JP2016203253A - Low hydrogen type coated arc welding rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low hydrogen type coated arc welding rod, excellent in stability of an arc, and excellent in low temperature toughness by providing high strength welding metal, in multi-layer welding of the steel pipe circumference of a 490 MPa-class or more.SOLUTION: A low hydrogen type coated arc welding rod includes metal carbonate:25-45%, metal fluoride:5-15%, rutile:2-7%, alumina:0.2-2.0%, zircon sand:0.3-1.5%, magnesium oxide:0.1-1.0%, hematite:0.1-1.0%, Si:5-10%, Mn:2.0-6.5%, Ni:0.8-1.8%, Ti:0.5-3.5%, a B alloy and a B compound:0.03-0.15% in a B conversion value and iron powder:15-35% in mass% to the coating agent whole mass, and applies a coating agent in the coating ratio of 28-42%.SELECTED DRAWING: None

Description

  The present invention relates to a low hydrogen-based coated arc welding rod in which a coating agent is applied to a mild steel core wire, and in particular, in a multi-layer welding of a steel pipe circumference of 490 MPa class or higher using a DC power source, the arc stability is excellent, The present invention relates to a low hydrogen-based coated arc welding rod excellent in weld metal strength and toughness at low temperatures.

  Low hydrogen-based coated arc welding rods composed mainly of metal carbonate and metal fluoride are easier to weld in all positions and have better mechanical properties than illuminite-based and lime-titania coated arc welding rods. In addition, low hydrogen-based coated arc welding rods have less diffusible hydrogen and superior crack resistance than high-cellulosic-coated arc welding rods that allow vertical downward welding. Are often used.

  Low hydrogen-based coated arc welding rods are often designed assuming that they are generally welded using an AC power source, but when steel pipes are circumferentially welded outdoors, a DC power source is used. There are many cases. When this DC power source is used for welding with a low hydrogen-based coated arc welding rod, there is a problem that magnetic blowing or partial melting of the coating material occurs, the arc becomes unstable, and a sound bead cannot be obtained. For this reason, even when a DC power source is used, there is a high demand for developing a low hydrogen-based coated arc welding rod that has excellent arc stability and good mechanical performance of the weld metal.

  With respect to the coated arc welding rod used for circumferential welding of steel pipes, for example, Patent Document 1 reduces the arc breakage by limiting the average particle size and content of potassium titanate in the coating, There is a disclosure of a technique for obtaining a weld bead continuously and uniformly by optimizing the content of components and improving general welding workability.

  Further, in Patent Document 2, by adjusting the content of potassium feldspar, rutile and alumina in the coating material, all layers from back wave welding to final layer welding can be efficiently welded. There is a technical disclosure that arc stability and bead shape can be obtained.

  However, the techniques described in Patent Document 1 and Patent Document 2 are both effective when an AC power source is used, but when welding using a DC power source with these low hydrogen-based coated arc welding rods, There was a problem that a magnetic bead or arc break occurred and the arc became unstable, and a healthy bead could not be obtained.

  On the other hand, Patent Document 3 discloses a technique relating to a low hydrogen-based coated arc welding rod for a DC power source. That is, the disclosed technique of Patent Document 3 focuses on the fact that the carbon content of a steel core wire used as a welding rod for a DC power supply greatly affects the oxygen content of the weld metal, and attempts to optimize the carbon content. It is. However, the technique described in Patent Document 3 is that a low temperature fracture toughness value of a weld metal welded in a downward posture using a DC power source can be obtained, and in multi-layer welding such as circumferential welding of a steel pipe, There was a problem that a good bead could not be obtained.

JP2012-143810A JP 2000-117487 A JP 2010-227968 A

  Therefore, the present invention has been devised in view of the above-described problems, and is excellent in arc stability and high-strength welding in multi-layer welding of a steel pipe circumference of 490 MPa class or higher using a DC power source. An object of the present invention is to provide a low hydrogen-based coated arc welding rod that provides a metal and is excellent in low-temperature toughness.

