JP7383513B2 - Covered arc welding rod for 9% Ni steel welding - Google Patents

Description

The present invention relates to a coated arc welding rod used for welding 9% Ni steel, which is mainly used in the construction of LNG storage tanks. The present invention also relates to a coated arc welding rod for welding 9% Ni steel, which provides a weld metal with excellent porosity defect resistance.

Because LNG storage tanks store LNG, the temperature inside the tank is always -196°C, so 9% Ni steel, a ferritic alloy steel with excellent low-temperature toughness, is often used. For welding, welding materials based on Ni-based alloys are often used because the weld metal has good toughness at extremely low temperatures.

In recent years, as LNG storage tanks have become larger, weld metals have been required to have high strength and high toughness, and there was a problem in that coated arc welding rods using conventional technology were unable to fully meet the required specifications. .

For example, Patent Document 1 discloses that by using a pure Ni core wire and specifying Ti, Al, Mg, and metal carbonate in the coating material, a coated arc with excellent mechanical performance of the weld metal and with fewer pore defects can be achieved. A welding rod is disclosed. However, although the porosity defect resistance is good, the metal carbonate content of the coating material is low, which improves downward welding workability, but there is a problem that welding workability in vertical upward welding tends to be poor. there were.

Moreover, Patent Document 2 discloses a coated arc welding rod that has excellent strength and toughness of weld metal by adding C, Nb+Ta, and W. However, although the strength of the weld metal can be ensured by adding C, Nb+Ta, and W, there are problems in that the toughness tends to vary, and the impact performance at -196° C. does not meet recent required specifications.

Japanese Patent Application Publication No. 2016-043395 JP2006-272432A

The present invention has been devised in view of the above-mentioned problems, and has good welding workability in all-position welding, horizontal fillet welding and vertical advancement welding, and has good cracking resistance. The object of the present invention is to provide a coated arc welding rod for welding 9% Ni steel, which can stably yield a weld metal with excellent porosity defect resistance and mechanical performance, especially toughness at low temperatures.

The gist of the present invention is as follows. In a coated arc welding rod for welding 9% Ni steel, the core is a Ni-based alloy containing 95% by mass or more of Ni, and the total of one or both of the core wire and coating material is the core wire mass ratio shown in the following formula. , Si: 0.1-1.0%, Mn: 1.5-4.0%, Cr: 8-12%, Mo: 2.5-8.0%, Nb: 0.5-2.5 %, Ta: 0.05 to 0.30%, Ti: 0.1 to 0.8%, W: 0.5 to 1.7%, and the coating material has a mass relative to the total mass of the coating material. %, total SiO ₂ equivalent value of Si oxide: 4 to 12%, total of one or more metal fluorides: 12 to 25%, total of one or more metal carbonates: 13 to 21%, the sum of Na and K equivalent values of Na oxide and K oxide: 1 to 5%, the remainder being Ni and Fe in the core wire and Fe in the iron alloy of the coating material. and unavoidable impurities.
Core wire mass ratio = Content % in the core + Content % in the coating × Coverage % / 100... formula (however, the content % in the core is the mass % of the total mass of the core, the coating The content in the agent is mass % based on the total mass of the coating material, and the coverage rate is the mass % of the coating material based on the total mass of the coated arc welding rod for welding 9% Ni steel)

According to the coated arc welding rod for welding 9% Ni steel of the present invention, welding workability is good in all position welding, horizontal fillet welding and vertical advancement welding, and cracking resistance and pore defect resistance are achieved. It is possible to improve the quality of the welded joint by stably obtaining weld metal with excellent toughness and mechanical performance, especially at low temperatures.

FIG. 1 is a diagram showing a welding test plate used in an example of the present invention.

In order to solve the above problems, the present inventors welded 9% Ni steel in order to improve the strength and toughness of the weld metal, improve cracking resistance and pore defect resistance, and improve welding workability in all position welding. Various studies were conducted on the composition of coated arc welding rods. As a result, in order to satisfy the target mechanical performance of the weld metal, especially toughness at low temperatures, the core wire must be made of a Ni-based alloy containing 95% by mass or more of Ni, and a balance of Cr, Mo, Nb, Ta, and W must be maintained. It was found that it was necessary to add an appropriate amount.

