JP7039353B2 - Low hydrogen coated arc welding rod - Google Patents

Description

The present invention relates to a low hydrogen-based shielded metal arc welding rod which is excellent in arc stability and bar burning resistance in vertical downward welding, and is excellent in the strength of the weld metal and the toughness at low temperature.

Low hydrogen-based shielded metal arc welding rods are widely used because welding metals having excellent mechanical properties can be obtained. On the other hand, this low hydrogen-based shielded metal arc welding rod lacks arc stability, has a slow melting rate, does not stretch beads, and becomes a convex bead, etc., compared to illuminating welding rods and lime titanian welding rods. It has the drawback of poor workability. Especially in vertical downward welding, high current welding is commonly used, and when welding is performed under high current welding conditions, deep penetration is obtained and welding work efficiency is improved, but the steel core wire is formed in the latter half of the welding rod. There is a drawback that heat is generated and the coating material is burnt, that is, a stick burning phenomenon (hereinafter referred to as stick burning) is likely to occur. When a welding rod with burnt rods is used, the arc becomes unstable during welding, which not only deteriorates the welding workability but also causes welding defects such as blow holes and insufficient penetration.

In recent years, since further improvement in welding work efficiency and quality of welded parts is required, it is excellent in arc stability while maintaining good mechanical performance of weld metal, and arc spraying is suitable. A low hydrogen-based shielded metal arc welding rod for downward welding has been requested, and various proposals have been made.

For example, Patent Document 1 defines the composition of components in a coating agent for a shielded metal arc welding rod and the bulk density after firing to prevent the coating from falling off during welding, and provides excellent arc stability and shielding effect. The technology to be obtained is disclosed.

Further, Patent Document 2 defines the content of V in the coating agent of the shielded metal arc welding rod.
A technique for improving the crack resistance of a weld metal is disclosed.

However, the shielded metal arc welding rods described in Patent Documents 1 and 2 can improve the arc stability and the mechanical performance of the weld metal, which have been problems of the conventional low hydrogen-based shielded metal arc welding rods. However, it was difficult to improve the bar burning resistance.

Further, Patent Document 3 describes a technique for preventing stick burning by using a high molar ratio water glass having a molar ratio of SiO ₂ / Na ₂ O in water glass as a fixing agent of 2.8 to 3.8. It has been disclosed. However, when the molar ratio of water glass is increased, drying cracks occur during production, and the content of alkali metal oxides such as Na ₂ O and K ₂ O decreases, so that the arc state deteriorates and the scattering of spatter increases. There was a problem.

Japanese Unexamined Patent Publication No. 57-72790 Japanese Unexamined Patent Publication No. 8-281474 JP-A-57-206595

The present invention has been devised in view of the above-mentioned problems, and is particularly excellent in arc stability in vertical downward welding, suitable arc spraying can be obtained, and bead shape and bar burning resistance. It is an object of the present invention to provide a low hydrogen-based shielded metal arc welding rod from which a weld metal having good performance and excellent mechanical performance can be obtained.

The gist of the present invention is a low hydrogen-based coated arc welding rod in which a coating material is coated on a steel core wire, and a low-hydrogen coating arc welding rod in which a coating agent is applied to a steel core wire. , Total Si conversion value of metal Si and Si alloy: 3 to 10%, Total Mn conversion value of metal Mn and Mn alloy: 1 to 5%, Tio of Ti oxide in mass% with respect to the total mass of the coating agent. Total of ₂ conversion values: 1 to 3%, total of SiO ₂ conversion values of Si oxide: 3 to 8%, total of one or more types of metal carbonate: 40 to 55%, F of metal fluoride Total of converted values: 1 to 5%, total of one or more kinds of organic substances: 0.1 to 2.0%, iron powder: 10 to 30%, Na ₂ O converted values of Na compounds and K compounds and A low hydrogen-based coated arc welding rod containing a _total of K2O conversion values: 1 to less than 4.6% , and the balance is composed of a coating agent, Fe content from an iron alloy, and unavoidable impurities. ..

According to the low hydrogen-based shielded metal arc welding rod of the present invention, excellent welding workability can be ensured, such as good arc stability and suitable arc spraying, especially in vertical downward welding, and the bead. Welded metal with good shape and bar burn resistance and excellent mechanical performance can be obtained. Therefore, it can greatly contribute to the improvement of welding work efficiency and the quality of the welded portion.

