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Martensite in Steels

Martensite in Steels. cml.postech.ac.kr/teaching.html Graduate Institute of Ferrous Technology (GIFT). http://cml.postech.ac.kr/. Materials, transformation temperatures & strength. Olson and Hartman, 1982. Olson and Hartman, 1982. Olson and Hartman, 1982. Diffusionless transformation?.

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Martensite in Steels

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  1. Martensite in Steels cml.postech.ac.kr/teaching.html Graduate Institute of Ferrous Technology (GIFT)

  2. http://cml.postech.ac.kr/

  3. Materials, transformation temperatures & strength

  4. Olson and Hartman, 1982

  5. Olson and Hartman, 1982

  6. Olson and Hartman, 1982

  7. Diffusionless transformation? Martensite can form at very low temperatures. Martensite can grow very rapidly. No composition change during transformation.

  8. Shape of martensite ?

  9. Irrational: why?

  10. Orientation relationships: irrational

  11. athermal transformation

  12. Creation of a bi-crystal cut and rotate by angle q about axis normal to diagram q

  13. Glissile interface

  14. Glissile interface cannot contain more than one set of dislocations. Martensitic transformation only possible if the deformation which changes the parent into the product leaves one line undistorted and unrotated, i.e. an invariant-line. Deformation is an invariant-line strain.

  15. 50 mm

  16. general invariant-plane strain simple shear uniaxial dilatation s s d d 1 1 1 s=0.26 d=0.03

  17. s d c r 1 Christian, 1957

  18. body-centred cubic cubic close-packed

  19. b a 3 3 a 2 b b 2 1 a 1 (a) (b) BAIN STRAIN (d) (c) Body-centered Body-centered cubic martensite tetragonal austenite

  20. [001] b b' [100] o a' a b (a) o b' (b) a,a'

  21. RB z w w z w z P Observed P 1 Martensite Austenite 2 shape, (wrong wrong y shape) structure x x y x y (a) (b) (c) LATTICE -INVARIANT DEFORMATION w w z z Twin Boundary x y x y Twinned Slipped Martensite Martensite Correct macroscopic shape, correct structure

  22. transformation twins (Wayman)

  23. hexagonal close-packed cubic close-packed

  24. z w w z P Observed 1 Austenite shape, correct y structure x x y (a) (b)

  25. Brooks, Loretto and Smallman, 1979

  26. a + strain a Free Energy g a ag ga x x x Carbon Concentration

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