JP2011025298A - Gas shielded arc welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method where welding efficiency is improved according to the welding operation conditions of high heat input/high interpass temperatures, welding operability is satisfactory, and a weld zone of high quality can be obtained. <P>SOLUTION: In the gas shielded arc welding method using a flux-cored wire, adopting a flux-cored wire comprising, by mass%, to the total mass of the wire, 0.03 to 0.10% C, 0.4 to 1.0% Si, 1.7 to 2.8% Mn, 0.1 to 0.3% Mo and 0.35 to 0.65% Mg, and in which the value of Ti oxide expressed in terms of TiO<SB>2</SB>is 4.8 to 6.5%, the value of Si oxide expressed in terms of SiO<SB>2</SB>is 0.3 to 0.8%, the value of Zr oxide expressed in terms of ZrO<SB>2</SB>is 0.2 to 0.5%, the total of the value of Al expressed in terms of Al<SB>2</SB>O<SB>3</SB>, and Al<SB>2</SB>O<SB>3</SB>is 0.4 to 1.2%, and the total of the value of an Na compound expressed in terms of Na<SB>2</SB>O and the value of a K compound expressed in terms of K<SB>2</SB>O is 0.06 to 0.20%, carbon dioxide gas-shielded arc welding is performed at a welding heat gain of 20 to 40 kJ/cm and at an interpass temperature of 200 to 350°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas shielded arc welding method for 490 to 520 MPa class high-strength steel, and in particular, when welding with high heat input and high pass temperature welding conditions using a flux-cored wire excellent in welding workability in all-position welding. The present invention relates to a gas shielded arc welding method capable of obtaining a weld metal with high efficiency and excellent mechanical performance.

  In recent years, in order to further improve the efficiency of welding in the building steel frame field, a solid wire for gas shielded arc welding corresponding to welding conditions with high heat input and high interpass temperature has been developed, and is specified in JIS Z3312 YGW18. Yes. This solid wire for gas shielded arc welding allows welding conditions with a maximum heat input of 40 kJ / cm and a maximum interpass temperature of 350 ° C. with respect to 490 MPa class high strength steel. For 520 MPa class high strength steel, welding conditions with a maximum heat input of 30 kJ / cm and a maximum interpass temperature of 250 ° C. are allowed.

  For example, Japanese Patent Laid-Open No. 10-230387 (Patent Document 1) and Japanese Patent Laid-Open No. 11-90678 (Patent Document 1) disclose a solid wire for gas shielded arc welding corresponding to such welding conditions of high heat input and high interpass temperature. Document 2) and Japanese Patent Application Laid-Open No. 2001-287086 (Patent Document 3). According to these, in order to ensure the strength even under welding conditions of large heat input and high pass temperature, it contains a large amount of Si, Mn, Mo, Cr, etc. as necessary, and Ti and B to ensure toughness. Contains.

  Moreover, in order to ensure slag peelability even under welding conditions with high heat input and high interpass temperature, JP 2006-26643 A (Patent Document 4), JP 2006-88187 A (Patent Document 5). As disclosed in Japanese Patent Application Laid-Open No. 2007-301597 (Patent Document 6) and the like, there is a disclosure of a technique for improving the slag peelability of the generated slag.

  However, since Patent Documents 1 to 6 are solid wires for gas shielded arc welding, there is a large amount of spatter generation, and there is a problem that the molten metal tends to sag particularly in the standing improvement posture welding.

  On the other hand, Japanese Patent Application Laid-Open No. 2005-279683 (Patent Document) discloses a technique that satisfies the mechanical performance under the welding conditions of high heat input and high pass temperature using a flux-cored wire for gas shield arc welding that can reduce the amount of spatter generated. Reference 7). However, the flux-cored wire for gas shielded arc welding described in Patent Document 7 is a metal powder based flux with very little slag agent. Similar to the above, there is a problem that the molten metal tends to sag. Furthermore, the amount of spatter generated was not satisfactory.

JP-A-10-230387 Japanese Patent Laid-Open No. 11-90678 JP 2001-287086 A JP 2006-26643 A JP 2006-88187 A JP 2007-301597 A JP 2005-279683 A

  The present invention improves welding efficiency by adopting welding conditions with high heat input and high interpass temperature, with low spatter generation and good welding workability in all position welding, and mechanical performance of weld metal An object of the present invention is to provide a gas shielded arc welding method capable of obtaining a high-quality welded portion such as excellent in quality.

