Manufacturing process of functional gradient welded INVAR and stainless steel and method for manufacturing the same

Abstract

The present embodiments may provide a gradient structure welded joint of Invar steel and stainless steel and a method for manufacturing the same, wherein the laminate comprises an Invar steel alloy and a stainless steel alloy, and the laminate comprises an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in the opposite direction at one end and the opposite end.

Description

Technology Field

[0001] These embodiments relate to a method for manufacturing a sloped weld joint of Invar steel and stainless steel. Background Technology

[0003] Invar steel refers to a metal that exhibits very low thermal expansion with temperature compared to other metallic materials. Fe-36Ni Invar steel is a well-known representative alloy composition, and thermal expansion characteristics can be controlled by adjusting the alloy composition. Due to these thermal expansion properties, Invar steel is widely used in industries such as display manufacturing and shipbuilding.

[0004] Invar steel alloys are primarily manufactured through traditional processes such as casting and rolling, and are mainly supplied in the form of plates. Invar steel is used either on its own or welded with other stainless steels. However, since there are differences in physical properties between Invar steel and stainless steel due to their alloy compositions, direct welding of the two materials results in differences in physical properties.

[0005] Therefore, the development of technology capable of reducing the difference in material properties that occurs when welding Invar steel and stainless steel is required. The problem to be solved

[0007] In this embodiment, we aim to provide a method for manufacturing an inclined weld joint of Invar steel and stainless steel that can mitigate the difference in physical properties that occurs when welding Invar steel and stainless steel. means of solving the problem

[0009] A gradient structure weld of Invar steel and stainless steel according to one embodiment comprises a laminate including an Invar steel alloy and a stainless steel alloy; and the laminate may include an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in opposite directions at both ends.

[0010] Invar steel alloy may be located at one end of the laminate where the concentration of Invar steel alloy is high, and stainless steel alloy may be located at the multi-stage of the laminate where the concentration of stainless steel alloy is high.

[0011] In addition, the thickness of the above inclined structure welded part may be in the range of 5 mm to 30 mm.

[0012] The above laminate comprises one or more unit laminates, and the unit laminate may include an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in the opposite direction at one end and the opposite other end, and the thickness of the unit laminate may be in the range of 0.1 mm to 0.5 mm.

[0013] In addition, the concentrations of the Invar steel alloy and stainless steel alloy in the adjacent unit laminates may change in stages.

[0014] A method for manufacturing a sloped structure weldment according to one embodiment of the present invention comprises: a step of preparing a metal specimen; a step of forming a molten pool in the metal specimen by laser beam irradiation; and a step of forming a sloped structure weldment by spraying metal powder into the molten pool; wherein, in the step of forming a sloped structure weldment by spraying metal powder into the molten pool, the metal powder comprises Invar steel alloy and stainless steel alloy powder, and the Invar steel alloy powder and the stainless steel alloy powder can be fed from respective feeding units.

[0015] The above Invar steel alloy powder and the above stainless steel alloy powder can each be supplied in a range of 0 wt% to 100 wt% based on the total mass of the mixture of the above Invar steel alloy powder and the above stainless steel alloy powder.

[0016] In addition, the Invar steel alloy powder and the stainless steel alloy powder can be fed at a feeding rate in the range of 2 to 10 g / min.

[0017] In addition, the above Invar steel alloy powder and the above stainless steel alloy powder may have an average particle size D (50) in the range of 50㎛ to 150㎛.

[0018] In the step of forming an inclined structure weld by spraying metal powder into the molten pool, the thickness of the inclined structure weld may be 5 mm to 30 mm.

[0019] In addition, in the step of forming a sloped structure weld by spraying metal powder into the molten pool, the sloped structure weld is composed of one or more unit laminates, and the thickness of the unit laminates may be in the range of 0.1 mm to 0.5 mm. Effects of the invention

[0021] According to the present embodiment, metal powders are fed by each feeding method, and a stable inclined structure weld can be manufactured using direct injection laser cladding.

