JPH0246314B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a flux-cored wire for welding.
Ru. [Prior Art] A flux-cored wire for welding has a tubular outer sheath filled with a flux consisting of a deoxidizer, an alloy component, an arc stabilizer, a slag agent, and the like. However, deoxidizers, alloy component agents, arc stabilizers,
As is well known, slag agents etc. have a direct effect on welding workability, etc., and are not filled in large quantities and are small in volume, so deoxidizers, etc.
It is not possible to fill the inside of the tubular sheath with flux using alloy component agents, arc stabilizers, slag agents, etc. alone, and voids are created within the tubular sheath. If such voids occur in the tubular sheath, flux will move longitudinally through the tubular sheath during wire processing such as wire drawing, annealing, and plating (in the case of seamless flux-cored wires), causing flux to flow in the longitudinal direction of the wire. uneven distribution may occur. If welding is performed using a wire with such unevenly distributed flux, not only will the components of the weld metal be segregated, but the arc will become unstable, and in short, it will not be possible to perform good welding. Therefore, in order to prevent the above-mentioned uneven distribution, in order to balance the flux composition more than before, we
As shown in No. 84696, measures such as adding iron powder to the flux have been taken. [Problems to be solved by the invention] However, the iron powder that has been conventionally used is reduced iron powder, which is relatively cheap and easily available. When welding is performed using a conventional wire that has no voids, there is a problem in that the toughness of the weld metal tends to vary. SUMMARY OF THE INVENTION An object of the present invention is to provide a flux-cored wire that has no variation in toughness in the weld metal and can be welded favorably. [Means for Solving the Problems] The present invention which solves the above problems has the following advantages: C≦0.2% by weight, the total amount of Al, Mn, and Si is 0.1 to 2% by weight, and the balance
The gist of this invention is a flux-cored wire characterized by adding atomized iron powder containing Fe and unavoidable impurities to flux. Incidentally, the addition of atomized iron powder or atomized metal powder to a welding material has been disclosed in Japanese Patent Publication No. 54-8340 and Japanese Patent Application Laid-open No. 54-8347. Japanese Patent Publication No. 54-8340 relates to coated arc welding rods, and contains C, Si, and Mn in the iron powder mixed in the coating material.
The occurrence of pits and blowholes is reduced by specifying the percentage ratio of C, Si, and Mn in the welding rod core wire for each element, and the use of atomized iron powder as the iron powder is This is to improve the adhesion of the coating material, and the purpose of adding the solvent material is also completely different from that of the present invention. On the other hand, JP-A No. 54-5837 relates to flux-cored wire, and contains an atomized metal powder containing B of more than 0.5% by weight and less than 10.0% by weight.
By filling the steel shell with flux containing 30.0% by weight, boron segregation is prevented, and the composition and purpose of addition are different from the atomized iron powder of the present invention. . The present invention is based on a technical idea completely different from that of the prior art, and uses a specific atomized iron powder in a flux-cored wire to reduce variations in the toughness of weld metal. [Function] As a result of numerous investigations into the causes of variation in the toughness of weld metal when reduced iron powder is used, including metal composition, inclusions, precipitates, and chemical composition, the inventor found that It was discovered that the variation in toughness is caused by oxygen, which is introduced from the reduced iron powder. Reduced iron powder is usually produced by reducing scale powder, so Figures 3 and 4 (Figure 3 is a scanning electron microscope (SEM) photograph showing the surface of reduced iron powder, and Figure 4 As shown in (a scanning electron micrograph showing a cross section of reduced iron powder), the outer shape has many irregularities, and there are many voids inside. However, if the outer shape has many irregularities, the specific surface area will increase,