  As a result of investigating the difference in the case of welding with an AC power source and a DC power source using a low hydrogen-based coated arc welding rod, the inventors have compared with the case of welding with a DC power source as compared with the case of welding with an AC power source. As a result, it has been found that magnetic arcing or partial melting of the coating tends to occur due to the length of the arc becoming long and the coating becomes brittle, and the arc becomes unstable and a healthy bead cannot be obtained.

  Therefore, in order to obtain a good bead shape without magnetic blowing or partial melting of the coating material even when the steel pipe circumference is welded with a DC power source using a low hydrogen based arc welding rod, Various preparations of the agent components were studied.

  As a result, by adding an appropriate amount of iron powder and setting the coverage ratio to an appropriate value, even when multi-layer welding is performed with a DC power source, magnetic blowing or partial melting of the coating does not occur, and metal carbonate, alumina, rutile and It has been found that by using an appropriate amount of hematite, the arc is stable and a good bead shape can be obtained, and by using an appropriate amount of metal fluoride, the bead shape and slag peelability can be improved. Further, it was found that adjusting the amount of zircon sand added has an effect of further preventing the coating from being partially melted.

  In order to ensure the low temperature toughness of the weld metal, the amount of coating component Si, Mn, Ni, Ti and B should be appropriate, and the strength of the weld metal can be ensured by making Mn and Ni appropriate. I found.

  That is, the gist of the present invention is a low hydrogen-based arc welding rod in which a coating agent is applied to a mild steel core wire, in a mass% with respect to the total mass of the coating agent, and a total of one or more metal carbonates: 25-45%, total of one or more metal fluorides: 5-15%, rutile: 2-7%, alumina: 0.2-2.0%, zircon sand: 0.3-1. 5%, magnesium oxide: 0.1 to 1.0%, hematite: 0.1 to 1.0%, Si: 5 to 10%, Mn: 2.0 to 6.5%, Ni: 0.8 to 1.8%, Ti: 0.5 to 3.5%, B alloy and B compound: 0.03 to 0.15% in total of one or more of B conversion values, iron powder: 15 to 35 And the balance is a slag forming agent, a deoxidizing agent, a coating agent, a coating agent composed of a solid content of water glass and inevitable impurities, and the mild steel core. By mass% with respect to the low hydrogen type covered electrode total mass on the outer periphery of, characterized by being coated with from 28 to 42% coverage.

  According to the low hydrogen-based coated arc welding rod of the present invention, in a multi-layer welding of a steel pipe circumference of 490 MPa class or more using a direct current power source, magnetic blowing or partial melting of the coating does not occur, and the arc stability is excellent. Thus, a good bead shape can be obtained, and the general welding workability is also good, so that the welding efficiency can be greatly improved, and the mechanical performance of the weld metal is also good, so that a high-quality weld is obtained.

  Hereinafter, the low hydrogen type | system | group covering arc welding rod to which this invention is applied is demonstrated in detail. In the low hydrogen-based coated arc welding rod to which the present invention is applied, a coating agent is applied to a mild steel core wire. The content of each component composition of the low hydrogen-based coated arc welding rod is expressed as mass% with respect to the total mass of the coating material, and is simply described as% below.

[Total of one or more metal carbonates: 25 to 45%]
Metal carbonate refers to calcium carbonate, magnesium carbonate, barium carbonate, manganese carbonate, etc., and has the function of shielding and protecting the deposited metal from the atmosphere by being decomposed in an arc to generate CO ₂ gas. If the total of one or more of the metal carbonates is less than 25%, the shielding effect is insufficient and blow holes are likely to occur. On the other hand, if the total of one or more of the metal carbonates exceeds 45%, the arc becomes unstable, the bead shape becomes convex in all-position welding, and the slag peelability is also deteriorated. Therefore, the total of one or more metal carbonates is 25 to 45%.

