JP6638529B2 - Weld joint by laser-arc hybrid welding method using Ni-base alloy-based welding material and method for producing the same - Google Patents

Description

  The present invention relates to a welding joint including a welding metal obtained by laser-arc hybrid welding in which a welding torch is preceded and a laser irradiation point is arranged behind the welding torch by using a welding material of a Ni-based alloy, and a method for manufacturing the same. Welding joints with excellent toughness of weld metal, no weld defects such as poor penetration, poor fusion, and hot cracking, and can reduce the number of welding passes by obtaining deep penetration. provide.

  In recent years, the use of liquefied natural gas as an energy source with less global warming exhaust gas has been increasing, and the construction of LNG tanks and LNG vessels for storing and transporting it has been active. The tank for storing LNG is required to have low-temperature toughness that does not cause brittle fracture even at an extremely low temperature of -162 ° C. Therefore, a high Ni steel containing 6 to 9% of Ni, which has excellent strength and low-temperature toughness, is used. Further, to increase the size of the tank, thickening of high Ni steel is also being studied.

  For welding high Ni steels, welding materials of Ni-base alloys are mainly used. Covered arc welding, TIG welding, and submerged arc welding are used as welding methods for high Ni steels. The coated arc welding method and the TIG welding method have very low welding efficiency and are not suitable for welding thick high Ni steel. On the other hand, although submerged arc welding has high welding efficiency, high-temperature cracks are easily generated in the weld metal and repair thereof is frequently required, so that the welding construction cost is still high.

Then, as an efficient welding method, application of gas shielded arc welding can be considered. However, in order to perform gas shielded arc welding in a stable arc state, it is necessary to include CO ₂ gas or O ₂ gas in the shield gas, but the weld metal obtained using the shield gas contains a large amount of oxygen. .
The toughness at -196 ° C is required for the steel material and the weld metal of the LNG tank, but the effect of oxygen on the toughness of the weld metal is great, and as the oxygen increases, the toughness deteriorates greatly.

  On the other hand, a method of welding by reducing the oxygen of the shielding gas as much as possible is also conceivable. However, if the molten weld metal has a small amount of oxygen, the molten pool does not spread, so that it tends to have a convex bead shape, and there is a problem that welding defects such as poor penetration, poor fusion, and hot cracking are likely to occur. In order to solve these problems, a flux cored wire of a Ni-based alloy applicable to gas shielded arc welding has been developed. However, in order to suppress hot cracking, a large amount of expensive alloying elements are added, and in addition, the manufacturing cost of flux cored wires is higher than that of solid wires, so that the cost of welding materials is high. is there. Therefore, there is a demand for a welding method that has a high welding efficiency and a low welding material cost.

  In recent years, for the purpose of increasing the efficiency of welding steel sheets, it has been studied to fabricate a welded joint having a narrow groove shape by using laser-arc hybrid welding combining laser and gas shielded arc welding (for example, Patent Document 1). 1-5).

  Patent Document 1 discloses that a steel plate of 4 to 12 mm having a tensile strength of 1100 MPa or more is subjected to one-pass welding by laser hybrid welding using a solid wire, so that the width W1 of the weld metal on the surface of the steel plate is set to 2. The weld metal has a cross-sectional shape of 0 to 7.0 mm, the width of the weld metal from the surface of the steel sheet to 3/4 of the plate thickness: W2 of 0.5 to 2.4 mm, and has a parameter Ceq (carbon equivalent) and Y = ｛. ([Si] + [Mn]) / 40+ [Al] + [Ti]} discloses a welding joint containing 1.0 to 9% of Ni, which is a predetermined value.

  As described in Document 1, this technique is a one-pass welding joint for high-strength steel sheets up to a thickness of 12 mm, and cannot be applied to welding thicker steel sheets.

