A multi-type precipitate synergistically strengthened heat-resistant alloy and a preparation method thereof

Abstract

The application discloses a multi-type precipitated phase synergistically reinforced heat-resistant alloy and a preparation method thereof, and belongs to the technical field of heat-resistant alloys. The alloy has the following chemical components in percentage by mass: C 0.01-0.04%, Si 0.1-0.4%, Mn 0.2-0.6%, Mo 0.8-1.6%, Cr 12-17%, Ni 28-33%, Ti 1.5-2.5%, Al 0.5-2.0%, Nb 0.2-0.8%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe. The heat-resistant alloy has the advantages that synergistic reinforcement is realized through more than 30% of multi-type nano-strengthening phases (γ' phase, (Ti, Nb)C and Fe2Ti type Laves phase) in volume fraction; the prepared heat-resistant alloy has a high-temperature tensile strength of no less than 486 Mpa, meets the use requirements of heat-resistant alloy materials such as automobile engine exhaust valves and fasteners, and is also applicable to the manufacture of load-bearing components of aero-engines and heat-resistant components of gas turbines.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat-resistant alloys, and relates to a multi-type precipitated phase synergistically strengthened heat-resistant alloy and a preparation method thereof, which is suitable for use of automobile engine exhaust valves. BACKGROUND

[0002] The automobile industry is one of the most important pillar industries in China, and the total production and sales of automobiles has ranked first in the world for 14 consecutive years. Fuel vehicles are still the mainstream of China's automobile market, and their sales and proportion are still much higher than those of pure electric vehicles. Automobile carbon emissions account for about 7.5% of total social carbon emissions. The large number of fuel vehicles, the combustion of fossil fuels in the use stage, and the low combustion efficiency are the main factors causing high carbon emissions of automobiles. In recent years, with the continuous improvement of energy saving and emission reduction requirements, higher requirements are put forward for the combustion efficiency of automobile engines. Valve steel is a key material for automobile engines. The annual production of valves in China has exceeded 500 million (equivalent to about 48,000 tons of raw materials). Automobile engine exhaust valves are subjected to high temperature and high pressure because they discharge high-temperature corrosive exhaust gas. The material of the exhaust valve is required to have excellent high-temperature strength, toughness, hardness, wear resistance, oxidation resistance and corrosion resistance at the working temperature, as well as microstructure stability and dimensional stability under the cold and hot alternating working conditions of the engine. At the same time, the valve material should have good cold and hot working and welding properties during processing.

[0003] At present, widely used valve alloy grades include high alloy steel 21-4N and 21-4NWNb, nickel-based high-temperature alloy GH4751 and Nimonic 80A, and the working temperature is 680-820℃. However, the above valve alloy materials are difficult to achieve a good match between high service temperature and high high-temperature strength, and do not have the advantage of low cost. With the wide application of technologies such as direct injection and turbocharging of automobile internal combustion engines to improve combustion efficiency, the exhaust valve material is required to have higher high-temperature corrosion resistance, oxidation resistance and high-temperature strength. The current automobile exhaust valve steel materials 21-4N and 21-4NWNb cannot meet the temperature requirement of 700℃ and above in the engine combustion chamber. The use of nickel-based valve alloy is also very high in cost. China's high-performance valve alloy for automobile internal combustion engines serving at 680-760℃ is entirely dependent on imports.

[0004] Therefore, it is urgent to develop a new type of valve alloy material that takes into account high performance and low cost. This has important strategic significance for solving the problem of material dependence on imports, and also provides protection for meeting the demand for future higher emission standard valve alloys. SUMMARY

[0005] To solve the above problems, the technical scheme of the present application provides a multi-type precipitated phase synergistically strengthened heat-resistant alloy and a preparation method thereof. The high-strength heat-resistant alloy is obtained by optimizing the alloy composition and formulating a reasonable production process. After electroslag remelting, homogenization treatment, forging, high-temperature solid solution and aging heat treatment, the prepared heat-resistant alloy has a grain size of 5-7 levels, and fine and dispersed multi-type strengthening phases (γ' phase, (Ti, Nb)C and Fe2Ti type Laves phase) are precipitated. The γ' phase strengthening phase is spherical in shape and has a volume fraction of 25%-35%, the small blocky (Ti, Nb)C has a volume fraction of 5%-8%, and the Fe2Ti type Laves phase is discontinuously distributed along the grain boundaries and has a volume fraction of 2%-5%.

