JP6939508B2 - Corrosion-resistant steel gas shield arc welding flux-cored wire and welding joint manufacturing method - Google Patents

Description

The present invention relates to a flux-cored wire for gas shielded arc welding suitable for welding corrosion-resistant steel, and a method for manufacturing a welded joint.

Weathering steels that have been exposed for extended periods of time in an air corrosive environment generally have a protective rust layer formed on their surface. Since this rust layer shields corrosive substances from the outside world, corrosion of steel materials after the formation of the rust layer is suppressed, and weather resistance is exhibited. Therefore, weathering steel is used for structures such as bridges as a steel material that can be used naked without painting.

However, in an environment with a large amount of flying salt, such as in the inland area where snow melting agents are sprayed in addition to the beach area, it is difficult for a protective rust layer to form on the surface of the weathering steel, which suppresses corrosion. It is difficult for the effect to be exhibited. Therefore, in these areas, weathering steel cannot be used naked and must be painted.

Further, in the above-mentioned environment with a large amount of flying salt, deterioration of the coating film causes scratches on the coating film, and the steel material directly under the scratched coating film is directly exposed to the corrosive environment. It shows a corrosive form in which the film swells. As the corrosion form progresses, the scratched part of the coating film gradually expands and the corrosion of the structure continues to progress. Therefore, repainting is carried out about every 10 years for the purpose of extending the life of the structure. Often. However, since repainting requires a large amount of man-hours, new corrosion-resistant steel has been developed that can reduce maintenance costs by extending the painting life and greatly extending the repair painting interval, and welding corresponding to this has been developed. There is a demand for the development of welding materials for gas shield welding.

As a welding material having excellent corrosion resistance, for example, in Patent Document 1, regarding welding of high Ni-based high weather resistant steel, by containing an appropriate amount of S and Bi in the wire, good welding workability, particularly excellent slag peeling Disclosed is a gas shielded arc welding solid wire that imparts corrosion resistance to sea salt without impairing the corrosion resistance of the base metal by containing Ni in the wire and suppressing Cr to a low level. There is.

However, although the solid wire for welding described in Patent Document 1 is superior in corrosion resistance of the weld metal as compared with the case of welding with a normal welding material, it is a new type used by painting in the above-mentioned environment with a large amount of flying salt. When used for welding corrosion-resistant steel, sufficient corrosion resistance of the weld metal cannot be obtained. Further, the coated portion of the welded steel sheet does not have a sufficient coating film life. Furthermore, horizontal fillet welding is mainly used for bridge welding, but when solid wire for welding is used for horizontal fillet welding, the appearance and shape of the bead deteriorates and the amount of spatter generated is large, so spatter removal There is a problem that work efficiency is poor due to a large amount of time and effort.

From this point of view, in horizontal fillet welding, a gas shielded arc welding flux-containing wire with a soft arc, a small amount of spatter, and a good bead appearance and shape is widely used, and the welding flux has excellent corrosion resistance. As an entry wire, for example, in Patent Document 2, welding is performed by adding an appropriate amount of Si, Mn, Al, and Mg while ensuring excellent corrosion resistance of the weld metal by adding an appropriate amount of Cu, Cr, and Ni to the wire. Welding workability such as metal sagging resistance is good by improving the mechanical performance of metal and _{adding appropriate amounts of TiO 2} , SiO ₂ , Al ₂ O ₃ , ZrO ₂ and Mg, and the entire posture of the fixed pipe. A flux-filled wire for gas shielded arc welding for corrosion-resistant steel that can be welded is disclosed.

However, although the flux-containing wire described in Patent Document 2 has the effect of improving the corrosion resistance of the weld metal by adding appropriate amounts of Cu, Cr, and Ni, it is used by coating in an environment with a large amount of flying salt. When used for welding new corrosion-resistant steel, sufficient corrosion resistance of the weld metal cannot be obtained. Further, the coating film on the surface of the steel sheet does not have a sufficient coating film life.

Further, Patent Document 3 discloses a flux-cored wire for electrogas arc welding, which can obtain durability and good weldability of resin coating by welding a resin coated steel sheet used in an environment where salt flying is unavoidable. Has been done.

