Manuel A. Pouchon :: Head of LNM :: Paul ScherrerInstitut · PDF file ·...
Transcript of Manuel A. Pouchon :: Head of LNM :: Paul ScherrerInstitut · PDF file ·...
WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN
Nuclear Fuels and Materials - 151-2017-00L
Manuel A. Pouchon :: Head of LNM :: Paul Scherrer Institut
Master of Nuclear Engineering ‐ Spring Semester 2016
Nuclear Fuels and Materials - 151-2017-00L ⌸ Lecture 2 - Page 2/112
• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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3
One Component Phase Diagram
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• Components:The elements or compounds that are mixed initially (Al and Cu).
• Phases:A phase is a homogenous, physically distinct and mechanically separable portion of the material with a given chemical composition and structure ( and ).
(darker phase)
(lighter phase)
Aluminum‐
Copper
Alloy
(fcc)
Components and Phases
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
The aluminum-copper phase diagram and the microstructures that may develop during cooling of an Al-4% Cu alloy.
Al-Cu diagram
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
The aluminum-rich end of the aluminum-copper phase diagram showing the three steps in the age-hardening heat treatment and the microstructures that are produced.
αSS:supersaturated solid solution
Al-Cu: Quenching, aging
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Phase Diagrams (1): Eutectics
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Constitution Point
Tie Line
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Phase Diagrams (2): Proportions of phases in two phase alloys
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Phase Diagrams (3): Metallic alloys – eutectics and eutectoids
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Fe-C Phase Diagram
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Not only carbon, but also the other alloying elements like:• Cr, • Ni, • Mo or • V• etc.affect microstructure and microstructural properties. Ternary phase diagrams (shown up) and the Schaeffler Diagram (next slide) provide important information particularly for welding (which is a local melting/solidification process)
Ternary diagram of Ni-Cr-Fe at 1000 oC
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Ternary Phase Diagrams
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The Schaeffler-Diagram I
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Nickel-Equivalent% Ni + 30 % C + 0,5 % Mn
Nickel is a former of austenite
Chromium-Equivalent% Cr + % Mo + 1,5 % Si + 0,5 % Nb + 2 % Ti
Chromium is a former of ferrite
The Nickel-Equivalent and the Chromium-Equivalent are the key parameters which determine the microstructure.
The Schaeffler-Diagram II
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The Schaeffler-Diagram III
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The Schaeffler-Diagram IV: Example for SS304
The Nickel and other elements that form Austenite, are plotted against Chrome and other elements thatform ferrite, using the following formula:
Nickel Equivalent = %Ni + 30%C + 0.5%Mn
Chrome Equivalent = %Cr + Mo + 1.5%Si + 0.5%Nb
Example, a typical 304L = 18.2%Cr, 10.1%Ni, 1.2%Mn, 0.4%Si, 0.02%C
Ni Equiv = 10.1 + 30 x 0.02 + 0.5 x 1.2 = 11.3
Cr Equiv = 18.2 + 0 + 1.5 x 0.4 + 0 = 18.8
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The Schaeffler-Diagram IV: Extension
Delong Diagram
This refines the Schaffler diagram by taking account of the strong austenite stabilizing tendency of nitrogen. The chromium equivalent is unaffected but the nickel equivalent is modified to
Ni (eq) = Ni + (30 x C) + (0.5 x Mn) + (30 x N)
The diagram, identifying the phase boundaries is shown below. This shows the ferrite levels in bands, both as percentages, based on metallographic determinations and as a ferrite number 'FN', based on magnetic determination methods.
