JP7651355B2 - Low hydrogen type covered electrode - Google Patents

Description

The present invention relates to a low-hydrogen covered metal arc welding rod, and in particular to a low-hydrogen covered metal arc welding rod with improved moisture resistance and coating drop-off resistance.

Low-hydrogen covered electrodes have good arc stability, excellent crack resistance, and excellent weld metal toughness, so they are widely used in areas with strong restraints and for welding high-tensile steel.

On the other hand, with the recent increase in the size of welded structures, there is a demand for higher strength steel materials. However, as the strength increases, management to prevent weld cracks becomes important in welding work, and in particular, to obtain a covered metal arc welding rod with excellent crack resistance, the main condition is that the diffusible hydrogen of the weld metal is extremely low. When using low-hydrogen covered metal arc welding rods, in order to maintain their characteristics, they are generally dried at 300 to 400°C for about 30 to 60 minutes before use, and stored in a container that can maintain a temperature of 100 to 150°C, from which they are taken out and used. If the rod is left in the air before use, it will absorb moisture depending on the environmental conditions, and if welding is performed in this state, the diffusible hydrogen will increase, and there is a risk of weld cracks occurring. In particular, for on-site welding, it is difficult to prepare multiple drying facilities, and the distance to and from the drying facilities becomes long, resulting in an increase in labor hours. In addition, when transporting the welding rod to the site or handling it during welding, the coating may partially fall off due to impact, making it unusable. For these reasons, there is a strong demand for the development of a low-hydrogen covered metal arc welding rod that has improved moisture absorption resistance, can be left in the air for long periods of time, and has improved resistance to shedding of the coating.

In response to this situation, various proposals have been made as a means for improving moisture absorption resistance and adhesion of the coating. For example, Patent Document 1 discloses a technology related to a covered metal arc welding rod that aims to reduce hydrogen and improve moisture absorption resistance by adjusting the weight ratio of Na ₂ O/K ₂ O, firing in a carbon dioxide gas atmosphere, and containing lithium. However, the technology described in Patent Document 1 has a problem with resistance to sheathing, with the coating adhesion being somewhat insufficient.

On the other hand, Patent Document 2 discloses a technology for a covered metal arc welding rod having excellent moisture absorption resistance due to AlF ₃ and LiF. However, the technology described in Patent Document 2 relates to a covered metal arc welding rod for temporary welding, and it is difficult to use it for actual welding or welded joints.

Patent Document 3 also discloses a technology for a covered metal arc welding rod that aims to improve the adhesion of the hectorite coating. However, although the technology described in Patent Document 3 has good resistance to shedding, it has a problem with low moisture absorption.

Japanese Patent Application Laid-Open No. 56-109191 JP 2018-89673 A Japanese Unexamined Patent Publication No. 57-160597

The present invention was devised in consideration of the above-mentioned problems, and aims to provide a low-hydrogen covered metal arc welding rod that has improved resistance to moisture absorption and sheath fall-off.

The gist of the present invention is
(1) In a low-hydrogen covered metal arc welding electrode in which a coating is applied to a steel core wire, the total of one or more metal carbonates: 30 to 55%, the total of one or more metal fluorides: 8 to 20%, the total of one or more of the total of Ti oxides in terms of TiO2 and the total of the total of Zr oxides in terms of ZrO2: 2 to 8%, the total of Si oxides in terms of SiO2: 5 to 8%, and the total of Al oxides in terms of Al2O3: 1 to ₁₀ %, and the total of the Ti oxides in terms of TiO2 and Zr oxides in terms of _ZrO2 : 1 to 10%, and the total of the Si oxides in terms of SiO2: 1 to 10%, and the total of the Al oxides in terms of Al2O3: 1 to 10%, and the total of the Al oxides in terms of Al2O3: 1 to 10%, and the total of the Ti oxides in terms of TiO2 _{and Zr} oxides in terms of ZrO2: 1 to 10%, and the total of the Al oxides in terms of _Al2O3 ... Al oxides in terms a total of one or more of Na oxide and Na fluoride in _Na equivalent value: 1.1 to 1.5%, a total of one or more of K oxide and K fluoride in K equivalent value: 0.8 to 1.0%, a total of one or more of Li oxide and Li fluoride in Li equivalent value: 0.02 to 0.07%, Si: 2 to 5%, Mn: 1 to 6%, Fe: 4 to 30%, Ti: 0.5 to 2.0%, hectorite: 0.1 to 1.0%, and the remainder being a coating agent and impurities, which is applied to a steel core wire at a coverage rate of 25 to 45% by mass relative to the total mass of the low hydrogen covered metal arc welding rod.

