JPH11138290A - Welding method and welding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method and a welding material capable of improving the fatigue strength of a welded joint even though a special after- treatment is not always executed after welding is executed. SOLUTION: Ferro-alloy containing, by weight, 0.025 % C, 0.33% Si, 0.70% Mn, 10.0% Ni, 10.0% Cr, 0.13 % Mo is used as the welding material. Only a weld zone of a main plate 1 is preheated, end parts ((1) and (2) in a figure) which face each other in the longitudinal direction 4 in a weld zone cross section 3 of a rib plate 2 are welded, and thereafter a residual part is welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method useful for manufacturing large structures such as ships and bridges.
The present invention relates to a welding method and a welding material capable of improving the fatigue strength of a welded joint when performing welding using a welding material.

[0002]

2. Description of the Related Art In ships, offshore structures, penstocks, bridges, and the like, the use of high-strength steel materials is required for the purpose of increasing the size and reducing the weight. As materials used for these structures, so-called low alloy steel materials containing less than 3.0% by weight of various alloying elements such as Cr, Ni, and Mo are used. These materials have a tensile strength level of 30 to 12%.
It is 0 kgf / mm ² .

[0003] In response to the demand for high strength, when a high-strength low-alloy steel material is used, the fatigue strength of the high-strength steel is reduced for the base material. It is said that the fatigue strength of welded joints does not improve even if the material strength increases (Summary of the National Meeting of J.W.S., No. 52, 1993,
P. 256-257).

For this reason, conventionally, the fatigue strength of a welded joint made of high-strength steel is the same as that of low-strength steel. Therefore, in a structure employing a joint joined by fillet welding or the like, even if high-strength steel is used. There was a problem that the design strength could not be increased. The reason why the fatigue strength is not improved in the welded joint of high-strength steel is that the tensile residual stress is large (Journal of the Japan Welding Society, Vol. 13, No. 3, PP. 438-).
443 (1995)).

The high notch sensitivity of a welded joint made of a high-strength steel material is also a factor that does not improve the fatigue strength. This is discussed in, for example, Japanese Patent Application Laid-Open No. 5-69128. As described, this can be prevented by smoothly grinding the weld toe with a grinding tool such as a grinder or a rotary cutter to increase the toe radius.

[0006] The tensile residual stress generated in the welded portion of the joint is caused by the fact that the weld metal after welding contracts when cooled. FIG. 18 is a diagram showing a contraction state of a weld metal in a cooling process after welding when welding is performed using a low-alloy steel material to be welded to the low-alloy steel material. The weld metal thermally contracts in the direction of the arrow in FIG. 18 after welding.

Here, when a conventional welding material made of a low alloy steel is used as the temperature decreases, the weld metal contracts due to heat and its elongation (length) decreases, but elongates (length) at around 500 ° C. Is present in some regions. This is 500
This is because martensitic transformation occurs at around 0 ° C., and the expansion of the weld metal accompanying this martensitic transformation occurs. When the martensitic transformation ends, only heat shrinkage occurs again, and the elongation decreases as the temperature decreases. When the weld metal is cooled from the freezing point to about 600 ° C., since the yield stress of the weld metal is low, the weld metal is cooled while undergoing plastic deformation. Therefore, tensile residual stress caused by shrinkage is relaxed by this plastic deformation. You. And about 60
When shrinking at 0 ° C. or lower, the yield stress of the weld metal is large, so that plastic deformation hardly occurs and tensile residual stress is introduced.

In FIG. 18, in the cooling process from about 500.degree. C. to about 400.degree. C., expansion occurs due to martensitic transformation, so that tensile residual stress is relaxed during this period. Will be introduced.

The above is the main reason why tensile residual stress is generated in the welded portion.
If the two workpieces have different sizes, the residual tensile stress is further promoted due to the difference in heat capacity of the workpieces.

When a T-shaped joint as shown in FIG. 19A is formed by fillet welding, as shown in FIG. 19B, the main plate 1 and the sub plate 2 are arranged along the longitudinal direction 4. Welding is performed in the direction of arrow A. During this welding operation, the temperatures of the main plate 1 and the sub-plate 2 increase due to the heat applied to the weld. When the main plate 1 and the sub plate 2 are different in size, the main plate 1 and the sub plate 2 have different degrees of heat diffusion. Since the sub plate 2 has a smaller volume than the main plate 1, the amount of temperature rise is larger. Therefore, the amount of thermal expansion generated during welding is larger in the sub-plate than in the main plate. Therefore, the weld (1)
During the construction, a difference in thermal expansion occurs between the main plate 1 and the sub plate 2 in the portion of the weld (2) to be welded. Since the welding of the welded portion (2) is performed in a state where the difference in thermal expansion is generated, a tensile residual stress is generated in the welded portion during the heat shrinkage process after the welding portion.

Further, as shown in FIGS.
In the case of a joint in which the sub-plate 2 is turned around the main plate 1 and fillet welding is performed, the conventional welding procedure is as shown in FIG. 20 (c), in which the long side in the welded section 3 of the sub-plate 2 (FIG. 20 (c)) Middle (1)) → Short side ((2) in FIG. 20 (c)) → ((3) in FIG. 20 (c))
In order. In addition, in the construction shown in FIG. 20 (c), since the welded section 3 of the sub-plate 2 is large, turning welding is performed in two parts. And also in this case, the secondary plate 2
Is smaller in volume than the main plate 1, so that the sub-plate 2 has a larger temperature rise than the main plate 1 during welding. Therefore, when welding the long sides, the sub-plate 2 has a larger amount of elongation in the longitudinal direction, and a tensile residual stress is generated in the welded portion in the cooling process after the end of welding.

When the above-described tensile residual stress caused by the difference in thermal expansion between the main plate and the sub-plate and the above-mentioned tensile residual stress caused by the thermal contraction of the weld metal are superimposed, the residual tensile stress is reduced to about the yield strength. May be rising.

As a method of reducing the tensile residual stress of such a welded joint, for example, as described in Japanese Patent Application Laid-Open No. Hei 4-21717, after turning a sub plate around a main plate and joining it by fillet welding, A method has been proposed in which a compressive stress is imparted by hitting a weld toe by shot peening, hammer peening, or the like to reduce residual tensile stress during welding of the weld toe.

