JP2020040094A - Coated electrode and coated arc welding method - Google Patents

Abstract

To provide a coated electrode which suppresses half-melting and deviation of arc, can smoothly translate a droplet, is excellent in arc stability and, thereby, provides superior welding operability.SOLUTION: A coated electrode includes a core wire and a coating agent with which the core wire is coated. Therein, the coating agent contains at least one kind of metal carbonate and metal fluoride and the sum of a content (in terms of CO) of the metal carbonate of particle size 75 μm or more Cand a content (in terms of F) of the metal fluoride of particle size 75 μm or more Cis 6.0 mass% or more with respect to total mass Cof the coating agent (therein, at least one side of Cand Cincludes the case of 0 mass%).SELECTED DRAWING: None

Description

  The present invention relates to a coated arc welding rod and a coated arc welding method, and more particularly, suppresses arc deflection and maintains good arc stability, thereby enabling droplets to be smoothly transferred, The present invention relates to a covered arc welding rod capable of obtaining improved welding workability, and a covered arc welding method for performing arc welding using the same.

  Covered arc welding is a covered arc welding rod in which a metal rod (core wire) is provided with a flux or a protective material called a coating agent (sometimes simply referred to as a "welding rod" or a "hand rod"). Is an electrode, an arc is generated between the base material and the base material, and the welding rod and the base material are melted by arc heat, thereby joining the objects. Covered arc welding is the simplest welding method that does not require a shielding gas, can be welded outdoors where wind is strong, and is widely used in various manufacturing plants, buildings, ships, vehicles, and the like.

  The coating material constituting the coated arc welding rod contains raw materials having functions such as a gas generating agent, a slag forming agent, a deoxidizing agent, an alloy additive, an arc stabilizer, and a fixing agent. In addition, coated arc welding rods are classified according to the type of coating agent, and include illuminite, high titanium oxide, lime titania, iron powder titanium oxide, high cellulose, low hydrogen, and iron powder low hydrogen. There are various systems.

  Among the various types of coated arc welding rods described above, as a low hydrogen-based coated arc welding rod, as described in Patent Document 1, the oxygen content in the core wire is limited, and the metal carbonate in the coating agent is limited. There has been proposed a coated arc welding rod in which the contents of metal, metal fluoride, and moisture are appropriately adjusted. Patent Literature 1 describes that by appropriately adjusting the components in the core wire and the coating agent in the coated arc welding rod, it is possible to secure good welding workability without impairing the physical properties of the weld metal. Have been.

JP-A-57-85696

  However, in welding using a covered arc welding rod, since the welding is performed in various welding positions such as an advance angle and a receding angle, when the welding rod is tilted, the coating agent in a portion close to the base material is easily melted ( This is called one-side melting), the arc is deflected, and the welding operation is deteriorated. The covered arc welding rod described in Patent Document 1 described above does not describe anything about one-side melting and arc deflection, and is applied specifically to a low hydrogen-based coated arc welding rod. For all other types of coated arc welding rods, the welding workability evaluated by droplet transferability and arc stability could not be improved.

  INDUSTRIAL APPLICABILITY The present invention suppresses one-side melting and arc deflection, enables smooth transfer of droplets, and has good arc stability, thereby providing excellent welding workability. The purpose is to provide a stick.

The covered arc welding rod according to the present invention has the following configuration (1).
(1) A coated arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are the following: 6.0% by mass or more based on the total mass C _{coat, total of the} coating agent (including the case where at least one of the C _{CO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass),
On the welding rod tip side after use of the coated arc welding rod,
And the tip portion of the core wire, the leading edge portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction and D _1,
And cutting edge portions of the coating remaining on the periphery of the core wire, the rearmost end portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction is D ₂ When
The _{D 2} ratio _(D 2 / _{D 1)} is covered electrode to satisfy the 0.40 or less (including 0) for the _{D 1.}

A preferred embodiment of the coated arc welding rod according to the present invention has the following configuration (2) or (3).
(2) wherein _{D 1} satisfies the following 2.2 mm, covered electrodes according to the above (1).
(3) covered electrode according to the ratio of the _{D 1} to diameter d of the core wire in the covered electrode _(D 1 / d) satisfies the 1.3 above (1) or (2).

Further, the covered arc welding rod according to the present invention has the following configuration (4).
(4) A coated arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are as follows. 6.0% by mass or more (including the case where at least one of the _{CCO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass) with _respect to _{the total} mass _{Ccoat , total of the} coating agent. Characterized covered arc welding rod.

Further, a preferred embodiment of the coated arc welding rod according to the present invention has the following configurations (5) to (10).
(5) In a section perpendicular to the longitudinal direction of the welding rod,
The cross-sectional area of the entire coating and S _1,
When the circle equivalent diameter of at least one of the total area of said metal carbonate and said metal fluoride is 30μm or more was S _2,
The ratio of _{S 2} relative to S _{1 (S} 2 / _{S 1)} is covered electrode as claimed in any one of the preceding satisfy 0.06 to 0.15 (1) to (4).
(6) The coating agent contains, as the metal carbonate, at least one selected from CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ ,
The total content of metal carbonate (CO ₂ converted value) C _{CO2, total} in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent satisfies 6.0 mass% or more and 26.0 mass% or less. The coated arc welding rod according to any one of (1) to (5).
(7) The coating agent contains at least one selected from CaF ₂ , BaF ₂ , SrF ₂ and MgF ₂ as the metal fluoride,
The total content (F conversion value) _{CF, total} of the metal fluoride in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent is 15.0% by mass or less (including 0% by mass). The coated arc welding rod according to any one of the above (1) to (6).
(8) The coating agent contains both a metal carbonate and a metal fluoride,
In the coating agent, the total content of metal fluorides relative to the total of the total content of metal carbonates (CO ₂ converted value) C _{CO2, total} and the total content of metal fluorides (F converted value) _{CF, total} (1) to (7) _{, wherein} the ratio of the amount (F-converted value) C _{F, total} {C _{F, total} / (C _{CO2, total} + C _{F, total} )} satisfies 0.10 to 0.30. A coated arc welding rod according to any one of the preceding claims.
(9) The coating agent further contains at least one of Si and a Si compound,
In the above (1), the total content of Si and the Si compound (in terms of Si) C _{Si, total} is 6.0% by mass to 9.0% by mass with respect to _{the total} mass C _{coat, total} of the coating agent. The coated arc welding rod according to any one of (1) to (8).
(10) The above-mentioned (1) to (9), wherein the coated arc welding rod is used in arc welding in a welding posture in which the base metal is perpendicular or has a receding angle of more than 0 ° and 30 ° or less. A coated arc welding rod according to any one of the preceding claims.

Further, the coated arc welding method according to the present invention has the following configuration (11).
(11) A covered arc welding method using a covered arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are as follows. 6.0% by mass or more (including the case where at least one of the _{CCO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass) with _respect to _{the total} mass _{Ccoat , total of the} coating agent. Characterized covered arc welding method.

A preferred embodiment of the coated arc welding method according to the present invention includes the following configurations (12) to (15).
(12) On the welding rod tip side after using the coated arc welding rod,
And the tip portion of the core wire, the leading edge portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction and D _1,
And cutting edge portions of the coating remaining on the periphery of the core wire, the rearmost end portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction is D ₂ When
The _{D 2} ratio _(D 2 / _{D 1)} is arc welding so that 0.40 or less (including 0), shielded metal arc welding method according to (11) for said _{D 1.}
(13) wherein _{D 1} is arc welding so as to satisfy the following 2.2 mm, shielded metal arc welding method according to (12).
(14) the ratio of the _{D 1} to diameter d of the core wire in the covered electrode _(D 1 / d) is arc welding so as to satisfy 1.3 or less, according to the above (12) or (13) Covered arc welding method.
(15) The above-mentioned (11) to (14), wherein the covered arc welding rod is arc-welded in a welding posture in which the base metal is perpendicular or has a receding angle of more than 0 ° and 30 ° or less. Covered arc welding method.

  According to the present invention, among the at least one kind of particles selected from the metal carbonates and metal fluorides contained in the coating agent, the particles are controlled such that the particles of a suitable size are contained in a predetermined amount. Since the coating material is uniformly melted, the protective cylinder is formed uniformly during welding, so that one-side melting is prevented and arc deflection is suppressed. As a result, the arc stability is better. Thus, it is possible to provide a coated arc welding rod and a coated arc welding method that can obtain excellent welding workability even with any type of coated arc welding rod.

FIG. 1A is a cross-sectional view illustrating a state of a covered arc welding rod when the deflection of an arc is suppressed during welding. FIG. 1B is a cross-sectional view showing a state of the covered arc welding rod when the deflection of the arc is remarkable during welding.

  Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

  The present inventors pay attention to the particle size (particle size) of the metal carbonate or metal fluoride contained in the coating agent, and can realize smooth droplet transfer and good arc stability. Intensive studies were conducted to obtain a coated arc welding rod. As a result, it has been found that it is effective to adjust the particle size of the metal carbonate or metal fluoride particles so that the particles have a large size.

