KR20210133141A - Welding wires for obtaining giga-grade welds, welding structures manufactured using them, and their welding methods - Google Patents

Abstract

Provided are a welding wire capable of obtaining a giga-level weld, a welded structure manufactured using the same, and a welding method thereof. According to the present invention, the welding wire, with respect to the whole wire, contains 0.08 to 0.15 wt% of C, 0.001 to 0.1 wt% of Si, 1.6 to 1.9 wt% of Mn, 0.015 wt% or less of P, 0.015 wt% or less of S, 4.0 to 5.2 wt% of Cr, 0.4 to 0.65 wt% of Mo, and balance consisting of Fe and unavoidable impurities. The value X defined by the following relational expression 1 satisfies the range of 0.7 to 1.1%, wherein the relational expression 1 is represented by X (%) = [Cr]/10 + [Mo] - 4x[Si]/[Mn].

Description

Welding wires for obtaining giga-grade welds, welding structures manufactured using the same, and welding methods thereof

The present invention relates to a welding wire applicable to gas shield arc welding of galvanized giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less applied to structural members of the lower body of an automobile, a welded structure manufactured using the same, and a welding method thereof it's about

In the automobile sector, research on light-weight technology for car bodies and parts is emerging as a big issue due to fuel economy regulation policies for environmental protection such as global warming. Chassis parts, which are important for automobile driving performance, also require the application of high-strength steel for weight reduction in accordance with this principle.

In order to achieve the weight reduction of such parts, it is essential to increase the strength of the material, and it is an important factor to guarantee the durability of parts made of high-strength steel in an environment where repeated fatigue loads are applied.

However, in the case of arc welding, which is mainly used to secure strength when assembling automobile chassis parts, since overlap joint welding is performed between parts by welding of a welding wire, it is unavoidable to provide a geometric shape of the joint. This acts as a repetitive fatigue stress concentration part (notch effect) and becomes a fracture origin, resulting in deterioration of the durability of the part, and thus has a limit in which the advantage of applying high-strength steel is lost.

Therefore, in order to improve the fatigue characteristics of the weld, it is most important to reduce the angle (toe angle) of the end of the bead, which is mainly a stress concentration part. In addition, it is important to control the material and stress of the toe part. In addition, as described above, the demand for rust prevention for penetration corrosion prevention is increasing due to the thinning of the material due to the high strength and light weight of parts, and the adoption of plated steel is increasing. Because it does not exist, it has a limit in that the corrosion resistance after painting is inferior compared to the base material. Accordingly, there is a problem that leads to deterioration of fatigue properties along with the occurrence of premature corrosion of the welded parts of the chassis parts made of the plated steel sheet in a severe corrosive environment during vehicle driving. On the other hand, during gas-shielded arc welding of galvanized steel, porous defects in the form of pits and blowholes are generated in large quantities in the weld bead due to the generation of steam such as zinc, which may decrease the strength of the welded part, thereby reducing the welding productivity. In addition, in the case of general uncoated steel materials, slag generated on the weld bead during gas shield arc welding causes paint defects and is a factor in lowering the corrosion resistance after painting. There is a problem of cost increase. Meanwhile, in order to effectively reduce the weight in preparation for the electric vehicle era, the application of giga steel with a tensile strength of 1 GPa or more is expected to be expanded, so securing the strength of the welded part is an important prerequisite.

As an example of the prior art for solving such a problem, the invention described in patent document 1 is mentioned. In Patent Document 1, it is disclosed that the blowhole and slag area ratio of the welding part can be controlled within 10%, respectively, through appropriate control of the Si, Mn, Ti and Al contents of the gas-shielded arc welding wire, but the actual high-strength steel In this case, when the blowhole area ratio of the welded part exceeds 5%, the tensile strength and fatigue strength of the weld metal may be significantly reduced. A more sensitive issue arises.

Patent Document 2 discloses that it is possible to secure the tensile strength of the weld metal portion of 800 MPa or more by controlling the carbon equivalent of the gas-shielded arc welding wire to 0.8 to 0.9%, but a method for reducing blowholes and slag in the welding portion is not suggested.

Patent Document 3 discloses that by controlling the content ratio of Si and Mn of the gas shielded arc welding wire to an appropriate range, the formation of Si-based slag in the weld bead is suppressed to improve the paintability and porosity of the welded part. However, in Patent Document 3, the maximum strength of the weld is 540 MPa for general steel, and there is a limitation in not suggesting a method for securing the strength of the weld of giga steel with a tensile strength of 1 GPa or more.

Patent Document 4 discloses that the slag area ratio of the welding part can be controlled within 5% through appropriate control of the Si, Al, Ti, Al, Sb and S content of the gas shielded arc welding wire, but pits and blows in the plated steel welding part Hall reduction measures are not suggested. On the other hand, a method for improving the strength of the welded part is suggested by adding an appropriate amount of B to the wire, but it has a limit in that the strength does not reach the 1GPa level or higher.

Patent Document 5 discloses that the total amount of Cr and Ni of the welding wire is controlled to 1% to 24%, so that the weld strength of the steel with a tensile strength of 980 MPa or higher is 90% or more compared to the base material, but slag reduction and porosity improvement of the welded part are improved It has a limitation that does not suggest a solution for it.

That is, the invention disclosed in Patent Documents 1 to 5 does not sufficiently consider welding of a galvanized steel sheet having a tensile strength of 1 GPa or more and a coating amount per side of 20 to 120 g/m ^{2 , so as to secure sufficient strength and} It was unclear whether slag reduction and porosity resistance were simultaneously secured.

Korean Patent Publication No. 2015-0108930 Korean Patent Publication No. 2016-0080096 Korean Patent Publication No. 2019-0047388 International Patent Publication No. WO2019-124305 Korean Patent Publication No. 2019-0134703

Accordingly, the present invention relates to a welding wire applicable to gas shield arc welding of galvanized giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less applied to structural members of the lower body of a vehicle, a welded structure manufactured using the same, and a welding method thereof is intended to provide.

In addition, the subject of this invention is not limited to the above-mentioned content. The subject of the present invention will be understood from the overall content of the present specification, and those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional subject of the present invention.

