Low-nickel heat-resistant steel as well as preparation method and application thereof

Abstract

The invention provides low-nickel heat-resistant steel and a preparation method and application thereof, and belongs to the technical field of mechanical casting. The invention provides low-nickel heat-resistant steel, which comprises the following element components in percentage by mass: 0.30 to 0.50 percent of C; si: 1.00 to 2.50%; cr: 21.00% to 23.00%; 1.00% to 5.80% of Ni; mn: 1.00 to 2.90%; nb: less than or equal to 1.80%; cu: less than or equal to 0.25%; 0.50% or less of N; 0.50% or less of Mo; p: less than or equal to 0.04%; less than or equal to 0.03% of S and the balance of Fe. By optimizing the proportion of stable austenite elements, an austenite matrix is realized, and the high-temperature mechanical properties and physical properties of the low-nickel heat-resistant steel are also obviously improved, so that the market competitiveness of the heat-resistant steel is improved.

Description

Technical Field

[0001] This invention relates to the field of mechanical casting technology, and in particular to a low-nickel heat-resistant steel, its preparation method, and its application. Background Technology

[0002] Currently, automotive turbine housings and exhaust pipes typically use chromium-nickel austenitic heat-resistant steel. This is primarily due to the stabilizing effect of nickel on austenite, achieving an austenitic microstructure at room temperature, while chromium provides excellent high-temperature mechanical properties and oxidation resistance. However, the high price of nickel makes the production cost of automotive turbine housings and exhaust pipes relatively high, necessitating the use of other inexpensive raw materials to replace it. Research has revealed that besides nickel, manganese and nitrogen can also stabilize austenite, and their prices are significantly lower than nickel's. Therefore, using inexpensive manganese and nitrogen to promote and stabilize austenite has become a major research direction. However, high levels of manganese and nitrogen in heat-resistant steel can impair microstructure stability and reduce the steel's high-temperature oxidation and carburization resistance. Therefore, their dosage in heat-resistant steel is low, and their substitution effect is extremely limited, resulting in a nickel content in heat-resistant steel still exceeding 6.0% by mass. Therefore, providing a technical solution to reduce the nickel content in heat-resistant steel without negatively impacting its mechanical properties and high-temperature resistance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a low-nickel heat-resistant steel, its preparation method, and its application. The heat-resistant steel provided by this invention has a low nickel content and excellent mechanical properties and high-temperature resistance.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a low-nickel heat-resistant steel, comprising the following elemental components by mass percentage: C: 0.30~0.50%; Si: 1.00~2.50%; Cr: 21.00~23.00%; Ni: 1.00~5.80%; Mn: 1.00~2.90%; Nb: ≤1.80%; Cu: ≤0.25%; N: ≤0.50%; Mo: ≤0.50%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

[0005] Preferably, the low-nickel heat-resistant steel comprises, by mass percentage, the following elemental composition: C: 0.32~0.48%; Si: 1.20~2.20%; Cr: 21.20~22.80%; Ni: 2.00~5.80%; Mn: 1.20~2.80%; Nb: 0.10~1.80%; Cu: 0.01~0.25%; N: 0.01~0.50%; Mo: 0.01~0.50%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

[0006] Preferably, the low-nickel heat-resistant steel comprises, by mass percentage, the following elemental composition: C: 0.35~0.45%; Si: 1.50~2.00%; Cr: 21.50~22.50%; Ni: 3.00~5.80%; Mn: 1.50~2.50%; Nb: 0.20~1.50%; Cu: 0.05~0.20%; N: 0.05~0.40%; Mo: 0.01~0.40%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

[0007] Preferably, the low-nickel heat-resistant steel comprises, by mass percentage, the following elemental composition: C: 0.4~0.45%; Si: 1.50~2.00%; Cr: 22.00~22.50%; Ni: 4.00~5.80%; Mn: 2.00~2.50%; Nb: 0.50~1.00%; Cu: 0.10~0.15%; N: 0.20~0.30%; Mo: 0.20~0.30%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

[0008] The present invention provides a method for preparing the low-nickel heat-resistant steel described in the above technical solution, comprising: mixing and melting alloy raw materials to obtain an alloy melt, and then casting the alloy melt to obtain low-nickel heat-resistant steel.

[0009] Preferably, the alloy raw materials include carbon raisers, nickel plates, micro-carbon ferrochrome alloys, ferroniobium alloys, ferrosilicon alloys, and ferromanganese alloys.

[0010] Preferably, the mixing and melting operation is as follows: the carbon raiser, nickel plate, micro-carbon ferrochrome alloy and ferroniobium alloy are mixed and melted at a temperature of 1430~1480°C to obtain carbon-nickel-chromium-niobium-iron melt; the carbon-nickel-chromium-niobium-iron melt is heated to 1500~1550°C, and then ferrosilicon alloy and ferromanganese alloy are added and mixed evenly to obtain alloy melt.

