JP2021167019A - Flux-cored wire for self-shielded arc welding - Google Patents

Abstract

To provide a flux-cored wire for self-shielded arc welding which can obtain a weld metal with high strength and excellent toughness, can suppress weld defect, and has good welding workability.SOLUTION: In a flux-cored wire for self-shielded arc welding contains, by mass % to a wire total mass, C: 0.05 to 0.25%, Mn: 0.5 to 1.5%, Al: 1.0 to 3.0%, and Si: 0.8% or less in total of steel outer skin and flux, and contains, in th flux, Mg: 1.0 to 3.0%, total of SiO2 conversion values: 0.1 to 0.5%, total of F conversion values: 1 to 5%, total of one or more kinds of metal carbonate:0.2 to 1.5%, and total of one or more kinds of Na2O conversion values and K2O conversion values: 0.02 to 0.15%.SELECTED DRAWING: None

Description

The present invention relates to a 590 MPa class high-strength steel flux-welded wire for self-shielded arc welding, in which a weld metal having high strength and excellent toughness can be obtained, and welding defects such as pits and blow holes do not occur, and welding work is performed. The present invention relates to a flux-containing wire for self-shielding arc welding having good properties.

In the self-shielded arc welding flux-filled wire, by adding a gas generator such as metal fluoride or metal carbonate to the welding wire, these metal fluoride and metal carbonate are decomposed by arc heat during welding. This is a welding method in which the molten pool is covered with the generated shielding gas, and the atmosphere is blocked and welding is performed without using the shielding gas. Since this welding method does not require equipment such as a cylinder or piping for sending out shield gas, the structure of the welding device is simple and easy to carry, and it is widely used in the fields of civil engineering and construction. For example, Patent Document 1 discloses a flux-cored wire for self-shielding arc welding capable of full-position welding.

However, in self-shielded arc welding, compared to general gas-shielded arc welding, the arc is unstable and welding workability is poor, pore defects such as pits and blow holes are likely to occur, and the mechanical performance of the weld metal is poor. There was a problem such as low.

As a means for solving this, Patent Document 2 contains Al, which has the effect of fixing N in the molten metal and improving the pore resistance, Mg, which has the effect of shielding the welded portion, metal fluoride, and metal carbonate. By adding an appropriate amount to the welding wire, the shield resistance is improved to prevent pore defects such as pits and blow holes, and the self-shielded arc welding flux-containing wire has good welding workability such as arc stabilization. It is disclosed.

Further, in Patent Document 3, welding workability such as making it easier to stabilize an arc by adding Al, Mg and Ba at the same time while preventing the occurrence of pore defects such as pits and blow holes by adding Al is provided. A flux-cored wire for self-shielding arc welding, which is good and can improve the toughness of the weld metal by adding appropriate amounts of Mn and Ni, is disclosed.

By using the self-shielded arc welding flux-containing wire disclosed in Patent Documents 2 and 3, it is possible to suppress pore defects such as pits and blow holes, stabilize the arc, and obtain good welding workability. However, since a large amount of Al is added, the microstructure of the weld metal tends to be coarsened, and it is difficult to obtain a weld metal having excellent mechanical performance. In particular, it is difficult to obtain sufficient toughness of the weld metal. rice field.

Further, in recent years, the strength of welded structures has been increasing in the fields of civil engineering and construction, and high-strength steels such as 590 MPa class steel are widely used. When welding these high-strength steels, the weld metal is also required to have considerable strength, so elements that improve the strength of the weld metal, such as Mo, are added to the welding wire used for self-shielding arc welding. However, when Mo or the like is contained in the weld metal, it becomes more difficult to obtain the toughness of the weld metal.

As a means for solving these problems, Patent Document 4 includes welding such as suppressing pore defects such as pits and blow holes by adding an appropriate amount of _{Al, BaF 2 and Sr composite oxides to stabilize the arc.} A flux-cored wire for self-shielding arc welding, which can improve workability and improve the strength and toughness of a weld metal by adding appropriate amounts of C, Mn, Ni and Mo, is disclosed. However, although the flux-cored wire for self-shielding arc welding disclosed in Patent Document 4 can obtain good welding workability such as stabilizing the arc and suppressing pore defects such as pits and blow holes, C.I. Since the addition amounts of Mn, Ni and Mo are increased, there is a problem that the strength of the weld metal becomes excessively high.

