JPH11192555A - Method for submerged arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a weld metal excellent in toughness and crack propagation stopping characteristic and at the same time suppressing own hardness. SOLUTION: Bonded flux contains by wt. per the total weight of the flux, 20-40% MgO, 15-35% Al2 O3 , 8-20% SiO2 , 5-15% CaF2 , 2-5% metal carbonate (expressed in terms of CO2 ), 1-2.5% metal Si and substantially no boron. Wire contains by wt. per the total weight of the wire, 0.03-0.08 C, 0.02-0.4% Si, 0.1-0.7% Mn, 3.5-6% Ni and the balance Fe consisting of inevitable impurities, N as the inevitable impurities is controlled to be <=0.007%. When a metal silicon content in the flux is [Si]f expressed by wt.%, a C content in the wire is [C]w expressed by wt.% and an Si content in the wire is [Si]w expressed by wt.%, the welding is executed in combinations with these fluxes and wires so that a value A calculated by formula, A=([Si]f +65×[C]w +15×[Si]w ) becomes 4-9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method applied to welding of low temperature aluminum killed steel or 1.5 to 3.5% by weight Ni steel used as a material for tanks and offshore structures. The present invention relates to a submerged arc welding method capable of obtaining good welding workability at the time of transverse welding using a direct current, having excellent crack propagation stopping characteristics and toughness, and obtaining a weld metal having a suppressed maximum hardness.

[0002]

2. Description of the Related Art Generally, when welding an LPG storage tank or the like in which low-temperature steel, which is a kind of carbon steel for welded structural steel, is used, a high toughness value is required to ensure safety. It is required to obtain a weld metal having the same. For example, in a temperature range up to about −60 ° C., C—Si—Mn—
A Ti-B-based weld metal or a component-based weld metal obtained by adding about 2% by weight of Ni to the weld metal is employed. In the temperature range up to -100 ° C, C-
Generally, a component-type weld metal in which about 3 to 4% by weight of Ni is added to a Mn-Si-based material is used. In any of the weld metals, the toughness is improved by reducing the oxygen content of the weld metal, and Mo may be added to improve the strength in some cases.

In recent years, in view of the safety of a cylindrical tank for storing butane, propane, and the like at normal pressure and low temperature, it is required to improve the toughness of a weld metal in a lower temperature range. Standards for structural materials in this low temperature range include:
For example, BS7777 was set in 1993,
Recently, this standard has been applied to the construction of cylindrical tanks and the like. Conventional propane tanks are generally required to have a toughness value of vE of 27 J or more at −46 ° C., which is the liquefaction temperature of propane. However, in BS7777, the propane tank is Ty
This propane tank has a value higher than the conventional toughness value, that is, vE-80 ° C. is 5
It is required to be 0 J or more.

In addition, for Type III weld metal,
In addition to the above specifications, as a crack propagation arresting property, the non-ductile transition temperature T _NDT in the drop weight test is −95 ° C. or less, that is, −
Non-breaking at 90 ° C. is often required. Further, in order to improve the corrosion resistance, the maximum hardness of the weld metal may be regulated.
It may be required to be 90 or less.

As a method for welding low-temperature steel, the present inventors have proposed a transverse submerged arc welding method capable of obtaining a high-toughness Ti-B-based weld metal (Japanese Patent Publication No. 3-78).
197 publication). This is to appropriately regulate the composition of the flux and the wire whose particle size has been adjusted.
The aim is to improve the toughness of the weld metal in the temperature range up to ° C.

[0006] When performing horizontal submerged arc welding, a direct current power supply (DC-EP) is usually used, and a direct current power source for low-temperature steel is used in which the weld metal is reduced in oxygen to improve mechanical properties. A bond flux for submerged arc welding is disclosed (JP-A-4-238695). This is one in which the flux composition is appropriately regulated. For example, improvement in toughness of a weld metal in a temperature region up to −40 ° C. is being studied.

[0007]

However, even when welding low-temperature steel by the method disclosed in Japanese Patent Publication No. 3-78197, the toughness of the weld metal in a temperature range lower than -60 ° C is sufficiently improved. In addition, there is a problem that high crack propagation stopping characteristics cannot be obtained.

