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
Date Issued
2005
Date
2005
Author(s)
王涵聖
DOI
zh-TW
Abstract
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.
Subjects
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
Type
thesis
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