However, the welding flux-containing wire described in Patent Document 3 is premised on resin coating of polyester, epoxy, urethane, etc., and is intended to reduce the promotion of corrosion of the resin coating defect portion. It is not related to the extension of the life of a normal coated steel sheet in which the agent is sprayed on the surface of the steel sheet, and there is a problem that the corrosion resistance of the weld metal and the life of the coating film cannot be sufficiently obtained.

Japanese Unexamined Patent Publication No. 2003-311471 Japanese Unexamined Patent Publication No. 2004-230456 Japanese Unexamined Patent Publication No. 2000-94185

INDUSTRIAL APPLICABILITY The present invention provides a flux for gas shielded arc welding, which is excellent in welding workability and mechanical performance (tensile strength and toughness) of the weld metal, and can obtain a weld metal having excellent corrosion resistance and coating film peeling resistance. It is intended to provide a welded wire.

The gist of the present invention is as follows.
(1) The flux-containing wire for gas-shielded arc welding of corrosion-resistant steel according to one aspect of the present invention includes a steel outer skin and a flux in the steel outer skin, and the flux-containing wire is the flux-containing wire of the flux-containing wire. C: 0.05 to 0.18%, Si: 0.40 to 1.60%, Mn: 1.50 to 2.50%, Cu: 0.05 to 0.50% in terms of mass% with respect to the total mass. , Ti: 0.10 to 0.30%, Sn: 0.05 to 0.40%, F conversion value of fluorine compound: 0.01 to 0.10%, SiO ₂ conversion value of Si oxide: 0. Contains 01 to 0.20%, _{the total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: 0.02 to 0.15%, and limits to Al: 0.010% or less. The rest consists of a steel hull, iron powder, Fe content of iron alloy powder, and impurities.
(2) The flux-cored wire for gas shielded arc welding of corrosion-resistant steel according to (1) above may further contain B: 0.0100% or less in mass% with respect to the total mass of the flux-cored wire. ..
(3) The flux-cored wire for gas shielded arc welding of the corrosion-resistant steel according to (1) or (2) above further contains Mo: 0.50% or less in mass% with respect to the total mass of the flux-cored wire. You may.
(4) The method for manufacturing a welded joint according to another aspect of the present invention uses the flux-cored wire for gas shielded arc welding of corrosion-resistant steel according to any one of (1) to (3) above. It is provided with a process of gas shielded arc welding of steel.

According to the flux-containing wire for gas shielded arc welding of corrosion-resistant steel of the present invention, welding workability and welding are performed in welding of corrosion-resistant steel having excellent corrosion resistance and coating peeling resistance even in an environment with a large amount of flying salt such as a beach area. It is possible to obtain a weld metal having excellent mechanical performance of the metal and excellent corrosion resistance and coating peeling resistance.

It is a figure which showed the sampling position of the corrosion test piece for evaluation of the corrosion resistance of a welded part. It is a figure which showed the outline of the shape and the cross cut of the corrosion test piece for evaluation of the coating film corrosiveness of a welded part. It is a figure which showed the outline of the corrosion test method (SAE J2334 test, execution condition per cycle).

The present inventors have excellent welding workability and mechanical performance of the weld metal, and a gas capable of producing a weld metal having excellent corrosion resistance and coating peeling resistance even in an environment with a large amount of flying salt such as a beach area. In order to obtain a flux-welded wire for shielded arc welding, the chemical components of various flux-welded wires for welding were changed and their effects were investigated.

As a result, it was found that the corrosion resistance of the weld metal in an environment with a large amount of flying salt can be improved by containing an appropriate amount of tin (Sn) and copper (Cu) in the wire.

The reason why Sn improves the corrosion resistance of the weld metal is that the metal Sn in the weld metal ^{is eluted as tin ions (II) (Sn 2+} ) and exhibits an inhibitory effect in the exposed portion, that is, in an acidic chloride solution. It is considered that this is because the corrosion at the anode where the pH is lowered is suppressed. Further, it is considered that the metal Sn in the weld metal has an effect ^{of reducing the concentration of iron (III) ion (Fe 3+} ) having a corrosion promoting action and improving the corrosion resistance in an environment with a large amount of flying salt.

