新型含铝奥氏体耐热钢相形成规律及高温变形行为研究
发布时间：2019-05-27 03:56
【摘要】：表面形成A1203保护层的新型奥氏体耐热钢(Alumina-forming Austenitic steel,简称AFA钢)在高温复杂服役环境下具有优异的抗氧化性能,非常有潜力成为新一代高温结构材料。因此,这种新型AFA钢近年来吸引了众多材料研究者的目光。但是,到目前为止关于此类AFA钢的研究工作主要集中在高温氧化机理方面,而对其高温变形行为及力学性能缺乏系统的、深入性的研究。本课题组前期成功研发出了高温抗氧化性能优异的新型AFA钢,但是其高温力学方面的研究不足,制约了其实际工程应用。为了理解该AFA钢的高温变形机制并提高其高温力学性能尤其是耐蠕变性能,本文在系统研究第二相的析出行为、预冷加工处理作用机理、再结晶行为等基础上,探索其高温变形机制以及成分、工艺条件等对高温力学性能的影响规律。 本文首先系统研究了AFA钢在高温条件下的流变行为,揭示了其高温变形机制。研究发现AFA钢的高温变形行为可用幂律规律描述,在考虑变形门槛力、弹性模量及晶格扩散影响的基础上,得出我们研究的AFA钢的应力指数为5,证实其高温蠕变是典型的回复型蠕变,主要受奥氏体晶格扩散过程的影响,而变形门槛力的存在表明了此AFA钢存在明显的第二相析出强化。同时发现,该AFA钢中的门槛力来源于位错绕过第二相颗粒所产生的额外阻力,可用Orowan机制描述。当实验温度由低于1023K上升到1023K以上的时,运动位错和第二相颗粒的交互作用能从163kJ/mol下降到34kJ/mol,表明强化效果发生了明显的改变。 其次,本文系统研究了AFA钢的第二相析出规律以及强化效果。实验结果表明,在1023K或更高温度下,我们研究的AFA钢中主要析出B2-NiAl、初生NbC、σ/δ-FeCr、Laves-Fe2Nb等相,高温强化效果主要来源于Laves-Fe2Nb的析出强化。但是由于Laves-Fe2Nb的粗化倾向大,其带来的强化效果随温度升高、服役时间延长而明显下降,因此该钢的高温耐蠕变性能明显不足。纳米NbC相具有较好的强化效果,其粗化倾向也远小于Laves-Fe2Nb相,但是这种纳米相在本文研究的AFA钢中只在较低的温度下稳定存在。研究发现通过改变Nb、C的加入量,调节Nb/C比至7.7-10时,AFA钢在1023K温度时也能析出大量的纳米NbC相,从而大幅度提高其高温耐蠕变性能。减少Si和Mo元素的加入量可有效地抑制σ-FeCr脆性相的析出,从而提高AFA钢的高温蠕变性能。 此外,本文还研究了工艺条件和再结晶过程对AFA钢的高温耐蠕变性能的影响。研究发现,10%左右的预冷加工处理可以促进我们研究的AFA钢中纳米NbC相的析出,并使其分布更加均匀弥散,从而使该AFA钢在1023K,100MPa条件下的蠕变断裂寿命提高1倍左右。研究还发现AFA钢的再结晶晶粒长大动力学指数为3,这说明晶粒长大过程受到了其他因素的阻碍。晶粒长大表观激活能为234.7kJ/mol,这与Nb在奥氏体晶界的扩散激活能(-225kJ/mol)非常接近,表明该AFA钢再结晶过程中发生了NbC纳米相的析出,这一推论也被TEM观察的结果所证实。 在上述研究的基础上,通过调节Nb/C比,适当降低Mo. Si元素的添加量,成功开发出了改进型的AFA钢,其化学成分为Fe-18Cr-25Ni-3Al-0.8Mo-0.5Nb-0.08Si-0.08C-0.01B-0.04P-0.lY-0.1Ti。并优化了工艺条件,使得改进的新型AFA钢在1023K和100MPa条件下的蠕变寿命提高到4500小时以上。这一水平超过了美国橡树岭国家实验室所开发HTUPS系列AFA钢。同时高温氧化实验表明,改进后的AFA钢仍然具有优异的高温抗氧化性能。
[Abstract]:AFA steel, a new type of austenitic heat-resistant steel (AFA steel), is a new generation of high-temperature structural material. Therefore, this new type of AFA steel has attracted many researchers' eyes in recent years. So far, the research work on such AFA steel mainly focuses on the high-temperature oxidation mechanism, and the high-temperature deformation behavior and the mechanical properties lack the systematic and in-depth study. The research group has successfully developed a new type of AFA steel with excellent high-temperature oxidation resistance, but the research on its high-temperature mechanics has limited its practical engineering application. In order to understand the high-temperature deformation mechanism of the AFA steel and to improve the high-temperature mechanical property, especially the creep resistance, this paper, on the basis of the system research on the precipitation behavior of the second phase, the mechanism of the pre-cooling treatment, the recrystallization behavior and so on, explores its high-temperature deformation mechanism and its components, The influence of process conditions on the mechanical properties of high temperature is studied. In this paper, the rheological behavior of AFA steel under high temperature is studied in this paper, and its high-temperature deformation machine is revealed. The results show that the high-temperature deformation behavior of AFA steel can be described by the law of power law. On the basis of considering the influence of the deformation threshold force, the elastic modulus and the lattice diffusion, the stress index of the AFA steel we have studied is 5, and it is proved that the high-temperature creep is a typical recovery type. The influence of the diffusion process of the austenite crystal lattice is mainly affected by the diffusion process of the austenite crystal lattice, and the existence of the deformation threshold force indicates that the second phase of the AFA steel has obvious second phase precipitation. It is also found that the threshold force in the AFA steel is derived from the additional resistance generated by the dislocations bypassing the second phase particles, The interaction between the moving dislocation and the second phase particles can be reduced from 163 kJ/ mol to 34 kJ/ mol when the experimental temperature is increased from below 1023 K to more than 1023 K, indicating that the strengthening effect has changed obviously. The second phase of AFA steel is also