KR101568542B1 - Welding Method - Google Patents

Abstract

The present invention relates to a welding method capable of improving the toughness of a base material without increasing the amount of heat input. The welding method includes a contact surface formed at a central portion for contacting two members, and a groove including a step surface formed between the outer surface of the member and the contact surface There is provided a welding method in which a welding structure formed by opposing two formed members is welded and molten metal is melted in the groove to directly weld the two members.

Description

{Welding Method}

The present invention relates to a welding method and relates to a welding method with improved impact toughness of a heat affected zone (HAZ).

1 (a) and 1 (b) show a welded portion welded by a conventional welding structure and a welding method. The two members 1 comprise a groove 5 formed by the outer surface 2 and the contact surface 4 and the inclined surface 3 between the outer surface 2 and the contact surface 4 and in many cases the groove 5 Is formed between the contact surface (4) and the upper surface and between the contact surface (4) and the lower surface. As the welding metal 10 is melted and supplied to the groove 5 formed in the two members 1, the member 1 is formed with the heat-affected portion 11 (HAZ) due to the melting of the welding metal, The heat affected zone 11 is known as a weak portion of the welded portion.

2 and 3 are photographs showing the results of impact test of the heat affected zone. As shown in FIGS. 2 and 3, when the thermal impact test is performed, the crack proceeds along the coarse austenite boundary of the fusion line of the heat affected zone.

Particularly, there is a problem that cracks do not propagate into the weld metal and propagate to the boundary of the austenite 12 in the nearby fusion line even if the notch is formed in the weld metal without being formed in the heat affected portion and then tested (b)).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a welding method capable of improving the toughness of a base material without increasing the amount of heat input.

In order to achieve the above object, the present invention provides a welding method as described below.

The present invention relates to a welding method for welding a welding structure formed by abutting two members formed with grooves including a contact surface formed at a central portion and a step surface formed between an outer surface of the member and a contact surface, A welding method is provided for melting molten metal to directly weld two members.

In this case, the stepped surface may alternatively include a plurality of first surfaces having an inclination angle with respect to the outer surface, and a plurality of second surfaces having an inclination angle with respect to the first surface.

In addition, the first surface may be orthogonal to the outer surface, the second surface may be orthogonal to the first surface, and the first surface and the second surface may have the same length.

In addition, the height of each end in the stepped surface may be 3 mm or more and less than 6 mm, and the width of each end in the stepped surface may be 2 mm or more and less than 6 mm.

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According to the present invention, it is possible to provide a welding method capable of improving the toughness of a base material without increasing the amount of heat input. In addition, when the above-described structure is filled with the welding metal, the austenite boundary is staggered to form a welded portion where crack propagation is not easy.

Fig. 1 (a) is a view showing a conventional welding structure, and Fig. 1 (b) is a cross-sectional view in which a welding metal is filled in the welding structure of Fig.
Figs. 2 and 3 are cross-sectional photographs in which a crack propagated when a conventional weld structure was subjected to an impact test.
Fig. 4 (a) is a sectional view showing the welding structure of the present invention, and Fig. 4 (b) is a sectional view of a welded portion in which the welding metal is filled in the welding structure of the present invention.
5 (a) is a schematic view of a crack propagating after welding with a conventional welding structure, and Fig. 5 (b) is a schematic view of a welding structure And a crack is propagated after welding.
6 is a diagram showing the impact energy according to the width A and the height B of the step portion in the structure of the present invention.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

Conventionally, in order to improve the impact toughness of the welded portion, the bead width is widened to increase the distance from the weld metal to the fusion line, thereby improving the impact energy or improving the toughness by delaying the propagation of the crack by crushing the grainboundary Has been proposed. However, when the bead width is widened, there is a limit to the increase of the heat input amount, and there is a problem that the technique of crushing the grain boundary is not applicable because the technology development is not enough yet.

The present invention improves the impact toughness of the welded portion by changing the welded structure without increasing the bead width. Fig. 4 (a) is a sectional view showing the welded structure of the present invention, Sectional view of a welded portion filled with a weld metal.

As shown in Fig. 4 (a), in the welding structure of the present invention, two members 1, which are base metals, are disposed in contact with each other, and a groove 5 is formed in the member 1. [ The groove 5 has a welded structure including a contact surface 4 formed at the center to contact the two members and a stepped surface 20 formed between the outer surface 2 of the member and the contact surface 4 .

The stepped surface 20 alternately includes a plurality of first surfaces 21 having an inclination angle with respect to the outer surface 2 and a plurality of second surfaces 22 having an inclination angle with respect to the first surface 21 . The first inclination angle of the first surface 21 with respect to the outer surface 2 and the second inclination angle of the second surface 22 with respect to the first surface 21 are 180 degrees, ) Or the second surface 22 are repeatedly implemented at the same angle.

