Title of the invention: Overlap welding method of galvanized steel sheet
Technical field
[One]
The present invention relates to an overlap welding method of a hot-dip galvanizing steel sheet having a tensile strength of 780 MPa or more and a thickness of 6 mm or less applied to automobile chassis parts. The present invention relates to a method of overlapping welding of galvanized steel sheets that can improve the strength of weld metal by effectively reducing weld porosity defects up to a welding speed of 100 cm/min without introducing existing constraints such as providing gaps and changing arc positions.
[2]
Background
[3]
In the automotive field, research on technology to reduce weight of vehicle bodies and parts is emerging as a major issue due to policies to regulate fuel economy according to environmental protection such as global warming. Chassis parts, which are important for vehicle driving performance, are also required to apply high-strength steel for weight reduction in accordance with this trend. In order to achieve weight reduction of parts, it is essential to increase the strength of the material, and guaranteeing the durability of parts 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 strength when assembling automobile chassis parts, overlapping joint welding between parts is performed by welding of welding wires, so it is particularly important to secure the strength of the weld metal in the case of high-strength steel. In addition, as described above, due to the thinning of the material due to the high strength and weight reduction of parts, the demand for rust prevention to prevent penetration corrosion has increased, so the adoption of plated steel is increasing. Porosity defects are sensitive, which is a factor that lowers the strength of the weld. In particular, the higher strength steel is, the greater the concern that the weld metal may be damaged due to insufficient strength due to pore defects in the weld metal part.
[4]
According to Patent Document 1, which is a conventional patent, it is proposed to set the gap of the overlapping joint in the range of 0.2 to 1.5 mm in order to suppress the occurrence of pore defects in the arc welding part of Zn-based galvanized steel sheet, but when the actual part is applied, the joint without gap There is a limit that cannot guarantee the welding properties of the structure. In addition, according to Patent Document 2, in order to solve the above problem, a ternary protective gas in which Ar is mixed with CO 2 and O 2 and a low-viscosity solid wire with limited contents of Si and Mn are applied, and in addition to the arc position It is proposed to float 1mm from the tip of the weld overlapping joint, but restrictions on the protective gas and welding material are inevitable, and there is a burden to keep the arc position constant when applying real parts.
[5]
[Prior technical literature]
[6]
[Patent Literature]
[7]
(Patent Document 1) Japanese Patent Laid-Open No. 2016-101593
[8]
(Patent Document 2) Japanese Patent Laid-Open No. 2015-167981
[9]
Detailed description of the invention
Technical challenge
[10]
Therefore, the present invention optimizes the polarity fraction of the arc welding current so as to effectively reduce the pore defects of the weld during overlap welding of galvanized steel sheets. It is an object of the present invention to provide a method of lap welding of galvanized steel sheets capable of providing welding parts of galvanized steel sheets having a tensile strength of 780 MPa or more and a thickness of 6 mm or less without constraints.
[11]
Means of solving the task
[12]
The present invention for achieving the above object,
[13]
In the method of overlapping a galvanized steel sheet using a welding material, when welding, a welding current of 150 to 300A, a mixed gas of Ar+10 to 30% CO2 as a protective gas, and a welding polarity fraction defined by the following relational formula 1 The present invention relates to a method of welding galvanized steel sheets capable of reducing pore defects in weld metal by alternately changing the welding polarity to satisfy the range of 0.25 to 0.35.
[14]
[Relationship 1]
[15]
EN R,% /(EP R,% +EN R,% )
[16]
Here, EN R,% represents the polarity fraction of cathode welding, and EP R,% represents the polarity fraction of anode welding.
[17]
[18]
The welding material may be E70C-GS Φ1.0 metal cored wire.
[19]
[20]
The gap between the welded joints may be 0 mm.
[21]
[22]
The welding current may be 200 to 270A.
[23]
[24]
The galvanized steel sheet may be HGI 780HB steel.
