Welding member, gas shielded arc welding wire, and automobile part having the welding member

Abstract

The present invention ensures excellent strength and toughness of the weld metal compared to gigasteel, which is mainly used in the automotive industry, while effectively ensuring the economy of welding components and welding materials that are essential for manufacturing parts. [Solution] The present invention relates to a welding member and a wire for gas shielded arc welding, which 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 (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 is characterized in that the weld contains the following relational expression 1: [Equation 1] 0.15≦([Ti] / [Nb]) / t≦0.65 (In the above formula, [Ti] and [Nb] indicate the weight percent content of each element in parentheses in the weld, and t indicates the thickness of the base material (mm).)

Description

[Technical field]

[0001] The present invention relates to a welding member and a wire for gas-shielded arc welding, and more particularly to a welding member and a wire for gas-shielded arc welding having excellent strength and toughness. [Background technology]

[0002] Development of lightweight chassis parts for next-generation automobiles is underway, utilizing Gigasteel with a tensile strength of 980 MPa or more. As the development of lightweight chassis parts for such ultra-high strength automobiles progresses, the development of welding technology that can improve the properties of welds while also ensuring economic efficiency is becoming an important issue.

[0003] Existing ultra-high strength welding materials for automotive Gigasteel contain a large amount of expensive Ni, making them less economical, which inevitably increases manufacturing costs. In addition, they have limitations in that the microstructure and mechanical properties of the Gigasteel thin plate weld metal are not optimized.

[0004] In particular, in the case of thin steel plates having a thickness of 2.0 mm or less, there is a lack of accurate and detailed understanding of the phase transformation and microstructural development mechanisms of the weld metal formed by the melting and dilution of the welding material and base metal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-220431 A Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a welding component and a wire for gas shielded arc welding.

[0007] More specifically, the objective is to ensure the excellent strength and toughness of the weld metal for gigasteel, which is mainly used in the automotive industry, while effectively ensuring the economy of welding components and welding materials that are essential for manufacturing parts.

[0008] The object of the present invention is not limited to the above. Further object of the present invention is described in the entire 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 contents described in the specification of the present invention. [Means for solving the problem]

[0009] The present invention relates to The base material and the welded portion are included. The welded portion 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 (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 is characterized in that it satisfies the following relational formula 1.

[0010] [Equation 1] 0.15≦([Ti] / [Nb]) / t≦0.65 (In the above formula, [Ti] and [Nb] indicate the weight percent content of each element in parentheses in the weld, and t indicates the thickness of the base material (mm).)

[0011] The present invention relates to The wire for gas-shielded arc welding contains, by weight, 0.05-0.16% C, 0.001-0.2% Si, 1.0-2.5% Mn, 0.4-6.0% Cr, 0.10-0.65% Mo, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.20% or less (excluding 0%) Al, 0.40% or less (excluding 0%) Ni, 0.20% or less (excluding 0%) Ti, 0.10% or less (excluding 0%) Nb, with the balance being Fe and other unavoidable impurities, and is characterized in that it satisfies the following relational formula 3.

[0012] [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 percent content of each element in parentheses with respect to the welding wire.)

[0013] The present invention also relates to an automobile part having the above welded member. Effect of the Invention

[0014] The present invention seeks to provide a welded component and a wire for gas shielded arc welding.

[0015] The present invention can effectively ensure the economy of welding components and welding materials that are essential for manufacturing parts while ensuring excellent strength and toughness of the weld metal compared to gigasteel, which is mainly used in the automotive industry.

[0016] The various and beneficial advantages and effects of the present invention are not limited to the above, but can be more easily understood in the course of describing specific embodiments of the present invention. [Brief description of the drawings]

[0017] [Figure 1]1 is an IQ (Image Quality) and IPF (Inverse Pole Figure) photograph of Example 1 of the present invention observed by EBSD. [Diagram 2] 1 is an IQ (Image Quality) and IPF (Inverse Pole Figure) photograph of Comparative Example 2 of the present invention observed by EBSD. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the embodiments of the present invention will be described. It goes without saying that the following embodiments can be modified in various ways by those having ordinary skill in the art to which the present invention belongs, without departing from the scope of the present invention. The following embodiments are provided for the purpose of understanding the present invention, and the scope of the present invention should not be limited to the following embodiments, but should be defined by the claims below as well as equivalents thereto.

