阅读说明：本技术 焊接区抗气孔性和疲劳特性优异的镀覆钢板的焊接构件及其制造方法 (Welded member of plated steel sheet having excellent weld porosity resistance and fatigue characteristics, and method for producing same ) 是由 裵规烈 李泰永 于 2018-06-18 设计创作，主要内容包括：公开了具有优异的焊接区抗气孔性和疲劳特性的镀覆钢板的焊接构件及其制造方法。根据本发明的一个实施方案的具有优异的焊接区抗气孔性和疲劳特性的镀覆钢板的焊接构件包括：通过将第一构件和第二构件交叠成第二构件部分交叠第一构件经电弧焊接形成的焊缝金属部,其中所述焊缝金属部的趾角(θ)为45°或更小,以及所述第一构件和所述第二构件为镀覆钢板。(Disclosed are a welded member of plated steel sheets having excellent weld-area porosity resistance and fatigue characteristics, and a method for producing the same. A welded member of plated steel sheets having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention includes: a weld metal portion formed by arc welding by overlapping a first member and a second member such that the second member partially overlaps the first member, wherein a toe angle (θ) of the weld metal portion is 45 ° or less, and the first member and the second member are plated steel sheets.)

1. A welded member of plated steel sheets having excellent weld zone porosity resistance and fatigue characteristics, comprising:

a weld metal portion formed by arc welding by overlapping a first member and a second member such that the second member partially overlaps the first member,

wherein a toe angle (θ) of the bead metal part is 45 ° or less, and the first member and the second member are plated steel sheets.

2. The welded member of plated steel sheet according to claim 1, wherein the plated steel sheet is a Zn-Mg-Al alloy plated hot rolled steel sheet or a zinc plated hot rolled steel sheet.

3. The welded member of plated steel sheet according to claim 2, wherein the hot rolled steel sheet has a tensile strength of 590MPa or more and a thickness of 6mm or less.

4. The welded member of plated steel sheet according to claim 3, wherein the hot rolled steel sheet is 590FB steel.

5. The welded member of plated steel sheet according to claim 1, wherein the hole area ratio of the weld metal portion is less than 0.5%.

6. The welded member of plated steel sheet according to claim 1, wherein the fatigue strength of the weld metal portion is 250MPa or more, and the fatigue life at a cyclic fatigue load of 10kN (minimum/maximum load ratio, R ═ 0.1) is 2,000,000 cycles or more.

7. A method of manufacturing a welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics, comprising:

forming a weld metal portion by overlapping a first member and a second member, which are plated steel sheets, such that the second member partially overlaps the first member and performing arc welding;

a welding current is applied to the solid wire to generate an arc,

wherein the welding current is a pulse current repeated with a first peak and a second peak having a current value smaller than the first peak as one pulse period, and

the welding molten metal stirring wave frequency defined by the following formula (1) is 20Hz to 30Hz,

1/(T_H+T_L) - - -formula (1)

Here, T_HIs the period of the first peak, and T_LIs the period of the second peak.

8. The method of claim 7, wherein the solid welding wire is fed to as comprising 10% to 30% CO₂Ar gas as a gas.

9. The method of claim 7, wherein the welding current is in a range of 200A to 300A.

10. The method of claim 7, wherein the solid wire has a diameter of 1.0mm to 1.2mm, a torch angle of 30 ° to 45 °, a push angle of 0 ° to 25 °, and a welding speed of 0.6 m/min to 1.0 m/min.

11. The method according to claim 7, wherein the first member and the second member are a Zn-Mg-Al alloy plated hot rolled steel sheet or a galvanized hot rolled steel sheet.

12. The method according to claim 11, wherein the hot rolled steel sheet has a tensile strength of 590MPa or more and a thickness of 6mm or less.

Technical Field

The present invention relates to a welded member of plated steel sheet and a method for manufacturing the same, and more particularly, to a welded member of plated steel sheet excellent in weld zone (weldzone) porosity resistance and fatigue characteristics, and a method for manufacturing the same.

