ORNL is managed by UT-Battelle for the US Department of Energy
RAFM Steels: Status and Enhancement for High-Temperature
Performance
L. Tan and Y. Katoh
Oak Ridge National Laboratory, USA
A.-A.F. Tavassoli
DMN/Dir, DEN, CEA, France
M. Rieth
Karlsruhe Institute of Technology, Germany
H. Tanigawa
Japan Atomic Energy Agency, Japan
Q. Huang
Institute of Nuclear Energy Safety Technology, China
ICFRM-17 | Aachen, Germany | 12-16 October 2015 Acknowledge all the persons who involved and contributed
to the tests and ideas during the R&D activities and the financial support by the respective funding sources in each county.
2
Outline
U Introduction to Reduced Activation Ferritic- Martensitic (RAFM) Steels
U Status of RAFM Research
U Enhancement of RAFM Steels U Summary
For Fe-based steels and alloys, many talks on ODS/NFA are given at this conference. There are also a few talks on some new types of alloys for potential use in fusion reactors, such as
Bainitic steels (O41 Wed.) and FeCrAl alloys.
This talk focuses on RAFM steels.
Po4-05 on Thursday
3
Development of RAFM Steels
U USA, Japan, and European Union initiated development of RAFM steels in 1980s, and came up with respective alloys such as 9Cr-2WVTa, F82H, and Eurofer97 (adopted in 1997). China, India, Korea, etc. started
relevant R&D activities afterwards.
U Despite comparable tensile properties as compared with the ASME
codified Grade 91, RAFM steels have significantly lower creep strength at temperatures above ~500°C.
0"
100"
200"
300"
400"
500"
600"
0" 200" 400" 600" 800"
Yield&Stress&(MPa)&
Temperature&(oC)&
Eurofer97"
F82H"
P91"
Eurofer97:"Rieth,"FZKA"6911"(2003)"
F82H:"Tavassoli,"et."al."FED"(2002)"
P91:"NIMS"Creep"Data"Sheet"
4
Typical Compositions of Representative RAFM Steels as Compared to T91
Element (1) T91 9Cr-2WVTa (2) F82H-BA07 (3) Eurofer97-2 (4) CLAM (5) CNAs (6)
C 0.09 0.11 0.09 0.11 0.10 0.08-0.12
N 0.044 0.021 0.017 0.038 0.04 <0.06
Cr 8.70 8.90 8.00 8.95 8.76 8.3-8.8
Mn 0.35 0.44 0.46 0.55 0.42 <1.0
V 0.22 0.23 0.19 0.20 0.22 0.10-0.25
W 2.01 1.88 1.04 1.40 1.0-1.5
Ta 0.06 0.04 0.14 0.16 0.05-0.15
Si 0.29 0.21 0.17 0.05 <0.2
Ti <0.003 <0.15
Nb 0.072 <0.01 <0.005 0.004 <0.01
Mo 0.90 0.01 <0.01 0.005 <0.01
Ni 0.28 <0.01 <0.01 0.03 <0.01
(1) All the elements have specific ranges for different steels. Other elements set to minimal, e.g., P/S/O/B/Al/Cu/Co/Zr/As/Sn/Sb.
(2) USA ORNL heat 3791.
(3) F82H-BA07 has ~2X of Ta and N as compared with the ITER-grade.
(4) Eurofer97-2 version (heat 993402) has ~2X of N in Eurofer97 (0.02).
(5) China Low-Activation Martensitic (CLAM), heat 1105.
(6) Cast nanostructured alloys (CNAs) – advanced RAFM steels developed at ORNL.
U L. Malerba: Why is radiation embrittlement minimum at 9Cr in FM steels (O14 at 15:00 on Monday)
U Q. Huang: Overall progress and strategy of the CLAM project for ITER- TBM procurement (O16 at 15:40 on Monday)
5
Limits on Alloying Elements and Impurities
U Restriction by disposal and recycle limits:
– Mo, Ag, and Nb
proved to be the most important of the
restricted elements.
