Welding materials

Abstract

To provide a welding member excellent in corrosion resistance of a weld zone.SOLUTION: A welding member includes a weld zone to which a steel material is welded. The zone includes a weld bead that is made of alloy steel containing 9-30 mass% of Cr and 3-25 mass% of Ni. The steel material includes a steel base material, and a zinc-containing plating layer provided on a surface at least on the side, on which the weld bead is formed, of the steel base material. On the surface on the side, on which the weld bead is formed, of the steel base material, the plating layer is formed with a space of 0.1-2.5 mm from a toe part of the weld bead.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to welded components. [Background technology]

[0002] MAG (Metal Arc Gas) welding, which uses a mixture of Ar and CO2 or O2 as the shielding gas, is widely used in various fields, including automobile manufacturing. For example, arc welding is often used for automobile suspension parts because they often have a continuous structure and require continuous welding to ensure the strength and rigidity of the parts.Suspension parts are manufactured by welding steel plates together, followed by chemical conversion treatment and electrodeposition coating, but arc welds are prone to corrosion and require countermeasures.

[0003] In gas-shielded arc welding, slag adheres to the surface of the weld bead. Slag is an oxide that precipitates on the surface of the weld bead and at the toe of the weld bead when deoxidizing elements (such as Si and Mn, which have a high affinity for oxygen) in the steel plate and welding wire react with oxidizing gases (CO2 and O2) in the shielding gas. Because slag is generally non-conductive, the slag area prevents the formation of an electrocoat film, resulting in poor coating, which allows corrosion factors such as salt water to penetrate and become the starting point for corrosion.

[0004] For example, Patent Document 1 discloses a gas-shielded metal welding method for welding carbon steel base materials together in order to suppress the generation of slag on the surface of the weld bead, in which a solid welding wire made of alloy steel containing, by weight, 15% or more of Cr and 1.2% or less of C is used in the welding process at least over the area to be subjected to electrodeposition coating in a subsequent process.

[0005] Furthermore, Patent Document 2 discloses an arc welding method for zinc-based alloy plated steel sheets, in which the alloy components are, in mass % relative to the total mass of the wire, C: 0.01 to 0.05%, Si: 0.1 to 0.5%, Mn: 0.5 to 3%, Ni: 7 to 12%, and Cr: 24 to 30%, and further limited to Mo: 1% or less and N: 0.1% or less, in order to improve the corrosion resistance and liquid metal embrittlement cracking resistance of the weld metal of stainless steel components, and which forms weld metal having an area fraction of ferrite phase of 25% or more in a joint of the zinc-based alloy plated steel sheets and having a tensile strength TSW that satisfies the following formula (1): TSW / TSB≦1.8 (1) However, TSB indicates the tensile strength (MPa) of the base material of the zinc-based alloy plated steel sheet, and TSW indicates the tensile strength (MPa) of the weld metal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-59059 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-35293 Summary of the Invention [Problem to be solved by the invention]

[0007] In welded components produced by welding steel materials by arc welding or the like, it is desirable for the welded parts to have higher corrosion resistance. An object of the present disclosure is to provide a welded member having excellent corrosion resistance at the welded portion. [Means for solving the problem]

[0008] The gist of the present disclosure is as follows. <1> A welded member including a welded portion where steel materials are welded, The welded portion includes a weld bead made of an alloy steel containing, by mass%, Cr: 9 to 30% and Ni: 3 to 25%, the steel material includes a steel base material and a zinc-containing plating layer on at least a surface of the steel base material on a side on which the weld bead is formed, A welded member, wherein the plating layer is formed on the surface of the steel base material on the side where the weld bead is formed, at a distance of 0.1 to 2.5 mm from the toe of the weld bead. <2> The steel base material is a steel plate <1> The welded member according to claim 1. [Effects of the Invention]

