JPH0455797B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a flux-cored wire for welding galvanized steel, and particularly to steel whose surface is coated with zinc or an alloy containing zinc (hereinafter referred to as "galvanized steel").
That's what it means. This invention relates to a flux-cored wire that can minimize the occurrence of pores such as pits (pores appearing on the surface of the weld metal) and blowholes (pores existing inside the weld metal) during welding. (Prior Art) In recent years, the use of galvanized steel sheets has been rapidly expanding in the automobile industry and housing industry in order to improve the durability of steel sheets and steel materials from the viewpoint of corrosion prevention. In the automobile industry, the purpose is to improve the rust resistance against salt spraying as an antifreeze agent in cold regions such as North America, and in the housing industry, the purpose is to improve the rust resistance of lightweight steel-framed houses. Although galvanized steel sheets have these excellent properties, the problem is that their weldability (mainly porosity resistance and amount of spatter) is extremely poor compared to ordinary steel sheets that have not been surface treated. There is. Therefore, at present, low-speed welding (approximately 30 cm/min) is performed using coated arc welding rods or solid wire.
We are dealing with this mainly through construction techniques based on experience, such as welding with gaps between steel plates (gap of about 0.5 mm). (Problem to be Solved by the Invention) As described above, in conventional arc welding of galvanized steel sheets, a coated arc welding rod or solid wire is used, and low-speed welding or welding with gaps between the steel sheets is performed. Therefore, measures have been taken to deal with the occurrence of pores (pits, blowholes, etc.) and an increase in the amount of spatter. However, such construction is inefficient due to the slow welding speed, and defects such as burn-through and undercuts are likely to occur due to the gaps between the steel plates. On the other hand, increasing the welding speed and decreasing the gap between the steel plates,
This results in an increase in the number of pores and an increase in the amount of spatter.
The cause of this phenomenon, that is, the cause of the low weldability of galvanized steel sheets, is mainly due to the influence of zinc in the plating layer.
It has been pointed out in various studies. That is, when galvanized steel sheets are arc welded, many pores are generated in the weld metal due to zinc vapor decomposed and dissipated by arc heat, which may significantly deteriorate the mechanical properties of the zinc joint. In addition, with regard to welding workability, there is a problem in that the arc is disturbed by the influence of zinc vapor, increasing the amount of spatter generated, and the welding work efficiency is significantly reduced due to the removal work. Furthermore, there is also the problem that zinc turns into zinc oxide due to arc heat, increasing welding fume. The present invention has been made in view of the above situation, and it is possible to arc weld galvanized steel sheets at a higher welding speed than before, and even when the gaps between the steel sheets are small or non-existent, the weld metal can be welded. It is an object of the present invention to provide a flux-cored wire for arc welding galvanized steel sheets that has extremely few pores such as pits and blowholes, and also has a low amount of spatter in terms of welding workability. (Means for Solving the Problems) In order to achieve the above object, the present inventors first determined the amount of zinc in the plating layer (hereinafter referred to as "zinc basis weight") that affects the formation of pores (pits, blowholes, etc.).