[25]
Effects of the Invention
[26]
According to the present invention, through the optimization of the polarity fraction of the arc welding current, it is possible to effectively reduce the pore defects of the overlap joint weld without a joint gap, thereby effectively improving the weld strength of the galvanized steel sheet component with a tensile strength of 780 MPa or more manufactured accordingly. I can. Therefore, it can have industrial significance that can expand the adoption of galvanized steel sheets for securing high strength of parts such as automobile chassis members and rust prevention due to thinning.
[27]
Brief description of the drawing
[28]
1 is a schematic diagram showing a polarity fraction of an arc welding current according to an embodiment of the present invention.
[29]
Figure 2 is a cross-sectional photograph of a weld bead before and after optimization of the polarity fraction of the galvanized steel sheet arc welding (the used welding base material is HGI 780Hyber Burring steel 2.0mmt, the tensile strength is 810MPa, and the plating amount is 100g/m 2 on one side ) .
[30]
3 is a photograph showing the appearance of the weld after optimizing the polarity fraction of the galvanized steel sheet arc welding and the result of X-ray transmission of the weld (degree of welding 100 cm/min).
[31]
4 is a graph showing the result of measuring the hardness of the weld after optimizing the polarity fraction of the galvanized steel sheet arc welding current.
[32]
5 is a graph showing the results of the tensile curve of the weld after optimizing the polarity fraction of the galvanized steel sheet arc welding current.
[33]
Best mode for carrying out the invention
[34]
Hereinafter, the present invention will be described.
[35]
The inventors of the present invention are able to effectively discharge zinc vapor to the outside by vibrating the molten paper formed by welding by optimally controlling the polar fraction of the arc welding current during overlap welding of galvanized steel sheets. It is confirmed that defects can be reduced and the present invention is presented.
[36]
That is, in the welding method of a galvanized steel sheet of the present invention, in a method of overlapping a galvanized steel sheet using a welding material, when welding, a welding current of 150 to 300A, a protective gas Ar+10 to 30% CO2 And it is characterized in that the welding polarity is alternately changed so that the welding polarity fraction defined by the following relational equation 1 satisfies the range of 0.25 to 0.35.
[37]
[38]
First, the present invention relates to an overlap welding method of a galvanized steel sheet.
[39]
The lap welding method refers to a method of welding the first galvanized steel sheet and the second galvanized steel sheet laminated to partially overlap the first galvanized steel sheet while forming a weld metal through lap arc welding.
[40]
In the present invention, the galvanized steel sheet includes a general galvanized hot-rolled or cold-rolled steel sheet, and further, the plated steel sheet may be a Zn-Mg-Al alloy-plated steel sheet.
[41]
In the present invention, a weld metal is formed by joining the first galvanized steel sheet and the second galvanized steel sheet laminated to partially overlap the first galvanized steel sheet through arc welding. That is, after preparing the first galvanized steel sheet and the second galvanized steel sheet, a welding line is formed by laminating the second plated steel sheet on the first plated steel sheet so that at least a portion thereof overlaps, and then If the welding current is supplied to the welding material while providing the shield gas along the formed welding line, an arc is generated to proceed with arc welding.
[42]
In the present invention, at this time, the overlapping width of the welding joint may be applied to about 25 mm, but is not limited thereto.
[43]
In addition, in the present invention, the welding material may be an E70C-GS Φ1.0 metal cored wire, and is not particularly limited to the type and component of the welding material.
[44]
[45]
And during welding, the welding current is preferably limited to 150A or more and 300A or less, and more preferably to 200A or more and 270A or less. If the current is too low, the effect of discharging the plating vapor decreases due to the reduction in arc force. On the contrary, if the current is too high, the molten welded metal part is unstable and the occurrence of pore defects may increase.
