An arc wire feeding additive manufacturing method for 321 stainless steel tissue gradient material

Abstract

An arc wire feeding additive manufacturing method for a 321 stainless steel tissue gradient material, which relates to the field of additive manufacturing. The purpose of the present invention is to address the problems of complex processes, high costs, low deposition efficiency, easy contamination, and limited forming size existing in the preparation process of existing tissue gradient materials. The present invention proposes to control the recrystallization degree of different deposition positions by matching different ultrasonic impact and arc wire feeding additive manufacturing process parameters, and then achieve the purpose of tissue structure gradient transition, so as to prepare a metal FGM with a tissue structure gradient in this way. The present invention can achieve a relatively continuous gradient transition of the tissue structure and function gradient material of large and complex structures, achieving the effects of improving deposition efficiency, simplifying the process flow, and reducing manufacturing costs.

Description

Technical Field

[0001] The present invention belongs to the field of additive manufacturing, and particularly relates to an arc wire feeding additive manufacturing method for 321 stainless steel tissue gradient materials. Background Art

[0002] Functional Graded Materials (FGM) is a kind of material with a continuous gradient in composition or structure. By continuously changing the composition and structure of the material, its interface disappears, so that the properties of the material change slowly with the change of the composition and structure of the material. In functional gradient materials, tissue gradient refers to the characteristic that the microstructure of the material shows a gradual change in space. Compared with the traditional physical vapor deposition method and electrochemical deposition method, the preparation of FGM by additive manufacturing has more advantages, mainly reflected in simple process, easy control of functional gradient and wide application range, etc.

[0003] Generally speaking, at the present stage, the methods for preparing FGM by additive manufacturing mainly focus on laser powder bed fusion and laser powder feeding additive manufacturing. For example, the functional gradient materials of 316L stainless steel and Inconel 718 superalloy with different composition change rates are prepared by laser coaxial powder feeding and directional energy deposition method (Li Pengfei, et al. Study on the Microstructure and Properties of 316L / IN718 Functional Gradient Materials with Different Composition Change Rates by Laser Additive Manufacturing [J]. Chinese Journal of Mechanical Engineering. 2022, 58, 17: 226-239). Another example is that W-Cu functional gradient materials are prepared by selective laser melting (Yan Anru. Research on the Selective Laser Melting Forming Process and Characteristics of W-Cu Composites [D]. Beijing University of Technology). Although laser additive manufacturing can better realize the deposition of different functional gradient materials, laser powder bed fusion additive manufacturing has problems such as low deposition efficiency and limited forming size, while laser powder feeding additive manufacturing has problems such as easy powder contamination and high forming cost. These two methods are difficult to meet the low-cost manufacturing requirements of large-scale complex structure functional gradient materials. Therefore, it is necessary to explore new process methods to prepare large-size tissue functional gradient materials with complex structures more efficiently and simply to meet the special application requirements in the fields of biomedicine, electricity, optics, magnetics, etc.

[0004] At the present stage, the preparation of functional gradient materials by laser additive manufacturing is mainly achieved by mixing different kinds of powders in a certain proportion, melting the mixed powders of different components under the action of a laser heat source, continuously changing the composition ratio of the metal powders during deposition, forming a metallurgical bond between dissimilar materials, and finally obtaining functional gradient materials. Although this method has flexible manufacturing methods and high forming accuracy, it has problems such as high manufacturing cost, low deposition efficiency and easy contamination. Summary of the Invention

[0005] The object of the present invention is to propose an arc wire - feeding additive manufacturing method for 321 stainless - steel tissue gradient materials in view of the problems existing in the preparation process of existing tissue gradient materials, such as complex process, high cost, low deposition efficiency, easy pollution and limited by the forming size.

[0006] An arc wire - feeding additive manufacturing method for 321 stainless - steel tissue gradient materials of the present invention is carried out according to the following steps:

[0007] Step 1: After surface pretreatment of the metal substrate, it is fixedly clamped.

[0008] Step 2: Fix the welding torch to the robotic arm and adjust the angle between the welding torch and the substrate surface.

[0009] Step 3: Set the arc wire - feeding additive manufacturing process and carry out arc wire - feeding additive manufacturing to complete the forming of one deposition layer.

