Gas-shielded arc welded metal and automotive parts having gas-shielded arc welded metal

Abstract

To provide a gas shielded arc weld metal having excellent weld strength and porosity resistance, which can ensure excellent weld strength and porosity resistance in the automotive industry. The present invention relates to a weld metal obtained by gas-shielded arc welding of a weld base metal, the weld metal containing, by weight%, C: 0.001 to 0.30%, Si: 0.25% or less (excluding 0%), Mn: 0.50 to 3.00%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Cr: 0.50% or less (excluding 0%), Mo: 0.60% or less (excluding 0%), Al: less than 0.07% (excluding 0%), Ni: 0.40% or less (excluding 0%), Cu: 0.50% or less (excluding 0%), Ti: less than 0.07% (excluding 0%), with the balance being Fe and other unavoidable impurities, and is characterized in that the weld metal satisfies Relational Formula 1 and Relational Formula 2.

Description

[Technical Field]

[0001] The present invention relates to a gas-shielded arc-welded metal, and more particularly to a gas-shielded arc-welded metal that not only has excellent weld strength and porosity resistance but also ensures the economy that is always required when manufacturing parts. [Background technology]

[0002] In the automotive industry, technological research into weight reduction of vehicle bodies and parts has emerged as a major issue due to fuel efficiency regulations imposed in response to environmental protection issues such as global warming. This trend has led to the need to apply high-strength steel to chassis parts, which are important for vehicle driving performance, in order to reduce weight.

[0003] To achieve such lightweight components, it is essential to increase the strength of the material, and it is important to ensure the durability of components made from high-strength steel in an environment where repeated fatigue loads are applied.

[0004] However, in the case of arc welding, which is mainly used to ensure strength when assembling automobile chassis parts, lap joints are formed between parts by welding a welding wire, so the geometric shape of the seam is unavoidable. This acts as a concentration point of repeated fatigue stress (notch effect) and becomes a fracture initiation point, resulting in a decrease in the durability of the part, and therefore has a limit where the benefits of using high-strength steel are lost.

[0005] Therefore, to improve the fatigue properties of welds, it is crucial to reduce the angle (toe angle) of the bead tip, which is the area where stress is concentrated. In addition, controlling the material and stress of the toe is also crucial. Furthermore, as mentioned above, the trend toward higher strength and lighter weight components has led to thinner materials, which has increased demand for rust resistance to prevent through-hole corrosion. This has led to an increased use of plated steel. However, the weld metal, particularly in arc welds, lacks a plated layer, which limits its corrosion resistance after painting on the base material. This leads to early corrosion of welds in chassis parts made of plated steel in the harsh corrosive environment of vehicle operation, leading to reduced fatigue properties. Meanwhile, gas-shielded arc welding of plated steel can generate a large number of porosity defects, such as pits and blowholes, in the weld bead due to the generation of zinc vapor, potentially reducing the strength of the weld and resulting in reduced welding productivity. Furthermore, in the case of general unplated steel materials, slag generated in the weld bead during gas shielded arc welding can cause coating defects and reduce corrosion resistance after coating. This can lead to a problem of increased costs due to post-processing steps such as pickling or brushing to remove slag after welding during part manufacturing.

[0006] Recently, there has been active development of lightweight chassis parts for next-generation eco-cars, and the development of welding technology that can improve the properties of welded joints while ensuring economic efficiency has become an especially important issue. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-118274 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a gas-shielded arc weld metal that has excellent weld strength and porosity resistance, which can ensure excellent weld strength and porosity resistance in the automotive industry. The weld metal refers to a metal formed by melting and mixing the base metal to be welded and the welding wire.

[0009] The object of the present invention is not limited to the above-mentioned matters. Further object of the present invention is described in the entire content of the specification, and a person skilled in the art to which the present invention pertains will have no difficulty in understanding the further object of the present invention from the entire content of the specification of the present invention. [Means for solving the problem]

[0010] The present invention provides The present invention relates to a gas-shielded arc weld metal obtained by gas-shielded arc welding of a weld base metal, which contains, by weight, C: 0.001 to 0.30%, Si: 0.25% or less (excluding 0%), Mn: 0.50 to 3.00%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Cr: 0.50% or less (excluding 0%), Mo: 0.60% or less (excluding 0%), Al: less than 0.07% (excluding 0%), Ni: 0.40% or less (excluding 0%), Cu: 0.50% or less (excluding 0%), Ti: less than 0.07% (excluding 0%), with the balance being Fe and other unavoidable impurities, and which satisfies the following relational expressions 1 and 2.

