JPH0525598B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to welding materials for steel with excellent fire resistance (hereinafter referred to as fire-resistant steel) used in various buildings in the fields of architecture, civil engineering, marine structures, etc. More specifically, the present invention relates to a submerged arc welding wire and flux that yields a weld metal with excellent high-temperature yield strength at 600°C and good toughness. (Prior Art) Conventionally, among various steel structures in the fields of architecture, civil engineering, and marine structures, the surfaces of steel members of buildings such as buildings, offices, and residences that are closely connected to daily life have been exposed to fire hazards. To prevent temperatures from exceeding 350℃,
Fireproof coating is applied. This is because at around 350°C, the yield strength decreases to 60-70% of that at room temperature, potentially causing the building to collapse. Incidentally, recently, fire-resistant steels are being developed that have a yield strength at an even higher temperature of 600°C that is 70% or more of that at room temperature, can be uncoated or lightly coated, and can lower construction costs. However, we obtained a weld metal with excellent high-temperature properties that can be applied to welding fire-resistant steel.
There is no conventional submerged arc welding material that is also cost-effective. For this reason, even if fire-resistant steel is used in a building, if construction is carried out using conventional submerged arc welding materials, the welded part will be made of slag wool, rock wool, glass wool, etc. as the base material, just like when conventional steel is used. It is necessary to carefully apply fireproof coatings such as spraying, spreading felt material, and covering with fireproof mortar to prevent thermal damage in the event of a fire, resulting in high construction costs. On the other hand, from the viewpoint of high-temperature properties only, Cr-Mo
There are submerged arc welding materials for steel, and for welding wires, for example, JP-A No. 53-95146 discloses an example containing a large amount of Cr, and for fluxes, for example, JP-A No. 59-4994 discloses a high-Cr content welding wire.
Fluxes with a specific basicity are disclosed for use in combination with Cr-containing wires. (Problems to be Solved by the Invention) As mentioned above, when welding fire-resistant steel, the welding materials used for conventional steel have a low yield strength of the weld metal at 600°C, so it is necessary to apply a large amount of fire-resistant coating. This poses the problem of increasing construction costs, reducing the usable space of buildings, and lowering economic efficiency. On the other hand, although the well-known welding materials for Cr-Mo steel have good high-temperature properties, the toughness of the weld metal is ensured by performing SR after welding, and the toughness as welded is extremely low. bad. Therefore, it cannot be applied for architectural purposes. Further, since the wire for Cr-Mo steel contains a large amount of alloying components, it is very expensive, and there is a disadvantage in that there is no cost advantage in omitting the fireproof coating. It should be noted that conventional fluxes for Cr--Mo steels have poor high-temperature properties when combined with conventional steel wires, making them unsuitable as fluxes for fire-resistant steels. The purpose of the present invention is to have excellent high temperature properties at 600℃,
Another object of the present invention is to provide a submerged arc welding wire and flux for fire-resistant steel, which yields a weld metal with good impact toughness as-welded. (Means for Solving the Problems) The present invention overcomes the above-mentioned problems and achieves the objects.In weight%, C: 0.01 to 0.15%, Si: 0.5%
Below, Mn: 0.4~2.5%, Mo: 0.06~0.80%,
Nb: Contains 0.003~0.030%, the remainder consists of Fe and inevitable impurities, (Mo+20Nb): 0.15~
1.25 is a submerged arc welding wire for refractory mesh. Furthermore, in the present invention, _SiO2 : 5 to 35% by weight,
MgO: 5-35%, CaO: 5-25%, F: 1-8
%, Mo: 0.1-1.0%, Nb: 0.01-0.14%, and (Mo+10Nb): 0.3-2.0. (Function) The currently developed fireproof steels are:
The composition has been designed so that the high temperature strength at 600℃ is 70% or more of that at room temperature. In order to obtain a submerged arc welding wire and flux for fire-resistant steel, the present inventors first studied existing welding materials and found that the weld metal has a yield strength at 600°C that satisfies 70% or more of that at room temperature. was difficult to put into practice. That is, the wire or flux that provides the necessary high-temperature proof strength has large amounts of expensive alloying elements added to it, increasing the cost of welding materials, which offsets the construction cost reduction effect achieved by reducing the fireproof coating. Furthermore, unlike Cr-Mo steel, which is originally used at high temperatures, weld metal that contains large amounts of alloying elements in building structures that are used at room temperatures becomes too strong, resulting in problems with cracking resistance, and It was also found that the toughness was very poor. Therefore, as a result of further detailed examination of the components, the wire and flux of the present invention were obtained. The component elements and their addition amounts in the present invention will be explained below. First, the major feature of the welding wire is that it has achieved sufficient high-temperature strength through the combined addition of Mo and a small amount of Nb. Mo and Nb form fine carbonitrides, and
Mo increases high-temperature yield strength through solid solution strengthening, but it is difficult to obtain sufficient yield strength at 600°C by adding Mo or Nb alone. In other words, the minimum amount of each component to obtain a combined effect is 0.06 Mo.
%, Nb needs to be contained at 0.003%. On the other hand, if the amounts of Mo and Nb are too large, the room temperature strength becomes too high and the toughness deteriorates, so the upper limits of the Mo and Nb contents need to be 0.80% and 0.030%, respectively. Further, even if Mo and Nb are each within the above specified values, if the total of these components is too small, the target high temperature proof strength cannot be obtained. Also, even if it is excessive,
