TWI436847B - Welded joint manufacturing method - Google Patents

Description

Fusion joint manufacturing method Field of invention

The present invention relates to a method of manufacturing a welded joint, and more particularly to a structure of a welded joint or a structure in which a structure of a welded structure is considered to be weldable only from one side of a steel material, and In the method of manufacturing a welded joint in which the fatigue strength of the welded side portion or the root portion on the side opposite to the welded side is increased, the welded side portion or the root portion on the side opposite to the welded side is difficult to perform a shot peening treatment or the like. Fatigue strength measures.

Background of the invention

The fatigue characteristics of the welded structure are extremely important in determining the life of the structure itself. As means for improving the fatigue strength of the welded structure, the shape of the welded side portion is smoothed to minimize stress concentration as much as possible, or the residual stress is locally suppressed by performing a peening treatment or the like. A method of imparting a position such as occurrence of fatigue. Further, as disclosed in Patent Document 1, there is also a method of improving the fatigue strength by reducing the abnormal temperature of the molten metal and reducing the residual stress by the deformation expansion.

However, the technique described in Patent Document 1 is the first technique, and the prior art does not disclose how to apply the joint in which the welded side portion is sealed.

Fig. 1 shows an example of a fusion splice and a welded structure. Fig. 1 is a schematic view showing a structure in which a member having a U-shaped cross section is attached to a flat plate by welding in order to secure bending rigidity. In the example shown in Fig. 1, the U-shaped member is welded to the flat plate at two positions, and the joint is a T-joint. At this time, since the fatigue crack system occurs in the stress concentration portion, the example shown in Fig. 1 occurs at four positions indicated by the symbols A to D. Among these, since the two positions indicated by the symbols A and B are located outside the welded structure, it is easy to perform the repair, and the shape of the welded side is processed to be smooth or subjected to hammering. The compressive residual stress is imparted, and the fatigue strength can be improved.

However, the symbols C and D in Fig. 1 indicate that the welded side portions of the two positions are structurally sealed, and the post-processing after the welding is completed cannot be performed. This is because the mechanical post-processing method such as hammering requires a very simple reason to deal with the part where the fatigue is problematic (refer to the position of the symbols C and D in Fig. 1). Therefore, the fatigue strength of the welded structure shown in Fig. 1 depends on the fatigue strength of the welded side portion indicated by the symbols C and D, and even if the fatigue strength of the welded side portion indicated by A and B is raised, it is welded. As a whole, there is a problem that the fatigue strength is not improved as a whole.

On the other hand, in the technique described in Patent Document 1 or 2, the technique disclosed in this document is only a technique for revealing a joint when the welded side portion is located outside. For example, when the actual welded structure is subjected to fatigue cracking at the welded side portion on the inner side, how to use the welded material disclosed in Patent Document 1 is not necessarily clear. In the case of Fig. 1, the welding of the T-joint is completed by two-way welding. At this time, the heat of the weld bead, that is, the outer welded bead, is formed, and the inner bead is destroyed. Generated Residual stress does not give the original effect. On the other hand, when a T-joint as shown in Fig. 1 is formed by one-pass welding, the butt joint solidification is caused, and the possibility of occurrence of high-temperature cracks in the welded portion becomes large. Further, when an alloying element capable of reducing the degree of residual stress is added to the weld metal, the high-temperature crack sensitivity becomes higher than that of a normal welded material, and a technique for improving the fatigue strength while avoiding this problem is considered to be necessary.

Prior technical literature Patent literature

Patent Document 1 Japanese Patent Publication No. 11-138290

Patent Document 2, JP-A-2001-246495

Summary of invention

As described above, the fatigue strength of the welded structure is a factor that determines the life of the structure itself, and in particular, the fatigue strength of the entire welded structure is determined in the portion where the fatigue strength is the lowest.

The present invention has been made in view of the above problems, and the welded side portion or the root portion which has a problem of fatigue strength due to the presence of a closed region or the like in the structure cannot be mechanically processed or formed by performing shot peening or the like. In order to improve the fatigue strength by welding a bead or the like, a method of manufacturing a welded joint capable of improving fatigue strength is provided.

The present inventors have been able to achieve an improvement from the above viewpoints. The means for reducing the fatigue strength of the welded joint in the case of the welded joint portion or the root portion of the structure in which the mechanical strength is improved, the fatigue strength is not repeated. It has been found that the fusion metal which is metamorphosed at a low temperature is formed on the side of the fusion side or the root side in advance, and the fusion metal is re-transformed by subsequent welding; or the fusion is performed by using induction heating or electric heating. When the metal is deformed again, the compressive residual stress temporarily disappearing once can be generated again, whereby the fatigue strength of the welded edge portion or the root portion can be improved. The present invention has conducted such research, and the gist thereof is as follows.

(1) A method of producing a welded joint, which is a method of producing a welded joint in which a joint portion of a steel material is welded by a plurality of passes, wherein the multi-pass welding system includes a first welding step, and the first pass is used a fusion material having a transformation starting temperature of 175 ° C to 400 ° C for fusion welding; and a second welding step of subsequently forming a portion of the fusion metal formed in the first welding step In the form of the molten portion, the welded metal is deposited and welded in one or two or more passes, and the unmelted portions are all re-transformed into austenite by the last welding heat.

(2) A method of producing a welded joint, which is a method of producing a welded joint in which a joint portion of a steel material is welded by a plurality of passes, wherein the multi-pass welding system includes a first welding step, and the first pass is used a fusion material having a transformation starting temperature of 175 ° C to 400 ° C for fusion welding; and a second welding step of subsequently forming a portion of the fusion metal formed in the first welding step In the way of melting the portion, the welded metal is deposited and welded in one or two passes; subsequently, it is carried out. The step of heat-treating all of the unmelted portions into a heat treatment of the Worth field.

(3) The method of manufacturing a fusion splice according to (1) or (2), wherein the joint portion of the fusion splice is formed only by welding from one side.

(4) The method of manufacturing a fusion splice according to (1) or (2), wherein the fusion splice is a structure capable of being welded only from one side of the fusion splice from the structure of the fusion splice or the structure of the welded structure.

(5) The method of manufacturing a fusion splice according to (1) or (2), wherein the fusion splice is a T-joint, a corner joint or a lap joint.

(6) The method of manufacturing a fusion splice according to (1), wherein the fusion splice is a T-joint, and the joint portion of the T-joint is an unwelded portion and a welded portion sandwiching both sides of the unwelded portion And the manufacturing method is to perform the multi-pass welding by partially melting and welding the welding portion from one side; and in the method, the length of the unwelded portion is the welding of the respective channels of the multi-pass welding. More than three times the maximum thickness of the weld bead.

(7) The method of manufacturing a fusion splice according to (1), wherein the fusion splice is a cross-shaped joint, and the joint portion of the cross-shaped joint is an unwelded portion and a welded portion sandwiching both sides of the unwelded portion And the manufacturing method is to perform multi-pass welding by partially melting and welding the aforementioned welded portion from one side; and in the method, the length of the unfused portion existing between the respective welded portions and forming the ten The minimum thickness of the steel plate of the glyph joint is more than three times the maximum value of the thickness of the welded bead of each of the multi-pass welds.

(8) The method of manufacturing a fusion splice according to (2), wherein the fusion splice joint is a T-shaped joint or a cross-shaped joint, and the joint portion of the welded joint is composed of an unwelded portion and a welded portion sandwiching both sides of the unwelded portion, and the manufacturing method only borrows the welded portion from one side The multi-pass welding is performed by partial melting welding; and in the method, the heat treatment is performed after all the multi-pass welding of all the welded portions is completed.

(9) The method of producing a fusion splice according to (2) or (8), wherein the heat treatment step is any one of induction heating or electric heating.

(10) The method for producing a welded joint according to any one of (1), (2), (6), (7), (8), wherein the component of the weld metal used in the first welding step is It contains C: 0.01 to 0.15%, Si: 0.2 to 0.8%, Mn: 0.4 to 2.0%, P: 0.03% or less, S: 0.02% or less, Ni: 7.0 to 11.5%, and contains Cu: 0.4, by mass%. % or less, Ti: 0.1% or less, Nb: 0.1% or less, V: 0.5% or less, Cr: 3.0% or less, and Mo: 2.0% or less.

(11) The method for producing a welded joint according to any one of the preceding claims, wherein the component of the welded metal used in the first welding step is C: 0.005 to 0.10%, Si: 0.1 to 0.7%, Mn: 0.1 to 2.0%, P: 0.03% or less, S: 0.02% or less, Ni: 4.0 to 8.0%, and Cr: 8.0 to 15.0, in terms of % by mass. %, and one or more of Mo: 2.0% or less, Cu: 0.4% or less, Ti: 0.1% or less, Nb: 0.1% or less, and V: 0.5% or less.

(12) The method of manufacturing a fusion splice according to any one of (1), (2), (6), (7), or (8), wherein after the second welding step, the side to be welded The side of the welded bead is subjected to post-treatment by a grinding process.

(13) The method of manufacturing a fusion splice according to any one of (1), (2), (6), (7), (8), wherein, after the second welding step, the side of the welded side is The side of the weld bead is welded and post-treated by a peening process.

(14) The method of manufacturing a fusion splice according to any one of (1), (2), (6), (7), (8), wherein after the second welding step, the fusion side is welded The side of the bead is subjected to reheating treatment using a TIG arc (Tungsten Inert Gas arc).

(15) A fusion splice manufactured by the method of producing a fusion splice according to any one of (1), (2), (6), (7), or (8).

According to the method of manufacturing a welded joint according to the present invention, even if there is a problem in the structure of the welded joint or the structure of the welded structure, there is a welded side portion of the structure which cannot be post-treated by mechanical or welding or In the case of the root portion, it is also possible to increase the fatigue strength of the welded joint, and to increase the service life of the entire welded structure, or to repair the already existing welded structure, thereby prolonging the service life of the welded structure. The meaning of the above is very significant.

Simple illustration

1 is a schematic view for explaining an example of a method of manufacturing a welded joint according to the present invention, and is a cross-sectional view showing an example of a welded joint in which a welded inner side of the structure is a sealed structure.

Fig. 2a is a schematic view for explaining another example of the method of manufacturing the welded joint of the present invention, and shows an example of a welded joint which can be welded only from one side to form a portion which is partially melted and has a root which is inaccessible from the outside. Sectional view.

Fig. 2b is a schematic view for explaining another example of the method of manufacturing the welded joint of the present invention, and shows that the joint portion of the T-joint is a welded portion on both sides sandwiching the unfused portion and the unfused portion. The welded portion is a cross-sectional view of an example of a welded joint formed by partial fusion welding and having a root portion that is inaccessible from the outside.

Figure 3 is a schematic view for explaining the definition of the thickness of the welded metal of the present invention.

Fig. 4 is a schematic view for explaining an example of a method of manufacturing the welded joint of the present invention, and is a cross-sectional view showing an example of a welded joint in which the inner welded side portion is a closed structure.

Fig. 5 is a schematic view for explaining an example of a method of manufacturing a welded joint of the present invention, and is a partially enlarged cross-sectional view showing a welded portion of the welded joint shown in Fig. 4.

