The present invention relates to a welding wire that can be applied to gas shielded arc welding such as galvanized giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less, which is applied to structural members of the lower body of an automobile, a welded structure manufactured using the same, and a welding method thereof. it's about
background art
[2]
In the automobile field, research on lightweight technology for car bodies and parts is emerging as a major issue due to fuel economy regulation policies in accordance with environmental protection such as global warming. Chassis parts, which are important for vehicle driving performance, also need to apply high-strength steel for weight reduction according to this trend.
[3]
In order to achieve such weight reduction, it is essential to increase the strength of materials, and guaranteeing the durability of parts made of high-strength steel materials in an environment where repeated fatigue loads are applied is an important factor.
[4]
However, in the case of arc welding, which is mainly used to secure strength when assembling automotive chassis parts, overlapping joints between parts are welded by welding wires, so it is inevitable to give geometric shapes to the joints. This serves as a repeated fatigue stress concentration (notch effect) and becomes the starting point of fracture, resulting in a decrease in the durability of the part, so the advantage of applying high-strength steel is lost.
[5]
Therefore, in order to improve the fatigue characteristics of the welding part, it is most important to reduce the angle (toe angle) of the end of the bead, which is mainly a stress concentration part, and in addition, controlling the material and stress of the toe part is an important factor. In addition, as described above, the adoption of plated steel materials is increasing as the demand for corrosion prevention for penetration corrosion prevention increases due to the thinning of materials due to the high strength and light weight of parts, but in particular, the welding metal of the arc welding part has a plating layer. Since it does not exist, the corrosion resistance after painting compared to the base material has a limit of inferiority. Accordingly, there is a problem of premature corrosion of a welded portion of a chassis part made of a plated steel sheet in a harsh corrosive environment while driving a vehicle, leading to a decrease in fatigue characteristics. On the other hand, during gas shielded arc welding of plated steel materials, a large amount of pit and blow hole defects are generated in the weld bead due to the generation of steam such as zinc, which may cause a decrease in the strength of the welded joint, thereby reducing welding productivity. Also, in the case of general uncoated steel materials, the slag generated in the welding bead during gas shielded arc welding causes painting defects and deteriorates corrosion resistance after painting. There is a problem of cost increase. On the other hand, as the application of giga steel with a tensile strength of 1GPa or more is expected to be expanded for effective weight reduction in preparation for the era of electric vehicles, securing the strength of welded parts is an important prerequisite.
[6]
An example of a prior art for solving this problem is the invention described in Patent Document 1. Patent Document 1 discloses that the blowhole and slag area ratio of the welded portion can be controlled to within 10%, respectively, through appropriate control of the Si, Mn, Ti, and Al contents of the gas shielded arc welding wire, but the actual high-strength steel If the blowhole area ratio of the welded part exceeds 5%, the tensile strength and fatigue strength of the welded metal may be significantly lowered. A more sensitive issue arises.
[7]
Patent Document 2 discloses that the tensile strength of the weld metal part can be secured at 800 MPa or more by controlling the carbon equivalent of the gas shielded arc welding wire to 0.8 to 0.9%, but the method for reducing blowholes and slag in the weld part is not suggested.
[8]
Patent Document 3 discloses controlling the content ratio of Si and Mn in the gas shielded arc welding wire to an appropriate range to suppress the formation of Si-based slag in the weld bead and improve the paintability and porosity resistance of the welded part. However, in Patent Document 3, the strength of the welded part is aimed at general steel materials with a maximum of 540MPa, and a method for securing the strength of the welded part of giga steel with a tensile strength of 1GPa or more has a limit.
[9]
Patent Document 4 discloses that the slag area ratio of the weld zone can be controlled to within 5% through appropriate control of the Si, Al, Ti, Al, Sb and S contents of the gas shielded arc welding wire, but pit and blow of the plated steel weld zone Hall reduction measures are not presented. On the other hand, a method of improving the strength of the welded part by adding an appropriate amount of B to the wire is proposed, but the strength does not reach 1GPa or higher.
