JP3586380B2 - Multi-layer welding method - Google Patents

Description

【００５３】
【表２】

【００５４】
【表３】

【００５５】
【表４】

【００５６】
【発明の効果】
以上のように、本発明によれば、溶接金属表面全体のの残留応力を低減させることが可能となり、溶接構造物の信頼性確保、向上がより確実となる。したがって、本発明は工業的価値の極めて高い発明であるといえる。
【図の簡単な説明】
【図１】図１は、溶接継手を作製したときの開先形状を示す断面図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-layer welding method, and more particularly to improving the reliability of a welded structure, particularly reducing residual stress in a weld metal portion and contributing to improvements in stress corrosion cracking, fatigue characteristics, brittle fracture characteristics, and the like. .
[0002]
[Prior art]
Conventionally, the most effective and frequently used method for reducing the residual stress in a weld is to perform stress relief annealing (SR) after welding is completed. This has the meaning of not only reducing the welding residual stress but also improving the metallurgical properties. However, SR has a problem of increasing the machining cost of a welded structure. If there is a method of reducing welding residual stress without performing SR, there is a great industrial advantage.
[0003]
Therefore, several methods for reducing residual stress have been proposed. Typical examples are a method that utilizes the transformation expansion that occurs when the weld metal transforms from austenite to martensite, a method that mechanically reduces residual stress after welding is completed (shot peening method, etc.), and problems with joint characteristics. A method of intentionally forming a new weld bead such that the residual stress of compression is distributed in a portion where the welding is performed.
[0004]
The latter two include the problem that a new work load is generated in the work load for producing the welded structure.
On the other hand, the method of lowering the temperature at which austenite is transformed into martensite (hereinafter referred to as the martensite transformation start temperature, ie, “Ms temperature”) and utilizing the transformation expansion is a method in which the material itself becomes a compressive residual stress Therefore, if the residual stress can be reduced by this, there is no problem that a new work load is generated. The reason why the transformation temperature must occur at a low temperature is to prevent the residual stress from increasing again due to the heat shrinkage after the transformation.
[0005]
However, this method has not yet been able to achieve a sufficient effect from the viewpoint of reliably reducing the residual stress. That is, when performing multi-layer welding, the residual stress of each weld bead of the final layer is not necessarily all reduced, and partially high residual stress is still generated even by using the low-temperature transformation expansion material. .
As described above, when the residual stress of the weld metal portion is not necessarily reduced, it means that there is a risk that a problem such as stress corrosion cracking may occur from that portion, which is referred to as the reliability of the entire welded structure. From a point of view, there is no guarantee that it is necessarily improving. Therefore, the conventional technique of reducing the residual stress by using the transformation expansion of the weld metal has not yet improved the reliability of the welded structure.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-layer welding method capable of solving the above-mentioned problems of the prior art and reducing the residual stress on the entire surface of the weld metal.
[0007]
[Means for Solving the Problems]
The present inventors have focused on the fact that, in the prior art, the transformation expansion at a low temperature is not sufficiently utilized for reducing residual stress, and the transformation expansion of a weld metal at a low temperature is surely effective. The present invention has been completed as a result of intensive research with an awareness of the problem of how to achieve this, and the gist is as follows.
[0008]
(1) A multi-layer welding method comprising forming a weld metal having an austenite-to-martensite transformation start temperature of 150 ° C. or more and 300 ° C. or less, and performing TIG remeltran welding on the surface of the final layer.
(2) A welding wire, wherein C, Ni, Cr and Mo are each represented by weight% and the range of the parameter Pa defined by the following equation is 0.95 or more and 1.30 or less. The multi-layer welding method according to the above (1), wherein
[0009]
Pa = C + Ni / 12 + Cr / 24 + Mo / 19
(3) The welding wire is in weight%
C: 0.01 to 0.2%,
Si: 0.1-0.5%,
Mn: 0.01-1.5%,
P: 0.03% or less,
S: 0.02% or less,
Ni: contains 8 to 12%,
Ti: 0.01 to 0.4%,
Nb: 0.01 to 0.4%,
V: The multi-layer welding method according to (2), further comprising one or more of 0.3 to 1.0%, and the balance being iron and unavoidable impurities.
