JP7744306B2 - Weld metal and its manufacturing method - Google Patents

Description

The present invention relates to weld metal formed by welding high-tensile steel materials, and to a method for manufacturing weld metal that can be welded to high-tensile steel materials in a single pass.

The most commonly used structural material for high-rise buildings is a box column, a structure made by joining the ends of four flat plates at a 90° angle to create a square cross section. Traditionally, ordinary steel was used for box columns, but in recent years, steel materials have become stronger in order to meet the demand for even higher-rise buildings. For example, 780 MPa-class steel (hereinafter referred to as HT780 steel or HT780) is now being used for extremely thick steel plates with a thickness of 50 to 100 mm.

When welding corner joints in the manufacture of box columns using ordinary steel, single-pass, high-heat-input welding, such as single-pass, two-electrode submerged arc welding (SAW), is widely used. Meanwhile, Patent Document 1 describes the use of multi-pass SAW as a corner joint welding method for manufacturing box columns using, for example, HT780. Multi-pass SAW, which is less efficient than single-pass, high-heat-input welding, is chosen because joining high-tensile steels such as HT780 using single-pass, high-heat-input welding is prone to solidification cracking in the final solidified portion, making it difficult to maintain mechanical properties. Furthermore, multi-pass SAW requires the laborious work of supplying and recovering flux and removing slag, resulting in poor work efficiency and hindering the widespread use of HT780 steel box columns.

From the perspective of construction efficiency, electroslag welding (ESW) is sometimes used as a construction method for large groove sections. Like SAW, ESW allows for high heat input welding. However, while SAW is generally used for flat welding, ESW is a construction method suitable for vertical welding. Due to the characteristics described above, ESW is often used to weld the internal diaphragms of box columns. The ESW method used for internal diaphragms involves inserting a long nozzle into the welded part, which is surrounded by steel plates on the bottom and four sides, and then filling the interior with molten metal as the nozzle is pulled up; however, the dimensions that can be welded are limited by the length of the nozzle.

Meanwhile, Patent Document 2 discloses an ESW that uses a sliding backing plate. The ESW described in Patent Document 2 can be applied to welding structures with long weld lines, ensuring sound penetration and preventing deterioration of the mechanical properties of the weld metal. Patent Document 3 describes a method of welding the corners of a four-sided box column using an ESW. When using the welding methods described in Patent Documents 2 and 3, the electrode is inserted from the groove surface side into the welded part, which has one side (groove surface) open, thereby shortening the length of the nozzle that secures the electrode. In this welding method, the nozzle that guides the electrode is called a torch. Furthermore, the entire torch securing device can be moved using a lifting mechanism that uses rails or the like, making it possible to accommodate long welds.

Japanese Patent Application Publication No. 04-339592 JP 2016-215214 A Japanese Patent Application Laid-Open No. 2018-001214

By the way, ESW has the advantage that it is relatively easy to ensure the mechanical properties of the weld metal because metal refining is possible in a slag bath. However, this is an advantage when using ordinary steel materials, and when using high-tensile steel materials, it is likely that the problem of solidification cracking will arise, just like with SAW.

The present invention was made in consideration of these problems, and aims to provide weld metal obtained by welding high-tensile steel, which has excellent mechanical properties and can suppress solidification cracking, even when single-pass, large-heat-input welding is applied to HT780 steel in particular. The present invention also aims to provide a method for manufacturing weld metal that can weld high-tensile steel with high efficiency in a single pass, suppress solidification cracking, and produce weld metal with excellent mechanical properties.

The above object of the present invention is achieved by the following configuration [1] relating to the weld metal.

[1] A weld metal formed by welding high-tensile steel materials,
Ti: 0.015 mass% or less,
The P content in the weld metal is represented by [P] in mass%, the S content by [S] in mass%, the Ni content by [Ni] in mass%, the C content by [C] in mass%, the Mn content by [Mn] in mass%, the Cu content by [Cu] in mass%, the Si content by [Si] in mass%, the Cr content by [Cr] in mass%, the Mo content by [Mo] in mass%, the V content by [V] in mass%, and the B content by [B] in mass%,
The value obtained by the formula A: [P] + [S] is (A),
The value obtained by the formula D1: [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D1),
The value obtained by the formula D2: 40-4 × [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D2),
The value obtained by the formula D3: 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D3),
When the value obtained by the formula E: [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 × [B] is represented as (E),
In the range where [Ni] is less than 7.0, (A) × (D1) is 0.1 or less;
In the range of 7.0≦[Ni]<10.0, (A)×(D2) is 0.1 or less;
In the range of [Ni]≧10.0, (A)×(D3) is 0.1 or less,
A weld metal characterized in that (E) is 0.25 or more.

Furthermore, a preferred embodiment of the present invention relating to weld metal relates to [2] below.

[2] The weld metal described in [1], characterized by containing REM: 0.005 mass% or more and 0.050 mass% or less.

The above object of the present invention relates to the following [3], which relates to a method for producing weld metal.

[3] A method for producing a weld metal produced by one-pass welding of high-tensile steel material,
The weld metal is
Ti: 0.015 mass% or less,
The P content in the weld metal is represented by [P] in mass%, the S content by [S] in mass%, the Ni content by [Ni] in mass%, the C content by [C] in mass%, the Mn content by [Mn] in mass%, the Cu content by [Cu] in mass%, the Si content by [Si] in mass%, the Cr content by [Cr] in mass% , the Mo content by [Mo], the V content by [V] in mass% , and the B content by [B] in mass% ,
The value obtained by the formula A: [P] + [S] is (A),
The value obtained by the formula D1: [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D1),
The value obtained by the formula D2: 40-4 × [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D2),
The value obtained by the formula D3: 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D3) ,
When the value obtained by the formula E: [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 × [B] is represented as (E),
In the range where [Ni] is less than 7.0, (A) × (D1) is 0.1 or less;
In the range of 7.0≦[Ni]<10.0, (A)×(D2) is 0.1 or less;
In the range of [Ni]≧10.0, (A)×(D3) is 0.1 or less,
(E) is 0.25 or more.

Furthermore, preferred embodiments of the present invention relating to the method for manufacturing weld metal relate to the following [4] to [10].

[4] The method for producing weld metal described in [3], characterized in that the weld metal is produced by vertical position electroslag welding.

[5] A method for producing weld metal as described in [4], characterized in that welding is performed within a groove made of the high-tensile steel material while weaving the tip position of the electrode wire within a plane approximately perpendicular to the weld line direction.

[6] A method for producing weld metal according to any one of [3] to [5], characterized in that welding is performed using multiple electrode wires.

[7] Using multiple electrode wires,
The method for producing a weld metal according to [4] or [5], characterized in that at least one of the plurality of electrode wires is a fixed electrode that is stationary within a plane in a direction substantially perpendicular to the weld line direction.

[8] A method for producing weld metal according to any one of [4], [5], and [7], characterized in that at least one of the plurality of electrode wires is powered by a DC power source and at least one of the plurality of electrode wires is powered by an AC power source.

[9] The method for producing weld metal described in [8], characterized in that the EN ratio in the electrode wire using the AC power source is 30% or more and 70% or less.

[10] The method for producing weld metal described in [7], wherein the current waveform of the fixed electrode is a pulse current waveform.

According to the present invention, it is possible to provide a weld metal that has excellent mechanical properties and can suppress solidification cracking, even when one-pass large heat input welding is applied to high-tensile steel materials.
Furthermore, according to the present invention, it is possible to provide a method for manufacturing a weld metal that can weld high-tensile steel materials with high efficiency in one pass, suppress solidification cracking, and obtain a weld metal having excellent mechanical properties.

