KR102020515B1 - Welded member having excellent welded portion porosity resistance and fatigue property and method of manufacturing the same - Google Patents

Abstract

Disclosed are a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics and a method of manufacturing the same. Plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an embodiment of the present invention is a welding metal part formed by overlapping arc welding the first member and the second member laminated so that a part of the first member is overlapped And a toe angle (θ) of the weld metal part is 45 ° or less, and the first member and the second member are plated steel sheets.

Description

Plated steel sheet welding member with excellent porosity resistance and fatigue characteristics of welded part and method for manufacturing thereof {WELDED MEMBER HAVING EXCELLENT WELDED PORTION POROSITY RESISTANCE AND FATIGUE PROPERTY AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a plated steel sheet welding member and a method for manufacturing the same, and more particularly, to a plated steel sheet welding member and a method for producing the same excellent weld resistance porosity and fatigue properties.

In the automotive sector, research on the weight reduction technology of car bodies and parts has emerged as a major issue due to the fuel economy regulation policy for environmental protection such as global warming. Chassis parts, which are important for automobile driving performance, also require high-strength steel applications for weight reduction. In order to achieve the part weight reduction, it is essential to increase the strength of the material, and it is important to guarantee the durability of parts made of high strength steel in an environment where repeated fatigue loads are applied.

In the case of arc welding, which is mainly used to secure strength when assembling automobile chassis parts, overlapping welding between parts is performed by welding of welding wires, so that the geometrical shape of the welding joint is inevitable. This acts as a cyclic fatigue stress concentration part (notch effect) and becomes a break point, resulting in a decrease in durability of the component, and thus has the limitation of losing the advantage of applying high strength steel.

As described above, in order to improve the fatigue characteristics of the welded part, it is important to reduce the angle of the end of the welded joint, that is, the stress concentration part, that is, the toe angle, and to control the material and stress of the toe part. It can be said.

In addition, as described above, the demand for anti-corrosion resistance for penetration corrosion is increasing due to the thinning of materials due to the high strength and light weight of parts, but the adoption of plated steel is increasing, but such as pits or blowholes during arc welding. Pore defect generation is sensitive, and there is a problem of lowering the strength and fatigue characteristics of the weld.

On the other hand, the application of Zn-Mg-Al-based high corrosion-resistant alloy plate steel, which has much higher corrosion resistance than the existing hot-dip galvanized steel sheet, has been proposed. As it is sensitive, it is necessary to develop a technology to suppress the occurrence of pore defects in the welded part.

Prior art 1 proposes to set the gap of overlapping joint to 0.2 ~ 1.5mm in order to suppress the occurrence of pore defects in the arc welded part of galvanized steel sheet. There is a limit that cannot be guaranteed.

In addition, in the prior document 2 to apply the three types of mixed gas containing CO ₂ and O ₂ mixed with Ar and low viscosity solid wire with limited content of Si and Mn in order to suppress the occurrence of pore defects in the arc welded portion of the galvanized steel sheet. In addition, it is proposed to float the arc position 1mm from the tip of the welded joint, but the restriction of the protective gas and the welding material is inevitable, and there is a burden of maintaining the arc position constant when applying the seal parts.

Japanese Patent Publication No. 2016-101593 Japanese Patent Publication No. 2015-167981

Embodiments of the present invention are to provide a plated steel sheet welding member having excellent weld resistance porosity and fatigue properties.

In addition, embodiments of the present invention is to provide a method for manufacturing a plated steel sheet welding member having excellent weld resistance porosity and fatigue properties.

The plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an embodiment of the present invention includes a weld metal formed by overlapping arc welding of a first member and a second member laminated so that a part of the first member overlaps the first member. And a toe angle (θ) of the weld metal portion is 45 degrees or less, and the first member and the second member are plated steel sheets.

In addition, according to an embodiment of the present invention, the plated steel sheet may be a Zn-Mg-Al-based alloy plating or galvanized hot rolled steel sheet.

In addition, according to an embodiment of the present invention, the hot rolled steel sheet may have a tensile strength of 590 MPa or more and a thickness of 6 mm or less.