  On the other hand, Patent Literatures 2 to 4 employ laser-arc hybrid welding in which a laser irradiation point is set to the front and a welding torch is arranged to the rear. In these technologies, laser welding is performed from the front in the welding direction, and arc welding is performed while melting the groove bottom and groove wall in front of the molten pool.Welding with a narrow groove shape and low heat input Even in this case, it is said that a good welded joint that does not cause welding defects at the boundary between the weld metal and the base material can be obtained. However, these Literatures 2 to 4 do not discuss a pear-shaped bead crack and a surface crack when forming a deep penetration weld metal.

  Patent Literature 5 discloses laser-arc hybrid welding in which a welding torch is arranged on the front side. This technique is a method of irradiating the weld metal with a laser after solidification is completed and re-melting the weld metal to obtain deep penetration. However, hot cracks (pear-shaped bead cracks, No consideration has been given to surface cracking.

International Publication No. 2011/155620 JP 2012020291A JP 2012-206144 A JP 2012-206145 A JP 2013-103259 A

  The present invention relates to welding of a thick steel base material such as a high Ni steel applied to a steel structure material exposed to a very low temperature environment such as an LNG tank or an LNG ship, in which poor penetration, poor fusion, high-temperature cracking, etc. Arc-hybrid welding joint that does not generate welding defects and does not cause poor fusion at the interface between the base metal and the weld metal, and a method for manufacturing the same, to reduce the number of laminations and the number of passes of welding It aims to remarkably improve welding efficiency and welding cost.

In order to solve the above-mentioned technical problem, the present inventor precedes a welding torch for gas shielded arc welding using a solid wire welding material such as a Ni-based alloy, and arranges a laser irradiation point behind the welding torch. We examined various welding conditions when using hybrid welding and found that welding with excellent toughness of the weld metal, no weld defects such as poor penetration, poor fusion, and high temperature cracking, and high welding efficiency could be obtained. I found the law.
The present invention is as described below.

(1) Multi-layer weld metal obtained by a welding method using laser-arc hybrid welding in which a welding torch for gas shielded arc welding using a Ni-based alloy welding material is preceded and a laser irradiation point is arranged behind the welding torch When the total area of the weld metal is WTA and the sum of the areas of the portions re-melted by laser welding subsequent to gas shielded arc welding is SWA, the area ratio SWA / WTA is 0.20 or more. When the width of the weld metal formed in each pass is W and the height is H, all H / Ws are less than 0.7, and the oxygen content of the obtained weld metal is 220 ppm or less. A welded joint characterized by the following.

(2) A method for producing a welding joint as described in (1) above, wherein a welding torch for gas shielded arc welding is preceded and laser-arc hybrid welding is performed with a laser irradiation point disposed behind the welding torch. In the gas shielded arc welding, a mixed gas composed of an Ar gas containing _{2 to} 5% O ₂ gas or 5 to 25% CO ₂ gas is used as a shielding gas, and the welding heat input is 14.0 to 21. 5 kJ / cm, and a laser having a wavelength of 0.78 to 1.60 μm was used for the rear laser welding. The target position of laser irradiation was P [mm], the welding speed was V [mm / sec], When the wire aiming position of the gas shielded arc welding is set to the origin 0, it is noted that P is in the range of V to 10 V [mm] in the direction opposite to the welding progress direction from the wire aiming position. It welded joint manufacturing method according to a laser-arc hybrid welding to.

  The welding joint of the present invention is a laser-arc hybrid welding in which a welding material of a Ni-based alloy is used in welding a thick steel base material such as a high Ni steel, a welding torch is arranged ahead, and a laser irradiation point is arranged behind the welding torch. Is a welded joint made of a multi-layered weld metal made by a welding method using, and has excellent toughness of the weld metal, no welding defects such as poor penetration, poor fusion, and hot cracking. -Since the number of passes can be greatly reduced, welding efficiency and welding cost can be greatly improved, and the industrial effect is extremely large.