[0022] The inclined structure welded part manufactured according to the present embodiment can mitigate the difference in physical properties that occurs when welding Invar steel and stainless steel. Brief explanation of the drawing

[0024] FIG. 1 is a schematic diagram of a system for manufacturing inclined structure welded parts according to the present invention. FIG. 2 is a schematic diagram of an inclined structure welded joint according to one embodiment. FIG. 3 is a schematic diagram of a method for manufacturing an inclined structure welded part according to one embodiment. Figure 4 is a vertical cross-sectional image of a slanted structure weld manufactured according to an example. Figure 5 is the result of a layer-by-layer composition analysis of a sloped structure weldment manufactured according to an example. Specific details for implementing the invention

[0025] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0026] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0027] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0028] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0030] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0032] FIG. 1 is a schematic diagram of a system for manufacturing inclined structure welded parts according to the present invention.

[0033] Referring to FIG. 1, the inclined structure weldment manufacturing system (10) according to the present invention includes a metal powder feeding device (100), a laser cladding device (200), a base plate (300), a CAD / CAM PC device (400), and a control unit (500).

[0034] First, the metal powder feeding device (100) will be explained.

[0035] In the present invention, the metal powder feeding device (100) may include a chamber for receiving metal powder, and the metal powder may be supplied to a laser cladding device (200) described later through a feeding pipe connected to the chamber.

[0036] Here, the metal powder feeding device (100) may include a first feeding unit (110) and a second feeding unit (120). The first feeding unit (110) is provided with a first feeding pipe (111), and the metal powder contained in the first feeding unit (110) is supplied to a laser cladding device (200) described later through the first feeding pipe (111). Additionally, the second feeding unit (120) is provided with a second feeding pipe (121), and the metal powder contained in the second feeding unit (120) is supplied to a laser cladding device (200) described later through the second feeding pipe (121).

[0037] Meanwhile, the first feed section (110) may receive Invar steel alloy powder, and the second feed section (120) may receive stainless steel alloy powder. At this time, the Invar steel alloy powder and the stainless steel alloy powder may be different or the same metal powder, and are not particularly limited. In addition, the average particle size of the Invar steel alloy powder and the stainless steel alloy powder may be within the same range or different ranges, and is not particularly limited.

[0038] Meanwhile, the first feed unit (110) and the second feed unit (120) are each electrically connected to the control unit (500), and the amount of metal powder supplied to the laser cladding device (200) can be adjusted by the control of the control unit (500).

[0039] In the first feeding section (110) and the second feeding section (120), the feeding amount of the Invar steel alloy powder and the stainless steel alloy powder may be 2 to 10 g / min, specifically 4 to 8 g / min. If the feeding amount of the metal powder is less than 2 g / min, a problem may arise where productivity for implementing the stacking section is reduced, and if the feeding amount of the metal powder is greater than 10 g / min, a problem may arise where it is difficult to control the powder for implementing the inclined structure.

[0040] The Invar steel alloy powder fed from the first feeding unit (110) and the stainless steel alloy powder fed from the second feeding unit (120) can each be fed in a range of 0 to 100 wt% based on the total mass of the Invar steel alloy powder and the stainless steel alloy powder.

[0041] In addition, the Invar steel alloy powder fed from the first feeding unit (110) and the stainless steel alloy powder fed from the second feeding unit (120) can be mixed in a mixing unit provided in the laser cladding device (200) described later and sprayed into a molten pool formed on a metal specimen described later.

[0042] Additionally, although FIG. 1 illustrates a first feed section (110) and a second feed section (120), additional feed sections may be included depending on the material composition and structural characteristics of the required inclined structure weld, and are not particularly limited.

[0044] Next, the laser cladding device (200) will be described.

[0045] In the present invention, the laser cladding device (200) may include a laser beam irradiation unit and a nozzle.

[0046] Here, the laser beam irradiation unit may include a laser generating unit, a laser beam transport unit, and a laser beam focusing unit. The laser beam irradiation unit may form a molten pool on the surface of a metal specimen placed on a base plate (300) described later. Additionally, the metal powder may form a laminate in the molten pool.

