2004-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/708174摘要：雙相不銹鋼具有良好的機械強度、抗應力腐蝕及孔蝕之特性，已大量地應用於建築、石油、化工及核能等工業，此優異性質來自其相同體積比的γ＋δ雙相結構。然而，本類不銹鋼在300℃以上溫度時效後會導致肥粒前鐵相產生相變態，分解成超微細的富鐵相(α)及富鉻相(α&#900;)，造成材料脆化。2205雙相不銹鋼為現代雙相不銹鋼之最原始鋼種，了解2205雙相不銹鋼的這種脆化現象，具有學術與工業之價值。我們實驗室先前已對2205雙相不銹鋼在600 - 975℃溫度範圍之時效相變態作一系列研究，發現相變態主要涉及相及相。目前正對2205雙相不銹鋼在400 - 500℃溫度範圍之時效相變態,這個溫度範圍δ肥粒鐵可能存在於所謂的混合間隙(miscibility gap)。 鐵-鉻合金系統之相圖，具有混合間隙(miscibility gap)已是大家耳熟能詳的事，在這混合間隙(miscibility gap)，肥粒鐵相以孕核與成長方式(nucleation and growth) 或 離相(spinodaldecomposition)方式分解成超微細奈米尺度的富鐵相(α)及富鉻相(α&#900;)。由於雙相<br> Abstract: Duplex stainless steels have been widely used in oil, chemical and nuclear industries due to their high strength, good weldability, and high resistance to stress corrosion and pitting. The superior properties of the duplex stainless steels come primarily from approximately equivalent amounts of austenite (γ) and δ-ferrite. However, these types of steels are intrinsically subject to embrittlement when exposed to temperatures above 300 ℃, because of solid-state reactions within the ferrite phase. The 2205 duplex stainless steel is a progenitor of modern duplex stainless steels, and it is worth understanding the embrittlement phenomena. Previous work has been carried out on the microstructural stability and toughness properties of a 2205 duplex stainless steel aged in the temperature range of 650 - 975 ℃, where the formation of σ and χ phase is found to promote severe deterioration in toughness. In the present work, an attempt is made to investigate the same steel aged in the temperature range of 400 - 500 ℃, where a miscibility gap for the decomposition of ferrite presumably exists. It is well known that in Fe-Cr alloys there is a miscibility gap, where the ferrite phase may decompose into an iron-rich BCC phase (α) and a chromium-enriched BCC phase (α&#900;) either by nucleation and growth of α&#900; precipitates or by spinodal decomposition. The complex chemistry of the original δ-ferrite in the duplex stainless steels would significantly affect the above mentioned phase transformation. Atom probe field ion microscopy has been performed on CF series of cast duplex stainless steels aged at 270-450 ℃, and the morphology, size distribution and chemical concentration profile of the α&#900; precipitates have been determined. However, a detailed high resolution transmission electron microscopy has not been reported. Our TEM result has shown the modulated structure of the decomposed -ferrite. The contrast mechanism of modulated structure is not clear, although it has been presumed to be due to differential oxidation of the two phases during the eletro-polishing preparation of the TEM thin foils. The purpose of this work is to investigate the decomposed -ferrite structure in electro-polishing thin foils and mechanical polishing thin foils. The atomic structure of decomposed δ-ferrite phase and the dislocation structure in this steel will be observed via a 300 kV field-emission-gun transmission electron microscope (FEG-TEM), Tecnai F30雙相不銹鋼離相反應奈米調幅結構差排組織Duplex stainless steelspinodal decompositionnanometer-scaled modulated structuredislocation structure.