[0008] Also, in the case where transverse submerged arc welding is performed using a bond flux described in Japanese Patent Application Laid-Open No. Hei 4-238699, the toughness of the weld metal in a temperature range lower than -40 ° C is insufficient. In addition, good crack propagation stopping characteristics cannot be obtained. This is because the oxygen content of the weld metal is affected by the composition of both the flux and the wire.
This is because, in Japanese Patent No. 238695, only the composition of the bond flux is specified. Therefore, the amount of oxygen in the weld metal cannot be sufficiently reduced depending on the composition of the wire to be combined.

Thus, when welding low temperature steel,
When high toughness at −80 ° C. and good crack arrestability at −90 ° C. are required, it is considered difficult to use a ferrite-based welding material, and Ni is contained in about 70% by weight. A high Ni austenitic welding material is used for welding Type III low temperature steel. When this welding material is used, the toughness and crack propagation arresting characteristics are good, but since different materials are welded between the ferritic base material and the austenitic welding metal, there is a problem in bending performance due to the difference in ductility. And the cost of the welding material increases significantly.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and can weld low-temperature steel such as a cylindrical tank at low cost, has excellent toughness and crack propagation stopping characteristics, and has a high hardness. It is an object of the present invention to provide a submerged arc welding method capable of obtaining a weld metal with reduced cracking.

[0011]

A submerged arc welding method according to the present invention is directed to a submerged arc welding method for welding by combining a wire and a bond flux.
Flux total weight per, MgO: 20 to 40 wt%, Al ₂ O _3: 15 to 35 wt%, SiO _2: 8 to 20 wt%, CaF _2: 5 to 15% by weight, metal carbonate (CO ₂ converted value ): 2.0 to 5.0% by weight and metal S
i: a bond flux containing 1.0 to 2.5% by weight and containing substantially no B, and
C: 0.03 to 0.08% by weight, Si: 0.02 to 0.40% by weight, Mn: 0.10 to 0.70% by weight, and Ni: 3.5 to 6.0% by weight. And the balance is Fe
And a wire composed of unavoidable impurities, wherein N of the unavoidable impurities is regulated to 0.0070% by weight or less, and a metal Si content in the flux by weight% [S
i] _f , when the C content in the wire is [C] _w in weight% and the Si content in the wire is [Si] _w in weight%, the formula A = ([Si] _f + 65 × [ C] _w + 15 × [S
i] It is characterized in that welding is performed in combination so that the A value calculated by _w ) is 4.0 to 9.0.

In the present invention, the flux does not substantially contain B in order to form a non-Ti-B-based weld metal, but specifically, the flux contains inevitable impurities as inevitable impurities in the flux. The B content is regulated to 0.02% by weight or less. However, the B content is a B-converted value from the B alloy and the B oxide in the flux.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors first disclosed
By applying the welding method described in -78197,
About 1.5% by weight of Ni was added to the wire to form a Ti-B-based weld metal, and the properties of the obtained weld metal were evaluated. As a result, good toughness at -80 ° C and -9
Although excellent crack propagation arrest characteristics (falling performance) at 0 ° C. could be obtained, the Vickers maximum hardness of the weld metal, Hv
Became a value greatly exceeding 290. That is, when the value of the hardness of the weld metal is not regulated, or when the regulation value is not strict even if the hardness is regulated, the welding method described in Japanese Patent Publication No. 3-78197 is used. It is possible to apply. However, in order to satisfy the maximum hardness Hv: 290 or less, which is an object of the present invention, it is necessary to take measures such as preheating and maintaining the interlayer temperature at a high temperature.

On the other hand, a non-Ti-B type alloy having a Ni content of 3.5
When a weld metal having a weight percent or more was formed and evaluated in the same manner, good results were obtained in the dropping performance at -90 ° C, but the toughness at -80 ° C was reduced, and the dropping performance at -90 ° C. In some cases exceeded 290. As described above, it was not possible to satisfy all of these characteristics only by optimizing the composition of the wire and the flux.

Therefore, the present inventors further obtained good toughness at -80 ° C., excellent dropping performance at -90 ° C., and a Vickers maximum hardness Hv of 2
In order to obtain a weld metal of 90 or less, intensive experiments and examinations were repeated. As a result, while appropriately controlling the composition of the flux and the wire, the value calculated from the metal Si content in the flux, which is a deacidifying element, and the C content and the Si content in the wire, must be appropriately defined. As a result, it has been found that it is possible to obtain a weld metal having excellent low-temperature toughness and dropping performance, and having a suppressed maximum hardness.

Hereinafter, the submerged arc welding method according to the present invention will be described in more detail. First, the reasons for limiting the composition of the bond flux will be described.