Further, as a method for reducing the residual stress in the welded portion, there is a welding method described in Japanese Patent Application Laid-Open No. 54-130451. In this welding method, at least the final layer of the weld metal is welded with a welding material made of an austenitic iron alloy having a martensitic transformation start temperature of room temperature or lower, and then, using liquid nitrogen, for example, at -60 ° C or lower. It is a method of cooling to a temperature.

[0015]

However, in the method for improving the fatigue strength of a welded portion (welded joint) described in Japanese Patent Application Laid-Open No. Hei 4-21717, a special post-process is required after welding. And equipment and operations that are not normally used in the welding work are required. Therefore, there is a problem that the method is not always efficient and economical.

Also, in the welding method described in the above-mentioned Japanese Patent Application Laid-Open No. 54-130451, it is necessary to perform an operation of cooling to, for example, -60 ° C. or lower using liquid nitrogen after ordinary welding. Further, considering application to a large welded joint of an extremely thick plate, which is a main application object of the present invention,
Cooling the entire weld to -60C or the like using liquid nitrogen is a daunting task.

The present invention has been made in view of such a problem, and a welding method and a welding material capable of improving the fatigue strength of a welded joint without performing toe treatment or quenching after ordinary welding. The challenge is to provide

[0018]

In order to solve the above-mentioned problems, the present invention provides a welding method for welding a low alloy steel material for a structure using a welding material. In addition, the present invention is characterized in that martensite transformation is caused in a cooling process after welding of a weld metal produced by welding, so that the metal is expanded at room temperature more than at the start of the martensite transformation.

As described above, when the martensitic transformation occurs in the cooling process, the iron alloy temporarily expands from the start of the martensitic transformation until the temperature drops to some extent. In the present invention, the martensitic transformation is caused in the cooling process after welding to the weld metal generated by welding, and moreover, at room temperature, the state is more expanded than at the start of the martensitic transformation. Relaxes the tensile residual stress generated in the weld metal by
Compressive residual stress can be given instead of tensile residual stress. Therefore, the fatigue strength of the welded joint at room temperature, which is the normal use temperature of the welded joint, is improved.

Next, a second aspect of the present invention is the first aspect.
The invention is characterized in that a martensitic transformation start temperature of less than 250 ° C. and 170 ° C. or more is used as the welding material.

FIG. 1 shows the transformation characteristics of the welding material according to the present invention (solid line in FIG. 1) and the transformation characteristics of the conventional welding material (FIG. 1).
(Middle, broken line). In the present invention, the expansion temperature of the weld metal due to martensitic transformation can be increased by using an iron alloy having a starting temperature of martensitic transformation of less than 250 ° C and 170 ° C or more as a welding material, and The state where the expansion amount is large becomes around room temperature, and when the cooling process of the weld metal ends, the metal is expanded more than when the martensitic transformation starts. For this reason, compressive residual stress is introduced by the expansion, and tensile residual stress generated in the process of cooling the weld metal is reduced, thereby improving the fatigue strength of the welded joint after welding.

The martensitic transformation start temperature of the weld metal depends on the chemical composition of the material to be welded and the chemical composition of the welding material. The present invention is directed to the case where the material to be welded is a low alloy steel material. Therefore, by adjusting the chemical composition of the welding material such that the martensitic transformation start temperature of the welding material is less than 250 ° C and 170 ° C or more, the martensitic transformation starting temperature of the weld metal is less than 250 ° C and 170 ° C or more. It is possible.

Here, the reason why the temperature of the martensite transformation start point is set to less than 250 ° C. is that the higher the martensite transformation start temperature is, the smaller the expansion amount due to the transformation is, and the maximum point of transformation expansion is higher than room temperature. Temperature, so heat shrinkage occurs again in the subsequent cooling process to room temperature,
This is because the effect of the transformation expansion cannot be sufficiently obtained (see the broken line in FIG. 1).

Also, the martensitic transformation onset temperature is 17
The reason why the temperature was set to 0 ° C. or higher was that the martensitic transformation starting temperature was 1
If the temperature is lower than 70 ° C., even if martensitic transformation starts, the amount of transformation expansion until the end of the cooling process is small, and the effect of the transformation expansion cannot be sufficiently obtained.

Next, the invention described in claim 3 is the first invention.
Or a welding material used in the welding method according to claim 2, wherein C, Cr, Ni, Si, Mn, Mo and Nb.
Is a ferrous alloy whose content is adjusted so as to satisfy the following formula (1).

170 ≦ 719−795 × C (% by weight) −23.7 × Cr (% by weight) −26.5 × Ni (% by weight) −35.55 × Si (% by weight) −13.25 × Mn (% By weight) -23.7 × Mo (% by weight) -11.85 Nb (% by weight) <250 (1) Generally, the martensitic transformation start temperature (Ms) of a steel material
Is known to be affected by the chemical composition. Murata et al., Transactions of the Japan Welding Society, Vol. 9 (1991) No. 1, "Effects of Alloying Elements and Transformation Temperature on Stress Relaxation"
In the relationship between the Ms point and the contents of various alloying elements, Ms (° C.) = 719−26.5 × Nieq−23.7 × Creq Nieq = 30 × C (% by weight) + 0.5 × Mn (weight) %) Creq = Cr (% by weight) + Mo (% by weight) + 1.5 × Si (% by weight) + 0.5 × Nb (% by weight)

As described above, when the working temperature of the welded joint is room temperature, the expansion of the weld metal due to martensitic transformation is performed by using an iron alloy having a martensitic transformation start temperature of less than 250 ° C. and 170 ° C. or more as a welding material. The state where the amount of expansion can be increased and the amount of expansion is large is around room temperature, and at the end of the cooling process of the weld metal, the weld metal is expanded more than at the start of martensitic transformation. For this reason, the compressive residual stress is introduced by the expansion, and the tensile residual stress generated in the process of cooling the weld metal is reduced, thereby improving the fatigue strength of the welded joint after welding. Therefore, C, Cr, Ni, S
By adjusting the contents of i, Mn, Mo and Nb, a welding material capable of improving the fatigue strength of a welded joint can be obtained.

