JP2002321059A - Welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method capable of improving fatigue strength of a welded joint without necessarily providing special after-treatment after welding. SOLUTION: The welding method comprises using, as welding materials, an alloy of iron which expands from the startup of martensitic transformation at room temperature by containing C of 0.025 wt.%, Si of 0.33 wt.%, Mn of 0.70 wt.%, Ni of 10.0 wt.%, Cr of 10.0 wt.%, and Mo of 0.13 wt.%, preheating only the welding part of a main plate 1, welding the ends (figure 3-(1) and (2)) facing each other in the longitudinal direction 4 at the cross-sectional surface 3 of the welding part of a rib plate 2, and thereafter welding the remaining part.

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 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, marine structures, penstocks, bridges and the like, high strength steel materials are required for the purpose of increasing the size and reducing the weight. As a material used for these structures, a so-called low alloy steel material containing less than 3.0% by weight of various alloying elements such as Cr, Ni, and Mo is used, and the tensile strength level of these materials is 294 to 1
176 N / mm ² (= 30 to 120 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 welded joints made of high-strength steel is the same as that of low-strength steel. There was a problem that it could not be raised. The reason why the fatigue strength is not improved in the high-strength steel welded joint is that the tensile residual stress is large.
No. 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 has been improved by improving the welding method or disclosed in, for example, JP-A-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. The tensile residual stress generated in the welded portion of the joint is caused by heat contraction when the weld metal after welding is 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.

[0005] Here, when a conventional welding material made of a low alloy steel is used as the temperature decreases, the weld metal thermally contracts and its elongation (length) decreases, but elongation (length) near 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 ° C. to about 400 ° C., expansion occurs due to martensitic transformation, so that the tensile residual stress is relaxed during this period. Will be introduced. The above is the main reason why tensile residual stress occurs in the welded portion. For example, when two pieces to be welded are different in size, such as fillet welding, due to a difference in heat capacity of the pieces to be welded. Thus, the tensile residual stress is further promoted.

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 moved 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 completion of the welded portion.

[0008] 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 tensile residual stress caused by the difference in thermal expansion between the main plate and the sub-plate and the tensile residual stress caused by the thermal contraction of the weld metal described above 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 on a main plate and joining it by fillet welding, a weld toe is used. A method has been proposed in which a compressive stress is imparted by hitting a portion by shot peening, hammer peening, or the like to reduce residual tensile stress at the time of welding of a 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.

[0011]

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. It requires equipment and work that are not normally used in the welding work. Therefore, there is a problem that the method is not always efficient and economical. Also, in the welding method described in the above-mentioned JP-A-54-130451, after normal welding,
For example, it is necessary to use liquid nitrogen to cool to a temperature of −60 ° C. or lower. Further, considering the application to a large-sized welded joint of an extremely thick plate, which is a main application object of the present invention, liquid nitrogen is used. Cooling the entire weld to -60 ° C or the like by using it is a difficult 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

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, a welding method of the present invention firstly comprises a welding method for welding a low alloy steel material for a structure using a welding material.
The present invention is characterized in that a martensite transformation is caused in a cooling process after welding of a weld metal generated by welding, so that the weld metal is expanded at room temperature as compared with the time of 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.

[0015] In order to make the "expanded state at room temperature than at the start of the martensitic transformation" as described in claim 3, the martensitic transformation starting temperature of the welding material is less than 250 ° C. It is good to use an iron alloy of at least ℃. FIG. 1 shows the transformation characteristics of the welding material used in the present invention (solid line in FIG. 1) in comparison with the transformation characteristics of the conventional welding material (dashed line in FIG. 1). In the present invention,
Starting temperature of martensitic transformation is less than 250 ° C and 170 ° C
By using the above iron alloy as a welding material, the amount of expansion of the weld metal due to martensitic transformation can be increased, and the state of the large amount of expansion becomes around room temperature. At the end, the metal is expanded more than at the start of the martensitic transformation. 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, but 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). The reason why the martensitic transformation start temperature is set to 170 ° C. or higher is that when the martensitic transformation start temperature is lower than 170 ° C., even when martensite transformation starts, the amount of transformation expansion until the end of the cooling process is small. Cannot be obtained sufficiently.

Here, as the welding material used in the welding method of the present invention, for example, C, Cr, Ni, Si, Mn, Mo
It is preferable to use an iron alloy in which the contents of Nb and Nb are adjusted to satisfy the following expression (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) Generally, the martensitic transformation onset temperature (Ms) of steel materials
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 above, regarding the relationship between the Ms point and the contents of various alloy elements, Ms (° C.) = 719−26.5 × Nieq−23.7 × C
req Nieq = 30 × C (% by weight) + 0.5 × Mn (% by weight) Creq = Cr (% by weight) + Mo (% by weight) + 1.5 ×
The following equation is obtained: 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 starting 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, and S of the iron alloy are set so that the Ms point according to the above equation is less than 250 ° C. and 170 ° C. or more.
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.

