WO2022148426A1 - High-aluminum austenitic alloy having excellent high-temperature anticorrosion capabilities and creep resistance - Google Patents

Abstract

The present invention provides 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. In weight percentage, 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％; the remainder being Fe and inevitable impurities. 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.

Description

High-alumina austenitic alloy with excellent high temperature corrosion resistance and creep resistance technical field

The invention relates to the field of austenitic alloys, in particular to high-alumina austenitic alloys with excellent high temperature (≥900° C.) corrosion resistance and creep resistance.

Background technique

Nickel-chromium austenitic heat-resistant alloys have been widely used in the petrochemical industry. The devices used in this industry (such as cracking tubes for steam cracking) are subject to combustion near 1100°C outside the furnace tube on the one hand, and materials are also subject to carburizing corrosion caused by hydrocarbon gas inside the furnace tube and external combustion. High temperature oxidation of the surface, so the material is required to have good high temperature resistance and corrosion resistance and high temperature mechanical properties in high temperature environment, such as creep resistance and high temperature plasticity.

The two most commonly used nickel-chromium austenitic heat-resistant alloys are ZG45Ni35Cr25NbM and ZG50Ni45Cr35NbM (35/45 is used to replace ZG50Ni45Cr35NbM below), of which 35/45 alloy is used in higher temperature and more severe corrosive environment conditions. During use, the corrosive gas will interact with the alloy to cause high temperature oxidation and corrosion, and a certain thickness of metal oxide layer will be formed on the inner surface of the furnace tube to protect the material from further oxidation and corrosion. The metal oxide layers formed in the 35/45 alloy are mainly Cr ₂ O ₃ +SiO ₂ composite oxide layers/films. The oxide layer is relatively stable when the temperature is lower than 1050°C, and can effectively prevent the oxidation and carburizing corrosion of the material. However, when the temperature is higher than 1050 °C, the thermal stability of chromium oxide becomes poor. When the furnace tube is subjected to stress, the oxide layer is prone to cracks, which reduces its continuity and compactness, and is not enough to continue to protect the material matrix, resulting in oxidation. Diffusion into the material and carburizing corrosion are accelerated until the oxide layer and the matrix are gradually cracked and peeled off.

The addition of Al element is one way to increase the resistance of 35/45 nickel-chromium austenitic alloy to oxidation and carburization. When the Al content is high, a layer of high-density alumina with a certain thickness can be formed on the surface of the alloy. Under the working condition of the cracking furnace, it is also stable when the temperature is higher than 1050 °C, so that the alloy can be heated at high temperature. It shows good anti-carburization and anti-oxidation properties in the environment. However, an increase in the Al content leads to a decrease in 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 a high aluminium content to ensure high resistance to the environment (eg oxidation and carburizing corrosion), while at the same time guaranteeing mechanical properties at least as high as the alloys known to date.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a high-alumina austenite alloy and a high-alumina austenitic centrifugal casting pipe, which have excellent performance at temperatures of 900° C. and above corrosion resistance and creep resistance, while having the required mechanical properties. The present invention also relates to a method for producing the high-alumina austenitic alloy and high-alumina austenitic centrifugally cast pipe of the present invention.

Specifically, in terms of weight percentage, the elemental composition of the high-alumina austenite alloy or high-alumina austenitic centrifugal casting pipe of the present invention is: 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%; the balance is Fe and inevitable impurities.

Preferably, in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe of the present invention, the C content is 0.4-0.65%.

Preferably, in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe of the present invention, the Mn content is 0-0.4%.

Preferably, in the high-alumina austenitic alloy or the high-alumina austenitic centrifugal casting pipe of the present invention, the Si content is 0-0.4%.

Preferably, in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe of the present invention, the Ti content is 0.04-0.3%.

Preferably, in the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe of the present invention, the Ta content is 0.07-2%, for example, 0.2-2%, 0.4-2%.

Preferably, in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe of the present invention, the Mo content is 0.2-1%.

Preferably, in the high-alumina austenite alloy or the high-alumina austenitic centrifugal casting pipe of the present invention, the W content is 0.4-1.9%.

Preferably, in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe of the present invention, the N content is 0.006-0.035%.

Preferably, in the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe of the present invention, Re is Y, Hf and Ce, and the content of each is 0.01-0.1%.

Preferably, in the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe of the present invention, the total content of Re is 0.08-0.3%.

Preferably or optionally, the high-alumina austenitic alloy or high-alumina 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. Preferably, in the high-alumina austenitic alloy or high-alumina austenite centrifugal casting pipe of the present invention, S≤0.005%, P≤0.005%, and O≤0.005%.

Preferably, in the high-alumina austenitic alloy or high-alumina 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%; inevitable impurities.

Preferably, the permanent life of the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe of the present invention measured under the test conditions of 1100° C. and 17MPa is ≥100 hours, preferably ≥110 hours, more preferably ≥115 hours.

