JP7084261B2 - Shielded metal arc welding rod and shielded metal arc welding method - Google Patents

Description

The present invention relates to a shielded metal arc welding rod and a shielded metal arc welding method, and more specifically, it is possible to smoothly transfer droplets by suppressing arc deflection and maintaining good arc stability, which is excellent. The present invention relates to a shielded metal arc welding rod capable of obtaining welding workability, and a shielded metal arc welding method for performing arc welding using the rod.

Shielded metal arc welding is a shielded metal arc welding rod in which a metal rod (core wire) is provided with a flux called a coating agent or a protective material (sometimes referred to simply as a "welding rod" or "hand rod"). Is a welding method in which an object is joined by generating an arc between the welding rod and the base metal and melting the welding rod and the base metal with the arc heat. Shielded metal arc welding is the simplest welding method that does not require shielded gas, and can be welded outdoors in strong winds, and is widely used in various manufacturing plants, buildings, ships, vehicles, and the like.

The coating agent constituting the shielded metal 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. Shielded metal arc welding rods are classified according to the type of coating agent, and are illuminate-based, high-titanium oxide-based, lime titania-based, iron powder titanium oxide-based, high-cellulose-based, low-hydrogen-based, and iron-powder low-hydrogen-based. There are various systems such as.

Among the various types of shielded metal arc welding rods described above, as the low hydrogen-based shielded metal arc welding rod, as shown in Patent Document 1, the oxygen content in the core wire is limited and the metal carbonate in the coating agent is used. , Metal fluoride, and shielded metal arc welding rods with appropriately adjusted water content have been proposed. Patent Document 1 describes that good welding workability can be ensured without impairing the physical properties of the weld metal by appropriately adjusting the core wire of the shielded metal arc welding rod and the components in the coating agent. Has been done.

Japanese Unexamined Patent Publication No. 57-85696

However, since welding using a shielded metal arc welding rod is performed in various welding postures such as advance angle and receding angle, the coating agent in the portion close to the base metal is easily melted when the welding rod is tilted (when the welding rod is tilted). This is called one-sided melting), the arc is deflected, and the welding work deteriorates. Since the shielded metal arc welding rod described in Patent Document 1 described above does not describe anything regarding one-sided melting or arc deflection, and is specifically applied to a low hydrogen-based shielded metal arc welding rod. For all other types of shielded metal arc welding rods, it was not possible to improve the welding workability evaluated by the droplet transferability and arc stability.

INDUSTRIAL APPLICABILITY According to the present invention, shielded metal arc welding can suppress one-side melting and arc deflection, smoothly transfer droplets, and have good arc stability, whereby excellent welding workability can be obtained. The purpose is to provide a stick.

The shielded metal arc welding rod according to the present invention has the following configuration (1).
(1) A shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. It is 6.0% by mass or more with respect to the total mass C _{coat, total} of the coating agent (provided that at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%).
On the tip side of the welding rod after using the shielded metal arc welding rod,
The distance between the tip of the core wire and the tip end portion of the coating material remaining around the core wire in the longitudinal direction of the welding rod is defined as D ₁ .
The distance between the most advanced portion of the coating agent remaining around the core wire and the rearmost end portion of the coating agent remaining around the core wire in the longitudinal direction of the welding rod was defined as D ₂ . When
A shielded metal arc welding rod, wherein the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) satisfies 0.40 or less (including the case of 0).

Further, a preferred embodiment of the shielded metal arc welding rod according to the present invention has the following configuration (2) or (3).
(2) The shielded metal arc welding rod according to (1) above, wherein D ₁ satisfies 2.2 mm or less.
(3) The shielded metal arc welding rod according to (1) or (2) above, wherein the ratio (D ₁ / d) of D ₁ to the diameter d of the core wire in the shielded metal arc welding rod satisfies 1.3 or less.

Further, the shielded metal arc welding rod according to the present invention has the following configuration (4).
(4) A shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. 6.0% by mass or more based on the total mass C _{coat and total} of the coating agent (including the case where at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%). Characterized coated arc welding rod.

Further, a preferred embodiment of the shielded metal arc welding rod according to the present invention has the following configurations (5) to (10).
(5) In the cross section perpendicular to the longitudinal direction of the welding rod
Let S ₁ be the cross-sectional area of the entire coating agent.
When the total area of at least one of the metal carbonate and the metal fluoride having a circle equivalent diameter of 30 μm or more is S ₂ .
The shielded metal arc welding rod according to any one of (1) to (4) above, wherein the ratio of S ₂ to S ₁ (S ₂ / S ₁ ) satisfies 0.06 or more and 0.15 or less.
(6) The coating agent contains at least one selected from CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ as the metal carbonate.
The total content of metal carbonate (CO ₂ conversion value) C _{CO2, total} in the coating agent with respect to the total mass C _{coat, total} of the coating agent satisfies 6.0% by mass or more and 26.0% by mass or less. , The shielded metal arc welding rod according to any one of (1) to (5) above.
(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 shielded metal arc welding rod according to any one of (1) to (6) above.
(8) The coating agent contains both a metal carbonate and a metal fluoride, and contains.
The total content of metal fluoride in the coating agent relative to the total content of metal carbonate (CO ₂ conversion value) C _{CO2, total} and the total content of metal fluoride (F conversion value) _{CF, total} . Amount (F conversion value) _{CF, total} ratio { _{CF, total} / (C _{CO2, total} + _{CF, total} )} satisfies 0.10 or more and 0.30 or less, (1) to (7) above. The coated arc welding rod according to any one of the above.
(9) The coating agent further contains at least one of Si and a Si compound.
The total content (Si conversion value) C _{Si, total} of the Si and the Si compound 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, as described above (1). )-(8). The shielded metal arc welding rod according to any one of (8).
(10) The above-mentioned (1) to (9), wherein the shielded metal arc welding rod is used in arc welding in a welding posture perpendicular to the base metal or with a receding angle of more than 0 ° and 30 ° or less. The shielded metal arc welding rod according to any one.

Further, the shielded metal arc welding method according to the present invention has the following configuration (11).
(11) A shielded metal arc welding method using a shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. 6.0% by mass or more based on the total mass C _{coat and total} of the coating agent (including the case where at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%). A featured coated arc welding method.

Further, a preferred embodiment of the shielded metal arc welding method according to the present invention comprises the following configurations (12) to (15).
(12) On the tip side of the welding rod after using the shielded metal arc welding rod
The distance between the tip of the core wire and the tip end portion of the coating material remaining around the core wire in the longitudinal direction of the welding rod is defined as D ₁ .
The distance between the most advanced portion of the coating agent remaining around the core wire and the rearmost end portion of the coating agent remaining around the core wire in the longitudinal direction of the welding rod was defined as D ₂ . When
The shielded metal arc welding method according to (11) above, wherein arc welding is performed so that the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) is 0.40 or less (including the case of 0).
(13) The shielded metal arc welding method according to (12) above, wherein arc welding is performed so that D ₁ satisfies 2.2 mm or less.
(14) The above-mentioned (12) or (13), wherein the arc welding is performed so that the ratio (D ₁ / d) of the D ₁ to the diameter d of the core wire in the shielded metal arc welding rod satisfies 1.3 or less. Shielded metal arc welding method.
(15) The above-mentioned one of (11) to (14), wherein the shielded metal arc welding rod is arc-welded vertically or in a welding posture with a receding angle of more than 0 ° and 30 ° or less with respect to the base metal. Shielded metal arc welding method.

