JP2000288728A - High fatigue strength welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a welded joint having high fatigue strength by a simple welding method utilizing a low temp. transformation expansion by forming the welded metal of weld beads so that the starting temp. of the transformation from austenite to martensite at the toe part of welding is located in a specified range. SOLUTION: The welded metal is formed so that the starting temp. of the transformation from austenite to martensite in the weld bead is located in a range of 150-350 deg.C. The welded metal whose yield strength becomes 40-120 kg/mm2 at the starting temp. of the transformation is formed. On a structural member receiving the fatigue load, an out-of-plane gusset, cover plate or stud is welded. At both end parts of the out-of-plane gusset, a bevel part is arranged over the range of >=5 mm from the end parts, and the area of undeposit portion is reduced by >=10% compared to the area in the case of arranging no bevel part. The content of C, Ni, Cr and Mo in the welded metal is, by wt.%, C+Ni/12+Cr/24+Mo/19=0.85-1.3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welded joint having high fatigue strength for improving the reliability of a welded structure.

[0002]

2. Description of the Related Art Fatigue cracks generated in welds have a significant effect on the reliability of the entire structure. Therefore, techniques for improving the fatigue properties have been attempted for some time. The portion where the fatigue crack is likely to occur is the welded portion. The reason for this is that the welded portion has a stress concentration portion, a tensile residual stress is generated, and the like. Solving these causes is effective for realizing a welded joint having high fatigue strength. Therefore, as a high fatigue strength welded joint in the prior art, a joint in which stress concentration is reduced by applying a decorative welding by a mechanical method or TIG welding, or compressive residual stress is introduced into a part where fatigue occurs by using peening, and at the same time, There were joints with reduced stress concentration. Since these joints directly increase the cost of manufacturing a structure, a welded joint having improved fatigue strength other than such a joint has been desired.

[0003] Recently, attention has been paid to a technique for utilizing a transformation expansion of a weld metal to reduce residual stress and thereby improve fatigue strength. For example, in Ohta et al., In the 61st meeting of the Japan Welding Society, pp. 520-521, reports on the improvement of the fatigue strength of square-turn welded joints utilizing the transformation expansion of weld metal. According to this report, by lowering the temperature at which transformation from austenite to martensite (Ms temperature) is started, expansion accompanying transformation becomes larger than heat shrinkage after transformation, and as a result, residual stress of compression is introduced. A high fatigue strength welded joint is obtained. According to Ohta et al., The main plate (flat plate) of the turning welding joint
Preheated and welded with the addition (vertical plate) at room temperature,
The improvement of fatigue strength has been confirmed. The welding joints reported by Ohta et al. Have many problems from the viewpoint of construction cost, such as preheating must be performed from the viewpoint of construction work, and the vertical plates are kept at room temperature.

[0004]

It is an existing finding that the lower the transformation temperature, the lower the residual stress tends to be, and it is easily presumed that the fatigue strength is affected by the residual stress. . However, high fatigue strength welded joints that can be manufactured using a simple construction method applicable to construction work have not yet been established. Although the method of Ota et al. Uses a technique of reducing residual stress, the employed construction method is not practical and cannot be said to be a welded joint suitable for implementation.
On the other hand, conventional joints on which decorative welding such as peening or TIG welding is performed are themselves a factor of increasing the construction cost of a welded structure. If a joint that achieves high fatigue strength is established by introducing compressive residual stress into a weld by simple construction and using it, the effect will be enormous from the viewpoint of improving the reliability of the welded structure.

An object of the present invention is to provide a high fatigue strength welded joint which utilizes low-temperature transformation expansion and can be manufactured by a simple welding method.

[0006]

Means for Solving the Problems In view of the above circumstances, the present inventors have studied various techniques for reducing the residual stress of the welded part and improving the fatigue strength, and have conducted intensive studies so far. As a result, the present invention has been completed, and the gist thereof is as follows. (1) At the weld toe where fatigue is a problem, a weld metal is formed at a temperature at which transformation from austenite to martensite starts at 350 ° C or lower and 150 ° C or higher with respect to a weld bead forming the weld toe. High fatigue strength welded joint characterized by: (2) At a temperature at which transformation from austenite to martensite starts, the yield strength is 40 kg / mm ² or more;
The high fatigue strength welded joint according to (1), wherein a weld metal of 120 kg / mm ² or less is formed. (3) The high fatigue strength according to the above (1) or (2), wherein one or two or more out-of-plane gussets, cover plates, or studs are welded to the structural member subjected to the fatigue load. Welded joints. (4) In the case where an out-of-plane gusset is welded to a structural member subjected to fatigue load, a groove is formed at both ends of the gusset over a range of 5 mm or more from the end, and the gusset and the gusset in the range where the groove is formed are formed. The high fatigue strength according to (3), wherein the area of the unwelded portion existing between the attached structural members is reduced by 10% or more with respect to the area of the unwelded portion when no groove is formed. Welded joints. (5) The high fatigue strength welded joint according to (1) or (2), wherein the structural member having a scallop and subjected to a fatigue load is welded to the structural member by rotary welding. (6) For a structural member having a scallop and subjected to a fatigue load, a groove is formed in a range of 5 mm or more from the end of the scallop, and between the structural member having the scallop in the range where the groove is formed and a structural member to which it is attached. The high fatigue strength welded joint according to the above (5), wherein the area of the unwelded portion existing in the above is reduced by 10% or more with respect to the area of the unwelded portion when no groove is formed. (7) A weld metal having a parameter Pa defined by the following equation in a range of 0.85 or more and 1.30 or less, where C, Ni, Cr and Mo are each represented by weight% of each component. (1), (2),
(3) The high fatigue strength welded joint according to (4), (5) or (6).

