JPH0520199B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a flux-cored wire for gas-shielded arc welding for welding fire-resistant steel used in the fields of architecture, civil engineering, and marine structures. The present invention relates to a highly efficient metal powder-based flux-cored wire for gas-shielded arc welding, which can yield a weld metal with excellent high-temperature yield strength, good toughness, and weather resistance. [Prior Art] Metal powder-based flux-cored wires have the advantage of generating less slag and achieving higher welding speeds than general flux-cored wires containing a large amount of slag agents such as titania-based wires. In recent years, there has been a tendency for its usage to increase more and more because it can reduce the total cost of welding. For example, Japanese Patent Laid-Open No. 169195/1982 and No. 180696/1987 disclose flux-cored wires mainly made of iron powder with a small amount of spatter. By the way, among various structures, welded parts in buildings, offices, residences, and other buildings that are closely connected to daily life are required to be covered with sufficient fireproof coating to ensure safety in the event of a fire.
Building-related laws and regulations require that the temperature of the welded part be 350℃ in the event of a fire.
It is specified that the temperature should not exceed ℃. This has a yield strength of 60 to 70% of that at room temperature at around 350℃.
This is because there is a risk that the amount of water may drop to a lower level and cause the building to collapse. For this purpose, in addition to spreading sprayed material or felt based on slag wool, rock wool, glass wool, asbestos, etc. on the surface of the welded part, there are also methods of covering the welded part with fireproof mortar and adding additional layers on top of the insulation layer. Fire-resistant coatings, such as protection with thin metal plates, such as aluminum or stainless steel plates, are carefully applied to prevent thermal damage in the event of a fire. On the other hand, the conventional metal powder-based flux-cored wires mentioned above were not designed with fire resistance in mind, so they have poor high-temperature properties and cannot be used with welded parts uncoated or lightly coated. However, it was necessary to apply a relatively expensive fireproof coating as described above. On the other hand, in recent years, buildings have become taller, and due to improvements in design technology and high reliability, fire-resistant design has been reviewed, and in 1985, a new fire-resistant design law for buildings was stipulated. The ability of fireproof coating can now be determined based on the high-temperature strength of the weld and the actual load applied to the building, without being limited by the 350℃ temperature limit, and in some cases it is also possible to use it without coating. It became. Along with this, new types of steel plates that have weather resistance in addition to fire resistance have been developed, and there has been a strong demand for the development of welding materials that can meet these requirements. [Problems to be Solved by the Invention] The present invention was developed in light of these circumstances, and its purpose is to solve the problem without losing the high efficiency characteristic of conventional metal powder-based flux-cored wires. The object of the present invention is to provide a metal powder-based flux-cored wire for gas-shielded arc welding for fire-resistant steel that provides a weld metal with excellent fire resistance and good impact toughness, and also has weather resistance. [Means for Solving the Problems] That is, the present invention overcomes the above-mentioned problems and achieves the objects, and specific means thereof are shown in the following section. A. In a flux-cored wire for gas-shielded arc welding in which a steel sheath is filled with flux, iron powder: 4.0~
16.0%, deoxidizer: 1.6~6.0%, arc stabilizer:
Metal powder flux composed of 0.05-1.1%, slag forming agent: 0.4-3.6%, Mo: 0.10-0.50%, Nb: 0.005 in one or both of the steel jacket and filling flux, based on the total weight of the wire. ~
Contains 0.025%, (0.5Mo+10Nb) is 0.1~0.4
% flux-cored wire for gas-shielded arc welding for fire-resistant steel. B: As additional components, Ti: 0.05 to 0.35%, B:
The flux-cored wire for gas-shielded arc welding for fire-resistant steel according to item (a) above, which contains one or both of 0.005 to 0.01% of the flux in one or both of the steel jacket and the filling flux. C. As additional components, Cu: 0.20-0.60%, Cr:
0.30-0.75%, Ni: 0.05-0.70% 1 or 2
The flux-cored wire for gas-shielded arc welding for fire-resistant steel according to item (a) or (b) above, wherein one or both of the steel jacket and the filling flux contain at least one of the following: [Function] The steel materials currently being developed as fire-resistant steels are
It is designed so that the high temperature proof strength at °C is 70% or more of that at room temperature. Therefore, the present inventors investigated various prototype wires with the aim of obtaining a weld metal that can secure a high-temperature yield strength equal to or higher than the above-mentioned fireproof steel at 600°C. As a result, even if the flux-cored wire for heat-resistant steel specified in JIS standard Z3318 does not contain large amounts of expensive alloying elements, trace amounts of
High-temperature properties can be improved by adding Mo and Nb together.
Furthermore, it was discovered that weather resistance could be imparted by adding Ni, Cr, and Cu. Furthermore, by limiting other components, we have developed a metal powder-based flux-cored wire for gas-shielded arc welding that has high efficiency and good welding workability. The reasons for limiting each component that characterizes the flux-cored wire of the present invention will be described below. Mo: 0.10~0.50%, Nb: 0.005~0.025% and
0.5Mo+10Nb: 0.1~0.4% Nb and Mo form fine carbonitrides, and further Mo
Although high temperature strength is increased by solid solution strengthening,
When Mo is added alone, it is difficult to obtain sufficient yield strength in the high temperature range of 600°C. As a result of test research using various prototype wires, the present inventors found that Mo
We have found that the combined addition of Nb and Nb is extremely effective. However, if the Nb and Mo contents are too large, weldability and toughness will deteriorate, so the upper limits of the Nb and Mo contents should be 0.025% and 0.50%, respectively, and the lower limit should be set to obtain a combined effect. The minimum amount is 0.005% and 0.10%, respectively. The amount of Mo and Nb is within the range mentioned above.
600℃ when the sum of (0.5Mo + 10Nb) is 0.1 to 0.4%
Its high-temperature yield strength is equivalent to or higher than that of fire-resistant steel, and its impact toughness is good.
The sum of (0.5Mo+10Nb) was limited to a range of 0.1% to 0.4%. Mo and Nb may be added to either or both of the outer shell and flux. The use of Mo to increase high-temperature strength is known in conventional wires for heat-resistant steel, but welding wire for fire-resistant steel with a compound addition of Nb in addition to a small amount of Mo is used for welding wire used in construction. No flux-cored wire is known for this purpose. Iron powder: 4.0 to 16.0% In order to fully achieve the effect of improving welding efficiency, which is a characteristic of metal powder-based flux-cored wire, iron powder must be
