JP5417098B2 - Submerged arc welding method for low temperature steel - Google Patents

Description

  The present invention relates to a submerged arc welding method for low-temperature steel such as 5.5% Ni steel and 9% Ni steel used as a construction material for storage tanks for cryogenic liquids. The present invention relates to a submerged arc welding method for low temperature steel suitable for obtaining a high quality welded joint.

  In the submerged arc welding method, a granular flux is dispersed in advance along a welding line, an electrode wire is continuously supplied therein, and an arc is generated between the tip of the electrode wire and the base material. This is a method of performing welding continuously. According to this submerged arc welding method, a high-efficiency and high-quality welded joint can be obtained, so that it is often used for welding low-temperature steel. In addition, because the welding speed is fast and the penetration is deep, it is very useful when welding large structures such as shipbuilding, pipe building, bridges, and vehicles.

  The actual welding posture for performing the submerged arc welding is a welding posture that is conventionally used when performing downward welding or horizontal fillet welding in the case of performing ordinary arc welding. In particular, the submerged arc welding at the time of construction of the storage tank for the cryogenic liquid may have to be carried out in a lateral posture welding. For this reason, a flux capable of welding in such a lateral posture has also been developed.

  By the way, the welded portion of low-temperature steel such as 5.5% Ni steel and 9% Ni steel is required to have low-temperature toughness in the state after completion of welding without performing heat treatment. Also, a Ni-based alloy wire having a high Ni content is applied. In addition, the submerged arc welding method can be applied when actually performing a downward posture or a welding posture by horizontal fillet welding in field construction, but in the case of a vertical posture welding, the flux is effectively dispersed. Therefore, such a method cannot be applied, and eventually it is unavoidable to carry out welding by a covering arc welding method or a TIG welding method. More recently, the development of flux-cored wire for gas shielded arc welding, which is highly efficient and excellent in welding workability, is in progress, but its crack resistance is insufficient. It has become mainstream.

However, this coated arc welding method has a problem in that the welding efficiency is low and the work period of the on-site construction cannot be shortened. For this reason, a submerged arc welding material and a welding method therefor have been proposed (see, for example, Patent Document 1), which is highly efficient and capable of vertical improvement welding with excellent weld metal crack resistance. According to the disclosed technique of Patent Document 1, it has been found that submerged arc welding can be performed in a vertical posture by reducing CaF ₂ and positively adding Al ₂ O _3. is there. Actually, by making CaF ₂ 40% or less, particularly in the vertical position welding, the arc length is suppressed to stabilize the arc state, and by making Al ₂ O ₃ 31% or more, welding slag is reduced. Therefore, it is expected that the bead shape will be smoothed even in vertical position welding.

  However, although it is possible to provide a submerged arc welding material that can surely be improved by the disclosed technique of Patent Document 1 described above, the dilution rate of the base material as a problem peculiar to the submerged arc welding method is low. There is a problem that it is difficult to improve the toughness due to the high Fe in the weld metal, and the tensile strength of the weld metal cannot be further improved.

  Further, as a submerged arc welding method for cryogenic steel, a welding method capable of obtaining a weld metal having excellent crack resistance and mechanical properties has been proposed (for example, see Patent Document 2). According to the technique disclosed in Patent Document 2, by optimizing the metal Al content coefficient, it is a technique that can improve the blowhole resistance during welding. However, this disclosed technique has a problem that crack resistance is insufficient because it contains a large amount of Cr.

JP 2009-39661 A Japanese Patent Publication No.59-6756

  Accordingly, the present invention has been devised in view of the above-described problems, and submerged arc welding is performed on 5.5% Ni steel, 9% Ni steel, and the like used for building materials for cryogenic liquid storage tanks. In this case, downward welding, horizontal fillet welding, lateral and vertical position welding can be realized, high tensile strength and toughness can be obtained, and high quality welded joints with excellent ductility and no blowholes and crack defects can be obtained. It is an object of the present invention to provide a submerged arc welding method for low temperature steel.