[Total of one or more metal fluorides: 5 to 15%]
Metal fluoride refers to fluorite, barium fluoride, magnesium fluoride, aluminum fluoride, etc., and has a function of lowering the viscosity of molten slag to improve slag fluidity and to improve the bead shape. If the total of one or more of the metal fluorides is less than 5%, an appropriate molten slag viscosity cannot be obtained, and the bead shape becomes poor in all-position welding. On the other hand, if the total of one or more metal fluorides exceeds 15%, the slag peelability becomes poor. Therefore, the total of one or more metal fluorides is 5 to 15%.

[Lucille: 2-7%]
Rutile acts as an arc stabilizer and adjusts the viscosity of the molten slag. If the rutile is less than 2%, the arc becomes unstable and the bead shape becomes poor in all-position welding. On the other hand, if the rutile exceeds 7%, the viscosity of the molten slag becomes high and the slag fluidity becomes poor, and the shape of the bead at the time of welding in the vertical posture and the upward posture becomes convex. Therefore, rutile is 2 to 7%.

[Alumina: 0.2-2.0%]
Alumina stabilizes the arc and adjusts the viscosity of the molten slag. When alumina is less than 0.2%, the arc becomes unstable, and the bead shape becomes poor in all-position welding. On the other hand, if alumina exceeds 2.0%, the slag becomes glassy and slag peeling becomes poor. Therefore, alumina is 0.2 to 2.0%.

[Zircon sand: 0.3-1.5%]
In addition to adjusting the viscosity of molten slag, zircon sand has a high melting point of 2700 ° C, so it has stable fire resistance even when the coating material and the core wire are overheated, and has the function of suppressing melting of the coating material. . In addition, because it has better mechanical strength than other oxides, it is less likely to be damaged even when the coating itself is subjected to a physical impact, and the coated arc welding rod can be used in an unstable welding posture such as an upward posture. Even when the tip of the steel plate contacts the steel plate groove, chipping is less likely to occur and stable welding is possible. If the zircon sand is less than 0.3%, partial melting of the coating tends to occur. In addition, the mechanical strength of the coating agent itself is weakened, and chipping is likely to occur. On the other hand, if the zircon sand exceeds 1.5%, the viscosity of the molten slag increases and the slag fluidity decreases, so that the bead shape becomes convex in the vertical posture and the upward posture welding. Therefore, the zircon sand is 0.3 to 1.5%.

[Magnesium oxide: 0.1 to 1.0%]
Since magnesium oxide is excellent in heat resistance, it has a function of suppressing partial melting of the coating agent. If the magnesium oxide is less than 0.1%, partial dissolution of the coating tends to occur. On the other hand, when magnesium oxide exceeds 1.0%, the viscosity of the molten slag becomes high and the slag fluidity decreases, and the bead shape becomes convex in the vertical posture and the upward posture welding. Therefore, the magnesium oxide is 0.1 to 1.0%.

[Hematite: 0.1 to 1.0%]
Hematite has the effect of stabilizing the arc. If hematite is less than 0.1%, the arc spray becomes weak and the arc becomes unstable. On the other hand, if hematite exceeds 1.0%, the amount of oxygen in the weld metal increases, and the low temperature toughness decreases. Therefore, hematite is 0.1 to 1.0%.

[Si: 5 to 10%]
Si is added from metals Si, Fe-Si, Fe-Si-Mn, etc., and is used for the purpose of deoxidation of weld metal. In particular, it has a large function to stabilize the arc and ensures welding workability. It is necessary from the aspect. If Si is less than 5%, deoxidation is insufficient, the low temperature toughness of the weld metal is lowered, and blow holes are likely to occur. In addition, the arc becomes unstable, and the bead shape becomes poor in all-position welding, and in particular, it is difficult to continue in welding in a vertical posture and an upward posture. On the other hand, when Si exceeds 10%, a low melting point oxide is precipitated at the grain boundary, and the low temperature toughness of the weld metal is lowered. Therefore, Si is 5 to 10%.

