RU2764624C1 - Coated electrode for arc welding and the method for arc welding with a coated electrode - Google Patents

Abstract

FIELD: welding technology.

SUBSTANCE: invention relates to arc welding of coated electrodes. The sum of the content of metal carbonate in the coating with a grain diameter of 75 microns or more in terms of CO₂ (C_{CO2, 75 microns}) and the content of metal fluoride with a grain diameter of 75 microns or more in terms of F (C_{F, 75 microns}) relative to the total mass of the coating (S_{tot. coat.}) is 6.0, wt. %, or more. The specified content of carbonate and metal fluoride is selected from the condition for obtaining a coating after welding at the far end of the electrode, the shape of which satisfies the ratio D₂/D₁, ranging from 0 to 0.4, where D₁ is the distance in the longitudinal direction of the electrode between the end of the electrode rod after welding and the furthest end of the coating remaining around the rod after welding, and D₂ is the distance in the longitudinal direction of the electrode between the ends of the coating remaining around the rod after welding.

EFFECT: electrode prevents unilateral melting and displacement of the arc and ensures uniform movement of the melt droplets.

15 cl, 5 tbl, 2 dwg

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to a coated electrode and a consumable coated electrode arc welding method, and more specifically, to a coated electrode in which droplets can be evenly transferred to prevent arc deviation and maintain good arc stability, and excellent weldability can be obtained, and a method of arc welding with a consumable coated electrode for performing arc welding using the coated electrode.

BACKGROUND OF THE INVENTION

[0002] Coated consumable arc welding is a welding method for connecting an object to a base metal using a coated electrode (also referred to simply as an "electrode", "welding electrode", or the like), in which a metal rod (electrode wire) there is a flux or protective material called coating composition, creating an arc between the coated electrode and the base metal, and melting the electrode and the base metal under the heat of the arc. The consumable coated arc welding is the simplest welding method that does not require a shielding gas. The consumable electrode arc welding can be performed even outdoors under strong wind, and is widely used in various manufacturing plants, construction, ships, vehicles, and the like.

[0003] The coating composition constituting the coated electrode contains raw materials with functions such as blowing agent, slag former, deoxidizer, dopant, arc stabilizer, and fixing agent. In addition, coated electrodes are classified according to the grade of coating compositions, and there are various types of coated electrodes, such as ilmenite-based coated electrode, titanium oxide-based coated electrode, lime-titanium dioxide-based coated electrode, coated electrode based on iron powder-titanium oxide, cellulose-based coated electrode, low hydrogen coated electrode, and low hydrogen coated electrode based on iron powder.

[0004] Among the various types of coated electrodes described above, a coated electrode in which the oxygen content of the electrode wire is limited and the contents of metal carbonates, metal fluorides and water in the coating composition are properly adjusted has been proposed as the low hydrogen coated electrode disclosed in the patent Document 1. Patent Document 1 describes that the components in the electrode wire and the coating composition of the coated electrode are properly adjusted to ensure good weldability without degrading the physical properties of the weld metal.

LIST OF CITATIONS

PATENT LITERATURE

[0005] Patent Document 1: JP-A-S57-85696

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0006] However, welding using the coated electrode is performed in various welding positions such as advance angle and retard angle. Thus, when the electrode is tilted, the part of the coating composition that is closer to the base metal is easily melted (this is called one-sided melting), and the arc is deflected, which disrupts the welding operation. As for the coated electrode described in the above-mentioned Patent Document 1, there is no indication of one-sided melting and arc deflection, and the coated electrode specifically refers to a low hydrogen coated electrode. Thus, the other coated electrodes described in Patent Document 1 could not improve the weldability as measured by the drop transfer capability and arc stability of other types of coated electrodes.

[0007] An object of the present invention is to provide a coated electrode by which excellent weldability can be obtained because one-sided melting and arc deflection can be prevented, droplets can be evenly transferred, and good arc stability is high.

THE SOLUTION OF THE PROBLEM

[0008] The coated electrode of the present invention has the following configuration (1).

(1) Coated electrode, comprising:

electrode wire; and

a coating composition that coats the electrode wire,

wherein the coating composition contains at least one of a metal carbonate and a metal fluoride,

the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total mass the coating composition (C _{coat, total} ) is 6.0 wt.% or more (wherein the case where at least one of C _{CO2, 75 μm} and C _{F, 75 μm} is 0 wt.%) is included, and

on the distal end side of the electrode after applying the coated electrode, the ratio of D ₂ to D ₁ (D ₂ /D ₁ ) is 0.40 or less (including the case where this ratio is 0),

where D ₁ is the distance between the far end portion of the electrode wire and the farthest end portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode, and

D ₂ is the distance between the farthest end portion of the coating composition remaining around the electrode wire and the rearmost portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode.

[0009] In addition, preferred embodiments of the coated electrode of the present invention provide for the following configuration (2) or (3).

(2) The coated electrode according to (1) above, wherein D ₁ is 2.2 mm or less.

(3) The coated electrode according to (1) or (2) above, wherein the ratio of D ₁ to the diameter d of the electrode wire in the coated electrode (D ₁ /d) is 1.3 or less.

[0010] In addition, the coated electrode of the present invention has the following configuration (4).

(4) Coated electrode, comprising:

electrode wire; and

a coating composition that coats the electrode wire,

wherein the coating composition comprises at least one of a metal carbonate and a metal fluoride, and

the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total mass the coating composition (C _{coating, total} ) is 6.0 wt.% or more (wherein the case when at least one of C _{CO2, 75 μm} and C _{F, 75 μm} is 0 wt.%) is included.

[0011] In addition, preferred embodiments of the coated electrode of the present invention provide for the following configurations (5)-(10).

(5) The coated electrode according to any of the above (1)-(4),

moreover, in a section perpendicular to the longitudinal direction of the electrode,

the ratio of S ₂ to S ₁ (S ₂ /S ₁ ) is 0.06 or more and 0.15 or less,

where S ₁ is the cross-sectional area of the entire coating composition, and

S ₂ is the total area of at least one of a metal carbonate and a metal fluoride, each having an equivalent circle diameter of 30 µm or more.

(6) The coated electrode according to any of the above (1)-(5),

moreover, as a metal carbonate, the coating composition contains at least one selected from CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ , and

the total content (CO ₂ conversion value) of metal carbonate in the coating composition ( _{CCO2, total} ) relative to the total weight of the coating composition ( _{Ccoat, total} ) is 6.0 mass% or more and 26.0 mass% or less.

(7) The coated electrode according to any of the above (1)-(6),

moreover, as the metal fluoride, the coating composition contains at least one selected from CaF ₂ , BaF ₂ , SrF ₂ and MgF ₂ , and

the total content (value of conversion F) of metal fluoride in the coating composition (C _{F, total} ) relative to the total weight of the coating composition (C _{coating, total} ) is 15.0 wt.% or less (including 0 wt.%).

(8) The coated electrode according to any of the above (1)-(7),

wherein the coating composition comprises a metal carbonate and a metal fluoride, and

the ratio of the total content (F conversion values) of metal fluoride in the coating composition (C _{F, total} ) relative to the sum of the total content (CO ₂ conversion values) of metal carbonate in the coating composition (C _{CO2, total} ) and the total content (F conversion values) of metal fluoride (C _{F, total} ) in the coating composition {C _{F, total} /(C _{CO2, total} +C _{F, total} )} is 0.10 or more and 0.30 or less.

(9) The coated electrode according to any of the above (1)-(8),

wherein the coating composition further comprises at least one of Si and a Si compound, and

the total content (Si conversion value) of Si and the Si compound (C _{Si, total} ) relative to the total weight of the coating composition (C _{coat, total} ) is 6.0 wt.% or more and 9.0 wt.% or less.

(10) The coated electrode according to any one of (1) to (9) above, wherein the coated electrode is used in arc welding at a welding position in which the coated electrode is perpendicular to the base metal or has a lag angle of more than 0° and 30° or less.

[0012] In addition, the consumable coated electrode arc welding method of the present invention has the following configuration (11).

(11) A coated electrode arc welding method using a coated electrode including an electrode wire and a coating composition that coats the electrode wire,

wherein the coating composition comprises at least one of a metal carbonate and a metal fluoride, and

the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total mass the coating composition (C _{coating, total} ) is 6.0 wt.% or more (wherein the case when at least one of C _{CO2, 75 μm} and C _{F, 75 μm} is 0 wt.%) is included.

[0013] In addition, preferred embodiments of the consumable coated electrode arc welding method of the present invention provide for the following configurations (12)-(15).

(12) The consumable electrode arc welding method according to (11) above,

wherein, on the distal end side of the electrode, after applying the coated electrode, the ratio of D ₂ to D ₁ (D ₂ /D ₁ ) is 0.40 or less (including the case where the ratio is 0),

where D ₁ is the distance between the far end portion of the electrode wire and the farthest end portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode, and

D ₂ is the distance between the farthest end portion of the coating composition remaining around the electrode wire and the rearmost portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode.

(13) The consumable electrode arc welding method according to (12) above, wherein the arc welding is performed such that D ₁ is 2.2 mm or less.

(14) The consumable coated electrode arc welding method according to (12) or (13) above, wherein the arc welding is performed such that the ratio D ₁ to the diameter d of the electrode wire in the coated electrode (D ₁ /d) is 1.3 or less.

(15) The consumable coated electrode arc welding method according to any of the above (11) to (14), wherein the arc welding is performed in a welding position in which the coated electrode is perpendicular to the base metal or has a lag angle of more than 0° and 30° or less .

ADVANTAGEABLE EFFECTS OF THE INVENTION

[0014] In the present invention, a predetermined number of grains having an appropriate size is contained to control the grain size of at least one kind of grains selected from metal carbonates and metal fluorides contained in the coating composition, and therefore, the coating composition is melted evenly, due to which during welding, a protective sheath is formed, one-sided melting is prevented, and arc deflection is prevented. Accordingly, it is possible to provide a coated electrode and a consumable coated electrode arc welding method by which excellent weldability can be obtained even for all types of coated electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1A is a sectional view illustrating the state of the coated electrode in the case where arc deflection is prevented during welding.

FIG. 1B is a sectional view illustrating the state of a coated electrode in a case where a significant arc deflection occurs during welding.

DESCRIPTION OF EMBODIMENTS

[0016] Embodiments of the present invention are described in detail below. It should be understood that the present invention is not limited to the embodiments described herein and may be optionally changed without departing from the scope of the present invention.

[0017] The inventors of the present invention have focused on the grain size (grain size) of the metal carbonate or metal fluoride contained in the coating composition, and have made intensive studies to obtain a coated electrode in which uniform droplet transfer and good arc stability can be achieved. As a result, the present inventors have found that it is effective to control the amount of grains having a large size among the grains of metal carbonate or metal fluoride.

[0018] First, the effect (i.e., operation and effect) of grain size (i.e., coarse grain diameter) of metal carbonate or metal fluoride on droplet transport is described in detail below.

