A nano-titanium nitride and oxide composite reinforced ODS steel and a preparation method thereof

Abstract

The application relates to the technical field of nuclear materials, in particular to a nano titanium nitride and oxide composite reinforced ODS steel and a preparation method thereof. The mass percentage of the alloy components of the ODS steel is as follows: Cr: 8.0-15.0%; W: 0.5-2.0%; Mn: 0.2-2.0%; TiN: 0.1-1.5%; Y2O3: 0.1%-0.5%; C<=0.01%; and Fe: the balance. TiN and Y2O3 powders are synchronously added in the master alloy powder to carry out mechanical alloying, high-volume-fraction and dispersedly-distributed nano TiN and Y2O3 (or Y-Ti-O) composite reinforced precipitated phases are obtained, the ODS steel has excellent high-temperature strength, high thermal stability and strong neutron irradiation resistance, the tensile strength at room temperature is greater than or equal to 1500 MPa, the tensile strength at 700 DEG C is greater than or equal to 420 MPa, and the creep rupture life at 700 DEG C / 150 MPa is greater than or equal to 3000 h.

Description

Technical Field

[0001] This invention relates to the field of nuclear materials technology, specifically to a nano-titanium nitride and oxide composite reinforced ODS steel and its preparation method. Background Technology

[0002] Nuclear energy is a clean, low-carbon, and efficient new energy source. Actively developing nuclear energy is beneficial for solving problems such as environmental pollution and the limited supply of fossil fuels. Currently, the sustainability, economy, and safety of fourth-generation nuclear fission and fusion reactors have been significantly improved. However, fourth-generation nuclear fission reactor fuel cladding materials and fusion reactor breeder blanket structure materials face higher service temperatures, stronger doses of neutron radiation, more complex corrosive environments, and alternating loads compared to existing reactors. Traditional nuclear structural materials can no longer meet service requirements; therefore, the development of structural materials with excellent service performance is extremely important. Oxide dispersion strengthened (ODS) steel, with its high number density and dispersed distribution of nano-sized oxides (generally yttrium oxides), has a pinning effect on dislocations and grain boundary migration, greatly improving the material's high-temperature strength. Simultaneously, the numerous interfaces between the nano-precipitated phase and the matrix can serve as trapping sites for irradiation vacancies and interstitial atoms, giving ODS high resistance to radiation damage. Therefore, ODS steel has become one of the most promising nuclear structural materials.

[0003] ODS steel typically contains 0.1–0.2 wt% carbon, which is converted into M during tempering. 23 C6-type carbides precipitate at grain boundaries. However, numerous studies have shown that M... 23 C6 type carbides undergo aging and growth under long-term high-temperature (≥600℃) aging or creep conditions. These coarse carbides easily become crack initiation sites, significantly reducing the material's toughness and creep life. CN108893580A avoids this by reducing the carbon content to below 0.03%. 23 The precipitation of C6 carbides improves the aging problem. Simultaneously, by adding 0.02%–0.08% N, 0.15–0.30% V, and 0.10–0.15% Ta or Nb to the master alloy, highly thermally stable nitrides such as TaN, VN, or NbN are formed, appropriately mitigating the strength reduction caused by carbon reduction in the material. Since N, V, Ta, and other alloying elements are added during the master alloy smelting process, and N is a gas, increasing the N content in the melt and precisely controlling its content presents significant technological challenges. Especially when the N content exceeds 0.1%, special smelting processes such as high-pressure smelting are required.

[0004] like Figure 1As shown, compared to TaN, NbN, and VN, titanium nitride (TiN) has the lowest aging rate (Reference: Yong Qilong, Second Phase in Steel Materials. Beijing: Metallurgical Industry Press, 2006). On the other hand, TiN has a high melting point of 2950℃, higher than most transition metal nitrides; its Mohs hardness is 8-9, similar to diamond, and it exhibits good thermal shock resistance. If a high content of TiN exists in steel as a nanoscale second phase, it can significantly improve both the material's strength and impact toughness. Therefore, utilizing the excellent mechanical properties and high-temperature stability of TiN, and combining it with nano-Y2O3 (or Y-Ti-O) in conventional ODS steel for composite strengthening, can further improve the material's mechanical strength, long-term high-temperature thermal stability, and creep life. Simultaneously, the dispersed, fine-sized TiN and Y2O3 (or Y-Ti-O) can also improve the material's radiation resistance.

