JP2006212676A - Two-electrode large heat input submerged arc welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-electrode large heat input submerged arc welding method capable of obtaining excellent and consistent weld metal toughness, and obtaining a sound penetration shape and bead appearance free from defective weld even when a high-tensile steel of 490-570 MPa class is subjected to the large heat input submerged arc welding of the welding heat input of ≥500 kJ/cm. <P>SOLUTION: In the two-electrode large heat input submerged arc welding method, welding is performed by using a wire having a composition consisting of, by mass, 0.02-0.18% C, 0.02-0.5% Si, 1.15-2.2% Mn, 0.1-1.0% Mo, 0.1-1.5% Ni, 0.005-0.05% Ti, ≤0.006% P, ≤0.003% S, and the balance Fe with inevitable impurities, and a flux having a composition consisting of 13-25% SiO<SB>2</SB>, 8-20% MgO, 5-13% CaO, 1-7% CaF<SB>2</SB>, 9-23% Al<SB>2</SB>O<SB>3</SB>, 3-11% TiO<SB>2</SB>, 11-25% Fe, 0.1-0.6% B<SB>2</SB>O<SB>3</SB>, 1-4.3% Mo, and 1-4.5% Ni. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high heat input submerged arc welding method for high-strength steel plates, and in particular, when welding various types of welded steel structures such as buildings, shipbuilding, bridges, marine structures, etc. The present invention relates to a two-electrode large heat input submerged arc welding method capable of obtaining a weld metal having better and stable toughness.

  From the viewpoint of preventing brittle fracture of a structure during an earthquake, there is an extremely great social demand for a toughened weld metal. On the other hand, box columns with thicker plates are being manufactured with the increase in the size of building structures, but the construction method using one-pass welding with large heat input is superior in terms of efficiency, and welding in one-pass welding with large heat input. There is a demand for high toughness of metals. Large heat input submerged arc welding of box column corner joints has a large welding heat input of 400 kJ / cm or more in the case of 1-pass welding with a plate thickness exceeding 50 mm, so the cooling rate of the weld metal is slow and austenite (γ) during the cooling process. Coarse pro-eutectoid ferrite (α) is easily generated from the grain boundaries, and it is difficult to obtain sufficient weld metal toughness.

  As for the toughness of the high heat input submerged arc welding of the box column corner joint, there is a technique for defining the component composition of the welding material, for example, in JP-A-11-170085 (Patent Document 1). It does not actively control the grain size, intragranular structure and grain boundary structure, and it is difficult to obtain sufficient weld metal toughness. As another method, a method is known in which a Ti oxide is generated by adding Ti to the weld metal, and fine acicular ferrite is generated using this as a nucleus to make the weld metal tough.

  However, in high heat input submerged arc welding, the molten pool is maintained for a longer time than in general arc welding, so even if a considerable amount of Ti is added to the weld metal, Ti oxide migrates into the slag bath. As a result, there are many portions that are separated from the molten metal, and it does not function sufficiently as an effective nucleation site of acicular ferrite, and it is difficult to ensure sufficient toughness of the weld metal only by this method.

  In JP 2002-283095 A (Patent Document 2), in order to improve the toughness of the weld metal, a large amount of alloy element is added to the wire for submerged arc welding. As a result, the tensile strength and hardness of the wire become excessively high, the wire feedability deteriorates during welding, and a sound penetration shape and a good bead appearance cannot be obtained.

  In Japanese Patent Laid-Open No. 2000-84672 (Patent Document 3), when submerged arc welding is performed on a steel sheet having a thickness of about 60 mm in one pass, the gap between the groove bottoms of the steel sheet is widened, and iron or iron is formed in the groove. There is a disclosure of a technique of spraying and welding alloy powder. However, with this technology, groove accuracy is important in assembling steel sheets, so it takes time to construct, and when the groove accuracy is inferior or the amount of iron or iron alloy sprayed in the groove is uniform. Otherwise, a stable penetration shape cannot be obtained, and a sound weld metal cannot be obtained.

