JPS594233B2 - Gas shield arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-shielded arc welding method for welding structural steel, and the present invention relates to a gas-shielded arc welding method for welding structural steel. The purpose of this invention is to realize welding in which welding defects such as pores are less likely to occur by applying it to welding work on welded objects with surfaces that are uneven.

Traditionally, as welded structures become larger, there has been a strong demand for shorter and labor-saving welding processes, and to meet this demand, various automatic welding methods, such as submerged arc welding, CO2 arc welding,
2-Ar arc welding, CO25-O2 arc welding and no gas arc welding methods have been widely applied. but,
All of these conventional automatic methods tend to produce a large number of pores when welding steel sheets coated with shop primer, which has often been a major problem.

As a result of investigating the cause of this, it became clear that the above-mentioned pore formation was due to the relationship between the oxygen level of the weld metal formed by these automatic methods and the hydrogen supplied from the high-molecular organic compound as the color vehicle of the shop primer. Summer.

That is, the weld metal produced by the conventional automatic welding method described above contains relatively large amounts of Si, At, Ti, and in some cases Mg and C.
Because of strong deoxidation by elements such as a, the oxygen content of weld metals produced by these conventional methods is generally 0.04 wt% or less, and dissolved hydrogen becomes extremely active in such a low oxygen content range.

As a result, gasification of dissolved hydrogen is promoted, so it is thought that pores are formed due to hydrogen gas.

Research has shown that pore formation in this case can be prevented by lowering the degree of deoxidation in the welding material or adding oxygen to the molten pool to increase the amount of oxygen in the weld metal compared to the conventional method. revealed.

However, in multilayer welding using any of the above methods that can form a weld metal with a high oxygen content, if hydrogen cannot be supplied from the primer, such as in one-bus fillet welding, so-called desorption due to an excessive amount of oxygen occurs. Forms acid-deficient pores.

Therefore, in order to be applicable not only to single-layer fillet welding of steel plates to which primer containing a hydrogen source is attached, but also to both sides of multi-layer joint welding, the oxygen content level in the weld metal must be lower than that of conventional methods. It seems effective to increase the hydrogen content as well as increase the hydrogen content.

From this point of view, it is considered that coated welding slags such as illuminite type, lime titania type, titania type, cellulose type, hexagram, and iron powder iron oxide type realize the above theory industrially. In other words, the oxygen and hydrogen content of the weld metal produced by these welding rods is higher than that of any of the current automatic welding methods. Defect-free weld metal can also be obtained.

However, welding work using these welding rods has disadvantages in that it is inferior in efficiency and does not suit the recent trend toward automation, and it goes without saying that automation is strongly desired. The present invention applies the above theory to automatic welding and has succeeded in industrializing it.

That is, the present invention is a gas-shielded arc welding method for welding structural steel using a flux-cored wire, in which the wire is 0.
It is characterized by using a shielding gas that contains 5 to 8.5 wt% of Mn element as an essential component, is filled with a flux to which 17 wt% or less of a hydrogen source compound is added, and has a total hydrogen content of more than 5v0t%. It is something.

The present invention will be explained in detail below.

(1) Mn element In the present invention, the level of wire deoxidation is lowered as much as possible, and the amount of oxygen in the weld metal is increased compared to the conventional automatic method.

i.e. conventional automatic methods, e.g. submerged arc welding, CO2
Many of the welding methods, inert gas welding methods, no-gas welding methods, etc. use large amounts of strong deoxidizing elements such as Si, At, Ti, Mg, etc. to reduce the oxygen level of the weld metal as much as possible. However, as mentioned above, when the oxygen level in the weld metal is reduced, the hydrogen that dissolves into the metal from moisture in the outside air, moisture in the welding material, and hydrogen sources adhering to the steel material becomes very active. This has the disadvantage that gas pores are likely to be formed.

Therefore, in all of the conventional automatic methods described above, it is necessary to remove the hydrogen source during welding, which makes the welding method itself difficult to handle. From this meaning, the present invention}
The deoxidizing element used in the process is characterized in that it does not extremely reduce the oxygen level, in other words, it is mainly composed of Mn, which has a low deoxidizing ability.

