Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics Comprehensive nuclear materials 2 08 nickel alloys properties and characteristics
Trang 12.08 Nickel Alloys: Properties and Characteristics
T Yonezawa
Tohoku University, Japan
ß 2012 Elsevier Ltd All rights reserved.
2.08.2.1.1 Chemical compositions, physical properties, and mechanical properties 235
2.08.2.2.1 Chemical compositions, physical properties, and mechanical properties 241
2.08.2.3.1 Chemical compositions, physical properties, and mechanical properties 250
2.08.2.4.1 Chemical compositions, physical properties, and mechanical properties 253
2.08.4 Corrosion Resistance and Stress Corrosion Cracking Resistance 258
BWR Boiling water reactor
CRDM Control rod drive mechanism EBW Electron beam welding
FCAW Flux cored arc welding GTAW Gas tungsten arc welding HTGR High-temperature gas-cooled reactor
233
Trang 2HTH Precipitation hardening at about 715C
after solution annealing at a high
temperature near 1075C
HTTR High-temperature engineering HTGR test
reactor
IGSCC Intergranular stress corrosion cracking
MAG Metal active gas welding
MIG Metal inert gas welding
PWR Pressurized water reactor
PWSCC Primary water stress corrosion cracking
SCC Stress corrosion cracking
SMAW Shielded metal arc welding
TT Thermally treated or thermal treatment
2.08.1 Introduction
Nickel was first used as an alloying element for steels
in the mid-eighteenth century The development of
corrosion-resistant steels was started in the nineteenth
century.1,2 These studies led to the development of
various kinds of stainless steels, particularly in the
early 1900s Particularly, the 300 series austenitic
stain-less steels were developed and became the ‘most widely
used tonnage’ materials in the twentieth century
The nickel–copper Alloy 400 (Monel 400, UNS
N04400) was developed as the first nickel-based alloy
at the beginning of the twentieth century.3This alloy
was developed as an alternative
chloride-corrosion-resistant material to austenitic stainless steel
Nickel is a less noble element than copper;
how-ever, it is more noble than iron and zinc It exhibits
higher corrosion resistance than iron in most
envir-onments due to the formation of denser and more
protective corrosion films with superior passivation
characteristics compared to iron
Nickel has superior corrosion resistance in caustic
or nonoxidizing acidic solutions, and in gaseous
halo-gens It can be relatively easily alloyed with various
elements such as chromium, molybdenum, iron, and
copper Many nickel-based alloys have been
devel-oped and applied as corrosion-resistant alloys in
var-ious environments, as well as creep-resistant alloys in
high-temperature applications.4
Based on their excellent properties, nickel-based
alloys have been widely applied in a number of fields,
for example, the aerospace industry, chemical
indus-tries, and electricity generation plants In the nuclear
power industry, nickel-based alloys have been used inpressurized water reactors (PWRs) and boiling waterreactors (BWRs) since their initial development inthe early 1950s In particular, Alloys X-750 (UNSN07750) and X-718 (UNS N07718) have been widelyapplied, for example, for jet-engine blades, due totheir excellent creep strength A high-creep-strengthmaterial is one that is highly resistant to stress relax-ation at high temperatures Alloys X-750 and 718have therefore been applied as bolting and springmaterials for PWRs and BWRs
Alloy 600 (UNS N06600) has superior resistance tostress corrosion cracking (SCC) in boiling 42% MgCl2solution as high-chloride solutions.5In the Shipping-port and Yankee Rowe reactors, 347 stainless steelwas used as a steam generator (SG) tube material.(The Shippingport reactor was the first full-scalenuclear powered electricity generation plant (proto-type reactor), and the Yankee Rowe reactor was the firstcommercial PWR.) Beginning with the ConnecticutYankee PWR, the next electricity generation plant,Alloy 600 was used as the SG tube material, and thensubsequently applied in PWRs worldwide, due to itssuperior SCC resistance in high-chloride solutions.Among the other superior properties of Alloy 600,its thermal expansion coefficient is noted to be betweenthat of ferritic steels and austenitic steels Based on this,the residual stress and strain for dissimilar weld joints