Next, the invention according to claim 4 provides the welding material according to claim 3 with 0.10% by weight or less of C, 8.0-13.0% by weight of Cr, From 5.0 to 1
It is characterized by containing 2.0% by weight.

Here, the content of C ensures the weldability,
The content is preferably as small as possible in order to reduce the hardness of martensite, and it is preferably 0.1% by weight or less, preferably 0.06% by weight or less in order not to cause weld cracking.

The martensitic transformation starting temperature can be changed by adjusting the contents of C, Cr, Ni, Si, Mn, Mo and Nb.
Of these elements, increasing Cr and Ni contents does not significantly affect the workability in the manufacturing process. Therefore, it is preferable to increase the Cr and Ni contents to adjust the martensitic transformation start temperature.

Here, the reason why the content of Cr is set to 8.0% by weight or more is that if the content is less than 8.0% by weight, the martensitic transformation starting temperature is set to less than 250 ° C .;
Also, it is necessary to contain a large amount of other components that deteriorate the workability during the production of the welding material. The reason why the content is set to 13.0% by weight or less is that if it exceeds 13.0% by weight, a ferrite structure appears in the structure of the weld metal, which is not preferable.

The Ni content is regulated to be 5.0 to 12.0% by weight. When the Ni content is less than 5.0% by weight, the martensitic transformation starting temperature is less than 250 ° C. It is necessary to contain a large amount of other components that deteriorate the processability of the steel. Also, Ni is an expensive element and it is not economically preferable to add a large amount of Ni.
The upper limit of the content was 12.0% by weight.

Conventionally, when producing thick steel plate welded joints used for ships, marine structures, penstocks, bridges, etc., the Ni content is less than 3.0% by weight and the Cr content is as a welding material. Was less than 1.0% by weight.

Next, according to the invention as set forth in claim 5, the welding material as set forth in claim 4 contains 0.2 to 1.
0% by weight, 0.4 to 2.5% by weight of Mn, and 4.0% of Mo.
% Of Nb and 1.0% by weight or less of Nb.

Here, the reason why the content of Si is set to 0.2 to 1.0% by weight is that 0.2% by weight is necessary because Si is added as a deoxidizing material, and 1.0% by weight is required. This is because, when the ratio exceeds, the workability in the welding material manufacturing process is reduced.

Similarly, the reason why the content of Mn is set to 0.4 to 2.5% by weight is that Mn is added as a deoxidizing agent, so that at least 0.4% by weight is required. %, The workability in the welding material manufacturing process is reduced.

Further, Mo can be added for the purpose of imparting corrosion resistance to the welded portion, but the content of Mo is 4.0.
If the amount exceeds Mo, the workability in the welding material manufacturing process is reduced. Therefore, the Mo content is set to 4.0 wt% or less.

Nb can be added because it has the effect of lowering the martensitic transformation onset temperature. However, if the Nb content exceeds 1.0% by weight, the workability in the welding material manufacturing process decreases. Therefore, the content of Nb is set to 1.0% by weight or less.

According to a sixth aspect of the present invention, there is provided a welding method for joining materials to be welded together by using a welding material. , And then the remainder is welded.

As described above, when the sizes of the materials to be welded are different from each other, a difference in thermal expansion between the materials to be welded occurs due to a difference in the amount of temperature rise during welding. Therefore, a tensile residual stress is generated in the weld metal due to a difference in shrinkage between the materials to be welded in a cooling process after welding.

In the present invention, when joining the materials to be welded, first, a part of the welded portion is partially welded at a predetermined interval. As a result, the materials to be welded are restrained by a number of welding points without increasing the temperature of the materials to be welded so much. Next, when the remaining unwelded portions are welded, the temperature of the material to be welded rises, but since the materials to be welded are restrained by the above welding points, the difference in expansion during welding is suppressed to a small value. Therefore, in the cooling process after welding, the difference in the amount of shrinkage between the materials to be welded becomes small, and the occurrence of tensile residual stress can be reduced.

Next, the invention described in claim 7 is applied to claim 6
In contrast to the welding method described in the above, the main plate and the sub-plate are used as the material to be welded, and before welding, preheating is performed so that the temperature of the joint of the main plate is higher than the temperature of the joint of the sub-plate. It is a feature.

That is, according to the present invention, before performing the welding according to the sixth aspect of the present invention, preheating is performed so that the temperature of the welded portion on the main plate side becomes higher than the temperature of the welded portion of the subplate. After that, in other words, by performing the welding after the main plate side is relatively thermally expanded more than the sub-plate in advance, the difference in thermal expansion between the main plate and the sub-plate due to a difference in temperature rise and restraint is reduced, Further, the tensile stress remaining in the welded joint after welding can be reduced.

Next, the invention according to claim 8 is different from the welding method according to claim 6 or 7 in the method for welding a low alloy steel material for a structure using a welding material. In addition, the present invention is characterized in that martensite transformation is caused in a cooling process after welding of a weld metal produced by welding, so that the metal is expanded at room temperature more than at the start of the martensite transformation.

That is, the present invention has the function of the invention described in claim 1 in addition to the function of the invention described in claim 6 or claim 7. Next, the invention according to claim 9 is characterized in that, in the welding method according to claim 8, an iron alloy having a martensitic transformation start temperature of less than 250 ° C and 170 ° C or more is used as the welding material. Is what you do.

The present invention has the function of the invention described in claim 2 in addition to the function of the invention described in claim 8.

[0047]

Next, embodiments of the present invention will be described with reference to the drawings. This embodiment uses the HT780MP
As shown in FIG. 2, a rib plate 2 as a sub-plate made of the same high-strength steel material is joined to a main plate 1 made of a-class high-strength steel plate by turning fillet welding to form a welded joint. Is what you do.

As welding materials, 0.025% by weight of C, 0.33% by weight of Si, 0.70% by weight of Mn, N
An iron alloy containing 10.0% by weight of i, 10.0% by weight of Cr, and 0.13% by weight of Mo is used. This welding material has a martensitic transformation start point Ms temperature of about 19
0 ° C. and has martensitic transformation characteristics as shown by the solid line in FIG.