http://www.bssa.org.uk/topics.php?article=121
DeLong constitution diagram for stainless steel weld metal. The Schaeffler austenite-martensite boundary is included for reference
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Time-Temperature-Transformation
TTT diagram for carbon steels
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TTP (time-temperature-precipitation)
M23C6 Precipitate
Precipitates
TTP-diagram of a martensitic 9-12% Cr steel
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TTP diagram from Powell
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Metals
Ferrous metals
Steels
Plain carbon steels
Low carbon steels
Medium carbon steels
High carbon steels
Low alloy steels
High alloy steelsStainless & Tool
steels
Cast Irons
Grey Iron
White Iron
Malleable & Ductile Irons
Non-ferrous metals
Steel Microstructures: http://www.threeplanes.net/SiteMap.html
2-6 % C
0.9-2.5 % C
0.05-0.3 % C
0.25-0.6 % C
Alloying element < 4-8%
Alloying element > 4-8%
Classification of metals
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Five main constituents:• Ferrite• Austenite• Cementite• Pearlite• Martensite
Microstructure of Steel
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Iron Carbon Phase Diagram
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• FerriteAllotropes of ferrite include:
• α-iron (Alpha ferrite, bcc)• δ-iron (Delta ferrite, high T, bcc)• β-iron (Beta ferrite, paramagnetic form of α ferrite)• ε-iron (Hexaferrum, hcp at high pressure)• γ-iron (Gamma ferrite, fcc)
• Austenite (γ-iron + carbon in solid solution)
• Cementite (iron carbide, Fe3C)
• Graphite (allotrope of carbon)
• Martensite (BCT, metastable phase, quenching of Aust.)
• ε-carbon (transitional carbide, Fe24C)
Iron-C System I: Allotropes
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The structure of pure iron. Has a body-centered cubic (BCC) crystal structure. It is soft and ductile and imparts these properties to the steel. Very little carbon (less than 0.01% carbon will dissolve in ferrite at room temperature). Often known as iron.
A photomicrograph of 0.1% carbon steel (mild steel). The light areas are ferrite.
Ferrite
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Ferrite is a body-centered cubic (BCC) form of iron, in which a very small amount(a maximum of 0.02% at 1333°F / 723°C) of carbon is dissolved. This is far less carbon than canbe dissolved in either austenite or martensite, because the BCC structure has much less interstitialspace than the FCC structure. Ferrite is the component which gives steel and cast iron theirmagnetic properties, and is the classic example of a ferromagnetic material. This is also the reasonthat tool steel becomes non-magnetic above the hardening temperature - all of the ferrite has beenconverted to austenite. Most "mild" steels (plain carbon steels with up to about 0.2 wt% C) consistmostly of ferrite, with increasing amounts of cementite as the carbon content is increased, whichtogether with ferrite, form the mechanical mixture pearlite. Any iron-carbon alloy will contain someamount of ferrite if it is allowed to reach equilibrium at room temperature.
Photomicrograph of Ferrite Structure
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Ferrite II
The interstitial site for dissolving a carbon atom in alpha-Fe (which is bcc) is the 1/2 0 1/2 type positions as shown here:
This drawing is not to scale as the carbon atom is actually more than four times too large for this site. Consequently carbon solubility in alpha-Fe is quite low. (~0.02%)atomic radius: Fe: 0.127 nm / C: 0.077 nm
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High temperature structure of pure iron:
This is the structure of iron at high temperatures (over 912 °C). Has a face-centre cubic (FCC) crystal structure. This material is important in that it is the structure from which other structures are formed when the material cools from elevated temperatures. Often known as iron. Not present at room temperatures.
Austenite
Interstitial solution of carbon in the high-temperature structure of gamma-Fe which is fcc. The largest interstitial site for a carbon atom is a 1/2 0 1 type position.
Homework:Determine by how much the C atom in gamma-Fe is oversize.atomic radius: Fe: 0.127 nm / C: 0.077 nm
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Austenite is a metallic, non-magnetic solid solution of carbon and iron that exists in steelabove the critical temperature of 1333°F ( 723°C). Its face-centred cubic (FCC) structureallows it to hold a high proportion of carbon in solution. As it cools, this structure eitherbreaks down into a mixture of ferrite and cementite (usually in the structural forms pearliteor bainite), or undergoes a slight lattice distortion known as martensitic transformation.The rate of cooling determines the relative proportions of these materials and thereforethe mechanical properties (e.g. hardness, tensile strength) of the steel. Quenching (toinduce martensitic transformation), followed by tempering (to break down some martensite andretained austenite), is the most common heat treatment for high-performance steels. Theaddition of certain other metals, such as manganese and nickel, can stabilize the austeniticstructure, facilitating heat-treatment of low-alloy steels. In the extreme case of austeniticstainless steel, much higher alloy content makes this structure stable even at roomtemperature. On the other hand, such elements as silicon, molybdenum, and chromium tend tode-stabilize austenite, raising the eutectoid temperature (the temperature where two phases,ferrite and cementite, become a single phase, austenite).