FIG. 1 is a schematic diagram showing an example of the configuration of a welding system according to this embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of a welding device using ESW used in this embodiment when applied to a butt joint. FIG. 3 is a block diagram showing the functional configuration of the traveling carriage control unit. FIG. 4 is a flowchart showing the control process of the traveling carriage control unit. FIG. 5 is a side cross-sectional view that schematically shows an example of a method for producing a weld metal when welding a corner of a box column using ESW. 6A is a top cross-sectional view schematically illustrating an example of the tip position of the welding wire illustrated in FIG. 5. FIG. FIG. 6B is a top cross-sectional view schematically showing another example of the tip position of the welding wire shown in FIG. 5 . 6C is a top cross-sectional view schematically showing yet another example of the tip position of the welding wire shown in FIG. 5. FIG. FIG. 7 is a side cross-sectional view that schematically shows another example of a method for producing a weld metal when welding corners of a box column using ESW. FIG. 8 is a top cross-sectional view schematically showing an example of the tip position of the welding wire shown in FIG. FIG. 9 is a side cross-sectional view that schematically shows yet another example of a method for producing a weld metal when welding corners of a box column using ESW. FIG. 10 is a schematic diagram showing the method of manufacturing the weld metal applied to the invention examples and comparative examples.

The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, they noticed that the Ni content in the weld metal has a significant effect on solidification cracking, and discovered parameters that can suppress solidification cracking depending on the Ni content. Specifically, they organized solidification cracking resistance using Formula A, which represents the content of impurity elements that are harmful to solidification cracking, and Formulas D1, D2, and D3, which are derived from elements that make solidification cracking more likely to occur depending on the Ni content. Furthermore, they found that solidification cracking resistance can be improved by controlling the value obtained by multiplying Formula A by Formulas D1, D2, and D3 depending on the Ni content.
The present invention was made based on these findings.

Embodiments of the present invention are described in detail below. Note that the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit and scope of the present invention.

<Weld metal>
The weld metal according to this embodiment is a weld metal formed by welding high-tensile steel materials. Below, values calculated using the contents of components contained in the weld metal according to this embodiment, as well as preferred ranges and reasons for limiting the contents of these components, will be specifically described.

In the following description, [P] is the P content in the weld metal expressed in mass%, [S] is the S content in the weld metal expressed in mass%, [Ni] is the Ni content in the weld metal expressed in mass%, [C] is the C content in the weld metal expressed in mass%, [Mn] is the Mn content in the weld metal expressed in mass%, [Cu] is the Cu content in the weld metal expressed in mass%, [Si] is the Si content in the weld metal expressed in mass%, [Cr] is the Cr content in the weld metal expressed in mass%, [Mo] is the Mo content in the weld metal expressed in mass%, [V] is the V content in the weld metal expressed in mass%, and [B] is the B content in the weld metal expressed in mass%.

Furthermore, formula A, formula D1, formula D2, formula D3, and formula E, which use the contents of each element, are defined as follows:
Formula A: [P] + [S]
Formula D1: [Ni]+30×[C]+0.5×[Mn]+0.25×[Cu]
Formula D2: 40-4×[Ni]+30×[C]+0.5×[Mn]+0.25×[Cu]
Formula D3: 30×[C]+0.5×[Mn]+0.25×[Cu]
Formula E: [C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5×[B]

Furthermore, the value obtained by formula A will be represented as (A), the value obtained by formula D1 as (D1), the value obtained by formula D2 as (D2), the value obtained by formula D3 as (D3), and the value obtained by formula E as (E).

((A) × (D1) is 0.1 or less in the range where [Ni] is less than 7.0)
The P and S elements in formula A are well known as impurity elements in metals, and are harmful to solidification cracking because they segregate in the final solidified portion, lowering the melting point of the residual liquid phase and weakening the grain boundaries. In other words, the larger the value of (A), the more likely solidification cracking occurs.
Furthermore, in the range where [Ni]<7.0, formula D1 indicates the ease of austenite formation. In austenite, the solid solubility limit of impurity elements such as P and S is lower than that in ferrite. Therefore, it is known that the closer the solidification form is to austenite single phase, the more the segregation of impurity elements in the final solidified portion is promoted, making solidification cracking more likely to occur. In other words, the larger the value of (D1), the more likely the steel is to undergo solidification cracking.

In the range where [Ni] < 7.0, if (A) x (D1) exceeds 0.1, solidification cracking is more likely to occur in the weld metal when high-tensile steel is welded in a single pass with a large heat input. Therefore, (A) x (D1) should be 0.1 or less, and preferably 0.09 or less.

[(A) × (D2) is 0.1 or less in the range of 7.0≦[Ni]<10.0]
Ni is known to be an element that easily forms austenite, and generally, as the Ni content in the weld metal increases, cracking becomes more likely to occur. On the other hand, Ni is also an element that changes the Ca yield and suppresses the aggregation of inclusions. The final location of inclusions is the microsegregation zone, which is the solidification cracking site, and reducing coarse inclusions in the microsegregation zone can have the effect of improving the solidification cracking resistance of the weld metal. Therefore, in this embodiment, the occurrence of solidification cracking can be suppressed by adjusting the Ni content as well as the austenite.
In the range of 7.0≦[Ni]<10.0, the higher the Ni content, the smaller the effect of Ni on solidification cracking. Therefore, the above formula (D2) was derived as a parameter that serves as an indicator of the occurrence of solidification cracking.

In the range of 7.0≦[Ni]<10.0, if (A) × (D2) exceeds 0.1, solidification cracking is more likely to occur in the weld metal when high-tensile steel is welded in a single pass with a large heat input. Therefore, (A) × (D2) should be 0.1 or less, and preferably 0.09 or less.

((A) × (D3) is 0.1 or less in the range of [Ni] ≧ 10.0)
In the range of [Ni]≧10.0, the influence of Ni on solidification cracking disappears, and therefore the above formula (D3) was derived as a parameter that serves as an index for the occurrence of solidification cracking.
In the range of [Ni]≧10.0, if (A)×(D3) exceeds 0.1, solidification cracking is likely to occur in the weld metal when high-tensile steel is welded with a large heat input in one pass. Therefore, (A)×(D3) is set to 0.1 or less, and preferably 0.09 or less.

[E]: 0.25 or more]
The formula E is a parameter that correlates with the strength of the weld metal, and the larger the value of [E], the higher the strength tends to be. In this embodiment, since the welding of high-tensile steel materials is the target, the strength of the weld must also be sufficiently improved. If [E] is less than 0.25, the desired strength cannot be obtained in the weld metal. Therefore, [E] is set to 0.25 or more, and preferably 0.28 or more.

[Ti: 0.015 mass% or less (including 0 mass%)]
Excessive Ti content in the weld metal can produce harmful coarse precipitates, which can reduce grain boundary strength. As a result, solidification cracking becomes more likely to occur. If the Ti content in the weld metal exceeds 0.015 mass%, the occurrence of solidification cracking cannot be suppressed. Therefore, the Ti content in the weld metal is set to 0.015 mass% or less, and preferably 0.010 mass% or less.

[REM: 0.005% by mass or more and 0.050% by mass or less]
Rare earth metals (REM) are not essential components in the weld metal according to this embodiment, but may be contained in the weld metal to improve the toughness of the weld metal. If the total content of REM in the weld metal is 0.005 mass % or more, the effect of improving the toughness of the weld metal can be obtained.
Therefore, when REM is contained in the weld metal, the total REM content is preferably 0.005 mass % or more, more preferably 0.007 mass % or more, and even more preferably 0.008 mass % or more.
Note that Ni, which will be described later, also has the effect of improving the toughness of the weld metal. However, regardless of the Ni content, in order to obtain the effect of improving toughness using REM alone, it is particularly preferable that the total amount of REM in the weld metal be 0.015 mass % or more.

On the other hand, if the REM content in the weld metal is excessive, it becomes difficult to obtain the desired toughness of the weld metal. Therefore, when REM is contained in the weld metal, the total REM content is preferably 0.050 mass% or less, more preferably 0.035 mass% or less, even more preferably 0.020 mass% or less, and particularly preferably 0.018 mass% or less.
Examples of REM include Y and lanthanides such as La and Ce, and in this embodiment, the REM analysis value is the total content of La and Ce because they are contained in high proportions in the applicable alloy. In addition to these elements, Y, Pr, Nd, etc. may be used alone or in combination.

In this embodiment, the content of each element in the weld metal is not particularly specified as long as the above (A) x (D1), (A) x (D2), (A) x (D3), and (E) and the Ti content in the weld metal are within the above ranges. However, the preferred content of each element is described below.

