HEAT-RESISTANT, OXIDATION-RESISTANT ALLOY AND METHOD OF PREPARATION

Abstract

This disclosure relates to a heat-resistant, oxidation-resistant alloy and a method of preparation, which belongs to the technical field of alloys, and solves the problems of conventional alloys where the oxygen, sulfur, and nitrogen contents are high, the proportion of Al2O3 film in the oxidation film on the surface of the alloy is low, and when the aluminum content is high, the hardness of the alloy is poor; The heat-resistant, oxidation-resistant alloy of the present disclosure, by mass percentage, comprises: 2.5%-6% Al, 24%-30% Cr, 0.3%-0.55% C, 30%-50% Ni, 2%-8% W, 0.01%-0.2% Ti, 0.01%-0.2% Zr, 0.01%-0.4% Hf, 0.01%-0.2% Y, 0.01%-0.2% V, N<0.05%, O<0.003%, S<0.003%, and Si<0.5%, the balance being Fe and unavoidable impurities; wherein merely one of Ti and V is comprised; the method for preparing the heat-resistant oxidation-resistant alloy comprises: melting with inactive element materials, refining, adding mixed rare earth, adding slag, alloying the active elements; the full oxidation-resistant level temperature of the heat-resistant oxidation-resistant alloy of the present disclosure reaches 1200°C, which makes it real that the alloy can serve below 1200°C for a prolonged and stable period.

Description

HEAT-RESISTANT, OXIDATION-RESISTANT ALLOY AND METHOD OF PREPARATION TECHNICAL FIELD This disclosure relates to the technical field of alloys, and particularly to a heat-resistant, oxidation-resistant alloy and method of preparation. BACKGROUND OF THE INVENTION Along with developments in fields such as aviation and petrochemicals, materials with excellent high-temperature oxidation resistance at 1000–1200°C are critically needed, such as for high-temperature components in aircraft engine combustion chambers and exhaust pipes, and for ethylene cracking furnace tubes. Furthermore, good weldability is required for connecting these components. Materials that actively serve as such components are primarily forged superalloys and heat-resistant steels, which possess good weldability. However, the high-temperature oxidation resistance of these alloys is mainly achieved by adding a high chromium content, and the oxide film formed at high temperatures is primarily Cr₂O₃.CrzO₂ below 1000°C is very stable and has good protective properties, but above 1000°C it is unstable, readily gasses to form pores, and loses its protective function for the alloy matrix. Al₂O₃ can remain stable in high-temperature environments above 1000°C. Therefore, to enable alloys to have excellent oxidation resistance above 1000°C, a compact Al₂O₃ film must form. A larger surface area of ​​Al₂O₃ in the oxide film formed on the alloy surface makes the film more difficult to peel off, thus improving the alloy's oxidation resistance. Adding a certain amount of aluminum to heat-resistant steels can form an Al₂O₃ film, which significantly improves the high-temperature oxidation resistance of the alloys. In the petrochemical industry, heat-resistant aluminum alloys have already begun to be used in ethylene cracking furnace tubes to replace traditional heat-resistant steels. The HTE alloy (ZL102187003B), developed by Schmidt-Clemens in Germany, is the most representative and offers optimal performance. Ethylene cracking furnace tubes made from the HTE alloy exhibit good oxidation resistance and resistance to... Q / frcnn / Lznz / Em coking, and both the furnace tube life and the decoking period are considerably improved compared to traditional heat-resistant steels. However, the high-temperature mechanical properties, oxidation resistance, and oxidation film stability of the alloy can still be improved further. Additionally, when the aluminum content is high, a sufficiently thick Al₂O₃ layer can form, preventing the Al₂O₃ layer from peeling off in high-temperature service. However, if the aluminum content is too high, the alloy's hardness is poor. Therefore, in high-temperature service, good oxidation resistance and good hardness cannot be achieved simultaneously in alloys. Unlike heat-resistant steels, when active elements such as aluminum and titanium are added, they readily form oxide and nitride inclusions with the oxygen and nitrogen in the alloys. This affects the alloy's mechanical properties and consumes the main elements, such as aluminum and titanium, hindering the formation of the aluminum-oxide film. Therefore, to achieve high-quality preparation and ensure excellent serviceability, it is necessary to strictly control the oxygen and nitrogen content of aluminum-containing alloys. Furthermore, sulfur strongly influences the adhesion between the oxide film and the alloy matrix. To ensure that the oxide film can adhere stably to the surface of the alloy matrix and provide protection, it is necessary to strictly control the sulfur content in the alloys.However, because it is restricted by the preparation process, in the preparation process of conventional aluminum-containing alloys, the range within which the harmful element nitrogen is controlled is very wide, and harmful elements such as oxygen and sulfur are not controlled, which seriously affects the performance and quality stability of the furnace tubes. In the technical field of alloys, it is relatively easy to improve the overall properties of alloys below 1050°C. However, improving the properties of alloys at service temperatures above 1050°C, especially as they approach 1200°C, presents a significant challenge. Because improving the properties of alloys at high service temperatures above 1050°C is so difficult, even if the service temperature is only to be increased by 50°C, the difficulty becomes exponential, and the cost of the work required is inconceivable for a skilled professional. An increase of just 50°C is a remarkable achievement, and industry experts should generally acknowledge and respect it. BRIEF DESCRIPTION OF THE INVENTION In view of the analysis described above, this disclosure is intended to provide a heat-resistant, oxidation-resistant alloy and a method of preparation, which can solve at least one of the following technical problems: (1) When the service temperature is above 1100°C, good oxidation resistance and good mechanical properties of the alloys cannot be obtained simultaneously; (2) Harmful elements such as oxygen, sulfur, and nitrogen are not effectively controlled, causing the alloys to have poor exhaust properties and unstable quality; and (3) The proportion of Al2O3 film in the oxide film formed on the surface of the alloys in high-temperature environments above 1100°C is low, and the Al2O3 film peels off easily, resulting in poor oxidation resistance of the alloys. One objective of this disclosure is to achieve primarily through the following technical solution: In one aspect, the present disclosure