In order to solve the above problems, the present inventors have produced a low hydrogen-based shielded metal arc welding rod, and first of all, in order to improve the welding workability and the mechanical performance of the weld metal in vertical downward welding, the rod burn resistance We investigated the sex in detail. As a result, in vertical downward welding, since welding is performed with a high current, the welding rod tends to become reddish due to welding heat. Therefore, the content of metal carbonate and the content of organic matter should be adjusted to accelerate the endothermic reaction. It was found that the stick burning can be prevented.

It was also found that the arc stability can be improved by optimizing the content of each of the arc stabilizers such as TiO ₂ and Na compound and K compound in the coating agent.

Regarding the mechanical performance of the weld metal, it was found that the mechanical performance of the weld metal can be improved by making the content of Si and Mn in the coating material appropriate and retaining the appropriate amount of Si and Mn in the weld metal. rice field.

Hereinafter, the component composition in the coating agent of the low hydrogen-based coated arc welding rod to which the present invention is applied and the reason for limiting the component composition will be described in detail. The content of each component composition shall be expressed in mass% with respect to the total mass of the coating agent, and when expressing the mass%, it shall be simply described as%.

[Total Si conversion value of metallic Si and Si alloy: 3 to 10%]
Si is added from a Si alloy such as metallic Si, Fe—Si, and Fe—Si—Mn, and is used for the purpose of deoxidizing the weld metal, but it is also necessary for ensuring welding workability. If the total Si conversion value of the metallic Si and the Si alloy is less than 3%, blowholes are likely to occur in the weld metal due to insufficient deoxidation, and the arc is unstable, making it difficult to continue welding. On the other hand, when the total Si conversion value of the metallic Si and the Si alloy exceeds 10%, a low melting point oxide is deposited at the grain boundaries of the weld metal structure and the toughness is lowered. Therefore, the total Si conversion value of the metallic Si and the Si alloy is set to 3 to 10%.

[Total of Mn conversion values of metal Mn and Mn alloy: 1 to 5%]
Mn is added from Mn alloys such as metal Mn, Fe-Mn, and Fe-Si-Mn, and is added as a deoxidizing agent in the same manner as Si, and is effective in improving the strength of weld metal. If the total of the Mn-converted values of the metal Mn and the Mn alloy is less than 1%, the strength of the weld metal decreases. On the other hand, when the total of the Mn-converted values of the metal Mn and the Mn alloy exceeds 5%, the strength of the weld metal becomes high and the toughness becomes low. Therefore, the total Mn conversion value of the metal Mn and the Mn alloy is 1 to 5%.

[Total of TiO ₂ conversion values of Ti oxide: 1 to 3%]
The Ti oxide is added from rutile, titanium oxide, sodium titanate, titanium slag and the like, acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and bead shape. If the total of the TiO ₂ conversion values of the Ti oxide is less than 1%, the arc becomes unstable, the slag fluidity becomes poor, and the bead shape becomes poor. On the other hand, when the total TiO ₂ conversion value of Ti oxide exceeds 3%, the viscosity of the molten slag becomes high during welding and the flow of slag decreases, so that the shape of the bead is convex and the penetration becomes shallow, resulting in poor fusion. Is likely to occur. Therefore, the total TiO ₂ conversion value of Ti oxide is set to 1 to 3%.

[Total SiO ₂ conversion value of Si oxide: 3-8%]
Si oxide is added from silica sand, feldspar, water glass and the like, acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and slag exfoliation property. When the total SiO ₂ conversion value of the Si oxide is less than 3%, the arc becomes weak and unstable, and the vitreous quality of the generated slag becomes small, resulting in poor slag peelability. On the other hand, when the total SiO ₂ conversion value of the Si oxide exceeds 8%, the viscosity of the slag becomes high and the bead shape becomes poor. Therefore, the total value of Si oxides in the coating material in terms of SiO ₂ is set to 3 to 8%.

[Total of one or more metal carbonates: 40-55%]
Metallic carbonate is added over one or more types from calcium carbonate, magnesium carbonate, barium carbonate, manganese carbonate, lithium carbonate, etc., and decomposes in an arc to generate CO ₂ gas to shield the weld metal from the atmosphere. Has the effect of protecting. If the total of one or more of the metal carbonates is less than 40%, the shielding effect is insufficient and blow holes are likely to occur, and stick burning is likely to occur. On the other hand, when the total of one or more of the metal carbonates exceeds 55%, the arc becomes unstable and becomes a convex bead, and the slag peeling property also deteriorates. Therefore, the total of one or more metal carbonates in the coating is 40-55%.

