Covered metal arc welding electrodes for galvanized steel sheets

Abstract

To provide a coated arc welding rod for galvanized steel sheet that has extremely few weld defects, and can obtain beautiful weld beads.SOLUTION: A coated arc welding rod for galvanized steel sheet, in which a mass ratio of a coating material to total mass of a weld rod is 20% or more and 45% or less, comprises by mass% to total mass of the coating material: C of 0.01 to 0.50%; Si of 0.01 to 0.50%; Mn of 2.0 to 7.0%; total of one or more metal carbonates of 5 to 20%; total TiO2 equivalent value of Ti oxide of 10 to 30%; total SiO2 equivalent value of Si oxide of 10 to 30%; total Al2O3 equivalent value of Al oxide of 0.1 to 5.0%; total CaO equivalent value of Ca oxide of 0.1 to 5.0%; total MgO equivalent value of Mg oxide of 0.1 to 5.0%; total of Na2O equivalent vaule of Na compound and K2O equivalent value of K compound of 1.0 to 5.0%; Fe of iron powder and iron alloy powder of 15 to 40%; organic substance of 1.0 to 8.0%; and so on.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a covered electrode for galvanized steel sheets, which can produce beautiful weld beads with extremely few welding defects such as porosity defects when welding galvanized steel sheets. [Background technology]

[0002] Galvanized steel sheets, which have excellent corrosion resistance due to the application of zinc plating to the steel sheet surface and are relatively inexpensive and economical, are widely used in the light steel frame fields of automobiles, buildings, etc. However, when these steel sheets are welded, the zinc coating layer evaporates due to the heat of the arc and turns into zinc vapor, which can lead to problems such as blowholes and other porosity defects, as well as increased spatter and welding fumes, and poor penetration.

[0003] In response to this situation, various proposals have been made as means for improving resistance to blowhole defects. For example, Patent Document 1 discloses a welding method for welding hot-dip galvanized steel sheets using a covered arc welding rod with few blowhole defects, preventing damage to the zinc coating even in the vicinity of the weld heat-affected zone. However, the welding rod in Patent Document 1 does not limit the total of the Na2O equivalent value and the K2O equivalent value, nor does it limit the total of the MgO equivalent value, resulting in an unstable arc, poor welding workability, and poor bead shape.

[0004] Furthermore, Patent Document 2 discloses an ilmenite-based covered metal arc welding rod that has excellent arc stability, provides suitable arc spray, has deep penetration without welding defects, and has good slag removability, bead shape, and hot cracking resistance, resulting in an excellent weld metal. However, the ilmenite-based covered metal arc welding rod described in Patent Document 2 has a low amount of Fe from the iron powder and iron alloy powder, so when welding is performed on a galvanized steel sheet, sufficient penetration is not obtained, resulting in poor penetration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-267846 [Patent Document 2] Japanese Patent Application Publication No. 2019-155472 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been devised in view of the above-mentioned problems, and has an object to provide a covered electrode for galvanized steel sheets, which has good welding workability such as arc stability, has very few welding defects such as porosity defects and poor penetration, and can produce beautiful weld beads in all-position welding using galvanized steel sheets. [Means for solving the problem]

[0007] The gist of the present invention is a covered metal arc welding electrode for galvanized steel sheets, in which a steel core wire is coated with a coating material, the mass ratio of the coating material to the total mass of the welding electrode being 20% ​​or more and 45% or less, and the mass % of the total mass of the coating material being C: 0.01 to 0.50%, Si: 0.01 to 0.50%, Mn: 2.0 to 7.0%, the total of one or more metal carbonates: 5 to 20%, the total of Ti oxides in terms of TiO2: 10 to 30%, the total of Si oxides in terms of SiO ... the sum of the values ​​of Al2O3 converted into Al2O3: 10 to 30%, the sum of the values ​​of Al oxides converted into Al2O3: 0.1 to 5.0%, the sum of the values ​​of Ca oxides converted into CaO: 0.1 to 5.0%, the sum of the values ​​of Mg oxides converted into MgO: 0.1 to 5.0%, the sum of one or more of the values ​​of Na compounds converted into Na2O and K compounds converted into K2O: 1.0 to 5.0%, Fe of iron powder and iron alloy powder: 15 to 40%, the sum of one or more of the values ​​of organic matter: 1.0 to 8.0%, and the balance is 5% or less The coating material is characterized by having less than 1% impurities.

