Automotive parts having welding components, gas shielded arc welding wires, and welding components.

Abstract

This invention provides welding components and gas shielded arc welding wires that effectively ensure the economic efficiency of welding components and welding materials, which are essential requirements in parts manufacturing, while ensuring excellent strength and toughness of weld metal for Gigasteel, which is mainly used in the automotive industry. [Solution] The welded member includes a base material and a weld, and the weld contains, by weight %, C: 0.05~0.16%, Si: 0.001~1.0%, Mn: 1.0~2.5%, Cr: 0.1~5.0%, Mo: 0.1~1.5%, P: 0.030% or less, S: 0.030% or less, Al: 0.20% or less, Ni: 0.40% or less, Ti: 0.10% or less, Nb: 0.10% or less, with the remainder being Fe and other unavoidable impurities. [Relationship 1] 0.15 ≤ ([Ti] / [Nb]) / t ≤ 0.65 The weld satisfies the following conditions: ([Ti] and [Nb] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base material (mm).)

Description

Technical Field

[0001] The present invention relates to a welded member and a wire for gas shielded arc welding, and more particularly to a welded member and a wire for gas shielded arc welding that are excellent in strength and toughness.

Background Art

[0002] The development of next-generation lightweight chassis parts for automobiles using gigasteel with a tensile strength of 980 MPa or more is underway. As the development of such ultra-high-strength lightweight chassis parts for automobiles progresses, the development of welding technology capable of improving the characteristics of the welded part while ensuring economic efficiency has become an important issue.

[0003] Existing ultra-high-strength welding materials for automotive gigasteel contain a large amount of expensive Ni, resulting in poor economic efficiency, inevitable increase in manufacturing costs, and limitations in that the microstructure and mechanical properties of gigasteel thin plate welded metal cannot be optimized.

[0004] In particular, in the case of thin steel plates with a thickness of 2.0 mm or less, there is a lack of accurate and detailed understanding of the phase transformation and microstructure development mechanism of the welded metal formed by melting and dilution of the welding material and the base material.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a welded member and a wire for gas shielded arc welding.

[0007] More specifically, the goal is to ensure the excellent strength and toughness of weld metal for Gigasteel, which is primarily used in the automotive industry, while effectively ensuring the economic efficiency of welding components and materials, which are essential during parts manufacturing.

[0008] The problems that the present invention will not address are not limited to those described above. Further problems that the present invention will address are described throughout the specification, and any person with ordinary skill in the art to which the present invention belongs will have no difficulty understanding these further problems from the contents of the specification. [Means for solving the problem]

[0009] The present invention Including the base material and the welded part, The above-mentioned welded portion contains, by weight percent, C: 0.05~0.16%, Si: 0.001~1.0%, Mn: 1.0~2.5%, Cr: 0.1~5.0%, Mo: 0.1~1.5%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Al: 0.20% or less (excluding 0%), Ni: 0.40% or less (excluding 0%), Ti: 0.10% or less (excluding 0%), and Nb: 0.10% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities, and is characterized by satisfying the following relational formula 1.

[0010] [Relationship 1] 0.15 ≤ ([Ti] / [Nb]) / t ≤ 0.65 (In the above relationship, [Ti] and [Nb] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base metal (mm).)

[0011] The present invention The present invention provides a gas shielded arc welding wire characterized by containing, by weight percent, C: 0.05~0.16%, Si: 0.001~0.2%, Mn: 1.0~2.5%, Cr: 0.4~6.0%, Mo: 0.10~0.65%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Al: 0.20% or less (excluding 0%), Ni: 0.40% or less (excluding 0%), Ti: 0.20% or less (excluding 0%), and Nb: 0.10% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities, and satisfying the following relational formula 3.

[0012] [Relationship 3] 490≦732-202×[C]+216×[Si]-85×[Mn]-37×[Ni]-47×[Cr]-39×[Mo]≦520 (In the above relational equation 3, [C], [Si], [Mn], [Ni], [Cr], and [Mo] represent the weight percentage content of each element in parentheses in the welding wire.)

[0013] Furthermore, the present invention relates to an automobile part having the above-mentioned welded member. [Effects of the Invention]

[0014] The present invention aims to provide welding components and wires for gas shielded arc welding.

[0015] This invention effectively ensures the economic efficiency of welding components and materials, which are essential during parts manufacturing, while maintaining excellent strength and toughness of weld metal for Gigasteel, which is mainly used in the automotive industry.

[0016] The diverse and beneficial advantages and effects of the present invention are not limited to those described above and can be more easily understood in the process of describing specific embodiments of the present invention. [Brief explanation of the drawing]

[0017] [Figure 1]IQ (Image Quality) and IPF (Inverse Pole Figure) photographs obtained by observing Invention Example 1 of the present invention with EBSD. [Figure 2] IQ (Image Quality) and IPF (Inverse Pole Figure) photographs obtained by observing Comparative Example 2 of the present invention with EBSD.