[0011] [Equation 1] 3.5≦[Si]×100 / [Mn]≦8.5

[0012] [Equation 2] [Ti]+[Al]<0.07 (In the above Relational Formula 1 and Relational Formula 2, [Si], [Mn], [Ti], and [Al] represent the weight percent contents of each element in parentheses in the weld metal.)

[0013] The weld metal may contain Si in the range of 0.05 to 0.15%.

[0014] The weld metal may further contain one or more of Nb: 0.10% or less, V: 0.10% or less, and Zr: 0.10% or less.

[0015] The weld metal may further contain B: 0.01% or less.

[0016] The weld metal can satisfy the requirement that the length fraction of porosity defects is 10% or less (including 0%) relative to the entire length of the weld metal.

[0017] The welding base material may be a hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on the surface thereof.

[0018] The above welding base metal has a composition, by weight percent, of C: 0.04 to 0.18%, Si: 2.0% or less (including 0%), Mn: 0.5 to 3.0%, Cr: 2.0% or less (including 0%), Mo: 2.0% or less (including 0%), Al: 0.01 to 0.1%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities.

[0019] The welding base metal may be further composed of one or more of Ti: 0.20% or less, Nb: 0.10% or less, and Cu: 0.10% or less.

[0020] The welding base metal may have a thickness of 0.8 to 4.0 mm.

[0021] The present invention also provides The present invention relates to an automobile part having the above weld metal. [Effects of the Invention]

[0022] According to the present invention, it is possible to effectively provide a gas shielded arc weld metal having excellent weld strength and porosity resistance as a next-generation welding technology that ensures performance / cost competitiveness in line with the popularization of electric vehicles. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described below. When welding galvanized steel sheets, zinc vapor generation can lead to porosity in the weld. Lowering the content of silicon (Si), a deoxidizer in the weld metal, beyond a certain level reduces the viscosity of the molten metal, facilitating the discharge of zinc vapor. At high welding temperatures, oxygen (O) generated by the dissociation of CO2 in the protective gas reacts more actively with the zinc in the coating layer to form Zn-based oxides. This effectively lowers zinc vapor pressure, stabilizes the arc, and reduces porosity. However, the inventors' research has shown that when titanium or aluminum (Ti or Al), a steel deoxidizer, is present in the weld metal at a certain level, it can interfere with the oxidation reaction of zinc, leading to arc instability, increased porosity, and reduced weld strength, even at low Si content. In particular, a Ti+Al ratio of 0.07% or more significantly increases porosity, making it difficult to obtain a weld metal with excellent weld strength and porosity resistance.

[0024] Therefore, the weld metal obtained by gas-shielded arc welding the welding base metal of the present invention contains, by weight%, C: 0.001 to 0.30%, Si: 0.25% or less (excluding 0%), Mn: 0.50 to 3.00%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Cr: 0.50% or less (excluding 0%), Mo: 0.60% or less (excluding 0%), Al: less than 0.07% (excluding 0%), Ni: 0.40% or less (excluding 0%), Cu: 0.50% or less (excluding 0%), Ti: less than 0.07% (excluding 0%), with the remainder being Fe and other unavoidable impurities, and satisfies the following relational formula 1 and relational formula 2.

[0025] [Equation 1] 3.5≦[Si]×100 / [Mn]≦8.5

[0026] [Equation 2] [Ti]+[Al]<0.07

[0027] The gas-shielded arc weld metal of the present invention will be described below. First, the reasons for adding each component and the reasons for limiting the content in the weld metal of the present invention will be described in detail. It should be noted that the contents of each component described below are all based on weight percent unless otherwise specified.

