JP5052997B2 - Multi-electrode submerged arc welding method - Google Patents

Description

  The present invention relates to a downward multi-electrode submerged arc welding method used for producing a weld metal that requires strength and toughness in welding of a high-strength line pipe or a high-strength hydraulic iron pipe.

  Downward multi-electrode submerged arc welding is a welding method that uses a plurality of electrodes to create a single weld pool, and can be welded at high speed and with a large amount of welding, so it is often used for welding steel pipes and large structures. This is an arc welding method.

  One of the characteristics required for the weld metal of this submerged arc welding is toughness. The fact that the toughness of weld metal can be improved by optimizing the amount of oxygen in the weld metal is said to be based on many research results, and based on this, the development of welding materials is underway. In recent years, steel materials used for the purpose of increasing the size of welded structures and reducing construction costs have been increasing in strength, and in connection with this, the strength of weld metals used has also been increasing. However, since the toughness generally tends to decrease as the strength of the weld metal increases, the method of controlling the amount of oxygen becomes more important to ensure the toughness of the weld metal as the strength of the steel increases.

  Conventionally, the oxygen content of the submerged arc weld metal has been controlled by adjusting the composition of the flux used. For example, in patent document 1, low temperature toughness is ensured by reducing Ti and oxygen of a weld metal with respect to X100 class high strength steel with a UO steel pipe. Moreover, in patent document 2, it is trying to improve the toughness of a weld metal by limiting the chemical composition of a base material and a weld metal, and using a flux. Further, in Patent Document 3, Patent Document 4, Patent Document 5 or Patent Document 6, the oxygen content of the weld metal is reduced by optimizing the composition of the flux as means for specifically reducing oxygen, and the bead shape. The weldability such as is secured. In Patent Document 7 or Patent Document 8, the weld metal having a strength of 800 MPa or more is used by ensuring the toughness of the weld metal by controlling the oxygen content of the weld metal and the ratio of Al to oxygen.

JP 2004-43911 A JP-A-3-285770 JP-A-5-375 JP 7-256488 A Japanese Patent Laid-Open No. 9-262692 JP 2004-154840 A JP-A-11-2678844 JP 2000-96187 A

  However, Patent Document 1 discloses in detail the effect of oxygen reduction of the weld metal, but does not disclose the method of oxygen reduction. Further, in Patent Document 2, an attempt is made to improve the toughness by controlling the structure of the weld metal by the chemical composition of the base metal or the chemical composition of the wire, but it is applicable only to the weld metal having a low Pcm of the weld metal, that is, a low strength. Can not. Furthermore, no specific prescription of the flux is disclosed. On the other hand, Patent Document 3, Patent Document 4, Patent Document 5 or Patent Document 6 specifically examines the components of the flux as a method for realizing hypoxia, clarifies the method, and further examines the chemical composition of the wire. Although the means for improving the toughness has been clarified, the premise of using these welding materials is a steel material or weld metal having a low strength equivalent to SM490 or X65.

  On the other hand, as described above, in recent years, there has been an increasing demand for application of high strength steel of 800 MPa or more to a welded structure. High strength weld metals of 800 MPa or higher applied to these steel materials have high alloying elements in order to obtain strength, and therefore physical properties such as viscosity of molten metal are different from those of low strength weld metals. Therefore, a high basicity flux having a composition premised on use for low-strength weld metal, such as disclosed in Patent Document 3, Patent Document 4, Patent Document 5, or Patent Document 6, is used for such a high strength. When used when producing a weld metal, a new problem has arisen that slag-in occurs at the top of the bead as shown in FIG. The top slag-in is a slag-in having a diameter of about 0.1 mm to 2.0 mm generated in the weld metal in the vicinity of the top of the weld beat surplus. This is because the molten slag in the weld metal melted during welding does not float up and remains inside the weld metal at the top of the weld bead and is recognized as a defect. In patent document 7, the strength of weld metal is secured by controlling the ratio of Al and oxygen and the basicity of the flux to be used for a weld metal having a strength of 800 MPa or more. Not added, again the problem of top slag in occurs. Patent Document 8 also attempts to ensure the toughness of the weld metal by controlling the ratio of the amount of Al and oxygen in the weld metal, but does not mention an oxygen control method. In particular, since a commercially available flux is used, the problem of the top slag in cannot be avoided.

  In order to solve this problem, the present inventors examined the tendency of top slag-in formation. As a result, it was found that the generation tendency of the top slag-in is mainly influenced by the viscosity of the weld metal, the viscosity of the molten slag, and the interfacial tension between the molten metal and the molten slag. The viscosity of the weld metal varies depending on the composition of the weld metal. In addition, the viscosity of the molten slag changes depending on the slag components. The interfacial tension between the molten metal and the molten slag also varies depending on the weld metal component and the molten slag component. On the other hand, the components of the weld metal are optimized to obtain the strength of the weld metal. The component of the molten slag is naturally determined by the component of the flux. Therefore, the inventors tried to sort out the tendency of the top slag in by the strength of the weld metal and the flux component.

  For that purpose, an index representing the component system of the flux is necessary. Controlling the amount of oxygen is an important aspect of the flux component design. The index indicating the relationship between the flux and the amount of oxygen in the weld metal is basicity, which is an important index for determining the flux component system. Therefore, we tried to organize the tendency of the occurrence of top slag in using basicity.

The result is shown in FIG. The horizontal axis in FIG. 2 represents the basicity calculated by the formula (1) using CaO, MgO, CaF ₂ , Al ₂ O ₃ and SiO ₂ among the components of the flux to be used, and the vertical axis represents the solid wire. It is the tensile strength of the created weld metal. Several formulas are used to express the basicity of the flux used for submerged arc welding. The formula (1) is a basicity formula proposed by Mori et al. The basicity is expressed using a mole fraction. For example, it is also used in Japanese Patent Application Laid-Open No. 60-191691, and is a formula that has been used for a long time as the basicity of the flux. The welding method used in the creation of FIG. 2 was three-electrode submerged arc welding, and a commercially available solid wire was used to adjust the strength of the weld metal depending on the chemical composition of the wire. The welding conditions shown in Table 1 were used as the welding conditions. As shown in FIG. 2, the tendency of the occurrence of top slag-in can be arranged by the basicity calculated by the formula (1) and the strength of the weld metal, and the top slag-in is generated at higher basicity as the strength of the weld metal increases. It becomes like this. In a weld metal having a strength of 800 MPa or more, top slag-in is generated unless the basicity calculated by the formula (1) is 1.1 or more.
B = 6.05N [CaO] + 4.0N [MgO] + 5.1N [CaF ₂ ] −0.2N [Al ₂ O ₃ ] −6.3N [SiO ₂ ] (1)
Here, in the formula (1), N [CaO], N [MgO], N [CaF ₂ ], N [Al ₂ O ₃ ], and N [SiO ₂ ] are respectively CaO, MgO, CaF ₂ , It means the molar fraction of Al ₂ O ₃ and SiO ₂ .