  In order to solve the above-mentioned problems, the present inventors have made various studies on the alloy components of the submerged arc welding wire and the firing flux. As a result, it was found that the tensile strength of the welded joint can be increased by increasing the amount of C. However, an excessive increase in the amount of C also causes C that cannot be dissolved to disperse and precipitate as iron carbide, facilitates the propagation of cracks, and causes a significant decrease in the toughness of the weld metal. That is, the present inventors have found that increasing the amount of C results in lower toughness as the strength of the welded joint is increased.

  Therefore, the balance between the tensile strength and toughness of the welded joint was maintained, and as a result of examining the components that can obtain high strength and high toughness, the excess that cannot be dissolved while increasing the tensile strength by increasing the C content We paid attention to the fact that the toughness can be improved while increasing the tensile strength of the weld metal by making C of manganese carbide a carbide that does not affect the mechanical performance, crack resistance and the like. For this reason, high tensile strength and toughness are obtained by optimizing the balance between C and Mn to produce such manganese carbide for the Ni-based alloy wire and the firing flux component to be combined. It was clarified that high-quality welded joints without holes and crack defects can be obtained.

The present invention has been made based on the above findings, and the gist of the present invention is that in a submerged arc welding method for welding low-temperature steel by combining a Ni-based alloy wire and a firing-type flux, a Ni-based alloy wire and a firing die. The M content of each component obtained from the following formula (1) of the flux is expressed by mass% with respect to the total mass of the wire and the total mass of the flux , C: 0.03 to 0.12%, Mn: 0.5 to 2% However, 10 × C / Mn: 1.5 or less, Ni: 60% or more, sum of either one or both of Mo and W: 19 to 27%, sum of either one or both of Al and Ti: 0 and .3～3%, Si, total Cr and Cu: 1% or less, the remainder of the Ni-based alloy wire as unavoidable impurities, to the firing type flux, by mass% with respect to the flux to the total mass, C: 0. Containing from 1 to 0.20%, the balance of the oxides of the calcined type flux, metal carbonates, characterized in that a metal fluoride and unavoidable impurities.
M = Mw + 0.5 × Mf (1)
Mw:% by mass of each component in the Ni-based alloy wire with respect to the total mass of the wire
Mf:% by mass with respect to the total mass of each component in the calcined flux
Further, it may be a submerged arc welding method for low-temperature steel, wherein the C content in the calcined flux is 0.01 to 0.20% by mass.

  According to the submerged arc welding method for low-temperature steels such as 5.5% Ni steel and 9% Ni steel of the present invention, submerged arc welding is performed using the Ni-based alloy wire and the firing flux having the above-described composition. Therefore, the tensile strength of the weld metal can be increased by increasing the amount of C. Further, excess C is made to be manganese carbide, and the carbide has no influence on mechanical performance, crack resistance, etc. Thus, it is possible to improve the toughness while increasing the tensile strength of the weld metal, and it is possible to obtain a high-quality welded joint that is excellent in ductility and free from blowholes and crack defects.

  Hereinafter, as a mode for carrying out the present invention, a submerged arc welding method for low-temperature steel such as 5.5% Ni steel and 9% Ni steel will be described in detail.

  In the present invention, the composition of each component of the Ni-based alloy wire and the calcining flux used for welding of low-temperature steel such as 5.5% Ni steel and 9% Ni steel can be achieved by a single effect and a synergistic effect due to their coexistence. It is a thing.

  Incidentally, in the present invention, the concept of M content is used in defining each component composition of the Ni-based alloy wire and the firing flux. This M content is a content converted based on M shown in the following formula (1).

M = Mw + 0.5 × Mf (1)
Mw: mass% of each component in the Ni-based alloy wire with respect to the total mass of the wire
Mf: mass% of each component in the calcined flux with respect to the total mass of the flux

This M is 1% of the weight of each component in the Ni-based alloy wire with respect to the total mass of the wire and the weight of the weld metal component and the mechanical performance of 1% by mass with respect to the total mass of the flux of each component in the firing type flux. : Converted as 0.5. The reason why this weighting is set to 1: 0.5 between the mass% of each component in the Ni-based alloy wire and the mass% of each component in the fired flux is that the weld metal component and mechanical performance are It takes into account the contribution ratio. In the submerged arc welding, the consumption of the firing type flux is about 1 with respect to the consumption 1 of the Ni-based alloy wire, but the firing type flux is melted by the arc heat and does not become slag. It is formed. For this reason , when the unmelted portion is subtracted, the actual firing-type flux contribution ratio is about 1/2 that of the Ni-based alloy wire, and thus the above-described weighting is performed.

