KR20140114878A - Method for fillet arc welding high-strength thin steel sheets - Google Patents

Abstract

Provided is a fillet arc welding method of a high strength steel sheet capable of improving the fatigue characteristics of a welded joint with a good welding end shape even when the welding speed is not less than 110 cm / min and not more than 150 cm / min. The steel sheet is subjected to fillet arc welding of a high strength steel sheet having a tensile strength of 700 MPa or more by gas shield arc welding at a welding speed of 110 cm / min or more and 150 cm / min or less, wherein C = 0.02 to 0.15% (Mass%) of the steel sheet is defined as Si (steel sheet), the Si content of the welding wire used for the fillet arc welding (as expressed in terms of% by mass), Si = 0.2 to 1.8%, Mn = 0.5 to 2.5% Si (steel plate) + 0.1 x Si (wire)} ≥ 0.32, where Si (wire)

Description

[0001] METHOD FOR FILLET ARC WELDING HIGH-STRENGTH THIN STEEL SHEETS [0002]

[0001] The present invention relates to a fillet arc welding method for a high strength steel sheet, and more particularly, to a fillet arc welding method for a fillet arc welded joint produced by gas shielded arc welding and improved fatigue characteristics of a fillet arc welded joint To a fillet arc welding method of a high strength steel sheet.

As a preferable object member to which the present invention can be applied, a vehicle body structural member of an automobile, particularly a wheel part member which is an important security component, can be mentioned.

In the gas shielded arc welding in the automotive industry or the like, in order to improve the efficiency of the manufacturing line, it is general that the welding speed is set higher than in other industrial fields. Generally, it is not less than 60 cm / min and not more than 100 cm / min.

The reason why arc welding with such a high welding speed is possible is that the thickness of the steel sheet used in the automobile industry is 6 mm or less in most cases and even in the case of a wheel part part having a relatively large thickness, It is often 4 mm or less. That is, since the plate is thin as described above, the weld amount in arc welding can secure at least a predetermined joint strength. In the case where the plate thickness is as thick as 6 mm or more and the arc welding capable of ensuring the welding amount necessary for obtaining the predetermined joint strength is to be performed at a welding speed of 60 cm / min or more, There is a problem that the welding voltage must be increased and the risk of adversely affecting the shape of the weld bead is increased. As described above, arc welding in the automotive industry is characterized in that the welding speed is higher than in other industries.

However, under the arc welding condition of high welding speed, the shape of the weld bead, particularly, the shape of the welded end portion is deteriorated, that is, the frank angle (see FIG. 2) of the welded end portion becomes large. As a result, And the fatigue strength of the welded joint is lowered. The reason why the shape of the weld bead is deteriorated at a high welding speed is because, if the welding speed is high, the molten metal becomes thinner and longer so that the molten metal tends to solidify while not being sufficiently widened. On the other hand, particularly in the automotive industry, reduction of CO ₂ emissions by improving fuel efficiency has become an urgent task in recent years due to heightened interest in the global environment. Reducing the weight of the vehicle itself is an effective means of improving the fuel economy, and reducing the thickness of the steel sheet forming the automobile can be an effective means. However, the reduction of the plate thickness of the steel plate means an increase in the stress applied to the steel plate, and the increase in stress not only causes a problem of static strength but also causes a problem of fatigue strength. That is, even if the static strength is sufficient, there arises a problem that the plate thickness feeling, that is, the weight reduction can not be promoted from the viewpoint of the fatigue strength.

Generally, it is said that the fatigue strength of a welded joint has little dependency on the material, and is dominated by mechanical factors such as stress concentration determined by the shape of the weld bead and residual stress of the welded portion. As described above, since the manufacturing efficiency improvement and the fatigue strength securing are often opposite to each other, as the means for improving the shape of the welded end portion at the high welding speed and the means for improving the fatigue strength of the welded joint, Or the like, or applying residual stress of compression to the welded end portion by shot peening or the like has been adopted. These are called so-called post-processes and are not desirable for increasing the production cost.

On the other hand, as one of the means for solving the fatigue problem of the welded joint, there has been proposed a method of designing a component so that the transformation temperature of the welding material is lowered and reducing the residual stress in the welded end portion to improve the fatigue strength (see Patent Document 1, 2, hereinafter referred to as high fatigue strength weld materials). Although this method defines the components of the welding material, it is a method of controlling the mechanical factors in the sense of reducing the residual stress, and it is an efficient method because a high fatigue strength joint can be obtained only by changing the welding material.

Further, as disclosed in Patent Documents 3 and 4 and Non-Patent Document 1, there is a technique of making the weld bead shape wide by restricting the components of the welding material and the steel sheet. For example, the technique disclosed in Patent Document 3 and Non-Patent Document 1 is a technique of adding S in an amount of more than 0.01% to 0.06% or less, thereby reducing the surface tension of the melt pool and improving the welded end shape. The technique disclosed in Patent Document 4 is a technique for adjusting the sum of Si and Mn of a steel sheet.

Patent Document 10 discloses a welding method in view of fatigue characteristics in the overlapping fillet gas shield arc welding of thin steel sheets. This technique defines the chemical composition of the weld metal to improve the bead tip shape.

Also, Patent Documents 5 to 9 disclose techniques relating to a steel sheet having excellent fatigue strength.

Japanese Patent Application Laid-Open No. 11-138290 Japanese Patent Application Laid-Open No. 2004-001075 Japanese Patent Application Laid-Open No. 2002-361480 Japanese Patent Application Laid-Open No. 2007-177279 Japanese Patent Application Laid-Open No. 2004-143518 Japanese Patent Application Laid-Open No. 2000-248330 Japanese Patent Application Laid-Open No. 11-189842 Japanese Patent Application Laid-Open No. 07-316649 Japanese Patent Application Laid-Open No. 2003-003240 Japanese Patent Application Laid-Open No. 2002-45963

Welding Society National Convention lecture summary, 2007, Vol. 81, pp. 236 ~ 237

However, even when the high fatigue strength welding material described in Patent Documents 1 and 2 is used, the fatigue strength of the welded joint deteriorates, which is not preferable. This is because residual stress and stress concentration, which are the two main factors controlling the fatigue strength of joints, are high residual stress welding materials, which focus on residual stresses and are not aimed at improving stress concentration. Particularly, 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 demand for welding at a higher speed. As the welding speed is increased in accordance with the demand, the shape of the bead is disturbed. Therefore, stress concentration is increased, which is not preferable from the viewpoint of fatigue strength improvement. As described above, there is a limit to improving the fatigue characteristics of welded joints by applying the high fatigue strength welding material described in Patent Documents 1 and 2 to the automobile industry.

In addition, the techniques described in Patent Documents 3 and 4 and Non-Patent Document 1 are all aimed at widening the weld bead width beyond that of the prior art. The width of the weld bead can be a good indicator for reliably representing the shape of the entire weld joint. However, the fatigue strength thereof greatly depends on the shape of the welded end portion which is the stress concentration portion. That is, the shape of a part of the weld joint tends to be unique to the fatigue strength which is not the static strength, which determines the characteristics of the entire weld joint. Therefore, in order to improve the fatigue strength, it is necessary to pay attention to the shape of a portion of the welded joint, which is referred to as a welded end shape, rather than the characteristics of the entire welded joint as the welded 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, but it is not clear whether or not the technique is effective for improving the fatigue strength.

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

Patent Document 9 discloses a technique relating to the fatigue strength of a heat-affected zone (also referred to as HAZ). However, the welded joint in question is a butt welded joint, It is not as high as an arc weld joint. However, most parts of automobile wheel parts are manufactured by fillet arc welding. From this, it is not 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 having a high stress concentration, which is widely used in the automotive industry or the like.

The techniques disclosed in the prior arts described in Patent Documents 5 to 9 relate to the fatigue strength of a base material having no weld joint or the fatigue strength of a butt joint having a relatively small stress concentration. In an actual structure, fatigue cracking occurs from the place where the stress concentration is greatest, and it determines the fatigue strength of the whole structure. That is, unless the fatigue strength of the overlapping fillet joint is greater than that of the butt joint, stress fatigue of the structure is not improved. Patent Document 10 aims at improving the fatigue strength of the overlapping fillet joints of thin steel sheets. However, the welding speed is an embodiment in which the welding speed is 80 to 110 cm / min, which is conventionally referred to as high-speed welding, It is not compatible with new high-speed welding, such as the one described above. Patent Document 10 provides a technique that the fatigue strength of the joint is 12% or more of the fatigue strength of the steel plate. Generally, the fatigue strength of the steel sheet is said to be proportional to the tensile strength of the steel sheet because of the flatness of the steel sheet itself and the absence of a stress concentration portion, and is about 60% or more and 70% or less of the tensile strength of the steel sheet. Therefore, the technique of Patent Document 10 is a technique of making the fatigue strength of the welded joint 780 x 0.7 x 0.12 = 66 MPa or more when the tensile strength of the steel sheet is 780 MPa. However, when the fatigue strength is about 66 MPa or more, it is a range that can also be achieved by a method such as appropriately selecting the welding conditions, particularly the welding speed.

From this background, development of an overlapping fillet joint of a high strength steel sheet capable of increasing the welding speed while securing the fatigue strength of the thin steel sheet which is further strengthened has become a critical issue. Specifically, it is possible not only to secure sufficient fatigue strength even at a welding speed of about 100 cm / min (80 cm / min to 110 cm / min) which is the present high speed welding speed, The fillet arc welded joint of the high strength steel sheet is improved in the shape of the bottom end of the fillet arc welded joint even when the welding speed is exceeded, and the fillet arc welding method of the steel sheet capable of securing the fatigue strength has been expected. Here, since the fatigue strength required for a weld joint of a thin steel plate is about 250 MPa, in the present invention, it is a passing goal to have a fatigue strength of at least 250 MPa. The reason why 250 MPa is intended for the present invention is as follows. The reason why uniform values are selected regardless of the strength of the steel is that the fatigue strength of the welded joint does not depend on the kind of the steel, that is, the characteristic that the joint fatigue strength is the same for a steel material of 490 MPa class or a steel material of 780 MPa class . The fatigue strength of the steel is dependent on the tensile strength of the steel but is not dependent on the steel in the case of a welded joint. Next, the fatigue strength of the welded joint in a welded state, that is, in a state in which the measures for improving fatigue are not made, is approximately 200 MPa. If the fatigue strength is 250 MPa, corresponding to a strength increase of 20% or more, fatigue design is preferable. In some cases, the possibility of plate thickness change is also a value. Therefore, the present invention aims at 250 MPa.

Therefore, in view of the problems of these prior arts, the present invention improves the shape of the welded end portion even when the welding speed is more than 80 cm / min, particularly more than 110 cm / min in the gas shielded arc welding, A method for improving the fatigue of a welded joint in a steel sheet having a tensile strength of 700 MPa or more which is strongly expected to realize the improvement of the fatigue strength, .

From the above viewpoints, the present inventors paid attention to the welding speed, the steel sheet and the welding wire component, and studied the influence of the shape of the welded end portion. In particular, it has been found out that the shape of the welded joint can be improved even when the welding speed is more than 80 cm / min, particularly more than 110 cm / min and not more than 150 cm / min, by limiting the amount of Si, The relationship between the amount of Si contained in the steel sheet and the amount of Si contained in the welded wire exhibiting the effect of improving the shape of the tip is also found. The present invention has been made by such studies, and the gist of the invention is as follows.

(1) A fillet arc welding method for a high strength steel sheet having a tensile strength of 700 MPa or more, characterized in that the welding speed is more than 80 cm / min, particularly more than 110 cm / min and not more than 150 cm /

The steel sheet according to claim 1,

C: 0.02 to 0.15%

0.2 to 1.8% of Si,

Mn: 0.5 to 2.5%

P: 0.03% or less,

S: not more than 0.02%

Wherein the thin steel sheet and the Si contained in the welding wire are combined so that the value of the following formula 1 is 0.32 or more.

Si (steel plate) + 0.1 x Si (wire) (Equation 1)

Note that Si (steel plate) represents the Si content of the thin steel sheet, and Si (wire) represents the total Si content of the welding wire.