[0008] According to the present invention, the coating agent may further contain, in mass % relative to the total mass of the coating agent, 4.0% or less of the total amount of manganese oxides converted into MnO.

[0009] According to the present invention, the coating agent may further contain, in mass % relative to the total mass of the coating agent, 4.0% or less of the total amount of Fe oxides calculated as FeO.

[0010] Furthermore, according to the present invention, the coating agent may further contain Ti: 3.0% or less in mass % relative to the total mass of the coating agent. [Effects of the Invention]

[0011] The covered electrode for galvanized steel sheets of the present invention provides good welding workability such as arc stability in all-position welding using galvanized steel sheets, minimizes welding defects such as porosity and poor penetration, and produces beautiful weld beads, thereby significantly improving the reliability of welded joints for various steel structures. DETAILED DESCRIPTION OF THE INVENTION

[0012] In order to solve the above-mentioned problems, the present inventors have produced a covered electrode and investigated in detail the strength and toughness of the deposited metal.

[0013] As a result, it was found that the strength of the weld metal can be ensured by optimizing the C and Mn contents, and further that the toughness of the weld metal can be ensured by optimizing the metal carbonate and Si contents and the coating rate on the steel core wire.

[0014] In addition, with regard to welding workability, it was found that the arc spray strength can be improved by optimizing the content of C and organic matter, and the arc can be stabilized and the amount of spatter reduced by optimizing the content of Si, metal carbonates, the sum of the TiO2 equivalent values ​​of Ti oxides, the sum of the Al2O3 equivalent values ​​of Al oxides, the sum of the CaO equivalent values ​​of Ca oxides, and the sum of the Na2O equivalent values ​​of Na compounds and the K2O equivalent values ​​of K compounds, and that the coverage rate on the steel core wire can be optimized.It was also found that the bead shape and bead appearance can be improved by optimizing the content of metal carbonates, the sum of the TiO2 equivalent values ​​of Ti oxides, the sum of the SiO2 equivalent values ​​of Si oxides, the sum of the Al2O3 equivalent values ​​of Al oxides, and the sum of the MgO equivalent values ​​of Mg oxides.

[0015] In addition, it was found that the slag removability and fluidity can be improved by optimizing the contents of metal carbonate, the total of Ti oxides in terms of TiO2, the total of Si oxides in terms of SiO2, and the total of Al oxides in terms of Al2O3.

[0016] In addition, it was discovered that rod burn, where the welding rod itself becomes red hot, can be prevented by adjusting the Fe content, that one-sided melting of the welding rod protective tube can be prevented by adjusting the total MgO equivalent value of Mg oxide and the Fe content, and that productivity of welding rods, such as the paintability of coating agents, can be improved by adjusting the total content of the Na2O equivalent value of Na compounds and the K2O equivalent value of K compounds.

[0017] Furthermore, it was found that by adjusting the total Mn oxides in MnO equivalent and the total Fe oxides in FeO equivalent, the arc blow strength can be improved and poor penetration can be further suppressed, and that by adjusting the Ti content, the arc stability can be further improved.

[0018] The composition of the components in the coating of the covered electrode for galvanized steel sheet according to the present invention and the reasons for limiting the composition of the components will be described in detail below. The content of each component will be expressed in mass% relative to the total mass of the coating, and when expressing mass%, it will be simply written as %. Hereinafter, galvanized steel sheet refers to a carbon steel sheet up to 490 MPa that has been hot-dipped, painted, and electroplated with zinc or a zinc-based alloy containing zinc as the main component.

[0019] [Covering rate: 20-45% by mass of coating material relative to the total mass of the covered electrode] The coverage rate of the coating material on the outer periphery of the steel core wire has a significant effect on the shielding resistance during welding. If the coverage rate is less than 20% by mass (hereinafter simply referred to as %) of the coating material relative to the total mass of the covered metal arc welding electrode, the coating material itself becomes insufficient, resulting in insufficient shielding, and the N content in the weld metal increases, reducing the toughness of the weld metal. On the other hand, if the coverage rate of the coating material exceeds 45%, the amount of slag becomes excessive, causing the arc to become unstable. Therefore, the coverage rate should be 20 to 45%.

