JP2015205304A - Flux-cored wire for gas shield arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux-cored wire for gas shield arc welding for vertical upward welding of a 590 Mpa-class high tensile steel, favorable in welding workability and capable of obtaining a weld metal excellent in mechanical performance.SOLUTION: A flux-cored wire for gas shield arc welding for vertical upward welding contains: in mass% based on total mass of wire, 0.02-0.08% C, 0.3-1.0% Si, 2.0-3.5% Mn, 0.1-1.0% Ni, 0.4-2.3% total of AlOconversion value of Al, and AlO, 0.2-1.1% Al, and 0.002-0.015% B; and a flux containing 5.5-6.8% TiOconversion value, 0.4-1.6% SiOconversion value, 0.1-0.6% ZrOconversion value, 0.1-0.3% Mg, 0.10-0.20% total of NaO and KO conversion values, and the balance Fe with inevitable impurities.

Description

  The present invention relates to a flux-cored wire for gas shielded arc welding of high-strength steel of 590 MPa class, and in particular, welding workability is improved in vertical welding with high heat input under high heat input welding conditions where high efficiency construction is possible. The present invention relates to a flux-cored wire for gas shielded arc welding for standing-up progress welding capable of obtaining a weld metal having excellent mechanical performance.

  The flux-cored wire for gas shielded arc welding has better welding workability such as a bead appearance than the solid wire, and further has excellent welding efficiency, so that its usage is increasing year by year. In recent years, in the steel frame field, with the increase in size of structures, higher strength of steel materials has been studied, and high-tensile steel of 590 MPa class has been used, and the demand for welding materials corresponding to this has increased. . Furthermore, for the purpose of improving the welding efficiency, even in multi-layered welding with a large heat input such as a heat input of 30 to 50 kJ / cm, good welding work can be obtained by standing up posture welding and toughness There is a demand for a weld metal that excels in resistance.

  However, under such welding conditions with high heat input, the welded portion of 590 MPa class high-strength steel tends to deteriorate the mechanical performance of the weld metal. There is a problem that the amount of generated metal is large and a phenomenon that the molten metal droops (hereinafter referred to as metal dripping) is likely to occur.

  Regarding the flux-cored wire for welding corresponding to the construction conditions of such a large heat input, for example, in Patent Document 1, a slag generating agent necessary for the standing improvement advance welding is added as an alloy component to the flux-cored wire for welding. By doing so, a flux-cored wire for welding is disclosed in which a weld metal having good toughness can be obtained by utilizing a deoxidizing action while suppressing metal sag in standing improvement posture welding. However, the flux-cored wire for welding described in Patent Document 1 is for 490 MPa class high strength steel and does not assume welding with 590 MPa class high strength steel. The required mechanical performance cannot be obtained.

  Further, in Patent Document 2, in welding of 490 to 520 MPa class high-tensile steel, welding is performed under welding conditions with large heat input by limiting the contents of alloy components and slag forming agents in the flux-cored wire for welding. Although a flux-cored wire for welding that does not cause deterioration in toughness even in a reheated part has been disclosed, it does not assume welding in a standing posture, so metal dripping occurs in welding in a standing posture It is easy to do and the bead shape tends to be bad.

  Further, in Patent Document 3, in welding of 490 to 520 MPa class high-tensile steel, high-performance and excellent welding workability can be obtained without degrading toughness and bead shape in vertical improvement welding. A flux cored wire is disclosed. However, since the flux-cored wire for welding described in Patent Document 3 does not assume welding with large heat input, the required strength cannot be obtained by welding under such large heat input welding conditions. There is a problem that metal dripping is likely to occur.

JP 2009-61474 A JP 2005-279683 A JP 2005-305531 A

  The present invention has been devised in view of the above-described problems, and relates to a flux-cored wire for gas shielded arc welding for 590 MPa class high-strength steel. It is an object of the present invention to provide a flux-cored wire for gas shielded arc welding for vertical improvement welding, which can obtain a weld metal having good welding workability in vertical improvement welding and excellent mechanical performance.

  In order to solve the above-described problems, the present inventors have achieved good welding workability even when welding is performed under high heat input welding conditions in 590 MPa class high-strength steel standing improvement welding. In order to obtain a weld metal having excellent mechanical properties such as strength and toughness, various investigations were made on the composition of the flux-cored wire for welding.

