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 car bodies and parts has emerged as a major issue due to fuel efficiency regulations in response to environmental protection issues such as global warming. In response to this trend, the application of high-strength steel materials to reduce weight is also required for chassis parts, which are important for the driving performance of automobiles.

[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 they are subjected to repeated fatigue loads.

[0004] However, in the case of arc welding, which is mainly used to ensure strength when assembling chassis parts for automobiles, lap joint welding between parts is performed by deposition of a welding wire, so it is inevitable to give the joint a geometric shape, which acts as a concentration point of repeated fatigue stress (notch effect) and becomes a fracture starting point, resulting in a decrease in the durability of the parts, and therefore has a limit where the benefits of using high-strength steel are lost.

[0005] Therefore, in order to improve the fatigue properties of a weld, it is most important to reduce the angle (toe angle) of the bead tip, which is the main stress concentration part, and in addition, it can be said that controlling the material and stress of the toe part is an important factor. As described above, the demand for rust prevention to prevent through-hole corrosion has increased due to the thinning of materials in accordance with the trend toward high strength and light weight of parts, and the use of plated steel has been increasing. However, the weld metal of an arc welded part in particular does not have a plated layer, and there is a limit to the deterioration of corrosion resistance after painting on the base material. This causes a problem of early corrosion of the welded parts of chassis parts made of plated steel sheets in the severe corrosive environment during vehicle operation, leading to a deterioration of fatigue properties. Meanwhile, during gas-shielded arc welding of plated steel, a large number of pore defects in the form of pits and blowholes are generated in the weld bead due to the generation of vapor such as zinc, which may reduce the strength of the welded part, resulting in a problem of reduced welding productivity. In addition, even in the case of general unplated steel materials, slag generated in the weld bead during gas shielded arc welding causes poor painting and reduces corrosion resistance after painting, which causes 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 welds while ensuring economic efficiency has become an important issue. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-118274 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims 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 weld metal means a metal obtained by melting and mixing the base material to be welded and the welding wire.

[0009] The object of the present invention is not limited to the above. Further object of the present invention is described in the entire contents of the specification, and a person having ordinary skill 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 contents of the specification of the present invention. [Means for solving the problem]

[0010] The present invention relates to 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 formula 1 and relational formula 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] indicate the weight percent content 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 above weld metal can satisfy the requirement that the length percentage occupied by porosity defects is 10% or less (including 0%) relative to the entire length of the weld metal.

[0017] The welding base metal 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: 0.04-0.18%, Si: 2.0% or less (including 0%), Mn: 0.5-3.0%, Cr: 2.0% or less (including 0%), Mo: 2.0% or less (including 0%), Al: 0.01-0.1%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), with the balance being Fe and other unavoidable impurities.

[0019] The weld 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 a method for producing a method for manufacturing a semiconductor device comprising the steps of: The present invention relates to an automobile part having the above weld metal. Effect of the Invention

[0022] According to the present invention described above, 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 the era of popularization of electric vehicles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described. When welding galvanized steel sheets, there is a problem that porosity defects occur in the welded portion due to the generation of zinc vapor. In this case, if the content of Si, which is a deoxidizing agent in the components of the weld metal, is reduced to a certain level, the viscosity of the molten metal is reduced, making it easier to discharge zinc vapor, and O generated by the dissociation of CO2 in the protective gas at high temperatures during welding reacts more actively with Zn in the coating layer to form Zn-based oxides, effectively lowering the zinc vapor pressure, stabilizing the arc, and suppressing the generation of porosity defects. However, the inventors have confirmed through their research results that when Ti or Al, which is a steel deoxidizing agent in the components of the weld metal, is contained in a certain level or more, it hinders the oxidation reaction of Zn, causing arc instability, an increase in porosity defects, and a decrease in weld strength even with a low Si content. In particular, it has been confirmed that when the Ti+Al value is 0.07% or more, the increase in porosity defects is obvious, and it is not possible to ensure 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-welded 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% The C is a main element that can lower the temperature at which the weld metal starts to transform into acicular ferrite, bainite, and martensite through diffusionless transformation caused by continuous cooling in the high-temperature austenite phase during solidification. If the C content is less than 0.001%, the hardening ability is reduced, making it difficult to ensure sufficient strength of the weld metal. In addition, due to the above-mentioned principle, the low-temperature transformation start temperature is not sufficiently low, and the effect of offsetting the tensile residual stress of the weld due to the low-temperature transformation expansion effect during the cooling process is significantly reduced, and a high-hardness grain boundary structure with a large difference in azimuth angle between grains is not formed. On the other hand, if the C content exceeds 0.30%, not only the viscosity of the molten metal is reduced, resulting in poor bead shape, but also the weld metal is excessively hardened, resulting in reduced toughness.