According to the present invention, among at least one kind of particles selected from the metal carbonate and the metal fluoride contained in the coating agent, a predetermined amount of particles having a suitable size is contained by controlling the particle size. As a result, the coating material melts uniformly, so that the protective cylinder is uniformly formed during welding, preventing one-sided melting and suppressing arc deflection. As a result, the arc stability is better. Thereby, it is possible to provide a shielded metal arc welding rod and a shielded metal arc welding method capable of obtaining excellent welding workability even for a shielded metal arc welding rod of any system.

FIG. 1A is a cross-sectional view showing a state of a shielded metal arc welding rod when the deflection of the arc is suppressed during welding. FIG. 1B is a cross-sectional view showing a state of a shielded metal arc welding rod when an arc deflection is remarkably generated during welding.

Hereinafter, embodiments of the present invention will be described in detail. 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. Diligent studies were conducted to obtain a shielded metal arc welding rod. As a result, it was found that it is effective to adjust the particles of the metal carbonate or the metal fluoride so as to contain a predetermined amount of the particles having a large size.

First, the effect (that is, the action effect) of the particle size (that is, the coarseness of the particle size) of the metal carbonate or the metal fluoride on the droplet transfer will be described in detail below.

We also influence the particle size of metal carbonates and metal fluorides on the shape of the protective tube formed during arc welding, thereby preserving arc directivity, i.e. arc deflection. It was found that good arc stability can be obtained by suppressing the above.
That is, if a metal carbonate or metal fluoride having a large particle size is contained in the coating material, the specific surface area becomes small and the coating material becomes difficult to melt. Therefore, the coating material melts uniformly during arc welding. The protective cylinder is uniformly formed during welding (see the contents below for details). Therefore, by maintaining the arc directivity, the arc stability becomes better.

Further, metal carbonate and metal fluoride are components that can be contained as a gas generating agent in the coating agent, and are shielded gas when an arc is generated between the coated arc welding rod as an electrode and the welding base material. Plays a role in preventing the invasion of weld metals such as oxygen and nitrogen in the atmosphere.
When the particle size of the metal carbonate or metal fluoride contained in the coating agent is adjusted to be large, the one with a large particle size is completely gas at the tip of the shielded metal arc welding rod (the arc generation point on the welding rod side). It will stay in one place until it becomes a metal. Due to this retention in one place, gas is intensively generated in one direction (direction of the molten core wire), and the volume expansion of the gas affects the formation of a constriction of droplets. Therefore, the shearing force for releasing the droplets such as the electromagnetic pinch force and the surface tension works efficiently, and the droplets can be separated in the state of small particles. Further, since the droplets are separated while keeping the release cycle stable, the arc stability is improved and excellent welding workability can be obtained.

On the other hand, when the particle size of the metal carbonate or the metal fluoride is small, the amount of gas generated is small, so that a small volume of gas is generated and the gas generation direction is not determined in one direction, so that the metal carbonate 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 droplets is also small.

Hereinafter, regarding the shielded metal arc welding rod according to the embodiment of the present invention, the particle size of the gas generating agent contained in the coating agent, the area ratio of the cross section in the longitudinal direction of the welding rod, the reason for adding other components, the reason for limiting numerical values, etc. Will be explained in detail.

The shielded metal arc welding rod according to this embodiment is
A shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. It is 6.0% by mass or more with respect to the total mass C _{coat, total} of the coating agent (provided that at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%).
On the tip side of the welding rod after using the shielded metal arc welding rod,
The distance between the tip of the core wire and the tip end portion of the coating material remaining around the core wire in the longitudinal direction of the welding rod is defined as D ₁ .
The distance between the most advanced portion of the coating agent remaining around the core wire and the rearmost end portion of the coating agent remaining around the core wire in the longitudinal direction of the welding rod was defined as D ₂ . When
The ratio of D ₂ to D ₁ (D ₂ / D ₁ ) satisfies 0.40 or less (including the case of 0).

[Coating agent]
First, the details of the coating agent will be described below.

<Content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and metal fluoride having a particle size of 75 μm or more with respect to the total mass C _{coat and total} of the coating agent. Content (F conversion value) CF, total _{of 75 μm} : 6.0% by mass or more>
Increasing the particle size of the metal carbonate or metal fluoride contained in the coating agent promotes the formation of a constriction of droplets during arc welding as described above, and smooth droplet transfer can be realized. Further, the coating material is uniformly melted during arc welding, so that the protective cylinder is uniformly formed during welding. Therefore, the deflection of the arc is suppressed and the arc directivity is maintained, so that the arc stability becomes better.

If the coating contains a metal carbonate having a particle size of 75 μm or more, or a metal fluoride having a particle size of 75 μm or more is contained in the coating, smooth droplets as described above are contained. The effects of migration and good arc stability can be obtained. However, since the content of a metal carbonate having a particle size of a predetermined value or more and a metal fluoride having a particle size of a predetermined value or more can affect smooth droplet transfer and arc stability, the shielded metal arc welding according to the present embodiment. 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 conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} If it is 6.0% by mass or more with respect to the total mass of the coating material, _{Ccoat, total} , the droplets can be smoothly transferred, the arc stability is good, and the welding workability is improved. The effect of making it can be sufficiently obtained.
However, the case where at least one of the above C _{CO 2,75} μm and _{CF, 75 μm} is 0% by mass is included.

The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} If it is too large for the total mass of the coating agent, _{Ccoat, total} , there is a concern that spatter may increase and the coating property may be affected in the manufacturing process. Therefore, the content should be 15.0% by mass or less. It is preferably present, and more preferably 12.0% by mass or less.

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

In order to further sufficiently obtain the effects of the above-mentioned smooth droplet transfer and good arc stability, the particle size is C CO _2,150 μm, which is the content of metal carbonate having a particle size of 150 μm or more (CO ₂ conversion value). The total content of the metal fluoride content (F conversion value) of 150 μm or more, _{CF, 150 μm} is preferably 2.5% by mass or more, preferably 3.0% by mass, based on the total mass of the coating material, _{Ccoat, total} . More preferably, it is by mass or more.
Further, the above value is preferably 5.0% by mass or less, preferably 4.0% by mass or less, because there is a concern that the above-mentioned spatter increases and the coating property is affected in the manufacturing process. It is more preferable to have.

The metal carbonate and the metal fluoride may be contained in at least one kind, but may be contained in both. Further, the "particle size" described in this embodiment is measured by using a measuring method according to JIS Z 8801-2006.
The particle size (particle size) of the metal carbonate and the metal fluoride contained in the coating agent is generally about 600 μm at the maximum.

<Ratio of D ₂ to D ₁ (D ₂ / D ₁ ): 0.40 or less (including the case of 0)>
As mentioned above, the particle size of metal carbonate and metal fluoride also affects the shape of the protective tube after arc welding. That is, by defining the particle size of the metal carbonate and the metal fluoride and the content thereof, the protective cylinder after arc welding can be formed in a good shape. As a result, the arc directivity becomes even better, and the arc stability is improved.

Here, the state of the shielded metal arc welding rod in the case where arc welding is performed using two types of shielded metal arc welding rods will be described with reference to the drawings. In FIGS. 1A and 1B, the same objects are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1A is a cross-sectional view showing a state of a shielded metal arc welding rod when the deflection of the arc is suppressed during welding. As shown in FIG. 1A, the shielded metal arc welding rod 1 has a core wire 2 and a coating agent 3 that coats the core wire 2. The coating agent 3 contains at least one compound selected from metal carbonates and metal fluorides. Then, the total of the content of the metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of the metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} , 6.0% by mass or more with respect to the total mass C _{coat, total} of the coating agent (however, including the case where at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%). The components of the coating agent 3 are specified in the above.