[0011] Preferably, the method further includes chemical composition analysis of the alloy melt; the chemical composition analysis is performed by heating the alloy melt to 1550°C and then taking a spectrophotometer for chemical composition analysis. When the elemental composition and content in the alloy melt do not meet the target values ​​for the required low-nickel heat-resistant steel, the alloy melt is adjusted, and then chemical composition analysis is performed again until the elemental composition of the alloy melt meets the elemental composition requirements for low-nickel heat-resistant steel.

[0012] Preferably, the temperature of the alloy melt during casting is 1580~1620℃.

[0013] This invention provides the application of the low-nickel heat-resistant steel described in the above technical solution or the low-nickel heat-resistant steel prepared by the preparation method described in the above technical solution in automobile turbine housings or exhaust pipes.

[0014] This invention provides a low-nickel heat-resistant steel, comprising the following elemental components by mass percentage: C: 0.30~0.50%; Si: 1.00~2.50%; Cr: 21.00~23.00%; Ni: 1.00~5.80%; Mn: 1.00~2.90%; Nb: ≤1.80%; Cu: ≤0.25%; N: ≤0.50%; Mo: ≤0.50%; P: ≤0.04%; S: ≤0.03% and the balance Fe. In this invention, silicon has a strong affinity for oxygen, effectively removing dissolved oxygen from the alloy melt, thus preventing porosity in the cast billet and improving the purity of the steel. Simultaneously, silicon selectively oxidizes at high temperatures, and its oxide, SiO2, integrates with and strengthens the surface oxide film, primarily composed of Cr2O3. SiO2 has an extremely low oxygen diffusion coefficient, significantly hindering the diffusion of oxygen and metal ions through the oxide film, making the oxide film denser, more stable, and slower-growing. Furthermore, the silicon-containing oxide film bonds more firmly to the substrate, making it less prone to peeling, thereby improving the high-temperature oxidation resistance of the heat-resistant steel and providing long-lasting protection. In addition, silicon produces a significant solid solution strengthening effect, improving the steel's strength at both room temperature and high temperatures. Nickel significantly lowers the ductile-brittle transition temperature of the steel, maintaining high impact toughness even at low temperatures. The solid solution of nickel reduces the stacking fault energy, promoting cross-slip and dislocation mobility, thus enhancing the plasticity of the heat-resistant steel. The invention enhances the heat-resistant steel's ability to form and resist crack propagation. Simultaneously, during high-temperature oxidation, the stable austenitic matrix formed by nickel better dissolves elements such as chromium, promoting the formation of a denser, more adhesive protective oxide film. This, combined with the solid solution strengthening and precipitation strengthening of carbon, improves the high-temperature resistance of the heat-resistant steel. Manganese preferentially reacts with sulfur to form high-melting-point manganese sulfide (MnS). MnS has a high melting point and typically exists in spherical or dot-like forms, fundamentally eliminating the hot brittleness caused by sulfur. Furthermore, manganese atoms can dissolve in the austenitic matrix, causing lattice distortion and providing a certain solid solution strengthening effect, which helps improve the room-temperature and high-temperature strength of the heat-resistant steel. By optimizing the proportion of stabilizing austenitic elements and the dosage of Ni and Mn, while adjusting the dosage of other elements, this invention significantly improves the high-temperature mechanical and physical properties of low-nickel heat-resistant steel, thereby enhancing its market competitiveness.

[0015] The results of the embodiments show that the low-nickel heat-resistant steel provided by the present invention has a tensile strength >700MPa, a yield strength >410MPa, and an elongation ≥13.0% at room temperature; a tensile strength >310MPa, a yield strength >185MPa, and an elongation ≥13.0% at 800℃; a tensile strength >170MPa, a yield strength >145MPa, and an elongation ≥26.0% at 900℃; and a tensile strength ≥100MPa, a yield strength >90MPa, and an elongation >38.0% at 1000℃, exhibiting excellent high-temperature resistance. Under stress of 60MPa at 900℃, the creep rupture time of the low-nickel heat-resistant steel reaches over 220 hours, demonstrating excellent high-temperature creep rupture performance. After holding at 1050℃ for 100 hours, the oxidation weight gain of the low-nickel heat-resistant steel is <15mg, and the average oxidation rate is ≤0.52g / mm². 2 h has excellent high-temperature oxidation performance. Detailed Implementation

[0016] This invention provides a low-nickel heat-resistant steel, comprising the following elemental components by mass percentage: C: 0.30~0.50%; Si: 1.00~2.50%; Cr: 21.00~23.00%; Ni: 1.00~5.80%; Mn: 1.00~2.90%; Nb: ≤1.80%; Cu: ≤0.25%; N: ≤0.50%; Mo: ≤0.50%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

