KR101719797B1 - Flux cored wire - Google Patents

Abstract

A flux cored wire is disclosed. In one aspect of the present invention, there is provided a flux cored wire filled with a flux in a metal sheath, wherein the flux has a composition of BaF2: 5.0 to 14.0%, a rare earth element converted to rare earth element: At least one selected from the group consisting of an Al-based reducing agent and a Mg-based reducing agent; 2.0 to 3.8%; alkali metal fluoride: 0.5 to 2.4%; alkali metal carbonate: 0.1 to 0.35%; iron oxide: 2.0 to 4.0% : 1.0 to 1.2%, and Ni + Zr: 0.8 to 2.2%.

Description

FLUX CORED WIRE

FIELD OF THE INVENTION The present invention relates to flux cored wires, and more particularly to flux cored wires that can be preferably applied to self-shielded arc welding.

In recent years, as the development of energy sources has moved beyond the offshore waters to deep sea and polar regions, it has become a very urgent task to secure stable welded parts at extremely low temperatures in the construction of energy development and transportation structures. In addition, as the energy use of emerging countries has increased rapidly, energy transport volume has increased, and new energy project pipeline projects have been launched frequently. Therefore, mechanical performance including stable low temperature impact toughness is required on the welded part of the energy transport pipe have.

In order to ensure the stable mechanical performance of welds at low temperature, conventional gas shielded arc welding methods have been used to reduce the oxygen content in the weld metal by filling the flux with basic flux, And is planning production.

However, self-shielded arc welding is used as an alternative to gas-shielded arc welding for piping in extreme ground because it is troublesome to transport and install shielding gas and gas connection pipes in addition to welding devices. However, At the time of welding, penetration of oxygen and nitrogen in the atmosphere is a major cause of detrimental effects on low temperature impact toughness and countermeasures are required.

It is an object of the present invention to provide a flux cored wire capable of securing a welded portion excellent in welding workability and excellent in impact resistance at low temperatures during self-shielded arc welding.

In one aspect of the present invention, there is provided a flux cored wire filled with a flux in a metal sheath, wherein the flux has a composition of BaF2: 5.0 to 14.0%, a rare earth element converted to rare earth element: At least one selected from the group consisting of an Al-based reducing agent and a Mg-based reducing agent; 2.0 to 3.8%; alkali metal fluoride: 0.5 to 2.4%; alkali metal carbonate: 0.1 to 0.35%; iron oxide: 2.0 to 4.0% : 1.0 to 1.2%, and Ni + Zr: 0.8 to 2.2%.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof will be more fully understood by reference to the following specific embodiments.

The flux cored wire of the present invention is advantageous in welding workability in a self-shielded arc welding.

In addition, the welded portion obtained by the self-shielded arc welding using the flux cored wire of the present invention has an advantage that the impact resistance at low temperature is very excellent.

The inventors of the present invention have repeatedly carried out experiments for manufacturing a flux cored wire for arc welding which can secure a welded portion excellent in welding workability and excellent in low temperature impact toughness at the time of self shielded arc welding, , A large amount of BaF ₂ is used as a slag forming agent, a large amount of Al and / or Mg is used as a reducing agent, and a rare earth oxide, an alkali metal oxide, an alkali metal fluoride, iron oxide, , It has been confirmed that the above object can be accomplished, and the present invention has been accomplished.

Hereinafter, the flux cored wire, which is one aspect of the present invention, will be described in detail.

First, the components and the composition range of the flux cored wire of the present invention will be described in detail. The content range of each component to be described below means the content range of the whole wire, and unless otherwise stated, it is all based on weight.

BaF ₂ : 5.0 to 14.0%

BaF ₂ is a basic slag forming agent, which significantly improves the alkalinity of slag and reduces impurity content in the deposited metal to improve the low temperature impact toughness of the weld. In particular, BaF ₂ is CaF _2, SrF _2, etc. in other than the slag-forming agent, and a volume transition and excellent shielding effect, and, BaF ₂ is effective for preventing vertical downward position when the welding bead drop. In order to exhibit such an effect in the present invention, it is preferable to contain 5.0% or more, more preferably 8.2% or more. However, when the content is excessive, slag formation is excessive, slag inclusion occurs, and weldability is deteriorated. Therefore, the content of BaF ₂ is preferably 14.0% or less, more preferably 10.0% or less.