When arc welding is performed on the base metal 5 using the shielded metal arc welding rod 1, a specific compound contained in the coating agent 3 (that is, at least one selected from metal carbonate and metal fluoride). Since the particle size and the total content thereof are limited as described above, the specific surface area of the compound becomes smaller, and as a result, it protrudes from the coating material 3, strictly speaking, the tip portion 2a of the core wire 2. Melting or softening of the protective cylinder 6 which is a part of the coating agent 3 which is a portion is difficult to proceed, and the protective cylinder 6 is likely to remain during arc welding.
Therefore, the one-sided melting of the coating agent 3 is suppressed, and the coating agent 3 melts uniformly over the entire circumferential direction of the shielded metal arc welding rod 1. As a result, during or after welding, the space surrounded by the inner peripheral surface of the protective cylinder 6 approaches a uniform conical shape in the cross-sectional view of the shielded metal arc welding rod. As a result, the distance D in the longitudinal direction of the welding rod between the tip 3a of the protective cylinder 6 and the tip 2a of the core wire 2 has almost the same length regardless of the position, and there is little variation. Therefore, the fluctuation of the arc 4 is suppressed during welding, the arc directivity becomes good, and the arc stability is improved.

Further, as will be described later, when both the metal carbonate and the metal fluoride are contained in the coating agent 3, the total content of the metal carbonate contained in the coating agent 3 (CO ₂ conversion value) C _CO2 . _{, Total} and total metal fluoride content (F conversion value) _{CF, total} of metal fluoride content (F conversion value) _{CF, total} ratio { _{CF, total} / (C _CO2 ) _{, Total} + _{CF, total} )}, the softening point of the coating material 3 can be increased, so that the shape of the protective cylinder 6 can be uniformly maintained up to an appropriate length. The protective cylinder 6 serves as a guide to enhance the directivity of the arc. As a result, the fluctuation (wobble) of the droplets 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 a state of the shielded metal arc welding rod when the deflection of the arc is remarkably generated during welding. As shown in FIG. 1B, when arc welding is performed using a shielded metal arc welding rod 11 having a coating agent 13 in which the particle sizes and contents of the metal carbonate and the metal fluoride are not adjusted as described above. The distance between the most advanced portion 13a and the rearmost end portion 13b of the coating material 13 (protection cylinder 16) remaining after welding varies from the tip portion 2a of the core wire 2. As a result, the deflection of the arc 14 is remarkably generated during welding, so that the arc stability is lowered.

In the present embodiment, variations in the lengths (or the lengths of the protective cylinders 6 and 16) of the coating agents 3 and 13 remaining around the core wire 2 after the use of the shielded metal arc welding rod are specified. do. Therefore, a method for quantifying the variation will be described in detail with reference to FIG. 1B.

As shown in FIG. 1B, on the tip end side of the welding rod (lower side of the shielded metal arc welding rod 11 in FIG. 1B) after using the shielded metal arc welding rod, around the tip portion 2a of the core wire 2 and around the core wire 2. The distance from the cutting edge 13a of the remaining coating material 13 in the longitudinal direction of the welding rod (vertical direction in FIG. 1B) is set to D ₁ , and the cutting edge of the coating material 13 remaining around the core wire 2. Let D2 be the distance between the portion 13a and the rearmost end portion 13b of the coating material 13 remaining around the core wire ₂ in the longitudinal direction of the welding rod.

When the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) satisfies 0.40 or less, it means that the protective cylinder 16 having little variation in length is formed in a good shape. When this requirement is met, arc directivity is obtained and arc stability is improved. The ratio of D ₂ to D ₁ (D ₂ / D ₁ ) is preferably 0.30 or less, more preferably 0.25 or less, and most preferably 0.

Here, the term "after the use of the shielded metal arc welding rod (that is, after the end of arc welding)" means a state in which the coating agent remains after a continuous arc generation period of 5 seconds or more has passed after the start of arc welding.
In general, a shielded metal arc welding rod may be used repeatedly even after it has been used once, as long as the coating material remains.
After using the shielded metal arc welding rod, slag may adhere to the tip of the core wire 2, but in the present embodiment, the tip portion 2a of the core wire 2 is defined with the slag removed, and its shape is defined. Is substantially flat.
Further, the "state-of-the-art portion" described in the present embodiment means the most protruding portion of the tips of the coating agents 3 and 13, and the "rearmost end portion" is the tip of the coating agents 3 and 13. Of these, the part that does not protrude the most.

<D ₁ : 2.2 mm or less>
On the tip end side of the welding rod after the use of the shielded metal arc welding rod, it is preferable that the coating agent 13 remains around the core wire 2 with a length of a certain length or more and the protective cylinder 16 is formed. However, when the distance D1 in the longitudinal direction of the welding rod between the tip portion 2a of the core wire 2 and the tip portion 13a of the coating material 13 remaining around the core wire ₂ exceeds 2.2 mm, the protective cylinder 16 The effect is that the core wire becomes excessively long, the distance between the core wire and the base metal increases, and the arc length becomes long. If this arc length becomes excessively long, the arc length tends to fluctuate, causing arc breakage and deterioration of arc stability. As a result, the appearance of the bead may be deteriorated, spatter may be increased, and the welding workability may be deteriorated. Therefore, the D ₁ is preferably 2.2 mm or less, and more preferably 1.7 mm or less. If the above D ₁ is extremely small, the directivity of the arc cannot be obtained and the arc stability deteriorates. Therefore, the D ₁ is preferably 1.0 mm or more, preferably 1.3 mm or more. More preferred.

<Ratio of D ₁ to the diameter d of the core wire in the shielded metal arc welding rod (D ₁ / d): 1.3 or less>
Generally, the diameter d of the core wire in the shielded metal arc welding rod (see d in FIG. _1B ) and the above D1 are in a proportional relationship. In order to maintain good arc stability, D ₁ / d is preferably 1.3 or less, more preferably 1.0 or less, and even more preferably 0.8 or less. Further, 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 is 0. It is more preferable that the value is 3 or more.
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 to S ₁ (S ₂ / S ₁ ): 0.06 or more and 0.15 or less>
The present embodiment described above is smooth by defining that a predetermined amount of particles having a large particle size is contained among at least one particle selected from the metal carbonate and the metal fluoride contained in the coating agent. Achieves good droplet migration and good arc stability.
On the other hand, in the present embodiment, the following is adopted as another regulation method for realizing these performances. Specifically, in the shielded metal arc welding rod, the cross-sectional area of the entire coating agent is S1 in the cross section perpendicular to the longitudinal direction of the welding rod, and at _least among the metal carbonates and metal fluorides having a circle equivalent diameter of 30 μm or more. When the total area of one type is S ₂ , the ratio of S ₂ to S ₁ (S ₂ / S ₁ ) is 0.06 or more and 0.15 or less.

When the ratio of S ₂ to S ₁ (S ₂ / S ₁ ) is 0.06 or more, the effect of promoting the detachment of droplets appears more remarkably, and smoother droplet migration can be realized. Therefore, the above S ₂ / S ₁ is preferably 0.06 or more, and more preferably 0.07 or more.
On the other hand, when the S ₂ / S ₁ is 0.15 or less, it becomes easy to obtain a weld metal having desired performance. Therefore, the above S ₂ / S ₁ is 0.15 or less, more preferably 0.10 or less.

The above effect can be obtained even if only the metal fluoride having a circle equivalent 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. Further, it is most preferable that both the metal carbonate and the metal fluoride are contained in the above range.

