An arc additive manufacturing method for a nuclear power pressure water reactor main pipe 316L-In718 functionally graded material

Abstract

An arc additive manufacturing method for a nuclear power water reactor main pipe 316L-In718 functional gradient material relates to the field of additive manufacturing, and aims at solving the problems of poor interlayer bonding capacity of dissimilar metals, uneven component distribution, poor size precision and stress corrosion cracking and the like in the process of preparing materials in the prior art.The nuclear power water reactor main pipe 316L-In718 functional gradient material is prepared by using the coaxial wire feeding arc additive manufacturing method, wherein the welding wire of the coaxial wire feeding is 316L-In718 stranded welding wire.The method can realize the relatively continuous component gradient transition of the 316L-In718 functional gradient material of the large nuclear power water reactor main pipe complex structure, and the effect of improving the deposition efficiency, forming size precision, corrosion resistance and interlayer bonding capacity is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of additive manufacturing, and particularly relates to an electric arc additive manufacturing method for a 316L-In718 functional gradient material of a nuclear power water reactor main pipe. BACKGROUND

[0002] Nuclear energy is the most promising clean energy, and the main pipe of the pressurized water reactor is a key part of the nuclear power field, which requires it to meet the service requirements under the very harsh conditions of high temperature, high pressure, chemical corrosion and radiation. The development of special materials and manufacturing methods for the main pipe is of great significance to ensure the long-term safe and stable operation of nuclear power facilities. The commonly used 316L stainless steel is prone to stress corrosion cracking and other problems under such conditions. The traditional cladding corrosion-resistant alloy (such as nickel-based alloy) method will cause stress concentration and poor interface bonding due to the thermal physical property differences of dissimilar materials.

[0003] To solve this problem, researchers have proposed a functional gradient transition method to realize the combination of dissimilar metal materials. Functional gradient materials are composed of two or more materials, and their composition, structure and performance all show a gradient change. By continuously changing the composition and structure of these materials, the interface disappears, so that the performance of the material changes slowly with the change of the composition and structure.

[0004] The traditional preparation methods of functional gradient materials mainly include vapor deposition, powder metallurgy, self-propagating high-temperature synthesis, centrifugal casting, electrodeposition and plasma spraying, etc. Although these preparation methods have been widely used in the preparation of component gradient functional gradient materials, they still face many problems: (1) high manufacturing cost and long production cycle; (2) low degree of automation and complex process; (3) only simple shape functional gradient materials can be prepared, and it is difficult to prepare complex shape and high precision parts; (4) lack of effective methods to prepare functional gradient materials with precise continuous changes in three-dimensional space. These problems have greatly restricted the application and development of metal functional gradient materials.

[0005] Additive Manufacturing (AM) technology is an advanced manufacturing technology based on the principle of layer-by-layer stacking, which effectively reduces material waste and enables rapid customization of individual parts. It can also produce multi-component, complex-shaped composite materials and functional gradient materials. The rapid development of this technology has made it possible to efficiently produce metal functional gradient materials. Laser additive manufacturing is a commonly used technology for preparing functional gradient materials at present. The prepared parts have excellent formability, and through precise design and control of the composition of different materials, powder delivery process, and laser melting forming process, the gradient distribution of material composition, microstructure, and performance can be achieved in theory, which has unique advantages in preparing functional gradient material parts.

[0006] However, the size of the parts formed by laser additive manufacturing is small, and the number of gradient layers is limited due to the forming principle and the cost of powder preparation, which is not conducive to eliminating interface stress, resulting in the performance of the formed parts cannot meet the requirements. Different materials have different physical properties such as density, thermal expansion coefficient, melting point, and laser absorption rate, which is one of the technical bottlenecks of laser additive manufacturing technology for preparing functional gradient materials. The metal functional gradient materials prepared by related technologies are difficult to meet the industrial manufacturing requirements of large and complex parts.

[0007] Compared with laser additive manufacturing technology, Wire and Arc Additive Manufacturing (WAAM) technology has the advantages of high material utilization, high deposition efficiency during forming, simple forming equipment, low cost, and no limitation on the size of the formed parts and material reflectivity, which is particularly suitable for rapid forming of large-scale components. WAAM is the most likely additive manufacturing technology to achieve batch manufacturing of large and complex metal parts.

