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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. Fatigue crack growth in moist air Fatigue crack growth in vacuum Crack growth by hydrogen embrittlement

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Examples of Steel Fractography

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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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

  42. 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

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