CN109735798B - Modified austenitic stainless steel with excellent high temperature creep resistance and preparation method thereof - Google Patents

Abstract

The invention discloses a modified austenitic stainless steel with excellent high-temperature creep resistance and a preparation method. The modified steel includes a steel matrix and a permeation layer, and the permeation layer includes an Al-containing Fe phase diffusion layer of 40-80 μm from the inside to the outside. , 50-100μm Fe-Al compound layer and 10-20μm Al ₂ O ₃ thin film. The preparation method includes: (1) electrolytic polishing; (2) aluminizing: treating at 400-600 DEG C and 900-1050 DEG C, respectively, and cooling in a furnace; (3) sandblasting: under 0.6-0.9 MPa nitrogen; ( 4) Annealing: annealing at 1000～1100℃, furnace cooling; (5) Laser shock strengthening: single pulse energy 4～7J, spot diameter 2.6～3mm, times 1～3 times. The modified steel of the invention has excellent creep resistance and corrosion resistance under the condition of molten aluminum-silicon alloy, no brittle phase in the infiltrating layer, strong bonding force with the matrix, good spalling resistance, toughness and strength.

Description

Modified austenitic stainless steel with excellent high temperature creep resistance and preparation method thereof

technical field

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.

Background technique

Solar thermal power generation (also known as Concentrating Solar Power, CSP) has the advantages of stable, continuous and controllable power output and complementary advantages with photovoltaic and wind power. It is used as a clean energy source in energy structure optimization. Representatives are widely valued. The heat storage system is the main link of the CSP power station. At present, the heat storage medium of commercial CSP power station mainly uses water vapor, molten salt and heat transfer oil. Due to the low heat storage capacity of water vapor, low thermal conductivity of molten salt, easy decomposition at high temperature and solid-liquid stratification, heat transfer oil has high temperature (above 400 ℃). ) is easy to decompose and other characteristics, so the thermal storage system has defects such as low thermal conductivity, poor thermal stability, and large subcooling degree, resulting in high power generation costs and limiting the development of solar thermal power generation. The latent heat of Al-Si alloy at 1079°C can reach 960J/g, and its thermal conductivity is more than twice that of salt. After 720 melting-solidification cycles at a melting point of 575°C, the latent heat of phase transition decreases from 505kJ/kg to 452kJ. /kg, the drop is only 10.5%, while the phase transition temperature is basically stable, and it has the characteristics of high oxidation resistance (after hundreds of hours of high temperature oxidation, the oxidation rate is less than 0.01%), it is considered to be a new generation of heat storage medium. Material.

However, in practical applications, the working conditions and application environment of solar thermal power generation heat exchange pipes are extremely harsh, and they need to withstand constant high stress loads and temperature fluctuations of 495 to 620 °C. deformation and damage, thereby shortening the service life of the thermal power generation system. Therefore, improving the high temperature creep resistance of heat exchange tube materials is an urgent problem to be solved in the research and development of CSP. At present, the method to alleviate the corrosion of molten aluminum-silicon alloy is to aluminize the austenitic stainless steel, which is the material of the heat exchange tube. As a mature chemical heat treatment process, aluminizing has been widely used in industrial production. However, in the ordinary aluminizing process, the composition of the surface phase of the aluminized coating is not easy to control, and brittle phases are easily generated. The strength and toughness of the material are reduced. It can be seen that the aluminized steel prepared by the existing aluminized process still has obvious deficiencies in mechanical properties. It is easy to nucleate on the surface and expand rapidly, resulting in aluminized specimens showing higher creep strain rate and shorter creep rupture life.

Laser shock peening is an advanced surface enhancement technology, which can refine the grains of the surface material, increase the dislocation density, and introduce high residual compressive stress, which can effectively inhibit the initiation and propagation of cracks and improve the mechanical properties of the material. However, the material treated by aluminizing and laser shock has the problems that the surface roughness increases, the coating is easy to peel off, and the resulting aluminized layer is easy to crack under high temperature load, which shortens the life of the workpiece. For example, the patent with the patent application number of 201310282671.7 discloses a method for composite treatment of aluminizing and laser shock. The process includes pre-cleaning, annealing at 550-780°C for 2-3 hours, shot peening, and aluminizing at 500-600°C for 4 ~6h, post-cleaning, and final laser shock, the composition of the infiltrated layer generated by this process is mainly Fe ₂ Al ₅ brittle phase, which does not solve the problem of the brittleness of the infiltrated layer. Due to the poor force, the residual compressive stress introduced by laser shock strengthening at high temperature is greatly released, and the effect of fretting fatigue resistance enhancement is poor.

