KR101639905B1 - Welding member having excellent welded portion fatigue characteristic and method for manufacturing the same - Google Patents

Abstract

A welded member excellent in fatigue characteristics of a welded portion and a method for manufacturing the same. According to an aspect of the present invention, A second member stacked on the first member so as to be at least partially overlapped with the first member; And a weld metal portion formed by lap-arc welding of the first member and the second member, wherein the toe angle of the weld metal portion is 35 DEG or less (excluding 0 DEG).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding member having excellent fatigue characteristics,

The present invention relates to a welding member excellent in fatigue characteristics of a weld zone and a manufacturing method thereof.

Recently, in the automobile industry, due to the global warming problem and the fuel economy regulation and the collision safety policy, the strengthening and lighter weight of the automobile body and its parts are emerging as a big issue. According to this trend, high-strength hot-rolled steels are also being applied to chassis parts of automobiles. Such high-strength hot-rolled steels are generally joined by arc welding and used as chassis parts. However, at this time, the weld metal portion formed by arc welding acts as a repetitive fatigue stress concentration portion (notch effect) and becomes a starting point of fracture, resulting in deterioration of durability of the chassis parts. Therefore, .

In this connection, Patent Document 1 discloses a technology for improving the fatigue characteristic by applying compression stress by forming a plastic deformation region by continuously blowing an end portion of a weld bead with a chipper (a striking pin) Discloses a technique for improving fatigue characteristics by re-melting an end of a weld bead through a post-plasma heat source. However, since these processes require additional processes after welding, there is an inevitable increase in process time and cost.

Japanese Patent Application Laid-Open No. 2014-014831 Japanese Patent Application Laid-Open No. 2014-004609

An object of the present invention is to provide a welding member excellent in fatigue characteristics of a welded portion and a method of manufacturing the same.

The object of the present invention is not limited to the above description. Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

According to an aspect of the present invention, A second member stacked on the first member so as to be at least partially overlapped with the first member; And a weld metal portion formed by lap-arc welding of the first member and the second member, wherein the toe angle of the weld metal portion is 35 DEG or less (excluding 0 DEG).

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: preparing a first member and a second member; Laminating at least a portion of the second member on the first member so as to form a weld line; (MIG) welding while providing a protective gas along the formed welding line, wherein the distance between the tip of the welding wire and the welding line is 1.5 to 2.0 mm, the torch angle is 35 to 60 mm, 45 °, push angle: 5 to 25 °, welding current: 82t to 90t (here, welding current is A (ampere) and t is thickness of second member (mm)) And a welding method for welding a workpiece.

The welding member according to the present invention has an advantage that the fatigue characteristic is very excellent.

The method of manufacturing a welding member according to the present invention is advantageous in that the process time and cost are reduced since no additional process is required after welding.

1 is a conceptual diagram for explaining the toe angle of the weld metal part.
2 is a conceptual diagram for explaining the distance between the tip of the welding wire and the welding line.
3 is a conceptual diagram for explaining the torch angle.
4 is a conceptual diagram for explaining the push angle.
5 is a photograph showing a cross section perpendicular to the welding line of the welding member manufactured according to the embodiment of the present invention.
Fig. 6 is a photograph showing a fracture position of a welded member manufactured according to Inventive Example 2 of the present invention after a tensile test at room temperature. Fig.

Hereinafter, a welding member having an excellent fatigue characteristic of a welded portion as an aspect of the present invention will be described in detail.

The welding member of the present invention comprises: a first member; A second member stacked on the first member so as to be at least partially overlapped with the first member; And a weld metal portion formed by lap-arc welding of the first member and the second member.

In the present invention, the kind, physical properties and thickness of the first member and the second member are not particularly limited, and the first member and the second member may have the same kind, physical property and thickness, The present invention can be applied even when it has physical properties and thickness. However, in order to suitably apply the welding member to chassis parts of an automobile, it is preferable that the first member and the second member are hot-rolled steel sheets having a tensile strength of 780 MPa or more and a thickness of 6 mm or less.