As shown in the experimental results of FIG. 1, the amount of Mn added to the wire used in the present invention is effectively within the range of 0.5 to 8.5 wt%. By the way, the test wire flat 1 used in the experiment shown in Fig. 1 contained 8.5 wt% rutile, 3.5 wt% silica sand, 3.3 wt% potassium feldspar, and 0% by weight of the total weight of the wire.
Mn was added in various proportions in the range of ~10.7 wt% by equivalent replacement with iron powder, and Wire Black 2 contained 4.0 wt% dolomite, 2.3 wt% rutile, 7.0 wt% silica sand, 2.0 wt% potassium feldspar, 0-10.7 wt% Mn
The wire flat plate 3 contains 1.0 wt% of fluorite, 4.0 wt% of rutile, 2.0 wt% of silica sand, and 3.
0 wt (fl) magnesium carbonate, 2.0 wt% lime carbonate, 0.5 wt% magnesium oxide, 0. , 5w
Add t% of SilO to 13.0wt% of Mn to replace the iron powder in an equivalent amount and add 2.4r! The diameter was m. The ratio of the flux to the total weight of the wire was -26%, the outer sheath of the wire was made of extremely mild steel, and the welding conditions were a current of 350 A (alternating current), a voltage of 31 to 33 V, and a speed of 20 to 35 cm/Rin.

Well, the shielding gas is 20v0t% hydrogen and 80v0t.
% CO2 mixed with 251/- was flowed. Furthermore, these wires were used for horizontal fillet welding of mild steel plates coated with a zinc-rich primer to a thickness of 20 μm, and the relationship between the occurrence of surface pores on the second bead side and the amount of Mn in the wires and q was determined. As shown in Figure 1, the amount of Mn in the wire is 0.5wt%.
If it is less than 8.5 wt %, pores are observed to be mainly caused by insufficient deoxidation, whereas if it exceeds 8.5 wt %, pores are generated which is thought to be due to excessive deoxidation.

Therefore, in the present invention, the amount of Mn added to the wire is 0.
It is defined as 5 to 8.5 wt%. )) Other deoxidizing elements A deoxidizing element having a greater affinity for oxygen than Mn can also be added to the wire used in the present invention, if necessary.

This may be due to the presence of a large amount of foreign matter that acts as an oxygen source, such as mill scale or rust, in the welded workpiece, or due to welding work that makes it difficult to remove debris that adheres to the inner surface of the gas nozzle, causing turbulence in the shielding gas and In cases where the effectiveness deteriorates, it is necessary to perform the work in a well-ventilated area, and the shielding effect is easily impaired by wind, etc. Oxygen and nitrogen in the weld metal increase inappropriately, making it difficult to prevent porosity with Mn deoxidation alone. sometimes effective.

The types of these strong deoxidizing elements are Si, Ti, Zr, At,
Any of the materials generally used for deoxidizing welding materials, such as Mg and ca, may be used, and the wire of the present invention may contain one or more of these.

As a result of examining various flux systems and welding conditions, it was determined that this addition amount should be limited to 2.0 wt%.
In other words, if more than 2.0 wt% is added, pores thought to be caused by hydrogen are likely to be generated due to excessive deoxidation under any conditions, and these strong deoxidizing properties are likely to occur in the weld metal. As a result of a large yield of elements, particularly Si, Ti, Zr, At, etc., the weld metal becomes hardened and brittle, which is not preferable. (3) Hydrogen-containing gasFurthermore, in the welding method of the present invention, unlike conventional gas-shielded arc welding methods, which take care to reduce the hydrogen in the weld metal, the welding method of the present invention does not contain hydrogen in any form. The feature is that a certain amount of hydrogen is added to the weld metal using the shielding gas contained in the weld metal.

By the way, the reason why hydrogen-containing gas is used in the method of the present invention is as follows.

In other words, one of the reasons is that by shielding the outside air with a gas containing reducing hydrogen, it prevents nitrogen from entering the metal, eliminates the embrittlement of the weld metal caused by nitrogen, and prevents the formation of pores due to excessive dissolved nitrogen. The goal is to solve the following problems. In addition, by increasing the hydrogen partial pressure in the arc atmosphere and increasing the amount of hydrogen dissolved in the metal, and promoting the floating and dissipation of air bubbles that form in the fillet weld metal of the brimer-coated steel plate, weld beads without pores are created. You can also get it.

In addition to the present invention, it can be seen that the total amount of hydrogen in the shielding gas that exhibits the greatest effect is 0.1V0t01) or more, as is clear from the experimental results shown in FIG.