provides a heat-resistant, oxidation-resistant alloy, by mass percentage, comprising: 2.5%-6% Al, 30%-50% Ni, 2%-8% W and 0.01%-0.4% Hf. Based on the above solution, this disclosure is improved as follows: Optionally, the alloy comprises: 2.5%-6% Al, 24%-30% Cr, 0.3%-0.55% C, 30%-50% Ni, 2%-8% W, 0.01%-0.2% Ti, 0.01%-0.2% Zr, 0.01%-0.4% Hf, 0.01%-0.2% Y, and 0.01%-0.2% V; wherein merely one of Ti and V is comprised. Optionally, the alloy comprises: N<0.05%, O<0.003%, S<0.003%, and Si<0.5%, the balance being Fe and unavoidable impurities. Optionally, the alloy comprises: 3.3%-5.5% Al, and 34%-46% Ni. Optionally, the alloy comprises: 3%-6% of W. Optionally, the alloy comprises: 0.01%-0.06% of Y. Optionally, in an oxidizing atmosphere of 1000-1200°C, not less than 90% of an area of ​​an oxidation film that forms on an alloy surface is an Al2O3 film. In another aspect, this disclosure also provides a method for preparing a heat-resistant, oxidation-resistant alloy, which comprises the following steps: Step 1: Melt carbon and inactive elements to obtain molten steel after it has been completely melted; Step 2: Heat the molten steel, and refine; Step 3: Add a mixed rare earth; Step 4: Add slag; and Step 5: Introduce an inert gas into a melting channel, place active elements such as aluminum, hafnium, titanium, zirconium, and yttrium into the melting channel, heat, pour molten steel into the melting channel, and introduce the molten steel into a melting trough. Optionally, the refining temperature in Step 2 is not less than 1640°C. Optionally, some of the carbon is first added in Step 1, and the remaining carbon is then added in Step 2 when the molten steel has been heated to no less than 1640°C. Optionally, the amount of rare mixed earth added is 0.05%-0.25% of the mass of molten steel. Optionally, the slag contains CaO. Optionally, the inert gas is argon, the argon pressure is 0.15-0.3MPa, and the flow rate is 1-5L / min. Optionally, the method also includes casting after Step 5, and the speed from steel threading to completion of casting is 60-100 kg / minute. The advantageous effects of this disclosure are as follows: (1) This disclosure, by adding an appropriate amount of element Al, ensures the formation of the Al2O3 film, and weldability and mechanical property can be obtained simultaneously; by adding an appropriate amount of element C, it ensures the precipitation of carbide which is used to strengthen the alloy; by adding an appropriate amount of element Cr, it facilitates the formation of the Al2O3 film at a low aluminum content, and the formation of carbide which is used to strengthen the alloy; by adding an appropriate amount of element Zr, it strengthens the grain boundary, to improve the mechanical property; and by adding an appropriate amount of element Ti or V, it thins the carbide, to improve the creep property of the alloy. (2) This disclosure reduces the formation of the Ni3Al phase by thoroughly adjusting the Ni content and Al content to allow the alloy to still have good hardness when the Al content is above 4%. (3) The present disclosure, by adding Hf, and by the combined function of Hf and Y, when the content of Y is below 0.06%, can still optimize the morphology and chemical composition of the oxide and relieve the degree of internal oxidation, to allow the oxidation film formed on the surface of the alloy to be continuous and compact, to improve the cohesion between the oxidation film and the matrix, and in turn greatly improve the high-temperature oxidation resistance of the alloy. (4) This disclosure, by adding W, and by controlling the W content, improves the high-temperature strength of the alloy, and prolongs the service life. (5) It is very difficult to improve the alloy's properties above 1050°C, especially when approaching 1200°C. Each time the temperature is increased by 20°C or 50°C, the difficulty increases exponentially, making it absolutely impossible to achieve through limited experimentation or conventional methods. In fact, this disclosure adjusts the composition and element content through extensive experimentation to enable the alloy to form a stable Al₂O₃ film in the high-temperature environment of 1100–1200°C. The alloy exhibits excellent oxidation resistance, good high-temperature strength, and good weldability, and its overall performance surpasses that of conventional heat-resistant aluminum alloys. (6) The preparation method provided by this disclosure, by adding carbon in different batches, performs deep and multi-time deoxidation and denitrification, thereby effectively reducing the N and O content in the alloy and, in turn, improving the alloy's properties. (7) This disclosure, by adding the mixed rare earth multiple times instead of adding it all at once, reduces oxidation and combustion loss of the rare earth, to ensure that the rare earth can be added effectively; and by controlling the amount of addition of the mixed rare earth, it can ensure a good desulfurization effect, and prevent the rare earth elements remaining in the molten steel from forming a low melting point phase with Ni, and affecting the high-temperature mechanical properties of the alloy. (8) This disclosure, by selecting the type of cover slag and controlling the amount of cover slag added, adsorbs and traps oxides, nitrides, sulfides and floating inclusions, thus obtaining a high-clean cast steel. (9) This disclosure, by controlling the refining temperature to not be less than 1640, allows the chemical reaction of CO generation by replacement reaction between carbon and oxide inclusions in molten steel to be carried out more easily, to obtain a better purification effect. (10) By adjusting the process steps and process parameters, this disclosure allows the N content in the alloy prepared by the preparation method in this disclosure to be below 0.05%, the O content to be below 0.003%, the S content to be below 0.003%, and the Si content to be below 0.5%. In this disclosure, the foregoing technical solutions may be combined to achieve more preferable combined solutions. Other features and advantages of this disclosure will be described below, and some of these advantages may become apparent from the description or upon implementation. The objectives and other advantages of this disclosure may be implemented and obtained from the content specifically outlined in the description and claims. BRIEF DESCRIPTION OF THE FIGURES The figures are merely for the purpose of illustrating the particular modalities and are not considered a limitation to the present disclosure. Throughout the figures, the same reference signs denote the same elements. Figure 1 shows the cyclic oxidation weight gain curves at 1100°C for the alloys of the forms described in this disclosure and for comparative material alloy No. 8; Figure 2 shows the cyclic