(2) The low hydrogen-based non-satisfactory arc welding rod according to (1) , further comprising Ni, the Ni content being 12.0% or less, in terms of mass % relative to the total mass of the coating material.

(3) A low hydrogen type covered metal arc welding rod according to (1) or (2), further comprising one or more of metal B, B alloy and B oxide, wherein the total of the B converted values of the one or more of metal B, B alloy and B oxide is 0.10% or less, in mass% based on the total mass of the coating material.

(4) The low hydrogen covered metal arc welding electrode according to any one of (1) to (3), further comprising one or both of Cr and Mo, the total amount of the one or both of Cr and Mo being 6.0% or less, in mass% based on the total mass of the coating material.

The low-hydrogen covered metal arc welding rod of the present invention can provide a low-hydrogen covered metal arc welding rod that has improved moisture absorption resistance and coating drop-off resistance, and that has good welding workability and mechanical performance, allowing for high-quality welded joints to be obtained.

In order to solve the above-mentioned problems, the inventors conducted detailed research into the composition of the coating material of low-hydrogen covered metal arc welding electrodes that have improved resistance to moisture absorption and to shedding of the coating.

As a result, it was found that moisture-resistant properties can be obtained by optimizing the contents of the Na-equivalent, K-equivalent, and Li-equivalent values of Na oxide, Na fluoride, K oxide, K fluoride, Li oxide, and Li fluoride, and that the resistance to shedding of the coating can be improved by optimizing the hectorite content. After further investigation, the present invention was completed.

The reasons for limiting the composition of each component in the coating material for the low-hydrogen covered metal arc welding rod of the present invention will be explained in detail below. Note that the content of each component in the low-hydrogen covered metal arc welding rod is expressed as mass% relative to the total mass of the coating material, and when expressing the mass%, it is simply written as %.

[Total of one or more metal carbonates: 30 to 55%]
Metal carbonates include calcium carbonate, magnesium carbonate, barium carbonate, etc., and are decomposed by the heat of the arc to generate _CO2 gas, which has the effect of protecting the weld metal from the atmosphere. If the total of one or more metal carbonates is less than 30%, the shielding effect is insufficient and blowholes are likely to occur. On the other hand, if the total of one or more metal carbonates exceeds 55%, the arc becomes unstable, the bead shape becomes poor, and slag removability also becomes poor. Therefore, the total of one or more metal carbonates is set to 30-55%.

[Total of one or more metal fluorides: 8 to 20%]
Metal fluorides refer to fluorite, magnesium fluoride, aluminum fluoride, etc., and have the effect of adjusting the fluidity of the molten slag to improve the bead shape. If the total of one or more metal fluorides is less than 8%, the fluidity of the molten slag will be poor, the slag encapsulation will be unstable, and the bead shape will be poor. On the other hand, if the total of one or more metal fluorides exceeds 20%, the shape of the covering tube will be incomplete, resulting in a one-sided melting state and an unstable arc. Therefore, the total of one or more metal fluorides is set to 8-20%.

[Total of one or both of the total of Ti oxides converted into _TiO2 and the total of Zr oxides converted into _ZrO2 : 2 to 8%]
Ti oxide and Zr oxide are added from rutile, titanium oxide, titanium slag, zircon sand, zirconia, etc., and have the effect of adjusting the viscosity of the molten slag to improve the bead shape. If the total of one or _two of the sum of the TiO2 converted values of Ti oxide and the sum of the _ZrO2 converted values of Zr oxide is less than 2%, the viscosity of the slag decreases and the bead shape becomes poor. On the other hand, if the total of one or two of the sum of the TiO2 converted values of Ti _oxide and the sum of the _ZrO2 converted values of Zr oxide exceeds 8%, the viscosity of the molten slag increases and the fluidity of the slag becomes poor, resulting in a poor bead shape. Therefore, the total of one or two of the sum of the TiO2 converted values of Ti _oxide and the sum of the ZrO2 converted values of Zr _oxide is set to 2-8%.