The document "Research on Aluminizing Process After Laser Shock Strengthening of 1Cr11NiWMoV Steel" (China Laser, 2011, 38(7), 126-130) discloses a method of first laser shock strengthening and then aluminizing at 510 ° C for 12 hours. The aluminizing temperature is relatively low, which can effectively avoid the release of residual compressive stress introduced by laser shock strengthening, and does not affect the thickness of the aluminizing layer, but the main component of the aluminizing layer is FeAl ₃ brittle phase. nucleation and will lead to a significant release of residual compressive stress, resulting in poor enhancement of high temperature mechanical properties. The patent with the application number of 20111006570.2 discloses a method of laser shock first, then aluminized, 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 cumbersome, the processing period is long, and the production cost is high.

The solar thermal power generation heat exchange tube using aluminum-silicon alloy as heat storage medium requires high temperature creep resistance at high temperature (620℃) in the use environment of molten aluminum-silicon alloy. Although the patent document with the application number of 201310282671.7 can introduce compressive residual stress on the surface of the aluminized layer to provide surface strength, but the obtained infiltration layer has a weak bonding force, and the composition of the infiltrated layer contains Fe ₂ Al ₅ brittle phase, and the compressive residual stress at high temperature The stress is greatly released, and the high temperature strengthening effect is poor, which cannot meet the long-term operation requirements of the heat exchange tube.

In view of the above-mentioned defects of the above technologies, the technical problem to be solved by the present invention is to provide a new process for co-processing of aluminizing and laser shock, which can obtain uniform structure, no brittle phase, strong bonding force of the infiltrating layer, and surface strengthening of the matrix. The toughened modified austenite can ensure excellent high temperature creep resistance of the heat exchange tube.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and to provide a kind of excellent creep resistance and corrosion resistance under the condition of molten aluminum-silicon alloy, the composition of the infiltration layer has no brittle phase, and the gap between the infiltration layer and the matrix is excellent. The modified austenitic stainless steel has strong bonding force, good spalling resistance, and good toughness and strength. It also provides a simple process, which can prepare the infiltration layer and the matrix with strong bonding force, good spalling 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.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

Modified austenitic stainless steel with excellent high temperature creep resistance, the modified austenitic stainless steel includes an austenitic stainless steel matrix and a seepage layer, and the seepage layer includes an Al-containing material with a thickness of 40-80 μm from the inside to the outside. The Fe phase diffusion layer, the Fe-Al compound layer with a thickness of 50-100 μm, and the Al ₂ O ₃ thin film with a thickness of 10-20 μm.

The above-mentioned modified austenitic stainless steel with excellent high temperature creep resistance, preferably, the Fe-Al compound layer is a non-brittle intermetallic compound of Fe and Al; the non-brittle intermetallic compound includes FeAl, FeAl ₂ and _Fe3Al .

The above-mentioned modified austenitic stainless steel with excellent high temperature creep resistance, preferably, the austenitic stainless steel matrix is 321 austenitic stainless steel; the surface hardness of the infiltrated layer is 625-1390HV, and the strengthening depth is 300 ~1600μm.

As a general inventive concept, a method for preparing a modified austenitic stainless steel with excellent high temperature creep resistance is also provided, comprising the following steps:

S1. Electrolytic polishing: 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;

S2. Aluminizing: Dry the electropolished austenitic stainless steel, and then use a solid powder infiltrating agent for aluminizing. ℃～1050℃ for 10～15h and then cooled to room temperature with the furnace;

S3. Sandblasting treatment: blast the aluminized sample under high pressure nitrogen of 0.6-0.9MPa;

S4. Annealing: anneal the sandblasted sample in an argon atmosphere at 1000-1100 °C, and take out the sample after cooling in the furnace;

S5. 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, and the number of laser shocks is 1~3 times. After the laser shock treatment , that is, the modified austenitic stainless steel is obtained.

The above-mentioned preparation method of modified austenitic stainless steel with excellent high temperature creep resistance, preferably, in the step S2, the solid powder infiltration agent includes a uniform mixture of the following components: aluminum powder with a particle size of 200 mesh, Al A filler composed of ₂ O ₃ and Cr powder and a penetration aid of powdered NH ₄ Cl, in the solid powder penetration agent, in terms of mass ratio, the aluminum powder accounts for 42-74%, and the Al ₂ O _3. The powder accounts for 20-40%, the Cr powder accounts for 5-15%, and the NH ₄ Cl accounts for 1-3%.

In the above-mentioned preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance, preferably, in the step S4, the annealing time is 0.5-3 hours.

The above-mentioned preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance, preferably, in the step S5, a pulsed high-energy laser is used, the black tape is used as the protective layer, and the water is used as the constraining layer; the wavelength of the laser is 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 sheet.