It is a joint sectional view at the time of obtaining a test piece from the welding joint of the present invention. It is a figure for explaining the laser-arc hybrid welding method adopted by the present invention. It is a figure for explaining a welding joint section shape after welding. 4 is a graph showing a correlation between a SWA / WTA ratio and the number of welding defects. It is a graph showing the influence which the amount of oxygen in a weld metal has on the Charpy absorbed energy value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A welding joint was manufactured by the following manufacturing method and evaluated. In FIG. 1, 9% Ni steel having a thickness of 20 mm manufactured by Nippon Steel & Sumitomo Metal Co., Ltd. was used as the steel plate 11, and 9% Ni steel having a thickness of 12 mm was used as the back plate 12. As the welding material 6 (see FIG. 2), a solid wire of a Ni-based alloy corresponding to Z3334-SNi6082 and Z3334-SNi6276 of the JIS standard was used. [Table 1-1] shows the components of the steel plate 11 used, and [Table 1-2] shows the components of the welding material (welding wire) 6.

  Using these steel plates and welding wires SW1 or SW2, the groove shape shown in FIG. 1 was obtained according to the method for producing a welded joint described in “Method of tensile and impact test of welded metal” in JIS Z3111-2005. Under the conditions (current, voltage, welding speed, heat input, shielding gas composition, laser medium, laser output, laser irradiation target position) shown in [Table 2-1] to [Table 2-2], Laser-arc hybrid welding combining welding and laser welding was performed to produce a multi-layer welded joint.

The thus obtained welded joint was cut in a direction perpendicular to the welding direction, and a cross section of the welded joint revealed a structure by mirror polishing and nital corrosion. It was visually observed and observed with an optical microscope, the entire area of the weld metal was measured and defined as WTA, the area of the remelted portion was measured, and the sum was defined as SWA, and SWA / WTA was calculated.
Regarding welding defects, the number of poor penetration, poor fusion, and hot cracking were counted, and the total was defined as the number of welding defects.
Further, the height and width of the weld metal for each pass were observed, and the one that maximized H / W was measured.
As a result of the observation, as shown in FIG. 4, SWA / WTA was 0.20 or more, that is, the area WTA of the entire weld metal was reduced by the area of the area remelted by laser welding subsequent to gas shielded arc welding. In the region where the sum SWA was 0.20 or more, no generation of welding defects was observed.

Next, as shown in FIG. 1, a No. A1 tensile test piece (round bar) (diameter = 12.5 mm) 15 based on JIS standard Z3111-2005 and a Charpy test piece (2 mm V notch test) based on Z2242-2005. 14) were sampled, and subjected to mechanical property tests to measure the tensile strength of the deposited metal and the Charpy absorbed energy vE _-196 [J] at -196 ° C (liquid nitrogen temperature).

The evaluation criteria for the mechanical properties were as follows.
-Tensile strength: The tensile strength required for the welded part according to the Electricity Business Law and the Gas Business Law of the LNG tank was 660 MPa or more.

  -Toughness: Charcoal absorbed energy of 80 J or more at -196 ° C was accepted for the inconel welding material SW1 of Z3334-SNi6082, and Charpy absorbed energy of 60J at -196 ° C for the Hastelloy-based welding material SW2 of Z3334-SNi6276. The above was passed.

The oxygen content of the weld metal is measured by cutting out an analytical sample pin for oxygen measurement of the weld metal from the center of the plate thickness and the center of the width of the weld metal in the longitudinal direction of the weld joint, using an inert gas-dissolved infrared absorption method. Was measured by As shown in the results in FIG. 5, for all the welding materials, the Charpy absorbed energy values in the acceptable range were obtained in the region where the oxygen content was 220 ppm or less.
The above test results are shown in [Table 3-1] to [Table 3-2].

  As shown in the test results of [Table 3-1] to [Table 3-2], test numbers T1 to T30, which are examples of the present invention, passed. On the other hand, the test numbers T31 to T42 as comparative examples failed in the comprehensive judgment.

