Method for manufacturing a martensitic stainless steel cored wire and a structural part

Abstract

The application discloses a martensitic stainless steel flux-cored wire, which comprises a core and a sheath, and the core is composed of the following components in percentage by mass: 12-15% of chromium powder, 2-4% of titanium powder, 6-8% of molybdenum powder, 2-4% of vanadium powder, 1-3% of niobium powder, 0.2% of carbon powder, 0.5-1% of tungsten carbide, 1-2% of manganese powder, 0.3-0.6% of silicon powder, 0.1-0.2% of rare earth oxide, and the rest is iron powder. The application further discloses a method for preparing a structural part by using the martensitic stainless steel flux-cored wire. The martensitic stainless steel structural part is prepared by using the martensitic stainless steel flux-cored wire and adopting MIG welding as a heat source for additive manufacturing. The martensitic stainless steel structural part is prepared by using a full-automatic welding robot, so that the efficiency is high; the arc is stable during the printing process, the weld formation is beautiful, the surface is smooth, and there is no air hole or slag inclusion.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of welding wire materials, and specifically relates to a martensitic stainless steel flux-cored wire, and also relates to a method for preparing a structural member by using the martensitic stainless steel flux-cored wire. BACKGROUND

[0002] With the continuous development of the aviation industry, the performance requirements for aircraft landing gears are becoming higher and higher, especially in terms of lightweight, high strength and corrosion resistance. Traditional manufacturing methods have been difficult to meet the demand of modern aircraft for high-performance materials.

[0003] Wire Arc Additive Manufacturing (WAAM) is a method of manufacturing complex structures by melting metal wires through an electric arc and depositing them layer by layer. First, the high deposition efficiency of WAAM technology is one of its notable features. WAAM can achieve very high deposition rates by using an electric arc as a heat source, typically reaching several kilograms to tens of kilograms of material deposition per hour, which is much higher than traditional laser additive manufacturing techniques. This high deposition rate greatly shortens the manufacturing time and improves production efficiency. Secondly, WAAM technology also performs well in terms of cost-effectiveness. Since WAAM uses welding equipment, which is relatively mature and reasonably priced, the initial investment and operating costs of the equipment are relatively low. Compared with expensive laser systems, WAAM technology has obvious advantages in equipment cost and maintenance cost, making it particularly suitable for industries that require large-scale production. In addition, WAAM technology also has high flexibility, which can achieve precise manufacturing of complex shapes by adjusting welding parameters and paths. This flexibility and large-size manufacturing capability make WAAM technology an ideal choice for many high-demand industrial fields.

[0004] Martensitic stainless steel has high strength, excellent corrosion resistance, good processability, and good weldability and machinability, and is widely used in the aerospace field. Flux-cored wire can flexibly adjust alloy elements, and has higher cladding efficiency than solid wire, so it is widely used in additive manufacturing.

[0005] By combining the advantages of wire arc additive manufacturing technology, precipitation-hardened martensitic stainless steel performance and flux-cored wire, the manufacturing of high-performance aircraft landing gears can be realized, meeting the demand of modern aviation industry for lightweight, high strength and corrosion resistance. With the continuous progress of technology, wire arc additive manufacturing of aircraft landing gears using precipitation-hardened martensitic stainless steel flux-cored wire will have a wide application prospect in the aviation industry. The progress of this technology will promote the development of the aviation industry and realize the efficient manufacturing of high-performance aircraft landing gears. SUMMARY

[0006] The first object of the present application is to provide a martensitic stainless steel flux-cored wire which can be used as a raw material for additive manufacturing of martensitic stainless steel, and the preparation process of the flux-cored wire is simple, pollution-free, and the composition is easy to control.

[0007] The second object of the present application is to provide a method for preparing a structural member using the martensitic stainless steel flux-cored wire, which can be used for additive manufacturing of an aircraft landing gear structural member.

