JPH054199B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a seamless flux-cored wire in which metal components and intermetallic compounds contained in the flux are not oxidized during wire annealing. [Prior Art] When diffusible hydrogen is present in the weld metal during welding of metals, there is a risk that the cracking resistance and porosity resistance of the welded object may be impaired. Therefore, as one means for suppressing the amount of diffusible hydrogen in the weld metal, it is required to reduce the potential moisture content of the flux filled into the welding wire as much as possible. Therefore, in the production of conventional flux-cored wire,
Dry thoroughly to reduce the potential moisture content to 10 to 70 ppm.
It was necessary to fill with a certain amount of flux. In this specification, potential moisture includes not only moisture but also oils and all other hydrogen sources. By the way, seamless flux-cored wire was developed with the main purpose of improving the wire feeding performance, and when manufacturing it, it is necessary to make sure that it is suitable for pipes such as drawn pipes, extruded pipes, welded pipes, etc. This is done by filling the strip with dry flux or by sprinkling flux on the strip, rolling the strip and welding the seam, and then going through the wire drawing and plating steps, but before the wire drawing step. It is generally added during or after the annealing process to reduce and make the hardness of the wire uniform. [Problems to be solved by the invention] Even when a drying flux with sufficiently suppressed potential moisture content is used as described above, 500%
When annealing is carried out at temperatures above ℃, the metal components such as Mg and Al added to the flux and their intermetallic compounds are extremely easily oxidized, which significantly impairs arc stability and deoxidizing properties, which are the purpose of their addition. invite. As a result of investigation by differential thermal analysis, it has been found that, for example, Mg and Al in the flux begin to oxidize when the annealing temperature exceeds 550°C. Therefore, the present inventors conducted an investigation on the oxidation of Mg and Al in the flux in an inert gas atmosphere by replacing the flux filling part with Ar and _N2 gas. As a result, it was found that oxidation of Mg and Al progressed in all cases of inert gas, and that the oxidation prevention of added metals in the flux was insufficient. Based on these facts, the present inventors have determined that in order to prevent the oxidation of the added metal during wire annealing, the atmosphere in the flux-filled part during wire annealing should not be simply an inert atmosphere, but a reducing atmosphere. I have come to the conclusion that this may be necessary. The present invention has been made in view of the above circumstances, and its purpose is to form a strong reducing atmosphere in the flux-filled part during wire annealing.
It is an object of the present invention to provide a method for producing a seamless flux-cored wire that prevents oxidation of additive metals and suppresses diffusible hydrogen in weld metal. [Means for Solving the Problems] The method for producing a seamless flux-cored wire according to the present invention is to adjust the potential water content of the wire to 80 to 3000 ppm before annealing, and to release atomic hydrogen when the wire is annealed. The gist is that a reducing atmosphere is formed in the flux filling section by generating the flux. [Function] As a method of forming a reducing atmosphere in the flux-filled part, it is possible to replace the flux-filled part with H ₂ gas.
Since H ₂ remains in the flux-filled portion as H ₂ gas even after wire annealing, a problem arises in that the amount of diffusible hydrogen in the weld metal increases. However, if a reducing atmosphere is formed using atomic hydrogen, atomic hydrogen has a much stronger reducing property than H ₂ gas, and since it is inherently highly diffusive, it can pass through the pipe wall to the outside after annealing and before it is cooled. Atomic hydrogen has the property of being easily dissipated, so that a large amount of atomic hydrogen does not remain in the wire. That is, it is a truly advantageous component that is present in the pipe during annealing and prevents the oxidation of Al, etc., and is quickly dissipated after annealing. Since atomic hydrogen is extremely unstable, it is difficult to add it to the inside of the wire before annealing. Therefore, in the present invention, atomic hydrogen is generated in the flux-filled portion by annealing. If the potential water content of the wire is appropriately controlled, atomic hydrogen is generated by heating during annealing according to the following reaction mechanism. Flux-added metal + H ₂ O Heating -> Metal oxide + H (atomic hydrogen) Organic matter thermal decomposition - -> H ₂ O + lower hydrocarbon + H (atomic hydrogen) As a result of studying and analyzing iron powder, which is one of the additive metals, it was confirmed by gas chromatography that the reaction starts at around 180℃, and at 600℃, about 80% of the water becomes atomic hydrogen. . The reaction is mainly the thermal decomposition of the potential moisture content of oil and fats adhering to the pipes in the flux filling section, but these reactions have traditionally been treated using organic solvents as sources of diffusible hydrogen in the weld metal. It was used to remove it. In this way, in the prior art, the addition of hydrogen sources such as water and oil to the flux was suppressed as much as possible, but in the present invention, on the contrary, it is actively added to achieve the above-mentioned object of the present invention. It is something to do. The potential moisture content of the wire is 80~3000ppm,
Preferably it is adjusted to 100 to 1000 ppm. If the potential moisture content of the wire is less than 80ppm, the amount of moisture generated during annealing is small.
Oxidation of filler metals such as Mg and Al cannot be prevented. On the other hand, the potential moisture content of the wire is
If it exceeds 3000 ppm, water that did not participate in the above reaction will remain in the product, increasing the amount of diffusible hydrogen in the weld metal. [Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. In the present invention, the method for measuring the potential water content of the wire is not particularly limited, but in the following examples, the Karl Fischer method and the inert gas extraction method were used. After cleaning the surface of the test wire before annealing using an organic solvent such as ether, the Karl Fischer method is performed in an oxygen atmosphere.
The amount of water is determined by extraction at 750 to 1000℃, and the inert gas extraction method reduces the hydrogen source contained in the wire by reacting with carbon, and the amount of hydrogen produced is determined using a gas chromatograph. This value is then converted into water content. The flux-cored wire was manufactured by filling a mild steel pipe with flux and using a conventional method to produce a wire with a diameter of 1.2 mm. Table 1 shows the composition of the mild steel pipe in weight percent. Table 2 also shows the amount of the flux composition in weight percent.