In the above-mentioned preparation method of modified austenitic stainless steel with excellent high temperature creep resistance, preferably, in the step S3, the abrasive for sandblasting is 300-500 mesh Al ₂ O ₃ particles; The time is 5 to 20 minutes, and the distance of sandblasting is 2 to 6 cm.

The above-mentioned preparation method of modified austenitic stainless steel with excellent high temperature creep resistance, preferably, in the step S1, the electrolyte includes concentrated sulfuric acid with a volume fraction of 60-80%, and a volume fraction of 15-37%. Concentrated phosphoric acid and distilled water with a volume fraction of 3-5%; the DC voltage of electrolysis is 5-6V, the temperature of the electrolyte is 60-80°C, and the electropolishing time is 2-5min.

The above-mentioned preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance, preferably, before the step S1, further comprising the step of performing surface mechanical polishing on the austenitic stainless steel; Polishing specifically includes: sanding with 80-1200-mesh sandpaper until there are no obvious scratches visible to the naked eye, then cleaning with acetone for 5-20 minutes in ultrasonic waves, degreasing, ultrasonic cleaning with absolute ethanol for 5-20 minutes, removing stains, and finally placing Put it in a drying oven at 80°C for 20-40min.

Compared with the prior art, the advantages of the present invention are:

1. The modified austenitic stainless steel of the present invention has excellent creep resistance under the condition of molten aluminum-silicon alloy and high temperature stress due to its excellent structure, and has high material strength and toughness. From the inside to the outside of the substrate surface, it includes an Al-containing Fe phase diffusion layer with a thickness of 40-80 μm, a Fe-Al compound layer with a thickness of 50-100 μm and an Al ₂ O ₃ film with a thickness of 10-20 μm. The composition of the structure, the infiltration layer does not contain brittle phase, the structure is uniform, the thickness is controllable, the components between the infiltration layer and the infiltration layer are gradient and smooth transition, which significantly reduces the interface stress and tissue defects between the matrix and the infiltration layer, effectively Improve the bonding force between the matrix and the infiltration layer, inhibit the infiltration layer from falling off, inhibit the initiation and expansion 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. The working requirements of solar thermal power generation heat exchange tubes with aluminum-silicon alloys as heat storage medium have great academic value and industrial application potential.

2. The infiltration layer of the modified austenitic stainless steel of the present invention does not contain brittle phases such as Fe ₂ Al ₅ , FeAl ₃ , etc., and has strong bearing capacity, good adhesion between the infiltration layers and between the infiltration layers and the matrix, without Flakes off easily.

3. The modified austenitic stainless steel infiltration layers of the present invention are closely combined, have no cracks, have obvious and neat boundaries, the surface hardness of the infiltrated layer is 625-1390HV, the strengthening depth is 300-1600 μm, and the surface strengthening effect of the material is good. .

4. The present invention processes 321 stainless steel organically in a specific order through specific process steps of electrolytic polishing, aluminizing, sandblasting, annealing and laser shock strengthening, and controls the aluminizing temperature, sandblasting pressure, and annealing temperature. , laser shock path, single pulse energy and spot intensity and other parameters, the Al ₂ O ₃ thin film with a thickness of 10-20 μm and a Fe-Al compound layer (FeAl, FeAl ₂ and Fe ₃ ) with a thickness of 50-100 μm were obtained from the outside Al) and 40-80 μm thick Al(Fe)-containing phase diffusion layer (ie, Al-containing Fe phase diffusion layer) infiltration layer, the infiltration layers are tightly bonded, without cracks, with clear and neat boundaries, and the interfaces between The stress is small, the interface stress between the matrix and the infiltrating layer is small, the macroscopic appearance of the infiltrating layer surface is good, the structure grain is fine, no cracks, the structure is uniform, the thickness is controllable, no Fe ₂ Al ₅ , FeAl ₃ and other brittle phases, the infiltrating layer and The modified austenitic stainless steel with the composition between the infiltration layers is gradient and smooth transition, which significantly reduces the interface stress and microstructure defects between the matrix and the infiltration layer, effectively improves the bonding force between the matrix and the infiltration layer, and inhibits the infiltration layer. Falling off, inhibiting the initiation and propagation of cracks, effectively improving 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 Change properties, and can improve the strength and toughness of austenitic stainless steel matrix.

5. The method of the present invention can further improve the control accuracy of the structure by further controlling the annealing time, the composition of the infiltrating agent, the process parameters of the laser shock, the sandblasting time, the sandblasting distance, the conditions of the 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 strength and other properties.