[0006] According to a first aspect of the technical scheme of the present application, a preparation method of a multi-type precipitated phase synergistically strengthened heat-resistant alloy is provided, which comprises the following steps:

[0007] (1) Smelting: vacuum induction furnace smelting → casting electrode rod → inert gas atmosphere protection electroslag remelting, or adopting electroarc furnace + LF + VD + electroslag remelting method to smelt, producing electroslag ingot, and then electroslag ingot hot sending annealing;

[0008] (2) Homogenization treatment: the homogenization treatment adopts two-stage heat preservation process, the first stage homogenization treatment temperature is 900-1050℃, the heat preservation time is 2-10h, so that the γ-γ' eutectic phase and Laves phase are fully dissolved; the second stage homogenization treatment temperature is 1100-1150℃, the heat preservation time is 2-16h, so that (Ti, Nb)C is fully dissolved, and Ti and Nb elements are uniformly diffused to eliminate element segregation; after the homogenization treatment is completed, the furnace is cooled to 1030℃ first, and then the furnace is discharged for air cooling;

[0009] (3) Forging: the electroslag ingot is kept at 1150-1180℃, and then forged; the open forging temperature is 1150-1180℃, the final forging temperature is not lower than 950℃, and the forging ratio is 3-4;

[0010] (4) Solid solution and aging: the forged alloy blank is subjected to high-temperature solid solution treatment + aging treatment, the high-temperature solid solution temperature is 950-1100℃, and the heat preservation time is 0.5-6h; the aging treatment temperature is 580-780℃, and the heat preservation time is 4-32h.

[0011] Further, the electroslag remelting smelting is carried out in an argon protection atmosphere. In order to prevent Ti burning loss in the electroslag process and at the same time ensure good surface quality of the electroslag ingot, a special slag system is adopted, and the slag system composition is as follows in terms of mass percentage: CaF2: 50-55%, CaO: 15-25%, Al2O3: 15-25%, MgO: 1-4%, TiO2: 2-5%, FeO≤0.5%, SiO2≤0.8%.

[0012] Further, for 50-200kg ingot type: the voltage is 25-30V and the current is 1500-3000A during the remelting stabilization; for 200-500kg ingot type: the voltage is 30-35V and the current is 3000-4000A during the remelting stabilization; for 500kg-1t ingot type: the voltage is 35-40V and the current is 4000-5000A during the remelting stabilization.

[0013] Further, after the electroslag remelting is finished, the electroslag ingot is demolded, the electroslag ingot is covered with a stainless steel heat preservation cover for slow cooling, and the cooling time is greater than 5h, so that the surface cracking of the electroslag ingot is effectively prevented.

[0014] Further, after the aging heat treatment, the alloy has the following microstructure characteristics: the grain size is 5-7, the spherical γ' phase (the size is not greater than 100nm, and the volume fraction is 25%-35%) is precipitated in the grain, the small blocky (Ti, Nb) C (the size is not greater than 200nm, and the volume fraction is 5%-8%) and the spherical or small blocky Fe2Ti type Laves phase (the size is not greater than 200nm, the volume fraction is 2%-5%, and the Laves phase is composed of Fe, Ti, Nb, Ni, Si and Mo elements) are precipitated at the grain boundary; the nanoscale γ' phase strengthening phase in the grain interacts with the dislocation, and the above mechanisms all work, and no matter which mechanism works, the quantity of the γ' phase strengthening phase is a fundamental influencing factor; the nanoscale (Ti, Nb) C and Fe2Ti type Laves phase precipitated at the grain boundary hinders the dislocation movement, inhibits the grain boundary migration and grain growth, and can improve the strength and toughness of the region near the grain boundary. Meanwhile, the existence of the nanoscale (Ti, Nb) C and Fe2Ti type Laves phase refines the alloy grain, and has the effect of fine-grain strengthening. The fine and dispersed nanoscale γ' phase, (Ti, Nb) C and Fe2Ti type Laves phase are precipitated after the aging treatment, and the multiple types of precipitated phases realize the synergistic strengthening.

[0015] Further, after the aging heat treatment, the alloy has the following mechanical properties: the high-temperature mechanical properties at 760℃ are as follows: the yield strength R p0.2 ≥432Mpa; the tensile strength R m ≥486Mpa.

[0016] According to the second aspect of the technical scheme of the present application, a multiple-type precipitated phase synergistically strengthened heat-resistant alloy is provided, and the multiple-type precipitated phase synergistically strengthened heat-resistant alloy is prepared by the preparation method according to any one of the above aspects,

[0017] The chemical composition of the multi-type precipitate phase synergistically reinforced heat-resistant alloy includes, in terms of mass percentage: C 0.01-0.04%, Si 0.1-0.4%, Mn 0.2-0.6%, Mo 0.8-1.6%, Cr 12-17%, Ni 28-33%, Ti 1.5-2.5%, Al 0.5-2.0%, Nb 0.2-0.8%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe.