The inclusion of Mo is for the purpose of imparting corrosion resistance. In the conventional welding materials, Ni and Cr are not added, or even if they are added, of the above additives. The amount is as small as less than 3.0% by weight and the Cr content is less than 1.0% by weight.

Before the welded portion of the rib plate 2 is brought into contact with the welded portion on the surface of the main plate 1, the welded portion on the main plate 1 side and its vicinity are heated by a burner to give preliminary heating, that is, After preheating only the welded portion of the main plate 1 to 110 ° C., the rib plate 2 is brought into contact with the welded portion of the main plate 1. Thereafter, the fillet welding by semi-automatic arc welding of the gas shield using the above welding material is performed to join the two, 1 and 2, and the welding joint 6
Is prepared.

As shown in FIG. 3, the order of the above-mentioned turning fillet welding is as follows. First, the ends 3a and 3b ((1) and (1) in FIG. (2)
Weld). Thereby, the longitudinal direction 4 of the rib plate 2
, The opposite end portions are fixed to the main plate 1.
That is, the elongation of the rib plate 2 in the longitudinal direction 4 of the welded section 3 is restricted by the main plate 1.

Next, welding is performed along the portion of the rib plate 2 that is opposed in the short side direction 5 in the cross section 3 of the welded portion, that is, along the long side ((3) and (4) in FIG. 3). As a result, the rib plate 2 is joined to the main plate 1 by fillet welding to form a weld joint 6.

At this time, the expansion mainly occurs due to thermal expansion in the longitudinal direction 4 which is the direction of the welding line when the long side portion is welded. , 3b are restrained by the main plate 1 by the previous welding, so that the elongation during heating is suppressed. For this reason, a difference in thermal expansion due to a difference in constraint between the main plate 1 and the rib plate 2 during welding,
In particular, the difference in thermal expansion generated in the longitudinal direction 4 at the welded section 3 of the rib plate 2 is suppressed to a small value.

The weld metal shrinks during the cooling process, but when it is cooled to 190 ° C. as described above, the martensitic transformation occurs and expands, and the cooling process ends at around room temperature where the maximum expansion has occurred (see FIG. 1). As a result, compression residual is given to the weld metal, and tensile residual stress is reduced.

Further, since the above-described welding is performed after the welded portion of the main plate 1 is slightly expanded from the welded portion of the rib plate 2 by preheating, the welding at the time of welding due to the difference in the temperature of the welded portion is performed. The difference in thermal expansion is kept small, which further reduces the residual tensile stress.

As a result, in the welded joint 6, the tensile residual stress generally generated near the weld toe is reduced or becomes the compressive residual stress. As a result, the fatigue strength of the welded joint 6 can be improved without performing any special post-processing such as grinding after welding.

Of course, a special post-treatment such as grinding may be performed after welding to reduce the notch sensitivity and further improve the fatigue strength of the welded joint 6. Here, in the welding method of the above embodiment, first, ends 3a and 3b facing each other in the longitudinal direction 4 in the welded section 3 of the rib plate 2 (in FIG. 3,
After welding (1) and (2)), welding is performed along the long side ((3) and (4) in FIG. 3).
It is preferable to perform welding along the long side while the weld metal applied to a and 3b ((1) and (2) in FIG. 3) has a melting point or less and is higher than the martensitic transformation start temperature.

That is, after the weld metal subjected to (1) and (2) is cooled to a temperature lower than the martensitic transformation start temperature and a compressive residual stress is introduced, the weld metal at positions (3) and (4) is welded. Then, due to the heat of the new weld metal, the weld metal at the end (1) or (2) (the angular position of the cross-section of the weld) in contact with the new weld metal is heated again in a constrained state. By doing so, the compressive residual stress is alleviated. For this reason, the effect of the above-described transformation expansion at the end of (1) or (2) is reduced. In contrast, (1) and
By performing welding at positions (3) and (4) while the weld metal applied in (2) is at a temperature higher than the martensitic transformation start temperature, the weld metal in (1) and (2) undergoes transformation expansion. Is reheated before the occurrence of the stress, and as a result, the effect of relaxing the tensile residual stress by the transformation expansion works effectively.

If it is difficult to complete the welding while the entire weld metal is at a temperature higher than the martensitic transformation start temperature, the entire weld metal is heated to the austenitizing temperature after the completion of the welding, Thereafter, by cooling, the martensitic transformation may be started simultaneously for all the weld metals.

The procedure for applying the welding material is not limited to the above procedure. For example, as shown in FIG. 4, end portions 3 opposed in the longitudinal direction 4 in the welded section 3 of the rib plate 2.
After welding a pair of opposed corners of a and 3b ((1) and (2) in FIG. 4), another pair of opposed corners are welded ((3) in FIG. 4). (4)) After the main plate 1 restricts the elongation of the rib plate 2 in the longitudinal direction 4, the remaining portion may be welded ((5) (6) in FIG. 4).

Further, in the above embodiment of the present invention, the main plate 1 and the rib plate 2 are welded in one layer without overlapping, but the lamination of the welding material in the present invention is not limited to this. . For example, as shown in FIG. 5, three layers may be stacked. In FIG. 5A, (1) to (18) show the welding lamination order. In this example, after welding the first layer of a pair of opposing corners among the ends 3a and 3b opposing each other in the longitudinal direction 4 in the welded section 3 of the rib plate 2 (FIG. 5A).
In the middle, (1) and (2)), the first layer of the other pair of corners facing each other is welded ((3) and (4) in FIG. In the longitudinal direction 4 is restricted. Thereafter, three layers of welding are performed along the longitudinal direction 4 (in FIG. 5A,
(5) (6) (7) and (8) (9) (10)). Finally, the second and third layers of the corner are welded ((11) to (1) in FIG. 5A).
8)).

Here, it is only necessary to first weld the opposite ends of the rib plate 2 in the longitudinal direction to restrict the longitudinal extension of the rib plate 2, and the order of lamination of the welding material thereafter is not particularly limited. Not done.