  Japanese Patent No. 2947731 (Patent Document 4) discloses a lead electrode (first electrode) wire for obtaining a sound penetration shape when a steel plate having a thickness of 50 mm or more is subjected to submerged arc welding with high heat input. There is a disclosure of technology for adjusting the diameter and improving it. However, according to this welding method, although the penetration shape has been improved, since a flux and welding wire for submerged arc welding having general components are used, a steel sheet having a thickness of 50 mm or more is 1 In pass large heat input submerged arc welding, the welding heat input becomes as large as 400 kJ / cm or more, so the hardenability of the weld metal becomes insufficient, coarse proeutectoid ferrite is generated, and the weld metal toughness is significantly deteriorated. is there.

Japanese Patent Laid-Open No. 11-170085 JP 2002-283095 A JP 2000-84672 A Japanese Patent No. 2947731

  In view of the above-mentioned problems, the present invention provides good and stable weld metal toughness even when high-tensile steel of 490 to 570 MPa class is subjected to high heat input submerged arc welding with a heat input of 500 kJ / cm or more. An object of the present invention is to provide a two-electrode large heat input submerged arc welding method capable of obtaining a sound penetration shape and a bead appearance without welding defects.

The present invention solves the above-mentioned problems, and the gist of the invention is as follows.
(1) By mass%, C: 0.02 to 0.18%, Si: 0.02 to 0.5%, Mn: 1.15 to 2.2%, Mo: 0.1 to 1.0% Ni: 0.1 to 1.5%, Ti: 0.005 to 0.05%, P: 0.006% or less, S: 0.003% or less, the balance being Fe and inevitable impurities a wire _{made, SiO 2: 13~25%, MgO} : 8~20%, CaO: 5~13%, CaF 2: 1~7%, Al 2 O 3: 9~23%, TiO 2: 3~11 %, Fe: 11 to 25%, B ₂ O ₃ : 0.1 to 0.6%, Mo: 1 to 4.3%, Ni: 1 to 4.5% 2 electrode large heat input submerged arc welding method characterized.

(2) One or more of Cr: 0.3% or less, Nb: 0.1% or less, and V: 0.1% or less are contained in the wire at 0.10 to 0.70% in Cr + 3Nb + 3V. The two-electrode large heat input submerged arc welding method according to (1) above.

  According to the two-electrode large heat input submerged arc welding method of the present invention, even in large heat input submerged arc welding with a welding heat input of 500 kJ / cm or more, the weld metal mechanical performance is excellent, and good welding workability is obtained. The safety of the building structure can be significantly increased, and at the same time the welding efficiency can be significantly increased.

First, the technical idea of the present invention will be described in terms of the weld metal structure.
FIG. 1 schematically shows weld metal structures (a) and (b) in the prior art and weld metal structures (c) and (d) in the present invention. In general, the structure of a weld metal transforms from a δ ferrite phase to an austenite phase in the cooling process after welding (melting) and solidification, and then transforms to an α ferrite phase to form a final structure. Conventionally, in high heat input submerged arc welding of 400 kJ / cm or more, since it transforms from a δ ferrite phase to an austenite phase in a high temperature range after solidification, as shown in FIGS. 1 (a) and 1 (b), austenite grains The grain size was coarsened by the growth of the boundary 2. Furthermore, in the transformation process from the austenite phase to the α ferrite phase, coarse proeutectoid (grain boundary) ferrite 1 harmful to toughness is formed around the austenite grain boundary 2, and coarse, hard, brittle coarse that is harmful to the austenite grain. Grainous cementite 6 was formed, and these significantly reduced the toughness of the weld metal.

Therefore, the present inventors have conducted intensive studies on welding metal component compositions for improving the above problems by welding experiments and the like.
As a result, Si, Mo, Cr, Nb, and V are effective as elements that thermodynamically stabilize the δ ferrite phase after welding (melting) and solidification to a low temperature region. When these elements are contained in the weld metal, At the same time, by reducing the elements (C, Mn, Ni) that stabilize austenite, after solidification of the weld metal, the δ ferrite phase is maintained up to a relatively low temperature region, and the transformation to the austenite phase is performed in the low temperature region. Thus, it was found that coarsening of austenite grains in the weld metal in submerged arc welding with high heat input can be suppressed, and the weld metal structure can be refined.

