Arc weld metal, welded joints, and automotive components

Abstract

An arc weld metal according to one aspect of the present invention contains, in unit mass%, C: 0.10-0.30%, Si: 0.30-1.00%, Mn: 1.30-3.00%, P: 0.0500% or lower, S: 0.0100% or lower, N: 0.01% or lower, and O: 0.02-0.07%, the remainder being iron or impurities, and the residual austenite volume ratio is 3.0-16.0%.

Description

[Technical Field]

[0001] The present invention relates to an arc weld metal, a welded joint, and an automobile component. This application claims priority based on Japanese Patent Application No. 2022-010976, filed on January 27, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In the manufacture of automotive components, particularly automotive undercarriage components, the steel sheets used as materials are becoming thinner and stronger. This leads to the achievement of weight reduction in automobiles and the improvement of automobile safety. Arc welding is mainly used to join steel sheets for automotive components.

[0003] However, it is known that the weld metal obtained by arc welding high-strength steel sheets is prone to hydrogen embrittlement cracking. Therefore, measures to prevent hydrogen embrittlement cracking are essential to promote the application of high-strength steel sheets to automotive suspension components.

[0004] Automotive parts are also required to have corrosion resistance, and therefore arc welds formed at joints in automotive parts are required to have not only hydrogen embrittlement resistance but also electrodeposition paintability.

[0005] As prior art related to arc welding, Patent Document 1 describes a weld metal formed by gas-shielded arc welding using a flux-cored wire, which contains C: 0.02 to 0.12% (meaning "mass %"; the same applies hereinafter to chemical composition), Si: 0.10 to 2.00%, Mn: 0.90 to 2.5%, Ni: 0.20 to 3.5%, Ti: 0.040 to 0.15%, N: 0.015% or less (not including 0%), and O: 0.030 to 0.10%, with the balance being iron and unavoidable impurities, and has a density of 2500 retained austenite particles per mm 2 The present invention discloses a weld metal having excellent resistance to hydrogen embrittlement susceptibility, characterized in that the above-mentioned components are present, the volume fraction of retained austenite particles is 4.0% or more, and the β value expressed by the following formula (1) is 75 or more. β value=320×[C]+50×[Si]+15×[Mn]+10×[Ni]+28×[Mo]...(1) Here, [C], [Si], [Mn], [Ni] and [Mo] mean the contents (mass%) of C, Si, Mn, Ni and Mo, respectively.

[0006] Patent Document 2 describes a steel sheet containing C: 0.02 to 0.12% (meaning "mass %"; the same applies hereinafter to the chemical composition), Si: 0.18 to 2.00%, Mn: 0.90 to 2.5%, Ni: 1.0 to 3.5%, Cr: 0.3 to 2.0%, Al: 0.030% or less (excluding 0%), N: 0.015% or less (excluding 0%), and O: 0.050% or less (excluding 0%), with the remainder being iron and unavoidable impurities, and containing 2500 retained austenite particles per mm with a circle equivalent diameter of 0.15 μm or more. 2 The present invention discloses a weld metal with excellent resistance to hydrogen embrittlement susceptibility, characterized in that the volume fraction of the retained austenite phase is 4.3% or more relative to the entire structure, and the ratio of the Cr and Mn contents [Cr] / [Mn] is 0.20 or more.

[0007] Patent Document 3 describes a weld metal formed by gas-shielded arc welding using a flux-cored wire, which contains C: 0.02 to 0.12% (meaning "mass %"; the same applies hereinafter to chemical composition), Si: 0.10 to 2.00%, Mn: 0.90 to 2.5%, Ni: 0.20 to 3.5%, Ti: 0.040 to 0.15%, N: 0.015% or less (not including 0%), and O: 0.030 to 0.10%, with the balance being iron and unavoidable impurities, and has a density of 2500 retained austenite particles per mm 2 The present invention discloses a weld metal having excellent resistance to hydrogen embrittlement susceptibility, characterized in that the above-mentioned components are present, the volume fraction of retained austenite particles is 4.0% or more, and the β value expressed by the following formula (1) is 75 or more. β value=320×[C]+50×[Si]+15×[Mn]+10×[Ni]+28×[Mo]...(1) Here, [C], [Si], [Mn], [Ni] and [Mo] mean the contents (mass%) of C, Si, Mn, Ni and Mo, respectively.

[0008] Patent Document 4 discloses an arc welding method for steel plates having a C content of 0.08 to 0.30 mass%, in which welding is performed using a welding wire having a total content of Cr and Ni of 1.00 mass% or more, under conditions where X, represented by the following formula (1), is 200 or less. X = 0.8 × (300 - 279 [C] W -25[Si] W -35[Mn] W -49[Ni] W -47[Cr] W -61[Mo] W ) + 0.2 × (300 - 279 [C] BM -25[Si] BM -35[Mn] BM -49[Ni] BM -47[Cr] BM -61[Mo] BM ) (1) (However, [C] W , [Si] W , [Mn] W , [Ni] W , [Cr] W , and [Mo] W respectively indicate the contents (mass%) of C, Si, Mn, Ni, Cr, and Mo in the welding wire, and [C] BM , [Si] BM , [Mn] BM , [Ni] BM , [Cr] BM , and [Mo] BM indicate the contents (mass%) of C, Si, Mn, Ni, Cr, and Mo in the steel sheet, respectively.)

[0009] Patent Document 5 discloses a high fatigue strength fillet welded joint in which at least one steel plate has a thickness of 1 to 4 mm, characterized in that (a) the volume fraction of martensite in the weld metal is 50% or more, and (b) the angle of the weld toe formed on the steel plate surface is 110 to 150°. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2013 / 129284 [Patent Document 2] Japanese Patent Application Publication No. 2014-133258 [Patent Document 3] Japanese Patent Publication No. 2013-173179 [Patent Document 4] Japanese Patent Application Publication No. 2018-187640 [Patent Document 5] Japanese Patent Publication No. 2005-238305 Summary of the Invention [Problem to be solved by the invention]

[0011] However, none of the inventions described in Patent Documents 1 to 5 address the issue of improving both the electrodeposition paintability and hydrogen embrittlement resistance of the welded portion, nor do they disclose any specific configurations for achieving this.

[0012] An object of the present invention is to provide an arc weld metal that can improve both the electrodeposition paintability and hydrogen embrittlement resistance of a weld, as well as a welded joint and an automotive component that have excellent electrodeposition paintability and hydrogen embrittlement resistance of a weld. [Means for solving the problem]

[0013] The gist of the present invention is as follows.