Preferably, the average rate of creep in the second stage of creep measured under the test conditions of 1050° C. and 15MPa for the high-alumina austenite alloy or high-alumina austenite centrifugal casting pipe of the present invention is ≤0.0005%/h, preferably ≤ 0.0003%/h.

Preferably, the average rate of creep in the second stage of creep measured under the test conditions of 1050° C. and 20MPa for the high-alumina austenitic alloy or high-alumina austenite centrifugal casting pipe of the present invention is ≤0.002%/h, preferably ≤ 0.0015%/h.

Preferably, the average rate of creep in the second stage of creep measured under the test conditions of 1050° C. and 25MPa for the high-alumina austenite alloy or high-alumina austenite centrifugal casting pipe of the present invention is ≤ 0.01%/h, preferably ≤ 0.007%/h.

Preferably, the average rate of creep in the second stage of creep measured under the test conditions of 1050° C. and 30MPa of the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe of the present invention is ≤0.05%/h, preferably ≤ 0.035%/h.

Preferably, the yield strength of the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe measured under the test condition of 850°C is ≥120MPa, preferably ≥124MPa; tensile strength ≥185MPa, preferably ≥189MPa; elongation The rate is ≥49%, preferably ≥50%.

Preferably, the yield strength of the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe of the present invention measured under the test condition of 1050°C is ≥53 MPa, preferably ≥ 55 MPa; the tensile strength is ≥ 65 MPa, preferably ≥ 67 MPa; Elongation ≥ 59%, preferably ≥ 61%.

Preferably, the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe of the present invention has a carbon increase of 0.5% or less, preferably 0.45% or less at a depth of 1 mm under the test condition of 1150° C./7 days. The carbon increase amount at a depth of 2 mm is 0.05% or less, preferably 0.03% or less.

Preferably, the high-alumina austenitic alloy centrifugal casting pipe of the present invention has an outer diameter of 60-250 mm and a wall thickness of 6-10 mm.

Preferably, the microstructure of the high-alumina austenite alloy or the high-alumina austenite centrifugal casting tube of the present invention includes columnar crystals with a volume fraction of ≥80% and equiaxed crystals with a volume fraction of ≤20%, or a volume fraction of ≥80%. % columnar crystals and volume fraction ≤ 20% equiaxed crystal composition.

Preferably, the high-alumina austenite centrifugal casting tube of the present invention has columnar crystals near the outer wall in the wall thickness direction, and uniform equiaxed crystals near the inner wall.

The present invention also provides a method for manufacturing the high-alumina austenite alloy or the high-alumina austenite centrifugal cast pipe of the present invention, comprising:

1) Smelting: according to the target chemical composition, smelting the chemical compositions other than Al, Re, Ti, Zr in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe in an intermediate frequency furnace to obtain molten steel;

2) Deoxidation and slagging: deoxidize and slag the molten steel obtained in step 1);

3) Add Al: add Al to the molten steel treated in step 2), and slag after the Al is dissolved;

4) Quenching and tempering: adding Re, Ti and Zr to the ladle, introducing the molten steel treated in step 3) into the ladle, and slag after Re, Ti and Zr are dissolved;

5) Pouring: slag before pouring, and then pour the molten steel into a metal mold, and after cooling, a high-alumina austenite alloy or a high-alumina austenite centrifugal casting tube is obtained.

Preferably, in step 1), raw materials are selected and formulated according to the target chemical composition, and the raw materials are smelted in the order of being not easily oxidized to easily oxidized.

Preferably, in step 1), Fe, Ni, C, Mn, Cr, Si are smelted in the order of Fe, Ni, C, Mn, FeCr, FeSi.

Preferably, in step 1), the content of harmful elements such as Pb, Sn, Sb, Zn, As, Bi and the like in the molten steel is controlled to be less than 50 ppm, respectively.

Preferably, in step 1), the sample is taken and sent to the laboratory for testing, and the chemical composition is adjusted according to the laboratory chemical analysis result.

Preferably, in step 2), the temperature of the molten steel is raised to 1650±50° C., and the slag is deoxidized by using a deoxidizer.

Preferably, in step 2), the slagging comprises: covering the molten steel in the furnace with a slag-forming agent, and starting to blow argon at the bottom of the furnace; and slagging after the argon blowing. It is preferable to blow argon for 3±1min before slagging. The oxides, impurities and gases in the molten steel are accelerated by blowing argon at the bottom of the furnace, and the slag-forming agent binds them and removes them together to improve the purity of the molten steel.

Preferably, in step 3), the argon furnace mouth is covered and protected to isolate the air from reacting with the molten steel surface.

Preferably, in step 3), during the process of adding Al for dissolution, the furnace bottom is blown with argon and the furnace mouth is covered with argon for protection. The purpose of blowing argon at the bottom of the furnace and covering the furnace mouth with argon is to ensure that the active elements added later are not burned and oxidized.

Preferably, in step 3), after the Al is dissolved, the molten steel is heated to 1680±50° C., and then a slag-forming agent is added to make slag.

