JP5706354B2 - Coated arc welding rod for duplex stainless steel - Google Patents

Description

  The present invention is used for welding inexpensive duplex stainless steel, and can provide a weld metal having mechanical performance comparable to that of the base metal, good corrosion resistance, excellent resistance to defects such as blow holes, and welding. The present invention relates to a coated arc welding rod for duplex stainless steel having good workability.

  Conventionally, duplex stainless steels represented by SUS329J3L and SUS329J4L are stainless steels having excellent corrosion resistance and strength characteristics. As the grade of this duplex stainless steel, the pitting corrosion resistance index PRE (Cr% + 3.3 Mo% + 16 N%) or PREW (Cr% + 3) is based on Cr, Mo, N, and W contained in the chemical composition. .3 (Mo% + 0.5 W%) + 1.6 N%). As applications, it is used as a corrosion-resistant material for chemical plants, chemical equipment, oil wells, gas wells and the like that require corrosion resistance, and because of its high strength, it is also used as a steel structural member.

  In recent years, a low-priced duplex stainless steel with a low pitting corrosion resistance index PRE has been developed. S32101 and S32304 have been put into practical use. The applicable welding material has an index equal to or higher than the pitting corrosion resistance index of these steel materials, and a sound weld metal and welding workability are required.

  Under such circumstances, development of a coated arc welding rod having excellent mechanical performance and good welding workability is desired. However, there is a problem that welding defects such as blow holes occur when duplex stainless steel containing a large amount of N is welded. In addition, the slag peelability is extremely poor, and there is a problem that it is necessary to add a process for removing slag by jet chisel or the like.

  As a technique for solving this problem, for example, Japanese Patent Application Laid-Open No. 2002-248598 (Patent Document 1) discloses a coated arc welding rod that defines Ni, Cr, Mo, and N and has good corrosion resistance. However, this coated arc welding rod contains a large amount of expensive Ni and Mo, and is expensive and unsuitable for inexpensive duplex stainless steel welding. In addition, oxides, fluorine compounds and metal carbonates that act on the superiority and inferiority of welding workability are not defined, and there is a problem that arc stability and slag peelability are inferior.

Japanese Patent Laid-Open No. 2003-1488 (Patent Document 2) discloses a coated arc welding rod in which the content of TiO ₂ , SiO ₂ , CaCO ₃ and AlF ₃ is limited as a coating agent to improve welding workability. Is disclosed. However, since this coated arc welding rod uses expensive duplex stainless steel for the core wire, it is unsuitable for practical use, and has good welding workability in conventional duplex stainless steel welding. However, when applied to the welding of inexpensive duplex stainless steel, there is a problem that the defect resistance deteriorates.

JP 2002-248598 A JP 2003-1488 A

  By using the present invention for welding of inexpensive duplex stainless steel, it is possible to obtain a weld metal having the same mechanical performance as the base metal, good corrosion resistance, and excellent defect resistance such as blowholes, It is another object of the present invention to provide a coated arc welding rod for duplex stainless steel having good welding workability.

The gist of the present invention is that, in a coated arc welding rod for duplex stainless steel in which a coating is coated on an austenitic stainless steel core wire, the mass is based on the total mass of the coated arc welding rod, and the total of the core wire and the coating agent. C: 0.04% or less, Si: 0.15-0.85%, Mn: 0.5-3.0%, Ni: 5-10%, Cr: 19-28%, Mo: 0.2 -1.0%, N: 0.05-0.2%, and furthermore, the sum of Bi and Bi converted value of Bi oxide in the coating agent: 0.02-0.05%, Ti TiO ₂ equivalent value of oxide: 10.0 to 15.0%, SiO ₂ equivalent value of Si oxide: 1.0 to 1.5%, ZrO ₂ equivalent value of Zr oxide: 0.1 to 0. 2% _Al 2 _{O 3} conversion value of Al oxide: 0.7 to 1.2% MgO converted value of Mg oxide: 0.1 to 0.2 percent, a metal carbonitride One or more of the total salt: 4.0 to 6.0%, F converted value of the fluorine compounds: 0.6 to 1.0%, _K of terms of Na ₂ O values and K compounds of Na Compound ₂ Total of one or two kinds of O converted values: 0.2 to 1.5%, the balance being Fe content of core wire, Fe content of iron alloy in coating agent and inevitable impurities It is in the coated arc welding rod for duplex stainless steel.

