Method for producing ferritic steel Fe-12 / 18 Cr strengthened by oxide dispersions
The method for producing ferritic steel Fe-12/18 Cr with oxide dispersion improves impact resistance and tensile properties by refining particle size through sieving and processing, resulting in enhanced mechanical performance.
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
- 2026-06-30
AI Technical Summary
Conventional methods for producing ferrite ODS steels with high chromium content (12%–18%) are limited in impact resistance and hot tensile strength, despite their good thermal creep properties and other advantages.
A method involving co-grinding ferritic steel powder Fe-12/18 Cr with oxide powder, followed by sieving to a predetermined initial size, reprocessing to a smaller final size, and then encapsulating and hot isostatic compression or sintering to produce ferritic steel with improved mechanical properties.
The method enhances impact resistance and hot tensile properties, increasing ductile energy levels and brittle/ductile transition temperatures, and improves mechanical strength at both room and high temperatures.
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Abstract
Description
Technical Field
[0001] The present invention relates to the metallurgy of ferrite steel Fe-Cr strengthened by an oxide dispersion.
[0002] In particular, the present invention relates to a method for manufacturing such steel.
Background Art
[0003] Conventional manufacturing methods for oxide-dispersion-strengthened ferrite steels (ODS steels, also known as "oxide dispersion strengthened" steels) are well-known and enable the production of materials with remarkable hot properties. The ferrite matrix offers many advantages (good electrical conductivity, low thermal expansion, high rigidity, excellent resistance to irradiation damage, etc.), and the oxide dispersion improves the thermal creep properties. Therefore, ferrite ODS steels are regarded as structural materials for future nuclear reactors (fast neutron reactors RNR-Na, fusion, etc.) or other components that require the quality of these materials.
[0004] Conventionally, the dispersion of oxides, most often nano-oxides, is achieved by mechanical synthesis of powders. The first step of this method consists of high-energy co-grinding of atomized steel powder and oxide powder, such as yttrium oxide Y2O3, enabling the oxide to dissolve inside the steel powder particles. After co-grinding, new powder is obtained. The coarsest powder (with an average size exceeding 150 - 200 microns) is removed by sieving, and then the remaining powder with an average diameter centered around about 100 microns is solidified. Solidification can be carried out using various techniques such as encapsulation (which can remove moisture and gas in this step) and subsequent hot isostatic pressing (HIP). This solidification can also be carried out by other methods, such as sintering. Flash sintering (also known as SPS, which means "spark plasma sintering"). In all cases, the solidification step enables densification of the material and precipitation of the oxide.
[0005] The objective is to enable the use of ferrite grades with high chromium content (12%–18%) and desirable mechanical properties, particularly in terms of impact resistance and hot tensile strength. However, current ferrite ODS steels, while performing well, remain limited in these respects. [Overview of the project]
[0006] One of the objectives of the present invention is to provide a method for producing ferritic steel Fe-12 / 18 Cr reinforced with an oxide dispersion, which enables improved impact resistance and hot tensile properties. It should be noted that ferritic steel Fe-12 / 18 Cr is a steel containing 12% to 18% chromium.
[0007] For this purpose, the present invention is a method for producing ferritic steel Fe-12 / 18 Cr strengthened with an oxide dispersion, a) A step of supplying ferritic steel powder Fe-12 / 18 Cr and oxide powder, b) A step of co-grinding ferrite steel powder Fe-12 / 18 Cr with oxide powder to obtain ferrite steel powder Fe-12 / 18 Cr reinforced with an oxide dispersion, c) A step of sieving the ferrite steel powder Fe-12 / 18 Cr, which has been strengthened with the oxide dispersion thus produced, to a predetermined initial average particle size, d) A step of reprocessing the ferrite steel powder Fe-12 / 18 Cr, which has been strengthened with an oxide dispersion derived from the powder thus sieved, in order to obtain a predetermined final average particle size that is strictly smaller than a predetermined initial average particle size, e) A step to produce ferritic steel Fe-12 / 18 Cr strengthened with an oxide dispersion derived from the reprocessed powder in this manner, We propose a method that includes this.