and the influence of welding conditions was investigated. As a result, it was found that the amount of zinc vapor generated by arc heat and the difficulty of releasing zinc vapor from the molten metal into the atmosphere greatly influenced the number of pores. That is, when the amount of zinc per unit area is small, naturally the amount of zinc vapor generated is small, and the number of pores generated thereby is also small. In addition, if it is extremely difficult to release zinc vapor into the atmosphere, for example, if the viscosity or cooling rate of the molten metal is extremely high, and the generation, growth, and floating of zinc vapor in the molten metal is suppressed, pores may be The number of occurrences will decrease. On the other hand, when release to the atmosphere is extremely easy, for example, when the viscosity or cooling rate of the molten metal is very low, and zinc vapor in the molten metal grows, floats, and is easily released to the atmosphere, pores may The number of occurrences will decrease. In light of these phenomena, and as a result of further intensive research, we determined that the characteristics that the wire should possess were to reduce the depth of penetration in order to suppress the generation of zinc vapor. In order to facilitate the floating of zinc vapor in the molten metal, the stability of the arc (droplet transfer, number of short circuits, etc.) is improved to promote stirring of the molten pool. Slag generation is suppressed to facilitate release of zinc vapor from molten metal. To suppress vaporization of molten zinc, a component that forms a compound with zinc is added to the wire. In order to suppress the generation and growth of zinc vapor, the viscosity is increased by lowering the amount of oxygen in the molten metal or adding trace components. As a welding material, we found that it has excellent porosity (pits, blowholes) resistance, and has excellent spatter generation, arc stability, slag generation, speed appearance, etc. This has led to the invention of a wire for gas-shielded arc melting for galvanized steel sheets that can be suppressed within a problem-free range. That is, the wire for gas-shielded arc welding of galvanized steel sheets according to the present invention contains 65 to 90% Fe,
A flux containing 5 to 30% of a deoxidizing agent mainly composed of Si and Mn and 0.1 to 10% of an arc stabilizer is filled into a steel shell so that the flux rate is 10 to 35%. Wire, and C: 0.10 to 0.30 per total wire weight
%, P: 0.025 to 0.15% and Zr: 0.01 to 0.15% as essential components, and further Ti: 0.01 as necessary.
~0.15% and Nb: 0.01~0.15%, one or both of which are included as essential components. The present invention will be explained in more detail below. (1) Type of wire As shown in Figure 1, wire for gas-shielded arc welding of galvanized steel sheets must be flux-cored, which has a shallower penetration depth than solid wire, in order to suppress the generation of zinc vapor. Wire is suitable. In addition, in order to stir the molten pool and promote the floating and release of zinc vapor, as shown in Figure 1, arc stability (droplet transfer, number of short circuits, etc. ) Flux-cored wire is more suitable. Table 1 shows the results using a 1.2 mmφ solid wire (JISYGW12) and a metal flux-cored wire (JISYFW24), using shielding gas (100% CO ₂ , 20/min),
Thyristor controlled power supply, 120A x 17~18V x
Galvanized steel sheets with a zinc weight of 90/90 g/m ² and a thickness of 2.3 mm were welded under the welding conditions of 60 cm/min, overhang length 15 mm, and the lap fillet joint shape shown in Figure 2. This is an example of comparing the results (penetration depth, arc stability, porosity) between solid wire and flux-cored wire. Furthermore, in order to reduce the amount of slag generation and promote the release of zinc vapor from the molten pool to the atmosphere, metal flux-cored wire is preferable to titanium-based flux-cored wire, as shown in Figure 3. Are suitable. Here, Fig. 3 shows a solid wire (JISYGW12), a metal flux-cored wire (JISYFW24), and a titanium flux-cored wire (JISYFW24), each having a diameter of 1.2 mm.
2.0mmφ self-shielded wire (JISYFW11)
and 3.2mmφ coated arc welding rod (JISD4313)
For gas shielded arc welding, use shielding gas (100% CO ₂ , 20/min).
With a thyristor controlled power supply, welding conditions are as follows:
For 1.2mmφ wire, 120A×60cm/min, 2.0
200A x 60cm/min for mmφ wire, 100A/40cm/min for coated arc welding rod,
In both cases, under the conditions of the lap fillet joint shape shown in Fig. 2, the zinc weight is 90/90 g/m ² and the plate thickness.