of ferritic steels and austenitic steels can be minimized
by the use of Alloy 600 and its compatible weld metals
In nuclear power plants, ferritic steels and austeniticsteels are widely used as the main component materi-als, especially for the pressure boundary Numerousdissimilar metal weld joints are therefore found innuclear power plants Alloy 600 and its weld metalssuch as Alloys 82, 132, and 182 have also found wide-spread application in such plants
Nickel-based alloys were developed not only
as corrosion-resistant materials but also as resistant materials These alloys are suitable forvarious components and parts in light water reactors,heavy water reactors, gas reactors, etc
heat-The detailed features and various physical ties of these nickel-based alloys are described in thefollowing sections
proper-2.08.2 Nickel and Nickel Alloy Systems
Nickel by itself is a very versatile corrosion-resistantmetal and has a higher strength at elevated tempera-tures than steel Nickel forms a complete solid solution
234 Nickel Alloys: Properties and Characteristics
Trang 3with copper (as shown inFigure 1), manganese, and
gold.6Nickel forms a peritectic with iron (as shown in
Figure 2) and eutectics with many elements, such as
chromium (as shown in Figure 3), molybdenum (as
shown inFigure 4), silicon, titanium, aluminum,
nio-bium.6Nickel can form solid solutions with many
ele-ments and intermetallic compound with aluminum,
titanium, niobium, and so on The ternary constitutional
diagram for the iron–nickel–chromium isothermal
sec-tion at 650C shown inFigure 5indicates a wide region
covered by the face-centered cubic (fcc) structure of
nickel But the fcc region is shrunk in the ternary
constitutional diagram at 600C for nickel–chromium–
molybdenum system, as shown inFigure 6 In this alloy
system, sigma phase and other intermetallic phases are
found based on a composition range.6The effects of
alloying elements on the properties of nickel-based
alloys are summarized inTable 1
Commercially pure nickel and various nickel-based
alloys are representative of the newly developed
mate-rials during the twentieth century These matemate-rials are
typically encountered in various industrial systems,
including chemical and petrochemical processing,
aerospace engineering, fossil fuel and nuclear power
generation, energy conversion, solar energy
conver-sion, thermal processing and heat treatment, oil and
gas production, pollution control and waste
processing, marine engineering, pulp and paperindustry, agrichemicals, industrial and domestic heat-ing, and electronics and telecommunication, amongothers
Various nickel-based alloys, including binary, nary, and other complex systems, were also devel-oped in the twentieth century The main features andapplications of these commercially pure nickel andnickel-based alloys are summarized inFigure 7.Detailed properties and features of these nickeland nickel-based alloys are described in the followingsections The several of these nickel-based alloyshave been applied or designed to various nuclearreactor materials as shown inTable 2
ter-2.08.2.1 Ni and Ni–Cu Alloys2.08.2.1.1 Chemical compositions, physicalproperties, and mechanical propertiesThe chemical compositions of nickel and typicalnickel–copper alloys are shown in Table 3, alongwith those of other nickel-based alloys
Alloy 200 (UNS N02200) is a commercially pure(99.6%) wrought nickel Alloy 201 (UNS N02201) isthe low-carbon version of Alloy 200 These alloyshave good mechanical properties and good resistance
to corrosion at low to moderate temperatures in
(Cu,Ni) L
Figure 1 Copper–nickel binary phase diagram.
Nickel Alloys: Properties and Characteristics 235
Trang 40 10 500
1345 ⴗC
1455 ⴗC
1863 ⴗC Atomic percent chromium
Weight percent chromium
Figure 2 Iron–nickel binary phase diagram.
