A high-nitrogen duplex stainless steel and its preparation method
High-nitrogen duplex stainless steel was prepared by laser additive manufacturing technology, which solved the problem of limited nitrogen content increase in existing technologies and achieved high PREN value, excellent corrosion resistance and mechanical strength.
Patent Information
- Application Number
- CN202610161033.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-04
- Publication Date
- 2026-05-26
AI Technical Summary
Existing smelting methods make it difficult to further increase the nitrogen content in duplex stainless steel, resulting in the inability to improve the pitting resistance equivalent (PREN) and stagnation in material development.
High-nitrogen duplex stainless steel is prepared by using laser additive manufacturing technology and specific forming parameters. Through ultra-fast solidification, nitrogen atoms are supersaturated and dissolved in the alloy matrix, avoiding Cr2N precipitation and achieving a high PREN value.
High-nitrogen duplex stainless steel with a nitrogen content of ≥0.6% was prepared, and the PREN value exceeded 50, reaching 52 or more, which significantly improved the material's corrosion resistance and mechanical strength.
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Figure CN122077023A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of high-nitrogen duplex stainless steel preparation technology, and particularly relates to a high-nitrogen duplex stainless steel and a method for preparing high-nitrogen duplex stainless steel. Background Technology
[0002] SAF 3207 duplex stainless steel, developed by the Swedish company SANDVIK, is designed for deep-water umbilical cables, applications requiring extremely high resistance to pitting and crevice corrosion, mechanical strength, and fatigue performance. Compared to super duplex steel, SAF 3207 HD offers higher yield strength, greater corrosion resistance, and superior fatigue performance, making it an excellent material choice for a range of other oil and gas applications. For example, when resistance to hydrogen sulfide is required, such as in raw seawater injection, control lines, and chemical injection lines, SAF 3207 HD provides high reliability and operational safety, thereby reducing operating costs.
[0003] Traditional smelting and casting methods for preparing duplex stainless steel have already reached the limit for nitrogen content (0.5 wt.%). Adding higher nitrogen content will result in the precipitation of a large amount of Cr2N in the alloy, making it impossible to obtain dissolved nitrogen and further improve the material's pitting corrosion equivalent (PREN).
[0004] Adding ≥0.5 wt% nitrogen to duplex stainless steel must be carried out under high temperature and high pressure conditions, requiring precise control of nitrogen partial pressure and melt temperature. If the pressure is unbalanced, nitrogen solubility will deviate from the equilibrium value, immediately leading to component segregation, porosity, or subsequent nitrogen escape. Nitrogen is a strong austenite-forming element; even slight changes can significantly alter the ferrite / austenite phase ratio. Literature indicates that when nitrogen >0.3 wt%, the synergistic balance of multiple elements such as Cr, Mn, and Ni must be adjusted simultaneously; otherwise, the phase ratio may easily shift to 1:1, causing a decrease in pitting corrosion equivalent (PREN). More seriously, during slow cooling, nitrogen easily migrates to ferrite grain boundaries, forming Cr₂N precipitates, which become localized corrosion sources, reducing corrosion resistance.
[0005] Previously developed high-nitrogen duplex stainless steels have nitrogen contents of 0.2 wt.%, SAF2707 0.4%, and SAF3207 0.5 wt.%. The next generation of high-nitrogen duplex stainless steels requires further increases in nitrogen content (≥0.5 wt.%), but existing smelting methods cannot achieve this, representing a technological bottleneck for the industry. Without increasing nitrogen content, the pitting corrosion resistance equivalent cannot be further improved, leading to stagnation in material development. Summary of the Invention
[0006] The purpose of this invention is to overcome at least one of the shortcomings of the prior art and to provide a high-nitrogen duplex stainless steel and a method for preparing high-nitrogen duplex stainless steel. The high-nitrogen duplex stainless steel is prepared by laser additive manufacturing technology. Combined with the set forming parameters, nitrogen is supersaturated and dissolved in the alloy matrix, no Cr2N precipitation occurs, and the pitting corrosion resistance is high.
