本文選題：Super304H奧氏體耐熱鋼 + 富Cu相　； 參考：《上海交通大學》2015年博士論文

【摘要】：隨著火力發(fā)電機組的迅速發(fā)展,機組運行的蒸汽壓力和溫度參數(shù)不斷提高,對機組用耐熱鋼的性能要求也越來越高。Super304H奧氏體耐熱鋼是在18/8Cr-Ni不銹鋼基礎(chǔ)上添加約3 wt%的Cu以及少量的Nb而開發(fā)的一種新型奧氏體鋼。由于Super304H奧氏體鋼具有良好的高溫強度和抗氧化性能,因此當前被廣泛應(yīng)用于國內(nèi)外超超臨界(UltraSupercritical-USC)機組中的過熱器和再熱器管。Super304H奧氏體鋼良好的高溫強度主要來源于其在高溫服役過程中析出的納米級富Cu相和MX相(Nb(C,N))的沉淀強化作用。此外,M23C6和Z相(NbCrN)在Super304H奧氏體鋼高溫服役過程也起到了輔助的強化作用。然而,到目前為止對于這些析出相在Super304H奧氏體鋼中的析出行為和強化機理還不甚清楚。對Super304H奧氏體鋼析出行為和強化機理的研究將會進一步完善人們對于Super304H鋼中析出相的認識,從而為該鋼種的高溫服役性能評估提供實驗依據(jù)。本文以Super304H奧氏體鋼為研究對象,利用掃描和透射電子顯微鏡對其顯微結(jié)構(gòu)進行深入觀察和分析,研究了Super304H奧氏體鋼的時效析出行為,并把時效析出行為和宏觀力學性能結(jié)合起來分析,探討了Super304H奧氏體鋼的沉淀強化機理。本文的主要研究結(jié)論如下:1.固溶態(tài)Super304H奧氏體鋼原始組織的奧氏體基體中存在有少量大塊狀的富Nb MX相和圓形夾雜物。經(jīng)650°C長時時效5000 h后的研究結(jié)果表明:Super304H奧氏體鋼在時效過程析出的析出相包括富Nb MX相、M23C6碳化物以及富Cu相。其中,納米尺寸的富Nb MX相與基體存在立方取向關(guān)系和非共格界面關(guān)系;M23C6可以在奧氏體晶粒內(nèi)以富Nb MX相為核心析出形成雙層結(jié)構(gòu),偶爾在基體內(nèi)單獨析出,M23C6與奧氏體基體存在立方取向關(guān)系;在奧氏體晶界析出不連續(xù)的鏈狀M23C6也與基體存在立方取向關(guān)系;奧氏體晶粒內(nèi)析出大量納米尺寸的富Cu相與基體存在立方取向關(guān)系和共格界面關(guān)系。2.富cu相的粗化行為研究結(jié)果表明:super304h奧氏體鋼在650~750°c溫度范圍內(nèi)時效后析出的富cu相在長大過程中始終與奧氏體基體保持立方取向關(guān)系和共格界面關(guān)系,富cu相顆粒的粗化行為遵循lifshitz-slyozov-wagner(lsw)理論;富cu相的長大激活能約為212±3kj/mol,其粗化長大主要由cu原子在奧氏體基體中的體擴散所控制。3.super304h奧氏體鋼在室溫~650°c溫度范圍內(nèi)的拉伸屈服行為研究結(jié)果表明:富cu相的沉淀強化作用對super304h奧氏體鋼屈服強度增量的貢獻約為17~23%;時效態(tài)super304h奧氏體鋼比固溶態(tài)具有更高的激活體積和激活能表明在拉伸變形過程中存在有位錯和富cu相之間的交互作用。super304h奧氏體鋼室溫拉伸變形過程中富cu相的沉淀強化主要來源于共格應(yīng)變強化以及部分來源于層錯強化,理論計算獲得的由于富cu相強化而引起的剪切應(yīng)力增量與實驗結(jié)果是一致的。super304h奧氏體鋼在650~750°c溫度范圍內(nèi)的時效硬化行為研究結(jié)果表明:在不同的時效溫度下,析出相的沉淀強化作用對super304h奧氏體鋼峰值硬度的貢獻約為17~25%,富cu相的沉淀強化同樣主要來源于共格應(yīng)變強化和部分來源于層錯強化。4.super304h奧氏體鋼在650~700°c及190~210mpa應(yīng)力水平條件下的蠕變行為研究結(jié)果表明:super304h奧氏體鋼蠕變變形的平均表觀應(yīng)力指數(shù)和激活能分別為21.5和687.3kj/mol;高的平均表觀應(yīng)力指數(shù)和激活能表明在蠕變變形過程中存在有一個位錯與富cu相的交互作用所引起的門檻應(yīng)力。在此溫度范圍內(nèi),super304h奧氏體鋼的蠕變變形機制為基體晶格擴散所控制的位錯攀移過程,蠕變過程中的門檻應(yīng)力主要來源于富cu相與奧氏體基體之間正的晶格常數(shù)錯配引起的共格應(yīng)變場,理論計算獲得的由于富cu相強化而引起的門檻應(yīng)力值與實驗結(jié)果基本一致。super304h奧氏體鋼在650°c及250mpa應(yīng)力水平條件下蠕變447h后mx相的析出行為研究結(jié)果表明:在奧氏體晶粒內(nèi)可以析出納米尺寸立方形狀的富nbmx相,富nbmx相與奧氏體基體的界面是非共格的;此外,納米尺寸的富nbmx相更容易在富cu相與奧氏體基體的界面處以及沿著奧氏體基體的位錯線析出。
[Abstract]:With the rapid development of thermal power generating sets, the steam pressure and temperature parameters of the unit are increasing, and the performance requirements for the heat resistant steel are getting higher and higher..Super304H austenitic heat-resistant steel is a new austenite steel which is opened by adding about 3 wt% Cu and a small amount of Nb on the base of 18/8Cr-Ni stainless steel. Due to Super304H austenite With good high temperature strength and antioxidant properties, the high temperature strength of the superheater and reheater tube.Super304H austenite steel in the super supersupercritical (UltraSupercritical-USC) unit at home and abroad is mainly derived from the nanoscale Cu phase and MX phase (Nb (C, N)) precipitated during the high temperature service. In addition, the M23C6 and Z phase (NbCrN) also plays an auxiliary strengthening role in the high temperature service of Super304H austenitic steel. However, the precipitation behavior and strengthening mechanism of these precipitates in Super304H austenite steel are not yet clear. Study on the precipitation behavior and strengthening mechanism of Super304H austenite steel The understanding of the precipitated phase in Super304H steel will be further improved, thus providing experimental basis for the evaluation of the high temperature service performance of the steel. In this paper, the microstructure of Super304H austenitic steel was investigated and analyzed by scanning and transmission electron microscopy, and the aging of Super304H austenite steel was studied. The precipitation behavior was analyzed and the precipitation strengthening mechanism of Super304H austenitic steel was discussed. The main conclusions of this paper are as follows: 1. the austenite matrix of Super304H austenite steel in solid solution state has a small amount of large Nb MX and circular inclusions in the austenite matrix. The results after 5000 h have shown that the precipitated phases precipitated in the aging process of Super304H austenitic steel include rich Nb MX phase, M23C6 