WO2020147490A1 - 抗高温蠕变性优良的改性奥氏体不锈钢及其制备方法 - Google Patents

抗高温蠕变性优良的改性奥氏体不锈钢及其制备方法 Download PDF

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WO2020147490A1
WO2020147490A1 PCT/CN2019/126131 CN2019126131W WO2020147490A1 WO 2020147490 A1 WO2020147490 A1 WO 2020147490A1 CN 2019126131 W CN2019126131 W CN 2019126131W WO 2020147490 A1 WO2020147490 A1 WO 2020147490A1
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stainless steel
austenitic stainless
layer
creep resistance
temperature creep
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PCT/CN2019/126131
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English (en)
French (fr)
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李微
陈荐
许栋梁
李传常
邱玮
任延杰
何建军
陈建林
彭卓寅
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长沙理工大学
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Priority to AU2019422376A priority Critical patent/AU2019422376B9/en
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/02—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
    • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
    • C23C10/36—Embedding in a powder mixture, i.e. pack cementation only one element being diffused
    • C23C10/48—Aluminising
    • C23C10/50—Aluminising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
    • C23C10/60—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/16—Polishing
    • C25F3/22—Polishing of heavy metals
    • C25F3/24—Polishing of heavy metals of iron or steel

Definitions

  • the invention relates to the technical field of heat exchange tube materials, in particular to a modified austenitic stainless steel with excellent high temperature creep resistance and a preparation method thereof.
  • Solar thermal power generation also known as Concentrating Solar Power, CSP
  • CSP Concentrating Solar Power
  • the heat storage system is the main link of the CSP power station.
  • the heat storage medium of commercial CSP power station mainly uses water vapor, molten salt and heat transfer oil.
  • the latent heat of aluminum-silicon alloy at 1079°C can reach 960J/g, and its thermal conductivity is more than twice that of salt.
  • phase change latent heat drops from 505kJ/kg to 452kJ /kg, the drop is only 10.5%, while the phase transition temperature remains basically stable, with high oxidation resistance characteristics (after hundreds of hours of high temperature oxidation, the oxidation rate is less than 0.01%), which is considered to be a new generation of heat storage medium replacement material.
  • the working conditions and application environment of the solar thermal power generation heat exchange pipe fittings are extremely harsh, and they need to withstand constant high stress loads and temperature fluctuations of 495 to 620 °C. They are corroded by the molten aluminum silicon alloy of the heat storage medium, and corrosion creep occurs. Deformation and damage, thereby shortening the service life of the thermal power generation system. Therefore, improving the high-temperature creep resistance of the molten aluminum-silicon alloy of the heat exchange tube material is an urgent problem for CSP research and development.
  • the current method to alleviate the corrosion of molten aluminum-silicon alloy is to conduct aluminizing on austenitic stainless steel, which is the material of the heat exchange tube.
  • aluminizing As a mature chemical heat treatment process, aluminizing has been widely used in industrial production.
  • the phase composition of the aluminized coating surface is not easy to control, and it is easy to produce brittle phases.
  • the thickness of the infiltrated layer is often too thin, loose, not closely combined with the substrate, and easy to peel off, which affects the surface strengthening effect, or during the treatment process The strength and toughness of the material decrease. It can be seen that the aluminized steel prepared by the existing aluminizing process still has obvious deficiencies in the mechanical properties.
  • the material toughness and strength are insufficient, and the micropores or microcracks in the aluminized layer It is easy to nucleate on the surface and expand rapidly, resulting in aluminized samples exhibiting a higher creep strain rate and a shorter creep rupture life.
  • Laser shock strengthening is an advanced surface enhancement technology that can refine the grains of the surface material, increase the dislocation density, and introduce a higher residual compressive stress, which can effectively inhibit the initiation and propagation of cracks to improve the mechanical properties of the material.
  • the material after aluminizing and laser shock treatment has increased surface roughness, the coating is easy to peel off, and the generated aluminized layer is easy to crack under high temperature load, which shortens the life of the workpiece.
  • the patent application number 201310282671.7 discloses a composite treatment method of aluminizing and laser shock.
  • the process is pre-cleaning, annealing at 550-780°C for 2 ⁇ 3h, shot peening, and aluminizing at 500-600°C4 ⁇ 6h, post-cleaning, and finally laser shock.
  • the composition of the permeated layer produced by this process is mainly Fe2Al5 brittle phase, which does not solve the problem of brittleness of the permeated layer.
  • the coating is easy to peel off during the laser shock process, and the bond between the permeated layer and the substrate is poor. As a result, the residual compressive stress introduced by laser shock strengthening at high temperatures is greatly released, and the fretting fatigue resistance enhancement effect is poor.
  • the patent application number 20111006570.2 discloses a method of first laser shock, then aluminizing, and finally laser shock.
  • the aluminized layer obtained by the method is easy to fall off during the laser shock process, the thickness of the aluminized layer is affected, the process is complicated, the processing period is long, and the production cost is high.
  • the heat exchange tube for solar thermal power generation using aluminum-silicon alloy as the heat storage medium requires high temperature creep resistance at high temperature (620°C) in the use environment of molten aluminum-silicon alloy.
  • 620°C high temperature
  • the patent document with application number 201310282671.7 can introduce compressive residual stress on the surface of the aluminized layer to provide surface strength, the obtained layer has a weak bonding force, and the composition of the layer contains Fe2Al5 brittle phases.
  • the compressive residual stress increases significantly at high temperatures. Release, the high temperature strengthening effect is poor, and it cannot meet the long-term operation requirements of the heat exchange tube.
  • the technical problem to be solved by the present invention is to provide a new process of aluminizing and laser shock treatment, which can obtain uniform structure, no brittle phase, strong bonding force of the infiltrated layer, and surface strengthening of the matrix.
  • the toughened modified austenite can ensure excellent high temperature creep resistance of the heat exchange tube.
  • the technical problem to be solved by the present invention is to overcome the shortcomings of the prior art, and provide an excellent creep resistance and corrosion resistance under the condition of molten aluminum-silicon alloy, no brittle phase in the composition of the infiltration layer, and between the infiltration layer and the substrate.
  • the modified austenitic stainless steel has strong bonding force, good peeling resistance, and good toughness and strength. It also provides a simple process that can prepare the permeable layer and the matrix with strong bonding force, good peeling resistance, and no brittle phase , The method of modifying austenitic stainless steel with excellent high temperature creep resistance and corrosion resistance under the condition of molten aluminum-silicon alloy, and good toughness and strength.
  • the technical solution adopted by the present invention is:
  • a modified austenitic stainless steel with excellent high-temperature creep resistance includes an austenitic stainless steel matrix and a permeated layer.
  • the permeated layer includes Al-containing alloys with a thickness of 40 to 80 ⁇ m from the inside to the outside.
  • the Fe-Al compound layer is a non-brittle intermetallic compound of Fe and Al; the non-brittle intermetallic compound includes FeAl, FeAl2 and Fe3Al .
  • the austenitic stainless steel matrix is 321 austenitic stainless steel; the surface hardness of the infiltrated layer is 625-1390HV, and the strengthening effect depth is 300 ⁇ 1600 ⁇ m.
