elevated temperature mechanical properties and corrosion

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Elevated temperature mechanical properties and corrosion Elevated temperature mechanical properties and corrosion

characteristics evaluation of alloy Ht-9 characteristics evaluation of alloy Ht-9

Bhagath Yarlagadda University of Nevada, Las Vegas

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ELEVATED TEMPERATURE MECHANICAL PROPERTIES AND CORROSION

CHARACTERISTICS EVALUATION OF ALLOY HT-9

by

Bhagath Yarlagadda

Bachelor of Technology in Mechanical (Manufacturing) Engineering J.N.T.U. College of Engineering, Hyderabad, India

June 2002

A thesis submitted in partial fulfillment of the requirements for the

Master of Science Degree in Mechanical Engineering Department of Mechanical Engineering

Howard R Hughes College of Engineering

Graduate College University of Nevada, Las Vegas

August 2004

R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission.

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ITNTV Thesis ApprovalThe Graduate College University of Nevada, Las Vegas

July 15 20 04

The Thesis prepared by

B hagath Y arlagad d a

Entitled

Elevated Temperature Mechanical Properties and CorroRion

C h a r a c t e r i s t i c s E v a liia t to n o f A l l o y HT-Q.

is approved in partial fulfillment of the requirements for the degree of

M aster o f S c ie n c e in M e ch a n ica l E n g in e e r in g .______

Examination Committee M em ber

£Examination Committee M em ber

Graauate C rllege Faculty Representative

Examination Committee Chair

Dean of the Graduate College

11


ABSTRACT

Elevated Temperature Mechanical Properties and Corrosion CharacteristicsEvaluation Alloy HT-9

by

Bhagath Yarlagadda

Dr. Ajit K.Roy, Examination Committee Chair Associate Professor of Mechanical Engineering

University of Nevada, Las Vegas

This thesis presents the results of tensile testing, stress corrosion cracking (SCC) and

localized corrosion studies of Alloy HT-9, which is currently being considered as a target

structural material for transmutation applications. The results of tensile testing indicate

that the yield strength and the ultimate tensile strength were gradually reduced with

increasing temperature, but the ductility parameters were enhanced due to increased

plastic deformation, irrespective of the tempering time. The results of SCC testing in the

90°C acidic solution, performed by the slow-strain-rate (SSR) technique, revealed higher

failure stress (of) at longer tempering time. Localized corrosion studies conducted by

polarization technique showed pitting and crevice corrosion in specimens exposed to both

neutral and acidic environments. The fractographic evaluations of the primary fracture

face of the broken tensile specimen by scanning electron microscopy revealed dimpled

microstructure indicating ductile failure. Branched secondary cracks were observed along

the gage length of the SCC test specimens, evaluated by optical microscopy.

Ill


TABLE OF CONTENTS

ABSTRACT.............................................................................................................................iii

LIST OF TABLES..................................................................................................................vi

LIST OF FIGURES................................................................................................................vii

ACKNOWLEDGEMENTS................................................................................................... ix

CHAPTER I INTRODUCTION..............................................................................................1

CHAPTER 2 MATERIALS AND ENVIRONMENTS..................................................... 72.1 Test Materials........................................................................................................... 72.2 Test Specimens........................................................................................................102.3 Test Environments.................................................................................................. 12

CHAPTER 3 EXPERIMENTAL PROCEDURES..............................................................133.1. Tensile Testing....................................................................................................... 133.2. Slow-Strain-Rate Testing....................................................................................... 173.3. Cyclic Potentiodynamic Polarization Testing...................................................... 213.4. Optical Microscopy.................................................................................................243.5. Scanning electron microscopy...............................................................................24

CHAPTER 4 RESULTS........................................................................................................264.1 Hardness vs. Tempering Time................................................................................264.2 Ambient-Temperatnre Mechanical Properties...................................................... 264.3 Elevated Temperature Tensile Testing..................................................................274.4 Fractographic Evaluations......................................................................................344.5 Slow Strain Rate (SSR) Testing............................................................................. 364.6 Localized Corrosion Study.....................................................................................394.7 Metallographic Evaluations....................................................................................43

CHAPTER 5 DISCUSSIONS..............................................................................................465.1 Effect of Thermal-Treatment................................................................................. 465.2 Effect of Temperature on Tensile Properties........................................................ 475.3 Slow Strain Rate Testing........................................................................................48

CHAPTER 6 SUMMARY AND CONCLUSIONS...........................................................50

CHAPTER 7 FUTURE W ORK.......................................................................................... 52

IV


APPENDIX A: TENSILE DATA USING SPECIMENS TEMPERED FOR1.25 HOURS............................................................................................... 53

APPENDIX B: TENSILE DATA USING SPECIMENS TEMPERED FOR1.75 HOURS............................................................................................... 58

APPENDIX C: TENSILE DATA USING SPECIMENS TEMPERED FOR2.25 HOURS............................................................................................... 63

APPENDIX D: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR1.25 HOURS............................................................................................... 68

APPENDIX E: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR1.75 HOURS............................................................................................... 69

APPENDIX F: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR2.25 HOURS............................................................................................... 70

BIBLIOGRAPHY................................................................................................................... 71

V ITA........................................................................................................................................73


LIST OF TABLES

Table 2.1 Physical and Thermal Properties of Alloy HT-9................................................... 9

Table 2.2 Chemical Composition (%wt) of Alloy HT-9......................................................10

Table 2.3 Chemical Composition of Test Environments (gram/liter).................................12

Table 3.1 Minimum Times Needed to Reach the Desired Temperature............................ 16

Table 4.1 Hardness Due to Thermal Treatments..................................................................26

Table 4.2 Ambient Temperature Tensile Properties of Alloy HT-9................................... 27

Table 4.3 UTS and YS of Alloy HT-9 at Different Temperatures..................................... 30

Table 4.4 %E1 and %RA of Alloy HT-9 at Different Temperatures.................................. 30

Table 4.5 YS vs. Uniform Strain at Different Temperatures............................................... 31

Table 4.6 Results of SSR Testing.......................................................................................... 37

Table 4.7 CPP Test Results.................................................................................................... 43

VI


LIST OF FIGURES

Figure 1.1 Approach to Spent Fuel Management..............................................................2

Figure 1.2 Different Components of Idealized Transmutation System........................... 3

Figure 1.3 Separation of Fission Products and Actinides................................................. 4

Figure 2.1 Schematic View of Smooth Cylindrical Tensile Specimen..........................11

Figure 2.2 Polarization Specimen..................................................................................... 11

Figure 3.1 Material Testing System (MTS)......................................................................15

Figure 3.2 CERT Machine for SSR Testing.....................................................................18

Figure 3.3 SSR Test Setup Showing Different Components...........................................18

Figure 3.4 Load Frame Compliance Test Data.................................................................19

Figure 4.1 Comparison of Stress-Strain Diagrams for at Different Temperatures 28

Figure 4.2 Comparison of Stress-Strain Diagrams at Different temperatures...............28

Figure 4.3 Comparison of Stress-Strain Diagrams at Different Temperatures..............29

Figure 4.4 UTS vs. Temperature........................................................................................31

Figure 4.5 YS vs. Temperature..........................................................................................32

Figure 4.6 %E1 vs. Temperature........................................................................................32

Figure 4.7 %RA vs. Temperature......................................................................................33

Figure 4.8 Uniform Strain vs. Temperature......................................................................33

Figure 4.9 SEM Micrograph of Alloy HT-9 at Room Temperature for SpecimenTempered for 1.25 hrs (35X)........................................................................ 34

Figure 4.10 SEM Micrograph of Alloy HT-9 at 600°C for Specimen Temperedfor 1.25 hrs (35X).......................................................................................... 34

Vll



Figure 4.12 SEM Micrograph of Alloy HT-9 at 600°C for Specimen Temperedfor 1.25 hrs (35X)..........................................................................................35


Figure 4.14 SEM Micrograph of Alloy HT-9 at 600°C for Specimen Temperedfor 2.25 hrs (35X).......................................................................................... 35

Figure 4.16 Failure Stress vs. Tempering Time................................................................. 37

Figure 4.17 Time to Failure vs. Tempering Time..............................................................38

Figure 4.18 %E1 vs. Tempering Time.................................................................................38

Figure 4.19 %RA vs. Tempering Time...............................................................................39

Figure 4.20 Calibration Curve using GAMRY Potentiostat............................................. 40

Figure 4.21 CPP Diagram in 30°C Neutral Solution........................................................41

Figure 4.22 CPP Diagram in 90°C Neutral Solution........................................................41

Figure 4.23 CPP Diagram in 30°C Acidic Solution.......................................................... 42

Figure 4.24 CPP Diagram in 90°C Acidic Solution.......................................................... 42

Figure 4.25 Epit vs. Temperature........................................................................................43

Figure 4.26 Optical Micrographs of Alloy HT-9 under Different Heat-Treat Conditions

................................................................................................................... 44

Figure 4.27 Optical Micrographs of Tensile Specimens Tempered for 1.25 hours.........45

Figure 4.28 Optical Micrographs of SSR Test specimens in 90°C Acidic Solution........45

vm


ACKNOWLEDGEMENTS

First and foremost, I wish to thank Dr. Ajit K.Roy, my research advisor, for his

valuable guidance, and for having been a constant source of inspiration for this work. I

really admire Professor Dr. Ajit K.Roy’s dedication to his research; I have learned a lot

from his approach of conducting research.

I also thank Dr. Anthony Hechanova, Director of Transmutation Research Program

(TRP), Dr. Brendan J.O’toole, Department of Mechanical Engineering and Dr.