On the other hand, in order to secure the toughness of a high strength weld metal having a strength of 800 MPa or more, it is important to control the amount of oxygen in the weld metal. For weld metals having a strength of 800 MPa or more, it has been found from the inventors' knowledge that stable toughness can be obtained with mass% and oxygen content in the range of 0.018% to 0.035%. This is because if the oxygen content is less than 0.018%, an oxide of an amount necessary for refining the structure is not formed, and toughness cannot be obtained. On the other hand, if it exceeds 0.035%, a coarse oxide is formed, which becomes the starting point of fracture and lowers toughness. FIG. 3 shows the basicity of the flux calculated by the formula (1) using CaO, MgO, CaF ₂ , Al ₂ O ₃ and SiO ₂ among the components of the flux used, and the weld metal created using the flux. The relationship of the amount of oxygen inside is shown. Among the flux components, CaO, MgO, CaF ₂ , Al ₂ O ₃ and SiO ₂ are used, and the basicity calculated by equation (1) is used to determine the flux components and the oxygen in the weld metal. The quantity can be well organized as shown in FIG. The welding method used for creating FIG. 3 was three-electrode submerged arc welding, and a commercially available solid wire was used to adjust the strength of the weld metal depending on the chemical composition of the wire. The welding conditions shown in Table 1 were used as the welding conditions. Solid wires generally contain only inevitable impurities of 0.01% or less. Therefore, in FIG. 3, the amount of oxygen in the weld metal is determined by the flux.

  From FIG. 3, in order to stably obtain an oxygen content in the weld metal of 0.018% or more, the basicity calculated by the equation (1) needs to be less than about 1.1. However, when the strength of the weld metal is 800 MPa or more from FIG. 2, when the basicity calculated by the formula (1) is less than 1.1, the top slag-in is generated, which causes a problem from the viewpoint of preventing welding defects.

  Thus, it has been found that it is difficult to achieve both weldability and toughness in a high-strength weld metal. Furthermore, as pointed out in the patent literature, the composition of the flux has an important influence on the weldability, and many ideas and costs are required to develop a flux that achieves both good weldability and toughness. Become. If the component design of the flux is performed only from the viewpoint of weldability to prevent defects such as bead shape and slag in, and oxygen control can be performed by another method, it is very important in designing the welding material for submerged arc welding. It can be an effective means.

  The present invention has been studied from such a viewpoint, and an object thereof is to provide a method for producing a high-strength weld metal having a good bead shape and excellent toughness by downward multi-electrode submerged arc welding. To do.

  In order to achieve the above-mentioned object, the present inventors have focused on the submerged arc welding method itself and studied a method for achieving both oxygen amount control and weldability. As a result, it has been found that the oxygen content of the weld metal can be easily controlled by partially changing the weld wire used to the metal cored wire, and as a result, a weld metal having good toughness can be obtained. Was completed.

  That is, the gist of the present invention is as follows.

A steel material having a tensile strength of 800 to 1200 MPa is filled with a high basic flux in the groove of the steel material, a molten pool is created using a plurality of electrodes, and submerged arc welding is performed. In a multi-electrode submerged arc welding method for forming a weld metal of ˜1200 MPa,
Any one electrode or two or more of the plurality of electrodes is a metal cored wire containing O: 0.03% to 0.50% by mass% with respect to the whole wire for each individual wire, and the rest While making the electrode a solid wire,
The component composition of the high basic flux is SiO ₂ : 5.0% to less than 20.0%, CaF ₂ : 30.0% to 50.0%, CaO: 5.0% by mass% with respect to the flux. _{~25.0%, MgO: 1.0% ~5.0} %, Al 2 O 3: containing 15.0% to 30.0%, and the component composition of the flux is the following equation (1) The calculated basicity B value satisfies 1.1 to 3.2,
The component composition of the weld metal is mass% with respect to the weld metal,
C: 0.03% to 0.12%,
Si: 0.03% to 0.40%,
Mn: 0.5% to 3.0%
Ti: 0.002% to 0.025%,
Al: 0.002% to 0.030%,
O: contains 0.018% to 0.035%,
Nb: limited to 0.04% or less,
Further, any one or more of Cr: 0.1% to 1.5%, Ni: 0.1% to 4.0%, and Mo: 0.1% to 2.0% The balance is Fe and inevitable impurities, and the chemical composition of the weld metal satisfies the value of Pcm determined by the following formula (2) satisfying 0.22 to 0.38, Multi-electrode submerged arc welding method.
B = 6.05 × N [CaO] + 4.0 × N [MgO] + 5.1 × N [CaF ₂ ] −0.2 × N [Al ₂ O ₃ ] −6.3 × N [SiO ₂ ] (1)
Pcm = [C] + [Si] / 30 + ([Mn] + [Cr]) / 20+ [Ni] / 60 + [Mo] / 15 (2)
However,
N [CaO], N [MgO], N [CaF ₂ ], N [Al ₂ O ₃ ], and N [SiO ₂ ] are CaO, MgO, CaF ₂ , Al ₂ O ₃ , and SiO, respectively. _Shows a mole fraction of ₂ ,
[C], [Si], [Mn], [Cr], [Ni], and [Mo] indicate mass% of C, Si, Mn, Cr, Ni, and Mo, respectively.

(2) The component composition of the steel material is mass%,
C: 0.03% to 0.15%,
Si: 0.01% to 0.50%,
Mn: 0.5% to 3.0%
Ti: 0.001% to 0.03%,
Al: 0.001% to 0.04 is contained,
The multi-electrode submerged arc welding method according to (1) above, wherein the balance is Fe and inevitable impurities.

  (3) The component composition of the steel material is mass%, and Cr: 0.1% to 1.5%, Ni: 0.1% to 2.5%, Mo: 0.1% to 2.0% %, And Nb: any one of 0.005% to 0.06%, or two or more kinds, and the multi-electrode submerged arc welding according to (1) or (2) above Method.

(4) The component composition of the solid wire is mass%,
C: 0.03% to 0.15%,
Si: 0.02% to 0.80%,
Mn: 0.2% to 4.0%,
Ti: 0.002% to 0.10%,
Al: 0.001% to 0.02% is contained,
Further, one or more of Cr: 0.25% to 3.0%, Ni: 0.25% to 8.0%, and Mo: 0.25% to 4.0% And the balance is Fe and inevitable impurities,
The component composition of the metal cored wire is mass%,
C: 0.03% to 0.15%,
Si: 0.02% to 0.80%,
Mn: 0.2% to 4.0% or less,
Ti: 0.002% to 0.10%,
Al: 0.001% to 0.02%,
O: 0.03% to 0.50% is contained,
Further, one or more of Cr: 0.25% to 3.0%, Ni: 0.25% to 8.0%, and Mo: 0.25% to 4.0% The multielectrode submerged arc welding method according to any one of (1) to (3) above, wherein the balance is Fe and inevitable impurities.

  (5) Any one of the above (1) to (4), wherein at least one electrode after the second electrode among the plurality of electrodes is the metal cored wire, and the remaining electrodes are the solid wires. The multi-electrode submerged arc welding method according to claim 1.

  The solid wire referred to in the present invention is a solid alloy steel wire welding material with a diameter of 1.6 mm to 6.4 mm, which is used in normal submerged arc welding, and is melted to form a weld metal. To do. At the same time, in submerged arc welding, it is used as an electrode for generating an arc.