FIG. 5B is a diagram showing a cross section AA ′ in FIG. 5A, and is a diagram showing the lamination positions of the three layers. In this embodiment, the first layer is laminated ((1) and (4) in FIG. 5B), and the second layer is laminated on the side of the rib plate along the welded portion of the first layer (FIG. 5B). Of (b), (11) and (1)
2)) The third layer is laminated on the main plate 1 (in FIG. 5B,
(13) and (14)).

As described above, when the lamination is a multilayer, FIG.
It is preferable that the final layer is in contact with the main plate 1 as in the example shown in FIG. This is for maximizing the compressive residual stress at the boundary (weld toe) between the main plate 1 and the welded portion where the fatigue crack is most likely to occur. This is because compressive residual stress decreases when heating is performed in the step (1).

For the same reason, and in order to perform welding in a state in which the longitudinal extension of the rib plate 2 is sufficiently restrained, the rib plate 2 should be solidified lastly at the opposite end in the longitudinal direction. Preferably, the last layer at the end is laminated last.

Further, the welding material is not limited to the above composition, and if the composition satisfies the above formula (1), more desirably, C is 0.10% by weight or less, preferably 0.06% by weight or less. 8.0 to 13.0% by weight, and Ni 5.0
Other weld metals may be used as long as they are martensite or a ferrous alloy having a structure of martensite and retained austenite.

In the above embodiment, preheating is performed only on the welded portion on the main plate 1 side. However, preheating may be performed on the rib plate 2 side to suppress welding cracks. Even in this case, it is preferable to keep the heating temperature lower than that of the main plate 1, such as by shortening the heating time of the rib plate 2.

In the above embodiment, the welding material according to the fifth aspect of the present invention is used, and the sixth and seventh aspects of the present invention are used.
Although the welding method based on the invention is adopted, it is not necessary to employ all of them depending on the material of the main plate 1 and the sub plate as the base material and the conditions of the fillet welding.

The above-described joining procedure by fillet welding is particularly effective when the welded section 3 of the rib plate 2 as the sub-plate is rectangular. The partial cross section 3 may be a square cross section or the like. In the case of a square section, as shown in FIG. 6, the diagonal corners are welded ((1) → (2) → (3) → (4) in FIG. 6) and ribs are attached to the main plate 1 as shown in FIG. After restraining the corners of the plate 2, the rest ((5) (6) (7)
(8)) may be welded. By doing this, (5)
The extension in the direction of the welding line when welding the sides such as is restricted by the main plate 1.

Further, in the above embodiment, the main plate 1 and the rib plate 2 as the sub plate are made of high-strength steel, but the present invention is not limited to this. It may be a low-strength steel material or the like. Further, as shown in FIG. 7, it is preferable to perform a groove process on an edge portion of the welded portion of the rib plate 2. FIG. 7 shows a case where a beveling process is performed in turning fillet welding of the main plate 1 and the rib plate 2 shown in FIGS. 2 and 3.

By this groove processing, the amount of the weld metal 5 that can be applied to one place is increased, and the compressive stress due to the above-described transformation expansion can be increased. Further, as shown in FIG. 8, a beveling process is performed on an edge portion of the welded portion of the rib plate 2, and 1 m is provided between the main plate 1 and the tip of the rib plate 2.
It is preferable to perform welding with a gap δ of not less than m and not more than 5 mm.

As a result, the amount of the weld metal 5 that can be applied to one place is further increased, and the compressive stress due to the above-described transformation expansion can be increased. Although the groove processing is used in the present embodiment, the groove processing is not necessarily performed. This is because the amount of the weld metal 5 can be increased only by providing a gap between the main plate 1 and the tip of the rib plate 2.

Next, a second embodiment will be described with reference to the drawings. The same members and the like as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted. In this embodiment,
This is an example in which the present invention is employed when a T-shaped joint used at room temperature is produced by fillet welding.

That is, as shown in FIG. 9, the main plate 1 and the sub-plate 2 which are the materials to be welded are positioned in a T-shape, and the welding material is applied to the welded portion of the main plate 1 and the sub-plate 2 along the longitudinal direction 4. Prosper. At this time, as in the case of the above embodiment, 0.025% by weight of C, 0.33% by weight of Si, M
n is 0.70% by weight, Ni is 10.0% by weight, and Cr is 1%.
An iron alloy containing 0.0% by weight and 0.13% by weight of Mo is used. First, the welding material 5a is partially applied to the weld at predetermined intervals in the order of (1) → (2) → (3) → (4) →. Similarly, for the welded portion of the sub plate 2 facing in the thickness direction, (1) ′ → (2) ′ → (3) ′ → (4) ′ →.
・ Partially perform welding at predetermined intervals. Thereby, the sub plate 2 is restrained by the main plate 1.

Next, a welding material 5b along the longitudinal direction 4 is applied in the order of arrows O, P, and Q. Similarly, arrows O ', P', and
Welding along the longitudinal direction 4 is performed in the order of Q ′. At this time, the temperature of the sub-plate 2 becomes higher than that of the main plate 1 due to heat generated by welding, but the sub-plate 2 and the main plate 1 are partially welded in advance ((1) to (4)... And ( 1) 'to (4)'...), The difference in thermal expansion between the welded portion of the sub-plate 2 and the welded portion of the main plate 1 is restricted. Therefore, in the cooling process after the end of welding, the tensile residual stress introduced due to the difference in shrinkage between the main plate 1 and the sub plate 2 can be reduced.

As welding materials, C was 0.025% by weight, Si was 0.33% by weight, Mn was 0.70% by weight,
Since an iron alloy containing 10.0% by weight of Ni, 10.0% by weight of Cr, and 0.13% by weight of Mo is used, martensitic transformation occurs when the weld metal is cooled to 190 ° C. after welding. This causes the weld metal to expand during the cooling process from the martensitic transformation start temperature to room temperature. Therefore, the tensile residual stress introduced by the contraction of the weld metal can be reduced or a compressive residual stress can be given.

Before welding (before welding (1))
Preferably, preheating is performed so that the temperature of the welded portion of the sub-plate 2 is higher than the temperature of the welded portion of the main plate 1.
This makes it possible to reduce the temperature difference between the main plate 1 and the sub-plate 2 during welding, reduce the occurrence of tensile residual stress due to the difference in thermal expansion, and increase the compressive residual stress introduced after welding. .