[0028] C:0.001~0.30% Carbon (C) is a key element that lowers the temperature at which acicular ferrite, bainite, and martensite transformations occur through diffusionless transformations during solidification of the high-temperature austenite phase during continuous cooling. If the C content is less than 0.001%, the hardening ability is reduced, making it difficult to ensure sufficient weld metal strength. Furthermore, due to the aforementioned principle, the low-temperature transformation start temperature is not sufficiently low, significantly reducing the offset effect of the low-temperature transformation expansion effect on the tensile residual stress in the weld during cooling. This can result in the failure to form a high-hardness grain boundary structure with a large difference in orientation angle between grains. On the other hand, if the C content exceeds 0.30%, the viscosity of the molten metal decreases, resulting in poor bead shape. Furthermore, the weld metal becomes excessively hard, reducing its toughness.

[0029] Si: 0.25% or less (excluding 0%) The above-mentioned Si is an element (deoxidizing element) that promotes deoxidation of molten metal during arc welding, which is advantageous in suppressing the occurrence of blowholes and raising the low-temperature transformation start temperature. However, when welding galvanized steel sheets, reducing the Si content among the weld metal components can promote the oxidation of Zn and reduce the zinc vapor pressure, thereby preventing the occurrence of porosity defects in the weld. On the other hand, if the Si content exceeds 0.25%, there may be disadvantages such as the generation of a large amount of non-conductive slag, which causes poor coating of the weld, and excessive deoxidation, which insufficiently activates the surface of the weld and reduces the penetration of the molten metal. Therefore, in the present invention, it is preferable to control the Si content to 0.25% or less. More preferably, the Si content is controlled to a range of 0.05 to 0.15%. If the Si content is too low, the deoxidizing effect may be insufficient, and blowholes may be more likely to occur.

[0030] Mn: 0.5 to 3.0% Mn is a deoxidizing element that promotes deoxidation of molten metal during arc welding, thereby preventing blowhole formation. Like C, it lowers the low-temperature transformation start temperature. A Mn content of less than 0.5% can result in insufficient deoxidation, potentially increasing blowhole formation. However, when welding galvanized steel sheets, an excessively high Mn content among the weld metal components can hinder the oxidation of Zn, increasing the zinc vapor pressure and promoting arc instability and the formation of porosity defects in the weld. On the other hand, a Mn content of more than 3.0% can result in excessively high molten metal viscosity, preventing proper flow of molten metal into the weld at high welding speeds, resulting in the formation of humping beads and potentially poor bead shape. More preferably, the Mn content is limited to 2.50% or less.

[0031] Cr: 0.50% or less (excluding 0%) Cr is a ferrite stabilizing element that lowers the low-temperature transformation start temperature and is advantageous for improving strength by ensuring the hardenability of the weld metal. If the Cr content exceeds 0.50%, there may be a disadvantage that the brittleness of the weld metal increases unnecessarily, making it difficult to ensure sufficient toughness. The Cr content is more preferably 0.30% or less, even more preferably 0.20% or less, and most preferably 0.10% or less.

[0032] Mo: 0.60% or less (excluding 0%) Mo is a ferrite stabilizing element and is an element advantageous in ensuring hardenability that improves the strength of the weld metal. If the Mo content exceeds 0.60%, there may be a drawback in some cases in that the toughness of the weld metal decreases.

[0033] P: 0.030% or less (excluding 0%) P is an element that is generally present in steel as an inevitable impurity and is also a common impurity in solid wires for arc welding. If the P content exceeds 0.030%, there may be a drawback in that high-temperature cracking of the weld metal becomes significant.

[0034] S: 0.030% or less (excluding 0%) S is an element that is generally found in steel as an unavoidable impurity and is also commonly found in solid wires for arc welding. If the S content exceeds 0.030%, the toughness of the weld metal may deteriorate and the surface tension of the molten metal may be insufficient during welding, which may cause the molten metal to flow excessively downward due to gravity during high-speed downward welding (vertical welding from top to bottom), resulting in poor weld bead shape.

