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CN-121992310-A - Heat-treatment-free duplex stainless steel member and preparation method thereof

CN121992310ACN 121992310 ACN121992310 ACN 121992310ACN-121992310-A

Abstract

The heat-treatment-free duplex stainless steel component is obtained by mixing duplex stainless steel powder with MnN powder and then performing laser melting printing through a selected area, wherein the microstructure of the heat-treatment-free duplex stainless steel mixed powder comprises an austenite phase and a ferrite phase, and the volume fraction of the austenite phase is 40% -60%. According to the invention, through cooperative control of an exogenous alloying strategy and a selective laser melting process, the duplex proportion of austenite and ferrite is regulated and controlled in situ, so that the duplex balanced stainless steel material without subsequent heat treatment is obtained, the material manufacturing process is simplified, excellent mechanical property and corrosion resistance are achieved, the tensile strength is more than or equal to 750 MPa, and the elongation after fracture is more than or equal to 30%.

Inventors

  • CHANG KEKE
  • Dong Haokai
  • JIANG XINYUE
  • ZHONG RUI

Assignees

  • 中国科学院宁波材料技术与工程研究所

Dates

Publication Date
20260508
Application Date
20260317

Claims (10)

  1. 1. The heat treatment-free duplex stainless steel member is characterized in that the heat treatment-free duplex stainless steel member is obtained by mixing duplex stainless steel powder and MnN powder and then performing selective laser melting printing; The microstructure of the heat-treatment-free duplex stainless steel member comprises an austenite phase and a ferrite phase, wherein the volume fraction of the austenite phase is 40% -60%.
  2. 2. The duplex stainless steel member of claim 1, wherein the duplex stainless steel member has a tensile strength of at least 750 MPa and an elongation after break of at least 30%.
  3. 3. The duplex stainless steel member of claim 1, wherein MnN powder comprises 7% -9% of the total mass of the mixed powder.
  4. 4. The duplex stainless steel member as claimed in claim 1, wherein the duplex stainless steel powder is 2205 duplex stainless steel powder having a chemical composition of ：Cr：21.0-24.0%,Ni：4.5-6.5%,Mo：2.5-3.5%,N：0.08-0.2%,Mn：≤2.0%,Si：≤1.0%,C：≤0.03%,S：<0.03%,P：<0.04%, weight percent balance of Fe and unavoidable impurities.
  5. 5. The duplex stainless steel member as claimed in claim 4, wherein the 2205 duplex stainless steel powder has a particle size in the range of 15-53 μm, and is spherical or nearly spherical.
  6. 6. The duplex stainless steel member of claim 1, wherein the laser power of the selective laser melt printing is 200-450W.
  7. 7. The duplex stainless steel member of claim 1, wherein the volumetric energy density E v is 150-190J/mm 3 .
  8. 8. The duplex stainless steel member according to claim 1, wherein the scanning pitch of selective laser melting printing is 0.05-0.1 mm, the powder layer thickness is 0.02-0.05 mm, and the scanning speed is 500-1000 mm/s.
  9. 9. The duplex stainless steel member of claim 1, wherein the scanning strategy employed for selective laser melt printing is 67 ° relative rotation of the upper and lower layers.
  10. 10. The duplex stainless steel member of claim 1, wherein the protective atmosphere for selective laser melting printing is argon and the oxygen content in the forming cavity is less than 100 ppm.

Description

Heat-treatment-free duplex stainless steel member and preparation method thereof Technical Field The invention belongs to the field of metal material preparation, and particularly relates to a heat-treatment-free duplex stainless steel member and a preparation method thereof. Background The duplex stainless steel has good strength, toughness and corrosion resistance due to the structure characteristics of the coexistence of austenite (gamma) and ferrite (delta) phases, and is widely applied to the fields of ocean engineering, petrochemical industry, energy equipment and the like. However, due to the high content of alloying elements in steel, the conventional preparation process has many challenges, such as special pressurizing equipment for smelting process, strict temperature control for forging-hot rolling process, strict heat input control for welding process, etc. These operations undoubtedly increase the cost of preparation of the material, while limiting its complex shaping. With the continuous progress of China from the ocean major country to the ocean strong country, the traditional cast-forge welding process is difficult to meet the requirements of sea tooling for precision, customization and structural function integration, so that a new process exploration is needed to be developed. Selective area laser melting (SLM) provides a revolutionary approach to the formation of complex duplex stainless steel components. However, the extremely high energy density and extremely fast cooling rate (typically up to 10 5-106 K/s) inherent to SLM process severely inhibit solid state transformation of delta-ferrite into austenite during solidification, which results in the formation of coarse columnar crystalline ferrite as the main structure of the conventional duplex stainless steel (e.g. 2205) powder after SLM forming, and serious shortage of austenite content (typically less than 2%) failing to meet the performance requirements of duplex stainless steel. Therefore, duplex stainless steel manufactured by SLM in the prior art generally requires subsequent solution heat treatment to regulate the ratio of two phases, which not only increases the production cycle and cost, but also may introduce deformation and residual stress. In order to be able to directly obtain a two-phase structure in which austenite (γ) and ferrite (δ) coexist during the molding process, various attempts have been made in the prior art, but there are significant drawbacks. For example, patent publication No. CN116219295A discloses a scheme for improving phase balance by adjusting equivalent ratio of Cr and Ni. However, this solution is based on laser Directed Energy Deposition (DED) with a cooling rate (10 2-103 K/s) 2-3 orders of magnitude lower than SLM, with fundamental differences in process principles. More importantly, this approach clearly acknowledges that laser additive manufacturing results in incomplete ferrite to austenite transformation, often requiring subsequent heat treatments, and thus does not achieve a true heat treatment free. In addition, the Ni content is as high as 8-8.5%, and the raw material cost is obviously increased. For another example, the invention patent publication No. CN116511530A discloses a method for preparing a high-nitrogen nickel-saving austenitic stainless steel component, which is based on various duplex/austenitic-ferritic stainless steel powders and adds MnN to prepare the high-nitrogen nickel-saving austenitic stainless steel. However, the target product of this approach is a fully austenitic structure, in contrast to the duplex equilibrium requirements sought for duplex stainless steels. The invention patent with publication number CN116652170A discloses a duplex stainless steel and an additive manufacturing method thereof, specifically 430 ferrite stainless steel and 316L austenitic stainless steel are mechanically mixed, and the phase proportion is regulated and controlled by adjusting the SLM scanning rate. However, the solution is purely physical mixing, lacks an in-situ alloying mechanism, has limited phase structure regulation and control capability, and cannot stably obtain an ideal biphase proportion. Therefore, based on the tissue characteristics of austenite (gamma) and ferrite (delta) two phases, the two-phase balance is regulated and controlled in situ and accurately in the forming process through the innovative exogenous alloying strategy and process cooperative control, so that a novel material system and method which completely eliminate the heat treatment process are developed, and the novel material system and method have urgent technical requirements and remarkable innovation value. Disclosure of Invention In order to solve the technical problems in the prior art, the invention provides a heat-treatment-free duplex stainless steel member and a preparation method thereof, wherein the duplex proportion of austenite and ferrite is controlled in situ by cooperative control of an