[0019] However, the terms used herein are for the purpose of describing the present invention and are not intended to limit the present invention. Furthermore, the singular forms used herein include the plural forms unless the relevant definition clearly indicates otherwise.

[0020] As used herein, the meaning of "comprise" is to specify features and does not exclude the presence or addition of other features.

[0021] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Dictionary-defined terms are to be interpreted as having a meaning consistent with the relevant technical literature and the presently 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. First, the alloy composition of the welded portion will be described. The content of the alloy composition described below is in "wt %".

[0023] C:0.05~0.16% The C is a main element that can lower the temperature at which the acicular ferrite, bainite and martensite transformations due to diffusionless transformations start as the weld metal is continuously cooled in the high-temperature austenite phase during solidification. If the C content is less than 0.05%, not only is the hardening ability reduced, making it difficult to ensure sufficient strength of the weld metal, but also the low-temperature transformation start temperature is not sufficiently low due to the above-mentioned principle, 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-angle grain boundary structure with a large difference in azimuth angle between grains is not formed. On the other hand, if the C content exceeds 0.16%, not only is the viscosity of the molten metal reduced and the bead shape is poor, but the weld metal is excessively hardened to reduce toughness, and the low-temperature transformation start temperature is excessively low, making it impossible to ensure compressive stress due to low-temperature transformation at temperatures near room temperature where the tensile residual stress of the weld reaches its maximum, and the residual austenite phase, which is an untransformed phase, may increase in the final weld metal structure. 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 may be 0.075%, or the upper limit of the C content may be 0.13%.

[0024] Silicon: 0.001 to 1.0% The Si is an element (deoxidizing element) that promotes deoxidation of molten metal during arc welding, is advantageous in suppressing the occurrence of blowholes, and increases the low-temperature transformation start temperature. If the Si content is less than 0.001%, there is a drawback that the deoxidizing effect is insufficient, making blowholes more likely to occur, and the low-temperature transformation start temperature is excessively low, which may reduce the effect of offsetting the tensile residual stress of the welded portion. On the other hand, if the Si content exceeds 1.0%, there is a drawback that a large amount of non-conductive slag is generated, causing poor painting of the welded portion, and the surface activation of the welded portion is insufficient due to excessive deoxidation, which may reduce the penetration of the molten metal, and the low-temperature transformation start temperature is increased, which may prevent sufficient 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 may be 0.22%, or the upper limit of the Si content may be 0.80%.

[0025] Mn: 1.0-2.5% 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 is an element that reduces the low temperature transformation start temperature like C. If the Mn content is less than 1.0%, there may be disadvantages that the deoxidizing effect is insufficient, blowholes are easily generated, the low temperature transformation start temperature increases, and sufficient compressive stress effect due to low temperature transformation cannot be obtained. On the other hand, if the Mn content exceeds 2.5%, there may be disadvantages that the viscosity of the molten metal becomes excessively high, and when the welding speed is fast, the molten metal cannot properly flow into the welded part, a humping bead is formed, and the low temperature transformation start temperature is too low, which reduces the effect of offsetting the tensile residual stress of the welded part. Meanwhile, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Mn content may be 1.4%, or the upper limit of the Mn content may be 2.4%.

[0026] Cr:0.1~5.0% The Cr is a ferrite stabilizing element, which lowers the low-temperature transformation start temperature and is advantageous in improving the strength by ensuring the hardening ability of the weld metal. If the Cr content is less than 0.1%, the ratio of high-angle grain boundaries in the weld metal decreases, making it difficult to obtain a sufficient compressive stress effect due to the low-temperature transformation, and it may also be difficult to ensure sufficient strength of the weld metal. On the other hand, if the Cr content exceeds 5.0%, the brittleness of the weld metal may increase unnecessarily in some cases, making it difficult to ensure sufficient toughness, and the low-temperature transformation start temperature may be too low to ensure sufficient compressive stress of the welded part. 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 may be 0.4%, or the upper limit of the Cr content may be 4.9%.