One aspect of the present invention is

As mass% of the entire wire, C: 0.08 to 0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less, Cr: 4.0 to 5.2%, Mo : It relates to a gas shielded arc welding wire that contains 0.4 to 0.65%, the remainder Fe, and unavoidable impurities, and the value X defined by the following relation 1 satisfies the range of 0.7 to 1.1%.

[Relational Expression 1]

X(%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn]

However, in relation 1, [Cr], [Mo], [Si] and [Mn] represent the mass% of each element.

A Cu plating layer may be formed on the surface of the welding wire.

Cu constituting the Cu plating layer, as a mass% of the entire wire including the plating layer, preferably has a content of 0.4% or less (excluding 0%), more preferably, limited to a content in the range of 0.1 to 0.3% will do

The welding wire is, by mass%, Cr: 4.2 to 4.9%, Mo: 0.45 to 0.48% and Mn: It is preferable to contain 1.65 to 1.75%, respectively.

The welding wire preferably includes a Si content in the range of 0.04 to 0.08%.

The welding wire may be a solid wire for gas shielded arc welding.

In addition, another aspect of the present invention,

A welded structure having a welding portion obtained by welding two or more welding base materials using the welding wire, wherein the welding portion, in area%, is 30-50% of martensite, 50-70% of bainite, and a residual of 5% or less It has a microstructure made of austenite, and the microstructure constituting the weld has an average effective grain size of 1 to 3 μm, and a high-hardness grain fraction of 47° or more is 35% or more It relates to a welded structure. .

At least one of the welding base materials may be a galvanized steel sheet.

The galvanized steel sheet may be one of an electro-galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.

The base steel sheet constituting the galvanized steel sheet, in its own mass%, Cr: 0.2 to 0.9% and Mo: may contain one or more of 0.1 to 0.2%.

In addition, another aspect of the present invention is

As a method of gas-shielded arc welding of a welding base material using the welding wire, 5-20% CO ₂ is mixed with Ar as a protective gas during the welding, and the thickness of the welding base material is t (mm). It relates to a gas shielded arc welding method, characterized in that welding is performed so that the range of the welding heat input Q (kJ/cm) defined by the following relational expression 2 satisfies 1.15t ≤ Q ≤ 1.6t.

[Relational Expression 2]

Q = (I × E) × 0.048 /υ

However, in Relation 2, I, E, and υ represent welding current [A], welding voltage [V], and welding speed (cm/min), respectively.

The welding wire may be a solid wire having a diameter of 0.9 to 1.2 mm.

According to the present invention having the above configuration, by reducing the slag area ratio and the blowhole area ratio of the gas shield arc welding part and the blowhole area ratio of Giga Steel with a tensile strength of 1 GPa or more and a thickness of 6 mm or less to 1% or less, separate pickling or brushing for removing slag from the welding part, etc. It is possible to omit the post-treatment process, and furthermore, it is possible to secure excellent paintability, thereby reducing the number of originals and improving the quality at the industrial manufacturing site.

In addition, there is an advantage that not only can effectively prevent pit and blowhole defects, but also secure weld strength of 1 GPa or more without breaking the weld metal or molten wire when welding the plating material.

Therefore, it can have industrial significance in that it can expand the adoption of Giga Steel by satisfying the needs for improvement of rust resistance and durability according to high strength and thinning of parts such as automobile chassis members.

1 is a wire No. in Table 2 in Example 1 of the present invention. It is a photograph showing the cross-sectional structure of the fractured portion after welding, hardness distribution, and static tensile test obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] welded using No. 7.
2 is a wire No. in Table 2 in Example 1 of the present invention. 32 is a photograph showing the cross-sectional structure of the fractured portion obtained from Comparative Example [X(%) = 0.55, Q(kJ/cm) = 2.6], hardness distribution and static tensile test.
3 shows each weld obtained after performing overlap joint welding with a galvanized steel sheet or overlap joint welding with an alloyed galvanized steel sheet using wires Nos 5, 7, 12, 34 and 36 of Table 2 in Example 1 of the present invention; RT (Radiographic Test) picture for
4 is the No. 4 of Table 4 in Example 2 of the present invention. 7 Wire and No. 1 These are the EBSD structure picture and inverse pole figure of the weld metal obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 3.2] in which steel materials were combined and welded.
5 is a No. 5 of Table 4 in Example 2 of the present invention. 32 wire and No. 1 These are the EBSD structure picture and inverse pole figure of the weld metal obtained from Comparative Example [X(%) = 0.55, Q(kJ/cm) = 3.2] in which steel materials were combined and welded.
6 is a No. of Table 4 in Example 2 of the present invention. 7 Wire and No. 1 By omitting the welding bead appearance photo obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] and post-treatment processes such as pickling or brushing to remove slag from the weld area, This is a picture of the exterior after painting.
Figure 7 (ab) in Example 2 of the present invention, Table 4 No. 7 wire and No. 1 High-speed tensile test (tensile speeds of 1 m/s and 15 m/s, respectively) by applying a load to the welds obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] in which steel materials were combined and welded This is a diagram showing the change in the load at the weld (b) compared to the change in the load in the steel, which is the welding base material (a).

Hereinafter, the present invention will be described.

The present invention can reduce the slag area ratio and the blowhole area ratio of the weld to less than 1%, respectively, when gas-shielded arc welding for giga steel with a tensile strength of 1 GPa or more and a thickness of 6 mm or less, and without breaking the weld metal or molten line It has the characteristic that it is possible to secure the weld strength of 1 GPa or more. To this end, as a result of repeated experiments and studies by the present inventors, among the components of the welding wire used for gas shielded arc welding, the contents of Cr and Mo, which are reinforcing elements for strength improvement, and Si and Mn, which are deoxidation elements, were determined above. It was confirmed that it is effective to control the X value defined by Relation 1 to satisfy the range of 0.7 to 1.1%.

In addition, the present inventors found that when the value of Relation 1 is used as a parameter, the X value has a great influence on weld slag, blowhole generation, and weld strength. In particular, as a component included in the welding wire, by controlling the individual content of each element as well as controlling the amount of each component so that the value of X is in the range of 0.7 to 1.1%, slag and blowholes of the weld bead are generated At the same time, the present invention is presented by confirming that the strength of the weld can be secured at least 1 GPa without breaking the weld metal or the molten wire.

