evaluation of temper embrittlement of 30cr2mov rotor...

Research ArticleEvaluation of Temper Embrittlement of 30Cr2MoV Rotor SteelsUsing Electrochemical Impedance Spectroscopy Technique

Zhang Shenghan Lv Yaling and Tan Yu

North China Electric Power University Baoding 071000 China

Correspondence should be addressed to Zhang Shenghan zhang shenghanyeahnet

Received 6 August 2014 Accepted 21 August 2014

Academic Editor Tifeng Jiao

Copyright copy Zhang Shenghan et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Temper embrittlement tends to occur in the turbine rotor after long running which refers to the decrease in notch toughness of alloysteels in a certain temperature range (eg 400∘C to 600∘C)The severity of temper embrittlementmust bemonitored timely to avoidfurther damagement and the fracture appearance transition temperature (FATT

50

) is commonly used as an indicator parameter tocharacterize the temper embrittlement Compared with conventional destructive methods (eg small punch test) nondestructiveapproaches have drawn significant attention in predicting the material degradation in turbine rotor steels without impairingthe integrity of the components In this paper laboratory experiments were carried out based on a nondestructive methodelectrochemical impedance spectroscopy (EIS) with groups of lab-charged specimens for predicting the temper embrittlement(FATT

50

) of turbine rotor steel The results show that there was a linear relationship of interfacial impedance of the specimens andtheir FATT

50

values The predictive error based on the experiment study is within the range of plusmn15∘C indicating the predictingmodel is precise effective and reasonable

1 Introduction

Thermal power stations are the most common electricitysources all over the world due to their low running costsand reliability However any failures in themain components(eg steam turbine rotor) of aged thermal power plantsoperating in many areas may cause significant costs longdowntime and even the loss of lifeTheprecisely predicting ofthe aging process or the remaining service life of turbine rotoris of great importance for safe operation and life extension [1]

Temper embrittlement in low alloy steels (eg Cr-Mo-V) of steamed turbine rotors is one of the typical materialdegradations (eg creep fatigue embrittlement and cor-rosion) [2 3] and is commonly characterized by fractureappearance transition temperature (FATT

50) at which the

fracture surface of the material is 50 brittle or cleavageand 50 ductile [1] The turbine rotor steel operated at ahigh temperature for long time may lose its flexibility and

ductility as the segregation of metalloid impurities such asphosphorus (P) tin (Sn) and antimony (Sb) at the grainboundaries which reduces the cohesion at grain boundaries[4ndash6] Among the impurity elements phosphorus (P) is con-sidered as the main impurity causing temper embrittlement[5 7 8] If the increase of FATT

50value is not detected in

time the rotor steel can be easily damaged or even broken andcauses severe safety accidents [4] Therefore it is essential tomake the accurate predictions and assessments on the temperembrittlement parameters of the turbine rotor material

To date different destructive and nondestructive meth-ods have been developed to detect the FATT

50value of

turbine rotors such as small punch test [1 9ndash12] electro-magnetic method [13] ultrasonic [14ndash16] auger electronspectroscopy [17 18] electrochemical method [5 19 20]and chemical corrosion [19] Destructive methods can pro-vide accurate results of mechanical properties (eg yieldstress tensile strength FATT

50 fracture toughness and creep

Hindawi Publishing CorporationJournal of SpectroscopyArticle ID 957868

2 Journal of Spectroscopy

properties) from the actual components [11 12] but theirapplication is highly-limited due to the damage to the turbinerotor

As a relatively high-precision nondestructive detectingmethod electrochemical approach has drawn significantattention in predicting the material degradation in turbinerotor steels without impairing the integrity of the com-ponents Mao and Zhao investigated the electrochemicalbehaviors of type 321 austenitic stainless steel in sulfuricacid solution and found that the electrochemical polarizationcurves can be used to estimate the aging embrittlementdegradation [21] Komazaki et al developed a methodologyfor thermal aging embrittlement and the results on electro-chemical polarization measurements in 1N KOH solutionrevealed that the peak current density ldquo119868prdquo value was foundto be increasing linearly with the degree of embrittlement asevaluated by impact absorbed energy at 0∘C [22 23] Anodicand single loop electrochemical potentiokinetic reactivation(SL-EPR) polarization curves of the embrittled specimenshave been evaluated difference in current density (IP2-E-Ipass-E) between active second peak and passive one in ananodic polarization curve of temper-embrittled specimensincreases linearly with increase in FATT in the range ofmode transfer over transgranular cleavage to intergranular ofCharpy impact fracture [24] Zhang et al developed a geneticprogramming (GP) for FATT