The reason why Cu improves the corrosion resistance of the weld metal is that the reaction rate of the dissolution reaction (corrosion reaction) of the weld metal itself containing Cu is reduced by Cu, and in the case of the weld metal containing Cu, the steel plate surface ( Corrosion products (rust) generated in the surplus portion, etc.) exhibit a characteristic fine and dense structure, so that a rust layer with high corrosion resistance that suppresses the permeation of water, oxygen, chloride ions, etc. is formed. It is thought that this is because. Furthermore, it was found that Cu has an effect of enhancing the corrosion resistance effect of Sn when coexisting with Sn.

_{Regarding welding workability, the total value of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound, and the total value of the F conversion value of the fluorine compound are made appropriate, and an appropriate amount of Si oxide is contained. As a result, it was found that the stability of the arc and the reduction of the amount of spatter generated can be achieved, and the appearance and shape of the bead can be improved. However, oxides may impair the mechanical properties of the weld metal.

Further, in order to simultaneously achieve appropriate strength and toughness improvement of the weld metal, the oxide which is a slag generating agent in the wire is reduced as much as possible within the range where the above-mentioned welding workability improvement effect can be secured, and the alloy component is formed. It was found that the optimization of the contents of each of C, Si, Mn, Ti, and Al was effective.

Furthermore, it has also been found that the toughness and strength of the weld metal can be further improved by containing appropriate amounts of B and Mo in the wire.

The flux-cored wire for gas shielded arc welding according to the present embodiment can be achieved by the synergistic effect of each component composition alone or coexisting, and the reasons for limiting each component composition will be described below. The% of the following components indicates the mass% with respect to the total mass of the flux-cored wire for welding.

[C: 0.05 to 0.18%]
C is an element necessary for improving the strength of the weld metal. If C is less than 0.05%, the required strength of the weld metal cannot be obtained. On the other hand, when C exceeds 0.18%, the strength of the weld metal becomes excessively high and the toughness decreases. Further, when C exceeds 0.18%, high temperature cracking is likely to occur. Therefore, C is set to 0.05 to 0.18%. Preferably, C is 0.07 to 0.15%, more preferably 0.08 to 0.12%. C may be contained in the steel outer skin or may be contained in the flux as metal powder, alloy powder or the like.

[Si: 0.40-1.60%]
Si is contained for deoxidizing the weld metal and ensuring the strength of the weld metal. If Si is less than 0.40%, deoxidation is insufficient and the strength and toughness of the weld metal are lowered. On the other hand, when Si exceeds 1.60%, the strength of the weld metal becomes excessively high and the toughness decreases. Further, when Si exceeds 1.60%, the amount of slag generated during welding increases, and welding defects such as slag entrainment are likely to occur. Therefore, Si is set to 0.40 to 1.60%. Preferably, Si is 0.70 to 1.30%, more preferably 0.80 to 1.10%. Si may be contained in the steel outer skin or may be contained in the flux as an alloy powder of metal Si, Fe-Si, Fe-Si-Mn or the like.

[Mn: 1.50 to 2.50%]
Mn is contained for ensuring the toughness of the weld metal and improving the strength. If Mn is less than 1.50%, the strength and toughness of the weld metal will decrease. On the other hand, when Mn exceeds 2.50%, the strength of the weld metal becomes excessively high and the toughness decreases. Further, when Mn exceeds 2.50%, the amount of slag generated increases and welding defects such as slag entrainment are likely to occur. Therefore, Mn is set to 1.50 to 2.50%. Preferably, Mn is 1.70 to 2.30%, more preferably 1.90 to 2.10%. Mn may be contained in the steel outer skin or may be contained in the flux as an alloy powder of metals Mn, Fe-Mn, Fe-Si-Mn and the like.

[Cu: 0.05 to 0.50%]
Like Sn, Cu is an element responsible for improving corrosion resistance and coating film peeling resistance. If Cu is less than 0.05%, a weld metal having sufficient corrosion resistance and coating film peeling resistance cannot be obtained. On the other hand, if Cu exceeds 0.50%, the toughness of the weld metal decreases. Therefore, Cu is set to 0.05 to 0.5%. Preferably, Cu is 0.15 to 0.45%, more preferably 0.20 to 0.40%. Cu may be contained in the steel outer skin, as a Cu plating component applied to the surface of the steel outer skin, or may be contained in the flux as an alloy powder of metal Cu, Fe—Si—Cu or the like. ..