Therefore, the welding wire, which is an aspect of the present invention, by its own mass%, C: 0.08 to 0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less , Cr: 4.0 to 5.2%, Mo: 0.4 to 0.65%, the remainder including Fe and unavoidable impurities, and the value X defined by the above relation 1 satisfies the range of 0.7 to 1.1%.

Hereinafter, the component composition of the gas shielded arc welding wire, which is an aspect of the present invention, and the reason for its limitation will be described, where % is mass% unless otherwise specified. Meanwhile, in the present invention, the welding wire is not limited to a specific type of the wire, and it can be used for a solid wire or a flux-filled wire, and is preferably used as a solid wire. And it is preferable that the Cu plating layer is formed on the surface of the said welding wire.

[C: 0.08~0.15%]

C is a component that stabilizes the arc and acts to atomize the volume. However, if the C content is less than 0.08%, the volume becomes large, the arc becomes unstable, the amount of spatter is increased, and it may be difficult to secure sufficient strength of the giga-grade steel weld metal having a tensile strength of 1 GPa or more. On the other hand, when the C content exceeds 0.15%, the viscosity of the molten metal is lowered, so that the bead shape becomes defective, and the weld metal is excessively hardened, thereby increasing brittleness. Therefore, in the present invention, it is preferable to limit the C content of the welding wire to 0.08 to 0.15%.

[Si: 0.001~0.1%]

Si is an element (deoxidation element) that promotes deoxidation of molten metal during arc welding, and is effective in suppressing the occurrence of blowholes. It is also an element that causes paint defects. When the Si content is less than 0.001%, deoxidation becomes insufficient and blowholes are easily generated, and when the Si content exceeds 0.1%, slag increases remarkably. Therefore, the Si content of the solid wire for welding was made into the range of 0.001 to 0.1 % from the balance point of generation|occurrence|production suppression of a blowhole, and a slag amount suppression.

In addition, limiting the Si content to the range of 0.04 to 0.08% is preferable in terms of being able to more effectively achieve both suppression of blowholes and suppression of slag amount.

[Mn: 1.6~1.9%]

Mn is also a deoxidation element, and has an effect of promoting deoxidation of molten metal during arc welding and suppressing the occurrence of blowholes, but on the other hand, it is also an element that increases the viscosity of molten metal. When the Mn content is less than 1.6%, deoxidation becomes insufficient within the appropriate range of the above-described Si content, and blowholes are likely to occur. On the other hand, if the Mn content exceeds 1.9%, the viscosity of the molten metal becomes excessively high, and when the welding speed is high, the molten metal cannot properly flow into the welding site, resulting in a humped bead, which tends to cause poor bead shape. lose Therefore, Mn content of the wire for welding was made into the range of 1.6 to 1.9%. In addition, in order to reliably suppress the occurrence of blowholes, it is preferable that the Mn content be limited within the range of 1.65 to 1.75%.

[Cr: 4.0~5.2%]

Cr is a ferrite stabilizing element and is a hardening element that improves the strength of the weld metal. In particular, it is necessary to limit the Cr content in the range of 4.0 to 5.2% in order to secure sufficient strength of the giga-grade steel weld metal having a tensile strength of 1 GPa or higher. If the Cr content is less than 4.0%, the problem of insufficient strength of the giga-grade steel weld metal tends to occur. On the other hand, when the Cr content exceeds 5.2%, there is a high risk of the formation of a δ ferrite structure or the precipitation of chromium carbide in the structure, resulting in embrittlement of the weld metal, that is, a decrease in toughness. In addition, limiting the Cr content in the range of 4.2 to 4.9% is preferable in terms of ensuring sufficient strength of the weld metal and suppressing embrittlement more effectively.

[Mo: 0.4~0.65%]

Mo is also a ferrite stabilizing element, and is a hardening element which improves the intensity|strength of a weld metal. In particular, it is necessary to limit the Mo content in the range of 0.4 to 0.65% in order to secure sufficient strength of the giga-grade steel weld metal having a tensile strength of 1 GPa or higher. If the Mo content is less than 0.4%, it is difficult to obtain sufficient strength of a giga-grade steel weld metal having a tensile strength of 1 GPa or higher within the above-described appropriate component range, and if the Mo content exceeds 0.65%, the toughness of the weld metal may be reduced is getting bigger In addition, limiting the Mo content to the range of 0.45 to 0.48% is preferable in terms of ensuring sufficient strength of the weld metal and suppressing embrittlement more effectively.

[P: 0.015% or less]

P is an element that is generally incorporated as an unavoidable impurity in steel, and is usually included as an impurity in an arc welding wire. Here, P is one of the main elements which generate|occur|produces hot cracking of a weld metal, and it is preferable to suppress it as much as possible, and when P content exceeds 0.015 %, hot cracking of a weld metal becomes remarkable. Therefore, in the present invention, it is preferable to limit the P content of the welding wire to 0.015% or less.

[S: 0.015% or less]

S is also generally incorporated as an unavoidable impurity in steel, and is usually included as an impurity in solid wire for arc welding as well. Here, S is an element that inhibits the toughness of the weld metal, and it is preferable to suppress it as much as possible. When the S content exceeds 0.015%, the toughness of the weld metal deteriorates. Therefore, in the present invention, it is preferable to limit the S content of the welding wire to 0.015% or less.

[Relational Expression 1]

In addition, in the gas-shielded arc welding wire of the present invention, it is important to control the content of Cr, Mo, Si, and Mn so that the X value defined by the following relation 1 satisfies the range of 0.7 to 1.1%.

[Relational Expression 1]

X(%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn]

However, in relation 1, [Cr], [Mo], [Si] and [Mn] represent the mass% of each element.

That is, according to the research results of the present inventors, it was found that the contents of Cr, Mo, Si and Mn contained in the wire strongly correlated not only with the strength of the weld, but also with the generation of blowholes and slag, and this relational expression 1 was devised. Specifically, by controlling the contents of Cr, Mo, Si and Mn so that the X value defined by the above relation 1 satisfies the range of 0.7 to 1.1%, the tensile strength of 1 GPa or more of giga-class steel welds is secured and porosity resistance Improvement and slag reduction were certainly obtained. That is, by applying the above relational expression 1 parameter, it is possible to reliably suppress the occurrence of slag and blowholes in the weld bead, and it is possible to secure the weld strength of 1 GPa or more without breaking the weld metal or the molten line.