[0047] The laser output irradiated from the laser beam irradiation unit may be 300 to 1000 W, specifically 500 to 700 W. If the laser output is less than 300 W, the powder may not melt and may remain in the stacking unit, and if the laser output is greater than 1000 W, the melting area of ​​the melting unit may become too large and difficult to control.

[0048] Meanwhile, the Invar steel alloy powder fed from the first feeding device (110) and the stainless steel alloy powder fed from the second feeding device (120) can be uniformly mixed and sprayed through the nozzle to form a laminate. At this time, the feeding amount of the metal powder mixed with the Invar steel alloy powder and the stainless steel alloy powder sprayed through the nozzle may be in the range of 2 to 10 g / min, and specifically may be 4 to 8 g / min.

[0049] Next, the base plate (300) will be explained.

[0050] In the present invention, the base plate (300) can be positioned horizontally below the laser cladding device (200).

[0051] A metal specimen can be placed on the top of the base plate (300), and the metal specimen can be freely transported. Additionally, it can be transported in the forward / backward direction or left / right direction of the transport direction. The base plate (300) may include a transport unit, and the transport unit is electrically connected to a control unit (500), so that the transport direction and transport speed can be controlled by the control unit (500). Meanwhile, the transport speed of the base plate (300) may be in the range of 300 m / s to 1000 m / s. If the transport speed is too slow, the heat input increases, and the size of the molten pool may increase; if the transport speed is too fast, the heat input decreases, and an unmelted area of ​​the powder may occur.

[0052] The CAD / CAM PC device (400) generates a work path through CAM conversion from 3D CAD data and transmits it to the control unit (500). The control unit (500) receives the work path from the CAD / CAM PC device (400) and performs a laser cladding operation.

[0053] The control unit (500) may include various input / output devices and may include a function to control all components constituting the inclined structure weldment manufacturing system (10) of the present invention and to monitor the status of each component in real time.

[0055] FIG. 2 is a schematic diagram of an inclined structure welded joint according to one embodiment.

[0056] Referring to FIG. 2, the inclined structure weld of Invar steel and stainless steel according to one embodiment of the present invention may include a laminate comprising an Invar steel alloy and a stainless steel alloy. In addition, the laminate may include an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in the opposite direction at one end and the opposite other end.

[0057] Meanwhile, an Invar steel alloy may be located at one end of the laminate where the concentration of the Invar steel alloy is high, and a stainless steel alloy may be located at the other end of the laminate where the concentration of the stainless steel alloy is high.

[0058] A hard magnetic structure welded portion having such a configuration can improve the welding efficiency of the Invar steel and the stainless steel by having a high concentration of Invar steel alloy, or by having one end where the Invar steel alloy is located face the Invar steel for welding, and the other end where the stainless steel alloy concentration is high face the stainless steel for welding.

[0059] The above laminate may include one or more unit laminates, and the unit laminate may include an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in the opposite direction at one end and the opposite other end. Additionally, if there are two or more unit laminates, two adjacent unit laminates may be adjacent in the same direction as the trend of change of the Invar steel alloy concentration or the stainless steel alloy concentration. That is, when two unit laminates are laminated, the laminate formed by the lamination of the two unit laminates and each of the unit laminates have the same trend of change of the Invar steel alloy concentration and the stainless steel alloy concentration in the lamination direction. This is advantageous for effectively welding the Invar steel and stainless steel to be welded.

[0060] In one embodiment of the present invention, the thickness of the inclined structure weld may be in the range of 5 mm to 30 mm, specifically in the range of 10 mm to 20 mm. If the thickness of the inclined structure weld is less than 5 mm, it is difficult to implement the incline through minimum powder spraying, and if the thickness of the inclined structure weld is greater than 30 mm, a problem may arise where the productivity required for inclined lamination decreases.