(2) The fillet arc welding method of high strength thin-rolled steel sheet according to (1), wherein the thin steel plate and the welding wire are combined so that the value of (formula 1) is 0.40 or more.

(3) The steel sheet according to any one of (1) to

Al: 0.005 to 0.1%

The fillet arc welding method of the high strength thin steel sheet according to the above (1) or (2), characterized by comprising:

(4) The steel sheet according to any one of (1) to

0.005 to 0.1% of Ti,

0.005 to 0.1% of Nb,

V: 0.01 to 0.2%

0.1 to 1.0% Cr,

Mo: 0.05 to 0.5%

(1) to (3), characterized in that the fillet arc welding method according to any one of (1) to (3)

(5) The welding wire as described above,

C: 0.03 to 0.15%

0.2 to 2.0% of Si,

Mn: 0.7 to 2.5%

P: not more than 0.05%

S: 0.08% or less,

Cu: 0.5% or less (including 0%)

(1) to (4), characterized in that a solid wire for welding consisting of a residual iron and an inevitable impurity is used as the filler arc welding method.

(6) The solid wire for welding according to any one of (1) to

Ti: 0.01 to 0.5%

0.01 to 0.1% Nb,

V: 0.05 to 0.3%

0.05 to 1.0% Cr,

Mo: 0.05 to 0.7%

Ni: 0.3 to 12.0%

(5) above, characterized in that the fillet arc welding method according to the item

(7) A method for producing a solid wire for welding,

Ni: 4.0 to 12.0%

Of the high strength steel sheet according to the item (6).

(8) The fillet of high strength steel sheet according to any one of (5) to (7) above, characterized in that S contained in the welding solid wire is limited to 0.02 to 0.08% Arc welding method.

(9) The flux-containing wire for gas-shielded arc welding in which the welding wire is formed by filling the flux in a slit-shaped,

In one or both of the forced shell and the flux, the total mass%

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: 0.06% or less,

Further, as the flux to be charged in the forced shell, in terms of mass% of the whole wire,

SiC: 0.05 to 1.2%

Characterized by comprising a flux-containing wire for welding comprising 0.05 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O in total, and the balance being iron and inevitable impurities (1) to (4) above.

(10) The flux-containing wire for welding according to any one of the above items (1) to

Graphite: 0.02% or more

, And the sum of the C-converted values defined in the following formula (2) is 0.15 to 0.45%. The fillet arc welding method according to item (9)

C converted value = [graphite] + 0.3 x [SiC] (formula 2)

However, [graphite] and [SiC] represent the mass% of graphite and SiC with respect to the whole wire, respectively.

(11) The method according to any one of (11) to (11), wherein the flux-containing wire for welding is one or both of a steel shell and a flux,

0.1 to 5.0% of Ni,

0.1 to 2.0% of Cr,

Mo: 0.1 to 2.0%

Cu: 0.1 to 0.5%

(9) or (10), wherein the total content of the filler metal is 0.1 to 6.0% by weight, based on the total weight of the steel sheet.

(12) The method according to any one of the above items (1) to (3), wherein the welded flux-containing wire is one or both of a steel shell and a flux,

B: 0.001 to 0.015%

(9) to (11), characterized in that the fillet arc welding method of the high strength steel sheet according to any one of the above (9) to (11)

(13) The method according to any one of the above items (1) to (4), wherein the welding flux-incorporating wire contains 0.005 to 0.3% in total of one or both of Nb, V and Ti in a total mass% of the wire on one or both of the steel shell and the flux And the fillet arc welding method of the high strength thin steel sheet according to any one of (9) to (12).

(14) The flux according to any one of (9) to (14), wherein the flux-containing wire for welding is filled in the steel shell with an arc stabilizer in an amount of 0.05 to 0.5% A fillet arc welding method of high strength thin steel sheet according to any one of the preceding claims.

(15) The method according to any one of (15) to (16), wherein the flux-containing wire for welding comprises, on one or both of the steel shell and the flux,

S: 0.02 to 0.06%

(9) to (14), characterized in that the fillet arc welding method of the high strength steel sheet according to any one of the above (9) to (14)

(16) The fillet arc welding method of the high strength thin steel sheet is gas shielded arc welding, wherein, as the shielding gas,

CO ₂ : 5% or more and 25% or less,

O ₂ : 4% or less (including 0%)

And a shield gas composed of a residual amount Ar and an inevitable impurity is used as the filler arc welding method for welding the high strength steel sheet according to any one of the above (1) to (15).

(17) A gas-shielded arc welded joint in a fillet arc welded joint of a high strength steel sheet having a tensile strength of 700 MPa or more at a welding speed of more than 80 cm / min, particularly more than 110 cm / min and not more than 150 cm /

The steel sheet according to claim 1,

C: 0.02 to 0.15%

0.2 to 1.8% of Si,

Mn: 0.5 to 2.5%

P: 0.03% or less,

S: not more than 0.02%

Wherein the thin steel sheet and the Si contained in the welding wire are combined so that the value of the formula (1) is 0.32 or more. The steel sheet according to any one of claims 1 to 3, Fillet arc welded joint of thin steel sheet.

(18) The fillet arc welded joint of the high strength thin steel sheet according to item (17), wherein the thin steel plate and the welding wire are combined so that the value of the above (formula 1) is 0.40 or more.

According to the present invention, in the overlapping fillet welding of a high-strength thin steel sheet having a strength of 700 MPa or more, even when high-speed welding is performed at a welding speed exceeding 80 cm / min, particularly above 110 cm / min and 150 cm / min or less, It is possible to reduce the concentration of stress in the welded end portion by that much, and the fatigue strength of the welded joint can be improved. Particularly, since the fillet arc welding method of a high strength steel sheet provided by the present invention is effective not only in the automobile industry but also in an industrial field in which there is a strong demand for an increase in welding speed and is a technology capable of both improving productivity and improving fatigue strength, The meaning of the prize is very large.

Fig. 1 is a conceptual diagram for explaining a case where Si having an atomic radius smaller than Fe is added to a steel material, and a positional change of Fe atoms before the addition. Fig.
Fig. 2 is a conceptual diagram for explaining the influence on the molten pool when a difference occurs in the expansion of the welding arc.
3 is a graph showing the relationship between the amount of Si of the welding solid wire and the amount of Si of the steel sheet and the frank angle when the overlap fillet welding is performed at the welding speeds of 100 cm / min, 112 cm / min, 120 cm / Fig.
4 is a conceptual diagram illustrating the angle of the flanks and the depth of the undercuts in the overlapping fillet arc welding joint.
5 is a conceptual diagram for explaining the relationship between the Frank angle and the fatigue strength.
Fig. 6 is a conceptual diagram for explaining the shape of the fatigue test piece and the stress load direction used in the embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

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

Metal fatigue is a phenomenon that, unlike static strength, the metal fatigue breaks in the state of stress added in the elastic range. The stress is added repeatedly, and the number of iterations determines the fatigue life. Generally, if the fatigue is not reached even if the stress is repeatedly repeated more than 2 million times, the additional stress at that time is called fatigue strength. Since metal fatigue is a phenomenon of breaking due to the additional stress in the elastic range, there are many differences from the static strength. For example, at static strength, it does not receive much of the effect of stress concentration or residual stress in the welded joint. Even if the grinder finish of the welded end portion which is very effective for improving the fatigue strength is carried out, the static strength does not mostly change. This is because the static strength involves plastic deformation. Even if there is a stress concentrating portion such as a welded end portion, plastic deformation only occurs in the portion, and from the viewpoint of static strength, only the portion other than the stress concentrating portion is required to bear the strength, maintain. In addition, even if a tensile stress already exists in a part such as a residual stress, considering the self-balancing characteristic of the residual stress, there is always a compressive residual stress canceling the tensile residual stress, State, the yield strength is not reached at the compressive residual stress portion, so that this portion will bear the static strength. For this reason, the static strength of the entire welded joint is not influenced by these factors. As a result, the overall strength of the weld bead, such as the weld bead width, becomes important.

On the other hand, the fatigue strength of the welded joint is a phenomenon in which the characteristics of the entire welded joint are determined in a very small stressed state of the welded joint. The portion where fatigue cracks occur is a welded portion with high stress concentration. There is also residual stress in the tensile. As described above, the residual stress is self-balancing, and the compressive residual stress that cancels this tensile residual stress necessarily exists inside the welded joint. However, since the fatigue strength is determined in a very small part of the stress state of the welded joint, even if compression residual stress is present, this residual compressive stress does not affect the fatigue strength unless it is present at the place where the fatigue crack occurs. This tendency is also suitable for stress concentration. That is, even if the weld joint exhibits a smooth shape as a whole, the fatigue strength of the entire welded joint is determined if there is a portion having a high stress concentration. Therefore, rather than improving the shape of the entire welded joint such as the welded bead width, improving the local shape, such as improvement of the welded end flange angle, contributes to improvement in 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 for improving the shape of the welded end portion contributing to improvement in fatigue strength. Actually, non-patent document 1 discloses a technique of increasing the width of the weld bead. According to this, it is not always clear that the frank angle is reduced by increasing the width of the weld bead.

As described above, the technique of increasing the width of the weld bead and the technique of narrowing the frank angle of the welded end portion are not necessarily the same. The present invention provides a technique aimed at improving the shape of a welded end portion, but its purpose is to improve fatigue strength of a welded joint. As to the static strength, since it does not depend on the stress concentration and the residual stress, it is possible to sufficiently secure the static strength as long as no defects occur in the welded joint, and in the scope of the present invention, factors There is no particular. In this respect, the object of the present invention is to provide technologies different from those of Patent Documents 3 and 4 and Non-Patent Document 1. On the other hand, the techniques of Patent Documents 1 and 2 are aimed at improving the fatigue strength of a welded joint and are the same as those of the present invention. However, as means for improving the fatigue strength of the welded joint, relaxation of stress concentration and relaxation of residual stress exist, and the techniques disclosed in Patent Documents 1 and 2 are techniques for improving fatigue strength using residual stress relaxation, This is different from the technique using the stress concentration relaxation disclosed in the invention. In addition, as a measure against fatigue of a welded joint, there is a technique of performing a pinning process or a grinder process after welding as a technique that has been used for a long time. These are post-process steps, and it is considered that there is a problem in terms of manufacturing efficiency.

Next, the process leading to the present invention will be described.

Generally, as a material factor for determining the shape of the weld bead including the shape of the welded tip, there is a surface tension of the molten pool and a gravitational force acting on the molten metal, and the shape of the weld bead has been determined by the mechanical balance. The surface tension of the molten pool is influenced by its chemical composition, for example C, Si, S, O and so on. Therefore, it has been considered that controlling these elements appropriately results in improvement in the shape of the weld bead. With this idea, it is preferable to lower the surface tension in order to reduce the frank angle of the welded end portion, but this also results in an effect of widening the width of the weld bead. As a result, there has been a tendency that the technique of increasing the width of the weld bead and the technique of increasing the contact angle of the welded end portion are equalized. As described above, it is preferable to reduce the frank angle of the welded end portion in order to improve the fatigue strength. However, according to the conventional thinking, this is also a technique of widening the weld bead width. Particularly, considering that the surface tension of the molten pool is determined by the components thereof, supply of each component from a steel sheet or supply from a welding material is not a problem, and as a result, If it is suppressed within a predetermined range, the shape of the weld bead can be improved. The invention described in Patent Document 10 is based on this thinking method.

From the prior art, as described above, the range of composition of the molten pool becomes a problem. For example, when the S component of the steel sheet is insufficient, it can be solved by replenishing it from the welding material. This means that one of the components of the steel sheet and the steel can be supplemented with the other component.

On the other hand, in the present invention, as described later, the phenomenon that components of such a steel sheet can not be supplemented with a welding material is used. In order to cause such a phenomenon, it is considered that there is a material factor other than the surface tension of the molten pool as a shape factor of the weld bead, but it is not necessarily clear by what mechanism it is affected.

However, as in the present invention, the fact that the material factor for determining the shape of the welded edge exists in addition to the components of the molten pool is the discovery of factors that have not attracted attention so far.