  • a method for preparing modified austenitic stainless steel with excellent high temperature creep resistance includes the following steps:
  • the austenitic stainless steel plate is electrolytically polished with the austenitic stainless steel plate as the anode and the insoluble conductive material as the cathode;
  • Aluminizing drying the austenitic stainless steel treated by electrolytic polishing, and then using solid powder infiltration agent for aluminizing.
  • the conditions for the aluminizing are: heat preservation at 400-600°C for 20-40 minutes, and then at 900 Keep it at °C ⁇ 1050°C for 10 ⁇ 15h and then cool to room temperature with the furnace;
  • Annealing Anneal the sand-blasted sample in an argon atmosphere at 1000 ⁇ 1100°C, and take out the sample after cooling in the furnace;
  • Laser shock strengthening The annealed sample is subjected to laser shock treatment.
  • the single pulse energy of laser shock is 4 ⁇ 7J
  • the spot diameter is 2.6 ⁇ 3mm
  • the number of laser shocks is 1 ⁇ 3 times.
  • laser shock strengthening treatment That is, modified austenitic stainless steel.
  • the solid powder penetrating agent includes a homogeneous mixture of the following components: aluminum powder with a particle size of 200 mesh, Al2O3 A filler composed of Cr powder and its powdery NH4Cl permeation aid.
  • the aluminum powder accounts for 42-74%
  • the Al2O3 powder accounts for 20-40%.
  • the Cr powder accounts for 5 to 15%
  • the NH4Cl accounts for 1 to 3%.
  • the annealing time is 0.5 to 3 hours.
  • step S5 a pulsed high-energy laser is used, black tape is used as a protective layer, and water is used as a constraining layer;
  • the wavelength of the laser It is 1064nm, the pulse width is 10-30ns, and the overlap rate is 40-70%;
  • the laser shock treatment is double-sided laser shock treatment; the path direction of the laser shock treatment is perpendicular to the rolling direction of the stainless steel plate.
  • the abrasive for sandblasting is 300-500 mesh Al2O3 particles; the sandblasting time is 5 ⁇ 20min, the distance of sandblasting is 2 ⁇ 6cm.
  • the electrolyte includes concentrated sulfuric acid with a volume fraction of 60 to 80% and a volume fraction of 15 to 37%.
  • the above-mentioned preparation method of modified austenitic stainless steel with excellent high temperature creep resistance further includes a step of mechanically polishing the surface of the austenitic stainless steel; Polishing specifically includes: sanding with 80-1200 mesh grit sandpaper until no obvious scratches are visible to the naked eye, then washing with acetone in ultrasonic for 5-20 minutes, degreasing, ultrasonic cleaning with absolute ethanol for 5-20 minutes, removing stains, and finally putting Put it into a drying oven at 80°C and dry for 20-40min.
  • the modified austenitic stainless steel of the present invention has an excellent structure, so that it has excellent creep resistance under the conditions of molten aluminum-silicon alloy and high-temperature stress, and has high material strength and toughness. From the inside to the outside of the substrate surface, it is composed of an Al-containing Fe phase diffusion layer with a thickness of 40 to 80 ⁇ m, a Fe-Al compound layer with a thickness of 50 to 100 ⁇ m, and an Al2O3 film with a thickness of 10 to 20 ⁇ m.
  • the infiltration layer does not contain brittle phases, the organization is uniform, and the thickness is controllable.
  • the components between the infiltration layer and the infiltration layer are in a gradient and smooth transition, which significantly reduces the interface stress and tissue defects between the matrix and the infiltration layer, and effectively improves the matrix and
  • the bonding force between the infiltrated layers can inhibit the peeling of the infiltrated layer, inhibit the initiation and propagation of cracks, and effectively improve the creep resistance of 321 austenitic stainless steel under the conditions of molten aluminum-silicon alloy and high temperature stress, which can meet the requirements of molten aluminum-silicon alloy
  • the solar thermal power generation heat exchange tube which is the heat storage medium, has great academic value and industrial application potential.
  • the modified austenitic stainless steel of the present invention does not contain brittle phases such as Fe2Al5 and FeAl3, has strong bearing capacity, has good adhesion between the infiltrated layers and between the infiltrated layers and the substrate, and is not easy to peel off.
  • the modified austenitic stainless steel infiltrated layer of the present invention is tightly bonded, has no cracks, has obvious boundaries, and is neat.
  • the surface hardness of the infiltrated layer is 625-1390HV, the depth of strengthening is 300-1600 ⁇ m, and the surface strengthening effect of the material is good. .
  • the present invention uses specific electrolytic polishing, aluminizing, sand blasting, annealing and laser shock strengthening process steps to organically combine 321 stainless steel in a specific order, and control the aluminizing temperature, sand blasting pressure, and annealing temperature.
  • the layer interface stress is small, the surface of the infiltrated layer has good macro morphology, the structure has fine grains, no cracks, uniform structure, controllable thickness, no brittle phases such as Fe2Al5, FeAl3, and the composition between the infiltrated layer and the infiltrated layer is smooth and gradient
  • the transitional modified austenitic stainless steel significantly reduces the interface stress and microstructure defects between the matrix and the cemented layer, effectively improves the bonding force between the matrix and the cemented layer, inhibits the peeling of the cemented layer, inhibits the initiation and propagation of cracks, and effectively improves
  • the creep resistance of 321 austenitic stainless steel under the conditions of molten aluminum silicon alloy and high temperature stress it has excellent creep resistance under the conditions of molten aluminum silicon alloy and high temperature stress, and can improve the austenitic stainless steel Matrix strength and toughness.
  • the method of the present invention can further improve the control precision of the tissue by further controlling the annealing time, the composition of the penetrating agent, the process parameters of the laser shock, the sandblasting time, the sandblasting distance, the conditions of electrolytic polishing, etc.
  • the compactness and integrity of the structure can obtain modified austenite with good surface strengthening and high matrix toughness, which can effectively improve the creep resistance, toughness and toughness of the modified austenitic stainless steel under the conditions of molten aluminum silicon alloy and high temperature stress. Strength and other properties.
  • the method of the present invention performs surface mechanical polishing treatment on the austenitic stainless steel sample before electrolytic polishing to remove impurities and coverings on the sample surface, improve the cleanliness of the sample surface, and create a better solution for subsequent aluminizing treatment. Surface condition.
  • Fig. 1 is a laser shock strengthening path diagram of the austenitic stainless steel sample of the present invention subjected to laser shock treatment.
  • FIG. 2 XRD comparison diagram of modified 321 austenitic stainless steel prepared in Example 3 of the present invention and unmodified 321 austenitic stainless steel.
  • Example 3 is a cross-sectional morphology of modified 321 austenitic stainless steel prepared in Example 3 of the present invention and an EDS energy spectrum analysis diagram of corresponding points.
  • Example 4 is a graph showing changes in the microhardness of the modified 321 austenitic stainless steel prepared in Example 3 of the present invention along the depth direction of the infiltration layer.
  • Figure 5 shows the high temperature creep of modified 321 austenitic stainless steel and unmodified 321 austenitic stainless steel prepared in Example 3 of the present invention at 620°C/210MPa and in a molten aluminum-silicon alloy environment at 620°C/210MPa Compare graphs.
  • the modified austenitic stainless steel includes an austenitic stainless steel matrix from the inside to the outside, and an Al-containing Fe phase diffused with a thickness of 40-80 ⁇ m Layer, a Fe-Al compound layer with a thickness of 50-100 ⁇ m and an Al2O3 thin film with a thickness of 10-20 ⁇ m.