6. In the method of the present invention, the surface of the austenitic stainless steel sample is mechanically polished before electropolishing to remove impurities and coverings on the surface of the sample, improve the cleanliness of the surface of the sample, and create a better surface for the subsequent aluminizing treatment. surface conditions.

Description of drawings

FIG. 1 is a diagram of the laser shock strengthening path of the austenitic stainless steel sample of the present invention subjected to laser shock treatment.

Figure 2 XRD comparison diagram of modified 321 austenitic stainless steel prepared in Example 3 of the present invention and unmodified 321 austenitic stainless steel.

FIG. 3 is the cross-sectional morphology of the modified 321 austenitic stainless steel prepared in Example 3 of the present invention and the EDS energy spectrum analysis diagram of the corresponding point.

FIG. 4 is a graph showing the change of the microhardness of the modified 321 austenitic stainless steel prepared in Example 3 of the present invention along the depth direction of the infiltrated layer.

Figure 5 shows the high temperature creep of the modified 321 austenitic stainless steel prepared in Example 3 of the present invention and the unmodified 321 austenitic stainless steel at 620°C/210MPa and in the molten aluminum-silicon alloy environment at 620°C/210MPa Compare graphs.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

A modified austenitic stainless steel with excellent high temperature creep resistance of the present invention, the modified austenitic stainless steel includes an austenitic stainless steel matrix from the inside to the outside, and a Fe phase diffusion containing Al with a thickness of 40-80 μm. layer, a Fe-Al compound layer with a thickness of 50-100 μm and an Al ₂ O ₃ thin film with a thickness of 10-20 μm.

The Fe-Al compound layer is a non-brittle intermetallic compound of Fe and Al, including FeAl, FeAl ₂ and Fe ₃ Al.

The austenitic stainless steel base is 321 austenitic stainless steel.

A preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance of the present invention, comprising the following steps:

(1) Surface mechanical polishing: The hot-rolled austenitic stainless steel plate is polished with sandpaper of different particle sizes (80-1200#) until there are no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic waves for 5-20 minutes to remove oil and no scratches. Ultrasonic cleaning with water ethanol for 5-20 minutes, remove stains, and finally put it in a drying oven at 80 °C for drying for 20-40 minutes; the 321 austenitic stainless steel is a rolled sheet, and its chemical composition mass fractions are C 0.04%, Si 0.38%, Mn 1.08%, Cr 17.02%, Ni 9.06%, N0.05%, P 0.03%, Ti 0.22%, and the rest are Fe. The mechanical properties of 321 stainless steel at room temperature are: tensile strength (σb) 667MPa, yield strength (σ0.2) 245MPa, elongation 56.5%, hardness 175HV.

(2) Electrolytic polishing: connect the 321 austenitic stainless steel plate to the anode, use an insoluble conductive material (graphite plate) for the cathode, and the distance between the cathode and anode is 50mm. ～6V DC voltage, after polishing in electrolysis for 2～5min, the austenitic stainless steel plate is taken out, rinsed, washed and dried. 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 15-37% (purity of 85%) and distilled water with a volume fraction of 3-5%.

(3) Aluminizing: The solid powder infiltrating agent is composed of aluminum source, filler, and penetration aid (activator). The aluminum source is aluminum powder with a particle size of 200 meshes, and Al ₂ O ₃ and Cr powder are used as fillers and powder. The composition of the penetration aid of NH ₄ Cl is fully mixed according to 5-15wt.%Cr, 42-74wt.%Al, _20-40wt .% _Al2O3 , and 1-3wt.% _NH4Cl . Put the infiltrating agent and the electropolished austenitic stainless steel plate into a heat-resistant stainless steel material tank, press down, seal with refractory mud, and carry out aluminizing: heat up with the furnace, dry at 150 ° C for 2 hours, and then keep at 400 ~ 600 ° C for heat preservation 20～40min, the heating rate is 10℃/min, then keep at 900℃～1050℃ for 10～15h, and then cool down to room temperature with the furnace.

(4) Sandblasting treatment: The austenitic stainless steel plate after aluminized is placed under high pressure nitrogen of 0.6-0.9MPa for sandblasting, and the abrasive is 300-500 mesh Al ₂ O ₃ particles. The sand distance is 2-6cm to remove loose infiltration layer and impurities.

(5) Annealing: The aluminized austenitic stainless steel plate is put into a vacuum tube furnace, annealed under high-purity argon gas at 1000-1100 ° C for 0.5-3 hours, and taken out as the furnace cools.

(6) Laser shock strengthening: double-sided laser shock treatment is performed 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 overlap rate is 40-70%, the black tape is the protective layer, the water is the constraining layer, and the number of laser shocks is 1-3 times (it can be 1, 2 or 3 times). Figure 1 shows the laser shock strengthening path, and the direction of the path is perpendicular to the rolling direction of the stainless steel sheet.

