Method of laser-welding metal base material, laser-welding apparatus, and welded metal structure formed using same

Abstract

The present invention provides a method of laser-welding a metal base material, a laser-welding apparatus, and a welded metal structure formed using same, wherein welding is performed using a laser to minimize the formation of a welding heat affected zone and thus maintain the strength and functionality of a welded part. The method of laser-welding a metal base material according to an embodiment of the present invention comprises: a step of providing a metal base material having an area to be welded; a step of injecting a powder filler metal into the welding target area; a step of irradiating the area to be welded with a laser so that the powder filler metal is melted to form a filler metal molten material; and a step of forming a welding part by allowing the filler metal molten material to solidify.

Description

Laser welding method for metal base material, laser welding device, and welded metal structure formed using the same

[0001] The technical idea of ​​the present invention relates to a method for welding a metal base material, and more specifically, to a method for laser welding a metal base material, a laser welding device, and a welded metal structure formed using the same.

[0002] This invention was conducted with the support of the Ministry of Trade, Industry and Energy as a 'International Cooperation in Industrial Technology' [Project Name: Development of Smart Clamping and Coupling Technology for Civil Structures Using Iron-Based Shape Memory Alloy, Project Number: NK230007, Project Identification Number: 1415189866, Project Management (Specialist) Organization Name: Korea Institute for Advancement of Technology, Project Execution Organization Name: Korea Institute of Industrial Technology].

[0003] Gas metal arc welding (GMAW) or gas tungsten arc welding (GTAW) are commonly used welding methods for assembling metal base materials. This arc welding method involves feeding a consumable electrode wire as a filler metal at a constant rate to the welding area while applying current, thereby generating an arc between the wire and the base material. The continuously fed wire is melted by the high heat of the arc and supplied to the welding area, and welding is accomplished while being protected from the surrounding atmosphere by a shielding gas. This type of arc welding has limitations, such as the risk of generating spatter that can adhere to the surface of the base material and damage its appearance, and the inability to weld in areas where the welding wire has difficulty approaching the welding area. In addition, the weld heat affected zone is formed very widely in the base material, which causes undesirable grain growth, and coarse dendrites are formed in the weld due to the low solidification rate, which causes very large solute segregation, and the desired properties such as strength may be significantly reduced, and in particular, the shape memory properties may be reduced or not expressed.

[0004] The technical problem to be achieved by the technical idea of ​​the present invention is to provide a method for laser welding a metal base material, a laser welding device, and a welded metal structure formed using the same, which welds using a laser so as to minimize the formation of a heat-affected zone of the weld and maintain the strength and functionality of the weld.

[0005] However, these tasks are exemplary and the technical idea of ​​the present invention is not limited thereto.

[0006] According to one aspect of the present invention, a method for laser welding a metal base material, a laser welding device, and a welded metal structure formed using the same are provided, which weld using a laser so as to minimize the formation of a heat-affected zone of the weld and maintain the strength and functionality of the weld.

[0007] According to one embodiment of the present invention, a method for laser welding a metal base material includes the steps of: providing a metal base material having a welding target area; introducing a powder filler metal into the welding target area; irradiating a laser onto the welding target area so that the powder filler metal melts to form a filler metal melt; and solidifying the filler metal melt to form a welded portion. In the step of introducing the powder filler metal and the step of introducing the laser, the laser may move along an extension direction of the welding target area, and the introduction of the powder filler metal may be performed at a tip of the laser by following the movement of the laser.

[0008] According to one embodiment of the present invention, the step of injecting the powdered filler material and the step of irradiating the laser are performed continuously while moving along the extension direction of the welding target area, thereby forming the welded part.

[0009] According to one embodiment of the present invention, the step of introducing the powdered filler metal and the step of irradiating the laser are performed intermittently while moving along the extension direction of the welding target area, thereby forming the welded part.

[0010] According to one embodiment of the present invention, the step of injecting the powder filler material and the step of irradiating the laser can be performed once or repeatedly multiple times while moving along the extension direction of the welding target area to form the welded part.

[0011] According to one embodiment of the present invention, the metal base material may include an Fe-Si-Mn shape memory alloy, and the powder filler material may include an Fe-Mn-Cr-C shape memory alloy.

[0012] According to one embodiment of the present invention, the metal base material contains 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0013] The above powdered filler may contain 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0014] According to one embodiment of the present invention, the content of manganese contained in the powder filler metal may be higher than the content of manganese contained in the metal base material.

[0015] According to one embodiment of the present invention, the laser can be irradiated with an output in a range of 150 W or more and less than 350 W.

[0016] According to one embodiment of the present invention, the powder filler may have an average particle diameter in the range of 50 μm to 150 μm.

[0017] According to one embodiment of the present invention, the metal base material may be a metal plate formed into a hollow cylindrical shape, and the welding target area may be an area where both ends of the metal base material are in contact with each other.

[0018] According to one embodiment of the present invention, the welded portion may be formed by stacking a plurality of layers along the extension direction of the welding target area, or may have a continuous shape or a discontinuous shape.

[0019] According to one embodiment of the present invention, the step of injecting powdered filler metal into the welding target area can be performed while changing the composition of the powdered filler metal over time.

[0020] According to one embodiment of the present invention, in the step of introducing the powder filler metal, a powder filler metal of a first composition is introduced, and a step of irradiating the laser is performed to form a lower weldment, and then, in the subsequent step of introducing the powder filler metal, a powder filler metal of a second composition different from the first composition is introduced, and a step of irradiating the laser is performed to form an upper weldment on the lower weldment.

[0021] According to one embodiment of the present invention, the welded portion may include a first composition welded portion and a second composition welded portion that are arranged along the extension direction of the welding target area and have different compositions.