Further, as the welding material used in the present invention, C is 0.10% by weight or less and Cr is 8.0 to 13.0%.
It is preferable to use an iron alloy containing 5.0% to 12.0% by weight of Ni. Here, the content of C is preferably as small as possible in order to secure weldability and reduce the hardness of martensite, and is 0.1% by weight or less, preferably 0.06% by weight in order not to cause weld cracking. % Is preferable.

The martensite transformation start 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. Where C
The reason why the content of r is set to 8.0% by weight or more is that if the content is less than 8.0% by weight, the martensitic transformation start temperature is set to 250 ° C.
This is because, in order to reduce the content to less than 1, it is necessary to contain a large amount of expensive Ni and 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 reason why the content of Ni is regulated to 5.0 to 12.0% by weight is that when the 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 welded joints of thick steel plates used for ships, marine structures, penstocks, bridges, etc., the Ni content of the welding material is less than 3.0% by weight and the Cr content is 1. Less than 0% by weight was used.

Further, as welding materials used in the present invention, 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, and Nb of 1.0% by weight or less. It is preferable to use an iron alloy containing 0% by weight or less. 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 agent.
If the content exceeds 0% by weight, 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. Mo can be added for the purpose of imparting corrosion resistance to the welded portion. However, if the content of Mo exceeds 4.0% by weight, the workability in the welding material manufacturing process is reduced. To 4.0% by weight 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. Next, the present invention described in claim 1 is a welding method for joining materials to be welded using the above-mentioned welding material, wherein a welding portion between the materials to be welded made of the low alloy steel material is formed by a predetermined method. Are welded partially at intervals, 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 materials to be welded, first, a part of a 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 smaller,
Generation of tensile residual stress can be reduced.

Next, according to the present invention, in addition to the above-mentioned structure, the main plate and the sub plate are made of a material to be welded made of the low-alloy steel material, and before welding with the above-mentioned welding material,
It is characterized in that 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.
That is, according to the present invention, before performing welding, preheating is performed so that the temperature of the welded portion on the main plate side is higher than the welded portion temperature of the sub plate, that is, the main plate side is relatively Welding is performed after the thermal expansion of the sub-plate is larger than that of the sub-plate, thereby reducing the difference in thermal expansion between the main plate and the sub-plate due to the rise in temperature and the difference in restraint. Stress can be reduced.

[0028]

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 a welding material, C was 0.025% by weight,
0.33% by weight of Si, 0.70% by weight of Mn, 10.0% by weight of Ni, 10.0% by weight of Cr, 0.1% of Mo
An iron alloy containing 3% by weight is used. This welding material has a martensitic transformation start point Ms temperature of about 190 ° C.
And has a martensitic transformation characteristic as shown by a solid line in FIG.

It is to be noted that Mo is contained for the purpose of imparting corrosion resistance. In the conventional welding materials, Ni and Cr are not added, or even if 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 end face which is the welded portion of the rib plate 2 is brought into contact with the welded portion of the main plate 1 surface, the welded portion on the main plate 1 side and the vicinity thereof are heated by a burner to give preliminary heating, that is, the main plate 1 Weld only 11
After preheating to 0 ° C., the rib plate 2 is brought into contact with the welded portion of the main plate 1. Then, the fillet welding by semi-automatic arc welding of the gas shield using the above welding material is performed, and the two are joined to form the weld joint 6.

As shown in FIG. 3, the order of the above-mentioned turning fillet welding is as follows. First, as shown in FIG. 3, the ends 3a, 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 facing the short side direction 5 in the welded section 3 of the rib plate 2, 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 elongation is mainly caused by the thermal expansion in the longitudinal direction 4 which is the welding line direction at the time of welding the long side portion. 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 the room temperature where the maximum expansion occurs (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 difference in thermal expansion during welding due to the difference in the temperature of the welded portion is small. It is suppressed, which also 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-described embodiment, first, the 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, 3b ((1) and (2) in FIG. 3) has a melting point or lower 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 onset temperature and 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 operation while the temperature of all the weld metals is higher than the martensitic transformation start temperature, all the weld metals are heated to the austenitizing temperature after the completion of the welding operation. 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, after welding a pair of opposing corners of the end portions 3a and 3b facing each other in the longitudinal direction 4 in the welded section 3 of the rib plate 2 ((1) and ( 2)),
The other pair of opposing corners is welded ((3) in FIG. 4).
(4)) After the main plate 1 restrains the extension of the rib plate 2 in the longitudinal direction 4, the remaining portion may be welded (FIG. 4).
Medium, (5) (6)).