This is an example of welding 2.3mm galvanized steel sheets and comparing the results (number of blowholes and pits). Therefore, in the present invention, a metal flux-cored wire is used as the wire. (2) Amount of Fe in the flux: 65-90% In order to have the characteristics of the metal flux-cored wire described above, first, the amount of iron powder in the flux must be 65-90%. If it is less than 65%, the amount of slag generated increases due to the increased content of deoxidizers, arc stabilizers, etc., and the release of zinc vapor to the atmosphere is hindered, making it easy for pores to occur. Moreover, if it exceeds 90%, the content of deoxidizing agent or arc stabilizer will be insufficient, and the viscosity of molten metal will decrease, and the stability of arc and melt transfer will decrease, resulting in pores (pits, blowholes) and The amount of spatter generated increases. Therefore, iron powder is 65-90% in the flux.
shall be contained. (3) Deoxidizing agent in flux: 5 to 30% Adjusts the viscosity of molten metal and the amount of slag generated to control the growth, floating, and release of zinc vapor to the atmosphere, and removes pores (pits, blowholes). In order to control the occurrence of
In order to manage mechanical performance such as toughness within a range that does not cause any practical problems, a deoxidizing agent is added to the flux.
Contain 30%. Note that Si and Mn are mainly used as deoxidizers, but there are no particular restrictions. However, the content of deoxidizer in the flux is 5
If it is less than %, the viscosity of the molten metal decreases due to an increase in the amount of oxygen in the molten metal, and the number of pores (pits, blowholes) increases. Additionally, when the content is extremely low, the viscosity of the molten metal becomes extremely low, making it easier for zinc vapor to float to the surface, reducing the number of pores (blowholes), but also reducing the viscosity of the droplets. Therefore, during or after transferring from the wire to the molten pool, the droplets tend to scatter due to the influence of zinc vapor, increasing the amount of spatter. In addition, poor speed appearance and decreased toughness of weld metal due to insufficient deoxidation, or
Problems such as a decrease in the strength of the weld metal due to insufficient content of Si, Mn, etc. occur. On the other hand, when it exceeds 30%, the amount of slag generated increases, which prevents zinc vapor from being released into the atmosphere.
The number of pores (pits) increases. Furthermore, since the yield of Si and Mn in the solution metal increases, the strength becomes too high and the toughness decreases as a result. Therefore, the deoxidizing agent is present in the flux at a concentration of 5 to 30%.
%. Note that deoxidizers such as Si and Mn can be added alone to the flux, or as Fe-Si, Fe-
It may be added as a compound such as Mn, Fe-Si-Mn, Fe-Si-Zr. Furthermore, it may be added to the outer metal. (4) Arc stabilizer in flux: 0.1 to 10% Arc stabilizer is used to suppress arc instability caused by zinc vapor, reduce the amount of spatter, and stabilize the bead appearance and shape. The agent is contained in the flux in an amount of 0.1 to 10%.
As the arc stabilizer, alkali metals, lithium, or compounds thereof are mainly used, but there is no particular restriction. However, if the content of arc stabilizer in the flux is less than 0.1%, the arc becomes unstable.
The amount of spatter will increase, and the bead appearance and shape will become defective. Moreover, if it exceeds 10%, the amount of slag generated increases, which prevents zinc vapor from being released into the atmosphere and increases the number of pores (pits). Therefore, the arc stabilizer is present in the flux.
It shall be added in an amount of 0.1 to 10%. (5) Flux rate: 10-35% In order to obtain the characteristics of the metal flux-cored wire shown in (1) using a flux composed of the above components (2) to (4), the flux rate (wire Flux weight to weight ratio) from 10 to 35
It needs to be in %. If the flux rate is less than 10%, the characteristics of a flux-cored wire, such as shallower penetration depth and superior arc stability compared to solid wire, will decrease, which will prevent the formation of pores (pits and blowholes). Alternatively, the effect of reducing the amount of spatter generated is reduced. On the other hand, when the flux rate exceeds 35%, the content of deoxidizing agent and arc stabilizer increases, so the amount of slag generated increases, and the effect of suppressing the generation of pores (pits) decreases. Also, as the outer metal becomes thinner, the current density there increases,
The melting of the skin metal precedes the melting of the flux. This makes the arc and droplet transfer unstable. Therefore, the flux rate should be 10-35%. (6) Amount of C in the whole wire: 0.10 to 0.30% As is clear from Figure 4, carbon in the wire (in the sheath metal and/or flux) is caused by the generation of CO or CO ₂ gas in the molten metal. It has the effect of stirring the molten pool by causing a deoxidizing reaction and by stabilizing the transfer of droplets from the wire to the molten pool. This action promotes the floating of zinc vapor in the molten metal and its release into the atmosphere, reducing the number of pores (pits, blowholes).