As a method of controlling the above 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 which is the raw material of the coating agent, the content of the metal carbonate or the metal fluoride is adjusted. There is a method of adjusting the coating pressure of the coating agent at the time of manufacturing the shielded metal arc welding rod. Then, the above S2 _/ S1 can be controlled by these _alone or in combination. However, the above manufacturing method is merely an example, and is not necessarily limited to these.

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

Here, the above S ₂ / S ₁ can be measured, for example, as follows. First, a welding rod cross section is analyzed using a WD / ED combine electron probe microanalyzer (EPMA) JXA-8200 manufactured by JEOL Ltd. 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, the region of at least one of the metal carbonate and the metal fluoride having a circle equivalent diameter of 30 μm or more and the other region are binar to the entire cross section of the welding rod. To 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 a circle equivalent diameter of 30 μm or more with respect to the cross-sectional area S ₁ of the entire coating agent is calculated. be able to.

<Total content of metal carbonate in the coating agent (CO ₂ conversion value) with respect to the total mass C _{coat and total} of the coating agent C _{CO2, total} : 6.0% by mass or more and 26.0% by mass or less>
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 shield gas (shielding gas) by thermal decomposition near the arc generation point, and oxygen in the atmosphere. It is a component that has the effect of protecting the molten pool from nitrogen and moisture. For example, CaCO ₃ decomposes at about 825 ° C to generate CaO and CO ₂ gas. If the content of metal carbonate in the coating agent is too low, poor shielding causes air entrainment, resulting in deterioration of welding workability, welding defects such as blow holes, and a decrease in the impact value of the weld metal. It causes.
On the other hand, if the total content of the metal carbonate in the coating agent is excessive, it becomes difficult for the coating material to melt during welding. That is, since the distance of D1 described above becomes long, the distance between the melting interface of the core wire and the molten pool becomes excessively large, and the arc length deviates from the appropriate condition. As a result, arc breakage may occur, arc stability may decrease, and spatter may increase.
Further, as described above, the droplet migration cycle can be stabilized by containing a metal carbonate having a predetermined size or more.

When the total content of metal carbonate in the coating agent (CO ₂ conversion value) C _{CO2 and total} with respect to the total mass C _{coat and total} of the coating agent is 6.0% by mass or more, these effects should be sufficiently obtained. Can be done. Therefore, the content C _{CO2 and total} of the metal carbonate is preferably 6.0% by mass or more in terms of _CO2 conversion value, and more preferably 10.0% by mass or more.
On the other hand, when the total content of metal carbonate (CO ₂ conversion value) C _{CO2 and total} with respect to the total mass C _{coat and total} of the coating agent is 26.0% by mass or less, the arc stability is more stable. It is improved and the amount of spatter generated is reduced. Therefore, the content C _{CO2 and total} of the metal carbonate is preferably 26.0% by mass or less in terms of _CO2 conversion value, and more preferably 25.0% by mass or less.
For the same reason as above, the total content of metal carbonate in the shielded metal arc welding rod (CO ₂ conversion value) with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod is 4.0% by 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, and 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 ). It is preferably at least one selected. 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 . The above-mentioned various metal carbonates may be used alone or in combination of two or more, but when a plurality of metal carbonates are used, the total content of the CO ₂ conversion value is 6.0% by mass. It is preferable that the content is within the range of 26.0% by mass or less.

When CaCO ₃ is contained in the coating as a metal carbonate, the content of CaCO ₃ in the coating 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. % Or less, more preferably 10.0% by mass or more and 25.0% by mass or less.
The content of CaCO ₃ in the shielded metal arc welding rod is preferably 10.0% by mass or more and 20.0% by mass or less, and 11.0% by mass or more, 19.0 per total mass of the welding rod. It is more preferably 11.0% by mass or more and 17.0% by mass or less, more preferably 11.0% by mass or less.

Further, when BaCO ₃ is contained in the coating as a metal carbonate, the content of BaCO ₃ in the coating is 0 in terms of CO ₂ conversion with respect to the total mass of the coating from the viewpoint of welding workability. It is preferably more than 9.0% by mass and less than 4.0% by mass.

<Total content of 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 and total} of the coating agent>
The metal fluoride such as CaF ₂ contained in the coating agent of the shielded metal 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, metal fluoride decomposes due to arc heat to generate a large amount of reducing shielding gas (fluorine gas), thereby suppressing an increase in the amount of oxygen and hydrogen in the weld metal and improving 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 hydrogen in the molten metal and molten slag, and the hydrogen partial pressure in the molten metal can be lowered, so that the weld metal can be reduced in hydrogen. You can also. Furthermore, as described above, the inclusion of a metal fluoride having a size equal to or larger than a predetermined value in the coating agent can improve the droplet transferability. However, if the content of the metal fluoride in the coating material is excessive, the fluidity of the slag becomes excessive, problems such as slag entrainment occur, and the welding quality may deteriorate.

Since the coating agent does not necessarily 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 metal fluoride, and the content thereof is preferably more than 0.0% by mass, preferably 3.0% by mass or more. More preferred.
On the other hand, when the total content of metal fluoride (F conversion value) _{CF, total} in the coating is 15.0% by mass or less with respect to the total mass C _{coat, total} of the coating, better arc stability is achieved. Can be 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 above, the total content of metal fluoride (F conversion value) in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod is 0.5% by mass or more, 2 It is preferably 0.7% by mass or less, more preferably 0.7% by mass or more and 2.5% by mass or less, and further 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 ). It is preferable that it is at least one kind. 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 . The above-mentioned various metal fluorides may be used alone or in combination of two or more, but when a plurality of metal fluorides are used, the total content of the F conversion value is 15.0% by mass or less. It is preferable that the content is within the range of (including 0% by mass).

When CaF ₂ is contained in the coating as a metal fluoride, the content of CaF ₂ in the coating 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. % Or less, more preferably 3.0% by mass or more and 7.5% by mass or less.
The content of CaF ₂ in the shielded metal arc welding rod is preferably 1.0% by mass or more and 6.0% by mass or less, and 1.5% by mass or more and 5.5% by mass, based on the total mass of the welding rod. It is more preferably mass% or less, and further preferably 1.8 mass% or more and 5.2 mass% or less.

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

When the above ratio { _{CF, total} / (C _{CO2, 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 sufficient. It can be left in the length, and the welding workability is improved. Therefore, the above ratio is preferably 0.10 or more. The ratio is preferably 0.30 or less, and more preferably 0.15 or less.

<Total content of Si and Si compounds in the coating agent (Si conversion value) C _{Si, total} : 6.0% by mass or more and 9.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Si and the Si compound are compounds that act as a catalyst in SiO ₂ in the coating agent and promote the decomposition of the metal carbonate (CaCO ₃ ). For example, CaCO ₃ produces 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 amount of CO ₂ gas generated per hour increases, and the pinch force works efficiently, which promotes the formation of a constriction of droplets.
Further, when CaCO ₃ is thermally decomposed, CaO generated thereby reacts with SiO ₂ , 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 fluoride gas. For example, 2CaF ₂ and SiO ₂ react to generate 2CaO and SiF ₄ gas. However, since the SiF ₄ gas generated by this reaction has a smaller volume than the CO ₂ gas produced by the metal carbonate using SiO ₂ as a catalyst, the action of releasing the droplets 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 a circle equivalent diameter of 30 μm or more in the cross section perpendicular to the longitudinal direction of the welding rod. It defines the total area of the metal fluoride, which means that a metal fluoride having a large particle size is contained in the coating agent. As a result, the amount of gas generated is increased and the formation of a constriction of droplets is promoted.
Further, the following effects can be obtained by containing a metal fluoride having a large particle size in the coating agent. 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 remarkable 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 that acts as a catalyst for the metal carbonate, and to promote smoother detachment of droplets. can.