  According to the coated arc welding rod for duplex stainless steel of the present invention, it is used for welding inexpensive duplex stainless steel, a weld metal having mechanical performance comparable to that of the base material is obtained, and the corrosion resistance is good. It is possible to provide a coated arc welding rod for duplex stainless steel having excellent defect resistance such as blowholes and good welding workability.

  In order to solve the above-mentioned problems, the inventors made various types of coated arc welding rods as prototypes, and applied each of them to mechanical performance, corrosion resistance, welding workability, and defect resistance when applied to duplex stainless steel welding. The effect of component composition was investigated in detail.

  As a result, the amount of Cr, Mo, and Si that are ferrite forming elements is adjusted, the crystallization of ferrite is stabilized, and N is dissolved in the ferrite phase to improve the corrosion resistance of the deposited metal, thereby improving the slag removability and blowing. Improved resistance to defects such as holes. Moreover, the mechanical performance of the deposited metal was made comparable to that of the base material by adjusting the amounts of C, Mn and Ni. Furthermore, it has been found that better welding workability can be obtained than addition of appropriate amounts of Ti oxide, metal carbonate, Na and K oxides and compounds as arc stabilizers and slag forming agents.

The present invention can be achieved by the synergistic effect of the austenitic stainless steel core wire and each component composition of the individual and the coexistence of the respective components. The following is a description of the coated arc welding rod for duplex stainless steel of the present invention. The reason for limiting the component composition will be described.
The following components can be contained in both the core wire and the coating agent.

[C: 0.04 mass% or less]
C easily bonds to Cr and precipitates as Cr carbide at the grain boundaries. As a result, a Cr-deficient layer is formed at the grain boundary and deteriorates the corrosion resistance. Therefore, the C content is 0.04% or less in terms of mass% (hereinafter referred to as%) with respect to the total mass of the coated arc welding rod. C of the coating agent is C containing a small amount of iron alloy powder such as Fe-Si, Fe-Mn, and Fe-Si-Mn.

[Si: 0.15-0.85%]
Si has the effect of reducing the viscosity of the molten metal and improving the bead shape. If Si is less than 0.15%, the effect is insufficient. On the other hand, if it exceeds 0.85%, precipitation of the σ phase is promoted and ductility is lowered. Therefore, Si is 0.15 to 0.85%. The coating Si is Si from metals Si, Fe-Si and Fe-Si-Mn.

[Mn: 0.5 to 3.0%]
Mn has the effect of increasing the solid solubility of N, improving the yield of N, and improving the strength of the deposited metal. If Mn is less than 0.5%, the effect is insufficient. On the other hand, if it exceeds 3.0%, precipitation of intermetallic compounds is promoted and corrosion resistance is deteriorated. Therefore, Mn is 0.5 to 3.0%. The coating Mn is Mn from metal Mn, Fe-Mn, Mn nitride, Fe-Si-Mn, and the like.

[Ni: 5 to 10%]
Ni has the effect of strengthening the matrix of the austenite phase and improving the toughness of the deposited metal. If Ni is less than 5%, the effect is insufficient. On the other hand, if it exceeds 10%, the amount of crystallization of austenite increases and the strength of the deposited metal decreases. Therefore, Ni is 5 to 10%. The coating Ni is Ni from metal Ni and Fe-Ni.

[Cr: 19-28%]
Cr is a component necessary for ensuring corrosion resistance. If Cr is less than 19%, the effect is insufficient. On the other hand, if it exceeds 28%, the σ phase is precipitated and the ductility of the deposited metal is lowered. Therefore, Cr is 19 to 28%. The coating Cr is Cr from metal Cr, Fe—Cr, nitride Fe—Cr and the like.