[0022] According to one embodiment of the present invention, in order to prevent oxidation of the filler material melt and the weld, an inert gas may be supplied to the filler material melt and the weld to perform purging.

[0023] According to one embodiment of the present invention, the welded metal structure includes a metal base material; and a weld formed at a portion where ends of the metal base materials are in contact with each other, wherein the metal base material is a shape memory alloy containing 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities, and the weld may contain 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0024] According to one embodiment of the present invention, the thickness of the weld heat-affected zone formed on the metal base material may be in a range of more than 0 μm and less than or equal to 50 μm.

[0025] According to one embodiment of the present invention, the average grain size of the weld heat-affected zone formed in the metal base material may be in the range of 30 μm to 50 μm or less.

[0026] According to one embodiment of the present invention, the welded portion may have a solidified structure formed by melting and then solidifying the powdered filler material.

[0027] According to one embodiment of the present invention, the welded metal structure may include a metal base material in the form of a plate formed into a hollow cylinder; and a tubular coupler including a welded portion formed in a portion where the ends of the metal base material are in contact with each other and extend in the longitudinal direction of the hollow cylinder of the metal base material.

[0028] According to the technical idea of ​​the present invention, the laser welding method according to the technical idea of ​​the present invention forms a weld by melting and solidifying a powder filler metal using a laser having a relatively low heat input. The formation of a wide weld heat-affected zone and the formation of coarse dendritic structures in the weld can be suppressed in conventional arc welding, and thus the integrity of the interface between the metal base material and the weld and the internal integrity of the weld can be secured, and the mechanical strength and functionality of the metal base material can be secured. In particular, the shape memory characteristics of a coupler made of a shape memory alloy can be secured.

[0029] Furthermore, unlike conventional arc welding, where it is difficult to change the composition of the filler metal during welding, welding can be performed by changing the composition of the powder filler metal during welding, thereby compensating for the lack of volatile substances by performing subsequent welding using a powder filler metal of a different composition to compensate for the change in composition due to volatilization of volatile substances. Furthermore, a welded joint with a different composition can be easily formed in real time during welding.

[0030] The effects of the present invention described above are illustrative, and the scope of the present invention is not limited by these effects.

[0031] FIG. 1 is a flowchart illustrating a method for laser welding a metal base material according to one embodiment of the present invention.

[0032] FIGS. 2 to 5 are schematic diagrams showing a weld formed by a laser welding method of a metal base material according to one embodiment of the present invention.

[0033] FIG. 6 is a schematic diagram illustrating a laser welding device that performs a method for laser welding a metal base material according to one embodiment of the present invention.

[0034] FIG. 7 and FIG. 8 show the microstructure of a welded metal structure formed using a laser welding method according to one embodiment of the present invention.

[0035] FIG. 9 is an external photograph showing the formation of a defect according to the laser output of a welded portion of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0036] FIGS. 10 to 12 are graphs showing the stress-elongation relationship of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0037] Fig. 13 is a graph showing the shape memory characteristics of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0038] FIG. 14 is a schematic diagram illustrating a process for forming a tubular coupler as a welded metal structure formed using a laser welding method according to one embodiment of the present invention.

[0039] FIG. 15 is a photograph showing a tubular coupler having shape memory characteristics formed using a laser welding method according to an embodiment of the present invention.

[0040] Fig. 16 is a photograph showing a state in which a pipe is coupled using a tubular coupler having shape memory characteristics formed using a laser welding method according to an embodiment of the present invention.

[0041] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Embodiments of the present invention are provided to more completely explain the technical idea of ​​the present invention to those skilled in the art. The following embodiments may be modified in various different forms, and the scope of the technical idea of ​​the present invention is not limited to the following embodiments. Rather, these embodiments are provided to more faithfully and completely convey the technical idea of ​​the present invention to those skilled in the art. Like reference numerals throughout this specification denote like elements. Furthermore, various elements and areas in the drawings are schematically drawn. Therefore, the technical idea of ​​the present invention is not limited by the relative sizes or intervals drawn in the attached drawings.

[0042] Laser welding method

[0043] FIG. 1 is a flowchart illustrating a method for laser welding a metal base material according to one embodiment of the present invention.

[0044] Referring to FIG. 1, a method for laser welding a metal base material (S100) includes a step of providing a metal base material having a welding target area (S110); a step of injecting a powder filler metal into the welding target area (S120); a step of irradiating a laser onto the welding target area so that the powder filler metal melts to form a filler metal melt (S130); and a step of solidifying the filler metal melt to form a weld (S140).

[0045] In the step of introducing the powder filler material (S120) and the step of irradiating the laser (S130), the laser moves along the extension direction of the welding target area, and the introduction of the powder filler material can be performed at the tip of the laser by following the movement of the laser.

[0046] The step (S110) of providing the above metal base material may be performed by providing a metal base material having a welding target area. The metal base material may be composed of a plurality of flat plates that are in contact with each other, and the welding target area may be an area where the flat plates are in contact with each other. Alternatively, the metal base material may be a hollow tube formed into a circular plate, and the welding target area may be both side ends that are in contact with each other.

[0047] The step of injecting the powdered filler material (S120) can be performed by injecting the powdered filler material into the welding target area.

[0048] The step (S130) of irradiating the laser may be performed by irradiating the welding target area with the laser. Accordingly, the powdered filler metal may be melted to form a filler metal melt. By the laser, a melting pool may be formed in the welding target area. The laser may be irradiated with an output in the range of 150 W or more and less than 350 W.

[0049] The step (S140) of forming the above welded portion can be performed by solidifying the melted filler material.