[0018] Further, the chemical composition of the multi-type precipitate phase synergistically reinforced heat-resistant alloy includes, in terms of mass percentage: C 0.02%, Si 0.2%, Mn 0.4%, Mo 1.2%, Cr 15%, Ni 30%, Ti 1.9%, Al 0.6%, Nb 0.5%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe.

[0019] Further, the chemical composition of the multi-type precipitate phase synergistically reinforced heat-resistant alloy includes, in terms of mass percentage: C 0.02%, Si 0.2%, Mn 0.4%, Mo 1.2%, Cr 15%, Ni 30%, Ti 2.0%, Al 1.4%, Nb 0.5%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe.

[0020] Further, the chemical composition of the multi-type precipitate phase synergistically reinforced heat-resistant alloy includes, in terms of mass percentage: C 0.02%, Si 0.2%, Mn 0.4%, Mo 1.2%, Cr 15%, Ni 30%, Ti 2.4%, Al 0.6%, Nb 0.5%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe.

[0021] The beneficial effects of the present application are as follows:

[0022] (1) A casting ingot homogenization kinetics model is established to guide the development of high-temperature homogenization process. Before homogenization treatment, the ingot structure is distributed with brittle γ-γ' eutectic phase, brittle Laves phase and large size (Ti, Nb) C.

[0023] The brittle γ-γ' eutectic phase and Laves phase are fully dissolved, and (Ti, Nb) C is fully dissolved through two-stage homogenization treatment of the electroslag ingot, effectively avoiding the occurrence of void defects in the alloy, and controlling the grain size from excessively growing. After two-stage homogenization treatment, the residual segregation coefficient δ of Ti and Nb elements is <0.2, and the Ti and Nb elements are fully diffused and uniform, improving the hot working plasticity of the alloy. The residual segregation coefficient of the elements is calculated according to the following formula:

[0024]

[0025] wherein and are the minimum and maximum concentration of the element in the ingot, and are the minimum and maximum concentration of the element in the ingot after high temperature diffusion annealing.

[0026] (2) Controlling the sum of Ti+Al+Nb content and the ratio of Ti / Al to control the volume fraction, size, antiphase boundary energy and misfit with the matrix of the γ' phase. The sum of Ti+Al+Nb content is 3%~5%

[0027] Guarantee the volume fraction of γ' phase is 25%~35%, add 0.5% of Nb element to enhance γ' phase

[0028] Thermal stability of Ni3(Ti,Al,Nb). Add 1.2% of Mo to slow down the diffusion speed of Ti and Al elements, control the ratio of Ti / Al to avoid the formation of harmful phase η phase after long time aging. Intra-grain nanoscale γ' phase strengthening phase strengthens through coherent strain strengthening, bypass mechanism strengthening, dislocation cutting mechanism strengthening and dislocation climbing mechanism strengthening, nanoscale (Ti,Nb)C and Fe2Ti type Laves phase precipitated at grain boundary improve the strength and toughness of the region near the grain boundary, realizing the synergistic strengthening effect of multiple types of precipitated phases.

[0029] (3) Strictly control the content of C, Ti, Nb, Mo, Si, avoid the continuous precipitation of (Ti,Nb)C and Fe2Ti type Laves phase at the grain boundary, so as to ensure the strength and toughness of the grain boundary. The (Ti,Nb)C and Fe2Ti type Laves phase in the alloy of the present application is discontinuously distributed along the grain boundary, the volume fraction of (Ti,Nb)C is 5%~8%, and the volume fraction of Fe2Ti type Laves phase is 2%~5%. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to the structures shown in the drawings without creative labor for those skilled in the art.

[0031] Figure 1 The preparation method flow chart of the multi-type precipitated phase synergistic strengthening heat-resistant alloy according to the technical solutions of the present application;

[0032] Figure 2 The equilibrium phase precipitation result in the heat-resistant alloy of the present application;

[0033] Figure 3 The nanoscale multi-type precipitates (γ' phase, (Ti, Nb)C and Fe2Ti type Laves phase) and matrix structure of the heat-resistant alloy of the present application after solution treatment and aging at 770℃ for 4 hours;

[0034] Figure 4 The nanoscale multi-type precipitates (γ' phase, (Ti, Nb)C and Fe2Ti type Laves phase) and matrix structure of the heat-resistant alloy of the present application after solution treatment and aging at 710℃ for 28 hours;

[0035] Figure 5 The nanoscale multi-type precipitates (γ' phase, (Ti, Nb)C and Fe2Ti type Laves phase) and matrix structure of the heat-resistant alloy of the present application after solution treatment and aging at 740℃ for 4 hours. DETAILED DESCRIPTION

