JP6829111B2 - Filling material for TIG welding - Google Patents

Description

The present invention relates to a filler material for TIG (Tungsten Inert Gas) welding. More specifically, the present invention relates to a filler material for TIG welding, which is useful as a TIG welding material for low-strength steel having a tensile strength of 400 N / mm class ² .

Conventionally, various steel materials have been used as rolled steel for welded structures. For example, a steel material (400 MPa class steel) having a tensile strength of 400 MPa class represented by rolled steel for welded structure SM400 (JIS G3106) has been used. There is. When a structure is welded, it is generally designed so that when a load is applied to the structure, the base metal portion is broken instead of the welded portion. Therefore, in general, the welded portion is required to have higher strength than the base metal. Here, JIS Z3316 defines standards for TIG welding filler rods and solid wires for mild steel, high-strength steel, and low-temperature steel.

Here, in TIG welding of carbon steel, high-purity argon (Ar) gas is generally used as the shield gas. Since the argon gas does not cause an oxidation reaction in the molten pool, the oxygen content of the weld metal is significantly lower than that of other welding methods. Therefore, the TIG weld metal has the property of having few inclusions such as oxides and being excellent in strength and toughness.

However, since carbon steel having a small amount of oxygen has a property of having a very high hardenability, there is a problem that the strength and hardness of the raw material portion of the weld metal are greatly increased. In particular, in the case of a thick plate, the cooling rate is faster than in the case of a thin plate, and as a result of further enhancing the hardenability, there is a problem that excess hardness is promoted.
In addition, in places that are not reheated by welding, such as the final layer in multi-layer welding and single-layer welding, the structure becomes the raw material, so the hardness may become excessively high, resulting in delayed cracking and sulfide stress corrosion cracking. (SSCC) may occur. These cracks depend on the amount of diffusible hydrogen in the weld metal and the binding force applied to the weld metal, but it is generally said that cracks are likely to occur when the Vickers hardness of the weld metal is HV350 or higher. ing.

Here, as a method for reducing the hardness of the welding material, a method is known in which the welding heat input is increased in order to reduce the cooling rate, and the preheating temperature and the interpass temperature are increased on the welding surface. Further, as a post-weld heat treatment (PWHT), a method is also known in which the structure is tempered by annealing the cured raw material portion to reduce the hardness.

However, these methods have a problem that the man-hours increase, so that the productivity decreases and the cost increases. Further, the increase in welding heat input affects the heat-affected zone (HAZ), and there is also a problem that the joint strength cannot be secured. Further, regarding the post-weld heat treatment (PWHT), there is also an equipment restriction that it is difficult to apply the heat treatment depending on the size of the furnace and the size of the welded structure.

Further, as welding materials, for example, Patent Document 1 states that C is 0.03% by weight or less, Si is 0.05% by weight or less, Mn is 0.80% by weight or less, and Ti is 0.008% by weight or less. A solid wire for gas shielded arc welding is described in which O is regulated to 0.025% by weight or less and the balance is composed of Fe and unavoidable impurities.

Japanese Unexamined Patent Publication No. 11-221672

The solid wire for gas shielded arc welding described in Patent Document 1 is effective for suppressing excessive hardness of the weld metal in single-layer welding. However, since the strength of the weld metal including the reheated portion such as multi-layer welding is softer than the strength of the steel plate, the solid wire for gas shielded arc welding described in Patent Document 1 is required as a welding material for 400 MPa class steel. There was a problem that the strength of the welded joint could not be satisfied. That is, all of the weld metals using the solid wire for gas shielded arc welding described in Patent Document 1 had a tensile strength lower than 400 MPa. Further, it is conceivable to reduce the hardness of the raw material portion by applying only the final layer having excessive hardness in multi-layer welding with the wire, but there are problems in terms of wire management and efficiency of welding work.

In view of the above-mentioned conventional problems, the present invention suppresses excess hardness of the weld metal that causes delayed cracking in single-layer welding, and weld joint performance (strength,) required as a welding material for 400 MPa class steel in multi-layer welding. It is an object of the present invention to provide a filler metal for TIG welding that satisfies (toughness, etc.).

