EP4276209A1 - Austenitische hochaluminiumlegierung mit hervorragenden hochtemperatur-korrosionsschutzeigenschaften und kriechfestigkeit - Google Patents

Austenitische hochaluminiumlegierung mit hervorragenden hochtemperatur-korrosionsschutzeigenschaften und kriechfestigkeit Download PDF

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EP4276209A1
EP4276209A1 EP22736588.9A EP22736588A EP4276209A1 EP 4276209 A1 EP4276209 A1 EP 4276209A1 EP 22736588 A EP22736588 A EP 22736588A EP 4276209 A1 EP4276209 A1 EP 4276209A1
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Prior art keywords
aluminum
aluminum austenitic
centrifugal casting
alloy
casting pipe
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EP22736588.9A
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English (en)
French (fr)
Inventor
Minghao Zhang
Kun Du
Jian PEI
Tianzhen DING
Guowei YE
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Yantai Manoir Heat Resistant Alloys Co Ltd
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Yantai Manoir Heat Resistant Alloys Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B22D11/002—Stainless steels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/006—Continuous casting of metals, i.e. casting in indefinite lengths of tubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
    • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
    • B22D21/04—Casting aluminium or magnesium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C22C1/023—Alloys based on nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

  • the present invention relates to the field of austenitic alloys, specifically to high-aluminum austenitic alloys with excellent high temperature ( ⁇ 900°C) corrosion resistance and creep resistance.
  • Ni-Cr austenitic heat resistant alloy has been widely used in petrochemical industry.
  • the devices used in this industry (such as cracking tubes for steam cracking) have to withstand the combustion near 1100°C outside the furnace tube, and on the other hand, the materials have to withstand the carburization corrosion brought by the hydrocarbon gas inside the furnace tube and the high temperature oxidation of the outer surface, so the materials are required to have good high temperature resistance, corrosion resistance and high temperature mechanical properties, such as creep resistance and high temperature plasticity, in high temperature environment.
  • the two most commonly used alloys in Ni-Cr austenitic heat resistant alloys are ZG45Ni35Cr25NbM and ZG50Ni45Cr35NbM (hereinafter, 35/45 is used instead of ZG50Ni45Cr35NbM), with 35/45 alloy being used at higher temperatures and in more severe corrosive environmental conditions.
  • 35/45 alloy When used, corrosive gas will react with the alloy to undergo high temperature oxidation and corrosion, and a metal oxide layer with a certain thickness will be formed on the inner surface of the furnace tube to protect the material from further oxidation and corrosion.
  • the metal oxide layer formed in 35/45 alloy is mainly Cr 2 O 3 + SiO 2 composite oxide layer/film.
  • the oxide layer is relatively stable below 1050°C and can effectively prevent oxidation and carburization corrosion of the material.
  • the temperature is higher than 1050°C, the thermal stability of chromium oxide becomes poor, and when the furnace tube is subjected to stress, the oxide layer is prone to crack, resulting in a decrease in its continuity and compactness, which is insufficient to continue protecting the material matrix. This leads to the diffusion of oxidation into the material and acceleration of carburization corrosion, until the oxide layer and the matrix gradually crack and peel off.
  • the addition of Al is one way to increase the resistance of the 35/45 Ni-Cr austenitic alloy to oxidation and carburization.
  • a layer of dense aluminum oxide with a certain thickness can be formed on the surface of the alloy, and it also exhibits stability at temperature above 1050°C under the working condition of a cracking furnace, so that the alloy has good carburization resistance and oxidation resistance in a high temperature environment.
  • the increase of Al content leads to the decrease of the ductility of the material. Therefore, the heat resistant alloys currently used in the petrochemical industry usually contain little or no aluminum.
  • the present invention proposes an austenitic alloy with high aluminum content to ensure high resistance to the environment (such as oxidation and carburization corrosion), while ensuring at least the same high mechanical properties as currently known alloys.
  • the purpose of the present invention is to provide a high-aluminum austenitic alloy and a high-aluminum austenitic centrifugal casting pipe.
  • the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe have excellent anti-corrosion capabilities and creep resistance at a temperature of 900°C or above, while having required mechanical properties.