[0035] Al: Less than 0.07% (excluding 0%) Al acts as a deoxidizing element, promoting deoxidation of molten metal during arc welding even in trace amounts, thereby improving the strength of the weld metal. To ensure the above-mentioned effects, 0% is excluded as the lower limit of the Al content. However, the deoxidizing effect of Al can hinder the oxidation reaction of Zn during welding of galvanized steel sheets, increasing zinc vapor pressure and inducing arc instability, which can promote the occurrence of porosity defects in the weld. If the Al content is 0.07% or more, the formation of Al-based oxides increases, which can potentially reduce the strength and toughness of the weld metal and increase the susceptibility of the weld to electrodeposition coating defects due to non-conductive oxides.

[0036] Ti: Less than 0.07% (excluding 0%) Ti acts as a deoxidizing element, promoting deoxidation of molten metal during arc welding even in trace amounts, thereby improving the strength of the weld metal. It also facilitates the development of acicular ferrite, which can improve the toughness of the weld. To ensure the above-mentioned effects, the lower limit of the Ti content is set to 0%. However, the deoxidizing effect of Ti can hinder the oxidation reaction of Zn during welding of galvanized steel sheets, increasing zinc vapor pressure and inducing arc instability, which can promote the occurrence of porosity defects in the weld. A Ti content of 0.07% or more can increase the formation of Ti-based oxides, potentially resulting in reduced strength and toughness of the weld metal.

[0037] Ni: 0.40% or less (excluding 0%) The Ni is an element that can improve the strength and toughness of the weld metal. To ensure the above-mentioned effects, the lower limit of the Ni content is set to 0%. However, if the Ni content exceeds 0.40%, there may be a drawback in that the weld metal becomes susceptible to cracking, so the Ni content is set to 0.40% or less. The Ni content is more preferably 0.30% or less, even more preferably 0.20% or less, and most preferably 0.10% or less.

[0038] Cu: 0.50% or less (excluding 0%) The Cu is an element effective in improving the strength of the weld metal. However, if the Cu content exceeds 0.50%, there may be a drawback in that the weld metal becomes more susceptible to cracking. The Cu content is more preferably 0.45% or less, even more preferably 0.40% or less, and most preferably 0.30% or less. On the other hand, in order to fully obtain the effect of improving strength, the Cu content in the weld metal can be 0.01% or more.

[0039] The weld metal of the present invention may further selectively contain one or more of Nb: 0.10% or less, V: 0.10% or less, and Zr: 0.10% or less.

[0040] Nb: 0.10% or less Nb is an element that can enhance hardening ability and densify the microstructure, thereby improving the strength and toughness of the weld metal. It also has the effect of improving the flow of molten metal during arc welding and stabilizing the arc. To ensure the above-mentioned effects, the lower limit of the Nb content is set to 0%. However, if the Nb content exceeds 0.10%, it may form low-melting-point compounds at grain boundaries, which can lead to the disadvantage of high-temperature cracking.

[0041] V:0.10% or less V is an element that can improve the strength and toughness of weld metal by increasing hardening ability and making the microstructure dense. It is also a precipitation strengthening element that can improve the strength of weld metal by forming carbonitrides. However, if the V content exceeds 0.10%, excessive strength due to excess precipitates can result in a decrease in the toughness of the weld metal. Therefore, the V content is limited to 0.10% or less.

[0042] Zr: 0.10% or less Zr is an element that promotes deoxidation of molten metal during arc welding (a deoxidizing element), and is therefore advantageous in suppressing the occurrence of blowholes. However, if the Zr content exceeds 0.10%, there is a possibility that the electrodeposition paintability of the welded portion may be reduced. Therefore, the Zr content is set to 0.10% or less.

[0043] The weld metal of the present invention may further contain B: 0.01% or less, selectively. B: 0.01% or less B is an element that can enhance the hardening ability and thereby improve the strength of the weld metal. However, if the B content exceeds 0.01%, the excessive hardening ability may result in a decrease in the toughness of the weld metal. Therefore, the B content is set to 0.01% or less.

[0044] The remaining component of the present invention is iron (Fe). However, during the normal manufacturing process, unintentional impurities may be inevitably mixed in from the raw materials or the surrounding environment, and this cannot be excluded. Since the above impurities are known to anyone skilled in the art, the present invention does not specifically mention all of them.