In addition, according to an embodiment of the present invention, the hot rolled steel sheet may be 590FB steel.

Further, according to one embodiment of the present invention, the pore area ratio formed in the weld metal portion may be less than 0.5%.

In addition, according to an embodiment of the present invention, the fatigue strength of the weld metal part is 250 MPa or more, and may be a fatigue life of 2,000,000 cycles or more at a repeated fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1).

According to an embodiment of the present invention, a method of manufacturing a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics may include: overlapping arc welding of a first member and a second member laminated so as to partially overlap on the first member. And forming a weld metal part, wherein the first member and the second member are plated steel sheets, and in the arc welding, a welding current is supplied to a solid wire to generate an arc, and the welding current is first. The pulsed current is repeated by applying a peak and a second peak having a current value smaller than the first peak at one pulse period, and the weld molten metal stirring wave frequency defined by Equation (1) is repeated at 20 to 30 Hz. Perform.

1 / (T _H + T _L ) --- Equation (1)

Here, T _H is the period of the first peak, T _L is the period of the second peak.

In addition, according to an embodiment of the present invention, the solid wire may be supplied to the shield gas which is Ar gas containing 10 to 30% of CO ₂ gas.

In addition, according to an embodiment of the present invention, the welding current may be 200 to 300A.

Further, according to one embodiment of the present invention, in the arc welding, the solid wire diameter: 1.0 to 1.2 mm, torch angle: 30 to 45 °, push angle: 0 to 25 °, welding speed: 0.6 to 1.0 m / min Can be done with

In addition, according to an embodiment of the present invention, the first member and the second member may be a Zn-Mg-Al-based alloy plating or galvanized hot rolled steel sheet.

In addition, according to an embodiment of the present invention, the hot rolled steel sheet may have a tensile strength of 590 MPa or more and a thickness of 6 mm or less.

In the manufacture of a plated steel sheet welding member having excellent weld porosity and fatigue characteristics according to embodiments of the present invention, it is possible to effectively reduce the weld metal portion pore defects by optimizing the wave frequency of the welding current and to control the toe angle of the weld metal portion. The fatigue stress concentration in the welding tow can be reduced. Therefore, in order to secure the high strength of the parts, such as automobile chassis member, anti-rusting according to the thinning, it can be used a high corrosion-resistant plated steel sheet, thereby obtaining a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics.

1 is a photograph of a cross section of a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an embodiment of the present invention.
Figure 2 is a photograph of the appearance of the welding portion according to an embodiment of the present invention.
3 is a X-ray photograph of the appearance of the weld portion according to an embodiment of the present invention.
Figure 4 is a photograph showing the tensile fracture test results of the plated steel sheet welding member according to an embodiment of the present invention.
5 is a schematic view for explaining a weld metal part of a plated steel sheet welding member according to an embodiment of the present invention.
6 is a graph for explaining a molten metal stirring wave frequency during arc welding of a plated steel sheet welding member according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are presented to sufficiently convey the spirit of the present invention to those skilled in the art. The present invention is not limited to the embodiments presented herein but may be embodied in other forms. The drawings may omit illustrations of parts not related to the description in order to clarify the present invention, and may be exaggerated to some extent in order to facilitate understanding.

1 is a photograph of a cross section of a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an embodiment of the present invention. Figure 2 is a photograph of the appearance of the welding portion according to an embodiment of the present invention. 3 is a X-ray photograph of the appearance of the weld portion according to an embodiment of the present invention. Figure 4 is a photograph showing the tensile fracture test results of the plated steel sheet welding member according to an embodiment of the present invention. 5 is a schematic view for explaining a weld metal part of a plated steel sheet welding member according to an embodiment of the present invention.

1 to 5, in accordance with a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an exemplary embodiment of the present disclosure, a second layer may be partially stacked on the first member and the first member. The welded metal portion is formed through overlapping arc welding of the member.

At this time, the toe angle θ of the weld metal part is 45 ° or less.

Methods for increasing the fatigue characteristics of the welding member can be largely divided into a method using the residual stress and a method of controlling the bead shape.