Fig. 6 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the first embodiment is performed.

Fig. 7 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the first embodiment is performed.

Fig. 8 is a schematic view for explaining a welded joint of the present invention, and is a partially enlarged view showing a welded portion of the joint of the fifth embodiment.

Fig. 9 is a schematic view for explaining an embodiment of a method of manufacturing a welded joint of the present invention, and shows a fatigue test of the joint of the embodiment 5; A cross-sectional view of the load-bearing direction of the test.

Fig. 10 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the lap joint of the fifth embodiment is performed.

Fig. 11 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the T-joint of the fifth embodiment is performed.

Figure 12 is a schematic view for explaining an embodiment of a method of manufacturing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when a fatigue test of a T-joint welded from both sides of Example 6 is performed. .

Figure 13 is a schematic view for explaining an embodiment of a method of manufacturing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when a fatigue test of a cross-shaped joint welded from both sides of Example 6 is performed. .

Form for implementing the invention

Hereinafter, an embodiment of the method of manufacturing the welded joint of the present invention will be described with reference to Figs. 1 to 13 as appropriate. Further, the present embodiment is described in detail for better understanding of the gravitational joint manufacturing method of the present invention, and the present invention is not limited thereto unless otherwise specified.

First, the technical idea of the present invention will be described.

The present invention roughly divides the method for improving fatigue strength into three types. The first type is a method of mechanically or mechanically treating an impact such as a beading on a surface, and the second type is a material such as a component of a steel material or a fusion material by adjusting a composition of a weld metal and using a metamorphic expansion of the weld metal or the like. Characteristic work Method; the third method is a method of heating after welding. Each of the methods of the present invention is referred to as a mechanical method, a material method, and a heat treatment method.

According to such classification, the present invention can be said to be a method using both a material method and a heat treatment method.

As described above, the present invention has an object of improving the fatigue strength of a welded joint having a structure in which fatigue strength cannot be improved by a mechanical treatment or the like. In general, as such a structure, the welded structure has a partial sealing structure, or a welded joint has a portion such as an unwelded portion that is melted or the like, and the hammering treatment or the polishing treatment cannot be directly performed. .

Further, a fatigue lifting technique using a metamorphic expansion of a fusion metal to reduce residual stress is applied (hereinafter, a fusion material of such a component system is referred to as a low temperature metamorphic melting material, and a fusion metal formed at this time is referred to as a low temperature metamorphic fusion welding. In the case of metal). When the number of welded tracks is one, the residual stress effect can be reduced, and the fatigue strength effect can be improved. However, most of the low-temperature metamorphic melting system contains Ni or Cr, and there are also component systems in which cracks are likely to occur at high temperatures. At this time, when the first welding is performed in accordance with the shape of the joint, the risk of occurrence of high temperature cracking is likely to occur when the welded metal is likely to be abutted and solidified.

When there is a crack in the welded portion, even if the residual stress of the welded side portion is compressed, fatigue cracking occurs from the crack inside the welded metal, and the fatigue strength of the entire joint is not affected. On the other hand, in the case of performing multi-pass welding in order to avoid high-temperature cracks, the relationship between the shape of the joint and the welded side or the root due to fatigue is formed by the first pass, The welding heat after the second pass causes a problem that the compressive residual stress disappears.

In this way, as a joint that cannot be used to improve the fatigue strength by mechanical treatment or the like, as shown in Fig. 1, when there is a closed space in the structure, the partial fusion fusion is shown as shown in Fig. 2a. In the welded joint, since there is no unwelded portion even if there is no closed space, it is considered that the stress concentration portion where fatigue is a problem (see the portion indicated by the symbol F in Fig. 2a) cannot be directly subjected to mechanical treatment. Happening. As shown in Fig. 1, the present invention is a position indicated by the symbols C and D in the first drawing in the case where the mechanical processing cannot be performed because of the presence of a sealed space, and is referred to as the inner welded side portion, and is as in the 2a As shown in the figure, the case where the unfused portion exists is referred to as a root portion.

The present invention solves the problem of the fatigue strength of the inner welded side portion 21 or the root portion 41 on the side of the sealed space as described below. The present invention discloses two types of methods in which heat treatment is not performed after welding (refer to item 1 of the patent application) and when heat treatment is performed (refer to item 2 of the patent application). In the present invention, the former is referred to as a non-heat treatment type, and the latter is referred to as a heat treatment type.

First, the non-heat treatment type will be described.

The manufacturing method of the non-heat-treated fusion splice of the present invention is as illustrated in Fig. 1 or Fig. 2, and the structure of the welded joint or the structure of the welded structure can only be obtained from the steel material 11 of the welded joint 10 (30). The one side of (31) is welded, and the inner welded side portion 21 covered by the welded structure 1 or the root portion 41 which is formed by partial fusion welding and which is inaccessible from the outside cannot be mechanically or welded. The method of the post-weld joint 10 (30) has a first welding step, which uses an abnormal starting temperature a weld metal in the range of 175 ° C to 400 ° C is formed to weld the inner weld edge portion 21 or the root portion 41; and a second weld step is heated to the inner weld edge portion 21 formed in the first fusion step or At least a part of the weld metal of the root portion 41 is an unmelted portion, and the unmelted portion is completely deformed to become a heat input for fusion of the Worth field body, thereby performing fusion using a stacked weld metal to introduce compression residual stress. The inner side is welded to the side portion 21 or the root portion 41.

In the non-heat treatment type method as described above, first, in order to prevent high-temperature cracking, a low-temperature metamorphic melting material is used to form a welded bead (inner welded side portion and root portion) for the purpose of preventing high-temperature cracking as the first welding. Welding beads. This is equivalent to the first welding step. Since this is a fusion metal formed using a low temperature metamorphic material, the fusion metal is a low temperature metamorphic metal. By the welded bead, the inner welded side portion or the root portion can be formed on the side where the mechanical treatment cannot be performed. However, since the state is insufficient to obtain a sufficient amount of welding, the static strength of the joint is insufficient. Therefore, the second weld bead (outer weld side) is formed as a subsequent bead. This is equivalent to the second welding step. For the formation of the second bead, a molten material commensurate with the strength of the material of the steel sheet forming the welded structure can be used, that is, a normal welding material can be used, and a low-temperature metamorphic melting material can be continuously used. Further, in the case of a material which is intended to select a low temperature cracking sensitivity, it is preferable to form a second bead by using a usual welding material. Moreover, it is not too difficult for a welding-related manufacturer to select a welding material that is commensurate with the strength of the steel.

In this way, it is meant to use two welds to form a welded joint, but only when the two welds are used, the first weld bead of the low temperature metamorphic melt is used. The resulting compressive residual stress may be lost due to the second bead, and in such a state, the fatigue strength cannot be expected to be improved. Therefore, when the second welding step is performed, it is necessary to generate the compressive residual stress again after the first occurrence of the compressive residual stress disappears. The use of the second welded bead to cause the compressive residual stress to occur again constitutes the fundamental technical idea of the present invention. That is, the compressive residual stress which increases the fatigue strength is not the residual stress generated after the low-temperature metamorphic melting material is welded, but the residual stress which occurs after the second welding.

The use of the low temperature metamorphic molten material of the prior art is a technique of introducing a compressive residual stress by utilizing metamorphic expansion, which occurs during a cooling process using fusion. In the present invention, the compressive residual stress corresponds to the compressive residual stress generated in the first pass welding, but in the present invention, the compressive residual stress disappears during the second welding. The basic technical idea of the present invention is that the compressive residual stress is generated again in the second welding, and the welding material used in the second welding is not necessarily limited to the low-temperature metamorphic melting material.

In the second welding step of using a welding material which is not necessarily a low-temperature metamorphic material, the second welding may not be performed without limitation in order to cause the compression residual stress to occur in the inner side of the welding edge or the root. That is, it is necessary to control the thermal influence of the second welding step. Specifically, in the second welding step, in order to regenerate the compressive residual stress, it is necessary to re-transform all of the low-temperature metamorphic weld metal formed by the first welding into the Vostian system by the thermal influence of the second welding. Conversely, if it can be completely transformed into a Worth field and re-expanded again in the subsequent cooling, it can be re- The compressive residual stress is generated, and as a result, the fatigue strength can be improved. In the second welding step, only a part of the low-temperature metamorphic welding metal formed in the first welding is transformed into a Worth field, and in the subsequent cooling, since the untransformed portion is only thermally contracted, it does not swell. Therefore, it is no longer possible to generate sufficient compressive residual stress. Further, even if the surface is welded only by coating the surface of the low-temperature metamorphic metal formed by the first welding, the low-temperature metamorphic welding metal formed by the first welding cannot be completely transformed into a Worthian body.

In the second welding step, part or all of the low-temperature metamorphic welding metal formed in the first welding step is necessary for the unmelting. When the low-temperature metamorphic welding metal is completely melted by the second welding, the residual stress is not re-introduced. On the other hand, at the last welding path of the second welding step, all of the unmelted low-temperature metamorphic welding metal must be heated to re-transformed into a Worthian body. It is not too difficult for the welding industry to discuss such conditions in advance. The welding joint is manufactured by preparing a test body having the same shape as the actual fusion joint in advance, and using the same welding material as the welding material which is suitably used for welding, and performing the first welding step and the second welding step, and then, When a macroscopic cross section is taken from the fusion splice and the microstructure of the macroscopic cross section is observed, it is possible to easily determine whether or not the unmelted portion of the low-temperature metamorphic weld metal is present, and it is possible to easily judge the unconformed portion from the last welded pass of the second welding step. Whether the molten low-temperature metamorphic welding metal is completely transformed into a Worth field. In this way, the welding condition is determined in advance, and the actual fusion joint can be welded under the conditions. Regarding the metamorphic onset temperature of the low temperature metamorphic fusion metal, it is also possible to take a test piece by measuring the untransformed off-temperature from the unmelted low-temperature metamorphic metal portion of the previously manufactured fusion joint. To confirm.

The above is the ability to increase the fatigue strength of the welded joint of Fig. 1 or Fig. 2a.

Subsequently, the T-joints that are welded from both sides are described.

In this case, in the case of FIG. 2b, in order to increase the fatigue strength of the root portion, the welded metal existing at the two positions is limited to be sufficiently separated, and the first and second welding steps for forming the respective welded metal are performed. The residual stress introduced in the welding step on the other side is not eliminated. That is, if the welded metal systems existing on both sides can be regarded as independent, the fatigue strength of the root portion can be improved by applying the non-heat treatment type technique described above. In Fig. 2b, as a joint of one of the T-joints of the fusion splice joint, since the present invention aims to increase the fatigue strength by controlling the residual stress, it is considered that the influence of the respective weld on the residual stress on the other side can be ignored. At the time, there are two welded portions that are only welded from one side. At this time, the unmelted portion corresponds to the sealed space sandwiched by the welded portions on both sides.

