CN102127672A - Method for preparing iron-base superalloy by extrusion forming of gas atomized powder - Google Patents

Abstract

A method for preparing nanophase-strengthened iron-based superalloys by extrusion molding of gas-atomized powders, using gas-atomized iron-based alloy powders with a particle size of ≤200 μm and an oxygen content of 0.05% to 0.20% (mass fraction) instead of mechanically alloyed powders , put into the ladle, degas at 100℃～300℃, vacuum degree of 10 ^-2 Pa, seal and weld the package, extrude at 850℃～1250℃, the extrusion ratio is (6～15):1, extrusion After the pressed bar is deformed and heat-treated, an iron-based superalloy with a nano-cluster strengthening phase is obtained. The invention has simple technological process, low cost, high purity of prepared alloy, no alloy pollution caused by mechanical alloying powder, density reaches 99%, room temperature strength σ _b ≥ 1200MPa, plasticity δ ≥ 8% after heat treatment; strength at 850°C σ _b ≥ 100MPa; high production efficiency, low cost, suitable for large-scale preparation of iron-based superalloys with nano-cluster strengthening phase.

Description

A method for preparing iron-based superalloy by gas atomized powder extrusion forming

technical field

The invention relates to a method for preparing nano-cluster reinforced iron-based high-temperature alloy by extrusion molding of gas atomized powder. It belongs to the field of metal materials.

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. A strengthening mechanism, with excellent high-temperature mechanical properties and oxidation resistance, is a class of high-performance powder metallurgy superalloys. At present, the preparation of oxide dispersion strengthened alloy is mainly obtained by mechanical alloying (MA) method to uniformly disperse ultrafine oxide particles into the alloy powder matrix, and then obtain it after consolidation forming and subsequent treatment.

Recently, in the study of mechanically alloyed oxide dispersion strengthened alloys (MA/ODS), it was found that the comprehensive properties of a few oxide dispersion strengthened iron-based alloys prepared by mechanical alloying have been greatly improved, and the service temperature has increased from 550 °C to 550 °C. The creep resistance at high temperature of 600-850°C is also greatly improved at 850°C. Analysis of its ultrastructure found that in the matrix of this iron-based alloy, there is a dispersion strengthening phase with a size of tens of nanometers, which has extremely high high-temperature stability, which is the reason for the substantial improvement in the performance of the iron-based alloy. Further analysis found that this strengthening phase exists in the form of nano-clusters enriched in elements such as Y, Ti and O, and is highly dispersed in the alloy matrix. This powder metallurgy iron-based superalloy developed on the basis of ODS alloys with nano-clusters as strengthening units has both the high strength and high oxidation resistance of oxide dispersion-strengthened superalloys and the high ductility and high strength of precipitation-strengthened superalloys. Toughness, good heat transfer performance and radiation swelling resistance, has broad application prospects in aero-engines, gas turbines, nuclear reactors, automobiles, glass and other industries, and is an important structural material for the development of fourth-generation nuclear reactors.

At present, the research on nanocluster-strengthened iron-based superalloys is in its infancy, and its preparation method mainly uses mechanical alloying (MA) alloy powder, which is prepared by thermal consolidation forming, subsequent deformation processing and heat treatment. First, the mechanical alloying (MA) method is used to mix element powder (pure metal powder), intermediate alloy powder, and refractory oxide particles such as Y ₂ O ₃ as a dispersed phase, and after a long time of high-energy ball milling, the synthetic oxide is dispersed Uniform alloy powder [Zeng Delin. Powder metallurgy materials. Beijing: Metallurgical Industry Press, 1997]. Due to the inherent limitations of the grinding process of the MA preparation process, this method has the following disadvantages: (1) The introduction of 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 , Contaminate the powder, reduce the mechanical properties of the alloy; (2) Oxygen content control is difficult: 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 seriously reduce the properties of the alloy. Since the MA powder 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) The process cycle is long: it is necessary to obtain a fully alloyed hard material with high thermal and chemical stability. Alloy powder with evenly dispersed oxides requires long-term high-energy ball milling, long process cycle, low output, and low production efficiency, which brings difficulties to large-scale industrial preparation; (4) Poor repeatability: the size and dispersion of oxides are restricted by The ball milling process and the original size of the oxide raw material have poor repeatability, resulting in unstable alloy quality.

