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

  Introduction to Reduced Activation Ferritic-Martensitic (RAFM) Steels  Status of RAFM Research  Enhancement of RAFM Steels  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   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.

  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&(M

Pa)&

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.

  L. Malerba: Why is radiation embrittlement minimum at 9Cr in FM steels (O14 at 15:00 on Monday)   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

  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]

  Fusion spectra result in extremely higher appm He/dpa ratio than fission spectra, leading to the limit of some elements.

6

Outline

  Introduction to Reduced Activation Ferritic-Martensitic (RAFM) Steels  Status of RAFM Research  Enhancement of RAFM Steels  Summary

0 100 200 300 400 500 6000

100

200

300

400

500

600

700

stre

ss, M

Pa

Temperature (°C)

(RP0.2)min

(Rm)min

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 1000120

140

160

180

200

应力，

MPa

断裂时间，h

-200 -150 -100 -50 0-20020406080100120140160180200220

Abs

orbe

d En

ergy

, J

Temperature, ℃

DBTT ≈ –80°C

Stress rupture results under 600°C

Tensile properties

Fatigue properties

Impact properties

Fracture toughness Rupture time, h

Stre

ss, M

Pa

Fatigue Properties of CLAM

1000000 1E7

230

240

250

260

270

280

290

300

310 550? 450?

Stre

ss a

mpl

itude

(MP

a)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 )

Tota

l axi

al st

rain

rang

e (%

)

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   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--11UUnnIIrrrr ((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--11UUnnIIrrrraaddiiaatteedd CCTT SSppeecciimmeennss

CIEMAT-0.5TNRG-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 Curve5% confidence95% confidence

KJC

(1T)

, MPa

√m

Temperature, °C

KJC(1T) = 30+70 Exp(0.019(T-To))(To = -95 °C)

5%

95%

  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

  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

  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.

  Richard Kurtz/PNNL: High dose He & dpa effects on microstructure and deformation mechanisms in RAFM and NFA (P8 at 09:10 on Wednesday).

  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).

  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

  Temperature: 480oC (DRAGON-I)   Flow rate : 0.10m/s   Samples : CLAM (0408B)   Test time : 10,000 h

  Temperature: 550°C (PICOLO)   Flow rate : 0.1m/s   Samples : CLAM and Eurofer   Test time : 12,000 h

î Corrosion rate of ~18.5 µm/yr at 480oC and ~220 µm/yr at 550oC (0.1 m/s), a little lower than that of Eurofer.

  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

  Ji-Ming Chen: Material development for ITER TBM and beyond in China (P7 at 08:30 on Wednesday).

  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=5D1

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  

OOuuttlliinnee

  Introduction to Reduced Activation Ferritic-Martensitic (RAFM) Steels  Status of RAFM Research  Enhancement of RAFM Steels  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

  Po4-02 (J. Hoffmann, et al.): Improvement of mechanical and microstructural properties of Eurofer through TMT   Po1-17 (U. Jäntsch, et al.): TEM at

samples of TMT-ed RAFM steels   O21 at 12:00 on Tue. (Y.B. Chun,

et al.): Influence of TMT on microstructure and mechanical properties of ARAA   Effect of non-standard heat

treatments on Eurofer97

21  

Highlights

Adjustment  of  EUROFER  proper�es  by  varying  heat  treatment  temperatures    Austeni�sa�on:  980  °C  –  1150  °C    Tempering:  700  °C  –  760  °C  

Tensile  Strength   Creep  Strength  Charpy  Proper�es  

22

Motivation of CNAs   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-o

n&

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

  Higher Cr23C6 amount results in greater creep rate.

High Cr23C6

Low Cr23C6

[F. Abe, Nature 2003]

Tested at 650°C/140MPa

Bet

ter P

erfo

rman

ce

  Coarse Z-phase forms by consuming fine MX during long-term services.

  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   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.

  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-o

n&

Temperature&(oC)&

M23C6"

Laves"

Z"MX"

""""""""""CNA1"""""""""""CNA2"""""""""""Eurofer97"

Po3-11 on Wednesday

25

Tensile and Creep Resistance of CNAs   CNAs exhibited ~100–300 MPa increases in yield strength compensated by some reductions in ductility as compared with the FM/RAFM steels.

  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&(M

Pa)&

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&(M

Pa)&

Creep&Life&(h)&

this work SS-3 Eurofer97

Gauge Cross-Section

650oC"

600oC"

F82H"

CNA"

26

Microstructure of CNAs   Lath boundary width (λsgb: 200–

500 nm) is comparable to or less than conventional FM/RAFM steels (350–500 nm).

  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).

  Free dislocation density (ρd: 1014 m–2) is comparable to that in FM/RAFM steels.

MX#(DF)(CNA2# Disloca3ons#(WBDF)#

12x12µm

[Klim

enko

v et

al.,

Pro

g.

Nuc

l. E

ner.

(201

2)]

Eurofer97

σ sgb ≈≈10Gb / λsgb

σ i ≈≈ aMGb dini

σ d ≈≈ 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   CNA1 (primarily MN) exhibited USE and DBTT comparable to Grade 91.

  CNA2 and CNA3 (primarily MC) showed significantly increased USE with comparable or lower DBTT as compared with Grade 91.

  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   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.

  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]