JP2007083292A - Two-electrode one-side one-pass high heat input submerged-arc welding method for obtaining weld metal with excellent toughness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding method capable of obtaining the high toughness in which the 2 mm V-notch Charpy absorbed energy at 0°C is ≥ 70J in the range of the entire thickness from the face side to the back side of a weld metal when performing the two-electrode, one-side, one-pass high heat input submerged arc welding of a thick high-tensile steel plate of the thickness of ≥ 40 mm. <P>SOLUTION: When performing the two-electrode, one-side, one-pass submerged arc welding of a steel plate of the thickness of ≥ 40 mm, the welding is performed under the condition that the diameter of a welding wire of a second electrode is 6-8 mm, and the ratio of the sectional area of a welding wire of a first electrode to the sectional area of the welding wire of the second electrode is 35-75% while each chemical composition of the steel plate, the flux and the welding wire is limited in an adequate range. The differential microstructure between the face side and the back side of the weld metal is set to be a permissible range without impairing the soundness of a joint. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high heat input submerged arc welding method used when building a welded structure requiring high safety such as a building, shipbuilding, bridge, and marine structure, and more particularly, a weld metal having good toughness. The present invention relates to a two-electrode single-sided one-pass large heat input submerged arc welding method of a high-tensile steel plate from which high temperature steel is obtained.

  When building large welded structures in the construction field, shipbuilding field, etc., it is required to increase the heat input during welding in order to increase the welding work efficiency. Among arc welding, there are many submerged arc weldings with high welding heat input. It is used. On the other hand, in construction, shipbuilding, etc., high safety is required for the welded structure at the same time, and particularly high toughness is required for the welded portion. In particular, in a building structure, a social demand for increasing the toughness of a welded portion, particularly a weld metal, has become extremely large from the viewpoint of preventing brittle fracture during an earthquake.

  Along with the recent increase in the size of building structures, when manufacturing box columns by welding thick steel plates with a thickness of 40 mm or more, one-sided large pass using one or two electrodes to improve the welding efficiency The application of heat input submerged arc welding is increasing. In such a large heat input submerged arc welding of such a thick steel plate, the welding heat input is 400 kJ / cm or more, and the cooling rate of the weld metal formed in the welded portion is slowed down. Therefore, austenite (γ ) Coarse pro-eutectoid ferrite (α) harmful to toughness tends to be generated from the grain boundary, resulting in a problem that the toughness of the weld metal is lowered.

  In addition, when the steel plate thickness is thick and the welding heat input is further increased, the weld metal on the weld root side (hereinafter also referred to as the weld back side) where the molten metal first solidifies in the thickness range of the weld metal As the heat history becomes more severe, the toughness deteriorates remarkably, and as a result, it becomes difficult to ensure good toughness equivalent to the center part in the thickness direction and the weld metal on the surface side.

  In general, as a method to ensure weld metal toughness during welding with relatively high heat input, it is known to refine the structure by adding a lot of alloying elements to the weld metal using a welding material to improve hardenability. ing.

  However, when a thick steel plate having a thickness of 40 mm or more is welded with a heat input of 400 kJ / cm or more and single-sided one-pass submerged welding, if the amount of alloy elements is increased in the weld metal using a welding material, However, the hardenability of the weld metal becomes excessive, and the problem arises that the toughness deteriorates.

  The non-uniformity of toughness in the weld metal thickness range at the time of large heat input submerged welding of the above-mentioned thick steel plate is obtained when using a multi-electrode submerged arc welding method with two or more electrodes and welding a thick steel with a plate thickness of 40 mm or more. Problems are likely to manifest.

  Conventionally, as a method of improving weld metal toughness at the time of submerged arc welding with large heat input for box column corner joints, bond flux and welding wire are used, and hardenability is improved by combined addition of Ti, B, and Mo in the weld metal. And the method of improving weld metal toughness is proposed (for example, refer patent document 1).

  However, with this method, the toughness of the weld metal can be improved to 47 J or more with the Charpy impact value at 0 ° C., but it is difficult to improve the toughness of 70 J or more.

  In addition, a method has been conventionally known in which Ti is added to a weld metal during high heat input welding to produce Ti oxide, and fine acicular ferrite is produced using this as a core to make the weld metal tough. It has been. However, in a welding method with a very large heat input, such as a large heat input submerged arc welding of a box column corner joint, the molten metal pool is maintained for a long time compared to general arc welding. Even if a considerable amount of Ti is added to the weld metal, the Ti oxide often moves into the slag bath and separates from the molten metal. For this reason, it is difficult to sufficiently improve the toughness of the weld metal by sufficiently functioning the Ti oxide in the weld metal as a nucleation site of acicular ferrite. In addition, since the cooling rate is very low in high heat input submerged arc welding, a large amount of intergranular ferrite is generated in the weld metal, and it is easy to coarsen. Therefore, even if fine acicular ferrite is generated in the grains, coarse grains are produced. There is also a problem that it is difficult to obtain sufficient toughness improvement because the boundary ferrite has a dominant influence on the toughness.

  Recently, there is also a technology that stabilizes the δ ferrite phase generated after solidification of the weld metal to refine the solidified austenite grain size and, as a result, refines the transformation structure of the weld metal to improve toughness. It has been proposed (see, for example, Patent Document 2). However, in 1-pass large heat input submerged arc welding of a thick steel plate having a thickness of 40 mm or more, it is difficult to make the entire weld metal uniform and tough.

  As described above, there is a limit to the conventional technology for improving the toughness of the weld metal by improving the weld metal structure by devising the weld material, and the toughness variation in the weld metal thickness range during one-pass large heat input submerged arc welding of thick steel plates It is difficult to improve sufficiently. Therefore, there is a demand for a new technique for uniformly improving the toughness not only in the weld metal center portion but also in the entire thickness range from the front surface side to the back surface side of the weld metal in one-pass large heat input submerged arc welding of thick steel plates.

Japanese Patent Laid-Open No. 11-170085 JP 2004-1028 A

  In view of the above-mentioned problems of the prior art, the present invention provides a high-strength steel plate having a thickness of 40 mm or more and a tensile strength of 490 MPa class or more. To provide a welding method in which the toughness is uniform over the entire thickness range from the front surface side to the back surface side of the weld metal during thermal submerged arc welding, and a high toughness with a 2 mmV notch Charpy absorbed energy at 0 ° C. of 70 J or more is obtained. Objective.

  In order to solve the above-mentioned problems, the inventors of the present invention based on the optimization of the weld metal composition by the welding material, and usually the weld metal that inevitably occurs in the two-electrode single-sided one-pass submerged arc welding on the thick steel plate. The difference in temperature history between the welding surface side and the back surface side is made as small as possible depending on the welding conditions, and it is uniform from the surface side to the back side of the weld metal without excessively increasing the alloy content of the weld metal. A new method for obtaining high toughness was studied.

  As a result, the welding wire used for two-electrode single-sided one-pass submerged arc welding and the composition of the flux are within an appropriate range, and the welding wire diameter of the first electrode (leading electrode) and the second electrode (following electrode) and its Knowledge that the ratio of the cross-sectional area can be optimized to control the cooling rate on the back side of the weld metal and avoid high-temperature cracking, while making the cooling rate on the back side almost the same as that on the front side. did.

  The present invention has been invented based on such new findings, and the gist of the invention is as follows.