[0014] (1) An arc weld metal according to one embodiment of the present invention contains, in mass%, C: 0.10% or more and 0.30% or less, Si: 0.30% or more and 1.00% or less, Mn: 1.30% or more and 3.00% or less, P: 0.0500% or less, S: 0.0100% or less, N: 0.0100% or less, O: 0.0200% or more and 0.0700% or less, and one or more elements selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg in a total amount of 5.00% or less, with the remainder being iron and impurities, and has a retained austenite volume fraction of 3.0% or more and 16.0% or less. (2) The arc weld metal described in (1) above may contain, in unit mass%, one or more elements selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg in a total amount of 0.03% or more and 5.00% or less. (3) In the arc weld metal described in (1) or (2) above, the Ni content, the Cr content, the Mo content, and the V content may satisfy Ni / 59+Cr / 52+Mo / 96+V / 51<0.0200%. In the above formula, each element symbol represents the content of each element in mass %. (4) The arc weld metal according to any one of (1) to (3) above may contain, in mass %, C: 0.13% or more and 0.30% or less. (5) The arc weld metal according to any one of (1) to (4) above may contain, in mass %, Ti: 0.025% or more and 0.120% or less. (6) The arc weld metal according to any one of (1) to (5) above may contain, in mass%, one or more selected from the group consisting of Al: 0.01% or more and 0.20% or less, Ti: 0.020% or more and 0.120% or less, Cu: 0.10% or more and 1.00% or less, Ni: 0.05% or more and 1.50% or less, Cr: 0.050% or more and 1.000% or less, Mo: 0.050% or more and 1.000% or less, V: 0.050% or more and 0.300% or less, B: 0.050% or more and 0.0600% or less, Nb: 0.005% or more and 0.100% or less, Zr: 0.005% or more and 0.050% or less, and Mg: 0.0005% or more and 0.0100% or less.

[0015] (7) A welded joint according to another aspect of the present invention includes a plurality of base steel plates and an arc weld metal joining the plurality of base steel plates, wherein the arc weld metal is the arc weld metal according to any one of (1) to (5) above, and the Si content of each of the plurality of base steel plates may be, in mass%, 0.60% or more and 2.00% or less, and at least one of the plurality of base steel plates may have a plate thickness of 4.0 mm or less. (8) A welded joint according to another aspect of the present invention includes a plurality of base steel plates and an arc weld metal joining the plurality of base steel plates, wherein the arc weld metal is the arc weld metal described in (6) above, and the Si content of each of the plurality of base steel plates may be, in mass%, 0.60% or more and 2.00% or less, and at least one of the plurality of base steel plates may have a plate thickness of 4.0 mm or less. (9) In the welded joint described in (7) above, at least one of the plurality of base steel plates may have a tensile strength of 980 MPa or more. (10) In the welded joint described in (8) above, at least one of the plurality of base steel plates may have a tensile strength of 980 MPa or more.

[0016] (11) An automobile component according to another aspect of the present invention includes the welded joint described in (7) above. (12) An automobile component according to another aspect of the present invention includes the welded joint described in (8) above. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an arc weld metal that can improve both the electrodeposition paintability and hydrogen embrittlement resistance of a weld, as well as a welded joint and an automotive component that have excellent electrodeposition paintability and hydrogen embrittlement resistance of a weld. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of an analytical method for measuring the chemical composition of a weld metal using optical emission spectroscopy. [Figure 2]FIG. 1 is a schematic diagram of an analytical method for measuring the chemical composition of a weld metal using chemical analysis. [Figure 3] FIG. 2 is a schematic diagram of an analysis method for measuring the amount of retained austenite in a weld metal. [Figure 4] FIG. 2 is a cross-sectional schematic diagram of a weld metal and a weld joint when the weld joint is a lap fillet joint. [Figure 5] 1 is a cross-sectional schematic diagram of a weld metal and a weld joint when the weld joint is a T-fillet joint. FIG. [Figure 6] FIG. 2 is a schematic diagram of a paintability evaluation area. DETAILED DESCRIPTION OF THE INVENTION

[0019] First, an arc weld metal according to a first embodiment of the present invention will be described. Hereinafter, the arc weld metal may be simply referred to as the weld metal. The inventors have discovered that hydrogen embrittlement resistance can be improved by forming retained austenite in the weld metal. Specifically, they have discovered that retained austenite can be used to trap hydrogen that penetrates into the weld metal and suppress hydrogen diffusion to stress concentration areas, thereby suppressing hydrogen embrittlement.

[0020] On the other hand, it was also discovered that Si, an element that stabilizes retained austenite, impairs electrodeposition paintability. When the inventors investigated welded joints with poor electrodeposition paint, they found that insulating welding slag containing Si and other elements had formed in the areas where poor electrodeposition paint had occurred. The insulating material adhering to the surface of the weld bead inhibits the formation of a coating film during electrodeposition paint, causing poor electrodeposition paint.

[0021] Increasing the Si content of arc weld metal inevitably increases the amount of insulating slag produced, impairing electrodeposition paintability. Therefore, the present inventors have intensively studied means for ensuring the amount of retained austenite in the weld metal without impairing the electrodeposition paintability of the weld metal, and have come up with the arc weld metal according to this embodiment, which will be described in detail below.

[0022] The arc weld metal according to the first embodiment of the present invention has, in unit mass%, C: 0.10% or more and 0.30% or less Si: 0.30% or more and 1.00% or less Mn: 1.30% or more and 3.00% or less P:0.0500% or less S: 0.0100% or less N: 0.0100% or less O: 0.0200% or more and 0.0700% or less One or more selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg, in a total content of 5.00% or less and the balance being iron and impurities. Furthermore, the arc weld metal according to this embodiment has a retained austenite volume fraction of 3.0% or more and 16.0% or less. Hereinafter, all "%" indicating the content of an element means "% by mass."

[0023] (C: 0.10% or more and 0.30% or less) Carbon (C) is an important element that affects the strength of the weld metal. If the C content of the weld metal is less than 0.10%, the strength of the weld metal will be insufficient. Furthermore, if the C content of the weld metal is less than 0.10%, the amount of retained austenite in the weld metal will be insufficient. On the other hand, if the C content of the weld metal is more than 0.30%, the toughness of the weld metal will be impaired. Therefore, the C content of the weld metal is set to 0.10% or more and 0.30% or less. The C content of the weld metal is preferably 0.12% or more, 0.13% or more, 0.14% or more, 0.15% or more, or 0.18% or more. The C content of the weld metal is preferably 0.28% or less, 0.25% or less, 0.22% or less, or 0.20% or less. The most preferable C content is considered to be in the range of 0.14% or more and 0.2% or less.

[0024] (Si: 0.30% or more and 1.00% or less) Si suppresses the formation of carbides and stabilizes retained austenite. Si also contributes to the deoxidation of the weld metal. If the Si content of the weld metal is less than 0.30%, these effects cannot be obtained. On the other hand, if the Si content of the weld metal exceeds 1.00%, the amount of insulating welding slag increases and the electrodeposition paintability of the weld metal is impaired. Therefore, the Si content of the weld metal is set to 0.30% or more and 1.00% or less. The Si content of the weld metal is preferably 0.35% or more, 0.40% or more, or 0.50% or more. The Si content of the weld metal is preferably 0.95% or less, 0.90% or less, or 0.80% or less.

