the electrochemical behavior and stress corrosion cracking...
TRANSCRIPT
The Electrochemical Behavior and Stress Corrosion Cracking
of Cold Rolled 316L Stainless Steel
in Simulated PWR Water Environments
Junjie Chen, Zhanpeng Lu*, Qian Xiao, Xiangkun Ru, Guangdong Han
Institute of Materials Science
School of Materials Science and Engineering, Shanghai University, China
[email protected], [email protected]
17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors
August 9-12, 2015, Ottawa, Ontario, Canada
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SCCCrack tip Interface reaction
Electrochemical mechanism
Mechanical property
Mircrostrurcture
OutlineAustenitic stainless steel is commonly used in nuclear power plant. Local corrosion of
austenitic stainless steel in high temperature water, such as stress corrosion cracking
(SCC), intergranular corrosion, pitting and so on, may occur in the process of nuclear
power plants service. Work hardening such as machining, bending, and rolling is known to
have an effect on austenitic stainless steel and its resistance to stress corrosion cracking
in high-temperature water environments.
● Effect of rolling orientation on mechanical properties of 1DCR 316L SS
● Effect of rolling orientation on SCC of 1DCR 316L SS
● Effect of single tensile overload on SCC of 1DCR 316L SS
● Effect of cold roll on electrochemical behavior of 316L SS
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● Experimental
Materials: solution annealed 316L SS (316L-SA) , one-directionally cold-rolled 20%
316L SS (1DCR 316L , 316L-CR)
C Si Mn S P Cr Ni Mo Fe
0.019 0.320 1.60 0.006 0.027 16.39 10.21 2.12 Bal.
Experimental solution: simulated PWR primary water containing 2 ppm Li+ (from LiOH) and 1200
ppm B3+ (from H3BO3), 310 °C, 12.20 MPa Pressure
Water chemistry: (a) DO<5ppb, 2.5 ppm DH, (b) 8ppm DO, (c) DO< 5 ppb, DH < 0.5 ppb
SCC test: constant loading, K was ~ 30 MPa.m0.5 in the beginning of the SCC test
Electrochemical test: 316L-SA and 316L-CR as working electrode, autoclave as count
electrode, 0.1 M KCl Ag/AgCl pressure-balanced external reference electrode.
Potentiodynamic polarization and electrochemical impedance spectrum (EIS) were applied.
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Nuclear materials environmental assisted cracking experiment
system in Shanghai University
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T-L orientation
L-T orientation
45D orientation
UTS (MPa) 721 770 712
Elongation (%) 62.9 52.4 56.3
Yield strength (MPa)
618 680 614
Reduction of area (%)
80.5 72.8 77.5
● Effect of rolling orientation on mechanical properties of 1DCR 316L SS
T-L L-T
45DSEM morphologies of the
fracture surfaces of 1DCR
316L SS specimen after
tensile test
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Specimen No. Water chemistry Loading mode
T-LHDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Step 1: immersed for 48 hStep 2: Tri. Loading, R = 0.7, 0.01 Hz, 864 cyclesStep 3: Constant loading (CL) , 500 h
T-LHOLDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Constant loading (CL), 500 h
L-THDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Step 1: immersed for 48 hStep 2: Tri. Loading, R = 0.7, 0.01 Hz, 864 cyclesStep 3: Constant loading (CL) , 500 h
L-THOLDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Constant loading (CL), 500 h
45DHDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Constant loading (CL), 500 h
45DHOLDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)
Constant loading (CL), 500 h
T-LNDH < 0.5ppb, DO < 5ppb(Deaerated)
Step 1: immersed for 48 hStep 2: Tri. Loading, R = 0.7, 0.01 Hz, 864 cyclesStep 3: Constant loading (CL) , 1122 h
L-TNDH < 2.5ppb, DO < 5ppb(Deaerated)
Step 1: immersed for 48 hStep 2: Tri. Loading, R = 0.7, 0.01 Hz, 864 cyclesStep 3: Constant loading (CL) , 1122 h
Procedures for the SCC tests of 1DCR 316L SS in a simulated PWR primary water at 310°C.
● Effect of rolling orientation on SCC of 1DCR 316L SS
A single triangle wave overload with a Kmax of about 48 MPa.m0.5 was applied within 180 s for specimens
T-LHOL, L-THOL and 45DHOL.
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SEM morphologies of the fracture surfaces of 1DCR
316L SS specimen (a) T-L orientation, (b) L-T orientation
and (c) 45D orientation after SCC test in hydrogenated
environment for 500 hours.
● Effect of rolling orientation on SCC of 1DCR 316L SS
The CGRs of specimen T-LH, L-TH and
45DH were 0.732μm/h, 0.534 μm/h and
0.262 μm/h.
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● Effect of rolling orientation on SCC of 1DCR 316L SS
SEM morphologies of the fracture surfaces of 1DCR 316L SS specimen (a) T-L orientation
and (b) L-T orientation after SCC test in deaerated environment for 1122 hours.
The CGR was 0.765 μm/h for specimen T-LN and 0.302 μm/h for specimen L-TN.
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● Effect of single tensile overload on SCC of 1DCR 316L SS
The CGR was 0.373 μm/h for specimen T-LHOL
SEM morphologies of the fracture surfaces of 1DCR
316L SS specimen (a) T-L orientation and (b) L-T
orientation and (c) 45D orientation with one single
tensile overload after SCC test in hydrogenated
environment for 500 hours.