In order to achieve the above object, the present invention contains C: 0.02 to 0.06% by mass, Si: 0.30 to 0.85% by mass, and Mn: 0.70 to 1.40% by mass. However, Ni: 0.10% by mass or less (however, including 0% by mass), Cr: 0.10% by mass or less (however, including 0% by mass), Mo: 0.10% by mass or less (however, 0% by mass) (Including mass%), V: 0.05% by mass or less (however, including 0% by mass), P: 0.030% by mass or less (however, not including 0% by mass), S: 0.030% by mass It is regulated to the following (however, 0% by mass is not included) and N: 0.0100% by mass or less (however, 0% by mass is not included), and the balance consists of Fe and unavoidable impurities, and the following formula Provided is a filler material for TIG welding in which the carbon equivalent Ceq represented by (1) is in the range of 0.15 to 0.35.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 (1)
(However, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] are the contents of C, Si, Mn, Ni, Cr, Mo and V, respectively. Mass%) is shown.)

Here, in the filler metal for TIG welding of the present invention, the carbon equivalent Ceq may be in the range of 0.20 to 0.33.

Further, the filler material for TIG welding of the present invention contains Al: 0.10% by mass or less (however, including 0% by mass), Ti: 0.10% by mass or less (however, including 0% by mass), and Zr. : At least one selected from the group consisting of 0.10% by mass or less (however, including 0% by mass) and O: 0.0100% by mass or less (however, not including 0% by mass) is further contained. Moreover, it may satisfy the relationship of the following equation (2).
[X] = ([Ti] + [Al] + [Zr]) × [O] × 10000 ≦ 10.0 (2)
(However, [Ti], [Al], [Zr], and [O] indicate the contents (mass%) of Ti, Al, Zr, and O, respectively.)

Further, the filler metal for TIG welding of the present invention may further contain Cu: 0.50% by mass or less (however, including 0% by mass).

The filler metal for TIG welding of the present invention suppresses excessive hardness of the weld metal that causes delayed cracking in single-layer welding, and has welded joint performance (strength and toughness) required as a welding material for 400 MPa class steel in multi-layer welding. Etc.) are satisfied. Therefore, the filler metal for TIG welding of the present invention is particularly useful as a TIG welding material for 400 MPa class steel.

1A and 1B are views showing the shape of a base metal used for multi-layer welding (total weld metal), FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view. 2A and 2B are explanatory views showing a state of single-layer fillet welding, FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view.

Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below.

The filler material for TIG welding of the present embodiment (hereinafter, also simply referred to as “welding material”) has C: 0.02 to 0.06% by mass, Si: 0.30 to 0.85% by mass, and Mn: 0.70 to 1.40% by mass, Ni: 0.10% by mass or less (however, including 0% by mass), Cr: 0.10% by mass or less (however, including 0% by mass) , Mo: 0.10% by mass or less (however, including 0% by mass), V: 0.05% by mass or less (however, including 0% by mass), P: 0.030% by mass or less (however, including 0% by mass) % Is not included), S: 0.030% by mass or less (however, 0% by mass is not included), and N: 0.0100% by mass or less (however, 0% by mass is not included), and the balance Is composed of Fe and unavoidable impurities, and the carbon equivalent Ceq represented by the following formula (1) is in the range of 0.15 to 0.35.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 (1)
(However, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] are the contents of C, Si, Mn, Ni, Cr, Mo and V, respectively. Mass%) is shown.)

Hereinafter, the reasons for limiting the chemical composition and the like of the filler metal of the present embodiment will be described. In the following, the percentages (%) in the description of the composition shall all represent the percentages (mass%) based on the mass unless otherwise specified. Further, in the present specification, it is assumed that mass% is the same as weight%.

(C: 0.02 to 0.06%)
C is an element having an effect of improving strength and hardness by being dissolved in a weld metal. When the C content in the filler metal is 0.02% or more, the effect of improving the strength is sufficiently exhibited, and it is possible to secure the strength of the weld metal suitable as a welding material for 400 MPa class steel. Further, when the C content in the filler metal is 0.06% or less, the hardness does not become too high, and delayed cracking due to excessive hardness can be prevented.
The C content is preferably 0.03% or more. The C content is preferably 0.05% or less.

(Si: 0.30 to 0.85%)
Si is an element that has the effect of improving strength and hardness by being dissolved in a weld metal. Si also has the effect of improving the familiarity of the bead toe. When the Si content in the filler metal is 0.30% or more, the effect of improving the strength is sufficiently exhibited, the strength can be made appropriate as a welding material for 400 MPa steel, and the bead toe is familiar. Can be good. Further, when the Si content in the filler metal is 0.85% or less, the hardness does not become too high, and delayed cracking due to excessive hardness can be prevented.
The Si content is preferably 0.40% or more, more preferably 0.50% or more. The Si content is preferably 0.80% or less, more preferably 0.70% or less.