In the present invention, the object of the present invention is to improve the fatigue characteristics of the welding member by controlling the bead shape. For this purpose, the toe angle of the weld metal part is 45 ° or less (excluding 0 °), more preferably. Is one technical feature of controlling to 35 ° or less (excluding 0 °), even more preferably 30 ° or less (excluding 0 °).

In this case, when the toe angle is defined as a weld toe, the contact point where the boundary between the first member and the second member meets the weld metal part in a cross section perpendicular to the welding line is defined as a weld toe. And an angle formed between the boundary line of the second member and the tangent of the bead curvature portion closest to the weld tow of the weld metal portion.

By forming the tow angle to 45 ° or less, stress concentrated on the weld metal portion can be alleviated, thereby improving fatigue characteristics of the welding member.

As described above, the fatigue properties of the welded part can be improved only by controlling the toe angle of the welded metal part. However, in order to maximize the effect, it is more preferable to properly control the penetration depth of the welded metal part. According to this, the penetration depth of the weld metal part may be controlled to 20% or more relative to the thickness of the second member. More preferably, the penetration depth of the weld metal portion may be controlled to 45% or more relative to the thickness of the second member. If the penetration depth of the weld metal portion is insufficient, the weld metal portion may break due to the repeated fatigue load starting from the bead root.

In addition, the first member and the second member is a plated steel sheet.

Therefore, by using a plated steel sheet instead of a general hot rolled steel sheet, it is possible to secure the anti-corrosion property to prevent penetration corrosion by thinning of the material due to the high strength and light weight of the recent parts.

For example, the plated steel sheet may be a Zn-Mg-Al-based alloy plating or galvanized hot rolled steel sheet. More preferably, the plated steel sheet may be a Zn-Mg-Al-based alloy plated hot rolled steel sheet having better corrosion resistance than galvanized hot rolled steel sheet.

For example, the hot rolled steel sheet may have a tensile strength of 590 MPa or more and a thickness of 6 mm or less, and the hot rolled steel sheet may be a 590FB steel having a microstructure including ferrite and bainite.

For example, the pore area ratio formed in the weld metal part may be less than 0.5%.

When welding a plated steel sheet welding member according to the conventional arc welding method, when the plated layer comes into contact with the welding arc, a large amount of pore defects such as pits or blowholes are generated due to the generation of plating vapor, thereby reducing the strength and fatigue characteristics of the welded portion. There is a problem. In addition, the Zn-Mg-Al-based high corrosion-resistant alloy plated steel sheet having excellent corrosion resistance compared to the existing galvanized steel sheet has much lower melting point and vaporization point of ternary alloy plating, resulting in higher amount of plating vapor, and thus pore defects. There is a problem that the incidence is higher.

However, according to the manufacturing method including the arc welding according to an embodiment of the present invention by minimizing such a problem, even in the case of using a Zn-Mg-Al-based high corrosion-resistant alloy plated steel sheet as well as the existing galvanized steel sheet, The pore area ratio formed in the weld metal portion may be limited to less than 0.5%, preferably 0%.

For example, the fatigue strength of the weld metal is 250 MPa or more, and the fatigue life of 2,000,000 cycles or more can be secured at a repeated fatigue load of 10 kN (minimum / maximum load ratio, R = 0.1), which shows that the weld fatigue properties are excellent. have. In this case, the fatigue strength (or fatigue limit) is defined as a value obtained by dividing the maximum fatigue load value at which the fatigue life is 2,000,000 cycles or more divided by the cross-sectional area of the member.

Further, according to the method for manufacturing a plated steel sheet welding member having excellent weld resistance porosity and fatigue characteristics according to an embodiment of the present invention, the arc overlapping the first member and the second member laminated so as to partially overlap on the first member. Forming a weld metal portion through welding.

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

The overlap width of the weld joint may be applied to about 5 to 50 mm, but is not limited thereto.

At this time, the arc welding is performed while providing a shield gas along the formed welding line, and during arc welding, an arc is generated by supplying a welding current to the solid wire to weld the arc.

For example, the solid wire may be fed into a shield gas, which is an Ar gas containing 10 to 30% of CO ₂ gas. More preferably, the shield gas may be an Ar gas including 10 to 20% of CO ₂ gas.