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The mechanical properties of cold-rolled 316L stainless steel exhibited anisotropy in
different rolling orientations.
In both hydrogenated and deaerated simulated PWR water environments, the SCC in
specimen T-L orientation is significantly more serious than that in specimen L-T
orientation.
The dependence of SCC growth rate is related to the intergranular SCC path in cold-
rolled stainless steel with microstructural anisotropy. There is a faster grain boundary
diffusion of the oxidizing species in the T-L rolling orientation than in the other
orientation [Arioka, K. et al, Lozano-Perez, S. et al.]. The grain boundary length is higher
along the L direction than along the T one. Once a crack is initiated at a GB, its
propagation is probably easier.
A single tensile overload would produce a residual plastic zone in both the stationary
and growing crack tips [Xue et al.]. This would decrease the plastic strain rate in the
crack tip thus the crack growth rate would decrease.
Summary I
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The electrode surface reaction kinetics
of 316L-SA and 316L-CR change with
time in hydrogenated simulated PWR
water and the surface reaction kinetics
change is different between 316L-SA
and 316L-CR.
The EIS of (a) 316L-SA and (b)
316L-CR in hydrogenated simulated
PWR water under OCP at different
immersion times.
● Effect of cold roll on electrochemical behavior of 316L SS
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The EIS of 316L-SA and 316L-CR in hydrogenated simulated PWR water at OCP: (a) in the
initial stage of immersion, (b) in the final stage of immersion.
The effect of cold roll on the surface reaction kinetics of 316L SS in hydrogenated simulated
PWR water is uncertain.
● Effect of cold roll on electrochemical behavior of 316L SS
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● Effect of cold roll on electrochemical behavior of 316L SS
The electrode surface reaction kinetics of 316L-
SA and 316L-CR changes with time in
oxygenated simulated PWR water and the
surface reaction kinetics of 316L-SA is not the
same as that of 316L-CR based on the
difference of shapes of EIS between 316L-SA
and 316L-CR .
The EIS of (a) 316L-SA and (b) 316L-CR
in oxygenated simulated PWR water
under OCP at different immersion times.
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The electrode surface reaction kinetics of 316L-SA and 316L-CR at open circuit state are
similar both in the initial and final stages of immersion but changes with immersion time. It also
implies that the cold rolling has a clear effect on the surface reaction kinetics of 316L SS.
The EIS of 316L-SA and 316L-CR in oxygenated simulated PWR water at OCP: (a) in the initial
stage of immersion, (b) in the final stage of immersion.
● Effect of cold roll on electrochemical behavior of 316L SS
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● Effect of cold roll on electrochemical behavior of 316L SS
The potentiodynamic polarization curves of 316L-SA and 316L-CR in oxygenated simulated
PWR water in the (a) early immersion stage and (b) final immersion stage.
The electrode surface reaction activity of 316L-CR is higher than that of 316L-CR both in
the early and final stages of immersion.
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● Effect of cold roll on electrochemical behavior of 316L SS
The change of electrode surface reaction kinetics of 316L-SA and 316L-CR with time is not
linearly in deaerated simulated PWR water
The EIS of (a) 316L-SA and (b) 316L-CR in deaerated simulated PWR water under open
circuit state at different immersion times.
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● Effect of cold roll on electrochemical behavior of 316L SS
The difference of surface reaction kinetics between 316L-SA and 316L-CR in deaerated
simulated PWR water is not significant.
The EIS of 316L-SA and 316L-CR in deaerated simulated PWR water with different immersion
time at OCP: (a) in the initial stage of immersion, (b) in the final stage of immersion.
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In low oxygen concentration (hydrogenated or deaerated) environments, 316L SS is in lowcorrosion potentials. The stability of the oxide film is not high, which may be difficult todistinguish the effect of cold roll 316L SS by electrochemical methods.
In oxygenated environment, 316L SS is in high corrosion potentials and the stability of theoxide film is higher than that in non-oxygenated environment. A relatively stable surfacestate may be good for distinguishing the effect of cold roll on the surface reaction kineticsof 316L SS by electrochemical methods.
The CGR of stainless steels and nickel alloys decreased with the decreasing of corrosionpotentials in high temperature pure water [Andresen, P. L. et al.].
Literature data showed that cold work would increase the SCC susceptibility of austeniticstainless steels in oxygenated primary water [Meng, F. et al.]. Present results showed thatcold rolled 316L SS had higher surface reaction activity.
Summary II
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The mechanical properties of cold-rolled 316L stainless steel exhibited anisotropy in
different rolling orientations.
In both hydrogenated and deaerated simulated PWR water, the intergranular SCC
CGR of 1DCR 316L SS specimen in the T-L orientation was faster than those in other
orientations.
A single tensile overload decreased the intergranular SCC CGR, lengths and numbers
of 1DCR 316L SS specimens in different cold rolling orientations in hydrogenated
simulated PWR water.
The electrode surface reaction kinetics of both the solution annealed and cold rolled
316L SS changed with immersion time in hydrogenated, deaerated and oxygenated
simulated PWR water. The effect of cold roll on the electrochemical behavior of 316L
SS was more significant in oxygenated environment than in hydrogenated or
deaerated environments.
● Conclusion
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Thank you very much for your attention!