In the modified austenitic stainless steel for enhancing the high temperature creep resistance of molten aluminum-silicon alloy and the preparation method of the present invention, after the austenitic stainless steel is aluminized and subjected to laser shock, the macroscopic appearance of the surface of the infiltrated layer is good, and its microstructure and crystal structure are good. The grains are small and without cracks. The infiltration layer is a multi-layer structure, and from the outside to the inside, there are Al ₂ O ₃ films with unevenness of 10-20 μm, Fe-Al compounds (FeAl, FeAl ₂ and Fe ₃ Al) with a thickness of 50-100 μm, and a thickness of 40-80 μm. The Al(Fe)-containing phase diffusion layer and matrix. And the infiltration layers are closely combined, without cracks, and the boundaries are obvious and neat. The surface hardness of the infiltration layer is 625-1390HV, and the strengthening depth is 300-1600μm. In the environment of molten aluminum-silicon alloy at 620℃, the high temperature tensile creep rupture time under the creep load of 210MPa is more than 94h, and the steady-state creep rate is less than ^1.1254x10-7 . Compared with 321 stainless steel (creep rupture time is 73h) , the steady-state creep rate is 2.7143×10 ^-7 ), and the steady-state creep rate is greatly reduced, showing excellent creep resistance of molten aluminum-silicon alloy at high temperature, which meets the requirements of solar thermal power generation based on molten aluminum-silicon alloy as heat storage medium. The working requirements of heat pipes have great academic value and industrial application potential.

Embodiment 1:

A preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance of the present invention, comprising the following steps:

(1) Surface mechanical polishing: The hot-rolled austenitic stainless steel plate samples are polished with sandpaper of different particle sizes (80 mesh to 1200 mesh) until there are no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic waves for 5 minutes to remove oil. Ultrasonic cleaning with absolute ethanol for 5 minutes, removing stains, and finally drying in a drying box at 80°C for 20 minutes; 321 austenitic stainless steel is a rolled sheet, and its chemical composition mass fraction is 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 are Fe. Heat treatment state: The mechanical properties of 321 stainless steel at room temperature are: tensile strength (σ _b ) is 667 MPa, yield strength (σ _0.2 ) is 245 MPa, elongation is 56.5%, and hardness is 175HV.

(2) Electrolytic polishing: connect the 321 austenitic stainless steel plate to the anode, use an insoluble conductive material (graphite plate) for the cathode, the distance between the cathode and anode is 50mm, the electrolyte is heated to 60°C, the two poles enter the electrolyte at the same time, and 5V DC is passed through. Voltage, soaked in electrolysis for 2min, the sample was taken out, washed with water, washed and dried; the composition of the electrolyte consists of concentrated sulfuric acid with a volume fraction of 60% (purity of 98%) and concentrated phosphoric acid with a volume fraction of 37% (purity of 85%). ) and distilled water with a volume fraction of 3%.

(3) Aluminizing: The solid powder infiltrating agent is composed of aluminum source, filler, and penetration aid (activator). The aluminum source is aluminum powder with a particle size of 200 meshes, and Al ₂ O ₃ and Cr powder are used as fillers and powder. The composition of the penetration aid of NH ₄ Cl is fully mixed according to 5wt.%Cr, 64wt.%Al, _28wt .% _Al2O3 and 3wt.% _NH4Cl . Put the infiltrating agent and the sample into a heat-resistant stainless steel tank, press it tightly, seal it with refractory mud, and perform aluminizing: heat up with the furnace, dry at 150 °C for 2 hours, keep at 400 °C for 20 minutes, the heating rate is 10 °C/min, at 900 °C ℃ for 15h and then cooled to room temperature with the furnace.

(4) Sandblasting treatment: place the aluminized sample under 0.6MPa high pressure nitrogen for sandblasting, the abrasive is 300 mesh Al ₂ O ₃ particles, the sandblasting time is 5min, the sandblasting distance is 6cm, and the loose infiltration layer and impurities.

(5) Annealing: Put the aluminized sample into a vacuum tube furnace, anneal for 1.5h under high-purity argon at 1000°C, and take out the sample as the furnace cools.

(6) Laser shock strengthening: double-sided laser shock treatment is performed on 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, and the overlap rate is 40%. The black tape is Protective layer, water is the constraining 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 obtained infiltration layer is closely combined with the matrix and the interlayer, and the infiltration layer is a 20μm thick Al ₂ O ₃ film with uneven thickness and an 80-100 μm thick Fe-Al compound layer (FeAl, FeAl ₂ and Fe ₃ Al), 60-70 μm thick Al-containing Fe phase diffusion layer and matrix, the infiltration layer does not contain Fe ₂ Al ₅ , FeAl ₃ and other brittle phases. The surface hardness of the infiltration layer is 600-700HV, and the strengthening depth is 300-400μm.