  • the present invention also relates to a method for manufacturing the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention is composed of the elements of: C, 0.3-0.7%; Mn, 0-0.5%; Si, 0-0.5%; Cr, 20-26%; Ni, 40-50%; Al, 3.5-5%; Ti, 0.01-0.3%; Zr, 0.01-0.3%; Nb, 0.1-1%; Ta, 0.01-2%; Mo, 0.01-1%; W, 0.01-1.9%; N, 0.001-0.04%; Re, 0.03-0.3%; and a balance of Fe and unavoidable impurities.
  • the C content ranges from 0.4% to 0.65%.
  • the Mn content ranges from 0 to 0.4%.
  • the Si content ranges from 0 to 0.4%.
  • the Ti content ranges from 0.04% to 0.3%.
  • the Ta content ranges from 0.07% to 2%, such as 0.2-2%, 0.4-2%.
  • the Mo content ranges from 0.2% to 1%.
  • the W content ranges from 0.4% to 1.9%.
  • the N content ranges from 0.006% to 0.035%.
  • Re is Y, Hf, and Ce, and the content of each is 0.01-0.1 %.
  • the total content of Re ranges from 0.08% to 0.3%.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention further contains one or more of Cu, V, Co, and B, wherein: Cu, ⁇ 0.1%; V, ⁇ 0.01%; Co, ⁇ 0.03%; B, ⁇ 0.1%.
  • the unavoidable impurities include one or more of S, P, and O.
  • S Preferably, in the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention, S ⁇ 0.005%, P ⁇ 0.005%, and O ⁇ 0.005%.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention C, 0.4-0.65%; Mn, 0-0.4%; Si, 0-0.4%; Cr, 20-26%; Ni, 40-50%; Al, 3.5-5%; Ti, 0.04-0.3%; Zr, 0.01-0.3%; Nb, 0.1-1%; Ta, 0.4-2%; Mo, 0.2-1%; W, 0.4-1.9%; N, 0.006-0.035%; Re, 0.08-0.3%; Cu, ⁇ 0.1%; V, ⁇ 0.01%; Co, ⁇ 0.03%; B, ⁇ 0.1%; and a balance of Fe and unavoidable impurities.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has a creep rupture life of ⁇ 100 hours, preferably ⁇ 110 hours, and more preferably ⁇ 115 hours, measured under testing conditions of 1100°C and 17MPa.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has an average creep rate of the second stage of creep of ⁇ 0.0005%/h, preferably ⁇ 0.0003%/h, measured under testing conditions of 1050°C and 15MPa.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has an average creep rate of the second stage of creep of ⁇ 0.002%/h, preferably ⁇ 0.0015%/h, measured under testing conditions of 1050°C and 20MPa.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has an average creep rate of the second stage of creep of ⁇ 0.01 %/h, preferably ⁇ 0.007%/h, measured under testing conditions of 1050°C and 25MPa.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has an average creep rate of the second stage of creep of ⁇ 0.05%/h, preferably ⁇ 0.035%/h, measured under testing conditions of 1050°C and 30MPa.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe has a yield strength of ⁇ 120MPa, preferably ⁇ 124MPa; a tensile strength of ⁇ 185MPa, preferably ⁇ 189MPa; and an elongation of ⁇ 49%, preferably ⁇ 50%, measured under a testing condition of 850°C.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has a yield strength of ⁇ 53MPa, preferably ⁇ 55MPa; a tensile strength ⁇ 65MPa, preferably ⁇ 67MPa; and an elongation ⁇ 59%, preferably ⁇ 61%, measured under a testing condition of 1050°C.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention has a carbon increment at a depth of 1mm of 0.5% or less, preferably 0.45% or less, and a carbon increment at a depth of 2mm of 0.05% or less, preferably 0.03% or less, under testing conditions of 1150°C/7 days.
  • the high-aluminum austenitic alloy centrifugal casting pipe of the present invention has an outer diameter of 60-250mm and a wall thickness of 6-10mm.
