Solidification of undercooled Fe-Cr-Ni alloys: Part I. Thermal behavior |
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Authors: | Toshihiko Koseki Merton C Flemings |
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Affiliation: | (1) Steel Research Laboratories, Nippon Steel Corporation, Futtsu, 293 Chiba, Japan;(2) Department of Materials Science and Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA |
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Abstract: | Solidification of undercooled Fe-Cr-Ni alloys was studied by high-speed pyrometry during and after recalescence of levitated,
gas-cooled droplets. Alloys were of 70 wt pct Fe, with Cr varying from 15 to 19.7 wt pct, balance was Ni. Undercoolings were
up to about 300 K. Alloys of Cr content less than that of the eutectic (18.1 wt pct) have face-centered cubic (fee) (austenite)
as their equilibrium primary phase, and alloys of higher Cr content have body-centered cubic (bcc) (ferrite) as their equilibrium
primary phase. However, except at low undercoolings in the hypoeutectic alloys, all samples solidified with bcc as the primary
phase; the bcc then transformed to fcc during initial recalescence for the lower Cr contents or during subsequent cooling
for the higher Cr contents. The bcc-to-fcc transformation, whether in the semisolid or solid state, was detected by a second
recalescence. In the hypoeutectic alloys, the growth of primary metastable bcc apparently results from preferred nucleation
of bcc. The subsequent nucleation of fcc may occur at bcc/bcc grain boundaries.
Formerly Graduate Student, Department of Materials Science and Engineering, Massachusetts Institute of Technology |
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