KR101957494B1 - Welding method for zinc plated steel improving anti-fatigue property - Google Patents

Abstract

The present invention provides a method of manufacturing a galvanized steel sheet, comprising: disposing a first galvanized steel sheet as an upper plate and a second galvanized steel sheet as a lower plate; And welding an overlapping portion of the first galvanized steel sheet and the second galvanized steel sheet, the welding comprising: performing a first welding using a first welding torch; And performing a second welding on at least a portion of the area melted by the first welding torch using a second welding torch spaced apart and subsequent to the first welding torch, The maximum depth of the recess extending in the direction of the second zinc plated steel sheet with respect to the uppermost surface of the first zinc plating steel is set at the interface between the heat affected zone (HAZ) of the steel sheet and the welded part h) of the first zinc coated steel sheet is controlled to be 6% or less of the first zinc coated steel sheet thickness (t).

Description

TECHNICAL FIELD [0001] The present invention relates to a method of welding a galvanized steel sheet,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method, and more particularly, to a welding method of a galvanized steel sheet for improving an endothelial property.

As a part of improving the quality of automobiles, the application of zinc plated steel sheet having excellent anti-rusting properties is expanding. However, the galvanized steel plate has a low vaporization temperature and zinc vapor is generated during welding. The zinc vapor causes porosity failure, and prevents stable generation of arc, thereby generating a large amount of spatters.

In recent years, two galvanized steel sheets are separated by about 150 mu m to form a predetermined gap, and then welding is performed. At this time, a method in which the zinc vapor escapes through the gap is welded most industrially. However, there is a problem that it is very difficult to form and maintain an appropriate gap of the clearance.

DISCLOSURE Technical Problem The present invention has been made to solve various problems including the above problems, and it is an object of the present invention to provide a welding method and a welding method, And a method of welding a galvanized steel sheet which improves the endothelial property through the steel sheet. However, these problems are exemplary and do not limit the scope of the present invention.

According to one aspect of the present invention, there is provided a method of welding a galvanized steel sheet that improves endothelial characteristics. A method of welding a galvanized steel sheet to improve the endothelial property includes the steps of disposing a first galvanized steel sheet as an upper plate and a second galvanized steel sheet as a lower plate; And welding an overlapping portion of the first galvanized steel sheet and the second galvanized steel sheet, the welding comprising: performing a first welding using a first welding torch; And performing a second welding on at least a portion of the area melted by the first welding torch using a second welding torch spaced apart and subsequent to the first welding torch, The maximum depth of the recess extending in the direction of the second zinc plated steel sheet with respect to the uppermost surface of the first zinc plating steel is set at the interface between the heat affected zone (HAZ) of the steel sheet and the welded part h) can be controlled to be 6% or less of the first zinc plated steel sheet thickness (t).

A method of welding a galvanized steel sheet to improve the endothelial property, characterized in that the step of performing the first welding comprises the steps of: at least a part of the first galvanized steel sheet and the second galvanized steel sheet overlap each other, And performing the first welding torch with a predetermined distance (Contact Tip to Work Distance, CTWD), and the predetermined distance CTWD may range from 10 mm to 20 mm.

A method of welding a galvanized steel sheet to improve the endothelial property, the step of performing the second welding is a step of joining at least a part of the first galvanized steel sheet and the second galvanized steel sheet to each other, And performing the second welding torch with a predetermined distance (CTWD), wherein the predetermined distance CTWD may range from 10 mm to 20 mm.

Wherein the first welding torch or the second welding torch is welded in an inclined manner with a predetermined angle with reference to the upper surface of the second galvanized steel sheet, , And the predetermined angle may have a range of 35 [deg.] To 55 [deg.].

A method of welding a galvanized steel sheet to improve the endothelial property, wherein a progress angle of the first welding and the second welding is performed in an inclined manner with a predetermined angle with respect to an upper surface of the second base material And the predetermined angle may have a range of 65 to 85 degrees.