Further, it is preferable to terminate the welding while all the welding materials applied to the welded portion are higher than the martensite transformation start temperature. This is because the weld metal applied earlier is
When the next welding is performed after cooling to a temperature lower than the martensitic transformation start temperature and compressive stress is introduced, the previously welded portion in contact with the new weld metal is heated by the heat of the new weld metal. By doing so, the compressive residual stress is relaxed, and the effect of the transformation expansion of the previously welded portion is reduced.

In the second embodiment, the welding procedure according to the sixth aspect is employed using the welding material according to the fifth aspect of the present invention. Depending on the material of the plate 2 and the conditions of fillet welding, it is not necessary to employ all of them.

Next, a third embodiment will be described with reference to the drawings. The same members as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted. This embodiment is an example in which the present invention is adopted for butt welding.

That is, as shown in FIG. 10, the ends of the extremely thick plates 10 and 11 which are the materials to be welded are opposed to each other at a predetermined interval, and many layers are overlapped in the gap. It was done.

Since the thickness is an electrode plate, welding metals are individually stacked from both sides in the plate thickness direction with the center of the plate thickness as a boundary.
That is, the final layer 20 is located on both sides of the plate. As the welding metal used for this welding, the welding material shown in the first embodiment is used. That is, in the cooling process, a welding material that maximizes martensitic transformation expansion near room temperature is used.

Thus, the residual tensile stress due to the heat shrinkage generated in the weld metal is reduced by the transformation expansion. In this case, it is preferable to repeat the next welding while the weld metal placed first is at or above the martensitic transformation start temperature.
By doing so, it becomes possible to effectively exert a residual stress relaxation effect due to transformation expansion of the weld metal placed earlier.

At this time, as shown in FIG.
The welding material shown in the first embodiment is used only for welding at 0 (hatched portion in FIG. 11), and the other layers are welded using a conventional welding material. You may.

In this case, although inferior to the above case, generally, the residual stress in the vicinity just below the final layer where the residual stress in the direction orthogonal to the welding direction (the thickness direction) is maximized is reduced by the effect of transformation expansion. The joint strength is improved.

The welding method shown in the second embodiment according to the present invention is not limited to the above embodiment. For example, as shown in FIG. 12, the present invention can be applied to a case where the sub-plate 2 has a pipe shape. In this case, the welding may be performed once as shown by an arrow N using the welding material shown in the first embodiment as shown in FIGS. As shown in FIGS. 12 (c) and 12 (d), a conventional welding material is used as the welding material, and the welding procedure is performed after the welding metal 5a is partially applied at predetermined intervals (see FIG. 12 (c)). ), (1) to (4)), arrows O, P,
The welding of the remaining weld metal 5b may be performed in the order of Q and R. It is more effective to employ the welding procedure shown in FIGS. 12C and 12D using the welding material shown in the first embodiment.

Similarly, a cruciform welded joint, a four-sided assembled box structure welded joint shown in FIGS.
The present invention is also effective when producing a welded H-section steel. As shown in FIGS. 13 (a) and 13 (b), FIGS. 14 (a) and 15 (a), a welded joint may be made using the welding material shown in the first embodiment. 13 (c) (d) and FIG. 14 using conventional welding materials.
(B), as shown in each of FIG. 15 (b), after the welding metal 5a is partially applied in advance, the welding metal 5b is
May be applied. When the welding procedure shown in each of FIGS. 13 (c) (d), 14 (b) and 15 (b) is performed, it is more preferable to use the welding material shown in the first embodiment. It is effective.

Further, the welding with the welding material shown in the first embodiment is not limited to arc welding, but can be applied to electroslag welding for forming a welded joint as shown in FIG.

Further, in the welding material shown in the first embodiment, when a fatigue crack is found in a steel material or the like, the fatigue crack portion is re-joined by welding or a defective portion of the base material is removed. It can also be applied as a welding material when performing repair welding such as build-up welding.

[0090]

EXAMPLES In order to confirm the improvement of the fatigue strength of a welded joint formed by fillet welding by the above method, the following was performed.

A main plate 1 and a rib plate 2 (sub-plate) each made of a 20 mm-thick HT780 MPa steel plate were joined by fillet welding according to the present invention and conventional fillet welding to produce a welded joint. Here, the dimensions of the main plate 1 and the rib plate 2 are as shown in FIGS. 20A and 20B, and the rib plate 2 is welded to both surfaces of the main plate 1.

At this time, as the welded joint, FIG.
In addition to the joint types shown in (a) and (b), as shown in Table 2 below, FIGS. 7, 8, 10, 11, 13, and 19 are used.
This is also performed according to the joint type shown in FIG.

Here, the welding materials used are those shown in Table 1 below. Welding materials A, B, C, D, E and F
Is a welding material according to any one of claims 3 to 5, and the welding material L is a conventionally used welding material. Also, welding materials G, H, I, J
And K are such that the content of each element does not satisfy the expression (1),
That is, it is a comparative example which does not satisfy the limited range of the welding material according to the present invention described in any of claims 3, 4 and 5.
The unit of numerical values in the table is% by weight, and the balance is iron and inevitable elements.

[0094]

[Table 1]

[0095] Weld joints were formed in the combinations shown in Table 2 below, and were subjected to a pulsating fatigue test at room temperature in the atmosphere. The results of the fatigue test are indicated by a fatigue strength corresponding to a rupture life of 2 × 10 ⁶ times.

[0096]

[Table 2]

Focusing on the welded joints manufactured by turning fillet welding of joints Nos. 1 to 12 in the table, as a welding material, the martensitic transformation starting temperature is 170 ° C. to 2 ° C.
Fatigue strength is improved by using welding materials A to F in the range of 50 ° C (joint Nos. 1 to 6) as compared with the case of using conventional welding material L (joint No. 12). I understand. Further, even when a welding material containing Ni or Cr is used as in the case of the joint Nos. 7 to 11, the welding material is out of any range of the present invention described in claims 3, 4 and 5. In the case of the above, it is understood that the fatigue strength is not improved. When the welding materials G, H, J and K were used as shown in the joint Nos. 7, 8, 10 and 11, the martensitic transformation start temperature Ms point was 2 as shown in Table 1.
Since the temperature is 50 ° C. or higher, it can be seen that the weld metal shrinks during the cooling process after the martensitic transformation and the fatigue strength is not improved. Further, when the welding material I is used as in the case of the joint No. 9, the martensitic transformation start temperature Ms point is lower than the room temperature. This is because a large tensile residual stress occurs because no site transformation occurs.

