JP5066370B2 - Rare earth metal alloy powder for coated arc welding electrode and low hydrogen-based coated arc welding electrode - Google Patents

Description

The present invention relates to a rare earth alloy powder for a coated arc welding rod that can provide a high-toughness weld metal with good productivity and welding workability in the manufacture of a low hydrogen-based coated arc welding rod of 590 N / mm grade ² or higher. And a low hydrogen-based coated arc welding rod (hereinafter referred to as a low hydrogen-based rod).

  Low hydrogen rods have good crack resistance and toughness in welds, so they are applied to steel for large structures, and are used for welding medium and thick plates for low temperature steel and heat resistant steel. Yes. In recent years, welding of offshore structures (jack-up rigs) for petroleum exploration has demanded severe low temperature toughness for weld metal while ensuring good welding workability for low hydrogen rods.

  Conventionally, various proposals have been made for improving the weld metal toughness of low hydrogen rods. For example, in Japanese Patent No. 3026899 (Patent Document 1), the components of the steel core wire and the main component of the coating agent are defined. In addition, the low-temperature toughness of high-strength steel is made excellent by the particle size regulation of metallic Mg as an additive. However, the application of metal Mg has a problem in that MgO increases in the welding slag, so that the viscosity of the slag is increased, the slag fluidity is deteriorated, and the welding workability is deteriorated. Furthermore, this technique has a problem that the metal Mg reacts with the water glass during the production of the low hydrogen rod to generate hydrogen gas and create cavities inside the coating.

  On the other hand, in Japanese Patent Application Laid-Open No. 61-273297 (Patent Document 2), a multilayered weld metal having a thickness of 5 to 15 mm containing Ni is heated to 700 to 950 ° C. and held within 30 seconds, and then constant. It is proposed that a low temperature toughness is obtained by a construction method in which a cooling bead is formed at a cooling rate, a weld bead is formed on a preceding bead, and the above process is repeated. However, this method has a problem that construction management is difficult, work efficiency is poor, and practicability is lacking.

In this way, the current low hydrogen rods have problems with productivity, welding workability, work efficiency, etc., with the existing coating material and construction technology improvement measures, and satisfy various performances. However, it has been difficult to ensure excellent weld metal toughness.
Japanese Patent No. 3026899 JP-A-61-273297

  The present invention relates to a rare earth metal alloy powder for a coated arc welding rod capable of ensuring a weld metal with satisfactory welding workability and excellent low-temperature toughness while satisfying the productivity of the coated arc welding rod, and a low-hydrogen coating using the same. An object is to provide an arc welding rod.

The gist of the present invention is as follows:
(1) Rare earth metal alloy powder added to a coating agent when producing a coated arc welding rod, containing 10 to 45 mass% of one or more rare earth metals and 25 to 65 mass% of Si In addition, the rare earth metal alloy powder for coated arc welding rods is composed of Fe and unavoidable impurities and has an average particle diameter of 50 to 200 μm.
(2) In a low hydrogen-based arc welding rod in which a coating agent is coated on a core wire made of mild steel or low alloy steel, the coating agent contains 10 to 45 mass% of one or more rare earth metals, Si 25 to 65% by mass of a rare earth metal alloy powder composed of Fe and unavoidable impurities and having an average particle size of 50 to 200 μm is contained in an amount of 1.5 to 9.0% by mass with respect to the total mass of the coating agent. The present invention provides a low hydrogen-based coated arc welding rod.

  According to the rare earth metal alloy powder for a coated arc welding rod and a low hydrogen-based coated arc welding rod of the present invention, the productivity of the coated arc welding rod is good and excellent low temperature toughness is obtained in welding construction of large structures and the like. Also, it is possible to build a safe structure even in a cold region, and even better welding workability can be obtained, which can contribute to improving the welding work efficiency.

  The present inventors have intensively studied means for improving the low temperature toughness of the weld metal while satisfying the productivity of low hydrogen rods and welding workability. As a means for this, we examined strong deoxidation raw materials among coating raw materials, tried to improve toughness by reducing the amount of oxygen in the weld metal and reducing non-metallic inclusions, and various performances such as welding workability and productivity. Also investigated.

First, focusing on Ti sources that are strong deoxidation components and can be expected to have a refined effect on the weld metal structure, in order to activate the deoxidation effect, a great effect can be achieved by reducing the particle size of the Ti raw material. Therefore, Fe—Ti and metal Ti were pulverized, and those having an average particle diameter of about 10 μm were used and applied to a low hydrogen rod for 780 N / mm grade ² high strength steel. As a result, the oxygen content of the weld metal could be reduced and the toughness was improved, but with this measure, coating cracks occurred during the drying process when producing low hydrogen rods, and the slag viscosity decreased excessively during welding. As a result, the welding workability deteriorated, for example, the beads became convex.