[0010]
(4) The weight of the welding wire is
Cu: 0.05 to 0.4%,
Cr: 0.1 to 3.0%,
Mo: 0.1 to 3.0%,
The multi-layer welding method according to the above (3), further comprising one or more of Co: 0.1 to 2.0%.
[0011]
(5) The welding wire is in weight%
C: 0.001 to 0.05%,
Si: 0.1-0.7%,
Mn: 0.4-2.5%,
P: 0.03% or less,
S: 0.02% or less,
Ni: 4 to 8%,
Cr: 10 to 15%,
N: 0.001 to 0.05%
C + N: 0.001 to 0.06%, the balance being iron and unavoidable impurities, the multi-layer welding method according to the above (2), wherein
[0012]
(6) Welding wire in weight%
Mo: 0.1 to 2.0%,
Cu: 0.05 to 0.4%,
Ti: 0.005 to 0.3%,
Nb: 0.005 to 0.3%,
V: The multi-layer welding method according to the above (6), further comprising one or more of 0.05 to 0.5%.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the reason why even when transformation expansion occurs at a sufficiently low temperature in a multi-layer welded joint, the residual stress of each weld bead may show a considerably high stress value will be described.
[0014]
When performing multi-layer welding, it is assumed that the residual stress of a certain weld bead is compression. Thereafter, when a new weld bead is placed adjacent to the weld bead, the bead transforms and expands, acting to pull the previous weld bead. This means that, even if the residual stress of one weld bead is reduced, the subsequent expansion of the subsequent weld bead will cause a tensile residual stress in the previous weld bead by continuing welding. However, the fact that the residual stress is eventually reduced means that only the final bead existing in the final layer and the other beads existing in the surface layer have a large residual tensile stress. However, if a material that does not cause low-temperature transformation expansion is used for the final bead, the residual stress of the final bead cannot be reduced as a matter of course.
[0015]
As described above, when a plurality of weld beads are placed on the surface, it is difficult to completely reduce the residual welding stress on the surface of the weld metal because each bead interacts with each other. . Therefore, it can be seen that the technique of reducing the residual stress of the weld metal by improving the welding material is not a technique that has been sufficiently completed.
[0016]
As can be seen from the above considerations, if the final layer can be finished with one bead, it can be seen that at least the surface of the weld metal portion can reduce the residual stress. However, finishing the final layer with one bead often results in too much welding heat input unless the groove can be made sufficiently narrow. Even if the residual stress is reduced, the joint characteristics are improved. From the viewpoint of ensuring the reliability of the welded structure, a desired result cannot always be obtained.
[0017]
The present inventors have conducted an in-depth analysis of such problems of the conventional technology and confirmed the effects of TIG remeltran welding. The TIG remeltran welding solves the conventional problem that the residual stress is not necessarily reduced even when the low-temperature transformation expansion occurs depending on the welding bead on the surface when performing multi-layer welding. That is, once the surface is redissolved with TIG, redistribution of the residual stress is generated, the weld metal surface is uniformly melted, and the same effect as when a new weld bead is formed is generated. Moreover, since the surface is once melted, then enters the cooling process, and there is no subsequent welding, the problem that occurs in the prior art, that is, even if the residual stress of a certain bead is reduced, it is again high in the subsequent weld bead. There is no problem that tensile residual stress occurs. Further, from a local point of view, there is an advantage that the stress concentration portion on the surface of the weld bead is reduced. As described above, the merit of performing TIG remeltran welding has a great economic merit from the viewpoint of improving joint performance.
[0018]
Next, the reason for limiting the component range of the welding wire will be described.