0" 5" 10" 15" 20"
Nb"
V"
Mo"
Ti"
316SS"
Al"
appm$He/dpa$
Fission"Spectra"
Fusion"Spectra"
[After G.L. Kulcinski of Univ. of Wisconsin]
[R.L. Klueh, et al., JNM 280 (2000) 353]
U Fusion spectra result
in extremely higher
appm He/dpa ratio
than fission spectra,
leading to the limit of
some elements.
6
Outline
U Introduction to Reduced Activation Ferritic- Martensitic (RAFM) Steels
U Status of RAFM Research
U Enhancement of RAFM Steels
U Summary
0 100 200 300 400 500 600 0
100 200 300 400 500 600 700
stress, MPa
Temperature (°C)
(RP0.2)min (Rm)mi n
Sm
Mechanical Properties of CLAM
q Fabrication technology has been mature.
q All-around mechanical property tests are in progress.
− Tensile (>700 specimens)
− Impact properties (>1,000, ~100 curves)
− Fracture toughness (~40 specimens )
− Fatigue properties (LCF/HCF) (~200 specimens)
− Creep Properties (>8,000 hrs, ~150 specimens)
10 100 1000
120 140 160 180 200
应力，MPa
断裂时间，h
-200 -150 -100 -50 0
-20 0 20 40 60 80 100 120 140 160 180 200 220
Absorbed Energy, J
Temperature, ℃
DBTT ≈ –80°C
Stress rupture results under 600°C
Tensile properties
Fatigue properties Impact properties
Fracture toughness
Rupture time, h Stress, MPa
Fatigue Properties of CLAM
1000000 1E7
230 240 250 260 270 280 290 300
310 550?
450?
Stress amplitude (MPa)
fatigue life (N)
1000 10000 100000
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
INEST(RT) IMR(RT) INEST(450 ) INEST(550 )
Total axial strain range (%)
Number of cycle to failure (Nf)
Low cycle fatigue (LCF) at different temperature High cycle fatigue (HCF) at different temperature
æ With the test temperature increases, fatigue life was slightly decreased under LCF, but significantly
decreased under the HCF condition.
Creep Properties of CLAM
Creep curve at 550°C Minimum creep rate vs. Stress
at 550 and 600°C Coarse M23C6 after creep test at 550°C for 1595h
æ The creep property of CLAM steel was similar to that of Eurofer97.
A series of creep tests were carried out at 500, 550, 600 and 650°C with stresses of 150–300 MPa (~200 specimens).
Mechanical proper�es of 20t-‐F82H Plates with Different Thicknesses
Tensile and Charpy impact proper�es of plates with difference thicknesses from 18 to 100 mm, which were made from F82H-‐BA12 heat melted in a 20 tons electric arc furnace.
No significant thickness dependence was observed in tensile property, but Charpy impact property degraded with increasing thickness of plate.
Tensile proper�es (Ttest=RT) Charpy impact proper�es
H. Sakasegwa /JAEA, Presented at ISFNT12 2015
Thermal Aging Effect on Impact Toughness
æ Aging-induced increase of DBTT and decrease of USE of CLAM is consistent with the F82H-IEA at 600°C, but not consistent at 650°C.
600°C
650°C
[Full-size L-T orientation F82H- IEA: K. Shiba, et al., Fus. Eng.
Des. 86 (2011) 2895.]
–63 J
+40°C –20 J
+30°C
12
Fracture Toughness of Eurofer97 at Transition Region
U The code RCC-MRx edition 2015 for Eurofer97 validates the full materials properties (irradiated section will be included in the next edition).