[0025] (Mn: 1.30% or more and 3.00% or less) Mn is an important element that improves the hardenability of weld metal. Furthermore, Mn, together with C, concentrates in the austenite phase and stabilizes it. If the Mn content of the weld metal is less than 1.30%, the hardenability and strength of the weld metal will be insufficient. On the other hand, if the Mn content of the weld metal exceeds 3.00%, the toughness of the weld metal will be impaired. Therefore, the Mn content of the weld metal should be 1.30% or more and 3.00% or less. The Mn content of the weld metal is preferably 1.50% or more, 1.80% or more, or 2.00% or more. The Mn content of the weld metal is preferably 2.80% or less, 2.50% or less, or 2.20% or less.

[0026] (P:0.0500% or less) P is an impurity. If the P content of the weld metal exceeds 0.0500%, P segregates at the grain boundaries of the weld metal, impairing the toughness of the weld metal. Therefore, the P content of the weld metal is set to 0.0500% or less. The P content is preferably 0.0450% or less, 0.0400% or less, or 0.0300% or less. From the viewpoint of ensuring the toughness of the welded joint, the smaller the P content, the better. Therefore, no lower limit for the P content is set. The lower limit for the P content may be 0%. However, taking into consideration the manufacturing cost of the welded joint, the P content of the weld metal may be 0.0005% or more, 0.0010% or more, or 0.0100% or more.

[0027] (S:0.0100% or less) S is an impurity. If the S content of the weld metal exceeds 0.0100%, S segregates at the grain boundaries of the weld metal, impairing the toughness of the weld metal. Therefore, the S content of the weld metal is set to 0.0100% or less. The S content is preferably 0.0080% or less, 0.0060% or less, or 0.0050% or less. From the viewpoint of ensuring the toughness of the welded joint, the smaller the S content, the better. Therefore, no lower limit for the S content is set. The lower limit for the S content may be set to 0%. However, taking into consideration the manufacturing cost of the welded joint, the S content of the weld metal may be 0.0005% or more, 0.0010% or more, or 0.0030% or more.

[0028] (N:0.0100% or less) N is an element that penetrates into the weld metal during welding. N contributes to increasing the strength of the weld metal, but if the N content is excessive, the toughness of the weld metal decreases. Therefore, the upper limit of the N content is set to 0.0100%. The N content may be 0.0080% or less, 0.0070% or less, or 0.0060% or less. In the arc weld metal according to this embodiment, the strength is ensured by elements other than N, so no lower limit of the N content is set. The lower limit of the N content may be 0%. On the other hand, the N content may be 0.0001% or more, 0.0010% or more, or 0.0030% or more.

[0029] (O: 0.0200% or more and 0.0700% or less) O is an element that penetrates into the weld metal during welding. Because O forms oxides in the weld metal, excessive O content reduces the toughness of the weld metal. Therefore, the upper limit of the O content is set to 0.07%. The O content may be set to 0.06% or less, 0.05% or less, or 0.04% or less. From the viewpoint of ensuring the toughness of the welded joint, a smaller O content is preferable. Therefore, the lower limit of the O content may be set to 0%. On the other hand, in order to reduce the O content of the weld metal, it is necessary to add a deoxidizing element to the weld metal. An increase in the amount of deoxidizing element increases the construction cost. Therefore, the O content of the weld metal is preferably set to 0.02% or more. The O content may be set to 0.025% or more, 0.03% or more, or 0.035% or more.

[0030] The balance of the chemical composition of the weld metal consists of iron and impurities. The impurities refer to components that are mixed in, for example, from raw materials such as ore or scrap when industrially producing the base metal and filler metal, or due to various factors in the manufacturing process, or components that are mixed in from the welding environment when welding the base metal, and are acceptable within a range that does not adversely affect the weld metal according to this embodiment. Furthermore, the weld metal may contain any of the following optional elements in place of a portion of the remaining iron.

[0031] (One or more optional elements selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg: preferably 0.03% or more and 5.00% or less in total) Al deoxidizes the weld metal. Ti deoxidizes the weld metal and refines the structure of the weld metal. Cu improves welding workability and the hardenability of the weld metal. Ni improves the low-temperature toughness of the weld metal. Cr, Mo, V, and B improve the hardenability of the weld metal. Nb refines the structure of the weld metal. Zr improves the strength of the weld metal. Mg deoxidizes the weld metal. Therefore, these elements may be contained in the weld metal. For example, the total content of these optional elements in the weld metal may be 0.03% or more, 0.10% or more, 0.50% or more, or 1.50% or more. On the other hand, reducing the content of alloying elements can ensure the toughness of the weld metal and further reduce construction costs. Therefore, the total content of these optional elements may be 5.00% or less, 3.50% or less, 2.50% or less, or 2.20% or less.

[0032] These optional elements are often contained in high-strength steel plates. Furthermore, weld metal is formed by melting and mixing a base metal on which the weld metal is provided and a filler metal. Therefore, when the base metal on which the weld metal is provided is a high-strength steel plate, these optional elements may migrate from the base metal to the weld metal. However, these optional elements are not essential from the viewpoint of ensuring the electrodeposition paintability and hydrogen embrittlement resistance of the weld.

[0033] Since insulating slag, which adversely affects electrodeposition coatability, is mainly composed of Si, electrodeposition coatability can be ensured by controlling the Si content within the above range.

[0034] Hydrogen trapping to improve hydrogen embrittlement resistance is achieved using retained austenite, as described below. However, the optional elements mentioned above do not significantly affect the amount of retained austenite. For example, in "Chemistry of Steel Materials" by Mitsuru Tanino et al. (Uchida, Rokakuho, 2001, pp. 103-104), C, N, Mn, Ni, and Cu are listed as examples of austenite-forming elements, with C being particularly important. Furthermore, in "Effect of Grain Size on Transformation-Induced Plasticity of Metastable Fe-Ni-C Austenite" by Masashi Maki et al. (Journal of the Japan Institute of Metals, Vol. 38, pp. 871-876, 1974), it is explained that the lower the Ms point, the more thermally stable the austenite becomes. The Ms point can be estimated, for example, using the following formula ("Formula for Calculating the Carbon Equivalent Transformation Temperature," Welding Information Center, Japan Welding Society, http: / / www-it.jwes.or.jp / weld_simulator / cal1.jsp). Ms=521-353C-22Si-24.3Mn-7.7Cu-17.3Ni-17.7Cr-25.8Mo In the formula for calculating Ms, it can be seen that the C content has a particularly large effect on the austenite stabilization effect.

