KR20140066040A - Materal for flux cored arc welding - Google Patents

Abstract

The present invention relates to a flux cored arc welding material having a core and an outer shell covering the core. The welding material includes; 0.05 to 1.30 wt% of C, 0.2 to 1.8 wt% of Si, 0.5 to 25 wt% of Mn, less than 0.031 wt% of one of or both P and S, 25 to 50 wt% of Ni, 1.5 wt% or less of Al, 3.5 to 15 wt% of TiO2, 0.01 to 1.3 wt% of one or more than one of K, Na and Li, 2.4 wt% or less of Ti, 0.001 to 10 wt% of one of or more than one of Mo, W and Co, and the remaining Fe and unavoidable impurities, and the outer shell includes 35 to 46 wt% of Ni, 0.05 wt% or less of other impurities, and the remaining Fe. According to the present invention, the flux cored arc welding material has excellent impact toughness in a cryogenic environment, high yield strength at room temperature, and excellent weldability.

Description

{MATERIAL FOR FLUX CORED ARC WELDING}

The present invention relates to a flux cored arc welding material.

Recently, explosive increase in LNG demand has caused explosive increase in transportation facilities and storage tanks for transportation and storage of cryogenic LNG. Tanks that transport or store LNG must, inevitably, be constructed to withstand impact at temperatures below -162 ° C, the LNG temperature. For this purpose, Al, 9% Ni steel, and stainless steel (hereinafter referred to as STS) are typically used as materials having high impact toughness at cryogenic temperatures.

However, in the case of Al, there is a problem that a thick plate is required due to a low tensile strength and weldability is poor.

In addition, in the case of 9% Ni steel, there is a problem that the welding material (Inconel 625: at least 50% by weight of Ni and at least 20% by weight of Cr) is expensive and the yield strength of weld portion is low. STS has a high price, There is a problem such that the cryogenic temperature can not be guaranteed.

Therefore, it is required to develop a high Mn-based welding material for cryogenic temperature which is capable of ensuring low cost and good weldability as compared with Ni as an austenite stabilizing element.

One aspect of the present invention is to provide a flux cored arc welding material having excellent low temperature impact toughness and room temperature yield strength by preventing high temperature cracking during welding while maintaining the toughness in an austenite phase even in a cryogenic environment.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, one aspect of the present invention is a welding material comprising a core and an outer envelope surrounding the core, wherein the core comprises 0.05 to 1.30% of C, 0.2 to 1.8% of Si, 0.5 to 1.2% of Mn, ~ 25%, P and at least one of S: less than 0.031%, Ni: 25 ~ 50 %, Al: 1.5% or _{less, TiO 2: 3.5 ~ 15%} , K, Na, and at least one of Li: 0.01 ~ 1.3%, Ti: 2.4% or less, at least one of Mo, W and Co: 0.001 to 10% The remainder Fe and other unavoidable impurities, wherein the shell comprises 35 to 46% by weight of Ni and 0.05% or less of other impurities, and the balance Fe.

According to one aspect of the present invention, it is possible to provide a flux cored arc welding material having excellent impact toughness, excellent room temperature yield strength, and excellent weldability in a cryogenic environment.

1 is a cross-sectional view of a welding material according to an embodiment of the present invention.

Hereinafter, the flux cored arc welding material of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

In general, high Mn steel for cryogenic temperature is high Mn added steel to replace 9% Ni steel and STS 304 steel used for LNG storage tanks. It forms stable austenitic structure even at very low temperatures, And it is known that it possesses the characteristic that there is no toughness deterioration in the heat affected zone (HAZ) part during welding.

The flux cored arc welding material of the present invention is designed to be capable of welding a cryogenic high Mn steel used in cryogenic marine structures, energy, shipbuilding, and pressure vessels, as well as a dissimilar material, yet having excellent low-temperature impact toughness. Therefore, it is possible to maintain the toughness in the austenite phase excellent in toughness in a cryogenic environment, and to control the components so as to prevent high-temperature cracking during welding, thereby achieving excellent electron weldability with excellent low temperature impact toughness.

As a means for realizing this, a composite wire composed of a core and an envelope containing alloy and flux powder was designed.

The welding material in the present invention has a double structure including a core made of a predetermined alloy and flux, and an outer shell surrounding the outer surface of the core.

