JPH0819860A - Method for welding boxing welding joint of construction steel - Google Patents

Abstract

PURPOSE:To stably improve the fatigue strength of a joint without requiring a special toe treatment in an improving means of the fatigue strength of the boxing welding joint. CONSTITUTION:In a method of welding a corner boxing welding part after fillet-welding a rib plate on a main plate, fillet welding is executed before the corner boxing welding part, after cooling to room temperature, then the corner boxing welding part is welded so that the length is made longer than (thickness of rib plate +2Xfillet weld length) by (2X fillet weld length). In such a way, the welding residual stress and the stress concentration are reduced and the fatigue strength of the joint are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method for improving the fatigue strength of a turn-welded joint which is frequently used in the construction of ships, offshore structures, steel towers and the like.

[0002]

2. Description of the Related Art Generally, the fatigue strength of a base material for structural steel plates increases as the strength of the base material increases, but the fatigue strength of welded joints (hereinafter referred to as joint fatigue strength) improves even when the strength of the base material increases. It was a popular theory not to do it. Therefore, the joint fatigue strength of structural high-strength steel is almost the same as that of low-strength steel, and for structures where fatigue fracture is a problem, even if high-strength steel is used, the design strength cannot be increased and the toe treatment A method of ensuring the joint fatigue strength of high-strength steel by an improvement treatment called as has been studied.

For example, as a method of smoothing the toe shape to reduce stress concentration at the toe where cracks occur, there is a method of increasing the toe radius by grinding the toe with a grinding tool such as a grinder. JP-A-2-152771 proposes a method of spraying high-pressure water mixed with abrasive grains. Some of the inventors of the present invention also proposed in JP-A-5-69128 an improvement in joint fatigue strength by grinding a specific position using a rotary cutter. Similarly, for the purpose of reducing stress concentration, a method of remelting the toe by a melting method such as TIG welding to make the toe shape smooth is proposed. For example, in Japanese Patent Publication No. 54-30386. In Japanese Patent Laid-Open No. 59-110490, TI
G arc is used as a heat source for melting.

Further, since tensile tough welding residual stress is generally present at the toe, the toe is hit by shot peening, hammer peening or the like for the purpose of reducing the welding residual stress, and compressive residual stress is applied to the toe. There is a method (for example, Japanese Patent Application Laid-Open No. 4-21717) of generating it. More recently, a welding wire that smoothes the toe shape and improves joint fatigue strength has also been used in CAMP-ISIJ, vol. 6
(1993).

[0005] The turning welding is, for example, a collection of papers of the Japan Shipbuilding Society,
No. 171, p. No. 623, it is a welding form used in the longitudinal rib material of a ship, and this weld toe has high welding residual stress and is increased to the yield strength of the structural steel used. In addition, since structural stress concentration due to the rib plate and local stress concentration at the turning weld toe become a large stress concentration due to weight, it is a joint with lower fatigue strength than the butt welded joint or the cross welded joint. A simple and effective measure for improving fatigue strength is desired.

[0006]

However, when considering a welded structure, all of the above-mentioned toe processing methods require enormous work. For example, in the method of mechanically grinding the toe, the worker holds the cutting tool and grinds it, so that the work efficiency is remarkably low and the processing welding length per working time is short. Furthermore, the degree of improvement in fatigue strength is not constant, but greatly depends on the position and degree of grinding. In the remelting method using a heat source such as TIG welding, the degree of fatigue strength improvement depends not only on the remelting position but also on the welding conditions such as heat input, and even when these are melted under certain conditions. Since the toe shape greatly varies depending on the flow state of metal, it is difficult to obtain a stable shape improving effect. In the method of reducing the residual welding stress, for example, shot peening cannot be applied to a large structure, and hammer peening has the same problem as the above-mentioned method by mechanical grinding. Further, the welding wire for smoothing the toe is not known to have the effect of improving the joint fatigue strength with respect to the price of the wire.

An object of the present invention is to improve fatigue strength of a turn-welded joint without requiring special toe treatment.
It is intended to stably improve joint fatigue strength.