[0029] Si: 0.25% or less (excluding 0%) The above-mentioned Si is an element (deoxidizing element) that promotes the deoxidation of molten metal during arc welding, which is advantageous in suppressing the occurrence of blowholes, and is an element that increases the low temperature transformation start temperature. However, when welding galvanized steel sheets, the Si content in the weld metal components can be reduced to promote the oxidation of Zn and reduce the zinc vapor pressure to prevent the occurrence of porosity defects in the weld. On the other hand, if the Si content exceeds 0.25%, there may be disadvantages in that a large amount of non-conductive slag is generated, causing poor painting of the weld, and the surface activation of the weld is insufficient due to excessive deoxidation, resulting in a decrease in 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: 0.5-3.0% The Mn is a deoxidizing element, which is advantageous in suppressing the occurrence of blowholes by promoting the deoxidation of molten metal during arc welding, and, like C, is an element that reduces the low-temperature transformation start temperature. If the Mn content is less than 0.5%, there may be a drawback that the deoxidizing effect is insufficient and blowholes are easily generated. However, if the Mn content of the weld metal components is excessively high during welding of galvanized steel sheets, it may hinder the oxidation of Zn and increase the zinc vapor pressure, which may promote arc instability and the occurrence of porosity defects in the welded parts. On the other hand, if the Mn content exceeds 3.0%, there may be a drawback that the viscosity of the molten metal becomes excessively high, and therefore, when the welding speed is high, the molten metal cannot properly flow into the welded part, and a humping bead is formed, which may cause a bead shape defect. More preferably, the Mn content is limited to 2.50% or less.

[0031] Cr: 0.50% or less (excluding 0%) The Cr is a ferrite stabilizing element, which is advantageous in lowering the low-temperature transformation start temperature and improving the strength by ensuring the hardening ability of the weld metal. If the Cr content exceeds 0.50%, there may be a drawback that the brittleness of the weld metal increases unnecessarily in some cases, 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%) The Mo element is a ferrite stabilizing element and is an element advantageous in securing hardening ability to improve the strength of the weld metal. If the Mo content exceeds 0.60%, there may be a drawback that the toughness of the weld metal decreases in some cases.

[0033] P: 0.030% or less (excluding 0%) The P is an element that is generally mixed into steel as an inevitable impurity, and is also contained as a normal impurity in solid wire for arc welding. If the P content exceeds 0.030%, there may be a drawback in that high-temperature cracks in the weld metal become prominent.

[0034] S: 0.030% or less (excluding 0%) The above S is an element that is generally mixed in steel as an unavoidable impurity, and is also a common impurity in solid wires for arc welding. If the S content exceeds 0.030%, the toughness of the weld metal may deteriorate in some cases, and the surface tension of the molten metal during welding may be insufficient, causing the molten part to flow down excessively 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%) The above-mentioned Al is an element that can improve the strength of the weld metal by promoting the deoxidation of the molten metal during arc welding even in a small amount as a deoxidizing element. In order to ensure the above-mentioned effect, 0% is excluded as the lower limit of the Al content. However, the deoxidizing effect of Al may hinder the oxidation reaction of Zn during welding of galvanized steel sheets, and promote the occurrence of porosity defects in the weld due to an increase in zinc vapor pressure and induction of arc instability. If the above-mentioned Al content is 0.07% or more, there may be a disadvantage that the generation of Al-based oxides increases, and in some cases the strength and toughness of the weld metal decreases, and the weld becomes sensitive to electrodeposition coating defects due to non-conductive oxides.

[0036] Ti: Less than 0.07% (excluding 0%) The Ti element acts as a deoxidizing element and can improve the strength of the weld metal even in trace amounts by promoting the deoxidation of the molten metal during arc welding. It also facilitates the development of acicular ferrite, which can improve the toughness of the weld. In order to ensure the above effects, the lower limit of the Ti content is set to 0%. However, the deoxidizing effect of Ti may hinder the oxidation reaction of Zn during welding of galvanized steel sheets, which may promote the occurrence of porosity defects in the weld due to an increase in zinc vapor pressure and an instability of the arc. If the Ti content is 0.07% or more, the generation of Ti-based oxides increases, which may result in a decrease in the 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. In order to ensure the above-mentioned effects, the lower limit of the Ni content is excluded from 0%. However, if the Ni content exceeds 0.40%, there may be a drawback in that the material becomes sensitive to cracks, 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 the strength, the Cu content in the weld metal may be 0.01% or more.