From the above viewpoints, the inventors of the present invention have focused on the speed at which the welding speed can exceed 110 cm / min, in particular, the welding speed exceeds 80 cm / min, in particular the conventional high speed welding speed, Has been repeatedly reviewed. As a result, it was found that the Si amount of the steel sheet greatly influences the shape of the welded end. The influence of the Si content of the steel sheet is not limited only to the effect of the dilution on the weld metal component. If the Si amount of the welding wire is adjusted by the dilution ratio, the same effect can be obtained. However, as described later, the effect of not controlling the amount of Si in the welding wire is not obtained .

The reason why the amount of Si in the steel sheet acts and why the same effect can not be obtained in the addition from the welding wire is not necessarily clear, but a possible interpretation is as follows.

First, the additive element Si in the steel sheet is a substitutional element, and Mn, Ni, Cr, and other substitutional elements usually contained in the steel sheet have the smallest atomic radius. In fact, in the periodic table, Si is arranged in the order of Na, Mg, Al, Si, P, S, Cl, and Ar. Since the number of atoms in the right side is larger than that in the right side, In order, the atomic radius decreases. P and S located on the right side of Si are smaller in atomic radius than Si. However, addition of a large amount of P or S leads to deterioration of characteristics of the steel itself and deterioration of weldability. Therefore, Can not be expected. Therefore, Si is practically regarded as an element having the smallest atomic radius among substitutional elements. The inventors of the present invention have focused on Si in the steel in this respect.

When an atom with a small atomic radius is added, the interatomic distance is naturally considered to be long. On the other hand, iron is a metal, and electrons move freely in the steel sheet, that is, free electrons exist. When these free electrons are in a region where the interatomic distance is long, that is, in the region where Si exists, the attracting force from the iron atoms tends to be reduced by that much, so that the electron emission from the steel sheet becomes easy.

The ease of electron emission from the steel sheet means that in the case of performing arc welding, the welding arc is apt to expand as far as it is. This means that the weld bead is easily enlarged. Further, the enlargement of the welding arc also serves to maintain the temperature of the surface of the molten pool at a high temperature. This also means that the surface tension of the grass can be kept small by this effect. By this effect, . Such an effect is an effect not obtained by a method of reducing the surface tension of the molten pool by adjusting the components of the welding material. Figs. 1 and 2 are conceptual diagrams illustrating this effect.

1 shows the positional relationship of Fe atoms (2) after Si addition when Si 3 having a small atomic radius is arranged on Fe atoms before Si addition where the iron atoms are regularly arranged (Circles indicated by black lines in Fig. 1). Since the radius of the Si atom is small, the position of the iron atom is slightly changed, and it can be understood that the interatomic distance, that is, the gap portion between atoms in FIG. 1, is large. Therefore, it is considered that the bond of free electrons is lowered and the electron emission becomes easier.

Fig. 2 is a conceptual diagram showing the influence of the free electrons on the shape of the weld bead when the arc of welding by the welding wire 4 is enlarged due to easiness. Fig. 2 (a) shows the case where Si is not added too much, and Fig. 2 (b) shows the arc phenomenon when Si is added. In FIG. 2 (b), since the welding arc is enlarged far, the steel plate is melted to a large extent, that is, the width of the weld bead tends to be widened. Further, the surface temperature of the molten pool existing in the rear portion of the arc It is possible to keep the surface tension of the molten pool low. As a result, the shape of the weld bead can be made smooth. 2 (a) shows a case where the welding arc is narrower than (b), and the amount of Si added is smaller. In this case, the area where the steel material can be melted is narrowed by the narrow part of the welding arc. Further, since the area where the surface of the molten pool behind the arc can be heated becomes narrower, the temperature of the pool surface tends to be lower than that in case of (b). If the temperature is low, the surface tension tends to become large. Therefore, in the region A2 in (b), the surface temperature of the molten pool is kept high due to the wide arc, thereby suppressing the surface tension to a low level. There is no loss. On the other hand, in FIG. 2 (a), since the arc is narrowed, the pool surface temperature in the region A1 in (a) can not be kept high and the surface tension tends to be restored and the pull width tends to become narrow. In the rear of the region A1, the pulling temperature is lowered from the viewpoint of heat conduction, and furthermore, the temperature of the outside portion of the pulling portion becomes lower than that of the inside portion, so that a difference occurs in the surface tension, and the pulling force is pulled toward the outer side where the temperature is low, The phenomenon occurs, and the full width is widened again. This is the B1 region in Fig. 2 (a). However, since the solution is narrow in the area A1, the tendency of the shape of the bead end portion to be difficult to be smoothed is not solved. In Fig. 2 (b), the decrease in the full width in the region A2 does not occur, so that the bead shape is in a good state. In order to solve this problem, in the prior art, a component system capable of keeping the surface tension low even if the temperature of the pool surface is lowered, or the welding speed is lowered as shown in Fig. 2 (c) A method has been employed in which the A1 region is allowed to enter the welding arc, that is, the area A3 in Fig. 2 (c). The present invention differs from the prior art in that this method is solved by widening the welding arc.

According to the above technique of the present invention, it is understood that the addition of Si should be made of a steel material and that a sufficient effect can not be obtained even if it is applied to a welding material. In other words, in order for the welding arc to be widened, an arc must first be generated between the steel and the steel before the steel or the steel is melted. For this purpose, electrons are required to be discharged from the steel material to flow electricity between the steel material and the steel material. The effect of Si in this phenomenon, that is, the effect of facilitating the release of electrons from the steel, can not be solved by means of adding Si from the molten pool and replenishing Si diluted from the steel material. That is, Si in the steel is important, and the same effect can not be obtained even if it is replenished from the molten steel.

For this reason, the present inventor defines Si in the steel.

The present inventors also clarified the relationship between the appropriate Si amount of the steel sheet and the Si amount of the welding wire. That is, when the Si amount of the welding wire is increased, the Si amount of the steel sheet tends to decrease as much as necessary in order to improve the welded end shape. However, when Si is not added to the steel sheet, even if the Si amount of the welding wire is increased, the shape of the welded end is not improved under the condition of high speed welding. As a countermeasure for improving the shape of the welded end portion in this case, it is necessary to sacrifice the manufacturing efficiency such as lowering the welding speed (for example, 80 cm / min or less). It is not necessarily clear why the minimum amount of Si in the steel sheet tends to decrease in order to improve the shape of the welded edge when the Si amount of the welding wire increases. However, It is considered that, when the area is narrowed to some extent, Si that reduces the surface tension is added from the welding material, thereby improving the weld bead end shape.

3 is a graph showing the relationship between the amount of Si of the welding solid wire and the amount of Si in the steel plate plotted on the abscissa axis and the amount of Si of the steel plate on the ordinate axis, Fig. Since there are several definitions of the Frank angle, the definition of the Frank angle in the present invention is shown in FIG. In FIG. 4, the Frank angle 5 defines the angle of the weld metal side, which is defined by the tangent of the weld bead and the extension of the surface of the steel plates 6 and 7, as the Frank angle. According to the document, the angle defined by the angle (180 DEG-Frank angle) using the Frank angle in Fig. 4, that is, the angle formed by the tangent of the weld bead and the extension line of the surface of the steel sheet, In the present invention, the angle of FIG. 4 is defined as a Frank angle. Fig. 3 shows the case where the Frank angle is 55 degrees or less and the case where the Frank angle is larger than 55 degrees. The overlapping fillet arc welding was carried out at a welding speed of 100 cm / min, 112 cm / min, 120 cm / min and 150 cm / min by preparing a steel plate having a thickness of 3.2 mm, did. The Frank angle at that time was measured according to Fig. Fig. 3 is a plot showing that the frank angle is 55 degrees or less and the frank angle is greater than 55 degrees for each welding speed. The Frank angle and fatigue strength are in good correlation, and a conceptual diagram illustrating this relationship is shown in FIG. This shows that the Frank angle is plotted on the abscissa and the fatigue strength is plotted on the ordinate, and the fatigue strength becomes A 'when the Frank angle is A. When the Frank angle is changed from B to A, the fatigue strength changes from B 'to A'. As shown in Fig. 5, the relationship between the Frank angle and the fatigue strength is represented by a straight line (or curved line) descending from the upper left side to the lower right side, so that it is understood that decreasing the Frank angle has an effect of improving the fatigue strength. This is because the Frank angle is a parameter for determining stress concentration. As the Frank angle increases, the stress concentration increases, so the fatigue strength decreases. On the contrary, when the frank angle becomes smaller, the stress concentration decreases and the fatigue strength increases. On the other hand, when the design fatigue strength of the welded joint is determined, the upper limit of the Frank angle is determined by itself. In FIG. 3, the Frank angle of 55 degrees has a fatigue strength of about 250 MPa.

In the fillet arc welding method of a steel sheet in the present invention, as shown in Fig. 3, a boundary line between a point of a flange angle of 55 degrees or less and a point of more than 55 degrees can be drawn. The upper portion of this boundary line is a range where the Frank angle is 55 degrees or less and the fatigue strength can be ensured. The upper part of this boundary line tends to have a smaller Frank angle. In FIG. 3, the frank angle tends to decrease under the four conditions of the welding speeds of 100, 112, 120 and 150 cm / min. However, as described in FIG. 2, as the welding speed decreases, the frank angle becomes smaller Loses. That is, the shape of the welded tip is improved.

It is an object of the present invention to reduce the frank angle, which has a large influence on the fatigue strength while securing the efficiency of welding work. Therefore, it has been confirmed that sufficient fatigue strength can be secured even at a welding speed of 110 cm / min or more, and more preferably 120 cm / min or more, at which the welding efficiency can be expected to be sufficiently high.

Next, the thickness of the thin steel sheet in the present invention will be described.

The thickness of the thin steel sheet to which the present invention is applied is not particularly limited. However, since the technique is limited to gas shielded arc welding using a solid wire for welding, the range of the plate thickness that can be practically applied, particularly the lower limit, is about 1.6 mm. This is because, for steel sheets thinner than 1.6 mm, spot welding or laser welding is often used rather than arc welding. The upper limit of the plate thickness was set to 4 mm. This is because the present invention is limited to steel plates of 700 MPa or more in which improvement in fatigue characteristics becomes particularly important, and is a steel sheet which does not need to have a large plate thickness because of its high strength.

Next, the reason for limiting each component of the steel sheet in the fillet arc welding method of the high strength steel sheet in the present invention will be described.

When C is less than 0.02%, it becomes difficult to secure strength, and therefore, the lower limit is set. On the other hand, if it is added in an amount exceeding 0.15%, the carbide formed is increased, and thus the hole expandability is deteriorated. Therefore, the upper limit is set to this value.

Mn is an element added to increase the strength of the steel. Excessive addition, however, leads to deterioration of ductility, so the upper limit is 2.5%. On the other hand, in order to secure strength, addition of 0.5% or more is required.

S is an impurity in the present invention. (JIS G0555) is formed by bonding with Mn to deteriorate ductility as well as hole ductility, so that the upper limit is set to 0.02%. In addition, lowering it to 0.0005% significantly increases the cost of steelmaking. Therefore, it is preferable to set 0.0005% as the lower limit value.

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

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

The point that the amount of Si in the steel sheet is limited is the basis of the present invention. As already described, the present inventors believe that the action of Si in the steel sheet is caused by enlarging the welding arc, but it is hardly sufficiently clear yet. However, the action of Si of the steel sheet described in the present invention is different from the action of influencing the amount of Si in the weld metal through the dilution of the base material. For example, when the base material 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% x 0.65 + 0.4% x 0.35 = 0.595 %. If the Si of the steel sheet is 0% and the dilution ratio of the base material is the same, in order to obtain the same weld metal, the Si amount of the welding wire can be set to 0.595% / 0.65 = 0.915%. In this case, the weld metal becomes the same Si, but the welded end shape is not the same. When the amount of Si in the steel sheet is 0.4%, the shape of the welded joint becomes better. This phenomenon has not been known until now. However, such a phenomenon occurs when the welding speed is higher than 80 cm / min, and the phenomenon can not be confirmed when the welding speed is lower than 80 cm / min.

The lower limit of 0.2% of the amount of Si in the steel sheet was determined as the action of Si, which is the improvement of the weld bead shape.