[0008] The first technical solution adopted by the present application is a martensitic stainless steel flux-cored wire, comprising a core and a sheath, wherein the core is composed of the following components in mass percentage: chromium powder 12-15%, titanium powder 2-4%, molybdenum powder 6-8%, vanadium powder 2-4%, niobium powder 1-3%, carbon powder 0.2%, tungsten carbide 0.5-1%, manganese powder 1-2%, silicon powder 0.3-0.6%, rare earth oxide 0.1-0.2%, and the rest is iron powder.

[0009] The sheath is a 0Cr18Ni9 austenitic stainless steel strip, and the filling amount of the core powder is 23wt%-26wt%.

[0010] The second technical solution adopted by the present application is a method for preparing a structural member using the martensitic stainless steel flux-cored wire, which is specifically carried out according to the following steps:

[0011] Step 1, according to mass percentage, the following raw materials are weighed respectively: chromium powder 12-15%, titanium powder 2-4%, molybdenum powder 6-8%, vanadium powder 2-4%, niobium powder 1-3%, carbon powder 0.2%, tungsten carbide 0.5-1%, manganese powder 1-2%, silicon powder 0.3-0.6%, rare earth oxide 0.1-0.2%, and the rest is iron powder.

[0012] Step 2, the raw material powder weighed in step 1 is heated and kept in an inert gas atmosphere to remove moisture;

[0013] Step 3, the sheath is placed on the tape placing machine of the wire forming machine, and the sheath is rolled into a U-shaped groove through the pressure groove of the forming machine, and the raw material powder obtained in step 2 is cooled to room temperature in the furnace, and then the powder is filled into the U-shaped groove, and the filling rate of the core powder is controlled at 23wt%-26wt%, and after passing through the closed forming roller, a 2.10mm wire is prepared, and finally a 1.20mm flux-cored wire is prepared by the step-by-step reducing method;

[0014] Step 4, the prepared flux-cored wire is assembled to a full-automatic welding robot, MIG welding is used as a heat source to obtain a structural member through additive manufacturing, with the movement of the welding head, the molten metal is accumulated on the base material layer by layer, and the thickness of each layer is usually controlled at 2-3 mm, so that the stability of the deposited layer and the density of the structure can be ensured. The welding path is accurately controlled through the pre-programmed robot system, and the robot can weld according to the set trajectory, so that the shape and size of each layer meet the design requirements. In the process of additive manufacturing, good bonding between layers is required, which requires controlling the interlayer temperature during welding. The interlayer temperature is fixed at 100-150 DEG C, and the generation of deformation or cracks caused by excessive heat accumulation is avoided. Finally, after the arc additive manufacturing is completed, the structural member may need to be treated, such as removing slag and polishing the surface to obtain the final product.

[0015] The second technical scheme of the present application is characterized in that,

[0016] The inert protective atmosphere in step 3 is pure argon with a purity of 99.999%;

[0017] In step 3, the outer skin is 0Cr18Ni9 austenitic stainless steel strip.

[0018] In step 2, the heating temperature is 150-200 DEG C, and the holding time is 2-2.5 h.

[0019] In step 4, the process parameters of MIG welding are as follows: welding speed 0.2-0.3 m / min; each layer of welding gun is lifted by 2-3 mm, and the protective gas is pure argon with a purity of 99.999%;

[0020] The third technical scheme adopted by the present application is a martensitic stainless steel structural member prepared by the above method.

[0021] The beneficial effects of the present application are:

[0022] 1. The martensitic stainless steel flux-cored wire has a short preparation period and high production efficiency, and the performance can be improved by adjusting the composition and proportion of the core, and the flux-cored wire production is pollution-free and the cladding efficiency is high during welding.