50prediction and single loop

electrochemical polarization reactivation (EPR) test has beenconducted [5] The multiple correlation coefficient betweenpredicted and measured FATT

50was 0990 indicating the

model obtained by GP can be used in predicting temperembrittlement of new rotor materials with a precision ofabout plusmn20∘C [5] Bayesian neural network was proposedto model the temper embrittlement of steam turbine rotorin service and the FATT

50was predicted as a function of

ratio of the two peak current densities (119868p119868pr) tested byelectrochemical potentiodynamic reaction method [25]

EIS as an effective electrochemical method originallywas used to study the electrical response characteristicfrequency of linear circuit network and has been used bymore and more researchers to study the electrode processwhich could provide more information of interface structurethan other methods [26ndash28]

In this paper EIS method was employed to study thethermal embrittlement of turbine rotor and a multiple linearregression analysis on interfacial impedance and other rel-evant parameters was carried out to build a predict modelof FATT

50 The predicted and measured values of FATT

50

were compared and the error was within an acceptable rangeindicating an effective and reasonable model was obtained

2 Experimental Method

21 Principle The test specimens in this paper were lab-charged phosphorus-doped 30Cr2MoV rotor steel and thechemical composition was shown in Table 1

To simulate the temper embrittlement during the long-term service of turbine rotor step cooling treatment was

used to promote the segregation of phosphorus to the grainboundary Their FATT

50values were measured by a stress

test according to relevant national standardThe result wouldbe used to verify the subsequent test Impedance of thespecimens was measured in a three-electrode system andanalyzed by the equivalent circuit method A predictivemodel was built based on the analysis results

22 Experiment FATT50values of specimens were measured

by stress test and the result is shown in Table 2To measure the impedance of the specimens a three-

electrode system was employed As shown in Figure 1 thespecimen was cut into cube with side length of 12mm andwas welded on a piece of copper wireThe specimen cube actsas the working electrode in the experiment In order for thereaction area of the working electrode to remain fixed fivesides of the cube including some parts of the copper wirewere sealed with epoxy resin the remaining side was coveredwith anticorrosion tape with a hole (diameter = 5mm) afterbeing grinded with sandpaper step by step to 2000

Platinumelectrodewas selected as auxiliary electrode andsaturated calomel electrode was used as reference electrodeElectrolyte was made of 001M Na

2MoO4with phosphoric

deployed to the pH value of 55 The three-electrode systemwas placed in a water bath filled with circulating hot water of25∘C to maintain a constant temperature

The three-electrode system was connected to the corre-sponding position of electrochemical workstation (model ofPARTAT 2273) A computer equipped with software of thatworkstation was used to record measurements

All specimens were anodic polarized the result showedthat those corrosion potentials are basically the same In orderto measure the EIS AC potential with amplitude of 5mVwas applied to working electrode at the corrosion potentialas input signal Sixty frequencies were logarithmic sweeplyselected from 100 kHz to 100mHz Impedance under thatcondition could be measured by comparing the measuredoutput current with the input potential

3 Results and Discussion

Figure 2 shows the Nyquist plot of measured impedance ofspecimenThe impedance was represented by a complexTheabscissa of plot in Figure 2 is the real part of the impedanceand the ordinate is the imaginary part The results showedthat the Nyquist plot of all specimens is similar In the highfrequency region the plots were arcs in the first quadrantbut the centers of arcs were in the fourth quadrant Somestudies claimed that high frequency region was dynamicscontrol district and the diameter of the arc represents thesize of charge transfer resistance of the electrode reactionThe higher the diameter of arc the more difficult the chargetransfer in electrode reaction and the slower the reactionIn the low frequency region the plots were straight lines ofdifferent lengths This region was considered mass transfercontrolled district If the line in this region was very long theelectrode reaction could be considered as led bymass transfer

Journal of Spectroscopy 3

Table 1 Chemical composition of 30Cr2MoV rotor steel (wt)