  • the Fe-Al compound layer is a non-brittle intermetallic compound of Fe and Al, including FeAl, FeAl2 and Fe3Al.
  • the austenitic stainless steel matrix is 321 austenitic stainless steel.
  • a method for preparing modified austenitic stainless steel with excellent high temperature creep resistance of the present invention includes the following steps:
  • the hot-rolled austenitic stainless steel plate is polished with sandpaper of different grain sizes (80 ⁇ 1200#) until there is no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic for 5 ⁇ 20min, degreasing, no Ultrasonic cleaning with water and ethanol for 5-20 minutes, removing stains, and finally drying in a drying oven at 80°C for 20-40 minutes;
  • the 321 austenitic stainless steel is a rolled plate with a mass fraction of C 0.04%, Si 0.38%, Mn 1.08%, Cr 17.02%, Ni 9.06%, N 0.05%, P0.03%, Ti 0.22%, and the rest is Fe.
  • the mechanical properties of 321 stainless steel at room temperature are: tensile strength ( ⁇ b) 667MPa, yield strength ( ⁇ 0.2) 245MPa, elongation rate 56.5%, hardness 175HV.
  • Electrolytic polishing connect the 321 austenitic stainless steel plate to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between the anode and the cathode, and heat the electrolyte to 60 ⁇ 80°C (heating by water bath), and pass in 5 ⁇ 6V DC voltage, after polishing for 2 ⁇ 5min in electrolysis, take out the austenitic stainless steel plate, rinse and blow dry.
  • the composition of the electrolyte is as follows: Concentrated sulfuric acid with a volume fraction of 60 ⁇ 80% (purity 98%) , Concentrated phosphoric acid with a volume fraction of 15 to 37% (purity 85%) and distilled water with a volume fraction of 3 to 5%.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al2O3 and Cr powder are used as fillers and powdered NH4Cl.
  • the composition of the penetration aid is fully mixed according to 5-15wt.% Cr, 42-74wt.% Al, 20-40wt.% Al2O3, and 1-3wt.% NH4Cl.
  • the penetrating agent and the electrolytically polished austenitic stainless steel plate into a heat-resistant stainless steel tank, press tightly, and seal the refractory mud for aluminizing: increase the temperature in the furnace, dry at 150°C for 2h, and then keep warm at 400 ⁇ 600°C 20-40min, the heating rate is 10°C/min, and then keep the temperature at 900°C ⁇ 1050°C for 10-15h, then cool to room temperature with the furnace.
  • Sandblasting treatment Place the aluminized austenitic stainless steel plate under 0.6 ⁇ 0.9MPa high pressure nitrogen for sandblasting, the abrasive is 300 ⁇ 500 mesh Al2O3 particles, the blasting time is 5 ⁇ 20min, the blasting distance is 2 ⁇ 6cm, remove loose infiltrated layer and impurities.
  • Annealing Put the aluminized austenitic stainless steel plate into a vacuum tube furnace, annealing at 1000-1100°C under high-purity argon for 0.5-3h, and take it out with the furnace cooling.
  • Laser shock strengthening double-sided laser shock strengthening treatment on the annealed austenitic stainless steel plate, the laser wavelength is 1064nm, the single pulse energy is 4 ⁇ 7J, the pulse width is 10 ⁇ 30ns, and the spot diameter is 2.6 ⁇ 3mm , The lap rate is 40-70%, the black tape is the protective layer, the water is the constraining layer, the number of laser shocks is 1 to 3 times (it can be 1, 2 or 3 times).
  • Figure 1 shows the laser shock strengthening path, which is perpendicular to the rolling direction of the stainless steel sheet.
  • the modified austenitic stainless steel with enhanced resistance to high-temperature creep of molten aluminum-silicon alloy and the preparation method of the present invention after aluminizing the austenitic stainless steel, after laser shock, the surface of the austenitic stainless steel has a better macroscopic morphology, and its microstructure The grains are small and no cracks.
  • the infiltration layer is a multilayer structure, from the outside to the inside, there are 10-20 ⁇ m uneven Al2O3 film, 50-100 ⁇ m thick Fe-Al compound (FeAl, FeAl2 and Fe3Al), 40-80 ⁇ m thick Al(Fe) Phase diffusion layer and matrix. Moreover, the permeable layers are tightly bonded, without cracks, and the boundaries are obvious and neat.
  • the surface hardness of the infiltration layer is 625-1390HV, and the depth of strengthening is 300-1600 ⁇ m.
  • the high-temperature tensile creep rupture time under 210MPa creep load is more than 94h, and the steady-state creep rate is less than 1.1254x10-7, compared with 321 stainless steel (creep rupture time 73h , The steady-state creep rate is 2.7143x10-7), the steady-state creep rate is greatly reduced, and it exhibits excellent resistance to high-temperature creep of molten aluminum-silicon alloy, which meets the requirements of solar thermal power generation based on molten aluminum-silicon alloy as the heat storage medium.
  • the work requirements of heat pipes have great academic value and industrial application potential.
  • a method for preparing modified austenitic stainless steel with excellent high temperature creep resistance of the present invention includes the following steps:
  • Electrolytic polishing connect the 321 austenitic stainless steel plate to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between the anode and the cathode, heat the electrolyte to 60°C, enter the electrolyte at the same time, and pass 5V DC Voltage, soak in the electrolysis for 2 minutes, take the sample out, rinse and blow dry; the composition of the electrolyte consists of 60% concentrated sulfuric acid (purity 98%) and 37% concentrated phosphoric acid (purity 85%) ) And 3% distilled water.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al2O3 and Cr powder are used as fillers and powdered NH4Cl.
  • the composition of the penetration aid is fully mixed according to 5wt.% Cr, 64wt.% Al, 28wt.% Al2O3, and 3wt.% NH4Cl.
  • Annealing Put the aluminized sample in a vacuum tube furnace, and anneal it under high-purity argon at 1000°C for 1.5h, and take out the sample as the furnace cools.
  • Laser shock strengthening double-sided laser shock strengthening treatment for aluminized stainless steel, the laser wavelength is 1064nm, the single pulse energy is 4J, the pulse width is 10ns, the spot diameter is 2.8mm, the overlap rate is 40%, and the black tape is Protective layer, water is the constrained layer, and the number of laser shocks is 1 time.
  • the path direction of the laser shock treatment is perpendicular to the rolling direction of the stainless steel sheet.
  • the prepared cemented layer is tightly bonded to the substrate and the interlayer, and the cemented layer from the outside to the inside is an uneven 20 ⁇ m thick Al 2O3 film, 80-100 ⁇ m thick Fe-Al compound layer (FeAl, FeAl2 and Fe3Al), 60 ⁇ 70 ⁇ m thick Al-containing Fe phase diffusion layer and matrix, without brittle phases such as Fe2Al5 and FeAl3 in the infiltration layer.
  • the surface hardness of the infiltrated layer is 600-700HV, and the depth of strengthening is 300-400 ⁇ m.
  • a method for preparing modified austenitic stainless steel with excellent high temperature creep resistance of the present invention includes the following steps:
  • Electrolytic polishing connect 321 austenitic stainless steel to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between anode and cathode, heat the electrolyte to 70°C, enter the electrolyte at the same time, and apply a 5V DC voltage. Soak in the electrolysis for 5 minutes, the sample is taken out, rinsed, and blown dry.