[0050] The step of introducing the powder filler metal (S120) and the step of irradiating the laser (S130) may be performed simultaneously or with a time difference. Alternatively, the step of introducing the powder filler metal (S120) may be performed after performing the step of introducing the powder filler metal (S130). Alternatively, the step of introducing the laser (S130) may be performed after performing the step of introducing the powder filler metal (S120).

[0051] The step of injecting the powdered filler (S120) and the step of irradiating the laser (S130) can be performed once or repeatedly multiple times while moving along the extension direction of the welding target area to form the welded part.

[0052] When the step of injecting the powder filler material (S120) and the step of irradiating the laser (S130) are performed repeatedly multiple times, the weld can be formed by stacking multiple layers along the extension direction of the welding target area (see Fig. 2). In this case, one layer can be formed for each performance. The multiple layers can remain as separate layers or be integrated. In addition, the weld can have a continuous shape or a discontinuous shape as described below.

[0053] The step of injecting the powdered filler material (S120) and the step of irradiating the laser (S130) can be performed continuously while moving along the extension direction of the welding target area to form the welded part (see Fig. 3). Accordingly, the welded part can have a continuous shape along the extension direction of the welding target area.

[0054] The step of injecting the powder filler metal (S120) and the step of irradiating the laser (S130) can be performed intermittently while moving along the extension direction of the welding target area, thereby forming the welded portion (see Fig. 4). Accordingly, the welded portion can have a discontinuous shape along the extension direction of the welding target area. In addition, spot welding of the welding target area can be implemented by the intermittent method described above.

[0055] The step (S120) of introducing the powder filler metal may be performed while changing the composition of the powder filler metal over time (see FIG. 5). Accordingly, the welded portion may be composed of regions having different compositions along the extension direction of the welding target region. The composition of the powder filler metal may be changed based on various requirements, such as changes in the components and shape of the metal base material, the filler metal supply speed, the welding environment such as temperature or humidity, and the welding progress time.

[0056] Additionally, to prevent oxidation of the filler metal melt and the weld, purging can be performed by supplying an inert gas such as nitrogen or argon to the filler metal melt and the weld.

[0057] The above metal base material and the above welded portion may have shape memory characteristics.

[0058] The above metal base material may include, for example, an Fe-Si-Mn shape memory alloy, and may include, for example, 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0059] The above powder filler and the above welded portion may include, for example, an Fe-Mn-Cr-C type shape memory alloy, and may include, for example, 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0060] Additionally, the powder filler metal and the welded portion may be the same metal alloy as the metal base material, and may contain, for example, 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0061] The manganese content contained in the powder filler metal may be higher than the manganese content contained in the metal base material. That is, since manganese may evaporate during the process of melting the powder filler metal to form the weld, the manganese content of the powder filler metal may be increased to compensate for the evaporated amount. Accordingly, the manganese content of the metal base material and the weld may be maintained to be similar or the same.

[0062] The above powdered filler may have an average particle diameter in the range of 50 μm to 150 μm.

[0063] The thickness of the weld heat-affected zone formed on the above metal base material may be in the range of more than 0 μm and less than or equal to 50 μm.

[0064] The average grain size of the weld heat-affected zone of the above metal base material may be in the range of 30 μm to 50 μm. Since grain growth hardly occurs in the weld heat-affected zone of the above metal base material, the above metal base material and the weld heat-affected zone of the above metal base material may have grains of almost the same size.

[0065] The above welded metal structure may be implemented as a tubular coupler. For example, the metal base material may be a metal plate formed into a hollow cylinder, and the welding target area may be an area where both ends of the metal base material are in contact with each other.

[0066] Figures 2 to 5 are schematic diagrams illustrating a weld formed by a laser welding method of a metal base material according to one embodiment of the present invention. Figure 2 is a cross-sectional view, and Figures 3 to 5 are top views.

[0067] Referring to FIG. 2, a weld (170) is formed by repeatedly introducing powder filler material and performing laser irradiation in a welding target area (180) of a metal base material (190) multiple times along the extension direction of the welding target area indicated by arrows. The powder filler material is introduced and the laser irradiation is performed once along the extension direction of the welding target area to form a lower weld (170_1), and then the powder filler material is introduced and the laser irradiation is performed a second time along the extension direction of the welding target area to form an upper weld (170_2) on the lower weld (170_1), thereby forming a weld (170). In this case, the powder filler material introduction and the laser irradiation may be performed multiple times more than twice.

[0068] In addition, the step (S130) of injecting powder filler metal into the welding target area can be performed while changing the composition of the powder filler metal over time. In the step (S130) of injecting powder filler metal, a powder filler metal of a first composition is injected, and the step (S140) of irradiating the laser is performed to form a lower weldment, and then in the subsequent step (S130) of injecting powder filler metal, a powder filler metal of a second composition different from the first composition is injected, and the step (S140) of irradiating the laser is performed to form an upper weldment (170_2) on the lower weldment (170_1).

[0069] For example, when the powder filler metal contains a volatile substance such as manganese, the content of the volatile substance in the formed lower weld (170_1) may be lower than the value set in the first composition of the powder filler metal. Therefore, in a subsequent process, an upper weld (170_2) may be formed using a powder filler metal having a second composition with an increased content of the volatile substance, thereby supplementing the insufficient content of the volatile substance by transferring it from the upper weld (170_2) to the lower weld (170_1).

[0070] Referring to FIG. 3, powder filler metal injection and laser irradiation are continuously performed in the welding target area (180) of the metal base material (190) along the extension direction of the welding target area indicated by the arrow to form a continuous weld (170_3). Accordingly, the continuous weld (170_3) can have a continuous shape along the extension direction of the welding target area. In addition, as described in FIG. 2, powder filler metal injection and laser irradiation can be performed repeatedly multiple times to form a continuous weld (170_3).