  • the microstructure of the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention comprises columnar grains with a volume fraction of 80% or more and equiaxed grains with a volume fraction of 20% or less, or consists of columnar grains with a volume fraction of 80% or more and equiaxed grains with a volume fraction of 20% or less.
  • columnar grains are located near the outer wall, and uniform equiaxed grains are located near the inner wall.
  • the present invention also provides a method for manufacturing the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention, comprising:
  • step 1) raw materials are selected and prepared according to the target chemical components, and the raw materials are smelted according to a sequence from being difficult to oxidize to being easy to oxidize.
  • step 1) Fe, Ni, C, Mn, Cr, Si are smelted in the order of Fe, Ni, C, Mn, FeCr and FeSi.
  • step 1) contents of harmful elements such as Pb, Sn, Sb, Zn, As and Bi in the molten steel are controlled to be less than 50 ppm respectively.
  • step 1) a sample is collected and sent to a laboratory for testing, and chemical compositions are adjusted based on the laboratory chemical analysis results.
  • step 2) after the molten steel is heated to 1650 ⁇ 50°C, deoxidation is performed with a deoxidizer and then deslagging is performed.
  • deslagging comprises: covering the molten steel in the furnace with a slagging agent, beginning to blow argon at the bottom of the furnace, and carrying out deslagging after blowing argon. It is preferable to blow argon for 3 ⁇ 1 minutes before deslagging.
  • the floating of oxides, impurities and gases in the molten steel is accelerated by blowing argon from the bottom of the furnace, and the oxides, impurities and gases are removed together after being bonded by the slagging agent, so that the purity of the molten steel is improved.
  • step 3 a furnace mouth is covered and protected with argon to block a reaction between air and the surface of the molten steel.
  • blowing argon at the bottom of a furnace and covering and protecting a furnace mouth with argon are performed during the process of adding Al and Al dissolution.
  • the purpose of blowing argon at the bottom of the furnace and covering and protecting the furnace mouth with argon is to ensure that the active elements added subsequently are not burned and oxidized.
  • step 3 after the dissolution of Al, the molten steel is heated to 1680 ⁇ 50°C, and then a slagging agent is added to form slag and deslagging is performed.
  • step 4 Re, Ti, and Zr are added to the steel ladle, the molten steel is introduced into the steel ladle, and the dissolution and homogenization processes of Re, Ti, and Zr are completed through the pouring process of the molten steel; and after the pouring of the molten steel is completed, the surface of the molten steel in the steel ladle is covered by slagging.
  • the molten steel in the steel ladle is rapidly poured into a metal mold rotating at a high speed on a centrifuge, and the molten steel is cooled to obtain the centrifugal casting pipe.
  • the pouring time should be as short as possible.
  • C is a carbide-forming element.
  • C and medium strong carbide-forming elements (Cr, Mo) or strong carbide-forming elements (Ti, V, Nb) form carbides such as M7C3, M23C6, and MC.
  • Cr, Mo medium strong carbide-forming elements
  • Ti, V, Nb strong carbide-forming elements
  • Mn can improve welding performance and slow down the diffusion of carbon.
  • the content of Mn in the alloy of the present invention is controlled equal to or below 0.5%.
  • the Mn content is expected to be as low as possible, and the Mn content in the alloy of the present invention is preferably equal to or below 0.4%. In some embodiments, the content of Mn is 0.01-0.4%.
  • Si in the process of molten steel smelting, Si as a strong deoxidizer can reduce the oxygen content in molten steel, thereby improving the purity of molten steel.
  • an appropriate Si content can enable the material to have good oxidation resistance and anti-carburization performance.
  • the binding force between Si and O is greater than that between Cr and O, and a passive film SiO 2 can be formed in the alloy just like Cr.
  • the oxidation resistance of SiOz is higher than that of Cr 2 O 3 , but excessive addition of Si can lead to poor mechanical properties of the alloy, affect its welding performance and reduce its creep rupture life.
  • the Si content in the alloy of the present invention is controlled equal to or below 0.5%, preferably equal to or below 0.4%. In some embodiments, the content of Si is 0.05-0.4%.