[0019] The inventors of the present invention have found that the grain size of the metal carbonate or metal fluoride also affects the shape of the protective sheath formed during arc welding, and thus the arc direction is maintained, that is, arc deflection is prevented, so that good arc stability can be obtained. . That is, when a metal carbonate or a metal fluoride having a large grain size is contained in the coating composition, the specific surface area becomes small and the coating composition melts with difficulty, which means that the coating composition melts evenly at the time of welding, thereby uniformly forming a protective shell at the time of welding ( see later discussion for details). Therefore, the directionality of the arc is maintained, so that the stability of the arc is further improved.

[0020] Metal carbonate or metal fluoride is a component that can be contained in the coating composition as a blowing agent, and plays a role in preventing oxygen, nitrogen or the like from the atmosphere from entering the weld metal by generating a shielding gas when the coated electrode is used an arc is created as a welding electrode and between the coated electrode and the base metal. When the grain size of the metal carbonate or metal fluoride contained in the coating composition is adjusted to a larger value, the metal carbonate or metal fluoride having a large grain size is held in place until it is completely gassed at the far end of the coated electrode (at the point where the arc is formed). on the side of the electrode). Due to this retention in place, the gas is intensively released in one direction (the direction of the melted electrode wire), and the manifestation of compression of the droplets as a result of the volumetric expansion of the gas is stimulated. On this basis, a droplet releasing shear force such as an electromagnetic compression force or surface tension is effective, and the droplets can be separated in a state of fine particles. In addition, the droplets are released while being stably held in the separation period, so that arc stability is improved and excellent weldability can be obtained.

[0021] On the other hand, in the case where the grain size of the metal carbonate or metal fluoride is small, the amount of outgassing becomes small. Therefore, a small amount of gas is generated, and the direction of the evolved gas is not fixed in one direction, and therefore the droplet separation assisting force is small compared with the case where the grain size of the metal carbonate or metal fluoride is large.

[0022] Further, with regard to the coated electrode in the embodiment of the present invention, the grain size, the ratio of the cross-sectional area of the electrode in the longitudinal direction, the reason for adding other components, the reason for the quantitative limitation, and the like are described in detail. according to the blowing agent contained in the coating composition.

[0023] The coated electrode in the present embodiment includes:

electrode wire; and

a coating composition which coats the electrode wire, wherein

the coating composition contains at least one of a metal carbonate and a metal fluoride,

the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total mass the coating composition (C _{coating, total} ) is 6.0 wt.% or more (wherein the case where at least one of C _{CO2, 75 μm} and C _{F, 75 μm} is 0 wt.%) is included, and

on the distal end side of the electrode after applying the coated electrode, the ratio of D ₂ to D ₁ (D ₂ /D ₁ ) is 0.40 or less (including the case where this ratio is 0),

where D ₁ is the distance between the far end portion of the electrode wire and the farthest end portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode, and

D ₂ is the distance between the farthest end portion of the coating composition remaining around the electrode wire and the rearmost portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode.

[Coating compound]

[0024] First, details regarding the coating composition are described below.

<Total content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to total weight of the coating composition (C _{coating, total} ): 6.0 wt.% or more>

[0025] When the grain size of the metal carbonate or metal fluoride contained in the coating composition is increased, it may contribute to the occurrence of droplet shrinkage during arc welding, and uniform droplet transfer as described above can be achieved. In addition, the coating composition is uniformly melted during arc welding so that a protective sheath is uniformly formed during welding. Therefore, deflection of the arc is prevented and the directionality of the arc is maintained, so that arc stability is further improved.

[0026] When the coating composition contains a metal carbonate having a grain diameter of 75 μm or more, or when the coating composition contains a metal fluoride having a grain diameter of 75 μm or more, the above-described effects of uniform droplet transfer and good arc stability can be obtained. In this case, since the content of metal carbonate having a grain diameter equal to or greater than the specified value or metal fluoride having a grain diameter equal to or greater than the specified value can also affect the uniform droplet transfer and arc stability, in the coated the electrode according to the present embodiment is also set to a content of metal carbonate or metal fluoride, each of which has a grain diameter equal to or greater than the set value.

[0027] That is, when the sum of the content (CO ₂ conversion value) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion value) of metal fluoride with a grain diameter of 75 µm or more (C _{F , 75 μm} ) relative to the total weight of the coating composition ( _{Ccoat, total} ) is 6.0 mass% or more, droplets can be evenly transferred, arc stability improves, and the effect of improving weldability can be effectively obtained. It should be noted that this includes the case where at least one of C _{CO2, 75 µm} and C _{F, 75 µm} is 0 wt.%.

[0028] When the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) is too large relative to the total weight of the coating composition (C _{coating, total} ), there is a fear of increasing spatter or affecting the adhesion of the coating composition during the manufacturing process. Therefore, the sum of C _{CO2, 75 µm} and C _{F, 75 µm is} preferably 15.0 mass% or less, and more preferably 12.0 mass% or less.

[0029] In order to better obtain the above-described effects of uniform droplet transfer and good arc stability, the sum of the content (CO ₂ conversion value) of metal carbonate with a grain diameter of 106 µm or more (C _{CO2, 106 µm} ) and the content (F conversion value) of fluoride metal with a grain diameter of 106 μm or more (C _{F, 106 μm} ) relative to the total weight of the coating composition (C _{cover, total} ) is preferably 5.0 wt.% or more. On the other hand, the above value is preferably 9.0 wt.% or less, since there is a fear that spattering will increase or the adhesiveness of the coating composition will be affected during the manufacturing process as described above.

[0030] In order to better obtain the above-described effects of uniform droplet transfer and good arc stability, the sum of the content (CO ₂ conversion value) of metal carbonate with a grain diameter of 150 µm or more (C _{CO2, 150 µm} ) and the content (F conversion value) of fluoride metal with a grain diameter of 150 μm or more (C _{F, 150 μm} ) relative to the total weight of the coating composition (C _{cover, total} ) is preferably 2.5 wt.% or more, and more preferably 3.0 wt.% or more. In addition, the above value is preferably 5.0 wt.% or less, and more preferably 4.0 wt.% or less, since there is a concern that spattering will increase or the adhesiveness of the coating composition will be affected during the manufacturing process as described above.

[0031] The coating composition must contain at least one of the above-described metal carbonate and the above-described metal fluoride, and may contain both of them. Described in the present embodiment, the "grain diameter" is measured by a measurement method in accordance with JIS Z 8801-2006. In addition, the grain size (grain diameter) of the metal carbonate and metal fluoride contained in the coating composition is typically about 600 µm maximum.

<D ₂ to D ₁ ratio (D ₂ /D ₁ ): 0.40 or less (including the case where the ratio is 0)>

[0032] As described above, the grain size of the metal carbonate and metal fluoride also affects the shape of the containment after arc welding. That is, the arc welding jacket can be formed with a good shape by setting the grain size and the content of metal carbonate and metal fluoride. As a result, the directivity of the arc is improved and the stability of the arc is improved.

[0033] Here, the state of the coated electrode in the case where arc welding is carried out using two types of coated electrodes is described with reference to the drawings. FIG. 1A and FIG. 1B, the same components are identified by the same reference numbers, and a detailed description of them is omitted.

[0034] FIG. 1A is a sectional view illustrating the state of the coated electrode in the case where arc deflection during welding is prevented. As illustrated in FIG. 1A, the coated electrode 1 includes an electrode wire 2 and a coating composition 3 which coats the electrode wire 2. The coating composition 3 contains at least one kind of compound selected from metal carbonates and metal fluorides. The components of the coating composition 3 are defined such that the sum of the content (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) and the content (F conversion values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total weight of the coating composition (C _{coating, total} ) is 6.0 wt.% or more (where the case is included when at least one of C _{CO2, 75 µm} and C _{F, 75 µm} is 0 wt. .%).

[0035] When arc welding is performed on the base metal 5 using the above-described coated electrode 1, the grain diameter and the total content of said compound (that is, at least one selected from metal carbonates and metal fluorides) contained in the coating composition 3 is limited. as above, and therefore the specific surface area of the above-described compound is reduced. As a result, melting or softening of the coating composition 3, strictly speaking, the protective sheath 6, which is the part protruding from the distal end portion 2a of the electrode wire 2 and is part of the coating composition 3, hardly occurs, and the protective sheath 6 tends to be preserved during arc welding. Therefore, one-sided melting of the coating composition 3 is prevented, and the coating composition 3 is evenly melted along the entire circumferential direction of the coated electrode 1. As a result, during or after welding, the space surrounded by the inner peripheral surface of the protective sheath 6 acquires a uniform conical shape in the cross-sectional view of the coated electrode. . As a result, the distance D between the distal end 3a of the protective sheath 6 and the distal end portion 2a of the electrode wire 2 in the longitudinal direction of the electrode is substantially the same at any position and exhibits little variation. Therefore, deflection of the arc 4 during welding is prevented, and the direction of the arc is improved, and the stability of the arc is improved.

[0036] As described later, in the case where both metal carbonate and metal fluoride are contained in the coating composition 3, and the ratio of the total content (F conversion value) of metal fluoride (C _{F, total} ) to the total content (value CO ₂ conversion) of the metal carbonate contained in the coating composition 3 (C _{CO2, total} ) and the total content (conversion value F) of metal fluoride (C _{F, total} ) can be increased in the softening point of the coating composition. Therefore, the shape of the containment shell 6 can be kept uniform up to a proper length, and the containment shell 6 serves as a guide for increasing the directivity of the arc. Accordingly, drop deflection is further prevented, and good arc stability can be maintained, thereby improving weldability.

[0037] On the other hand, FIG. 1B is a sectional view illustrating the state of a coated electrode in a case where a noticeable arc deflection occurs during welding. As illustrated in FIG. 1B, in the case where arc welding is performed using the coated electrode 11 having the coating composition 13 in which the grain diameter and the content of metal carbonate and metal fluoride are not adjusted as described above, there is a difference between the distance between the distal end portion 2a of the electrode wire 2 and a farthest end portion 13a of the coating composition 13 (sheath 16) remaining after welding, and a distance between the distal end portion 2a of the electrode wire 2 and the farthest portion 13b of the coating composition 13 (sheath 16). As a result, during welding, there is a noticeable deflection of the arc 14, which means that the stability of the arc is reduced.

[0038] In the present embodiment, variations in the lengths of the coating compositions 3, 13 remaining around the electrode wire 2 (or the lengths of the protective sheaths 6, 16) after application of the coated electrode are given. Therefore, a method for converting a variation into a digital form is described in detail with reference to FIG. 1B.

[0039] As illustrated in FIG. 1B, on the distal end side of the electrode (lower side of the coated electrode 11 in FIG. 1B), after applying the coated electrode, the distance between the distal end portion 2a of the electrode wire 2 and the distal end portion 13a of the coating composition 13 remaining around the electrode wire 2 in the longitudinal direction electrode (from top to bottom in FIG. 1B) is defined as D ₁ , and the distance between the portion 13a of the farthest end of the coating composition 13 remaining around the electrode wire 2 and the rearmost portion 13b of the coating composition 13 remaining around the electrode wire 2 in the longitudinal direction of the electrode is defined as D ₂ .

