JP2010120022A - Fillet arc welding method of thin steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fillet arc welding method of a thin steel sheet, in which a weld toe shape is excellent even in the case of a welding speed of >80 to ≤150 cm/min and fatigue characteristic of a weld joint can be enhanced. <P>SOLUTION: In this welding method, fillet arc welding of a steel sheet having a thickness of 1.6-6 mm is performed by gas shield arc welding at a welding speed of >80 to ≤150 cm/min using a flux cored wire, wherein the steel sheet and the flux cored wire for the arc welding are combined so as to satisfy äSi(steel sheet)+0.1×Si(wire)}≥0.32. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fillet arc welding method for a thin steel plate. More specifically, the toe shape of a fillet arc welded joint produced by gas shielded arc welding is improved, and the fillet arc welded joint The present invention relates to a fillet arc welding method for thin steel sheets, which can improve fatigue characteristics.

  Preferred target members to which the present invention can be applied include vehicle body structural members of automobiles, particularly suspension parts that are important safety parts. The undercarriage part of an automobile is a strength member, and the thickness is almost 1.6 to 6 mm. Therefore, the thickness range targeted by the present invention is set to 1.6 to 6 mm. In addition, the welding speed targeted by the present invention is set to a range of more than 80 cm / min and not more than 150 cm / min as a range of the welding speed that does not reduce the manufacturing efficiency of the suspension part.

  In gas shielded arc welding in the automotive industry field and the like, the welding speed is usually set higher than in other industrial fields in order to improve the efficiency of the production line. Generally, it is 60 cm / min or more, and is often set to 100 cm / min or more.

  The reason why arc welding at such a high welding speed is possible is that the plate thickness of the steel plate used in the automobile industry is often 6 mm or less, for example, even in the case of a suspension part having a relatively large plate thickness. This is because it is usually 4 mm or less in many cases. That is, because the plate is thin as described above, a predetermined joint strength can be ensured even if the amount of welding in arc welding is small. In addition, if the plate thickness is as thick as over 6 mm, if arc welding is performed at a welding speed of 60 cm / min or more so as to secure a welding amount necessary to obtain a predetermined joint strength, it is only that The welding current and welding voltage must be increased, which increases the risk of adversely affecting the weld bead shape. Thus, it can be said that arc welding in the automotive industry field has a higher welding speed than other industries.

However, under such arc welding conditions of high welding speed, the weld bead shape, particularly the shape of the weld toe, deteriorates, that is, the flank angle (see FIG. 2) of the weld toe increases. As a result, stress concentration is caused at the weld toe, and the problem is that the fatigue strength of the welded joint decreases. The reason that the weld bead shape deteriorates at a high welding speed is that the faster the welding speed, the longer the molten pool becomes, and the molten metal tends to solidify before it spreads sufficiently. On the other hand, recently, due to increasing interest in the global environment, reduction of CO ₂ emissions by improving fuel efficiency has become an urgent issue even in the automobile industry. Reducing the weight of the automobile itself is an effective means for improving fuel efficiency, and reducing the thickness of the steel sheet forming the automobile can be an effective means. However, the reduction in the thickness of the steel sheet means an increase in the stress applied to the steel sheet, and the increase in stress causes not only a problem of static strength but also a problem of fatigue strength. That is, there is a problem that even if the static strength is sufficient, the plate thickness is reduced, that is, the weight cannot be reduced from the viewpoint of fatigue strength.

  In general, it is said that the fatigue strength of a welded joint has almost no material dependence and is governed by mechanical factors such as stress concentration determined by the weld bead shape and residual stress in the weld. In addition, as described above, since improvement in production efficiency and securing of fatigue strength are often contradictory to each other, the weld toe is used as a means for improving the shape of the weld toe at high welding speeds and as means for improving the fatigue strength of welded joints. There have been adopted methods such as smoothing by finishing or applying a compressive residual stress to the weld toe by shot peening or the like. These are so-called post-processes and are not preferable because they increase manufacturing costs.

  On the other hand, as one of the means for solving the fatigue problem of welded joints, a method of improving the fatigue strength by designing the components so that the transformation temperature of the welding material is lowered and reducing the residual stress at the weld toe is proposed. (See Patent Documents 1 and 2. Hereinafter, such a welding material is referred to as a high fatigue strength welding material.) Although this method defines the components of the welding material, it is a method of controlling mechanical factors in the sense of reducing the residual stress, and a high fatigue strength joint can be obtained simply by changing the welding material. It can be said that this is a good method.

  In addition, as disclosed in Patent Documents 3 and 4 and Non-Patent Document 1, there is a technique for widening the weld bead shape by limiting the components of the welding material and the steel plate. For example, the technique disclosed in Patent Document 3 and Non-Patent Document 1 is a technique of adding S to more than 0.1% and not more than 0.6%, thereby reducing the surface tension of the molten pool to form a weld toe shape. It is a technology that improves The technique disclosed in Patent Document 4 is a technique for adjusting the sum of Si and Mn of a steel sheet.

  Patent Documents 5 to 9 disclose techniques relating to steel sheets having excellent fatigue strength.

  Among these conventional techniques, even when the high fatigue strength welding materials described in Patent Documents 1 and 2 are used, there is no guarantee that a fatigue improvement effect can be sufficiently obtained if the toe shape of the welded joint deteriorates. This is because, among the residual stress and stress concentration, which are the two major factors governing the fatigue strength of the joint, the high fatigue strength welding material is a technique that focuses on the residual stress and does not aim to improve the stress concentration. Even if one of the two major factors of fatigue strength is improved, if the other deterioration is severe, it is not known whether the fatigue strength is improved. Therefore, when using a high fatigue strength welding material, it must be limited to a welding condition range that does not deteriorate the bead shape. In the automobile industry and the like, as already described, welding is performed at a higher welding speed than other industries, and there is a strong need for welding at a higher speed. As the welding speed is increased in accordance with the needs, the bead shape is disturbed, which is not preferable from the viewpoint of improving the fatigue strength.

  Moreover, all of the techniques described in Patent Documents 3 and 4 and Non-Patent Document 1 are techniques aimed at making the weld bead width wider than that of the conventional technique. The weld bead width can certainly be a convenient index for representing the overall shape of the weld joint, but its fatigue strength largely depends on the shape of the weld toe that is the stress concentration portion. That is, there is a tendency peculiar to fatigue strength that is not present in static strength, in which the shape of a part of the welded joint determines the characteristics of the entire welded joint. Therefore, in order to improve fatigue strength, it is necessary to pay attention to the shape of a part of the welded joint called the weld toe shape rather than the characteristic of the entire welded joint called the weld bead width. The techniques disclosed in Patent Documents 3 and 4 and Non-Patent Document 1 are suitable for improving the static strength, that is, the tensile fracture strength of the welded joint. Not clear.

  Moreover, all the prior arts described in Patent Documents 5 to 8 relate to the fatigue strength of the base material. Since it is said that the fatigue strength of the steel material is proportional to the static strength of the steel material because there is no stress concentration portion, these techniques are not necessarily effective techniques for improving the fatigue strength of the welded joint.

  Further, Patent Document 9 discloses a technique related to fatigue strength of a weld heat affected zone (also referred to as heat-affected zone, HAZ), but the welded joint being taken up is a butt welded joint. Stress concentration is not as high as fillet arc welded joints. By the way, most of automobile underbody parts and the like are manufactured by fillet arc welding. From this, it is clear whether or not the technique described in Patent Document 9 can improve the fatigue strength of a structure having a fillet arc welded joint that is frequently used in the automotive industry and the like and has a high stress concentration. Absent.

  The techniques disclosed in the prior arts described in Patent Documents 5 to 9 relate to the fatigue strength of a base material without a welded joint or the fatigue strength of a butt joint having a relatively small stress concentration. In an actual structure, a fatigue crack is generated from the place where the stress concentration is the largest, and this determines the fatigue strength of the entire structure. That is, unless the fatigue strength of the lap fillet joint having a higher stress concentration than the butt joint is improved, the fatigue of the structure will not be improved.

  As described above, in the range of the prior art, there are still many problems to be improved in order to perform high-speed welding and improve joint fatigue strength.

JP 11-138290 A JP 2004-001075 A JP 2002-361480 A JP 2007-177279 A JP 2004-143518 A JP 2000-248330 A JP-A-11-189842 JP 07-316649 A JP 2003-003240 A JP 2007-136547 A Outline of National Welding Society Conference Lecture, 2007, Vol. 81, pp 236-237

  Against such a background, the fillet of the steel sheet in which the toe shape of the fillet arc welded joint is good even when the welding speed is high, specifically, when the welding speed of more than 80 cm / min and not more than 150 cm / min is set. An arc welding method has been desired.

  Therefore, in view of these problems of the prior art, the present invention provides a good shape of the weld toe even when the welding speed is more than 80 cm / min and not more than 150 cm / min in gas shielded arc welding, and fillet arc welding. An object of the present invention is to provide a fillet arc welding method for a thin steel sheet, which can improve the fatigue characteristics of a joint.

  From the above viewpoint, the present inventors have focused on the welding speed, the steel plate, and the welding wire component, and have intensively studied the influence of the weld toe shape. And among steel plates and welding wires, it has been found that the shape of the weld toe can be improved even when the welding speed is more than 80 cm / min and not more than 150 cm / min by limiting the amount of Si. The present inventors have also found a relationship between the amount of Si contained in the steel sheet and the amount of Si contained in the welding wire, where the shape improvement effect is manifested. This invention is made | formed by such a research, The summary is as follows.

