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Accession Number:
ADA114716
Title:
FCC and BCC Solidification Products in a Rapidly Solidified Austenitic Steel.
Descriptive Note:
Technical rept. Oct 80-Sep 81,
Corporate Author:
MASSACHUSETTS INST OF TECH CAMBRIDGE
Report Date:
1981-12-01
Pagination or Media Count:
8.0
Abstract:
The microstructures and local composition variations in centrifugally atomized high-sulfur stainless steel powder are investigated. Both fcc and bcc are found to be primary solidification phases in the as-solidified powder of this nominally austenitic steel where the smaller powder particles approx. 70 micron diameter tend to be bcc. Cellular solidification structures, with sulfide precipitates 100 to 200 nm diameter in size at the cell walls, are observed in both fcc and bcc particles. The bcc structure, however, has many small sulfide precipitates 10 to 20 nm diameter in the cell interior with few larger sulfide precipitates at the cell walls. The small precipitates, observed only in the bcc structures, form on cooling from a supersaturated solid solution that results from reduced solute partitioning during solidification. partitioning of chromium and nickel is minimal in these cellular structures. A non-cellular bcc structure is also observed with small sulfide precipitates throughout the entire structure. This non-cellular bcc structure results from smooth-front massive solidification. Analysis of the nucleation process for solidification indicates that a transition from fcc nucleation to bcc nucleation occurs with increasing wetting angle in heterogeneous nucleation. Thus bcc should nucleate in the smaller droplets of a liquid dispersion where catalytic surfaces of low potency large wetting angle tend to be the only heterogeneous nucleants available. Author
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