The method of increasing the fatigue characteristics of the welded member can be roughly divided into a method using residual stress and a method of controlling bead shape. According to the present invention, it is an object of the present invention to improve the fatigue characteristics of a welded member by controlling a bead shape. To this end, the toe angle of the welded metal portion is set to 35 ° or less (excluding 0 °) Is controlled to be 25 DEG or less (excluding 0 DEG), more preferably 20 DEG or less (except 0 DEG). Herein, the toe angle refers to a contact angle at which the boundary between the first member and the second member and the weld metal portion is defined as a weld toe at a cross section perpendicular to the weld line, And the angle formed by the tangent of the boundary line of the second member and the bead curvature portion closest to the welding toe of the weld metal portion. 1 is a conceptual diagram for explaining the toe angle of the weld metal portion for the sake of understanding.

Meanwhile, by controlling the toe angle of the weld metal portion as described above, it is possible to improve the fatigue characteristic of the weld portion. However, in order to maximize the effect, it is more preferable to control the penetration depth of the weld metal portion appropriately. According to the example, it is preferable to control the penetration depth of the weld metal portion to 20% or more of the thickness of the second member, more preferably 30% or more. If the penetration depth of the weld metal portion is insufficient, there is a fear that the weld metal portion may be broken starting from the bead route due to the repeated fatigue load.

According to one embodiment of the present invention, the welded member according to the present invention has a fatigue life of 2,000,000 cycles at a fatigue strength of 250 MPa or more, a repetitive fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1 and frequency, And the fatigue characteristics of the welded part are excellent. Here, the fatigue strength (or fatigue limit) is defined as a value obtained by dividing the maximum fatigue load value at which the fatigue life exceeds 2,000,000 cycles divided by the cross-sectional area of the member.

According to an embodiment of the present invention, the welding member according to the present invention is advantageous in that the tensile strength of the weld metal portion is 100% or more of the tensile strength of the first member and the second member, and the strength of the weld metal portion is extremely excellent. In this case, the term "100% or more" means that the tensile strength of the weld metal portion is higher than the tensile strength of the first member and the tensile strength of the second member.

The welding member described above can be manufactured by various methods, and the manufacturing method thereof is not particularly limited. However, as one embodiment thereof, it can be produced by the following method.

Hereinafter, a method of manufacturing a welded member having excellent fatigue characteristics of welded portions according to another aspect of the present invention will be described in detail.

First, after preparing the first member and the second member, a second member is laminated on the first member so that at least a part thereof overlaps to form a welding line. Here, the welding line means the end portion of the second member among the regions where the first member and the second member overlap.

Then, MIG (Metal Inert Gas) welding is performed while providing a protective gas along the formed welding line. The reason why the welding method is limited to MIG welding as described above in the present invention is that since arc length and width are relatively large, spreadability and wettability of the molten pool during welding are excellent and the strength of the weld metal portion is excellent .

At this time, in order to obtain the desired bead shape, it is preferable to control the distance between the tip of the welding wire and the welding line, the torch angle and the push angle during MIG welding as follows.

Distance between the tip of the welding wire and the welding line: 1.5 to 2.0 mm

Fig. 2 is a conceptual view for explaining the distance between the tip of the welding wire and the welding line, and shows the position of the tip of the welding wire at the time of welding. The distance between the tip of the welding wire and the welding line is closely related to the toe angle of the weld metal portion. If the distance is less than 1.5 mm, the flow characteristic of the welding solution to the first member is limited, On the other hand, when the thickness exceeds 2.0 mm, there is a problem that the strength of the bead root portion is lowered due to insufficient melting and deposition of the second member.

Torch angle: 35 to 45 °

2 is a conceptual diagram for explaining a torch angle. The torch angle is also closely related to the toe angle of the weld metal. If the torch angle is less than 35, the bead spreadability, that is, the reduction effect of the toe angle is reduced. On the other hand, There is a problem that the heat pinch force is reduced and the penetration of the weld metal is reduced, so that the strength of the bead root portion is lowered.

Push angle: 5 to 25 °

3 is a conceptual diagram for explaining the push angle. The push angle is also closely related to the toe angle of the welded metal part like the torch angle. If the push angle is less than 5 degrees, the bead spreadability, that is, the reduction effect of the toe angle is reduced. On the other hand, The arc heat pinch force per area is reduced, so that the penetration of the weld metal is reduced, and the strength of the bead root portion is lowered.