Pa = C + Ni / 12 + Cr / 24 + Mo / 19 (8) By weight%, C: 0.01 to 0.2%, Si: 0.
1 to 0.5%, Mn: 0.01 to 1.5%, P: 0.0
(1), (2), wherein a weld metal containing 3% or less, S: 0.02% or less, Ni: 8 to 12%, and the balance being iron and unavoidable impurities is formed. ,
(3) The high fatigue strength welded joint according to (4), (5), (6) or (7). (9) By weight%, Ti: 0.01 to 0.4%, Nb:
The high fatigue strength according to (8), wherein a weld metal further containing one or more of 0.01 to 0.4% and V: 0.1 to 1.0% is formed. Welded joints. (10) By weight%, Cu: 0.05 to 0.4%, Cr:
0.1-3.0%, Mo: 0.1-3.0%, Co:
The high fatigue strength welded joint according to (8) or (9), wherein a weld metal further containing 0.1% to 2.0% of one or more kinds is formed. (11) By weight%, C: 0.001-0.05%, S
i: 0.1 to 0.7%, Mn: 0.4 to 2.5%, P:
0.03% or less, S: 0.02% or less, Ni: 4 to 8
%, Cr: 8 to 15%, N: 0.001 to 0.05%, C + N: 0.001 to 0.06%, with the balance being a weld metal consisting of iron and unavoidable impurities. (1), (2), (3),
(4) The high fatigue strength welded joint according to (5), (6) or (7). (12) Mo: 0.1 to 2.0% by weight, Ti:
0.005 to 0.3%, Nb: 0.005 to 0.3%,
V: A high fatigue strength welded joint according to (11), wherein a weld metal further containing one or more of 0.05 to 0.5% is formed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, the technical concept of the present invention will be described. The first technical concept of the present invention is to obtain a high fatigue strength welded joint by reducing the residual stress at the bead toe where a fatigue crack occurs.

When the weld metal transforms from austenite to martensite during the cooling process, the volume increases, that is, expands. At this time, compressive stress is generated in the weld metal because it is constrained from surrounding parts. However, the introduction of the compressive stress accompanying the transformation expansion also returns to the tensile stress state during cooling to room temperature if the subsequent thermal contraction is large. Except for some stainless steel materials, welding materials used for ordinary steel materials always undergo transformational expansion at a certain temperature, but due to the high temperature, subsequent thermal shrinkage ultimately generates tensile residual stress. I do. Since the thermal shrinkage is obtained by multiplying the temperature change by the thermal expansion coefficient, in order to make the residual stress as small as possible and, in some cases, into a compressed state, the temperature change may be made small.

There are two methods for reducing the temperature change. One is to use a material that lowers the Ms temperature, and the other is to preheat the plate. Since the method of preheating the plate eventually cools to the outside air temperature, it is considered that the change in temperature does not seem to be small at first glance.
However, if preheating is performed, the temperature distribution of the plate becomes uniform in a temperature region higher than room temperature, and in the subsequent cooling process, a uniform temperature is maintained, so that no thermal stress is generated. The temperature difference in this case is the temperature change in this case. This is because if the temperature distribution of the plate is uniform,
Due to the fact that thermal stress does not occur on heating or cooling. In ordinary materials, the Ms temperature is around 450 ° C., but it is not practical to set the preheating to a value close to that.
Therefore, as a method of reducing the temperature change, that is, the heat shrinkage after the transformation, it is indispensable to select a material having a low Ms temperature. But,
If the value of the Ms temperature is inappropriate, or if the material selection is inappropriate, the residual stress cannot be reduced by using only the material, and additional measures such as the use of preheating are required. In fact, Ota et al. Achieve high fatigue strength welded joints by preheating.

[0011] In order to apply a material having a low Ms temperature to the working, it is desirable that the welding can be performed without preheating to reduce the residual stress and achieve a high fatigue strength welded joint. It is not only the construction cost, but unlike the case of fatigue test specimens, the preheating of the actual structure must be performed only in the vicinity of the welded part, so-called local preheating, and the introduction of residual stress and deformation due to preheating construction itself This is because there is concern. Therefore, an object of the present invention is to provide a welded joint in which residual stress is reduced to such an extent that high fatigue strength can be expected without preheating.

In the present invention, as described above, an object of the present invention is to improve the fatigue strength by using the transformation expansion caused by lowering the Ms temperature of the weld metal.
In order to further reduce the residual stress, a second technical idea of the present invention is to set the yield strength of the weld metal at an Ms temperature to an appropriate value. In general,
It is necessary to add C, Ni, Cr and the like to the material having a low Ms temperature, and it is considered that a certain level of strength is secured. However, in order to reliably achieve a high fatigue strength welded joint, it is desirable to set the strength in an appropriate range. This technical idea of controlling the strength is based on the fact that even if transformation expansion occurs, there is a limit to the compressive elastic strain caused by the expansion, and the value is the value obtained by dividing the yield strength by the Young's modulus. It is.

Here, for example, consider the case where the transformation expansion amount of the weld metal is 3%. Assuming that the weld metal is completely constrained from the surroundings, a 3% transformation expansion introduces a 3% compressive strain, resulting in a total strain of 0%. At this time, the compressive strain of 3% can be classified into plastic strain and elastic strain, but the elastic strain has a limit as described above, and the rest must be plastic strain. The weld metal then undergoes thermal shrinkage, which in turn introduces tensile strain into the weld metal. Due to this tensile strain, the amount of elastic compressive strain introduced at the time of transformation expansion decreases, and depending on the amount of thermal shrinkage, it may become tensile strain.

It is understood from this consideration that even if the amount of heat shrinkage is reduced, that is, even if the Ms temperature is lowered, the residual stress cannot be reduced if the compression elastic strain limit (maximum value) is small. . This means that, by conversely, by increasing the compression elastic strain limit, the residual effect can be surely reduced and, consequently, can be brought into a compressed state, thereby achieving the high fatigue strength welded joint which is the object of the present invention more reliably. Means you can do it. The reason why such a discussion always holds is due to the fact that the transformation expansion strain is always larger than the elastic strain limit. To increase the elastic strain limit, the yield strength may be increased. For that purpose, the yield strength of the weld metal must be set to an appropriate value. This is the second technical concept of the present invention.

The present invention provides two technical ideas described above, namely, the use of a weld metal having a low Ms temperature and an increase in the elastic strain limit by increasing the yield strength of the weld metal, as well as the welding of steel. Heat affected zone (HAZ)
There is a third technical idea that the residual stress can be reduced by utilizing the transformation expansion of the weld metal. The fatigue crack does not necessarily propagate from the weld toe where fatigue occurs to the steel HAZ, but rather to the weld metal, but in the present invention, the steel itself is not necessarily a low Ms temperature material. However, in the present invention, it is considered that by forming a low Ms temperature weld metal on the bead forming the toe, a residual stress equivalent to that of the weld metal can be introduced into the steel material HAZ as a reaction force. Since the residual stress is a stress distribution in a situation where no external force acts, it has a feature that the resultant force is zero as a whole. Thus, introducing compressive residual stress also means introducing tensile residual stress somewhere else in the weld. However, fatigue is mainly caused by stress concentration on the surface (bead toe)
Since the value of the residual stress is important, the residual stress in the fatigue occurrence part is reduced, and if the high residual stress is distributed to the part where there is no danger of fatigue, a high fatigue strength welded joint can be realized. .