(1) Fillet arc welding of a thin steel plate having a thickness of 1.6 to 6 mm is performed by gas shielded arc welding with a welding speed of 80 cm / min or more and 150 cm / min or less using a flux-cored wire. In the arc welding method,
The thin steel sheet, in mass%,
C: 0.001 to 0.15%,
Si: 0.2-2.0%,
Mn: 0.5 to 2.5%
P: 0.03% or less,
S: 0.02% or less, consisting of the balance iron and inevitable impurities, and a thin steel plate having a tensile strength of 280 MPa class to 600 MPa class,
The flux-cored wire,
A flux-cored wire for gas shielded arc welding in which a slit-like seamless steel outer shell with a risk of intrusion of outside air is filled with flux,
In one or both of the steel sheath and flux, the total mass% of the entire wire,
C (excluding C in SiC): 0.01 to 0.20%,
Si (excluding Si in SiC and SiO ₂ ): 0.05 to 1.2%
Mn: 0.2 to 2.5%
P: 0.03% or less,
S: 0.08% or less,
Further, as a flux filled in the steel outer sheath, it contains SiC: 0.05 to 1.2% by mass% of the whole wire, and includes SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O. 1 type or 2 types or more in total containing 0.05 to 0.4%,
The balance is a flux-cored wire for arc welding consisting of iron and inevitable impurities,
Furthermore, the corner of the thin steel sheet, characterized in that the thin steel sheet and the flux-cored wire for arc welding are combined so that the total Si amount defined by the following (formula 1) is 0.32 or more. Meat arc welding method.
Total Si amount = Si (steel plate) + 0.1 × Si (wire) (Equation 1)
However, Si (steel plate) represents the Si amount of the thin steel plate, and Si (wire) represents the total Si amount of the flux-cored wire for arc welding.

  (2) Said (1) characterized by combining said thin steel plate and said flux-cored wire for arc welding so that the value of total Si amount of said (Formula 1) may be 0.40 or more. Fillet arc welding method for thin steel sheets.

(3) The thin steel sheet is further in mass%,
Al: 0.005 to 0.1%
The fillet arc welding method for a thin steel sheet according to the above (1) or (2), characterized by comprising:

(4) The thin steel sheet is further in mass%,
Ti: 0.005 to 0.1%,
Nb: 0.005 to 0.1%,
V: 0.01-0.2%
Cr: 0.1 to 1.0%,
Mo: 0.05-0.5%
The fillet arc welding method for thin steel sheets according to any one of the above (1) to (3), comprising any one or more of the above.

(5) The flux-cored wire for arc welding is a mass% of the whole wire, and further contains graphite: 0.02% or more as a flux filled in the steel outer sheath, and the following (formula 2) It is a flux-cored wire for arc welding whose total amount of C conversion value defined is 0.20 to 0.45%, Any one of said (1) thru | or (4) characterized by the above-mentioned. Fillet arc welding method for thin steel sheet.
Total amount of C conversion value = [graphite] + 0.3 × [SiC] (Formula 2)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.

(6) The flux-cored wire for arc welding is, in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
Ni: 0.1 to 5.0%,
Cr: 0.1 to 2.0%,
Mo: 0.1 to 2.0%,
Cu: 0.1 to 0.5%
The fillet arc welding method for a thin steel sheet according to any one of (1) to (5) above, wherein one or more of the above are contained in a total of 0.1 to 6.0% .

(7) The flux-cored wire for arc welding is, in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
B: 0.001 to 0.015%
The fillet arc welding method for a thin steel sheet according to any one of the above (1) to (6), characterized by comprising:

  (8) The flux-cored wire for arc welding is 0.005 in total of one or more of Nb, V, and Ti in one or both of the steel outer sheath and the flux in the mass% of the whole wire. The fillet arc welding method for thin steel sheets according to any one of the above (1) to (7), characterized by comprising -0.3%.

(9) The flux-cored wire for arc welding is, in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
S: more than 0.02 to 0.08%
The fillet arc welding method for a thin steel sheet according to any one of the above (1) to (8), characterized by comprising:

  (10) The flux-cored wire for arc welding contains 0.05 to 0.5% of an arc stabilizer other than an oxide based on the mass% of the whole wire as a flux filled in the steel outer sheath. The fillet arc welding method for a thin steel sheet according to any one of (1) to (9) above, characterized in that:

(11) As a shielding gas for the gas shielded arc welding, in mass%,
CO ₂ : 5% or more and 25% or less,
O ₂ : 4% or less (including 0%)
The fillet arc welding method for a thin steel sheet according to any one of (1) to (10) above, wherein a shielding gas comprising the remainder Ar and inevitable impurities is used.

  According to the present invention, even when the welding speed is more than 80 cm / min and not more than 150 cm / min, the shape of the weld toe becomes smooth, the stress concentration at the weld toe can be reduced, and the fatigue strength of the welded joint can be reduced. Can be improved. In particular, the fillet arc welding method for thin steel sheets provided by the present invention is particularly effective not only in the automobile industry but also in industrial fields where there is a strong need for increased welding speed, and is a technology that can achieve both productivity improvement and fatigue strength improvement. Therefore, the industrial significance is extremely large.

  The present invention is described in detail below.

  First, the fatigue characteristics of the welded joint, which is the subject of the present invention, will be described.

  Unlike fatigue strength, metal fatigue is a phenomenon that breaks in a state where stress within an elastic range is applied. Stress is repeatedly applied, and the number of repetitions determines the fatigue life. In general, if a fracture does not occur even when a stress is repeatedly applied 2 million times or more, the applied stress at that time is called fatigue strength. Metal fatigue is a phenomenon that breaks due to an applied stress within the elastic range, and thus is often different from static strength. For example, static strength is not significantly affected by stress concentration or residual stress existing in a welded joint. Even if the grinder finish of the weld toe is extremely effective in improving fatigue strength, the static strength is almost unchanged. This is because static strength is accompanied by plastic deformation. Even if there is a stress-concentrated part such as a weld toe, only plastic strain occurs in that part, and from the standpoint of static strength, the part other than the stress-concentrated part only bears the strength. The strength of the joint as a whole is maintained. Also, even if tensile stress already exists in some parts, such as residual stress, considering the self-equilibrium characteristic of residual stress, there is always compressive residual stress that cancels the tensile residual stress. Even if the yielding state is reached immediately in the tensile residual stress portion, the yielding state is not reached in the compressive residual stress portion, so this portion bears the static strength. For this reason, static strength is not influenced by these factors in the entire welded joint. Therefore, the shape of the entire weld bead, such as the weld bead width, is important for static strength.

  On the other hand, the fatigue strength of a welded joint is a phenomenon in which the characteristics of the entire welded joint are determined by a very small stress state of the welded joint. The portion where the fatigue crack occurs is a weld toe portion where stress concentration is high. There is also a tensile residual stress. As described above, the residual stress is self-equilibrium, and a compressive residual stress that cancels out this tensile residual stress always exists inside the welded joint. However, since the fatigue strength is determined by a small part of the stress state of the welded joint, even if a compressive residual stress is present, this compressive residual stress will be the fatigue strength if it does not exist at the place where the fatigue crack occurs. Does not affect. This trend is also true for stress concentrations. That is, even if the welded joint as a whole has a smooth shape, if there is a part where stress concentration is high in part, the fatigue strength of the welded joint as a whole is determined. Therefore, rather than improving the overall shape of the welded joint such as the weld bead width, improving the local shape, such as improving the weld toe flank angle, contributes to improving fatigue strength. In this sense, it is unclear whether the techniques disclosed in Patent Documents 3 and 4 and Non-Patent Document 1 are effective in improving the shape of the weld toe portion that contributes to improving fatigue strength.

  As described above, the technique for widening the weld bead width and the technique for narrowing the flank angle of the weld toe are not necessarily the same. The present invention provides a technique aimed at improving the shape of the weld toe, and its purpose is to improve the fatigue strength of the welded joint. As for static strength, since it does not depend on stress concentration or residual stress, it can be sufficiently ensured unless there is a defect in the welded joint. In the scope of the present invention, such a welded joint defect is generated. There are no such factors.

  In addition, in order to achieve fatigue strength improvement, this invention also utilizes the knowledge of the high fatigue strength welding material which is a prior art. Until now, high-fatigue-strength welding materials have not always had a good bead shape at high-speed welding, and it has been far preferable to use limited welding conditions to improve fatigue strength. In this case, the present inventors have positively utilized both of the two major factors of fatigue strength, namely stress concentration relaxation and residual stress reduction.

  In general, the material factors that determine the weld bead shape including the weld toe shape include the surface tension of the molten pool and the gravity acting on the molten metal, and the weld bead shape is determined by the mechanical balance between these factors. I came. The surface tension of the molten pool is affected by its chemical components, such as C, Si, S, O, and the like. Therefore, it has been considered that appropriately controlling these elements has an effect on improving the weld bead shape. From this point of view, the surface tension may be lowered in order to reduce the flank angle of the weld toe, but this also brings about the effect of widening the weld bead width as it is. Therefore, the technique for increasing the weld bead width and the technique for increasing the contact angle of the weld toe portion tend to be identified. As described above, it is preferable to reduce the flank angle of the weld toe for improving the fatigue strength. However, according to the conventional idea, this is also a technique for widening the weld bead width. In particular, considering that the surface tension of the molten pool is determined by its components, it does not matter whether each component is supplied from the steel plate or from the welding material. If it falls within the predetermined range, the weld bead shape can be improved.