That is, in the present invention, each component of the Ni-based alloy wire and the firing-type flux is not individually defined, but the component is defined through one parameter M by combining the Ni-based alloy wire and the firing-type flux. Is. When actually welding, since this Ni-based alloy wire and firing-type flux are combined, the components are also defined in a combined state, and the components in the Ni-based alloy wire are weighted for the reasons described above. Is heavy.

  Hereinafter, the reason for adding each component composition and the reason for limiting the M content will be described. The mass% in the composition is simply described as%.

C: 0.03-0.12%
C is added from ferromanganese, ferrosilicon manganese, graphite, and the like contained in the Ni-based alloy wire and the firing-type flux for the purpose of increasing the tensile strength of the weld metal and realizing deoxidation. When the M content of C obtained by the above-described equation (1) is less than 0.03%, the tensile strength of the weld metal that can be sufficiently improved and can be shifted becomes low. On the other hand, when M content of C calculated | required by (1) formula exceeds 0.12%, C is excessive and C which cannot be dissolved is dispersed and precipitated as iron carbide, and this deteriorates the toughness of a weld metal remarkably. . Therefore, the M content of C is set to 0.03 to 0.12%.

Further, a part of C reacts with oxygen in the arc and is released as CO ₂ gas, which has an effect of reducing the oxygen content of the weld metal. In order to make deoxidation by C work effectively, the effect of adding from the firing type flux is larger than that of the Ni-based alloy wire, and if the amount of C in the firing type flux is less than 0.01%, a sufficient deoxidation effect is obtained. It is not obtained and blow holes are likely to occur. On the other hand, if the amount of C in the calcined flux exceeds 0.20%, the CO ₂ gas becomes excessive, and the stability of the arc is impaired, which tends to cause blow holes. Therefore, it is desirable that the amount of C in the fired flux be 0.01 to 0.20%. In addition, although Al and Ti which will be described later are also added for the purpose of deoxidation, inclusions such as nitrides are likely to be inherent in the weld metal if added excessively, so in order to perform more effective deoxidation, It is necessary to add C together with Al and Ti.

Mn: 0.5-2%
Mn fixes S of the low melting point sulfide in the weld metal and becomes MnS to improve the crack resistance of the weld metal, and ferromanganese, ferrosilicon manganese, and the like contained in the Ni-based alloy wire and the fired flux Add from metallic manganese. If M content of Mn calculated | required by (1) Formula mentioned above is less than 0.5%, the effect is not fully acquired but the crack resistance of a weld metal is low. On the other hand, if the M content of Mn exceeds 2%, a large amount of Mn oxide is inherent in the weld metal, and when bending stress is applied, this opens as a starting point of cracks, deteriorating bending ductility. Let Therefore, the M content of Mn is set to 0.5 to 2%.

10 × C / Mn: 1.5 or less Tensile strength without degrading the toughness of the weld metal by setting the above-mentioned M converted value of C and 10 × C / Mn of M converted to M to 1.5 or less. Can be increased. As the M content of C increases, it can be dissolved in the weld metal to improve the tensile strength. However, if this C content is excessively added, C that cannot be dissolved dissolves and precipitates as iron carbide, and the propagation of cracks. And the toughness of the weld metal is impaired. For this reason, while adding the M content of Mn in an appropriate amount, the tensile strength of the weld metal is improved, and C that cannot be dissolved is changed to manganese carbide by Mn, and mechanical properties, crack resistance, etc. are not affected. By using carbides, the toughness can be increased while the tensile strength of the weld metal is increased. When 10 × C / Mn exceeds 1.5, the M content of C becomes excessive compared with the M content of Mn, and the tensile strength of the weld metal can be increased, but excessive C Is left without being converted to manganese carbide by Mn, and the toughness is lowered by precipitation of iron carbide.