  First, the effect of the particle size (ie, particle size roughness) of the metal carbonate or metal fluoride on droplet transfer (ie, the effect) will be described in detail below.

The present inventors have found that the particle size of the metal carbonate or metal fluoride also affects the shape of the protective cylinder formed during arc welding, thereby maintaining the directivity of the arc, that is, the deflection of the arc. It has been found that by suppressing the above, good arc stability can be obtained.
In other words, when the metal carbonate or metal fluoride having a large particle size is contained in the coating agent, the specific surface area becomes small and the coating agent becomes difficult to melt, so that the coating agent is uniformly melted during arc welding. During the welding, the protective cylinder is formed uniformly (for details, refer to the contents described later). For this reason, the arc stability is further improved by maintaining the arc directivity.

In addition, metal carbonates and metal fluorides are components that can be contained as a gas generating agent in the coating agent, and when a coated arc welding rod is used as an electrode to generate an arc between the coating material and a welding base material, a shielding gas is generated. To prevent entry of oxygen and nitrogen in the atmosphere into the weld metal.
If the particle size of the metal carbonate and metal fluoride contained in the coating agent is adjusted to be large, at the tip of the coated arc welding rod (the arc generating point on the welding rod side), the one with the large particle size is completely gaseous. Will stay in one place until it is transformed. Due to this stagnation, the gas is intensively generated in one direction (in the direction of the molten core wire), and the volume expansion of the gas affects, thereby promoting the constriction of the droplet. For this reason, the shearing force for detaching the droplet such as the electromagnetic pinch force and the surface tension works efficiently, and the droplet can be detached in a small particle state. Further, since the droplets are detached while keeping the detachment cycle stable, arc stability is improved and excellent welding workability can be obtained.

  On the other hand, when the particle size of the metal carbonate or metal fluoride is small, a small volume of gas is generated because the amount of generated gas is small, and the generation direction of the gas is not determined in one direction. As compared with the case where the particle size of the metal fluoride or the metal fluoride is large, the force for promoting the detachment of the droplet becomes small.

  Hereinafter, for the coated arc welding rod according to the embodiment of the present invention, in the gas generating agent contained in the coating agent, the particle size, the area ratio of the cross section in the longitudinal direction of the welding rod, other reasons for addition of components and reasons for numerical limitation, etc. Will be described in detail.

The coated arc welding rod according to the present embodiment,
A coated arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are the following: 6.0% by mass or more based on the total mass C _{coat, total of the} coating agent (including the case where at least one of the C _{CO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass),
On the welding rod tip side after use of the coated arc welding rod,
And the tip portion of the core wire, the leading edge portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction and D _1,
And cutting edge portions of the coating remaining on the periphery of the core wire, the rearmost end portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction is D ₂ When
The ratio of the _{D 2} for _{D 1 (D} 2 / _{D 1)} satisfies the 0.40 or less (including 0).

(Coating agent)
First, details of the coating agent will be described below.

<Content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 , 75 μm, and metal fluoride having a particle size of 75 μm or more, based on the total mass C _{coat, total} of the coating material (F conversion value) _CF, total of _{75 μm} : 6.0% by mass or more>
When the particle size of the metal carbonate or the metal fluoride contained in the coating material is increased, as described above, the formation of the constriction of the droplet at the time of arc welding is promoted, and the smooth droplet transfer can be realized. In addition, since the coating material is uniformly melted at the time of arc welding, the protective cylinder is uniformly formed during welding. For this reason, the deflection of the arc is suppressed, and the arc directivity is maintained, so that the arc stability is further improved.

  If a metal carbonate having a particle size of 75 μm or more is contained in the coating material, or a metal fluoride having a particle size of 75 μm or more is contained in the coating material, a smooth droplet as described above is obtained. The effect of transition and good arc stability can be obtained. However, the content of a metal carbonate having a particle size of a predetermined value or more and a content of a metal fluoride having a particle size of a predetermined value or more can also affect smooth droplet transfer and arc stability. In the rod, the content of metal carbonate or metal fluoride having a particle size of a predetermined value or more is also specified.

That is, the total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are obtained. When the amount is 6.0% by mass or more with respect to the total mass C _{coat and total of} the coating agent, the droplet can be smoothly transferred, and the arc stability becomes good, thereby improving the welding workability. The effect of causing this to occur can be sufficiently obtained.
However, this includes the case where at least one of the above-mentioned _{CCO2 , 75 μm} and _{CF, 75 μm} is 0% by mass.

The sum of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are given by: If it is too large relative to _{the total} mass C _{coat, total} of the coating agent, there is a concern that the coating agent may have an adverse effect on the coating properties during the manufacturing process, and therefore, the content is not more than 15.0% by mass. Preferably, it is 12.0 mass% or less.

Further, in order to more sufficiently obtain the effects of the smooth droplet transfer and the good arc stability described above, the content of the metal carbonate having a particle size of 106 μm or more (CO ₂ converted value) C CO2, 106 μm is _defined as: It is preferable that the sum of the content (F conversion value) _{CF and 106 μm} of the metal fluoride having a particle size of 106 μm or more is 5.0% by mass or more based on the _total mass C _{coat and total of} the coating agent. On the other hand, the above-mentioned value is preferably 9.0% by mass or less, since there is a concern about an increase in the above-mentioned spatter and an influence on the coatability of the coating agent in the manufacturing process.

To obtain more fully smooth droplet transfer and good arc stability effect as described above, the content of metal carbonate particle size is 150μm or more and (CO ₂ conversion _value) C CO2,150μm, particle size The total of the content (F conversion value) _{CF and 150} μm of the metal fluoride of 150 μm or more is preferably 2.5% by mass or more based on the _total mass C _{coat and total of} the coating agent, and is preferably 3.0%. It is more preferred that the content be at least mass%.
In addition, the above value is preferably 5.0% by mass or less, and more preferably 4.0% by mass or less, since there is a concern that the above-mentioned increase in spatter and the influence on the coating property of the coating agent during the manufacturing process are concerned. More preferably, there is.

It is sufficient that at least one of the metal carbonate and the metal fluoride is contained in the coating agent, but both may be contained. The “grain size” described in the present embodiment is measured using a measuring method according to JIS Z 8801-2006.
Further, the particle size (particle size) of the metal carbonate and the metal fluoride contained in the coating agent is generally at most about 600 μm.

<Ratio of _{D 2} for _{D 1 (D 2 / D 1} ): 0.40 or less (including 0)>
As described above, the particle size of the metal carbonate and the metal fluoride also affects the shape of the protective cylinder after arc welding. That is, by defining the particle size and the content of the metal carbonate and the metal fluoride, the protection cylinder after the arc welding can be formed in a good shape. As a result, the arc directivity is further improved, and the arc stability is improved.

  Here, the state of the covered arc welding rod when two types of covered arc welding rods are used to perform arc welding will be described with reference to the drawings. 1A and 1B, the same components are denoted by the same reference numerals, and a detailed description thereof will be omitted.

FIG. 1A is a cross-sectional view illustrating a state of a covered arc welding rod when the deflection of an arc is suppressed during welding. As shown in FIG. 1A, the covered arc welding rod 1 has a core wire 2 and a coating agent 3 that covers the core wire 2. The coating agent 3 contains at least one compound selected from metal carbonates and metal fluorides. Then, the sum of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are as follows. The total mass C _{coat, total of} the coating agent is 6.0% by mass or more (including the case where at least one of the C _{CO2,75 μm and} the _{CF, 75 μm} is 0% by mass). Defines the components of the coating agent 3.

When the base material 5 is subjected to arc welding using the coated arc welding rod 1, a specific compound contained in the coating agent 3 (that is, at least one selected from metal carbonates and metal fluorides) Is limited as described above, and as a result, the specific surface area of the compound is reduced, and as a result, the compound 3 protrudes more than the tip 2 a of the core wire 2. Melting or softening of the protective cylinder 6, which is a part of the coating agent 3, is difficult to progress, and the protective cylinder 6 tends to remain during arc welding.
For this reason, one-side melting of the coating agent 3 is suppressed, and the coating agent 3 is uniformly melted over the entire circumferential direction of the coated arc welding rod 1. As a result, during or after welding, the space surrounded by the inner peripheral surface of the protection cylinder 6 approaches a uniform conical shape in a sectional view of the covered arc welding rod. As a result, the distance D in the longitudinal direction of the welding rod between the distal end 3a of the protective tube 6 and the distal end portion 2a of the core wire 2 is almost equal at any position, and the dispersion is small. Therefore, the fluctuation of the arc 4 during welding is suppressed, the arc directivity is improved, and the arc stability is improved.