[0036] The embodiments of the present application will be described below in detail with the embodiments of the present application, so that the advantages and features of the present application can be better understood by those skilled in the art. Obviously, the following described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0037] The application discloses a multi-type precipitated phase synergistically reinforced heat-resistant alloy and a preparation method thereof, and belongs to the technical field of heat-resistant alloys. The alloy has the following chemical components in percentage by mass: C 0.01-0.04%, Si 0.1-0.4%, Mn 0.2-0.6%, Mo 0.8-1.6%, Cr 12-17%, Ni 28-33%, Ti 1.5-2.5%, Al 0.5-2.0%, Nb 0.2-0.8%, N <0.004%, P <0.005%, S <0.004%, and the balance of Fe. The alloy is smelted by a vacuum induction smelting and atmosphere protection electroslag remelting duplex process, the electroslag ingot is subjected to two-stage homogenization treatment at 900-1150 DEG C, and after the homogenization treatment, the electroslag ingot is furnace-cooled to 1030 DEG C and then taken out and air-cooled. The electroslag ingot after the homogenization treatment is kept at 1150-1180 DEG C, and then subjected to forging; the open forging temperature is 1150-1180 DEG C, the final forging temperature is not lower than 950 DEG C, and the forging ratio is 3-4; the forged blank is subjected to solid solution treatment at 950-1100 DEG C for 0.5-6 hours; and the blank is subjected to aging treatment at 580-780 DEG C for 4-32 hours. Thus, synergistic reinforcement is realized by more than 30% of multi-type nano-strengthening phases (gamma prime phase, (Ti, Nb)C and Fe2Ti type Laves phase); the prepared heat-resistant alloy has a high-temperature tensile strength of not lower than 486 MPa, meets the use requirements of heat-resistant alloy materials such as automobile engine exhaust valves and fasteners, and is also applicable to the manufacture of load-bearing parts of aero-engine and heat-resistant parts of a gas turbine.

[0038] Specifically, the technical scheme of the application first provides a preparation method of a multi-type precipitated phase synergistically reinforced heat-resistant alloy, as shown in the formula: Figure 1 The method comprises the following steps:

[0039] (S101) smelting process: the vacuum induction smelting and atmosphere protection electroslag remelting duplex process is adopted for smelting; the electroslag remelting smelting is carried out in an argon protection atmosphere, and the remelting process is ensured to be carried out under the condition that the electrode melting rate is low, so as to ensure the cleanliness and homogeneity of the heat-resistant alloy ingot and improve the mechanical properties of the alloy.

[0040] (S102) homogenization treatment: element segregation inevitably exists in the electroslag ingot, brittle gamma-gamma prime eutectic phase, brittle Laves phase and large-size (Ti, Nb)C are precipitated. The existence of these low-melting-point brittle phases and large-size (Ti, Nb)C will reduce the hot working plasticity of the alloy, leading to forging cracking. Therefore, the electroslag ingot must be subjected to homogenization treatment before forging, so as to dissolve the large-size eutectic phase and eliminate element segregation.

[0041] Therefore, based on thermodynamic equilibrium calculation, Figure 2) and combining with production practice, the two-stage homogenization process is determined. The first stage homogenization treatment temperature is 900-1050℃, the holding time is 2-10h, so that the γ-γ' eutectic phase and Laves phase are fully dissolved; the second stage homogenization treatment temperature is 1100-1150℃, the holding time is 2-16h, so that (Ti, Nb) C is fully dissolved, and Ti and Nb elements are uniformly diffused, and element segregation is eliminated. After high-temperature diffusion annealing, first furnace cooling to 1030℃, then furnace cooling to 1030℃, and then air cooling.

[0042] Here, it should be noted that if a one-stage homogenization process is used, the temperature is higher than the initial melting temperature of the Laves phase and (Ti, Nb) C, and the precipitated phase will melt, and the internal cavity defects of the alloy will be produced.

[0043] (S103) forging: the electroslag ingot is heated at 1150-1180℃, and then forged. The open forging temperature is 1150-1180℃, the final forging temperature is not lower than 950℃, and the forging ratio is 3-4.

[0044] (S104) solid solution and aging: the solid solution treatment is mainly used for controlling the dissolution of precipitated phase, the uniformity of structure and the grain size, and the aging treatment is mainly used for controlling the quantity, size and distribution of strengthening phases γ', (Ti, Nb) C and Laves phase. The high-temperature solid solution temperature is 950-1100℃, and the holding time is 0.5-6 hours; the aging treatment temperature is 580-780℃, and the holding time is 4-32 hours.