(1) When a steel plate having a thickness of 40 mm or more is subjected to one-pass one-pass welding by two-electrode submerged arc welding,
C: 0.02 to 0.2%,
Si: 0.01 to 1%,
Mn: 0.1 to 2.5%
Al: 0.002 to 0.1%,
N: 0.001 to 0.015% is contained,
P: 0.02% or less,
S: 0.01% or less,
O: limited to 0.01% or less,
A steel plate with the balance being Fe and inevitable impurities,
% By mass
SiO ₂ : 10 to 25%,
MgO: 5 to 20%,
CaO: 5 to 15%,
CaF ₂ : 1 to 10%,
Al ₂ O ₃ : 5 to 25%,
TiO ₂ : 2 to 20%,
Fe: 10 to 25%,
B ₂ O ₃ : a flux composed of 0.1% to 2.5%,
% By mass
C: 0.02 to 0.2%,
Si: 0.01 to 1%,
Mn: 0.5 to 2.5%
Al: 0.002 to 0.1%,
Ti: 0.005 to 0.3%,
N: 0.001 to 0.015% contained,
P: 0.02% or less,
S: 0.01% or less,
O: Limiting to 0.01% or less, using the welding wire of the first electrode and the second electrode, the balance being Fe and inevitable impurities, the diameter of the welding wire of the second electrode is 6 to 8 mm, and the second Welding is performed under the condition that the ratio of the cross-sectional area of the welding wire of the first electrode to the cross-sectional area of the welding wire of the electrode is 35 to 75%. Submerged arc welding method.

(2) The steel sheet is mass%,
Ti: 0.002 to 0.05%,
B: 0.0003 to 0.015%,
Mo: 0.01 to 1.5%,
Cr: 0.01 to 1.5%
W: 0.01 to 1.5%
Ni: 0.01-6%,
Cu: 0.01 to 1.5%,
Nb: 0.002 to 0.1%,
V: 0.002-0.5% and
Ta: 0.002 to 0.5% of one type or two or more types, the two-electrode single-sided one-pass high-heat-input submerged arc welding excellent in toughness of the weld metal according to (1) above Method.

(3) The steel sheet is in mass%, and
Ca: 0.0002 to 0.01%
Mg: 0.0002 to 0.01%, and
REM: 0.0002 to 0.01% of 1 type or 2 types or more, 2 electrode single sided 1 pass large insertion with excellent toughness of weld metal according to (1) or (2) Thermal submerged arc welding method.

(4) The flux is mass%,
Mo: 1-5%, and
Ni: 1 to 5% of 1 type or 2 types, The two-electrode single-sided one-pass large heat input submerged excellent in toughness of the weld metal according to any one of the above (1) to (3) Arc welding method.

(5) The welding wire is in% by mass, and
Ni: 0.1 to 6%,
Cu: 0.01 to 1.5%,
Cr: 0.01 to 1.5%
Mo: 0.1 to 3%,
W: 0.01-2%
Nb: 0.002 to 0.05%,
V: 0.005 to 0.5%,
Ta: 0.002 to 0.2%, and
B: One electrode 1 having excellent toughness of weld metal according to any one of (1) to (4), characterized by containing one or more of 0.001 to 0.05%. Pass large heat input submerged arc welding method.

(6) The welding wire is in% by mass, and
Ca: 0.0002 to 0.01%,
Mg: 0.0002 to 0.01%, and
REM: 1 type or 2 types or more of 0.0002-0.01% 2 electrode single side | surface 1 excellent in the toughness of the weld metal in any one of said (1)-(5) characterized by the above-mentioned Pass large heat input submerged arc welding method.

  According to the present invention, in high heat input submerged arc welding in which a thick high strength steel plate having a plate thickness of 40 mm or more and a tensile strength of 500 to 600 MPa class is welded by two-pass single-sided one-pass welding with a heat input of 400 kJ / cm or more. The toughness can be made uniform in the entire thickness range from the front surface to the back surface of the metal, and high toughness with 2 mmV notch Charpy absorbed energy at 70 ° C. of 70 J or more can be obtained. Therefore, by applying the present invention, it is possible to improve the welding construction efficiency of welded structures such as buildings, shipbuilding, bridges, marine structures and the like, and to increase the safety thereof, so that the industrial utility value is very high. Is.

  Normally, when performing two-electrode single-sided one-pass submerged arc welding, using the same wire for the first electrode (leading electrode) and the second electrode (following electrode) and welding under the same heat input conditions, Since the back side is affected by the welding heat input by the second electrode (following electrode) in addition to the welding heat input by the first electrode (leading electrode), the cooling rate on the back side of the weld metal after welding is on the front side. Compared with inevitably slow. In particular, since the cooling rate from 800 ° C. to 500 ° C. on the back side of the weld metal, which influences the structure of the weld metal, is slower than that on the surface side, a structure having a high transformation point is likely to be formed on the back side of the weld metal. Actually, the structure on the back surface side of the weld metal has a higher proportion of intergranular ferrite than the front surface side, and the toughness tends to decrease.

  When two-electrode single-sided one-pass submerged arc welding is performed on a steel plate with a limited thickness, the welding material is selected, and the chemical composition of the weld metal is kept within a certain range very strictly. It is also possible to minimize the difference in the structure of the weld metal and maintain high toughness uniformly in the thickness range. However, since a special welding material is used and the target steel plate thickness is limited, there is a problem in practical use.

  Moreover, in order to improve the hardenability of the back surface side of the weld metal whose cooling rate becomes slow, a method of increasing the alloy component of the wire of the first electrode (leading electrode) compared to the second electrode (following electrode) is also conceivable. . However, according to the study by the present inventors, when a thick steel plate having a thickness of 40 mm or more is welded, the welding metal formed by the first electrode (leading electrode) can be obtained only by controlling the alloy component of the wire. It has been confirmed that the weld metal formed by the second electrode (following electrode) is mixed in a molten state, and a great effect due to the difference in the component composition between the front surface side and the back surface side of the weld metal cannot be expected.

  Furthermore, by making a difference in the amount of welding heat input between the first electrode (leading electrode) and the second electrode (following electrode), and reducing the difference in cooling rate between the front side and the back side of the weld metal, the cooling rate can be reduced. Although a method of reducing the difference in toughness between the front side and the back side of the weld metal can be considered, control of welding heat input cannot be said to be a preferable method from the viewpoint of welding stability and ensuring the bead shape.

  Therefore, the present inventors have maintained the welding stability and the bead shape well when the thick steel plate having a thickness of 40 mm or more is subjected to the two-electrode single-sided one-pass submerged arc welding, while maintaining the welding stability and the bead shape from the back side to the back side. Metal composition control of welding wire, flux and steel plate to obtain uniform and high toughness up to the thickness range up to, and weld metal by wire of first electrode (leading electrode) and second electrode (following electrode) The effective heat input control method on the back side was studied.

  As a result, the diameter of the wire of the first electrode (leading electrode) is changed to the second electrode (following electrode) so that the ratio of the wire cross-sectional areas of both is within a predetermined range without changing the welding input due to the welding current or the like. It was confirmed that the bead width on the back surface side of the weld metal can be narrowed within an allowable range by making it thinner than the wire of this type, and as a result, the cooling rate on the back surface side can be increased to the same level as the front surface side. . In addition to effective heat input control on the back side of the weld metal, the composition of the welding wire, flux, and steel sheet controls the weld stability and bead shape, while maintaining good weld stability and bead shape. It was confirmed that uniform and high toughness can be obtained in the thickness range up to the side.

  The present invention has been made based on the above knowledge and technical idea.

  The reasons for limiting the technical matters of the present invention necessary to achieve the intended effect based on the above technical idea will be described below.

  In the present invention, as described above, by changing the diameter of the wire of the first electrode (leading electrode) compared to the wire of the second electrode (following electrode) without changing the welding input due to the welding current or the like, The technical idea is to reduce the bead width on the back side of the weld metal and increase the cooling rate on the back side to the same level as the front side.

  However, if the bead width on the back surface side of the weld metal becomes excessively narrow due to a decrease in the diameter of the wire of the first electrode (leading electrode), there is a high possibility that hot cracking or poor fusion will occur or the welding efficiency will decrease. . Therefore, the cross-sectional area of the welding wire of the first electrode (leading electrode) and the welding wire of the second electrode (following electrode) used in the two-electrode single-sided one-pass submerged arc welding so that such a problem does not occur. It is necessary to optimize both the ratio of 35 to 75% and the diameter of the welding wire of the second electrode (following electrode) of 6 to 8 mm.