Venkatesan Muthukumar, Department of Electrical & Computer Engineering, UNLV, for

their direct and indirect contributions for the research and serving on my thesis

committee. I would also like to thank Dr. Mohamed B.Trabia, chairman of department of

mechanical engineering,.

Acknowledgement is made to the support of the United States Department of Energy

(USDOE) under contract no: DEFG042001AL67358.

I would like to thank my parents, Mr. Subba Rao and Mrs. Chandra Sahaja for all

their support and belief in me, and my brother Pramod for supporting me during rough

times.

I would like to acknowledge the support and help of my friends, Srinivasa Rao

Kukatla, Venkata Nagarjuna Potluri, Satish Babu Dronavalli, Narendra Kothapalli,

Suresh Babu Sadineni, Sudheer Sama and many colleagues throughout this research.

IX


CHAPTER 1

INTRODUCTION

Over the past two decades, extensive efforts have been focused to determine the

suitability of the Yucca Mountain site, near Las Vegas, Nevada to contain highly

radioactive nuclear waste inside a geologic repository. The purpose of this repository is to

safely dispose highly radioactive nuclear waste such as spent nuclear fuel (SNF) and

defense high-level-radioactive waste (HLW) for at least 10,000 years. The primary goal

to build this repository is to isolate the SNF/HLW from the near-field environment.^’

Nuclear waste is comprised of used fuel discharged from operating nuclear reactors.

Currently, nearly 20% of the nation’s electricity is being produced from nuclear power

using the existing operating plants. Over 87,000 metric tons of SNF are expected to be

produced from approximately 100 operating nuclear power plants over their lifetimes in

the proposed Yucca Mountain repository. Approximately 70,000 tons of SNF and HLW

are designed to be disposed of in Yucca Mountain. This amount represents nuclear waste

produced by the past and present day reactors. However, by the year 2050, almost 1

million tons of nuclear waste may require disposal worldwide. Such projection would

indicate the need to build and commission a repository of the scale of the Yucca

Mountain somewhere in the world roughly every three to four years.

Actually, in the SNF, only about 1% of its content is harmful. Therefore, this 1%

poses a severe risk to the future generations, requiring long-term disposal of these

1


hazardous materials. This 1% of SNF is primarily made up of americium (Am),

plutonium (Pu), neptunium (Np) and curium (Cm), and also long-lived isotopes of iodium

(I) and technetium (Tc) created as by-products resulting from the fission process inside

the nuclear reactors. Am, Pu, Np and Cu are called as trasuranic elements. The long term

toxicity of the nuclear waste depends on these transuranic elements. The toxic nature of

SNF can be reduced below that of uranium ore within a period of several hundred of

years by removing these transuranic elements from SNF/HLW. Different approaches

proposed for spent fuel management are shown in Figure 1.1.

Spent Fuel Fmrn OommerdalPlmib r

OkeotDisposa

Spentfuel

Recytie

PU

Tam, «vaneat,

Residing

--- -- - ► OUREX ----- * SiparMlcnsP i\/u ra n lu m P u A / u r a i u m

W M deYRecyrle ^

(Existing Fleet)

Long Tam

m yssPu AcUmües

PmductsmepD$#y

J Transuîiter , (laênlVFaAReaiA:/I ÂtceteratorDiwenSysieiw)

t Tmoe PuL TmceAdlnldes

FisekmPittWt %@Wtov

Figure 1.1 Approach to Spent Fuel Management

Removal of Pu and other transuranic elements from SNF can minimize the long-term

heat management issues within the geologic repository. The possibility of penetration of

radioactive materials into the biosphere in future can be reduced or eliminated by


removal of Np, Tc and I. Further, the removal of Pu from the SNF could enable the

recovery of Pu for nuclear proliferation. In essence, the development of a large nuclear

waste repository is driven by the presence of this small amount of long-lived highly toxic

materials contained in SNF. Thus, in order to store the SNF for a much shorter duration

in the potential repository, and to avoid construction of additional geologic repository in

future, these long-lived isotopes and fission products must be minimized or eliminated.

This goal can be accomplished through a process known as transmutation. Different

stages involved in the transmutation process are shown in Figure

s p a t t i

JL.

rqpm«c«M

■pu, MkmcAc-tinittes

fud ?

t r a n s m w l a l i o n r e a K t e r

Eadwmjclidt» Impsacliœa! to Tt:aasmute

s h f i r t a m S m c d i u m - l i v e i t - » S s s i o a p r o j e t s

noit ttanwritMatlK» wiâ

W a s t e M a i H f a n a A

storage for centtirks Of repositoty

t o w 4 s » t e l w a s t e c sposal

{ioteimctWetevd w a s t e d i s p o s a l

Figure 1.2 Different Components of Idealized Transmutation System


Transmutation occurs when the nucleus of an atom changes because of natural

radioactive decay, nuclear fission, nuclear fusion, neutron capture, or numerous other

processes. The United States transmutation program objective is to transform the long-

lived actinides and fission products into stable or significantly shorter-lived nuclides. The

goal is to have wastes, which may become radiologically innocuous in only a few

hundred years. Elimination or minimization of long-lived actinides and fission products

irom SNF is accomplished by impingement of neutron flux onto it, thus inducing

transmutation. Most transmutation processes involve the use of nuclear reactors or

particle accelerators. Some radiotoxic nuclides, such as Pu-239 and the long-lived fission

products Tc-99 and 1-129, can be transmuted (fissioned, in the case of Pu-239) with

thermal (slow) neutrons. The process of separation of fission products (FP) and minor

actinides (MA) are shown in Figure 1.3.

Initial Materials: UraniumCladding & Structures

fp

/ I I

n

f i

fp

uPu or MA

e è fp

Resulting Materials:UraniumPlutonium & Minor Actinides (MA)Fission ProductsActivated Cladding & Structures

X \ •Pu or \ U

• i'-èPu or • w MA \ U

Figure 1.3 Separation of Fission Products and Actinides


The minor actinides including Np, Am and Cm, and the higher isotopes of Pu, which

are all highly radiotoxic, can be more readily destroyed by fissioning with a fast-neutron

energy spectrum, where they can also contribute to the generation of power

With repeated recycling in a transmutation system, the radiotoxicity of SNF can be

reduced to a point that, after a decay period of less than 1000 years, it is less toxic than

the uranium ore originally used to produce the fuel. The need for a waste repository is

certainly not eliminated, but the hazard posed by the disposed waste materials is greatly

reduced, thus, requiring shorter disposal period.

Transmutation involves bombarding a target material such as molten lead-bismuth-

eutectic (LBE) by protons generated by an accelerator, thereby producing neutrons or in a

nuclear reactor. These neutrons are then impinged upon HLW and SNF at a very high

speed, thus minimizing or isolating highly radioactive isotopes and fission products. This

enables the storage of SNF/HLW for much shorter durations in the repository due to their

reduced half-lives. The advantages associated with the use of a transmutation process are

the reduction of the volume, toxicity and fissile content of the waste requiring disposal,

minimization of materials that may create proliferation and environmental risks, and

development of a simple repository. During transmutation, significant amounts of heat

can be generated in the target material (molten LBE). However, the molten LBE will be

contained in a sub-system structural container made of a martensitic stainless steel, such

as Alloy HT-9. Since the molten LBE will be subjected to stresses during neutron

generation at elevated temperatures ranging between 400 and 600°C, the target structural

material (Alloy HT-9) may also undergo plastic deformation in this temperature regime.


Thus, this investigation is focused on the evaluation of the tensile properties of

martensitic Alloy HT-9 at elevated temperatures. Mechanical properties of Alloy HT-9

have been evaluated using a mechanical testing system (MTS) in the presence of nitrogen

at temperatures ranging from ambient to 600°C as a function of different tempering times.

Corrosion studies have also been performed to evaluate the stress corrosion cracking

(SCC) and localized corrosion (pitting and crevice) behavior of this alloy. Metallurgical

microstructures, and the extent and morphology of failures at different testing

temperatures were analyzed by optical microscopy and scanning electron microscopy

(SEM), respectively.


CHAPTER 2

MATERIALS AND ENVIRONMENTS

2.1 Test Materials

The material tested in this study is Alloy HT-9 which is a martensitic stainless steel.

Alloy HT-9 is also called a 12Cr-lMoVW steel. It has a high chromium (Cr) content of

about 12%. Hence Alloy HT-9 is also called a high-chromium martensitic stainless steel.

Presence of increased Cr content in this steel provides excellent resistance to atmospheric

corrosion and resistance to degradation in many organic media. The presence of

molybdenum (Mo) enhances the localized corrosion resistance in environments

containing deleterious species by preventing the breakdown of protective oxide films.

Alloy HT-9 has a body-centered-cubic (BCC) structure. Physical and thermal properties

of this alloy are given in the Table 2.1.

Martensitic stainless steels are considered to be potential candidates for the blanket

and first wall structures of a fusion reactor. "* Several factors need to be considered in

selecting the structural material for transmutation applications. These factors include

mechanical, thermal, physical and chemical properties, cost, availability, capability of

withstanding radiation damage and some neutronic factors. Alloy HT-9 can be used up to

a temperature of 500°C in Pb-Li coolant.^^^


Martensitic alloys are also finding increased application in the fast breeder reactor

systems. Alloy HT-9 possesses better corrosion and swelling resistance and provides

excellent resistance to irradiation embrittlement at 60°C. A major concern on the effect of

extremely high electromagnetic fields on a ferromagnetic structure was alleviated when it

was realized that a ferromagnetic material would behave paramagnetically in an

extremely strong magnetic field.