[0009] According to the present disclosure, a welded component having excellent corrosion resistance at the welded portion is provided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing an increase in cathodic current due to the progression of corrosion. [Figure 2] 1 is a graph showing the relationship between each type of shielding gas and the Zn plating evaporation distance. [Figure 3] FIG. 2 is a schematic diagram showing the shape of a corrosion resistance test piece. [Figure 4] FIG. 1 is a diagram showing the contents of the JASO M609-91 test. [Figure 5] 1 is a graph showing the measurement results of maximum erosion depth. [Figure 6] This is a cross-sectional SEM image of the weld bead and HAZ of a GA arc-welded material (Ar + 1% CO2 shielding gas) using SUS wire. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment that is an example of the present disclosure will be described. In this disclosure, the "%" used to indicate the content of each element means "% by mass." In addition, in this disclosure, unless otherwise specified, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In addition, when the numerical values ​​written before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit. In the numerical ranges described in stages in the present disclosure, the upper limit of a certain numerical range may be replaced with the upper limit of another numerical range described in stages or a value shown in an Example. Also, in the numerical ranges described in stages in the present disclosure, the lower limit of a certain numerical range may be replaced with the lower limit of another numerical range described in stages or a value shown in an Example. Furthermore, the term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0012] The present inventors have conducted extensive research to improve the corrosion resistance of welds, and have found that when arc welding is performed on plated steel material having a zinc-based plating layer formed thereon, the corrosion resistance of the welds can be significantly improved by using a specific SUS wire (welding wire) and a specific shielding gas, and by keeping the Cr and Ni contents of the weld bead in the welds within specific ranges and restricting the plating loss area around the toe of the weld bead within specific ranges. First, the experiments that led to the welded member according to the present disclosure will be described.

[0013] (A) Weld bead Table 1 shows the combination of steel material (steel plate) used as the welded material and wire used as the arc welding rod, as well as the average composition of the weld bead (EDX quantitative analysis results, average wt% of five or more measurement points). The shielding gas used was Ar + 20% CO2 when using regular wire, and Ar + 1% O2 when using SUS wire.

[0014] [Table 1]

[0015] In Table 1, the steel materials refer to the following steel plates. 980 cold rolled: 980MPa class cold rolled steel plate 980GA: 980MPa grade galvannealed steel sheet 590 hot rolled: 590MPa class hot rolled steel plate 440GA: 440MPa grade galvannealed steel sheet Regular wire: Nippon Steel Welding Co., Ltd., mild steel wire "YM-24T" SUS wire: Nippon Steel Welding Co., Ltd., "YM-309L"

[0016] When ordinary steel wire (normal wire) is used, the weld bead is almost entirely steel, as shown in Table 1, and is therefore prone to red rust due to corrosion. Figure 1 shows the increase in cathodic current as corrosion progresses. When red rust forms, as shown in Figure 1, the cathodic current increases significantly (unplated steel sheet after red rust has formed), further accelerating corrosion. On the other hand, when SUS wire is used, the weld bead has a stainless steel composition as shown in Table 1, so red rust is less likely to occur compared to when regular wire is used, and the increase in cathode current mentioned above is less likely to occur, improving the corrosion resistance of the weld bead.

[0017] (B) HAZ (heat affected zone) Slag forms at the toe of the weld bead, which makes it easy for poorly painted areas to occur. When unplated steel sheets are used, iron scale forms in the HAZ, and corrosion factors penetrate through the poorly painted areas at the toe of the weld bead, causing iron rust to form early and causing corrosion to progress. On the other hand, when GA steel sheets are used, the Zn coating evaporates due to heat and Fe scale forms near the toe of the weld bead. The Zn coating remains at a distance of several hundred micrometers to several millimeters from the toe of the weld bead, and this sacrificial protection effect is thought to inhibit the progression of corrosion.

