The Electrochemical Behavior and Stress Corrosion Cracking ...envdeg2015.org/final-proceedings/ENVDEG/presentations/ENVDEG_PPT… · (SCC), intergranular corrosion, pitting and so

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


School of Materials Science and Engineering

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



● 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.



Nuclear materials environmental assisted cracking experiment

system in Shanghai University



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



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)


L-THOLDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)


45DHDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)


45DHOLDH ~ 2.5ppm, DO < 5ppb(Hydrogenated)


T-LNDH < 0.5ppb, DO < 5ppb(Deaerated)


L-TNDH < 2.5ppb, DO < 5ppb(Deaerated)


Procedures for the SCC tests of 1DCR 316L SS in a simulated PWR primary water at 310°C.


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.



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.


The CGRs of specimen T-LH, L-TH and

45DH were 0.732μm/h, 0.534 μm/h and

0.262 μm/h.




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.



● 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.



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



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.




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.





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.



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.





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.




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.




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.



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



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



Thank you very much for your attention！

Documents

The Electrochemical Behavior and Stress Corrosion Cracking ...envdeg2015.org/final-proceedings/ENVDEG/presentations/ENVDEG_PPT… · (SCC), intergranular corrosion, pitting and so