[0017] The low-nickel heat-resistant steel provided by this invention comprises 0.30~0.50% C by mass percentage. As one embodiment of this invention, the mass percentage of C can be 0.30%, 0.32%, 0.34%, 0.35%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.45%, 0.46%, 0.48%, or 0.50%. In this invention, C acts as a strengthening element, improving the strength and hardness of the steel at high temperatures through solid solution strengthening and precipitation strengthening. Carbon is also an important austenite stabilizing element, helping to maintain a single austenitic structure from room temperature to high temperatures, thus providing excellent ductility, toughness, oxidation resistance, and high-temperature strength. However, excessive carbon content can impair high-temperature oxidation resistance and carburization resistance, promoting microstructure deterioration. Therefore, the mass percentage of C is controlled within the range of 0.30~0.50%.

[0018] The low-nickel heat-resistant steel provided by this invention comprises 1.00~2.50% Si by weight percentage. As one embodiment of this invention, the weight percentage of Si can be 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, or 2.50%. In this invention, silicon has a strong affinity for oxygen, effectively removing dissolved oxygen from the alloy melt, thus preventing porosity in the cast billet and improving the purity of the steel. Simultaneously, silicon selectively oxidizes at high temperatures, and its oxide, SiO2, integrates with and strengthens the surface oxide film, primarily composed of Cr2O3. SiO2 has an extremely low oxygen diffusion coefficient, significantly hindering the diffusion of oxygen and metal ions through the oxide film, making the oxide film denser, more stable, and slower to grow. Furthermore, the silicon-containing oxide film bonds more firmly to the alloy, making it less prone to peeling, thereby improving the high-temperature oxidation resistance of the heat-resistant steel and providing long-lasting protection. In addition, silicon produces a significant solid solution strengthening effect, improving the steel's room temperature and high-temperature strength. Since excessive Si content severely impairs the room temperature and medium temperature toughness, high-temperature creep strength, and endurance strength of the heat-resistant steel, the mass percentage of Si is controlled within the range of 1.00% to 2.50%.

[0019] The low-nickel heat-resistant steel provided by this invention comprises 21.00~23.00% Cr by mass percentage. As one embodiment of this invention, the mass percentage of Cr can be 21.20%, 21.40%, 21.50%, 21.60%, 21.80%, 22.00%, 22.20%, 22.40%, 22.50%, 22.60%, or 22.80%. In this invention, chromium is the most important alloying element in heat-resistant steel. At high temperatures, chromium has a strong affinity for oxygen and selectively oxidizes, forming an extremely thin (micrometer-scale), dense, continuous, and firmly bonded Cr2O3 film on the steel surface. This "passivation film" effectively blocks the inward diffusion of oxygen and the outward diffusion of metal ions, greatly slowing down or even stopping the continuous oxidation process, thereby improving the high-temperature oxidation resistance of heat-resistant steel. It also improves the heat-resistant steel's resistance to high-temperature corrosion (such as carburization, sulfidation, and vanadium corrosion). Chromium is a major carbide-forming element and can form various carbides with carbon, such as M... 23 Carbides such as C6 and M7C3 precipitate during long-term high-temperature service, effectively pinning dislocations and grain boundaries, providing secondary hardening and high-temperature creep strength; chromium atoms are dissolved in the austenitic matrix, providing a certain solid solution strengthening effect and enhancing the mechanical properties of heat-resistant steel.

[0020] The low-nickel heat-resistant steel provided by this invention comprises Ni: 1.00~5.80% by mass percentage. As one embodiment of this invention, the mass percentage of Ni can be 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%, or 5.50%. In this invention, nickel significantly reduces the ductile-brittle transition temperature of steel, maintaining high impact toughness even at low temperatures. Furthermore, the solid solution of nickel reduces the lattice stacking fault energy, promoting cross-slip and dislocation mobility, thereby enhancing the plastic deformation capacity and crack propagation resistance of the heat-resistant steel. Simultaneously, during high-temperature oxidation, the stable austenitic matrix formed by nickel better dissolves elements such as chromium, promoting the formation of a denser, more adhesive protective oxide film (such as Cr2O3), and, combined with solid solution strengthening and precipitation strengthening, improves the high-temperature resistance of the heat-resistant steel. Because excessive Ni content not only promotes sulfide embrittlement and the precipitation of brittle phases, impairing toughness after long-term service, but also significantly increases production costs, the mass percentage of Ni is controlled within the range of 1.00~5.80%.