(Mn: 0.70 to 1.40%)
Mn is an element that has the effect of improving strength and hardness by being dissolved in a weld metal. Mn also has the effect of improving toughness. When the Mn content in the filler metal is 0.70% or more, the effect of improving the strength is sufficiently exhibited, the strength can be made appropriate as a welding material for 400 MPa class steel, and excellent toughness is obtained. be able to. Further, when the Mn content in the filler metal is 1.40% or less, the hardness does not become too high, and delayed cracking due to excessive hardness can be prevented.
The Mn content is preferably 0.80% or more, more preferably 1.00% or more. The Mn content is preferably 1.30% or less, more preferably 1.25% or less.

(Ni: 0.10% or less (however, including 0%), Cr: 0.10% or less (however, including 0%), Mo: 0.10% or less (however, including 0%), and V: 0.05% or less (however, including 0%))
Ni, Cr, Mo and V are elements having an effect of improving hardness, but if they are contained in excess, the hardness becomes too high, and delayed cracking due to excess hardness may occur.
Therefore, these elements may or may not be contained in the filler metal, but even if they are contained, the respective contents in the filler metal are Ni. It is regulated to 0.10% or less, 0.10% or less for Cr, 0.10% or less for Mo, and 0.05% or less for V.
The Ni content is preferably regulated to 0.05% or less.
The Cr content is preferably regulated to 0.05% or less.
The Mo content is preferably regulated to 0.05% or less.
The V content is preferably regulated to 0.02% or less.

(Carbon equivalent Ceq: 0.15-0.35)
The filler metal of the present embodiment has a carbon equivalent Ceq represented by the following formula (1) in the range of 0.15 to 0.35.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 (1)
(However, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] are the contents of C, Si, Mn, Ni, Cr, Mo and V, respectively. Mass%) is shown.)

When the carbon equivalent Ceq is 0.15 or more, an appropriate strength improving effect can be obtained, and the strength can be made suitable as a welding material for 400 MPa class steel. Further, when the carbon equivalent Ceq is 0.35 or less, the hardness does not become too high, and delayed cracking due to excessive hardness can be prevented.
The carbon equivalent Ceq is preferably 0.20 or more. The carbon equivalent Ceq is preferably 0.33 or less.

(P: 0.030% or less (however, 0% is not included), and S: 0.030% or less (however, 0% is not included))
P and S are elements that are inevitably present in the filler metal, but have the effect of increasing the sensitivity to high temperature cracking and lowering the toughness. Therefore, the P content in the filler metal is regulated to 0.030% or less, and the S content is regulated to 0.030% or less. The P content is preferably regulated to 0.025% or less. Further, the S content is preferably regulated to 0.025% or less. It is preferable that the contents of P and S are as small as possible, but it is usually difficult to prevent the filler metal from containing these elements at all. Therefore, if the lower limit of the contents of P and S is specified, it is, for example, more than 0%.

(N: 0.0100% or less (however, 0% is not included))
N is an element that is inevitably present in the filler metal, but has the effect of reducing toughness. Therefore, the N content in the filler metal is restricted to 0.0100% or less. The N content is preferably regulated to 0.0070% or less. The N content is preferably as small as possible, but it is usually difficult to prevent the filler metal from containing N at all. Therefore, if the lower limit of the N content is specified, it is, for example, more than 0%.

Further, the filler metal of the present embodiment may further contain the following elements in addition to the above-mentioned elements as long as the content is not more than a predetermined content.

(Al: 0.10% or less (however, including 0%), Ti: 0.10% or less (however, including 0%), Zr: 0.10% or less (however, including 0%), and O: At least one selected from the group consisting of 0.0100% or less (however, 0% is not included)
Al, Ti and Zr are elements that have the effect of increasing the strength of the weld metal by solid solution and precipitation, but on the other hand, they combine with O to form oxides in the weld metal, resulting in elongation and toughness. It is also an element that lowers it. Further, when they are discharged to the outside of the weld metal, they form slag, which causes welding defects such as slag entrainment, and further becomes a factor of impairing the appearance of the bead. Further, O is an element that is inevitably present in the filler metal, but when a large amount of O is present, the above-mentioned effect is promoted.
Therefore, Al, Ti and Zr may or may not be contained in the filler metal, but even if they are contained, the respective contents in the filler metal are Al. If there is, it is 0.10% or less, if it is Ti, it is 0.10% or less, and if it is Zr, it is 0.10% or less.
The Al content is preferably 0.05% or more. The Al content is preferably 0.01% or less.
The Ti content is preferably 0.05% or more. The Ti content is preferably 0.01% or less.
The Zr content is preferably 0.05% or more. The Zr content is preferably 0.01% or less.
The O content is 0.0100% or less, preferably 0.0070% or less. The content of O is preferably as small as possible, but it is usually difficult to prevent the filler metal from containing O at all. Therefore, if the lower limit of the O content is specified, it is, for example, more than 0%.

