JP2012143809A - Ni POWDER FOR COVERED ARC WELDING ELECTRODE, AND LOW-HYDROGEN TYPE COVERED ARC WELDING ELECTRODE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Ni powder for a covered arc welding electrode and a low-hydrogen type covered arc welding electrode, which are excellent in productivity, are excellent in arc stability and welding workability such as reduction of a spatter generation quantity, and can ensure the toughness of a weld metal.SOLUTION: Ni powder, to be added to a coating flux when manufacturing a covered arc welding electrode, has the content of C of ≤0.020 mass%, and the balance Ni with inevitable impurities, while the average particle diameter is 35-120 μm. Further, in the low-hydrogen type covered arc welding electrode, Ni powder of 3.5-12.5 mass% is contained to the total mass of the coating flux.

Description

  The present invention relates to Ni powder added as a coating material for a coated arc welding rod and a low hydrogen-based coated arc welding rod, and in particular, improves the stability of the arc, reduces the amount of spatter, and increases the productivity. The present invention relates to a Ni powder for a coated arc welding rod capable of ensuring excellent and good weld metal toughness and a low hydrogen-based coated arc welding rod (hereinafter referred to as a low hydrogen-based rod) using the same.

  Low hydrogen rods mainly composed of metal carbonates and metal fluorides have good cracking resistance and toughness, so they are applied to steel for large structures and are used for welding low temperature steels and heat resistant steels. Yes.

  The low hydrogen rod may use a high current for the purpose of improving work efficiency. In that case, while deep penetration into the work piece is obtained, the arc force becomes excessively strong, the amount of spatter generated increases, the adhesion to the steel plate becomes intense, and the spatter removal work takes time. there were.

  Various measures for improving the problems of such low hydrogen rods have been proposed. For example, Japanese Patent Application Laid-Open No. 58-209499 (Patent Document 1) proposes a technique for stabilizing the arc and reducing the amount of spatter generated by using a fine atomized material in the coating. The agent becomes dense, resulting in coating cracks in the drying process, resulting in productivity problems.

  Japanese Patent Application Laid-Open No. 5-169296 (Patent Document 2) proposes a technique for stabilizing the arc and reducing the amount of spatter generated by limiting the average particle size of silica sand used for the coating material. However, since silica sand is applied, the amount of Si in the weld metal increases, and good weld metal toughness cannot be obtained, and there is a problem in crack resistance.

On the other hand, in JP-A-58-116991 (Patent Document 3), the amount of spatter is reduced by limiting the amount of Mn in the steel core wire and coating and the amount of C in the steel core wire. However, this proposal relates to a non-low hydrogen welding rod, and even if this method is applied to a low hydrogen welding rod, almost no effect was observed. In addition, it is known to use raw materials (such as potassium feldspar and wollastonite) containing K ₂ O and CaO having a low ionization voltage as a coating material to reduce the amount of spatter generated. As a result, the amount of diffusible hydrogen increases, leading to deterioration of crack resistance.

  As described above, it has been very difficult to improve the arc stability and reduce the amount of spatter generated while satisfying various performances of the current low hydrogen rod. Each industry using low hydrogen rods strongly demanded welding rods with less spatter generation from the viewpoint of work efficiency.

JP 58-209499 A JP-A-5-169296 JP 58-116991 A

  The present invention is excellent in welding workability such as good productivity, reduced arc stability and spatter generation, and can ensure the toughness of the weld metal. Ni powder for coated arc welding rod and low hydrogen-based coated arc The object is to provide a welding rod.

The gist of the present invention is as follows.
(1) Ni powder added to a coating agent when manufacturing a coated arc welding rod, C is 0.020% by mass or less, the balance is Ni and inevitable impurities, and the average particle size is 35 to 120 μm. Ni powder for coated arc welding rods, characterized in that
(2) In a low hydrogen-based coated arc welding rod in which a coating is applied to the steel core wire, the coating comprises 0.020% by mass or less of C, the balance is Ni and inevitable impurities, and the average particle size is 35 Ni powder which is ~ 120 μm is contained in an amount of 3.5 to 12.5% by mass based on the total mass of the coating agent, and the others are metal carbonate, metal fluoride, arc stabilizer, slag generator, deoxidizer, A low hydrogen-based arc welding rod characterized by being an alloying agent, a fixing agent and inevitable impurities.

