Phase transformations in aged CF 8 and CF 8M stainless steels

Conference · Thu Jan 01 04:00:00 EST 1987

OSTI ID:6376792

Bentley, J; Miller, M K

The mechanical properties of CF 8 and CF 8M cast stainless steels used for the primary coolant pipes in pressurized light-water nuclear reactors (service temperature about 300C) may be degraded by extended aging at 300 to 400C. Of particular concern is the dramatic loss in impact properties to approximately 15% of the initial value. The cast steels have a duplex microstructure consisting of austenite (el) with 15 to 20% delta-ferrite. The ferrite increases the yield strength and reduces the susceptibility to hot cracking. During aging, the ferrite decomposes spinodally into a fine scaled interconnected network of iron-rich phase and chromium-enriched ' phase. In addition, fine particles of G-phase, a complex silicide, are formed in the ferrite. In some cases, extensive carbide formation at el-delta interfaces occurs. These fine scale phase transformations are believed to be responsible for the degradation of mechanical properties. This paper describes the results of microstructural analysis by atom-probe field-ion microscopy and analytical electron microscopy which provide a powerful combination for a complete characterization of these steels for reliable structure-property correlations.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6376792
• Report Number(s): CONF-870733-7; ON: DE87012522
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
AGING
ALLOYS
CARBON ADDITIONS
CHROMIUM ALLOYS
CORROSION RESISTANT ALLOYS
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
FERRITE
ION MICROSCOPY
IRON ALLOYS
IRON BASE ALLOYS
MICROSCOPY
MICROSTRUCTURE
PHASE TRANSFORMATIONS
STAINLESS STEELS
STEELS
TRANSMISSION ELECTRON MICROSCOPY