WO2023134292A1 - 铸造铁基奥氏体抗蠕变钢及其制备方法、应用 - Google Patents

铸造铁基奥氏体抗蠕变钢及其制备方法、应用 Download PDF

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WO2023134292A1
WO2023134292A1 PCT/CN2022/131885 CN2022131885W WO2023134292A1 WO 2023134292 A1 WO2023134292 A1 WO 2023134292A1 CN 2022131885 W CN2022131885 W CN 2022131885W WO 2023134292 A1 WO2023134292 A1 WO 2023134292A1
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creep
resistant steel
austenitic
austenite
present
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PCT/CN2022/131885
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English (en)
French (fr)
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王寅杰
宫高全
陈小华
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科华控股股份有限公司
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Priority to EP22871096.8A priority Critical patent/EP4234744A1/en
Publication of WO2023134292A1 publication Critical patent/WO2023134292A1/zh

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/005—Selecting particular materials
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D25/00—Component parts, details, or accessories, not provided for in, or of interest apart from, other groups
    • F01D25/24—Casings; Casing parts, e.g. diaphragms, casing fastenings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/08—Other arrangements or adaptations of exhaust conduits
    • F01N13/10—Other arrangements or adaptations of exhaust conduits of exhaust manifolds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/16—Selection of particular materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/02—Selection of particular materials
    • F04D29/023—Selection of particular materials especially adapted for elastic fluid pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/40—Casings; Connections of working fluid
    • F04D29/403—Casings; Connections of working fluid especially adapted for elastic fluid pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2220/00—Application
    • F05D2220/40—Application in turbochargers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2240/00—Components
    • F05D2240/10—Stators
    • F05D2240/14—Casings or housings protecting or supporting assemblies within
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2300/00—Materials; Properties thereof
    • F05D2300/10—Metals, alloys or intermetallic compounds
    • F05D2300/17—Alloys
    • F05D2300/171—Steel alloys

Definitions

  • the invention belongs to the technical field of austenitic creep-resistant steel, and in particular relates to a cast iron-based austenitic creep-resistant steel and its preparation method and application.
  • Austenitic steel is a steel that has an austenitic structure after normalizing.
  • the alloying elements (Ni, Mn, N, Cr, etc.) added to the steel can make the normalized metal have a stable austenite structure.
  • Iron-based austenitic creep-resistant steel refers to a heat-resistant steel that has an austenitic structure at room temperature and has special requirements for high-temperature creep properties of materials. Based on Fe, the steel contains about 20% to 25% of Cr, about 9% to 40% of Ni, about 0.3% to 0.5% of C, about 0.5% to 2% of Nb and a certain amount of Mo, W, and B elements. Among the three austenitic matrix heat-resistant steels (high-temperature alloys) of Fe, Co, and Ni, the cost of iron-based heat-resistant raw materials is the lowest, but the thermal stability of the austenitic matrix is the worst, and the TCP phase is precipitated during long-term high-temperature use. Fastest and therefore least creep resistant.
  • the invention provides a cast iron-based austenitic creep-resistant steel and its preparation method and application.
  • the present invention provides an austenitic creep-resistant steel, comprising the following components in mass percentage: C: 0.2-0.5; Si: 0.5-2.0, Mn ⁇ 0.5; Cr: 20-28 ; Ni: 8 ⁇ 13; P ⁇ 0.04; S ⁇ 0.3; W: 0.5 ⁇ 2; N: 0.2 ⁇ 0.4; the balance is iron and other unavoidable impurity elements.
  • the present invention also provides a method for preparing an austenitic creep-resistant steel. After melting the above-mentioned raw materials in an intermediate frequency furnace, they are cast into a mold to prepare the austenitic creep-resistant steel.
  • the present invention also provides an application of the aforementioned austenitic creep-resistant steel in an automobile engine exhaust manifold or a turbocharger housing.