Secondly, the current thermal consolidation forming methods are mainly aimed at hot isostatic pressing, hot pressing sintering or molding-sintering, deformation processing and other processes of mechanically alloyed alloy powders. For example:

Chinese patent CN200810021329.0, oxide dispersion strengthened low-activation martensitic steel material and its preparation method, discloses a composition (mass fraction) of 8.5-9.5% Cr, 1.3-1.7% W, 0.15-0.25% V, 0.12-0.18% Ta, 0.4.-0.5.Mn, 0.08-0.12% C, 0.1.-0.50% Ti, 0.2-0.5% Y ₂ O ₃ , the balance is Fe oxide dispersion strengthened low activation martensitic steel The material preparation method uses mechanical alloying powder, hot isostatic pressing at 1323~1473k/100~200MPa/2~5h or hot pressing sintering at 1323~1573k/40~70MPa/2~5h to prepare green body, and then hot Extrusion or forging, hot rolling and other processing and forming processes to prepare the required materials.

Chinese patent CN200910083638.5, a method for preparing oxide dispersion strengthened austenitic stainless steel, discloses a mechanical alloying preparation composition (mass fraction) 17-19% Cr, 7-9% Ni, 1.5-2.5 %W, 0.5-1.0% Ti, 0.3-0.6% Y ₂ O ₃ , the balance being Fe oxide dispersion strengthened stainless steel powder, a method for preparing oxide dispersion strengthened stainless steel by hot pressing and sintering at 1200°C/80MPa/2h.

U.S. Patent 5032190, ODS iron-based alloy plate processing method, discloses a composition (mass fraction) of 74% Fe, 20% Cr, 4.5% Al, 0.5% Ti and 0.5% Y ₂ O ₃ mechanically alloyed iron-based alloy A method for preparing plates by powder hot pressing-hot rolling-cold rolling forming.

Chinese patent CN200610031607.1, a production process for dispersion-strengthened copper alloy materials, discloses a process for preparing alloy powders by using MA - high-temperature sintering to make green bodies - hot extrusion forming to prepare oxide dispersion-strengthened copper alloy materials.

Alloys prepared by hot isostatic pressing and hot pressing sintering processes have low density, complex equipment, and the limited size of the prepared materials, which limits their application fields and prevents their excellent properties from being fully utilized.

The highly dispersed nanoclusters in nanocluster-strengthened iron-based alloys are a composite oxide formed by enriched Ti, Y, O and other elements. The formation of such nanoscale oxides requires a combination of Y/Ti/O The distribution is very uniform. The MA method adds Y ₂ O ₃ oxides, and the oxides are dispersed into the alloy matrix by MA ball milling. Only a few nano-scale oxides may meet the conditions for forming nano-clusters and form nano-clusters; At the same time, Y ₂ O ₃ will become the nuclei of heterogeneous nucleation of Ti, Y, O composite oxide during high temperature sintering for a long time in the process of preparing green bodies, and Y ₂ O ₃ +Ti+O in the powder will form Y ₂ O ₃ aggregates and grows as the core. Affected by the uniformity of Y ₂ O ₃ distribution, the formation of nanoclusters and the uniformity of distribution become complex and difficult to control. Therefore, the reproducibility of nanoclusters formed in the iron-based alloy prepared by the above method is poor.

Aiming at the consolidation forming of atomized iron-based alloy powder, Chinese invention patent CN101265530A, a preparation method of nano-cluster dispersion strengthened iron-based alloy, discloses a method of using atomized iron-based pre-alloy powder for room temperature molding, 1350 ° C / 2h A method for preparing a forged green body by sintering and forging a cluster dispersion-strengthened iron-based alloy by forging at a temperature of 900°C to 1200°C. This method has a simple preparation process, but it is difficult to prepare high-performance nanocluster-strengthened iron-based alloys. The main disadvantages are as follows: (1) Due to the high degree of powder alloying and difficult deformation, the molded body at room temperature has low density and poor porosity. At the same time, long-term high-temperature sintering oxidizes the powder surface. These factors hinder the bonding of the powder interface and reduce the bonding strength, thereby reducing the mechanical properties of the alloy; The film is not easily damaged, and the residual oxide film is easy to form the original particle boundary, which reduces the strength of the material; (3) the solid dissolved oxygen in the powder forms a stable oxide during the long-term high-temperature sintering (1350°C/2h) stage of the compacted body, and loses Conditions for the formation of nanoclusters. In particular, the sintered porosity of the green body is difficult to eliminate through forging with a small amount of deformation, and the performance of the prepared iron-based alloy is low.

