Method for producing austenitic steel Fe-Cr-Ni reinforced with oxide dispersions
Cryogenic grinding and co-grinding with oxide powder, followed by sieving and optional hot isostatic pressing, address the yield and quality issues in austenitic ODS steel production, resulting in improved mechanical properties and corrosion resistance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
- Filing Date
- 2025-12-10
- Publication Date
- 2026-06-24
AI Technical Summary
Current methods for producing austenitic ODS steel face challenges such as powder agglomeration, contamination, and reduced mechanical properties due to oxide growth and carbon contamination, leading to low yield and poor chemical homogeneity.
A method involving cryogenic grinding of austenitic Fe-Cr-Ni powder followed by co-grinding with oxide powder, combined with sieving and optional steps like hot isostatic pressing or sintering, to enhance oxide dispersion reinforcement in austenitic steel.
This method improves yield and maintains powder quality by achieving finer particle sizes and homogeneous distribution of oxide dispersions, enhancing mechanical properties and corrosion resistance.
Smart Images
Figure 2026103856000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the metallurgy of austenitic steel Fe-Cr-Ni strengthened by an oxide dispersion. In particular, the present invention relates to a method for producing such steel.
Background Art
[0002] Currently, the production of austenitic ODS (oxide dispersion strengthened) steel by powder metallurgy involves a mechanical milling stage. This stage is currently essential for the production of certain classes of steel such as ODS steel. ODS steels are typically steels strengthened by nanometer oxide dispersions. They are of interest in industry for their high properties in terms of corrosion resistance and mechanical strength at high temperatures, and also in the nuclear industry for their resistance to radiation damage.
[0003] Today, methods for producing ODS steel include powder metallurgy and co-milling (also known as mechanosynthesis) of austenitic steel powder with oxide powder, such as yttrium oxide Y2O3. When mechanosynthesis is carried out correctly, the oxide dissolves in the matrix. This step is well established for ferritic steels. On the other hand, the high ductility of austenitic steel makes this mechanosynthesis step difficult. This is because the powder can "stick" together and agglomerate without the mechanosynthesis step occurring, or can "coat" the milling beads or the milling tank.
[0004] Attempts have been made to solve this problem by varying the chemical composition of the powder and / or the processing parameters.
[0005] Currently, there is no consensus on design parameters that mainly affect the dynamics or energy of the system. Parameters such as rotational speed, bead / powder mass ratio, media filling rate, blade shape, etc. depend on the technology and materials being studied.
[0006] However, for the dissolution of oxides in the matrix and mechanical alloy to be effective, the strength of the mechanosynthesis must be high enough to deform the powder.
[0007] Solutions have been proposed to reduce most adhesion: the use of surfactants or PCA (process control agents). However, these cause significant contamination of the treated material. For example, the use of stearic acid as a PCA has been shown to induce significant carbon contamination and adversely affect the behavior of the resulting steel. The addition of carbon is known to impair corrosion resistance and weaken the material, particularly with crude carbides. 23 This leads to the precipitation of C6. Similarly, the precipitation of M7C3 type carbides is detected at grain boundaries, which may affect mechanical strength. Resistance under irradiation is also reduced by oxide growth, and this oxide growth is accelerated by carbon contamination due to the diffusion of elements into the carbides.
[0008] It has also been proposed to perform co-grinding in two steps. This involves a first co-grinding with ferrite Fe-Cr steel powder and oxide powder (lasting 20-40 hours), followed by a second co-grinding with the addition of pure nickel powder (lasting 3-30 hours). The result is an austenitic alloy Fe-Cr-Ni. However, the addition of the co-grinding step with pure nickel induces significant clumping, affecting yield and chemical homogeneity.
[0009] Furthermore, it has been suggested to use crushed beads made of hard materials such as zirconia ZrO2 or tungsten carbide WC to prevent the powder from adhering to the beads. However, fragments of beads trapped in the solidified powder significantly reduce the mechanical properties of the austenitic ODS steel produced in this manner, particularly its toughness and ductility.