Example 2:

A preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance of the present invention, comprising the following steps:

(1) Surface mechanical polishing: The hot-rolled austenitic stainless steel samples are polished with sandpaper of different particle sizes (80 mesh to 1200 mesh) until there are no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic waves for 10 minutes to remove oil and no scratches. Ultrasonic cleaning with water ethanol for 10min, remove stains, and finally put it in a drying oven at 80℃ for 30min drying; 321 austenitic stainless steel is a rolled plate, and its chemical composition mass fractions are 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 (σ _b ) is 667 MPa, yield strength (σ _0.2 ) is 245 MPa, elongation is 56.5%, and hardness is 175HV.

2) Electrolytic polishing: connect 321 austenitic stainless steel to the anode, use an insoluble conductive material (graphite plate) for the cathode, the distance between the cathode and anode is 50mm, the electrolyte is heated to 70°C, the two poles enter the electrolyte at the same time, and a 5V DC voltage is applied. Immerse in electrolysis for 5 minutes, take out the sample, rinse with water, wash and blow dry. The composition of the electrolyte consists of concentrated sulfuric acid with a volume fraction of 70% (purity of 98%) and concentrated phosphoric acid with a volume fraction of 26% (purity of 85%). ) and distilled water with a volume fraction of 4%.

(3) Aluminizing: The solid powder infiltrating agent is composed of aluminum source, filler, and penetration aid (activator). The aluminum source is aluminum powder with a particle size of 200 meshes, and Al ₂ O ₃ and Cr powder are used as fillers and powder. The composition of the penetration aid of NH ₄ Cl is fully mixed according to 15wt.%Cr, _44wt .%Al, 40wt.% _Al2O3 , 1wt.% _NH4Cl . Put the infiltrating agent and the sample into a heat-resistant stainless steel tank, press it tightly, seal it with refractory mud, and perform aluminizing: heat up with the furnace, dry at 150 °C for 2 hours, keep at 600 °C for 40 minutes, the heating rate is 10 °C/min, and at 1050 ℃ for 10h and then cooled to room temperature with the furnace.

(4) Sandblasting treatment: Put the aluminized sample under 0.8MPa high pressure nitrogen for sandblasting, the abrasive is 400 mesh Al ₂ O ₃ particles, the sandblasting time is 10min, the sandblasting distance is 4cm, and the loose infiltration layer and impurities.

(5) Annealing: Put the aluminized sample into a vacuum tube furnace, anneal for 0.5h under high-purity argon at 1100°C, and take out the sample as the furnace cools.

(6) Laser shock strengthening: double-sided laser shock treatment is carried out on aluminized stainless steel. The laser wavelength is 1064nm, the single pulse energy is 6J, the pulse width is 30ns, the spot diameter is 3mm, the overlap rate is 70%, and the black tape is used for protection. layer, water is the confinement layer, and the number of laser shocks is 3 times. FIG. 1 is a laser shock strengthening path of this embodiment, and the direction of the path is perpendicular to the rolling direction of the stainless steel plate.

The obtained infiltration layer is closely combined with the substrate and the interlayer, and the infiltration layer is a 10 μm thick Al ₂ O ₃ film with uneven thickness and a 70-80 μm thick Fe-Al compound layer (FeAl, FeAl ₂ and Fe, respectively, from outside to inside). ₃ Al), 50-60 μm thick Al-containing Fe phase diffusion layer and matrix, the infiltration layer does not contain Fe ₂ Al ₅ , FeAl ₃ and other brittle phases. The surface hardness of the infiltration layer is 700-800HV, and the strengthening depth is 800-1400μm.

Example 3:

A preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance of the present invention, comprising the following steps:

(1) Surface mechanical polishing: The hot-rolled austenitic stainless steel samples are polished with sandpapers of different particle sizes (80 mesh to 1200 mesh) until there are no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic waves for 20 minutes to remove oil and no scratches. Ultrasonic cleaning with water ethanol for 20min, remove stains, and finally put it in a drying oven at 80°C for drying for 40min; the 321 austenitic stainless steel is a rolled plate, and its chemical composition mass fractions are 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 (σb) is 667 MPa, yield strength (σ0.2) is 245 MPa, elongation is 56.5%, and hardness is 175HV.

