JPH01143775A - Arc welding method for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To obtain a weld zone with less pits by using a solid wire of the Fe having a specified chemical composition as a positive electrode, transferring the globule to the base metal when a base current is applied, and carrying out welding in a shielding gas of Ar mixed with specified amts. of CO2 or O2. CONSTITUTION:The solid wire consisting, by weight, of 0.02-0.12% C, 0.10-0.80% Si, 0.20-1.20% Mn, 0.003-0.03% P, 0.003-0.03% S, and the balance Fe is used, and a shielding gas consisting essentially of Ar and contg., by volume, 5-50% CO2 or 2-20% O2 is used. A periodically repeated pulse DC current is projected on the zinc plating layer 7 by the heavy-current arc column 3 when a peak current is applied to melt and vaporize the layer 7, the globule 4 is short-circuited and transferred to the base metal from the tip of the solid wire 2 when a base current is applied and welding is carried out. By this method, pits are not generated, a welded metal part with an extremely small number of blowholes is obtained, the strength of a structure is not decreased, and the appearance is also ameliorated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to gas shield welding of steel materials that have been previously subjected to anti-corrosion treatment, and is a welding method that produces a sound welded metal part with fewer pits and blowholes. Regarding the method.

[Conventional technology]

Galvanized steel sheets are usually hot-rolled or cold-rolled steel materials coated with zinc to prevent corrosion and improve corrosion resistance, and are used in construction materials such as roofing sheets, gasoline conversion, and washing machine parts. , used in automobiles, etc.

When this galvanized steel sheet is welded, its boiling point is 9
The combustion and gasification of zinc at temperatures as low as 0.6°C disturbs the arc and increases the occurrence of spatter, and when zinc is present in the molten pool, the zinc vapor bumps and solidifies the weld metal, causing pits and blowholes in the weld. This causes frequent welding defects.

Welded metal parts without weld defects such as pits and blowholes do not have any particular problems with the material, but pins and blowholes cause cross-sectional defects in the necessary weld metal, which is undesirable from the perspective of ensuring the strength of the structure. etc. are unfavorable in appearance and not only reduce the commercial value but also lead to a decrease in productivity. This is not a problem when welding with illuminite-based welding rods or titania-based welding rods because pits and blowholes are less likely to occur, but pits and blowholes occur when welding with gas shield using solid wire. is remarkable.

JP-A No. 59-45096 targets a steel plate coated with a primer containing zinc powder, and uses 7i, Ss, Sb, and S to prevent defects such as focus and blowholes.
Although a welding material containing an appropriate amount of is proposed, it is considered to be less effective for welding galvanized steel sheets, which is the object of the present invention.

[Problem that the invention seeks to solve]

The present invention has been made to solve the above-mentioned problems, and it solves the problem that when galvanized steel plates are welded with solid wire for gas shield welding, welding defects such as pits and blowholes occur in the welded part. It is something to be solved.

[Means for solving problems]

In the welding method of the present invention, as the composition of the solid wire, C, Si, and Mnl, which are LJ-like and deoxidizing elements that reduce the activity of zinc vapor generated during welding, are superimposed on each other. 0.12%, Si: 0.10-0.
80%, Mn: 0.20 to 1.20%, and the shielding gas is 5 to 50 voj in Ar! % CO
Arc using a shielding gas mixed with □ or 2 to 20 vol% 0□, using the wire as the positive electrode, and using a pulsed direct current without periodically repeating the current at the peak current and the small current at the base current. During welding, the zinc on the surface of the base metal is irradiated and melted by the high current arc at the peak time, without transferring droplets from the wire to the base metal, and the zinc on the plated part is actively evaporated, and then the base metal is removed. This is an arc welding method for galvanized steel sheets, characterized by short-circuiting droplets from the tip of a solid wire to the base metal side when current is applied, and welding while repeating this state.

That is, the present invention appropriately selects the composition of the wire components, uses pulsed DC current without periodically repeating the peak current and base current, and limits the welding transition form, and furthermore appropriately selects the shielding gas composition. Even when gas shield welding is performed, pits and blowholes are likely to occur.

[For production]

As mentioned above, the inventors believe that the reason why pits and blowholes are particularly likely to occur in galvanized steel sheets during gas shield welding using solid wire is as follows: (a) Zinc has a low boiling point of 906°C; When the weld metal is in a molten state, zinc vapor is bumped to form bullholes.