FIG. 1 shows a turning welding joint which is considered to be the most severe in view of the fatigue problem. When the hatched weld bead of FIG. 1 undergoes transformation expansion at a low temperature, as can be seen from the figure, a compressive stress is introduced as a reaction force into the steel material HAZ, for example, the regions A and B in FIG. It can be understood. Here, it should be noted that the compressive stress of the steel material HAZ is not introduced because the steel material itself has undergone transformation expansion, but is a reaction force against the transformation expansion of the weld metal. Accordingly, the residual stress in the direction perpendicular to the weld bead can be reduced in the region A in FIG. 1, and the residual stress in both the weld bead direction and the direction perpendicular to the bead can be reduced in the region B. Since the fatigue crack occurs from the bead toe, the residual stress here is reduced. On the other hand, the HAZ located below the weld bead, that is, existing inside the steel material, is conversely subjected to tensile stress due to the expansion of the bead. However, since this portion is not a fatigue crack initiation site, improvement in fatigue strength of the welded joint as a whole can be expected.

Next, a fourth technical concept of the present invention will be described. In the present invention, the fatigue strength of the bead toe is improved by the first, second, and third technical ideas described above. However, even if the fatigue strength of the bead toe is improved in the weld joint as a whole, if fatigue cracks occur in other parts, the weld joint as a whole is determined by the fatigue strength there. Normally, fatigue cracks occur from the bead toe because the fatigue strength there is the lowest, and therefore, in the present invention, the first and second fatigue cracks are generated.
Further, the third technical concept aims at improving the fatigue strength of the bead toe. With this alone, the improvement of the fatigue strength of the welded part can be expected, but the improvement in the fatigue strength of the bead toe may cause the fatigue strength of other parts to determine the fatigue strength of the welded joint as a whole. . In order to further improve the fatigue strength of the welded joint, it is desirable to improve the fatigue strength of a portion where a fatigue crack may occur outside the toe portion. In the joints dealt with in the present invention, the portion where the fatigue crack is likely to occur at portions other than the bead toe portion is an unwelded portion existing inside the rotary welded portion. For example, the unwelded portion existing between the gusset and the structural member when the out-of-plane gusset is attached to the structural member by welding and welding, particularly the unwelded portion near the corner turning portion, itself forms a stress concentration portion. Therefore, there is a risk that fatigue cracks may be generated therefrom.

Therefore, in the present invention, there is a fourth technical concept of reducing the unwelded portion near the corner turning portion and improving the fatigue strength there. This fourth technical idea is
Since it does not necessarily improve the fatigue strength of the bead toe where fatigue cracks occur in ordinary welded joints, a technique that can be expected to have an effect when used in combination with the first, second, and third technical ideas of the present invention. It is. Conversely, by using these technical ideas in combination, it is possible to reliably realize a high fatigue strength welded joint.

The present inventors have found a mechanism for reducing the residual stress at the fatigue crack initiation site as described above, and have conducted intensive studies on the relationship with the fatigue strength of the welded joint. Has led to the discovery of a high fatigue strength welded joint. Next, the reason for limiting the Ms temperature range and the yield strength range of the weld metal at the Ms temperature will be described.

The Ms temperature shows a value of 500 ° C. or less even in ordinary steel materials and weld metals, and is often 450 ° C. or less in many cases. This value depends on the component, for example, welding CCT of steel for welding structural use issued by the Iron and Steel Institute of Japan.
As can be seen from the diagram, if Ni is added at about 5%, Ms
The temperature can be reduced to about 350 ° C. But,
When the Ms temperature is higher than 350 ° C., the effect of reducing the residual stress is not sufficient, and the effect of improving the fatigue strength cannot be expected. On the other hand, setting the Ms temperature to 150 to 350 ° C. can be realized with a material having an industrial value, and is within a range in which improvement in fatigue strength by reduction of residual stress can be expected. The lower limit of 150 ° C. of the Ms temperature was set as a lower limit that can be realized with a material having industrial value. According to the second technical concept of the present invention, the upper limit of the Ms temperature, 350 ° C., can be expected to reduce the residual stress if the yield strength is sufficiently high even if this value is higher than 350 ° C., and consequently the fatigue strength can be improved. Although it is possible, there is also a problem of whether a too high yield strength can also be realized with a material having industrial value, so the upper limit was set to 350 ° C. Since a lower Ms temperature is preferable for reducing the residual stress, it is preferable to set the Ms temperature to preferably 300 ° C. or lower.

Next, the reason why the shape of the welded joint is limited will be described. In the present invention, a case is considered in which the out-of-plane gusset, the cover plate, and the stud are welded to a structural member subjected to fatigue load, and a scallop turning welded joint is present in the structural member subjected to fatigue load. In the present invention, as described above, the Ms temperature of the weld metal is reduced, and further, by controlling the strength range, the residual stress is reduced and the fatigue strength is improved. The reaction force against the transformation expansion of the weld metal is used to reduce the residual stress of the weld metal. Since the method utilizing this reaction force cannot be applied to all welded joints, it must be limited to a welded joint for which this method is effective. This technique is effective with a joint shape as shown in FIG. Moreover, such a joint is a joint in which fatigue is often a problem in a welded structure. The welded joint in the present invention, that is, a joint in which an out-of-plane gusset, a cover plate, or a stud is welded to a structural member subjected to fatigue load, or a welded joint in which a structural member having scallops is attached by turning welding, FIG.
The present invention is a welded joint capable of reducing the residual stress of the steel material HAZ as shown in the following by the action of the reaction force against the transformation expansion of the weld metal and determines the fatigue strength of the welded structure. Limited to.

Next, the reason why the range of the groove from the end of the structural member having the out-of-plane gusset and scallops is limited will be described. There are two stress concentration portions existing at the ends, that is, a bead toe portion and an unwelded portion existing inside the turning welded portion. From the viewpoint of fatigue, the bead toe portion is usually a more severe portion, but the present invention has achieved improvement in fatigue strength at this portion. Therefore, it is apparent that a higher fatigue strength can be realized by improving the fatigue strength of the unwelded portion near the end, which is another stress concentration portion, that is, the root portion. The reason for forming a groove from the end of the structural member having the gusset and scallops is to reduce this unwelded portion and to keep the stress concentration low. Therefore, since the groove is not intended to improve the static strength of the joint, it is not always necessary to make a groove for the entire welded portion. However, if the range of the groove is too small, the stress concentration cannot be suppressed, and the fatigue strength may be the same as when the groove is not formed. The groove range of 5 mm or more was set as the lowest value at which the effect of forming a groove could be expected. In addition, from the viewpoint of suppressing stress concentration, it is desirable that the groove range is preferably set to 2 cm or more.