Austenite can contain far more carbon than ferrite, between 0.8% at 1333°F (723°C) and2.08% at 2098°F (1148°C). Thus, above the critical temperature, all of the carbon contained inferrite and cementite (for a steel of 0.8% C) is dissolved in the austenite.
http://threeplanes.net/austenite.html
Austenite II
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A compound of iron and carbon, iron carbide (Fe3C).
It is hard and brittle and its presence in steels causes an increase in hardness and a reduction in ductility and toughness.
Orthorhombic (Pnma)http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cementite
Cementite
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Cementite is iron carbide with the formula Fe3C, and an orthorhombic crystal structure. It is a hard, brittle material, essentially a ceramic in its pure form. It forms directly from the melt in the case of white cast iron. In carbon steel, it either forms from austenite during cooling or from martensite during tempering. Cementite contains 6.67% Carbon by weight; thus above that carbon content in the Fe-C phase system, the alloy is no longer steel or cast iron, as all of the available iron is contained in cementite. Cementite mixes with ferrite, the other product of austenite, to form lamellar structures called pearlite and bainite. Much larger lamellae, visible to the naked eye, make up the structure of Damascus steel. Fe3C is also known as cohenite, particularly when found mixed with nickel and cobalt carbides in meteorites.
Photomicrograph of Pearlite Structure(Dark bands are cementite)
http://threeplanes.net/cementite.html
Cementite II
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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A laminated structure formed of alternate layers of ferrite and cementite.
It combines the hardness and strength of cementite with the ductility of ferrite and is the key to the wide range of the properties of steels. The laminar structure also acts as a barrier to crack movement as in composites. This gives it toughness.
Two-dimensional view of pearlite, consisting of alternating layers of cementite and ferrite.
Pearlite
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Pearlite is a lamellar structure consisting of alternating bands of ferrite and cementite. Pearlite exists in equilibrium in carbon steels at normal temperatures.
Dark bands are cementite,light bands are ferrite
http://threeplanes.net/pearlite.html
Pearlite II
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Schematic illustration of the microstructures for an iron–carbon alloy of eutectoid composition (0.77% carbon), above and below the eutectoid temperature of 727°C
Pearlite III
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Photomicrographs of samples quenched from 1200oC, deformed, annealed at 800oC in different times and air cooled: • a) and b) 1 min, c) and d) 180 min• 2% Nital: a) and c) OM; b) and d) SEM
Ferrite / Pearlite1 m
in180 m
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
The evolution of the microstructure of • hypoeutectoid and • hypereutectoid steels during cooling. In relationship to the Fe-Fe3C phase diagram.
Fe-C diagram: Hypo- & Hpyer-Eutectoid
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Bainitic steel
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A very hard needle-like structure of iron and carbon.
Only formed by very rapid cooling from the austenitic structure (i.e. above upper critical temperature). Needs to be modified by tempering before acceptable properties reached.
The needle-like structure of martensite, the white areas are retained austenite.
Body Centered Tetragonal Unit Cell (BCT)
Martensite – What is it, how does it form
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Martensite is a body-centered tetragonal form of iron in which some carbon isdissolved. Martensite forms during quenching, when the face centered cubic latticeof austenite is distored into the body centered tetragonal structure without the lossof its contained carbon atoms into cementite and ferrite. Instead, the carbon isretained in the iron crystal structure, which is stretched slightly so that it is nolonger cubic. Martensite is more or less ferrite supersaturated with carbon.Compare the grain size in the micrograph with tempered martensite.