Rare earth element converted amount of rare earth oxide: 0.4 to 1.5%

The rare earth oxide not only reduces the melting point of slag by reacting with BaF ₂ during welding but also reduces the content of residual Al in the molten metal to suppress the formation of AlN, thereby improving the low temperature impact toughness of the weld.

In order to exhibit such an effect in the present invention, the rare earth element preferably has a rare earth element conversion amount of 0.4% or more, more preferably 0.48% or more. However, when the content is excessive, the flowability of the flux is excessively lowered, which may adversely affect the productivity of the flux cored wire. Therefore, the rare earth element in terms of the rare earth element is preferably 1.5% or less, more preferably 1.0% or less. In the present invention, there is no particular limitation on the kind of rare earth oxide, but it may preferably be Ce oxide or La oxide.

Al-based and / or Mg-based reducing agents: 2.0 to 3.8%

Al-based reducing agents and Mg-based reducing agents are powerful deoxidizers, denitrating agents, and nitrogen fixing agents, and play a role in inhibiting the penetration of oxygen or nitrogen in the atmosphere into the melting zone. In order to exhibit such effects in the present invention, the content of the Al-based and / or Mg-based reducing agent is preferably 2.0% or more, more preferably 2.4% or more. However, if the content is excessive, the oxygen content in the melting paper is excessively lowered due to an excessive deoxidizing action during welding, so that there is a problem that the impurities are not removed due to the formation of the oxide slag. Further, when the content of the Al-based reducing agent is excessive, there is a fear that the impact toughness of the deposited metal is lowered due to crystal grain coarsening, and when the content of the Mg-based reducing agent is excessive, fume and spatter are excessively generated , The viscosity of the slag may excessively increase, and the shielding ability of the slag may be reduced. Therefore, the content of the Al-based reducing agent and / or the Mg-based reducing agent is preferably 3.8% or less, more preferably 3.2% or less.

Specific examples of the Al-based reducing agent include Al, Fe-Al based alloys, Al-Mg based alloys, Al-Li based alloys and Al-Zr based alloys. Mg, Al-Mg alloys, Mg-Si alloys, Mg-Si-Ca alloys, Ni-Mg alloys and Li-Mg alloys.

Alkali metal fluoride: 0.5 to 2.4%

Alkali metal fluorides properly control the slag melting point and viscosity, deepen the penetration, and strengthen and stabilize the arc. This prevents defects such as slag inclusion and incomplete melting. In order to exhibit such an effect in the present invention, the content is preferably 0.5% or more, more preferably 1.0% or more. However, when the content is excessive, the slag fluidity excessively increases, the slag shape in the vertical posture becomes poor, and the bead flows down. Therefore, the content of the alkali metal fluoride is preferably 2.4% or less, more preferably 1.4% or less.

On the other hand, some alkali metal fluorides have strong hygroscopicity and have the problem of forming pores in the deposited metal when absorbing moisture. Therefore, it is preferable to use alkali metal fluorides with low hygroscopicity, and use them singly or in combination, Specific examples of the alkali metal fluoride include Na ₂ ZrF ₆ , K ₂ SiF ₆ , Na ₂ SiF ₆ , Na ₃ AlF ₆ , RbSiF ₆ , K ₂ TiF ₆ , K ₂ ZrF ₆ , LiF and LiBaF ₃ .

Alkali metal carbonate: 0.1 to 0.35%

The alkali metal carbonate serves as a slag forming agent to promote the formation of a healthy slag, thereby improving the slag releasing property. In order to exhibit such an effect in the present invention, it is preferable to contain 0.1% or more, more preferably 0.2% or more. However, when the content is excessive, the amount of carbon dioxide generated due to the decomposition of the alkali metal carbonate during welding explosively increases, thereby deteriorating the arc stability. Therefore, the content of the alkali metal carbonate is preferably 0.35% or less, more preferably 0.3% or less. Specific examples of the alkali metal carbonate include Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ and Cs ₂ CO ₃ .

