KR100611787B1 - Covered electrode for welding fire resistance steel - Google Patents

Abstract

A coated arc welding rod for refractory steel is provided.

The present invention is a coating arc welding rod coated with a coating material on a steel core wire, wherein the coating agent is in its own weight%, metal carbonate: 20 to 60%, metal fluoride: 10 to 30%, TiO ₂ : 5 to 10 %, Si: 2-6%, Mn: 2-6%, Mo: 0.5-2.5%, 1 or 2 or more selected from Ni, Cr, Cu: 0.5-3%, Nb, Ti, V, N Of the selected one or two or more of the sum: 0.01% to 0.5%, and relates to a coated arc electrode comprising a residual iron and a fixing agent.

According to the coated arc welding rod of this invention, the outstanding fire resistance characteristic with little intensity | strength fall at high temperature can be obtained.

Low hydrogen system, high temperature strength, fire resistance

Description

Covered electrode for welding fire resistance steel}

1 is a schematic diagram showing an improved shape and a lamination method of a welded test piece,

2 is a schematic diagram showing a test piece for measuring room temperature and high temperature strength.

The present invention relates to a coating arc welding rod for high-temperature refractory steel, which has a low strength drop at high temperatures even when the temperature of the steel rises during a fire in a construction or civil engineering structure such as a high-rise building, and more particularly, a low-hydrogen-based coating having excellent high temperature fire resistance. It relates to an arc welding rod.

In general, steels used in construction and civil engineering structures include general structural rolled steels (KS D 3503), welded structural rolled steels (KS D 3515), weather-resistant hot rolled steels (KS D 3529), and high weather-resistant rolled steels (KS D 3503). D 3542), general structural carbon steel pipes (KS D 3566), and general structural square steel pipes (KS D 3568) are mainly used.

Buildings constructed with such steel structures have a reduced strength as a building due to a decrease in strength of steel due to heat when a fire occurs. Therefore, to prevent the building from collapsing in the event of fire, the Building Standards Act stipulates to protect the steel frame with fireproof coating so that the temperature of the steel member does not rise above a certain temperature within a certain time. However, the thickening of the fireproof coating increases the construction cost and construction air of the building, and reduces the space used in the actual building. Therefore, the necessity of reducing the fireproof coating construction has emerged from the viewpoint of reducing the construction cost, reducing the air, and effectively using the actual area.

According to this need, 600 ℃ refractory steel with excellent high temperature characteristics has been developed and used, and the demand is gradually increasing. In general construction steel, the yield strength at 350 ℃ falls below 2/3 of the standard yield strength standard and falls short of the strength required in the structure. Therefore, thick fireproof coating should be applied to prevent thermal damage in case of fire. On the other hand, 600 ℃ refractory steel is a yield strength up to 600 ℃ 2/3 or more of the room temperature yield strength standard value, characterized in that it does not collapse even if the steel temperature increases to 600 ℃. Therefore, when using refractory steel, even if the refractory coating is thin enough, it does not collapse within the standard refractory time, so it is possible to obtain a great advantage such as reducing construction cost and shortening the air due to the reduction of the refractory coating.

Meanwhile, as the coated arc welding rod used together with the steel for general building structures described above, the coated arc welding rod for mild steel (KS D 7004), the coated arc welding rod for high tensile steel (KS D 7006), the molybdenum steel, and the chromium molybdenum steel coated arc welding rod (KS D 7022), coated arc welding rod for weathering steel (KS D 7101), etc. are mainly used.

However, since general welding materials do not exhibit high temperature characteristics equivalent to that of refractory steels, the fire resistance coating should be performed mainly on the welded part. For this reason, the molybdenum steel and chromium molybdenum steel coated arc welding rods (KS D 7022), which are commercially available coated arc welding rods for heat resistance steel, have been obtained, but the effect on high temperature characteristics is very high. It is rather unreasonable to use it widely in the construction field.

It is well known that Ni, Cr, Mo, Nb, Ti, V, N, etc. should be added in addition to the basic five-component system (C, Si, Mn, P, S) to have high temperature heat and fire resistance characteristics. As an example of the coated arc welding electrode which has been added, many methods have already been proposed in addition to Japanese Patent Application Laid-Open No. 2-182396 or 11-170087.

However, when the hardenable elements Cr, Mo, Nb, Ti, V are used, the strength of the welded portion at room temperature is very high, which causes cracking during welding. In addition, since moisture contained in the coating material of the electrode is a major hydrogen source, there is a possibility that low temperature cracks are generated by hydrogen during welding. Therefore, the arc coating electrode having a high temperature characteristic must be a low hydrogen electrode, and the coating material must be in the air. There is a problem that the moisture absorption rate from the to be minimized.

 Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and to provide a coating arc welding rod that is economically and fireproof by appropriately adjusting components exhibiting excellent characteristics at high temperature strength.

The present invention for achieving the above object is a coating arc welding rod coated with a coating material on the core wire, the coating agent in its own weight%, metal carbonate: 20 to 60%, metal fluoride: 10 to 30%, TiO ₂ : 5-10%, Si: 2-6%, Mn: 2-6%, Mo: 0.5-2.5%, one or more selected from Ni, Cr, Cu: 0.5-3%, Nb The present invention relates to a coated arc welding rod comprising one or two or more selected from Ti, V, and N: 0.01 to 0.5%, residual iron, and a fixing agent.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by providing a coating arc welding rod that has excellent high temperature fire resistance properties and can prevent the occurrence of low temperature cracking by hydrogen by minimizing the water absorption in the coating material, the coating material constituting the welding rod of the present invention The composition components of and the reason for limitation thereof are explained.

First, in the present invention, metal carbonate (CaCO ₃ , BaCO ₃ , MgCO _3, etc.) is a component that serves to shield the welding arc atmosphere from the atmosphere by generating a gas, the content of which is 20-60% by weight of the coating agent Limited to If the content is less than 20%, there is little gas generation and the shielding effect is weakened, so there is a risk of defects such as blow holes in the welded part, and if it exceeds 60%, the slag fluidity is worsened, resulting in poor bead shape. .

Metal fluoride (CaF ₂ , MgF _2, etc.) is a component that improves toughness by increasing the basicity of the slag and lowering harmful gases such as oxygen and hydrogen in the weld metal, and improving fluidity by lowering the melting point of the slag. Limit to 10-30%. If the content is less than 10%, the slag basicity is low, and not only the harmful gas remaining in the weld metal increases, but also the slag fluidity deteriorates. In particular, the bead shape becomes poor during vertical upward welding. And if the content exceeds 30%, the arc is unstable, there is a risk of arc short.

TiO ₂ is a component that stabilizes the arc and increases the viscosity of the slag to beautify the appearance of the beads. The content is limited to 5-10%. If the content is less than 5%, the arc becomes unstable, the slag does not completely cover the deposited metal, and the exposed part appears and the undercut increases, whereas if the content exceeds 10%, the slag viscosity becomes large and the deposited bead shape becomes poor. to be.

Si and Mn are elements added as a deoxidizer or an alloying agent and in the present invention, their contents are limited to 2-6%, respectively.

If the Si content is less than 2%, there is a risk of defects such as blow holes in the weld metal due to lack of deoxidation. If the content is more than 6%, impact toughness may be lowered. In addition, when the Mn content is less than 2%, the impact toughness worsens, and when the Mn content exceeds 6%, there is a risk of high temperature cracking of the weld metal and the weldability is also deteriorated.

Mo is an element that exists in the weld metal in the form of fine carbides to increase the high temperature strength, and is effective for improving the room temperature strength by improving the hardenability. However, if the content is less than 0.5%, it is difficult to secure the target high temperature strength, and if it exceeds 2.5%, the weldability may worsen and the occurrence of high temperature crack may increase.

Therefore, in the present invention, the content of Mo is limited to 0.5-2.5%.

Ni, Cr, and Cu are elements added to improve low temperature toughness and to improve corrosion resistance and weather resistance of the weld metal. In the present invention, Ni, Cr, and Cu are limited to 0.5-3.0% of one or two or more selected from the group. do. If the sum is less than 0.5%, the effect of the addition cannot be expected, and if it exceeds 3%, the weldability is deteriorated.

In the present invention, in order to form fine carbonitrides to improve the high temperature strength, one or two or more selected from Nb, Ti, V, and N are limited to 0.01-0.5%. If the sum is less than 0.01%, the effect of the addition cannot be expected, and if it exceeds 0.5%, the impact toughness is lowered.

In particular, N is an element which helps to form nitrides of Nb, Ti, and V, and when N is added, the content thereof is preferably limited to 0.01-0.2%.

In addition, the coating agent for the coated arc electrode of the present invention may contain iron, slag generating agent and arc stabilizer in addition to the above-described components.

Iron is an indispensable element and may be included in the flux component or may be contained separately. A small amount of iron does not significantly affect the achievement of the object of the present invention, but it is necessary to contain an appropriate amount separately in order to improve the welding efficiency.

And the slag generating agent and the arc stabilizer may contain Ti oxide, Si oxide, Al oxide and the like.

Meanwhile, the coating agent for the coated arc welding rod of the present invention includes a fixing agent.