  Moreover, after filling either or both of metal powder and alloy powder into a hollow steel pipe called an outer shell as a metal core wire as referred to in the present invention, wire drawing is further added as necessary. It is a linear welding material manufactured to a diameter. Even when the metal powder and alloy powder are filled into the steel pipe, even after the shape of the steel pipe is formed, the metal powder and the alloy powder are filled into the steel pipe at the same time during the forming process of the steel pipe. The metal cored wire manufactured by the method including any filling method is also included in the metal cored wire referred to in the present invention. In the present invention, this metal cored wire is also used as an electrode in submerged arc welding in the same manner as a solid wire, and is used for the purpose of forming a weld metal.

  The outer shell includes a caulking die in which a seam portion is joined by mechanical caulking, and a seamless die that is a seamless seamless steel pipe or a welded steel pipe in which seams are joined by welding. The seamless type referred to in the present invention means that there is no seam, or that the outer and inner sides of the steel pipe are metallurgically cut off against gas or moisture at the seam portion of the steel pipe which is the outer skin. Therefore, it is generally superior in moisture absorption resistance compared to the caulking type. It is difficult to absorb moisture even for long-term storage in a place with high humidity, and as a result, it is suitable as a welding material for high-strength weld metal that is particularly sensitive to cold cracking.

  In FIG. 4, the schematic diagram of the cross section of a metal cored wire is shown. 4 (a) and 4 (b) are examples of a cross section of a metal cored wire which is a caulking type steel pipe in which the seam portion of the outer skin A has a mechanical caulking portion K. FIG. 4 (c) is a schematic diagram of a metal cored wire using a seamless steel pipe as the outer skin B, and FIG. 4 (d) shows a steel pipe having a seam portion joined by welding W as the outer skin B. It is the used metal cored wire.

  In the present invention, a metal cored wire whose outer skin A is crimped as shown in the examples of FIGS. 4A and 4B is called a crimped metal cored wire. A metal cored wire having a seamless outer sheath B as shown in the examples of FIGS. 4C and 4D is referred to as a seamless metal cored wire. Further, the caulking type metal cored wire and the seamless metal cored wire are collectively referred to as a metal cored wire.

  From the viewpoint of formability and workability in the wire drawing process, the metal cored wire skin A or B is generally made of mild steel composed of C, Si, Mn, and other Fe and inevitable impurities. An alloying element necessary as a welding material is added from metal powder or alloy powder filled inside. However, in the case of a metal cored wire with a lot of alloying elements, an alloy component may be added from the outer skin as needed. The oxygen content of the outer skin generally contains only inevitable impurities of 0.01% or less.

  The metal powder and alloy powder C to be put into the metal cored wire are specifically pure metal powders such as Fe, Ni, Cr, Mo and Ti or alloy powders containing these, and are selected as necessary. Monkey. These powders are appropriately selected and used. Among metal powders, especially Fe, unlike other metal powders and alloy powders, easily adsorbs oxygen on the surface, and the surface of the powder is easily oxidized to form a small amount of iron oxide. In the present invention, oxygen is supplied. Plays an important role as a powder. Moreover, in order to improve the manufacturability of metal cored wires as required, production aids such as water glass in addition to metal powder, and arc stabilizers such as oxides and fluorides for further improving weldability However, this does not affect the effect of the present invention. Further, these components are included as impurities unavoidable as components of the metal cored wire. Examples of the element include Na or Ca.

The average composition of the alloy elements of the metal cored wire can be calculated by formula (3) if the chemical composition of the outer skin, the average composition of the metal powder, and the mass ratio of the outer core to the metal powder of the metal cored wire determined by the manufacturing equipment and manufacturing process are determined. Determined by
M (CW) = M (g) × a (g) + M (p) × a (p) (3)
However,
M (CW): average mass% of element M of the metal cored wire,
M (g): mass% of element M of the outer skin,
a (g): ratio of the mass of the unit length of the skin to the sum of the mass of the unit length of the metal powder and the skin,
M (p): average mass (%) of element M in the metal powder,
a (p): ratio of the mass of the unit length of the metal powder to the sum of the mass of the unit length of the metal powder and the outer skin,
a (g) + a (p) = 1

  According to the submerged arc welding method of the present invention, by using a metal cored wire in addition to the solid wire used as an electrode, the oxygen amount of the weld metal can be easily controlled, and a good bead shape without causing top slag in Can be welded. As a result, there is a remarkable effect that a high-strength weld metal having good weldability and excellent toughness can be obtained.

  The present invention is premised on being applied to a weld metal having a tensile strength of 800 MPa to 1200 MPa. This is because a weld metal having a strength of less than 800 MPa has a small amount of alloy of the weld metal, and a weld with good toughness and a good bead shape can be obtained even in the prior art. In addition, a weld metal of more than 1200 MPa has a martensitic structure, and it becomes difficult to ensure toughness only by the technique of the present invention.

  As a welding method, downward multi-electrode submerged arc welding is used. This is an indispensable prerequisite for the present invention to use a plurality of types of wires, solid wires and metal cored wires. The number of electrodes is not particularly specified as long as it is 2 or more, but usually 2 to 5 electrodes are desirable.

  As for the combination of the solid wire and the metal cored wire, at least one electrode among the plurality of electrodes of multi-electrode submerged arc welding was a metal cored wire and the remaining electrodes were solid wires. The reason for this will be described next.

  As described above, in the submerged arc weld metal, it is important to control the amount of oxygen in the weld metal in order to obtain good toughness. In a weld metal with a tensile strength of 800 MPa to 1200 MPa, the oxygen content of the weld metal needs to be in the range of 0.018% to 0.035% by mass, but as shown in FIG. 2 and FIG. When the oxygen amount is controlled within the range, top slag in is generated. Therefore, in the present invention, the amount of oxygen in the weld metal is increased by a method other than the flux.

  In the present invention, in order to stably bring the oxygen content of the weld metal into a range of 0.018% to 0.035% by mass%, the oxygen content is increased using a metal cored wire. The amount of oxygen supplied from the metal cored wire can be adjusted by the amount of oxygen in the metal cored wire, the number of electrodes using the metal cored wire, and the current distribution at each electrode. Since the amount of oxygen contained in the solid wire is generally about unavoidable impurities of 0.01% or less, oxygen cannot be supplied from the wire as long as the solid wire is used.

  Specifically, if a metal cored wire with a large amount of oxygen is used, the amount of oxygen supplied to the weld metal increases.

  FIG. 5 shows the relationship between the basicity calculated by the flux equation (1) and the amount of oxygen in the weld metal when one or more metal cored wires are used for electrodes of three-electrode submerged arc welding. The welding method used for creating FIG. 5 was three-electrode submerged arc welding, in which welding was performed using solid wires and metal cored wires as electrodes. The welding conditions used are those shown in Table 1. The horizontal axis of FIG. 5 shows the basicity of the flux calculated by equation (1), and the vertical axis shows the amount of oxygen in the weld metal. The circles in the figure are the results when all three electrodes shown in FIG. 3 are welded with solid wires. In the figure, ●, ■, and ◆ are the results when welding using one, two, and three metal cored wires. As shown in FIG. 5, when at least one metal cored wire is used, oxygen is supplied from the metal cored wire to the weld metal. Therefore, the basicity flux calculated by the same equation (1) is used. Even so, the amount of oxygen in the weld metal can be increased.

  The oxygen of the metal cored wire is mainly supplied from oxygen adsorbed on the surface of Fe powder contained in the metal powder or iron oxide generated on the surface. Like the solid wire, the outer skin contains oxygen only to the extent of inevitable impurities, so it does not serve as a source of oxygen. Further, the oxygen amount of the metal cored wire can be changed by changing the mass ratio of the metal powder and the skin material.