【table】

[Table] <Control of Potential Moisture Content> The potential moisture content of the wire was controlled by a method in which the flux to be filled was made to absorb moisture. <Determination of Arc Stability> Arc stability was investigated by comprehensively examining arc strength, variation in spread, arc flapping, variation in wire protrusion length, and amount of spatter and fume generation. In the following tables, ◯: good, △: slightly poor, ×: poor, respectively. <Measurement of diffusible hydrogen amount> Measured by gas chromatography. Example 1 A pipe with the composition shown in Table 1 A-1 was combined with the composition shown in Table 2 B-
A flux-cored wire was manufactured by filling the wire with a flux having the composition shown in 1. The flux filling rate for the wire was 14%. The moisture content (ppm) of the wire before annealing was measured by the Karl Fischer method (oxygen atmosphere, extraction at 750°C). Welding was performed under the following conditions. <Welding conditions> Power source: DC/reverse polarity Current: 250A Voltage: 27~28V Posture: Downward Speed: 30cm/min Shielding gas: 100% CO ₂ 25/min Test plate: SM50A Note that numbers are rounded to the nearest whole decimal place. This is the value. The test results are shown in Table 3.

【table】

[Table] As is clear from Table 3, in test numbers 1 and 2, Mg in the flux was oxidized due to the low moisture content of the wires, and as a result, deterioration of arc stability was observed. In test numbers 9 and 10, the amount of diffusible hydrogen was large due to excessive moisture content in the wire, and the arc stability was also slightly degraded. Test Nos. 3 to 8 completely satisfied the conditions of the present invention, and all had good arc stability and a low amount of diffusible hydrogen. Example 2 A pipe with the composition shown in Table 1 A-2 and Table 2 B-
A flux-cored wire was manufactured by filling the wire with a flux having the composition shown in 2. The flux filling rate for the wire was 15%. The measurement of the moisture content of the wire before annealing was the same as in Example 1. Also,
The amount of welding current was 280A, and other welding conditions were the same as in Example 1. The test results are shown in Table 4.

[Table] As is clear from Table 4, in test number 1, the Mg alloy powder in the flux was oxidized due to the low moisture content of the wire, and as a result, deterioration of arc stability was observed. In test number 10, the amount of diffusible hydrogen was large due to excessive moisture content in the wire, and the stability of the arc was also slightly degraded. Test Nos. 2 to 9 satisfied all the conditions of the present invention, and all had good arc stability and a low amount of diffusible hydrogen. Example 3 A pipe with the composition shown in Table 1 A-1 was combined with Table 2 B-
A flux-cored wire was manufactured by filling the wire with a flux having the composition shown in No. 3. The flux filling rate for the wire was 12%. The moisture content of the wire before annealing was measured by the inert gas extraction method described above. Further, the welding conditions were the same as in Example 2. The test results are shown in Table 5.

[Table] As is clear from Table 5, in test number 1, because the moisture content of the wire was small, the A1 powder in the flux was oxidized, and as a result, deterioration of arc stability was observed. In test number 8, the amount of diffusible hydrogen was large due to the excessive moisture content of the wire, and the arc stability was also slightly deteriorated. Test Nos. 2 to 7 satisfied all the conditions of the present invention, had good arc stability, and had a low amount of diffusible hydrogen. [Effects of the Invention] According to the method for producing a flux-cored wire according to the present invention, hydrogen sources such as moisture and oil, which should be suppressed as much as possible from being added to flux in the conventional technology, can be added to the flux. On the contrary, by actively adding the flux to the flux, it is possible to prevent the added metal in the flux from being oxidized even during the annealing process during wire manufacturing. Therefore, the above-mentioned additive metals sufficiently perform their functions as arc stabilizers and deoxidizers, which are the purposes for which they are added.
Moreover, in combination with the effect of suppressing the amount of diffusible hydrogen in the weld metal to a low level, a seamless flux-cored wire exhibiting excellent welding workability can be obtained.

Claims (1)

[Claims] 1. A seamless flux-cored wire characterized in that the potential water content of the wire before annealing is adjusted to 80 to 3000 ppm, and the wire is annealed to generate atomic hydrogen to form a reducing atmosphere in the flux-filled part. Production method.