  Next, as described above, metal Mg reacts with water glass during the production of low hydrogen rods, causing gas blistering in the coating and reducing the degree of adhesion of the coating. Went. As a result, the oxygen content of the weld metal could be reduced and excellent toughness could be secured and the productivity was good, but the welding workability became worse, such as poor arc condition and increased spatter scattering.

  Therefore, the other components were examined, and the rare earth metal having a very high deoxidation effect as compared with Ti, Al, Ca, Mg and the like was examined. Rare earth metals ignite at low temperatures in the powder state, so they cannot be applied as they are as coating materials. Furthermore, during production, the reaction with water glass is intense, causing gas blistering due to hydrogen in the coating materials, and the adhesion of the coating deteriorates, so it is alloyed. I thought it was necessary. In order to satisfy these problems and various performances of rare earth metals, the present inventors have conducted extensive research to determine the selection of components and their contents in rare earth metal alloys.

  The alloying of rare earth metals is used as a coating material, so that the grindability is important. However, the rare earth metals alone are too viscous and difficult to grind. It has been found that the addition of Si is effective as a countermeasure. However, coupled with the fact that this alloy contains Si, the reactivity with water glass is extremely stronger than that of metal Mg, and the adhesion of the coating is deteriorated.

  Therefore, as a result of various investigations of this improvement measure, if the content of rare earth metal and Si is appropriate, after pulverization, firing at 700 to 900 ° C. in an oxidizing atmosphere to form an oxide film on the powder surface It became clear that there was no reaction with water glass. The oxidizing atmosphere may be, for example, the atmosphere. If the temperature is less than 700 ° C., the formation of an oxide film is insufficient, and if it exceeds 900 ° C., it becomes hardened by sintering and cannot be maintained in a powder state. The time for maintaining the above temperature is not particularly limited, but may be 1 minute or longer.

  If the total of one or more of the rare earth metals in the rare earth metal alloy powder is less than 10% by mass (hereinafter referred to as%), the oxygen content of the weld metal is not lowered and the impact toughness is poor. On the other hand, if it exceeds 45%, it reacts with water glass at the time of production of a low hydrogen rod, gas swells on the coating, and the fixing property is deteriorated, resulting in poor productivity. Further, the welding workability is deteriorated, for example, the arc voltage is excessively lowered during welding, the arc does not spread and the bead shape is deteriorated.

  If the Si content in the rare earth metal alloy powder is less than 25%, the grindability during the production of the alloy powder will be poor. On the other hand, if it exceeds 65%, even if an oxide film is produced by firing, it reacts with water glass during the production of a low hydrogen rod and gas swells on the coating, resulting in poor productivity.

  Further, when the average particle size of the rare earth metal alloy powder is less than 50 μm, it easily reacts with water glass during the production of the low hydrogen rod, gas swells in the coating, and the fixing property is deteriorated, resulting in poor productivity. On the other hand, if the average particle size exceeds 200 μm, flux slippage is deteriorated in the coating process at the time of production of the low hydrogen rod, and the productivity is deteriorated.

  As a result of applying the rare earth metal alloy powder thus obtained to a low hydrogen rod, it was found that the low temperature toughness is extremely good, the welding workability is satisfactory, and the productivity is also good. The content of the rare earth metal alloy powder in the coating agent is 1.5 to 9.0% with respect to the total mass of the coating agent. When the content in the coating agent is less than 1.5%, it does not function as a deoxidizer and it is difficult to ensure high toughness of the weld metal. On the other hand, if it exceeds 9.0%, the arc state is disturbed and welding workability is deteriorated.

  Note that the rare earth metal referred to in the present invention refers to a metal having Sc, Y, and an atomic number of 57 (La) to 71 (Lu). The rare earth metal alloy powder includes Fe and inevitable impurities other than one or more of the rare earth metals and Si.

  The main raw materials for the coating agent for the low hydrogen rod of the present invention are metal carbonates such as calcium carbonate, metal fluorides such as calcium fluoride, and the like. Metal carbonate is added to block the atmosphere, but if the content is small, oxygen and nitrogen in the weld metal will increase, and if added excessively, the arc state and bead shape will deteriorate, so the metal carbonate content The amount is desirably 20 to 60%. In addition, metal fluoride is indispensable for obtaining good slag fluidity, and if its content is small, it is ineffective, and if it is excessively large, the arc state and slag peelability deteriorate, so the amount added. Is desirably 13 to 30%. In addition, arc stabilizers, slag forming agents, deoxidizing agents, and alloying agents are generally used as coating materials for low-hydrogen rods.

  The effects of the present invention will be specifically described with reference to examples. After examining the pulverizability of various rare earth metal alloys having the components shown in Table 1 by ball milling, firing was performed at 800 ° C. in the atmosphere to form an oxide film on the surface. Alloy powder was used.

