1. Interface-related micromechanics in TWIP steels
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe
28. October 2009, MS&T, Pittsburgh
Acknowledgements:
SFB 761 “Steel ab initio”;
discussions with Marty Crimp and Tom Bieler
(Michigan State University)
see also: talk at 2 pm Thursday room 328, EBSD session

2. Overview
Dierk Raabe, MS&T, Pittsburgh, 28. Oct. 2009, MPIE

3. 2
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
0
10
20
30
40
50
60
70
80
totalelongationtofracture[%]
ultimate tensile strength [MPa]
TRIP and
complex phase
martensitic
maraging
TRIP
dual phase
ferritic
Ductility-strength profile for sheet steels
austenitic
stainless
advanced
TWIP and
TRIP
www.mpie.de
www.mpie.de
www.mpie.de

4. 3
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
0
10
20
30
40
50
60
70
80
totalelongationtofracture[%]
ultimate tensile strength [MPa]
TRIP and
complex phase
martensitic
maraging
TRIP
dual phase
ferritic
Ductility-strength profile for sheet steels
austenitic
stainless
advanced
TWIP and
TRIP

5. Characterization
Dierk Raabe, MS&T, Pittsburgh, 27. Oct. 2009, MPIE

6. 5
Scaling issue in microscopy
?
TEM EBSD
EBSD orientation contrast
is not lattice defect contrast
Large scale mapping of lattice
defects
TEM information in SEM
Electron Channeling Contrast Imaging
Example: Fe-22Mn-0.6C (wt%), TWIP

7. 6
EBSD
High spatial and
angular resolution
ECCI
1 nm
10 nm
100 nm
1000 nm
0.001º 0.01º 0.1º 1º
Spatial
resolution
Angular
resolution
Limited spatial and
angular resolution
Good spatial and
angular resolution
TEM
Overview characterization

8. Electron channeling contrast mechanism
Dislocation imaging
[A.J. Wilkinson, P.B. Hirsch, Micron 28 (1997) 279]
Requirement: Crystal at Bragg condition
Imaging under controlled diffraction conditions

9. 8
Fe-22Mn-0.6C (wt%) TWIP steel
High resolution EBSD ECCI
twins
Dislocation cells
Comparison EBSD-ECCI
Electron Channeling Contrast Imaging

10. 9
SEM

11. 10
SEM
TEM

12. 11
ECCI / SEM
(-220)
Dislocation cells are clearly seen by ECCI
TEM-Bright Field
Fe-22Mn-0.6C (wt%) TWIP steel
Electron Channeling Contrast Imaging
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740

13. 12
0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stress
Hardening (MPa)
Hardening/Stress(MPa)
True strain
YS: 210 MPa
UTS: 1200 MPa
Ductility: 51%
strain rate: 2.5x10-4 s-1
tensile test, room temperature
10%
20%
40%
TA
twins
TA
step size: 50 nm
twins do not provide much
strain but the 2nd
hardening plateau
EBSD: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740

14. 0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stress
Hardening (MPa)
Hardening/Stress(MPa)
True strain
YS: 210 MPa
UTS: 1200 MPa
Ductility: 51%
strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
2nd hardening stage:
2%<e< 10%
-Planar slip structures + wavy structures
-Few mechanical twins*
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia et al. Scripta Mater. 61 (2009) 737-740

15. 2nd hardening stage:
2%<e< 10%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

16. 0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stress
Hardening (MPa)
Hardening/Stress(MPa)
True strain
YS: 210 MPa
UTS: 1200 MPa
Ductility: 51%
strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
3rd hardening stage:
10%<e< 25%
-Wavy structures: dislocation cells
-Mechanical twins
-3 Types of grains
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

17. 3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

18. 0
500
1000
1500
2000
2500
3000
3500
4000
0 0.1 0.2 0.3 0.4 0.5
True stress
Hardening (MPa)
Hardening/Stress(MPa)
True strain
YS: 210 MPa
UTS: 1200 MPa
Ductility: 51%
strain rate: 2.5x10-4 s-1
2% 10% 25% 35%
5th hardening stage:
35%<e< 50%
-Wavy structures: dislocation cells
-Mechanical twins
-3 Types of grains
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

19. 5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

20. Type I
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

21. Type II
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

22. Type III
5th hardening stage:
35%<e< 50%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

23. 0
20
40
60
80
100
0.05 0.1 0.2 0.4
DDW+Cells
DDW+Cells+Twins
Type I
Type II
Type III
%
True strain
Type of grain
Interface statistics
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

24. Most of the grains follow
the Schmid’s Law (3/4)
True strain: 40%
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

25. True strain: 40%
Some of the grains follow
the Schmid’s Law
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

26. True strain: 40%
1-2activated twinning
systems nucleated at
grain boundaries
No twins inside the grain (few degrees from [001])
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

27. Grains with “low” twinning activity:
-Short twins (less than 5 microns length)
-Few twins
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

28. Grains with “high” twinning activity:
-Long twins
-Thick bundles of twins
-High population of twins
These results suggest a
Sslip/Stwinning relationship
on twin growth
EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

29. Type I
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

30. Type II
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

31. Type III
3rd hardening stage:
10%<e< 25%
ECCI: Work hardening of TWIP steels, Fe-22Mn-0.6C (wt%)
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

32. 31
Fe22Mn0.6C TWIP steel
Mechanical twins
Dislocation cells
Electron Channeling Contrast Imaging
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

33. EBSD: Growth of deformation twins in TWIP steels
I. Gutierrez-Urrutia, et al. Mater. Sc. Engin. A 527 (2010) 3552

34. Dierk Raabe, MS&T, Pittsburgh, 27. Oct. 2009, MPIE
Summary

35. 34
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe: Scripta Mater. 61 (2009) 737-740
Electron channeling contrast imaging of twins and dislocations in twinning-
induced plasticity steels under controlled diffraction conditions in a scanning
electron microscope
I. Gutierrez-Urrutia, S. Zaefferer, D. Raabe: Mater. Sc. Engin. A 527 (2010)
3552-3560
The effect of grain size and grain orientation on deformation twinning in a
Fe–22 wt.% Mn–0.6 wt.% C TWIP steel
References