Further, as described later, when both the metal carbonate and the metal fluoride are contained in the coating material 3, the total content of the metal carbonate (the CO ₂ conversion value) C _CO2 contained in the coating material 3 _{, Total} and the total content of metal fluoride (converted to F) C _{F, total} of the total content of metal fluoride (converted to F) _{CF, total} ｛ _{CF, total} / (C _{CO2) , Total} + C _{F, total} )} is appropriately adjusted, the softening point of the coating material 3 can be increased, so that the shape of the protective cylinder 6 can be maintained uniformly to an appropriate length. The protection cylinder 6 serves as a guide to enhance the directivity of the arc. Thereby, the fluctuation (fluctuation) of the droplet is further suppressed, and good arc stability can be maintained, so that welding workability is improved.

  On the other hand, FIG. 1B is a cross-sectional view showing the state of the covered arc welding rod when the deflection of the arc is remarkable during welding. As shown in FIG. 1B, when the particle size and the content of the metal carbonate and the metal fluoride are subjected to arc welding using the coated arc welding rod 11 having the coating agent 13 which is not adjusted as described above. In the coating agent 13 (protective cylinder 16) remaining after welding, the distance from the leading end 2a of the core wire 2 varies between the leading end 13a and the trailing end 13b. As a result, the arc 14 is significantly deflected during welding, and the arc stability is reduced.

  In the present embodiment, variations in the lengths of the coating materials 3 and 13 (or the lengths of the protection cylinders 6 and 16) remaining around the core wire 2 after using the coated arc welding rod are specified. I do. Therefore, a method of digitizing the variation will be described in detail with reference to FIG. 1B.

As shown in FIG. 1B, at the tip end side of the welding rod after use of the covered arc welding rod (under the covered arc welding rod 11 in FIG. 1B), the distal end portion 2 a of the core wire 2 and the periphery of the core wire 2 are formed. the leading edge portion 13a of the residual to that coating 13, welded (in FIG. 1B, the vertical direction) rod longitudinal distance in the D _1, state-of-the-art coating 13 remaining on the periphery of the core wire 2 and section 13a, the rearmost end portion 13b of the coating 13 remaining on the periphery of the core wire 2, the distance in the welding rod longitudinal direction and D _2.

When the ratio of _{D 2} for _{D 1 (D 2 / D 1} ) satisfies 0.40 or less, it means that the variation in the length is less protecting cylinder 16 is formed in a good shape. When this requirement is satisfied, the directivity of the arc is obtained, and the arc stability is improved. The ratio of _{D 2} for _{D 1 (D 2 / D 1} ) is preferably 0.30 or less, more preferably 0.25 or less, and most preferred is if 0.

Here, after using the covered arc welding rod (that is, after the end of the arc welding) means a state in which the coating agent remains after a continuous arc generation period of 5 seconds or more after the start of the arc welding.
Generally, the coated arc welding rod may be used repeatedly even after it has been used once as long as the coating agent remains.
After the use of the covered arc welding rod, slag may adhere to the tip of the core wire 2. In the present embodiment, the tip 2 a of the core wire 2 is defined in a state where the slag is removed, and its shape is determined. Has a substantially planar shape.
In addition, the “most distal portion” described in the present embodiment refers to the most protruding portion of the tips of the coating materials 3 and 13, and the “rearmost portion” refers to the distal end of the coating materials 3 and 13. Of these, the least protruding part.

<D ₁ : 2.2 mm or less>
It is preferable that the coating material 13 remains around the core wire 2 at a certain length or more on the distal end side of the welding rod after use of the coated arc welding rod, and the protective cylinder 16 is formed. However, the tip portion 2a of the core 2, the welding rod longitudinal distance D ₁ of the leading-edge portion 13a of the coating 13 remaining on the periphery of the core wire 2 is more than 2.2 mm, the protective tube 16 Becomes excessively long, the distance between the core wire and the base material increases, and the arc length increases. If the arc length is excessively long, the arc length is liable to fluctuate, causing arc breakage and deteriorating arc stability. As a result, there is a possibility that welding workability may deteriorate, such as deterioration of bead appearance and increase of spatter. Therefore, it is preferable that the above _{D 1} is 2.2mm or less, and more preferably to less 1.7 mm. If D ₁ is too small, the directivity of the arc cannot be obtained, and the arc stability is deteriorated. Therefore, D ₁ is preferably 1.0 mm or more, and preferably 1.3 mm or more. More preferred.

<Ratio of _{D 1} to the diameter d of the core wire in the covered electrode _(D 1 _/d):1.3 less>
Generally, the diameter of the core wire d (see d in FIG. 1B) in the covered electrode, the D ₁ is proportional. In order to maintain good arc stability, D ₁ / d is preferably at most 1.3, more preferably at most 1.0, even more preferably at most 0.8. If D ₁ is extremely small with respect to the diameter d, the directivity of the arc cannot be obtained, and the arc stability deteriorates. Therefore, D ₁ / d is preferably 0.1 or more, and 0/0. It is more preferably at least 3.
In the present embodiment, the diameter d is not particularly limited, but is preferably 3.0 to 5.0 mm from the range of the generally used diameter d.

<Ratio of _{S 2} relative to _{S 1 (S 2 / S 1} ): 0.06 to 0.15>
In the above-described embodiment, among the at least one kind of particles selected from the metal carbonates and the metal fluorides contained in the coating agent, the particles having a large particle size are defined so as to be contained in a predetermined amount, so that the particles are smoothly contained. The transfer of the droplets and the good arc stability are realized.
On the other hand, in the present embodiment, the following is adopted as another defining method for realizing these performances. Specifically, covered electrode, in a cross section perpendicular to the welding rod longitudinally, the cross-sectional area of the entire coating and S _1, at least one equivalent circle diameter of the metal carbonate and metal fluoride is 30μm or more one of the total area when the _{S 2,} the ratio of _{S 2} relative to _{S 1 (S 2 / S 1} ) , characterized in that satisfy 0.06 to 0.15.

The ratio of _{S 2} relative to _{S 1 (S 2 / S 1} ) it is, if it is less than 0.06, appears more remarkable effect of promoting droplet detachment can Smoother droplet transfer. Therefore, the ratio S ₂ / S ₁ is preferably 0.06 or more, and more preferably 0.07 or more.
On the other hand, when S ₂ / S ₁ is 0.15 or less, it becomes easy to obtain a weld metal having desired performance. Therefore, the ratio S ₂ / S ₁ is set to 0.15 or less, and more preferably 0.10 or less.

  In the coating agent, the above effect can be obtained even if only the metal fluoride having an equivalent circle diameter of 30 μm or more is contained in the above range, but only the metal carbonate is contained in the above range. Is more preferable. Most preferably, both the metal carbonate and the metal fluoride are contained in the above range.

As a method of controlling the S ₂ / S ₁ as described above, in addition to the method of adjusting the particle size of the metal carbonate or the metal fluoride used as the raw material of the coating agent, the method of adjusting the content of the metal carbonate or the metal fluoride And a method of adjusting the coating pressure of the coating agent during production of the coated arc welding rod. By combining or these alone, it is possible to control the S _{2 /} S _1. However, the above-described manufacturing method is merely an example, and the present invention is not necessarily limited thereto.

In the present embodiment, the “equivalent circle diameter” refers to the diameter of a circle having an area equal to the projected area of a particle as defined in JIS Z 8827-1, and is obtained by image analysis software using a computer. be able to.
In addition, the particle size (equivalent circle diameter) of the metal carbonate and the metal fluoride contained in the coating agent is generally about 600 μm at the maximum.

Here, the S _{2 /} S ₁ is for example, can be measured as follows. First, using a WD / ED combine electron probe microanalyzer (EPMA) JXA-8200 manufactured by JEOL Ltd., the welding rod cross section is analyzed at an acceleration voltage of 15 kV and an irradiation current of 5 × 10 ⁻¹⁰ A ( Magnification is 400 times). Then, using the image analysis software JTrim, at least one region of a metal carbonate and a metal fluoride having an equivalent circle diameter of 30 μm or more and the other region are binary-coded with respect to the entire cross section of the welding rod. Become Thereby, the total area S ₂ (that is, S ₂ / S ₁ ) of at least one of the metal carbonate and the metal fluoride having the equivalent circle diameter of 30 μm or more with respect to the cross-sectional area S ₁ of the entire coating material is calculated. be able to.

<Total mass of metal carbonate in the coating agent (CO ₂ equivalent value) C _{CO2, total} : 6.0 mass% or more and 26.0 mass% or less based on the total mass C _{coat and total} of the coating material>
Metal carbonates such as CaCO ₃ and BaCO ₃ contained in the coating agent of the coated arc welding rod generate CO ₂ , which is a shielding gas (shielding gas), by thermal decomposition near the arc generating point, and oxygen in the atmosphere It is a component that has the effect of protecting the molten pool from nitrogen, moisture. For example, CaCO ₃ decomposes at about 825 ° C., generating CaO and CO ₂ gas. If the content of metal carbonate in the coating agent is too low, poor shielding may cause entrapment of air, resulting in deterioration of welding workability, welding defects such as blow holes, and lower impact value of weld metal. Cause.
On the other hand, when the total content of the metal carbonate in the coating agent is excessive, the coating agent becomes difficult to melt during welding. That is, since the distance of D1 described above is long, the distance between the molten interface of the core wire and the molten pool is excessively large, and the arc length is out of proper conditions. As a result, the occurrence of arc breakage or a decrease in arc stability occurs, and there is a possibility that spatter may increase.
Further, as described above, by containing a metal carbonate having a predetermined size or more, the droplet transfer cycle can be stabilized.