[0010] The conditions of the arc wire - feeding additive manufacturing process are as follows: the wire diameter is 0.8 mm - 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 14 V - 22 V, the current is 126 A - 198 A, the wire - feeding speed is 3.0 m / min - 8.0 m / min, the running speed is 0.1 m / min - 0.4 m / min, the wire extension is 12 - 15 mm, the inter - layer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min - 20 L / min.

[0011] Step 4: After the forming of one deposition layer is completed, ultrasonic impact treatment is carried out; after ultrasonic impact, after adjusting the wire - feeding speed, welding voltage and welding current in the arc wire - feeding additive manufacturing process in Step 3, continue to deposit on the basis of the completed one deposition layer until the deposition is completed; among them, adjusting the arc wire - feeding additive manufacturing process in Step 3 means that the values of the wire - feeding speed, welding voltage and welding current increase in a gradient with the increase of the deposition layer.

[0012] Further, in Step 2, the angle between the welding torch and the substrate surface is adjusted to 10° - 15°.

[0013] Further, the parameters of the arc wire - feeding additive manufacturing process in Step 3 are that the wire diameter is 1.0 mm - 1.4 mm, the substrate thickness is greater than 5 mm, the welding voltage is 16 V - 20 V, the current is 140 A - 180 A, the wire - feeding speed is 5.0 m / min - 7.0 m / min, the running speed is 0.2 m / min - 0.3 m / min, the wire extension is 13 - 15 mm, the inter - layer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min - 20 L / min.

[0014] Further, the process parameters of the arc wire feeding additive manufacturing in step 3 are as follows: the wire diameter is 1.0 mm to 1.2 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15 V to 18 V, the current is 130 A to 160 A, the wire feeding speed is 4.0 m / min to 6.0 m / min, the running speed is 0.2 m / min to 0.3 m / min, the wire elongation is 13 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

[0015] Further, the gradient increase as the deposition layer increases in step 4 means that for every 4-layer increase in the deposition layer, the values of the wire feeding speed, welding voltage, and welding current in the arc wire feeding additive manufacturing process in step 3 increase by one gradient.

[0016] Further, after adjusting the wire feeding speed, welding voltage, and welding current in the arc wire feeding additive manufacturing process in step 3, continue the deposition on the basis of completing one deposition layer until the deposition is completed, which is carried out in the following manner:

[0017] When the deposition layer is 1 to 4 layers, the process parameters of the arc wire feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 14 V to 15 V, the current is 126 A to 139 A, the wire feeding speed is 4.0 m / min to 5.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min;

[0018] When the deposition layer is 5 to 8 layers, the process parameters of the arc wire feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15 V to 15.5 V, the current is 139 A to 165 A, the wire feeding speed is 5.0 m / min to 6.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min;

[0019] When the number of deposited layers is 9 to 12, the process parameters of arc wire - feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15.5 V to 16 V, the current is 165 A to 195 A, the wire - feeding speed is 6.0 m / min to 8.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the inter - layer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

[0020] When the number of deposited layers is more than 12, the process parameters of arc wire - feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 16 V to 22 V, the current is 165 A to 198 A, the wire - feeding speed is 6.0 m / min to 8.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the inter - layer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

[0021] Furthermore, in step 4, the ultrasonic impact device for ultrasonic impact treatment is perpendicular to the substrate, and the angle with the deposited layer is 90°.

[0022] Furthermore, the ultrasonic impact parameters in step 4 for ultrasonic impact treatment are as follows: the impact power is 600 W to 1200 W, the impact frequency is 18 to 25 kHz, the impact running speed is 0.05 m / min to 0.2 m / min, and the external load is 40 N to 100 N.

[0023] Furthermore, the ultrasonic impact parameters in step 4 for ultrasonic impact treatment are as follows: the impact power is 800 W to 1000 W, the impact frequency is 20 to 25 kHz, the impact running speed is 0.1 m / min to 0.2 m / min, and the external load is 60 N to 100 N.

