JP2012081514A - Fillet arc welding method of galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high joint strength by stabilizing fillet arc welding of a high strength galvanized steel sheet, as cracks due to hydrogen embrittlement occurs even when a low temperature transformation welding material is used for the steel sheet, and a droplet transforming mode is unstable even when a flux-cored wire having high rates of Oand metal powder is used, in arc welding of a high strength galvanized steel sheet (pulse MAG welding, in particular).SOLUTION: In this fillet arc welding method of a galvanized steel sheet, welding wire components include: 0.15-0.5% C; 0.3-1.5% Si; 0.2-3.0% Mn; 0.1-0.4% SiO, AlO, TiO, NaO, and KO; 0.05-0.25% O; and the remainder being Fe. The flux-cored welding wire having a filling rate of 5-12% is used, and a cracking parameter (PcmS) of the steel sheet and a cracking parameter (PcmW) of the welding wire have the following relation: -0.86×PcmS+0.51≤PcmW≤-1.9×PcmS+1.0.

Description

  The present invention relates to welding of galvanized steel sheets used as structural members for automobiles and the like, and in particular, corners of galvanized steel sheets capable of obtaining good joint fatigue strength while preventing the occurrence of welding defects such as blow holes and pits. The present invention relates to a meat arc welding method (particularly, a pulse MAG welding method) and a welded joint thereof.

In recent years, in the automobile field, from the viewpoint of improving fuel consumption by reducing the weight of a vehicle body, the thickness of a steel material has been reduced by applying a high-tensile steel plate. Further, as the thickness of the steel material is reduced, there is a concern about the perforation of the steel material due to corrosion, and the application of a high-strength galvanized steel sheet is being studied from the viewpoint of preventing corrosion.
As the strength characteristics of the welded portion, it is necessary to ensure the fatigue strength of the welded joint. However, even if a high strength steel plate of 780 MPa class is used, for example, it is said that the joint fatigue strength can be ensured only as high as that of a mild steel of about 440 MPa. This is an issue of improving the joint fatigue strength of high-strength steel sheets.
Regarding the improvement of joint fatigue strength, the application of a low-temperature transformation welding material is known as a prior art. This technique lowers the martensitic transformation temperature of the weld metal, transforms and expands the weld metal on the low temperature side during cooling of the weld metal, and introduces compressive residual stress into the weld. (See Patent Document 1 and Patent Document 2)
In Patent Document 1, a welding material component that can be transformed at a low temperature is specified, and a flux component for reducing welding slag is proposed.
In Patent Document 2, the transformation temperature is reduced with a relatively low-cost alloy component, and the weld bead shape is improved and the joint fatigue strength is improved by applying pure Ar to the shielding gas at the time of welding.

  On the other hand, in arc welding of galvanized steel sheets, an increase in spatter during welding and blowhole defects in the weld are problematic because the joint strength is reduced (FIG. 1). That is, since a large amount of zinc plating evaporates due to heat input accompanying welding, the state of droplet transfer during welding becomes unstable and spatter 11 increases, and zinc vapor is mixed into the molten metal 14, thereby causing the blowhole 12. And pits 13 are generated. For example, Patent Document 3 and Patent Document 4 are known as techniques for reducing spatter and blow holes during galvanized steel sheet welding.

In Patent Document 3, the amount of oxygen (O ₂ ) in the shielding gas is increased as means for suppressing blowholes in pulse MAG welding, which is widely used in the automobile field as a welding method with relatively little spatter.

In Patent Document 4, a CO ₂ gas shielded arc using a metal-based flux-cored wire in which the O ₂ addition amount is 500 to 5000 ppm, the C addition amount is 0.15 to 0.35%, and the metal powder in the flux component is 70% or more. By welding, zinc vapor discharge from molten metal is promoted to reduce blowholes. However, when pulse MAG welding is performed using this welding material, there is a problem that the droplet transfer form becomes unstable and spatter increases.
In Patent Document 4, blowholes reduced by Ar + CO ₂ mixed gas shielded welding using flux-cored wire optimizing the metal system in the range of 2000~10000ppm the O ₂ amount in accordance with the coating weight of the galvanized steel sheet I am trying.