[0071] Referring to FIG. 4, powder filler metal injection and laser irradiation are performed intermittently along the extension direction of the welding target area (180) of the metal base material (190) along with the arrows to form a discontinuous weld (170_4). Accordingly, the discontinuous weld (170_4) may have a discontinuous shape along the extension direction of the welding target area. In addition, as described in FIG. 2, powder filler metal injection and laser irradiation may be performed repeatedly multiple times to form a discontinuous weld (170_4).

[0072] Referring to FIG. 5, a powder filler metal having a first composition is injected into a welding target area (180) of a metal base material (190) and laser irradiation is performed along the extension direction of the welding target area to form a weld (170_5) having a first composition. Subsequently, by changing the composition over time, a powder filler metal having a second composition different from the first composition is injected into the welding target area and laser irradiation is performed along the extension direction of the welding target area to form a weld (170_6) having a second composition. Accordingly, the weld (170) may be arranged along the extension direction of the welding target area (180) and may include a weld (170_5) having a first composition and a weld (170_6) having a second composition that have different compositions.

[0073] Each of the first composition weld (170_5) and the second composition weld (170_6) may be formed by stacking multiple layers along the extension direction of the welding target area as described above, or may have a continuous shape or a discontinuous shape.

[0074] laser welding device

[0075] FIG. 6 is a schematic diagram illustrating a laser welding device that performs a method for laser welding a metal base material according to one embodiment of the present invention.

[0076] Referring to FIG. 6, the laser welding device (100) includes a laser unit (120), a welding material supply unit (130), a driving unit (140), a control unit (150), and a purging unit (160).

[0077] The laser welding device (100) can form a molten filler material by simultaneously supplying the powdered filler material from the filler material supply unit (130) to the welding target area (180) while moving along the extension direction of the welding target area (180) and irradiating the laser from the laser unit (120).

[0078] The receiving space (110) can provide a receiving space for performing laser welding of a metal base material (190). The receiving space (110) can be, for example, a chamber.

[0079] The laser unit (120) is positioned so as to face the welding target area (180) provided on the metal base material (190) within the receiving space (110), and can irradiate a laser (122) toward the welding target area (180). The laser unit (120) may be configured as at least one of, for example, a neodymium yag (Nd:YAG) laser, a fiber laser, and a diode laser. The laser unit (120) may have an output in the range of, for example, 100 W to 1000 W. Accordingly, the laser unit (120) may have a relatively low heat input and may reduce the range of the formed welding heat-affected zone.

[0080] The above-mentioned filler material supply unit (130) is arranged to be linked with the laser unit (120) within the receiving space (110), and can supply the powder filler material (133) toward the welding target area (180) in real time so that the powder filler material (133) is melted and solidified by the laser (122) to weld the welding target area (180).

[0081] The above-mentioned filler material supply unit (130) may include a filler material receiving unit (131) that receives the powder filler material (133); and a nozzle unit (132) that is arranged toward the welding target area (180) and injects the powder filler material (133) provided from the filler material receiving unit (131) into the welding target area (180). The filler material receiving unit (131) may include components such as a compressor, a pump, etc., so as to be able to inject the powder filler material (133) into the nozzle unit (132).

[0082] The above-mentioned filler material receiving portion (131) may include a first filler material receiving portion (131_A) for receiving a powdered filler material of a first composition; and a second filler material receiving portion (131_B) for receiving a powdered filler material of a second composition different from the first composition. The filler material receiving portion (131) may include components such as pipes and valves for selectively providing the powdered filler material.

[0083] However, this is exemplary, and the filler material receiving portion (131) according to the technical idea of ​​the present invention can provide powder filler material by mixing the powder filler material of the first composition received in the first filler material receiving portion (131_A) and the powder filler material of the second composition received in the second filler material receiving portion (131_B), and for this purpose, the filler material receiving portion (131) can include a filler material mixing element.

[0084] Although the above-mentioned filler material receiving portion (131) is illustrated as having two sub-filler material receiving portions, namely, a first filler material receiving portion (131_A) and a second filler material receiving portion (131_B), it should be noted that this is an example of including a plurality of sub-filler material receiving portions.

[0085] The above nozzle part (132) may have a hollow shape with the path of the laser (122) at the center, and may be, for example, a hollow cylinder.

[0086] The above powder filler (133) may have a powder form. However, this is merely exemplary, and the filler may also have various forms, such as a paste or solid, within the technical scope of the present invention.

[0087] The powder filler metal (133) can be introduced into the welding target area (180) from the nozzle unit (132) by means of a carrier gas (134). A component that provides the carrier gas (134) can be installed in the filler metal receiving unit (131), installed in the nozzle unit (132), or separately connected to the nozzle unit (132). The carrier gas (134) can be an inert gas, and can be, for example, nitrogen gas, argon gas, or a mixed gas thereof.

[0088] The above driving unit (140) is connected so that the laser unit (120) and the filler material supply unit (130) can move in conjunction with each other along the welding target area (180) and can move forward and backward in the welding progress direction. The driving unit (140) can be placed within the receiving space (110) or outside the receiving space (110).

[0089] The control unit (150) can control the operation of at least one of the laser unit (120), the filler material supply unit (130), and the driving unit (140). The control unit (150) can be placed within the receiving space (110) or outside the receiving space (110).

[0090] The above control unit (150) may include a laser control unit (151), a filler supply control unit (152), and a driving control unit (153).

[0091] The laser control unit (151) is electrically connected to the laser unit (120) and can provide a first control signal to the laser unit (120) that controls the output and scan speed of the laser (122). The output and scan speed of the laser (122) can be changed depending on the components of the metal base material (190) and the components and input amount of the powder filler material (133).