[0061] In addition, the thickness of the unit laminate may be in the range of 0.1 mm to 0.5 mm, and specifically in the range of 0.2 mm to 0.4 mm. If the thickness of the inclined structure unit laminate is less than 0.1 mm, it is difficult to implement the incline through minimum powder spraying, and if the thickness of the inclined structure weld is greater than 0.5 mm, the productivity required for inclined lamination decreases.

[0063] Figure 3 is a schematic diagram of a method for manufacturing a sloped structure welded part according to an embodiment.

[0064] Referring to Fig. 3, a method for manufacturing a sloped structure welded joint will be explained in more detail.

[0065] A method for manufacturing a sloped structure weldment according to an embodiment of the present invention may include a step of preparing a metal specimen (S1), a step of forming a molten pool on the metal specimen (S2), and a step of forming a sloped structure weldment (S3).

[0066] First, in the metal specimen preparation step (S1), a metal specimen is placed on the upper surface of the base plate. At this time, the metal specimen is placed horizontally and transported by the movement of the base plate. Additionally, it can be transported to a vertically downward position of a laser cladding device located above the base plate.

[0067] Next, a laser beam is irradiated from the cladding device to form a molten pool on the surface of the metal specimen. At this time, the laser beam irradiation from the cladding device may have a laser output of 300 to 1,000 W, specifically a laser output of 300 to 1,000 W. The reason for selecting such a laser output range is omitted as it has been described in detail above.

[0068] Next, the metal powder fed from the metal powder feeding device is sprayed into the molten pool at a constant speed. At the same time, the metal specimen is transported by the movement of the base plate to form a continuous laminate on the metal specimen. Here, a carrier gas may be used for feeding the metal powder. The carrier gas may be an inert gas and may serve to prevent oxidation of the metal powder or the molten pool by the external atmosphere.

[0069] Meanwhile, the metal powder may be a mixture of Invar steel alloy powder and stainless steel alloy powder. The Invar steel alloy powder may be fed by a first feeding unit, and the stainless steel alloy powder may be fed to a laser cladding device by a second feeding unit. Here, the feeding amount of the Invar steel alloy powder and the stainless steel alloy powder may be 2 to 10 g / min, and specifically 4 to 8 g / min.

[0070] Meanwhile, the average particle size D (50) of the Invar steel alloy powder and the metal powder may be 50㎛ to 150㎛, specifically 80㎛ to 120㎛. If the average particle size D (50) is less than 50㎛, the feeding performance of the nozzle may be reduced due to a large amount of fine particles, and if the average particle size D (50) is greater than 150㎛, the resolution for realizing the minimum unit stacked structure decreases.

[0071] At this time, the Invar steel alloy powder and the stainless steel alloy powder can be uniformly mixed in the laser cladding device.

[0072] The above Invar steel alloy powder and stainless steel alloy powder can be fed at a feeding ratio ranging from 0 to 100% each based on the total mass of the mixture. The mixing ratio can be controlled according to the requirements of the inclined structure weld to be manufactured.

[0073] In addition, the above feed rate can be adjusted by the control unit.

[0074] In addition, by measuring the thickness of the laminate formed in the CAD device and transmitting an electrical signal to the control unit, the control unit can adjust the feed amount of Invar steel alloy powder and the feed amount of stainless steel alloy powder.

[0075] In this way, by varying the feeding ratio of the above Invar steel alloy powder and stainless steel alloy powder, a sloped structure weldment can be formed in which unit laminates having different compositions are stacked on a metal specimen.

[0076] In the present invention, the thickness of the manufactured inclined structure weldment may be in the range of 5 to 30 mm, specifically in the range of 10 mm to 20 mm. If the thickness of the inclined structure weldment is less than 5 mm, it is difficult to achieve an inclined shape through minimal powder spraying, and if the thickness of the inclined structure weldment is greater than 30 mm, a problem may arise where the productivity required for inclined lamination decreases.