If the X value is less than 0.7%, it is difficult to secure sufficient strength of the weld metal as well as the porosity resistance and slag reduction effect of the giga-grade steel welded portion. Even if the slag reduction effect is satisfied, the weld metal is too brittle, and the weld metal or the molten wire may be susceptible to fracture, resulting in poor physical properties of the weld.

[impurities]

An impurity is a component contained in a raw material, or a component mixed in the process of manufacture, and refers to the component which is not intentionally contained in the welding wire.

On the other hand, it is preferable that the Cu plating layer is formed on the surface of the welding wire of this invention. Cu is usually contained in about 0.02% as an impurity in the steel constituting the wire. In the case of the arc welding wire of the present invention, it is mainly derived from copper plating applied to the surface of the wire.

In a wire for arc welding, copper plating is an important surface treatment method for stabilizing wire feedability and conductivity, and when copper plating is performed, a certain amount of Cu may inevitably be contained.

In the present invention, at this time, the Cu content contained in the plating layer is preferably controlled to be 0.4% or less (excluding 0%) by mass% with respect to the entire wire including the Cu plating layer. If the content of Cu exceeds 0.4%, the crack susceptibility of the weld metal may increase. A more preferable Cu content that can more effectively reduce the crack susceptibility of the weld metal while stabilizing the feedability and conductivity of the wire is to be controlled in the range of 0.1 to 0.3%. When the Cu content is excessively low, the necessary wire feedability and conductivity may not be obtained.

Next, a welded structure manufactured using the welding wire, which is another aspect of the present invention, will be described.

The welded structure of the present invention is a welded structure having a welded portion obtained by welding two or more welding base materials using the welding wire, and the welded portion is, in area%, martensite 30-50%, bainite 50-70% and a microstructure consisting of residual austenite of less than 5%. In addition, in the microstructure constituting the weld, the average effective grain size is 1-3 μm, and the high-hardness grain fraction of 47° or more is 35% or more.

First, the welding part of the present invention has a microstructure consisting of 30-50% martensite, 50-70% bainite, and residual austenite of 5% or less in area%. In the present invention, if the martensite fraction is excessive, the weld metal may be too hard to be sensitive to brittleness, and if it is too small, there is a problem that the strength of the weld metal may be insufficient.

On the other hand, in general, bainite constituting a weld formed by low-temperature transformation at a temperature of 550° C. or less may include both upper bainite and lower bainite. In the case of prior austenite, there are many high-hardness grains that are inter-locking with each other. Therefore, when such lower bainite is mixed with martensite, toughness is relatively improved compared to when martensite is present alone. It works.

In consideration of this point, in the present invention, the microstructure constituting the weld portion has an average effective grain size of 1 to 3 μm, and a high-hardness grain fraction of 47° or more is controlled to be 35% or more. If the average effective grain size of the microstructure constituting the weld is less than 1 μm, there is a risk that the toughness of the weld metal may be insufficient. there is In addition, if the high-hardness crystal grain fraction of 47° or more is less than 35%, there is a problem in that the strength and toughness of the weld metal may be reduced.

In addition, the welding portion may have an average hardness of 370 to 400 Hv, and a tensile strength of 940 MPa or more, preferably, 1 GPa or more, which is 95% or more compared to the welding base material.

In addition, the microstructure characteristics of the weld metal improve the mechanical properties of the weld, and as described above, when a tensile load is applied, the weld metal or molten wire does not break, and in the case of sub-frames, which are front collision members, automobiles It is possible to secure sufficient strength and toughness to prevent fracture of the weld metal part even in a high-speed collision (high-speed tensile load applied) with an acceleration of 3.6 to 54 km/h.

In the present invention, the high-speed tensile strength of the welded portion may be 95% and 80% or more, respectively, compared to the base material at tensile speeds of 3.6 km/h and 54 km/h.

On the other hand, the welding part of the present invention can be obtained by welding two or more welding base materials using the welding wire.

On the other hand, in the present invention, the type or component composition of the steel sheet to be subjected to gas shielded arc welding using the welding wire is not particularly limited. For example, it is preferable that at least one of the welding base materials is a galvanized steel sheet, because when gas-shielded arc welding of the galvanized steel sheet is performed using the welding wire of the present invention, the effect becomes remarkable. Specifically, when a zinc or zinc alloy plated steel sheet having a single-sided coating amount of 20 to 120 g/m ² is used as the base steel sheet, in particular, when there is no gap in the overlap joint during welding and is closely adhered, zinc vapor generated in a large amount is melted Even in a situation in which lice cannot be sufficiently discharged before solidification, the use of the gas shielded arc welding wire of the present invention can reliably reduce blowholes.

In addition, the galvanized steel sheet may be one of an electro-galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.

Furthermore, the base steel sheet constituting the galvanized steel sheet, in its own mass%, Cr: 0.2 to 0.9% and Mo: It is preferable to contain at least one of 0.1 to 0.2%.

Next, a method of welding giga steel using the welding wire, which is another aspect of the present invention, will be described.

The present invention is a method of gas-shielded arc welding of a welding base material using the welding wire, and 5 to 20% CO ₂ is mixed with Ar as a protective gas during the welding, and the thickness of the welding base material is t ( mm), welding can be performed so that the range of the welding heat input Q (kJ/cm) defined by the following relation 2 satisfies 1.15t ≤ Q ≤ 1.6t.

[Relational Expression 2]

Q = (I × E) × 0.048 /υ

However, in Relation 2, I, E, and υ represent welding current [A], welding voltage [V], and welding speed (cm/min), respectively.

The present invention is not particularly limited in the specific form (welding posture) of the welding, and may be applied, for example, to lap fillet welding in the form of an overlap joint or fillet welding of a T-joint.