[0039] The weld metal of the present invention may selectively further 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 The above-mentioned Nb is an element that can enhance the hardening ability and make the microstructure dense to improve 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. In order to ensure the above-mentioned effects, the lower limit of the Nb content is excluded to 0%. However, if the above-mentioned Nb content exceeds 0.10%, there may be a drawback that a low melting point compound is formed at the grain boundary, making high-temperature cracks more likely to occur.

[0041] V:0.10% or less The V element is capable of increasing the hardening ability and making the microstructure dense to improve the strength and toughness of the weld metal. It is also a precipitation strengthening element that can form carbonitrides to improve the strength of the weld metal. However, if the V content exceeds 0.10%, there may be a drawback that the toughness of the weld metal may decrease in some cases due to the excessive strength caused by the excess of precipitates. Therefore, the V content is set to 0.10% or less.

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

[0043] The weld metal of the present invention may further selectively contain B: 0.01% or less. B: 0.01% or less The B element is capable of increasing the hardening ability and improving the strength of the weld metal. However, if the B content exceeds 0.01%, there may be a drawback that the toughness of the weld metal may decrease due to the excessive hardening ability. Therefore, the B content is set to 0.01% or less.

[0044] The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, there is a possibility that unintended impurities are inevitably mixed in from the raw materials or the surrounding environment, and this cannot be excluded. Since the above impurities are known to any ordinary technician, the present invention does not specifically mention all the contents thereof.

[0045] Meanwhile, the weld metal of the present invention contains Mn and Si 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 is insufficient, and the problem of insufficient strength due to reduced porosity resistance may occur. If it exceeds 8.5, not only the viscosity of the weld metal increases, but also the zinc vapor pressure during welding increases due to the above-mentioned principle, which may cause arc instability and reduced porosity resistance, resulting in insufficient strength. As a result, the problem of deterioration of electrodeposition paintability due to an increase in Si-based non-conductive oxides may occur. 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 Formula 1, [Si] and [Mn] indicate the weight percent content of each element in parentheses in the weld metal.)

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

[0048] When welding galvanized steel sheets, zinc vapor is generated and porosity defects occur in the welded part. If the content of Si, a deoxidizing agent in the weld metal, is reduced to a certain level, the viscosity of the molten metal is reduced, making it easier to discharge zinc vapor, and the Zn in the coating layer reacts more actively with O (oxygen) generated by dissociation of CO2 in the protective gas at high temperatures during welding to form Zn-based oxides, effectively lowering the zinc vapor pressure and stabilizing the arc and suppressing the occurrence of porosity defects. However, when Ti or Al, a steel deoxidizing agent in the weld metal, is contained in a certain level or higher, it hinders the oxidation reaction of Zn, causing arc instability, an increase in porosity defects, and a decrease in weld strength even with a low Si content. In particular, when the Ti+Al value is 0.07% or more, the increase in porosity defects is obvious, and it is not possible to ensure a weld metal with excellent weld strength and porosity resistance.

[0049] More specifically, the affinity of metals with oxygen, i.e., the thermodynamic stability when each metal element combines with oxygen at a certain temperature, can be easily understood through the well-known Ellingham diagram, and the Gibbs free energy decreases in the order of Al>Ti>Si>Zn, so that it is easier to combine with oxygen, and the stability of the oxide increases. Meanwhile, the temperatures at which each of the above metal elements starts to combine with oxygen, i.e., the boiling points, are Al2O3: 2,977°C, TiO2: 2,972°C, SiO2: 2,230°C, and ZnO: 2,360°C, and Al and Ti are thermodynamically stable at high temperatures compared to Si and Zn, and can easily combine with oxygen first. Therefore, the weld metal melted at about 3,000 to 5,000°C, which is the central temperature of the arc during welding, gradually cools and solidifies, lowering the Si content, and before Zn can more easily combine with O, the increase in the Al and Ti content causes oxidation to occur before Zn, which may increase the sensitivity of the weld to porosity defects caused by the increase in Zn vapor pressure.

[0050] [Equation 2] [Ti]+[Al]<0.07 (In the above formula 2, [Ti] and [Al] indicate the weight percent content of each element in parentheses in the weld metal.)