Specifically, the shell enveloping the core is a single shell structure composed of Fe-group strips containing 35 to 46% Ni by weight.

In order to achieve the above object, the present invention provides a welding material comprising a core and an outer envelope surrounding the core, wherein the core comprises 0.05 to 1.30% of C, 0.2 to 1.8% of Si, 0.5 to 25% of Mn, or more of: 0.031% to less than, Ni: 25 ~ 50%, Al: 1.5% or _{less, TiO 2: 3.5 ~ 15%} , K, Na, and at least one of Li: 0.01 ~ 1.3%, Ti : 2.4% or less, Mo, W and Co: 0.001 to 10% by weight, The balance Fe, and other unavoidable impurities.

The reason for limiting the numerical values of the above components will be described as follows. Hereinafter, it is necessary to pay attention that the content unit of each component is weight% unless otherwise stated.

Carbon (C): 0.05 to 1.30 wt%

Carbon is the most powerful element existing as an austenite stabilizing element which ensures the strength of the weld metal and ensures the cryogenic impact toughness of the weld metal, and is an essential element in the present invention. However, in the welding wire, even if such a carbon component is low, a sufficient amount of carbon can be incorporated from the flux. The lower limit of the carbon content may be limited to 0.05 wt%. However, if the carbon content is less than 0.05% by weight, austenite does not appear at a very low temperature, and toughness tends to decrease. If the content of carbon is more than 1.30 wt%, carbon dioxide gas may be generated during welding, which may cause defects in the welding part. When the content of carbon is greater than 1.30 wt%, carbides such as MC, M ₂₃ C ₆ , And the impact toughness is deteriorated at a low temperature. Therefore, the content of carbon is preferably limited to 0.05 to 1.30% by weight.

silicon( Si ): 0.2 to 1.8 wt%

If the content of silicon is less than 0.2% by weight, the deoxidizing effect in the weld metal is insufficient and the flowability of the weld metal may be deteriorated. On the other hand, when the content of silicon exceeds 1.8% by weight, segregation or the like in the weld metal is caused, which lowers the impact resistance at low temperatures and adversely affects the weld crack susceptibility. Therefore, the content of silicon is preferably limited to 0.3 to 1.8 wt%.

manganese( Mn ): 0.5 to 25 wt%

Manganese is a main element that generates austenite which is a stable low-temperature phase, and is an element which is essential to be added in the present invention and is a very low element compared to nickel. When the content of manganese is less than 0.5% by weight, sufficient austenite is not produced and the toughness is extremely low at a very low temperature. On the other hand, if the content of manganese exceeds 25 wt%, segregation may occur excessively, causing high-temperature cracks, and harmful fumes may be generated. Therefore, the content of manganese is preferably limited to 0.5 to 25 wt%.

At least one of sulfur (P) and phosphorus (S): less than 0.031%

Sulfur (P) and phosphorus (S) are segregated at the final solidification site during solidification after welding. This element forms a low melting point compound, and there is a problem that cracks are generated by the stress generated at the welding at these sites. Therefore, the content of at least one of sulfur (P) and phosphorus (S) is preferably limited to less than 0.031 wt%.

nickel( Ni ): 25-50 wt%

Nickel is an element to be added as an austenite stabilizing element in the present invention. It should be added in an amount of 25% or more in order to guarantee a cryogenic toughness, and it is preferable that it is contained in an amount of 50% by weight or less considering the manufacturing cost. Therefore, the content of nickel is preferably limited to 25 to 50% by weight.

aluminum( Al ): 1.5% by weight or less

Aluminum reduces strength, but it also increases SFE (Stacking Fault Energy) to ensure toughness at low temperatures. However, when the content of aluminum is more than 1.5% by weight, Ti (C, N) is formed by reducing TiO ₂ to the welded portion, and the cryogenic impact toughness is extremely reduced. Therefore, the content of aluminum is preferably limited to 1.5% by weight or less.

TiO ₂ (Titanium dioxide): 3.5 to 15 wt%

The TiO ₂ serves as a slag forming agent and functions to prevent the liquid weld metal from solidifying and allowing the liquid weld metal to flow down before it coagulates so that the weld metal can be electronically welded. In order to exhibit such an effect, it is preferable to add at least 3.5 wt% in the present invention. However, when the content exceeds 15% by weight, the oxide content in the weld metal increases sharply and the cryogenic impact toughness is deteriorated. Therefore, the content of TiO ₂ is preferably limited to 3.5 to 15% by weight.