That is, the shield gas is an Ar gas, and contains 10 to 30% of CO ₂ gas, when containing less than 10% of CO ₂ gas, the arc heat pinch force effect due to the arc expansion is reduced, thereby reducing the plating vapor discharge effect. If it contains more than 30% of the CO ₂ gas, the arc heat pinch force effect by the arc contraction is excessive, thereby reducing the effect of plating vapor discharge.

When the first member and the second member to be welded is a plated steel sheet, for example, in the case of a galvanized steel sheet, a zinc-plated layer having a low boiling point becomes an arc of zinc due to arc heat during arc welding, which rises to the top of the molten portion. Most of this is released, but some remain in the melt to form blowholes, spherical cavities upon solidification, and pits, small pits, when zinc gas solidifies near the base metal surface. For example, by using an Ar gas containing a predetermined amount of CO ₂ gas as the shield gas, the arc force generated between the solid wire and the base material during the gas shield arc welding is increased, so that the weld directly under the solid wire is greatly dug up. You can go down. Accordingly, it is possible to facilitate the release of the zinc gas generated in the lower portion of the molten portion, and to increase the penetration depth of the weld metal portion during gas shield arc welding, and finally, to improve weld fatigue characteristics and pore defects. Can be suppressed.

As the welding material, the solid wire may be used. For example, ER70S-3 (KC-25M) Φ1.2 soild wire may be used, but is not particularly limited thereto.

For example, the welding current is a pulse current which is repeated with one pulse period of energization of a first peak and a second peak having a current value smaller than the first peak.

The pulsed current is repeatedly supplied with a weld molten metal stirring wave frequency defined by the following equation (1) at 20 to 30 Hz to perform welding.

1 / (T _H + T _L ) --- Equation (1)

Here, T _H is the period of the first peak, T _L is the period of the second peak.

6 is a graph for explaining a molten metal stirring wave frequency during arc welding of a plated steel sheet welding member according to an embodiment of the present invention.

The weld molten metal stirring wave frequency is defined as 1 / (T _H + T _L ) as shown in FIG. 6. Accordingly, the frequency is repeatedly supplied in the range of 20 to 30 Hz. If the frequency range is too low or too high, there is a problem in that the reduction of the pore defects due to the reduced plating vapor discharge effect.

For example, the welding current may range from 200 to 300A.

More preferably, the lower limit of the welding current may be 225 A or more, and the upper limit may be 270 A or less. If the current is too low, the plating vapor discharge effect is reduced by reducing the arc force, on the contrary, if the current is too high, there is a problem that the incidence rate of pore defects increases because the molten weld metal part is unstable.

For example, the arc welding may be performed at a solid wire diameter of 1.0 to 1.2 mm, torch angle of 30 to 45 °, push angle of 0 to 25 °, and welding speed of 0.6 to 1.0 m / min.

In the embodiment of the present invention, the gap of the welded joint is applied to 0mm, but is not particularly limited thereto.

In addition, the first member and the second member is a plated steel sheet, the plated steel sheet is a Zn-Mg-Al-based alloy plating or galvanized hot rolled steel sheet, the hot rolled steel sheet may have a tensile strength of 590MPa or more and 6mm or less in thickness. . Detailed descriptions of the first member and the second member are the same as described above and will be omitted below.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

Example  1 to 4 and Comparative example  1 to 6

Two 590FB steel plates of Zn-Mg-Al plated with a thickness of 90 g / m ² plated on the both sides of the steel plate were arranged so that 20 mm overlap each other, and then the joints were arc-welded according to the conditions shown in Table 1 below to weld metal. To form a weld member.