Mode for Carrying Out the Invention

[0018] Hereinafter, examples of the present invention will be described. Needless to say, the following examples can be variously modified within the scope not departing from the scope of the present invention by those having ordinary knowledge in the technical field to which the present invention pertains. The following examples are for understanding the present invention, and the scope of rights of the present invention should not be defined limited to the following examples, but should be defined by not only the scope of claims described later but also equivalents thereof.

[0019] On the other hand, the terms used in this specification are for explaining the present invention and are not intended to limit the present invention. Further, the singular forms used in this specification also include plural forms unless the relevant definition clearly indicates the opposite meaning.

[0020] The meaning of "including" used in this specification does not specify a configuration and does not exclude the existence or addition of other configurations.

[0021] Unless otherwise defined, all terms including technical terms and scientific terms used in this specification have the same meaning as generally understood by those having ordinary knowledge in the technical field to which the present invention pertains. Terms defined in a dictionary are interpreted as having a meaning consistent with the related technical literature and the currently disclosed content.

[0022] The welded member of the present invention will be described. The welded member of the present invention includes a base material and a welded portion. At this time, first, the alloy composition of the above welded portion will be described. The content of the alloy composition described below is "wt%".

[0023] C:0.05~0.16% The above-mentioned carbon (C) is a key element that, during the solidification process of the weld metal, can lower the temperature at which acicular ferrite, bainite, and martensitic transformations via diffusionless transformation begin, due to continuous cooling in the high-temperature austenite phase. If the C content is less than 0.05%, the hardening ability decreases, making it difficult to ensure sufficient strength of the weld metal. Furthermore, due to the principle described above, the low-temperature transformation initiation temperature does not become sufficiently low, significantly reducing the effect of canceling out tensile residual stress in the weld due to the low-temperature transformation expansion effect during the cooling process. This can result in the formation of high-angle grain boundary structures with large differences in orientation angles between grains. On the other hand, if the C content exceeds 0.16%, the viscosity of the molten metal decreases, resulting in poor bead shape. In addition, the weld metal hardens excessively, reducing toughness. The low-temperature transformation initiation temperature becomes excessively low, making it impossible to secure compressive stress through low-temperature transformation at temperatures near room temperature where the tensile residual stress in the weld reaches its maximum. This can lead to an increase in the retained austenite phase, which is the untransformed phase, in the final weld metal structure. On the other hand, although not particularly limited, from the viewpoint of further improving the effects described above, the lower limit of the C content can be 0.075%, or the upper limit of the C content can be 0.13%.

[0024] Si: 0.001~1.0% The above-mentioned Si is an element that promotes deoxidation of molten metal during arc welding (a deoxidizing element), which is advantageous in suppressing the occurrence of blowholes and is an element that increases the low-temperature transformation initiation temperature. If the Si content is less than 0.001%, there is a disadvantage that the deoxidation effect is insufficient and blowholes are more likely to occur, and the low-temperature transformation initiation temperature may become excessively low, potentially reducing the effect of offsetting the tensile residual stress in the weld. On the other hand, if the Si content exceeds 1.0%, a large amount of non-conductive slag is generated, causing poor coating of the weld, and excessive deoxidation may lead to insufficient surface activation of the weld, potentially reducing the penetration of the molten metal. Furthermore, the low-temperature transformation initiation temperature may rise, potentially resulting in insufficient compressive stress effect due to low-temperature transformation. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Si content can be 0.22%, or the upper limit of the Si content can be 0.80%.

[0025] Mn: 1.0~2.5% The above-mentioned Mn is a deoxidizing element that promotes the deoxidation of molten metal during arc welding, which is advantageous in suppressing the occurrence of blowholes, and it is an element that reduces the low-temperature transformation initiation temperature, similar to C. If the above-mentioned Mn content is less than 1.0%, the deoxidizing effect is insufficient, blowholes are easily formed, the low-temperature transformation initiation temperature rises, and a disadvantage may be that a sufficient compressive stress effect due to low-temperature transformation cannot be obtained. On the other hand, if it exceeds 2.5%, the viscosity of the molten metal becomes excessively high, and if the welding speed is high, the molten metal cannot flow properly into the weld area, and a humping bead is formed, making it easy for defects in bead shape to occur, and a disadvantage may be that the low-temperature transformation initiation temperature becomes too low, reducing the effect of offsetting the tensile residual stress in the weld area. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Mn content can be 1.4%, or the upper limit of the above-mentioned Mn content can be 2.4%.

[0026] Cr:0.1~5.0% The above-mentioned Cr is a ferrite-stabilizing element that lowers the low-temperature transformation initiation temperature and is advantageous for improving strength by ensuring the hardening ability of the weld metal. If the Cr content is less than 0.1%, the proportion of high-angle grain boundaries in the weld metal decreases, making it difficult to obtain a sufficient compressive stress effect due to low-temperature transformation, and potentially making it difficult to ensure sufficient strength of the weld metal. On the other hand, if the Cr content exceeds 5.0%, in some cases the brittleness of the weld metal may increase unnecessarily, making it difficult to ensure sufficient toughness, and the low-temperature transformation initiation temperature may become too low, making it difficult to ensure sufficient compressive stress in the weld. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Cr content can be 0.4%, or the upper limit of the Cr content can be 4.9%.

