JP2011206795A - Fe-Si ALLOY POWDER FOR COVERED ELECTRODE AND LOW-HYDROGEN TYPE COVERED ELECTRODE FOR BACK-BEAD WELDING - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Fe-Si alloy powder for covered electrodes and low-hydrogen type covered electrodes for back-bead welding, which are excellent in arc stability while satisfying various performances in initial layer welding in pipe etc., and which can secure a superior back bead shape.SOLUTION: The Fe-Si alloy powder is added to a coating agent when covered electrodes are manufactured, containing 17.0-55.5 mass% Si and having an average grain size of 5-35 μm. The low-hydrogen type covered electrode for back-bead welding contains 3.5-10.0 mass% Fe-Si alloy powder in terms of Si relative to the total mass of the coating agent.

Description

  The present invention relates to an Fe-Si alloy powder added as a coating material for a coated arc welding rod and a low hydrogen-based coated arc welding rod for back wave welding, particularly excellent arc stability in the first layer welding of a pipe, The present invention relates to a Fe—Si alloy powder for a coated arc welding rod which can provide a good backside bead and a coated arc welding rod for backside welding using the same.

  Low hydrogen coated arc welding rods (hereinafter referred to as low hydrogen rods) mainly composed of metal carbonates and metal fluorides (hereinafter referred to as low hydrogen rods) are more suitable for back wave welding than illuminite or lime titania coated arc welding rods. , Mechanical properties are excellent. Furthermore, since it has less diffusible hydrogen and excellent crack resistance compared to high-cellulosic-coated arc welding rods that can be welded in the back-and-forth direction, it is often used for back-wave welding in pipelines and the like. .

  In recent years, in order to prevent the electric shock of welding workers, especially, the number of welding machines in which the no-load voltage on the secondary side is controlled to a low voltage has been increasing. When back wave welding is performed with a rod, the arc becomes unstable, arc breakage occurs, and it is difficult to obtain a sound back wave bead.

  As a method for improving arc breakage of low hydrogen rods for backside welding, it is known to add an arc stabilizer, Al-Mg, Mg, or the like to the coating material. Although it can be reduced, there is a problem that the arc force becomes too weak to form a sufficient back bead. Japanese Patent No. 2579860 (Patent Document 1) proposes a technique that can add stable potassium feldspar with a regulated particle size to the coating agent to reduce arc breakage and secure a stable back bead. Since potassium feldspar contains crystal water, there is a problem that the amount of diffusible hydrogen increases and crack resistance deteriorates.

  Furthermore, Japanese Patent Laid-Open No. 2000-117487 (Patent Document 2) proposes a technique for improving the stability of the arc and the back bead by appropriately setting rutile and alumina in the coating material. When the machine's no-load voltage was low, the arc break could not be reduced.

  Thus, it is difficult to obtain a low hydrogen rod for backside welding that satisfies various performances, prevents arc breakage, has a good backside bead shape, and can secure a stable backside bead. It was.

Japanese Patent No. 2579860 JP 2000-117487 A

  The present invention provides a Fe-Si alloy powder for a coated arc welding rod that is excellent in arc stability while satisfying various performances in the first layer welding of a pipe, etc., and can ensure a good backside bead shape, and backside welding using the same An object of the present invention is to provide a low hydrogen-based coated arc welding rod.

The gist of the present invention is as follows.
(1) Fe-Si alloy powder added to the coating agent when producing a coated arc welding rod, containing 17.0 to 55.5% by mass of Si, and the other consists of Fe and inevitable impurities, And the average particle diameter is 5-35 micrometers, Fe-Si alloy powder for covering arc welding rods characterized by the above-mentioned.
(2) In a low hydrogen-based arc welding rod for back wave welding in which a coating is coated on a mild steel core wire, the coating contains 17.0 to 55.5% by mass of Si, and the others are Fe and inevitable Fe-Si alloy powder consisting of impurities and having an average particle diameter of 5 to 35 μm is contained in an amount of 3.5 to 10.0% by mass in terms of Si with respect to the total mass of the coating agent. Low hydrogen coated arc welding rod for wave welding.

  According to the Fe—Si alloy powder for a coated arc welding rod of the present invention and the low hydrogen-based coated arc welding rod for back wave welding using the same, a welding machine having a low secondary no-load voltage in the first layer welding of a pipe, etc. Can prevent arc breakage, which is a drawback of conventional welding rods, and can provide a uniform back bead. Also, it has good general welding workability and can greatly improve welding efficiency. It is a great thing to do.

  As a means for preventing arc breakage when using a low hydrogen rod for back wave welding and obtaining a sound back bead, the present inventors have made use of metal powder that also affects the welding workability of the low hydrogen rod. Research focused on the particle size.