Shield gas Welding material Welding condition Weld Pulse Current Frequency (Hz) Example 1 Ar + 20% CO ₂ KC-25MΦ1.2 200 A, 60 cm / min 30 Example 2 Ar + 20% CO ₂ KC-25MΦ1.2 225A, 60cm / min 30 Example 3 Ar + 20% CO ₂ KC-25MΦ1.2 225A, 80cm / min 30 Example 4 Ar + 20% CO ₂ KC-25MΦ1.2 225A, 100cm / min 30 Comparative Example 1 Ar + 30% CO ₂ MIX-ZnΦ1.0 200 A, 80 cm / min 20 Comparative Example 2 Ar + 30% CO ₂ MIX-ZnΦ1.0 220A, 80cm / min 20 Comparative Example 3 Ar + 20% CO ₂ KC-25MΦ1.2 200 A, 100 cm / min 0 Comparative Example 4 Ar + 20% CO ₂ KC-25MΦ1.2 300 A, 100 cm / min 0 Comparative Example 5 Ar + 20% CO ₂ KC-25MΦ1.2 200 A, 60 cm / min 20 Comparative Example 6 Ar + 20% CO ₂ KC-25MΦ1.2 250 A, 80 cm / min 20

The weld metal part of the said welding member was observed, the presence or absence of a pit generation, and the pore area ratio were measured, and it is shown in following Table 2.

Feet occurrence Pore area ratio (%) Example 1 X 0.0 Example 2 X 0.0 Example 3 X 0.0 Example 4 X 0.0 Comparative Example 1 O 2.5 Comparative Example 2 O 7.4 Comparative Example 3 O 1.6 Comparative Example 4 O 4.1 Comparative Example 5 O 0.6 Comparative Example 6 O 2.4

5 is a schematic view for explaining a weld metal part of a plated steel sheet welding member according to an embodiment of the present invention.

Referring to FIG. 5, the width of the weld metal portion, that is, the weld leg length is represented by L, the thickness of the second member is represented by h1, and the upper surface edge of the second member to the toe portion on the first member. D is the distance from the straight line of the first and second members to the contact point of the weld metal part, d is the distance from the highest surface of the weld metal part to r, penetration depth is represented by p, and the toe angle is represented by θ. It was. Accordingly, the results of observing the size and the like of the weld metal part of the embodiments of the present invention are shown in Table 3 below.

h1 (mm) L (mm) r (mm) d (mm) p (mm) Tow angle (°) Example 1 2.2 6.0 1.8 1.6 1.2 38 Example 2 2.2 6.2 1.8 1.6 1.4 33 Example 3 2.2 5.9 1.8 1.7 2.1 30 Example 4 2.2 4.8 1.4 1.7 One 44

Referring to the above, the tow angle of the welded metal part of the welding member according to an embodiment of the present invention can be ensured to less than 45 °, and the pit and pores do not occur in the welded metal portion in the plated steel sheet welding member Its porosity is improved, the welded metal portion can secure a fatigue strength of 250MPa or more, it is possible to increase the application range of high-strength plated hot-rolled sheet steel for thinning and lightweighting parts such as automobile chassis member.

Claims (12)

delete delete delete delete delete delete Forming a weld metal part through the overlapping arc welding of the first member and the second member partially overlapped on the first member;
The first member and the second member is a Zn-Mg-Al alloy plated hot rolled steel sheet,
In the arc welding, a welding current of 200 to 270 A is supplied to the solid wire to generate an arc, and the welding current is pulsed by applying a first peak and a second peak having a current value smaller than the first peak. As a pulse current repeated in cycles, the weld molten metal stirring wave frequency defined by the following formula (1) is repeatedly performed at 30 Hz,
A method for manufacturing a plated steel sheet welding member having excellent porosity resistance and fatigue characteristics of a welded portion for supplying the solid wire to a shield gas, which is an Ar gas containing 10 to 20% of CO ₂ gas.
1 / (T _H + T _L ) --- Equation (1)
Here, T _H is the period of the first peak, T _L is the period of the second peak. delete delete The method of claim 7, wherein
In the arc welding, the welded pores and fatigue characteristics of the solid wire diameter: 1.0 to 1.2 mm, torch angle: 30 to 45 °, push angle: 0 to 25 °, welding speed: 0.6 to 1.0 m / min. Method for producing an excellent plated steel sheet welding member. delete The method of claim 7, wherein
The hot rolled steel sheet is a method of manufacturing a welded plate steel member excellent in porosity resistance and fatigue properties of the welded portion having a tensile strength of 590MPa or more and 6mm or less.

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