JP2015085341A - Low-hydrogen type coated arc welding electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-hydrogen type coated arc welding electrode which shows excellent arc stability, without occurrence of arc breakage, in back wave welding, e.g. circumferential welding of steel pipes by using a DC power supply and provides a good back wave bead.SOLUTION: In a low-hydrogen type coated arc welding electrode consisting of a steel core wire coated with a coating agent, a coating agent which comprises, by mass% relative to the total mass of the coating agent, 0.20-0.35% of C, a total content of 40-55% of one or more metal carbonates, a total content of 4-11% of one or more metal fluorides, 3-9% rutile, 4-10% potassium feldspar, 4-7%, based on the Si conversion value, of one or more metallic Si and Si alloys and 1.5-5.0%, based on the Mn conversion value, of one or more metallic Mn and Mn alloys is applied to a steel core wire containing 0.06-0.11%, by mass% relative to the total mass of the steel core wire, of C.

Description

  The present invention relates to a low hydrogen-based coated arc welding rod, and particularly suitable for obtaining a good back bead in arc back welding such as circumferential welding of a 490 MPa class steel pipe using a DC power source. The present invention relates to a low hydrogen-based coated arc welding rod.

  Low hydrogen coated arc welding rods composed mainly of metal carbonates and metal fluorides are easier to back weld in all positions and have better mechanical properties than illuminite and lime titania coated arc welding rods. Yes. In addition, the low hydrogen-based coated arc welding rod has less diffusible hydrogen content and excellent crack resistance than the high cellulose-based coated arc welding rod capable of vertical downward welding. For this reason, low hydrogen-based coated arc welding rods are often used for reverse wave welding such as circumferential welding of steel pipes.

  However, low hydrogen-based coated arc welding rods are generally designed to be welded using an AC power supply. However, when steel pipes are circumferentially welded outdoors, a DC power supply must be used. There are many. When this DC power source is used for welding with a low hydrogen-based coated arc welding rod, there is a problem in that a magnetic blow or arc breakage occurs, the arc becomes unstable, and a healthy back bead cannot be obtained. For this reason, even when a DC power source is used, there is a high demand for development of a low hydrogen-based coated arc welding rod that is excellent in arc stability and that provides a good back bead.

  A coated arc welding rod for first layer welding such as circumferential welding of a steel pipe is disclosed in Patent Document 1, for example, by limiting the average particle size of potash feldspar in the coating material to reduce arc break during back wave welding. There is a disclosure of technology for obtaining wave beads continuously and uniformly.

  In addition, Patent Document 2 limits the average particle size of potassium titanate in the coating material to reduce arc breakage during back wave welding and obtain a back wave bead continuously and uniformly. There is a disclosure of a technique for improving the property.

  Furthermore, in Patent Document 3, by adjusting the content of potash feldspar, rutile and alumina in the coating material, all layers from back wave welding to final layer welding can be efficiently welded, which is favorable. There is a technical disclosure that arc stability and bead shape can be obtained.

  However, the techniques described in Patent Documents 1 to 3 are all effective when an AC power source is used. However, when welding is performed using a DC power source with these low hydrogen-based coated arc welding rods, There was a problem that blowing and arc breakage caused the arc to become unstable and a sound back-bead could not be obtained.

  On the other hand, Patent Document 4 discloses a technique relating to a low hydrogen-based coated arc welding rod for a DC power source. That is, in the disclosed technique of Patent Document 4, the carbon amount of the steel core wire used as a welding rod for a DC power source has a great influence on the oxygen amount of the weld metal, and the carbon amount is optimized. Is. However, in the technique described in Patent Document 4, a low temperature fracture toughness value of a weld metal welded in a downward posture using a DC power source can be obtained. In the wave welding, there is a problem that the stability of the arc and a good back bead cannot be obtained.

JP-A-5-212586 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 when performing reverse wave welding such as circumferential welding of a steel pipe using a DC power source, the arc is excellent in arc stability and arc breakage. An object of the present invention is to provide a low hydrogen-based coated arc welding rod that does not occur and can provide a good back bead.

  The gist of the present invention is that, in a low hydrogen-based coated arc welding rod in which a coating material is coated on a steel core wire, the mass% with respect to the total mass of the coating material, C: 0.20 to 0.35%, Total of one or more types: 40 to 55%, total of one or more types of metal fluorides: 4 to 11%, rutile: 3 to 9%, potassium feldspar: 4 to 10%, metallic Si and 1 type or 2 types or more of Si alloy: 4 to 7% in total of Si conversion value, 1 type or 2 types or more of metal Mn and Mn alloy: 1.5 to 5.0% in total of Mn conversion value And the balance is a steel core wire containing C: 0.06 to 0.11% by mass% with respect to the total mass of the steel core wire, with the coating agent comprising the slag generator, deoxidizer, coating agent and inevitable impurities. It is characterized by being applied to.