[0018] Furthermore, when the evaporation distance of the zinc coating was investigated when GA steel sheet was gas-shielded with SUS wire, it was found that the evaporation distance of the zinc coating differed depending on the type of shielding gas. Figure 2 shows the zinc coating disappearance distance (evaporation distance) for each type of shielding gas. Here, the steel material was 980 MPa-grade GA steel sheet, and the coating weight was 45 g / m on one side. 2 Gas shielded arc welding was performed with a plate thickness of 1.6 mm and a welding current of 120A. As shown in Figure 2, when the amount of oxygen source in the shielding gas is reduced, the Zn plating loss distance increases. This is thought to be because the reduction in the amount of oxygen source in the shielding gas increases the spread of the arc plasma, dispersing the energy and expanding the Zn evaporation range. Therefore, if arc welding is performed on zinc-based coated steel sheets using stainless steel wire and a shielding gas that suppresses the spread of arc plasma, the coating layer remaining near the toe of the weld bead will provide a sacrificial corrosion protection effect, and it is thought that the corrosion resistance of the weld will be improved. The welded member according to the present disclosure was discovered based on the above-mentioned experiments and considerations.

[0019] [Welding material] A welded member according to the present disclosure is a welded member including a weld zone formed by welding steel materials, the weld zone including a weld bead made of an alloy steel containing, by mass %, 9-30% Cr and 3-25% Ni, and the steel material including a steel base material and a zinc-containing plating layer on at least the surface of the steel base material on which the weld bead is formed, with a distance of 0.1-2.5 mm from the toe of the weld bead on the surface of the steel base material on which the weld bead is formed.

[0020] <Steel> The steel material to be welded includes a steel base material and a zinc-containing plating layer on at least one surface of the steel base material (the surface on which the weld bead is formed). The shape of the steel material is not particularly limited, and may be a plate-shaped steel material (steel plate), a tubular steel material (steel pipe), a rod-shaped steel material (steel bar), or a steel material (shaped steel) formed into a specific cross-sectional shape such as an H-shape or L-shape. The welded member according to the present disclosure may be, for example, two steel sheets (sometimes referred to as "zinc-based plated steel sheets" or simply "plated steel sheets" in the present disclosure) with a zinc-containing plating layer formed thereon, welded together at their ends, or may be a member formed by welding the end of a zinc-based plated steel sheet to the surface of another steel sheet. It may also be a tubular member formed by forming a zinc-based plated steel sheet into a tubular shape and joining both ends together, or a tubular member formed by joining the ends of two steel pipes with zinc-based plating applied to the outer periphery thereof. The size, thickness, diameter, etc. of the steel material are not particularly limited. Below, as a typical example, the case where the steel material is a zinc-based plated steel sheet will be mainly described.

[0021] From the viewpoint of corrosion resistance of portions other than the welded portion, the steel sheet is a plated steel sheet (zinc-based plated steel sheet) including a base steel sheet and a zinc-containing plating layer (zinc-based plating) on ​​at least the surface of the base steel sheet on the side where the weld bead is formed. The zinc-based plating may be formed on both sides of the base steel sheet.

[0022] The zinc-based coating may be hot-dip galvanizing or electrogalvanizing. The zinc-based coating may contain elements other than Zn, such as Mg, Al, or Si, in order to improve corrosion resistance.

[0023] When the steel material is a zinc-based plated steel sheet, it is preferable that the thickness of the base steel sheet is 0.5 mm to 9.0 mm and the thickness of the plated layer is 3 to 100 μm, for example. If the thickness of the plating layer is 3 μm or more, the plating layer remains after processing, making it easier to maintain high corrosion resistance even in areas other than the welds. Also, if the thickness of the plating layer is 100 μm or less, it can be manufactured on a continuous plating line. The zinc-based plated steel sheet may be a hot-dip galvanized steel sheet (GI material) or a galvannealed steel sheet (GA material) that has been alloyed after plating. In particular, the GA material is preferred from the viewpoint of preventing the zinc plating from adhering to tools during processing.