Preferably, in step 4), Re, Ti and Zr are added to the ladle, molten steel is introduced into the ladle, and the process of dissolving and homogenizing Re, Ti and Zr is completed through the pouring process of molten steel; after the pouring of molten steel is completed, the ladle The inner molten steel surface is covered with slag.

Preferably, in step 5), the molten steel in the ladle is rapidly poured into a metal mold rotating at a high speed on a centrifuge, and a centrifugal casting tube is obtained after the molten steel is cooled. The casting time should be as short as possible.

Description of drawings

Figure 1 : Average creep rate of the second stage of creep for the alloys of Example 1, Example 3 and Example 4 and Alloy No. 11 (35/45 alloy).

Figure 2: Cyclic oxidation weight gain curves of the alloys of Example 1, Example 3 and Example 4 of the present invention and Alloy No. 11 (34/45 alloy).

Figure 3: High temperature short-time tensile curves of the alloy of Example 1 of the present invention at 850, 950, 1050, and 1150°C, respectively.

Figure 4: High temperature short-time tensile curves of alloy No. 11 (34/45 alloy) at 850, 900, 1000, and 1050 °C, respectively.

Figure 5: Carburizing percentages at different depths for the alloys of Examples 1-4 of the present invention and alloy No. 11 (34/45 alloy) under the test conditions of 1150°C/7 days.

Detailed ways

In order for those skilled in the art to understand the features and effects of the present invention, general descriptions and definitions of terms and expressions mentioned in the specification and claims are hereunder. Unless otherwise specified, all technical and scientific terms used in the text have the ordinary meaning understood by those skilled in the art to the present invention, and in case of conflict, the definitions in this specification shall prevail.

Herein, all features such as numerical values, amounts, amounts, and concentrations defined as numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible sub-ranges and individual numerical values (including integers and fractions) within the ranges.

Herein, when embodiments or examples are described, it should be understood that it is not intended to limit the invention to those embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are intended to be included within the scope of the appended claims. It should be understood that, within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (eg, embodiments) can be combined with each other, thereby constituting a preferred technical solution.

In the present invention, the role of each element in the high-alumina austenite alloy and the centrifugally cast pipe is as follows.

C: carbide-forming element, C and medium-strong carbide-forming elements (Cr, Mo) or strong carbide-forming elements (Ti, V, Nb), etc., form carbides M7C3, M23C6, and MC. During the high temperature aging process, the supersaturated solid solution carbon in the matrix is precipitated in the form of finely dispersed secondary M23C6, thereby improving the durability of the alloy. However, too high carbon content will reduce the toughness of the alloy, and the content of C needs to be properly selected to ensure the high temperature durability and high temperature plasticity of the material.

Mn: It can improve the welding performance and slow down the diffusion of carbon. The content of Mn in the alloy of the present invention is controlled below 0.5%. The Mn content is desirably as low as possible, and the Mn content in the alloy of the present invention is preferably 0.4% or less. In some embodiments, the content of Mn is 0.01-0.4%.

Si: In the process of molten steel smelting, as a strong deoxidizer, Si can reduce the oxygen content in molten steel, thereby improving the purity of molten steel. Appropriate Si content can make the material have good oxidation resistance and carburization resistance during high temperature service. The bonding force between Si and O is greater than that of Cr, and it can form a passivation film SiO ₂ in the same alloy as Cr. Its oxidation resistance is higher than that of Cr ₂ O ₃ , but too much Si addition will lead to poor mechanical properties of the alloy. To affect the welding performance and reduce the lasting life, the content of Si in the alloy of the present invention is controlled below 0.5%, preferably below 0.4%. In some embodiments, the Si content is 0.05-0.4%.

Cr: It is the main element of high temperature oxidation resistance and high temperature corrosion resistance, which can improve the thermal strength of the alloy. When the Cr content is sufficient, an oxide film will be formed on the surface of the alloy, which will inhibit the formation of coke deposition and increase the carburization resistance of the alloy. The Cr content in the alloy of the invention is controlled to be 20-26%. Excessive Cr content will lead to the rapid or gradual precipitation of ferrite phase in the material, the microstructure stability of the material will decrease under high temperature conditions, and the high temperature mechanical properties of the material, especially the lasting properties will decrease; at the same time, it will promote the formation of ferrite phase, It will also lead to the deterioration of the welding performance of the material, making it impossible to replace spare parts by welding in the later stage.

Ni: It is one of the most important alloying elements in heat-resistant alloys. The main function of Ni is to stabilize the γ region, so that the alloy can obtain a complete austenite structure, so that the alloy has a high combination of strength, plasticity and toughness, and Ensure that the alloy has good high temperature strength and creep resistance. The price of Ni element is relatively high, which directly determines the final price of the product. Considering the two aspects of cost and performance comprehensively, the content of Ni in the alloy of the invention is controlled to be 40-50%.