When the coating agent further contains at least one of Si and the Si compound, the total content of Si and the Si compound in the coating agent (Si conversion value) with respect to the total mass _{Ccoat and total} of the coating agent C _Si . _{When the total} is 6.0% by mass or more, the generation of CO ₂ gas and fluorinated gas can be further promoted. Therefore, the C _{Si and total} are preferably 6.0% by mass or more.
On the other hand, when the C _{Si and total} are 9.0% by 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 and total} are preferably 9.0% by mass or less, and more preferably 8.0% by mass or less.

Subsequently, the coating agent according to the present embodiment may contain alloys, oxides and the like in addition to the above-mentioned metal carbonates, metal fluorides, Si and Si compounds. 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 shielded metal arc welding rod is defined as the content per total mass of the welding rod.

<Fe in the coating agent: 0.0% by mass or more (including 0% by mass), 35.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Fe is a component added to a coating agent for a coated arc welding rod for the purpose of improving the mechanical properties of the weld metal by deoxidizing action and adding an alloy, and improving the welding efficiency by increasing the amount of metal welded, and is coated. In addition to being contained as iron powder in the agent, it is also contained as Fe—Si, Fe—Mn and the like. Fe in the coating agent may be arbitrarily added according to the necessity of the above effect, and it is not necessary to specify a lower limit, and it may be 0.0% by mass or more. However, when considering further improvement in 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, by setting Fe in the coating agent to 35.0% by mass or less, the size of the droplets transferred to the molten pool can be reduced, and the welding workability is further improved.
Therefore, the lower limit of the Fe content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is more preferably 0.1% by mass or more. Further, the upper limit of the Fe content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 35.0% by mass or less, preferably 32.0% by mass or less, based on the total mass of the coating agent. More preferably, it is more preferably 30.0% by mass or less.
For the same reason as above, the Fe content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod is 60.0% by mass or more and 85.0% by mass or less. It is more preferably 70.0% by mass or more and 85.0% by mass or less, and further preferably 72.0% by mass or more and 85.0% by mass or less.

<Al in the coating agent: 0.0% by mass or more (including 0% by mass), 1.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Al (metal Al) is a component that has the effect of improving the crack resistance of the weld metal and also the corrosion resistance and oxidation resistance, and may be added as needed, and it is necessary to specify a lower limit in particular. However, it may be 0.0% by mass or more. When Al is added to the coating agent, if the Al content in the coating agent is 1.0% by mass or less, in addition to the above effects, the weld metal can obtain sufficient ductility.
Therefore, the Al content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and 0.6. It is more preferably mass% or less.
For the same reason as above, the Al content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod may be 0.50% by mass or less (including 0% by mass). It is more preferably 0.30% by mass or less, and even 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 with respect to the total mass C _{coat and 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 it is not necessary to specify a lower limit, and it may be 0.0% by mass or more. When Ni is added to the coating agent, if the Ni content in the coating agent is 4.0% by mass or less, high-temperature cracking of the weld metal can be further suppressed. Therefore, the Ni content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 4.0% by mass or less, and is 3.0% by mass or less and 2.5% by mass or less. Is more preferable.
For the same reason as described above, the Ni content in the shielded metal arc welding rod with respect to the total mass _{Electrode and total} of the shielded metal arc welding rod is preferably 1.00% by mass or less, preferably 0.60% by mass. It is more preferably less than or equal to, and even more preferably 0.30% by mass or less.

<Mn in the coating agent: 1.5% by mass or more and 6.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Mn is a component having an effect of improving the strength of the alloy material, and may be added as needed. It is not necessary to specify a 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, high-temperature cracking can be suppressed while maintaining the strength of the weld metal. Therefore, the Mn content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 1.5% by mass or more and 6.0% by mass or less, and 1.7% by mass or more and 4. It 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 above, the Mn content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod may be 0.8% by mass or more and 1.8% by mass or less. It is more preferably 0.8% by mass or more and 1.6% by mass or less, and further preferably 0.8% by mass or more and 1.4% by mass or less.

<Si in the coating agent: 1.0% by mass or more and 9.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Si (metal Si) is a deoxidizing agent and is a component having an effect of reducing the oxygen content and improving the strength of the weld metal. It may be added as needed, and it is not necessary to specify a lower limit. It may be 0% by 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 transferred 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 and 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. It is more preferably 0% by mass or less, and further preferably 2.8% by mass or more and 6.6% by mass or less.
For the same reason as above, the Si content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod may be 0.8% by mass or more and 2.2% by mass or less. It is more preferably 1.0% by mass or more and 2.0% by mass or less, and further preferably 1.1% by mass or more and 1.9% by mass or less.

<Mo in the coating agent: 0.0% by mass or more (including 0% by mass), 2.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
Mo is a component having an effect of improving the strength of the weld metal, and may be added as needed. It is not necessary to specify a lower limit, and Mo may be 0.0% by mass or more. When Mo is added to the coating agent, if the Mo content in the coating agent is 2.0% by mass or less, welding cracking can be further suppressed while maintaining the strength. Therefore, the Mo content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 2.0% by mass or less, more preferably 1.2% by mass or less, and 0.8. It is more preferably mass% or less.
For the same reason as above, the Mo content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod may be 0.65% by mass or less (including 0% by mass). It is more preferably 0.45% by mass or less, and even more preferably 0.30% by mass or less.

<Al ₂ O ₃ : 0.02% by mass or more and 3.0% by mass or less in the coating agent with respect to 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 _Al2O3 content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 0.02% by mass or more and 3.0% by mass or less, preferably 0.03% by mass or more. It is more preferably 2.6% by mass or less, and further preferably 0.05% by mass or more and 2.0% by mass or less.
For the same reason as above, the _Al2O3 content in the _shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod is 0.01% by mass or more and 0.90% by mass or less. It is preferably 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 : 1.5% by mass or more and 15.0% by mass or less in the coating with respect to the total mass C _{coat and total} of the coating>
SiO ₂ is a component that acts as a slag-forming agent or an adhesive. When SiO ₂ in the coating agent is 1.5% by mass or more, the above-mentioned effect can be sufficiently obtained. Further, when the SiO ₂ in the coating agent is 15.0% by mass or less, the slag peelability is further improved. Therefore, the SiO ₂ content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 1.5% by mass or more and 15.0% by mass or less, and 2.0% by mass or more and 10% by mass. It is more preferably 9.0% by mass or less, and further preferably 4.0% by mass or more and 8.0% by mass or less.
For the same reason as above, the content of SiO ₂ in the shielded metal arc welding rod with respect to the total mass _{Selectrode and total} of the shielded metal arc welding rod is 0.40% by mass or more and 4.00 per mass of the shielded metal arc welding rod. It is preferably 0% by mass or less, more preferably 0.60% by mass or more and 3.60% by mass or less, and further preferably 0.80% by mass or more and 3.20% by mass or less.

