An ultra-high strength steel and a 3D printing forming process of thin-walled components thereof

Abstract

The scheme discloses a kind of ultra-high strength steel in the technical field of ultra-high strength steel component design optimization and 3D printing forming, and the mass percentage of Mn element in the element it contains is 0.55%~0.60%, by improving the alloy composition of ultra-high strength steel D406A, reduce the Mn content in alloy, reduce the evaporation when printing, so that it becomes the alloy material suitable for 3D printing forming.Can print out the complex thin-walled sample piece with only 1mm wall thickness without cracking, the density is more than 99.5%, and the tensile property of the sample piece printed can be comparable with forged D406A ultra-high strength steel.

Description

Technical Field

[0001] This invention belongs to the field of ultra-high strength steel composition design optimization and 3D printing forming technology, and specifically relates to a 3D printing forming process for ultra-high strength steel and its thin-walled components. Background Technology

[0002] The development level of high-end materials is an important measure of a nation's comprehensive strength, and it is related to national security and the people's livelihood. A new generation of materials, a new generation of equipment, a new generation of fields, and a new generation of development—the importance of materials is self-evident. Generally, steel with a yield strength greater than 550 MPa at room temperature is called ultra-high-strength steel. It is usually also required to have good plasticity and toughness, excellent fatigue performance, fracture toughness, and resistance to stress corrosion. Ultra-high-strength steel is an important type of steel with a wide range of applications, widely used in fields with special performance requirements such as rocket engine casings, aircraft landing gear, and bulletproof steel plates.

[0003] D406A ultra-high strength steel has excellent comprehensive properties and is widely used in aerospace and military products such as solid rocket engine casings, aircraft landing gear, and certain components of conventional weapons. However, D406A ultra-high strength steel is difficult to machine and has poor weldability, and is prone to serious defects such as cold cracks after welding. Although D406A has excellent performance, it currently faces the following prominent problems: (1) Although the application market for D406A materials is very wide, the supply is seriously insufficient due to high technical barriers. (2) At present, D406A products are mainly produced by traditional vacuum induction melting + vacuum self-consumption refining to produce high-purity ingots, which are then forged, heat-treated, and machined into final products. The traditional method of producing products is complex, lengthy, costly, and wastes a lot of materials. (3) D406A is an ultra-high strength steel. Due to its high strength, it is difficult to machine and has very low processing efficiency. (4) When processing complex thin-walled D406A parts, the scrap rate is high and they cannot be integrally formed. Welding and riveting are required. It is difficult to solve the sealing problem by riveting, and D406A has poor weldability.

[0004] 3D printing, also known as additive manufacturing, is a manufacturing technology that integrates computer-aided design, material processing and forming technology. Based on digital model files, it uses software and CNC machinery to deposit specialized materials layer by layer through methods such as extrusion, sintering, melting, photopolymerization, and spraying to create physical objects. Unlike traditional processing methods that involve removing raw materials, cutting, and assembling, it is a bottom-up, material accumulation manufacturing method. Metal 3D printing, as the most cutting-edge and promising technology in the entire 3D printing system, is an important development direction for advanced manufacturing technology. With the development of technology and the need for wider application, manufacturing functional metal parts using direct rapid prototyping has become a major development direction for rapid prototyping. In recent years, China has developed the capability to manufacture high-end products through 3D printing; however, the alloy compositions and processes suitable for 3D printing are still not perfect.

[0005] Existing D406A ultra-high strength steel has high strength but poor weldability, making it prone to defects such as voids and cracks when 3D printed. Therefore, the purpose of this invention is to adjust and optimize the composition of D406A alloy and the corresponding 3D printing technology to overcome the problems of existing technology and obtain complex thin-walled components with strength comparable to forgings. Summary of the Invention

[0006] This invention aims to address the problem that existing D406A steel, with its high strength and poor weldability, is unsuitable for 3D printing of complex thin-walled structural components. This invention provides an ultra-high strength steel suitable for 3D printing and a corresponding 3D printing technology. By adjusting the alloy composition of D406A ultra-high strength steel and employing electron beam 3D printing technology, the invention solves the problems of poor weldability, high internal stress, and defects such as voids and cracks that easily occur when using laser 3D printing to fabricate complex thin-walled structural components with ultra-high strength steel.

[0007] This solution discloses a 3D printing process for thin-walled components, characterized in that the thin-walled components are prepared using ultra-high-strength steel. The ultra-high-strength steel comprises the following elements and their mass percentages: C 0.29%~0.32%, Mn 0.55%~0.60%, Si 1.53%~1.66%, Cr 1.26%~1.30%, Ni 0.24%~0.26%, Mo 0.48%~0.52%, V 0.10%~0.15%, S≤0.005, P≤0.005, Cu≤0.10, As≤0.01, Sn≤0.005, Pb≤0.003, Sb≤0.003, Bi≤0.003, with the remainder being Fe. The total addition amount of alloying elements is 4.30%~5.00%. The process includes the following steps:

[0008] S1 Ingredients: Weigh the raw materials according to the elemental composition and dosage requirements of the ultra-high strength steel described in this invention and mix them.