Since the toughness of the weld metal may deteriorate, it is necessary to limit the content of Mo and Nb in the wire. That is, in the wire, Nb is about 20% more than Mo.
It was found that the effect was equivalent to twice the amount added.
By setting Mo+20Nb in the range of 0.15 to 1.25, it is possible to obtain adequate room temperature strength and good toughness while obtaining sufficient high temperature proof strength of the weld metal. Next, the reason for limiting the components other than Mo and Nb in the wire of the present invention will be explained in detail. C is necessary to ensure strength and to exhibit the effect of adding Mo and Nb, and for this purpose 0.01%
is the lower limit. Moreover, if it exceeds 0.15%, hot cracking susceptibility increases and toughness deteriorates, so the upper limit of C is set to 0.15%. Si can be added to the weld metal from the welding flux to be combined, and there is no particular lower limit specified for the welding wire. However, if Si exceeds 0.5%, the toughness of the weld metal decreases, so Si must be kept at 0.5% or less. Mn is an essential element for ensuring strength and toughness, and must be contained at 0.4% or more.
On the other hand, if it exceeds 2.5%, it increases hot cracking susceptibility and deteriorates toughness, so the upper limit of Mn
The rate shall be 2.5%. The basic components of the wire of the present invention are as described above,
The remainder consists of Fe and unavoidable impurities. Next, the flux of the present invention will be explained in detail. As for the flux, Mo
It is important to add Nb and Nb in combination.
By this combined addition, a weld metal with sufficient high-temperature proof strength can be obtained, whereas the addition of Mo or Nb alone is insufficient. In order to obtain this combined effect, Mo must be at least 0.1% and Nb must be at least 0.1% of the total weight of the flux.
0.01% or more is required. Furthermore, if Mo and Nb are too large, the strength at room temperature becomes too high and the toughness deteriorates, so Mo needs to be 1.0% or less and Nb needs to be 0.14% or less. Further, even if Mo and Nb are each within the above specified values, if the total of these components is too small, the target high temperature proof strength cannot be obtained. Also, even if it is excessive,
Since the toughness of weld metal may deteriorate, Mo
and the total Nb content must be limited. In other words, in the flux, Nb is about the same as Mo.
It was found that it has an effect equivalent to 10 times the amount added, and by setting Mo + 10Nb in the range of 0.3 to 2.0,
It is possible to obtain adequate room temperature strength and good toughness while obtaining sufficient high temperature proof strength of the weld metal. Mo or Nb is added to the flux using metal powder or a compound containing these elements, such as an oxide or nitride. Note that the values specified above apply to Mo or Nb.
Shows the value converted to . Next, _SiO2 is a necessary component to adjust the slag viscosity and obtain a good bead appearance.
If SiO ₂ is less than 5%, the viscosity is too low, resulting in rough bead waveforms and uneven bead widths. On the other hand, when SiO ₂ exceeds 35%, the amount of oxygen in the weld metal increases and the toughness decreases. SiO ₂ is silica sand,
It is added with ores or compounds containing SiO ₂ such as wollastonite, siyamoto, zircon sand, and olivine sand. Furthermore, MgO is a necessary component to enable highly efficient welding using a large current due to its effect of increasing the slag melting point. To obtain this effect of MgO, a minimum of 5% is required; if it is less than 5%, the bead waveform becomes rough. On the other hand, when MgO is added in excess of 35%, irregularities and pockmarks occur at the bead toe ends.
MgO is added as an ore or synthetic material containing MgO, such as magnesia clinker or olivine sand. Further, CaO is an effective component for obtaining good toughness of weld metal, and a minimum content of 5% is required. However, when CaO exceeds 25%, the melting point of the slag becomes too high, causing spot marks. CaO is added by carbonate lime, wollastonite, etc. Finally, F as an essential component is necessary to reduce the amount of oxygen in the weld metal and obtain good toughness.
Addition of 1% or more is effective. On the other hand, if it is added in excess of 8%, the melting point of the slag will increase, causing pockmarks. The addition of F to the flux is
Metal fluorides such as CaF ₂ , AlF ₃ , MgF ₂ , BaF ₂ , Na ₃ AlF ₆ are used as raw materials. The specific components in the flux of the present invention have been described above, but in addition to the above-mentioned components, the flux of the present invention may also contain ordinary flux components as appropriate. First, MnO and Al ₂ O ₃ are added as components for adjusting the fluidity of the slag. however,
When MnO exceeds 15%, it deteriorates the slag removability.
When Al ₂ O ₃ exceeds 20%, the slag melting point increases,
Undercuts are likely to occur. For MnO, ores and synthetic materials such as manganese silicate, manganese carbonate, manganese dioxide, and manganese slag are used. Next, TiO ₂ and B ₂ O ₃ can be added as appropriate for the purpose of improving the toughness of the weld metal, and TiO ₂ uses rutile, titanium slag, etc., and B ₂ O ₃ uses borax, colemanite, etc. Other carbonates such as BaCO ₃ and Na ₂ CO ₃ , Fe, Al,
Metals such as Ti, Ca, Mg, Mn, Si, and V can also be added as appropriate. The flux of the present invention is produced by granulating each raw material using a suitable adhesive such as water glass, alumina sol, silica gel, etc., and drying or firing at a high temperature. (Example) Example 1 Wires (wire diameter: 4.8 mmφ) having 19 types of compositions W1 to W19 shown in Table 1 were produced. Of these, W1
-W10 are the wires of the present invention, and W11 to W19 are comparative examples. Next, the fire-resistant steel with the chemical composition shown in Table 2 was added to the
Groove shape shown in the figure (t ₁ = 25 mm, θ1 = 20°, d = 16
mm), multi-layer welding was performed under the welding conditions shown in Table 3. The fluxes combined with these wires are SiO ₂ = 40%, MnO = 20%, CaO
It is a molten flux (particle size 20×D mesh) with a composition of 25% TiO ₂ , 4% TiO 2 , and 5% F.

