Fractography Resource - 1 Examples of Steel Fractography Professor M Neil James Department of Mechanical & Marine Engineering University of Plymouth Drake Circus, Plymouth PL4 8AA ENGLAND

Fractography Resource - 2 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 - 3 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 Linear growth rate regime ~ mm/cycle Original magnification 2kx

Fractography Resource - 4 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 Linear growth rate regime ~ mm/cycle Original magnification 5kx

Fractography Resource - 5 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 – ductile transgranular with some evidence of underlying structure Threshold growth rate regime ~ mm/cycle Original magnification 2kx

Fractography Resource - 6 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 – ductile transgranular with some evidence of underlying structure Threshold growth rate regime ~ mm/cycle Original magnification 5kx

Fractography Resource - 7 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 – ductile transgranular Threshold growth rate regime ~ mm/cycle Original magnification 2kx

Fractography Resource - 8 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 – ductile transgranular with some environment (moisture) induced IG facets 'Knee' of growth rate regime ~ mm/cycle Original magnification 2kx

Fractography Resource - 9 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 – ductile transgranular with some moisture-induced oxide build-up by fretting 'Knee' of growth rate regime ~ mm/cycle Original magnification 1.15kx Mechanism of oxide- induced fatigue crack closure

Fractography Resource - 10 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 – ductile transgranular with some moisture-induced oxide build-up by fretting 'Knee' of growth rate regime ~ mm/cycle Original magnification 7.6kx Mechanism of oxide- induced fatigue crack closure

Fractography Resource - 11 Fatigue in Air 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 Threshold growth rate regime < mm/cycle Original magnification 500x

Fractography Resource - 12 Fatigue in Air 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 Threshold growth rate regime < mm/cycle Original magnification 500x

Fractography Resource - 13 Fatigue in Air 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 Threshold growth rate regime < mm/cycle Original magnification 2kx Back to Contents

Fractography Resource - 14 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 500x

Fractography Resource - 15 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 2kx

Fractography Resource - 16 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 500x

Fractography Resource - 17 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 2kx

Fractography Resource - 18 Fatigue in Vacuum 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 2kx

Fractography Resource - 19 Fatigue in Vacuum 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 to mm/cycle. No IG facets in absence of moist air Growth rate ~ mm/cycle Original magnification 5kx Back to Contents

Fractography Resource - 20 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, H 2 concentration and its effect on plasticity Quasi-cleavage at initiation site changes to IG as crack tip stress decreases Bend loading + H 2 charging Original magnification given by micron bar

Fractography Resource - 21 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, H 2 concentration and its effect on plasticity Quasi-cleavage at initiation site shown at higher magnification Bend loading + H 2 charging Original magnification given by micron bar

Fractography Resource - 22 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, H 2 concentration and its effect on plasticity Quasi-cleavage at initiation site changes to IG as crack tip stress decreases Bend loading + H 2 charging Original magnification given by micron bar

Fractography Resource - 23 Crack Growth by Hydrogen Embrittlement 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) 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 - 24 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles Fatigue performance is no worse than grades that do not show IG fatigue Original magnification given by micron bar

Fractography Resource - 25 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles Fatigue striations on an IG facet Original magnification given by micron bar

Fractography Resource - 26 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles Fatigue striations on IG facets Original magnification given by micron bar

Fractography Resource - 27 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles IG facets at crack initiation site Original magnification given by micron bar

Fractography Resource - 28 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles IG facets at crack initiation site (although damaged by surface contact) Original magnification given by micron bar

Fractography Resource - 29 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles Striation growth once crack is established and plasticity levels are higher at crack tip Original magnification given by micron bar

Fractography Resource - 30 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa Some of these steels show IG fatigue at low levels of plasticity (e.g. during crack initiation, and at long lives) N f = cycles Fatigue striations at higher magnification Original magnification given by micron bar

Fractography Resource - 31 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa An extra-low carbon grade does not show IG fatigue N f = cycles No IG facets near crack initiation site Original magnification given by micron bar

Fractography Resource - 32 Low Carbon Interstitial-Free Steel Typically 0.002C 0.15Mn + Ti, Nb or B additions - YS = MPa An extra-low carbon grade does not show IG fatigue N f = cycles Higher magnification view of crack initiation site Original magnification given by micron bar Back to Contents

Fractography Resource - 33 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

Fractography Resource - 34 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

Fractography Resource - 35 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

Fractography Resource - 36 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

Fractography Resource - 37 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

Fractography Resource - 38 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

Fractography Resource - 39 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 Back to Contents

Fractography Resource - 40 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 Back to Contents

Fractography Resource - 41 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 Back to Contents

Fractography Resource - 42 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 Back to Contents