  • Cr is the main element that is resistant to high-temperature oxidation and high-temperature corrosion, and can improve the thermal strength of the alloy. When the Cr content is sufficient, an oxide film will form on the surface of the alloy, inhibiting the formation of coke deposition and increasing the carburization resistance of the alloy.
  • the Cr content in the alloy of the present invention is controlled at 20-26%. Excessive Cr content will lead to the rapid or gradual precipitation of ferrite phase in the material, which will reduce the stability of the microstructure of the material under high temperature conditions, and reduce the mechanical properties of the material at high temperature, especially the creep rupture properties. At the same time, it will promote the formation of ferrite phase, and also lead to the decline of the welding performance of the material, resulting in the inability to replace spare parts by welding in the later period.
  • Ni is one of the most important alloy elements in the heat-resistant alloy.
  • the main function of Ni is to stabilize the ⁇ zone, so that the alloy can obtain a complete austenite structure, and then the alloy has a combination of high strength, plasticity and toughness, and ensures that the alloy has good high-temperature strength and creep resistance.
  • the higher price of Ni element directly determines the final price of the product, and the Ni content in the alloy of the invention is controlled to be 40-50% by comprehensively considering the two aspects of cost and performance.
  • Al is a necessary element for forming an aluminum oxide layer in the alloy of the present invention under high temperature conditions.
  • the Al content in the alloy of the present invention is relatively high, and is equal to or higher than 3.5%, which can ensure the formation of a continuous and dense alumina layer on the surface of the alloy.
  • the Al content in the alloy of the present invention is controlled at 3.5-5%.
  • Ti During the high-temperature aging process of the product, secondary precipitated carbides gradually appear.
  • the addition of Ti element can improve the thermal dynamic stability of the secondary precipitate M23C6, thereby maintaining a uniform dispersion distribution for a long time and improving the high-temperature creep resistance of the alloy; in addition, Ti can inhibit the transformation of the primary precipitate MC into G phase, indirectly improving the stability of the primary precipitate, and also improving the high-temperature creep strength of the alloy.
  • the Ti content in the alloy of the present invention is controlled to be 0.01-0.3%, preferably 0.04-0.3%.
  • Zr As a strong oxidant, the addition of Zr can reduce the oxygen content in molten steel during the smelting process, thereby ensuring the absorption of other core elements.
  • the Zr content in the alloy of the present invention is controlled to be 0.01-0.3%.
  • Nb is one of the precipitation strengthening elements, which can reduce the creep rate and improve the creep resistance.
  • Nb is also one of the main forming elements of carbides M7C3, M23C6, and MC, and its carbides are very stable at high temperatures.
  • Nb can also form carbonitrides, change the morphology of carbides, refine M23C6, and make it uniformly dispersed, thereby improving the high-temperature creep strength of the alloy.
  • the content of Nb in the alloy of the present invention is controlled equal to or below 1%, preferably 0.1-1%.
  • Ta plays a role of solid solution strengthening and precipitation strengthening. Ta has a very high affinity with C and other interstitial atoms, and the precipitates formed are very stable at high temperature. Ta also helps to improve the high-temperature instantaneous strength and creep performance of the alloy. The addition of Ta can significantly improve the creep rupture life of the alloy under high temperature and high pressure.
  • the content of Ta in the alloy of the present invention is control to be 0.01-2%, preferably 0.4-2%. In some preferred embodiments, the content of Ta in the alloy of the present invention is 0.07-2%, such as 0.1%, 0.15%, 0.2%, 0.23%, 0.4%, 0.6%, 0.8%, 0.9%, 1%, 1.2%, 1.5% and 1.7%.
  • Mo atoms are mostly dissolved in the ⁇ matrix, and Mo atoms are larger than Ni and Fe atoms, which can also improve the yield strength.
  • the addition of Mo can form M 6 C carbides, which is fine and dispersed, and can also play a strengthening role.
  • Mo can also refine austenitic grains, and fine grains are beneficial for improving the plasticity of the alloy.
  • the content of Mo in the alloy of the present invention is control to be 0.01-1%, preferably 0.2-1%.