oxidation release curves at 1100°C of the alloys of the forms in this disclosure and the comparative material alloy No. 9; Figure 3 shows the cyclic oxidation release curves at 1150°C of the alloys of the forms in this disclosure and the comparative material alloy No. 9; Figure 4 shows the cyclic oxidation release curves at 1200°C of the alloys of the forms in this disclosure and the comparative material alloy No. 9; Figure 5 is the scanning electron microscope photograph of the surface oxidation film of Alloy No. 3 of an embodiment of the present disclosure after cyclic oxidation at 1200°C for 100 h; Figure 6 is the scanning electron microscope photograph of the surface oxidation film of comparative alloy No. 9 after cyclic oxidation at 1200°C for 100 h; Figure 7 is the scanning electron microscope photograph section of the oxidation film of Alloy No. 3 of one modality of the present disclosure after cyclic oxidation at 1200°C for 100 h; Figure 8 is the scanning electron microscope photograph section of the oxidation film of comparative alloy No. 9 after cyclic oxidation at 1200°C during 100 h. DETAILED DESCRIPTION OF THE INVENTION The preferred forms of this disclosure will be described in particular below with reference to the figures. The figures that form a portion of this disclosure are intended to explain the principle of this disclosure in conjunction with the forms of this disclosure and are not intended to limit the scope of this disclosure. In this disclosure, unless otherwise stated, all contents refer to mass percentage contents. The functions of the elements in the high-temperature, oxidation-resistant, heat-resistant, iron-nickel-based alloy of this disclosure are described in detail as follows: Ni: Ni can stabilize the austenite structure and expand the austenite phase regions, allowing the alloy to have high strength and plasticity, and ensuring good high-temperature strength and creep resistance. However, a very high Ni content affects nitrogen solubility in the matrix, exacerbates the tendency for nitrides to precipitate in the alloy, and impairs its creep resistance. Furthermore, very high Ni content readily forms the NisAl phase with the Al in the alloy. The NisAl phase affects the alloy's hardness and machinability. If the Ni content exceeds 60%, even if the Al content is controlled to be below 4%, the NisAl phase will form, negatively impacting the alloy's hardness and machinability.Furthermore, nickel (Ni) is expensive, and a very high content will affect the cost of preparing the alloy. Therefore, the Ni content in the material of this disclosure is controlled to be 30%–50%, preferably 34%–46%. Aluminum (Al): Aluminum is a prerequisite for the formation of a highly stable Al₂O₃ film on the surface of the alloy when it is oxidized at high temperatures. However, if the Al content is very high, it readily forms an intermetallic compound phase, NisAl, with Ni. While the NisAl phase can improve the alloy's strength, it negatively impacts hardness and machinability. Above 1000°C, the NisAl phase redissolves and disappears, thus not contributing to the alloy's high-temperature strength or service life. At medium and low temperatures, the presence of NisAl improves the alloy's strength, but this improvement in strength at room or medium-low temperatures is detrimental to the alloy's service life. Furthermore, the resulting decrease in room-temperature hardness and machinability will significantly affect the casting and processing costs of the components.Therefore, for this disclosure, it is necessary to jointly adjust and control the Ni and Al content to prevent the formation of the Ni3Al phase. Because the Ni content in this disclosure is not high, the Ni3Al phase has not yet formed when the Al content is above 4%. At the same time, to form a stable Al2O3 film at higher temperatures, the Al content in this disclosure is controlled to be 2.5%–6%, preferably 3.3%–5.5%. Cr: In this disclosure, the addition of Cr can reduce the critical amount of Al required for the formation of an Al₂O₃ film. This allows for a decrease in the amount of Al needed to form an Al₂O₃ film layer on the alloy surface, thus facilitating the formation of the protective Al₂O₃ layer. Furthermore, Cr is a carbide-forming element, and carbide formation improves the high-temperature strength of the alloy. However, Cr is also a strong ferrite-forming element, and a very high addition imparts austenite phase stability, which is detrimental to the alloy's high-temperature strength. Therefore, the Cr content in this disclosure should be controlled to be 24%–30%. Carbon (C): Carbon is a carbide-forming element and forms carbide phases in the alloy described herein. These carbide phases have a strengthening effect. If the carbide content is low, the amount of carbide phases is low, which affects the strengthening effect. If the carbide content is too high, the amount of carbide phases is too high, which is detrimental to the alloy's hardness. Therefore, the carbon content in the material described herein is controlled to be 0.3%–0.55%. W: W can dissolve in the alloy matrix to strengthen the solid solution and form carbides to strengthen the dispersion, effectively improving the alloy's high-temperature strength. However, a very high W content will negatively affect the alloy's hardness. Therefore, the W content in this disclosure is controlled to be 2%-8%, preferably 3%-6%. Ti and V: Ti and V can change the morphology of grain boundary carbides and thin them, allowing them to disperse and distribute more evenly, thus improving the alloy's high-temperature creep resistance. Very high levels of Ti and V are detrimental to carbide morphology and readily form an N13(Al, Ti) phase, which negatively impacts the alloy's hardness. Therefore, the Ti content in this disclosure should be controlled to 0.01%–0.2%, and the V content should also be controlled to 0.01%–0.2%. Zr: Zr segregates at grain boundaries and strengthens them. However, very high levels readily form a low-melting-point NbZr phase, which negatively impacts the alloy's high-temperature properties. Therefore, the Zr content in the material described herein is controlled to be 0.01%–0.2%. Hf and Y: In this disclosure, adding an appropriate amount of the elements Hydrogen (Hf) and uranium (Y) can influence the morphology and chemical composition of the oxides and the degree of internal oxidation, improve the adhesive strength of the oxide film, and greatly enhance the high-temperature oxidation resistance of the alloy. When used together, the effect is even better. Because the rare earth element Y is highly reactive, in non-vacuum alloy casting, Y is easily lost through combustion or oxidation, its content is difficult to control effectively in engineering, and service stability cannot be