CN102248171A - Gas atomization method for preparing oxygen supersaturated iron-based alloy powder - Google Patents

Abstract

The gas atomization preparation method of oxygen supersaturated iron-based alloy powder adopts the gas atomization method to prepare iron-based alloy powder. By comprehensively controlling the oxygen content of the atomization medium, atomization pressure and melt superheat, the alloy melt is processed at high speed Gas atomization, rapid cooling, introducing oxygen during the atomization process, and controlling the oxygen content of the atomized powder by controlling the oxygen content in the atomization gas, using the characteristics of rapid solidification of gas atomization to obtain high-concentration solid-dissolved oxygen , and high-concentration vacancies, preventing oxygen and alloy elements from forming stable oxides, providing high-purity and high-quality powder raw materials for the preparation of nanocluster reinforced alloys; the gas atomized iron-based alloy powder prepared by the present invention has an oxygen content of less than ≤ 1.00% The content is controllable within the range, no oxides are formed, and it is especially suitable for the preparation of iron-based alloy powders containing rare earth, Ti, Cr and other highly active alloying elements. The method has the advantages of simple preparation process, high production efficiency and low cost, and is suitable for large-scale production.

Description

Gas atomization preparation method of oxygen supersaturated iron-based alloy powder

technical field

The invention relates to a method for preparing gas-atomized iron-based alloy powder, in particular to a gas-atomized method for preparing oxygen-supersaturated iron-based alloy powder; it belongs to the technical field of metal powder material preparation.

Background technique

Oxide dispersion strengthened (ODS) alloy is an alloy (called ODS alloy) that uses ultrafine oxides with high thermal and chemical stability to strengthen the alloy matrix. It has both dispersion strengthening and precipitation strengthening. With multiple strengthening mechanisms, it has excellent high-temperature mechanical properties and oxidation resistance, good heat transfer and radiation swelling resistance, and is widely used in aero-engines, gas turbines, nuclear reactors, automobiles, glass and other fields. At present, ODS alloys are mainly prepared by mechanical alloying (MA) method to uniformly disperse oxide particles into the alloy powder matrix, and then obtain them after consolidation forming and subsequent treatment. Recently, in the study of MA/ODS alloys, it was found that nano-sized dispersion strengthening phases that exist in the form of clusters and have good high-temperature stability can significantly improve the service temperature and high-temperature creep resistance of high-temperature iron-based alloys. These strengthening phases are nano-clusters composed of specific atoms, which are highly dispersed in the alloy matrix, and the content and existence of oxygen play a key role in the formation of nano-clusters. At present, mechanical alloying powder is mainly used in the preparation of this alloy. The preparation process of alloy powder MA is to mix element powder (pure metal powder), intermediate alloy powder, and refractory compound powder such as _Y2O3 as a dispersed _phase , and then perform high-energy ball milling to synthesize alloy powder with uniform oxide dispersion [Zeng Delin. Powder metallurgy materials. Beijing: Metallurgical Industry Press, 1997]. Due to the inherent limitations of the MA grinding process, the MA method shows obvious deficiencies:

(1) Introducing impurities: During the mechanical alloying grinding process, solid impurities are introduced due to the long-term interaction between the alloy raw materials, grinding balls and grinding barrels, polluting the powder, and reducing the mechanical properties of the alloy;

(2) It is difficult to control the oxygen content: the oxygen content is controlled by the oxygen content of the raw material powder and the MA process. The MA technology introduces sufficient oxygen required to form dispersed oxides by adding oxides. The oxygen introduced from the raw material powder and the MA process will become impurities and reduce the performance of the alloy. Since MA powder making needs to control the oxygen content of the raw material powder and the oxygen increase in the MA process at the same time, it is difficult to control the oxygen content of the powder in the MA process;

(3) Long process cycle: To obtain alloy powders that are fully alloyed and have high thermal and chemical stability and uniformly dispersed hard oxides, it takes a long time for high-energy ball milling, long process cycle, low output, and low production efficiency. Large-scale industrial preparation brings difficulties;

(4) Poor repeatability: The size and dispersion of oxides are limited by the ball milling process and the original size of oxide raw materials, and the repeatability is poor, resulting in unstable alloy quality.