[10]
Patent Document 5 discloses that the weld strength of a steel having a tensile strength of 980 MPa or more is 90% or more compared to the base material by controlling the total amount of Cr and Ni of the welding wire to 1% to 24%, but reducing slag and improving porosity of the welded part It has limitations that do not suggest solutions for
[11]
That is, in the inventions disclosed in Patent Documents 1 to 5, sufficient consideration is not made for welding of galvanized steel sheets having a tensile strength of 1 GPa or more and a coating weight per side of 20 to 120 g/m 2 , so that sufficient strength of the giga steel weldment is secured and It was unclear whether slag reduction and porosity were secured at the same time.
[12]
[Prior art literature]
[13]
[Patent Literature]
[14]
(Patent Document 1) Korean Patent Publication No. 2015-0108930
[15]
(Patent Document 2) Korean Patent Publication No. 2016-0080096
[16]
(Patent Document 3) Korean Patent Publication No. 2019-0047388
[17]
(Patent Document 4) International Patent Publication No. WO2019-124305
[18]
(Patent Document 5) Korean Patent Publication No. 2019-0134703
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[19]
Therefore, the present invention is a welding wire that can be applied to gas shield arc welding such as galvanized giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less, which is applied to structural members of the lower body of an automobile, a welded structure manufactured using the same, and a welding method thereof. It is intended to provide
[20]
On the other hand, the subject of the present invention is not limited to the above. The subject of the present invention will be understood from the entire contents of this specification, and those skilled in the art will have no difficulty in understanding the additional subject of the present invention.
means of solving the problem
[21]
One aspect of the present invention,
[22]
In terms of mass% of the total wire, C: 0.08 to 0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less, Cr: 4.0 to 5.2%, Mo : 0.4 to 0.65%, the balance includes Fe and unavoidable impurities, and relates to a wire for gas shielded arc welding in which the value X defined by the following relational expression 1 satisfies the range of 0.7 to 1.1%.
[23]
[Relationship 1]
[24]
X(%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn]
[25]
However, [Cr], [Mo], [Si] and [Mn] in relational expression 1 represent the mass % of each element.
[26]
A Cu plating layer may be formed on the surface of the welding wire.
[27]
Cu forming the Cu plating layer preferably has a content of 0.4% or less (excluding 0%) in mass% with respect to the total wire including the plating layer, more preferably, limited to a content in the range of 0.1 to 0.3%. is to do
[28]
The welding wire preferably contains Cr: 4.2 to 4.9%, Mo: 0.45 to 0.48%, and Mn: 1.65 to 1.75%, respectively, in terms of mass%.
[29]
The welding wire preferably includes a Si content in the range of 0.04 to 0.08%.
[30]
The welding wire may be a solid wire for gas shielded arc welding.
[31]
Another aspect of the present invention is
[32]
A welded structure having a welded portion obtained by welding two or more welding base materials using the welding wire, wherein the welded portion, in area%, contains 30 to 50% of martensite, 50 to 70% of bainite, and a residual of 5% or less. It has a microstructure made of austenite, and the microstructure constituting the welded part has an average effective grain size of 1 to 3 μm, and a high angle crystal grain fraction of 47 ° or more is 35% or more. .
[33]
At least one of the welding base materials may be a galvanized steel sheet.
[34]
The galvanized steel sheet may be one of an electric galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.
[35]
The base steel sheet constituting the galvanized steel sheet may contain one or more of Cr: 0.2 to 0.9% and Mo: 0.1 to 0.2%, in terms of its own mass%.
[36]
In addition, another aspect of the present invention,
[37]
As a method of gas-shielded arc welding the welding base material using the welding wire, 5 to 20% CO 2 is mixed with Ar as a protective gas during the welding, and the thickness of the welding base material is referred to as t (mm) At this time, it relates to a gas shielded arc welding method characterized in that welding is performed so that the range of the welding heat input Q (kJ / cm) defined by the following relational expression 2 satisfies 1.15t ≤ Q ≤ 1.6t.
