新型含鋁奧氏體耐熱鋼相形成規(guī)律及高溫變形行為研究
發(fā)布時(shí)間：2019-05-27 03:56
【摘要】：表面形成A1203保護(hù)層的新型奧氏體耐熱鋼(Alumina-forming Austenitic steel,簡稱AFA鋼)在高溫復(fù)雜服役環(huán)境下具有優(yōu)異的抗氧化性能,非常有潛力成為新一代高溫結(jié)構(gòu)材料。因此,這種新型AFA鋼近年來吸引了眾多材料研究者的目光。但是,到目前為止關(guān)于此類AFA鋼的研究工作主要集中在高溫氧化機(jī)理方面,而對其高溫變形行為及力學(xué)性能缺乏系統(tǒng)的、深入性的研究。本課題組前期成功研發(fā)出了高溫抗氧化性能優(yōu)異的新型AFA鋼,但是其高溫力學(xué)方面的研究不足,制約了其實(shí)際工程應(yīng)用。為了理解該AFA鋼的高溫變形機(jī)制并提高其高溫力學(xué)性能尤其是耐蠕變性能,本文在系統(tǒng)研究第二相的析出行為、預(yù)冷加工處理作用機(jī)理、再結(jié)晶行為等基礎(chǔ)上,探索其高溫變形機(jī)制以及成分、工藝條件等對高溫力學(xué)性能的影響規(guī)律。 本文首先系統(tǒng)研究了AFA鋼在高溫條件下的流變行為,揭示了其高溫變形機(jī)制。研究發(fā)現(xiàn)AFA鋼的高溫變形行為可用冪律規(guī)律描述,在考慮變形門檻力、彈性模量及晶格擴(kuò)散影響的基礎(chǔ)上,得出我們研究的AFA鋼的應(yīng)力指數(shù)為5,證實(shí)其高溫蠕變是典型的回復(fù)型蠕變,主要受奧氏體晶格擴(kuò)散過程的影響,而變形門檻力的存在表明了此AFA鋼存在明顯的第二相析出強(qiáng)化。同時(shí)發(fā)現(xiàn),該AFA鋼中的門檻力來源于位錯(cuò)繞過第二相顆粒所產(chǎn)生的額外阻力,可用Orowan機(jī)制描述。當(dāng)實(shí)驗(yàn)溫度由低于1023K上升到1023K以上的時(shí),運(yùn)動位錯(cuò)和第二相顆粒的交互作用能從163kJ/mol下降到34kJ/mol,表明強(qiáng)化效果發(fā)生了明顯的改變。 其次,本文系統(tǒng)研究了AFA鋼的第二相析出規(guī)律以及強(qiáng)化效果。實(shí)驗(yàn)結(jié)果表明,在1023K或更高溫度下,我們研究的AFA鋼中主要析出B2-NiAl、初生NbC、σ/δ-FeCr、Laves-Fe2Nb等相,高溫強(qiáng)化效果主要來源于Laves-Fe2Nb的析出強(qiáng)化。但是由于Laves-Fe2Nb的粗化傾向大,其帶來的強(qiáng)化效果隨溫度升高、服役時(shí)間延長而明顯下降,因此該鋼的高溫耐蠕變性能明顯不足。納米NbC相具有較好的強(qiáng)化效果,其粗化傾向也遠(yuǎn)小于Laves-Fe2Nb相,但是這種納米相在本文研究的AFA鋼中只在較低的溫度下穩(wěn)定存在。研究發(fā)現(xiàn)通過改變Nb、C的加入量,調(diào)節(jié)Nb/C比至7.7-10時(shí),AFA鋼在1023K溫度時(shí)也能析出大量的納米NbC相,從而大幅度提高其高溫耐蠕變性能。減少Si和Mo元素的加入量可有效地抑制σ-FeCr脆性相的析出,從而提高AFA鋼的高溫蠕變性能。 此外,本文還研究了工藝條件和再結(jié)晶過程對AFA鋼的高溫耐蠕變性能的影響。研究發(fā)現(xiàn),10%左右的預(yù)冷加工處理可以促進(jìn)我們研究的AFA鋼中納米NbC相的析出,并使其分布更加均勻彌散,從而使該AFA鋼在1023K,100MPa條件下的蠕變斷裂壽命提高1倍左右。研究還發(fā)現(xiàn)AFA鋼的再結(jié)晶晶粒長大動力學(xué)指數(shù)為3,這說明晶粒長大過程受到了其他因素的阻礙。晶粒長大表觀激活能為234.7kJ/mol,這與Nb在奧氏體晶界的擴(kuò)散激活能(-225kJ/mol)非常接近,表明該AFA鋼再結(jié)晶過程中發(fā)生了NbC納米相的析出,這一推論也被TEM觀察的結(jié)果所證實(shí)。 在上述研究的基礎(chǔ)上,通過調(diào)節(jié)Nb/C比,適當(dāng)降低Mo. Si元素的添加量,成功開發(fā)出了改進(jìn)型的AFA鋼,其化學(xué)成分為Fe-18Cr-25Ni-3Al-0.8Mo-0.5Nb-0.08Si-0.08C-0.01B-0.04P-0.lY-0.1Ti。并優(yōu)化了工藝條件,使得改進(jìn)的新型AFA鋼在1023K和100MPa條件下的蠕變壽命提高到4500小時(shí)以上。這一水平超過了美國橡樹嶺國家實(shí)驗(yàn)室所開發(fā)HTUPS系列AFA鋼。同時(shí)高溫氧化實(shí)驗(yàn)表明,改進(jìn)后的AFA鋼仍然具有優(yōu)異的高溫抗氧化性能。
[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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG142.73
本文編號：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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG142.73
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