[0008] The University of Anna in India based on Cold Metal Transfer (CMT) to realize the Wire and Arc Additive Manufacturing of In825-SS316L functional gradient material, got the thin-walled wall structure and evaluated its mechanical properties, see Figure 1 for specific morphology. The University of Tennessee in the United States uses Gas Metal Arc Welding (GMAW) to complete the Wire and Arc Additive Manufacturing of SS316L-In625 bimetallic functional structural material, which can replace the functional structural parts manufactured by traditional welding process to a certain extent, see Figure 2 for specific morphology.

[0009] But the functionally gradient material formed by the above form is not strictly continuous functionally gradient function, and there is still obvious interface when the dissimilar metals are combined, and the organization, structure and performance cannot be smoothly transitioned, so it is difficult to meet the actual engineering requirements.

[0010] In view of this problem, Wang Lin et al. of Shanghai Jiaotong University adopts a double-wire electric arc additive strategy, and respectively sends Al wire and Ti wire into the molten pool to prepare TiAl alloy, and realizes the component transition of TiAl alloy by changing the wire feeding speed of Al wire, and the principle diagram is as shown in Figure 3 Zhang Guoyang et al. of Tianjin University of Science and Technology adopts a double-wire strategy, and respectively sends TA1 and Ti6Al4V wires with equal mass fraction into the molten pool to in-situ synthesize a defect-free Ti3Al2V single-wall component, and the double-wire electric arc additive manufacturing system and the obtained component are as shown in Figure 4 .

[0011] Although the electric arc wire melting additive manufacturing of the functionally gradient material can realize the component transition of the functionally gradient material to some extent in this way, the overall equipment structure is complex, the flexibility of the double-wire feeding mechanism is poor during operation when preparing complex components, and the wire feeding stability is difficult to guarantee, so that the size of the molten pool fluctuates greatly, and then the forming size precision of the component is affected. In addition, due to the fact that the two materials are simultaneously fed into the molten pool from two different directions, the fusion between the dissimilar materials may be uneven to some extent, resulting in component segregation and transition distribution difference.

[0012] From the above research progress of preparing metal functionally gradient material, it can be seen that there are few methods for efficiently and low-costly preparing large and complex structure metal functionally gradient material by additive manufacturing at home and abroad. SUMMARY

[0013] In view of the above problems, the present application aims to provide an electric arc additive manufacturing method for 316L-In718 functionally gradient material of nuclear pressurized water reactor main pipeline, so as to solve the problems of poor interlayer bonding ability of dissimilar metals, uneven component distribution, poor size precision and stress corrosion cracking and the like in the process of preparing materials in the prior art.

[0014] To achieve the above purpose, the present application adopts the following technical scheme:

[0015] A coaxial stranded welding wire electric arc additive manufacturing method for 316L-In718 functionally gradient material of nuclear pressurized water reactor main pipeline, the coaxial stranded welding wire electric arc additive manufacturing method is carried out in the following way:

[0016] The method for preparing the nuclear pressure water reactor main pipeline 316L-In718 functional gradient material by using the coaxial wire feeding arc additive manufacturing method, wherein the coaxial wire feeding welding wire is a 316L-In718 stranded welding wire.

[0017] The specific scheme is as follows:

[0018] Step 1: according to the physical characteristics and actual working conditions of 316L and In718, a component transition mode is designed, and a special wire for arc additive manufacturing of the nuclear pressure water reactor main pipeline 316L-In718 functional gradient material is prepared, the special welding wire is formed into a twisted rope shape by rotating a plurality of thin wires, and a 316L-In718 stranded welding wire is formed.

