cf8c plus: a new cast stainless steel for high-temperature diesel
TRANSCRIPT
CF8C-Plus: A New Cast Stainless
Steel for High-Temperature Diesel
Exhaust Components
P.J. Maziasz, and J.P Shingledecker
Oak Ridge National Laboratory, and
M.J. Pollard
Caterpillar Technical Center
Research sponsored by the Heavy Vehicle Propulsion
Materials Program, DOE Office of FreedomCAR and
Vehicular Technology Program, under contract
DE-AC05-00R22725 with UT-Battelle, LLC
CF8C-Plus cast stainless steel was developed to provide higher temperature capability and reliability for
advanced diesel engine
• Cast stainless upgradefor SiMo cast-iron diesel engine exhaust components
turbo-housing
exhaust manifold
C-15, 14.6L HD On-Highway Diesel Engine
Materials Need: High Performance Low-Cost Alloy was Needed to Replace SiMo Cast Iron
Some Candidate Alloy Compositions (wt%)Some Candidate Alloy Compositions (wt%) • SiMo Cast Iron: Fe-3.45C-4Si-0.6Mo-0.3Mn • CF8C: Fe-19Cr-10Ni-0.07C-1.0Nb-0.7Mn-1Si • CF8C-Plus: Fe-19Cr-12Ni-0.07C-0.07Nb-0.4Si-+Mn+N • Ni-Resist: Fe-2Cr-35Ni-0.5Mn-5Si-1.9C
Improving the properties of less expensive alloys without the costly addition of Ni offered the best opportunity
CF8C-Plus = Best Results
Alloy Development: Mn and N were the “Plus” added to improve austenite stability
• Lower cost Mn and N were added instead of costly Ni for fully austenitic stainless steel
• CF8C = 15-25% Delta Ferrite, CF8C-Plus = 0% Delta Ferrite
CF8C-Plus Cast Stainless Steel won a 2003 R&D100 Award for Outstanding Heat-Resistance at 850oC, and
Successful Commercial Scale-Up in only 1.5 years
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60
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300
18,000 20,000 22,000 24,000 26,000 28,000
CF8C CF8C-Plus SiMo Cast Iron Ni-Resist
STR
ESS
(MPa
)
LMP (C=20)
CF8C CF8C-Plus
SiMo Cast Iron
Ni-Resist
LMP (Larson-Miller Parameter) is calculated using creep-rupture time and temperature
Creep-Rupture at 550-850oC
Engineered Microstructure • CF8C-Plus Has “Super” Creep Resistance at 850oC
Because Abundant, Stable Nano-NbC Precipitates Pin Dislocations
(TEM, as cast)
500 nm
Creep Tested 850°C/500 h
NbC
CF8C-Plus
500 nm
Creep Tested 850°C/23,000 h
NbC
Std CF8C
CF8C-Plus Has Great Castability for Defect-Free Parts
• CF8C-Plus (<0.5Si) shows as-good or better fluidity compared to CF8M (1.5Si) at equivalent pour temperatures
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25
30
35
Leng
th, i
n.
2500 2600 2700 2800 2900 3000 Pour Temperature, F
CF8C Plus #1 CF8C Plus #2 CF8M
Fluidity
From Ron Bird, Stainless Foundry and Engineering
CF8C-Plus Fluidity Spiral:
•Round-top trapezoid, 3/8” w (bottom), ¼” w (top), ¼” high •Length = linear length of spiral
Better
In May, 2007, CF8C-Plus was submitted to ASTM for approval of a new heat-
resistant cast alloy grade – HG10MNN
Welds of CF8C-Plus passed U-bendDuctility test (SF&E)
Welds of CF8C-Plus passed RT tensiletests for UTS and ductility, with 20%Better YS than base metal
Commercial Applications – Direct Replacement of NiResist for Natural Gas Reciprocating Engines at Reduced
Cost (Cost of CF8C-Plus = 80% of NiResist)
45 lb static sand-cast CF8C-Plus exhaust component castby Stainless Foundry and Engineering, Inc.
Caterpillar is now using CF8C-Plus steel for the CRS components which are on all heavy-duty
highway truck diesel engines in 2007
CF8C-Plus steel
SiMo Cast-iron
• Exhaust combustor (turbo exhaust + injected fuel) to clean out particulate filters: high temperature and rapid cycling conditions
New Work on Step-Castings to get mechanical properties data on thin-sections, to support turbocharger
and manifold applications
ORNL is using step-castings of CF8C-Plus and CF8C-Plus Cu/W to measure mechanical properties of the thin sections
representative of heavy-diesel exhaust components
• Stainless Foundry & Engineering made step castings of CF8C-Plus and CF8C-Plus Cu/W in late 2006
CF8C-Plus thin sections have YS as good or better than thicker sections
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0 200 400 600 800 1,000
400 800 1200 1600
CF8C: YS CF8C: UTS CF8C-Plus: YS CF8C-Plus: UTS
CF8C-Plus Step Cast: YSCF8C-Plus Step Cast: UTSCF8C-Plus+Cu/W Step Cast: YSCF8C-Plus+Cu/W Step Cast: UTS
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STR
ESS
(MP
a)
TEMPERATURE (oC)
TEMPERATURE (oF)
STR
ESS
(ksi
)
YS CF8C-Plus Cu/W
0
0.5
1
1.5
2
0 200 400 600 800 1,000
CR
EEP
STR
AIN
(%)
TIME (hrs)
1.0%
0.5%
CF8C-Plus Cu/W has improved creep resistance compared to CF8C-Plus
• Good creep resistance in thin-section casting is important for turbochargerand manifold applications
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0 200 400 600 800 1,000 1,200 1,400 1,600
CF8C-Plus CF8C-Plus+Cu/W
CR
EEP
STR
AIN
(%)
TIME (hrs)
Step Castings (1/2" Thick) Creep Test: 800 oC 75MPa
Conclusions for New CF8C-Plus cast austenitic stainless steel
• Castable, even as thin sheets • Weldable • Outstanding Creep Performance • Cost-Effective • Applications
– Caterpillar CRS components (on-highway in 2007) – Exhaust components for NG engines – Turbocharger housings – Numerous other potential spin-offs