  If the Ni-based alloy wire contains Fe as an impurity and the weld metal has no parent dilution, it is easy to increase both the tensile strength and toughness of the weld metal. There is a base metal dilution of 5.5% Ni steel and 9% Ni steel, the amount of Fe in the weld metal is high, and iron carbide is likely to be deposited, which tends to impair the toughness of the weld metal. Therefore, it is necessary not only to satisfy the M content of C and the M content of Mn, but also to maintain an appropriate balance between the M content of C and the M content of Mn as described above. Therefore, 10 × C / Mn of the M content of C and the M content of Mn is 1.5 or less.

Ni: 60% or more Ni is added from ferronickel and metallic nickel contained in the Ni-based alloy wire and the fired flux for the purpose of increasing the toughness of the weld metal. If the M content of Ni obtained by the above formula (1) is less than 60%, the toughness of the weld metal is lowered. Therefore, the M content of Ni is set to 60% or more. On the other hand, the upper limit is not particularly limited, but in order to increase the tensile strength of the weld metal, crack resistance, blow hole resistance, etc., Mo, W, Mn, Al, Ti, etc. are added. In consideration of the total amount, the upper limit is about 85%.

Total of either one or both of Mo and W: 19 to 27%
Mo and W are added from ferromolybdenum and metal tungsten contained in the Ni-based alloy wire and the fired flux for the purpose of increasing the tensile strength by dissolving in the weld metal. If the sum of one or both of the M content of Mo and the M content of W calculated by the above formula (1) is less than 19%, the effect cannot be sufficiently obtained, and the tensile strength of the weld metal is low. turn into. On the other hand, if added over 27%, the elongation of the weld metal becomes low. Therefore, the total of either one or both of the M content of Mo and the M content of W is set to 15 to 27%. Although the effects of Mo and W are the same, it is preferable that the M content of Mo is in the range of 15 to 25% and the M content of W is in the range of 1 to 4% in consideration of economic efficiency and wire productivity.

Total of either one or both of Al and Ti: 0.3 to 3%
Al and Ti are deoxidized and denitrogenated from ferroaluminum, metal aluminum, ferrotitanium, metal titanium, etc. contained in Ni-based alloy wires and fired fluxes for the purpose of improving blowhole resistance in weld metals. Added. If the sum of one or both of the M content of Al and the M content of Ti determined by the above formula (1) is less than 0.3%, the effect cannot be obtained and blowholes are generated. On the other hand, when it is added in excess of 3%, a large amount of Al and Ti nitride is inherent in the weld metal, and when bending stress is applied, it opens as a starting point of a crack and deteriorates bending ductility. Therefore, the total of one or both of the M content of Al and the M content of Ti is set to 0.1 to 3%. Both Al and Ti have a deoxidizing and denitrifying effect, but Al has a higher deoxidizing ability and Ti is slightly inferior. On the other hand, the denitrification ability is higher in Ti and Al is slightly inferior. Therefore, in order to perform both deoxidation and denitrification, addition of both elements is preferable, the M content of Al is 0.3 to 2%, and the M content of Ti is 0.05 to 1.5%. A range is preferable.

Total of Si, Cr, and Cu: 1% or less Si, Cr, and Cu increase the solidification temperature width, promote the formation of low melting point inclusions such as P and S, and easily cause hot cracks. preferable. Therefore, the sum of the M content of Si, the M content of Cr, and the M content of Cu is 1% or less.

  In addition, since it is easy to generate | occur | produce a hot crack, so that P and S are high, it is preferable that the sum total of P and S of a Ni base alloy wire shall be less than 0.01%. Moreover, it is preferable to use a raw material with low P and S as the firing flux.

The main chemical component other than the metal component of the cermet type flux used in submerged arc welding method of low-temperature steel of the present invention, both in terms of _{mass%, Al 2 O 3: 30~60} %, CaF 2: 10~40 _{%, SiO 2: 1~10%,} Na 2 O: 0.1~5%, MgO: 1~10%, CaCO 3: 1~10%, CaO: is preferably 1-20%.

Al ₂ O ₃ is added to form a bead having a wide bead width and good fit. When the added amount of Al ₂ O ₃ is less than 30%, the familiarity deteriorates, and when it exceeds 60%, the bead cannot be flattened. Therefore, the Al ₂ O ₃ content is 30 to 60%. Is desirable.