Al: It is an essential element for the alloy of the present invention to form an aluminum oxide layer in a high temperature environment. The content of Al in the alloy of the present invention is relatively high, higher than 3.5%, which can ensure the formation of a continuous and dense aluminum oxide layer on the surface of the alloy. At the same time, considering that too high aluminum content will reduce the toughness of the alloy at room temperature, making machining difficult and increasing the machining cost, 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 appeared. The addition of Ti element can improve the thermodynamic stability of the secondary precipitate M23C6, so that it can maintain a uniform dispersion distribution for a long time, thereby improving the high temperature creep strength of the alloy; in addition, Ti can inhibit the transformation of the primary precipitate MC into G phase, which indirectly improves the stability of the primary precipitate and also improves 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 invention is controlled to be 0.01-0.3%.

Nb: one of the precipitation strengthening elements, which can reduce the creep rate and improve the creep resistance; at the same time, 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 carbonitride, change the carbide morphology, refine M23C6, make it evenly dispersed, and then improve the high temperature creep strength of the alloy. At the same time, considering the high cost of Nb, the content of Nb in the alloy of the present invention is controlled below 1%, preferably 0.1-1%.

Ta: It acts as solid solution strengthening and precipitation strengthening. Ta has a very high affinity with interstitial atoms such as C, and the formed precipitate is very stable at high temperature. Ta also helps to improve the high temperature transient strength and creep properties of the alloy. The addition of Ta can significantly improve the durable life of the alloy under high temperature and high pressure. The present invention controls the Ta content in the alloy to be 0.01-2%, preferably 0.4-2%. In some preferred embodiments, the Ta content in the alloys 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%, 1.7%.

Mo: Mo atoms are mostly dissolved in the γ matrix, and molybdenum atoms are larger than nickel and iron atoms, which can also improve the yield strength. At the same time, the addition of molybdenum can form M ₆ C carbide, which is finely dispersed and can also play a strengthening role. In addition, molybdenum can also refine austenite grains, and the fine grains are beneficial to the improvement of alloy plasticity. The present invention controls the Mo content in the alloy to be 0.01-1%, preferably 0.2-1%.

W: It acts as a solid solution strengthening. W dissolves in the γ matrix, and the atomic radius of tungsten is relatively large, which causes the lattice to expand significantly in the matrix, prevents the movement of dislocations, and improves the yield strength. At the same time, tungsten can reduce the stacking fault energy of γ matrix, and the reduction of stacking fault energy can effectively improve the creep properties of superalloys. In the present invention, the content of W in the alloy is controlled at 0.01-1.9%, preferably 0.4-1.9%.

N: N element can form carbonitride with Nb and C, change the form of carbide, refine M23C6, make it evenly dispersed, and then improve the high temperature creep strength of the alloy. The N content in the alloy of the present invention is controlled at 0.001-0.04%, preferably 0.006-0.035%.

Re (rare earth element): The rare earth element in the heat-resistant alloy of the present invention includes at least one of Ce, Y, and Hf. Rare earth elements help to refine and stabilize the secondary precipitation phase, thereby improving the high temperature mechanical properties of the material. In addition, rare earth elements also help to promote the densification of the oxide layer dominated by chromium oxide and silicon oxide, thereby improving the high-temperature oxidation resistance of the product. In the alloy of the present invention, 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 may each be 0.01-0.1%.

The high-alumina austenitic alloy or the high-alumina austenitic centrifugal casting pipe of the present invention can be manufactured by a method comprising the following steps:

1) Smelting: according to the target chemical composition, smelting the chemical compositions other than Al, Re, Ti, Zr in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe in an intermediate frequency furnace to obtain molten steel;

2) Deoxidation and slagging: deoxidize and slag the molten steel obtained in step 1);

3) Add Al: add Al to the molten steel treated in step 2), and slag after the Al is dissolved;

4) Quenching and tempering: adding Re, Ti and Zr to the ladle, introducing the molten steel treated in step 3) into the ladle, and slag after Re, Ti and Zr are dissolved;

5) Pouring: slag before pouring, and then pour the molten steel into a metal mold, and after cooling, a high-alumina austenite alloy or a high-alumina austenite centrifugal casting tube is obtained.

In step 1), the preparation raw materials can be selected according to the target chemical composition. The raw materials are preferably smelted in the order of being less oxidizable to easily oxidizing, for example, Fe, Ni, C, Mn, Cr, and Si are smelted in the order of Fe, Ni, C, Mn, FeCr, and FeSi. In step 1), the content of harmful elements such as Pb, Sn, Sb, Zn, As, Bi and the like in the molten steel can be controlled to be less than 50 ppm respectively by optimizing the raw materials. In step 1), the sample can be taken and sent to the laboratory for testing, and the chemical composition can be adjusted according to the laboratory chemical analysis result.

In step 2), the molten steel can be heated up, and then deoxidized by a deoxidizer, followed by slag removal. Preferably, the temperature of molten steel is raised to 1650±50° C., and then deoxidation and slag are carried out. In step 2), the slagging preferably includes: covering the molten steel in the furnace with a slag-forming agent, and starting to blow argon at the bottom of the furnace; and slagging after the argon blowing. It is preferable to blow argon for 3±1min before slagging. In the slag process, by adding a slag-forming agent and blowing argon at the bottom of the furnace, the oxides, impurities and gases in the molten steel are removed, and the purity of the molten steel is improved. Before deoxidation, the molten steel temperature in the furnace is controlled by controlling the power of the intermediate frequency furnace.