[Ti: 0.10 to 0.30%]
Ti acts as a deoxidizer and has the effect of forming fine oxides of Ti in the weld metal to improve the toughness of the weld metal. If Ti is less than 0.10%, the toughness of the weld metal decreases. On the other hand, when Ti exceeds 0.30%, the amount of solid solution Ti in the weld metal increases, and the toughness of the weld metal decreases. Therefore, Ti is set to 0.10 to 0.30%. Ti is preferably 0.10 to 0.25%, more preferably 0.12 to 0.23%. Ti may be contained in the steel outer skin or may be contained in the flux as an alloy powder of metal Ti, Fe—Ti or the like.

[Al: 0.010% or less]
Al may be added because it has a deoxidizing effect. On the other hand, when Al exceeds 0.010%, it remains as an oxide in the weld metal and lowers the toughness of the weld metal. Further, when Al exceeds 0.010%, the arc becomes unstable and the amount of spatter generated increases. Therefore, the Al content is limited to 0.010% or less in total of the steel outer skin and the flux. The upper limit of Al may be 0.008% or 0.005%.

[Sn: 0.05 to 0.40%]
Sn is an important element for improving the corrosion resistance and the coating film peeling resistance of the weld metal. If Sn is less than 0.05%, the effect of improving corrosion resistance and coating film peeling resistance cannot be obtained. On the other hand, when Sn exceeds 0.40%, the crack sensitivity of the weld metal becomes high, and high-temperature cracking is likely to occur. Further, when Sn exceeds 0.40%, Sn segregates at the grain boundaries in the weld metal and the toughness of the weld metal decreases. Therefore, Sn is set to 0.05 to 0.40%. Preferably, Sn is 0.10 to 0.25%. From the viewpoint of improving corrosion resistance and coating film peeling resistance, Sn is preferably 0.10 to 0.30%. Sn may be contained in the steel outer skin or may be contained in the flux as metal Sn or alloy Sn powder, but it is preferable that Sn is contained in the flux.

[Fluorine compound: 0.01 to 0.10% in F conversion value]
Fluoride compounds (fluoride) have the effect of concentrating and stabilizing arcs. If the F conversion value of the fluorine compound is less than 0.01%, this effect cannot be obtained, the arc becomes unstable, and the amount of spatter generated increases. On the other hand, when the F conversion value of the fluorine compound exceeds 0.10%, the arc becomes rough and unstable, and the amount of spatter generated increases. Therefore, the F conversion value of the fluorine compound is set to 0.01 to 0.10%. Preferably, the F conversion value of the fluorine compound is 0.01 to 0.07%. The fluorine compound can be contained in the flux as _{CaF 2} , NaF, LiF, MgF ₂ , K ₂ SiF ₆ , Na ₃ AlF ₆ , AlF _{3, and the like.} The elements constituting these fluorides are not included in the content of the alloy components described above. The F conversion value is the total amount of F contained in the flux. _{For example, when CaF 2} of n% by mass with respect to the total mass of the flux-cored wire is contained in the flux-cored wire, _{the F conversion value of CaF 2} is calculated by the following formula.
( _{F conversion value of CaF 2} ) = n × (19.00 × 2 / 78.08)
In the above formula, "19.00" is the atomic weight of F, "2" is the number of F atoms contained in _{one CaF 2} , and "78.08" is the molecular weight of _{CaF 2.} be. For _{fluorides other than CaF 2} , the F conversion value can be calculated in the same manner. When a plurality of types of fluorides are contained in the flux, the total value of the F-converted values of each fluoride is regarded as the F-converted value of the fluorides contained in the flux. The lower limit of the F conversion value of the fluorine compound may be 0.03% or 0.04%. The upper limit of the F conversion value of the fluorine compound may be 0.09% or 0.08%.