When the total content of the metal carbonate in the coating agent (CO ₂ converted value) C _{CO2, total} is 6.0% by mass or more with respect to _{the total} mass C _{coat, total} of the coating agent, these effects are sufficiently obtained. Can be. Therefore, the content C _{CO2, total} of the metal carbonate is preferably 6.0% by mass or more, more preferably 10.0% by mass or more in terms of CO ₂ .
On the other hand, when the total content (CO ₂ converted value) C _{CO2, total} of the metal carbonate in the coating material is 26.0% by mass or less with respect to _{the total} mass C _{coat, total} of the coating material, the arc stability becomes higher. And the amount of spatter generated is reduced. Therefore, the content C _{CO2, total} of the metal carbonate is preferably 26.0% by mass or less, more preferably 25.0% by mass or less in terms of CO ₂ .
Incidentally, the same reason as described above, the total mass _{C Electrode} covered _electrodes, for _total, the total content of metal carbonate in the covered electrode (CO ₂ conversion value) is 4.0 mass% or more, It is preferably 10.0% by mass or less, more preferably 4.5% by mass or more and 9.0% by mass or less, further preferably 4.5% by mass or more and 7.5% by mass or less. preferable.

The metal carbonate used as the coating agent of the present embodiment includes calcium carbonate (CaCO ₃ ), barium carbonate (BaCO ₃ ), strontium carbonate (SrCO ₃ ), magnesium carbonate (MgCO ₃ ), and manganese carbonate (MnCO ₃ ). Preferably, at least one selected from them is used. From the viewpoint of manufacturing cost, it is more preferable to use CaCO ₃ and BaCO ₃ , and it is most preferable to use CaCO ₃ . Any of the above various metal carbonates may be used alone or in combination of two or more. When a plurality of metal carbonates are used, the total content in terms of CO ₂ is 6.0% by mass. It is preferable that the content be in the range of not less than 26.0% by mass.

When CaCO ₃ is contained in the coating agent as a metal carbonate, the content of CaCO _{3 in} the coating agent is 6.0% by mass or more and 26.0% by mass in terms of CO _{2 with} respect to the total mass of the coating agent. %, More preferably 10.0% by mass or more and 25.0% by mass or less.
The content of CaCO ₃ in the covered arc welding rod is preferably 10.0% by mass or more and 20.0% by mass or less, preferably 11.0% by mass or more and 19.0% by mass, based on the total mass of the welding electrode. %, More preferably 11.0% by mass or more and 17.0% by mass or less.

Further, when containing BaCO ₃ as metal carbonate in the coating agent, the content of BaCO ₃ in the coating, from the viewpoint of weldability, the total weight coating agent, in terms of CO ₂ values, 0 It is preferable to be more than 0.0% by mass and 4.0% by mass or less.

<Total mass of the metal fluoride in the coating agent (F conversion value) _{CF, total} : 15.0% by mass or less (including 0% by mass) with respect to _{the total} mass C _{coat, total} of the coating agent>
Metal fluoride such as CaF ₂ contained in the coating agent of the coated arc welding rod is a component having an effect of lowering the melting point of the slag, improving the fluidity of the slag, and improving the bead shape. In addition, the metal fluoride is decomposed by the arc heat to generate a large amount of reducing shielding gas (fluoride gas), thereby suppressing an increase in the amount of oxygen and hydrogen in the weld metal and improving the arc stability. It is a component that has the effect of causing
Furthermore, when metal fluoride is added to the coating agent, the decomposed fluorine reacts with the hydrogen in the molten metal or molten slag, and the hydrogen partial pressure in the molten metal can be reduced. Can also. Furthermore, as described above, droplet transferability can be improved by including a metal fluoride having a size equal to or larger than a predetermined size in the coating material. However, if the content of the metal fluoride in the coating agent is excessive, the fluidity of the slag becomes excessive, and problems such as entrainment of the slag may occur, and the welding quality may be deteriorated.

Since it is not always necessary for the coating agent to contain metal fluoride, the lower limit is not particularly set and may be 0.0% by mass. However, in order to sufficiently obtain these effects, it is better to add a metal fluoride, and the content is preferably more than 0.0% by mass, and more preferably 3.0% by mass or more. More preferred.
On the other hand, when the total content (F conversion value) _{CF, total} of the metal fluoride in the coating material is 15.0% by mass or less with respect to _{the total} mass C _{coat, total} of the coating material, better arc stability is obtained. And welding workability is improved. Therefore, the content _{CF, total} of the metal fluoride is preferably 15.0% by mass or less, and more preferably 7.5% by mass or less.
For the same reason as described above, the total content (F conversion value) of the metal fluoride in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod is 0.5% by mass or more, 0.7% by mass or less, more preferably 0.7% by mass or more and 2.5% by mass or less, even more preferably 0.9% by mass or more and 2.3% by mass or less. .

The metal fluoride used as the coating agent of the present embodiment is selected from calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ), strontium fluoride (SrF ₂ ), and magnesium fluoride (MgF ₂ ). Preferably, at least one of them is used. From the viewpoint of manufacturing cost, it is more preferable to use CaF ₂ and BaF ₂ , and it is most preferable to use CaF ₂ . Any of the above various metal fluorides may be used alone or in combination of two or more. When a plurality of metal fluorides are used, the total content in terms of F is 15.0% by mass or less. (Including 0% by mass).

When CaF ₂ is contained in the coating material as a metal fluoride, the content of CaF _{2 in} the coating material is more than 0.0% by mass and 15.0% by mass in terms of F with respect to the total mass of the coating material. %, More preferably 3.0% by mass to 7.5% by mass.
The content of CaF ₂ in the covered arc welding rod is preferably not less than 1.0% by mass and not more than 6.0% by mass, and preferably not less than 1.5% by mass and 5.5% by mass, based on the total mass of the welding rod. It is more preferably at most 1.8 mass%, more preferably at least 1.8 mass% and not more than 5.2 mass%.

<Total content of metal fluoride in the coating agent, based on the total content of metal carbonate (CO ₂ converted value) C _{CO2, total} and total content of metal fluoride (F converted value) _{CF, total} Amount (F conversion value) Ratio of _{CF and total} { _{CF, total} / ( _{CCO2, total} + _{CF, total} )}: 0.10 or more and 0.30 or less>
When the coating agent contains both a metal carbonate and a metal fluoride, the softening point of the flux can be increased by appropriately adjusting the mass ratio between the metal fluoride and the metal carbonate. As a result, the protection cylinder can be formed stably with a desired length, and the arc directivity can be improved. Thereby, the swing of the droplet becomes smaller, good arc stability is obtained, and welding workability is improved.

If the above ratio { _{CF, total} / ( _{CCO2, total} + _{CF, total} )} is 0.30 or more and is in the range of 0.10 or less, the softening point of the flux is appropriate, and the protective cylinder is sufficiently provided. It can be left in the length, and the welding workability becomes better. Therefore, the above ratio is preferably 0.10 or more. Further, the ratio is preferably 0.30 or less, and more preferably 0.15 or less.

<Total mass C Si _{, total} of Si and the Si compound in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent (Si conversion value) C _{Si, total} : 6.0 mass% or more and 9.0 mass% or less>
Si and the Si compound are compounds that become SiO ₂ in the coating agent and act as a catalyst to promote the decomposition of metal carbonate (CaCO ₃ ). For example, CaCO ₃ generates CaO.SiO ₂ and CO ₂ gas in the presence of SiO ₂ , but when CaCO ₃ having a particle size of 75 μm or more is contained in a predetermined content or more, the unit is as described above. The increase in the amount of CO ₂ gas generated per time and the efficient operation of the pinch force promotes the formation of necking of droplets.
When CaCO ₃ is thermally decomposed, CaO and SiO ₂ generated thereby react with each other, and the heat of reaction promotes the thermal decomposition of undecomposed CaCO ₃ .
Further, Si and the Si compound become SiO ₂ in the coating agent and react with the metal fluoride to generate a fluorinated gas. For example, 2CaF ₂ and SiO ₂ react to generate 2CaO and SiF ₄ gas. However, the volume of the SiF ₄ gas generated by this reaction is smaller than that of the CO ₂ gas generated by the metal carbonate using SiO ₂ as a catalyst, so that the effect of releasing the droplet is relatively small.