  It is also possible to easily increase the number of electrodes using metal cored wires.

  Furthermore, the degree of contribution of the wire component of each electrode to the chemical composition of the weld metal can be controlled by the current distribution of each electrode. Therefore, by increasing the current of the electrode using the metal cored wire, the contribution ratio of the metal cored wire is increased, and the amount of oxygen supplied to the weld metal can be increased. The slight decrease is also possible by adjusting the current value. Although the distribution of the welding current supplied to each electrode is not particularly defined, it is desirable that the smallest electric value among the welding currents of each electrode is 25% or more of the largest current value because of the balance.

Next, the reason for limiting the amount of SiO ₂ in the flux will be described.

Of the components constituting the flux used for submerged arc welding, the ratio of SiO ₂ was mass%, and was limited to 5.0% to less than 20.0%. FIG. 6 shows the influence of the amount of SiO ₂ in the flux on the tendency to generate top slag in each strength, with the horizontal axis representing the amount of SiO ₂ in the flux and the vertical axis representing the strength of the weld metal. For welding, three-electrode submerged arc welding was used, and all the welding wires were solid wires. The welding conditions shown in Table 1 were used as the welding conditions. In addition, among the fluxes used in FIG. 6, the SiO ₂ is in the range of 15.5% to 31.0%. is there. Further, the flux SiO ₂ is not less than 34.5% is outside the scope of the present invention in basicity calculated by Equation (1) is -0.4～0.8.

When the tensile strength of the weld metal is 800 MPa or more, the top slag-in is generated when the amount of SiO ₂ is about 20.0% or more. This is because, if SiO ₂ is added excessively, the molten slag becomes more vitreous, and it becomes difficult to float from the weld metal and easily remains on the top of the weld bead. Further, SiO ₂ is to increase the softening and melting temperature of the molten slag, the slag viscosity is also increased. Therefore, the upper limit is made less than 20.0%. The lower limit is not particularly limited from the effect of the present invention, but since SiO ₂ is a glass component, if it is small, the flux becomes crystalline and easily absorbs moisture, and particularly at high strength, it inhibits cold cracking resistance and is 5.0% or more. It was.

Next, the reason for limiting the amount of CaF _{2 in the} flux will be described.

Of the components constituting the flux used for submerged arc welding, the CaF ₂ ratio was 3% by mass, and was 30.0% to 50.0%. FIG. 7 shows the influence of the amount of CaF ₂ in the flux on the tendency of the occurrence of top slag in each strength, with the horizontal axis representing the amount of CaF ₂ in the flux and the vertical axis representing the strength of the weld metal. In all the fluxes used in FIG. 7, the basicity calculated by the equation (1) is 1.1 to 3.2.

When the tensile strength of the weld metal is 800 MPa or more, the amount of CaF ₂ is less than about 30%, and the top slag is generated. This is because CaF ₂ has the effect of lowering the softening and melting temperature of the molten slag to lower the viscosity, but if less than 30%, the effect cannot be obtained. Therefore, the lower limit was made 30.0%. The upper limit is not necessarily limited for the effect of the present invention, but is limited to 50.0% or less because the stability of the arc is impaired when the amount of CaF ₂ is excessive.

  Next, the reason for limiting the CaO of the flux will be described.

  Among the components constituting the flux used for submerged arc welding, the CaO ratio was 5.0% to 25.0% by mass%. CaO is added to adjust the basicity calculated by the formula (1), but if it is 5.0% or less, the basicity calculated by (1) becomes too small, so 5.0% or more is necessary. Further, CaO affects the weld bead shape of the weld metal, and if it is less than 5.0%, the softening and melting temperature becomes high, leading to poor appearance of the surface of the weld bead such as the occurrence of flapping due to the inhibition of the diffusion of the molten gas. On the other hand, if it is excessive, the excess of the weld bead becomes high and the bead shape is deteriorated. In addition, the slag removability is reduced. Therefore, the upper limit was made 25%.

  Next, the reasons for limiting the MgO flux will be described.

  Of the components constituting the flux used for submerged arc welding, the MgO ratio was 1.0% to 5.0% by mass. MgO is added for adjusting the basicity. If it is less than 1%, the basicity becomes too small, so 1.0% or more is necessary. If it exceeds 5.0%, the bead shape becomes a convex bead and undercut occurs. Therefore, the upper limit was made 5%.

Next, the reason for limiting the Al ₂ O ₃ flux will be described.

Of the components constituting the flux used for submerged arc welding, the ratio of Al ₂ O ₃ was 15.0% to 30.0% by mass.

Al ₂ O _{3 is} also added for adjusting the basicity. If it is less than 15.0%, the basicity becomes too high, so 15% or more is necessary. On the other hand, if adding over 30%, the basicity becomes too small, so the upper limit was made 15.0%. In addition, Al ₂ O ₃ has an influence on welding workability, and if it is excessive, undercuts or horse-like projections are generated on the top of the weld bead, so the upper limit was made 30.0%.

  Next, the reason for limiting the basicity calculated by the flux equation (1) will be described.

CaO among the components constituting the flux used, _MgO, basicity of the flux calculated by CaF 2, _Al 2 _{O 3} and SiO ₂ in using the molar fraction equation (1) is from 1.1 to 3.2 Limited to.

As a component of the highly basic flux to be used, in addition to SiO ₂ and CaF ₂ , oxides such as Al ₂ O ₃ , MgO, CaO, LiO ₂ , TiO ₂ and FeO, or CaCO _{3 and the} like are slag generation, basicity It is used for the purpose of adjusting the shape and the effect of adjusting the weld bead shape. Components other than SiO ₂ and CaF ₂ do not affect the formation of top slag in the mass ratio of the carrier, but among these components, SiO ₂ , CaF ₂ , CaO, MgO and Al ₂ O ₃ Slag-in is likely to occur depending on the blending ratio. Specifically, when the tensile strength of the weld metal is 800 MPa or more, the basicity calculated by the formula (1) using the molar fraction is 1. even if the SiO ₂ amount and the CaF ₂ amount are in appropriate ranges. If it is less than 1, top slag-in is generated as shown in FIG. Therefore, the lower limit was set to 1.1. Several formulas are used to express the basicity of the flux used for submerged arc welding. The formula (1) is a basicity formula proposed by Mori et al. The basicity is expressed using a mole fraction.

The upper limit of the basicity calculated by the formula (1) is not particularly limited from the effect of the present invention, but the flux becomes more crystalline as the basicity increases, so the surface area of the flux increases and the amount of adsorbed water increases. As a result, the hydrogen in the weld metal increases and the frequency of occurrence of defects such as cracks increases. For this reason, it is necessary to take measures for drying the flux and storing it after drying, which is disadvantageous in terms of cost. Therefore, the upper limit was set to 3.2.
B = 6.05N [CaO] + 4.0N [MgO] + 5.1N [CaF ₂ ] −0.2N [Al ₂ O ₃ ] −6.3N [SiO ₂ ] (1)
Here, N [CaO], N [MgO], N [CaF ₂ ], N [Al ₂ O ₃ ], and N [SiO ₂ ] are CaO, MgO, CaF ₂ , Al ₂ O ₃ , and It means the molar fraction of SiO ₂ .