[0040] When the ratio of D ₂ to D ₁ (D ₂ /D ₁ ) is 0.40 or less, it means that the protective sheath 16 is formed with good shape with little variation in length. 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.

[0041] Here, the state after application of the coated electrode (i.e., the state after the end of arc welding) refers to the state in which the coating composition remains after the end of a continuous arc generation period of 5 seconds or longer after the start of arc welding. Generally, even after the coated electrode has been used once, the coated electrode can be reused as long as the coating composition is retained. It should be noted that after applying the coated electrode, slag may adhere to the distal end portion of the electrode wire 2, and in the present embodiment, the distal end portion 2a of the electrode wire 2 is described in a state in which the slag is removed, and the shape of the distal end portion 2a is substantially flat. . In addition, the “most distal end portion” described in the present embodiment refers to the most protruding portion of the distal ends of the coating compositions 3, 13, and the “rearmost portion” refers to the least protruding portion of the distal ends of the coating compositions 3, 13.

<D ₁ : 2.2 mm or less>

[0042] It is preferable that, on the distal end side of the electrode, after applying the coated electrode, the coating composition 13 around the electrode wire 2 remains with a length equal to or greater than a certain length, and a protective sheath 16 is formed. However, when the distance D ₁ between the far end portion 2a the end of the electrode wire 2 and the section 13a of the farthest end of the coating composition 13 remaining around the electrode wire 2 in the longitudinal direction of the electrode is more than 2.2 mm, the distance between the electrode wire and the base metal increases and the arc length increases due to the excessive length of the protective sheath 16. When the arc length is excessively large, the arc length tends to change. This means that an intermittent arc occurs, and the stability of the arc decreases. As a result, weldability may deteriorate due to deterioration in the appearance of the weld bead and increased spatter. Accordingly, the above D _{1 is} preferably 2.2 mm or less, and more preferably 1.7 mm or less. When the above value of D ₁ is extremely small, the arc directionality is not achieved and the arc stability deteriorates. Therefore, D _{1 is} preferably 1.0 mm or more, and more preferably 1.3 mm or more.

<Ratio of D ₁ to electrode wire diameter d of coated electrode (D ₁ /d): 1.3 or less>

[0043] Typically, the above value of D ₁ is proportional to the diameter d (see d in FIG. 1B) of the electrode wire of the coated electrode. 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. When D ₁ is extremely small with respect to the above-described diameter d, arc directionality is not achieved and arc stability deteriorates. Therefore, D ₁ /d is preferably 0.1 or more, and more preferably 0.3 or more. In the present embodiment, the diameter d is not particularly limited, but is preferably 3.0 to 5.0 mm based on the range of commonly used diameters d.

<S ₂ to S ₁ ratio (S ₂ /S ₁ ): 0.06 or more and 0.15 or less>

[0044] In the present embodiment described above, uniform droplet transfer and good arc stability are achieved by setting the requirement that the coating composition contains a predetermined amount of grains having a large grain size among at least one kind of grains selected from metal carbonates and metal fluorides. contained in the coating composition. On the other hand, in the present embodiment, the following is adopted as another setting method to achieve these characteristics. More specifically, in a coated electrode, in a section perpendicular to the longitudinal direction of the electrode, when the cross-sectional area of the entire coating composition is defined as S ₁ and the total area of at least one of a metal carbonate and a metal fluoride, each of which has an equivalent circle diameter of 30 μm or more, defined as S ₂ , the ratio of S ₂ to S ₁ (S ₂ /S ₁ ) is 0.06 or more and 0.15 or less.

[0045] When the ratio of S ₂ to S ₁ (S ₂ /S ₁ ) is 0.06 or more, the droplet release promoting effect is more pronounced, and more uniform droplet transfer can be achieved. Accordingly, the above S ₂ /S ₁ ratio is preferably 0.06 or more, and more preferably 0.07 or more. On the other hand, when the above S ₂ /S ₁ ratio is 0.15 or less, it is easy to obtain a weld metal having desirable characteristics. Accordingly, the above S ₂ /S ₁ ratio is 0.15 or less, and more preferably 0.10 or less.

[0046] The above-described effects can be obtained even when only metal fluoride having an equivalent circle diameter of 30 µm or more is contained in the coating composition within the above-described range, but more preferably, only metal carbonate is contained within the above-described range. In addition, it is most preferred that both the metal carbonate and the metal fluoride are contained within the above range, respectively.

[0047] Examples of the method for adjusting the above S ₂ /S ₁ ratio as described above include a method for adjusting the grain diameter of metal carbonate or metal fluoride as a raw material of the coating composition, a method for controlling the content of metal carbonate or metal fluoride, and a method for controlling pressure when coating coating composition during the manufacture of the coated electrode. The above ratio S ₂ /S ₁ can be adjusted using one of these methods alone or using these methods in combination. However, the above production method is only an example, and the present invention is not limited to this example.

[0048] In the present embodiment, the term "equivalent circle diameter" refers to the diameter of a circle having an area equal to the grain projection area as defined in JIS Z 8827-1, and can be determined using image analysis software or the like. P. computer based. The grain size (equivalent circle diameter) contained in the coating composition of metal carbonate and metal fluoride is typically about 600 µm maximum.

[0049] Here, the above ratio S ₂ /S ₁ can be measured, for example, as follows. First, the electrode cross-section (at 400-fold magnification) is analyzed at an accelerating voltage of 15 kV and an irradiation current of 5×10 ^-10 A using an electron probe microanalyzer (EPMA) JXA-8200 manufactured by JEOL Ltd., for combined energy dispersive (ED) and wave (WD) analysis. Then, for the entire cross section of the electrode, the area of at least one of metal carbonate and metal fluoride, each having an equivalent circle diameter of 30 µm or more, and other areas are binarized using JTrim image analysis software. Accordingly, the ratio of the total area S ₂ of at least one of the metal carbonate and the metal fluoride, each having an equivalent circle diameter of 30 µm or more, to the _{cross-sectional area S 1 of the} entire coating composition (i.e., S ₂ /S ₁ ) can be calculated.

<Total content (CO ₂ conversion value) of metal carbonate in the coating composition ( _{CCO2, total} ) relative to the total weight of the coating composition ( _{Ccoat, total} ): 6.0 mass% or more and 26.0 mass% or less>

[0050] A metal carbonate such as CaCO ₃ and BaCO ₃ , which is contained in the coating composition of the coated electrode, is a component having the function of protecting the molten bath from oxygen, nitrogen, and moisture from the atmosphere by releasing CO ₂ , which is a protective gas, as a result of thermal decomposition at a temperature close to the arc generation temperature. For example, CaCO ₃ decomposes at about 825° C. to form CaO and gaseous CO ₂ . When the metal carbonate content of the coating composition is too low, entrainment of the atmosphere occurs due to poor shielding, which causes deterioration in weldability, formation of weld defects such as gas pockets, and reduction in toughness of the weld metal. In contrast, when the total metal carbonate content of the coating composition is excessive, the coating composition is less likely to melt during welding. That is, the above-described distance D ₁ increases, which means that the distance between the consumable interface of the electrode wire and the molten pool becomes excessively large, and the arc length deviates from the proper condition. Accordingly, an unstable arc may occur, or arc stability may decrease, and spatter may increase. As described above, by containing a metal carbonate with a size equal to or greater than a given size, the droplet transfer period can be stabilized.

[0051] When the total content (CO ₂ conversion value) of metal carbonate in the coating composition ( _{CCO2, total} ) relative to the total weight of the coating composition ( _{Ccoat, total} ) is 6.0 mass% or more, these effects can be obtained in to a sufficient extent. Accordingly, the content of the above-described metal carbonate (C _{CO2, total} ) as a CO ₂ conversion value is preferably 6.0 mass% or more, and more preferably 10.0 mass% or more. On the other hand, when the total content (CO ₂ conversion value) of the metal carbonate in the coating composition ( _{CCO2, total} ) relative to the total weight of the coating composition ( _{Ccoat, total} ) is 26.0 mass% or less, arc stability is further improved, and reduced spatter. Accordingly, the content of the above-described metal carbonate (C _{CO2, total} ) as a CO ₂ conversion value is preferably 26.0 mass% or less, and more preferably 25.0 mass% or less. For the same reason as described above, the total content (CO ₂ conversion values) of metal carbonate in the coated electrode relative to the total weight of the coated electrode C _{electrode, the total is} preferably 4.0 mass% or more and 10.0 mass% or less, more preferably 4.5 wt.% or more and 9.0 wt.% or less, and even more preferably 4.5 wt.% or more and 7.5 wt.% or less.

[0052] The metal carbonate used in the coating composition in the present embodiment is preferably at least one selected from calcium carbonate (CaCO ₃ ), barium carbonate (BaCO ₃ ), strontium carbonate (SrCO ₃ ), magnesium carbonate (MgCO ₃ ) and manganese carbonate (MnCO ₃ ). For reasons of manufacturing costs, the use of CaCO ₃ and BaCO ₃ is more preferred, and the use of CaCO _{3 is} most preferred. Any variety of the various metal carbonates described above may be used, or multiple different metal carbonates may be used in combination. In the case where a plurality of metal carbonates are used, the total content, as a CO ₂ conversion value, is preferably within the range of 6.0 mass% or more and 26.0 mass% or less.

_{[0053] In the case where CaCO 3 is} contained in the coating composition as the metal carbonate, the content of CaCO ₃ as the CO ₂ conversion value in the coating composition relative to the total weight of the coating composition is preferably 6.0 mass% or more and 26.0 wt.% or less, and more preferably 10.0 wt.% or more and 25.0 wt.% or less. The content of CaCO ₃ in the coated electrode relative to the total weight of the coated electrode is preferably 10.0 mass% or more and 20.0 mass% or less, more preferably 11.0 mass% or more and 19.0 mass% or less , and even more preferably 11.0 wt.% or more and 17.0 wt.% or less.

_{[0054] When BaCO 3 is} contained in the coating composition as the metal carbonate, the content of BaCO ₃ as the CO ₂ conversion value in the coating composition relative to the total weight of the coating composition is preferably more than 0.0 wt.% and 4.0 wt.% or less, for reasons of weldability.

<Total content (conversion value F) of metal fluoride in the coating composition (C _{F, total} ) relative to the total weight of the coating composition C _{coating, total} : 15.0 mass% or less (including 0 mass%)>

[0055] A metal fluoride such as CaF ₂ contained in the coated electrode coating composition is a component having an effect of improving the shape of the weld bead by lowering the melting point of the slag and improving the fluidity of the slag. In addition, metal fluoride is a component having a function of preventing an increase in the amount of oxygen or hydrogen in the weld metal and improving arc stability by releasing a large amount of reducing shielding gas (fluorine derivative gas) when metal fluoride is decomposed by arc heat. When metal fluoride is added to the coating composition, the fluorine-containing decomposition product reacts with hydrogen in the molten metal or molten slag, and the partial pressure of hydrogen in the molten metal can be reduced. Therefore, the amount of hydrogen in the weld metal can also be reduced. As described above, when the coating composition contains metal fluoride with a size equal to or greater than a given size, droplet tolerance can be improved. However, when the metal fluoride content of the coating composition is excessive, the slag flow becomes excessive, and a defect such as slag inclusion may occur, which may degrade the welding quality.