[0008]

Means for Solving the Problems In order to solve the above problems, according to the present invention, during welding of a turn-welded joint, after performing corner fillet welding up to the front of a corner-turned welded part, the temperature is cooled to room temperature,
After that, by turning so that the welded part becomes longer,
This is aimed at improving joint fatigue strength. That is, the gist of the present invention is, in the method of welding the corner turning weld after fillet welding the rib plate to the main plate, in which the fillet welding is performed before the corner turning weld, and after cooling to room temperature, A welding method for a structural steel-screw-welded joint is characterized in that the corner-turn welding portion is welded to be longer than (rib plate thickness + 2 x fillet weld leg length) by (2 x fillet weld leg length) or more.

[0009]

The present invention will be described in detail below. The turn welding joint is a joint in which a rib plate 2 is welded to the main plate 1 on three sides or more by fillet welding, and FIG. 3 shows a plan view of a normal turn welding joint. In the normal welding method, as shown in this figure, the fillet welds 4A, 4A on both sides of the rib plate 2 are
Welding is continuously performed from B to the corner turning weld portion 3. Therefore, the tensile residual stress at the toe 5 of the corner turning welded portion 3 reaches the yield stress level due to the longitudinal contraction of the bead of the long fillet welded portion, which is one of the factors that greatly reduce the fatigue strength.

1 (a) to 1 (c) are plan views of a turn-welded joint showing the method of the present invention in the order of steps. According to the method of the present invention, first, fillet welding 6A up to the corner turning welding portion,
6B is performed (FIG. 1A). In this case, fillet welding on the opposite side of the rib plate 2 is also performed. Then, it is cooled to room temperature before performing the corner turning welding. The reason for cooling is that the fillet weld bead is sufficiently shrunk so as not to affect the residual stress at the toe of the later corner turning weld. At this time, due to the contraction of the bead of the fillet welding, the rib plate 2 also slightly contracts as shown by elastic deformation 7 in FIG. However, a high tensile welding residual stress occurs at the toe of this bead. After the fillet welding is cooled, the square-turn welding portion 10 is then welded (FIG. 1 (c)). This welding is performed linearly without turning. Further, the welding length 8 is made longer than (rib plate thickness + 2 x fillet weld leg length) (reference numeral 9) by (2 x leg length) or more, and welding is performed so as to sufficiently protrude from the corner turning portion. The reason why the welding length is increased by (2 × leg length) or more is to reduce the structural stress concentration in the vicinity of the corner turning welding.

Although FIG. 1 (c) shows a method of welding the corner turning welded portion 10 in two passes from both ends of the welding length toward the central portion, such welding method is used. It is not limited. That is, the corner turning weld is
Fig. 1 (c) when the welding work on the actual structure is limited
As shown in FIG. 2, if there is no particular limitation on the welding work, welding may be performed in one pass from either one direction as shown in FIG. The same effect can be obtained regardless of the direction.

FIG. 4 is a schematic diagram showing the flow of stress in the fillet weld, where (a) is the conventional welding method and (b) is the method of the present invention. (2 x leg length) If the welding length of the corner turning weld is increased, the welding start end of the straight bead will be located outside 45 ° from the rib plate corner, including the elliptical shape of the crater (Fig. 4 (b)). Therefore, the stress flowing from the main plate to the rib plate can be dispersed over the entire length of the bead. That is, it is possible to shift the position of local stress concentration at the toe of the welding start end and the position of structural stress concentration due to the rib plate (square turning welding central part), and it is possible to reduce stress concentration. The weld length here means the entire bead length including the welding start and end points.

The tensile welding residual stress at the toe of the corner turning welded portion in the present invention is smaller than that of the usual turning welding joint and is almost the same as that of the rib cross joint because only the lateral shrinkage of the linear bead acts. . The tensile residual stress due to the longitudinal shrinkage of the bead in the fillet welding performed previously is melted by the welding of the corner turning portion and disappears. Thus, the present invention is a method for improving the fatigue strength by reducing the welding residual stress at the toe to the extent of a rib cross joint and reducing the stress concentration.

The method of the present invention separates the fillet weld and the corner turn weld to reduce the welding residual stress and stress concentration, so that the chemical composition and mechanical properties of the structural steel (main plate and rib plate) are determined. Not affected. Although the chemical composition and mechanical properties affect the absolute value of the welding residual stress itself, the effect of reducing the welding residual stress can be similarly obtained.