[0005] However, for steels prepared by conventional smelting methods (such as high-carbon chromium bearing steel), Ti readily combines with N during the smelting process to form large primary nitrides or inclusions. These large, hard, and brittle precipitates or inclusions easily lead to stress concentration during processing and become crack initiation points during service, severely impairing material properties. Therefore, high-content TiN is not suitable for addition via smelting. Summary of the Invention

[0006] In view of the above background, the purpose of this invention is to provide a nano-titanium nitride and oxide composite reinforced ODS steel and its preparation method, so that the material simultaneously has excellent high-temperature strength, high-temperature stability and resistance to strong neutron irradiation.

[0007] This invention is achieved through the following technical solution:

[0008] A nano-titanium nitride and oxide composite reinforced ODS steel, wherein the alloy composition of the ODS steel by mass percentage is: Cr: 8.0-15.0%; W: 0.5-2.0%; Mn: 0.2-2.0%; TiN: 0.1-1.5%; Y2O3: 0.1%-0.5%; C≤0.01%; Fe balance.

[0009] The aforementioned nano-titanium nitride and oxide composite reinforced ODS steel achieves excellent high-temperature strength, high-temperature stability, and resistance to strong neutron irradiation through composite reinforcement of high volume fraction, dispersed distribution, and nano-sized TiN and Y2O3 or Y-Ti-O precipitates.

[0010] The preparation method of the nano-titanium nitride and oxide composite reinforced ODS steel includes the following steps:

[0011] (1) Master alloy smelting: Add Cr, W, Mn, C and Fe elements to the raw materials according to the composition of ODS steel alloy to smelt the master alloy;

[0012] (2) Atomization powder preparation: The smelted master alloy is prepared into powder by gas atomization. The atomization process is protected by argon gas with a volume purity of 99.99%. The particle size of the atomized master alloy powder is ≤200μm.

[0013] (3) Mechanical ball milling: The atomized master alloy powder, TiN and Y2O3 powder are ball milled at high speed in a ball mill. The particle size of TiN powder is ≤1μm and the particle size of Y2O3 powder is ≤100nm. The ball milling atmosphere is argon gas with a volume purity of 99.99%. The ball-to-material mass ratio is (5~20):1. The ball milling time is 20~100h and the rotation speed is 150~500r / min.

[0014] (4) Vacuum degassing: The mechanically ball-milled alloy powder is loaded into a container for degassing. The vacuum pressure of the container is ≤10. -1 Pa, temperature 200–500℃, time 2–20h;

[0015] (5) Curing and molding: The alloy powder after vacuum degassing is cured and molded by hot isostatic pressing. The pressure is 100-200MPa, the temperature is 1000-1200℃, and the holding time is 1-10h.

[0016] (6) Thermomechanical processing: After solidification and molding, hot processing is carried out by any one or more of hot forging, hot rolling, and hot extrusion to improve the density and mechanical properties of the material; the initial hot processing temperature is 1100-1200℃ and the final hot processing temperature is 900-950℃.

[0017] (7) Heat treatment: After thermomechanical processing, normalizing and tempering heat treatment are carried out. The normalizing temperature is 1050~1200℃ and the holding time is 30~120min; the tempering temperature is 600~800℃ and the tempering time is 30~120min.

[0018] The method for preparing nano-titanium nitride and oxide composite reinforced ODS steel has the following properties: room temperature tensile strength ≥1500MPa, elongation ≥6%; 700℃ tensile strength ≥420MPa, elongation ≥10%; and creep rupture life ≥3000h at 700℃ / 150MPa.

[0019] The design concept of this invention is:

[0020] A novel ODS steel was obtained by introducing dispersed, fine, and high-density nano-sized TiN and Y2O3 (or Y-Ti-O) precipitates using powder metallurgy. TiN and Y2O3 powders were simultaneously added to the atomized master alloy powder for mechanical alloying, resulting in high volume fraction and dispersed distribution of nano-sized TiN and Y2O3 (or Y-Ti-O) composite reinforced precipitates. Through composite strengthening, a novel ODS steel was obtained, which also exhibits excellent high-temperature strength, high-temperature stability, and resistance to strong neutron irradiation.