[Total of Si oxides converted into _SiO2 : 5 to 8%]
Silicon oxides are added from silica sand, zircon sand, feldspar, water glass, etc., and have the effect of increasing the viscosity of the molten slag, ensuring slag with appropriate viscosity, and improving the bead shape. If the total of the silicon oxides in terms of _SiO2 is less than 5%, the viscosity of the molten slag will be low and the bead shape will be poor. On the other hand, if the total of the silicon oxides in terms of _SiO2 exceeds 8%, the slag will become glassy and the slag removability will be poor. Therefore, the total of the silicon oxides in terms of _SiO2 is set to 5-8%.

[Total _Al2O3 converted value of Al _oxide : 0.2 to 1.5%]
Aluminum oxide is added from alumina and the like, and has the effect of stabilizing the arc and improving the bead shape. If the total of the aluminum _oxides in terms of _Al2O3 is less than 0.2%, the arc becomes unstable and the bead shape becomes poor. On the other hand, if the total of _the aluminum oxides in terms of _Al2O3 exceeds 1.5%, the slag becomes glassy and slag removal becomes poor. Therefore, the total of the aluminum _oxides in terms of _Al2O3 is set to 0.2-1.5%.

[Total of one or more of Na oxides and Na fluorides in terms of Na: 1.1 to 1.5%]
Na oxide is mainly added from sodium silicate of water glass, etc., and has the effect of improving the paintability during the manufacturing of welding rods and the stability of the arc during welding. It is also added from sodium fluoride and sodium silicofluoride of Na fluorides, and from albite and sodium borate of Na oxides, and is necessary for ensuring welding workability. If the total Na equivalent value of one or more of Na oxides and Na fluorides is less than 1.1%, the arc becomes unstable. If the total Na equivalent value is less than 1.1%, the paintability during production becomes poor and the resistance to shedding of the coating also decreases. On the other hand, if the total Na equivalent value of one or more of Na oxides and Na fluorides exceeds 1.5%, the moisture absorption property decreases, and the arc blow becomes too strong and unstable. Therefore, the total Na equivalent value of one or more of Na oxides and Na fluorides is 1.1 to 1.5%.

[Total of K-equivalent value of one or more of K oxides and K fluorides: 0.8 to 1.0%]
K oxide is mainly added from potassium silicate of water glass, etc., and has the effect of improving the stability of the arc during welding. It is also added from potassium silicofluoride and potassium fluoride of K fluorides, and potassium feldspar of K oxide, and is necessary for ensuring welding workability. If the total of the K-converted values of one or more of K oxide and K fluoride is less than 0.8%, the arc becomes unstable. On the other hand, if the total of the K-converted values of one or more of K oxide and K fluoride exceeds 1.0%, the hygroscopicity decreases, and the arc blow becomes weak and unstable. Therefore, the total of the K-converted values of one or more of K oxide and K fluoride is set to 0.8-1.0%.

[Total of one or more of Li oxides and Li fluorides in terms of Li: 0.02 to 0.07%]
Li oxide and Li fluoride are added from lithium fluoride, aluminum fluoride, lithium silicate of water glass, etc., and have the effect of improving the hygroscopicity of the coating. If the total of the Li-equivalent values of one or more of Li oxide and Li fluoride is less than 0.02%, the hygroscopicity is not obtained. On the other hand, if the total of the Li-equivalent values of one or more of Li oxide and Li fluoride exceeds 0.07%, the hygroscopicity is improved, but the drying speed after painting becomes too fast during the production of the welding rod, causing microcracks on the surface of the coating, and the resistance to falling off is also reduced. Therefore, the total of the Li-equivalent values of one or more of Li oxide and Li fluoride is set to 0.02 to 0.07%.

[Si: 2 to 5%]
Silicon is added from metal Si, Fe-Si, Fe-Si-Mn, etc., and is used for the purpose of deoxidizing the weld metal, and is also necessary from the viewpoint of welding workability. If the silicon content is less than 2%, deoxidation is insufficient and blowholes are likely to occur in the weld metal. On the other hand, if the silicon content exceeds 5%, low melting point oxides are precipitated at the grain boundaries of the weld metal, reducing the toughness of the weld metal. Therefore, the silicon content is set to 2-5%.