[0035] For the above reasons, the total content of these optional elements may be 0%. Furthermore, when the total content of various optional elements is specified as described above, it is not necessary to specify the content of each optional element independently. Instead of or in addition to specifying the total content of various optional elements, the content of each optional element may be specified independently as follows:

[0036] (Al: preferably 0.01% or more and 0.20% or less) Al deoxidizes the weld metal. Therefore, Al may be contained in the weld metal. The Al content may be 0%, but the above effect can be preferably obtained by setting the Al content to 0.01% or more, for example. The Al content may be 0.05% or more, 0.08% or more, or 0.10% or more. On the other hand, the Al content may be 0%. Furthermore, setting the Al content of the weld metal to 0.20% or less prevents excessive precipitation of alumina-based oxides in the weld metal, thereby further improving the toughness of the weld metal. The Al content may be 0.18% or less, 0.15% or less, or 0.12% or less.

[0037] (Ti: preferably 0.020% or more and 0.120% or less) Ti deoxidizes the weld metal and refines its structure. Additionally, Ti contained in the filler metal, which is the source of the weld metal, improves the electrical conductivity of the slag adhering to the weld metal surface, further enhancing electrodeposition paintability. Therefore, Ti-containing weld metal obtained from a Ti-containing filler metal has high electrodeposition paintability. While the Ti content may be 0%, these effects can be preferably achieved by, for example, setting the Ti content of the weld metal to 0.020% or more. The Ti content may also be 0.025% or more, 0.030% or more, 0.050% or more, 0.060% or more, or 0.100% or more. On the other hand, setting the Ti content of the weld metal to 0.120% or less reduces the amount of coarse precipitates in the weld metal, further improving the toughness of the weld metal. The Ti content may also be 0.100% or less, 0.080% or less, or 0.060% or less.

[0038] (Cu: preferably 1.00% or less) Plating Cu on the surface of the welding wire, which is the material for the weld metal, improves welding workability. Cu also improves the hardenability of the weld metal. Therefore, Cu may be contained in the weld metal. The Cu content may be 0%, but the above-mentioned effects can be preferably obtained by setting the Cu content to, for example, 0.10% or more, 0.20% or more, or 0.30% or more. On the other hand, setting the Cu content of the weld metal to 1.00% or less can further improve the toughness of the weld metal. The Cu content may also be 0.90% or less, 0.80% or less, or 0.60% or less.

[0039] (Ni: preferably 1.50% or less) Ni improves the low-temperature toughness of the weld metal. Therefore, Ni may be contained in the weld metal. The Ni content may be 0%, but the above-mentioned effects can be preferably obtained by setting the Ni content to, for example, 0.05% or more, 0.10% or more, or 0.12% or more. On the other hand, setting the Ni content of the weld metal to 1.50% or less can prevent excessive hardening of the weld metal and ensure stable toughness of the weld metal. The Ni content may also be 1.00% or less, 0.95% or less, 0.50% or less, 0.20% or less, 0.19% or less, or 0.15% or less.

[0040] (Cr: preferably 1.000% or less) Cr improves the hardenability of the weld metal. Therefore, Cr may be contained in the weld metal. The Cr content may be 0%, but the above-mentioned effects can be preferably achieved by setting the Cr content to, for example, 0.050% or more, 0.100% or more, or 0.120% or more. On the other hand, when the Cr content of the weld metal is 1.000% or less, the cost of the alloy is reduced, which is economically advantageous. Furthermore, by setting the Cr content of the weld metal to 1.000% or less, the toughness of the weld metal can be further improved. The Cr content may also be 0.900% or less, 0.800% or less, or 0.600% or less.

[0041] (Mo: preferably 1.000% or less) Mo improves the hardenability of the weld metal. Therefore, Mo may be contained in the weld metal. The Mo content may be 0%, but the above-mentioned effects can be preferably obtained by setting the Mo content to, for example, 0.050% or more, 0.100% or more, or 0.120% or more. Furthermore, when the Mo content of the weld metal is 1.000% or less, the cost of the alloy is reduced, which is economically advantageous. Furthermore, by setting the Mo content of the weld metal to 1.000% or less, the toughness of the weld metal can be further improved. The Mo content may also be 0.900% or less, 0.800% or less, or 0.600% or less.

[0042] (V: preferably 0.300% or less) V improves the hardenability of the weld metal. Therefore, V may be contained in the weld metal. The V content may be 0%, but the above-mentioned effects can be preferably obtained by setting the V content to, for example, 0.050% or more, 0.100% or more, or 0.120% or more. On the other hand, when the V content of the weld metal is 0.300% or less, the cost related to the alloy is reduced, which is economically advantageous. Furthermore, by setting the V content of the weld metal to 0.300% or less, the toughness of the weld metal can be further improved. The V content may be 0.280% or less, 0.250% or less, or 0.200% or less.

[0043] (B: preferably 0.0600% or less) B improves the hardenability of the weld metal. Therefore, B may be contained in the weld metal. The B content may be 0%, but the above-mentioned effects can be preferably obtained by setting the B content to, for example, 0.0005% or more, 0.0010% or more, or 0.0050% or more. On the other hand, by setting the B content of the weld metal to 0.0600% or less, the toughness of the weld metal can be further improved. The B content may also be 0.0500% or less, 0.0450% or less, or 0.0400% or less.

[0044] (Nb: preferably 0.100% or less) Nb forms carbonitrides in the weld metal, contributing to the refinement of the structure of the weld metal and the improvement of its strength. Therefore, Nb may be contained in the weld metal. The Nb content may be 0%, but the above-mentioned effects can be preferably obtained by setting the Nb content to 0.005% or more, 0.010% or more, or 0.020% or more, for example. On the other hand, by setting the Nb content of the weld metal to 0.100% or less, the toughness of the weld metal can be further improved. The Nb content may also be 0.080% or less, 0.050% or less, or 0.040% or less.

[0045] (Zr: preferably 0.050%) Zr precipitates as fine nitrides in the weld metal, improving the strength of the weld metal. Therefore, Zr may be contained in the weld metal. The Zr content may be 0%, but the above-mentioned effects can be preferably achieved by setting the Zr content to, for example, 0.005% or more, 0.006% or more, or 0.007% or more. On the other hand, setting the Zr content in the weld metal to 0.050% or less can prevent the formation of coarse precipitates in the weld metal and further improve the toughness of the weld metal. The Zr content may also be 0.040% or less, 0.035% or less, or 0.030% or less.

[0046] (Mg: preferably 0.0100% or less) Mg is an element added to deoxidize the weld metal. Therefore, Mg may be contained in the weld metal. The Mg content may be 0%, but the above-mentioned effects can be preferably obtained by setting the Mg content to, for example, 0.0005% or more, 0.0007% or more, or 0.0010% or more. On the other hand, setting the Mg content of the weld metal to 0.0100% or less can prevent a decrease in the toughness of the weld metal. The Mg content may also be 0.0050% or less, or 0.0030% or less.