  Further, in the transformation process from the austenite phase to the α ferrite phase, fine bainite 8 or acicular ferrite 5 is formed in the austenite grains as shown in FIGS. When covered, cementite, which is the starting point of the occurrence of brittle cracks, is finely dispersed as fine cementite 10 in the grains, and in addition to the effect of fragmentation of fracture surface units during the progress of brittle cracks due to the above-mentioned refinement of crystal grains. It has been found that the toughness of the weld metal can be greatly improved. Thus, in order to produce fine bainite 8 or acicular ferrite 5 in the austenite grains, it has been found that improvement in hardenability by adding appropriate amounts of Si, Mo, Cr, Nb and V is effective. It was.

  Further, in order to make the toughness improving effect brought about by the fine dispersion of fine cementite 10 utilizing the above-described refinement of crystal grains and the formation of fine bainite 8 or acicular ferrite 5 structure of the intragranular structure to be more remarkable. In addition, a method of suppressing the formation of coarse proeutectoid (grain boundary) ferrite 1 at the austenite grain boundary 2 with the refinement of the austenite grain using the segregation action of B to the austenite grain boundary 2 is effective. I found out.

  Further, in addition to the above means, the transformation process from the austenite phase to various ferrite phases by suppressing the amount of C added to the weld metal or adding an appropriate amount of Si having the effect of suppressing the formation of coarse cementite 6. Alternatively, it was clarified that, after completion of the transformation, the formation of coarse cementite 6 which is coarse, hard and brittle, which is harmful to the toughness generated in the grains, can be reduced, and the toughness of the weld metal can be further improved. In addition, according to the present invention, as shown in FIGS. 1C and 1D, the bainite 8 or acicular ferrite 5 main structure in which the crystal grain of the weld metal structure is fine and the grain structure is fine is shown. A fine cementite 10 is finely dispersed, and a structure with less proeutectoid (grain boundary) ferrite 1 and excellent toughness is obtained.

  The present invention has been made based on the above knowledge. Si, Mo, and further Cr, which are elements that stabilize the δ ferrite phase of the weld metal obtained by high heat input submerged arc welding and improve the hardenability. To improve the toughness of the weld metal by containing a predetermined amount of B containing Nb and V in a predetermined amount and having an effect of suppressing the formation of coarse proeutectoid (grain boundary) ferrite 1 at the austenite grain boundary 2 Can do. Further, in order to suppress the formation of coarse cementite 6 that impairs the toughness in the crystal grains, the toughness of the weld metal can be improved by suppressing the C content in the welding wire and increasing Si. is there.

  However, it was confirmed that the toughness was improved if the above weld metal structure was adopted. However, as the plate thickness increased, a tendency that the toughness values differed between the weld metal surface portion and the root portion was recognized. This is because, as the plate thickness increases, the welding heat input increases, so the dilution rate of the base material increases, and in the case of submerged arc welding, the groove cross-sectional area of the base material increases from the root to the surface. It was confirmed that the consumption of the molten material was larger on the surface portion than on the root portion, and the hardenability effect was different.

  Then, improvement examination was carried out about the toughness and welding workability of the surface part and the root part of the weld metal. The reason why the toughness value is different between the surface portion and the root portion of the weld metal is because the consumption of the molten metal is different, and in order to obtain the weld metal toughness where the surface portion and the root portion are uniformly stable, the flux for submerged arc welding is used. The balance in wire combination was considered important. Usually, two-electrode submerged arc welding is frequently used for welding a box column having a large plate thickness. Accordingly, in order to obtain a uniform and good toughness between the surface portion of the weld metal and the root portion, it was considered that the hardenability effect of the surface portion of the weld metal and the root portion must be equal.

  First, an attempt was made by changing the flux composition. However, since the flux consumption was different between the surface portion and the root portion, the hardenability effect was different and the toughness value varied. Next, as a result of examining combinations of wires having different components for the first electrode and the second electrode, the toughness of the surface portion and the root portion of the weld metal can be made uniform and favorable. That is, in the two-electrode submerged arc welding, an alloy element necessary for improving the hardenability of the root portion is added to the first electrode wire, and the second electrode wire is required to improve the hardenability of the surface portion. It has been found that the hardenability effect of the surface portion and the root portion of the weld metal can be made equal by adding the alloy element.