[0045] Meanwhile, the weld metal of the present invention contains Mn and Si so as to satisfy the following relational expression 1. By satisfying the following relational expression 1, the strength and porosity resistance of the weld metal can be improved. If the value defined by the above relational expression 1 is less than 3.5, the deoxidation effect of the weld metal may be insufficient, resulting in a decrease in porosity resistance and a lack of strength. If the value exceeds 8.5, not only will the viscosity of the weld metal increase, but the zinc vapor pressure during welding may also increase due to the above-mentioned principle, resulting in arc instability and a decrease in porosity resistance, resulting in a lack of strength. This may lead to a problem of deterioration in electrodeposition paintability due to an increase in Si-based non-conductive oxides. More preferably, the upper limit of the value defined by the above relational expression 1 is controlled to 6.0.

[0046] [Equation 1] 3.5≦[Si]×100 / [Mn]≦8.5 (In the above relational expression 1, [Si] and [Mn] represent the weight percent contents of each element in parentheses in the weld metal.)

[0047] The weld metal of the present invention is also required to contain Ti and Al so as to satisfy the following relational expression 2.

[0048] When welding galvanized steel sheets, zinc vapor generation can cause porosity in the weld. However, lowering the content of silicon (Si), a deoxidizer in the weld metal, reduces the viscosity of the molten metal, facilitating the discharge of zinc vapor. At high welding temperatures, oxygen (O) generated by the dissociation of CO2 in the protective gas reacts more vigorously with the zinc in the coating to form zinc-based oxides. This effectively lowers the zinc vapor pressure, stabilizes the arc, and reduces porosity. However, when titanium or aluminum (Ti or Al), a steel deoxidizer, is present in the weld metal at a higher content, it can interfere with the oxidation reaction of zinc, leading to arc instability, increased porosity, and reduced weld strength, even at low silicon content. In particular, a Ti+Al value of 0.07% or higher significantly increases porosity, preventing the weld metal from achieving excellent weld strength and porosity resistance.

[0049] More specifically, the affinity of metals for oxygen, i.e., the thermodynamic stability of each metal element when it combines with oxygen at a certain temperature, can be easily understood using the well-known Ellingham diagram. The Gibbs free energy decreases in the order Al > Ti > Si > Zn, which allows each element to more easily combine with oxygen, resulting in increased oxide stability. The boiling points at which each element begins to combine with oxygen are Al2O3: 2,977°C, TiO2: 2,972°C, SiO2: 2,230°C, and ZnO: 2,360°C. Al and Ti are thermodynamically more stable than Si and Zn at higher temperatures, allowing them to more easily combine with oxygen first. Therefore, as the weld metal molten at the arc center temperature of approximately 3,000–5,000°C gradually cools and solidifies, the Si content decreases. Before Zn can more easily combine with oxygen, the increased Al and Ti content oxidizes before Zn, potentially increasing the susceptibility to porosity due to increased Zn vapor pressure.

[0050] [Equation 2] [Ti]+[Al]<0.07 (In the above relational expression 2, [Ti] and [Al] represent the weight percent contents of each element in parentheses in the weld metal.)

[0051] Furthermore, in the present invention, the weld metal can satisfy the requirement that the length fraction of porosity defects relative to the entire length of the weld metal is 10% or less (including 0%). Therefore, the present invention can effectively provide automobile parts and other components having welds with excellent porosity resistance.

[0052] In the present invention, a hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on its surface can be used as the welding base material used to form the weld metal, and the hot-dip galvanized layer has a thickness of 1 to 20 μm and a single-side coating amount of 1 to 120 g / m 2 It is preferable that:

[0053] Furthermore, the present invention is not limited to the alloy composition of the weld base metal, and as an example, the weld base metal may contain, by weight percent, C: 0.04 to 0.18%, Si: 2.0% or less (including 0%), Mn: 0.5 to 3.0%, Cr: 2.0% or less (including 0%), Mo: 2.0% or less (including 0%), Al: 0.01 to 0.1%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), with the balance being Fe and other unavoidable impurities.

[0054] The welding base metal may optionally further contain one or more of Ti: 0.2% or less, Nb: 0.1% or less, and Cu: 0.1% or less. Furthermore, the welding base material may have a thickness of 0.8 to 4.0 mm.