Background

In the automotive field, research on weight reduction techniques for vehicle bodies and components has become a major issue in fuel efficiency control strategies for environmental protection against problems such as global warming. The tendency is also followed as a chassis component important for the traveling performance of automobiles, and it is required to apply a high-strength steel material to reduce the weight. In order to achieve weight reduction of the component, it is necessary to increase the strength of the material, and it can be said that ensuring the durability performance of the component made of high-strength steel in an environment where repeated fatigue loads are applied is an important factor.

In the case of arc welding, which is mainly used to secure the strength of a combination of automobile chassis parts, lap welding is performed between the parts by welding of a welding wire, and therefore formation of a geometric shape of a welded joint (welded joint) is inevitable. It acts as a repeated fatigue stress concentration portion (notch effect) and becomes a starting point of fracture, and therefore, the durability of the part is lowered, and thus the advantage of applying the high-strength steel material is lost.

As described above, in order to improve the fatigue characteristics of the weld, it is important to reduce the angle of the end portion (which is the main stress concentration portion) of the welded joint, i.e., toe angle (weld corner). At the same time, it is important to control the material and stress of the toe.

Further, as described above, since the demand for rust prevention characteristics to prevent penetration corrosion (corrosion) due to material thinning caused by high strength and light weight of parts is increasing, there is an increasing tendency to increase adoption of plated steel materials as in prior art 1. The use of plated steel materials is sensitive to the occurrence of hole defects (e.g., craters or blowholes) upon arc welding, and has the problem of reducing the strength and fatigue characteristics of the weld.

On the other hand, although the application of Zn-Mg-Al plated high corrosion resistance alloy steel having much higher corrosion resistance than existing hot dip galvanized steel sheets has been proposed, the melting point and evaporation point of the ternary alloy plating layer are lower than those of the conventional zinc plating layer, the generation of plating vapor is more sensitive, and thus the development of a technique for suppressing the occurrence of hole defects in the weld is required.

Although prior art 1 proposes setting the gap of the lap portion in the range of 0.2mm to 1.5mm to suppress the generation of hole defects of the galvanized steel sheet arc welded portion, there is a limitation that the welding characteristics of the joint structure without the gap cannot be ensured when the actual parts are applied.

Further, in prior art 2, in order to suppress the occurrence of hole defects in the galvanized steel sheet arc-welded seam, it is proposed to use CO mixed with Ar₂And O₂Triple mixed gas and low viscosity solid wire, which limits the content of Si and Mn. Furthermore, it is proposed that the arc position is 1mm at the tip of the weld lap. However, the limitation of the shielding gas and the welding material is inevitable, and the arc position must be kept constant when the actual part is applied.

(patent document 0001) Japanese patent laid-open publication No. 2016-

(patent document 0002) Japanese patent laid-open publication No. 2015-

Disclosure of Invention

Technical problem

One embodiment of the present invention seeks to provide a welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics.

Further, embodiments of the present invention seek to provide a method of manufacturing a welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics.

Technical scheme

A welded member of plated steel sheets having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention includes: a weld metal part formed by arc welding the first member by overlapping the first member and the second member such that the second member partially overlaps (overlap), wherein a toe angle (θ) of the weld metal part is 45 ° or less, and the first member and the second member are plated steel plates.

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

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

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

Further, according to an embodiment of the present invention, the hole area ratio of the weld metal part may be less than 0.5%.

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

A method of manufacturing a welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention includes: forming a weld metal portion by overlapping a first member and a second member, which are plated steel sheets, such that the second member partially overlaps the first member and performing arc welding; applying a welding current to the solid wire to generate an arc, wherein the welding current is a pulse current repeating with a first peak and a second peak having a current value smaller than the first peak as one pulse period, and a welding molten metal stirring wave frequency defined by the following formula (1) is 20Hz to 30 Hz.

1/(T_H+T_L) - - -formula (1)

Here, T_HIs the period of the first peak, and T_LThe period of the second peak.

Further, according to an embodiment of the present invention, the solid welding wire may be fed to as containing 10% to 30% of CO₂Ar gas as a gas.