Potassium (K), sodium ( Na ), Lithium ( Li ): 0.01 to 1.3 wt%

The alkali metal lowers the ionization potential of the arc during welding to facilitate the generation of arc and can maintain a stable arc during welding. The alkali metal should be added in an amount of 0.01 wt% or more to exhibit such effects. However, if the content exceeds 1.3% by weight, a high vapor pressure may cause excessive welding fumes. Here, the alkali metal includes at least one of potassium (K), sodium (Na) and lithium (Li) alkali metals, and the effect of addition of alkali metal in the present invention is independent of the respective content ratios.

titanium( Ti ): 2.4 wt% or less

The wire of the present invention preferably contains 2.4 wt% or less of titanium (Ti). Ti is a powerful deoxidizer and can strongly remove oxides in the weld metal. However, when the amount of Ti (C, N) is excessively increased, there is a disadvantage that the cryogenic impact toughness is extremely reduced. Therefore, the content of aluminum is preferably limited to 2.4 wt% or less.

molybdenum( Mo ), Tungsten (W), and cobalt ( Co ): 0.001 to 10 wt%

Molybdenum, tungsten, and cobalt are elements capable of improving the strength of the matrix, and are preferably contained in an amount of 0.001% by weight or more in the present invention. However, when the content of the above elements exceeds 10% by weight, carbides are excessively generated and the cryogenic toughness is lowered. Therefore, the content of at least one of molybdenum (Mo), tungsten (W) and cobalt (Co) is preferably limited to 0.001 to 10 wt%.

In addition to the above essential components, the welding material of the present invention, Cr in weight percent: at least one of 0.001 ~ 10%, Nb and V: 0.001 ~ 1.2%, SiO 2, ZrO 2 And Al ₂ O ₃ 0.01 to 7.0% of at least one of F and 0.01 to 1.0% of at least one of F and Ca, and 0.01 to 0.5% of N, to further improve the effect of the present invention .

chrome( Cr ): 0.001 to 10 wt%

Chromium is a ferrite stabilizing element and is an element that improves strength and corrosion properties. In order to exhibit such an effect, it is preferable that the content is 0.001% by weight or more. On the other hand, when the content of chromium exceeds 10% by weight, chromium-based carbides are excessively produced, and cryogenic toughness is lowered. Therefore, the content of chromium is preferably limited to 0.001 to 10% by weight.

Niobium ( Nb ) And vanadium (V): 0.001 to 1.2 wt%

Niobium and vanadium are elements capable of improving the strength of the base, and are preferably contained in an amount of 0.001% by weight or more in the present invention. However, when the content of the above elements exceeds 1.2% by weight, carbides are excessively generated and the cryogenic toughness is lowered. Therefore, the content of at least one of niobium (Nb) and vanadium (V) is preferably limited to 0.001 to 1.2% by weight.

SiO ₂ (Silicon dioxide), ZrO ₂ (Zirconium dioxide) and Al ₂ O ₃ (Aluminum oxide): 0.01 to 7.0 wt%

If less than 0.01% by weight of at least one of SiO ₂ , ZrO ₂ and Al ₂ O ₃ is used, slag coating and peelability and arc stability are deteriorated, resulting in deteriorated elaboratory workability and weld bead formation. The amount of slag is rapidly increased and the viscosity of the slag is increased, so that the electron weldability and the bead shape are poor. Further, transition of silicon, aluminum, etc. to the deposited metal is increased, and impact toughness is lowered. Therefore, the content of at least one of SiO ₂ , ZrO ₂ and Al ₂ O ₃ is preferably limited to 0.01 to 7.0% by weight.

Fluorine (F) and calcium ( Ca ): 0.01 to 1.0 wt%

The welding wire of the present invention can further improve the effect of the present invention when fluorine (F) and potassium (Ca) are additionally added in the alkali metal and alkaline earth metal fluorine compounds. Since 0.01% by weight or more of the fluorine compound is added to the inside of the welding wire, fluorine is generated in the arc in a high-temperature arc and reacts with hydrogen during welding to cause a dehydrogenation reaction, thereby effectively reducing diffusible hydrogen. However, , Fume is excessively generated due to high vapor pressure characteristics, and TiO ₂ excessively reduces the slag viscosity of the molten pool in the rutile system, which is a main slag component, to form an unstable bead. Therefore, the content thereof is preferably limited to 0.01 to 1.0% by weight.