  From the prior art, as described above, the component range of the molten pool becomes a problem. For example, when the S component of the steel sheet is insufficient, the problem can be solved by supplementing it with the welding material. This means that one of the components of the steel plate and the molten material can be supplemented with the other component. However, in the present invention, as described later, a phenomenon in which such a steel plate component cannot be supplemented with a welding material is used.

  From the above viewpoints, the present inventors have made extensive studies on factors that determine the shape of the weld toe after the welding speed is limited to more than 80 cm / min and not more than 150 cm / min. As a result, it was found that the Si amount of the steel plate greatly affects the weld toe shape. The influence of the Si content of the steel sheet is not limited to the influence on the weld metal component due to dilution. If this is the case, the same result should be obtained even if the Si amount of the welding wire is adjusted according to the dilution rate, but it can be obtained only by adjusting the Si amount in the welding wire as described later. No effect.

Although it is not necessarily clear why the Si amount of the steel sheet is essential and why the same effect cannot be exhibited by simply supplementing with the addition from the wire, a possible interpretation is described here.
As a possible interpretation, the present inventors consider the temperature distribution of the molten metal that determines the electron emission from the steel sheet and the surface tension of the molten metal. Generally, when gas shield welding is performed using a welding wire, the wire is set as a positive electrode and the steel plate is set as a negative electrode. This is because an electron collision occurs in the wire, and the wire melting becomes more efficient and the wire supply can be increased. In order for electrons to move from the steel plate to the wire, the steel plate needs to emit electrons. The ease of electron emission is a characteristic that does not depend on the wire component but depends only on the steel plate component. The present inventors consider that there is Si in the steel sheet as a component that makes electron emission from this steel sheet a preferable condition for the bead shape. That is, the interpretation is that the electron emission behavior when Si within the scope of the present invention is added to the steel sheet affects the temperature distribution of the molten pool, and the surface tension determined by the temperature distribution forms a preferred bead shape. Regarding the surface tension, there is Etebeche's law, and it can be seen that the surface tension strongly depends on the temperature of the material in addition to the material itself. So far, studies have been made on the surface tension and bead shape of the molten pool, but the component system of the molten pool has been discussed as a factor that determines the surface tension itself, but it is caused by the electron emission of the steel sheet. Little is discussed about the temperature distribution in the molten pool. In addition, the bead shape improvement effect by such a mechanism is not dependent on the wire component, so even for materials that have not been recognized as having a good bead shape, such as high fatigue strength welding materials. Applicable.

  The present inventors have further clarified the relationship between the appropriate Si amount of the steel sheet and the Si amount of the welding wire. That is, as the amount of Si in the welding wire increases, the minimum amount of Si in the steel sheet necessary to improve the weld toe shape tends to decrease. However, when Si is not added to the steel plate, the shape of the weld toe is not improved under the high-speed welding conditions even if the Si content of the welding wire is increased. As measures for improving the weld toe shape in this case, it is necessary to sacrifice production efficiency such as a welding speed of 80 cm / min or less.

  FIG. 1 is a diagram explaining this. Fig. 1 plots the Si content of the flux-cored wire for welding on the horizontal axis and the Si content of the steel plate on the vertical axis. Among fillet arc welding, it is the most commonly used stacking fillet for automobile undercarriage parts. It is the figure which showed the state of the welding toe shape when performing arc welding. Since there are some definitions of the flank angle, FIG. 2 shows the definition of the flank angle in the present invention. In FIG. 2, the flank angle 3 defines the angle on the weld metal side as the flank angle among the angles formed by the tangent line of the weld bead 4 where the steel plate 1 and the steel plate 2 are welded and the extension line of the steel plate surface. . Depending on the literature, using the flank angle of FIG. 2, the angle represented by (180 ° -flank angle), that is, the angle formed by the tangent line of the weld bead and the extension line of the steel plate surface, the opposite side of the weld metal. In the present invention, the angle in FIG. 2 is defined as the flank angle. FIG. 1 shows a distinction between the case where the flank angle is 55 ° or less and the case where the flank angle exceeds the flank angle. Lap fillet arc welding was performed by preparing a steel plate having a thickness of 3.2 mm and performing welding at a welding speed of 100 cm / min. A cross-section macro specimen was taken from the welded joint, and the flank angle at that time was measured according to FIG. 1 indicates that the flank angle is 55 ° or less, and ● in FIG. 1 indicates that the flank angle is greater than 55 °. The flank angle and fatigue strength have a good correlation, and FIG. 3 is a conceptual diagram illustrating this relationship. This plots the flank angle on the horizontal axis and the fatigue strength on the vertical axis, and indicates that when the flank angle is A, the fatigue strength is A '. When the flank angle is changed from B to A, the fatigue strength changes from B 'to A'. Since the relationship between the flank angle and the fatigue strength is represented by a straight line (or curve) that goes down from the upper left to the lower right as shown in FIG. 3, reducing the flank angle may have an effect of improving the fatigue strength. Recognize. Conversely, when the design fatigue strength of the welded joint is determined, the upper limit of the flank angle is naturally determined.

  In the fillet arc welding method for steel sheets according to the present invention, the upper part of the boundary line in FIG. The flank angle tends to be smaller as the position becomes higher. Note that even if the welding speed is set to 80 cm / min or less even under conditions outside the scope of the present invention, the flank angle is gradually reduced, that is, the weld toe shape is improved. Therefore, in the present invention, the welding speed is 80 cm / min. The condition below min is excluded.

  Next, the reason for limiting the plate thickness of 1.6 to 6 mm in the present invention will be described.

  The present invention deals with a technique limited to gas shielded arc welding using a flux-cored wire for welding. Therefore, the plate thickness range, particularly the lower limit, is limited to 1.6 mm. The reason for this was set for steel sheets thinner than 1.6 mm because spot welding and laser welding are often used rather than arc welding. The upper limit of the plate thickness was set to 6 mm. This is because it is extremely difficult to make the welding speed higher than 80 cm / min when trying to weld by 1-pass welding for a plate thickness exceeding 6 mm. The present invention intends to provide a technique aiming at improving the welding efficiency and improving the fatigue characteristics by improving the weld toe shape. Therefore, the range in which the condition where the welding speed exceeds 80 cm / min is difficult is not handled in the present invention.

  Next, the reason why the components of the steel plate are limited in the fillet arc welding method of the thin steel plate will be described.

  If C is less than 0.001%, it is difficult to ensure strength, so this is the lower limit. On the other hand, if added over 0.15%, the amount of carbide formed increases and the hole expandability deteriorates, so the upper limit was set to this value.

  Mn is an element added to increase the strength of steel. However, excessive addition causes deterioration of ductility, so the upper limit is made 2.5%. On the other hand, addition of 0.5% or more is necessary to ensure strength.

  In the present invention, S is an impurity. An A-based inclusion (JIS G0555) is formed by bonding with Mn and deteriorates not only the hole expandability but also the ductility, so 0.02% is made the upper limit. In addition, making it lower than 0.0005% raises the cost in steelmaking significantly. Therefore, it is preferable to set 0.0005% as the lower limit.

  P is also an impurity in the present invention. When the P content is increased, not only the ductility is lowered but also the secondary workability is deteriorated, so the upper limit is set to 0.03%.

  Next, the reason why Si of the steel plate is limited will be described.

  The point of limiting the amount of Si in the steel sheet is the basis of the present invention. As already stated, it is still unclear how Si in the steel plate functions. However, the function of Si in the steel sheet described in the present invention is different from the function of affecting the amount of Si in the weld metal through the base material dilution. For example, when the base metal dilution ratio is 35%, when the Si amount of the welding wire is 0.7% and the Si amount of the steel sheet is 0.4%, the Si amount of the weld metal is 0.7%. % × 0.65 + 0.4% × 0.35 = 0.595% can be estimated. If the base metal dilution rate is the same when the Si of the steel plate is 0%, to obtain the same weld metal, the Si amount of the welding wire is 0.595% ÷ 0.65 = 0. 915% would be enough. In this case, the weld metal is the same Si, but the weld toe shape is not the same. When the steel sheet Si content is 0.4%, the weld toe shape is improved. Such a phenomenon has not been known so far. However, such a phenomenon occurs when the welding speed exceeds 80 cm / min. Such a phenomenon cannot be confirmed at 80 cm / min or less. The lower limit of the Si content, 0.2%, is less than this, and the steel toe shape does not become smooth regardless of the Si content of the welding wire under high welding speed conditions. This value was set because the welding speed had to be sacrificed. The upper limit of 2.0% was set to this value because the improvement of the weld toe shape would be saturated even if addition exceeding the upper limit was performed.

  Next, the reason for limiting the relationship between the Si amount of the steel sheet and the total Si amount of the welding wire will be described.

  As described above, the function of Si in the steel sheet is different from the function of adjusting the Si amount of the weld metal. In general, it has been said that Si affects the viscosity and surface tension of molten iron and, through this function, affects the shape of the weld toe. However, when Si is not added to the steel sheet, the effect of improving the weld toe shape is not seen. However, this is a case where the welding speed is a high welding speed exceeding 80 cm / min. That is, when the welding speed is not so high, the weld toe shape can be controlled by improving the viscosity, surface tension, etc., but it is considered that the control becomes difficult as the welding speed increases. However, when the welding wire Si amount changes, the minimum steel plate Si amount necessary for improving the weld toe shape also changes. Therefore, the relationship between the Si amount of the steel sheet and the Si amount of the welding wire is limited. That is, if it can be satisfied that the value of the total Si amount defined by the following (formula 1) is 0.32 or more, the weld toe shape can be improved.

