A method for preparing a high-nitrogen nickel-saving austenitic stainless steel component

Abstract

The application provides a high-nitrogen nickel-saving austenitic stainless steel component preparation method. The method is based on the nitrogen-containing austenite-ferrite type stainless steel S21953, S22253, S22053, S23043, S22553, S25554 and S27603 powder recorded in GB / T 20878-2007, and high-nitrogen nickel-saving austenitic stainless steel components are prepared through in-situ MnN laser additive manufacturing, so as to solve the problems of complex traditional preparation process, high cost, long cycle and the like of the existing high-nitrogen nickel-saving austenitic stainless steel components, the problem that laser additive manufacturing powder raw materials are difficult to obtain, and the problem that special high-nitrogen nickel-saving austenitic stainless steel component development is not mature, and belongs to the field of additive manufacturing.

Description

Technical Field

[0001] This invention relates to a method for preparing high-nitrogen, nickel-saving austenitic stainless steel components, specifically to the design of the composition ratio of high-nitrogen, nickel-saving austenitic stainless steel and the laser additive manufacturing process for preparing high-nitrogen, nickel-saving austenitic stainless steel components, belonging to the field of additive manufacturing. Background Technology

[0002] Austenitic stainless steel refers to stainless steel that has an austenitic structure at room temperature. Due to its excellent mechanical properties and corrosion resistance, it has become the most widely used structural engineering alloy. Austenitic stainless steel typically uses Ni (approximately 8%–25%) as the austenite-forming and stabilizing element. Its austenite-forming ability can be measured by the chromium-nickel equivalent ratio of Cr. eq / Ni eq Make predictions (Cr) eq =%Cr + 1.5 × %Si + %Mo, Ni eq =%Ni+30×(%C+%N)+0.5×%Mn), where Cr eq / Ni eq A fully austenitic structure can be obtained when the temperature is less than 1.25.

[0003] However, Ni is expensive and has poor biocompatibility, making it increasingly important to find ways to replace Ni with other elements to obtain austenitic stainless steel. According to the nickel equivalent calculation formula, nitrogen's austenite-forming ability is 30 times that of Ni, making it a strong austenite-forming and stabilizing element. Furthermore, nitrogen acts as an interstitial atom, providing solid solution strengthening and grain refinement. Therefore, high-nitrogen, nickel-saving austenitic stainless steel, which offers advantages such as low cost, high strength, high toughness, high corrosion resistance, and excellent biocompatibility, is an ideal substitute for traditional Cr-Ni stainless steel and has promising application prospects in defense, energy and chemical industries, transportation, and medical devices.

[0004] High-nitrogen nickel-saving austenitic stainless steel contains more than 0.4% nitrogen by mass; however, the equilibrium solubility of nitrogen in the various phases of the steel is low (2.8 wt.% in γ-austenite, 0.04 wt.% in L-liquid, and 0.0128 wt.% in δ-ferrite). Therefore, high-nitrogen nickel-saving austenitic stainless steel is currently typically prepared using high-pressure melting and other methods. The conventional high-pressure manufacturing process is complex, and the high strength and hardness of high-nitrogen nickel-saving austenitic stainless steel make it difficult to process complex components using traditional methods, thus limiting its development and application.

[0005] Laser additive manufacturing, as an emerging manufacturing technology, can rapidly manufacture complex three-dimensional structural parts using a layer-by-layer additive process, making it one of the most promising research directions for the preparation of high-nitrogen, nickel-efficient austenitic stainless steel components. However, existing processes struggle to produce high-nitrogen, nickel-efficient austenitic stainless steel powder for laser additive manufacturing at low cost, and there are currently no commercially available high-nitrogen, nickel-efficient austenitic stainless steel powders of various standard grades. Therefore, obtaining high-nitrogen stainless steel powder is a prerequisite for laser additive manufacturing of high-nitrogen, nickel-efficient austenitic stainless steel and a key to the successful preparation of high-nitrogen, nickel-efficient austenitic stainless steel components.