Further, according to an embodiment of the present invention, the welding current may be in a range of 200A to 300A.

Further, according to an embodiment of the present invention, at the time of arc welding, the diameter of the solid wire may be 1.0mm to 1.2mm, the torch angle (torch angle) may be 30 ° to 45 °, the push angle (push angle) may be 0 ° to 25 °, and the welding speed may be 0.6 m/min to 1.0 m/min.

Further, according to an embodiment of the present invention, the first member and the second member may be a Zn-Mg-Al alloy plated hot rolled steel sheet or a Zn-plated hot rolled steel sheet.

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

Advantageous effects

In the production of a welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention, hole defects in the weld metal portion can be effectively reduced by optimizing the wave frequency of the welding current. The fatigue stress concentration on the weld toe can be reduced by controlling the toe angle of the weld metal portion. Therefore, a high corrosion-resistant plated steel sheet can be used to ensure high strength of parts (e.g., chassis members of automobiles) and rust-proof properties due to thinning of the parts. Therefore, a welded member of plated steel sheets having excellent weld-zone porosity resistance and fatigue characteristics can be obtained.

Drawings

Fig. 1 is a photograph of a cross section of a welded member of a plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention.

FIG. 2 is a photograph of the appearance of a weld according to one embodiment of the present invention.

FIG. 3 is an X-ray photograph of the appearance of a weld according to one embodiment of the present invention.

Fig. 4 is a photograph showing the tensile rupture test result of a welded member of a plated steel sheet according to an example of the present invention.

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

Fig. 6 is a diagram for explaining a molten metal agitation wave frequency (molten metal agitation wave frequency) at the time of arc welding of a welding member of a plated steel sheet according to an embodiment of the present invention.

Best mode for carrying out the invention

A welded member of plated steel sheet having excellent weld-zone porosity resistance and fatigue characteristics, comprising: a weld metal portion formed by arc welding by overlapping a first member and a second member such that the second member partially overlaps the first member, wherein a toe angle (θ) of the weld metal portion is 45 ° or less, and the first member and the second member are plated steel sheets.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are put forth so as to fully convey the spirit of the invention to those skilled in the art to which the invention pertains. The present invention is not limited to the embodiments set forth herein, but may be embodied in other forms. For the sake of clarity of the present invention, the drawings omit illustration of parts irrelevant to the description, and the size of components may be expressed in a slightly exaggerated manner for easy understanding.

Fig. 1 is a photograph of a cross section of a welded member of a plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention. FIG. 2 is a photograph of the appearance of a weld according to one embodiment of the present invention. FIG. 3 is an X-ray photograph of the appearance of a weld according to one embodiment of the present invention. Fig. 4 is a photograph showing the tensile rupture test result of a welded member of a plated steel sheet according to an example of the present invention. Fig. 5 is a schematic view for explaining a weld metal portion of a welded member of a plated steel sheet according to an embodiment of the present invention.

Referring to fig. 1 to 5, a welded member of plated steel sheets having excellent weld zone porosity resistance and fatigue characteristics according to an embodiment of the present invention includes: a weld metal portion formed by arc welding by overlapping a first member and a second member such that the second member partially overlaps the first member.

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

Methods of improving fatigue characteristics of welded members can be broadly classified into a method of utilizing residual stress and a method of controlling the shape of a bead.

In the context of the present invention, it is an object of the invention to improve the fatigue properties of welded components by controlling the shape of the weld. For this reason, the toe angle of the weld metal portion is set to 45 ° or less (excluding 0 °), preferably 35 ° or less (excluding 0 °), and more preferably 30 ° or less (excluding 0 °).

Here, the toe angle refers to an angle formed by a tangent line of the weld curved portion closest to a boundary line between the first member and the second member and a toe of the weld metal portion, with the toe as a reference point. At this time, a contact point of a boundary line between the first member and the second member and the weld metal portion in a cross section perpendicular to the weld line is defined as a weld toe (weld toe).

By forming the toe angle of 45 ° or less, stress concentrated on the weld metal portion can be relieved, and at the same time, fatigue characteristics of the welded member can be improved.