Sample P C Si Mn S Cr Ni Mo Cu V As Sn Sb41 0045 028 036 066 0013 162 006 062 008 029 0013 0004 0001342 0107 03 037 069 0014 165 005 073 007 029 0013 0004 0001543 0063 028 036 069 0014 168 005 068 01 029 0015 0006 0001944 0204 03 037 069 0015 166 005 075 01 029 0015 0007 0002A2 0065 028 043 068 0012 179 028 07 008 03 0013 0004 00012A3 0019 024 04 062 0001 16 025 069 012 027 0007 0008 00015

Table 2 The FATT50 values of different rotor samples

Sample Original state Heat-treated state Difference41 675 956 28142 1987 2117 1343 1036 1422 38644 235 2754 404A2 82 1271 451A3 minus709 minus541 168

REWE

AE

Electrochemicalworkstation

Recorddevice

Input

OutputHot water

Electrolyte

Figure 1 A three-electrode system for measuring the impedance ofthe specimens

An equivalent circuit based on impedance plots wasshown in Figure 3119877119871is the solution impedance between working elec-

trode and auxiliary electrode CPE is constant-phase-elementwhich could be expressed by parameters 119884

0and 119899 119877ct is

the charge transfer impedance of the electrode reaction119882 is mass transfer impedance and can be expressed byparameter 1198841015840

0

The impedance of the equivalent circuit couldbe calculated by (1) as follows

119885 = 119885119877119871+

1

119884CPE + 119884(CPE(119877ct119882))

= 119877119871+

1

1198840(119895120596)minus119899

+ (1 (119877ct + (11198841015840

0

radic119895120596)))

(1)

The impedance value calculated by the formula matchedwell the experimental results Figure 4 showed the calculatedand measured curves and the fitting error of each equivalentcircuit component parameter was less than 5

By analyzing the component parameter values of equiv-alent circuit it could be found that the solution impedanceof specimens was essentially unchanged but the interfaceimpedance varied greatly Figure 5 shows the linear relation-ship of interfacial impedance of specimen and its FATT

50

at a frequency of 100 kHz The abscissa of Figure 5 wasinterfacial impedance value in ohms ordinate was FATT

50

value in degree Celsius Their fitting formula was in theupper left corner The 119910 in formula represented FATT

50and

119909 interfacial impedance The 119877 in formula is the correlationcoefficient and it was calculated as 0836 by 1198772 = 06983119877min the correlation coefficient threshold could be looked upfrom corresponding table as 0567 [29] Since 119877 was greaterthan 119877min it could be believed that there was a close linearrelationship between the interfacial impedance and FATT

50

and the FATT50could be described by linear equations

In addition to the interfacial impedance FATT50also has

linear correlationship with other parameters [29] which wereshown in Table 3

By multivariate linear regression analysis using excelsoftware the regression equation could be expressed by (2)where Z was interfacial impedance One has

FATT50= minus2002 + 1264 lowast Z + 178 lowast P + 4106 lowast C

+ 1318 lowastMn minus 9214 lowast S minus 06 lowast 120595(2)

Significant test using Excel software showed that the equationwas credible and there was significant linear relationshipbetween FATT

50and other variables

Table 3 shows that the residuals of predicted value wereplusmn15∘C the error was small and themodel was reasonable andeffective

4 Conclusions

In this work the EIS of turbine rotor at the corrosionpotential in 001MNa

2MoO4was studied through laboratory

experiments and the following conclusions are obtainedTheelectrode reaction of rotor in electrolyte could be representedby an equivalent circuit The total impedance of the circuit


0

200

400

0 200 400 600 800 1000

Imag

inar

y

Real (Ω)FATT = 2754

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000Real (Ω)

Imag

inar

y

FATT = 2117

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

yReal (Ω)

FATT = 2754

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


(a)

Figure 2 Continued


0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

(b)

Figure 2 Nyquist diagrams of the impedance of different samples

Table 3 FATT50-related parameters

Sample Measured FATT50 Impedance 119885 (Ω) P () C () Mn () S () Reduction 120595 () Predicted value DifferenceA31 minus709 007 0019 024 062 0001 722 minus73432 minus2532A32 minus541 009 0019 024 062 0001 7133 minus48674 5426411 675 01 0045 028 066 0013 6447 7087 337A21 82 009 0065 028 068 0012 603 94862 12862412 956 012 0045 028 066 0013 6233 94866 minus0734431 1036 011 0063 028 069 0014 5657 1123 87A22 1271 011 0065 028 068 0012 5257 115504 minus11596432 1422 013 0063 028 069 0014 5533 136836 minus5364421 1987 011 0107 03 069 0014 528 19999 129422 2117 012 0107 03 069 0014 5417 213452 1752441 235 013 0204 03 069 0015 4665 229632 minus5368442 2754 018 0204 03 069 0015 305 283142 7742