Total Si amount = Si (steel plate) + 0.1 × Si (wire) (Equation 1)
That (Formula 1) is 0.32 or more must be satisfied regardless of the base material dilution. This is because the present invention is not a technique that simply uses component adjustment of the weld metal. In FIG. 1, a straight line of (Equation 1) = 0.32 is drawn. As can be seen from FIG. 1, when the value of (Expression 1) is 0.32, the flank angle is 55 ° or less. The lower limit 0.32 of (Equation 1), which is determined by the Si amount of the steel sheet and the Si amount of the welding wire, is less than this value, so that the shape improvement effect of the weld toe cannot be obtained at a high welding speed. It was set. In addition, although the upper limit is not specifically defined, the range is naturally limited from the upper limit value of the Si amount of the steel plate and the welding wire. The value of (Equation 1) is determined by the Si amount of both the steel plate and the welding solid wire, and the respective Si amounts cannot be determined independently, but those skilled in the art can easily determine them. This is not a problem.

  In the fillet arc welding method for thin steel sheets in the present invention, the value of (Equation 1) is further limited so that the weld toe shape can be improved more reliably.

  As a method of securing the value of (Formula 1), there are a method of securing with the Si amount of the steel sheet and a method of securing with the Si amount of the flux-cored wire for welding. In (Equation 1), since the coefficient of the steel sheet Si amount is large, it seems that the method of securing with a steel sheet seems to be excellent. However, in general, the weight of a steel sheet is about 100 times that of a weld metal in a welded structure. Therefore, it is often economically preferable to secure the value of (Formula 1) with a solid wire for welding even when the coefficient of the steel sheet Si amount of (Formula 1) is large. However, in addition to the effect of improving the weld toe shape which is an object of the present invention, when Si is added to the steel sheet, it is not always necessary to sufficiently add Si to the welding solid wire. Therefore, the amount of Si in the welding solid wire is limited by the amount of Si in the steel plate to ensure the value of (Equation 1). That is, if the value of the total Si amount in (Equation 1) is 0.40 or more, the flank angle is further reduced. The upper limit is determined by the amount of Si in both the steel plate and the welding solid wire. FIG. 1 also shows a line when the value of (Equation 1) is 0.40, but it can be seen that the region is shifted upward as compared with the case where the value of (Equation 1) is 0.32. . In this case, the flank angle can be further reduced, and the effect of improving fatigue strength is further increased. The lower limit of (Equation 1) is limited to 0.40 because values less than this limit are not so different from the case where the value of (Equation 1) is 0.32 or more. When the value of (Expression 1) is set to 0.40 or more, the effect of reducing the flank angle is large, so it is desirable to set the lower limit of the welding speed to 100 cm / min from the viewpoint of manufacturing efficiency.

  The above is the reason for limiting the essential components of the steel sheet in the present invention. In the present invention, the following elements can be selectively added as necessary, but these are all for ensuring the strength and workability of the steel sheet, and improving the weld toe shape. Not for.

  The upper limit of the welding speed was set to 150 cm / min. This is because, as already described, the welding speed is one of the factors that determine the manufacturing efficiency of the welded structure, and the higher the speed, the higher the efficiency. On the other hand, an excessively high speed is not preferable from the viewpoint of the weld bead shape, for example, the movement of the molten pool becomes intense. In particular, the undercut in FIG. An object of the present invention is to improve the fatigue strength of a welded joint, and to improve the weld toe shape, such as reducing the flank angle, is the means. From the viewpoint of improving fatigue strength, if undercut occurs, the fatigue strength decreases. Therefore, the upper limit of the welding speed was set to 150 cm / min.

  Next, selective elements of the steel sheet will be described.

  The reason why Al is added to the steel sheet in the present invention is from the viewpoint of deoxidation, not from the viewpoint of improving the shape of the weld toe portion, which is the object of the present invention, and is also disclosed in Patent Document 5 and the like. Belongs to the technology. The lower limit of Al was set to 0.005% as the minimum value at which the effect of deoxidation can be exhibited. On the other hand, excessive addition of Al remains in the steel sheet as an oxide. In this case, the problem of the hole expandability of the steel plate arises. In general, when gas shield arc welding is performed in the automobile field, since it is often applied to undercarriage parts, hole expansibility is one of the important characteristics required for steel sheets. Ensuring the hole expandability is not the object of the present invention, but ensuring the hole expandability was judged to be industrially significant. The upper limit of 0.1% of Al addition was set as a value that can ensure hole expandability.

  The purpose of adding Ti, Nb, V, Cr, and Mo to the steel sheet is to ensure the strength of the steel sheet. These elements combine with C to form carbides and increase the strength of the steel sheet. However, since the degree of influence of each element on the strength increase is different, different component ranges are set for each element.

  The lower limit of 0.005% of Ti and Nb was set as the minimum value at which an increase in strength can be expected. The upper limit of 0.1% for Ti and Nb was set to this value because excessive addition deteriorates the ductility of the steel sheet.

  V is also an element having the same function as Ti and Nb. However, since Ti and Nb do not have precipitation strengthening, lower and upper limits are set to values different from Ti and Nb. The lower limit of 0.01% of V was set as the minimum value at which an increase in strength can be expected. The upper limit of 0.2% was set to this value because excessive addition deteriorates the ductility of the steel sheet.

  Cr is an element that forms carbides and increases the strength in the same way as Ti, but Cr has an effect of not only precipitation hardening but also solid solution hardening. On the other hand, since the influence of precipitation hardening is not as great as that of Ti, Nb, and V, the range of addition can be set wider than these elements. The lower limit of 0.1% was set as the minimum value at which an increase in strength can be expected. The upper limit of 1.0% was set to this value because excessive addition deteriorates the ductility of the steel sheet.

  Mo is an element having the same effect as Cr. The lower limit of 0.05% of Mo was set as a minimum value at which an increase in strength can be expected. On the other hand, the upper limit of 0.5% was set to this value because excessive addition deteriorates the ductility of the steel sheet.

  Next, the reason why the welding wire is limited to the flux-cored wire will be described.

  Generally, a wire used for thin plate welding in the automobile field or the like is a solid wire. The reason is that the solid wire is cheaper than the flux-cored wire, and the solid wire is preferable from the viewpoint of painting because it has a small amount of slag generated after welding. Among these, the advantage that the solid wire is cheaper is the case where the production amount of the wire is large to some extent. When the production amount of the wire is small, the flux-cored wire can be manufactured at a lower cost than the solid wire. The reason for this is that when it is necessary to change the wire composition, the wire material itself must be recreated for solid wires, whereas for flux-cored wires, only the flux components to be filled need to be adjusted. This is because the components of the entire wire can be changed.

  An object of the present invention is to improve the fatigue strength of a welded joint. As means for this, improvement of the weld toe shape by limiting the Si of the steel plate and Si of the steel plate and welding wire defined by (Equation 1), and reducing the residual stress in the weld by limiting the components of the welding wire There are two technologies. The second technique is a selection technique in the present invention and is a conventionally known technique. In order to achieve this, there is no particular problem with a solid wire. However, the wire component system that reduces the residual stress in the welded portion has to set the alloy element high, resulting in high wire cost. Therefore, in order to reduce the manufacturing cost of the welded structure, it is desirable to keep such a high cost wire to a minimum application. This means that the amount of wire used is reduced. In such a situation, the flux-cored wire is economically superior to the solid wire, so it is limited to the flux-cored wire.

  Next, the reason why the steel core of the flux-cored wire is limited to a slit-like seamless outer shell that may be invaded by outside air will be described.

  Compared with the solid wire, the problem with the flux-cored wire is that the amount of hydrogen is increased in addition to the slag generation problem. Therefore, when manufacturing a flux-cored wire, the flux filled in the wire is dried in advance to reduce the amount of hydrogen. However, even after the flux is dried and filled in the wire, if there is a slit-like seam in the steel outer sheath of the flux-cored wire that has a risk of entering the outside air, the flux absorbs moisture from the seam, resulting in hydrogen. Increase the amount. As a technique for improving fatigue in the present invention, there is a residual stress reduction by adjusting the component of the flux-cored wire, but this has to be a component system that contains a relatively large amount of alloy elements, and so-called cold cracking sensitivity is present. High component system. Cold cracking can be prevented by reducing the amount of hydrogen. Therefore, the moisture absorption of the flux is prevented by limiting the crack to a skin without a slit-like seam that may be invaded by outside air.

  Next, the reasons for limiting the composition of each component of the flux-cored wire will be described.

  C other than SiC is contained mainly in the steel outer sheath in the flux-cored wire, and contained for the purpose of preventing disconnection in the wire drawing process during wire manufacture. C other than SiC also has the effect of reducing the transformation temperature of the weld metal, but in the present invention, the content of SiC in the flux filled in the steel outer shell is adjusted according to the component system, and the weld metal The transformation temperature can be sufficiently reduced. In order to obtain an effect of preventing disconnection in the wire drawing step by C in the steel outer shell, the lower limit of the C content other than SiC needs to be 0.01%. On the other hand, if C is excessively added to the steel outer shell, it will harden during drawing and cause breakage, so the upper limit of the C content other than SiC is set to 0.20%.

  In addition, when iron powder is filled in the steel outer shell as a flux, C in the iron powder is included as C other than SiC. Therefore, from the point of reducing the hardening in wire drawing caused by C in the steel outer shell, the iron content in which the C content in the steel outer shell is 0.15% and the remaining C amount is added as a flux. It is desirable to supplement with the C content.

