JP4481873B2 - Iron powder for coated arc welding rod and coated arc welding rod for tacking - Google Patents

Description

  The present invention relates to an iron powder for a coated arc welding rod and a temporary coating added to a coating agent when manufacturing a low hydrogen-based coated arc welding rod which is often used in tack welding in structures such as shipbuilding, bridges and buildings. For coated arc welding rods for welding, especially for coated arc welding rods that maintain good welding workability and also provide excellent re-arcing and good side arc resistance even after welding with a welding machine with an electric shock prevention device The present invention relates to a coated arc welding rod for iron powder and tacking (hereinafter referred to as a tacking welding rod), and particularly to a coated arc welding rod for low hydrogen-based tacking.

  Because tack welding rods have excellent crack resistance and mechanical properties, they are often used for tack welding of important structures using high-strength steel and low-temperature steel and large structures using thick plates. Has been. Temporary welding, where intermittent welding is performed, interrupts the arc in the middle of welding and generates an arc again, and the arc is generated by crushing the coated cylinder and bringing the core wire into contact with the steel sheet, but if the coating is partially missing Since welding defects such as pits and blowholes are likely to occur in the weld metal, it is desirable that the arc be easily generated by lightly contacting the coated tube formed by welding with the steel plate.

  In addition, a normal welding machine has a no-load voltage of about 60 to 90 V, but an electric shock prevention device is used to prevent electric shock, and about 10 to 25 V is applied to the holder when welding is stopped. The electric shock prevention device detects the welding current and is released (within 0.06 seconds), and an arc voltage due to the drooping characteristic of the power source is applied to the holder during welding. Further, when the arc is stopped, the no-load voltage of the welding machine is maintained at about 60 to 90 V for about 1 second, but after that, it becomes about 10 to 25 V by the electric shock prevention device. Thus, the electric shock prevention device is very difficult to generate a re-arc because the voltage at the time of stopping welding is low for safety. In addition, if only the re-arcing property is taken into account and excessively high-conductivity iron powder or the like is contained, an arc is likely to be generated from the covering portion of the welding rod (hereinafter referred to as a side arc) during welding. There are safety issues.

  In order to satisfy the re-arcing property and side arc resistance of the tack welding rod, there are proposals for tack welding rods using various iron powders for the purpose of improving the conductivity of the coated cylinder. Has been. For example, Japanese Patent Application Laid-Open No. 11-22679 (Patent Document 1) discloses a low hydrogen-based covered arc welding rod that improves re-arcability by limiting the average particle size and specific surface area of iron powder. . However, with this technique, the insulation of the coating deteriorates, so that a side arc is likely to occur even before welding.

  Japanese Patent Application Laid-Open No. 2004-306094 (Patent Document 2) limits the content of metal carbonate, metal fluoride, iron powder, organic matter, coverage and insulation resistance in the coating agent, There is a disclosure of a technique for improving re-arcing property and side arc resistance by inclusion. However, this technique has side arc resistance before welding and does not satisfy the side arc resistance after welding.

Further, Japanese Patent Laid-Open No. 10-263878 (Patent Document 3) discloses that the specific resistance of the core wire and the contact resistance between the core wire and the welder holder are limited, regardless of the amount of coating metal added. There is a disclosure of a technique that can improve arc performance. However, since the side arc resistance is inferior, it does not improve the re-arcing property and the tack welding rod that satisfies the side arc resistance after welding.
Japanese Patent Laid-Open No. 11-226779 Japanese Patent Laid-Open No. 2004-306094 JP-A-10-263878

  The present invention possesses good welding workability, has very good re-arcing property with a welding machine with an electric shock prevention device, and also satisfies side arc resistance after welding with a welding machine without an electric shock prevention device. It is an object to provide a tack welding rod and iron powder for a coated arc welding rod used in the production thereof.

The gist of the present invention is as follows.
(1) Iron powder added to a coating agent when a coated arc welding rod is manufactured, and 2 to 25% by mass of organic matter is converted into solid mass on the surface of the iron powder at a ratio to the mass of the coated iron powder. Thus, the iron powder for coated arc welding rods is coated with 0.3 to 8.0% by mass of water glass.
(2) In a coated 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 has a solid mass of 2 to 25 mass% of organic matter in a ratio to the mass of the coated iron powder. 30 to 60% by mass of iron powder coated on the surface with 0.3 to 8.0% by mass of water glass in terms of the total mass of the coating agent.
Further, the coating agent further contains 20 to 50% by mass of metal carbonate and 0.5 to 3.5% of metal fluoride, and the others are deoxidizer, arc stabilizer, slag generator and inevitable impurities. Further, the present invention is a low arc hydrogen arc-coated electrode welding rod characterized by the above.