[0009] Among the raw materials, metallic Ni is added as pure nickel with a purity of ≥99.0%, metallic Cr is added according to the provisions of GB / T 3211-2007, ferrosilicon is added according to the provisions of GB / T 2272-2009, metallic Mn is added as pure manganese with a purity of ≥99.0%, metallic Al is added as Al with a purity of ≥99.0%, ferromolybdenum is added according to the provisions of GB / T 3649-87, ferrovanadium is added according to the provisions of GB / T4139-2012, carbon is added as pure graphite blocks with a purity of 100%, and iron is added as pure iron with a purity of 99.5%.

[0010] S2 Casting: Casting is divided into two steps: vacuum induction melting and vacuum consumable refining. Before vacuum consumable melting, the surface of the raw material is cleaned and rusted, and then dried in a drying oven at 200~250℃. The drying temperature for pure nickel is 750~900℃. After induction melting, the induction ingot is cooled, and its circumferential surface and end face are polished. It is then welded to a dummy electrode for vacuum consumable refining.

[0011] In this step, since the D406A casting method is already very mature, the contents of the other alloys in this invention are not much different from those of this alloy, except for the Mn content, which is significantly different from that of this alloy. Therefore, the casting process of D406A is suitable for this alloy.

[0012] S3 Annealing and Hot Deformation: After cooling, the consumable ingot is subjected to stress-relief annealing at a temperature of 660~690℃ and held for 20~30h; the refined ingot after stress-relief annealing is hot-deformed and processed into electrode rods of specified dimensions.

[0013] S4 Powder Preparation: The blank of the electrode rod is used to prepare printing powder by plasma rotating electrode atomization. The plasma rotating electrode atomization powder preparation process is as follows: arc initiation at 23000~25000 r / min, electrode rod rotation speed at 24000~26000 r / min, feed speed at 0.5~3 mm / s, current at 700-1500 mA, and argon gas as the atomization medium and protective atmosphere; powder with a particle size of 53~100 μm is sieved for later use and then filled with argon gas for protection.

[0014] S5 Sample Printing: Samples were printed using a powder bed electron beam selective melting 3D printing system. Preheating was performed in two stages before printing. The first stage preheated to 600~650℃ and held for 15 min. The second stage preheated to 800~850℃. During printing, the layer thickness was 40~50 μm, the surface indentation was 0.05~0.10 mm, the scanning interval was 0.1~0.2 mm, the power was 10~15mA, the speed was 3~5 m / s, and the defocusing amount was 0.35~0.5V.

[0015] S6 Performance Heat Treatment: The printed parts are subjected to normalizing and high-temperature tempering heat treatment.

[0016] Furthermore, the electrode rod is a round rod with a diameter of Φ30~100 mm and a length of 230~260 mm.

[0017] Furthermore, the normalizing process involves holding at 700~740℃ for 2.5~3.5 hours, holding at 900~940℃ for 7~8 hours, and then air cooling.

[0018] Furthermore, the high-temperature tempering process involves holding at 720~760℃ for 9~11 hours, followed by furnace cooling to below 600℃ and air cooling.

[0019] Furthermore, after printing, the sample is cooled in a helium atmosphere and removed from the furnace when the temperature drops to 40~70℃.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) By improving the alloy composition of ultra-high strength steel D406A, the Mn content in the alloy is reduced, and the evaporation during printing is reduced, making it an alloy material suitable for 3D printing.

[0022] (2) Through powder bed electron beam 3D printing technology, using special 3D printing technology, complex thin-walled structural parts with a wall thickness of only 1mm, a density greater than 99.5%, and a strength comparable to forgings can be printed. Such complex thin-walled structural parts can be applied to aerospace and weapon equipment. Attached Figure Description

[0023] Figure 1 The macroscopic morphology of the high-strength steel tensile specimen obtained in this invention;

[0024] Figure 2 The defects of the high-strength steel printed parts obtained by this invention are shown below;

[0025] Figure 3 The metallographic structure of the high-strength steel printed part obtained by this invention;

[0026] Figure 4 This is the macroscopic morphology of the high-strength steel printed part obtained by the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further defined below with reference to specific embodiments, but the scope of protection is not limited to the description.

