, the present inventors have made it difficult for metal powders to be bonded together by pressure molding, that is, to prevent them from becoming lumps, and even if metal powders become lumps, wire drawing It is concluded that it is necessary that the bond can be easily released due to the progress of processing.

As a result of various examinations from the above viewpoints, the intended purpose was achieved by the above-mentioned constitution. The reasons for limiting the present invention will be described below. Usually, as the flux supplied into the tubular body, various raw material powders are selected according to the purpose of use of the flux-cored wire and used as it is, that is, non-granulated or granulated. The two-part split prescription flux must be a granulated product. The filling with the granulation flux is to fully exhibit the wire drawability improving effect of the ultrafine powdery iron oxide, which is a feature of the present invention. Further, when the granulated flux is filled, the component segregation is less than when the raw material powder having different particle diameters and specific gravities is blended as it is.

The flux used for the flux-cored wire for welding includes: -rutile sand, magnesia clinker, etc. as a slag forming agent-potassium titanate, sodium silicate, etc. as an arc stabilizer-Fe-Si, Fe as a deoxidizing agent and an alloying agent -Si-M
n, Al-Mg and other weak magnetic raw material powders are blended to further improve the welding speed,
Ferromagnetic material powder such as iron powder is mixed for adjusting the flux filling rate and welding workability. Normally, all the raw material powders are contained in the case of granulation, and all the raw material powders are mixed as a single powder in the case of non-granulation. Therefore, when granulating, iron powder, ferromagnetic material powder such as iron alloy constitutes flux particles together with other weak magnetic material powder, and when non-granulating, iron material, ferromagnetic material powder such as iron alloy, etc. It is blended as it is. That is, there is a sufficient risk that the flux particles will be magnetically attached to the opening edge surface which is poled at the time of high-frequency welding in both cases of granulated and non-granulated flux. Due to the nature of the flux particles themselves that are easily affected by the magnetic field, the basic prescription is divided into a ferromagnetic raw material powder and a weak magnetic raw material powder, and the ferromagnetic raw material powder as the second type divided prescription is provided on the lower side of the tubular body. Is supplied, and the weak magnetic raw material powder is supplied to the upper layer side as a first type divided prescription. This reduces the magnetic susceptibility of the flux located on the upper layer side, which is easily affected by the magnetic field, and suppresses the soaring of the ferromagnetic raw material powder located on the lower layer side due to the magnetic field by shielding the type 1 split prescription flux on the upper layer side. .

FIG. 3 shows a state immediately after the flux is supplied, in which the lower layer side is the second type divided prescription flux 6 containing the ferromagnetic raw material powder, and the upper layer side is the first mixture containing the weak magnetic raw material powder.
The seed division prescription flux 5 is supplied in a substantially layered manner.
Therefore, even when a flux containing a relatively large amount of iron powder, which is a ferromagnetic raw material powder, is supplied to the tubular body, the flux particles do not become magnetically attached to the opening edge surface of the tubular body that is magnetically poled during high frequency welding.

FIG. 1 is a diagram schematically showing a state in which ultrafine powdery iron oxide is adhered to the surface of the granulated flux of the second type divided formulation filled in the lower layer side. In some cases, the ultrafine powdery iron oxide 2 is scattered on the surface of the granulated flux particles 1, or the ultrafine powdery iron oxide covers the entire surface thinly.
In the case of the granulation flux, it is easy to uniformly distribute the ultrafine powdery iron oxide.

Due to the action of the ultrafine powdery iron oxide adhering to the surface of the granulation flux, the binding of the metal powders is less likely to occur. Further, since the ultrafine powdery iron oxide exists between the metal powders, the binding force between the metal powders can be reduced.

In the present invention, the particle size of the ultrafine powdery iron oxide is limited to 1.0 μm or less. The reason is that the finer the powder, the easier it is to adhere to the surface of the granulating flux, and even a small amount effectively prevents the disconnection due to the agglomeration of the metal powder. If the particle size is coarser than 1.0 μm,
It is difficult to adhere to the surface of the granulated flux, and it becomes easy to separate before the flux is supplied, so that the above effects cannot be sufficiently exhibited. Regarding the content of ultrafine powdery iron oxide, if the content is less than 0.2% with respect to the total weight of the filling flux, the above effect cannot be obtained, and if it exceeds 2.0%, the welding performance is adversely affected.