[0008] The methods according to the present invention may, either alone or in combination, have at least one of the following features: -Step d) includes one or more sieving steps. -Step d) includes a first sieving step at a predetermined intermediate average particle size between the initial average particle size and the final average particle size, followed by a second sieving step at a predetermined final average particle size. - The initial average particle size is 80-100 microns. - The average intermediate particle size is 60-80 microns, for example, about 70 microns. -Step d) is a grinding step, so-called cryogenic grinding, of the ferritic steel powder Fe-12 / 18 Cr reinforced with oxide dispersions derived from the sieved powder, which is carried out at a temperature of -40°C to -180°C for a period of 4 to 48 hours. - Cryogenic grinding is carried out over a period of 8 to 24 hours, preferably 10 to 18 hours. - The final average particle size is 40-60 microns, for example, about 50 microns. -Process e) is e1) A step of encapsulating and degassing the ferrite steel powder Fe-12 / 18 Cr, which has been reprocessed in this manner and therefore has a final average particle size, and then e2) A process of performing hot isostatic compression, Includes. -Step e) is a sintering process, such as flash sintering. - The oxide powder supplied in step a) is selected from yttrium oxide powder (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 more preferably less than 100 nm. [Brief explanation of the drawing]
[0009] Other features and advantages of the present invention will become apparent from the description made with reference to the accompanying drawings. [Figure 1] This is a flowchart of a method for producing Fe-12 / 18 Cr ferritic steel reinforced with an oxide dispersion according to the present invention. [Figure 2]This photograph shows the difference between particle size obtained by a conventional method (a, left) and particle size obtained by the method in Figure 1 (b, right). [Figure 3] This graph shows the particle size distribution of powder reprocessed by the method shown in Figure 1 and conventional powder obtained by the conventional method. [Figure 4] This graph shows the ductile-brittle transition curves of materials obtained by CIC from untreated powder (conventional technology) and powder treated by the method shown in Figure 1. [Figure 5] This graph shows the tensile curves of materials obtained by CIC from untreated powder and powder treated by the method shown in Figure 1. [Modes for carrying out the invention]
[0010] Detailed explanation Throughout the following explanation, particle size (also called particle size distribution) is derived from dry laser particle size measurement. The principle of this measurement is as follows: a certain amount of powder is placed on a diaphragm, and when the diaphragm is activated, the powder falls into a vertical column (in this case, the column is filled with a gas, e.g., air: dry method), 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 relates the scattering angle to the size of the powder. This physical model is, for example, the Mie scattering model. The typical error range for powder size obtained with dry laser particle size measurement is less than 5%. More specifically, the measurements derived in this explanation were obtained using a Horiba Jobin-Yvon LA-950 machine.
[0011] Referring to Figure 1, a method for producing Fe-12 / 18 Cr ferritic steel reinforced with an oxide dispersion according to the present invention will be described.
[0012] A method for producing ferritic steel Fe-12 / 18 Cr reinforced with an oxide dispersion according to the present invention comprises a first step 100 (step a) of supplying ferritic steel powder Fe-12 / 18 Cr and oxide powder, for example, yttrium oxide powder (Y2O3). Other oxide powders, such as zirconium oxide powder or titanium oxide powder, can be used. The oxide powder used 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 dissolve the oxide powder in the ferritic steel powder.
[0013] Next, the method for producing oxide dispersion-reinforced ferritic steel Fe-12 / 18 Cr according to the present invention includes a second step 200 (step b) in which ferritic steel powder Fe-12 / 18 Cr and oxide powder are co-ground to obtain oxide dispersion-reinforced ferritic steel powder Fe-12 / 18 Cr. This co-grounding step includes mechanosynthesis of the powder, which dissolves the oxide inside the particles of the ferritic steel powder Fe-12 / 18 Cr (matrix).
[0014] Next, the method for producing ferritic steel Fe-12 / 18 Cr reinforced with an oxide dispersion according to the present invention includes a third step 300 (step c) of sieving the ferritic steel powder Fe-12 / 18 Cr reinforced with an oxide dispersion thus produced to a predetermined initial average particle size. The initial average particle size is, for example, 100 microns or less, particularly 80 to 100 microns. The result of this third step 300 (step d) is shown, for example, in Figure 2a), which is a scanning electron microscope (SEM) image of steel powder Fe-14 Cr.
[0015] Next, a method for producing a ferrite steel Fe-12 / 18 Cr strengthened by a sieved oxide dispersion according to the present invention includes a fourth step 400 (step d) of reprocessing a ferrite steel powder Fe-12 / 18 Cr strengthened by a sieved oxide dispersion in order to obtain a predetermined final average particle size that is strictly smaller than a predetermined initial average particle size. The final average particle size is typically 40 to 60 microns, for example about 50 microns.