  Moreover, it exists in the low hydrogen type | system | group covering arc welding rod characterized by containing hematite: 0.2-1.5% in the mass% with respect to the coating material total mass.

  According to the low hydrogen-based coated arc welding rod to which the present invention is applied, when performing reverse wave welding such as circumferential welding of a steel pipe using a DC power source, the arc stability is excellent and arc breakage does not occur. A good back bead is obtained and 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.

  The present inventors investigated in detail the difference in the case of welding using an AC power source and a DC power source using a low hydrogen-based coated arc welding rod. As a result, when welding using a DC power supply, compared to welding using an AC power supply, magnetic arcing or arc breakage occurs due to the weakening of the arc, making the arc unstable and healthy. It was found that wave beads could not be obtained.

  Therefore, in order to obtain a good back bead without causing arc breakage and stable arcs even when back welding such as circumferential welding of steel pipes is performed with a DC power source using a low hydrogen-based coated arc welding rod. In addition, various prototypes of the steel core wire component and the coating agent component were studied.

  As a result, by making the amount of C in the steel core wire and the amount of C in the coating material appropriate, even when back wave welding is performed with a DC power supply, the arc blowing is good, and each content of metal carbonate and rutile By adjusting the amount of slag, the arc is stabilized and a good back bead can be obtained, and by adjusting each content of metal fluoride and potassium feldspar, the shape of the surface bead and slag peelability can be improved. I found out. It was also found that the arc is further stabilized by adjusting the amount of hematite added.

  Hereinafter, the low hydrogen-based coated arc welding rod of the present invention will be described in detail with respect to the amount of C in the steel core wire with respect to the total mass of the steel core wire and the reason for limiting the content of each component composition in the coating material with respect to all the coating agent components. To do. Hereinafter, the mass% in each component composition is simply described as%.

[C of steel core wire: 0.06 to 0.11%]
C of the steel core wire is an element that dominates the strength of the weld metal and is necessary for maintaining a stable arc even when welding is performed with a DC power source. When the C of the steel core wire is less than 0.06%, the arc spray becomes weak and the arc becomes unstable, and a stable back bead cannot be obtained even under a DC power source. On the other hand, if C of the steel core wire is less than 0.06%, the strength of the weld metal is lowered. On the other hand, if C of the steel core wire exceeds 0.11%, the arc spray becomes too strong, the amount of spatter generated increases, and the shape of the surface bead becomes uneven. Moreover, the strength of the weld metal becomes excessive and the toughness is lowered. Therefore, C of the steel core wire with respect to the total mass of the steel core wire is 0.06 to 0.11%.

  The other components of the steel core wire are: Si: 0.03% or less, Mn: 0.40 to 0.60%, P: 0.009% or less, S: 0.005% or less, N: 0.00. It is preferably 065% or less.

[C of coating agent: 0.20 to 0.35%]
The coating material C, like the steel core wire C, is necessary for maintaining a stable arc even when welding is performed with a DC power source, and is an extremely important component in securing the strength of the weld metal. When C of the coating agent is less than 0.20%, the arc spray becomes weak and the arc becomes unstable, and a stable back bead cannot be obtained even under a DC power source. On the other hand, if the C content of the coating is less than 0.20%, the strength of the weld metal is lowered. On the other hand, when C of the coating agent exceeds 0.35%, the strength of the weld metal becomes excessive and the toughness is lowered. Accordingly, the C of the coating with respect to the total mass of the coating is 0.20 to 0.35%.

[Total of one or more metal carbonates: 40 to 55%]
Metal carbonate refers to calcium carbonate, barium carbonate, manganese carbonate, magnesium carbonate, etc., and decomposes in the arc to generate CO ₂ gas, blocking the deposited metal from the atmosphere and reducing the hydrogen partial pressure in the arc atmosphere. is there. When the total of one or two of the metal carbonates is less than 40%, the shielding effect due to the generation of CO ₂ gas is insufficient as described above, and blow holes are likely to occur. If the total of one or two metal carbonates is less than 40%, the amount of diffusible hydrogen increases and crack resistance deteriorates. On the other hand, if the total of one or two of the metal carbonates exceeds 55%, the arc spray becomes weak, the arc becomes unstable, and a stable back bead cannot be obtained. Therefore, the total of one or more metal carbonates with respect to the total mass of the coating agent is 40 to 55%.

