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    Fractography

    George F. Vander Voort, Consultant

    Principal Engineer

    P.O. Box 10

    Wadsworth, IL 60083-0010

    [email protected]

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    Fracture Modes

    Transgranular: Cracking across grains

    without preference for grain boundaries

    Intergranular: Cracking between grains, the

    crack propagates in the grain boundaries

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    Fracture Mechanisms

    Ductile

    Brittle

    Fatigue

    Torsion

    Stress Corrosion Cracking

    Liquid Metal Embrittlement

    Hydrogen Embrittlement and HIC

    Creep

    Wear

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    Ductile Fracture in Tension

    Top View Side View

    Large shear lips, substantial necking down

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    Ductile FractureCharpy V Notch Specimen

    2% Nital Etch

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    Ductile Fracture

    Microvoid Coalescence

    SEM SEIPH 13-8Mo Stainless Steel Tensile Fracture

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    Ductile Fracture: X-750 Rising Load Test

    Bright field (left) and dark field (right) light microscope images of a

    ductile fracture in an X-750 Ni-base superalloy rising load test fracture.

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    Ductile Fracture Popsac Vessel

    70 F, Burst at 8500 psi

    -50 F, Burst at 9000 psi

    7.375 inch diameter, 0.125 inch thick 1030

    carbon steel vessel, design strength 4475 psi

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    Tensile Fractures Begin Internally

    Partially Broken Tensile Specimen

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    Brittle Fracture

    Brittle fractures suggest that the

    design, manufacture or materialsquality were improper for the safe use

    of the part.

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    Brittle Fracture in Tension

    Top View Side View

    Small shear lips, no visible necking down

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    Brittle FractureCharpy V Notch Specimen

    2% Nital

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    Brittle FractureCharpy V Notch Specimen

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    Cleavage Fracture in Carbon Steel

    100 m50 m

    Fracture profile of brittle fracture of a carbon steel specimen (nickel

    plated, 2% nital etch).

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    Cleavage Cracks in Carbon Steel

    Cleavage cracks in a carbon steel (nital). Cracks off of the main fracture.

    20 m 20 m

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    Cleavage Cracks in a Low-Carbon Steel

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    Cleavage Cracks in a Low-Carbon Steel

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    Direct and Indirect Views of a Brittle Fracture

    LOM - Profile LOM - Fracture SEM - Fracture

    LOM - Replica SEM - Replica TEM - Replica

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    Charpy V-

    Notch Series to

    Evaluate the

    Ductile-to-

    BrittleTransition

    Temperature

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    T il d CVN C f

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    Tensile and CVN Curves for

    NiCrMoV Forging Grade

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    Brittle Fracture of Fe2.2% Si Slab

    Brittle fracture of a silicon electrical steel slab during mill handling. The

    slab measured 8.5-inch thick x 41-inch wide (21.6-cm x 104-cm).

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    Brittle Fracture of Fe2.2% Si Slab

    Coarse columnar grain structure of the Fe2.2% Si electrical steel slab,

    etched with nital. The rolling direction is vertical.

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    CVN Curves for RMS Titanic Plate Steel

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    Brittle Fracture of Fe-Al-Cr Ingot

    Note that the ingots grain structure can be clearly seen in the fracture pattern.

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    Large Brittle Fracture of Steel Part

    Fracture was initiated at the stress concentrator (arrow)

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    Boyds Model for Chevron Cracks

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    Boyds Model for Chevron Crack Growth

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    Brittle Fracture of a Railroad Rail

    The apex of the chevrons point back to the origin of the fracture

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    Ship Steel Drop-Weight Test Fractures

    Note transition from ductile to chevron to flat cleavage fracture with

    decreasing temperature. Chevrons are most pronounced at50 F (-45 C).

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    Cleavage in Fe2.5% Si

    Bright field (left) and dark field (right) views by light microscopy of a

    brittle cleavage fracture in Fe2.5% Si broken at173 C.

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    Cleavage Fracture of Fe-2.5% Si

    SEM SEI, 14 mm WD SEM BSEI, 14 mm WD

    Same area viewed with the Everhard-Thornley detector;

    the backscattered image is easier to interpret

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    X-60 Line Pipe Tested 8 F Above DWTT

    Full scale line pipe test, loaded to 40% of the yield strength, tested at 56 F, 8

    F above the 50% shear area drop-weight tear test transition temperature

    (+48 F). A 30-grain charge was detonated beneath an 18-inch notch cut in

    the pipe. The crack speed was 279 fps. The crack propagated 33-inch in full

    shear and then 18-inch in tearing shear before stopping.

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    X-60 Line Pipe Tested 2 F Below DWTT

    After a small amount of brittle fracture, the crack became ductile and stopped;

    average crack speed was 566 fps.

