Carbide-oxide composite dispersion strengthened steel and preparation method thereof

Abstract

The invention provides carbide-oxide composite dispersion strengthened steel and a preparation method thereof. ZrC nanopowder smaller than 30 microns is added into pre-alloyed iron powder, and by controlling the volume fraction of Ar gas in a ball-milling protective atmosphere, spark plasma sintering is adopted for consolidation to obtain the alloy steel synergistically strengthened by carbides and oxides. Raw materials of the steel comprise the following elements in percentage by mass: 0.150% < = C < = 0.170%, 10.00% < = Cr < = 11.08%, 0.90% < = W < = 1.30%, 0.32% < = V < = 0.34%, 0.15% < = Ta < = 0.25%, 1.30% < = Zr < = 1.50%, 0.65% < = Mn < = 0.67%, 0.49% < = Si < = 0.54%, 0.030% < = O < = 0.060%, less than 0.015% of P, less than 0.015% of S and the balance of Fe matrix. On the premise that good tensile strength / yield strength of the dispersion strengthened steel is guaranteed, the ductility, high-temperature creep resistance and high-temperature thermal stability of the dispersion strengthened steel are further improved, and the dispersion strengthened steel is suitable for being used as a structural material for a fourth-generation advanced nuclear reactor.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, specifically relating to a carbide-oxide composite dispersion-strengthened steel and its preparation process. It is an effective process for improving the strength-elongation ratio, high-temperature creep resistance, and high-temperature thermal stability of dispersion-strengthened steel. Background Technology

[0002] With the development of nuclear energy, the emergence of fourth-generation nuclear reactor technology has facilitated the progress of human society, but the safety issues involved cannot be ignored. The reliability and stability of structural materials are crucial to the economic advantages of fourth-generation nuclear reactors. They typically face harsh operating conditions such as high temperature, high pressure, and neutron irradiation, and must also withstand corrosion from high-velocity, high-density liquid coolants. Currently, the commonly used structural materials in nuclear reactors are austenitic stainless steel and ferritic / martensitic steel. However, austenitic stainless steel is prone to radiation swelling in irradiated environments, while the high-temperature mechanical properties of ferritic / martensitic steel are insufficient to meet the operating requirements of advanced nuclear reactors. In recent years, nanoparticle dispersion-strengthened steel has attracted much attention from scholars.

[0003] Nanoparticle dispersion-strengthened steel refers to alloy steel in which high-thermal-stability, high-hardness, and high-melting-point nano-oxide, carbide, or nitride particles are added to a metal matrix material through powder metallurgy. This dispersion strengthening enhances the matrix and significantly improves high-temperature mechanical properties. ODS steel with added Y₂O₃ is the most common example. In ODS steel, the Y₂O₃ content is typically 0.20-0.50 wt.%. Adding too much Y₂O₃ can lead to the formation of insoluble amorphous Y₂O₃ nanoparticles in the matrix, which not only hinders further strength improvement but also deteriorates plasticity. Furthermore, excessive oxygen can cause the formation of coarse oxide particles in the steel. These oxide particles contribute very little to strength but are prone to forming crack initiation sites. Adding nano-ZrC, compared to Y₂O₃, can more significantly reduce the particle size of the dispersed phase, decrease the area fraction of coarse phase particles, and improve the room temperature and high-temperature strength of dispersion-strengthened steel, achieving good high-temperature creep resistance and high-temperature thermal stability. However, achieving a balance between strength and plasticity remains a challenge.

[0004] Therefore, it is crucial to design the elemental composition of steel and optimize the preparation process to obtain a dispersion-strengthened steel that simultaneously possesses good high-temperature mechanical properties, a good strength-plasticity balance, resistance to high-temperature creep, and high-temperature thermal stability. Summary of the Invention

[0005] The purpose of this invention is to use dispersion-strengthened steel as a base, and through optimized composition and preparation process, to enable the in-situ precipitation of nano-oxide particles in the dispersion-strengthened steel, and to introduce a large number of dispersed nano-carbide particles, so as to achieve a synergistic strengthening effect, overcome the problem of strength-plasticity matching, and further improve the high-temperature mechanical properties of steel.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The elements in the raw materials of dispersion-strengthened steel, by mass percentage, are as follows: 0.150%≤C≤0.170%, 10.00%≤Cr≤11.08%, 0.90%≤W≤1.30%, 0.32%≤V≤0.34%, 0.15%≤Ta≤0.25%, 1.30%≤Zr≤1.50%, 0.65%≤Mn≤0.67%, and 0.49%≤Si≤0.54%. 0.030%≤O≤0.060%, P<0.015%, S<0.015%, balance is Fe matrix and unavoidable impurities; C is an indispensable element for the formation of martensite in steel; Cr can improve the corrosion resistance and high-temperature creep resistance of steel; Si and Mn have significant solid solution strengthening effects and are indispensable elements in dispersion-strengthened steel; The addition of nano ZrC not only retains ZrC nanoparticles in the steel, but also introduces Zr, which precipitates in situ with O during ball milling and sintering, synergistically achieving a strength-plasticity balance in steel.