[0006] Adding nitrides as a nitrogen source to nitrogen-containing / high-nitrogen stainless steels (austenitic stainless steel, austenitic-ferritic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation-hardening stainless steel) according to the grades specified in GB / T 20878-2007 is an effective method for preparing high-nitrogen, nickel-saving austenitic stainless steel. However, the content of elements such as C, Si, Mn, P, S, Cr, Mo, Al, and Ti in stainless steel has a significant impact on the formation of the austenite phase, chromium-nickel equivalent, nitrogen solubility, and carbides. Therefore, it is crucial to select appropriate grades from among the many nitrogen-containing / high-nitrogen stainless steels, as well as to choose the appropriate nitride and determine the addition ratio. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing high-nitrogen nickel-saving austenitic stainless steel components, in order to solve the problems of complex, costly, and long-cycle traditional preparation processes for high-nitrogen nickel-saving austenitic stainless steel components, the difficulty in obtaining laser additive manufacturing powder raw materials, and the immature development of special high-nitrogen nickel-saving austenitic stainless steel components.

[0008] To address the aforementioned issues, a method for preparing high-nitrogen, nickel-saving austenitic stainless steel components is proposed. This method is based on nitrogen-containing austenitic-ferritic stainless steel powders S21953, S22253, S22053, S23043, S22553, S25554, and S27603 as described in GB / T 20878-2007, and high-nitrogen, nickel-saving austenitic stainless steel components are prepared by in-situ addition of MnN laser additive manufacturing.

[0009] The specific weight ratio is as follows: 5%~10% MnN is added to S21953, S22253, S23043, S22553, and S25554; 4%~10% MnN is added to S22053 and S27603. The specific addition ratio of MnN is adjusted according to the N content, mechanical properties, and corrosion resistance requirements of the formed component. Specifically, the yield strength...

[0010] The pitting equivalent PREN = 1[Cr] + 3.3[Mo] + 30[N] can be calculated based on the mechanical properties, corrosion resistance requirements, yield strength, and pitting equivalent of the formed component. The optimal MnN addition ratio can be obtained.

[0011] Laser additive manufacturing processes can be either powder-spreading or powder-feeding. Powder-spreading mainly involves selective laser melting, while powder-feeding mainly involves laser melting deposition. When the formed component is small in size, requires high surface precision, and has a complex structure, selective laser melting is preferred; otherwise, laser melting deposition is preferred.

[0012] The particle size range of S21953, S22253, S22053, S23043, S22553, S25554, S27603, and MnN powders is between 20 and 100 μm. Selective laser melting process selects powders with a particle size of 20 to 50 μm, while laser melting deposition process selects powders with a particle size of 50 to 100 μm.

[0013] The specific principle is as follows:

[0014] 1) Reasons for selecting base powders: S21953, S22253, S22053, S23043, S22553, S25554, and S27603 have low nickel content and moderate Cr content. Austenitic stainless steel usually contains more than 18% Cr to ensure the corrosion resistance of stainless steel. The carbon content is low. In the laser additive manufacturing process, excessive carbon content is easy to form carbides, which is not conducive to corrosion resistance. The low carbon content ensures that no carbide is formed. There are no Al and Ti elements. In the laser additive manufacturing process, N easily forms AlN, TiN and other nitrides with Al and Ti. On the one hand, it reduces the solid solution N content, which is not conducive to the formation of austenitic phase. On the other hand, it is not conducive to corrosion resistance. The absence of Al and Ti elements ensures that no nitride is formed.