Also, the type of shielding gas to be used is not particularly limited, and 100% CO ₂ gas, Ar+20CO ₂ gas, Ar+10%CO ₂ gas, Ar+5%CO ₂ gas, Ar+2%O ₂ gas, etc. are used. but it can be used as shielding gas, in particular, as a shielding gas, in the case of using the _{Ar + 5 ~ 20% CO 2} , can exert a remarkable effect of the present invention. That is, in the present invention, in order to secure a tensile strength of 1 GPa or more at the weld without breaking the weld metal or molten line, it is preferable to mix _{5 to 20% of CO 2 with Ar as a protective gas during the welding.}

In addition, when the thickness of the welding base material is t (mm), it is required that the range of the welding heat input Q (kJ/cm) defined by the relation 2 above satisfies 1.15t ≤ Q ≤ 1.6t. If the welding heat input Q value is less than 1.15t, there is a risk that the strength and toughness of the weld metal of giga-grade steel and the coarse grained heat affected zone may be insufficient. Conversely, if it exceeds 1.6t, , there is a problem that not only the insufficient strength of the weld metal and the decrease in the strength of the heat-affected zone of the weld become excessive, but also back bead and melt-out easily occur in the weld, resulting in a defect.

In addition, in the present invention, the welding wire may use a solid wire having a diameter of 0.9 to 1.2 mm, and the description of the welding base material is as described above.

As described above, in the present invention, the contents of Cr, Mo, Si and Mn are controlled so as to satisfy the above relation (1). In addition, while suppressing the Cr content in the welding wire relatively high within the range of 4.0 to 5.2%, and suppressing the Si content as low as 0.001 to 0.1%, it is possible to secure sufficient strength of the welded portion, reduce slag and secure porosity at the same time. can

Hereinafter, the present invention will be described in detail through examples.

(Example 1)

After vacuum melting an ingot having the composition components shown in Table 2 below, a wire was prepared by annealing after being fresh at room temperature through hot rolling. Then, a Cu plating layer was formed on the surface of the wire, and at this time, the copper content was plated in a range of 0.15 to 0.36% by mass% with respect to the entire wire including the plating layer. Then, the copper-plated wire was wire-drawn, and a solid wire for welding with a diameter of 0.9 to 1.2 mm was manufactured.

Using the solid wire produced as described above, galvanized steel sheets having a tensile strength of 1050MP using the base steel No. At this time, for comparison, by using the wire Nos 5, 7, 12, 34 and 36 of Table 2 below, the above-mentioned galvanized steel sheet is used as a welding base material for overlap joint welding, and, in addition, an alloyed galvanized steel sheet is used as a welding base material. Lap joint welding was performed using the

On the other hand, at this time, the zinc or zinc alloy plated steel sheet used is that the base steel sheet is galvanized on both sides, the thickness of the base steel sheet is 2.0 mm, and the plating amount is 100 g/m ² and 45 g/ m ² .

In addition, as a standard condition for welding, _{a mixed shielding gas of Ar+20%CO 2} (flow rate 20l/min) was applied, and two identical steel plates were used as overlapping joints without gaps, and the wire protrusion length was 15mm, pulse It was welded with MAG and welding speed of 80 cm/min. At this time, the Q (kJ/cm) value defined by Relation 2 as described above was made to be 1.5 to 3.4.

After solidification of the weld metal obtained by the above-mentioned overlap joint welding, observation of the bead appearance of the welded part, RT test for investigating the blowhole occurrence situation, hardness measurement and static/dynamic tensile test, etc. were conducted, and the evaluation results are shown in Table 2-3 and FIG. 3 .

At this time, the case where the average hardness of the weld metal was 370~400 as Vickers hardness (Hv, load 500gf, measured at 0.2mm intervals) was evaluated as ○ (Pass), and the case of 330~370 was △, and more than 400 or less than 330 was rated as X (fail). In addition, after the static tensile test (speed 10mm/min) of the weld, when the tensile strength is 1 GPa or more and when the fracture location is not the weld metal or molten wire, ○ (Pass) was evaluated, and X (Fail) was evaluated otherwise. did.

In addition, in the case of the RT test for the observation of the bead appearance and blowhole investigation of the above-mentioned welded part, the bead surface and RT photo were taken for the bead of the central 50mm length excluding the part from the beginning and the end 50mm of the weld bead 150mm. Burns were taken. Then, the slag and blowhole sites were marked, the sum of the areas of the marked sites was calculated, and the slag area ratio was calculated from the following relational expression 3 from the total image area.

[Relational Expression 3]

Slag (or blowhole) area ratio (%) = [Sum of slag (or blowhole) site area/total image area] × 100

And in the evaluation of the slag generation situation shown in Table 2 below, the reference value of the slag area ratio was 1%, and the case of 1% or less was evaluated as ○ (pass), and the others were evaluated as X (failed). This is to completely omit post-slag removal post-treatment processes such as separate pickling or mechanical abrasive brushing (both pickling and brushing if necessary) after welding to improve paint adhesion and corrosion resistance after painting when manufacturing parts. It is a set of goals for

In addition, when evaluating the blowhole occurrence situation, the reference value of the blowhole area ratio was evaluated as ○ (pass) when it was 1% or less based on the ISO 5817 standard, and X (failed) was evaluated otherwise. In the case of high-strength steel with a tensile strength of 590 MPa or higher, when the blowhole area ratio of the weld bead exceeds 5%, there is a concern for a sudden decrease in the static strength and fatigue strength of the welded part. In the case of steel, it is a target standard set to completely prevent the deterioration of the strength of the weld metal due to the increase in the blowhole area ratio of the weld bead.