Further, the welding residual stress varies depending on the thickness of the main plate of the structural steel, but in the case of the rib cross weld joint, if the same heat input and the same welding, the main plate thickness becomes smaller,
Since the welding residual stress becomes smaller than the yield stress and the difference from the welding residual stress of the turn-welded joint becomes large, the smaller the plate thickness, the more effective. Specifically, the welding heat input is Q [MJ
/ Mm], the present invention works more effectively as long as the main plate has a plate thickness of square root Q [mm] or less. With respect to the thickness of the rib plate, the thicker the plate has the same shape as that of the rib cross joint, the method of the present invention becomes ineffective. Specifically, when (rib plate thickness + 2 x fillet weld leg length) becomes 1/2 or more of the plate width of the main plate (in this case, whether or not it is defined as a turn weld joint), Since the welding residual stress does not reach the yield stress level, it is judged that the effect of the present invention is not exerted.

Further, the welding residual stress is affected by the welding method and heat input, but basically, the effect of reducing the welding residual stress by the method of the present invention is effective regardless of the welding method and heat input. Since the welding residual stress tends to decrease as the heat input increases, the difference between the welding residual stresses of the rib cross joint and the turn welding joint increases as the heat input increases. Therefore, in the present invention, for example, when the thickness of the main plate is t [mm], the heat input is t ² [MJ / m].
m] or more, and in such large heat input welding, the welding residual stress at the toe can be made smaller than in the conventional turn-welded joint, and the present invention works more effectively.

[0017]

[Example] 490 MPa with plate thicknesses of 25 mm and 15 mm
A turn-welded joint of class TMCP steel (shipping standard K36A) was produced by CO ₂ welding with a heat input of 17 kJ / cm by the welding method of the present invention and a conventional welding method. The welding wire used had the same strength level as the steel material. Figure 5
It is a figure showing the shape and dimensions of the test piece of the spiral welded joint, (a)
Is a plan view and (b) is a front view. The fatigue test was carried out at room temperature and in the atmosphere with axial load control, a stress ratio of 0.1 and a frequency of 10 Hz.

The test results are shown in Table 1. The fatigue strength in the table is shown by the number of repetitions at which the breaking life becomes 2 × 10 ⁶ . The turn-welded joint according to the method of the present invention shows a fatigue strength of about 1.3 to 1.6 times when compared with the fatigue strength of 2 × 10 ⁶ times as compared with the joint of the conventional welding method of the same plate thickness,
It is recognized that the fatigue strength is greatly improved. Further, when the welding length of the corner turning weld is short, fatigue cracks occur at the toes at the beginning and end of the corner turning welding, and significant fatigue strength improvement cannot be expected.

[0019]

[Table 1]

[0020]

As described above, the method of the present invention is
By separating fillet welding and corner turning welding and increasing the welding length of corner turning welding, it is possible to improve the fatigue strength of the turning welded joint over a wide range regardless of the type of steel material, welding material and welding method. . Therefore, when used in a structure in which fatigue fracture is a problem, it is possible to stably obtain high fatigue strength without requiring special consideration in terms of design and materials, and the effect is industrially great.

[Brief description of drawings]

FIG. 1 is a plan view of a welded joint showing a method of the present invention, where (a), (b), and (c) show a process sequence.

FIG. 2 is a plan view of a welded joint showing another method of the present invention different from FIG. 1 (c).

FIG. 3 is a plan view of a welded joint showing a normal turning welding method.

FIG. 4 is a schematic diagram of stress flow in (a) a conventional method and (b) the method of the present invention.

5A and 5B are a plan view and a front view, respectively, showing the shape and dimensions of a test piece of a turn-welded joint in Examples.

[Explanation of symbols]

 1 Main Plate 2 Rib Plate 3 Square Turn Weld 4A, 4B, 6A, 6B Fillet Weld 5 Toe of Square Turn Weld 7 Elastic Deformation 8 Weld Length 9 Rib Plate Thickness + 2 × Fillet Weld Leg Length 10 Square Turn Weld (In the present invention)

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area // B23K 31/00 F

Claims (1)

[Claims] 1. A method of welding a corner plate welded portion after a rib plate is fillet welded to a main plate. In the method, fillet welding is performed up to the front of the corner welded portion, and after cooling to room temperature, the corner welded portion is A welding method for a structural steel screw-welded joint, characterized in that welding is performed so as to be (2 × fillet weld leg length) or more longer than (rib plate thickness + 2 × fillet weld leg length).