[0020] [C: 0.01 to 0.50%] C is added from C-containing alloy powder, graphite, etc., and has the effect of improving the strength of the weld metal as well as the effect of improving the arc blast strength, and is particularly effective in suppressing poor penetration when welding to galvanized steel sheets. If C is less than 0.01%, the strength of the weld metal will be insufficient, and when welding galvanized steel sheets, the arc blast strength will be insufficient, resulting in poor penetration. On the other hand, if C exceeds 0.50%, the strength of the weld metal will be excessively high and the toughness will decrease. Therefore, C is set to 0.01 to 0.50%. The C content is preferably 0.05 to 0.30%.

[0021] [Si: 0.01 to 0.50%] Si is added in the form of metallic Si, Fe-Si, Fe-Si-Mn, etc., and is used for the purpose of deoxidizing the weld metal. If the Si content is less than 0.01%, deoxidation is insufficient, making blowholes more likely to occur in the weld metal and making the arc unstable. On the other hand, if the Si content exceeds 0.50%, low-melting-point oxides are precipitated at the grain boundaries of the weld metal, reducing the toughness of the weld metal. Therefore, the Si content is set to 0.01 to 0.50%. The Si content is preferably 0.05 to 0.30%.

[0022] [Mn: 2.0-7.0%] Mn is added in the form of metallic Mn, Fe-Mn, Fe-Si-Mn, etc., and, like Si, is an important deoxidizer, increasing the strength of the weld metal. If the Mn content is less than 2.0%, the strength of the weld metal will be insufficient, and blowholes will be more likely to occur in the weld metal due to insufficient deoxidation. On the other hand, if the Mn content exceeds 7.0%, the strength of the weld metal will be excessively high and the toughness will decrease. Therefore, the Mn content is set to 2.0 to 7.0%. The Mn content is preferably 3.0 to 6.0%.

[0023] [Total of one or more metal carbonates: 5-20%] Metal carbonates are added from calcium carbonate, magnesium carbonate, barium carbonate, etc., and decompose under the heat of the arc to generate CO2 gas, which protects the weld metal from the atmosphere. If the total content of one or more metal carbonates is less than 5%, the shielding effect is insufficient and blowholes are more likely to occur. If the total content of one or more metal carbonates is less than 5%, nitrogen from the atmosphere is mixed into the weld metal, reducing the toughness of the weld metal. On the other hand, if the total content of one or more metal carbonates exceeds 20%, the arc becomes unstable, the bead shape becomes convex, and slag removability is also impaired. Therefore, the total content of one or more metal carbonates is set to 5 to 20%. The total content of one or more metal carbonates is preferably 8 to 14%.

[0024] [Total TiO2 equivalent value of Ti oxides: 10-30%] Ti oxides are added from rutile, titanium oxide, titanium slag, calcium titanate, etc., and have the effect of stabilizing the arc and adjusting the viscosity of the molten slag to improve the bead shape. If the total Ti oxides in terms of TiO2 is less than 10%, the arc becomes unstable and the bead shape becomes poor. On the other hand, if the total Ti oxides in terms of TiO2 exceeds 30%, the viscosity of the molten slag increases, reducing the slag's fluidity and resulting in a convex bead shape. Therefore, the total Ti oxides in terms of TiO2 should be 10 to 30%. The total Ti oxides in terms of TiO2 is preferably 12 to 22%.

[0025] [Total of silicon oxides converted to SiO2: 10-30%] Silicon oxides are added from silica sand, zircon sand, potassium feldspar, solid components of water glass such as sodium silicate and potassium silicate, and wollastonite. They increase the viscosity of the molten slag, ensuring a slag with appropriate viscosity and improving the bead shape. If the total SiO2 equivalent of silicon oxides is less than 10%, the viscosity of the molten slag decreases, resulting in a poor bead shape. On the other hand, if the total SiO2 equivalent of silicon oxides exceeds 30%, the slag becomes glassy, ​​resulting in poor slag removability. Therefore, silicon oxide content is set to 10-30%. The total SiO2 equivalent of silicon oxides is preferably 14-24%.