Martensitic stainless steels have been developed for both in-core applications in

advanced liquid metal fast breeder reactors (LMFBR) and for first wall and structural

materials applications for commercial fusion reactors. Alloy HT-9 has been extensively

tested for LMFBR applications and has shown to resist radiation damage, providing a

creep and swelling resistant alternative to austenitic stainless steels. Degradation in

fi-acture toughness and charpy impact properties have been observed with this alloy, but

these properties are sufficient to provide reliable service performance. Tungsten-

stabilized martensitic stainless steels have appropriate properties for fusion applications.

Radioactivity levels become benign after less than 500 years of service, giving excellent

radiation damage resistance. Moderate strength, ample corrosion resistance, and excellent

resistance to swelling in the fast neutron environment has made Alloy HT-9 a primary

candidate material for use as cladding in the current U.S. fast reactor designs.^^^


Table 2.1 Physical and Thermal Properties of Alloy HT-9

Property Value

Thermal Conductivity, W/m*K 28

Modulus of Elasticity, Gpa (10^ psi) 160

Poisson’s Ratio 0.33

Coefficient of Thermal Expansion per °C (°F) * 10 ^ 12.5

Experimental heats of Alloy HT-9, tested in this investigation, were melted by a

vacuum-induction-melting practice at the Timken Research Laboratory, Canton, OH,

followed by different fabricating processes that included forging, hot rolling and cold

rolling. Since significant amount of residual or internal stresses were generated during

these manufacturing processes, the test materials were subsequently thermally-treated to

relieve these internal stresses and achieve the desired metallurgical microstructures.

These thermal treatments included austenitizing at 1850°F, followed by an oil-quench

(OQ). Subsequently, they were tempered at 1150°F, followed by air-cooling (AC). These

types of thermal-treatments resulted in a fully-tempered fine-grained microstructure

characteristics of a martensitic stainless steel without the formation of any retained

austenite. The chemical compositions of two experimental heats of Alloy HT-9 are

shown in Table 2.2.


Table 2.2 Chemical Composition (%wt) of Alloy HT-9

Material / Heat No.

C Mn P S Si Cr Ni Mo Cu V W

HT-92048

0.18 0.40 .012 0.004 0.20 12.6 0.49 1.00 0.01 0.30 0.46

HT-92049

0.19 0.41 0.012 0.004 0.20 12.31 0.50 1.00 0.01 0.30 0.47

2.2 Test Specimens

The heat-treated materials, in the form of round bars, were subsequently machined to

fabricate smooth cylindrical specimens having 4-inch overall length, 1-inch gage length

and 0.25-inch gage diameter, as illustrated in Figure 2.1. These specimens were machined

in such a way that the gage section was parallel to the longitudinal rolling direction. The

gage length to the diameter (1/d) ratio of these specimens was maintained at 4 according

to the ASTM Designation E 8 .^ The tensile properties were determined by using these

specimens in an MTS machine (Model 319.25). Specimens for localized corrosion

studies were also manufactured from these materials according to the ASTM designation

G 5. * Since the corrosion properties of engineering materials depend on the surface

finish of the test specimens, the polarization specimens were properly polished prior to

their testing. The schematic view of the polarization specimen is shown in Figure 2.2.

10


7 /1 6 - 2 0 UNF-2AIZ^ôîTbI# 3 CENTER DRILL

BOTH ENDS (OPTIONAL)

R ~ 0 .Q 01[^

L a b e l to o th e n d s o f t h e sp e c im e n a c c o r d in g t o t h e a t t a c h e d s p e c l f l c a t i o t

C y lin d ric a l T h r e a d e d Dob B o n e I e n s i le S p ec im en

iDHC-gQ0 3 / 2 6 / 0 2A p p ro v e d FPr. Roy

Figure 2.1 Schematic View of Smooth Cylindrical Tensile Specimen

N D H O L E10

S E C T I O N A - A

S C A L E 1 . 0 0

- 0 . 375± O , O O 5

S C A L E A . 00

OIHCNSIONS AKE IN IIKNES UNLESS OTHEIWISE SPECIFIED

SURFACE R0U6NNE3S g T

DO NOT SCALE DRAtING

U N V E R S T Y O F N E V A D A . L A S V E G A S D E P A R T M E N T O F M E C H A N I C A L E N G M E E R N G

E L E C F R O C H E M I C A L P O L A R I Z A T I O N S P E C I M E N

DRAIING BT: MARTIN LEVIS è t f 1 I o n 1 REVA 1 1 O O O l l o i

EFFECTIVE DATE 08/08/01 | S C « 4: 1 & NOTlD I SHEET 1 OF 1

T

Figure 2.2 Polarization Specimen

11


2.3 Test Environments

Molten LBE is surrounded by target structural material such as Alloy HT-9. This

target structural material can undergo corrosion in molten LBE environment. Due to lack

of facilities to accommodate testing in the molten LBE environment at the University of

Nevada Las Vegas (UNLV), the corrosion experiments in the presence of molten LBE

were performed at the Los Alamos National Laboratory (LANL). Corrosion testing at

UNLV has been performed in neutral and acidic solutions to evaluate the susceptibility of

Alloy HT-9 to SCC, and localized corrosion such as pitting and crevice. Corrosion

studies have been performed at ambient temperature, 60 and 90°C. These tests are aimed

at generating a corrosion database in aqueous environments for comparison purposes.

The chemical compositions of two aqueous environments used in corrosion testing are

given in Table 2.3.

The tensile testing using smooth cylindrical specimens was performed at ambient and

elevated temperatures in the presence of nitrogen to avoid oxidation.

Table 2.3 Chemical Composition of Test Environments (gram/liter)

Environment(pH)

CaClz K2SO4 MgSOj NaCl NaNOj Na2S04 HCl

Neutral (6-6.5) 2.769 7.577 4.951 39.973

31.529 56.742

Acidic (2-2.2) 2.769 7.577 4.951 39.973

31.529 56.742 Added to attain the desired

pH

12


CHAPTER 3

EXPERIMENTAL PROCEDURES

The high temperature tensile properties of Alloy HT-9 were evaluated by using an

axial/torsional material testing system (MTS). The susceptibility to SCC in neutral and

acidic aqueous environments was evaluated by using slow-strain-rate (SSR) testing

technique at ambient temperature and 90°C. The localized corrosion behavior was

evaluated by using the electrochemical cyclic potentiodynamic polarization (CPP)

technique using a potentiostat manufactured by the Gamry Instruments. Finally,

fractographic and metallographic evaluations were performed by SEM and optical

microscopy, respectively. The detailed experimental techniques are discussed next in the

following subsections.

3.1. Tensile Testing

The tensile properties including the ultimate tensile strength (UTS), yield strength

(YS) and ductility parameters such as percentage elongation (%E1) and percentage

reduction in area (%RA) were evaluated at ambient temperature, 100, 300, 400, 500 and

600°C using an MTS unit. The smooth cylindrical specimens were strained in tension at a

strain rate of lO'^/sec according to the ASTM Designation E 8. ^ A minimum of two

specimens were tested under each experimental condition and an average value was

determined. The experimental data such as the load, time, and extensometer reading were

13


recorded in the data file at the rate of 100/sec. The engineering stress versus engineering

strain curves were developed using these data. The magnitude of the yield strength (YS)

was determined by the point of intersection of a line drawn parallel to the linear portion

of this curve at a strain offset value of 0.2% of strain. UTS, %E1, %RA and uniform

elongation were determined using this plot and the dimensions of the cylindrical

specimen before and after testing.

The MTS unit (Model 319.25), shown in Figure 3.1, had an axial load transducer of

55 kip (250 kN) and a torsional load transducer of 20,000 Ibf-in (2200 N-m) capacity. It

had a hydraulically-controlled actuator with 5.5” stroke and approximately 55° angular

rotation. It consisted of a large heavy-duty load frame with an adjustable crosshead

attached to the wedge grip at the top, and a movable actuator with another wedge grip at

the bottom to enable loading and unloading of the test specimen. The axial motion can be

controlled by force, displacement, or an external signal from the strain gage. The

torsional motion can be controlled by torque, angular position, or an external signal from

the strain gage. The specimen was mounted between two wedge grips and was pulled by

the movable actuator. The load cell, contained in the crosshead, measured the applied

force on the tensile specimen. The movement of the crosshead relative to the locked

crosshead generates the strain within the specimen and consequently, the corresponding

load.

14


tr 4# 11

ifI ( (.T iim ic 1 k 'a im u Laser

Extensometer( T ia m n e r

High Temperature Grip System

/Nitrogen Supply System

ManualControl( P O D )

IComputer That Controls MTS

Figure 3.1 Material Testing System (MTS)

15


The MTS machine was equipped with an 8-channel signal-conditioning box for

monitoring the strain gages, extensometers, and temperature sensors. Signals from this

box were processed directly by the MTS control software programs (Test Star 790.00 v

4.0E and Test Ware SX v 4.0D) that automatically controlled all signals during testing. A

laser extensometer having a scan rate of 100 scans/sec was added to this MTS unit to

measure the elongation of the gage section of test specimen during plastic deformation

under tensile loading. The MTS unit was modified to accommodate high-temperature

testing in the presence of nitrogen using a ceramic-lined custom-made chamber. The

testing temperature inside this chamber was monitored by two K-type thermocouples. A

pair of custom-built water-cooled specimen grips made of maraging steel (M250) was

attached to the MTS machine to prevent these grips from being heated during testing at

elevated temperatures. Temperature profiles were developed to determine the times

needed to achieve the desired test temperatures as a part of the furnace calibration

process. The resultant times and the environment-chamber set point temperatures for

different target temperatures in the presence of nitrogen gas at 20 bar on Argon scale are

shown in Table 3.1.