CaF ₂ is added to lower oxygen and improve toughness. If this CaF ₂ is less than 10%, oxygen cannot be reduced sufficiently, and if it exceeds 60%, the arc will be destabilized.

SiO ₂ is added to form a good bead by increasing the viscosity of the slag. If the SiO ₂ content is less than 1%, such an effect cannot be achieved. If the SiO ₂ content exceeds 10%, the amount of oxygen increases, and sufficient deoxidation is achieved even if the deoxidation element described above is added. Inability to do so is a factor that reduces toughness. Therefore, the SiO ₂ is desirably set to 1-10%.

Na ₂ O is added from the viewpoint of improving the stability and concentration of the arc, but if it is less than 0.1%, the effect cannot be sufficiently obtained in the vertical posture welding. Moreover, when the content of Na ₂ O exceeds 5%, the slag removability deteriorates. For this reason, it is desirable that Na ₂ O be 0.1 to 5%.

  MgO is added for the purpose of increasing the melting point of the slag and adjusting the bead shape, and such an effect can be expressed at 1% or more. However, if the addition amount exceeds 10%, the peelability of the slag deteriorates. End up. For this reason, it is desirable that MgO be 1 to 10%.

CaCO ₃ is added to generate CO ₂ gas during welding and shield the weld metal. In order to exhibit such an effect, it is necessary to contain CaCO ₃ in an amount of 1% or more. However, since the arc state becomes unstable when the content of CaCO ₃ exceeds 10%, the content of CaCO ₃ is desirably 1 to 10%.

  CaO is added from the viewpoint of lowering oxygen and improving toughness. If the CaO content is less than 1%, oxygen cannot be lowered, and if it exceeds 20%, the bead shape cannot be optimized. For this reason, it is desirable that the content of CaO is 1 to 20%.

  The reasons for limiting the M content of each component composition of the Ni-based alloy wire and the firing flux used in the low-temperature steel submerged arc welding method of the present invention have been described above. By performing submerged arc welding using the Ni-based alloy wire and the firing flux having the above-described composition, the tensile strength of the weld metal can be increased by increasing the amount of C, and excessive C With regard to, it is possible to improve toughness while increasing the tensile strength of the weld metal by using manganese carbide and making it carbide that does not affect mechanical performance, crack resistance and the like.

  Furthermore, referring to the method for producing the calcined flux, the powder raw material is blended and stirred, and then a fixing agent (sodium silicate and / or potassium silicate aqueous solution) is added, followed by fluid drying and calcining to form a bond. Use flux. For the purpose of improving welding workability, a melt flux that has been dissolved and pulverized in advance may be used as a raw material.

  In addition to being able to be embodied as a submerged arc welding method, the present invention may also be embodied as a welding material for submerged arc welding composed of a Ni-based alloy wire and a fired flux. is there. In such a case, it is applied to a welding kit in which the composition of each component of the Ni-based alloy wire and the firing type flux is adjusted so as to achieve the M content described above.

  An embodiment of a submerged arc welding method to which the present invention having the above-described configuration is applied will be described in detail.

  First, as a test material, a Ni-based alloy wire having a component composition defined by the wire symbols W1 to W6 shown in Table 1 and a fired flux having a component composition shown in Table 2 were used.

  Table 3 shows the M content converted when submerged arc welding is performed by combining these Ni-based alloy wires and firing-type flux. The wire diameters of the Ni-based alloy wires shown in Table 1 are 2.4 mm for downward and lateral position welding, and 1.2 mm for vertical position welding.

  In actual submerged arc welding, a 9% Ni steel plate thickness of 16 mm was used, and a downward posture welding and a lateral posture welding were performed in accordance with a welding specimen for collecting a bending specimen of a welded joint of JIS Z 3333. For the vertical position welding, the groove shape was the same as the downward position welding. About the presence or absence of a blowhole and a crack generation, the radiation transmission test was done according to JISZ3106, the transmission photograph was observed, and the presence or absence of a blowhole and a crack was investigated.