The so-called separation of the residual stress does not affect the degree of separation, but also depends on the heat input to the fusion. When the heat input to the welding is high, since the thickness of the welded metal formed by the welded passage is also large, in the present invention, the thickness of the welded metal is used instead of the input heat. In the present invention, the thickness of the weld metal is defined as shown in Fig. 3. First, set 1 point of the surface of the welded metal to A. A tangent to the surface of the welded metal of A is set, and then a straight line crossing the tangent and passing through point A is obtained. The intersection of the straight line and the fusion metal is set to B, and the distance between points A and B is defined as the thickness at point A. Do this to define the thickness of each point in the weld metal, and The maximum value is set to the thickness of the welded metal. Further, in this definition, when the subsequent welding is performed, since the surface of the welded metal disappears, it is necessary to take care that the thickness must be determined after the respective fusion paths are performed and before the subsequent welding paths are performed. Further, it has been found that among the thicknesses of the welded metal formed in each of the welded tracks, the maximum value and the length of the unwelded portion are compared, and when the length of the unwelded portion is more than three times the maximum value, the welded metal existing on both sides Can be considered to be independent of each other without affecting residual stress. Here, the length of the unwelded portion means the minimum value of the distance between the portion in contact with the one side of the weld metal and the portion in contact with the other side of the weld metal. If the unwelded portion is shorter than this value, the melting step on one side may affect the residual stress on the other side, and the fatigue strength may not necessarily increase, so this value is set.

Subsequently, the cross-shaped joint is described.

Regarding the cross-shaped joint, it can be considered that the front side and the back side of one steel sheet are welded from both sides to form a T-shaped joint. At this time, the conditions for forming the respective T-joints are necessary to satisfy the qualification conditions set when the T-joint is formed. Regarding the cross-shaped joint, in addition to this condition, attention must be paid to the heat of fusion transmitted through the steel sheet. It is found that the thickness of the plate is so thick that it does not affect the residual stress, that is, the length of the unwelded portion and the minimum thickness of the steel plate forming the cross-shaped joint are the thickness of the welded metal formed in each welded channel. When the maximum value is more than three times, the newly formed welded metal system can be regarded as being independent of each other without affecting the residual stress. If the unwelded portion is shorter than this, the melting step on one side will affect the residual stress on the other side, so that the fatigue strength may not be mentioned. The situation is raised, so the value is set.

The above is the technical idea of the present invention in the non-heat treatment type lifting fatigue strength method.

The metamorphosis of the low-temperature metamorphic weld metal may be a metamorphosis of the volume expansion at a low temperature specified in the present invention. Although it is not necessarily limited to a particular metamorphosis, it is generally effective, but the metamorphosis that usually occurs within the temperature range of the present invention is a martensite metamorphosis. The metamorphic onset temperature of the metamorphic iron in the field is different from that of the bainite metamorphosis or the ferrite pearlite metamorphosis. It is characterized by not depending on the cooling rate during welding but only on the weld metal. ingredient. Moreover, a formula for using a component is also known, and for example, a proposal is disclosed as follows.

Ms=719-795C-20Cr-32Ni-35.6Si-13.3Mn-23.7Mo-11.9Nb

Further, Ms indicates the metamorphic starting temperature (°C) of the granulated iron, and C indicates the value of the welded metal component (% by mass). The existence of such a presumptive formula can be a convenient indicator for the welding material to be a reference for material development. Further, the metamorphosis which occurs in the temperature range of the present invention is mainly the metamorphism of the granulated iron, and the heat treatment type described below is also the same.

Subsequently, a method of improving the fatigue strength of the heat treatment type of the present invention will be described.

The method for producing a heat-sealing type welded joint according to the present invention is a method for producing a welded joint 10 (30) having the above-described welded joint or a structure considered to be a welded structure, comprising: a first welding step, Performing the fusion of the inner weld edge portion 21 or the root portion 41 using a weld metal having a transformation starting temperature of 175 ° C to 400 ° C; and a second welding step of forming the inner side formed by the first welding step Welded edge 21 or root The at least one portion of the weld metal of the portion 41 is welded to the deposited metal by one or two or more passes in a manner of being unmelted; subsequently, there is a heat treatment step; the fusion formed by the first welding step is performed by applying All the unmelted portions of the metal are further transformed into a heat treatment of the Worth field, and the compressive residual stress is introduced into the inner welded side portion 21 or the root portion 41.

In the non-heat treatment type, the low-temperature metamorphic fusion metal formed in the first fusion step is heated to the entire re-transformation to become a Worth field by the second welding step; and the heat treatment type is the shape of the joint. When it is difficult to re-transform all of them into a Worthian body, it is judged that it is not necessary to reliably introduce the residual residual stress, and heat treatment is performed after welding, and the low-temperature metamorphic welding of the metal portion is surely performed by the heat. Metamorphosis becomes the method of the Worth field. Therefore, when compared with the non-heat treatment type, the first welding step is the same as the heat treatment type, and the second welding step is performed such that a part of the low-temperature metamorphic welding metal formed by the first welding step is in an unmelted state, and It is not necessary to use a low-temperature metamorphic melting material for the welding material, and it is the same at this point. However, as the heat treatment type second welding step, in the last welding path of the second welding step, all or a part of the unmelted portion of the low-temperature abnormal-welded metal formed by the first welding step does not necessarily need to be transformed into a Worthian body. This is because in the heat treatment step after the second welding step, all of them are re-transformed into a Worthian body. That is, in the heat-treated type of fatigue-strengthening method of the present invention, the low-temperature metamorphic fusion metal re-transformation becomes a heat treatment after the welding of the Vostian system, and before that, it is necessary to become a Worth field without re-transformation.

Determining in advance the method for improving the fatigue strength of the heat treatment type of the present invention The fusion application conditions or heat treatment conditions are not too difficult for the welding related industry. In the same manner as in the case of the non-heat treatment type, the first welding step and the second welding step are performed by preparing a test body having the same shape as the actual fusion joint in advance and using the same welding material as the welding material which is suitably used for welding. Then, in the heat treatment step, the welded joint to be produced is processed, and when the macroscopic cross section is taken from the welded joint and the microstructure of the macroscopic cross section is observed, it is possible to easily judge whether or not the unmelted portion of the low temperature metamorphic weld metal exists, and further, judge Whether or not the unmelted low-temperature metamorphic fusion metal is completely deformed into a Worth field by heat treatment. In this way, the welding condition or the heat treatment condition is determined in advance, and the actual fusion joint can be applied under the conditions. The abnormality onset temperature of the low-temperature metamorphic fusion metal can also be confirmed by taking a test piece from the unmelted low-temperature metamorphic metal portion of the previously manufactured fusion splice and measuring the metamorphic shutdown temperature.

The above is the technical idea of the non-heat treatment type and heat treatment type lifting fatigue strength method of the present invention. Further, in the non-heat treatment type, when the second welding step is two or more, since the last pass of the second welding step is pulled away from the welded metal formed in the first welding step, the second welding step of the non-heat treatment type is performed. It is preferable to limit the welding to one pass.

[Reasons for the method of manufacturing the welded joint]

Hereinafter, the reasons for limitation of the present invention will be described.

[Transformation starting temperature of the sputter metal used in the first fusing step]

First, the reason for defining the abnormal onset temperature of the low temperature metamorphic fusion metal will be described.

In the present invention, it is impossible to implement by mechanical or melting After the post-treatment is performed to raise the fatigue weld strength, the inner weld edge or the root portion is formed to form a low-temperature metamorphic weld metal, and the compressive residual stress is introduced into the welded joint portion or the root portion by the metamorphic expansion of the low-temperature metamorphic weld metal. Therefore, it is necessary to reduce the heat shrinkage after the end of the metamorphosis. The upper limit of the abnormality onset temperature is 400 ° C. Since the thermal contraction after the end of the metamorphosis becomes larger than the metamorphic onset temperature of this temperature, the compressive stress introduced when the metamorphosis is expanded disappears, so this value is set. On the other hand, the lower limit is 175 ° C, because even if the transformation start temperature is lower than the temperature, the effect is substantially the same, and in order to obtain an abnormality onset temperature lower than 175 ° C, it is necessary to add more than the limit of the present invention. The alloy element raw material is set to this value in terms of the manufacturing cost of the welded material and the risk of occurrence of high temperature cracking.

[heat treatment method in heat treatment step]

Subsequently, a heat treatment method in a heat treatment type will be described.

As a method of heat-treating the welded joint, a method using heating by a gas burner, electric heating using an electric heater, or a method of mounting a heat treatment line on the entire structure may be considered. In the present invention, a heat treatment method using electric heating or induction heating is preferred. Electric heating or induction heating and heating using a gas burner or an electric heater are significantly different in the following respects.

The electric heating is a method in which a welding current flows and a Joule heat generated at this time is used for heating, and the induction heating causes an eddy current to be generated and used to heat and the heat is generated inside the fusion splice. On the other hand, a gas burner or the like utilizes heat conduction from the surface of the joint, and heat is conducted to the inside of the joint. The present invention is targeted because the structure cannot be constructed by The fatigue of the inner welded edge or the root of the structure that is mechanically or welded for post-treatment cannot be directly baked using a gas burner during heat treatment. Therefore, in order to re-transform the low-temperature metamorphic metal into a Worth field by heat treatment, continue Heating to heat conduction to the low temperature metamorphic metal system is necessary. Therefore, not only the low temperature metamorphic metal is welded, but also the surrounding portion is heated considerably. This means that not only is the heat treatment efficiency poor, but there is also the risk of new significant residual stresses during heat treatment. On the other hand, since electric heating or induction heating generates heat inside, heat conduction and heat transfer to the low-temperature metamorphic metal are less problematic, and the problem of newly occurring residual stress is less than that of the gas burner heating. Therefore, the present invention preferably uses electric heating or induction heating.

[Component of welded metal (low temperature metamorphosis): 1st welding step]

Next, the reason for limiting the composition of the low-temperature metamorphic weld metal used in the first welding step will be described.

In the present invention, a component system mainly composed of Ni and a component mainly composed of Cr and Ni are provided as a low-temperature metamorphic fusion metal. In the present invention, the former is referred to as Ni-based and the latter is referred to as Cr-Ni-based.

In addition, in the following description, the "%" indicating the content of each element is "% by mass" unless otherwise specified.

"Ni-based ingredients"

First, regarding the Ni system, the reason for limiting the range of the components will be described.

(C: carbon) 0.01~0.15%

The effect of C is to lower the Ms temperature by adding it to iron. However, on the other hand, the toughness of the welded metal is deteriorated due to excessive addition. For the problem of welding metal cracks, the upper limit is set to 0.15%. However, when C is not added, it is difficult to obtain the granulated iron, and it is not economical to use other expensive elements to reduce the residual stress. When C is limited to 0.01% or more, an inexpensive element C is used, and the minimum limit of economic advantage is set. Further, from the viewpoint of welding metal cracks, the upper limit of C is more preferably set to 0.10%.

(Si: 矽) 0.2~0.8%

Si is known as a deoxidizing element. The Si system has an effect of lowering the oxygen level of the weld metal. In particular, in the welding construction, it is important to control the amount of Si to an appropriate value because of the risk of air being mixed in the welding. First, regarding the lower limit of Si, when Si is less than 0.2%, the amount of Si in the low-temperature metamorphic welding material also decreases. At this time, the deoxidizing effect is small, so that the oxygen level in the welded metal becomes too high, which may cause deterioration in mechanical properties, particularly toughness. Therefore, the present invention sets the lower limit to 0.2%. On the other hand, since the toughness is deteriorated when Si is excessively added, the upper limit is set to 0.8%.