Iron oxide: 2.0 to 4.0%

The iron oxide reacts with the residual Al in the melting paper formed at the time of welding to suppress the formation of AlN, thereby improving the low-temperature impact toughness of the welded portion. In order to exhibit such effects in the present invention, the content is preferably 2.0% or more, more preferably 2.8% or more. However, if the content is excessive, the interfacial affinity between the deposited metal and the slag may be improved to deteriorate the slag peeling property. Therefore, the content of the iron oxide is preferably 4.0% or less, more preferably 3.2% or less. Specific examples of the iron oxide include FeO, Fe ₂ O ₃ and Fe ₃ O ₄ .

Mn: 1.0 to 1.2%

Manganese increases the strength of the deposited metal and reduces the surface tension of the molten metal to improve the bead shape. In order to exhibit such an effect in the present invention, the content of Mn contained in the flux cored wire is preferably controlled to 1.0% or more. However, if the content is excessive, the strength of the deposited metal becomes excessively high, which may lower the impact toughness. Therefore, the content of Mn contained in the flux cored wire is preferably controlled to 1.2% or less. The Mn may be added in the form of the metal Mn, Fe-Mn-based alloy a flux, such as Fe-Si-Mn-based _{alloy, MnO, Li 2 MnO 3,} SrMnO 3, Ba (MnO 4) 2.

Ni + Zr: 0.8 to 2.2%

Nickel is an austenite stabilizing element. It plays a role of reinforcing impact toughness by preventing ferrite crystal coarsening with a large amount of reducing agent, and zirconium strengthens impact toughness of weld metal by nitrogen fixation and grain refinement. In order to exhibit such an effect in the present invention, it is preferable to control the sum of the Ni and Zr contents in the flux cored wire to 0.8% or more. However, if the content is excessive, the strength of the deposited metal becomes excessively high, which may lower the impact toughness. Therefore, it is preferable to control the sum of the content of Ni and Zr contained in the flux cored wire to 2.2% or less. Wherein Ni is the metal Ni, Fe-Ni-Cr-based alloy a flux, Mg-Ni based alloy, NiO, NiO ₂ Ba ₄ may be introduced in the form of the Zr-based alloy is the flux in Fe-Zr, Zr- Si-based alloy, Al-Zr-based alloy, K ₂ ZrF ₆ , Na ₂ ZrF ₆ , ZrO ₂ , ZrSiO ₄ , Li ₂ ZrO ₃ and the like.

In addition to the above composition, the remainder includes Fe and unavoidable impurities in the metal shell. However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically referred to in this specification, as they are known to one of ordinary skill in the art.

The flux cored wire according to the present invention has an advantage of excellent arc stability and slag peelability, and the weld metal formed by using the flux cored wire according to the present invention has an advantage of excellent impact resistance at low temperature.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example )

A flux cored wire for a self-shielded arc welding having a diameter of 2.0 mm having the composition shown in Table 1 (weight% based on the total weight of the wire) was prepared by filling the steel shell with a flux. At this time, a soft steel material containing 0.02% of C, 0.002% of Si, 0.20% of Mn, 0.010% of P and 0.009% of S was used as a steel material in weight percent. On the other hand, in all the examples, CeO ₂ as the rare earth oxide, metal Al and metal Mg (50:50 by weight) as the reducing agent, K ₂ SiF ₆ as the alkali metal fluoride, Na ₂ CO ₃ was used.

Thereafter, each of the manufactured wires was subjected to specimen welding according to the American Welding Association Standard (AWS A5.29 / A5.29M) under the welding conditions shown in Table 2 below, and the welding workability was evaluated. And the results are shown in Table 3 below.

More specifically, the welding workability was evaluated by comparing the arc stability and the slag releasability through the sensory evaluation of the welding worker, and the results were classified into excellent (?), Normal (?), And poor (X) , Impact toughness results were obtained by preparing five specimens for each example and performing a Charpy V notch impact test at -40 DEG C to obtain the average of the remaining three results except for the maximum value and the minimum value And the results were evaluated as excellent when the value was 60 J or more.