[Mn: 1 to 6%]
Mn is added from metal Mn, Fe-Mn, Fe-Si-Mn, etc., and is important as a deoxidizer like Si, and has the effect of refining the weld metal structure and increasing the toughness and strength of the weld metal. If Mn is less than 1%, the strength and toughness of the weld metal will decrease. Also, if Mn is less than 1%, deoxidization will be insufficient and blowholes will easily occur in the weld metal. On the other hand, if Mn exceeds 6%, the hardenability will be strongly affected and the toughness of the weld metal will decrease. Therefore, Mn is set to 1 to 6%.

[Fe: 4-30%]
Fe is added from iron powder, iron alloy powder such as Fe-Mn or Fe-Mo, or iron oxide, and has the effect of reducing the arc potential gradient, shortening the arc length, and preventing one-sided melting of the coating material. Fe also has the effect of improving work efficiency by increasing the amount of deposition. If Fe is less than 4%, the arc length becomes too long, the arc is likely to disappear during welding, one-sided melting of the coating material occurs, and the arc becomes unstable. On the other hand, if Fe exceeds 30%, the amount of slag material decreases, the slag encapsulation becomes uneven, and the bead shape becomes poor. Therefore, Fe is set to 4-30%.

[Ti: 0.5-2.0%]
Ti is added from metallic Ti, Fe-Ti, etc., and is effective as a deoxidizer, and at the same time, has the effect of lowering the potential gradient of the arc and stabilizing the arc. Ti also has the effect of refining the microstructure of the weld metal and improving its toughness. If Ti is less than 0.5%, the microstructure of the weld metal is not refined, and the toughness of the weld metal decreases. On the other hand, if Ti exceeds 2.0%, the precipitation of Ti oxide in the weld metal increases, and the toughness of the weld metal decreases. Therefore, Ti is set to 0.5 to 2.0%.

[Hectorite: 0.1-1.0%]
Hectorite is a type of clay mineral, and has a composition such as Na _0.3 (MgLi) ₃ Si ₄ O ₁₀ (F,OH) _2. Hectorite has good dispersibility in the coating agent, and increases the viscosity of the coating agent during production, preventing scratches and chipping immediately after coating, and improving paintability. Hectorite also improves the adhesion of the coating agent and improves the resistance to falling off of the coating agent. If the hectorite content is less than 0.1%, the coating ability and resistance to falling off cannot be obtained. On the other hand, if the hectorite content exceeds 1.0%, the coating ability is good and the coating agent does not fall off, but the coating tube becomes too strong, the arc voltage increases during welding, making the arc more likely to break, and the arc becomes unstable. Therefore, the hectorite content is set to 0.1 to 1.0%.

[Covering rate: 25 to 45% by mass of coating material relative to the total mass of low-hydrogen covered metal arc welding rod]
The coverage of the steel core wire with the coating agent has a large effect on the shielding resistance during welding. If the coverage is less than 25% by mass (hereinafter simply referred to as %) of the coating agent relative to the total mass of the low-hydrogen covered metal arc welding electrode, the amount of coating agent itself will be reduced, resulting in insufficient shielding, and the N content in the weld metal will increase, reducing the toughness of the weld metal. On the other hand, if the coverage of the coating agent exceeds 45%, the amount of slag will be excessive, causing the arc to become unstable. Therefore, the coverage is set to 25-45%.

[Ni: 12.0% or less]
Ni is added from metallic Ni and is an element that improves the strength and toughness of the weld metal. On the other hand, if Ni exceeds 12.0%, the toughness of the weld metal decreases. Therefore, Ni is set to 12.0% or less.

[Total of B-converted values of one or more of metal B, B alloy and B oxide: 0.10% or less]
B is added from metal B, Fe-B, Fe-Mn-B, borax, colemanite, etc., and is an element that improves hardenability in small amounts and is effective in suppressing the formation of grain boundary ferrite, and is effective in improving the toughness of the weld metal. On the other hand, if the total of the B-equivalent values of one or more of metal B, B alloy, and B oxide exceeds 0.10%, the toughness of the weld metal decreases. Therefore, the total of the B-equivalent values of one or more of metal B, B alloy, and B oxide is set to 0.10% or less.