[46]
[47]
In addition, in the present invention, it is necessary to mix 10 to 30% CO2 with Ar as a protective gas during welding. That is, the shielding gas is Ar gas, and contains 10 to 30% of CO2 gas, but if the CO2 gas is less than 10%, the arc thermal pinch force effect due to arc expansion is reduced, thereby reducing the plating vapor discharge effect. In addition, when the CO2 gas is included in an amount exceeding 30%, the arc heat pinch force effect due to arc contraction is excessive, and the effect of discharging the plating vapor is deteriorated.
[48]
[49]
In addition, in the present invention, during the arc welding, it is preferable to manage the welding torch angle in the range of 30 to 45° and the proceeding angle in the range of 0 to 25°.
[50]
In addition, in the present invention, a gap of 0 mm may be applied to the welding joint, but is not particularly limited thereto.
[51]
[52]
On the other hand, in the case of overlap welding of galvanized steel sheets, during arc welding, the zinc plated layer with a low boiling point becomes zinc gas due to arc heat and floats to the top of the molten paper. A hollow blowhole is formed. Accordingly, there is a problem in that the weld metal produced by welding has pore defects, and thus, the weld metal having excellent tensile strength cannot be obtained.
[53]
Accordingly, the present invention is to solve this problem, and is characterized in that the welding polarity is alternately changed so that the welding polarity fraction defined by the following relational equation 1 satisfies the range of 0.25 to 0.35. Accordingly, by vibrating the molten paper formed by welding to discharge zinc vapor, it is possible to reduce pore defects of the weld metal.
[54]
[Relationship 1]
[55]
EN R,% /(EP R,% +EN R,% )
[56]
Here, EN R,% represents the polarity fraction of cathode welding, and EP R,% represents the polarity fraction of anode welding.
[57]
1 is a schematic diagram showing a polarity fraction of an arc welding current according to an embodiment of the present invention. As shown in FIG. 1, by appropriately mixing and varying the welding polarity fraction, the melting ground vibration increases due to an increase in arc pressure and volume transition frequency, thereby promoting an increase in zinc vapor discharge.
[58]
[59]
In the present invention, in the case of overlap welding of galvanized steel sheets, the anode polarity fraction (EP R,% ) of the welding material and the cathode polarity fraction (EN R,% ) of the welding base material are determined in order to effectively discharge zinc vapor from the molten sheet . It is characterized by controlling the value of the relational expression 1 to be an appropriate value, and the introduction of this concept is due to the following technical idea.
[60]
In the case of a general DCEP (Direct Current Electrode Positive) Pulse, the volume of the molten paper increases due to an increase in heat input due to arc contraction, and thus there is a limitation in that the discharge of pores due to zinc vapor generated during welding is reduced. On the other hand, when DCEP and DCEN (Direct Current Electrode Negative) polarity are mixed in an appropriate fraction and changed, arc contraction and oxygen atmosphere increase can increase the activation of the negative electrode of the wire in the DCEN cycle. That is, during the DCEN cycle, the wire is heated due to frequent occurrence of the cathode point and the arc concentration at the top of the wire, and an arc is generated at the top of the wire while the current path is maintained in the subsequent DCEP cycle. At this time, the globular and spray volume transfer modes occur, which increases the volume transfer frequency and simultaneously increases the arc pressure pressurization frequency, thereby maximizing the discharge of pores generated in the melt.
[61]
Therefore, in the case of a variable polarity arc, since the arc pressure and volume transfer are irregular and high frequency, the pore discharge effect is excellent. However, when the DCEN polarity fraction is lower than the appropriate value, the effect is reduced if the value defined by the above relational equation 1 is less than 0.25.