  When the wire diameter is less than 6 mm, the bead width becomes excessively small as a whole and the bead shape becomes vertically long (none). As a result, high temperature cracking is likely to occur, which is not preferable from the viewpoint of suppressing welding defects. On the other hand, if the wire diameter is larger than 8 mm, the welding workability such as the current density becomes excessive due to the limited capacity of the welding machine and the arc becomes unstable is deteriorated, and the weld metal composition excessively influences the steel composition. Therefore, it becomes difficult to secure a stable material.

  For this reason, in the present invention, the diameter of the welding wire of the second electrode is set to 6 to 8 mm.

  In the present invention, the diameter of the welding wire of the second electrode (following electrode) is limited to the above range, and the cross-sectional area of the welding wire of the second electrode (following electrode) and the first are based on the following examination results. The ratio of the electrode (leading electrode) to the cross-sectional area of the welding wire is set to 35 to 75%.

The present inventors have confirmed that when a relatively thin steel plate having a thickness of less than 40 mm is subjected to two-electrode single-sided one-pass large heat input submerged arc welding, a weld metal with good toughness can be formed. The thickness range of the weld metal after welding is changed by changing the diameters of the welding wires of the first electrode and the second electrode without changing the welding heat input of the first electrode and the second electrode under the conditions of the component composition of the steel plate. The toughness was measured.
That is, the chemical composition is 0.12% C-0.25% Si-1.41% Mn-0.009% P-0.004% S-0.016% Al-0.0035% N-0. A steel plate having a plate thickness of 55 mm with 0029% O-0.007% Nb-0.011% Ti-0.0020% Ca and a chemical composition of SiO ₂ : 18%, MgO: 12.3%, CaO: 11 .8%, CaF ₂ : 3.7%, Al ₂ O ₃ : 12%, TiO ₂ : 11%, Fe: 18.5%, B ₂ O ₃ : 0.8%, Ni: 1.5% And a chemical composition of 0.06% C-0.15% Si-2.0% Mn-0.01% P-0.004% S-0.006% Al-0.0051% N-0 .Use of welding wire made of 95% Ni-0.46% Mo-0.023% Ti-0.0031% O When performing merge arc welding, the welding heat input is approximately constant at about 540 to 550 kJ / cm, and the diameters of the welding wires of the first electrode (leading electrode) and the second electrode (following electrode) are variously changed. Welded joints were created under the above conditions. Moreover, about the obtained welded joint, 2 mmV notch Charpy impact test pieces shown in FIG. 1 were collected from various positions of the weld metal, and the toughness distribution in the thickness range of the weld metal was measured and evaluated. The diameter of the welding wire of the second electrode (following electrode) is three types of 8 mm, 7 mm, and 6.4 mm, and the first electrode (leading electrode) having a different wire diameter for each welding wire diameter of each second electrode. A joint was made by combining several types of welding wires.

  FIG. 2 shows the difference between the 0 ° C. absorbed energy at the 7 mm position on the back surface of the weld metal and the 0 ° C. absorbed energy at the 7 mm position below the surface of the weld metal, and the difference between this 0 ° C. absorbed energy and the first electrode ( The result which arranged the relationship between the ratio of the welding wire cross-sectional area of a 2nd electrode (following electrode) and a 2nd electrode (following electrode) is shown.

  In addition, when the steel plate used in this experiment was welded with a flack and a welding wire, good toughness of 100 J or more was obtained for all 0 ° C. absorbed energy at a position 7 mm below the surface of the weld metal.

  As apparent from FIG. 2, the first electrode (leading electrode) with respect to the wire cross-sectional area of the second electrode (following electrode) on the precondition that the welding wire diameter of the second electrode (following electrode) is 6 to 8 mm. ) Is within the range of 0.35 to 0.75, no hot cracks or poor weld defects occur, and the toughness of the back side of the weld metal is almost the same as the surface side. It can be increased to the same extent. Under these conditions, there was no deterioration in welding workability.

  On the other hand, if the ratio of the wire cross-sectional area of the first electrode (leading electrode) to the wire cross-sectional area of the second electrode (following electrode) is more than 0.75, the lack of hardenability on the back side of the weld metal is resolved. Since the cooling rate on the back surface side becomes slower than that on the front surface side, the toughness deterioration at 7 mm on the back surface is remarkable as a result of the formation of grain boundary ferrite that deteriorates toughness or the coarsening of crystal grains due to grain growth. .

  Further, when the ratio of the wire cross-sectional area of the first electrode (leading electrode) to the wire cross-sectional area of the second electrode (following electrode) becomes less than 0.35, the structure of 7 mm above the back surface of the weld metal is almost 7 mm below the surface. Although it is refined equally, the cooling rate on the back side of the weld metal becomes excessively high, so segregation of diffusible hydrogen, or the back side bead width becomes narrow, resulting in hot cracking (when the bead width is narrow). Cracks caused by solidification structure growth and solidification shrinkage of the weld metal) and welding defects such as poor fusion are likely to occur. Due to the presence of these defects, the absorbed energy of 7 mm on the back surface of the weld metal is slightly lower than when the ratio of the wire cross-sectional areas is in the proper range (0.35 to 0.75).

  Based on the above investigation results, in the present invention, the toughness on the back side of the weld metal is defined as the front side without causing welding defects such as hot cracks and poor fusion and without deteriorating welding workability. In order to increase to the same extent, the diameter of the welding wire of the second electrode (following electrode) is assumed to be 6 to 8 mm, and the first electrode (leading electrode) with respect to the cross-sectional area of the welding wire of the second electrode (following electrode) ) Welding wire cross-sectional area ratio is 35 to 75%. It becomes possible.

  In the present invention, in addition to appropriately controlling the welding wire conditions of the first electrode (leading electrode) and the second electrode (following electrode), in order to increase the overall toughness of the weld metal to a target level. In order to appropriately control the weld metal composition, it is necessary to limit the respective component compositions of the steel plate, the flux and the welding wire as follows.

In the two-electrode single-sided one-pass large heat input submerged arc welding method, the amount of welding heat input is higher than that of ordinary arc welding, so the component composition of the weld metal formed during welding is partially mixed with the steel plate components. Since the ratio, that is, the dilution ratio of the steel sheet increases, the contribution of the steel sheet composition to the weld metal composition cannot be ignored.
Therefore, in this invention, a steel plate is the mass%, C: 0.02-0.2%, Si: 0.01-1%, Mn: 0.1-2.5%, Al: 0.002- 0.1%, N: 0.001 to 0.015%, P: 0.02% or less, S: 0.01% or less, O: 0.01% or less, as required , Ti: 0.002 to 0.05%, B: 0.0003 to 0.015%, Mo: 0.01 to 1.5%, Cr: 0.01 to 1.5%, W: 0.01 -1.5%, Ni: 0.01-6%, Cu: 0.01-1.5%, Nb: 0.002-0.1%, V: 0.002-0.5%, and Ta: 0.002 to 0.5%, or one or more of them, and if necessary, Ca: 0.0002 to 0.01%, Mg: 0.0002 to 0.01%, And REM: 0 From 0,002 to 0.01%, containing one or more.

First, C in the steel plate needs to be contained by 0.02% or more in order to secure the strength of the steel plate. On the other hand, if more than 0.2% is contained in the steel sheet, the deterioration of the toughness of the steel sheet, the weld heat affected zone toughness, and further the resistance to weld cracking will be impaired, and the safety as structural steel will be impaired. Therefore, the upper limit of the C content of the steel sheet is set to 0.2% in the present invention.
Si is an element effective as a deoxidizing element and for securing the strength of the steel sheet. If the content is less than 0.01%, deoxidation becomes insufficient and it is disadvantageous for securing the strength. On the other hand, an excessive content exceeding 1% forms a coarse oxide and causes the ductility and toughness of the steel sheet to deteriorate. In addition, the Si content in the weld metal may be excessive and the toughness of the weld metal may be impaired. Then, the range of Si content in a steel plate was 0.01 to 1%.