[0015] 2) The effects of adding MnN include: First, based on the in-situ melting, decomposition, diffusion, and mass transfer of MnN, it serves as a N source to achieve in-situ N and Mn addition in the molten pool (MnN→[Mn]+[N]); Second, it compensates for the loss of dissolved N in nitrogen-containing austenitic-ferritic stainless steel during laser additive manufacturing (N has low solubility in high-temperature molten pools, only 0.04 wt.%, and some of the supersaturated N will inevitably precipitate out); Third, it compensates for the loss of low-boiling-point Mn in nitrogen-containing austenitic-ferritic stainless steel during the thermal process of laser additive manufacturing (Mn has a boiling point of only 1962℃, while the peak temperature of the molten pool is usually above 2000℃, which will inevitably cause some MnN to volatilize); Fourth, as an austenite phase forming and stabilizing element, increasing the Mn content is more conducive to ensuring the formation of the austenite phase. Meanwhile, increasing the proportion of austenite phase is more conducive to increasing the N content in the molten pool (the solubility of N in the L liquid phase, δ ferrite phase, and γ austenite phase during the high-temperature molten pool solidification process is 0.04 wt.%, 0.0128 wt.%, and 2.8 wt.%, respectively, with γ austenite phase having the highest solubility), and conversely, increasing the N content in the molten pool promotes the formation of the austenite phase; fifth, as an element that reduces the N activity coefficient and increases the N solubility in stainless steel, increasing the Mn content is more conducive to increasing the N content in the molten pool and Sixth, the addition of MnN can promote the transformation of the solidification mode of the molten pool from type F (L→L+δ→δ→δ+γ), type FA (L→L+δ→L+δ+γ→δ+γ), type AF (L→L+γ→L+γ+δ→δ+γ) to type A (L→L+γ→γ), avoiding "ferrite traps" (N has extremely low solubility in the ferrite phase, causing N precipitation loss), reducing N loss and nitrogen porosity defects (N element precipitates in the form of N2, which easily forms nitrogen porosity defects).

[0016] 3) Reasons for choosing MnN nitride: MnN powder is moderately priced, can be used as a N source while also supplementing Mn element, Mn can promote the formation of austenite phase and improve the solubility of N, and has low carbon content and no Al or Ti elements.

[0017] Compared with existing technologies, this invention uses nitrogen-containing austenitic-ferritic stainless steel powders S21953, S22253, S22053, S23043, S22553, S25554, and S27603 as a base, as described in GB / T 20878-2007, to prepare high-nitrogen nickel-saving austenitic stainless steel components through in-situ MnN addition laser additive manufacturing. This method can obtain the forming powder raw material for high-nitrogen nickel-saving austenitic stainless steel components by laser additive manufacturing at low cost, while ensuring the relevant performance requirements of the designed material composition of the formed components (stainless steel listed in national standards has good comprehensive performance). Compared with developing high-nitrogen nickel-saving austenitic stainless steel separately, it can reduce development costs and save development time, while also having a better nickel-saving effect. Due to the increased N content and lower nickel content, the formed components have low cost, good mechanical properties, good corrosion resistance and biocompatibility, and a certain amount of nickel content ensures the high-temperature performance of the formed components. It has good application prospects in the fields of national defense, energy and chemical industry, transportation, and medical devices. Attached Figure Description

[0018] Figure 1 It is a single-pass, single-layer formed sample;

[0019] Figure 2 This is a schematic diagram of the microstructure characteristics of the molten pool boundary in the longitudinal cross-section of the formed sample;

[0020] Figure 3 and Figure 4 This is a map showing the elemental distribution in the middle of the sedimentary layer;

[0021] Figure 5 This is a distribution map of N and Mn elements in the middle of the sedimentary layer;

[0022] Figure 6 This is an EDS energy spectrum of the middle part of the sedimentary layer. Detailed Implementation