[Ni: 22.5% by mass or less]
As described above, when the Ni content in the weld metal increases, cracking becomes more likely to occur. However, by appropriately controlling the value obtained from the formula according to the Ni content and adjusting the austenite, it is possible to suppress the occurrence of solidification cracking even when the Ni content in the weld metal is increased.
In this embodiment, it is not necessary for the weld metal to contain Ni, and the Ni content may be 0 mass %. However, since the Ni content in the weld metal is an effective component for improving strength even in small amounts, the Ni content in the weld metal is preferably more than 0 mass %, and more preferably 3.5 mass % or more.

Ni is a component that has the effect of improving the toughness of the weld metal together with REM. However, in order to obtain the effect of improving toughness using Ni alone, regardless of the REM content, it is more preferable that the Ni content in the weld metal be 4.75 mass% or more.
On the other hand, if the Ni content in the weld metal is 22.5 mass% or less, a decrease in solidification cracking resistance can be suppressed. Therefore, the Ni content in the weld metal is preferably 22.5 mass% or less, and more preferably 20.0 mass% or less.

[C: 0.13% by mass or less]
C is a component that has the effect of improving the strength of the weld metal. If the C content in the weld metal is 0.13 mass% or less, the strength of the weld metal can be improved without causing weld cracks. Therefore, the C content in the weld metal is preferably 0.13 mass% or less, more preferably 0.10 mass% or less, and even more preferably 0.07 mass% or less.

[Si: 1.00% by mass or less]
Si is a component that can ensure the strength of the weld metal and also has a deoxidizing effect. If the Si content in the weld metal is 1.00 mass% or less, the strength of the weld metal can be improved without reducing the toughness of the weld metal. Therefore, the Si content in the weld metal is preferably 1.00 mass% or less, and more preferably 0.60 mass% or less.

[Mn: 2.25% by mass or less]
Mn is a component that can ensure the strength of the weld metal and has a deoxidizing effect. If the Mn content in the weld metal is 2.25 mass% or less, the strength of the weld metal can be improved without reducing the toughness of the weld metal. Therefore, the Mn content in the weld metal is preferably 2.25 mass% or less, and more preferably 1.80 mass% or less.

[P: 0.030% by mass or less]
P is an element that reduces the cracking resistance and mechanical properties of the weld metal. If the P content in the weld metal is 0.030 mass% or less, it is possible to prevent an extreme decrease in cracking resistance and mechanical properties. Therefore, the P content in the weld metal is preferably 0.030 mass% or less, and more preferably 0.025 mass% or less.

[S: 0.030% by mass or less]
S is an element that reduces the cracking resistance of the weld metal. If the S content in the weld metal is 0.030 mass% or less, an extreme decrease in cracking resistance can be suppressed. Therefore, the S content in the weld metal is preferably 0.030 mass% or less, and more preferably 0.025 mass% or less.

[Cu: 0.50% by mass or less]
Cu is a component that has the effect of improving the strength of the weld metal. If the Cu content in the weld metal is 0.50 mass% or less, the strength of the weld metal can be improved without causing hot cracking. Therefore, the Cu content in the weld metal is preferably 0.50 mass% or less, and more preferably 0.40 mass% or less.

[Cr: 1.00% by mass or less]
Cr is a component that has the effect of ensuring the desired strength of the weld metal. If the Cr content in the weld metal is 1.00 mass% or less, the strength of the weld metal can be improved without reducing the toughness of the weld metal. Therefore, the Cr content in the weld metal is preferably 1.00 mass% or less, and more preferably 0.60 mass% or less.

[V: 0.08% by mass or less]
V is a component that has the effect of ensuring the desired strength of the weld metal. If the V content in the weld metal is 0.08 mass% or less, the strength of the weld metal can be improved without reducing the toughness of the weld metal. Therefore, the V content in the weld metal is preferably 0.08 mass% or less, and more preferably 0.05 mass% or less.

[Mo: 2.50% by mass or less]
Mo is a component that has the effect of ensuring the strength of the weld metal at a desired level. If the Mo content in the weld metal is 2.50 mass% or less, the strength can be improved without reducing the toughness of the weld metal. Therefore, the Mo content in the weld metal is preferably 2.50 mass% or less, more preferably 2.30 mass% or less, and even more preferably 2.00 mass% or less.

[B: 0.050% by mass or less]
B is a component that has the effect of ensuring the strength of the weld metal at a desired level. If the B content in the weld metal is 0.050 mass% or less, the desired toughness can be ensured without reducing crack resistance. Therefore, the B content in the weld metal is preferably 0.050 mass% or less, and more preferably 0.030 mass% or less.

[Other components: Fe and inevitable impurities]
In this embodiment, the remainder excluding the above elements is preferably Fe and unavoidable impurities. "Impurities" refers to elements that are not intentionally added, and examples of elements other than the above include O, N, Sn, Co, Sb, As, Zr, Li, and Bi. The impurity contents in the weld metal are 0.02 mass% or less for O, 0.02 mass% or less for N, 0.02 mass% or less for Sn, Sb, As, Zr, Li, and Bi, respectively, and 0.30 mass% or less for Co. The total content of the above impurities is preferably 0.50 mass% or less, more preferably 0.30 mass% or less. The upper limit of the Co content is high because Ni and Co have similar properties and are difficult to separate, resulting in the Ni containing a relatively large amount of Co as an impurity. Because Co has properties similar to Ni, Co alone does not cause changes in the weld metal properties at this level.

In this embodiment, the weld metal is obtained by welding high-tensile steel materials, and as long as the composition of the weld metal and the relationship between each component are as described above, the welding method (method for producing weld metal), welding materials, etc. are not particularly limited. An example of a method for producing weld metal is described below in detail.

<Method of manufacturing weld metal>
The method for producing a weld metal according to this embodiment is a method for producing a weld metal by one pass on a high-tensile steel material, and the weld metal is as described above.

(Material to be welded)
In the weld metal manufacturing method according to this embodiment, the material to be welded is a high-tensile steel material. As described above, when welding ordinary steel material, the occurrence of solidification cracking can be easily suppressed by using ESW, but when high-tensile steel material is welded with a large heat input, solidification cracking is more likely to occur. In this embodiment, by adjusting the composition of the weld metal, the occurrence of solidification cracking can be suppressed even in one-pass high-heat-input welding, and therefore high-tensile steel material can be welded with high efficiency.

The high-tensile steel material to be welded preferably has a strength of 780 N/ ^mm2 or more and 930 N/mm2 or ^less , and a Ni content of 4.5 mass% or less relative to the total mass of the steel material. The Ni content of the total mass of the steel material is more preferably 3.5 mass% or less, even more preferably 3.0 mass% or less, and particularly preferably 2.5 mass% or less. In the present invention, the thickness of the material to be welded is not particularly limited, but it is preferably a thick steel plate that can benefit from the improved efficiency of single-pass high-heat-input welding and that can exhibit the advantage of suppressing the occurrence of solidification cracking even when high-heat-input welding is used. Specifically, it is preferable to target a thick steel plate with a groove thickness (plate thickness) of, for example, 50 mm or more and 100 mm or less.

The specific welding method used in the weld metal manufacturing method is not particularly limited, but as a welding method that applies this embodiment, which can suppress the occurrence of solidification cracking even with high heat input welding in a single pass, it is preferable to use vertical position ESW, which can achieve highly efficient welding in a single pass. As an example, a welding method using vertical position ESW is described below.

An overall overview of the welding system 500 used in this embodiment will be described. Figure 1 is a schematic diagram showing an example configuration of the welding system 500 according to this embodiment. The welding system 500 includes a welding device 100, a welding power source 200, a wire feeder 300, and a control box 400. The welding device 100 and the other devices are connected via various cables, such as a power cable and a signal cable.

(welding equipment)
2 is a schematic diagram showing an example of the configuration of a welding device using ESW used in this embodiment when applied to a butt joint. The welding device 100 is an electroslag welding device using ESW.

Figure 2 shows a coordinate system consisting of three axes: X, Y, and Z. In the following explanation, the axial directions shown in each figure correspond to each other. Arrow Z indicates the direction along the weld line of the base material 3, i.e., the up-down direction. Arrow X indicates the thickness direction of the base material 3. Arrow Y indicates the direction in which the pair of base materials are aligned, i.e., the horizontal direction along the surface of the base material 3. Therefore, "up" refers to the upper side relative to the plane of Figure 2, and "down" refers to the lower side relative to the plane of Figure 2. Furthermore, "front" refers to the left side relative to the plane of Figure 2, and "rear" refers to the right side relative to the plane of Figure 2. Assuming that a sliding welding copper pad 30 (hereinafter also referred to as "copper pad 30") is positioned on the surface of the base material 3, arrow Z refers to the longitudinal direction of the sliding welding copper pad 30, i.e., the longitudinal direction of the pad body. Arrow X refers to the thickness direction of the sliding welding copper pad 30, i.e., the thickness direction of the pad body. Arrow Y indicates the width direction of the sliding welding copper backing 30, i.e., the width direction of the backing body.

As shown in FIG. 2, the welding apparatus 100 used in this embodiment includes a backing metal 1, a sliding welding copper backing metal 30, a welding torch 4, a molten slag bath detector 13, a flux supply device 14, a flux supply control device 15, a traveling carriage 16, and a traveling carriage control device 17. Furthermore, although not shown in FIG. 2, the welding apparatus 100 also includes front-rear and left-right sliders for adjusting the position of the welding torch 4 mounted on the traveling carriage 16, a slider for adjusting the left-right position of the sliding welding copper backing metal 30, and traveling rails. Note that "front-rear" here refers to the X-axis direction, and "left-right" refers to the Y-axis direction. These sliders are preferably electrically operated using a motor (not shown), but are not limited to electrical operation and may be configured to be manually operated.

In the welding device 100, a fixed backing metal 1 is placed on the back side of the groove between a pair of base materials 3 made of high-tensile steel, and a copper backing metal 30 is placed on the front side of the groove. The backing metal 1 may be copper, a steel material that is integrated with the weld metal, or a backing material made of heat-resistant ceramic. The front-side copper backing metal 30 is a copper backing metal that slides up and down and is cooled, for example, by water cooling. While this embodiment uses copper as the material for the sliding welding copper backing metal 30, it is not limited to copper. Generally, any material with good thermal conductivity can be used for the sliding backing metal. For convenience, in this embodiment, the side where the fixed backing metal 1 is placed is referred to as the "back side of the groove," and the side where the sliding welding copper backing metal 30 is placed is referred to as the "front side of the groove." However, sliding copper backing metals 30 may be placed on both sides of the groove.

The welding torch 4 supplies a welding current 8 supplied from the welding power source 200 to the welding wire (electrode wire) 6 to weld the base material 3. The welding torch 4 also has a contact tip 5, which guides the welding wire 6 and supplies the welding current 8 to the welding wire 6.

A welding wire 6 is fed from the tip of the contact tip 5 of the welding torch 4 into the groove surrounded by the base material 3, backing metal 1, and copper backing metal 30, and is then fed into the molten slag bath 7 formed in the groove. A welding current 8 flows from the welding wire 6 through the molten slag bath 7 to the base material 3. At this time, Joule heat is generated by the welding current 8 flowing through the welding wire 6 and molten slag bath 7, and welding progresses while melting the welding wire 6 and base material 3, forming molten metal 9.

The molten slag bath detector 13 detects the position of the molten slag bath 7. The flux supply device 14 supplies flux 12 to the molten slag bath 7. Since the flux 12 melts to form molten slag, supplying the flux 12 increases the amount of the molten slag bath 7.

The flux supply control device 15 controls the operation of the flux supply device 14 and adjusts the amount of flux 12 supplied to the molten slag bath 7. If the molten slag bath detector 13 determines that the molten slag bath 7 has not reached the appropriate position, the flux supply control device 15 controls the flux supply device 14 to supply flux 12. On the other hand, if the molten slag bath detector 13 determines that the molten slag bath 7 has reached the appropriate position, the flux supply control device 15 controls the flux supply device 14 to stop supplying flux 12. In this way, the flux supply device 14 supplies flux 12 and adjusts the depth of the molten slag bath 7 according to the detection results of the molten slag bath detector 13.

The reason for this adjustment is that as welding progresses, the molten metal 9 cools to form the weld metal 10. A portion of the molten slag bath 7 forms a molten slag layer between the backing metal 1 and the weld metal 10, and between the copper backing metal 30 and the weld metal 10 (if a copper backing metal 1 is used). This molten slag layer cools to form solidified slag 11. As welding progresses, the molten slag is consumed, and the depth Ls of the molten slag bath 7 decreases. The amount of solidified slag 11 covering the bead surface varies depending on the bead width and the width of the welding groove. The amount of solidified slag 11 also varies depending on the degree of adhesion between the backing metal 1 or copper backing metal 30 and the workpiece (hereinafter also referred to as the workpiece to be welded or the base metal) and the cooling state of the backing metal 1 or copper backing metal 30. Therefore, the amount of solidified slag 11 is not constant, and the amount of flux 12 supplied must also be adjusted to maintain a constant depth Ls of the molten slag bath 7. However, because the depth Ls of the molten slag bath 7 is unknown, if the amount of flux 12 supplied is inappropriate, the depth Ls of the molten slag bath 7 will fluctuate.

Therefore, in this embodiment, in addition to supplying flux 12 using the molten slag bath detector 13, control is performed to keep the depth Ls of the molten slag bath 7 constant. Here, "constant" does not necessarily mean that the depth Ls of the molten slag bath 7 always has a single value, but also means that the depth Ls of the molten slag bath 7 may exhibit a value within a certain range, taking into account error. In other words, the depth Ls of the molten slag bath 7 is controlled to be maintained within a predetermined depth range.

The first requirement for maintaining a constant depth Ls of the molten slag bath 7 is to control the welding wire length Ld (hereinafter referred to as the dry extension Ld) from the tip of the contact tip 5 to the top surface of the molten slag bath 7 to a predetermined length. The second requirement for maintaining a constant depth Ls of the molten slag bath 7 is for the traveling carriage control device 17 to control the traveling speed of the traveling carriage 16 so that the welding current 8 has a predetermined relationship with a reference current value determined according to the wire feed speed, i.e., so that the reference current value and the welding current 8 are equal. At a given wire feed speed, there is a correlation between (Ld + Ls) and the welding current 8. By having the traveling carriage control device 17 control the traveling speed of the traveling carriage 16 so that the reference current value and the welding current 8 are equal, (Ld + Ls) is kept constant.

The dry extension Ld can be controlled by detecting the molten slag bath 7 with the molten slag bath detector 13. In the above, the dry extension Ld is defined as the distance from the top surface of the molten slag bath 7 to the tip of the contact tip 5, but this assumes that the tip of the contact tip 5 is generally the current-carrying position between the welding wire 6 and the contact tip 5. For example, if the tip of the contact tip 5 is protected by ceramic or the like and the current-carrying portion between the welding wire 6 and the contact tip 5 is located above the tip of the contact tip 5, the position of this current-carrying portion will be the basis for determining the dry extension Ld.

(Traveling cart)
The traveling carriage 16 is configured to carry the sliding welding copper backing 30, the welding torch 4, the molten slag bath detector 13, the flux supply device 14, the flux supply control device 15, the traveling carriage control device 17, and the lifting/lowering drive unit 19. The traveling carriage 16 moves upward on rails (not shown), i.e., in the Z direction, while welding, thereby raising the welding device 100. That is, the traveling carriage 16 moves in the Z direction together with the sliding welding copper backing 30, the welding torch 4, the molten slag bath detector 13, the flux supply device 14, the flux supply control device 15, the traveling carriage control device 17, and the lifting/lowering drive unit 19, so that the relative positions of each component do not change except for the parts that can be adjusted by the sliders. As the traveling carriage 16 rises, vertical welding is performed in the upward direction.

The traveling carriage control device 17 controls the lifting drive unit 19 provided on the traveling carriage 16 to increase or decrease the traveling speed (hereinafter also referred to as the lifting speed or the rising speed) of the traveling carriage 16, thereby controlling the operation of the traveling carriage 16. The flux supply control device 15 controls the flux supply amount by deriving a control variable based on the detection value detected by the molten slag bath detector 13 and outputting it to the flux supply device 14. The lifting drive unit 19 drives the traveling carriage 16 based on the control signal from the traveling carriage control device 17.

(Sliding copper pad for welding)
The sliding welding copper pad 30 is placed at the welding point of the workpiece, i.e., on one side of the groove surface, and slides on the groove surface in accordance with the lifting and lowering movement of the welding device 100 .

(Welding power source and wire feeder)
The welding power source 200 is connected to the welding device 100 via a power cable (not shown) so as to energize the welding wire 6, which is a consumable electrode. Furthermore, the welding power source 200 is connected to a workpiece via a power cable (not shown). A relay box (not shown) may be provided as an interface between the welding power source 200 and the welding device 100. The relay box may be equipped with various control cables, such as those for supplying power to the traveling carriage 16, and an emergency stop switch. The provision of the relay box, for example, facilitates cable removal, contributing to the efficiency of the welding operation. The relay box may also be equipped with a mechanism for installing a removable memory, such as an SD card, and records of welding operations, such as the welding current and arc voltage, may be written to the memory. The welding power source 200 and the wire feeder 300 for feeding the welding wire 6 are connected by a signal line, either directly or via the relay box, to control the feed speed of the welding wire 6. When using multiple electrodes, a welding power source may be provided for each electrode, multiple welding power sources may be used for one electrode, or one welding power source may be used for multiple electrodes.

(operation box)
The operation box 400 outputs various commands to the welding device 100 based on operations by an operator. Examples of items that can be operated using the operation box 400 include construction information such as the welding method and welding materials, and welding conditions such as the welding current, arc voltage, wire feed speed, and extension length. The operation box 400 is equipped with a UI (User Interface) for inputting the operable items. In addition, the operation box 400 may be configured to be capable of monitoring the welding current, arc voltage, etc.

In this embodiment, the welding device 100 is configured to include a control device that performs various processes. However, a control device configured to perform some or all of the processes of the welding device 100 described above may be provided separately from the welding device 100. In this case, the control device may be configured to be connected to the welding system 500 or the welding device 100 via a wired or wireless network (not shown).

The control device provided separately from the welding device 100 may be realized, for example, by an information processing device comprising a control unit, memory unit, and input/output unit (not shown). The control unit may be composed of a CPU (Central Processing Unit), MPU (Micro Processing Unit), DSP (Digital Single Processor), or dedicated circuitry. The memory unit is composed of volatile and non-volatile storage media such as an HDD (Hard Disk Drive), ROM (Read Only Memory), or RAM (Random Access Memory), and is capable of inputting and outputting various information in response to instructions from the control unit. The input/output unit is capable of inputting and outputting various information from and to the outside. The input/output unit is composed of a display device such as an LCD display, and outputs various information to the worker in response to instructions from the control unit. There are no particular limitations on the output method used by the input/output unit, and it may, for example, be an auditory output using voice or a visual notification using a screen output. The input/output unit may also be a network interface with communication capabilities, and may perform output operations by transmitting data to an external device (not shown) via a network (not shown).

(Functional configuration for control)
In this embodiment, the set value of the extension length or the set value of the feed speed is kept constant, and the welding operation is stabilized by controlling the rising speed based on the difference between the detected welding current and the preset target value of the welding current.

Figure 3 is a diagram illustrating an example of the functional configuration of the traveling bogie control device 17. Note that Figure 3 only shows the parts corresponding to the functions related to this embodiment, and parts related to other controls are omitted to simplify the explanation.

The traveling bogie control device 17 is configured to include a parameter management unit 441, a reference value calculation unit 442, and a control amount calculation unit 443. Note that the parameter management unit 441, the reference value calculation unit 442, and the control amount calculation unit 443 are not necessarily limited to configurations provided in the traveling bogie control device 17; for example, some or all of their functions may be realized by the operation box 400 or an external information processing device (not shown).

In this embodiment, the parameter management unit 441 has at least one database (hereinafter also referred to as DB), and this DB is configured to contain data associating at least construction information and coefficient information. Construction information 410 includes, for example, information such as welding method 411, welding material 412, placement of sliding copper backing, material of backing metal, workpiece material, workpiece thickness, and groove shape. In this embodiment, at least the items of welding method 411 and welding material 412 are included. Note that welding material 412 is information on a combination of welding wire and flux. Furthermore, coefficient information indicates coefficients related to functions described below, and in this embodiment, at least two or more coefficients are included.

In this embodiment, construction information 410, which includes at least the items welding method 411 and welding material 412, is associated with coefficient information containing at least two or more coefficients. The at least two or more coefficients associated with each combination of welding method and welding material are set so that a constant relationship is maintained even when the values of at least the feed speed, welding current, and extension length change.

The reference value calculation unit 442 uses a predefined function to calculate the reference value used by the control amount calculation unit 443, using at least the specified welding condition setting information 420 and information from the parameter management unit 441 as input. Note that the function according to this embodiment may be predefined by the reference value calculation unit 442, or may be configured to call up a corresponding function from a memory unit depending on the welding method specified as the construction information 410.

The welding condition setting information 420 includes, for example, conditions related to welding current 421, feed speed 422, extension length 423, arc voltage, and weaving (also known as oscillation). When specifying the welding current, it may be simply entered as amperes (A), or it may be entered as the current density, which is the welding current value per unit area. Examples of oscillation-related conditions include oscillation length and oscillation period. In this embodiment, the welding conditions are set to at least two of the welding current, feed speed, and extension length. The reference value item calculated by the reference value calculation unit 442 is derived from one of the welding conditions based on a predefined function. Therefore, in this embodiment, the reference value is not limited to the welding current, and reference values for other items, such as the feed speed and extension length, can be calculated, allowing for highly flexible control.

The control quantity calculation unit 443 outputs a control quantity based on a preset control formula or table for the reference value output from the reference value calculation unit 442. The control formula or table may be stored in advance in the control quantity calculation unit 443, or the corresponding control formula or table may be called from a memory unit in response to specified conditions. The control quantity calculation unit 443 also acquires measured values of the actual operation of the lift drive unit 19 and other components from the measurement unit 430 and uses this information to calculate the control quantity. For example, PI control (proportional-integral control) may be performed using the measured values from the measurement unit 430 as feedback. There is no particular restriction on the object controlled by the control quantity calculated here. For example, if it is desired to correct the lift speed, the control quantity may be input to the lift drive unit 19. If it is desired to control welding conditions such as the welding current or arc voltage, the control quantity may be input to the welding power source 200. Furthermore, the controlled object does not have to be limited to one; for example, the control amount calculation unit 443 may use a control formula to output control amounts for multiple elements, such as the rising speed and welding current.

(Control Method)
While the present embodiment focuses on the lift control of the traveling carriage 16, the welding power source 200 and the wire feeder 300 can also be controlled in a similar manner. While FIG. 3 illustrates the lift drive unit 19, the welding power source 200, and the wire feeder 300 as destinations to which the controlled variable is output from the traveling carriage control device 17, this is not limiting. For example, the controlled variable calculation unit 443 may be configured to output information regarding the controlled variable to the flux supply control device 15. In this case, the flux supply control device 15 may calculate the amount of flux 12 to be supplied by the flux supply device 14 based on the controlled variable received by the controlled variable calculation unit 443 and the detection result of the molten slag bath detector 13. More specifically, the amount of flux 12 to be supplied may be calculated so that the extension length is a value set in the welding conditions or a reference value calculated by the reference value calculation unit 442. Furthermore, a method of increasing or decreasing the controlled variable calculated by the calculation unit relative to a reference flux supply amount depending on the groove cross-sectional area may also be possible.

The processing flow according to this embodiment will be explained using Figure 4. This processing flow may be implemented by a control unit (not shown) provided in the traveling bogie control device 17 in this embodiment reading and executing a program stored in a memory unit (not shown). To simplify the explanation, the processing will be collectively described as being performed by the traveling bogie control device 17.

In S701, the traveling carriage control device 17 acquires construction information from the worker via the operation box 400. Here, the construction information includes the specification of the welding method and welding materials. The construction information may be specified, for example, by selecting an option from multiple options. Alternatively, multiple modes corresponding to the setting values of each item of the construction information may be defined in advance, allowing the worker to select from these.

At S702, the traveling carriage control device 17 receives the setting values for each welding condition item from the operator via the operation box 400. Here, the welding conditions used are welding current, feed speed, and extension length, and the system receives specification of values for two of these items. Note that the extension length referred to here may also be referred to as dry extension in the case of ESW. Furthermore, the number of items that must be entered is determined based on the total number of items used as welding conditions. Therefore, if the setting values for the required items have not been entered, the system may be configured to notify the operator to enter them.

In S703, the traveling bogie control device 17 uses the construction information values acquired in S701 and a pre-defined database to determine coefficient information, which is a parameter for calculating the reference value.

In S704, the traveling carriage control device 17 uses the values of the construction information acquired in S701 and a predefined database to determine constants, which are parameters used by the control amount calculation unit 443 to calculate the control amount of the lift drive unit 19. Examples of constants include gain numbers. When determining the gain number, a predefined fixed value may be used, or a relationship between certain conditions and gain numbers may be established in the database, and the gain number may be read for each condition. For example, if a relationship between the feed rate and gain number is established, an appropriate gain number is determined according to the set feed rate. This step may be omitted depending on the content of the construction information set in S701. In that case, parameter notification from the parameter management unit 441 shown in FIG. 3 to the control amount calculation unit 443 is omitted. The constants may also be determined by further considering the welding conditions acquired in S702.

In S705, the traveling carriage control device 17 sets the coefficient information determined in S703 as each coefficient of a predefined function. At this time, the traveling carriage control device 17 may be configured to determine the function to be used from multiple predefined functions based on the construction information acquired in S701. For example, in this embodiment, the following formula (1) can be used as the function for calculating the reference value.

However, in the above formula (1),
W _f : Feed speed I : Welding current Ext : Extension length
a, b, c, d: Coefficients specified using DB.

As shown in formula (1), there is a correlation between the items of the welding conditions. For example, if the feed speed and extension length are specified as welding conditions, the reference values of the welding conditions can be calculated. In other words, formulas are specified corresponding to the items entered in S702, and reference values can be calculated for items that have not been entered. In addition, in the case of formula (1), the constants a, b, c, and d correspond to the items of coefficient information determined in S703.

In S706, the traveling carriage control device 17 calculates the reference values for the undetermined welding conditions by inputting the welding conditions acquired in S702 into the function for which the coefficient information was set in S705.

In S707, the traveling carriage control device 17 acquires the actual measurement values for the current operating conditions. For example, the actual measurement values when operating under the welding conditions acquired in S702 are acquired as feedback values.

In S708, the traveling carriage control device 17 calculates the control amount of the lifting drive unit 19 using the reference value calculated in S706, the actual measurement value acquired in S707, and the constant determined in S704. The control amount here may be a target value for the lifting speed of the traveling carriage 16. For example, the constant determined in S704 may be a gain number, and the control amount may be obtained by PI control. For example, the control amount may be calculated using the following equation (2). When equation (2) is used, the constants _Kp and _K1 may be set by the parameter management unit 441. Note that a known method can be applied to PI control, so a detailed description thereof will be omitted here.

However, in the above formula (2),
_If : Actual measured current value (feedback value)
I _c : Reference value (target value) of current
K _p : Proportional gain (constant)
K _I : Integral gain (constant)

In S709, the traveling carriage control device 17 controls the lifting/lowering drive unit 19 based on the control amount calculated in S708. This processing flow then ends. Note that this processing flow is repeatedly executed while the welding device 100 is performing a welding operation.

The above-described welding method allows for automatic control of optimal feed speed, extension length, flux supply amount, etc., thereby improving work efficiency and welding quality. However, the welding equipment and welding methods that can be applied to the weld metal manufacturing method according to this embodiment are not limited to the above-described equipment and methods, and various other types can be used.

The weld metal manufacturing method according to this embodiment can be applied to the grooves of a pair of base materials 3 arranged opposite each other, as described above, but it can also be applied to grooves such as those used when welding the corners of a box column.

Figure 5 is a side cross-sectional view that schematically illustrates an example of a method for producing weld metal when welding the corners of a box column using ESW. Figures 6A to 6C are top cross-sectional views that schematically illustrate examples of the tip positions of the welding wire shown in Figure 5. In Figures 5 and 6A to 6C, the same components as those shown in Figure 2 are designated by the same reference numerals, and detailed descriptions of these components will be omitted or simplified.

As shown in Figures 5 and 6A, when welding the corners of a box column using ESW, the base material 3 shown in Figure 2 will be described as steel plates 23a and 23b. The surface of the end of steel plate 23a is positioned opposite the end face of steel plate 23b (not shown in Figure 5) so that the surfaces of steel plate 23a and steel plate 23b are perpendicular to each other, and a groove is formed. A backing metal 1 with a length approximately equal to the Z-direction height of steel plates 23a and 23b is placed on the back side of groove 27, i.e., the position inside the box column. A sliding welding copper backing metal 30 is placed on the position outside the box column, i.e., the front side of groove 27, and slides in the Z direction, which is the direction of the weld line. The end face of steel plate 23b is cut so that it forms an inclined plane relative to the surface of steel plate 23a, resulting in a groove shape that is wider on the front side of groove 27.

In this embodiment, when welding using a single welding wire 6, the tip 6a of the welding wire 6 is positioned near the center of the groove 27 to create molten metal 9. At this time, as shown in FIG. 6B, it is preferable to position the tip 6a of the welding wire 6 in the weld line direction, i.e., in the XY plane perpendicular to the Z-axis direction, while performing welding, as this results in more uniform molten metal 9 being formed in the wide groove 27. The tip 6a of the welding wire 6 may be weaved in a repetitive linear motion in the XY plane, as shown in FIG. 6B, or may be made to trace a triangular trajectory in the XY plane along the groove shape, as shown in FIG. 6C.

The position to which the tip 6a of the welding wire 6 moves does not necessarily have to be within a plane perpendicular to the welding line direction; it may move within a plane approximately perpendicular to the welding line direction. A plane approximately perpendicular to the welding line direction can be, for example, within a range of 10° or less from the plane perpendicular to the welding line direction.

Figure 7 is a side cross-sectional view that schematically shows another example of a method for producing weld metal when welding the corners of a box column using ESW. Figure 8 is a top cross-sectional view that schematically shows an example of the tip position of the welding wire shown in Figure 7. In Figures 7 and 8, the same components as those shown in Figures 5 and 6A-6C are designated by the same reference numerals, and detailed descriptions thereof will be omitted or simplified.

In this embodiment, welding is performed using two welding wires: a welding wire 6 held by a welding torch 4 and a welding wire (electrode wire) 26 held by a welding torch 24. This increases the speed at which molten metal 9 is formed, enabling more efficient welding. Furthermore, using multiple welding wires allows the heat input to be distributed over a wider area, preventing incomplete fusion.

In addition, in the method shown in Figure 8, the welding wire 26 closest to the backing metal 1 is used as a fixed electrode held stationary in a plane approximately perpendicular to the weld line direction, while the other welding wire 6 is weaved in a plane approximately perpendicular to the weld line direction. In this way, for example, by holding the tip 26a of the welding wire 26 closest to the backing metal 1 near the root stationary in the above plane and moving only in the weld line direction, the high-temperature thermal history near the root can be limited to a monotonous decrease, thereby reducing the susceptibility to reheat liquation cracking. Furthermore, by weaving the tip 6a of the other welding wire 6, insufficient fusion on the surface side within the groove 27 can be prevented.

As the welding wire to be fixed near the tip 26a of the welding wire 26, it is preferable to select the welding wire 26 whose tip is located closest to the backing metal 1. By using the welding wire 26 as a fixed electrode in this way, it is possible to obtain the effect of preventing microcracks near the root.
8, the tip 6a of the welding wire 6 is weaved in a reciprocating motion, but it may be weaved in a rotational motion as in Fig. 6C. The weaving direction is preferably in the thickness direction of the steel plate 23b, i.e., moving alternately toward the backing metal 1 and the sliding copper welding backing metal 30, because this allows the heat generated by welding to be distributed to areas where insufficient fusion is likely to occur, such as near the root or on the surface side of the groove.

Figure 9 is a cross-sectional side view that schematically illustrates another example of a method for producing weld metal when welding the corners of a box column using ESW. In Figure 9, the same components as those in Figure 7 are designated by the same reference numerals, and detailed descriptions of these components will be omitted or simplified.

In the embodiment shown in Figure 9, welding is performed using three welding wires: welding wire 6 held by welding torch 4, welding wire 26 held by welding torch 24, and welding wire 36 held by welding torch 34. In this way, in this embodiment, multiple welding wires (electrode wires) 6, 26, and 36 can also be used.

When multiple welding wires are used in this way, from the perspective of the reheat liquation cracking susceptibility of the weld metal, it is preferable that at least one welding wire be stationary in a plane generally perpendicular to the welding line direction. Furthermore, from the perspective of suppressing the occurrence of insufficient fusion, it is preferable that welding be performed while weaving the tip position of at least one of the other welding wires in a plane generally perpendicular to the welding line direction.

Furthermore, when multiple welding wires are used and the currents flowing through these welding wires are in phase and approach each other, mutual interference can create attractive or repulsive forces, which can result in penetration abnormalities. Therefore, it is preferable to use a DC power supply for at least one welding wire and an AC power supply for at least one welding wire, as this cancels out the mutual interference and allows for proper penetration. Furthermore, as shown in Figure 8, when one welding wire 26 is used as a fixed electrode and the other welding wire 6 is used for weaving, it is preferable to use an AC power supply for the welding wire 26 that serves as the fixed electrode.

When an AC power supply is used with one welding wire as described above, the degree of mutual interference between two or more wires can be controlled by appropriately controlling the relationship between the current value (EN) during the period when a negative voltage is applied to the wire side and the current value (EP) during the period when a positive voltage is applied to the wire side. In other words, from the perspective of suppressing abnormal penetration due to mutual interference, the EN ratio is preferably 30% or more and 70% or less, more preferably 35% or more and 65% or less, and even more preferably 38% or more and 62% or less. The EN ratio here is calculated as the time integral of EN / (time integral of EN + time integral of EP).

Furthermore, when using multiple welding wires, as mentioned above, penetration is particularly required on the root side, so it is preferable to use a fixed electrode for the welding wire near the root. If the current waveform passed through this fixed electrode is a pulsed current waveform, this creates rigidity in the strong heat input at high currents, allowing for appropriate penetration.

In the above embodiment, an example was described in which multiple welding wires were used in a method for producing weld metal using ESW. However, multiple welding wires can also be used when other welding methods are used. For example, the present invention can also be applied to multi-electrode SAW. As such, according to the present invention, regardless of the welding wire and welding method, high-tensile steel can be welded highly efficiently in a single pass, solidification cracking is suppressed, and weld metal with excellent mechanical properties can be obtained. Furthermore, because the present invention can produce weld metal with the above-mentioned excellent properties, it is also possible to obtain a weld joint in which high-tensile steel plates are joined together with the weld metal. In other words, solidification cracking in the weld metal can be suppressed, and a weld joint with weld metal with excellent mechanical properties can be obtained.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples and can be implemented with modifications within the scope of the present invention, all of which are within the technical scope of the present invention. Furthermore, the welding conditions described here are merely examples, and the present embodiment is not limited to the following welding conditions.

[Weld metal production]
Figure 10 is a schematic diagram showing the manufacturing method of weld metal applied in the invention example and comparative example. As shown in Figure 10, steel plates 23a and 23b, each 60 mm thick and made of HT780 steel, were prepared. The steel plates 23a and 23b were arranged so that the surface of the end of the steel plate 23a faced the end face of the steel plate 23b, forming a groove 27. A backing metal 1 made of ordinary steel was placed on the back side of the groove 27. Furthermore, a welding sliding copper backing metal 30, which slides in the direction of the weld line, was placed on the outer side of the box column, i.e., on the front side of the groove 27. The end face of the steel plate 23b was cut so as to be inclined relative to the surface of the steel plate 23a, with a groove angle of 20° and a root gap of 12 mm.

ESW was performed on the workpieces configured as described above using one or two electrodes (hereinafter referred to as welding wire) under the various conditions shown in Table 1 to produce weld metals. A highly basic flux with a high _CaF2 content was used to ensure stable ESW. Metal-based flux-cored wires with various additive alloys were used as welding wires to obtain the weld metals of the invention examples, with the additive alloys varied to match the compositions of the steel plates 23a and 23b and to obtain the desired weld metals.

In the example using one electrode, the electrode (welding wire 6) was weaved so as to move repeatedly in a linear direction within the groove 27, as shown in Figure 6B. In Table 1 below, this electrode is referred to as electrode W1. In the example using two electrodes, in addition to electrode W1, an electrode (welding wire 26) was placed as a fixed electrode near the root of the groove 27, as shown in Figure 8, and this is referred to as electrode W2 in Table 1 below. In Table 1 below, DCEP (direct current electrode positive) represents direct current electrode positive, AC (Alternating Current) represents alternating current, and DCEP-Pulse represents the case where the welding current is pulsed when the direct current electrode is positive.

The contents of each component of the obtained weld metal, the values of (A), (D1), (D2), (D3), and (E), and the calculation results of (A)×(D1), (A)×(D2), and (A)×(D3) are shown in Tables 2 and 3 below.
Here, (A) is the value obtained by the formula A: [P] + [S],
(D1) is the value obtained by the formula D1: [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu],
(D2) is a value obtained by the formula D2: 40-4×[Ni]+30×[C]+0.5×[Mn]+0.25×[Cu],
(D3) is the value obtained by the formula D3: 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu],
(E) is the value obtained by the formula E: [C] + [Si]/30 + ([Mn] + [Cu] + [Cr])/20 + [Ni]/60 + [Mo]/15 + [V]/10 + 5 × [B].

However, because the formula used differs depending on the range of Ni content, when the Ni content is less than 7.0% by mass, the value calculated using formula D1 is entered in the (D1) column of Table 3, and a "-" is entered in the (D2) and (D3) columns. Furthermore, when the Ni content is 7.0% by mass or more but less than 10.0% by mass, the value calculated using formula D2 is entered in the (D2) column of Table 3, and a "-" is entered in the (D1) and (D3) columns. Similarly, when the Ni content is 10.0% by mass or more, the value calculated using formula D3 is entered in the (D3) column of Table 3, and a "-" is entered in the (D1) and (D2) columns. Furthermore, in the (A) x (D1), (A) x (D2), and (A) x (D3) columns of Table 3, the value obtained by multiplying (A) by the value entered in (D1) to (D3) is entered.

In the above formulas, [P] is the P content in the weld metal expressed in mass%, [S] is the S content in the weld metal expressed in mass%, [Ni] is the Ni content in the weld metal expressed in mass%, [C] is the C content in the weld metal expressed in mass%, [Mn] is the Mn content in the weld metal expressed in mass%, [Cu] is the Cu content in the weld metal expressed in mass%, [Si] is the Si content in the weld metal expressed in mass%, [Cr] is the Cr content in the weld metal expressed in mass%, [Mo] is the Mo content in the weld metal expressed in mass%, [V] is the V content in the weld metal expressed in mass%, and [B] is the B content in the weld metal expressed in mass%.

In Tables 2 and 3 below, the analytical values for each component are listed up to the lower analytical limit, and values below the lower limit are indicated with an inequality sign, indicating the lower analytical limit. Furthermore, if the content of a component used in the calculations of Formula A, Formula D1, Formula D2, Formula D3, or Formula E was below the lower analytical limit, the content of the corresponding component was treated as 0.

[Weld metal evaluation]
The obtained weld metals were evaluated for tensile strength, toughness, solidification cracking resistance, and reheat liquation cracking resistance. The evaluation methods and evaluation criteria are shown below, and the measured or calculated values in each experiment and the evaluation results are shown in Tables 4 and 5 below.

(Tensile test)
A tensile test was carried out on the weld metal to evaluate the tensile strength.
From the obtained weld metal, an A1 test piece specified in JIS Z 3111:2005 was taken along the weld line direction, and the tensile strength was measured and the yield stress (0.2% proof stress) was calculated in accordance with the tensile test method for metallic materials specified in JIS Z 2241:2011.
The evaluation criteria were as follows: a tensile strength measurement result of 780 (MPa) or more was rated A (good: pass), and a measurement result of less than 780 (MPa) was rated C (poor: fail). Furthermore, a yield stress of 630 (MPa) or more was rated A (good), and a measurement result of less than 630 (MPa) was rated B (pass).