CPE

RL

Rct W

Figure 3 Constructed equivalent circuit in accordance withFigure 1

0

100

200

300

400

500

0 200 400 600 800 1000

Red-calculatedBlack-measured

Imag

inar

y

Real (Ω)

Figure 4 Comparison of the calculated and measured curve

y = 00002x + 00879

0

005

01

015

02

minus100 minus50 0 50 100 150 200 250 300

Z (i

nter

faci

al im

peda

nce)

FATT50

R2 = 06983

Figure 5 Relationship of interface impedance and FATT50

values

includes two parts solution impedance between workingelectrode and auxiliary electrode and interfacial impedancebetween the rotor and electrolyte At higher frequency thereis a linear relationship between the interfacial impedance andits FATT

50 The larger the interfacial impedance value the

lower the FATT50 An effective predictive model could be

built by a series of parameters and the error is small enoughindicating the model is reasonable and effective


Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

This paper is supported by the ldquoFundamental Research Fundsfor the Central Universities of Chinardquo (Grant no 13MS85)

References

[1] J S Ha and E Fleury ldquoSmall punch tests to estimate themechanical properties of steels for steam power plant IIFracture toughnessrdquo International Journal of Pressure Vesselsand Piping vol 75 no 9 pp 707ndash713 1998

[2] Y Kadoya T Goto M Takei N Haruki T Ikuno and YNishimura ldquoNondestructive evaluation of temper embrittle-ment in Cr-Mo-V rotor steelrdquo Transactions of the Japan Societyof Mechanical Engineers Part A vol 57 no 537 pp 1085ndash10901991

[3] H Uemura andM Kohno ldquoTemper embrittlement characteris-tic of Cr-Mo-V steel steam turbine rotors in long term servicerdquoJournal of the Iron and Steel Institute of Japan vol 93 no 4 pp324ndash329 2007

[4] Y-M Chen Y Long Z-G Han and Y-H Wang ldquoPredictthe temper embrittlement extent of turbine rotor steel byusing chemical corrosion methodrdquo in Proceedings of the Asia-Pacific Power and Energy Engineering Conference (APPEEC rsquo09)Wuhan China March 2009

[5] S-H Zhang Y-Z Fan Y-M Chen and S-L Zhou ldquoA newnondestructive test technique for predicting the temper embrit-tlement of turbine rotor steel with genetic programmingrdquo inProceedings of the IEEE International Conference on IndustrialTechnology (ICIT rsquo05) pp 768ndash771 Hong Kong December2005

[6] A Fujita M Shinohara H Yokota K Kaku K Soeda and YKuroda ldquoEffect of chemical composition and manufacturingprocedure on toughness of CrMoV HP rotor forgingsrdquo Journalof the Iron and Steel Institute of Japan vol 84 no 3 pp 236ndash2411998

[7] J Kameda and R Ranjan ldquoNondestructive evaluation of steelsusing acoustic and magnetic barkhausen signals-I Effect ofcarbide precipitation and hardnessrdquo Acta Metallurgica vol 35no 7 pp 1515ndash1526 1987

[8] J Kameda and R Ranjan ldquoNondestructive evaluation of steelsusing acoustic and magnetic barkhausen signals-II Effect ofintergranular impurity segregationrdquo Acta Metallurgica vol 35no 7 pp 1527ndash1531 1987

[9] A Shekhter S Kim D G Carr A B L Croker and S P RingerldquoAssessment of temper embrittlement in an ex-service 1Cr-1Mo-025V power generating rotor by Charpy V-Notch testing KIcfracture toughness and small punch testrdquo International Journalof Pressure Vessels and Piping vol 79 no 8ndash10 pp 611ndash615 2002

[10] S-I Komazaki T Shoji and K Takamura ldquoEvaluation ofthermal aging embrittlement in directionally solidified Ni-basesuperalloy by small punch testrdquo Journal of EngineeringMaterialsand Technology Transactions of the ASME vol 127 no 4 pp476ndash482 2005