Japanese Unexamined Patent Publication No. 62-238097 Japanese Unexamined Patent Publication No. 3-118993 Japanese Unexamined Patent Publication No. 2000-301382 Japanese Unexamined Patent Publication No. 2009-119497

Therefore, the present invention has been devised in view of the above-mentioned problems, and a weld metal having high strength and excellent toughness can be obtained with respect to a flux-welded wire for self-shielding arc welding of 590 MPa class high-tensile steel. It is an object of the present invention to provide a flux-containing wire for self-shielding arc welding, which can suppress pore defects such as pits and blow holes and has good welding workability.

The gist of the present invention is that in a wire containing a flux for self-shielding arc welding in which a steel outer skin is filled with flux, the total mass of the steel outer skin and the flux is C: 0.05 to 0, which is the mass% with respect to the total weight of the wire. .25%, Mn: 0.5-1.5%, Al: 1.0-3.0%, Si: 0.8% or less, and in mass% of the total weight of the wire in the flux. , Mg: 1.0 to 3.0%, _{total SiO 2} conversion value of Si oxide: 0.1 to 0.5%, total F conversion value of metal fluoride: 1 to 5%, metal carbonate Total of 1 or 2 or more of: 0.2 to 1.5%, Na ₂ O conversion value of Na oxide and K oxide and total of 1 or 2 of _{K 2 O conversion value: 0.02} It is characterized by containing ~ 0.15%, and the balance is composed of Fe content of a steel outer skin, iron powder, Fe content of iron alloy powder, and impurities.

Further, it is characterized in that the total mass of the steel outer skin and the flux is 0.5% or less in terms of mass% with respect to the total mass of the wire.

Further, the flux-cored wire for self-shielding arc welding is characterized in that the total mass of the steel outer skin and the flux is 1.0% or less in terms of mass% with respect to the total mass of the wire.

According to the self-shielded arc welding flux-filled wire to which the present invention is applied, a weld metal having a high strength of 590 MPa or more and excellent toughness can be obtained, and pore defects such as pits and blow holes do not occur, and welding work is performed. It is possible to provide a wire containing a flux for self-shielding arc welding having good properties.

It is sectional drawing of the ear with flux for self-shielding arc welding prototyped in the Example of this invention.

In order to solve the above-mentioned problems, the present inventors have obtained a weld metal having a high strength of 590 MPa or more and excellent toughness in a wire containing flux for self-shielded arc welding, and pores such as pits and blow holes. The composition of the flux-welded wire for self-shielded arc welding, which does not generate defects, stabilizes the arc, and has excellent welding workability, was examined in detail.

As a result, by adding an appropriate amount of Al to the flux-containing wire for self-shielded arc welding, N in the molten metal can be fixed as AlN and the occurrence of pore defects such as pits and blow holes can be suppressed, but Al is welded. It was found that the microstructure of the metal was coarsened to reduce the toughness of the weld metal. Therefore, as a result of various studies on methods for improving the strength of the weld metal while suppressing the coarsening of the microstructure, metal fluorides, metal carbonates and Mg that generate gas in the flux-containing wire for self-shielded arc welding were found. By adding a large amount, it is possible to improve the shielding property and reduce the amount of Al added, it is possible to suppress the coarsening of the microstructure, and by adding an appropriate amount of C and Mn, the strength of the weld metal And found that toughness can be improved. It was also found that when the amount of Mn added was increased in order to obtain the required toughness of the weld metal, the strength of the weld metal became too high.

Therefore, as a result of further studies to suppress the occurrence of pore defects such as pits and blow holes, and to obtain a weld metal having a strength of 590 MPa class and good toughness, the amount of metal carbonate added was reduced. The amount of slag generated is suppressed, the amount of Al added is kept to a minimum, and the amount of Mg and metal fluoride added is increased to ensure high shielding properties and suppress the occurrence of pore defects such as pits and blow holes. However, it was found that by adjusting the addition amount of C while suppressing the addition amount of Mn to a small amount, the strength of the weld metal of 590 MPa class can be obtained and the weld metal having good toughness can be obtained. Furthermore, it was also found that the strength can be improved without lowering the toughness of the weld metal by adding appropriate amounts of Mo and Ni.

