JPS5951388B2 - Method for manufacturing welded joints with non-welded parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a welded joint having a non-welded part, and particularly to a method for manufacturing a welded joint having a non-welded part, and in particular, a method for manufacturing a welded joint having a non-welded part with improved strength against fatigue fracture and brittle fracture from the tip of the non-welded part. The present invention relates to a method for manufacturing a welded joint.

Note that in this invention, a joint means a part where members are joined.

This invention can improve the strength against fatigue fracture and brittle fracture, and the strength against fatigue fracture will be explained below as an example.

In general, welded joints with non-welded parts, such as cross joints and T-joints, which are formed by joining the side surface of one workpiece to the end face of another workpiece, are the most frequently used joints due to their simplicity. However, it is known that its fatigue strength is significantly lower than that of the smooth base material, which limits its use in important structures subject to repeated loads.

FIG. 1I is a front view showing a cross joint as a typical example of welded joints having non-welded parts, in which 1 and 1' are the materials to be welded, 2 is the weld metal, 3 is the non-welded part, 4 indicates a fatigue crack generated from the tip 5 of the unwelded portion, and the arrow indicates the direction of repeated loading. The reason why the fatigue strength of welded joints having unwelded parts is low has been investigated using fracture mechanics. FIG. 11 is a partial cross-sectional view enlarged around the area marked with a broken line in FIG. 1I, and as shown in FIG. The main cause is said to be the large stress concentration caused by the sharp notches. Therefore, the conventional method for improving the fatigue strength of such welded joints has been to create a large groove in the joint and create a welded joint with no unwelded parts and completely molten S. However, even if this method could be adopted, it had drawbacks such as inevitably doubling the amount of weld metal and causing large welding distortion. In order to solve the above-mentioned drawbacks of the conventional method, this invention welds the materials to be welded together while applying internal pressure with gas to the unwelded portion between the materials to be welded, As shown in Fig. 2, an attempt is made to ensure an appropriate radius of the recess in the weld metal at the tip 5 of the unwelded part, reduce stress concentration on the root part, and improve the fatigue strength of the welded joint having the unwelded part. It is something to do.

Note that FIG. 2 is a partial sectional view corresponding to FIG. 1, and is a diagram for explaining the present invention.

FIG. 3 is a perspective view illustrating one embodiment of the method of the present invention.

1 is a material to be welded, which is installed with a space of 3 mm above the material to be welded 1'.

Between the materials to be welded 1 and 1', there is an appropriate spacer piece (3 mm in height).
(not shown) are placed. Reference numeral 3 denotes a portion that is not welded, that is, a non-welded portion, and a movable gas shield member 6 is placed except for an open portion 8 into which gas 7 is sent to surround this portion.

7 is a gas that applies internal pressure to the non-welded part 3 so that the weld metal does not hang into the non-welded part 3 during welding, and is an inert gas such as argon Ar or helium He, CO, gas, or CO.

Gas and 0. It is a mixed gas of two or three gases and an inert gas. 11 is a welding torch.

The table below shows examples of single gases or gas mixtures used and their ratios.

In the gas (f), the ratio of Ar gas and CO2 gas may be freely changed. During welding, the unwelded part 3 between the welded material 1 and the welded material 1' is surrounded by a gas shield member 6, and the gas 7 is fed into the unwelded part 3 through the open part 8. A slight internal pressure of about 0.02 atm higher than atmospheric pressure, that is, about 1.02 atm when atmospheric pressure is 1 atm, is applied.

Next, welding is performed, and as welding progresses, welding is performed while moving the gas shield member 6 at the part to be welded. At this time, since internal pressure is applied within the non-welded portion 3, when the gas shield member 6 is moved, the internal gas blows out from the moved portion. Therefore, when welding is performed on the moved part, the weld metal 2 does not hang down to the unwelded part 3, and a groove-shaped depression 9 is formed in the weld metal at the tip of the unwelded part (unwelded part). As a result, at the boundary between the weld metal and the unwelded area, a depression 9 is formed, the cross-sectional shape of which is a truncated circle having an arc with an appropriate radius, and this radius (hereinafter referred to as <the radius of the depression) is 0. The thickness is preferably 5 mm or more, preferably in the range of 1.0 mm to 2.0 mm. If the concave radius is smaller than 0.5 mm, it will not be possible to reduce the stress concentration at the weld root, and if the concave radius is too large, weld metal will increase and the unwelded area will increase unnecessarily. become. A fatigue test was conducted to demonstrate the effectiveness of a welded joint with a non-welded portion manufactured by the method of the present invention.