  As a result, in order to ensure sufficient strength and toughness of the weld metal under welding conditions of heat input of 30-50 kJ / cm, the contents of C, Si, Mn and Mo in the flux-cored wire for welding are appropriate. As a result, it was found that the strength and toughness of the weld metal required can be obtained by ensuring the strength of the weld metal and making the contents of Ni, B, Mg and Al appropriate.

As for the welding workability in vertical upward advance position _{welding, TiO 2, SiO 2, ZrO} 2, Al of welding flux cored in the _wire, Al 2 O 3, Mg, the content of Na ₂ O and _{K 2} O By making it appropriate, it is possible to improve the arc state, spatter generation amount, slag encapsulation, slag peelability, bead appearance and bead shape in the vertical improvement welding, and prevent metal dripping, welding defects, and hot cracking. I found out.

  Furthermore, it also discovered that slag peelability can be improved by making the content of Bi in the flux-cored wire for welding appropriate.

  The present invention has been completed based on these findings, and the gist of the invention is as follows.

(1) In a flux-cored wire for gas shielded arc welding formed by filling a steel sheath with flux, the total of the steel sheath and flux
C: 0.02 to 0.08%,
Si: 0.3 to 1.0%,
Mn: 2.0 to 3.5%
Ni: 0.1 to 1.0%,
Total of Al ₂ O ₃ equivalent and Al ₂ O ₃ : 0.4 to 2.3%, and Al: 0.2 to 1.1%,
B: contains 0.002 to 0.015%,
To the flux,
TiO ₂ conversion value of Ti oxide: 5.5 to 6.8%,
SiO ₂ conversion value of Si oxide: 0.4 to 1.6%,
ZrO ₂ conversion value of Zr oxide: 0.1 to 0.6%,
Mg: 0.1 to 0.3%
The sum of the _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound: containing 0.10 to 0.20%,
A flux-cored wire for gas shielded arc welding for rapid improvement welding under welding conditions of heat input of 30 to 50 kJ / cm, characterized in that the balance consists of Fe and inevitable impurities.

  (2) In mass% with respect to the total mass of the wire, the flux further includes Mo: 0.1 to 0.3%, and the sum of Bi and Bi oxide Bi converted values: 0.003 to 0.02% A flux-cored wire for gas shielded arc welding.

  According to the flux-cored wire for gas shielded arc welding of the present invention, the welding workability is good even when welding is performed under a high heat input welding condition in a standing posture advance welding with a 590 MPa class high-tensile steel plate, and It becomes possible to obtain a weld metal excellent in mechanical performance.

Hereinafter, the present invention will be described in detail.

  First, the reasons for limiting the welding conditions for welding in the standing improvement posture of the flux-cored wire for gas shielded arc welding according to the present invention will be described.

[Amount of heat input: 30-50 kJ / cm]
The amount of heat input is a parameter indicating the amount of heat given by welding, and is calculated from the welding current, welding voltage, and welding speed. When this heat input becomes high, the amount of welding for each pass of multi-layer welding increases, and the welding efficiency can be improved. If the heat input is less than 30 kJ / cm, the welding amount per pass is also small, and the number of layers is inevitably increased, so that the welding efficiency is lowered. On the other hand, if the heat input exceeds 50 kJ / cm, the temperature of the welded part becomes very high and the cooling rate of the welded part becomes slow, so that the weld metal structure becomes coarse and the necessary weld metal strength and toughness are obtained. It becomes difficult to generate hot cracks. Therefore, the heat input is 30 to 50 kJ / cm.

  In addition, the temperature between passes for each layer is preferably set to 150 ° C. or less from the viewpoint of preventing deterioration of mechanical properties due to coarsening of the structure of the weld metal.

  Next, the reason for limiting the component composition of the flux-cored wire of the present invention will be described. The composition of each component is expressed by mass% with respect to the total mass of the wire, and when expressing the mass%, it is simply expressed as%.