[38]
[Relationship 2]
[39]
Q = (I × E) × 0.048 /υ
[40]
However, in relational expression 2, I, E and υ represent welding current [A], welding voltage [V], and welding speed (cm/min), respectively.
[41]
The welding wire may be a solid wire having a diameter of 0.9 to 1.2 mm.
Effects of the Invention
[42]
According to the present invention having the above-described configuration, separate pickling or brushing to remove weld slag by reducing the slag area ratio and blowhole area ratio of the gas shielded arc welded part of giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less to within 1%, respectively. The post-processing process can be omitted, and furthermore, it is possible to secure excellent paintability, thereby reducing raw materials and improving quality at industrial manufacturing sites.
[43]
In addition, pit and blowhole defects can be effectively prevented when welding plated materials, and weld strength of 1 GPa or more can be secured without breaking the weld metal or the molten line.
[44]
Therefore, high-strength, thin-walled components such as automobile chassis members
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5,000 character limit. Use the arrows to translate more.It can have industrial significance that can expand the adoption of giga steel by satisfying the needs for improving rust prevention and durability according to materialization.
Brief description of the drawing
[45]
1 is in Example 1 of the present invention, the wire No. of Table 2. It is a photograph showing the cross-sectional structure of the welded part obtained from the example of welding [X (%) = 0.85, Q (kJ / cm) = 2.6] welded using 7, hardness distribution, and fractured cross-sectional structure after a static tensile test.
[46]
2 is in Example 1 of the present invention, the wire No. of Table 2. It is a photograph showing the cross-sectional structure of the welded part obtained from the comparative example [X (%) = 0.55, Q (kJ / cm) = 2.6] welded using 32, hardness distribution, and fractured cross-sectional structure after a static tensile test.
[47]
3 is each weld obtained after lap joint welding with galvanized steel sheets or lap joint welding with alloyed galvanized steel sheets using wires Nos. 5, 7, 12, 34 and 36 of Table 2 in Example 1 of the present invention. This is a radiographic test (RT) picture for
[48]
Figure 4 shows No. 4 in Table 4 in Example 2 of the present invention. 7 wire and no. 1 It is an EBSD structure photograph and an inverse pole figure of the weld metal obtained from the example of welding by combining steel materials [X (%) = 0.85, Q (kJ / cm) = 3.2].
[49]
5 is Example 2 of the present invention, Table 4 No. 32 wire and no. 1 It is an EBSD structure photograph and an inverse pole figure of the weld metal obtained from a comparative example [X (%) = 0.55, Q (kJ / cm) = 3.2] in which steel materials are combined and welded.
[50]
6 shows No. 4 in Table 4 in Example 2 of the present invention. 7 wire and no. 1 Weld bead appearance photograph obtained from the example of welding by combining steel materials [X (%) = 0.85, Q (kJ / cm) = 2.6], and post-treatment processes such as pickling or brushing for removing weld slag are omitted. This is a picture of the exterior after painting.
[51]
Figure 7 (a-b) is in Example 2 of the present invention, No. 7 wire of Table 4 and No. 1 A high-speed tensile test (tensile speed of 1 m/s and 15 m/s, respectively) was performed by applying a load to the welded portion obtained from the example of welding by combining steel materials [X (%) = 0.85, Q (kJ / cm) = 2.6] When welding, the load change (b) of the welding part is compared with the load change (a) of the steel material, which is the base material for welding.
BEST MODE FOR CARRYING OUT THE INVENTION
[52]
Hereinafter, the present invention will be described.
[53]
According to the present invention, when performing gas shielded arc welding of giga steel having a tensile strength of 1 GPa or more and a thickness of 6 mm or less, it is possible to reduce the slag area ratio and the blowhole area ratio of the welded part to within 1%, respectively, and without breaking the weld metal or the molten line. It has a feature that can secure a weld strength of 1GPa or more. To this end, as a result of repeated experiments and examinations by the present inventors, among the components of the welding wire used for gas shielded arc welding, the contents of Cr and Mo, which are reinforcing elements for strength improvement, and Si and Mn, which are deoxidizing elements, are described above. It was confirmed that it is effective to control the X value defined by relational expression 1 to satisfy the range of 0.7 to 1.1%.