http://threeplanes.net/martensite.html
Photomicrograph of Martensite Structure
Martensite II - Description
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Martensitic Transformation: Mysterious Properties ExplainedThe difference between austenite and martensite is, in some ways, quite small:while the unit cell of austenite is a perfect cube, in the transformation to martensitethis cube is distorted so that it's slightly longer than before in one dimension andshorter in the other two.The mathematical description of the two structures is quite different, for reasons ofsymmetry, but the chemical bonding remains very similar.Unlike cementite, which has bonding reminiscent of ceramic materials, the hardnessof martensite is difficult to explain in chemical terms.The explanation hinges on the crystal's subtle change in dimension, and the speed ofthe martensitic transformation. Austenite is transformed to martensite on quenchingat approximately the speed of sound - too fast for the carbon atoms to come out ofsolution in the crystal lattice. The resulting distortion of the unit cell results incountless lattice dislocations in each crystal, which consists of millions of unit cells.These dislocations make the crystal structure extremely resistant to shear stress -which means, simply that it can't be easily dented and scratched. Picture thedifference between shearing a deck of cards (no dislocations, perfect layers of atoms)and shearing a brick wall (even without the mortar).
http://threeplanes.net/martensite.html
Martensite III –How does the transformation work
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Atomic movements during transformation are cooperative in a regimented fashion with distance less than one interatomic spacing
Cause shape change in the transformed region
Surface tilt if the product ’ phase intersects a free surface of the parent phase
Martensite IV
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Surface tilting:Large change in shape would cause large strain.Minimized by deformationo Twinning o Slipwith no crystal structure change
Martensite V
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Martensite Transformation
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When martensite is tempered, it partially decomposes intoferrite and cementite. Tempered martensite is not as hard asjust-quenched martensite, but it is much tougher. Note alsothat it is much finer-grained than just-quenched martensite.
Tempered Martensite
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TTT Diagram: Time-Temperature-Transformation
Dynamics of Phase Transformation I
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Temperature vs time (sec, then min)
TTT diagram for isothermal transformation of steel W 1 (1% C)A = austeniteB = bainiteP = pearlite Ms = start of martensite
transformation,M50 = 50% M
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Dynamics of Phase Transformation II
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• Quenching in a liquid bath at 700 oC; holding time 4 min. During this interval the C has separated out, partly as pearlite lamellae and partly as spheroidizedcementite. Hardness 225 HV.
• Quenching to 575 oC, holding time 4 s. A very fine, closely spaced pearlite as well as some bainite has formed. Note that the amount of spheroidized cementite is much less than in the preceding case. Hardness 380 HV.
• Quenching to 450 oC, holding time 60 s. The structure consists mainly of bainite. Hardness 410 HV.
• Quenching to 20 oC (room temperature). The matrix consists of, roughly, 93% martensite and 7% retained austenite. There is some 5% cementite as well which has not been included in the matrix figure. Hardness 850 HV.
Dynamics of Phase Transformation III
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The unit cells for:
(a) Austenite(b) ferrite, and(c) martensite.
The effect of percentage of carbon (by weight) on the lattice dimensions for martensite is shown in (d). Note the interstitial position of the carbon atoms. (Note also the increase in dimension c with increasing carbon content; this effect causes the unit cell of martensite to be in the shape of a rectangular prism.
The Unit Cells
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
The effect of transformation temperature on the properties of an eutectoid steel.
Fe-C Mechanical properties
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• Extremely important class of austenitic (fcc) materials based on nickel
• Strengthening Solid solution strengthened and particle strengthened (gamma prime)
• Highly corrosion resistant
• «The» high temperature alloys • IN-600, X-750, 182/82 (RPV cladding)• Will be discussed in detail for advanced nuclear
plants (Autumn course)
Nickel-base alloys
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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ASM Materials Handbook on‐line 2008
Mechanical properties
• Strength- Tensile strength (ultimate strength)- Yield strength- Compressive strength
• Hardness
• Toughness- Notch toughness- Fracture toughness
• Ductility- Total elongation- Reduction in area
• Fatigue resistance
Other properties/characteristics
• Formability- Drawability- Stretchability- Bendability
• Wear resistance- Abrasion resistance- Gallic resistance- Sliding wear resistance- Adhesive wear resistance
• Machinability
• Weldability
Typical Criteria for Materials Selection
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• Irradiation Damage: Hardening, embrittlement, radiation induced segregation, radiation induced phase transformation
• Corrosion damage:Uniform, Pitting, stress-corrosion cracking, irradiation assisted stress corrosion cracking
• Fatigue damage
• Different types of crack growth
What Damage occurs in Generation II/III-plants
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• Strength • Ductility • Toughness • Fatigue
Properties of metallic materials
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Deformation of Single Crystals
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http://www.msm.cam.ac.uk/doitpoms/
Critical resolved shear stress (Schmids Law)
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Why are there slip planes?