[0023] Example

[0024] This embodiment mainly improves the preparation method of high-nitrogen nickel-saving austenitic stainless steel components. The improved method is as follows: Based on the nitrogen-containing austenitic-ferritic stainless steel powders S21953, S22253, S23043, S22553, and S25554 described in GB / T 20878-2007, high-nitrogen nickel-saving austenitic stainless steel components are prepared by in-situ addition of 5%~10% MnN using laser additive manufacturing. The grades and chemical compositions of the austenitic-ferritic stainless steel are shown in Table 1 below. The designed MnN addition ratio can ensure the preparation of high-nitrogen nickel-saving austenitic stainless steel (Cr eq / Ni eq<1.25); The specific addition ratio of MnN is adjusted according to the N content, mechanical properties, corrosion resistance, and other requirements of the formed component. Among them, the yield strength The pitting equivalent PREN = 1[Cr] + 3.3[Mo] + 30[N]. Based on the mechanical properties, corrosion resistance requirements, yield strength, and pitting equivalent calculation formula of the formed component, the optimal addition ratio of MnN can be calculated. The chemical composition of MnN is shown in Table 2 below.

[0025] Table 1. Grades and Chemical Compositions of Austenitic-Ferritic Stainless Steel

[0026]

[0027] Table 2 Chemical composition of MnN

[0028]

[0029] Methods and rationale for determining the MnN addition ratio: The method for determining the MnN addition ratio needs to comprehensively consider the requirements of chromium-nickel equivalent (to ensure austenitic phase formation), nitrogen content (greater than the requirements of high-nitrogen austenitic stainless steel, with a mass fraction exceeding 0.4%), mechanical properties (measured by yield strength), and corrosion resistance (measured by pitting corrosion equivalent). However, due to the unavoidable loss of dissolved nitrogen during the thermal process of laser additive manufacturing (the solubility of N during melting exceeds its saturation solubility), the addition of MnN must ensure a 10% N margin. Calculations show that the nitrogen content mass fraction of the designed powder needs to reach 0.45%. However, excessively high N content in the powder will strengthen the tendency for supersaturated nitrogen precipitation, easily leading to nitrogen porosity defects. Therefore, the N content mass fraction in the powder needs to be lower than 1.1%. The addition ratio, chromium-nickel equivalent, and powder composition mass fraction are determined based on the above, as shown in Table 3.

[0030] Laser additive manufacturing processes can be either powder-spreading or powder-feeding processes. Powder-spreading processes are represented by selective laser melting (SLM), while powder-feeding processes are represented by laser melting deposition (LMD). When the formed component is small in size, has high surface precision requirements, and a complex structure, selective laser melting is preferred; otherwise, laser melting deposition (LMD) is preferred. The particle size range of S21953, S22253, S22053, S23043, S22553, S25554, S27603, and MnN powders is between 20 and 100 μm. Selective laser melting (SLM) processes prefer powders with a particle size of 20 to 50 μm, while laser melting deposition (LMD) processes prefer powders with a particle size of 50 to 100 μm.

[0031] Table 3. Powder ratio, chromium-nickel equivalent, and chemical composition of high-nitrogen, nickel-saving austenitic stainless steel for laser additive manufacturing.

[0032]

[0033]

[0034] Example 2

[0035] This embodiment represents an improvement to the preparation method of high-nitrogen, nickel-saving austenitic stainless steel components. The improved method uses nitrogen-containing austenitic-ferritic stainless steel powders S22053 and S27603 as described in GB / T20878-2007 as a base. High-nitrogen, nickel-saving austenitic stainless steel components are prepared by in-situ addition of 4%~10% MnN via laser additive manufacturing. The MnN addition ratio ensures the production of high-nitrogen, nickel-saving austenitic stainless steel (Cr... eq / Ni eq <1.25); The specific addition ratio of MnN is adjusted according to the N content, mechanical properties, corrosion resistance, and other requirements of the formed component. Among them, the yield strength The pitting equivalent PREN = 1[Cr] + 3.3[Mo] + 30[N] can be calculated based on the mechanical properties, corrosion resistance requirements, yield strength, and pitting equivalent of the formed component. The optimal MnN addition ratio can be obtained.