  • the electrolyte is composed of 70% concentrated sulfuric acid (purity 98%) and 26% concentrated phosphoric acid (85% purity). ) And distilled water with a volume fraction of 4%.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al2O3 and Cr powder are used as fillers and powdered NH4Cl.
  • the composition of the penetration aid is fully mixed according to 15wt.% Cr, 44wt.% Al, 40wt.% Al2O3, and 1wt.% NH4Cl.
  • Sandblasting Put the aluminized sample under 0.8MPa high pressure nitrogen for sandblasting, the abrasive is 400 mesh Al2O3 particles, the sandblasting time is 10min, the sandblasting distance is 4cm, and the loose infiltration layer and impurities are removed.
  • Annealing Put the aluminized sample in a vacuum tube furnace, and anneal it under high-purity argon at 1100°C for 0.5h. Take out the sample as the furnace cools.
  • Laser shock strengthening double-sided laser shock strengthening treatment for aluminized stainless steel, laser wavelength is 1064nm, single pulse energy is 6J, pulse width is 30ns, spot diameter is 3mm, overlap rate is 70%, black tape is for protection Layer, water is the constrained layer, the number of laser shocks is 3 times.
  • Figure 1 shows the laser shock strengthening path of this embodiment, and the path direction is perpendicular to the rolling direction of the stainless steel sheet.
  • the prepared cemented layer is tightly bonded to the substrate and between the layers, and the cemented layer from the outside to the inside is a 10 ⁇ m thick Al 2O3 film, a 70-80 ⁇ m thick Fe-Al compound layer (FeAl, FeAl2 and Fe3Al), 50 ⁇ 60 ⁇ m thick Al-containing Fe phase diffusion layer and matrix, without brittle phases such as Fe2Al5 and FeAl3 in the infiltration layer.
  • the surface hardness of the infiltrated layer is 700-800HV, and the depth of strengthening is 800-1400 ⁇ m.
  • a method for preparing modified austenitic stainless steel with excellent high temperature creep resistance of the present invention includes the following steps:
  • Electrolytic polishing connect 321 austenitic stainless steel to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between anode and cathode, heat the electrolyte to 80°C, enter the electrolyte at the same time, and apply 5V DC voltage , Soak in the electrolysis for 3 minutes, take the sample out, rinse and blow dry; the composition of the electrolyte is 80% concentrated sulfuric acid (purity 98%), 15% concentrated phosphoric acid (purity 85%) and It is composed of 5% distilled water by volume.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al2O3 and Cr powder are used as fillers and powdered NH4Cl.
  • the composition of the penetration aid is fully mixed according to 10wt.% Cr, 58wt.% Al, 30wt.% Al2O3, and 2wt.% NH4Cl.
  • Sandblasting treatment Put the aluminized sample under 0.9MPa high pressure nitrogen for sandblasting, the abrasive is 500 mesh Al2O3 particles, the sandblasting time is 5min, the sandblasting distance is 2cm, and the loose infiltration layer and impurities are removed. .
  • Annealing Put the aluminized sample in a vacuum tube furnace, and anneal it under high-purity argon at 1050°C for 1 hour, and take out the sample as the furnace cools.
  • Laser shock strengthening double-sided laser strengthening treatment on aluminized stainless steel with pulsed high energy laser, laser wavelength is 1064nm, single pulse energy is 7J, pulse width is 20ns, spot diameter is 2.6mm, overlap rate is 50% , Black tape is the protective layer, water is the constraining layer, and the number of laser shocks is 3 times.
  • Figure 1 shows the laser shock strengthening path of this embodiment, and the path direction is perpendicular to the rolling direction of the stainless steel sheet.
  • the phase composition of the cemented layer is mainly composed of FeAl, FeAl2 and Fe3Al, and the cemented layer does not contain brittle phases such as Fe2Al5 and FeAl3.
  • the SEM analysis of the infiltrated layer prepared in this example shows that the results are shown in Figure 3.
  • the infiltrated layer is tightly bonded to the substrate and between the layers without cracks, and the boundary is clear and neat, indicating that the aluminized layer and the substrate have formed a metallurgical bond.
  • four points A, B, C, and D are taken from the outside to the inside along the depth direction of the permeable layer.
  • the EDS diagrams are shown in Figure 3(b), 3(c), 3(d), 3 (e) shown (ie in Figure 3, (a) is the cross-sectional topography; (b) is the EDS energy spectrum corresponding to point A; (c) is the EDS energy spectrum corresponding to point B; (d) is the corresponding point C (E) is the EDS energy spectrum corresponding to point D), in which the content of Al element gradually decreases, and the content of Fe element gradually increases. From the outside to the inside, the permeated layers are respectively an uneven 10 ⁇ m thick Al2O3 film, a 50-60 ⁇ m thick Fe-Al compound (including FeAl, FeAl2 and Fe3Al), a 40-50 ⁇ m thick Al-containing Fe phase diffusion layer and a matrix.
  • Figure 4 shows the variation of the microhardness produced by this example with the depth direction of the infiltration layer.
  • the surface microhardness is 1390HV, which is 7.95 times the hardness (175HV) of the 321 stainless steel before modification, and the depth of strengthening reaches 1600 ⁇ m.
  • Figure 5 shows the high-temperature compression creep curves of the modified 321 austenitic stainless steel and the unmodified 321 austenitic stainless steel prepared in this example under a 620°C/210MPa creep load, and in a molten aluminum-silicon alloy environment , Comparison chart of high temperature compression creep curve under 620°C/210MPa creep load. It can be seen from Figure 5 that the high temperature creep rupture time of 321 stainless steel at 620°C and 210MPa is 105h, and the steady-state creep rate is 1.3285 ⁇ 10-7.
  • molten aluminum silicon alloy will reduce the 321 stainless steel Creep resistance, the corresponding creep rupture time in the molten aluminum-silicon environment is 73h, and the steady-state creep rate is 2.7143 ⁇ 10-7; while the modified 321 austenitic stainless steel prepared in this example is in molten aluminum-silicon alloy The creep rupture time in the environment is 124h, and the steady-state creep rate is 6.0575 ⁇ 10-8.
  • the creep resistance is improved by an order of magnitude; at the same time, it is compared with the modified 321 Austrian steel prepared in this example.
  • the influence of the molten aluminum alloy environment is negligible.