[0056] The coating composition does not necessarily contain metal fluoride, and the lower limit is not specifically set and may be 0.0 wt.%. However, in order to sufficiently obtain these effects, it is preferable to add metal fluoride, and the content of metal fluoride is preferably more than 0.0 mass%, and more preferably 3.0 mass% or more. On the other hand, when the total content (conversion value F) of the metal fluoride in the coating composition (C _{F, total} ) relative to the total weight of the coating composition C _coating is 15.0 mass% or less in total, better arc stability can be obtained, and improved weldability. Accordingly, the content of metal fluoride (C _{F, total} ) is preferably 15.0 mass% or less, and more preferably 7.5 mass% or less. For the same reason as described above, the total content (conversion value F) of metal fluoride in the coated electrode (C _{electrode, total} ) is preferably 0.5 mass% or more and 2.7 mass% or less, more preferably 0.7 wt.% or more and 2.5 wt.% or less, and even more preferably 0.9 wt.% or more and 2.3 wt.% or less.

[0057] The metal fluoride used in the coating composition in the present embodiment is preferably at least one selected from calcium fluoride (CaF ₂ ), barium fluoride (BaF ₂ ), strontium fluoride (SrF ₂ ), and magnesium fluoride (MgF ₂ ). For reasons of manufacturing costs, the use of CaF ₂ and BaF ₂ is more preferable, and the use of CaF _{2 is} most preferred. Any variety of the various metal fluorides described above may be used, or multiple different metal fluorides may be used in combination. In the case where a plurality of metal fluorides are used, the total content, as the F conversion value, is preferably within the range of 15.0 mass% or less (including 0 mass%).

_{[0058] In the case where CaF 2 is} contained as the metal fluoride in the coating composition, the content, as conversion value F, in the coating composition relative to the total weight of the coating composition is preferably more than 0.0 wt.% and 15.0 wt.% or less, and more preferably 3.0 wt.% or more and 7.5 wt.% or less. The content of CaF ₂ in the coated electrode relative to the total weight of the coated electrode is preferably 1.0 mass% or more and 6.0 mass% or less, more preferably 1.5 mass% or more and 5.5 mass% or less , and even more preferably 1.8 wt.% or more and 5.2 wt.% or less.

<The ratio of the total content (F conversion values) of metal fluoride (C _{F, total} ) to the sum of the total content (CO ₂ conversion values) of metal carbonate (C _{CO2, total} ) and the total content (F conversion values) of metal fluoride (C _{F, total} ) in the coating composition {C _{F, total} /(C _{CO2, total} +C _{F, total} )}: 0.10 or more and 0.30 or less>

[0059] When the coating composition contains both metal carbonate and metal fluoride, the softening point of the flux can be increased by appropriately controlling the weight ratio between metal fluoride and metal carbonate. As a result, a protective sheath with a desired length can be stably formed, and arc directivity can be improved. Accordingly, drop deflection is further reduced, good arc stability is obtained and weldability is improved.

[0060] When the above ratio {C _{F, total} /(C _{CO2, total} +C _{F, total} )} is 0.10 or more and 0.30 or less, the softening temperature of the flux can be appropriate, the containment can be maintained with sufficient length, and the weldability is further improved. Therefore, the above ratio is preferably 0.10 or more. The above ratio is preferably 0.30 or less, and more preferably 0.15 or less.

<Total content (Si conversion value) of C _{Si, total} Si and Si compounds in the coating composition (C _{Si, total} ) relative to the total weight of the coating composition C _{coating, total} : 6.0 wt.% or more and 9.0 wt.% or less>

[0061] Silicon (Si) and Si compounds are compounds that are in the coating composition in the form of SiO ₂ and act as a catalyst to promote the decomposition of metal carbonate (CaCO ₃ ). For example, CaCO ₃ in the presence of SiO ₂ forms CaO∙SiO ₂ and gaseous CO ₂ , and when CaCO ₃ having a grain diameter of 75 µm or more is present at a content equal to or greater than a given amount, the amount of gaseous CO ₂ increases. formed per unit time, and the compression force effectively acts, thereby stimulating the manifestation of droplet compression. When thermal decomposition of CaCO ₃ occurs, the resulting CaO reacts with SiO ₂ and the heat of this reaction promotes thermal decomposition of undecomposed CaCO ₃ . Si and the Si compound are in the coating composition in the form of SiO ₂ and react with metal fluoride to form a fluorine-containing gas. For example, 2CaF ₂ reacts with SiO ₂ to form 2CaO and gaseous SiF ₄ . In this case, the gaseous SiF ₄ formed by this reaction has a smaller volume than the volume of the gaseous CO ₂ formed from the metal carbonate using SiO ₂ as a catalyst, so that the gaseous SiF ₄ has a relatively small effect on droplet release.

[0062] As described above, in the present embodiment, the total content of metal fluoride with a grain diameter of 75 µm or more in the coating composition or the total area of metal fluoride with an equivalent circle diameter of 30 µm or more in a section perpendicular to the longitudinal direction of the electrode is set, and this means that the coating composition contains metal fluoride with a large grain diameter. Thus, the amount of gas formed increases, stimulating the manifestation of droplet compression. When a metal fluoride with a large grain diameter is contained in the coating composition, the following effects can be additionally obtained. Namely, since the large grain diameter metal fluoride has a small specific surface area, the large grain diameter metal fluoride can inhibit the reaction between the metal fluoride (eg, CaF ₂ ) and SiO ₂ compared to the small grain diameter metal fluoride. As described above, the amount of gaseous SiF ₄ generated by the reaction between metal fluoride and SiO ₂ is not significant compared to the amount of gaseous CO ₂ generated from the above-described metal carbonate using SiO ₂ as a catalyst. Therefore, for example, by inhibiting the reaction between CaF ₂ and SiO ₂ , the amount of SiO ₂ acting as a catalyst for the metal carbonate can be sufficiently ensured, and more uniform droplet release can be promoted.

[0063] In the case where the coating composition further contains at least one of Si and Si compounds, and the total content (Si conversion value) of Si and Si compounds in the coating composition (C _{Si, total} ) relative to the total weight of the coating composition (C _{coating , total} ) is 6.0 wt.% or more, you can further promote the release of gaseous CO ₂ and fluorine-containing gas. Therefore, the above-described value of C _{Si, the total is} preferably 6.0 wt.% or more. On the other hand, when the above-described C _{Si total} is 9.0 wt.% or less, it is easier to maintain the desired mechanical properties and stable shape of the weld bead in the weld metal. Therefore, the above-described C _{Si total is} preferably 9.0 mass% or less, and more preferably 8.0 mass% or less.

[0064] Further, the coating composition in the present embodiment may contain an alloy, an oxide, and the like, in addition to metal carbonate, metal fluoride, Si, and Si compounds. These other components are described below. In the following description, the amount of each component in the coating composition is given as the content relative to the total weight of the coating composition. The content of each component in the entire coated electrode is given as content relative to the total weight of the electrode.

<The content of Fe in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.0 wt.% or more (including 0 wt.%) and 35.0 wt.% or less>

[0065] Fe is a component added to the coating composition of the coated electrode for the purpose of improving the mechanical properties of the weld metal by deoxidizing action, or adding an alloy and improving the welding efficiency by increasing the amount of weld metal, and Fe is contained in the form of Fe-Si, Fe -Mn or the like, in addition to being contained in the coating composition in the form of iron powder. Fe in the coating composition may optionally be added depending on the need for the above-described effect, and the lower limit need not be specifically set, and it may be 0.0 mass%. However, in the case of further improvement in mechanical properties, it is preferable to add Fe in an amount of 0.1 mass% or more in order to reduce the O content in the weld metal. When the content of Fe in the coating composition is 35.0 mass% or less, it is possible to reduce the droplet size transferred to the molten bath and further improve the weldability. Accordingly, in terms of the lower limit of the Fe content of the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ), the Fe content is more preferably 0.1 wt.% or more. With respect to the upper limit of the Fe content of the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ), the Fe content relative to the total weight of the coating composition is preferably 35.0 mass% or less, more preferably 32.0 mass% or less, and even more preferably 30.0 mass% or less. For the same reason as described above, the Fe content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 60.0 mass% or more and 85.0 mass% or less, more preferably 70. 0 wt.% or more and 85.0 wt.% or less, and even more preferably 72.0 wt.% or more and 85.0 wt.% or less.

<Al content of the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.0 mass% or more (including 0 mass%) and 1.0 mass% or less>

[0066] Al (Al metal) is a component having the effect of improving the crack resistance of the weld metal and improving the corrosion resistance and oxidation resistance, and can be added as needed. The lower limit of Al need not be specified and may be 0.0 wt%. In the case where Al is added to the coating composition and the content of Al in the coating composition is 1.0 mass% or less, the weld metal can have sufficient ductility in addition to the above-described effects. Accordingly, the content of Al in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ) is preferably 1.0 wt.% or less, more preferably 0.8 wt.% or less, and even more preferably 0.6 wt.% or less. For the same reason as described above, the Al content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.50 mass% or less (including 0 mass%), more preferably 0.30 mass .% or less, and even more preferably 0.10 wt.% or less.

<Ni content in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.0 mass% or more (including 0 mass%), and 4.0 mass% or less>

[0067] Ni is a component showing the effect of improving the fatigue strength of the weld, and can be added if necessary. The lower limit of Ni need not be set and may be 0.0 wt%. In the case where Ni is added to the coating composition and the content of Ni in the coating composition is 4.0 mass% or less, hot cracks in the weld metal can be further prevented. Accordingly, the content of Ni in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ) is preferably 4.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 2.5 mass% or less. For the same reason as described above, the content of Ni in the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 1.00 mass% or less, more preferably 0.60 mass% or less, and still more preferably 0.30 mass% or less.

<Content of Mn in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 1.5 mass% or more and 6.0 mass% or less>

[0068] Mn is a component showing the effect of improving the strength of the alloy material, and can be added as needed. The lower limit of Mn need not be set and may be 0.0 wt%. When the content of Mn in the coating composition is within the range of 1.5 mass% or more and 6.0 mass% or less, hot cracking can be prevented while maintaining the strength of the weld metal. Accordingly, the content of Mn in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 1.5 wt.% or more and 6.0 wt.% or less, more preferably 1.7 wt.% or more and 4 .8 wt.% or less, and even more preferably 1.8 wt.% or more and 4.2 wt.% or less. For the same reason as described above, the Mn content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.8 mass% or more and 1.8 mass% or less, more preferably 0. 8 wt.% or more and 1.6 wt.% or less, and even more preferably 0.8 wt.% or more and 1.4 wt.% or less.