[0027] Mo: 0.1 to 1.5% The Mo 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 Mo content is less than 0.1%, the ratio of high-angle grain boundaries in the weld metal is reduced, making it difficult to obtain a sufficient compressive stress effect due to the low-temperature transformation, and it may also be 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 start temperature may become too low, making it difficult to ensure sufficient compressive stress of 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 Mo content may be 0.23%, or the upper limit of the Mo content may be 1.2% or 0.38%.

[0028] P: 0.030% or less (excluding 0%) The above P is an element that is generally mixed in as an unavoidable impurity, and the lower limit does not include 0%. However, if the P content exceeds 0.030%, there may be a drawback that hot cracking of the weld metal becomes 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 may be 0.001%, or the upper limit of the P content may be 0.013%.

[0029] S: 0.030% or less (excluding 0%) The above S is an element that is generally mixed in as an inevitable impurity, and the lower limit does not include 0%. However, if the S content exceeds 0.030%, in some cases, the toughness of the weld metal may deteriorate, and the surface tension of the molten metal during welding may be insufficient, causing the molten part to excessively flow down due to gravity during high-speed downward welding (vertical welding, welding from top to bottom), resulting in a defective 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 may be 0.001%, or the upper limit of the S content may be 0.010%.

[0030] Al: 0.20% or less (excluding 0%) The Al is a deoxidizing element, and even a small amount of it can promote the deoxidation of the molten metal during arc welding, thereby improving the strength of the weld metal. In order to ensure the above-mentioned effects, the lower limit of the Al content is excluded to be 0%. However, if the Al content exceeds 0.20%, there may be a drawback that the generation of Al-based oxides increases, and in some cases, the strength and toughness of the weld metal decreases, and the welded part becomes sensitive to electrodeposition coating defects due to non-conductive oxides. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Al content may be 0.010%, or the upper limit of the Al content may be 0.055%.

[0031] 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 weld metal becomes sensitive to cracking, so the Ni content is set to 0.40% or less. The Ni content is more preferably 0.30% or less, further 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 Ni content may be 0.008%, or the upper limit of the Ni content may be 0.10% or 0.053%.

[0032] Ti: 0.10% or less (excluding 0%) The Ti is a deoxidizing element, and even a small amount of Ti can promote the deoxidation of the molten metal during arc welding, thereby improving the strength of the weld metal. It also facilitates the development of acicular ferrite, which can improve the toughness of the weld. In order to ensure the above-mentioned effects, the lower limit of the Ti content is set to 0%. However, if the Ti content exceeds 0.10%, the generation of Ti-based oxides increases, and in some cases, there may be a drawback that the strength and toughness of the weld metal decreases. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Ti content can be 0.008%, or the upper limit of the Ti content can be 0.058%.

[0033] Nb: 0.10% or less (excluding 0%) The Nb is an element that can enhance 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 be 0%. However, if the Nb content exceeds 0.10%, there may be a drawback that a low melting point compound is formed at the grain boundary, making hot cracking more likely to occur. Therefore, the Nb content is set to 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 Nb content can be 0.026%, or the upper limit of the Nb content can be 0.050%.

[0034] Although not particularly limited, in the present invention, the above-mentioned welded member may selectively further include, by weight percent, one or more 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%).

[0035] V: 0.20% or less (including 0%) The V element can enhance the hardening ability and make 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 0.20%, there may be a drawback that the toughness of the weld metal may be reduced in some cases due to excessive strength caused by excess precipitates. Therefore, the V content is set to 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 may be 0.001%, or the upper limit of the V content may be 0.018% or 0.009%.

