JP2020078816A - Low-hydrogen type coated arc welding electrode - Google Patents

Abstract

To provide a low-hydrogen type coated arc welding electrode which has suitable arc stability, can provide a preferable penetration bead, is free from a welding defect and provides excellent welded metal even when performing back-bead welding with all posture by using either power source of AC power source and DC power source.SOLUTION: A low-hydrogen type coated arc welding electrode contains, by mass % with respect to coating agent all mass, C of 0.01 to 0.15%, metal carbonates of 35 to 55%, metal fluorides of 4 to 12%, TiOconversion value of 3 to 9%, SiOconversion value of 10 to 20%, AlOconversion value of 0.5 to 3.0%, Si of 3 to 9%, Mn of 1.0 to 5.0%, Ti of 0.1 to 2.5% and the sum of NaO conversion value and KO conversion value of 1.5 to 5.0%.SELECTED DRAWING: None

Description

  The present invention relates to a low-hydrogen-based coated arc welding rod, and when using backside welding in all positions such as circumferential welding of a steel pipe using either AC power source or DC power source, suitable arc stability The present invention relates to a low hydrogen-based coated arc welding rod which can obtain a favorable back bead, has no welding defects, and can obtain a weld metal excellent in strength and low temperature toughness.

  Low-hydrogen coated arc welding rods containing metal carbonates and metal fluorides as main components are in all positions compared to non-low-hydrogen coated arc welding rods such as illuminate type coated arc welding rods and lime titania type coated arc welding rods. Backside welding is easy, and because the atmosphere is shut off by a gas generating agent, it has excellent mechanical properties, a small amount of diffusible hydrogen in the deposited metal, and excellent crack resistance. It is often used for back seam welding in posture.

  Low-hydrogen coated arc welding rods are generally designed for welding using an AC power source. However, when circumferentially welding steel pipes or the like outdoors, a DC power source is often used, and there is the problem that a magnetic back blow occurs or the arc becomes unstable, and a healthy back bead cannot be obtained. .. For this reason, there has been a strong demand for the development of a low-hydrogen-based coated arc welding rod that can be applied to both AC and DC power sources.

  A coated arc welding rod for first layer backside welding in all positions, such as circumferential welding of steel pipe, is disclosed in Patent Document 1 by adjusting the contents of potassium feldspar, rutile and alumina in the coating agent. There is a disclosure of a technique capable of efficiently welding all layers from the reverse side welding to the welding of the final layer and obtaining good arc stability and bead shape.

Further, Patent Document 2 contains a mineral (silica stone, etc.) containing a SiO ₂ component in a proportion of 90% by mass or more, a metal carbonate, a metal fluoride, and rutile, and contains particles having a particle size of less than 53 μm in the mineral. There is a disclosure of a technique for suppressing the occurrence of arc breakage by defining the rate.

  Further, Patent Document 3 discloses a technique of stabilizing the arc by adjusting the amount of hematite added in the coating material.

  However, both Patent Document 1 and Patent Document 2 are technologies of low-hydrogen coated arc welding rods when an AC power source is used, but when welding is performed using a DC power source with these low-hydrogen coated arc welding rods. However, there is a problem in that the magnetic blow and the arc become unstable and a sound back bead and good low temperature toughness cannot be obtained. Further, Patent Document 3 is a technology of a low hydrogen-based coated arc welding rod when a DC power source is used, but when welding is performed using an AC power source with such a low hydrogen-based coated arc welding rod, it is equivalent to a DC power source. There was a problem that the arc stability and good back bead could not be obtained.