In addition to the MA method, currently suitable methods for preparing iron-based alloy powders include centrifugal atomization, water atomization, and gas atomization [Huang Peiyun, Principles of Powder Metallurgy, Beijing: Metallurgical Industry Press, 2000]. Centrifugal atomization method is to use centrifugal force to break metal melt, and throw it out as atomized liquid droplets and solidify it into powder particles. The cost of the bar is high, the prepared powder is relatively coarse, the cost is high, the production efficiency is low, the energy consumption is high, and the oxygen content cannot be adjusted by atomization. The water atomization method is to use high-pressure water flow to crush and cool the molten metal fluid to prepare powder. It is a widely used low-cost powder making method at present, but the prepared powder has low purity and irregular particle shape, especially for alloys. When the active elements such as RE, Ti, Zr, Cr, V etc. are contained in the powder, these elements will react with water or water vapor, xMe+yH ₂ O=M _x O _y +yH ₂ (↑), on the powder surface Difficult-to-reduce oxides are formed, and the oxygen content cannot be controlled. These oxides will form the original grain boundaries in the subsequent consolidation forming process and reduce the mechanical properties of the alloy. Gas atomization is currently the main method used to prepare high-purity alloy powders, especially an important method for preparing low-oxygen or oxygen-free powders. Exist in the form of oxides, reducing the performance of the alloy.

There are no relevant research reports at home and abroad on the gas atomization preparation method of oxygen supersaturated iron-based alloy powder.

Contents of the invention

The object of the present invention is to provide a gas atomization preparation of oxygen supersaturated iron-based alloy powder in which oxygen exists in a supersaturated form in the prepared iron-based alloy powder, which is simple in process, high in production efficiency, low in cost, suitable for large-scale production method.

The gas atomization preparation method of oxygen supersaturated iron-based alloy powder of the present invention comprises the following steps:

The first step: ingredients, smelting

According to the designed iron-based alloy composition, the pure metal or intermediate alloy of each component is used to prepare the alloy raw material; after vacuum heating and melting, it is filled with a protective atmosphere; the vacuum degree is above 10 ^-1 Pa;

Step 2: Atomization

The alloy melt obtained in the first step is placed in an atomizing bag and heated to 100°C to 150°C above the melting point of the alloy; after uniform temperature, atomization is carried out; the atomizing gas used is argon containing oxygen; the atomizing gas pressure 2MPa ~ 6MPa; atomization gas injection speed 2Mach ~ 4Mach;

The third step: take powder

After the atomization is completed, the container containing the powder is removed, sieved in the glove box, and packaged to obtain the oxygen supersaturated iron-based alloy powder.

In the present invention, the atomization is carried out by a close-coupled atomization device, and the structural parameters of the close-coupled atomization device are air outlet area S=30mm ² , spray angle α=50°, catheter outer diameter D=12mm, The shape of the catheter is cylindrical, the diameter of the metal liquid flow is d=4mm, and the length L of the catheter protruding from the air outlet of the atomizing nozzle is 2.1-2.3mm.

In the present invention, the iron-based alloy powder is a Fe-Cr-Ti-W-Y alloy.

In the present invention, the volume content of oxygen in the oxygen-containing argon gas is 1.0-2.0 times of the oxygen content of the designed alloy powder.

In the present invention, after the atomization bag is preheated to 100° C. to 150° C. above the melting point of the alloy, the alloy melt is placed therein.

In the present invention, the atomization temperature is 100°C to 150°C above the melting point of the alloy.

The oxygen content and X-ray diffraction phase analysis of the iron-based alloy powder prepared by the invention shows that the oxygen content of the obtained iron-based alloy powder is 60-70% of the oxygen content in the atomizing gas and has no oxide.