  In general, metal Mn powder, Fe-Si alloy powder, or the like, which is a deoxidizer, is mainly used as a metal powder used as a coating for a low hydrogen rod for back wave welding. Therefore, first, metal Mn powder was prepared by changing the pulverization conditions so that the average particle diameter was 10 to 150 μm as measured by a laser diffraction method, and applied to a low hydrogen rod for back wave welding. The arc state was investigated. As a result, it was confirmed that the metal Mn powder had a weak arc force in the fine grain region and a strong arc in the coarse grain region, but no change was observed in the stability of the arc and no load was applied. No effect was found to prevent arc breakage with a low voltage welding machine. Moreover, although the Fe-Mn alloy powder which is a Mn source was also investigated, the effect of improving the arc stability as with the metal Mn powder could not be obtained.

  Next, the welding workability was investigated using the Fe-Si alloy powder having a Si content of 42% by mass and the average particle size changed to 10 to 150 μm. As a result, it has been found that in the fine-grained area, the droplets become fine and the arc is extremely stable, and in particular, arc breakage hardly occurs. In addition, fine-grained Fe-Si alloy powder has the effect of improving the conformability between the weld metal and the base metal, and if the Si content in the Fe-Si alloy powder is an appropriate amount, it can form an excellent back bead. Also turned out. On the other hand, Fe-Si alloy powder easily reacts with water glass (sodium silicate, potassium silicate, etc.), which is a fixing agent of the coating agent, in the drying process when manufacturing the low hydrogen rod, and voids are generated in the coating material on the coating surface. It has also been found that it is necessary to bake and apply an oxide film because irregularities are seen and the appearance is poor and the coating is likely to fall off.

  That is, by using an appropriate amount of fine-grained Fe-Si alloy powder that has undergone surface treatment, productivity is good, excellent arc stability can be secured, arc breakage can be prevented, and a good back bead can be obtained. It was found that other characteristics were satisfactory.

  Hereinafter, the reason for limiting the component composition of the Fe—Si alloy powder, the particle size, and the content in the coating agent will be described for the Fe—Si alloy powder for a coated arc welding rod and the low-hydrogen welding rod for back wave welding of the present invention. .

  When the Si content in the Fe—Si alloy powder is less than 17.0% by mass (hereinafter referred to as “%”), the grindability during the production of the Fe—Si alloy powder is poor, and a good back bead cannot be obtained during welding. Slag releasability also deteriorates. On the other hand, if it exceeds 55.5%, the arc voltage becomes high, the arc spray becomes excessively strong, and the arc breakage is likely to occur.

  The particle size of the Fe—Si alloy powder is the most important part in the present invention. When the average particle size is less than 5 μm, it is difficult to treat the surface oxide film to prevent the reactivity with water glass, and the alloy powder tends to aggregate during firing. On the other hand, when the average particle size exceeds 35 μm, the arc stability is poor, the spatter is scattered, and the arc breaks frequently occur in a welding machine having a low secondary no-load voltage.

  The surface oxide film treatment of the Fe—Si alloy powder may be performed by putting the powder in a container and heating at 500 to 1000 ° C. in an oxidizing atmosphere. As the oxidizing atmosphere, an atmosphere containing 5 to 25% oxygen is appropriate, and air may be used. When the heating temperature is less than 500 ° C., the formation of the oxide film is insufficient, and when it exceeds 1000 ° C., the tendency of the alloy powder to aggregate during firing increases. Further, if the amount of oxygen in the atmosphere is less than 5%, formation of an oxide film is insufficient, and if it exceeds 25%, oxidation may proceed to the inside of the powder particles. Moreover, the heating time should just be 10 minutes or more in the said temperature range. The formation state of the oxide film can be known by X-ray diffracting the alloy powder and detecting the diffraction line of the oxide.

  The content of the Fe—Si alloy powder in the coating agent is 3.5 to 10.0% in terms of Si with respect to the total mass of the coating agent. When the Si conversion value is less than 3.5%, the familiarity with the base material is poor and the slag removability is poor, and the arc stability is poor and a good back bead shape cannot be obtained. On the other hand, if it exceeds 10.0%, the arc is too strong and the back bead shape is deteriorated.

Also, among other raw materials used for coatings, metal carbonate is added to block the atmosphere, but if the content is low, oxygen and nitrogen in the weld metal will increase, and if added excessively, the arc state Since the bead shape deteriorates, the metal carbonate content is preferably 35 to 60%. Furthermore, metal fluoride is indispensable for obtaining good slag fluidity, and if its content is low, there is no effect, and if it is excessive, the arc state and slag peelability deteriorate, so the amount added is 5-15% is desirable. In addition, arc stabilizers such as Na ₂ O, K ₂ O, and Li ₂ O, and slag generators such as TiO ₂ , SiO ₂ , Al ₂ O ₃ , and ZrO ₂ are usually used as low hydrogen-based coating raw materials. . In addition, in order to acquire the effect of the component of the coating material in this invention demonstrated above, 20-50% is suitable for a coverage (mass% of the coating material with respect to the total mass of a welding rod).