In addition, for the evaluation of the brittleness of the weld metal obtained using the wires and the simulation evaluation of the high-speed collision situation of the front part, the low-speed (3.6 km/h) and high-speed (54 km/h) conditions, that is, the tensile speeds of 1 m/s and 15 m A high-speed tensile test was performed on the weld specimen under the condition of /s to confirm the fracture location. And the maximum load value at this time was compared with the physical properties of the steel. At this time, the case where no fracture occurred in the weld metal and the maximum load value of the welded part under high-speed conditions was 80% or more compared to the base material was evaluated as ○ (pass), and the others were evaluated as X (failed). When these criteria are satisfied, it was judged that the robustness of the welding part can be sufficiently secured in the high-speed collision situation of front parts of automobiles.

steel
No. Chemical composition (mass %) of steel (welding base material) C Si Mn P S Cr Mo Fe One 0.070 1.100 2.10 0.009 0.001 0.90 - balance 2 0.090 0.900 2.00 0.009 0.001 0.20 0.20 balance

Wire No. division Welding wire chemical composition (% by mass) X value (%) average hardness Seal
burglar break location C Si Mn Ni Cr Mo One invention example 0.085 0.030 1.75 - 4.20 0.48 0.83 ○ ○ ○ 2 invention example 0.085 0.002 1.70 - 4.90 0.50 0.99 ○ ○ ○ 3 invention example 0.080 0.010 1.75 - 5.00 0.50 0.98 ○ ○ ○ 4 invention example 0.090 0.040 1.70 - 4.00 0.45 0.76 ○ ○ ○ 5 invention example 0.080 0.010 1.70 - 5.00 0.62 1.10 ○ ○ ○ 6 invention example 0.100 0.001 1.60 - 4.00 0.40 0.80 ○ ○ ○ 7 invention example 0.085 0.020 1.75 - 4.20 0.48 0.85 ○ ○ ○ 8 invention example 0.085 0.085 1.70 - 4.90 0.50 0.79 ○ ○ ○ 9 invention example 0.080 0.080 1.75 - 5.00 0.50 0.84 ○ ○ ○ 10 invention example 0.090 0.090 1.70 - 4.50 0.48 0.72 ○ ○ ○ 11 invention example 0.080 0.060 1.70 - 5.00 0.65 1.01 ○ ○ ○ 12 invention example 0.100 0.040 1.60 - 4.00 0.40 0.70 ○ ○ ○ 13 invention example 0.085 0.100 1.85 - 5.00 0.65 0.93 ○ ○ ○ 14 invention example 0.080 0.080 1.90 - 5.00 0.40 0.73 ○ ○ ○ 15 invention example 0.087 0.090 1.88 - 4.90 0.50 0.80 ○ ○ ○ 16 invention example 0.082 0.050 1.90 - 5.00 0.65 1.04 ○ ○ ○ 17 invention example 0.085 0.040 1.72 - 5.20 0.54 0.97 ○ ○ ○ 18 invention example 0.15 0.040 1.70 - 4.80 0.50 0.89 ○ ○ ○ 19 comparative example 0.075 0.010 1.07 - 1.37 0.56 0.66 X X X 20 comparative example 0.081 0.030 1.90 - 1.45 0.54 0.62 X X X 21 comparative example 0.087 0.020 1.82 - 5.20 0.67 1.15 X X X 22 comparative example 0.092 0.005 1.88 - 5.80 0.62 1.19 X X X 23 comparative example 0.092 0.040 1.89 - 5.60 0.72 1.20 X X X 24 comparative example 0.070 0.860 1.53 - - - -2.25 X X X 25 comparative example 0.070 0.490 1.02 - - - -1.92 X X X 26 comparative example 0.050 0.510 1.37 2.640 0.16 0.47 -1.00 X X X 27 comparative example 0.070 0.270 1.37 2.880 0.50 0.30 -0.44 X X X 28 comparative example 0.080 0.530 1.68 1.400 0.05 0.24 -1.02 X X X 29 comparative example 0.100 0.800 1.80 1.900 0.33 0.54 -1.20 X X X 30 comparative example 0.075 0.59 1.07 - 1.37 0.56 -1.51 X X X 31 comparative example 0.090 0.45 0.47 0.060 4.97 0.51 -2.82 △ X X 32 comparative example 0.075 0.02 1.63 - 1.17 0.48 0.55 X X X 33 comparative example 0.088 0.31 1.90 - 4.80 0.45 0.28 X X X 34 comparative example 0.010 0.16 1.75 - 4.90 0.51 0.63 X X X 35 comparative example 0.095 0.22 1.82 - 5.00 0.55 0.57 X X X 36 comparative example 0.099 0.38 1.87 - 4.70 0.49 0.15 X X X 37 comparative example 0.087 0.42 1.75 - 5.00 0.46 0.00 X X X

*In Table 1, the remaining components are Fe and unavoidable impurities.

wire No. division X value (%) zinc alloy plating
Blow hole area ratio (%) Zinc cover
Blow hole area ratio (%) slag
Area rate (%) high-speed tensile properties One invention example 0.83 ○ ○ ○ ○ 2 invention example 0.99 ○ ○ ○ ○ 3 invention example 0.98 ○ ○ ○ ○ 4 invention example 0.76 ○ ○ ○ ○ 5 invention example 1.10 ○ ○ ○ ○ 6 invention example 0.80 ○ ○ ○ ○ 7 invention example 0.85 ○ ○ ○ ○ 8 invention example 0.79 ○ ○ ○ ○ 9 invention example 0.84 ○ ○ ○ ○ 10 invention example 0.76 ○ ○ ○ ○ 11 invention example 1.01 ○ ○ ○ ○ 12 invention example 0.70 ○ ○ ○ ○ 13 invention example 0.93 ○ ○ ○ ○ 14 invention example 0.73 ○ ○ ○ ○ 15 invention example 0.80 ○ ○ ○ ○ 16 invention example 1.01 ○ ○ ○ ○ 17 invention example 0.97 ○ ○ ○ ○ 18 invention example 0.89 ○ ○ ○ ○ 19 comparative example 0.66 ○ ○ ○ X 20 comparative example 0.62 ○ ○ ○ X 21 comparative example 1.15 ○ ○ ○ X 22 comparative example 1.19 ○ ○ ○ X 23 comparative example 1.20 ○ ○ ○ X 24 comparative example -2.25 X X X X 25 comparative example -1.92 X X X X 26 comparative example -1.00 X X X X 27 comparative example -0.44 X X X X 28 comparative example -1.02 X X X X 29 comparative example -1.20 X X X X 30 comparative example -1.51 X X X X 31 comparative example -2.82 X X X X 32 comparative example 0.55 ○ ○ ○ X 33 comparative example 0.28 X X X X 34 comparative example 0.63 X X X X 35 comparative example 0.57 X X X X 36 comparative example 0.15 X X X X 37 comparative example 0.00 X X X X

As can be seen from Table 2-3, the X value defined by Relation 1 as well as the solid wire composition component satisfies the range of 0.7 to 1.1%. In all of 1-18, it can be confirmed that the average hardness of the weld, the tensile strength of the weld, and the fracture location meet the standards. 1 is a wire No. in Table 2 above. It is a photograph showing the cross-sectional structure of the fractured portion after welding, hardness distribution, and static tensile test obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] welded using No. 7.