As described above, in the present embodiment, the total content of the metal fluoride having a particle size of 75 μm or more in the coating material, or the metal fluoride having an equivalent circle diameter of 30 μm or more in a cross section perpendicular to the longitudinal direction of the welding rod. , Which means that a metal fluoride having a large particle size is contained in the coating material. Thus, the amount of generated gas is increased, and the formation of constriction of the droplet is promoted.
The following effects can be further obtained by including a metal fluoride having a large particle size in the coating material. That is, since the metal fluoride having a large particle size has a small specific surface area, the reaction between the metal fluoride (for example, CaF ₂ ) and SiO ₂ can be suppressed as compared with the metal fluoride having a small particle size.
As described above, the amount of SiF ₄ gas generated by the reaction between the metal fluoride and SiO ₂ is not so significant as compared with the CO ₂ gas generated by the metal carbonate using SiO ₂ as a catalyst. Therefore, for example, by suppressing the reaction between CaF ₂ and SiO ₂ , it is possible to sufficiently secure the amount of SiO ₂ acting as a catalyst for the metal carbonate, and to promote smoother droplet detachment. it can.

When the coating material further contains at least one of Si and a Si compound, the total content of Si and the Si compound in the coating material (in terms of _Si ) C _{Si with} respect to the _total mass C _{coat, total} of the coating material _{, Total} is 6.0% by mass or more, the generation of CO ₂ gas and fluoride gas can be further promoted. Therefore, the content of C _{Si, total} is preferably 6.0% by mass or more.
On the other hand, when the C _{Si, total} is 9.0 mass% or less, it becomes easier to secure a predetermined mechanical performance and a stable bead shape in the weld metal. Therefore, the C _{Si, total} is preferably at most 9.0% by mass, more preferably at most 8.0% by mass.

Subsequently, in addition to the above-mentioned metal carbonate, metal fluoride, Si and the Si compound, the coating material according to the present embodiment can contain an alloy, an oxide, and the like. Other components will be described below.
In the following description, the amount of each component in the coating agent is defined as the content per total mass of the coating agent. Further, the amount of each component in the entire covered arc welding rod is defined as the content per total mass of the welding rod.

<Fe in the coating material: 0.0% by mass or more (including 0% by mass), 35.0% by mass or less based on the total mass C _{coat, total} of the coating material>
Fe is a component added to the coating agent of the coated arc welding rod for the purpose of improving the mechanical properties of the weld metal by deoxidizing action or adding an alloy, and improving welding efficiency by increasing the amount of metal deposited. It is contained as iron powder in the agent, as well as Fe-Si and Fe-Mn. Fe in the coating agent may be arbitrarily added according to the necessity of the above effect, and it is not necessary to particularly define the lower limit, and it is sufficient if it is 0.0% by mass or more. However, in order to further improve the mechanical performance, it is preferable to add 0.1% by mass or more in order to reduce the O content in the weld metal. Further, when Fe in the coating agent is 35.0% by mass or less, the size of droplets transferred to the molten pool can be reduced, and welding workability is further improved.
Therefore, the lower limit of the Fe content in the coating agent relative to _{the total} mass C _{coat, total} of the coating agent is more preferably 0.1% by mass or more. In addition, the upper limit of the Fe content in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent is preferably 35.0% by mass or less, and preferably 32.0% by mass or less, based on the total mass of the coating agent. More preferably, it is still more preferably 30.0% by mass or less.
In addition, for the same reason as described above, the Fe content in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod may be 60.0% by mass or more and 85.0% by mass or less. Preferably, it is 70.0% by mass or more and 85.0% by mass or less, and more preferably 72.0% by mass or more and 85.0% by mass or less.

<Al in coating material: 0.0% by mass or more (including 0% by mass), 1.0% by mass or less based on total mass C _{coat, total} of coating material>
Al (metallic Al) is a component that has the effect of improving the crack resistance of the weld metal and also improving the corrosion resistance and oxidation resistance, and may be added as needed, and it is particularly necessary to define the lower limit. But not more than 0.0% by mass. In the case where Al is added to the coating material, if the Al content in the coating material is 1.0% by mass or less, the weld metal can obtain sufficient ductility in addition to the above-described effects.
Therefore, the Al content in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and 0.6% by mass or less. It is more preferable that the content be not more than mass%.
In addition, for the same reason as described above, the Al content in the coated arc welding rod with respect to the _total mass of the coated arc welding rod C _{electode, total} may be 0.50% by mass or less (including 0% by mass). Preferably, it is 0.30% by mass or less, more preferably 0.10% by mass or less.

<Ni in the coating agent: 0.0% by mass or more (including 0% by mass), 4.0% by mass or less based on the total mass C _{coat, total} of the coating agent>
Ni is a component having an effect of improving the fatigue strength of the welded portion, and may be added as needed, and there is no particular need to define the lower limit, and it is sufficient if it is 0.0% by mass or more. In the case where Ni is added to the coating material, if the Ni content in the coating material is 4.0% by mass or less, hot cracking of the weld metal can be further suppressed. Therefore, the Ni content in the coating material is preferably 4.0% by mass or less, and preferably 3.0% by mass or less and 2.5% by mass or less with respect to _{the total} mass C _{coat and total} of the coating material. Is more preferred.
For the same reason as described above, the Ni content in the coated arc welding rod with respect to the _total mass of the covered arc welding rod C _{electode, total} is preferably 1.00% by mass or less, more preferably 0.60% by mass. The content is more preferably not more than 0.30% by mass, more preferably not more than 0.30% by mass.

<Mn in the coating agent based on the total weight C _{coat, total} of the coating agent: 1.5% by mass or more and 6.0% by mass or less>
Mn is a component having an effect of improving the strength of the alloy material, and may be added as needed. There is no particular need to define the lower limit, and Mn may be 0.0% by mass or more. When the Mn content in the coating agent is in the range of 1.5% by mass or more and 6.0% by mass or less, hot cracking can be suppressed while maintaining the strength of the weld metal. Therefore, the Mn content in the coating material with respect to _{the total} mass C _{coat, total} of the coating material is preferably 1.5% by mass or more and 6.0% by mass or less, and is preferably 1.7% by mass or more and 4.0% by mass or less. The content is more preferably 8% by mass or less, and further preferably 1.8% by mass or more and 4.2% by mass or less.
For the same reason as described above, the Mn content in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod may be 0.8% by mass or more and 1.8% by mass or less. Preferably, it is 0.8% by mass or more and 1.6% by mass or less, more preferably 0.8% by mass or more and 1.4% by mass or less.

<Si in the coating agent based on the total weight C _{coat, total} of the coating agent: 1.0% by mass or more and 9.0% by mass or less>
Si (metallic Si) is a deoxidizing agent and is a component having an effect of reducing the amount of oxygen in the weld metal and improving the strength, and may be added as necessary. What is necessary is just 0 mass% or more. However, when the Si content in the coating agent is in the range of 1.0% by mass or more and 9.0% by mass or less, the droplet size that transfers to the molten pool can be made smaller, and the welding workability is good. become. Therefore, the Si content in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent is preferably 1.0% by mass or more and 9.0% by mass or less, preferably 2.4% by mass or more and 7.0% by mass or less. The content is more preferably 0% by mass or less, further preferably 2.8% by mass or more and 6.6% by mass or less.
For the same reason as described above, the Si content in the coated arc welding rod with respect to the _total mass C _{electronode, total} of the coated arc welding rod may be 0.8% by mass or more and 2.2% by mass or less. Preferably, it is 1.0% by mass or more and 2.0% by mass or less, more preferably 1.1% by mass or more and 1.9% by mass or less.

<Mo in the coating material relative to _{the total} weight C _{coat, total} of the coating material: 0.0% by mass or more (including 0% by mass), 2.0% by mass or less>
Mo is a component having an effect of improving the strength of the weld metal, and may be added as needed, and there is no particular need to define the lower limit, and it is sufficient if it is 0.0% by mass or more. When Mo is added to the coating material, if the Mo content in the coating material is 2.0% by mass or less, welding cracks can be further suppressed while maintaining strength. Therefore, the Mo content in the coating agent relative to _{the total} mass C _{coat, total} of the coating agent is preferably 2.0% by mass or less, more preferably 1.2% by mass or less, and 0.8% by mass or less. It is more preferable that the content be not more than mass%.
For the same reason as described above, the Mo content in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod may be 0.65% by mass or less (including 0% by mass). Preferably, it is 0.45% by mass or less, more preferably 0.30% by mass or less.

<Al ₂ O ₃ in the coating agent: 0.02% by mass or more and 3.0% by mass or less based on the total mass C _{coat and total} of the coating agent>
Al ₂ O ₃ is a component having an arc stabilizing effect and an effect as a slag forming agent. When the Al ₂ O ₃ content in the coating agent is 3.0% by mass or less, a higher arc stabilizing effect can be obtained. Therefore, the content of Al ₂ O ₃ in the coating material relative to _{the total} weight C _{coat, total} of the coating material is preferably 0.02% by mass or more and 3.0% by mass or less, and more preferably 0.03% by mass or more. , 2.6% by mass or less, more preferably 0.05% by mass or more and 2.0% by mass or less.
For the same reason as above, the content of Al ₂ O ₃ in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod is 0.01% by mass or more and 0.90% by mass or less. Preferably, it is 0.02% by mass or more and 0.80% by mass or less, and further preferably 0.02% by mass or more and 0.70% by mass or less.