  However, the use of wires having different chemical components for the first electrode and the second electrode may cause troubles due to wire setting mistakes and a reduction in work efficiency. Usually, in the case of two-electrode welding, since the main current is that the welding current of the first electrode is higher than that of the second electrode, the wire consumption is different between the first electrode and the second electrode. When wires with different chemical components are used, wire consumption is different between the first electrode and the second electrode, so inventory management must be performed separately. Therefore, combining wires with different chemical components in the first electrode and the second electrode can equalize the hardenability effect of the surface portion and the root portion and improve toughness, We thought that it was difficult to apply because there were concerns about troubles due to wire setting mistakes and a decrease in work efficiency.

  Therefore, the work efficiency is good, and as a result of study for improvement to obtain excellent weld metal toughness and weld workability, it is confirmed that lowering the P and S components in the wire is extremely effective for weld metal toughness. I found it. This is because it is possible to reduce segregation and inclusions in the weld metal and further improve the toughness of the ferrite matrix by lowering the P and S components in the wire. Therefore, even if wires with different chemical components are not used for the first and second electrodes, it is equivalent to adjusting the hardenability of the weld metal surface and root by reducing the P and S components in the wire. Good toughness can be obtained as described above, and troubles due to wire setting mistakes and work efficiency are not lost.

  In designing the chemical composition of the weld metal, in consideration of the yield of stable alloy elements, alloy elements are often added to wires. However, excessive addition of alloying elements results in excessively high tensile strength and hardness of the wire, poor wire flexibility during welding, deteriorated wire feedability, unstable arc, bead appearance and penetration The weld metal shape becomes worse, such as lack. Therefore, the wire is supplemented by adding alloy elements in an amount that does not hinder welding workability, and alloy elements that are insufficient for improving the toughness of the weld metal are added to the flux. It was possible to improve both toughness.

The reasons for limiting the flux and welding wire in the present invention will be described below.
In addition, the following% shows the mass%. The flux SiO ₂ is the most important component for forming a good weld bead in high heat input submerged arc welding. However, if it is excessive, the amount of oxygen and Si in the weld metal will increase and the toughness will deteriorate. . That is, if it is less than 13%, the familiarity of the end portion of the bead heel becomes worse, the slag peelability is deteriorated, and undercutting occurs. On the other hand, if it exceeds 25%, the oxygen content of the weld metal increases and the toughness deteriorates, so the content is made 13 to 25%.

The flux MgO improves the fire resistance of the slag. In the high heat input submerged arc welding, it is necessary to increase the fire resistance of the slag, and if it is less than 8%, the bead shape becomes poor. On the other hand, if it exceeds 20%, protrusions are generated on the bead surface, and the slag removability and the bead appearance become poor. Therefore, the content of MgO is 8 to 20%.
The flux CaO is an important component for adjusting the melting point and fluidity of the slag. If it is less than 5%, the fit of the end of the bead collar is poor, the bead appearance is poor, and undercutting occurs. On the other hand, if it exceeds 13%, the slag fluidity becomes poor, the bead height is uneven, and the slag peelability is also poor, so the content is made 5 to 13%.

The CaF ₂ flux is effective in improving toughness, but since the melting point is low, if it is excessive, the smoothness of the beads is impaired. If it is less than 1%, there is no effect of improving toughness, and if it exceeds 7%, the bead becomes defective, so its content is made 1 to 7%.
The flux Al ₂ O ₃ has the effect of improving the slag peelability. If the content is less than 9%, the slag peelability deteriorates and undercutting occurs. On the other hand, if it exceeds 23%, it becomes a convex bead and the slag peelability becomes poor, so the content is made 9 to 23%.