[0016] In a first embodiment of the fourth reprocessing step 400, the reprocessing is performed by screening (sieving) the ferrite steel powder of Fe-12 / 18 Cr strengthened by the sieved oxide dispersion obtained during the third step 300 of the method for producing a ferrite steel Fe-12 / 18 Cr strengthened by the oxide dispersion according to the present invention.
[0017] Thus, only the finest powder is retained.
[0018] This screening is performed using one or more sieving steps 410, 420, in this example double sieving.
[0019] Thus, the fourth step 400 of the method for producing a ferrite steel Fe-12 / 18 Cr strengthened by a sieved oxide dispersion includes a first sieving step 410 of a predetermined intermediate average particle size that is between the initial average particle size and the final average particle size. Typically, the intermediate average particle size is 60 to 80 microns, for example about 70 microns. Next, the fourth step 400 of the method for producing a ferrite steel Fe-12 / 18 Cr strengthened by an oxide dispersion includes a second sieving step 420 of the ferrite steel powder Fe-12 / 18 Cr strengthened by the oxide dispersion sieved to the intermediate particle size in order to obtain a ferrite steel powder Fe-12 / 18 Cr strengthened by the oxide dispersion having a predetermined final average particle size, following the first sieving step 410.
[0020] For example, the first sieving step 410 makes it possible to obtain an intermediate particle size of 70 microns, which is then picked up in the second sieving step 420 to retain only the finest powder with a particle size of less than 50 microns.
[0021] Figure 2b) shows the results of this fourth reprocessing step 400 of the method for producing ferritic steel Fe-12 / 18 Cr strengthened with oxide dispersion according to the present invention.
[0022] Figure 3 shows the size distribution (particle size) of ferritic steel powder Fe-12 / 18 Cr strengthened by oxide dispersions of conventional powder (prior art) and optimized powder, i.e., powder reprocessed between the methods according to the present invention.
[0023] Therefore, the effectiveness of this fourth step 400 powder size of the method for producing ferritic steel Fe-12 / 18 Cr strengthened by oxide dispersion according to the present invention is evident.
[0024] In a second embodiment of the fourth reprocessing step 400, this is carried out by taking the conventional powder after grinding, which is obtained from the third step 300 of the method for producing sieved oxide dispersion-reinforced ferritic steel Fe-12 / 18 Cr, by cold grinding. Such cold grinding is typically carried out at -40°C to -180°C for a period of 4 to 48 hours, preferably 8 to 24 hours, and even more preferably 10 to 18 hours. This grinds the oxide dispersion-reinforced ferritic steel powder Fe-12 / 18 Cr, which has an initial average particle size, to obtain a finer oxide dispersion-reinforced ferritic steel powder Fe-12 / 18 Cr, which has a final average particle size.
[0025] Finally, a method for producing ferritic steel Fe-12 / 18 Cr strengthened by an oxide dispersion according to the present invention includes a fifth step 500 for producing ferritic steel Fe-12 / 18 Cr strengthened by an oxide dispersion derived from the powder thus reprocessed.
[0026] This fifth step 500 can be carried out in various ways. Therefore, the following steps are conceivable: e1) encapsulating and degassing the reprocessed, and therefore having the final average particle size, oxide dispersion-enhanced ferrite steel powder Fe-12 / 18 Cr, and then e2) hot isostatic compression. During vacuuming, water vapor and any gases are evacuated.
[0027] Alternatively, a fifth step 500 of the method for producing ferritic steel Fe-12 / 18 Cr reinforced with an oxide dispersion, reprocessed according to the present invention, is e) a sintering step, for example, flash sintering (also known by the acronym SPS, meaning "spark plasma sintering").
[0028] It is clear that the use of the method for producing Fe-12 / 18 Cr ferritic steel reinforced with oxide dispersions according to the present invention, as described above, enables the resulting steel grade to have improved impact properties, as shown in Figure 4.
[0029] From the same batch of co-ground ferrite steel powder Fe-12 / 18 Cr reinforced with oxide dispersions, two steel ODSs were obtained: one without reprocessing step 400 (conventional powder, prior art) and the other with reprocessing step 400 (optimized powder according to the present invention). Figure 4 shows that the ductile energy level increased from approximately 3 joules (conventional powder) to 6.8 joules (optimized powder). The brittle / ductile transition temperature increased from around -10°C to around -50°C, demonstrating a significant improvement in impact resistance. The curves in Figure 4 were obtained from 3 × 4 × 27 mm mini Charpy specimens.