(Mn: manganese) 0.4~2.0%

The Mn system is known as an element for improving strength. The lower limit of Mn is 0.4%, and is set to a minimum value at which the effect of ensuring strength can be obtained. On the other hand, even if the amount is more than the above, in particular, excessive addition is not expected to increase the fatigue strength, and the upper limit is set to 2.0%.

(P: phosphorus) below 0.03% (S: sulfur) 0.02% or less

P and S are inevitable impurities in the present invention. However, if these elements are present in a large amount of welded metal, the toughness will deteriorate, and the upper limit will be Set to 0.03% and 0.02%.

(Ni: nickel) 7.0~11.5%

The Ni-based monomer is a Worstian body, that is, a metal having a face-center structure, and by adding a weld metal, the Worstian body can be made into a more stable state. The iron itself is a Worth field in the high temperature region, and becomes a ferrite iron core in the low temperature region. Ni is made to have a more stable structure in the high-temperature region of iron by adding it, and it has a face-center structure even in a lower temperature region than in the case of no addition. This means that the metamorphosis becomes a decrease in the temperature of the body structure. The lower limit of Ni is 7.0%, which is determined based on the intention of reducing the amount of addition of the minimum residual stress effect. The upper limit of Ni is 1.5% because the effect is not changed much from the viewpoint of reducing the residual stress, and when the amount is added or more, an economic disadvantage due to expensive Ni occurs, and high temperature cracking occurs. The danger. Further, in order to surely increase the fatigue strength, the lower limit of Ni is preferably 8.0%.

The above is the reason for limiting the essential components of the Ni system of the present invention. Further, in the Ni system, in addition to the above-described essential components, the following components may be selectively added as necessary.

(Cu: copper) 0.05~0.4%

When the welding material is a metal wire, since Cu is plated to enhance the electrical conductivity, it is an effective element for improving the welding workability. However, the effect of improving the workability when excessively added is saturated, and the manufacturing cost of the manufacturing metal wire is increased, which is also unsatisfactory in the industry. The upper limit of Cu is 0.4%, which is set for such reasons. On the other hand, the lower limit of Cu is 0.05%. It is set so that the minimum value which makes a favorable electroconductivity effect can be acquired.

(Nb: 铌) 0.005~0.1%

Nb is bonded to C in the weld metal to form a carbide. The Nb carbide has a function of increasing the strength of the base material and the weld metal by using a small amount, and therefore, its economic advantage is significant when it is effectively utilized. However, on the other hand, since excessive precipitation hardening occurs when excessive carbides are formed, it is naturally necessary to set an upper limit. The lower limit of Nb is set to a minimum value of the effect of increasing the strength of the carbide formation, and is 0.005%. Further, since the strength is remarkably increased, the problem of welding cracks is caused, and even if the welding crack can be avoided, the effect of increasing the strength is gradually saturated, and the upper limit of Nb is set to 0.1%.

(V: vanadium) 0.01~0.5%

The V system acts on the same elements as Nb. However, in order to expect the same precipitation effect, unlike Nb, the addition amount is more necessary than Nb. Therefore, the lower limit of addition of V is 0.01%, and is set to the lowest value at which precipitation hardening can be expected by addition. In addition, when the addition is larger than the amount, the precipitation hardening becomes excessively remarkable, and even if excessive addition is performed, the saturation is improved from the viewpoint of improving the fatigue effect, and the fusion crack occurs due to excessive precipitation hardening. The problem is set to 0.5%.

(Ti: titanium) 0.005~0.1%

Ti also forms carbides and precipitates and hardens similarly to Nb and V. However, the precipitation hardening of V is different from the precipitation hardening of Nb, and the precipitation hardening of Ti is also different from the precipitation hardening of Nb and V. Therefore, the range of addition amount of Ti is also set to a range different from Nb and V. The lower limit of the amount of Ti added is 0.005%. It is set to the minimum amount at which the effect can be expected, and the upper limit of Ti is 0.1%. When the amount is larger than this amount, the effect of improving the fatigue strength is saturated, and the problem of cracking occurs due to an excessive precipitation effect. The value.

(Cr: chromium) 0.1~3.0%

Like the Nb, V, and Ti, the Cr system precipitates a hardening element. Further, since the Cr system has an effect of lowering the temperature of Ms, it is an element that should be effectively utilized. However, since the low-temperature metamorphic welding metal system of the present invention mainly reduces the Ms temperature by adding Ni, the amount of Cr added should be less than that of Ni. Excessive addition of Cr does not necessarily improve the effect of reducing residual stress. Moreover, because the Cr system is expensive, it is not industrially good. The lower limit of the amount of addition of Cr is 0.1%, and it is set such that the minimum value of the residual stress can be obtained by adding it. In addition, the upper limit of the amount of addition of Cr is 3.0%. With respect to the Ni system, the Ms temperature is lowered by the addition of Ni, and the strength can be ensured by other precipitation elements. Therefore, even if the amount is increased or more, the effect of reducing the residual stress is also Not changed, but set to this value.

(Mo: molybdenum) 0.1~2.0%

The Mo system also has the same effect as Cr. However, since Mo is capable of expecting an element of precipitation hardening of Cr or more. Therefore, the addition range is also set to be narrower than Cr. The lower limit of 0.1% is set to a minimum amount at which the effect of addition of Mo can be expected. Further, the upper limit of Mo is 2.0%, because even if the amount is added or more, the amount of the fatigue strength is increased and set.

The above is the reason for limiting the Ni-based component of the present invention. Further, regarding the Ni system, since the metamorphic onset temperature is mainly achieved by Ni, from the viewpoint of preventing high temperature cracking, the metamorphic initial temperature of the Ni-based low-temperature metamorphic metal is welded. The lower limit of the degree is preferably set to 200 ° C.

[Component of Cr-Ni system]

Subsequently, regarding [Cr-Ni system], the reason for limiting the range of the components will be explained.

(C: carbon) 0.005~0.10%

The effect of C is to lower the Ms temperature by adding it to iron. However, on the other hand, since the addition of excessively causes a problem of deterioration of weld cracking or toughness, in the Cr-Ni system of the present invention, since the temperature of Ms is lowered by adding Cr and Ni, the upper limit of C should be It is set to be lower than the Ni system. Therefore, the upper limit of the Cr-Ni system C is set to 0.10% from the viewpoint of preventing high temperature cracking and toughness. However, when C is not added, it is difficult to obtain the granulated iron and it is necessary to use other expensive elements to reduce the residual stress, which is not economical. When C is limited to 0.005% or more, an inexpensive element C is used, and the minimum limit of economic advantage is set.

(Si: 矽) 0.1~0.7%

Si is known as a deoxidizing element. In particular, it is very important to control the amount of Si to an appropriate value because of the danger of mixing air in the welding. First, regarding the lower limit of Si, when the amount of Si of the low-temperature metamorphic material is less than 0.1%, it means that the amount of Si in the low-temperature metamorphic welding material is also lowered. At this time, the deoxidizing effect is small, so that the oxygen level in the welded metal becomes too high, which may cause deterioration in mechanical properties, particularly toughness. Therefore, the lower limit of the amount of Si of the low-temperature metamorphic fusion metal is set to 0.1%. Further, since the Si system has an effect of improving the workability at the time of welding in addition to the deoxidation effect, the lower limit of Si is preferably 0.30%. On the other hand, even if Si is added in an amount of more than 0.7%, the effect of improving the workability is gradually saturated, and the upper limit is set to 0.7%.

(Mn: manganese) 0.1~2.0%

It is known that Mn is generally used as an element for improving strength. Since the Cr-Ni system of the present invention is obtained by Cr or the like, the effect has been obtained. Therefore, the addition of Mn is the same as that of Si, and the main purpose is the deoxidation effect. The lower limit of Mn is 0.1%, and is set to a minimum value at which the effect of deoxidizing effect can be obtained. On the other hand, the upper limit is set to 2.0% because the amount of deoxidation effect is gradually saturated and the upper limit is set to 2.0% even when the addition amount is more than this.

(P: phosphorus) below 0.03% (S: sulfur) 0.02% or less

P and S are inevitable impurities in the present invention. However, when these elements are present in a large amount in the base material and the weld metal, the toughness is deteriorated, and the upper limit is made 0.03% and 0.02%, respectively.

(Ni: nickel) 4.0~8.0%

The Ni-based monomer is a Worth field body, that is, a metal having a face-center structure. The iron itself is a Worth field in the high temperature region, and becomes a fat iron in the low temperature region, that is, a body center structure. Ni is made to have a more stable structure in the high-temperature region of iron by adding it, and it has a face-center structure even in a lower temperature region than in the case of no addition. This means that the metamorphosis becomes a decrease in the temperature of the body structure. Further, Ni has an effect of improving the toughness of the welded metal by adding it. The lower limit of the amount of Ni added to the Cr-Ni-based low-temperature metamorphic welding metal is 4.0%, which is determined from the viewpoint of reducing the amount of addition of the residual stress effect and ensuring the toughness. The upper limit of the amount of addition of Ni is 8.0% because the Cr-based metal wire is added to the Cr described later, and the Ms temperature is somewhat lowered, and from the viewpoint of reducing the residual stress. Even if the amount is added or more, the effect is not changed much, and when the amount is added or more, an economic disadvantage due to the high cost of Ni occurs, so this value is set.

(Cr: chromium) 8.0~15.0%

Unlike the Ni, the Cr system is a ferrite former. However, when Cr is added to iron, the ferrite is formed in the high temperature region, but the Worth field is formed in the middle temperature region, and the ferrite iron is formed again when the temperature is lowered. In fact, it is usually impossible to obtain the ferrite iron on the low temperature side, but to obtain the granulated iron. The reason for this is that the advantage of adding Cr is an increase in quenching property. That is to say, the addition of Cr has two points in the metamorphic system of the granulated iron, one point is that the quenching property is increased without the ferrite iron metamorphism, and the other is that the Ms temperature itself is lowered. As the effect of both of them can be satisfied, the Cr addition range of the metamorphic expansion for reducing the residual stress is effectively utilized, and the lower limit is set to 8.0. Further, the upper limit of Cr is 15.0%, because when the amount is larger than the amount, the metamorphic temperature is lowered too much, and the amount of metamorphic expansion is small, so that the effect of improving the fatigue strength tends to decrease, so this value is set.

The above is the reason for limiting the essential components of the Cr-Ni system of the present invention.

In the Cr-Ni system of the present invention, the following elements can be selectively added. The addition of the following components is not necessarily aimed at improving the fatigue strength, and the judgment of whether or not to add is easily judged by the welding company.