The upper limit of the amount of Si in the steel sheet is such that the amount of Si to be diluted from the base material, that is, the amount of Si in the weld metal increases and the Si bonds with oxygen to form SiO ₂ , thereby increasing the amount of slag generated on the surface of the weld metal after welding 1.8%. Generally, in the field of automobiles and the like, a coating process is arranged after welding, but slag present on the surface of the welding metal is not preferable in the coating process. Therefore, we set this value.

Next, the reason why the relationship between the Si content of the steel sheet and the Si content of the welding wire is limited will be described.

As described above, the action of Si in the steel sheet has an action different from the action of adjusting the amount of Si in the weld metal. Generally, Si has been said to affect the viscosity and surface tension of molten iron and affect the shape of welded ends through this action. However, when Si is not added to the steel sheet, the effect of improving the welded end shape is not seen. However, this is a case where the welding speed is a high welding speed exceeding 80 cm / min, and the higher the welding speed, the more remarkable the tendency becomes. That is, when the welding speed is not so high (in the case of 80 cm / min or less), it is possible to control the shape of the welded portion by improving the viscosity and the surface tension. However, do. However, when the amount of Si of the welding wire is changed, the minimum amount of Si sheet necessary for improving the shape of the welded end is also changed. As a result, the relationship between the amount of Si in the steel sheet and the amount of Si in the welding wire was limited. That is, if the value of the following expression (1) is satisfied to be 0.32 or more, the shape of the welded tip can be improved even at high speed welding of 120 cm / min or more and 110 cm / min or more.

Si (steel plate) + 0.1 x Si (wire) (Equation 1)

(Equation 1) of 0.32 or more must be satisfied regardless of the dilution of the base material. This is because the present invention is not a technique using a simple adjustment of the composition of the weld metal. This point is very different from the prior art.

In Fig. 3, a straight line of (Equation 1) = 0.32 is drawn. As can be seen from Fig. 3, when the value of (Equation 1) is 0.32 or more, the Frank angle becomes 55 deg. Or less. That is, the lower limit of 0.32 of (formula 1), which is determined by the amount of Si in the steel sheet and the amount of Si in the welding wire, was set at a value below this value because the effect of improving the shape of the welded end was not obtained at the high welding speed . The upper limit is not specifically defined, but the range is naturally limited from the upper limit of the Si content of the steel sheet and the welding wire.

The value of (formula 1) is determined by the amount of Si on both the steel sheet and the welding wire, and the amount of each Si can not be determined independently. However, those skilled in the art can easily determine the value.

In the fillet arc welding method of the high strength steel sheet according to the present invention, the value of (Eq. 1) is further limited and the improvement of the welded end shape can be more surely achieved.

As a method of securing the value of (Expression 1), there is a method of securing by the amount of Si of the steel sheet and securing by the amount of Si of the welding wire. (Equation 1), it is considered that the method of ensuring the steel sheet is superior because the coefficient of the amount of Si in the steel sheet is large. However, the weight of the steel sheet is generally 100 times larger than that of the weld metal. Therefore, even when the coefficient of the steel sheet amount in (formula 1) is large, it is economically preferable to secure the value of (formula 1) with a welding wire in many cases. However, apart from the effect of improving the welded end shape of the 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 wire. Therefore, the amount of Si in the welding wire is limited by the amount of Si in the steel sheet to secure the value of (formula 1). (Equation 1) can be expressed by Si (wire)? 0.40-Si (steel plate) / 0.1 (Equation 1-1), the Si amount contained in the welding wire satisfies (Equation 1-1) A welding wire is used.

Further, when the value of (formula 1) is set to 0.40 or more, the Frank angle is further reduced. In FIG. 3, a line when the value of (Equation 1) is 0.40 is drawn, but it can be seen that the region is moving upward as compared with the case where the value of (Equation 1) is 0.32. In this case, the frank angle can be further reduced, and the effect of improving the fatigue strength is much greater. When the value of (Expression 1) is set to 0.40 or more, the frank angle reduction effect is large, so that the welding speed can be further increased. For example, the welding speed may be 120 cm / min or more.

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 required, but these are all for securing the strength and processability of the steel sheet and not for improving the shape of the welded end portions.

The upper limit of the welding speed was set at 150 cm / min. This is because, as described above, the welding speed is one of the factors determining the manufacturing efficiency of the welded structure, and the higher the speed, the better the efficiency.

On the other hand, excessive speeding up is not preferable from the viewpoint of the shape of the weld bead, such as a severe movement of the molten pool. Particularly, the undercut 8 in Fig. 4 tends to be easily released. It is an object of the present invention to improve the fatigue strength of a welded joint and to improve the shape of a welded end portion such as a reduction in frank angle. From the viewpoint of improving the fatigue strength, when the undercut occurs, the fatigue strength is lowered. Therefore, the upper limit of the welding speed was set at 150 cm / min. Of course, exceeding the welding speed of 150 cm / min does not directly lower the fatigue strength of the joint. Depending on the welding conditions, there is no problem even if the welding speed is higher than this. However, as shown in Fig. 3, according to the present invention, it has been confirmed that sufficient fatigue strength can be ensured even at a high speed welding of 150 cm / min.

Next, the selected 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 and is not added from the viewpoint of the improvement of the shape of the welded end portion for the purpose of the present invention but belongs to the technique disclosed in Patent Document 5 and the like. The lower limit value of Al was set to 0.005% as the minimum value capable of exhibiting the effect of deoxidation. On the other hand, excessive addition of Al remains as an oxide in the steel sheet. In this case, there arises a problem of hole expandability of the steel sheet. In general, when gas shielded arc welding is performed in an automobile field, it is often applied to wheel part parts, so hole expandability is one of the important characteristics required for a steel sheet. Securing the hole expandability is not an object of the present invention, but it has been determined that securing the hole expandability is industrially significant. The upper limit of 0.1% of the Al content was set as a value capable of ensuring hole expandability.

The purpose of adding Ti, Nb, V, Cr, and Mo to the steel sheet is to secure the strength of the steel sheet. These elements combine with C and form carbides to increase the strength of the steel sheet. However, since the effect on the increase in the strength of each element 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 the increase in strength can be expected. The upper limit of 0.1% of Ti and Nb is set to this value because excessive addition deteriorates the ductility of the steel sheet.

V is also an element that acts like Ti and Nb. However, since there is no precipitation strengthening as Ti or Nb, the lower limit and the upper limit are set to values different from Ti or Nb. The lower limit of V of 0.01% is set as the minimum value at which the increase in strength can be expected. This value was set at 0.2% of the upper limit, since excessive addition deteriorates the ductility of the steel sheet.

Cr is an element that forms a carbide so as to be equal to Ti and increases the strength, but Cr has effects of hardening as well as precipitation hardening. On the other hand, since the effect of precipitation hardening is not as large as Ti, Nb and V, the range of addition can be set wider than these elements. 0.1% of the lower limit is set as the minimum value at which the increase in strength can be expected. This value was set to 1.0% of the upper limit because excessive addition deteriorates the ductility of the steel sheet.

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

The above is the reason for limiting the steel sheet component in the present invention.

Next, the reason for limiting the components of the welding wire will be described.

In the present invention, two types of welding wire are considered, namely solid wire and flux-containing wire.

First, the reasons for limiting the components of the solid wire for welding will be described.

C is added to secure the strength of the weld metal. Unlike a steel plate, in the case of a weld metal, it is necessary to secure the strength in the welded state, and therefore, the lower limit value needs to be set higher than the base metal. 0.03% of the lower limit was set because it would be difficult to obtain strength when it is below this value. On the other hand, if 0.15% of the upper limit is added in excess, it is set to this value because there is a risk of high-temperature cracking of the weld metal.

Mn is also an element added to increase the strength of the weld metal. Excessive addition, however, leads to excessive curing, so the upper limit is 2.5%. On the other hand, since the steel material of the present invention is intended for the generally required steel material of 700 MPa class or higher, its own strength is required for the welded joint. In order to secure the strength, 0.7% or more of addition is required, and therefore this value is set to the lower limit value.

Si is an element having an effect of deoxidizing the weld metal. Since the lower limit of 0.2% of Si is inferior to deoxidization at a lower addition amount, and blowholes and the like are likely to occur in the weld metal, this value is set. In order to improve the shape of the welded end portion, which is an object of the present invention, the effect is obtained even if Si is added in excess of the value defined by the present invention. However, the present invention deals with the plate thickness range used in the automobile field and the like. When the amount of Si of the welding solid wire becomes excessive, the amount of Si in the welding metal increases and bonds with oxygen to form SiO ₂ , thereby increasing the amount of slag generated on the surface of the welding metal. In the field of automobiles and the like, the post-welding painting process is arranged, but the slag present on the surface of the weld metal is not preferable in the coating process. In addition, in order to reduce the amount of spatter generated during welding, the shield gas may be an Ar-based gas. In this case, Si, which is a deoxidizing element, is preferably set to a small value. Therefore, in the present invention, the upper limit for reducing the amount of slag formation and the amount of spatter formation is set at 0.7%. The upper limit value is preferably set to 0.6%, more preferably 0.5%.

S is generally an impurity. Excessive addition increases the risk of deterioration of the weld metal toughness and also high temperature cracking of the weld metal, so the upper limit is 0.08%.

P is an impurity in the present invention. As the content of P increases, the risk of weld metal toughness deteriorates and the risk of weld metal high-temperature cracks increases, resulting in an upper limit of 0.05%.

Cu has two effects of plating the solid wire for welding, increasing the conductivity and preventing the rust of the wire. Therefore, from the viewpoint of the effect of improving the shape of the welded end portion of the object of the present invention, it is not necessarily required to be added. However, since there is a risk that the melted wire may cause problems such as blow holes and the like, the present invention limits the value thereof. In recent years, however, from the viewpoint of the environment, there is a case that Cu addition is disliked, and even if the conductivity is somewhat sacrificed, there is an accident that it is better not to perform Cu plating. Therefore, in the present invention, the lower limit of Cu is not specifically provided including the case where Cu plating is not performed, and it is assumed that 0% is included. In order to exhibit the effect of Cu plating, it is preferable to set the lower limit of Cu addition to 0.05%. The upper limit of 0.5% of the Cu content is set so that even when added in an amount exceeding the above range, the effects such as conductivity become saturated and the risk of Cu cracking increases.

Next, selection elements of the solid wire for arc welding will be described.

Ti, Nb, V, Cr, Mo, and Ni, which are the selective elements of the welding solid wire, are added as elements for ensuring the strength of the weld metal as the first object. Among them, It can be added for purposes other than securing strength.

The lower limit of 0.01% of Ti was set as the minimum value that can increase the strength and stabilize the welding arc. 0.5% of the upper limit, the addition amount exceeding the upper limit, the weld metal is excessively hardened, and a problem arises in the nature of the joint, so this value is set. The reason why the upper limit and the lower limit of Ti are higher than the upper limit and the lower limit of the Ti addition amount of the steel sheet specified by the present invention is considered to be a phenomenon in which Ti of the welding solid wire is oxidized by the welding arc.

The lower limit of 0.01% of Nb was set as the minimum value at which the increase in strength could be expected. 0.1% of the upper limit of the above amount is added because the welding metal is excessively hardened to cause a problem in the nature of the joint.

V is an element having an action of securing the same strength as Ti and Nb. However, since there is no precipitation strengthening as Ti or Nb, the lower limit and the upper limit are set to values different from Ti or Nb. The lower limit of V of 0.05% was set as the minimum value at which the increase in strength can be expected. 0.3% of the upper limit is set so that excessive addition deteriorates the ductility of the steel sheet.

Cr is an element that forms carbide and increases the strength in the same manner as Ti, but Cr has an effect of not only precipitation hardening but also hardening of hardening. On the other hand, since the effects of precipitation hardening are not as large as Ti, Nb and V, the range of addition can be set wider than these elements. The lower limit of 0.05% is set as the minimum value at which the increase in strength can be expected, but it is preferably 0.1%. If the upper limit of 1.0% is exceeded, this causes curing of the weld metal, which causes problems such as toughness.