  • the beneficial effect of the present invention is that the austenitic creep-resistant steel prepared by the present invention suppresses the high-temperature ferrite phase and eliminates the precipitation-type nitrogen pore defect; the addition range of nitrogen and carbon elements is optimized, so that the processing cost of the casting is low Compared with ordinary chromium-nickel austenitic heat-resistant steel; excellent mechanical properties at high temperature, long creep rupture time. Under the condition that the cost of raw materials is reduced by more than 60%, the high-temperature creep rupture time, thermal conductivity and linear expansion coefficient reach the level of 1.4849 heat-resistant steel.
  • Fig. 1 is the sample diagram of the austenitic creep-resistant steel that embodiment 1 of the present invention makes;
  • Fig. 2 is a sample diagram of the austenitic creep-resistant steel prepared in Comparative Example 1 of the present invention.
  • nickel is the main austenitizing element. Its main function is to form and stabilize austenite, so that austenitic steel can obtain good high-temperature mechanical properties and anti-oxidation and corrosion resistance. Phase transition occurs when cooled to room temperature and prevents precipitation of TCP phase when used at high temperature for a long time.
  • Nickel is a precious metal element and is a strategic resource. The production of austenitic creep-resistant steel consumes a large amount of nickel, resulting in high product prices. The development of low-nickel austenitic creep-resistant steel that replaces nickel in whole or in part with other cheap alloying elements is beneficial to reduce costs and improve the market competitiveness of heat-resistant steel products.
  • Nitrogen and carbon are strong austenite-forming elements. When they are interstitial solid-solution elements, their effect on stabilizing austenite is about 30 times that of nickel, which can greatly reduce the amount of nickel used in austenitic creep-resistant steel. , thereby reducing raw material costs. However, in actual production, the addition of nitrogen often causes nitrogen pore defects in castings, and seriously affects the cutting performance of materials. When carbon is excessive, it will also form carbides, which will increase the cost of processing tools, resulting in an increase in overall production costs, which is not worth the candle.
  • the present invention provides an austenitic creep-resistant steel, comprising the following components in mass percentage: C: 0.2-0.5; Si: 0.5-2.0, Mn ⁇ 0.5; Cr: 20-28 ; Ni: 8 ⁇ 13; P ⁇ 0.04; S ⁇ 0.3; W: 0.5 ⁇ 2; N: 0.2 ⁇ 0.4; the balance is iron and other unavoidable impurity elements.
  • the austenitic creep-resistant steel of the present invention eliminates precipitation-type nitrogen pore defects by suppressing the high-temperature ferrite phase; optimizes the addition range of nitrogen and carbon elements, and adds an appropriate amount of easy-cutting elements, so that the processing cost of castings is lower than Ordinary chromium-nickel austenitic creep-resistant steel; the creep rupture time at 1000°C and 35MPa is better than that of 1.4849 heat-resistant steel, and the cost of raw materials is greatly reduced.
  • C in the austenitic creep-resistant steel of the present invention, C can form carbides with high thermal stability at the grain boundaries with Cr and W elements, which can precipitate and strengthen the grain boundaries and reduce grain boundary creep. Speed, thereby increasing the service life of parts.
  • C and N together replace the precious metal Ni to stabilize the austenite matrix and reduce the cost of raw materials.
  • the as-cast matrix contains about 3% (volume percentage) of TCP phase, and more TCP phases are precipitated after aging treatment at 900-1000°C (>5% ), which shortens the creep rupture time of the material by about 80% at 1000°C.
  • the mass percentage of C in the austenitic creep-resistant steel described in the present invention is controlled at 0.2-0.5%.
  • the role of Si is to assist deoxidation during smelting to improve the fluidity of molten steel, reduce casting slag hole defects, and slightly improve high-temperature oxidation resistance and corrosion resistance.
  • Si is > 2.0% or ⁇ 0.5%, the fluidity of molten steel drops sharply, and the defects of casting slag holes increase sharply.
  • Si is the main ferrite forming element, if the content is too high, the ferrite phase will appear in the as-cast state, and reduce the high temperature stability of the austenite matrix and carbides, and reduce the service life of the parts.
  • the mass percentage of Si is controlled at 0.5-2.0%.
  • the content of Mn needs to be controlled ⁇ 0.5%.