[0028] An ultra-high strength steel, wherein the ultra-high strength steel comprises the following elements and their mass percentages: C 0.29%~0.32%, Mn 0.55%~0.60%, Si 1.53%~1.66%, Cr 1.26%~1.30%, Ni 0.24%~0.26%, Mo 0.48%~0.52%, V 0.10%~0.15%, S≤0.005, P≤0.005, Cu≤0.10, As≤0.01, Sn≤0.005, Pb≤0.003, Sb≤0.003, Bi≤0.003, with the remainder being Fe.

[0029] The following example uses a 18×50×80 mm long tensile specimen as an example:

[0030] Example 1: A type of ultra-high strength steel that can be 3D printed, with the following elemental composition by mass percentage: C 0.32%, Mn 0.56%, Si 1.53%, Cr 1.26%, Ni 0.25%, Mo 0.48%, V 0.11%, S≤0.005%, P≤0.005%, Cu≤0.10%, As≤0.01%, Sn≤0.005%, Pb≤0.003%, Sb≤0.003%, Bi≤0.003%, and the remainder being Fe. The total amount of alloying elements added to the ultra-high strength steel is 4.30%~5.00%.

[0031] Example 2: A tensile specimen of ultra-high strength steel that can be 3D printed, the preparation method of which includes the following steps:

[0032] Step 1, Ingredient Preparation: Weigh the raw materials according to the above formula requirements. Specifically, the raw materials include: Ni (≥99.0% purity) pure nickel; Cr (≥99.0% purity) chromium; ferrosilicon (≥99.0% purity) ferrosilicon; Mn (≥99.0% purity) manganese; Al (≥99.0% purity) Al; ferromolybdenum (≥99.0% purity) ferromolybdenum (≥99.0% purity) ferromolybdenum (≥99.0% purity) ferrovanadium (≥99.5% purity) ferromolybdenum (≥99.0% purity) ferromolybdenum (≥99.0% purity) ferrovanadium (≥99.5% purity) carbon; and iron (≥99.5% purity) iron.

[0033] Step 2, Casting: Casting consists of two steps: vacuum induction melting and vacuum arc refining. Before vacuum arc refining, the surface of the raw material is cleaned and rust-removed, and then dried in a drying furnace at 200-250℃ for 1-3 hours, with the drying temperature for pure nickel being 750-900℃. After induction melting, the induction ingot is completely cooled in a pit for 30-40 hours. The circumferential surface and end face of the induction ingot are then polished white and welded to a dummy electrode for vacuum arc refining. Since the casting method for D406A is already mature, the content of other alloys in this invention is not significantly different from that of the alloy except for the Mn content, which differs considerably. Therefore, the casting process of this alloy is suitable for this alloy.

[0034] Step 3, Annealing and Hot Deformation: After the consumable ingot is completely cooled in a pit for 30-40 hours, it undergoes stress-relief annealing at 660-690℃ for 20-30 hours. The stress-relief annealed refined ingot is then hot-deformed and machined into electrode rods of specified dimensions.

[0035] Step 4, Powder Preparation: The electrode rod blank processed in step (3) is used to prepare printing powder using the plasma rotating electrode atomization method. The powder preparation blank is a round rod with a diameter of Φ30~50 mm and a length of 230~260 mm, with a roundness deviation of less than 0.08 mm and a straightness deviation of less than 0.04 mm / m. The printing powder is prepared using the plasma rotating electrode atomization method. The process is as follows: arc initiation at 23000~25000 r / min, electrode rod rotation speed of 24000~26000 r / min, feed speed of 0.5~3 mm / s, current of 700~1500 mA, and argon gas is used as the atomization medium and as the protective atmosphere.

[0036] Step 5, powder sieving: The powder is sieved using a vibrating sieve under argon protection to select powder with a particle size of 53~100 μm for later use. The powder is then placed in a powder storage bottle and filled with argon for protection.

[0037] Step 6, Sample Printing: The sample was printed using a powder bed electron beam selective melting 3D printer. Preheating was performed in two stages: first, preheating to 600-650℃ and holding for 15 min; second, preheating to 800-850℃. During printing, the layer thickness was 40-50 μm, the surface indentation was 0.05-0.10 mm, the scanning spacing was 0.1-0.2 mm, the power was 10-15 mA, the speed was 3-5 m / s, and the defocusing amount was 0.35-0.5V. After printing, helium was introduced into the forming cavity for furnace cooling, and the sample was removed from the furnace when the temperature dropped to 40-70℃. The tensile sample after printing is shown below. Figure 1As shown, no cracks were found, and the surface quality was good, indicating that this process can be used for 3D printing of D406A ultra-high strength steel in this invention. After cleaning away the loose layer on the surface, a density test was conducted, and the density was determined to be 7.8 g / mm³ according to the standard. 3 The calculated density of the printed part is 99.6%. Metallographic observation of the printed part will be performed, such as... Figure 2 As shown, no obvious defects such as pores, cracks, or unmelted spheres were found.