Table 3.1 Minimum Times Needed to Reach the Desired Temperature

Material Target temperatureCO

Environmental chamber set point temperature

CO

Minimum time to reach the target temperature

(minutes)

AlloyHT-9

100 143 60300 363 60400 467 55500 563 50600 658 50

16


3.2. Slow-Strain-Rate Testing

Slow-strain-rate (SSR) testing was performed using a specially-designed system

known as a constant-extension-rate-testing (CERT) machine, as shown in Figure 3.2.

This equipment enabled testing to simulate a broad range of load, temperature, strain-rate

and environmental conditions using both mechanical and electrochemical corrosion

testing techniques.^^^ These machines, designed and manufactured by the Cortest Inc,

offered accuracy and flexibility in testing the effect of strain rate, providing up to 7500

lbs of load capacity with linear extension rates ranging from 10' to 10 * in/sec. To ensure

the maximum accuracy in the test results, this apparatus was comprised of a heavy duty

load-frame that minimized the system compliance while maintaining precise axial

alignment of the load train. An all-gear drive system provided consistent extension rate.

Added features included a quick-hand wheel to apply a pre-load prior to the operation.

The SSR test setup used in this investigation consisted of a top-loaded actuator,

testing chamber, linear variable differential transducer (LVDT) and load cell, as shown in

Figure 3.3. The top-loaded actuator was intended to pull the specimen at a specified strain

rate, so that the spilled solution, if any, would not damage the actuator. A heating coil

was connected to the bottom cover of the environmental chamber for elevated-

temperature testing. A thermocouple was coimected through the top cover of this

chamber to monitor the testing temperature. The load cell was intended to measure the

load through an interface with the front panel. The LVDT was used to record the

displacement of the gage section during testing.

17


Constant Extension, Rate Testing MacWncs

A -L V D T B - Top Actuator C - Environmental Chamber D " Bottom Actuator

Figure 3.2 CERT Machine for SSR Testing

Load cell

.Thermooupie/ s te p p e r m otor pow er drive

/LVDT0 I / - ' yBeld point

/eating coil

user in te rface

Testing c lia m b e r

Figure 3.3 SSR Test Setup Showing Different Components

18


Prior to the performance of SCC testing, the load-frame-compliance factor (LFCF,

the deflection in the frame per unit load) was determined by using ferritic Type 430

stainless steel specimen. The generated LFCF data, shown in the Figure 3.4, were input to

a load frame data acquisition system prior to testing.

Frame Compliance Test

0.70

0.60

Frame -1 (LFCF=4e-l

y = 4E.06x + 06380.50

.5 0.40

Frame-3 (LFCF=5e-6) y = 5E-06x + 0.2309

0.30

0.20

0.10Frame-2 (LFCF=5e-6

y = 5E-06x + 0.12480.00

0 1000 2000 3000 4000 5000 6000 80007000

Load (lb)

Figure 3.4 Load Frame Compliance Test Data

Smooth cylindrical specimens were used to evaluate the SCC susceptibility of Alloy

HT-9. Since the application of a too fast or a too slow strain rate can adversely influence

the role of mechanical and environmental factors in promoting SCC, a strain rate of

3.3x10'^ sec ' was used to optimize the combined effect of the applied load and the

testing environment. Selection of this strain rate was based on prior research performed at

the Lawrence Livermore National Laboratories.^'*'^ During SCC testing by the SSR

19


method, the specimen was continuously strained in tension until fracture, in contrast to

more conventional SCC test conducted under a sustained loading condition. The

application of a slow dynamic strain during the SSR testing to the specimen produced

failure that probably might not occur under a constant load or might have taken a

prohibitively longer duration to initiate cracking in the tested specimens.

Load versus displacement, and stress versus strain curves were plotted during these

tests. Dimensions (length and diameter) of the test specimens were measured before and

after testing. The cracking tendency in the SSR tests was characterized by the time-to-

failure (TTF), and the ductility parameters such as the percent elongation (%E1) and the

percent reduction in area (%RA). Further, the maximum stress (Om) and the true failure

stress (Of) obtained from the stress-strain diagram were taken into consideration. %E1,

%RA, Gm and Of were calculated using the following equations:

% El = -^0V y

xlOO

%RA = Xl OO

(Equation 3.1)

(Equation 3.2)

f A ,(Equation 3.3)

crm A

m

(Equation 3.4)

- 7TX £)„(Equation 3.5)

f (Equation 3.6)

20


Where,

4 = Initial cross sectional area

= Cross sectional area at the maximum load

Aj- = Cross sectional area at failure

P„ = Ultimate tensile load

P/ = Failure load

= Initial length

L f = Final length

D„ - Initial diameter

D f = Final diameter

3.3. Cyclic Potentiodynamic Polarization Testing

The susceptibility of Alloy FIT-9 to pitting and crevice corrosion was determined by

performing CPP experiments in neutral and acidic aqueous environments using a

GAMRY potentiostat. This type of testing is based on a three-electrode polarization

concept, in which the working electrode (specimen) acted as an anode and two graphite

electrodes (counter electrodes) acted as cathodes, as shown in Figure 3.5.

The reference electrode was made of Ag/AgCl solution contained inside a Luggin

probe having the test solution in it that acted as a salt-bridge. The tip of the Luggin probe

was placed at a distance of 2 to 3 mm from the test specimen, as shown in Figure 3.6. At

the onset, the corrosion or the open circuit potential (Ecorr) of the test specimen was

determined with respect to the Ag/AgCl reference electrode, followed by forward and

21


reverse potential scans at the ASTM specifie4’^ rate of 0.17 mV/sec. An initial delay of

50 minutes was given to attain a stable Ecorr value. The magnitudes of the critical pitting

potential (Epit) and protection potential (Eprot), if any, were determined from the CPP

diagram.

Reference Electrode

Graphite Counter Electrodes

orking Electrode (Test Specimen)

Figure 3.5 Electrochemical Testing Setup

Before conducting the CPP test, the potentiostat was calibrated according to the

ASTM Designation G 5. * Calibration of the potentiostat was performed to generate a

characteristic potentiodynamic polarization curve (Figure 3.7) for ferritic Type 430

22


stainless steel specimen in IN (1 Normal) H2SO4 solution at 30°C. Small cylindrical test

specimens made of ferritic Type 430 SS were used to generate the calibration curves.

WxyWn*2 -3 mm LuQ9#n C#pW##y

Figure 3.6 Luggin Probe Arrangement

3 ""ÎTT!»,, , ..T g

0.6 v/h

i ta s i l I s 1 1 : « 1 s i n i t l 1 j .L listi:

Figure 3.7 Standard Potentiodynamic Polarization Plot (ASTM G 5)'18)

23


3.4. Optical Microscopy

Characterization of metallurgical microstructures of the test specimens before and

after testing by optical microscopy is of paramount importance. The principle of an

optical microscope is based on the impingement of a light source perpendicular to the test

specimen. The light rays pass through the system of condensing lenses and the shutters,

up to the half-penetrating mirror. This brings the light rays through the objective to the

surface of the specimen. Light rays reflected off the surface of the sample then return to

the objective, where they are gathered and focused to form the primary image. This

image is then projected to the magnifying system of the eyepiece. The contrast observed

under the microscope results from either an inherent difference in intensity or wavelength

of the light absorption characteristics of the phases present. It may also be induced by

preferential staining or attack of the surface by etching with a chemical reagent.

The test specimens were sectioned and mounted using the standard metallographic

techniques, followed by polishing and etching to reveal the microstructures including the

grain boundaries. The polished and etched specimens were rinsed in deionized water, and

dried with acetone and alcohol prior to their evaluation by a Leica optical microscope. A

resolution of up to lOOOX can be achieved in this microscope.

3.5. Scanning electron microscopy

In a scanning electron microscope (SEM), electrons from a metal filament are

collected and focused, just like light waves, into a narrow beam. The beam scans across

the subject, synchronized with a spot on a computer screen. Electrons scattered from the

subject are detected and create a current, the strength of which makes the spot on the

24


computer brighter or darker. This creates a photograph-like image with an exceptional

depth of field. Magnifications of several thousand times are possible in SEM. Normally,

SEM provides black and white micrographs. A JEOL-5600 scanning electron

microscope, capable of resolution of up to 50 nm at magnifications of up to 100,000

times, was used for fractographic evaluations.

The extent and morphology of failure in the tested specimens were determined by

SEM. Analysis of failure in metals and alloys involves identification of the type of

failure. The test specimens were sectioned into Vi to 3/4 of an inch in length to

accommodate them in the vacuum chamber of the SEM. Usually, failure can occur by

one or more of the several mechanisms, including surface damage, such as corrosion or

wear, elastic or plastic deformation and fracture. Failures can be classified as ductile or

brittle. Dimpled microstructure is a characteristic of ductile failure. Brittle failure can be

of two types, intergranular and transgranular. An intergranular brittle failure is

characterized by crack propagation along the grain boundaries while a transgranular

failure is characterized by crack propagation across the grains.

25


CHAPTER 4

RESULTS

4.1 Hardness vs. Tempering Time

The measured hardness values in Rockwell C scale (Rc) resulting from austenitizing

and tempering of Alloy HT-9 for three different time periods are shown in Table 4.1.

This table shows the average hardness values based on three measurements along the

diameter of the round bar specimen. As anticipated, the hardness value was reduced due

to tempering, showing gradual reduction with increasing tempering time.