[0023] 2. The martensitic stainless steel flux-cored wire has a strengthening effect, that is, a plurality of precipitated phase elements are added to the welding wire, Cr and Ni elements are used as main alloy components, a certain amount of V, Mo, Nb, Ti and other trace alloy elements are added, WC hard phase and a small amount of rare earth oxides are added, and the proportion of each element is strictly controlled, so as to obtain a martensitic stainless steel flux-cored wire with excellent performance.

[0024] 3.The method for preparing structural parts by using the martensitic stainless steel flux-cored wire, which is a method for preparing martensitic stainless steel by using MIG welding as a heat source and flux-cored wire as a raw material; the uniformly mixed flux-cored powder is placed in a tube furnace, argon is continuously introduced, and the temperature is kept at 150-200 DEG C for 2-2.5 hours; the full-automatic welding robot is programmed to realize the additive manufacturing of the martensitic stainless steel structural parts, and the efficiency is high; the arc is stable during the printing process, the weld is formed in a beautiful and smooth surface, and the burr is only 2-3 mm without pores and slag inclusions.

[0025] 4.The martensitic stainless steel structural parts prepared by the additive manufacturing have a beautiful shape and excellent mechanical properties, and perfectly meet the use requirements of the airplane landing gear. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a stress-strain curve diagram of the martensitic stainless steel prepared by the flux-cored wire of example 5.

[0027] Figure 2 is a microstructure diagram of the martensitic stainless steel structural parts prepared by example 5. DETAILED DESCRIPTION

[0028] The application will be described in detail below in combination with the drawings and specific examples.

[0029] Example 1

[0030] The application provides a martensitic stainless steel flux-cored wire, which comprises a core and a sheath, wherein the core is composed of the following components in percentage by mass: chromium powder 12-15%, titanium powder 2-4%, molybdenum powder 6-8%, vanadium powder 2-4%, niobium powder 1-3%, carbon powder 0.2%, tungsten carbide 0.5-1%, manganese powder 1-2%, silicon powder 0.3-0.6%, rare earth oxide 0.1-0.2%, and the rest is iron powder; the sheath is a 0Cr18Ni9 austenitic stainless steel strip, and the filling amount of the flux-cored powder is controlled at 20wt%-25wt%.

[0031] The functions and effects of the components in the flux-cored wire are as follows:

[0032] Cr element: the Cr element is a necessary element for improving corrosion resistance. During welding, the Cr atom generally has a strong affinity with the C atom, and in a long-term high-temperature environment, the C atom will migrate to the high-C area to form a carbide accumulation area, which has a great hardening tendency in subsequent processing. At the same time, the Cr element is also a ferrite-forming element, which can reduce the Ms point;

[0033] Ni element: Ni element mainly promotes the formation of austenite in the weld structure, Ni element will make the gamma phase zone move to the direction of higher Cr element, avoid too much ferrite in the weld. But when the content of Ni element is too high, it will reduce the Ms point, make it difficult to transform the martensite in the structure, and more residual austenite structure, reduce the strength of the weld metal;

[0034] Mo element: Mo element can improve the strength and corrosion resistance. The molybdenum-rich phase precipitates during aging to improve the strength of the weld. Mo can prohibit other precipitates in the weld metal from diffusing and precipitating at the grain boundary, avoiding intergranular fracture. Mo and Cr can interact to improve the corrosion resistance of the weld;

[0035] Nb element: Nb element and Ti element have aging strengthening effect, but the influence of Nb element on toughness is less than that of Ti element. Because Nb(C, N) precipitates at the grain boundary, the deformation ability of the crystal interior is still large, while the precipitates of Ti are uniformly distributed in the grain interior, the deformation ability is weakened, which leads to the decrease of toughness.

[0036] Ti element: The strengthening effect of Ti element mainly reflects in two aspects: fine grain strengthening and precipitate strengthening. Appropriate addition of Ti can act as nucleation sites during the solidification process of the molten pool, promoting the refinement of the structure. A large number of small grain boundaries can effectively hinder the movement of dislocations, thereby limiting deformation and crack propagation, and improving the yield strength and impact toughness of the steel.