According to one embodiment of the present invention as described above, the process is simple, the generation of spatter generated at the welding is suppressed, the formation of defects of internal and external pores is prevented, A method of welding a galvanized steel sheet can be realized. Of course, the scope of the present invention is not limited by these effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view and a cross-sectional view of a base material schematically shown for explaining a welding method of a galvanized steel sheet for improving endothelial characteristics according to an embodiment of the present invention. FIG.
2 is a photograph of a welded portion of a sample produced by a method of welding a galvanized steel sheet for improving the endothelial property according to Comparative Examples and Examples of the present invention.
Fig. 3 is a photograph of the fracture surface of the samples prepared by the welding method of the zinc-plated steel sheet for improving the endothelial property according to the comparative examples and the examples of the present invention by the fatigue test.
FIG. 4 is a graph showing the results of analysis of fatigue characteristics according to respective welding conditions of samples prepared by a method of welding a galvanized steel sheet to improve endothelial characteristics according to Comparative Examples and Examples of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, for convenience of explanation, the components may be exaggerated or reduced in size.

Generally, when two or more galvanized steel sheets are welded, since the boiling point (906 ° C) of zinc plated on the steel plate is lower than the melting point of iron (1500 ° C), if the welding is performed, Zinc is first vaporized. As a result, the zinc vapor explodes instantaneously as the steel plate melts, generating spatters. In addition, a pit hole is formed on the inner pore and the surface on the welded part, resulting in a very poor weldability.

In order to solve this problem, the present invention can reduce the pores of the welded portion by using two welding torches and suppress the generation of spatters, thereby achieving high-quality welding, And a method of welding a galvanized steel sheet.

The method of welding a galvanized steel sheet to improve the endothelial property according to the present invention comprises the steps of disposing the first galvanized steel sheet 10 as an upper plate and the second galvanized steel sheet 20 as a lower plate, 10) and the second galvanized steel sheet 20 may be welded to each other. Wherein the welding step includes performing a first welding using a first welding torch and a second welding torch having a second welding torch spaced apart from and spaced apart from the first welding torch, And performing a second weld to at least a portion of the region. The first welding torch may be a DC MAG torch, and the second welding torch may be a pulse MAG torch.

Hereinafter, a method of welding a galvanized steel sheet to improve the endothelial property will be described in detail with reference to FIGS. 1 to 4. FIG.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view and a cross-sectional view of a base material schematically shown for explaining a welding method of a galvanized steel sheet for improving endothelial characteristics according to an embodiment of the present invention. FIG.

1 (a) is a cross-sectional view of a first zinc-plated steel sheet 10 and a second zinc-coated steel sheet 20 in order to weld the first zinc-plated steel sheet 10 and the second zinc- (20) are arranged so as to overlap each other. FIG. 1 (b) is a plan view of the first zinc-plated steel sheet 10 and the second zinc-coated steel sheet 20 shown in FIG. 1 (a) on the y-axis and the z-axis. 1 (c) is a plan view of the first galvanized steel sheet 10 and the second galvanized steel sheet 20 shown in FIG. 1 (a) as viewed along the y-axis and the x-axis plane.

1 (a), a method of welding a zinc-plated steel sheet to improve the endothelial property of the present invention is a method in which at least a part of the first zinc-coated steel sheet 10 and the second zinc- Are arranged so as to overlap each other. Here, the region where the first zinc-plated steel sheet 10 and the second zinc-coated steel sheet 20 overlap each other can be widened or narrowed depending on the welding conditions. Alternatively, the first zinc-plated steel sheet 10 and the second zinc-coated steel sheet 20 may be spaced apart from each other within a range in which they can be welded, or may be arranged so as to be in contact with each other.

Then, as shown in FIG. 1 (b), welding can be performed while the welding torch 30 approaches the region constituting the joint by a predetermined distance and then proceeds along the x-axis. Here, the welding direction may be performed not only in the x-axis direction but also in the direction opposite to the x-axis direction.

Meanwhile, the welding torch 30 may include a first welding torch 32 and a second welding torch 34, as shown in Fig. 1 (c). First, the first welding torch 32 is preceded along the x-axis, and the first welding is performed in an inclined shape with a predetermined angle in a direction perpendicular to the y-axis with reference to the upper surface of the second galvanized steel sheet 20 can do. At the same time, the second welding torch 34 is inclined at a predetermined angle in the direction perpendicular to the y-axis with respect to the upper surface of the second zinc plated steel sheet 20, like the first welding torch 32 A first welding can be performed. At this time, the first welding torch 32 and the second welding torch 34 can be separated from each other by a predetermined distance and can simultaneously perform the second welding.