JP 2007-136547 A JP 2007-289965 A JP-A-10-258367 Japanese Unexamined Patent Publication No. 64-31596 JP-A-8-66792

  In pulse MAG welding of high-strength galvanized steel sheets, hydrogen embrittlement is likely to occur due to hardening of the weld metal even if joint fatigue strength is improved by lowering the transformation temperature of the weld metal as described in Patent Documents 1 and 2. This contributes to a decrease in joint fatigue strength. That is, even if a low-temperature transformation welding material is applied to a high-strength galvanized steel sheet to improve joint fatigue strength, there is a problem that cracks occur in the weld due to hydrogen embrittlement.

In addition, as described in Patent Documents 3 and 4, even if an attempt is made to reduce the blowhole and spatter of the weld by optimizing the amount of oxygen (O2) of the welding material component in pulse MAG welding, the present inventors As a result, in the method of Patent Document 3, the addition of a large amount of O ₂ causes the droplet transfer form to become unstable and an irregular bead with an uneven weld bead shape occurs. In the method of Patent Document 4, the droplet transfer form is unstable. In addition to the increase in spatter, it was confirmed that there was a problem that the weld bead shape was irregular because the oxygen content of the welding material was too high, as in Patent Document 3. In other words, a metal-based flux-cored wire with a high O ₂ content is used to suppress blowholes caused by galvanizing, and furthermore, a solidified slag covering the welded portion by increasing the ratio of metal powder in the flux component. Even if the reduction and promotion of blowhole discharge are promoted, an increase in spatter due to instability of the droplet transfer form becomes a problem.

  In order to solve the above problems, the present invention aims to realize high strength joint strength by stabilizing pulse MAG welding of a high strength galvanized steel sheet, particularly pulse MAG fillet welding, and to realize a welding material suitable for it. And

The inventors of the present invention have reported that cracking occurs during welding of a galvanized steel sheet by pulse MAG welding with a welding material component capable of low-temperature transformation and a metal-based flux-cored wire in which the amount of oxygen (O ₂ ) in the welding material component is increased. As a result of detailed analysis and examination of the state of occurrence of spatter and sputtering, hydrogen embrittlement is suppressed by adapting the cracking susceptibility index of the welding material according to the cracking susceptibility index of the base metal, and SiO in the flux-cored wire Stable liquid droplet transfer characteristics can be obtained by setting the slag agent components such as ₂ and Na ₂ O low and reducing the ratio of the slag agent and metal powder filled in the steel outer sheath of the welding wire. The headline and the present invention were made. The gist of the present invention is as follows.

(1) In fillet arc welding method (especially pulse MAG welding method) of galvanized steel sheet,
The component of the flux-cored welding wire that combines the outer sheath of the welding wire and the flux is mass%
C: 0.15-0.5%
Si: 0.3 to 1.5%,
Mn: 0.2 to 3.0%
0.1 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , TiO ₂ , Na ₂ O and K ₂ O,
O: 0.05-0.25%
Remaining Fe and unavoidable impurities,
Filling rate of metal powder and oxide filled in the outer sheath of the welding wire: 5 to 12%
The crack sensitivity index (PcmS) and the crack sensitivity index (PcmW) of the welding wire satisfy the following relationship, using a metal-based flux-cored welding wire: Fillet arc welding method for galvanized steel sheet.
−0.86 × PcmS + 0.51 ≦ PcmW ≦ −1.9 × PcmS + 1.0
(2) In the component of the welding wire, Ni: 0.5 to 5%
Cr: 0.1-3.0%
Among them, the fillet arc welding method for a galvanized steel sheet according to (1), comprising one or two of them.
(3) The galvanized steel sheet is a galvanized steel sheet having a plate thickness of 1.0 to 4.0 mm, a tensile strength of 440 to 980 MPa, and a zinc plating adhesion amount of 20 to 60 g / m ² per one surface of the steel sheet. Fillet arc welding of the galvanized steel sheet according to (1) or (2).
(4) In fillet arc welded joints (particularly pulse MAG welded joints) of galvanized steel sheets,
The component of the flux-cored welding wire that combines the outer sheath of the welding wire and the flux is mass%
C: 0.15-0.5%
Si: 0.3 to 1.5%,
Mn: 0.2 to 3.0%
0.1 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , TiO ₂ , Na ₂ O and K ₂ O,
O: 0.05-0.25%
Remaining Fe and unavoidable impurities,
Filling rate of metal powder and oxide filled in the outer sheath of the welding wire: 5 to 12%
The crack sensitivity index (PcmS) and the crack sensitivity index (PcmW) of the welding wire satisfy the following relationship, using a metal-based flux-cored welding wire: Fillet arc welded joint of galvanized steel sheet.
−0.86 × PcmS + 0.51 ≦ PcmW ≦ −1.9 × PcmS + 1.0