  Mn is an element necessary for enhancing the hardenability of the steel sheet and ensuring strength and toughness, and it is necessary to contain Mn at least 0.1%. However, an excessive content exceeding 2.5%, as with an excessive C content, significantly deteriorates the toughness of the steel sheet, and also deteriorates the toughness and cracking properties of the weld heat affected zone. Further, since the weld metal toughness is also adversely affected, the upper limit is set to 2.5%.

  Al is an element effective for deoxidation of steel sheets, refinement of the grain size of heated austenite, etc., and in order to exert the effect, it is necessary to contain 0.002% or more, but exceeding 0.1% excessively If it is included, a coarse oxide is formed and the toughness and ductility of the steel sheet are extremely deteriorated. Also, the amount of Al in the weld metal becomes excessive, and upper bainite that is harmful to toughness is formed, resulting in weld metal. In the present invention, the amount of Al in the steel sheet is limited to a range of 0.002% to 0.1%.

  N is combined with Al and Ti and effectively works to refine the austenite grains and contributes to the improvement of the toughness of the steel sheet, but in order to clarify the effect, it is necessary to contain 0.001% or more, but excessively contained If it does, solid solution N will increase and it will lead to the deterioration of the toughness of a steel plate. Further, if the N amount of the steel sheet is excessively high, the N amount of the weld metal also becomes excessive, and B and nitride are formed to reduce the amount of solid solution B effective for refining the structure. Both tend to coarsen the structure, which is not preferable. In the present invention, the upper limit of the N content of the steel sheet is 0.015% as the content in the steel sheet that can tolerate the adverse effect of N on the weld metal.

  P is an impurity element and is preferably reduced as much as possible with respect to the properties of the steel sheet and the weld metal. However, the upper limit is set to 0.02% as an allowable amount from the viewpoint of securing toughness.

  Since S is also an impurity element and deteriorates both the ductility and toughness of the steel plate and the weld metal, reduction is necessary. As the upper limit that is practically acceptable without significant deterioration in ductility and toughness, the content is 0.01% or less.

  O is an impurity element in a steel sheet, and is not preferable because it adversely affects the ductility and toughness of the steel sheet due to the adverse effects of oxides. Further, since there is a concern that the amount of O of the weld metal is excessively increased to similarly deteriorate the ductility and toughness of the weld metal, the content is limited to 0.01% or less.

  The above are the basic components of the steel sheet used in the present invention. In the present invention, Ti, B, Mo, Ni, Cr, W are further added to the steel sheet for the purpose of adjusting the strength of the steel sheet. Cu, Nb, V, and Ta can be contained in the following content range.

  Ti is an element effective in improving the toughness of steel sheets by refining austenite grains by the formation of TiN, and it also has an effect on refining the structure of weld metal by being contained in the weld metal by dilution. In order to exhibit the above effect, the steel sheet needs to contain 0.002% or more. On the other hand, if the content in the steel sheet exceeds 0.05%, coarse oxides and nitrides are formed to deteriorate the toughness and ductility of the steel sheet, and depending on the composition of the welding material, the Ti content in the weld metal Therefore, the upper limit is made 0.05%.

  B is an element that enhances hardenability in a very small amount and is effective for increasing the strength of a steel sheet. Further, when an appropriate amount of B is contained in the steel plate, it is also contained in the weld metal by dilution, and is effective in suppressing the grain boundary ferrite of the weld metal. In order to clearly exhibit these effects, B needs to be contained in the steel sheet in an amount of 0.0003% or more. On the other hand, if it is included in the steel sheet in excess of 0.015%, a coarse precipitate is often formed in the heating stage at the time of steel slab production or steel sheet production, so the effect of improving the hardenability becomes insufficient. In addition, there is an increased risk of toughness degradation due to cracks and precipitates in the steel slab. Therefore, in the present invention, the range of B is set to 0.0003 to 0.015%.

  Mo is an element effective for improving the strength of a steel sheet by improving hardenability and precipitation strengthening. Further, when a proper amount of Mo is contained in the steel sheet, it is also contained in the weld metal by dilution, and the hardenability of the weld metal is enhanced, which is effective in suppressing grain boundary ferrite and refining acicular ferrite. In order to produce a clear effect, 0.01% or more is necessary. On the other hand, when Mo is contained excessively exceeding 1.5%, the strength is excessively increased and the toughness of the steel sheet is deteriorated. Therefore, in the present invention, the Mo content in the steel sheet is 0.01 to 1.5%.

  Since Cr has substantially the same effect and action as Mo, the content in the steel sheet is limited to 0.01 to 1.5% for the same reason as Mo.

  Since W has the same effects and actions as Mo and Cr, the content in the steel sheet is limited to 0.01 to 1.5% for the same reason.

  Ni is an element that can essentially increase the toughness of the matrix, and can be improved at the same time in strength and toughness without depending largely on the microstructure. Therefore, Ni is a very effective element in both steel sheets and weld metals. In order to exhibit the effect of improving the toughness of the steel plate, it is necessary to contain 0.01% or more in the steel plate. When the content increases, the strength and toughness are improved, but even if the content exceeds 6%, the effect is saturated, so the upper limit is made 6% in consideration of economy.

  Cu is an element effective for improving the strength of the steel sheet mainly by improving the hardenability and strengthening the solid solution, but in order to exert the effect, it is necessary to contain 0.01% or more. On the other hand, if the content exceeds 1.5%, there is a problem in hot workability, and the hot cracking resistance of the weld metal is deteriorated, so the Cu content in the steel sheet is 0.01 to 1.5%. Limited to.

  Nb is an element effective for increasing the strength of a steel sheet in a small amount by precipitation strengthening and transformation strengthening, and also effective for improving the toughness of the steel sheet by refining the heated austenite grain size. 0.002% or more is necessary. However, if it is excessively contained exceeding 0.1%, the toughness of the steel sheet is deteriorated, and there is also a concern that excessive Nb is contained in the weld metal due to dilution, and the toughness of the weld metal is deteriorated. In the present invention, the Nb content in the steel sheet is limited to a range of 0.002 to 0.1%.

  V is an element which is effective for increasing the strength of a steel sheet in a small amount mainly by precipitation strengthening, and 0.002% or more is necessary to exert the effect. However, if it is contained excessively exceeding 0.5%, coarse precipitates are formed and the toughness of the steel sheet is deteriorated, and excessive V is also contained in the weld metal due to dilution, and the toughness of the weld metal. In the present invention, the V content in the steel sheet is limited to a range of 0.002 to 0.5%.

  Ta is an element that is effective for increasing the strength of a steel sheet in a small amount mainly by precipitation strengthening, and 0.002% or more is necessary to exert the effect. However, if it exceeds 0.5% and contains excessively, coarse precipitates are formed and the toughness of the steel sheet is deteriorated, and excessive Ta is also contained in the weld metal due to dilution, and the toughness of the weld metal In the present invention, the Ta content in the steel sheet is limited to a range of 0.002 to 0.5%.

  In the invention, in addition to the steel plate component, one or more of Ca, Mg and REM can be contained for the purpose of improving the ductility of the steel plate. Also in the selectable element, it is necessary to limit each composition range as follows.

  Ca, Mg, and REM are all effective in improving ductility by suppressing the extension of sulfide during hot rolling. It effectively works to improve the heat affected zone toughness of welded joints by refining oxides. The lower limit content for exhibiting the effect is 0.0002% in terms of the content in the steel sheet. On the other hand, excessive inclusion causes coarsening of sulfides and oxides, leading to deterioration of ductility, toughness, and fatigue characteristics. Also, excessive inclusion in the weld metal due to dilution inhibits weldability. Therefore, the upper limit of the content in the steel sheet is 0.01%.

  The above is the reason for limitation in the chemical composition of the steel sheet used in the present invention.