[0055] Furthermore, the present invention is not limited to a specific compositional component of the welding wire that forms the weld metal. One example of the compositional component of the welding wire that can be used is a welding solid wire that contains, by weight, C: 0.001 to 0.30%, Si: 0.25% or less (excluding 0%), Mn: 0.50 to 3.00%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Cr: 1.50% or less (excluding 0%), Mo: 0.60% or less (excluding 0%), Al: less than 0.10% (excluding 0%), Ni: 0.40% or less (excluding 0%), Cu: 0.50% or less (excluding 0%), Ti: less than 0.10% (excluding 0%), with the balance being Fe and other unavoidable impurities. Optionally, the wire composition may further contain one or more of Nb: 0.10% or less, V: 0.10% or less, and Zr: 0.10% or less, or may further contain B: 0.01% or less.

[0056] Meanwhile, in the present invention, the type of shielding gas used in welding the above-mentioned base metal is not particularly limited, and 100% CO2 gas, Ar + 20% CO2 gas, Ar + 10% CO2 gas, Ar + 5% CO2 gas, Ar + 2% O2 gas, etc. can be used as the shielding gas, but the effects of the present invention can be particularly pronounced when Ar + 5 to 20% CO2 is used as the shielding gas. That is, in the present invention, in order to ensure the tensile strength of the weld without causing fracture of the weld metal or fusion line, it is preferable to use a mixture of Ar and 5 to 20% CO2 as the protective gas during the above-mentioned welding.

[0057] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are merely for the purpose of illustrating and embodying the present invention, and are not intended to limit the scope of the present invention, as the scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0058] (Example) The alloy composition is as shown in Table 1 below, and the thickness is 2.0 mm, the length is 200 mm, the width is 150 mm, and the plating amount on one side is 85 g / m 2Two sheets of each of three types of hot-dip galvanized steel sheets with tensile strengths of 540 MPa (Steel 1), 670 MPa (Steel 2), and 780 MPa (Steel 3) were prepared as base materials. A large number of solid wires for gas shielded arc welding with various alloy compositions were also prepared.

[0059] Next, the above hot-dip galvanized steel sheets were lap-welded using each of the above welding solid wires. Pulse DC (protective gas: Ar + 10-20% CO2) was used as the welding method, with a shielding gas flow rate of 20 l / min, a welding torch angle of 45° relative to the perpendicular direction of the base metal, a wire protrusion length of 15 mm, and welding current / voltage / speed conditions of 200 A, 20 V, and 80 cm / min. The gap of the lap joint was 0 mm, and the length of the lap joint was 10 mm.

[0060] Meanwhile, in the longitudinal direction of the welding base material, welding was started at a position 10 mm from the starting point, and after welding proceeded for a length of 180 mm, welding was finished at a position 10 mm from the finishing point on the opposite side to the welding start position.

[0061] For each weld formed by the above welding, the microstructure of a cross section perpendicular to the longitudinal direction at the longitudinal center of the weld was observed using an optical microscope to identify the weld metal region in advance, and that region was machined into the form of fine chips. Next, for each chip sample, the chemical composition of the weld metal was measured using emission spectroscopy using high-frequency inductively coupled plasma (ICP). The results are shown in Table 2 below.

[0062] The porosity of each weld formed by the above welding was measured, and the results are shown in Table 3 below. The specific porosity measurement method is as follows. The prepared welded test piece was irradiated with X-rays to measure the length of each pore distributed in the weld, and the porosity of the weld was calculated by adding up all of these lengths and dividing the total length by the entire length of the weld. In this case, sections of 10 mm from the start and end points of the weld were excluded from the measurement, and the porosity was calculated as the average value of the measurements for three welded test pieces.

[0063] In addition, a tensile test was performed on the welded joints, and the location of the fracture was visually observed. If the fracture occurred in the weld base metal or heat-affected zone, it was evaluated as pass (◯), and if the fracture occurred in the weld metal, it was evaluated as fail (×). The specific tensile test method is as follows: Tensile test specimens 30 mm wide and 250 mm long were processed from each of the welded test specimens prepared above, and a uniaxial tensile test was performed at a speed of 10 mm / min, after which the fracture location was investigated. The tensile test results were evaluated for reproducibility by evaluating three welded test specimens.