  According to the iron powder for the coated arc welding rod and the welding rod for tacking of the present invention, since the surface of the iron powder is coated with an organic substance, when the coating agent to which the iron powder is added is coated on the steel core wire, Good welding workability can be obtained during welding, re-arcing is excellent even in a welding machine equipped with an electric shock prevention device, and side arc resistance after welding is obtained even in a welding machine with a high no-load voltage. This greatly contributes to the improvement of work efficiency in the welding process.

  In order to solve the above-mentioned problems, the inventors of the present invention have an effect on various arc coating materials on re-arcing property in a welding machine with an electric shock prevention device and side arc resistance after welding in a welding machine without an electric shock prevention device. investigated. As a result, it was found that both the re-arcing property and the side arc resistance are improved by including in the coating agent an iron powder obtained by coating the surface of the iron powder with an organic substance using water glass.

  Hereinafter, with respect to the iron powder for the coated arc welding rod and the welding rod for tacking in the present invention, the coating amount of the organic matter on the iron powder, the solid mass of water glass, the content in the coating of the welding rod for tacking, etc. will be described To do.

  By coating the organic material with water glass so as to cover the surface of the iron powder, the iron powder is insulated with the organic material, so the side arc resistance after welding is improved, and even during re-arcing, only near the protective cylinder due to arc heat Since the coating of the organic substance on the surface of the iron powder is broken and the carbide is formed from the organic substance, the rearcability can be improved.

  If the organic substance that coats the surface of the iron powder exceeds 25% by mass with respect to the mass of the coated iron powder, an organic substance lump is formed, and the product yield deteriorates during production as a raw material for the welding rod for tacking. On the other hand, if it is less than 2% by mass, it becomes impossible to coat the iron powder surface so as to completely cover the surface, so that the side arc resistance is deteriorated. The organic substance referred to in the present invention refers to cellulose, dextrin, birch powder, starch, starch, sodium alginate and the like.

  In the water glass used as a fixing agent for organic coating, the solid mass composed of one or two kinds of potassium silicate and sodium silicate is greatly related to the fixing property of the organic material and side arc resistance. When the solid mass of the water glass is less than 0.3% by mass with respect to the mass of the coated iron powder, the iron powder is not coated with an organic substance and the side arc resistance is also inferior because of poor adhesion. On the other hand, when it exceeds 8.0 mass%, the solid mass with high insulation will increase and re-arcing property will be inferior. In addition, the adhesiveness becomes too strong, and the particle size of the iron powder coated with organic matter becomes large, so that the product yield is deteriorated during the production as a raw material for the welding rod for tacking.

  The iron powder for a coated arc welding rod of the present invention is, for example, mixed with an organic substance in iron powder, added with water glass composed of one or two kinds of potassium silicate and sodium silicate, and granulated after 150 to 300 ° C. To dry and manufacture. The particle size is preferably 150 to 1000 μm.

  The content of the iron powder coated with an organic substance in the coating agent is 30 to 60% by mass with respect to the total mass of the coating agent. When the content of the iron powder coated with an organic substance in the coating agent is less than 30% by mass, both the re-arcing property and the side arc resistance are poor. On the other hand, when the content of the iron powder coated with the organic substance in the coating agent exceeds 60% by mass, the rod burn resistance is deteriorated and the side arc resistance after welding is also deteriorated. Furthermore, since the amount of diffusible hydrogen increases, the cold cracking resistance deteriorates.

The metal carbonate in the coating is decomposed in the arc to generate CO ₂ gas to protect the deposited metal and molten slag from the atmosphere, prevent the intrusion of nitrogen, oxygen and hydrogen, and ensure the arc force. 20 to 50% by mass is necessary for the total mass of the coating agent. If the metal carbonate is less than 20% by mass, the amount of generated CO ₂ gas is small and hydrogen in the atmosphere is easily involved, and the amount of diffusible hydrogen increases, which may cause cold cracking. In addition, the increase in nitrogen and oxygen in the weld metal also deteriorates the mechanical performance. On the other hand, if the metal carbonate exceeds 50% by mass, the arc becomes too strong and the amount of spatter generated increases.

  The metal fluoride in the coating agent needs to be 0.5 to 3.5% by mass with respect to the total mass of the coating agent in order to lower the melting point of the slag and obtain a slag having good fluidity. If the metal fluoride is less than 0.5% by mass, satisfactory slag fluidity cannot be obtained and the slag encapsulation is inferior, so that the bead shape is deteriorated. On the other hand, when the metal fluoride exceeds 3.5% by mass, the fluidity is excessively improved, the slag encapsulation is inferior, and the bead shape is deteriorated.

  In addition to the above components, the coating agent contains a deoxidizing agent such as ferrosilicon, an arc stabilizer such as wollastonite, a slag forming agent such as magnesite, and inevitable impurities. The iron powder for the coated arc welding rod of the present invention is not limited to the low hydrogen-based tacking rod containing the above-mentioned amount of metal carbonate and metal fluoride, but also illuminite, lime titania, high titanium oxide, etc. It can be applied to any of the above non-low hydrogen based coated arc welding rods.