Further, when the relationship between the martensitic transformation start point Ms of the welding material and the fatigue strength was determined based on Tables 1 and 2, the results shown in FIG. 17 were obtained. The following can be seen from FIG.

That is, when attention is paid to welded joints Nos. 1 to 12 using conventional welding methods other than the welding material, there is a relationship indicated by a chain line, and the martensitic transformation start point Ms
It can be seen that the use of the welding material based on the present invention, which is not more than 250 ° C., effectively improves the fatigue strength even when the conventional method is used for the construction procedure and the like.

Further, paying attention to welded joint Nos. 12 and 14, it can be seen that the fatigue strength is effectively improved only by changing the welding procedure. In addition, welded joint No. 1
Focusing on Nos. 3 and 15, it can be seen that the fatigue strength is effectively improved by preheating only the main plate 1.
Also, in the comparison of welded joint Nos. 29 and 31, it can be seen that fatigue strength is effectively improved by preheating only main plate 1.

Further, paying attention to the welded joint Nos. 16 and 17, it is assumed that the preheating of only the main plate 1 and the welding procedure are performed by the method based on the present invention, and that the welding material based on the present invention is also used. It can be seen that the fatigue strength is greatly improved.

Further, paying attention to the welded joints Nos. 16 and 20, it can be seen that the bevel working further improves the fatigue strength.

Further, paying attention to the welded joints Nos. 12 and 21, it can be seen that even when only the groove processing and the welding material are based on the present invention, the fatigue strength is greatly improved.

Further, focusing on welded joints Nos. 16 and 22, or welded joints Nos. 19 and 23, it can be seen that fatigue strength is further improved only by adding welding in a state where a gap is opened. .

Focusing on welded joints Nos. 20 and 24, it can be seen that the combined use of beveling and welding with a gap opened further improves fatigue strength. At this time, paying attention to the welded joint No. 25, it can be understood that the same fatigue strength as that of the welded joint No. 20 can be obtained even if preheating is applied to the rib plate side in order to prevent welding crack of the rib plate. .

Further, focusing on welded joint No. 28,
This welding method is a case where all the welded metals are finished in a state where the applied welding metal is at or above the martensitic transformation start temperature, but all the weld metals at the time of completion of the application are at or above the martensitic transformation start temperature. , It can be seen that the fatigue strength is further improved as compared to the welded joint No. 24.

Focusing on welded joint No. 46, fatigue strength can be further improved by heating the entire welded portion to 720 ° C., which is higher than the austenitizing temperature, and then cooling it after welding. I understand.

Focusing on welded joint Nos. 23 and 26, it can be seen that the fatigue strength is improved by setting the gap between the main plate and the rib plate to 5 mm and further performing beveling. .

In the welded joint No. 27, the gap between the main plate and the rib plate is set to 7 mm.
The fatigue strength is not so much improved as compared with the case where the gap between the main plate and the rib plate is 5 mm.

Further, welded joint Nos. 29 to 33 are examples in which the present invention is applied to the case of performing three-layer welding as shown in FIG. 5 in turning fillet welding. In addition, welded joint No. 34
Is an example of a case where three layers are laminated by repeating the welding procedure of (1) to (6) of FIG. 20B three times.

Focusing on welded joint No. 34 and welded joint No. 31, it can be seen that the fatigue strength is improved by employing the welding procedure shown in FIG. Focusing on welded joint Nos. 29 to 31, it can be seen that fatigue strength is further improved by using welding material A based on the present invention as a welding material. Furthermore, welded joint No. 33
Focusing on, it can be seen that the fatigue strength is greatly improved by setting the gap between the main plate and the rib plate to 2 mm and performing groove processing.

The joint Nos. 35 to 38 are examples in which the welding method of the present invention is applied to a T-shaped joint. Welded joint No. 3
Focusing attention on No. 7, by adopting a welding procedure shown in FIG.
It can be seen that the fatigue strength is improved as compared with O.39.

Focusing on welded joints Nos. 36 and 35, it can be seen that the use of welding material A according to the present invention as a welding material and the preheating of only the main plate further improves the fatigue strength.

Further, as can be seen from the welded joints Nos. 40 to 42, it can be seen that the fatigue strength is greatly improved when adopted for butt welding. At this time, paying attention to the welded joint Nos. 41 and 42, it can be understood that it is effective to carry out only the final layer by the welding method based on the present invention.

Further, as can be seen from welded joints Nos. 43 and 45, even when the welding method by fillet welding according to the present invention is applied to the cruciform joint, the fatigue strength is greatly improved.

Further, the welded joints shown in FIGS. 20 (a) and 20 (b) were prepared by using the welding material L according to the procedure shown in FIG. 20 (c), and subjected to a pulsating tensile fatigue test under a stress of 120 MPa. The test was interrupted at the same time that the occurrence of fatigue cracks at the weld toe portions opposed in the longitudinal direction was visually confirmed. Thereafter, repair welding was performed on both weld toe portions facing each other in the longitudinal direction by overlaying using welding materials A and L, and a re-fatigue test was performed.

As a result, the fatigue strength of 2 million times after the build-up repair welding was 1 when the welding material A was used for the repair welding.
70 MPa, and 82 MPa when the welding material L was used for repair welding.

[0118]

As described above, in the welding method of the present invention, the martensitic transformation expansion can be effectively achieved without performing post-processing (special toe treatment) such as grinding or cooling after welding. There is an effect that the fatigue strength of the formed welded joint can be improved by utilizing the same.

At this time, by adopting any one of the first to fifth aspects of the present invention, the fatigue strength of the welded joint can be improved even if ordinary welding is performed only by specifying the welding material. is there.