[0026] [Total Al oxides converted to Al2O3: 0.1-5.0%] Al oxides are added from alumina, potassium feldspar, etc., and have the effect of stabilizing the arc and improving the bead shape. If the total Al2O3 content of Al oxides is less than 0.1%, the arc becomes unstable and the bead shape becomes poor. On the other hand, if the total Al2O3 content of Al oxides exceeds 5.0%, the slag becomes glassy and slag removability becomes poor. Therefore, the total Al2O3 content of Al oxides is set to 0.1 to 5.0%. The total Al2O3 content of Al oxides is preferably 0.5 to 4.0%.

[0027] [Total of Ca oxides converted to CaO: 0.1-5.0%] Ca oxides are added from calcium titanate, wollastonite, etc., and are effective in stabilizing the arc and reducing spatter generation. If the total Ca oxides in CaO equivalent is less than 0.1%, the arc becomes unstable and spatter increases. On the other hand, if the total Ca oxides in CaO equivalent exceeds 5.0%, the arc becomes weak and unstable, making welding defects such as poor penetration more likely to occur. Therefore, the total Ca oxides in CaO equivalent is set to 0.1 to 5.0%. The total Ca oxides in CaO equivalent is preferably 0.5 to 3.5%.

[0028] [Total of Mg oxides converted to MgO: 0.1-5.0%] Mg oxide is added from magnesium oxide, magnesia clinker, etc., and has excellent heat resistance and is effective in suppressing the dissolution of the coating material as a single component. If the total of Mg oxides in terms of MgO is less than 0.1%, the coating material will dissolve as a single component. On the other hand, if the total of Mg oxides in terms of MgO exceeds 5.0%, the viscosity of the molten slag will increase, resulting in a convex bead shape. Therefore, the total of Mg oxides in terms of MgO is set to 0.1 to 5.0%. The total of Mg oxides in terms of MgO is preferably 0.5 to 3.5%.

[0029] [Total of one or more of the NaO equivalent values ​​of sodium compounds and KO equivalent values ​​of potassium compounds: 1.0 to 5.0%] Na is added from solid components of water glass, such as sodium silicate, or sodium fluoride. K is added from solid components of water glass, such as potassium silicate, potassium silicofluoride, and potassium feldspar. These components improve the paintability of welding rods during production and the stability of the arc during welding. If the sum of the NaO equivalent value of the Na compound and the KO equivalent value of the K compound is less than 1.0%, the arc becomes unstable, paintability during production deteriorates, and cracks are more likely to occur on the coating surface during welding rod production, reducing the productivity of covered arc welding rods. On the other hand, if the sum of the NaO equivalent value of the Na compound and the KO equivalent value of the K compound exceeds 5.0%, the arc blow becomes stronger and the amount of spatter increases. Therefore, the sum of the NaO equivalent value of the Na compound and the KO equivalent value of the K compound should be 1.0 to 5.0%. The sum of the NaO equivalent value of the Na compound and the KO equivalent value of the K compound is preferably 1.5 to 4.0%.

[0030] [Fe in iron powder and iron alloy powder: 15-40%] Fe is added from iron powder, iron alloy powder such as Fe-Mn or Fe-Mo, or iron oxide, and has the effect of lowering the potential gradient of the arc, shortening the arc length, and preventing one-sided melting of the coating material. Furthermore, by increasing the deposition amount, it is effective in suppressing poor penetration, especially when welding to galvanized steel sheets. If Fe is less than 15%, the arc length becomes long, making one-sided melting of the coating material more likely to occur. On the other hand, if Fe exceeds 40%, welding with a covered arc welding rod will cause the rod itself to glow red (hereinafter referred to as rod burn) in the latter half of welding, making welding difficult and causing poor penetration. Therefore, Fe is set to 15-40%. The Fe content is preferably 20-35%.

[0031] [Total of one or more organic substances: 1.0-8.0%] The organic substance is added from cellulose, dextrin, wheat flour, starch, cornstarch, etc., and has the effect of strengthening the arc blow and deepening the penetration. It is particularly effective in suppressing poor penetration when welding to galvanized steel sheets. If the total content of one or more organic substances is less than 1.0%, the arc blow will be weak and poor penetration will occur. On the other hand, if the total content of one or more organic substances exceeds 8.0%, the arc will become coarse and the amount of spatter will increase. Therefore, the total content of one or more organic substances is set to 1.0 to 8.0%. The total content of one or more organic substances is preferably 2.5 to 6.5%.