Table 4.1 Hardness Due to Thermal Treatments

Heat-Treating Conditions Hardness (Rc)

Austenitized at 1850°F/1 hr/Oil-Quenched (OQ) 52

Quenched and Tempered at 1150°F/1.25 hrs/Air Cooled (AC) 31

Quenched and Tempered at 1150°F/1.75 hrs/AC 28

Quenched and Tempered at 1150°F/2.25 hrs/AC 27

4.2 Ambient-Temperature Mechanical Properties

The results of ambient-temperature mechanical properties of Alloy HT-9 using an

MTS machine are given in the Table 4.2. These data indicate that no significant variation

26


in UTS, YS, %E1 and %RA was observed due to different tempering times, even though

the hardness value was reduced with longer tempering time, as indicated above.

Table 4.2 Ambient Temperature Tensile Properties of Alloy HT-9

Tensile Tempering RoomProperties Time Temperature

1.25 hr 138.5UTS (ksi) 1.75 hr 137.4

2.25 hr 135.11.25 hr 111.4

YS (ksi) 1.75 hr 111.22.25 hr 110.51.25 hr 21.07

%E1 1.75 hr 19.652.25 hr 20.481.25 hr 58.54

%RA 1.75 hr 58.692.25 hr 58.52

4.3 Elevated Temperature Tensile Testing

Comparative analyses of the stress-strain diagrams for Alloy HT-9 at different

temperatures are shown in Figures 4.1 through 4.3 as a function of different tempering

times.

27


UTS Alloy HT-9, Q u en ched /T em pered (Q&T)H eat No: 2049Tem pering Time: 1.25 hours

140YS

120

FS100 500°C

600°CCO

2

0.2 0.25 0 .3 0.35 0.40.05 0.1 0 .150Strain

Figure 4.1 Comparison of Stress-Strain Diagrams at Different Temperatures

RT UTS140 YS

Alloy HT-9, Q&THeat No: 2049T em pering Time: 1.75 hours

100°C

120

FS100

500°C

CO

I I00°C60

40

20

0.2 0.3 0.40.05 0.1 0.15 0.25 0.350

Strain

Figure 4.2 Comparison of Stress-Strain Diagrams at Different temperatures

28


140 1Y S Alloy HT-9, Q&T

H eat No: 2049Tem pering Time: 2 .2 5 hours

120 -300°C

100 -

500°C

I iOO°Ca>

20

0 0.1 0.2 0 .25 0.350.05 0 .15 0.3 0 .4 0.45

Strain

Figure 4.3 Comparison of Stress-Strain Diagrams at Different Temperatures

A careful review of these stress-strain diagrams indicate that the YS and UTS were

gradually reduced with increasing temperatures, as expected. However, the extent of this

reduction was more pronounced at temperatures above 400°C. It is interesting to note

that, even though the failure stress was also gradually reduced at higher testing

temperatures, the failure strain in the temperature regime of ambient to 300°C was

gradually reduced. This phenomenon is commonly explained by strain hardening effect in

martensitie stainless steels, especially in this temperature regime. Beyond 300°C, the

strain value was enhanced, showing significantly higher strains at 600°C, irrespective of

the tempering time.

As indicated in the previous section, the ductility in terms of %E1 and %RA was

determined using these stress-strain diagrams, and the initial and final dimensions of the

test specimen. The magnitudes of UTS, YS, %E1 and %RA, determined from these

tensile testing, are shown in Tables 4.3 and 4.4 as a function of the tempering time.

29


Table 4.3 UTS and YS of Alloy HT-9 at Different Temperatures

Temperature( ° C )

Ultimate Tensile Strength (ksi)

Yield Strength (ksi)

Tempering Time (hours) Tempering Time (hours)1.25 1.75 2 .2 5 1.25 1.75 2.25

RT 138.5 137.4 135.1 111.4 111.2 110.5100 132.6 127.4 125.5 107.2 101.6 101.5300 119 115.3 114.3 97.9 95.1 94.3400 112 109.8 107.3 91.7 90.4 89.1500 94.8 92.1 91.2 8 7 .2 85.2 84.7600 66.5 64.7 6 3 .8 65 63.2 6 2 .2

Table 4.4 %E1 and %RA of Alloy HT-9 at Different Temperatures

Temperature

C C )

% Elongation % Reduction in AreaTempering Time (hours) Tempering Time (hours)

1.25 1.75 2 .2 5 1.25 1.75 2 .2 5RT 21.07 19.65 20.48 58.54 58.69 5 8 .5 2100 19.33 20.60 19.93 62.16 62.27 6 2 .8 4300 17.36 17.62 17.80 62.48 63.15 62.11400 18.50 18.42 18.07 63.30 64.07 64.35500 26.90 26.45 25.81 77.60 78.41 78.50600 35.80 36.11 37.39 87.50 8 8 .3 9 8 8 .8 5

The room temperature tensile data have also been included in these tables for

comparison purpose. Also, the magnitude of uniform elongation determined from stress-

strain diagrams are shown in Table 4.5 for all testing temperatures at different tempering

times.

30


Table 4.5 YS vs. Uniform Elongation at Different Temperatures

Temperaturem

Uniform ElongationTempering Time (hours)

1.25 1.75 2.25RT 0.0681 0.0638 0.0626100 0.0581 0.0616 0.0571300 0.0483 0.0495 0.0483400 0.0487 0.0465 0.0445500 0.0296 0.0273 0.02775600 0.0162 0.0118 0.0128

These data indicate that the uniform strain was gradually reduced with increasing testing

temperature irrespective of the tempering time.

The data shown in Tables 4.3 and 4.4 are reproduced in a graphical format showing

the effect of temperature on the different tensile properties including UTS, YS, %E1 and

%RA. The effects of temperature on UTS and YS are shown in Figures 4.4 and 4.5,

respectively, once again showing a gradual decline in UTS and YS with increasing

temperature due to lower resistance to deformation at elevated temperatures.

160.0Alloy HT-9, Q&T

Heat No: 2049140.0

120.0

100.0Î “ 80.0

60.0Tempering Time

40.0. 1.25 hr• 1.75 hr* 2.25 hr

20.0

0.0500 600 700200 300 4000 100

Temperature(°C)

Figure 4.4 UTS vs. Temperature

31


120.0 -

Alloy HT-9, Q&T Heat No; 2049

100.0

80.0

60.0

40.0 Tempering Time

♦ 1.25 hr• 1.75 hr

» 2 .25 hr

20.0

0.0600300 500 7004000 100 200

Temperature(°C)

Figure 4.5 YS vs. Temperature

Simultaneously, the enhanced ductility at elevated temperatures in terms of %E1 and

%RA, shown in Figures 4.6 and 4.7, can be attributed to enhanced plastic flow at these

temperatures.

40 .00 n

Aiioy HT-9, Q&T H eat No: 204935.00

30.00

25.00

^ 20.00 -

15.00Tempering Time

10.00 -

. 1.25 hr

■ 1.75 hr A 2 .25 hr

5 .00 -

0.00600 700300 500200 4000 100

Tem perature(°C )

Figure 4.6 %E1 vs. Temperature

32


100.00 1Alloy HT-9, Q&T

H eat No: 204990.00

80.00

70.00 -

60.00

^ 50.00 -

40 .00 -

Tempering Time30.00

20.00 - . 1.25 hr ■ 1.75 hr * 2 .25 hr

10.00

0.00300 500 6000 100 200 400 700

Tem perature(°C )

Figure 4.7 %RA vs. Temperature

It should be noted that the drop in UTS and YS, as well as increase in ductility were more

pronounced at temperatures exceeding 400°C. The variation of uniform elongation with

testing temperature is shown in Figure 4.8 for specimens tempered for three different

times.

0.08 1

0.07Alloy HT-9, Q&T Heat No: 20490.06 -

m 0.05

LO 0.04

>5 0.03Tempering Time

0.02-* -1 .25 hr

1.75 hr -*-2 .25 hr

0.01

500 700200 400 600100 3000

Temperature (°C)

Figure 4.8 Uniform Elongation vs. Temperature

33


4.4 Fractographic Evaluations

The SEM micrographs of broken specimens tempered for different time periods and

tested at ambient temperature and 600°C are shown in Figures 4.9 through 4.14. An

examination of these micrographs reveals that at ambient temperature, the primary

fracture face contained a large number of cracks showing very little plastic deformation.

However, the primary fracture surface was characterized by a very large dimpled area

indicating enhanced ductility at 600°C. A similar behavior was observed with specimens

tested at other elevated temperatures. Those micrographs are shown in the appendix

section.

Figure 4.9 SEM Micrograph of Alloy HT-9 at Room Temperature for Specimen Tempered for 1.25 hrs (35X)

Figure 4.10 SEM Micrograph of Alloy HT-9 at 600°C for Specimen Tempered for 1.25 hrs (35X)

34






35


4.5 Slow Strain Rate (SSR) Testing

Stress-strain diagrams for Alloy HT-9 tested in the 90°C acidic solution using the

SSR technique are shown in Figure 4.15. These tests were performed using smooth

cylindrical specimens tempered for 1.25 and 2.25 hours, respectively. The magnitudes of

different tensile parameters were derived from these stress-strain diagrams, which are

shown in Table 4.6. These data indicate that the failure stress (of) was increased, but the

ductility parameters were reduced with specimens tempered for longer time. The effects

of tempering time on Of, TTF, % El and % RA are graphically shown in Figures 4.16

through 4.19, respectively.