_{[SiO 2} conversion value of Si oxide: 0.01 to 0.20%]
The Si oxide has the effect of increasing the viscosity of the molten slag, improving the slag encapsulation property and the familiarity of the bead toe, and improving the appearance and shape of the bead. _{If the SiO 2} conversion value of the Si oxide is less than 0.01%, the bead toe of the weld bead will not fit well, and the appearance and shape of the bead will be poor. On the other hand, when the SiO ₂ conversion value of the Si oxide exceeds 0.20%, the amount of oxygen in the weld metal increases and the toughness decreases. In addition, the amount of slag generated increases, and welding defects such as slag entrainment are likely to occur. _{Therefore, the SiO 2} conversion value of the Si oxide is set to 0.01 to 0.20%. Preferably, the SiO ₂ conversion value of the Si oxide is 0.03 to 0.12%, more preferably 0.05 to 0.10%. _{The SiO 2} conversion value of the Si oxide may be contained in the flux as a solid component of water glass composed of silica sand, sodium silicate and potassium silicate. The SiO ₂ conversion value, when the Si in the Si oxide contained in a flux cored wire is assumed that all of the SiO _2, a SiO ₂ content of the flux cored wire. The elements constituting these Si oxides shall not be included in the content of the alloy components described above.

_{[Total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: 0.02 to 0.15%]
The Na compound and the K compound have the effect of softening and stabilizing the arc. _{If the total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound is less than 0.02%, the arc becomes unstable and the amount of spatter generated increases. _{On the other hand, when the total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound exceeds 0.15%, the arc becomes too strong and the amount of spatter generated increases. In addition, the fit of the toe of the bead becomes poor, and the appearance and shape of the bead become poor. _{Therefore, the total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound is 0.02 to 0.15%. _{The total of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound is preferably 0.03 to 0.10%, more preferably 0.04 to 0.08%. The Na compound and the K compound may be contained in the flux as a powder of a solid component of water glass composed of sodium silicate and potassium silicate, K ₂ SiO ₃ , Na ₂ SiO ₃ , NaF, K ₂ SiF _{6, and the like.} .. Terms of Na 2 _O values A, when the Na of Na compound contained in the flux cored wire is assumed to be all Na 2 _O, a content of Na 2 _O of the flux cored wire. K The 2 _O converted value, when the K a K compound contained in the flux cored wire is assumed to be all K _{2 O,} a K _{2 O} content of the flux cored wire.

[B: 0.0100% or less]
Since B is not essential for solving the problem of the flux-cored wire according to the present embodiment, the B content may be 0%, but B has the effect of further improving the toughness by refining the structure of the weld metal. Since it is present, it may be contained. However, when B exceeds 0.0100%, segregation occurs at the grain boundaries and the toughness decreases. Therefore, B is set to 0.0100% or less. In order to obtain the effect of improving the toughness of the weld metal, it is preferable that B is 0.0015% or more. Further, B may be contained in the steel outer skin or may be contained in the flux as an alloy powder of Fe-B, Fe-Mn-B or the like.

[Mo: 0.50% or less]
Since Mo is not essential for solving the problem of the flux-cored wire according to the present embodiment, the Mo content may be 0%, but Mo is an important element for further improving the strength of the weld metal. Therefore, it may be contained. However, when Mo exceeds 0.50%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, Mo is 0.50% or less. In order to obtain the effect of improving the strength of the weld metal, it is preferable that Mo is 0.10% or more. Further, Mo may be contained in the steel outer skin or may be contained in the flux as metal Mo powder.

The flux-cored wire for gas shielded arc welding according to the present embodiment can be manufactured by the same process as the usual method for manufacturing a flux-cored wire. That is, the steel outer skin is formed into a pipe shape, and the inside thereof is filled with flux. The types of wires are seamless wire (so-called seamless wire) obtained by welding the seams of the molded steel outer skin and steel without welding the seams to the steel outer skin. It can be roughly divided into wires with seams on the outer skin. In this embodiment, a wire having any cross-sectional structure can be adopted, but a wire having a seamless steel outer skin can be heat-treated for the purpose of reducing the total amount of hydrogen in the wire, and can be manufactured. Since there is no subsequent moisture absorption of the flux, the amount of diffusible hydrogen in the weld metal can be reduced and the low temperature crack resistance can be improved, which is more preferable.

The rest of the flux-filled wire for gas shielded arc welding according to this embodiment is Fe of the steel outer skin, iron powder added for component adjustment, and iron alloy powder such as Fe-Si, Fe-Mn, and Fe-Ti alloy. Fe content and impurities. The impurity is a component mixed by a raw material such as ore or scrap, or various factors in the manufacturing process when the flux-filled wire is industrially manufactured, and has an adverse effect on the flux-filled wire according to the present embodiment. Means what is allowed within the range that does not give. For example, since S and P are harmful to the flux-cored wire according to the present embodiment, the content thereof is preferably 0%, but the flux is set as a range that does not adversely affect the flux-cored wire according to the present embodiment. A maximum of 0.1% by mass with respect to the total mass of the incoming wire is allowed.

