JP2012076141A - Fillet welding joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fillet welding joint which is greatly contributable to reduction in operation time and welding cost while having high fatigue resistance.SOLUTION: In the fillet welding joint including one base metal 1 and the other base metal 2 joined to a surface of the one base metal by welding, a welding material 3 having an intensity ratio to the base metals 1, 2 smaller than 1 is used to restrict heat input during the welding.

Description

  The present invention relates to a load non-transmission fillet welded joint made of structural steel including high-strength steel, and is suitable for use, for example, in a fillet welded portion of a non-strength member in a bridge or ship. The present invention relates to a meat weld joint.

  Generally, the fatigue strength of structural steel is improved as the tensile strength of the steel material increases, but the fatigue strength of the fillet welded joint is not significantly improved even if the tensile strength of the steel material is increased. Factors that do not improve the fatigue strength of this fillet welded joint include stress concentration that occurs in the shape discontinuity of the weld toe and residual stress that occurs during welding.

  Conventionally, in order to relieve the stress concentration at the weld toe, an operation of grinding the weld toe by a grinder to increase the toe radius is performed at the welding site, and in order to reduce residual stress, Work to perform shot peening is performed at the welding site.

  In addition to this, as a technique for relaxing the stress concentration at the weld toe, there is a method of remelting the weld toe by TIG welding and plasma treatment described in Patent Document 1 to smooth the shape, As a technique for reducing the residual stress, there is a method using low-temperature transformation expansion described in Patent Document 2.

Japanese Patent Laid-Open No. 01-301823 JP-A-54-130451

  However, the method of grinding the weld toe by the above grinder, remelting the weld toe by TIG welding, etc., and the method of performing the shot peening treatment add construction after welding. There is a problem that the man-hour is increased correspondingly, and the working time cannot be shortened and the welding cost cannot be reduced.

  In addition, the method using low-temperature transformation expansion is limited to steel materials and welding materials having a special composition, and the welding material becomes expensive, and a predetermined transformation expansion effect cannot be obtained depending on welding conditions. There is a problem that there is a possibility, and it has been a conventional problem to solve these problems.

  The present invention has been made paying attention to the above-described conventional problems, and provides a fillet welded joint that has high fatigue strength and can greatly contribute to shortening of working time and reduction of welding costs. It is an object.

Here, it is known that a material having a low tensile strength has ductility as compared with a high-strength material, for example, high-strength steel, and is excellent in wettability during welding.
In order to achieve the above object, the present inventors use a material having a tensile strength lower than that of the base material as a welding material. For example, in the case of arc welding, the current and voltage are reduced or the welding speed is reduced. If speeded up, it is thought that at least one of the ductility and wettability properties of the material with low tensile strength functions, so that stress concentration at the weld toe can be reduced and residual stress can be reduced. It came to make this invention.

  That is, the invention according to claim 1 of the present invention is formed by joining the other base material to one base material surface by welding (welding such as arc welding, laser arc hybrid welding, laser welding, laser hot wire welding). The fillet welded joint is characterized in that a welding material whose strength ratio to the base material does not exceed 1 is used and a heat input restriction is applied at the time of welding. As a means for solving the conventional problems.

In the fillet welded joint according to the present invention, the strength ratio is the ratio of the strength of the welding material to the strength of the base material, the strength of the base material is steel strength, and the strength of the welding material is the total molten metal strength. is there.
At this time, if a welding material having a strength ratio with respect to the base material exceeding 0.8 is used, the shape of the weld toe portion is not smooth, so that relaxation of stress concentration and reduction of residual stress cannot be expected.
Therefore, in the fillet welded joint according to claim 2 of the present invention, a welding material having a strength ratio with respect to the base material of 0.8 or less is used.
Here, even if a welding material having a strength ratio of about 0.3 is used, it is considered that the stress concentration at the weld toe can be reduced and the residual stress can be reduced. Therefore, the strength ratio, particularly the lower limit value, is appropriately determined depending on the tensile strength of the welding material to be used based on the design required strength.

  In the fillet welded joint according to the present invention, fillet weld includes not only T-shaped fillet weld and cross fillet weld but also rotating weld. In the fillet welded joint according to the present invention, As the material, structural steel including high-tensile steel can be adopted, while as the welding material, carbon steel having a tensile strength lower than that of the base material can be used.

  Here, the heat input during welding (welding heat input [J / mm]) is obtained from (current [A] × voltage [V]) / welding speed [mm / s]. Based on the heat input required for ordinary arc welding, the heat input is kept low by reducing the current and voltage or increasing the welding speed.

For example, in the case of laser arc hybrid welding, if the heat input by the arc exceeds 15% of the heat input supplied by normal arc welding, stress concentration relaxation and residual stress reduction cannot be expected. It is desirable to suppress the heat input by the arc to 15% or less of the heat input supplied by normal arc welding.
Here, even if the heat input amount is suppressed to 10% or less, it is considered that the stress concentration at the weld toe portion can be relaxed and the residual stress can be reduced. Therefore, based on the required design strength, the lower limit of the heat input is determined as appropriate.

  In this laser arc hybrid welding or laser welding, the heat input by the laser can be limited by lowering the laser power.

  In this heat input restriction at the time of welding, the reduction width of the current and voltage, the reduction width of the laser power, and the increase amount of the welding speed can be determined according to the type and thickness of the base materials to be joined.

  In the fillet welded joint according to the present invention, since a heat input restriction is performed at the time of welding after using a welding material having a tensile strength lower than that of the base material, the ductility and wetting of the welding material having a low tensile strength are performed. One or both of these properties will function to alleviate stress concentration at the weld toe and reduce residual stress. As a result, conventional fillet welding using high-strength welding materials Fatigue strength is increased compared to the joint.