[0077] In addition, the thickness of the unit laminate may be in the range of 0.1 mm to 0.5 mm, and specifically in the range of 0.2 mm to 0.4 mm. If the thickness of the inclined structure unit laminate is less than 0.1 mm, it is difficult to implement the incline through minimum powder spraying, and if the thickness of the inclined structure weld is greater than 0.5 mm, the productivity required for inclined lamination decreases.

[0078] Meanwhile, the above Invar steel alloy powder and stainless steel alloy powder may be composed of compositions included in different metal members to be welded, and may be powders obtained by pulverizing said different metal members. It is not particularly limited thereto.

[0080] Embodiments of the present invention will be described in detail below. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0082] Example 1

[0083] A welded joint of Invar steel and stainless steel with an inclined structure was manufactured using the manufacturing method shown in Fig. 3.

[0084] The Invar steel alloy powder used in Example 1 is STS316L powder, and the stainless steel alloy powder is IN625 powder. The average particle size D (50) of the STS316L powder and the IN625 powder may be in the range of 50 to 150 μm.

[0085] First, an STS316L specimen is placed on a base plate and transported to a lower position of the laser cladding device. When the shear portion of the STS316L specimen reaches a vertically lower position of the laser cladding device, the laser cladding device irradiates a laser beam to form a molten pool on the surface of the STS316L specimen. At this time, the laser output for irradiating the laser beam is 700W.

[0086] Next, the STS316L powder contained in the first feed section is fed to the laser cladding device and sprayed into the molten pool through the nozzle of the laser cladding device to form the first laminate (#1). Here, the feeding speed at which the STS316L powder fed to the laser cladding device is sprayed into the molten pool through the nozzle is 4 g / min. At the same time, the STS316L specimen is transported by the movement of the base plate. At this time, the rear end of the STS316L specimen is positioned vertically downward from the front end of the laser cladding device.

[0087] After the first laminate (#1) is formed, the amount of STS316L powder contained in the first feeder is reduced, and IN625 powder contained in the second feeder is supplied simultaneously. At this time, the STS316L powder and IN625 powder are fed in a ratio of 80:20 by mass. Meanwhile, the feeding speed at which the metal powder mixed with STS316L powder and IN625 powder fed to the laser cladding device is sprayed through the nozzle of the laser cladding device is 4 g / min. In addition, the second laminate (#2) is formed in the same manner as the first laminate (#1).

[0088] Next, STS316L powder and IN625 powder were fed in ratios of 60:40, 40:60, and 20:80 by mass to form the third laminate (#3), the fourth laminate (#4), and the fifth laminate (#5), respectively.

[0089] Finally, the feeding of STS316L powder was stopped, and only IN625 powder was fed to form the 6th laminate (#6).

[0090] In this way, a cross-sectional image of the inclined structure weld of Invar steel and stainless steel formed by sequentially stacking the first laminate (#1) to the sixth laminate (#6) is shown in FIG. 4.

[0092] Examples 2, 3 and Comparative Examples 1, 2

[0093] When forming the first laminate (#1) to the sixth laminate (#6), the feed speed sprayed through the nozzle of the laser cladding device was adjusted as shown in Table 1 below, except that the inclined structure welded part of Invar steel and stainless steel was manufactured in the same way as in Example 1.

[0094] Examples 4, 5 and Comparative Examples 3, 4

[0095] When forming the first laminate (#1) to the sixth laminate (#6), the laser output was adjusted as shown in Table 1 below, except that the inclined structure welded part of Invar steel and stainless steel was manufactured in the same way as in Example 1.

[0096]

[0097] Test Example 1

[0098] A cross-section of the inclined structure weld of Invar steel and stainless steel manufactured according to Example 1 is shown in FIG. 4, and the layer composition of the first laminate (#1) to the sixth laminate (#6) shown in the cross-section was analyzed, and the results are shown in FIG. 5.