  According to the Ni powder for a coated arc welding rod of the present invention and a low hydrogen rod using the same, the productivity, welding workability and toughness of the weld metal are good, and the spatter generation amount is small, so the welding work efficiency is greatly improved. There are significant areas that can be improved and contribute to the industry.

The present inventors diligently studied means for reducing the amount of spatter generated from a low hydrogen rod while ensuring various performances.
The cause of spatter is known to be caused by excessively strong plasma flow or arc force at the time of arc generation, or by gas explosion of droplets, etc., especially when welding at high currents The arc becomes unstable and the amount of spatter generated increases. Therefore, it is considered effective to improve the detachment of the droplets and reduce the size of the spatter, and attention was paid to the particle size and impurities of the coating material.

  First, the particle size of the metal carbonate calcium carbonate and metal fluoride fluorite, which are the main raw materials for low-hydrogen rods, was examined. By using fine particles, the arc was stabilized and the amount of spatter generated was reduced. Was found to be reduced. However, since the particle size composition of the entire coating agent is reduced, there is a problem that the coating becomes dense and dry cracks occur during production. In addition, fluorite was also studied for high-purity products with few impurities such as crystal water, S, and P, but was not effective in reducing the amount of spatter generated.

  Next, the particle size of Fe-Si generally used as a deoxidizer was also examined, but the reverse of calcium carbonate and fluorite, the more stable the arc, the lower the amount of spatter generated. However, the arc was weakened excessively, resulting in insufficient penetration.

  Furthermore, Ni powder effective for low-temperature toughness of weld metal of low hydrogen rods was investigated, the average particle size was changed by sieving, and the amount of spatter generated and various performances were investigated. It was found out that the amount of generation decreased. Ni powder is easily oxidized in the fine-grained region, and Ni oxide is formed on the surface. The melting point of Ni oxide is higher than about 1450 ° C and about 2000 ° C. Therefore, when fine Ni powder is used for the coating, the viscosity of the slag of the droplets increases during welding, and the melting point is increased accordingly. Since the drop detachment becomes worse, the amount of spatter generated increases.

  Conversely, when Ni powder is excessively rough, the oxidation reaction is reduced, so the viscosity of the slag of the droplets is reduced, the detachment of the droplets is facilitated and the amount of spatter is reduced, but the coating agent is fixed when the welding rod is manufactured. Deteriorates and the coating is easily removed during transportation. Therefore, it is important to set an appropriate average particle diameter. Furthermore, limiting the C content of the Ni powder is indispensable for reducing the spatter generation amount of the low hydrogen rod together with the average particle size. It has been found that if the C content of the Ni powder is high, the viscosity of the molten slag increases and the slag tends to precede and a stable arc cannot be obtained, causing spattering.

Hereinafter, the reason for limiting the average particle diameter of Ni powder, the component composition, and the content in the coating agent of the Ni powder for a coated arc welding rod and the low hydrogen rod of the present invention will be described.
If the average particle size of the Ni powder is less than 35 μm, the detachment of the droplets becomes worse, so the arc becomes unstable and the amount of spatter generated increases. On the other hand, if the thickness exceeds 120 μm, the coating agent is not tightened, and the coating is cracked in the manufacturing drying process, and the coating comes off.

On the other hand, when the C content of the Ni powder exceeds 0.020 mass% (hereinafter referred to as “%”), the viscosity of the molten slag becomes high, the slag is preceded and the arc becomes unstable, and the amount of spatter generated increases.
When the content of the Ni powder in the coating material is less than 3.5% with respect to the total mass of the coating material, good low temperature toughness cannot be obtained. On the other hand, if it exceeds 12.5%, the arc force becomes excessively weak, the detachment of the droplets deteriorates, the amount of spatter increases, the bead does not spread, and the bead shape becomes poor.

  In addition, among other raw materials used for the coating agent, metal carbonate is added to block the atmosphere, but if the content is low, oxygen and nitrogen in the weld metal will increase, while on the other hand if excessively added Since the arc state and the bead shape deteriorate, the content of the metal carbonate 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 10 to 35% is desirable. In addition, arc stabilizers, slag forming agents, and sticking agents 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 welding rod total mass).