[Total of one or both of Cr and Mo: 6.0% or less]
Cr is added as metallic Cr, Fe-Cr, etc., and Mo is added as metallic Mo, Fe-Mo, etc., and has the effect of further improving the strength of the weld metal. On the other hand, if the total of one or both of Cr and Mo exceeds 6.0%, the toughness of the weld metal decreases. Therefore, the total of one or both of Cr and Mo is set to 6.0% or less.

The coating material of the low-hydrogen covered metal arc welding electrode of the present invention is impurities contained in the paint and alloy powder as the balance other than the above components.

The coating agent is included from the viewpoint of productivity, and the coating agent content is, for example, 0.1 to 1.0%.

Impurities are components contained in raw materials or components mixed in during the manufacturing process, but are not intentionally included in the coating. Impurities contained in coatings include organic matter, alloy powders, and P and S contained in paints. The total amount of impurities is preferably 2% or less, and more preferably 1% or less.

The steel core wire used may be, for example, JIS G3523 SWY11, mild steel, or low alloy steel. The P content of the steel core wire is 0.010% or less because it reduces toughness, S content is 0.010% or less because it reduces the fluidity of the slag, and N content is 0.01% or less because it has a strong bond with B and reduces hardenability.

The effects of the present invention will be specifically explained below using examples.

In this example, a welding rod coating machine was used to coat a steel core wire with a diameter of 4 mm and a length of 400 mm, and the composition shown in Table 1, with a coating agent with the composition shown in Tables 2 and 3 at the coverage shown in Table 2, and then the wire was dried to produce various low-hydrogen covered electrodes.

In addition, in Tables 1, 2, and 3, the notation "-" means that the component is not intentionally included.

The manufactured welding rods were investigated for moisture absorption, diffusible hydrogen, coating loss rate, welding workability, mechanical performance, and welding defects.

[Moisture absorption amount]
The moisture absorption resistance was evaluated based on the amount of moisture absorbed. After drying the welding rod at 350°C for 1 hour, it was left in a thermo-hygrostat chamber maintained at a temperature of 30°C and a humidity of 80% for 7 hours. The weight ratio of the coating before and after drying was measured, and those within 0.4% were considered good.

[Diffusible hydrogen content]
For the measurement of the amount of diffusible hydrogen, a welding rod was used that had been dried at 350°C for 1 hour and then left for 7 hours in a constant temperature and humidity chamber maintained at a temperature of 30°C and a humidity of 80%. Welding was performed with an alternating current polarity, a welding current of 160A, and a welding speed of 18cm/min. The amount of diffusible hydrogen was measured according to JIS Z 3118, and a value of 8ml/100g or less was considered good.

[Coating loss rate]
The resistance to shedding was evaluated by the percentage of shedding of the coating. A welding rod weighing about 1.5 kg was placed in a steel box measuring 55 mm x 300 mm x 500 mm and made with a plate thickness of 6 mm, and the box was rotated for 5 minutes at a speed of 40 revolutions per minute around its longitudinal axis, and the weight percentage of the shedding of the coating was measured. A shedding rate of less than 2.0% was considered good.

[Welding workability]
The welding workability was evaluated by using JIS G 3106 SM490A steel plates having a thickness of 16 mm, a width of 100 mm and a length of 450 mm, and performing AC welding in flat, horizontal fillet and vertical upward welding, and performing a comprehensive sensory evaluation.

(Arc state)
The welding was judged to be good when the arc was stable during welding, the arc did not disappear during welding, a constant arc length was obtained, and there was no disturbance in the straightness of the arc.

(Bead shape)
Welds with both toes aligned and consistent weld height, bead width, waviness and surface condition were deemed good.

(Slag fluidity)
A good condition was determined when a healthy molten pool was obtained during welding, the molten slag did not penetrate into the molten pool, and the molten slag did not come into contact with the tip of the welding rod.

(Slag removability)
After welding, when the solidified slag was struck with a chipping hammer, if the slag cracked and could then be easily removed, it was judged to be good.

[Evaluation of machine performance]
Using JIS G 3106 SM490A steel plate having a thickness of 20 mm, weld metal test specimens were prepared in accordance with JIS Z 3211, using AC current polarity, a welding current of 150 to 170 A, and a preheat/interpass temperature of 90 to 110°C.

Mechanical performance was evaluated based on the tensile strength of the weld metal and the absorbed energy in a Charpy impact test at -20°C, with a tensile strength of 490 MPa or more and an absorbed energy of 80 J or more being considered good.