Next, the reasons for limiting the flux composition will be described below. In high heat input submerged arc welding, the flux contributes greatly to the composition and structure of the weld metal. To achieve stable and high weld metal toughness, not only the welding wire and steel plate but also the flux composition It needs to be optimized. That is, in the present invention, in _{mass%, SiO 2: 10~25%,} MgO: 5~20%, CaO: 5~15%, CaF 2: 1~10%, Al 2 O 3: 5~25% TiO ₂ : 2 to 20%, Fe: 10 to 25%, B ₂ O ₃ : 0.1% to 2.5%, Mo: 1 to 5%, Ni: 1 if necessary It is necessary to contain -5% of 1 type or 2 types.

SiO ₂ is the most important component for improving the conformability of the bead toe in high heat input submerged arc welding and forming a good weld bead. In order to obtain this effect, 10% of SiO ₂ is added to the flux. % Or more. On the other hand, if the SiO ₂ content in the flux exceeds 25%, oxygen and Si in the weld metal increase and the toughness deteriorates, so the upper limit of the content is specified to 25%.

  MgO is contained in the flux in an amount of 5% or more in order to improve the fire resistance of the slag and improve the bead shape in welding with high heat input such as submerged arc welding. On the other hand, if the MgO content exceeds 20%, protrusions are generated on the bead surface and the bead shape deteriorates, so the upper limit of the MgO content in the flux is 20%.

  CaO is an important component for adjusting the melting point and fluidity of the slag and improving the conformability of the bead toe. To obtain this effect, CaO contains 5% or more of CaO. On the other hand, when the CaO content in the flux exceeds 15%, the slag fluidity becomes poor and the bead height becomes non-uniform, so the upper limit of the CaO content in the flux is set to 15%.

CaF ₂ is effective in improving toughness. To obtain this effect, the flux contains 1% or more of CaF ₂ . On the other hand, since CaF ₂ has a low melting point and excessively exceeds 10%, high heat input submerged arc welding impairs the smoothness of the beads and results in poor beads, so the upper limit of the CaF ₂ content in the flux is limited. 10%.

Al ₂ O ₃ has an effect of improving the slag peelability, and in order to obtain this effect, the flux contains 5% or more of Al ₂ O ₃ . On the other hand, when the Al ₂ O ₃ content exceeds 25%, a convex bead is formed and the bead shape is poor. Therefore, the upper limit of the Al ₂ O ₃ content in the flux is set to 25%.

TiO ₂ is effective in improving the smoothness and toughness of the bead surface. To obtain these effects, TiO ₂ is contained in the flux in an amount of 2% or more. On the other hand, if the TiO ₂ content exceeds 20%, the rising angle of the bead toe portion becomes large and the bead shape is deteriorated. In addition, TiO ₂ is excessively present in the weld metal and adversely affects the toughness. Therefore, the upper limit of the TiO ₂ content in the flux is set to 20%.

  Fe is effective in improving the welding efficiency and reducing the welding heat input. In order to obtain these effects, Fe in the flux is contained by 10% or more. On the other hand, if the Fe content exceeds 25%, protrusions are generated on the bead surface, so the upper limit of the Fe content in the flux was set to 25%. In the present invention, Fe may be pure Fe, for example, an Fe alloy with Mn or Si, and the effect is exhibited if the total content of Fe in the flux is within the above range.

B ₂ O ₃ precipitates a B compound such as BN at the interface of the Ti oxide formed in the weld metal, further promotes the ability of the Ti oxide to form fine acicular ferrite. As a segregation to austenite grain boundaries, it has the effect of suppressing the formation of coarse grain boundary ferrite. In order to use these functions and refine the weld metal structure, it is necessary to contain B ₂ O ₃ in the flux in an amount of 0.1% or more, preferably 0.6% or more. As will be described later, it is possible to add B from the welding wire to the weld metal, but an increase in the B content in the welding wire is not preferable because it deteriorates workability at the time of manufacturing the welding wire. For this reason, in the present invention, the addition of B to the weld metal is basically performed in the form of B ₂ O ₃ from the flux, and in addition to this, B is added from the welding wire as needed. Add to weld metal. On the other hand, when the content of B ₂ O ₃ in the flux exceeds 2.5%, the surface side weld metal is sintered when the toughness in the thickness direction of the weld metal in high heat input submerged arc welding is made uniform at a high level. The permeability is excessively increased, and the formation of a hard and coarse upper bainite structure becomes remarkable, and conversely, the toughness is deteriorated. For this reason, the upper limit of the B ₂ O ₃ content in the flux is defined as 2.5%.

In the present invention, the reason why the form of B in the flux is B ₂ O ₃ is that B ₂ O ₃ has a better yield of B in the weld metal than the form of metal B or other B compounds. It is.

  In the present invention, in addition to the above basic components of the flux, in order to stably improve the mechanical properties of the weld metal, particularly toughness, Mo and Ni may be added in the following ranges as selective components. .

  Mo is an element that has a higher effect of refining the effective crystal grain size of acicular ferrite or bainite of the weld metal than other hardenability improving elements. In particular, due to the difference in heat history and cooling rate in the thickness direction of the weld metal in high heat input submerged arc welding, the surface layer is likely to generate upper bainite that is harmful to toughness when improving the hardenability of the entire thickness range of the weld metal. In the side weld metal, the upper bainite crystal grain size can be refined and toughness deterioration can be suppressed, so that it is an effective element for uniformizing the toughness of the entire range of the weld metal. Further, Ni is the only hardenability-enhancing element and has the only solid solution toughening effect and can essentially improve toughness. The higher the Ni content, the better the toughness. Compared with other austenite stabilizing elements, Ni has a greater effect of expanding the bainite nose in the CCT diagram. Therefore, Ni in the weld metal has a cooling rate in the weld metal thickness direction during high heat input submerged arc welding. It is an effective element for uniformizing the toughness of the entire range of the weld metal because the difference in structure between the front side and the back side due to the difference and the toughness difference due to the change can be reduced.

  In the present invention, Mo and Ni are basically added from the wire into the weld metal, but in addition to this, Mo and Ni are added from the flux to the weld metal as a result of the action of Mo and Ni described later. In order to obtain the effect of refinement of the microstructure of the weld metal and improvement of toughness more stably, when containing one or two of Mo and Ni in the flux, the lower limit of each content should be 1%. Is preferred.

  On the other hand, if the content of each of Mo and Ni exceeds 5%, depending on the welding wire composition and steel plate composition, there is a concern that the hardness of the weld metal becomes excessive and the toughness is deteriorated. When one or two of these are contained, the upper limit of each content is preferably 5%.

  The form of Mo and Ni in the flux may be any form of pure metal, alloy, and oxide as long as the contents of Mo and Ni are within the above ranges. In order to reduce the amount of oxygen in the weld metal, it is more preferable to contain metal Mo, metal Ni, or an alloy containing Mo and Ni.

  The above is the reason for limiting the main component composition of the flux for achieving the object and technical idea of the present invention, but does not deviate from the object and technical idea of the present invention and does not impair the mechanical properties of the weld metal. In addition, other components of the flux component and a binder component can be contained.

  Next, the reason for limiting the component composition of the welding wire will be described. In the high heat input submerged arc welding of thick steel plates, the contribution to the structure and mechanical properties of the weld metal due to the composition of the welding wire as well as the flux is large. Therefore, in order to limit the composition of the weld metal and achieve high toughness uniformly from the front surface side to the back surface side, it is necessary to optimize not only the flux and the steel plate but also the composition of the welding wire as follows: is there. In the two-electrode single-sided one-pass large heat input submerged arc welding according to the present invention, it is important to use welding wires having different wire diameters for the first electrode and the second electrode. If the first electrode and the second electrode are each within the chemical composition range of the present invention, the first electrode and the second electrode may impair the effects of the present invention regardless of whether the chemical composition is the same or different. is not.