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Abstract

一种抗高温蠕变性优良的改性奥氏体不锈钢及制备方法，该改性钢包括钢基体和渗层，渗层由内至外包括40～80μm的含Al的Fe相扩散层、50～100μm的Fe-Al化合物层和10～20μm的Al 2O 3薄膜。制备方法包括：(1)电解抛光；(2)渗铝：分别于400～600℃和900℃～1050℃下处理，炉冷；(3)喷砂：于0.6～0.9MPa氮气下进行；(4)退火：1000～1100℃下退火，炉冷；(5)激光冲击强化：单脉冲能量4～7J，光斑直径2.6～3mm，次数1～3次。改性钢在熔融铝硅合金条件下抗蠕变性能和抗腐蚀性能优良、渗层无脆性相、与基体结合力强、抗剥落性能及韧性和强度好。

Description

抗高温蠕变性优良的改性奥氏体不锈钢及其制备方法 技术领域
本发明涉及换热管材料技术领域，尤其涉及一种抗高温蠕变性优良的改性奥氏体不锈钢及其制备方法。
背景技术
太阳热能发电(也称聚焦型太阳能热发电，Concentrating Solar Power，CSP)因具有出稳定、连续、可控的电力输出以及可实现与光伏、风电互补的优势，在能源结构优化中作为清洁能源的代表受到广泛的重视。储热系统是CSP发电站的主要环节。目前商业化CSP发电站储热介质主要采用水蒸气、熔融盐以及导热油，由于水蒸气储热容量低，熔融盐导热系数低、高温易分解和固液分层，导热油高温(在400℃以上)易分解等特点，因此储热系统存在导热效率低、热稳定性差、过冷度大等缺陷，导致发电成本高，限制了太阳能热发电的发展。铝硅合金在1079℃的潜热可达960J/g，其导热系数是盐的2倍以上，在熔点为575℃下经720次熔融-凝固循环后，其相变潜热由505kJ/kg下降至452kJ/kg，降幅只有10.5％，而相变温度基本保持稳定，具有抗氧化性能高的特点(经几百小时的高温氧化后，其氧化率小于0.01％)，被认为是储热介质新一代替代材料。
但是在实际应用中，太阳能热发电换热管件的工作条件和应用环境极其恶劣，需要承受恒定的高应力载荷以及495～620℃的温度波动，受到储热介质熔融铝硅合金腐蚀，发生腐蚀蠕变变形损伤，进而缩短热发电系统的使用寿命。因此提高换热管材料的抗熔融铝硅合金高温蠕变性能是CSP研发亟待解决的问题。目前缓解熔融铝硅合金腐蚀的方法是在换热管材料奥氏体不锈钢上进行渗铝。渗铝作为一种成熟的化学热处理工艺现已广泛应用于工业生产。但普通的渗铝工艺中渗铝涂层表面物相组成不易控制，容易产生脆性相，渗层厚度往往过薄、疏松、与基体结合不紧密、易剥落，影响表面强化效果，或处理过程中材料的强度和韧性降低。可见，采用现有渗铝工艺制备的渗铝钢在力学性能上还存在明显的不足，例如：由于渗铝层的承载性较低，材料韧性和强度不够，渗层中的微孔或微裂纹易在表面形核并快速扩展，导致渗铝试样表现出更高的蠕变应变速率和更短的蠕变断裂寿命。
激光冲击强化是一种先进的表面增强技术，能够使得表层材料晶粒细化，位错密度提高，并引入较高的残余压应力，能够有效抑制裂纹萌生和扩展，以提高材料的力学性能。然而，渗铝和激光冲击共同处理后的材料存在表面粗糙度增加，涂层易剥落，生成的渗铝层在高温载荷下容易开裂，缩短工件寿命的问题。例如，专利申请号为201310282671.7的专利公开了一种渗 铝与激光冲击复合处理的方法，工艺过程为前清洗、在550～780℃退火2～3h、喷丸、在500～600℃渗铝4～6h、后清洗、最后激光冲击，该工艺生成的渗层成分主要以Fe2Al5脆性相为主，没有解决渗层脆性问题，激光冲击过程中涂层易剥落，且渗层与基体结合力差，使得高温下激光冲击强化引入的残余压应力大幅释放，微动疲劳抗力增强效果差。
文献《1Cr11NiWMoV钢激光冲击强化后渗铝工艺研究》(中国激光，2011，38(7)，126～130)公开了一种先激光冲击强化、后在510℃下渗铝12h的方法，该工艺渗铝温度比较低，可有效避免激光冲击强化引入残余压应力的释放，不影响渗铝厚度，但是渗层的主要成分为FeAl3脆性相，在高温下加载后，裂纹容易在渗层处形核且会导致残余压应力大幅释放，导致高温力学性能增强效果不好。申请号为20111006570.2的专利公开了一种先激光冲击，再渗铝，最后激光冲击的方法。该方法获得渗铝层在激光冲击过程中容易脱落，渗铝厚度受到影响，工艺繁琐，处理周期长，生产成本高。
以铝硅合金作为储热介质的太阳能热发电换热管要求高温下(620℃)在熔融铝硅合金的使用环境下具有较高的抗高温蠕变性能。申请号为201310282671.7的专利文献虽能在渗铝层表面引入压缩残余应力，提供表面强度，但所获得的渗层结合力不强，渗层成分含Fe2Al5脆性相，高温下随压缩残余应力的大幅释放，高温强化效果差，不能满足换热管长时运行要求。
有鉴于以上技术的上述缺陷，本发明所要解决的技术问题是提供一种渗铝和激光冲击共同处理的新工艺，该工艺可获得组织均匀、无脆性相，渗层结合力强，表面强化基体韧化的改性奥氏体，可以保证换热管耐高温蠕变性能优良。
发明内容
本发明要解决的技术问题是克服现有技术的不足，提供一种在熔融铝硅合金的条件下抗蠕变性能和抗腐蚀性能优良、渗层成分无脆性相、渗层与基体之间的结合力强、抗剥落性能好，且韧性和强度好的改性奥氏体不锈钢，还提供了一种工艺简单、能制备出渗层与基体结合力强、抗剥落性能好、不含脆性相、在熔融铝硅合金的条件下抗高温蠕变性能和抗腐蚀性能优良，且韧性和强度好的改性奥氏体不锈钢的方法。
为解决上述技术问题，本发明采用的技术方案是：
抗高温蠕变性优良的改性奥氏体不锈钢，所述改性奥氏体不锈钢包括奥氏体不锈钢基体和渗层，所述渗层由内至外包括厚度为40～80μm的含Al的Fe相扩散层、厚度为50～100μm的Fe-Al化合物层和厚度为10～20μm的Al2O3薄膜。
上述的抗高温蠕变性优良的改性奥氏体不锈钢，优选地，所述Fe-Al化合物层为Fe和Al的非脆性金属间化合物；所述非脆性金属间化合物包括FeAl、FeAl2和Fe3Al。
上述的抗高温蠕变性优良的改性奥氏体不锈钢，优选地，所述奥氏体不锈钢基体为321奥氏体不锈钢；所述渗层的表面硬度为625～1390HV，强化作用深度为300～1600μm。
作为一个总的发明构思，还提供一种抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，包括如下步骤：
S1、电解抛光：以奥氏体不锈钢板为阳极、以不溶性导电材料为阴极，对奥氏体不锈钢板进行电解抛光处理；
S2、渗铝：对经电解抛光处理的奥氏体不锈钢进行干燥，再采用固体粉末渗剂进行渗铝，所述渗铝的条件为：先于400～600℃保温20～40min，再于900℃～1050℃保温10～15h后随炉冷却至室温；
S3、喷砂处理：将渗铝后的试样于0.6～0.9MPa的高压氮气下进行喷砂；
S4、退火：将经喷砂处理的试样在1000～1100℃的氩气气氛下退火，随炉冷却取出试样；
S5、激光冲击强化：将经退火处理的试样进行激光冲击处理，激光冲击的单脉冲能量为4～7J，光斑直径为2.6～3mm，激光冲击次数1～3次，经激光冲击强化处理后，即得改性奥氏体不锈钢。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，所述步骤S2中，所述固体粉末渗剂包括以下组分的均匀混合物：粒度为200目的铝粉，Al2O3和Cr粉组成的填充剂及其粉末状NH4Cl的助渗剂，所述固体粉末渗剂中，按质量比计，所述铝粉占42～74％，所述Al2O3粉占20～40％，所述Cr粉占5～15％，所述NH4Cl占1～3％。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，所述步骤S4中，所述退火的时间为0.5～3h。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，所述步骤S5中，采用脉冲大能量激光器，以黑胶布为保护层，以水为约束层；激光的波长为1064nm，脉宽为10～30ns，搭接率40～70％；所述激光冲击处理为双面激光冲击处理；所述激光冲击处理的路径方向与不锈钢板材的轧制方向垂直。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，所述步骤S3中，所述喷砂的磨料为300～500目的Al2O3颗粒；所述喷砂的时间为5～20min，喷砂的距离2～6cm。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，所述步骤S1中，电解液包括体积分数为60～80％的浓硫酸，体积分数为15～37％的浓磷酸和体积分数为3～5％的蒸馏水；电解的直流电压为5～6V，电解液的温度为60～80℃，电解抛光的时间为2～5min。