<The content of Si in the coating composition relative to the total weight of the coating composition (C _{coating, total} ): 1.0 wt.% or more and 9.0 wt.% or less>

[0069] Si (metal Si) is a deoxidizer and is a component having an effect of reducing the amount of oxygen in the weld metal and improving the strength of the weld metal. Si can be added as needed. The lower limit Si need not be set and may be 0.0 mass%. However, when the content of Si in the coating composition is within the range of 1.0 mass% or more and 9.0 mass% or less, the droplet size transferred to the molten bath can be further reduced and weldability improved. Accordingly, the content of Si in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ) is preferably 1.0 wt.% or more and 9.0 wt.% or less, more preferably 2.4 wt.% or more and 7 .0 wt.% or less, and even more preferably 2.8 wt.% or more and 6.6 wt.% or less. For the same reason as described above, the Si content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.8 mass% or more and 2.2 mass% or less, more preferably 1. 0 wt.% or more and 2.0 wt.% or less, and even more preferably 1.1 wt.% or more and 1.9 wt.% or less.

<Content of Mo in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.0 wt.% or more (including 0 wt.%) and 2.0 wt.% or less>

[0070] Mo is a component having an effect of improving the strength of the weld metal, and may be added as needed. The lower limit of Mo does not have to be set and may be 0.0 mass%. In the case where Mo is added to the coating composition and the Mo content of the coating composition is 2.0 mass% or less, cracking can be further prevented while maintaining strength. Accordingly, the content of Mo in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ) is preferably 2.0 wt.% or less, more preferably 1.2 wt.% or less, and even more preferably 0.8 wt.% or less. For the same reason as described above, the content of Mo in the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.65 mass% or less (including 0 mass%), more preferably 0.45 mass .% or less, and even more preferably 0.30 wt.% or less.

<The content of Al ₂ O ₃ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ): 0.02 wt.% or more and 3.0 wt.% or less>

[0071] Al ₂ O ₃ is a component exhibiting an arc stabilizing effect and a slag forming effect. When the content of Al ₂ O ₃ in the coating composition is 3.0 mass% or less, a higher arc stabilization effect can be obtained. Accordingly, the content of Al ₂ O ₃ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 0.02 wt.% or more and 3.0 wt.% or less, more preferably 0.03 wt.% or more and 2.6 wt.% or less, and even more preferably 0.05 wt.% or more and 2.0 wt.% or less. For the same reason as described above, the content of Al ₂ O ₃ in the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.01 mass% or more and 0.90 mass% or less, more preferably 0.02 mass% or more and 0.80 mass% or less, and even more preferably 0.02 mass% or more and 0.70 mass% or less.

<The content of SiO ₂ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ): 1.5 wt.% or more and 15.0 wt.% or less>

[0072] SiO ₂ is a component that acts as a melting agent or adhesive. When the content of SiO ₂ in the coating composition is 1.5 mass% or more, the above-described effects can be sufficiently obtained. In addition, when the content of SiO ₂ in the coating composition is 15.0 mass% or less, the peelability of the slag is further improved. Accordingly, the content of SiO ₂ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 1.5 wt.% or more and 15.0 wt.% or less, more preferably 2.0 wt.% or more, and 10.0 wt.% or less, and even more preferably 4.0 wt.% or more and 8.0 wt.% or less. For the same reason as described above, the content of SiO ₂ in the coated electrode relative to the total mass of the coated electrode (C _{electrode, total} ) is preferably 0.40 mass% or more and 4.00 mass% or less, more preferably 0 .60 wt.% or more and 3.60 wt.% or less, and even more preferably 0.80 wt.% or more and 3.20 wt.% or less, relative to the total weight of the coated electrode.

<Content of TiO ₂ in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.2 mass% or more and 10.0 mass% or less>

[0073] TiO ₂ is a component having a slag-forming action in the coating composition of the coated electrode, forming a slag with good fluidity, imparting a gloss to the surface of the weld bead, and imparting excellent appearance to the weld metal. In addition, TiO _{2 is} also a component that helps to prevent arc deflection (fluctuation) and obtain good weldability. When the content of TiO ₂ in the coating composition relative to the total weight of the coating composition is within the range of 0.2 mass% or more and 10.0 mass% or less, the above-described effects are further improved. Accordingly, the content of TiO ₂ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 0.2 wt.% or more and 10.0 wt.% or less, more preferably 0.5 wt.% or more, and 8.0 wt.% or less, and even more preferably 1.0 wt.% or more and 6.0 wt.% or less. For the same reason as described above, the content of TiO ₂ in the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 1.00 mass% or more and 4.00 mass% or less, more preferably 1 20 wt% or more and 3.00 wt% or less, and even more preferably 1.40 wt% or more and 2.60 wt% or less.

<The content of MgO in the coating composition relative to the total mass of the coating composition ( _{Ccoat, total} ): more than 0.01 wt.% and 4.0 wt.% or less>

[0074] MgO is a component exhibiting the effect of increasing the peelability of the slag. When the content of MgO in the coating composition is more than 0.01 mass% and 4.0 mass% or less, the above-described effects are further improved. Accordingly, the content of MgO in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably more than 0.01 wt.% and 4.0 wt.% or less, more preferably 0.2 wt.% or more and 1. 0 wt.% or less, and even more preferably 0.5 wt.% or more and 0.8 wt.% or less. For the same reason as above, the MgO content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.01 mass% or more and 1.00 mass% or less, more preferably 0. 01 wt% or more and 0.80 wt% or less, and even more preferably 0.01 wt% or more and 0.50 wt% or less.

<Total content of K ₂ O, Li ₂ O and Na ₂ O in the coating composition relative to the total weight of the coating composition (C _{coating, total} ): 1.6 wt.% or more and 3.6 wt.% or less>

[0075] K ₂ O, Li ₂ O and Na ₂ O are components contained in a large amount in water glass used as an inorganic binder in a coating composition, and are also added as powdered raw materials and are effective components for improving stability arc to obtain good arc stability and proper arc pressure. 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 composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 1.6 wt.% or more and 3.6 wt.% or less, more preferably 1.8 wt.% or more and 3.2 wt.% or less, and even more preferably 2.0 wt.% or more and 3.0 wt.% 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 electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.20 mass% or more and 1, 40% by mass or less, more preferably 0.40% by mass or more and 1.20% by mass or less, and even more preferably 0.60% by mass or more and 1.00% by mass or less. In addition, Li ₂ O also has the effect of improving the moisture absorption resistance of the coated electrode and reducing the diffusible hydrogen in the weld metal.

<Content of C in the coating composition relative to the total weight of the coating composition ( _{Ccoat, total} ): 0.0 wt.% or more (including 0 wt.%) and 0.15 wt.% or less>

[0076] C (carbon) is a component that helps improve the strength of the weld metal, and can be added if necessary. The lower limit of the C content does not have to be set and may be 0.0 mass%. In the case where C is added to the coating composition, the content of C is preferably 0.15 wt% or less to prevent the weld metal from degrading and cracking. Accordingly, the content of C in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 0.0 wt.% or more and 0.15 wt.% or less. For reasons of improving weldability, the C content is more preferably 0.01 mass% or more and 0.10 mass% or less, and even more preferably 0.02 mass% or more and 0.08 mass% or less. Examples of the C source include organics, various minerals, dopants, graphite, and the like. For the same reason as described above, the C content of the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ) is preferably 0.15 mass% or less (including 0 mass%), more preferably 0.01 mass .% or more and 0.10 wt.% or less, and even more preferably 0.02 wt.% or more and 0.08 wt.% or less.

<Other>

[0077] The rest of the coating composition of the present embodiment is unavoidable impurities. 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. The total content of unavoidable impurities in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) is preferably 5.0 wt.% or less (including 0 wt.%). In addition, it is more preferable that the content of Nb ₂ O ₅ in the coating composition relative to the total weight of the coating composition (C _{coating, total} ) be limited to 0.3 wt.% or less (including 0 wt.%), the content of V ₂ O ₅ was limited to 0.3 mass% or less (including 0 mass%), the content of ZrO ₂ was limited to 0.4 mass% or less (including 0 mass%), and the content of Fe ₂ O ₃ ∙FeO was limited to 3.50 wt.% or less (including 0 wt.%). It should be noted that the concept of impurities also includes those that are not provided for in the design of the electrode. For example, ilmenite raw materials are added to the coating composition of an ilmenite-based coated electrode, which means that Fe ₂ O ₃ ∙FeO not provided in the design of the electrode can be contained in an amount of 3.50 wt.% maximum, and they are defined as impurities.

[0078] The following describes the electrode wire and the proportion of the coating.

[electrode wire]

[0079] The electrode wire in the present embodiment is not particularly limited, and for example, an electrode wire having a diameter d of 2.6 mm to 6.0 mm can be used, and an electrode wire with a diameter of 4.0 mm can be particularly preferably used. mm. The composition of the electrode wire in the present embodiment is described below.

<O content: 0.0005 mass% or more and 0.0150 mass% or less>

[0080] When the O content of the electrode wire is excessive, the amount of O in the resulting weld metal becomes excessive, and the fracture toughness of the weld metal may decrease. In addition, since the oxygen in the electrode wire reacts with Fe-Si or Fe-Mn, which is a deoxidizer added to the coating composition, to form slag, the amount of slag increases, which may cause deterioration in slag flowability and weldability, and further may cause deterioration of mechanical properties due to a decrease in the amount of Si or Mn in the weld metal or an increase in the amount of oxygen. In addition, the fluidity of the molten metal increases, and it may not be possible to hold the weld metal at the time of welding in a standing position, an up position, or the like, and therefore weldability may deteriorate. On the other hand, when the O content of the electrode wire is too low, the spreading of the melt pool under the arc pressure becomes insufficient, and a weld metal in which the alloying components are uniformly distributed cannot be obtained. Based on the above considerations, the O content of the electrode wire relative to the total weight of the electrode wire is preferably 0.0005 mass% or more, more preferably 0.0013 mass% or more, and even more preferably 0.0016 mass% or more. The O content of the electrode wire is preferably 0.0150 mass% or less, more preferably 0.0125 mass% or less, and even more preferably 0.0100 mass% or less.

<Other Components>

[0081] Although not specifically limited, as the electrode wire in the present embodiment, for example, an iron-based electrode wire containing Fe as a main component can be preferably used. More specifically, SWRY11 specified in JIS G 3503:2006 can be used as the electrode wire. In addition to O and Fe, C, Si, Mn, P, S, N, Cu and the like may be contained in the electrode wire. Preferably, the C content of the electrode wire relative to the total weight of the electrode wire is limited to 0.09 wt% or less, the Si content is limited to 0.03 wt% or less (including 0 wt%), the Mn content is limited to 0.35 wt% or more and 0.65 wt% or less, the P content was limited to 0.020 wt% or less (including 0 wt%), the S content was limited to 0.023 wt% or less ( including 0 mass %), and the content of Cu was limited to 0.20 mass % or less (including 0 mass %).

[Share coverage]

[0082] In the present embodiment, the coating ratio of the coating composition on the outer surface of the electrode wire is not particularly limited, but, for example, it is preferably 20% or more, more preferably 22% or more, and even more preferably 24% or more, for reasons ensuring the strength of the coating composition. In addition, for reasons of arc stability and the like, the coverage ratio is, for example, preferably 40% or less, more preferably 38% or less, and even more preferably 36% or less.