(Cu: copper) 0.05~0.4%

When the low-temperature metamorphic welding material is a metal wire, since Cu is capable of improving electrical conductivity by plating it, it is an effective element for improving welding workability. The lower limit of Cu is 0.05% because when the amount of Cu in the low-temperature metamorphic fusion metal is less than this amount, the amount of Cu plated on the metal wire is also lowered. It is a minimum value necessary to improve workability by increasing electrification. However, the excessive addition of Cu is not only an effect of improving workability, but also an improvement in the manufacturing cost of manufacturing metal wires. The upper limit of Cu is 0.4%, which is set for such reasons. Moreover, when the hand is welded, the low-temperature metamorphic welding material is not particularly necessary for plating the Cu system. In the present invention, the Cu-based selective element is not only a measure for improving fatigue strength, but also can be selected from the viewpoint of workability, and it can be easily judged whether or not Cu should be added as long as it is a welding-related company. .

(Nb: 铌) 0.005~0.1%

Nb is bonded to C in the weld metal to form a carbide. The Nb carbide has a function of increasing the strength of the welded metal by using a small amount, and therefore, its economic advantage is significant when it is effectively utilized. However, on the other hand, since excessive precipitation hardening occurs when excessive carbides are formed, it is naturally necessary to set an upper limit. The lower limit of Nb is a minimum value at which carbide formation can be expected to increase the strength, and is set to 0.005%. Further, the upper limit of Nb is capable of preventing the problem of cracking, and does not impair the reliability of the welded portion due to deterioration of toughness, and is set to 0.1%.

(V: vanadium) 0.05~0.5%

The V system acts on the same elements as Nb. However, in order to expect the same precipitation effect, unlike Nb, the addition amount is more necessary than Nb. Therefore, the lower limit of addition of V is 0.01%, and is set to the lowest value at which precipitation hardening can be expected by addition. Further, the reason for setting the upper limit value of V is the same as in the case of Nb, and when the addition is larger than this amount, precipitation hardening becomes excessively significant and toughness is caused. The upper limit is made 0.5% from the viewpoint of deterioration and occurrence of weld cracking due to excessive precipitation hardening.

(Ti: titanium) 0.005~0.1%

Ti also forms carbides and precipitates and hardens similarly to Nb and V. However, the precipitation hardening of V is different from the precipitation hardening of Nb, and the precipitation hardening of Ti is also different from the precipitation hardening of Nb and V. Therefore, the range of addition amount of Ti is also set to a range different from Nb and V. The lower limit of the Ti addition amount is 0.005%, which is set to the lowest amount at which the effect can be expected, and the upper limit of Ti is 0.1%, which is determined from the viewpoint of deterioration of toughness or excessive weld cracking of steel.

(Mo: molybdenum) 0.1~2.0%

Mo is also an element which can be expected to be precipitated and hardened similarly to Nb, V, and Ti. However, in order to obtain the same effect as Nb, V, and Ti, it is necessary to add Nb, V, or Ti to Mo. The lower limit of the amount of addition of Mo is 0.1%, and is set to a minimum value at which the yield strength can be expected to be increased by precipitation hardening. Further, the upper limit of Mo is 2.0%, because even if the amount is increased or more, the amount of the fatigue strength is saturated and set to this value.

[used to improve fatigue strength after treatment]

Subsequently, the reason for limiting the measure of the lifting fatigue strength of the inner welded side portion on the welded side will be described.

The present invention relates to a method for improving the fatigue strength of an inner welded side portion or a root portion which cannot be subjected to a measure for improving fatigue strength by mechanical treatment or the like. Therefore, the welded edge portion on the welded side is not necessarily the object of the present invention. However, if the fatigue cracking system can increase the fatigue strength of a certain part, the fatigue strength of other parts determines the fatigue strength of the joint as a whole. because Therefore, the inventors of the present invention thought that it is impossible to perform the post-treatment by mechanical or welding, and the fatigue strength of the inner welded side portion or the root portion of the measures for improving the fatigue strength is improved, and the fatigue fatigue strength of the welded side portion on the opposite side is further provided. Countermeasures are meaningful in the industry.

The measures for improving the fatigue strength can be roughly classified into a method of reducing residual stress and a method of mitigating stress concentration. As an example of the method of reducing the residual stress, the method of heating the entire welded structure and then slowly cooling it. However, in this method, since the compressive residual stress which is intentionally introduced by the low-temperature metamorphic welding metal disappears, it cannot be used as a measure for improving the fatigue strength without limitation. In the present invention, it is necessary to limit the measures for improving the fatigue strength which do not affect the residual stress introduced by the low-temperature metamorphic welding metal.

In the present invention, mechanical post-treatment can be performed by one or both of the outer welded side portions 22 (42) on both sides of the welded bead on the welded side formed in the second welding step (see the first The symbols 22a, 22b, 42a, and 42b) in Fig. 2 are subjected to post-machining processing using a polishing process or the like, and the shape of the outer side welded side portion 22 (42) after the post-treatment is processed into a state other than the original welding state. More smooth.

The method of processing the welded edge portion to be smoother than the original state by welding using a post-machining treatment such as grinding treatment is to relax the stress concentration method because of the residual stress of the low-temperature metamorphic welding metal. The influence of the joint application as the object of the present invention is a suitable method for improving the fatigue strength.

Moreover, in the present invention, both sides of the welded bead on the welded side are One or both of the outer welded side portions 22 (42) can be processed by a hammering process such as beading, ultrasonic hammering, or air hammering, and can be used as a side of the side after the post-treatment is performed. The shape of 22 (42) is processed to be smoother than the original state of fusion, and a method of mechanical post-treatment for introducing the compressive residual stress to the outer welded side portion 22 (42).

Since the fatigue strength countermeasure by the post-treatment of the hammering treatment by using ultrasonic hammering or the like is to relieve the stress concentration, the compressive residual stress is also introduced into the treated portion, so that the fatigue improvement effect is higher than the usual grinding treatment. Big. Further, since the influence of the residual stress introduced into the low-temperature metamorphic metal is not large, it is a suitable method for the joint application of the present invention as a method for improving the fatigue strength.

Further, in the present invention, it is possible to perform a post-welding process in which one or both of the outer welded side portions 22 (42) on both sides of the welded bead are subjected to TIG welding without using a weld filler material ( In the TIG eutectic welding, the shape of the outer side welded side portion 22 (42) to which the TIG welding is performed can be processed to be smoother than the original state of welding.

The TIG eutectic welding system does not use a welding material, but re-melts the surface of the joint by welding arc heat to reduce the stress concentration of the welded portion and the like. Since the method of heating the welded joint is generally possible, there is a possibility that the compressive residual stress introduced by the low-temperature metamorphic welding metal disappears, and the use thereof is necessary. However, in the TIG eutectic welding, even if it is a method of heating, it is possible to achieve a suitable method for the joint of the present invention by sufficiently reducing the stress concentration by inputting a small amount of heat. Further, in the heat treatment type of the method for improving fatigue strength of the present invention, When the method is applied, when the TIG co-melting is performed before the heat treatment, the problem of the disappearance of the compressive residual stress introduced by the low-temperature metamorphic welding metal is completely absent. Therefore, in the heat treatment type, the TIG fusion welding is performed before the heat treatment. The treatment is better.

Further, in the present invention, it is possible to employ a method of performing post-treatment by welding by applying a forming component and a metamorphic start to one or both of the welded side edges 22 (42) on both sides of the welded bead. The temperature is considered to be the same as the weld metal (the cosmetic bead) which is the same as the weld metal used in the first welding step, and the introduced compressive residual stress is introduced to the side of the welded side which is subjected to the post-treatment. 22 (42).

By using the same welding material as the low-temperature metamorphic welding metal forming the first welding step, a method of forming a cosmetic bead on the welded side portion of the welded side is used, and since the amount of welding is small, the heat of application to the welded joint can be suppressed to Lower is a suitable method that can be applied to the joint of the present invention. However, this method is a method of controlling the residual stress. On the other hand, the method of imparting the above-described TIG eutectic fusion of the joint heat is a method of mitigating the stress concentration, and the method of improving the fatigue strength is different. Therefore, in the heat-treated type of fatigue-strengthening method of the present invention, the TIG co-melting method can be carried out before or after the heat treatment, but the method of forming the cosmetic beads is required to be carried out after the heat treatment. Since the cosmetic beads are formed before the heat treatment, the compressive residual stress formed by the cosmetic beads during the heat treatment disappears. When the cosmetic bead is formed before the heat treatment, it is necessary to set the heat treatment condition during the heat treatment so that both the low-temperature metamorphic weld metal formed at the first welding step and the weld metal of the cosmetic bead are changed again. In the case of the Worth field, at this time, the heating range is widened, and the risk of introduction of residual stress or deformation due to heat treatment is increased. Therefore, in the present invention, when the heat treatment type fatigue strength increasing method is employed, the cosmetic beads are preferably subjected to heat treatment.

As described above, according to the method for manufacturing a welded joint according to the present invention, even if there is a problem in the structure of the welded joint or the structure of the welded structure, there is a inside of the structure which cannot be post-treated by mechanical or welding. When the edge portion or the root portion is welded, it is also possible to increase the fatigue strength of the welded joint, and it is possible to increase the service life of the entire welded structure, or to repair the existing welded structure, thereby prolonging the service life of the welded structure. The significance of the industry is very significant.

Example

Hereinafter, the present invention will be more specifically described by way of examples of the method for producing a welded joint according to the present invention, but the present invention is not limited to the following examples, and can be carried out in a range suitable for the purpose of the foregoing and the following description. Any suitable ones are included in the technical scope of the present invention.

[Example 1]

Example 1 is an example of a non-heating type measure for improving fatigue strength.

First, a structure as shown in Fig. 4 is assembled by welding, and is a structure that can be welded only from one side. At this time, the state of the welded portion is as shown in Fig. 5. Since the number of welded tracks in the non-heating type is limited to two, the thickness in the upper portion of Fig. 4 is set to 6 mm. Moreover, in order to manufacture the joint of Fig. 5, various welding materials are experimentally produced. First, as the first welding step, The inner side welded side portion on the side where the mechanically improved fatigue strength measure cannot be performed as shown in Fig. 5 forms a bead. Subsequently, the second welded splice (outer welded side) was produced as the second welding step, and the left and right joints shown in Fig. 5 were welded using the same welding conditions.

The welding method to be used is two types of hand welding (SMAW) and carbon dioxide gas welding (GMAW), and the welding conditions at this time are as follows.

1st SMAW: 130A-23V-14cm/min

Track 2 SMAW: 140A-190V-25~30V

1st road GMAW: 200A-27V-23cm/min

Track 2 GMAW: 250A-31V-18.5cm/min

Further, regarding the welding condition of the second SMAW, since the case of re-transformation or the case of no re-transformation is produced, and the embodiment in which the unmelted portion does not remain or only one of the unmelted portions is not deformed, in order to manufacture the Wortfield body, The current and voltage in the above range are selected for the purpose of changing the input heat, and the welding speed is controlled to change the input heat. In the table of the examples shown later, the second SMAW is described. Further, when the second welding material is the same as the first welding material, that is, the welding material having a strength level of 490 MPa to 780 MPa may be selected. In either case, the welding conditions are those using the above conditions. Further, the welding condition of the second pass is to impart a thermal influence to the welded metal formed in the first pass, and in order to achieve the purpose of re-transformation into a Worthfield, if the object can be achieved, the welding condition is not limited. Moreover, as a normal welding material, the following (fused metal component) uses the following.