[0007] The technical solution of this invention is: a method for preparing high-nitrogen duplex stainless steel, comprising the following steps: Raw material preparation steps: Prepare stainless steel powder, wherein the nitrogen content of the stainless steel powder is greater than or equal to 0.6% by weight; Forming steps: The stainless steel material powder is placed in a laser additive manufacturing equipment for forming, and the parameters of the laser additive manufacturing equipment when forming high-nitrogen duplex stainless steel are set as follows: laser power is set to 150W-350W, laser scanning distance is 60-150 μm, laser scanning layer thickness is 30-65 μm, and laser scanning rate is 200-1200 mm / s.
[0008] Optionally, the stainless steel powder comprises, by weight: Cr: 30–34%; Ni: 7–14%; Mo: 3.0–4.0%; N: 0.60–0.95%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe.
[0009] Optionally, the stainless steel powder comprises, by weight: Cr: 32%; Ni: 12%; Mo: 3.5%; N: 0.60–0.90%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe.
[0010] Optionally, the stainless steel powder contains 0.7% nitrogen by weight.
[0011] Optionally, the stainless steel powder is prepared by gas atomization powder preparation.
[0012] Optionally, when forming high-nitrogen duplex stainless steel, the laser additive manufacturing equipment controls the solidification rate of the material to allow nitrogen atoms in the molten region to dissolve in the alloy matrix.
[0013] Optionally, the laser additive manufacturing equipment uses a material solidification rate of 10 during forming. 5 -10 7 K / s.
[0014] Optionally, the laser scanning rate is 500-800 mm / s, and the laser scanning spacing is 80-100 μm.
[0015] The present invention also provides a high-nitrogen duplex stainless steel, which is prepared by the above-mentioned method for preparing high-nitrogen duplex stainless steel, wherein the nitrogen content in the high-nitrogen duplex stainless steel is greater than or equal to 0.6% by weight.
[0016] Optionally, the high-nitrogen duplex stainless steel has a PREN value ≥ 52.
[0017] Traditional smelting of duplex steels involves slow cooling, which allows nitrogen to easily precipitate as the Cr2N phase, resulting in a decrease in effective dissolved nitrogen and limiting the improvement of PREN. This invention provides a high-nitrogen duplex stainless steel and a method for preparing it, utilizing laser additive manufacturing to produce 10... 5 -10 7 The K / s ultra-fast solidification of the alloy matrix allows for the supersaturation of w(N) ≥ 0.6% in the alloy matrix, resulting in no Cr2N precipitation and enabling PREN to exceed 50, reaching over 52, a significant improvement. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a typical microstructure diagram of a high-nitrogen duplex stainless steel provided in an embodiment of the present invention; Figure 2 This refers to the room temperature tensile properties of materials under different printing parameters in the preparation method provided in this embodiment of the invention. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0021] It should be noted that the terms "setup" and "connection" should be interpreted broadly. For example, they can refer to direct setup or connection, or indirect setup or connection through centered components or centered structures.
[0022] Furthermore, in embodiments of this invention, terms such as "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" are used to indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, or in a conventional placement or usage state. These terms are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the structures, features, devices, or elements referred to must have a specific orientation or positional relationship, nor that they must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0023] The various specific technical features and embodiments described in the detailed embodiments can be combined in any suitable manner without contradiction. For example, different implementation methods can be formed by combining different specific technical features / embodiments. In order to avoid unnecessary repetition, the various possible combinations of the various specific technical features / embodiments in this invention will not be described separately.
[0024] This invention provides a method for preparing high-nitrogen duplex stainless steel, comprising the following steps: Raw material preparation steps: Prepare stainless steel powder with a nitrogen content greater than or equal to 0.6 wt%, that is, the nitrogen content in the stainless steel powder is greater than or equal to 0.6% by weight; Forming Steps: Stainless steel powder with a nitrogen content greater than 0.6 wt% is placed in a laser additive manufacturing equipment for forming. The parameters for forming high-nitrogen duplex stainless steel are set as follows: laser power 150W-350W, laser scanning spacing 60-150 μm, laser scanning layer thickness 30-65 μm, and laser scanning rate 200-1200 mm / s. Traditional smelting of duplex steel results in slow cooling, leading to the easy precipitation of nitrogen as the Cr2N phase, which reduces the effective dissolved nitrogen and limits the improvement of PREN. This invention provides a high-nitrogen duplex stainless steel and its preparation method. By utilizing laser additive manufacturing to create an alloy matrix, w(N) ≥ 0.6% is supersaturated and dissolved in the alloy matrix, preventing Cr2N precipitation and enabling PREN to exceed 50, reaching over 52, representing a significant improvement.
