JPS6330112B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas-encapsulated arc welding method, and in particular uses argon (Ar) as a shielding gas (encapsulation gas).
This relates to a gas-encapsulated arc welding method that uses a strongly oxidizing gas containing a high concentration of oxygen (O ₂ ) exceeding 20%. Conventionally, in gas encapsulated arc welding of steel,
The shielding gas is carbon dioxide (CO ₂ ),
Single component gas such as Ar, CO ₂ - O ₂ , Ar - CO ₂ ,
Ar―O ₂ , Ar―hydrogen (H ₂ ), Ar―CO ₂ ―O ₂ , Ar―
Various mixed gases such as O ₂ -H ₂ have been proposed and put into practical use. However, these conventional shielding gases have advantages and disadvantages, and each has various problems that need to be solved. for example,
Welding using CO ₂ or CO ₂ - O ₂ has the disadvantage that there are many spatters, and therefore it is necessary to remove the spatters that adhere to the vicinity of the welding area, which increases welding costs. If they cannot be completely removed, there are inherent problems that will cause negative effects such as deterioration of product appearance. In addition, Ar, Ar-O ₂ welding has the disadvantage of producing a large number of pores (blow holes), and Ar-CO ₂ welding also has the disadvantage of high gas costs.
Furthermore, Ar--CO ₂ ---O ₂ , Ar--He, and Ar--H ₂ welding had the fatal drawback of causing cracks in high carbon steel welds. Moreover, the shielding gas
In the case of mixed gases such as CO ₂ - O ₂ and Ar - CO ₂ , it is difficult to liquefy the mixed gas, transport it, and supply it to the welding area because the boiling points of the mixed components differ greatly. This is also one of the causes of rising gas costs. In this respect, the Ar-O _2- based mixed gas is Ar,
Since both O ₂ and O 2 have similar boiling points, it is possible to vaporize the liquefied material with a predetermined gas composition that has been liquefied and transported and immediately introduce it to the welding area as a shielding gas, and it is possible to use a large amount of O ₂ . For example, it is expected that it will be possible to further reduce gas costs. However, increasing the O ₂ concentration in this Ar-O ₂ mixed gas has traditionally been thought to cause various problems in welding operations. For example, in the case of welding low alloy steel or austenitic steel, it is difficult to increase the In order to improve the transition state and the penetration shape of the bead cross section, it is said that the O ₂ concentration needs to be 20% or less, and according to Japanese Patent Publication No. 46-36442, If the amount exceeds 25%, the strength value is still sufficient, but sputtering and bubble formation are found to increase sharply. It was believed that the strongly oxidizing gas contained therein was inappropriate as a shielding gas in arc welding. Here, the present inventors discovered that Ar--O containing a large amount of oxygen, exceeding 20% by volume, makes the shielding gas a strong oxidizer, which has traditionally been considered difficult to use as described above. ₂ As a result of various studies on mixed gases, we found that welding using such a strong oxidizing Ar-O ₂ mixed gas greatly suppresses the generation and adhesion of spatter and cleans the weld metal. They discovered that in addition to preventing cracks and the formation of pores, they can also have beneficial rather than harmful effects in improving the appearance, leading to the completion of the present invention. That is, the present invention provides a gas-encapsulated arc welding method in which an Ar-O ₂ mixed gas with an O 2 volume fraction of more than 20% and 75% or less is used as a shielding gas, and an Ar-O ₂ mixed gas with an O 2 volume fraction of 1% or less is used as a shielding gas. Carbon (C),
Contains 0.2-2% silicon (Si), 1.7-25% manganese (Mn), 0.05-1.0% titanium (Ti) and 0.1
The purpose of this method is to use a steel wire that contains less than 2% of one or more of the above aluminum (Al) and 0.01 or more magnesium (Mg) in a total amount of less than 2%.This is the first method to reduce spatter and prevent the formation of pores. This made it possible to weld high carbon steel without cracking, with low gas costs. In other words, the present invention provides high concentrations of more than 20%
By combining a shielding gas consisting of an Ar-O ₂ mixed gas containing O ₂ and a welding wire (conductive welded filler wire) consisting of a C-Si-Mn-Ti-Al/Mg wire with a specific composition. , improves the stability of the arc and improves the transfer state of droplets, suppresses the generation of spatter under strongly oxidizing Ar-O ₂ gas, which has been considered a problem in the past, and also improves the welding area of such spatter. By suppressing adhesion in the vicinity, it was possible to improve the appearance of the product. Furthermore, according to the present invention,
The oxidizing ability of O ₂ , which is said to be 10 times that of CO ₂ gas, can effectively burn away the carbon in high carbon steel, significantly contributing to improving the prevention of cracking, and furthermore, liquefaction of Ar and O ₂ . (Vaporization) Since the temperature difference is small, it is possible to liquefy a gas mixture of a predetermined composition for transportation, then vaporize it and supply it as it is to welding, which not only makes it possible to supply large amounts of Al at low cost. ,Ti,
Due to the presence of a certain amount of deoxidizing elements such as Si and Mn,
The generation of pores could be effectively prevented. In addition, according to the present invention, it is possible to significantly suppress the generation rate of pores in fillet welds of coated steel sheets, which are said to occur on a principle different from that of ordinary pores, and also to reduce the ease of slag peeling and the formation of welds. Significant improvements were also made in various performances such as cleanliness, weld toughness, and bead appearance. Here, the volume fraction (concentration) of O ₂ in the Ar-O ₂ mixed gas as the shielding gas used in the present invention is maintained at a ratio exceeding 20% in order to achieve the above-mentioned object of the present invention. It is necessary to However, when the O ₂ concentration exceeds 75%,
O ₂