[0024] Furthermore, the ultrasonic impact parameters in step 4 for ultrasonic impact treatment are as follows: the impact power is 600 W to 800 W, the impact frequency is 18 to 22 kHz, the impact running speed is 0.05 m / min to 0.1 m / min, and the external load is 40 N to 80 N.

[0025] The main technical solution of the present invention is as follows: during the arc wire - feeding additive manufacturing process, ultrasonic impact means are introduced. By matching different deposition parameters and ultrasonic impact parameters, a controllable degree of recrystallization is obtained, and then a tissue gradient transition is realized at different deposition stages, and finally the purpose of preparing a tissue gradient transition is achieved.

[0026] The theoretical basis on which this technical solution is based is as follows:

[0027] After introducing ultrasonic impact during the arc wire and arc additive manufacturing process, it can have two important effects on the deposited layer: First, under the action of ultrasonic impact, severe plastic deformation will occur on the surface of the deposited layer, resulting in a large amount of dislocation multiplication, obvious lattice distortion, and thus introducing a large amount of deformation energy storage into the microstructure. The magnitude of the deformation energy storage directly affects the strength of the driving force for recrystallization. Specifically, as shown in Equation (1), the grain boundary driving force ΔE can be expressed as:

[0028]

[0029] τ is the energy per unit length of the dislocation line, ρ NR is the dislocation density before recrystallization, ρ(x) is the dislocation density after grain boundary migration, and r is the grain radius. Under the influence of the subsequent thermal effect of arc wire and arc additive manufacturing, these changes will undergo recrystallization, achieving a certain degree of grain refinement. However, under the combined action of different deformation energy storage and the interlayer thermal effect of arc wire and arc additive manufacturing, due to the difference in recrystallization activation energy, there will be obvious differences in the degree of recrystallization of the deposited layer. The Zener - Hollomon parameter Z can be expressed as:

[0030]

[0031] is the strain rate, T is the deformation temperature, Q is the recrystallization activation energy, and R is the gas constant. Second, in addition to surface plastic deformation, ultrasonic impact can also generate ultrasonic oscillation under the action of high strain in a very short time. The ultrasonic oscillation will break a part of the dislocation bondage and promote the movement of dislocations. During the movement of dislocations, a large amount of combination and annihilation will occur, forming a large number of sub - structures. The proportion of sub - structures f LAGB has the following relationship with the recrystallization percentage A:

[0032] f LAGB ∝A(3)

[0033] This means that the change in the proportion of sub - structures caused by ultrasonic impact will directly affect the recrystallization percentage. Considering the internal changes in the deposited layer caused by ultrasonic impact above, under the combined action of ultrasonic impact and the interlayer thermal effect of arc wire and arc additive manufacturing, a certain degree of recrystallization will occur, and the occurrence of recrystallization will cause grain refinement. The specific schematic diagram is shown in the figure.

[0034] Based on this principle, the present invention proposes to control the degree of recrystallization at different deposition positions by matching different ultrasonic impact and arc wire and arc additive manufacturing process parameters, and then achieve the purpose of gradient transition of the organizational structure, and prepare a metal FGM with an organizational structure gradient in this way.

[0035] The present invention focuses on the additive manufacturing of nuclear metal tissue gradient materials. Aiming at the problems existing in the preparation of tissue functional gradient materials at the present stage, such as complex processes, high costs, and limitations in forming size, it proposes to achieve differences in the recrystallization degree of different deposition layers by combining ultrasonic impact with arc wire additive manufacturing technology, so as to achieve the purpose of tissue gradient transition. Combining the physical properties of the deposited metal and the recrystallization conditions, the ultrasonic impact process (introducing deformation and substructure) and the forming process (introducing interlayer thermal effects) are scientifically matched according to different designed tissue transition conditions, and high deposition efficiency, high quality, and high performance arc wire additive manufacturing of organizational structure functional gradient materials are realized by means of arc wire melting.