[11] K Turba R C Hurst and P Hahner ldquoAnisotropic mechanicalproperties of the MA956 ODS steel characterized by the small

punch testing techniquerdquo Journal of Nuclear Materials vol 428no 1ndash3 pp 76ndash81 2012

[12] X Mao T Shoji and H Takahashi ldquoCharacterization of frac-ture behavior in small punch test by combined recrystallization-etch method and rigid plastic analysisrdquo Journal of Testing andEvaluation vol 15 no 1 pp 30ndash37 1987

[13] G Dobmann ldquoNDE for material characterisation of ageing dueto thermal embrittlement fatigue and neutron degradationrdquoInternational Journal of Materials and Product Technology vol26 no 1-2 pp 122ndash139 2006

[14] H Jeong S-H Nahm K-Y Jhang and Y-H Nam ldquoEvaluationof fracture toughness degradation of CrMoV rotor steels basedon ultrasonic nonlinearity measurementsrdquo KSME InternationalJournal vol 16 no 2 pp 147ndash154 2002

[15] H Jeong S-H Nahm K-Y Jhang and Y-H Nam ldquoA non-destructive method for estimation of the fracture toughness ofCrMoV rotor steels based on ultrasonic nonlinearityrdquoUltrason-ics vol 41 no 7 pp 543ndash549 2003

[16] C-HHsuH-Y Teng and S-CChiu ldquoUltrasonic evaluation oftemper-embrittlement for martensitic stainless steelrdquoMaterialsTransactions vol 44 no 11 pp 2363ndash2368 2003

[17] R Ding A Islam S Wu and J Knott ldquoEffect of phosphorussegregation on fracture properties of two quenched and tem-pered structural steelsrdquo Materials Science and Technology vol21 no 4 pp 467ndash475 2005

[18] S H Song J Wu L Q Weng and T H Xi ldquoPhosphorusgrain boundary segregation under an intermediate appliedtensile stress in a Cr-Mo low alloy steelrdquo Materials Science andEngineering A vol 520 no 1-2 pp 97ndash100 2009

[19] Y Z Fan Y M Chen and S H Zhang ldquoDevelopment ofnondestructive inspecting of temper embrittlement of turbineroter steelrdquo Turbine Technology Article ID 100125884 2004

[20] Y Kadoya T Goto M Takei N Haruki K Ikuno and YNishimura ldquoNondestructive evaluation of temper embrittle-ment in Cr-Mo-V rotor steelrdquoThe American Society of Mechan-ical Engineers Power Division (Publication) PWR vol 13 pp229ndash234 1991

[21] X Mao and W Zhao ldquoElectrochemical polarization method todetect aging embrittlement of 321 stainless steelrdquo Corrosion vol49 no 4 pp 335ndash342 1993

[22] S-I Komazaki S Kishi T Shoji H Chiba and K SuzukildquoThermal aging embrittlement of tungsten-alloyed 9Cr fer-ritic steels and electrochemical evaluationrdquo Materials ScienceResearch International vol 9 no 1 pp 42ndash49 2003

[23] S-I Komazaki S Kishi T Shoji H Chiba and K SuzukildquoThermal aging embrittlement ofW alloyed 9Cr ferritic steelsand its evaluation by electrochemical techniquerdquo Journal of theSociety of Materials Science vol 49 no 8 pp 919ndash926 2000

[24] T Shibuya and T Misawa ldquoElectrochemical evaluation of thedegree of temper-embrittlement with mode transfer in impactfracture surface of 225Cr-1Mo low alloy steelsrdquo CorrosionEngineering vol 48 no 3 pp 146ndash154 1999

[25] S-H Zhang Y-Z Fan and Y-M Chen ldquoPredicting the temperembrittlement of steam turbine rotor steels with Bayesian neu-ral networkrdquo inProceedings of the IEEE International Conferenceon Industrial Technology (ICIT rsquo05) pp 991ndash994 Hong KongDecember 2005

[26] K Darowicki S Krakowiak and P Slepski ldquoEvaluation of pit-ting corrosion bymeans of dynamic electrochemical impedancespectroscopyrdquo Electrochimica Acta vol 49 no 17-18 pp 2909ndash2918 2004