[Total F conversion value of metal fluoride: 1-5%]
The metal fluoride is added from fluorite, barium fluoride, magnesium fluoride, aluminum fluoride and the like, and the F conversion value is the total of the F conversion values contained therein. All of these fluorine compounds reduce the viscosity of the molten slag to form slag with good fluidity and give it an excellent bead shape. If the total F conversion value of the metal fluoride is less than 1%, the appropriate viscosity of the molten slag cannot be obtained and the shape of the bead deteriorates. On the other hand, when the total F conversion value of the metal fluoride exceeds 5%, the slag peelability deteriorates. Therefore, the total F conversion value of the metal fluoride is 1 to 5%.

[Total of one or more organic substances: 0.1-2.0%]
The organic substance is added over one or more kinds from sodium alginate, wheat flour, starch, cornstarch and the like, and has an effect of strengthening the spraying of the arc, deepening the penetration and suppressing welding defects such as blow holes. When the total of one or more kinds of organic substances is less than 0.1%, the spraying of the arc becomes weak, the penetration becomes shallow, and welding defects such as blow holes are likely to occur. On the other hand, when the total of one or more kinds of organic substances exceeds 2.0%, stick burning is likely to occur and the amount of spatter generated is also large. Therefore, the total of one or more organic substances in the coating is 0.1 to 2.0%.

[Iron powder: 10 to 30%]
Since iron powder increases the amount of weld metal, it is extremely effective in improving welding efficiency. If the iron powder is less than 10%, the welding efficiency is lowered and the bead shape is deteriorated. On the other hand, if the iron powder exceeds 30%, the rod is burnt in the latter half of the welding and welding cannot be completed until the end. Therefore, the iron powder is 10 to 30%.

[Total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound: 1 to less than 4.6% ]
The Na compound and the K compound are added from sodium silicate, potassium silicate, potassium feldspar and the like in water glass, and have an effect of acting as an arc stabilizer to stabilize the arc. If the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound is less than 1%, the arc becomes unstable. On the other hand, when the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound is 4.6 % or more, the arc spraying becomes excessively strong and the bead shape becomes poor. Therefore, the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound in the coating agent shall be 1 to less than 4.6% .

The remainder of the low hydrogen-based shielded metal arc welding rod to which the present invention is applied can contain at least one type of coating agent such as hectrite and mica in a total amount of 5% or less in terms of mass% with respect to the total mass of the coating agent. Others are Fe content and unavoidable impurities from iron alloys such as Fe—Si, Fe—Mn, and Fe—Si—Mn.

Further, it is preferable to use JIS G3523 SWY11 as the mild steel core wire to be used. Further, the coverage of the coating material on the mild steel core wire is preferably 25 to 38% by mass of the coating agent with respect to the total mass of the welding rod.

Hereinafter, examples of the low hydrogen-based shielded metal arc welding rod provided by the present invention will be specifically described.

Various low hydrogen-based coated arc welding rods were prototyped by applying a coating agent having each component composition shown in Table 2 to the mild steel core wire of JIS G3523 SWY11 with a diameter of 4.0 mm and a length of 400 mm shown in Table 1 and drying it. ..

Using these prototype welding rods, welding workability and mechanical performance were investigated.

For the evaluation of welding workability, a test piece made of JIS G 3101 SS400 mild steel plate with a thickness of 9 mm, width of 75 mm, and length of 450 mm assembled in a T shape was used, and a small welding machine with a secondary side no-load voltage of 60 V was used. Then, vertical downward welding was performed with a welding current of 170 to 190 A, and the presence or absence of arc spraying, arc stability, slag peelability, bead shape, and stick burning was investigated. Further, as for the bar burning resistance, the one in which the steel core wire generates heat and does not burn when vertical downward welding is performed at 210 A is good.

For the evaluation of mechanical performance, a welding metal test was conducted using a JIS G 3106 SM490A with a plate thickness of 19 mm using an AC welder according to JIS Z Z3111, and a tensile test piece (A0) and an impact test piece (V notch test piece). Was collected and subjected to a tensile test and an impact test.