  The composition of the welding wire is mass%, C: 0.02 to 0.2%, Si: 0.01 to 1%, Mn: 0.5 to 2.5%, Al: 0.002 to 0.1. %, Ti: 0.005 to 0.3%, N: 0.001 to 0.015%, P: 0.02% or less, S: 0.01% or less, O: 0.01% or less Limiting is a basic requirement, and if necessary, Ni: 0.1 to 6%, Cu: 0.01 to 1.5%, Cr: 0.01 to 1.5%, Mo: 0.1 to 0.1% 3%, W: 0.01-2%, Nb: 0.002-0.05%, V: 0.005-0.5%, Ta: 0.002-0.2%, and B: 0 0.001 to 0.05% of one kind or two or more kinds, and, if necessary, Ca: 0.0002 to 0.01%, Mg: 0.0002 to 0.01%, and REM : 0.0002 ~ .01%, characterized in that it contains one or more.

  C is a component that improves the strength of the weld metal, and in particular, 0.02% or more is contained in the welding wire in order to ensure a tensile strength of 500 to 800 MPa as a weld metal for high-strength steel. On the other hand, if the content of C in the welding wire exceeds 0.2%, the amount of C in the weld metal becomes excessive and the toughness of the weld metal deteriorates, which is not preferable. Therefore, in the present invention, the C content in the welding wire is limited to 0.02 to 0.2%.

  Si is a deoxidizing element, reduces the amount of oxygen in the weld metal, suppresses defects due to inclusions in the weld metal, and suppresses material deterioration due to oxygen. In order to exert these effects, 0.01% or more of Si is contained in the welding wire. However, if Si is contained in the wire exceeding 1%, the hardness of the weld metal is excessively increased and the toughness is deteriorated, so the upper limit of the Si content in the wire is set to 1%.

  Mn has a strength improvement and deoxidation action of the weld metal. If the content in the welding wire is less than 0.5%, sufficient deoxidation action and sufficient strength of the weld metal cannot be obtained. Since the oxygen content of the weld metal is increased, the toughness of the weld metal is deteriorated. Therefore, the lower limit of the Mn content in the wire is set to 0.5%. On the other hand, if the Mn content in the wire exceeds 2.5%, the weld metal structure becomes a coarse bainite structure and the toughness is likely to deteriorate. Therefore, in the present invention, the Mn content in the welding wire Is set to 2.5%.

  Al acts as a deoxidizing element and is an element effective for controlling the amount of oxygen in the weld metal. In order to effectively contribute to deoxidation of the weld metal, Al is contained in the welding wire in an amount of 0.002% or more. On the other hand, if Al is excessively contained in the weld metal, the formation of fine acicular ferrite is suppressed, the weld metal structure is coarsened, and the toughness is deteriorated. Therefore, the upper limit of the Al content in the weld wire is 0.1. %.

Ti is an important element in the present invention that forms a Ti oxide in a weld metal and acts as a production nucleus of fine acicular ferrite, thereby contributing to refinement of the weld metal structure. In the present invention, even in high heat input submerged arc welding in which the molten metal pool is maintained for a long time, B added to the weld metal from the flux described later is a B compound such as BN and Fe ₂₃ (C, B) _6. Precipitating at the Ti oxide interface makes it possible to enhance the ability to produce fine acicular ferrite. In the present invention, in order to sufficiently secure these effects, 0.005% or more of Ti is contained in the welding wire. On the other hand, if the Ti content in the welding wire exceeds 0.3%, the weld metal deteriorates the toughness of the weld metal by forming coarse Ti-containing oxides and nitrides that can cause brittle fracture. Therefore, in the present invention, the upper limit of the Ti content in the welding wire is set to 0.3%.

  N is an unavoidable impurity element in the welding wire, but N is a useful element for forming austenite and fine acicular ferrite by forming nitrides with Ti and B in the weld metal. In order to obtain these effects, the N content needs to be 0.001% or more. On the other hand, when the N content of the welding wire exceeds 0.015%, the N content in the weld metal is increased, and the toughness of the ferrite matrix is deteriorated when N in the weld metal is in a solid solution state. In addition, B is fixed as a nitride, which inhibits the transformation of proeutectoid ferrite (grain boundary ferrite) at the austenite grain boundary due to the segregation of grain boundaries of the solid solution B and the toughness effect thereby. Therefore, in the present invention, the upper limit of the content in the welding wire is set to 0.015%.

  P is an unavoidable impurity element, and P in the weld metal deteriorates the toughness of the weld metal. Therefore, the P content in the welding wire is preferably reduced as much as possible. In the present invention, the upper limit of the P content in the welding wire is set to 0.02% as an allowable upper limit from the viewpoint of ensuring the toughness of the weld metal.

  S is also an inevitable impurity element, and both the ductility and toughness of the weld metal are deteriorated. Therefore, the S content in the welding wire needs to be reduced as much as possible. In the present invention, the upper limit of the S content in the welding wire is set to 0.01% as an upper limit that is practically acceptable from the viewpoint of ensuring the ductility and toughness of the weld metal.

  Oxygen (O) is also an unavoidable impurity element in the welding wire, and if the O content is excessive, the productivity of the welding wire is hindered, and the O content in the weld metal is increased and welding is performed. This is not preferable because it deteriorates the ductility and toughness of the metal. In the present invention, the upper limit of the O content in the welding wire is set to 0.01% in order to improve the manufacturability of the welding wire and not deteriorate the ductility and toughness of the weld metal.

  In the present invention, in addition to the basic components of the welding wire, in order to adjust the mechanical properties of the weld metal, particularly strength and toughness, one of Ni, Cu, Cr, Mo, W, Nb, V, Ta and B is further added. Two or more species can be contained in the welding wire within a predetermined range.

  Ni has the only solid solution toughening effect among the hardenability improving elements and can essentially improve toughness. The higher the amount of Ni, the better the toughness. Further, Ni has a greater effect of expanding the bainite nose in the CCT diagram than other austenite stabilizing elements. For this reason, Ni in the weld metal reduces the change in the weld metal structure between the front side and the back side due to the cooling rate difference in the thickness direction of the weld metal during the one-pass large heat input submerged arc welding of the thick steel plate, As a result, it is an effective element for achieving uniform toughness in the entire thickness range of the weld metal. In order to fully express these effects, when Ni is contained in the welding wire, it is necessary to contain 0.1% or more. On the other hand, even if Ni is included in the welding wire in excess of 6%, the effect is saturated, but the hardenability of the weld metal becomes excessive, and there is a possibility that the strength becomes excessive and deteriorates the toughness. In the present invention, the upper limit of the Ni content in the welding wire is limited to 6%.

  Cu is an austenite stabilizing element, and is an element effective in suppressing the formation of coarse grain boundary ferrite by increasing the hardenability of the weld metal and making the weld metal structure finer and improving the strength and toughness. In order to obtain these effects, the Cu content in the welding wire is preferably 0.01% or more. On the other hand, if the Cu content in the welding wire is more than 1.5%, hot cracking is likely to occur, and the manufacturability of the welding wire is deteriorated, so the upper limit of the Cu content is 1.5%. preferable. Even if Cu is contained in the welding wire or plated on the surface of the wire, the substantial effect does not change.

  Cr, like Mo, is an element effective for improving hardenability. When Cr is contained in the welding wire in order to improve the strength of the weld metal, it is necessary to contain 0.01% or more. On the other hand, if the Cr content in the welding wire is more than 1.5%, the toughness of the weld metal is significantly deteriorated, so the upper limit of the Cr content is preferably 1.5%.

  Mo is an element having an effect of refining the effective crystal grain size of acicular ferrite or bainite of a weld metal as compared with other hardenability improving elements. In particular, due to the difference in heat history and cooling rate in the thickness direction of the weld metal in high heat input submerged arc welding, the surface layer is likely to generate upper bainite that is harmful to toughness when improving the hardenability of the entire thickness range of the weld metal. In the side weld metal, the upper bainite crystal grain size can be refined and toughness deterioration can be suppressed, so that it is an element that is particularly effective for uniformizing the toughness of the entire range of the weld metal. When Mo is contained in the welding wire in anticipation of the effect, it is necessary to contain 0.1% or more. However, if Mo is excessively contained in the weld metal exceeding 3%, the weld metal is excessively hardened and the toughness of the weld metal is remarkably deteriorated. Therefore, in the present invention, the upper limit of the Mo content in the weld wire is limited. 3%.