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 so as to restrain 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 cross-sectional view taken along the line A in FIG.
It is a figure which shows -A 'and is a figure which shows the lamination position of the above-mentioned three layers. In this embodiment, the first layer is laminated (FIG. 5).
In (b), (1) and (4)), the second layer is laminated on the rib plate side along the welded portion of the first layer ((11) and (1) in FIG. 5B).
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). In addition, in order to perform welding for the same reason and in a state where the longitudinal extension of the rib plate 2 is sufficiently restrained, the rib plate 2 is so shaped that the opposite end in the longitudinal direction is finally solidified. It is preferable to laminate the last layer of the part 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. Also,
In the above-described embodiment, preheating is performed only on the welded portion on the main plate 1 side, but 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.

Depending on the material of the main plate 1 and the sub plate as the base material and the conditions of the fillet welding, it is not necessary to adopt all of the above. In addition, the construction procedure in the joining method by the fillet welding is particularly effective when the welded section 3 of the rib plate 2 as the sub-plate is rectangular. May have 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.

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. This groove processing increases the amount of the weld metal 5 that can be applied to one location, and can increase the compressive stress due to the above-described transformation expansion.

Further, as shown in FIG. 8, the edge of the welded portion of the rib plate 2 is grooved, and a gap δ of 1 mm or more and 5 mm or less is formed between the main plate 1 and the tip of the rib plate 2.
It is preferable to perform welding in a state where the wire is opened. Thereby, 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 laid along the longitudinal direction 4 on the welded portion of the main plate 1 and the sub-plate 2. . At this time, as in the case of the above-described embodiment, 0.025% by weight of C, 0.33% by weight of Si, 0.70% by weight of Mn, and 10% of Ni were used as welding materials.
An iron alloy containing 0% by weight, 10.0% by weight of Cr, and 0.13% by weight of Mo is used. First, (1) → (2) → (3) →
(4) The welding material 5a is partially applied to the welding portion at predetermined intervals in the order of →. Similarly, for the welded portion of the sub plate 2 facing in the plate thickness direction, (1) ′ → (2) ′ →
(3) ′ → (4) ′ →... Are partially welded at predetermined intervals. Thereby, the sub-plate 2 becomes the main plate 1
Is bound by

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 ′,
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 when the previously applied weld metal is cooled to a temperature lower than the martensitic transformation start temperature and the next welding is performed after compressive stress is introduced, the heat of the new weld metal causes the new welding metal to perform the new welding. This is because, by heating the previously welded portion in contact with the metal, the above-mentioned compressive residual stress is relaxed, and the effect of the transformation expansion of the previously welded portion is reduced.

It is not necessary to employ all of the above depending on the material of the main plate 1 and the sub plate 2 as the base material and the conditions of the fillet welding. 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 will be 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 were opposed to each other at a predetermined interval, and welding was performed so that many layers were overlapped in the gap. Things.

Because of the thickness of the electrode, the weld metal is individually overlapped from both sides in the thickness direction with the center of the 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. Thereby, the tensile residual stress due to the heat shrinkage generated in the weld metal is reduced by the transformation expansion.

In this case, it is preferable that the next weld be repeated before 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. 11, the welding material shown in the first embodiment is used only for welding the final layer 20 (hatched portion in FIG. 11), and for welding other layers, Alternatively, welding may be performed using a conventional welding material.

In this case, although it is inferior to the above case, generally, the residual stress in the vicinity just below the final layer where the residual stress in the direction perpendicular to the welding direction (the thickness direction) becomes maximum is relaxed by the effect of transformation expansion. The joint strength is improved. The welding method shown in the second embodiment based on 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 was used as the welding material, and the welding procedure was performed after the welding metal 5a was partially applied at predetermined intervals (FIG. 12).
(C), (1) to (4)), and the remaining weld metal 5b may be welded in the order of arrows O, P, 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, as 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.

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 weld-welded. It can also be applied as a welding material when performing repair welding in such cases.

[0053]

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. 20 mm thick HT780MPa by fillet welding based on the present invention and conventional fillet welding
The main plate 1 made of the steel plate and the rib plate 2 (sub plate) were joined 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.
(A) In addition to the joint types shown in (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. The welding materials A, B, C, D, E and F are iron alloys having a martensitic transformation start temperature of less than 250 ° C and 170 ° C or more, and the welding material L is a conventionally used welding material. The unit of numerical values in the table is% by weight, and the balance is iron and inevitable elements.