[0030] Tensile properties are also improved. At ambient temperature, the ductility of the material having powder reprocessed using the method for producing ferritic steel Fe-12 / 18 Cr reinforced with oxide dispersion according to the present invention is much higher than that of the grade having conventional powder (prior art). This increase in ductility is beneficial for the formability of the material at room temperature. At high temperatures (600°C / 700°C), as shown in Figure 5, the mechanical strength of the material obtained using the method for producing ferritic steel Fe-12 / 18 Cr reinforced with oxide dispersion according to the present invention is even greater than that of the material having conventional powder. Figure 5 shows the tensile curves of the material obtained using conventional powder (dotted line, prior art) and reprocessed / optimized powder (solid line, present invention). At room temperature, the optimized material has nearly 25% elongation at break compared to 15% of the conventional material. At high temperatures (600°C / 700°C), the mechanical strength of the optimized material is greater than that of the conventional material.
Claims
1. A method for producing ferritic steel Fe-12 / 18 Cr strengthened with an oxide dispersion, a) A step (100) of supplying ferrite steel powder Fe-12 / 18 Cr and oxide powder, b) A step of co-grinding (200) the ferrite steel powder Fe-12 / 18 Cr and the oxide powder to obtain ferrite steel powder Fe-12 / 18 Cr strengthened by an oxide dispersion, c) A step (300) of sieving the ferrite steel powder Fe-12 / 18Cr, which has been strengthened with the oxide dispersion thus produced, to a predetermined initial average particle size, d) A step (400) to reprocess the ferrite steel powder Fe-12 / 18 Cr, which has been reinforced with an oxide dispersion derived from the powder thus sieved, in order to obtain a predetermined final average particle size that is strictly smaller than a predetermined initial average particle size, e) A step (500) to produce the ferritic steel Fe-12 / 18 Cr strengthened with the oxide dispersion derived from the powder reprocessed in this manner, Methods that include...
2. The method according to claim 1, wherein step d) includes one or more sieving steps (410, 420).
3. The method according to claim 2, wherein step d) includes a first sieving step (410) at a predetermined intermediate average particle size between the initial average particle size and the final average particle size, and a second sieving step (420) at the predetermined final average particle size thereafter.
4. The method according to any one of claims 1 to 3, wherein the initial average particle size measured by dry laser particle size measurement is 80 to 100 microns.
5. The method according to claim 3, wherein the intermediate average particle size measured by dry laser particle size measurement is 60 to 80 microns, for example, about 70 microns.
6. The method according to claim 1, wherein step d) is a grinding step of the ferrite steel powder Fe-12 / 18Cr reinforced with the oxide dispersion derived from the powder thus sieved, so-called cryogenic grinding, and the cryogenic grinding is carried out at a temperature of -40°C to -180°C for a period of 4 to 48 hours.
7. The method according to claim 6, wherein the cryogenic grinding is carried out over a period of 8 to 24 hours.
8. The method according to any one of claims 1 to 3, wherein the final average particle size measured by dry laser particle size measurement is 40 to 60 microns.
9. The aforementioned step e) e １ ) The ferrite steel powder Fe-12 / 18Cr, which has been reprocessed in this manner and thus has a final average particle size, and is strengthened with an oxide dispersion, is encapsulated and degassed, and then e ２ ) A process of performing hot isostatic compression, The method according to any one of claims 1 to 3, including
10. The method according to any one of claims 1 to 3, wherein step e) is a sintering step.
11. The oxide powder supplied in step a) is yttrium oxide (Y ２ O ３ The method according to any one of claims 1 to 3, wherein the powder is selected from zirconium oxide or titanium oxide.
12. The method according to any one of claims 1 to 3, wherein the oxide powder supplied in step a) has an average particle size of less than 5 microns, and the average particle size is measured by dry laser particle size measurement.
13. The method according to any one of claims 1 to 3, wherein the oxide powder supplied in step a) has an average particle size of less than 1 micron, and the average particle size is measured by dry laser particle size measurement.
14. The method according to any one of claims 1 to 3, wherein the oxide powder supplied in step a) has an average particle size of less than 100 nm, and the average particle size is measured by dry laser particle size measurement.