[C: 0.02 to 0.08%]
C contributes to the stabilization of the arc during welding and also contributes to increasing the strength of the weld metal by increasing the yield in the weld metal and increasing the hardenability. When C is less than 0.02%, this effect is not sufficiently obtained, and in the vertical improvement welding under large heat input welding conditions, the arc state becomes unstable and the amount of spatter generated increases. The required weld metal strength cannot be obtained. On the other hand, when C exceeds 0.08%, C is excessively yielded in the weld metal, the strength of the weld metal is excessively increased, and the toughness is lowered. In addition, the cracking sensitivity of the weld metal is increased and high temperature cracking is likely to occur. Therefore, C is 0.02 to 0.08% in total of the steel outer shell and the flux. Note that C is added from a steel outer shell, metal powder in a flux, alloy (ferroalloy) powder, or the like.

[Si: 0.3-1.0%]
Si is partly slag during welding to improve the bead appearance and bead shape of the weld bead and contribute to the improvement of welding workability, and the yield in the weld metal improves the strength and toughness of the weld metal. effective. When Si is less than 0.3%, the effect of improving the bead appearance and bead shape is not sufficiently obtained in the standing improvement welding under the high heat input welding conditions, and the required strength of the weld metal is not obtained. Cannot be obtained. On the other hand, if Si exceeds 1.0%, Si is excessively yielded in the weld metal and the toughness is lowered. Therefore, Si is 0.3 to 1.0% in total of the steel outer shell and the flux. In addition, Si is added from Si alloy (ferroalloy) etc. like Fe-Si and Fe-Si-Mn other than steel outer skin and metal Si in the flux.

[Mn: 2.0 to 3.5%]
Mn, like Si, becomes part of the slag during welding to improve the bead appearance and bead shape of the weld bead and contribute to improving the workability of the weld, while yielding to the weld metal and the strength and toughness of the weld metal. There is an effect of improving. When Mn is less than 2.0%, these effects cannot be obtained sufficiently in the standing improvement welding under the high heat input welding conditions, the bead appearance and the bead shape become poor, and the necessary weld metal Strength and toughness cannot be obtained. On the other hand, when Mn exceeds 3.5%, since Mn is excessively yielded in the weld metal, the strength of the weld metal is excessively increased and the toughness is lowered. Therefore, Mn is 2.0 to 3.5% in total of the steel outer shell and the flux. In addition, Mn is added from Mn alloys (ferroalloy) such as Fe—Mn and Fe—Si—Mn, in addition to the steel outer sheath and metal Mn in the flux.

[Ni: 0.1 to 1.0%]
Ni has the effect of improving the toughness of the weld metal. If Ni is less than 0.1%, this effect cannot be sufficiently obtained, and the toughness of the weld metal is lowered in the standing improvement posture welding under the high heat input welding conditions. On the other hand, if Ni exceeds 1.0%, the toughness of the weld metal decreases. Moreover, it becomes easy to generate | occur | produce a hot crack. Therefore, Ni is 0.1 to 1.0% in total of the steel outer shell and the flux. In addition, Ni is added from Ni alloy (ferroalloy) etc. like Fe-Ni other than steel outer shell and metal Ni in the flux.

[Total Al ₂ O ₃ conversion value of Al and Al ₂ O ₃ : 0.4 to 2.3% and Al: 0.2 to 1.1%]
Al and Al ₂ O ₃ adjusts the viscosity and melting point of the slag by being included as Al ₂ O ₃ in the melt pool, in particular, the effect of preventing metal sagging in vertical upward advance position welding. This effect is not sufficiently obtained when the total of Al converted to Al ₂ O ₃ and Al ₂ O ₃ is less than 0.4%. Dripping easily occurs, and the bead appearance and bead shape become poor. On the other hand, if the total of Al ₂ O ₃ converted value of Al and Al ₂ O ₃ exceeds 2.3%, welding defects such as poor fusion and slag entrainment tend to occur. In addition, Al oxide remains in the weld metal as inclusions and the toughness decreases. Therefore, the total of Al ₂ O ₃ converted value of Al and Al ₂ O ₃ is 0.4 to 2.3% in the total of the steel outer shell and the flux.