<TiO ₂ : 0.2% by mass or more and 10.0% by mass or less in the coating agent with respect to the total mass C _{coat and total} of the coating agent>
TiO ₂ is a component having the effect of producing slag with good fluidity, giving gloss to the bead surface, and giving a beautiful appearance to the weld metal in a coating agent for a shielded metal arc welding rod. It is also a component that suppresses the deflection (wobble) of the arc and contributes to obtaining good welding workability. When the TiO ₂ content in the coating agent 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 agent, the above effect is further improved. Therefore, the TiO ₂ content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 0.2% by mass or more and 10.0% by mass or less, and 0.5% by mass or more, 8 It is more preferably 0.0% by mass or less, and further preferably 1.0% by mass or more and 6.0% by mass or less.
For the same reason as above, the TiO ₂ content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod shall be 1.00% by mass or more and 4.00% by mass or less. It is more preferably 1.20% by mass or more and 3.00% by mass or less, and further preferably 1.40% by mass or more and 2.60% by mass or less.

<MgO in the coating agent: more than 0.01% by mass and 4.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
MgO is a component having an effect of enhancing the peelability of slag. When the MgO content in the coating agent is more than 0.01% by mass and 4.0% by mass or less, the above effect is further improved. Therefore, the MgO content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably more than 0.01% by mass and 4.0% by mass or less, and is 0.2% by mass or more and 1. It is more preferably 0% by mass or less, and further preferably 0.5% by mass or more and 0.8% by mass or less.
For the same reason as above, the MgO content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod is 0.01% by mass or more and 1.00% by mass or less. It is more preferably 0.01% by mass or more and 0.80% by mass or less, and further preferably 0.01% by mass or more and 0.50% by mass or less.

<Total content of K ₂ O, Li ₂ O and Na ₂ O in the coating agent with respect to _{the total mass C coat and 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 abundantly contained in water glass used as an inorganic binder for coating agents, and are also added as a powder raw material, and have high-quality arc stability and moderateness. It is an effective component for improving arc stability by obtaining a stable arc spraying force. In order to further enhance the above effect, the total content of K ₂ O, Li ₂ O and Na ₂ O in the coating agent with respect to _{the total mass C coat and total} of the coating agent is 1.6% by mass or more. It is preferably 6% by mass or less, more preferably 1.8% by mass or more and 3.2% by mass or less, and further preferably 2.0% by mass or more and 3.0% by mass or less.
For the same reason as above, the total content of K ₂ O, Li ₂ O and Na ₂ O in the shielded metal arc welding rod is 0.20% by mass with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod. As mentioned above, it is preferably 1.40% by mass or less, more preferably 0.40% by mass or more and 1.20% by mass or less, and more preferably 0.60% by mass or more and 1.00% by mass or less. Is more preferable.
Li ₂ O also has the effect of improving the moisture absorption resistance of the shielded metal arc welding rod and reducing the diffusible hydrogen in the weld metal.

<C in the coating agent: 0.0% by mass or more (including 0% by mass), 0.15% by mass or less with respect to the total mass C _{coat and total} of the coating agent>
C is a component that contributes to improving the strength of the weld metal, and may be added as needed. It is not necessary to specify a lower limit, and C may be 0.0% by mass or more. When C is added to the coating agent, it is preferably 0.15% by mass or less in order to reduce the ductility of the weld metal and suppress welding cracks. Therefore, the C content in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 0.0% by mass or more and 0.15% by mass or less. Further, from the viewpoint of improving welding workability, 0.01% by mass or more and 0.10% by mass or less are more preferable, and 0.02% by mass or more and 0.08% by mass or less are further preferable. Examples of the C source include organic substances, various minerals, alloying agents, graphite and the like.
For the same reason as above, the C content in the shielded metal arc welding rod with respect to the total mass _{Selectrod and total} of the shielded metal arc welding rod may be 0.15% by mass or less (including 0% by mass). It is more preferably 0.01% by mass or more and 0.10% by mass or less, and further preferably 0.02% by mass or more and 0.08% by mass or less.

<Remaining>
The rest of the coating in this embodiment is an unavoidable impurity. Examples of unavoidable impurities include Nb ₂ O ₅ , V ₂ O ₅ , ZrO ₂ , Fe ₂ O ₃ · FeO, SnO, P, S and the like. Further, the total content of unavoidable impurities in the coating agent with respect to _{the total mass C coat and total} of the coating agent is preferably 5.0% by mass or less (including 0% by mass). Further, Nb ₂ O ₅ in the coating agent is 0.3% by mass or less (including 0% by mass) and V ₂ O ₅ is 0.3% by mass or less (0 mass%) with respect to the total mass C _{coat and total} of the coating agent. %), ZrO ₂ is limited to 0.4% by mass or less (including 0% by mass), and Fe _{2O 3}・ FeO is limited to 3.50% by mass or less (including 0% by mass). preferable. Impurities include those unintended in the design of the welding rod. For example, in an illuminant-based shielded metal arc welding rod, since the illuminant raw material is added to the coating agent, Fe ₂ O ₃ and FeO unintended in the design of the welding rod may be contained in a maximum of 3.50% by mass. There are, but these are impurities.

Next, the core wire and the coverage will be described.

[Core line]
The core wire in the present embodiment is not particularly limited, but for example, one having a diameter d of 2.6 mm to 6.0 mm can be used, and in particular, one having a diameter of 4.0 mm can be preferably used. The composition of the core wire of this embodiment will be described below.

<O: 0.0005% by mass or more, 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 decrease. In addition, oxygen in the core wire reacts with Fe-Si and Fe-Mn, which are deoxidizers added to the coating agent, to generate slag, which increases the amount of slag and improves slag fluidity and welding workability. There is a risk of deterioration, and further deterioration of mechanical properties due to a decrease in the amount of Si and Mn of the weld metal and an increase in the amount of oxygen.
In addition, the fluidity of the molten metal becomes high, and when welding is performed in an upright or upward posture, the weld metal tends to drip down, which may reduce welding workability. On the other hand, if the O content of the core wire is too small, the sales expansion of the molten pool by the arc force becomes insufficient, and the weld metal in which the alloy component is uniformly distributed cannot be obtained.
From the above viewpoint, the O content of the core wire with respect to the total mass of the core wire 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. The O content of the core wire is preferably 0.0150% by mass or less, more preferably 0.0125% by mass or less, and further 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, and specifically, SWRY11 specified in JIS G 3503: 2006 can be used. It can be used as a core wire.
In addition to the above O and Fe, the core wire may contain C, Si, Mn, P, S, N, Cu and the like. The C content of the core wire with respect to the total mass of the core wire 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. .65% by mass or less, P content is 0.020% by mass or less (including 0% by mass), S content is 0.023% by mass or less (including 0% by mass), Cu content is 0.20% by mass. It is preferable to be limited to% or less (including 0% by mass).

[Coverage]
In the present embodiment, the coverage of the coating material on the outer periphery of the core wire is not particularly limited, but is preferably 20% or more, preferably 22% or more, from the viewpoint of ensuring the strength of the coating agent. More preferably, it is more preferably 24% or more. Further, from the viewpoint of arc stability and the like, for example, it is preferably 40% or less, more preferably 38% or less, and further preferably 36% or less.

The present embodiment also relates to an arc welding method using a shielded metal 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 (particle size, area ratio, etc.) in the coating material of the welding rod to be used, the length of the coating material remaining after using the arc, etc. are as described above. Therefore, the description is omitted. Hereinafter, the welding posture in the arc welding method according to the present embodiment will be described in particular.