Here, the first welding torch 32 is a DC MAG torch and the second welding torch 34 is a torch for a pulse MAG. The first welding torch 32 and the second welding torch 34 may be used for the same purpose and the first welding torch 32 may be a pulse MAG torch, The torch 34 may be used as a DC MAG torch. However, in this case, the internal pores are not controlled better than the configuration according to the present invention, and the welding characteristics are relatively poor.

As described above, when the first welding and the second welding are performed, the first zinc-plated steel sheet 10 (or the first zinc-coated steel sheet 10) is adhered to the interface between the heat affected zone (HAZ) The maximum depth of the recess extending in the direction of the second zinc plated steel sheet 20 (the -y axis direction shown in FIG. 2 (a)) (refer to FIG. 2 (a) The illustrated h) can be controlled to be about 6% or less of the thickness of the first galvanized steel sheet 10 (t shown in FIG. 2 (a)). If the maximum depth of the recess (h shown in (a) of FIG. 2) is more than 6%, it serves as a starting point of fatigue failure by the recess, .

Therefore, the maximum depth of the recess (h shown in FIG. 2A) should be controlled to 6% or less, and preferably close to 0%, that is, the uppermost surface of the first zinc plated steel sheet 10 Should be controlled to be as horizontal as possible. The present invention performs the first welding and the second welding at the same time so that the notch structure is not formed at the interface between the heat affected zone (HAZ) of the first zinc plated steel sheet 10 and the welded portion, The endothelial property can be improved.

Further, when performing the first welding and the second welding in the welding method of the zinc-plated steel sheet of the present invention, the following equations 1 and 2 can be satisfied. The reason why the following equations 1 and 2 should be satisfied will be described below.

(식 1)

(Equation 1)

(식 2)

(Equation 2)

(Where D is the spacing between the first welding torch 32 and the second welding torch 34, V _A is the wire feed rate of the first welding torch 32 and V _B is the second welding torch 34 ) Wire feed rate, and V _W is the velocity of the first and second welds)

First, the first welding is performed by arranging at least a part of the first zinc-plated steel sheet 10 and the second zinc-coated steel sheet 20 so as to overlap with each other, and the first zinc-coated steel sheet 10 and the second zinc- The first welding torch 32 may be spaced apart from the first welding torch 32 by a predetermined distance CTWD. The purpose of performing the first welding is to perform a function of melting a part of the region constituting the joint so as to be joined by the following second welding. A part of the first galvanized steel sheet 10 and the second galvanized steel sheet 20 are melted and the zinc vapor starts to be discharged. After the zinc vapor is discharged, the second welding is continuously performed.

Here, the predetermined distance may have a range of 10 mm to 20 mm. If the distance between the first welding torch 32 and the region constituting the joint is shorter than 10 mm, the distance between the first welding torch 32 and the second zinc coating steel sheet 20 Is very high and there is a possibility that the welded portion is damaged. On the other hand, when the distance between the first welding torch 32 and the region constituting the joint is longer than 20 mm, the distance between the first welding torch 32 and the second zinc plating steel plate 20 So that the welding failure may occur.

At this time, the first welding torch 32 can perform welding in an inclined form with a predetermined angle in the y-axis direction with reference to the upper surface of the second galvanized steel sheet 20 (on the z-axis basis). Here, the predetermined angle alpha may have a range of 35 DEG to 55 DEG. The predetermined angle? Can be understood as an angle of welding (hereinafter referred to as a welding angle). As the welding angle is lower, the discharge of the zinc vapor from the molten pool is facilitated. Therefore, if the welding angle exceeds 55 °, the probability of occurrence of spatter due to the zinc vapor increases relatively, which may cause welding failure. On the other hand, when the welding angle is too low, i.e., 35 DEG or less, it is difficult for the welding itself to proceed smoothly.