It has also been found that in order to improve crack resistance and pore defect resistance, it is necessary to add Si and Mn in appropriate amounts with a good balance. In order to improve welding workability in all-position welding, we have found that it is effective to add appropriate amounts of Si oxide, metal fluoride, and metal carbonate.

The present invention was achieved through the individual effects and synergistic effects of the coexistence of each component of the Ni-based alloy core wire containing 95% by mass or more of Ni and the coating material.The reasons for adding each component are as follows. and state the reason for limiting the quantity. Note that the % of the amount of each component described below refers to the mass ratio of the core wire, and is calculated by the following formula for the mass % of the content of one or both of the core wire and the coating material. However, the content of the cord in the same formula means the proportion to the total mass of the cord, and the compounding ratio in the coating means the proportion to the total mass of the coating. Further, the coverage ratio means the ratio of the coating agent to the total mass of the welding rod.
Core wire mass ratio = Content % in the core + Content % in the coating material x Coverage %/100...Formula

[Si: 0.1 to 1.0% in core wire mass ratio]
Si has the effect of improving the pore defect resistance in the weld metal. If Si is less than 0.1% in terms of core mass ratio, the effect cannot be sufficiently obtained and pore defects are likely to occur. On the other hand, if Si exceeds 1.0% in terms of core wire mass ratio, cracks are likely to occur. Therefore, Si is set to 0.1 to 1.0% in terms of core wire mass ratio. Note that Si can be added from a core wire, metal Si, Fe-Si, Fe-Si-Mn, or the like.

[Mn: 1.5-4.0% in core wire mass ratio]
Mn has the effect of improving the cracking resistance of weld metal. If Mn is less than 1.5% in terms of core wire mass ratio, cracks are likely to occur. On the other hand, when Mn exceeds 4.0% in terms of core wire mass ratio, the toughness of the weld metal decreases. Therefore, Mn is set to 1.5 to 4.0% in terms of core wire mass ratio. Note that Mn can be added from a core wire, metal Mn, Fe--Mn, Fe--Si--Mn, etc.

[Cr: 8-12% in core wire mass ratio]
Cr has the effect of improving the strength of weld metal. When the Cr content is less than 8% in terms of core mass ratio, the strength of the weld metal decreases. On the other hand, when Cr exceeds 12% in terms of core wire mass ratio, the toughness of the weld metal decreases. Therefore, the Cr content in the core mass ratio is set to 8 to 12%. Note that Cr can be added from a core wire, metal Cr, Fe--Cr alloy powder, and the like.

[Mo: 2.5 to 8.0% in core wire mass ratio]
Mo has the effect of improving the strength of weld metal. When Mo is less than 2.5% in terms of core mass ratio, the strength of the weld metal decreases. On the other hand, when Mo exceeds 8.0% in terms of core wire mass ratio, the toughness of the weld metal decreases. Therefore, Mo is set to 2.5 to 8.0% in terms of core wire mass ratio. Note that Mo can be added from a core wire, metal Mo, Fe--Mo, and the like.

[Nb: 0.5 to 2.5% in core wire mass ratio]
Nb has the effect of improving the strength of weld metal. When Nb is less than 0.5% in terms of core mass ratio, the strength of the weld metal decreases. On the other hand, if Nb exceeds 2.5% in terms of core wire mass ratio, the toughness of the weld metal decreases. Therefore, Nb is set to 0.5 to 2.5% in terms of core wire mass ratio. Note that Nb can be added from a core wire or an alloy powder such as Fe--Nb.

[Ta: 0.05 to 0.30% in core wire mass ratio]
Ta has the effect of improving the strength of weld metal. When Ta is less than 0.05% in terms of core wire mass ratio, the strength of the weld metal decreases. On the other hand, when Ta exceeds 0.30% in terms of core wire mass ratio, the toughness of the weld metal decreases. Therefore, Ta is set to 0.05 to 0.30% in terms of core wire mass ratio. Note that Ta can be added from a core wire, metal Ta, Nb--Ta, and the like.

