Phase transformations in aged CF 8 and CF 8M stainless steels
Abstract
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.
- Authors:
- Publication Date:
- Research Org.:
- Oak Ridge National Lab., TN (USA)
- OSTI Identifier:
- 6376792
- Report Number(s):
- CONF-870733-7
ON: DE87012522
- DOE Contract Number:
- AC05-84OR21400
- Resource Type:
- Conference
- Resource Relation:
- Conference: Pacific workshop and meeting on analytical electron microscopy, Kona, HI, USA, 12 Jul 1987; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 36 MATERIALS SCIENCE; STAINLESS STEELS; AGING; PHASE TRANSFORMATIONS; FERRITE; ION MICROSCOPY; MICROSTRUCTURE; TRANSMISSION ELECTRON MICROSCOPY; ALLOYS; CARBON ADDITIONS; CHROMIUM ALLOYS; CORROSION RESISTANT ALLOYS; CRYSTAL STRUCTURE; ELECTRON MICROSCOPY; IRON ALLOYS; IRON BASE ALLOYS; MICROSCOPY; STEELS; 360102* - Metals & Alloys- Structure & Phase Studies
Citation Formats
Bentley, J, and Miller, M K. Phase transformations in aged CF 8 and CF 8M stainless steels. United States: N. p., 1987.
Web.
Bentley, J, & Miller, M K. Phase transformations in aged CF 8 and CF 8M stainless steels. United States.
Bentley, J, and Miller, M K. 1987.
"Phase transformations in aged CF 8 and CF 8M stainless steels". United States.
@article{osti_6376792,
title = {Phase transformations in aged CF 8 and CF 8M stainless steels},
author = {Bentley, J and Miller, M K},
abstractNote = {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.},
doi = {},
url = {https://www.osti.gov/biblio/6376792},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 1987},
month = {Thu Jan 01 00:00:00 EST 1987}
}