The second welding can be performed while the first welding is performed and the first welding torch 32 and the second welding torch 34 are kept at a predetermined distance from each other. Here, the interval D between the first welding torch 32 and the second welding torch 34 can be the first welding and the second welding while maintaining the range of 3 mm to 9 mm. If the interval D is smaller than 3 mm, the second welding is performed before the zinc vapor discharged from the first zinc-plated steel sheet 10 and the second zinc-coated steel sheet 20 melted by the first welding passes out So that the zinc vapor can not completely escape and is trapped, resulting in a large number of porosity defects. On the other hand, if the distance D is larger than 9 mm, the molten region is cooled, and the interaction with the molten portion due to the first welding is limited during the second welding, which may deteriorate the welding quality.

The step of performing the second welding may include disposing the second welding torch 34 at a predetermined distance CTWD in a region constituting a joint in which the first galvanized steel sheet 10 and the second galvanized steel sheet 20 are overlapped, . The purpose of performing the second welding is to perform the function of joining after the zinc vapor is discharged in the molten region by the preceding first welding.

Here, the predetermined distance CTWD may have a range of 10 mm to 20 mm. If the distance between the second welding torch 34 and the region constituting the joint is shorter than 10 mm, the distance between the first and second zinc-plated steel plates 10 and 20 Is very high and there is a possibility that the welded portion is damaged. On the other hand, when the distance between the second welding torch 34 and the region constituting the joint is longer than 20 mm, the distance between the second welding torch 34 and the second galvanized steel plate 20 is too long to be transmitted to the first galvanized steel sheet 10 and the second galvanized steel sheet 20 So that the welding failure may occur.

At this time, the second welding torch 34 can perform the welding in an inclined form with a predetermined angle alpha in the y-axis direction on the reference (z-axis) upper surface of the second galvanized steel plate 20. [ Here, the predetermined angle alpha may have a range of 35 DEG to 55 DEG. The predetermined angle? Can be understood as an angle of welding (hereinafter referred to as a welding angle). As the welding angle is lower, discharging of zinc vapor from the molten pool is facilitated. Therefore, if the welding angle exceeds 55 °, pore discharge due to zinc vapor may not be smooth and weld failure may occur. On the other hand, when the welding angle is too low, i.e., 35 DEG or less, it is difficult for the welding itself to proceed smoothly.

Also, as shown in Fig. 1 (c), the progress angle of the first welding and the second welding can be made to be inclined at a predetermined angle with respect to the upper surface of the second base material. Here, the progressing angle of the first welding and the second welding is such that the first welding torch 32 and the second welding torch 34 are positioned on the basis of the upper surface of the second zinc-coated steel plate 20 (on the x-axis basis) It is possible to perform welding with each predetermined angle. The predetermined angle means β and γ in FIG. 1 (c), and β and γ may have different angles, but the same angle may be applied to the region constituting the joint have. The predetermined angle shows good welding quality in an appropriate range (65?? 85, 65?? 85), and the angle determined by the predetermined angle? Shown in FIG. 1 (b) Can be changed and settled. If the traveling angle exceeds 85 DEG, welding failure may occur. On the other hand, if the traveling angle is too low, i.e., less than 65 DEG, the welding itself is difficult to proceed smoothly.

On the other hand, referring to Equation 2, it can be seen that the porosity is increased or decreased by the welding speed V _W , the wire feeding speed V _{A of} the first welding torch and the wire feeding speed V _B of the second welding torch, And shape may be changed. The smaller the porosity, the greater the tensile strength. Therefore, the porosity should be controlled. The porosity is influenced by the shape and behavior of the molten pool formed according to the feed rate of the welding wire, and the shape and behavior thereof can be optimized by appropriately adjusting the welding speed (V _W ). Therefore, in order to decrease the porosity, the welding speed (V _W ) should be controlled within a suitable range.

That is, the wire feed speed (V _A ) of the first welding torch and the wire feeding speed (V _B ) of the second welding torch should maintain a ratio within a certain range with the welding speed (V _W ). As a result of the experiment, it is found that the porosity can be kept to be the least when the formula 2 is satisfied, the welding characteristic is excellent, and the tensile strength and endothelial property can be improved. Hereinafter, the experimental examples are compared and described in detail.