As the specific surface area increases, the rate at which the iron powder is oxidized increases during the flux granulation process, wire annealing process, and the like. Therefore, reduced iron powder must contain a high proportion of oxygen as an oxide, and if there are many voids inside, oxygen will easily enter those voids, and the iron powder will be in a state that contains oxygen. I have no choice but to become From the above, in order to prevent the incorporation of oxygen from iron powder, effective measures include reducing the specific surface area of iron powder, suppressing oxidation of iron powder, and reducing voids in iron powder. I discovered something. Based on this knowledge, when atomized iron powder was added in place of reduced iron powder, very good results were obtained. This is because atomized iron powder has a nearly spherical shape, a smooth particle surface, and the same particle size, not only because it has a smaller surface area than reduced iron powder, but also because atomized iron powder has almost no voids inside the particle. This is thought to be due to the fact that it has a small specific surface area because it does not have . Incidentally, the fact that the bulk density of atomized iron powder is generally 3±1 g/cm ³ , which is higher than that of reduced iron powder, 2.5±1 g/cm ³ , proves that atomized iron powder does not have voids inside the grains. ing. FIGS. 1 and 2 show scanning electron micrograph images of the surface and cross section of atomized iron powder. As is clear from FIG. 1, the shape of the atomized iron powder is close to spherical, and as is clear from FIG. 2, there are almost no voids inside the particles. In addition, since electrolytic iron powder also has almost no voids inside the particles, when electrolytic iron powder was applied in place of reduced iron powder, good results were obtained as in the case of atomized iron powder. However, electrolytic iron powder is expensive;
Since it is often difficult to apply due to cost, the present invention is limited to atomized iron powder. In the present invention, the composition of the atomized iron powder is C≧0.2% by weight, 0.1% by weight≦(total of Al, Mn, and Si)≦2% by weight, and the balance is Fe and unavoidable impurities. The reason for this composition is as follows. First, with regard to C, if it exceeds 0.2%, air bubbles will often form inside the atomized iron powder due to the reaction between C and oxygen, regardless of other chemical compositions, and the surface will become more uneven. , the specific surface area increases, and the rate at which the amount of oxygen in the iron powder increases during the granulation and annealing steps increases. Therefore, C≦0.2% by weight. Next, regarding Al, Mn, and Si, since C mainly reacts with oxygen in molten steel, in order to reduce the porosity and surface roughness of atomized iron powder, the amount of free oxygen present in molten steel must be reduced by Al. , Mn, and Si, based on the knowledge that Al,
The total amount of Mn and Si was 0.1% by weight or more. On the other hand, if the total exceeds 2% by weight, there is no problem with the voids inside the iron powder, but Al, Mn, and Si form oxides, and the amount of oxygen in the atomized iron powder increases due to the formed oxides. Al, Mn, Si
The total amount shall be 2% by weight or less. Of course, it is not limited to this. In addition, in cases where the toughness is greatly affected by the oxygen content of the weld metal, the chemical composition of the atomized iron powder applied to the flux-cored wire used is C<0.1%, 0.2≦Al, Mn, Si≦ 1.0
It is more desirable to set it to %. In addition, in order to reduce the amount of oxide film on the powder surface, elements that tend to form an oxide film on the metal surface, such as elements such as B, should be kept at less than 0.5%. In order to obtain toughness, it is more desirable to keep the content to 0.1% or less. In addition, especially when it is necessary to reduce the oxygen content of weld metal,
By washing the atomized iron powder with an inorganic acid or an organic acid and drying it after granulation in a non-oxidizing or reducing atmosphere, it is possible to further reduce oxygen. In addition, the flux-cored wire in the present invention may be a so-called seamless wire,
It may also be a seamed wire. In addition, the flux may be granulated,
It may also be one that is not granulated. When the Fe content in the flux is 5% or more,
Iron powder in the form of flux brings a large amount of oxygen into the weld metal, which tends to cause variations in toughness.
It is particularly effective when applied to flux-cored wires with an Fe content of 5% or more. Furthermore, the present invention found that the amount of oxygen in the wire sheath also affects the toughness of the weld metal, although it is not as pronounced as iron powder, and found that reducing the amount to 150 ppm or less is effective in improving toughness. did. However, there are nonmetallic inclusions (mainly oxides) in the outer skin.