236 Nickel Alloys: Properties and Characteristics
Trang 5α α
+
90 80
σ + γ
γ
σ + α α⬘ + σ α⬘ + γα⬘
σ 70
60 50 40 30 20 10 Cr
Figure 4 Nickel–molybdenum binary phase diagram.
Nickel Alloys: Properties and Characteristics 237
Trang 6caustic solutions such as NaOH or dilute deaerated
solutions of common nonoxidizing mineral acids
such as HCl, H2SO4, or H3PO4.7
The mechanical properties of Alloy 200 at
ele-vated temperatures are shown inFigures 8 and 9.3
Alloy 200 is typically limited to use at temperatures
below 315C At higher temperatures, Alloy 200
products can suffer from graphitization, which can
severely compromise the properties of the material
Alloy 200 is susceptible to embrittlement after
long-term heating in the range of 425–760C, due to
carbide precipitation along grain boundaries.4 For
service above 315C, Alloy 201 is preferred.7
The reason for the good corrosion resistance of
Alloys 200 and 201 is the fact that the standard
oxidation–reduction potential of nickel is more
noble than that of iron and less noble than that of
copper Due to nickel’s high overpotential for
hydro-gen evolution, hydrohydro-gen is not easily discharged from
any of the common nonoxidizing acids, and a supply
of oxygen is necessary for rapid corrosion to occur
Hence, in the presence of oxidizing species such
as ferric ions, cupric ions, nitrates, peroxides, or
oxy-gen, nickel can corrode rapidly The outstanding
corrosion-resistance characteristics of Alloy 200 to
caustic soda and other alkalis have led to its ful use in caustic evaporator tubes.7
success-The nickel–copper Alloy 400 is a complete solution alloy that can be hardened only by cold-working Alloy 400 contains about 30–33% copper
solid-in a nickel matrix and has similar characteristics asthose of Alloy 200 It has high strength and toughnessover a wide temperature range and good resistance tomany corrosive environments Alloy 400 exhibitsexcellent resistance to corrosion in many reducingmedia It is also generally more resistant to attack byoxidizing environments compared to higher copper-content alloys It is also widely used in marine appli-cations Alloy 400 products exhibit low corrosionrates in flowing seawater, whereas in stagnant condi-tions, crevice and pitting corrosion can be induced It
is also resistant to SCC and pitting in most fresh andindustrial waters Alloy 400 is highly resistant tohydrofluoric acid at all concentrations and at alltemperatures up to their boiling points It is thereforewidely used in components for seawater applications,salt units, crude distillation, and as a structural mate-rial in chemical plants.8
Alloy K-500 (UNS N05500) is a hardened version of Alloy 400 It contains aluminum
precipitation-10
90 80 70 60
50
A P
Weight percent chromium
W eight per
cent molybdenum
Weight percent nickel
50 60 70 80 90
10 20 30 40 50 60 70 80 90 Mo
γ
γ + σ
γ+A
σ A
Figure 6 Nickel–chromium–molybdenum ternary phase diagram (at 600C).