[Ti: 0.1 to 0.8% in core wire mass ratio]
Ti has the effect of removing excess oxygen contained in the alloy and stabilizing the strength and toughness of the weld metal. If Ti is less than 0.1% in terms of core wire mass ratio, the effect cannot be sufficiently obtained, and pore defects are likely to occur in the weld metal. On the other hand, if Ti exceeds 0.8% in terms of core mass ratio, a large amount of Ti will be distributed as metal oxides in the weld metal, resulting in a decrease in strength and toughness. Therefore, Ti is set to 0.1 to 0.8% in terms of core wire mass ratio. Note that Ti can be added from a core wire, metal Ti, Fe-Ti, or the like.

[Wire mass ratio: W: 0.5 to 1.7%]
W has the effect of improving the strength of the weld metal without reducing its toughness. If W is less than 0.5% in terms of core wire mass ratio, the strength of the weld metal cannot be obtained. On the other hand, when W exceeds 1.7% in terms of core wire mass ratio, the strength of the weld metal becomes too high and the toughness decreases. Therefore, W in terms of core wire mass ratio is set to 0.5 to 1.7%. Note that W can be added from a core wire, metal W, WC, etc.

The component composition contained in the coating material is as follows in mass % based on the total mass of the coating material.

[Total SiO ₂ equivalent value of Si oxide: 4 to 12%]
Si oxide has the effect of improving slag removability. If the total SiO ₂ equivalent value of the Si oxide is less than 4%, the arc becomes unstable and the slag removability becomes poor. On the other hand, if the total SiO ₂ equivalent value of the Si oxide exceeds 12%, the melting point of the molten slag will drop excessively, resulting in metal sag during vertical position welding and poor bead shape. Therefore, the content of Si oxide is 4 to 12%. Note that Si oxide can be added from silica sand, feldspar, sodium silicate, potassium silicate, etc. in water glass.

[Total of one or more metal fluorides: 12 to 25%]
Metal fluorides have the effect of optimizing arc spraying, slag viscosity and fluidity, and improving welding workability. If the total amount of one or more metal fluorides is less than 12%, the effect will not be obtained and the slag removability and bead shape will be poor. On the other hand, if the total content of one or more metal fluorides exceeds 25% or more, the arc becomes unstable, a large amount of spatter is generated, and the bead shape becomes poor. Furthermore, metal sag is more likely to occur during vertical advancement welding. Therefore, the total amount of one or more metal fluorides is 12 to 25%. Note that the metal fluoride can be added from fluorite, barium fluoride, magnesium fluoride, aluminum fluoride, and the like.

[Total of one or more metal carbonates: 13-21%]
Metal carbonates, like metal fluorides, have the effect of optimizing arc spraying, slag viscosity and fluidity, and improving welding workability. If the total amount of one or more metal carbonates is less than 13%, the effect cannot be obtained, and the arc becomes unstable and the bead shape becomes poor. On the other hand, if the total content of one or more metal carbonates exceeds 21%, the arc becomes unstable and the amount of spatter generated increases, resulting in poor slag removability and bead shape. Furthermore, metal sag is more likely to occur during vertical advancement welding. Therefore, the total amount of one or more metal carbonates is 13 to 21%. Note that the metal carbonate can be added from calcium carbonate, magnesium carbonate, barium carbonate, manganese carbonate, lithium carbonate, and the like.

[Total of Na and K equivalent values of Na oxide and K oxide: 1 to 5%]
Na oxide and K oxide have the effect of stabilizing the arc. If the sum of the Na and K equivalent values of the Na oxide and K oxide is less than 1%, the arc becomes unstable and the bead shape becomes poor. On the other hand, when the sum of the Na and K equivalent values of the Na oxide and K oxide exceeds 5%, the arc becomes unstable and the amount of spatter generated increases. Therefore, the total of the Na and K equivalent values of Na oxide and K oxide is 1 to 5%. Note that Na oxide and K oxide can be added from sodium silicate and potassium silicate, feldspar, etc. in water glass.

