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NEET FY 12 Project
Accelerated Development of Zr-Containing New Generation Ferritic Steels
for Advanced Nuclear Reactors Lizhen Tan
Materials Science and Technology Division Oak Ridge National Laboratory
DOE-NE Materials Crosscut Coordination Meeting
August 20, 2013
Tasks and Team Members
n Team Members – Lizhen Tan and Ying Yang (ORNL) – Todd Allen and Kumar Sridharan (UW-Madison)
n Tasks
Alloy Design Thermodynamic database development (Yang) Alloy design & fabrication (Tan, Yang)
Recommendation
Yes
Yes
Testing & Characterization Mechanical testing (Tan)
Microstructural characterization (Tan) Microstructural simulation (Yang)
Radiation Resistance Proton and heavy ion irradiations (Allen/Sridharan, Tan) Microstructure and hardness (Sridharan, Tan)
No
No
The Need for Advanced Material Development
n The escalating global clean-energy need drives higher operating temperatures of power plants for improved thermal efficiency.
n Advanced materials with superior high-temperature strength can effectively improve plant economics (reduced commodities, increased thermal efficiency, longer lifetimes), safety margins, and design flexibility.
200 mm Dia.593.3°C32 MPa~320°C
~50%
Ferritic Steels Have Outstanding Properties for Engineering Design
n Ferritic steels are important structural materials for nuclear reactors – Advantages of FM steels over austenitic stainless steels
High resistance to radiation-induced void swelling (e.g., ~10 times better at temperatures above 300°C) High thermal conductivity and
low thermal expansion Low-cost
0 200 400 600 8000
5
10
15
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25
30
35
40
10
15
20
25
30
NF616X20CrMoV121T91
P22
TP316
Ther
mal
Con
duct
ivity
(W/K
m)
Temperature (oC)
P22
T91
NF616
X20CrMoV121
TP316
Mea
n C
oeffi
cien
t of L
inea
r Exp
ansi
on (1
0-6/K
)
500 700 800 600
100
10
1
Ni-base
F/FM Steels
ODS Ferritic Steels
New Steels
Cur
rent
Allo
y C
ost (
$/lb
)
Use Temperature (°C)
Austenitic Steels
[Source: adapted from B.A. Pint]
n Higher Cr23C6 amount results in greater creep rate.
Concerns of The Current FM Steels
High Cr23C6
Low Cr23C6
[F. Abe, Nature 2003]
Tested at 650°C/140MPa
Bet
ter P
erfo
rman
ce
n Coarse Z-phase forms by consuming fine MX.
n Laves phase coarsening deteriorates 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.
n Refine grain size by ZrC Improve strength, toughness, etc. n Reduce the amount of Cr23C6 Improve creep resistance, reduce
sensitization, etc. n Reduce radiation-induced segregation (RIS) Reduce potential
SCC/IASCC. n Form Zr-bearing Laves phase Unclear. n Form new phases, e.g., Fe23Zr6 Unclear.
n Difficulty in alloy impurity control (oxygen): contrary effects – Low enough oxygen à better fracture toughness – High oxygen à poor fracture toughness, ductility, etc.
Potential Effects of Zr Alloying
Approach to Accelerate The Development of Zr-Containing Ferritic Steels
Now/Future: Materials-by-Design; High efficient and low-cost
Past: Trial and Error Method; Time-consuming and expensive
Experiment Microstructure Property
Computational Tools (Software + Database)
Computational Microstructural Modeling
Microstructural Simula�on & Valida�on
Computational Thermodynamics
Kinetics Simulation
Phase stability, frac�on, composi�on
Precipitate size, distribution
CALPHAD (CALculation of PHAse Diagram)
Nucleation, Growth and Coarsening Theory
NEW thermodynamic property (G) and Mobility (D) databases of
the Zr-containing Fe-base system