Mo is an element having an effect similar to that of Cr. The lower limit of 0.05% of Mo is set as the minimum value at which the increase in strength can be expected. On the other hand, in the case of 0.7% of the upper limit, this value is set to be 0.5%, because excessive addition deteriorates toughness of the weld metal.

The purpose of adding Ni is mainly twofold. That is, securing the strength of the weld metal and securing the fatigue strength of the welded part are two points. From the point of securing the second fatigue strength, it is necessary to limit the range of Ni to a narrower range, and the range of Ni with respect to this point will be described later. From the viewpoint of securing the strength of the weld metal, the lower limit of Ni was set at 0.3%. This lower limit is set as a minimum value at which the increase in strength can be expected. The upper limit of 12.0% of the upper limit is set because the microstructure of the weld metal becomes austenite and there is a risk that the strength is lowered, and further there is a risk of occurrence of hot cracks.

In the present invention, the range of the S of the welding solid wire is set so as to be positively usable so as not to adversely affect the joint characteristics. S can reduce the viscosity of the weld metal and can be expected to improve the shape of the welded joint. There are two methods of ensuring the S amount of the weld metal, that is, a method of adding S to the steel sheet and a method of adding the steel to the welding wire. However, since the method of adding the steel to the steel sheet causes a problem in the steel sheet characteristics, It is preferable to add it to the above. However, if the addition to the solid wire is also excessively added, the problem of high temperature cracking occurs as described above, so the upper limit is set to 0.08%. S is positively used to improve the shape of the welded joint, the amount of S added may be set to 0.02% or more. Generally, when S is added in an amount of 0.02% or more, toughness of the weld metal may become a problem. However, this depends on the characteristics required for the weld joint, and it can be appropriately selected by comparing the shape of the welded joint and the required toughness.

In the present invention, in addition to securing the strength of the weld metal, Ni of the solid wire for welding is also lowered by lowering the transformation start temperature of the weld metal and positively reducing the residual stress at the welded end, Is improved. This method positively introduces the technique of the high fatigue strength welding material into the present invention, and the technique of the high fatigue strength welding material is a technique already disclosed in Patent Documents 1 and 2 and the like. This technique and the technique provided by the present invention can be used as needed, not particularly canceling each other. The lower limit of 4.0% of Ni added to the solid wire for welding was set as a minimum value at which fatigue strength improvement due to the addition of Ni could be expected. In the case of 12.0% of the upper limit of the upper limit, the amount of austenite as a microstructure of the weld metal is increased in the case of an addition amount exceeding the upper limit, so that there is a possibility that the transformation expansion amount of the weld metal is small, It can not be anticipated. Therefore, this value is set to the upper limit.

When the content of Ni is in the range of 4.0 to 12.0%, the upper limit of S added to the solid wire for welding is preferably 0.01%, more preferably 0.006% .

These are the basic components of the solid wire for welding in the present invention.

Next, the flux-containing wire will be described.

Generally, the wire used for the thin plate welding in the automobile field is a solid wire. This is because the solid wire is cheaper than the flux-containing wire, and the solid wire is preferable from the viewpoint of coating because the amount of slag generated after welding is small. Among them, the advantage of the solid wire being inexpensive is that the production amount of the wire is somewhat large, and when the wire production is small, the flux built-in wire can be manufactured at a lower cost than the solid wire. The reason for this is that, when the wire component needs to be changed, the wire material itself needs to be re-formed for the solid wire. With respect to the flux built-in wire, by adjusting the component of the flux to be charged, Because the components can be changed. In this situation, the inventors believed that it would be meaningful to provide a technique in which the fatigue strength improvement with flux-built-in wire is more achieved.

Next, a description will be given of the reason why the outer shell is a slit-like seamless shell having a risk of entering the outside air as the forced shell of the flux-containing wire.

In contrast to the solid wire, the problem with the flux built-in wire is that there is a problem of increasing the amount of hydrogen in addition to the above-mentioned slag generation problem. Therefore, in the case of manufacturing a flux-containing wire, the flux filling the wire is dried in advance to reduce the amount of hydrogen. However, even when the flux is dried and charged into the wire, if there is a slit-like joint present in the forced shell of the flux-containing wire, there is a danger of entering the outside air, the flux absorbs moisture from the joint and consequently increases the amount of hydrogen. As the fatigue-improving technique in the present invention, there is a reduction in residual stress due to the adjustment of the component of the flux-containing wire. However, this must be a component system containing a relatively large amount of alloying elements, resulting in a so-called low temperature cracking susceptibility component system. The low-temperature crack can be prevented by lowering the amount of hydrogen, so that it is limited to a slit-like seamless shell having a risk of entering the outside air, thereby preventing moisture absorption of the flux.

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

C other than SiC is contained mainly in the steel shell in the flux-containing wire for the purpose of preventing breakage in the wire-making process during wire production. C other than SiC also has an effect of reducing the transformation temperature of the weld metal. In the present invention, however, the transformation temperature of the weld metal can be sufficiently reduced by adjusting the content of SiC in the flux to be filled in the steel shell. The lower limit of the C content other than SiC needs to be set to 0.01% in order to obtain a disconnection prevention effect in the wiring process by C in the forced shell. On the other hand, if C is excessively added to the steel shell, the wire is hardened during drawing the line this time, which causes a disconnection. Therefore, the upper limit of the C content other than SiC is set to 0.20%.

When iron powder is charged as a flux in the steel shell, C in the iron powder is included as C other than SiC. Therefore, it is preferable that the C content in the steel shell is set to 0.15%, and the remaining C amount is supplemented with the C content in the iron powder to be added as the flux from the point of alleviating the curing in wire drawing caused by C in the steel shell.

Si other than SiC and Si other than SiO ₂ have a lower limit of the content of 0.05% in order to obtain deoxidation effect of the weld metal during arc welding. On the other hand, when Si other than SiC and Si other than SiO ₂ is excessively added, the weld metal is cured and is not preferable from the viewpoint of joint properties, so that the upper limit of its content is set at 1.2%.

Mn is an element necessary for securing the strength of the weld metal. If the content is less than 0.2%, it becomes difficult to secure the strength of the weld metal, so that the lower limit of the Mn content is set to 0.2%. The reason why the lower limit of Mn can be set lower than that of the solid wire for welding in the present invention is that the strength can be secured to some extent by the addition of C. On the other hand, if the Mn content is excessively high, the toughness of the weld metal tends to deteriorate, 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, the presence of a large amount of these elements in the weld metal deteriorates the toughness. Therefore, the upper limit of the content of P is set to 0.03%.

Generally, S, like P, is an inevitable impurity element of the weld metal, but it is said that S contributes to the improvement of the bead shape by reducing the surface tension of the molten pool. Therefore, the present invention is effectively used. However, since the flux-containing wire in the present invention is limited to the range of the component that achieves the reduction of the residual stress, C is high and therefore the content of S is lower than that of the solid wire in the present invention It is necessary to set it low. Therefore, the upper limit of S was set at 0.06%.

SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O contained in the flux are usually called slag materials. In these steps, in the step of finishing the role of the binder when granulating the flux component before manufacture of the flux-containing wire, and after filling the flux component in the forced shell, drawing a line up to a predetermined wire diameter, And acts as a lubricant for reducing the resistance between the inner surface and the flux. In the present invention, by containing SiC having a lubricating action, the workability in the wire drawing process can be ensured even if the slag material, which is an oxide thereof, is reduced as compared with the prior art. However, when 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 is difficult to maintain the above processability, and problems arise in wire quality and manufacturing efficiency The lower limit of the total amount was 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 0.4%, the amount of slag generated in the welded portion increases, The upper limit of the total amount was set at 0.4%.

The SiC according to the present invention has an action as SiC having lubricating and deoxidizing properties, securing a proper amount of Si in the flux-containing wire, further acting as a main element C source for reducing the transformation starting temperature of the weld metal, It is an essential component in the present invention.

The lower limit of SiC, 0.05%, is such that the effect of improving the workability of the wire and the effect of reducing the amount of slag due to the lubrication action and deoxidation action of SiC are insufficient. On the other hand, if the content of SiC in the flux is increased, there is a problem of curing of the weld metal and a possibility that the weld metal may not be transformed due to an increase in austenite structure. In this case, the advantage of adding SiC specifically to the flux-containing wire is eliminated. As a result, the upper limit of the SiC content in the flux-containing wire was limited to 1.2%. Further, in the case of a flux-containing wire, the amount of Si in the wire tends to be higher than the upper limit of the solid wire. This is because C in SiC is combined with oxygen to form CO and relieves out of the welding arc. Therefore, even if the amount of Si exceeding the upper limit of the solid wire is contained in the flux-containing wire, Because it does not have much effect on the quantity.

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

Next, the reason for selection of the flux-incorporated wire selection element will be described.

The action of the graphite in the present invention is an alternative to SiC. As the C source, the graphite is cheaper than SiC, while the graphite is lighter, and therefore, there is a manufacturing problem that the graphite is scattered during manufacture of the flux-containing wire. However, not only inexpensiveness but also graphite is more effective than SiC in the sense of the action of a lubricant in the wire, the present inventors have decided to treat the graphite as a selective element. However, since SiC and graphite also have the same function as the C source, in order to take this point into consideration, the total amount of C converted values of the following (Equation 2) is made to limit the total amount of C.

C converted value = [graphite] + 0.3 x [SiC] (formula 2)

The lower limit of the graphite, 0.02%, was such that the effect of graphite addition could not be exhibited when the graphite was smaller than the lower limit of 0.02%. Although the upper limit of the graphite is not specifically provided in the present invention, since the range of (Formula 2) is limited, the upper limit of the graphite is limited by itself. Further, when the lower limit of 0.15% of the formula (2) is set to be lower than the lower limit, the content of the graphite should be less than 0.02%. Therefore, this value is set. On the other hand, the upper limit of 0.45% is set at such a value that the C level of the weld metal becomes excessively high at an amount exceeding the upper limit, which causes a problem of hardenability, toughness and crack susceptibility of the weld metal.

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

Ni is an element that is effective for improving the joint fatigue strength by lowering the transformation starting temperature of the weld metal, and is an element for improving joint characteristics such as strength and toughness. The lower limit of the Ni content in the case of containing Ni is 0.1% as the minimum amount which can sufficiently improve the effect of improving the joint fatigue strength in the low SiC system, but is preferably 0.5%. The upper limit of the Ni content is sufficiently attained in the effect of reducing the transformation starting temperature of the weld metal. When the Ni content exceeds 5.0%, there is a possibility that the cooling of the weld metal is stopped in a state where the weld metal does not transform into bainite or martensite transforming at a low temperature due to an interaction with C contained in the weld metal and is austenite , An improvement in fatigue strength can not be expected. 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 starting temperature of the weld metal and increasing the strength and the quenching. Particularly, since Cr and Mo have higher effect of strengthening the weld metal and securing the quenching property than Ni, it is possible to transform the weld metal into a structure having a low transformation temperature such as martensite by using this effect, The content of Cr and Mo must be 0.1% or more, respectively. On the other hand, since Cr and Mo have a lower effect of improving the toughness of the weld metal than Ni, there is a possibility that the toughness of the weld metal may be lowered if it is contained excessively. Therefore, the upper limit of Cr and Mo is 2.0% did.

Like Cu and Mo, Cu is an element having the effect of reducing the transformation starting temperature of the weld metal, improving the strength and securing the quenching property. In addition, Cu may be plated on the wire surface in order to secure the conductivity. It is necessary to set the lower limit of the Cu content to 0.1% in order to obtain the effect of the improvement of the strength of the weld metal by the Cu, the improvement of the quenching property and the effect of securing the conductivity. However, when 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 0.5%.

In the present invention, the upper limit of the total amount of at least one of Ni, Cr, Mo, and Cu is set to 6.0%. This is because if the total content exceeds 6.0% and the weld metal is contained excessively, the weld metal is not transformed into bainite or martensite which transforms at low temperature in the cooling process after welding, and becomes a state of austenite structure, The improvement becomes difficult. Therefore, the upper limit of the total content is preferably set to 6.0%. In the present invention, the lower limit when one or more of Ni, Cr, Mo, and Cu is added is not particularly specified, but the lower limit is set for each of the additional elements. exist. When it is necessary to increase the fatigue strength in addition to the effect of improving the shape of the tip in the present invention, it is preferable to set the lower limit of the total content to 1.5%. The addition of less than 1.5% is added for the purpose of improving the mechanical properties such as Charpy characteristics, but it is the object of the person skilled in the art using the present invention to improve Charpy characteristics or improve fatigue characteristics, It is not particularly difficult to determine the addition amount.