Further, regarding other welding workability, it was found that it is effective to add an appropriate amount of Na oxide and K oxide in order to stabilize the arc.

Furthermore, it was found that the viscosity of the molten slag can be adjusted and the slag encapsulation property and the bead shape of the weld bead can be improved by adding an appropriate amount of Si oxide.

The flux-cored wire for self-shielding arc welding of the present invention can be achieved by the synergistic effect of each component alone or coexisting. The reasons for adding each component and the reasons for limitation will be described below. In the following, the chemical composition of the flux-cored wire for self-shielding welding shall be represented by mass%, which is a ratio to the total mass of the wire, and the description regarding the mass% shall be simply described as%.

[Total of steel outer skin and flux C: 0.05 to 0.25%]
C has the effect of improving the strength of the weld metal by strengthening the solid solution. In addition, CO and CO ₂ generated during welding have the effect of blocking the atmosphere into the melting pool, enhancing the shielding property, and suppressing the occurrence of pore defects such as pits and blow holes. If C is less than 0.05%, the effect cannot be sufficiently obtained and the strength of the weld metal cannot be obtained. Further, if C is less than 0.05%, the shielding property cannot be sufficiently ensured, and pore defects such as pits and blow holes are likely to occur. On the other hand, when C exceeds 0.25%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, the total of the steel outer skin and the flux is set to 0.05 to 0.25%. In addition to the components contained in the steel outer skin, C can be added from the flux as metal powder, alloy powder, or the like.

[Mn: 0.5 to 1.5% in total of steel outer skin and flux]
Mn acts as a deoxidizer for the weld metal and has the effect of improving the strength and toughness of the weld metal. If Mn is less than 0.5%, the effect cannot be sufficiently obtained, and the strength and toughness of the weld metal are lowered. On the other hand, when Mn exceeds 1.5%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, the total Mn of the steel outer skin and the flux is set to 0.5 to 1.5%. In addition to the components contained in the steel outer skin, Mn can be added from the flux as an alloy powder such as metal Mn, Fe-Mn, and Fe-Si-Mn.

[Total of steel outer skin and flux Al: 1.0-3.0%]
Al acts as a deoxidizing agent to improve the toughness of the weld metal, and has the effect of fixing N that has penetrated into the molten metal as AlN and suppressing the occurrence of pore defects such as pits and blow holes. If Al is less than 1.0%, the effect cannot be sufficiently obtained, and pore defects such as pits and blow holes are likely to occur. On the other hand, when Al exceeds 3.0%, Al in the weld metal is excessively retained, the microstructure becomes coarse, and the toughness of the weld metal decreases. Therefore, the total of the steel outer skin and the flux is set to 1.0 to 3.0%. In addition to the components contained in the steel outer skin, Al can be added from the flux as an alloy powder of metals Al, Fe-Al, Al-Mg and the like.

[Total of steel outer skin and flux Si: 0.8% or less]
If Si is excessively left in the weld metal, it causes a decrease in the toughness of the weld metal. Therefore, the total of the steel outer skin and the flux is set to 0.8% or less. In addition to the components contained in the steel outer skin, Si can be added from the flux by alloy powders such as metal Si, Fe-Si, and Fe-Si-Mn.

[Mg in flux: 1.0 to 3.0%]
Mg acts as a deoxidizing agent, promotes deoxidation of the weld metal, suppresses the occurrence of pore defects such as pits and blow holes, and has the effect of improving the toughness of the weld metal. If Mg is less than 1.0%, the effect cannot be sufficiently obtained, pore defects such as pits and blow holes are likely to occur, and the toughness of the weld metal is lowered. On the other hand, when Mg exceeds 3.0%, the arc becomes excessively strong and becomes unstable. Therefore, the total of the steel outer skin and the flux is set to 1.0 to 3.0%. In addition, Mg can be added from flux as an alloy powder of metal Mg, Al—Mg and the like.