    X 60 Li Pi T t d 10 F B l DWTT

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    X-60 Line Pipe Tested 10 F Below DWTT

    Fracture was brittle, ending in ductile shear; average crack speed was 1550 fps.

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    X-60 Line Pipe Tested 40 F Below DWTT

    This line pipe fractured in a wave pattern for a full wave-length by cleavage

    with

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    SEM 1000x

    SEM 1000x

    SEM 5000x

    SEM 5000x

    TEM Replica 5000x

    TEM Replica 5000x

    Brittle (Top) and Ductile (Bottom) Fractures

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    Unusual Intergranular Fracture in Fe-Cr-Al Alloy

    LOMBright Field LOMDark Field

    SEM SEI

    i C

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    Unusual Intergranular Fracture in Fe-Cr-Al Alloy

    Dark Field LOM SEM SE Image

    Two additional views of the unusual stepped intergranular fracture in the

    Fe-Cr-Al alloy.

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    Intergranular Cracking in Ni-Base Alloy

    Bright field (left) and dark field (right) light microscopy images of an

    intergranular fracture in a Ni-base superalloy.

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    Intergranular Fracture in Ni-Base Alloy

    Secondary electron (left) and backscattered electron (E-T) SEM images of the

    intergranular fracture in a Ni-base superalloy.

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    Fatigue Fractures

    Fatigue fractures occur due to repeated

    cyclic loading below the static yieldstrength. It is important to determine if

    fatigue was high-cycle or low-cycle, as the

    remedies for each are different.

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    U idi ti l B di F ti i B lt

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    Unidirectional Bending Fatigue in Bolt

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    Reversed Bending Fatigue

    Railroad Coupling Pins

    Rotating Torsional Fatig e of 4320 Shaft

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    Rotating Torsional Fatigue of 4320 Shaft

    Failure started at keyway (B) and ended at Csmall size of final rupture

    zone indicates a relatively low load

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    Torsional Fatigue Fracture in 51B60

    Railroad Spring

    1.625 inch diameter spring (arrow points to the origin)

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    Fatigue Cracks in Al

    Broken specimen, Kellers reagent

    Non-broken specimen, Kellers reagent

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    Fatigue in Carbon Steel

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    Fatigue Crack in Carbon Steel

    2% Nital

    Fatig e in Carbon Steel

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    Fatigue in Carbon Steel

    Fatigue crack grown from a notch in a

    carbon steel (above and above right, 2%

    nital).

    F ti C k i C b St l

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    Fatigue Crack in Carbon Steel

    Ni Plating

    2% Nital

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    Fatigue Fracture of Carbon Steel

    Fatigue fracture in a carbon steel fracture covered with electroless nickel

    (nital). Crack moving left to right.

    100 m 50 m

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    Fatigue Crack in 304 Stainless Steel

    Glyceregia, Bright Field

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    Fatigue Crack in 304 Stainless Steel

    15 HCl10 Acetic10 HNO3; Nomarski DIC

    50 m

    Fatigue Crack in 304 Stainless Steel

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    Fatigue Crack in 304 Stainless Steel

    Glyceregia, Bright Field

    Fatigue in 316 SS

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    100 m

    20 m

    20 m

    Fatigue in 316 SS

    Fatigue crack grown from a notch

    (above and above right) and the carck

    path through the microstructure

    (glyceregia).

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    Fatigue Crack in 304 Stainless Steel

    15 mL HCl10 mL Acetic10 mL HNO3, DIC

    Fatigue Crack in 304 Stainless Steel

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    Fatigue Crack in 304 Stainless Steel

    Left: Glyceregia, Bright Field; Right: 15 mL HCl10 mL Acetic

    10 mL HNO3, DIC

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    Examples of Striation Patterns

    F t f P lit St i ti

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    Fracture of Pearlite vs Striations

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    Fatigue Fracture: X-750 Rising Load Test

    Bright field (left) and dark field (right) light microscopy images of an X-750

    Ni-base superalloy fatigue fracture.

    F ti F t X 750 Ri i L d T t

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    Fatigue Fracture: X-750 Rising Load Test

    Secondary electron SEM image of a fatigue pre-cracked surface in an X-750

    Ni-base superalloy specimen.