Experimental examples for grasping the relevance of the endothelial property by the heat affected zone (HAZ) in the welding method of the galvanized steel sheet for improving the endothelial property will be described below. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and that the present invention is not limited to the following examples.

Table 1 shows a method of welding a galvanized steel sheet to improve the endothelial property according to an embodiment of the present invention. The prepared first galvanized steel sheet base material and second galvanized steel sheet base material are arranged so as to overlap each other. At this time, the first zinc-plated steel plate base material is disposed on the second zinc-coated steel plate base material so that the overlapping region overlaps by about 30 mm. Then, the results of simultaneous pulse MAG with the DC MAG and the trailing weld are shown.

On the other hand, in order to comparatively compare the degree of the endothelial property, the base material of the zinc-plated steel sheet and the same member as used in the above Experimental Example were bonded by a single welding method and tested in the same manner as in the above Experimental Example. Here, the DC MAG welding was performed on the zinc-coated steel plate base material as Comparative Example 1, and the pulse MAG welding was performed on the zinc-coated steel plate base material as Comparative Example 2, respectively.

As shown in Fig. 1 (b), the working angle in Table 1 can be understood as a predetermined angle?, And the traveling angle can be understood as predetermined angles? And? As shown in Fig. 1 (c) have. In Table 1, the distribution represented by the circle (●) represents an excellent value, and the distribution represented by an equilateral triangle (▲) represents a bad value.

2 is a photograph of a welded portion of a sample produced by a method of welding a galvanized steel sheet for improving the endothelial property according to Comparative Examples and Examples of the present invention.

2 (a) and 2 (b) are photographs showing a weld portion of a sample according to Comparative Example 1 of the present invention, and FIGS. 2 (c) and 2 1 is a photograph of a weld portion of a sample. FIG. 2B is an enlarged view of the area A in FIG. 2A. It can be seen that a notch is formed in the heat affected zone (HAZ) of the first zinc-plated steel plate base material and the interface part of the weld zone . 2 (d) is an enlarged view of the area A in FIG. 2 (c), in which no notch is formed in the heat affected zone (HAZ) of the first zinc-plated steel plate base material and the interface part of the weld zone .

In the case of the sample realized by the welding method of the zinc-plated steel sheet improving the endothelial characteristics according to the embodiment of the present invention, the discharge of the zinc vapor is easily controlled so that the notch structure at the interface between the heat- As a result.

Fig. 3 is a photograph of the fracture surface of the samples prepared by the welding method of the zinc-plated steel sheet for improving the endothelial property according to the comparative examples and the examples of the present invention by the fatigue test.

3 (a) is a photograph of a fracture surface of a welded portion of a sample according to Comparative Example 1 of the present invention, and FIG. 3 (b) is a photograph of a sample according to Experimental Example 1 of the present invention And the fracture surface of the welded portion is observed.

3 (a) shows that the fracture is formed by the notch structure in the heat affected zone (HAZ) of the first zinc-plated steel plate base material and the interface part of the welded part. On the other hand, FIG. 3 (b) shows that the fracture is formed at the interface between the heat affected zone (HAZ) of the first zinc-plated steel plate base material and the notch structure at a distance of a predetermined distance in the direction of the weld. In the fatigue test of the sample, the bending moment acts in addition to the uniaxial compressive stress and the tensile stress. The influence of the bending moment becomes large at a high stress ratio of about 50% or more of the tensile strength, and the influence of the bending moment is relatively small at a low stress ratio It is considered that the location of stress concentration varies.

FIG. 4 is a graph showing the results of analysis of fatigue characteristics according to respective welding conditions of samples prepared by a method of welding a galvanized steel sheet to improve endothelial characteristics according to Comparative Examples and Examples of the present invention.