_{[Total SiO 2} conversion value of Si oxide in flux: 0.1 to 0.5%]
The Si oxide has the effect of adjusting the viscosity and melting point of the molten slag and improving the slag encapsulation property. _{If the total SiO 2} conversion value of the Si oxide is less than 0.1%, this effect cannot be sufficiently obtained and the slag encapsulation property deteriorates. On the other hand, when _{the total SiO 2} conversion value of the Si oxide exceeds 0.5%, the basicity of the molten slag decreases, the amount of oxygen in the weld metal increases, and the toughness of the weld metal decreases. Therefore, the total value of Si oxides in the flux in _{terms of SiO 2} is set to 0.1 to 0.5%. The Si oxide can be added from the flux as silica sand, potash glass, fluorite and the like.

[Metal fluoride contained in flux: 1 to 5% in total of F conversion value]
The metal fluoride acts as a gas generating agent and has the effect of enhancing the shielding property of the molten pool from the atmosphere. If the total F conversion value of the metal fluoride is less than 1%, the effect cannot be sufficiently obtained, the shielding effect becomes insufficient, pore defects such as pits and blow holes are likely to occur, and the arc is unstable. become. On the other hand, when the total F conversion value of the metal fluoride exceeds 5%, the arc becomes excessively strong and becomes unstable. Therefore, the total F-converted value of the metal fluoride contained in the flux is 1 to 5%. The metal fluoride can be added from the flux as fluorite, sodium fluoride, lithium fluoride, magnesium fluoride, potassium siliceous fluoride, cryolite, aluminum fluoride, etc., and the F conversion value is contained therein. It is the total amount of F.

[Total of one or more metal carbonates contained in the flux: 0.2 to 1.5%]
Metal carbonate acts as a gas generator and is decomposed by arc heat during welding _{to generate CO and CO 2} gas, which blocks the molten pool from the atmosphere and enhances the shielding property, and pore defects such as pits and blow holes. Has the effect of suppressing the occurrence of. If the total of one or more of the metal carbonates is less than 0.2%, the effect cannot be sufficiently obtained, and pore defects such as pits and blow holes are likely to occur. Further, if the total of one or more of the metal carbonates is less than 0.2%, the toughness of the weld metal is lowered. On the other hand, if the total of one or more of the metal carbonates exceeds 1.5%, the arc becomes excessively strong and unstable, and slag entrainment occurs in the welded portion. Therefore, the total of one or more metal carbonates contained in the flux is 0.2 to 1.5%. The metal carbonate can be added from the flux as calcium carbonate, barium carbonate, lithium carbonate, manganese carbonate, magnesium carbonate and the like.

[Total of 1 or 2 types of _{Na 2} O conversion value and K ₂ O conversion value of Na oxide and K oxide contained in the flux: 0.02 to 0.15%]
Na oxide and K oxide have the effect of stabilizing the arc state. _{If the sum of one or two of the Na 2} O conversion value and the K ₂ O conversion value of Na oxide and K oxide is less than 0.02%, the arc becomes unstable. On the other hand, if _{the total of one or two of the Na 2} O conversion value and the K ₂ O conversion value of Na oxide and K oxide exceeds 0.15%, the bead toe becomes unfamiliar and the bead shape. Becomes defective. Therefore, the total of one or two _{of the Na 2} O conversion value and the K ₂ O conversion value of the Na oxide and the K oxide contained in the flux is 0.02 to 0.15%. In addition, Na oxide and K oxide can be added from flux as powder of potash glass, soda glass and the like.

[Total of steel outer skin and flux: Mo: 0.5% or less]
Mo has the effect of increasing the strength of the weld metal. However, when Mo exceeds 0.5%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, the total Mo of the steel outer skin and the flux is 0.5% or less. In order to obtain the effect of increasing the strength of the weld metal, Mo is preferably 0.1% or more. Mo can be added from the flux as an alloy powder such as metal Mo powder and Fe-Mo, in addition to the components contained in the steel outer skin.

[Total of steel outer skin and flux Ni: 1.0% or less]
Ni has the effect of improving the strength and toughness of the weld metal. However, when Ni exceeds 1.0%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, Ni is 1.0% or less. In order to obtain the effect of improving the strength and toughness of the weld metal, Ni is preferably 0.1% or more. Ni can be added from the flux as an alloy powder of metal Ni, Fe—Ni, etc., in addition to the components contained in the steel outer skin.