  • Mn can replace Ni to reduce the cost of raw materials, and can also react with S to form spherical MnS, reducing the hot brittleness of grain boundary FeS.
  • the mass percentage is greater than 0.5%, the precipitated porosity defects increase significantly, and the absorption rate of N during smelting decreases greatly. Since the N element is added to the molten steel through the N-containing alloy, other alloy elements will be brought in.
  • the main function of Cr is to provide oxidation resistance and corrosion resistance at 900-1050 ° C, and to increase the solubility of N in molten steel, thereby increasing the absorption of N when N-containing alloys are added rate, reduce the boiling phenomenon of molten steel at high temperature, and reduce casting porosity defects.
  • Cr is a ferrite-forming element, and if the content is too high, the ferrite phase will appear in the cast state. When the ferrite is above 900°C, the tensile strength is less than one-tenth of that of austenite, which seriously reduces the high-temperature mechanical properties of the parts. performance.
  • Cr is also a TCP phase-forming element, and the number of electron vacancies reaches 4.66.
  • the mass percentage of Cr is less than 20%, the solubility of N in molten steel is less than 0.3%, resulting in the appearance of sigma phase in the as-cast structure and the increase of casting pore defects.
  • the mass percentage of Cr is greater than 28%, the ferrite phase will also appear in the as-cast state when the contents of other alloy elements meet the requirements. Based on this, in the technical solution of the present invention, the mass percentage of Cr is controlled at 20-28%.
  • Ni is the main austenite-forming element, and the number of electron vacancies is 0.66, which is the strongest element for inhibiting the TCP phase among the main alloying elements of the iron-based heat-resistant steel.
  • Ni is the alloying element with the highest proportion in raw material cost. Ni also reduces the solubility of N, which increases casting porosity defects at higher levels of both elements.
  • the mass percentage of Ni is controlled at 8-13%.
  • the main function of W is to form carbides with C to play the role of precipitation strengthening, and the W solid solution in the matrix can play the role of solid solution strengthening and improve the creep fracture Time and suppression of nitrogen porosity defects.
  • Mo which has a similar effect
  • W has a smaller chromium equivalent coefficient and has less side effects on the stability of the austenite matrix.
  • the addition of W exceeds 2%, continue to increase W, the creep rupture time does not increase, but the material chromium equivalent and the average number of electron vacancies increase. Based on this, in the technical solution of the present invention, the quality of W is controlled The percentage is between 0.5% and 2%.
  • N is the main austenite forming element, and solid solution N can replace about 30 times of Ni.
  • the mass percentage of N is >0.4%, the addition of >25% Cr and >2% W cannot suppress the precipitation-type nitrogen pore defects, and at the same time, the processability deteriorates. Based on this, in the technical solution of the present invention, the mass percentage of N is controlled at 0.2-0.4%.
  • the tensile strength of the austenitic creep-resistant steel at 1000°C is not lower than 110MPa, the yield strength is not lower than 40MPa, and the elongation after fracture is not lower than 15%.
  • the creep rupture time of the austenitic creep-resistant steel at 1000°C and 35MPa is not less than 77h.
  • the thermal conductivity of the austenitic creep resistant steel is 22-24W/(m ⁇ K) at 800°C, and 26-27W/(m ⁇ K) at 1000°C.
  • the average linear expansion coefficient of the austenitic creep-resistant steel is (17-18) ⁇ 10 -6 at 25-800°C, and (17-19) ⁇ 10 -6 at 25-1000°C.
  • the present invention also provides a method for preparing austenitic creep-resistant steel. After adding the above-mentioned raw materials into an intermediate frequency furnace for melting, they are cast into molds to obtain austenitic creep-resistant steel. steel.
  • the present invention also provides an application of the aforementioned austenitic creep-resistant steel in an automobile engine exhaust manifold or a turbocharger housing.
  • the working temperature of the austenitic creep-resistant steel can reach 1050°C.
  • Austenitic creep-resistant steels were prepared with reference to the components and ratios in Table 1.