[0025] Optionally, the stainless steel powder comprises, by weight: Cr: 30–34%; Ni: 7–14%; Mo: 3.0–4.0%; N: 0.60–0.95%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe and unavoidable impurities.
[0026] In specific applications, the Ni content can be 7%, 8%, 9%, 10%, 11%, 12%, 13%, or 14%, etc.
[0027] Optionally, the stainless steel powder comprises, by weight: Cr: 32%; Ni: 12%; Mo: 3.5%; N: 0.60–0.90%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe and unavoidable impurities.
[0028] Optionally, the stainless steel powder contains, by weight, Cr: 32%; Ni: 12%; Mo: 3.5%; N content: 0.7%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; with the balance being Fe and unavoidable impurities.
[0029] Optionally, the stainless steel powder is prepared using a gas atomization powder preparation method. In this method, high-pressure nitrogen gas is used to impact the molten metal flow at supersonic speed, instantly completing the "liquid → powder" conversion, equivalent to rapid solidification in "micro-casting". The "nitrogen atomization" itself carries a nitrogen partial pressure of 0.1-0.2 MPa, which can continue to dissolve nitrogen into the droplets during the flight phase, achieving "secondary nitrogen enrichment". This increases the nitrogen content of the powder by 0.05-0.08 wt% compared to the master alloy. Gas atomization not only obtains highly spherical, low-oxygen, and precisely composed powder in one step, but also utilizes the dual effect of "high-pressure nitrogen + rapid cooling" to push the nitrogen content to the range of 0.6-0.95%, laying the raw material foundation for subsequent laser additive manufacturing to achieve high-nitrogen duplex stainless steel with no Cr2N and PREN ≥ 52.
[0030] Optionally, when forming the high-nitrogen duplex stainless steel, the laser additive manufacturing equipment controls the solidification rate of the material so that nitrogen atoms in the molten region are dissolved in the alloy matrix.
[0031] Optionally, the laser additive manufacturing equipment uses a material solidification rate of 10 during forming. 5 -10 7 K / s. Nitrogen diffuses only a few tens of times the lattice spacing in ferrite, which is insufficient to grow to form Cr2N crystal nuclei.
[0032] Optionally, in this embodiment, selective laser melting (SLM) printing is used, with a laser power P=250W, a scanning distance H=80 μm, a laser scanning rate of 500-800 mm / s, and a laser scanning distance of 80-100 μm. This utilizes the ultra-fast solidification characteristics of selective laser melting additive manufacturing (10... 5 -10 7 The K / s ratio allows nitrogen atoms in the molten region to be dissolved (locked) in the alloy matrix, avoiding the precipitation of Cr2N phase in the alloy caused by slow cooling in traditional smelting methods, which steals the N atoms dissolved in the matrix, resulting in a new type of duplex stainless steel with high PREN value.
[0033] The present invention also provides a high-nitrogen duplex stainless steel, which is prepared by the above-mentioned method for preparing high-nitrogen duplex stainless steel, and has a nitrogen content ≥0.6 wt.%, that is, the nitrogen content in the high-nitrogen duplex stainless steel is greater than or equal to 0.6% by weight.
[0034] Optionally, the high-nitrogen duplex stainless steel has a PREN value ≥ 52, a material strength of up to 1300 MPa, and an elongation at break of up to 24%. Specifically, PREN = Cr + 3.3(Mo + 0.5W) + 16N.
[0035] Traditional smelting of duplex steels involves slow cooling, which allows nitrogen to easily precipitate as the Cr2N phase, resulting in a decrease in effective dissolved nitrogen and limiting the improvement of PREN. This invention provides a high-nitrogen duplex stainless steel and a method for preparing it, utilizing laser additive manufacturing to produce 10... 5 -10 7 The K / s ultra-fast solidification of the alloy matrix allows for the supersaturation of w(N) ≥ 0.6% in the alloy matrix, resulting in no Cr2N precipitation and enabling PREN to exceed 50, reaching over 52, a significant improvement.