The gist of the present invention is that, in a gas shielded arc welding method using a flux-cored wire in which a steel sheath is filled with a flux, C: 0.03 to 0.10%, Si: 0 with respect to the total mass of the wire. 0.4 to 1.0%, Mn: 1.7 to 2.8%, Mo: 0.1 to 0.3%, Mg: 0.35 to 0.65%, TiO ₂ equivalent value of Ti oxide: 4.8 to 6.5%, SiO ₂ conversion value of Si oxides: 0.3~0.8%, ZrO ₂ conversion value of Zr oxide: 0.2 to 0.5%, Al of _Al 2 O ₃ one or of the sum of the converted values and _Al 2 _{O 3: 0.4~1.2%,} the terms of Na ₂ O values and _{K 2} O conversion value of Na compounds and K compounds one or two Total: 0.06 to 0.20% contained, F compound value of fluorine compound is 0.03% or less, balance is iron powder, iron alloy Carbon dioxide shielded arc welding under the welding conditions of welding heat input of 20-40 kJ / cm and interpass temperature of 200-350 ° C. using a flux-cored wire consisting of Fe content of steel, Fe content of steel outer sheath and inevitable impurities A gas shielded arc welding method characterized by Here, the flux-cored wire has no seam penetrated through the steel-making outer shell, and has a copper plating with a thickness of 0.3 to 0.9 μm on the wire surface, and the flux-cored wire has a total hydrogen content of 20 ppm or less. It is also characterized.

  According to the gas shielded arc welding method of the present invention, the component composition of the flux-cored wire to be used is appropriate when welding is performed on 490 to 520 MPa class high strength steel under welding conditions of high heat input and high pass temperature. By doing so, spatter generation amount is small even in all position welding, and good welding workability can be obtained. As a result, it is possible to achieve high-efficiency welding by reducing the number of welding passes and shortening the cooling waiting time for each pass, and it is possible to obtain a welded portion with good mechanical performance.

In order to obtain a weld metal having excellent mechanical performance even when welding is performed with high efficiency under welding conditions of high heat input and high pass temperature, the present inventors have good welding workability in all-position welding. Various studies were made on the component composition of the flux-cored wire. As a result, in order to ensure the strength and toughness when performing multi-layer welding under conditions where welding can be performed at a high efficiency of a maximum heat input amount of 40 kJ / cm and a maximum interpass temperature of 350 ° C., It has been found effective to use Si, Mn, and Mo in appropriate amounts, to contain relatively large amounts of Mg, which is a strong deoxidizer, to contain TiO ₂ in appropriate amounts, and to further reduce fluorine compounds.

Moreover, weldability in all position welding has been found to be a good by containing an appropriate amount of _{TiO 2, SiO 2, ZrO 2} , Al 2 O 3, Na 2 O and _{K 2} O in the flux in the wire . Furthermore, by limiting the copper plating thickness on the wire surface, the arc is stable even under high current welding conditions, and by limiting the total hydrogen content of the wire, crack resistance in multi-layer welding can be improved. It was.
Hereinafter, the construction conditions of the gas shield arc welding method of the present invention and the reasons for limiting the flux-cored wire component composition to be used will be described.

[Welding heat input: 20 to 40 kJ / cm]
If the welding heat input is increased, the welding amount per pass increases, so that the welding efficiency is improved. If the welding heat input is less than 20 kJ / cm, the amount of welding per pass is small, so the number of welding passes increases and the welding efficiency decreases. On the other hand, when the welding heat input is large, the cooling rate is slowed, and generally the structure of the weld metal is coarsened and the strength and toughness are lowered. Moreover, it becomes easy to produce a hot crack. Even if the flux-cored wire used in the present invention to be described later is used, the strength and toughness cannot be ensured with a heat input of welding exceeding 40 kJ / cm, and hot cracking is likely to occur. Therefore, the welding heat input is 20 to 40 kJ / cm.