[0037] Mn element and Si element: In the welding process, the main role of Mn and Si is deoxidation and desulfurization, which can reduce the content of oxygen and sulfur in the surfacing alloy, prevent the formation of pores and other defects in the surfacing metal, and cause the decrease of forming quality.

[0038] WC element: WC as a high-strength hard phase can not only act as a nucleation site in the molten pool to refine the grain and improve the strength of the material. At the same time, WC can also be precipitated to strengthen and improve the strength and toughness of the martensitic stainless steel.

[0039] Rare earth element (Re): Rare earth elements can combine with impurity elements in the weld to produce solid solution strengthening effect and increase strength. Re element can increase the volume fraction of lath martensite in the weld metal, refine the grain size, reduce the proportion of residual austenite, and inhibit the formation of sheet martensite, so that the carbide is spheroidized and dispersedly distributed on the ferrite matrix. Re can modify impurities and purify grain boundaries to improve impact toughness

[0040] The application also provides a method for preparing a structural part by using the martensitic stainless steel flux-cored wire, which is prepared according to the following steps:

[0041] Step 1, the following raw materials are weighed according to mass percentage: chromium powder 12-15%, titanium powder 2-4%, molybdenum powder 6-8%, vanadium powder 2-4%, niobium powder 1-3%, carbon powder 0.2%, tungsten carbide 0.5-1%, manganese powder 1-2%, silicon powder 0.3-0.6%, rare earth oxide 0.1-0.2%, and the rest is iron powder;

[0042] Step 2, the raw material powder weighed in step 1 is heated and kept in an inert gas atmosphere to remove moisture;

[0043] In step 2, the heating temperature is 150℃~200℃, and the holding time is 2h~2.5h.

[0044] Step 3, place the outer skin on the tape machine of the welding wire forming machine, roll the outer skin into a U-shaped groove through the pressure groove of the forming machine, and then cool the raw material powder obtained in step 2 to room temperature in the furnace, and then fill the powder into the U-shaped groove, the filling rate of the core powder is controlled at 20wt%-25wt%, and then the 2.10mm welding wire is obtained after the closed forming roller, and finally the 1.20mm flux-cored wire is obtained by gradually reducing the diameter.

[0045] In step 3, the inert atmosphere is 99.999% pure argon; in step 3, the outer skin is 0Cr18Ni9 austenitic stainless steel tape.

[0046] Step 4, assemble the prepared flux-cored wire to the full-automatic welding robot, use MIG welding as the heat source to carry out additive manufacturing to obtain a structural part, wherein the specific parameters of the welding process are: the welding speed is 0.2m / min-0.3m / min; the welding gun is lifted by 2mm-3mm per layer; the protective gas is 99.999% argon. With the movement of the welding head, the molten metal is deposited on the substrate layer by layer, and the thickness of each layer is usually controlled at 2-3mm, which can ensure the stability of the deposited layer and the density of the structure. The welding path is precisely controlled by the pre-programmed robot system, and the robot can weld according to the set trajectory to ensure that the shape and size of each layer meet the design requirements. In the process of additive manufacturing, good bonding between layers is required, which requires controlling the interlayer temperature during welding. The interlayer temperature is fixed at 100-150℃ to avoid the accumulation of excessive heat leading to deformation or cracking. Finally, after the arc additive manufacturing is completed, the structural part may need to be treated, such as removing the welding slag and polishing the surface to obtain the final product.

[0047] Example 2

[0048] Step 1: Take the following components by mass percentage: chromium powder 12%, titanium powder 2%, molybdenum powder 8%, vanadium powder 2%, niobium powder 1%, carbon powder 0.2%, tungsten carbide 0.5%, manganese powder 1%, silicon powder 0.6%, rare earth oxide 0.1%, and the rest is iron powder. The sum of the mass percentages of the above components is 100%.