It is considered difficult to reduce the amount of oxygen in the outer skin to 20 ppm or less in terms of cost, etc., so it is desirable to keep it within the range of 150 to 20 ppm. Example 1 When producing atomized iron powder, the composition of iron as a raw material was variously adjusted to create atomized iron powder having the composition shown in Table 1. A granulated flux for seamless flux-cored wire was produced using the above atomized iron powder in a conventional manner to obtain a flux having the composition shown in Table 2 (a). The drying temperature of the granulated flux is 350℃×
It was set as 1 hour. The obtained granulated flux was adjusted to a flux rate of 15%.
Filled into a pipe (welded pipe) having the composition shown in Table 2 (b), the wire is drawn, annealed, wire drawn, plated, finished and wound, and a seamless flux-cored wire with a final wire diameter of 1.2 mmφ is obtained. Manufactured. Welding was performed using this wire under the following welding conditions. Welding conditions Voltage: 29V Current: 280A Speed: 25~40cpm Polarity: DC-RP Shielding gas: CO ₂ gas Bevel shape: Bevel angle 45° (Figure 5) Material: SM41B Welding layers: 5 layers, 10 passes or more After welding, the toughness of the weld metal was investigated, and the results shown in Table 3 were obtained. The toughness was evaluated by a Charpy test based on JISZ2242 using a JISZ2202 No. 4 test piece. Note that the Charpy test was conducted at -20°C. A test piece was taken at a position 7 mm from the surface. As is clear from Table 3, test No. 1 using reduced iron powder
4, 1-9, although the amounts of C, Si, Mn, and Al are within the range of the present invention, the amount of oxygen increases during the wire manufacturing process due to the surface and internal properties of the reduced iron powder. As a result, the amount of oxygen in the weld metal increases, leading to greater variations in toughness. In addition, Test No. 1-5, 1-6, and 1-12 are examples using atomized iron powder, but Test No. 1-5
In Test No. 1-6, the sum of Si, Mn, and Al amounts exceeds the upper limit of the invention, and in Test No. 1, the sum of Si, Mn, and Al amounts exceeds the upper limit of the invention. −12
Since the amount of C exceeds the upper limit of the range of the present invention, the amount of oxygen in the weld metal increases and the variation in toughness also increases. In contrast, Test Nos. 1-1, 1-2, 1-3, 1-7, in which all conditions are within the scope of the present invention,
1-8, 1-10, 1-11 are low levels of oxygen,
It shows toughness values with small variations. Example 2 Similar to Example 1, granulated flux for seamless flux-cored wire was produced using the various iron powders shown in Table 1 in a conventional manner, and a flux having the composition shown in Table 4 (a) was prepared. Obtained. The drying temperature of the granulated flux is 350℃×
It was set as 1 hour. The obtained flux was subjected to a fourth process at a flux rate of 14%.
A pipe (welded pipe) having the composition shown in Table (b) was filled with the final wire diameter in the same manner as in Example 1.
A seamless flux-cored wire with a diameter of 1.2 mm was manufactured. Using the thus obtained seamless flux-cored rewire, welding was performed under the following conditions. Welding conditions Voltage: 29V Current: 280A Speed: 26~42cpm Polarity: DC-RP Shielding gas: 80%Ar-20%CO ₂ gas Groove shape: Groove angle 45° (Fig. 6) Material: SM41B Welding layer: After welding 5 layers and 10 passes or more, the toughness of the weld metal was investigated in the same manner as in Example 1, and the results shown in Table 5 were obtained. As is clear from Table 5, in Tests Nos. 2-4 and 2-9 using reduced iron materials, reduced iron Due to the surface and internal properties of the powder, the amount of oxygen increases during wire manufacturing, and as a result, the amount of oxygen in the weld metal also increases, leading to greater variations in toughness. Test Nos. 2-5, 2-6, and 2-12 are examples using atomized iron powder, but Test No. 2-5 uses Si,
In Test No. 2-6, the sum of Mn and Al amounts is smaller than the lower limit of the present invention, and in Test No. 2-12, the sum of Si, Mn, and Al exceeds the upper limit of the present invention. Since the amount exceeds the upper limit of the present invention range, the amount of oxygen in the weld metal increases and the variation in toughness also increases. In contrast, Test Nos. 2-1, 2-2, 2-3, 2-7, in which all conditions are within the scope of the present invention,
Nos. 2-8, 2-10, and 2-11 have low levels of oxygen content and small variations in toughness values. In addition, test No. 2-3 is an example in which a mixture of reduced iron powder Fe-3 and Fe-3 was applied at a weight ratio of 1:1. Small toughness values were obtained. Example 3 Similar to Examples 1 and 2, a granulated flux for seamless flux-cored wire was produced using the various iron powders shown in Table 1 by a conventional method, and a flux having the composition shown in Table 6 (a) was produced. I got it. The drying temperature of the granulated flux is 350℃×
It was set as 1 hour. The obtained flux was applied to the 6th flux at a flux rate of 15%.