http://practicalmaintenance.net/?p=1135
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Plane designation: Miller index
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DOI: http://dx.doi.org/10.1103/PhysRevB.89.144105
Slip modes in fcc, bcc, and hcp
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One gliding plane
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Example for large pillar compression –AISI 316
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Two gliding planes
http://dx.doi.org/10.1016/j.matlet.2013.01.118
Example for small pillar compression –AISI 316
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Slip Lines on a Deformed Sample
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The mechanical „baseline“
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Upper and lower yield stressContinuous yielding
Typical Stress-Strain Curves
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S. Kyriakides, Transactions of the ASME (2000)
Function of grain size (↓σU, σL & ∆ɛL ↑ ) and composition.
Extracted Single grain ?
Lüders strain
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600
700
800
900
0 2 4 6 8 10 12 14 16 18 20
Strain (%)
Str
ess
(MP
a)
∆ɛLσL
2 µm
JRQ Reference Sample – In-Situ Test
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• Elastic Modulus (Hook‘s law)• Yield Stress (offset)• Hardening• Ultimate Tensile Stress• (Fracture) Elongation• Reduction of Area• Fracture appearance
• Elastic Modulus (Hook‘s law)• Yield Stress (offset)• Hardening• Ultimate Tensile Stress• (Fracture) Elongation• Reduction of Area• Fracture appearance
Important Tensile Test Parameters
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http://practicalmaintenance.net/?p=1135 Stress Strain Curve
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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PHWT: Post-Weld Heat Treatment
Toughness
Brittle fracture of a steel pressure vessel during proof test. (The vessel walls were 149 mm thick, and a 2-tonnefragment was thrown 46 m).DOI: 10.1098/rsta.2014.0126
Brittle fracture of a steel pressure vessel during proof test. (The vessel walls were 149 mm thick, and a 2-tonnefragment was thrown 46 m).DOI: 10.1098/rsta.2014.0126
The above picture is of a new pressure vessel that failed during its hydraulic test. The vessel had been stress relieved, but some parts of it did not reach the required temperature and consequently did not experience adequate tempering. This coupled with a small hydrogen crack, was sufficient to cause catastrophic failure under test conditions. It is therefore important when considering PWHT or its avoidance, to ensure that all possible failure modes and their consequences are carefully considered before any action is taken. (http://www.gowelding.com/met/pwht.htm)
The above picture is of a new pressure vessel that failed during its hydraulic test. The vessel had been stress relieved, but some parts of it did not reach the required temperature and consequently did not experience adequate tempering. This coupled with a small hydrogen crack, was sufficient to cause catastrophic failure under test conditions. It is therefore important when considering PWHT or its avoidance, to ensure that all possible failure modes and their consequences are carefully considered before any action is taken. (http://www.gowelding.com/met/pwht.htm)
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When dropping a ceramic piece to ground it breaks – metals usually not. The quantity relating the resistance of a material to sudden (impact) loads is called Toughness.
Construction materials must have high toughness. For many metallic materials (including RPV-steels) the toughness is temperature dependent with a sudden change at a so-called transition temperature. This transition temperature can change during service (ageing) which means an increase of failure risk.
Toughness is measured with impact testing machines or with fracture mechanics samples as shown in the next viewgraphs.