[0047] (Residual austenite volume fraction: 3.0% to 16.0%) Generally, hydrogen embrittlement cracking occurs at stress-concentrated areas, such as near the root of a lap fillet joint or a T-fillet joint.

[0048] The retained austenite phase contained in the weld metal traps hydrogen that has entered the weld metal during arc welding, thereby reducing the hydrogen concentration at stress-concentrated regions such as the root tip and improving the hydrogen embrittlement resistance of the weld metal. The above-mentioned effects can be achieved when the volume fraction of retained austenite is 3.0% or more. The volume fraction of retained austenite may be 4.0% or more, 5.0% or more, or 8.0% or more. While there is no particular upper limit for the volume fraction of retained austenite, considering the chemical composition of the weld metal according to this embodiment, it is estimated that it would be difficult to achieve a volume fraction of retained austenite exceeding 16.0%. Therefore, the volume fraction of retained austenite may be 16.0% or less, 15.0% or less, or 13.0% or less.

[0049] The remainder of the metallurgical structure of the weld metal is not particularly limited. It is sufficient that the remainder of the metallurgical structure is composed of, for example, ferrite and martensite. It is more preferable that the volume fraction of martensite in the weld metal is less than 50%, 48% or less, 45% or less, or 40% or less. This prevents excessive hardening of the weld metal, further improving the hydrogen embrittlement resistance of the weld metal.

[0050] (Ni / 59+Cr / 52+Mo / 96+V / 51: preferably less than 0.0200%) While Ni, Cr, Mo, and V contained in the weld metal have the effect of improving the hardenability of the weld metal, they may form precipitates in the weld metal and reduce the toughness of the weld metal. Therefore, it is preferable that the parameter A, which is obtained by substituting the Ni content, Cr content, Mo content, and V content into the following formula, is less than 0.0200%. Parameter A = Ni / 59 + Cr / 52 + Mo / 96 + V / 51 In other words, the Ni content, the Cr content, the Mo content, and the V content are Ni / 59+Cr / 52+Mo / 96+V / 51<0.0200% It is preferable that the parameter A satisfies the following: The parameter A is more preferably less than 0.0100%, or less than 0.0050%. In the above formula, each element symbol represents the content of each element in mass %.

[0051] The weld metal may be subjected to a surface treatment. For example, a chemical conversion coating, plating, paint film, etc. may be provided on the surface of the weld metal. Suitable examples of plating include hot-dip galvanizing, alloyed hot-dip galvanizing, electrogalvanizing, hot-dip aluminizing, and electroaluminizing. Suitable examples of paint film include electrodeposition coating, etc. The weld metal may also be subjected to blasting treatments such as shot blasting and wet blasting, peening treatments such as UIT and hammer peening, and grinding using a grinder, etc. Hydrogen embrittlement cracking of the weld metal occurs within a relatively short time after the completion of welding. Therefore, post-treatment performed some time after the completion of welding is thought to have no effect on the frequency of hydrogen embrittlement cracking of the weld metal.

[0052] The chemical composition of weld metal can be measured using either optical emission spectroscopy or chemical analysis. Optical emission spectroscopy is suitable for joints where a wide analysis surface can be secured, while chemical analysis is suitable for joints where a large amount of test pieces can be collected. The two measurement methods can be used depending on the actual condition of the joint. Regardless of which method is used, the analysis results will be nearly identical. However, when optical emission spectroscopy is used, it is preferable to perform measurements, for example, three or more times and consider the average value to be the chemical composition of the weld metal.

[0053] A method for optical emission spectroscopy will be described using FIG. 1. FIG. 1 is a diagram illustrating a method for measuring the chemical composition of weld metal 1 in a welded joint 2 formed by lap fillet welding two base steel plates 21 by optical emission spectroscopy. FIG. 1 is a diagram schematically illustrating a portion of a cross section of welded joint 2 in a direction perpendicular to the longitudinal direction of weld metal 1. When optical emission spectroscopy is used, first, weld metal 1 is cut and appropriately prepared so as to expose the interior of weld metal 1. For example, if welded joint 2 in which weld metal 1 is arranged is a lap fillet joint, as shown in FIG. 1, one base steel plate 21 (base steel plate 21 shown by a dashed line) of welded joint 2 is removed, and weld metal 1 is cut and polished so that the surface of the other base steel plate 21 (base steel plate 21 shown by a solid line) and the cross section of weld metal 1 are included in the same plane. Next, optical emission spectroscopy is performed on weld metal 1. In this case, the fusion boundary, which is the boundary between the weld metal 1 and the base steel plate 21, and its vicinity are not included in the analysis area. In the case of a normal arc-welded joint 2, it is sufficient to exclude the area within 100 μm from the fusion boundary from the analysis area. This is because the components of the base steel plate 21 tend to be concentrated near the fusion boundary, and have a different composition from the average composition of the weld metal 1. Even if the shape of the welded joint is not a lap fillet joint as exemplified in FIG. 1, it is sufficient to exclude the area within 100 μm from the fusion boundary from the analysis area and perform optical emission spectroscopy analysis on the cross section of the weld metal.

[0054] Next, a chemical analysis method will be described using FIG. 2 . FIG. 2 is a diagram illustrating a method for chemically analyzing the chemical composition of weld metal 1 in a welded joint 2 formed by lap fillet welding two base steel plates 21. FIG. 2 is a schematic diagram illustrating a portion of a cross section of welded joint 2 perpendicular to the longitudinal direction of weld metal 1. When chemical analysis is performed, weld metal 1 is first sampled from welded joint 2. The sampled position of weld metal 1 is at least 100 μm away from the fusion boundary. For example, if welded joint 2 containing weld metal 1 is a lap fillet joint, weld metal 1 may be sampled as shown in FIG. 2 . The hatched area in FIG. 2 indicates the location where weld metal 1 was sampled. Furthermore, because the surface of weld metal 1 may be contaminated with slag or other contaminants, the outermost layer of weld metal 1 is not subject to analysis. Therefore, the surface of weld metal 1 must be ground before sampling. Then, the sampled weld metal 1 is subjected to a conventional chemical analysis. Even if the shape of the welded joint is not the lap fillet joint shown in FIG. 2, good measurement results can be obtained by sampling the weld metal 1 while avoiding the area within 100 μm of the fusion boundary. For example, the fusion boundary can be clearly identified by performing appropriate corrosion on the cross section of the welded joint including the weld metal. By clearly identifying the fusion boundary in this way, we can sample the weld metal while avoiding the area within 100 μm of the fusion boundary, regardless of the shape of the welded joint. Note that the location from which the weld metal is sampled is preferably the steady bead portion.