[54]
In addition, the present inventors have found that when the value of relational expression 1 is used as a parameter, the X value has a great influence on weld slag, blowhole generation, and weld strength. In particular, as a component included in the welding wire, not only the individual content of each element is controlled, but also the amount of each component is controlled so that the value of X is in the range of 0.7 to 1.1%, thereby generating slag and blowholes of the welding bead. It is possible to reliably suppress it, and at the same time, it is confirmed that the strength of the welded part can be secured at 1 GPa or more without breaking the weld metal or the molten line, and the present invention is proposed.
[55]
Therefore, in the welding wire, which is one aspect of the present invention, in terms of mass%, C: 0.08 to 0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less , Cr: 4.0 to 5.2%, Mo: 0.4 to 0.65%, the balance including Fe and unavoidable impurities, and the value X defined by the above relational expression 1 satisfies the range of 0.7 to 1.1%.
[56]
Hereinafter, the composition of the components of the wire for gas shielded arc welding, which is one aspect of the present invention, and the reason for its limitation will be described, where % is mass % unless otherwise specified. On the other hand, in the present invention, the welding wire is not limited to a specific type of the wire, and can be used for a solid wire or a flux-filled wire, and preferably, a solid wire. And it is preferable that the Cu plating layer is formed on the surface of the said welding wire.
[57]
[C : 0.08~0.15%]
[58]
C is a component that has an effect of stabilizing the arc and atomizing the volume. However, if the C content is less than 0.08%, the volume becomes large, the arc becomes unstable, the amount of spatter increases, and it may be difficult to secure sufficient strength of the giga-grade steel weld metal having a tensile strength of 1 GPa or more. On the other hand, if the C content exceeds 0.15%, the viscosity of the molten metal is lowered, resulting in a defective bead shape, and excessive hardening of the weld metal, resulting in increased brittleness. Therefore, in the present invention, the C content of the welding wire is preferably limited to a range of 0.08 to 0.15%.
[59]
[Si : 0.001~0.1%]
[60]
Si is an element that promotes deoxidation of molten metal during arc welding (deoxidation element), and is effective in suppressing the occurrence of blowholes. It is also an element that causes paint defects. When the Si content is less than 0.001%, deoxidation becomes insufficient and blowholes tend to occur, and when the Si content exceeds 0.1%, slag increases remarkably. Therefore, from the viewpoint of the balance between suppression of generation of blowholes and suppression of the amount of slag, the Si content of the solid wire for welding was set within the range of 0.001 to 0.1%.
[61]
In addition, limiting the Si content to the range of 0.04 to 0.08% is preferable in terms of more effectively suppressing blowholes and suppressing the amount of slag.
[62]
[Mn: 1.6~1.9%]
[63]
Mn is also a deoxidizing element, and has an effect of promoting deoxidation of molten metal during arc welding and suppressing the occurrence of blowholes, but is also an element that increases the viscosity of molten metal. If the Mn content is less than 1.6%, insufficient deoxidation occurs within the appropriate range of the above-mentioned Si content, and blowholes tend to occur. On the other hand, if the Mn content exceeds 1.9%, the viscosity of the molten metal becomes excessively high, and when the welding speed is high, the molten metal cannot properly flow into the welded part, resulting in a humping bead, which tends to cause bead shape defects. lose Therefore, the Mn content of the welding wire was within the range of 1.6 to 1.9%. In addition, in order to reliably suppress the occurrence of blowholes, the Mn content is preferably limited within the range of 1.65 to 1.75%.