The reasons for limiting the constituent requirements of the coated arc welding rod for welding 9% Ni steel of the present invention have been described above, and the remainder is the Ni and Fe content in the core wire, the Fe content in the iron alloy of the coating material, and unavoidable impurities. . Further, the unavoidable impurities C, P, and S are preferably as low as possible from the viewpoint of toughness and cracking resistance, and C is preferably 0.05 or less.

The method for producing coated arc welding rods involves preparing a coating compounded and mixed with a Ni-based alloy core wire containing 95% or more of Ni, and then adding a fixing agent (an aqueous solution of potassium silicon and sodium silicate) to the coating. It can be produced by performing wet mixing, coating the core wire with a coating agent, and then drying and baking at 150 to 450° C. for about 1 to 3 hours after coating.

The effects of the present invention will be specifically explained using examples.

After coating a core wire of a Ni-based alloy containing 95% by mass or more of Ni with a diameter of 4.0 mm and a length of 350 mm shown in Table 1 with the coating agent shown in Table 2 at a coverage rate of 45 to 50%, a dried 9% Ni A prototype coated arc welding rod for steel welding was produced.

Using these prototype welding rods, welding workability, weld defects, mechanical performance of deposited metal, and crack resistance were investigated.

Welding workability was evaluated using a test specimen made of SM490B steel plates specified in JIS G 3106 with a plate thickness of 9 mm, width of 100 mm, and length of 450 mm assembled in a T shape, and horizontal fillet welding was performed under the welding conditions shown in Table 3. Then, vertical advancement welding was performed, and the arc stability, slag removability, bead shape, amount of spatter generation, and presence or absence of metal sag were visually inspected.

The mechanical performance of weld metal was evaluated using a steel plate specified in JIS G 3127 SL9N590 with a plate thickness of 19 mm, and after conducting a weld metal test according to AWS A5.11 ENiCrMo-6 and an X-ray transmission test, A tensile test and an impact test were conducted.

In the X-ray transmission test, if slag entrainment, blowholes, or poor penetration were observed, the type of defect was indicated, and if the above defects were not observed at a joint welding length of 500 mm, it was determined that there was no defect.

In the tensile test evaluation, tensile strength of 690 MPa or more was considered good. For evaluation of the impact test, the Charpy impact test was repeated three times at a test temperature of -196°C, and an average value of absorbed energy of 70 J or more was considered good.

In the investigation of crack resistance, as shown in Fig. 1, grooves 2 with a depth of 18 mm were formed in a steel plate 10 specified in JIS G 3127 SL9N590, which had a thickness of 26 mm and an opening angle of 40°, and were restrained by strong back. A test bead 1 was formed in the groove 2 by welding the steel plate 10 for 500 mm in a horizontal position under the welding conditions shown in Table 3, and a penetrant test was conducted by grinding the bead surface three times at approximately 1 mm intervals to detect cracks. The presence or absence was determined. The results are summarized in Table 4.

In Tables 2 and 4, welding rod No. 1~No. 12 is an example of the present invention, welding rod No. 13~No. 25 is a comparative example.

Welding rod No. which is an example of the present invention. 1~No. In No. 12, Si, Mn, Cr, Mo, Nb, Ta, Ti, and W are appropriate in the core wire mass ratio, and the coating material is the sum of the SiO ₂ equivalent value of Si oxide, one or two metal fluorides. Since the sum of the above species, the sum of one or more metal carbonates, and the Na-equivalent value and K-equivalent value of Na oxide and K oxide are appropriate, the arc is stable and the amount of spatter generation is reduced. The slag removal property was excellent, the bead shape was good, and good welding workability was obtained in horizontal fillet welding and vertical advancement welding. Furthermore, there were no welding defects, and the tensile strength and absorbed energy of the welded metal were good, giving very satisfactory results.

Welding rod No. in the comparative example. In No. 13, blowholes occurred because Si was small in terms of core mass ratio. In addition, since Ta was large in the core mass ratio, the absorbed energy of the weld metal was low.

Welding rod no. In No. 14, cracks occurred because the fiber mass ratio was high in Si. Furthermore, since the amount of Ti was large in terms of core mass ratio, the tensile strength and absorbed energy of the weld metal were low.