[0008] Preferably, the alloying elements of the steel, by mass percentage, include: 0.163% C, 10.64% Cr, 1.11% W, 0.34% V, 0.20% Ta, 0.66% Mn, 0.52% Si, 1.34% Zr, 0.48% O, P < 0.015%, S < 0.015%, with the balance being Fe matrix.

[0009] This invention relates to the preparation of the aforementioned dispersion-strengthened steel. It mainly includes the following steps:

[0010] (1) In a high-energy planetary ball mill, the ball milling was completed with the following parameters: the ball milling speed was 350 rpm, the ball milling time was 50 h, the ball-to-material ratio was 10:1, and the filling rate was 40%.

[0011] (2) The ball-milled powder was solidified by spark plasma sintering (SPS) at a sintering temperature of 1050°C, a sintering heating rate of 100°C / min, a holding time of 5 minutes after reaching the temperature, and an axial pressure of 50 MPa.

[0012] (3) First, the sintered steel is hot rolled three times at 1100±10℃, with a total deformation of 18%.

[0013] (4) Then keep it at 1100±10℃ for 60 minutes, take it out of the furnace and place it in water to cool to room temperature (quenching).

[0014] (5) Then reheat to 700±10℃ and hold for 90 minutes, and finally cool to room temperature in air (tempering).

[0015] The present invention provides a process for preparing dispersion-strengthened steel with good strength-plasticity balance, high-temperature creep resistance and high-temperature thermal stability. The characteristic is that carbides are directly added through powder metallurgy, and nano-oxides are formed in situ during ball milling or sintering, which achieves a synergistic strengthening effect of carbide and oxide dispersion phase particles, so that the carbide-oxide composite dispersion-strengthened steel of the present invention has good mechanical properties. Attached Figure Description

[0016] The present invention will now be further described with reference to the accompanying drawings.

[0017] Figure 1 This is a flowchart illustrating the preparation process described in an embodiment of the present invention;

[0018] Figure 2 and Figure 3 This is a scanning electron microscope image as described in the embodiment of this discovery. Detailed Implementation

[0019] The following detailed description, in conjunction with specific embodiments, further illustrates the carbide-oxide composite dispersion-strengthened steel and its production method of the present invention. The embodiments described below are exemplary and intended to illustrate the invention, and should not be construed as limiting the invention.

[0020] This invention proposes a carbide-oxide composite dispersion-strengthened steel and its preparation process. The mass percentages of each alloying element in the steel are as follows: 0.150%≤C≤0.170%, 10.00%≤Cr≤11.08%, 0.90%≤W≤1.30%, 0.32%≤V≤0.34%, 0.15%≤Ta≤0.25%, 1.30%≤Zr≤1.50%, 0.65%≤Mn≤0.67%, and 0.49%≤Si≤0.54%. 0.030%≤O≤0.060%, P<0.015%, S<0.015%, balance is Fe matrix and unavoidable impurities; C is an indispensable element for the formation of martensite in steel; Cr can improve the corrosion resistance and high-temperature creep resistance of steel; Si and Mn have significant solid solution strengthening effects and are indispensable elements in dispersion-strengthened steel; The addition of nano ZrC not only retains ZrC nanoparticles in the steel, but also introduces Zr, which precipitates in situ with O during ball milling and sintering, synergistically achieving a strength-plasticity balance in steel.

[0021] According to an embodiment of the present invention, the mass percentage of each alloying element in the selected dispersion-strengthened steel is as follows: 0.163% C, 10.64% Cr, 1.11% W, 0.34% V, 0.20% Ta, 0.66% Mn, 0.52% Si, 1.34% Zr, 0.48% O, P < 0.015%, S < 0.015%, with the remainder being Fe and unavoidable impurities.

[0022] For this dispersion-strengthened steel, the present invention proposes a novel preparation process, the flowchart of which is shown below. Figure 1 As shown, the following refers to specific embodiments.

[0023] Example

[0024] (1) The pre-alloyed powder of the present invention is prepared by aerosol method.

