JPH0453639B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a flux-cored wire for arc welding, and more particularly to a flux-cored wire for self-shielded arc welding that has good porosity resistance against pits, blowholes, etc. (Prior art and problems to be solved) Conventionally, a method using metallic Li as a denitrifying agent has been proposed as one of the flux-cored wires for self-shielded arc welding (U.S. Patent No.
3691340). However, since metallic Li is extremely active, it is difficult to keep it stably present in the atmosphere for long periods of time.
The above method is considered impractical. Therefore, there is a method of adding Li to the flux in the form of Li compounds such as carbonates, oxides, fluorides, or composite compounds containing these, and reducing the Li compounds with a reducing agent using arc heat to obtain elemental Li. Proposed. For example, in JP-A-48-4347 and JP-A-48-8627, ferrates, silicates, manganates, and aluminates are used as Li compounds. However, as is clear from the fact that the industrial method for producing Li is by molten salt electrolysis, Li is an element that is extremely difficult to reduce. Pits and blowholes often occurred. The present invention was made in order to solve the problems of the prior art described above, and it is a self-shield that suppresses the reactivity of Li metal, does not change wire performance over a long period of time, and has excellent porosity resistance. The object of the present invention is to provide a flux-cored wire for arc welding. (Means for Solving the Problem) In order to achieve the above object, the present inventors initially made full use of various coating methods and surface treatment techniques such as microencapsulation in order to suppress the reactivity of Li metal. However, with either method, it has been impossible to stably maintain metallic Li in the atmosphere for a long period of time. Therefore, we began investigating the possibility of reducing the concentration of metallic Li, that is, alloying metallic Li, to suppress its reactivity. First, from the phase diagram, the elements that metal Li can dissolve are Al, Ca, Cu, Mg, K, Na, Sn, Zn, Ni,
Since Si and Co are considered, metal Li was dissolved in these metal elements to produce various Li-containing metal powders. When various physical properties such as density, oxidation resistance, and moisture absorption were investigated for the obtained metal powder, it was found that Al, Mg-based Li-containing metal powder is relatively promising as a Li source. Next, in consideration of safety in handling metal powder (during storage and wire manufacturing), a Hartmann metal dust explosion test was conducted. As a result, it was found that Al-Li alloys are safer than Mg-Li alloys as Li-containing metal powders. Based on the above investigation results, we conducted further research on the porosity resistance when the flux contains an Al-Li alloy, and hereby the present invention was created. That is, the flux-cored wire for self-shielded arc welding according to the present invention replaces Li with an Al-Li alloy (however, the Li content in the alloy is 0.1 to 50 at%).
It is characterized by adding 1 to 50 wt% of water to the flux in the form of 1 to 50 wt%, and further setting the water content per total weight of the wire to 100 to 4000 ppm. The present invention will be explained in more detail below. In the present invention, as Li contained in the flux,
The main feature is that it uses an Al-Li alloy. The amount of Al-Li added to the flux depends on arc stability (arc flapping, arc spread, arc strength, etc.), slag covering, amount of fume generation,
Judging from the bead shape, the amount of nitrogen in the weld metal, etc., a range of 1 to 50 wt% is preferable. If it is less than 1 wt%, the effect of reducing the amount of nitrogen in the weld metal by Al-Li cannot be obtained, which is not preferable. If it exceeds 35wt%, the arc stability will deteriorate a little and the amount of nitrogen in the weld metal will tend to increase slightly, but 50wt%
Exceeding this is undesirable because the shielding effect of Li becomes excessive and the amount of fume generated becomes extremely large. Therefore, the amount of Al-Li in the flux is in the range of 1 to 50 wt%. In addition, if the amount of nitrogen in the weld metal is considered, it is more preferably 5 to 5.
It is 35wt%. Here, the amount of metallic Li added in the flux can be determined by the following simple method.
That is, as shown in FIG. 1, an ammonia measuring device is used that inserts a quartz tube 2 into an electric furnace 1 and introduces _N2 gas into the quartz tube via distilled water 3. - A flux-cored wire 4 containing a Li alloy is heated under a humid nitrogen stream, for example.
When heated to 400°C, the metal Li in the Al-Li alloy reacts with nitrogen to generate Li ₃ N. The generated Li ₃ N
is very unstable and reacts with water to form NH ₃ (ammonia). This NH ₃ is absorbed into distilled water and the generated NH ₃ is measured to determine the amount of metallic Li added in the flux. In this case, the AL-Li alloy content in the flux is 1~
If it is 50wt%, _NH3 per 100g of wire is
It corresponds to 0.005 to 1 mg. Even in the case of Li-based alloys other than AL-Li alloys, the amount of Li added in the flux can be determined from the determined amount of NH ₃ in the same manner. Therefore, this simple method can be used when adjusting the flux. In addition to Al-Li, Al-Li alloys include Fe, Zr, Cu, Si, Mg, Ca,
Addition of Zn, Mn, etc. singly or in combination (several ppm to
Al-Li alloy (patent application 1982-
202677), and the component system is not particularly limited. According to the experimental research conducted by the present inventors, the addition of a third component did not significantly affect the denitrification effect.
Even a trace addition of 1wt% or less has the effect of increasing the safety (resistance to metal dust explosion) of Al-Li alloy powder. Such Al-Li alloys are manufactured by appropriate methods such as the REP method, gas atomization method, and mechanical crushing method, but from the viewpoint of preventing segregation during flux mixing and metal dust explosion, the particle size must be 45 μm or more.
Desirably 500μm or less. In particular, if the particle size is 45 μm or more, metal dust explosions will not occur. The Li content (concentration) in the Al-Li alloy needs to be an appropriate amount. In this regard, the present inventors produced Al-Li alloy powders with various Li concentrations, used them to prototype flux-cored wires for self-shielded arcs, and investigated the amount of nitrogen in the weld metal. −If the Li content in Li is 0.1 at% or more,