[Total of one or more metal fluorides: 4 to 11%]
Metal fluoride refers to fluorite, barium fluoride, magnesium fluoride, aluminum fluoride, etc., all of which reduce the viscosity of molten slag to make slag with good fluidity and make an excellent bead shape. Metal fluoride also improves crack resistance by lowering the hydrogen partial pressure in the arc atmosphere. If the total of one or more of the metal fluorides is less than 4%, a suitable molten slag viscosity cannot be obtained, the surface bead shape is inferior, and the amount of diffusible hydrogen increases, resulting in crack resistance. Deteriorates. On the other hand, if the total amount of metal fluorides exceeds 11%, the slag peelability becomes poor. Accordingly, the total of one or more metal fluorides relative to the total mass of the coating agent is 4 to 11%.

[Lucille: 3-9%]
Lucille adjusts the viscosity of the arc stabilizer and slag. If the rutile is less than 3%, the arc becomes unstable and it becomes difficult to obtain a good back bead. On the other hand, if the rutile exceeds 9%, the viscosity of the molten slag becomes high and the flow of the slag decreases during welding in the upright posture and the upward posture, so that the shape of the front bead becomes convex. Therefore, the content of rutile relative to the total mass of the coating agent is 3 to 9%.

[Kari feldspar: 4-10%]
Potassium feldspar increases the viscosity of the molten slag and can obtain a slag having an appropriate viscosity at the time of back welding, and improves the concentration of the arc, so that a good back bead can be obtained. However, since potassium feldspar is a hydrous mineral, the amount of diffusible hydrogen increases and crack resistance deteriorates. If the potassium feldspar is less than 4%, the viscosity of the molten slag is low and the arc is not concentrated, so that it is difficult to obtain a good back bead. On the other hand, if potassium feldspar exceeds 10%, the amount of diffusible hydrogen increases and crack resistance deteriorates. Therefore, the content of potassium feldspar relative to the total mass of the coating agent is 4 to 10%.

[One or more of metal Si and Si alloy: 4 to 7% in total in terms of Si]
Si is added from metal Si and Si alloys such as Fe-Si and Fe-Si-Mn, and is used for the purpose of deoxidation of the weld metal, but is also necessary for ensuring welding workability. When the total of one or more of Si conversion values of metal Si and Si alloy is less than 4%, blow holes are likely to occur in the weld metal due to insufficient deoxidation, and the arc is unstable and welding in a vertical position It will be difficult to continue. On the other hand, when the sum of Si conversion values exceeds 7%, low melting point oxides are precipitated at the grain boundaries of the weld metal structure, and the toughness is lowered. Therefore, the total of one or two or more Si-converted values of metal Si and Si alloy with respect to the total mass of the coating agent is 4 to 7%.

[One or more of metal Mn and Mn alloy: 1.5 to 5.0% in total of Mn conversion values]
Mn is added from metal Mn and Mn alloys such as Fe-Mn and Fe-Si-Mn, and is added as a deoxidizer in the same manner as Si, and is effective in improving the strength of the weld metal. If the total of one or more Mn equivalents of metal Mn and Mn alloy is less than 1.5%, the strength of the weld metal is lowered. On the other hand, if the total Mn conversion value exceeds 5.0%, the strength of the weld metal increases and the toughness decreases. Accordingly, the total of one or more Mn-converted values of the metal Mn and the Mn alloy with respect to the total mass of the coating agent is 1.5 to 5.0%.

[Hematite: 0.2-1.5%]
Because hematite is a low-grade oxide, it is effective in supplying oxygen, strengthening the blowing of the arc, and increasing the concentration. If hematite is less than 0.2%, the effect is not obtained and the back bead becomes slightly unstable. On the other hand, if hematite exceeds 1.5%, the spray of arc becomes too strong and the amount of spatter generated increases. Therefore, the content of hematite with respect to the total mass of the coating agent is 0.2 to 1.5%. Incidentally, the desired effect described above can be obtained without adding hematite to the coating material, but it is desirable to adjust the amount of hematite added to the above range from the viewpoint of arc stability.

  In addition, the coating agent other than the above-mentioned coating agent composition is 15% or less in total of at least one kind of solid components such as silica sand, wollastonite, alumina, sericite, sodium silicate and potassium silicate from water glass as a slag forming agent. In addition, one or more of magnesium, aluminum magnesium, ferroaluminum and the like as deoxidizers is 3% or less in total, and one or more of mica, sodium alginate and the like as coating agents is 4% or less in total.

  Inevitable impurities are impurities inevitably mixed, such as the Fe content of the Si alloy and Mn alloy.

  Further, the coverage of the coating material on the mild steel core wire (mass% of the coating material with respect to the total mass of the welding rod) is 25 to 38%.

  Examples of the low hydrogen-based coated arc welding rod to which the present invention is applied will be specifically described.

  Low hydrogen type coated arc welding rods coated on steel core wires with a coverage of 32% using steel core wires N1 to N5 with outer diameter of 4 mm having chemical components shown in Table 1 and various coating agents shown in Table 2 Various prototypes were made.