By controlling the toe angle of the weld metal portion as described above, the fatigue characteristics of the weld portion can be improved. However, in order to maximize the effect, it is preferable to appropriately control the penetration depth of the weld metal portion. According to an embodiment of the present invention, the penetration depth of the weld metal part may be controlled to 20% or more of the thickness of the second member. More preferably, the penetration depth of the weld metal part may be controlled to 45% or more of the thickness of the second member. If the penetration depth of the weld metal portion is insufficient, the fatigue load may cause cracking of the weld metal portion from the weld path (bead route) due to the repeated fatigue load.

Further, the first member and the second member are plated steel sheets.

Therefore, by using a plated steel sheet instead of a general hot rolled steel sheet, it is possible to secure rust preventive properties to prevent the breakthrough corrosion due to material thinning caused by high strength and light weight of the parts.

For example, the plated steel sheet may be a hot rolled steel sheet plated with an alloy based on Zn-Mg-Al or a galvanized hot rolled steel sheet. More preferably, the plated steel sheet may be a hot rolled steel sheet plated with a Zn-Mg-Al alloy, which is more corrosion resistant than the galvanized hot rolled steel sheet.

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

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

In the case of welding a welded member of a plated steel sheet according to a conventional arc welding method, a large number of hole defects such as craters or blowholes are formed due to generation of plating vapor when a plating layer comes into contact with a welding arc, and there is a problem that the strength and fatigue characteristics of the welded portion are lowered. In addition, in the case of a steel sheet plated with a Zn — Mg — Al type high corrosion resistance alloy, which is superior in corrosion resistance to conventional galvanized steel sheets, the melting point and evaporation point of the ternary alloy plating layer are much lower. Therefore, there are problems in that the amount of plating vapor generated is larger and the occurrence rate of hole defects is higher.

However, according to the manufacturing method including arc welding according to one embodiment of the present invention, not only the existing galvanized steel sheet but also the Zn-Mg-Al high corrosion resistance alloy-plated steel sheet is used to minimize these problems. In any case, the hole area ratio of the weld metal portion may be limited to less than 0.5%, preferably 0%.

For example, the fatigue strength of the weld metal portion is 250MPa or more, and a fatigue life of 2,000,000 cycles or more can be ensured at a cyclic fatigue load of 10kN (minimum/maximum load ratio, R ═ 0.1). It can be seen that the component fatigue characteristics are excellent. At this time, the fatigue strength (or fatigue limit) is defined as a value obtained by dividing a maximum fatigue load value at which the fatigue life becomes 2,000,000 cycles or more by the sectional area of the member.

According to the method of manufacturing a welded member of a plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics, the method includes the step of forming a weld metal portion by overlapping a first member and a second member such that the second member partially overlaps the first member and performing arc welding.

First, after preparing the first member and the second member, a welding line (welding line) is formed by laminating the second member on the first member so that at least a portion thereof overlaps. Here, the weld line means an end portion of the second member in a region where the first member overlaps the second member.

The overlapping width of the welding joint parts may be about 5mm to 50mm, but is not limited thereto.

At this time, arc welding is performed along the formed welding line while supplying a shielding gas, and at the time of arc welding, a welding current is supplied to the solid wire to generate an arc for welding.

For example, a solid wire may be fed to the wire as containing 10% to 30% CO₂Ar gas as a gas. More preferably, the shielding gas may be a gas containing 10% to 20% CO₂Ar gas of gas.

That is, the shielding gas is Ar gas and contains 10% to 30% of CO₂A gas. If CO is present₂If the gas content is less than 10%, the effect of arc heat shrink force (arc heat pinch force) due to arc shrinkage is reduced, and the effect of discharging plating vapor is reduced. If CO is present₂If the gas content is more than 30%, the effect of the thermal contraction force of the arc due to the arc expansion becomes excessive, and the effect of discharging the plating vapor is reduced.