([X] ≤ 10.0)
Further, when the filler material of the present embodiment contains at least one of Al, Ti, Zr and O within the above range, it is preferable to satisfy the relationship of the following formula (2).
[X] = ([Ti] + [Al] + [Zr]) × [O] × 10000 ≦ 10.0 (2)
(However, [Ti], [Al], [Zr], and [O] indicate the contents (mass%) of Ti, Al, Zr, and O, respectively.)

When [X] represented by the above formula (2) is 10.0 or less, the amount of slag formed can be satisfactorily suppressed, welding defects such as slag entanglement can be prevented, and the appearance is excellent. You can get a bead.

(Cu: 0.50% or less)
Cu is an element having an effect of improving the strength, but if it is added in an excessive amount, the strength becomes too high and the sensitivity to high temperature cracking increases. Therefore, Cu may or may not be contained in the filler metal, but even if it is contained, the Cu content in the filler metal is 0.50% or less. ..
The Cu content is preferably 0.35% or more. The filler metal of the present embodiment may be subjected to Cu plating if desired. Here, in the present specification, the Cu content when the filler metal is Cu-plated is the Cu content in the filler metal and the Cu plating film with respect to the entire total of the filler metal and the Cu plating film. It shall mean the content.

The balance of the filler metal of the present embodiment is composed of Fe and unavoidable impurities. Elements other than the above elements, such as Nb, Sn, and B, are present as unavoidable impurities. Since these elements increase the strength of the weld metal by solid solution and precipitation and increase the sensitivity to high temperature cracking, it is preferable to reduce them as much as possible, but the content of each element is up to 0.1%. If it is within the range, inclusion is allowed.

Examples of the form of the filler metal of the present embodiment include welding rods and wires. In this embodiment, the presence or absence of Cu plating on the surface of the filler metal, the surface form such as intergranular oxidation, and the properties of the surface coating oil are not particularly limited. Further, in the present embodiment, the winding shape of the wire is not particularly limited, and for example, a spool winding wire, a packed wire, or the like can be used.

In manufacturing the filler material of the present embodiment, various conventionally known methods for producing the filler metal can be applied without particular limitation.

The filler metal of the present embodiment suppresses the excessive hardness of the weld metal that causes delayed cracking in single-layer welding, and has welded joint performance (strength, toughness, etc.) required as a welding material for 400 MPa class steel in multi-layer welding. To be satisfied. Therefore, the filler metal of the present embodiment is particularly useful as a TIG welding material for 400 MPa class steel. The filler metal of the present embodiment can be appropriately used as a TIG welding material for various steels other than 400 MPa class steel. Further, the filler metal of the present embodiment can be appropriately applied to various welding methods other than TIG welding.

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

(All weld metal tensile test, Charpy impact test and slag amount evaluation)
1A and 1B are views showing the shape of a base metal used for multi-layer welding (total weld metal), FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view. As shown in FIG. 1, first, two JIS G3106 SM400B steel plates 1 having an inclined notch on the end surface are prepared, and the inclined surfaces 1a face each other and the tips of the inclined surfaces 1a are separated by 10 mm. By arranging the two steel plates 1, a groove 2 having a groove angle of 45 ° was formed between the two steel plates 1. Next, after arranging the backing material 3 made of JIS G3106 SM400B on the back surface side of the groove 2, the filler material (wire) having various compositions shown in Tables 3 and 4 with respect to the groove 2. Was used to perform multi-layer welding (total weld metal) under the welding conditions shown in Table 1 below. In this test, the thickness of the steel plate 1 was 16 mm, the length of the steel plate 1 in the direction parallel to the inclined surface 1a was 300 mm, and the length in the direction orthogonal to the inclined surface 1a was 125 mm. Further, the plate thickness of the backing material 3 was set to 6 mm. In addition, "-" in Tables 3 and 4 indicates that the amount of the component was less than the detection limit. The rest of the composition is Fe and unavoidable impurities.