Next, when a groove is formed from the end of the structural member having the out-of-plane gusset or scallops, the area of the unwelded portion inside the turning welded portion in the grooved area is not formed. The reason for limiting the amount of reduction for the case will be described. The reason for forming the groove from the end of the structural member having the out-of-plane gusset or scallops is that the first, second and third technical ideas of the present invention achieve high fatigue strength of the bead toe, This is because the fatigue strength of the stress-concentrated portion formed by the unwelded portion inside the turning welded portion where the fatigue strength is relatively low, that is, the fatigue strength of the root portion is improved. Therefore, unless the stress concentration is suppressed until the effect of improving the fatigue strength becomes remarkable, this object cannot be achieved. For this reason, it has already been mentioned that the invention has limited the groove range. However, if the unwelded part remains at the same level as when the groove is not formed due to the inappropriate groove shape, stress concentration cannot be suppressed even if the groove range is appropriate. It is not enough to further increase the overall fatigue strength. The lower limit of the decrease in the area of the unwelded portion relative to the case where no groove is formed is 1
The setting of 0% was set as the minimum condition under which the effect of creating a groove was recognized. In addition, from the viewpoint of suppressing stress concentration and improving the fatigue strength of the root portion, it is desirable that the lower limit of the reduction amount is preferably set to 20%.

Next, the reason for limiting the range of the yield strength will be described. When the yield strength is less than the lower limit of 40 kg / mm ² , the Ms temperature must be lower than 150 ° C. so that the residual stress reduction effect can be reliably expected. If the Ms temperature is lower than this, the material is limited to those having low industrial value, and this is contrary to the intention of the present invention, so the lower limit was set to 40 kg / mm ² . Preferably, the lower limit of the yield strength is 50 kg / mm.
It is desirable that it be ² or more. 120kg / mm of upper limit
^{In the case of No. 2} , in order to obtain a higher yield strength than this, many special alloy elements must be added, and the industrial value is also low, so the upper limit is set to 120 kg / mm ² .

Next, the reason for introducing the parameter P shown in the following formula and limiting the range of the value will be described. Pa = C + Ni / 12 + Cr / 24 + Mo / 19 (i) The parameter Pa is calculated by the component values of C, Ni, Cr and Mo. These components have the function of improving strength and lowering the Ms temperature by being added to the weld metal. In particular, C, Ni, Cr and Mo are the elements to be used most effectively in terms of elements that lower the Ms temperature. From the viewpoint of improving the strength, it is conceivable to effectively use elements that form carbides, such as Ti, Nb and V. However, if Ti, Nb and V are added to such an extent that the Ms temperature becomes sufficiently low, the joint properties will be reduced. A major problem occurs, which is not preferable. On the other hand, C, Ni, C
Since the functions of lowering the Ms temperature of r and Mo and lowering the residual stress are not necessarily the same, it is industrially necessary to determine coefficients according to the respective functions and create an index representing the effect as a whole of the four elements. It is determined that the value is high, and Pa as shown in Expression (i) is created.

However, the value of Pa also has an appropriate range.
For example, if Pa is too small, it is difficult to reduce the Ms temperature, and even if it becomes possible by adding other elements, it is not preferable from the viewpoint of securing welded joint characteristics. Conversely, a large Pa means that the Ms temperature is lower, but a Pa that is too large is uneconomical because the addition of alloying elements must be increased accordingly. From the above, the range of Pa is 0.85 or more and 1.30.
It was as follows. In addition, in order to secure a higher fatigue strength welded joint, it is desirable to set the lower limit of Pa to 0.95.

Further, in the present invention, since the technique of increasing the yield strength of the weld metal and reducing the residual stress more reliably is used together, the yield strength of the weld metal at the Ms temperature is 50 kg / mm ² or more. In the case of, the upper limit of Pa is preferably set to 1.25 from the viewpoint of the possibility of the existence of residual austenite in the weld metal and the economic efficiency. Further, when the yield strength of the weld metal at the Ms temperature is 60 kg / mm ² or more, the upper limit of Pa is preferably set to 1.20 from the viewpoint of economy.

Next, use of the weld metal with limited components will be described. Actually, the number of component systems for obtaining the Ms temperature and the yield strength described above is not necessarily one. The weld metal according to the present invention includes a component system mainly using Ni described in the above (8), (9) and (10);
(12) can be divided into two types of component systems mainly using Cr. Hereinafter, the former will be referred to as a Ni-based weld metal, and the latter will be referred to as a Cr-based weld metal.

First, the reason for limiting the component range of the Ni-based weld metal will be described. C acts to lower the Ms temperature by adding it to iron. But,
On the other hand, excessive addition causes problems such as deterioration of toughness of the weld metal and cracks in the weld metal.
2%. However, when C is not added, martensite is hardly obtained, and the residual stress must be reduced only by other expensive elements, which is not economical. The reason for limiting to the case where C is added in an amount of 0.01% or more is that C, which is an inexpensive element, is used, and is set as the minimum value at which the economic merit is obtained. The upper limit of C is preferably set to 0.15% from the viewpoint of weld metal cracking.

[0030] Si is known as a deoxidizing element. Si
Has the effect of lowering the oxygen level of the weld metal. In particular, during welding, there is a risk of air being mixed in during welding, so it is extremely important to control the amount of Si to an appropriate value. First, regarding the lower limit of Si, if the amount of Si added to the weld metal is less than 0.1%, the deoxidizing effect is weakened, the oxygen level in the weld metal becomes too high, and the mechanical properties, particularly the toughness, are reduced. There is a risk of causing deterioration. Therefore, the lower limit of the weld metal is set to 0.1%. On the other hand, the excessive addition of Si also causes toughness degradation, so the upper limit was made 0.5%.

Mn is known as an element for increasing the strength. Therefore, it is an element that should be used effectively from the viewpoint of ensuring the yield strength during transformation expansion, which is the residual stress reduction mechanism in the present invention. The lower limit of Mn, 0.01%, was set as the minimum value at which the effect of securing strength was obtained. On the other hand, excessive addition causes toughness degradation of the base metal and the weld metal, so the upper limit was made 1.5%.