MgO: 20 to 40% by weight MgO is a component having an effect of improving the toughness of the weld metal by increasing the basicity and reducing the amount of oxygen in the weld metal. If the MgO content in the flux is less than 20% by weight based on the total weight of the flux, the above effects cannot be sufficiently obtained. On the other hand, MgO in the flux
If the content exceeds 40% by weight, the fluidity of the slag is deteriorated, the appearance of the bead becomes poor, and the slag is likely to be involved. Therefore, MgO in the flux
The content is 20 to 40% by weight based on the total weight of the flux.

Al ₂ O ₃ : 15 to 35% by weight Al ₂ O ₃ is a component necessary for improving the bead appearance and maintaining the welding workability. If the Al ₂ O ₃ content in the flux is less than 15% by weight or more than 35% by weight based on the total weight of the flux, the above effects cannot be obtained. Therefore, the content of Al ₂ O ₃ in the flux is 15 to 35% by weight based on the total weight of the flux.

SiO ₂ : 8 to 20% by weight SiO ₂ acts as a slag forming agent and has an effect of adjusting the appearance and shape of the bead. S in flux
If the iO ₂ content is less than 8% by weight based on the total weight of the flux, the above effects cannot be sufficiently obtained. on the other hand,
When the SiO ₂ content in the flux exceeds 20% by weight, glass-like seizure occurs on the surface of the bead. Therefore, the content of SiO ₂ in the flux is set to 8 to 20% by weight based on the total weight of the flux.

CaF ₂ : 5 to 15% by weight CaF ₂ increases the basicity of the slag, raises the basicity of the weld metal, and reduces the amount of oxygen in the weld metal.
It is a component having the effect of improving the toughness of the weld metal.
If the content of CaF ₂ in the flux is less than 5% by weight, the above effects cannot be sufficiently obtained. On the other hand, if the content of CaF ₂ in the flux exceeds 15% by weight, the stability of the arc decreases, and slag is likely to be involved. Therefore, the content of CaF ₂ in the flux is 5 to 15% by weight based on the total weight of the flux.

Metal carbonate (CO ₂ equivalent): 2.0 to
5.0% by weight of CO ₂ is contained in the flux in the form of carbonates such as CaCO ₃ and BaCO ₃ , and these carbonates are thermally decomposed into CO ₂ during welding to shield the arc atmosphere. This has the effect of preventing nitrogen from entering the weld metal. If the content of the metal carbonate in the flux is less than 2.0% by weight based on the total weight of the flux in terms of CO ₂ , the above effect cannot be sufficiently obtained. On the other hand, when the metal carbonate in the flux exceeds 5.0% by weight in terms of CO _{2, the} amount of generated gas increases and a pock mark is easily generated on the surface of the bead. Therefore, the content of the metal carbonate in the flux is 2.0 to 5.0% by weight based on the total weight of the flux in terms of CO ₂ .

Metallic Si: Metallic Si in a flux of 1.0 to 2.5% by weight acts as a deoxidizing agent. If the content of metal Si in the flux is less than 1.0% by weight based on the total weight of the flux, the effect cannot be sufficiently obtained. On the other hand, even if metal Si is added to the flux in an amount exceeding 2.5% by weight, the deoxidizing effect is saturated and oxygen cannot be further reduced. Further, the toughness of the weld metal decreases and the maximum hardness increases. Therefore,
The content of metal Si in the flux is 1.0 to 2.5% by weight based on the total weight of the flux. In addition, metal Si
Is usually added to the flux in the form of an alloy such as Fe-Si and Ca-Si.

Next, the reasons for limiting the composition of the wire will be described.

C: 0.03 to 0.08% by weight C is a component necessary for improving the strength of the weld metal, and also has the effect of reducing the amount of oxygen in the weld metal. The C content in the wire is 0.0
If it is less than 3% by weight, the amount of oxygen in the weld metal will increase significantly, and the desired toughness cannot be obtained. On the other hand, if the C content in the wire exceeds 0.08% by weight, the hardenability increases, the strength of the weld metal increases significantly, the maximum hardness Hv increases, and the toughness decreases. Therefore, the C content in the wire is from 0.03 to 0.
08% by weight.