[Interpass temperature: 200-350 ° C]
The temperature between passes affects the welding efficiency as well as the welding heat input. When the temperature between passes is lowered, particularly in welding of a member having a short welding length, the cooling waiting time for each pass becomes long, so that the welding efficiency is lowered. If the interpass temperature is less than 200 ° C., the effect of improving the welding efficiency which is the object of the present invention cannot be obtained. On the other hand, when the interpass temperature exceeds 350 ° C., the strength and toughness are significantly reduced. Therefore, the interpass temperature is 200 to 350 ° C.

  In the gas shielded arc welding method of the present invention, carbon dioxide is used as the shielding gas. This is because carbon dioxide gas is cheaper than a mixed gas containing argon as a main component, and even when carbon dioxide gas is used as a shielding gas, the advantage of the flux-cored wire that less spatter is generated can be exhibited. For these reasons, the flux-cored wire used in the present invention is a component that can exhibit its performance to the maximum when carbon dioxide is used as the shielding gas.

[C: 0.03-0.10 mass%]
C is an important element for enhancing the hardenability of the weld metal and ensuring strength and toughness. C is contained in one or both of the steel outer sheath and the flux, but the total of these is less than 0.03% by mass (hereinafter referred to as “%”) with respect to the total mass of the wire (the same applies to the following components). Necessary strength and toughness cannot be obtained. On the other hand, when it exceeds 0.10%, the hot cracking sensitivity of the weld metal becomes high. Therefore, C is 0.03 to 0.10%.

[Si: 0.4 to 1.0%]
Si is an important element for improving the toughness by reducing the oxygen content of the weld metal. However, when the amount is too large, the weld metal is embrittled under welding conditions with high heat input and high pass temperature. In addition, although there is a large amount of Si consumption under the welding conditions with high heat input and high interpass temperature, it is necessary to secure the strength by yielding an appropriate amount of Si in the weld metal. When the total amount of Si contained in one or both of the steel outer shell and the flux is less than 0.4%, a predetermined strength cannot be obtained and the toughness is also lowered. On the other hand, if it exceeds 1.0%, the toughness of the weld metal becomes worse. Therefore, Si is 0.4 to 1.0%. Si is added as a flux component such as ferrosilicon, metal Si, or silicon manganese.

[Mn: 1.7 to 2.8%]
Mn is an important element for obtaining toughness by lowering the oxygen content of the weld metal. It is also an effective element for improving the strength. Furthermore, MnS having a high melting point is formed to prevent the sulfide from crystallizing out at the grain boundaries of the weld metal and to suppress cracking. On the other hand, if the amount is too large, the weld metal is embrittled under the welding conditions of high heat input and high-pass temperature in the same manner as Si. When the total amount of Mn contained in one or both of the steel outer shell and the flux is less than 1.7%, the predetermined strength and stable toughness cannot be obtained. On the other hand, if it exceeds 2.8%, the toughness of the weld metal decreases. Therefore, Mn is set to 1.7 to 2.8%. Mn is added as a flux component as ferromanganese, metal Mn, silicon manganese or the like.

[Mo: 0.1 to 0.3%]
Mo is an element that enhances the hardenability of the weld metal. In particular, it is an indispensable element for securing strength because the hardenability of the weld metal is insufficient under the welding conditions of high heat input and high pass temperature. If the total amount of Mo contained in one or both of the steel outer shell and the flux is less than 0.1%, the required strength cannot be obtained. On the other hand, if it exceeds 0.3%, the strength becomes too high and the toughness decreases. Therefore, Mo is 0.1 to 0.3%. Mo is added as a flux component such as ferromolybdenum.

[Mg: 0.35-0.65%]
Mg as a strong deoxidizer reduces oxygen in the weld metal and improves the toughness of the weld metal. Especially in welding conditions with high heat input and high interpass temperature, the molten pool becomes large and the consumption of other deoxidizers (C, Si, Mn) is large. To do. Mg is added to the flux as metallic Mg or Al—Mg alloy, but if Mg is less than 0.35%, the oxygen of the weld metal increases and the toughness decreases. On the other hand, if it exceeds 0.65%, the amount of spatter generated increases. Therefore, Mg is 0.35 to 0.65%.