First, the reason for limiting the Ms temperature will be described.
The welding wire must be capable of forming a weld metal having a low Ms temperature such that residual welding stress can be expected when the bead of the final layer is one bead. For that purpose, the Ms temperature needs to be 150 ° C. or more and 300 ° C. or less. The reason why the upper limit of the Ms temperature is set to 300 ° C. is that if the Ms temperature is higher than this, the Ms is transformed into martensite, and the transformation expansion causes the stress at the temperature at that time, ie, the Ms temperature, to reduce the compressive residual stress This is because, even if the tensile stress is reduced, the state of high tensile stress is again caused by thermal shrinkage in the process of cooling to room temperature. Since the amount of heat shrinkage after transformation is proportional to the difference between room temperature and the Ms temperature, if Ms becomes higher than a certain level, the amount of heat shrinkage increases and it becomes impossible to reduce the stress state at room temperature, that is, the residual stress. . The upper limit of the Ms temperature of 300 ° C. was set because the residual stress cannot be reduced by using a welding material at a higher Ms temperature.
[0019]
In order to reduce the thermal shrinkage after the martensitic transformation, it is considered that the lower the Ms temperature is, the more advantageous it is at room temperature or higher. However, in an actual weld metal, if the Ms temperature is too low, even if the value is equal to or higher than room temperature, the entire weld metal is not necessarily transformed. An increase in the ratio of retained austenite means that the amount of transformation expansion decreases accordingly. Since the present invention utilizes the transformation expansion of the weld metal to reduce the residual stress, the effectiveness of the present invention cannot be exhibited unless the martensitic transformation is securely performed. The lower limit of the Ms temperature, 150 ° C., was set to suppress generation of retained austenite and to surely generate martensitic transformation.
[0020]
As described above, the components of the welding wire should be determined as a component system that keeps the Ms temperature within a predetermined range. In order to use this transformation expansion effectively and effectively, the welding metal strength at the time of transformation is required. However, there is also a problem that some degree must be secured. The strength of the weld metal generally tends to decrease with increasing temperature. Thus, for example, if, during transformation expansion, the weld metal strength becomes extremely low, the transformation expansion itself will only result in plastic strain, mostly unrelated to residual stress, and will be introduced by subsequent heat shrinkage and strength recovery. This is because only tensile stress is applied. Therefore, it is necessary to limit the welding wire component not only in securing a low Ms temperature but also in securing strength.
[0021]
For a welding wire capable of forming a weld metal having such characteristics, it is necessary to pay close attention to the selection of its components.
Next, the reason for introducing the parameter P shown in the following formula and limiting the range of the value will be described.
Pa = C + Ni / 12 + Cr / 24 + Mo / 19 (i)
The parameter Pa is calculated from the component values of C, Ni, Cr and Mo. These components have the function of improving strength and lowering the Ms temperature by being added to the weld metal. In particular, C, Ni, Cr and Mo are the elements to be used most effectively in terms of elements that lower the Ms temperature. On the other hand, the functions of lowering the Ms temperature and lowering the residual stress of C, Ni, Cr and Mo are not always the same, so that the coefficients corresponding to the respective functions are determined and an index representing the effect is created for the four elements as a whole. That is, it is judged that the industrial value is high, and Pa as shown by the equation (i) is created. However, the value of Pa also has an appropriate range. For example, if Pa is too small, it is difficult to reduce the Ms temperature. Conversely, a large Pa means that the Ms temperature is further reduced and the residual stress is also reduced, but austenite may remain in the weld metal, which is preferable from the viewpoint of securing joint characteristics. I'm sorry. From the above, the range of Pa was set to 0.95 or more and 1.30 or less.
[0022]
Such a component system is not necessarily only one type. This is because there are a plurality of components such as Ni and Cr that can lower the Ms temperature. The welding steel according to the present invention is composed of a component system mainly using Ni described in the above (3) and (4) and a component system mainly using Cr described in the above (5) and (6). The former is hereinafter referred to as a Ni-based welding wire, and the latter as a Cr-based welding wire. Hereinafter, the reasons for limiting each element will be described in detail.