carbide and Cu rich phase. Among them, there is a cubic orientation relationship and a non common interface relationship with the matrix rich Nb MX phase and the matrix, and M23C6 can be precipitated at the core of the austenite grain at the core of the rich Nb MX phase. Double structure, occasionally precipitated in the matrix, there is a cubic orientation relationship between M23C6 and austenite matrix, and the discontinuous chain M23C6 precipitated from the austenite grain boundary also has a cubic orientation relationship with the matrix, and a large number of nanoscale Cu phases are precipitated in the austenite grain and there are vertical and common interface relations between the matrix and the matrix.2. rich Cu phase. The results of the coarsening study show that the rich Cu phase precipitated in the Super304H austenite steel after aging in the 650~750 C temperature range has always maintained the cubic orientation relationship and the common interface relationship with the austenite matrix during the growing process. The coarse-grained behavior of the rich Cu phase particles follows the lifshitz-slyozov-wagner (LSW) theory, and the activation energy of the rich Cu phase is about 212. The results of the tensile yield behavior of.3.super304h austenitic steel at room temperature ~650 degree C are mainly controlled by the Cu atom in the austenite matrix. The results show that the contribution of the precipitation strengthening of the rich Cu phase to the increment of the yield strength of the Super304H austenite steel is 17~23%; the aging state Super304H austenite. There is a higher activation volume and activation energy in the steel than the solid solution state. The interaction between the dislocation and the rich Cu phase exists in the tensile deformation process. The precipitation enhancement of the rich Cu phase in the tensile deformation process of the.Super304h austenite steel is mainly due to the common lattice strain strengthening and the part of the stacking fault hardening. The theoretical calculation obtained is due to the results. The results of the aging hardening behavior of the.Super304h austenitic steel in the 650~750 degree C temperature range are consistent with the experimental results. The results show that the contribution of precipitation strengthening to the peak hardness of the Super304H austenite steel is about 17~25% and the precipitate of rich Cu phase is strong at different aging temperatures. The results show that the creep behavior of.4.super304h austenite steel at 650~700 degree C and 190~210mpa stress level is mainly derived from the common lattice strain strengthening and partly from the stacking fault reinforcement. The results show that the average apparent stress index and the activation energy of the creep deformation of Super304H austenite steel are 21.5 and 687.3kj/mol; the high average apparent stress The force index and activation energy indicate that there is a threshold stress caused by the interaction of the dislocation and the rich Cu phase during the creep deformation process. In this temperature range, the creep deformation mechanism of Super304H austenite steel is the dislocation climbing process controlled by the matrix lattice diffusion, and the threshold stress in the creep process is mainly derived from the rich Cu phase and the Ordovician. The common lattice strain field caused by the mismatch of the positive lattice constant between the body matrix, the theoretical calculation of the threshold stress caused by the enrichment of the rich Cu phase is basically in agreement with the experimental results. The analysis of the.Super304h phase of the MX phase after the creep 447h under the conditions of 650 degree C and 250Mpa stress level shows that: in the austenite grain The interface between the rich nbmx phase and the austenite matrix is non common in order to precipitate the rich nbmx phase in the nanoscale cubic shape. In addition, the nanoscale rich nbmx phase is more easily precipitated in the interface between the rich Cu phase and the austenite matrix and along the dislocation lines along the austenite matrix.

【學位授予單位】：上海交通大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG142.1

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