Wolfgang Bleck Wenwen Song Alireza Saeed

A5
Microstructure and Mechanism Maps
Wolfgang Bleck
Wenwen Song
Alireza Saeed-Akbari
Institut für Eisenhüttenkunde der RWTH Aachen
Motivation
In the second period of SFB 761 project, 2D and 3D
mechanism maps have been developed to describe the
deformation mechanisms in high Manganese steels in
Fe-Mn-C and Fe-Mn-Al-C system. The effect of chemical
composition and the temperature on the deformation
mechanisms is revealed in 2D and 3D regimes. The
deformation modes and the strain hardening behaviors
of the high manganese steels were characterized and
further discussed in terms of microstructural features.
2D&3D Mechanism Maps
Research 2. Phase
SFE Calculations
The composition-dependent stacking fault energy (SFE) maps
of high Manganese austenitic steels were calculated based on a
subregular solution thermodynamics model. In the model, the
stacking fault energy was calculated by:
γ→ε
Γ=2ρ∆Geff +2σγ/ε
γ/ε
where ρ is the molar surface density along the {111} plane, σ
γ→ε
is the γ/ε interfacial energy, ∆Geff is the effective Gibbs free
energy change during the austenite→martensite transformation.
Synchrotron Results
Synchrotron X-ray method has been applied in order to follow the
strain hardening behavior during tensile test.
Fe-17Mn-1.5Al-0.6C
strain rate 0.001 s-1
 2D and 3D composition-dependent stacking fault energy (unit,
mJ/m²) map of Fe-Mn-Al-C steel at 300 K
 The synchrotron X-ray diffraction results show the dynamic
grain refinement by the deformation twins.
g
f
e
d
c
b
a
 The synchrotron X-ray diffraction tracks the dynamic twinning
evolution during tensile test.
 Changing of iso-SFE surface with the increase of temperature
Summary
• The composition-dependent SFE maps can facilitate in 2D and
3D regimes to predict the deformation mechanisms in high
Manganese steels.
• The mechanism map describes the deformation modes, i.e. TRIP,
TWIP, MBIP in high Manganese steels.
• The synchrotron X-ray results show the dynamic grain refinement
by deformation twins.
 Effect of Al and C on composition-dependent SFE
[1] W. Song; T. Ingendahl; W. Bleck: Acta Metall. Sin. (Engl. Lett.), 27 (2014) 3 546-556.
[2] A. Saeed-Akbari; A. K. Mishra; J. Mayer; W. Bleck: Metall. Mater. Trans. A, 43A (2012) 1705-1723.