studied in this paper. The experimental results show that, at the temperature of 1023 K or higher, the main precipitation of B2-NiAl, primary NbC, Fe/ Fe-Cr, Laves-Fe2Nb and other phases in the AFA steel is mainly from the analysis of the Laves-Fe2Nb. However, because the coarsening tendency of the Laves-Fe2Nb is large, the strengthening effect of the steel is increased with the temperature, and the service time is prolonged and the service time is obviously reduced, so that the high-temperature creep resistance of the steel The nano-NbC phase has a good reinforcing effect, and its coarsening tendency is much smaller than that of the Laves-Fe2Nb phase, but the nano-phase is only stable at a lower temperature in the AFA steel studied in this paper. It is found that by changing the addition of Nb and C and adjusting the Nb/ C ratio to 7.7 -10, the AFA steel can also precipitate a large amount of nano-NbC phase at the temperature of 1023 K, so that the high-temperature resistance of the AFA steel can be greatly improved. Reducing the addition of Si and Mo elements can effectively inhibit the precipitation of the brittle phase of the Al-FeCr, so as to improve the high temperature of the AFA steel. In addition, the high-temperature creep resistance of AFA steel was studied by the process conditions and the recrystallization process. It is found that the pre-cooling treatment of about 10% can promote the precipitation of the nano-NbC phase in the AFA steel and make the distribution of the AFA steel more uniform and disperse, so that the creep rupture life of the AFA steel under the condition of 1023 K and 100 MPa is improved. It is also found that the growth kinetics of the recrystallized grains of AFA steel is 3, which indicates that the grain growth process is affected by other factors. The apparent activation energy of grain growth is 234.7 kJ/ mol, which is very close to the activation energy (-225 kJ/ mol) of the diffusion activation energy (-225 kJ/ mol) of Nb in the austenite grain boundary, indicating that the precipitation of the NbC nano-phase occurs during the recrystallization of the AFA steel, which is also observed by the TEM. The results show that, on the basis of the above research, the modified AFA steel is successfully developed by adjusting the ratio of Nb/ C and the addition of Mo. Si. The chemical composition is Fe-18Cr-25Ni-3Al-0.8Mo-0.5Nb-0.08 Si-0.08 C-0.01B-0.04P-0.1. The process conditions are optimized and the creep life of the modified AFA steel under the conditions of 1023 K and 100 MPa is increased to 4 Over 500 hours. This level exceeds the HTUP developed by the American Oak Ridge National Laboratory. The results of high temperature oxidation show that the modified AFA steel is still excellent.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.73
本文编号：2485888
[Abstract]:AFA steel, a new type of austenitic heat-resistant steel (AFA steel), is a new generation of high-temperature structural material. Therefore, this new type of AFA steel has attracted many researchers' eyes in recent years. So far, the research work on such AFA steel mainly focuses on the high-temperature oxidation mechanism, and the high-temperature deformation behavior and the mechanical properties lack the systematic and in-depth study. The research group has successfully developed a new type of AFA steel with excellent high-temperature oxidation resistance, but the research on its high-temperature mechanics has limited its practical engineering application. In order to understand the high-temperature deformation mechanism of the AFA steel and to improve the high-temperature mechanical property, especially the creep resistance, this paper, on the basis of the system research on the precipitation behavior of the second phase, the mechanism of the pre-cooling treatment, the recrystallization behavior and so on, explores its high-temperature deformation mechanism and its components, The influence of process conditions on the mechanical properties of high temperature is studied. In this paper, the rheological behavior of AFA steel under high temperature