[0023]
First, the reason for limiting the component range in the Ni-based welding wire will be described.
C acts to lower the Ms temperature by adding it to iron. However, on the other hand, excessive addition causes problems of toughness deterioration of the weld metal and cracks in the weld metal, so the upper limit was made 0.2%. However, when C is not added, martensite is hardly obtained, and residual stress must be reduced only by other expensive elements, which is not economical. The reason for limiting the case where C is added at 0.01% or more is that C, which is an inexpensive element, is used, and is set as a minimum value at which an economic merit is obtained. Note that the upper limit of C is preferably set to 0.15% from the viewpoint of weld metal cracking.
[0024]
Si is known as a deoxidizing element. Si has the effect of lowering the oxygen level of the weld metal. In particular, during welding work, there is a risk of air being mixed during welding, so it is extremely important to control the amount of Si to an appropriate value. First, regarding the lower limit of Si, when the amount of Si added to the welding wire is less than 0.1%, the deoxidizing effect is weakened, the oxygen level in the weld metal becomes too high, and the mechanical properties, particularly the toughness, are reduced. There is a risk of causing deterioration. Therefore, the lower limit of the welding wire is set to 0.1%. On the other hand, since the excessive addition of Si also causes toughness degradation, the upper limit is set to 0.5%.
[0025]
Mn is known as an element for increasing the strength. Therefore, it is an element that should be used effectively from the viewpoint of ensuring the yield strength during transformation expansion, which is the residual stress reduction mechanism in the present invention. The lower limit of Mn, 0.01%, was set as the minimum value at which the effect of securing strength was obtained. On the other hand, excessive addition causes toughness deterioration of the base metal and the weld metal, so the upper limit was made 1.5%.
[0026]
P and S are impurities in the present invention. However, if these elements are present in a large amount in the weld metal, the toughness deteriorates. Therefore, the upper limits are set to 0.03% and 0.02%, respectively.
Ni is a single element of austenite, that is, a metal having a face-centered structure, and is an element that makes the state of austenite more stable by adding it to a welding wire. Iron itself has an austenitic structure in a high temperature range, and has a ferrite or body core structure in a low temperature range. Addition of Ni makes the face-centered structure of iron in a high-temperature range more stable, so that it has a face-centered structure even in a lower temperature range as compared with the case without addition. This means that the temperature at which the body transforms into a body-core structure becomes lower. The lower limit of Ni, 8%, was determined to mean the minimum amount of addition in which the residual stress reduction effect was exhibited. The upper limit of 12% of Ni is because, from the viewpoint of reducing the residual stress, the effect does not change so much even if it is further added, and if it is added more than that, there is an economic disadvantage that Ni is expensive.
[0027]
Cu is an element effective for improving welding workability because Cu has an effect of improving electrical conductivity by plating on a welding wire. Further, since Cu is also a hardenable element, an effect of promoting martensitic transformation can be expected. The lower limit of 0.05% of Cu was set as a minimum value necessary for improving workability and promoting martensitic transformation. However, excessive addition is not industrially preferable because it not only has no effect of improving workability but also increases wire manufacturing cost. The upper limit of Cu, 0.4%, was set for such a reason.
[0028]
Nb combines with C in the weld metal to form carbide. Nb carbide has the function of increasing the strength of the weld metal in a small amount, and therefore has a great economic merit of effective use. Further, there is a great merit from the viewpoint of increasing the yield strength at the Ms temperature, which is the residual stress reduction technique in the present invention. However, on the other hand, excessive carbide formation causes a deterioration in toughness, so that an upper limit is naturally set. The lower limit of Nb was set to 0.01% as a minimum value at which carbides were formed and an effect of increasing strength was expected. The upper limit is set to 0.4% as a value that does not impair the reliability of the weld due to deterioration in toughness.