【table】

【table】

【table】

[Table] After welding was completed under the above conditions, a tensile test piece and a Charpy impact test piece were taken from the position shown in FIG. 2 (e=7 mm), and a mechanical test was conducted. The results are shown in Table 4. Here, the proof stress at 600℃, which is the heaviest when evaluating weld metal performance, is the minimum yield point at room temperature of SM50 steel specified in JIS G3106 Type 233
The goal was to secure 70% or more of Kgf/mm ² . In other words, it was determined that a yield strength of 23 Kgf/mm ² or more is applicable for the weld metal at 600°C. As is clear from the results shown in Table 4, all of the wires of the present invention have good room temperature strength and high temperature yield strength, as well as high impact values, whereas the comparative wires lack high temperature strength and tensile strength at room temperature. Some wires have excessive strength and low impact values, and are not satisfactory as wires for fireproof steel.

【table】

[Table] Example 2 Next, the flux is F1 to F13 shown in Table 5.
Bond fluxes with different compositions were prepared. Of these, F1 to F6 are the fluxes of the present invention, and F7 to F13 are comparative examples. To produce these fluxes, first, the flux raw materials are blended and mixed, then granulated using water glass as a binding agent, and fired at 400℃ for 2 hours.
The grains were sized to 12 to 100 mesh pieces. The test method was to use fire-resistant steel with the chemical composition shown in Table 2, with the groove shape shown in Figure 3 (t ₂ = 32 mm, θ ₂ = 70°,
θ ₃ = 60°, a = 12 mm, b = 7 mm, c = 13 mm), and one pass welding was performed for each layer under the two-electrode welding conditions shown in Table 6. The wire used in combination with these fluxes is W15 in Table 1, and this wire is a Mn-based wire that is used in conventional welding of structural steel. After welding was completed under the above conditions, a tensile test piece and a Charpy impact test piece were taken from the position shown in FIG. 4, and a mechanical test was conducted. The appearance of the bead was also inspected, and the results are shown in Table 7. As with wire, the yield strength of weld metal at 600°C for flux is 23 kg.
It was determined that f/mm ² or higher was applicable.

【table】

[Table] As is clear from the results shown in Table 7, all of the fluxes of the present invention have good high-temperature yield strength and room-temperature strength, high impact values, and no problems with bead appearance. Comparative fluxes, on the other hand, lack high-temperature yield strength, have excessive tensile strength at room temperature, have low impact values, and even have problems with bead appearance, making them unsatisfactory as fluxes for fire-resistant steel. There is nothing.

【table】

[Table] (Effects of the Invention) As described above, the wire and flux of the present invention can provide weld metal with good high-temperature strength characteristics and impact toughness, and also have good welding workability, and can be used for fire-resistant steel structures. It is possible to significantly reduce the cost of fireproofing the welded parts.

[Brief explanation of the drawing]

FIGS. 1 and 3 are front views showing the groove shape used in the example, and FIGS. 2 and 4 are front sectional views showing the test piece sampling position.

Claims (1)

[Claims] Contains 1% by weight, C: 0.01 to 0.15%, Si: 0.5% or less, Mn: 0.4 to 2.5%, Mo: 0.06 to 0.80%, Nb: 0.003 to 0.030%, and the balance is Consisting of Fe and inevitable impurities, (Mo
+20Nb): Submerged arc welding wire for fire-resistant steel, characterized in that it is 0.15 to 1.25. Contains _SiO2 : 5-35%, MgO: 5-35%, CaO: 5-25%, F: 1-8%, Mo: 0.1-1.0%, Nb: 0.01-0.14% at 2% by weight. A submerged arc welding flux for fire-resistant steel, characterized in that (Mo+10Nb): 0.3 to 2.0.