Welding current: 82t to 90t (where the unit of welding current is A (ampere) and t is the thickness of the second member in mm)

The welding current is closely related to the toe angle and penetration depth of the weld metal portion. If the welding current is too low, the strength of the weld portion may be lowered. Therefore, the welding current is preferably 82t or more. However, when the welding current is excessively high, the fatigue characteristics may be deteriorated due to the decrease in the hardenability of the welded portion due to the heat input and the formation of the convex beads due to excessive wear. Therefore, the welding current is preferably 90t or less, and more preferably 88t or less.

On the other hand, as a means for maximizing the effect of improving the fatigue characteristics of the welded part, the kind of the protective gas, the diameter of the welding wire, the protrusion length of the welding wire, and the welding speed at the time of welding the arc (GMA, Gas Metal Arc) Can be controlled.

Type of protective gas: 100% argon (Ar) gas

In general, the protective gas used for arc welding includes argon (Ar) gas, argon (Ar) and oxygen (O ₂ ) mixed gas, argon (Ar) and carbon dioxide (CO ₂ ) mixed gas. In the present invention, it is preferable to use 100% argon (Ar) gas, which restricts the heat shrinkage of the arc which may occur when using a mixed gas with oxygen (O ₂ ) or carbon dioxide (CO ₂ ) This is because not only the bead spreadability and wettability can be maximized, but also oxidation of the curing elements in the steel is effectively suppressed, which is advantageous in securing the strength of the weld metal part.

Diameter of welding wire (Φ): 1.0 to 1.2 mm

The diameter of the welding wire is closely related to the stability of the arc. If it is less than 1.0 mm or exceeds 1.2 mm, it may be difficult to derive the correct heat input to the plate thickness.

Extrusion length of welding wire: 12 ~ 15mm

The protruding length of the welding wire is closely related to the resistance heat and the melting rate of the wire. If it is less than 12 mm, the spatter is likely to adhere to the nozzle, thereby deteriorating the appearance of the weld metal portion. On the other hand, , There is a fear that the protective effect by the protective gas is lowered and the arc becomes unstable.

Welding speed: 0.6 ~ 0.8m / min

The welding speed is closely related to the welding amount and the depth of penetration of the weld metal. If the welding speed is too slow, the fatigue characteristics are degraded by the decrease of the hardenability of the welded portion due to the heat input and the formation of the convex bead There is a concern. Therefore, the welding speed is preferably 0.6 m / min or more, and more preferably 0.7 m / min or more. However, when the welding speed is excessively high, the strength and fatigue characteristics of the welded portion may be deteriorated due to occurrence of bead undercut. Therefore, the welding speed is preferably 0.8 m / min or less.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate and specify the present invention and not to limit the scope of the present invention. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

( Example )

Eight pairs of FB780 steel plates (thickness: 3.4 mm), which are widely used as hot-rolled steel for automobiles, were prepared as welding base materials. Thereafter, a total of eight pairs of FB780 steel plates were laminated so as to partially overlap each other to form a welding line, and MIG welding was performed under the conditions shown in Table 1 below. On the other hand, at the time of MIG welding, the protective gas was 100% argon (Ar), the diameter of the welding wire was 1.2 mm, and the protruding length of the welding wire was 15 mm. The cross section perpendicular to the welding line of each of the manufactured welding members was observed, and it was shown in FIG. 5, and the tow angle was measured and shown in Table 1 below. In the following Table 1, the penetration depth means the penetration depth with respect to the thickness of the first member.

No. Welding condition Toe angle
(°) Penetration depth
(%) Remarks electric current
(A) speed
(m / min) Torch angle
(°) Push angle
(°) The tip of welding wire
Distance to welding line (mm) One 280 0.8 25 5 0 54 54 Comparative Example 1 2 280 0.8 35 5 0 43 42 Comparative Example 2 3 280 0.8 45 5 0 54 44 Comparative Example 3 4 280 0.8 35 25 0 42 34 Comparative Example 4 5 280 0.8 45 25 0 42 27 Comparative Example 5 6 280 0.8 45 25 2.0 20 36 Inventory 1 7 280 0.6 45 25 2.0 24 44 Inventory 2 8 300 0.8 45 25 2.0 35 37 Inventory 3

Table 1 shows the change of the toe angle according to the welding condition change. First, in Comparative Examples 1 to 3, when the push angle was fixed at 5 °, when the torch angle was increased from 25 ° to 35 °, the toe angle was reduced from 54 ° to 43 °, , The tow angle increases from 43 ° to 54 °. This is presumed to be due to the fact that the molten pool flow and deposition are relatively shifted toward the overlapping part upper plate (second member) side and can not flow to the lower plate (first member), resulting in a narrower bead width and an increased tow angle.