Nitrogen (N): 0.01 to 0.5 wt%

In addition, the welding wire of the present invention can further improve the effect of the present invention when nitrogen (N) is additionally added. Nitrogen is an element showing the same characteristics as carbon. In order to exhibit such an effect, nitrogen is preferably contained in an amount of 0.01 wt% or more. On the other hand, when the content of nitrogen exceeds 0.5% by weight, excessive nitrides are formed and the impact toughness is deteriorated. Therefore, the content of nitrogen is preferably limited to 0.01 to 0.5% by weight.

The remainder of the present invention is iron (Fe). 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 mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

The outer shell of the welding material is composed of 35 to 46% by weight of Ni and 0.05% or less of other impurities, and the balance Fe. The shell is a high Ni-containing steel having a function of increasing the content of Ni The reason for limiting the content of Ni and other impurities as described above is to secure toughness at a very low temperature and to reduce defects such as cracks during welding.

The diameter of the welding material is preferably about 0.9 to 1.6 mm, and the weight fraction of the sheath is preferably about 50 to 90% in terms of the weight fraction of the entire welding material in consideration of the density of the sheath and the density of the core.

This type of sheath is shown in FIG. 1 and can be represented by a single sheath structure that surrounds the core of the alloy component.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are only for illustrating the present invention in more detail and do not limit the scope of the present invention.

[ Example ]

A welding material having the components shown in the following Table 1 was prepared. The content unit of each component is% by weight.

The composition of the jacket of the inventive material and the comparative material and the composition of the jacket are the same and the content of the entire welding material is different. The shell of the welding material is composed of 35 to 46% by weight of Ni, 0.05% or less of other impurities, and the balance Fe.

Flux Cored Arc Welding (FCAW) was performed on each welding material.

For FCAW, welding was performed at 1.7 kJ / mm in 100% CO ₂ condition. The diameter of the FCAW wire was 1.2 mm.

After that, the weldability, the crack porosity of the welded joint, the impact toughness at -196 DEG C, and the yield strength at room temperature were measured and are shown in Table 1 below. The unit of impact toughness (CVN) value is J, and the unit of yield strength is MPa. Also, the components connected by '+' mean the content of one or more of the components.

The results of Table 1 indicate that the inventive material satisfying the alloy composition of the present invention exhibited good weldability and no uniform pores. The impact toughness was 27J or more at a cryogenic temperature of -196 ° C, All exhibited a performance of 360 MPa or more.

On the other hand, the comparative material was found to be inapplicable as a welding material, showing the result of heating in at least one of weldability, crack pore, impact toughness and yield strength.

11: core 12: sheath (high Ni content)

Claims (5)

1. A welding material comprising a core and an envelope enclosing the core, wherein: C: 0.05 to 1.30%, Si: 0.2 to 1.8%, Mn: 0.5 to 25%, at least one of P and S: Ni: 25 to 50%, Al: 1.5% or less, TiO ₂ : 3.5 to 15%, at least one of K, Na and Li: 0.01 to 1.3%, Ti: 2.4% Species or more: 0.001 to 10% by weight, The balance Fe and other unavoidable impurities,
Wherein the shell comprises 35 to 46% of Ni by weight%, and 0.05% or less of other impurities, and the balance Fe. The method according to claim 1,
The welding material of Cr by weight%: 0.001 ~ 10%, Nb and V more than 1 kind _{of: 0.001 ~ 1.2%, SiO 2} , ZrO 2 And Al ₂ O ₃ 0.01 to 7.0% of one or more of F and 0.01 to 1.0% of at least one of F and Ca, and 0.01 to 0.5% of N. The flux cored arc welding material according to claim 1, The method according to claim 1,
Wherein the impact toughness of the welded joint using the welding material is at least 27 J at a cryogenic temperature of -196 캜. The method according to claim 1,
Wherein the welded joint using the welding material has a room temperature yield strength of 360 MPa or more. The method according to claim 1,
Wherein the shell is 50 to 90% in weight fraction of the weld material.

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