[0049] Step 2: Mix all the raw materials weighed in Step 1 uniformly and place them in a tube furnace. Under the condition of continuous argon gas inflow, heat at 200℃ for 2.5h.

[0050] Step 3: Place the 0Cr18Ni9 austenitic stainless steel strip (composition as shown in Table 1) with a width of 7mm and a thickness of 0.3mm on the strip placing machine of the wire forming machine. Roll the steel strip into a U-shaped groove through the pressure groove of the forming machine. Put the core powder obtained in Step 2 into the U-shaped groove, and control the filling rate of the core powder to be 24wt%. Then use the forming machine to roll and close the U-shaped groove. Wipe clean with acetone or anhydrous ethanol, and draw the wire to a diameter of 2.1mm. Then reduce the diameter to 1.20mm. Wipe the oil on the wire with cotton cloth dipped in acetone or anhydrous ethanol. Finally, straighten the wire, coil it into a disc, seal it, and package it to obtain the martensitic stainless steel cored wire for additive manufacturing.

[0051] Table 1: Chemical composition of the 0Cr18Ni9 austenitic stainless steel strip used (mass fraction %)

[0052]

[0053] Step 4: Put the prepared martensitic stainless steel cored wire for additive manufacturing into a fully automatic welding robot, and use MIG welding as the heat source to perform additive manufacturing to obtain a structural part. The specific parameters of the welding process are as follows: welding speed is 0.2m / min-0.3m / min; the welding gun is lifted by 2mm-3mm per layer; the protective gas is 99.999% argon. As the welding head moves, the molten metal is deposited on the substrate layer by layer, with the thickness of each layer usually controlled at 2-3mm, which can ensure the stability of the deposited layer and the density of the structure. The welding path is precisely controlled by the pre-programmed robot system, and the robot can weld according to the set trajectory, ensuring that the shape and size of each layer meet the design requirements. During the additive manufacturing process, good bonding between layers is required, which requires controlling the interlayer temperature during welding. The interlayer temperature is fixed at 100-150℃ to avoid excessive heat accumulation that may cause deformation or cracking. Finally, after arc additive manufacturing is completed, the structural part may need to be treated, such as removing slag and polishing the surface to obtain the final product.

[0054] The martensitic stainless steel formed part prepared in this example has an attractive appearance and no obvious spatter. The tensile strength can reach 883.6MPa, and the elongation is 10.5%.

[0055] Example 3

[0056] Step 1: Take the chromium powder 14%, titanium powder 2%, molybdenum powder 6.5%, vanadium powder 3%, niobium powder 1.5%, carbon powder 0.2%, tungsten carbide 0.6%, manganese powder 1.5%, silicon powder 0.5%, rare earth oxide 0.1% by mass percentage respectively, and the rest is iron powder;

[0057] Step 2: Mix all the raw materials weighed in step 1 uniformly and place them in a tube furnace, continuously pass argon under the condition of 200℃ for 2.5h.

[0058] Step 3: Place the 0Cr18Ni9 austenitic stainless steel strip (composition as shown in Table 1) with a width of 7mm and a thickness of 0.3mm on the strip placing machine of the wire forming machine, roll the steel strip into a U-shaped groove through the pressure groove of the forming machine, put the core powder obtained in step 2 into the U-shaped groove, and control the filling rate of the core powder to be 23wt%, then use the forming machine to roll and close the U-shaped groove, wipe it clean with acetone or anhydrous ethanol, and draw it into a welding wire with a diameter of 2.1mm, then reduce the diameter to 1.20mm, wipe the oil stains on the welding wire with cotton cloth dipped in acetone or anhydrous ethanol, and finally straighten, coil into a disc, and seal package through the wire drawing machine to obtain the martensitic stainless steel cored wire for additive manufacturing.