Next, when comparing the comparative examples 2 and 4 and the comparative examples 3 and 5, it can be seen that when the push angle is increased from 5 ° to 25 °, the toe angle decreases slightly with the torch angle being fixed.

Next, in consideration of the concept of controlling the molten pool flow and welding to the lower plate (first member) side relatively under the conditions of Comparative Example 5, which is the most improved condition among the Comparative Examples 1 to 5, Welding was performed at a distance of 2.0 mm from the welding line. Comparing Comparative Example 5 and Inventive Example 1, it can be seen that the tow angle is significantly reduced. On the other hand, Examples 2 and 3 are cases in which welding is performed by slightly changing the welding current or the welding speed.

Then, the fatigue characteristics of the welding members obtained according to Comparative Example 1 and Inventive Example 1 were evaluated. The results are shown in Table 2 below. The fatigue tests were carried out with a tensile fatigue R (minimum / maximum load ratio) = 0.1 and f (frequency) = 20Hz and rated up to 2,000,000 cycles.

Maximum load (kN) Fatigue life (cycles) Comparative Example 1 Inventory 1 8.0 2,000,000 2,000,000 8.5 1,257,617 2,000,000 9.0 369,197 2,000,000 9.5 330,195 2,000,000 10.0 282,479 2,000,000

Referring to Table 2, it can be seen that Inventive Example 1 has significantly improved weld fatigue characteristics compared to Comparative Example 1.

Thereafter, a test piece was prepared on the basis of the standard of JIS 13B with respect to the welding member obtained according to Inventive Example 2, and a room temperature tensile test was conducted.

Fig. 6 is a photograph showing a fracture position of a welded member manufactured according to Inventive Example 2 of the present invention after a tensile test at room temperature. Fig. 6, it can be confirmed that the tensile strength of the weld metal portion is 100% or more of the tensile strength of the base material portion in that first the fracture occurred in the base material portion (the first member or the second member) rather than the weld metal portion .

1: welding member
10: first member
20: second member
30: welded metal part
100: welding wire

Claims (9)

A first member;
A second member stacked on the first member so as to be at least partially overlapped with the first member; And
And a weld metal portion formed by lap-arc welding of the first member and the second member,
Wherein the toe angle of the weld metal portion is less than or equal to 35 ° (excluding 0 °), and the tensile strength of the weld metal portion is 100% or more of the first member and 100% or more of the tensile strength of the second member.
The method according to claim 1,
Wherein the penetration depth of the weld metal portion is 20% or more of the thickness of the first member.
The method according to claim 1,
Wherein the first member and the second member are hot-rolled steel sheets having a tensile strength of 780 MPa or more and a thickness of 6 mm or less.
delete The method according to claim 1,
Wherein the welded member has a fatigue strength of 250 MPa or more and a fatigue life of 2,000,000 cycles or more at a repetitive fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1).
Preparing a first member and a second member;
Laminating at least a portion of the second member on the first member so as to form a weld line;
And performing MIG (Metal Inert Gas) welding while providing a protective gas along the formed welding line,
In the MIG welding, the distance between the tip of the welding wire and the welding line is 1.5 to 2.0 mm, the torch angle is 35 to 45 degrees, the push angle is 5 to 25 degrees, the welding current is 82 to 90 t Is A (ampere), and t is the thickness (mm) of the second member).
The method according to claim 6,
Wherein the protective gas is 100% argon (Ar) gas.
The method according to claim 6,
Wherein the welding wire has a diameter of 1.0 to 1.2 mm and a protruding length of 12 to 15 mm.
The method according to claim 6,
Wherein the MIG welding is performed at a welding speed of 0.6 to 0.8 m / min.

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