本文選題：逆向奧氏體相變 + 組織遺傳�。� 參考：《清華大學(xué)》2016年博士論文

【摘要】：本文選取Fe-13Cr-5Ni馬氏體不銹鋼,作為研究對象,從實(shí)驗(yàn)以及相場模擬兩個(gè)方面著手,研究了高溫下的逆向奧氏體相變行為,特別是導(dǎo)致組織遺傳現(xiàn)像的相變過程。同時(shí)深入討論了,相場方法在研究逆向奧氏體相變(固態(tài)相變)中的數(shù)值優(yōu)勢。通過對不同熱處理?xiàng)l件下奧氏體的行為研究,揭示了不同加熱溫度以及不同保溫時(shí)間對逆向奧氏體相變的影響。結(jié)果表明,高溫下奧氏體在原奧氏體晶界球狀形核,在馬氏體板條界針狀形核,且針狀?yuàn)W氏體與基體間存在K-S晶體學(xué)位向關(guān)系。逆向奧氏體相變過程中,存在合金元素的配分行為,尤其是Ni元素。隨著退火溫度的升高,奧氏體中Ni的含量降低,從而降低奧氏體的穩(wěn)定性;同時(shí),隨著退火溫度的升高,奧氏體的轉(zhuǎn)變量增加。兩種機(jī)制共同影響,決定了室溫下殘余奧氏體的量,隨退火溫度升高先增加再減少的趨勢。保溫時(shí)間對室溫下殘余奧氏體的量的影響,與退火溫度一樣。為了更直觀研究高溫下奧氏體的相變行為,使用相場方法,建立描述降溫馬氏體相變及隨后升溫逆向奧氏體相變過程的相場模型。在新相與母相間為共格界面,且存在K-S位向關(guān)系的前提下,模擬了高溫下奧氏體的形核與長大過程。并詳細(xì)討論了相變過程中,初始組織、相變誘導(dǎo)應(yīng)變以及外加力學(xué)條件等因素,對相變熱力學(xué)、動(dòng)力學(xué)以及組織演化過程的影響。結(jié)合實(shí)驗(yàn)與模擬結(jié)果,同一原奧氏體晶粒內(nèi)形成的,與馬氏體板條間存在K-S位向關(guān)系的針狀?yuàn)W氏體,沿著馬氏體板條界不斷長大且保持這一位向關(guān)系,由此減小相變引起的體系應(yīng)變能增量,直致這些針狀?yuàn)W氏體相遇合并,最終導(dǎo)致組織遺傳的發(fā)生。奧氏體與馬氏體板條間的共格界面以及K-S位向關(guān)系,是導(dǎo)致組織遺傳的關(guān)鍵。模擬結(jié)果還表明,通過增加初始馬氏體組織的缺陷畸變能,以增加利于奧氏體形核的位置與驅(qū)動(dòng)力;以及在逆向奧氏體相變過程中對試樣施加外應(yīng)力作用,以抑制奧氏體相變長大過程,都有助于消除組織遺傳現(xiàn)像的發(fā)生,得到細(xì)小的奧氏體組織。最后研究了相場方法在研究逆向奧氏體相變中的優(yōu)勢。除了可以彌補(bǔ)實(shí)驗(yàn)表征手段在對高溫下奧氏體相變過程直觀觀測中的不足,研究結(jié)果還表明,相場方法中使用的基于傅立葉變換的FSIPM算法,在模擬固態(tài)相變中具有很高的計(jì)算精度、同時(shí)具有明顯優(yōu)勢的計(jì)算效率。
[Abstract]:In this paper, Fe-13Cr-5Ni martensitic stainless steel is selected as the research object. The reverse austenitic transformation behavior at high temperature, especially the phase transformation process leading to the genetic phenomenon of the microstructure, is studied from two aspects of experiment and phase field simulation. At the same time, the numerical advantages of phase field method in the study of reverse austenitic transformation (solid phase transformation) are discussed. By studying the behavior of austenite under different heat treatment conditions, the effects of different heating temperature and holding time on the reverse austenite transformation were revealed. The results show that austenite nucleates at the grain boundary of the original austenite at high temperature and acicular nucleation at the martensite lath boundary, and there is a K-S crystal orientation relationship between the acicular austenite and the matrix. During reverse austenitic transformation, there are alloy elements, especially Ni. With the increase of annealing temperature, the content of Ni in austenite decreases and the stability of austenite decreases, and the amount of austenite transformation increases with the increase of annealing temperature. The two mechanisms affect the amount of retained austenite at room temperature, which increases first and then decreases with the increase of annealing temperature. The effect of holding time on the amount of retained austenite at room temperature is the same as the annealing temperature. In order to study the transformation behavior of austenite at high temperature more intuitively, a phase field model was established to describe the martensite transformation at low temperature and the reverse austenite transformation process after heating up by using the phase field method. The nucleation and growth process of austenite at high temperature was simulated under the premise of the coherent interface between the new phase and the parent phase and the existence of K-S orientation. The effects of the initial microstructure, phase transition induced strain and applied mechanical conditions on the thermodynamics, kinetics and microstructure evolution of phase transition are discussed in detail. Combined with the experimental and simulation results, acicular austenite formed in the same austenite grain with K-S orientation relationship with martensite lath grows up along the martensite lath boundary and maintains this orientation relationship. Therefore, the strain energy increment of the system caused by transformation is reduced, and the acicular austenite meets and merges directly, which leads to the occurrence of microstructure heredity. The coherent interface between austenite and martensite lath and the K-S orientation are the key factors leading to tissue inheritance. The simulation results also show that the position and driving force of austenite nucleation are increased by increasing the defect distortion energy of the initial martensite, and the external stress is applied to the specimen during the reverse austenitic transformation. The inhibition of austenitic transformation can help to eliminate the genetic phenomenon of the microstructure and obtain fine austenitic structure. Finally, the advantage of phase field method in the study of reverse austenitic transformation is studied. In addition to the deficiency of experimental characterization in the direct observation of austenitic transformation process at high temperature, the results also show that the FSIPM algorithm based on Fourier transform is used in the phase field method. In the simulation of solid phase transition, it has high calculation accuracy and obvious advantage of calculation efficiency.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG142.71

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本文編號：1841974