[0032] [Total of Mn oxides converted to MnO: 4.0% or less] Mn oxides, added from manganese ore and the like, have the effect of improving bead shape and arc blast strength, and particularly when welding to galvanized steel sheets, they are effective in further suppressing poor penetration. However, if the total Mn oxides in terms of MnO exceeds 4.0%, the arc blast strength becomes excessive and spatter increases. Therefore, the total Mn oxides in terms of MnO is set to 4.0% or less. The total Mn oxides in terms of MnO is preferably 2.5% or less.

[0033] [Total of Fe oxides (FeO equivalent): 4.0% or less] Fe oxides, such as hematite, magnetite, and wustite, are added to improve the arc blow strength and further suppress poor penetration, especially when welding to galvanized steel sheets. However, if the total amount of Fe oxides (as converted into FeO) exceeds 4.0%, the viscosity of the molten slag decreases, slag removability deteriorates, and the bead shape deteriorates. Therefore, the total amount of Fe oxides (as converted into FeO) is set to 4.0% or less. The total amount of Fe oxides (as converted into FeO) is preferably 2.5% or less.

[0034] [Ti:3.0% or less] Ti is added as metallic Ti, Fe-Ti, etc., and is effective as a deoxidizer while also stabilizing the arc by lowering the arc potential gradient. This arc stabilizing effect is particularly pronounced when welding to galvanized steel sheets. However, if Ti exceeds 3.0%, the precipitation of Ti oxides in the weld metal increases, reducing the toughness of the weld metal. Therefore, Ti is set to 3.0% or less. The Ti content is preferably 1.5% or less.

[0035] The remainder of the coating material in the covered metal arc welding electrode for galvanized steel sheets of the present invention is impurities contained in the coating material and alloy powder. Hectorite, mica, etc. are used as the coating material, and it is preferable that one or more of them be present in a total amount of 5% or less. Impurities contained in the alloy powder include P, S, Cu, Nb, V, B, etc., and P and S in particular both form low-melting point compounds that reduce the toughness of the weld metal, so the total amount of impurities is adjusted to 1% or less.

[0036] The steel core wire used is preferably JIS G3523:1980 SWY11, with a C content of 0.10% or less, and the C content can be adjusted appropriately from the coating material to adjust strength. P in the steel core wire reduces toughness, so it is preferable that it be 0.010% or less, and S, which reduces the fluidity of the slag, is 0.010% or less. [Example]

[0037] The effects of the present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. Although an AC power supply is used in the examples, the present invention is not limited to AC power supplies.

[0038] A JIS G3523 SWY11 steel core wire (C: 0.08 mass%, Si: 0.02 mass%, Mn: 0.46 mass%, P: 0.009 mass%, S: 0.006 mass%) having a diameter of 4.0 mm and a length of 400 mm was coated with a coating agent having the composition shown in Table 1 at the coverage shown in Table 1, and then dried to produce prototypes of various covered metal arc welding electrodes for galvanized steel sheets.

[0039] [Table 1]

[0040] [Table 2]

[0041] Using the above-mentioned prototype welding electrodes, weld metal specimens were prepared from 20mm-thick steel plates with the chemical compositions shown in Table 2, with a 20° groove angle, a 16mm root gap, and a backing groove. The welding conditions were an AC current of 170A, a welding heat input of 17kJ / cm, and preheating and interpass temperatures of 100-150°C. Tensile test specimens (JIS Z 2241:2011 No. 10) and V-notch impact test specimens (JIS Z 2242:2018) were taken from the center of the plate thickness. Tensile tests were performed using a tensile strength of 400-550MPa, and toughness was evaluated using a Charpy impact test at a test temperature of -20°C. An average absorbed energy of 70J or greater was considered good for three tests. Weldability was evaluated by visual inspection of arc stability, spatter generation, bead shape and appearance, slag removability, and the presence or absence of one-sided melting of the coating material and rod burn. The productivity of the welding rods was also investigated by product inspection after production. Furthermore, using the galvanized steel sheets and each prototype welding rod shown in Table 3, horizontal fillet welding tests were carried out using an AC power source with a welding current of 170 A and a welding heat input of 17 kJ / cm. After welding was completed, the horizontal fillet welded test specimen was cut 100 mm from the start of the weld bead and the cross-sectional shape was observed to investigate the state of penetration. The test results are summarized in Table 5.