Science-based approaches
Multicomponent Thermodynamics (CALulation of PHAse Diagram-CALPHAD)
Binary phase diagram Thermochemical Data G=f(T,P,xB)
G=f(T,P,xB,xC) Ternary phase diagram Thermochemical Data
𝐺𝐺=∑↑▒𝑋𝑋𝑋𝑋𝑋𝑋𝐺𝐺𝑋𝑋𝑋𝑋𝑋↑0𝑋𝑋+RT∑↑▒𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋
+𝐵𝐵𝑋𝑋𝑋𝑋𝐵𝐵𝐵𝐵𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋
+𝐵𝐵𝑋𝑋𝑋𝑋𝐵𝐵𝐵𝐵𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋+𝑇𝑇𝐺𝐺𝐵𝐵𝑋𝑋𝐵𝐵𝐵𝐵𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋
+𝐵𝐵𝑋𝑋𝑋𝑋𝐵𝐵𝐵𝐵𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋+𝑇𝑇𝐺𝐺𝐵𝐵𝑋𝑋𝐵𝐵𝐵𝐵𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋 +𝑋𝑋𝑛𝑛𝑛 𝑜𝑜𝐵𝐵𝑜𝑜𝐺𝐺𝐵𝐵 𝐺𝐺↑𝐺𝐺𝐺𝐺𝑋 Thermodynamics Phase diagram
Computational diffusivity
𝐷𝐷𝑋𝐷𝐷𝑋↑∗𝑋=RTM𝐷𝐷 (𝐷𝐷=𝐴𝐴,𝐵𝐵) 𝐷𝐷𝑋𝐷𝐷𝑋=RTM𝑋k𝑋 𝑋𝐷𝐷𝑋; 𝑋𝐷𝐷𝑋=1+𝜕𝜕ln( 𝑓𝑓𝑋𝐷𝐷𝑋)/𝜕𝜕ln( 𝑋𝑋𝑋𝐷𝐷𝑋)𝑋;(𝐷𝐷=𝐴𝐴,𝐵𝐵) 𝐷𝐷𝑋=𝐺𝐺𝐵𝐵𝐷𝐷𝐴𝐴+𝐺𝐺𝐴𝐴𝐷𝐷𝐵𝐵
Computational tools used in this study
Thermodynamic property OCTANT (in-house)
Mobility MCFe (Non-encrypt)
Database
Computational thermodynamics Matcalc 5.51 Pandat 8.0
Precipitation kinetics Matcalc 5.51
Software
OCTANT: ORNL Computational Thermodynamics for Applied Nuclear Technology
Thermodynamic database Fe-C-Cr-Mo-Nb-Ti-W-Zr
C Cr Mo Nb Ti W Zr Fe Fe-C Fe-Cr Fe-Mo Fe-Nb Fe-Ti Fe-W Fe-Zr C C-Cr C-Mo C-Nb C-Ti C-W C-Zr Cr Cr-Mo Cr-Nb Cr-Ti Cr-Ti Cr-Zr Mo Mo-Nb Mo-Ti Mo-W Mo-Zr Nb Nb-Ti Nb-W Nb-Zr Ti Ti-W Ti-Zr W W-Zr
Binaries
Thermodynamic database Fe-C-Cr-Mo-Nb-Ti-W-Zr
Cr Mo Nb Ti W Zr Fe-C Fe-C-Cr Fe-C-Mo Fe-C-Nb Fe-C-Ti Fe-C-W Fe-C-Zr Fe-Cr Fe-Cr-Mo Fe-Cr-Nb Fe-Cr-Ti Fe-Cr-W Fe-Cr-Zr Fe-Mo Fe-Mo-Nb Fe-Mo-Ti Fe-Mo-W Fe-Mo-Zr Fe-Nb Fe-Nb-Ti Fe-Nb-W Fe-Nb-Zr Fe-Ti Fe-Ti-W Fe-Ti-Zr Fe-W Fe-W-Zr
Mo Nb Ti W Zr Cr-C Cr-Mo-C Cr-Nb-C Cr-Ti-C Cr-W-C Cr-Zr-C Mo-C Mo-Nb-C Mo-Ti-C Mo-W-C Mo-Zr-C Nb-C Nb-Ti-C Nb-W-C Nb-Zr-C Ti-C W-Ti-C Ti-Zr-C W-C W-Zr-C
Fe-X-Y Ternaries
X-Y-C Ternaries
From literature
From this work
Design of Alloys Containing Zr
n Class I: Intermetallics-strengthened alloys – Support fundamental Zr-bearing thermodynamic database development – Explore Zr-bearing Laves phase and potential Fe23Zr6 effects
n Class II: 9Cr ferritic steels – Better phase stability than 12Cr – With Grade 91 and 92 as references
n Class III: High-Cr ferritic steels – Better corrosion resistance than lower Cr steels, negligible SCC issue – With AISI 439/444 and 304 as references
n Three intermetallics (Fe2Zr) strengthened alloys Z3, Z4, and Z5 were designed with
– Phase transformation of Fe2Zr from C14-type at high-temperature to C15-type at low-temperature
– Similar amount of Fe2Zr in Z3 and Z4, but about ½ amount reduced in Z5. n Conditions
– As-received: 1150°C + 50% reduction deformation + AC – Aging: 750°C for 1800 h to obtain C15-type in Z3 and Z5, comparing its effect to C14-
type in Z4.
Z3 Z4 Z5
Class I: Intermetallics-Strengthened Alloys
Class I: Intermetallics-Strengthened Alloys
n Intermetallics in as-received: – Z3 is primarily composed of
dispersive fine intermetallics with a few large size intermetallics.
– Z4 is dominated by dispersive fine intermetallics with minor orientations (or texture) in different grains.
– Z5 has less amount of fine intermetallics forming a network.
n The aging did not lead to noticeable changes to the microstructures of Z3 and Z5. But the texture in Z4-AR was eliminated by the aging.
Z3-AR Z3-Aged
Z4-AR Z4-Aged
Z5-AR Z5-Aged
10µm 10µm
10µm 10µm
10µm 10µm
Class I: Intermetallics-Strengthened Alloys
n Tensile testing results: – Yield stresses of Z3 are
similar to Z4, about 40-60% higher than P92. Yield stress of Z5 is comparable to P92.