In step 3), it is preferable to cover the furnace mouth with argon to prevent the air from reacting with the molten steel surface. In step 3), during the process of adding Al block to dissolve, it is preferable to keep the furnace bottom blowing argon and furnace mouth argon covering protection. Argon blowing at the bottom of the furnace is to bubbling argon gas at the bottom of the furnace to make the oxide slag in the molten steel stick together and help to remove the oxide slag. The argon cover protection of the furnace mouth is to replace the air at the furnace mouth with argon to prevent the added Al from being oxidized by oxygen in the air. One of the characteristics of the alloy of the present invention is that it contains Al, and the present invention adopts argon blowing at the bottom of the furnace and argon gas covering the furnace mouth when adding Al for dissolution, so as to ensure that the added Al is not burned and oxidized. In the process of Al dissolution, the temperature of molten steel in the furnace can be controlled by controlling the power of the intermediate frequency furnace to avoid accidents caused by excessive temperature. In step 3), after the Al is dissolved, the molten steel can be heated, and then a slag-forming agent is added to form slag. Preferably, after the molten steel is heated to 1680±50°C, slag is performed.

In step 4), Re, Ti and Zr can be added to the ladle, and molten steel can be introduced into the ladle. The process of dissolving and homogenizing raw materials such as Re is completed through the pouring process of molten steel. After the molten steel is poured, the surface of the molten steel in the ladle is covered with slag. One of the characteristics of the alloy of the present invention is that it contains Re. By adding Re in the molten steel, the present invention improves the pourability of the molten steel and simultaneously improves the performance of the alloy.

In step 5), slag can be carried out when the molten steel temperature reaches the pouring temperature. Those skilled in the art can determine the pouring temperature according to the amount of molten steel, the size of the mold, and the like. After slagging, the molten steel in the ladle can be poured into the metal mold rotating at high speed on the centrifuge, and the centrifugal casting tube can be obtained after the molten steel is cooled. The casting time should be as short as possible.

In some embodiments, the high alumina austenitic centrifugal cast pipe of the present invention is manufactured using a method comprising the steps of:

Step 1: Select and prepare raw materials according to the target chemical composition, and the raw materials are smelted in the order of being not easily oxidized to easily oxidized (for example, smelting Fe, Ni, C, Mn, Cr, Si in the order of Fe, Ni, C, Mn, FeCr, FeSi) ), the chemical composition except Al, Re, Ti, Zr is melted to obtain molten steel; The content of harmful elements such as Pb, Sn, Sb, Zn, As, Bi in the preferred raw material control molten steel is respectively lower than 50ppm; Laboratory inspection, according to the results of laboratory chemical analysis, adjust the chemical composition;

Step 2: After the chemical composition is verified, the molten steel is heated to 1650±50°C, deoxidized with a deoxidizer, and then slag is removed, the molten steel in the furnace is covered with a slag-forming agent, and argon blowing is started at the bottom of the furnace; slag slag is carried out after blowing argon for 3±1 min;

Step 3: Cover and protect the furnace mouth with argon gas to isolate the air from reacting with the surface of the molten steel; add Al blocks to dissolve, and keep the bottom of the furnace blowing argon and cover the furnace mouth with argon gas during this process; After heating up to 1680±50℃, add slag-forming agent to make slag and prepare to release;

Step 4: adding rare earth, Ti and Zr into the ladle; introducing molten steel into the ladle, and completing the process of dissolving and homogenizing the rare earth and other raw materials through the pouring process of the molten steel; after the pouring of the molten steel, the surface of the molten steel in the ladle is covered with slag ;

Step 5: Before transferring the ladle to the centrifuge, after the molten steel temperature reaches the pouring temperature, slag in the ladle is carried out for the last time, and then the molten steel in the ladle is quickly poured into the metal mold rotating at high speed on the centrifuge, and the centrifugal casting tube is obtained after the molten steel is cooled. .

The microstructure of the high-alumina austenite alloy and the high-alumina austenite centrifugal casting pipe of the present invention includes columnar crystals with a volume fraction of ≥80% and equiaxed crystals with a volume fraction of ≤20%, or columnar crystals with a volume fraction of ≥80% The composition of equiaxed crystals and volume fraction ≤ 20%. In a preferred embodiment, the high-alumina austenite centrifugal casting tube of the present invention has columnar crystals near the outer wall in the wall thickness direction, and uniform equiaxed crystals near the inner wall.

The outer diameter of the high-alumina austenitic alloy centrifugal casting tube of the present invention may be 60-250 mm, such as 60-70 mm, and the wall thickness may be 6-10 mm, such as 7-8 mm.