The flux filling rate is not particularly limited, but is preferably 8 to 20% with respect to the total mass of the wire from the viewpoint of productivity.

A method for manufacturing a welded joint according to another aspect of the present invention includes a step of gas shielded arc welding of corrosion-resistant steel using a flux-welded wire for gas shielded arc welding according to the present embodiment. The application of the welded joint to which the flux-welded wire for gas shielded arc welding of the corrosion-resistant steel of the present invention is applied is not particularly limited, but structural steel materials, particularly port facilities, bridges, construction / civil engineering structures, are preferable. Welded joints that make up steel structures such as objects, tanks, ships / marine structures, railways, and containers.
Further, the material of the steel material to which the flux-containing wire for gas shielded arc welding of the corrosion-resistant steel according to the present embodiment is applied is not particularly limited to the steel type, and may be an ordinary steel material such as carbon steel or low alloy steel. Weathering steel (for example, "welding structural weathering hot rolled steel" specified in JIS G 3114) and low alloy steel containing Ni, Sn, etc. are advantageous from the viewpoint of weather resistance and coating corrosion resistance. be.

In the method for manufacturing a welded joint, the shield gas is not particularly limited, but 100% carbon dioxide gas is preferable. This is because when the shield gas is carbon dioxide gas, spatter is likely to occur, but the welding cost can be reduced. The flux-cored wire according to the present embodiment has an optimized content of Na compound, K compound, fluoride, etc. in order to suppress the amount of spatter generated, so that even if the amount of spatter is easily increased, 100% carbon dioxide gas Welding workability can be ensured even when the gas is used as a shield gas. As a matter of course, it is not hindered to use a gas that does not easily generate spatter, such as a mixed gas of _{Ar and CO 2, in combination with the flux-cored wire according to the present embodiment.} The flow rate of the shield gas is not particularly limited, and normal welding conditions can be appropriately selected depending on the situation. For example, the flow rate of the shield gas is preferably 20 to 35 liters / minute in order to prevent welding defects and nitrogen from the atmosphere. Other welding conditions, such as welding current, welding voltage, welding speed, preheating temperature, interpass temperature, heat input, etc., are not particularly limited, and depend on the situation to which the welding joint manufacturing method according to the present embodiment is applied. Can be selected as appropriate.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples.

SPCC specified in JIS G 3141 is used for the steel outer skin, and after forming it into a U shape in the process of forming the steel outer skin, a seamless wire is formed by welding the seams of the steel outer skin. The wire was drawn and a wire containing flux of various components shown in the table was prototyped. The wire diameter was 1.2 mm. The symbol "-" in the table indicates that the element was not intentionally added. In addition, values outside the scope of the invention and values that do not meet the pass / fail criteria are underlined.

Gas shielded arc welding was performed using the prototype flux-cored wire shown in the table, and welding workability, the presence or absence of welding defects and cracks, weld metal performance and corrosion resistance were investigated.

In the evaluation of welding workability and weld metal performance, C: 0.15%, Si: 0.27%, Mn: 1.15%, P: 0.008%, S: 0.001% as the material to be welded. , Sn: 0.13%, Cu: 0.012%, using corrosion resistant steel (plate thickness: 20 mm), conforming to JIS Z 3111, by performing a weld metal test under the welding conditions shown in Table 2. , The mechanical performance and welding workability of the weld metal were investigated.

Welding workability was evaluated by visually confirming arc stability, spatter generation amount, bead appearance shape, and presence / absence of cracks during the weld metal test.

The mechanical performance of the weld metal is as follows: A tensile test piece (JIS Z 2241 A0) and an impact test piece (JIS Z 2242 V notch test piece) are taken from the center of the center of the plate thickness of the welded test piece, and the machine is used for these. It was evaluated by conducting a test. A flux-cored wire having a weld metal in the range of 490 to 670 MPa in tensile strength was accepted as acceptable in terms of tensile strength. When the Charpy impact test at 0 ° C. was repeated three times, the flux-cored wire from which a weld metal having an average value of absorbed energy of 80 J or more could be obtained was judged to have good toughness.

