JPH07164184A - Flux cored wire for gas shielded arc welding - Google Patents

Abstract

PURPOSE:To provide the flux cored wire for gas shielded arc welding which is improved in low-temp. toughness by assuring good welding workability, drastically decreasing the amt. of the oxygen in weld metal and precipitating a large amt. of Ti oxides constituting the nuclei for forming intra-granular ferrite. CONSTITUTION:This flux cored wire contains, by weight % of the total weight of the wire, 4.0 to 7.0% TiO2, 0.2 to 1.6% Si, 1.8 to 2.4% Mn, 0.3 to 0.5% Mg, 0.04 to 0.06% Ti, 0.006 to 0.012% B and <=8.0% oxide (including TiO2), and further, contains 0.03 to 0.06% C and 0.3 to 0.5% Ni at need in the flux filled in the wire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux-cored wire for gas shielded arc welding, which has good welding workability and can obtain a weld metal having excellent low temperature toughness.

[0002]

Flux-cored wire for gas shield arc welding, which uses a titania-based flux as a filler and a single or mixed gas such as carbon dioxide, argon, helium, etc. as a shield gas, has an excellent bead appearance and bead. It is widely used for welding structures such as mild steel and high-strength steel of 50 kg class because it gives a shape and improves workability and work efficiency. However, the biggest drawback of the titania-based flux is that the amount of oxygen in the weld metal is large and the low temperature toughness is low.

In Japanese Patent Publication No. 56-6840,
Although Ti and B were added to the titania-based flux to improve toughness, good toughness was not obtained at -40 ° C. Further, as a method of improving the low temperature toughness, which is a drawback thereof, while maintaining the characteristics of the titania-based flux-cored wire, in JP-B-59-44159, the amount of oxygen in the weld metal, which has been about 700 to 900 ppm, is conventionally used. , Ti, and B were added together to reduce the low temperature toughness to 500 ppm or less, but good toughness was not obtained at -40 ° C.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to secure good welding workability, which is a characteristic of titania-based flux, and to secure low temperature toughness in a lower temperature range. , Mg, Ti, B, TiO ₂ , the amount of oxides, and C and Ni, drastically reduced the oxygen content in the weld metal, which was the greatest drawback of the titania-based flux. By precipitating a large amount of Ti oxide, which is a generation nucleus, to improve the low temperature toughness, eliminate the defects of the conventional wire, and provide a flux-cored wire that can be applied to a wider range of fields.

[0005]

Means for Solving the Problems The present invention is to solve the above problems, and in a flux-cored wire for gas shield arc welding, comprising a steel shell filled with flux, the total weight of the wire in the filled flux is To% by weight
_{In, TiO 2: 4.0~7.0%, Si} : 0.2~1.
6%, Mn: 1.8 to 2.4%, Mg: 0.3 to 0.5
%, Ti: 0.04 to 0.06%, B: 0.006 to
A flux-cored wire for gas shield arc welding, which contains 0.012% and oxide: 8.0% or less (including TiO ₂ ). Also here,
The filling flux further contains C: 0.03 to 0.06% by weight based on the total weight of the wire, and the filling flux further contains Ni: 0 by weight% based on the total weight of the wire. It is also characterized by containing 0.3 to 0.5%.

[0006]

As described above, the titania-based flux-cored wire has the greatest feature in that it has excellent welding workability. However, Ti and B, which are simply effective in forming intragranular ferrite in the conventional wire composition, are used. Even with the combined addition, the amount of oxygen in the weld metal was not reduced, a large amount of intragranular ferrite was not formed, and grain boundary ferrite and lath-like bainite structure were formed, so the low temperature toughness could not be improved. Therefore, the present inventors further conducted experiments and found the following facts.

(1) The generation nucleus of intragranular ferrite is Ti oxide.

(2) The Ti oxide, which is the nuclei for formation, is reduced and formed by the deoxidizing agent added with TiO ₂ which is the main component of the titania-based flux when the molten pool is formed.
i is oxidized again into Ti oxide in the solidification process. The oxidized Ti oxide and the remaining Si and Mn are solidified during the redox reaction, and Si and Mn are present in the Ti oxide in a pierced form.

(3) Ti oxide that does not serve as a nucleus for forming intragranular ferrite has the same TiO ₂ content as the nucleus for forming intragranular ferrite.
Are reduced to Ti to form Ti oxide. However, it is a substance solidified during the redox reaction with Al remaining after the formation of Ti oxide, and a large amount of Al is present in the Ti oxide. Further, in the Ti oxide having a form in which Al is stuck, the Ti oxide becomes coarse.

(4) Al, which is a strong deoxidizer, is not added to the wire.
When an experiment was performed to add Al in the range of 0.12%,
As the addition amount increases, a large complex oxide is formed and the toughness deteriorates.