[0083] The present embodiment also relates to a coated electrode arc welding method in which the components in the above-described coating composition are adjusted. In the arc welding method of the present embodiment, the reasons for limiting the components (grain diameter, area ratio, and the like) in the coating composition of the electrode used, the length of the coating composition remaining after applying the arc, and the like are as described above, and therefore their description omitted. Next, the welding position in the arc welding method in the present embodiment will be specifically described.

[Welding position]

<The coated electrode is perpendicular to the base metal or has a lag angle of more than 0° and 30° or less relative to the base metal>

[0084] The coated electrode in the present embodiment is preferably used in arc welding in a welding position in which the coated electrode is perpendicular to the base metal (i.e., the coated electrode is perpendicular to the base metal), or the lag angle of the coated electrode relative to the base metal is more than 0° and 30 ° or less. As described above, welding using a coated electrode is often performed in different welding positions such as lead angle and lag angle, and in the case where welding is carried out in these welding positions (i.e., in the case where the covered electrode is correspondingly inclined), a noticeable one-sided melting compared to the case when the coated electrode is perpendicular to the base metal. In consumable coated electrode arc welding, in the case of a lagging angle of more than 0° and 30° or less, the coated electrode in the present embodiment can achieve essentially the same effect as when the coated electrode is perpendicular to the base metal. The above-described lagging angle is more preferably 5° or more and 25° or less. Even in the case where the welding position is perpendicular, the molten pool itself may in some cases not be horizontal with respect to the base metal. However, the coated electrode in the present embodiment is highly reliable and can prevent one-sided melting even if some disturbance or error occurs.

[0085] The coated electrode in the present embodiment can be applied as a welding electrode based on various types of electrodes, such as ilmenite-based coated electrode, titanium oxide-based coated electrode, lime-titanium dioxide-based coated electrode, iron powder-titanium oxide coated electrode, cellulose coated electrode, low hydrogen coated electrode and low hydrogen iron powder coated electrode. Since a large amount of gasifier is added to the coating composition of the low hydrogen coated electrode to reduce diffusible hydrogen, the droplet releasing effect of the gasifier becomes excellent when the coated electrode of the present embodiment is used as the low hydrogen coated electrode. In addition, a large amount of iron powder is added to the coating composition of the low-hydrogen iron powder coated electrode in order to obtain a desirable amount of weld metal, and this iron powder causes strong droplet growth. Therefore, there is such a problem that uniform droplet tolerance cannot be obtained, and heavy droplet splashing occurs. Accordingly, it is most preferable that the coated electrode of the present embodiment, with which droplet release can be improved, is used as a low hydrogen iron powder coated electrode.

[0086] The method for producing the coated electrode described here is not particularly limited. For example, the coated electrode of the present embodiment can be obtained by mixing the raw material of the coating composition together with water glass, applying the resulting mixture to the outer surface of the electrode wire, and performing drying and firing.

Examples

[0087] Hereinafter, the present invention is described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to them.

[Production of coated electrode, arc welding and calculation of various parameters]

[0088] SWRY 11 with a diameter of 3.2 to 5.0 mm was used as the electrode wire, and coating compositions (coating compositions Nos. C1-C15) having the chemical composition shown in Table 1 were applied to the outer surfaces of the electrode wires, with coverage rates of 26.9% to 35.6% as shown in Table 3, respectively, followed by drying to obtain various coated electrodes (Test Nos. T1-T19 shown in Table 3).

[0089] Table 1 shows the content of each component in the coating composition relative to the total weight of the coating composition (C _{pcr, total} ). In Table 1, the rest is unavoidable impurities, and the amount of each component in the coating composition indicates the content (wt.%) relative to the total weight of the coating composition (C _{CO, total} ). Table 4 shows the content of each component in the coated electrode relative to the total weight of the coated electrode (C _{electrode, total} ). In Table 4, the rest is unavoidable impurities, and the amount (wt.%) of each component in the coated electrode indicates the content (wt.%) relative to the total mass of the electrode (C _{electrode, total} ).

[0090] In addition, Table 2 shows a list of values of various physical properties related to the content of metal carbonate contained in the coating composition, or the content of metal fluoride contained in the coating composition. In Table 2, C[CO ₂ , 75 µm] means the total content (CO ₂ conversion value) of metal carbonate with a grain diameter of 75 µm or more, C[F, 75 µm] means the total content (F conversion value) of metal fluoride with a grain diameter grains 75 µm or more, C[CO ₂ , 106 µm] means the total content (CO ₂ conversion value) of metal carbonate with a grain diameter of 106 µm or more, C[F, 106 µm] means the total content (F conversion value) of metal fluoride with a grain diameter of 106 µm or more, C[CO ₂ , 150 µm] means the total content (CO ₂ conversion value) of metal carbonate with a grain diameter of 150 µm or more, and C[F, 150 µm] means the total content (F conversion value ) metal fluoride with a grain diameter of 150 µm or more. In addition, C[CO ₂ , total] means the total content (CO ₂ conversion value) of metal carbonates contained in the coating composition, and C[F, total] means the total content (F conversion value) of metal fluorides contained in the coating composition. C[cover, total] means the total weight of the coating composition, and C[Si, total] means the total content (Si conversion value) of Si and the Si compound.

[0091] Here, for example, C[CO ₂ , 75 μm]/C[CO ₂ , total] shown in column (1) in Table 2 means the content ratio (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 μm or more (C _{CO2, 75 µm} ) relative to the total content (CO ₂ conversion values) of metal carbonates contained in the coating composition (C _{CO2, total} ). The same applies to other columns.

[0092] In addition, "(5)+(6)" shown in column (7) in Table 2 means the total amount of C[CO ₂ , 75 µm]/C[cover, total] shown in column (5 ), and C[F, 75 µm]/C[cover, total] shown in column (6), that is, the total content ratio (CO ₂ conversion values) of metal carbonate with a grain diameter of 75 µm or more (C _{CO2 , 75 µm} ) relative to the total weight of the coating composition (C _{cover, total} ) and the ratio of the content (conversion values F) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total weight of the coating composition (C _{cover, total} ) . Similarly, "(8)+(9)" shown in column (10) in Table 2 shows the total content ratio (CO ₂ conversion values) of metal carbonate with a grain diameter of 106 µm or more (C _{CO2, 106 µm} ) relative to the total weight of the coating composition (C _{cover, total} ) and the ratio of the content (values of conversion F) of metal fluoride with a grain diameter of 106 μm or more (C _{F, 106 μm} ) relative to the total weight of the coating composition (C _{cover, total} ). Similarly, "(11)+(12)" shown in column (13) in Table 2 shows the total content ratio (CO ₂ conversion values) of metal carbonate with a grain diameter of 150 µm or more ( _{CCO2, 150 µm} ) relative to the total weight of the coating composition (C _{cover, total} ) and the ratio of the content (values of conversion F) of metal fluoride with a grain diameter of 150 μm or more (C _{F, 150 μm} ) relative to the total weight of the coating composition (C _{cover, total} ).

[0093] Then, arc welding was performed using the obtained coated electrode under the following welding conditions, and the power supply was optionally turned off 10 seconds after the start of welding. As shown in Table 5, in tests Nos. T9 and T10, the tests were performed with various changes in the angle of retardation within the range from 5° to 25°. In other test examples than Test Nos. T9 and T10, the tests were performed with the lagging angle fixed at 15°.

[0094] <Welding Conditions>

Power supply polarity: DCEP (DC positive electrode)

Welding position: bead from top to bottom on the plate

Weld object: SM490 steel sheet with dimensions of 12mm thick × 70mm wide × 450mm long

Welding current: 150A (target) ± 10A

Arc voltage: 21V (target) ± 2V

[0095] Thereafter, the length was measured from the distal end portion of the coating composition (sheath) remaining around the electrode wire on the distal end side of the electrode to the rear end portion of the electrode on the holder side (rear end side), and the length was measured from the rearmost portion coating composition (protective sheath) remaining around the electrode wire on the side of the distal end of the electrode, to the area of the rear end of the electrode on the side of the holder. In addition, the protective shell coating composition and the slag remaining on the end portion of the electrode wire were removed, and the length from the distal end portion of the electrode wire to the rear end portion of the electrode on the holder side was measured. Then, these measured values were used to calculate the distance D1 between the distal end portion of the electrode wire and the distal end portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode, and the distance D2 between the distal end portion of the coating composition remaining around the electrode wire and the most the back portion of the coating composition remaining around the electrode wire, in the longitudinal direction of the electrode (see Table 5).

[0096] The coated electrode obtained by the above method was immersed in resin so that the section perpendicular to the longitudinal direction served as the surface to be examined, and examined with a scanning electron microscope (SEM). An SEM-based study was performed using reflected electron (BSE) imaging at 50x magnification and an accelerating voltage of 15 kV. Then, the cross section of the coating composition was subjected to elemental analysis using energy dispersive X-ray spectroscopy (EDX), and the area ratio of grains with an equivalent circle diameter of 30 μm or more, that is, the ratio of S ₂ to S ₁ (S ₂ /S ₁ ), in which S ₁ was the cross-sectional area of the entire coating composition, and S ₂ was the total area of at least one of a metal carbonate and a metal fluoride each having an equivalent circle diameter of 30 µm or more.

[0097] SEM-based EDX analysis can be performed as follows. For example, using a TM3030 Miniscope manufactured by Hitachi High-Tech Corporation, the cross section of the coated electrode was analyzed (magnification: 50 times, four rectangular areas of 1.61 mm×1.21 mm). The field of view is desirably chosen such that the cross section of the coating composition is 70% or more in each field of view. Then, binarized 1024 × 768 pixels (number of pixels: 786432) with respect to one field of view using a software for image analysis Image J, we can calculate the proportion of the area of grains having an area of 706.8 m ² or more (equivalent circle diameter: 30 µm or more). The threshold value during binarization is, for example, 60.

[0098] The measurement results of the electrode wire diameter d and S ₂ /S ₁ in the coated electrode 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.

[0099] In addition, the coated electrodes of Tests Nos. T1-T15 (Examples) and Tests Nos. T16-T19 (Comparative Examples) were used for welding under the same welding conditions at the time of measuring the above D ₁ and D ₂ and were evaluated in terms of the evaluation of one-sided melting (presence or absence of one-sided melting), arc deflection prevention effect, and weldability according to the following evaluation criteria.

[Assessment of unilateral melting (presence or absence of unilateral melting)]

[0100] In the case where D ₂ /D ₁ ≦0.40 is satisfied: none

In the case where D ₂ /D ₁ >0.40 is satisfied: present

[Arc deflection prevention effect]

[0101] The presence or absence of arc deflection and the appearance of the weld bead were visually assessed. The case of determining that the arc did not deviate and the bead appearance was good was rated ○○ (excellent), the case of determining that the arc was slightly deviated but the bead appearance was good was rated ○ (good), and the case of determining that the arc deviated and the appearance of the roller was poor, was evaluated as × (poor).

[Weldability (organoleptic evaluation)]

[0102] The case of visually determining that droplets were intermittently transferred during welding and only small spatter was formed was rated as ○○ (excellent), the case of determining that drops were intermittently transferred during welding, but spatter of moderate size was generated was rated as ○ (good ), and the case of determining that the droplets were not intermittently transferred during welding and coarse spatter was generated was rated as × (poor).