The effects of the present invention will be specifically described with reference to examples.
Various low-hydrogen rods were made by adding Ni powders having different average particle sizes and C contents as shown in Table 2 to the coating for the 780 MPa class low-hydrogen rods shown in Table 1. . JIS G3523 SWY11 steel core wire having a diameter of 4.0 mm and a length of 400 mm was coated and then dried to a coverage of 31%, and productivity, spatter generation, welding workability, and weld metal toughness were investigated.

  The productivity test consists of manufacturing approximately 100 kg of welding rods, making good ones with no wrinkles, dents or cracks in the coating or in the drying process, and making the production yield the ratio of good products to all manufactured welding rods. A value of 99.0% or more was regarded as good, and a value less than 99.0% was regarded as defective.

  The amount of spatter generated was investigated by placing a 490 MPa class test steel plate having a thickness of 20 mm, a width of 50 mm, and a length of 450 mm inside a copper plate collection box having a width of 200 mm, a length of 600 mm, and a height of 200 mm. A slit was opened in the direction, and an inspection welding rod was inserted here to weld the plate thickness surface of the test steel plate. The welding conditions were a current of 190 A, a speed of 15 cm / min, and a sputter generation amount of 1.5 g / min or less.

  Welding workability survey was conducted by assembling a T-shaped 780MPa class steel plate with a plate thickness of 16mm, width of 100mm and length of 450mm, using an AC welding machine, horizontal fillet welding with a current of 170A, and vertical position welding of 150A. did. As a result, the arc state (stability, spray strength), slag peelability (fluidity, encapsulation, peelability), bead shape, and the like were investigated.

  The weld metal has an impact toughness of 170 A (AC) current, 90-130 ° C pre-pass / pass temperature, 17 kJ / cm average heat input, and welded according to the weld metal test of JIS Z3211. Thus, a No. 4 impact test piece of JIS Z2202 was collected. The test temperature was −40 ° C., and six tests were performed, and the average value of the absorbed energy was 70 J or more. These results are also summarized in Table 2.

  In Table 2, 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 average particle diameter of the Ni powder in the coating material and the C content in the Ni powder were appropriate, the arc stability was excellent and the amount of spatter generated was small. Further, since the amount of Ni powder added to the coating material was appropriate, welding workability such as arcing was good and the absorbed energy of the deposited metal was high, which was a very satisfactory result.

In the comparative example, the welding rod No. In No. 9, since the average particle diameter of the Ni powder was fine, the transferability of the droplets was poor, the arc became unstable, and the amount of spatter generated was large.
Welding rod no. In No. 10, since the average particle diameter of the Ni powder was coarse, the fixability of the coating agent was poor at the time of production, and the coating cracked at the time of drying, resulting in a low production yield.

  Welding rod no. 11 and welding rod no. In No. 12, since the C content of the Ni powder was large, the viscosity of the molten slag was high, the slag was preceded, the arc became unstable, and the amount of spatter was large.

Welding rod no. No. 13 had a low absorbed energy because the amount of Ni powder added in the coating was small.
Welding rod no. In No. 14, since the amount of Ni added in the coating was large, the arc was weakened, the droplets were not easily detached, and the amount of spatter was large. Moreover, the bead did not spread and the bead shape was also poor.

Claims (2)

Ni powder added to a coating agent when manufacturing a coated arc welding rod, C is 0.020% by mass or less, the balance is Ni and inevitable impurities, and the average particle size is 35 to 120 μm. Ni powder for a coated arc welding rod characterized by the above. In a low hydrogen-based coated arc welding rod in which a coating material is coated on a steel core wire, the coating material has a C content of 0.020% by mass or less, the balance is made of Ni and inevitable impurities, and the average particle size is 35 to 35%. Ni powder of 120 μm is contained in an amount of 3.5 to 12.5% by mass with respect to the total mass of the coating agent, and the others are metal carbonate, metal fluoride, arc stabilizer, slag generator, deoxidizer, alloy A low hydrogen-based coated arc welding rod characterized by being an agent, a fixing agent and inevitable impurities.