[0036] The present invention has the following beneficial effects:

[0037] The present invention adopts the method of ultrasonic impact combined with arc wire additive manufacturing to prepare organizational structure functional gradient materials. The key technical points that can be achieved by this invention are: reasonably setting the organizational structure gradient transition method (including the organizational structure composition and transition efficiency of each deposition layer) according to the characteristics of the deposited metal, scientifically matching the ultrasonic impact process (including impact power, impact frequency, impact running speed, external load, and treatment times) under different organizational structures and the arc wire additive manufacturing forming process (including welding voltage, welding current, wire feeding speed, running speed, interlayer waiting time, and elongation, etc.), and formulating process control points specifically applicable to the preparation of organizational structure functional gradient materials.

[0038] Compared with laser additive manufacturing for preparing organizational structure 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;

[0039] Compared with traditional physical vapor deposition and electrochemical deposition methods, this technology has the advantages of simple process flow and high stability when forming complex structure parts;

[0040] Compared with conventional ultrasonic impact treatment-assisted arc wire additive manufacturing, the present invention can not only achieve the purposes of grain refinement, stress state improvement, defect repair, and anisotropy reduction, but also can realize the control of organizational structure gradient by reasonably matching with the interlayer thermal effect of arc wire additive manufacturing.

[0041] The present invention can realize relatively continuous gradient transition of organizational structure functional gradient materials for large complex structures, achieving the effects of improving deposition efficiency, simplifying the process flow, and reducing manufacturing costs. Brief Description of the Drawings

[0042] Figure 1 Schematic diagram of the principle of tissue gradient transition;

[0043] Figure 2 Schematic diagram of ultrasonic impact treatment on the workpiece after deposition;

[0044] Figure 3 Comparison diagrams of the formed tissue gradient materials of the present invention and conventional arc wire and arc additive manufacturing; among them, (a-c) are the tissue of the deposited layer untreated by the present invention, and (d-f) are the tissue of the deposited layer treated by the present invention;

[0045] Figure 4 Comparison diagrams of the formed tissue of the present invention and traditional arc wire and arc additive manufacturing; among them, (a) is the tissue of traditional arc wire and arc additive manufacturing, and (b) is the tissue of the deposited layer treated by the present invention;

[0046] Figure 5 Morphology diagram of recrystallized grains inside the formed parts of the present invention;

[0047] Figure 6 Comparison diagrams of the recrystallization degree of the parts of the present invention and traditional arc wire and arc additive manufacturing: among them, (a) is the recrystallization distribution of traditional arc wire and arc additive manufacturing, and (b) is the recrystallization distribution of the deposited layer treated by the present invention;

[0048] Figure 7 Schematic process flow diagram of the present invention. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer and more understandable, the spirit of the content disclosed by the present invention will be described in detail below. After any person skilled in the art understands the embodiments of the content of the present invention, they can change and modify it according to the technology taught by the content of the present invention, and it does not deviate from the spirit and scope of the content of the present invention.

[0050] The illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but do not limit the present invention.

[0051] Example 1:

[0052] The present invention uses ultrasonic impact and arc wire and arc additive manufacturing to prepare a tissue structure gradient material of 321 stainless steel, achieving the purpose of high-efficiency and low-cost manufacturing of a metal matrix tissue structure gradient material. The specific implementation steps are as follows:

[0053] (1) Design of tissue structure gradient transition

[0054] To effectively achieve the functional gradient transition of the tissue structure between different deposited layers, designing the tissue structure according to the characteristics of the deposited metal and the recrystallization conditions is one of the important factors affecting the transition effect. The present invention scientifically matches the ultrasonic impact process parameters and the arc wire and arc additive manufacturing process parameters according to formulas (1) to (3). During the actual forming process, the ultrasonic impact process parameters are set as shown in Table 1.

[0055] Table 1 Ultrasonic impact process parameter settings

[0056]

[0057] Correspondingly, the process parameter settings of arc wire additive manufacturing are shown in Table 2

[0058] Table 2 Arc wire additive manufacturing process settings

[0059]

[0060] (2) Forming method

[0061] After completing the process matching of the above ultrasonic impact and arc wire additive manufacturing, using 304 stainless steel as the substrate (thickness 5 mm) and 321 stainless steel wire (diameter 1.2 mm) as the deposited metal, the chemical compositions of the substrate and the wire are shown in Table 3

[0062] Table 3 Chemical compositions of the substrate and the wire (mass percentage)

[0063]