It was found that the amount of nitrogen in the weld metal was significantly reduced and the porosity resistance of the wire was improved. When the Li content is gradually increased, the amount of nitrogen in the weld metal gradually decreases as the Li content increases, but this tendency is not significant. However, when the concentration exceeds 50 at%, Al-Li metal powder no longer exists stably in the atmosphere. Therefore, the Li concentration is preferably in the range of 0.1 to 50 at%, and furthermore, if it is 3 to 20 at%, the denitrification effect is significant. Next, the moisture content of the flux-cored wire in the present invention will be explained. In order to maintain the Al-Li alloy powder in a stable state for a long period of time in the wire, it is necessary to keep the moisture content of the wire above a certain value. In other words, Al-Li alloy powder is unstable because highly active metal Li is exposed on the surface of the metal powder, so it is necessary to change the metal Li into a stable form beforehand. For example, Al-Li alloy powder can be maintained in a stable state for a long period of time. Specifically, a preferred method is to react the metal Li exposed on the surface of the Al-Li alloy powder with carbon dioxide gas (CO ₂ ) in the air, and coat the Al-Li alloy powder with Li ₂ CO ₃ . For this purpose, it is necessary for the metal Li to become a hydroxide and to easily absorb carbon dioxide gas, and it is advisable to increase the moisture content of the flux-cored wire. The inventors of the present invention forced the flux to absorb moisture and investigated various flux moisture contents, and found that if the moisture content per total wire weight is 100 ppm or more,
It was found that the Al-Li alloy powder remained stable for a long period of time in the wire, and the wire performance could also be maintained constant for a long period of time. However, when the moisture content per total weight of the wire exceeds 4000 ppm, the wire itself naturally becomes susceptible to rust, and wire feedability, current conductivity, arc stability, etc. tend to deteriorate. Therefore, the moisture content per total weight of wire is
Regulated within the range of 100-4000ppm. Note that the amount of water per total weight of the wire here refers to the amount of water extracted at 750° C. in an O ₂ atmosphere and determined by the Karl Fischer method. In the present invention, it goes without saying that the hoop material, wire dimensions, cross-sectional shape, flux rate, applicable welding materials, etc. are not particularly limited. (Example) Next, an example of the present invention will be shown. Example 1 Al-Li alloys with various Li concentrations shown in Table 1 were produced as prototypes. The obtained Al--Li alloy powder was appropriately mixed with 100 parts by weight of a mixed flux having the flux composition shown in Table 2 to prepare a filling flux for self-shielded arc welding. At this time, the moisture content per total wire weight was controlled by changing the moisture content of the raw material flux. Specifically, we may mix the same raw materials with different moisture content (the moisture content may vary greatly depending on the production area or refining process), or we may use hydrated minerals that do not affect welding workability. It was added separately to the composition shown in Table 2. A hoop material having the chemical composition shown in Table 3 was formed into a pipe shape and filled with the thus obtained filling flux at a flux filling rate of 14% to produce a flux-cored wire by a conventional method. Type of Al-Li alloy used, weighed and mixed
Al-Li addition amount {(parts by weight of Al-Li alloy) ÷ (100
+ parts by weight of Al--Li alloy) x 100} and the moisture content of the wire were as shown in Table 5. Next, these flux-cored wires (wire diameter
1.2mmφ), and the thickness is as shown in Figure 2.
12mm thick, 500mm with 20μm zinc primer
Fillet weld joints of long steel plates to be welded were welded under the welding conditions shown in Table 4. Table 5 also shows the results of investigations regarding pore resistance, fume content, and arc stability. In addition, the porosity resistance is determined by the presence or absence of pits on the surface of the 2nd pass (Figure 2).
If there was a pit, an x mark was added for evaluation. The welding conditions in this case are 280A x 30cpm. The amount of hume was measured according to JISZ3930, and the evaluation was made by marking ○ if the amount of hume generated was 1500 mg/min or less, and marking × if it was more than 1500 mg/min. The welding conditions in this case are 280A x 30cpm. Arc stability is determined by investigating the arc length during welding (downward bead-on-plate) using high-speed video. If the variation in arc length is within twice the wire diameter, it is marked ○, and if it is more than twice the wire diameter, it is marked ○. It was evaluated by marking it with an x. As is clear from Table 5, test No. 1 in which the Li concentration in the Al-Li alloy was less than 0.1 at%, and
0.1at% or more, but Al-Li alloy addition amount is 1wt
In Tests Nos. 3, 5, and 12 where the lithium oxide was less than %, the pore resistance deteriorated because the shielding by Li was insufficient. In addition, in Test Nos. 8 and 14 where the amount of Al-Li alloy added exceeds 50wt%, the shielding effect of Li was excessive, and the amount of fume generated was extremely large, resulting in a large amount of fume generated in places where there is no strong exhaust equipment. It is difficult to weld. In test No. 9.17 in which the water content per total weight of the wire was less than 100 ppm, the porosity resistance and arc stability deteriorated due to the instability of the Al-Li alloy. This is considered to be because the Al-Li alloy is in a state where it is very easily oxidized and is oxidized before being exposed to the arc atmosphere, reducing the shielding effect of Li. In addition, the moisture content per total wire weight is 4000ppm.
In test No. 15 in which the wire exceeded the above, the wire became susceptible to rust due to the high moisture content, rust occurred on the inner and outer surfaces of the wire, resulting in poor conduction and significantly deteriorating the stability of the arc. In contrast, test No. 2, 4, 6 of the present invention example
Nos. 7, 10 to 11, 13, 16, and 18 had excellent pore resistance, a small amount of fume generation, and excellent arc stability.