  Next, the reason for limiting the chemical composition of the weld metal will be described. In submerged arc welding, the properties of the weld metal are determined by its chemical composition, so the component range is important.

C: 0.03% to 0.12%
C is an important element for securing the hardenability of the weld metal and obtaining strength and toughness. If it is less than 0.03%, strength cannot be obtained. On the other hand, if it exceeds 0.12%, the strength becomes excessive. In addition, carbides are formed and toughness is reduced. Therefore, it was made into 0.12% or less.

Si: 0.03% to 0.40%
Si is necessary as a deoxidizing element, and 0.03% or more is necessary. On the other hand, if added over 0.40%, the Si becomes excessive, and the excess Si dissolves in the weld metal and lowers the toughness. Therefore, the upper limit is made 0.40%.

Mn: 0.5% to 3.0%
Mn is required to be 0.5% or more in order to improve the hardenability and obtain the strength of the weld metal. On the other hand, if it exceeds 3.0%, the strength becomes excessive and the toughness decreases, so the upper limit was made 3.0%.

Ti: 0.002% to 0.025%
Ti must be at least 0.002% or more to refine the microstructure of the weld metal. However, if it exceeds 0.025%, the solid solution Ti increases and the toughness of the weld metal decreases. Therefore, the upper limit was made 0.025%.

Al: 0.002% to 0.030%
Since Al migrates from the base material, the wire, and the flux, it exists as an impurity in the weld metal. However, if it exceeds 0.030%, a coarse oxide is formed and the toughness of the weld metal is lowered. Therefore, the upper limit was made 0.030%. The lower limit is not particularly limited from the effect of the present invention, but 0.002% or more is included as an inevitable impurity such as a base material or a flux.

Nb: 0.04% or less Nb is contained only in an inevitable impurity level in the welding material. However, since Nb may be added to the base material, it is supplied from the base material to the weld metal. However, if it is excessively contained in the weld metal, carbides are formed and the toughness is lowered. Therefore, the upper limit was made 0.04%.

O: 0.018% to 0.035%
O is an important element for ensuring the toughness of the weld metal. If it is less than 0.018%, an oxide necessary for refining the structure and improving toughness cannot be formed. Therefore, 0.018% or more is necessary. However, if it exceeds 0.035%, a coarse oxide is formed, and the toughness of the weld metal is lowered. Therefore, the upper limit was made 0.035%.

Cr: 0.1% to 1.5%, Ni: 0.1% to 4.0%, and Mo: 0.1% to 2.0%, including one or more :
Since Cr, Ni and Mo are elements that improve the strength of the weld metal, they are added. However, the upper limit was determined because excessive addition reduces toughness or weldability.
Cr is added to improve the hardenability and obtain the strength of the weld metal. In order to obtain this effect, 0.1% or more is necessary. However, if it exceeds 1.5%, excess Cr reduces the toughness of the weld metal. Therefore, the upper limit is made 1.5%.

  Ni is added to improve the strength and toughness of the weld metal. In order to obtain this effect, 0.1% or more is necessary. However, if it exceeds 4.0%, the risk of hot cracking during welding increases. Therefore, the upper limit was made 4.0%.

  Mo is added to improve the hardenability and obtain the strength of the weld metal. In order to obtain this effect, 0.1% or more is necessary. However, if it exceeds 2.0%, the excessive Mo excessively increases the strength of the weld metal and decreases the toughness. Therefore, the upper limit was made 2.0%.

  Next, the value of Pcm calculated by Formula (2) using the chemical composition of the weld metal was set to 0.22 to 0.38. If it is less than 0.22, the strength of the weld metal is less than 800 MPa, so the lower limit was set to 0.22. Moreover, since the intensity | strength of a weld metal will become high too much when it exceeds 0.38, the upper limit was set to 0.38.

  Next, the reasons for limiting the chemical composition of the base material according to claims 2 and 3 will be described. In submerged arc welding, since the base metal has a high dilution rate, the chemical composition of the weld metal in submerged arc welding is affected by both the chemical composition of the base metal and the chemical composition of the welding material. The strength and toughness of the weld metal are almost determined by its chemical composition. Therefore, it is possible to easily obtain a weld metal having an appropriate chemical composition by defining the chemical composition of the base material. Further, by limiting the chemical composition of the base material to be used, the characteristics of the base material can be improved, and a better welded joint can be obtained.

C: 0.03% to 0.15%
C is an important element for enhancing the hardenability and miniaturizing the structure. In order to ensure the strength of the base material, 0.03% or more is necessary. Further, in order to stably supply C to the weld metal, 0.03% or more is necessary. On the other hand, if it exceeds 0.15%, C becomes excessive. Therefore, the welding heat affected zone of the base material is significantly hardened, which adversely affects toughness. Therefore, the upper limit was made 0.15%.

Si: 0.01% to 0.50%
Si is necessary as a deoxidizing element during the production of the base material, and 0.005% or more is necessary to obtain the effect. On the other hand, if added over 0.50%, the toughness of the base material decreases. In addition, since the amount of Si transferred to the weld metal is excessive and there is a risk of reducing the toughness of the weld metal, the upper limit is set to 0.5%.

Mn: 0.5% to 3.0%
Mn is an element necessary for increasing the hardenability of the base material and obtaining strength, and is required to be at least 0.5% or more. On the other hand, if added over 3.0%, the strength becomes too high and the toughness is lowered. In addition, segregation increases and the steel structure becomes non-uniform. Therefore, the upper limit was made 3.0%.

Ti: 0.001% to 0.02%
Ti is required to be added 0.001% or more in order to improve the strength of the base material and improve the toughness by adding a small amount. However, excessive Ti makes the base material strength excessive. Therefore, the upper limit was made 0.02%.

Al: 0.001% to 0.04%
Al is necessary for the base material as a deoxidizing element, and it is necessary to add 0.001% or more. However, if added over 0.04%, a coarse oxide is formed and the toughness of the base material is lowered, so the upper limit was made 0.04%.

  Furthermore, it is effective to add the following elements in order to obtain a good balance between strength and toughness of the base material.

Cr: 0.1% to 1.5%, Ni: 0.1% to 2.5%, Mo: 0.1% to 2.0%, Nb: 0.005% to 0.05% Contains one or more:
Any one of Cr, Ni, Mo, and Nb is added in order to improve the strength of the base material. However, the upper limit is determined in order to reduce the toughness of the base material due to excessive addition.

  Cr is added to improve the hardenability and ensure the strength. In order to obtain this effect, 0.1% or more is necessary. However, if added over 1.5%, the toughness of the base material is lowered. Therefore, the upper limit is made 1.5%.

  Ni is added to improve the strength of the base material. In order to obtain this effect, 0.1% or more is necessary. However, if added over 2.5%, Ni transferred to the weld metal becomes excessive, and hot cracking is likely to occur in the weld metal. Moreover, since addition excessively is not preferable also from an economical viewpoint, the upper limit was made 2.5%.

  Mo is added to improve the strength of the base material. In order to obtain this effect, 0.1% or more is necessary. However, if added over 2.0%, the strength of the base material becomes excessive and the toughness of the base material decreases. Moreover, since excessive addition is not preferable also from an economical viewpoint, the upper limit was made 2.0%.