In view of the above problems, this patent proposes to prepare nano-cluster reinforced iron-based superalloys by using gas atomized iron-based alloy powder extrusion molding process.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing nanocluster reinforced iron-based superalloy by extrusion molding of gas atomized alloy powder. A method for the preparation of iron-based superalloys.

The invention provides a method for preparing nanophase-strengthened iron-based superalloy by extrusion molding of gas atomized powder. The gas atomized powder is taken, packed into a sheath, degassed, sheathed and welded, and the sheathed powder is sealed. Heating and extruding to obtain a bulk iron-based superalloy comprises the following steps:

Step 1: Select gas-atomized iron-based alloy powder with an average oxygen content of 0.05% to 0.20% (mass fraction), and put the powder into a steel ladle with an average particle size of ≤200 μm; vacuumize the inside of the ladle to 10 ^-2 After Pa, heat the jacketed alloy powder to 100°C-300°C and continue vacuuming to 10 ^-2 Pa, degas for more than 60 minutes, and seal the jacket;

Step 2: Heat the sealed sheath and alloy powder obtained in the first step at 850°C to 1250°C for 15min to 45min. After the sheath powder is completely heated and uniform, extrude. The extrusion ratio is (6~15 ): 1 to obtain high-density iron-based superalloy rods;

Step 3: After the rod obtained in the second step is machined to remove the jacket, it is subjected to vacuum annealing treatment at 1050°C to 1200°C for 1h to 1.5h, and then cooled in the air to obtain nanocluster-strengthened iron-based Superalloy.

In the present invention, the composition of the iron-based alloy powder is Fe-(13.5-14.5%) Cr-(2.8-3.5)%W-(0.35-0.42%)Ti-(0.2-0.6%)Y-(0.05-0.15%) %)O (mass fraction), and the specific oxygen content is determined according to the composition of the alloy and the amount of nano-oxide formed in the design.

In the present invention, the sheath is tightly welded and sealed; the sheath is provided with an air extraction pipe, and a filter screen is arranged in the air extraction pipe, and a group of conical flasks are connected between the air extraction pipe of the vacuum unit and the air extraction pipe of the sheath to filter The device prevents the powder in the sheath from being drawn out during air extraction; after the degassing is completed, the part 40mm~60mm above the bottom of the sheath exhaust pipe is heated locally, and the seal is quickly hammered when it is heated to a temperature that can be welded by hammering Pipe, repeat several times to completely weld the inner wall of the exhaust pipe, remove the excess exhaust pipe, and completely weld the seal of the exhaust pipe with a welding machine;

In the present invention, the extrusion is carried out in an extruder; the extrusion die is preheated to 300-400° C., and graphite powder is used as a lubricant.

The invention adopts gas atomized oxygen-containing alloy powder instead of mechanical alloying powder, and by optimizing the alloy composition, introducing an appropriate concentration of vacancies and controlling its distribution state, an iron-based superalloy with diffusely distributed nano-clusters or nano-oxides is prepared .

First, the oxygen element introduced by atomization is used as an alloy element to replace the metal oxide, and dispersed nano-clusters or nano-oxides are precipitated by heat treatment.

Gas atomized powder is prepared by rapidly cooling the alloy melt with uniform composition to room temperature through high-speed gas, which avoids segregation caused by equilibrium solidification, and the distribution of alloy elements and oxygen in the powder matrix is uniform. Nucleation is formed to ensure that the formed composite oxide is highly dispersed; during the powder extrusion process, high-concentration deformation defects are formed through shear deformation, and the high-concentration vacancies provided by the atomization process can effectively hinder the formation of this oxide. Gather and grow. Therefore, by controlling the formation and growth process of oxides, the final product can be effectively controlled to form dispersed nano-clusters or nano-oxides.