As a method for adhering the ultrafine powdery iron oxide to the surface of the granulation flux, it is sufficient to mix it with the second type divided prescription flux, or after wet granulation, the second type in a semi-dried state. It may be mixed with the divided prescription flux and attached.

[0019]

EXAMPLES The effects of the present invention will be more specifically described below with reference to examples. Shown in Table 3 on the lower layer side so that the basic prescription shown in Table 1 is obtained at the stage of forming a U-shaped strip steel (SPHC, C = 0.05%) with a plate thickness of 2.0 mm and a width of 75.0 mm. The first-class split prescription flux shown in Table 2 is shown on the upper layer side.
A flux-filled tube (filling rate 15.5%) was supplied by supplying the seed-divided prescription flux, followed by rolling and drawing to reduce the diameter (final linear velocity 1100 m / min) to make a flux-cored wire as a prototype (wire diameter 1.2 mm). Seam welding was performed by high frequency induction welding, and intermediate annealing for stress relief was performed at the diameter reduction stage.

The ultra-fine powdery iron oxide was prepared by mixing both the second-class split prescription flux on the lower layer side which had been granulated and dried (105 ° C.) and the ultra-fine powdery iron oxide in the ratio shown in Table 4. It was put into a machine and mixed.

For each prototype wire, 270 A-26
V, CO ₂ gas flow rate 20 l / min, wire protrusion length 25
A welding workability test (plate thickness 12 mm, T-shaped fillet improvement welding) was performed under welding conditions of mm.

Table 4 collectively shows the occurrence of wire breakage of the trial wire and the results of the welding test. Test No. Nos. 1 to 4 were according to the present invention, and there was no disconnection even in high-speed wire drawing, and welding workability was good. Test No. No. 5 was a case in which no ultrafine powdery iron oxide was contained, and because wire breakage occurred frequently, welding was stopped. Test No. When the particle size of the ultrafine powdery iron oxide is too large, the test No. 6 was used. No. 7 was a case where the content of the ultrafine powdery iron oxide was too small, and disconnection occurred in each case. Test No. No. 8 was a case where the content of ultrafine powdery iron oxide was too large, and although wire breakage did not occur, welding workability deteriorated.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

As described above, according to the present invention, in the production of a welding flux-cored wire, it is possible to prevent the cracking of the outer skin portion due to the rising of the powder of the ferromagnetic material, and to cause a problem in the case of the high-speed wire drawing. It is possible to provide a method for manufacturing a flux-cored wire for welding which has high productivity and which is prevented from being broken.

[Brief description of drawings]

FIG. 1 is a schematic view showing an adhered state of ultrafine powdery iron oxide according to the present invention.

FIG. 2 is a cross-sectional view in the longitudinal direction of the flux-cored wire in the vicinity of the disconnection occurrence portion.

FIG. 3 is a cross-sectional shape of a flux-cored wire.

[Explanation of symbols]

 1 Granulation Flux 2 Ultrafine Powdered Iron Oxide 3 Metal Skin 4 Massive Flux 5 Type 1 Split Prescription Flux 6 Type 2 Split Prescription Flux

Claims (1)

[Claims] 1. A method for manufacturing a flux-cored wire for welding, wherein flux is supplied to a tubular body during forming of a metal strip into a tubular body, the abutting portions of the tubular body are joined by high frequency welding, and then the diameter is reduced. The flux has a basic prescription of a flux composed of a ferromagnetic raw material powder and a weak magnetic raw material powder in a predetermined mixing ratio, and the basic prescription comprises a first-class divided prescription flux containing a weak magnetic raw material powder and a ferromagnetic raw material powder. A plurality of divided prescription fluxes that are configured by dividing the compounded second type divided prescription flux into at least two, wherein the first type divided prescription flux is on the upper layer side of the tubular body, and the second type divided prescription flux of the tubular body is It is supplied to the lower layer side, and at least the second type divided prescription flux is a granulated product, and the second type divided prescription flux is filled with ultra-fine powdery iron oxide having a particle size of 1.0 μm or less. Scan the total weight for the 0.2 to 2.0%
A method of manufacturing a flux-cored wire for welding, characterized by containing it.