[0010] As a final example, low-temperature grinding of austenitic steel has also been proposed. Unfortunately, once solidified, the material is porous and has a bimodal microstructure. Furthermore, the oxides are particularly coarse (visible under an optical microscope).
[0011] Due to these problems, where the austenitic steel powders stick together, the yield is very low. This yield is relative to the amount of powder actually used to produce the austenitic steel, compared to the amount of powder initially supplied. [Overview of the Initiative]
[0012] One of the objectives of the present invention is to provide a method for producing austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion, which can improve the yield described above.
[0013] For this purpose, the present invention is a method for producing an oxide dispersion-enhanced austenitic steel Fe-Cr-Ni, a) A step of supplying austenitic steel Fe-Cr-Ni powder, b) So-called cryogenic grinding, i.e., grinding austenitic steel Fe-Cr-Ni powder at temperatures of -50°C to -196°C The grinding process, c) A step of supplying oxide powder, d) A step of co-grinding austenitic steel Fe-Cr-Ni powder with the oxide powder supplied in this manner to obtain austenitic steel Fe-Cr-Ni powder reinforced with an oxide dispersion, e) A step to produce an austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion from the powder produced in this manner, We propose a method that includes this.
[0014] The methods according to the present invention may, either alone or in combination, have at least one of the following features: - The grinding process lasts from 10 minutes to 20 hours, particularly from 10 minutes to 15 hours, and more specifically from 10 minutes to 100 minutes. -This method includes a further step between step d) and step e), which involves sieving the austenitic steel powder reinforced with an oxide dispersion to an initial predetermined average particle size of less than 250 microns. -Process e) is e1) a sub-step of encapsulating and degassing the austenitic steel powder strengthened by the oxide dispersion, and then e2) a sub-step of performing hot isostatic pressing, is included. - Step e) is a sintering step, such as flash sintering. - Step e) is a melt spinning step. - The oxide powder supplied in step c) is selected from powders of yttrium oxide (Y2O3), zirconium oxide or titanium oxide. - The oxide powder supplied in step a) has an average particle size of less than 5 microns, preferably less than 1 micron, and even more preferably less than 100 nm.
Brief Description of the Drawings
[0015] [[ID=十九]] [Figure 1] It is a flowchart of a method for manufacturing austenitic steel Fe-Cr-Ni strengthened by the oxide dispersion according to the present invention. [Figure 2] It is a graph showing the comparative distribution of the particle sizes of the particles by laser particle size analysis. [Figure 3] It is a photograph showing the difference between the particle sizes obtained by the method according to the prior art and the particle sizes obtained by the method of FIG. 1. [Figure 4] It is a photograph showing the comparison between the new grinding beads and the grinding beads after using the method shown in FIG. 1 and the prior art method.
Embodiments for Carrying Out the Invention
[0016] Detailed Description Throughout the following description, the particle size (also referred to as the particle size distribution) is provided based on dry laser particle size measurement. The principle of this measurement is as follows: A certain amount of powder is placed on a vibrating plate, and then when the plate is activated, the powder falls into a vertical column (in this case, the column is filled with a gas, such as air: dry method), and a collimated laser beam passes through the vertical column, interacts with the powder, and then diffuses as a result of this interaction. The angle at which the light is scattered then provides information about the size of the powder using a physical model that associates the scattering angle with the size of the powder. This physical model is, for example, the Mie scattering model. The typical error range of the powder size obtained using dry laser particle size is typically less than 5%. More specifically, the measured values provided in this description were obtained using a Horiba Jobin - Yvon LA - 950 machine.
[0017] Referring to Figure 1, a method for manufacturing an austenitic steel Fe - Cr - Ni strengthened by an oxide dispersion according to the present invention will be described.