[0064] During the deposition process, the surface of the substrate is cleaned with alcohol to remove oil stains and oxide layers. The substrate is clamped and fixed, and the welding torch, ultrasonic impact equipment and robotic arm are connected. The forming and ultrasonic impact treatment of the deposited metal are completed through path planning software and control unit. First, the deposition of 321 stainless steel material is realized. After a certain interlayer waiting time, the deposited layer is cooled to below 100 °C (this is mainly to consider that too high a temperature of the deposited layer will damage the ultrasonic impact equipment). At this time, after a certain cleaning treatment of the deposited layer, the external load and running trajectory of the ultrasonic impact equipment are controlled through the robotic arm. After the impact is completed, the deposition continues on the previously treated deposited layer. Under the combined action of ultrasonic impact and the interlayer thermal effect of arc wire, certain recrystallization will occur, achieving a certain grain refinement effect. After obtaining 1-4 deposited layers under this process, the parameter matching of ultrasonic impact and arc wire additive manufacturing is adjusted, and the previous process is repeated to achieve a higher degree of recrystallization, making the structure more refined. The 5-8 deposited layers obtained form an obvious organizational structure gradient compared with the initial 1-4 deposited layers. After adjusting the specific parameter matching according to this mode, the deposition of the 9-12 deposited layers is continued, and finally the organizational structure gradient transition is realized. The specific effect is shown in Figure 3 .

[0065] (3) Grain refinement and recrystallization

[0066] Compared with the 321 stainless steel organizational structure gradient (hereinafter referred to as the traditional workpiece) metal workpiece manufactured by the arc wire additive manufacturing method without the ultrasonic impact process in Example 1, the structure obtained by the present invention has been significantly refined, and obvious columnar crystal to equiaxed crystal transformation has occurred in the structure under the action of recrystallization. The specific situation is as follows Figure 4 shown. After recrystallization occurs, a large number of typical recrystallized grains will be formed in the structure. The specific situation is as follows Figure 5 shown (BF is the bright field image, and DF is the dark field image). The recrystallization comparison situation is as follows Figure 6 shown.

[0067] (4) Tensile properties

[0068] The tensile properties of the workpiece formed by the present invention are significantly improved in the X, Y, and Z directions compared with the traditional arc wire additive manufacturing workpiece, as shown in Table 4 specifically.

[0069] Table 4 Comparison of tensile properties between traditional arc wire additive manufacturing workpieces and workpieces of the present invention

[0070]

[0071] (5) Impact properties

[0072] The impact properties of the workpiece formed by the present invention (specimen size: 10mm×10mm×55mm, room temperature) are significantly improved in the X, Y, and Z directions compared with the traditional arc wire additive manufacturing workpiece, as shown in Table 5 specifically.

[0073] Table 5 Comparison of impact properties between traditional arc wire additive manufacturing workpieces and workpieces of the present invention

[0074]

[0075]