  • Table 1 Element composition and ratio of austenitic creep-resistant steel in each embodiment and comparative example
  • the austenitic creep-resistant steel prepared by the present invention suppresses the high-temperature ferrite phase and eliminates the precipitation-type nitrogen pore defects; the addition of nitrogen and carbon elements is optimized range, making the casting processing cost lower than that of ordinary chromium-nickel austenitic heat-resistant steel; excellent mechanical properties at high temperatures, and long creep rupture time.
  • the austenitic creep-resistant steel prepared by the present invention suppresses the high-temperature ferrite phase, eliminates the precipitation-type nitrogen pore defects; optimizes the addition range of nitrogen and carbon elements, making the processing cost of castings lower than ordinary Chromium-nickel austenitic heat-resistant steel; excellent mechanical properties at high temperatures and long creep rupture time. Under the condition that the cost of raw materials is reduced by more than 60%, the high-temperature creep rupture time, thermal conductivity and linear expansion coefficient reach the level of 1.4849 heat-resistant steel.

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Abstract

本发明属于奥氏体抗蠕变钢技术领域，具体涉及一种铸造铁基奥氏体抗蠕变钢及其制备方法、应用。本发明的奥氏体抗蠕变钢，包括以下质量百分比的各组分：C：0.2～0.5；Si：0.5～2.0，Mn<0.5；Cr：20～28；Ni：8～13；P≤0.04；S≤0.3；W：0.5～2；N：0.2～0.4；余量为铁及其他不可避免的杂质元素。本发明制得的奥氏体抗蠕变钢，抑制了高温铁素体相，消除了析出型氮气孔缺陷；优化氮、碳元素的加入范围，使得铸件加工成本低于普通铬镍奥氏体耐热钢；高温下机械性能优异，蠕变断裂时间长。

Description

铸造铁基奥氏体抗蠕变钢及其制备方法、应用 技术领域
本发明属于奥氏体抗蠕变钢技术领域，具体涉及一种铸造铁基奥氏体抗蠕变钢及其制备方法、应用。
背景技术
奥氏体钢是正火后具有奥氏体组织的钢。钢中加入的合金元素(Ni、Mn、N、Cr等)能将使正火后的金属具有稳定的奥氏体组织。
