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Fractography Resource - [email protected]
Examples of Steel Fractography
Professor M Neil [email protected]
Department of Mechanical & Marine Engineering
University of Plymouth
Drake Circus, Plymouth PL4 8AA
ENGLAND
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
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 – 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
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 evidence of underlying structure
Threshold growth rate regime ~ 10-7 mm/cycle
Original magnification 2kx
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 evidence of underlying structure
Threshold growth rate regime ~ 10-7 mm/cycle
Original magnification 5kx
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
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
Fractography Resource - [email protected]
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
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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
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
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
Fractography Resource - [email protected]
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
Fractography Resource - [email protected]
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
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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 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 performance is no worse than grades that do not show IG fatigue
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 an IG facet
Original magnification given by micron bar
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
Fatigue striations on IG facets
Original magnification given by micron bar
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
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 = 24 371 cycles
IG facets at crack initiation site (although damaged by surface contact)
Original magnification given by micron bar
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 = 24 371 cycles
Striation growth once crack is established and plasticity levels are higher at crack tip
Original magnification given by micron bar
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 = 24 371 cycles
Fatigue striations at higher magnification
Original magnification given by micron bar
Fractography Resource - [email protected]
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
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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 showing MVC 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 where plastic 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 occur at 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 reversed component
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 low cycle fatigue situation; this is the reversed bend area.
Original magnification given by micron bar
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Fatigue in a High Tensile Bolt
High tensile bolt with Q&T microstructure
High magnification view of fatigue striations in the main fatigue region.
Original magnification given by micron bar
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