Mechanism of the present invention is briefly described below:

The formation process of metal oxide is the process completed by the reaction formula xMe+yO=M _x O _y , including gas-phase oxygen molecules colliding with metals, oxygen molecules form physical adsorption with metals by van der Waals force, oxygen molecules decompose into oxygen atoms and bond with matrix metals. Free electrons interact to form four stages of chemisorption or dissolution and oxide formation [Li Tiefan. Metal high temperature oxidation and thermal corrosion. Beijing: Chemical Industry Press, 2003]. This is a kinetic process, and oxygen does not form oxides when the process is time-controlled and cannot be completed. According to the phase diagram, the solubility of oxygen can reach 0.010wt% under the pressure of 0.1MPa in the iron melt at 1528℃～2000℃ [T B Massalski, H Okamoto, P R Subramanian, L Kacprazak. Binary Alloy Phase Diagrams. ASM International, 1990 ], it can be predicted that the solubility of oxygen (from the atomization medium) in the iron melt will be significantly improved under the atomization pressure of 3MPa～6MPa. When the iron alloy melt is rapidly solidified to room temperature by the high-speed gas atomization method, the oxide It is too late to complete the formation process, and the high-concentration dissolved oxygen in the melt will rapidly cool down to room temperature with the melt to form an oxygen supersaturated solid solution. At the same time, the high-concentration vacancies in the melt will also remain at room temperature, forming high-concentration vacancies in the solid alloy .

G S Painter，X Q Chen.Phys Rev Lett 99(2007)225502]，而氩气雾化的冷却速度高(大于10⁵k/s)，可以将具有高浓度空位的铁基合金熔体快速冷却到室温，并保持高浓度的空位。在这种用氩气雾化制备的具有高浓度空位的铁基合金体系中，氧主要以三种方式存在：一部分氧以过饱和状态固溶于合金基体中；由于O-空位对的形成能低，一部分氧以O-空位对的方式存在；其余的氧形成O-Y对、O-Ti对，或以其它方式存在。因此，采用高压高速气体雾化，可以有效防止铁基合金中的氧与合金元素生成氧化物。In iron-based alloys, the formation energy of O-vacancy pairs is lower than that of OY pairs and O-Ti pairs [CL Fu, M

G S Painter, X Q Chen. Phys Rev Lett 99(2007) 225502], and the cooling rate of argon atomization is high (greater than 10 ⁵ k/s), which can rapidly cool the iron-based alloy melt with high concentration of vacancies to room temperature , and maintain a high concentration of vacancies. In this iron-based alloy system with a high concentration of vacancies prepared by argon atomization, oxygen mainly exists in three ways: a part of oxygen is solid-dissolved in the alloy matrix in a supersaturated state; due to the formation energy of O-vacancy pairs Low, part of the oxygen exists in the form of O-vacancy pairs; the rest of the oxygen forms OY pairs, O-Ti pairs, or exists in other ways. Therefore, the use of high-pressure and high-speed gas atomization can effectively prevent the oxygen and alloy elements in the iron-based alloy from forming oxides.

The atomizing gas pressure of the present invention is 3MPa-6MPa, and the gas velocity will reach 2Mach-4Mach in the atomizing region of the close-coupled atomizing device. Control the gas velocity by controlling the atomizing gas pressure.