上述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，优选地，在所述步骤S1前，还 包括对所述奥氏体不锈钢进行表面机械抛光处理的步骤；所述表面机械抛光具体包括：采用80目～1200目粒度的砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min，除油，无水乙醇超声波清洗5～20min，去渍，最后放入干燥箱80℃干燥20～40min。
与现有技术相比，本发明的优点在于：
1、本发明的改性奥氏体不锈钢为由于具有优异的组织结构，使得其具在熔融铝硅合金和高温应力的条件下，具有优良的抗蠕变性能，且材料强度和韧性高，其通过从由基体表面由内至外依次包括厚度为40～80μm的含Al的Fe相扩散层、厚度为50～100μm的Fe-Al化合物层和厚度为10～20μm的Al2O3薄膜的组织结构的组成，渗层不含脆性相，组织均匀，厚度可控，渗层与渗层之间的组分呈梯度平滑过渡，显著降低了基体与渗层之间的界面应力和组织缺陷，有效提高基体与渗层之间的结合力，抑制渗层脱落、抑制裂纹萌生和扩展，有效提高321奥氏体不锈钢在熔融铝硅合金和高温应力的条件下的抗蠕变性能，能满足基于熔融铝硅合金为储热介质的太阳能热发电换热管的工作需求，极具学术价值和工业应用潜力。
2、本发明的改性奥氏体不锈钢的渗层内不含Fe2Al5、FeAl3等脆性相，承载能力强，渗层之间及渗层与基体之间的粘合性好，不容易剥落。
3、本发明的改性奥氏体不锈钢渗层之间结合紧密、无裂缝、界限明显且整齐，渗层的表面硬度为625～1390HV，强化作用深度为300～1600μm，材料的表面强化效果好。
4、本发明通过特定的电解抛光、渗铝、喷砂、退火和激光冲击强化这几个工艺步骤按特定的顺序有机结合对321不锈钢进行处理，并控制渗铝温度、喷砂压力、退火温度、激光冲击路径、单脉能量和光斑强度等参数，获得了从外往里依次为10～20μm的Al2O3薄膜、50～100μm厚的Fe-Al化合物层(FeAl、FeAl2和Fe3Al)和40～80μm厚的含Al(Fe)相扩散层(即含Al的Fe相扩散层)的渗层，渗层之间结合紧密、无裂缝、界限明显且整齐、各界面之间的应力小，基体与渗层界面应力小、渗层表面宏观形貌较好、组织晶粒细小，无裂纹、组织均匀，厚度可控、无Fe2Al5、FeAl3等脆性相、渗层与渗层之间的组分呈梯度平滑过渡的改性奥氏体不锈钢，显著降低了基体与渗层之间的界面应力和组织缺陷，有效提高基体与渗层之间的结合力，抑制渗层脱落、抑制裂纹萌生和扩展，有效提高321奥氏体不锈钢在熔融铝硅合金和高温应力的条件下的抗蠕变性能，其在熔融铝硅合金和高温应力的条件下，具有优良的抗蠕变性能，且能提高奥氏体不锈钢基体强度和韧性。
5、本发明的方法通过进一步控制退火时间、渗剂组成、激光冲击的工艺参数、喷砂时间、喷砂距离、电解抛光的条件等工艺参数，能进一步提高对组织的调控精度，从而进一步提高组织的致密性和完整性，获得表面强化好和基体韧性高的改性奥氏体，有效提高改性奥氏体不锈 钢在熔融铝硅合金和高温应力的条件下的抗蠕变性能、韧性和强度等性能。
6、本发明的方法通过对奥氏体不锈钢试样在电解抛光前进行表面机械抛光处理，除去试样表面的杂质和覆盖物，提高试样表面的洁净度，为后续的渗铝处理创造好的表面条件。
附图说明
图1为本发明的奥氏体不锈钢试样进行激光冲击处理的激光冲击强化路径图。
图2本发明实施例3制备的改性321奥氏体不锈钢与未经改性的321奥氏体不锈钢的XRD对比图。
图3为本发明实施例3制备的改性321奥氏体不锈钢的截面形貌及对应点的EDS能谱分析图。
图4为本发明实施例3制备的改性321奥氏体不锈钢的显微硬度沿渗层深度方向的变化图。
图5为本发明实施例3制备的改性321奥氏体不锈钢与未经改性的321奥氏体不锈钢在620℃/210MPa下和在熔融铝硅合金环境620℃/210MPa下的高温蠕变对比曲线图。
具体实施方式
以下将结合说明书附图和具体实施例对本发明做进一步详细说明。
一种本发明的抗高温蠕变性优良的改性奥氏体不锈钢，所述改性奥氏体不锈钢由内至外包括奥氏体不锈钢基体、厚度为40～80μm的含Al的Fe相扩散层、厚度为50～100μm的Fe-Al化合物层和10～20μm厚的Al2O3薄膜。
所述Fe-Al化合物层为Fe和Al的非脆性金属间化合物，包括FeAl、FeAl2和Fe3Al。
所述奥氏体不锈钢基体为321奥氏体不锈钢。
一种本发明的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，包括以下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢板经不同粒度(80～1200#)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min，除油，无水乙醇超声波清洗5～20min，去渍，最后放入干燥箱80℃干燥20～40min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P0.03％，Ti 0.22％，其余为Fe。321不锈钢常温下的力学性能为：抗拉强度(σb)667MPa，屈服强度(σ0.2)245MPa，延伸率56.5％，硬度175HV。
(2)电解抛光：将321奥氏体不锈钢板接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至60～80℃(可通过水浴加热)，通入5～6V直流电压，在电解中抛光2～5min后，将奥氏体不锈钢板取出冲水清洗吹干，其中电解液的成分如下：体积分数为60～80％的浓硫酸(纯度为98％)、体积分数为15～37％的浓磷酸(纯度为85％)和体积分数为3～ 5％的蒸馏水。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al2O3和Cr粉作填充剂为和粉末状NH4Cl的助渗剂组成，按照5～15wt.％Cr，42～74wt.％Al，20～40wt.％Al2O3，1～3wt.％NH4Cl充分混合。将渗剂与经电解抛光的奥氏体不锈钢板装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，于150℃干燥2h，然后于400～600℃保温20～40min，升温速率为10℃/min，再在900℃～1050℃保温10～15h后随炉冷却至室温。
(4)喷砂处理：将渗铝后的奥氏体不锈钢板放在0.6～0.9MPa高压氮气下进行喷砂，磨料为300～500目的Al2O3颗粒，喷砂时间5～20min，喷砂距离2～6cm，去除疏松的渗层以及杂质。
(5)退火：将经渗铝的奥氏体不锈钢板放入真空管式炉中，在1000～1100℃下高纯氩气下退火时间0.5～3h，随炉冷却取出。
(6)激光冲击强化：对退火后的奥氏体不锈钢板进行双面激光冲击强化处理，激光波长为1064nm，单脉冲能量为4～7J，脉宽为10～30ns，光斑直径为2.6～3mm，搭接率40～70％，黑胶布为保护层，水为约束层，激光冲击次数1～3次(可以为1次、2次或3次)。图1为激光冲击强化路径，该路径方向与不锈钢板材的轧制方向垂直。