JP 2000-117487 A JP, 2018-114512, A JP, 2005-85341, A

  Therefore, the present invention has been devised in view of the above-mentioned problems, and it is preferable to use any of an AC power source and a DC power source to perform backside welding in all positions such as circumferential welding of a steel pipe. Provided is a low-hydrogen coated arc welding rod which has excellent arc stability, does not cause arc breakage, can obtain a good backside bead, has no welding defects, and can obtain a weld metal excellent in strength and low temperature toughness. The purpose is to

The gist of the present invention is a low hydrogen-based coated arc welding rod in which a coating material is applied to a steel core wire, wherein the coating material is C: 0.01 to 0.15 in mass% with respect to the total mass of the coating material. %, the total of one or two or more metal carbonates: 35 to 55%, the total of one or two or more metal fluorides: 4 to 12%, the total TiO ₂ conversion value of Ti oxide: 3 ˜9%, total of SiO ₂ converted values of Si oxide: 10 to 20%, total of Al ₂ O ₃ converted value of Al oxide: 0.5 to 3.0%, Si: 3 to 9%, Mn : 1.0 to 5.0%, Ti: 0.1 to 2.5%, Na ₂ O converted value of Na compound and K compound and total of K ₂ O converted value: 1.5 to 5.0% It is characterized in that it contains and the balance consists of coating agent, Fe content from iron alloy and inevitable impurities.

  Further, the low-hydrogen coated arc welding rod is characterized in that it contains one or two of Al and Mg in total of 0.2 to 3.0% by mass% based on the total mass of the coating material.

  According to the low-hydrogen coated arc welding rod of the present invention, suitable arc stability is obtained even when the first layer is back-wave welded in all positions such as circumferential welding of a steel pipe using either an AC power source or a DC power source. Since it has good properties, arc breakage does not occur, good back bead is obtained, and general welding workability is also good, welding efficiency can be greatly improved, and there are no welding defects, strength and low temperature toughness. Since excellent weld metal can be obtained, the quality of the welded portion can be improved.

  The present inventors have investigated in detail the difference between welding using an AC power supply and a DC power supply using a low-hydrogen coated arc welding rod.

  As a result, when the backside welding is performed using a DC power supply, magnetic arcing and arc breakage occur due to the arc becoming weaker than when welding is performed using an AC power supply, and the arc is unstable. It turns out that you can't get a healthy Uranami bead. It was also found that C, Si, and Mn of the weld metal were reduced, and the strength and the low temperature toughness of the weld metal were reduced as compared with the AC power source.

  On the other hand, when the backside welding was performed with an AC power supply using a low hydrogen type covered arc welding rod designed for a DC power supply, the arc was too strong and the bead shape was found to be bad for both the front bead and the backside bead. did. It was also found that C, Si, and Mn of the weld metal increased, the strength of the weld metal became excessive, and the low temperature toughness decreased.

  Therefore, it has suitable arc stability when performing backside welding using either an AC power source or a DC power source, arc breakage does not occur, and a good backside bead is obtained, and strength and low-temperature toughness are obtained. In order to obtain an excellent weld metal, various compositions of low hydrogen system coated arc welding rods were investigated.

  As a result, by adjusting the contents of C, Ti oxide, Si oxide, Al oxide, Ti, Na compound, and K compound to proper amounts, it is possible to use either one of AC power supply and DC power supply by their synergistic effect. Even when the backside welding is performed in all positions using the power source, the arc is stable and good backside bead and front bead shapes are obtained, and the metal carbonate and metal fluoride contents are set to appropriate amounts. It was found that the amount of diffusible hydrogen decreases. It was also found that the mechanical properties of the weld metal can be improved by making the respective contents of C, Si, Mn, and Ti appropriate amounts. It was also found that the low temperature toughness is further improved by adding an appropriate amount of Al or Mg.

  Hereinafter, the composition of each component with respect to the total mass of the coating material and the reason for limiting the content of the low-hydrogen coated arc welding rod of the present invention will be described in detail. Hereinafter, the content of each component composition will be represented by mass% with respect to the total mass of the coating material, and the mass% will be simply described as %.