238 Nickel Alloys: Properties and Characteristics
Trang 7and titanium, and is hardened by the formation of
submicroscopic particles of intermetallic compounds,
Ni3(Ti, Al) The formation of intermetallic
com-pounds occurs as a solid-state reaction during the
thermal aging (precipitation hardening) treatment
Prior to the aging treatment, the alloy component
needs to be solution-annealed to dissolve any phases
that may have formed during previous processing
The solution annealing and aging are normally
car-ried out in the temperature range 980–1040C and
540–590C, respectively Alloy K-500 has the
excel-lent corrosion-resistant features of Alloy 400 with the
added benefits of increased strength up to 600C and
hardness The alloy has low magnetic permeability
and is nonmagnetic up to 134C
Some typical applications of Alloy K-500 include
pump shafts, impellers, medical blades and scrapers,
oil well drill collars and instruments, nonmagnetic
housings and other complementary tools, electroniccomponents, springs, and valve trains.9
The mechanical and various physical properties ofnickel and typical nickel–copper alloys are shown inTables 4 and 5, respectively, along with those ofother nickel-based alloys Physical properties at ele-vated temperature are shown inTables 6–8.2.08.2.1.2 Applications to nuclear powerindustrial fields
Based on the high thermal conductivity (seeTable 6)and high corrosion resistance of nickel–copper alloys
in seawater, Alloy 400 has been widely applied inboiler feed water heat exchanger tubes and shells,and Alloy 500 has found wide use for pump shaftsand impellers in seawater pumps Based on suchindustrial applications, Alloy 400 was used for SGtubes in some CANDU reactors
Table 1 The effects of alloying elements various properties of nickel-based alloys
Ni Provides corrosion resistance to caustic
solutions and dilute deaerated solutions
of nonoxidizing mineral acids Improves
chloride SCC
Stabilization of austenitic phase.
Provides precipitation of g0
Thermal stability and fabricability
Cr Provides resistance to oxidizing media Provides solid solution hardening
Enhances localized corrosion resistance Provides precipitation of M 23 C 6 , as
benefit for notched rupture resistance
Mo Provides resistance to reducing media Provides solid solution hardening;
provides precipitation of M 6 C Enhances localized corrosion resistance
W Behaves similar to Mo but less effective Provides solid solution hardening Detrimental to
thermal stability Provides precipitation of M 6 C
(Ni 3 Ti)
Deoxidizer in melting process Provides oxidation resistance
casting process
C Affects detrimental effect for sensitization Provides solid solution hardening Mechanical
properties Provides precipitation of M 23 C 6 , M 6 C,
MC, etc., much precipitation of MC decreases precipitation of g0and g00
and mechanical properties
Suppress precipitation of Z phase
melting processNickel Alloys: Properties and Characteristics 239
Trang 8Ni–Cu alloy
Ni–Cr–Fe alloy
Alloy 200 Alloy 201
Applicable to the components for sea water, salt unit, crude distillation, etc.
Commercial pure Ni Applicable in caustic solution below 315 ⬚C
Alloy 400 Alloy R-405 Alloy K-500
Free machining grade of Alloy 400 P.H version of Alloy 400, up to 600 ⬚C Applicable to pump-shaft, impellers, scrapers, etc.
Low C commercial pure Ni Applicable in caustic solution above 315⬚C
Excellently resistant to in chloride SCC Applicable to structural materials Alloy 600
Alloy 601 Alloy 690
Excellently resistant to high-temperature oxidation Applicable to oxidation-resistant parts Excellently resistant to many corrosive aqueous media, etc Applicable to structural materials Highly resistant to high-temperature oxidation Applicable to components for high-temperature use Alloy 800
Alloy X-750 Alloy 718
Typical P.H Ni-based alloy Applicable to parts which need high tensile, creep and creep rupture properties Higher strength level than Alloy X-750 Applicable to parts which need high tensile, creep and creep rupture, etc.
Improved on corrosion resistance in heat affected zone after welding of Alloy B Minimized fabrication problems for Alloy B-2 Not applicable to the environment with ferric or cupric salt
Advanced Alloy B Superior corrosion resistance to oxidizing environment compared to Alloy B
Alloy C Alloy C-276 Alloy C-4
Excellent high resistance to oxidation, corrosion in chlorine, compounds with chlorine, oxidizing acid, etc.