guaranteed. Furthermore, hydrogen (Hf) is relatively stable, and its content is easily controlled in casting. Additionally, Hf can significantly improve the adhesive strength of the oxide film in high-temperature environments above 1000°C.However, if the Hf and Y contents are too high, this increases the material cost, and Hf and Y readily form a low-melting-point phase with Ni, which negatively impacts the alloy's high-temperature mechanical properties. Therefore, when Hf and Y are added to the material of this disclosure, the Hf content is controlled to be 0.01%–0.4%, and the Y content is controlled to be 0.01%–0.2%. Si: Si is readily introduced into the alloy by raw materials such as ferrochromium, and Si facilitates the precipitation of the detrimental σ phase, which reduces the alloy's strength life. Therefore, the Si content must be strictly controlled, and this disclosure achieves the purpose of controlling the Si content in the alloy by preferentially selecting raw materials. The Si content in this disclosure is controlled to be below 24% ± 0.5%. Oxygen and Nitrogen: Because the alloy compositions of this disclosure include active elements such as Al, Hf, Y, Zr, and Ti, high oxygen and nitrogen contents readily cause inclusions such as oxides and nitrides to form, impairing the alloy's hardness and consuming useful elements such as Al and Hf, thus affecting aluminum-oxide film formation. Therefore, the oxygen and nitrogen contents should be kept as low as possible. The oxygen content in the alloy of this disclosure is controlled to be below 0.003%, and the nitrogen content is controlled to be below 0.05%. S: S segregates at the grain boundary, which disrupts the continuity and stability of the grain boundary, significantly reduces the long-term creep properties and tensile plasticity of the alloy, impairs the adhesion of the surface oxide film, readily causes the oxide film to detach, and reduces the alloy's oxidation resistance. Therefore, the S content should be controlled to be as low as possible, and the S content in the alloy of this disclosure is controlled to be below 0.003%. This disclosure provides a heat-resistant, oxidation-resistant alloy, by mass percentage, comprising: 2.5%-6% of Al, 24%-30% of Cr, 0.3%-0.55% of C, 30%-50% of Ni, 2%-8% of W, 0.01%-0.2% of Ti, 0.01%-0.2% of Zr, 0.01%-0.4% of Hf, 0.01%-0.2% of Y, and 0.01%-0.2% of V, N<0.05%, O<0.003%, S<0.003%, and Si<0.5%, the equilibrium being Fe and unavoidable impurities; wherein merely one of Ti and V is comprised. In comparison with prior art, the present disclosure, by adjusting the alloy compositions and addition quantities, allows the alloy to have excellent oxidation resistance, good high-temperature strength, and good weldability. Specifically, the advantageous effects of the heat-resistant, oxidation-resistant alloy of this disclosure are as follows: (1) This disclosure, by adding an appropriate amount of element Al, ensures the formation of the Al2O3 film, and weldability and mechanical property can be obtained simultaneously; by adding an appropriate amount of element C, it ensures the precipitation of carbide which is used to strengthen the alloy; by adding an appropriate amount of element Cr, it facilitates the formation of the Al2O3 film at a low aluminum content, and the formation of carbide which is used to strengthen the alloy; by adding an appropriate amount of element Zr, it strengthens the grain boundary, to improve the mechanical property; and by adding an appropriate amount of element Ti or V, it thins the carbide, to improve the creep property of the alloy. (2) This disclosure reduces the formation of the N13AI phase by thoroughly adjusting the Ni content and Al content to allow the alloy to still have good hardness when the Al content is above 4%. (3) The present disclosure, by adding Hf, and by the combined function of Hf and Y, when the content of Y is below 0.06%, can still improve the morphology and chemical composition of the oxide and the degree of internal oxidation, to allow the oxidation film formed on the surface of the alloy to be continuous and compact, to improve the cohesion between the oxidation film and the matrix, and in turn greatly improve the high-temperature oxidation resistance of the alloy. (4) This disclosure, by adding W, and by controlling the W content, improves the high-temperature strength of the alloy, and prolongs the service life. (5) Improving the alloy's properties above 1050°C is extremely difficult, especially at around 1200°C. Each increase in temperature of 20°C or 50°C exponentially increases the difficulty, making such improvements impossible to achieve through limited experimentation or conventional methods. Therefore, this disclosure adjusts the composition and elemental content through extensive experimentation to enable the alloy to form a stable Al₂O₃ film in the high-temperature environment of 1100–1200°C. The alloy exhibits excellent oxidation resistance, good high-temperature strength, and good weldability, and its overall performance surpasses that of conventional heat-resistant aluminum alloys. For illustrative purposes, the composition and mass percentages of the alloy in this disclosure may also be 4.5%-5.5% Al, 34%-46% Ni, 3%-6% W, and 0.01%-0.06% Y. The method for preparing a heat-resistant, oxidation-resistant alloy of this disclosure varies with the use, and if used for high-temperature components used in the aerospace field, it must employ vacuum induction casting and casting, and comprises the following steps: 1. Preparation of materials: Select electrolytic nickel, metallic aluminum, metallic chromium (or ferrochrome), pure iron, metallic tungsten, graphite, hafnium sponge, titanium sponge, zirconium sponge and metallic trium as raw materials, and weigh the proportion of the same to be used. 2. Add materials: Place the electrolytic nickel, chromium metal (or ferrochrome), pure iron, and tungsten metal in the crucible, and add the other elements from a hopper. 