The high-alumina austenitic alloy and the high-alumina austenitic centrifugal casting pipe of the present invention have excellent corrosion resistance and creep resistance at temperatures of 900° C. and above, and have required mechanical properties at the same time.

Compared with the 35/45 alloy, the high-alumina austenitic alloy and high-alumina austenitic centrifugal cast pipe of the present invention have:

(1) Longer lasting life: The lasting life measured under the test conditions of 1100°C and 17MPa is ≥100 hours, preferably ≥110 hours, more preferably ≥115 hours;

(2) Smaller creep rate: the average creep rate of the second stage of creep measured under the test conditions of 1050°C and 15MPa is ≤0.0005%/h, preferably ≤0.0003%/h; at 1050°C, 20MPa The average creep rate of the second stage of creep measured under the test conditions is ≤0.002%/h, preferably ≤0.0015%/h; the average creep rate of the second stage of creep measured under the test conditions of 1050℃ and 25MPa≤ 0.01%/h, preferably ≤0.007%/h; the average creep rate of the second stage of creep measured under the test conditions of 1050°C and 30MPa is ≤0.05%/h, preferably ≤0.035%/h;

(3) Better oxidation resistance: increase the air temperature to 950°C at a rate of 600°C/h, hold for 4 hours, and then cool to room temperature to measure the weight gain. After 19 cycles of this process, the weight gain of the alloy is ≤ 0.3g/m ² , preferably ≤0.15g/m ² ;

(4) Better carburization resistance: under the test conditions of 1150°C/7 days, the carburization amount at a depth of 1mm is less than 0.5%, preferably less than 0.45%, and the carburization amount at a depth of 2mm is less than 0.05% , preferably 0.03% or less.

At the same time, the high-alumina austenitic alloy and high-alumina austenitic centrifugal casting pipe of the present invention have good strength and elongation at high temperature: the yield strength measured under the test condition of 850°C is ≥120MPa, for example, ≥124MPa, Tensile strength ≥185MPa, such as ≥189MPa; elongation ≥49%, such as ≥50%; yield strength measured under test conditions of 1050°C ≥53MPa, such as ≥55MPa; tensile strength ≥65MPa, such as ≥67MPa; Elongation ≥ 59%, eg ≥ 61%.

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

The high-alumina austenitic centrifugal casting tubes of Examples 1-7, Comparative Examples 8-10, Comparative Examples 13-16 and Examples 17-20 were manufactured by the following methods:

Step 1: Select and prepare raw materials according to the target chemical composition, the raw materials are smelted in the order of being not easily oxidized to easily oxidized, and the chemical compositions other than Al, Re, Ti, Zr are melted to obtain molten steel, wherein, according to Fe, Ni, C, Mn , FeCr, FeSi sequentially smelting Fe, Ni, C, Mn, Cr, Si; control the content of Pb, Sn, Sb, Zn, As, Bi and other harmful elements in molten steel to be less than 50ppm respectively; take chemical composition samples and send them to the laboratory Inspection, according to the laboratory chemical analysis results, adjust the chemical composition of the furnace;

Step 2: After the chemical composition is verified, the molten steel is heated to 1650°C, deoxidized with a deoxidizer, and then slag is removed, the molten steel in the furnace is covered with a slag-forming agent, and argon blowing is started at the bottom of the furnace;

Step 3: Cover and protect the furnace mouth with argon gas to isolate the air from reacting with the surface of the molten steel; add Al blocks to dissolve, and keep the bottom of the furnace blowing argon and cover the furnace mouth with argon gas during this process; After heating up to 1680℃, add slag-forming agent to make slag and prepare to release;

Step 4: adding rare earth, Ti and Zr into the ladle; introducing molten steel into the ladle, and completing the process of dissolving and homogenizing the rare earth and other raw materials through the pouring process of the molten steel; after the pouring of the molten steel, the surface of the molten steel in the ladle is covered with slag ;

Step 5: Before transferring the ladle to the centrifuge, after the temperature reaches the pouring temperature, carry out the last slag in the ladle, and then pour the molten steel in the ladle quickly into the metal mold rotating at high speed on the centrifuge, and the molten steel is cooled to obtain a centrifugal casting tube.

The outer diameter of the centrifugal casting tube in the embodiment of the present invention is 66 mm, the wall thickness is 7 mm, the microstructure is composed of columnar crystals with a volume fraction of ≥80% and equiaxed crystals with a volume fraction of ≤20%, and columnar crystals are formed near the outer wall in the direction of wall thickness. , near the inner wall is a uniform equiaxed crystal.

The chemical components and contents of the centrifugal casting tubes of the examples of the present invention and the comparative examples are shown in Table 1. In this paper, Alloys No. 1-7 correspond to Examples 1-7 respectively, Alloys No. 8-10 correspond to Comparative Examples 8-10 respectively, and Alloy No. 11 is an existing alloy material ZG50Ni45Cr35NbM (35/45 Alloy), No. 12 alloy is the existing alloy material ZG50Ni45Cr35NbM (35/45 alloy) with a C content of 0.45%, No. 13-16 alloys correspond to Comparative Examples 13-16 respectively, and No. 17-20 alloys correspond to Example 17 respectively -20.