In addition, when Al is added as a simple substance of Al, the deoxidizing power is very strong, and oxygen in the molten pool is taken in earlier than other deoxidizing agents, so the yield rate of Si and Mn in the weld metal is increased. It has the effect of increasing the strength and toughness of the weld metal. If the Al content is less than 0.2%, the effect cannot be obtained, and in the vertical improvement welding under the high heat input welding conditions, the yield of Si and Mn in the weld metal decreases, and the required weld metal strength And toughness is not obtained. On the other hand, if Al exceeds 1.1%, the arc state becomes rough and the amount of spatter generated increases. Moreover, it remains as an inclusion in the weld metal and the toughness decreases. Therefore, Al is 0.2 to 1.1% in total of the steel outer shell and the flux. In addition, Al and Al ₂ O ₃ are made of steel outer shell or metal Al in the flux, Al alloy (ferroalloy) such as Fe—Al, etc., and Al ₂ O ₃ is alumina in the flux, etc. From.

[B: 0.002 to 0.015%]
B has an effect of refining the microstructure of the weld metal by adding a small amount and improving the toughness of the weld metal. If B is less than 0.002%, this effect cannot be obtained sufficiently, and the toughness of the weld metal is lowered in the standing improvement posture welding under the high heat input welding conditions. On the other hand, if B exceeds 0.015%, the weld metal is excessively hardened, so that the toughness of the weld metal is lowered and hot cracking is likely to occur. Therefore, the total B of the steel outer shell and the flux is set to 0.002 to 0.015%. B is added from a steel alloy or a B alloy (ferroalloy) such as Fe—B or Fe—Mn—B in the flux.

[TiO ₂ converted value of Ti oxides: 5.5 to 6.8%]
Ti oxide contributes to the stabilization of the arc during welding and also has the effect of improving the welding workability by forming a bead appearance and bead shape of the weld bead as a slag during welding. In addition, in the vertical improvement welding, there is an effect of adjusting the viscosity and melting point of the slag and preventing metal dripping. When the TiO ₂ equivalent value of the Ti oxide is less than 5.5%, these effects cannot be obtained sufficiently, and in the standing posture advance welding under the high heat input welding conditions, the arc state becomes unstable, Spatter generation increases. Also, metal dripping is likely to occur, and the bead shape and bead appearance also become poor. On the other hand, when the TiO ₂ equivalent value of the Ti oxide exceeds 6.8%, the Ti oxide remains excessively in the weld metal and the toughness is lowered. Therefore, the TiO ₂ equivalent value of the Ti oxide in the flux is set to 5.5 to 6.8%. The Ti oxide is added from rutile, titanium oxide, titanium slag, illuminite or the like in the flux.

[SiO ₂ converted value of Si oxide: 0.4 to 1.6%]
Si oxide has the effect of adjusting the viscosity and melting point of molten slag to improve slag encapsulation and slag peelability. If the SiO ₂ equivalent value of the Si oxide is less than 0.4%, this effect cannot be obtained sufficiently, and the slag encapsulation and slag peelability are not improved in the standing improvement advance welding under the welding conditions with high heat input. breaking bad. On the other hand, if the SiO ₂ equivalent value of the Si oxide exceeds 1.6%, the basicity of the molten slag decreases, the oxygen content of the weld metal increases, and the toughness decreases. Accordingly, the SiO ₂ equivalent value of the Si oxide in the flux is 0.4 to 1.6%. Si oxide is added from silica sand, zircon sand or the like in the flux.

[ZrO ₂ converted value of Zr oxide: 0.1 to 0.6%]
The Zr oxide is included in the slag as Zr oxide during welding, thereby adjusting the viscosity and melting point of the slag, and in particular, has an effect of preventing metal sag in the standing improvement posture welding. If the ZrO ₂ conversion value of the Zr oxide is less than 0.1%, this effect cannot be obtained sufficiently, and metal dripping is likely to occur in the standing improvement posture welding under the high heat input welding conditions. On the other hand, when the ZrO ₂ conversion value of the Zr oxide exceeds 0.6%, the slag becomes dense and hardens, resulting in poor slag removability. In addition, the oxygen content of the weld metal increases and the toughness decreases. Therefore, the ZrO ₂ conversion value of the Zr oxide in the flux is set to 0.1 to 0.6%. The Zr oxide is added from zircon sand and zirconium oxide in the flux.

[Mg: 0.1-0.3%]
Mg functions as a strong deoxidizer, thereby reducing the amount of oxygen in the weld metal and increasing the toughness of the weld metal. If Mg is less than 0.1%, this effect cannot be sufficiently obtained, and in the standing improvement posture welding under the high heat input welding conditions, the amount of oxygen in the weld metal does not decrease, and the toughness decreases. On the other hand, if Mg exceeds 0.3%, the arc state becomes rough, the amount of spatter generation increases, and metal dripping is likely to occur. Therefore, Mg in the flux is 0.1 to 0.3%. In addition, Mg is added from Mg alloy (ferroalloy) etc. like Al-Mg other than metal Mg in a flux.