120

2.25 hr100 -

80

Alloy HT-9, Q&T H eat No: 204960

I40 - Tem pering Time

1.25 hr2 .25 hr

20 -

0.1 0.120.06 0.080 0.02 0.04Strain

Figure 4.15 Comparison of Stress-Strain Diagrams in SSR Testing

36


Table 4.6 Results of SSR Testing

Environment/Temperature

Tempering Time (hrs)

%E1 %RA Pf(lbs)

Om(ksi)

Of

(ksi)TTF(hrs)

Acidic Solution (pH-

2.21)/90°C

1.25 10.68 9.86 3870.97 108 96.97 12.10

2.25 10.19 7.88 4313.56 108.18 102.83 11.47

Where,

%E1

%RA

Pf

Om

O f

TTF

Percentage Elongation

Percentage Reduction in Area

: Failure Load

Maximum Tensile Stress

: Failure Stress

: Time-to-Failure

120

100

80 -

60

40

20

0

Alloy HT-9, Q&T Heat No: 2049

0.5 1 1.5Tempering Time (Hrs)

2.5

Figure

4.16 Failure Stress vs. Tempering Time

37


14 1

12 -

10 -

o 6

Ei- 4 4

Alloy HT-9, Q&T Heat No: 2049

0.5 1 1.5

Tempering Time (Hrs)

2.5

Figure

4.17 Time to Failure vs. Tempering Time

12 1

10

2 -

Alloy HT-9, Q&T H eat No: 2049

0.5 1 1.5

Tem pering Time (Hrs)

2 .5

Figure 4.18 %E1 vs. Tempering Time

38


12

10

2 -

Alloy HT-9, Q&T Heat No; 2049

0.5 1 1.5

Tempering Time (Hrs)

2.5

Figure 4.19 %RA vs. Tempering Time

4.6 Localized Corrosion Study

The calibration curve for the Gamry potentiostat, used in localized corrosion study

according to the ASTM Designation G 5 ^ is shown in Figure 4.20. This curve closely

matches the standard potentiodynamic polarization curve shown in the ASTM

Designation G indicating the accuracy of the potentiostat in evaluating the localized

corrosion behavior of Alloy FIT-9. The cyclic potentiodynamic polarization (CPP)

diagrams for this alloy generated in neutral and acidic solutions at 30 and 90°C are shown

in Figures 4.21 through 4.24. The magnitude of the corrosion potential (Ecorr) and the

critical pitting potential (Epit), determined from these cyclic polarization diagrams, are

shown in Table 4.7. The effect of temperature on Epufor Alloy HT-9 in neutral and acidic

environments is shown in Figure 4.25. An examination of these data indieates that the Epu

value became more active (negative) in the acidic solution, compared to that in the

neutral solution, as expected. This phenomenon may be attributed to a synergistic effect

39


of pH and temperature on the localized corrosion susceptibility of this martensitie

stainless steel. No protection potential (Eprot) was observed in these tests.

1000

8 0 0

4 0 0

200

-200

-e o o

-1000

-12000-2 13-5 - 4

Kliigraji riT'2)j

Figure 4.20 Calibration Curve using GAMRY Potentiostat

40


CycNc Waozatioci Scan

Ëpit

IEcorr

iœ .O p I ÛQOfi ie.00n 100.0n 1.£B0p 10.00p IDÜ.Op 1.000 m 10.00m 100.0m 1.000

j(Afcfn*3

Figure 4.21 CPP Diagram in 30“C Neutral Solution

Gyde Pofafàaiiop Semi

Epit

#V '

t :

I Ecorr

lOjIOp WOJOp I j W n 1ÔÀ)n lOOjOn, I.OOOp lOJQOp lOOuOp iOOOm lOnOm 1000m IJÎOO

Figure 4.22 CPP Diagram in 90°C Neutral Solution

41


Çy<*c Scars

DOOOV

Ecorr

100 .0)1

Figure 4.23 CPP Diagram in 30°C Acidic Solution

Cÿcfic Pofaswrfran Sear

Epit

Ecorr

I

100.0 m

f (Aknf)

Figure 4.24 CPP Diagram in 90°C Acidic Solution

42


Table 4.7 CPP Test Results

Material/ Heat No Environment Temperature (°C)

Scan Rate (mV/sec)

Ecorr 5 m V(Ag/AgCl)

Epit, mV (Ag/AgCl)

Alloy HT-9/ 2048

NeutralSolution

30 0.166 -570 -890 0.166 -625 -347

AcidicSolution

30 0.166 -495 -12290 0.166 -475 -440

uf

0 -, -50

-100 -

-150

-200

-250

-3 0 0 -

-3 5 0 -

-400

-4 5 0 -

-50020

N eutral Solu tion A cidic Solution

4 0 6 0

T e m p e ra u re (°C)

80 100

Figure 4.25 Epit vs. Temperature

4.7 Metallographic Evaluations

The microstructural evaluation of Alloy HT-9 was performed using optical

microscopy (OM). The optical micrograph of the austenitized and quenched material is

shown in Figure 4.26 (a). The micrographs for Alloy HT-9, quenched and tempered for

three different times of 1.25, 1.75 and 2.25 hours are shown in Figures 4.26 (b), (c) and

(d) respectively. The results of OM on specimens tested at ambient temperature and

43


600°C are shown in Figure 4.27 (a) and (b), respectively. The examination of all these

micrographs indicates that fine-grained fully-tempered martensitic microstructure was

observed in all cases. The results of OM involving the SSR test specimens revealed

secondary cracks with some branching, as shown in Figures 4.28 (a), and (b).

(a) Austenitized and Quenched (b) 1.25 hours Tempering Time

(c) 1.75 hours Tempering Time (d) 2.25 hours Tempering

Figure 4.26 Optical Micrographs of Alloy HT-9 under Different Heat-Treat Conditions

44


(a) Tested at Ambient temperature (b) Tested at 600°C

Figure 4.27 Optical Micrographs of Tensile Specimens Tempered for 1.25 hours

(a) 1.25 Hours of Tempering (b) 2.25 Hours of Tempering

Figure 4.28 Optical Micrographs of SSR Test specimens in 90°C Acidic Solution

45


CHAPTER 5

DISCUSSIONS

Ambient and elevated temperature tensile properties of Alloy HT-9 were determined

to understand the deformation mechanism of this alloy as a function of temperature. The

susceptibility to SCC of this alloy was evaluated in 90°C acidic solution using the SSR

testing technique. Also, the localized corrosion behavior including pitting and crevice

corrosion was determined by electrochemical cyclic potentiodynamic polarization (CPP)

technique.

5.1 Effect of Thermal-Treatment

As anticipated, the hardness of Alloy HT-9 following the austenitizing and quenching

treatment was substantially high due to the formation of hard, but brittle martensite. The

purpose of tempering was to reduce the hardness value so that significant ductility could

be induced in this alloy due to the homogenization of metallurgical microstructure.

Different tempering times were given to the austenitized and quenched material to see if

the tempering time could influence the resultant ductility. As indicated in an earlier

section, the hardness value gradually became reduced with longer tempering time, as

anticipated. However, this reduction in hardness value was not reflected in the tensile

properties of Alloy HT-9 both at the ambient and the elevated temperatures.

46


Nevertheless, a uniform microstructure consisting of fine-grained and fully tempered

martensite was observed with specimens tempered for three different times.

5.2 Effect of Temperature on Tensile Properties

The results of tensile testing, presented in the previous section, clearly indicate that

the magnitudes of UTS, YS, %E1 and %RA were significantly influenced by the variation

in temperature during tensile testing. The reduced UTS and YS values with increasing

temperature could be attributed to enhanced movement of lattice imperfections such as

dislocations through the grain boundaries to the neighboring grains of this alloy due to

increased plastic flow with increasing temperature. At elevated temperatures, this alloy

was able to undergo plastic deformation more readily due to the enhanced plastic flow.

This reduction in strength at elevated temperatures was usually associated with increased

ductility in terms of %E1 and %RA, as observed by other investigators.^’ ’

In the temperature regime of ambient to 300°C, the ductility of this material was

reduced to some extent. This was characterized by reduced strain in the stress-strain

diagrams for this alloy, shown in the previous section. This behavior can be attributed to

the strain hardening p h e n o m e n o n * ^ ' t h a t can produce large number of defects

such as dislocations and voids, thus, increasing the resistance of this material to plastic

deformation and reducing the extent of ductility. However, beyond 300°C, the ductility of

this material was gradually increased, showing substantially higher %E1 and %RA values

at 500 and 600°C.

The magnitude of YS and UTS became significantly reduced at temperamres above

400°C, suggesting that a temperature in the vicinity of 400°C may represent the critical

47

R eproduced with perm ission o f the copyright owner. Further reproduction prohibited without perm ission.

temperature beyond which the strength of Alloy HT-9 may be drastically reduced due to

enhanced plasticity. For the same reason, the ductility parameters were also enhanced at

temperatures beyond 400°C. With respect to the effect of tempering time on the tensile

properties, the magnitude of UTS, YS %E1 and %RA was not at all influenced by the

changes in tempering time irrespective of the testing temperature.

5.3 Slow Strain Rate Testing

The results of SCC testing, conducted in a 90°C acidic solution by using the SSR

technique, showed that the failure stress (of) was increased but the ductility was reduced

as the tempering time was increased from 1.25 to 2.25 hours. It is well known that a

longer tempering time can produce improved ductility due to relaxation of internal

stresses that were generated during the quenching operation. This phenomenon can

possibly explain the cause of higher failure stress (of) with specimens tempered for 2.25

hours. However, some discrepancy was observed with ductility in terms of %E1 and

%RA, in that reduced ductility was observed despite increased Of value. Ideally, these

specimens should have given enhanced ductility values with increased tempering time.