It is necessary to add 4.0% or more. If it is less than 4.0%, the wire welding speed will be slow and the welding efficiency will be reduced. On the other hand, if it exceeds 16.0%, the absolute amounts of other components in the flux, such as slag forming agents, deoxidizers, alloying agents, etc., will be insufficient, resulting in deterioration of the bead shape and failure to obtain the desired strength. Therefore, the iron powder should be in the range of 4.0 to 16.0%. Deoxidizing agent: 1.0 to 6.0% As the name suggests, deoxidizing agent is an effective ingredient for reducing non-metallic inclusions in weld metal and improving the physical properties of weld metal through its deoxidizing action. Examples include metals such as Mn, Si, A, and Mg, or iron alloys thereof. If the deoxidizing agent is less than 1.0%, deoxidizing will be insufficient and the X-ray performance will deteriorate, so it is necessary to contain more than this. But 6.0
%, the deoxidation becomes excessive and the toughness and cracking resistance of the weld metal decrease. Therefore, the amount of deoxidizer should be 1.0 to 6.0%. Arc stabilizer: 0.05-1.1% In the wire of the present invention, which is mainly composed of iron powder, it is essential to add an arc stabilizer in order to stabilize the arc and reduce the amount of spatter generated. If the arc stabilizer content is less than 0.05, the arc is unstable and spatter occurs frequently, which is unfavorable in terms of welding workability. On the other hand, if it exceeds 1.1%, the arc length becomes extremely long, which impedes droplet migration, resulting in coarse droplets and frequent spatter. Therefore, the arc stabilizer is 0.05~
The rate shall be 1.1%. The arc stabilizer mentioned here is
Examples include alkali metals such as Li, Na, K, Rb, and Cs and their compounds. Slag forming agent: 0.4 to 3.6% The slag forming agent must be added within a range that does not reduce the welding speed in order to improve the bead shape. If it is less than 0.4%, no bead shape improvement effect will be observed, and if it exceeds 3.6%, the amount of slag will increase, causing defects such as slag entrainment and reducing welding efficiency. Therefore, the slag forming agent, excluding the arc stabilizer, should be 0.4 to 3.6%. The slag forming agents include TiO ₂ , SiO ₂ , A ₂ O ₃ , MnO, FeO,
Oxides such as MgO, fluorides such as CaF ₂ , BaF ₂ and LiF, and carbonates such as CaCO ₃ and Li ₂ CO ₃ can be used. The above is the main structure of the wire of the present invention, and the reason why Ti and B are added to the wire will be further explained. Ti forms Ti oxide, refines the microstructure of weld metal, and is effective in improving toughness, but 0.05
If it is less than %, there is no effect, so the lower limit is set at 0.05%.
On the other hand, if it exceeds 0.35%, toughness will be significantly impaired, so the upper limit is set at 0.35%. Since B is a strong deoxidizing carbide forming element,
By adding this to the wire, crystal nucleation in the weld metal is promoted, growth of columnar crystals is inhibited, and as a result, crystal grains become finer. Also, it has the effect of increasing the hardenability of the weld metal, and in order to obtain this effect, a minimum B content of 0.005% is required; less than that is ineffective, and too much B may cause hot cracking in the weld metal. is likely to occur, so set an upper limit.
It shall be 0.01%. Incidentally, like Mo and Nb, Ti and B may also be added to one or both of the outer shell and flux. The above are means for improving fire resistance performance, but the present inventors further considered whether it would be possible to use the material without a fire resistant coating (expansion of the field of application) and to have weather resistance as well. As a result, if the composition range of PW type flux-cored wire for carbon dioxide gas arc welding for weathering steel (JIS Z 3320) is used, the as-welded strength is somewhat high, but the high-temperature properties at 600°C, which is the objective of the present invention, are was confirmed to be fully satisfactory. Accordingly
Cu: 0.20-0.60%, Cr: 0.30-0.75%, Ni: 0.05
~0.70% of one or more types can be contained in one or both of the steel shell and the filling flux. If Cu, Cr, and Ni are less than the above-mentioned lower limit, no weather resistance effect can be obtained, and if it exceeds the upper limit, the strength becomes too high and the cracking resistance deteriorates. Incidentally, Cu can also be added as a wire surface plating component. Further, the flux filling rate of the flux-cored wire according to the present invention is preferably 8 to 25%. The reason for this is that if the filling rate exceeds 25%, wire breakage problems occur frequently during wire drawing and productivity deteriorates, and if it falls below 8%, the absolute amount of flux is insufficient and the specified strength cannot be obtained. Or,
This is because the stability of the arc is impaired. There are no restrictions on the cross-sectional shape of the wire; in the case of a wire with a small diameter of 2 mm or less, a relatively simple cylindrical shape is used, and in the case of a wire with a large diameter of about 2.4 to 3.2 mm, the sheath material is placed inside. Those with a complicated folded structure are common. Furthermore, it is also effective to plate the surface of the seamless wire with Cu or the like. Hereinafter, the effects of the present invention will be illustrated in more detail with reference to Examples. [Example] Table 1 shows typical fire-resistant steel materials used in the test, Table 2 shows the steel shell components used in the test, and Table 3 shows the composition of flux-cored wire for welding fire-resistant steel. After processing a 25 mm thick steel plate shown in Table 1 into the groove shape (t = 25 mm, G = 5 mm, φ45°) shown in Figure 1, using the flux-cored wire shown in Table 3,
Welded joints were produced under the welding conditions shown in Table 4. In addition, in addition to checking the welding workability during welding,
Defects such as slag entrainment and blowholes were investigated by wire tests. Tensile test pieces and Charpy test pieces were taken from the test materials and their welding properties were investigated. In addition, flat plate welding was performed using the flux-cored wire shown in Table 3 on the steel plate shown in Table 1 with a thickness of 20 mm under the welding conditions shown in Table 4. The speed was measured. At the same time, the amount of spatter was also measured using a copper spatter collecting box. Summarizing the above results, the fifth
Shown in the table. As is clear from Table 5, the welded joints using the wire of the present invention show good values in both room temperature and high temperature 600°C strength properties, impact toughness, X-ray performance, welding speed, and amount of spatter. In contrast, all comparison wires have problems such as too high strength at room temperature, insufficient high temperature strength, and low impact toughness, as well as poor X-ray performance and low welding speed. Not suitable as steel wire.