Referring to FIG. 4, a graph comparing the fatigue life of welds according to the number of fatigue test cycles in Experimental Example 1, Comparative Example 1 and Comparative Example 2 of the present invention shows a single DC MAG welding and a pulse MAG welding As a result, the shape of the graph was not significantly different, and it was found to have an average value of 61 MPa and 92 MPa, respectively, over 10 ⁶ cycles. On the other hand, Experimental Example 1 was found to have an average value of 122 MPa in the same cycle number. This is because the first welding and the second welding are continuously performed while the respective torch intervals are kept constant as shown in the photographs shown in Figs. 2B and 3B, so that the heat of the first zinc- Since the notch structure is not formed at the interface between the affected part (HAZ) and the welded part, the position where the stress is concentrated is different from the case where the single MAG welding is performed, and the fatigue life is relatively large.

As described above, the present invention applies the leading DC MAG and the trailing MAG to the fillet welds arranged in an overlapping manner with no gaps. In this case, it is possible to prevent the occurrence of spatter by preceding the evaporation of zinc plated on the fillet and prevent the formation of defects in the inner and outer pores of the weld, and to perform high quality welding without a notch structure . That is, according to the present invention, the notch structure is not formed in the heat affected zone (HAZ) of the first galvanized steel sheet 10 and the welded part at the welded part by simultaneously performing the preceding DC MAG and the trailing pulse MAG, The position of concentration can be changed to improve the characteristics of the endothelium.

According to the present invention, in performing the preceding MAG process and the post-MAG process, it is possible to realize a high-quality welded portion by deriving and controlling the optimal process conditions with the parameters of Equations 1 and 2 below. In summary, the present invention is directed to a method of manufacturing a welded joint, comprising: performing a first weld using a first weld torch; and performing at least one of the regions melted by the first weld torch using a second weld torch spaced- To a method of welding a galvanized steel sheet that improves the endothelial property, including a step of performing a second welding on a part of the steel sheet.

In this case, the first welding torch is a DC MAG torch, and the second welding torch is a pulse MAG torch. The distance between the first welding torch and the second welding torch between the welding speed V _W , the wire feeding speed V _A of the first welding torch, the wire feeding speed V _{B of} the second welding torch, 1 and formula 2 are satisfied, the process is simple, the occurrence of spatter generated at the welding is suppressed, the formation of defects of inner and outer pores is prevented, and the characteristics of the inner film which can suppress the occurrence of notches and defects are improved A method of welding a galvanized steel sheet can be implemented.

(식 1)

(Equation 1)

(식 2)

(Equation 2)

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: First galvanized steel sheet
20: Second galvanized steel sheet
30: welding torch
32: First welding torch
34: Second welding torch

Claims (5)

Disposing a first galvanized steel sheet as an upper plate and a second galvanized steel sheet as a lower plate; And
And welding the overlapping portions of the first zinc plated steel sheet and the second zinc plated steel sheet,
Wherein the welding step comprises:
Performing a first welding using a first welding torch; And
And performing a second welding on at least a portion of the area melted by the first welding torch using a second welding torch spaced apart from and following the first welding torch,
The heat-affected zone (HAZ) of the first zinc-plated steel sheet and the interface portion of the welded portion are controlled to be horizontal with the uppermost surface of the first zinc-
Wherein the first welding torch or the second welding torch performs welding in an inclined shape with an angle ranging from 35 to 55 degrees with respect to the upper surface of the second galvanized steel sheet, 2 The welding angle of the welding torch is in the range of 65 to 85 degrees with respect to the upper surface of the second base material,
(METHOD OF WELDING ZINC PLATED STEEL SHEET). The method according to claim 1,
Wherein performing the first welding comprises:
Performing at least a part of the first zinc-plated steel sheet and the second zinc-coated steel sheet overlap each other, and separating the first welding torch by a predetermined distance CTWD in a region constituting the joint,
The predetermined distance CTWD is a distance of 10 mm to 20 mm,
(METHOD OF WELDING ZINC PLATED STEEL SHEET). The method according to claim 1,
Wherein performing the second welding comprises:
Performing at least a part of the first galvanized steel sheet and the second galvanized steel sheet to overlap each other and to separate the second welding torch by a predetermined distance CTWD in a region constituting the joint,
The predetermined distance CTWD is in the range of 10 mm to 20 mm,
(METHOD OF WELDING ZINC PLATED STEEL SHEET). delete delete

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