B is a quenching element and secures the quenching of the weld metal to make the microstructure of the weld metal a higher strength structure and also inhibits the formation of the start of the transformation at high temperatures, . Since the weld metal has a higher oxygen content than the steel sheet, B may be bonded to oxygen and lose its effect, so that the quenching by B in the weld metal and the tensile strength and fatigue strength by microstructure control are improved , The lower limit of the B content is preferably 0.001%. On the other hand, the upper limit of the amount of B added was set at 0.015% because the risk of causing cracks in the weld metal occurs when an amount exceeding this amount is added.

Nb, V, and Ti are elements having an effect of increasing the strength by forming carbide in the weld metal. By containing at least one of Nb, V, and Ti in a small amount in the weld metal, do. If the lower limit of the total content of at least one of Nb, V and Ti is less than 0.005%, improvement of the joint strength can not be expected to be expected. Therefore, the lower limit of the total content is preferably 0.005%. On the other hand, if the total content exceeds 0.3%, the strength of the weld metal becomes excessive, which causes a problem in the characteristics of the joint. Therefore, the upper limit of the total content is preferably 0.3%. In addition, since Ti has an effect of improving the strength of the weld metal and stabilizing the welding arc, Ti is preferably contained preferably in an amount of 0.003% or more.

In the present invention, the S of the flux-containing wire is set to a range that can be positively used so as not to adversely affect the joint characteristics. S can reduce the viscosity of the weld metal and can be expected to have an effect on the improvement of the welded end shape. There are two methods of ensuring the amount of S of the weld metal, that is, the method of adding S to the steel sheet and the method of adding to the welding wire. However, since the method of adding the steel to the steel sheet causes problems in the steel sheet characteristics, It is preferable to add it to the wire. However, in the method of adding to the flux-containing wire too, if it is added excessively, the problem of high temperature cracking occurs as described above, so the upper limit is set to 0.06%. S is positively used to improve the shape of the welded joint, the amount of S added may be set to 0.02% or more. Generally, when S is added in an amount of 0.02% or more, toughness of the weld metal may become a problem. However, this depends on the characteristics required for the welded joint, and it can be appropriately selected by comparing the shape of the welded joint and the required toughness. However, when one or more of Ni, Cr, Mo and Cu is added within the range of the present invention, it is preferable to set the upper limit of S to 0.03% from the viewpoint of crack susceptibility.

The arc stabilizer is an element having an action of stabilizing a welding arc by being contained in a flux to be charged in a forced shell. Na ₂ O and K ₂ O contained in the above-mentioned flux also act as an arc stabilizer. Therefore, these components are preferably contained to such an extent as not to hinder the reduction in the amount of slag generated in the welded portion of the object of the present invention. In addition, since the arc stabilizing effect is obtained when the compound is a compound of Na, Al, F such as giltstone (Na ₃ AlF ₆ ) without forming an oxide such as Na ₂ O or K ₂ O, From the viewpoint of reduction in the amount of the generated oxides, it is preferable to contain them as compounds other than oxides.

The lower limit of the content of the arc stabilizer other than the oxide system is preferably 0.05% in order to reduce the amount of slag generated in the welded part and to obtain the effect of stabilizing the arc. On the other hand, when the content of the arc stabilizer other than the oxide system exceeds 0.5%, the arc stabilizing effect is not changed, so that 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.

CO ₂ or Ar is used as the gas used for the shield gas, but it is still impossible to use 100% Ar for the shield gas because of the stability of the arc. In contrast, a method of using a 100% CO _2, upon effectively using the Si, such as a deoxidizing element, and sufficiently available in a range of prior art, also within the scope of Si, which discloses the present invention, the shield of 100% CO ₂ can be used as the gas, there is also the advantage that said CO ₂ gas side is less expensive than Ar gas. However, the use of a shield gas mainly composed of Ar gas has an advantage that the number of spatters can be reduced. However, since the Ar gas is an inert gas, a minimum amount of CO ₂ gas is required. For the shield gas mainly composed of Ar gas, the lower limit of 5% of the mass% of the CO ₂ gas is set so that the welding arc becomes unstable when the lower limit is 5%. 25% of the upper limit is larger than this, spatters are increased, and this value is set because there is no significant difference from the case where 100% CO ₂ gas is used as a shielding gas.

In the present invention, it is also possible to add O ₂ to the shielding gas. However, the reason for adding the O ₂ gas is to suppress the cost of the shielding gas, and it is not directly related to the effect of improving the shape of the welded end for the purpose of the present invention. Generally, in order to make the Ar gas 100%, the O ₂ gas needs to be removed (to 0%), but this increases the cost of the shield gas. On the other hand, Ar gas containing a certain amount of O ₂ can be produced at a relatively low cost. The effect of improving the shape of the welded joint is not lost even if the O ₂ gas is contained to some extent. Since the lower limit of 2% of the O ₂ gas component limit range affects the cost of the Ar gas, it is preferable to set this content to a lower value. In the case of 4% of the upper limit, in the case of the addition amount exceeding the upper limit, the oxygen amount of the weld metal is increased to cause a problem of toughness, so this value is set.

The above is the limiting reason for the fillet arc welding method of the high strength steel sheet according to the present invention.

≪ Embodiment 1 >

Hereinafter, an embodiment of the present invention will be described.

Table 1 is a table of the steel sheet components used in the first embodiment. The first embodiment aims at examining hole expandability of a steel sheet.

The steel strip having the components shown in Table 1 was heated to a heating temperature of 1150 to 1250 占 폚 and hot rolled at a finishing temperature of 820 to 900 占 폚 and then cooled at a cooling rate of 35 to 75 占 폚 / To 550 캜 to obtain a hot-rolled steel sheet having a thickness of 2.6 mm. Since various tensile strengths are obtained by controlling the cooling rate and the like, Table 1 also shows the tensile strength of the steel sheet.

From these hot-rolled steel sheets, a test piece having a square of 250 mm x 250 mm was taken, and a circular hole having a diameter of 30 mm was punched in the center portion. Thereafter, a hole expansion test was conducted with a conical punch having a vertical angle of 60 DEG. The hole expandability was measured by measuring the diameter d at the time when the cracks penetrated to the plate surface and the surface, observing cracks occurring on the punching surface by widening the hole with a conical punch, and calculating the increase rate of the diameter d by {(d-30) 30}. When the diameter is doubled to 60 mm, the hole expandability is 100%.

Table 1 shows the components of the steel sheet, tensile strength and hole expandability. In general, the hole expandability tends to decrease as the steel strength increases. Therefore, in comparison with the steel material of 700 MPa or more in the present invention and the steel material of 400 MPa in a lower strength, for example, It is not valid. It is necessary to compare the steel materials of 700 MPa or more and evaluate the superiority thereof. For this reason, except for B13 and B14, the steel materials shown in Table 1 were selected so that the strength was 700 MPa or more.

On the other hand, with respect to comparative examples B01 and B12, the hole expandability is more than 70%, and it is found that good characteristics are exhibited. The reason why these steel sheets are comparative examples is that Si is out of the scope of the present invention, but it is understood that even if Si is below the lower limit of the present invention, the hole expandability is good. The reason why such a phenomenon occurs is that the lower limit of Si is set from the viewpoint of securing the hole expandability and is set for improving the welded end shape to be compared in the second and subsequent embodiments. This is because the legitimacy of one lower Si is not shown.

In Comparative Examples B13 and B14, Si is within the range of Examples of the present invention, but Mn and C are out of the range of the present invention, and the strength is not 700 MPa. B13 and B14 are comparative examples in the present invention because the present invention targets a steel material of 700 MPa or more in which the fatigue problem becomes remarkable.

≪ Embodiment 2 >

The second embodiment related to the improvement of the shape of the welded portion and the fatigue test is shown below.

In the first embodiment, an overlapping fillet arc welded joint was manufactured using a steel plate having hole expandability of more than 70%, and the welded end shape and fatigue test were conducted. Overlapped fillet arc welded joints are one of the plate thickness ranges of the present invention, particularly the welded joint shapes most commonly used for automotive wheel part parts. Table 2 shows the components of the welding solid wire used when the welded joint was manufactured.

Tables 3 to 5 show the welding conditions and the composition of shield gas used. The results of the examples of Tables 3 to 5 are all the cases where the thickness of the steel sheet is 2.6 mm. It is possible to investigate the influence by changing the welding speed. The current at this time is a condition capable of forming a weld joint by one-pass welding, and 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.

An overlapping fillet arc welded joint was made, from which a section macro was taken and the flange angle and undercut depth defined in FIG. 2 were measured. If there is no undercut, the undercut depth is defined as zero. Further, the plane bending fatigue test piece shown in Fig. 6 was sampled from the same weld joint, and fatigue test was carried out. In the case of the second embodiment, the plate thickness 10 and the plate thickness 11 in Fig. 6 are 2.6 mm. When the fatigue test was carried out, a strain gauge was attached to the vicinity of the welded portion of the surface of the test piece to check the stress state on the surface. The cyclic stress was given under the condition of the stress ratio, R = 0.1. In this case, when the stress amplitude is 100 MPa, the maximum stress is 111 MPa, the lowest 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 was not induced even when the stress of 2,000,000 cycles was applied.

Tables 3 to 5 show test results of Frank angle, undercut depth, and fatigue strength. Tables 3 to 5 show a series of examples. As described above, since the fatigue strength required for an overlapping fillet welded joint of a thin steel plate is about 250 MPa, it is aimed to evaluate that the fatigue strength becomes 250 MPa or more.

No. 1 is an example in which the value of the steel sheet Si and (formula 1) is out of the range of the present invention but the fatigue strength is 270 MPa because the welding speed is as low as 70 cm / min and the welded end shape is good. In other words, it is possible to improve the shape of the welded edge by making the welding speed slower according to the components of the steel sheet, but it is understood that the welding construction efficiency must be sacrificed as much. Similarly, in the case of Nos. 2 and 43 in which the welding speed is high even in the case of combination of the steel plate and the welding wire, the shape of the welded ends was not improved, and the fatigue strengths were lowered to 180 MPa and 170 MPa, respectively. No.3, No.4 and No.44 show the same results. However, in No. 3, No. 4 and No. 44, the steel sheet Si is as low as 0.17%, but the wire Si is increased to 1.55%, so that the value of (Formula 1) is within the range of the present invention. However, the fatigue strength is high at No. 3, but at No. 44, since the welding speed is 120 cm / min, the fatigue strength is as low as 180 MPa. That is, the amount of Si in the steel sheet has such an effect that it has such an effect that it can not be supplemented by the wire Si.

On the other hand, Nos. 5 and 19 are examples in which blowholes due to Si shortage of the wire are within the scope of the present invention, and the shape of the welded joint and the fatigue strength are not measured.

No.13 was in the range of the present invention although it was in the range of the present invention. However, it was found that the welding speed was 170 cm / min and the Frank angle was relatively small at 55, Yes. In No. 13, when the welding speed is set within the range of the present invention as in No. 12, the fatigue improving effect can be expected. In addition to No. 13, No. 11 in Table 3 and No. 21 and No. 23 in Table 4 all exhibited an undercut of more than 150 cm / min at the welding speed, and the fatigue strength Does not reach 250 MPa.

In No. 16, both the steel sheet Si and the wire Si are within the range of the present invention, but the value of (Formula 1) is out of the scope of the present invention. That is, it is an example showing that not only the Si amount of the steel sheet and the wire but also the value of (Equation 1) should be within the range of the present invention. No. 25 is an example in which the amount of Si in the steel sheet is low and the value of (formula 1) is also lowered. In these comparative examples, all of the Frank angles exceed 55 DEG and the fatigue strength does not reach 250 MPa, except for the case where the welding speed is 70 cm / min.