The flux TiO ₂ is effective in obtaining the smoothness of the bead surface and is also effective in improving toughness. If the content is less than 3%, there is no effect of improving the smoothness and toughness of the bead surface, and if it exceeds 11%, the rising angle of the bead end becomes large, and the bead appearance and slag peelability become poor. The content is 3 to 11%.
The flux Fe is effective in improving the welding efficiency and reducing the heat input of welding. If its content is less than 11%, no effect can be obtained in improving the welding efficiency and reducing the heat input of welding, and if it exceeds 25%, protrusions are generated on the bead surface, resulting in poor slag releasability. The amount is 11-25%.

The flux B ₂ O ₃ is effective in improving toughness. If the content is less than 0.1%, the effect of improving toughness cannot be obtained. If the content exceeds 0.6%, the weld metal is hardened and the toughness is deteriorated. %.
Mo in the flux is an important component as an element for increasing the hardenability of the weld metal. If its content is less than 1%, there is no effect in improving the toughness of the weld metal. If it exceeds 4.3%, the hardenability of the weld metal becomes excessive, and the hardness becomes excessive and the toughness deteriorates. Is 1 to 4.3%.

  Ni in the flux is an element necessary for improving the toughness of the ferrite matrix in the weld metal. If its content is less than 1%, there is no effect in improving the toughness of the weld metal. If it exceeds 4.5%, it is also an austenite stabilizing element, so the austenite grain size is coarsened and toughness deteriorates. Therefore, the Ni content is set to 1 to 4.5% in order to refine the austenite grain size.

C of the wire is an important component for obtaining good weld metal toughness, and its content needs to be 0.02% to 0.18% in order to obtain good toughness. If the content is less than 0.02%, deoxidation is insufficient and toughness deteriorates. If it exceeds 0.18%, the hardness becomes excessive and the toughness deteriorates. In addition, when C is excessively contained in the weld metal, a large amount of coarse cementite (Fe ₃ C) harmful to toughness is generated in the austenite grains. Therefore, the upper limit of the C content is set to 0.14%. It is preferable for improving.

The Si in the wire is a deoxidizing element and reduces the amount of oxygen in the weld metal. If the content is less than 0.02%, the deoxidation effect cannot be obtained, and the toughness deteriorates. If it exceeds 0.5%, the hardness of the weld metal becomes excessive and the toughness deteriorates. Si is contained in the wire as an effective element to suppress austenite coarsening as a stabilizing element of δ ferrite and to refine the austenite grain size, but the effect of miniaturizing the austenite grain size In addition to the above, there is an effect of suppressing the formation of coarse cementite (Fe ₃ C) harmful to toughness generated in the austenite grains, and in order to obtain the effect, the lower limit of the Si content is set to 0.15% It is preferable to do.

  Mn of the wire is an important component for improving the strength of the weld metal and as a deoxidizing effect element. If the content is less than 1.15%, sufficient strength of the weld metal cannot be obtained, and the oxygen content of the weld metal increases and the toughness deteriorates. If it exceeds 2.2%, the hardness of the weld metal becomes excessive and the toughness deteriorates, so the content is made 1.15 to 2.2%.

  Mo of the wire is an important component as an element for increasing the hardenability of the weld metal. If its content is less than 0.1%, there is no effect in improving the toughness of the weld metal, and if it exceeds 1.0%, the tensile strength and hardness of the wire become excessively high, and the wire feedability during welding deteriorates. As a result, the arc becomes unstable and the bead appearance and penetration shape become poor, resulting in poor welding workability. Moreover, the hardenability of the weld metal becomes excessive, the hardness becomes excessive, and the toughness deteriorates.

  Ni in the wire is an important element that improves the toughness of the ferrite matrix of the weld metal. Therefore, if the content is less than 0.1%, there is no effect in improving the toughness of the weld metal, and if it exceeds 1.5%, the tensile strength and hardness of the wire are remarkably improved. Degradation makes the arc unstable, resulting in poor welding workability such as poor bead appearance and penetration shape. Further, it is also an austenite stabilizing element, and if contained excessively, the austenite grain size is coarsened, so that toughness deteriorates. Therefore, the Ni content is set to 0.1 to 1.5% in order to refine the austenite grain size and improve the welding workability.