[0029]
V is an element that functions similarly to Nb. However, unlike Nb, in order to expect the same precipitation effect, it is necessary to increase the amount of Nb added. The lower limit of 0.3% of the addition of V is set as the minimum value at which precipitation hardening can be expected by adding V. The upper limit of V is set to 1.0% because if more than this, precipitation hardening becomes too remarkable and toughness deteriorates.
[0030]
Ti, like Nb and V, also forms carbides and causes precipitation hardening. However, just as the precipitation hardening of V differs from that of Nb, the precipitation hardening of Ti is also different from Nb and V. Therefore, the range of the addition amount of Ti is set to a range different from Nb and V. The lower limit of 0.01% of the addition amount of Ti is determined as a minimum amount at which the effect can be expected, and the upper limit of 0.4% is determined in consideration of deterioration of toughness.
[0031]
Cr is a precipitation hardening element like Nb, V, and Ti. Further, Cr is an element to be effectively utilized because it also has the effect of reducing the Ms temperature. However, since the welding wire in the present invention achieves the reduction of the Ms temperature mainly by adding Ni, the amount of Cr added should be smaller than that of Ni. Excessive addition of Cr does not necessarily improve the effect of reducing residual stress, and is not industrially preferable because Cr is expensive. The lower limit of 0.1% of the amount of Cr added was set as the minimum value at which the effect of adding Cr was obtained and the effect of reducing residual stress was obtained. The upper limit of 3.0% of the added amount of Cr is more than that of the Ni-based welding wire because the Ms temperature has already been reduced by the addition of Ni and the strength is secured by other precipitated elements. The value was also set because the effect of reducing the residual stress did not change much and the deterioration in toughness became remarkable.
[0032]
Mo is also an element having the same effect as Cr. However, Mo is an element in which precipitation hardening can be expected more than Cr. Therefore, the addition range was set narrower than Cr. The lower limit of 0.1% was set as the minimum value at which the effect of Mo addition can be expected. The upper limit of 3.0% was set because, if added more than this, the composition would be excessively hardened and the toughness would be significantly deteriorated.
[0033]
Co, unlike Ti or the like, is not an element that causes strong precipitation hardening. However, Co is an element that should be effectively used because it is a more preferable element than Ni from the viewpoint of increasing the strength by adding it and securing the toughness while expecting the strength increase. However, since Ni is added to the welding wire in order to ensure a low Ms temperature at which a residual stress reduction effect can be expected, the lower limit of 0.1% of the Co addition amount is the minimum at which the effect of Co addition can be expected. Was set as the limit value. On the other hand, excessive addition results in excessive increase in strength and deterioration of toughness, so the upper limit was made 2.0%.
[0034]
Next, the reason for limiting the component range of the Cr-based welding wire will be described. C acts to lower the Ms temperature by adding it to iron. However, on the other hand, excessive addition causes problems of weld cracking and deterioration of toughness, so the upper limit was made 0.05%. However, when C is not added, martensite is hardly obtained, and residual stress must be reduced only by other expensive elements, which is not economical. The reason for limiting the case where C is added at 0.005% or more is that C, which is an inexpensive element, is used, and is set as a minimum value at which the economic merit is obtained.
[0035]
Si is known as a deoxidizing element. Si has the effect of lowering the oxygen level of the weld metal or steel. Particularly, in the case of a weld metal, it is extremely important to control the amount of Si to an appropriate value because there is a risk of air being mixed during welding. First, regarding the lower limit of Si, when the amount of Si added to the welding wire is less than 0.1%, the deoxidizing effect is weakened, the oxygen level in the weld metal becomes too high, and the mechanical properties, particularly the toughness, are reduced. There is a risk of causing deterioration. Therefore, the lower limit of the welding wire is set to 0.1%. On the other hand, excessive addition of Si also causes toughness degradation, so the upper limit was set to 0.7%.