[0045] The technical scheme of the present application further provides a multi-type precipitated phase synergistically reinforced heat-resistant alloy, characterized in that the chemical composition of the heat-resistant alloy contains, in terms of mass percentage: C 0.01-0.04%, Si 0.1-0.4%, Mn 0.2-0.6%, Mo 0.8-1.6%, Cr 12-17%, Ni 28-33%, Ti 1.5-2.5%, Al 0.5-2.0%, Nb 0.2-0.8%, N<0.004%, P<0.005%, S<0.004%, and the balance is Fe.

[0046] Among them, the optimized and controlled Al+Ti mass percentage is: 2.5%≤Al+Ti≤3.4%, and at the same time, the Ti / Al ratio is 1.4≤Ti / Al≤4.

[0047] Here, the preferred alloy composition Al content is controlled at 0.5% to 1.4%, and the Ti content is controlled at 1.9% to 2.4%. Increasing the Al content promotes the precipitation of γ' phase, and Al is an important element for improving the oxidation resistance of the alloy. Ti is a strong carbide-forming element. In addition to forming γ' phase, Ti added to the alloy is used to fix carbon, form stable and not easily decomposed carbides, eliminate the depletion of Cr at the grain boundary, thereby eliminating the intergranular corrosion of the alloy. At the same time, the generated nanoscale carbides can play a role in precipitation strengthening. The Ti / Al ratio determines the antiphase boundary energy of the γ' phase, and increasing the Ti / Al ratio of the alloy increases the antiphase boundary energy of the γ' phase. Increasing the Ti content and increasing the Ti / Al ratio increases the lattice constant of the γ' phase, and the mismatch between the γ' phase and the substrate increases. Adding 0.5% Nb enhances the thermal stability of the γ' phase.

[0048] It should be noted that, in addition to the base iron, the specific selection reasons for the above main chemical components are as follows (the alloy components in this specification are in mass percent):

[0049] Carbon (C): C can form and stabilize austenite and form carbides with other elements. If the C content in the alloy is too high, on the one hand, large-size eutectic carbides such as M 23 C6, MC and M6C, etc. will continuously precipitate on the grain boundary, reducing the grain boundary strength and adversely affecting the toughness of the alloy. On the other hand, it will form a network of excess carbides, increase the susceptibility of the weld heat-affected zone to liquation cracking, and reduce the welding performance of the alloy. Controlling the appropriate C content in the alloy, and aging treatment makes the carbides discontinuously precipitate on the grain boundary, which is beneficial to hinder the grain boundary slip and crack propagation, and the alloy endurance life is improved. However, too low C content will reduce the nucleation driving force of the carbide, making it difficult to precipitate, reducing the strength and toughness of the grain boundary. At the same time, too low C content will weaken the solid solution strengthening effect of C element. Therefore, the C content in the present application is strictly controlled at 0.01% to 0.04%.

[0050] Silicon (Si): Adding Si to the heat-resistant alloy is beneficial to improve the strength of the γ matrix, the steam corrosion resistance and the high temperature oxidation resistance. However, too high Si content promotes the precipitation of intermetallic phase σ phase, reduces the grain boundary strength, and is not conducive to the impact toughness and endurance life of the alloy. Considering that the present heat-resistant alloy is used in high-temperature steam corrosion and high-temperature exhaust gas corrosion environments, at least 0.1% Si needs to be added to enhance the corrosion resistance and high-temperature oxidation resistance of the alloy. Therefore, the Si content in the present alloy is strictly controlled at 0.1% to 0.4%.

[0051] • Manganese (Mn): Mn can form and stabilize austenite. The addition of Mn in the alloy can improve the strength, hot working, corrosion resistance and welding performance. But excessive Mn will form MnS with S, which reduces the cleanliness of the alloy. Mn is easy to segregate at the grain boundary, which leads to the weakening of the grain boundary strength and the reduction of the alloy's endurance strength. Considering that forging is an essential step in the production of the alloy, at least 0.2% of Mn needs to be added to enhance the hot working performance of the alloy. Therefore, the content of Mn in the alloy of the present application is strictly controlled in the range of 0.2-0.6%.

[0052] • Chromium (Cr): Cr added to the heat-resistant alloy can have a solid solution strengthening effect. Cr in the matrix causes lattice distortion, producing an elastic stress field and interacting with dislocations, thereby improving the strength of the γ solid solution. Cr forms a dense Cr2O3 type oxide film during the service of the heat-resistant alloy, improving the high-temperature oxidation resistance and hot corrosion resistance. However, too high a Cr content will promote the precipitation of intermetallic phase σ phase, destroy the organizational stability, and damage the mechanical properties of the alloy. At least 12% of Cr needs to be added to the present heat-resistant alloy to form a Cr2O3 type oxide film. In view of the above, the content of Cr in the alloy of the present application is in the range of 12-17%.