JIS G3523 SWY11 having a diameter of 4.0 mm and a length of 400 mm obtained by adding the rare earth metal alloy powders shown in Tables 1 and 2 to the coating material of the low hydrogen rod for 780 N / mm grade ² low temperature steel shown in Table 3. The production of low hydrogen rods was confirmed by coating the steel core wire and drying it to make various low hydrogen rods. Furthermore, welding was performed using this welding rod, and the impact toughness and welding workability of the deposited metal were investigated.

  Judgment of the pulverization property of the rare earth metal alloy was good when it was easily pulverized, and marked when it took time for pulverization. For evaluation of the productivity of the low hydrogen rod, the appearance of the coating was observed, and the case where no gas bulging due to the reaction gas with water glass did not occur was marked as good, and the case where it occurred was marked as x.

  The impact toughness of the weld metal was investigated by conducting welding according to the weld metal test of JIS Z 3212, with a current of 170 A (AC), a preheating / pass temperature of 100 ± 10 ° C., and an average heat input of 17 kJ / cm. A JIS Z 2202 No. 4 impact test piece was collected from the center. The test was conducted at -40 ° C. for 5 tests, and the average value of the absorbed energy was 90 J or more.

Furthermore, the welding workability survey was conducted by assembling a 780 N / mm grade ² steel plate with a plate thickness of 16 mm, a width of 100 mm, and a length of 450 mm into a T-shape, using an AC welding machine, with horizontal fillet welding with a current of 170 A and with vertical posture welding Welding was performed under a welding condition of 150 A, and the arc state, the slag state, the degree of spatter, and the like were investigated. The determination was made by comprehensively evaluating the evaluation of each position welding, and “good” was marked with “good” and inferior was marked with “x”. The results are also summarized in Table 2.

In Tables 1 and 2, the welding rod No. 1-No. 10 is an example of the present invention, welding rod No. 11-No. 18 is a comparative example.
The welding rod no. 1-No. No. 10 is a combination of one or more rare earth metals in the rare earth metal alloy powder, the Si content and the average particle size are appropriate, so the grindability as a raw material is good, and the production of low hydrogen rods Since the content of the rare earth metal alloy powder added to the coating material is also appropriate, the low temperature toughness of the weld metal is extremely excellent and the welding workability is also good.

In the comparative example, the welding rod No. No. 11 had a large total of rare earth metals in the rare earth metal alloy powder, and thus it reacted with water glass during the production of low hydrogen rods, resulting in gas expansion in the coating, resulting in poor adhesion and poor productivity. Further, the arc voltage is excessively lowered during welding, the arc does not spread, the bead shape is deteriorated, and welding workability is poor.
Welding rod no. No. 12 had a low absorption energy because the total amount of rare earth metals in the rare earth metal alloy powder was small.

Welding rod no. No. 13 has a large amount of Si in the rare earth metal alloy powder, so that it reacted with water glass during the production of the low hydrogen rod and gas swelled in the coating, resulting in poor productivity.
Welding rod no. No. 14 had poor pulverizability at the time of producing the alloy powder because there was little Si in the rare earth metal alloy powder.

Welding rod no. No. 15 had a large average particle size of the rare earth metal alloy powder, so that the slipping of the flux deteriorated in the coating during the production of the low hydrogen rod, resulting in poor productivity. In addition, spatter was scattered during welding and welding workability was also poor.
Welding rod no. No. 16 has a small average particle size of the rare earth metal alloy powder, so that it reacted with water glass at the time of production of the low hydrogen rod and gas swelled in the coating, resulting in poor productivity.

Welding rod no. In No. 17, since the content of the rare earth metal alloy powder in the coating material was large, the arc state was disturbed and the welding workability was deteriorated.
Welding rod no. No. 18 had a low absorption energy because the content of the rare earth metal alloy powder in the coating material was small.

Claims (2)

A rare earth metal alloy powder added to a coating agent when producing a coated arc welding rod, containing one or more rare earth metals in an amount of 10 to 45 mass%, Si in an amount of 25 to 65 mass%, and others A rare earth metal alloy powder for a coated arc welding rod, comprising Fe and inevitable impurities and having an average particle diameter of 50 to 200 μm. In a low hydrogen-based arc welding rod in which a coating agent is coated on a core wire made of mild steel or low alloy steel, the coating agent is 10 to 45% by mass of one or more rare earth metals and 25 to Si. A rare earth metal alloy powder containing 65% by mass, composed of other Fe and inevitable impurities, and having an average particle size of 50 to 200 μm is contained in an amount of 1.5 to 9.0% by mass with respect to the total mass of the coating agent. Features a low hydrogen-based coated arc welding rod.