0 50 100 150 200 250 300 350 400
-200 -150 -100 -50
EEuurrooffeerr 9977--11 UUnnIIrrrr ((EEPPFFLL && NNRRGG))
KJC (1T), MPa√m
Temperature, °C KJC(1T) = 12+88 Exp(0.019(T-To)
(To = -90 °C) 0
100 200 300 400 500
-200 -150 -100 -50
EEuurrooffeerr 9977--11
UUnnIIrrrraaddiiaatteedd CCTT SSppeecciimmeennss
CIEMAT-0.5T NRG-0.2T (8 mm) NRG-0.2T (14 mm) NRG-0.2T (25 mm) NRG-0.4T (14 mm) NRG-0.4T (25 mm) EPFL-0.35T (L-T) EPFL-0.35T (T-L) EPFL-0.87T (L-T) Master Curve 5% confidence 95% confidence
KJC (1T), MPa√m
Temperature, °C
KJC(1T) = 30+70 Exp(0.019(T-To)) (To = -95 °C)
5%
95%
U The updated tests of fracture toughness indicate that the lower bound curve does not adequately cover the scatter of the data, leading to the proposal of using a lower
median curve.
High-Energy Spallation Neutron Irradiation of CLAM
æ ~20dpa high energy spallation neutron irradiation properties of
CLAM are similar to those of the other RAFMs.
Post irradia�on tensile proper�es above 80dpa
Target design window and HFIR irradia�on condi�ons
ü Con�nuous irradia�on hardening was observed above 80 dpa even at 400 and 500 ˚C, where so�ening was observed at the FFTF/MOTA experiment.
RAFM (F82H, etc) Irradia�on experiment JP-‐28 & 29 in HFIR over a period of 8+ years, supported by the U.S. DOE – JAEA Collabora�on on Fusion Materials.
Tensile tests of F82H at irradia�on temp.
500oC 400oC 300oC
Eurofer97 BOR60@330°C
U T. Hirose/JAEA: I21 at 11:00 on Tue.
15
Effect of He on RAFM
O56 at 15:10 on Wednesday
Po1-66 on Monday
U Effect of He on 9Cr-2WVTa (USA) has been studied by doping 2 wt% Ni-58 and Ni-60 isotopes. They were irradiated in HFIR to >80 dpa at 300–500°C through the U.S. DOE–JAEA Collaboration.
U Richard Kurtz/PNNL: High dose He & dpa effects on
microstructure and deformation mechanisms in RAFM and NFA (P8 at 09:10 on Wednesday).
U Yong Dai/PSI: Deformation mechanisms of FM after irradiation to a wide dpa and He range in spallation neutron targets (I14 at 14:30 on Monday).
U ORNL and KIT are collaborating on investigating the effect of He on Eurofer97 and CNAs by
alloying 54Fe isotope in the two types of alloys to be irradiated in HFIR.
Long-term Corrosion Test in Flowing Pb-Li
Po2-14 on Tuesday
U Temperature: 480oC (DRAGON-I) U Flow rate : 0.10m/s
U Samples : CLAM (0408B) U Test time : 10,000 h
U Temperature: 550°C (PICOLO) U Flow rate : 0.1m/s
U Samples : CLAM and Eurofer U Test time : 12,000 h
î Corrosion rate of ~18.5 µm/yr at 480
oC and
~220 µm/yr at 550
oC (0.1 m/s), a little lower than that of Eurofer.
U Compared to the 475°C limit for DCLL blanket, preliminary study indicates FeCrAl alloy can work at 550°C and up to 800°C in Pb-Li.
CLAM: Z. Jiang – O86 at 9:10 on Friday.
§ First Wall § Cover and Cooling Plates
Fabrication Technologies for TBM
v Fabrication of key components of blankets using the EB and HIP welding
v Blanket Module Assembling
Cover Plates
Cooling Plates
§ Fabrication of 1/3 scale DFLL-TBM
ü Validation of the welding and assembly techniques
ü Validation of the feasibility of the assembly procedure
æ The key technologies for TBM fabrication have been successfully tested and developed.
1/3-scale DFLL-TBM
U-type plates and tubes EB welding
Water and Gas Elimination HIP welding
U Ji-Ming Chen: Material development for ITER TBM and beyond in China (P7 at 08:30 on Wednesday).
U Arun Kumar Bhaduri: RAFM steel and fabrication technologies for the Indian TBM for ITER-issues and challenges (O94 at 11:20 on Friday).