Improved on fabricability and long range aging characteristics of Alloy C
Improved on corrosion resistance of Alloy C-276 in oxidizing environment Alloy C-22
Alloy 625 Alloy 625LCF
High creep rupture strength and high resistance to corrosion and pitting in oxidizing environment Improved on low cycle fatigue properties and cold formability of Alloy 625
Improved on aqueous corrosion resistance in a wide variety of corrosion media, modified by Alloy 800 Alloy 825
Alloy 686 High Cr content of Alloy C-276 Excellent resistance to SCC, pitting and crevice corrosion in aggressive media
Superior corrosion resistance to oxidizing environment, inferior corrosion resistant to reducing environment Alloy G
Alloy G-3 Improved on bending characteristics of weld joints for Alloy G
Improved on corrosion resistance in wet phosphoric acid for Alloy G Alloy G-30
Alloy N Alloy 230
Excellent corrosion resistance to liquid fluoride
High strength at high temperatures and good resistance to oxidation in high temperature air Alloy X
Alloy XR Alloy A286
Originally developed as a structural material for high temperature gas-cooled reactors
Age-hardenable alloy Good strength and oxidation resistance up to 700 ⬚C
Ni > 99.0
Ni > 99.0, C < 0.02 Ni–31Cu–2Fe (S £ 0.024) Ni–31Cu–2Fe–0.04S Ni–30Cu–2Fe–0.6Ti–2.7Al Ni–15Cr–8Fe
Ni–23Cr–8Fe–1.4Al Ni–29Cr–9Fe Fe–33Ni–21Cr Ni–15Cr–7Fe–2.5Ti–1Nb–0.7Al Ni–19Cr–17Fe–3Mo–0.9Ti–0.5Al–5.1Nb
Ni–28Mo–5Fe–2Co Ni–28Mo–4Fe–2Co–Low Si, Low C Ni–30Mo–2Fe–2Co–2Cr–2W–2Mn Chemical compositions
Ni–17Mo–16.5Cr–4.5W–5.3Fe–0.3V Ni–16Mo–15.5Cr–5Fe–3.7W–2Co
Ni–21Cr–13.5Mo–4Fe–3W–2Co Ni–21.5Cr–9Mo–4Fe
Ni–22Cr–14W–4Co–2Mo–2Fe Ni–22Cr–18.5Fe–9Mo–0.6W–2Co
Alloy 59 Ni–23Cr–15.7Mo–1Fe–0.3Al Pure Ni–Cr–Mo alloy Excellent corrosion resistance and thermal stability
Excellent resistance to oxidation and nitriding, as well as high strength at high temperatures
Trang 92.08.2.2 Ni–Cr–Fe and Ni–Cr–Fe–Mo Alloys
2.08.2.2.1 Chemical compositions, physical
properties, and mechanical properties
The chemical compositions of typical nickel–
chromium–iron and nickel–chromium–iron–
molybdenum alloys are shown inTable 3, together
with those of other nickel-based alloys
As described earlier, nickel is a very versatile
corrosion-resistant metal The addition of chromium
confers resistance to sulfur compounds and also
pro-vides resistance to oxidizing conditions at high
tem-peratures or in corrosive solutions, with the
exceptions of nitric acid and chloride solutions In
addition, chromium confers resistance to oxidation
and sulfidation at high temperatures
Alloy 600 consists of about 76% nickel, 15%
chromium, and 8% iron The alloy is not
precipitation-hardenable and can only be hardened and strengthened
by cold-working It has excellent resistance to hot
halogen gases and has been used in processes
involv-ing chlorination It has excellent resistance to
oxida-tion and chloride SCC It is widely applied as a
structural material in many industrial fields owing
to its strength and corrosion resistance.10
The thermal expansion coefficient of Alloy 600 is
smaller than those of austenitic stainless steels and
somewhat larger than those of ferritic steels, as shown
inTable 7 It is also highly resistant to sensitization in
heat-affected zones during welding The alloy and its
weld metals such as Alloys 82, 132, and 182 have
there-fore been widely used for dissimilar metal weld joints
to reduce residual stresses and strains after welding
Alloy 601 has a higher chromium content (about