Fill a pipe (welded pipe) with the composition shown in Table (b),
In the same manner as in Examples 1 and 2, the final wire diameter
A seamless flux-cored wire with a diameter of 1.2 mm was manufactured. Using the thus obtained seamless flux-cored rewire, welding was performed under the following welding conditions. Welding conditions Voltage: 30V Current: 270A Speed: 30cpm Polarity: DC-RP Shielding gas: 80%Ar-20%CO ₂ gas Bevel shape: Bevel angle 45° (Fig. 7) Material: SM41B Welding layer: 6 layers After welding for 13 passes or more, the toughness of the weld metal was investigated in the same manner as in Example 1, and the results shown in Table 7 were obtained. As is clear from Table 7, as in Examples 1 and 2, Test No. 3-4 and 3-
9, even though the amounts of C, Si, Mn, and Al are all within the range of the present invention, the amount of oxygen increases during wire manufacturing due to the surface and internal properties of the reduced iron powder, which causes welding. The amount of oxygen in metals has also increased, leading to greater variations in toughness. Test Nos. 3-5, 3-6, and 3-12 are examples using atomized iron powder, but Test No. 3-5 is
In Test No. 3-6, the sum of Si, Mn, and Al amounts is smaller than the lower limit of the present invention, and in Test No. 3-12, the sum of Si, Mn, and Al exceeds the upper limit of the present invention. Since the amount of C exceeds the upper limit of the range of the present invention, the amount of oxygen in the weld metal increases and the variation in toughness also increases. In contrast, Test Nos. 3-1, 3-2, 3-3, 3-7, in which all conditions are within the scope of the present invention,
3-8, 3-10, 3-11 are low level oxygen amounts,
It shows toughness values with little variation. Example 4 In order to investigate the influence of the amount of oxygen in the wire sheath,
A seamless flux-cored wire with the same flux composition and welded pipe composition as Test No. 3-1 of Example 3, but with a different amount of oxygen in the pipe, was prototyped, and the welding conditions were the same as in Example 3. A welding test was conducted. The test results are shown in Table 8. As is clear from the results in Table 8, test No. 4-
Tests No. 2 and 4-3 show much better toughness of the weld metal than Test No. 4-1. [Effects of the Invention] Since the present invention is configured as described above, the following effects can be obtained. The oxygen content in the flux is low, so there is no variation in the toughness of the weld metal even when welding is performed. Flux is not unevenly distributed during wire processing, and there is no segregation of components in the weld metal even when welding is performed.

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【table】 [Brief explanation of drawings]

1 and 2 are scanning electron micrographs showing the particle structure of atomized iron powder. FIGS. 3 and 4 are scanning electron micrographs showing the particle structure of reduced iron powder. FIGS. 5 to 7 are conceptual diagrams showing the groove shape during welding in the embodiment.

Claims (1)

[Claims] 1 C≦0.2% by weight, the sum of Al, Mn, and Si is 0.1 to
A flux-cored wire for welding, characterized in that atomized iron powder consisting of 2% by weight, the balance being Fe and unavoidable impurities is added to the flux. 2. The flux-cored wire for welding according to claim 1, wherein the amount of oxygen in the wire sheath is 150 to 20 ppm.