Table 1: Composition of Example and Comparative Alloys (wt%, balance Fe)

Endurance life: According to ASTM E139-11, the endurance life of the alloy was measured under the test conditions of 1100℃/17MPa. The results are shown in Table 2.

It can be seen from Table 2 that the lasting life of the alloy of the embodiment of the present invention at 1100°C/17MPa is overall better than that of the alloys of the comparative example (alloy No. 8-10 and alloy No. 13-16) and the alloy No. 11 and No. 12 in the prior art alloy. Alloys 13-16 do not contain Ta, and their lasting life is much lower than that of the alloys of the present invention.

Table 2: Endurance life of each alloy at 1100℃/17MPa

alloy	Endurance life (h)
1	127
2	131
3	138
4	118
5	154
6	123
7	126
8	86
9	104
10	97
11	108
12	100
13	18
14	15
15	twenty two
16	19
17	89
18	96
19	112

20

104

Creep rate: At 1050 °C, different stresses are applied to the alloy respectively, and the length of time at different times is measured by an extensometer. The deformation is derived from the time to obtain the deformation rate. The average result of the deformation rate in the second stage of creep is as follows: shown in Table 3. For the convenience of comparison, after taking the logarithm of the average rate of creep in the second stage of pressure and creep, Figure 1 is obtained. The 35/45 alloy in Table 3 and Figure 1 is a No. 11 alloy.

It can be seen from Table 3 and Figure 1 that at the same pressure and temperature, the average creep rate of the alloy of the present invention in the second stage of creep is significantly lower than that of the comparative alloy, so the creep resistance of the alloy of the present invention is significantly better than that of the comparative alloy 35/ 45.

Table 3: Average rate of creep in the second stage of creep of alloys under different pressures at 1050°C

Cyclic oxidation: In order to simulate the actual conditions of the alloy during use, the alloy was subjected to a cyclic oxidation test. The air temperature was raised to 950°C at a rate of 600°C/h, maintained for 4 hours, and then cooled to room temperature to measure its weight gain. Cycle During this process, the test results are shown in Table 4 and Figure 2. The 35/45 alloy in Table 4 and Figure 2 is a No. 11 alloy.

It can be seen from Table 4 and Figure 2 that the oxidation resistance of the alloy of the present invention is obviously better than that of the 35/45 alloy.

Table 4: Weight gain of alloy after cyclic oxidation

High temperature short-time tensile: refer to ASTM E21-05 to measure the yield, tensile and elongation tests of the alloy at 850, 950, 1050, and 1150 °C. 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 11.

By comparing the alloy of Example 1 with the 35/45 alloy, it can be seen that the alloy of Example 1 has good strength and elongation at high temperature even with a higher content of aluminum.

Table 5-1: High-temperature and short-time tensile test results of example alloys and comparative alloys at different temperatures

Table 5-2: High-temperature and short-time tensile test results of example alloys and comparative alloys at different temperatures

Carburizing test: put the solid carburizing agent into the test pipe section, dry it, weld and seal it, put it in an environment of 1150 °C, and keep it warm for 7 days, measure the increase in carbon content per millimeter from the inner surface to the outer surface of the alloy. The results are shown in Table 6. and shown in Figure 5. The 35/45 alloy in Figure 5 is a No. 11 alloy.

It can be seen from Table 6 and Figure 5 that the carburization amount of the alloy of the present invention is significantly lower than that of the comparative alloy, indicating that the alloy of the present invention has good anti-carburization properties.

Table 6: 1150 ℃, 7 days carburizing test results (%) of the example alloys and the comparative alloys

alloy

1mm depth

2mm depth

3mm depth

4mm depth

	Carbon increase (%)	Carbon increase (%)	Carbon increase (%)	Carbon increase (%)
1	0.35	0.01	0	0
2	0.39	0.03	0.01	0
3	0.44	0.01	0	0
4	0.31	0.02	0	0
5	0.37	0.02	0.01	0
6	0.29	0	0	0
7	0.3	0.01	0	0
11	1.12	0.3	0.04	0.01

Claims (10)

1. A high-alumina austenitic alloy or a high-alumina austenitic centrifugal casting tube, characterized in that, in weight percentage, the elemental composition of the high-alumina austenite alloy or high-alumina austenite centrifugal casting tube is: 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%; Fe and inevitable impurities.
2. The high-alumina austenite alloy or high-alumina austenitic centrifugal casting pipe according to claim 1, wherein the elemental composition of the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe has one of the following: one or more features:

   C content is 0.4-0.65%;

   Mn content is 0-0.4%;

   Si content is 0-0.4%;

   Ti content is 0.04-0.3%;

   Ta content is 0.07-2%, such as 0.4-2%;

   Mo content is 0.2-1%;

   W content is 0.4-1.9%;

   The N content is 0.006-0.035%;