[0053] • Nickel (Ni): Ni can stabilize and expand the austenite phase region to obtain single-phase austenite structure. The addition of Ni can improve the composition and performance of the Cr2O3 type oxide film, and the high-temperature oxidation resistance of the alloy is improved. The addition of Ni improves the corrosion resistance and plasticity and toughness of the alloy. However, too high a content of Ni will increase the coarsening rate of NbNi3, reduce the hot strength, and increase the cost of the alloy. Considering that the present heat-resistant alloy is used in high-temperature oxidation environment, at least 28% of Ni needs to be added to meet the performance requirements of the alloy's high-temperature oxidation resistance. Therefore, the content of Ni in the alloy of the present application is in the range of 28-33%.

[0054] • Molybdenum (Mo): Mo in the heat-resistant alloy mainly plays a solid solution strengthening role. Mo can slow down the diffusion rate of Cr, Al and Ti at high temperature, improve the atomic binding force of the γ solid solution, and significantly improve the hot strength of the alloy. The aging of fine Mo-rich intermetallic compounds (Laves phase) can improve the hardness of the alloy. The segregation coefficient of Mo element is less than 1, and it is segregated in the interdendritic region during solidification. Excessive Mo content will cause serious segregation, which will promote the precipitation of large-size M6C type carbides on one hand, and easily generate TCP harmful phases such as μ phase on the other hand. At least 0.8% of Mo needs to be added to the present heat-resistant alloy to slow down the diffusion rate of Al and Ti elements at high temperature and inhibit the coarsening of γ' strengthening phase. Therefore, the content of Mo in the alloy of the present application is strictly controlled in the range of 0.8-1.6%.

[0055] • Titanium (Ti): Ti added in the heat resistant alloy forms about 90% of γ'-Ni3(Ti, Al) and about 10% enters γ solid solution to play a solid solution strengthening role. Under the condition of a certain Al content, increasing Ti content promotes γ' phase precipitation and improves the high temperature strength of the alloy. Ti is also a key element for enhancing the alloy's resistance to hot corrosion and improving the stability of the surface layer structure. However, if the Ti / Al ratio is too high, it increases the tendency of γ' phase to η-Ni3Ti phase. After long-term aging, needle-shaped η phase is formed at the grain boundary, which destroys the structure stability and reduces the impact toughness of the alloy. At least 1.5% of Ti needs to be added to the heat resistant alloy of the present application to form γ' phase, Fe2Ti type Laves phase and (Ti, Nb) C strengthening phase. Therefore, the Ti content in the alloy of the present application is strictly controlled at 1.5-2.5%.

[0056] • Aluminum (Al): Al added in the heat resistant alloy forms about 80% of γ'-Ni3(Ti, Al) and about 20% enters γ solid solution to play a solid solution strengthening role. Increasing Al content promotes γ' phase precipitation, and Al is an important element for improving the oxidation resistance of the alloy and increasing the surface structure stability of the alloy. However, too high Al content may precipitate harmful β-NiAl phase. In order to ensure the high temperature strength of the alloy, at least 0.5% of Al needs to be added to precipitate γ' strengthening phase with a volume fraction of at least 15%. At the same time, 0.5% of Al cooperates with Cr element to further enhance the high temperature oxidation resistance of the alloy. Therefore, the Al content in the alloy of the present application is strictly controlled at 0.5-2.0%.

[0057] • Niobium (Nb): The atomic radius of Nb is larger than that of Mo, and the solid solution strengthening effect is good. Nb can replace Ti and Al in γ' phase, increase the mismatch degree between γ' phase and γ matrix, and improve the strengthening ability of γ' phase. Adding Nb is beneficial to increasing the thermal stability and volume fraction of γ' phase, and Nb and C can form fine and dispersed nanoscale MC carbide to improve the structure stability and creep strength of the alloy. However, too high Nb content will form a large amount of micron-sized eutectic carbide, which is not conducive to the plasticity, toughness, welding performance and corrosion resistance of the alloy. In addition, too high Nb content will reduce the oxidation resistance of the alloy, especially the cyclic oxidation resistance. At least 0.2% of Nb needs to be added to the present application to enhance the thermal stability of γ' phase. At the same time, Nb combines with C element to form fine and dispersed nanoscale carbide to strengthen the grain boundary. Therefore, the Nb content in the alloy of the present application is strictly controlled at 0.2-0.8%.

[0058] In addition, in order to ensure the performance of the alloy, the content of the five harmful elements and other impurity elements should be as low as possible.