Remarks Flux component (% by weight) Rare earth metal oxides:
Rare earth element converted value Iron oxide BaF2 reducing agent Alkali metal fluoride Mn Ni + Zr Alkali metal carbonate Comparative Example 1 0.16 2 10 3 2 One 2 0 Comparative Example 2 0.16 2 8.6 4.09 1.2 One 2.11 0 Comparative Example 3 0.45 2 7.2 3.79 2.2 1.28 2.11 0 Comparative Example 4 0.16 4.5 6.9 2 2.4 One 2.06 0.3 Comparative Example 5 0.16 2 7.7 3.79 2.4 One 2.31 0 Comparative Example 6 0.45 4.5 4.8 3.79 2.4 One 2.11 0.2 Comparative Example 7 0.45 2 6.4 4.49 3 One 2.11 0.2 Comparative Example 8 0.49 2 7.2 4.09 2.4 One 2.11 0 Comparative Example 9 0.16 2 10 3.8 0 One 2.4 0 Comparative Example 10 0.45 2 15 2 0.5 0.5 One 0.1 Comparative Example 11 0.81 2 7.4 4.09 2.4 One 2.11 0 Comparative Example 12 0.45 2.6 6.4 4.49 2.4 0.64 2.11 0 Comparative Example 13 0.45 2.6 6.2 4.49 2.4 0.64 2.11 0.05 Comparative Example 14 0.65 3.2 8 3.4 1.2 One 2 0.4 Inventory 1 0.48 3.2 8.78 2.4 1.4 1.2 2.2 0.3 Inventory 2 One 3 8.2 2.89 1.2 1.2 2.11 0.2 Inventory 3 0.81 2.8 10 3.2 One One 0.8 0.2

Welding condition Welding voltage (V) Welding current (A) Protective gas polarity 19-22 200 to 250 none DCEN

Remarks Welding workability Impact Toughness (J) Arc stability Slag peelability Comparative Example 1 O △ 16.8 Comparative Example 2 O △ 18.8 Comparative Example 3 O △ 28.1 Comparative Example 4 O △ 30.1 Comparative Example 5 X X 20.56 Comparative Example 6 X X 50.58 Comparative Example 7 O X 52.58 Comparative Example 8 O △ 55.66 Comparative Example 9 △ △ 54.5 Comparative Example 10 O X 63.7 Comparative Example 11 O △ 57.04 Comparative Example 12 O △ 57.08 Comparative Example 13 O △ 53.58 Comparative Example 14 △ O 61.2 Inventory 1 O O 80.78 Inventory 2 O O 80.14 Inventory 3 O O 135.3

It can be seen from the results shown in Table 3 that Inventive Examples 1 to 3, which satisfy all of the composition ranges proposed by the present invention, not only have excellent welding workability, but also have excellent low-temperature impact toughness at the welded portion.

On the other hand, in Comparative Examples 1, 2, 4, 5 and 9, the low-temperature impact toughness of the weld portion was low due to the insufficient rare earth oxide content. In Comparative Example 3, Due to the deficiency of BaF 2, Comparative Examples 7 and 8 and 11 to 13 showed low cold impact toughness at the welded part due to excessive reductant content.

In Comparative Examples 1 to 3, 5, 8 and 9 and 11 to 13, owing to the deficiency or lack of alkali metal carbonate, Comparative Examples 4 and 6 were due to excessive iron oxide, Comparative Example 7 was due to excessive alkali metal fluoride, In Comparative Example 10, the slag peeling property was found to be normal or poor due to excessive BaF 2.

In Comparative Examples 5 and 9, due to the excessive content of Ni + Zr, in Comparative Example 6, due to the lack of BaF2, in Comparative Example 14, the arc stability was found to be normal or poor due to excessive alkali metal carbonate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. .

Claims (1)

A flux cored wire filled with a flux in a metal sheath, wherein the flux comprises, by weight based on the total weight of the wire, BaF2: 5.0 to 14.0%, rare earth element converted to rare earth element content: 0.4 to 1.5% Mg-based reducing agent, 2.0 to 3.8% of alkali metal fluoride, 0.5 to 2.4% of alkali metal fluoride, 0.1 to 0.35% of alkali metal carbonate, 2.0 to 4.0% of iron oxide, 1.0 to 1.2% of Mn, Ni + Zr: 0.8 to 2.2%.