Next, the obtained weld metal was subjected to a tensile test of all the weld metals under the conditions shown in Table 2 below to obtain tensile strength (MPa), 0.2% proof stress (MPa) and elongation (%). Measured and evaluated. These results are shown in Tables 5 and 6.
Here, the tensile strength was evaluated as good when it was in the range of 430 to 600 MPa, and evaluated as defective in other cases.
The 0.2% proof stress was evaluated as good when it was 330 MPa or more and defective when it was less than 330 MPa.
Regarding the elongation, the case of 20% or more was evaluated as good, and the case of less than 20% was evaluated as poor.

Further, the obtained weld metal was subjected to a Charpy impact test under the conditions shown in Table 2 below to measure and evaluate the absorbed energy (J). The results are shown in Tables 5 and 6. Here, the case where the absorbed energy was 100 J or more was evaluated as good, and the case where the absorbed energy was less than 100 J was evaluated as poor.

In addition, the amount of slag of the obtained weld metal was visually evaluated. The results are shown in Tables 5 and 6. Here, the case where the amount of slag is small and the appearance is evaluated to be excellent is good (○), the amount of slag is large and the appearance is inferior, and fusion failure (welding defect) such as slag entrainment occurs in ultrasonic flaw detection. The case was evaluated as defective (x).

(Vickers hardness test)
2A and 2B are explanatory views showing a state of single-layer fillet welding, FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view. As shown in FIG. 2, the JIS G3106 SM400B steel plate having a width of 150 mm × the length of 200 mm × the plate thickness of 50 mm as the steel plate 4 and the JIS G3106 SM400B steel plate having a width of 70 mm × the length of 200 mm × the plate thickness of 6 mm as the steel plate 5 I prepared. For these lower plates and standing plates, a filler metal (wire) having various compositions shown in Tables 3 and 4 was used to form a single-layer fillet welded portion 6 under the welding conditions shown in Table 1 below. Made.

Next, the Vickers hardness HV of the obtained weld metal was measured and evaluated by carrying out a Vickers hardness test at the center of the cross section of the weld metal under the conditions shown in Table 2 below. The results are shown in Tables 5 and 6. Here, the case where the Vickers hardness was HV350 or less was evaluated as good, and the case where the Vickers hardness exceeded HV350 was evaluated as defective (x).

Experimental Examples 1 to 11 are Examples, and Experimental Examples 12 to 25 are Comparative Examples.
As shown in Tables 3 to 6, since each filler metal of Experimental Examples 1 to 11 has an appropriate chemical composition, the tensile strength in the tensile test of all weld metals is in the range of 430 to 600 MPa. At the same time, good mechanical performance with a 0.2% proof stress of 330 MPa or more and an elongation of 20% or more was obtained. Further, the Vickers hardness of the single-layer fillet weld metal was also HV350 or less, which was good. Therefore, each filler metal of Experimental Examples 1 to 11 suppresses the excessive hardness of the weld metal, which causes delayed cracking in single-layer welding, and has welded joint performance required as a welding material for 400 MPa class steel in multi-layer welding. Strength, toughness, etc.) were satisfied.
In Experimental Examples 4 and 9, since [X] was as large as 12.7 and 11.9, respectively, the amount of slag generated was large and the appearance was inferior.

On the other hand, in Experimental Example 12, the Mn content is smaller than the range specified in the present invention, and Ceq is smaller than the range specified in the present invention. Therefore, the 0.2% proof stress and tensile strength of the total weld metal were insufficient, and the evaluation result was poor.
In Experimental Example 13, the Si content is smaller than the range specified in the present invention. Therefore, the tensile strength of the fully welded metal was insufficient, and the evaluation result was poor.
In Experimental Example 14, the C content and the Mn content are smaller than the range specified in the present invention, and the Ceq is smaller than the range specified in the present invention. Therefore, the 0.2% proof stress and tensile strength of the total weld metal were insufficient, and the evaluation result was poor.