Therefore, the amount of C in the entire wire is set to 0.10 to 0.30%. However, if the amount of C in the total wire is less than 0.10%, the above-mentioned stirring action of the molten pool will not be sufficient, and no effect will be seen in reducing the number of pores (pits, blowholes). In addition, if it exceeds 0.30%, the amount of CO or CO ₂ gas generated increases.
On the contrary, pores are generated due to them. Furthermore, the gas pressure generated in the droplets causes the droplets to explode, increasing the amount of spatter and fume generated. Therefore, the amount of C in the total wire is 0.10 to 0.30
%. Incidentally, carbon may be added to the flux as a single carbon, or may be added in the form of being contained in other raw materials such as Fe--Mn--C. Furthermore, it may be added to the outer metal. Here, Figure 4 shows 1.2mm with varying C amount.
Using φ metal flux-cored wire,
Using a shielding gas (100% CO ₂ , 20/min), a thyristor-controlled power supply, welding conditions of 120A x 60cm/min, and the lap fillet joint shape shown in Fig. Fabric weight 90/
This is an example in which galvanized steel plates of 90 g/m ² and 2.3 mm thickness were welded, and the results (number of blowholes and pits) were investigated in relation to the C content. (7) Amount of P in the whole wire: 0.025 to 0.15% As is clear from Figure 5, P in the wire is a stable compound with zinc (P-Zn system, P-Zn system) at temperatures above the melting point of zinc. -Fe series, etc.). Therefore, the amount of zinc vapor generated decreases,
The generation of pores (pits, blowholes) is suppressed. For that purpose, P in all wires is 0.025~
Contain 0.15%. However, the amount of P in the whole wire is less than 0.025% (usually 0.01-0.20% if not intentionally added)
(containing a certain amount), the amount of the compound formed with zinc is insufficient, so the effect of suppressing the generation of pores is extremely small. In addition, if it exceeds 0.15%, the amount of P that is concentrated during the final solidification of the molten metal will increase, making it more susceptible to cracking (especially hot cracking), and making it difficult to control welding conditions, development gaps (root gaps), etc. Depending on the conditions, cracks may occur. Therefore, the content of P in the total wire is
Set to 0.025-0.10%. Note that phosphorus may be added to the flux as a single phosphorus substance, or may be added in the form of being contained in other raw materials such as Fe-P. Furthermore, it may be added to the outer metal. Here, Fig. 5 shows 1.2 mm with varying P amount.
Using φ metal flux-cored wire,
Other conditions were the same as in the test shown in Figure 3.
This is an example in which the results (number of blowholes and pits) were investigated in relation to the amount of P. (8) Amount of Zr in the whole wire: 0.01~0.15% As is clear from Figure 6, Zr in the wire
Similarly to P, at temperatures above the melting point of zinc,
Generates stable compounds (Zr-Zn system, etc.) with zinc. Therefore, the amount of zinc vapor generated is reduced, and the generation of pores (pits, blowholes) is suppressed. Zr also has a deoxidizing effect, which lowers the amount of oxygen in the molten metal and increases its viscosity. Furthermore, Zr itself has the effect of increasing the viscosity of molten iron. Since the viscosity of the molten metal increases in this way, the growth of zinc vapor is suppressed and the number of pores (pits, blowholes) is reduced.