No valid explanation can be provided at this time as to this unusual behavior related to

the ductility parameter. In view of these results, it is suggested that further study be

pursued in future to address this issue.

5.4 Electrochemical Polarization Testing

The results of localized corrosion study using the CPP technique revealed that the

magnitude of the critical pitting potential became more active in the acidic solution at

48


90°C. The more active potential is usually associated with increased susceptibility to

pitting and crevice corrosion due to the synergistic effect of the elevated temperature and

the acidic pH. The evaluation of the polarized specimens by visual examination showed

that the extent of localized attack was more pronounced in the 90°C acidic solution due to

the increased hydrogen ion (H^) concentration in the acidic solution, compared to that in

the neutral solution.

49


CHAPTER 6

SUMMARY AND CONCLUSIONS

The effect of tempering time on the tensile properties of quenched and tempered

martensitic Alloy HT-9 has been evaluated at temperatures ranging from ambient to

600°C in the presence of nitrogen. SSR testing has been performed to evaluate the SCC

behavior of this alloy in a 90°C acidic environment. The susceptibility to localized

corrosion including pitting and crevice corrosion has been determined by electrochemical

CPP method. Optical microscopy has been utilized to characterize the secondary cracks

during SCC. Fractographic evaluations of the tensile specimens have been performed by

SEM. The significant conclusions derived from this investigation are given below.

> The longer tempering time resulted in reduced hardness of this alloy due to

relaxation of internal stresses resulting from the quenching operation. However,

the metallurgical microstructure and the tensile properties at different

temperatures were not significantly influenced by the variation in tempering time.

> The tensile strength of Alloy HT-9 in terms of YS, UTS and Of was gradually

reduced with increasing temperature, showing significant reduction at

temperatures above 400°C.

> At temperatures, ranging from ambient to 300°C, the magnitude of failure strain

was reduced to some extent due to the strain hardening effect. However, the

50


ductility parameters in terms of %E1 and %RA were gradually enhanced at

temperatures above 300°C due to enhanced plastic flow.

> The dimpled area became larger with increasing test temperature indicating

enhanced ductility at elevated temperature.

> The failure stress in the SSR testing was higher for specimens tempered for a

longer time.

> All polarized specimens showed pitting and crevice corrosion, irrespective of the

testing environment. The magnitude of Epit became more active at elevated

temperature in both the test environments.

51


CHAPTER 7

FUTURE WORK

/ The effect of tempering time on the SCC susceptibility of Alloy HT-9 needs

further studies.

SCC data using aqueous environments should be correlated to those obtained in

the molten LBE environment.

/ Transmission electron microscopy should be used to analyze defects and their

interactions in Alloy HT-9 as a function of the testing temperature.

52


APPENDIX A: TENSILE DATA USING SPECIMENS TEMPERED FOR 1.25 HOURS

AS A FUNCTION OF TESTING TEMPERATURE

Material : Alloy HT-9 Heat Number : 2049 Austenitized I hr at I850F and OQ Tempered at II50F for I.25hrs and AC Testing Temp: Room TemperatureSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_RT#I 3.9998 in 0.2498 in 136.1160 ksi 109.5236 ksi 20.84 % 5&53 94

Alloy HT-9 2049 Stress vs Strain

140 n

120100

20

0.2500.100 0.150 0.2000.000 0.050

S train

Material : Alloy HT-9 Heat Number : 2049 Austenitized I hr at 1850F and OQ Tempered at II50F for 1.25hrs and AC Testing Temp: Room TemperatureSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H49I RT#2 4.0003 in 0.2499 in 137.5 ksi IIO.I ksi 22.13 % 59.68 %

A ky HT-9 2049 Stress vs Strain

140

120100

£CO

0.150 0.200 0.2500.050 0.1000.000

S train

53


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.25hrs and AC Testing Temp: Room TemperatureSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_RT#4 4.0002 in 0.2506 in 142 ksi 114.7 ksi 20.25 % 59.42 %


160 1

140 -

120 100

stn

0,2500.100 0.150 0.2000,000 0.050

S tra in

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.25hrs and AC Testing Temperature; 100°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_100#5 4.0013 in 0.2509 in135.3 ksi111.3 ksi 1R79%6 6154 94


160 -

140 -

120 "5 100 ■

0.200 0.2500.100 0.1500.000 0.050

S train

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.25hrs and AC Testing Temperature: 100°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_100#6 4.0022 in 0.2505 in 131.7334 ksi 105.3942 ksi 1R81%6 61.72%

Altay HT-9 2049 Stress vs Strain

160 1

140 -

120 -

100

60 -

40

2

0.2500.100 0.150 0.2000.000 0.050

S train

54


Material ; Alloy HT-9 Heat Number : 2049 Austenitized Ihr at I850F and OQ Tempered at 1150F for 1.25hrs and AC Testing Temperature: 100°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_100#7 4.0002 in 0.2502 in 130.8 ksi 105.0 ksi 20.40 % 61.21 %


160 -|

140 -

120 ■

100 -

4 0 -

0.2500.000 0.050 0.100 0.150 0.200S train

Material ; Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.25hrs and AC Testing Temperature: 300°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491 300#8 4.0010 in 0.2507 in118.3 ksi 97.0 ksi17.03 % 6258 94


160 1

140

120 -

100

CO

0.2500.100 0.150 0.2000.000 0.050

S train

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 115GF for 1.25hrs and AC Testing Temperature: 300°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_300#9 4.0000 in 0.2503 in 119.7 ksi 98.8 ksi 17.69 % 6238 94

A ky HT-9 2049 Stress vs Strain

160 1 140 120- 100

0.2500.000 0.100 0.150 0.2000.050

Strain

55


Material : Alloy HT-9 Heat Number ; 2049 Austenitized Ihr at 1850F and OQ Tempered at 115OF for 1.25hrs and AC Testing Temperature: 400°CSpeeimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491_400#10 3.9972 in 0.2500 in 111.7 ksi 91.9 ksi 18.57% 62.94 %

Alloy Hr-9 2049 Stress vs Strain

160 n140 -

_120- « 100

0.100 0.200 0.2500.050 0.1500.000S train


H491_400#13 4.0022 in 0.2508 in 112.1958 ksi 91.4095 ksi 18.44% 63.67 %


160-,

140

120 -100

%S

CO

0.2500.100 0.150 0.2000.0500.000Strain


H491_500#ll 4.0000 in 0.2506 in 94.6 ksi 88.2 ksi 25.96 % 76.37 %


160 n

140

120100

S 60-

" 40

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

S train

56


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 115OF for 1.25hrs and AC Testing Temperature; 500°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H491 500#14 3.9955 in 0.2512 in 94.9 ksi 86.2 ksi 2%89%6 7&86 94


160

140120100

0.000 0,050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain


H491_600#13 3.9972 in 0.2497 in 66.9 ksi 65.2 ksi 3548%6 8 7 .8 6 %


160140

_ 120

« 100

£

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain

57


APPENDIX B: TENSILE DATA USING SPECIMENS TEMPERED FOR 1.75 HOURS


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at I I 5OF for 1.75hrs and AC Testing Temp: Room TemperatureSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H492_RT#I 4.0002 in 0.2511 in 140.1 ksi 115.0 ksi 21.14% 59.05 %


160 n

140

120 -

100

Î“ 40 -

0.100 0.150 0.200 0.2500.000 0.050

Strain


H492_RT#2 4.0005 in 0.2510 in 134.7 ksi 110.1 ksi 18.15% 5833 94


160 1

140

1 2 0 -

100

m

0.150 0.200 0.2500.000 0.050 0.100Strain

58


Material : Alloy HT-9 Heat Number ; 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 100°C Specimen ID : H492_100#3Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

3.9965 in 0.2511 in 128.8 ksi 97.3 ksi 2L37 94 62.21 %


160

140

12010080

60

40

200 f— 0.000 0,050 0.100 0.200 0.2500.150

Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 100°C Specimen ID : H492 100#9Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

4.0017 in 0.2517 in 127.2 ksi 103.1ksi 20.27 % 62.48 %


160

140

120100

40

0.2500.000 0.050 0.100 0.150 0.200Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 100°C Specimen ID : H492_100#10Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

4.0140 in 0.2513 in126.3 ksi104.3 ksi 20.15% 62T2 94


160 1

140

120 -100-

I 40 -

0.2500.000 0.050 0.100 0.150 0.200S train

59


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 300°C Specimen ID : H492 100#4Length : 3.9967 inDiameter : 0.2496 inUltimate Tensile Strength Yield Strength %Elongation % Reduction in Area

116.2 ksi 96.0ksi17.78 %63.79 %


160

140

12010080

60

40

200 4— 0.000 0.200 0.2500.1500.050 0.100

Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature; 300°C Specimen ID : H492 400# 11Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

4.0103 in 0.2512 in 114.3 ksi 94.1 ksi 17.45 % 62.50 %


160

140 - 120 100 80 -

0.2500.2000.050 0.100 0.1500.000Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 400°C Specimen ID : H492_400#5Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

4.0000 in 0.2521 in 108.5 ksi 91.1 ksi 1&63Ï6 63.49 %


160 1

140 -

120

100

£ 60CO

0.200 0.2500.100 0.1500.000 0.050

Strain

60


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature; 400°C Specimen ID : H492 5GO# 12Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

4.0093 in 0.2512 in 111.1 ksi 89.7 ksi 18.19 % 64.65 %


160 1

140

120 -

100 -£S.</)

0.150 0.200 0.2500.000 0.050 0.100

Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 500°C Speeimen ID : H492_500#13Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