P and S are impurities in the present invention.
However, when these elements are present in a large amount in the weld metal, the toughness is deteriorated.
0.02%. Ni is a single element of austenite, that is, a metal having a face-centered structure, and is an element that makes the state of austenite more stable by adding it to the weld metal. Iron itself has an austenitic structure in a high temperature range, and has a ferrite or body core structure in a low temperature range. Addition of Ni makes the face-centered structure of iron in a high-temperature range more stable, so that it has a face-centered structure even in a lower temperature range as compared with the case without addition.
This means that the temperature at which the structure transforms into a body-core structure becomes lower. The lower limit of Ni, 8%, was determined to mean the minimum amount of addition in which the residual stress reduction effect appears. The upper limit of Ni, 12%, is that, from the viewpoint of reducing the residual stress, the effect does not change so much even if it is added further, and if added more, there is an economic disadvantage that Ni is expensive.

Cu is an effective element for improving welding workability because Cu has an effect of improving electric conductivity by plating on a welding wire. Further, since Cu is also a hardenable element, an effect of promoting martensitic transformation by adding it to the weld metal can be expected. Cu
The lower limit of 0.05% was set as a minimum value necessary for improving workability and promoting martensitic transformation. But,
Excessive addition not only has no effect of improving workability but also increases the wire manufacturing cost, which is not preferable in industry.
The upper limit of Cu, 0.4%, was set for such a reason.

Nb combines with C in the weld metal,
Form carbides. Nb carbide has the function of increasing the strength of the weld metal in a small amount, and therefore has a great economic merit of effective use. Further, the second technical idea of the present invention has a great advantage in terms of increasing the yield strength at the Ms temperature. However, excessive carbide formation on the other hand naturally sets an upper limit because toughness degradation occurs. The lower limit of Nb was set to 0.01% as a minimum value at which carbides were formed and an effect of increasing strength was expected. The upper limit is set to 0.4% as a value that does not impair the reliability of the welded portion due to deterioration in toughness.

V is an element having the same function as Nb.
However, unlike Nb, in order to expect the same precipitation effect, it is necessary to increase the amount of Nb added. The lower limit of 0.3% of the addition of V is set as the minimum value at which precipitation hardening can be expected by adding V. The upper limit of V is set to 1.0% because if more than this, precipitation hardening becomes too remarkable and toughness deteriorates.

Ti, like Nb and V, forms carbides and causes precipitation hardening. However, just as the precipitation hardening of V was different from that of Nb, the precipitation hardening of Ti was also Nb, V
And different. Therefore, the range of the addition amount of Ti is set to a range different from Nb and V. Lower limit of Ti addition amount 0.01
% Is the minimum amount at which the effect can be expected, and the upper limit of 0.
4% was determined in consideration of toughness deterioration.

Cr is a precipitation hardening element like Nb, V and Ti. Further, Cr is an element to be effectively utilized because it also has the effect of reducing the Ms temperature. However, the Ni-based weld metal in the present invention is mainly composed of Ms
Since the temperature is reduced, the amount of Cr added should be smaller than that of Ni. Excessive addition of Cr does not necessarily improve the effect of reducing residual stress, and is not industrially preferable because Cr is expensive. The lower limit of 0.1% of the amount of Cr added was set as the minimum value at which the effect of adding residual Cr to obtain the residual stress reduction effect was obtained. The upper limit of 3.0% of the added amount of Cr is more than that of Ni-based weld metal because the Ms temperature is already reduced by the addition of Ni and the strength is secured by other precipitated elements. The value was also set because the residual stress reduction effect did not change much and the toughness deteriorated significantly.

Mo is an element having the same effect as Cr.
However, Mo is an element for which precipitation hardening can be expected more than Cr. Therefore, the addition range was set narrower than Cr.
The lower limit of 0.1% was set as the minimum value at which the effect of Mo addition can be expected. The upper limit of 3.0% was set because, if added more than this, the composition would be excessively hardened and the toughness would be significantly deteriorated.

Co, unlike Ti and the like, is not an element that causes strong precipitation hardening. However, Co is an element that should be used effectively because it is a more preferable element than Ni from the viewpoint of increasing the strength by adding it and securing the toughness while expecting the increase in the strength. However, since Ni is added to the weld metal in order to secure a low Ms temperature at which a residual stress reduction effect can be expected, the lower limit of 0.1% of the Co addition amount is the minimum at which the effect of Co addition can be expected. It was set as the limit value. On the other hand, excessive addition results in excessive increase in strength and deterioration of toughness, so the upper limit was made 2.0%.

Next, the reason for limiting the component range of the Cr-based weld metal will be described. C acts to lower the Ms temperature by adding it to iron. But,
On the other hand, excessive addition causes problems of weld cracking and toughness deterioration, so the upper limit was made 0.05%. However, when C is not added, martensite is hardly obtained, and the residual stress must be reduced only by other expensive elements, which is not economical. C is 0.00
The reason for limiting to the case where 1% or more is added is to use C, which is an inexpensive element, and set it as the minimum value at which the economic merit is obtained.

[0041] Si is known as a deoxidizing element. Si
Has the effect of lowering the oxygen level of the weld metal. Particularly, in welding work, it is extremely important to control the amount of Si to an appropriate value because there is a risk of air being mixed during welding. First, regarding the lower limit of Si,
If the amount of Si added to the weld metal is less than 0.1%, the deoxidizing effect is weakened, and the oxygen level in the weld metal becomes too high, and there is a risk that mechanical properties, particularly toughness, may be deteriorated. Therefore, the lower limit of the weld metal is set to 0.1%. On the other hand, excessive addition of Si also causes toughness degradation, so the upper limit was set to 0.7%.

Mn is known as an element for increasing the strength. Therefore, it is an element to be effectively used from the viewpoint of securing the yield strength at the time of transformation expansion, which is the second technical idea of the present invention. The lower limit of Mn, 0.4%, was set as the minimum value at which the effect of securing the strength was obtained. On the other hand, excessive addition causes toughness degradation of the weld metal, so the upper limit was made 2.5%.

P and S are impurities in the present invention. However, if these elements are present in a large amount in the weld metal, the toughness is deteriorated.
2%. Ni is austenitic, that is, a metal having a face-centered structure by itself. Iron itself has an austenitic structure in a high temperature range, and has a ferrite or body core structure in a low temperature range. Addition of Ni makes the face-centered structure of iron in a high-temperature range more stable, so that it has a face-centered structure even in a lower temperature range as compared with the case without addition. This means that the temperature at which the structure transforms into a body-core structure becomes lower. Ni has the effect of improving the toughness of the weld metal by adding Ni.
The lower limit of 4% of the amount of Ni added to the Cr-based weld metal was determined from the viewpoint of the minimum amount of addition in which the effect of reducing residual stress appears and securing of toughness. The upper limit of 8% of the addition amount of Ni is that the Cr-based weld metal has the Ms temperature reduced to some extent by the addition of Cr described below, and from the viewpoint of reducing the residual stress, the effect does not change much even if added more. This value is set because there is no economical disadvantage that Ni is expensive if added further.