[0036] Zr: 0.10% or less (including 0%) The Zr is an element (deoxidizing element) that promotes deoxidation of molten metal during arc welding, and is an element that is advantageous in suppressing the occurrence of blowholes. However, if the Zr content exceeds 0.10%, there may be a drawback that the electrodeposition paintability of the welded portion decreases. Therefore, the Zr content is set to 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 may be 0.001%, or the upper limit of the Zn content may be 0.09%.

[0037] B: 0.01% or less (including 0%) The B content is an element that can enhance the hardenability and improve 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 decreases in some cases due to the excessive hardenability. Therefore, the B content is set to 0.01% 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 B content may be 0.001%, or the upper limit of the B content may be 0.009%.

[0038] Alternatively, but not limited to, the above-mentioned welded member may selectively further contain, by weight percent, one or more 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%).

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

[0040] Cu: 0.50% or less (including 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 obtain a sufficient strength improving effect, the Cu content in the weld metal may be 0.01% or more.

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

[0042] 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. The above impurities are known to any ordinary technician, so the present invention does not specifically mention all of them.

[0043] Meanwhile, according to the present invention, the welded portion can satisfy the following Relational Expression 1. By satisfying the following Relational Expression 1, the strength and toughness of the weld metal can be improved at the same time. This is because the effect of the alloying elements varies depending on the dilution ratio between the base metal of the steel plate and the welding wire by more precisely controlling the microstructure of the weld metal, and therefore there is a correlation with the thickness of the base metal.

[0044] [Equation 1] 0.15≦([Ti] / [Nb]) / t≦0.65 (In the above formula, [Ti] and [Nb] indicate the weight percent content of each element in parentheses in the weld, and t indicates the thickness of the base material (mm).)

[0045] Although not particularly limited, the welded portion may satisfy the following Relational Expression 2. By satisfying the following Relational Expression 2, the strength and toughness of the weld metal described above can be further improved, and the formation of non-conductive oxides that deteriorate the electrodeposition paintability of the welded portion can be suppressed.

[0046] [Equation 2] 3.68≦([Ti] / [Nb])×t / ([Si] / [Mn])≦17.0 (In the above formula, [Ti], [Nb], [Si] and [Mn] indicate the weight percent content of each element in parentheses in the weld, and t indicates the thickness of the base metal (mm).)

[0047] Although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the value of ([Ti] / [Nb])×t / ([Si] / [Mn]) in the above Relational Formula 2 can be 4.50 (i.e., 4.50 or more).

[0048] In addition, although not particularly limited, the welded portion of the welded member may have a microstructure including at least one selected from the group consisting of bainite, acicular ferrite, granular ferrite, martensite, and retained austenite. By utilizing the lower bainite transformation including acicular ferrite in the prior austenite grains generated during the cooling process after welding, the microstructure of the welded metal portion is made to have a dense structure in which acicular ferrite and bainite are interlocked in a complex form, i.e., a structure in which the azimuth angle between the grains is high, and the low-temperature transformation start temperature is lowered, so that the compressive residual stress of the welded portion generated by the low-temperature transformation expansion can offset the contraction tensile stress generated during solidification of the molten pool, or can add additional compressive stress.

[0049] Although not particularly limited, the microstructure of the weld may have an average effective grain size of 10 μm or less (excluding 0 μm). By finely controlling the average effective grain size in this manner, it is possible to obtain an effect of ensuring relatively excellent strength and toughness of the weld metal. If the average effective grain size exceeds 10 μm, as described above, it may be difficult to simultaneously ensure sufficient strength and toughness of the weld metal.

[0050] Meanwhile, in the present invention, the alloy composition of the base material is not particularly limited. However, as an example, the base material 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: 0.01-0.10%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), and the balance may be Fe and other inevitable impurities. In addition, 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 welded member may contain 0.5 to 2.0% by area of ​​retained austenite. By satisfying this condition, it is possible to obtain an effect of simultaneously improving the strength and toughness of the weld metal. This is due to the improvement in ductility caused by the transformation-induced plasticity of the retained austenite during deformation, and it is possible to exhibit excellent resistance to defect generation even when stress is applied.