On the other hand, wire No. In the case of 19-23, the Si content is controlled to 0.001 to 0.1% or less, and as shown in Table 3, the blowhole and slag area ratios are at acceptable levels, but the above-mentioned value of X is outside the required range. , the average hardness, tensile strength, rupture value and high-speed tensile properties of the weld metal were not good. In particular, wire No. In 21-23, the average hardness of the weld metal part exceeded 400, and as a result, fracture occurred in the weld metal during static or high-speed tensile tests. This was judged as a result of excessively increased brittleness, as the fraction of martensite in the weld metal exceeded 50%.

In addition, wire No. In 24-31, the value of X largely deviated from the range of 0.7 to 1.1%, and as a result, as shown in Tables 2 and 3, wire No. It did not meet the criteria in all items except for the average hardness △ determination of weld metal parts in No. 31.

Also, wire No. In the case of 32, the Si content was controlled to be 0.001 to 0.1% or less, and as shown in Table 3, the blowhole and slag area ratios were excellent, respectively, but as shown in Table 2, the average hardness of the weld metal was Vickers. With a hardness of 320, it was too low compared to the base material of steel, so the tensile strength of the weld was much lower than that of the base material, and the fracture value was also a weld metal part, so it did not meet the standards. 2 is a wire No. in Table 2 above. 32 is a photograph showing the cross-sectional structure of the fractured portion obtained from Comparative Example [X(%) = 0.55, Q(kJ/cm) = 2.6], hardness distribution and static tensile test.

In addition, wire No. In 33-37, the X value does not satisfy the above-mentioned appropriate range, so that the average hardness value of the weld metal part exceeds 400, and the Si content also exceeds 0.1%. It can be seen that both the blowhole and slag area ratio do not meet the standards. In particular, some of them show the result of breaking at the molten line during tension, confirming that the brittleness of the weld metal part is increased.

On the other hand, as described above, in FIG. 3, using the wires Nos. 5, 7, 12, 34 and 36 of Table 2, the overlap joint welding is performed with the galvanized steel sheet described above, and the overlap joint welding is performed with the alloyed galvanized steel sheet. , are RT (Radiographic Test) photos of each weld metal obtained.

As shown in FIG. 3, the content of Si is out of the range of 0.001 to 0.1%, and the above-described X value is also out of the range of 0.7 to 1.1% of the wire No. In the case of the welds obtained using 34 and 36, as can be seen from the RT results, the blowhole area ratio was greatly increased. On the other hand, the Si and X values satisfies the appropriate range of the present invention. It can be seen that in the case of the welds obtained using 5, 7, and 12, very good results can be obtained in which the blowhole area ratio is within 1%.

(Example 2)

steel
No. wire
No. division heat input
(kJ/cm) weld
Tensile strength (MPa) Microstructure Characteristics of Welded Metal M fraction
(%) B/γ fraction
(%) Average effective grain size (㎛) High inclination angle of more than 47°
Grain fraction (%) One 7 comparative example 1.6 950 50 41/9 1.5 27 One 7 comparative example 2.0 958 46 47/7 1.8 29 One 32 comparative example 3.2 930 14 80/6 4.4 24 One 7 invention example 2.3 1009 43 52/5 2.2 35 One 7 invention example 2.6 1022 38 58/4 2.6 37 One 7 invention example 2.8 1017 32 64/4 2.8 36 One 7 invention example 3.2 1015 30 66/3 2.9 36 2 12 invention example 2.4 1008 42 53/5 2.3 38 2 12 invention example 2.6 1021 37 59/4 2.5 35 2 12 invention example 2.8 1020 31 66/3 2.9 39 2 12 invention example 3.2 1018 30 68/2 3.0 37

*In Table 4, M stands for martensite, B stands for bainite, and γ stands for retained austenite. And in Table 4, the steel No. refers to the steel No. in Table 1, and the wire No. refers to the wire No. in Table 2.

By using the solid wires as shown in Table 4, the steel materials of Table 4 were welded by overlap joint welding to obtain a weld metal. At this time, the steel was a galvanized steel sheet with zinc plated on the surface, and a thickness of 2.0 mm was used. In addition, specific welding conditions during this welding were the same as in Example 1, and only the welding heat input was applied differently as shown in Table 4 above for each wire and steel material combination. And the tensile strength of each weld metal obtained by applying different welding heat input as described above was measured and shown in Table 4, and microstructure characteristics of the weld metal were also measured and shown in Table 4 above.

On the other hand, in the present invention, the tensile strength is measured by processing three tensile specimens according to JIS-5 standard from the welded specimens of the overlap joint at the center of the bead, and installing an extensometer under the condition of a tensile speed of 10 mm/min. It was set as the average value of each measurement value obtained afterward.

And the microstructure of the welding part was measured from the result of performing Lepera etching on the weld metal part, taking an optical picture, and analyzing each low-temperature transformation phase divided by color difference, and the average effective grain size and 47˚ The fraction of the above high-hardness grains was also measured through EBSD analysis.

As shown in Table 4, the invention examples in which the Q value according to Relation 2 satisfies the range of 2.3 ~ 3.2 kJ / cm based on the thickness of the steel sheet base material of 2.0 mm obtained the result that the tensile strength of the weld exceeds 1 GPa, , the ratio of tensile strength to the base material of the welded part was 95-96%.

On the other hand, it can be seen that the comparative examples in which the value of Q is less than 2.3 kJ/cm exhibits less than 1 GPa of weld tensile strength. In addition, when the Q value exceeds 3.2 kJ/cm, back beads are formed or melted due to excessive welding heat input compared to the thickness of the steel sheet, so it was excluded from this analysis.

On the other hand, when the value of X defined by the above-mentioned relation 1 is in the range of 0.7 to 1.1%, the development of upper and lower bainite is possible in a temperature range of about 400 to 250 ° C. , compared to martensite alone, a large number of high-hardness grains developed in an inter-locking structure within the old austenite grains, and mixed with martensite, so it was judged to be effective in improving strength and toughness.