[Sum of the _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound: 0.10 to 0.20%]
Na compound and K compound act as an arc stabilizer and a slag forming agent during welding. When the sum of the K _{2 O} conversion value of terms of Na 2 _O values and K compounds of Na compound is less than 0.10%, in the vertical upward advance position welding in welding conditions high heat input arc state not As a result, the amount of spatter generated becomes stable, and the bead appearance and bead shape become poor. On the other hand, if the total of the K _{2 O} conversion value of terms of Na 2 _O values and K compounds of Na compound exceeds 0.20%, the slag removability is poor, so the metal dripping is likely to occur. Therefore, the sum of _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound in flux, and 0.10 to 0.20%. The Na compound and the K compound are added from a potassium feldspar, a solid component of water glass made of sodium silicate or potassium silicate, or a fluorine compound such as sodium fluoride fluoride or sodium silicate in the flux.

[Mo: 0.1 to 0.3%]
Mo has the effect of increasing the hardenability and refining the structure by increasing the yield in the weld metal, and increasing the strength and toughness of the weld metal. If Mo is less than 0.1%, this effect cannot be obtained sufficiently, and the required strength of the weld metal cannot be obtained in the stand-up improvement posture welding under the high heat input welding conditions. On the other hand, when Mo exceeds 0.3%, Mo is excessively yielded in the weld metal, the strength of the weld metal is excessively increased, and the toughness is reduced. Therefore, Mo in the flux is 0.1 to 0.3%. In addition, Mo is added from Mo alloy (ferroalloy) etc. like Fe-Mo other than the metal Mo in a flux.

[Total with Bi converted value of Bi and Bi oxide: 0.003 to 0.02%]
Bi has the effect of facilitating the slag peeling from the weld metal and improving the slag peelability in multi-layer welding. If the sum of Bi and Bi oxide with Bi converted value is less than 0.003%, the effect cannot be obtained, and the slag peelability becomes poor in the standing improvement posture welding under the high heat input welding conditions. . On the other hand, if the total of Bi and Bi oxide with Bi converted value exceeds 0.02%, the toughness of the weld metal is lowered and hot cracking is likely to occur. Therefore, the sum of Bi in the flux and Bi converted value of Bi oxide is set to 0.003 to 0.02%. Bi and Bi oxide are added from metal Bi, oxide Bi, etc. in the flux.

  The reason for limiting the constituent requirements of the component composition of the flux-cored wire for gas shielded arc welding according to the present invention has been described above. Fe is a steel outer shell Fe, iron powder of flux, Fe of iron alloy (ferroalloy) powder such as Fe-Mn, Fe-Si, Fe-Si-Mn alloy, etc. An appropriate amount can be added for the purpose of adjusting the flux filling rate of the cored wire. Inevitable impurities are impurities inevitably mixed in such as P and S. From the viewpoint of hot cracking resistance, P: 0.050% or less and S: 0.05% or less are preferable.

  In addition, the flux cored wire for welding consists of a steel outer shell formed into a pipe shape and filled with flux inside, and a seamless seamless type in which the ends of the steel outer shell are welded to each other, and the end of the steel outer shell. There is a caulking type in which the parts are caulked together, but when used in welding in a low temperature environment, a seamless type with excellent moisture absorption resistance is preferable because of low temperature cracking prevention and preheating temperature reduction. It is preferable that it is a flux-cored wire for welding to which copper plating having good properties is applied.

The flux-cored wire for gas shielded arc welding of the present invention preferably uses CO ₂ as the shielding gas. Moreover, the wire diameter of the flux-cored wire for welding is 1.2 to 1.6 mm, and the filling rate of the flux is not particularly limited, but is preferably 11 to 20% from the viewpoint of productivity.

Hereinafter, the effect of the present invention will be described in detail with reference to examples.
SPHC (C: 0.02%, Si: 0.01%, Mn: 0.40%, P: 0.02%, S: 0.01%) described in JIS G 3141 is used as a steel outer shell. No. 1 filled with various fluxes shown in Table 1 at a flux filling rate of 15% and reduced in diameter to 1.2 mm. Various types of flux-cored wires for welding having components of 1 to 24 were produced.