[Welding posture]
<The shielded metal arc welding rod is perpendicular to the base metal or has a receding angle of more than 0 ° and less than 30 °>
The shielded metal arc welding rod according to the present embodiment is welded perpendicular to the base metal (that is, the shielded metal arc welding rod is arranged perpendicular to the base metal) or with a receding angle of more than 0 ° and 30 ° or less. It is preferably used in arc welding by posture. As described above, welding using a shielded metal arc welding rod is often performed in various welding postures such as advance angle and receding angle, and when welding is performed in these welding postures (that is, the shielded metal arc welding rod is appropriately used). When tilted), one-sided melting becomes more remarkable than when it is tilted. The shielded metal arc welding rod according to the present embodiment has the same effect as when the shielded metal arc welding rod is perpendicular to the base metal in the shielded metal arc welding when the receding angle is more than 0 ° and 30 ° or less. Can be done. The receding angle is more preferably 5 ° or more and 25 ° or less.
Although the molten pool itself may not be horizontal to the base metal even when the welding posture is vertical, the shielded metal arc welding rod according to the present embodiment has high robustness, and has some disturbance and error. Even if this occurs, it is possible to suppress one-sided melting.

The shielded metal arc welding rod according to the present embodiment has various systems such as illuminate type, high titanium oxide type, lime titania type, iron powder titanium oxide type, high cellulose type, low hydrogen type and iron powder low hydrogen type. It can be applied as a welding rod. However, since the low hydrogen type welding rod contains a large amount of 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 welded with a low hydrogen type. When applied to a rod, the effect of droplet release by the gas generating agent becomes remarkable.
Further, in the iron powder low hydrogen type welding rod, a large amount of iron powder is added to the coating agent in order to obtain a desired amount of weld metal, and the iron powder causes the droplets to grow significantly. There is a problem that smooth droplet transferability cannot be obtained and large spatters are scattered. Therefore, it is most preferable that the shielded metal arc welding rod according to the present embodiment, which can improve the droplet release property, is applied as an iron powder low hydrogen type welding rod.

The method for manufacturing the shielded metal arc welding rod described above is not particularly limited. For example, the shielded metal arc welding rod according to the present embodiment can be manufactured by kneading the coating material raw material together with water glass, applying the coating material to the outer periphery of the core wire, drying and firing.

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

[Manufacturing of shielded metal 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 agents No. C1 to C15) having the chemical composition shown in Table 1 was prepared as shown in Table 3 and 26. Various shielded metal arc welding rods were manufactured by applying the coating to the outer periphery of the core wire with a coverage of 9.9 to 35.6% and 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 and total} of the coating agent. In Table 1, the balance is an unavoidable impurity, and the amount of each component in the coating agent indicates the content (% by mass) per total mass C _{coat and total} of the coating agent.
In addition, Table 4 shows the content of each component in the shielded metal arc welding rod with respect to the total mass _{Electrode and total} of the shielded metal arc welding rod. In Table 4, the balance is an unavoidable impurity, and the amount of each component in the shielded metal arc welding rod indicates the content (% by mass) per total mass of the welding rod, _{Electrode, total} .

Further, Table 2 shows a list of various physical property values relating to the content of metal carbonate or the content of metal fluoride contained in the coating agent.
In Table 2, C [CO 2,75 μm] is the total content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value), and C [F, 75 μm] has a particle size of 75 μm or more. The total content of metal fluoride (F conversion value), C [CO 2,106 μm] is the total content of metal carbonate having a particle size of 106 μm or more (CO ₂ conversion value), and C [F, 106 μm]. ] Is the total content of metal fluoride having a particle size of 106 μm or more (F conversion value), and C [CO 2,150 μm] is the total content of metal carbonate having a particle size of 150 μm or more (CO ₂ conversion value). ), 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.
Further, C [CO2, total] is the total content of metal carbonate contained in the coating agent ( _CO2 conversion value), and C [F, total] is the metal fluoride contained in the coating agent. Total content (F conversion value). Further, C [coat, total] is the total mass of the coating agent, and C [Si, total] is the total content (Si conversion value) of Si and the Si compound.

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

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

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

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

After that, the length from the most advanced part of the coating agent (protective cylinder) remaining around the core wire on the tip side of the welding rod to the rear end part of the welding rod on the holder side (rear end side) is measured and welded. The length from the rearmost end of the coating material (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 material forming the protective cylinder and the slag remaining at the end of the core wire were removed, and the length from the tip 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 tip of the core wire and the tip end of the coating material remaining around the core wire is around the core wire. The distance D2 in the longitudinal direction of the welding rod between the most advanced portion of the remaining coating material and the rearmost end portion of the coating material remaining around the core wire was calculated (see Table ₅ ).

Further, the shielded metal arc welding rod obtained by the above method was embedded in a resin so that the cross section perpendicular to the longitudinal direction was the observation surface, and was observed with a scanning electron microscope (SEM). The observation by SEM was an observation by a backscattered electron (BSE) image with a magnification of 50 times and an acceleration voltage of 15 kV.
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 cutoff of the entire coating material. The ratio of S ₂ to S ₁ (S ₂ / S ₁ ) when the area is S ₁ and the total area of at least one of the metal carbonates and metal fluorides having a circle equivalent diameter of 30 μm or more is S ₂ . ) Was calculated.

EDX analysis by SEM can be performed as follows. For example, using TM3030 Miniscope manufactured by Hitachi High-Technologies Corporation, the cross section of the shielded metal arc welding rod is analyzed (magnification 50 times, 1.61 mm × 1.21 mm rectangular areas at 4 locations). For the selection of the visual field, it is desirable that the cross section of the coating material is 70% or more in each visual field. Then, by binarizing 1024 × 768 pixels (786432 pixels) using the image analysis software ImageJ for one field of view, the area of the particles becomes 706.8 μm ² or more (circle equivalent diameter 30 μm or more). The area ratio can be calculated. The threshold value at the time of binarization is, for example, 60.

_The measurement results of the diameter d of the core wire and S2 / S1 in the _shielded metal arc welding rod are shown in Table 3 below. The measurement results of D ₂ / D ₁ , D ₁ and D ₁ / d are shown in Table 5 below.

Furthermore, the test No. T1 to T15 (Examples) and Test No. The shielded metal arc welding rods T16 to T19 (comparative example) are welded in the same manner as the welding conditions at the time of measurement of D ₁ and D ₂ , and one-sided melting evaluation (presence or absence of one-sided melting) and arc are performed according to the following evaluation criteria. The effect of suppressing deflection and welding workability were evaluated.

[Evaluation of one-sided melting (presence or absence of one-sided melting)]
When D ₂ / D ₁ ≤ 0.40 is satisfied: None When D ₂ / D ₁ > 0.40 is satisfied: Yes

[Effect of suppressing arc deflection]
The presence or absence of arc deflection and the appearance of the bead were visually evaluated. If the arc is not deflected and the bead appearance is judged to be good ◎ (excellent), if the arc is slightly deflected but the bead appearance is judged to be good ○ (good), the arc is deflected and Those judged to have a bad bead appearance were marked with x (bad).

[Welding workability (sensory evaluation)]
Visually, droplets are periodically transferred during welding, and those that are judged to generate only fine spatters are ◎ (excellent), and droplets are periodically transferred during welding, but they are conspicuous. ○ (good) indicates that medium-grain spatter is generated, and it is judged that a large amount of large-grain spatter is generated, not the droplets that are periodically transferred during welding. Those were marked as x (defective).

Test Nos. In Tables 3 to 5. T1 to T15 (Examples) have the requirements of the present invention (that is, the content of metal carbonate having a particle size of 75 μm or more (CO ₂ equivalent value) C CO _2,75 μm with respect to _{the total mass C cot, total} of the coating agent. , The content of metal fluoride having a particle size of 75 μm or more (F conversion value) CF, the total of _{75 μm} is 6.0% by mass or more) is satisfied (see column (7) in Table 2). Coating agent No. 1 or Table 2 No. This is an example using C1 to C11. These test Nos. As shown in Table ₅ , T1 to T15 satisfy D2 / D1 ≤ 0.40 (no _one -sided melting), and are excellent or good in both the effect of suppressing arc deflection and the welding workability. Results were obtained.

