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標題: | 沃斯田鐵在不鏽鋼及合金鋼之Displacive相變態與其衍生之顯微組織研究 |
作者: | Han-ShenWang 王涵聖 |
指導教授: | 楊哲人 |
關鍵字: | 沃斯田鐵,麻田散鐵,316L不鏽鋼超細鋼線,17-4PH不鏽鋼,雙相鋼,TRIP鋼,機械安定化, reversed austenite,martensite,316L untra-fine stainless steel wire,17-4PH stainless steel,dual phase steel,TRIP steel, |
出版年 : | 2005 |
學位: | 博士 |
摘要: | 摘 要
沃斯田鐵與鋼鐵最終的顯微組織及性質有著密切不可分的關係。Displacive相變態為原子晶格藉由剪切作用使其結構產生變化的一種相變態方式。當沃斯田鐵相依循Displacive相變態分解時,主要的產物可分為麻田散鐵及變韌鐵,兩者的差異在於相變過程之中,格隙固溶的碳原子是否發生擴散。 本研究藉由17-4PH不鏽鋼的reversed austenite研究、316L超細不鏽鋼線的冷抽顯微結構、雙相鋼的軋延組織及TRIP(Transformation Induced Plasticity)鋼的熱機處理等四個不同的鋼種來了解沃斯田鐵在1.合金添加及非平衡合金元素分佈、2.熱處理流程設計、3.冷加工及4.熱機處理等不同狀態之下,其displacive相變態的行為及其衍生的顯微組織。 目前對於17-4PH不鏽鋼的研究發現,合金添加及非平衡合金元素分佈可改變沃斯田鐵相的安定性,甚至使沃斯田鐵在低於Ac1溫度時發生成核及成長,且其晶體方位亦循原displacive相變態之variant逆向回復而有晶體方位記憶效應,使得擴散型相變態產物之方位因先前displacive相變態而受限。在雙相鋼研究中的熱處理流程設計,則藉由displacive相變態產物的特性而能夠達到晶粒細化及改變顯微組織型態的目的。冷抽線加工則可以在沃斯田鐵相中誘發麻田散鐵的生成;應變的角色除可誘發displacive相變態之外,亦可藉由缺陷來抑制displacive相變態而得到所謂的沃斯田鐵相的機械安定化。熱機處理則藉由在高溫沃斯田鐵相內部導入大量缺陷結構,以提供displacive相變態所需的成核位置。 Abstract Austenite phase is of deciding importance on the microstructural development in steels. Displacive phase transformation, whrere the atoms undergo a shear movement, can form a new phase such as martensite or bainite. After displacive transformation, the interstitial atoms can diffuse (e.g. upper bainite with interpolate carbides, lower bainite with interpolate carbides, and auto-tempered martensite with intralath carbides). In this study, the displacive transformation of austenite are investigated through (i) observations of reversed austenite in 17-4PH stainless steel, (ii) TEM(transmission electron microscope) specimen preparation and observations of ultra-fine 316 stainless steel wires, (iii) cold rolling structure in dual-phase steels and (iv) microstructure evaluations of TRIP-aided steels with thermo-mechanical treatment. The results can be discussed by the nature of displacive transformation and conluded via the following aspects: 1. alloying and non-equilibrium distributions, 2. heat treatments, 3. cold working and 4. thermo-mechanical treatment. Alloying and non-equilibrium distribution in 17-4PH stainless steel result in reversed austenite formation below Ac1 temperature. The reverse transformation from martensite crystals to the same austenite orientation suggests the effect of crystal memory. Intermediate quenching of dual-phase steel can control the initial structure before inter-critical annealing (IA) and refine the grian size and morphology in final microstructure. Cold drawing of 316L stainless steel wire can induce the martensitic reaction. Strain, as a role of displacive transformation, not only promotes the reaction ifself, but also inhibit the reaction by highly strain induced dislocated structure. Thermo-mechanical treatment in TRIP-aided steels accelerates the decomposition of austenite by increasing the nucleation sites. Retardation of displacive transformation under strain, which is known as mechanical stabilization of austenite, is observed and discussed. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/35924 |
全文授權: | 有償授權 |
顯示於系所單位: | 材料科學與工程學系 |
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