[Welding defects]
For weld defects (blowholes, etc.), defects in the weld metal were judged using JIS Z 3104 "Radiographic examination method for steel welded joints" before mechanical test pieces were taken. From the radiographic photographs, it was determined which of the 1st to 4th types of defects in "Annex 4, Table 1, Types of Defects" the defect fell into, and in "6. Classification of Defects" the defects were classified into Classes 1 to 4. Of these, Class 1 was A, Class 2 was B, Class 3 and Class 4 was C, with A and B being good and C being bad.

These analysis results and survey results are summarized in Table 4.

In Tables 2, 3 and 4, welding rods No. 1 to No. 27 are examples of the present invention, and welding rods No. 28 to No. 48 are comparative examples. In No. 27, the total of one or two of the total of metal carbonates, the total of metal fluorides, the total of Ti oxides in _TiO2 equivalent, and the total of Zr oxides in _ZrO2 equivalent, the total of Si oxides in _SiO2 equivalent, the total of Al oxides in _Al2O3 equivalent, the total of one _or more of Na oxides and Na fluorides in Na equivalent, the total of one or more of K oxides and K fluorides in K equivalent, the total of one or more of Li oxides and Li fluorides in Li equivalent, Si, Mn, Fe, Ti, and hectorite were appropriate, and the coating rate of the coating agent was also appropriate, so that the moisture absorption amount and the diffusible hydrogen amount were low, the coating drop rate was low, the arc was stable, the bead shape was good, and the slag fluidity and slag removability were good. In addition, the tensile strength and absorbed energy of the deposited metal were both good, and there were no welding defects in the deposited metal, so the results were satisfactory.

Welding rod No. 10 contains an appropriate amount of Ni and the total B equivalent value of one or more of metal B, B alloy, and B oxide, so the deposited metal has a tensile strength of 700 MPa or more and an absorbed energy of 170 J or more.

Welding rod No. 14 contains an appropriate amount of Ni, Cr, and/or Mo, so even though the deposited metal has a high tensile strength of 780 MPa or more, the absorbed energy of the deposited metal is 80 J or more.

Welding rod No. 17 contains an appropriate amount of Ni, metal B, B alloy, and B oxide, one or more of which are added in B equivalent, and one or more of which are added in Cr and Mo. Therefore, even though the tensile strength of the weld metal is high at 780 MPa or more, the absorbed energy of the weld metal is high at 152 J, which is an extremely satisfactory result.

Welding rods No. 22 and No. 24 contain appropriate amounts of one or both of Cr and Mo, resulting in a tensile strength of the deposited metal of 700 MPa or more.

Welding rods No. 23 and No. 25 have an appropriate amount of Ni added to them, so the tensile strength of the weld metal is 700 MPa or more, and the absorbed energy of the weld metal is 150 J or more.

Welding rods No. 26 and No. 27 contain an appropriate amount of the total B-equivalent value of one or more of metal B, B alloy, and B oxide, and therefore have an absorbed energy of 150 J or more.

In the comparative example, welding rod No. 28 had a large total _SiO2 equivalent value, so the slag became glassy and the slag removability was poor. In addition, because the Fe content was small, the arc length became long, the arc was easily extinguished during welding, one-sided melting of the coating occurred, and the arc was unstable.

Welding rod No. 29 had a high total Al ₂ O ₃ conversion value, so the slag became glassy and slag removal was poor.

Welding rod No. 30 had a low total metal fluoride content, which resulted in poor fluidity of the molten slag, unstable slag encapsulation, and poor bead shape.

Welding rod No. 31 had a poor bead shape because the total _SiO2 equivalent value was low. Also, the total B equivalent value of one or two of metal B, B alloy, and B oxide was high, so the absorbed energy of the deposited metal was low.

Welding rod No. 32 had a high total metal fluoride content, so it melted one-sidedly and the arc was unstable.

Welding rod No. 33 had a low total of one or two of the _TiO2 and _ZrO2 converted values, so the viscosity of the slag was low and the bead shape was poor. Also, the total of one or two of the Cr and Mo was high, so the absorbed energy of the deposited metal was low.

Welding rod No. 34 had a high total metal carbonate content, which caused the arc to become unstable, resulting in poor bead shape and poor slag removability.