[0055] Next, a method for measuring the retained austenite volume fraction of a weld metal will be described with reference to FIG. 3 . FIG. 3 is a diagram illustrating a method for measuring the retained austenite volume fraction of a weld metal 1 in a welded joint 2 formed by lap fillet welding two base steel plates 21. FIG. 3 is a schematic diagram illustrating a portion of a cross section of the welded joint 2 in a direction perpendicular to the longitudinal direction of the weld metal 1. The method for measuring the retained austenite volume fraction of the weld metal 1 is as follows. First, the weld metal 1 is cut to expose the interior of the weld metal 1, and the cut surface is appropriately prepared. For example, if the welded joint 2 to which the weld metal 1 is disposed is a lap fillet joint, the weld metal 1 may be cut perpendicular to the welding direction as shown in FIG. 3 . Then, an analysis is performed using an X-ray diffraction device in a region at least 100 μm away from the outer periphery of the weld metal 1. The outer periphery of the weld metal 1 conceptually includes both the fusion boundary between the weld metal 1 and the base steel plate 21 and the surface of the weld metal 1. In FIG. 3 , the region surrounded by a dashed line is the analysis region. The austenite phase fraction is calculated based on the integrated intensity ratio between the peak of the (110) lattice plane of the ferrite phase and the peak of the (111) lattice plane of the austenite phase. Specifically, the X-ray diffraction results are substituted into the following formula to calculate the austenite phase fraction. V=l γ / (l α +l γ ) V: Retained austenite fraction l α : Integrated intensity of the peak of the (110) lattice plane of the ferrite phase l γ : Integrated intensity of the peak of the austenite phase (111) lattice plane Although the weld metal 1 according to this embodiment may contain martensite, in this measurement method, the martensite fraction is included in the ferrite fraction because the crystal structure of martensite formed in steel with C: 0.10% or more and 0.30% or less is almost the same as the crystal structure of ferrite.

[0056] The method for measuring the martensite area ratio of weld metal is as follows. First, a cross-sectional observation sample of the weld metal is prepared. Next, the cross-section is etched with nital to reveal the structure. Then, the cross-section of the weld metal is observed using a scanning electron microscope (SEM) in five fields of view to determine the area of ​​the martensite structure within the fields of view. The area ratio of martensite is then calculated by dividing the area of ​​martensite by the area of ​​the fields of view. The measurement region is a region at least 100 μm away from the outer periphery of the weld metal 1. In other words, the area ratio of martensite is measured within the region surrounded by the dashed line in Figure 3.

[0057] Next, a welded joint according to a second embodiment of the present invention will be described. As shown in Fig. 4 or 5, the welded joint 2 according to the second embodiment includes a plurality of base steel plates 21 and an arc weld metal 1 that joins the plurality of base steel plates 21. This arc weld metal 1 is the arc weld metal 1 according to the first embodiment described above. Note that the figure shows an example in which there are two base steel plates 21, but the number of base steel plates 21 may be any number as long as it is more than one, and three or more base steel plates may be joined by the arc weld metal 1. Furthermore, the Si content of each of the plurality of base steel plates 21 is 0.60% or more and 2.00% or less.

[0058] There are no particular limitations on the shape of the welded joint 2. For example, the welded joint 2 according to this embodiment may be a lap fillet joint as shown in Fig. 4 or a T-fillet joint as shown in Fig. 5. In addition, various shapes such as a butt welded joint can be applied to the welded joint 2 according to this embodiment.

[0059] In the welded joint 2, a plurality of base steel plates 21 are joined by the arc weld metal 1 according to the first embodiment. As a result, the welded joint 2 according to this embodiment has high hydrogen embrittlement resistance and high electrodeposition paintability in the weld metal 1. The thickness of at least one of the plurality of base steel plates is set to 4.0 mm or less. More preferably, the thickness of at least one of the plurality of base steel plates is set to 3.8 mm or less, 3.5 mm or less, or 3.0 mm or less. This can increase the strength of the welded joint 2. Naturally, various preferred aspects of the welded metal 1 according to the first embodiment can be applied to the welded metal 1 of the welded joint 2 according to this embodiment.

[0060] The Si content of each of the multiple base steel plates 21 constituting the weld joint 2 must be 0.60% or more and 2.00% or less. If the Si content of the base steel plate 21 exceeds 2.00%, even if the Si content of the weld metal 1 is within the above-mentioned range, insulating slag containing Si as a main component will form on the surface of the weld metal 1 near the base steel plate 21, impairing the electrodeposition paintability of the weld metal 1. The Si content of the base steel plate 21 is preferably 1.80% or less, 1.60% or less, or 1.40% or less. On the other hand, if the Si content of the base steel plate 21 is less than 0.60%, the adhesion of the oxide scale formed on the surface of the base steel plate 21 during arc welding will be impaired, and the paint film will peel off along with the oxide scale, impairing the electrodeposition paintability of the base steel plate 21. The Si content of the base steel plate 21 is preferably 0.80% or more, 1.00% or more, or 1.20% or more.

[0061] As long as the Si content and thickness are within the above-mentioned ranges, the configuration of the base steel sheet is not particularly limited, but preferred examples are listed below.

[0062] The tensile strength of the base steel plate is not particularly limited, but for example, it is preferable that the tensile strength of at least one of the plurality of base steel plates is 980 MPa or more, 1000 MPa or more, 1200 MPa or more, or 1400 MPa or more, which makes it easy to apply the welded joint according to this embodiment to automobile parts.

[0063] The base steel sheet may be subjected to a surface treatment. For example, the base steel sheet may have a chemical conversion coating, plating, paint film, etc. Suitable examples of plating include hot-dip galvanizing, galvannealed hot-dip galvanizing, electrogalvanizing, hot-dip aluminizing, and electroaluminizing. Suitable examples of paint film include electrodeposition coating, etc. The weld metal may also be subjected to blasting treatments such as shot blasting and wet blasting. For example, blasting treatments may be performed on the base steel sheet and weld metal after welding to remove scale and other particles adhering to the steel sheet surface before welding. Furthermore, peening treatments such as UIT and hammer peening, as well as grinding with a grinder, may be performed on the weld metal and its surrounding base metal. Hydrogen embrittlement cracking of weld metal occurs relatively quickly after the completion of welding. Therefore, post-treatments performed some time after the completion of welding are not considered to affect the frequency of hydrogen embrittlement cracking of weld metal.

[0064] Next, an automobile component according to a third embodiment of the present invention will be described. The automobile component according to the third embodiment includes the welded joint according to the second embodiment. As a result, the automobile component according to this embodiment has high hydrogen embrittlement resistance and high electrodeposition paintability in both the weld metal and the base steel plate. Naturally, various preferred aspects of the welded joint according to the second embodiment can be applied to the welded joint of the automobile component according to this embodiment. Furthermore, it is not necessary for all of the joints of the automobile component to be the welded joint according to the second embodiment.

