Containerless processing of stainless steel
Author(s)Bui, Quoc Cuong, 1974-
Merton C. Flemings.
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The rapid solidification of a Fe-12 wt% Cr-16 wt% Ni alloy in containerless processing conditions was investigated using an electromagnetic levitation facility. High-speed video and pyrometry allowed the study of phase selection and secondary nucleation mechanisms for that alloy as well as measurements of delay times and growth velocities. Double recalescence events were observed for the first time at temperatures near the To temperature of the metastable ferritic phase, defining a value of the critical undercooling for metastable bee nucleation significantly lower than previously reported. Phase selection during recalescence was successfully performed by use of different trigger materials: at temperatures below the bee To , a bee Fe trigger induced the primary nucleation of the metastable bee phase which subsequently transformed into the stable fee phase while an fee Ni trigger caused the nucleation of the equilibrium fee phase. Growth velocities were characterized for the 6 phase growing into the undercooled liquid, the [delta] phase growing into the undercooled liquid and the [gamma] phase growing into the semi-solid primary bee. It was found that a critical undercooling exists at which the growth velocity of the primary ferritic phase is equal to that of the secondary austenitic phase into the primary semi-solid. At undercoolings below this critical value, the equilibrium, can overwhelm the primary a and break into the undercooled liquid. Such a double recalescence event can therefore appear as a single event depending on the geometry of the detection equipment. From this observation, a model based on velocity and delay time arguments was proposed to explain discrepancies with earlier works.
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Vita.Includes bibliographical references (leaves 74-75).
DepartmentMassachusetts Institute of Technology. Department of Materials Science and Engineering
Massachusetts Institute of Technology
Materials Science and Engineering