Welding rod No. 35 had a low total _Al2O3 content, _which resulted in an unstable arc and poor bead shape. Also, because of the low Si content, blowholes occurred in the deposited metal.

Welding rod No. 36 had a low total metal carbonate content, which caused blowholes. Also, because it had a high Ni content, the absorbed energy of the weld metal was low.

Welding rod No. 37 had a high total of one or both of the TiO2 _- converted values and the _ZrO2- converted values, which resulted in poor slag fluidity and a poor bead shape.

Welding rod No. 38 had a high total Na equivalent value of one or more of sodium oxides and sodium fluorides, so it had a high amount of hygroscopic moisture and diffusible hydrogen, and the arc spray was too strong and unstable. In addition, because it had a high amount of silicon, the absorbed energy of the deposited metal was low.

Welding rod No. 39 had a low total Li-equivalent value of one or more types of Li oxide and Li fluoride, so the amount of moisture absorbed and the amount of diffused hydrogen were high.

Welding rod No. 40 had a low total Na equivalent value of one or more of Na oxides and Na fluorides, so the arc was unstable and the rate of coating shedding was high. Furthermore, because it contained a lot of Ti, the absorbed energy of the deposited metal was low.

Welding rod No. 41 had a high total K-equivalent value for one or more of K oxides and K fluorides, so it had a high amount of absorbed moisture and diffused hydrogen, and the arc spray was weak and unstable. In addition, because it had a high Mn content, the absorbed energy of the deposited metal was low.

Welding rod No. 42 had a high total Li-equivalent value of one or more of Li oxides and Li fluorides, so the rate of sheathing loss was high. In addition, because it had a low Mn content, blowholes occurred in the weld metal, and the tensile strength and absorbed energy of the weld metal were low.

Welding rod No. 43 had a low total K-equivalent value for one or more of K oxides and K fluorides, so the arc was unstable. Also, because it had a low Ti content, the absorbed energy of the deposited metal was low.

Welding rod No. 44 contains a lot of Fe, which causes the slag to be coated unevenly, resulting in a poor bead shape.

Welding rod No. 45 contains a lot of hectorite, so the arc voltage rises during welding, causing arc interruptions and making the arc unstable.

Welding rod No. 46 had a low coverage rate, so the absorbed energy of the weld metal was low.

Welding rod No. 47 had a high rate of coating loss because it contained less hectorite.

Welding rod No. 48 had a high coverage rate, so the arc was unstable.

Claims (4)

In low-hydrogen covered electrodes in which a coating is applied to the steel core wire,
The coating agent is, in mass% based on the total mass of the coating agent,
Total of one or more metal carbonates: 30 to 55%,
Total of one or more metal fluorides: 8 to 20%,
Sum of one or both of the sum of Ti oxides converted into _TiO2 and the sum of Zr oxides converted into _ZrO2 : 2 to 8%,
Total of Si oxides converted into _SiO2 : 5 to 8%,
Sum of Al oxides converted into Al ₂ O ₃ : 0.2 to 1.5%,
Sum of one or more of Na oxides and Na fluorides in terms of Na: 1.1 to 1.5%,
The total of one or more of K oxides and K fluorides converted into K: 0.8 to 1.0%,
The total of one or more of Li oxides and Li fluorides converted into Li: 0.02 to 0.07%;
Si: 2 to 5%,
Mn: 1 to 6%,
Fe: 4 to 30%,
Ti: 0.5-2.0%,
Hectorite: 0.1-1.0%,
A low-hydrogen covered metal arc welding rod, characterized in that a coating material, the balance of which is impurities, is applied to a steel core wire at a coverage rate of 25 to 45% by mass based on the total mass of the low-hydrogen covered metal arc welding rod. Further containing Ni,
In mass% based on the total mass of the coating material,
2. The low hydrogen type covered metal arc welding electrode according to claim 1, characterized in that Ni: 12.0% or less. Further containing one or more of metal B, B alloy and B oxide,
In mass% based on the total mass of the coating material,
3. The low hydrogen type covered metal arc welding electrode according to claim 1, wherein the total of the B converted values of one or more of metal B, B alloy and B oxide is 0.10% or less. Further containing one or both of Cr and Mo,
In mass% based on the total mass of the coating material,
The low hydrogen type covered metal arc welding electrode according to any one of claims 1 to 3, characterized in that the total content of one or both of Cr and Mo is 6.0% or less.