[0019] Step 2: before deposition, the surface of the 316L stainless steel substrate is pretreated to remove oil stains and oxides on the surface of the substrate, and then the pretreated 316L stainless steel substrate is fixed and clamped;

[0020] Step 3: the welding gun is fixed with the mechanical arm, and the angle between the welding gun and the substrate surface is adjusted;

[0021] Step 4: based on the interlayer stress during the transition of different components, the number of deposited layers during the transition of each component is set;

[0022] Step 5: based on the molten pool flow characteristics under different components, the welding voltage, welding current, wire feeding speed, running speed, wire elongation and interlayer waiting time are set;

[0023] Step 6: the deposition model is imported into the arc wire melting additive manufacturing path planning software, and the deposition process parameters in step 5 are set through the control unit to complete the formation under one component;

[0024] Step 7: according to the component gradient transition design result in step 4, steps 5 and 6 are repeated to realize the deposition and transition of the functional gradient material under different components, and the 316L-In718 functional gradient material is obtained.

[0025] Further, the substrate and the 316L-In718 functional gradient material are repeatedly cleaned and wiped with alcohol.

[0026] Further, the special welding wire designed in step 1 is a 316L-In718 stranded welding wire, the diameter D of the welding wire is 1.2mm-1.6mm, the lay length L of the welding wire is 11mm-13mm, the helical angle of the welding wire is 18°-24°, and the single wire diameter R is 0.72mm-0.81mm.

[0027] Further, the 316L-In718 stranded welding wire has 3 strands, wherein the strand combination of 316L-In718 is one or more of 3-0, 0-3, 1-2, 2-1.

[0028] Further, the special welding wire of step 1 is composed of 4 ways, i.e. 3x316L, 2x316L+1xIn718, 1x316L+2xIn718 and 3xIn718.

[0029] Further, the chemical composition of 316L in the special welding wire of step 1 is C≤0.03%, Si: 0.3%-0.65%, Mn: 1%-2.5%, P≤0.025%, S≤0.02%, Cr: 18%-20%, Ni: 11%-14%, Mo: 2%-3%, Cu≤0.75%, and the balance is Fe. The chemical composition of In718 in the special welding wire of step 1 is C≤0.08%, Si≤0.35%, Mn≤0.35%, P≤0.015%, S≤0.015%, Al: 0.2%-0.8%, Cr: 17%-21%, Ni: 50%-55%, Mo: 2.8%-3.3%, Co≤1%, Ti: 0.65%-1.15%, Cu≤0.3%, and the balance is Fe.

[0030] Further, the angle between the welding gun and the substrate in step 3 is 10°-15°.

[0031] Further, in step 5, the deposition 3x316L welding voltage is 17V-24V, the current is 152A-191A, the wire feeding speed is 4.5m / min-7m / min, the running speed is 0.2m / min-0.5m / min, and the interlayer waiting time is 1min-2min; the deposition 2x316L+1xIn718 welding voltage is 16V-23V, the current is 148A-187A, the wire feeding speed is 4.2m / min-6.5m / min, the running speed is 0.2m / min-0.5m / min, and the interlayer waiting time is 2min-3min; the deposition 1x316L+2xIn718 welding voltage is 15V-22V, the current is 124A-168A, the wire feeding speed is 4.0m / min-6.2m / min, the running speed is 0.2m / min-0.5m / min, and the interlayer waiting time is 3min-4min; the deposition 3xIn718 welding voltage is 14V-21V, the current is 116A-152A, the wire feeding speed is 3.8m / min-6m / min, the running speed is 0.2m / min-0.5m / min, and the interlayer waiting time is 3min-5min; the wire elongation is 12-15mm, and the shielding gas is Ar with a flow rate of 15L / min-20L / min.

[0032] The present application is around the additive manufacturing of nuclear pressurized water reactor main pipe material, aiming at the problems of poor interlayer bonding ability of dissimilar metals, uneven component distribution, poor size precision, low deposition efficiency and stress corrosion cracking and the like existing in the preparation of functional gradient materials at the present stage, the transition of different components between dissimilar materials is realized by twisting 316L and In718 materials in different proportions, the forming process is scientifically matched according to the molten pool characteristics under the transition condition of different components in combination with the thermophysical characteristics of 316L and In718, and the coaxial wire feeding mode is adopted to realize the high deposition efficiency, high size precision, high quality and high performance electric arc wire additive manufacturing of 316L-In718 functional gradient material for nuclear pressurized water reactor main pipe.