  The amount of diffusible hydrogen was measured according to JIS Z 3118 using a prototype low hydrogen-based coated arc welding rod.

  Also, a 490 MPa class steel pipe (plate thickness: 9 mm, inner diameter: 150 mm, groove angle: 60 °, gap: 2.5 mm, root face: 1.5 mm) was used as a horizontal fixed pipe, and a welding current of 85 A using a DC welding machine. In JIS Z 3104, welding was performed in all positions sequentially from the upward position using six prototype welding rods, and after investigating the welding workability such as the back bead shape, arc stability, and slag peelability. The X-ray transmission test was conducted according to the above.

  Further, using 490 MPa class steel (plate thickness: 16 mm), weld metal was applied with a DC welding machine in accordance with JIZ Z3111, and a tensile test piece (A2) and an impact test piece were collected to investigate the mechanical performance.

  The amount of diffusible hydrogen was 5 ml / 100 g or less. Tensile strength of the tensile test was good at 550 to 650 MPa, and the impact test was repeated at a test temperature of −40 ° C., and a five Charpy impact test was conducted. These test results are summarized in Table 3.

  In Tables 2 and 3, the welding rod No. 1 to 10 are examples of the present invention, welding rod Nos. 11 to 19 are comparative examples. Since the welding rod symbols 1 to 10 which are examples of the present invention are steel core C, coating C, metal carbonate, metal fluoride, rutile, potassium feldspar, Si equivalent value and Mn equivalent value, The results were very satisfactory, such as low diffusible hydrogen, stable arc, less spatter generation, good back bead shape, front bead shape and slag peelability, and no weld defects such as blow holes. The tensile strength and absorbed energy of the weld metal were also good values.

  It should be noted that the welding rod no. 1, 4, 5, 8 and welding rod no. No. 10 has a very stable arc.

  In the comparative example, the welding rod No. No. 11 had less C in the coating, so the arc was weakly sprayed, the arc was unstable, and the back bead was non-uniform. Moreover, the tensile strength of the weld metal was low. Furthermore, since there are many potash feldspars, the amount of diffusible hydrogen was large.

  Welding rod no. No. 12 had a high tensile strength of the weld metal and a low absorption energy because there was much C in the coating. Moreover, since there were few potash feldspars, the arc was unstable and the back bead was not uniform.

  Welding rod no. No. 13 had a large amount of diffusible hydrogen because the total amount of metal carbonate was small. In addition, blow holes occurred. Further, since there was little rutile, the arc was unstable and the back bead was non-uniform.

  Welding rod no. No. 14 had a large total of metal carbonates, so the arc was unstable and the back bead was non-uniform. Moreover, since there were many Si conversion values, the absorbed energy of the weld metal was low.

  Welding rod no. No. 15 had a large amount of diffusible hydrogen because the total amount of metal fluorides was small. Further, the shape of the front bead was poor. Furthermore, since the Mn conversion value is small, the tensile strength of the weld metal was low.

  Welding rod no. No. 16 had poor slag removability because of the large amount of metal fluoride. Moreover, since there was much hematite, there was much spatter generation amount.

  Welding rod no. No. 17 had a lot of rutile, so the surface bead shape was poor. Moreover, since there were many Mn conversion values, the tensile strength of the weld metal was high and the absorbed energy was low.

  Welding rod no. In No. 18, since the C of the steel core wire N4 was small, the spray of the arc was weak, the arc was unstable, and the back bead was non-uniform. Moreover, the tensile strength of the weld metal was low. In addition, since there is little hematite, the effect which stabilizes an arc was not acquired.

  Welding rod no. No. 19 had a large amount of spatter due to a large amount of C in the steel core wire N5, and the surface bead shape was poor. Moreover, the tensile strength of the weld metal was high and the absorbed energy was low. Furthermore, since the Si conversion value is small, the arc is unstable and blow holes are generated.

Claims (2)

In low hydrogen-based arc welding rods with coatings coated on steel cores,
In mass% with respect to the total mass of the coating agent,
C: 0.20 to 0.35%,
Total of one or more metal carbonates: 40-55%,
Total of one or more metal fluorides: 4 to 11%,
Lucille: 3-9%
Potassium feldspar: 4-10%,
1 type or 2 types or more of metal Si and Si alloy: 4-7% in total of Si conversion value,
1 type or 2 types or more of metal Mn and Mn alloy: It contains 1.5-5.0% in the total of Mn conversion value,
Apply the coating material consisting of the slag generator, deoxidizer, coating agent and inevitable impurities to the steel core containing C: 0.06-0.11% in mass% with respect to the total mass of the steel core. A low-hydrogen-coated arc welding rod characterized by   2. The low hydrogen-based coated arc welding rod according to claim 1, further comprising hematite: 0.2 to 1.5% by mass% with respect to the total mass of the coating agent.