[27] C Boissy C Alemany-Dumont and B Normand ldquoEIS evalua-tion of steady-state characteristic of 316L stainless steel passivefilm grown in acidic solutionrdquo Electrochemistry Communica-tions vol 26 no 1 pp 10ndash12 2013

[28] S Krakowiak K Darowicki and P Slepski ldquoImpedance inves-tigation of passive 304 stainless steel in the pit pre-initiationstaterdquo Electrochimica Acta vol 50 no 13 pp 2699ndash2704 2005

[29] J T Zhang Nondestructive Method for the Evaluation of theEmbrittlement of the Turbine Rotor Steels North China ElectricPower University Baoding China 2004

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


properties) from the actual components [11 12] but theirapplication is highly-limited due to the damage to the turbinerotor

As a relatively high-precision nondestructive detectingmethod electrochemical approach has drawn significantattention in predicting the material degradation in turbinerotor steels without impairing the integrity of the com-ponents Mao and Zhao investigated the electrochemicalbehaviors of type 321 austenitic stainless steel in sulfuricacid solution and found that the electrochemical polarizationcurves can be used to estimate the aging embrittlementdegradation [21] Komazaki et al developed a methodologyfor thermal aging embrittlement and the results on electro-chemical polarization measurements in 1N KOH solutionrevealed that the peak current density ldquo119868prdquo value was foundto be increasing linearly with the degree of embrittlement asevaluated by impact absorbed energy at 0∘C [22 23] Anodicand single loop electrochemical potentiokinetic reactivation(SL-EPR) polarization curves of the embrittled specimenshave been evaluated difference in current density (IP2-E-Ipass-E) between active second peak and passive one in ananodic polarization curve of temper-embrittled specimensincreases linearly with increase in FATT in the range ofmode transfer over transgranular cleavage to intergranular ofCharpy impact fracture [24] Zhang et al developed a geneticprogramming (GP) for FATT

50prediction and single loop

electrochemical polarization reactivation (EPR) test has beenconducted [5] The multiple correlation coefficient betweenpredicted and measured FATT

50was 0990 indicating the

model obtained by GP can be used in predicting temperembrittlement of new rotor materials with a precision ofabout plusmn20∘C [5] Bayesian neural network was proposedto model the temper embrittlement of steam turbine rotorin service and the FATT

50was predicted as a function of

ratio of the two peak current densities (119868p119868pr) tested byelectrochemical potentiodynamic reaction method [25]

EIS as an effective electrochemical method originallywas used to study the electrical response characteristicfrequency of linear circuit network and has been used bymore and more researchers to study the electrode processwhich could provide more information of interface structurethan other methods [26ndash28]

In this paper EIS method was employed to study thethermal embrittlement of turbine rotor and a multiple linearregression analysis on interfacial impedance and other rel-evant parameters was carried out to build a predict modelof FATT

50 The predicted and measured values of FATT

50

were compared and the error was within an acceptable rangeindicating an effective and reasonable model was obtained

2 Experimental Method

21 Principle The test specimens in this paper were lab-charged phosphorus-doped 30Cr2MoV rotor steel and thechemical composition was shown in Table 1

To simulate the temper embrittlement during the long-term service of turbine rotor step cooling treatment was

used to promote the segregation of phosphorus to the grainboundary Their FATT

50values were measured by a stress

test according to relevant national standardThe result wouldbe used to verify the subsequent test Impedance of thespecimens was measured in a three-electrode system andanalyzed by the equivalent circuit method A predictivemodel was built based on the analysis results

22 Experiment FATT50values of specimens were measured

by stress test and the result is shown in Table 2To measure the impedance of the specimens a three-

electrode system was employed As shown in Figure 1 thespecimen was cut into cube with side length of 12mm andwas welded on a piece of copper wireThe specimen cube actsas the working electrode in the experiment In order for thereaction area of the working electrode to remain fixed fivesides of the cube including some parts of the copper wirewere sealed with epoxy resin the remaining side was coveredwith anticorrosion tape with a hole (diameter = 5mm) afterbeing grinded with sandpaper step by step to 2000

Platinumelectrodewas selected as auxiliary electrode andsaturated calomel electrode was used as reference electrodeElectrolyte was made of 001M Na

2MoO4with phosphoric

deployed to the pH value of 55 The three-electrode systemwas placed in a water bath filled with circulating hot water of25∘C to maintain a constant temperature