[TiO ₂ converted value of Ti oxides: 4.8 to 6.5%]
Ti oxides such as rutile and titanium slag in the flux are an arc stabilizer and improve the bead shape. Further, in the vertical advance welding, molten metal is prevented from dripping due to slag having an appropriate viscosity and melting point. Furthermore, a part of the titanium oxide is retained in the weld metal and becomes a nucleus of recrystallization, whereby the microstructure of the weld metal is refined and the toughness is improved. When the TiO ₂ equivalent value of the Ti oxide is less than 4.8%, the arc is unstable, the spatter is large, and the bead shape is also poor. In addition, the molten metal drips during the vertical improvement welding. Furthermore, the yield of Ti oxide to the weld metal is reduced, the microstructure is coarsened, and the toughness is reduced. On the other hand, if it exceeds 6.5%, the arc is stable and the amount of spatter is reduced, but the amount of slag is increased by multi-layer welding, resulting in poor slag peelability. In addition, the yield of Ti oxide to the weld metal becomes excessive, non-metallic inclusions increase, and toughness decreases. Therefore, the TiO ₂ equivalent value of the Ti oxide is 4.8 to 6.5%.

[SiO ₂ converted value of Si oxide: 0.3 to 0.8%]
Si oxides such as silica sand, zircon sand, and sodium silicate in the flux increase the viscosity of the molten slag and improve the slag encapsulation even under welding conditions of high heat input and high pass temperature. Improves peelability. When the SiO ₂ conversion value of the Si oxide is less than 0.3%, the viscosity of the molten slag is lowered, the slag encapsulation is poor, the bead shape is poor, and the slag is seized. On the other hand, if it exceeds 0.8%, the hardened phase formation of the microstructure of the weld metal is promoted and the toughness of the weld metal is lowered. Therefore, the SiO ₂ equivalent value of the Si oxide is set to 0.3 to 0.8%.

[ZrO ₂ converted value of Zr oxide: 0.2 to 0.5%]
Zr oxide such as zircon sand and zircon oxide in the flux raises the solidification temperature of the molten slag and makes it difficult for the molten metal to sag during the vertical improvement welding. In addition, the slag encapsulation is improved during downward welding to improve the bead shape. When the ZrO ₂ conversion value of the Zr oxide is less than 0.2%, the molten metal tends to sag in the vertical improvement posture welding, and in the downward welding, the slag encapsulation is poor and the bead shape is poor. On the other hand, if it exceeds 0.5%, the slag becomes dense and hard, resulting in poor slag peelability. Therefore, the ZrO ₂ conversion value of the Zr oxide is 0.2 to 0.5%.

[Total Al ₂ O ₃ conversion value of Al and one or two of Al ₂ O ₃ : 0.4 to 1.2%]
Al is added from one or both of the steel outer shell and the flux, but the flux is added as metal Al, Al—Mg alloy, ferroaluminum, or the like. Also sometimes added to the flux as _Al 2 _{O 3.} Al becomes an oxide and, together with Al ₂ O ₃ , adjusts the viscosity and freezing point of the molten slag to improve the slag encapsulation and improve the bead shape. If the Al ₂ O ₃ conversion value of Al and the total of one or two of Al ₂ O ₃ is less than 0.4%, the slag encapsulation of the downward welding is poor and the bead shape is poor. On the other hand, if it exceeds 1.2%, Al ₂ O ₃ remains in the weld metal as non-metallic inclusions and the toughness is lowered. In addition, the molten metal is liable to sag during the vertical improvement welding. Therefore, the Al ₂ O ₃ equivalent value of Al and the total of one or two of Al ₂ O ₃ is 0.4 to 1.2%.

[Total of one or two Na ₂ O converted values and K ₂ O converted values of Na compound and K compound: 0.06 to 0.20%]
Solid components of water glass composed of potassium feldspar, sodium silicate and potassium silicate, and Na and K from fluorine compounds such as sodium fluoride and potassium silicofluoride act as arc stabilizers and slag forming agents. When the total of one or two of the Na ₂ O equivalent value and the K ₂ O equivalent value of the Na compound and K compound is less than 0.06%, the arc is unstable and the amount of spatter generated increases. On the other hand, if it exceeds 0.20%, the slag peelability becomes poor. In addition, the molten metal is liable to sag during the vertical improvement welding. Accordingly, the total of one or two of the Na ₂ O converted value and the K ₂ O converted value of the Na compound and K compound is 0.06 to 0.20%.