[0021] The low-nickel heat-resistant steel provided by this invention comprises Mn: 1.00~2.90% by mass percentage. As one embodiment of this invention, the mass percentage of Mn can be 1.20%, 1.40%, 1.50%, 1.60%, 1.80%, 2.00%, 2.20%, 2.40%, 2.50%, 2.60%, or 2.80%. In this invention, manganese preferentially reacts with sulfur to form high-melting-point manganese sulfide (MnS). MnS has a high melting point and usually exists in spherical or dot-like forms, fundamentally eliminating the hot brittleness caused by sulfur. Simultaneously, manganese atoms can dissolve in the austenitic matrix, causing lattice distortion and providing a certain solid solution strengthening effect, which helps improve the room temperature and high temperature strength of the heat-resistant steel. Since excessive Mn content promotes the precipitation of brittle intermetallic compounds, impairs the structural stability and toughness, and reduces the steel's high-temperature oxidation and carburization resistance, the mass percentage of Mn is controlled within the range of 1.00~2.90%.

[0022] The low-nickel heat-resistant steel provided by this invention comprises Nb: ≤1.80% by mass percentage. As one embodiment of this invention, the mass percentage of Nb can be 0.10~1.80%, or 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, or 1.70%. In this invention, niobium precipitates as extremely fine, dispersed MX-type carbonitrides (mainly NbC or Nb-rich Nb(C,N)) during high-temperature service, typically at the nanoscale (<10nm), exhibiting extremely high thermal stability. These nanoparticles can extremely effectively pin dislocations and subgrain boundaries, which are effective barriers to dislocation movement and crack propagation at high temperatures, thereby improving the high-temperature strength and toughness of the heat-resistant steel, as well as its long-term high-temperature creep strength and endurance strength. Because excessive Nb content leads to coarse carbides and reduced toughness, and because Nb is expensive, excessive content will significantly increase the cost of heat-resistant steel. Therefore, the mass percentage of Nb is controlled below 1.80%.

[0023] The low-nickel heat-resistant steel provided by this invention comprises Cu: ≤0.25% by mass percentage. As one embodiment of this invention, the mass percentage of Cu can be 0.01~0.25%, or even 0.05%, 0.10%, 0.15%, 0.20%, or 0.25%. In this invention, supersaturated copper precipitates from the alloy as extremely fine, dispersed ε-copper-rich phases (e-Cu, a type of pure copper or copper-rich particles with a face-centered cubic structure). These nanoscale copper-rich particles maintain a coherent or semi-coherent relationship with the alloy, effectively pinning dislocations and providing a strong precipitation strengthening effect, significantly improving the creep strength and endurance strength of the heat-resistant steel at high temperatures. Because Cu has limited solid solubility in iron, the enriched copper has a low melting point and will penetrate into the austenite grain boundaries in the form of a liquid film, severely weakening the grain boundary bonding force and causing the steel surface to crack during hot working. At the same time, in high-chromium steel, excessive copper content will promote the formation of brittle phases. Therefore, the mass percentage of Cu element is controlled below 0.25%.

[0024] The low-nickel heat-resistant steel provided by this invention comprises N: ≤0.50% by mass percentage. As one embodiment of this invention, the mass percentage of N can be 0.01~0.50%, or 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, or 0.45%. In this invention, nitrogen can closely synergize with strong carbonitride forming elements (Nb, Cr, etc.) to form MX-type carbonitrides. These fine MX particles can extremely effectively pin dislocations and subgrain boundaries, are extremely stable at high temperatures, have extremely strong resistance to coarsening, and can provide long-term high-temperature creep strength and endurance strength. Since excessive N content easily forms harmful nitrides and porosity in the heat-resistant steel, and nitrogen combines with chromium, reducing the "effective chromium content" in the solid solution and negatively impacting high-temperature oxidation resistance, the mass percentage of N is controlled below 0.50%.

[0025] The low-nickel heat-resistant steel provided by this invention comprises Mo: ≤0.50% by mass percentage. As one embodiment of this invention, the mass percentage of Mo can be 0.01~0.50%, or 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, or 0.45%. In this invention, molybdenum can comprehensively improve the high-temperature strength and creep resistance of steel through two core mechanisms: solid solution strengthening and carbide formation. Molybdenum atoms have a large size and can strongly integrate into heat-resistant steel, causing significant lattice distortion, thereby effectively pinning dislocations and improving the alloy's resistance to plastic deformation at high temperatures. Molybdenum is a medium-strength carbide-forming element; in chromium-containing steel, molybdenum first dissolves into Mo. 23 C6-type carbides enhance stability and delay their aggregation and growth at high temperatures. In more complex steels (such as those containing V and Nb), molybdenum participates in the formation of more stable M6C (such as Fe3Mo3C) and MC-type carbides. These fine, dispersed carbides are key to precipitation strengthening, effectively hindering dislocation movement and grain boundary slip, thus improving creep strength and endurance strength. Because Mo is expensive, excessive addition can significantly increase the cost of heat-resistant steel; therefore, the mass percentage of Mo in heat-resistant steel is controlled below 0.50%.