[0021] The advantages and beneficial effects of this invention are:

[0022] 1) During mechanical ball milling, appropriate amounts of TiN and Y2O3 powders are added simultaneously. Through high-energy ball milling, they are fully dissolved in the matrix. During subsequent hot working and heat treatment, TiN and Y2O3 (or Y-Ti-O) are redeprecipitated at the nanoscale and dispersed. Through composite strengthening and dispersion strengthening, the material obtains high strength.

[0023] 2) The present invention achieves uniform precipitation of high-content TiN in steel at nanoscale size by adding TiN powder and mechanical ball milling. This solves the problem that the N content in smelting is difficult to exceed 0.1wt%, resulting in a limited number of nitrides. It also solves the problem that TiN easily forms large-size primary precipitates or inclusions during smelting, leading to high brittleness of the material.

[0024] 3) The general order of stability of precipitated phases is: oxides > nitrides > carbides. This invention strictly controls the carbon content, inhibits the precipitation of carbides, and avoids the performance degradation problem caused by high aging of carbide-containing materials.

[0025] 4) Compared with the addition of other NbN, TaN and VN to steel, the TiN precipitate used in this invention has a lower ripening rate, which effectively improves the long-term high-temperature stability of the material.

[0026] 5) The novel ODS steel prepared by this invention has a room temperature tensile strength ≥1500MPa, a 700℃ tensile strength ≥420MPa, and a creep rupture life ≥3000h at 700℃ / 150MPa, all of which exceed those of similar ODS steels currently available. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 A graph showing the ripening and growth rates of various carbides and nitrides;

[0029] Figure 2The table shows the room temperature tensile stress-strain curves of the titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. The horizontal axis represents strain, and the vertical axis represents stress (MPa).

[0030] Figure 3 The tensile stress-strain curve at 700℃ is shown for the titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. The horizontal axis represents strain and the vertical axis represents stress (MPa).

[0031] Figure 4 The image shows the EBSD-IPF of the titanium nitride and oxide composite reinforced ODS steel obtained in Example 1.

[0032] Figure 5 The image shows the TiN precipitate morphology of the titanium nitride and oxide composite reinforced ODS steel obtained in Example 1.

[0033] Figure 6 The image shows the morphology of the Y2O3 precipitate phase in the titanium nitride and oxide composite reinforced ODS steel obtained in Example 1.

[0034] Figure 7 The image shows the morphology of the large-size (1 μm) TiN inclusion phase in the material obtained in Comparative Example 1. Detailed Implementation

[0035] 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 embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0036] The present invention will be described in detail below through examples and comparative examples.

[0037] Example 1:

[0038] In this embodiment, a nano-titanium nitride and oxide composite reinforced ODS steel has an alloy composition of 11% Cr, 0.6% W, 1% Mn, 0.01% C, 0.3% Y2O3, 1.5% TiN, and the remainder being Fe.

[0039] The preparation process of the ODS steel is as follows:

[0040] (1) Master alloy smelting: Add Cr, W, Mn, C and Fe elements to the raw materials according to the requirements of ODS steel alloy composition to smelt the master alloy;

[0041] (2) Atomization powder preparation: The smelted master alloy is prepared into powder by gas atomization. The atomization process is protected by argon gas with a volume purity of 99.99%. The average particle size of the atomized master alloy powder is 140μm.

[0042] (3) Mechanical ball milling: 1.5% by mass of TiN powder with a size of 500 nm, 0.3% by mass of Y2O3 powder with a size of 100 nm, and atomized master alloy powder were ball milled at high speed in a planetary ball mill for 30 h. The ball-to-material mass ratio was 6:1, and the rotation speed was 300 r / min. Argon gas with a volume purity of over 99.99% was used for protection throughout the process to obtain alloy powder.

[0043] (4) Vacuum degassing: The mechanically alloyed powder is placed in a container for degassing at 300℃ for 2 hours. The vacuum pressure in the container is maintained at ≤3.2×10⁻⁶. -2 Pa;

[0044] (5) Curing and molding: The alloy powder is cured and molded by hot isostatic pressing at a pressure of 100MPa and a temperature of 1100℃ for 3 hours.

[0045] (6) Thermomechanical processing: After forming, hot rolling is carried out, and the rolling deformation is 50%;

[0046] (7) Heat treatment: After thermomechanical processing, normalizing and tempering heat treatment are performed. The normalizing process parameters are 1100℃ / 60min / air cooling to room temperature, and the tempering process parameters are 770℃ / 60min / air cooling to room temperature.