In Experimental Example 15, the C content, Si content, Mn content and Mo content are larger than the range specified in the present invention, and Ceq is larger than the range specified in the present invention. Therefore, the tensile strength of the fully welded metal was high, the evaluation result was poor, the Vickers hardness also exceeded HV350, and the evaluation result was also poor.
In Experimental Example 16, the Si content and the Mn content are larger than the range specified in the present invention, and the Ceq is larger than the range specified in the present invention. Therefore, the tensile strength of the fully welded metal was high, the evaluation result was poor, the Vickers hardness also exceeded HV350, and the evaluation result was also poor.
In Experimental Example 17, the C content is larger than the range specified in the present invention, and Ceq is larger than the range specified in the present invention. Therefore, the tensile strength of the fully welded metal was high, the evaluation result was poor, the Vickers hardness also exceeded HV350, and the evaluation result was also poor.

In Experimental Example 18, the N content is larger than the range specified in the present invention. Therefore, the absorbed energy of all the weld metals was insufficient, and the evaluation result was poor.

In Experimental Example 19, the Si content is smaller than the range specified in the present invention, and the S content is larger than the range specified in the present invention. Therefore, the tensile strength and absorbed energy of the fully welded metal were insufficient, and the evaluation result was poor.

In Experimental Example 20, the Mn content is smaller than the range specified in the present invention, and the Ni content is larger than the range specified in the present invention. Therefore, the tensile strength and 0.2% proof stress of the fully welded metal were insufficient, and the evaluation result was poor.

In Experimental Example 21, the Cr content is larger than the range specified in the present invention, and Ceq is also larger than the range specified in the present invention. Therefore, the tensile strength and Vickers hardness of the fully welded metal were high, and the evaluation result was poor.
In Experimental Example 22, the Mo content is larger than the range specified in the present invention. Therefore, the tensile strength and Vickers hardness of the fully welded metal were high, and the evaluation result was poor.
In Experimental Example 23, the Cr content, V content and N content are larger than the range specified in the present invention. Therefore, the absorbed energy of the total weld metal was insufficient, the Vickers hardness was high, and the evaluation result was poor.

In Experimental Example 24, the C content is larger than the range specified in the present invention, and Ceq is also larger than the range specified in the present invention. Therefore, the tensile strength and Vickers hardness of the fully welded metal were high, and the evaluation result was poor.

In Experimental Example 25, the P content is larger than the range specified in the present invention. Therefore, the absorbed energy of all the weld metals was insufficient, and the evaluation result was poor. In addition, the amount of slag generated was large and the appearance was inferior.

1 Steel plate 1a Inclined surface 2 Groove 3 Backing material 4 Lower plate 5 Standing plate 6 Welded metal

Claims (4)

C: 0.02 to 0.06% by mass,
It contains Si: 0.30 to 0.85% by mass and Mn: 0.70 to 1.40% by mass.
Ni: 0.10% by mass or less (however, including 0% by mass),
Cr: 0.10% by mass or less (however, including 0% by mass),
Mo: 0.10% by mass or less (however, including 0% by mass),
V: 0.05% by mass or less (however, including 0% by mass),
P: 0.030% by mass or less (however, 0% by mass is not included),
S: 0.030% by mass or less (however, 0% by mass is not included) ,
N: 0.0100% by mass or less (however, 0% by mass is not included) , and
O: Regulated to 0.0100% by mass or less (however, 0% by mass is not included)
The balance consists of Fe and unavoidable impurities, and
A filler material for TIG welding in which the carbon equivalent Ceq represented by the following formula (1) is in the range of 0.15 to 0.35.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 (1)
(However, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] are the contents of C, Si, Mn, Ni, Cr, Mo and V, respectively. Mass%) is shown.) The filler metal for TIG welding according to claim 1, wherein the carbon equivalent Ceq is in the range of 0.20 to 0.33. Al: 0.10% by mass or less (however, including 0% by mass),
Ti: 0.10% by mass or less (however, including 0% by mass), and Zr: 0.10% by mass or less (however, including 0% by mass )
And at least one selected from Ranaru group or,
Cu: 0.50% by mass or less (however, 0% by mass is not included),
The TIG welding filler material according to claim 1 or 2, which further contains the above and satisfies the relationship of the following formula (2).
[X] = ([Ti] + [Al] + [Zr]) × [O] × 10000 ≦ 10.0 (2)
(However, [Ti], [Al], [Zr], and [O] indicate the contents (mass%) of Ti, Al, Zr, and O, respectively.) The filler material for TIG welding according to claim 1 or 2, further containing Cu: 0.50% by mass or less (however, including 0% by mass).

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