[0036] Methods and rationale for determining the MnN addition ratio: The method for determining the MnN addition ratio needs to comprehensively consider the requirements of chromium-nickel equivalent (to ensure austenitic phase formation), nitrogen content (greater than the requirements of high-nitrogen austenitic stainless steel, with a mass fraction exceeding 0.4%), mechanical properties (measured by yield strength), and corrosion resistance (measured by pitting corrosion equivalent). However, due to the unavoidable loss of dissolved nitrogen during the thermal process of laser additive manufacturing (the solubility of N during melting exceeds its saturation solubility), the addition of MnN must ensure a 10% N margin. Calculations show that the nitrogen content mass fraction of the designed powder needs to reach 0.45%. However, excessively high N content in the powder will strengthen the tendency for supersaturated nitrogen precipitation, easily leading to nitrogen porosity defects. Therefore, the N content mass fraction in the powder needs to be lower than 1.1%. The addition ratio, chromium-nickel equivalent, and powder composition mass fraction are determined based on the above, as shown in Table 3.

[0037] Laser additive manufacturing processes can be either powder-spreading or powder-feeding processes. Powder-spreading processes are represented by selective laser melting (SLM), while powder-feeding processes are represented by laser melting deposition (LMD). When the formed component is small in size, has high surface precision requirements, and a complex structure, selective laser melting is preferred; otherwise, laser melting deposition (LMD) is preferred. The powder particle size range is 20~100um. Selective laser melting (SLM) prefers powder with a particle size of 20~50um, while laser melting deposition (LMD) prefers powder with a particle size of 50~100um.

[0038] The above embodiments utilize nitrogen-containing austenitic-ferritic stainless steel powder as described in GB / T 20878-2007. High-nitrogen, nickel-saving austenitic stainless steel components are prepared through in-situ MnN addition laser additive manufacturing. This approach provides a low-cost raw material for laser additive manufacturing of high-nitrogen, nickel-saving austenitic stainless steel components while ensuring the performance requirements of the designed material composition. The stainless steel listed in national standards exhibits good overall performance. Compared to developing high-nitrogen, nickel-saving austenitic stainless steel separately, this method reduces development costs and time while also offering significant nickel savings. The formed components, due to the increased N content and lower nickel content, possess low cost, good mechanical properties, excellent corrosion resistance, and biocompatibility. The certain amount of nickel content also ensures the high-temperature performance of the formed components, making them promising for applications in defense, energy and chemical industries, transportation, and medical devices.

[0039] Experimental example:

[0040] I. Materials and Experiments

[0041] Based on 022Cr19Ni5Mo3Si2N (code: S21953) austenitic-ferritic stainless steel, high-nitrogen, nickel-saving austenitic stainless steel was prepared by in-situ addition of 7% by mass of MnN powder via laser melting deposition. Single-pass, single-layer forming experiments were conducted using a laser power of 1000W, a scanning speed of 8mm / s, and a powder feed rate of 8g / min. The formed samples are shown below. Figure 1 As shown in the figure, the weld width and depth of the formed sample are suitable, and there are no obvious defects.

[0042] II. Microstructural Features

[0043] The schematic diagram of the microstructure characteristics of the molten pool boundary in the longitudinal cross-section of the formed sample is shown in the figure below. As can be seen from the figure, the deposited layer is dominated by austenite phase, and the microstructure consists of columnar dendrites and equiaxed grains. There are few pores and cracks, and the microstructure characteristics are relatively good.

[0044] III. Nitrogen Content and Distribution

[0045] EDS energy dispersive spectroscopy was performed on the middle part of the sediment layer. Figure 3 , Figure 4 It can be seen that, based on 022Cr19Ni5Mo3Si2N (code: S21953) austenitic-ferritic stainless steel, the high-nitrogen, nickel-saving austenitic stainless steel deposit prepared by in-situ addition of 7% by mass of MnN powder via laser melting deposition exhibits uniform element distribution and no compositional segregation. Figure 5The EDS energy dispersive spectroscopy (EDS) spectrum of the middle layer shows that the N content is 0.55% by mass, the Mn content is 7.5% by mass, and the Ni content is 3.2% by mass, meeting the composition requirements for high-nitrogen austenitic stainless steel components and exhibiting good nickel-saving effects. The N and Mn contents of the deposited layer are somewhat reduced compared to the designed composition. This is due to the precipitation of supersaturated dissolved N and the evaporation loss of Mn during laser melting deposition. However, through margin design, it can be ensured that high-nitrogen, nickel-saving austenitic stainless steel can still be produced even after the loss of N and Mn elements.