<SiO ₂ in the coating agent: 1.5% by mass or more and 15.0% by mass or less based on the total mass C _{coat, total} of the coating agent>
SiO ₂ is a component that acts as a slag-making agent and an adhesive. When the content of SiO ₂ in the coating agent is 1.5% by mass or more, the above-described effects can be sufficiently obtained. When the content of SiO ₂ in the coating agent is 15.0% by mass or less, the slag removability is further improved. Therefore, the content of SiO ₂ in the coating material with respect to _{the total} weight C _{coat, total} of the coating material is preferably from 1.5% by mass to 15.0% by mass, more preferably from 2.0% by mass to 10% by mass. It is more preferably not more than 0.0% by mass, and further preferably not less than 4.0% by mass and not more than 8.0% by mass.
For the same reason as described above, the content of SiO ₂ in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod is 0.40% by mass or more based on the total mass of the welding _electrode, and 4.00%. % By mass, preferably 0.60% by mass or more and 3.60% by mass or less, more preferably 0.80% by mass or more and 3.20% by mass or less.

<Total mass _{C coat} of the _coating, for _{total, TiO} in the coating 2: 0.2 wt% or more, 10.0% by mass or less>
TiO ₂ is a component having a function of generating a slag having good flowability, giving a luster to a bead surface, and giving a beautiful appearance to a weld metal in a coating agent for a coated arc welding rod. It is also a component that suppresses arc deflection (wandering) and contributes to obtaining good welding workability. When the TiO ₂ content in the coating is in the range of 0.2% by mass or more and 10.0% by mass or less based on the total mass of the coating, the above-mentioned effect is further improved. Therefore, the content of TiO ₂ in the coating material with respect to _{the total} weight C _{coat, total} of the coating material is preferably 0.2% by mass or more and 10.0% by mass or less, and 0.5% by mass or more and 8% by mass or less. The content is more preferably 0.0% by mass or less, and even more preferably 1.0% by mass or more and 6.0% by mass or less.
For the same reason as described above, the content of TiO ₂ in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod is 1.00% by mass or more and 4.00% by mass or less. , Preferably 1.20% by mass or more and 3.00% by mass or less, more preferably 1.40% by mass or more and 2.60% by mass or less.

<MgO in the coating agent relative to _{the total} mass C _{coat, total} of the coating agent: more than 0.01% by mass, 4.0% by mass or less>
MgO is a component having an effect of enhancing the slag removability. When the MgO content in the coating agent is more than 0.01% by mass and not more than 4.0% by mass, the above-mentioned effect is further improved. Therefore, the content of MgO in the coating material with respect to _{the total} mass C _{coat, total} of the coating material is preferably more than 0.01% by mass and 4.0% by mass or less, more preferably 0.2% by mass or more. The content is more preferably 0% by mass or less, further preferably 0.5% by mass or more and 0.8% by mass or less.
For the same reason as described above, the content of MgO in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod may be 0.01% by mass or more and 1.00% by mass or less. Preferably, it is 0.01% by mass or more and 0.80% by mass or less, further preferably 0.01% by mass or more and 0.50% by mass or less.

<Total mass of K ₂ O, Li ₂ O, and Na ₂ O in the coating agent based on the total mass C _{coat, total} of the coating agent: 1.6% by mass or more and 3.6% by mass or less>
K ₂ O, Li ₂ O and Na ₂ O are components that are contained in a large amount in water glass used as an inorganic binder of a coating agent, and are also added as a powder raw material, and provide good arc stability and moderate It is an effective component for improving arc stability by obtaining a suitable arc spraying force. In order to further enhance the above effects, the total content of K ₂ O, Li ₂ O, and Na ₂ O in the coating material with respect to _{the total} weight C _{coat, total} of the coating material is 1.6% by mass or more. The content is preferably 6% by mass or less, more preferably 1.8% by mass or more and 3.2% by mass or less, even more preferably 2.0% by mass or more and 3.0% by mass or less.
For the same reason as described above, the total content of K ₂ O, Li ₂ O and Na ₂ O in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod is 0.20% by mass. As described above, the content is preferably 1.40% by mass or less, more preferably 0.40% by mass or more and 1.20% by mass or less, and 0.60% by mass or more and 1.00% by mass or less. Is more preferred.
Li ₂ O also has the effect of improving the moisture absorption resistance of the coated arc welding rod and reducing the diffusible hydrogen in the weld metal.

<C in the coating material: 0.0% by mass or more (including 0% by mass), 0.15% by mass or less based on the total mass C _{coat, total} of the coating material>
C is a component that contributes to the improvement of the strength of the weld metal, and may be added as needed. There is no particular need to define the lower limit, and it is sufficient if it is 0.0% by mass or more. When C is added to the coating agent, the content is preferably 0.15% by mass or less in order to reduce the ductility of the weld metal and suppress weld cracking. Therefore, it is preferable that the C content in the coating agent is 0.0% by mass or more and 0.15% by mass or less based on the total mass C _{coat and total} of the coating agent. In addition, from the viewpoint of improving welding workability, the content is more preferably 0.01% by mass or more and 0.10% by mass or less, and still more preferably 0.02% by mass or more and 0.08% by mass or less. Examples of the C source include organic substances, various minerals, alloying agents, graphite, and the like.
In addition, for the same reason as described above, the C content in the coated arc welding rod with respect to the _total mass C _{electode, total} of the coated arc welding rod may be 0.15% by mass or less (including 0% by mass). Preferably, it is 0.01% by mass or more and 0.10% by mass or less, more preferably 0.02% by mass or more and 0.08% by mass or less.

<Remainder>
The balance of the coating agent in the present embodiment is inevitable impurities. Examples of inevitable impurities include Nb ₂ O ₅ , V ₂ O ₅ , ZrO ₂ , Fe ₂ O ₃ .FeO, SnO, P, and S. Further, the total content of inevitable impurities in the coating material relative to _{the total} mass C _{coat, total} of the coating material is preferably 5.0% by mass or less (including 0% by mass). Further, based on the total mass C _{coat, total} of the coating agent, Nb ₂ O ₅ in the coating agent was 0.3% by mass or less (including 0% by mass), and V ₂ O ₅ was 0.3% by mass or less (0% by mass). %, ZrO ₂ is limited to 0.4% by mass or less (including 0% by mass), and Fe ₂ O ₃ .FeO is limited to 3.50% by mass or less (including 0% by mass). preferable. The impurities include those that are not intended in the design of the welding rod. For example, in the case of an illuminite-coated arc welding rod, since the illuminite raw material is added to the coating material, the undesired Fe ₂ O ₃ .FeO in the design of the welding rod may contain 3.50 mass% at the maximum. However, these are impurities.

  Next, the cord and the coverage will be described.

(Core wire)
The core in the present embodiment is not particularly limited. For example, a core having a diameter d of 2.6 mm to 6.0 mm can be used, and a core having a diameter d of 4.0 mm can be preferably used. The composition of the core wire of the present embodiment will be described below.

<O: 0.0005% by mass or more and 0.0150% by mass or less>
If the O content of the core wire is excessive, the O content in the obtained weld metal becomes excessive, and the toughness of the weld metal may be reduced. In addition, since oxygen in the core wire reacts with Fe-Si or Fe-Mn, which is a deoxidizing agent added to the coating agent, to generate slag, the amount of slag increases, and slag fluidity and welding workability are increased. This may cause deterioration, and may further cause deterioration in mechanical properties due to a decrease in the amount of Si and Mn in the weld metal and an increase in the amount of oxygen.
Further, the fluidity of the molten metal is increased, and in welding in a vertical or upward position, dripping of the weld metal is likely to occur, and welding workability may be reduced. On the other hand, if the O content of the core wire is too small, the expansion of the molten pool by the arc force becomes insufficient, and a weld metal in which alloy components are uniformly distributed cannot be obtained.
From the viewpoints described above, the O content of the cord with respect to the total mass of the cord is preferably 0.0005% by mass or more, more preferably 0.0013% by mass or more, and 0.0016% by mass or more. Is more preferable. Further, the O content of the core wire is preferably 0.0150% by mass or less, more preferably 0.0125% by mass or less, and even more preferably 0.0100% by mass or less.

<Other ingredients>
Although not particularly limited, as the core wire in the present embodiment, for example, an iron-based core wire containing Fe as a main component can be preferably used. Specifically, SWRY11 specified in JIS G 3503: 2006 is used. It can be used as a cord.
The core wire may contain C, Si, Mn, P, S, N, Cu, etc. in addition to the above O and Fe. The C content of the cord relative to the total mass of the cord is 0.09% by mass or less, the Si content is 0.03% by mass or less (including 0% by mass), the Mn content is 0.35% by mass or more, and 0% or less. 0.65% by mass or less, P content 0.020% by mass or less (including 0% by mass), S content 0.023% by mass or less (including 0% by mass), Cu content 0.20% by mass % Or less (including 0% by mass).