[C: 0.01 to 0.15%]
C is added from metal powder and alloy powder from the coating agent, and has the effect of maintaining the stability of the arc when welding is performed with an AC power supply and a DC power supply. C is also an extremely important component for ensuring the strength of the weld metal. If the C content is less than 0.01%, the arc spraying becomes weak and the arc becomes unstable, so that a uniform back bead cannot be obtained. If the C content is less than 0.01%, the strength of the weld metal will be low. On the other hand, when the content of C exceeds 0.15%, the strength of the weld metal becomes excessive and the low temperature toughness decreases. Therefore, C is set to 0.01 to 0.15%.

[The total of one or more metal carbonates: 35 to 55%]
The metal carbonate is added from calcium carbonate, barium carbonate, manganese carbonate, magnesium carbonate, etc., decomposes in the arc to generate CO ₂ gas, and shields the molten metal from the atmosphere to protect it from hydrogen. It has the effect of lowering the pressure. If the total amount of one or more metal carbonates is less than 35%, the shielding effect is insufficient and blowholes are easily generated, the amount of diffusible hydrogen increases, and the crack resistance deteriorates. On the other hand, if the total amount of one or more metal carbonates exceeds 55%, the arc spraying becomes weak and the arc in the low current region becomes unstable, especially when an AC power source is used, and good back It becomes difficult to form wave beads. Therefore, the total amount of one or more metal carbonates is 35 to 55%.

[The total of one or more metal fluorides: 4 to 12%]
Metal fluoride is added from fluorspar, barium fluoride, magnesium fluoride, aluminum fluoride, etc. to reduce the viscosity of the molten slag and adjust the fluidity of the slag to improve the bead shape, and in an arc atmosphere. The hydrogen partial pressure is reduced to improve crack resistance. If the total of one kind or two or more kinds of metal fluorides is less than 4%, an appropriate viscosity of the molten slag cannot be obtained and the shape of the surface bead becomes poor. Further, if the total of one kind or two or more kinds of metal fluorides is less than 4%, the amount of diffusible hydrogen increases and the crack resistance deteriorates. On the other hand, if the total of one or more metal fluorides exceeds 12%, the slag removability deteriorates. Therefore, the total of one kind or two or more kinds of metal fluorides is 4 to 12%.

[Total of TiO ₂ converted values of Ti oxide: 3 to 9%]
Ti oxide is added from rutile, titanium oxide, titanium slag, ilmenite, etc. to stabilize the arc. If the total of the TiO ₂ converted values of the Ti oxide is less than 3%, the arc becomes unstable and it becomes difficult to obtain a good backside bead. On the other hand, when the sum of the TiO ₂ conversion values of Ti oxide exceeds 9%, the slag becomes dense and the slag removability deteriorates. If the total TiO ₂ conversion value of the Ti oxide exceeds 9%, the viscosity of the molten slag increases and the fluidity of the slag decreases during vertical and upward position welding, so the shape of the surface bead is convex. Becomes Therefore, the total of TiO ₂ converted values of Ti oxide is 3 to 9%.

[Total SiO ₂ converted value of Si oxide: 10 to 20%]
Si oxide is added from silica sand, potassium silicate, sodium silicate, potassium feldspar, wollastonite, etc. to strengthen the spraying of the arc and stabilize the arc. If the total of the SiO ₂ converted values of the Si oxide is less than 10%, the arc becomes weak and the shape of the back bead becomes poor, especially when a DC power source is used. On the other hand, if the total of the SiO ₂ converted values of Si oxide exceeds 20%, the arc becomes too strong, especially when an AC power source is used, and the shape of both the back bead and the front bead becomes defective. Therefore, the total SiO ₂ conversion value of the Si oxide is set to 10 to 20%.

[Total Al ₂ O ₃ conversion value of Al oxide: 0.5 to 3.0%]
Al oxide is added from alumina, feldspar, silica sand, mica, etc. to adjust the viscosity of the molten slag. If the total of Al ₂ O ₃ conversion values of Al oxides is less than 0.5%, the viscosity of the molten slag is reduced and it becomes difficult to perform welding in the vertical and upward postures. On the other hand, when the total of Al ₂ O ₃ conversion values of Al oxide exceeds 3.0%, the arc spraying becomes strong and the amount of spatter generation increases. Therefore, the total of Al ₂ O ₃ conversion values of Al oxides is 0.5 to 3.0%.