[0025] (2) Add the pre-alloyed iron powder and nano ZrC powder to the ball mill jar in a ratio of 100:1.5 and purge with argon gas.

[0026] (3) The powder from step (2) is ball-milled with a ball milling speed of 350 rpm, a ball milling time of 50 h, a ball-to-material ratio of 10:1, and a filling rate of 40%.

[0027] (4) The ball mill powder obtained in step (3) is solidified by spark plasma sintering (SPS) and heated to 1050°C at an axial pressure of 50 MPa and a rate of 100°C / min.

[0028] (5) After reaching 1050℃, hold for 5 minutes, then cool with the furnace to room temperature to obtain a cylindrical sintered steel with a height of 10mm and a diameter of 20mm.

[0029] (6) The sintered steel is hot rolled three times at 1100±10℃, with a total deformation of 18%.

[0030] (7) Keep at 1100±10℃ for 60 minutes, remove from the furnace and place in water to cool to room temperature to complete the quenching.

[0031] (8) Reheat to 700±10℃ and hold for 90 minutes, then cool to room temperature in air to complete the tempering.

[0032] Evaluation indicators:

[0033] The scanning electron microscope microstructure of the carbide-oxide composite dispersion-strengthened steel obtained by the above-described embodiments is shown in the figure. Figure 2 and Figure 3 .Depend on Figure 2 and Figure 3It can be seen that the grain size of the dispersion-strengthened steel is significantly refined after being pinned by nanoparticles, with an average grain size of 0.81±0.25μm. In the examples, the main nanoparticles in the dispersion-strengthened steel are nano-oxides and nano-carbides, which achieve synergistic strengthening of the dispersion-strengthened steel.

[0034] Mechanical property testing:

[0035] The mechanical properties at room temperature and high temperature were determined according to GB / T228.1-2010 "Metallic materials - Tensile testing - Part 1: Test method at room temperature" and GBT 4338-2006 "Metallic materials - Tensile testing method at high temperature".

[0036] Measurement results:

[0037] At room temperature, the tensile strength reaches 1608 MPa, the yield strength reaches 1373 MPa, and the elongation after fracture is 11.9%.

[0038] At 600℃, the tensile strength reaches 987MPa, the yield strength reaches 844MPa, and the elongation after fracture is 12.2%.

[0039] At 700℃, the tensile strength reaches 522MPa, the yield strength reaches 470MPa, and the elongation after fracture is 13.7%.

[0040] It should be noted that, according to the above embodiments of the present invention, those skilled in the art can fully implement the entire scope of claim 1 and the dependent claims of the present invention, and the implementation process and method are the same as those in the above embodiments. Furthermore, the parts of the present invention not described in detail belong to known technologies in the art. The above description is merely a part of specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbide-oxide composite dispersion-strengthened steel, characterized in that, The mass percentages of each alloying element in the steel are as follows: 0.150%≤C≤0.170%, 10.00%≤Cr≤11.08%, 0.90%≤W≤1.30%, 0.32%≤V≤0.34%, 0.15%≤Ta≤0.25%, 1.30%≤Zr≤1.50%, 0.65%≤Mn≤0.67%, and 0.49%≤Si≤0.54%. 0.030%≤O≤0.060%, P<0.015%, S<0.015%, the balance being Fe matrix and unavoidable impurities, the preparation method of this carbide-oxide composite dispersion-strengthened steel is characterized by the following steps: (1) ball milling is completed in a high-energy planetary ball mill with the following parameters: ball milling speed is 350 rpm, ball milling time is 50 h, ball-to-material ratio is 10:1, and filling rate is 40%; (2) the powder after ball milling is sintered by spark plasma (SP). S) Consolidation, using a sintering temperature of 1050°C, a sintering heating rate of 100°C / min, a holding time of 5 minutes after reaching the temperature, and an axial pressure of 50MPa; (3) First, the sintered steel is hot rolled three times at 1100±10°C, with a total deformation of 18%; (4) Then, it is held at 1100±10°C for 60 minutes, then removed from the furnace and placed in water to cool to room temperature; (5) Subsequently, it is reheated to 700±10°C and held for 90 minutes, and finally cooled to room temperature in air.

2. The carbide-oxide composite dispersion-strengthened steel according to claim 1, characterized in that, The mass percentages of each alloying element are as follows: 0.16% C, 10.64% Cr, 1.11% W, 0.34% V, 0.20% Ta, 0.66% Mn, 0.52% Si, 1.34% Zr, 0.48% O, P < 0.015%, S < 0.015%, with the balance being matrix Fe and unavoidable impurities.

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