[0033] The present application comprises the following beneficial effects:

[0034] The present application adopts coaxial electric arc wire additive manufacturing to realize the preparation of 316L-In718 functional gradient material for nuclear pressurized water reactor main pipe, and the key technical points that can be realized by the present application are that: the 316L-In718 component transition mode (including the component composition of each deposition layer and the transition efficiency) is reasonably set, the coaxial electric arc wire additive manufacturing forming process under different components (including welding voltage, welding current, wire feeding speed, running speed, interlayer waiting time and elongation, etc.) is scientifically matched, and the process control points specially suitable for the preparation of 316L-In718 functional gradient material are formulated.

[0035] Compared with traditional cladding or welding, the present invention can achieve a smooth transition between 316L and In718, solving the problems of dissimilar metal interface bonding and stress corrosion cracking during the operation of the main pipeline of nuclear pressurized water reactor.

[0036] Compared with the laser additive manufacturing method for preparing 316L-In718 functional gradient materials, the present invention has the advantages of high forming efficiency, low cost, no limitation on the size of the formed parts, and no dust pollution.

[0037] Compared with dual-axis wire feeding laser or arc additive manufacturing, this technology has the advantages of simple process flow and high stability when forming complex structural parts;

[0038] Compared with solid wire additive manufacturing, the twisting of dissimilar wires can better achieve the functional gradient transition of 316L-In718. The stirring effect of the molten pool brought by this method also helps to evenly distribute the dissimilar metals in the molten pool.

[0039] The present invention can realize relatively continuous component gradient transition of 316L-In718 functional gradient material of complex structure of main pipeline of large nuclear pressurized water reactor, thereby improving deposition efficiency, forming dimensional accuracy, corrosion resistance and interlayer bonding ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Figure 1: In825-SS316L functional gradient material prepared by WAAM technology; (a) top view of the product; (b)

[0041] (c) Schematic diagram of the workpiece;

[0042] Figure 2 Figure 1: SS316L-In625 functional structural material prepared by WAAM technology; (a) schematic diagram; (b) actual image;

[0043] Figure 3 Schematic diagram of component transition materials for twin-wire arc additive manufacturing;

[0044] Figure 4 Figure 1 shows a twin-wire arc additive manufacturing system and a thin-walled part; (a) Schematic diagram of the working principle; (b) actual picture;

[0045] Figure 5 is the variation of interlaminar stress with the number of wire strands;

[0046] Figure 6 Schematic diagram of characteristic parameters of 316L-In718 functional gradient material welding wire;

[0047] Figure 7 is the variation of interlaminar stress with the number of strands of special welding wire;

[0048] Figure 8 The 316L-In718 functional gradient material thin-wall wall sample pattern is shown in Figure 1;

[0049] Figure 9 The transition zone between different component layers is shown in Figure 2;

[0050] Figure 10 The 316L-In718 functional gradient material before and after corrosion is shown in Figure 3;

[0051] Figure 11 The coaxial arc additive manufacturing method flow chart of the metal functional gradient material is shown in Figure 4;

[0052] Figure 12 The principle schematic diagram of the present application is shown in Figure 5. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear and explicit, the spirit of the present application will be described in detail below, and any person skilled in the art can make changes and modifications to the technology taught by the present application without departing from the spirit and scope of the present application.

[0054] The schematic embodiments of the present application and the descriptions thereof are used to explain the present application, but not as a limitation of the present application.

[0055] Embodiment:

[0056] The present application combines 316L and In718 in different components by twisting, realizes the arc melting wire additive manufacturing of 316L-In718 functional gradient material by the coaxial wire feeding mode, and achieves the manufacturing purposes of high quality, high efficiency, high dimensional accuracy and high corrosion resistance of the material for the main pipe of the pressurized water reactor, and the specific implementation steps are as follows:

[0057] (1) Component gradient transition design and special wire manufacturing

[0058] In order to effectively realize the functional gradient transition between 316L and In718, the component design is one of the important factors affecting the transition effect, and the present application comprehensively considers the interlayer stress level, deposition transition efficiency, manufacturing difficulty and process cost of the special welding wire under different component transition conditions. The interlayer stress under different 316L-In718 component transition conditions is simulated by using simulation software, and the specific results are shown in Figure 6. Figure 5The chemical composition of 316L in the special welding wire is: C≤0.03%, Si: 0.3%-0.65%, Mn: 1%-2.5%, P≤0.025%, S≤0.02%, Cr: 18%-20%, Ni: 11%-14%, Mo: 2%-3%, Cu≤0.75%, and the balance is Fe. The chemical composition of In718 in the special welding wire described in step 1 is: C≤0.08%, Si≤0.35%, Mn≤0.35%, P≤0.015%, S≤0.015%, Al: 0.2%-0.8%, Cr: 17%-21%, Ni: 50%-55%, Mo: 2.8%-3.3%, Co≤1%, Ti: 0.65%-1.15%, Cu≤0.3%, and the balance is Fe.

[0059] From the simulation results, for both 316L and In718 materials, as the number of twisted strands of the special welding wire increases, the composition transition speed between 316L and In718 gradually decreases, making the thermal physical property difference between the dissimilar materials more moderate. This way can effectively reduce the interlayer stress, but when the number of twisted strands is higher than 3, the efficiency of reducing the interlayer stress gradually decreases. At this time, although increasing the number of twisted strands can still reduce the interlayer stress, this way will reduce the transition efficiency on the one hand, and will greatly increase the manufacturing difficulty and process cost of the special welding wire on the other hand. Therefore, after comprehensively considering the interlayer stress level, deposition transition efficiency, and manufacturing difficulty and process cost under different composition transition conditions, the number of twisted strands of the special welding wire is designed to be 3, and the specific mode is shown in Table 1.

[0060] Table 1 Combination mode of 316L-In718 special welding wire

[0061]

[0062] According to the composition design results of the 316L-In718 functional gradient material for the main pipe of the pressurized water reactor, combined with the physical properties and processing characteristics of 316L and In718, the manufacturing mode of the special welding wire is designed according to formula (1),

[0063]

[0064] wherein α is the spiral angle, D is the diameter of the special welding wire, and L is the lay length, and the specific case is shown in Figure 6 The spiral angle is finally selected to be 22.73°, the diameter of the special welding wire is 1.6 mm, the lay length is 12 mm, and the diameter of the thin wire is 0.76 mm. Manufacturing the special welding wire in this process mode can meet the requirements of arc welding wire additive manufacturing of 316L-In718 functional gradient material.

[0065] (2) Forming method

[0066] After the completion of the 316L-In718 component gradient transition design and the manufacture of the special welding wire, the composition transition of the 316L-In718 functional gradient material is realized by the deposition of the special welding wire using the coaxial wire feeding arc additive manufacturing method. The 316L stainless steel substrate is used as the substrate, the substrate surface is cleaned with alcohol to remove oil stains and oxide layers, the substrate is clamped and fixed, the welding gun is connected with the mechanical arm, and the formation of the 316L-In718 functional gradient material is completed through the path planning software and the control unit. First, the deposition of 316L material is realized (3x316L special welding wire is used), which mainly considers that the nickel-based alloy is prone to serious heat accumulation and large crack sensitivity during the arc wire deposition process. In the initial stage of deposition, the use of substrates and wires with similar compositions can effectively avoid the formation of poor conditions under large temperature gradients. After depositing a certain number of layers of 316L, 2x316L+1xIn718 special welding wire is selected for deposition on this basis, and after deposition, the purpose of 100% 316L to 2 / 3 316L+1 / 3 In718 transition is achieved. According to this mode, 1x316L+2xIn718 and 3xIn718 special welding wires are deposited, and finally the composition transition from 100% 316L to 100% In718 is realized.

[0067] (3) Process control points

[0068] During the deposition process, the number of deposited layers under each component is crucial for the 316L-In718 transition efficiency and interlayer stress control. Without the support of a corresponding process database, a large number of process designs and comparisons are carried out, and the relationship between the number of different component transition layers and interlayer stress is obtained. The specific situation is as follows: Figure 7 As can be seen from the figure, with the increase of the number of deposited layers in the component gradient transition, the interlayer stress gradually decreases, but when the number of deposited layers under each component is greater than 4, the degree of reduction of interlayer stress with the change of the number of deposited layers has become smaller and smaller. Therefore, based on the comprehensive consideration of interlayer stress control and component transition efficiency, the number of deposited layers under each component is set to 4 layers.