(2) Electrolytic polishing: connect 321 austenitic stainless steel to the anode, use an insoluble conductive material (graphite plate) for the cathode, the distance between cathode and anode is 50mm, the electrolyte is heated to 80°C, the two poles enter the electrolyte at the same time, and a 5V DC voltage is applied , soaked in electrolysis for 3 minutes, the sample was taken out, washed with water, washed and dried; the composition of the electrolyte consists of concentrated sulfuric acid with a volume fraction of 80% (purity of 98%), concentrated phosphoric acid with a volume fraction of 15% (purity of 85%) and Distilled water with a volume fraction of 5%.

(3) Aluminizing: The solid powder infiltrating agent is composed of aluminum source, filler, and penetration aid (activator). The aluminum source is aluminum powder with a particle size of 200 meshes, and Al ₂ O ₃ and Cr powder are used as fillers and powder. The composition of the penetration aid of NH ₄ Cl is fully mixed according to 10wt.%Cr, 58wt.%Al, 30wt.% _Al2O3 and _2wt .% _NH4Cl . Put the infiltrating agent and the sample into a heat-resistant stainless steel tank, press it tightly, seal it with refractory mud, and carry out aluminizing: heat up with the furnace, dry at 150 °C for 2 hours, keep at 500 °C for 30 minutes, the heating rate is 10 °C/min, and the temperature is 950 °C. ℃ for 12h and then cooled to room temperature with the furnace.

(4) Sandblasting treatment: Put the aluminized sample under 0.9MPa high pressure nitrogen for sandblasting, the abrasive is 500 mesh Al ₂ O ₃ particles, the sandblasting time is 5min, and the sandblasting distance is 2cm to remove loose infiltration. layers and impurities.

(5) Annealing: put the aluminized sample into a vacuum tube furnace, anneal for 1 hour under high-purity argon at 1050°C, and take out the sample as the furnace cools.

(6) Laser shock strengthening: Double-sided laser strengthening treatment of aluminized stainless steel by a pulsed high-energy laser. The laser wavelength is 1064nm, the single pulse energy is 7J, the pulse width is 20ns, the spot diameter is 2.6mm, and the overlap rate is 50%. , the black tape is the protective layer, the water is the constraining layer, and the number of laser shocks is 3 times. FIG. 1 is a laser shock strengthening path of this embodiment, and the direction of the path is perpendicular to the rolling direction of the stainless steel plate.

XRD analysis was carried out on the infiltrated layer prepared in this example. The results are shown in Figure 2. The phase composition of the infiltrated layer is mainly composed of FeAl, FeAl ₂ and Fe ₃ Al, and the infiltration layer does not contain Fe ₂ Al ₅ and FeAl ₃ Equal brittle phase.

The SEM analysis of the infiltrated layer obtained in this example is carried out, and the results are shown in Figure 3. The infiltration layer is closely combined with the substrate and the interlayer, without cracks, and the boundaries are obvious and neat, indicating that the aluminized layer and the substrate have formed a metallurgical bond, such as As shown in Figure 3(a), four points A, B, C, and D are taken from the outside to the inside along the depth direction of the seepage layer, and the EDS map is shown in Figures 3(b), 3(c), 3(d), and 3. As shown in (e) (that is, in Figure 3, (a) is the cross-sectional morphology; (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 The EDS energy spectrum of ; (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. The infiltrated layers are, from outside to inside, a 10-μm-thick Al ₂ O ₃ film with unevenness, a 50-60 μm-thick Fe-Al compound (including FeAl, FeAl ₂ and Fe ₃ Al), and a 40-50 μm-thick Al-containing Fe Phase diffusion layer and matrix.

Figure 4 shows the variation of microhardness with the depth of the infiltrated layer obtained in this example. The surface microhardness is 1390HV, which is 7.95 times the hardness of 321 stainless steel before modification (175HV), and the strengthening depth reaches 1600 μm.

Figure 5 shows the high-temperature compressive creep curves of the modified 321 austenitic stainless steel and unmodified 321 austenitic stainless steel prepared in this example under the creep load of 620°C/210MPa, and the high temperature compressive creep curves in the molten aluminum-silicon alloy environment , Comparison of high temperature compression creep curves under 620℃/210MPa creep load. It can be seen from Figure 5 that the high temperature creep rupture time of 321 stainless steel at 620 ℃ and 210MPa is 105h, and the steady-state creep rate is 1.3285×10 ^-7 . Under the same creep load (210MPa), molten aluminum-silicon alloy will reduce 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 ; and the modified 321 austenitic stainless steel obtained in this example is in the molten aluminum-silicon alloy. The creep rupture time in the environment is 124h, and the steady-state creep rate is 6.0575×10 ^-8 . Compared with 321 stainless steel, the creep resistance is improved by an order of magnitude; Compared with the ordinary high temperature creep properties of tensite stainless steel (creep rupture time is 128h), the influence of the molten aluminum alloy environment is negligible.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above, or modify it into an equivalent implementation of equivalent changes. example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention should fall within the protection scope of the technical solutions of the present invention.