  The Ti of the wire forms a nucleation site for generating fine grained acicular ferrite that is effective in improving strength and toughness by producing Ti oxides and the like even in a trace amount with a weld metal. In order to obtain it, the lower limit of the content in the wire was made 0.005%. However, if it exceeds 0.05% and contained in the wire, Ti that has not been fixed as an oxide or nitride will dissolve in the ferrite matrix and deteriorate the toughness, so the upper limit of the content is 0. .05%.

P in the wire is a component harmful to weld metal toughness. When the content is increased, the weld metal toughness is remarkably deteriorated due to segregation and a decrease in toughness of the ferrite matrix. Therefore, it is effective to make the content of P extremely low, and the content is made 0.006% or less.
S in the wire is a component harmful to weld metal toughness, has a large tendency to segregate, and easily generates sulfides. If the S content increases, the weld metal toughness deteriorates remarkably, so it is effective to make the content extremely low. Therefore, to obtain excellent weld metal toughness, the content is made 0.003% or less.

  As a component of the wire used in the present invention, one or more of Cr is 0.3% or less, Nb is 0.1% or less, and V is 0.1% or less, and Cr + 3Nb + 3V is 0.10 to 0.70. By containing%, the hardenability of the weld metal can be increased and the toughness can be improved. If Cr + 3Nb + 3V is less than 0.10%, there is no effect in improving the toughness of the weld metal. Also, if Cr + 3Nb + 3V exceeds 0.70%, Cr exceeds 0.3%, Nb exceeds 0.1% and V exceeds 0.1%, the hardenability of the weld metal becomes excessive and the hardness becomes excessive. And toughness deteriorates.

Hereinafter, the effects of the present invention will be described in detail by way of examples.
A steel plate having a thickness of 60 mm having the chemical composition shown in Table 1 is used, and the corner joint groove shown in FIG. 2 is used. Various combinations of these were performed, and one-pass square joint welding by two-electrode submerged arc welding was performed under the welding conditions shown in Table 4.

  From the weld metal part shown in FIG. 3, 7 mm below the surface of the steel sheet (hereinafter referred to as the surface layer part), 30 mm of the steel sheet center part (hereinafter referred to as the central part), and 7 mm above the steel sheet lower surface part (hereinafter referred to as the root part). A Charpy impact test piece (JIS Z22424 No. 4) and a tensile test piece (JIS Z2201 A1 No.) centered on 10 mm below the steel sheet surface were collected and subjected to mechanical tests. The toughness was evaluated by a Charpy impact test at 0 ° C., and the average of three repetitions was evaluated. The tensile strength was 490 MPa or higher, and the Charpy absorbed energy was 100 J or higher in all locations of the surface layer portion, the central portion, and the root portion. Welding workability was evaluated by examining arc stability, slag peelability, bead appearance, weld defects, and penetration shape. Regarding the arc stability, there was no fluctuation in current and voltage, and it was judged as good if it was a stable wire feed, and marked as bad if it was unstable.

  The slag peelability was evaluated as “good” if the slag was easily peeled off with a hammer or a chisel to easily peel off the slag, and poor if the slag did not peel off with a light hit. The bead appearance was good if the bead surface had fine waviness, a uniform and beautiful bead shape, and the case where even one was inferior was rated as x. Regarding the weld defect evaluation, it was judged as good if there were no weld defects such as undercuts and blowholes. Regarding the penetration shape evaluation, there was no poor penetration or poor fusion inside the groove, and it was good if it was a healthy penetration shape, and x was poor if there was a poor penetration or poor fusion. Table 5 summarizes the results of these tests.