[62]
On the other hand, in the case of a galvanized steel sheet such as HGI, the arc is eccentric in the DCEN polarity due to the influence of the galvanized layer, and the arc effective radius decreases as the cathode point is distributed over a wide area on the surface of the base material, or the cathode point is a specific area. The phenomenon that is concentrated on occurs reduces the welding heat input efficiency. In addition, the higher the DCEN polarity fraction, the more coarse and unstable globular transitions and arcs occur, and the exposure time of the cathode point to the volume increases. Appears as. In other words, if the DCEN polarity fraction exceeds the red bluish value (the value defined by the relational equation 1 exceeds 0.35), it has an adverse effect on suppressing the occurrence of pore defects in the weld zone.
[63]
Mode for carrying out the invention
[64]
Hereinafter, the present invention will be described in detail through examples.
[65]
(Example)
[66]
Two 2.0mmt HGI 780Hyber Burring steel sheets with a plating amount of 100g/m 2 on one side were made to overlap each other by 25mm, and the connection was welded. Specifically, using the welding materials and welding conditions as shown in Table 1-2, respectively, the HGI 780HB steel was lap-welded. In addition, the presence or absence of pit generation and the pore area ratio were measured and shown in Table 1 below, and the tensile strength and fracture unit value of the welded portion were measured and shown in Table 2.
[67]
[Table 1]
Mark Welding material Welding conditions (welding current-voltage-speed) Current characteristics feet Pore ​​area ratio Remark
One ER70S-6Φ1.2 202A-20.6V-0.6m/min EP:EN=100:0 X 1.55% Comparative Example 1
2 ER70S-6Φ1.2 242A-23.7V-0.8m/min EP:EN=100:0, Pulse O 12.67% Comparative Example 2
3 ER70S-6Φ1.2 263A-25.6V-1.0m/min EP:EN=100:0, Pulse O 20.60% Comparative Example 3
4 ER70S-3Φ1.0 162A-26.4V-0.6m/min EP:EN=100:0, Pulse X 4.46% Comparative Example 4
5 ER70S-3Φ1.0 217A-28.9V-0.8m/min EP:EN=100:0, Pulse X 5.70% Comparative Example 5
6 ER70S-3Φ1.0 257A-30.0V-1.0m/min EP:EN=100:0, Pulse O 8.25% Comparative Example 6
7 E70C-GSΦ1.0 214A-24.0V-1.0m/min EP:EN=50:50, Pulse X 2.51% Comparative Example 7
8 E70C-GSΦ1.0 213A-24.0V-1.0m/min EP:EN=60:40, Pulse X 2.34% Comparative Example 8
9 E70C-GSΦ1.0 214A-24.0V-1.0m/min EP:EN=65:35, Pulse X 0.97% Invention Example 1
10 E70C-GSΦ1.0 209A-24.0V-1.0m/min EP:EN=70:30, Pulse X 0.87% Invention Example 2
11 E70C-GSΦ1.0 216A-24.2V-1.0m/min EP:EN=75:25, Pulse X 0.94% Invention Example 3
12 E70C-GSΦ1.0 210A-24.0V-1.0m/min EP:EN=80:20, Pulse X 1.52% Comparative Example 9
[68]
[Table 2]
Mark Welding material Welding conditions (welding current-voltage-speed) Current characteristics The tensile strength Wave unit Remark
One ER70S-6Φ1.2 202A-20.6V-0.6m/min EP:EN=100:0 625 MPa Welding metal Comparative Example 1
2 ER70S-6Φ1.2 242A-23.7V-0.8m/min EP:EN=100:0, Pulse 599 MPa Welding metal Comparative Example 2
3 ER70S-6Φ1.2 263A-25.6V-1.0m/min EP:EN=100:0, Pulse 473 MPa Welding metal Comparative Example 3
4 ER70S-3Φ1.0 162A-26.4V-0.6m/min EP:EN=100:0, Pulse 690 MPa Heat affected zone Comparative Example 4
5 ER70S-3Φ1.0 217A-28.9V-0.8m/min EP:EN=100:0, Pulse 678 MPa Heat affected zone Comparative Example 5
6 ER70S-3Φ1.0 257A-30.0V-1.0m/min EP:EN=100:0, Pulse 670 MPa Heat affected zone Comparative Example 6
7 E70C-GSΦ1.0 214A-24.0V-1.0m/min EP:EN=50:50, Pulse 692 MPa Heat affected zone Comparative Example 7
8 E70C-GSΦ1.0 213A-24.0V-1.0m/min EP:EN=60:40, Pulse 696 MPa Heat affected zone Comparative Example 8