Cr, unlike Ni, is a ferrite former. However, when Cr is added to iron,
Although it is ferrite in a high temperature range, it forms austenite in a medium temperature range, and forms ferrite again when the temperature is further lowered. In the case of a welded part, ferrite on a lower temperature side is generally not obtained in the heat history due to the heat input amount of welding, and martensite is obtained. This is C
The advantage of adding r is due to the increased hardenability. That is, the martensitic transformation by adding Cr does not cause ferrite transformation due to an increase in hardenability, and also lowers the Ms temperature itself.
There are two points. The lower limit of 8% was set as a Cr addition range that effectively utilizes transformation expansion for reducing residual stress while satisfying both effects. The upper limit of 15% is set because the effect does not increase even if an amount exceeding the upper limit is added and the demerit increases economically.

Cu is an effective element for improving welding workability because Cu has an effect of improving electric conductivity by plating on a welding wire. Further, since Cu is also a hardenable element, an effect of promoting martensitic transformation by adding it to the weld metal can be expected. Cu
The lower limit of 0.05% was set as a minimum value necessary for improving workability and promoting martensitic transformation. But,
Excessive addition not only has no effect of improving workability but also increases the wire manufacturing cost, which is not preferable in industry.
The upper limit of Cu, 0.4%, was set for such a reason.

Nb combines with C in the weld metal,
Form carbides. Nb carbide has the function of increasing the strength of the weld metal in a small amount, and therefore has a great economic merit of effective use. Further, there is a great merit from the viewpoint of increasing the yield strength at the Ms temperature, which is the residual stress reduction technique in the present invention. However, excessive carbide formation on the other hand naturally sets an upper limit because toughness degradation occurs. The lower limit of Nb was set to 0.005% as a minimum value at which a carbide was formed and the effect of increasing strength was expected.
The upper limit is set to 0.3% as a value that does not impair the reliability of the weld due to deterioration in toughness.

V is an element having the same function as Nb.
However, unlike Nb, in order to expect the same precipitation effect, it is necessary to increase the amount of Nb added. The lower limit of 0.05% of the addition of V was set as the lowest value at which precipitation hardening can be expected by adding V. The upper limit of V is set to 0.5% because if more than this, precipitation hardening becomes too remarkable and toughness deteriorates.

Ti, like Nb and V, also forms carbides and causes precipitation hardening. However, just as the precipitation hardening of V was different from that of Nb, the precipitation hardening of Ti was also Nb, V
And different. Therefore, the range of the addition amount of Ti is set to a range different from Nb and V. Lower limit of Ti addition amount 0.00
5% is determined as the minimum amount in which the effect can be expected, and the upper limit of 0.3% is determined in consideration of toughness deterioration.

Mo, like Nb, V and Ti, is also an element for which precipitation hardening can be expected. However, Mo is Nb, V, Ti
In order to obtain the same effect as above, it is necessary to add Nb, V, and Ti or more. The lower limit of 0.1% of the Mo content was set as the lowest value at which an increase in yield strength due to precipitation hardening can be expected. The upper limit of 2.0% is the same as Nb, V, and Ti.
It was determined in consideration of toughness deterioration.

N is an element known as an austenite former. Since addition of N also makes it easier to obtain martensite, a minimum addition is necessary. The lower limit of N, 0.001%, was set as the minimum value for obtaining a low Ms temperature similarly to C. However, an excessive addition forms a nitride and causes a problem of deterioration in toughness and ductility. Therefore, the upper limit is set to 0.05%.

C and N have similar functions, such as forming carbides and nitrides and being austenite formers, respectively. Their total, that is, the amount of C + N is also an upper limit.
You need to set a lower limit. Lower limit of C + N, 0.001
% Is a minimum value for easily obtaining martensite and lowering the Ms temperature, and 0.06% of the upper limit.
Is defined as a limit value at which the problems of toughness deterioration and ductility deterioration due to carbides and nitrides do not occur.

The reason for limiting the range of the components of the weld metal has been described above. As a method of controlling the components of the weld metal within these ranges, a method of controlling the components of the welding wire, a component of the welding wire and the components of the flux, and the like. Or the method of controlling the components of the welding core wire and the coating flux, etc., but in the present invention, regardless of these methods, if the components of the weld metal are set within the above-mentioned range, high fatigue Strength welding joints can be realized. Further, a welding wire forming a weld metal that is a component range in the present invention, a combination of a welding wire and a flux, or a combination of a welding core wire and a coating flux can be easily formed by those skilled in the art. is there.

If a weld metal according to the present invention is formed on a weld bead forming a weld toe, a high fatigue strength welded joint can be realized. However, after the weld bead is formed, another bead is formed. If so, the distribution of the residual stress may change. When this bead is newly formed as a bead forming a weld toe, a welded joint may be produced by selecting a material for the bead so as to be a weld metal according to the present invention. However, if this is not the case, the residual stress distribution may change, so that the weld bead forming the weld toe is finally solidified, i.e. becomes the final bead, compared to other weld beads nearby. It is desirable to have a welded joint with a selected welding order.

[0054]

EXAMPLES Table 1 shows the component values of Ni-based and Cr-based weld metals used for examining residual stress and fatigue strength. Table 1 shows the Ms temperature (° C.) and the yield strength at the Ms temperature. Former test specimens and tensile test specimens were directly taken from each weld metal.
This is the result of measuring the s temperature and then performing a tensile test at that temperature.

FIG. 2 shows a view of a corner turning welded joint prepared for measuring the residual stress at the bead toe. 2 is 5c from both ends of the out-of-plane gusset.
Turning welding is performed within the range of m with the groove shown in FIG. The main bead at the weld portion uses a normal welding material, but is a joint in which, after the completion of the main welding, the weld metal of WF, WA, WB, and WH shown in Table 1 is formed as an additional bead. The residual stress was measured by a so-called cutting method in which a strain gauge having a gauge length of 2 mm was attached to the weld toe as shown in the figure and the stress was relaxed by machining.