[0069] In the process of 316L-In718 functional gradient material electric arc wire additive manufacturing, due to the significant difference in metal composition under each component condition, which further causes the difference in the pool flow and characteristics, which leads to the difference between the deposition of 316L-In718 functional gradient material and the conventional deposition. In order to obtain good dimensional accuracy under different components, the deposition layer forming process under different component conditions needs to be scientifically matched according to the pool characteristics in the deposition process of each component. The geometry of the pool depends on the convective flow of the liquid metal in the pool. There is a significant difference in the surface tension and viscosity of the liquid metal under different component conditions. The forming process is designed by formula (2),

[0070]

[0071] In the formula, Ma is the Marangoni coefficient, which is usually used to represent the ratio of surface tension and viscous force, and is a measure of the convective flow intensity of liquid metal in the pool. μ is the viscosity of the liquid metal, α is the thermal diffusivity of the metal, L is the characteristic length of the pool, that is, the melt width we usually say, and ΔT is the difference between the highest temperature in the liquid metal pool and the solidus temperature, is the sensitivity of surface tension to temperature. According to the calculation and process optimization for many times, the finally formulated 316L-In718 functional gradient material electric arc wire additive manufacturing process parameters are shown in Table 2.

[0072] Table 2 316L-In718 functional gradient material electric arc wire additive manufacturing forming process

[0073]

[0074] In the forming process, in order to successfully complete the deposition and obtain good dimensional accuracy and surface quality, a larger heat input is required. Therefore, in order to avoid excessive heat accumulation, the interlayer temperature needs to be controlled, and a certain interlayer waiting time needs to be set. With the increase of the number of deposited layers, the interlayer waiting time should be gradually increased. The specific process parameters are shown in Table 3.

[0075] Table 3 316L-In718 functional gradient material electric arc wire additive manufacturing interlayer waiting time

[0076]

[0077] (4) Sample physical object

[0078] After depositing 316L-In718 functional gradient material by the above process and method, a thin-walled wall sample is obtained, the sample size is, the sample size is uniform, the step effect is well controlled, and no obvious pores and cracks are found, the overall quality is good, and the specific situation is as follows Figure 8In addition, the transition zones between different component layers are combined well, the component distribution is uniform, and no inclusions, un-melting or other defects are found, and the specific conditions are as shown in Figure 9

[0079] (5) Deposition efficiency

[0080] After the 316L-In718 functional gradient material is deposited by the above process and method, the deposition efficiency is greatly improved compared with laser additive manufacturing, and the specific conditions are as shown in Table 4

[0081] Table 4 Comparison of deposition efficiency of the method of the present application and laser additive manufacturing

[0082]

[0083] (6) Dimensional accuracy

[0084] The 316L-In718 functional gradient material obtained by the above process and method has higher dimensional accuracy compared with the off-axis wire feeding electric arc wire additive manufacturing, and the specific comparison is shown in Table 5:

[0085] Table 5 Comparison of dimensional accuracy of the method of the present application and off-axis wire feeding electric arc wire additive manufacturing

[0086]

[0087] (7) Corrosion resistance

[0088] The uniform corrosion test and stress corrosion test of the conventional 316L and the 316L-In718 functional gradient material obtained in the present application are compared under the typical corrosion environment of the nuclear pressurized water reactor main pipe, and the uniform corrosion results are shown in Table 6. From Table 6, it can be seen that the corrosion weight gain of 316L is obviously higher than that of 316L-In718 functional gradient material, and the unit area corrosion weight gain ratio is 28.8:1, which shows that the 316L-In718 functional gradient material formed under the technology process proposed in the present application can greatly improve the corrosion resistance of the nuclear pressurized water reactor main pipe.

[0089] Table 6 Comparison of uniform corrosion of conventional 316L and 316L-In718 functional gradient material of the present application

[0090]

[0091] At the same time, since the pressurized water reactor main pipe is prone to stress corrosion cracking and other problems at the position of large angle bending, therefore, the stress corrosion of 316L and 316L-In718 functional gradient material after large angle bending under working condition is compared, and the specific conditions are as shown in Figure 9 From the figure, it can be seen that the bending part of 316L after corrosion can find obvious corrosion products​Figure 10 b), which is very likely to cause subsequent stress corrosion cracking, while the 316L-In718 functional gradient material does not show obvious changes in the severe working condition corrosion conditions at the large angle bending part Figure 10 d), which shows that the 316L-In718 functional gradient material formed under the technical process proposed in the application can greatly improve the stress corrosion cracking resistance of the nuclear pressurized water reactor main pipe.