[0036]
Mn is known as an element for increasing the strength. Therefore, it is an element that should be used effectively from the viewpoint of ensuring the yield strength during transformation expansion, which is the residual stress reduction mechanism in the present invention. The lower limit of Mn, 0.4%, was set as the minimum value at which the effect of securing strength was obtained. On the other hand, excessive addition causes toughness deterioration of the base metal and the weld metal, so the upper limit was made 2.5%.
[0037]
P and S are impurities in the present invention. However, if these elements are present in a large amount in the base metal and the weld metal, the toughness deteriorates. Therefore, the upper limits are set to 0.03% and 0.02%, respectively.
Ni is austenitic, that is, a metal having a face-centered structure by itself. Iron itself has an austenitic structure in a high temperature range, and has a ferrite or body core structure in a low temperature range. Addition of Ni makes the face-centered structure of iron in a high-temperature range more stable, so that it has a face-centered structure even in a lower temperature range as compared with the case without addition. This means that the temperature at which the body transforms into a body-core structure becomes lower. Ni has the effect of improving the toughness of the weld metal by adding it. The lower limit of 4% of the amount of Ni added to the Cr-based welding wire was determined from the viewpoint of the minimum amount of addition of the residual stress reducing effect and the securing of toughness. The upper limit of 8% of the addition amount of Ni is that the Cr-based welding wire has the Ms temperature reduced to some extent by the addition of Cr described below, and from the viewpoint of reducing the residual stress, the effect does not change much even if added more. This value is set because there is no economic disadvantage that Ni is expensive if added further.
[0038]
Cr is a ferrite former unlike Ni. However, when Cr is added to iron, it forms ferrite in a high temperature range, forms austenite in a medium temperature range, and forms ferrite again at a lower temperature. In the case of a welded part, ferrite on the lower temperature side is generally not obtained in the heat history due to the heat input, and martensite is obtained. This is because the advantage of adding Cr is due to an increase in hardenability. That is, the martensitic transformation due to the addition of Cr has two points: no ferrite transformation due to an increase in hardenability, and a decrease in the Ms temperature itself. The lower limit of 10% was set as a Cr addition range that effectively utilizes transformation expansion for reducing residual stress while satisfying both of these effects. The upper limit of 15% is set because the effect is not increased even if an amount exceeding the upper limit is added, and the disadvantage is increased economically.
[0039]
Cu is an element effective for improving welding workability because Cu has an effect of improving electrical conductivity by plating on a welding wire. Further, since Cu is also a hardenable element, an effect of promoting martensitic transformation can be expected. The lower limit of 0.05% of Cu was set as a minimum value necessary for improving workability and promoting martensitic transformation. However, excessive addition is not industrially preferable because it not only has no effect of improving workability but also increases wire manufacturing cost. The upper limit of Cu, 0.4%, was set for such a reason.
[0040]
Nb combines with C in the weld metal to form carbide. Nb carbide has the function of increasing the strength of the weld metal in a small amount, and therefore has a great economic merit of effective use. Further, there is a great merit from the viewpoint of increasing the yield strength at the Ms temperature, which is the residual stress reduction technique in the present invention. However, on the other hand, excessive carbide formation causes a deterioration in toughness, so that an upper limit is naturally set. The lower limit of Nb is set to 0.005% as a minimum value at which carbides are formed and the effect of increasing strength can be expected. The upper limit is set to 0.3% as a value that does not impair the reliability of the weld due to deterioration in toughness.
[0041]
V is an element that functions similarly to Nb. However, unlike Nb, in order to expect the same precipitation effect, it is necessary to increase the amount of Nb added. The lower limit of 0.05% of the addition of V is set as the minimum value at which precipitation hardening can be expected by adding V. The upper limit of V is set to 0.5% because if more than this, precipitation hardening becomes too remarkable and toughness deteriorates.