  Nb is added to improve the strength of the base material. In order to obtain this effect, 0.005% or more is necessary. However, if added over 0.06%, the strength becomes excessive and the risk of lowering toughness increases, so the upper limit was made 0.06%.

  Next, the reasons for limiting the chemical composition of the solid wire used according to claim 4 and the average chemical composition of the metal cored wire will be described. The chemical composition of the weld metal is determined by the base material and the weld material. Therefore, the composition of the weld metal can be easily designed by defining the chemical composition of the solid wire or metal cored wire used for welding. Except for the amount of oxygen, the range of chemical composition of the solid wire and the metal cored wire is the same. The amount of oxygen is limited to metal cored wires only.

C: 0.03% to 0.15%
C is an important element for enhancing the hardenability and ensuring the strength of the weld metal. In order to supply the C amount necessary for the weld metal, 0.03% or more is necessary. However, if added over 0.15%, the C content of the weld metal becomes excessive, the strength increases, and the toughness decreases. In addition, since the solid wire becomes hard, manufacturability is hindered. Therefore, the upper limit was made 0.15%.

Si: 0.02% to 0.80%
Si is an element that increases the viscosity of the molten weld metal, and 0.02% or more is necessary from the viewpoint of workability. However. If added over 0.80%, the amount of Si in the weld metal becomes excessive and the toughness decreases, so the upper limit was made 0.80%.

Mn: 0.2% to 4.0%
Mn, like C, is an element added to increase the hardenability of the weld metal and ensure strength. Therefore, 0.2% or more is necessary. However, if added over 4.0%, the amount of Mn in the weld metal becomes excessive and the toughness decreases, so the upper limit was made 4.0%.

Ti: 0.002-0.10%
Ti combines with oxygen to form an oxide, and is an important element that helps refine the structure of the weld metal. If it is less than 0.002%, the added amount from the wire is insufficient and the effect cannot be obtained, so that the toughness of the weld metal is lowered. Therefore, 0.002% or more is necessary. However. If it exceeds 0.10% and is added to the wire, Ti or more necessary for forming an oxide is supplied to the weld metal, so that the solid solution Ti increases in the weld metal and the toughness of the weld metal decreases. Therefore, the upper limit was made 0.10%.

Al: 0.001% to 0.02%
Al reduces the toughness of the weld metal by forming an oxide. Naturally, the upper limit was set in order to move from the wire to the weld metal. If it exceeds 0.02% and is contained in the wire, the Al content of the weld metal becomes excessive and the toughness is lowered. The lower limit is not particularly required from the viewpoint of the toughness of the weld metal, but usually 0.001% or more is included as an inevitable impurity.

Cr: 0.25% to 3.0%, Ni: 0.25% to 8.0%, and Mo: 0.25% to 4.0%, including one or more of:
One, two or more Cr, Ni, and Mo are added to ensure the strength of the weld metal. Therefore, the shortage of the amount supplied from the base material is supplied from the welding material.

  Cr is an element added to the wire as necessary to enhance the hardenability of the weld metal and ensure the strength. In order for the weld metal to obtain this effect, the wire needs to be 0.25% or more. However, excess Cr reduces toughness. If added over 3.0%, Cr in the weld metal becomes excessive and the toughness of the weld metal decreases. Therefore, it was made 3.0% or less.

  Ni, like Cr, is an element that is added from the wire to the weld metal as necessary in order to increase the hardenability and ensure the strength. In order for the weld metal to obtain this effect, the wire needs to be 0.25% or more. However, if Ni is added in excess of 8.0%, the amount of Ni in the weld metal becomes excessive, causing hot cracking. Therefore, the upper limit is set to 8.0%.

  Mo, like Ni and Cr, is an element that is added from the wire to the weld metal as necessary in order to increase the hardenability and ensure the strength. In order for the weld metal to obtain this effect, the wire needs to be 0.25% or more. However, if Mo is added in excess of 4.0%, the strength of the weld metal becomes excessive and the toughness decreases. Therefore, the upper limit was made 4.0%.

  Next, the reason for limiting the oxygen content of the metal cored wire will be described.

O: 0.03% to 0.50%
The amount of oxygen of the metal cored wire was limited to 0.03% to 0.50% in mass% with respect to the whole wire for each individual wire . The object of the present invention is to add oxygen from the metal cored wire to the weld metal. Therefore, the oxygen amount of the metal cored wire is specified. If it is less than 0.03%, the amount of oxygen is small, and a sufficient amount of oxygen is not supplied into the weld metal. Therefore, 0.03% or more is necessary. On the other hand, if it exceeds 0.50%, the amount of oxygen becomes excessive, resulting in an increase in gas components and the occurrence of defects such as blow holes. Therefore, the upper limit was made 0.50% or less. Preferably it is 0.20 to 0.50%. Further, if the metal cored wire has an oxygen content of 0.50% or less, the weld metal will not be in excess of oxygen as long as the basicity calculated by the formula (1) is within the range of the present invention. .

  Next, claim 5 will be described. As described in claim 5, a deep penetration shape can be obtained by using a solid wire for the first electrode. In a metal cored wire, a welding arc is mainly generated from the outer skin. Therefore, as shown in the schematic diagram of FIG. 8A, the penetration Wb becomes shallow and the cross-sectional shape becomes wide. By using it, the penetration Wb can be deepened as shown in the schematic diagram of FIG. In recent years, in order to reduce the area of the weld heat affected zone, in the welding of high-strength steel, there is a tendency to reduce the heat input of the welding heat, but if the welding heat input is reduced, the penetration becomes shallower and the welding is insufficient. The possibility of the occurrence of defects increases. Therefore, a welding method with deeper penetration is beneficial.

  Hereinafter, the present invention will be described using examples.

  The welding method used in the examples mainly used 3-electrode submerged arc welding, and partially used 4-electrode and 5-electrode submerged arc welding. Table 2 shows the welding conditions used in the examples. Condition 1 is a basic condition, and condition 2 is a condition in which the current and voltage distribution of condition 1 is changed. Condition 3 is a four-electrode condition. Condition 4 is a five-electrode condition. As the groove shape, a V groove shown in FIG. 9 was used. The groove angle was 80 degrees, and the groove depth d was a groove depth corresponding to heat input as shown in Table 3. One-layer welding was performed on the groove under the welding conditions shown in Table 2.

Table 4 shows the solid wires used in the examples. Sixteen types of solid wires having different chemical compositions were used. Among these, the wires S1 to S11 are solid wires having the component range described in claim 4 .

Table 5 shows the metal cored wires used in the examples. Twenty kinds of metal cored wires having different chemical compositions were prepared. A wire having a strength level of less than 1000 MPa was a caulking type metal cored wire, and a wire having a strength level of 1000 MPa or more was a seamless metal cored wire. The wires C1 to C13 are metal cored wires having a written range according to claim 4 of the present invention. C12 is a CW with a small amount of oxygen because it uses iron powder that is not opened until just before use and stored in a state that prevents oxygen adsorption to the surface. Moreover, since C13 has increased the amount of iron powder, the amount of oxygen in CW is high. All wire diameters are 4.0 mm.