[F conversion value of fluorine compound: 0.03% or less]
Fluorine compounds such as sodium fluoride and potassium silicofluoride in the flux increase the directivity of the arc to form a stable molten pool, but the amount of spatter generated under high heat input and high pass temperature welding conditions Will increase. Therefore, the F converted value of the fluorine compound is set to 0.03% or less.

[Copper plating thickness on the wire surface: 0.3 to 0.9 μm]
Copper plating on the surface of the wire improves the electrical conductivity at the tip of the chip and stabilizes the arc. When the thickness of the copper plating is less than 0.3 μm, the arc becomes unstable particularly under welding conditions of high heat input and high pass temperature. On the other hand, when the copper plating thickness exceeds 0.9 μm, the copper plating scraped by the contact between the wire surface and the conduit tube during welding is accumulated in the chip and finally clogs the chip, and the arc stops. Therefore, the copper plating thickness on the wire surface is preferably 0.3 to 0.9 μm. In addition, since it immerses in a plating solution when copper plating is performed on the surface of the wire, a wire having no seam penetrated through the steel outer shell is used.

[Total hydrogen content: 20 ppm or less]
Since the hydrogen of the wire becomes a diffusible hydrogen source of the weld metal, it must be reduced as much as possible, and the total hydrogen content is preferably 20 ppm or less. When the total amount of hydrogen in the wire exceeds 20 ppm, the amount of diffusible hydrogen (JIS Z3118) exceeds 4 ml / 100 g, so that the sensitivity to cold cracking increases when multi-layer welding is performed. The total amount of hydrogen in the wire can be measured by an inert gas melting thermal conductivity method or the like.

  In addition, the flux-cored wire used in the present invention is a structure in which a steel strip is formed into a pipe shape and filled with a flux therein, and a seamless seam welded with a steel outer shell formed in the manufacturing process, and It can be roughly divided into wires having seams that penetrate through the steel outer skin without welding. In the present invention, any cross-sectional structure can be adopted, but it is necessary to select a filling flux having a low hydrogen content for a wire having a seam penetrating the steel outer shell. The seamless wire that penetrates the steel outer shell can be heat-treated at 650-1000 ° C. for the purpose of reducing the total hydrogen content of the wire, and has no moisture absorption after production. Since the amount can be reduced and crack resistance can be improved, it is more preferable.

  Other components of the flux-cored wire used in the gas shielded arc welding method of the present invention include iron powder added for component adjustment, Fe content of steel outer sheath, Fe content of iron alloys (ferrosilicon, ferromanganese, etc.) and Inevitable impurities.

  Hereinafter, the effect of the present invention will be described in detail with reference to examples. Using a steel strip of JIS G3141 SPCC for the steel outer sheath, a flux-cored wire having a wire diameter of 1.4 mm shown in Tables 1 and 2 was manufactured. Each prototype wire was annealed at 650 to 800 ° C. during wire drawing, but wire symbols W4, W8, W11 and W18 having seams penetrating the steel outer shell were annealed in an Ar atmosphere to produce wires. After that, it was sealed in a plastic bag and stored until welding. The wire symbol W21 was not annealed and sealed in a vinyl bag. The seamless wire that penetrated the steel outer skin was subjected to copper plating on the wire surface.

  The total amount of hydrogen was measured for each prototype wire using a hydrogen analyzer manufactured by HORIBA, Ltd .: EMGA-621. In addition, we measured the amount of diffusible hydrogen, the amount of spatter generated for each prototype wire, the welding workability in standing up position welding, the welding workability in multi-layer welding, and the mechanical performance. The amount of diffusible hydrogen was measured according to JIS Z3118. The amount of diffusible hydrogen was 4 ml / 100 g or less.

  The spatter generation amount was measured using a copper collection box under condition Nos. Shown in Table 3. At T1, JIS G3136 SN490B steel, 12 mm thick test plate was welded for 30 seconds × 5 times, the spatter was collected, and the amount of spatter generated per minute was calculated. The amount of spatter generated per minute was determined to be 1.0 g or less.

  The investigation of welding workability in vertical improvement welding is conducted under the condition No. shown in Table 3. At T2, JIS G3136 SN490B steel, a steel plate having a thickness of 12 mm was welded as a T-shaped fillet specimen, and the stability of the arc, the presence or absence of molten metal sagging, and slag peelability were investigated.