No. 42 is an example in which the wire Ni is high and high temperature cracks are generated thereby making it impossible to perform the test. In order to further improve the fatigue strength by adding Ni, it is necessary to set the amount of wire Ni within the range of the present invention as in No. 35. [ In No. 41, the wire Mn is 3.0%, which exceeds the range of the present invention. In the case of this welded joint, it was found that the weld metal hardness exceeds the Vickers hardness of 400 and there is a problem of softness. Therefore, the measurement of the shape of the welded tip and the fatigue strength was not carried out.

On the other hand, in the examples of Tables 3 to 5, the Frank angle is all 55 degrees or less, and the fatigue strength exceeds 250 MPa. In particular, when the value of (Equation 1) is 0.40 or more, the Frank angle is 45 degrees or less, and the fatigue strength is all 280 MPa or more. There are two methods of ensuring the value of (formula 1) to 0.40 or more, that is, a method of securing the steel sheet by Si and a method of securing by wire Si. It is not particularly difficult for a person skilled in the art. Nos. 37, 38 and 39 show the influence of the shielding gas. However, the shape of the welded end is slightly improved in the case of Ar + 20% CO ₂ and Ar + 7% CO ₂ gas than in the case of 100% CO ₂ gas. In addition, in addition to the improvement of the shape of the welded joint, the addition of Ni to the wire and the reduction of the residual stress in the welded end portion are also used in combination. Therefore, the fatigue strength is 380 MPa, to be. No. 40 is an example in which W08 is used as a wire to which 0.05% of S is added, but the Frank angle of the welded end is the smallest at 38 °. However, S is not preferable from the viewpoint of toughness of the weld joint. Therefore, when the fatigue improving effect can be sufficiently obtained without adding 0.05% of S, it is preferable to suppress S to 0.01% or less.

≪ Third Embodiment >

Next, the influence of the plate thickness was examined by using the steel plate B03 and the welding solid wire W05 used in the second embodiment. The plate thickness was set to 2.0, 2.6, 4.0, and 7.0 mm, respectively, by performing the rolling conditions as shown in the first embodiment. The test method is the same as in the second embodiment. Table 6 shows the results. Steel sheet and wire all have a component system within the scope of the present invention, and the value of (Formula 1) is also within the scope of the present invention. In No. 101, 102, 106, and 108, which are plate thicknesses within the range of the present invention, the Frank angle was 50 ° or less and the fatigue strength was a good value of 280 MPa or more. In No. 105, the fatigue test results are good, but in order to manufacture the weld joint by one-pass welding, the welding speed is set to 40 cm / min. It is apparent from No.1 of the second embodiment and the like that the steel plate and the welding wire do not have to fall within the scope of the present invention particularly in this welding speed condition. From the practical point of view, when applying the present invention, it is found that the preferable plate thickness range is 4 mm or less. It is considered that the welding method is about 1.6 mm from a practical point of view in consideration of the plate thickness range in which spot welding or laser welding becomes the mainstream, although the lower limit is not particularly carried out. Reference numeral 106 denotes an embodiment in which the steel sheet 6 and the steel sheet 7 in Fig. 4 have different thicknesses. Even if the plate thicknesses are different, if they are within the range of the present invention, the fatigue strength exceeds 250 MPa and the frank angle is less than 50 degrees, and good results are obtained.

It can be seen from the above that the combination of the steel sheet and the welding solid wire within the scope of the present invention can improve the welded end shape and the fatigue strength is also good.

<Fourth Embodiment>

In the fourth embodiment, the purpose is to investigate the components of the flux-containing wire and their characteristics. Table 7 and Table 8 show the results of examining the mass%, the filling rate, the wire drawability, and the Charpy absorbed energy of each component with respect to the total wire mass in the flux-containing wire. B06 of Table 1 was used as a steel material.

As can be seen from Tables 7 and 8, many test items are listed in Table 2, which is the table of the embodiment of the solid wire for welding. This is because there is a possibility that the Charpy characteristic of the weld metal becomes a problem because the flux is contained in the flux-containing wire characteristic of the flux-containing wire, and in the flux-containing wire according to the present invention, the amount of C added is set higher than that of the solid wire for welding , Charpy characteristics are shown in Table 7 and Table 8, and the number of items to be evaluated is larger than that of the solid wire, such as the wire wire, the amount of slag, and the scattering property when graphite is used .

First, the wires in Table 7 will be described.

It is within the scope of the present invention that the wire symbols are between 100 and 110, and the wire elements between 150 and 165 are outside the scope of the present invention.

For the wires in Table 7, the non-acidity of the flux, the sound of the wire, the Charpy absorbed energy, and the amount of slag were measured. The non-acidity of the flux means the ratio of the amount of graphite prepared for producing the flux and the ratio of the amount of graphite in the flux immediately before charging the wire. If the graphite does not scatter, the scattering rate becomes 0% because they coincide with each other. However, when the graphite is scattered, the graphite is reduced immediately before wire charging. Non-acidity was evaluated at this reduction rate. Wire wire The voice was evaluated based on whether wire breakage occurred during wire production. The Charpy absorbed energy was obtained as follows. A steel plate having a plate thickness of 3.2 mm was welded to each wire, and a 1/4 size Charpy test piece obtained by machining a 2 mm V notch on the center portion of the weld metal was sampled. . The amount of slag was evaluated by the bead-on-plate welding with a weld bead length of 250 mm and the weight of the slag generated on the weld metal surface at that time.

The wires 150, 151, and 159 show that the slag material is out of the range of the present invention, the slag generation amount exceeds 0.1 g, and there is a problem in paintability. On the other hand, in the wires 100 to 105 within the scope of the present invention, all of the slag production amounts are found to be less than 0.1 g, and in order to secure the paintability, it is necessary to limit the slag materials within the scope of the present invention. However, wire 150 had a good weld bead. Therefore, Charpy test pieces were sampled by using the earpieces and Charpy test was carried out. As a result, it was found that the Charpy test pieces were 7J. This is because, in the wire 150, the Mn exceeds the range of the present invention. Therefore, in order to obtain good mechanical properties, Mn must be within the range of the present invention.

On the other hand, the wire 151 is also below the scope of the present invention. In such a case, there is a problem that the wire 154 is broken due to difficulty in cutting the wire during the manufacturing process. However, since the wire 151 is excessively added with the slag material, there is no disconnection problem. Therefore, when the amount of slag was measured using the wire 151, the occurrence of slag exceeded 0.34 g and 0.1 g. That is, in order to prevent disconnection while suppressing occurrence of slag, it is necessary to use SiC instead of slag material.

Wire 152 is an example in which SiC exceeds the range of the present invention, and as a result, (Formula 2) also exceeds the range of the present invention and cracks are generated in the welded portion. Even if SiC was within the range of the present invention, the same cracks were also generated in the wire 165 in which (Formula 2) exceeded the range of the present invention. In the wire 153, the Si exceeded the range of the present invention, and the Charpy test was less than 10 J due to the Si excess. The wire 155 is a case where C exceeds the range of the present invention, and the Charpy value is also less than 10J. In the wire 156, Si is below the range of the present invention, and defects such as blow holes are generated in the welded portion.

On the other hand, in the wire 157, C was below the range of the present invention. Since the strength of the steel shell was insufficient, wire breakage occurred during wire production, and wire production could not be performed. The wire 158 has a Mn lower than the range of the present invention, and the wire 157 has a problem of disconnection due to the same reason.

In the wires 160 to 162 and 164, the total of Nb, V and Ti exceeded the range of the present invention, and the Charpy value was less than 10J. In the wire 163, B has exceeded the range of the present invention, and cracks have occurred in the welded portion.

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

Next, the wires in Table 8 will be described.

The wire in Table 8, and the wire within the scope of the present invention is 200 to 210. [ These wires have a relatively large amount of Cu, Ni, Cr, and Mo added thereto as compared with the wires in Table 7. [ The wires 250 to 255 are comparative examples.

The wire 250 had a slag content exceeding the range of the present invention, and the amount of slag exceeded 0.3 g and 0.1 g. This tendency is also confirmed in the examples of Table 2, but a component system to which Cu, Ni, Cr, and Mo are added is also confirmed.

The wires 251 and 252 are such that the sum of these four elements exceeds the range of the present invention, but no problem occurs in particular. This point will be described later in the fifth embodiment.

The wire 253 has a total of Nb, V and Ti exceeding the range of the present invention. As a result, the Charpy value became less than 6J and less than 10J.

The wire 254 is made of graphite in order to prevent disconnection of the wire because SiC is not added and the slag material is limited within the scope of the present invention. As a result, the graphite non-acidity became 40%. If the non-acidity becomes as high as this, it becomes very difficult to manage the wire manufacturing process, and there is a risk that the wire component is largely changed due to a slight change of the manufacturing process. In this case, it means that it is difficult to produce a wire of good quality.

Wire 255 has a problem of wire breakage because the amount of SiC added is below the range of the present invention.

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

<Fifth Embodiment>

In the fifth embodiment, among the steel materials and wires used in the first and fourth embodiments, there is no problem, that is, in the remarks column of Tables 1, 8 to 9, &quot; present invention &quot; And the effects of the present invention were confirmed, the overlap fillet welding was carried out by using those described in some &quot; comparative examples &quot;, and fatigue tests were conducted.

In addition, the table also shows the composition of the shield gas used. The results of the examples of Tables 10 to 11 are all the cases where the thickness of the steel sheet is 2.6 mm. It is possible to investigate the influence by changing the welding speed, but the current at this time is a condition capable of forming a weld joint 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.

Under these conditions, an overlapping fillet arc welded joint was made, from which a cross section macro was taken and the flange angle and undercut depth defined in FIG. 4 were measured. When there is no undercut, the undercut depth is defined as zero. Further, the plane bending fatigue test piece 9 shown in Fig. 6 was taken from the same welded joint and subjected to fatigue test. When the fatigue test was carried out, a strain gauge was attached to the vicinity of the welded portion of the surface of the test piece to check the stress state on the surface. The cyclic stress was given under the condition of the stress ratio, R = 0.1. In this case, when the stress amplitude is 100 MPa, the maximum stress is 111 MPa, the lowest 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 carried out under these conditions and the fatigue fracture was not broken even when the stress of 2,000,000 cycles was applied.

Tables 9 to 11 show test results of Frank angle, undercut depth, and fatigue strength. The thicknesses 10 and 11 of the steel plates 6 and 7 shown in Fig. 6 are 2.6 (thickness) and 10 (mm), respectively, except Table 11 in which influence of the plate thickness is examined. Mm.

Table 9 shows B01 to B10, B25 and B26 and B01 and B12 which are described as &quot; comparative examples &quot; in the remarks column of Table 1, And the welding wire used in the wire 100 to 110 shown in Table 2 was used to fabricate an overlapping fillet welded joint and the fatigue test piece was taken therefrom and the fatigue test was carried out. The reason for using B01 and B12, which are comparative examples of the steel, is that no problem occurs particularly at the stage of Table 1. The reason for not using the wires of wires 150 to 165 is that before the fatigue test, problems such as the Charpy value, wire wire noise, and slag generation amount have already occurred.

Nos. 1 and 2 in Table 9 are examples in which the Si of the steel is below the present invention. In the case of No. 1 having a welding speed of 70 cm / min, the Frank angle was 48 °, no undercut occurred, the shape of the tip 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 shape of the leading edge can be improved regardless of the amount of Si in the steel sheet. As described above, it is known in the art that the shape of the zipper is improved when the welding speed is lowered, so that the welding rate of 80 cm / min or less is out of the scope of the present invention. On the other hand, No. 2 is the case where the steel material and the wire are the same and the welding speed is as high as 100 cm / min. However, the Frank angle increases to 65 °, undercut occurs, and the fatigue strength is as low as 200 MPa. This is because the steel Si is below the range of the present invention.

However, in the case of No. 3 in which the Si of the steel sheet is lower than the present invention even when the steel sheet is welded at a high rate of 100 cm / min using the wire 101 having a high Si content, improvement in fatigue strength can not be confirmed. The wire 101 contains Si more than twice as much as the wire 100. However, the fact that the shape of the wire is not improved means that the influence of the steel sheet Si can not be supplemented by the wire Si as well as the influence of the simple base material dilution .