[0046] Therefore, based on 022Cr19Ni5Mo3Si2N (code: S21953) austenitic-ferritic stainless steel, high-nitrogen nickel-saving austenitic stainless steel deposited samples were prepared by in-situ addition of 7% by mass of MnN powder via laser melting deposition. The nitrogen content and microstructure of the deposited samples met the requirements of high-nitrogen nickel-saving austenitic stainless steel and had a good nickel-saving effect. High-nitrogen nickel-saving austenitic stainless steel components can be successfully prepared by selecting appropriate process parameters such as overlap rate, scanning path, and Z-axis lifting amount for multiple passes and multiple layers.

[0047] Meanwhile, appropriately increasing or decreasing the MnN addition ratio at 7% mass fraction can also prepare high-nitrogen, nickel-saving austenitic stainless steel by laser melting deposition. Theoretical calculations show that an addition ratio of 5-10% can better balance nitrogen content, microstructure, and defects. Furthermore, 022Cr22Ni5Mo3N (code: S22253), 022Cr23Ni5Mo3N (code: S22053), 022Cr23Ni4MoCuN (code: S23043), 022Cr25Ni6Mo2N (code: S22553), 03Cr25Ni6Mo3Cu2N (code: S25554), 022Cr25Ni7Mo4WCUN (code: S27603), and 022Cr19Ni5Mo3Si2N (code: S21953) are all austenitic-ferritic stainless steels with similar chemical compositions. Based on austenitic-ferritic stainless steels such as 022Cr22Ni5Mo3N (code: S22253), 022Cr23Ni5Mo3N (code: S22053), 022Cr23Ni4MoCuN (code: S23043), 022Cr25Ni6Mo2N (code: S22553), 03Cr25Ni6Mo3Cu2N (code: S25554), and 022Cr25Ni7Mo4WCUN (code: S27603), high-nitrogen nickel-saving austenitic stainless steels can also be successfully prepared by in-situ adding a certain amount of MnN. Theoretical calculations show that high-nitrogen, nickel-saving austenitic stainless steel can be prepared by adding 5-10% MnN to 022Cr22Ni5Mo3N (code: S22253), 022Cr23Ni4MoCuN (code: S23043), 022Cr25Ni6Mo2N (code: S22553), and 03Cr25Ni6Mo3Cu2N (code: S25554) as a base. Similarly, high-nitrogen, nickel-saving austenitic stainless steel can be prepared by adding 4-10% MnN to 022Cr23Ni5Mo3N (code: S22053) and 022Cr25Ni7Mo4WCUN (code: S27603) as a base.

[0048] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing high-nitrogen nickel-saving austenitic stainless steel components, wherein the method is based on any one of the nitrogen-containing austenitic-ferritic stainless steel powders S21953, S22253, S22053, S23043, S22553, S25554, and S27603 as described in GB / T 20878-2007, and high-nitrogen nickel-saving austenitic stainless steel components are prepared by in-situ addition of MnN laser additive manufacturing; Add 5%~10% MnN to S21953, S22253, S23043, S22553, and S25554; add 4%~10% MnN to S22053 and S27603. Laser additive manufacturing processes can be either powder-spreading or powder-feeding processes. Powder-spreading is a selective laser melting process, while powder-feeding is a laser melting deposition process. The particle size range of S21953, S22253, S22053, S23043, S22553, S25554, S27603, and MnN powders is between 20 and 100 μm. Selective laser melting process selects powders with a particle size of 20 to 50 μm, while laser melting deposition process selects powders with a particle size of 50 to 100 μm.

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