[0038] Step 7, Performance Heat Treatment: The printed parts undergo normalizing + high-temperature tempering heat treatment. The normalizing process involves holding at 700~740℃ for 2.5~3.5h + holding at 900~940℃ for 7~8h, followed by air cooling. The high-temperature process involves holding at 720~760℃ for 9~11h, followed by furnace cooling to below 600℃ and then air cooling.

[0039] The printed parts that underwent performance heat treatment were subjected to tensile tests and chemical composition analysis using a universal testing machine, and their metallographic structure was observed. The results are as follows: Figure 3 As shown in Tables 1 and 2, the results analysis shows that the chemical composition of the printed parts meets the design composition range, no overheated structure or obvious delamination was found in the microstructure, and the room temperature mechanical properties are comparable to those of forgings.

[0040] Table 1 Chemical composition (wt.%) of high-strength steel printed parts

[0041]

[0042] Table 2 Tensile properties of high-strength steel printed parts and forgings

[0043]

[0044] A sample of a complex thin-walled structure with a wall thickness of 1 mm after printing. Figure 4 As shown, after cleaning away the loose layer on the surface and observing, no obvious pores or cracks were found, indicating that the process can form complex thin-walled components of D406A ultra-high strength steel for aerospace applications.

Claims

1. A 3D printing process for thin-walled components, characterized in that, The thin-walled component is prepared using an ultra-high strength steel. The ultra-high strength steel contains the following elements and their mass percentages: C 0.29%~0.32%, Mn 0.55%~0.60%, Si 1.53%~1.66%, Cr 1.26%~1.30%, Ni 0.24%~0.26%, Mo 0.48%~0.52%, V 0.10%~0.15%, S≤0.005, P≤0.005, Cu≤0.10, As≤0.01, Sn≤0.005, Pb≤0.003, Sb≤0.003, Bi≤0.003, with the remainder being Fe. The total amount of alloying elements added is 4.30%~5.00%. The process includes the following steps: S1 Ingredients: Weigh the raw materials according to the stated elemental composition and dosage requirements; S2 Casting: Casting is divided into two steps: vacuum induction melting and vacuum consumable refining. Before vacuum consumable melting, the surface of the raw material is cleaned and rusted, and then dried in a drying oven at 200~250℃. The drying temperature for pure nickel is 750~900℃. After induction melting, the induction ingot is cooled, and its circumferential surface and end face are polished. It is then welded to a dummy electrode for vacuum consumable refining. S3 Annealing and Hot Deformation: After cooling, the consumable ingot is subjected to stress-relief annealing at a temperature of 660~690℃ and held for 20~30h; the refined ingot after stress-relief annealing is hot-deformed and processed into electrode rods of specified dimensions. S4 Powder Preparation: The blank of the electrode rod is used to prepare printing powder by plasma rotating electrode atomization. The plasma rotating electrode atomization powder preparation process is as follows: arc initiation at 23000~25000 r / min, electrode rod rotation speed at 24000~26000 r / min, feed speed at 0.5~3 mm / s, current at 700-1500 mA, and argon gas as the atomization medium and protective atmosphere; powder with a particle size of 53~100 μm is sieved for later use and argon gas is introduced for protection. S5 Sample Printing: Samples were printed using a powder bed electron beam selective melting 3D printing system. Preheating was performed in two stages before printing. The first stage was preheating to 600~650℃ and holding for 15 min. The second stage was preheating to 800~850℃. During printing, the layer thickness was 40~50 μm, the surface indentation was 0.05~0.10 mm, the scanning interval was 0.1~0.2 mm, the power was 10~15 mA, the speed was 3~5 m / s, and the defocusing amount was 0.35~0.5V. S6 Performance Heat Treatment: The printed parts are subjected to normalizing and high-temperature tempering heat treatment.

2. The 3D printing process for a thin-walled component according to claim 1, characterized in that: The electrode rod is a round rod with a diameter of Φ30~100 mm and a length of 230~260 mm.

3. The 3D printing forming process for a thin-walled component according to claim 2, characterized in that: The normalizing process involves holding at 700~740℃ for 2.5~3.5 hours, holding at 900~940℃ for 7~8 hours, and then air cooling.

4. The 3D printing forming process for a thin-walled component according to claim 3, characterized in that: The high-temperature tempering process involves holding at 720~760℃ for 9~11 hours, followed by furnace cooling to below 600℃ and air cooling.

5. The 3D printing process for a thin-walled component according to claim 4, characterized in that: After printing, the sample is cooled in a helium atmosphere and removed from the furnace when the temperature drops to 40~70℃.

6. A thin-walled component prepared by the process described in any one of claims 1 to 5.

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