[Mo: 0.2 to 1.0%]
Mo has the effect of improving the corrosion resistance, strengthening the matrix of the weld metal, and improving the strength of the deposited metal. If Mo is less than 0.2%, the effect is insufficient. On the other hand, if it exceeds 1.0%, precipitation of the σ phase is promoted and the ductility of the deposited metal is lowered. Therefore, Mo is 0.2 to 1.0%. The coating Mo is Mo from metal Mo and Fe-Mo.

[N: 0.05 to 0.2%]
N is an austenite-generating component and has the effect of strengthening the matrix and improving the strength and toughness of the deposited metal. If N is less than 0.05%, the effect is insufficient. On the other hand, if it exceeds 0.2%, blow holes frequently occur and defects increase. Further, since a large amount of nitride precipitates, the toughness of the deposited metal deteriorates. Therefore, N is set to 0.05 to 0.2%. N of the coating is N from Mn nitride and Fe-Cr nitride.
The following components are contained in the coating agent.

[Sum of Bi and Bi converted value of Bi oxide: 0.02 to 0.05%]
Bi and Bi oxide have a low melting point and improve slag removability. If the sum of Bi and Bi converted value of Bi oxide is less than 0.02%, the effect is insufficient. On the other hand, when it exceeds 0.05%, it precipitates as an oxide and deteriorates the toughness of the deposited metal. Therefore, the sum of Bi and Bi converted value of Bi oxide is 0.02 to 0.05%.

[TiO ₂ converted value of Ti oxides: 10.0 to 15.0%]
Ti oxides such as rutile and titanium slag are added in order to form a slag with good encapsulation. When the TiO ₂ equivalent value of the Ti oxide is less than 10.0%, the effect is insufficient, and the bead appearance is poor. On the other hand, if it exceeds 15.0%, a large amount of slag is generated, the slag interferes with the molten pool being welded, and the arc becomes unstable. Therefore, the TiO ₂ equivalent value of the Ti oxide is set to 10.0 to 15.0%.

[Si oxide SiO ₂ equivalent value: 1.0 to 1.5%]
Si oxides such as silica sand and zircon sand are added to reduce the viscosity of the slag and make the bead alignment uniform. If the SiO ₂ conversion value of the Si oxide is less than 1.0%, the effect is insufficient. On the other hand, if it exceeds 1.5%, the solidification of the slag becomes slow and the beads are likely to sag, and the alignment of the end portions of the beads becomes uneven. Therefore, the SiO ₂ equivalent value of the Si oxide is 1.0 to 1.5%.

[ZrO ₂ converted value of Zr oxide: 0.1 to 0.2%]
Zr oxides such as zircon sand and zircon oxide are added to increase the viscosity of the slag and smooth the beads. Since Ti oxide having a high melting point is added, it is added in an auxiliary role. If the ZrO ₂ conversion value of the Zr oxide is less than 0.1%, the effect is insufficient. On the other hand, when it exceeds 0.2%, it becomes easy to combine with N and the slag peelability deteriorates. Therefore, the ZrO ₂ conversion value of the Zr oxide is set to 0.1 to 0.2%.

[Al ₂ O ₃ converted value of Al oxide: 0.7 to 1.2%]
Al oxide such as alumina is added for the purpose of strengthening the arc spray and stabilizing the arc. Terms _{of Al} 2 _{O 3} value of Al oxide is less than 0.7%, the effect is insufficient. On the other hand, if it exceeds 1.2%, the arc spraying becomes strong and the amount of spatter generated increases. Therefore, the Al ₂ O ₃ equivalent value of the Al oxide is set to 0.7 to 1.2%.

[MgO converted value of Mg oxide: 0.1 to 0.2%]
Mg oxides such as magnesia clinker and natural magnesia are added to improve the fluidity of the slag and smooth the beads. If the MgO equivalent value of the Mg oxide is less than 0.1%, the effect is insufficient. On the other hand, if it exceeds 0.2%, the bead becomes convex and the shape deteriorates. Accordingly, the MgO equivalent value of the Mg oxide is set to 0.1 to 0.2%.