(5) When the deoxidizing agent is insufficient, B is generated in the coagulation process.
Is consumed by oxidation, the amount of free B that suppresses the generation of grain boundary ferrite decreases, and grain boundary ferrite is generated.

Therefore, in order to reduce the amount of oxygen in the weld metal in order to improve the low temperature toughness and generate a large amount of intragranular ferrite to achieve high toughness, the oxide serving as the oxygen source is limited. The amount of TiO ₂ that is a source of Ti oxide that serves as a generation nucleus of intragranular ferrite is made appropriate, and the deoxidizer S
It was found that proper addition of i, Mn, Mg and Ti is important. This reduces the amount of oxygen in the weld metal,
We succeeded in improving the low temperature toughness by producing a large amount of intragranular ferrite. The reasons for limiting the components in the present invention will be described below.

TiO ₂ : 4.0-7.0% TiO ₂ is a main component of the titania-based flux-cored wire and exhibits properties as a slag forming agent and an arc stabilizer for welding beads. In addition, the Ti oxide, which serves as the nuclei for the generation of intragranular ferrite, is generated by the reduction of TiO ₂ during the formation of the molten pool, and the generated Ti is oxidized again during the solidification process.
It is an oxide. Further, a complex oxide is formed with the oxidized Ti oxide and the remaining deoxidizing agent (Mn, Si). If a certain amount of this Ti oxide is secured, an intragranular ferrite structure with high toughness is obtained, but if it is less than 4.0% with respect to the total weight of the wire, an effective Ti oxide cannot be secured and grain boundary ferrite is formed. Since it is generated, high toughness cannot be obtained. Further, if it exceeds 7.0%, the amount of oxygen increases in the weld metal and the toughness decreases, so that TiO ₂ is 4.0 to 7.0.
%.

Si: 0.2-0.6% Used as a deoxidizing agent and effective in reducing the oxygen content of the weld metal. However, if it is less than 0.2%, deoxidation is insufficient and blowholes are generated, and if it exceeds 0.6%, toughness decreases, so the range was made 0.2 to 0.6%.

Mn: 1.8 to 2.4% It is effective in promoting deoxidation and improving the fluidity of the molten metal, and also in improving the strength. further,
Helps to form intragranular ferrite for structural control. 1.
If it is less than 8%, a large amount of grain boundary ferrite is generated and the toughness deteriorates. On the other hand, if it is 2.4% or more, lath-like bainite is formed and the toughness deteriorates, so the content was made 1.8 to 2.4%.

Mg: 0.3-0.5% Mg reacts with oxygen in a high temperature arc, and a deoxidation reaction is performed at the stage of droplets at the tip of the wire. As a result, the deoxidation product does not remain in the molten pool, and further, it assists the deoxidation reaction of Si and Mn that react in the molten pool, and is effective in reducing the oxygen content of the weld metal. However, if it is less than 0.3%, the above effect is insufficient, and if it exceeds 0.5%, the arc length becomes excessive and the molten metal hangs down in vertical welding, so that bead formation becomes impossible. It was set to 0.5%.

Ti: 0.04 to 0.06% Ti is a strong deoxidizer and suppresses the oxidative consumption of the weld metal.
Further, since TiN is formed and N is fixed, B is a component necessary for preventing B from becoming BN and ensuring free B that suppresses the generation of grain boundary ferrite at the γ grain boundary. However, if it is less than 0.04%, most of it is consumed by oxidation and TiN cannot be formed in the weld metal, so grain boundary ferrite cannot be suppressed, a large amount of grain boundary ferrite is generated, and toughness deteriorates. Further, if it exceeds 0.06%, TiC is formed and the weld metal is hardened, so that the toughness deteriorates. Therefore, Ti is set to 0.04 to 0.06%.

B: 0.006 to 0.012% B has the effect of suppressing the generation of grain boundary ferrite growing from the γ grain boundary by making it free B in the γ grain boundary, and assisting the generation of intragranular ferrite. is there. However, 0.006
If it is less than%, there is no effect of suppressing the grain boundary ferrite and no effect of improving the toughness. If it exceeds 0.012%, carbides are formed and the toughness deteriorates, so 0.006 to 0.012%
And

Oxide: 8.0% or less In the present invention, as a slag forming agent, in addition to TiO ₂ , Si
O ₂ , FeO, Al ₂ O ₃ , ZrO ₂ , Na ₂ O, K ₂
O oxides can be used together, but if the total addition of oxides exceeds 8.0%, the amount of slag produced is increased and slag entrainment easily occurs, and the amount of oxygen in the weld metal is increased. In order to deteriorate the toughness, the amount of oxide added was set to 8.0% or less.

C: 0.03 to 0.06% C is preferably added for strength adjustment. If the addition amount is less than 0.03%, the strength cannot be obtained, and a large amount of grain boundary ferrite is generated to deteriorate the toughness. Also, 0.
If it exceeds 06%, carbides are formed and hardened, and a lath-like bainite structure is formed to deteriorate toughness.
It was set to 03 to 0.06%.