[0065] Next, a preferred example of a method for producing arc weld metal according to the first embodiment will be described. The preferred example of the method for producing arc weld metal includes a step of arc-welding a plurality of base steel plates to obtain arc weld metal. Here, the Si content of each of the plurality of base steel plates is set to 2.00% or less. The composition of the arc weld metal is set to be within the range of chemical composition of the arc weld metal according to the first embodiment. Furthermore, when the arc welding is completed and the weld metal is cooled, the average cooling rate from 800°C to 300°C is set to be 40°C / s to 15°C / s.

[0066] First, a plurality of base steel plates are arc-welded to form an arc weld metal. The Si content of each of the plurality of base steel plates to be arc-welded must be 2.00% or less. This prevents insulating slag from being formed on the surface of the weld metal in the vicinity of the base steel plate, thereby ensuring electrodeposition paintability. When it is necessary to ensure not only the weld metal but also the electrodeposition paintability of the base steel plate, the lower limit of the Si content of the base steel plate is set to 0.60% or more. The preferred Si content of the base steel plate is the same as that of the base steel plate of the weld joint according to the second embodiment.

[0067] Arc welding is a fusion welding process that uses an electric arc as a heat source. If necessary, filler metal, such as welding wire or welding rod, may be added to the arc weld. Weld metal refers to the metal that melts and solidifies during welding. Weld metal is formed by the mixing and solidification of the molten base steel sheet and filler metal. Therefore, the composition of the weld metal can be controlled by the chemical composition of the base steel sheet, the chemical composition of the filler metal, and the mixing ratio of the base steel sheet and filler metal. The mixing ratio of the base steel sheet and filler metal can be controlled by the filler metal feed rate, heat input, welding speed, etc. during arc welding. Furthermore, the yield rate of alloying elements can also be taken into consideration when controlling the composition of the weld metal. The yield rate refers to the amount of elements remaining in the weld metal after welding relative to the amount of elements contained in the base steel sheet and filler metal before welding. For example, the yield rate of aluminum, which is prone to oxidization and slag formation, is low. The yield rate under certain welding conditions can be estimated by producing a welded joint under the same welding conditions and analyzing the composition of the weld metal. Taking these factors into consideration comprehensively, the composition of the arc weld metal may be set within the range of the composition of the arc weld metal according to the first embodiment.

[0068] Furthermore, the cooling rate of the arc weld metal obtained by arc welding must be within a predetermined range. Specifically, when the weld metal is cooled after arc welding, the average cooling rate from 800°C to 300°C is set to 40°C / sec to 15°C / sec. This average cooling rate is calculated by dividing 500°C (=800°C-300°C) by the time required for the temperature of the weld metal to decrease from 800°C to 300°C. In order to control the amount of retained austenite, it is extremely important to control the cooling rate from when the temperature of the weld metal drops below the A3 point to when it drops below the Ms point. Therefore, in the method for producing weld metal according to this embodiment, it is preferable to control the average cooling rate from 800°C to 300°C.

[0069] If the average cooling rate of the arc weld metal exceeds 40°C / sec, the phase transformation from austenite to martensite is accelerated, and the amount of retained austenite may be insufficient. On the other hand, if the average cooling rate of the arc weld metal is less than 15°C / sec, the phase transformation from austenite to ferrite is accelerated, and the amount of retained austenite may be insufficient.

[0070] The cooling rate of arc weld metal is determined by the heat input during arc welding, the atmospheric temperature after arc welding, and the total thickness of multiple base steel plates. The greater the total thickness of the base steel plates, the greater the amount of heat transferred from the weld metal to the base steel plate, resulting in a higher average cooling rate. The lower the atmospheric temperature, the greater the amount of heat transferred from the weld metal to the atmosphere, resulting in a higher average cooling rate. The greater the heat input, the higher the temperature of the base steel plate, the smaller the amount of heat transferred from the weld metal to the base steel plate, resulting in a lower average cooling rate. Therefore, by appropriately combining these factors, the average cooling rate of arc weld metal can be kept within the above-mentioned range. The heat input is determined by the current value, voltage value, and welding speed during arc welding. As long as the average cooling rate of arc weld metal is within the above-mentioned range, various welding conditions can be adopted depending on the thickness, composition, etc. of the steel plate. [Example]

[0071] The effects of one embodiment of the present invention will be explained in more detail using examples. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0072] Example 1 Various welded joints with arc weld metal were produced by arc welding 2.9 mm thick steel plates A to D. Table 1 shows the tensile strength and Si content of steel plates A to D.

[0073] [Table 1]

[0074] The arc welding conditions were as follows: Welding type: lap fillet weld Shape of the upper plate, i.e. the plate whose end face is welded: rectangular, 150mm wide and 40mm long Shape of the bottom plate, i.e. the plate to be welded on the surface: rectangular, 150mm wide and 60mm long Overlap between upper and lower plates: 10mm Welding current: 220~235A Welding voltage: 21~26V Welding speed: 0.8m / min Welding length: 100mm Current mode: DC pulse mode Shielding gas type: The following two types (1) Ar+20%CO2 shielding gas with H2 added to make the partial pressure 0.5% (2) Ar+20%CO2 shielding gas with H2 added to make the partial pressure 1.0% During arc welding, the composition of the weld metal was adjusted appropriately using a filler metal. After arc welding under the above conditions, the average cooling rate of the weld metal from 800°C to 300°C was set to a range of 30°C / s to 17°C / s.

[0075] The hydrogen embrittlement resistance of the weld metal was evaluated as follows. After 24 hours had passed since the completion of arc welding, the welded joint was cut perpendicular to the welding direction, and the root was observed to check for the presence or absence of cracks. The evaluation criteria were as follows: Weld metal where cracks occurred due to shielding gas type (1): C Weld metal where no cracks occurred with shielding gas type (1) but cracks occurred with shielding gas type (2): B Weld metal in which no cracks occurred with either shielding gas type (1) or (2): A

[0076] The paintability of the weld metal and base steel plate was evaluated as follows. First, electrodeposition coating was applied to the weld joint. Next, a photograph of the weld metal and base steel plate was taken from a direction perpendicular to the surface of the base steel plate. In this photograph, a paintability evaluation area including the weld metal and base steel plate was set. Figure 6 shows a schematic diagram of the paintability evaluation area. For ease of explanation, the left-to-right direction in Figure 6 is referred to as the horizontal direction, and the up-to-down direction in Figure 6 is referred to as the vertical direction. The paintability evaluation area is a rectangular area with the following horizontal and vertical ranges, including a portion of the weld metal 1 and each of the two base steel plates 21 welded by the weld metal 1. The horizontal range of the paintability evaluation area is 30 mm along the longitudinal direction of the weld metal 1. The vertical range of the paintability evaluation area is the range from a position "60% of the width direction length of weld metal 1 (weld bead width)" away from one weld toe of weld metal 1 to a position "60% of the width direction length of weld metal 1 (weld bead width)" away from the other weld toe of weld metal 1.