  Using various prototype wires shown in Table 1, gas shielded arc welding was performed in a standing improvement posture under the welding conditions (W1 to W5) shown in Table 2 to investigate welding workability and mechanical properties.

  JIS G3136 SM570 steel with a plate thickness of 20 mm is used as a test plate, and a gas shielded arc welding is performed on a test piece with a groove angle of 35 °, a root interval of 7 mm, and a backing material in a standing improvement posture under the welding conditions shown in Table 2. The arc stability, spatter generation amount, slag encapsulation, slag peelability, bead appearance and bead shape, presence of metal dripping, presence of hot cracking, etc. were investigated. For welding defects such as poor fusion and slag entrainment, an X-ray transmission test was conducted in accordance with JIS Z 3104 to investigate the presence or absence of welding defects.

  In the weld metal test, a tensile test piece (JIS Z 2201 A0) and an impact test piece (JIS Z 2204 No. 4) were collected from the central part of the thickness of the weld metal, and a tensile test and an impact test were performed. In the tensile test, the tensile strength was 610 to 710 MPa or more, and in the impact test, the average value of three absorbed energy at a test temperature of −20 ° C. was 60 J or more. The results are summarized in Table 3. In addition, No. shown in Table 3 No. of the flux-cored wire component shown in Table 1. Is shown.

  In Table 3, No. 1-9 are examples of the present invention, No. 10 to 26 are comparative examples.

No. which is an example of the present invention. 1-5, C of the sum of the steel sheath and the flux in the flux cored wire, Si, Mn, Ni, Al , the sum of terms _{of Al} 2 _{O 3} value and _Al 2 _{O 3} of Al, the content of B Appropriate amounts of TiO ₂ converted value, SiO ₂ converted value, ZrO ₂ converted value, Mg, Na ₂ O converted value, and K ₂ O converted value in the flux, and Bi converted values of Mo, Bi, and Bi oxides The total amount of heat is appropriate and the heat input is also appropriate, so the welding conditions for large heat input are improved and the arc state is stable, the spatter generation is small, slag encapsulation, and slag peelability The bead appearance and bead shape were good, there was no metal dripping, no hot cracking occurred, and the welding workability was good. In addition, welding defects such as poor fusion and slag entrainment did not occur, and the tensile strength and absorbed energy of the weld metal were good, which was a very satisfactory result. In addition, No. 6 and no. In No. 7, since Mo was not contained in the flux, the tensile strength and absorbed energy of the weld metal were slightly low, but there was no problem in product quality. No. 8 and no. In No. 9, since Bi and Bi oxide were not contained in the flux, the slag peelability was slightly poor, but the bead shape was good and the quality as a product was satisfactory.

No. in the comparative examples. No. 10, because the total C of the steel outer shell and the flux is small, the arc state is unstable, the spatter generation amount is large, and the tensile strength of the weld metal in the vertical improvement welding under the high heat input welding conditions. Was low. In addition, since there is little in terms of ZrO ₂ value in the flux, metal dripping has occurred. Furthermore, since there is little Mg in a flux, the absorbed energy of the weld metal was low.

No. No. 11 had a high total of C of the steel outer shell and the flux, and therefore hot cracking occurred. Moreover, the tensile strength of the weld metal was high and the absorbed energy was low. Further, since the total of Na ₂ O converted value and K ₂ O converted value in the flux was small, the arc state was unstable, the amount of spatter was increased, and the bead appearance and bead shape were poor.

No. In No. 12, since the total amount of Si in the steel outer shell and the flux was small, the bead appearance and bead shape were poor, and the tensile strength of the weld metal was low. Also, since there are many terms of SiO ₂ value in the flux was less absorbed energy of the weld metal.

  No. No. 13 had a large amount of Si in the steel outer shell and flux, so the absorbed energy of the weld metal was low. Moreover, since there was much Mg in a flux, the arc state was rough, spatter generation amount was large, and metal dripping also generate | occur | produced. Furthermore, since Mo is not contained in the flux, the tensile strength of the weld metal was low.