The evaluation of welding defects was carried out by conducting an X-ray transmission test on the welding test piece after the welding test in accordance with JIS Z 3106 and investigating the presence or absence of welding defects such as slag entrainment.

The corrosion resistance evaluation of the weld metal was carried out by the corrosion resistance test described below. A sample for producing a corrosion test piece (thickness 3 mm × width 60 mm × length 150 mm) shown in FIG. 1 was sampled from a sampling position 3 at a depth of 1 mm from the surface of the base metal 1 so that the weld metal 2 was at the center. After the shot blasting treatment, the material was heat-dried at a furnace temperature of 80 ° C. to prepare a corrosion test piece material. Both sides of the corrosion test piece material are coated with either paint A (Banno # 200 manufactured by China Paint Co., Ltd.) or paint B (Neo Gosei Primer HB manufactured by Shinto Paint Co., Ltd.), and the film thickness is 200 to 200. A 350 μm corrosion test piece was prepared. As shown in FIG. 2, the corrosion test piece was cross-cut 4 so as to straddle the weld metal 2, to prepare a corrosion test piece 5 simulating a scratch on the coating film. The cross cut 4 was created by applying a scratch knife from the top of the coating film to the surface of the underlying steel with a cutter knife.

Then, the obtained corrosion test piece 5 was subjected to a test in accordance with SAE (SAE International Engineers) J2334 to evaluate its corrosion resistance. Here, the SAE J2334 test is wet: 50 ° C., 100% RH, 6 hours, salt adhesion: 0.5% by mass NaCl, 0.1% by mass CaCl ₂ , 0.075% by mass NaHCO ₃ aqueous solution immersion, 0. .25 hours, drying: 60 ° C., 50% RH, 17.75 hours, and this is an accelerated test conducted under the condition of repeating dry and wet with one cycle (24 hours in total) of three processes. The outline of one cycle is shown in FIG. The SAE J2334 test is a test that simulates a severe corrosive environment where the amount of flying salt exceeds 1 mdd. This corrosion form is said to be similar to the atmospheric exposure test (see Hiroo Nagano, Masato Yamashita, Hitoshi Uchida: Environmental Materials Science, Kyoritsu Shuppan (2004), p.74).

After 80 cycles of the SAE J2334 test, the coating film peeling / swelling area ratio of each test piece was measured and calculated. Then, the residual coating film on the surface and the generated rust layer were removed, the corrosion depth of the coating film flaws was measured, and then the average corrosion depth of the coating film scratches was calculated. Flux-filled wire obtained of weld metal with a coating film peeling / swelling area ratio of less than 50% and an average coating film scratched corrosion depth of less than 0.50 mm passed the test in terms of corrosion resistance and coating film peeling resistance. Judged.

The results of these tests are shown in the table.

The wire symbols A1 to A16 in the table are examples of the present invention, and the wire symbols B1 to B21 are comparative examples. In the wire symbols A1 to A16 of the example of the present invention, C, Si, Mn, Sn, Cu, Ti and Al in the flux-filled wire are appropriate, and the F-converted values of the fluorine compounds in the flux are SiO ₂ , Na compounds. _{Since the sum of the Na 2} O conversion value and the K ₂ O conversion value of the K compound is an appropriate amount, the arc is stable, the amount of spatter generated is small, the bead appearance and shape are good, there are no welding defects and cracks, and welding is performed. The tensile strength and absorption energy of the metal were good, the peeling / swelling area ratio of the coating film and the average corrosion depth of the scratched portion of the coating film were small, and the results were extremely satisfactory. The wire symbols A12 to A16 had a tensile strength of 620 MPa or more because Mo was added in an appropriate amount. Further, the wire symbols A10 to A12, A14 and A16 had an absorption energy of 110 J or more because B was added in an appropriate amount.