Claims (9)

1. The modified austenitic stainless steel with excellent high temperature creep resistance is characterized in that, the modified austenitic stainless steel includes an austenitic stainless steel matrix and a permeation layer, and the infiltration layer includes a thickness of 40 mm from the inside to the outside. A Fe phase diffusion layer containing Al of ~80 μm, a Fe-Al compound layer with a thickness of 50 to 100 μm, and an Al ₂ O ₃ film with a thickness of 10 to 20 μm; the Fe-Al compound layer is a non-brittle metal of Fe and Al intermetallic compounds; the non-brittle intermetallic compounds include FeAl, FeAl ₂ and Fe ₃ Al; the surface hardness of the infiltrated layer is 625-1390HV, and the strengthening depth is 300-1600 μm. 2 . The modified austenitic stainless steel with excellent high temperature creep resistance according to claim 1 , wherein the austenitic stainless steel matrix is 321 austenitic stainless steel. 3 . 3. The preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance is characterized in that, comprising the following steps: S1. Electrolytic polishing: Electrolytic polishing is performed on austenitic stainless steel with austenitic stainless steel as anode and insoluble conductive material as cathode; S2. Aluminizing: Dry the electropolished austenitic stainless steel, and then use a solid powder infiltrating agent for aluminizing. ℃～1050℃ for 10～15h and then cooled to room temperature with the furnace; the solid powder infiltration agent includes a uniform mixture of the following components: aluminum powder with a particle size of 200 meshes, a filler composed of Al ₂ O ₃ and Cr powder and its powder The penetration aid of NH ₄ Cl; S3. Sandblasting treatment: blast the austenitic stainless steel after aluminizing under high pressure nitrogen of 0.6-0.9MPa; S4. Annealing: anneal the sandblasted austenitic stainless steel in an argon atmosphere of 1000-1100 °C, and take it out after cooling in the furnace; S5. Laser shock strengthening: The annealed austenitic stainless steel 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, and the laser shock is strengthened by laser shock. After treatment, the modified austenitic stainless steel is obtained. 4. The preparation method of modified austenitic stainless steel with excellent high temperature creep resistance as claimed in claim 3, characterized in that, in the step S2, in the solid powder infiltration agent, by mass ratio, the The aluminum powder accounts for 42-74%, the Al ₂ O ₃ powder accounts for 20-40%, the Cr powder accounts for 5-15%, and the NH ₄ Cl accounts for 1-3%. 5 . The method for preparing a modified austenitic stainless steel with excellent high temperature creep resistance according to claim 3 , wherein, in the step S4 , the annealing time is 0.5-3 hours. 6 . 6. The preparation method of the modified austenitic stainless steel with excellent high temperature creep resistance as claimed in claim 3, characterized in that, in the step S5, a pulsed high-energy laser is used, and a black tape is used as a protective layer, and the Water is the constraining layer; the wavelength of the laser is 1064 nm, the pulse width is 10-30 ns, 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 the same as that of the stainless steel plate. The rolling direction is vertical. 7. The preparation method of modified austenitic stainless steel with excellent high temperature creep resistance according to any one of claims 3 to 6, characterized in that, in the step S3, the abrasive for the sandblasting is 300～ 500 mesh Al ₂ O ₃ particles; the sandblasting time is 5-20min, and the sandblasting distance is 2-6cm. 8. The preparation method of modified austenitic stainless steel with excellent high temperature creep resistance according to any one of claims 3 to 6, characterized in that, in the step S1, the electrolyte contains a volume fraction of 60 to 80 % concentrated sulfuric acid, 15-37% concentrated phosphoric acid and 3-5% distilled water; the DC voltage of electrolysis is 5-6V, the temperature of the electrolyte is 60-80°C, and the electropolishing time is 2 to 5 minutes. 9 . The method for preparing a modified austenitic stainless steel with excellent high temperature creep resistance according to any one of claims 3 to 6 , characterized in that, before the step S1 , further comprising: The step of mechanically polishing the surface of the stainless steel; the mechanical polishing of the surface specifically includes: grinding with sandpaper with a particle size of 80 mesh to 1200 mesh until no obvious scratches are visible to the naked eye, and then using acetone in ultrasonic waves for 5 to 20 minutes to remove oil, no obvious scratches. Ultrasonic cleaning with water ethanol for 5 to 20 minutes to remove stains, and finally drying at 80°C for 20 to 40 minutes.

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