[Si: 3-9%]
Si is added from Fe-Si, metallic Si, Fe-Si-Mn, and the like, and is added for the purpose of deoxidizing the weld metal, but it is also necessary for ensuring welding workability. If the Si content is less than 3%, deoxidation becomes insufficient, blowholes are easily generated in the weld metal, the arc becomes unstable, and the shape of both the front bead and the backside bead becomes poor. On the other hand, if the Si content exceeds 9%, low-melting-point oxides are precipitated at the grain boundaries in the molten metal, lowering the low temperature toughness. Therefore, the Si content is set to 3 to 9%.

[Mn: 1.0 to 5.0%]
Mn is added from metal Mn, Fe-Mn, Fe-Si-Mn, etc., and is added as a deoxidizing agent like Si, and has the effect of improving the strength and low temperature toughness of the weld metal. If the Mn content is less than 1.0%, deoxidation becomes insufficient, and blowholes are likely to occur in the weld metal. Further, if the Mn content is less than 1.0%, the strength and low temperature toughness of the weld metal decrease. On the other hand, when the content of Mn exceeds 5.0%, the viscosity of the molten slag decreases, making it difficult to perform welding in the upright and upright positions, and the strength of the weld metal increases and the low temperature toughness decreases. Therefore, the Mn content is set to 1.0 to 5.0%.

[Ti: 0.1-2.5%]
Ti is added from metallic Ti, Fe-Ti, etc., and has the effect of reducing the ionization frequency of the arc and stabilizing the arc. Further, it not only acts as a deoxidizer, but also has the effect of refining the microstructure of the weld metal to improve low temperature toughness. If the Ti content is less than 0.1%, the arc becomes unstable, especially when an AC power source is used, and a good backside bead cannot be obtained. Further, if the Ti content is less than 0.1%, deoxidation becomes insufficient, blowholes are easily generated in the weld metal, and the effect of improving the low temperature toughness of the weld metal cannot be obtained. On the other hand, when Ti exceeds 2.5%, an upper bainite structure that inhibits the toughness is generated, and the low temperature toughness of the weld metal decreases. Therefore, Ti is 0.1 to 2.5%.

[Sum of Na ₂ O converted value and K ₂ O converted value of Na compound and K compound: 1.5 to 5.0%]
The Na compound and K compound are added from sodium silicate, potassium silicate, potassium feldspar, potassium glass, soda feldspar in water glass, and have the effect of stabilizing the arc. If the total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound is less than 1.5%, the arc becomes unstable and a stable backside bead shape cannot be obtained. On the other hand, when the total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound exceeds 5.0%, the arc becomes too strong especially when an AC power source is used, and the front bead and the back bead are formed. In both cases, the bead shape becomes defective. Therefore, the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound is 1.5 to 5.0%.

[The total of one or two of Al and Mg: 0.2 to 3.0%]
Al is added from metals Al, Fe-Al, Al-Mg, etc., and Mg is added from metals Mg, Al-Mg, etc., which act as strong deoxidizers and have the effect of reducing the oxygen content of the weld metal. Have. If the total of one kind or two kinds of Al and Mg is less than 0.2%, the effect of improving the low temperature toughness of the weld metal and the effect of suppressing blowhole generation cannot be obtained. On the other hand, if the total amount of one or two of Al and Mg exceeds 3.0%, the arc becomes unstable, the shapes of the front bead and the back bead become poor, and the amount of spatter generation increases. Therefore, the total of one or two of Al and Mg is set to 0.2 to 3.0%.