[64]
[Cr : 4.0~5.2%]
[65]
Cr is a ferrite stabilizing element and a hardenable element that improves the strength of the weld metal. In particular, it is necessary to limit the Cr content to the range of 4.0 to 5.2% in order to secure sufficient strength of the giga-class steel weld metal having a tensile strength of 1 GPa or more. If the Cr content is less than 4.0%, the problem of insufficient strength of the giga-grade steel weld metal tends to occur. On the other hand, when the Cr content exceeds 5.2%, there is a high risk of formation of a δ ferrite structure or precipitation of chromium carbide in the structure, resulting in embrittlement of the weld metal, that is, reduction in toughness. In addition, limiting the Cr content to the range of 4.2 to 4.9% is preferable in terms of ensuring sufficient strength of the weld metal and suppressing embrittlement more effectively.
[66]
[Mo : 0.4~0.65%]
[67]
Mo is also a ferrite stabilizing element and is a hardenable element that improves the strength of the weld metal. In particular, it is necessary to limit the content of Mo to the range of 0.4 to 0.65% in order to secure sufficient strength of the giga-class steel weld metal having a tensile strength of 1 GPa or more. If the Mo content is less than 0.4%, it becomes difficult to obtain sufficient strength of the giga-class steel weld metal with a tensile strength of 1 GPa or more within the above-mentioned appropriate component range, and if the Mo content exceeds 0.65%, the toughness of the weld metal may deteriorate gets bigger In addition, limiting the Mo content to the range of 0.45 to 0.48% is preferable in terms of ensuring sufficient strength of the weld metal and suppressing embrittlement more effectively.
[68]
[P: 0.015% or less]
[69]
P is an element that is generally mixed as an unavoidable impurity in steel, and is usually included as an impurity in an arc welding wire. Here, P is one of the main elements that cause hot cracking of the weld metal, and it is preferable to suppress it as much as possible. When the P content exceeds 0.015%, hot cracking of the weld metal becomes remarkable. Therefore, in the present invention, it is preferable to limit the P content of the welding wire to 0.015% or less.
[70]
[S: 0.015% or less]
[71]
S is also an element that is generally mixed as an unavoidable impurity in steel, and is usually included as an impurity in a solid wire for arc welding. Here, S is an element that impairs the toughness of the weld metal, and it is preferable to suppress it as much as possible. When the S content exceeds 0.015%, the toughness of the weld metal deteriorates. Therefore, in the present invention, it is preferable to limit the S content of the welding wire to 0.015% or less.
[72]
[Relationship 1]
[73]
In addition, in the gas shielded arc welding wire of the present invention, it is important to control the contents of Cr, Mo, Si, and Mn so that the X value defined by the following relational expression 1 satisfies the range of 0.7 to 1.1%.
[74]
[Relationship 1]
[75]
X(%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn]
[76]
However, [Cr], [Mo], [Si] and [Mn] in relational expression 1 represent the mass % of each element.
[77]
That is, according to the research results of the present inventors, contained in the wire
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5,000 character limit. Use the arrows to translate more.found that the contents of Cr, Mo, Si, and Mn strongly correlated not only with the strength of the weld but also with the generation of blowholes and slag, and derived this relational expression 1. Specifically, by controlling the contents of Cr, Mo, Si, and Mn so that the X value defined by the above relational expression 1 satisfies the range of 0.7 to 1.1%, sufficient strength of the giga-grade steel welded joint having a tensile strength of 1 GPa or more is secured and resistance to porosity is maintained. Improvement and slag reduction were definitely obtained. That is, by applying the relational expression 1 parameter, it is possible to reliably suppress the generation of slag and blowholes of the weld bead, and to secure the strength of the welded part of 1 GPa or more without occurrence of weld metal or molten line fracture.

we claims

[Claim 1]
In mass% of the whole wire, C: 0.08~0.15%, Si: 0.001% to 0.1%, Mn: 1.6 to 1.9%, P: 0.015% or less, S: 0.015% or less, Cr: 4.0 to 5.2%, Mo: 0.4 to 0.65%, the balance including Fe and unavoidable impurities, , A wire for gas shielded arc welding in which the value X defined by the following relational expression 1 satisfies the range of 0.7 to 1.1%. [Relational Expression 1] X (%) = [Cr] / 10 + [Mo] - 4 x [Si] / [Mn] However, [Cr], [Mo], [Si] and [Mn] in Relational Expression 1 are each represents the mass % of the element in
[Claim 2]
The gas shielded arc welding wire according to claim 1, wherein a Cu plating layer is formed on the surface of the welding wire.