[0051] In addition, in the weld metal of the present invention, the length ratio of porosity defects to the entire length of the weld metal can be 10% or less (including 0%). Therefore, the present invention can effectively provide parts such as automobile parts 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 weight of 1 to 120 g / m 2 It is preferable that:

[0053] In addition, 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: 0.04-0.18%, Si: 2.0% or less (including 0%), Mn: 0.5-3.0%, Cr: 2.0% or less (including 0%), Mo: 2.0% or less (including 0%), Al: 0.01-0.1%, 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 weld base metal may selectively 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 metal may have a thickness of 0.8 to 4.0 mm.

[0055] Further, in the present invention, the specific composition of the welding wire forming the weld metal is not limited, and as an example, a welding solid wire 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: 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, can be used. 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] On the other hand, in the present invention, the type of shielding gas used in welding the above-mentioned welding base metal is not particularly limited, and 100% CO2 gas, Ar+20CO2 gas, Ar+10%CO2 gas, Ar+5%CO2 gas, Ar+2%O2 gas, etc. can be used as the shielding gas, but particularly when Ar+5-20%CO2 is used as the shielding gas, the present invention can exhibit remarkable effects. That is, in the present invention, in order to ensure the tensile strength of the welded part without causing fracture of the weld metal or fusion line, it is preferable to use a mixture of Ar and 5-20% 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 illustrating and embodying the present invention, and are not intended to limit the scope of the present invention, since 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. 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 2Three types of base metals 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, two of each type. A large number of solid wires for gas shielded arc welding with various alloy compositions were also prepared.

[0059] Next, the above-mentioned hot-dip galvanized steel sheets were lap-welded using the above-mentioned solid welding wires. At this time, the welding method used was Pulse DC (protective gas: Ar+10-20% CO2), the shielding gas flow rate was 20 l / min, the welding torch angle was 45° with respect to the vertical direction of the base material, the wire protrusion length was 15 mm, and the welding current / voltage / speed conditions were 200 A-20 V-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 weld base material, welding was started at a position 10 mm from the starting point, and after welding had progressed for a length of 180 mm, welding was ended at a position 10 mm from the ending point on the opposite side to the welding start position.

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

[0062] In addition, 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 is irradiated with X-rays to measure the length of each pore distributed in the weld, and the porosity of the weld is calculated by adding up all the lengths and dividing the total length of the weld. At this time, 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] A tensile test was also conducted on the welds formed above, and the location of the fracture was visually observed. If the fracture occurred in the weld base material 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 at this time is as follows. Tensile test pieces 30 mm wide and 250 mm long were machined from each of the welded test pieces produced above, and a uniaxial tensile test was conducted at a speed of 10 mm / min, after which the fracture location was investigated. The results of the tensile test were evaluated for reproducibility by evaluating three welded test pieces.

[0064] [Table 1] *The residual components in Table 1 are Fe and unavoidable impurities.

[0065] [Table 2] TIFF2025514822000003.tif170170*The residual components in Table 2 are Fe and unavoidable impurities.

[0066] [Table 3] TIFF2025514822000005.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 Formulas 1 and 2, the length fraction of porosity relative to the total length of the weld metal is all 10% or less (including 0%), and further, it can be seen that the fracture locations of the welds are 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 in which 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 of the weld also occurs in the weld metal.

[0069] In addition, Comparative Examples 2 to 3, 9 to 10, 12 to 13, and 19 to 20 did not satisfy Relation 2, and therefore showed high porosity in the weld with any of the protective gases, and showed high porosity in the weld with all of the protective gases, and as a result, the fracture position of the weld also occurred in the weld metal.

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

Claims

1. A weld metal obtained by gas-shielded arc welding of a weld base material, 1. A gas shielded arc weld metal comprising, 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 satisfying the following relational expressions 1 and 2. [Relationship 1] 3.5≦[Si]×100 / [Mn]≦8.5 [Relationship 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.)

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

3. The gas shielded arc welded 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 welded metal according to claim 1, wherein the length fraction of porosity relative to the entire length of the weld metal is 10% or less (including 0%).

6. 2. The gas shielded arc welding metal according to claim 1, wherein the weld base metal is a hot-dip galvanized steel sheet having a hot-dip galvanized layer formed on a surface thereof.

7. 2. The gas shielded arc welding metal according to claim 1, characterized in that the weld base metal contains, 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.

8. The gas shielded arc welding metal according to claim 7, 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.

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

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

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