[0052] In addition, although not particularly limited, the retained austenite contained in the welded portion of the welded member may have an average ratio (Ll / Ls) of the major axis length (Ll) to the minor axis length (Ls) of 8.0 to 12.0. By satisfying this, the effect of further improving the strength and toughness of the weld metal can be exhibited. This is because the retained austenite developed in the form of a long and thin film at the grain boundaries of the dense microstructure exhibits the above-mentioned transformation induced plasticity effect and can more effectively improve the resistance to cracking of the welded portion. In this case, the method of measuring the major and minor axis lengths is not separately defined in this specification because they can be measured using a method commonly used in the technical field.

[0053] In addition, the present invention does not particularly limit the manufacturing method of the welded member. However, one advantageous method for manufacturing the welded member of the present invention will be described as follows. For example, when preparing two or more base materials and then performing gas-shielded arc welding using a welding wire to manufacture the welded member, it is preferable that the welding wire satisfies the alloy composition described below, and the base materials also satisfy the above-mentioned alloy composition.

[0054] The wire for gas-shielded arc welding of the present invention will be described below. First, the reasons for adding each component and limiting the content in the wire 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.

[0055] C:0.05~0.16% The C element is advantageous in stabilizing the arc and atomizing the droplets, and is also advantageous in ensuring hardening ability. If the C content is less than 0.05%, the droplets become coarse, the arc becomes unstable, and the amount of spatter increases, and it may be 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, and not only the bead shape becomes poor, but also the weld metal is excessively hardened, resulting in 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 may be 0.06%, or the upper limit of the C content may be 0.15%.

[0056] Silicon: 0.001 to 0.2% The Si is an element (deoxidizing element) that promotes deoxidation of molten metal during arc welding, and is an element that is advantageous in suppressing the occurrence of blowholes. If the Si content is less than 0.001%, there is a drawback that the deoxidizing effect is insufficient and blowholes are easily generated, and if it exceeds 0.2%, there may be a drawback that a large amount of non-conductive slag is generated, causing poor painting of the welded part, and the surface activation of the welded part is insufficient due to excessive deoxidation, resulting in 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 may be 0.005%, or the upper limit of the Si content may be 0.15% or 0.10%.

[0057] Mn: 1.0-2.5% The Mn is a deoxidizing element, and is advantageous in preventing the occurrence of blowholes by promoting the deoxidation of molten metal during arc welding. If the Mn content is less than 1.0%, there is a drawback that the deoxidizing effect is insufficient and blowholes are easily generated, and if it exceeds 2.5%, there is a drawback that the viscosity of the molten metal becomes excessively high, and when the welding speed is fast, the molten metal cannot flow properly into the welded part, and a humping bead is formed, which makes it easy for a defective bead shape to occur. Meanwhile, from the viewpoint of further improving the above-mentioned effects, although not particularly limited, the lower limit of the Mn content may be 1.6%, or the upper limit of the Mn content may be 1.9%.

[0058] Cr:0.4~6.0% The Cr is a ferrite stabilizing element and is an element advantageous in ensuring hardening ability to improve the strength of the weld metal. If the Cr content is less than 0.4%, there is a drawback that it is difficult to ensure sufficient strength of the weld metal, and if it exceeds 6.0%, there may be a drawback that in some cases the brittleness of the weld metal increases unnecessarily and it is 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 may be 0.6%, or the upper limit of the Cr content may be 5.9%.

[0059] Mo: 0.1 to 0.65% The Mo content is a ferrite stabilizing element, and is an element advantageous in ensuring hardening ability to improve the strength of the weld metal. If the Mo content is less than 0.1%, there is a drawback that it is difficult to ensure sufficient strength of the weld metal, and if it exceeds 0.65%, there may be a drawback that the toughness of the weld metal decreases 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 may be 0.3%, or the upper limit of the Mo content may be 0.64%.

[0060] P: 0.030% or less (excluding 0%) The above-mentioned P is an element that is generally mixed into steel as an unavoidable impurity, and is also contained as a normal impurity in solid wire for arc welding. If the content of P exceeds 0.030%, there may be a drawback that hot cracking of the weld metal becomes significant.