[0026] The low-nickel heat-resistant steel provided by this invention comprises P: ≤0.04% by mass percentage. In this invention, phosphorus has a very low solid solubility in heat-resistant steel and tends to segregate at interfaces such as grain boundaries, thereby affecting the mechanical properties of heat-resistant steel. It is a harmful impurity element. Therefore, the mass percentage content of P in heat-resistant steel is controlled to be below 0.04%.

[0027] The low-nickel heat-resistant steel provided by this invention comprises S: ≤0.03% by mass percentage. In this invention, sulfur forms "sulfide inclusions" in the steel. These inclusions severely impair the toughness, ductility, fatigue resistance, and high-temperature performance of the heat-resistant steel, and are harmful impurity elements. Therefore, the mass percentage content of S in the heat-resistant steel is controlled to be below 0.03%.

[0028] The low-nickel heat-resistant steel provided by this invention comprises the balance Fe by weight percentage. In this invention, iron is the base element of the heat-resistant steel.

[0029] In this invention, the microstructure of the low-nickel heat-resistant steel is preferably austenite with a small amount of carbides.

[0030] In this invention, silicon has a strong affinity for oxygen, effectively removing dissolved oxygen from the alloy melt, thereby preventing porosity in the billet and improving the purity of the steel. Simultaneously, silicon selectively oxidizes at high temperatures, and its oxide, SiO2, integrates with and strengthens the surface oxide film, which is primarily composed of Cr2O3. SiO2 has an extremely low oxygen diffusion coefficient, significantly hindering the diffusion of oxygen and metal ions through the oxide film, making the oxide film denser, more stable, and slower to grow. Furthermore, the silicon-containing oxide film bonds more firmly to the substrate, making it less prone to peeling, thus improving the high-temperature oxidation resistance of the heat-resistant steel and providing long-lasting protection. In addition, silicon produces a significant solid solution strengthening effect, improving both the room-temperature and high-temperature strength of the steel. Nickel significantly lowers the ductile-brittle transition temperature of steel, maintaining high impact toughness even at low temperatures. Furthermore, the solid solution of nickel reduces lattice stacking fault energy, promoting cross-slip and dislocation mobility, thereby enhancing the plastic deformation capacity and crack propagation resistance of heat-resistant steel. Simultaneously, during high-temperature oxidation, the stable austenitic matrix formed by nickel better dissolves elements such as chromium, promoting the formation of a denser, more adhesive protective oxide film. This, combined with solid solution strengthening and precipitation strengthening, improves the high-temperature resistance of heat-resistant steel. Manganese preferentially reacts with sulfur to form high-melting-point manganese sulfide (MnS). MnS has a high melting point and typically exists in spherical or dot-like forms, fundamentally eliminating the hot brittleness caused by sulfur. At the same time, manganese atoms can dissolve in the austenitic matrix, causing lattice distortion and providing a certain solid solution strengthening effect, contributing to improved room-temperature and high-temperature strength of heat-resistant steel.

[0031] This invention achieves an austenitic matrix by optimizing the proportion of stabilizing austenitic elements, and the high-temperature mechanical and physical properties of low-nickel heat-resistant steel are also significantly improved, thereby enhancing the market competitiveness of heat-resistant steel.

[0032] The present invention also provides a method for preparing the low-nickel heat-resistant steel described in the above technical solution, comprising: mixing and melting alloy raw materials to obtain an alloy melt, and then casting the alloy melt to obtain low-nickel heat-resistant steel.

[0033] In this invention, the alloy raw materials preferably include a carbon raiser, nickel plate, low-carbon ferrochrome alloy, ferroniobium alloy, ferrosilicon alloy, and ferromanganese alloy. This invention does not impose any particular limitation on the dosage relationship of the carbon raiser, nickel plate, low-carbon ferrochrome alloy, ferroniobium alloy, ferrosilicon alloy, and ferromanganese alloy. Based on the technical knowledge of those skilled in the art, it is sufficient that the elemental composition of the alloy melt meets the elemental composition requirements of low-nickel heat-resistant steel. As one embodiment of this invention, the carbon raiser can be a material with a fixed carbon content ≥99% and a sulfur content ≤0.05% obtained by graphitizing and calcining petroleum coke at 2800℃; the crystal structure of the carbon element in the carbon raiser can be a hexagonal layered graphite structure.

[0034] In this invention, the mixing and melting are preferably carried out in an induction furnace. This invention does not impose any particular limitation on the specific model or source of the induction furnace; any commercially available induction furnace well-known to those skilled in the art can be used.