[Mn: 2.0 to 6.5%]
Mn is added from metals Mn, Fe—Mn, Fe—Si—Mn, etc., and is added as a deoxidizer in the same manner as Si, and is effective in improving the strength of the weld metal. If Mn is less than 2.0%, the strength of the weld metal decreases. Also, deoxidation is insufficient and blow holes are likely to occur in the weld metal. On the other hand, if Mn exceeds 6.5%, the strength of the weld metal becomes excessively high and the low-temperature toughness becomes low. Therefore, Mn is set to 2.0 to 6.5%.

[Ni: 0.8 to 1.8%]
Ni is an element which is added from the metal Ni and improves the strength and low temperature toughness of the weld metal. If Ni is less than 0.8%, the required weld metal strength and low temperature toughness cannot be ensured. On the other hand, if Ni exceeds 1.8%, the strength of the weld metal becomes excessively high, and the low-temperature toughness decreases. Therefore, Ni is made 0.8 to 1.8%.

[Ti: 0.5 to 3.5%]
Ti is added from metal Ti, Fe—Ti, or the like, and has a function of stabilizing the arc by reducing the potential gradient of the arc. Moreover, it is effective as a deoxidizer, and has a function of improving the low temperature toughness by yielding in the weld metal and refining the microstructure of the weld metal. When Ti is less than 0.5%, the arc becomes unstable and the arc length is increased, and the coating material is likely to be partially melted. Moreover, the microstructure of the weld metal is not refined, and the low temperature toughness of the weld metal is reduced. On the other hand, when Ti exceeds 3.5%, precipitation of Ti oxide in the weld metal increases, and the low temperature toughness of the weld metal decreases. Therefore, Ti is 0.5 to 3.5%.

[B alloy and B compound: 0.03 to 0.15% in total of one or more of B conversion values]
B is added from Fe-B, Fe-Mn-B, borax, sodium borate, etc., and enhances the hardenability of the weld metal to suppress the formation of intergranular ferrite and is effective in improving the low temperature toughness of the weld metal. It is. If the total of one or more of B conversion values of B alloy and B compound is less than 0.03%, the effect of suppressing grain boundary ferrite by B does not work, and the ferrite grains become coarse, and the low temperature toughness of the weld metal Decreases. On the other hand, when the total of one or more of B conversion values of the B alloy and the B compound exceeds 0.15%, the weld metal becomes a coarse lath structure, and the low temperature toughness of the weld metal is lowered. Accordingly, the total of one or more of the B converted values of the B alloy and the B compound is 0.03 to 0.15%.

[Iron powder: 15-35%]
Iron powder is a very important raw material in welding with a DC power source because it reduces the arc potential gradient, shortens the arc length, and prevents partial melting of the coating material. If the iron powder is less than 15%, the arc length becomes long and unstable, and the coating material is partially melted. On the other hand, if the iron powder exceeds 35%, the welding rod becomes red hot (hereinafter referred to as “bar burning”) in the latter half of welding, and welding to the end becomes difficult. Therefore, the iron powder is 15 to 35%.

[Coating ratio of coating material on the outer periphery of the mild steel core wire: 28 to 42% by mass% with respect to the total mass of the low hydrogen based arc welding rod]
The covering ratio (mass% with respect to the total mass of the low hydrogen-based coated arc welding rod) on the mild steel core wire greatly affects the melting of the coating material and the slag state. If the coating rate of the coating agent is less than 28% by mass% (hereinafter simply referred to as%) with respect to the total mass of the low hydrogen-based coated arc welding rod, the coating itself becomes brittle and partial melting of the coating occurs. On the other hand, when the coating rate of the coating agent exceeds 42%, the amount of slag becomes excessive, and it is difficult to continue the vertical posture or the upward posture welding. Therefore, the coverage to the mild steel core wire is 28 to 42%.