In order to obtain the deoxidation effect of the weld metal during arc welding, the lower limit of the content of Si other than SiC and SiO ₂ is set to 0.05%. On the other hand, if Si other than SiC and SiO ₂ is added excessively, the weld metal is hardened, which is not preferable from the viewpoint of joint characteristics, so the upper limit of its content was set to 1.2%.

  Mn is an element necessary for ensuring the strength of the weld metal. If the content is lower than 0.2%, it becomes difficult to ensure the strength of the weld metal. Therefore, the lower limit of the Mn content is set to 0.2%. On the other hand, if the Mn content is excessively high, the toughness of the weld metal is deteriorated, so the upper limit of the Mn content is set to 2.5%.

  P is an inevitable impurity element of the weld metal. In the present invention, if these elements are present in the weld metal in a large amount, the toughness deteriorates. Therefore, the upper limit of the P content is set to 0.03%.

  Generally, like P, S is an inevitable impurity element of the weld metal, but S contributes to the improvement of the bead shape by reducing the surface tension of the molten pool. When S is contained for that purpose, in the present invention, the S content is set to 0.08% as the upper limit that does not deteriorate the toughness of the joint. That is, in order to acquire the said effect, S can contain more than 0.02 to 0.08%.

The SiO ₂ , Al ₂ O ₃ , Na ₂ O, and K ₂ O contained in the flux are usually called slag materials. These serve as a binder when granulating the flux component before production of the flux-cored wire, and after filling the flux component in the steel outer shell, drawing to a predetermined wire diameter, It acts as a lubricant that reduces the resistance between the inner surface of the skin and the flux. In the present invention, by containing SiC having a lubricating action, the workability in the wire drawing step can be ensured even if the slag material that is these oxides is reduced as compared with the conventional case. However, if the total amount of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O is less than 0.05%, it becomes difficult to maintain the workability and the wire quality. In order to cause problems in production efficiency, the lower limit of the total amount is set to 0.05%. On the other hand, when the total amount of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O, and K ₂ O exceeds 0.40%, the amount of slag generated in the welded portion increases and the paintability is increased. Since the problem of deterioration occurs, the upper limit of the total amount is set to 0.4%.

  The SiC in the present invention has an appropriate amount of Si in the flux-cored wire, and further serves as a main element C source for reducing the transformation start temperature of the weld metal, and also serves as SiC having lubricity and deacidification. In the present invention, it is an essential component.

  The lower limit of SiC, 0.05%, was set to this value because the effect of improving wire workability and reducing the amount of slag due to the lubricating action and deoxidizing action of SiC was not sufficient. On the other hand, if the SiC content in the flux increases, there is a possibility that the weld metal hardens and the austenite structure increases and the weld metal does not transform. In such a case, SiC is purposely added to the flux-cored wire. There is no merit. For this reason, the upper limit of the SiC content in the flux-cored wire is limited to 1.2%.

  The above is the reason for limiting the essential components of the flux-cored wire in the present invention.

  Next, the reasons for limitation of the selected elements of the flux-cored wire will be described.

  The function of graphite in the present invention is an alternative to SiC. As a C source, graphite is cheaper than SiC, but on the other hand, since graphite is light, it has a manufacturing problem that graphite is scattered during the manufacture of a flux-cored wire. However, not only is it cheap, but graphite is more effective than SiC in terms of the function of the lubricant in wire drawing, and the present inventors decided to treat graphite as a selective element. However, since SiC and graphite have the same function as a C source, in order to take this point into consideration, the total amount of C converted values of the following (Formula 2) was created to limit the total amount of C.

Total amount of C converted value = [graphite] + 0.3 × [SiC] (Equation 2)
The lower limit of graphite, 0.02%, was set to this value because the effect of adding graphite cannot be achieved with less graphite. Although the upper limit of graphite is not particularly provided in the present invention, the upper limit of graphite is naturally limited because the range of (Equation 2) is limited. Moreover, since the lower limit of (Formula 2), 0.20%, if the lower limit lower than this is set, the graphite content must be less than 0.02%, this value was set. On the other hand, the upper limit of 0.6% is set at an addition amount exceeding this value, because the C level of the weld metal becomes too high, causing problems of the curability, toughness, and crack sensitivity of the weld metal.

  In the present invention, Ni, Cr, Mo, and Cu are added for the purpose of improving the mechanical strength of the weld metal such as Charpy characteristics and lowering the transformation start temperature of the weld metal and improving the fatigue strength. As for Cu, there is another purpose of improving conductivity by plating the wire with Cu.

  Ni is an element that lowers the transformation start temperature of the weld metal and is effective for improving joint fatigue strength, and also improves joint characteristics such as strength and toughness. When Ni is contained, the lower limit of the Ni content needs to be 0.1% as the minimum amount at which the improvement effect of joint fatigue strength can be sufficiently expected in a low SiC component system, but preferably 0.5% It is. As for the upper limit of the Ni content, the effect of reducing the transformation start temperature of the weld metal is sufficiently obtained. When the Ni content exceeds 5.0%, the interaction with C contained in the weld metal allows the cooling to end while the austenite remains austenite without transformation to bainite or martensite where the weld metal transforms at low temperatures. Therefore, the upper limit of the Ni content is set to 5.0%.

  Cr and Mo are elements having an effect of reducing the transformation start temperature of the weld metal and increasing the strength and hardenability. In particular, Cr and Mo are more effective than Ni in improving the strength of the weld metal and ensuring hardenability. Therefore, using this effect, the weld metal is transformed into a structure having a low transformation temperature such as martensite, and the weld joint In order to further improve the fatigue strength, the content of Cr and Mo needs to be 0.1% or more. On the other hand, since Cr and Mo are less effective in improving the toughness of the weld metal than Ni, if excessively contained, the toughness of the weld metal may decrease, so the upper limit of the Cr and Mo content is 2 0.0%.

  Cu, like Cr and Mo, is an element that has the effect of reducing the transformation start temperature of the weld metal, improving the strength, and ensuring hardenability. Cu may also be plated on the surface of the wire to ensure normal electrical conductivity. In order to obtain the effect of improving the strength and hardenability of the weld metal by Cu and the effect of ensuring electric conductivity, the lower limit of Cu content needs to be 0.1%. However, if Cu is excessively added to the weld metal, there is a risk of causing Cu cracks in the weld metal, so the upper limit of the Cu content is set to 0.5%.

  In the present invention, 6.0% is set as the upper limit of the total amount of one or more of Ni, Cr, Mo and Cu. This is because if the total content exceeds 6.0% and is excessively contained, the weld metal does not transform into bainite or martensite that transforms at a low temperature in the cooling process after welding, and remains in an austenitic structure. Therefore, it is difficult to improve the joint fatigue strength. For this reason, it is preferable to make the upper limit of content of the said total content 6.0%. In the present invention, there is no particular lower limit when adding one or more of Ni, Cr, Mo and Cu, but since a lower limit is set for each additive element, Naturally there is a lower limit of 0.1%. In addition to the toe shape improvement effect in the present invention, when it is necessary to further increase the fatigue strength, it is desirable to set the lower limit of the total content to 1.5%. Addition of less than 1.5% is added for the purpose of improving mechanical properties such as Charpy properties, but whether to improve Charpy properties or fatigue properties depends on the purpose of those skilled in the art using the present invention. In addition, it is not particularly difficult for those skilled in the art to determine the addition amount.

  B is a hardenable element, which ensures the hardenability of the weld metal, makes the microstructure of the weld metal a stronger structure, and suppresses the formation of a structure that starts transformation at a high temperature and transforms at a lower temperature. Has the effect of making the microstructure. Since the weld metal has a higher oxygen content than steel sheets, B may bind to oxygen and lose its effect. Therefore, the hardenability by B in the weld metal and the tensile strength and fatigue strength by microstructure control. In order to improve the content, the lower limit of the B content is preferably 0.001%. On the other hand, the upper limit of the amount of B added is set to 0.015% because adding more than this causes the risk of cracking in the weld metal.

  Nb, V, and Ti are all elements that have the function of forming carbides in the weld metal to increase the strength, and by containing a small amount of one or more of Nb, V, and Ti in the weld metal. The joint strength can be improved. If the lower limit of the total content of one or more of Nb, V, and Ti is less than 0.005%, improvement in joint strength cannot be expected so much, so the lower limit of the total content is 0.005%. Is preferable. On the other hand, if the total content exceeds 0.3%, the strength of the weld metal becomes excessive and a problem occurs in joint characteristics. Therefore, the total content upper limit is preferably set to 0.3%. In addition, regarding Ti, in addition to the effect of improving the strength of the weld metal, it has a function of stabilizing the welding arc. Therefore, when Ti is contained, it is preferable to contain 0.003% or more of Ti.

  In the present invention, the flux-cored wire S is set to a range that can be actively used to the extent that the joint characteristics are not adversely affected. S can be expected to reduce the viscosity of the weld metal and improve the weld toe shape. There are two methods for securing the amount of S in the weld metal: a method of adding S to the steel plate and a method of adding S to the welding wire. However, the method of adding S to the steel plate causes a problem in the steel plate characteristics. Therefore, it is preferable to add to the flux-cored wire. However, the method of adding to the flux-cored wire too causes the problem of hot cracking as already described, so the upper limit was made 0.08%. When S is positively used and it is desired to further improve the weld toe shape, the amount of S should be 0.02% or more. Generally, when S is added in an amount of 0.02% or more, the toughness of the weld metal may become a problem. However, this depends on the characteristics required for the welded joint and may be selected as appropriate by comparing the weld toe shape improvement with the required toughness. However, when one or more of Ni, Cr, Mo and Cu are added within the scope of the present invention, the upper limit of S is preferably set to 0.03% from the viewpoint of crack sensitivity.