[0059] Example 1

[0060] Table 1 shows the alloy composition (weight percentage) of the embodiments; Table 2 shows the slag composition (weight percentage) used in smelting the heat-resistant alloy of the present invention; Table 3 shows the comparison of the high-temperature mechanical properties of each embodiment and comparative example at 760℃.

[0061] According to the composition shown in Table 1 for heat-resistant alloy #1, alloy ingots were smelted using a dual process of vacuum induction melting and atmosphere-protected electroslag remelting. The electroslag ingots underwent a two-stage homogenization treatment: the first stage homogenization temperature was 930℃, and the holding time was 4 hours; the second stage homogenization temperature was 1140℃, and the holding time was 6 hours. The homogenized electroslag ingots were held at 1160℃ and then forged. The initial forging temperature was 1160℃, the final forging temperature was not lower than 950℃, and the forging ratio was 4. The resulting alloy billet was solution treated at 1015℃, held for 1 hour, and then water-cooled to room temperature; subsequently, it was held at an aging temperature of 770℃ for 4-16 hours and then air-cooled to room temperature, thus obtaining a multi-type precipitate-strengthened heat-resistant alloy.

[0062] Table 1

[0063]

[0064] Table 2

[0065]

[0066] like Figure 3 The image shows a scanning electron microscope (SEM) image of the typical microstructure of heat-resistant alloy 1# after aging treatment at 770℃ for 4 hours. The γ' phase has a spherical morphology with a volume fraction of approximately 29%, (Ti,Nb)C has a blocky morphology with a volume fraction of approximately 7%, and the Fe2Ti type Lvaes phase has a blocky morphology with a volume fraction of approximately 3%.

[0067] Example 2

[0068] According to the composition of heat-resistant alloy #2 shown in Table 1, alloy ingots were smelted using a dual process of vacuum induction melting and atmosphere-protected electroslag remelting. The electroslag ingots underwent a two-stage homogenization treatment: the first stage homogenization temperature was 980℃, and the holding time was 8 hours; the second stage homogenization temperature was 1140℃, and the holding time was 12 hours. The homogenized electroslag ingots were held at 1160℃ and then forged. The initial forging temperature was 1160℃, the final forging temperature was not lower than 950℃, and the forging ratio was 4. The resulting alloy billet was solution treated at 1050℃, held for 0.5 hours, and then water-cooled to room temperature; subsequently, it was held at an aging temperature of 710℃ for 4-32 hours and then air-cooled to room temperature, thus obtaining a multi-type precipitate-strengthened heat-resistant alloy.

[0069] like Figure 4The image shows a scanning electron microscope (SEM) image of the typical microstructure of heat-resistant alloy #2 after aging at 710℃ for 28 hours. The γ' phase has a spherical morphology with a volume fraction of approximately 34%, while the (Ti,Nb)C and Fe2Ti type Lvaes phases have a blocky morphology.

[0070] Example 3

[0071] According to the composition of heat-resistant alloy #3 shown in Table 1, alloy ingots were smelted using a dual process of vacuum induction melting and atmosphere-protected electroslag remelting. The electroslag ingots underwent a two-stage homogenization treatment: the first stage homogenization temperature was 900℃, and the holding time was 6 hours; the second stage homogenization temperature was 1140℃, and the holding time was 10 hours. The homogenized electroslag ingots were held at 1160℃ and then forged. The initial forging temperature was 1160℃, the final forging temperature was not lower than 950℃, and the forging ratio was 4. The resulting alloy billet was solution treated at 1015℃, held for 1 hour, and then water-cooled to room temperature; subsequently, it was held at an aging temperature of 740℃ for 4-16 hours and then air-cooled to room temperature, thus obtaining a multi-type precipitate-strengthened heat-resistant alloy.

[0072] like Figure 5 The image shows a scanning electron microscope (SEM) image of the typical microstructure of heat-resistant alloy #3 after aging at 740℃ for 4 hours. The γ' phase has a spherical morphology and a volume fraction of about 30%. The (Ti,Nb)C and Fe2Ti type Laves phases have a blocky morphology.

[0073] The high-temperature tensile properties of the heat-resistant alloys in the comparative examples of this invention after different aging times and their comparisons are shown in Table 3. Table 3 includes the high-temperature tensile property data of alloy A286 and another 15Cr-30Ni-3.3Cu heat-resistant alloy developed by the inventors, which are compared with the alloys of this invention.