  According to the method for joining galvanized steel sheets according to the present invention, there is no occurrence of cracks in the weld due to hydrogen embrittlement even when arc welding (particularly pulse MAG welding) with a low-temperature transformation welding material is performed. Even with a high oxygen content welding material for suppressing generation, the droplet transfer mode is stable, and the occurrence of spatter can be suppressed. Thereby, in fillet welding of a galvanized steel sheet, a high-strength and high-quality welded joint with few defects can be obtained.

The figure which shows the outline | summary of a lap fillet joint. The figure which shows the relationship between a flux filling factor and the amount of sputtering. The figure which shows the outline | summary of the cross section of a lap fillet joint, and a hydrogen embrittlement crack. The figure which shows the relationship between the crack sensitivity of a steel plate, the crack sensitivity of a welding material, and the presence or absence of hydrogen embrittlement crack. The figure which shows the point of the fillet welding in an Example.

The details of the present invention will be described by way of an example of lap fillet pulse MAG welding of a galvanized steel sheet.
First, an appropriate welding material for reducing spatter during pulse MAG welding was examined. A flux-cored wire is manufactured by filling a steel powder with metal powder and an oxide, and the wire component is defined as a total value of the steel shell and a filling component. However, by adjusting the components of the steel outer sheath and the metal powder to be filled, flux-cored wires having the same wire component but different flux filling rates can be manufactured. The inventors of the present invention evaluated the pulse MAG of the galvanized steel sheet by paying attention to the flux filling rate, and found that the spatter can be reduced by setting the flux filling rate low. The examination results are shown below.

As a test steel material, a high-strength galvanized steel sheet obtained by subjecting a 780 MPa class steel sheet having a thickness of 2.3 mm to galvannealing with a galvanized coating amount of 45 g / m ² per side of the steel sheet was used. The welding material was a metal-based flux-cored wire and was evaluated by pulse MAG welding using Ar + 20% CO 2 gas. The joint type was a lap fillet joint as shown in FIG.

Alloy components in the flux are mainly composed of Fe, Si, and Mn, and oxide (slag agent) components in the flux are SiO ₂ and K ₂ O. The welding material composition including the welding wire shell and flux component is C: 0.35%, Si: 0.5%, Mn: 2.5%, Ni: 2.0%, Cr: 1.0% The oxide components were SiO ₂ : 0.2% and K ₂ O: 0.1%. The flux filling rate was changed in the range of 5 to 18% by adjusting the balance of the welding wire sheath and flux components. Further, the oxygen amount in the welding material was adjusted to be in the range of 1000 to 2500 ppm by changing the ratio of Fe and FeO added as flux components.

  FIG. 2 shows the amount of spatter generated when the flux filling rate of the welding wire is changed. In the welding of non-plated materials, even when the flux filling rate was increased, there was no significant increase in the amount of spatter, but in the welding of galvanized steel sheets, the spatter increased significantly when the flux filling rate exceeded 12%. Was confirmed. In pulse MAG welding, the droplet at the tip of the welding wire is moved to the base metal side in synchronization with the pulse current waveform. However, if the filling rate of the flux (metal powder) increases, the internal gas generated when the metal powder melts This is considered to be due to the fact that the molten form of the welding wire becomes unstable and the amount of heat input increases, so that the generation of zinc vapor at the time of welding is increased and the welding wire is easily affected. For this reason, the flux filling rate is desirably 12% or less.

On the other hand, if the flux filling rate is less than 5%, it is not practical because variations in the quality of the welding wire are likely to occur. Therefore, the lower limit of the filling rate is 5%.
That is, it has been found that by setting the flux filling rate to 5 to 12%, the droplet transfer form is stabilized and the amount of spatter can be kept low. In order to stabilize the droplet transfer form and reduce the amount of spatter, the flux filling rate is desirably 5 to 10%, and further 5 to 9%.

