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Examples of Steel Fractography. Professor M Neil James mjames@plymouth.ac.uk Department of Mechanical & Marine Engineering University of Plymouth Drake Circus, Plymouth PL4 8AA ENGLAND. Fatigue crack growth in moist air Fatigue crack growth in vacuum Crack growth by hydrogen embrittlement

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examples of steel fractography

Examples of Steel Fractography

Professor M Neil James

mjames@plymouth.ac.uk

Department of Mechanical & Marine Engineering

University of Plymouth

Drake Circus, Plymouth PL4 8AA

ENGLAND

Fractography Resource - mjames@plymouth.ac.uk

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

Contents – Use the hyperlinks to navigate around this resource

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – vestigial striations present

Fatigue in Air

Linear growth rate regime ~ 10-4 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air4

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – vestigial striations present

Fatigue in Air

Linear growth rate regime ~ 10-4 mm/cycle

Original magnification 5kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air5

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular with some evidence of underlying structure

Fatigue in Air

Threshold growth rate regime ~ 10-7 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air6

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular with some evidence of underlying structure

Fatigue in Air

Threshold growth rate regime ~ 10-7 mm/cycle

Original magnification 5kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air7

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular

Fatigue in Air

Threshold growth rate regime ~ 10-7 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air8

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular with some environment (moisture) induced IG facets

Fatigue in Air

'Knee' of growth rate regime ~ 10-6 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air9

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular with some moisture-induced oxide build-up by fretting

Fatigue in Air

'Knee' of growth rate regime ~ 10-6 mm/cycle

Original magnification 1.15kx

Mechanism of oxide-induced fatigue crack closure

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air10

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Quenched & Tempered - YS = 653 MPa – Grain size 10m – ductile transgranular with some moisture-induced oxide build-up by fretting

Fatigue in Air

'Knee' of growth rate regime ~ 10-6 mm/cycle

Original magnification 7.6kx

Mechanism of oxide-induced fatigue crack closure

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air11

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – microstructure has bigger influence (e.g. bainite packets) – clear IG facets

Fatigue in Air

Threshold growth rate regime < 10-6 mm/cycle

Original magnification 500x

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air12

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – microstructure has bigger influence (e.g. bainite packets) – clear IG facets

Fatigue in Air

Threshold growth rate regime < 10-6 mm/cycle

Original magnification 500x

Fractography Resource - mjames@plymouth.ac.uk

fatigue in air13

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – microstructure has bigger influence (e.g. bainite packets) – ductile transgranular

Fatigue in Air

Threshold growth rate regime < 10-6 mm/cycle

Original magnification 2kx

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – 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

Fatigue in Vacuum

Growth rate ~ 10-4 mm/cycle

Original magnification 500x

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum15

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – 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

Fatigue in Vacuum

Growth rate ~ 10-4 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum16

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – 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

Fatigue in Vacuum

Growth rate ~ 10-7 mm/cycle

Original magnification 500x

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum17

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T CGHAZ simulation – Grain size 58m – 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

Fatigue in Vacuum

Growth rate ~ 10-7 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum18

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – 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

Fatigue in Vacuum

Growth rate ~ 10-7 mm/cycle

Original magnification 2kx

Fractography Resource - mjames@plymouth.ac.uk

fatigue in vacuum19

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – 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

Fatigue in Vacuum

Growth rate ~ 10-7 mm/cycle

Original magnification 5kx

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

crack growth by hydrogen embrittlement

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – Hydrogen can cause cleavage, quasi-cleavage, MVC or IG fracture, depending on crack tip stress, H2 concentration and its effect on plasticity

Crack Growth by Hydrogen Embrittlement

Quasi-cleavage at initiation site changes to IG as crack tip stress decreases

Bend loading + H2 charging

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

crack growth by hydrogen embrittlement21

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – Hydrogen can cause cleavage, quasi-cleavage, MVC or IG fracture, depending on crack tip stress, H2 concentration and its effect on plasticity

Crack Growth by Hydrogen Embrittlement

Quasi-cleavage at initiation site shown at higher magnification

Bend loading + H2 charging

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

crack growth by hydrogen embrittlement22

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – Hydrogen can cause cleavage, quasi-cleavage, MVC or IG fracture, depending on crack tip stress, H2 concentration and its effect on plasticity

Crack Growth by Hydrogen Embrittlement

Quasi-cleavage at initiation site changes to IG as crack tip stress decreases

Bend loading + H2 charging

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

crack growth by hydrogen embrittlement23

Q1N Steel (HY 80) – 0.2C 2.5Ni 1.5Cr 0.5 Mo

Q&T - Grain size 10m – Comparison between IG and cleavage (induced by fracture at cryogenic temperatures)

Crack Growth by Hydrogen Embrittlement

IG region is on the left, and cleavage is on the right. Line demarcates the boundary.

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

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)

Low Carbon Interstitial-Free Steel

Nf = 1 196 172 cycles

Fatigue performance is no worse than grades that do not show IG fatigue

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel25

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)

Low Carbon Interstitial-Free Steel

Nf = 1 196 172 cycles

Fatigue striations on an IG facet

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel26

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)

Low Carbon Interstitial-Free Steel

Nf = 1 196 172 cycles

Fatigue striations on IG facets

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel27

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)

Low Carbon Interstitial-Free Steel

Nf = 1 196 172 cycles

IG facets at crack initiation site

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel28

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)

Low Carbon Interstitial-Free Steel

Nf = 24 371 cycles

IG facets at crack initiation site (although damaged by surface contact)

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel29

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)

Low Carbon Interstitial-Free Steel

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 - mjames@plymouth.ac.uk

low carbon interstitial free steel30

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)

Low Carbon Interstitial-Free Steel

Nf = 24 371 cycles

Fatigue striations at higher magnification

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel31

Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa

An extra-low carbon grade does not show IG fatigue

Low Carbon Interstitial-Free Steel

Nf = 37 782 cycles

No IG facets near crack initiation site

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

low carbon interstitial free steel32

Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = 160-200 MPa

An extra-low carbon grade does not show IG fatigue

Low Carbon Interstitial-Free Steel

Nf = 37 782 cycles

Higher magnification view of crack initiation site

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Low temperature fracture showing cleavage

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture34

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Low temperature fracture showing cleavage – twist and tilt grain boundaries evident

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture35

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Ductile fracture at room temperature showing MVC

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture36

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Room temperature fracture showing MVC and regions of brittle inter-pearlitic fracture

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture37

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Room temperature fracture showing MVC at high magnification with inclusion in hole

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture38

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Shear micro-voids can occur where plastic constraint is lower, towards the specimen edges

Original magnification given by micron bar

Fractography Resource - mjames@plymouth.ac.uk

charpy impact fracture39

Plain medium carbon steel (0.4%C) with a normalised microstructure

Charpy Impact Fracture

Smooth featureless shear can also occur at specimen edges

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

fatigue in a high tensile bolt

High tensile bolt with Q&T microstructure

Fatigue in a High Tensile Bolt

Fatigue in bend with a slightly reversed component

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

fatigue in a high tensile bolt41

High tensile bolt with Q&T microstructure

Fatigue in a High Tensile Bolt

Clear striations are present in this low cycle fatigue situation; this is the reversed bend area.

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk

fatigue in a high tensile bolt42

High tensile bolt with Q&T microstructure

Fatigue in a High Tensile Bolt

High magnification view of fatigue striations in the main fatigue region.

Original magnification given by micron bar

Back to Contents

Fractography Resource - mjames@plymouth.ac.uk