[Total of one or more metal carbonates: 4.0 to 6.0%]
Metal carbonates such as CaCO _3, BaCO _3, and MgCO ₃ are added for smooth transition of droplets and good arc stability and bead shape. If the total of one or more metal carbonates is less than 4.0%, the effect is insufficient and the bead shape deteriorates. On the other hand, if it exceeds 6.0%, the droplets grow greatly and the amount of spatter generated increases. Therefore, the total of one or more metal carbonates is 4.0 to 6.0%.

[F conversion value of fluorine compound: 0.6 to 1.0%]
F from fluorine compounds such as fluorite, aluminum fluoride, sodium fluoride and potassium fluoride is added to make the slag fluidity proper. When the F-converted value of the fluorine compound is less than 0.6%, the flow of slag is poor and the arc is difficult to sustain and becomes unstable. On the other hand, if it exceeds 1.0%, the amount of spatter generated increases. Therefore, the F converted value of the fluorine compound is set to 0.6 to 1.0%.

[One or two sum of _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compounds 0.2 to 1.5%
Na compounds such as Na oxides and K compounds such as K oxides from sodium silicate, potassium silicate, potassium feldspar and the like are added to improve the arc stability. One or total, the effect is less than 0.2 K _{2 O} conversion value of the terms of Na 2 _O values and K compounds of Na compound is insufficient. On the other hand, if it exceeds 1.5%, the coating agent in the coated arc welding rod absorbs moisture and the arc becomes unstable. Therefore, the sum of one or two _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound to 0.2 to 1.5%.

  In the coated arc welding rod for duplex stainless steel of the present invention, the component composition other than the above components is not particularly defined. Accordingly, the composition of Cu, Nb, W, etc. can be variously adjusted in consideration of the mechanical performance, corrosion resistance and welding workability of the deposited metal. However, P and S that promote hot cracking are preferably as small as possible, and P + S is preferably 0.045% or less.

  The coverage applied to the core wire of the coating agent is not particularly limited, but it is 30% or more in consideration of the stability of welding workability, and 40% or less in order to ensure the manufacturability of the coated arc welding rod. preferable.

Hereinafter, the present invention will be described in detail by way of examples.
Using the austenitic stainless steel core wires having chemical components shown in Table 1, coated arc welding rods for duplex stainless steels having various compositions shown in Table 2 were produced. The core wire diameter was 4.0 mm, and the coating rate was 30 to 40%.

  In the welding test, a two-layer buttering was performed in the groove based on JIS Z 3221 using SM490A defined in JIS G 3106, and a weld metal test was performed. After welding, an X-ray transmission test was performed based on JIS Z 3106, and the state of blowhole generation in the weld metal part was confirmed. The weld metal performance was based on JIS Z 3111, and a tensile test and an impact test were performed. The corrosion test was based on JIS G 0577.

  In the X-ray transmission test, the first type scratch score was less than 5 points. As for the weld metal performance, the tensile strength of the tensile test: 690 MPa or more, the elongation: 20% or more, the absorbed energy at −20 ° C. of the impact test: 27 J or more, and the pitting corrosion potential of the corrosion test: 350 mV or more.

  For welding workability, horizontal fillet welding was performed using duplex stainless steels having chemical components shown in Table 3, and the arc stability, spatter generation state, bead appearance, and bead shape were examined. In addition, the welding current of the welding metal test and the investigation of welding workability was performed at 120 to 160A. The results are summarized in Table 4.

  In Tables 2 and 4, the welding rod No. 1 to 10 are examples of the present invention, welding rod Nos. Reference numerals 11 to 24 are comparative examples. The welding rod no. Nos. 1 to 10 have appropriate component composition amounts, so the X-ray transmission test is good, the tensile strength, elongation, absorbed energy and pitting potential of the weld metal are high, and the welding workability is also very satisfactory. It was a result.