铁基奥氏体抗蠕变钢是指在常温下具有奥氏体组织，对材料高温蠕变性能有特殊要求的耐热钢。钢中以Fe为基础，含有Cr约20％～25％，Ni约9％～40％，C约0.3％～0.5％，Nb约0.5％～2％及一定量的Mo、W、B元素。在Fe、Co、Ni三种奥氏体基体耐热钢(高温合金)中，铁基耐热原料成本最低，但奥氏体基体的热稳定性最差，长时间高温使用时析出TCP相的速度最快，因此抗蠕变性能最差。
发明内容
本发明提供了一种铸造铁基奥氏体抗蠕变钢及其制备方法、应用。
为了解决上述技术问题，本发明提供了一种奥氏体抗蠕变钢，包括以下质量百分比的各组分：C：0.2～0.5；Si：0.5～2.0，Mn<0.5；Cr：20～28；Ni：8～13；P≤0.04；S≤0.3；W：0.5～2；N：0.2～0.4；余量为铁及其他不可避免的杂质元素。
又一方面，本发明还提供了一种奥氏体抗蠕变钢的制备方法，将如前各原料加入中频炉内熔炼后，浇铸至模具中，制得奥氏体抗蠕变钢。
第三方面，本发明还提供了一种如前所述的奥氏体抗蠕变钢在汽车发动机排气歧管或涡轮增压器壳体中的应用。
本发明的有益效果是，本发明制得的奥氏体抗蠕变钢，抑制了高温铁素体相，消除了析出型氮气孔缺陷；优化氮、碳元素的加入范围，使得铸件加工成本低于普通铬镍奥氏体耐热钢；高温下机械性能优异，蠕变断裂时间长。在原材料成本降低超过60％的情况下，高温蠕变断裂时间、热导率及线膨胀系数达到1.4849耐热钢的水平。
本发明的其他特征和优点将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点在说明书以及附图中所特别指出的结构来实现和获得。
为使本发明的上述目的、特征和优点能更明显易懂，下文特举较佳实施例，并配合所附附图，作详细说明如下。
附图说明
为了更清楚地说明本发明具体实施方式或现有技术中的技术方案，下面将对具体实施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是本发明的实施例1制得的奥氏体抗蠕变钢的样品图；
图2是本发明的对比例1制得的奥氏体抗蠕变钢的样品图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合附图对本发明的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
铁基奥氏体钢中，镍是主要的奥氏体化元素，其主要作用是形成并稳定奥氏体，使得奥氏体钢获得良好的高温机械性能及抗氧化、耐腐蚀性能，既避免冷却到室温时出现相变又抑制高温下长时间使用时析出TCP相。镍是一种贵重的金属元素，属于战略资源，奥氏体抗蠕变钢的生产消耗了大量的镍元素，造成其产品价格居高不下。发展以其它廉价合金元素全部或部分代替镍的低镍奥氏体抗蠕变钢有利于降低成本，提高耐热钢产品市场竞争力。
氮、碳作为强烈的奥氏体形成元素，在作为间隙型固溶元素时，其稳定奥氏体的作用是镍的30倍左右，可以大幅降低奥氏体抗蠕变钢中镍的使用量，从而降低原材料成本。但是在实际生产中，氮的加入往往使铸件产生氮气孔缺陷，并且严重影响材料加工切削性能，碳在过量时也会形成碳化物从而增加加工刀具成本，造成生产综合成本上升，得不偿失。
为了解决上述技术问题，本发明提供了一种奥氏体抗蠕变钢，包括以下质量百分比的各组分：C：0.2～0.5；Si：0.5～2.0，Mn<0.5；Cr：20～28；Ni：8～13；P≤0.04；S≤0.3；W：0.5～2；N：0.2～0.4；余量为铁及其他不可避免的杂质元素。
具体的，本发明的奥氏体抗蠕变钢通过抑制高温铁素体相，消除了析出型氮气孔缺陷；优化氮、碳元素的加入范围，加入适量易切削元素，使得铸件加工成本低于普通铬镍奥氏体抗蠕变钢；在1000℃、35MPa下的蠕变断裂时间优于1.4849耐热钢材质，而原材料 成本大幅降低。
其中，在本发明的奥氏体抗蠕变钢中，C可与Cr、W元素在晶界处形成热稳定性高的碳化物，对晶界起到沉淀强化的作用，降低晶界蠕变速度，从而提高零件使用寿命。同时在本发明中，C与N一同取代贵重金属Ni，起到稳定奥氏体基体并降低原材料成本的作用。在本发明规定成分下，C在小于0.2％时，铸态下基体中含有3％(体积百分比)左右的TCP相，在900～1000℃做时效处理后析出的TCP相更多(>5％)，使材料在1000℃下的蠕变断裂时间缩短80％左右。当C含量超过0.4％时晶粒内部出现碳化物，加工性能严重恶化，加工刀具成本增加100％～900％。基于此，在本发明所述的奥氏体抗蠕变钢中C的质量百分比控制在0.2～0.5％。