[0042]
Ti, like Nb and V, also forms carbides and causes precipitation hardening. However, just as the precipitation hardening of V differs from that of Nb, the precipitation hardening of Ti is also different from Nb and V. Therefore, the range of the addition amount of Ti is set to a range different from Nb and V. The lower limit of 0.005% of the added amount of Ti is determined as the minimum amount at which the effect can be expected, and the upper limit of 0.3% is determined in consideration of deterioration in toughness.
[0043]
Mo is also an element in which precipitation hardening can be expected like Nb, V and Ti. However, Mo needs to be added to Nb, V, and Ti or more in order to obtain the same effect as Nb, V, and Ti. The lower limit of 0.1% of the Mo content was set as the lowest value at which an increase in yield strength due to precipitation hardening can be expected. Further, the upper limit of 2.0% was determined in consideration of deterioration in toughness, similarly to Nb, V, and Ti.
[0044]
N is an element known as an austenite former. Since addition of N also makes it easier to obtain martensite, a minimum addition is necessary. The lower limit of N, 0.001%, as in C, was set as the minimum value for obtaining a low Ms temperature. However, an excessive addition forms a nitride and causes a problem of deterioration in toughness and ductility. Therefore, the upper limit is set to 0.05%.
[0045]
C and N have similar functions, such as forming carbides and nitrides and being austenite formers, respectively, and the sum of them, that is, the amount of C + N, also needs to have upper and lower limits. The lower limit of C + N, 0.001%, is a minimum value for easily obtaining martensite and lowering the Ms temperature, and the upper limit of 0.06% is toughness deterioration and ductility deterioration due to carbides and nitrides. It was set as the limit value that does not cause the problem.
[0046]
【Example】
First, an embodiment using a Ni-based welding wire will be described.
Table 1 shows the TIG welding wire components, Ms temperature, and Pa used for producing the welded joint. The Ms temperature shown in Table 1 is a value measured by collecting a test piece from a weld metal portion of a welded joint prepared for measuring residual stress. Two welding joints were produced using the wires shown in Table 1 under welding conditions of 250A-12V-12 cpm, and using the groove shape shown in FIG. 1 under the same conditions. One of the two welded joints was further subjected to TIG remeltran welding.
[0047]
The residual stress of the weld metal part of the weld joint thus manufactured was measured. The residual stress measurement method uses a stress relaxation method in which a strain gauge is attached to the surface of a weld metal, and then the part where the strain gauge is attached is mechanically cut to release the residual stress, and the released strain is measured using a strain gauge. Was.
Since the welded joint without TIG remeltran welding may have different residual stress for each weld bead, a strain gauge was attached to the center of each bead. Since the surface of the joint subjected to TIG remeltran welding was once melted, the strain gauge was attached so as to be at the same position as the joint not subjected to TIG remeltran welding.
[0048]
Table 2 shows the residual stress measurement results. Measurement positions 1, 2, and 3 in Table 2 show the first bead, the second bead, and the third bead of the final layer, respectively, and the third bead is the final bead of the final layer.
As can be seen from Table 2, in the case of Ni-WA and Ni-WB in which the weld metal Ms temperature (and the wire component and Pa) does not fall within the range of the present invention, the residual stress is welded even when performing TIG remeltran welding. Not reduced over the entire metal surface. In the case of Ni-WA, when the TIG remeltran welding is not performed, the reason why the first bead becomes the compressive residual stress is that the initial residual stress is relaxed by the welding heat of the second bead and the third bead. The heat shrinkage of the bead acts in the direction in which a compressive stress is generated in the first bead, and the residual stress is not necessarily compressed due to the properties of the welding material.