Secondly, the above-mentioned powder pressing-high temperature sintering-deformation processing, or powder hot isostatic pressing-deformation processing, or powder hot pressing sintering-deformation processing and other processing technologies are adopted to replace the above-mentioned powder pressing-high temperature sintering-deformation processing technology, which realizes powder consolidation and Synchronous forming, oxide precipitation and heat treatment are synchronized, which reduces the mechanical alloying process and high-temperature sintering process, and shortens the process flow.

The present invention has the following advantages:

(1) Using gas atomized powder instead of mechanical alloying powder, the prepared alloy has high purity, and there is no alloy pollution problem caused by mechanical alloying powder;

(2) The material prepared by extrusion molding method has high density and large powder deformation, which is beneficial to improve the bonding state of the powder interface and improve the mechanical properties of the alloy;

(3) The solid dissolved oxygen in the powder is evenly distributed, which is beneficial to the finer and uniform dispersion of the precipitated oxides;

(4) Using gas atomized powder instead of mechanical alloying powder can control the oxygen content more accurately, and the properties of different batches of alloys are uniform and repeatable;

(5) The preparation process is simple, the production efficiency is high, the cost is low, and large-sized materials can be prepared, which is conducive to large-scale preparation and application.

In summary, the present invention provides a method for preparing nanophase-strengthened iron-based superalloys by extrusion molding of gas-atomized alloy powders. The density of the prepared alloys _can reach 99%. ≥8%; 850°C strength σ _b ≥100MPa.

Description of drawings:

Accompanying drawing 1 is the alloy prepared in Example 1 of the present invention, extrusion ratio is 6: 1, the TEM picture of structure after annealing 1h at 1050 ℃, alloy composition is Fe-13.8%Cr-3.1%W-0.42%Ti-0.27 %Y-0.08%O (mass fraction).

In Fig. 1: 1, 2, 3 are the formed nano-oxides.

Detailed ways

The present invention adopts gas-atomized iron-based alloy powder to prepare nano-phase-strengthened iron-based superalloy through hot extrusion. The specific implementation mode of the present invention will be further described below in conjunction with examples and accompanying drawings:

Example 1:

The atomized powder with an oxygen content of 0.08% (mass fraction) was used to prepare a nanophase-strengthened iron-based superalloy with an extrusion ratio of 6:1.

Select gas-atomized Fe-13.8%Cr-3.1%W-0.42%Ti-0.27%Y-0.08%O iron-based alloy powder with a particle size of ≤200μm and an average oxygen content of 0.08% (mass fraction), and load it into a ladle After covering, use a vacuum unit to vacuum degas the package with the powder, the vacuum degree reaches 10 ^-2 Pa and continues to pump for more than 30 minutes, then heat the package powder to 150°C and continue to vacuum to 10 ^-2 Pa Afterwards, degassing for more than 60 minutes, heat locally and rapidly at the part 40mm ~ 60mm above the bottom of the exhaust pipe of the sheath, and hammer it quickly after heating to a temperature that can be completely welded by hammering, repeating several times to completely weld the inner wall of the exhaust pipe , remove the excess exhaust pipe, and use a welding machine to weld the exhaust pipe seal.

The sealed sheathing powder is heated at 1100°C for 20 minutes, so that the sheathing powder is completely heated evenly, and then extruded to obtain a high-density rod. The extrusion ratio is 6:1, and the extrusion die is heated to 300-400°C , using graphite powder as a lubricant. The sheath on the periphery of the extruded bar is removed by machining to obtain an iron-based superalloy with a material density of 7.75×10 ³ kg/m ³ and a relative density of over 99%. After subsequent deformation and heat treatment, a nanocluster-strengthened iron-based superalloy is obtained, with room temperature strength σ _b ≥ 1200 MPa, plasticity δ ≥ 8%, and strength σ _b ≥ 100 MPa at 850°C. .