3.9980 in 0.2522 in92.5 ksi85.6 ksi 26H8 94 78.11 %


180

140

120

to

0.000 0.050 0.100 0.150 0.200 0.250 0.300

Strain


4.0005 in 0.2510 in91.7 ksi84.7 ksi 26.71% 78.71 %


160

140

120~ 100

20

0.000 0.050 0.100 0.150 0.200 0.250 0.300

S train

61


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 1.75hrs and AC Testing Temperature: 600°C Specimen ID : H492_600#7Length : 3.9977 inDiameter : 0.2504 inUltimate Tensile Strength Yield Strength %Elongation % Reduction in Area

66.1 ksi64.1 ksi 35H8 94 87.93 %


160

140

120100

(O

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain


4.0025 in 0.2515 in63.2 ksi62.3 ksi37.04 % 88.85 %


160

140

120 ~ 100

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain

62


APPENDIX C: TENSILE DATA USING SPECIMENS TEMPERED FOR 2.25 HOURS


Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 1150F for 2.25hrs and AC Testing Temperature: Room TemperatureSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H493_RT#1 3.9965 in 0.2513 in 132.8557 ksi 105.5616 ksi 20.40 % 57.66 %


160-,

140

120

100

OT

0.050 0.200 0.2500.000 0.100 0.150

Strain


H493_RT#2 3.9937 in 0.2510 in 139.0038 ksi 110.4325 ksi 20.29 % 58J6 94

Aiioy HT-9 2049 Stress vs Strain

160

140

120100JS

sCO

0.050 0.200 0.2500.000 0.100 0.150

Strain

63



H493_RT#3 3.9958 in 0.2509 in 133.461 ksi 115.444 ksi 20.75 % 59.15 %


140 -

120

f 100

0.2000.150 0.2500.000 0.050 0.100

Strain


H493 100#4 4.0080 in 0.2510 in 125.4905 ksi 101.1477 ksi

6L3694


160-,

140

120

100

%

0.150 0.200 0.2500.050 0.1000.000

S train


H493_100#5 3.9977 in 0.2522 in 125.4883 ksi 101.9283 ksi 18.99% 64.32%


160-,

140 -

120

100 -,

« ®o- 60

40

stn

0.150 0.200 0.2500.050 0.1000.000

Strain

64

R eproduced with perm ission o f the copyright owner. Further reproduction prohibited without perm ission.


H493_300#6 4.0090 in 0.2515 in 114.3509 ksi 93.8788 ksi 183494 6Z5194


160 1

140 120 -

100 -

0.050 0.150 0.200 0.2500.000 0.100

Strain


H493_300#7 4.0022 in 0.2513 in 114.2185 ksi 94.5891 ksi 17.25 % 61.70%

Aloy HT-9 2049 Stress vs Strain

160 -,

140

120

100 ■

£OT

0.150 0.200 0.2500.000 0.050 0.100

Strain

Material : Alloy HT-9 Heat Number : 2049 Austenitized Ihr at I850F and OQ Tempered at 1150F for 2.25hrs and AC Testing Temperature: 400°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H493_400#8 4.0128 in 0.2510 in 106.5091 ksi 87.4098 ksi 18.17% 65.22 %


160-,

140-

120

=5 100

40

0.2500.150 0.2000.000 0.050 0.100

Strain

65


Material ; Alloy HT-9 Heat Number : 2049 Austenitized Ihr at 1850F and OQ Tempered at 115OF for 2.25hrs and AC Testing Temperature: 400°CSpecimen ID Length Diameter Ultimate Tensile Strength Yield Strength %Elongation % Reduction in Area

H493_400#9 4.0105 in 0.2509 in 108.1399 ksi 90.7809 ksi 17.96 % 63.47 %


160

140

120

100£

m

0.100 0.2500.000 0.050 0.150 0.200

S train


H493_500#10 4.0160 in 0.2510 in 91.3207 ksi 84.4779 ksi 25.28 % 7&39T4

160

140

120

=5 100

% 80 £ 60

40

20

<o

00.000


0.050 0,100 0.150

Strain

0.200 0.250 0.300


H493_500#ll 4.0017 in 0.2507 in 91.0894 ksi 84.9419 ksi 25.54 % 7&59 94


160

140

120 M 100

80

60

40

20

Strain

0.250 0.300

66



H493_600#12 4.0083 in 0.2508 in 63.1944 ksi 61.3020 ksi 3735 89H4 94


160 -

140

120 -

^ 100

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain


H493_600#13 4.0075 in 0.2513 in 64.4086 ksi 63.1046 ksi 37.42 % 8R5694


160 -j

140

120

“ 100

£ 60

" 40

0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400

Strain

67


APPENDIX D: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR 1.25

HOURS AS A FUNCTION OF TESTING TEMPERATURE

(a) Tested at IOO°C (b) Tested at 300°C

m a m

(c) Tested at 400°C (d) Tested at 500°C

SEM Micrographs of Alloy HT-9 Tempered for 1.25 hours

68


APPENDIX E: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR 1.75


&(a) Tested at IOO°C (b) Tested at 300°C



69


APPENDIX F: SEM MICROGAPHS FOR SPECIMENS TEMPERED FOR 2.25


m - Æ -

m

(a) Tested at IOO°C (b) Tested at 300°C



70


BIBLIOGRAPHY

1) Transmutation Tour, Advanced Fuel Cycle Initiative (http://apt.lanl.gov/atw/)

2) Hisham Zeriffi, Annie Makhijani, “Nuclear Alchemy Gamble: An Assessment of Transmutation as Nuclear Waste Management Strategy”, Institute of Energy and Environmental Research, May 2000.

3) “Processing of Nuclear Wastes”, UIC Nuclear Issues Briefing Paper# 72, December 2001.

4) M.Victoria, D.Gavillet, P.Spatig, F.Rezai-Aria, S.Rossman, “Microstructure and Mechanical Properties of Newly Developed Low Activation Martensitic Steels”, Journal of Nuclear Materials, Vol.233-237, p 326-330, 1996.

5) “Choice of First Wall Material Physical Mechanical Thermal Chemical Neutronic Radiation Damage Cost Availability”, Lecture42, University of Wisconsin (fti.neep.wisc.edu/neep423/FALL98/Lecture42.pdf).

6) R.J.DiMelfi, E.E.Gruber, J.M.Kramer, “Microstructural Evaluation in a Ferritic- Martensitic Stainless Steel and its Relation to High-Temperature Deformation and Rupture Model”, RE-207, Argonne National Laboratory, Argonne, IL.

7) ASTM Designation E 8, “Standard Test Methods for Tensile Testing of Metallic Materials”.

8) ASTM Designation G 5, “Standard Test Methods for Tensile Testing of Metallic Materials”.

9) Corrosion Testing Equipment, Cortest, Incorporated (www.cortest.com)

10) A. K. Roy et., al. Cracking of Titanium Alloys under Cathodic Applied Potential , Framatome Cogema Fuels, September 1999.

11) ASTM Designation: G61-78, Standard Practice for Conducting CyclicPotentiodynamic Polarization Measurements for Localized Corrosion.

12) J.L. Martin and M. Victoria, ‘Deformation Mechanisms of Ferritic - Martensitic Steel between 290 and 870K’, Material Science & Engineering. A. structural materials; properties, microstructure and processing, p 159 - 163, May 30, 1993.

71


http://apt.lanl.gov/atw/

http://www.cortest.com

13)M. Victoria, D. Gavillet, P. Spating, F. Rezai-Aria, S. Rossmann, “Microstructure and Mechanical Properties of Newly Developed Low Activation Martensitic Steels”, Journal of nuclear materials, Vol.233-237, p 326-330, 1996.

14) Yu. Lakhtin, “Engineering Physical Metallurgy and Heat-Treatment”, MIR Publishers, Moscow.

15)R. Dutton and M. P. Puls, in A. W. Thompson and I. M. Bernstein (eds.). Effect of Hydrogen on Behavior of Materials, TMS-AIME, 1976, p. 516.

16) A. K. Roy, et. al., "Electromechanical Corrosion Studies of Container Materials in Repository-Relevant Environments," LLNL Report UCRL-ID-122860, December 1995.

17) Ajit K. Roy, Srinivas R. Kukatla, Bhagath Yarlagadda, “High Temperature Deformation Characteristics of Martensitic Stainless Steels,” SAMPE 2004, Long Beach, CA, USA

72


VITA

Graduate College University of Nevada, Las Vegas

Bhagath Yarlagadda

Local Address:4214 Grove Circle Apt # 3 Las Vegas, Nevada 89119

Degrees:Bachelor of Technology, Mechanical Engineering, 2002 Jawaharlal Nehru Technological University, Hyderabad, India

Master of Science, Engineering, 2004 University of Nevada, Las Vegas

Publications:Ajit. K. Roy, Srinivas R. Kukatla, Bhagath Yarlagadda, “High Temperature Deformation Characteristics of Martensitic Stainless Steels,” SAMPE 2004, Long Beach, CA, USA

S. R. Kukatla, B. Yarlagadda, V. N. Potluri, “Temperature Effect on Mechanical Properties of Target Structural Materials,” ANS Student Conference 2004, UW, Madison, WI, USA

Thesis Title: Elevated Temperature Mechanical Properties and Corrosion Characteristics of Alloy HT-9

Thesis Examination Committee:Chair Person, Dr. Ajit K.Roy, Ph. D.Committee Member, Dr. Anthony Hechanova, Ph. D.Committee Member, Dr. Brendan J.O’Toole, Ph. D.Graduate Faculty Representative, Dr. Venkatesan Muthukumar, Ph. D.

73


elevated temperature mechanical properties and corrosion

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