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

[0062] Al: 0.20% or less (excluding 0%) The Al is a deoxidizing element, and even a small amount of it can promote the deoxidation of molten metal during arc welding, thereby improving the strength of the weld metal. In order to ensure the above-mentioned effects, the lower limit of the Al content is excluded to be 0%. However, if the Al content exceeds 0.20%, the generation of Al-based oxides increases, and in some cases, the strength and toughness of the weld metal decreases, and the welded part becomes sensitive to electrodeposition coating defects due to non-conductive oxides. Meanwhile, from the viewpoint of further improving the above-mentioned effects, although not particularly limited, the lower limit of the Al content may be 0.001%, or the upper limit of the Al content may be 0.10% or 0.020%.

[0063] Ti: 0.20% or less (excluding 0%) The Ti is a deoxidizing element, and even a small amount of Ti can promote the deoxidation of the molten metal during arc welding, thereby improving the strength of the weld metal. It also facilitates the development of acicular ferrite, which can improve the toughness of the weld. In order to ensure the above-mentioned effects, the lower limit of the Ti content is set to 0%. However, if the Ti content exceeds 0.20%, the generation of Ti-based oxides increases, and in some cases, there may be a drawback that the strength and toughness of the weld metal decreases. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Ti content may be 0.001%, or the upper limit of the Ti content may be 0.10% or 0.050%.

[0064] Nb: 0.10% or less (excluding 0%) The Nb is an element that can enhance 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 be 0%. However, if the Nb content exceeds 0.10%, there may be a drawback that a low melting point compound is formed at the grain boundary, making hot cracking more likely to occur. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the lower limit of the Nb content can be 0.01%, or the upper limit of the Nb content can be 0.06%.

[0065] 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 does not include 0%. However, if the Ni content exceeds 0.40%, there may be a drawback in that the weld metal becomes sensitive to cracking, so the Ni content is set to 0.40% or less. On the other hand, although not particularly limited, from the viewpoint of further improving the above-mentioned effects, the Ni content (i.e., the upper limit of the Ni content) may be 0.30% or less, or 0.20% or less, or 0.10% or less. Alternatively, the lower limit of the Ni content may be 0.005% or 0.01%.

[0066] According to the present invention, the welding wire may selectively further contain, by weight percent, one or more 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%).

[0067] V: 0.20% or less (including 0%) The V element can enhance the hardening ability and densify the microstructure 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 0.20%, there may be a drawback that the toughness of the weld metal may be reduced in some cases due to excessive strength caused by excess precipitates. Therefore, the V content is set to 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 may be 0.001%, or the upper limit of the V content may be 0.15% or 0.10%.

[0068] Zr: 0.10% or less (including 0%) The Zr is an element (deoxidizing element) that promotes deoxidation of molten metal during arc welding, and is an element that is advantageous in suppressing the occurrence of blowholes. However, if the Zr content exceeds 0.10%, there may be a drawback that the electrodeposition paintability of the welded portion decreases. Therefore, the Zr content is set to 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 may be 0.001%, or the upper limit of the Zr content may be 0.09%.

[0069] B: 0.01% or less (including 0%) The B content is an element that can enhance the hardenability and improve 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 decreases in some cases due to the excessive hardenability. Therefore, the B content is set to 0.01% 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 B content may be 0.001%, or the upper limit of the B content may be 0.009%.

[0070] According to the present invention, the welding wire may selectively further include, by weight percent, one or more 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%).

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

[0072] Cu: 0.50% or less (including 0%) The Cu is generally an impurity in steel forming wire, and is usually contained at about 0.02%, but in the case of arc welding solid wire, the content can be determined mainly due to the copper plating applied to the wire surface. The Cu is an element that can stabilize the wire feedability and electrical conductivity. However, if the Cu content exceeds 0.50%, there may be a drawback that the weld metal becomes highly 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.