Toughness of materials
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• Impact testing (Charpy)• Fracture Appearance Transition Temperature (FATT)• Ductile Brittle Transition Temperature (DBTT)• Fracture Toughness (KIC)• J-Integral (JIC)
Remark for difference between DBTT and FATT:
The temperature at which behavior of the material is 50% brittle and 50% ductile is called the ductile-to-brittle-transition temperature (DBTT) while the temperature at which the fracture surface of the material is 50% flat (indication of brittle fracture) is known as fracture appearance transition temperature (FATT). In most cases, the DBTT and FATT are nearly the same. (http://dc231.4shared.com/doc/ATghg806/preview.html)
Toughness Measures
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Impact Fracture Testing
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Ductile-to-Brittle Transition – WWII Liberty Ships
Some of the first Liberty Ships completed suffered from hull and deck cracks and some were actually lost to these early defects. During the course of WWII there were nearly 1,500 instances of significant brittle fractures due to low grade of steel which suffered from embitterment. It was discovered by Constance Tipper of Cambridge University that ships that were used in the North Atlantic were exposed to temperatures that could fall below a critical point and cause the hull to fracture quite easily. One of the most common types of crack began at the square corner of a hatch with coincided with a welded seam with both the weld and the corner acting as stress concentrators. Along with the poor quality of steal the ships were usually grossly overloaded and many of the problems occurred during severe storms at sea that placed the ships and crew in even more danger. Various reinforcements were applied to the design to deal with the cracks.
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See also : Impact testing
http://www.twi.co.uk/technical-knowledge/job-knowledge/job-knowledge-71-mechanical-testing-notched-bar-or-impact-testing/
Ductile to Brittle Transition Temperature
Impact Testing
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The typical SEM images of different impact fracture surface of steel: (a) fracture 1 (brittle fracture, tempered at 200 °C); (b) fracture 2 (mixed ductile–brittle fracture, tempered at 300 °C); (c) fracture 3 (ductile fracture, tempered at 400 °C); (d) fracture 4 (ductile fracture, tempered at 500 °C).
Fracture surface
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[1] http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_lefm_K.cfm[2] http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_lefm_stress.cfm
Crack tips produce a 1/√r singularity. The stress fields near a crack tip of an isotropic linear elastic material can be expressed as a product of 1/√r and a function of θ with a scaling factor K:
where the superscripts and subscripts I, II, and III denote the three different modes that different loadings may be applied to a crack. The detailed breakdown of stresses and displacements for each mode are summarized in [2]. The factor K is called the Stress Intensity Factor.
Stress Intensity Factor and Crack Tip Stresses
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“Goofy duck” analog for three modes of crack loading. (a) Crack/beak closed. (b) Opening mode. (c) Sliding mode. (d) Tearing mode. (Courtesy of M. H. Meyers.)
Goofy Duck Analog for Modes of Crack Loading
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Fracture Toughness: a quantitative impact measure
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http://www.keytometals.com/page.aspx?ID=CheckArticle&site=ktn&NM=184
Development of a crack
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J-Integral
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Fatigue
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R = σmin/σ max
Fatigue Basics
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High Cycle Fatigue
(HCF)
Low Cycle Fatigue
(LCF)
N~5000
HCF: Loading far below yield stress,Caused by vibrations, crack initiation is important. Usually, stress controlled tests
LCF: Plastic strains occur, caused by transient loads or on notches, crack propagation Is important. Usually, strain controlled tests
(or strain)
HCF-LCF
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Fatigue curves
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Creep fatigue life
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Parts in a nuclear reactor
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Welding sections in RPV
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http://engineers.ihs.com/document/abstract/VYJOIBAAAAAAAAAA
Low Alloy Steels
• Fine-grained structural steels with bainitic (BCC) microstructure and high toughness
• Quenched + tempered (Q+T) + post-weld heat treatment (PWHT)
• Mn-Mo-Ni-type (SA-508 Cl. 3 forgings, SA-533 Gr. B Cl. 1 plates, …)
• Ni-Mo-Cr-typ (SA 508 Cl. 2 forgings, …)
• S ≤ 0.01% (in very old plants up to 0.04% S)
• S ↑ EAC susceptibility ↑, fracture toughness ↓
• Cu ≤ 0.05% (in old plants, weldments contained up to 0.35% Cu)
• Cu ↑ irradiation embrittlement ↑, toughness ↓
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Development of manufacturing tech. in JSW
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In the this process, both acid and basic, the necessary heat for melting and working the charge is supplied by oil or gas. But the gas and air are preheated by regenerators, two on each side of the furnace, alternatively heated by the waste gases. The regenerators are chambers filled with checker brickwork, brick and space alternating. The furnaces have a saucer-like hearth, with a capacity which varies from 600 tonnes for fixed, to 200 tonnes for tilting furnaces . The raw materials consist essentially of pig iron (cold or molten) and scrap, together with lime in the basic process. To promote the oxidation of the impurities iron ore is charged into the melt although increasing use is being made of oxygen lancing. The time for working a charge varies from about 6 to 14 hours, and control is therefore much easier than in the case of the Bessemer process. The Basic Open Hearth process was used for the bulk of the cheaper grades of steel, but there is a growing tendency to replace the OH furnace by large arc furnaces using a single slag process especially for melting scrap and coupled with vacuum degassing in some cases.