[0059] Step 4: Put the prepared martensitic stainless steel cored wire for additive manufacturing into a full-automatic welding robot, and use MIG welding as the heat source to carry out additive manufacturing to obtain a structural part, wherein the specific parameters of the welding process are: the welding speed is 0.2m / min-0.3m / min; the welding gun is lifted by 2mm-3mm per layer; the protective gas is 99.999% argon. As the welding head moves, the molten metal is deposited on the substrate layer by layer, and the thickness of each layer is usually controlled at 2-3mm, which can ensure the stability of the deposited layer and the density of the structure. The welding path is precisely controlled by the pre-programmed robot system, and the robot can weld according to the set trajectory to ensure that the shape and size of each layer meet the design requirements. During the additive manufacturing process, good bonding between layers is required, which requires controlling the interlayer temperature during welding to be fixed at 100-150℃ to avoid the accumulation of excessive heat leading to deformation or crack. Finally, after the arc additive manufacturing is completed, the structural part may need to be treated, such as removing the welding slag and polishing the surface to obtain the final product.

[0060] The martensitic stainless steel formed part prepared in this example has good mechanical properties and no obvious spatter, and the tensile strength can reach 915.2MPa and the elongation is 11.6%.

[0061] Example 4

[0062] Step 1: Take the following components by mass percentage: chromium powder 13%, titanium powder 3%, molybdenum powder 8%, vanadium powder 4%, niobium powder 2.5%, carbon powder 0.2%, tungsten carbide 1%, manganese powder 1%, silicon powder 0.6%, rare earth oxide 0.15%, and the rest is iron powder. The sum of the mass percentages of the above components is 100%.

[0063] Step 2: Mix all the raw materials weighed in Step 1 uniformly and place them in a tube furnace. Under the condition of continuous argon gas inflow, heat at 200°C for 2.5h.

[0064] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (composition as shown in Table 1) with a width of 7mm and a thickness of 0.3mm on the strip placing machine of the wire forming machine. Roll the steel strip into a U-shaped groove through the pressure groove of the forming machine. Put the core powder obtained in Step 2 into the U-shaped groove, and control the filling rate of the core powder to be 26wt%. Then use the forming machine to roll and close the U-shaped groove. Wipe clean with acetone or anhydrous ethanol, and draw the wire to a diameter of 2.1mm. Then reduce the diameter to 1.20mm. Wipe the oil on the wire with cotton cloth dipped in acetone or anhydrous ethanol. Finally, straighten the wire, coil it into a disc, seal it, and package it to obtain a martensitic stainless steel cored wire for additive manufacturing.

[0065] Step 4: Put the prepared martensitic stainless steel cored wire for additive manufacturing into a fully automatic welding robot, and use MIG welding as the heat source to perform additive manufacturing to obtain a structural part. The specific parameters of the welding process are as follows: welding speed is 0.2m / min-0.3m / min; the welding gun is lifted by 2mm-3mm per layer; the protective gas is 99.999% argon. As the welding head moves, the molten metal is deposited on the substrate layer by layer, and the thickness of each layer is usually controlled at 2-3mm, which can ensure the stability of the deposited layer and the density of the structure. The welding path is precisely controlled by the pre-programmed robot system, and the robot can weld according to the set trajectory to ensure that the shape and size of each layer meet the design requirements. During the additive manufacturing process, good bonding between layers is required, which requires controlling the interlayer temperature during welding. The interlayer temperature is fixed at 100-150°C to avoid the accumulation of excessive heat leading to deformation or cracking. Finally, after arc additive manufacturing is completed, the structural part may need to be treated, such as removing the slag and polishing the surface to obtain the final product.

[0066] The martensitic stainless steel formed part prepared in this example has no cracks and pores on the surface, and there is no obvious spatter during welding. The tensile strength can reach 964.2MPa, and the elongation is 8.2%.