A fixing agent is an adhesive liquid added to attach a mixture (coating agent) of the flux of the above-described composition to the core, and the main component is one or two selected from Na ₂ O, K ₂ O, and Li ₂ O in addition to SiO _2. It is an alkali silicate aqueous solution comprised including the above component.

Among the fixing agents, SiO ₂ is effective as a slag generating agent, and Na ₂ O, K ₂ O, and Li ₂ O are added as arc stabilizers, but in order to obtain a constant viscosity of the fixing agent, the molar ratio of the fixing agent [SiO ₂ / (Na ₂ O + K ₂ O + Li ₂ O)] is preferably limited to 2.0-5.0. If the molar ratio is less than 2.0, the adhesion of the coating is reduced due to the decrease in viscosity, and the dropout of the coating increases, and the diffusion of hydrogen content in the weld metal increases due to the increase of moisture absorption in the atmosphere of the coating, which causes cracking. And when it exceeds 5.0, the viscosity is too high, the flux is fixed and the dry crack increases, the productivity is lowered.

It is also of (the sum on the one member of _{Na 2 O, Li 2 O)} / K 2 O of the fixing agent is from 0.2 to 8.0 is preferred. If the ratio is less than 0.2, the wet mixed state of the flux (coating agent) is bad and the fastening rate is high, so that the dry cracking increases and productivity is lowered. In addition, if it exceeds 8.0, the arc may become unstable and the shape of the bead deteriorates.

Hereinafter, the present invention will be described in detail through examples.

(Example 1)

 A fixing agent was added to the flux (coating agent) prepared as shown in Table 3, and coated with a steel core wire having a composition as shown in Table 1 to prepare a coated arc welding rod. The welding rod prepared in this way was welded to the test piece for refractory steel processed in the improved shape as shown in FIG. 1 with a welding current of 170 A and a flat posture, and the chemical composition of the refractory steel welding base material used was shown in Table 2.

After such welding, the weldability was evaluated and the results are shown in Table 4, and the weld metal was processed as shown in FIG. 2 to measure room temperature and high temperature strength, and the results are also shown in Table 4.

At this time, the evaluation of welding workability was evaluated by horizontal fillet and vertical upward welding on SM-400 steel of 13mm thickness, and the high temperature strength was good when securing 50% or more of room temperature strength at 600 ℃. Was evaluated as good (○) and bad (×) according to slag fluidity, bead shape, and the presence or absence of defects.

Chemical content (% by weight) C Si Mn P S Cu 0.06 0.04 0.50 0.015 0.017 0.015

Chemical content (% by weight) C Si Mn Cr Mo Nb V Ti Al 0.08 0.35 1.10 0.30 0.30 0.029 0.031 0.011 0.029

division Flux composition (% by weight) Metal carbonate Metal fluoride TiO ₂ Si Mn Mo Ni Cr Cu Nb Ti V N Etc Inventive Example One 39.5 24.6 9.4 4.0 3.5 0.8 0.5 1.2 - 0.03 - 0.15 0.05 16.3 2 36.4 20.6 7.5 5.1 5.4 2.1 - 2.0 0.8 - 0.03 0.31 0.08 19.7 3 54.6 12.3 5.2 2.3 4.1 1.5 0.7 - - 0.15 - 0.26 0.06 18.8 4 45.8 19.2 6.5 3.5 5.0 1.1 - 2.3 0.5 0.21 0.02 - 0.05 15.8 5 38.8 27.5 7.1 3.0 5.1 1.6 0.6 1.8 - 0.1 - 0.21 - 14.2 Comparative example One 50.1 13.1 6.8 3.4 4.9 0.4 1.1 1.2 - 0.3 0.04 - 0.04 18.6 2 43.9 21.2 6.5 3.5 5.3 1.5 - 0.3 - 0.15 - 0.21 0.04 17.4 3 48.5 19.5 5.8 2.9 5.5 1.8 0.9 1.7 0.3 - - - - 13.1 4 23.9 38.5 8.1 3.3 4.1 0.9 0.6 1.8 - 0.15 0.02 0.26 0.05 18.3 5 38.5 27.6 4.6 5.1 5.4 1.5 0.5 1.9 - 0.18 - 0.22 0.02 14.5 6 51.0 16.8 7.5 1.6 5.1 1.9 1.1 1.5 - 0.08 0.03 0.18 0.05 13.2