In the comparative example, the welding rod No. No. 11 had a low pitting corrosion potential because of a small amount of Cr. Further, since N is large, the number of scratches by the X-ray transmission test was high, and the absorbed energy of the deposited metal was low. Furthermore, the arc was unstable because the total of Na ₂ O converted value and K ₂ O converted value was small.
Welding rod no. No. 12 had a large amount of Cr, so the elongation of the deposited metal was low. Further, the arc was unstable because TiO ₂ converted value is large.

Welding rod no. No. 13 had a poor bead shape because of its large SiO ₂ conversion value. Moreover, since there was much C, the pitting corrosion potential was low.
Welding rod no. No. 14 had a low pitting potential because of a large amount of Mn. Moreover, since there was little Si, the bead shape was unsatisfactory.

Welding rod no. No. 15 had a low tensile strength of the weld metal because of the large amount of Ni. Moreover, the slag removability was poor because terms of ZrO ₂ value is large.
Welding rod no. No. 16 had a low tensile strength of the deposited metal because of a small amount of Mn. Moreover, since there were many MgO conversion values, the bead shape was unsatisfactory. In addition, the amount of spatter generated was large due to the large amount of metal carbonate.

Welding rod no. Since No. 17 had a large sum of Bi and Bi-converted value of Bi oxide, the absorbed energy of the weld metal was low. Further, peeling of the slag was poor because SiO ₂ converted value is small.
Welding rod no. In No. 18, since the amount of Si was large, the elongation of the deposited metal was low. Moreover, since the Al ₂ O ₃ conversion value is large, the amount of spatter generated was large. In addition, the bead shape was poor because there was little metal carbonate.

Welding rod no. In No. 19, since there was much Mo, the elongation of the deposited metal was low. Further, the bead shape was poor because terms of Na 2 _O values and K sum is often the _{2 O} equivalent.
Welding rod no. No. 20 had low Mo, so the tensile strength of the deposited metal was low. Moreover, since the Al ₂ O ₃ conversion value was small, the arc was unstable.

Welding rod no. No. 21 had low N, so the tensile strength of the weld metal was low. Moreover, since the MgO conversion value was small, the bead shape was poor.
Welding rod no. No. 22 had low Ni, so the absorbed energy of the deposited metal was low. Further, since the ZrO ₂ conversion value was small, the bead shape was poor.

Welding rod no. Since No. 23 had little sum of Bi and Bi conversion value of Bi oxide, slag peelability was unsatisfactory. Further, since the F conversion value is large, the amount of spatter generated is large.
Welding rod no. No. 24 had a poor TiO ₂ conversion value, so the slag encapsulation was poor and the bead appearance was poor. Moreover, since the F conversion value is small, the arc is unstable.

Claims (1)

In the coated arc welding rod for duplex stainless steel, where the coating agent is coated on the austenitic stainless steel core wire, in mass% with respect to the total mass of the coated arc welding rod,
C: 0.04% or less,
Si: 0.15-0.85%,
Mn: 0.5 to 3.0%
Ni: 5 to 10%
Cr: 19 to 28%,
Mo: 0.2 to 1.0%,
N: 0.05-0.2%
In addition, the coating agent
Sum of Bi and Bi converted value of Bi oxide: 0.02 to 0.05%,
TiO ₂ conversion value of Ti oxide: 10.0 to 15.0%,
SiO ₂ conversion value of Si oxide: 1.0 to 1.5%,
ZrO ₂ conversion value of Zr oxide: 0.1 to 0.2%,
Al ₂ O ₃ conversion value of Al oxide: 0.7 to 1.2%,
MgO converted value of Mg oxide: 0.1-0.2%,
Total of one or more metal carbonates: 4.0 to 6.0%,
F conversion value of fluorine compound: 0.6 to 1.0%,
One or two of a total of _{K 2} O conversion value of terms of Na ₂ O values and K compounds of Na compound: 0.2 to 1.5%
And the balance is the Fe content of the core wire, the Fe content of the iron alloy in the coating agent, and the inevitable impurities, and a coated arc welding rod for duplex stainless steel.