[0064] [Table 1] *Residual components in Table 1 are Fe and unavoidable impurities

[0065] [Table 2] TIFF0007767644000003.tif170170*The residual components in Table 2 are Fe and unavoidable impurities.

[0066] [Table 3] TIFF0007767644000005.tif170150

[0067] As shown in Tables 1 to 3 above, in the case of Examples 1 to 15 of the invention, which satisfy both the weld metal alloy composition and Relational Expressions 1 and 2, the length fraction of porosity defects relative to the total length of the weld metal is 10% or less (including 0%) in all cases, and it can be seen that the fracture locations of the welds are also excellent as weld base metals or heat-affected zones.

[0068] In contrast, Comparative Examples 1, 11, 4-5, 14-15, and 21-30 are cases where Relational Formulas 1 and 2 are outside the range of the present invention, and show high porosity in the weld with any protective gas, and show high porosity in the weld with all protective gases. As a result, it can be confirmed that the fracture position in the weld also occurs in the weld metal.

[0069] Furthermore, Comparative Examples 2 to 3, 9 to 10, 12 to 13, and 19 to 20 did not satisfy Relational Formula 2, and therefore showed high porosity in the weld with any protective gas, and showed high porosity in the weld with all protective gases, and as a result, the fracture location in the weld also occurred in the weld metal.

[0070] Comparative Examples 6 to 8 and 16 to 18 are cases where Relational Formula 1 was not satisfied, and showed high porosity in the weld for all protective gases. As a result, it was confirmed that the fracture position in the weld also occurred in the weld metal.

Claims

1. A weld metal obtained by gas-shielded arc welding two welding base materials, The alloy contains, by weight, C: 0.001 to 0.30%, Si: 0.25% or less (excluding 0%), Mn: 0.50 to 3.00%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Cr: 0.50% or less (excluding 0%), Mo: 0.60% or less (excluding 0%), Al: less than 0.07% (excluding 0%), Ni: 0.40% or less (excluding 0%), Cu: 0.50% or less (excluding 0%), and Ti: less than 0.07% (excluding 0%), with the balance being Fe and other unavoidable impurities, and satisfies the following relational formula 1 and relational formula 2: The weld metal satisfies the requirement that the length fraction of porosity defects is 10% or less (including 0%) relative to the entire length of the weld metal, 1. A gas-shielded arc welding metal, wherein at least one of the two welding base materials is a hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on its surface. [Relationship 1] 3.5≦[Si]×100 / [Mn]≦8.5 [Relationship 2] [Ti]+[Al]<0.07 (In the above-mentioned Relational Formula 1 and Relational Formula 2, [Si], [Mn], [Ti], and [Al] represent the weight percent contents of each element in parentheses in the weld metal.)

2. 2. The gas-shielded arc weld metal according to claim 1, wherein the weld metal contains, by weight, Si in the range of 0.05 to 0.15%.

3. The gas-shielded arc weld metal according to claim 1, further comprising, by weight percent, one or more of Nb: 0.10% or less, V: 0.10% or less, and Zr: 0.10% or less.

4. The gas-shielded arc weld metal according to claim 1, further comprising, by weight percent, B: 0.01% or less.

5. 2. The gas-shielded arc weld metal according to claim 1, characterized in that the weld base metal contains, by weight%, C: 0.04 to 0.18%, Si: 2.0% or less (including 0%), Mn: 0.5 to 3.0%, Cr: 2.0% or less (including 0%), Mo: 2.0% or less (including 0%), Al: 0.01 to 0.1%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), and the balance being Fe and other unavoidable impurities.

6. The gas-shielded arc weld metal according to claim 5, wherein the weld base metal further contains, by weight percent, one or more of Ti: 0.20% or less, Nb: 0.10% or less, and Cu: 0.10% or less.

7. The gas-shielded arc weld metal according to claim 1, wherein the weld base metal has a thickness of 0.8 to 4.0 mm.

8. An automobile part comprising the gas-shielded arc welded metal according to claim 1.

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