Retained Austenite in TRIP-Assisted Steels role of transformation plasticity China Steel

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Transcript of Retained Austenite in TRIP-Assisted Steels role of transformation plasticity China Steel

  • Slide 1
  • Retained Austenite in TRIP-Assisted Steels role of transformation plasticity China Steel
  • Slide 2
  • Shape deformations due to transformations
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  • Fe-30.5Ni-0.32C wt% Forsik, 2004 Invariant-plane strain
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  • s 1 s 1 1 uniaxial dilatation simple shear general invariant-plane strain s=0.26 =0.03
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  • Minimum requirement for martensitic transformation there must exist an invariant-line at interface i.e., one set of dislocations which can glide conservatively can be more than one invariant-line
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  • body-centred cubic cubic close-packed
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  • (a) BAIN STRAIN (c) Body-centered tetragonal austenite (d) Body-centered cubic martensite a a a 1 2 3 b 3 b 1 b 2 (b)
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  • [100] [001] o a a' b b' o b a,a' (a) (b)
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  • Austenite Martensite (wrong shape) Twinned Martensite Slipped Martensite Twin Boundary Observed shape, wrong structure RB P LATTICE -INVARIANT DEFORMATION Correct macroscopic shape, correct structure (a) (b)(c) w x y z w x z y x wz y x w z y x wz y P 1 2
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  • Bhadeshia & Edmonds, (1980) Typical composition: Fe-0.15C-1.5Si- 1.5Mn wt% polycrystalline
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  • Bhadeshia & Edmonds, (1980) b
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  • Is the shear important in a polycrystalline sample?
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  • How can we bias the microstructure? By transforming under the influence of stress.
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  • s 1 s 1 1 uniaxial dilatation simple shear general invariant-plane strain s=0.26 =0.03
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  • 50 m polycrystalline austenite Bhadeshia, 1982
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  • What is the maximum tensile strain obtained from TRIP? in a fully austenitic sample which transforms completely into martensite.
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  • s z3z3 z1z1
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  • u v
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  • Sakuma et al. (1991)
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  • absorbed energy / kJ Yoshitake et al. (1996)
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  • Retained Austenite in TRIP-Assisted Steels Slide 1 ..very small contribution to elongation.
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  • Bhadeshia & Edmonds, (1980) Composite of soft and hard phase
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  • Bhadeshia & Edmonds, (1980) strain in soft phase Strain in hard phase
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  • Tomota (1976)
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  • Bhadeshia & Edmonds, (1980)
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  • low silicon high silicon Jacques et al. (2001) silicon causes scale
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  • Summary Assistance from TRIP is less than 1.4% of total strain Emphasis could be shifted from retained austenite to studies of composite deformation Low silicon steels can perform well (Jacques)
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  • Sherif et al. 2003
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