[0067] Example 5

[0068] Step 1: Take the following powders by mass percentage: chromium powder 16%, titanium powder 4%, molybdenum powder 7%, vanadium powder 2%, niobium powder 3%, carbon powder 0.2%, tungsten carbide 0.6%, manganese powder 2%, silicon powder 0.4%, rare earth oxide 0.2%, and the rest is iron powder. The sum of the mass percentages of the above components is 100%.

[0069] Step 2: Mix all the raw materials weighed in Step 1 uniformly and place them in a tube furnace. Under the condition of continuous argon gas inflow, heat at 200°C for 2.5h.

[0070] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (composition as shown in Table 1) with a width of 7mm and a thickness of 0.3mm on the strip placing machine of the wire forming machine. Roll the steel strip into a U-shaped groove through the pressure groove of the forming machine. Put the core powder obtained in Step 2 into the U-shaped groove, and control the filling rate of the core powder to be 25wt%. Then use the forming machine to roll and close the U-shaped groove. Wipe clean with acetone or anhydrous ethanol, and draw the wire to a diameter of 2.1mm. Then reduce the diameter to 1.20mm. Wipe the oil on the wire with cotton soaked in acetone or anhydrous ethanol. Finally, straighten the wire, coil it into a disc, seal it, and package it to obtain a martensitic stainless steel cored wire for additive manufacturing.

[0071] Step 4: Put the prepared martensitic stainless steel cored wire for additive manufacturing into a fully automatic welding robot, and use MIG welding as the heat source to perform additive manufacturing to obtain a structural part. The specific parameters of the welding process are as follows: welding speed is 0.2m / min-0.3m / min; the welding gun is lifted by 2mm-3mm per layer; the protective gas is 99.999% argon. As the welding head moves, the molten metal is deposited on the substrate layer by layer, and the thickness of each layer is usually controlled at 2-3mm, which can ensure the stability of the deposited layer and the density of the structure. The welding path is precisely controlled by the pre-programmed robot system, and the robot can weld according to the set trajectory to ensure that the shape and size of each layer meet the design requirements. During the additive manufacturing process, good bonding between layers is required, which requires controlling the interlayer temperature during welding. The interlayer temperature is fixed at 100-150°C to avoid the accumulation of excessive heat leading to deformation or cracking. Finally, after the arc additive manufacturing is completed, the structural part may need to be treated, such as removing the slag and polishing the surface to obtain the final product.

[0072] The martensitic stainless steel structure obtained in this embodiment is aesthetically pleasing. The macroscopic morphology shows that the stacked part exhibits obvious layering, and the layers are well metallurgically bonded without pores, inclusions, and other defects. The microstructure is shown in Figure 2

[0073] Example 6 ​

[0074] Based on the embodiment 5,

[0075] In the process of additive manufacturing, the additive tissue is changed from the delta-ferrite distributed on the austenite matrix to the lath martensite tissue, the high-density lattice defects are formed in the crystal inside of the martensite in the weld tissue when the martensite is formed, the high-density dislocations in the lath martensite can play the role of pinning dislocations, so that the martensite is strengthened.

[0076] Through the mechanical property test, the stress-strain curve of the stainless steel structural part is as shown in Figure 1 The tensile strength of the formed part in the embodiment can reach 977.8 MPa, and the elongation is 14.5%. In summary, the martensitic stainless steel obtained by the application has good mechanical property indexes, and fully meets the use requirements of the aircraft landing gear.

[0077] The alloy powder of Cr, V, Nb and the like added in the welding wire of the application can be combined with the C element to form carbide, so as to improve the performance of the martensite as a reinforcing phase. At the same time, the reinforcing phase is generated in situ, and the grain is more fine, so that the toughness of the martensitic structural part is also improved. The proportion of the C element in the martensitic stainless steel is more important. When the carbon element is less than 0.2%, it is lath martensite, and the toughness is better. When the carbon element is greater than 1.0%, it is lamellar martensite, which is more brittle and not easy to use in additive manufacturing. Therefore, the content of the carbon element in the powder of the application is kept at 0.2%, and the powder rate is 25%. The content of the C element in the application is less than 0.2%. The addition of WC should not be too much. Excessive WC can cause the martensitic stainless steel additive manufacturing structural part to crack in the process of additive manufacturing. However, a small amount of addition can also be a very strong reinforcing phase to improve the mechanical properties, improve the mechanical properties and tissue of the overall structural part, and a small amount of addition of rare earth oxides can improve the fluidity of the overall metal powder, improve the fracture toughness and elongation.