23%) than Alloy 600 and about 1.4% aluminum The
alloy is resistant to high-temperature oxidation and
has good resistance to aqueous corrosion Oxidation
resistance is further enhanced by its aluminum
con-tent The alloy has been applied to the muffles of
heat-treatment furnaces and in catalytic convertors
for exhaust gases in automobiles.11
Alloy X-750 contains titanium, aluminum, andniobium, and is hardened by precipitation of the g0phase as Ni3(Ti, Al, Nb).12 Alloy 718, on the otherhand, contains niobium, molybdenum, titanium, andaluminum, and is hardened by the precipitation ofboth the g0phase as Ni3(Ti, Al, Nb) and the g00phase
as Ni3Nb.13 These alloys were developed as highcreep-strength and high creep-rupture-strengthmaterials for jet-engine blades and vanes in the1940s These precipitation-hardened materials havealso been used in industrial gas-turbine materials Inaddition, Alloy X-750 has been used as a boltingmaterial and Alloy 718 has been applied to bellows,springs, etc for industrial products
Alloy 690 (UNS N06690) was developed in thelate 1960s and has a higher chromium content (about30%) than Alloys 600 and 601 It exhibits excellentresistance to many corrosive aqueous media andhigh-temperature atmospheres The properties ofAlloy 690 are useful in a range of applications involv-ing nitric or nitric/hydrofluoric acid production,and as heating coils and tanks for nitric/hydrofluoricsolutions used in the pickling of stainless steels, forexample.14
Alloy 800 (UNS N08800) is an iron-based nickel–chromium alloy This alloy has been compared
to Alloys 600 and 690 from the view point of itscorrosion resistance in many environments It wasintroduced for industrial use in the 1950s as anoxidation-resistant alloy and for high-temperatureapplications requiring optimum creep and creep-rupture properties Alloy 800 has been widely used
as an oxidation-resistant material and is suitable forhigh-temperature applications due to its high resis-tance to s-phase embrittlement after heating in therange of 650–870C.15
Alloy 825 (UNS N08825) was developed from alloy
800 by the addition of molybdenum (about 3%),copper (about 2%), and titanium (about 0.9%) forimproved aqueous corrosion resistance in a wide vari-ety of corrosive media In this alloy, the nickel contentconfers resistance to chloride-ion SCC Nickel in con-junction with molybdenum and copper gives outstand-ing resistance to reducing environments such as thosecontaining sulfuric and phosphoric acids Molybde-num also enhances its resistance to pitting and crevicecorrosion In both reducing and oxidizing environ-ments, the alloy resists general corrosion, pitting, crev-ice corrosion, intergranular (IG) corrosion, and SCC.Some typical applications include various componentsused in sulfuric acid pickling of steel and copper, com-ponents in petroleum refineries and petrochemical
Table 2 Main applications or candidates of
nickel-based alloys for nuclear reactors
Type of nuclear reactor Alloys
Trang 10Table 3 Chemical compositions of nickel-based alloys
34.0
33.0 0.35–0.85 2.30–
1.20
718 N07718 50.0–
55.0 a 17.0–
21.0 2.80–
3.30 17.0 b – ≦0.080 ≦0.35 ≦1.0 ≦0.35 – ≦0.015 ≦0.015 ≦0.30 0.65–1.15 0.20–
0.80 4.75–
5.50
Reference A286 S66286 24.00–
27.00 13.50–
16.00 1.00–
3.0
98.0 Ni–Mo–
Cr–Fe
16.5 15.0–
17.0 4.0–
7.0 3.0–
Trang 1114.5 2.0–
6.0 2.5–
3.5
625 N06625 ≧58.0 20.0–
23.0 8.0–
23.5 2.5–
7.5 18.0–
8.0 18.0–
6.0 13.0–
17.0 1.5–
3.0
≦3.0 13.0–
15.0 0.05–