Hereinafter, the iron powder for a coated arc welding rod and the tack welding rod of the present invention will be described in detail by way of examples.
Table 1 shows iron powder (hereinafter referred to as coated iron powder) obtained by coating the surface of the iron powder with various organic substances. In addition, the coating iron powder shown in Table 1 adds water glass to an organic substance so that it may become the solid mass of Table 1, and after granulating, it dries at 200 degreeC so that a particle size may be in the range of 150-1000 micrometers. Sifted. Table 1 also shows the yield during sieving.

  Using the coating iron powder shown in Table 1, the coating agent having various compositions shown in Table 2 was coated on a steel core wire of JIS G3523 SWY11 having a diameter of 4.0 mm and a length of 400 mm, and then at a temperature of 400 ° C. After drying, a trial welding rod was made and investigated for re-arcability, side arc resistance and welding workability.

  First, the re-arc property was evaluated by welding for 10 seconds using a welding machine equipped with an electric shock prevention device, and after the covering portion at the tip of the welding rod reached room temperature, the coated rod of the welding rod was SM490B and the plate thickness was 9 mm. Each of the 20 pieces was examined by lightly contacting the fillet portion of the test body in which the steel plate was assembled in a T shape. Immediately when an arc was generated, it was determined to be acceptable, and the number of acceptable samples was 16 or more.

  In addition, the side arc resistance after welding is evaluated by using a welding machine without an electric shock prevention device until welding is performed until the welding rod length reaches 250 mm, and then immediately touching the corner of the steel plate 75 mm from the tip of the welding rod. Those in which no arc was generated were judged to be acceptable, and even one out of 20 samples in which an arc was generated from the coating was regarded as defective.

  Welding workability is investigated by assembling the above steel plates into a T shape and conducting horizontal fillet welding and vertical downward welding at a welding current of 200 A to investigate the arc state, slag state, bead shape, rod burn resistance, etc. did. These survey results are summarized in Table 3.

  In Table 3, welding rod no. 1-No. 6 is an example of the present invention, welding rod No. 7-No. 12 is a comparative example. The welding rod no. 1-No. 6 is equipped with an electric shock prevention device because the amount of organic matter in the coating of organic matter on iron powder, the solid mass of water glass and the amount added to the tack welding rod, and the addition amount of metal carbonate and metal fluoride are appropriate. The results showed very satisfactory results with good re-arcing with a welding machine, side arc resistance after welding with a welding machine without an electric shock prevention device, and welding workability. Also, the amount of diffusible hydrogen was small in the results of measuring the amount of diffusible hydrogen separately conducted.

  The welding rod No. in the comparative example. No. 7 had poor side arc resistance after welding because there was little organic matter in the coated iron powder E. Moreover, since there were many metal carbonates, there was much spatter generation amount.

  Welding rod no. No. 8 had a lot of organic matter of the coated iron powder F, so that the mass of the organic matter could be extremely large, and the yield when producing the coated iron powder was low. Further, since there are many metal fluorides, the slag fluidity is excessively improved, the slag encapsulation is inferior, and the bead shape is deteriorated.

  Welding rod no. No. 9 had poor side arc resistance after welding because the solid mass of the water glass of the coated iron powder G was small. Further, since the amount of metal fluoride is small, satisfactory slag fluidity cannot be obtained, slag encapsulation is deteriorated, and the bead shape is deteriorated.

  Welding rod no. No. 10 has a large solid mass of the water glass of the coated iron powder H, so that a large amount of organic matter can be produced, and the yield at the time of producing the coated iron powder is low. Further, the re-arcing property was poor. Furthermore, since there were few metal carbonates, the amount of diffusible hydrogen was large as a result of measuring the amount of diffusible hydrogen implemented separately.

Welding rod no. In No. 11, since the amount of coated iron powder in the coating agent was large, the anti-sticking property deteriorated, so the side arc resistance after welding was poor.
Welding rod no. No. 12 had poor re-arcing properties because it had less coating iron powder.

Claims (3)

An iron powder added to a coating agent when a coated arc welding rod is manufactured, and 0 to 25% by weight of organic matter is converted to a solid mass on the surface of the iron powder at a ratio to the mass of the coated iron powder. Iron powder for coated arc welding rods, which is coated with 3 to 8.0% by weight of water glass. In a coated 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 converts 2 to 25% by mass of organic matter into a solid mass in a ratio to the mass of the coated iron powder. A coated arc welding rod for temporary attachment, comprising 30 to 60% by mass of iron powder coated on the surface with 0.3 to 8.0% by mass of water glass. The coating further contains 20-50% by weight of metal carbonate and 0.5-3.5% of metal fluoride, and the others are deoxidizers, arc stabilizers, slag generators and inevitable impurities. The covered arc welding rod for temporary attachment according to claim 2 characterized by the above-mentioned.