skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Creep Behavior of a New Cast Austenitic Alloy

Abstract

A new cast austenitic alloy, CF8C-Plus, has been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar for a wide range of high temperature applications including diesel exhaust components and turbine casings. The creep strength of the CF8C-Plus steel is much greater than that of the standard cast CF8C stainless steel and is comparable to the highest strength wrought commercial austenitic stainless steels and alloys, such as NF709. The creep properties of CF8C-Plus are discussed in terms of the alloy design methodology and the evaluation of some long-term creep tested specimens (over 20,000 hours). Microcharacterization shows that the excellent creep strength is due mainly to the precipitation of very fine nano-scale and stable MC carbides, without the formation of deleterious intermetallic phases.

Authors:
 [1];  [1];  [1];  [2]
  1. ORNL
  2. Caterpillar Technical Center
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
931256
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: International Journal of Pressure Vessels and Piping; Journal Volume: 84
Country of Publication:
United States
Language:
English
Subject:
creep; austenitic alloys; stainless steels; castings; engineered microstructure; MC carbides

Citation Formats

Shingledecker, John P, Maziasz, Philip J, Evans, Neal D, and Pollard, Michael J. Creep Behavior of a New Cast Austenitic Alloy. United States: N. p., 2007. Web. doi:10.1016/j.ijpvp.2006.09.014.
Shingledecker, John P, Maziasz, Philip J, Evans, Neal D, & Pollard, Michael J. Creep Behavior of a New Cast Austenitic Alloy. United States. doi:10.1016/j.ijpvp.2006.09.014.
Shingledecker, John P, Maziasz, Philip J, Evans, Neal D, and Pollard, Michael J. Mon . "Creep Behavior of a New Cast Austenitic Alloy". United States. doi:10.1016/j.ijpvp.2006.09.014.
@article{osti_931256,
title = {Creep Behavior of a New Cast Austenitic Alloy},
author = {Shingledecker, John P and Maziasz, Philip J and Evans, Neal D and Pollard, Michael J},
abstractNote = {A new cast austenitic alloy, CF8C-Plus, has been developed by Oak Ridge National Laboratory (ORNL) and Caterpillar for a wide range of high temperature applications including diesel exhaust components and turbine casings. The creep strength of the CF8C-Plus steel is much greater than that of the standard cast CF8C stainless steel and is comparable to the highest strength wrought commercial austenitic stainless steels and alloys, such as NF709. The creep properties of CF8C-Plus are discussed in terms of the alloy design methodology and the evaluation of some long-term creep tested specimens (over 20,000 hours). Microcharacterization shows that the excellent creep strength is due mainly to the precipitation of very fine nano-scale and stable MC carbides, without the formation of deleterious intermetallic phases.},
doi = {10.1016/j.ijpvp.2006.09.014},
journal = {International Journal of Pressure Vessels and Piping},
number = ,
volume = 84,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The microstructure of a new and improved high-temperature creep-resistant cast austenitic alloy, CF8C-Plus, was characterized after creep-rupture testing at 1023 K (750 C) and 100 MPa. Microstructures were investigated by detailed scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). Principal component analysis of EDS spectrum images was used to examine the complex precipitate morphology. Thermodynamic modeling was performed to predict equilibrium phases in this alloy as well as the compositions of these phases at relevant temperatures. The improved high-temperature creep strength of CF8C-Plus over its predecessor CF8C is suggested to be due to the modified microstructure andmore » phase stability in the alloy, including the absence of {delta}-ferrite in the as-cast condition and the development of a stable, slow-growing precipitation hardening nitride phase - the tetragonal Z-phase - which has not been observed before in cast austenitic stainless steels.« less
  • Micro- and nanoindentation experiments were conducted to investigate the deformation mechanisms in a Fe79.4Cr13Mo5V1C1.6 (wt. %) cast alloy. This alloy consists of an as cast microstructure mainly composed of austenite, martensite, and a complex carbide network. During microhardness testing, metastable austenite transforms partially into martensite confirmed by electron backscatter diffraction. For nanoindentation tests, two different indenter geometries were applied (Berkovich and cube corner type). Load-displacement curves of nanoindentation in austenitic dendrites depicted pop-ins after transition into plastic deformation for both nanoindenters. Characterizations of the region beneath a nanoindent by transmission electron microscopy revealed a martensitic transformation as an activated deformationmore » mechanism and suggest a correlation with the pop-in phenomena of the load-displacement curves. Furthermore, due to an inhomogeneous chemical composition within the austenitic dendrites, more stabilized regions deform by mechanical twinning. This additional deformation mechanism was only observed for the cube corner indenter with the sharper geometry since higher shear stresses are induced beneath the contact area.« less