  As apparent from Table 5, the test symbols W1 to W10, which are examples of the present invention, indicate that the combined fluxes F1, F2, F3, and F4 and the wires a, b, c, r, u, and v satisfy the constituent requirements of the present invention. Since it was satisfied, good values were obtained for the tensile strength of the weld metal and the Charpy absorbed energy at all locations in the surface layer portion, the central portion, and the root portion. In addition, the arc stability and slag peelability were excellent, and a beautiful bead appearance and a sound penetration shape without welding defects such as undercut could be obtained. In addition, since the Cr of the wire r was slightly high, the test symbol W8 was slightly hardened, and the Charpy absorbed energy of the weld metal was 100 J, which was just below the target value. Moreover, since the Cr + 3Nb + 3V of the wire u was slightly low, the test symbol W9 was slightly inferior in hardenability, and the Charpy absorbed energy of the weld metal was 100 J, which was just below the target value. In addition, the test symbol W10 was slightly higher in Cr + 3Nb + 3V of the wire v, so that the hardenability was slightly excessive, and the Charpy absorbed energy of the weld metal was 100 J, which was just below the target value.

On the other hand, the test symbol W11 which is a comparative example was low in deoxidation because C of the wire d was low, and the amount of oxygen in the weld metal increased and the Charpy absorbed energy was low. Further, since the SiO ₂ of the combined flux F5 was low, the familiarity of the end portion of the bead became worse, the slag peelability was deteriorated, and undercut occurred. In the test symbol W12, since the C of the wire e was high, the hardness of the weld metal was excessive and the Charpy absorbed energy was low. Moreover, since MgO of the combined flux F8 was high, protrusions were generated on the bead surface, and the slag peelability and the bead appearance deteriorated.

In test symbol W13, since Si of wire f was low, deoxidation was insufficient, the amount of oxygen in the weld metal was increased, and Charpy absorbed energy was reduced. Moreover, since CaO of the combined flux F10 was high, the slag fluidity was poor, the bead height was non-uniform, and the bead appearance and slag peelability were deteriorated.
In the test symbol W14, since the Si of the wire g is high, the hardness of the weld metal is excessive and the Charpy absorbed energy is low. In addition, since the CaO of the combined flux F9 was low, the familiarity of the bead edge became worse, the bead appearance deteriorated, and an undercut occurred.

In the test symbol W15, since the Mn of the wire h was low, the weld metal could not obtain sufficient strength, and deoxidation was insufficient, the amount of oxygen increased, and the Charpy absorbed energy decreased. Moreover, since TiO ₂ of the combined flux F16 is high, the rising angle of the bead end portion is increased, and the slag peelability is also deteriorated.
In the test symbol W16, since the Mn of the wire i is high, the hardness of the weld metal is excessive and the Charpy absorbed energy is low. Further, since the Al ₂ O ₃ of the combined flux F13 was low, the slag peelability deteriorated and undercut occurred.

In the test symbol W17, since the P value of the wire j is high, the Charpy absorbed energy of the weld metal is reduced due to segregation and a decrease in the toughness of the ferrite matrix. Moreover, since MgO of the combined flux F7 was low, the bead shape became non-uniform.
In the test symbol W18, since the S of the wire k is high, the Charpy absorbed energy of the weld metal is low due to segregation and the generation of sulfide. Further, since high CaF ₂ of the combined flux F12, smoothness of the bead is impaired by bead appearance deteriorated.

In the test symbol W19, since the Mo of the wire l is low, the hardenability of the weld metal is inferior and the Charpy absorbed energy is low. Moreover, since the Fe of the combined flux F17 was low, the amount of welding was insufficient.
In test symbol W20, the wire m has a high Mo, so the tensile strength and hardness of the wire are excessively high, the wire feedability during welding deteriorates, the arc becomes unstable, and the bead appearance and penetration shape also It became defective. At the same time, the hardenability of the weld metal became excessive, the hardness became excessive, and the Charpy absorbed energy was lowered.

In the test symbol W21, since the Ni of the wire n is low, the hardenability of the weld metal is inferior and the Charpy absorbed energy is low. Further, since the Fe of the combined flux F18 was high, protrusions were generated on the bead surface and the slag peelability was also deteriorated.
In the test symbol W22, since the Ni of the wire o is high, the tensile strength and hardness of the wire are excessively high, the wire feeding property during welding is deteriorated, the arc becomes unstable, and the bead appearance and the penetration shape are also obtained. It became defective. At the same time, the Charpy absorbed energy of the weld metal decreased due to the coarsening of the austenite grain size.