在本发明的奥氏体抗蠕变钢中，Si的作用是熔炼时的辅助脱氧以改善钢水流动性，减少铸造渣孔缺陷，并略微改善高温抗氧化性能及耐腐蚀性能。Si在>2.0％或<0.5％时钢水流动性大幅下降，铸造渣孔缺陷急剧增加。Si是主要的铁素体形成元素，含量过高会使铸态下出现铁素体相，并降低奥氏体基体及碳化物的高温稳定性，降低零件使用寿命。在本发明所述奥氏体抗蠕变钢中，Si的质量百分比控制住0.5～2.0％。
在本发明的奥氏体抗蠕变钢中，Mn需要控制其含量<0.5％。通常来说Mn具有取代Ni降低原材料成本的作用，也可以与S反应生成球形MnS，降低晶界FeS的热脆性。但在本发明中当其质量百分比大于0.5％时，析出性气孔缺陷显著增加，且熔炼时N的吸收率大幅降低。由于N元素是通过含N合金加入钢水中，会带入其他合金元素，N的吸收率降低导致含N合金加入量增加，带入的其他合金元素亦增加，从而使钢水成分调整更加困难。在大批量生产时，由于铸造返材中也含有N，在Mn过高时，返材中的N在钢水熔炼过程中也损失严重，该部分N也需要含N合金补充，从而降低了铸造返材的使用比例，在实际工艺出品率较低时会造成铸造返材积压，无法循环使用。根据Pauling理论，Mn的电子空位数是3.66，在奥氏体形成元素中最高，在镍当量较低的铁基奥氏体抗蠕变钢中会显著促进TCP相的形成，降低奥氏体基体的稳定性，使得蠕变速度增加。所以必须使用低锰原料，来降低Mn含量。
在本发明的奥氏体抗蠕变钢中，Cr的主要作用是提供900～1050℃的抗氧化性及耐腐蚀性，以及提高钢水中N的溶解度，从而提高含N合金加入时N的吸收率，减少高温下钢水的沸腾现象，减少铸造气孔缺陷。但Cr是铁素体形成元素，含量过高会使铸态下出现铁素体相，铁素体在900℃以上时抗拉强度不足奥氏体的十分之一，严重降低零件的高温机械性能。Cr也是TCP相形成元素，电子空位数达到4.66，当Cr质量百分比小于20％ 时，N在钢水中的溶解度小于0.3％，导致铸态组织出现西格玛相，铸造气孔缺陷增大。当Cr质量百分比大于28％时，在其余合金元素含量满足要求时，铸态下也会出现铁素体相。基于此，在本发明所述的技术方案中，控制Cr的质量百分比在20～28％。
在本发明的奥氏体抗蠕变钢中，Ni是主要的奥氏体形成元素，电子空位数是0.66，是铁基耐热钢主要合金元素中最强的抑制TCP相的元素。Ni是原材料成本中占比最高的合金元素。Ni也会降低N的溶解度，在这两种元素含量都较高时，会增加铸造气孔缺陷。在其余合金元素含量满足要求时，Ni质量百分比小于8％时，铸态时材料基体中含有1％(体积百分比)左右的TCP相，在900～1000℃做时效处理后析出的TCP相更多(>3％)，该比例的TCP相会使材料在1000℃下的蠕变断裂时间缩短60％左右。但当Ni含量超过13％时，继续增加Ni含量，蠕变断裂时间反而开始降低。基于此，在本发明所述的技术方案中，控制Ni的质量百分比在8～13％。
在本发明的奥氏体抗蠕变钢中，W的主要作用是与C形成碳化物起到沉淀强化的作用，固溶在基体中的W可以起到固溶强化的作用，提高蠕变断裂时间及抑制氮气孔缺陷。和具有类似作用的Mo相比，W的铬当量系数更小，对奥氏体基体稳定性的副作用更小。当W的加入量超过2％时，继续增加W，蠕变断裂时间并不增加，材料铬当量及平均电子空位数却增加，基于此，在本发明所述的技术方案中，控制W的质量百分比在0.5～2％。
在本发明的奥氏体抗蠕变钢中，N是主要的奥氏体形成元素，固溶的N可以取代约30倍的Ni。但N的质量百分比>0.4％时，加入>25％的Cr和>2％的W都无法抑制析出型氮气孔缺陷，同时加工性能恶化。基于此，在本发明所述的技术方案中，控制N的质量百分比在0.2～0.4％。
其中，所述奥氏体抗蠕变钢在1000℃下的抗拉强度不低于110MPa，屈服强度不低于40MPa，断后延伸率不低于15％。
所述奥氏体抗蠕变钢在1000℃、35MPa下的蠕变断裂时间不小于77h。