490MPa grade SMAW: C: 0.07%, Si: 0.62%, Mn: 1.2%, P: 0.011%, S: 0.006%

490MPa grade GMAW: C: 0.10%, Si: 0.52%, Mn: 1.2%, P: 0.010%, S: 0.008%

590MPa grade SMAW: C: 0.07%, Si: 0.40%, Mn: 1.2%, P: 0.011%, S: 0.006%, Ni: 0.76%, Mo: 0.23%

590MPa grade GMAW: C: 0.07%, Si: 0.38%, Mn: 1.4%, P: 0.005%, S: 0.008%, Mo: 0.35%

780MPa grade SMAW: C: 0.05%, Si: 0.44%, Mn: 1.4%, P: 0.011%, S: 0.008%, Ni: 2.56%, Mo: 0.51%, Cr: 0.18%

780MPa grade GMAW: C: 0.07%, Si: 0.54%, Mn: 1.3%, P: 0.006%, S: 0.007%, Ni: 2.26%, Mo: 0.48%

As the welding material at this time, various welding materials are used, for example, the same welding material as the first welding step, or a 590 MPa welding material. Further, several such welded joints are manufactured, some of which are used for component analysis of the welded metal produced in the first welding step, measurement of the abnormality onset temperature, and determination of the shape of the Worthfield by observing the macroscopic structure. Metamorphosis, the rest is used as a test body for fatigue testing.

Fig. 6 is a schematic view showing the load direction of the load when the fatigue test is performed, and the arrow in Fig. 6 indicates the direction of the load. The fatigue test was carried out by a four-point bending test, and the fatigue load was measured by attaching a strain gauge to the inner welded side of the welded metal formed in the first welding step. Moreover, since the test piece can be attached to the strain gauge, it is considered that it is difficult to measure the stress using the strain gauge when the actual welded structure is welded.

Table 1 below shows the measurement results of the components of the weld metal and the abnormality onset temperature formed in the first welding step. The weld metal component is measured by directly taking a test piece for component analysis from the formed weld metal after welding. Further, the abnormality onset temperature is a result of taking a FORMASTER test piece from the formed weld metal after welding and measuring the abnormal onset temperature. That is, the expansion and contraction of the weld metal were measured by taking a test piece of a round bar shape from the weld metal, heating and cooling, and measuring the length of the test piece at each temperature, and thereby determining the abnormality onset temperature. In Table 1, the number 1 to 14 is a weld metal component or an abnormality onset temperature which is within the range of the present invention. Since the present invention relates to a method for improving fatigue strength, it is not necessarily the case of the present invention that only the weld metal component and the abnormality onset temperature are within the scope of the present invention. However, for reference, in the following Table 1, the case where the weld metal component and the abnormality onset temperature are within the scope of the present invention is described as an example of the present invention. When the components of the numbers 1 to 14 in the following Table 1 were observed, it was found that the components of the weld metal shown in Table 1 below are examples of the Ni-based component of the present invention.

Further, in the following Table 1, the numbers 51 to 60 are outside the scope of the present invention. Since these cracks occurred in the welded metal, the portion where no crack occurred was selected to take a test piece and measure. The number 51 is C. 0.2%, which exceeds the range of the present invention and causes weld cracks (high temperature cracks). The number 52 is Ni outside the range of the present invention, and similar to the number 51, weld cracking occurs. The number 56 is Nb outside the range of the present invention, and the weld crack (low temperature crack) occurs due to the strength being too high. The number 57 is V outside the range of the present invention, and similar to the number 56, a weld crack occurs. The number 59 is Ti outside the range of the present invention, and similar to the numbers 56 and 57, weld cracking occurs. The number 60 is Si is outside the scope of the present invention. Although the weld crack did not occur, defects occurred due to insufficient deoxidation.

The numbers 1 to 14 within the scope of the present invention are such that cracks or defects do not occur and the abnormality onset temperature is within the scope of the present invention. Further, the numbers 53, 54, 55, and 58 of the comparative example have no problem such as cracks, but the components are outside the range of the present invention. Therefore, the abnormality onset temperature is also outside the range of the present invention. These evaluations can be judged from the results of the fatigue test.

Table 2 below shows the composition and metamorphic start of the weld metal formed in the first welding step when the welded joint shown in Fig. 5 is produced using the test body as shown in Fig. 4, in the same manner as in Table 1. temperature. A welded joint is present on the left and right sides of Figs. 4 and 5, and the joint is produced using the same melting conditions. In the following Table 2, the numbers 101 to 116 are the weld metal in the range of the present invention, which is the same as in Table 1. Since the present invention relates to the method for improving the fatigue strength, only the weld metal component and the abnormality onset temperature are within the scope of the present invention. In the meantime, it is not necessarily an example of the present invention. However, for reference, in the following Table 2, the case where the weld metal component and the abnormality onset temperature are within the scope of the present invention is described as an example of the present invention. Further, the numbers 151 to 162 are comparative examples of the present invention. Here, the numbers 152, 155, 160, 161, and 162 are examples in which cracks or defects occur in the welded metal, and the abnormality onset temperature is selected by selecting a welded metal portion where cracking has not occurred. Although cracks did not occur in the other comparative examples, since the components were outside the scope of the present invention, the abnormal onset temperature became outside the scope of the present invention.

In the following Table 3, the weld metal of the component system shown in Tables 1 and 2 was formed in the first welding step, and the test body shown in Fig. 4 was produced through the second welding step. It indicates the fatigue strength when the fatigue load as shown in Fig. 6 is applied. The fatigue strength at this time is determined in the form of a stress range that does not break when 2 million fatigue loads are applied. Further, the stress range is a value measured by sticking the strain gauge to the vicinity of the side of the welded metal formed by the first pass welding before the fatigue test is performed. Here, the fatigue strength is 200 MPa, which means that the load does not break even when the load is applied in the range of 0 to 200 MPa for 2 million times. At this time, the welding method selects two types of SMAW (hand welding method) and GMAW (gas shielding welding method). The welding conditions are set to the first SMAW: 130A-23V-14cm/min, the second SMAW: 140A-190V-25~30V, the first pass GMAW: 200A-27V-23cm/min, the second pass GMAW: 250A -31V-18.5cm/min. At this time, the right and left joints shown in Fig. 5 were welded under the same conditions. The welding method [1] shown in the following Table 3 means the first welding step, and [2] means the second welding step. The components of the weld metal formed in the first welding step are described in Tables 1 and 2, and the weld metal number ([1] weld metal number) for each joint is shown in Table 3 below. In the second welding step, the same welding material as the first welding step is not necessarily used, and a general welding material of the 590 MPa class may be used. The welding material used in the second welding step is also shown in Table 3. Further, by observing the macroscopic test, whether or not the welded metal system formed in the first welding step was re-transformed to the Vostian body, the results are also shown in Table 3.

The numbers in Table 3, J1 to J36, are the components in the first welding step which are formed within the scope of the present invention and the fusion metal at the abnormal initial temperature, and the result of the macroscopic test piece observation is that the welded metal is in the second welding step. From the joints of the Worthfield body, it is known from Table 3 that the fatigue strength is all greater than 250 MPa. J133 to J136 are different from J1 to J32 in the strength of the welded metal used in the second welding step. Since the welded metal formed in the first welding step can be re-transformed, it is known that the fatigue strength can be improved.

On the other hand, J101 to J116 are comparative examples because the abnormality onset temperature is outside the range of the present invention and the fatigue strength is not up to 250 MPa. Among them, J101, J103, J105, J108, and J109 are joints formed by welding metal of the numbers 53 and 55 of Table 1 and the numbers 151, 156 and 157 of Table 2 in the first welding step, and the transformation starting temperature ratio is The scope of the invention is low. It is considered that such a joint is incapable of obtaining a sufficient amount of metamorphic expansion because the abnormal initial temperature is too low, resulting in an insufficient effect of improving fatigue strength. On the other hand, in the first welding step of J102, J104, J106, J107, J110, and J111, the joints of the numbers 54 and 58 of Table 1 and the numbers 153, 154, 158, and 159 of Table 2 are formed, and these are the joints. The joint is because the abnormal initial temperature is higher than the range of the present invention, resulting in a decrease in residual stress. Further, it is within the scope of the present invention that only the four joints of J112 to J115 are in the range of the initial temperature of the low-temperature metamorphic weld metal formed in the first welding step, but it is known by macroscopic observation that the second pass is The input heat is small, and the low-temperature metamorphic fusion metal is not deformed to the joint of the Worth body in a part of the second fusion step. At this time, since the compressive residual stress introduced in the first welding step disappears and the compressive residual stress is not introduced again in the second welding step, The fatigue strength is not improved. In the comparative example of J116, although the abnormality onset temperature is within the scope of the present invention, since the heat input of the second pass is not appropriate, the unmelted portion of the weld metal formed in the first pass is not present and is completely melted. An example is an example where fatigue strength is not improved.

From the above, the case of the present invention is all confirmed to have an effect of improving the fatigue strength, and the industrial significance is clear.

[Embodiment 2]

Example 2 is an example of a method for improving the fatigue strength of the heat treatment of the present invention. In the heat treatment type of the present embodiment, the welding path of the second welding step is two, and the thickness of the upper portion of the third drawing is set to 8 mm, and is set to be thicker than that of the first embodiment, and is carried out 2 Road welding. The total welding is one lane in the first welding step and two lanes in the second welding step, and the total is three lanes. Further, as the heating method at the time of heat treatment, two types of induction heating and electric heating are selected. Induction heating was performed at 2.0 kHz of 20 kW, and energized heating was performed by energizing a current of 250 A to the welded bead.

Table 4 below shows the results of Example 2, and in Table 4 below, the meanings of [1] and [2], [1] weld metal number, and [2] weld material of the welding method are the same as those in Table 3. However, the judgment of the metamorphosis is different from that of the first embodiment. Further, the fatigue test was carried out in the same manner as in Example 1, and the stress range which was used 2 million times without breaking was taken as the fatigue strength. In the following Table 4, the numbers J201 to J230 are the examples of the present invention in which the 590 MPa grade welding material is used in the second welding step and heat treatment is performed by induction heating, and the fatigue strength is all greater than 250 MPa. Further, J231 and J232 are examples of the present invention in the case where the same welding material as the first welding step is used in the second welding step, and it is known that the fatigue is improved. The effect of labor intensity. Further, J232 to 235 is an example of the present invention in which heat treatment is used for heat treatment, and it is confirmed that it has an effect of improving fatigue strength. J236 to J239 are the same as J201 formed in the first welding step, but the strength of the welding material used in the second welding step is 490 MPa and 780 MPa, which is different from J201. However, the induction metal formed in the first welding step reliably achieves the re-transformation of the weld metal by the induction heating, and the fatigue strength is more than 250 MPa or more, and the embodiment having the effect of improving the fatigue strength can be confirmed.