Welding rod no. No. 15 had a small amount of Mn in the fiber mass ratio, so cracking occurred. Furthermore, since the core wire mass ratio W was small, the tensile strength of the welded metal was low.

Welding rod no. Since No. 16 had a large amount of Mn in the core mass ratio, the absorbed energy of the weld metal was low.

Welding rod no. In No. 17, the tensile strength of the weld metal was low because the Cr content was low in the core wire mass ratio. Furthermore, since the sum of Na and K equivalent values of Na oxide and K oxide was large, the arc was unstable and a large amount of spatter was generated.

Welding rod no. No. 18 had a large amount of Cr in the core wire mass ratio, so the absorbed energy of the weld metal was low. Furthermore, since the sum of Na and K equivalent values of Na oxide and K oxide was small, the arc was unstable and the bead shape was poor.

Welding rod no. In No. 19, the tensile strength of the weld metal was low because the Mo content was small in terms of the core wire mass ratio. Furthermore, since the total amount of one or more metal carbonates was large, the arc was unstable and a large amount of spatter was generated. Furthermore, since the total amount of one or more metal carbonates was large, slag peeling and bead shape were poor, and metal sag occurred during vertical advancement welding.

Welding rod no. In No. 20, the absorbed energy of the weld metal was low because the core mass ratio was high in Mo. Furthermore, since the total amount of one or more metal carbonates was small, the arc was unstable and the bead shape was poor.

Welding rod no. In No. 21, the tensile strength of the welded metal was low because the Nb content was low in terms of core wire mass ratio. Further, since the total amount of one or more metal fluorides was large, the arc was unstable, a large amount of spatter was generated, the bead shape was poor, and metal sag occurred during vertical advancement welding.

Welding rod no. No. 22 had a large amount of Nb in the core wire mass ratio, so the absorbed energy of the weld metal was low. Furthermore, since the total amount of one or more metal fluorides was small, slag peeling and bead shape were poor.

Welding rod no. In No. 23, the tensile strength of the weld metal was low because Ta was low in the core mass ratio. Further, since the total amount of Si oxides converted to SiO ₂ was large, metal sag occurred during vertical advancement welding, resulting in poor bead shape.

Welding rod no. In No. 24, the tensile strength of the welded metal was high and the absorbed energy was low because the wire mass ratio had a large amount of W. Furthermore, since the total SiO ₂ equivalent value of Si oxide was small, the arc was unstable and the slag removability was poor.

Welding rod no. No. 25 had a low Ti content in terms of core wire mass ratio, so blowholes occurred and the tensile strength and absorbed energy of the weld metal were low.

1 test bead 2 groove

Claims (1)

In a coated arc welding rod for welding 9% Ni steel with a core made of a Ni-based alloy containing 95% by mass or more of Ni, the total of the core wire and one or both of the coating material has a core wire mass ratio shown in the following formula: in,
Si: 0.1-1.0%,
Mn: 1.5-4.0%,
Cr: 8-12%,
Mo: 2.5-8.0%,
Nb: 0.5-2.5%,
Ta: 0.05-0.30%,
Ti: 0.1 to 0.8%,
Contains W: 0.5 to 1.7%,
The coating material is mass% based on the total mass of the coating material,
Total _SiO2 equivalent value of Si oxide: 4 to 12%,
Total of one or more metal fluorides: 12 to 25%,
Total of one or more metal carbonates: 13-21%,
Contains a total of Na equivalent value and K equivalent value of Na oxide and K oxide: 1 to 5%,
A coated arc welding rod for welding 9% Ni steel, characterized in that the remainder consists of Ni and Fe in the core wire, Fe in the iron alloy of the coating, and unavoidable impurities.

Core wire mass ratio = Content % in the core + Content % in the coating × Coverage % / 100... formula (However, the content % in the core is the mass % of the total mass of the core, the coating The content in the agent is mass % based on the total mass of the coating material, and the coverage rate is the mass % of the coating material based on the total mass of the coated arc welding rod for welding 9% Ni steel)

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