0.15 0.25–
10.0 17.0–
20.0 0.20–
1.0 0.05–
10.0 17.0–
20.0 0.20–
1.0 0.07–
0.15 0.3–
Trang 12plants (tanks, valves, pumps, agitators), equipment used
in the production of ammonium sulfate, pollution
con-trol equipment, oil and gas recovery, and acid
production
Alloy A-286 (UNS S66286) is an iron-based
nickel–chromium alloy with added molybdenum
and titanium The alloy is age-hardenable to achievesuperior mechanical properties It maintains goodstrength and oxidation resistance at temperatures up
to about 700C.16The mechanical and physical properties of typicalnickel–chromium–iron and nickel–chromium–iron–molybdenum alloys are shown in Tables 4 and 5,respectively, together with those of other nickel-based alloys
2.08.2.2.2 Applications to nuclear powerindustrial fields
Alloys 600, 690, 800, X-750, and 718 have been used
as materials for components and parts of nuclearpower plants These alloys are representative alloysfor nuclear power plant applications
In the General Requirements of the first edition ofASME Sec III (1963) Rules for Nuclear Vessels, thefollowing terms are included ‘‘The Code rules
do not cover deterioration which may occur inservice as a result of radiation effects, instability ofthe material, or the effects of mechanical shock orvibratory loading These effects shall be taken intoaccount with a view to obtaining the design or thespecified life of the vessel It is recommended thatthe increase in the brittle fracture transition tem-perature due to neutron irradiation be checkedperiodically by means of surveillance specimens.The combined effects of fabrication, stress, andintegrated neutron flux should be considered.’’ Con-sequently, materials for the pressure boundary ofnuclear power plants are selected from those thathave been demonstrated to have excellent proper-ties from experience.17
Alloy X-750 was selected as the bolting and spring material for water reactors (light and heavywater reactors) based on practical experience withthe material in jet-engine applications as well as itsexcellent creep resistance (i.e., excellent resistance
coil-to stress relaxation) Wires and strips used for cal and flat springs are typically produced usingAlloy X-750.Table 9shows an example of the designstresses for springs at elevated temperatures.12Alloy A286 was also selected as a bolting materialfor water reactors based on similar reasons as thosedescribed for Alloy X-750
heli-Alloy 718 was selected as a material for springsand bellows for water reactors based on experiencewith the material in jet engines as well as its excellentcreep resistance (i.e., excellent resistance to stressrelaxation), and its high yield strength in the temper-ature range of up to 400C
Figure 8 High-temperature tensile properties of annealed
Alloy 200.
10
0.1 0.01
Minimum creep rate (% per 1000 h)
200 300 400 600
Figure 9 Typical creep strength of annealed Alloy 200.
244 Nickel Alloys: Properties and Characteristics
Trang 13Table 4 Mechanical properties of nickel-based alloys
strength (MPa)
Yield strength (0.2% offset) (MPa)
Elongation (%) ASTM
690 N06690 Seamless tube, cold drawn
B163
Type1
and annealed
Trang 14Table 5 Physical properties of nickel-based alloys
Alloy systems Alloys UNS no Density
(g cm3)
Melting point (C)
Coefficient of thermal expansion
to 100C (106C1)
Thermal conductivity
at 100C (W m1C)
Specific heat
at 100C (J kg1C)
Electric resistivity
at 100C (108V m)
Young’s modulus
at R.T.
(10 3 N mm1)
Poisson’s ratio at R.T.