[0024] <Weld bead> The weld bead in a weld is the raised portion of the weld mark formed when the steel (welded member) and welding wire melt and solidify. The chemical composition of the weld bead is affected by the steel plate (welded member), the composition of the welding wire, and the type of shielding gas, with the latter having the greatest influence. The weld bead in the present disclosure is made of an alloy steel containing, by mass%, 9-30% Cr and 3-25% Ni. The chemical composition of the weld bead may be the remainder Fe and impurities, or may contain optional elements such as C, Si, and Mn. When the weld bead in the weld has a chemical composition containing 9-30% Cr and 3-25% Ni, it can exhibit high corrosion resistance. Each component of the weld bead will be explained below.

[0025] Cr: 9~30% The Cr in the weld bead is mainly derived from the SUS wire. When the Cr content in the weld bead is 9% or more, corrosion resistance is improved. When the Cr content in the weld bead is 30% or less, a significant increase in wire costs can be prevented. From this perspective, the Cr content in the weld bead is preferably 9 to 30%, and more preferably 9 to 20%.

[0026] Ni: 3 to 25% The Ni in the weld bead is mainly derived from the SUS wire. When the Ni content in the weld bead is 3% or more, corrosion resistance is improved. When the Ni content in the weld bead is 25% or less, a significant increase in wire costs can be prevented. From this perspective, the Ni content in the weld bead is preferably 3 to 25%, and more preferably 3 to 15%.

[0027] Remainder: Fe and impurities The alloy steel of the weld bead may contain C, Si, Mn, etc. in addition to Cr and Ni, which have a large effect on corrosion resistance, for the purpose of improving strength, etc. The balance is Fe and impurities. In addition to the alloy elements such as Cr and Ni in the weld bead, Fe and impurities are contained in the weld bead from the SUS wire, steel material, and shielding gas. Impurities include P, S, N, O, etc.

[0028] (Gap between the toe of the weld bead and the plating layer) In the welded member according to the present disclosure, the plating layer is formed at a distance of 0.1 to 2.5 mm from the toe of the weld bead toward the surface of the plated steel sheet. When plated steel sheets are arc-welded, the heat generated during welding causes the plating layer to disappear by at least 0.1 mm from the toe of the weld bead in positions close to the weld. However, in the welded member according to the present disclosure, the distance between the toe of the weld bead and the plating layer is 2.5 mm or less, in other words, the plating layer disappearance distance is 2.5 mm or less, and the sacrificial corrosion protection effect of the plating layer remaining near the weld suppresses the progression of corrosion. To suppress corrosion of the weld due to the sacrificial corrosion protection effect, it is even more preferable that the distance between the toe of the weld bead and the plating layer is 1.5 mm or less. The distance between the toe of the weld bead and the coating layer (coating loss distance) is measured by observing a cross section of the weld bead cut in the welding direction and thickness direction of the steel sheet under a microscope (magnification: 300x). The weld bead is cut at two random locations in the welding direction, and the distance from the toe of the weld bead to the coating layer on both sides of each cross section (coating loss distance) is measured. The average of the four coating loss distances is taken as the distance between the toe of the weld bead and the coating layer for that weld bead.

[0029] <Application> The use of the welded member according to the present disclosure is not particularly limited, but it is suitable, for example, as an automobile suspension part. By providing a welded member according to the present disclosure that has excellent corrosion resistance after painting at the welded portion by electrodeposition coating, it is possible to achieve long-term rust prevention for the automobile suspension part.

[0030] [Method of manufacturing welded components] Next, a method for manufacturing a welded member according to the present disclosure will be described. Although the method for manufacturing a welded member according to the present disclosure is not particularly limited, the welded member according to the present disclosure can be manufactured by arc welding a plated steel sheet, particularly by using a stainless steel wire and a specific shielding gas. As a welding method, it is preferable to apply MAG using a SUS wire and an Ar-O2 mixed gas or an Ar-CO2 mixed gas containing Ar and 3 to 20% by volume of O2 or CO2.