That is, in this experiment, the total amount of hydrogen in the shielding gas was varied in each of the methods described above, and a 20 m thick mild steel plate coated with a 20 μ thick zinc-rich primer was welded in the following manner. The relationship between the number of surface pores per unit length of fillet bead and the total amount of hydrogen in the shielding gas is clarified. As is clear from FIG. 2, when the total amount of hydrogen in the shielding gas is 0.1 V0t% or more, the number of surface pores in the fillet weld bead becomes zero in all cases.

By the way, the test wire Haruka 1 in the experiment shown in Fig. 2 contains 8wt% of rutile, 3.5wt% of silica sand, 4.0wt% of potassium feldspar, 2.0wt% of rhodonite, and 5.5wt% of Mnl3 based on the total weight of the wire. ．． Qwt% iron powder, wire flat 2 5.0wt% dolomite, 3.0wt% rutile, 2.0wt% lime carbonate, 5.0wt% silica sand,
2.0wt% potassium feldspar, 4.0wt%0Mr1, 5.
0 wt% iron powder, Wire Haruka 3 is 4.5 wt% rutile, 2.0 wt% silica sand, 3.5 wt% magnesium carbonate, 2.0 wt% lime carbonate, 1.0 wt% magnesium oxide, 0 .5wt% fluorite, 0.5wt% Zrl
2. A very mild steel strip material is filled with 26wt% of iron powder of MnllOwt% and finished to a diameter of 2.4rn1n.

The welding conditions are: current 350A (AC), voltage 31-33V, speed 20-35 (-In/Mh), shielding gas: CO
2 was used as the basic gas, and various proportions of hydrogen gas were added thereto, and 25 t/- of this was flowed. The results were judged based on the number of surface pores generated per unit length of a horizontal fillet weld bead of a 20μ thick zinc-rich primer coated steel plate. By the way, the experiments shown in Figures 1 and 2 were conducted when hydrogen gas was added to CO2 gas, but the basic shielding gas could also be CO2, Ar, He, O2, etc. Generally speaking, hydrogen sources other than hydrogen gas include methane, ethane, propane, butane, bentane, hexane, heptane, octane, nonane, decane, etc. of the methane hydrocarbon organic compound group represented by the general formula CnH2n+2, and ethylene type represented by CnH2n. Hydrocarbon organic compounds such as ethylene, propylene, butadienes (isobutane, 1,3-butadiene), butylenes (isobutylene, n-butylene), and C2.

Even if one or more types of water vapor are mixed in addition to acetylene of the acetylenic hydrocarbon organic compound group represented by H2n, methylacetylene, vinyl acetylene, etc., the total amount of hydrogen in the shielding gas is 0.1V0t% or more. However, from the viewpoint of actual welding workability, the present invention requires that the content exceeds 5V0t%. In particular, the reason why the above effects can be obtained by using the above hydrocarbon organic compounds and water vapor is that these compounds are easily decomposed by arc heat and increase the hydrogen partial pressure in the arc atmosphere, similar to when hydrogen gas is added alone. This is thought to be because the effect of

(4) Hydrogen Source Compound As another means of increasing the hydrogen partial pressure in the arc atmosphere, a hydrogen source compound can be added to the flux filling the wire.

These hydrogen source compounds used in the present invention are generally organic compounds commonly used as welding flux materials such as cellulose, starch, and wood flour, inorganic compounds such as talc, mica, asbestos, and powdered water glass, and magnesium hydroxide and hydroxide. These include inorganic compounds with hydroxyl groups such as aluminum calcium hydroxide, barium hydroxide, sodium hydroxide, and iron hydroxide. Furthermore, the hydrogen source compound can be added to the wire by filling it with oils and fats or moisture-absorbing flux that adhere to the wire during the wire making or coiling process.