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

[0074] 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. The above impurities are known to any ordinary technician, so the present invention does not specifically mention all of them.

[0075] Meanwhile, according to the present invention, the welding wire can satisfy the following Relational Expression 3. By satisfying the following Relational Expression 3, the strength and toughness of the weld metal described above can be improved, and the formation of non-conductive oxides that deteriorate the electrodeposition paintability of the welded portion can be suppressed.

[0076] [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 percent content of each element in parentheses with respect to the welding wire.)

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

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

[0079] [Equation 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 expression 3-2, and by satisfying this, the effect ensured by the above-mentioned relational expression 3 can be optimized.

[0081] Furthermore, although not particularly limited, according to the present invention, the welding wire can satisfy the following Relational Expression 4. By satisfying the following Relational Expression 4, the microstructure of the weld metal described above can be more precisely controlled, and the strength and toughness of the weld can be improved at the same time.

[0082] [Equation 4] Ti+Nb≧0.04 (In the above formula, [Ti] and [Nb] indicate the weight percent 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 intended to illustrate and embody the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0084] (Example) Two steel plates having a tensile strength of 980 MPa or more or 1180 MPa or more and having the alloy composition and thickness shown in Table 1 below were prepared as base materials. A wire for gas-shielded arc welding having an alloy composition shown in Table 2 below was also prepared. Then, gas-shielded arc welding was performed while applying the welding heat input shown in Table 4 below, and a welded member having a welded part having an alloy composition shown in Table 3 below was manufactured. At this time, for each welded part formed by the above welding, the microstructure of the cross section perpendicular to the longitudinal direction at the longitudinal center of the welded part was observed with an optical microscope to confirm the weld metal area in advance, and the area was machined into the form of a fine chip. Then, the chemical composition of the welded metal was measured using each chip sample by using emission spectroscopy using high-frequency inductively coupled plasma (ICP).

[0085] The microstructure, strength and toughness of the welded parts manufactured in this way were measured, and the results are shown in Tables 4 to 5 below. At this time, a micro tensile test piece with a width of 1.6 mm, a length of 20 mm and a thickness of 0.5 mm was processed at the center of the welded part, and the strength of the welded metal was measured by a tensile test. In addition, the toughness of the welded part was prepared by preparing a butt joint welded part using the above-mentioned steel plate and welding wire, and processing a V-notch impact test piece with a length of 55 mm according to the JIS Z 2242 standard. The V-notch was positioned at the center of the welded metal, and the impact absorption energy was measured by an impact test at -40°C. At this time, each test was performed three times for each test piece, and the average value was taken as the measured value.

[0086] The microstructure was observed under an optical microscope after a test specimen was taken from the welded joint, the cross-sectional structure was finely polished, and etched with a Nital solution. In addition, the Kikuchi pattern was analyzed through EBSD (Electron Backscattered Diffraction) to obtain IQ (Image Quality) and IPF (Inverse Pole Figure) maps that visualize the grain boundaries and grain orientation information. The grains were then classified using the EBSD IQ and IPF maps along with the microstructure photographs observed under the optical microscope, and the average effective grain size was measured by calculating the average grain size converted from the number of grains per unit area.

[0087] In addition, by applying the above-mentioned observation method in a similar manner, in the case of the retained austenite (RA) fraction, the ratio of the sum of the areas of the retained austenite distributed in the observation region of the weld metal to the total area of ​​the observation region was measured for each of 10 regions of the weld metal, and the average value of these was calculated. In the case of the average ratio (Ll / Ls) of the major axis length (Ll) to the minor axis length (Ls) of the retained austenite, the minor axis length and major axis length of the retained austenite were measured for any 100 retained austenite particles in the observation region of the above-mentioned weld metal, and the average value of these was calculated and shown respectively 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 by 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 case of Examples 1 to 12 of the invention, which satisfy the composition range of the weld of the present invention and Relational Formula 1 (or Relational Formulas 1 and 2) and satisfy the composition range of the wire and Relational Formula 3 (or Relational Formulas 3 and 4), it was confirmed that the strength and toughness of the weld are simultaneously excellent.