The rest of the flux-containing wire for self-shielding arc welding of the present invention is Fe of iron alloy powder such as Fe content of steel outer skin, iron powder, Fe-Si, Fe-Mn, Fe-Si-Mn, and Fe-Al alloy. Minutes and impurities. Iron powder is contained in the flux for adjusting the flux filling rate. The impurities are not particularly limited, but P is preferably 0.010% or less from the viewpoint of preventing high temperature cracking.

The flux-cored wire for self-shielding arc welding of the present invention has a so-called E cross section in which a steel outer skin is formed into a U shape, the inside is filled with flux, and then the outer skin is woven inside to form a wire. It is a wire.

The flux filling rate is not particularly limited, but is preferably 10 to 30% with respect to the total mass of the wire from the viewpoint of productivity.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples.

Steel hull (C: 0.001 to 0.10%, Si: 0.05% or less, Mn: 0.1 to 0.6%, P: 0.05% or less, S: 0.05% or less) The steel outer skin is formed into a U shape, and various fluxes shown in Table 1 are filled with a filling rate of 15 to 25%. We made a prototype wire containing flux. The wire diameter was 3.2 mm. The flux to be filled was dried before filling.

Self-shielded arc welding was carried out using a prototype self-shielded arc welding flux-cored wire, and a weld metal test and welding workability evaluation were performed.

The weld metal test was carried out under the welding conditions shown in Table 2 according to JIS Z 3111 and JIS Z 3313. The steel plate used is JIS G 3106 SM570 (plate thickness 20 mm). A0 tensile test piece and V-notch impact test piece were collected from the center of the thickness of the welded metal of the obtained test piece and subjected to the tensile test and the impact test, respectively.

As the quality judgment criteria in the evaluation of the tensile properties of the weld metal, those having a tensile strength in the range of 590 to 770 MPa were considered to be good. Further, as a criterion for evaluating the impact characteristics of the weld metal, those having an average value of three absorbed energy values at 20 ° C. of 27 J or more were considered to be good.

In addition, after preparing a test piece for the weld metal test, the surplus and the backing metal were ground to smooth the surface of the steel sheet, and then an X-ray transmission test according to JIS Z 3104 was conducted to investigate the presence or absence of welding defects. .. These results are summarized in Table 3.

Welding workability was evaluated for arc stability, slag encapsulation, and bead shape during welding in the weld metal test.

The stability of the arc was evaluated by measuring the voltage fluctuation for 10 seconds during welding and measuring the magnitude of the voltage. When ± 4V is set as the threshold value with respect to the average voltage, arc stability is defined as the time when the voltage fluctuation exceeds the threshold value is 80% or less in 10 seconds, and the time when the voltage fluctuation exceeds the threshold value exceeds 20% in 10 seconds. Made the arc unstable. For the slag encapsulation property, the area without slag on the bead that can be visually confirmed was estimated, and the area without slag on the bead was set to be good at 10% or less. The bead shape is good if it is a welded bead sound part and there is no undercut or overlap that needs to be repaired.

Wire symbols 1 to 12 in Tables 1 and 3 are examples of the present invention, and wire symbols 13 to 24 are comparative examples. In wire symbols 1 to 12 which are examples of the present invention, C, Mn, Al and Si in the slag-containing wire for self-shielding arc welding are appropriate, and _{the sum of the SiO 2} conversion values of Mg and Si oxide in the flux, the metal. Since the total F conversion value of the fluoride, the total metal carbonate, the total Na ₂ O conversion value and the K ₂ O conversion value of Na oxide and K oxide are appropriate, the arc is stable, and the slag encapsulation property and slag encapsulation property and The bead shape was good, welding defects such as pits, blow holes and slag entanglement did not occur, and both the tensile strength and absorption energy of the weld metal were good.

Since the amount of Mo added to the wire symbols 3 and 6 is appropriate, the tensile strength of the weld metal is 700 MPa or more, and the absorption energy is 27 J or more. Further, since the amount of Ni added to the wire symbols 1 and 12 is appropriate, a welded metal having a high strength of 700 MPa or more was obtained, and an absorption energy of 50 J or more was obtained. Further, since the amounts of Mo and Ni added to the wire symbols 8, 10 and 11 are appropriate, a welded metal having a high strength of 750 MPa or more was obtained, and an absorption energy of 50 J or more was obtained.