[0042] [Welding workability] (Arc stability) When the arc was stable during welding and did not disappear, it was judged as good, and when the arc disappeared even once, it was judged as bad.

[0043] (amount of spatter generated) It is preferable to generate as little spatter as possible during welding. Specifically, a copper collection box was used to measure the weight of spatter generated during one minute of welding, and the value per unit time (g / min) was calculated. Spatter was measured five times under the welding conditions shown in Table 4, and the average value was calculated. A value of 2.0 g / min or less was considered good.

[0044] (Bead shape and appearance) It is preferable that the bead waveform of the deposited metal is uniform and free of disturbance, and that undercuts and overlaps that require rework do not occur. It is also preferable that the deposited metal has a bead shape with excellent uniformity in the reinforcement height and bead width. Specifically, cases where the bead waveform of the deposited metal is disturbed or where undercuts and overlaps that require rework occur on the bead surface of the deposited metal were judged to be defective.

[0045] (Slag removability) After welding, it is preferable that the solidified slag on the weld bead surface can be easily removed. After welding, the solidified slag on the weld bead surface was struck with a chipping hammer (total length 300 mm, weight 350 g) by lightly swinging it down in an arc around the handle. If the slag cracked and could then be easily removed, the result was rated as good, and if the slag did not crack, the result was rated as poor.

[0046] (Partial dissolution of coating material) It is preferable that the arc is generated parallel to the welding rod without any chipping of the coating material during welding, and that the arc spread is uniform and stable. If part of the coating material is chipped during welding, the arc is deflected in a direction other than parallel to the welding rod, and the arc spread is non-uniform, it is rated as "fail."

[0047] (stick burn) It is preferable that the coating does not fall off during welding because the welding rod becomes red hot. If the color of the welding rod does not change during welding, it is rated as good, and if the color of the welding rod becomes red during welding, it is rated as bad.

[0048] [Welding defects] Specifically, radiographic testing was conducted in accordance with JIS Z 3104:1995 to check for the presence of welding defects such as blowholes and poor penetration.

[0049] [Productivity] Productivity was determined to be poor if the welding rod was inspected after production and showed any coating material falling off, chipping, or cracking, and the product yield was 90% or less.

[0050] [Table 3]

[0051] [Table 4]

[0052] [Table 5]

[0053] Welding rods No. 1 to No. 10 in Tables 1 and 5 are examples of the present invention, and welding rods No. 11 to No. 20 are comparative examples. The welding rods No. 1 to No. 10, which are examples of the present invention, had appropriate amounts of the coating rate of the coating agent, the sum of C, Si, Mn, metal carbonates, the sum of Ti oxides in terms of TiO2, the sum of Si oxides in terms of SiO2, the sum of Al oxides in terms of Al2O3, the sum of Ca oxides in terms of CaO, the sum of Mg oxides in terms of MgO, the sum of one or more of Na compounds and K compounds in terms of Na2O and KO2O, and the sum of Fe and organic substances. Therefore, the welding workability was good, with good arc conditions, little spatter generation, good protective sleeve conditions, no rod burn, and good bead appearance, bead shape, and slag removability. Productivity was also good, there were no welding defects, and the tensile strength and absorbed energy of the deposited metal were good. There was also no poor penetration when welding galvanized steel sheets, resulting in extremely satisfactory results. Furthermore, Nos. 1, 3, 6, 7, and 10 had appropriate amounts of the total of Mn oxides converted to MnO, the total of Fe oxides converted to FeO, and Ti or the total of these, so poor penetration was further suppressed when welding galvanized steel sheets.

[0054] Among the comparative examples, welding electrode No. 11 had a high coverage rate, resulting in an unstable arc. Also, because of the high C content, the tensile strength of the deposited metal was excessive, resulting in low absorbed energy. Furthermore, because of the high TiO2 content, the bead shape was convex.

[0055] Welding rod No. 12 had a low coverage rate, so the absorbed energy of the deposited metal was low. Also, because it contained little carbon, the tensile strength of the deposited metal was insufficient. In addition, poor penetration occurred when welding galvanized steel sheets. Furthermore, because the total TiO2 equivalent value of titanium oxide was low, the arc was unstable and the bead shape was poor.