division Room temperature strength  High temperature strength (600 ℃) Welding workability Yield strength (Kgf / ㎡) Tensile Strength (Kgf / ㎡) Yield strength (Kgf / ㎡) Tensile Strength (Kgf / ㎡)   evaluation Inventive Example One 52.6 67.5 28.6 36.6    Good ○ 2 53.4 68.5 29.5 37.2    Good ○ 3 51.9 66.5 29.4 37.5    Good ○ 4 54.6 68.9 30.5 38.8    Good ○ 5 55.2 69.5 31.2 39.5    Good ○ Comparative example One 49.5 62.3 21.2 30.5    Defective ○ 2 50.2 62.5 21.5 29.9.    Defective ○ 3 48.2 61.0 20.9 28.8    Defective ○ 4 54.1 66.5 29.5 36.9    Defective × 5 53.0 65.9 28.8 37.1    Defective × 6 52.9 65.0 29.2 36.6    Defective ×

As shown in Table 4, Inventive Examples (1 to 5), the high temperature strength at 600 ℃ secured more than 50% of the room temperature strength, it can be seen that the welding workability is good.

On the contrary, Comparative Examples (1 to 3) lacked an essential element to secure high temperature strength, and thus the high temperature strength was less than 50% of the room temperature strength at 600 ° C. Lack of TiO ₂ and deoxidizer resulted in poor slag fluidity and bead shape and defects.

(Example 2)

The coated arc welding rod was changed by changing the molar ratio of the fixing agent and the ratio of (the sum of one or more of Na ₂ O and Li ₂ O) / K ₂ O in the composition of the flux (coating agent) corresponding to Inventive Example (3) of Table 3. After manufacturing, according to whether there is a problem such as dropping of coating material, dry cracking, deterioration of welding workability, it is evaluated as very good (◎), good (○), normal (△), bad (×). Indicated.

At this time, the moisture content of the flux was measured after exposing the prepared electrode to an atmosphere of temperature 27 ° C. and humidity 80% for 24 hours and evaluated to be within 1.0% as good.

division Molar ratio of fixer [SiO ₂ / (Na ₂ O + K ₂ O + Li ₂ O)] (Sum of one or more of Na ₂ O and Li ₂ O) / K ₂ O ratio Flux moisture content (wt%) evaluation Inventive Example One 2.1 8.4 0.95 ○ 2 1.9 5.8 1.02 ○ 3 3.5 3.2 0.72 ◎ 4 4.6 0.5 0.56 ◎ Comparative example One 1.7 8.1 1.21 △ 2 5.3 0.1 0.52 △ 3 1.5 9.6 1.92 × 4 5.9 9.9 0.52 ×

As shown in Table 5, Inventive Example (3-4) shows good water absorption, coating loss, dry cracking, and welding workability, and Inventive Example (2) shows a relatively low molar ratio of the fixing agent. The moisture content was rather high, but the workability was good.

In addition, although the welding arc was somewhat unstable in the invention example (1), the paintability (dropping of the coating, dry cracking, etc.) was good.

On the other hand, Comparative Examples (1, 3) was excessively increased the water content of the flux, poor weldability, Comparative Examples (2, 4) were dry cracks and dropping of the coating material, especially Comparative Example In (4), the arc was unstable and the bead shape was also poor.

As described above, the present invention has a useful effect in providing a coating arc electrode having excellent fire resistance at high temperatures by appropriately adjusting the components exhibiting excellent properties at high temperature strength, minimizing the water absorption of the coating material, By increasing the basicity, it is possible to prevent the occurrence of low temperature cracking by hydrogen.

Claims (5)

In the coated arc welding rod coated with a coating material on the steel core, The coating agent, in terms of its own weight%, metal carbonate: 20 to 60%, metal fluoride: 10 to 30%, TiO ₂ : 5 to 10%, Si: 2 to 6%, Mn: 2 to 6%, Mo: 0.5-2.5%, one or two or more sums selected from Ni, Cr, Cu: 0.5-3%, one or two or more sums selected from Nb, Ti, V, N: 0.01-0.5%, residual iron and Contains fixing agent, The binder is SiO ₂ in addition to _{Na 2 O, K 2 O,} Li 2 O as a silicate alkaline aqueous solution that is configured to include a selected one or two or more components _{of, SiO 2 / (Na 2 O} + K 2 O + Li 2 A coated arc electrode whose molar ratio defined by O)] is controlled from 2.0 to 5.0. The coated arc electrode as claimed in claim 1, wherein when N is added, the amount is controlled to be 0.01-0.2%. delete The coated arc welding electrode according to claim 1, wherein the fixing agent (the sum of one or more of Na ₂ O and Li ₂ O) / K ₂ O is controlled at 0.2 to 8.0. The coated arc welding rod according to claim 1 or 2, wherein the coated arc welding rod is a low hydrogen system having excellent fire resistance.

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