[0092] The above-mentioned filler material supply control unit (152) is electrically connected to the filler material supply unit (130) and can provide a second control signal for controlling the components and input amount of the powder filler material (133) to the filler material supply unit (130).

[0093] The above driving control unit (153) is electrically connected to the driving unit (140) and can provide a third control signal to the driving unit (140) that controls the driving of the laser unit (120) and the filler material supply unit (130).

[0094] The purging unit (160) is disposed within the receiving space (110) and can supply an inert gas to the welding target area (180) to prevent oxidation of the metal base material (190) during welding. The supply of the inert gas can be selectively performed. The inert gas can be, for example, nitrogen gas, argon gas, or a mixed gas thereof. The purging unit (160) can be controlled by the control unit (150), and the supply of the inert gas can be controlled accordingly.

[0095] The powder filler metal (133) injected into the welding target area (180) is melted by the laser (122) to form a filler metal melt and then solidifies to form the welding portion (170). As the laser portion (120) and the filler metal supply portion (130) move in conjunction with each other along the welding target area (180) by the driving portion (140), the welding portion (170) can be formed along the extension direction of the welding target area.

[0096] Welded metal structures of Fe-Mn-Si-based iron-based shape memory alloys

[0097] Below, as an example of applying the laser welding method of a metal base material, a welded metal structure of an Fe-Mn-Si-based iron-based shape memory alloy is described.

[0098] Although Fe-Mn-Si based iron-based shape memory alloys exhibit lower shape memory properties than Ni-Ti alloys, they are much cheaper, so they have great advantages in mass production, high recovery stress, and other applications in large structures. Therefore, they are receiving a lot of attention for applications such as pipe couplings and vibration damping members in civil engineering structures. After the iron-based shape memory alloy is made into a sheet, it is bent and welded to make a hollow pipe, so that a coupler used for water pipes and gas pipes can be formed. After expanding a coupler with an inner diameter smaller than the outer diameter of the pipe, pipes are inserted into the coupler from both sides and heated, and the shape memory properties and high recovery stress can strongly bind the two pipes. Welding is required to form such a coupler.

[0099] Welding methods that use an arc as a heat source, such as conventional gas tungsten arc welding, are easy to access, but they generate a very wide heat-affected zone, which causes grain growth and, due to the low solidification rate, forms a coarse dendrite structure with very large solute segregation in the fusion zone, which can significantly reduce strength and shape memory properties or prevent them from being developed at all.

[0100] Welding of iron-based shape memory alloys, such as those used in couplers, requires more than simply physically connecting two metals; it also requires maintaining their inherent functionality. Therefore, utilizing a laser welding method using a laser as a heat source according to the technical concept of the present invention can minimize deterioration in the strength and shape memory properties of the weld and weld heat-affected zone.

[0101] The above laser welding method can achieve deep local weld penetration in a short period of time, thereby minimizing the occurrence of a heat-affected zone. Furthermore, the extremely rapid cooling rate after melting prevents, or at least minimizes, solute segregation, thereby maintaining the strength and functionality of the weld.

[0102] In particular, the laser welding method according to the present invention forms a weld by stacking layers formed by melting and cooling powder filler metal using a relatively low laser output, thereby reducing the weld heat-affected zone, thereby ensuring the integrity of the interface between the metal base material and the weld and the integrity of the inside of the weld. Therefore, if a ferrous shape memory alloy coupler is manufactured using the laser welding method according to the present invention, the on-site welding process can be reduced in the installation of water and sewage pipes, gas pipes, etc., thereby significantly reducing the process time and cost, and can also be applied to reinforcing bar couplers used in construction sites. In addition, the laser welding method according to the present invention can suppress the formation of a wide weld heat-affected zone and the formation of coarse dendritic structures in the weld, which are formed in conventional arc welding, and can secure the mechanical strength and functionality of the shape memory alloy.

[0103] When welding metal materials, maintaining the strength of the weld and the weld heat-affected zone is crucial. Maintaining strength and functionality is particularly important for iron-based shape memory alloys. The formation of a weld heat-affected zone around the weld is primarily related to heat input, which can be inferred using the following equation.

[0104] Q = P / v

[0105] (Here, Q is the heat input, P is the laser power, and v is the welding speed)

[0106] In the case of conventional arc welding, a wide and shallow melting pool is formed compared to laser welding, so the welding speed is slow to obtain sufficient penetration, so the heat input increases, and thus a wide weld heat-affected zone is formed. At this time, the grains in the wide weld heat-affected zone coarsen, and the strength is reduced accordingly. In addition, shape memory alloys that improve strength and shape memory properties through carbide precipitation, such as Fe-Mn-Si-Cr-Ni-(V,C), experience coarse precipitates, which deteriorate the shape memory properties.

[0107] In the case of the laser welding method according to the present invention, since it has a high energy density, a high welding speed can be implemented, and accordingly, the change in the structure of the metal base material due to the heat generated during welding can be minimized. In addition, it has a high temperature gradient and 10 5 Because it has a very fast cooling rate of more than ℃ / sec, it can exhibit a fine cellular structure instead of a coarse dendritic structure and also minimize solute segregation.

[0108] The output of the laser generator for laser welding with these advantages can range from several hundred W to several kilowatts. For example, high-power laser welding using a high output of 1 kW or more can achieve very thin and deep penetrations, such as keyholes.