[0035] In this invention, the preferred method for the mixing and melting operation is as follows: the carbon raiser, nickel plate, micro-carbon ferrochrome alloy and ferroniobium alloy are mixed and melted at a temperature of 1430~1480°C to obtain carbon-nickel-chromium-niobium-iron melt; the carbon-nickel-chromium-niobium-iron melt is heated to 1500~1550°C, and then ferrosilicon alloy and ferromanganese alloy are added and mixed evenly to obtain alloy melt.

[0036] In this invention, the melting temperature is 1430~1480℃, preferably 1440~1460℃, and more preferably 1450℃. This invention does not have a specific limitation on the melting time; it can be determined based on the technical knowledge of those skilled in the art, as long as it allows all elemental components to completely melt.

[0037] In this invention, the heating temperature is 1500~1550℃, preferably 1510~1540℃, and more preferably 1520~1530℃. This invention, by heating the molten carbon-nickel-chromium-niobium-iron alloy, facilitates the melting of ferrosilicon and ferromanganese alloys.

[0038] The present invention does not have any special limitations on the specific operation of the uniform mixing. Conventional mixing methods can be used to ensure that the components are mixed evenly.

[0039] After obtaining the alloy melt, the present invention preferably further includes chemical composition analysis of the alloy melt; the preferred method of chemical composition analysis is to heat the alloy melt to 1550°C and then take spectrophotometric samples for chemical composition analysis. If the elemental composition and content in the alloy melt do not meet the target values ​​for the desired low-nickel heat-resistant steel, the alloy melt is adjusted, and then chemical composition analysis is performed again until the elemental composition of the alloy melt meets the elemental composition requirements for low-nickel heat-resistant steel. Through the above operations, the present invention can ensure the acquisition of low-nickel heat-resistant steel with the desired composition.

[0040] In this invention, the temperature of the alloy melt during casting is preferably 1580~1620℃, more preferably 1590~1610℃, and even more preferably 1600℃. This invention does not impose any special limitations on the specific casting operation; casting operations well-known to those skilled in the art can be used.

[0041] The preparation method provided by this invention can obtain the required low-nickel heat-resistant steel by mixing and casting the raw materials. The preparation process is simple and easy to operate, which is conducive to large-scale industrial promotion.

[0042] The present invention also provides the application of the low-nickel heat-resistant steel described in the above technical solution or the low-nickel heat-resistant steel prepared by the preparation method described in the above technical solution in automobile turbine housings or exhaust pipes.

[0043] The present invention does not impose any special limitations on the specific operation of the application, and any application method known to those skilled in the art can be used.

[0044] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] Example 1 A low-nickel heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.38%; Si: 1.25%; Cr: 21.50%; Ni: 5.80%; Mn: 2.50%; Nb: 1.20%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the low-nickel heat-resistant steel is as follows: Carbon raiser, nickel plate, micro-carbon ferrochrome alloy, and ferroniobium alloy are mixed in an induction furnace, and then heated to 1450℃ for melting to obtain a carbon-nickel-chromium-niobium-iron molten liquid; the carbon-nickel-chromium-niobium-iron molten liquid is heated to 1520℃, and then ferrosilicon alloy and ferromanganese alloy are added and mixed evenly to obtain an alloy molten liquid; the alloy molten liquid is heated to 1550℃, and a spectrophotometric sample is taken for chemical composition analysis. When the content of a certain element in the alloy molten liquid does not reach the target value of the required low-nickel heat-resistant steel, the corresponding ferroalloy is added for adjustment, and then chemical composition analysis is performed again until the elemental composition of the alloy molten liquid meets the elemental composition requirements of low-nickel heat-resistant steel; finally, the alloy molten liquid is heated to 1600℃ for casting to obtain the low-nickel heat-resistant steel.

[0046] Comparative Example 1 A heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.38%; Si: 1.25%; Cr: 21.50%; Ni: 10.50%; Mn: 0.50%; Nb: 1.20%; Cu: 0.06%; N: 0.15%; Mo: 0.031%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the heat-resistant steel is the same as that in Example 1.

[0047] Comparative Example 2 A heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.38%; Si: 1.25%; Cr: 21.50%; Ni: 7.50%; Mn: 0.50%; Nb: 1.20%; Cu: 0.05%; N: 0.25%; Mo: 0.025%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the heat-resistant steel is the same as that in Example 1.

[0048] Comparative Example 3 A heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.48%; Si: 2.50%; Cr: 21.50%; Ni: 6.50%; Mn: 2.50%; Nb: 1.20%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the heat-resistant steel is the same as that in Example 1.

[0049] Comparative Example 4 A heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.65%; Si: 2.50%; Cr: 21.50%; Ni: 6.50%; Mn: 2.50%; Nb: 1.20%; Cu: 0.04%; N: 0.25%; Mo: 0.022%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the heat-resistant steel is the same as that in Example 1.

[0050] The mechanical properties of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4 were tested at different temperatures, and the results are shown in Tables 1 and 2: Table 1. Mechanical properties of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4 at room temperature and 800°C.