[0018] The method for manufacturing an austenitic steel Fe - Cr - Ni strengthened by an oxide dispersion according to the present invention includes a first step 100 of supplying austenitic steel Fe - Cr - Ni powder.
[0019] Next, the method for manufacturing an austenitic steel Fe - Cr - Ni strengthened by an oxide dispersion according to the present invention includes a second step 200 of performing a grinding operation on the supplied austenitic steel Fe - Cr - Ni powder at a so - called cryogenic grinding temperature, that is, at a temperature of - 50°C to - 196°C. This second step 200 lasts for several tens of minutes, for example, 10 minutes to 100 minutes. However, this step may need to last longer, for example, several hours. More generally, this step is expected to last for 10 minutes to 20 hours, particularly 10 minutes to 15 hours. Austenitic steel Fe - Cr - Ni powder having a predetermined initial average particle size is obtained.
[0020] Next, the method for producing an austenitic steel Fe-Cr-Ni strengthened by an oxide dispersion according to the present invention includes a third step 300 of supplying an oxide powder, for example, yttrium oxide (Y2O3) powder. Other oxide powders such as zirconium oxide powder or titanium oxide can be used. The supplied oxide powder has an average particle size of less than 5 microns, preferably less than 1 micron, and more preferably less than 100 nm. The smaller the particle size of the oxide powder, the easier it is to insert the oxide powder into the steel powder.
[0021] Next, the method for producing austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion according to the present invention includes a fourth step 400 in which austenitic steel Fe-Cr-Ni powder obtained by cryogenic grinding is co-ground with oxide powder to obtain austenitic steel Fe-Cr-Ni powder reinforced with an oxide dispersion. This co-grounding step includes mechanosynthesis of the powder. This enables the dissolution of oxides within the particles of the austenitic steel Fe-Cr-Ni powder.
[0022] The results of this co-grinding process are shown, for example, in Figure 3b). This is a scanning electron microscope (SEM) image of oxide dispersion-strengthened steel powder 316L obtained by the method for producing oxide dispersion-strengthened austenitic steel Fe-Cr-Ni according to the present invention. This is compared with the same powder obtained by a prior art method (Figure 3a).
[0023] Finally, the method for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni according to the present invention includes a fifth step 500 for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni from the powder thus pulverized and sieved. This fifth step 500 is a solidification step. For example, this may include a sub-step of encapsulating and degassing the pulverized oxide dispersion-reinforced austenitic steel Fe-Cr-Ni powder, which thus has a final average particle size, and a sub-step of performing hot isostatic compression (CIC).
[0024] Alternatively, the fifth step 500 of the method for producing an austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion according to the present invention may be carried out by sintering, for example, flash sintering (commonly known by the acronym SPS, which stands for "spark plasma sintering").
[0025] Process 500 may also be carried out by melt spinning or other suitable solidification techniques.
[0026] It should be noted that an additional and optional step may be included between step 400 and step 500, in which the austenitic steel Fe-Cr-Ni powder reinforced with oxide dispersion is sieved to a predetermined final average particle size, for example, 250 microns or less. This may be useful when hot isostatic compression (CIC) is desired in step 500. Other final average particle size values, such as 100 microns, can be selected depending on the application.
[0027] By using the method for producing austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion according to the present invention as described above, it is possible to obtain a larger quantity (yield) of austenitic steel Fe-Cr-Ni powder reinforced with an oxide dispersion without degrading the powder quality, as is the case with certain prior art methods.
[0028] Figure 4 shows the improvement in performance. In a), the grinding beads are new. In b), the grinding beads are simply capped and used in the fourth grinding step 400 of the method for producing austenitic steel Fe-Cr-Ni reinforced with oxide dispersion according to the present invention. In c), the grinding beads have a surface to which austenitic steel powder adheres during co-grinding by the conventional method.