is studied in this paper, and its high-temperature deformation machine is revealed. The results show that the high-temperature deformation behavior of AFA steel can be described by the law of power law. On the basis of considering the influence of the deformation threshold force, the elastic modulus and the lattice diffusion, the stress index of the AFA steel we have studied is 5, and it is proved that the high-temperature creep is a typical recovery type. The influence of the diffusion process of the austenite crystal lattice is mainly affected by the diffusion process of the austenite crystal lattice, and the existence of the deformation threshold force indicates that the second phase of the AFA steel has obvious second phase precipitation. It is also found that the threshold force in the AFA steel is derived from the additional resistance generated by the dislocations bypassing the second phase particles, The interaction between the moving dislocation and the second phase particles can be reduced from 163 kJ/ mol to 34 kJ/ mol when the experimental temperature is increased from below 1023 K to more than 1023 K, indicating that the strengthening effect has changed obviously. The second phase of AFA steel is also studied in this paper. The experimental results show that, at the temperature of 1023 K or higher, the main precipitation of B2-NiAl, primary NbC, Fe/ Fe-Cr, Laves-Fe2Nb and other phases in the AFA steel is mainly from the analysis of the Laves-Fe2Nb. However, because the coarsening tendency of the Laves-Fe2Nb is large, the strengthening effect of the steel is increased with the temperature, and the service time is prolonged and the service time is obviously reduced, so that the high-temperature creep resistance of the steel The nano-NbC phase has a good reinforcing effect, and its coarsening tendency is much smaller than that of the Laves-Fe2Nb phase, but the nano-phase is only stable at a lower temperature in the AFA steel studied in this paper. It is found that by changing the addition of Nb and C and adjusting the Nb/ C ratio to 7.7 -10, the AFA steel can also precipitate a large amount of nano-NbC phase at the temperature of 1023 K, so that the high-temperature resistance of the AFA steel can be greatly improved. Reducing the addition of Si and Mo elements can effectively inhibit the precipitation of the brittle phase of the Al-FeCr, so as to improve the high temperature of the AFA steel. In addition, the high-temperature creep resistance of AFA steel was studied by the process conditions and the recrystallization process. It is found that the pre-cooling treatment of about 10% can promote the precipitation of the nano-NbC phase in the AFA steel and make the distribution of the AFA steel more uniform and disperse, so that the creep rupture life of the AFA steel under the condition of 1023 K and 100 MPa is improved. It is also found that the growth kinetics of the recrystallized grains of AFA steel is 3, which indicates that the grain growth process is affected by other factors. The apparent activation energy of grain growth is 234.7 kJ/ mol, which is very close to the activation energy (-225 kJ/ mol) of the diffusion activation energy (-225 kJ/ mol) of Nb in the austenite grain boundary, indicating that the precipitation of the NbC nano-phase occurs during the recrystallization of the AFA steel, which is also observed by the TEM. The results show that, on the basis of the above research, the modified AFA steel is successfully developed by adjusting the ratio of Nb/ C and the addition of Mo. Si. The chemical composition is Fe-18Cr-25Ni-3Al-0.8Mo-0.5Nb-0.08 Si-0.08 C-0.01B-0.04P-0.1. The process conditions are optimized and the creep life of the modified AFA steel under the conditions of 1023 K and 100 MPa is increased to 4 Over 500 hours. This level exceeds the HTUP developed by the American Oak Ridge National Laboratory. The results of high temperature oxidation show that the modified AFA steel is still excellent.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.73
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