The three-electrode system was connected to the corre-sponding position of electrochemical workstation (model ofPARTAT 2273) A computer equipped with software of thatworkstation was used to record measurements

All specimens were anodic polarized the result showedthat those corrosion potentials are basically the same In orderto measure the EIS AC potential with amplitude of 5mVwas applied to working electrode at the corrosion potentialas input signal Sixty frequencies were logarithmic sweeplyselected from 100 kHz to 100mHz Impedance under thatcondition could be measured by comparing the measuredoutput current with the input potential

3 Results and Discussion

Figure 2 shows the Nyquist plot of measured impedance ofspecimenThe impedance was represented by a complexTheabscissa of plot in Figure 2 is the real part of the impedanceand the ordinate is the imaginary part The results showedthat the Nyquist plot of all specimens is similar In the highfrequency region the plots were arcs in the first quadrantbut the centers of arcs were in the fourth quadrant Somestudies claimed that high frequency region was dynamicscontrol district and the diameter of the arc represents thesize of charge transfer resistance of the electrode reactionThe higher the diameter of arc the more difficult the chargetransfer in electrode reaction and the slower the reactionIn the low frequency region the plots were straight lines ofdifferent lengths This region was considered mass transfercontrolled district If the line in this region was very long theelectrode reaction could be considered as led bymass transfer






REWE

AE


Recorddevice

Input

OutputHot water

Electrolyte




0and 119899 119877ct is


0


119885 = 119885119877119871+

1

119884CPE + 119884(CPE(119877ct119882))

= 119877119871+

1

1198840(119895120596)minus119899

+ (1 (119877ct + (11198841015840

0

radic119895120596)))

(1)



50


50


50and


50










4 Conclusions





0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000Real (Ω)

Imag

inar

y

FATT = 2117

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

yReal (Ω)

FATT = 2754

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


(a)

Figure 2 Continued


0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

(b)




CPE

RL

Rct W


0

100

200

300

400

500

0 200 400 600 800 1000


Imag

inar

y

Real (Ω)


y = 00002x + 00879

0

005

01

015

02

minus100 minus50 0 50 100 150 200 250 300

Z (i

nter

faci

al im

peda

nce)

FATT50

R2 = 06983


values








Acknowledgment


References









































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






REWE

AE


Recorddevice

Input

OutputHot water

Electrolyte




0and 119899 119877ct is


0


119885 = 119885119877119871+

1

119884CPE + 119884(CPE(119877ct119882))

= 119877119871+

1

1198840(119895120596)minus119899

+ (1 (119877ct + (11198841015840

0

radic119895120596)))

(1)



50


50


50and


50










4 Conclusions





0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000Real (Ω)

Imag

inar

y

FATT = 2117

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

yReal (Ω)

FATT = 2754

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


(a)

Figure 2 Continued


0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

(b)




CPE

RL

Rct W


0

100

200

300

400

500

0 200 400 600 800 1000


Imag

inar

y

Real (Ω)


y = 00002x + 00879

0

005

01

015

02

minus100 minus50 0 50 100 150 200 250 300

Z (i

nter

faci

al im

peda

nce)

FATT50

R2 = 06983


values








Acknowledgment


References









































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000Real (Ω)

Imag

inar

y

FATT = 2117

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

yReal (Ω)

FATT = 2754

0

200

400

0 200 400 600 800 1000

Imag

inar

y


0

200

400

0 200 400 600 800 1000

Imag

inar

y


(a)

Figure 2 Continued


0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

(b)




CPE

RL

Rct W


0

100

200

300

400

500

0 200 400 600 800 1000


Imag

inar

y

Real (Ω)


y = 00002x + 00879

0

005

01

015

02

minus100 minus50 0 50 100 150 200 250 300

Z (i

nter

faci

al im

peda

nce)

FATT50

R2 = 06983


values








Acknowledgment


References









































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

0

200

400

0 200 400 600 800 1000Real (Ω)

Imag

inar

y

FATT = 2754

(b)




CPE

RL

Rct W


0

100

200

300

400

500

0 200 400 600 800 1000


Imag

inar

y

Real (Ω)


y = 00002x + 00879

0

005

01

015

02

minus100 minus50 0 50 100 150 200 250 300

Z (i

nter

faci

al im

peda

nce)

FATT50

R2 = 06983


values








Acknowledgment


References









































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Acknowledgment


References









































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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