75% will be adopted as the upper limit. Among these, an O ₂ concentration of 25 to 50% is preferably employed in the present invention.
Note that even when the O ₂ concentration is lower than 20%, it has been observed that many pores occur. Also, the best residual gas other than O ₂ is Ar,
Such Ar reduces the potential gradient and allows spray transfer welding. If all Ar is used as the residual gas, the volume fraction of Ar in the shielding gas will be 25 to 80%.
However, the inclusion of nitrogen gas as an impurity is unavoidable, and therefore Ar-
It is desirable to adjust and maintain the nitrogen gas concentration in the O ₂ mixed gas to 1% or less. Generally, pores caused by O ₂ are formed by deoxidizing elements C, Si,
It can be sufficiently prevented by mixing Mn, Ti, Al/Mg, and the pores caused by nitrogen can be prevented by the denitrifying element Ti,
This can be prevented when Al/Mg is present, but if the amount of nitrogen exceeds 1%, the effect of preventing pores cannot be achieved sufficiently and also causes a decrease in toughness and ductility. Furthermore, if approximately 0.001 to 10% of methane (CH ₄ ) is contained in the Ar-O ₂ mixed gas, it will contribute to suppressing the generation of pores in the fillet welds of painted steel sheets and improve cracking resistance. Contribute. The Ar-O ₂ mixed gas with this gas composition is generally liquefied and transported to the target welding location, where it is vaporized and supplied to the welding torch as is, making it effective as a protective gas for the welding area. It can be used for On the other hand, the steel wire used in the present invention as a welding wire (conductive weld filler wire) must first contain C in an amount not exceeding 1%.
This carbon is a strong deoxidizing element that combines with O ₂ to lower the oxygen concentration in the welded steel, and its deoxidizing ability in the welded metal is as strong as that of Si, but its content is If it is too large, cracks tend to occur in the welded area, so it must be kept at 1% or less. In addition, Si and Mn work together to deoxidize, effectively contributing to the prevention of pore formation in gases with high O ₂ concentration, and when they combine with O ₂ , they cause an exothermic reaction. At the same time, since the molten steel is heated to a high temperature, inclusions in the steel are brought to the surface and removed from the system (slag-off), which improves the peeling off of the slag that is generated, which in turn has the effect of increasing toughness.
However, if the Si content is less than 0.2%, the generation of pores cannot be sufficiently prevented, while if it exceeds 2%,
In the present invention, Si is contained in the wire in the range of 0.2 to 2% because excessive deoxidation has an adverse effect on the porosity resistance and deteriorates the toughness of the welded steel. In addition, Mn is an important element that is involved in solving various problems caused by gas with high O ₂ concentration, but if its content in the wire is less than 1.7%, it is not sufficiently effective. On the other hand, if it exceeds 25%, corrosion resistance deteriorates or becomes economically disadvantageous, so the Mn content is set to 1.7 to 25%, preferably 2.0% to 5.0%. Furthermore, Ti, Al, and Mg act as strong oxygen scavengers, and at least one of them is essential for Ar--O ₂ welding, and prevents the formation of pores. especially,
Ti also improves arc stability and contributes to less spatter under high O ₂ concentrations. In addition, the O ₂ concentration in the weld metal part is
Although it can only be reduced to about 0.07%, by adding Ti, Al, and Mg, it can be reduced to 0.05%.
It can be lowered to below, which is useful for improving the performance of weld metal. For this, at least 0.05 ~
In addition to containing 1.0% Ti in the wire,
It is necessary that the wire contains one or more of 0.1% or more Al and 0.01% or more Mg in a total amount of 2% or less. It should be noted that if the total amount of Al and Mg exceeds 2%, a problem arises in that the toughness decreases. Furthermore, such C-Si-Mn-Ti-Al/Mg
Mo, Cr,
Elements such as Ni, Co, and W may be contained as appropriate. By incorporating about 0.1 to 5% Mo into the wire, the toughness and ductility of the weld metal can be improved, and the strength can also be improved. Also, Co,
Ni, Co, and W are each contained in an amount of up to 25% to improve the oxidation resistance, low-temperature toughness, high-temperature strength, room-temperature strength, etc. of the steel. It should be noted that these components may be contained in the steel wire as alloy components or may be contained in a form present on the surface of the steel wire by a method such as plating, and there is no problem. The present invention attempts to perform normal arc welding in the above-mentioned Ar-O ₂ mixed gas atmosphere with a high O ₂ concentration using a steel wire having such a composition, and thereby achieves the following: It exhibits such excellent characteristics. (1) The transfer form of droplets is improved, and spatter is reduced to about 1/10 of CO ₂ welding. Furthermore, even if spatter occurs, it will not adhere to the weld area, improving the appearance of the product.
Also, there is no need to remove spatter. (2) The occurrence of pores is reduced, and S55C, carburized steel,
Even when welding galvanized steel plates and painted steel plates, the generation of pores can be effectively suppressed. (3) The bead becomes clean. For example, like flux-cored wire, the entire surface of the bead is covered with slag, so the appearance of the bead is excellent. (4) It becomes possible to weld high carbon content materials.
When welding high carbon steel, carburized steel, or high carbon equivalent steel, carbon is released from the weld metal, resulting in a sound weld. (5) Gas costs will become cheaper. Liquefaction also saves on transportation costs. Examples will be shown below to clarify the present invention more specifically. In addition, the steel wire used in the example
The No. and the components contained therein are as shown in Tables 1 to 4 below, and the expression "the present invention" in the classification column in these tables indicates the wire composition according to the present invention, and The designation "comparison" indicates the steel wire composition used for comparison with the present invention.