【table】

【table】

【table】

【table】

[Table] Example 2 In the same manner as in Example 1, the results shown in Table 1 were
An Al--Li alloy was appropriately mixed with 100 parts by weight of a mixed flux having a flux composition shown in Table 6 to prepare a filling flux for self-shielded arc welding. Type of Al-Li alloy used, weighed and mixed
The amount of Al--Li alloy added and the amount of water in the wire are as shown in Table 9. The moisture content of the wire was adjusted by changing the moisture content of the raw material flux to be filled. A hoop material having the chemical composition shown in Table 7 was formed into a pipe shape and filled with the obtained filling flux at a flux filling rate of 13% to produce a flux-cored wire by a conventional method. Using these manufactured flux-cored wires for self-shielded arc welding, welding was performed under the welding conditions shown in Table 8, and the porosity resistance, fume generation amount, and arc of the wire were determined in the same manner as in Example 1. Stability was investigated. The results are also listed in Table 9. As is clear from Table 9, test No. 1 in which the Li concentration in the Al-Li alloy was less than 0.1 at%, and
0.1at% or more, but Al-Li alloy addition amount is 1wt
In Test No. 3 with less than %, poor porosity resistance was obtained due to insufficient shielding by Li. In addition, in test No. 5 where the amount of Al-Li alloy added exceeds 50wt%, the shielding effect of Li becomes excessive, and the amount of fume generated is extremely large. Welding is difficult. In test No. 11 where the moisture content per total wire weight was less than 100 ppm, the arc was likely to become unstable due to the instability of the Al-Li alloy, and the porosity resistance deteriorated. In addition, in test No. 10 where the moisture content per total weight of the wire exceeds 4000 ppm, as in Example 1, the wire is prone to rust, and rust occurs on the inner and outer surfaces of the wire, resulting in poor conduction and arc failure. It was easy to become stable and the pore resistance deteriorated. On the other hand, in contrast to these, test No. 2 of the present invention example,
In No. 4, No. 6 to No. 9, all had excellent pore resistance, little amount of fume generation, and excellent arc stability.

【table】

【table】

【table】

[Table] (Effects of the Invention) As detailed above, according to the present invention, a flux-cored wire for self-shielded arc welding can be used to flux Li in a specific amount in the form of an Al-Li alloy with an appropriate Li concentration. At the same time, since the amount of water per total weight of the wire is regulated, it is possible to provide a wire with excellent porosity resistance, no change in wire performance over a long period of time, and excellent workability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an ammonia measuring device for determining the amount of Al--Li alloy added in a flux-cored wire, and FIG. 2 is a diagram illustrating the welding method used in the example. 1... Electric furnace, 2... Quartz tube, 3... Distilled water,
4... Sample (flux-cored wire), 5... Power supply.

Claims (1)

[Claims] 1 Li is added to the flux in the form of an Al-Li alloy (however, the Li content in the alloy is 0.1 to 50 at%).
A flux-cored wire for self-shielded arc welding characterized by adding 50wt% and further increasing the moisture content to 100 to 4000ppm per total wire weight.