The present invention has following advantage and positive effect:

The invention adopts the gas atomization method to prepare the iron-based alloy powder, and performs high-speed gas atomization and rapid cooling on the alloy melt by comprehensively controlling the oxygen content of the atomization medium, the atomization pressure, and the superheat of the melt. Oxygen is introduced to control the oxygen content of the atomized powder by controlling the oxygen content in the atomized gas. Using the characteristics of rapid solidification of gas atomization, a high concentration of solid solution oxygen and a high concentration of vacancies are obtained to prevent the formation of oxygen and alloy elements. Stable oxides provide high-purity and high-quality powder raw materials for the preparation of nano-cluster reinforced alloys; especially iron-based alloy powders containing highly active alloying elements such as RE, Ti, and Cr. The present invention has the following advantages:

(1) The prepared iron-based alloy powder has high purity and no impurities introduced by mechanical ball milling;

(2) The oxygen content of the prepared iron-based alloy powder is controllable, which can effectively prevent oxygen from forming stable oxides with alloy components, and provide the necessary oxygen conditions for the precipitation of uniformly dispersed nano-oxides in the subsequent process;

(3) It can provide a high concentration of vacancies, which provides the necessary conditions for the formation of nano-cluster strengthening phases when sintering and preparing iron-based alloys;

(4) The prepared iron-based alloy powder has good sphericity, which is beneficial to consolidation and forming;

(5) The preparation process is simple, the production efficiency is high, the cost is low, and it is suitable for large-scale production.

In summary, the present invention provides a gas atomized iron-based alloy powder oxygen content and its existence mode control method, which can provide high-quality powder raw materials for the preparation of high-performance nano-cluster reinforced iron-based alloys. The method is simple and easy, It can realize large-scale and low-cost preparation.

Description of drawings:

Accompanying drawing 1 is the relationship curve between the oxygen content of the iron-based alloy powder and the oxygen content in the atomizing gas established by the present invention.

Accompanying drawing 2 is the morphology of the iron-based alloy powder prepared in Example 1 of the present invention.

Accompanying drawing 3 is the oxygen distribution of the iron-based alloy powder prepared in Example 1 of the present invention with an average oxygen content of 0.31%wt and a particle size of 75-150, 45-75, <45 μm.

Accompanying drawing 4 is the X-ray phase analysis result of the iron-based alloy powder prepared in Examples 1 and 2 of the present invention.

Curve 1 in accompanying drawing 3 is the distribution of oxygen in iron-based alloy powders with a particle size of <45 μm, curve 2 is the distribution of oxygen in iron-based alloy powders with a particle size of 45-75 μm, and curve 3 is the distribution of iron with a particle size of 75-150 μm Oxygen distribution of base alloy powder

Curve 1 in accompanying drawing 4 is the X-ray physical phase analysis result of the iron-based alloy powder of oxygen content 0.31%wt, does not appear oxide peak; Curve 2 is the X-ray physical phase analysis of the iron-based alloy powder of oxygen content 1.06%wt As a result, no oxide peak appeared; Curve 3 is the X-ray phase analysis result of the iron-based alloy powder with an oxygen content of 0.31%wt after heating and oxidation, and an oxygen content of 0.83%wt, and an oxide peak appeared.

According to the energy spectrum analysis results of accompanying drawing 3, it shows that the distribution of oxygen in the prepared powder is relatively uniform.

According to the XRD phase analysis results of accompanying drawing 4, the iron-based alloy powders prepared in Example 1 and Example 2 do not have oxide diffraction peaks, indicating that in the prepared powders, oxygen is mainly dissolved in the powder matrix.

Detailed ways

The present invention adopts the gas atomization method to prepare various alloy powders with controllable oxygen content and no oxide formation. The present invention will be further described in conjunction with typical examples below.

Example 1: Preparation of Fe-14.15Cr-0.50Ti-3.19W-0.25Y iron-based alloy powder with an oxygen content of 0.31%