In addition, a hydrogen source compound can also be added to the wire by adding suitable water glass as a fixing agent to the flux, granulating it with a suitable device, drying it at low temperature, and then exposing it to light. By the way, the hydrogen generated from these hydrogen source compounds filled in the wire, in addition to the auxiliary effect of hydrogen in the outside air shielding gas as mentioned above, also causes droplets to become finer due to Q exposure when hydrogen is released at high temperatures. can be measured and the arc phenomenon can be improved. The amount of hydrogen source compound added to the wire according to the present invention is limited to 17 wt%. Exceeding this is rather undesirable because it causes problems such as deterioration of the arc condition, increased amount of spatter, and deterioration of the bead shape. Furthermore, in addition to the deoxidizing elements and hydrogen source compounds mentioned above, the wire used in the present invention also contains other flux materials for welding to form a slag and to stabilize the gas-generating arc.
Needless to say, it can be added for the purpose of weld metal zero alloying.

However, if these flux materials are added in an amount of 3 to 40 wt% based on the total weight of the wire having a mild steel outer shell, the above-mentioned effects can be obtained.

Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples Table 1 shows hydrogen source-containing gases G-1 to G-2 used in the present invention.
The composition of the shielding gas and the comparative shielding gas Q are shown.

The shielding gas used in this case is carbon dioxide gas produced for welding by Jyoto, and its total hydrogen content is below the scope of the present invention. Table 2 also shows wires W-1 to W-6 used in the present invention.
shows the wire components of

Furthermore, the table also shows two types of comparative wires: CW-1 and CW-2.
The ingredients are also listed.

All of these wires were flux-cored wires having a mild steel outer shell, and had an outer diameter of 2.0 mf. Hereinafter, the gases in Table 1 and the wires in Table 2 are combined as appropriate, and each wire has a current of 300A (8 DC voltages, 30 to 3
2V, speed 20-35C7r1/Fun, gas flow rate 25
The results of various types of welding performed under the condition of t/7 nm will be explained.

First, a combination of the various shielding gases of the present invention shown in Table 1 and the wire W-3 shown in Table 2, zinc-rich braimer (20
When fillet welding was performed on a coated steel plate (20rfr1T1 thickness), a fillet bead with no surface pores was obtained as shown in FIG. 3.

The figure also shows the results of welding using carbon dioxide gas in which the total amount of hydrogen is less than the range of the gas used in the present invention. From this figure, it is clear that carbon dioxide gas as a shielding gas used in the conventional method cannot prevent surface pores.
On the other hand, under similar welding conditions, welded mild steel (20 standard thickness) in a downward position.
Joint welding was performed to obtain a welded part with no X-ray defects.

Table 3 shows the results of determining the impact absorption energy of the weld metal at 0° C. by 2wmV notch sial. Next, gas G-1 shown in Table 1 and various wires shown in Table 2 were combined to perform fillet welding, resulting in a weld bead with no surface pores as shown in FIG. 4.

Furthermore, the same figure also shows the welding results of the comparison wire.
The problem is that the comparison wire cannot prevent the generation of surface pores. On the other hand, joint welding was performed in a downward position under the same welding conditions, and a welded part free from X-ray defects was obtained.

Table 4 shows the impact absorption energy of the weld metal in this case at 0°C. Although the embodiments of the present invention have been described above based on the results obtained by direct current welding, a similar study was separately conducted for alternating current welding, and it was confirmed that there was no significant difference in the results.

As described above, by using the welding method of the present invention, it is possible to obtain a fillet bead with excellent toughness and no surface pores during fillet welding of steel plates to which shovel primer, rust, moisture, oil, etc. have adhered. I understand. This is something that cannot be achieved using conventional gun shield arc welding methods, and it is an extremely significant contribution to the development of various industries.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the amount of n in the wire and the surface pores of the fillet weld bead, and Figure 2 is a diagram showing the relationship between the total amount of hydrogen in the shielding gas and the number of surface pores of the fillet weld bead. , FIG. 3 is a diagram showing the relationship between the shielding gas composition and the number of surface pores of the fillet weld bead, and FIG. 4 is a diagram showing the relationship between the wire composition and the number of surface pores of the fillet weld bead.

Claims (1)

[Claims] 1. A flux-cored wire containing 0.5 to 8.5 wt% of Mn element as an essential component is used, and the total amount of hydrogen is 5 vol.
A gas-shielded arc welding method for welding structural steel, characterized by using a shielding gas of more than 1%. 2 Using a flux cored wire in which 17 wt% or less of a hydrogen source compound is added to a flux containing 0.5 to 8.5 wt% of Mn element as an essential component, the total hydrogen amount is 5 vol.
A gas-shielded arc welding method for welding structural steel, characterized by using a shielding gas of more than 1%.