Table 6 shows the composition of the flack used in the examples. The balance is a binder (water glass). The flux used was a melt type flux. From the flux a to the slack g, the CaF ₂ content, the SiO ₂ content and the basicity calculated by the formula (1) are within the scope of the present invention. On the other hand, the basicity calculated by the equation (1) from the flux h to the flux k is outside the scope of the present invention. Further, slacks h is greater than or equal scope of the invention CaF ₂ content with basicity calculated by Equation (1). The amount of SiO _{2 in the} flux j is out of the scope of the present invention together with the basicity calculated by the equation (1). The amount of CaF _{2 and the} amount of SiO ₂ are outside the scope of the present invention as well as the basicity calculated by Equation (1). On the other hand, from the flux 1 to the flux n, the basicity calculated by the formula (1) is within the scope of the present invention, but the content of either one or both of CaF ₂ and SiO ₂ is outside the scope of the present invention. is there. All of these fluxes were used after drying at 250 ° C. for 1 hour before use. In order to prevent moisture absorption after drying, some fluxes were kept sealed in containers until just before use.

  Table 7 shows the base materials used in the examples. As the base material, steel plates having a thickness of 20 mm, a length of 1000 mm, and a width of 150 mm and strengths of 850 MPa, 950 MPa, and 1000 MPa were used. The base material B is a base material having a component in the range of claim 2. From the base material C to the base material L is a base material that satisfies the components in the range of claim 3 of the present invention. A single-sided V groove shown in FIG. 9 was processed over these steel plates over the entire length in the direction of 1000 mm length and subjected to welding.

  The strength of the weld metal was adjusted by adjusting the chemical composition of the weld metal by combining these base materials having different chemical compositions, solid wires having different chemical compositions, and metal cored wires having different chemical compositions.

  The evaluation was performed based on the presence or absence of generation of top slag in, presence or absence of internal defects other than the top slag in, bead shape, penetration depth, structure observation, weld metal tensile strength, and weld metal absorbed energy at −30 ° C. The bead shape was evaluated by the visual appearance of the created weld bead. The presence or absence of the top slag-in was first investigated by performing a radiation transmission test over the entire length while welding. Then, after removing thicknesses other than the top slag in by reducing the thickness by 15 mm from the back surface opposite to the surface having the weld bead, a radiation transmission test was performed again to determine the presence or absence of the top slag in. At this time, internal defects such as cracks other than the top slag-in were also evaluated by two radiation transmission tests. For the depth of penetration and the soundness of the structure, three specimens for structure observation were collected under each welding condition from three locations on the start side, half the bead length and crater side from one welded joint. The measurement was investigated. As shown in FIG. 10, the tensile test piece for the tensile test is a round bar type JISA No. 2 tensile test piece Ts from the center of the weld metal at a position 5 mm from the surface, and the parallel part of the tensile test piece is parallel to the weld line. It collected so that it might become. As shown in FIG. 11, the test piece for the impact test was measured by taking a 2 mm V Charpy impact test piece Tp so that the notch direction becomes the weld line direction from a position of 6 mm from the surface layer. Two welded joints were prepared for each condition for the radiation transmission test and for other evaluations.

  Tables 8 and 9 show examples. Table 8 is an invention example, and Table 9 is a comparative example.

  First, the invention examples in Table 8 will be described. In any of the examples of the invention, since at least one electrode uses a metal cored wire, oxygen is supplied to the weld metal from the metal cored wire, and the oxygen amount of the weld metal is within the appropriate range. As a result, the weld metal has good toughness. Moreover, since the basicity and component calculated by the formula (1) of the flux used are within the scope of the present invention, no top slag in is generated. In addition, since Invention Example 10 to Invention Example 12 and Invention Example 35 to Invention Example 46 use a solid wire for the first electrode, compared to the case where no solid wire is used for the first electrode, The penetration depth is about 2 mm deeper.

  Inventive Example 33 and Inventive Example 45 are invention examples of 4-electrode submerged arc welding, and Inventive Example 34 and Inventive Example 46 are invention examples in the case of 5-electrode submerged arc welding. The effect is obtained, the oxygen amount of the weld metal is in an appropriate range, good toughness is obtained, and no top slag in is generated.

  Invention Example 25 is an invention example in which the same base material, flux and wire combination as in Invention Example 24 are used, but the welding conditions are different. Similarly, Invention Example 38 is an invention example in which the same base material, flux and wire combination as in Invention Example 36 are used, but the welding conditions are different. In either case, the amount of oxygen in the weld metal can be changed by changing the welding conditions. However, the oxygen content of the weld metal falls within an appropriate range, and since the flux components and the basicity calculated by the formula (1) are also appropriate, good toughness is obtained and no top slag in is generated. .

  Inventive Example 30, Inventive Example 33 and Inventive Example 34 are examples of the invention using the metal cored wire C13 having a large amount of oxygen, and accordingly, the oxygen amount in the weld metal is different from C9 only in the oxygen amount in the wire. It is increased as compared with Invention Example 29, Invention Example 45 and Invention Example 46 used. The amount of oxygen increases the amount of Fe powder. Inventive Example 43 is an example using a metal cored wire C12 with a small amount of oxygen, and the oxygen content in the weld metal is lower than that in Inventive Example 42 using C9 which differs only in the oxygen content in the wire. C12 used the raw material which prevented the adsorption | suction of oxygen without opening raw material Fe powder until just before use, and reduced the amount of oxygen of a metal cored wire. In this way, the amount of oxygen in the weld metal can also be changed by changing the amount of oxygen in the metal cored wire.

  Next, comparative examples shown in Table 9 will be described. Comparative Examples 1 to 10 are examples of a multi-electrode submerged arc weld metal prepared using a solid wire for all electrodes and using a flux having a basicity calculated by Equation (1) of 1.1 or more. It is. The strength of the weld metal is 800 MPa or more because the chemical composition and Pcm of the weld metal are within the scope of the present invention. Moreover, since the basicity of the flux calculated by the equation (1) is within the scope of the present invention, no top slag in is generated. However, since all solid wires are used, the amount of oxygen in the weld metal is insufficient and the toughness is low. Comparative Example 11 to Comparative Example 15 are multi-electrode submerged arcs using solid wires for all electrodes and using flux i or flux j having a basicity calculated by Equation (1) of less than 1.1. It is an example of a weld metal. Although the oxygen amount in the weld metal is appropriate, the toughness is good, but the top slag-in is generated.

Comparative Example 16 and Comparative Example 17 are examples of a multi-electrode submerged arc weld metal produced using a flux k having a low basicity calculated by Formula (1). Since the basicity calculated by the formula (1) is below the range of the present invention, and the amount of SiO ₂ in the flux exceeds the range of the present invention, the top slag in is generated. In addition, the toughness is reduced due to the excessive amount of oxygen in the weld metal.

Comparative Example 18 is an example in which a metal cored wire is used for the first electrode and a solid wire is used for the second and third electrodes, the same as in Invention Example 1. The target strength of the weld metal is the same. However, since the amount of CaF _{2 in} the flux 1 used is excessive, the arc is disturbed, arc blowing occurs during welding, and the weld bead meanders. Further, since the amount of SiO ₂ in the flux 1 is small, the flux was dried and sealed in a container to prevent moisture absorption of the flux until just before welding.

Comparative Example 19 is an example in which a metal cored wire is used for the first electrode and the third electrode, and a solid wire is used for the second electrode, as in Invention Example 6. The target strength of the weld metal is the same. However, since the amount of CaF ₂ in the flux m is small, the top slag in is generated.