FIG. 4 shows the measurement results of the residual stress.
As is clear, in the example of the present invention, WA, WB, and WH are compressive residual stresses, whereas WF is a tensile stress due to insufficient addition of Ni. FIG. 5 shows the fatigue strength of a welded joint in which the out-of-plane gusset shown in FIG. The fatigue load application direction is the arrow direction in FIG. 2, that is, the out-of-plane gusset longitudinal direction. When investigating the fatigue strength, in order to be able to compare the case with the groove and the case without the groove, the case with the groove shown in Fig. 3 within 5 cm from the end of the gusset and the case without the groove Were manufactured, and a weld metal of WA was formed as an additional bead shown in FIG. WF, WB and WH in Table 1 were formed as an additional bead to the grooved joint. In the case of a grooved joint, fatigue occurs at the weld toe where the additional bead is formed, and the crack propagates through the steel HAZ. If the groove is not formed, the unwelded portion inside the corner turning weld is Propagated from the end where the stress concentration portion exists. FIG. 5 shows the fatigue life by a dotted line and a solid line. As shown in FIG.
WB and WH have clearly improved fatigue life and fatigue limit compared to WF as a comparative example, and even the same weld metal of the present invention, as can be seen from the example of WA, has a groove with a groove. The life is longer.

FIG. 6 shows a welded joint in which an out-of-plane gusset having a shape similar to that of FIG. However, a fatigue test was performed on the welded joint of FIG. 6 by applying a load as a fatigue load in a direction perpendicular to the out-of-plane gusset (the direction of the arrow in FIG. 5). In FIG. 6, the out-of-plane set is not particularly grooved. In this case, the weld bead forming the weld toe where fatigue becomes a problem is the actual bead of the welded portion. Therefore, in the joint of FIG. 6, the weld metal of WF, WA, WB, and WH shown in Table 1 was formed on the present bead to produce a joint. FIG. 7 shows the fatigue strength. The example of the present invention clearly has a higher fatigue strength.

Next, the fatigue strength of a joint where the cover plate is welded to a member subjected to fatigue load, in which fatigue is often a problem as in the case of a corner turning weld, was examined. FIG. 8 shows a test piece shape for which the fatigue strength was examined. The additional beads in the figure are beads formed after joining the cover plates by welding, that is, final beads. The weld metal of WC, WD, WE, and WG shown in Table 1 was formed on the additional bead, and a joint was produced. FIG. 9 shows the fatigue strength of the welded joint of FIG. Similar to FIG. 5, the fatigue life is indicated by a dotted line and a solid line. Also in the welded joint to which the cover plate was attached, it was demonstrated that the joint of the example of the present invention had higher fatigue life and fatigue limit than the comparative example.

Next, the fatigue strength of a joint in which a welded joint with a stud causing a problem of fatigue was welded to a member subjected to fatigue load, as in the case of the corner-turned joint and the cover plate-attached joint, was examined. FIG.
The test piece shape for which the fatigue strength was examined is shown. The hatched portions in the figure are weld beads, and WF, WC, WB, and WH weld metals shown in Table 1 were formed in these portions to produce joints. FIG. 11 shows the fatigue strength of the welded joint of FIG. As in FIG. 5, the fatigue life is indicated by a dotted line and a solid line. As can be seen from FIG. 11, the welded joint of the present invention also has a higher fatigue life and fatigue limit as compared with the comparative example in the joint with the stud attached.

FIG. 12 shows a welded joint shape having scallops. The welded metal of WC, WF, WB, WE, and WH shown in Table 1 was formed in the additional bead portion in FIG. 12 to produce a joint. Also, as in the case of the out-of-plane gusset (FIG. 2), a joint having a groove as shown in FIG. 3 within a range of 5 cm from the end of the scallop in order to reduce the unwelded portion inside the turning welded portion. And joints without making a groove were produced. The weld metals WC, WF, WB, and WH in Table 1 are formed as an additional bead shown in FIG. 12 for a grooved joint, and WE is formed as an additional bead for a grooveless joint. I was sorry. FIG. 13 shows the fatigue strength. Similar to FIG. 5, the fatigue life is indicated by a dotted line and a solid line. As shown in FIG. 13, the joint of the present invention has higher fatigue limit and fatigue life than the comparative example, and the effect of improving the fatigue strength when a groove is formed is more remarkable.

Next, the weld metal, WJ, WK, WL, WM, and WN shown in Table 1 were formed as additional beads on the joint to which the structural member subjected to fatigue load by turning the out-of-plane gusset was welded. The fatigue strength of the welded joint was investigated. At this time, some out-of-plane gussets have a groove as shown in FIG. 3 and some do not. However, the range of the groove is variously changed so that the effects can be compared. As the fatigue load, the nominal stress range was set to 200 MPa, and the fatigue life at that time is shown in Table 2. From the results in Table 2, the effect of the additional bead and the effect of the groove can be understood.

In Table 2, no. 1 to 4 show the fatigue life when the weld metal WI of Table 1 was formed as an additional bead. No. Comparing 1-4, N with no groove
o. N with a fatigue life of 1 and a groove range of 5 cm and 3 cm
o. The fatigue life of Nos. 2 and 3 is clearly no. It can be seen that the fatigue strength is improved when the groove is formed in the out-of-plane gusset, with the length of the grooves being longer. This is No. In the case of No. 1, the fatigue crack is generated from the stress concentrated portion at the end of the unwelded portion inside the turning weld, that is, from the root portion. However, no. When the groove range is as narrow as 4 mm as in No. 4, no groove is formed. The result was not much different from 1. In addition, No. Nos. 1 to 4 are comparative examples. 10
16 had a longer fatigue life.

No. 5, 6, and 7 are additional beads as shown in Table 1.
4 shows the results of examining the fatigue life when a WJ weld metal was formed. No. As in Nos. 1 to 4, no. The life of No. 5 is no. Shorter than 6 However, no. The life of No. 5 was No. 5 of the comparative example. 1
The fatigue life was longer than any of the cases 0 to 16. N
o. No. 7 shows a case where a groove was formed in a range of 3 cm. However, the width of the unwelded portion was reduced only by 5%. 5 had the same fatigue life.

In Table 2, No. 8 and 9 show the fatigue life of the joint when the weld metal WK shown in Table 1 was formed as an additional bead.
Longer life than 10-16. No. 10 to 16 are shown in Table 1.
Shows the fatigue life when the weld metals WL, WM, and WN are formed as additional beads. As can be seen from Table 2, the No. 1 sample of the present invention. Shorter than the fatigue life of 1-9.