[0031] <SUSワイヤ> The SUS wire (stainless steel welding wire) is not particularly limited as long as it can form a weld bead in the welded member according to the present disclosure when arc-welding steel materials. During arc welding, the components of the SUS wire are diluted by the steel material to form a weld, so it is preferable to use a SUS wire with a higher Cr and Ni content than the respective contents in the desired weld bead. Depending on the components of the steel material, a suitable SUS wire is, for example, a SUS solid wire with a chemical composition of 18-30% Cr and 6-25% Ni relative to the total mass of the wire.

[0032] <Shielding gas> Examples of shielding gases include CO2 gas, O2 gas, Ar-O2 mixed gas, and Ar-CO2 mixed gas. From the viewpoint of suppressing the loss of the zinc plating layer near the weld, it is particularly preferable to use an Ar-O2 mixed gas or Ar-CO2 mixed gas containing Ar and 3 to 30 volume % of O2 or CO2, and more preferably 5 to 20 volume % of O2 or CO2.

[0033] The zinc-based plated steel sheet, which is the member to be welded, is the same as that described above for the welded member, and therefore a description thereof will be omitted here.

[0034] There are no particular limitations on the welding conditions other than the welding wire and shielding gas, but it is preferable to satisfy the following conditions in order to keep the distance from the toe of the weld bead during arc welding to 2.5 mm or less. Welding current: less than 200A Welding voltage: less than 23V Welding speed: over 50cm / min [Example]

[0035] Examples of the welded member according to the present disclosure will be described below, but the welded member according to the present disclosure is not limited to the following examples.

[0036] [Example 1] <Production of welding components> (steel plate) The test materials used were an unplated hot-rolled steel sheet (hereinafter sometimes referred to as hot-rolled 590 or unplated material) with the chemical composition (mass%) shown in Table 2, a thickness of 2.3 mm, and a tensile strength of 590 MPa, and a GA steel sheet (hereinafter sometimes referred to as GA440 or GA material) with a tensile strength of 440 MPa.

[0037] [Table 2]

[0038] (welding wire) The welding wires used were mild steel wire (YM-24T, hereinafter referred to as normal wire) and SUS wire (YM-309L) manufactured by Nippon Steel Welding Co., Ltd., having the chemical compositions (mass %, the remainder being Fe and impurities) shown in Table 3.

[0039] [Table 3]

[0040] Bead-on welding was carried out on the corrosion resistance test piece having the shape shown in Figure 3 under the conditions shown in Table 4.

[0041] [Table 4]

[0042] <Corrosion resistance test> After bead-on welding, the welds were degreased (Nihon Parkerizing FC-E2001), surface conditioned (Nippon Paint PL-ZT), chemically treated (Nippon Paint PBL-3080), and electrocoated (Nippon Paint PN-1010E, targeting a 25μm film thickness). The edges and both ends of the bead were then sealed, and corrosion resistance was evaluated. Corrosion resistance was evaluated using the JASO M609-91 test shown in Figure 4. Specifically, the welds were cycled through two hours of salt spray (5% NaCl) at 35°C, four hours of dry (25% humidity) at 60°C, and two hours of wet (95% humidity) at 50°C, and the occurrence of red rust was evaluated.

[0043] The paint was peeled off and rust removed from the samples using conventional wire after 240 and 360 cycles, and from the samples using SUS wire after 360, 480, 600, and 720 cycles. After that, the maximum erosion depth was measured using a laser displacement meter, excluding approximately 10 mm from both ends of the weld bead. For conventional wire, the average value for each cycle (n=2) is calculated, and for SUS wire, the value for each cycle (n=1) is calculated.

[0044] <Evaluation results> The measurement results of the maximum erosion depth are shown in Figure 5. Table 5 also shows the results of EDX quantitative analysis (energy dispersive X-ray analysis) of the composition of each bead (average mass % of five or more measurement points).