[0099] Referring to Figure 5, the average Fe content of the first laminate (#1) to the sixth laminate (#6) of the inclined structure welded joint of the manufactured Invar steel and stainless steel showed a decreasing trend. The average Fe content for each laminate was found to be as follows: 54.2 wt% for the second laminate (#2), 43.4 wt% for the third laminate (#3), 32.3 wt% for the fourth laminate (#4), and 23.3% for the fifth laminate (#5). It can be confirmed that the average Fe content shows a linear change trend depending on the mixing ratio of STS316 powder and IN625 powder.

[0100] From this, it can be confirmed that the gradient structure welded portion of Invar steel and stainless steel manufactured according to Example 1 is formed by stacking unit laminates of uniform composition to form a compositional gradient structure.

[0101] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 A laminate comprising an Invar steel alloy and a stainless steel alloy; wherein the laminate comprises an Invar steel alloy and a stainless steel alloy in which the concentrations gradually decrease in opposite directions at both ends, and the Invar steel alloy is located at one end of the laminate where the concentration of the Invar steel alloy is high, and the stainless steel alloy is located at the other end of the laminate where the concentration of the stainless steel alloy is high, and the inclined structure weld of Invar steel and stainless steel. Claim 2 delete Claim 3 An inclined structure weld of Invar steel and stainless steel according to claim 1, wherein the thickness of the inclined structure weld is in the range of 5 mm to 30 mm. Claim 4 A gradient structure weld of Invar steel and stainless steel according to claim 1, wherein the laminate comprises one or more unit laminates, and the unit laminate comprises an Invar steel alloy and a stainless steel alloy in which the concentration gradually decreases in the opposite direction at one end and the opposite other end. Claim 5 In paragraph 4, the inclined structure weld of Invar steel and stainless steel, wherein the thickness of the unit laminate is in the range of 0.1 mm to 0.5 mm. Claim 6 In paragraph 5, the adjacent unit laminate is a gradient structure weld of Invar steel and stainless steel in which the concentrations of the Invar steel alloy and the stainless steel alloy change in steps. Claim 7 A method for manufacturing a sloped weld, comprising: a step of preparing a metal specimen; a step of forming a molten pool in the metal specimen by laser beam irradiation; and a step of forming a sloped weld by spraying metal powder into the molten pool; wherein, in the step of forming a sloped weld by spraying metal powder into the molten pool, the metal powder comprises Invar steel alloy and stainless steel alloy powder, and the Invar steel alloy powder and the stainless steel alloy powder are fed from respective feeders; and the sloped weld comprises a laminate comprising an Invar steel alloy and a stainless steel alloy; wherein the laminate comprises an Invar steel alloy and a stainless steel alloy in which the concentrations gradually decrease in opposite directions from both ends, and the Invar steel alloy is located at one end of the laminate where the concentration of the Invar steel alloy is high, and the stainless steel alloy is located at the other end of the laminate where the concentration of the stainless steel alloy is high. Claim 8 A method for manufacturing a sloped structure weldment according to claim 7, wherein the Invar steel alloy powder and the stainless steel alloy powder are each fed in a range of 0 wt% to 100 wt% based on the total mass of the mixture of the Invar steel alloy powder and the stainless steel alloy powder. Claim 9 A method for manufacturing an inclined structure weldment according to claim 7, wherein the Invar steel alloy powder and the stainless steel alloy powder are fed at a feeding speed in the range of 2 to 10 g / min. Claim 10 In claim 7, the above Invar steel alloy powder and the above stainless steel alloy powder have an average particle size D (50) in the range of 50㎛ to 150㎛, a method for manufacturing a sloped structure weldment. Claim 11 A method for manufacturing an inclined structure weldment according to claim 7, wherein, in the step of forming an inclined structure weldment by spraying metal powder into the molten pool, the thickness of the inclined structure weldment is in the range of 5 mm to 30 mm. Claim 12 A method for manufacturing a sloped structure weldment according to claim 7, wherein, in the step of forming a sloped structure weldment by spraying metal powder into the molten pool, the sloped structure weldment comprises one or more unit laminates, and the thickness of the unit laminates is in the range of 0.1 mm to 0.5 mm.

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