(Coverage)
In the present embodiment, the coating rate of the coating agent on the outer periphery of the core wire is not particularly limited, but is preferably, for example, 20% or more, and more preferably 22% or more, from the viewpoint of ensuring the strength of the coating agent. More preferably, it is still more preferably at least 24%. In addition, from the viewpoint of arc stability and the like, the content is preferably, for example, 40% or less, more preferably 38% or less, and still more preferably 36% or less.

  The present embodiment also relates to an arc welding method using a coated arc welding rod in which the components in the coating agent are controlled. In the arc welding method according to the present embodiment, the reasons for limiting the components (grain size and area ratio, etc.) in the coating material of the welding rod used and the length of the coating material remaining after the use of the arc are as described above. Therefore, the description is omitted. Hereinafter, particularly the welding position in the arc welding method according to the present embodiment will be described.

(Welding posture)
<The coated arc welding rod is perpendicular to the base metal or has a receding angle of more than 0 ° and 30 ° or less>
The covered arc welding rod according to the present embodiment is welded such that the covered arc welding rod is perpendicular to the base material (that is, the covered arc welding rod is disposed perpendicular to the base material) or has a receding angle of more than 0 ° and 30 ° or less. It is preferably used in position-dependent arc welding. As described above, welding using a covered arc welding rod is often performed in various welding positions such as advancing angle and receding angle, and when welding is performed in these welding positions (that is, the covered arc welding rod is One-side melting is more remarkable than in the case of vertical. The covered arc welding rod according to the present embodiment has the same effect as in the case where the covered arc welding rod is perpendicular to the base material in covered arc welding when the receding angle is set to more than 0 ° and 30 ° or less. Can be. Note that the receding angle is more preferably 5 ° or more and 25 ° or less.
In addition, even when the welding position is vertical, although the molten pool itself may not be horizontal with respect to the base material, the coated arc welding rod according to the present embodiment has high robustness and some disturbance or error. Can be suppressed even if a crack occurs.

In addition, the coated arc welding rod according to this embodiment includes various systems such as an illuminite system, a high titanium oxide system, a lime titania system, an iron powder titanium oxide system, a high cellulose system, a low hydrogen system, and an iron powder low hydrogen system. It can be applied as a welding rod. However, since the low-hydrogen welding rod contains a large amount of a gas generating agent in the coating agent for the purpose of reducing diffusible hydrogen, the coated arc welding rod according to the present embodiment is used for low-hydrogen welding. When applied to a rod, the effect of droplet separation by the gas generating agent becomes significant.
Further, in the iron powder low-hydrogen welding rod, a large amount of iron powder is added to the coating agent in order to obtain a desired amount of deposited metal. There is a problem that a smooth droplet transfer property cannot be obtained and large spatters are scattered. Therefore, it is most preferable that the coated arc welding rod according to the present embodiment, which can improve the droplet detachment property, be applied as an iron powder low hydrogen-based welding rod.

  The method for manufacturing the above-described coated arc welding rod is not particularly limited. For example, the coating material is kneaded with water glass, applied to the outer periphery of the core wire, dried and fired, whereby the coated arc welding rod according to the present embodiment can be manufactured.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Production of coated arc welding rod, arc welding and calculation of various parameters]
SWRY 11 having a diameter of 3.2 to 5.0 mm was prepared as a core wire, and a coating agent (coating agent No. C1 to C15) having a chemical component composition shown in Table 1 was coated as shown in Table 3 to form 26. Various coated arc welding rods were produced by applying the coating at a coating rate of 0.9 to 35.6% on the outer periphery of the core wire and then drying (test Nos. T1 to T19 in Table 3).

Table 1 shows the content of each component in the coating agent with respect to the _total mass C _{coat, total} of the coating agent. In Table 1, the remainder is unavoidable impurities, and the amounts of each component in the coating agent indicate the content (% by mass) per the _total mass C _{coat of the} coating agent _{and total} .
Also, Table 4 shows the content of each component in the coated arc welding rod with respect to the _total mass _{Celectrode, total} of the coated arc welding rod. In Table 4, the balance is unavoidable impurities, and the amount of each component in the covered arc welding rod indicates the content (% by mass) per the _total mass of the welding rod C _{Electrode, total} .

Further, Table 2 lists various physical property values related to the content of the metal carbonate or the content of the metal fluoride contained in the coating agent.
In Table 2, C [CO2, 75 μm] is the total content (in terms of CO ₂ ) of metal carbonates having a particle size of 75 μm or more, and C [F, 75 μm] is a particle size of 75 μm or more. a total content of metal fluoride (F-converted value), C [CO2,106μm] is the total content of the metal carbonate particle size is not less than 106 [mu] m (CO ₂ conversion value), C [F, 106 [mu] m ] Is the total content (F conversion value) of the metal fluoride having a particle size of 106 μm or more, and C [CO2, 150 μm] is the total content (CO ₂ conversion value) of the metal carbonate having a particle size of 150 μm or more. ), And C [F, 150 μm] is the total content (F conversion value) of the metal fluoride having a particle size of 150 μm or more.
Furthermore, C [CO2, total] is the total content of the metal carbonate contained in the coating agent (CO ₂ conversion value), C [F, total] is a metal fluoride contained in the coating agent It is the total content (F conversion value). C [coat, total] is the total mass of the coating agent, and C [Si, total] is the total content of Si and the Si compound (in terms of Si).

Here, for example, C shown in (1) column in Table 2 [CO2,75μm] / C [CO2 , total] is total content of metal carbonate contained in the coating agent (CO ₂ conversion value) C _CO2, for _total, the particle size indicates the content of the metal carbonate is 75μm or more (CO ₂ conversion _{value) C CO2,75μm.} The same applies to other columns.

Also, “(5) + (6)” shown in column (7) in Table 2 indicates C [CO2, 75 μm] / C [coat, total] shown in column (5) and column (6). The total amount of C [F, 75 μm] / C [coat, total], that is, the content (CO ₂ converted value) of the metal carbonate having a particle size of 75 μm or more with respect to the _total mass C _{coat, total} of the coating agent C _It shows the total amount of _CO2 , 75 μm, and the content (F conversion value) of the metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} . Similarly, “(8) + (9)” shown in column (10) in Table 2 represents the content (CO ₂₎ of the metal carbonate having a particle size of 106 μm or more with respect to the _total mass C _{coat, total} of the coating agent. It shows the total amount of (converted value) _CCO2 , 106 μm and the content (F converted value) of the metal fluoride having a particle size of 106 μm or more (F converted value) _{, 106 μm} . Similarly, “(11) + (12)” shown in column (13) of Table 2 indicates the content (CO) of the metal carbonate having a particle size of 150 μm or more with respect to the _total mass C _{coat, total} of the coating agent. ₂ converted value) _{CCO2 , 150 μm and} the total amount of the content (F converted value) _{CF, 150 μm} of the metal fluoride having a particle size of 150 μm or more are shown.

  Subsequently, using the obtained coated arc welding rod, arc welding was performed under the following welding conditions, and the power was arbitrarily turned off after 10 seconds from the start of welding. In addition, as shown in Table 5, Test No. In T9 and T10, tests were performed in which the sweepback angle was varied in the range of 5 to 25 °. Test No. The test examples other than T9 and T10 were performed with the receding angle fixed at 15 °.

<Welding conditions>
Power polarity: DCEP
Welding posture: Downward bead-on-plate Welding target: 12 mmt x 70 mmt x 450 mm SM490 steel plate Welding current: 150 A (target) ± 10 A
Arc voltage: 21V (target) ± 2V

After that, measure the length from the foremost end of the coating agent (protective tube) remaining around the core wire on the tip end side of the welding rod to the rear end of the welding rod on the holder side (rear end side), and perform welding. The length from the rearmost end of the coating agent (protective cylinder) remaining around the core wire on the rod tip side to the rear end of the welding rod on the holder side was measured.
Further, the coating agent forming the protective tube and the slag remaining at the end of the core wire were removed, and the length from the front end of the core wire to the rear end of the welding rod on the holder side was measured. Then, using these measured values, the distance D ₁ in the longitudinal direction of the welding rod between the leading end of the core wire and the tip of the coating agent remaining around the core wire, and the distance around the core wire, a distal end portion of the residual to that coating, the rearmost end portion of the coating remaining on the periphery of the core wire, and calculates the distance D ₂ in the welding rod longitudinal direction (see Table 5).

Further, the coated arc welding rod obtained by the above method was embedded in a resin such that a cross section perpendicular to the longitudinal direction became an observation surface, and observed with a scanning electron microscope (SEM). The observation by the SEM was performed with a magnification of 50 times, an acceleration voltage of 15 kV, and a backscattered electron (BSE) image.
Then, the cross section of the coating material is subjected to elemental analysis using energy dispersive X-ray spectroscopy (EDX), and the area ratio of particles having a circle-equivalent diameter of 30 μm or more, that is, the entire coating material is cut off. the area and _{S 1,} when at least one of the total area of the circle equivalent diameter of the metal carbonate and metal fluoride is 30μm or more was _{S 2,} the ratio of _{S 2} relative to _{S 1 (S} 2 / _{S 1} ) Was calculated.