【table】

【table】

【table】

【table】

[Table] Example 1 CO ₂ gas or Ar-O ₂ mixed gas containing 30% O ₂ was used as the shielding gas, and steel wire A containing 0.15% C, 0.6% Si, and 1.2% Mn was used as the welding wire.
or 0.03%C, 0.7%Si, 3.3%Mn, 0.3%Ti,
Using steel wire B containing 0.51% Al, welding current: 350A, arc voltage: 33V, welding speed: 30
cm/min, gas supply amount: 25/min, polarity: DC reverse polarity, SM50C was gas-encapsulated arc welded, and the obtained welded product (30cm in the welding direction x What is the welding method? 10 perpendicularly
The number of spatters adhering to the sample (cm) was determined and the results are shown in Table 5.

[Table] As is clear from the results in Table 5, by using the shielding gas composition and welding wire according to the present invention, adhesion of spatter to the surface of the base plate is significantly suppressed. Example 2 Using wires No. 1 to 4 (1.2 mmφ), Ar + 5%
Rimmed steel, killed steel, and low alloy steel with a thickness of 16 mm were arc welded using a mixed gas of O ₂ to Ar + 90% O ₂ as a shielding gas at a welding current of 300 A, an arc voltage of 30 to 34 V, and DC reverse polarity. Figure 1 shows the results of inspecting the occurrence of pores in the welded area using X-ray photographs.
is wire No. 3, killed steel base material; 4 is wire No. 4,
30 pieces per 200mm welding length (Ar + 5% O ₂
It can be seen that when the amount of O ₂ in the mixed gas exceeds 20%, the number of pores decreases to 0, and when the amount of O 2 in the mixed gas exceeds 75%, the number increases again to 35 or more.
In addition, when using the conventional wire No. 1 for Ar + O ₂ gas, the number of pores becomes minimal when the O ₂ content is around 15%, and when it exceeds 20%, the number of pores increases significantly again. I also found out. Furthermore, the mechanical properties of the weld metal investigated by multilayer welding using wires Nos. 3 and 4 according to the present invention are shown in Table 6, and are suitable for welding steel, especially HT and low alloy steel. The results were tolerable.
Further, the surface of the bead was uniformly covered with black slag, and the slag peelability was extremely good, and the bead appearance was as beautiful as that of flux-cored wire.