  W is qualitatively an element having the same effect as Cr, and when W is contained in the welding wire in order to improve the strength of the weld metal, 0.01% or more is contained in order to exert the effect. It is preferable to do this. On the other hand, if the W content in the welding wire is more than 2%, the toughness of the weld metal is remarkably deteriorated, so the upper limit of the W content is preferably 2%.

  Nb is an element effective for improving the strength of the weld metal by improving the hardenability and precipitation strengthening of the weld metal. In order to exhibit this effect reliably, the Nb content in the welding wire is preferably 0.002% or more. On the other hand, if the Nb content in the welding wire exceeds 0.05%, the strength of the weld metal becomes excessive, and because coarse Nb precipitates are formed, the toughness deterioration of the weld metal becomes significant. It is not preferable. Therefore, it is preferable that the upper limit of the Nb content in the welding wire is 0.05%.

  V is an element effective for improving the strength of the weld metal by precipitation strengthening of the weld metal. In order to exhibit this effect reliably, the V content in the welding wire is preferably 0.005% or more. On the other hand, if the V content in the welding wire exceeds 0.5%, the strength of the weld metal becomes excessive, and the toughness of the weld metal becomes significantly deteriorated. Therefore, the upper limit of the V content in the welding wire is preferably 0.5%.

  Ta is an element having substantially the same action as V, and is an element effective for improving the strength of the weld metal by precipitation strengthening of the weld metal. When Ta is contained in the welding wire in order to reliably exhibit this effect, the Ta content in the welding wire is preferably 0.002% or more. On the other hand, if the Ta content in the welding wire exceeds 0.2%, the strength of the weld metal becomes excessive and the toughness of the weld metal is significantly deteriorated, which is not preferable. Therefore, the upper limit of the Ta content in the welding wire is set to 0.2%.

  B segregates at the austenite grain boundaries as solid solution B in the weld metal, suppresses the formation of coarse grain boundary ferrite, precipitates as a B compound such as BN at the same time as the Ti oxide, and interacts with the Ti oxide. This has the effect of promoting the formation of fine acicular ferrite. Using these actions, B is essential in the weld metal in order to refine the weld metal structure and to uniformly improve the toughness of the entire thickness range from the front side to the back side of the weld metal in high heat input submerged arc welding. It is an element.

  In the present invention, B is basically added from the flux, but it is also possible to supplementarily add B from the welding wire into the weld metal in order to obtain the effect of B stably. In that case, in order to exhibit an effect reliably, it is preferable to make B content in a welding wire 0.001% or more. On the other hand, when the B content in the welding wire exceeds 0.05%, a coarse upper bainite structure is generated in the weld metal, the toughness of the weld metal is deteriorated, and the workability at the time of manufacturing the wire is deteriorated. Therefore, it is not preferable. Therefore, when B is contained in the welding wire, the upper limit of the B content is preferably 0.05%.

  Ca, Mg, and REM are effective elements for changing the sulfide structure in the weld metal, reducing the size of the sulfide and oxide, and improving the ductility and toughness of the weld metal. It can be contained in the welding wire as required. In order to exhibit these effects, the content of one or more of Ca, Mg, and REM in the welding wire is preferably 0.0002% or more. On the other hand, if the content of one or more of Ca, Mg and REM exceeds 0.01%, the sulfides and oxides in the weld metal are coarsened, and the ductility and toughness of the weld metal deteriorate. In addition, since the weld bead shape and weldability may be deteriorated, the upper limit of the content of one or more of Ca, Mg and REM in the welding wire is set to 0.01%. .

  The above is the reason for limiting the requirements of the present invention. Further, the operation and effects of the present invention will be described with reference to examples.

  As shown in FIG. 1, a joint is formed by abutting a steel plate having a component composition shown in Table 1 with a plate thickness shown in Table 1 that has been grooved in advance at the end of the steel plate. 2 electrode single-sided 1-pass large heat input submerged arc welding was performed under the welding conditions shown in Table 4 using welding wires having the composition shown in Table 3. Thereafter, in the welded joint, 2 mm V-notch Charpy impact test specimens were collected from three locations, 7 mm below the surface of the steel plate at the center of the weld metal shown in FIG. The toughness of the weld metal was evaluated by a Charpy impact test at 0 ° C., and the number of repetitions: the average value of three measured values.

  In Table 1, steel plates A1 to A8 are steel plates having a chemical composition within the range of the present invention, and steel plates B1 to B4 are steel plates having a chemical composition outside the range of the present invention. In Table 2, fluxes A1 to A9 are fluxes having a chemical composition within the scope of the present invention, and fluxes B1 to B5 are fluxes having a chemical composition outside the scope of the present invention. Furthermore, in Table 3, wires A1-a to A9-b are wires having a chemical composition within the scope of the present invention, and wires B1-a to B5-b are wires having a chemical composition outside the scope of the present invention. Note that the wire is drawn from the same ingot to a wire having a different wire diameter (4 to 8 mm), and the same symbol on the left side of the wire symbol-indicates that the wire is machined from the same ingot. ing. The chemical composition of the wire is an analytical value after wire drawing.

  As shown in Table 4, various steel plates, fluxes, and wires are combined to produce a joint. At that time, the toughness of 7 mm below the steel plate surface, the center of the plate thickness, and 7 mm above the back surface at the center of the weld metal is Charpy impact at 0 ° C. Evaluation was based on absorbed energy. In addition, the presence or absence of welding defects was investigated by X-ray transmission tests of joints, cross-sectional structure observations, and the like. Among Table 4, joints A1 to A33 are joints satisfying the present invention. Absorbed energy sufficiently higher than 70J is obtained at any position of the weld metal, and the front side to the back side of the weld metal. It is clear that high toughness is obtained stably.

  On the other hand, in Table 4, joints B1 to B18 are joints that do not satisfy the requirements of the present invention, and as described below, the toughness level of the entire weld metal is low, or the position of a part of the weld metal Therefore, the toughness is lowered or / and weld defects are generated, and the soundness of the joint is impaired.

  That is, in the joint B1, since the C amount of the steel plate is excessive, the C amount of the weld metal is also excessive, the hardness of the weld metal is excessive, and coarse cementite (Fe3C) or island-like that is harmful to toughness. Since a lot of martensite is generated, the toughness of the weld metal is inferior regardless of the position of the weld metal.

  In the joint B2, since the P amount of the steel plate is excessive, the P amount of the weld metal is also excessive, so that the toughness of the weld metal is inferior regardless of the position of the weld metal.

  In the joint B3, since the S amount of the steel plate is excessive, the S amount of the weld metal is also excessive, so that the toughness of the weld metal is inferior regardless of the position of the weld metal.

  In the joint B4, since the N amount of the steel plate is excessive, the N amount of the weld metal is also excessive. Therefore, the amount of solute B in the weld metal is not sufficient, and it is relatively good at 7 mm below the surface by adjusting the alloy composition. Although fine toughness is obtained, the structure is not sufficiently refined at the thickness 7 mm from the center of the plate thickness to the back surface, and the toughness is greatly deteriorated compared to 7 mm below the surface. That is, it is an insufficient achievement level for the purpose of achieving high toughness in the entire weld metal.

  Since the joint B5 does not contain B2O3 in the flux composition, the amount of B in the weld metal is too small. Therefore, in the weld metal structure, the generation of acicular ferrite is not sufficient, and the grain boundary ferrite The toughness is low as compared with the present invention and the toughness of the grain boundary ferrite formation behavior is largely dependent on the cooling rate. The difference is also large and undesirable.