Evalua�on of HIP joint in first wall mockup
HIP: 1100°C /150 MPa
Normalizing (PHHT) at 960°C, tempering as second PHHT at 750°C.
T. Hirose, et al., Fusion Eng. Des. 83 (2008) 1176
D0=5 D1
6
11 3
R0.5
6SQ-‐5D w/ hole
Unit: mm
3mm thick torsion specimens were machined out from HIP joints between cooling channels of a HIPed First wall component, and evaluated successfully.
Trial HIP joint component
Hardening of the base metal seemed to be suppressed by the presence of the HIP
joint, causing ~22%
reduc�on of total work during torsion process.
Base metal: τyield=425MPa, τmax=565MPa HIP joint: τyield=458MPa, τmax=564MPa
T. Nozawa /JAEA, Presented at ASTM-‐SSTT 2014
O
Ouuttlliinnee
U Introduction to Reduced Activation Ferritic- Martensitic (RAFM) Steels
U Status of RAFM Research
U Enhancement of RAFM Steels
U Summary
Advanced Steels
Ø Steels for Water Cooling
u 4 new heats produced, characterisation started
Ø Steels for High Temperature Applications
u Alternative heat treatment and TMT on EUROFER à VERY SUCCESSFUL !!!
u 14 new heats produced, characterisation started
20
EUROfusion – WPMAT Progress/Status
O22 at 12:20 on Tuesday U Po4-02 (J. Hoffmann, et al.):
Improvement of mechanical and microstructural properties of Eurofer through TMT
U Po1-17 (U. Jäntsch, et al.): TEM at samples of TMT-ed RAFM steels U O21 at 12:00 on Tue. (Y.B. Chun,
et al.): Influence of TMT on microstructure and mechanical properties of ARAA
U Effect of non-standard heat treatments on Eurofer97
21
Highlights
Adjustment of EUROFER proper�es by varying heat treatment temperatures
U Austeni�sa�on: 980 °C – 1150 °C U Tempering: 700 °C – 760 °C
Tensile Strength Creep Strength Charpy Proper�es
22
Motivation of CNAs
U The significant recovery of T91 at 600°C and 100 MPa suggests that the less amount of MX in the current RAFM steels (e.g., Eurofer97) would have worse resistance to recovery.
0"
0.01"
0.02"
400" 600" 800" 1000" 1200" 1400"
Phase&Mole&Frac-on&
Temperature&(oC)&
M23C6"
Laves"
Z" MX"
""""""""""T91"
""""""""""Eurofer97"
T91@600°C/100MPa/34,141h
[K. Kimura, et al., Key Eng. Mater.
171-174 (2000) 483]
Noticeable aging-induced softening in F82H-IEA at T > 500°C.
[K. Shiba, et al., Fus. Eng. Des.
86 (2011) 2895.]
23
U Higher Cr
23C
6amount results in greater creep rate.
High Cr23C6
Low Cr23C6 [F. Abe, Nature 2003]
Tested at 650°C/140MPa
Better Performance
U Coarse Z-phase forms by consuming fine MX during long-term services.
U Laves phase coarsening degrades strength.
/70MPa
[K. Sawada, MST 2013]
[Q. Li, Metall Mater Trans A 2006]
637°C
Early stage (Fine Laves)
Long-term (Coarse Laves)
Fe2(Mo,W)
Stress accelerates the replacement of MX by Z-phase.
Concerns of Current 9-12Cr FM Steels
(V/Nb/Ta)N Cr(V/Nb/Ta)N
T91 T92
V, wt% 32.4 34.8
Cr 44.0 44.2
Nb 19.4 16.3
Fe 4.2 4.7
@600°C 34,141h 39,540h Size 166 nm 155 nm Fraction 0.7% 0.3%
[K. Sawada, et. al. ISIJ Inter. 46 (2006) 769.]