本发明的增强抗熔融铝硅合金高温蠕变性能的改性奥氏体不锈钢及制备方法，对奥氏体不锈钢渗铝后在进行激光冲击后，渗层表面宏观形貌较好，其组织晶粒细小，无裂纹。渗层为多层结构，从外往里依次分别是凹凸不平10～20μm的Al2O3薄膜、50～100μm厚的Fe-Al化合物(FeAl、FeAl2和Fe3Al)、40～80μm厚的含Al(Fe)相扩散层以及基体。且渗层之间结合紧密、无裂缝、界限明显且整齐。渗层的表面硬度为625～1390HV，强化作用深度为300～1600μm。620℃熔融铝硅合金环境下，210MPa蠕变载荷下的高温拉伸蠕变断裂时间为94h以上，稳态蠕变速率为1.1254x10-7以下，与321锈钢相比(蠕变断裂时间73h，稳态蠕变速率为2.7143x10-7)，稳态蠕变速率大大降低，表现出优异的抗熔融铝硅合金高温蠕变性能，满足基于熔融铝硅合金为储热介质的太阳能热发电换热管的工作需求，极具学术价值和工业应用潜力。
实施例1:
一种本发明的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，包括以下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢板试样经不同粒度(80目～1200目)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5min，除油，无水乙醇超声波清洗 5min，去渍，最后放入干燥箱80℃干燥20min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％，Ti 0.22％，其余为Fe。热处理状态：321不锈钢常温下的力学性能为：抗拉强度(σb)为667MPa，屈服强度(σ0.2)为245MPa，延伸率为56.5％，硬度为175HV。
(2)电解抛光：将321奥氏体不锈钢板接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至60℃，两极同时进入电解液中，通入5V直流电压，在电解中浸泡2min，试样取出冲水清洗吹干；电解液的成分由体积分数为60％的浓硫酸(纯度为98％)，体积分数为37％的浓磷酸(纯度为85％)和体积分数为3％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al2O3和Cr粉作填充剂为和粉末状NH4Cl的助渗剂组成，按照5wt.％Cr，64wt.％Al，28wt.％Al2O3，3wt.％NH4Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，400℃保温20min，升温速率为10℃/min，在900℃保温15h后随炉冷却至室温。
(4)喷砂处理：将渗铝后试样放在0.6MPa高压氮气下进行喷砂，磨料为300目的Al 2O3颗粒，喷砂时间5min，喷砂距离6cm，去除疏松的渗层以及杂质。
(5)退火：将渗铝试样放入真空管式炉中，在1000℃下高纯氩气下退火时间1.5h，随炉冷却取出试样。
(6)激光冲击强化：对渗铝不锈钢进行双面激光冲击强化处理，激光波长为1064nm，单脉冲能量为4J，脉宽为10ns，光斑直径为2.8mm，搭接率40％，黑胶布为保护层，水为约束层，激光冲击次数1次。激光冲击处理的路径方向与不锈钢板材的轧制方向垂直。
制得的渗层与基体以及层间结合紧密、渗层从外往里依次分别是凹凸不平的20μm厚Al 2O3薄膜、80～100μm厚的Fe-Al化合物层(FeAl、FeAl2和Fe3Al)、60～70μm厚的含Al的Fe相扩散层以及基体，渗层内不含Fe2Al5、FeAl3等脆性相。渗层的表面硬度为600～700HV，强化作用深度为300～400μm。
实施例2：
一种本发明的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，包括以下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢试样经不同粒度(80目～1200目)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗10min，除油，无水乙醇超声波清洗10min，去渍，最后放入干燥箱80℃干燥30min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％， Ti 0.22％，其余为Fe。321不锈钢常温下的力学性能为：抗拉强度(σb)为667MPa，屈服强度(σ0.2)为245MPa，延伸率为56.5％，硬度为175HV。
2)电解抛光：将321奥氏体不锈钢接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至70℃，两极同时进入电解液中，通入5V直流电压，在电解中浸泡5min，试样取出冲水清洗吹干，其中，电解液的成分由体积分数为70％的浓硫酸(纯度为98％)，体积分数为26％的浓磷酸(纯度为85％)和体积分数为4％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al2O3和Cr粉作填充剂为和粉末状NH4Cl的助渗剂组成，按照15wt.％Cr，44wt.％Al，40wt.％Al2O3，1wt.％NH4Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，600℃保温40min，升温速率为10℃/min，在1050℃保温10h后随炉冷却至室温。
(4)喷砂处理：将渗铝后试样放在0.8MPa高压氮气下进行喷砂，磨料为400目的Al2O3颗粒，喷砂时间10min，喷砂距离4cm，去除疏松的渗层以及杂质。
(5)退火：将渗铝试样放入真空管式炉中，在1100℃下高纯氩气下退火时间0.5h，随炉冷却取出试样。
(6)激光冲击强化：对渗铝不锈钢进行双面激光冲击强化处理，激光波长为1064nm，单脉冲能量为6J，脉宽为30ns，光斑直径为3mm，搭接率70％，黑胶布为保护层，水为约束层，激光冲击次数3次。图1为本实施例的激光冲击强化路径，该路径方向与不锈钢板材的轧制方向垂直。
制得的渗层与基体以及层间结合紧密、渗层从外往里依次分别是凹凸不平的10μm厚Al 2O3薄膜、70～80μm厚的Fe-Al化合物层(FeAl、FeAl2和Fe3Al)、50～60μm厚的含Al的Fe相扩散层以及基体，渗层内不含Fe2Al5、FeAl3等脆性相。渗层的表面硬度为700～800HV，强化作用深度为800～1400μm。
实施例3：
一种本发明的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，包括以下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢试样经不同粒度(80目～1200目)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗20min，除油，无水乙醇超声波清洗20min，去渍，最后放入干燥箱80℃干燥40min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％，Ti 0.22％，其余为Fe。321不锈钢常温下的力学性能为：抗拉强度(σb)为667MPa，屈服强 度(σ0.2)为245MPa，延伸率为56.5％，硬度为175HV。
