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Thursday, October 17

Production of Stainless Steel for High-Temperature Reactor Uses

Iver E. Anderson, Ames Laboratory, Ames, Iowa
ASM Oak Ridge Chapter Meeting
5:30 PM — 8:00 PM, Rothchild's Conference Center, 8807 Kingston Pike, Knoxville
Contact: Lindsay Kolbus (kolbuslm@ornl.gov), 865.368.3603

Abstract

Abstract:
Oxide dispersion strengthened (ODS) ferritic stainless steel microstructures were processed by a simplified powder-based method that was recently developed at Ames Laboratory, to replace mechanical alloying and extensive hot working that proved too costly for commercial use. Precursor ferritic powders were oxidized in situ using gas atomization reaction synthesis to form a kinetically favored (i.e., typically Cr-enriched) metastable surface oxide, encapsulating the as-atomized powders and serving as a distributed reservoir for an oxygen addition. In the reactive sintering step, this surface layer became a source for oxygen to diffuse into the as-consolidated alloy microstructure when heat treatments promoted oxygen exchange (driven by thermodynamic stability differences) between metastable prior particle boundary oxides and dissolved Y and secondary additions. These exchange reactions produced nano-metric Y-enriched oxide dispersoids that vary in composition depending on the type of secondary oxide dispersoid forming element, e.g., Ti or Hf, that form on the site of previously formed (during droplet solidification) intermetallic phases. It also will be shown that the size, spatial distribution, and thermal stability of the oxide dispersoids depends on the "parent" intermetallic phases and, by extension, the secondary elements. Subsequent thermal-mechanical processing that promoted strengthening by sub-grain formation and recovery processes also was demonstrated. Transmission electron microscopy, high-energy X-ray diffraction, and 3-D atom probe helped characterize the powders and dispersoid evolution to quantify the thermal stability of the composite microstructures. This microstructure analysis and some initial high temperature tensile test results also indicated progress toward tolerance of ultra-high combustion temperatures, along with the potential for radiation tolerance.

About the Author:
Dr. Anderson is a Senior Metallurgist at Ames Laboratory and an ASM 2012-2015 Trustee.