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Title: The effect of ageing on the magnetic properties of 316L stainless steel
Other Titles: Shi xiao dui 316L bu xiu gang ci xing de ying xiang
時效對 316L 不銹鋼磁性的影響
Authors: Lai, Man-wang (黎萬宏)
Department: Dept. of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 1999
Publisher: Dept. of Physics and Materials Science, City University of Hong Kong
Subjects: Steel, Stainless -- Magnetic properties
Notes: CityU Call Number: TA479.S7 L35 1999
Includes bibliographical references (leaves 53-54)
Thesis (M.Phil.)--City University of Hong Kong, 1999
viii, 54 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: This thesis is composed of two major parts: the transformation characteristics of AISI 316L stainless steel under isothermal ageing conditions and the effect of ageing on the magnetic properties of the alloy. Commercial grade AISI 3 16L stainless steel specimens have been aged at temperatures in the range 500°C - 900°C for various periods from 24 hours up to 10000 hours. The time-temperature-precipitation (TTP) diagram of the alloy has been constructed. The types of precipitation are well defined by the ageing temperature. The transformation products below 650°C are M23C6 and laves-phase. Between 700°C to 800°C, the transformation sequence is formation of M23C6 and chi-phase, followed by the precipitation of laves-phase, and finally the formation of sigma-phase. Above 800°C, sigma precipitates predominantly after the formation of M23C6. The magnetic properties of the alloy were studied by using an a. c. susceptometer. Unaged alloy exhibits a paramagnetic-to-antiferromagnetic transition at 40K. It was observed that the transition temperature of bulk alloy varied systematically with ageing time and temperatures. The phenomenon was suggested to be related to the precipitation of various intermetallic phases. The intermetallic chi-phase was extracted electrochemically from the bulk alloy previously aged at 800°C for 500 hours. Magnetic susceptibility of the extracted residues was measured using various fields and driving frequencies. Magnetic transition was observed at around 1 lOK. Transition temperature of chi-phase was found to be field and frequency sensitive. A survey of literature shows that the magnetic properties of the chi-phase has never been studied. This work represents the first ever research effort on the magnetic properties of this intermetallic phase.
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