An arc stabilizer is an element which has the effect | action which stabilizes a welding arc by making it contain in the flux with which it fills in the steel outer_layer | skin. Since Na ₂ O, K ₂ O, and the like contained in the flux described above also have a function as an arc stabilizer, these components are contained to the extent that they do not hinder the reduction in the amount of slag generated in the weld of the present invention. It is preferable to do this. Further, the arc stabilizer can function as long as it is a compound of Na, Al, F, such as cryolite (Na ₃ AlF ₆ ), without using an oxide such as Na ₂ O or K ₂ O. Since a stabilizing effect is obtained, it is preferable to contain it as a compound other than an oxide from the viewpoint of reducing the amount of slag generated.

  In order to reduce the amount of slag generated in the weld and to obtain the effect of arc stabilization, the lower limit of the content of the arc stabilizer other than the oxide type is preferably 0.05%. On the other hand, if the content of arc stabilizers other than oxides exceeds 0.5%, the arc stabilizing effect will not change, so the upper limit of the content is preferably 0.5%.

  Next, the reason for limiting the shielding gas in the present invention will be described.

The gas used for the shielding gas is CO ₂ or Ar. However, with respect to Ar, it is still impossible to use 100% Ar for the shielding gas because of the stability of the arc. On the contrary, the method using 100% CO ₂ is sufficiently possible within the range of the prior art if Si or the like, which is a deoxidizing element, is used effectively, and also within the range of Si disclosed in the present invention. 100% CO ₂ can be used as a shielding gas, and there is an advantage that CO ₂ gas is cheaper than Ar gas. Nevertheless, the reason why the shielding gas mainly composed of Ar gas is used is that there is a merit that sputtering can be reduced. However, since Ar gas is an inert gas, a minimum amount of CO ₂ gas is required. The lower limit of 5% by mass of the CO ₂ gas with respect to the shielding gas mainly composed of Ar gas is set to this value because the welding arc becomes unstable when the lower limit is less than 5%. When the upper limit of 25% is exceeded, the amount of sputtering increases, and this value is set because it is not much different from the case where 100% CO ₂ gas is used as the shielding gas.

In the present invention, the shielding gas can contain O ₂ . However, the reason for including O ₂ gas is to reduce the cost of the shielding gas, and is not directly related to the effect of improving the weld toe shape intended by the present invention. Generally, in order to make Ar gas 100%, it is necessary to remove O ₂ gas, but this increases the cost of shielding gas. On the other hand, Ar gas containing a certain amount of O ₂ can be manufactured at a relatively low cost. Even if O ₂ gas is contained to some extent, the effect of improving the weld toe shape is not lost. The lower limit of the component limitation range of O ₂ gas can be 0%, but the lower limit is preferably 2%. That is, since the content ratio lower than this affects the cost of Ar gas, this value was set. 4% of the upper limit is set as the upper limit of the allowable value because an oxygen amount of the weld metal increases and a problem on toughness occurs when the addition amount exceeds the upper limit.

  The above is the reason for limitation regarding the fillet arc welding method for thin steel sheets in the present invention.

Examples of the present invention will be described below.
Example 1

  Table 1 is a table of steel plate components used in Example 1. The purpose of Example 1 is to investigate the hole expandability of a steel plate. In addition, since this invention makes the claim the combination of a steel plate and a welding wire, it cannot judge whether it is in the range of this invention only with a steel plate. Accordingly, the distinction between “comparative example” and “example of the present invention” in the remarks column is provided for reference.

  The steel slab having the components shown in Table 1 is heated to a heating temperature of 1150 to 1250 ° C., hot-rolled to a finishing temperature of 820 to 900 ° C., and then cooled at a cooling rate of 25 to 55 ° C./second. The steel sheet was wound at a winding temperature of 450 to 550 ° C. to obtain a hot rolled steel sheet having a thickness of 2.6 mm.

  From these hot-rolled steel plates, a square test piece of 250 mm × 250 mm was sampled, a circular hole with a diameter of 30 mm was punched in the center portion, and then a hole expansion test was performed with a conical punch having a vertex angle of 60 °. The hole expandability is determined by expanding the hole with a conical punch, observing a crack generated in the punched surface, measuring the diameter (d) when the crack penetrates to the front and back surfaces of the plate, and increasing the diameter {(d− 30) x100 / 30}. When the diameter is doubled to 60 mm, the hole expandability is 100%.

  Table 1 lists steel plate components, tensile strength, and hole expandability. As for B02 to B16, B25, and B26, which are component systems within the scope of the present invention, it can be seen that the hole expandability exceeds 100%. On the other hand, B17 to B24 of the comparative examples are out of the component range of the steel sheet in the present invention, and it is understood that the hole expandability is less than 100%. That is, it can be seen that the hole expandability is inferior.

  On the other hand, regarding the comparative examples B01 and B12, the hole expansibility exceeds 100%, indicating that the characteristics are good. These steel sheets are comparative examples because Si is outside the scope of the present invention, but it can be seen that the hole expandability is good even if Si is below the lower limit of the present invention. Such a phenomenon occurred because the lower limit of Si was not set from the viewpoint of ensuring hole expandability, but was set to improve the weld toe shape compared in Example 2. For this reason, only Example 1 does not show the validity of the lower limit of Si set in the present invention.

  In Comparative Examples B13 and B14, C and Mn are below the range of the present invention, respectively, but the hole expandability exceeds 100%, indicating a sufficient value. However, the strength does not reach 300 MPa. With this strength, it is necessary to lower the stress design of the actual welded structure, in which case the fatigue problem is not particularly emphasized. Since the object of the present invention is to improve fatigue strength, this range deviates from the spirit of the present invention.

（実施例２）

(Example 2)

  The purpose of Example 2 is to investigate the components of the flux-cored wire and its characteristics. Tables 2 and 3 show the results of investigating the mass% of each component, the filling rate, the wire drawability, and the Charpy absorbed energy with respect to the total wire mass in the flux-cored wire. In the present invention, a combination of a steel plate and a welding wire is included in the scope of claims, and therefore it cannot be determined whether or not the wire component alone is within the scope of the present invention. Therefore, it can be seen that the “comparative example” in the remarks column is outside the scope of the present invention with only the wire component, but what is described as “the present invention example” is the present invention in consideration of the combination of steel materials. A distinction should be made between examples. “Example of the present invention” in the remarks column is provided for reference.

  First, the wires in Table 2 will be described.

  The wire symbols of 100 to 110 are flux-cored wires within the scope of the present invention, and 150 to 165 have wire components already outside the scope of the present invention.

  For the wires in Table 2, the flux scattering property, wire drawing property, Charpy absorbed energy, and slag amount were measured. The flux scattering property is a comparison of the ratio of the amount of graphite prepared for producing the flux and the amount of graphite in the flux just before filling the wire. If the graphite does not scatter, these coincide with each other, and the scattering rate becomes 0%. However, when the graphite scatters, the graphite decreases just before the wire filling. Scatterability was evaluated by this reduction rate. The wire drawability was evaluated based on whether or not a breakage occurred during wire production. For Charpy absorbed energy, a steel plate with a thickness of 3.2 mm was butt welded with each wire, and a 1/4 size Charpy test piece with a 2 mm V notch machined into the center of the weld metal was sampled, and a Charpy test was conducted at 0 ° C. The value was evaluated. The amount of slag was evaluated by the weight of slag generated on the surface of the weld metal when bead-on-plate welding with a weld bead length of 250 mm was performed.

  As for the wires 150, 151, and 159, the slag material is out of the scope of the present invention, and the slag generation amount exceeds 0.1 g, and it can be seen that there is a problem in paintability. On the other hand, in the wires 100 to 105 within the scope of the present invention, it can be seen from Table 2 that the amount of slag produced is less than 0.1 g, and in order to ensure paintability, the slag material is limited within the scope of the present invention. There is a need to. However, the wire 150 had a good weld bead. Then, when Charpy test piece was extract | collected using this wire and the Charpy test was implemented, it turned out that it is 7J. This is because Mn exceeds the range of the present invention in the wire 150. In order to obtain good mechanical properties, Mn needs to be within the range of the present invention.

  On the other hand, SiC of the wire 151 is also below the range of the present invention. In such a case, as in the case of the wire 154, it may be difficult to draw the wire during manufacture, and a problem of disconnection should occur. However, since the slag material is excessively added to the wire 151, a disconnection problem occurs. There wasn't. Then, when the amount of slag was measured using the wire 151, slag generation exceeded 0.34g and 0.1g. That is, in order to prevent disconnection while suppressing slag generation, it is necessary to use SiC instead of slag material.

  The wire 152 is an example in which SiC exceeds the range of the present invention, and as a result, (Equation 2) also exceeds the range of the present invention, and a crack occurs in the welded portion. Even when SiC was within the range of the present invention, the same cracking occurred in the wire 165 in which (Equation 2) exceeded the range of the present invention. The wire 153 had Si exceeding the range of the present invention, and due to excessive Si, the Charpy test was less than 10 J. The wire 155 is a case where C exceeds the range of the present invention, and the Charpy value is also less than 10 J. In the wire 156, Si was less than the range of the present invention, and defects such as blow holes occurred in the welded portion.

  On the other hand, since the wire 157 had C below the range of the present invention and the strength of the steel outer shell was insufficient, a wire breakage problem occurred during wire production, and the wire could not be produced. The wire 158 had Mn below the range of the present invention, and the disconnection problem occurred for the same reason as the wire 157.