[0051] In Table 1, "-" indicates that the mechanical properties were not tested at 800℃ due to poor creep performance.

[0052] Table 2 shows the mechanical properties of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4 at 900°C, 950°C, and 1000°C.

[0053] As can be seen from Tables 1 and 2, the low-nickel heat-resistant steel provided in Example 1 of the present invention has a tensile strength of 106.4 MPa and a yield strength of 96.6 MPa at a temperature of 1000℃, which is higher than that of Comparative Examples 1 to 4, and has excellent mechanical properties.

[0054] The high-temperature creep rupture properties of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4 were tested, and the results are shown in Table 3: Table 3. High-temperature creep resistance of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4.

[0055] As shown in Table 3, the low-nickel heat-resistant steel provided in Example 1 can achieve a creep rupture time of 246 h under stress of 900 °C and 60 MPa, while Comparative Example 1 is only 203 h, Comparative Example 2 is only 94 h, Comparative Example 3 is only 138 h, and Comparative Example 4 is only 178 h. The low-nickel heat-resistant steel provided in Example 1 of this invention significantly improves the ductility of the material by increasing the Mn content and decreasing the Ni content. The creep elongation rate increases from 7.0% to 17.5%, and the creep reduction of area increases from 11.0% to 31.0%. Therefore, its creep rupture time is significantly improved, indicating that this invention improves the high-temperature creep rupture performance of heat-resistant steel by optimizing the chemical composition of the heat-resistant steel.

[0056] The high-temperature oxidation properties of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1 to 4 were tested according to the test method for determining the oxidation resistance of steel and high-temperature alloys in HB 5258-2000. The results are shown in Table 4. Table 4 shows the oxidation weight gain of the low-nickel heat-resistant steel provided in Example 1 and the heat-resistant steels provided in Comparative Examples 1-4.

[0057] As shown in Table 4, the low-nickel heat-resistant steel provided in Example 1, after being kept at 1050℃ for 100 hours, showed an oxidation weight gain of only 12.56 mg, while the oxidation weight gain of Comparative Example 1 was 18.92 mg and that of Comparative Example 4 was 17.01 mg. It can be seen that the high-temperature oxidation performance of the low-nickel heat-resistant steel provided by the present invention has been significantly improved. This is because the low-nickel heat-resistant steel provided in Example 1 of the present invention has a high nitrogen content and a low carbon content, which helps to form a protective multilayer oxide film structure, enhances the adhesion between the oxide film and the substrate, prevents oxide scale peeling, effectively blocks the inward diffusion of oxygen atoms and the outward diffusion of metal ions, thereby slowing down the oxidation reaction rate.

[0058] Example 2 A low-nickel heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.38%; Si: 1.23%; Cr: 21.30%; Ni: 5.70%; Mn: 2.42%; Nb: 1.19%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the low-nickel heat-resistant steel is the same as that in Example 1.

[0059] Example 3 A low-nickel heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.32%; Si: 1.50%; Cr: 22.40%; Ni: 5.65%; Mn: 1.25%; Nb: 1.21%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the low-nickel heat-resistant steel is the same as that in Example 1.

[0060] Example 4 A low-nickel heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.45%; Si: 2.00%; Cr: 22.80%; Ni: 5.74%; Mn: 2.05%; Nb: 0.90%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the low-nickel heat-resistant steel is the same as that in Example 1.

[0061] Example 5 A low-nickel heat-resistant steel, by mass percentage, is composed of the following elemental components: C: 0.42%; Si: 2.35%; Cr: 21.05%; Ni: 5.55%; Mn: 2.75%; Nb: 1.00%; Cu: 0.04%; N: 0.25%; Mo: 0.023%; P: ≤0.04%; S: ≤0.03% and the balance Fe; The preparation method of the low-nickel heat-resistant steel is the same as that in Example 1.

[0062] The mechanical properties of the low-nickel heat-resistant steels provided in Examples 2-5 were tested at different temperatures, and the results are shown in Tables 5 and 6. Table 5 shows the mechanical properties of the low-nickel heat-resistant steels provided in Examples 2-5 at room temperature and 800°C.

[0063] Table 6 shows the mechanical properties of the low-nickel heat-resistant steels provided in Examples 2-5 at 900°C and 1000°C.

[0064] As can be seen from Tables 5 and 6, the low-nickel heat-resistant steel provided by this invention has a tensile strength > 700 MPa, a yield strength > 410 MPa, and an elongation ≥ 13.0% at room temperature; a tensile strength > 310 MPa, a yield strength > 185 MPa, and an elongation ≥ 13.0% at 800℃; a tensile strength > 170 MPa, a yield strength > 145 MPa, and an elongation ≥ 26.0% at 900℃; and a tensile strength ≥ 100 MPa, a yield strength > 90 MPa, and an elongation > 38.0% at 1000℃, exhibiting excellent high-temperature resistance.