[0045] [Table 5]

[0046] As can be seen in Figure 5, for both unplated and GA materials, the maximum erosion depth is significantly reduced when stainless steel wire is used ((C) and (D)) compared to when regular wire is used ((A) and (B)). One reason for this is thought to be that the amount of slag formed is reduced by reducing the amount of oxygen source in the shielding gas, which suppresses coating defects and extends the red rust generation cycle (the start of erosion). On the other hand, when SUS wire is used, as shown in Figure 5, although there is some variation for each cycle number, the change in maximum erosion depth over time (slope) is smaller compared to when regular wire is used. This is thought to be due to the fact that the bead part when SUS wire is used has a composition similar to SUS304L, as shown in Table 5, and the corrosion resistance of the bead part is improved.

[0047] Furthermore, for both wires, the erosion depth tended to be smaller for the GA material compared to the unplated material, which is thought to be due to the sacrificial corrosion protection effect of the Zn coating remaining around the bead edge. The distance between the toe of the weld bead and the coating layer (distance at which the coating layer disappeared) was measured and found to be 2.3 mm for the combination of (D) GA material and SUS wire.

[0048] [Example 2] The grooves of two steel plates shown in Table 6 were gas-shielded arc-welded using the respective welding wires and shielding gases. After welding, degreasing, surface conditioning, chemical conversion treatment, and electrodeposition coating were performed in the same manner as in Example 1, and then the end faces and both ends of the bead were sealed and corrosion resistance was evaluated. Each measurement was performed using the method described above. In Table 6, the meanings of each symbol are as follows. Furthermore, underlines in Table 6 indicate that the results are outside the scope of the present disclosure or outside the range of preferred conditions.

[0049] (Bead composition) 〇: Cr: 9% to 30% and Ni: 3% to 25% ×: At least one of Cr and Ni is outside the above range

[0050] (Plating loss distance) The distance of plating loss was calculated by cross-sectional SEM observation of the area around the weld bead. Figure 6 shows an example of such an observation. At position (a), the plating on the base metal surface has disappeared, while at positions (b) and (c), the plating remains. In Figure 6, reference number 24 denotes a backing plate used when embedding in resin for cross-sectional SEM observation. ◎: 1.5mm or less ○: More than 1.5mm, less than 2.5mm △:More than 2.5mm

[0051] <Evaluation> (Corrosion resistance after painting of welded parts) -Erosion depth- Maximum erosion depth after 360 cycles of JASO M609-91 test ○: 0.4mm or less △: More than 0.4mm, less than 0.6mm ×: More than 0.6mm

[0052] -Erosion depth of chipping area- ◎: 0.5mm or less ○: More than 0.5mm, less than 0.7mm △: More than 0.7mm, less than 1.0mm ×: More than 1.0mm The erosion depth of the chipped area is the erosion depth when chipping damages the coating around the weld. Scratches simulating chipping were made using a test in accordance with SAE J400, and then the JASO M609-91 test was performed to evaluate the maximum erosion depth after 360 cycles.

[0053] [Table 6]

[0054] The steel sheets and wires in Table 6 are as shown in Tables 7 and 8, respectively. The balance of each component is Fe and impurities.

[0055] [Table 7]

[0056] [Table 8]

[0057] All of the examples of the present disclosure that met the requirements of the present disclosure had superior corrosion resistance compared to the comparative examples.

Claims

1. A welded member including a welded portion where steel materials are welded, The welded portion includes a weld bead made of an alloy steel containing, by mass%, Cr: 9 to 30% and Ni: 3 to 25%; the steel material includes a steel base material and a zinc-containing plating layer on at least a surface of the steel base material on a side on which the weld bead is formed, a welded member, wherein the plating layer is formed on a surface of the steel base material on which the weld bead is formed, at a distance of 0.1 to 2.5 mm from the toe of the weld bead.

2. 2. The welded component of claim 1, wherein the steel base material is a steel plate.

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