【table】

【table】

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【table】

[Table] is shown below.

【table】

【table】

〔Effect of the invention〕

As described above, according to the wire of the present invention, the weld metal obtained not only has excellent high-temperature properties and good impact toughness, but also has good welding workability during welding work.
It has good welding efficiency, bead appearance, and shape, and can significantly reduce the cost of fireproofing welded areas.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view showing the groove shape used in the example.

Claims (1)

[Claims] 1. Iron powder: 4.0 to 16.0% Deoxidizing agent: 1.0 to 6.0% Arc stabilizer: 0.05 to 1.1% Slag forming agent other than arc stabilizer: 0.4 ~3.6% In a flux-cored wire for gas-shielded arc welding that is filled with a flux composed of other alloys and unavoidable impurities, one or both of the steel sheath and the filling flux contains Mo: 0.10 to 0.50 based on the total weight of the wire. % Nb: 0.005 to 0.025%, and (0.5Mo+10Nb) is 0.1 to 0.4%, a flux-cored wire for gas-shielded arc welding for fire-resistant steel. 2. Gas-shielded arc welding for fire-resistant steel according to claim 1, wherein one or both of Ti: 0.05 to 0.35% and B: 0.005 to 0.01% are contained as additional components in one or both of the steel outer skin and the filling flux. Flux-cored wire for use. 3. Claim 1 or 2, wherein one or more of Cu: 0.20 to 0.60%, Cr: 0.30 to 0.75%, and Ni: 0.05 to 0.70% are contained in one or both of the steel outer skin and the filling flux as additional components. Flux-cored wire for gas-shielded arc welding for fire-resistant steel.