For this purpose, Zr is contained in the wire in an amount of 0.01 to 0.15%. However, if the amount of Zr in the entire wire is less than 0.01%, the amount of compounds with zinc produced is small, so the amount of zinc vapor generated hardly decreases. Also, the increase in viscosity of the molten metal is not sufficient to suppress the growth of zinc vapor. Therefore, stomata (pits,
Blowholes) are not effective for low frequencies. Moreover, if it exceeds 0.15%, slag due to Zr oxide increases, which prevents the release of zinc vapor from the molten metal to the atmosphere and increases the number of pores (pits). In addition, the diameter of the droplets increases due to their increased viscosity, and the transfer to the molten pool becomes unstable due to the influence of zinc vapor, and they tend to scatter as large spatters. In other words, it is not effective in reducing the number of pores (pits),
On the contrary, it reduces welding workability in terms of spatter generation and droplet transfer. From the above, Zr is contained in the entire wire in an amount of 0.01 to 0.15%. Note that Zr may be added alone to the flux, or may be added in the form of a compound such as Fe-Zr-Si, Fe-Zr, or other raw material. Furthermore, it may be added to the outer skin metal. Here, Figure 6 shows 1.2 mm with varying Zr content.
Using φ metal flux-cored wire,
Other conditions were the same as in the test shown in Figure 3.
The results (number of blowholes and pits)
This is an example investigated in relation to the Zr content. Regarding only reducing the number of pores (pits and blowholes), when the zinc weight is small (for example, 10 to 30 g/m ² ), the addition of C, P, and Zr alone is also effective. can get. However, if the zinc basis weight is large (for example, 60 to 90
g/m ² ), the effect is insufficient when added alone, but a practically sufficient effect is obtained by adding them in combination. (9) Ti amount in all wires: 0.01 to 0.15%, Nb in all wires: 0.01 to 0.15% Compared to the above-mentioned C-P-Zr system, it further improves porosity resistance and increases the strength of weld metal. When necessary, one or both of Ti and Nb are contained in an amount of 0.01 to 0.15% in the total wire and 0.01 to 0.15% in the total wire. Like Zr, both Ti and Nb have the effect of forming compounds with zinc and increasing the viscosity of molten metal, so they are effective in reducing the number of pores (pits, blowholes). However, when the content of Ti and Nb in the total wire is less than 0.01%, the amount of compounds formed with zinc is small, and the amount of zinc vapor generated is not sufficiently reduced. Also, the increase in viscosity of the molten metal is not sufficient to suppress the growth of zinc vapor. Therefore, no effect on reducing the number of pores (pits, blowholes) is observed. Additionally, if the Ti content exceeds 0.15%, Ti
The increase in slag due to oxides prevents the release of zinc vapor from the molten metal to the atmosphere, resulting in an increase in the number of pores (pits). In addition, since the amount of Ti oxide remaining in the weld metal increases,
Mechanical performance such as crack resistance of weld metal deteriorates. Further, Nb has the effect of increasing the strength of the weld metal, but if it is contained in an amount exceeding 0.15%, it becomes excessive and the mechanical performance such as elongation and toughness of the weld metal decreases. From the above, Ti and Nb can be contained in one or two types in the range of 0.01 to 0.15%, respectively, in the whole wire as necessary.
It shall contain seeds. Note that Ti and Nb may be added alone to the flux, or may be added in the form of a compound or other raw materials. Furthermore, it may be added to the outer shell metal. These elements (C, P, Zr, Ti, Nb), which are determined by the content in the entire wire, can be contained in one or both of the flux and the outer metal, and either can be contained. The flux-cored wire having the above composition is mainly used for mild steel and 50Kgf/mm ² class high tensile strength steel, but there are no particular restrictions on the steel type, and there are no restrictions on the cross-sectional shape of the wire. , various shapes shown in FIGS. 7A, B, C, D, etc. can be used. In addition, the wire diameter and shielding gas composition can be changed depending on the application: 0.8mmφ, 1.2mmφ, 1.4mmφ, 1.6mmφ.