  The downward multi-layer welding is performed under conditions No. 1 shown in Table 3 using JIS G3136 SN490B steel, a steel plate with a thickness of 20 mm as a test plate with a backing angle of 45 degrees and a root interval of 12 mm. Welding was performed while changing the welding heat input and interpass temperature in each test within the range of welding conditions of T3. The number of welding passes, arc stability, slag peelability, bead shape, and presence of hot cracks were investigated.

  In the downward multi-layer welding, a tensile test piece (JIS Z2201 A1) and a Charpy impact test piece (JIS Z22024) were further collected from the central part of the weld metal plate thickness and evaluated. Tensile strength passed 540-680MPa, and the Charpy impact test was made 5 each at a test temperature of 0 ° C, and the average value passed 70J or more. The results are summarized in Table 4 and Table 5.

In Table 4 and Table 5, Test No. 1 to 10 are examples of the present invention, test Nos. 11 to 26 are comparative examples.
Test No. which is an example of the present invention. In Nos. 1 to 10, since the component composition of the flux-cored wire used was an appropriate amount, the amount of spatter generation was small, and the welding workability in the standing improvement posture welding was good. In downward multi-layer welding, the welding heat input and inter-pass temperature are appropriate, so the number of welding passes is small, welding workability is good, there is no high temperature, and the tensile strength and absorbed energy of the weld metal are very good. It was a satisfactory result. In addition, since any flux-cored wire used had a low total hydrogen content, the amount of diffusible hydrogen was also low. In addition, Test No. 4 and no. 8 shows the flux-cored wire No. used. W4 and W8 had joints that penetrated the cross section of the steel outer shell, and the copper surface was not plated with copper, so that the arc was somewhat unstable in both the vertical improvement welding and the downward multi-layer welding.

Test No. in Comparative Examples. 11 is the flux-cored wire No. used. Since there is little C of W11, the tensile strength was low and the absorbed energy was also low in the mechanical test of the downward multi-layer welding. Further, since the amount of ZrO ₂ is small, the molten metal drips in the vertical improvement welding, and in the downward multi-layer welding, the slag encapsulation is poor and the bead shape is poor. Furthermore, since the seam penetrated through the cross section of the steel outer shell and copper plating was not applied, the arc was somewhat unstable in both the vertical improvement welding and the downward multi-layer welding.

Test No. 12 is the flux-cored wire No. used. Since there was much C of W12, the hot crack occurred in the downward multilayer overlay welding. Further, the absorbed energy in the mechanical testing of downward multipass welding was low values since SiO ₂ is large.

Test No. 13 is the flux-cored wire No. used. Since there is little Si of W13, the tensile strength was low and the absorbed energy was also low in the mechanical test of the downward multi-layer welding. Moreover, since the total of Al ₂ O ₃ conversion value of Al and Al ₂ O ₃ was small, the enveloping property of slag was poor and the bead shape was poor in the downward multi-layer welding.

Test No. 14 is the flux-cored wire No. used. Since there is much Si of W14, the absorbed energy was a low value in the mechanical test of downward multilayer overlay welding. In addition, since the amount of SiO ₂ is small, the slag peelability is poor in both the vertical improvement welding and the downward multi-layer welding, and in the downward multi-layer welding, the encapsulation of the slag is poor and the bead shape is also poor.

  Test No. 15 is the flux-cored wire No. used. Since the Mn of W15 is small, the tensile strength was low and the absorbed energy was also low in the mechanical test of the downward multi-layer welding. Further, since the F-converted value of the fluorine compound is large, the amount of spatter generated was large.

Test No. 16 is the flux-cored wire No. used. Since there was much Mn of W16, the absorbed energy was a low value in the mechanical test of the downward multi-layer welding. In addition, since the total of Na ₂ O converted value and K ₂ O converted value of Na compound and K compound is large, the slag peelability is poor in both vertical improvement welding and downward multilayer build-up welding. Molten metal also dripped.

Test No. 17 is the flux-cored wire No. used. Since there is little Mo of W17, the tensile strength was low in the mechanical test of downward multilayer overlay welding. Further, since there is no addition of K compound to other less terms of Na 2 _O values of Na metal compound the amount of occurrence of spatter many, arc was unstable in the welding both vertical upward advance position welding and downstream multi-pass.