No. In No. 14, since the total Mn of the steel outer shell and the flux was small, metal sagging occurred, the bead appearance and the bead shape were poor, and the tensile strength and absorbed energy of the weld metal were low. Also, since less in terms of SiO ₂ value in the flux, the slag encapsulated and the slag removability was poor.

No. In No. 15, since the total amount of Mn of the steel outer shell and the flux was large, the tensile strength of the weld metal was high and the absorbed energy was low. Further, since the sum of the terms of Na 2 _O values and K _{2 O} conversion value of the flux is large, the slag removability is bad, metal sagging occurs.

  No. No. 16 had a low absorbed energy of the weld metal because the total Ni of the steel outer shell and the flux was small. Moreover, since Bi and Bi oxide were not contained in the flux, the slag peelability was poor.

  No. In No. 17, since the total amount of Ni of the steel outer shell and the flux was large, hot cracking occurred and the absorbed energy of the weld metal was low.

No. 18, since the sum of terms of Al ₂ O ₃ value and Al ₂ O ₃ of a total of Al steel sheath and the flux is small, the metal sag occurs, bead appearance and the bead shape was also poor. Moreover, since the total Al of the steel outer shell and the flux was small, the tensile strength and absorbed energy of the weld metal were low.

No. In No. 19, since the sum of Al of the steel outer shell and flux and the Al ₂ O ₃ conversion value of Al and the total of Al ₂ O ₃ were large, slag entrainment occurred and the absorbed energy of the weld metal was low. Moreover, since there was much Al of the sum total of a steel outer_layer | skin and a flux, the arc state was rough and there was much spatter generation amount.

No. In No. 20, since the total B of the steel outer shell and the flux was small, the absorbed energy of the weld metal was low. Further, since the TiO ₂ equivalent value in the flux was small, the arc state was unstable, the amount of spatter was large, metal dripping occurred, and the bead appearance and bead shape were also poor.

  No. In No. 21, since the total B of the steel outer shell and the flux was large, hot cracking occurred. Also, the absorbed energy of the weld metal was low. Furthermore, since the heat input was low, the welding efficiency was poor.

No. 22, since there are many terms of TiO ₂ values in the flux was less absorbed energy of the weld metal.

No. 23, since there are many terms of ZrO ₂ value in the flux, the slag removability is poor, was less absorbed energy of the weld metal.

  No. No. 24 had a high heat input, so the tensile strength and absorbed energy of the weld metal were low.

No. No. 25 had poor slag encapsulation and slag removability because the SiO ₂ conversion value in the flux was small. Moreover, since there was much Mo in a flux, the tensile strength of the weld metal was high and the absorbed energy was low.

No. No. 26 had a small TiO ₂ conversion value, so the arc state was unstable, the amount of spatter was large, metal dripping occurred, and the bead appearance and bead shape were poor. Moreover, since there were many sum totals with the Bi conversion value of Bi and Bi oxide in a flux, the high temperature crack generate | occur | produced and the absorbed energy of the weld metal was low.

Claims (2)

In the flux-cored wire for gas shielded arc welding formed by filling the steel outer shell with flux,
The total of steel outer shell and flux,
C: 0.02 to 0.08%,
Si: 0.3 to 1.0%,
Mn: 2.0 to 3.5%
Ni: 0.1 to 1.0%,
Total of Al ₂ O ₃ equivalent and Al ₂ O ₃ : 0.4 to 2.3%, and Al: 0.2 to 1.1%,
B: contains 0.002 to 0.015%,
To the flux,
TiO ₂ conversion value of Ti oxide: 5.5 to 6.8%,
SiO ₂ conversion value of Si oxide: 0.4 to 1.6%,
ZrO ₂ conversion value of Zr oxide: 0.1 to 0.6%,
Mg: 0.1 to 0.3%
The sum of the _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound: containing 0.10 to 0.20%,
A flux-cored wire for gas shielded arc welding for stand-up improvement welding under welding conditions with a heat input of 30 to 50 kJ / cm, wherein the balance is made of Fe and inevitable impurities.   In the mass% with respect to the total mass of the wire, the flux further contains Mo: 0.1 to 0.3%, and the sum of Bi and Bi oxide Bi converted values: 0.003 to 0.02%. The flux-cored wire for gas shielded arc welding for stand-up advance welding under welding construction conditions with a heat input of 30 to 50 kJ / cm according to claim 1.