[0027] Mo: 0.1~1.5% The above-mentioned Mo is a ferrite-stabilizing element that lowers the low-temperature transformation initiation temperature and is advantageous for improving strength by ensuring the hardening ability of the weld metal. If the Mo content is less than 0.1%, the proportion of high-angle grain boundaries in the weld metal decreases, making it difficult to obtain a sufficient compressive stress effect due to low-temperature transformation, and potentially making it difficult to ensure sufficient strength of the weld metal. On the other hand, if the Mo content exceeds 1.5%, the toughness of the weld metal may decrease in some cases, and the low-temperature transformation initiation temperature may become too low, making it difficult to ensure sufficient compressive stress in the weld. While not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Mo content can be 0.23%, or the upper limit of the Mo content can be 1.2% or 0.38%.

[0028] P: 0.030% or less (excluding 0%) The above-mentioned P is an element that is generally present as an unavoidable impurity, and its lower limit is excluding 0%. However, if the P content exceeds 0.030%, there is a drawback in that high-temperature cracking of the weld metal may become significant. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the P content can be 0.001%, or the upper limit of the P content can be 0.013%.

[0029] S: 0.030% or less (excluding 0%) The above-mentioned sulfur (S) is an element that is generally present as an unavoidable impurity, and its lower limit is 0%. However, if the S content exceeds 0.030%, in some cases the toughness of the weld metal may deteriorate, resulting in insufficient surface tension of the molten metal during welding. This can lead to the disadvantage of excessive flow of the molten material due to gravity during high-speed downward welding (vertical welding, welding from top to bottom), resulting in a poor weld bead shape. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the S content can be 0.001%, or the upper limit of the S content can be 0.010%.

[0030] Al: 0.20% or less (excluding 0%) The above-mentioned Al is a deoxidizing element, and even in trace amounts, it can improve the strength of the weld metal by promoting the deoxidation of the molten metal during arc welding. To ensure the above-mentioned effect, 0% is excluded as the lower limit of the Al content. However, if the above-mentioned Al content exceeds 0.20%, the formation of Al-based oxides increases, which may have the disadvantage of potentially reducing the strength and toughness of the weld metal and making the electrodeposition coating of the weld more susceptible to defects due to non-conductive oxides. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effect, the lower limit of the above-mentioned Al content can be 0.010%, or the upper limit of the above-mentioned Al content can be 0.055%.

[0031] Ni: 0.40% or less (excluding 0%) The above-mentioned Ni is an element that can improve the strength and toughness of the weld metal. In order to ensure the above-mentioned effects, 0% is excluded as the lower limit of the Ni content. However, if the above-mentioned Ni content exceeds 0.40%, there is a disadvantage that it may become sensitive to cracking, so the Ni content should be 0.40% or less. The above-mentioned Ni content is more preferably 0.30% or less, even more preferably 0.20% or less, and most preferably 0.10% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Ni content can be 0.008%, or the upper limit of the above-mentioned Ni content can be 0.10% or 0.053%.

[0032] Ti: 0.10% or less (excluding 0%) The above-mentioned Ti is a deoxidizing element that, even in trace amounts, can improve the strength of the weld metal by promoting the deoxidation of the molten metal during arc welding. It also facilitates the development of needle-shaped ferrite, which can improve the toughness of the weld. To ensure the above-mentioned effects, 0% is excluded as the lower limit of the Ti content. However, if the above-mentioned Ti content exceeds 0.10%, the formation of Ti-based oxides increases, which may have the disadvantage of potentially reducing the strength and toughness of the weld metal. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Ti content can be 0.008%, or the upper limit of the above-mentioned Ti content can be 0.058%.

[0033] Nb: 0.10% or less (excluding 0%) The above-mentioned Nb is an element that can enhance hardening ability, densify the microstructure, and 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, 0% is excluded as the lower limit of Nb content. However, if the above-mentioned Nb content exceeds 0.10%, there is a disadvantage that low-melting-point compounds will form at the grain boundaries, making hot cracking more likely. Therefore, the Nb content should be 0.10% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Nb content can be 0.026%, or the upper limit of the above-mentioned Nb content can be 0.050%.

[0034] While not particularly limited, the present invention may further selectively include one or more welded members selected from the group consisting of V: ​​0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%), in weight percent.

[0035] V: 0.20% or less (including 0%) The element V mentioned above is an element that can enhance hardening ability and improve the strength and toughness of the weld metal by densifying the microstructure. It is also a precipitation strengthening element that can improve the strength of the weld metal by generating carbonitrides. However, if the V content exceeds 0.20%, there is a drawback that the toughness of the weld metal may decrease in some cases due to excessive strength caused by excess precipitates. Therefore, the V content should be 0.20% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the V content can be 0.001%, or the upper limit of the V content can be 0.018% or 0.009%.

[0036] Zr: 0.10% or less (including 0%) The above-mentioned Zr is an element that promotes deoxidation of molten metal during arc welding (a deoxidizing element), and is advantageous in suppressing the occurrence of blowholes. However, if the Zr content exceeds 0.10%, there is a drawback that the electrodeposition coating properties of the welded area will decrease. Therefore, the Zr content should be 0.10% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Zr content can be 0.001%, or the upper limit of the Zn content can be 0.09%.