  Next, hydrogen embrittlement cracking in the weld zone, which is a problem when applying low temperature transformation welding materials, was examined. The low temperature transformation welding material is designed to have a high C equivalent in order to lower the martensitic transformation temperature. In conventional welding of non-plated steel sheets, hydrogen embrittlement cracking did not occur, but in welding of galvanized steel sheets, the root portion of the weld bead (the upper plate 31, the lower plate 32 and the weld metal in fillet welding of the steel plates). In some cases, cracks 33 occur in the boundary portion of the weld metal 14 on the opposite side of the weld metal 14 from the welding wire 15 (FIG. 3).

  In galvanized steel sheets, it is considered that moisture is likely to be adsorbed on the plating surface, and that diffusible hydrogen is likely to collect at the welded part because the plating layer becomes a barrier in the hydrogen release process after welding. Therefore, suppression of hydrogen cracking is an important issue in welding galvanized steel sheets. Therefore, cracks occurred in galvanized steel plate welds using the crack sensitivity index Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B as an index. The situation was investigated. Here, the crack sensitivity index of the steel sheet is PcmS, and the crack sensitivity index of the welding wire is PcmW.

  First, the crack occurrence state was investigated by changing the cracking sensitivity index PcmW of the welding wire in the range of 0.14 to 0.26. Note that 780 MPa class (PcmS = 0.19), 590 MPa class (PcmS = 0.26), and 440 MPa class (PcmS = 0.14) alloyed hot-dip galvanized steel sheets were used as the base material. The crack sensitivity index PcmS of each steel plate is 0.19, 0.26, and 0.14.

  The results are shown in FIG. In the case of a galvanized steel sheet, hydrogen embrittlement cracking occurred in a region where both the steel PcmS and the welding material PcmW were high. From the experimental results, it was derived that a relationship of PcmW ≦ −1.9 × PcmS + 1.0 is necessary to suppress hydrogen embrittlement.

On the other hand, in the region where the PcmW of the welding material is low, a sufficient low temperature transformation effect could not be obtained. From this experimental result, it was derived that the relationship of −0.86 × PcmS + 0.51 ≦ PcmW is necessary.
That is, if the relationship between the crack sensitivity (PcmW) of the welding wire and the crack sensitivity (PcmS) of the base material of the galvanized steel sheet is −0.86 × PcmS + 0.51 ≦ PcmW ≦ −1.9 × PcmS + 1.0 It has been found that hydrogen embrittlement cracking does not occur and a sufficient low temperature transformation effect is obtained.
In addition, when an unplated steel plate was used, hydrogen embrittlement cracking did not occur in any combination of steel plates and welding materials.

Next, the range of various components of the welding material will be described.
C: 0.15-0.5%
It is an important element for lowering the martensitic transformation point (Ms point) and achieving low temperature transformation of the weld metal. In order to obtain a low temperature transformation effect, 0.15% or more of carbon (C) is required. The lower limit of C is desirably 0.16%, and more desirably 0.18%.

  On the other hand, since C is an element having high hardenability and high cracking sensitivity, if it exceeds 0.5%, hydrogen embrittlement cracking is likely to occur during welding of the galvanized steel sheet, so the upper limit was made 0.5%. In order to suppress the occurrence of hydrogen embrittlement cracking as much as possible, the upper limit of C is desirably 0.48%, and more desirably 0.45% or less.

Si: 0.3 to 1.5%
In order to obtain the deoxidizing effect of the weld metal and the effect of smoothing the weld bead shape, the lower limit was made 0.3%. On the other hand, when Si exceeds 1.5%, the viscosity of the molten metal increases, and blowholes are likely to remain in the welded portion. For this reason, the upper limit was made 1.5%. Desirably, the lower limit is 0.5%, and the upper limit is 1.4%.

Mn: 0.2 to 3.0%
It is an element necessary for ensuring the strength of the weld metal, and the lower limit was 0.2%. Since excessive addition reduces the toughness of the weld metal, the upper limit was made 3%. Desirably, the lower limit is 0.5%, and the upper limit is 2.5%.

Ni: 0.5-5%
It is an effective element for lowering the transformation start temperature of the weld metal to improve the joint fatigue strength and improving the toughness of the weld metal. In order to obtain this effect, the lower limit was made 0.5%. On the other hand, if added excessively, the upper limit was made 5% in order to raise the transformation start temperature.