[0109] On the other hand, since the tubular coupler has a curved shape, the two ends may not be completely sealed, so the gap can be filled using a powder filler material to secure the integrity of the interface and weld. In addition, the formation of the weld heat-affected zone can be suppressed by applying a low heat input using a fiber laser with a relatively low output of about 100 W to 250 W. In addition, even with a low laser output, the heat-affected zone can be reduced by 10 5It can achieve extremely high cooling rates of more than ℃ / sec. Therefore, it forms a fine cellular structure instead of a coarse dendritic structure and suppresses solute segregation, thereby preserving mechanical strength and shape memory properties. Furthermore, its low vapor pressure allows it to preserve the content of highly volatile manganese during melting.

[0110] Representative elements used in iron-based shape memory alloys include iron (Fe), manganese (Mn), silicon (Si), chromium (Cr), and nickel (Ni). Manganese (Mn) is present in the highest content among alloying elements excluding iron, at 15 to 30 wt%, and has a significant impact on phase stability and stacking fault energy, making it the most crucial element. In cases where high energy is injected, such as in laser welding, manganese (Mn) has a low vapor pressure and high volatility, which can significantly reduce the manganese (Mn) content in the weld zone. When manganese (Mn) is present in less than 15 wt%, the stacking fault energy increases, suppressing martensitic transformation, which exhibits shape memory characteristics during deformation, and reducing plastic deformation by accommodating twinning or dislocation slip. Therefore, by using a powder filler metal with a high manganese content, the manganese (Mn) content of the formed weld can be secured at a desired level, thereby maintaining the shape memory properties by keeping the stacking fault energy low.

[0111] In addition, when the integrity of the interface and weld is secured in a dissimilar joint with a high-manganese weld having a different composition from the metal base material, functionality can be imparted to the weld using powder having desired mechanical properties or functionality, such as stress-induced plasticity steel or stress-induced twin-induced plasticity steel.

[0112] A welded metal structure formed by the above-described laser welding method, wherein the welded metal structure comprises: a metal base material including a shape memory alloy; and a welded portion formed by melting and solidifying powdered filler material by a laser at a portion where the ends of the metal base materials are in contact with each other, and including a shape memory alloy.

[0113] The thickness of the weld heat-affected zone formed on the above metal base material may be in the range of more than 0 μm and less than or equal to 50 μm.

[0114] The average grain size of the above-mentioned weld heat-affected zone may be in the range of 30 μm to 50 μm or less.

[0115] The above metal base material and the above welded portion may have shape memory properties.

[0116] The above metal base material may include, for example, an Fe-Si-Mn shape memory alloy, and may include, for example, 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0117] The above powder filler and the above welded portion may include, for example, an Fe-Mn-Cr-C type shape memory alloy, and may include, for example, 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0118] Additionally, the powder filler metal and the welded portion may be the same metal alloy as the metal base material, and may contain, for example, 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0119] The aforementioned unavoidable impurities cannot be excluded, as unintended impurities from raw materials or the surrounding environment may inevitably be mixed in during the normal manufacturing process. Since these impurities are readily apparent to anyone skilled in the art of manufacturing, their full details are not specifically addressed in this specification.

[0120] Experimental example

[0121] Below, experimental examples are described to aid understanding of the present invention. The following experimental examples are presented to aid understanding of the invention, and the present invention is not limited to the following experimental examples.

[0122] First, as a metal matrix, shape memory alloy Fe-17Mn-5Si-10Cr-4Ni-0.7V-0.3C was prepared.

[0123] The above Fe-17Mn-5Si-10Cr-4Ni-0.7V-0.3C means that it contains 17 wt% manganese (Mn), 5 wt% silicon (Si), 10 wt% chromium (Cr), 4 wt% nickel (Ni), 0.7 wt% vanadium (V), 0.3 wt% carbon (C), and the remainder is iron (Fe) and unavoidable impurities.

[0124] Powdered filler metals were prepared as Fe-18.5Mn-4Cr-0.4C and Fe-24Mn-4Cr-0.4C powders.

[0125] The above Fe-18.5Mn-4Cr-0.4C means that it contains 18.5 wt% manganese (Mn), 4 wt% chromium (Cr), 0.4 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities. The above Fe-24Mn-4Cr-0.4C means that it contains 24 wt% manganese (Mn), 4 wt% chromium (Cr), 0.4 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities.

[0126] The manganese content of the above powdered filler may be greater than the manganese content of the above metal base material, and thus, a decrease in the manganese content due to volatilization may be prevented.

[0127] After forming a plate formed from the above metal base metal into a hollow pipe shape, both ends of the plate are brought into contact with each other in a butt-to-weld manner to form a welding target area, and using the laser welding method described above, the powder filler metal is melted and solidified by a laser to form a weld part in the welding target area. The output of the laser is varied from 100 W to 400 W.

[0128] In the drawings below, “18.5 wt% Mn” means a welded metal structure (Experimental Example 1) including a weld formed using Fe-18.5Mn-4Cr-0.4C powder filler metal, and “24 wt% Mn” means a welded metal structure (Experimental Example 2) including a weld formed using Fe-24Mn-4Cr-0.4C powder filler metal.

[0129] FIG. 7 and FIG. 8 show the microstructure of a welded metal structure formed using a laser welding method according to one embodiment of the present invention.

[0130] Referring to Figure 7, the microstructures of the base metal and weld part of Experimental Examples 1 and 2 are shown as inverse pole figure maps using backscatter electron diffraction. The black line indicates the interface between the base metal and the weld part.

[0131] Experimental Examples 1 and 2 show that the interface between the metal base material and the weld and the integrity of the weld are secured. The average grain size of the weld heat-affected zone of the metal base material adjacent to the weld was measured to be in the range of about 30 μm to 50 μm. Since the average grain size of the weld heat-affected zone of the metal base material and other regions of the metal base material are almost the same, it is analyzed that grain growth will hardly occur in the weld heat-affected zone of the metal base material. It can be seen that the weld has relatively large grains in the region far from the interface, and the average grain size of the weld was measured to be in the range of about 100 μm to 300 μm.