The first surface 21 and the second surface 22 are alternately arranged in one groove 5 more than once so that the step surface 20 has at least two stages.

As shown in FIG. 4 (a), the grooves 5 are respectively disposed on the upper and lower surfaces, and each of the grooves 5 has at least two stepped surfaces 20, The boundary surface of the weld metal 10 has a zigzag shape when the weld metal 10 is filled in the groove 5 as shown in Fig. 4 (b).

When the weld metal 10 is charged, the stepped surface 20 (see FIG. 4 (a)) of the welded structure is partially melted by the weld metal 10, Can be formed in a zigzag manner. At this time, the austenite crystals grown in the heat affected zone 11 grow in opposite directions and meet with each other, so that the grain growth does not have a constant directionality.

As described above, the cracks are transmitted along the austenite interface of the heat-affected zone. In the case of the welded structure of the present invention, since the austenite interface does not have a certain direction, it is difficult to transfer along the austenite interface, The impact toughness can be increased.

5 (a) is a schematic view showing a state where a crack is propagated after welding with a conventional welding structure, and Fig. 5 (b) A crack is propagated after welding with a welded structure of FIG.

As shown in FIG. 5 (a), when the inclined plane 3 is formed as shown in FIG. 1, the austenite 12 grown in the heat affected zone grows in a certain direction, and the interface is formed so as to be close to a straight line. However, in the case of the present invention, the austenite 12 grown in the heat affected zone by the stepped surface 20 does not have a constant directional orientation due to mutual interference, and accordingly, it is confirmed that crack propagation is difficult .

6 is a graph showing the impact energy according to the width A and the height B of the step portion in the structure of the present invention.

As shown in FIG. 6, the height of each end of the stepped surface 20 is less than 3 mm and less than 6 mm, and the impact toughness is improved when the width of each end of the stepped surface is less than 2 mm and less than 6 mm.

As the width A of the second surface 22 becomes longer, the bead width increases and the impact value increases, and the amount of heat input increases. When the width exceeds 6 mm, the performance is deteriorated sensitively . In addition, in the case of having a width of 2 mm or less, the shape is not maintained by the welding metal at the time of welding, and the heat affected portion also has no influence on the austenite growth.

Table 1 shows an embodiment of the structure according to the present invention.

As shown in Table 1, an experiment was conducted using a comparative example in which the stepped surface 20 was not formed, and an experiment was performed in which the stepped surface 20 was formed.

The thickness of the sheet material, that is, the member 1 was experimentally constant at 19 mm, and the height B of the first surface 21, the width A of the second surface 22, ) And the second surface 22 were varied while changing the second inclination angle &thetas;

As shown in Table 1, in the case of the comparative example, the inclination angle was 30 degrees, and the impact energy was 68J. However, in Example 1, the width and height of the first surface 21 and the second surface 22 were the same , An impact energy value of 96 J corresponding to about 1.5 times of the comparative example was obtained.

On the other hand, it can be confirmed that the second inclination angle? Formed by the first surface 21 and the second surface 22 is the most preferable when the first and second surfaces 21 and 22 are orthogonal as shown in the first and sixth embodiments. In the case of exceeding 12 mm, welding was not carried out and the impact energy could not be measured.

As can be seen in Examples 1, 4 and 5 and Examples 1, 2 and 3, when the width A and the height B of the first surface 21 and the second surface 22 are the same, And as shown in Examples 1 and 7, the impact energy can be improved when the thickness is approximately 15 to 25% of the thickness of the member.

1: member 2: outer face
4: contact surface 5: groove
20: step face 21: first face
22: second side

Claims (8)

There is provided a welding method for welding a welding structure formed by abutting two grooved members including a contact surface formed at a central portion and a step surface formed between an outer surface of the member and a contact surface,
And melting the molten metal in the groove to directly weld the two members.
The method according to claim 1,
Wherein the stepped surface alternately comprises a plurality of first surfaces having a first inclination angle with respect to the outer surface and a plurality of second surfaces having a second inclination angle with respect to the first surface.
3. The method of claim 2,
Wherein the first surface is orthogonal to the outer surface,
And the second surface is orthogonal to the first surface.
The method of claim 3,
Wherein the first surface and the second surface have the same length.
The method according to claim 1,
The height of each end on the step face is 3 mm or more and less than 6 mm,
Wherein a width of each end on the step face is less than 2 mm and less than 6 mm.
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