  For the mechanical properties of the weld metal, a test piece was collected using a welded joint prepared according to JIS Z 3333. In the tensile test, JIS Z 3111 A2 No. was taken from the weld metal (taken from the weld line direction) and tested, and the tensile strength was 690 MPa or more and the elongation was 25% or more. In addition, for the impact test, JIS Z 3111-4 (the notch position is the center of the weld metal) was sampled and subjected to an impact test at a test temperature of 196 ° C., and the absorbed energy was 50 J or more. Further, in the bending test, a longitudinal bending test piece was collected in accordance with JIS Z 3122, a bending radius of 3.1 / 3t (33R) was tested, and the bending performance was confirmed.

  The welding conditions were such that the polarity of the electrode was DC (+), the welding current was 300 to 400 A in the downward posture welding and the lateral posture welding, and the welding current was 150 to 230 A in the vertical posture welding. The results are summarized in Table 3. In Table 3, test no. 1-8 are examples of the present invention, test Nos. 9 to 15 are comparative examples. Test No. which is an example of the present invention. 1 to 8 are the above-described M contents of C, Mn, Ni, Mo, W, Al, Ti, Si, Cr, Cu, the ratio of 10 × C / Mn, and the amount of C in the fired flux. Since it was within the range specified in the present invention, the tensile strength, elongation, absorbed energy, bending ductility, crack resistance and blowhole resistance of the weld metal were all good, and the results were extremely satisfactory.

  Test No. in Comparative Examples. In No. 9, the M content of C was less than 0.03%, so the tensile strength of the welded joint was low. In addition, since the total of the M content of Al and the M content of Ti was less than 0.3%, blowholes were generated.

  Test No. In No. 10, the M content of C is more than 0.12%, so the absorbed energy of the weld metal is 42J, which is low. Moreover, since the sum of the M content of Al and the M content of Ti is more than 3%, the bending performance was poor.

  Test No. In No. 11, the M content of Mn was less than 0.5%, so cracking occurred. Moreover, since the sum of the M content of Mo and the M content of W was less than 19% and was low, the tensile strength of the weld metal was low.

  Test No. In No. 12, the M content of Mn was over 2%, and the bending performance was poor. Moreover, since the sum of the M content of Si, the M content of Cr, and the M content of Cu is more than 1%, cracking occurred.

  Test No. In No. 13, the M content of Ni was less than 60%, so the absorbed energy was low. Moreover, since the sum of the M content of Mo and the M content of W exceeds 27% and is large, the elongation of the weld metal was low. Furthermore, blow holes were generated because the amount of C in the calcined flux was 0% and was small.

  Test No. No. 14 had a low ratio of 10 × C / Mn, which was high because it was higher than 1.5, so the absorbed energy was low.

  Test No. No. 15 had a low ratio of 10 × C / Mn, which was high because it was higher than 1.5, so the absorbed energy was low. Also. Since the amount of C in the fired flux was over 0.2%, the arc became unstable and blow holes were generated.

  From the above experimental results, all of the examples of the present invention have a good overall evaluation (◯), whereas the comparative examples deviating from the range defined in the present invention have an overall evaluation of (×). I understand that there is. For this reason, it has been verified that satisfactory results can be obtained by adjusting the M content within the range defined in the present invention.

Claims (1)

In a submerged arc welding method of welding a low temperature steel by combining a Ni-based alloy wire and a firing type flux,
M content of each component calculated | required from the following (1) formula of both Ni base alloy wire and a firing type | mold flux with the mass% with respect to the wire total mass and flux total mass ,
C: 0.03-0.12%,
Mn: 0.5-2%
However, 10 × C / Mn: 1.5 or less,
Ni: 60% or more,
Sum of one or both of Mo and W: 19-27%,
Total of either one or both of Al and Ti: 0.3 to 3%,
Total of Si, Cr and Cu: 1% or less,
The remainder of the Ni-based alloy wire is an inevitable impurity,
In the calcination type flux, in mass% with respect to the total mass of the flux,
C: 0.01 to 0.20% contained,
A submerged arc welding method for low temperature steel, characterized in that the balance of the calcined flux is oxide, metal carbonate, metal fluoride and inevitable impurities.
M = Mw + 0.5 × Mf (1)
Mw:% by mass of each component in the Ni-based alloy wire with respect to the total mass of the wire
Mf:% by mass with respect to the total mass of each component in the calcined flux