[0095] On the other hand, in the case of Comparative Examples 1 to 7, which do not satisfy one or more of the composition range of the welded portion of the present invention and Relational Formula 1 (or Relational Formulas 1 and 2), and do not satisfy one or more of the composition range of the wire and Relational Formula 3 (or Relational Formulas 3 and 4), it was confirmed that one or more of the strength and toughness of the welded portion were inferior.

[0096] In particular, FIG. 1 shows IQ (Image Quality) and IPF (Inverse Pole Figure) photographs of Example 1 observed by EBSD, and the black color (i.e., the part shown in black on the right side of FIG. 1) indicates retained austenite.

[0097] FIG. 2 shows IQ (Image Quality) and IPF (Inverse Pole Figure) photographs of Comparative Example 2 observed by EBSD, and black (i.e., the part shown in black on the right side of FIG. 2) indicates retained austenite.

Claims

1. Including the base material and the welded part, The 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%), Nb: 0.10% or less (excluding 0%), with the remainder being Fe and other unavoidable impurities, and is a welded member characterized in that it satisfies the following relational expression 1. [Relationship 1] 0.15≦([Ti] / [Nb]) / t≦0.65 (In the above formula, [Ti] and [Nb] represent the weight percent content of each element in parentheses in the weld, and t represents the thickness (mm) of the base material.)

2. The welded member according to claim 1 , wherein the welded portion satisfies the following Relational Expression 2. [Relationship 2] 3.68≦([Ti] / [Nb])×t / ([Si] / [Mn])≦17.0 (In the above formula, [Ti], [Nb], [Si] and [Mn] represent the weight percent content of each element in parentheses in the weld, and t represents the thickness (mm) of the base material.)

3. 2. The welded member according to claim 1, further comprising, by weight percent, one or more of V: ​​0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%).

4. The welded member according to claim 1, wherein the welded portion further contains, by weight percent, Cu: 0.50% or less (including 0%).

5. The weld has a microstructure of Bainite, Acicular ferrite, and 2. The welded component according to claim 1, comprising at least one selected from the group consisting of granular ferrite, martensite, and retained austenite.

6. 2. The welded member according to claim 1, wherein the microstructure of the weld has an average effective grain size of 10 μm or less (excluding 0 μm).

7. 2. The welded member according to claim 1, wherein the weld contains, in area percentage, 0.5 to 2.0% retained austenite.

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 the major axis length (Ll) to the minor axis length (Ls) of 8.0 to 12.

0.

9. 2. The welded member according to claim 1, characterized in that the 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 0.10%, P: 0.05% or less (excluding 0%), S: 0.05% or less (excluding 0%), and the balance being Fe and other unavoidable impurities.

10. The welded member according to claim 9, wherein the base material further contains, by weight percent, 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%).

11. 1. A gas-shielded arc welding wire comprising, by weight, 0.05-0.16% C, 0.001-0.2% Si, 1.0-2.5% Mn, 0.4-6.0% Cr, 0.1-0.65% Mo, 0.030% or less (excluding 0%) P, 0.030% or less (excluding 0%) S, 0.20% or less (excluding 0%) Al, 0.40% or less (excluding 0%) Ni, 0.20% or less (excluding 0%) Ti, 0.10% or less (excluding 0%), with the balance being Fe and other inevitable impurities, and satisfying the following relational expression 3: [Relationship 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 percent content of each element in parentheses with respect to the welding wire.)

12. The wire for gas shielded arc welding according to claim 11, further satisfying the following relational expression 4: [Relationship 4] Ti+Nb≧0.04 (In the above formula, [Ti] and [Nb] indicate the weight percent content of each element in parentheses in the welding wire.)

13. The wire for gas-shielded arc welding according to claim 11, further comprising, by weight percent, one or more of V: ​​0.20% or less (including 0%), Zr: 0.10% or less (including 0%), and B: 0.01% or less (including 0%).

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

15. An automobile part comprising the welded member according to claim 1.

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