(U) In particular, in solid wires that do not use coatings or flux, large amounts of Si, Mn, etc. are added to strengthen the deoxidizing effect, but in weld metals that are rich in deoxidizing elements such as Si and Mn, the It was considered that it increases the activity of zinc and promotes (a). And this idea! , (To make the pit, sol'l-ball January 1-, (
c) Reduce the amount of deoxidizing elements such as Si and Mn added as much as possible to reduce the activity of zinc in the molten state of the weld metal.

(d)1! Suppose that the boiling point of 1-menzated zinc is 906
℃ is lower than that of steel, so if this zinc is actively evaporated with an arc before it penetrates into the weld metal, the effect of zinc on the weld metal will be reduced.

Considering this idea, the composition system of solid wire used for welding galvanized steel sheets is low C-low Si-
Considering that a low Mn system is suitable, we attempted to control the arc generation and droplet transfer conditions in arc welding of galvanized steel sheets, and as a result, we have constructed the present invention.

The reason for limiting the wire components will be described below.

C is determined depending on the amount of Si and Mn added, and the amount of Si and Mn added in the present invention is less than 0.02% and 0.12%.
Since blowholes occurred frequently when exceeding 0.02, the lower limit was set to 0.02.
%, with an upper limit of 0.12%.

S1+ Mn is added as a deoxidizing agent like C, but when it is added beyond the range of the present invention, pits and blowholes occur frequently, probably because the activity of zinc increases, so Si is added.

The upper limits of Mn were 0.80% and 1.20%, respectively. Also, if Si is less than 0.10% and Mn is less than 0.20%, deoxidation will basically be insufficient, and bits and blowholes other than those caused by galvanizing will occur frequently.
The lower limits of n were set to 0.10% and 0.20%, respectively.

In the present invention, P and S are added for the purpose of reducing the amount of spatter generated and improving the bead shape, but 0.003
% or less, and if it exceeds 0.030%, this effect will decrease and sensitivity to high temperatures will increase, so 0.003 to 0.03%.
03%.

The shielding gas used in the present invention is an inert gas containing 5 to 50 vol% carbon in order to stabilize the arc, suppress the occurrence of spatter, and ensure bead formation.
Ot or 2-20 voj! A shielding gas mixed with 0° active gas is used.

This ensures good arc stability, droplet migration, etc.

Figures 1 and 2 show the arc conditions and droplet transfer conditions at peak current and base current in arc welding of °C2 galvanized steel (reverse arc welding) as an example of the present invention, respectively.
1 is a direct current welding torch, 2 is a solin 1, 3 is a
4 is a droplet generated from the tip of the solid wire and transferred to the base metal, 5 is the weld metal, 6 is the shielding gas, 7 is the zinc layer coated on the surface of the base metal, 8
In the present invention, periodically repeated pulsed DC current is applied to a large current arc at the peak current as shown in Fig. 1, and the zinc plated on the base metal surface near the arc is irradiated and melted. After evaporation, welding is performed while short-circuiting the droplets from the tip of the solid wire to the base metal side when the base current is applied as shown in FIG. This method reduces harmful effects on arc welding such as burning and gasification of zinc, stabilizes the arc, and reduces welding defects such as blowholes inherent in the weld metal and pits that occur on the surface of the weld metal. Beautiful weld metal can always be formed.

Note that this effect is effective when the diameter is 1. When using a sm solid wire, the current value at the peak current should be 400Δ or more.The current value at the base current should be less than IQOA, so that the droplet 4 smoothly transfers to the base material at the base current. To do this, use 5 to 50 vol in Ar as shield gas 6!
It is necessary to use a mixture of 2 to 20 vol% of Nishima or 2 to 20 vol% of 0□.

In the present invention, it is necessary to select the chemical composition of the solid wire because the chemical composition of the solid wire also affects the welding defects of bits and blowholes.

〔Example〕

Table 1 shows the present invention and comparative examples.
It is shown by 32.