[Claim 3]
3. The wire for gas shielded arc welding according to claim 2, wherein the Cu constituting the Cu plating layer has a mass% of 0.4% or less (excluding 0%) of the total wire including the plating layer.
[Claim 4]
[Claim 4] The wire for gas shielded arc welding according to claim 3, wherein Cu constituting the Cu plating layer has a content in the range of 0.1 to 0.3%, in mass% with respect to the total wire including the plating layer.
[Claim 5]
The gas shielded arc welding wire according to claim 1, wherein the welding wire contains Cr: 4.2 to 4.9%, Mo: 0.45 to 0.48%, and Mn: 1.65 to 1.75%, respectively.
[Claim 6]
The gas shielded arc welding wire according to claim 1, wherein the welding wire has a Si content in the range of 0.04 to 0.08%.
[Claim 7]
The wire for gas shielded arc welding according to claim 1, wherein the welding wire is a solid wire for gas shielded arc welding.
[Claim 8]
A welded structure having a welded portion obtained by welding two or more welding base materials using the welding wire according to any one of claims 1 to 7, wherein the welded portion has, in area%, 30 to 50% martensite, bay It has a microstructure consisting of 50 to 70% of nite and retained austenite of 5% or less remaining, and the microstructure constituting the welded part has an average effective grain size of 1 to 3㎛, and a high angle crystal grain fraction of 47˚ or more is 35 A welded structure characterized in that % or more.
[Claim 9]
The welded structure according to claim 8, wherein at least one of the welding base materials is a galvanized steel sheet.
[Claim 10]
The welded structure according to claim 9, wherein the galvanized steel sheet is one of an electro-galvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet.
[Claim 11]
The welded structure according to claim 10, wherein the base steel sheet constituting the galvanized steel sheet contains at least one of Cr: 0.2 to 0.9% and Mo: 0.1 to 0.2%, in terms of its own mass%.
[Claim 12]
The welded structure according to claim 8, wherein the welded part has an average hardness of 370 to 400 Hv, and a tensile strength of 1 GPa or more, which is 95% or more of that of the base material.
[Claim 13]
[Claim 9] The welded structure according to claim 8, wherein the welded portion has a high-speed tensile strength of 95% and 80% or more of that of the base metal at tensile speeds of 3.6 km/h and 54 km/h, respectively.
[Claim 14]
A method of gas-shielded arc welding a welding base material using the welding wire according to any one of claims 1 to 7, wherein 5 to 20% CO 2 is mixed with Ar as a protective gas during the welding and used, When the thickness of the weld base material is t (mm), the range of welding heat input Q (kJ / cm) defined by the following relational expression 2 satisfies 1.15t ≤ Q ≤ 1.6t Gas, characterized in that for welding Shield arc welding method. [Relational expression 2] Q = (I × E) × 0.048 /υ However, in relational expression 2, I, E and υ represent welding current [A], welding voltage [V], and welding speed (cm/min), respectively.
[Claim 15]
15. The gas shielded arc welding method according to claim 14, wherein the welding wire is a solid wire having a diameter of 0.9 to 1.2 mm.
[Claim 16]
15. The gas shielded arc welding method according to claim 14, wherein the welding base material contains, by mass%, at least one of Cr: 0.2 to 0.9% and Mo: 0.1 to 0.2%.
[Claim 17]
15. The gas shielded arc welding method according to claim 14, wherein the welding base material is a galvanized steel sheet.
[Claim 18]
18. The gas shielded arc welding method according to claim 17, wherein the galvanized steel sheet is one of an electric galvanized steel sheet, a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet.