TW202320955A - Method for producing laser/arc hybrid welded joint - Google Patents

Abstract

The purpose of the present invention is to provide a method for producing a laser/arc hybrid welded joint having a welded metal portion with excellent low-temperature strength. In this method, a steel sheet contains Ti and also contains, in terms of mass%, 0.025% or less of AI, and 0.008% or less of O, and a welding wire contains Ti, and also contains, in terms of mass%, 0.080% or less of AI and 0.015% or less of O. Furthermore, the arc welding is gas metal arc welding in which a mixed gas, obtained by mixing a carbon dioxide gas and an inactive gas at a ratio [alpha], is used as a shield gas. The hybrid welding is carried out such that [beta], which is defined as [beta] = (0.8 * [Al]B + 0.2 * (1-0.9 * [alpha]) * [Al]WI) / (0.005 + 0.8 * [O]B + 0.2 * [O]WI + 0.02 * [alpha]), satisfies 1.1 or less through adjustment of [Al]B (Al content in the steel sheet), [Al]WI (Al content in the welding wire), [O]B (O content in the steel sheet), [O]WI (O content in the welding wire), and [alpha] (carbon dioxide mixing ratio (volume ratio)).

Description

Manufacturing method of laser-arc hybrid welding joint

The present invention relates to a manufacturing method of a laser-arc composite welded joint, and in particular relates to improving the toughness of the welded metal part of the welded joint.

For example, tanks for storage of cryogenic liquids such as liquefied petroleum gas (LPG) and liquefied ammonium are generally constructed by welding construction using thick steel plates with good low-temperature toughness. From the viewpoint of improving construction efficiency, construction by high heat input welding such as submerged arc welding is more desirable than construction by low heat input and multi-pass welding. However, if high heat input welding is applied and the welding heat input increases, the structure of the welding heat affected zone (Heat Affected Zone, HAZ) of the base metal will be coarsened, the toughness of the welding heat affected zone will decrease, and the welding deformation and strain will also increase.

Regarding the decrease in toughness of such a welded heat-affected zone, for example, Patent Document 1 describes a high heat input welding steel material having high HAZ toughness. The steel material described in Patent Document 1 is assumed to contain Al: 0.001% to 0.070%, Ti: 0.005% to 0.030%, B: 0.0002% to 0.0050%, and N: 0.0010% to 0.0100% in mass %. Composition, and set the carbon equivalent Ceq to 0.30% to 0.35% to reduce the HAZ hardness, adjust the amount of solid solution B to 0.0002% to 0.0010% to suppress the coarsening of grain boundary ferrite, and reduce the grain boundary ferrite fraction Adjusted to 1% to 20%. Thereby, the toughness of the welded heat-affected zone with a heat input of 20 kJ/mm to 100 kJ/mm is improved.

In addition, recently, as a construction method with low heat input and high efficiency, a laser-arc hybrid welding method combining laser welding and arc welding has been developed. Compared with laser welding alone, the laser-arc hybrid welding method has advantages such as increased groove accuracy and margin for gaps, and easy control of molten metal composition because the weld metal is supplied from the welding wire. In addition, compared with the case of only arc welding, there is also an advantage that deep penetration of the welded portion can be obtained. However, in laser-arc hybrid welding, arc welding conditions and laser welding conditions are closely related to porosity. In order to suppress the occurrence of porosity, it is necessary to pay careful attention to welding conditions.

In view of such a problem, Patent Document 2 describes a steel material excellent in hybrid laser-arc weldability that can suppress generation of pores during laser-arc hybrid welding. In the steel materials described in Patent Document 2, the contents of C, Si, Mn, Al, O, P, and S are optimized. Furthermore, when the Al content is defined as [Al], the amount of non-solid-solution Al (insol.Al) is optimized in the range of 0.1×[Al] to 0.7×[Al]. Furthermore, the Al content and the Si content are increased within a possible range to satisfy [Al]+[Si]/2.5≧0.05. Thereby, during laser-arc hybrid welding, pores can be prevented from being generated in the welded part. [Prior art literature] [Patent Document]

Patent Document 1: Japanese Patent Laid-Open No. 2005-336602 Patent Document 2: Japanese Patent Laid-Open No. 2007-146210

[Problem to be Solved by the Invention]

However, according to studies by the inventors of the present invention, in the steel materials described in Patent Document 2, the desired low-temperature toughness may not be ensured in the weld metal portion of the laser-arc hybrid welded joint. Therefore, laser-arc hybrid welding cannot be applied as a welding technique for constructing cryogenic tanks.

An object of the present invention is to solve the above problems and provide a method for manufacturing a laser-arc hybrid welded joint having a weld metal portion excellent in low temperature toughness and a welded joint portion excellent in low temperature toughness. It should be noted that "excellent low temperature toughness" here refers to the case where the absorbed energy vE _-60 of the V-notch Charpy impact test at the test temperature: -60°C is 27 J or more. In the V-notch Charpy impact test of the welded joint carried out in the present invention, since cracks tend to deviate to the base metal side, fracture path deviation (Fracture Path Deviation, FPD), as shown in Fig. 2 It is implemented using a Charpy impact test piece (10 mm square) with side grooves. [Means to solve the problem]

In order to achieve the object, the inventors of the present invention studied the influence of the microstructure on the toughness of the weld metal portion of the laser-arc hybrid welded joint. As a result, in the weld metal portion where the low-temperature toughness is lowered, a structure in which coarse upper ductile iron is formed from the grain boundaries of the original wursfield iron is formed, and the oxide formed in the weld metal is Al ₂ O ₃ .

Therefore, the inventors of the present invention conceived that in order to improve the low-temperature toughness of the weld metal, it is preferable to form the weld metal into an acicular ferrite structure. In order to make the weld metal have an acicular ferrite structure, it is preferable to nucleate ferrite from oxides formed in the weld metal. Therefore, it is considered that the weld metal contains Ti, and the oxide formed in the weld metal contains Ti. Furthermore, it was found that it is necessary to limit the ratio of the Al content [Al] _WE to the oxygen content [O] _WE in the weld metal, [Al] _WE /[O] _WE, to 1.1 or less. This is because when [Al] _WE / [O] _WE exceeds 1.1, all O (oxygen) in the weld metal is bonded to Al, so even if Ti is contained, Ti cannot be bonded to O (oxygen) to form Formation of Ti-containing oxides is effective for the acicular ferrite structure.

Through further studies by the inventors of the present invention, it was found that in order to make the [Al] _WE /[O] _WE in the weld metal of the laser-arc hybrid welding joint be 1.1 or less, it is effective to limit the Al content in the weld metal [ Al] _WE , and increase the O content [O] _WE in the weld metal. Furthermore, it was found that in laser-arc hybrid welding, since the dilution from the base metal (steel plate) is large, in order to limit the Al content [Al] _WE in the weld metal, it is effective to set the Al content of the base metal (steel plate) to [ Al] _B is limited to 0.025% by mass or less.

It was also found that an increase in the O content [O] _WE in the weld metal can be increased by increasing the mixing ratio α of carbon dioxide _CO2 in the shielding gas in arc welding (gas metal arc welding).

In addition, through further research by the inventors of the present invention, it was found that the following (1) formula β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8× [O] _B +0.2×[O] _WI +0.02×α) ・・・(1) Here, [Al] _B : Al content of the steel plate (mass %), [Al] _WI : Al content of the welding wire _{Definition _} When the β of β satisfies 1.1 or less, the ratio of Al content [Al] _WE to oxygen content [O] _WE in the weld metal, [Al] _WE / [O] _WE can be adjusted to 1.1 or less, and the low temperature toughness of the weld metal improve.

The present invention is based on the above-mentioned findings and further studies. That is, the gist of the present invention is as follows. [1] A method of manufacturing a laser-arc hybrid welded joint, characterized in that, when a steel plate is manufactured by laser-arc hybrid welding in which laser welding and arc welding are combined to manufacture a welded joint, the arc welding device For gas metal arc welding using a mixed gas containing carbon dioxide at a mixing ratio α (volume ratio) and the remainder being an inert gas as a shielding gas, the steel sheet is set to have the following steel sheet composition, that is, contains C in mass % : 0.04%～0.15%, Si: 0.04%～0.60%, Mn: 0.5%～2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.006% or less, and further contains Al: 0.025% or less, Ti : 0.005% to 0.030%, O (oxygen): 0.008% or less, and the remainder is composed of a steel plate containing Fe and unavoidable impurities. The welding wire used in the gas metal arc welding is set to have the following welding wire composition, That is, by mass %, it contains C: 0.03% to 0.12%, Si: 0.30% to 1.00%, Mn: 1.2% to 2.5%, P: 0.015% or less, S: 0.010% or less, N: 0.012% or less, and further contains Al: 0.080% or less, Ti: 0.020% to 0.300%, O: 0.015% or less, the remainder of which includes Fe and unavoidable impurities, so that β defined by the following formula (1) satisfies 1.1 or less The laser-arc hybrid welding is performed. β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8×[O] _B +0.2×[O] _WI +0.02×α)・・・(1) Here, [Al] _B : Al content (mass %) of the steel plate, [Al] _WI : Al content (mass %) of the welding wire, [O] _B : O content (mass %) of the steel plate, [O ] _WI : O content (mass %) of welding wire, α: Carbon dioxide mixing ratio (volume ratio). [2] The method for producing a laser-arc hybrid welded joint according to [1], wherein the steel sheet contains, in mass %, Cu: 1.0% or less, in addition to the composition of the steel sheet, Ni: 2.0% or less, Cr: 0.50% or less, Mo: 0.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, Rare Earth Metals (REM): 0.050% or less, B: One or more of 0.0030% or less. [3] The method for manufacturing a laser-arc hybrid welded joint as described in [1] or [2], wherein, in addition to the composition of the welding wire, the welding wire also contains, in mass %, selected from Cu: 1.0% or less, Ni: 2.0% or less, Cr: 0.50% or less, Mo: 0.80% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, REM: 0.080% or less, B: One or more of 0.0060% or less. [4] The method for manufacturing a laser-arc hybrid welded joint according to any one of [1] to [3], wherein the weld metal of the laser-arc hybrid welded joint has a The weld metal composition is as follows, that is, C: 0.04% to 0.15%, Si: 0.10% to 0.60%, Mn: 0.8% to 2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.010% by mass % % or less, Ti: 0.004% to 0.040%, Al: 0.025% or less, O: 0.008% to 0.040%, the remainder contains Fe and unavoidable impurities, and the content of Al [Al] _WE is equal to that of O The ratio of content [O] _WE , [Al] _WE /[O] _WE satisfies 1.1 or less. [5] The method for manufacturing a laser-arc hybrid welded joint as described in [4], wherein, in addition to the weld metal composition, the weld metal also contains Cu: 1.0% by mass % Below, Ni: below 2.0%, Cr: below 0.50%, Mo: below 0.50%, Nb: below 0.10%, V: below 0.10%, Ca: below 0.004%, REM: below 0.060%, B: below 0.0040% one or more of two. [Effect of the invention]

According to the present invention, it is possible to manufacture a laser-arc hybrid welded joint having excellent toughness of the weld metal and the toughness of the welded joint, which has a significant industrial effect.

This embodiment is a manufacturing method of a laser-arc hybrid welded joint in which a welded joint is produced by performing laser-arc hybrid welding in which laser welding and arc welding are combined between butted steel plates. Furthermore, from the viewpoint of welding stability, the steel plates to be butted are preferably steel plates with a plate thickness of 6 mm to 36 mm.

First, the steel plate of the welded joint of the present embodiment has the following composition: C: 0.04% to 0.15%, Si: 0.04% to 0.60%, Mn: 0.5% to 2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.006% or less, further contains Al: 0.025% or less, Ti: 0.005% to 0.030%, O (oxygen): 0.008% or less, and the remainder contains Fe and unavoidable impurities. The reasons for limiting the component composition of the steel sheet are as follows. Hereinafter, "mass %" related to the composition is abbreviated as "%".

C: 0.04% to 0.15% C is an element effective in improving the strength of the steel sheet at low cost, and in the present embodiment, the C content is set to 0.04% or more. On the other hand, if the C content exceeds 0.15%, the welded heat-affected zone hardens, and the toughness of the welded heat-affected zone including the welded joint decreases. Therefore, the C content is set at 0.04% to 0.15%. Furthermore, the C content is preferably 0.05% to 0.13%, more preferably 0.06% to 0.12%.

Si: 0.04% to 0.60% Si is an element that functions as a deoxidizing element and effectively contributes to improving the strength of the steel sheet. In order to obtain such an effect, the Si content is set to 0.04% or more. On the other hand, if the Si content exceeds 0.60%, a hard second phase (island-shaped mosaic iron) is formed in the welded heat-affected zone, and the toughness of the welded heat-affected zone (including the welded joint) decreases. Therefore, the Si content is set to 0.04% to 0.60%. Furthermore, the Si content is preferably 0.08% to 0.50%, more preferably 0.10% to 0.45%.

Mn: 0.5%～2.0% Mn is an element useful for improving the strength of the steel sheet. In order to obtain such an effect, the Mn content is set to 0.5% or more. On the other hand, if the Mn content exceeds 2.0%, the welded heat-affected zone will harden and the toughness of the welded heat-affected zone (including the welded joint) will decrease. Therefore, the Mn content is set to 0.5% to 2.0%. Furthermore, the Mn content is preferably 0.6% to 1.8%, more preferably 0.7% to 1.7%.

P: less than 0.015% P is an element that lowers the toughness of the steel sheet, and is diluted by the base material (steel sheet) at the time of welding and mixed into the weld metal to induce high-temperature cracking of the weld metal. Therefore, in this embodiment, the P content is preferably reduced as much as possible, but if it is 0.015% or less, it can be tolerated, and it is 0.015% or less. Furthermore, an excessive reduction of P will lead to an increase in refining cost. Therefore, the P content is preferably adjusted to 0.003% or more. The P content is more preferably 0.004% to 0.012%.

S: less than 0.010% S forms MnS in the steel sheet, becomes MnS that is stretched and elongated during rolling, and becomes a factor for lamellar tearing. Therefore, in this embodiment, the S content is preferably reduced as much as possible, but it is acceptable if it is 0.010% or less. Therefore, the S content is made 0.010% or less. Furthermore, excessive reduction will lead to high refining costs. Therefore, the S content is preferably adjusted to 0.001% or more. The S content is more preferably 0.002% to 0.008%.

N: less than 0.006% N is an element mixed as an impurity, and the solid solution of N reduces the toughness, so the N content is preferably as small as possible, but it is acceptable if it is 0.006% or less. Therefore, the N content is made 0.006% or less. Furthermore, excessive reduction will lead to high scouring costs, so the N content is preferably 0.002% or more. The N content is more preferably 0.003% to 0.005%.

Al: less than 0.025% Al functions as a deoxidizing element, contributes to the refinement of the microstructure, and has an effect of improving the toughness of the steel sheet (base material). In order to obtain such an effect, the Al content is preferably set at 0.004% or more. On the other hand, if the Al content exceeds 0.025%, the toughness of the weld metal will decrease. Therefore, the Al content is made 0.025% or less. Furthermore, the Al content is preferably from 0.004% to 0.020%, more preferably from 0.005% to 0.018%.

Furthermore, in the case of laser-arc hybrid welding, since the dilution from the base material (steel plate) increases, the contribution of the Al content of the steel plate to the Al content of the weld metal increases. As a result, when the Al content of the steel sheet increases, the amount of Al [Al] _WE in the weld metal increases, making it difficult to keep [Al] _WE / [O] _WE in the weld metal to 1.1 or less, and the toughness of the weld metal decreases. Therefore, in order to improve the toughness of the weld metal, it is necessary to limit the Al content [Al] _WE in the weld metal. In order to make [Al] _WE /[O] _WE in the weld metal 1.1 or less, the Al content [Al] _B of the base material (steel plate) is limited to 0.025 in consideration of the increase in the O content [O] _WE in the weld metal % or less, and adjust β defined by the following formula (1) to be 1.1 or less. β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8×[O] _B +0.2×[O] _WI +0.02×α)・・・(1) Here, [Al] _B : Al content (mass %) of the steel plate, [Al] _WI : Al content (mass %) of the welding wire, [O] _B : O content (mass %) of the steel plate, [O ] _WI : O content (mass %) of welding wire, α: Carbon dioxide mixing ratio (volume ratio).

Ti: 0.005% to 0.030% Ti is a nitride-forming element, bonds with N to form TiN, functions as pinning particles, suppresses the coarsening of Wastian iron grains, and contributes to the improvement of the toughness of the heat-affected zone. In order to obtain such an effect, the Ti content is set to 0.005% or more. On the other hand, if the Ti content exceeds 0.030%, the amount of solid solution Ti increases, and the toughness of the base material decreases. Therefore, the Ti content is set to 0.005% to 0.030%. Furthermore, the Ti content is preferably from 0.008% to 0.025%, more preferably from 0.010% to 0.022%.

O (oxygen): 0.008% or less O (oxygen) forms oxides in the steel sheet and becomes the origin of fracture. Therefore, in the present embodiment, it is preferable to reduce the O content as much as possible, but it is acceptable if it is 0.008% or less, so it is made 0.008% or less. Furthermore, an excessive reduction will lead to an increase in scouring costs, so O is preferably adjusted to 0.002% or more. More preferably, it is 0.003% to 0.006%.

The above components are the basic components of the steel sheet of this embodiment, but in addition to the above basic components, Cu: 1.0% or less, Ni: 2.0% or less, Cr: 0.50% or less, Mo : 0.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, REM: 0.050% or less, and B: 0.0030% or less.

Cu: 1.0% or less Cu is an element that increases the strength of the steel sheet and improves the corrosion resistance, and in order to obtain such an effect, it is necessary to contain 0.1% or more. On the other hand, if it is contained in excess of 1.0%, red hot brittleness will be exhibited, surface cracking of the steel sheet will occur, and the manufacturability of the steel sheet will decrease. Therefore, when Cu is contained, it is preferable to limit it to 1.0% or less. More preferably, it is 0.2% to 0.8%.

Ni: less than 2.0% Ni is an element that increases the strength of the steel sheet without reducing the toughness of the steel sheet and also improves the toughness of the welded heat-affected zone. In order to obtain this effect, it needs to be contained in an amount of 0.1% or more. On the other hand, the content of more than 2.0% will increase the production cost. Therefore, when Ni is contained, it is preferable to limit it to 2.0% or less. More preferably, it is 0.2% to 1.8%.

Cr: less than 0.50% Cr is an element that increases the strength of the base material. In order to obtain such an effect, it is necessary to contain 0.01% or more, but the content of more than 0.50% will reduce the toughness of the steel sheet. Therefore, when contained, Cr is preferably limited to 0.50% or less. More preferably, it is 0.02% to 0.45%.

Mo: less than 0.50% Mo is an element that increases the strength of the base material. In order to obtain such an effect, Mo needs to be contained in an amount of 0.01% or more, but the content of Mo in excess of 0.50% decreases the toughness of the steel sheet. Therefore, when Mo is contained, it is preferable to limit it to 0.50% or less. More preferably, it is 0.02% to 0.45%.

Nb: less than 0.10% Nb is an element that increases the strength of the base metal by improving the hardenability. In order to obtain this effect, it needs to be contained in an amount of 0.01% or more, but the content of more than 0.10% will reduce the toughness of the steel sheet. Therefore, when Nb is contained, it is preferable to limit it to 0.10% or less. More preferably, it is 0.02% to 0.08%.

V: less than 0.10% V is an element that precipitates fine carbides to increase the strength of the base metal. In order to obtain this effect, it is necessary to contain 0.01% or more, but the content of more than 0.10% will reduce the toughness of the steel sheet. Therefore, when contained, V is preferably limited to 0.10% or less. More preferably, it is 0.02% to 0.08%.

Ca: 0.004% or less Ca is an element that bonds with S to form spherical CaS, and is an element that contributes to the shape control of sulfides, and prevents lamellar tearing from occurring when tensile stress acts in the sheet thickness direction. In order to obtain such an effect, Ca needs to be contained in an amount of 0.001% or more. On the other hand, the content of Ca exceeding 0.004% increases the coarse CaS, which becomes the origin of fracture and reduces the toughness of the steel sheet. Therefore, when contained, Ca is preferably limited to 0.004% or less. More preferably, it is 0.002% to 0.003%.

REM: less than 0.050% REM bonds with S to form sulfides. The sulfide has ferrite nucleation ability, and ferrite grains are formed from the Wostian iron grains, which contributes to the miniaturization of the microstructure. In order to obtain this effect, REM needs to contain more than 0.001%. On the other hand, if the content exceeds 0.050%, REM will segregate in the grain boundary of Worth field iron, so that the ductility will be lowered, and it will become a factor of cracking, and the manufacturability of the steel sheet will be lowered. Therefore, when contained, REM is preferably limited to 0.050% or less. More preferably, it is 0.002% to 0.045%.

B: less than 0.0030% B and N are bonded to form BN in the Vossfield iron particles. The BN formed in the heat-affected zone becomes the nucleation site of ferrite, so the microstructure is refined, which contributes to the improvement of the toughness of the heat-affected zone. In order to obtain such an effect, it is necessary to contain 0.0005% or more of B. On the other hand, if the content exceeds 0.0030%, it will segregate at the grain boundary of Worsfield iron during casting solidification, forming a liquid phase, and inducing cracking. Therefore, when contained, B is preferably limited to 0.0030% or less. More preferably, it is 0.0008% to 0.0025%. The remainder other than the above-mentioned components contains Fe and unavoidable impurities.

In the method of manufacturing a welded joint according to the present embodiment, steel plates having the above steel plate composition are butted together, grooves of a predetermined shape are formed, and laser-arc hybrid welding is performed to manufacture a laser-arc hybrid welded joint. In addition, as the groove of a predetermined shape, an I groove, a Y groove, a V groove, etc. can be illustrated.

Laser-arc hybrid welding used in the method of manufacturing a welded joint according to the present embodiment uses arc welding as gas metal arc welding using a mixed gas containing carbon dioxide and an inert gas as a shielding gas, and combines it with laser welding. The laser source of the laser welding to be used is not particularly limited, but it is preferably used for laser welding of a fiber laser that can easily achieve high output while maintaining the beam quality.

As shown in Fig. 1, the combination of laser welding and arc welding is to arrange the arc electrode (arc welding torch) in front of the welding traveling direction for arc welding. That is, it is preferable to arrange the laser head behind the arc electrode (arc welding torch) to irradiate the laser beam to perform laser welding, so-called first: arc welding, and later: laser welding. However, there is no problem in an arrangement where laser welding is performed first and arc welding is performed last. Furthermore, for the purpose of preventing interference with the arc, it is preferable to set the target position of the laser beam at the time of advanced: arc welding and backward: laser welding to be 1 mm to 5 mm behind the center point of the arc electrode. Location.

In addition, the welding conditions of laser welding are preferably appropriately selected according to the plate thickness of the material to be welded. For example, in the range of plate thickness: 6 mm or more and less than 12 mm, it is better to set laser output: 5 kW to 10 kW, welding speed 0.8 m/min to 2.0 m/min, and plate thickness: 12 mm In the range above and below 24 mm, it is better to set laser output: 8 kW to 30 kW, welding speed 0.6 m/min to 1.4 m/min, and plate thickness: within the range of 24 mm or more and less than 36 mm , preferably set to laser output: 20 kW-60 kW, welding speed 0.3 m/min-1.0 m/min.

In addition, considering the stability of the arc, the welding conditions of the arc welding (gas metal arc welding) are preferably set to a downward posture, welding wire protrusion length: 10 mm to 25 mm, current: 220 A to 380 A, voltage: 28 V～46 V, welding speed: range from 0.3 m/min to 1.8 m/min. In addition, the shielding gas used for arc welding (gas metal arc welding) is a mixed gas containing carbon dioxide at a mixing ratio α (volume ratio) and an inert gas such as Ar gas as the remainder. Furthermore, from the viewpoint of arc stability, the mixing ratio α is preferably in the range of 0.05 to 1.00, more preferably 0.20 to 1.00.

In the method of manufacturing a welded joint according to this embodiment, the welding wire used in arc welding (gas metal arc welding) is a welding wire having a welding wire composition containing C: 0.03% to 0.12%, Si: 0.30% to 1.00 %, Mn: 1.2% to 2.5%, P: 0.015% or less, S: 0.010% or less, N: 0.012% or less, further containing Al: 0.080% or less, Ti: 0.020% to 0.300%, O: 0.015% or less, The balance consists of Fe and unavoidable impurities in the wire composition. Furthermore, from the viewpoint of arc stability, the welding wire used is preferably a welding wire set at 0.9 mmϕ to 1.6 mmϕ. Next, reasons for limiting the composition of the welding wire (wire composition) will be described.

C: 0.03% to 0.12% C is an element that increases the strength of the weld metal at low cost, and in order to obtain such an effect, the C content is set to 0.03% or more. On the other hand, if the C content exceeds 0.12%, the weld metal hardens, so the toughness decreases. Therefore, the C content of the welding wire is set to 0.03% to 0.12%. Furthermore, the C content is preferably 0.05% to 0.12%, more preferably 0.06% to 0.11%.

Si: 0.30% to 1.00% Si is an element that functions as a deoxidizer and contributes to an increase in the strength of the weld metal. In order to obtain such an effect, the Si content is set to 0.30% or more. On the other hand, if the Si content exceeds 1.00%, a hard second phase (island-like mosaic iron) is formed between laths of acicular ferrite in the weld metal, so the toughness of the weld metal decreases. Therefore, the Si content of the welding wire is set to 0.30% to 1.00%. Furthermore, the Si content is preferably 0.40% to 0.90%, more preferably 0.45% to 0.85%.

Mn: 1.2%～2.5% Mn is an element that functions as a deoxidizer and contributes to improving the strength of the weld metal. In order to obtain such an effect, the Mn content is set to 1.2% or more. On the other hand, if the Mn content exceeds 2.5%, the weld metal will harden and the toughness of the weld metal will decrease. Therefore, the Mn content of the welding wire is set to 1.2% to 2.5%. Furthermore, the Mn content is preferably 1.4% to 2.3%, more preferably 1.5% to 2.2%.

P: less than 0.015% P is an element that segregates at crystal grain boundaries during solidification of the weld metal and induces high-temperature cracking. It is preferable to reduce it as much as possible, but it is acceptable if the P content is 0.015% or less. Therefore, the P content of the welding wire is limited to 0.015% or less. Furthermore, excessive reduction will lead to high refining costs. Therefore, the P content is preferably adjusted to 0.003% or more. The P content is more preferably 0.004% to 0.013%.

S: less than 0.010% S is an element that segregates at crystal grain boundaries during solidification of the weld metal and induces high-temperature cracking. In the present invention, it is preferable to reduce it as much as possible, but it is acceptable if the S content is 0.010% or less. Therefore, the S content of the welding wire is set to 0.010% or less. Furthermore, excessive reduction will lead to high refining costs. Therefore, the S content is preferably adjusted to 0.001% or more. The S content is more preferably 0.002% to 0.008%.

N: less than 0.012% N is inevitably mixed into the welding wire, but if the amount of solid solution N increases, the ductility will deteriorate and the wire drawability will decrease. Therefore, the N content is preferably reduced as much as possible, but it is acceptable if it is 0.012% or less. Therefore, the N content of the welding wire is set to 0.012% or less. Furthermore, excessive reduction will lead to a rise in scouring costs, so the N content is preferably adjusted to 0.002% or more. The N content is more preferably 0.003% to 0.010%.

Al: 0.080% or less Al is a strong deoxidizing element, and by containing Al, oxides can be reduced, and the wire drawability of the wire material can be improved. In order to obtain such an effect, the Al content is set to 0.004% or more. On the other hand, if the Al content exceeds 0.080%, coarse Al ₂ O ₃ increases and becomes a starting point of fracture, so wire drawability decreases. Therefore, the Al content of the welding wire is set to 0.080% or less. Furthermore, the Al content is preferably at most 0.070%, more preferably 0.008% to 0.060%.

Ti: 0.020%～0.300% Ti forms Ti oxide in the weld metal, which serves as the nuclei of acicular ferrite, and contributes to the miniaturization of the structure. In order to obtain such an effect, the Ti content of the welding wire needs to be 0.020% or more. On the other hand, when the Ti content exceeds 0.300%, the toughness of the weld metal decreases. Therefore, the Ti content of the welding wire is set to 0.020% to 0.300%. Furthermore, the Ti content is preferably from 0.040% to 0.250%, more preferably from 0.050% to 0.220%.

O: less than 0.015% O is an element mixed as an impurity, but forms oxides in the welding wire to reduce wire drawability. Therefore, it is preferable to reduce it as much as possible, but it is acceptable if the O content is 0.015% or less, so the O content of the welding wire is made 0.015% or less. Furthermore, excessive reduction will lead to high scouring costs, so the O content is preferably at least 0.002%, more preferably 0.003% to 0.012%.

The above-mentioned components are the basic components of the welding wire, but in the method of manufacturing a welded joint according to this embodiment, in addition to the above-mentioned basic composition, it may also contain Cu: 1.0% or less, Ni: 2.0% or less, One or more of Cr: 0.50% or less, Mo: 0.80% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, REM: 0.080% or less, B: 0.0060% or less.

Cu: 1.0% or less Cu is an element that contributes to the improvement of the strength and corrosion resistance of the weld metal. In order to obtain this effect, it needs to be contained at least 0.1%, but if it is contained in excess of 1.0%, a liquid phase will be formed at the grain boundary of Worth field iron during solidification. Induce high temperature rupture. Therefore, when contained, the Cu content of the welding wire is preferably limited to 1.0% or less. More preferably, it is 0.2% to 0.8%.

Ni: less than 2.0% Ni is an element that increases the strength without reducing the toughness of the weld metal. In order to obtain this effect, Ni needs to be contained in an amount of 0.1% or more, but the content exceeding 2.0% leads to an increase in manufacturing costs. Therefore, when it is contained, the Ni content of the welding wire is preferably limited to 2.0% or less. More preferably, it is 0.2% to 1.8%.

Cr: less than 0.50% Cr is an element that increases the strength of the weld metal. In order to obtain this effect, it needs to be contained in an amount of 0.01% or more, but the content of more than 0.50% will reduce the toughness of the weld metal. Therefore, when contained, the Cr content of the welding wire is preferably limited to 0.50% or less. More preferably, it is 0.02% to 0.45%.

Mo: less than 0.80% Mo increases the strength of the weld metal, and also suppresses the formation of low-toughness grain boundary ferrite or ferrite side plates. In order to obtain this effect, it is necessary to contain 0.01% or more, but the content of more than 0.80% will harden the weld metal and reduce the toughness of the weld metal. Therefore, when Mo is contained, it is preferable to limit it to 0.80% or less. More preferably, it is 0.02% to 0.70%.

Nb: less than 0.10% Nb improves hardenability and suppresses the formation of low-toughness grain boundary ferrite or ferrite side plates. In order to obtain this effect, it is necessary to contain 0.01% or more, but the content of more than 0.10% will reduce the toughness of the weld metal. Therefore, when it is contained, the Nb content of the welding wire is preferably limited to 0.10% or less. More preferably, it is 0.02% to 0.08%.

V: less than 0.10% V is an element that contributes to improving the strength of the weld metal by precipitating fine carbides. In order to obtain this effect, it is necessary to contain 0.01% or more, and the content of more than 0.10% will reduce the toughness of the weld metal. Therefore, when containing, the V content of the welding wire is preferably limited to 0.10% or less. More preferably, it is 0.02% to 0.08%.

Ca: 0.004% or less Ca is an element that bonds with S to form CaS and contributes to suppression of cracking at high temperatures. In order to obtain this effect, it is necessary to contain 0.001% or more. On the other hand, if the content exceeds 0.004%, coarse CaS will be formed, which will become the origin of fracture and lead to a decrease in the toughness of the weld metal. Therefore, when contained, the Ca content of the welding wire is preferably limited to 0.004% or less. More preferably, it is 0.002% to 0.003%.

REM: less than 0.080% REM is an element that improves the electron emission energy of the cathode. In the case of arc welding using a welding wire containing REM with negative and positive polarity of the welding wire, the arc is stabilized, and the sputtering is significantly reduced. In order to obtain this effect, it is necessary to contain 0.010% or more. On the other hand, the addition of more than 0.080% reduces the hot ductility and the manufacturability of welding wires. Therefore, when contained, the REM content of the welding wire is preferably limited to 0.080% or less. More preferably, it is 0.002% to 0.070%.

B: less than 0.0060% B segregates at the grain boundary of Worthfield iron in the weld metal, and by reducing the energy of the grain boundary, it has the effect of suppressing grain boundary ferrite or ferrite side plates with low toughness. In order to obtain this effect, it is necessary to contain 0.0005% or more. On the other hand, if it contains more than 0.0060%, it will induce cracking at the time of casting of the welding wire raw material (steel ingot), and will reduce yield. Therefore, when contained, the B content of the welding wire is preferably limited to 0.0060% or less. More preferably, it is 0.0010% to 0.0050%.

The remainder other than the above-mentioned components contains Fe and unavoidable impurities. Furthermore, the bonding wire may be any one of solid bonding wire, metal cored bonding wire, and flux cored bonding wire.

In the present invention, the steel plates composed of the steel plates are butted to each other, and laser-arc hybrid welding is performed. In laser-arc hybrid welding, as arc welding, gas metal arc welding using a welding wire composed of the welding wire described above is mixed with carbon dioxide (mixing ratio α) and an inert gas such as Ar gas. For protective gas. Furthermore, in gas metal arc welding, from the standpoint of interference with the laser and arc stability, it is preferable to incline the welding torch by 20° to 60° relative to the direction opposite to the direction of welding progress. Solder down.

Furthermore, in the welded joint of the present embodiment, the Al content [Al] _B of the steel plate, the O content [O] _B of the steel plate, and the Al content of the welding wire [ Al] _WI , the O content [O] _WI of the welding wire, and the mixing ratio α of carbon dioxide in the mixed gas are adjusted to perform laser-arc hybrid welding. β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8×[O] _B +0.2×[O] _WI +0.02×α)・・・(1) Here, [Al] _B : Al content (mass %) of the steel plate, [Al] _WI : Al content (mass %) of the welding wire, [O] _B : O content (mass %) of the steel plate, [O ] _WI : O content (mass %) of welding wire, α: Carbon dioxide mixing ratio (volume ratio).

If β defined by the formula (1) becomes larger than 1.1, the ratio of the Al content [Al] _WE to the oxygen content [O] _WE in the weld metal, [Al] _WE / [O] _WE cannot be adjusted to 1.1 After that, the low-temperature toughness of the weld metal decreases. Therefore, the combination of the Al and O content of the steel plate, the Al and O content of the welding wire, and the mixing ratio α of carbon dioxide in the mixed gas is adjusted so that β is 1.1 or less, and laser-arc hybrid welding is performed. For example, if the steel plate used is constant, the mixing ratio α of each component of the welding wire and carbon dioxide is selected so that β is 1.1 or less, and laser-arc hybrid welding is performed.

Furthermore, in the laser-arc hybrid welded joint obtained by the laser-arc hybrid welding, the central portion of the weld metal preferably has a weld metal composition that contains C: 0.04% by mass % ～0.15%, Si: 0.10%～0.60%, Mn: 0.8%～2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0.004%～0.040%, Al: 0.025% Below, O: 0.008% to 0.040%, the remainder contains Fe and unavoidable impurities, and the ratio of Al content [Al] _WE to O content [O] _WE , [Al] _WE / [O] _WE satisfies 1.1 The following weld metal composition. Next, the reasons for limiting the preferable range of the weld metal composition will be described.

C: 0.04% to 0.15% C is an element that increases the strength of the weld metal at low cost. If the C content is less than 0.04, the aforementioned strength improvement cannot be achieved sufficiently. Therefore, the C content is set to 0.04% or more. On the other hand, if the C content exceeds 0.15%, the weld metal hardens, so the toughness decreases. Therefore, the C content is set at 0.04% to 0.15%. Furthermore, the C content is preferably 0.05% to 0.13%.

Si: 0.10% to 0.60% Si is an element that contributes to an increase in the strength of the weld metal. In order to obtain such an effect of increasing the strength, the Si content is set to 0.10% or more. On the other hand, if the Si content exceeds 0.60%, a hard second phase (island-like mosaic iron) is formed between laths of acicular ferrite in the weld metal, so the toughness of the weld metal decreases. Therefore, the Si content is set to 0.10% to 0.60%. Furthermore, the Si content is preferably 0.15% to 0.50%.

Mn: 0.8%～2.0% Mn is an element that contributes to improving the strength of the weld metal. In order to obtain such an effect of improving the strength, the Mn content is set to 0.8% or more. On the other hand, when the Mn content exceeds 2.0%, the weld metal hardens and the toughness of the weld metal decreases. Therefore, the Mn content is set to 0.8% to 2.0%. Furthermore, the Mn content is preferably 1.0% to 1.8%.

P: less than 0.015% P is an element that segregates at crystal grain boundaries during solidification of the weld metal to induce high-temperature cracking. In order to suppress such high-temperature cracking, the P content is set to 0.015% or less. The P content is preferably at most 0.012%.

S: less than 0.010% S is an element that segregates at crystal grain boundaries during solidification of the weld metal and induces high-temperature cracking. In order to suppress such high-temperature cracking, the S content is set to 0.010% or less. The S content is preferably at most 0.008%.

N: less than 0.010% N deteriorates the toughness of the weld metal. In order to suppress such a decrease in toughness, the N content is made 0.010% or less. The N content is preferably at most 0.008%.

Ti: 0.004% to 0.040% Ti forms Ti oxide in the weld metal, which serves as the nuclei for the formation of acicular ferrite, and the structure becomes finer. In order to obtain such a micronization effect of the structure, the Ti content is set to 0.004% or more. On the other hand, when the Ti content exceeds 0.040%, the toughness of the weld metal decreases. Therefore, the Ti content is set to 0.004% to 0.040%. The Ti content is preferably 0.006% to 0.030%.

Al: 0.025% or less Al functions as a deoxidizing element to reduce oxides. In order to obtain such a deoxidizing effect, the Al content is preferably set to 0.004% or more. On the other hand, if the Al content exceeds 0.025%, coarse Al ₂ O ₃ increases and toughness decreases. Therefore, the Al content is made 0.025% or less. The Al content is more preferably 0.005% to 0.022%.

O: 0.008% to 0.040% O is mixed from the steel plate, welding wire, and shielding gas to form oxides in the weld metal and become nucleation sites of acicular ferrite, so it needs to be contained at least 0.008%. On the other hand, if the O content exceeds 0.040%, coarse oxides are formed, which become the origin of fracture, thereby reducing toughness. Therefore, the O content is set to 0.008% to 0.040%. The O content is more preferably 0.010% to 0.035%.

The above-mentioned components are basic components of the weld metal, but in the welded joint of the present embodiment, in addition to the above-mentioned basic composition, it is preferable to also contain Cu: 1.0% or less and Ni: 2.0% or less in mass %. , Cr: 0.50% or less, Mo: 0.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, REM: 0.060% or less, B: 0.0040% or less.

Cu: 1.0% or less Cu is an element that improves the strength and corrosion resistance of the weld metal. In order to obtain this effect, it is preferably 0.1% or more. If the Cu content exceeds 1.0%, high temperature cracking will be induced during solidification. Therefore, the Cu content is made 1.0% or less. The Cu content is more preferably 0.2% to 0.8%.

Ni: less than 2.0% Ni is an element that increases the strength without decreasing the toughness of the weld metal. In order to obtain the effect of improving the strength, the Ni content is preferably set to 0.1% or more. If the Ni content exceeds 2.0%, the manufacturing cost will increase. Therefore, the Ni content is made 2.0% or less. The Ni content is more preferably 0.2% to 1.8%.

Cr: less than 0.50% Cr is an element that improves the strength of the weld metal. In order to obtain the effect of improving the strength, the Cr content is preferably set to 0.01% or more. If the Cr content exceeds 0.50%, the toughness of the weld metal will decrease. Therefore, the Cr content is made 0.50% or less. The Cr content is more preferably 0.02% to 0.45%.

Mo: less than 0.50% Mo improves the strength of the weld metal, and also suppresses the formation of grain boundary ferrite and ferrite side plates that cause a decrease in toughness. In order to obtain this effect, the Mo content is preferably at least 0.01%. When the Mo content exceeds 0.50%, the weld metal hardens and the toughness of the weld metal decreases. Therefore, the Mo content is made 0.50% or less. The Mo content is more preferably 0.01% to 0.45%.

Nb: less than 0.10% Nb improves the hardenability and suppresses the formation of grain boundary ferrite and ferrite side plates that cause a decrease in toughness. In order to obtain such an effect, the Nb content is preferably set at 0.01% or more. When the Nb content exceeds 0.10%, the toughness of the weld metal decreases. Therefore, the Nb content is made 0.10% or less. The Nb content is more preferably 0.02% to 0.08%.

V: less than 0.10% V improves the strength of the weld metal by precipitating fine carbides. In order to obtain the effect of improving the strength, the V content is preferably set at 0.01% or more. When the V content exceeds 0.10%, the toughness of the weld metal decreases. Therefore, the V content is made 0.10% or less. The V content is more preferably 0.02% to 0.08%.

Ca: 0.004% or less Ca bonds with S to form CaS, which suppresses cracking at high temperatures. In order to obtain such an effect, the Ca content is preferably set to 0.001% or more. On the other hand, if the Ca content exceeds 0.004%, coarse CaS will be formed and the toughness of the weld metal will decrease. Therefore, the Ca content is made 0.004% or less. The Ca content is more preferably 0.002% to 0.003%.

REM: less than 0.060% REM bonds with S to form sulfides, making the microstructure finer. In order to obtain the effect of micronizing the structure, the REM content is preferably set to 0.001% or more. On the other hand, if the REM content exceeds 0.060%, it will become a cracking factor. Therefore, the REM content is set to 0.060% or less. The REM content is more preferably 0.002% to 0.050%.

B: less than 0.0040% B segregates at the grain boundary of Worsfield iron in the weld metal, suppresses the formation of low-toughness grain boundary ferrite or ferrite side plates, and improves hardenability. In order to obtain this effect, the B content is preferably at least 0.0005%. On the other hand, if the B content exceeds 0.0040%, cracking will be induced. Therefore, the B content is made 0.0040% or less. More preferably, it is 0.0008% to 0.0026%.

The composition of the weld metal in the laser-arc hybrid welding joint is mainly determined by the composition of the welding wire used in the arc welding and the dilution from the steel plate used in turn, and is characterized in that, containing Ti, [Al] _WE / [O] _WE satisfies Below 1.1. Thereby, the structure of the weld metal can be made into an acicular ferrite structure, and the toughness of the weld metal can be improved. If [Al] _WE / [O] _WE exceeds 1.1, all O in the weld metal is bonded to Al, so even if Ti is contained, Ti cannot bond to O, and the structure of the weld metal cannot be acicular ferrite organization, the toughness of the weld metal decreases.

Hereinafter, an embodiment of the present invention will be further described based on examples. [Example]

The molten metal having the composition shown in Table 1 was melted in an arc melting furnace and poured into a mold to form a steel ingot. Then, the steel ingot was hot-rolled to form a steel plate with a thickness of 14 mm. In addition, the molten metal with the composition shown in Table 2 was melted in an arc melting furnace, poured into a mold to form an ingot, and the ingot was hot-rolled to produce a wire rod (5.5 mmϕ), followed by cold drawing and annealing. A welding wire (solid welding wire) of 1.2 mmϕ is made.

Two test panels were prepared from each of the obtained steel plates. The transverse end faces of the two test plates were butted together to form an I-groove (root gap: 0 mm), and laser-arc hybrid welding was performed to fabricate laser-arc hybrid welded joints. Furthermore, the cutting process was performed on the transverse end surface of the test plate which was butted.

In addition, the laser-arc hybrid welding used is set as follows, that is, as shown in FIG. 1 , the laser-arc hybrid welding is arranged in a downward posture relative to the arc electrode (arc welding torch) in the direction of welding progress. The laser head irradiates the laser beam, so-called first: arc welding, and last: laser welding.

As for the welding conditions of arc welding (gas metal arc welding), the welding wire protrusion length: 15 mm in downward posture, current: 300 A, voltage: 32 V, welding speed: 1.0 m/min, and shielding gas A mixed gas containing carbon dioxide having a mixing ratio α (volume ratio) shown in Table 3 and the remainder being argon Ar (inert gas) was used. In addition, in arc welding, when the welding wire is used as a welding wire containing REM (welding wire No.m), the welding wire is set to negative positive polarity, and when other welding wires are used, it is set as welding wire Line positive and reverse polarity.

In addition, regarding laser welding (fiber laser welding), the conditions of laser output: 10 kW, and welding speed 1.0 m/min were set. Furthermore, the focal point of the laser beam was set at a position 3 mm behind from the center point of the arc electrode.

Table 3 shows combinations of the mixing ratio α of the steel plate, the welding wire, and the carbon dioxide in the mixed gas in laser-arc hybrid welding. In addition, in Table 3, the value of β defined by Formula (1) is also described.

For each of the obtained welded joints, chips were collected from the center of the width of the weld metal in the range of ϕ1 mm from the center of the plate thickness, and elemental analysis was performed by wet analysis. The obtained results are shown in Table 4 as weld metal compositions.

In addition, at the center of the plate thickness of the welded joint, a Charpy impact test piece (V-shaped notch) is collected from the center of the weld metal and the joint, and the Charpy impact test is performed at the test temperature: -60°C to obtain the absorption Energy vE _-60 (J). In addition, in order to avoid the phenomenon of FPD (Fracture Path Deviation) that the crack deviates to the base material side, the V-notch Charpy impact test piece used was the test piece with side grooves shown in FIG. 2 . The obtained results are described together and shown in Table 4.

[Table 1] Steel plate No. Chemical composition (mass%) C Si mn P S Al Ti o N other A 0.06 0.30 1.5 0.010 0.008 0.015 0.030 0.003 0.004 Tr. B 0.07 0.27 1.4 0.012 0.009 0.024 0.008 0.008 0.004 Tr. C 0.08 0.20 1.4 0.010 0.004 0.018 0.010 0.003 0.006 Tr. D. 0.04 0.04 2.0 0.008 0.003 0.025 0.005 0.002 0.004 Tr. E. 0.15 0.10 1.2 0.009 0.008 0.000 0.030 0.006 0.002 Tr. f 0.12 0.60 0.5 0.005 0.010 0.004 0.005 0.008 0.004 Cu: 1.0, Ni: 2.0, Mo: 0.30 G 0.07 0.35 1.4 0.015 0.010 0.012 0.020 0.006 0.004 Cu: 0.5, Ni: 1.2 h 0.08 0.42 1.0 0.012 0.005 0.008 0.012 0.007 0.006 Cr: 0.50 I 0.04 0.09 1.0 0.015 0.003 0.016 0.014 0.006 0.005 Mo: 0.50 J 0.09 0.14 1.6 0.010 0.004 0.008 0.015 0.003 0.004 Nb: 0.10 K 0.10 0.09 1.4 0.005 0.006 0.010 0.018 0.004 0.004 V: 0.10 L 0.12 0.12 1.5 0.008 0.009 0.012 0.019 0.008 0.004 Ca: 0.004 m 0.14 0.07 1.2 0.003 0.006 0.011 0.025 0.008 0.003 REM: 0.050 N 0.07 0.48 1.5 0.008 0.009 0.009 0.030 0.005 0.003 Ca: 0.002, B: 0.0030 o 0.10 0.27 1.3 0.011 0.007 0.030 0.009 0.006 0.004 Tr. P 0.17 0.27 1.5 0.012 0.008 0.012 0.008 0.008 0.005 Tr. Q 0.14 0.75 1.7 0.007 0.009 0.004 0.012 0.003 0.003 Tr. R 0.05 0.37 2.4 0.008 0.007 0.010 0.015 0.004 0.002 Tr. ※Tr.: below the lower limit of analysis

[Table 2] Wire No. Chemical composition (mass%) C Si mn P S al Ti o N other a 0.06 0.60 1.8 0.010 0.008 0.020 0.150 0.005 0.004 Tr. b 0.12 0.50 1.6 0.009 0.008 0.000 0.300 0.006 0.002 Tr. c 0.09 0.40 1.6 0.010 0.004 0.008 0.040 0.003 0.004 Mo: 0.10, Nb: 0.10 d 0.06 1.00 1.3 0.005 0.007 0.020 0.040 0.008 0.004 Cu: 1.0, Ni: 2.0 e 0.08 0.35 1.8 0.015 0.010 0.020 0.020 0.006 0.004 Cu: 0.5, Ni: 0.8 f 0.03 0.30 2.5 0.008 0.003 0.080 0.120 0.003 0.004 Tr. g 0.08 0.42 1.4 0.012 0.005 0.014 0.060 0.005 0.006 Cr: 0.50 h 0.10 0.93 1.8 0.003 0.006 0.025 0.120 0.003 0.003 Tr. i 0.07 0.70 1.6 0.012 0.009 0.008 0.240 0.015 0.004 Tr. j 0.04 0.51 1.2 0.015 0.003 0.016 0.120 0.006 0.005 Mo: 0.80 k 0.10 0.60 1.5 0.005 0.006 0.051 0.100 0.004 0.004 Cr: 0.10, V: 0.10 l 0.07 0.48 1.5 0.008 0.009 0.017 0.180 0.005 0.003 Mo: 0.20, Nb: 0.02, B: 0.0060 m 0.08 0.40 1.6 0.010 0.004 0.012 0.040 0.008 0.012 REM: 0.080 no 0.12 0.80 1.5 0.008 0.009 0.012 0.020 0.008 0.004 Ca: 0.004, B: 0.0040 o 0.07 0.50 1.6 0.009 0.008 0.160 0.120 0.004 0.004 Tr. p 0.10 0.80 1.8 0.008 0.004 0.250 0.100 0.004 0.003 Tr. ※Tr.: below the lower limit of analysis

[table 3] Connector No. steel plate welding wire mixed composition β* No. [Al] _B [O] _B No. [Al] _WI [O] _{WI CO2} ratio α 1 A 0.015 0.003 a 0.020 0.005 1.00 0.4 2 B 0.024 0.008 b - 0.006 0.80 0.7 3 C 0.018 0.003 c 0.008 0.003 0.70 0.7 4 D. 0.025 0.002 d 0.020 0.008 0.60 1.1 5 E. - 0.006 e 0.020 0.006 0.50 0.1 6 f 0.004 0.008 f 0.080 0.003 0.50 0.5 7 G 0.012 0.006 g 0.014 0.005 0.80 0.4 8 h 0.008 0.007 h 0.025 0.003 0.40 0.5 9 I 0.016 0.006 i 0.008 0.015 0.20 0.8 10 J 0.008 0.003 j 0.016 0.006 0.80 0.3 11 K 0.010 0.004 k 0.051 0.004 1.00 0.3 12 L 0.012 0.008 l 0.017 0.005 0.80 0.4 13 m 0.011 0.008 m 0.012 0.008 1.00 0.3 14 N 0.009 0.005 no 0.012 0.008 0.60 0.4 15 A 0.015 0.003 a 0.020 0.005 0.10 1.5 16 B 0.024 0.008 b - 0.006 0.05 1.4 17 C 0.018 0.003 c 0.008 0.003 0.10 1.6 18 o 0.030 0.006 a 0.020 0.005 0.40 1.4 19 P 0.012 0.008 a 0.020 0.005 0.60 0.5 20 Q 0.004 0.003 a 0.020 0.005 0.50 0.3 twenty one R 0.010 0.004 a 0.020 0.005 0.50 0.5 twenty two A 0.015 0.003 o 0.160 0.004 0.20 3.1 twenty three A 0.024 0.008 p 0.250 0.004 0.20 4.3 *) β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8×[O] _B +0.2×[O] _WI +0.02×α)… …(1)