[0077] Defective electrodeposition coating areas within the paintability evaluation area were identified. Then, image analysis software was used to calculate the percentage of defective electrodeposition coating areas within the paintability evaluation area. The evaluation criteria were as follows: The percentage of defective electrodeposition coating areas exceeds 10% by area: C The percentage of defective electrodeposition coating areas is over 5% by area and 10% by area or less: B The percentage of defective electrodeposition coating areas is 5% or less by area: A

[0078] Furthermore, the chemical composition of the weld metal was determined by optical emission spectroscopy and listed in the table. Measurements were performed three times, and the average values ​​were listed in the table. The remainder of the chemical composition was iron and impurities. For elements whose contents were below the detection limit, the detection limit value was marked with a "<" sign and listed in the table. Furthermore, the total amounts of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg were also listed in the table. When calculating this total amount, elements whose contents were below the detection limit were considered to have a content of 0 mass%.

[0079] In addition, the amounts of retained austenite and martensite in the weld metal were determined using the methods described above. The amounts of retained austenite in the weld metal are shown in the table. The amounts of martensite in the weld metal were all within the range of 30 area % or more and 45 area % or less, so they were not included in the table.

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4]

[0083] In No. 3, the amount of retained austenite was insufficient due to an insufficient Mn content in the weld metal, and as a result, No. 3 failed the evaluation of hydrogen embrittlement resistance.

[0084] In No. 8, the amount of retained austenite was insufficient due to an insufficient Si content in the weld metal, and as a result, No. 8 failed the evaluation of hydrogen embrittlement resistance.

[0085] No. 12 had an insufficient carbon content in the weld metal, resulting in an insufficient amount of retained austenite. As a result, No. 12 failed the evaluation of hydrogen embrittlement resistance. Furthermore, No. 12 had an excessive silicon content. As a result, poor electrodeposition coating occurred on the surface of the weld metal, resulting in a failure in the paintability evaluation.

[0086] In No. 13, the base steel sheet had an insufficient Si content. As a result, poor electrodeposition coating occurred on the base steel sheet, and the paintability evaluation result for No. 13 was unacceptable. However, no poor electrodeposition coating occurred on the weld metal in No. 13. Therefore, it was determined that the weld metal of No. 13 had good hydrogen embrittlement resistance and good paintability.

[0087] Furthermore, when parameter A was less than 0.0200%, the evaluation of cracking was particularly excellent. This is thought to be because the toughness of the weld metal was improved when parameter A was less than 0.0200%.

[0088] On the other hand, in the inventive examples in which the chemical composition of the weld metal, the retained austenite volume fraction of the weld metal, and the Si content of the base steel plate were appropriate, the hydrogen embrittlement resistance of the weld metal and the paintability of the base steel plate and weld metal were all good.

[0089] Example 2 A welded joint was produced using the same base steel plate, filler metal, and welding conditions as in Example No. 1 of the invention disclosed in the table. However, after welding, the welded joint was immersed in liquid nitrogen to rapidly cool the weld metal. As a result, the average cooling rate of the weld metal from 800°C to 300°C was 100°C / s or more and 200°C / s or less.

[0090] The amount of retained austenite in the resulting weld metal was measured and found to be 1.04%. In other words, if the cooling rate of the weld metal is inappropriate, the necessary amount of retained austenite cannot be secured. Furthermore, when the hydrogen embrittlement resistance of this weld metal was evaluated according to the above-mentioned procedure and evaluation criteria, it was rated as "X." [Explanation of symbols]

[0091] 1. Arc welding metal (weld metal) 11 Root 2. Welded joints 21 Base material steel plate

Claims

1. In mass %, C: 0.10% or more and 0.30% or less, Si: 0.30% or more and 1.00% or less, Mn: 1.30% or more and 3.00% or less, P: 0.0500% or less, S: 0.0100% or less, N: 0.0100% or less, O: 0.0200% or more and 0.0700% or less, one or more elements selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg, in a total content of 5.00% or less; and the remainder being iron and impurities, The retained austenite volume fraction is 3.0% or more and 16.0% or less. Arc welding metal.

2. The arc weld metal described in claim 1, characterized in that it contains, by mass%, one or more elements selected from the group consisting of Al, Ti, Cu, Ni, Cr, Mo, V, B, Nb, Zr, and Mg in a total amount of 0.03% or more and 5.00% or less.

3. Ni content, Cr content, Mo content, and V content are Ni / 59+Cr / 52+Mo / 96+V / 51<0.0200% 2. The arc weld metal according to claim 1, wherein the above formula satisfies the above formula. In the above formula, each element symbol represents the content of each element in mass %.

4. In mass %, C: 0.13% or more and 0.30% or less The arc weld metal according to claim 1, further comprising:

5. In mass %, Ti: 0.025% or more and 0.120% or less, The arc weld metal according to claim 1, further comprising:

6. In mass %, Al: 0.01% or more and 0.20% or less, Ti: 0.020% or more and 0.120% or less, Cu: 0.10% or more and 1.00% or less, Ni: 0.05% or more and 1.50% or less, Cr: 0.050% or more and 1.000% or less, Mo: 0.050% or more and 1.000% or less, V: 0.050% or more and 0.300% or less, B: 0.050% or more and 0.0600% or less, Nb: 0.005% or more and 0.100% or less, Zr: 0.005% or more and 0.050% or less, and Mg: 0.0005% or more and 0.0100% or less The arc weld metal according to any one of claims 1 to 5, characterized in that it contains one or more selected from the group consisting of:

7. A plurality of base steel plates; an arc weld metal that joins the plurality of base steel plates; Equipped with The arc weld metal is the arc weld metal according to any one of claims 1 to 5, The Si content of each of the plurality of base steel plates is, in mass%, 0.60% or more and 2.00% or less, At least one of the plurality of base steel plates has a plate thickness of 4.0 mm or less. Welded joints.

8. A plurality of base steel plates; an arc weld metal that joins the plurality of base steel plates; Equipped with The arc weld metal is the arc weld metal according to claim 6, The Si content of each of the plurality of base steel plates is, in mass%, 0.60% or more and 2.00% or less, At least one of the plurality of base steel plates has a plate thickness of 4.0 mm or less. Welded joints.

9. The welded joint according to claim 7, wherein at least one of the plurality of base steel plates has a tensile strength of 980 MPa or more.

10. The welded joint according to claim 8, wherein at least one of the plurality of base steel plates has a tensile strength of 980 MPa or more.

11. An automobile component comprising the welded joint according to claim 7.

12. An automobile component comprising the welded joint according to claim 8.

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