Si: 0.02 to 0.40% by weight Si in the wire has a deoxidizing effect like metal Si in the flux. If the Si content in the wire is less than 0.02% by weight based on the total weight of the wire, the effect cannot be sufficiently obtained. On the other hand, if the Si content in the wire exceeds 0.40% by weight, the toughness of the weld metal decreases, and the maximum hardness Hv of the weld metal also increases. Therefore,
The Si content in the wire is from 0.02 to 0.40% by weight based on the total weight of the wire.

Mn: 0.10 to 0.70 wt% Mn is a component having an effect of improving the toughness of the weld metal. When the Mn content in the wire is 0.1% based on the total weight of the wire.
If the content is less than 10% by weight, the effect cannot be sufficiently obtained. On the other hand, if the content of M exceeds 0.70 wt% in the wire,
Even if n is contained, the toughness cannot be further improved. Further, the maximum hardness Hv of the weld metal also increases. Therefore, the Mn content in the wire is set to 0.10 to 0.70% by weight based on the total weight of the wire.

Ni: 3.5 to 6.0% by weight Ni is a component necessary for improving toughness and dropping performance. When the Ni content in the wire is less than 3.5% by weight based on the total weight of the wire, the dropping performance at -90 ° C is reduced. On the other hand, if the Ni content in the wire exceeds 6.0% by weight, hot cracking occurs during welding of the first layer. Therefore, the Ni content in the wire is set to 3.5 to 6.0% by weight based on the total weight of the wire.

N: 0.0070 wt% or less Most of N in the wire is retained in the weld metal. If the content of N as an unavoidable impurity in the wire exceeds 0.0070% by weight based on the total weight of the wire, the toughness of the weld metal decreases. Therefore, the N content in the wire is restricted to 0.0070% by weight or less based on the total weight of the wire.

The remainder of the wire defined in the present invention is composed of Fe and inevitable impurities such as Cu, Cr, Mo, Ti, Al, P and S. However, when the surface of the wire is plated with Cu for the purpose of preventing rust of the wire, the Cu is mixed in the weld metal in an amount of about 0.05 to 0.20% by weight, depending on the wire diameter.

In the present invention, the metal S in the flux
By appropriately defining the content of i, and the values calculated by the C content and the Si content in the wire, the low-temperature toughness and the dropping performance of the weld metal are improved, and the maximum hardness is suppressed. I have. Hereinafter, the reasons for limiting the values calculated based on these contents will be described.

[Si] _f + 65 × [C] _w + 15 × [S
i] _w : 4.0 to 9.0 In the case where welding is performed by combining a flux whose composition is regulated as described above and a wire, the content of metal Si in the flux is [Si] _f by weight%, and The content of C in weight% is [C] _w , and the content of Si in the wire is weight% [S
i] _{Assuming w} , the formula A = ([Si] _f + 65 × [C]
_w + 15 × [Si] _w ), when the A value is 4.0 to 9.0, the maximum hardness Hv of the weld metal can be set to 290 or less, and good toughness and dropping performance can be obtained. Can be obtained. If this A value is less than 4.0,
Even if the composition of the flux and the wire is within the range of the present invention, oxygen in the weld metal increases due to insufficient deoxidation, and the toughness decreases. On the other hand, when the A value exceeds 9.0, the hardenability increases, and the yield of C and Si in the wire and the metal Si in the flux to the weld metal increases,
These synergistic effects significantly increase the strength of the weld metal. As a result, the maximum hardness Hv of the weld metal increases and the toughness decreases. Therefore, the C content and the Si content in the wire and the metal S in the flux are adjusted so that the A value calculated by the above equation is 4.0 to 9.0.
Adjust the content of i.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the submerged arc welding method according to the present invention will be specifically described below in comparison with comparative examples.

First, using a bond flux having the composition shown in Table 1 below and a wire having a wire diameter of 2.4 mm and having the composition shown in Table 2 below, a low temperature containing 1.5% by weight of Ni was used. Multi-layer welding was carried out on steel sheets for industrial use. However, in the chemical composition of the wire shown in Table 2 below,
P, S and Cu are inevitable impurities. FIG. 1 is a cross-sectional view showing a groove shape and a size of a steel plate, and FIG. 2 is a schematic view showing a horizontal multi-layer welding method. As shown in FIG. 1, the steel plates 11 and 12 each having a thickness of 19 mm are provided with inclined notches 11a and 12a extending from the surfaces thereof to the end surfaces. V-shaped groove 13 is formed. In this embodiment, the thickness of the root surface is set to 4 mm,
Side bevel angle is 30 °, steel plate 2 side bevel angle is 15
°. The composition of this steel sheet is shown in Table 3 below.