On the other hand, the test Nos. In Tables 3 to 5 T16 to T19 (comparative example) do not satisfy the requirements of the present invention (see column (7) in Table 2), and the coating agent No. 1 in Table 1 or Table 2 is not satisfied. This is an example using C12 to C15. These test Nos. As shown in Table 5, T16 to T19 do not satisfy D ₂ / D ₁ ≤ 0.40 (with one-sided melting), and poor results are obtained in terms of both the arc deflection suppressing effect and the welding workability. Was done.

As described in detail above, according to the shielded metal arc welding rod of the present invention, by preventing one-sided melting and suppressing the deflection of the arc, the droplets can be smoothly transferred and the arc stability is good. Therefore, it can be seen that excellent welding workability can be obtained.

1, 11 Shielded metal arc welding rod 2 Core wire 2a Tip part 3, 13 Coating agent 3a Tip 4, 14 Arc 5 Base material 6, 16 Protective cylinder 13a Cutting edge part 13b Last end d Diameter of core wire in shielded metal arc welding rod D Distance between the tip of the protective cylinder and the tip of the core wire in the longitudinal direction of the welding rod D ₁ Longitudinal direction of the welding rod between the tip of the core wire and the tip of the coating material remaining around the core wire. Distance D ₂ The distance between the leading edge of the coating material remaining around the core wire and the rearmost end portion of the coating material remaining around the core wire in the longitudinal direction of the welding rod.

Claims (15)

A shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. It is 6.0% by mass or more with respect to the total mass C _{coat, total} of the coating agent (provided that at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%) .
The C content in the coating agent is 0.01% by mass or more and 0.15% by mass or less with respect to the total mass C _{coat and total} of the coating agent.
Content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _{2,75 μm} is 4.6% by mass or more with respect to the total mass _{Ccoat, total} of the coating agent.
The total of the content of metal carbonate having a particle size of 150 μm or more (CO ₂ conversion value) C CO _2,150 μm and the content of metal fluoride having a particle size of 150 μm or more (F conversion value) _{CF, 150 μm} is the above. A shielded metal arc welding rod characterized in that it is 2.5% by mass or more and 4.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent. In the cross section perpendicular to the longitudinal direction of the welding rod
Let S ₁ be the cross-sectional area of the entire coating agent.
When the total area of at least one of the metal carbonate and the metal fluoride having a circle equivalent diameter of 30 μm or more is S ₂ .
The shielded metal arc welding rod according to claim 1, wherein the ratio of S ₂ to S ₁ (S ₂ / S ₁ ) satisfies 0.06 or more and 0.15 or less. The coating agent contains at least one selected from CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ as the metal carbonate.
The total content of metal carbonate (CO ₂ conversion value) C _{CO2, total} in the coating agent with respect to the total mass C _{coat, total} of the coating agent satisfies 6.0% by mass or more and 26.0% by mass or less. , The shielded metal arc welding rod according to claim 1 or 2 . 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 shielded metal arc welding rod according to any one of claims 1 to 3 . The coating contains both metal carbonates and metal fluorides,
The total content of metal fluoride in the coating agent relative to the total content of metal carbonate (CO ₂ conversion value) C _{CO2, total} and the total content of metal fluoride (F conversion value) _{CF, total} . Any of claims 1 to 4 , wherein the ratio of quantity (F conversion value) _{CF, total} { _{CF, total} / (C _{CO2, total} + _{CF, total} )} satisfies 0.10 or more and 0.30 or less. The coated arc welding rod according to item 1. The coating agent further contains at least one of Si and a Si compound.
Claim 1 is that the total content (Si conversion value) C _{Si, total} of the Si and the Si compound 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 shielded metal arc welding rod according to any one of 5 to 5 . A shielded metal arc welding method using a shielded metal 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, and contains.
The total of the content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _2,75 μm and the content of metal fluoride having a particle size of 75 μm or more (F conversion value) _{CF, 75 μm} is the total. It is 6.0% by mass or more with respect to the total mass C _{coat, total} of the coating agent (provided that at least one of the C _{CO 2,75} μm and the _{CF, 75 μm} is 0 mass%) .
The C content in the coating agent is 0.01% by mass or more and 0.15% by mass or less with respect to the total mass C _{coat and total} of the coating agent.
Content of metal carbonate having a particle size of 75 μm or more (CO ₂ conversion value) C CO _{2,75 μm} is 4.6% by mass or more with respect to the total mass _{Ccoat, total} of the coating agent.
The total of the content of metal carbonate having a particle size of 150 μm or more (CO ₂ conversion value) C CO _2,150 μm and the content of metal fluoride having a particle size of 150 μm or more (F conversion value) _{CF, 150 μm} is the above. A shielded metal arc welding method characterized in that it is 2.5% by mass or more and 4.0% by mass or less with respect to the total mass C _{coat and total} of the coating agent. On the tip side of the welding rod after using the shielded metal arc welding rod,
The distance between the tip of the core wire and the tip end portion of the coating material remaining around the core wire in the longitudinal direction of the welding rod is defined as D ₁ .
The distance between the most advanced portion of the coating agent remaining around the core wire and the rearmost end portion of the coating agent remaining around the core wire in the longitudinal direction of the welding rod was defined as D ₂ . When
The shielded metal arc welding method according to claim 7 , wherein arc welding is performed so that the ratio of D ₂ to D ₁ (D ₂ / D ₁ ) is 0.40 or less (including the case of 0). The shielded metal arc welding method according to claim 8 , wherein arc welding is performed so that D ₁ satisfies 2.2 mm or less. The shielded metal arc welding method according to claim 8 or 9 , wherein the arc welding is performed so that the ratio (D ₁ / d) of D ₁ to the diameter d of the core wire in the shielded metal arc welding rod satisfies 1.3 or less. The shielded metal arc welding method according to any one of claims 7 to 10 , wherein the shielded metal arc welding rod is arc-welded vertically or in a welding posture with a receding angle of more than 0 ° and 30 ° or less with respect to the base metal. Content of metal carbonate having a particle size of 106 μm or more (CO) ₂ Converted value) C _{CO 2,106 μm} And the content of metal fluoride having a particle size of 106 μm or more (F conversion value) C _{F, 106 μm} Is the total mass of the coating material C _{cot, total} The shielded metal arc welding rod according to any one of claims 1 to 6, wherein the amount is 5.0% by mass or more and 9.0% by mass or less. Total mass of coating material C _{cot, total} In contrast to Al in the coating ₂ O ₃ : The shielded metal arc welding rod according to any one of claims 1 to 6, wherein the amount is 0.02% by mass or more and 3.0% by mass or less. Content of metal carbonate having a particle size of 106 μm or more (CO) ₂ Converted value) C _{CO 2,106 μm} And the content of metal fluoride having a particle size of 106 μm or more (F conversion value) C _{F, 106 μm} Is the total mass of the coating material C _{cot, total} The covered arc welding method according to any one of claims 7 to 11, wherein the amount is 5.0% by mass or more and 9.0% by mass or less. Total mass of coating material C _{cot, total} In contrast to Al in the coating ₂ O ₃ : The shielded metal arc welding method according to any one of claims 7 to 11, wherein the amount is 0.02% by mass or more and 3.0% by mass or less.

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