No. 4 is an example in which the steel sheet Si and the wire Si are within the range of the present invention and the Frank angle is less than 55 degrees and the fatigue strength is 300 MPa or more even if the welding speed is 140 cm / However, in No. 5 where the welding speed was 170 cm / min, the fatigue strength was lowered because the Frank angle exceeded 55 ° and undercut occurred. That is, when the welding speed exceeds the range of the present invention, the fatigue strength improving effect can not be exhibited.

As shown in Table 1 of the first embodiment, even if these elements are added to such a degree that the mechanical properties can be secured, An improvement effect can be obtained. Of these, No. 9 and 10 are obtained by adding 3% of oxygen to the shield gas, but the fatigue improving effect is sufficiently obtained.

In the No. 15, the value of (formula 1) is within the range of the present invention, but the value of Si of the steel sheet is below the range of the present invention. In this case, the fatigue strength can not be attained to 300 MPa, and it can be understood that the fatigue strength improvement effect can not be expected. In other words, fatigue-improving effect can not be obtained only by satisfying the formula (1), and it is also necessary to satisfy the Si amount of the steel sheet at the same time.

In Nos. 16 to 20, the steel was used as the component system B02 within the range of the present invention, and the wire was changed to 100, 102 to 105 within the range of the present invention, and Nb, V and Ti . As shown in Table 2 of the second embodiment, all of these wire components are within the scope of the present invention, and even if the selective element is added within this component range, the fatigue strength improving effect is sufficiently obtained, and the total fatigue strength is 300 MPa or more Respectively.

No. 21 is an example using 100% CO ₂ as a shielding gas, but the fatigue improving effect was confirmed as in the case of the other examples.

Nos. 22 and 23 were conducted to compare the case where the value of (Equation 1) was less than 0.40. In this case, the Frank angle is slightly larger than 50 DEG, and the fatigue strength is 290 MPa in either case, which is slightly less than 300 MPa in the present invention. However, in the case of the comparative example, the effect of improving the fatigue is obvious in consideration of the fact that it is lower than 250 MPa in all cases.

Nos. 24 to 28 are Examples using wires of 106 to 110 in which S is added to a large amount of wire. Compared with No. 8 in which the value of (Equation 1) is equivalent, the Frank angle is slightly small, The increase was also somewhat recognized. This is thought to be due to the addition of S in large amounts. The wires 106 to 110 are examples in which S is higher than that of the wire 100 in Table 2. However, since the Charpy value tends to decrease, it is preferable that the improvement of fatigue and the guarantee of Charpy be given priority. It may be determined according to the required characteristics, and those skilled in the art can easily judge it.

Nos. 29 to 31 are examples in which a steel material having a relatively high Si content of steel is used, which is characterized in that the value of the formula (1) is large and fatigue strength is improved.

Whether or not the fatigue strength of the actual structure is required depends on the fatigue design. Those skilled in the art can adjust the value of (Expression 1) according to the design concept.

Table 10 is mainly for the purpose of investigating the influence of the selective elements of the wire, Cu, Ni, Cr and Mo. The data shown in Table 5 are obtained by combining the steel sheets B01, B04 and B06 in Table 1 of the first embodiment using the wires 200 to 210, 251 and 252 in Table 8 of the second embodiment, The fatigue test result at the time of manufacture. No. 51 is the case where the Si content of the steel sheet is below the range of the present invention, but the Frank angle is more than 55 °, which is not preferable from the viewpoint of the fatigue strength. However, the fatigue strength was more than 300 MPa. This is because the wire 200 itself is set to have a relatively high total of 4.5% of the selected elements, and it is considered that the same effect as that of the conventional high fatigue strength welding material is exhibited. However, the fatigue strength of No. 51 is about the same as the fatigue strength of the present example as shown in Table 4. That is, even if an alloy element such as Ni, which is expensive and particularly expensive, is not added, the fatigue strength can be sufficiently improved by the wire of inexpensive component system by adding Si to the steel sheet, so that industrial advantage is shown in Table 4 . Therefore, No. 51 is a comparative example in the present invention.

On the other hand, No. 52 indicates that the Si content of the steel sheet is within the range of the present invention and (Formula 1) is within the scope of the present invention. In this case, when the wire 200 having a large amount of addition of elements such as Cu, Ni, Cr, Mo, etc. is used, the fatigue strength is further improved to be more than 400 MPa. This tendency was also confirmed in Nos. 53, 54, 55 and 57. This is considered to be an increase in the residual stress reducing effect due to the addition amount of elements such as Cu, Ni, Cr, Mo, and the like, thereby increasing the fatigue improving effect. In No. 56 and 58, the fatigue strength was sufficient to improve to 360 MPa, but not until reaching 400 MPa as in No. 52. This is an improvement due to the effect of improving the shape of the leading end in consideration of the fatigue strength of the present invention shown in Table 10, and it is considered that the wires 204 and 206 have not reached the residual stress reducing effect. Therefore, the addition amount of elements such as Cu, Ni, Cr, and Mo needs to be 1.5% or more in order to further improve the fatigue strength. The addition amount of less than the above may be added for the purpose of ensuring mechanical properties such as Charpy value.

Nos. 59 and 60 are within the scope of the present invention, but the amounts of elements such as Cu, Ni, Cr, and Mo added to the wire exceed the range of claim 11 of the present invention. Both of the fatigue strengths exceed 400 MPa, and the improvement effect is large. Therefore, it has been shown that the fatigue countermeasure has a sufficient effect. However, although the wires 251 and 252 contain many alloying elements, the fatigue strength is equivalent to that of No.52. This indicates that further fatigue improvement can not be obtained even if the total amount of these elements added exceeds 6%. In this sense, it can be judged that the wires 251 and 252 have a high manufacturing cost for the wire and have a small industrial advantage. Therefore, it is preferable that the wire component range is within the scope of Claim 11 of the present invention.

Nos. 61 to 65 are examples in which S is relatively high and 207 to 210 are used. Among them, No. 61 has a high fatigue strength of 430 MPa, which is considered to be because the alloying element of the wire is relatively high, and the residual stress reducing effect is exhibited in addition to the effect of improving the shape of the tip. Nos. 62 to 65 have a fatigue strength of 360 MPa or more, but they do not reach 400 MPa. This is considered to be because the fatigue enhancement is expressed by the effect of improving the shape of the tip, and the effect of the residual stress reduction effect is not applied. However, No. 61 to No. 65 all had a Frank angle of less than 40 °. It is considered that this satisfies the range of Si in the present invention and that the effect by S is filled. In general, however, adding a large amount of S may cause problems such as a Charpy value and a crack. Therefore, it is necessary to determine the use while considering the required characteristics of the joint.

Table 11 shows the influence of plate thickness. The steel sheet is B02, the steel sheet component is within the range of the present invention, the wire is 100, and the wire component is within the range of the present invention. First, when the plate thickness 10 and the plate thickness 11 are the same, the joints are No. 101, 102, and 108, respectively. When the plate thickness was 7.0 mm, welding could not be performed unless the welding speed was 40 cm / min. If we try to exceed 110cm / Min, the fillet leg length is short enough to be 2 passes. The fatigue strength of Nos. 101, 102 and 108 is 290 MPa or more. When the plate thickness was 4.0 mm, the result was slightly less than 300 MPa. However, because the leg length was long, the melt pool was stretched and the Frank angle tended to become larger than Nos. 101, 102 and 108 to be. In No.105, the tendency became larger and the fatigue strength was less than 250 MPa. In order to obtain the fatigue strength of about No.101, 102, and 108 in No. 105, it is desirable to improve the frank angle by performing 2-pass welding. However, in the thin plate field to which the present invention is applied, Welding.

Nos. 106 and 109 are examples in which the plate thickness 10 and the plate thickness 11 are different from each other. However, it has been found that the fatigue strength is improved if the thickness of both plates is within the preferable range of application of the present invention.

From the above, it can be seen that the combination of the steel sheet within the scope of the present invention and the wire with built-in flux for welding can improve the welded end shape and the fatigue strength exceeds 250 MPa.

1: Fe atom before Si addition
2: Fe atoms after Si addition
3: Si
4: Wire
5: Frank angle
6: Steel plate
7: Steel plate
8: Undercut depth
9: Specimen
10: plate thickness
11: plate thickness

Claims (11)

A fillet arc welding method of a high strength steel sheet having a tensile strength of 700 MPa or more, wherein a welding speed is 120 cm / min to 150 cm /
The steel sheet according to claim 1,
C: 0.02 to 0.15%
0.2 to 1.8% of Si,
Mn: 0.5 to 2.5%
P: 0.03% or less,
S: not more than 0.02%
The steel sheet comprising:
A flux-built-in wire for gas-shielded arc welding, comprising a slit-shaped,
In one or both of the forced shell and the flux, the total mass%
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: 0.06% or less,
Further, as a flux to be charged in the forced shell,
SiC: 0.05 to 1.2%
And at least one of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O in a total amount of 0.05 to 0.4%, the balance being iron and inevitable impurities,
Characterized in that the steel sheet is subjected to fillet arc welding using a welding wire satisfying the following formula (1-1), wherein the amount of Si contained in the welding wire is subjected to fillet arc welding.
Si (wire) ≥ {0.40 - Si (steel plate)} / 0.1 (Equation 1-1)
Note that Si (steel plate) represents the Si mass% of the steel sheet, and Si (wire) represents the total Si mass percentage of the welding wire The steel sheet according to claim 1, wherein the steel sheet further comprises, by mass%
Al: 0.005 to 0.1%
Wherein the fillet arc welding method comprises the steps of: The steel sheet according to claim 1, wherein the steel sheet further comprises, by mass%
0.005 to 0.1% of Ti,
0.005 to 0.1% of Nb,
V: 0.01 to 0.2%
0.1 to 1.0% Cr,
Mo: 0.05 to 0.5%
, Wherein the fillet arc welding method comprises the steps of: 2. The flux according to claim 1, wherein the flux-containing wire for welding is filled in a mass% of the entire wire,
Graphite: 0.02% or more, and the total amount of C-converted values defined in the following formula (2) is 0.15 to 0.45%.
C converted value = [graphite] + 0.3 x [SiC] (formula 2)
However, [graphite] and [SiC] represent the mass% of graphite and SiC with respect to the whole wire, respectively. The method according to claim 1, wherein the welded flux-containing wire is provided on one or both of the steel shell and the flux, in mass% of the whole wire,
0.1 to 5.0% of Ni,
0.1 to 2.0% of Cr,
Mo: 0.1 to 2.0%
Cu: 0.1 to 0.5%
By weight or more, and 0.1 to 6.0% by weight in total of at least one of them. The method according to claim 1, wherein the welded flux-containing wire is provided on one or both of the steel shell and the flux, in mass% of the whole wire,
B: 0.001 to 0.015%
Wherein the fillet arc welding method comprises the steps of: The method according to claim 1, wherein the welding flux-incorporating wire comprises, on one or both of the steel shell and the flux, one or more of Nb, V and Ti in a total mass% of the wire in a total amount of 0.005 to 0.3 % By weight of a high-strength steel sheet. The high-strength steel sheet according to any one of claims 1 to 3, characterized in that the flux for filling the welding flux-containing wire is filled in the steel shell and contains 0.05 to 0.5% of an arc stabilizer other than an oxide- Fillet arc welding method. The method according to claim 1, wherein the welding flux-containing wire is provided on one or both of the steel shell and the flux,
S: 0.02 to 0.06%
Wherein the fillet arc welding method comprises the steps of: The method as claimed in claim 1, wherein the fillet arc welding method of the high-strength steel sheet is gas shielded arc welding,
CO ₂ : 5% or more and 25% or less,
O ₂ : 4% or less (including 0%)
And a shield gas composed of a remaining amount Ar and inevitable impurities is used. A fillet arc welded joint of a high strength steel sheet having a tensile strength of 700 MPa or more,
A fillet arc welded joint of a high strength steel plate, characterized by being manufactured using the fillet arc welding method according to any one of claims 1 to 10.

Images