Artigo - Fractography and Mechanism of Hydrogen Cracking (Fisheye)
Fractography Steel
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Transcript of Fractography Steel
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Fractography Resource - [email protected]
Examples of Steel Fractography
Professor M Neil James
Department of Mechanical & Marine Engineering
University of Plymouth
Drake Circus, Plymouth PL4 8AA
ENGLAND
mailto:[email protected]:[email protected] -
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Fractography Resource - [email protected]
Contents Use the hyperlinks to navigate around this resource
Fatigue crack growth in moist air
Fatigue crack growth in vacuum
Crack growth by hydrogen embrittlement
Low carbon interstitial-free steels
Charpy impact fracture
Fatigue in a high tensile bolt
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m vestigial
striations present
Linear growth rate
regime ~ 10-4
mm/cycle
Original
magnification 2kx
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m vestigial
striations present
Linear growth rate
regime ~ 10-4
mm/cycle
Original
magnification 5kx
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular with some evidence of underlying structure
Threshold growth
rate regime ~ 10-7
mm/cycle
Original
magnification 2kx
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular with some evidence of underlying structure
Threshold growth
rate regime ~ 10-7
mm/cycle
Original
magnification 5kx
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Fractography Resource - [email protected]
Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular
Threshold growth
rate regime ~ 10-7
mm/cycle
Original
magnification 2kx
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Fractography Resource - [email protected]
Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular with some environment (moisture) induced IG facets
'Knee' of growth rate
regime ~ 10-6
mm/cycle
Original
magnification 2kx
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular with some moisture-induced oxide build-up by fretting
'Knee' of growth rate
regime ~ 10-6
mm/cycle
Original
magnification 1.15kx
Mechanism of oxide-
induced fatigue
crack closure
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Quenched & Tempered - YS = 653 MPa Grain size 10m ductile
transgranular with some moisture-induced oxide build-up by fretting
'Knee' of growth rate
regime ~ 10-6
mm/cycle
Original
magnification 7.6kx
Mechanism of oxide-
induced fatigue
crack closure
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m microstructure has bigger
influence (e.g. bainite packets) clear IG facets
Threshold growth
rate regime < 10-6
mm/cycle
Original
magnification 500x
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m microstructure has bigger
influence (e.g. bainite packets) clear IG facets
Threshold growth
rate regime < 10-6
mm/cycle
Original
magnification 500x
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Fatigue in Air
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m microstructure has bigger
influence (e.g. bainite packets) ductile transgranular
Threshold growth
rate regime < 10-6
mm/cycle
Original
magnification 2kx
Back to Contents
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Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m no 'knee' in da/dN curve,
implying no mechanism change over range of growth rate 10-4 to 10-7
mm/cycle. No IG facets in absence of moist air
Growth rate ~ 10-4
mm/cycle
Original
magnification 500x
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Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m no 'knee' in da/dN curve,
implying no mechanism change over range of growth rate 10-4 to 10-7
mm/cycle. No IG facets in absence of moist air
Growth rate ~ 10-4
mm/cycle
Original
magnification 2kx
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Fractography Resource - [email protected]
Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m no 'knee' in da/dN curve,
implying no mechanism change over range of growth rate 10-4 to 10-7
mm/cycle. No IG facets in absence of moist air
Growth rate ~ 10-7
mm/cycle
Original
magnification 500x
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Fractography Resource - [email protected]
Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T CGHAZ simulation Grain size 58m no 'knee' in da/dN curve,
implying no mechanism change over range of growth rate 10-4 to 10-7
mm/cycle. No IG facets in absence of moist air
Growth rate ~ 10-7
mm/cycle
Original
magnification 2kx
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Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m no 'knee' in da/dN curve, implying no
mechanism change over range of growth rate 10-4 to 10-7 mm/cycle. No
IG facets in absence of moist air
Growth rate ~ 10-7
mm/cycle
Original
magnification 2kx
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Fatigue in Vacuum
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m no 'knee' in da/dN curve, implying no
mechanism change over range of growth rate 10-4 to 10-7 mm/cycle. No
IG facets in absence of moist air
Growth rate ~ 10-7
mm/cycle
Original
magnification 5kx
Back to Contents
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Crack Growth by Hydrogen Embrittlement