9 E70C-GSΦ1.0 214A-24.0V-1.0m/min EP:EN=65:35, Pulse 700 MPa Heat affected zone Invention Example 1
10 E70C-GSΦ1.0 209A-24.0V-1.0m/min EP:EN=70:30, Pulse 702 MPa Heat affected zone Invention Example 2
11 E70C-GSΦ1.0 216A-24.2V-1.0m/min EP:EN=75:25, Pulse 701 MPa Heat affected zone Invention Example 3
12 E70C-GSΦ1.0 213A-24.0V-1.0m/min EP:EN=80:20, Pulse 698 MPa Heat affected zone Comparative Example 9
[69]
As shown in Table 1-2, Comparative Example 1-3 in which the polarity fraction value defined by the relation 1 as well as the welding conditions such as welding current satisfies the range of 0.25 to 0.35 is not Comparative Example 1-8 Compared to that, it can be seen that the effect of discharging zinc vapor is reduced, thereby reducing pore defects in the weld, thereby improving the tensile strength of the weld.
[70]
[71]
Meanwhile, FIG. 2 is a cross-sectional photograph of a welding bead before (Comparative Example 8) and after (Inventive Example 2) optimization of the polarity fraction of the galvanized steel sheet arc welding, and FIG. 3 is It is a photograph showing the appearance of the weld after optimization and the result of X-ray transmission of the weld (connection diagram 100 cm/min), and FIG. 4 is a graph showing the result of measuring the hardness of the weld after optimizing the polarity fraction of the galvanized steel sheet arc welding current of Inventive Example 2, And Figure 5 is a graph showing the results of the tensile curve of the weld after optimizing the arc welding current polarity fraction of the galvanized steel sheet of Example 2 of the present invention.
[72]
As can be seen in FIGS. 4 and 5, it can be seen that even at a welding speed of 100 cm/min, the hardness value of the weld metal part is quite constant without a large decrease in width due to pore defects. It can be seen as a result of suppressing the occurrence of pore defects in the weld metal due to fracture in the weld heat-affected zone without.
[73]
[74]
As described above, in the detailed description of the present invention, preferred embodiments of the present invention have been described, but those of ordinary skill in the art to which the present invention pertains, various modifications may be made without departing from the scope of the present invention. Of course it is possible. Therefore, the scope of the present invention is limited to the described embodiments and should not be determined, and should not be determined by the claims to be described later, as well as those equivalent thereto.
Claims
[Claim 1]
In the method of overlapping a galvanized steel sheet using a welding material, when welding, a welding current of 150 to 300A, a mixed gas of Ar+10 to 30% CO2 as a protective gas, and the welding polarity fraction defined by the following relation The welding method of galvanized steel sheet that can reduce the pore defects of the weld metal by alternately changing the welding polarity to satisfy the range of 0.25 to 0.35. [Relationship 1] EN R,% /(EP R,% +EN R,% ) Here, EN R,% denotes the negative polarity fraction, and EP R,% denotes the positive polarity fraction.
[Claim 2]
The method of claim 1, wherein the welding material is E70C-GS Φ1.0 metal cored wire.
[Claim 3]
The welding method for a galvanized steel sheet according to claim 1, wherein the gap between the weld joints formed by the overlap welding is 0 mm.
[Claim 4]
The method of claim 1, wherein the welding current is 200 to 270A.
[Claim 5]
The method of claim 1, wherein the galvanized steel sheet is HGI 780HB steel.