   Re content of 0.08-0.3%; and

   Re is Y, Hf and Ce, and the content of each of Y, Hf and Ce is 0.01-0.1%.
3. The high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe according to claim 1, wherein the high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe further contains Cu, V, One or more of Co and B.
4. The high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe according to claim 3, wherein the elemental composition of the high-alumina austenite alloy or high-alumina austenite centrifugal casting pipe has one of the following: one or more features:

   Cu content≤0.1%;

   V content≤0.01%;

   Co content ≤ 0.03%; and

   B content≤0.1%.
5. The high-alumina austenitic alloy or high-alumina austenitic centrifugal casting pipe according to claim 1, wherein the inevitable impurities include one or more of S, P and O; preferably, The S content of the high-alumina austenite alloy or the high-alumina austenite centrifugal casting tube is ≤0.005%, the P content is ≤0.005%, and the O content is ≤0.005%.
6. The high-alumina austenitic alloy or high-alumina austenitic centrifugal casting tube according to claim 1, wherein the high-alumina austenitic alloy or high-alumina austenite centrifugal casting tube has one or more of the following: Item performance:

   The long-lasting life of the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe measured under the test conditions of 1100° C. and 17MPa is ≥100 hours, preferably ≥110 hours, more preferably ≥115 hours;

   The average creep rate of the second stage of creep measured under the test conditions of 1050° C. and 15MPa for the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe is ≤0.0005%/h, preferably ≤0.0003%/h ;

   The average creep rate of the second stage of creep measured under the test conditions of 1050° C. and 20MPa for the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe is ≤0.002%/h, preferably ≤0.0015%/h ;

   The average creep rate of the second stage of creep measured under the test conditions of 1050° C. and 25MPa for the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe is ≤0.01%/h, preferably ≤0.007%/h ;

   The average creep rate of the second stage of creep measured under the test conditions of 1050° C. and 30MPa for the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe is ≤0.05%/h, preferably ≤0.035%/h ;

   The yield strength of the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe measured under the test condition of 850°C is ≥120MPa, the tensile strength is ≥185MPa, and the elongation is ≥49%;

   The yield strength of the high-alumina austenitic alloy or the high-alumina austenitic centrifugal cast pipe measured under the test condition of 1050°C is ≥53 MPa, the tensile strength is ≥ 65 MPa, and the elongation is ≥ 59%; and

   The high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe under the test conditions of 1150 ℃ / 7 days, the carbon increase in the depth of 1mm is less than 0.5%, and the carbon increase in the depth of 2mm is less than 0.05%.
7. The high-alumina austenitic centrifugal casting pipe according to claim 1, wherein the outer diameter of the high-alumina austenitic alloy centrifugal casting pipe is 60-250 mm, and the wall thickness is 6-10 mm.
8. The high-alumina austenite centrifugal casting tube according to claim 1, wherein the microstructure of the high-alumina austenite alloy or the high-alumina austenite centrifugal casting tube comprises columnar crystals with a volume fraction of ≥80% and Equiaxed crystals with a volume fraction of ≤20%; preferably, columnar crystals near the outer wall in the wall thickness direction of the high-alumina austenite centrifugal casting tube, and uniform equiaxed crystals near the inner wall.
9. The method for manufacturing the high-alumina austenitic alloy or high-alumina austenitic centrifugal cast pipe of claims 1-8, comprising the following steps:

   1) Smelting: according to the target chemical composition, smelting the chemical compositions other than Al, Re, Ti and Zr in the high-alumina austenite alloy or the high-alumina austenite centrifugal casting pipe in an intermediate frequency furnace to obtain molten steel;

   2) Deoxidation and slagging: deoxidize and slag the molten steel obtained in step 1);

   3) Add Al: add Al to the molten steel treated in step 2), and slag after the Al is dissolved;

   4) Quenching and tempering: adding Re, Ti and Zr to the ladle, introducing the molten steel treated in step 3) into the ladle, and slag after Re, Ti and Zr are dissolved;

   5) Pouring: slag before pouring, and then pour the molten steel into a metal mold, and after cooling, a high-alumina austenitic alloy or a high-alumina austenite centrifugal casting tube is obtained.
10. The method of claim 9, wherein the method has one or more of the following features:

    In step 1), control the content of Pb, Sn, Sb, Zn, As, Bi in molten steel to be lower than 50ppm respectively;

    In step 2), after heating the molten steel to 1650±50°C, use a deoxidizer to deoxidize and slag;

    In step 2), the slagging comprises: using a slag-forming agent to cover the molten steel in the furnace, starting to blow argon at the bottom of the furnace, and slagging after the argon blowing, and the argon blowing time is preferably 3±1min;

    In step 3), carry out argon gas furnace mouth covering protection, isolate air and molten steel surface reaction;

    In step 3), during the process of adding Al and Al dissolving, keep furnace bottom blowing argon and furnace mouth argon covering protection; and

    In step 3), after the Al is dissolved, the temperature is raised to 1680±50° C., and then a slag-forming agent is added to form slag.

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