24
Design of Strengthening Precipitates
U The superior stability of TaC under thermal, stress, and irradiation as
compared with TaN and VN, inspired the development of MC-strengthened in
compared with MN-strengthened CNAs.
U The CNAs are designed to have
– Increased MX, e.g., MN (with Z-phase) in CNA1 and MC (without Z-phase) in CNA2;
– Reduced M23C6;
– Comparable amount Laves phase.
[L. Tan, et al. J. Nucl. Mater. 445 (2014) 104; Acta Mater. 71 (2014) 11]
(c) VN (b) TaN
(a) TaC 20 dpa 20 dpa 20 dpa
0"
0.01"
0.02"
400" 600" 800" 1000" 1200" 1400"
Phase&Mole&Frac-on&
Temperature&(oC)&
M23C6"
Laves"
Z"
MX"
""""""""""CNA1"
""""""""""CNA2"
""""""""""Eurofer97"
Po3-11 on Wednesday
25
Tensile and Creep Resistance of CNAs
U CNAs exhibited ~100–300 MPa increases in yield strength compensated by some reductions in ductility as compared with the FM/RAFM steels.
U Creep at 650°C showed superior creep resistance of CNAs as compared with Eurofer97 and F82H.
0"
10"
20"
30"
40"
50"
60"
70"
80"
90"
100"
0"
100"
200"
300"
400"
500"
600"
700"
800"
0" 200" 400" 600" 800"
Total&Elonga*on&(%)&
Yield&Stress&(MPa)&
Temperature&(oC)&
Eurofer97"
CNA2"
F82H"
CNA1"
P91"
CNA3"
SS-3 (this work) Eurofer97 (FZKA6911) Gauge Cross-Section
0"
20"
40"
60"
80"
100"
120"
140"
160"
180"
10" 100" 1000" 10000"
Stress&(MPa)&
Creep&Life&(h)&
this work SS-3 Eurofer97
Gauge Cross-Section
650oC"
600oC"
F82H"
CNA"
26
Microstructure of CNAs
U Lath boundary width (λsgb: 200–
500 nm) is comparable to or less than conventional FM/RAFM steels (350–500 nm).
U MX nanoprecipitate (di: ~5 nm) density (ni: 1022 m-3) in CNA2 is two orders of magnitude higher than that in Eurofer97 (≥~20 nm;
1020 m–3).
U Free dislocation density (ρd: 1014 m–2) is comparable to that in FM/
RAFM steels.
MX#(DF)(CNA2# Disloca3ons#(WBDF)#
12x12µm
[Klimenkov et al., Prog. Nucl. Ener. (2012)]
Eurofer97
σsgb ≈≈10Gb / λsgb
σi ≈≈ aMGb dini
σd ≈≈ 0.5MGb ρd
>2X
>1X
~1X
~700 vs. ~500 MPa
~200 vs. ~80 MPa
~300 vs. ~300 MPa
~780 vs. ~580 MPa ~200MPa
27
Charpy Impact Toughness of CNAs
U CNA1 (primarily MN) exhibited USE and DBTT comparable to Grade 91.
U CNA2 and CNA3 (primarily MC) showed significantly increased USE with comparable or lower DBTT as compared with Grade 91.
U The CNAs and FM steel have remarkably higher USE as compared to the general value of 12-14Cr ODS/NFA.
0"
10"
20"
30"
40"
50"
60"
70"
80"
+150" +100" +50" 0" 50" 100" 150" 200"
Energy,"J"
Temperature,"oC"
G91"
CNA3"
CNA2"
ODS/NFA"
CNA1"
5"mm"
5"mm" 4"mm"
28
Radiation Hardening and Softening of CNA1
U HFIR irradiation of CNA1, primarily strengthened by (V,Ta)N, exhibited
– Slight hardening at 300°C with negligible changes in total elongation.
– Significant softening with increased total elongations at 500 and 650°C.
U The behavior is generally consistent with the modified Grade 92 FM steels under the same irradiation conditions, as well as CLAM (HFETR irradiation) at 300°C.
[Courtesy of T.S. Byun of PNNL]