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m Hydrogen can cause cleavage, quasi-cleavage,
MVC or IG fracture, depending on crack tip stress, H2 concentration and
its effect on plasticity
Quasi-cleavage at
initiation site
changes to IG as
crack tip stress
decreases
Bend loading + H2
charging
Original
magnification given
by micron bar
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Crack Growth by Hydrogen Embrittlement
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m Hydrogen can cause cleavage, quasi-cleavage,
MVC or IG fracture, depending on crack tip stress, H2 concentration and
its effect on plasticity
Quasi-cleavage at
initiation site shown
at higher
magnification
Bend loading + H2
charging
Original
magnification given
by micron bar
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Crack Growth by Hydrogen Embrittlement
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m Hydrogen can cause cleavage, quasi-cleavage,
MVC or IG fracture, depending on crack tip stress, H2 concentration and
its effect on plasticity
Quasi-cleavage at
initiation site
changes to IG as
crack tip stress
decreases
Bend loading + H2
charging
Original
magnification given
by micron bar
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Crack Growth by Hydrogen Embrittlement
Q1N Steel (HY 80)
0.2C 2.5Ni 1.5Cr 0.5 Mo
Q&T - Grain size 10m Comparison between IG and cleavage (induced
by fracture at cryogenic temperatures)
IG region is on the
left, and cleavage is
on the right. Line
demarcates the
boundary.
Original
magnification givenby micron bar
Back to Contents
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf
= 1 196 172
cycles
Fatigue performance
is no worse than
grades that do not
show IG fatigue
Original
magnification givenby micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf
= 1 196 172
cycles
Fatigue striations on
an IG facet
Original
magnification given
by micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf
= 1 196 172
cycles
Fatigue striations on
IG facets
Original
magnification given
by micron bar
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Fractography Resource - [email protected]
Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf
= 1 196 172
cycles
IG facets at crack
initiation site
Original
magnification given
by micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf= 24 371 cycles
IG facets at crack
initiation site
(although damaged
by surface contact)
Original
magnification given
by micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf= 24 371 cycles
Striation growth
once crack is
established and
plasticity levels are
higher at crack tip
Original
magnification givenby micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
Some of these steels show IG fatigue at low levels of plasticity (e.g. during
crack initiation, and at long lives)
Nf= 24 371 cycles
Fatigue striations at
higher magnification
Original
magnification given
by micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
An extra-low carbon grade does not show IG fatigue
Nf= 37 782 cycles
No IG facets near
crack initiation site
Original
magnification given
by micron bar
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Low Carbon Interstitial-Free Steel
Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa
An extra-low carbon grade does not show IG fatigue
Nf= 37 782 cycles
Higher magnification
view of crack
initiation site
Original
magnification given
by micron bar
Back to Contents
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Low temperature
fracture showing
cleavage
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Low temperature
fracture showing
cleavage twist and
tilt grain boundaries
evident
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Ductile fracture at
room temperature
showing MVC
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Room temperature
fracture showing
MVC and regions of
brittle inter-pearlitic
fracture
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Room temperature
fracture showingMVC at high
magnification with
inclusion in hole
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Shear micro-voids
can occur whereplastic constraint is
lower, towards the
specimen edges
Original
magnification given
by micron bar
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Charpy Impact Fracture
Plain medium carbon steel (0.4%C) with a normalised microstructure
Smooth featureless
shear can also occurat specimen edges
Original
magnification given
by micron bar
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Fatigue in a High Tensile Bolt
High tensile bolt with Q&T microstructure
Fatigue in bend with
a slightly reversedcomponent
Original
magnification given
by micron bar
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Fatigue in a High Tensile Bolt
High tensile bolt with Q&T microstructure
Clear striations are
present in this lowcycle fatigue
situation; this is the
reversed bend area.
Original
magnification given
by micron bar
Back to Contents
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Fatigue in a High Tensile Bolt
High tensile bolt with Q&T microstructure
High magnification
view of fatiguestriations in the main
fatigue region.
Original
magnification given
by micron bar
Back to Contents