[0037] B: 0.01% or less (including 0%) Element B, as described above, is an element that can enhance hardening ability and improve the strength of the weld metal. However, if the content of B exceeds 0.01%, excessive hardening ability may lead to a decrease in the toughness of the weld metal in some cases. Therefore, the content of B should be 0.01% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the effects described above, the lower limit of the B content can be 0.001%, or the upper limit of the B content can be 0.009%.

[0038] Alternatively, although not particularly limited, the above-mentioned welded member may further selectively include one or more types selected from the group consisting of V: ​​0.20% or less (excluding 0%), Zr: 0.10% or less (excluding 0%), and B: 0.01% or less (excluding 0%), in weight percent.

[0039] Furthermore, although not particularly limited, according to one embodiment of the present invention, the welded member may selectively further contain Cu: 0.50% or less (including 0%) by weight.

[0040] Cu: 0.50% or less (including 0%) The above-mentioned Cu is an effective element for improving the strength of the weld metal. However, if the Cu content exceeds 0.50%, there is a drawback that the weld metal may become 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 obtain a sufficient strength-improving effect, the weld metal can contain 0.01% or more of the above-mentioned Cu.

[0041] Alternatively, although not particularly limited, according to the present invention, the welded member may further selectively contain Cu: 0.50% or less by weight (excluding 0%).

[0042] The remaining component of this invention is iron (Fe). However, in the normal manufacturing process, unintended impurities may inevitably be mixed in from the raw materials or the surrounding environment, and therefore cannot be eliminated. Since the above-mentioned impurities are recognizable to any ordinary technician, this invention does not specifically mention all of them.

[0043] On the other hand, according to the present invention, the above-mentioned welded joint can satisfy the following relational expression 1. By satisfying the following relational expression 1, the strength and toughness of the weld metal are simultaneously improved. This is because, by more precisely controlling the microstructure of the weld metal, the effect of the alloying elements differs depending on the dilution ratio between the base material of the steel plate and the welding wire, and therefore has a correlation with the thickness of the base material.

[0044] [Relationship 1] 0.15 ≤ ([Ti] / [Nb]) / t ≤ 0.65 (In the above relationship, [Ti] and [Nb] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base metal (mm).)

[0045] While not particularly limited, the above-mentioned weld can satisfy the following relational equation 2. By satisfying the following relational equation 2, the strength and toughness of the weld metal described above are further improved, and the formation of non-conductive oxides that reduce the electrodeposition coating properties of the weld is suppressed.

[0046] [Relationship 2] 3.68≦([Ti] / [Nb])×t / ([Si] / [Mn])≦17.0 (In the above relational equation, [Ti], [Nb], [Si], and [Mn] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base material (mm).)

[0047] While not particularly limiting, from the perspective of further improving the effects described above, the lower limit of the value of ([Ti] / [Nb])×t / ([Si] / [Mn]) in relational equation 2 above can be 4.50 (i.e., 4.50 or greater).

[0048] Furthermore, although not particularly limited, the welded portion of the welded member may have a microstructure that includes one or more elements selected from the group consisting of bainite, acicular ferrite, granular ferrite, martensite, and retained austenite. By utilizing the lower bainite transformation, which includes acicular ferrite, that occurs within the prior austenite grains during the cooling process after welding, the microstructure of the weld metal can be made to have a dense structure in which acicular ferrite and bainite are interlocked in a complex manner, that is, a structure in which the azimuthal angles between grains have a high inclination angle. This lowers the low-temperature transformation initiation temperature, and the compressive residual stress of the weld generated by the low-temperature transformation expansion can offset the shrinkage tensile stress generated during the solidification of the molten pool, or it can add further compressive stress.

[0049] While not particularly limited, the microstructure of the welded joint described above can have an average effective grain size of 10 μm or less (excluding 0 μm). By finely controlling the average effective grain size in this way, it is possible to ensure relatively good strength and toughness of the weld metal. If the average effective grain size exceeds 10 μm, as mentioned above, it may become difficult to simultaneously ensure sufficient strength and toughness of the weld metal.

[0050] On the other hand, the present invention does not particularly limit the alloy composition of the base material. However, as an example, the base material may contain, by weight %, 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: 0.01~0.10%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities. Furthermore, the base material may selectively further contain one or more of Ti: 0.20% or less (including 0%), Nb: 0.10% or less (including 0%), and Cu: 0.10% or less (including 0%). Although not particularly limited, the base material may have a thickness of 0.8~4.0 mm.

[0051] Furthermore, although not particularly limited, the welded portion of the above-mentioned welded member may contain 0.5 to 2.0% retained austenite by area percentage. By satisfying this condition, it is possible to simultaneously improve the strength and toughness of the weld metal. This is due to the improvement in ductility caused by the transformation-induced plasticity of retained austenite during deformation, and it can also exhibit excellent resistance to defect formation when stress is applied.