[0103] Table 1

Coating composition No. The content of each component in the coating composition relative to the total mass of the coating composition (C _{coating, total} ) (wt.%) metal carbonate metal fluoride Si Mn Fe SiO Al ₂ O ₃ TiO ₂ MgO Na ₂ O +
K ₂ O +
Li ₂ O C Ni Mo Al CaCO ₃ BaCO ₃ Total Total CO _{2 Conversion} CaF ₂ F conversion value C1 53.5 0.0 53.5 23.5 17.1 8.3 6.60 2.44 9.3 5.87 0.22 0.79 0.00 2.41 0.06 0.00 0.000 0.124 C2 43.2 9.2 52.4 21.1 16.7 8.1 5.08 1.98 7.2 7.35 0.08 5.74 0.26 2.78 0.05 0.00 0.000 0.095 C3 51.2 3.8 55.0 23.4 16.3 7.9 5.74 2.91 8.3 1.74 0.47 6.19 0.53 2.61 0.07 0.00 0.000 0.108 C4 47.0 0.0 47.0 20.7 6.7 3.3 4.51 4.68 7.0 14.13 2.58 8.07 0.00 2.79 0.05 0.00 0.000 0.083 C5 53.7 0.0 53.7 23.6 0.0 0.0 6.36 1.85 19.7 6.05 0.28 5.82 0.33 2.00 0.05 0.00 0.000 0.119 C6 32.1 0.0 32.1 14.1 12.2 5.9 3.68 3.06 27.8 6.43 0.28 5.46 1.13 2.62 0.04 1.21 0.557 0.148 C7 32.0 0.0 32.0 14.1 12.1 5.9 3.67 3.05 27.7 6.42 0.60 5.44 1.13 2.62 0.04 1.21 0.555 0.148 C8 32.1 0.0 32.1 14.1 12.2 5.9 3.68 3.06 27.8 6.37 0.28 5.46 1.13 2.69 0.04 1.21 0.557 0.148 C9 32.0 0.0 32.0 14.1 12.1 5.9 3.67 3.05 27.7 6.36 0.60 5.44 1.13 2.69 0.04 1.21 0.555 0.148 C10 32.0 0.0 32.0 14.1 12.1 5.9 3.67 3.05 27.7 6.36 0.60 5.44 1.13 2.69 0.04 1.21 0.555 0.148 C11 32.6 0.0 32.6 14.4 12.2 5.9 3.74 3.11 28.3 6.61 0.30 5.55 0.39 2.62 0.04 1.23 0.567 0.233 C12 27.3 0.0 27.3 12.0 1.5 0.7 2.73 7.00 4.8 5.43 1.32 41.16 0.22 2.84 0.06 0.00 0.000 0.049 C13 28.1 1.9 30.0 12.8 15.6 7.6 3.38 2.76 28.6 6.68 0.80 6.66 0.21 3.05 0.07 0.00 0.000 0.062 C14 24.0 0.0 24.0 10.6 19.3 9.4 3.28 2.47 33.0 5.55 0.30 6.06 0.47 2.86 0.06 0.00 0.000 0.157 C15 26.7 0.0 26.7 11.7 17.8 8.7 3.82 3.18 28.8 6.19 0.25 5.67 0.39 2.62 0.04 1.26 0.578 0.154

[0104] Table 2

Coating composition No. Values of various physical properties related to the content of metal carbonate or the content of metal fluoride contained in the coating composition (wt.%) (one) (2) (3) (4) (5) (6) (7) (eight) (9) (10) (eleven) (12) (thirteen) (14) (15) C[CO ₂ , 75 µm]/C[CO ₂ , total] C[F, 75 µm]/C[F, total] C[CO ₂ , total]/C[cover, total] C[F, total]/C[cover, total] C[CO ₂ , 75 µm]/C[coated, total] C[F, 75 µm]/ C[coated, total] (5)+(6) C[CO ₂ , 106 µm]/C[coated, total] C[F, 106 µm]/C[coated, total] (8)+(9) C[CO ₂ , 150 µm]/C[coated, total] C[F, 150 µm]/C[coated, total] (11)+(12) C[F, total]/{C[CO ₂ , total] + C[F, total]} C[Si, total]/ C[cover, total] C1 33.8 33.0 23.5 8.3 7.9 2.8 10.7 5.8 2.3 8.1 3.1 1.6 4.7 0.26 9.34 C2 34.8 28.3 21.1 8.1 7.3 2.3 9.6 5.3 1.8 7.1 2.9 1.2 4.1 0.28 8.52 C3 42.9 21.4 23.4 7.9 10.0 1.7 11.7 7.3 1.2 8.5 3.9 0.7 4.6 0.25 6.55 C4 32.5 23.1 20.7 3.3 6.7 0.8 7.5 4.9 0.5 5.4 2.6 0.3 2.9 0.14 11.11 C5 40.5 0.0 23.6 0.0 9.6 0.0 9.6 6.9 0.0 6.9 3.8 0.0 3.8 0.00 9.18 C6 32.4 43.2 14.1 5.9 4.6 2.6 7.2 3.3 2.3 5.6 1.8 1.7 3.5 0.30 6.69 C7 32.4 43.2 14.1 5.9 4.6 2.5 7.1 3.3 2.3 5.6 1.8 1.7 3.5 0.30 6.67 C8 32.4 43.2 14.1 5.9 4.6 2.6 7.2 3.3 2.3 5.6 1.8 1.7 3.5 0.30 6.66 C9 32.4 43.2 14.1 5.9 4.6 2.5 7.1 3.3 2.3 5.6 1.8 1.7 3.5 0.30 6.64 C10 32.5 43.3 14.1 5.9 4.6 2.6 7.2 3.3 2.3 5.6 1.8 1.7 3.5 0.30 6.64 C11 40.5 52.9 14.4 5.9 5.8 3.1 8.9 4.2 3.0 7.2 2.3 2.3 4.6 0.29 6.83 C12 29.0 22.9 12.0 0.7 3.5 0.2 3.7 2.5 0.1 2.6 1.4 0.1 1.5 0.06 5.26 C13 27.0 23.1 12.8 7.6 3.5 1.8 5.3 2.5 1.2 3.7 1.4 0.7 2.1 0.37 6.50 C14 35.4 23.1 10.6 9.4 3.7 2.2 5.9 2.8 1.5 4.3 1.5 0.9 2.4 0.47 5.88 C15 16.2 23.0 11.7 8.7 1.9 2.0 3.9 1.4 1.4 2.8 0.7 0.8 1.5 0.42 6.71

[0105] Table 3

Test No. Coated electrode Note Coating composition Share of coverage Diameter d of the electrode wire in the coated electrode S ₂ / S ₁ Coating composition No. Wt% mm - T1 C1 30.0 4.0 0.087 Example T2 C2 30.0 4.0 0.077 Example T3 C3 27.0 4.0 0.078 Example T4 C4 26.9 4.0 0.068 Example T5 C5 27.6 4.0 0.077 Example T6 C6 35.0 4.0 0.064 Example T7 C7 35.0 4.0 0.081 Example T8 C8 35.0 4.0 0.079 Example T9 C9 35.0 4.0 0.087 Example T10 C10 35.0 4.0 0.079 Example T11 C11 35.0 4.0 0.110 Example T12 C1 31.0 3.2 0.086 Example T13 C2 30.0 3.2 0.070 Example T14 C4 26.9 3.2 0.068 Example T15 C3 28.0 5.0 0.078 Example T16 C12 35.6 4.0 0.059 Comparative Example T17 C13 34.0 4.0 0.059 Comparative Example T18 C14 350 4.0 0.078 Comparative Example T19 C15 35.0 4.0 0.055 Comparative Example

[0106] Table 4

Test No. The content of each component in the coated electrode relative to the total mass of the coated electrode (C _{electrode, total} ) (wt.%) Note metal carbonate metal fluoride Si Mn Fe SiO ₂ Al ₂ O ₃ TiO ₂ MgO Na ₂ O +
K ₂ O +
Li ₂ O C Ni Mo Al CaCO ₃ BaCO ₃ Total General
_{CO 2} conversion value CaF ₂ F conversion value T1 16.0 0.0 16.0 7.1 5.1 2.5 2.0 1.0 72.5 1.76 0.07 0.24 0.00 0.72 0.06 0.00 0.00 0.04 Example T2 13.0 2.8 15.7 6.3 5.0 2.4 1.5 0.9 71.8 2.20 0.02 1.72 0.08 0.83 0.06 0.00 0.00 0.03 Example T3 13.8 1.0 14.8 6.3 4.4 2.1 1.6 1.1 74.9 0.47 0.13 1.67 0.14 0.70 0.06 0.00 0.00 0.03 Example T4 12.6 0.0 12.6 5.6 1.8 0.9 1.2 1.6 74.7 3.80 0.69 2.17 0.00 0.75 0.06 0.00 0.00 0.02 Example T5 14.8 0.0 14.8 6.5 0.0 0.0 1.8 0.8 77.5 1.67 0.08 1.61 0.09 0.55 0.06 0.00 0.00 0.03 Example T6 11.2 0.0 11.2 4.9 4.3 2.1 1.3 1.3 74.4 2.25 0.10 1.91 0.40 0.92 0.05 0.42 0.19 0.05 Example T7 11.2 0.0 11.2 4.9 4.2 2.1 1.3 1.3 74.4 2.25 0.21 1.90 0.40 0.92 0.05 0.42 0.19 0.05 Example T8 11.2 0.0 11.2 4.9 4.3 2.1 1.3 1.3 74.4 2.23 0.10 1.91 0.40 0.94 0.05 0.42 0.19 0.05 Example T9 11.2 0.0 11.2 4.9 4.2 2.1 1.3 1.3 74.4 2.23 0.21 1.90 0.40 0.94 0.05 0.42 0.19 0.05 Example T10 11.2 0.0 11.2 4.9 4.2 2.1 1.3 1.3 74.4 2.23 0.21 1.90 0.40 0.94 0.05 0.42 0.19 0.05 Example T11 11.4 0.0 11.4 5.0 4.3 2.1 1.3 1.4 74.6 2.31 0.11 1.94 0.13 0.92 0.05 0.43 0.20 0.08 Example T12 16.4 0.0 16.4 7.2 5.3 2.6 2.0 1.0 71.5 1.99 0.11 0.28 0.00 0.78 0.06 0.00 0.00 0.04 Example T13 12.8 2.7 15.6 6.3 5.1 2.5 1.5 0.9 71.8 1.95 0.05 1.72 0.36 0.85 0.06 0.00 0.00 0.03 Example T14 12.7 0.0 12.7 5.6 1.8 0.9 1.2 1.6 74.7 3.82 0.69 2.17 0.00 0.69 0.06 0.00 0.00 0.02 Example T15 14.3 1.1 15.4 6.5 4.6 2.2 1.6 1.1 74.0 0.49 0.13 1.73 0.15 0.73 0.06 0.00 0.00 0.03 Example T16 9.7 0.0 9.7 4.3 0.5 0.3 1.0 2.8 65.8 1.93 0.47 14.65 0.08 1.01 0.06 0.00 0.00 0.02 Compar. example T17 9.6 0.6 10.2 4.3 5.3 2.6 1.2 1.2 75.4 2.27 0.27 2.26 0.07 1.04 0.06 0.00 0.00 0.02 Compar. example T18 8.4 0.0 8.4 3.7 6.7 3.3 1.2 1.1 76.3 1.94 0.11 2.12 0.16 1.00 0.06 0.00 0.00 0.05 Compar. example T19 9.3 0.0 9.3 4.1 6.2 3.0 1.3 1.4 74.8 2.17 0.09 1.98 0.14 0.92 0.05 0.44 0.20 0.05 Compar. example