3. Melting: Melting in an intermediate frequency induction vacuum melting furnace, supplying energy with a small power for 10 minutes to dehydrogenate, then supplying energy with a large power to melt completely, and starting the refining, where the refining temperature is 1530-1580°C, the refining period is set according to the amount of molten steel, and is controlled to be 10-60 minutes, and during refining the degree of vacuum should be below 5 Pa. 4. Melting: After complete melting, stir vigorously for 1-2 minutes, and pour when the molten steel temperature is controlled to 1450-1580 °C. The preparation of the alloy described herein using the vacuum induction melting method described above can precisely control active elements such as Al and Y, and can reduce harmful elements such as O, N, and S to a very low level. However, the preparation method is expensive, and the components that can be prepared are limited by current vacuum furnaces. Therefore, vacuum melting is only suitable for precision casting in aerospace foundries. If the method is used for ethylene cracking furnace tubes in the petrochemical field, because the length of a single furnace tube can reach several meters, performing both smelting and centrifugal casting under vacuum is difficult to implement due to equipment limitations and prohibitively high costs. Therefore, smelting and centrifugal casting can only be carried out in non-vacuum environments. However, because the raw materials for preparing the alloy described herein have high contents of active elements, it is very difficult to prepare a qualified alloy under non-vacuum conditions. This disclosure also provides a method for preparing the oxidation-resistant heat-resistant alloy under a non-vacuum condition, which comprises the following steps: Step 1: Melt carbon and inactive elements to obtain molten steel after it has been completely melted; Step 2: Heat the molten steel to no less than 1640°C to perform the refining; Step 3: Add a mixed rare earth; Step 4: Add slag; and Step 5: Place the active elements such as aluminum, hafnium, titanium, zirconium, and yttrium in the melting channel, introducing an inert gas into the melting channel, and when the temperature of the molten steel has increased to 1650-1750 °C, pour the molten steel into the melting channel, and introduce the molten steel into a trough to perform centrifugal casting. Compared to the prior art, the advantageous effects of the method for preparing the oxidation-resistant heat-resistant alloy provided by this disclosure are as follows: (1) By adding carbon in different batches, the method performs deep deoxidation and denitrification at various times, thereby effectively reducing the N and O content in the alloy and, in turn, improving the alloy's properties. (2) This disclosure, by adding the mixed rare earth multiple times instead of adding it all at once, reduces oxidation and combustion loss of the rare earth, to ensure that the rare earth can be added effectively; and by controlling the amount of addition of the mixed rare earth, it can ensure a good desulfurization effect, and prevent the rare earth elements remaining in the molten steel from forming a low melting point phase with Ni, and affecting the high-temperature mechanical properties of the alloy. (3) This disclosure, by selecting the type of cover slag and controlling the amount of cover slag added, adsorbs and traps oxides, nitrides, sulfides and floating inclusions, thus obtaining a high-clean cast steel. (4) By controlling the refining temperature to not be less than 1640, this disclosure allows the chemical reaction of CO generation by replacement reaction between carbon and oxide inclusions in molten steel to be carried out more easily, to obtain a better purification effect. (5) By adjusting the process steps and process parameters, this disclosure allows the N content in the alloy prepared by the preparation method in this disclosure to be below 0.05%, the O content to be below 0.003%, the S content to be below 0.003%, and the Si content to be below 0.5%. Specifically, when carbon and oxygen react in molten steel to generate CO gas, the method can, in one aspect, deoxidize the steel and, in another aspect, perform denitrification with air bubbles by utilizing the CO formed. When mixed rare earth elements and free oxygen and sulfur react in free steel to generate oxides or sulfides, the method can desulfurize and also deoxidize the steel. Considering that elements such as aluminum, hafnium, titanium, zirconia, and trium are highly reactive, if melted directly, they can undergo chemical reactions with oxygen in the air to generate oxides, thus consuming the alloying elements. Therefore, in this preparation method, the elements are not melted directly. Instead, the reactive elements are placed in a melting channel shielded by inert gas. Molten steel obtained from melting the inactive elements is poured onto the reactive elements. The reactive elements melt using the superheat of the molten steel, and the kinetic energy of the steel threading homogenizes them within the melting channel. This process effectively reduces the oxidation of the reactive elements, thereby protecting the alloying elements from further degradation. In order to further reduce the nitrogen and oxygen content in molten steel, the carbon is added gradually in the preparation method described herein. This is because smelting is carried out in air, and oxygen continuously enters the molten steel during the smelting process. In this method, some of the carbon is initially added to perform preliminary deoxidation and denitrification. The remaining carbon is then added once the molten steel has been heated to at least 1640°C. When used at high temperatures, the free energy of carbon is lower than that of oxides such as NiO, Fe₂O₃, and Cr₂O₃. Any oxygen present in the oxides is replaced, resulting in thorough deoxidation and protecting the alloying elements from being consumed.Furthermore, if too much carbon is added at once, fire and combustion loss easily occur, resulting in the carbon not being able to effectively enter the molten steel, thus affecting the deoxidation and denitrification effect. In the preparation method, the pouring temperature varies depending on the casting. For example, when casting a centrifuge tube, high pouring temperatures are used to ensure the molten steel has sufficient fluidity to facilitate the formation of the tube. If the centrifuge tube is thinner, the pouring temperature must be higher. While a higher temperature improves the fluidity of the molten steel, it also increases the likelihood of element loss through combustion. Therefore, considering both the fluidity of the molten steel and the potential for element loss through combustion, the pouring temperature for centrifuge tube casting is selected to be 1650–1750°C. In order to prevent the reaction between the molten steel (the alloy melt) and the crucible in the subsequent deoxidation by high-temperature melting, in the preparation method, the crucible is made of aluminum oxide, which has good high-temperature stability. It should be noted that, in order to adsorb and trap floating oxides, nitrides, and sulfides, in the method of preparation of the present disclosure, a coating slag containing CaO is added to the surface of the molten steel, which, in one aspect, is further desulfurized using the CaO, to remove more oxygen, nitrogen, and sulfur, and in another aspect, can also effectively remove inclusions, thus obtaining a high-clean molten steel. Specifically, CaO and S react to perform earlier stage desulfurization, where the reaction equation is: CaO+[S]=CaS+[O], and the reaction process is: first, the desulfurization reaction occurs on the surface, desulfurization generates CaS, which covers the surface of the CaO, after the CaS completely coats the CaO powder, the product layer diffuses inwards to the desulfurization reaction, and gradually thickens the layer of CaS on the surface of the CaO, and the diffusion desulfurization reaction gradually slows down until it ends. Whereas if the amount of slag added is too small, it cannot completely cover the surface of the molten steel, and if the amount added is too much, it causes waste and increases the cost, in the method of preparation of the present disclosure, the amount of slag addition is controlled to be 3% to 5% of the mass of the molten steel, which allows the slag to remove oxygen, nitrogen, and sulfur well, and effectively remove inclusions, thus obtaining a high-cleanliness molten steel. The mixed rare earth element used in the preparation method described herein is a mixture of the rare earth elements La and Ce, added at a concentration of 0.05%–0.25% of the molten steel mass. This is because if the amount of mixed rare earth element is too small, the number of chemical reactions involved in desulfurization will be insufficient, resulting in poor desulfurization. Conversely, if the amount is too large, the remaining rare earth elements in the molten steel readily form a low-melting-point phase with Ni, negatively impacting the high-temperature mechanical properties of the alloy. Therefore, in this preparation method, the amount of mixed rare earth element is selected to be 0.05%–0.25%.25% of the mass of the molten steel, which can ensure a good desulfurization effect, and prevent the remaining rare earth elements in the molten steel from forming a low melting point phase with Ni, which affects the high-temperature mechanical property of the alloy. In the preparation method, introducing fluid argon to the upper surface of the casting channel forms an argon curtain to protect the molten steel containing easily oxidized elements, thus slowing down oxidation. Specifically, the argon pressure is selected to be 0.15–0.3 MPa, and the flow rate to be 1–5 L / min. This is because if the argon pressure is too low, it cannot effectively form an argon curtain to isolate the molten steel from the air and prevent oxidation, while if the argon pressure is too high, it can easily cause waste, increase production costs, and jeopardize the safety of the operating equipment.In the present disclosure, after qualified composition molten steel is obtained using the above method, the centrifugal casting process is as follows: Qualified composition molten steel, a suitable degree of superheat and a suitable weight in the trough is rapidly melted into a metal mold that is rotating at a high speed, and the molten steel solidifies in a centrifugal casting tube. Specifically, the alloy obtained using the preparation method of the present disclosure can, apart from being used to cast centrifugal tubes, can also be used to cast other castings that are required to serve at high temperatures, especially castings that are required to serve in severe high-temperature environments of 1100-1200°C and high oxidizability. Given that the alloy composition includes a large number of active elements, to prevent losses due to combustion and oxidation of these elements, the entire steel threading process must be carried out very quickly. Specifically, the threading speed for completing the casting is controlled to be 60-100 kg / minute. The chemical composition and elemental content of the forms in this disclosure can be seen in Table 1, the process parameters of the preparation methods can be seen in Table 2, the amounts of alloy release after oxidation at different temperatures for 100 h can be seen in Table 3, the content of aluminum oxides in the oxidation films of the alloys formed after high-temperature cyclic oxidation at different temperatures can be seen in Table 4, and the lifetime of the alloys at 1100°C / 17MPa can be seen in Table 5. The first modality corresponds to Alloy No. 1, the second modality to Alloy No. 2, and the remainder can be reduced accordingly. To facilitate comparison, Alloy No. 8 and Alloy No. 9 are used as prior art benchmarks. Among them, Alloy No. 8 is the weldable superalloy GH3230, which has the highest service temperature and is widely used for high-temperature components in aerospace engine combustion chambers, and Alloy No. 9 is the HTE alloy, currently the best material for ethylene cracking furnace tubes in the petrochemical field. The heat-resistant oxidation-resistant alloys of the first to the seventh modes are prepared using the following method: Step 1: Weigh the raw materials; Step 2: Place the electrolytic nickel, pure iron, and part of the graphite in the crucible of a non-vacuum intermediate-frequency smelting furnace that has a fixed-point casting function, and obtain molten steel after it is completely melted; Step 3: Heat the molten steel to the refining temperature, and add the remaining graphite; Step 4: Add a certain amount of the mixed rare earth; Step 5: Add a certain amount of the slag containing CaO; Step 6: Introduce fluid argon into the upper surface of the casting channel, place active elements such as metallic aluminum, hafnium sponge, titanium sponge, zirconium sponge, and metallic yttrium into the casting channel, and when the chemical composition of the molten steel in Step 2 is qualified, and the temperature of the molten steel has risen to the pouring temperature, place the molten steel into the casting channel from the opening at the top of the casting channel, and introduce the molten steel into the trough from the opening at the bottom of the casting channel for centrifugal casting; and (7) Centrifuge tube casting: Quickly pour the molten steel into the trough into a metal mold that rotates at high speed, to make an experimental centrifuge tube. TABLE 1 The preparation of raw materials and contents of the elements of the first to the modalities. Alloy Al Cr C Ni W Ti Hf Zr YVONS Si Fe 1 4.5 25 0.32 32 4.5 0.05 0.05 0.05 0.15 - 0.001 0.035 0.001 0.4 remainder 2 4.1 28 0.45 35 5 0.1 0.15 0.01 0.03 - 0.001 0.032 0.002 0.4 remainder 3 3.7 26 0.43 44 5.7 0.11 0.05 0.05 0.05 - 0.001 0.038 0.002 0.33 remainder 4 3.8 28 0.35 46 5 0.18 0.39 0.05 0.01 - 0.001 0.038 0.001 0.4 remainder 5 2.9 27 0.41 49 7.8 - 0.15 0.03 0.18 0.01 0.001 0.002 0.001 0.2 remainder 6 2.5 27 0.4 45 2 - 0.1 0.19 0.1 0.09 0.001 0.03 0.001 0.16 rest 7 5.9 29.5 0.5 35 3.1 - 0.05 0.04 0.02 0.2 0.001 0.03 0.001 0.3 rest Cl Process parameters of the JADRO 2 modalities of the present disclosure Modality serial number Refining temperature / °C Amount of mixed earth addition / % Amount of slag addition / % Pouring temperature / °C Argon pressure / MPa Argon flow rate / L / min Melting speed / kg / min 1-2 1640 0.15 4 1750 0.25 5 80 3-5 1680 0.25 3 1650 0.15 1 100 6-7 1660 0.05 5 1700 0.3 3.5 60 o / frcnn / Lznz / E / Yii Under the same experimental conditions, the amounts of detachment after oxidation at different temperatures for 100 h of the alloys of the modalities of the present disclosure and the two alloys of the prior art are individually measured, the experimental results of which are listed in Table 3. The integrity states of the oxidation films after oxidation at different temperatures for 100 h are listed in Table 4, the high-temperature strength properties are listed in Table 5, and the high-temperature tensile elongations of the alloys of the modalities of the present disclosure are listed in Table 6. TABLE 3 The amounts of release of the alloys of the forms in this disclosure and the comparative materials after oxidation to different Temperatures for 100 h fmc i / cm2j Test temperature / °C Alloy No. 3 Alloy No. 9 1000 0.04 0.07 1050 0.035 0.10 1100 0.024 0.26 1150 0.064 0.35 1200 0.077 2.09 TABLE 4 The relationships between the areas of aluminum oxides and the surfaces of the alloys after oxidation at different temperatures for 100 h Test temperature / °C 1100 1150 1200 Alloy No. 1 94% 91% 90% Alloy No. 2 95% 93% 93% Alloy No. 3 96% 93% 92% Alloy No. 4 96% 93% 92% Alloy No. 5 94% 92% 91% Alloy No. 6 95% 94% 92% Alloy No. 7 96% 94% 93% Alloy No. 9 80% 70% 25% Note: Alloy No. 8 cannot form an aluminum oxide film at the high temperature of 1150°C, so the chart does not have data for Alloy No. 8. TABLE 5 The service life of the alloys at 1100°C / 17MPa Alloy 1 2 3 4 5 6 7 8 9 Service life / h 95 98 111 99 120 97 92 40 11, 27, 53 TABLE 6 The tensile elongations of the alloys of this disclosure at 1000°C Alloy 1 2 3 4 5 6 7 Tensile elongation / % 41 43 46 46 40 49 45 It can be seen from Figure 1 that, as analyzed in terms of oxidation rates for weight gain, the oxidation resistances at 1100°C of the alloy materials of the embodiments of the present disclosure are 2.5 to 4 times those of the prior art comparator material of Alloy No. 8. Above 1100°C, Alloy No. 8 cannot form a continuous and stable oxidation film, and the oxidizability decreases drastically. It can be seen from Table 3, Figure 2, Figure 3, and Figure 4 that, in the temperature range of 1000–1200°C, with increasing oxidation temperature, the amplitudes of the increase in the amount of oxidation release from the alloys in this disclosure are very small, indicating that all the alloys in this disclosure have excellent oxidation resistance below 1200°C. However, the oxidation resistance of the comparative material alloy No. 9 decreases rapidly with increasing temperature, and particularly above 1150°C, the amplitude of the decrease in oxidation resistance is particularly significant. After 100 h of oxidation, with the oxidation temperature increasing from 1150°C to 1200°C, the amount of oxidation release increases fivefold.After cyclic oxidation at 1100°C for 100 h, the oxidation release of the alloy of prior art material No. 9 is 5 to 10 times that of the alloy materials of the embodiments of this disclosure, and after cyclic oxidation at 1200°C for 100 h, the oxidation release of the alloy of prior art material No. 9 is 27 times greater than that of the alloy materials of the embodiments of this disclosure. This indicates that the cohesion between the oxidation film and the matrix of the alloys of the embodiments of this disclosure is much greater than the cohesion between the oxidation film and the matrix of alloy No. 9, and at higher temperatures, the advantage of the alloys of this disclosure becomes even more pronounced. Further analysis of the oxidation film states formed on the surfaces after alloy oxidation reveals (see Table 4, Figure 5, and Figure 6) that, in the alloys described herein, after oxidation in high-temperature environments below 1200°C for 100 h, aluminum oxide constitutes more than 90% of the oxidation films formed on the sample surfaces, and these films are continuous and compact. Furthermore, with increasing temperature, the aluminum oxide film does not decrease substantially; at 1200°C, it remains above 90%.The high-temperature stability of aluminum oxide is very good. The compact aluminum oxide films can protect alloy matrices from further oxidation, and when used in ethylene cracking furnace tubes, the aluminum oxide films can provide good resistance to carburization and coking. However, in the comparative material alloy No. 9 of the prior art, aluminum oxide constituted 80% of the oxide film formed after oxidation at 1100°C for 100 hours. After the test temperature was increased to 1150°C, the aluminum oxide in the oxide film decreased to 70%, and after the test temperature was further increased to 1200°C, the aluminum oxide in the oxide film decreased sharply to 25%, along with a large amount of oxide film being shed.This indicates that, above 1100°C, the advantage of the oxidation resistance of the alloys in this disclosure over those of prior art materials gradually increases, and the higher the temperature, the greater the advantage. In Figure 5 and Figure 6, the white areas represent the peel area, the black areas represent the aluminum oxide film, and the gray-white areas represent the composite oxidation film. Upon further observation of the sections of the oxidation films formed after cyclic oxidation at 1200°C for 100 h (see Figure 7 and Figure 8), it was found that the oxidation film formed by the alloy of the modality of the present disclosure is continuous and compact, closely coherent with the matrix, has a regular cohesive interface, and has an oxidation film thickness of approximately 6 pm, whereas the oxidation film of the alloy of comparative material No. 9 of the prior art is discontinuous and loose, has a non-compact cohesion between the residual oxidation film and the matrix, has an irregular cohesive interface, has evident detachment, and has a residual oxide layer thickness of approximately 3 pm.When comparing the two oxidation films, the protective effect of the oxidation film formed by the material of the present disclosure to the alloy matrix is ​​obviously better than that of the alloy of comparative material No. 9 of the prior art. As evaluated according to HB5258-2000 (Experimental Method for Measuring the Oxidation Resistance of Steel and Superalloys), the full oxidation resistance level temperatures of the alloys in the forms described herein reach 1200°C, while the full oxidation resistance level temperature of the prior art comparison material No. 9 alloy is only 1050°C. The full oxidation resistance level temperatures of the alloys described herein are 150°C higher than those of conventional alloys. In the technical field of alloys, when the