In the comparative example, the wire symbol 13 has a small amount of C, so that a blow hole is generated in the welded portion. Moreover, since C was small, the tensile strength of the weld metal was low. Furthermore, since the amount of Mg was large, the arc became excessively strong and became unstable. Since the amount of Ni was small, the effect of improving the tensile strength and absorption energy of the weld metal could not be obtained.

Since the wire symbol 14 has a large amount of C, the tensile strength of the weld metal is high and the absorbed energy is low. Further, _{since the total value of Si oxides converted to SiO 2} is small, the slag encapsulation property is poor.

Since the wire symbol 15 has a small amount of Mn, the tensile strength and absorption energy of the weld metal are low. Moreover, since the total F-converted value of the metal fluoride was small, the arc became unstable. In addition, since the total F conversion value of the metal fluoride is small, blow holes are generated in the welded portion. Since the amount of Mo was small, the effect of improving the tensile strength of the weld metal could not be obtained.

Since the wire symbol 16 has a large amount of Mn, the tensile strength of the weld metal is high and the absorption energy is low. In addition, since the total F conversion value of the metal fluoride was large, the arc became excessively strong and unstable.

Since the wire symbol 17 has a small amount of Al, a blow hole is generated in the welded portion.

Since the wire symbol 18 contains a large amount of Al, the absorption energy of the weld metal was low. _{Moreover, since the sum of the Na 2} O conversion value and the K ₂ O conversion value of Na oxide and K oxide was small, the arc became unstable.

Since the wire symbol 19 contains a small amount of Mg, a blow hole is generated in the welded portion. Moreover, since the amount of Mg was small, the absorption energy of the weld metal was low.

Since the wire symbol 20 contains a large amount of Si, the absorption energy of the weld metal was low. _{Further, since the total of the Na 2} O conversion value and the K ₂ O conversion value of Na oxide and K oxide is large, the bead toe portion is not well fitted and the bead shape is poor.

Since the wire symbol 21 has a _{large total of the SiO 2} conversion values of the Si oxide, the absorption energy of the weld metal was low. In addition, since the total amount of metal carbonate is large, the arc is excessively strong and unstable, and slag entrainment occurs in the welded portion.

The wire symbol 22 has a small total amount of metal carbonates, so that the absorbed energy of the weld metal is low. In addition, since the total amount of metal carbonate was small, blow holes were generated in the welded portion.

Since the wire symbol 23 has a large total F-converted value of the metal fluoride, the arc becomes excessively strong and unstable. Further, since the amount of Mo was large, the tensile strength of the weld metal was high and the absorbed energy was low.

As for the wire symbol 24, the arc became unstable because the sum _{of the Na 2} O conversion value and the K ₂ O conversion value of the Na oxide and the K oxide was small. Further, since the amount of Ni was large, the tensile strength of the weld metal was high and the absorption energy was low.

Claims (3)

In a wire with flux for self-shielding arc welding, which is made by filling a steel outer skin with flux, the total of the steel outer skin and flux is the mass% of the total weight of the wire.
C: 0.05 to 0.25%,
Mn: 0.5-1.5%,
Al: 1.0 to 3.0%,
Si: Contains 0.8% or less,
In addition, in the flux, in mass% of the total mass of the wire,
Mg: 1.0-3.0%,
_{Total SiO 2} equivalent of Si oxide: 0.1-0.5%,
Total F conversion value of metal fluoride: 1-5%,
Total of one or more metal carbonates: 0.2-1.5%,
_{Contains 1 or 2 of Na 2} O conversion value and K ₂ O conversion value of Na oxide and K oxide: 0.02 to 0.15%.
A flux-containing wire for self-shielding arc welding, wherein the balance is composed of Fe content of a steel outer skin, iron powder, Fe content of iron alloy powder, and impurities. The flux-cored wire for self-shielding arc welding according to claim 1, wherein the total mass of the steel outer skin and the flux is 0.5% or less in terms of mass% with respect to the total mass of the wire. The flux-cored wire for self-shielding arc welding according to claim 1 or 2, wherein the total mass of the steel outer skin and the flux is 1.0% or less in terms of mass% with respect to the total mass of the wire.

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