  The balance of the coating material of the low hydrogen-based coated arc welding rod to which the present invention is applied includes, as a coating material, one or more kinds of mica, sodium alginate, etc. in a total amount of 4% or less by mass% based on the total mass of the coating material. , And others are Fe content and unavoidable impurities from the iron alloy.

  Moreover, it is preferable to use JIS G3523 SWY11 as the mild steel core wire to be used. Further, the coating rate of the coating material on the mild steel core wire is preferably 25 to 40% by mass% of the coating material with respect to the total mass of the welding rod.

  The effects of the present invention will be specifically described with reference to examples.

  Mild steel core wire having an outer diameter of 3.2 mm and a length of 400 mm specified in JIS G3523 SWY11 (C: 0.06 mass%, Si: 0.02 mass%, Mn: 0. 51% by mass, P: 0.008% by mass, S: 0.003% by mass), using various coating agents shown in Table 1, a coating rate of 20 to 35% is applied to a steel core wire to form a low hydrogen system. A coated arc welding rod was prototyped.

  The diffusible hydrogen content was measured according to JIS Z3118 using the low-hydrogen coated arc welding rod shown in Table 1.

  In addition, JIS G3106 SM490A steel with a plate thickness of 9 mm has a groove shape with a groove angle of 45°, a gap of 2 mm and a root face of 1.5 mm, and the welding workability is the most problematic in all position welding. AC power source (hereinafter referred to as AC) and DC power source (hereinafter referred to as DC) are used as the power source, and the back welding is performed with a welding current of 85 A for a welding length of 500 mm to achieve arc stability, back bead shape, and front bead shape. Also, the slag removability was visually examined. Then, an X-ray transmission test was carried out according to JIS Z3104 to investigate the presence or absence of welding defects.

  Further, using a JIS G3106 SM490A steel having a plate thickness of 12 mm, a weld metal test was performed by AC in accordance with JIS Z3211, and a tensile test (No. A2) and an impact test piece were sampled to investigate the mechanical performance.

  A diffusible hydrogen amount of 8 ml/100 g or less was regarded as good. The tensile strength of the tensile test was 520 to 620 MPa, and the impact test was carried out by repeating the five Charpy impact test at a test temperature of −40° C., and the average absorbed energy was 30 J or more. These results are summarized in Table 2.

Welding rod Nos. in Tables 1 and 2 1 to 12 are examples of the present invention, welding rod Nos. 13 to 25 are comparative examples. The welding rod No. which is an example of the present invention. 1 to 12 are C in the coating material, the total of metal carbonates, the total of metal fluorides, the total of TiO ₂ conversion values of Ti oxide, the total of SiO ₂ conversion values of Si oxide, and the Al oxide Al _Since the sum of ₂ O ₃ conversion values and the sum of Si, Mn, Ti, Na compounds and K compounds Na ₂ O conversion values and K ₂ O conversion values are appropriate, the amount of diffusible hydrogen is low and both AC and DC are low. The arc was stable, the amount of spatter generated was small, the shape of the backside bead, the shape of the front bead, and the slag removability were good, and there were no welding defects such as blowholes. The tensile strength and absorbed energy of the deposited metal were also good values.

  The welding rod No. 1, No. 2, No. 5, No. 7, No. 8, No. 9 and No. Since No. 10 contains an appropriate amount of one or two of Al and Mg, the absorbed energy of the deposited metal was 50 J or more, which was a very satisfactory value.

The welding rod No. in the comparative example. In No. 13, since the total of TiO ₂ converted values of Ti oxide was small, the arc was unstable in both AC and DC, and the backside bead shape was poor in both AC and DC. In addition, since Mn is small, the tensile strength and absorbed energy of the deposited metal are low, and blowholes are also generated. Furthermore, since the total amount of Al and Mg is small, the effect of improving the absorbed energy of the deposited metal and the effect of suppressing blowholes were not obtained.