Ni: 0.3 to 0.5% Ni is preferably added because it forms a solid solution in the matrix to obtain high toughness. However, if it is less than 0.3%, there is no effect, and if it exceeds 0.5%, hot cracking tends to occur, so the content was made 0.3 to 0.5%.

As the steel shell, cold rolled steel or hot rolled steel having good deep drawability is used from the viewpoint of filling workability. The filling rate of the flux is not particularly limited, but considering wire drawability, it is 10 to 30 with respect to the wire weight.
The range of% is most suitable. There is no limitation on the cross-sectional shape of the wire, and a relatively simple cylindrical shape is preferable for a small diameter of 2.0 mm or less, and a hoop for a large diameter wire of about 2.4 to 3.2 mm. It is common for the structure to be complicatedly folded inside. It is also effective to apply a plating treatment such as Cu to the seamless wire. Further, the steel type to be welded can be applied to the welding of low temperature steel.

[0023]

EXAMPLES Table 1 shows the composition of the wire, and Table 2 shows the test results. In Tables 1 and 2, No. 1 to 8 are comparative examples,
No. 9 to 18 are examples of the wire of the present invention. In each case, a wire finished with a diameter of 1.2 mm using a mild steel outer shell was used to prepare a weld metal according to JIS Z3313, and a tensile test and an impact test were performed. The welding conditions are direct current reverse polarity, welding current: 270 A, arc voltage: 27 V, welding speed: 25 cm / min, shielding gas: Ar-20%.
CO ₂ 25 liter / min, distance between chip and base metal: 20 m
m, and the base material is JIS G3106 with a plate thickness of 20 mm.
The SM490B stacking method is 6 layers 12 passes.

[0024]

[Table 1]

[0025]

[Table 2]

As is clear from the test results in Table 2, No. No. 1 had a small amount of TiO ₂ and had poor slag encapsulation. Furthermore, since the amount of B is small, the generation of intragranular ferrite is small and the toughness is poor. No. No. 2 has a large amount of TiO ₂ and oxides, and does not contain Ti as a deoxidizer, and therefore has a large amount of oxygen in the deposited metal and is inferior in toughness.

No. In No. 3, since the addition amount of Si, which is a deoxidizing agent, is small and Mg is not added, the deoxidizing power is lowered, the amount of oxygen in the deposited metal is large, and the toughness is poor. No. 4 is Si
However, good toughness was not obtained due to the formation of nitrides and carbides. No. In No. 5, an excessive amount of Ti was added to form carbides, and good toughness was not obtained.

No. In No. 6, since Ti was not added, TiN was not generated and BN was generated, and free B that suppresses the grain boundary ferrite was not formed at the γ grain boundary, so that a large amount of grain boundary ferrite was generated and the toughness was deteriorated. Furthermore, M
Since a large amount of n was added, over-deoxidation occurred and pits and blow holes were generated. No. In No. 7, since the addition amount of Mg was small, deoxidation was insufficient and the amount of oxygen in the deposited metal was large, so that good toughness was not obtained. No. In No. 8, since the amount of Mg added was large, the arc length became long, the molten metal drooped in vertical welding, and it became impossible to form beads.

On the other hand, No. 1 within the scope of the present invention. The wire Nos. 9 to 18 have good welding workability, and as shown in FIG. 1, the amount of oxygen in the deposited metal can be 420 ppm or less, and the performance is particularly low.
It was confirmed that the low temperature toughness at 40 ° C. was excellent.

[0030]

EFFECTS OF THE INVENTION The flux-cored wire for gas shielded arc welding of the present invention is constituted as described above, and the combination of the additive components and the addition amount of the titania-based flux-cored wire having excellent welding workability are defined. By this, the low temperature toughness can be improved by reducing the amount of oxygen in the weld metal, and by further producing a large amount of Ti oxide, which serves as a production nucleus for forming intragranular ferrite, to produce a large amount of intragranular ferrite in the weld metal. .

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of oxygen in the deposited metal and vE- _40.

Claims (3)

[Claims] 1. A flux-cored wire for gas shield arc welding, comprising a steel shell filled with flux, wherein the weight of the filled flux is relative to the total weight of the wire.
_{In, TiO 2: 4.0~7.0% Si:} 0.2~1.6% Mn: 1.8~2.4% Mg: 0.3~0.5% Ti: 0.04~0 .06% B: .006 to .012% oxide: 8.0% or less gas shielded arc welding flux cored wire, characterized by containing (including TiO _2). 2. The flux for gas shielded arc welding according to claim 1, wherein the filling flux further contains C: 0.03 to 0.06% by weight% with respect to the total weight of the wire. Cored wire. 3. The gas shielded arc welding according to claim 1, wherein the filling flux further contains Ni: 0.3 to 0.5% by weight with respect to the total weight of the wire. Wire for flux.