In the evaluation of the tensile test, the tensile strength was good at 440 to 550 MPa. In addition, the toughness was evaluated by conducting a Charpy impact test at a test temperature of −30 ° C., and the average value of absorbed energy three times each was set to be good at 60 J or more.

For welding defects, the test piece after the weld metal test was subjected to an X-ray transmission test according to JIS Z 3106, and the presence or absence of blow holes and fusion defects was investigated. The results of these surveys are summarized in Table 3.

In Tables 2 and 3, the welding rod symbols R1 to R6 and R8 to R12 are examples of the present invention, and the welding rod symbols R13 to R25 are comparative examples.

In the welding rods R1 to R6 and R8 to R12, which are examples of the present invention, the total Si conversion values of the metal Si and the Si alloy in the coating agent, the total Mn conversion values of the metal Mn and the Mn alloy, and the TIO ₂ of the Ti oxide are used. Total conversion value, total SiO ₂ conversion value of Si oxide, total of one or more types of metal carbonate, total F conversion value of metal fluoride, total of one or more types of organic substances, Since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of iron powder, Na compound and K compound is appropriate, the arc spraying is appropriate, the arc is stable, the slag peeling property is excellent, and the bead shape is good. It was good. In addition, no stick burning occurred, and the tensile strength and absorption energy of the weld metal were good, which was an extremely satisfactory result.

In the comparative example, the welding rod R13 had a large TiO ₂ conversion value of the Ti oxide, so that the viscosity of the molten slag became high, the beads became convex, and fusion failure occurred.

Since the welding rod R14 has a large sum of the Si conversion values of the metallic Si and the Si alloy, the minimum value of the absorption energy of the welded metal was low. Also, because there was a lot of iron powder, it was burnt on a stick.

Since the sum of the Si conversion values of the metallic Si and the Si alloy is small in the welding rod R15, the arc is weak and unstable, and blow holes are generated.

Since the welding rod R16 has a high Mn conversion value of the metal Mn and the Mn alloy, the tensile strength of the weld metal is high and the absorption energy is also low. Further, since the total amount of one or more kinds of metal carbonates is large, the arc is unstable, the slag peelability is poor, and the bead shape is also convex.

Since the total of the Mn-converted values of the metal Mn and the Mn alloy of the welding rod R17 is small, the tensile strength of the welded metal is low. Further, since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound was large, the arc spraying was excessively strong and the bead shape was poor.

Since the total of the TiO ₂ conversion values of the Ti oxide of the welding rod R18 was small, the arc was unstable and the bead shape was poor.

The welding rod R19 had a poor bead shape because the total value of the Si oxide in terms of SiO ₂ was large. In addition, since the total amount of one or more kinds of organic substances is large, stick burning occurred.

Since the total amount of one or more of the metal carbonates of the welding rod R20 is small, the rod is burnt and blow holes are also generated in the weld metal.

Since the welding rod R21 has a large total F-converted value of the metal fluoride, the slag peelability was poor. In addition, since the amount of iron powder was small, the amount of welding was insufficient and the bead shape was poor.

The welding rod R22 had a poor bead shape because the F conversion value of the metal fluoride was small.

Since the total amount of one or more kinds of organic substances in the welding rod R23 is small, the arc spraying is weak and the penetration becomes shallow, and blow holes are generated in the weld metal.

Since the total of the SiO ₂ conversion values of the Si oxide of the welding rod R24 is small, the arc is weak and unstable, and the slag peelability is also poor.

The arc of the welding rod R25 was unstable because the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound was small.

Claims (1)

In a low hydrogen-based shielded metal arc welding rod in which a coating agent is applied to the steel core wire,
The coating agent is a mass% based on the total mass of the coating agent.
Total of Si conversion values of metallic Si and Si alloy: 3 to 10%,
Total of Mn conversion values of metal Mn and Mn alloy: 1-5%,
Total of TIO ₂ conversion values of Ti oxide: 1-3%,
Total SiO ₂ conversion value of Si oxide: 3-8%,
Total of one or more metal carbonates: 40-55%,
Total F conversion value of metal fluoride: 1-5%,
Total of one or more organic substances: 0.1-2.0%,
Iron powder: 10-30%,
The total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound: 1 to less than 4.6% ,
The balance is a low hydrogen-based shielded metal arc welding rod characterized by being composed of a coating agent, Fe content from an iron alloy, and unavoidable impurities.