In the comparative example, the wire symbol B1 had a small amount of C, so that the tensile strength of the weld metal was low.
Since the wire symbol B2 has a large amount of C, the tensile strength of the weld metal is excessive and the absorbed energy is low.
Since the wire symbol B3 has a small amount of Si, the tensile strength of the weld metal is low and the absorbed energy is also low.
Since the wire symbol B4 contains a large amount of Si, the tensile strength of the weld metal is excessive and the absorbed energy is low. Further, in the wire symbol B4, slag entanglement occurred in the welded portion.
Since the wire symbol B5 has a small amount of Mn, the tensile strength of the weld metal is low and the absorbed energy is also low.
Since the wire symbol B6 has a large amount of Mn, the tensile strength of the weld metal is excessive and the absorbed energy is low. Further, in the wire symbol B6, slag entanglement occurred in the welded portion.
Since the wire symbol B7 has a large amount of Sn, the absorbed energy of the weld metal was low. In addition, crater cracking occurred.
Since the wire symbol B8 contains a large amount of Cu, the absorbed energy of the weld metal was low.
Since the wire symbol B9 has a small amount of Ti, the absorbed energy of the weld metal is low.
Since the wire symbol B10 has a large amount of Ti, the absorbed energy of the weld metal is low.
Since the wire symbol B11 contains a large amount of Al, the absorbed energy of the weld metal is low. Further, in the wire symbol B11, the arc was unstable and the amount of spatter generated was large.
Since the wire symbol B12 contains a large amount of Si oxide, the absorbed energy of the weld metal was low. Further, in the wire symbol B12, slag was involved in the welded portion.
Since the wire symbol B13 has a large amount of Mo, the tensile strength of the weld metal is excessive and the absorbed energy is low.
Since the wire symbol B14 has a large amount of B, the absorbed energy of the weld metal was low.
Since the wire symbol B15 contains a small amount of Cu, the coating film peeling / swelling area ratio is large, and the average corrosion depth of the coating film scratched portion is deep.
Since the wire symbol B16 has a small amount of Sn, the coating film peeling / swelling area ratio is large, and the average corrosion depth of the coating film scratched portion is deep.
In the wire symbol B17, since the total F conversion value of the fluorine compound was small, the arc was unstable and the amount of spatter generated was large.
Since the wire symbol B18 has a _{large sum of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound, the arc is too strong, the amount of spatter generated is large, and the bead appearance and shape are also poor.
Since the wire symbol B19 has a large total of F-converted values of the fluorine compounds, the arc is unstable and the amount of spatter generated is large.
Since the wire symbol B20 contains a small amount of Si oxide, the bead appearance and shape are poor.
As for the wire symbol B21, _{since the sum of the Na 2} O conversion value and the K ₂ O conversion value of the Na compound and the K compound was small, the arc was unstable and the amount of spatter generated was large.

1 Base metal 2 Welded metal 3 Corrosion test piece collection position 4 Cross cut 5 Corrosion test piece

Claims (4)

Corrosion-resistant steel gas-shielded arc welding flux-cored wire
It is provided with a steel outer skin and a flux in the steel outer skin.
The flux-cored wire is a mass% of the total mass of the flux-cored wire.
C: 0.05 to 0.18%,
Si: 0.40-1.60%,
Mn: 1.50 to 2.50%,
Cu: 0.05 to 0.50%,
Ti: 0.10 to 0.30%,
Sn: 0.05 to 0.40%,
F conversion value of fluorine compound: 0.01 to 0.10%,
_{SiO 2} conversion value of Si oxide: 0.01 to 0.20%,
_{The total of Na 2} O conversion value and K ₂ O conversion value of Na compound and K compound: 0.02 to 0.15%,
Al: Limited to 0.010% or less,
The balance is a flux-filled wire for gas shielded arc welding of corrosion-resistant steel, which is composed of Fe of a steel outer skin, Fe of iron powder, and Fe of an iron alloy powder, and impurities. By mass% of the total mass of the flux-cored wire,
B: The flux-cored wire for gas shielded arc welding of corrosion-resistant steel according to claim 1, further containing 0.0100% or less. By mass% of the total mass of the flux-cored wire,
Mo: A flux-cored wire for gas shielded arc welding of corrosion-resistant steel according to claim 1 or 2, further containing 0.50% or less. A method for manufacturing a welded joint comprising a step of gas-shielding arc-welding the corrosion-resistant steel using the flux-welded wire for gas-shielded arc welding of the corrosion-resistant steel according to any one of claims 1 to 3.

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