J301 to J316 of Table 4 are comparative examples of the present invention, and the fatigue strength is different from the example of the present invention, and is not up to 250 MPa. However, since the transformation starting temperature of the weld metal formed in the first welding step of J301, J303, J305, J308, and J309 is lower than the range of the present invention and the expansion expansion is insufficient, it is considered that the residual stress is insufficient. On the other hand, the transformation starting temperature of the weld metal formed by the J302, J304, J306, J307, J310, and J311 in the first welding step is higher than the range of the present invention, and it is considered that the effect of reducing the residual stress is small. Further, although the abnormal starting temperature of the J312 to J315 low-temperature metamorphic welding metal is within the range of the present invention, since the heat treatment is insufficient, only a part of the unmelted portion is not metamorphosed to the Vostian body, and it is not confirmed that the fatigue is improved. Intensity. In the last comparative example J316 of Table 4, the welded metal of the first pass was completely melted at the time of welding of the second pass, and the unmelted portion disappeared. Therefore, the fatigue strength was not improved.

From the above, in the case of the present invention, all of the effects of improving the fatigue strength can be confirmed, and the industrial significance is clear.

[Example 3]

In the third embodiment of the present invention, the post-processing of the side of the welded metal formed on the outer side of the welded metal formed in the second welding step is performed as a measure for improving the fatigue strength.

In the first and second embodiments, the fatigue strength on the side of the welded metal formed in the first welding step was regarded as a problem, and the fatigue test was as shown in Fig. 6, and the two points on the inner side of the four-point bending test were made. The interval is narrow, and a difference is given to the stress of the welded metal side portion formed in the first welding step and the second welding step. In this regard, in the third embodiment, in order to make the same level of stress, As shown in Fig. 7, the position of the two fulcrums on the inner side of the 4-point bending test was placed outside the fusion splice. Further, the stress is measured by attaching a strain gauge. Further, the arrow in Fig. 7 indicates the direction of the load.

The measures for improving the fatigue strength applied to the welded side of the welded metal formed in the second welding step are welding bead, TIG eutectic welding, ultrasonic hammering, formation of low temperature abnormal welding metal, grinding treatment, by Local heating to remove any of the stresses. Further, the welding material used for forming the low-temperature abnormal-welding metal can be the same as the welding material used in the first welding step. Among these measures, a welded bead, an ultrasonic hammer, and a method of forming a low-temperature metamorphic welding metal to introduce a compressive residual stress, the first two of which have the effect of improving the shape of the welded edge. Moreover, the TIG eutectic welding and the grinding process are methods for improving the shape of the side portion to relieve stress concentration. Finally, the stress is removed by local heating, which means that the tensile residual stress of the welded portion is eliminated. However, there is a risk that the compressive residual stress introduced in the first welding step also disappears, and the present invention compares example.

Table 5 below shows the results of Example 3. The joint number in Table 5 below corresponds to the joint number in Table 3, which means that the joint fatigue strength is applied to the outer welded side portion of the second welding step side. Moreover, the processing method shown in the following Table 5 refers to the method of measures for improving the fatigue strength at this time. In addition, in the fatigue crack occurrence position in Table 5 below, [1] means that the fatigue crack system occurs on the inner weld side of the first welding step side, and [2] means that the fatigue crack system is The outer welded edge portion on the second welding step side occurs,

In Table 5, numbers K1 to K4 and K101 to K104 are examples of the present invention, and K51 and K151 are comparative examples. The fatigue strength of the K1 system was 290 MPa, which was approximately the same value as J1 of Table 3, and the crack occurrence position was [1]. It is considered that the fatigue strength of [2] is higher than [1] by the bead shot. The same tendency can also be observed in K3 and K4. In addition, the fatigue cracks of the numbers K2 and K5 are generated in [2]. Although the fatigue strength [2] is lower than [1], the fatigue strength itself is approximately the same as J1 of Table 3, and it is considered that These conditions are approximately the same fatigue strength as [1] and [2]. The same tendency as this is also observed for K101~K104.

K51 and K151 are heated by partial removal of stress, that is, SR, and the heating method is performed using a gas burner. At this time, the fatigue strength did not reach 250 MPa. Moreover, the fatigue cracking occurs from the [1] side, that is, from the inner welded side portion where the low-temperature metamorphic welding metal is formed. In this example, it is compared to in embodiment 1. The fatigue strength of Table 3 (the J1 joint is 280 MPa and the J28 joint is 350 MPa) is low. For this reason, it is considered that the compressive residual stress introduced in the first welding step by local heating is lost by local heating.

[Example 4]

The fourth embodiment is an embodiment in which the non-heating type measures for improving the fatigue strength are different from the first embodiment in the case where the number of the fusion paths is three or more.

In Example 4, the welding method employed SMAW. In the test body production system at this time, the structure shown in Fig. 4 was used in the same manner as in the second embodiment. The thickness of the upper portion was 8 mm in the same manner as in the second embodiment. The first two welds were made using a 3.2 mm diameter weld bar. The composition values of the weld metal at this time are as shown in Table 6. As shown in Table 6, four types of welding were performed. The welding conditions are 120A-22V-25cm/min in each lane.

Subsequently, the welding of the third pass is performed on the four types of joints. In the welding of the third pass, in order to change the influence of the input heat, when the input heat is 1.5 kJ/mm or more, the welding rod diameter is 4 mm, and the following is 3.2 mm. The welding condition is 170A-25V for a 4mm rod diameter and 120A-22V for a 3.2mm rod, and the input heat is adjusted by changing the welding speed. As a result, the number of fusion paths of the joint used in the fourth embodiment was all three-way welded, and the number of corresponding passages was larger than that of the two-way welding shown in the first embodiment. Table 7 shows the results of the fatigue test of the test body produced in this manner.

In Table 7, L1 to L8 are the present invention, and L51 to L56 are comparative examples. The input heat of the third channel shown in Table 7 is determined by the third pass, and the fusion metal of the first track is re-deformed. The macro test piece is judged by macroscopic observation. As is apparent from Table 7, in the example of the present invention, it was confirmed that all of the welded metal systems of the first track were subjected to re-metamorphism. On the other hand, in Comparative Examples L51 to L55, since the input heat was low, only a part of the welded metal of the first track was not deformed. In Comparative Example L56, since the input heat was high, the unmelted portion disappeared. The fatigue strength was carried out by using the load method shown in Fig. 5. In the example of the present invention, as shown in Table 7, all were 250 MPa or more, and the fatigue improvement system was remarkable when compared with the comparative example. In the comparative examples L51 to L55, even if the welding metal components of the first track and the second track are the same, the heat input of the third channel is not suitable, that is, when the re-transformation of the first molten metal cannot be achieved. The fatigue strength does not necessarily increase the obvious. The last comparative example L56 of Table 7 is an example in which the welded metal of the first pass is completely melted by the third pass welding, and therefore, the unmelted portions are all lost, and the fatigue strength is not improved.

[Example 5]

Example 5 is an example of investigating the influence of the shape of the joint. Embodiments 1 to 4 are formed in the first pass to form the welded metal provided by the present invention, and then, in the final fusion path, since the effect of verifying the re-deformation of the welded metal formed in the first pass is set, the joint is designed. The shape is welded to the joint of the flat plate using a U-shaped rib structural member. However, the essence of the present invention is to re-transform the low-temperature welded metal formed in the first pass by the final welding, and is not limited to such a joint. In the fifth embodiment, the effects of the present invention were verified by using a corner joint, a lap joint, and a T-joint which can be welded only from one side due to the presence of an unwelded portion.

The joints used in the fifth embodiment are the three types of joints shown in Figs. 8, 10, and 11, each of which is a corner joint, a lap joint, and a T joint. Further, in the corner joint of Fig. 8, since it is difficult to perform the fatigue test, as shown in Fig. 9, the welding is first performed on the one side without the unwelded portion, and then the corresponding fatigue characteristics are set. The welded joint of the corner joint of the purpose. The lap joint of Fig. 10 is manufactured such that the distance between the right and left lap joint portions is 200 mm. The T-joint of Fig. 11 is only capable of beveling the shape welded from the left side to the shape of the joint which can be welded only from one side.

The welding system is SMAW, and the welding condition of the first pass is the same as that of the embodiment, which is 130A-23V-14cm/min, and the welding condition of the second pass (last pass) is 150A-25V-9cm/min (the input heat is 2.5kJ). /mm), and 2A conditions of 150A-25V-20cm/min (input heat is 11kJ/mm). As the welding material of the first track, the number 1 of Table 1 and the number 102 of Table 2 are used. The same fusion material, but because of the dilution from the base material, several components were different, and a weld metal having the composition of Table 8 was formed. As the welding material of the second pass, the SMAW welding material for 590 MPa shown in Example 1 was used.

In Table 9, the results of the fatigue test are described. In Table 9, M1 to M6 are examples of the present invention, and M51 to 59 are comparative examples. Whether or not to perform the metamorphosis is confirmed by taking a macro test piece from the joint and observing the macroscopic structure. Table 9 shows the fatigue results of the joints made with the conditions of the last weld fusion input of 2.5 kJ/mm and the lower 1.1 kJ/mm for each joint. Table 9 shows that the weld metal formed in the first pass at 2.5 kJ/mm is completely deformed, but in the case of 1.1 kJ/mm, only a part of the weld metal formed in the first pass is not deformed. The fatigue test was also compared with the comparative example, and it was confirmed that the fatigue strength of the present invention was improved. Further, unlike Example 1 and the like, the fatigue strength in Table 9 is the value of the fatigue joint divided by the welded joint of the welded portion with respect to the corner joint, and the other values are divided by the steel sheet cross-section. The reason for this is that it is difficult to attach a strain gauge to the vicinity of the welded metal formed by the welding of the first pass because of the joint used in the fifth embodiment. In the three comparative examples of Table 9, any of M57, M58, and M59 is an example in which the welded metal formed in the first pass is melted and disappears due to the second pass, and the fatigue strength is not improved.

As is apparent from Table 9, the fatigue strength of the present invention was high as compared with the comparative example, and it was confirmed that the effect of the present invention is not only a T-joint but also effective for other joints.

[Embodiment 6]

Embodiment 6 is an embodiment relating to a T-joint and a cross-shaped joint welded from both sides. In the present invention, even in the case of a T-joint and a cross-shaped joint welded to both sides, the fusion of one side does not affect the fusion of the other side, that is, if it does not affect the residual stress, it can be Each is considered as an independent weld. Therefore, the thickness of the welded metal in each of the welded tracks is defined, and the thickness thereof is compared with the length of the unwelded portion existing between the welded portions on both sides. Also, regarding the cross-shaped joint, a comparison with the plate thickness is also considered.