– Total elongations of the alloys are comparable or better than P92 at high temperatures, but poor at room temperature.
n Creep testing at 600°C indicated different levels of improvement in creep resistance in both life and ductility.
n The aging slightly reduced the hardness of the alloys.
n The aging may alter the mechanical properties of the alloys, e.g., room temperature ductility.
0"
100"
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600"
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800"
0" 200" 400" 600" 800"
Yield&Stress&(M
Pa)&
Temperature&(oC)&
Z3"Z4"Z5"P92.MJP"
0"
50"
100"
150"
200"
250"
300"
350"
Vickers(H
ardn
ess((HV
1)(
Z3(((((((((((((((((((((Z4(((((((((((((((((((((Z5(
ini)al"750C1800h"
0"
5"
10"
15"
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25"
30"
0.1" 1" 10" 100"
Creep%Strain%(%
)%
Time%to%Rupture%(h)%
Z3@300MPa"Z4@260MPa"Z5@260MPa"Gr92@260MPa"
600oC
0"
10"
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30"
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70"
0" 200" 400" 600" 800"
Total&Elonga*
on&(%
)&
Temperature&(oC)&
Z3"Z4"Z5"
Class II: 9Cr Ferritic Steels
n Aims: – Eliminate Z-phase and reduce M23C6. – Changes to Laves phase content is not considered.
400 600 800 1000 1200 1400 16000.00
0.01
0.02
0.03
MX2
MX1
M23C6
Pha
se F
ract
ion
Temperature (oC)
Laves
T3
400 600 800 1000 1200 1400 16000.00
0.01
0.02
0.03
Z
MX
M23C6
Laves
Pha
se F
ract
ion
Temperature (oC)
P92
n Tensile testing results of alloy T3 showed moderate increase in yield strength (10-15%) and comparable or slightly lower total elongation, but noticeably improved uniform elongation.
0"1"2"3"4"5"6"7"8"9"
0" 200" 400" 600" 800"
Uniform
(Elonga-
on((%
)(
Temperature((oC)(
0"
5"
10"
15"
20"
25"
30"
35"
40"
0" 200" 400" 600" 800"
Total&Elonga*
on&(%
)&
Temperature&(oC)&
Class II: 9Cr Ferritic Steels
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100"
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300"
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600"
700"
0" 200" 400" 600" 800"
Yield&Stress&(M
Pa)&
Temperature&(oC)&
Solid:"T3"Open:"References"
Class III: High-Cr Ferritic Steels
n High-Cr (15Cr) ferritic alloys were designed to have Laves-phase strengthening.
n The poor control of oxygen and nitrogen in LZ1 alloy resulted in a lot of large particles, harmful to mechanical properties.
10µm
LT1
LZ1
10µm
LTZ1
10µm
400 600 800 1000 1200 1400 16000.00
0.02
0.04
0.06
0.08
0.10
Pha
se F
ract
ion
Temperature (oC)
f(LIQUID) f(FCC_A1) f(BCC_A2)_1 f(LAVES_C14) f(BCC_A2)_2
400 600 800 1000 1200 1400 16000.00
0.02
0.04
0.06
0.08
0.10
Pha
se F
ract
ion
Temperature (oC)
f(LIQUID) f(FCC_A1) f(BCC_A2)_1 f(LAVES_C14)_1 f(SIGMA) f(BCC_A2)_2 f(LAVES_C14)_2
LT1
LZ1
Class III: High-Cr Ferritic Steels
n The alloys’ strength is adjustable by thermomechanical treatment, which is comparable or superior to AISI 304. – The increased strength would be primarily
attributable to the significantly increased amount of ultrafine precipitates.
n The alloys showed decent ductility. – The occasional low ductility was resulted
from aggregated Zr-oxide inclusions.
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Yield Stress (M
Pa)
Temperature (oC)
LT1C15LTZ1C15LT1C3R1-‐3LTZ1C3R1-‐3
05
101520253035404550
0 200 400 600 800
Total Elongation (%
)
Temperature (oC)
LT1C15LTZ1C15LT1C3R1-‐3LTZ1C3R1-‐3
LT1C15 LT1C3R1-3
Ion-Irradiation Experiments
n Radiation resistance of the alloys is to be evaluated using proton and heavy ion (e.g., Fe2+) irradiations.
– Radiation-hardening, radiation-induced phase stability and segregation will be studied. n Radiation resistance screening of the first set of samples has been initiated.
1.7 MV Tandem Accelerator Ion Beam @ UW-Madison
Summary
FY 2013 FY 2014 FY 2015
n Three classes of alloys are being explored by experiments assisted with computational thermodynamics. – Intermetallics-
strengthened – 9Cr ferritic – Higher-Cr (15Cr) ferritic
n Ion irradiation experiments of selected alloy samples are initiated.
n Development and down selection of the 3-class of alloys for larger heats production and mechanical property assessment.
n Ion irradiation study of selected alloy samples.
Zr-alloying would improved mechanical properties and radiation resistance. Approaches to solve the difficulty in alloy chemistry control will be explored by collaborating with commercial vendors, e.g., Carpenter Tech.
n Continue testing, ion-irradiation, and characterization of the down-selected alloys.
n Recommend superior alloy(s) for further investigation.