Get pure metal, intermediate alloy preparation alloy raw material according to alloy composition requirement; According to alloy oxygen content requirement, determine to adopt the argon that contains 0.45% (volume ratio) oxygen as atomization medium according to accompanying drawing 1; In the melting crucible coupled with the atomization equipment, the vacuum degree is pumped to above 10 ^-1 Pa, and then filled with a protective atmosphere for melting, and at the same time, the atomization package is heated to 1600°C for heat preservation; when the alloy is completely alloyed, the alloy melt After the temperature is adjusted to 120°C-130°C above the melting point of the alloy and stabilized, the melt is poured into the atomization bag, and the atomization gas valve is opened for atomization; the atomization is carried out in a close-coupled atomization device, and the structural parameters of the atomization device It is: air outlet area S=30mm ² , spray angle α=50°, outer diameter of catheter tube D=12mm, shape of catheter tube is cylindrical, diameter of metal liquid flow d=4mm, extension of catheter tube is 2.1～2.3mm; the atomizing gas pressure used is 3.5MPa; after the atomization is completed, remove the container containing the powder at the bottom of the atomization device, sieve and package in the glove box, and test the oxygen content, X According to the X-ray diffraction phase analysis, the iron-based alloy powder with an oxygen content of 0.31% and no oxide is obtained.

Example 2: Preparation of Fe-14.13Cr-0.48Ti-3.01W-0.36Y iron-based alloy powder with an oxygen content of 1.06%

According to alloy oxygen content requirement, according to accompanying drawing 1, determine to adopt the argon gas that contains 1.80% (volume ratio) oxygen as atomization medium, then according to the method and step of example 1, prepare the iron that oxygen content is 1.06%, oxide-free Base alloy powder, the atomizing gas pressure used is 4.0MPa.

Example 3: Preparation of Fe-12.35Cr-0.49Ti-2.5W-0.25Y iron-based alloy powder with an oxygen content of 0.41%

According to alloy oxygen content requirement, according to accompanying drawing 1, determine to adopt the argon gas that contains 0.60% (volume ratio) oxygen as atomizing medium, then according to the method and step of example 1, prepare the iron that oxygen content is 0.41%, oxide-free Base alloy powder, the atomizing gas pressure used is 5.5MPa.

Claims (6)

1. The gas atomization preparation method of oxygen supersaturated iron-based alloy powder, comprising the following steps: The first step: ingredients, smelting According to the designed iron-based alloy composition, the pure metal or intermediate alloy of each component is used to prepare the alloy raw material; after vacuum heating and melting, it is filled with a protective atmosphere; the vacuum degree is above 10 ^-1 Pa; Step 2: Atomization The alloy melt obtained in the first step is placed in an atomizing bag and heated to 100°C to 200°C above the melting point of the alloy; after uniform temperature, atomization is carried out; the atomizing gas used is argon containing oxygen; the atomizing gas pressure 3MPa～6MPa; The third step: take powder After the atomization is completed, the container containing the powder is removed, sieved in the glove box, and packaged to obtain the oxygen supersaturated iron-based alloy powder. 2. The gas atomization preparation method of oxygen supersaturated iron-based alloy powder according to claim 1, characterized in that: the atomization is carried out by a close-coupled atomization device, and the structural parameter of the close-coupled atomization device is air flow Outlet area S=30mm ² , injection angle α=50°, outer diameter of catheter tube D=12mm, shape of catheter tube is cylindrical, diameter of metal liquid flow d=4mm, extension of catheter tube (catheter tube The length protruding from the air outlet end of the atomizing nozzle) L = 2.1-2.3 mm. 3. The gas atomization preparation method of oxygen supersaturated iron-based alloy powder according to claim 1, characterized in that: the volume content of oxygen in the oxygen-containing argon gas is 1.0-2.0% of the oxygen content of the designed alloy powder times. 4. The gas atomization preparation method of oxygen supersaturated iron-based alloy powder according to claim 1, characterized in that: after the atomization bag is preheated to 100°C-150°C above the melting point of the alloy, the alloy melt is placed in it. 5 . The gas atomization preparation method of oxygen supersaturated iron-based alloy powder according to claim 1 , characterized in that: the atomization temperature is 100° C. to 150° C. above the melting point of the alloy. 6. The gas atomization preparation method of oxygen supersaturated iron-based alloy powder according to any one of claims 1-5, characterized in that: the iron-based alloy powder is a Fe-Cr-Ti-W-Y alloy.

Images