FIG. 4 is an S-N diagram showing the results of the fatigue test, in which the horizontal axis shows the number of repetitions N, and the vertical axis shows the stress amplitude S on a logarithmic scale. The test piece shape was a cross simple fillet joint shown in FIG. 1, and the test was performed using a oscillating tensile load. a in the diagram
is an S-N diagram of a welded joint with a non-welded part welded using the conventional covered arc welding method, and b is an S-N diagram of a welded joint with a non-welded part manufactured by the method of the present invention for the same test piece. Fig. 2 shows an S-N diagram for a welded joint having a welded joint. In the figure, the fatigue limit of a normal cruciform fillet joint is extremely small at approximately 3.2 kg/1 due to the large stress concentration at the tip of the unwelded part, whereas the fatigue limit of b using the method of this invention is approximately This has doubled to 6 kg/1, and the effect of the method of this invention is remarkable. In addition, in this demonstration test, if the fatigue strength at the root part is improved, fatigue failure from the fillet gong end {number 10 in Figure 1} may occur before fatigue failure from the root part. , to prevent that,
After polishing the ends of the fillet gongs in both A and B, a fatigue test was conducted. As explained above, in this invention, the materials to be welded are welded while applying internal pressure with gas to the portions between the materials to be welded that are not welded, so that welding does not occur after welding. A depression is formed in the weld metal at the tip of the part where the welding is not performed.

Therefore, stress concentration on the root portion can be reduced, and the fatigue strength of a welded joint having an unwelded portion can be improved.
It goes without saying that the strength against brittle fracture is also improved for the same reason as the above-mentioned improvement in fatigue strength. Furthermore, a fully penetrated welded joint with no unwelded areas has the drawbacks of doubling the amount of weld metal and generating large welding distortions, but the method of the present invention does not have such problems and the degree of such problems is small. It is something that decreases.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a cross joint, which is a typical example of a welded joint having a non-welded part, and FIG. 11 is a partial cross-sectional view enlarged around the area marked with a broken line in FIG. FIG. 2 is a partial sectional view corresponding to FIG. 1 11 illustrating the present invention, and FIG. 3 is a perspective view illustrating one embodiment of the method of the present invention.
FIG. 4 is an SN (stress amplitude-repetition number) diagram showing the effects of the present invention. In the figure, 1 and 1'' are the materials to be welded, 2 is the weld metal, 3 is the unwelded part, 5 is the tip of the unwelded part, 6 is the gas shield member, 7 is the gas, 8 is the open part, and 9 is the weld metal. The recess 11 is a welding torch.

Claims (1)

[Claims] 1. A method for manufacturing a welded joint, such as a cruciform joint or a T-joint, in which the side surface of one workpiece is joined to the end face of the other workpiece, and has a non-welded part. A movable gas shield member is placed at a welding corner other than one open portion of the non-welded portion formed in the interposed space, and gas is pressurized from the open portion to weld the welded corner. A method for manufacturing a welded joint having a non-welded portion, characterized in that a cross-sectional shape is truncated and a concave groove-like depression is formed at a boundary portion of the weld metal with the non-welded portion. 2 Claim 1 using an inert gas as the gas
A method for manufacturing a welded joint having a non-welded portion as described in 1. 3. A method for manufacturing a welded joint having a non-welded portion according to claim 1, wherein CO_2 gas is used as the gas. 4. The method for manufacturing a welded joint having a non-welded portion according to claim 1, using a mixture of at least two of CO_2 gas, O_2 gas, and an inert gas as the gas.