That is, in T31, the laser output was insufficient, and in T32, the welding speed was too high, and the area ratio SWA / WTA of the re-melted portion by laser irradiation was less than 0.20, and welding defects occurred.
Further, in T33 and T34, since the content of oxygen or carbon dioxide in the shielding gas was insufficient, the arc became unstable, and welding defects were caused due to poor weld bead shape. , And Charpy test did not occur.

  In contrast to T33 and T34, T35 to T38 are comparative examples in which an excess oxygen or carbon dioxide is contained in the shielding gas or the joint is welded with a shielding gas of 100% carbon dioxide. In these comparative examples, the oxygen content in the weld metal was 220 ppm or more, and as a result, the Charpy absorbed energy value at -196 ° C was less than 60 J, and the specified toughness could not be secured.

T39 to T41 are comparative examples in which a welding defect was caused by an inappropriate laser irradiation position subsequent to gas shielded arc welding. In T39, the target positions are too close, and in T40 and T41, the target positions are too far, and neither can obtain an appropriate remelting state, and the area ratio SWA / WTA is less than 0.2. No welding defect occurred.
Further, T42 was an excessive voltage and current in the relative comparison with the welding speed, so that the amount of heat input per unit length of the welding line became excessive, so that the welding amount increased and remelting was insufficient. And a welding defect was generated, and the test was rejected.

  According to the present invention, in welding of a thick steel base material such as high Ni steel, laser-arc hybrid welding using a welding material of a Ni-based alloy, preceding a welding torch, and arranging a laser irradiation point behind the welding torch is performed. By forming a welded joint consisting of multiple layers of weld metal created by the used welding method, sound welding with excellent toughness of weld metal and no weld defects such as poor penetration, poor fusion, and hot cracking Since the joint can be manufactured with the number of laminations and the number of passes greatly reduced, welding efficiency and welding cost can be significantly improved.

DESCRIPTION OF SYMBOLS 1 Front and back of steel plate 2 Weld metal 3 Molten pool 4 Transfer droplet 5 Target position of arc welding 6 Welding wire 7 Gas shield arc welding torch 8 Laser torch 9 Laser beam 10 Laser irradiation point 11 Steel plate 12 Backing metal 13 Weld metal 14 Charpy test Piece (2mm V notch test piece)
15 Tensile test piece (round bar)

Claims (2)

  Welding with a multi-layer weld metal obtained by a welding method using laser-arc hybrid welding in which a welding torch of gas shielded arc welding using a Ni-based alloy welding material is preceded and a laser irradiation point is arranged behind it In the joint, when the area of the entire weld metal is WTA and the sum of the areas of the portions re-melted by the subsequent laser welding of gas shielded arc welding is SWA, the area ratio SWA / WTA is 0.20 or more; Assuming that the width of the weld metal formed for each pass is W and the height is H, all H / W is less than 0.7 and the oxygen content of the obtained weld metal is 220 ppm or less. Characterized welding joint. 2. A method for producing a welding joint according to claim 1, wherein a welding torch of gas shielded arc welding is preceded and laser-arc hybrid welding is performed with a laser irradiation point disposed behind the welding torch. In welding, a mixed gas composed of Ar gas containing _{2 to} 5% O ₂ gas or 5 to 25% CO ₂ gas is used as a shielding gas, and the welding heat input is 14.0 to 21.5 kJ / cm. There is a laser with a wavelength of 0.78 to 1.60 μm for the rear laser welding. The target position of laser irradiation is P [mm], the welding speed is V [mm / sec], and the preceding gas shield arc is used. When the wire aiming position of welding is set to the origin 0, P is in the range of V to 10 V [mm] in the direction opposite to the welding progress direction from the wire aiming position. Weld joint manufacturing method according to the Za-arc hybrid welding.