temperature is above 1000°C, particularly above 1100°C, the oxidation resistance of alloys decreases drastically due to the poor stability of the oxidation film and the poor cohesion between the matrix and the oxidation film. For example, for alloy No.Alloy No. 9, which exhibits excellent oxidation resistance in the prior art, shows that when the test temperature is increased from 1150°C to 1200°C, the proportion of aluminum oxide in the oxide film decreases from 70% to 25%, and the amount of oxide film detachment increases fivefold. At 1050°C, Alloy No. 9 is at the level of complete oxidation resistance; at 1100°C, it decreases to the level of oxidation resistance; and at 1200°C, it decreases to the level of sub-oxidation resistance. Those skilled in the art know that it is very difficult to improve the oxidation resistance of alloys above 1100°C, and that for every 20°C or 50°C increase in temperature, the difficulty increases exponentially.However, it can be considered a milestone in the field of oxidation-resistant alloys that the temperature of the full oxidation resistance level of the alloy of the present disclosure reaches 1200°C, which is achieved by a large amount of experimentation to repeatedly adjust the composition and content of the alloy, and by continuously optimizing the process steps and process parameters. It can be seen from Table 5 that the service life strength at 1100°C / 17 MPa of the alloy materials of the modalities of this disclosure is 2.4 to 3 times that of the comparative alloy material No. 8 of the prior art. The values ​​11, 27, and 53 in Table 5 indicate that the service life strength of the three No. 9 alloy tubes differs from one another, and the differences between the service life strengths of the alloy tubes are large, indicating that the quality stability of the No. 9 alloy is poor, and the difference in properties among the different tubes is significant. Q / hcnn / ι 7n7 / E / YL, which also indicates that the overall quality of Alloy No. 9 is low. However, the differences in service life strength of multiple alloy tubes of the same type in this disclosure do not exceed 3 hours, indicating that the quality stability of the alloys in the types in this disclosure is good, and the overall quality of the alloys in the types in this disclosure is good. Consequently, it can be seen that the high-temperature mechanical properties of the materials in this disclosure are obviously better than those of Alloy No. 8 and Alloy No. 9, and the quality stability of the alloys in the types in this disclosure is better than that of Alloy No. 9. It can be seen from Table 6 that the tensile elongations at 1000°C of the alloys in this disclosure are 40%-50%, which indicates that, when the aluminum contents are high, the hardness of the alloys in this disclosure is still good. In conclusion, the heat-resistant oxidation-resistant alloy described herein has advantages such as a higher service temperature, more excellent high-temperature oxidation resistance, a more compact oxidation film formed, a larger aluminum oxide film area, and better high-temperature mechanical properties. This heat-resistant oxidation-resistant alloy can serve stably below 1200°C for a long period, can form an aluminum oxide film of over 90% in oxidizing atmospheres at 1000-1200°C, belongs to the level of complete oxidation resistance below 1200°C according to HB5258-2000, and is superior to conventional high-temperature weldable materials. The alloy of the present disclosure has excellent exhaustive properties, and apart from being able to be used to melt ethylene cracking furnace tubes, it can also be used to melt other castings that are required to serve at high temperatures, especially castings that are required to serve in severe high-temperature environments of 1100-1200°C and high oxidizability. The foregoing are merely preferred particular modalities of the present disclosure, and the scope of protection of the present disclosure is not limited to them. All variations or substitutions that a person skilled in the art may provide within the technical scope disclosed by this disclosure shall fall within the scope of protection of this disclosure.

Claims

NOVELTY OF THE INVENTION CLAIMS 1.- A heat-resistant, oxidation-resistant alloy, by mass percentage, the heat-resistant, oxidation-resistant alloy is characterized in that it comprises: 2.5%-6% of Al, 24%-30% of Cr, 0.3%-0.55% of C, 30%-50% of Ni, 2%-8% of W, 0.01%-0.2% of Ti, 0.01%-0.2% of Zr, 0.01%-0.4% of Hf, 0.01%-0.2% of Y, and 0.01%-0.2% of V; wherein merely one of Ti and V is comprised. 2 - The heat-resistant, oxidation-resistant alloy according to claim 1, further characterized in that the alloy comprises: N<0.05%, O<0.003%, S<0.003%, and Si<0.5%, the balance being Fe and unavoidable impurities. 3 - The heat-resistant, oxidation-resistant alloy according to claim 1, further characterized in that the alloy comprises: 3.3%-5.5% Al, and 34%-46% Ni.

4. The heat-resistant, oxidation-resistant alloy according to claim 1, further characterized in that the alloy comprises: 3%-6% of W. 5 - The heat-resistant, oxidation-resistant alloy according to claim 1, further characterized in that the alloy comprises: 0.01%-0.06% of Y. 6 - The heat-resistant, oxidation-resistant alloy according to claim 1, further characterized in that in an oxidizing atmosphere of 1000-1200°C, not less than 90% of an area of ​​an oxidation film that forms on a surface of the alloy is an Al2O3 film. 7 - A method for preparing a heat-resistant, oxidation-resistant alloy, wherein the method is for preparing the alloy according to any one of claims 1 to 6, and characterized in that it comprises the following steps: Step 1: melting carbon and inactive elements to obtain molten steel after being completely melted; Step 2: heating the molten steel and refining it; Step 3: adding a mixed rare earth; Step 4: adding molten slag; and Step 5: introducing an inert gas into a melting channel, placing active elements such as aluminum, hafnium, titanium, zirconium, and yttrium into the melting channel, heating, pouring the molten steel into the melting channel, and introducing the molten steel into a melting trough. 8 - The method for preparing a heat-resistant, oxidation-resistant alloy according to claim 7, further characterized in that the amount of addition of the mixed rare earth is 0.05%-0.25% of the mass of the molten steel. 9 - The method for preparing a heat-resistant, oxidation-resistant alloy according to claim 7, further characterized in that the slag comprises CaO. 10 - The method for preparing a heat-resistant, oxidation-resistant alloy according to claim 7, further characterized in that the method further comprises casting after Step 5, and the speed from steel threading to completion of casting is 60-100 kg / minute.