Further, when the invention of claim 6 is employed, there is an effect that conventionally, when joining materials to be welded, the fatigue strength of the welded joint can be improved only by changing the welding procedure.

At this time, when the invention of claim 7 is adopted,
By applying the preheating, there is an effect that the fatigue strength of the welded joint can be further improved. Furthermore, by utilizing the transformation expansion caused by the welding material as in the invention according to any one of claims 8 and 9, even in the case where the stress remains higher than the conventional yield strength, it is ensured. There is an effect that the fatigue strength of the welded joint can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing transformation characteristics of a welding material (solid line) according to an embodiment of the present invention and a conventional welding material (dashed line).

FIG. 2 is a diagram showing a state in which a rib plate is welded to the main plate according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a construction procedure of a welding method according to the embodiment of the present invention.

FIG. 4 is a diagram for explaining another example of a construction procedure of the welding method according to the embodiment of the present invention.

5A and 5B are diagrams illustrating another example of a procedure for performing the welding method according to the embodiment of the present invention, wherein FIG.
(B) is a sectional view taken along the line AA '.

FIG. 6 is a diagram for explaining another example of a procedure for performing the welding method according to the embodiment of the present invention.

FIG. 7 is a side view showing the shape and joining of a test piece according to an example.

FIG. 8 is a diagram illustrating an example in which a groove processing and a gap are provided according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of joining a main plate and a sub-plate in a T-shape according to the embodiment of the present invention.

10A and 10B are diagrams illustrating an example in which the present invention is applied to the butt welding according to the embodiment of the present invention, wherein FIG. 10A is a plan view and FIG. 10B is a side view.

FIG. 11 is a diagram illustrating another example in which the present invention is applied to the butt welding according to the embodiment of the present invention.

12A and 12B are diagrams illustrating a case where a sub-plate according to an embodiment of the present invention has a pipe shape, and FIG.
(B) is a side view thereof, (c) is a plan view thereof, and (d) is a side view thereof.

FIG. 13 is a diagram showing an example applied to a cruciform joint;
(A) is a plan view, (b) is a side view, (c) is a plan view, and (d) is a side view.

FIG. 14 is a diagram applied to a four-sided assembly box structure;
(A) is an example of the welding, and (b) is another example of the welding.

FIG. 15 is a diagram applied to a welded H-section steel, where (a) is an example of the welding and (b) is another example of the welding.

FIG. 16 is a diagram applied to electroslag welding.

FIG. 17 is a diagram showing the relationship between the temperature at the martensitic transformation start point and the fatigue strength.

FIG. 18 is a view showing a contracted state of a weld metal in a cooling process after welding.

19A and 19B are diagrams illustrating a case where a T-shaped joint is formed by fillet welding, wherein FIG. 19A is a perspective view thereof, and FIG. 19B is a perspective view thereof.

FIG. 20 is a view for explaining the construction of the welding method, and (a)
Is a plan view thereof, (b) is a side view thereof, and (c) is a diagram for explaining a construction procedure of a conventional welding method.

[Explanation of symbols]

 Ms Martensitic transformation starting point 1 Main plate 2 Rib plate (sub-plate) 3 Welded section 3a, 3b Ends opposed in longitudinal direction 4 Longitudinal direction 5 Short side direction 6 Welded joint (1)-(18) Construction procedure

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C22C 38/00 302 C22C 38/00 302Z 38/48 38/48 (72) Inventor Akihiko Ota 1-chome Sengen, Tsukuba-shi, Ibaraki Pref. No. 1 in the National Institute for Metals Science and Technology Agency (72) Inventor Chiaki Shiga 1-2-1 Sengen in Tsukuba City, Ibaraki Prefecture Inside the National Institute for Metals Technology Research Institute of Science and Technology Agency (72) Inventor Satoshi Nishijima Sengen in Tsukuba City, Ibaraki Prefecture No. 1-2-1 in Science and Technology Agency, Metal Materials Research Laboratory

Claims (9)

[Claims] In a welding method for welding a low alloy steel material for a structure using a welding material, a weld metal produced by welding undergoes martensitic transformation in a cooling process after welding, and the martensite transforms at room temperature. A welding method characterized by being in a state of being more expanded than at the start of the site transformation. 2. The welding method according to claim 1, wherein an iron alloy having a martensite transformation start temperature of less than 250 ° C. and 170 ° C. or more is used as the welding material. 3. A welding material used in the welding method according to claim 1 or 2, wherein C, Cr, Ni, S
A welding material characterized by being an iron alloy in which the contents of i, Mn, Mo and Nb are adjusted to satisfy the following formula (1). 170 ≤ 719-795 x C (wt%)-23.7 x Cr (wt%)-26.5 x Ni (wt%)-35.55 x Si (wt%)-13.25 x Mn (wt%) ) -23.7 × Mo (% by weight) -11.85 Nb (% by weight) <250 (1) 4. C content of 0.10% by weight or less and Cr content of 8.0.
The welding material according to claim 3, wherein the welding material contains 0.1 to 13.0% by weight of Ni and 5.0 to 12.0% by weight of Ni. 5. An alloy comprising 0.2 to 1.0% by weight of Si, 0.4 to 2.5% by weight of Mn, 4.0% by weight or less of Mo, Nb
5. The composition of claim 4, wherein the content is 1.0% by weight or less.
Welding material described in. 6. A welding method for joining materials to be welded together by using a welding material, wherein a welding portion between the materials to be welded is partially welded at a predetermined interval, and then the remaining portion is welded. Characteristic welding method. 7. The method according to claim 7, wherein the main plate and the sub-plate are the materials to be welded, and pre-heating is performed before welding so that the temperature of the junction of the main plate becomes higher than the temperature of the junction of the sub-plate. The welding method according to claim 6. 8. A welding method for welding a low-alloy steel material for a structure using a welding material, wherein a martensitic transformation is caused in a cooling process after the welding to form a weld metal produced by welding, The welding method according to claim 6, wherein the welding is performed in a state in which the expansion is performed more than at the start of the site transformation. 9. The welding method according to claim 8, wherein an iron alloy having a martensite transformation start temperature of less than 250 ° C. and 170 ° C. or more is used as the welding material.