EDX analysis by SEM can be performed as follows. For example, the cross section of the coated arc welding rod is analyzed using TM3030 Miniscope (manufactured by Hitachi High-Technologies Corporation) (four rectangular areas of 50 ×, 1.61 mm × 1.21 mm). The selection of the visual field is desirably such that the coating material cross section is 70% or more in each visual field. By binarizing 1024 × 768 pixels (the number of pixels is 786,432) with respect to one visual field using image analysis software Image J, particles having an area of 706.8 μm ² or more (equivalent circle diameter of 30 μm or more) are obtained. The area ratio can be calculated. The threshold value at the time of binarization is, for example, 60.

Table 3 below shows the measurement results of the core diameter d and S ₂ / S ₁ of the coated arc welding rod. Table 5 below shows the measurement results of D ₂ / D ₁ , D _1, and D ₁ / d.

Further, in Test No. T1 to T15 (Example) and Test No. For covered electrode of T16～T19 (comparative example), and welded in the same manner as the welding conditions at the time of measurement of the D ₁ and D _2, according to the following evaluation criteria, (whether single melted) single melt rating, the arc The effect of suppressing deflection and the workability of welding were evaluated.

[Evaluation of one-side melting (presence of one-side melting)]
When D ₂ / D ₁ ≦ 0.40 is satisfied: No When D ₂ / D ₁ > 0.40 is satisfied: Yes

[Arc deflection suppression effect]
The presence or absence of arc deflection and the bead appearance were visually evaluated. If the arc is not deflected and the bead appearance is judged to be good, ◎ (excellent), the arc is slightly deflected, but if the bead appearance is judged to be good, o (good), the arc is deflected, Those judged to have poor bead appearance were evaluated as x (defective).

[Welding workability (sensory evaluation)]
When the droplets are visually observed to be periodically transferred during welding and only fine spatters are generated, ◎ (excellent), the droplets are transferred periodically during welding. If it is judged that medium-grain spatter has occurred, it is judged as good (good). It is judged that droplets are not periodically transferred during welding, and large-grain spatter has occurred in large quantities. Was evaluated as x (bad).

Test No. in Tables 3 to 5 T1～T15 (example), the requirements of the present invention (i.e., total mass _{C coat} of the _coating, for _total, the content of metal carbonate particle size is 75μm or more (CO ₂ conversion _value) and _{C CO2,75myuemu} And the content of metal fluoride having a particle size of 75 μm or more (F-converted value) _{, and} the sum of _{CF and 75 μm} is 6.0% by mass or more (see column (7) in Table 2). 1 or coating No. 1 in Table 2. This is an example using C1 to C11. These test Nos. As shown in Table 5, T1 to T15 satisfy D ₂ / D ₁ ≦ 0.40 (no melting), and are excellent or excellent in any of the arc deflection suppressing effect and the welding workability. The result was obtained.

On the other hand, the test Nos. T16 to T19 (Comparative Examples) do not satisfy the requirements of the present invention (see column (7) in Table 2). This is an example using C12 to C15. These test Nos. As shown in Table 5, T16 to T19 did not satisfy D ₂ / D ₁ ≦ 0.40 (single melting was present), and poor results were obtained in both the arc deflection suppressing effect and the welding workability. Was done.

  As described in detail above, according to the coated arc welding rod of the present invention, by preventing one-side melting and suppressing the deflection of the arc, the droplet can be smoothly transferred, and the arc stability is good. This shows that excellent welding workability can be obtained.

1, 11 covered arc welding rod 2 core wire 2a tip 3, 13 coating agent 3a tip 4, 14 arc 5 base metal 6, 16 protective cylinder 13a tip end 13b last end d diameter of core wire in covered arc welding rod D Distance in the longitudinal direction of the welding rod between the distal end of the protective cylinder and the distal end of the core wire D1 The longitudinal direction of the welding rod between the distal end of the _single core wire and the tip of the coating agent remaining around the core wire of the cutting edge portion of the coating remaining on the periphery of the distance D ₂ core wire, the rearmost end portion of the coating remaining on the periphery of the core wire in the distance in the welding rod longitudinal direction

Claims (15)

A coated arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are the following: 6.0% by mass or more based on the total mass C _{coat, total of the} coating agent (including the case where at least one of the C _{CO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass),
On the welding rod tip side after use of the coated arc welding rod,
And the tip portion of the core wire, the leading edge portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction and D _1,
And cutting edge portions of the coating remaining on the periphery of the core wire, the rearmost end portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction is D ₂ When
The _{D 2} ratio _(D 2 / _{D 1)} is covered electrode to satisfy the 0.40 or less (including 0) for the _{D 1.} Wherein _{D 1} satisfies the following 2.2 mm, covered electrode of claim 1. 3. The covered arc welding rod according to claim ₁ , wherein a ratio (D ₁ / d) of the D ₁ to a diameter d of a core wire of the covered arc welding rod satisfies 1.3 or less. 4. A coated arc welding rod having a core wire and a coating agent for coating the core wire,
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are as follows. 6.0% by mass or more (including the case where at least one of the _{CCO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass) with _respect to _{the total} mass _{Ccoat , total of the} coating agent. Characterized covered arc welding rod. In a cross section perpendicular to the longitudinal direction of the welding rod,
The cross-sectional area of the entire coating and S _1,
When the circle equivalent diameter of at least one of the total area of said metal carbonate and said metal fluoride is 30μm or more was S _2,
The ratio of _{S 2} relative to _{S 1 (S 2 / S 1} ) is covered electrode according to claim 1, satisfying 0.06 to 0.15. The coating agent contains, as the metal carbonate, at least one selected from CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ ,
The total content of metal carbonate (CO ₂ converted value) C _{CO2, total} in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent satisfies 6.0 mass% or more and 26.0 mass% or less. The coated arc welding rod according to any one of claims 1 to 5. The coating agent contains, as the metal fluoride, at least one selected from CaF ₂ , BaF ₂ , SrF ₂ and MgF ₂ ,
The total content (F conversion value) _{CF, total} of the metal fluoride in the coating agent with respect to _{the total} mass C _{coat, total} of the coating agent is 15.0% by mass or less (including 0% by mass). The covered arc welding rod according to any one of claims 1 to 6. The coating agent contains both a metal carbonate and a metal fluoride,
In the coating agent, the total content of metal fluorides relative to the total content of metal carbonates (CO ₂ converted value) C _{CO2, total} and total content of metal fluorides (F converted value) _{CF, total} The ratio of the amount (F conversion value) _{CF, total} { _{CF, total} / ( _{CCO2, total} + _{CF, total} )} satisfies 0.10 or more and 0.30 or less. Item 2. A covered arc welding rod according to item 1. The coating agent further contains at least one of Si and a Si compound,
2. The total content of Si and the Si compound (Si conversion value) C _{Si, total with} respect to _{the total} mass C _{coat, total} of the coating agent is 6.0% by mass or more and 9.0% by mass or less. The coated arc welding rod according to any one of claims 1 to 8.   The said covered arc welding rod is used in the arc welding by the welding attitude | position which made perpendicular or a receding angle more than 0 degree and 30 degrees or less with respect to a base metal, The Claims 1-9 characterized by the above-mentioned. Covered arc welding rod. Core wire, a coating agent for coating the core wire, and a coated arc welding method using a coated arc welding rod having:
The coating agent contains at least one of a metal carbonate and a metal fluoride,
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ converted value) C _CO2 and 75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F converted value) _{CF and 75 μm} are as follows. 6.0% by mass or more (including the case where at least one of the _{CCO2 , 75 μm and} the _{CF, 75 μm} is 0% by mass) with _respect to _{the total} mass _{Ccoat , total of the} coating agent. Characterized covered arc welding method. On the welding rod tip side after use of the coated arc welding rod,
And the tip portion of the core wire, the leading edge portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction and D _1,
And cutting edge portions of the coating remaining on the periphery of the core wire, the rearmost end portion of the coating remaining on the periphery of the core wire, the distance in the welding rod longitudinal direction is D ₂ When
The _{D 2} ratio _(D 2 / _{D 1)} is arc welding so that 0.40 or less (including 0) for the _{D 1,} shielded metal arc welding method according to claim 11. Wherein _{D 1} is arc welding so as to satisfy the following 2.2 mm, shielded metal arc welding method according to claim 12. The ratio of the D ₁ to diameter d of the core wire in the covered electrode (D 1 _{/ d)} is arc welding so as to satisfy 1.3 or less, shielded metal arc welding method according to claim 12 or 13.   The covered arc welding method according to any one of claims 11 to 14, wherein the covered arc welding rod is arc-welded to the base material in a welding posture in which the base metal has a perpendicular or receding angle of more than 0 ° and 30 ° or less.

Images