[0107] Table 5

Test No. Welding conditions Grade Note Welding position and angle Evaluation of one-sided melting Arc deflection prevention effect Weldability D ₂ / D ₁ Presence or absence of unilateral melting D ₁ D ₁ / d - - - mm - - - T1 Lag angle: 15° 0.22 Missing 2.9 0.7 ○○ ○ Example T2 Lag angle: 15° 0.36 Missing 1.6 0.4 ○ ○ Example T3 Lag angle: 15° 0.32 Missing 2.6 0.7 ○ ○ Example T4 Lag angle: 15° 0.25 Missing 2.1 0.5 ○○ ○ Example T5 Lag angle: 15° 0.35 Missing 2.8 0.7 ○ ○ Example T6 Lag angle: 15° 0.18 Missing 2.8 0.7 ○○ ○ Example T7 Lag angle: 15° 0.12 Missing 1.5 0.4 ○○ ○○ Example T8 Lag angle: 15° 0.21 Missing 1.3 0.3 ○○ ○○ Example T9 Lag angle: 5° 0.10 Missing 2.0 0.5 ○○ ○○ Example Lag angle: 10° 0.26 Missing 1.9 0.5 ○○ ○○ Example Lag angle: 15° 0.23 Missing 2.0 0.5 ○○ ○○ Example Lag angle: 20° 0.24 Missing 1.9 0.5 ○○ ○○ Example Lag angle: 25° 0.33 Missing 2.0 0.5 ○○ ○○ Example T10 Lag angle: 5° 0.23 Missing 1.6 0.4 ○○ ○○ Example Lag angle: 10° 0.15 Missing 2.0 0.5 ○○ ○○ Example Lag angle: 15° 0.24 Missing 1.9 0.5 ○○ ○○ Example Lag angle: 20° 0.29 Missing 1.7 0.4 ○○ ○○ Example Lag angle: 25° 0.39 Missing 1.9 0.5 ○○ ○○ Example T11 Lag angle: 15° 0.28 Missing 1.6 0.4 ○○ ○ Example T12 Lag angle: 15° 0.34 Missing 3.6 1.1 ○ ○ Example T13 Lag angle: 15° 0.28 Missing 3.6 1.1 ○○ ○ Example T14 Lag angle: 15° 0.11 Missing 2.1 0.7 ○○ ○ Example T15 Lag angle: 15° 0.36 Missing 4.1 0.8 ○ ○ Example T16 Lag angle: 15° 0.42 Present 1.2 0.3 × × Comparative Example T17 Lag angle: 15° 0.42 Present 2.4 0.6 × × Comparative Example T18 Lag angle: 15° 0.60 Present 1.8 0.5 × × Comparative Example T19 Lag angle: 15° 0.62 Present 1.4 0.4 × × Comparative Example

[0108] Test Nos. T1-T15 (Examples) in Tables 3-5 represent cases using coating compositions Nos. C1-C11 in Table 1 or Table 2 that meet the requirements of the present invention (i.e., the sum of the content (CO conversion values ₂ ) metal carbonate with a grain diameter of 75 µm or more (C _{CO2, 75 µm} ) relative to the total weight of the coating composition (C _{coating, total} ) and the content (conversion F values) of metal fluoride with a grain diameter of 75 µm or more (C _{F, 75 µm} ) relative to the total weight of the coating composition (C _{pok, total} ) is 6.0 wt.% or more) (see column (7) in Table 2). For these tests Nos. T1-T15, as shown in Table 5, the condition D ₂ /D ₁ ≤ 0.40 (no one-sided melting) was satisfied, and excellent or good results were obtained in all of the arc deflection prevention effect and weldability.

[0109] In contrast, Test Nos. T16-T19 (Comparative Examples) in Tables 3-5 represent cases using coating formulations Nos. C12-C15 in Table 1 or Table 2 that do not satisfy the requirements of the present invention (see column (7) in Table 2). For these test Nos. T16-T19, as shown in Table 5, the condition D ₂ /D ₁ ≤ 0.40 was not satisfied (one-sided melting occurred), and poor results were obtained in terms of both the arc deflection prevention effect and weldability.

[0110] As detailed above, with respect to the coated electrode of the present invention, it is found that by preventing one-sided melting and suppressing arc deflection, droplets can be evenly transferred and arc stability is good, thereby obtaining excellent weldability.

[0111] Although embodiments of the invention have been described above with reference to the drawings, it is needless to say that the present invention is not limited to such examples. Those skilled in the art will appreciate that various changes and modifications may be conceivable within the scope of the claims. The essential features in the embodiments described above may be freely combined within a range without departing from the spirit of the present invention.

[0112] The present application is based on Japanese Patent Application No. 2018-170066, filed September 11, 2018, and its contents are incorporated herein by reference.

LIST OF REFERENCES

[0113] 1, 11 coated electrode

2 electrode wire

2a far end section

3, 13 coating composition

3a far end

4, 14 arc

5 base metal

6, 16 protective shell

13a farthest end section

13b rearmost section

d is the diameter of the electrode wire in the coated electrode

D is the distance between the distal end of the protective sheath and the distal end portion of the electrode wire in the longitudinal direction of the electrode

D ₁ distance between the distal end portion of the electrode wire and the distal end portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode

D _{2 the} distance between the portion of the farthest end of the coating composition remaining around the electrode wire and the rearmost portion of the coating composition remaining around the electrode wire in the longitudinal direction of the electrode

Claims (37)

1. Coated welding electrode, comprising: an electrode rod and a coating that contains at least one of a metal carbonate and a metal fluoride, wherein the sum of the carbonate content of a metal with a grain diameter of 75 µm or more in terms of CO ₂ (C _{CO2, 75 µm} ) and the content of metal fluoride with a grain diameter of 75 µm or more in terms of F (C _{F, 75 µm} ) relative to the total mass of the coating ( C _{cover, total} ) is 6.0 wt.% or more, moreover, the specified content of carbonate and fluoride of the metal is selected from the condition of obtaining after welding at the far end of the electrode a coating, the shape of which satisfies the ratio D ₂ /D ₁ , which is from 0 to 0.4, where D ₁ is the distance in the longitudinal direction of the electrode between the end of the electrode rod after welding and the farthest end of the coating remaining around the rod after welding, and D ₂ is the distance in the longitudinal direction of the electrode between the ends of the coating remaining around the rod after welding. 2. Coated electrode according to claim 1, wherein D ₁ is 2.2 mm or less. 3. Coated electrode according to claim 1 or 2, wherein the ratio D ₁ to the diameter d of the electrode rod in the coated electrode (D ₁ /d) is 1.3 or less. 4. Coated welding electrode, comprising: an electrode rod and a coating that contains at least one of a metal carbonate and a metal fluoride, wherein the sum of the carbonate content of a metal with a grain diameter of 75 µm or more in terms of CO ₂ (C _{CO2, 75 µm} ) and the content of metal fluoride with a grain diameter of 75 µm or more in terms of F (C _{F, 75 µm} ) relative to the total mass of the coating ( C _{cover, total} ) is 6.0 wt.% or more. 5. Coated electrode according to claim 1 or 4, wherein in a section perpendicular to the longitudinal direction of the electrode, the ratio S ₂ /S ₁ is from 0.06 to 0.15, where S ₁ is the coverage area, and S ₂ is the total area of grains of at least one of metal carbonate and metal fluoride, each of which has an equivalent circle diameter of 30 µm or more. 6. Coated electrode according to claim 1 or 4, wherein as metal carbonate, the coating contains at least one selected from the group: CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ and MnCO ₃ , and the total content of metal carbonate, based on the CO ₂ in the coating (C _{CO2, total)} based on the total weight of the coating (C _{pokr General)} is from 6.0 to 26.0 wt.%. 7. Coated electrode according to claim 1 or 4, in which as metal fluoride, the coating contains at least one selected from CaF ₂ , BaF ₂ , SrF ₂ and MgF ₂ , and the total content of metal fluoride in terms of F in the coating (C _{F, total} ) relative to the total mass of the coating (C _{coating, total} ) is from 0 to 15.0 wt.%. 8. Coated electrode according to claim 1 or 4, in which the coating contains metal carbonate and metal fluoride, while the ratio of the total metal fluoride content as F (C _{F, total} ) to the sum of the total metal carbonate content as CO ₂ (C _{CO2, total} ) and the total metal fluoride content as F (C _{F, total} ) in the coating { C _{F total} /(C _{CO2 total} + C _{F total} )} is 0.10 to 0.30. 9. Coated electrode according to claim 1 or 4, in which the coating further comprises at least one of Si or a Si compound, wherein the total content of Si and the Si compound in terms of Si (C _{Si, total} ) relative to the total weight of the coating (C _{coating, total} ) is from 6.0 to 9.0 wt.%. 10. Coated electrode according to claim 1 or 4, which is designed for arc welding in a welding position in which it is perpendicular to the surface of the base metal or at an angle back of 30 ° or less. 11. A method for arc welding with a consumable coated electrode, including the use of a coated welding electrode containing an electrode rod and a coating containing at least one of a metal carbonate and a metal fluoride, the content of which is selected from the condition of obtaining the sum of the content of metal carbonate with a grain diameter of 75 μm or more in terms of CO ₂ (C _{CO2, 75 µm} ) and the content of metal fluoride with a grain diameter of 75 µm or more in terms of F ( _{CF, 75 µm} ) relative to the total weight of the coating (C _{coating, total} ) of 6.0 wt .% or more. 12. The method of arc welding with a consumable coated electrode according to claim 11, in which the specified content of carbonate and fluoride of the metal is selected from the condition of obtaining after welding at the far end of the electrode a coating, the shape of which satisfies the ratio D ₂ /D ₁ of 0 to 0.4, where D ₁ is the distance in the longitudinal direction of the electrode between the end of the electrode rod after welding and the farthest end of the coating remaining around the rod after welding, and D ₂ is the distance in the longitudinal direction of the electrode between the ends of the coating remaining around the rod after welding. 13. The consumable coated electrode arc welding method according to claim 12, wherein the arc welding is performed to obtain a D _{1 of} 2.2 mm or less. 14. The consumable coated electrode arc welding method according to claim 12 or 13, wherein the arc welding is performed to obtain a ratio D ₁ to the diameter d of the electrode wire in the coated electrode (D ₁ /d) of 1.3 or less. 15. The coated electrode arc welding method according to claim 11 or 12, wherein the arc welding is performed in a welding position in which the coated electrode is perpendicular to the surface of the base metal or at an angle back of 30° or less.

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