[0047] like Figure 2 The table shows the room temperature tensile stress-strain curve of the nano-titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. It can be seen that its room temperature tensile strength is 1520 MPa and its elongation is 6.5%.

[0048] like Figure 3 The figure shows the tensile stress-strain curve of the nano-titanium nitride and oxide composite reinforced ODS steel obtained in Example 1 at 700℃. It can be seen that the tensile strength at 700℃ is 438 MPa, and the elongation is 13%.

[0049] like Figure 4 The image shows the EBSD-IPF pattern of the nano-titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. It can be seen that its grain size ranges from 0.3 to 2 μm, with an average size of 0.6 μm.

[0050] like Figure 5 The image shows the morphology of the TiN precipitated phase in the nano-titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. It can be seen that the size of the TiN precipitated phase is 20–40 nm, and the number density is 3.0 × 10⁻⁶. 22 m -3 .

[0051] like Figure 6The image shows the morphology of the Y₂O₃ precipitate phase in the nano-titanium nitride and oxide composite reinforced ODS steel obtained in Example 1. It can be seen that the average size of the Y₂O₃ precipitate phase is 10 nm, and the number density is 4.1 × 10⁻⁶. 23 m -3 .

[0052] The nano-titanium nitride and oxide composite reinforced ODS steel obtained in this embodiment has a creep rupture life of 3560h at 700℃ / 150MPa.

[0053] Example 2:

[0054] In this embodiment, a nano-titanium nitride and oxide composite reinforced ODS steel is prepared with the following alloy composition by mass percentage: 13% Cr, 1% W, 0.8% Mn, 0.005% C, 0.4% Y₂O₃, 1.0% TiN, and the remainder being Fe. The preparation process is the same as in Example 1. The titanium nitride and oxide composite reinforced ODS steel obtained in this embodiment has a tensile strength and elongation of 1510 MPa and 7% at room temperature, respectively, a tensile strength and elongation of 429 MPa and 14% at 700℃, respectively, and a creep rupture life of 3218 h at 700℃ / 150 MPa.

[0055] Example 3:

[0056] In this embodiment, a nano-titanium nitride and oxide composite reinforced ODS steel has an alloy composition of 14% Cr, 0.5% W, 0.5% Mn, 0.008% C, 0.3% Y2O3, 1.2% TiN, and the remainder being Fe.

[0057] The preparation process of the nano-titanium nitride and oxide composite reinforced ODS steel is as follows:

[0058] (1) Master alloy smelting: Add Cr, W, Mn, C and Fe elements to the raw materials according to the requirements of ODS steel alloy composition to smelt the master alloy;

[0059] (2) Atomization powder preparation: The smelted master alloy is prepared into powder by gas atomization. The atomization process is protected by argon gas with a volume purity of 99.99%. The average particle size of the atomized master alloy powder is 30μm.

[0060] (3) Mechanical ball milling: 1.2% by mass of TiN powder with a size of 500 nm, 0.3% by mass of Y2O3 powder with a size of 90 nm, and atomized master alloy powder were ball milled at high speed in a planetary ball mill for 30 h. The ball-to-material mass ratio was 6:1, and the rotation speed was 400 r / min. Argon gas with a volume purity of over 99.99% was used for protection throughout the process to obtain alloy powder.

[0061] (4) Vacuum degassing: The mechanically alloyed powder is placed in a container for degassing at a temperature of 200℃ for 10 hours. The vacuum pressure in the container is maintained at 3.9 × 10⁻⁶. -2 Below Pa;

[0062] (5) Curing and molding: The vacuum-degassed alloy powder is cured and molded by hot isostatic pressing at a pressure of 110MPa, a temperature of 1100℃, and a holding time of 3h.

[0063] (6) Hot mechanical processing: Hot forging is carried out, with a deformation of 80%;

[0064] (7) Heat treatment: After thermomechanical processing, normalizing and tempering heat treatment are performed. The normalizing process parameters are 1150℃ / 60min / air cooling to room temperature, and the tempering process parameters are 800℃ / 120min / air cooling to room temperature.

[0065] Finally, the room temperature tensile strength and elongation of the titanium nitride and oxide composite reinforced ODS steel obtained in this embodiment are 1608 MPa and 6.0%, respectively. The tensile strength and elongation of the material at 700℃ are 450 MPa and 12%, respectively, and the creep rupture life at 700℃ / 150 MPa is 3847 h.