In addition, the remainder of the low hydrogen-based coated arc welding rod to which the present invention is applied is a total of 15% or less of one or more solid substances such as silica sand, sodium silicate and potassium silicate from slag forming agent, As a deoxidizer, one or more of magnesium, aluminum, aluminum magnesium, etc. is 3% or less in total. As a coating agent, one or more of sodium alginate, mica, etc. is 4% or less in total, Na ₂ O, K of water glass ₂ O solid content and inevitable impurities.
Moreover, it is preferable to use JIS G3523 SWY11 for the mild steel core wire to be used, but C in the mild steel core wire is preferably 0.05 to 0.08% in mass% with respect to the total mass of the mild steel core wire. The content of C can be adjusted appropriately from the coating material in order to adjust the strength. However, the C content is mass% with respect to the total mass of the low hydrogen-based coated arc welding rod, and the total of the mild steel core wire and the coating material is 0.06 to 0. 20% is preferable. Since P of the mild steel core deteriorates toughness, it is 0.010% or less in terms of mass% with respect to the total mass of the mild steel core, and S deteriorates the fluidity of slag. Since 010% or less and N has a strong bonding force with B and deteriorates the hardenability, it is preferably 0.005% or less in terms of mass% with respect to the total mass of the mild steel core wire.

  Hereinafter, specific examples of the low hydrogen-based coated arc welding rod to which the present invention is applied will be described.

  JIS G3523 SWY11 soft steel core wire having a diameter of 4.0 mm and a length of 400 mm (C: 0.06 mass%, Si: 0.01 mass%, Mn: 0.48 mass%, P: 0.009 mass%, S : 0.005% by mass, N: 0.0023% by mass), a coating material having the composition shown in Table 1 was applied to the outer periphery and dried to produce various low hydrogen-based coated arc welding rods.

  Using these various types of coated arc welding rods, we investigated the welding workability and weld metal performance.

  Welding workability was evaluated for each of the 490 MPa class steel pipes (plate thickness: 9 mm, inner diameter: 150 mm, groove angle: 60 °, gap: 1.0 mm, route face: 1.0 mm) for each prototype welding. Using 6 rods, using a DC welder, welding in all positions sequentially from the upward position with a welding current of 123A, and after visually examining the bead shape, arc stability, slag peelability, etc., welding About the defect, the X-ray transmission test was done according to JISZ3104.

  Weld metal performance was evaluated by using 490MPa class steel (plate thickness 20mm), welding metal with DC welding machine according to JIZ Z3111, and using tensile test piece (A0) and impact test piece (V notch test piece). Samples were collected and examined for mechanical performance.

  The strength of the weld metal was evaluated as good when the tensile strength was 550 to 650 MPa. For the evaluation of toughness, a Charpy impact test was conducted at a test temperature of −40 ° C., and the average value of the absorbed energy three times was 110 J or more. These test results are summarized in Table 2.

  In Tables 1 and 2, the welding rod No. 1 to 10 are examples of the present invention, welding rod Nos. 12 to 22 are comparative examples.

  The welding rod no. 1-No. 10 is a total of one or more metal carbonates in the coating, a total of one or more metal fluorides, rutile, alumina, zircon sand, magnesium oxide, hematite, Si, Mn, Ni , Ti, B alloy and B compound total of one or more of B conversion value and iron powder are appropriate amount and covering rate is also appropriate, so that the arc is stable and the coating material melts and burns In addition, the bead shape and slag peelability were good, there were no weld defects such as blowholes, and the tensile strength and absorbed energy of the deposited metal were also good values, which was a very satisfactory result.