Further, in the comparative example, it can be seen that the fatigue life is almost the same when the groove is formed in the out-of-plane gusset and when the groove is not formed. This is because the fatigue crack is generated at the weld bead toe, and the fatigue strength of the joint is determined by the bead toe even if the concentration of stress in the root portion inside the turning weld is suppressed. On the other hand, in the present invention example No. In Nos. 1 to 9, it was found that the fatigue life can be improved even when the groove is not formed, and that the groove as a whole further improves the fatigue life of the joint.

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

As described above, according to the present invention, it is possible to improve the fatigue strength of the weld toe, and to provide a high fatigue strength welded joint that can be manufactured only by a practical construction method. is there. Therefore, it can be said that the present invention is an invention having extremely high industrial value.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a steel material HAZ region in which a residual stress is reduced by a transformation expansion direction of a weld metal and a reaction force thereof.

FIGS. 2 (1) and 2 (2) are perspective views showing a welded joint in which an out-of-plane gusset is attached to a structural member subjected to fatigue load by corner turning welding, and further an additional bead is formed; It is the (2) top view explaining the residual stress measurement position in the welded joint.

FIG. 3 is a cross-sectional view showing a groove shape of a structural member having an out-of-plane gusset or scallops.

4 (1) to 4 (4) show (1) W shown in Table 1 as additional beads in the welded joint of FIG.
It is sectional drawing which showed the residual stress measurement result at the time of forming the weld metal of F, (2) WA, (3) WB, and (4) WH.

5 is a graph showing the fatigue strength of the welded joint of FIG. 2 when the weld metal of WF, WA, WB, and WH shown in Table 1 is formed as an additional bead. .

FIG. 6 is a perspective view showing the joint when the out-of-plane gusset is mounted on a structural member that receives a fatigue load by turning the corner by welding.

7 is a graph showing the fatigue strength of the welded joint of FIG. 6 when WF, WA, WB, and WH weld metals shown in Table 1 are formed in a welded portion.

FIG. 8 is a perspective view illustrating a welded joint in which a cover plate is attached to a structural member subjected to a fatigue load by welding and an additional bead is formed.

FIG. 9 is a graph showing the fatigue strength of the welded joint of FIG. 8 when the weld metal of WD, WC, WE, and WG shown in Table 1 was formed as an additional bead. .

FIG. 10 is a perspective view illustrating a welded joint in which a stud is rotated and welded to a structural member for planting a fatigue load.

11 is a graph showing the fatigue strength of the welded joint of FIG. 10 when the weld metal of WF, WC, WB, and WH shown in Table 1 was formed as a welded portion. .

FIG. 12 is a diagram illustrating a joint in which a structural member having scallops is attached by turning welding and an additional bead is formed in a corner turning portion.

FIG. 13 shows WC, WF, WB, WE, and WC shown in Table 1 as additional beads in the welded joint of FIG.
It is the perspective view which showed the fatigue strength in the weld joint at the time of forming the weld metal of WH.

Claims (12)

[Claims] 1. At the weld toe where fatigue is a problem,
The temperature at which transformation from austenite to martensite is initiated at 350 ° C. or less1
A high-fatigue-strength welded joint comprising a weld metal having a temperature of 50 ° C. or higher. 2. At a temperature at which transformation from austenite to martensite starts, the yield strength is 40 kg / mm.
^2. The high fatigue strength welded joint according to claim 1, wherein a weld metal of not less than ^{2 and not} more than 120 kg / mm ² is formed. 3. A structural member subjected to a fatigue load, wherein one or more of an out-of-plane gusset, a cover plate, or a stud is provided.
The high fatigue strength welded joint according to claim 1 or 2, wherein at least one is welded. 4. A case where an out-of-plane gusset is welded to a structural member subjected to a fatigue load.
A groove is formed over a range of 5 mm or more from the end, and the area of the unwelded part existing between the gusset and the structural member to which the gusset is attached in the grooved area is defined as the area of the unwelded part when the groove is not formed. 10 per area
The high-fatigue-strength welded joint according to claim 3, wherein the ratio is reduced by at least%. 5. The high fatigue strength welded joint according to claim 1, wherein the structural member having a scallop and subjected to a fatigue load is welded to the structural member by rotary welding. 6. A structural member having a scallop in a range of 5 mm or more from an end of a scallop with respect to a structural member having a scallop and receiving a fatigue load, and a structural member having a scallop in a range where the groove is formed and a structural member to which the scallop is attached. The high-fatigue-strength welded joint according to claim 5, wherein the area of the non-welded portion existing between them is reduced by 10% or more with respect to the area of the non-welded portion when no groove is formed. 7. A weld metal is formed wherein C, Ni, Cr and Mo are each represented by weight% of each component, and a parameter Pa defined by the following formula has a range of 0.85 or more and 1.30 or less. Claims 1 and 2,
The high fatigue strength welded joint according to 3, 4, 5 or 6. Pa = C + Ni / 12 + Cr / 24 + Mo / 19 8. C: 0.01 to 0.2% by weight, S:
i: 0.1 to 0.5%, Mn: 0.01 to 1.5%,
P: 0.03% or less, S: 0.02% or less, Ni: 8 to
A weld metal containing 12% and a balance of iron and unavoidable impurities is formed.
The high fatigue strength welded joint according to 2, 3, 4, 5, 6, or 7. 9. Ti in weight%: 0.01 to 0.4%;
Nb: 0.01 to 0.4%, V: 0.1 to 1.0%
The high fatigue strength welded joint according to claim 8, wherein a weld metal further containing one or more kinds is formed. 10. Cu: 0.05 to 0.4 by weight%.
%, Cr: 0.1 to 3.0%, Mo: 0.1 to 3.0
%, Co: 0.1 to 2.0%, wherein a weld metal further containing one or more of 0.1 to 2.0% is formed. 11. C: 0.001 to 0.05 by weight%
%, Si: 0.1 to 0.7%, Mn: 0.4 to 2.5
%, P: 0.03% or less, S: 0.02% or less, Ni:
4 to 8%, Cr: 8 to 15%, N: 0.001 to 0.0
The weld metal containing 5%, C + N: 0.001 to 0.06% and the balance being iron and unavoidable impurities is formed.
The high fatigue strength welded joint according to 5, 6, or 7. 12. Mo: 0.1 to 2.0% by weight.
Ti: 0.005 to 0.3%, Nb: 0.005 to 0.
The high fatigue strength welded joint according to claim 11, wherein a weld metal further containing one or more of 3% and V: 0.05 to 0.5% is formed.