Test No. 18 is the flux-cored wire No. used. Since there is much Mo of W18, the tensile strength was high and the absorbed energy was a low value in the mechanical test of the downward multi-layer welding. In addition, because of the large amount of ZrO ₂ , both the vertical improvement welding and the downward multi-layer welding have poor slag removability, and there is a seam penetrating the cross section of the steel outer shell and copper plating is not applied, so there is a slight arc. It was unstable.

Test No. 19 is the flux-cored wire No. used. Since there was little Mg of W19, the absorbed energy was a low value in the mechanical test of the downward multilayer overlay welding. Further, the molten metal in the vertical upward advance position welding sag because the sum of terms _{of Al} 2 _{O 3} value and _Al 2 _{O 3} of Al is large.

  Test No. No. 20 shows the flux-cored wire No. used. Since there was much W20 Mg, there was much spatter generation amount. Moreover, since the copper plating thickness on the wire surface was thin, the arc was slightly unstable in both the vertical improvement welding and the downward multilayer welding.

Test No. 21 is the flux-cored wire No. used. Since the total hydrogen amount of W21 is large, the amount of diffusible hydrogen was large. Moreover, the slag removability was poor in standing both improve advance position welding and downstream multipass welding because TiO ₂ is large. In addition, since there was a seam penetrating in the cross section of the steel outer shell and copper plating was not applied, the arc was somewhat unstable, and the absorbed energy was also low in a mechanical test of downward multilayer welding.

Test No. No. 22 is the flux-cored wire No. used. Since TiO ₂ of W22 is small, amount of occurrence of spatter arc is unstable within the weld both many elevational improve advance position welding and downstream multi-pass, the bead shape in the downward multipass welding dripping molten metal in vertical upward advance position welding The absorbed energy in the mechanical test was low. Furthermore, since the copper plating thickness on the wire surface was thick, there was a portion where the copper plating on the wire surface that passed through the conduit tube was peeled off.

Test No. In No. 23, since the welding heat input was low, the number of welding passes increased, and the time required for welding was long.
Test No. No. 24 had high welding heat input, so high temperature cracking occurred, and the mechanical test showed low tensile strength and low absorbed energy.

Test No. No. 25 has a long welding waiting time because the temperature between passes is low. In addition, the flux-cored wire No. used was used. Since TiO ₂ of W21 is larger slag removability is bad, since copper plating is not subjected to the wire surface has a seam that passes through the cross section of the steel sheath, was slightly arc also unstable.
Test No. Since the temperature between passes was high, the tensile strength was low and the absorbed energy was also low in the mechanical test.

Claims (3)

In the gas shielded arc welding method using a flux-cored wire filled with a flux in the steel outer sheath, in mass% with respect to the total mass of the wire,
C: 0.03-0.10%,
Si: 0.4 to 1.0%,
Mn: 1.7-2.8%,
Mo: 0.1 to 0.3%,
Mg: 0.35-0.65%,
TiO ₂ conversion value of Ti oxide: 4.8 to 6.5%,
SiO ₂ conversion value of Si oxide: 0.3 to 0.8%,
ZrO ₂ conversion value of Zr oxide: 0.2 to 0.5%,
Al ₂ O ₃ equivalent value of Al and total of one or two of Al ₂ O ₃ : 0.4 to 1.2%,
One or of the sum of terms of Na ₂ O values of Na compounds and K compounds and _{K 2} O converted value: from 0.06 to 0.20 percent
Containing
The F-converted value of the fluorine compound is 0.03% or less, and the balance is made of iron powder, Fe content of the iron alloy, Fe content of the steel outer sheath, and flux-cored wire consisting of inevitable impurities, and the welding heat input is 20 to 40 kJ / A gas shielded arc welding method, characterized in that carbon dioxide shielded arc welding is performed under a welding condition of cm and an interpass temperature of 200 to 350 ° C. The method for gas shielded arc welding according to claim 1, wherein the flux-cored wire has no seam penetrated through the steel-making outer skin and has a copper plating with a thickness of 0.3 to 0.9 µm on the surface of the wire. The gas-shielded arc welding method according to claim 1 or 2, wherein the flux-cored wire has a total hydrogen content of 20 ppm or less.