Cr: 0.1-3.0%
This has the effect of reducing the transformation start temperature of the weld metal and increasing the strength of the weld metal. In order to obtain this effect, 0.1% or more is necessary. On the other hand, if added excessively, the upper limit was made 3% in order to reduce the toughness of the weld metal.
Since both Ni and Cr have the effect of reducing the transformation start temperature and increasing the weld metal strength, the effect can be obtained by selectively adding either one or both.

Next, the flux component will be described.
One or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O, and K ₂ O: 0.1 to 0.4%
These oxide elements are called slag agents and act as arc stabilizers to ensure the workability in the process of drawing to a predetermined wire diameter in the welding wire manufacturing process and to stably generate a welding arc. To do. In order to obtain these effects, 0.1% or more in total of one or more of these oxides is required.

  On the other hand, excessive addition increases the solidification slag of the welded portion, so that the amount of spatter during welding of the galvanized steel sheet is increased and zinc vapor is difficult to escape. Desirably, the lower limit is 0.2%, and the upper limit is 0.3%.

O: 0.05-0.25%
By reducing the viscosity of the molten metal during welding and promoting the discharge of zinc vapor, there is an effect of reducing blowholes. In order to obtain this effect, 0.05% or more is necessary. On the other hand, excessive addition increases solidification slag, so the upper limit was made 0.25%. Desirably, the lower limit is 0.07%, and the upper limit is 0.18%.

  The galvanized steel sheet effective for the present invention is not limited to the above-described test material according to the present invention, and other than galvannealed steel, general galvanized steel, electroplated steel, galvanized steel For example, a Zn-Al-Mg-Si plated steel plate known as high corrosion-resistant plating can be used. If the steel plate has a plated layer containing zinc on the steel plate surface, the effect of the present invention can be obtained by applying the present invention. Obtainable. Further, the shape is not necessarily a plate, and a steel pipe and a steel plate can be combined.

Examples of the present invention are shown below. Table 1 shows steel plates used in the examples.
The steel plate was an alloyed hot-dip galvanized steel plate having a thickness of 2.3 mm (plating adhesion amount per side of 45 g / m 2), and the strength classes were 780 MPa class, 590 MPa class, and 440 MPa.

  Table 2 shows the components and crack sensitivity (PcmW) of the welding wire used. Each of the wire diameters is 1.2 mmφ, A to I are welding wires of the present invention, and J to Q are welding wires of comparative examples. P and Q were solid wires.

  As the welding power source, a pulse MAG welding power source was used, and lap fillet welding was performed as shown in FIG. The welding conditions were a torch height of 15 mm, a torch angle of 60 °, a welding current of 200 A, an arc voltage of 24 V, and a welding speed of 100 cm / min.

  Table 3 shows the results of the examples. No1 to No12 are the results of the present invention, and No13 to No23 are comparative examples. Evaluation items were presence / absence of hydrogen embrittlement cracking, spatter generation amount, joint fatigue strength, blowhole generation status, and slag adhesion amount on the weld bead surface.

  For hydrogen embrittlement cracking, the cross section of the weld bead was observed to check for cracks in the root portion of the weld bead.

  The spatter generation situation was compared by the sputter weight per unit time. The spatter generation amount of 3 g / min or less was judged to be good based on the spatter weight when using a solid wire.

  The joint fatigue strength was evaluated based on the stress amplitude of 2 million times in the repeated bending fatigue test of both swings. Fatigue strength of welded joints using conventional solid wires was about 210 MPa, 190 MPa, and 150 MPa for steel plates of 780 MPa, 590 MPa, and 440 MPa, respectively. did. That is, the case where the joint fatigue strength of 273 MPa, 247 MPa, 195 MPa or more was obtained for each of the 780 MPa class, the 590 MPa class, and the 440 MPa class steel sheet was determined to be good.

The state of blowhole occurrence was evaluated by X-ray transmission imaging of the weld bead and the ratio of the sum of the blowhole length to the weld bead length. By setting the blowhole ratio to 15% or less, the joint strength equivalent to the static strength of the base material is satisfied, so that the blowhole ratio is 15% or less.
The slag adhesion amount was evaluated by the slag generation amount with respect to the weld bead length of 250 mm, and the slag adhesion amount at the time of using the solid wire was 0.1 g or less.