[Table 4] Connector No. Weld metal chemical composition (mass%) Weld metal [Al] _WE / [O] _WE Absorbed energy vE _-60 (J) exam preparation C Si mn P S Al Ti o N other weld metal join 1 0.06 0.32 1.5 0.010 0.008 0.012 0.027 0.028 0.005 Tr. 0.4 104 121 Example of the invention 2 0.08 0.28 1.4 0.011 0.009 0.020 0.011 0.029 0.005 Tr. 0.7 141 84 Example of the invention 3 0.08 0.21 1.4 0.010 0.004 0.014 0.008 0.022 0.007 Mo: 0.02, Nb: 0.02 0.7 128 118 Example of the invention 4 0.04 0.24 1.8 0.007 0.004 0.020 0.004 0.020 0.005 Cu: 0.2, Ni: 0.5 1.0 153 140 Example of the invention 5 0.14 0.12 1.3 0.010 0.008 0.001 0.026 0.021 0.003 Cu: 0.1, Ni: 0.1 0.1 57 46 Example of the invention 6 0.11 0.54 0.8 0.005 0.009 0.008 0.004 0.022 0.005 Cu: 0.9, Ni: 1.7, Mo: 0.26 0.4 128 103 Example of the invention 7 0.07 0.33 1.4 0.014 0.009 0.010 0.015 0.027 0.006 Cu: 0.4, Ni: 0.9, Cr: 0.13 0.4 120 105 Example of the invention 8 0.08 0.50 1.1 0.010 0.005 0.008 0.011 0.019 0.005 Cr: 0.41 0.4 107 102 Example of the invention 9 0.05 0.20 1.1 0.014 0.004 0.013 0.012 0.017 0.005 Mo: 0.40 0.8 154 92 Example of the invention 10 0.08 0.18 1.5 0.011 0.004 0.007 0.014 0.025 0.005 Mo: 0.14, Nb: 0.08 0.3 102 82 Example of the invention 11 0.10 0.16 1.4 0.005 0.006 0.009 0.016 0.029 0.004 Cr: 0.02, V: 0.10 0.3 86 74 Example of the invention 12 0.11 0.17 1.5 0.008 0.009 0.010 0.018 0.028 0.004 Mo: 0.05, Nb: 0.01, Ca: 0.003, B: 0.0012 0.3 106 97 Example of the invention 13 0.13 0.09 1.2 0.004 0.006 0.010 0.022 0.033 0.004 REM: 0.055 0.3 82 74 Example of the invention 14 0.08 0.51 1.5 0.008 0.009 0.008 0.026 0.022 0.003 Ca: 0.002, B: 0.0025 0.4 152 49 Example of the invention 15 0.06 0.35 1.6 0.010 0.008 0.012 0.025 0.010 0.005 Tr. 1.2 15 52 comparative example 16 0.08 0.31 1.4 0.011 0.009 0.020 0.007 0.014 0.004 Tr. 1.4 12 46 comparative example 17 0.08 0.24 1.4 0.010 0.004 0.014 0.008 0.010 0.008 Mo: 0.02, Nb: 0.02 1.4 17 38 comparative example 18 0.09 0.32 1.4 0.011 0.007 0.025 0.008 0.019 0.004 Tr. 1.3 10 35 comparative example 19 0.15 0.32 1.5 0.012 0.008 0.010 0.008 0.024 0.005 Tr. 0.4 42 9 comparative example 20 0.12 0.69 1.7 0.008 0.009 0.004 0.011 0.018 0.004 Tr. 0.2 19 8 comparative example twenty one 0.05 0.39 2.3 0.008 0.007 0.009 0.014 0.019 0.003 Tr. 0.5 11 12 comparative example twenty two 0.06 0.33 1.5 0.010 0.008 0.015 0.024 0.012 0.004 Tr. 1.2 14 32 comparative example twenty three 0.07 0.39 1.6 0.010 0.007 0.016 0.024 0.012 0.004 Tr. 1.3 12 25 comparative example ※Tr.: below the lower limit of analysis

The weld metal portion of the example of the present invention has an acicular ferrite structure. In the example of the present invention, in the welded metal and welded part, the test temperature: the absorbed energy vE _-60 of the Charpy impact test at -60°C is more than 27 J, which can be said to be a welded joint with excellent low temperature toughness.

On the other hand, in comparative examples that deviated from the scope of the present invention, the absorbed energy vE _-60 of the weld metal and/or joint was less than 27 J, the low-temperature toughness of the weld metal decreased, and a welded joint excellent in the target low-temperature toughness could not be obtained.

S: material to be welded (steel plate) 1: arc welding torch 2: welding wire 3: Laser beam 4: Welding direction

FIG. 1 is an explanatory diagram schematically showing an embodiment of a laser-arc hybrid welding method. FIG. 2 is an explanatory view schematically showing the size and shape of a V-notch Charpy impact test piece with side grooves used in Examples.

1: arc welding torch

2: welding wire

3: Laser beam

4: Welding direction

S: material to be welded (steel plate)

Claims (5)

A method for manufacturing a laser-arc hybrid welded joint, characterized in that, when a steel plate is combined with laser welding and arc welding to manufacture a welded joint, the arc welding is set to include Gas metal arc welding in which a mixed gas of carbon dioxide at a mixing ratio α (volume ratio) and the rest is an inert gas is a shielding gas, and the steel plate is set to have the following steel plate composition, that is, C: 0.04% by mass % ～0.15%, Si: 0.04%～0.60%, Mn: 0.5%～2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.006% or less, further contains Al: 0.025% or less, Ti: 0.005% ～0.030%, O (oxygen): 0.008% or less, and the rest contains Fe and unavoidable impurities. The welding wire used in the gas metal arc welding is set to have the following welding wire composition, that is, by mass % includes C: 0.03% to 0.12%, Si: 0.30% to 1.00%, Mn: 1.2% to 2.5%, P: 0.015% or less, S: 0.010% or less, N: 0.012% or less, and further contains Al: 0.080% % or less, Ti: 0.020% to 0.300%, O: 0.015% or less, and the remainder contains Fe and unavoidable impurities. The β defined by the following formula (1) satisfies 1.1 or less. Laser-arc hybrid welding, β=(0.8×[Al] _B +0.2×(1-0.9×α)×[Al] _WI )/(0.005+0.8×[O] _B +0.2×[O] _WI + 0.02×α)・・・(1) Here, [Al] _B : Al content (mass %) of the steel plate, [Al] _WI : Al content (mass %) of the welding wire, [O] _B : O content of the steel plate (mass %), [O] _WI : O content of welding wire (mass %), α: carbon dioxide mixing ratio (volume ratio). The method for manufacturing a laser-arc hybrid welded joint according to claim 1, wherein, in addition to the composition of the steel sheet, the steel sheet also contains Cu: 1.0% or less, Ni: 2.0% or less in mass % , Cr: less than 0.50%, Mo: less than 0.50%, Nb: less than 0.10%, V: less than 0.10%, Ca: less than 0.004%, rare earth metals: less than 0.050%, B: less than 0.0030% or more . The manufacturing method of the laser-arc hybrid welding joint according to claim 1 or claim 2, wherein, in addition to the welding wire composition, the welding wire also contains Cu: 1.0% or less in mass % , Ni: 2.0% or less, Cr: 0.50% or less, Mo: 0.80% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, rare earth metals: 0.080% or less, B: 0.0060% or less one or more of two. The method for manufacturing a laser-arc hybrid welded joint according to any one of claim 1 to claim 3, wherein the central portion of the weld metal of the laser-arc hybrid welded joint has the following weld metal composition, namely Contains C: 0.04% to 0.15%, Si: 0.10% to 0.60%, Mn: 0.8% to 2.0%, P: 0.015% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0.004% by mass % % to 0.040%, Al: less than 0.025%, O: 0.008% to 0.040%, the remainder contains Fe and unavoidable impurities, and the content of Al [Al] _WE and the content of O [O] _WE are The ratio, [Al] _WE / [O] _WE satisfies 1.1 or less. The manufacturing method of the laser-arc hybrid welding joint as described in claim 4, wherein, in addition to the weld metal composition, the weld metal also contains Cu: 1.0% or less, Ni: 2.0% or less, Cr: 0.50% or less, Mo: 0.50% or less, Nb: 0.10% or less, V: 0.10% or less, Ca: 0.004% or less, rare earth metal: 0.060% or less , B: one or more of 0.0040% or less.

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