  Welding rod No. Since No. 14 had a small amount of Ti, the arc was unstable in AC and the backside bead shape was poor. Also, blowholes were generated and the absorbed energy of the deposited metal was low. Furthermore, since the total amount of Al and Mg is small, the effect of improving the absorbed energy of the deposited metal and the effect of suppressing blowholes were not obtained.

  Welding rod No. Since No. 15 had a large amount of C, the tensile strength of the deposited metal was high and the absorbed energy was low. Further, since the total amount of metal carbonate was large, the arc was weak in AC and the backside bead shape was poor.

Welding rod No. In No. 16, since C was small, both AC and DC had weak arcs, the backside bead shape was poor, and the tensile strength of the deposited metal was also low. Further, since the total of TiO ₂ converted values of Ti oxide was large, the surface bead shape was convex for both AC and DC, and the slag removability was also poor.

Welding rod No. In No. 17, since the total amount of metal carbonate was small, the amount of diffusible hydrogen was large and blowholes were generated. Moreover, since the total of the SiO ₂ converted values of the Si oxide was small, the arc weakened at DC and the backside bead shape was poor.

Welding rod No. In No. 18, the total amount of metal fluoride was large, so the slag removability was poor. In addition, since the total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound was small, both AC and DC arcs were unstable and the backside bead shape was poor.

Welding rod No. In No. 19, since the total of Al ₂ O ₃ conversion values of Al oxides was small, the viscosity of the slag decreased and the slag fluidity became excessive, which made sustaining difficult in upright posture welding. Further, since the amount of Si is large, the absorbed energy of the deposited metal is lowered.

  Welding rod No. Since No. 20 had a large amount of Mn, the viscosity of the slag decreased and the fluidity of the slag became excessive, making it difficult to sustain it in the upright posture welding. The tensile strength of the deposited metal was high and the absorbed energy was low.

Welding rod No. No. 21 had a large amount of diffusible hydrogen because the total amount of metal fluorides was small, and the surface bead shape was poor in both AC and DC. Further, since the total of Al ₂ O ₃ conversion values of Al oxides is large, both AC and DC have a strong arc and a large amount of spatter is generated.

Welding rod No. In No. 22, since the total of the SiO ₂ converted values of Si oxide was large, the arc was strong in AC and the backside bead shape and the front bead shape were poor.

  Welding rod No. In No. 23, since the amount of Si was small, the arc was unstable in both AC and DC, the shape of the backside bead and the shape of the front bead were poor, and blow holes were also generated.

Welding rod No. In No. 24, since the total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound was large, the arc was strong in AC and the backside bead and front bead shape were poor.

  Welding rod No. Since No. 25 had a large amount of Ti, the absorbed energy of the deposited metal was low. Further, since the total amount of Al and Mg was large, the arc was unstable in both AC and DC, the amount of spatter was large, and the backside bead shape and the front bead shape were poor.

Claims (2)

In a low hydrogen type coated arc welding rod in which a coating agent is applied to the steel core wire,
The coating material is a mass% based on the total mass of the coating material,
C: 0.01 to 0.15%,
One or more total of metal carbonates: 35-55%,
Total of one kind or two or more kinds of metal fluorides: 4 to 12%,
Sum of TiO ₂ converted values of Ti oxide: 3 to 9%,
Sum of SiO ₂ converted values of Si oxide: 10 to 20%,
Sum of Al ₂ O ₃ conversion values of Al oxide: 0.5 to 3.0%,
Si: 3-9%,
Mn: 1.0 to 5.0%,
Ti: 0.1 to 2.5%,
Containing Na ₂ O converted value and K ₂ O converted value of Na compound and K compound: 1.5 to 5.0%,
The balance is a coating agent, Fe content from iron alloy, and unavoidable impurities, which is a low-hydrogen coated arc welding rod.   The low hydrogen system coated arc welding according to claim 1, further comprising: a total of one or two of Al and Mg: 0.2 to 3.0% by mass% based on the total mass of the coating agent. rod.