  Hydrogen embrittlement cracks occur in the root part of the weld bead and reduce the static strength characteristics of the joint. Weld spatter is generated in the welding process, and if it adheres to the periphery of the welding equipment or weld, it is necessary to remove the spatter, which reduces productivity. Fatigue cracks in the joint occur at the toe of the weld bead and reduce the durability of the joint. The blow hole is generated at the root portion of the weld bead and deteriorates the static strength characteristic of the joint. The weld slag adheres to the surface of the weld bead and reduces the adhesion of the anticorrosive paint, thus reducing the corrosion resistance of the welded member. Since these items are all important items in the quality and productivity of the joint, the case where all these items are satisfied was regarded as the present invention.

No. Since No. 13 was designed with a low weld wire crack PcmW, the joint fatigue strength decreased as a result of the high martensitic transformation temperature. No. No. 14 had high PcmW and cracks occurred. No. Although PcmW of 15 is an appropriate range, since PcmS of the steel plate is high, cracks occurred in this combination. No. Since the total amount of slag agent in the wire 16 was high, the slag of the weld bead also increased. No. In No. 17, since the total amount of slag agent was low, the arc became unstable and spatter increased. No. Since No. 18 has a high flux filling rate to the wire, the pulse arc weldability was lowered and the spatter increased. No. In No. 19, since the amount of oxygen in the wire was small, the ability to discharge blowholes from the molten metal decreased, and the blowhole rate increased. No. In No. 20, since there was a lot of oxygen gas in the welding wire, oxidation of the molten metal progressed and slag increased.
In addition, No. 14, no. 15, no. No. 19 has a high fatigue strength despite the occurrence of hydrogen embrittlement cracks and blowholes in the weld bead. This is because a test was conducted for the purpose of fatigue evaluation of the weld toe where fatigue cracks are likely to occur in actual members.
No. 21, no. 22, no. Although 23 is a conventional solid wire, the joint fatigue strength is low, and the blow blow hole rate is also increased.

  As mentioned above, although this invention was demonstrated in detail including the Example, it cannot be overemphasized that embodiment of this invention is not limited to embodiment described above.

  The present invention can be used in any industry that uses arc welding of a galvanized steel sheet.

Claims (4)

In the fillet pulse MAG welding method of galvanized steel sheet,
The component of the flux-cored welding wire that combines the outer sheath of the welding wire and the flux is mass%
C: 0.15-0.5%
Si: 0.3 to 1.5%,
Mn: 0.2 to 3.0%
0.1 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , TiO ₂ , Na ₂ O and K ₂ O,
O: 0.05-0.25%
Remaining Fe and unavoidable impurities,
Filling rate of metal powder and oxide filled in the outer sheath of the welding wire: 5 to 12%
The crack sensitivity index (PcmS) and the crack sensitivity index (PcmW) of the welding wire satisfy the following relationship, using a metal-based flux-cored welding wire: Fillet arc welding method for galvanized steel sheet.
−0.86 × PcmS + 0.51 ≦ PcmW ≦ −1.9 × PcmS + 1.0 In the components of the welding wire, Ni: 0.5 to 5%
Cr: 0.1-3.0%
The fillet arc welding method for galvanized steel sheet according to claim 1, wherein one or two of them are contained. The galvanized steel sheet is a galvanized steel sheet having a thickness of 1.0 to 4.0 mm, a tensile strength of 440 to 980 MPa, and a galvanized coating amount of 20 to 60 g / m ² per one surface of the steel sheet. Or fillet arc welding of the galvanized steel sheet according to 2; In fillet pulse MAG welding joint of galvanized steel sheet,
The component of the flux-cored welding wire that combines the outer sheath of the welding wire and the flux is mass%.
C: 0.15-0.5%
Si: 0.3 to 1.5%,
Mn: 0.2 to 3.0%
0.1 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , TiO ₂ , Na ₂ O and K ₂ O,
O: 0.05-0.25%
Remaining Fe and unavoidable impurities,
Filling rate of metal powder and oxide filled in the outer sheath of the welding wire: 5 to 12%
The crack sensitivity index (PcmS) and the crack sensitivity index (PcmW) of the welding wire satisfy the following relationship, using a metal-based flux-cored welding wire: Fillet arc welded joint of galvanized steel sheet.
−0.86 × PcmS + 0.51 ≦ PcmW ≦ −1.9 × PcmS + 1.0

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