  In the joint B6, since B2O3 is excessively contained in the flux composition, the amount of B in the weld metal is excessive, the hardenability of the weld metal is excessive, the strength is excessive, and the joint is coarse. Since precipitates are formed, the toughness of the weld metal is inferior to that of the present invention regardless of the position of the weld metal. Moreover, a hot crack is also observed in the weld metal, and the soundness as a joint is inferior.

  In the joint B7, the amount of Mo is excessive together with the TiO2 in the flux, so the amount of Ti and Mo in the weld metal is excessive, so that coarse precipitates increase and the weld metal hardens excessively. The toughness of the weld metal is inferior to that of the present invention regardless of the position of the weld metal.

  In the joint B8, since the content of Ni in the flux in addition to TiO2 is excessive, both the amount of Ti and Ni in the weld metal are excessive. As a result, coarse precipitates increase and the weld metal strength is increased. It becomes excessively high and the toughness of the weld metal is not sufficient regardless of the position of the weld metal.

  Since the amount of TiO2 in the flux is excessive, the joint B9 is not preferable because the rising angle of the bead toe is increased and the bead shape is deteriorated. Further, TiO2 is excessively present in the weld metal and coarse TiO2 is also increased, so that the toughness of the weld metal is deteriorated regardless of the position.

  In the joint B10, since the C content of the welding wire is excessive, the C amount of the weld metal is excessive, the hardness of the weld metal is excessive, and coarse cementite (Fe3C) or island martens which are harmful to toughness. Since many sites are generated, the toughness of the weld metal is inferior regardless of the position of the weld metal.

  In the joint B11, since the N content of the welding wire is excessive, the N content in the weld metal is also excessive. Therefore, the amount of solute B cannot be secured, the toughness fluctuation is large, and particularly the toughness of 7 mm on the back surface is remarkable. Since it is inferior, it is not preferable.

  In the joint B12, since the P amount of the welding wire is excessive, the P amount of the weld metal is also excessive, and therefore the toughness of the weld metal is inferior regardless of the position of the weld metal.

  In the joint B13, since the Ti content of the welding wire is excessive, the amount of Ti in the weld metal also becomes excessive. Therefore, coarse Ti precipitates are generated in the weld metal, and the toughness of the weld metal is remarkably deteriorated.

  In the joint B14, since the welding wire does not contain Ti, the generation of acicular ferrite in the weld metal structure is not sufficient, and the structure becomes coarse. Therefore, the toughness is greatly inferior regardless of the position of the weld metal.

  The joint B15 has relatively good toughness on the surface side, but since the welding wire diameter is the same, the cooling rate decreases from the weld metal surface side to the back surface side, so the structure becomes coarser toward the back surface side. It has become. For this reason, the toughness decreases with increasing distance from the front surface side to the back surface side, and the absorbed energy at 7 mm on the back surface is low, which is not preferable.

  In the joint B16, the first electrode has a smaller diameter than the second electrode, but the wire cross-sectional area of the first electrode is not sufficiently smaller than the wire cross-sectional area of the second electrode. The effect of the present invention is not sufficiently exhibited. Therefore, as with the joint B17, the toughness decreases as it goes from the front surface side to the back surface side, and the absorbed energy at 7 mm on the back surface is low, which is not preferable.

  On the other hand, the joint B17 is not preferable because the wire cross-sectional area of the first electrode is excessively smaller than the wire cross-sectional area of the second electrode, and the bead cross-sectional shape becomes poor and high-temperature cracking occurs.

  In the joint B18, since the wire diameter of the second electrode is excessively small, the weld metal has good toughness, but poor fusion occurs and the soundness of the joint is impaired.

   From the results of the above examples, according to the present invention, when a thick high-tensile steel plate having a thickness of 40 mm or more is welded with a heat input of 400 kJ / cm or more and single-sided high-pass submerged arc welding on one side, the weld metal It is clear that excellent toughness of 70 J or more can be obtained uniformly over the entire thickness range from the front surface side to the back surface side with 2 mmV notch Charpy absorbed energy.

It is a figure which shows the collection position and direction of the welding groove shape used for the Example of this invention, and a 2 mmV notch Charpy impact test piece. It is a figure which shows the relationship between the toughness difference (difference of 0 degreeC absorption energy) between 7 mm below the surface, and 7 mm above the back surface, and the cross-sectional area ratio of a 1st electrode and a 2nd electrode.

Claims (6)

When one-sided one-pass welding of steel plates with a thickness of 40 mm or more by two-electrode submerged arc welding,
% By mass
C: 0.02 to 0.2%,
Si: 0.01 to 1%,
Mn: 0.1 to 2.5%
Al: 0.002 to 0.1%,
N: 0.001 to 0.015% is contained,
P: 0.02% or less,
S: 0.01% or less,
O: limited to 0.01% or less,
A steel plate with the balance being Fe and inevitable impurities,
% By mass
SiO ₂ : 10 to 25%,
MgO: 5 to 20%,
CaO: 5 to 15%,
CaF ₂ : 1 to 10%,
Al ₂ O ₃ : 5 to 25%,
TiO ₂ : 2 to 20%,
Fe: 10 to 25%,
B ₂ O ₃ : a flux composed of 0.1% to 2.5%,
% By mass
C: 0.02 to 0.2%,
Si: 0.01 to 1%,
Mn: 0.5 to 2.5%
Al: 0.002 to 0.1%,
Ti: 0.005 to 0.3%,
N: 0.001 to 0.015% contained,
P: 0.02% or less,
S: 0.01% or less,
O: Limiting to 0.01% or less, using the welding wire of the first electrode and the second electrode, the balance being Fe and inevitable impurities, the diameter of the welding wire of the second electrode is 6 to 8 mm, and the second Welding is performed under the condition that the ratio of the cross-sectional area of the welding wire of the first electrode to the cross-sectional area of the welding wire of the electrode is 35 to 75%. Submerged arc welding method. The steel sheet is in mass%, and
Ti: 0.002 to 0.05%,
B: 0.0003 to 0.015%,
Mo: 0.01 to 1.5%,
Cr: 0.01 to 1.5%
W: 0.01 to 1.5%
Ni: 0.01-6%,
Cu: 0.01 to 1.5%,
Nb: 0.002 to 0.1%,
V: 0.002-0.5% and
Ta: 0.002 to 0.5% of 1 type or 2 types or more, The two-electrode single-sided single-pass large heat input submerged arc welding method with excellent toughness of the weld metal according to claim 1 . The steel sheet is in mass%, and
Ca: 0.0002 to 0.01%
Mg: 0.0002 to 0.01%, and
REM: 0.0002-0.01% of 1 type or 2 types or more are contained, The 2 electrode single side | surface 1 pass large heat input submerged arc excellent in the toughness of the weld metal of Claim 1 or 2 characterized by the above-mentioned. Welding method. The flux is mass%, and
Mo: 1-5%, and
Ni: 1-5% of 1 type or 2 types are contained, The 2 electrode single side | surface 1 pass large heat input submerged arc welding method excellent in the toughness of the weld metal in any one of Claims 1-3 characterized by the above-mentioned. . The welding wire is in% by mass;
Ni: 0.1 to 6%,
Cu: 0.01 to 1.5%,
Cr: 0.01 to 1.5%
Mo: 0.1 to 3%,
W: 0.01-2%
Nb: 0.002 to 0.05%,
V: 0.005 to 0.5%,
Ta: 0.002 to 0.2%, and
B: One type or two or more types of 0.001 to 0.05% are contained. The two-electrode single-sided one-pass large-diameter excellent in weld metal toughness according to any one of claims 1 to 4 Thermal submerged arc welding method. The welding wire is in% by mass;
Ca: 0.0002 to 0.01%,
Mg: 0.0002 to 0.01%, and
REM: 1 type or 2 types or more of 0.0002-0.01% is contained, The 2 electrode single side | surface 1 pass large insertion excellent in the toughness of the weld metal in any one of Claims 1-5 characterized by the above-mentioned Thermal submerged arc welding method.

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