Shear modulus
at R.T (GPa)
Trang 15In the case of austenitic stainless steels, SCC
has often been observed in environments that include
chlorides However, high SCC resistance in chloride
solutions was observed for high nickel-content alloys
in the late 1950s, as indicated inFigure 10.5
To avoid SCC in chloride-containing ments, Alloy 600 was adopted as an SG tube mate-rial, based on experience with the material usedfor SG tubes in the Connecticut Yankee reactor inthe late 1950s Subsequently, Alloy 600 was used
environ-Table 6 Thermal conductivity (W m1C) of nickel-based alloys at elevated temperatures
Alloy 600
Alloy 690
Alloy 800
Alloy C-22
Alloy A286
316 stainless steel
Carbon steel (0.23C–0.64Mn–0.11Si)
Table 8 Specific heat (J kg1C) of nickel-based alloys at elevated temperatures
Trang 16Table 9 Design stresses for springs at elevated temperatures
of coiling
Thermal treatment ( C h1)
Up to 204–232 232–260 260–288 288–316 316–343 343–371 371–399 399–427 427–454 454–482 482–510 510–538 538–566 566–593 593–621 621–649 Helical springs
Trang 17worldwide for SG tubes for PWRs and for some
CANDU reactors
Coriou reported as early as 1959 the possibility of
IG stress corrosion cracking (IGSCC) in
high-temperature, high-purity water for high nickel-based
alloys, such as Alloys 600 and X-750, as shown in
Figures 11 and 12.18,19 However, this type of
IGSCC could not be reproduced by other researchers
for more than 15 years Nevertheless, IGSCC was
eventually detected in SG tubes made of Alloy 600
in the Obrigheim reactor in 1972,20 and it was alsodetected in support pins (split pins) and flexure pinsmade of Alloy X-750 in the Mihama No 3 reactor in
1978.21 Subsequently, IGSCC has been detected
in numerous SG tubes made from Alloy 600 andsupport pins made of Alloy X-750 In addition, it wasdetected in PWR reactor-vessel internal bolts made
of Alloy A286
After these experiences, this type of IGSCC wascalled ‘primary water stress corrosion cracking(PWSCC)’; many studies of PWSCC have been car-ried out As a result of these studies, thermally treated(TT: heated at about 700C for more than 10 h aftermill annealing) Alloy 600 was developed.22The TTAlloy 600 was used for SG tubes as an improvedIGSCC-resistant material from mill-annealed (MA)Alloy 600, toward the end of the 1970s TT Alloy 690was developed for SG tubes in the early 1980s as amaterial with excellent IGSCC resistance in PWRprimary water The thermal treatment chosen for
TT Alloy 690 also consisted of heating at about
700C for more than 10 h after mill annealing.23This alloy has been and still is used for SG tubesand control rod drive mechanism (CRDM) nozzles, etc
in PWRs as an alternative material to MA Alloy 600
In the case of conventional Alloy X-750, variousheat-treatment conditions have been specified fordifferent applications In the case of support pinsand flexure pins for PWRs, only mechanical proper-ties such as yield, tensile strength, or hardness werespecified for Alloy X-750 when used for bolts andsprings Several different heat treatments wereselected by the suppliers of the material; the effects
of heat-treatment conditions on PWSCC resistanceare shown in Figure 13 Precipitation hardening
at about 715C after solution annealing at a hightemperature near 1075C (the so-called HTH condi-tion) was selected for fabricating the most PWSCC-resistant Alloy X-750.24 Alloy X-750 HTH has beenapplied as a bolting material not only for PWRs butalso for BWRs due to its excellent IGSCC resistanceand high strength.25
However, the effects of heat treatment on IGSCCresistance have not been so clearly delineated inAlloys A-286 and 718 In particular, Alloy A-286was replaced in many cases with Alloy X-750 HTH
as a bolting material
Alloy 800 is an iron-based nickel–chromiumalloy However, it has good IGSCC resistance inhigh-temperature, high-purity water and causticsolutions A number of studies have been carried
Minimum time to cracking
Indicates commercial wire Did not crack in 30 days
Figure 10 Effect of increasing the nickel content on the
susceptibility of iron–18% chromium base wires in boiling
Pure
water
Figure 11 Schematic diagram showing the influence of
nickel content on the cracking processes occurring in 18%
chromium austenitic alloys, when stressed slightly above
the yield point in 350C water (demineralized or containing
1 g l1chloride ions).
Nickel Alloys: Properties and Characteristics 249