所述奥氏体抗蠕变钢在800℃时的热导系数为22～24W/(m·K)，1000℃时的热导系数为26～27W/(m·K)。
所述奥氏体抗蠕变钢在25～800℃的平均线膨胀系数为(17～18)×10 -6，25～1000℃的平均线膨胀系数为(17～19)×10 -6。
又一方面，本发明还提供了一种奥氏体抗蠕变钢的制备方法，将如前所述的各原料加入中频炉内熔炼后，浇铸至模具中，制得奥氏体抗蠕变钢。
本发明还提供了一种如前所述的奥氏体抗蠕变钢在汽车发动机排气歧管或涡轮增压器壳体中的应用。
其中，所述奥氏体抗蠕变钢的工作温度可达1050℃。
参照表1中的各组分及比例制备奥氏体抗蠕变钢。
表1各实施例及对比例中奥氏体抗蠕变钢的元素组成及比例
  C Si Mn P S W Ni N Cr
实施例1 0.33 1.3 0.2 0.015 0.012 0.6 12.5 0.39 23.9
实施例2 0.25 0.53 0.21 0.013 0.01 1.9 8.1 0.26 20.5
实施例3 0.49 1.98 0.21 0.016 0.013 2.9 12.8 0.26 27.9
对比例1 0.42 1.2 1.1 0.018 0.011 0.02 38.7 0.03 19.2
对比例2 0.35 1.2 0.21 0.014 0.01 0 11.2 0.26 24.2
对比例3 0.36 1.1 0.25 0.014 0.009 1.4 14 0.27 23.9
对比例4 0.34 1.3 0.24 0.011 0.012 1.3 7.8 0.28 24.1
对比例5 0.1 0.9 0.24 0.010 0.012 1.5 9.9 0.27 23.8
对表1中各实施例及对比例中相关性能测试后，数据汇总于表2。
表2各实施例及对比例中奥氏体抗蠕变钢的性能数据
Figure PCTCN2022131885-appb-000001
由图1和图2以及表2中的数据可知，本发明制得的奥氏体抗蠕变钢，抑制了高温铁素体相，消除了析出型氮气孔缺陷；优化氮、碳元素的加入范围，使得铸件加工成本低于普通铬镍奥氏体耐热钢；高温下机械性能优异，蠕变断裂时间长。
综上所述，本发明制得的奥氏体抗蠕变钢，抑制了高温铁素体相，消除了析出型氮气孔缺陷；优化氮、碳元素的加入范围，使得铸件加工成本低于普通铬镍奥氏体耐热钢；高温下机械性能优异，蠕变断裂时间长。在原材料成本降低超过60％的情况下，高温蠕变断 裂时间、热导率及线膨胀系数达到1.4849耐热钢的水平。
以上述依据本发明的理想实施例为启示，通过上述的说明内容，相关工作人员完全可以在不偏离本项发明技术思想的范围内，进行多样的变更以及修改。本项发明的技术性范围并不局限于说明书上的内容，必须要根据权利要求范围来确定其技术性范围。

Claims (4)

  1. 一种奥氏体抗蠕变钢，其特征在于，包括以下质量百分比的各组分：C：0.2～0.5；Si：0.5～2.0，Mn＜0.5；Cr：20～28；Ni：8～13；P≤0.04；S≤0.3；W：0.5～2；N：0.2～0.4；余量为铁及其他不可避免的杂质元素；所述奥氏体抗蠕变钢在1000℃、35MPa下的蠕变断裂时间不小于77h；所述奥氏体抗蠕变钢在800℃时的热导系数为22～24W/(m·K)，1000℃时的热导系数为26～27W/(m·K)；所述奥氏体抗蠕变钢在25～800℃的平均线膨胀系数为(17～18)×10 -6/K，25～1000℃的平均线膨胀系数为(17～19)×10 -6/K。
  2. 如权利要求1所述的奥氏体抗蠕变钢，其特征在于，所述奥氏体抗蠕变钢在1000℃下的抗拉强度不低于110MPa，屈服强度不低于40MPa，断后延伸率不低于15％。
  3. 一种奥氏体抗蠕变钢的制备方法，其特征在于，将如权利要求1中各原料加入中频炉内熔炼后，浇铸至模具中，制得奥氏体抗蠕变钢。
  4. 一种如权利要求1所述的奥氏体抗蠕变钢在汽车发动机排气歧管或涡轮增压器壳体中的应用。
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