  The wires 160 to 162 and 164 have a total of Nb, V, and Ti exceeding the range of the present invention, and have a Charpy value of less than 10 J. The wire 163 is one in which B exceeds the range of the present invention, and a crack is generated in the welded portion.

  On the other hand, all the wires 100 to 110 within the scope of the present invention did not cause a disconnection problem, the amount of slag generated was less than 0.1 g, and the Charpy value exceeded 10J.

  Next, the wires in Table 3 will be described.

  The wires in Table 3 are 200-210 within the scope of the present invention. These wires contain a relatively large amount of Cu, Ni, Cr, and Mo as compared to the wires in Table 2. Wires 250 to 255 are comparative examples.

  In the wire 250, the slag material exceeded the range of the present invention, and the slag amount exceeded 0.3g and 0.1g. Although this tendency is also observed in the examples in Table 2, it was confirmed also in the component system to which Cu, Ni, Cr, and Mo were added.

  The wires 251 and 252 are those in which the total of these four elements exceeds the range of the present invention, but from Table 3, there is no particular problem. This point will be described in Example 3 to be described later.

  The wire 253 has a total of Nb, V, and Ti exceeding the range of the present invention. Therefore, Charpy values were less than 6J and 10J.

  The wire 254 is made by adding no SiC and the slag material is limited within the scope of the present invention, and uses graphite to prevent wire breakage. Therefore, the graphite scattering property is 40%. When the scattering property is so high, it becomes extremely difficult to manage the wire manufacturing process, and there is a risk that a slight change in the manufacturing process may greatly change the wire component. In such a case, it means that it is difficult to produce a high-quality wire.

  The wire 255 has a SiC addition amount that is below the range of the present invention, which causes a problem of wire breakage.

  In contrast to these comparative examples, the wires 200 to 210 had a slag generation amount of less than 0.1 g, had no problem with wire drawing and scattering, and had a Charpy value of 20 J or more.

（実施例３）

(Example 3)

  In Example 3, there is no problem among the steel materials and wires used in Examples 1 and 2, that is, “Example of the present invention” is described in the remarks column of Tables 1 to 3 as a reference. In order to confirm the effects of the present invention and the present invention, lap fillet welding was performed using a part of which is described as “Comparative Example”, and a fatigue test was performed.

The table also shows the composition of the shielding gas used. In addition, the result of the Example of Tables 4-6 is a thing when the plate | board thickness of a steel plate is 2.6 mm altogether. The influence of the welding speed can be investigated by changing the welding speed. At this time, the current is set so that a welded joint can be formed by one-pass welding. Specifically,
60 cm / min: 120 A, 85 cm / min: 170 A
100 cm / min: 200 A, 120 cm / min: 240 A
130 cm / min: 260 A, 140 cm / min: 280 A
170 cm / min: 320 A
Was set.

  Under these conditions, a lap fillet arc welded joint was prepared, a cross-sectional macro was taken therefrom, and the flank angle and undercut depth defined in FIG. 2 were measured. When there was no undercut, the undercut depth was defined as 0. Moreover, the plane bending fatigue test piece shown in FIG. 4 was extract | collected from the same welded joint (steel plates 1, 2 and plate thickness 6, 7), and the fatigue test was implemented. When carrying out the fatigue test, a strain gauge was attached in the vicinity of the weld toe on the surface of the test piece to check the stress state on the surface. The repetitive stress was applied under the condition of stress ratio, R = 0.1. In this case, when the stress amplitude is 100 MPa, the maximum stress is 111 MPa, the minimum stress is 11 MPa, the stress amplitude is 111 MPa-11 MPa = 100 MPa, and the stress ratio is R = 11/111 = 0.1. The fatigue strength was defined as the maximum stress range in which the fatigue test was performed under these conditions and the fatigue fracture did not occur even when the stress was applied 2 million times.

  Tables 4 to 6 show the test results of flank angle, undercut depth, and fatigue strength. Tables 4 to 6 show a series of examples. Except for Table 6 in which the influence of the plate thickness was investigated, the plate thickness 6 and the plate thickness 7 in FIG. 4 are each 2.6 mm.

  Table 4 is described as "Example of the present invention" in the remarks column of Table 1 among the steel materials in Table 1, B02 to B11, B25, B26 and "Comparative example" in the remarks column of Table 1. B01 and B12 are used, and welding wires are prepared in lap fillet welded joints using the wires 100 to 110 described in Table 2 as “examples of the present invention” in the remarks column, and subjected to fatigue tests therefrom. It shows the test results when a piece was taken and a fatigue test was carried out. The reason for using B01 and B12, which are comparative examples of steel materials, is that no particular problems have occurred at the stage of Table 1. The reason why the wires 150 to 165 in Table 2 were not used is that problems such as Charpy value, wire drawability, and slag generation amount had already occurred before the fatigue test was performed.

  In Table 4, No. 1 and 2 are examples in which the Si of the steel material was lower than the example of the present invention. No. with welding speed of 70 cm / min. In the case of 1, the flank angle was 48 °, no undercut was generated, the toe shape was good, and the fatigue test was 340 MPa and 300 MPa or more. This is because when the welding speed is 80 cm / min or less, the toe shape can be improved regardless of the amount of steel sheet Si. Thus, since it has been known that the shape of the toe is improved when the welding speed is lowered, 80 cm / min or less is out of the scope of the present invention. On the other hand, no. No. 2 is the case where the steel material and the wire are the same, and the welding speed is as fast as 100 cm / min, but the flank angle is as large as 65 °, undercut occurs, and the fatigue strength is as low as 200 MPa. This is because the steel material Si is below the scope of the present invention.

  However, even if welding is performed at 100 cm / min using the same steel sheet 101 and a wire 101 having a high Si, Si of the steel sheet is lower than the present invention. In example 3, fatigue strength improvement cannot be confirmed. The wire 101 contains Si twice or more than the wire 100, but the shape of the toe is still not improved. The influence of the steel plate Si is not only the influence of the base material dilution, but also the wire Si. It means that it cannot be supplemented with.

  No. No. 4 is within the scope of the present invention for both the steel plate Si and the wire Si, and is an example in which the flank angle is less than 55 ° and the fatigue strength is 300 MPa or more even at a welding speed of 140 cm / min. However, no. In No. 5, the flank angle exceeded 55 °, and undercutting occurred, so the fatigue strength was low. That is, if the welding speed exceeds the range of the present invention, the effect of improving fatigue strength cannot be realized.

  No. 6 to 14 are all examples of the present invention, and the influence of the selected elements in the steel sheet was observed. However, as already shown in Table 1 of Example 1, these elements can be secured to the extent that mechanical characteristics can be secured. It was shown that the fatigue improvement effect can be obtained even with the addition of. Of these, No. 9 and 10 are examples in which 3% of oxygen was added to the shielding gas, and the fatigue improvement effect was sufficiently obtained.

  No. Although the value of (Formula 1) is within the range of the present invention, the value of Si of the steel sheet is below the range of the present invention. In this case, it can be seen that the fatigue strength does not reach 300 MPa, and the fatigue strength improvement effect cannot be expected. That is, the fatigue improvement effect can be obtained only by satisfying (Equation 1), and the Si amount of the steel sheet must be satisfied at the same time.

  No. 16-20, using B02 which is a component system within the scope of the present invention for the steel sheet, and changing the wire to 100, 102-105 within the scope of the present invention, among the selected elements of the wire component, Nb, This shows the effect of V and Ti. As shown in Table 2 of Example 2, all of these wire components are within the scope of the present invention, and even if a selective element is added within this component range, a sufficient fatigue doctrine effect is obtained, and all fatigue components are fatigued. The strength is 300 MPa or more.

No. No. 21 is an example using 100% CO ₂ as the shielding gas, and the fatigue improvement effect was confirmed as in the other examples of the present invention.

  No. 22 and 23 were carried out in order to compare the case where the value of (Equation 1) is less than 0.40. In this case, the flank angle slightly exceeds 50 °, and the fatigue strength is 290 MPa in both cases, which is an example that is slightly less than 300 MPa in the examples of the present invention. However, in consideration of the fact that all the comparative examples are below 250 MPa, the fatigue improvement effect is obvious.

  No. Nos. 24-28 are examples using 106-110 wires in which a large amount of S was added to the wires. Compared to 8, the flank angle was slightly smaller, and as a result, the fatigue strength was slightly increased. This is considered to be due to the addition of a large amount of S. In addition, although the wires 106 to 110 are examples in which S is higher than the wire 100 of Table 2, since the Charpy value tends to decrease, whether to give priority to improving fatigue or securing Charpy is: What is necessary is just to determine according to the required characteristic with respect to the coupling of an applied structure, and it can be easily judged by those skilled in the art.

  Whether or not the actual fatigue strength of the structure is necessary is related to the fatigue design, and those skilled in the art may adjust the value of (Equation 1) according to the design concept.

  Table 5 is carried out mainly for the purpose of investigating the influence of wire selection elements, Cu, Ni, Cr, and Mo. The data shown in Table 5 is obtained by combining the steel plates B01, B04, and B06 in Table 1 of Example 1 using the wires 200 to 210, 251, and 252 in Table 3 of Example 2, and overlapping them. It is a fatigue test result when producing a fillet joint. No. 51 is the case where the Si content of the steel sheet is below the range of the present invention, but the flank angle exceeds 55 °, which is not preferable from the viewpoint of fatigue strength. However, the fatigue strength was 300 MPa or more. This is presumably because the wire 200 itself is set to a relatively high total of 4.5% of the selected elements, and an effect equivalent to that of the high fatigue strength welding material as the prior art is exhibited. However, no. The fatigue strength of 51 is comparable to the fatigue strength in the examples of the present invention shown in Table 4. That is, even if an expensive alloy element such as Ni is not added to the wire, the addition of Si to the steel sheet improves the fatigue strength sufficiently with an inexpensive component-based wire. These are examples of the present invention shown in Table 4. Therefore, no. 51 is a comparative example in the present invention.