[0132] For reference, in conventional arc welding, grain growth occurs in the weld heat-affected zone, and accordingly, the average grain size of the weld heat-affected zone of the metal base material may be 4 to 5 times larger than that of other areas of the metal base material, and may be in the range of, for example, 120 μm to 250 μm.

[0133] Referring to Fig. 8, as an optical microscope photograph, the thickness of the weld heat-affected zone formed on the metal base material was measured to be 26.1 μm, 28.7 μm, and 46.3 μm. Therefore, the thickness of the weld heat-affected zone may be in the range of more than 0 μm and less than or equal to 50 μm. In conventional arc welding, the thickness of the weld heat-affected zone may be about 200 μm. In this way, by forming the weld heat-affected zone with a small thickness, the properties including the formation memory properties of the metal base material can be preserved or secured.

[0134] FIG. 9 is an external photograph showing the formation of a defect according to the laser output of a welded portion of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0135] Referring to Fig. 9, in Experimental Example 1 with a low manganese content, the integrity of the interface between the metal base material and the weld was confirmed at a laser output of 250 W. On the other hand, it was confirmed that defects such as cracks and pores were formed at the interface at a laser output of 300 W or more. In Experimental Example 2 with a high manganese content, the integrity of the interface between the metal base material and the weld was confirmed at laser outputs of 250 W and 300 W. On the other hand, it was confirmed that defects such as cracks and pores were formed at the interface at a laser output of 350 W or more. In addition, interface integrity could be secured at 150 W or more, but welding of the metal base material was not performed at a laser output of less than 150 W. Therefore, it is preferable that the laser be irradiated with an output in the range of 150 W or more and less than 350 W.

[0136] In addition, it can be seen that the above welded portion has a solidified structure formed by the melting and solidification of the injected powdered filler metal. It can be seen that the solidified structure has a shape similar to fish scales.

[0137] FIGS. 10 to 12 are graphs showing the stress-elongation relationship of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0138] Referring to Fig. 10, in the case of manufacturing by laminating powder filler material alone, Experimental Example 2 showed higher stress at the same elongation compared to Experimental Example 1, and also showed greater fracture stress and final elongation.

[0139] Referring to Fig. 11, the stress-strain relationship of Experimental Example 1 is shown when the laser power was changed to 200 W, 300 W, 350 W, and 400 W. The overall stress-strain behavior was similar, but the fracture stress and final elongation were the highest at 200 W. This result is analyzed to be due to the excellent soundness exhibited at 200 W. On the other hand, it is analyzed that the fracture occurred at low stress due to the formation of defects such as cracks and pores at laser powers of 300 W, 350 W, and 400 W.

[0140] Referring to Fig. 12, the stress-strain relationship of Experimental Example 2 is shown when the laser power was changed to 200 W, 300 W, 350 W, and 400 W. The overall stress-strain behavior was similar, but the fracture stress and final elongation were the highest at 200 W, and the second highest at 300 W. These results are analyzed to be due to the excellent soundness exhibited at 200 W and 300 W. On the other hand, at laser powers of 350 W and 400 W, it is analyzed that the specimen was destroyed at low stress due to the formation of defects such as cracks or pores.

[0141] Table 1 is a table showing the yield strength and tensile strength of a welded metal structure formed using a laser welding method according to one embodiment of the present invention.

[0142] Classification Yield strength (MPa) Tensile strength (MPa) Fe-18.5Mn-4Cr-0.4C single-layer 367689 Fe-24Mn-4Cr-0.4C single-layer 354560 Fe-18.5Mn-4Cr-0.4C welded joint application (Experimental example 1) 486787 Fe-24Mn-4Cr-0.4C welded joint application (Experimental example 2) 465883

[0143] Referring to Table 1, compared to cases where filler metal was laminated alone, cases where filler metal was applied to the weld joint showed a decrease in elongation, but an increase in yield strength and tensile strength. This is analyzed to be due to the effect of the metal base material. In addition, it can be confirmed that the soundness of the interface between the metal base material and the weld and within the weld joint was secured. Therefore, it has the advantage of being able to directly transfer the material properties designed during the alloy design stage to the weld joint. Therefore, it has the advantage of being able to impart desired functionality and properties to the joint, beyond simply joining the metal base material.

[0144] Fig. 13 is a graph showing the shape memory characteristics of a welded metal structure formed using a laser welding method according to an embodiment of the present invention.

[0145] Referring to Fig. 13, it can be seen that the base metal and weld part of the welded metal structure have similar shape memory characteristic behavior. Accordingly, it can be confirmed that the weld part also has shape memory characteristics after being formed.

[0146] FIG. 14 is a schematic diagram illustrating a process for forming a tubular coupler as a welded metal structure formed using a laser welding method according to one embodiment of the present invention.

[0147] Referring to Fig. 14, a metal plate is provided as a metal base material (10). The metal base material (10) is formed into a hollow cylindrical shape. Accordingly, both ends of the metal base material (10) are brought into contact with each other to form a welding target area (20). A powder filler metal is injected into the welding target area (20) and a laser is irradiated to form a weld (30). The weld (30) extends in the length direction of the hollow cylindrical shape of the metal base material (10) and is formed at a portion where the ends of the metal base material (10) are brought into contact with each other. Accordingly, a tubular coupler (40) is completed.

[0148] The metal base material (10) and the weld (30) may have shape memory characteristics, and accordingly, the tubular coupler (40) may have shape memory characteristics.

[0149] FIG. 15 is a photograph showing a tubular coupler having shape memory characteristics formed using a laser welding method according to an embodiment of the present invention.