The T-joint is formed using the welded beads 1, 2, 3, and 4 as shown in Fig. 12, and the welding sequence is performed in the order of 1, 2, 3, and 4. Among them, 1, 3 are low temperature metamorphic weld metals and are the component systems of 206 shown in Table 8. That is, the fusion lands 1 and 3 are applied using the same material as that used in the embodiment 5. These welding constructions were carried out under the same conditions as those carried out in the T-joint of Example 5. Table 10 is an example of a T-joint. In Table 10, in the respective embodiment numbers, the different parameters are the thickness of the welded bead 4 and the length W of the unwelded portion. Further, as is clear from Table 10, in the welding beads 1, 2, 3, and 4, the largest thickness is the welded bead 4. As is clear from Table 10, when the length W of the unwelded portion is three times or more the thickness of the welded bead 4, the present invention is an example, and the improvement in fatigue strength can be confirmed. On the other hand, the results of the improvement in fatigue strength were not observed in the comparative examples. Further, in the comparative example of Table 10, it was found that all of the fatigue cracking system occurred from the side of the welded bead 1 . This is considered to be because the residual stress on the side of the welded bead 1 is affected by the welded bead 3, 4, so that the effect of the low-temperature metamorphic fusion metal disappears.

Table 11 is an example of a cross-shaped joint. Manufacturing order of cross joints It can be considered that the manufacturing order of the T-joint is performed twice and back. Therefore, in the present embodiment, the low temperature metamorphic fusion metal of the cross joint is manufactured using the manufacturing method of the T-joint. Therefore, the composition of the low-temperature metamorphic weld metal is the same as that of 206 of Table 8 of Example 5. Regarding the cross-shaped joint, it is considered that the length of the plate thickness t2 as shown in Fig. 13 is necessary. Further, in Fig. 13, since the thickness t1 is not shorter than the length W of the unwelded portion, it is not shown in Table 11. In Fig. 13, the weld metal 1, 3, 5, and 7 are low-temperature metamorphic weld metals, and the composition thereof is the same as 206 of Table 8. Further, as the welding order, the welding bead 1 is applied, and the welding is performed in the same order as the bead number. At this time, since the T-joint is manufactured by using the welded bead 1 to 4, and then the T-joint of the back side is manufactured using 5 to 8, the manufacturing order of the table 10, that is, either of N1 and N2 is used as the respective T-shape. Joint manufacturing order. According to the manufacturing sequence of the T-joints, as shown in Table 10, since the length of the unwelded portion is sufficiently long, the manufacturing order for improving the fatigue strength can be expected. Regarding the cross-shaped joint, in addition to the influence of the residual stress in the horizontal plate (thickness t2) of Fig. 13, it is necessary to consider the influence of t2 in the embodiment of the cross-shaped joint. In Table 11, P1 and P2 are examples of the present invention, and P51, P52, P53, and P54 are comparative examples. In Comparative Examples P51 and P52, the T-joint of the front side T-joint, the back T-joint, and the T-joint manufacturing method of Table 10 having the effect of improving the fatigue strength were used, but the thickness was t2. It is 10mm, 12mm, and does not reach 3 times the thickness of the maximum welded bead, so the fatigue strength is not achieved. This reason can be considered to be because the welding heat penetrates the surface through the cross plate when the welding beads 5, 6, 7, and 8 are welded. Similarly, Comparative Examples P53 and P54 are also t2 for the thickness of the welded bead. The maximum value is 3 times (21 mm) or less of 7 mm, so the fatigue strength is not improved. In the example of the present invention, since the condition can be achieved, it is confirmed that the effect of improving the fatigue strength is obtained.

From the above, in the case of the examples of the present invention, all of the effects of improving the fatigue strength were confirmed, and the industrial significance was clear. Further, regarding the TIG eutectic welding, since the joint is heated, it should be noted that the compressive residual stress introduced in the inner welded side portion of the first welding step does not disappear, and it is preferably confirmed before application to the actual structure. Moreover, it is not too difficult to confirm in advance for the welding-related company. At this time, it is preferable to measure the residual stress after the formation of the TIG eutectic fusion, or to perform the fatigue test as in the third embodiment, and it is preferable to compare with the fatigue test result of the first embodiment.

1‧‧‧welded structure

11, 12, 31, 32‧ ‧ steel

21‧‧‧Inside welded edge

22, 42‧‧‧ outside welded edge

22a, 22b, 42a, 42b‧‧‧ one or both of the ends of the bead on the outer side of the weld

41‧‧‧ Root

10, 30‧‧‧weld joints

T1, t2‧‧‧ board thickness

W1, W2‧‧‧ unwelded length

A~F‧‧‧ Stress Concentration Department

1~8‧‧‧welding metal

1 is a schematic view for explaining an example of a method of manufacturing a welded joint according to the present invention, and is a cross-sectional view showing an example of a welded joint in which a welded inner side of the structure is a sealed structure.

Fig. 2a is a schematic view for explaining another example of the method of manufacturing the welded joint of the present invention, and shows an example of a welded joint which can be welded only from one side to form a portion which is partially melted and has a root which is inaccessible from the outside. Sectional view.

Fig. 2b is a schematic view for explaining another example of the method of manufacturing the welded joint of the present invention, and shows that the joint portion of the T-joint is a welded portion on both sides sandwiching the unfused portion and the unfused portion. The welded portion is a cross-sectional view of an example of a welded joint formed by partial fusion welding and having a root portion that is inaccessible from the outside.

Figure 3 is a schematic view for explaining the definition of the thickness of the welded metal of the present invention.

Figure 4 is a view for explaining a method of manufacturing the welded joint of the present invention A schematic view of an example, and is a cross-sectional view showing an example of a welded joint in which the inner welded side portion is a sealed structure.

Fig. 5 is a schematic view for explaining an example of a method of manufacturing a welded joint of the present invention, and is a partially enlarged cross-sectional view showing a welded portion of the welded joint shown in Fig. 4.

Fig. 6 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the first embodiment is performed.

Fig. 7 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the first embodiment is performed.

Fig. 8 is a schematic view for explaining a welded joint of the present invention, and is a partially enlarged view showing a welded portion of the joint of the fifth embodiment.

Fig. 9 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the joint of the fifth embodiment is performed.

Fig. 10 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the lap joint of the fifth embodiment is performed.

Fig. 11 is a schematic view for explaining an embodiment of a method for producing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when the fatigue test of the T-joint of the fifth embodiment is performed.

Fig. 12 is a schematic view for explaining an embodiment of a method of manufacturing a welded joint of the present invention, and shows a T which is welded from both sides in the sixth embodiment. A cross-sectional view of the load direction of the joint during fatigue testing.

Figure 13 is a schematic view for explaining an embodiment of a method of manufacturing a welded joint of the present invention, and is a cross-sectional view showing a direction of load load when a fatigue test of a cross-shaped joint welded from both sides of Example 6 is performed. .

A~D‧‧‧stress concentration department

Claims (15)

A method for producing a welded joint, which is a method for producing a welded joint in which a joint portion of a steel material is welded by using a plurality of welds, characterized in that the multi-pass welding system includes a first welding step, which uses a welded metal of the first pass a welding material having a transformation starting temperature in a range of 175 ° C to 400 ° C for performing welding; and a second welding step of subsequently forming a portion of the welding metal formed in the first welding step to be an unmelted portion The welded metal is deposited and welded in one or two or more passes, and the unmelted portions are all re-transformed into austenite by the last welding heat. A method for producing a welded joint, which is a method for producing a welded joint in which a joint portion of a steel material is welded by using a plurality of welds, characterized in that the multi-pass welding system includes a first welding step, which uses a welded metal of the first pass a welding material having a transformation starting temperature in a range of 175 ° C to 400 ° C for performing welding; and a second welding step of subsequently forming a portion of the welding metal formed in the first welding step to be an unmelted portion In the manner, the welded metal is deposited and welded in one or two or more passes. Subsequently, a step of heat-treating the entire unmelted portion to form a Worstian body is provided. For example, the manufacturing method of the fusion joint of claim 1 or 2 is only There is a joint portion of the aforementioned welded joint formed by welding from one side. The method of manufacturing a fusion splice according to claim 1 or 2, wherein the fusion splice is of a structure capable of being welded only from one side of the fusion splice from the structure of the fusion splice or the structure of the welded structure. The method of manufacturing a fusion splice according to claim 1 or 2, wherein the fusion splice is a T-joint, a corner joint or a lap joint. The method of manufacturing a fusion splice according to claim 1, wherein the fusion splice is a T-joint, and the joint portion of the T-joint is an unwelded portion and a welded portion that sandwiches both sides of the unwelded portion. And the manufacturing method is to perform the multi-pass welding by partially melting and welding the welding portion from one side; and in the method, the length of the unwelded portion is the welding of the respective channels of the multi-pass welding. More than three times the maximum thickness of the weld bead. The method of manufacturing a fusion splice according to claim 1, wherein the fusion splice is a cross-shaped joint, and the joint portion of the cross-shaped joint is an unwelded portion and a welded portion sandwiching both sides of the unwelded portion. And the manufacturing method is to perform multi-pass welding by partially melting and welding the aforementioned welded portion from one side; and in the method, the length of the unfused portion existing between the respective welded portions and forming the ten The minimum thickness of the steel plate of the glyph joint is more than three times the maximum value of the thickness of the welded bead of each of the multi-pass welds. The method of manufacturing a fusion splice according to claim 2, wherein the fusion splice is a T-shaped joint or a cross-shaped joint, and the joint portion of the welded joint is an unwelded portion and sandwiches both sides of the unwelded portion. The welding portion is configured, and the manufacturing method is performed by partially melting and welding the welded portion from one side to perform multi-pass welding; and in the method, after the multi-pass welding of all the welded portions is completed, the heat treatment is performed. . The method of manufacturing a fusion splice according to claim 2, wherein the heat treatment step is any one of induction heating or electric heating. The method for producing a fusion splice according to any one of claims 1, 2, 6, 7, or 8, wherein the component of the weld metal used in the first welding step contains C: 0.01% by mass%. 0.15%, Si: 0.2 to 0.8%, Mn: 0.4 to 2.0%, P: 0.03% or less, S: 0.02% or less, Ni: 7.0 to 11.5%, and Cu: 0.4% or less, Ti: 0.1% or less, Nb: 0.1% or less, V: 0.5% or less, Cr: 3.0% or less, and Mo: 2.0% or less. The method for producing a fusion splice according to any one of claims 1, 2, 6, 7, or 8, wherein the component of the weld metal used in the first welding step contains C: 0.005 by mass%. ~0.10%, Si: 0.1 to 0.7%, Mn: 0.1 to 2.0%, P: 0.03% or less, S: 0.02% or less, Ni: 4.0 to 8.0%, Cr: 8.0 to 15.0%, and Mo: 2.0% In the following, one or two or more of Cu: 0.4% or less, Ti: 0.1% or less, Nb: 0.1% or less, and V: 0.5% or less. The method of manufacturing a fusion splice according to any one of claims 1, 2, 6, 7, or 8, wherein after the second welding step, the side of the welded bead on the side to be welded is utilized Grinding is performed to perform post treatment. The method of manufacturing a fusion splice according to any one of claims 1, 2, 6, 7, or 8, wherein after the second welding step, the side of the welded bead on the side to be welded is utilized Peening (peening) Post-treatment. The method of manufacturing a fusion splice according to any one of claims 1, 2, 6, 7, or 8, wherein after the second welding step, the side of the welded bead on the side to be welded is utilized A TIG arc (Tungsten Inert Gas arc) is used for reheating. A fusion splice manufactured by the method of manufacturing a splice joint according to any one of claims 1, 2, 6, 7, and 8.