[0055]

[Table 1]

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

[0057]

[Table 2]

Focusing on the welded joints manufactured by turning fillet welding of joints Nos. 1 to 12 in the table, the martensitic transformation onset temperature is 170 ° C. to 2 ° C. as the welding material.
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 if a welding material containing Ni or Cr is used as in the case of the joint Nos. 7 to 11, if the welding material is out of the range of the present invention, the fatigue strength is not improved. You can see that. As shown in the joint Nos. 7, 8, 10, and 11, when the welding materials G, H, J, and K are used, as can be seen from Table 1, the martensitic transformation start temperature Ms point is 250 ° C. or more. It can be seen that in the cooling process after the martensitic transformation, the weld metal shrinks and the fatigue strength does not improve. 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 as indicated by a dashed line, and the martensitic transformation start point Ms is based on the invention of the present application of 250 ° C. or less. It can be seen that the use of the welding material improves the fatigue strength.

Further, paying attention to the welded joints 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, focusing on 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. Focusing on welded joints Nos. 16 and 20, it can be seen that performing beveling further improves fatigue strength. Also, paying attention to welded joints Nos. 12 and 21, it can be seen that the fatigue strength is greatly improved even when only the groove processing and the welding material are based on the present invention.

Further, paying attention to the welded joints Nos. 16 and 22 or the welded joints Nos. 19 and 23, it can be seen that the fatigue strength is further improved only by adding the welding with the gap opened. . In addition, welded joint Nos. 20 and 24
It can be seen that the fatigue strength is further improved by using the groove processing and the welding in a state where the gap is opened in combination. At this time, focusing on welded joint No. 25,
It can be seen that even if preheating is applied to the rib plate side in order to prevent the welding crack of the rib plate, the same fatigue strength as that of welded joint No. 20 can be obtained.

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, it can be seen that fatigue strength is further improved by heating the entire weld to 720 ° C., which is higher than the austenitizing temperature after welding, and then cooling.

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. . Further, in the welded joint No. 27, the gap between the main plate and the rib plate is 7 mm, but the fatigue strength is much smaller than when the gap between the main plate and the rib plate of the welded joint No. 26 is 5 mm. Not improved.

Further, the 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, FIG.
It can be seen that the fatigue strength is improved by employing the welding procedure shown in FIG.

Focusing on the welded joints Nos. 29 to 31, it can be seen that the use of the welding material A according to the present invention as the welding material further improves the fatigue strength.
Furthermore, paying attention to welded joint No. 33, 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.
Further, joint Nos. 35 to 38 are examples in which the welding method of the present invention is applied to a T-shaped joint.

Focusing on welded joint No. 37, the fatigue strength is improved by employing the welding procedure shown in FIG. 9 as compared with welded joint No. 39 which is a conventional example of a T-shaped joint. You can see that. In addition, welded joint No. 36
Paying attention to and 35, it is understood that the use of the welding material A based on the present invention as a welding material and the use of only the main plate for preheating further improves the fatigue strength.

Further, as can be seen from welded joint 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. Also,
As can be seen from welded joints Nos. 43 and 45, even if the welding method by fillet welding based on the present application is adopted for the cruciform joint,
It can be seen that the fatigue strength is greatly improved.

The welding 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 2,000,000 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.

[0071]

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, when the invention of claim 1 is adopted, there is an effect that the fatigue strength of the welded joint can be improved only by changing the welding procedure when joining the materials to be welded. Also,
When the invention of claim 2 is adopted, there is an effect that the fatigue strength of the welded joint can be improved by adding preheating.

[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, in which 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 Martensite transformation start point 1 Main plate 2 Rib plate (sub plate) 3 Welded section 3a, 3b Ends facing in longitudinal direction 4 Longitudinal direction 5 Short side direction 6 Welded joint (1)-(18) Construction procedure

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akihiko Ota 1-2-1, Sengen, Tsukuba, Ibaraki Prefecture Within the National Institute for Materials Science (72) Inventor Chiaki Shiga 1-2-1, Sengen, Tsukuba, Ibaraki No. 1 Independent Administrative Institution, National Institute for Materials Science (72) Inventor Satoshi Nishijima 1-1-1, Sengen, Tsukuba, Ibaraki Pref.

Claims (3)

[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. As a state that is more expanded than at the start of the site transformation, a weld portion between the materials to be welded, which is the low-alloy steel material, is partially welded at a predetermined interval, and then the remaining portion is welded. And welding method. 2. 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, As a state expanded from the start of the site transformation, the main plate and the sub-plate are welded materials made of the low-alloy steel material, and before welding, the temperature of the joint of the main plate and the temperature of the joint of the sub-plate A welding method characterized by preheating to a temperature higher than the temperature. 3. The welding method according to claim 1, wherein 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.