[0052] Furthermore, although not particularly limited, the retained austenite contained in the welded portion of the above-mentioned welded member may have an average ratio (Ll / Ls) of the long axis length (Ll) to the short axis length (Ls) of 8.0 to 12.0. Satisfying this condition can provide the effect of further improving the strength and toughness of the weld metal. This is because the retained austenite that has developed in the form of elongated films at the grain boundaries of the dense microstructure exhibits the transformation-induced plasticity effect described above, and can more effectively improve the resistance to cracking in the weld. In this case, the method for measuring the long axis and short axis lengths can be measured using conventional methods in the art, and therefore is not defined separately in this specification.

[0053] Furthermore, the present invention does not particularly limit the method for manufacturing the welded member. However, one advantageous method for manufacturing the welded member of the present invention is described below. For example, when manufacturing a welded member by gas-shielded arc welding using a welding wire after preparing two or more base materials, it is preferable that the welding wire satisfies the alloy composition described later, and that the base materials also satisfy the alloy composition described above.

[0054] The gas shielded arc welding wire of the present invention will be described below. First, the reasons for adding each component and the reasons for limiting their content in the wire of the present invention will be explained in detail. It should be noted that the content of each component described later is all based on weight percent unless otherwise specified.

[0055] C:0.05~0.16% The above-mentioned C is advantageous in stabilizing the arc and atomizing molten droplets, and is also advantageous in ensuring hardening ability. If the C content is less than 0.05%, the molten droplets become coarser, the arc becomes unstable, and not only does the amount of spatter increase, but it may also become difficult to ensure sufficient strength of the weld metal. On the other hand, if the C content exceeds 0.16%, the viscosity of the molten metal decreases, resulting in poor bead shape, and not only does it cause excessive hardening of the weld metal, but it may also cause a decrease in toughness. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the C content can be 0.06%, or the upper limit of the C content can be 0.15%.

[0056] Si: 0.001~0.2% The above-mentioned Si is an element that promotes deoxidation of molten metal during arc welding (a deoxidizing element), and is advantageous in suppressing the occurrence of blowholes. If the Si content is less than 0.001%, there is a disadvantage that the deoxidation effect is insufficient and blowholes are more likely to occur. If it exceeds 0.2%, there is a disadvantage that a large amount of non-conductive slag is generated, causing poor coating of the weld, and excessive deoxidation may lead to insufficient surface activation of the weld and a decrease in the penetration of the molten metal. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Si content can be 0.005%, or the upper limit of the Si content can be 0.15% or 0.10%.

[0057] Mn: 1.0~2.5% The above-mentioned Mn is a deoxidizing element that promotes the deoxidation of molten metal during arc welding, which is advantageous in suppressing the occurrence of blowholes. If the Mn content is less than 1.0%, the deoxidizing effect is insufficient, which has the disadvantage of making blowholes more likely to occur. If it exceeds 2.5%, the viscosity of the molten metal becomes excessively high, and if the welding speed is high, the molten metal may not be able to flow properly into the weld area, resulting in the formation of a humping bead, which can lead to defects in bead shape. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Mn content can be 1.6%, or the upper limit of the Mn content can be 1.9%.

[0058] Cr:0.4~6.0% The above-mentioned Cr is a ferrite-stabilizing element and is advantageous in ensuring hardening ability to improve the strength of the weld metal. If the Cr content is less than 0.4%, it is difficult to ensure sufficient strength of the weld metal, and if it exceeds 6.0%, in some cases the brittleness of the weld metal may increase unnecessarily, making it difficult to ensure sufficient toughness. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Cr content can be 0.6%, or the upper limit of the Cr content can be 5.9%.

[0059] Mo: 0.1~0.65% The above-mentioned Mo is a ferrite-stabilizing element and is advantageous in ensuring hardening ability to improve the strength of the weld metal. If the Mo content is less than 0.1%, it is difficult to ensure sufficient strength of the weld metal, and if it exceeds 0.65%, it may have the disadvantage of reducing the toughness of the weld metal in some cases. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Mo content can be 0.3%, or the upper limit of the Mo content can be 0.64%.

[0060] P: 0.030% or less (excluding 0%) The above-mentioned P is an element that is generally present as an unavoidable impurity in steel, and is also an element that is normally contained as an impurity in solid wire for arc welding. If the P content exceeds 0.030%, a disadvantage may be that high-temperature cracking of the weld metal becomes more pronounced.

[0061] S: 0.030% or less (excluding 0%) The above-mentioned sulfur (S) is an element that is generally present as an unavoidable impurity in steel, and is also an element that is normally contained as an impurity in solid wire for arc welding. If the content of S exceeds 0.030%, in some cases the toughness of the weld metal may deteriorate, resulting in insufficient surface tension of the molten metal during welding. This can lead to the disadvantage that, during high-speed downward welding (welding from top to bottom in vertical welding), the molten part may flow excessively due to gravity, resulting in a poor weld bead shape.