(2)电解抛光：将321奥氏体不锈钢接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至80℃，两极同时进入电解液中，通入5V直流电压，在电解中浸泡3min，试样取出冲水清洗吹干；电解液的成分由体积分数80％的浓硫酸(纯度为98％)，体积分数为15％的浓磷酸(纯度为85％)和体积分数5％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al2O3和Cr粉作填充剂为和粉末状NH4Cl的助渗剂组成，按照10wt.％Cr，58wt.％Al，30wt.％Al2O3，2wt.％NH4Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，500℃保温30min，升温速率为10℃/min，在950℃保温12h后随炉冷却至室温。
(4)喷砂处理：将渗铝后试样放在0.9MPa高压氮气下进行喷砂，磨料为500目的Al2O3颗粒，喷砂时间为5min，喷砂距离为2cm，去除疏松的渗层以及杂质。
(5)退火：将渗铝试样放入真空管式炉中，在1050℃下高纯氩气下退火时间1h，随炉冷却取出试样。
(6)激光冲击强化：采用脉冲大能量激光器对渗铝不锈钢进行双面激光强化处理，激光波长为1064nm，单脉冲能量为7J，脉宽为20ns，光斑直径为2.6mm，搭接率50％，黑胶布为保护层，水为约束层，激光冲击次数3次。图1为本实施例的激光冲击强化路径，该路径方向与不锈钢板材的轧制方向垂直。
对本实施例制得的渗层进行XRD分析，其结果如图2所示，渗层物相组成成分主要由FeAl、FeAl2和Fe3Al组成，渗层内不含Fe2Al5、FeAl3等脆性相。
对本实施例制得的渗层进行SEM分析，其结果如图3所示，渗层与基体以及层间结合紧密、无裂缝、界限明显且整齐，说明渗铝层与基体已形成冶金结合，如图3(a)所示，沿渗层深度方向由外往里取A、B、C、D四个点，EDS图依次如图3(b)、3(c)、3(d)、3(e)所示(即图3中，(a)为截面形貌；(b)为A点对应的EDS能谱；(c)为B点对应的EDS能谱；(d)为C点对应的EDS能谱；(e)为D点对应的EDS能谱)，其中Al元素含量逐渐降低，Fe元素含量逐渐增加。渗层从外往里依次分别是凹凸不平的10μm厚Al2O3薄膜、50～60μm厚的Fe-Al化合物(包括FeAl、FeAl2和Fe3Al)、40～50μm厚的含Al的Fe相扩散层以及基体。
图4为本实施例制得的显微硬度随渗层深度方向的变化，其表面显微硬度为1390HV，是改性前的321不锈钢硬度(175HV)的7.95倍，强化作用深度达1600μm。
图5为本实施例制得的改性321奥氏体不锈钢与未经改性的321奥氏体不锈钢在 620℃/210MPa蠕变载荷下的高温压缩蠕变曲线，及在熔融铝硅合金环境、620℃/210MPa蠕变载荷下的高温压缩蠕变曲线对比图。由图5可知，321不锈钢在620℃、210MPa下的高温蠕变断裂时间105h，稳态蠕变速率为1.3285×10 -7，相同蠕变载荷下(210MPa)，熔融铝硅合金会降低321不锈钢抗蠕变性能，熔融铝硅环境下对应的蠕变断裂时间为73h，稳态蠕变速率为2.7143×10 -7；而本实施例制得的改性321奥氏体不锈钢在熔融铝硅合金环境中的蠕变断裂时间为124h，稳态蠕变速率为6.0575×10 -8，与321锈钢相比，抗蠕变性能提高1个数量级；同时与本实施例制得的改性321奥氏体不锈钢的普通高温蠕变性能相比(蠕变断裂时间为128h)，熔融铝合金环境的影响可忽略不计。
虽然本发明已以较佳实施例揭示如上，然而并非用以限定本发明。任何熟悉本领域的技术人员，在不脱离本发明技术方案范围的情况下，都可利用上述揭示的技术内容对本发明技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本发明技术方案的内容，依据本发明技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均应落在本发明技术方案保护的范围内。

Claims (10)

  1. 抗高温蠕变性优良的改性奥氏体不锈钢，其特征在于，所述改性奥氏体不锈钢包括奥氏体不锈钢基体和渗层，所述渗层由内至外包括厚度为40～80μm的含Al的Fe相扩散层、厚度为50～100μm的Fe-Al化合物层和厚度为10～20μm的Al2O3薄膜。
  2. 如权利要求1所述的抗高温蠕变性优良的改性奥氏体不锈钢，其特征在于，所述Fe-Al化合物层为Fe和Al的非脆性金属间化合物；所述非脆性金属间化合物包括FeAl、FeAl2和Fe3Al。
  3. 如权利要求1或2所述的抗高温蠕变性优良的改性奥氏体不锈钢，其特征在于，所述奥氏体不锈钢基体为321奥氏体不锈钢；所述渗层的表面硬度为625～1390HV，强化作用深度为300～1600μm。
  4. 抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，包括如下步骤：S1、电解抛光：以奥氏体不锈钢为阳极、以不溶性导电材料为阴极，对奥氏体不锈钢进行电解抛光处理；S2、渗铝：对经电解抛光处理的奥氏体不锈钢进行干燥，再采用固体粉末渗剂进行渗铝，所述渗铝的条件为：先于400～600℃保温20～40min，再于900℃～1050℃保温10～15h后随炉冷却至室温；S3、喷砂处理：将渗铝后的奥氏体不锈钢于0.6～0.9MPa的高压氮气下进行喷砂；S4、退火：将经喷砂处理的奥氏体不锈钢在1000～1100℃的氩气气氛下退火，随炉冷却后取出；S5、激光冲击强化：将经退火处理的奥氏体不锈钢进行激光冲击处理，激光冲击的单脉冲能量为4～7J，光斑直径为2.6～3mm，激光冲击次数1～3次，经激光冲击强化处理后，即得改性奥氏体不锈钢。
  5. 如权利要求4所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，所述步骤S2中，所述固体粉末渗剂包括以下组分的均匀混合物：粒度为200目的铝粉，Al2O3和Cr粉组成的填充剂及其粉末状NH4Cl的助渗剂，所述固体粉末渗剂中，按质量比计，所述铝粉占42～74％，所述Al2O3粉占20～40％，所述Cr粉占5～15％，所述NH4Cl占1～3％。
  6. 如权利要求4所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，所述步骤S4中，所述退火的时间为0.5～3h。
  7. 如权利要求4所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，所述步骤S5中，采用脉冲大能量激光器，以黑胶布为保护层，以水为约束层；激光的波长为1064nm，脉宽为10～30ns，搭接率40～70％；所述激光冲击处理为双面激光冲击处理；所述激光冲击处理的路径方向与不锈钢板材的轧制方向垂直。
  8. 如权利要求4～7任意一项所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备 方法，其特征在于，所述步骤S3中，所述喷砂的磨料为300～500目的Al2O3颗粒；所述喷砂的时间为5～20min，喷砂的距离2～6cm。
  9. 如权利要求4～7任意一项所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，所述步骤S1中，电解液包括体积分数为60～80％的浓硫酸，体积分数为15～37％的浓磷酸和体积分数为3～5％的蒸馏水；电解的直流电压为5～6V，电解液的温度为60～80℃，电解抛光的时间为2～5min。
  10. 如权利要求4～7任意一项所述的抗高温蠕变性优良的改性奥氏体不锈钢的制备方法，其特征在于，在所述步骤S1前，还包括对所述奥氏体不锈钢进行表面机械抛光处理的步骤；所述表面机械抛光具体包括：采用80目～1200目粒度的砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min，除油，无水乙醇超声波清洗5～20min，去渍，最后于80℃干燥20～40min。
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