  • W plays a role in solid solution strengthening. W dissolved in ⁇ Matrix. The atomic radius of W is relatively large, which causes obvious lattice expansion in the matrix, prevents dislocation movement, and improves the yield strength. At the same time, W can reduce the stacking fault energy of ⁇ matrix, and the reduction of stacking fault energy can effectively improve the creep performance of high-temperature alloys.
  • the content of W in the alloy of the present invention is control to be 0.01-1.9%, preferably 0.4-1.9%.
  • N element can form carbonitrides with Nb and C, change the morphology of carbides, refine M23C6, and make it uniformly dispersed, thereby improving the high-temperature creep strength of the alloy.
  • the content of N in the alloy of the present invention is controlled to be 0.001-0.04%, preferably 0.006-0.035%.
  • the rare earth elements in the heat-resistant alloy of the present invention include at least one of Ce, Y, and Hf.
  • the rare earth elements are helpful to refine and stabilize the secondary precipitates, thereby improving the high-temperature mechanical properties of the material.
  • the rare earth elements also help to promote the compactness of the oxide layer mainly composed of chromium oxide and silicon oxide, thereby improving the high-temperature oxidation resistance of the product.
  • the total Re content may be in the range of 0.03-0.3%, preferably 0.08-0.3%, and the addition amounts of Ce, Y, and Hf can each be 0.01-0.1%.
  • the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention can be manufactured by a method comprising the following steps:
  • step 1) raw materials can be selected and prepared according to the target chemical composition.
  • the raw materials are preferably smelted according to the sequence from being difficult to oxidize to being easy to oxidize, for example, Fe, Ni, C, Mn, Cr, Si are smelted in the order of Fe, Ni, C, Mn, FeCr and FeSi.
  • the content of harmful elements such as Pb, Sn, Sb, Zn, As, Bi in the molten steel can be controlled to be less than 50ppm respectively by optimizing the raw materials.
  • a sample can be collected and sent to a laboratory for testing, and chemical compositions can be adjusted based on the laboratory chemical analysis results.
  • the molten steel can be heated, and then deoxidized with a deoxidizer before deslagging.
  • the molten steel is heated to 1650 ⁇ 50°C, followed by deoxidation and deslagging.
  • deslagging preferably comprises: covering the molten steel in the furnace with a slagging agent, beginning to blow argon at the bottom of the furnace, and carrying out deslagging after blowing argon. It is preferable to blow argon for 3 ⁇ 1 minutes before deslagging.
  • oxides, impurities and gases in the molten steel are removed by adding slagging agent and blowing argon at the bottom of the furnace, so that the purity of the molten steel is improved.
  • the temperature of the molten steel in the furnace is controlled by controlling the power of the intermediate frequency furnace.
  • step 3 it is preferable to cover and protect the furnace mouth with argon to block the reaction between air and the surface of the molten steel.
  • step 3 it is preferable to keep blowing argon at the furnace bottom and covering and protecting the furnace mouth with argon during the process of adding Al blocks and Al dissolution.
  • Blowing argon at the bottom of the furnace is to introduce argon bubbling at the bottom of the furnace to make the oxide slag in the molten steel adhere, which is helpful to remove the oxide slag.
  • Covering and protecting the furnace mouth with argon is to replace the air at the furnace mouth with argon to prevent the added Al from being oxidized by the oxygen in the air.
  • One of the characteristics of the alloy of the present invention is that it contains Al.
  • the present invention uses blowing argon at the furnace bottom and covering and protecting the furnace mouth with argon to ensure that the added Al is not burned or oxidized.
  • the temperature of the molten steel in the furnace can be controlled by controlling the power of the intermediate frequency furnace to avoid accidents caused by excessive temperature.
  • the molten steel can be heated up, and then a slagging agent can be added to form slag and deslagging can be performed.
  • the molten steel is heated to 1680 ⁇ 50°C then performing deslagging.
  • step 4 Re, Ti, and Zr can be added to the steel ladle and the molten steel is introduced into the steel ladle.
  • the dissolution and homogenization of raw materials such as Re are completed through the pouring process of the molten steel.
  • the surface of the molten steel in the steel ladle is covered by slagging.