Claims

1. An arc additive manufacturing method for 316L-In718 functionally graded materials used in nuclear pressurized water reactor main pipes, characterized in that The arc additive manufacturing method of coaxial stranded welding wire is carried out as follows: A 316L-In718 functionally graded material for a nuclear pressurized water reactor main pipe is prepared by a coaxial wire feeding arc additive manufacturing method, wherein the coaxial wire feeding welding wire is a 316L-In718 stranded welding wire; the number of strands of the 316L-In718 stranded welding wire is 3, wherein the number of strands of the 316L-In718 is one or more of 3-0, 0-3, 1-2, and 2-1; The 316L-In718 twisted strand welding wire is used in coaxial wire-feed arc additive manufacturing in the following manner: 1) three strands of 316L welding wire are selected for deposition; 2) two strands of 316L welding wire and one strand of In718 welding wire are selected for deposition based on the deposition layer in step 1); 3) one strand of 316L welding wire and two strands of In718 welding wire are selected for deposition based on the deposition layer in step 2); 4) three strands of In718 welding wire are selected for deposition based on the deposition layer in step 3), thereby completing the use of the twisted strand welding wire. Deposition conditions in step 1): welding voltage 17V~24V, current 152A~191A, wire feed speed 4.5m / min~7m / min, running speed 0.2m / min~0.5m / min, and inter-layer waiting time 1min~2min; Deposition conditions in step 2) are: welding voltage 16V~23V, current 148A~187A, wire feed speed 4.2m / min~6.5m / min, running speed 0.2m / min~0.5m / min, and inter-layer waiting time 2min~3min; Deposition conditions in step 3) are: welding voltage 15V~22V, current 124A~168A, wire feed speed 4.0m / min~6.2m / min, running speed 0.2m / min~0.5m / min, and inter-layer waiting time 3min~4min; Deposition conditions in step 4) are as follows: welding voltage of 14 V to 21 V, current of 116 A to 152 A, wire feed speed of 3.8 m / min to 6 m / min, operating speed of 0.2 m / min to 0.5 m / min, interlayer waiting time of 3 min to 5 min; wire elongation of 12 to 15 mm, and shielding gas of Ar with a flow rate of 15 L / min to 20 L / min.

2. The method according to claim 1, characterized in that The chemical composition of 316L in the 316L-In718 stranded welding wire is: C≤0.03%, Si: 0.3%~0.65%, Mn: 1%~2.5%, P≤0.025%, S≤0.02%, Cr: 18%~20%, Ni: 11%~14%, Mo: 2%~3%, Cu≤0.75%, and the balance is Fe; The chemical composition of In718 in the 316L-In718 stranded welding wire is: C≤0.08%, Si≤0.35%, Mn≤0.35%, P≤0.015%, S≤0.015%, Al: 0.2%~0.8%, Cr: 17%~21%, Ni: 50%~55%, Mo: 2.8%~3.3%, Co≤1%, Ti: 0.65%~1.15%, Cu≤0.3%, and the balance is Fe.

3. The method according to claim 1 or 2, characterized in that The diameter D of 316L-In718 stranded welding wire is 1.2mm~1.6mm, the wire lay length L is 11mm~13mm, the wire spiral angle is 18°~24°, and the single wire diameter R is 0.72mm~0.81mm.

4. The method according to claim 1, characterized in that The angle between the welding gun and the substrate in coaxial wire arc additive manufacturing is 10°~15°.

5. The method according to claim 1, characterized in that In the coaxial wire arc additive manufacturing of 316L-In718 functional gradient materials for the main pipe of a nuclear pressurized water reactor, a 316L stainless steel substrate is selected as the substrate, and the 316L stainless steel substrate is repeatedly cleaned and wiped with alcohol.

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