[0056] Welding rod No. 13 had a high Si content, which resulted in low absorbed energy in the deposited metal. Also, because it contained a high total amount of metal carbonates, the arc was unstable, the bead shape was convex, and slag removability was poor.

[0057] Welding rod No. 14 had a low Si content, which resulted in an unstable arc and the occurrence of blowholes. It also had a high Mn content, which resulted in excessive tensile strength of the deposited metal and low absorbed energy. Furthermore, the total amount of organic matter was high, which increased spatter. On the other hand, the total amount of Fe oxides (FeO equivalent) was high, which resulted in poor slag removability and a poor bead shape.

[0058] Welding rod No. 15 contained a small amount of Mn, which resulted in insufficient tensile strength of the deposited metal and the occurrence of blowholes. Also, the total amount of silicon oxides converted to SiO2 was high, which resulted in poor slag removability. Furthermore, the total amount of aluminum oxides converted to Al2O3 was low, which resulted in an unstable arc and poor bead shape.

[0059] Welding rod No. 16 had a low total metal carbonate content, which resulted in blowholes and low absorbed energy of the weld metal. It also had a low total SiO2 equivalent of silicon oxides, which resulted in poor bead shape. On the other hand, it had a high total Mn oxide equivalent of manganese oxides, which resulted in increased spatter.

[0060] Welding rod No. 17 had a high total CaO equivalent value of calcium oxide, which caused the arc to be unstable and resulted in poor penetration. In addition, poor penetration occurred when welding galvanized steel sheets. Also, due to the high Fe content, rod burn occurred. Furthermore, due to the high Ti content, the absorbed energy of the deposited metal was low.

[0061] Welding rod No. 18 had poor slag removability due to a high total Al2O3 equivalent value. Also, the total CaO equivalent value of the Ca oxide was low, resulting in an unstable arc and increased spatter. Furthermore, the total MgO equivalent value of the Mg oxide was high, resulting in a convex bead shape.

[0062] Welding rod No. 19 had a low total MgO equivalent value of Mg oxides, resulting in one-sided melting. Also, the total of one or more of the NaO equivalent value and the KO equivalent value of the Na compounds and K compounds was low, resulting in an unstable arc and poor productivity. Furthermore, the total organic matter content was low, resulting in poor penetration. Furthermore, poor penetration occurred when welding galvanized steel sheets.

[0063] Welding rod No. 20 had a high total of one or more of the Na2O equivalent and K2O equivalent values ​​of sodium and potassium compounds, which resulted in increased spatter. Also, because it contained a small amount of iron, one-sided dissolution occurred. Furthermore, poor penetration occurred when welding galvanized steel sheets.

Claims

1. A covered metal arc welding electrode for a galvanized steel sheet, in which a steel core wire is coated with a coating material, wherein a mass ratio of the coating material to a total mass of the welding rod is 20% or more and 45% or less, In mass % relative to the total mass of the coating material, C: 0.01-0.50%, Si: 0.01 to 0.50%, Mn: 2.0 to 7.0%, Total of one or more metal carbonates: 5 to 20%, Ti oxide TiO 2 Total conversion value: 10-30%, Si oxide SiO 2 Total conversion value: 10-30%, Al in Al oxide 2 O 3 Total conversion value: 0.1 to 5.0%, Total Ca oxides converted into CaO: 0.1 to 5.0%, Total Mg oxides converted into MgO: 0.1 to 5.0%, Na in Na compounds 2 O equivalent value and K of K compounds 2 Total of one or more of O equivalent values: 1.0 to 5.0% Fe in iron powder and iron alloy powder: 15 to 40% Contains 1.0 to 8.0% of one or more organic substances in total, The balance of the covered electrode for galvanized steel sheets is 5% or less of a coating agent and 1% or less of impurities.

2. The coating agent is, in mass % based on the total mass of the coating agent, Total Mn oxides converted to MnO: 4.0% or less The covered metal arc welding electrode for galvanized steel sheets according to claim 1, further comprising:

3. The coating agent is, in mass % based on the total mass of the coating agent, Total of Fe oxides converted to FeO: 4.0% or less The covered metal arc welding rod for galvanized steel sheets according to claim 1 or 2, further comprising:

4. The coating agent is, in mass % based on the total mass of the coating agent, Ti: 3.0% or less The covered metal arc welding rod for a galvanized steel sheet according to any one of claims 1 to 3, further comprising:

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