In the test symbol W23, Ti of the wire p was low, so that a nucleation site for generating fine acicular ferrite effective for improving the toughness of the weld metal could not be formed, and Charpy absorbed energy was low.
In the test symbol W24, since Ti of the wire q was high, Ti that was not fixed as an oxide or nitride of the weld metal was dissolved in the ferrite matrix, and Charpy absorbed energy was low.

In the test symbol W25, since the Nb of the wire s was slightly high, the hardenability of the weld metal was slightly increased, the hardness was excessive, and the Charpy absorbed energy was 100 J, which was just below the target value. Moreover, because of the high Al ₂ O ₃ of the combined flux F14, were also degraded slag removability becomes convex bead.
In the test symbol W26, since the Ni of the combined flux F24 is high, the hardenability of the weld metal is excessive, the hardness is excessive, and the Charpy absorbed energy is low.

Test symbol W27 has low Charpy absorbed energy due to the low TiO ₂ of the combined flux F15, and the smoothness of the bead surface deteriorated.
In the test symbol W28, the SiO ₂ of the combined flux F6 is high, so that the amount of oxygen in the weld metal increases and the Charpy absorbed energy decreases.
In the test symbol W29, since the combined flux F19 does not contain B ₂ O ₃ , the Charpy absorbed energy of the weld metal is low.

In the test symbol W30, since the B ₂ O ₃ of the combined flux F20 was high, the hardness was excessive and the Charpy absorbed energy of the weld metal was low.
In the test symbol W31, since the Mo of the combined flux F21 is low, the Charpy absorbed energy of the weld metal is low.
In the test symbol W32, since the CaF ₂ of the combined flux F11 was not added, the Charpy absorbed energy of the weld metal was low.

In the test symbol W33, since the Ni of the combined flux F23 is low, the Charpy absorbed energy of the weld metal is low.
In the test symbol W34, since the Mo of the combined flux F22 is high, the hardenability of the weld metal is excessive, the hardness is excessive, and the Charpy absorbed energy is low.
In the test symbol W35, since the V of the wire t is slightly high, the hardenability of the weld metal is slightly increased, the hardness is excessive, and the Charpy absorbed energy is 100 J, which is just below the target value. Moreover, since MgO of the combined flux F8 was high, protrusions were generated on the bead surface, and the slag peelability and the bead appearance deteriorated.

It is a conceptual diagram of a weld metal structure. It is a figure which shows the welding groove shape used for the Example of this invention. It is a figure which shows the weld metal mechanical performance test piece collection position used for the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pre-deposition (grain boundary) ferrite 2 Austenite grain boundary 3 Coarse bainite or acicular ferrite 4 Coarse bainite 5 Acicular ferrite 6 Coarse cementite 7 Fine bainite or acicular ferrite 8 Fine bainite 9 Oxidation Product 10 Fine cementite 11 Flange plate 12 Web plate 13 Back plate 14 Weld metal 15 Charpy impact test piece 16 Tensile test piece


Patent Applicant Nippon Steel & Sumikin Welding Industry Co., Ltd.
Attorney Attorney Shiina and others 1

Claims (2)

% By mass
C: 0.02 to 0.18%,
Si: 0.02 to 0.5%,
Mn: 1.15 to 2.2%,
Mo: 0.1 to 1.0%,
Ni: 0.1 to 1.5%,
Ti: 0.005 to 0.05%
Containing
P: 0.006% or less,
S: 0.003% or less,
A wire the balance being Fe and inevitable _{impurities, SiO 2: 13~25%, MgO} : 8~20%, CaO: 5~13%, CaF 2: 1~7%, Al 2 O 3: 9~23% , TiO ₂ : 3 to 11%, Fe: 11 to 25%, B ₂ O ₃ : 0.1 to 0.6%, Mo: 1 to 4.3%, Ni: 1 to 4.5% A two-electrode large heat input submerged arc welding method characterized in that welding is used. One or more of Cr: 0.3% or less, Nb: 0.1% or less, and V: 0.1% or less are contained in the wire, and Cr + 3Nb + 3V contains 0.10 to 0.70%. The two-electrode large heat input submerged arc welding method according to claim 1.

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