Claims

1. An arc wire feeding additive manufacturing method for a 321 stainless steel tissue gradient material, characterized in that It is carried out according to the following steps: Step 1: After surface pretreatment of the metal substrate, it is fixed and clamped; Step 2: Fix the welding torch to the robotic arm and adjust the angle between the welding torch and the substrate surface; Step 3: Set the arc wire feeding additive manufacturing process and perform arc wire feeding additive manufacturing to complete the forming of a deposition layer; The conditions of the arc wire feeding additive manufacturing process are as follows: the wire diameter is 0.8 mm - 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 14 V - 22 V, the current is 126 A - 198 A, the wire feeding speed is 3.0 m / min - 8.0 m / min, the running speed is 0.1 m / min - 0.4 m / min, the wire elongation is 12 - 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min - 20 L / min; Step 4: After completing the forming of a deposition layer, perform ultrasonic impact treatment; after ultrasonic impact treatment, adjust the wire feeding speed, welding voltage, and welding current in the arc wire feeding additive manufacturing process in Step 3, and then continue to deposit on the basis of the completed deposition layer until the deposition is completed; among them, adjusting the arc wire feeding additive manufacturing process in Step 3 means that the values of the wire feeding speed, welding voltage, and welding current increase in a gradient with the increase of the deposition layer; After adjusting the wire feeding speed, welding voltage, and welding current in the arc wire feeding additive manufacturing process in Step 3 in Step 4, and then continuing to deposit on the basis of the completed deposition layer until the deposition is completed, it is carried out in the following manner: When the deposition layer is 1 - 4 layers, the parameters of the arc wire feeding additive manufacturing process are: the wire diameter is 0.8 mm - 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 14 V - 15 V, the current is 126 A - 139 A, the wire feeding speed is 4.0 m / min - 5.0 m / min, the running speed is 0.1 m / min - 0.4 m / min, the wire elongation is 12 - 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min - 20 L / min; When the deposition layer is 5 - 8 layers, the parameters of the arc wire feeding additive manufacturing process are: the wire diameter is 0.8 mm - 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15 V - 15.5 V, the current is 139 A - 165 A, the wire feeding speed is 5.0 m / min - 6.0 m / min, the running speed is 0.1 m / min - 0.4 m / min, the wire elongation is 12 - 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min - 20 L / min; When the number of deposited layers is 9 to 12, the process parameters of arc wire feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15.5 V to 16 V, the current is 165 A to 195 A, the wire feeding speed is 6.0 m / min to 8.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min; When the number of deposited layers is more than 12, the process parameters of arc wire feeding additive manufacturing are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 16 V to 22 V, the current is 165 A to 198 A, the wire feeding speed is 6.0 m / min to 8.0 m / min, the running speed is 0.1 m / min to 0.4 m / min, the wire elongation is 12 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

2. The arc wire - feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 1, characterized in that In step 2, adjust the angle between the welding torch and the substrate surface to 10° to 15°.

3. The arc wire feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 1, characterized in that The process parameters of the arc wire feeding additive manufacturing described in step 3 are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 16 V to 20 V, the current is 140 A to 180 A, the wire feeding speed is 5.0 m / min to 7.0 m / min, the running speed is 0.2 m / min to 0.3 m / min, the wire elongation is 13 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

4. The arc wire feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 1, characterized in that The process parameters of the arc wire feeding additive manufacturing described in step 4 are as follows: the wire diameter is 0.8 mm to 1.6 mm, the substrate thickness is greater than 5 mm, the welding voltage is 15 V to 18 V, the current is 130 A to 160 A, the wire feeding speed is 4.0 m / min to 6.0 m / min, the running speed is 0.2 m / min to 0.3 m / min, the wire elongation is 13 to 15 mm, the interlayer waiting time is 1 min, and the shielding gas is Ar + CO2 with a flow rate of 15 L / min to 20 L / min.

5. The arc wire feeding additive manufacturing method for a 321 stainless steel tissue gradient material according to claim 1, characterized in that In step 4, the gradient increase with the increase of the deposited layer means that for every 4 layers increase in the deposited layer, the process of arc wire feeding additive manufacturing in step 3 refers to an increase in the values of the wire feeding speed, welding voltage, and welding current by one gradient.

6. The arc wire feeding additive manufacturing method for a 321 stainless steel tissue gradient material according to claim 1, characterized in that In step 4, the ultrasonic impact device for ultrasonic impact treatment is perpendicular to the substrate, and the angle with the deposited layer is 90°.

7. The arc wire feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 1 or 6, characterized in that The ultrasonic impact parameters of the ultrasonic impact treatment in step 4 are as follows: the impact power is 600 W to 1200 W, the impact frequency is 18 to 25 kHz, the impact running speed is 0.05 m / min to 0.2 m / min, and the external load is 40 N to 100 N.

8. The arc wire feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 7, characterized in that The ultrasonic impact parameters in Step 4 are as follows: impact power 800W - 1200W, impact frequency 20 - 25kHz, impact running speed 0.05m / min - 0.15m / min, external load 60N - 100N.

9. The arc wire feeding additive manufacturing method of a 321 stainless steel tissue gradient material according to claim 1, characterized in that The ultrasonic impact parameters in Step 4 are as follows: impact power 1000W - 1200W, impact frequency 22 - 25kHz, impact running speed 0.05m / min - 0.1m / min, external load 80N - 100N.

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