[0062] Al: 0.20% or less (excluding 0%) The above-mentioned Al is a deoxidizing element, and even in trace amounts, it can improve the strength of the weld metal by promoting the deoxidation of the molten metal during arc welding. To ensure the above-mentioned effect, 0% is excluded as the lower limit of the Al content. However, if the above-mentioned Al content exceeds 0.20%, the formation of Al-based oxides increases, which may have the disadvantage of potentially reducing the strength and toughness of the weld metal and making the electrodeposition coating of the weld more susceptible to defects due to non-conductive oxides. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effect, the lower limit of the above-mentioned Al content can be 0.001%, or the upper limit of the above-mentioned Al content can be 0.10% or 0.020%.

[0063] Ti: 0.20% or less (excluding 0%) The above-mentioned Ti is a deoxidizing element that, even in trace amounts, can improve the strength of the weld metal by promoting the deoxidation of the molten metal during arc welding. It also facilitates the development of needle-shaped ferrite, which can improve the toughness of the weld. To ensure the effects described above, 0% is excluded as the lower limit of the Ti content. However, if the above-mentioned Ti content exceeds 0.20%, the formation of Ti-based oxides increases, which may have the disadvantage of potentially reducing the strength and toughness of the weld metal. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Ti content can be 0.001%, or the upper limit of the above-mentioned Ti content can be 0.10% or 0.050%.

[0064] Nb: 0.10% or less (excluding 0%) The above-mentioned Nb is an element that can enhance hardening ability, densify the microstructure, and 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, 0% is excluded as the lower limit of Nb content. However, if the above-mentioned Nb content exceeds 0.10%, there is a disadvantage that low-melting-point compounds will form at the grain boundaries, making high-temperature cracking more likely. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the above-mentioned Nb content can be 0.01%, or the upper limit of the above-mentioned Nb content can be 0.06%.

[0065] Ni: 0.40% or less (excluding 0%) The above-mentioned Ni is an element that can improve the strength and toughness of the weld metal. In order to ensure the above-mentioned effects, 0% is excluded as the lower limit of the Ni content. However, since a Ni content exceeding 0.40% may result in the disadvantage of increased susceptibility to cracking, the Ni content should be 0.40% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the above-mentioned Ni content (i.e., the upper limit of the above-mentioned Ni content) can be 0.30% or less, or 0.20% or less, or 0.10% or less. Alternatively, the lower limit of the above-mentioned Ni content can be 0.005% or 0.01%.

[0066] Furthermore, according to the present invention, the welding wire may further selectively contain one or more elements selected from the group consisting of V: ​​0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%), in weight percent.

[0067] V: 0.20% or less (including 0%) The element V mentioned above is an element that can enhance hardening ability and improve the strength and toughness of the weld metal by densifying the microstructure. It is also a precipitation strengthening element that can improve the strength of the weld metal by generating carbonitrides. However, if the V content exceeds 0.20%, there is a drawback that the toughness of the weld metal may decrease in some cases due to excessive strength caused by excess precipitates. Therefore, the V content should be 0.20% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the effects mentioned above, the lower limit of the V content can be 0.001%, or the upper limit of the V content can be 0.15% or 0.10%.

[0068] Zr: 0.10% or less (including 0%) The above-mentioned Zr is an element that promotes deoxidation of molten metal during arc welding (a deoxidizing element), and is advantageous in suppressing the occurrence of blowholes. However, if the Zr content exceeds 0.10%, there is a drawback that the electrodeposition coating properties of the welded area will decrease. Therefore, the Zr content should be 0.10% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Zr content can be 0.001%, or the upper limit of the Zr content can be 0.09%.

[0069] B: 0.01% or less (including 0%) Element B, as described above, is an element that can enhance hardening ability and improve the strength of the weld metal. However, if the content of B exceeds 0.01%, excessive hardening ability may lead to a decrease in the toughness of the weld metal in some cases. Therefore, the content of B should be 0.01% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the effects described above, the lower limit of the B content can be 0.001%, or the upper limit of the B content can be 0.009%.

[0070] Furthermore, according to the present invention, the welding wire may further selectively contain one or more elements selected from the group consisting of V: ​​0.20% or less (excluding 0%), Zr: 0.10% or less (excluding 0%), and B: 0.01% or less (excluding 0%), in weight percent.

[0071] Furthermore, according to the present invention, the welding wire may selectively further contain Cu: 0.50% or less (including 0%) by weight.

[0072] Cu: 0.50% or less (including 0%) The above-mentioned Cu is generally an impurity in the steel that makes up the wire, and is usually present in a concentration of about 0.02%. However, in the case of solid wire for arc welding, its content can be determined mainly by the copper plating applied to the wire surface. The above-mentioned Cu is an element that can stabilize the wire's feeding and conductivity. However, if the Cu content exceeds 0.50%, there is a disadvantage that the weld metal becomes more susceptible to cracking. The above-mentioned Cu content is more preferably 0.45% or less, even more preferably 0.40% or less, and most preferably 0.30% or less.

[0073] Alternatively, according to the present invention, the welding wire may further selectively contain Cu: 0.50% or less by weight (excluding 0%).

[0074] The remaining component of this invention is iron (Fe). However, in the normal manufacturing process, unintended impurities may inevitably be mixed in from the raw materials or the surrounding environment, and therefore cannot be eliminated. Since the above-mentioned impurities are recognizable to any ordinary technician, this invention does not specifically mention all of them.