When the first member and the second member to be welded are plated steel sheets, for example, in the case of a galvanized steel sheet, arc heat causes a galvanized layer having a low boiling point to float as zinc gas on the upper portion of the melted portion during arc welding. Most of the zinc is released but a part thereof remains in the molten portion, and when the zinc gas near the surface of the substrate solidifies, pits are formed as small pits. Most of the zinc gas is released, but a part of the zinc gas remains in the melted portion and forms spherical bubble holes when solidified and pits when the zinc gas condenses near the surface of the substrate. For example, by makingWith a gas containing CO₂The Ar gas as a shielding gas can thoroughly weld a weld joint under a solid wire by increasing an arc force generated between the solid wire and a base material in gas-shielded arc welding. Therefore, the discharge of the zinc gas generated in the lower portion of the molten metal portion can be promoted, and the penetration depth of the weld metal portion can be further increased during the gas-shielded arc welding. Finally, it is possible to suppress the occurrence of the dishing defect and improve the fatigue characteristics of the welded portion.

As the welding material, a solid wire may be used. For example, ER70S-3(KC-25M)1.2 solid wire may be applied, but is not particularly limited thereto.

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

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

1/(T_H+T_L) - - -formula (1)

Here, T_HIs the period of the first peak, and T_LThe period of the second peak.

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

The welding molten metal stirring wave frequency is limited to 1/(T)_H+T_L) As shown in fig. 6. Therefore, the pulse current is repeatedly supplied in the range of 20Hz to 30 Hz. If the frequency range is too low or too high, the effect of discharging plating vapor may be reduced, which may make it difficult to reduce hole defects.

For example, the welding current may be in the range of 200A to 300A.

More preferably, the lower limit of the welding current may be 225A or more, and the upper limit may be 270A or less. If the current is too low, the effect of discharging the plating vapor is reduced due to the reduction in arc power. On the other hand, if the current is too high, the weld metal portion becomes unstable, and the incidence of hole defects increases.

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

In the embodiment of the present invention, although the gap of the welded joint is 0mm, it is not limited thereto.

Further, the first member and the second member may be a Zn-Mg-Al alloy plated hot rolled steel sheet or a Zn-plated hot rolled steel sheet. Also, the hot rolled steel sheet may have a tensile strength of 590MPa or more and a thickness of 6mm or less. The detailed description of the first member and the second member is the same as above, and thus will not be described again.

Hereinafter, the present invention will be described in more detail by examples.

Inventive examples 1 to 4 and comparative examples 1 to 6

Two pieces were coated with Zn-Mg-Al in an amount of 90g/m²590FB plates of 2.2mm thickness are placed on both sides of the steel plate so that they overlap each other by 20 mm. Then, the connection members were welded by arc welding according to the conditions shown in table 1 below.

[ Table 1]

The presence of the crater and the hole area ratio were measured by observing the weld metal portion of the welded member, and are shown in table 2 below.

[ Table 2]

	Pit occurrence	Aperture area ratio (%)
			Inventive example 1	X	0.0
Inventive example 2	X	0.0
			Inventive example 3	X	0.0
Inventive 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

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

In fig. 5, the width of the bead metal part, i.e., the fillet (leg) length, is L, the thickness of the second member is h1, the distance from a straight line from the upper surface edge of the second member to the toe on the first member to the contact point of the first member and the second member with the bead metal part is denoted by d, the distance to the highest surface of the bead metal part is r, and the penetration depth is p, and the toe angle is denoted by θ, respectively. Table 3 shows the observation results of the size of the weld metal part according to one embodiment of the present invention.

[ Table 3]

Referring to the above, the toe angle of the bead metal part of the welded member according to one embodiment of the present invention may be maintained at 45 ° or less, and no crater and hole are generated in the bead metal part, and thus, the porosity resistance of the welded member of the plated steel sheet may be improved. The strength of the weld metal portion can be ensured at 250MPa or more, and the range of application of the high-strength plated hot-rolled sheet steel for making parts such as automobile chassis members thinner and lighter can be increased.

Industrial applicability

The welded member of plated steel sheet having excellent weld zone porosity resistance and fatigue characteristics and the method of manufacturing the same according to the embodiments of the present invention may be applied to parts such as automobile chassis members.