[0049]
For Ni-WC and Ni-WD in which the temperature of the weld metal Ms (and the welding wire and Pa) falls within the range of the present invention, when TIG remeltran welding is not performed, the third bead, that is, the final bead is used. It is clear that the residual stress is reduced. This indicates that the residual stress is reduced by the components of the welding wire. However, as can be seen from comparison with the present invention example in which TIG remeltran welding was performed, from the viewpoint of reducing the residual stress on the surface of the weld metal as a whole, the first and second comparative examples in which TIG remeltran welding was not performed were performed. High tensile residual stress is generated in the two beads, and by comparing this, the effectiveness of TIG remeltran welding can be understood.
[0050]
Next, an embodiment using a Cr-based welding wire will be described.
Table 3 shows the TIG welding wire components, Ms temperature, and Pa used for producing the welded joint. The Ms temperature shown in Table 3 is a value measured by collecting a test piece from a weld metal portion of a welded joint prepared for measuring residual stress. Table 4 shows the results of producing a welded joint using the wires of Table 3 under the same conditions as those described for the Ni-based welding wire and measuring the residual stress by the same method.
[0051]
As can be seen from Table 4, in the joint obtained by performing TIG remeltran welding using each of the Cr-WA, Cr-WB, and Cr-WD wires within the scope of the present invention, the residual stress is reduced uniformly over the entire weld metal surface. You can see that it is. When TIG remeltran welding is not performed using these Cr-WA, Cr-WB, and Cr-WD which are within the scope of the present invention, the third bead (final bead) has a reduced residual stress but has a reduced first stress. The residual stress of the bead and the second bead is not reduced. Regarding Cr-WC and Cr-WD wires that are outside the scope of the present invention, TIG remeltran welding may be performed, but whether or not TIG remeltran welding is performed, the residual stress on the entire weld metal surface is not uniformly reduced.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
[Table 3]

[0055]
[Table 4]

[0056]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the residual stress on the entire surface of the weld metal, and the reliability and improvement of the reliability of the welded structure are further ensured. Therefore, it can be said that the present invention is an invention having extremely high industrial value.
[Brief explanation of the figure]
FIG. 1 is a cross-sectional view showing a groove shape when a welded joint is manufactured.

Claims (6)

A multilayer welding method comprising forming a weld metal having a transformation start temperature from austenite to martensite of 150 ° C. or more and 300 ° C. or less, and performing TIG remeltran welding on the surface of the final layer. Using C, Ni, Cr and Mo as the weight percent of each component, and using a welding wire characterized in that the range of the parameter Pa defined by the following equation is 0.95 or more and 1.30 or less. The method according to claim 1, wherein:
Pa = C + Ni / 12 + Cr / 24 + Mo / 19 Welding wire in weight%
C: 0.01 to 0.2%,
Si: 0.1-0.5%,
Mn: 0.01-1.5%,
P: 0.03% or less,
S: 0.02% or less,
Ni: contains 8 to 12%,
Ti: 0.01 to 0.4%,
Nb: 0.01 to 0.4%,
The multi-layer welding method according to claim 2, further comprising one or more of V: 0.3 to 1.0%, and the balance being iron and unavoidable impurities. Welding wire in weight%
Cu: 0.05 to 0.4%,
Cr: 0.1 to 3.0%,
Mo: 0.1 to 3.0%,
The multi-layer welding method according to claim 3, further comprising one or more of Co: 0.1 to 2.0%. Welding wire in weight%
C: 0.001 to 0.05%,
Si: 0.1-0.7%,
Mn: 0.4-2.5%,
P: 0.03% or less,
S: 0.02% or less,
Ni: 4 to 8%,
Cr: 10 to 15%,
N: 0.001 to 0.05%
The multi-layer welding method according to claim 2, wherein C + N: 0.001 to 0.06%, and the balance consists of iron and inevitable impurities. Welding wire in weight%
Mo: 0.1 to 2.0%,
Cu: 0.05 to 0.4%,
Ti: 0.005 to 0.3%,
Nb: 0.005 to 0.3%,
The multilayer welding method according to claim 6, further comprising one or more of V: 0.05 to 0.5%.

Images