[0075] On the other hand, according to the present invention, the welding wire can satisfy the following relational equation 3. By satisfying the following relational equation 3, the strength and toughness of the weld metal described above are improved, and the formation of non-conductive oxides that reduce the electrodeposition coating properties of the weld is suppressed.

[0076] [Relationship 3] 490≦732-202×[C]+216×[Si]-85×[Mn]-37×[Ni]-47×[Cr]-39×[Mo]≦520 (In the above relational equation 3, [C], [Si], [Mn], [Ni], [Cr], and [Mo] represent the weight percentage content of each element in parentheses in the welding wire.)

[0077] On the other hand, in the above relational equation 3, it is preferable to control the value of "732-202×[C]+216×[Si]-85×[Mn]-37×[Ni]-47×[Cr]-39×[Mo]" (i.e., the value of R below) to be between 495 and 515, and more preferably between 500 and 510.

[0078] That is, R = 732 - 202 × [C] + 216 × [Si] - 85 × [Mn] - 37 × [Ni] - 47 × [Cr] - 39 × [Mo]

[0079] [Relationship 3-2] 500≦732-202×[C]+216×[Si]-85×[Mn]-37×[Ni]-47×[Cr]-39×[Mo]≦510

[0080] Although not particularly limited, according to the present invention, the welding wire can also satisfy the following relational equation 3-2, and by satisfying this, the effect ensured by relational equation 3 described above can be optimized.

[0081] Furthermore, although not particularly limited, according to the present invention, the welding wire can satisfy the following relational equation 4. By satisfying the following relational equation 4, the microstructure of the weld metal described above can be controlled more precisely, and the strength and toughness of the welded joint are simultaneously improved.

[0082] [Relationship Equation 4] Ti + Nb ≥ 0.04 (In the above relational equation, [Ti] and [Nb] represent the weight percentage content of each element in parentheses in the welding wire.) [Examples]

[0083] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are for illustrative purposes and to illustrate the present invention, and are not intended to limit the scope of the rights of the present invention. The scope of the rights of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0084] (Examples) Two steel plates with tensile strengths of 980 MPa or higher or 1180 MPa or higher, having the alloy composition and thickness described in Table 1 below, were prepared as base materials. In addition, a gas shielded arc welding wire with the alloy composition described in Table 2 below was prepared. Subsequently, gas shielded arc welding was performed while applying the welding heat input described in Table 4 below to produce welded members having welds with the alloy composition described in Table 3 below. At this time, for each weld formed by the above welding, the microstructure of the cross-section perpendicular to the length direction at the center of the weld was observed with an optical microscope to confirm the area of ​​weld metal in advance, and that area was cut into the form of a fine chip. Subsequently, the chemical composition of the weld metal was measured using emission spectroscopy with inductively coupled plasma (ICP) analysis on each chip sample.

[0085] The microstructure, strength, and toughness of the welded parts manufactured in this manner were measured, and the results are shown in Tables 4-5 below. At this time, a micro-tensile test specimen measuring 1.6 mm horizontally, 20 mm vertically, and 0.5 mm thick was prepared in the center of the weld, and the strength of the weld metal was measured by tensile testing. Furthermore, the toughness of the weld was measured by preparing a butt joint weld using the steel plate and welding wire described above, and preparing a V-notch impact test specimen with a length of 55 mm according to the JIS Z 2242 standard. The V-notch was positioned in the center of the weld metal, and the impact absorption energy was measured by impact testing at -40°C. At this time, each test was performed three times per test specimen, and the average value was taken as the measured value.

[0086] The microstructure was examined by taking specimens from the weld, micro-polishing the cross-sectional structure, etching it with a Nital solution, and then observing it with an optical microscope. Furthermore, Kikuchi patterns were analyzed via EBSD (Electron Backscattered Diffraction) to obtain IQ (Image Quality) and IPF (Inverse Pole Figure) maps, visualizing grain boundaries and grain orientation information. Subsequently, the grains were classified using the EBSD IQ and IPF maps along with the photographs of the microstructure observed with the optical microscope. The average effective grain size was then measured by calculating the average grain size based on the number of grains per unit area.

[0087] Furthermore, applying the observation methods described above, in the case of retained austenite (RA) fraction, the ratio of the total area of ​​retained austenite distributed in the observation area of ​​the weld metal to the total area of ​​the observation area was measured for 10 areas of the weld metal, and the average value of these was calculated. In the case of the average ratio of the long axis length (Ll) to the short axis length (Ls) of retained austenite (Ll / Ls), the short axis length and long axis length of retained austenite were measured for any 100 retained austenites in the above observation area of ​​the weld metal, and the average value of these was calculated and shown in Table 4 below.

[0088] [Table 1] (In Table 1 above, "-" indicates that the content of the element is 0%.)

[0089] [Table 2] (In Table 2 above, "-" indicates that the content of the element is 0%.)

[0090] [Table 3]

[0091] [Table 4] AF: Acicular ferrite, B: Bainite, M: Martensite, RA: Retained austenite

[0092] The welding heat input Q (kJ / cm) is calculated using the formula Q = (I × E) × 0.048 / υ, where I is the welding current (A), E is the welding voltage (V), and υ is the welding speed (cm / min). (In Table 4 above, "-" indicates that the corresponding value is 0.)