[Table] Example 3 Using wires A and B of Example 1, welding current:
350A, arc voltage: 32V, welding speed: 30cm/min
Arc welding was performed on steel plates coated with wash primer, and the tendency of porosity in fillet welds was investigated.
The results are shown in Table 7 as the pore generation rate (=Σli·100/L; where L is the length of the weld on the observation surface, and li is the length of each pore in the L direction at the observation point). From Table 7 it is clear that the results of the combination of shielding gas and wire according to the invention are excellent. It was also found that by mixing a small amount of CH ₄ into the shielding gas, good results regarding the rate of porosity generation could be obtained.

[Table] Example 4 Using wire No. 27 (1.6mmφ), 40%O ₂ -60%
360A using Ar200Kg liquefied cylinder gas
Arc welding was performed under the condition of 32V-40cm/min. As a result, no pores were observed in the weld zone, the weld bead surface was beautiful, and sound welding was achieved.
At this time, the fluctuations in the gas composition at the initial stage when the gas was taken out from the liquefied gas cylinder and after 95% use were within ±5% as shown in Figure 2, making it clear that the liquefied gas supply was industrially possible. In addition,
The properties of the welded portion were excellent as shown in Table 8.

[Table] Example 5 Welding current using wire No. 5 to 50 (1.2 mmφ)
300A, arc voltage 30~34V, welding speed 30cm/min
Various welding tests were conducted under the following conditions, and the results are shown in Tables 9 to 11. From these tables, the effectiveness of the present invention was confirmed.

【table】

【table】

[Table] Example 6 0.03%C-0.5%Si-2.7%Mn-0.05%Ti-0.3%
The preheating temperature that can prevent cracking was investigated using a Y-type cracking test (JIS-Z-3158) for each welded product obtained using Al steel wire, and the results are shown in Table 12. As is clear, according to the present invention, cracking can be effectively prevented even if the preheating temperature is low.

【table】

[Table] ○: No cracks
×: Cracking Example 7 Arc welding was performed in the same manner as in the previous examples using the wire and shielding gas shown in Table 13, and the degree of slag coverage in the resulting welded area, the time until slag peeling, JIS-G-0555
(1977), weld cleanliness, toughness, and bead appearance were evaluated. The results are also shown in Table 13. As is clear from the results in Table 13, according to the present invention, the slag is easily peeled off, the welded area is clean, the toughness is high, and the bead appearance is beautiful.

【table】 [Brief explanation of drawings]

Figure 1 is a graph showing the number of pores generated in each wire under the use of Ar-O ₂ gas with various O ₂ mixing ratios determined in Example 2, and Figure 2 is a graph showing the number of pores generated in each wire using Ar-O 2 gas with various O 2 mixing ratios determined in Example 2. 2 is a graph showing changes in O ₂ concentration with respect to the usage rate of liquefied gas packed in a cylinder.

Claims (1)

[Claims] 1. An argon-oxygen mixed gas with an oxygen volume percentage of more than 20% and 75% or less is used as a shielding gas, and as a welding wire, carbon of 1% or less, 0.2~
2% silicon, 1.7-25% manganese, 0.05-1.0%
of titanium and 0.1% or more of aluminum,
An arc welding method using a shielding gas containing a high concentration of oxygen, characterized by using a steel wire containing at least 2% of one or more types of magnesium in a total amount of 0.01% or more. 2. The method according to claim 1, wherein the volume fraction of nitrogen gas in the argon-oxygen mixed gas is maintained at 1% or less. 3. The method of claim 1, wherein the argon-oxygen gas mixture is supplied by vaporizing a liquefied product of the gas mixture. 4 The argon-oxygen mixed gas is 0.001 to 10
% of methane. 5. The steel wire as the welding wire further contains up to 5% molybdenum and/or up to 25% each of one or more of chromium, nickel, cobalt and tungsten. Any method described.