[0036] The alloy matrix prepared in this embodiment has Cr of 32 wt%, Ni of 12 wt%, Mo of 3.5 wt%, and N of 0.6 wt%. It was manufactured using laser additive manufacturing (L-PBF) with 10 5 -10 7 A cooling rate of K / s inhibits Cr2N precipitation and locks in an α / γ ratio of approximately 1:1, achieving a PREN value ≥52. This enables ultra-high nitrogen content to be dissolved into duplex stainless steel, maintaining a supersaturated solution state without precipitation. Actual nitrogen content can reach 0.60 wt% (or higher), with no Cr2N, and tensile properties meeting 1300 MPa. Figure 1 This is a typical microstructure of the alloy matrix prepared in this invention. Red: ferrite; green: austenite. The two phases are in a ratio of 55:45, close to 1:1, which is typical of duplex stainless steel. Figure 2 The room temperature tensile properties of the alloy obtained under different printing parameters in the preparation method of this invention are shown. From the tensile curves, printing parameters 2, 13, 4, and 24# show the best results, exhibiting high strength and high elongation at break. The microstructure is a typical dual-phase structure (ferrite + austenite). Selective laser melting (SLM) with a scan speed of 500-800 m / s and a scan spacing of 80-100 μm yields excellent results. This embodiment also provides a nitrogen, oxygen, and hydrogen analyzer test report, as shown in the table below: It is evident that the nitrogen content reaches over 0.6 wt.%, which is higher than that of the existing SAF3207 steel (0.5 wt.%), indicating a promising future for its application and promotion.
[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing high-nitrogen duplex stainless steel, characterized in that, Includes the following steps: Raw material preparation steps: Prepare stainless steel powder, wherein the nitrogen content of the stainless steel powder is greater than or equal to 0.6% by weight; Forming steps: The stainless steel material powder is placed in a laser additive manufacturing equipment for forming, and the parameters of the laser additive manufacturing equipment when forming high-nitrogen duplex stainless steel are set as follows: laser power is set to 150W-350W, laser scanning distance is 60-150 μm, laser scanning layer thickness is 30-65 μm, and laser scanning rate is 200-1200 mm / s.
2. The method for preparing high-nitrogen duplex stainless steel as described in claim 1, characterized in that, The stainless steel powder comprises, by weight: Cr: 30–34%; Ni: 7–14%; Mo: 3.0–4.0%; N: 0.60–0.95%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe.
3. The method for preparing high-nitrogen duplex stainless steel as described in claim 1, characterized in that, The stainless steel powder comprises, by weight: Cr: 32%; Ni: 12%; Mo: 3.5%; N: 0.60–0.90%; C: ≤0.03%; Si: ≤0.8%; Mn: ≤1.5%; P: ≤0.035%; S: ≤0.01%; Balance Fe.
4. The method for preparing high-nitrogen duplex stainless steel as described in claim 1, characterized in that, The stainless steel powder contains 0.7% nitrogen by weight.
5. The method for preparing high-nitrogen duplex stainless steel as described in claim 1, characterized in that, The stainless steel powder is prepared by gas atomization powder preparation.
6. A method for preparing high-nitrogen duplex stainless steel according to any one of claims 1 to 5, characterized in that, When forming high-nitrogen duplex stainless steel, the laser additive manufacturing equipment controls the solidification rate of the material, so that nitrogen atoms in the molten region are dissolved in the alloy matrix.
7. The method for preparing high-nitrogen duplex stainless steel as described in claim 6, characterized in that, During the forming process, the laser additive manufacturing equipment has a material solidification rate of 10. 5 -10 7 K / s.
8. A method for preparing high-nitrogen duplex stainless steel according to any one of claims 1 to 5, characterized in that, The laser scanning rate is 500-800 mm / s, and the laser scanning spacing is 80-100 μm.
9. A high-nitrogen duplex stainless steel, characterized in that, The high-nitrogen duplex stainless steel is prepared by any one of the methods described in claims 1 to 8, wherein the nitrogen content in the high-nitrogen duplex stainless steel is greater than or equal to 0.6% by weight.
10. A high-nitrogen duplex stainless steel as described in claim 9, characterized in that, The PREN value of the high-nitrogen duplex stainless steel is ≥52.