Wire such as mmφ, 2.0mmφ, or 100% CO ₂ , Ar
- Can be arbitrarily determined from CO ₂ mixed gas, etc. Furthermore, although there are no particular restrictions on the welding power source, as shown in Figure 8, by using an inverter power source that is effective in maintaining arc stability, it is possible to improve porosity resistance and reduce the amount of spatter. In this respect, the effects of the present invention are further exhibited, which is preferable. Here, Fig. 8 uses a 1.2 mmφ metal flux-cored wire, shielding gas (100% CO ₂ , 80% Ar + 20% CO ₂ , 20/min), 120 A + 60 cm/min, Fig. 2. Under the overlap fillet joint conditions shown below, welded galvanized steel sheets with a zinc weight of 90/90 g/ ^m2 and a thickness of 2.3 mm using various power sources, and the results (number of blowholes and pits) This is an example of examining the relationship between the power supply type and the type of power supply. Next, examples of the present invention will be shown. (Example) Flux-cored wires having the compositions and flux rates shown in Tables 1 and 2 were manufactured. The wire diameter was 1.2 mmφ, and mild steel was used for the outer shell metal. Therefore, C, P, Zr, Ti, and Nb were mainly added and adjusted from flux. Also, Fe is iron powder,
An iron alloy of Si and Mn was used as the deoxidizing agent. Using these wires, a gas shielded arc welding test was conducted according to the following welding procedure. <Welding instructions> ●Wire: metal flux-cored wire,
1.2mmφ ●Shield gas: 100% CO ₂ , 20/min ●Steel plate: Zinc weight 90/90g/m ² , plate thickness 2.3mm ●Joint shape: Overlap fillet (see Figure 2) ●Welding conditions: 120A× 60cm/min, protrusion length 15
mm ●Power source: Thyristor controlled type The results of each welding test (number of pits, arc stability, spatter amount, slag amount, penetration depth, bead appearance, fume amount, cracking resistance, etc.) are also listed in each table. As is clear from each table, even at high welding speeds, all the examples of the present invention have extremely few pores such as pits in the weld metal, have good arc stability, good bead appearance, and have little spatter and slag. ,
Shows excellent welding workability.

【table】

【table】

[Table] (Effects of the invention) As detailed above, according to the present invention, when arc welding galvanized steel sheets with various zinc coating weights,
Even when welding speeds are higher than conventional ones and the gaps between steel plates are minute or non-existent, there are extremely few pores such as pits and blowholes in the weld metal.
Furthermore, excellent welding workability such as less spatter generation can be obtained.

[Brief explanation of drawings]

Figure 1 shows the penetration depth and arc stability in the case of gas-shielded arc welding using solid wire and metallic flux-cored wire. Figure 2 shows the joint shape and overlap fillet welding procedure, Figure 3 shows the relationship between various welding wires and penetration depth, and Figure 4 shows the relationship between the amount of C in the whole wire and the pores (pits, blowholes). ) Figure 5 is a diagram showing the relationship between the amount of P in all wires and the number of pores (pits, blowholes) generated, and Figure 6 is a diagram showing the relationship between the amount of Zr in all wires and the number of pores (pits, blowholes) generated.
Figure 7 A to D are diagrams showing examples of cross-sectional shapes of flux-cored wires, and Figure 8 shows the relationship between the number of blowholes (pits and blowholes) generated when using various power sources. It is a figure showing a number. 1... Test plate (galvanized steel plate), 2... Galvanized layer, 3... Torch, M... Shell metal, F...
...Flux.

Claims (1)

[Claims] 1% by weight (the same applies hereinafter), 65 to 90% Fe;
A flux-cored wire made by filling a steel shell with a flux containing 5-30% of a deoxidizing agent mainly composed of Si and Mn and 0.1-10% of an arc stabilizer so that the flux rate is 10-35%. And, per total wire weight, C: 0.10 to 0.30
%, P: 0.025 to 0.15%, and Zr: 0.01 to 0.15% as essential components. 2. The flux-cored wire further contains Ti: 0.01-0.15% and Nb: 0.01-0.01% based on the total weight of the wire.
The flux-cored wire according to claim 1, which contains 0.15% of one or two kinds as essential components.