  Welding rod no. No. 11 had blowholes because the total amount of metal carbonate was small. Moreover, since there was much magnesium oxide, the bead shape became convex shape by standing posture and upward posture welding. Further, since Ti is small, the arc length becomes long, the arc becomes unstable, the coating material melts, and the absorbed energy of the deposited metal is low.

  Welding rod no. In No. 12, since the total amount of metal carbonate was large, the arc was unstable, the bead shape became convex in all-position welding, and the slag peelability was also poor. Moreover, since the coating rate was low, partial melting of the coating agent occurred. Furthermore, since there is much Si, the absorbed energy of the weld metal was low.

  Welding rod no. No. 13 had a poor bead shape in all-position welding because the total amount of metal fluoride was small. In addition, because there was a lot of iron powder, bar burning occurred. Furthermore, since there is much hematite, the absorbed energy of the weld metal was low.

  Welding rod no. No. 14 had a poor total slag removability because of the large amount of metal fluoride. Further, since the amount of Si is small, the arc becomes unstable, and the bead shape becomes poor in all position welding, and it becomes difficult to sustain particularly in the vertical position and upward position welding. Furthermore, the absorbed energy of the weld metal was low and blow holes were generated.

  Welding rod no. In No. 15, since there was little rutile, the arc became unstable and the bead shape was poor in all-position welding. Moreover, since Mn was small, the tensile strength of the weld metal was low, and blow holes were also generated.

  Welding rod no. Since No. 16 had a lot of rutile, the bead shape became convex by vertical and upward posture welding. Moreover, since there was little hematite, the arc was unstable. Furthermore, since there was much Mn, the tensile strength of the weld metal was high and the absorbed energy was low.

  Welding rod no. In No. 17, since the amount of alumina was small, the arc became unstable and the bead shape was poor in all-position welding. Moreover, since there was little Ni, the tensile strength and absorbed energy of the deposit metal were low.

  Welding rod no. No. 18 was poor in slag removability because of the large amount of alumina. Moreover, since there was much Ni, the tensile strength of the weld metal was high and the absorbed energy was low.

  Welding rod no. In No. 19, since the zircon sand was small, partial melting of the coating agent and lack of coating occurred. Moreover, since there is much Ti, the absorbed energy of the weld metal was low.

  Welding rod no. No. 20 has a large amount of zircon sand, so that the bead shape became convex by welding in an upright posture and an upward posture. Moreover, since the total of B conversion value was small, the absorbed energy of the weld metal was low.

  Welding rod no. No. 21 had a small amount of magnesium oxide, so that partial dissolution of the coating agent occurred. Moreover, since the total of B conversion values was large, the absorbed energy of the weld metal was low.

  Welding rod no. In No. 22, since there was little iron powder, arc length became long and became unstable, and the piece of coating material melted. Moreover, since the coverage was high, the amount of slag generation increased, and it was difficult to sustain in the vertical posture and upward posture welding. Only a part of the steel plate was welded, and the weld metal test was stopped.

Claims (1)

In a low hydrogen-based coated arc welding rod with a coating applied to a mild steel core wire,
In mass% of the total mass of the coating
Total of one or more metal carbonates: 25 to 45%,
Total of one or more metal fluorides: 5 to 15%,
Lucille: 2-7%,
Alumina: 0.2-2.0%
Zircon sand: 0.3-1.5%
Magnesium oxide: 0.1 to 1.0%,
Hematite: 0.1-1.0%,
Si: 5 to 10%
Mn: 2.0 to 6.5%,
Ni: 0.8 to 1.8%,
Ti: 0.5 to 3.5%
B alloy and B compound: 0.03 to 0.15% in total of one or more of B conversion values,
Containing iron powder: 15-35%,
The remainder is a slag former, deoxidizer, coating agent, water glass solids and a coating composed of unavoidable impurities in mass% with respect to the total mass of the low hydrogen-based coated arc welding rod on the outer periphery of the mild steel core wire. A low hydrogen-based arc welding rod characterized by being applied at a coverage of 28 to 42%.