Then, as shown in FIG. 2, a direct current (D
Using C-EP), the groove portion 13 is moved from the groove surface 14a side.
Metal 15a by performing horizontal multi-layer welding with 5 passes
Was formed, a groove was formed on the groove back surface 14b side by gouging, and the groove was welded to the groove in three passes to form a weld metal 15b. In FIG. 2, the numerical values in the weld metals 15a and 15b indicate the lamination order of the weld metals formed for each pass of the horizontal multi-layer welding. Table 4 below shows the welding conditions for each pass.

Thereafter, a No. 4 test piece for Charpy impact test was collected from the weld metal 15a formed on the groove surface 14a side according to JIS Z3111, and the ASTM
A P-3 test piece for a drop test was collected according to E208, and a Charpy impact test and a drop test were performed using these test pieces. For the Charpy impact test,
The absorption energy at -80 ° C was measured with the number of repetitions being 5, and the average value was calculated. As for the dropping performance, a dropping test was carried out at −90 ° C. with the number of repetitions being 3.

Further, the groove surface 14a side and the groove back surface 14b
The Vickers hardness of the weld metals 15a and 15b formed on the sides was measured. FIG. 3 is a schematic diagram showing a measurement position of Vickers hardness. As shown in FIG. 3, in the weld metals 15a and 15b, the position at a depth of 1.0 mm from the groove surface 14a side of the steel plates 11 and 12 is measured at the measurement position 16
a, 16b, Vickers hardness was measured by applying a load of 5 kgf at 0.5 mm intervals.

Tables 5 and 6 below show the combinations of wires and fluxes used, the A values, and the evaluation results of various tests. The A value refers to the content of metal Si in the flux in weight% [Si] _f , the content of C in the wire in weight% [C] _w , and the content of Si in the wire in weight% [Si]. _{Assuming w} , the formula A = ([Si] _f + 65 × [C] _w +1
5 × [Si] _w ).

In the evaluation results shown in Table 5 below,
The maximum hardness column shows the maximum value measured by the Vickers hardness test. However, as an evaluation criterion of toughness, the case where the average value of the absorbed energy is 50 J or more is regarded as a pass, and as the evaluation criterion of the dropping performance, a case where all the specimens are not broken in three dropping tests is considered as a pass. did. In addition, as the evaluation standard of the maximum hardness, a case where Hv was 290 or less was regarded as acceptable.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

As shown in Tables 1 to 3, 5 and 6,
Example No. In Nos. 1 to 8, since the chemical composition of wire and flux and the A value are within the range of the present invention, the toughness and the dropping performance of the weld metal are good, and the maximum hardness Hv is 290 or less. was gotten.

On the other hand, in Comparative Example No. Nos. 9 to 11 apply the wire and the flux described in Japanese Patent Publication No. 3-78197. The wire and the flux are selected so that a Ti-B-based weld metal is formed, and the C in the wire is selected. And Mn are set to appropriate amounts to be added to the Ti-B-based weld metal. Comparative Example No. Comparative Example No. 9 did not contain Ni added to the wire. Nos. 10 and 11 are obtained by adding about 1.0% by weight and about 1.5% by weight of Ni to the wire, respectively. With an increase in the Ni content, the toughness and the dropping performance were improved. In No. 11, the results satisfy these performances, but the maximum hardness Hv increases with an increase in the Ni content, and Hv greatly exceeds 290.

Comparative Example No. 12 is Comparative Example No. 12. In order to lower the maximum hardness of No. 11, an attempt was made to lower the C and Mn contents in the wire. Although the maximum hardness was a good value, since the C and Mn contents in the weld metal deviated from the proper amounts of the Ti-B system, the toughness and the dropping performance were reduced.
As described above, when Ni is added to a wire by applying the technique disclosed in Japanese Patent Publication No. 3-78197, good values of toughness and dropping performance can be obtained, but the maximum hardness Hv exceeds 290. , And a result satisfying all of these performances could not be obtained.

Comparative Example No. In No. 13, since the Ni content in the wire exceeded the upper limit of the range of the present invention, hot cracking occurred over the substantially entire length of the bead when the first layer (first pass) on the groove face side was formed. Therefore, the subsequent evaluation test was stopped.
Comparative Example No. In No. 14, since the Ni content in the wire was less than the lower limit of the range of the present invention, the dropping performance was poor. Comparative Example No. In No. 15, since the Si content in the wire exceeds the upper limit of the range of the present invention and the A value also exceeds the upper limit of the range of the present invention, the toughness is reduced and the maximum hardness is also good. could not.