[0093] [Table 5]

[0094] As can be seen from the experimental results in Table 5 above, in the cases of Invention Examples 1 to 12, where the composition range of the welded part of the present invention satisfies relation 1 (or relation 1 and 2), and the composition range of the wire satisfies relation 3 (or relation 3 and 4), it was confirmed that the strength and toughness of the welded part are simultaneously excellent.

[0095] On the other hand, in Comparative Examples 1 to 7, where the composition range of the welded part of the present invention does not satisfy one or more of the relational formulas 1 (or relational formulas 1 and 2), and the composition range of the wire does not satisfy one or more of the relational formulas 3 (or relational formulas 3 and 4), it was confirmed that the welded part was inferior in one or more properties of strength and toughness.

[0096] In particular, Figure 1 shows the IQ (Image Quality) and IPF (Inverse Pole Figure) images of Invention Example 1 observed using EBSD, where the black areas (i.e., the black areas on the right side of Figure 1) indicate retained austenite.

[0097] Furthermore, Figure 2 shows the IQ (Image Quality) and IPF (Inverse Pole Figure) images of Comparative Example 2 observed using EBSD, where the black areas (i.e., the black areas on the right side of Figure 2) indicate retained austenite.

Claims

1. Including the base material and welded parts, The welded portion is characterized by containing, by weight percent, C: 0.05 to 0.16%, Si: 0.001 to 1.0%, Mn: 1.0 to 2.5%, Cr: 0.1 to 5.0%, Mo: 0.1 to 1.5%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Al: 0.20% or less (excluding 0%), Ni: 0.40% or less (excluding 0%), Ti: 0.10% or less (excluding 0%), Nb: 0.10% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities, and satisfying the following relational formula 1. [Relationship 1] 0.15≦([Ti] / [Nb]) / t≦0.65 (In the above relational expression, [Ti] and [Nb] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base material (mm).)

2. The welded portion is characterized in that it satisfies the following relational expression 2, as described in claim 1. [Relationship Equation 2] 3.68≦([Ti] / [Nb])×t / ([Si] / [Mn])≦17.0 (In the above relational formula, [Ti], [Nb], [Si], and [Mn] represent the weight percentage content of each element in parentheses in the weld, and t represents the thickness of the base material (mm).)

3. The welded portion further comprises one or more of the following by weight percent: V: 0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%), as described in claim 1.

4. The welded portion further comprises, by weight %, Cu: 0.50% or less (including 0%), as described in claim 1.

5. The aforementioned welded joint has the following microstructure: Baynight, Needle-shaped ferrite, and The welding member according to claim 1, characterized by comprising one or more selected from the group consisting of granular ferrite, martensite, and retained austenite.

6. The welded member according to claim 1, characterized in that the microstructure of the welded portion has an average effective grain size of 10 μm or less (excluding 0 μm).

7. The welded portion is characterized in that it contains 0.5 to 2.0% retained austenite by area percentage, as described in claim 1.

8. The welded member according to claim 1, characterized in that the retained austenite contained in the weld has an average ratio (Ll / Ls) of major axis length (Ll) to minor axis length (Ls) of 8.0 to 12.

0.

9. The welding member according to claim 1, characterized in that the base material comprises, 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 0.10%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), with the remainder being composed of Fe and other unavoidable impurities.

10. The welding member according to claim 9, characterized in that the base material further comprises one or more of the following by weight percent: Ti: 0.20% or less (including 0%), Nb: 0.10% or less (including 0%), and Cu: 0.10% or less (including 0%).

11. A gas shielded arc welding wire characterized by containing, by weight percent, C: 0.05-0.16%, Si: 0.001-0.2%, Mn: 1.0-2.5%, Cr: 0.4-6.0%, Mo: 0.1-0.65%, P: 0.030% or less (excluding 0%), S: 0.030% or less (excluding 0%), Al: 0.20% or less (excluding 0%), Ni: 0.40% or less (excluding 0%), Ti: 0.20% or less (excluding 0%), Nb: 0.10% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities, and satisfying the following relational formula 3. [Relationship Equation 3] 490≦732-202×[C]+216×[Si]-85×[Mn]-37×[Ni]-47×[Cr]-39×[Mo]≦520 (In the above relational formula 3, [C], [Si], [Mn], [Ni], [Cr], and [Mo] represent the weight percentage content of each element in parentheses in the welding wire.)

12. The gas shielded arc welding wire according to claim 11, further characterized by satisfying the following relational expression 4. [Relational Equation 4] Ti+Nb≧0.04 (In the above relational expression, [Ti] and [Nb] represent the weight percentage content of each element in parentheses in the welding wire.)

13. The welding wire according to claim 11 is characterized in that it further comprises one or more of the following in weight percent: V: 0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%).

14. The welding wire according to claim 11, further comprising, by weight %, Cu: 0.50% or less (including 0%).

15. An automobile part characterized by having the welded member described in claim 1.

Images