    Fatigue Striations in Rising Load Test

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    Fatigue Striations in Rising Load Test

    Specimen of Ni-Base Superalloy

    Fatigue Failure of Rail at FAST

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    Fatigue Failure of Rail at FAST

    Top View

    Side View

    Fracture made

    in lab to reveal

    extent offatigue crack

    propagation

    Circular Spall in Hardened Steel Roll

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    Circular Spall in Hardened Steel Roll

    A large inclusion was found at the origin (arrow)

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    Line Spall in

    Hardened SteelRoll

    Section Cut From Failed HSR

    Re-Austentized Regions at Spalls

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    Re Austentized Regions at Spalls

    Frictional heat from fatigue crack growth can re-austenitize regions

    (arrow) producing as-quenched martensite upon cooling (3% nital)

    Spalled Section of Hardened Steel Roll

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    Area A, 5x

    Spalled Section of Hardened Steel Roll

    Spalled Hardened Steel Roll

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    Area B, 10x Area C, 10x

    Spalled Hardened Steel Roll

    Close-up views of fatigue propagation marks at initiation

    site areas B and C on the roll fracture.

    Spalled Hardened Steel Roll

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    Spalled Hardened Steel Roll

    Fatigue propagation marks at initiation site D.

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    Examples of Fatigue Pre-Cracked

    Charpy V-Notch Specimens ofDifferent Materials Broken at 0 F

    Fatigue Pre-Crack and Ductile

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    Fracture of Al CVN Specimen

    TEM Replica 10,000x SEM 10,000x

    Images of the fatigue pre-cracked part of the Charpy

    V-notch impact specimen

    Fatigue Pre-Crack and Ductile Fracture of

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    g

    Al CVN Specimen

    TEM Replica, 5000xSEM SE Image, 2000x

    Views of the ductile rupture portion of the fatigue pre-

    cracked Charpy V-notch specimen

    Fatigue Pre-Crack and Ductile Fracture of

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    Fatigue Pre Crack and Ductile Fracture of

    304 Austenitic Stainless Steel CVN Specimen

    TEM Replica, 5000x LOM Image, 500x SEM SE Image, 5000x

    Views of the fatigue pre-cracked portion of a 304 austenitic stainless steel

    Charpy V-notch specimen

    Fatigue Pre-Crack and Ductile Fracture of

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    Fatigue Pre Crack and Ductile Fracture of

    304 Austenitic Stainless Steel CVN Specimen

    SEM SE Image, 2000xTEM Replica, 5000x

    Views of the ductile overload fracture of the fatigue

    pre-cracked Charpy V-notch specimen

    Fatigue Pre-Crack and Ductile Fracture of a

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    g

    Carbon Steel CVN Specimen

    TEM Replica, 5000x

    Views of the fatigue pre-cracked portion of the carbon

    steel Charpy V-notch specimen

    SEM SE Image, 5000x

    Fatigue Pre Crack and Ductile Fracture of a

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    Fatigue Pre-Crack and Ductile Fracture of a

    Carbon Steel CVN Specimen

    TEM Replica, 5000x LOM Image, 500x SEM SE Image, 5000x

    Views of the brittle fracture portion of the fatigue pre-cracked carbon steel

    Charpy V-notch specimen broken at 0 F

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    Corrosion and Embrittlement

    Failures

    SCC of 4340 in Salt Water

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    SCC of 4340 in Salt Water

    Two regions along SCC secondary cracks in a 4340 fastener used on an oil rig

    raiser in salt water. The fracture face was badly corroded, destroying the fine

    details, but appeared to be intergranular. It was too hard at 38 HRC for this

    application. Etched with saturated picric acid + 0.5% HCl and a wetting agent at

    80C (500x).

    20 m

    SCC in 4340 in Salt Water

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    Secondary cracks in 4340 fasteners that failed by SCC in sea water; etched with

    saturated picric acid + 0.5% HCl + wetting agent at 80C to show the PGBs.

    500x

    Intergranular SCC in 304 Stainless

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    g

    Mixed AcidsSEM SEI of Fracture

    304 stainless steel wire tested in boiling MgCl2

    I t l Ri i L d F t

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    Intergranular Rising Load Fracture

    SEM SEI, 15 mm WD, 15Tilt SEM ET-BSEI, 15 mm WD, 15Tilt

    Fatigue-Intergranular Interface in an X-

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    Fatigue Intergranular Interface in an X

    750 Rising-Load Test Specimen

    Bright field (left) and dark field (right) light microscopy views of the interface

    between the fatigue-pre-crack zone (left side) and the intergranular test fracture

    (right side) in an X-750 Ni-base rising load test specimen.

    Fatigue-Intergranular Interface in an X-

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    g g

    750 Rising-Load Test Specimen

    SEM SEI, 13 mm WD, 4Tilt SEM ET-BSEI, 13 mm WD, 4Tilt

    SEM views of the interface between the fatigue pre-crack zone (left side of

    fracture) and the intergranular test fracture (right side) in an X-750 rising load

    test specimen.

    Unusual Intergranular Fracture

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    Unusual Intergranular Fracture

    LOM - DF SEM SE Image