  On the other hand, no. No. 52 is that the Si amount of the steel sheet is within the scope of the present invention and (Equation 1) is also within the scope of the present invention. In this case, it can be seen that the fatigue strength is further improved and exceeds 400 MPa when the wire 200 having a large amount of addition of elements such as Cu, Ni, Cr, and Mo is used. This tendency is 53, 54, 55 and 57 were also confirmed. This is considered that the effect of reducing the residual stress due to the addition amount of elements such as Cu, Ni, Cr, and Mo is added, and the fatigue improvement effect is increased. No. Nos. 56 and 58 have a fatigue strength of 360 MPa, which is sufficiently improved. It was not until it reached 400 MPa like 52. This is an improvement due to the toe shape improvement effect, considering the same degree of fatigue strength of the present invention example in Table 4. In the case of the wires 204 and 206, the residual stress reduction effect is not realized. It is thought that. Therefore, the element addition amount of Cu, Ni, Cr, Mo or the like needs to be added by 1.5% or more in order to further improve the fatigue strength. The addition amount below that may be added for the purpose of securing mechanical properties such as Charpy value.

  No. 59 and 60 are cases where the added amount of elements such as Cu, Ni, Cr, and Mo in the wire exceeds the range of the present invention. Both fatigue strengths exceed 400 MPa, and the improvement effect is great. However, the wires 251 and 252 have no fatigue strength. 52. This indicates that even if these element addition amounts exceed 6% in total, no further improvement in fatigue can be obtained. In that sense, it can be determined that the wires 251 and 252 have a high wire manufacturing cost and little industrial merit.

  No. 61 to 65 are examples using wires 207 to 210 having a relatively high S. Of these, No. No. 61 has a high fatigue strength of 430 MPa because the alloying element of the wire is relatively high, and the effect of reducing the residual stress in addition to the effect of improving the shape of the toe is considered. No. 62-65 has a fatigue strength of 360 MPa or more, but does not reach 400 MPa. This is thought to be due to the fact that fatigue improvement was manifested in the toe shape improvement effect and no effect on the residual stress reduction effect was added. However, no. 61 to 65 were all good with a flank angle of less than 40 °. This is considered that the effect of S was filled in addition to satisfying the range of Si in the present invention. However, in general, adding a large amount of S may cause problems such as Charpy value and cracking, so it is necessary to determine the usage considering the required characteristics of the joint. It can be judged.

  Table 6 shows the effect of the plate thickness. The steel plate is B02, the steel plate component is within the scope of the present invention, the wire is 100, and the wire component is also within the scope of the present invention. First, when the plate thickness 1 and the plate thickness 2 are the same, the joint is No. 101-105. When the plate thickness was 7.0 mm, the welding speed could not be 80 cm / min. If it tried to exceed 80 cm / min, the fillet leg length was insufficient, resulting in two passes. No. 101 to 105 are within the scope of the present invention, and the fatigue strength is 290 MPa or more. When the plate thickness is 5.0 mm, the result is slightly less than 300 MPa. However, since the leg length is long, the phenomenon that the molten pool sags occurs, and the flank angle is no. It is because the tendency which becomes large compared with 101-103 was seen. No. In 105, the tendency was further increased, and the fatigue strength was less than 250 MPa. No. 105, no. In order to obtain fatigue strength of about 101 to 104, two-pass welding may be performed to improve the flank angle. However, in the thin plate field targeted by the present invention, single-pass welding is used to improve manufacturing efficiency. Yes. Therefore, in the present invention, the upper limit of the plate thickness is set to 6.0 mm.

  No. 106 and 107 are examples in which the plate thickness 1 and the plate thickness 2 are different, but it has been found that if the plate thickness is within the range of the present invention, the fatigue strength is improved.

  From the above, it was found that the weld toe shape can be improved and the fatigue strength is good in the combination of the steel sheet and the flux-cored wire for welding within the scope of the present invention.

It is the figure which showed the relationship between the amount of Si of the solid wire for welding, the amount of Si of a steel plate, and a flank angle when performing a fillet arc welding at a welding speed of 100 cm / min. It is the conceptual diagram explaining the flank angle and undercut depth in a lap fillet arc welding joint. It is the conceptual diagram explaining the relationship between a flank angle and fatigue strength. It is the conceptual diagram explaining the shape and stress load direction of the fatigue test piece used in the Example of this invention, (a) is a top view, (b) is a front view.

Explanation of symbols

1 steel plate 2 steel plate 3 flank angle 4 weld bead 5 undercut depth 6 plate thickness 7 plate thickness

Claims (11)

Fillet arc welding method for thin steel sheet, in which fillet arc welding of a thin steel sheet having a thickness of 1.6 to 6 mm is performed by gas shielded arc welding using a flux-cored wire at a welding speed of more than 80 cm / min and not more than 150 cm / min. In
The thin steel sheet, in mass%,
C: 0.001 to 0.15%,
Si: 0.2-2.0%,
Mn: 0.5 to 2.5%
P: 0.03% or less,
S: 0.02% or less, consisting of the balance iron and inevitable impurities, and a thin steel plate having a tensile strength of 280 MPa class to 600 MPa class,
The flux-cored wire,
A flux-cored wire for gas shielded arc welding, in which a slit-like seamless steel outer shell with a risk of intrusion of outside air is filled with flux,
In one or both of the steel sheath and flux, the total mass% of the entire wire,
C (excluding C in SiC): 0.01 to 0.20%,
Si (excluding Si in SiC and SiO ₂ ): 0.05 to 1.2%
Mn: 0.2 to 2.5%
P: 0.03% or less,
S: 0.08% or less,
Furthermore, as a flux filled in the steel outer sheath, it contains SiC: 0.05 to 1.2% by mass% of the whole wire, and includes SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O. 1 type or 2 types or more in total containing 0.05 to 0.4%,
The balance is a flux-cored wire for arc welding consisting of iron and inevitable impurities,
Further, the corner of the thin steel sheet, characterized in that the thin steel sheet and the flux-cored wire for arc welding are combined so that the total Si amount defined by the following (formula 1) is 0.32 or more. Meat arc welding method.
Total Si amount = Si (steel plate) + 0.1 × Si (wire) (Equation 1)
However, Si (steel plate) represents the Si amount of the thin steel plate, and Si (wire) represents the total Si amount of the flux-cored wire for arc welding.   2. The thin steel sheet according to claim 1, wherein the thin steel sheet and the flux-cored wire for arc welding are combined so that the value of the total Si amount in the (Expression 1) is 0.40 or more. Fillet arc welding method. The thin steel sheet is further in mass%,
Al: 0.005 to 0.1%
The fillet arc welding method for thin steel sheets according to claim 1 or 2, characterized by comprising: The thin steel sheet is further in mass%,
Ti: 0.005 to 0.1%,
Nb: 0.005 to 0.1%,
V: 0.01-0.2%
Cr: 0.1 to 1.0%,
Mo: 0.05-0.5%
The fillet arc welding method for a thin steel sheet according to any one of claims 1 to 3, wherein any one or more of the above are contained. The flux-cored wire for arc welding is defined by the following (formula 2), containing 0.02% or more of graphite as a flux filled in the steel outer shell in mass% of the whole wire. The fillet arc of a thin steel sheet according to any one of claims 1 to 4, wherein the flux-cored wire for arc welding has a total amount of C converted values of 0.20 to 0.45%. Welding method.
Total amount of C conversion value = [graphite] + 0.3 × [SiC] (Formula 2)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively. The arc-welded flux-cored wire is in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
Ni: 0.1 to 5.0%,
Cr: 0.1 to 2.0%,
Mo: 0.1 to 2.0%,
Cu: 0.1 to 0.5%
The fillet arc welding method for a thin steel sheet according to any one of claims 1 to 5, wherein one or more of the above are contained in a total of 0.1 to 6.0%. The arc-welded flux-cored wire is in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
B: 0.001 to 0.015%
The fillet arc welding method for a thin steel sheet according to any one of claims 1 to 6, characterized by comprising:   The flux-cored wire for arc welding is 0.005 to 0.00 in a total of one or more of Nb, V, and Ti in one or both of the steel outer sheath and the flux in the mass% of the whole wire. The fillet arc welding method for thin steel sheets according to any one of claims 1 to 7, characterized in that the content is 3%. The arc-welded flux-cored wire is in one or both of the steel outer sheath and the flux, in mass% of the whole wire,
S: more than 0.02 to 0.08%
The fillet arc welding method for a thin steel sheet according to claim 1, wherein the fillet arc welding process is performed.   The flux-cored wire for arc welding contains 0.05 to 0.5% of an arc stabilizer other than an oxide based on the mass% of the whole wire as a flux filled in the steel outer sheath. The fillet arc welding method for a thin steel sheet according to any one of claims 1 to 9, wherein the fillet arc welding is performed. As a shielding gas for the gas shielded arc welding, in mass%,
CO ₂ : 5% or more and 25% or less,
O ₂ : 4% or less (including 0%)
The fillet arc welding method for a thin steel sheet according to any one of claims 1 to 10, characterized in that a shielding gas comprising the remainder Ar and inevitable impurities is used.

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