All wire diameters are 1.2mm-φ, and by combining the shielding gas composition with pulsed arc welding using a pulsed DC power supply and normal DC arc welding using a constant voltage DC power supply,
Galvanized steel sheets shown in the table (thickness t: 2,3 mm),
Plate width w: 50 long, length l: 300 ■-, zinc stitched needle:
60 gr/rrr) were stacked on top of each other as shown in Figure 3, and gas shield welding was performed at the fillet. The current value of the arc condition is 450A at high current and 5A at low current in pulsed arc welding.
The average current value of 0A is shown.

After welding is completed, the number of weld defect pits that have occurred on the weld metal surface is visually measured, and then the welded area is measured as shown in Table 2. We investigated the occurrence of blowholes.

After counting the number of pits, the number of pits generated per meter of bead length (number of pits/m) is evaluated.
The blowhole width in the bead length direction was measured from the film of the 3-pass test, and the blowhole occurrence rate (%) was calculated from the total blowhole width with respect to the bead length.

Test number 1-12.19.25-27.31 is the present invention, 1
1h13-18.20-24.28-30.32 show comparative examples.

Yang IN! 1m12, 19.25 to 27.31 is pulsed arc welding, and there is less equipment for adding deoxidizing elements such as Si and Mn in the wire chemical components, and the equipment for zinc in the weld metal molten state is smaller, which may have caused the number of pits and blowholes to increase. The incidence is decreasing.

Tests 11m13 to 17 were pulsed arc welding, but due to the excessive addition of deoxidizing elements C, Si, and Qn,
Alternatively, the amount is too low, resulting in insufficient deoxidation, resulting in an increase in the number of pits and blowholes. Test positive 1B and Arashi 20-24.29-30゜32 are for DC arc welding, and even if the wire exceeds the wire chemical composition range of the present invention, the number of pits and blowhole occurrence rate are , since the zinc on the base metal surface is intervening in the molten pool and causing harmful effects, the amount of zinc is very large (28).Furthermore, the wire chemical composition is within the range of the present invention due to pulsed arc welding, but the shielding gas is changed to 008. Although no pits were generated, the blowhole generation rate was high.Although not specifically mentioned in Table 1, Nal 8.Na21.m2B using COt as the shielding gas had a high sputtering rate compared to other examples. It was judged that the number of cases was significantly large and that it was not practically preferable.

Based on this result, in the method of the present invention, the chemical composition of the wire is C: 0.02 to 0.12%, Si: 0.10%.
~0.80%, Mn: 0.20-1.20% p.

S is appropriately selected from 0.003% to 0.03%, respectively, and a pulsed direct current that periodically repeats a peak current and a base current is used to limit the droplet transfer form, and the shielding gas composition is further adjusted appropriately. If selected, even when welding galvanized steel sheets, a sound welded metal part that is not focused and has very few blowholes can be obtained.

〔Effect of the invention〕

As described above, in the present invention, even when galvanized steel sheets subjected to anti-corrosion treatment are welded with gas shield using solid wire, a sound welded metal part with no pits and very few blowholes can be obtained. , weld metal section cutout tn
The strength of the structure will not deteriorate. Furthermore, since no pits are generated, a welded metal part that is pleasing in appearance can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the arc status and droplet status at peak current during arc welding of galvanized steel sheets, and Figure 2 is a schematic diagram showing the arc status and droplet transfer status at base current, same as Figure 1. FIG. 3 is a perspective view of a downward lap fillet weld joint. 1: Direct current welding torch, 2: Solid wire, 3: Arc column at peak current, 4: Droplet, 5:
Weld metal, 6: Shielding gas, 7: Galvanized layer, 8:
Base metal, W: welding direction. Patent applicant Nippon Steel Corporation

Claims (1)

[Claims] Chemical components are C: 0.02 to 0.12% by weight, Si: 0
．． 10 to 0.80% by weight, Mn: 0.20 to 1.20% by weight, P: 0.003 to 0.03% by weight, S: 0.003 to 0.03% by weight, with the balance being Fe and Using a solid wire consisting of unavoidable impurities, using a shielding gas containing 5 to 50 vol% CO_2 or 2 to 20 vol% O_2 in Ar, a pulsed direct current is used to generate droplets using the wire as a positive electrode. A method for arc welding galvanized steel sheets, characterized in that welding is performed while transferring the welding material to the base metal side at the base current without transferring it to the base metal side at the peak current.