  • One of the characteristics of the alloy of the present invention is that the alloy contains Re, and by adding Re into molten steel, the castability of molten steel is improved, and simultaneously, the performance of the alloy is improved.
  • deslagging can be carried out when the temperature of the molten steel reaches the pouring temperature.
  • Technicians in this field can determine the pouring temperature based on the amount of steel, mold size, etc.
  • the molten steel in the steel ladle can be poured into a metal mold rotating at a high speed on a centrifuge, and the molten steel is cooled to obtain the centrifugal casting pipe.
  • the casting time should be as short as possible.
  • the high-aluminum austenitic centrifugal casting pipe of the present invention is manufactured using a method comprising the following steps:
  • the microstructure of the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention comprises columnar grains with a volume fraction of 80% or more and equiaxed grains with a volume fraction of 20% or less, or consists of columnar grains with a volume fraction of 80% or more and equiaxed grains with a volume fraction of 20% or less.
  • columnar grains are located near the outer wall and uniform equiaxed grains are located near the inner wall.
  • the outer diameter of the high-aluminum austenitic alloy centrifugal casting pipe of the present invention can be 60-250mm, such as 60-70mm, and the wall thickness can be 6-10mm, such as 7-8mm.
  • the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention have excellent anti-corrosion capabilities and creep resistance at a temperature of 900°C or above, and at the same time having required mechanical properties.
  • the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention have:
  • the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention have good strength and elongation at high temperatures: a yield strength measured at 850°C is ⁇ 120MPa, such as ⁇ 124MPa; a tensile strength measured at 850°C is ⁇ 185MPa, such as ⁇ 189MPa; an elongation measured at 850°C is ⁇ 49%, for example ⁇ 50%; a yield strength measured at 1050°C is ⁇ 53MPa, such as ⁇ 55MPa; a tensile strength measured at 1050°C is ⁇ 65MPa, for example ⁇ 67MPa; an elongation measured at 1050°C is ⁇ 59%, for example ⁇ 61%.
  • the high-aluminum austenitic centrifugal casting pipes of Examples 1-7, Comparative Examples 8-10, Comparative Examples 13-16, and Examples 17-20 are manufactured by the following method:
  • the outer diameter of the centrifugal casting pipes in the Examples of the present invention is 66mm, and the wall thickness is 7mm.
  • the microstructure of the centrifugal casting pipes in the Examples of the present invention consists of columnar grains with a volume fraction of ⁇ 80% and equiaxed grains with a volume fraction of ⁇ 20%, and in the direction of wall thickness, columnar grains are located near the outer wall, while uniform equiaxed grains are located near the inner wall.
  • alloys No.1-7 respectively correspond to Examples 1-7; alloys No.8-10 respectively correspond to Comparative Examples 8-10; alloy No.11 is an existing alloy material ZG50Ni45Cr35NbM (35/45 alloy) having a C content of 0.44%; alloy No. 12 is an existing alloy material ZG50Ni45Cr35NbM (35/45 alloy) with a C content of 0.45%; alloys No.13-16 respectively correspond to Comparative Examples 13-16; alloys No.17-20 respectively correspond to Examples 17-20.
  • Table 1 Compositions of the alloys of Examples and Comparative Examples (weight%, with a balance of Fe) Allo y C Mn Si Cr Ni Al Ti Zr Nb Ta Mo W N Re 1 0.4 0.3 3 0.0 7 24 48 4. 5 0.2 0.2 4 0. 5 0.4 0.5 0. 8 0.03 4 0.08 2 0.32 0.2 5 0.2 6 25 40 4 0.2 7 0.2 5 0. 9 0.9 0.6 0. 4 0.00 6 0.18 3 0.63 0.2 8 0.4 24 50 3. 5 0.0 8 0.1 1 1.2 1 1. 5 0.02 4 0.22 4 0.52 0.0 4 0.3 4 26 47 4. 3 0.2 0.2 3 0. 7 0.6 0.2 1. 9 0.00 9 0.08 5 0.47 0.2 1 0.1 20 44 3. 8 0.1 0.0 9 0. 1 2 0.8 1.