Claims

1. A martensitic stainless steel flux cored wire, characterized by, The welding wire comprises a core and a sheath, and the core component consists of the following components in percentage by mass: 12-15% chromium powder, 2-4% titanium powder, 6-8% molybdenum powder, 2-4% vanadium powder, 1-3% niobium powder, 0.2% carbon powder, 0.5-1% tungsten carbide, 1-2% manganese powder, 0.3-0.6% silicon powder, 0.1-0.2% rare earth oxide, and the rest is iron powder.

2. The martensitic stainless steel wire according to claim 1, characterized in that, The sheath is a 0Cr18Ni9 austenitic stainless steel belt, and the filling rate of the core powder is controlled at 23wt%-26wt%.

3. A method of making a structural component using a martensitic stainless steel flux cored wire, characterized in that, The specific operation steps are as follows: Step 1, respectively take the chromium powder 12-15%, titanium powder 2-4%, molybdenum powder 6-8%, vanadium powder 2-4%, niobium powder 1-3%, carbon powder 0.2%, tungsten carbide 0.5-1%, manganese powder 1-2%, silicon powder 0.3-0.6%, rare earth oxide 0.1-0.2%, and the rest is iron powder; Step 2, heat and keep the alloy powder weighed in step 1 in an inert gas atmosphere for a period of time to remove moisture; Step 3, after keeping the alloy powder obtained in step 2, cool it to room temperature in the furnace, then fill the powder into the U-shaped groove of the sheath, pass through the closed forming roller to make a 2.10mm welding wire, and make a 1.20mm core welding wire through the step-by-step reducing method; Step 4, assemble the prepared core welding wire to the full-automatic welding robot, use MIG welding as the heat source to obtain the structural part through additive manufacturing; as the welding head moves, the molten metal is deposited on the substrate layer by layer, the thickness of each layer is controlled at 2-3mm to ensure the stability of the deposited layer and the density of the structure; the welding path is accurately controlled by the robot system, and the welding is carried out according to the set trajectory to ensure that the shape and size of each layer meet the design requirements; after the arc additive manufacturing is completed, remove the slag from the structural part, polish the surface to obtain the final product.

4. The method of making a structure from a martensitic stainless steel flux cored welding wire according to claim 3, wherein The heating temperature in step 2 is 150-200℃, and the holding time is 2-2.5h.

5. The method of making a structural component using a martensitic stainless steel flux cored welding wire of claim 3, wherein, The inert atmosphere in step 3 is 99.999% argon.

6. The method of making a structural component using a martensitic stainless steel flux cored welding wire as defined in claim 3, wherein, The sheath in step 3 is a 0Cr18Ni9 austenitic stainless steel belt.

7. The method of making a structural component using a martensitic stainless steel flux cored welding wire as defined in claim 3, wherein, In step 4, the process parameters of MIG welding are as follows: welding speed 0.2m / min-0.3m / min; each layer of welding gun is lifted by 2mm-3mm, and the protective gas is 99.999% pure argon.

8. The method of making a structural component using a martensitic stainless steel flux cored wire of claim 3, wherein, In step 4, the interlayer temperature is fixed at 100-150℃ during the additive manufacturing process.

9. A structural member prepared using a martensitic stainless steel flux cored wire, characterized by, The method for preparing a structural part using the martensitic stainless steel core welding wire according to any one of claims 3-7.

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