Comparative Example 20 is an example in which a metal cored wire is used for the first electrode and the third electrode, and a solid wire is used for the second electrode, as in Invention Example 7. The target strength of the weld metal is the same. However, since the amount of SiO ₂ in the flux n exceeds the range of the present invention, the top slag in is generated.

  Comparative Example 21 is an example in which a metal cored wire is used for the first electrode and the third electrode, and a solid wire is used for the second electrode. The target strength of the weld metal is the same. However, the amount of oxygen in the metal cored wire used is more than the range of the present invention. Therefore, oxygen is excessive and weldability is reduced. Further, the gas component is excessive, and holes called pits are generated on the bead surface.

  Comparative Example 22 is an example in which a metal cored wire is used for the first electrode and the third electrode as in Invention Example 7, and a solid wire is used for the second electrode. The target strength of the weld metal is the same. However, the oxygen content of the metal cored wire used is below the range of the present invention. Therefore, the increase in oxygen in the weld metal is insufficient and the toughness of the weld metal is low.

Since the comparative example 23 uses the flux h in which the amount of CaF ₂ is excessive, the arc is not stabilized during welding, arc blowing occurs, and the weld bead meanders. In addition, since the basicity calculated by the formula (1) of the flux h is more than 3.2 and the surface of the flux is crystalline and easily adsorbs moisture, it is sealed again in the container until the flux is used after drying so as not to absorb moisture. Special attention was required.

  From Comparative Example 24 to Comparative Example 38, the welding method is three-electrode submerged arc welding, and a metal cored wire is used for any one or more electrodes. Therefore, the amount of oxygen in the weld metal is in the range of 0.018% to 0.035%. Further, the flux of the present invention is used as the flux, and the basic slag-in is not generated because the basicity calculated by the formula (1) is within the scope of the present invention. However, since the chemical composition of the weld metal is out of the scope of the present invention, there are problems such as insufficient weld metal strength, excessive weld metal strength, low weld metal toughness or fine hot cracks during welding. Occurred.

  As described above, by using the present invention, it is possible to easily obtain a multi-electrode submerged weld portion having no top slag in which is excellent in toughness, which greatly contributes industrially.

It is a schematic diagram of a top slag in. It is a figure which shows the relationship between the basicity calculated by Formula (1), and the generation | occurrence | production tendency of top slag in. It is a figure which shows the relationship between the basicity calculated by Formula (1), and the oxygen content in a weld metal. It is sectional drawing of a metal cored wire. It is a figure which shows the oxygen amount in a weld metal at the time of using a metal cored wire. Is a diagram showing the relationship between amount of SiO ₂ and the top Suraguin in the flux. It is a diagram showing the relationship between CaF ₂ content and the top Suraguin in the flux. It is a schematic diagram of a penetration shape. It is a figure which shows the groove shape used for the Example. It is a figure which shows the tension test piece collection point. It is a figure which shows the impact test piece collection point.

Explanation of symbols

S: Top slag in A: Outer skin of caulking type metal cored wire B: Outer skin of seamless metal cored wire C: Metal powder or alloy powder W: Welded portion of outer skin of seamless metal cored wire K: Caulking type metal cored wire Caulking portion d: groove depth Wb: penetration Ts: tensile test piece Tp: Charpy test piece

Claims (5)

A steel material having a tensile strength of 800 to 1200 MPa is filled with a high basic flux in the groove of the steel material, a molten pool is created using a plurality of electrodes, and submerged arc welding is performed. In a multi-electrode submerged arc welding method for forming a weld metal of ˜1200 MPa,
Any one electrode or two or more of the plurality of electrodes is a metal cored wire containing O: 0.03% to 0.50% by mass% with respect to the whole wire for each individual wire, and the rest While making the electrode a solid wire,
The component composition of the high basic flux is SiO ₂ : 5.0% to less than 20.0%, CaF ₂ : 30.0% to 50.0%, CaO: 5.0% by mass% with respect to the flux. _{~25.0%, MgO: 1.0% ~5.0} %, Al 2 O 3: containing 15.0% to 30.0%, and the component composition of the flux is the following equation (1) The calculated basicity B value satisfies 1.1 to 3.2,
The component composition of the weld metal is mass% with respect to the weld metal,
C: 0.03% to 0.12%,
Si: 0.03% to 0.40%,
Mn: 0.5% to 3.0%
Ti: 0.002% to 0.025%,
Al: 0.002% to 0.030%,
O: contains 0.018% to 0.035%,
Nb: limited to 0.04% or less,
Further, any one or more of Cr: 0.1% to 1.5%, Ni: 0.1% to 4.0%, and Mo: 0.1% to 2.0% The balance is Fe and inevitable impurities, and the chemical composition of the weld metal satisfies the value of Pcm determined by the following formula (2) satisfying 0.22 to 0.38, Multi-electrode submerged arc welding method.
B = 6.05 × N [CaO] + 4.0 × N [MgO] + 5.1 × N [CaF ₂ ] −0.2 × N [Al ₂ O ₃ ] −6.3 × N [SiO ₂ ] (1)
Pcm = [C] + [Si] / 30 + ([Mn] + [Cr]) / 20+ [Ni] / 60 + [Mo] / 15 (2)
However,
N [CaO], N [MgO], N [CaF ₂ ], N [Al ₂ O ₃ ], and N [SiO ₂ ] are CaO, MgO, CaF ₂ , Al ₂ O ₃ , and SiO, respectively. _Shows a mole fraction of ₂ ,
[C], [Si], [Mn], [Cr], [Ni], and [Mo] indicate mass% of C, Si, Mn, Cr, Ni, and Mo, respectively.
The component composition of the steel material is mass%,
C: 0.03% to 0.15%,
Si: 0.01% to 0.50%,
Mn: 0.5% to 3.0%
Ti: 0.001% to 0.03%,
Al: 0.001% to 0.04 is contained,
The multi-electrode submerged arc welding method according to claim 1, wherein the balance is Fe and inevitable impurities. The component composition of the steel material is mass%, and
Cr: 0.1% to 1.5%, Ni: 0.1% to 2.5%, Mo: 0.1% to 2.0%, and Nb: 0.005% to 0.06% The multi-electrode submerged arc welding method according to claim 1 or 2, wherein any one or more of them is included. The component composition of the solid wire is mass%,
C: 0.03% to 0.15%,
Si: 0.02% to 0.80%,
Mn: 0.2% to 4.0%,
Ti: 0.005% to 0.10%,
Al: 0.001% to 0.02% is contained,
Further, one or more of Cr: 0.25% to 3.0%, Ni: 0.25% to 8.0%, and Mo: 0.25% to 4.0% And the balance is Fe and inevitable impurities,
The component composition of the metal cored wire is mass%,
C: 0.03% to 0.15%,
Si: 0.02% to 0.80%,
Mn: 0.2% to 4.0% or less,
Ti: 0.005% to 0.10%,
Al: 0.001% to 0.02%,
O: 0.03% to 0.50% is contained,
further,
Including any one or more of Cr: 0.25% to 3.0%, Ni: 0.25% to 8.0%, and Mo: 0.25% to 4.0% The multi-electrode submerged arc welding method according to claim 1, wherein the balance is Fe and inevitable impurities.   5. The multi-electrode according to claim 1, wherein at least one electrode after the second electrode among the plurality of electrodes is the metal cored wire and the remaining electrode is the solid wire. 6. Submerged arc welding method.

Images