Example 2:

The atomized powder with an average oxygen content of 0.15% (mass fraction) was used to prepare a nanophase-strengthened iron-based superalloy with an extrusion ratio of 9:1.

Select the gas atomized Fe-13.5Cr-3%W-0.35Ti-0.6Y-0.15O iron-based alloy powder whose particle size is≤200 μm and average oxygen content of 0.15% (mass fraction), then according to the method of example 1 and The steps include sealing and welding the sheathing powder, heating and heat preservation, applying graphite powder, and then extruding with an extrusion ratio of 9:1. After removing the sheath, the obtained material has a density of 7.77×10 ³ kg/m ³ and a relative density of over 99%. After subsequent deformation and heat treatment, a nanocluster-strengthened iron-based superalloy is obtained.

Example 3:

The atomized powder with an average oxygen content of 0.11% (mass fraction) was used to prepare a nanophase-strengthened iron-based superalloy with an extrusion ratio of 15:1.

Select the gas-atomized Fe-(14.5%Cr-3%W-0.4%Ti-0.3%Y-0.11%O iron-based alloy powder with a particle size of ≤200 μm and an average oxygen content of 0.11% (mass fraction), and then follow the The method and steps of example 1 complete the sealing and welding of the envelope powder, heat insulation, smear graphite powder, and then adopt the extrusion ratio of 15: 1 to extrude. After removing the envelope, the material density obtained is 7.78 × 10 ³ kg/ m ³ , the relative density reaches over 99%. After subsequent deformation and heat treatment, an iron-based superalloy strengthened by nano-clusters is obtained.

Claims (4)

1. a gas atomization powder extrusion molding prepares the method for iron-base superalloy, comprises the steps:

The first step: select the oxygen-containing gas atomizing iron(-)base powder of median size≤200 μ m for use, the Steel Capsule of packing into; To being evacuated to 10 in the jacket ^-2Behind the Pa, Steel Capsule and powdered alloy are heated to 100 ℃～300 ℃ and continue to be evacuated to 10 ^-2Behind the Pa, more than the degasification 60min, Steel Capsule is sealed;

Second step: the jacket of the good seal that the first step is obtained and powdered alloy are at 850 ℃～1250 ℃ insulation 15min～45min, after treating the complete homogeneous heating of jacket powder, push, extrusion ratio is (6～15): 1, and the iron-base superalloy bar of acquisition high-compactness;

The 3rd step: after second bar that obtain of step removed jacket by machining, under 1050 ℃～1200 ℃, carry out vacuum annealing and handle 1.0h～1.5h, in air, cool off then, obtain the iron-base superalloy that nanocluster is strengthened.

2. a kind of atomized powder extrusion molding according to claim 1 prepares the method for iron-base superalloy, it is characterized in that: described iron(-)base powder is that gas atomization contains the oxygen powder, averaged oxygen content 0.05%～0.20% (massfraction), described iron(-)base powder composition are Fe-(13.5～14.5%) Cr-(2.8～3.5) %W-(0.35～0.4%) Ti-(0.2～0.6%) Y-(0.05～0.15%) O (massfraction).

3. a kind of atomized powder extrusion molding according to claim 1 prepares the method for iron-base superalloy, it is characterized in that: the close employing welded seal of described Steel Capsule; Described Steel Capsule is provided with extraction pipe, in described extraction pipe filtering net is set, and is connected one group of Erlenmeyer flask filtration unit between vacuum machine assembly air-exhausting pipe and the Steel Capsule extraction pipe, and the powder when preventing to bleed in the jacket is drawn out of; After finishing degasification, in Steel Capsule extraction pipe bottom above 40mm～60mm position local fast heating, when be heated to can be by the temperature of hammering seam after rapid hammering tube sealing, repeat repeatedly to make the complete seam of extraction pipe inwall, remove unnecessary extraction pipe, and extraction pipe is sealed complete seam with welding machine.

4. a kind of atomized powder extrusion molding according to claim 1 prepares the method for nanophase reinforced iron-base superalloy, it is characterized in that: described being squeezed in the extrusion machine carried out; Extrusion mould is preheated to 300～400 ℃, uses Graphite Powder 99 as lubricant.

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