Figure 4 is Table 4 No. 7 Wire and No. 1 The EBSD structure picture and the inverse pole figure of the weld metal obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 3.2] in which steel materials were combined and welded, this point is well explained. On the other hand, FIG. 5 shows No. 5 in Table 4. 32 wire and No. 1 As an EBSD structure picture and inverse pole figure of the weld metal obtained from Comparative Example [X(%) = 0.55, Q(kJ/cm) = 3.2] in which steel materials were combined and welded, although the amount of welding heat input is within the scope of the present invention, It can be seen that the value of X is outside the scope of the present invention and the desired microstructure cannot be obtained.

On the other hand, Figure 6 is Table 4 No. 7 Wire and No. 1 By omitting the welding bead appearance photo obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] and post-treatment processes such as pickling or brushing to remove slag from the weld area, This is a picture of the exterior after painting. In particular, it can be confirmed that the slag area ratio of the weld bead is very reduced to less than 1% even when 20% of carbon dioxide gas is mixed as the shielding gas, and accordingly, it can be confirmed that the paintability of the weld and the corrosion resistance after painting can be improved.

And Figure 7 (a-b) is Table 4 No. 7 Wire and No. 1 A high-speed tensile test (tensile speed of 1 m/s and 15 m/s, respectively) was performed by applying a load to the weld obtained from the invention example [X(%) = 0.85, Q(kJ/cm) = 2.6] in which steel materials were combined and welded. This is a diagram showing the change in load (b) of the welded part in comparison with the change in load (a) of the steel material, which is the welding base material. Specifically, in a relatively low-speed collision (3.6 km/h) situation, the maximum load ratio of the weld to the steel plate base material was very good at 95%, and the result was confirmed that fracture did not occur in the weld metal or molten line, and high-speed collision (54 km/h) /h), the maximum load ratio of the welded part to the steel plate base material is 82%, and it can be confirmed that the welded part load ratio can be secured by 80% or more without breaking the weld metal even in this case. As a result of supporting the microstructure characteristics of the above-described weld metal, it can be seen that a gas-shielded arc weld of a giga-grade steel having a tensile strength of 1 GPa or higher can be effectively obtained.

As described above, in the detailed description of the present invention, a preferred embodiment of the present invention has been described, but a person skilled in the art may make various modifications within the limit without departing from the scope of the present invention. Of course it is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims to be described later as well as equivalents thereof.

Claims (18)

By mass% of the whole wire, C: 0.08 to 0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less, Cr: 4.0 to 5.2%, Mo : A gas shielded arc welding wire that contains 0.4 to 0.65%, the remainder Fe and unavoidable impurities, and the value X defined by the following relational expression 1 satisfies the range of 0.7 to 1.1%.
[Relational Expression 1]
X(%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn]
However, in relation 1, [Cr], [Mo], [Si] and [Mn] represent the mass% of each element.
The gas shielded arc welding wire according to claim 1, wherein a Cu plating layer is formed on the surface of the welding wire.
The gas shielded arc welding wire according to claim 2, wherein Cu constituting the Cu plating layer has a content of 0.4% or less (excluding 0%) as a mass% of the entire wire including the plating layer.
The gas shielded arc welding wire according to claim 3, wherein Cu constituting the Cu plating layer is in a mass% of the entire wire including the plating layer, and has a content in the range of 0.1 to 0.3%.
The gas shielded arc welding wire according to claim 1, wherein the welding wire contains Cr: 4.2 to 4.9%, Mo: 0.45 to 0.48%, and Mn: 1.65 to 1.75%, respectively.
The gas shielded arc welding wire according to claim 1, wherein the welding wire has a Si content in the range of 0.04 to 0.08%.
The gas shielded arc welding wire according to claim 1, wherein the welding wire is a solid wire for gas shielded arc welding.
A welded structure having a welding portion obtained by welding two or more welding base materials using the welding wire according to any one of claims 1 to 7,
The weld portion, in area%, has a microstructure consisting of 30 to 50% martensite, 50 to 70% bainite, and residual austenite of less than 5%, and the microstructure constituting the weld is the size of the average effective grain size is 1-3㎛, and the high-hardness crystal grain fraction of 47˚ or more is 35% or more.
The welded structure according to claim 8, wherein at least one of the welding base materials is a galvanized steel sheet.
10. The welded structure according to claim 9, wherein the galvanized steel sheet is one of an electric galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.
The welded structure according to claim 10, wherein the base steel sheet constituting the galvanized steel sheet contains at least one of 0.2 to 0.9% Cr: 0.2 to 0.9% and Mo: 0.1 to 0.2% by mass%.
The welded structure according to claim 8, wherein the weld has an average hardness of 370 to 400 Hv, and a tensile strength of 1 GPa or more, which is 95% or more compared to the base material to be welded.
The welded structure according to claim 8, wherein the high-speed tensile strength of the welded part is 95% and 80% or more, respectively, compared to the base material at tensile speeds of 3.6 km/h and 54 km/h.
A method of gas-shielded arc welding of a welding base material using the welding wire according to any one of claims 1 to 7,
In the welding, 5-20% CO ₂ is mixed with Ar as a protective gas and used,
When the thickness of the welding base material is t (mm), the welding heat input Q (kJ/cm) defined by the following Relation 2 is 1.15t ≤ Q ≤ 1.6t Gas characterized in that the welding is performed Shielded arc welding method.
[Relational Expression 2]
Q = (I × E) × 0.048 /υ
However, in Relation 2, I, E, and υ represent welding current [A], welding voltage [V], and welding speed (cm/min), respectively.
15. The gas shielded arc welding method according to claim 14, wherein the welding wire is a solid wire having a diameter of 0.9 to 1.2 mm.
15. The gas shielded arc welding method according to claim 14, wherein the welding base material contains at least one of 0.2 to 0.9% of Cr and 0.1 to 0.2% of Mo, in terms of its own mass%.
15. The gas shielded arc welding method according to claim 14, wherein the welding base material is a galvanized steel sheet.
The gas shielded arc welding method according to claim 17, wherein the galvanized steel sheet is one of an electric galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.

Images