The effects of the present invention will be specifically described with reference to examples.
After investigating the grindability of the Fe-Si alloy powders of the components shown in Table 1 with a ball mill, the state was confirmed by firing at 700 to 900 ° C. to confirm the situation, and Fe—Si having various average particle diameters. Alloy powder was used. The average particle size was measured by a laser beam diffraction method.

  After coating the steel core wire of JIS G3523 SWY11 having a diameter of 3.2 mm and a length of 400 mm by adding the Fe—Si alloy powder shown in Table 1 to the coating material of the low hydrogen rod for back wave welding shown in Table 2. Various low hydrogen rods for backside welding with a coverage rate of 31% were made as prototypes, and the number of arc breaks, backside bead shape, and general welding workability were investigated.

  In the determination of pulverizability during the production of the Fe—Si alloy powder, those that could be easily pulverized were marked with good ◯ marks, and those that required time for pulverization were marked with X. In addition, the surface oxide film treatment status by firing was marked with a mark where no agglomeration was observed, and an x mark when agglomeration was observed.

  The number of arc breaks is as follows: mild steel pipe (wall thickness: 9 mm, inner diameter: 150 mm, groove angle: 60 °, gap: 2.5 mm, root face: 1.5 mm) is a horizontal fixed tube, and the secondary side no-load voltage is Using a 70V AC welding machine, welding was performed in all postures starting from the upward posture at the lower end of the circumference using six prototype welding rods with a welding current of 85A, and the average number of arc breaks per piece was investigated. The ones that were completely absent were considered good.

  Further, the back bead shape and general welding workability were evaluated under the test conditions used in the above-mentioned arc breakage number test. The back bead shape was evaluated as a good ○ mark when the bead width was uniform and uniform with no irregularities, and a non-uniform and lack of uniformity was evaluated as a poor X mark. For general welding workability, the arc state (stability, spray strength), spatter generation amount, slag peelability, surface bead shape, etc. are investigated, and these are comprehensively evaluated. Marked. These results are also summarized in Table 1.

  In Table 1, welding rod no. 1-No. No. 8 is an example of the present invention, welding rod no. 9-No. 14 is a comparative example. The welding rod no. 1-No. In No. 8, since the Si content in the Fe—Si alloy powder and the average particle diameter of the Fe—Si alloy powder were appropriate, the productivity during the production of the Fe—Si alloy powder was excellent. Furthermore, since the amount of Si equivalent to the total mass of the coating material is appropriate, it satisfies the various performances in the first layer welding of the pipe and has excellent arc stability, no arc breakage, and excellent back bead shape. It was a satisfactory result.

In the comparative example, the welding rod No. In No. 9, since the Si content in the Fe—Si alloy powder was small, the grindability during the production of the Fe—Si alloy powder was poor. Moreover, the back bead at the time of welding was not uniform, and the slag peelability was also poor.
Welding rod no. No. 10 had a large amount of Si in the Fe—Si alloy powder, so that the arc became strong, arc breakage occurred, and the amount of spatter generated was large.

Welding rod no. No. 11 had a small average particle diameter of the Fe—Si alloy powder, so that the powder particles aggregated during the firing process during the oxide film treatment, and the yield was low.
Welding rod no. No. 12 had a large average particle diameter of the Fe—Si alloy powder, so that the arc was unstable, arc breakage occurred frequently, the amount of spatter was large, and the uniformity of the back bead was also lacking.

Welding rod no. No. 13 had a low Si equivalent value in the coating agent, so that the familiarity with the base material and the slag peelability were poor, and the back bead was also poor.
Welding rod no. No. 14 had a large Si-converted value in the coating material, so the arc was too strong and the back bead shape was poor.

Claims (2)

Fe—Si alloy powder added to a coating agent when producing a coated arc welding rod, containing 17.0 to 55.5% by mass of Si, the other being composed of Fe and inevitable impurities, and an average grain A Fe—Si alloy powder for a coated arc welding rod, having a diameter of 5 to 35 μm. In a low hydrogen-based arc welding rod for back wave welding in which a coating is applied to a mild steel core wire, the coating contains 17.0 to 55.5% by mass of Si, and the other consists of Fe and inevitable impurities. In addition, Fe-Si alloy powder having an average particle diameter of 5 to 35 μm is contained in an amount of 3.5 to 10.0% by mass in terms of Si with respect to the total mass of the coating material. Low hydrogen type coated arc welding rod.