[0066] Comparative Example 1:

[0067] The method of adding TiN in this comparative example differs from that in Example 1. Ti and N alloying elements are added during the smelting of the master alloy, while the composition and other processes are the same as in Example 1. Figure 7 As shown, the results revealed that the material of Comparative Example 1 contained a large number of TiN inclusions with a size of about 1 μm, which is completely different from the TiN precipitates with a size of less than 50 nm in Example 1. Therefore, this will lead to a decrease in both the strength and plasticity of the material. The room temperature tensile strength and elongation of Comparative Example 1 were 1034 MPa and 3%, respectively, and the high temperature tensile strength and elongation at 700℃ were 260 MPa and 5%, respectively, while the creep rupture life at 700℃ / 150 MPa was only 891 h.

[0068] Comparative Example 2:

[0069] In this comparative example, no TiN powder was added during the smelting and ball milling of the master alloy. Only atomized master alloy powder and Y2O3 powder were added during ball milling. All other processes were the same as in Example 1. No nano-TiN precipitates were found in the material; the main reinforcement was Y2O3 dispersion. The room temperature tensile strength and elongation of Comparative Example 2 were 956 MPa and 12%, respectively. The high-temperature tensile strength and elongation at 700°C were 231 MPa and 18%, respectively, while the creep rupture life at 700°C / 150 MPa was 708 h.

Claims

1. A nano-titanium nitride and oxide composite reinforced ODS steel, characterized in that, The alloy composition of ODS steel, by mass percentage, is: Cr: 8.0~15.0%; W: 0.5~2.0%; Mn: 0.2~2.0%; TiN: 0.1~1.5%; Y2O3: 0.1%~0.5%; C≤0.01%; Fe balance; ODS steel has a room temperature tensile strength ≥1500 MPa and an elongation ≥6%; a 700 ℃ tensile strength ≥420 MPa and an elongation ≥10%; and a creep rupture life ≥3000 h at 700 ℃ / 150 MPa.

2. The nano-titanium nitride and oxide composite reinforced ODS steel according to claim 1, characterized in that, ODS steel achieves excellent high-temperature strength, high-temperature stability, and resistance to strong neutron irradiation through composite strengthening with high volume fraction, dispersed distribution, and nanoscale TiN and Y2O3 or Y-Ti-O precipitates.

3. The method for preparing nano-titanium nitride and oxide composite reinforced ODS steel according to claim 1 or 2, characterized in that, Includes the following steps: (1) Smelting of master alloy: Smelting master alloy by adding Cr, W, Mn, C and Fe elements according to the composition of ODS steel alloy; (2) Atomization powder preparation: The smelted master alloy is prepared into powder by gas atomization. The atomization process is protected by argon gas with a volume purity of 99.99%. The particle size of the atomized master alloy powder is ≤200 μm. (3) Mechanical ball milling: The atomized master alloy powder, TiN and Y2O3 powder are ball milled at high speed in a ball mill. The particle size of TiN powder is ≤1 μm and the particle size of Y2O3 powder is ≤100 nm. The ball milling atmosphere is argon gas with a volume purity of 99.99%. The ball-to-material mass ratio is (5~20):

1. The ball milling time is 20~100 h and the rotation speed is 150~500 r / min. (4) Vacuum degassing: The mechanically ball-milled alloy powder is loaded into a container for degassing. The vacuum pressure of the container is ≤10. -1 Pa, temperature 200–500 ℃, time 2–20 h; (5) Curing and molding: The alloy powder after vacuum degassing is cured and molded by hot isostatic pressing at a pressure of 100-200 MPa and a temperature of 1000-1200 ℃, and the holding time is 1-10 h. (6) Thermomechanical processing: After solidification and molding, hot forging, hot rolling, hot extrusion or any combination of two or more hot processing is used to improve the density and mechanical properties of the material; the initial hot processing temperature is 1100-1200 ℃ and the final hot processing temperature is 900-950 ℃. (7) Heat treatment: After thermomechanical processing, normalizing and tempering heat treatment are carried out. The normalizing temperature is 1050-1200 ℃ and the holding time is 30-120 min; the tempering temperature is 600-800 ℃ and the tempering time is 30-120 min.

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