http://www.steelmelters.com/steel.htm#hearth_
Open
hearth furnace
Electric Arc Furnace
Steel Making: Open-hearth processes
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Video of steel making process
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A ladle containing 150 tons of liquid steel is lowered into the tank degasser at Pennsylvania Steel Technologies to remove hydrogen from steel for harder railheads.
http://www.memagazine.org/backissues/membersonly/april98/features/vacuum/vacuum.html
Ladle degassing
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Ring Forging Penetration welding
Reactor pressure vessel production steps
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http://radona.de/index.htm
Austenitic Cladding Application
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Welding techniques
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A weld consists of:• Base metal• Heat affected zone• Fusion line• Weld metal
Different kinds of steel can develop. Particularly for dissimilar welds. After welding proper post weld heat treatment (PWHT) is important
A weld consists of:• Base metal• Heat affected zone• Fusion line• Weld metal
Different kinds of steel can develop. Particularly for dissimilar welds. After welding proper post weld heat treatment (PWHT) is important
Dissimilar weld (microstructure)
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Production
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End of (Design) Life n-Fluence (E > 1 MeV)
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• Phase diagramso Eutectic and Eutectoid
• Ternary Phase Diagram / Scheffler Diagram• Phase Transformation Diagrams (Dynamics) - Introduction• Fe-C system
o Ferriteo Austeniteo Cementiteo Bainite, Perliteo Martensiteo Phase Transformation Diagrams – Microstructure Formation
• Criteria for material selection• Deformation• Toughness• Intro to Fatigue & Creep-Fatigue• Reactor pressure vessel (RPV)• Irradiation damage
TOC
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Defect formation
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An illustration of cascade primary-damage production (iron atoms not shown in a–c and f): (a–c) MD simulation snapshots of initial intermediate and final dynamic stage of a displacement cascade; (d–e) vacancy and self interstitial defects; (f) vacancy-solute cluster complex formed after long-term cascade aging
Cascade development is depending on lattice type
Cascade illustration
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ν(T) = T/2.Eth
Displacement per atom «dpa»
Irradiation Damage
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Point defect reactions
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Typical isochronous annealing curves for pure Cu after irradiation at 4.2 K with fast neutrons to typical doses of 10' dpa. The annealing temperature T is normalized to the melting temperature of Cu. The Romain numbers refer to the different recovery stages. (FD means Frenkel Defects), replotted from [5.1]
Frenkel defect retention
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Effect Consequence in material Kind of degradation in component
Displacement damageFormation of point defect clusters and dislocation loops
Hardening, embrittlement
Irradiation-induced segregationDiffusion of detrimental elements to grain boundaries
Embrittlement, grain boundary cracking
Irradiation-induced phase transitions
Formation of phases not expected according to phase diagram, phase dissolution
Embrittlement, softening
SwellingVolume increase due to defect clusters and voids
Local deformation, eventually residual stresses
Irradiation creep Irreversible deformationDeformation, reduction of creep life
Helium formation and diffusionVoid formation (inter- and intra-crystalline)
Embrittlement, loss of stress rupture life and creep ductility
Radiation Damage
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a = b = c, α = β = γ= 90°
a = b ≠ c, α = β = γ= 90°
a ≠ b ≠ c,α = β = γ= 90°
a = b = c, α = β = γ ≠ 90°
a = b ≠ c, α = β = 90°, γ = 120°
a ≠ b ≠ c, α ≠ β ≠ γ
a ≠ b ≠ c, α = γ = 90°, β ≠ 90°
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Appendix: Explanation Burgers Vector