  In addition, a low-strength material such as carbon steel that is inexpensive and easily available can be used as the welding material, so that welding costs can be reduced, and after welding, grinder processing, shot peening processing, etc. Since there is no need to add work, the number of work steps can be reduced.

  Since the fillet welded joint according to the present invention has the above-described configuration, it has a very excellent effect that it can contribute to shortening the working time and reducing the welding cost while maintaining high fatigue strength. Brought about.

It is front explanatory drawing which shows one Example of the fillet welded joint which concerns on this invention. It is the graph (b) which showed the test point explanatory drawing at the time of conducting the fatigue strength test of the fillet welded joint in FIG. 1, and the fatigue strength test result.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of a fillet welded joint according to the present invention. In this embodiment, a case where the fillet welded joint according to the present invention is a T-shaped fillet welded joint will be described as an example. .

  As shown in FIG. 1, the T-shaped fillet welded joint is formed by joining the other base material 2 to the surface of one base material 1 by laser arc hybrid welding. A material having a lower tensile strength than 1 and 2 is used.

  In this case, high strength steel of HT780 steel (780 MPa class steel) is used for the base materials 1 and 2, and a welding material whose strength ratio to the base materials 1 and 2 does not exceed 1 is used for the welding material 3. MG-S50 (590 MPa grade steel) is used.

In this case, the strength ratio is the ratio of the strength of the welding material 3 to the strength of the base materials 1 and 2, the strength of the base materials 1 and 2 is the steel strength, and the strength of the welding material 3 is the total molten metal strength. It is.
In this embodiment, the strength of the base materials 1 and 2 is 780 MPa, whereas the strength of the welding material 3 is 580 MPa, and thus the strength ratio is 0.756.

  In this fillet welded joint, heat input is restricted during welding. In the case of this embodiment, the heat input by the arc of laser arc hybrid welding with respect to the base materials 1 and 2 each having a wall thickness of 12 mm is the heat input supplied by normal arc welding (1000 J / when the leg length is 6 mm). The heat input restriction so as to be 10 to 15% of the (mm), that is, the heat input restriction so as to be about 108 J / mm was performed.

  In addition, in the case of this embodiment, the heat input limit by which the heat input by the laser of the laser arc hybrid welding is 50% or less of the heat input supplied by the above-mentioned normal arc welding, that is, about 450 J / mm. The heat input restriction was implemented.

  In this heat input restriction, in addition to reducing the arc current and laser output respectively, a method of increasing the welding speed can also be used. It can be determined according to the type and thickness of 1 and 2.

  Therefore, as shown in FIG. 2A, when the fillet welded joint supported by the two fulcrums p and p was subjected to a four-point bending test in which a load in the direction of the arrow was repeatedly applied from above, FIG. The results indicated by ▼ are obtained.

  In the graph of FIG. 2 (b), ◇ indicates the test results of the fillet welded joint manufactured by laser welding using HT780 steel high-tensile steel as both the base material and the welding material. , Is a test result of a fillet welded joint produced by laser arc hybrid welding using HT780 steel high-strength steel as the base material and YM80 steel as the welding material, and △ marks indicate the high tensile strength of HT780 steel as the base material. It is a test result of the fillet welded joint manufactured by laser arc hybrid welding using MG-S50 as a welding material while using steel.

  As shown in FIG. 2 (b), the fillet welded joint (marked with a ▼ in the figure) of this example is in a range of Δσ ≦ 200 MPa (particularly Δσ = in comparison with other fillet welded joints for comparison). It is remarkable that the D grade is sufficiently satisfied at around 100 MPa). In other words, when considering the strength level of HT780 steel, it can be understood that it can be treated as a D grade without any practical problems. When a load cycle is applied to the fillet welded joint of this example, fatigue cracks in the base materials 1 and 2 are observed. Can be avoided.

In the above-described embodiment, the case where the fillet welded joint according to the present invention is a T-shaped fillet welded joint has been described as an example, but the present invention can also be applied to cross fillet welding and rotary welding.
In the above-described embodiment, the case where the high-strength steel of HT780 steel is used as the base materials 1 and 2 has been described as an example. However, as the base materials 1 and 2, other structural steels should be adopted. In addition, as the welding material 3 having a low tensile strength, carbon steel having a lower strength can be used.

  Furthermore, in the above-described embodiment, the case where a fillet welded joint is manufactured using laser arc hybrid welding has been described as an example, but various types of welding such as arc welding, laser welding, and laser hot wire welding are also employed. can do.

  The configuration of the fillet welded joint according to the present invention is not limited to the configuration of the above-described embodiment.

  In the fillet welded joint according to the present invention, a material having a tensile strength lower than that of the base material is used as the welding material.For example, in the case of arc welding, by reducing the current and voltage or increasing the welding speed, The stress concentration at the weld toe is reduced and the residual stress is reduced, but the work management by the toe radius and flank angle, which affects the fatigue strength of the weld toe, and the work management by hardness and proof stress. It is also considered effective to improve the fatigue strength of the weld toe in the fillet welded joint.

1 Base material 2 Other base material 3 Welding material

Claims (2)

In a fillet welded joint formed by welding the other base material to one base material surface,
Using a welding material whose strength ratio to the base material does not exceed 1,
A fillet welded joint, which is limited in heat input during welding.   The fillet welded joint according to claim 1, wherein a weld material having a strength ratio with respect to the base material of 0.8 or less is used.

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