Comparative Example No. No. 16 has a maximum hardness of 29 since the Mn content in the wire exceeds the upper limit of the range of the present invention.
The value exceeded 0. Comparative Example No. In No. 17, the maximum hardness exceeded 290 because the C content in the wire exceeded the upper limit of the range of the present invention. Comparative Example No. 18 has a C content and an A value in the wire of less than the lower limit of the range of the present invention, so that the maximum hardness could be sufficiently reduced.
Insufficient deoxidation reduced toughness. Comparative Example No. 19 is M
Since the n content was less than the lower limit of the range of the present invention, the toughness was lowered.

Comparative Example No. In No. 20, since the N content in the wire exceeded the upper limit of the range of the present invention, the toughness was lowered.
Comparative Example No. In Comparative Examples Nos. 21 and 22, the wire composition and the flux composition were within the scope of the present invention. 21 is A
Since the value exceeds the upper limit of the range of the present invention, the maximum hardness Hv
Became a value exceeding 290. Comparative Example No. In No. 22, since the A value was less than the lower limit of the range of the present invention, deoxidation was insufficient and toughness was lowered.

Comparative Example No. 23 is metal S in the flux
Since the content of i exceeded the upper limit of the range of the present invention, the toughness was reduced. In addition, since the A value exceeded the upper limit of the range of the present invention, the maximum hardness exceeded 290. Comparative Example No. In No. 24, since the content of metallic Si in the flux was less than the lower limit of the range of the present invention, deoxidation was insufficient and toughness was lowered. Comparative Example No. 25 is such that the content of Al ₂ O ₃ in the flux is less than the lower limit of the range of the present invention and the content of CaF ₂ and CO ₂ exceeds the upper limit of the range of the present invention.
The arc became unstable, causing slag entrainment defects and pock marks. Therefore, the subsequent evaluation test was stopped. When the other flux components were out of the range of the present invention, the welding workability was reduced, and the external shape of the bead was deteriorated.

Comparative Example No. In No. 26, since the Si in the wire was less than the lower limit of the range of the present invention, the maximum hardness could be sufficiently reduced, but the toughness was lowered due to insufficient deoxidation. Comparative Example No. In No. 27, since the B content in the flux exceeded the upper limit of the range of the present invention, the toughness was lowered.

[0053]

As described in detail above, according to the present invention,
While properly defining the chemical composition of the wire and flux during submerged arc welding, the A value calculated from the content of the specific component contained in the wire and flux is appropriately regulated, and the high Ni content Since it is not necessary to use an austenitic welding material, welding can be performed at low cost, and the toughness and dropping performance of the obtained weld metal can be improved, and the maximum hardness Hv of the weld metal can be set to a desired value. The following can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a groove shape and a size of a steel plate.

FIG. 2 is a schematic view showing a horizontal multilayer welding method.

FIG. 3 is a schematic view showing a measurement position of Vickers hardness.

[Explanation of symbols]

 11, 12; steel plate 13; groove 15a, 15b; weld metal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B23K 35/362 310 B23K 35/362 310B 310C

Claims (1)

[Claims] 1. A submerged arc welding method in which a wire and a bond flux are combined and welded, wherein MgO: 20 to 40% by weight, Al ₂ O ₃ : 15 to 35% by weight, SiO ₂ : 8 to 8% by weight based on the total weight of the flux. 20% by weight, CaF ₂ : 5 to 15% by weight, metal carbonate (in terms of CO ₂ ): 2.0 to 5.0% by weight, and metal S
i: a bond flux containing 1.0 to 2.5% by weight and containing substantially no B; C: 0.03 to 0.08% by weight, and Si: 0.02 to 0 based on the total weight of the wire .40% by weight, Mn: 0.1
0 to 0.70% by weight and Ni: 3.5 to 6.0% by weight, the balance being Fe and unavoidable impurities,
A wire in which N is regulated to 0.0070% by weight or less among the inevitable impurities, and a metal Si content in the flux by weight% [Si].
_f , when the C content in the wire is [C] _w in weight% and the Si content in the wire is [Si] _w in weight%,
Formula A = ([Si] _f + 65 × [C] _w + 15 × [Si]
A submerged arc welding method characterized in that welding is performed in combination so that the A value calculated by _w ) is 4.0 to 9.0.