[0150] Fig. 16 is a photograph showing a state in which a pipe is coupled using a tubular coupler having shape memory characteristics formed using a laser welding method according to an embodiment of the present invention.

[0151] Referring to Figures 15 and 16, a tubular coupler having shape memory properties formed using a laser welding method is illustrated. Furthermore, two pipes were coupled to each other at both ends using the tubular coupler having shape memory properties, indicated by the dotted lines.

[0152] The above coupling method is as follows. Pipes are inserted into each end of the tubular coupler, and the tubular coupler is heated. By this heating, the tubular coupler contracts due to its shape memory properties and comes into close contact with the inserted pipes.

[0153] It will be apparent to a person skilled in the art to which the technical idea of ​​the present invention pertains that the technical idea of ​​the present invention described above is not limited to the above-described embodiments and the attached drawings, and that various substitutions, modifications, and changes are possible within a scope that does not depart from the technical idea of ​​the present invention.

[0154] According to the technical idea of ​​the present invention, a coupler that secures shape memory characteristics can be provided.

Claims

1. A step of providing a metal base material having a welding target area; A step of injecting powdered filler metal into the above welding target area; A step of irradiating a laser to the welding target area so that the powdered filler metal melts to form a filler metal melt; and A step of solidifying the above-mentioned molten metal to form a weld, In the step of injecting the powder filler metal and the step of irradiating the laser, the laser moves along the extension direction of the welding target area, and the injection of the powder filler metal is performed at the tip of the laser by following the movement of the laser. Laser welding method of metal base materials.

2. In paragraph 1, The step of injecting the powder filler material and the step of irradiating the laser are as follows: By continuously performing the welding process while moving along the extension direction of the above welding target area, the welding part is formed. Laser welding method of metal base materials.

3. In paragraph 1, The step of injecting the powder filler material and the step of irradiating the laser are as follows: By performing intermittently while moving along the extension direction of the above welding target area, the above welding part is formed. Laser welding method of metal base materials.

4. In paragraph 1, The step of injecting the powder filler material and the step of irradiating the laser are performed once or repeatedly multiple times while moving along the extension direction of the welding target area to form the welded part. Laser welding method of metal base materials.

5. In paragraph 1, The above metal base material includes a Fe-Si-Mn shape memory alloy, The above powder filler comprises a Fe-Mn-Cr-C type shape memory alloy. Laser welding method of metal base materials.

6. In paragraph 1, The above metal base material contains 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities. The above powder filler contains 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities. Laser welding method of metal base materials.

7. In paragraph 1, The manganese content contained in the powder filler metal is higher than the manganese content contained in the metal base material. Laser welding method of metal base materials.

8. In paragraph 1, The above laser is irradiated with an output in the range of 150W or more and less than 350W, Laser welding method of metal base materials.

9. In paragraph 1, The above powder filler has an average particle diameter in the range of 50 μm to 150 μm. Laser welding method of metal base materials.

10. In paragraph 1, The above metal base material is a metal plate formed into a hollow cylinder shape, The above welding target area is the area where both ends of the metal base material are in contact with each other. Laser welding method of metal base materials.

11. In paragraph 1, The above welding part, Along the extension direction of the above welding target area, a plurality of layers are laminated and formed, or have a continuous shape or a discontinuous shape. Laser welding method of metal base materials.

12. In paragraph 1, The step of injecting powdered filler metal into the above welding target area is as follows: The process is performed by changing the composition of the above powder filler material over time. Laser welding method of metal base materials.

13. In paragraph 1, In the step of injecting the powder filler metal, the powder filler metal of the first composition is injected, and the step of irradiating the laser is performed to form the lower weldment, In the subsequent step of injecting the powder filler material, a powder filler material of a second composition different from the first composition is injected, and the step of irradiating the laser is performed to form an upper weld on the lower weld. Laser welding method of metal base materials.

14. In paragraph 1, The above welding part, A weld portion having a first composition and a weld portion having a second composition, which are arranged along the extension direction of the above welding target area and have different compositions, Laser welding method of metal base materials.

15. In paragraph 1, In order to prevent oxidation of the above-mentioned filler metal melt and the above-mentioned weld, an inert gas is supplied to the above-mentioned filler metal melt and the above-mentioned weld to purge the same. Laser welding method of metal base materials.

16. Metal base material; and It includes a weld formed at a part where the ends of the above metal base materials are in contact with each other, The above metal base material is a shape memory alloy containing 16 to 18 wt% manganese (Mn), 4 to 6 wt% silicon (Si), 9 to 11 wt% chromium (Cr), 3 to 5 wt% nickel (Ni), 0.5 to 1 wt% vanadium (V), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities. The above welded part contains 16.5 to 24 wt% manganese (Mn), 3 to 5 wt% chromium (Cr), 0.1 to 0.5 wt% carbon (C), and the remainder iron (Fe) and unavoidable impurities. Welded metal structures.

17. In paragraph 16, The thickness of the weld heat-affected zone formed on the above metal base material is in the range of 0 μm to 50 μm. Welded metal structures.

18. In paragraph 16, The average grain size of the weld heat-affected zone formed on the above metal base material is in the range of 30 μm to 50 μm. Welded metal structures.

19. In paragraph 16, The above welding part, Having a solidified structure formed by melting and solidifying the powdered filler metal. Welded metal structures.

20. In paragraph 16, The above welded metal structure is, A metal base material in the form of a plate formed into a hollow cylinder; and A tubular coupler including a weld formed in a portion where the ends of the metal base material are in contact with each other and extending in the longitudinal direction of the hollow cylinder of the metal base material, Welded metal structures.

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