[0029] Furthermore, as shown in Figure 2, the volume distribution of the average diameter (particle size) of the oxide dispersion-reinforced austenitic steel Fe-Cr-Ni powder is given for two batches of powder. The curve with a circle represents the conventional production of ODS steel 316L using the prior art method. The curve with a cross represents the production of the same ODS steel 316L using the method for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni according to the present invention. Note that the co-grinding in the fourth step 400 is carried out under the same conditions for both trials. A clear decrease in particle size was observed between the conventional co-grinding and double grinding (cryogenic grinding + co-grinding) of the method for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni according to the present invention. The powder is often sieved to less than 250 micrometers in order to solidify the material using hot isostatic compression (HIC). The sieving results for particles smaller than 250 μm show a yield of 1.48% with conventional grinding and 70.26% with double co-grinding in the method for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni according to the present invention. This demonstrates the potential of the method for producing oxide dispersion-reinforced austenitic steel Fe-Cr-Ni according to the present invention to significantly increase the yield of this method, because sieving down to 250 microns makes it possible to retain 70% of the ground powder compared to only 1.5% in the case of conventional methods.
[0030] Finally, by carrying out the method according to the present invention, in this case, it was possible to perform SAXS (small-angle X-ray scattering) measurements on the product obtained after solidification using step 500 of flash sintering. SAXS technique can be used to detect nanometer-sized objects in the matrix. For example, the inventors detected a volume fraction of 0.65%, i.e., about 1.6 × 10⁻⁶. +22 particles / m 3 The average powder particle size (i.e., average precipitate diameter) of 4.55 nm was observed at the number density.
[0031] Therefore, the present invention relates to the classically expected nanoprecipitation state for ODS steel, i.e., 10 +22 particles / m 3 ~×10 +23 particles / m 3 This allows for obtaining an average oxide powder particle size of less than 20 nm, and generally even smaller, at a number density of approximately 0.3% by volume fraction, and typically even smaller, at 4-10 nm.
Claims
1. A method for producing an oxide dispersion-reinforced austenitic steel Fe-Cr-Ni, a) A step (100) of supplying austenitic steel Fe-Cr-Ni powder, b) A step (200) in which the austenitic steel Fe-Cr-Ni powder is subjected to a grinding operation, so-called cryogenic grinding, at a temperature of -50°C to -196°C, c) A step of supplying oxide powder (300), d) A step (400) of co-grinding the austenitic steel Fe-Cr-Ni powder with the oxide powder supplied in this manner to obtain austenitic steel Fe-Cr-Ni powder reinforced with an oxide dispersion, e) A step (500) to produce the austenitic steel Fe-Cr-Ni reinforced with an oxide dispersion from the powder produced in this manner, Methods that include...
2. The method according to claim 1, wherein the grinding step lasts for 10 minutes to 20 hours, particularly 10 minutes to 15 hours, and more specifically 10 minutes to 100 minutes.
3. Between step d) and step e), there is an additional step of sieving the austenitic steel powder reinforced with an oxide dispersion to an initial predetermined average particle size of less than 250 microns. The method according to claim 1 or 2, wherein the average particle size is the average particle size measured by dry laser particle size measurement.
4. The aforementioned step e) e １ ) A sub-step of encapsulating and degassing the austenitic steel powder reinforced with an oxide dispersion, and then e ２ ) A sub-process in which hot isostatic compression is performed, The method according to any one of claims 1 to 3, including
5. The method according to any one of claims 1 to 3, wherein step e) is a sintering step, for example, flash sintering.
6. The method according to any one of claims 1 to 3, wherein step e) is a melt spinning step.
7. The oxide powder supplied in step c) is yttrium oxide (Y ２ O ３ The method according to any one of claims 1 to 6, wherein the powder is selected from zirconium oxide or titanium oxide.
8. The oxide powder supplied in step a) has an average particle size of less than 5 microns, preferably less than 1 micron, and more preferably less than 100 nm. The method according to any one of claims 1 to 7, wherein the average particle size is the average particle size measured by dry laser particle size measurement.