[0074] Table 3 Comparison of high-temperature mechanical properties (760℃)

[0075]

[0076] The performance data of the alloys in the comparative examples of this invention are shown in Table 3. By further optimizing the alloy composition and rationally controlling the electroslag smelting, diffusion annealing, hot working, solution treatment, and aging heat treatment processes, this invention enables the alloy to possess excellent high-temperature strength and plasticity. Compared to the A286 alloy and the 15Cr-30Ni-3.3Cu alloy, the high-temperature strength and plasticity of the heat-resistant alloy of this invention are significantly improved, fully meeting the requirements for heat-resistant alloy materials used in automotive engine exhaust valves, fasteners, etc., and can also be used to manufacture load-bearing components for aero-engines and heat-resistant parts for gas turbines, thus broadening its application scope. Furthermore, compared to nickel-based alloys, it has a significant cost advantage.

[0077] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the above-described specific embodiments, and the above-described specific embodiments are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection of the present application.

Claims

1. A method of producing a multi-type precipitate co-strengthened heat resistant alloy, characterized by: The method comprises the following steps: (1) smelting: vacuum induction furnace smelting → casting electrode bar → inert gas atmosphere protection electroslag remelting smelting, or adopting electroslag remelting smelting by adopting an electric arc furnace + LF + VD + electroslag remelting method to produce electroslag ingot, and then hot sending the electroslag ingot for annealing; (2) homogenization treatment: adopting a two-stage homogenization treatment process to treat the electroslag ingot, and first furnace cooling to a certain temperature after the homogenization treatment and then air cooling; (3) forging: first heat preservation and then forging the electroslag ingot treated in the step (2) to produce alloy billets; (4) solid solution and aging: high-temperature solid solution treatment + aging heat treatment are performed on the alloy billets, and thus a multi-type precipitated phase synergistic strengthening heat-resistant alloy is obtained, In the step (4), the high-temperature solid solution temperature is 950-1100 ℃, the holding time is 0.5-6 hours; the aging treatment temperature is 580-780 ℃, and the holding time is 4-32 hours; and after the aging heat treatment, the alloy organization features are as follows: the grain size is 5-7 levels, the intracrystalline precipitation is spherical γ' phase with a size of not greater than 100 nm and a volume fraction of 25%-35%; small blocky (Ti, Nb) C with a size of not greater than 200 nm and a volume fraction of 5%-8%; and spherical or small blocky Fe2Ti type Laves phase with a size of not greater than 200 nm and a volume fraction of 2%-5%. In the multi-type precipitated phase synergistic strengthening heat-resistant alloy, the chemical components include, in terms of mass percentage: C 0.01-0.04%, Si 0.1-0.4%, Mn 0.2-0.6%, Mo 0.8-1.6%, Cr 12-17%, Ni 28-33%, Ti 1.5-2.5%, Al 0.5-2.0%, Nb 0.2-0.8%, N <0.004%, P <0.005%, S <0.004%, and the balance is Fe.

2. The production method according to claim 1, characterized by: In the step (1), the electroslag remelting smelting is performed in an argon protection atmosphere and by using a special slag system, and the slag system composition includes, in terms of mass percentage: CaF2: 50-55%, CaO: 15-25%, Al2O3: 15-25%, MgO: 1-4%, TiO2: 2-5%, FeO≤0.5%, and SiO2≤0.8%.

3. The production method according to claim 2, characterized by: For 50-200 kg ingot type: the stable remelting voltage is 25-30 V, and the current is 1500-3000 A; for 200-500 kg ingot type: the stable remelting voltage is 30-35 V, and the current is 3000-4000 A; and for 500 kg-1 t ingot type: the stable remelting voltage is 35-40 V, and the current is 4000-5000 A.

4. The production method according to claim 2, characterized by: In the step (1), after the electroslag remelting is completed, the electroslag ingot is covered with a stainless steel heat preservation cover for slow cooling, and the cooling time is greater than 5 h, so that the surface cracking of the electroslag ingot is effectively prevented.

5. The method of claim 1, wherein: In the step (2), the two-stage homogenization treatment process specifically comprises: The first-stage homogenization treatment temperature is 900-1050 ℃, and the holding time is 2-10 h; The second-stage homogenization treatment temperature is 1100-1150 ℃, and the holding time is 2-16 h.

6. The method of claim 1, wherein, In the step (3), the forging temperature is 1150-1180 DEG C, the final forging temperature is not lower than 950 DEG C, and the forging ratio is 3-4.

7. The production method according to claim 1, wherein: In the step (4), the mechanical properties of the alloy after the aging heat treatment meet: 760 °C high temperature mechanical properties: yield strength R p0.2 ≥ 432 Mpa; tensile strength R m ≥ 486 Mpa.

8. A multi-type precipitate co-strengthened heat resistant alloy, characterized by: The multi-type precipitate phase synergistically strengthened heat-resistant alloy is prepared by the preparation method according to any one of claims 1-7.

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