[0065] The high-temperature creep rupture properties of the low-nickel heat-resistant steels provided in Examples 2-5 were tested, and the results are shown in Table 7. Table 7 High-temperature creep resistance of the low-nickel heat-resistant steels provided in Examples 2-5

[0066] As can be seen from Table 7, the low-nickel heat-resistant steel provided by the present invention has a creep rupture time of more than 220 hours under stress of 900℃ and 60MPa, and has excellent high-temperature creep rupture performance.

[0067] The high-temperature oxidation properties of the low-nickel heat-resistant steels provided in Examples 2-5 were tested, and the results are shown in Table 8. Table 8. High-temperature oxidation properties of the low-nickel heat-resistant steels provided in Examples 2-5

[0068] As shown in Table 8, the low-nickel heat-resistant steel provided by this invention, after being held at 1050℃ for 100 hours, exhibits an oxidation weight gain of <15mg and an average oxidation rate of ≤0.52g / mm. 2 h has excellent high-temperature oxidation performance.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-nickel heat-resistant steel, comprising, by mass percentage, the following elemental composition: C: 0.30~0.50%; Si: 1.00~2.50%; Cr: 21.00~23.00%; Ni: 1.00~5.80%; Mn: 1.00~2.90%; Nb: ≤1.80%; Cu: ≤0.25%; N: ≤0.50%; Mo: ≤0.50%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

2. The low-nickel heat-resistant steel according to claim 1, characterized in that, By mass percentage, it includes the following elemental components: C: 0.32~0.48%; Si: 1.20~2.20%; Cr: 21.20~22.80%; Ni: 2.00~5.80%; Mn: 1.20~2.80%; Nb: 0.10~1.80%; Cu: 0.01~0.25%; N: 0.01~0.50%; Mo: 0.01~0.50%; P：≤0.04%； S: ≤0.03% and the balance Fe.

3. The low-nickel heat-resistant steel according to claim 1, characterized in that, By mass percentage, it includes the following elemental components: C: 0.35~0.45%; Si: 1.50~2.00%; Cr: 21.50~22.50%; Ni: 3.00~5.80%; Mn: 1.50~2.50%; Nb: 0.20~1.50%; Cu: 0.05~0.20%; N：0.05~0.40%； Mo: 0.01~0.40%; P：≤0.04%； S: ≤0.03% and the balance Fe.

4. The low-nickel heat-resistant steel according to claim 1, characterized in that, By mass percentage, it includes the following elemental components: C: 0.4~0.45%; Si: 1.50~2.00%; Cr: 22.00~22.50%; Ni: 4.00~5.80%; Mn: 2.00~2.50%; Nb: 0.50~1.00%; Cu: 0.10~0.15%; N：0.20~0.30%； Mo: 0.20~0.30%; P: ≤0.04%; S: ≤0.03% and the balance Fe.

5. A method for preparing the low-nickel heat-resistant steel according to any one of claims 1 to 4, comprising: The alloy raw materials are mixed and melted to obtain an alloy melt, which is then cast to obtain low-nickel heat-resistant steel.

6. The preparation method according to claim 5, characterized in that, The alloy raw materials include carbon raisers, nickel plates, micro-carbon ferrochrome alloys, ferroniobium alloys, ferrosilicon alloys, and ferromanganese alloys.

7. The preparation method according to claim 5, characterized in that, The mixing and melting operation is as follows: the carbon raiser, nickel plate, micro-carbon ferrochrome alloy and ferroniobium alloy are mixed and melted at a temperature of 1430~1480℃ to obtain carbon-nickel-chromium-niobium-iron melt; the carbon-nickel-chromium-niobium-iron melt is heated to 1500~1550℃, and then ferrosilicon alloy and ferromanganese alloy are added and mixed evenly to obtain alloy melt.

8. The preparation method according to claim 5, characterized in that, It also includes chemical composition analysis of the alloy melt; the method of chemical composition analysis is to heat the alloy melt to 1550°C and then take a spectrophotometer for chemical composition analysis. When the elemental composition and content in the alloy melt do not meet the target values ​​of the required low-nickel heat-resistant steel, the alloy melt is adjusted and then chemical composition analysis is performed again until the elemental composition of the alloy melt meets the elemental composition requirements of low-nickel heat-resistant steel.

9. The preparation method according to claim 5, characterized in that, The temperature of the alloy melt during casting is 1580~1620℃.

10. The application of the low-nickel heat-resistant steel according to any one of claims 1 to 4 or the low-nickel heat-resistant steel prepared by the preparation method according to any one of claims 5 to 9 in automobile turbine housings or exhaust pipes.

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