  • Creep rupture life According to ASTM E139-11, the creep rupture life of the alloys was measured under the testing conditions of 1100°C/17MPa, and the results are shown in Table 2.
  • Creep rate At 1050°C, different stresses were applied to the alloy, and its length at different times was measured with an extensometer. The deformation amount is differentiated with respect to time to obtain the deformation rate. The average results of the deformation rate in the second stage of creep are shown in Table 3. For the convenience of comparison, after taking the logarithm of the average creep rate of the second stage of creep and pressure, Figure 1 is obtained. The 35/45 alloy in Table 3 and Figure 1 is alloy No.11.
  • Table 3 Average creep rate of the second stage of creep of alloys under different pressures at 1050 °C Pressure (MPa) Average creep rate of the second stage of creep (%/h)
  • Example 1 Example 3
  • Example 4 35/45 alloy 35 0.0201837 - - 0.1896310 30 0.0123634 0.0316228 0.0079433 0.0701448 25 0.0034995 0.0064565 0.0025119 0.0216346 20 0.0010276 0.0013646 0.0007943 0.0051277 15 0.0001754 0.0002630 0.0000883 0.0008014 10 0.0000141 - - 0.0000586
  • Cyclic oxidation In order to simulate the actual conditions of the alloy during use, the cyclic oxidation test was carried out on the alloy. The air temperature was raised to 950°C at a rate of 600 °C, and held for 4 hours. Then, it was cooled to room temperature to measure the weight gain. This process is repeated. The test results are shown in Table 4 and Figure 2 .
  • the 35/45 alloy in Table 4 and Figure 2 is alloy No.11.
  • Table 4 Weight gain of alloys after cyclic oxidation Number of cycles Weight gain (g/m 2 )
  • Example 1 Example 3
  • Example 4 35/45 alloy 0 0 0 0 0 1 0.01 0.01 0 0.26 2 0.02 0.01 0.01 0.35 3 0.02 0.03 0.02 0.35 4 0.04 0.02 0.09 0.3 5 0.18 0.11 0.07 0.51 6 0.11 0.17 0.09 0.41 7 0.15 0.06 0.08 0.62 8 0.05 0.08 0.1 0.51 9 0.04 0.06 0.05 0.68 10 0.1 0.11 0.07 0.51 11 0.17 0.1 0.08 0.48 12 0.11 0.07 0.12 0.48 13 0.08 0.11 0.06 0.62 14 0.06 0.07 0.1 0.42 15 0.1 0.06 0.1 0.62 16 0.08 0.1 0.08 0.51 17 0.12 0.13 0.07 0.51 18 0.11 0.11 0.06 0.62 19 0.09 0.1 0.14 0.68
  • High-temperature short-term tensile test Yield, tensile, and elongation tests of the alloy were measured at 850°C, 950°C, 1050°C, and 1150°C according to ASTM E21-05. The results are shown in Table 5, Figure 3, and Figure 4 .
  • the alloy in Figure 3 is alloy No.1.
  • the alloy in Figure 4 is alloy No. 11.
  • Table 5-1 High-temperature short-term tensile test results of alloys of Examples and Comparative Examples at different temperatures Alloy 850°C 950°C Yield strength (MPa) Tensile strength (MPa) Elongation (%) Yield strength (MPa) Tensile strength (MPa) Elongation (%) 1 124 192 50 89 106 61 2 125 198 50 92 108 60 3 131 201 49 93 106 60 4 124 189 52 89 104 62 5 120 195 51 90 106 61 6 124 190 51 91 110 61 7 126 200 50 94 113 59 11 121 205 27.5 - - - Table 5-2: High-temperature short-term tensile test results of alloys of Examples and Comparative Examples at different temperatures Alloy 1050°C
  • Carburization test A solid carburizing agent was placed into the test pipe section, and after drying treatment, the test pipe section was welded, sealed, and placed in an environment of 1150°C. After heat preservation for 7 days, carbon content increment per millimeter from the inner surface to the outer surface of the alloy was measured. The results are shown in Table 6 and Figure 5 .
  • the 35/45 alloy in Figure 5 is alloy No.11.

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