(Charpy impact test)
The weld metal was subjected to a Charpy impact test to evaluate its toughness.
From the obtained weld metal, impact test specimens specified in JIS Z 3111:2005 were taken along the plate width direction of the steel plate 23b, and a notch was formed in the center of the weld metal so as to fracture it in the weld line direction, and the absorbed energy was measured in accordance with the Charpy impact test method for metallic materials specified in JIS Z 2242:2018. Note that the absorbed energy was measured for three test specimens at a test temperature of 0°C, and the average value of these was calculated.
The evaluation criteria were as follows: an average absorbed energy of 47 (J) or more was rated as AA (particularly good); an average absorbed energy of 27 (J) or more but less than 47 (J) was rated as A (good); and an average absorbed energy of less than 27 (J) was rated as B (fair).

(ultrasonic flaw detection test)
Flaws in the center of the weld metal were detected using the incident angle probe method in accordance with the ultrasonic testing method for steel welds specified in JIS Z 3060: 2015. The length in the weld length direction was then measured, divided by the inspection length, and multiplied by 100 to calculate the length of solidification cracks per 100 mm of inspection length, and solidification crack resistance was evaluated.
The evaluation criteria were as follows: a solidification crack length of 0 (mm/100 mm) was rated A (good: pass); a solidification crack length of more than 0 (mm/100 mm) and less than 10 (mm/100 mm) was rated B (fair: pass); and a solidification crack length of 10 (mm/100 mm) or more was rated C (poor: fail).

(Reheat liquation cracking inspection test)
For a representative portion of the test specimen, the back surface of the steel plate 23b was used as the reference surface, and defects were detected on the surface ground 1.3 mm away from the reference surface in accordance with the magnetic particle testing method specified in JIS Z 2320-1:2017. The total number of defects detected within a predetermined inspection length was counted, divided by the inspection length, and multiplied by 100 to calculate the number of defects per 100 mm of inspection length, and reheat liquefaction cracking resistance was evaluated. Note that for some of the inventive examples and comparative examples, reheat liquefaction cracking inspection tests were not performed, and these are indicated by "-" in Tables 4 and 5 below.
The evaluation criteria were as follows: AA (particularly good) was given for a sample with 0 flaws (per 100 mm); A (good) was given for a sample with visible flaws but with fewer than 5 flaws (per 100 mm); and B (fair) was given for a sample with 5 flaws or more (per 100 mm).

As shown in Tables 1 to 5 above, in Invention Examples 1 to 25, the Ti content in the weld metal was within the range specified by the present invention, and the values of (A) x (D1), (A) x (D2), (A) x (D3), and (E), calculated from the contents of each component in the weld metal, were also within the ranges specified by the present invention. This resulted in excellent mechanical properties and suppression of solidification cracking in the weld metal. In particular, Invention Examples 2, 3, 5, and 9 to 25 had REM or Ni contents in the weld metal within the preferred ranges specified by the present invention for the purpose of improving the toughness of the weld metal, and therefore achieved excellent toughness evaluation results of A or AA. Furthermore, in Invention Examples 21 to 25, welding was performed using two electrodes, and therefore the proportion of samples that received a particularly good result in the penetrant testing to evaluate reheat liquation cracking resistance increased.

In Comparative Example No. 1, the value calculated by (A) x (D1) exceeded the upper limit specified by the present invention, resulting in reduced solidification cracking resistance. In Comparative Example No. 2, (E) was less than the lower limit specified by the present invention, resulting in reduced tensile strength. In Comparative Example No. 3, the value calculated by (A) x (D2) exceeded the upper limit specified by the present invention, resulting in reduced solidification cracking resistance. In Comparative Example No. 4, the Ti content in the weld metal exceeded the upper limit specified by the present invention, resulting in reduced solidification cracking resistance.

As described above in detail, the weld metal and weld metal manufacturing method according to the present invention achieved excellent mechanical properties and suppressed solidification cracking in the weld metal, particularly when single-pass, large heat input welding was applied to HT780 steel.

REFERENCE SIGNS LIST 1 Backing metal 3 Base material 4, 24, 34 Welding torch 5 Contact tip 6, 26, 36 Welding wire 7 Molten slag bath 8 Welding current 9 Molten metal 10 Weld metal 23a, 23b Steel plate 27 Groove 30 Sliding copper welding backing

Claims (9)

A weld metal formed by welding high-tensile steel materials having a strength of 780 N/mm ² or more,
Ti: 0.015 mass% or less,
REM: Contains 0.005% by mass or more and 0.050% by mass or less,
The P content in the weld metal is represented by [P] in mass%, the S content by [S] in mass%, the Ni content by [Ni] in mass%, the C content by [C] in mass%, the Mn content by [Mn] in mass%, the Cu content by [Cu] in mass%, the Si content by [Si] in mass%, the Cr content by [Cr] in mass%, the Mo content by [Mo] in mass%, the V content by [V] in mass%, and the B content by [B] in mass%,
The value obtained by the formula A: [P] + [S] is (A),
The value obtained by the formula D1: [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D1),
The value obtained by the formula D2: 40-4 × [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D2),
The value obtained by the formula D3: 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D3),
When the value obtained by the formula E: [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 × [B] is represented as (E),
In the range where [Ni] is less than 7.0, (A) × (D1) is 0.1 or less;
In the range of 7.0≦[Ni]<10.0, (A)×(D2) is 0.1 or less;
In the range of [Ni]≧10.0, (A)×(D3) is 0.1 or less,
A weld metal characterized in that (E) is 0.25 or more. A method for producing a weld metal by one-pass welding of a high-tensile steel material having a strength of 780 N/mm2 or ^more ,
The weld metal is
Ti: 0.015 mass% or less,
REM: Contains 0.005% by mass or more and 0.050% by mass or less,
The P content in the weld metal is represented by [P] in mass%, the S content by [S] in mass%, the Ni content by [Ni] in mass%, the C content by [C] in mass%, the Mn content by [Mn] in mass%, the Cu content by [Cu] in mass%, the Si content by [Si] in mass%, the Cr content by [Cr] in mass% , the Mo content by [Mo], the V content by [V] in mass% , and the B content by [B] in mass% ,
The value obtained by the formula A: [P] + [S] is (A),
The value obtained by the formula D1: [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D1),
The value obtained by the formula D2: 40-4 × [Ni] + 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D2),
The value obtained by the formula D3: 30 × [C] + 0.5 × [Mn] + 0.25 × [Cu] is (D3) ,
When the value obtained by the formula E: [C] + [Si] / 30 + ([Mn] + [Cu] + [Cr]) / 20 + [Ni] / 60 + [Mo] / 15 + [V] / 10 + 5 × [B] is represented as (E),
In the range where [Ni] is less than 7.0, (A) × (D1) is 0.1 or less;
In the range of 7.0≦[Ni]<10.0, (A)×(D2) is 0.1 or less;
In the range of [Ni]≧10.0, (A)×(D3) is 0.1 or less,
(E) is 0.25 or more. The method for producing a weld metal according to claim 2 , wherein the weld metal is produced by vertical position electroslag welding. 4. The method for producing a weld metal according to claim 3 , wherein welding is performed in the groove formed of the high-tensile steel material while weaving a tip position of the electrode wire in a plane in a direction substantially perpendicular to the weld line direction. The method for producing a weld metal according to any one of claims 2 to 4 , wherein welding is carried out using a plurality of electrode wires. Use multiple electrode wires
5. The method for producing a weld metal according to claim 3 , wherein at least one of the plurality of electrode wires is a fixed electrode that is stationary within a plane that is substantially perpendicular to the direction of the weld line. The method for producing a weld metal according to claim 6 , wherein at least one of the plurality of electrode wires is powered by a DC power source and at least one of the plurality of electrode wires is powered by an AC power source. The method for producing a weld metal according to claim 7 , wherein an EN ratio in the electrode wire using the AC power source is set to 30% or more and 70% or less. 7. The method for producing a weld metal according to claim 6 , wherein the current waveform of the fixed electrode is a pulse current waveform.