Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
140 Chapter IV. STRAIN PARTITIONING
IV.6.1.2 Widmanstätten morphology
The influence of the temperature has been studied for the Widmanstätten morphology, using exactly
the same procedure as for the equiaxed morphology.
IV.6.1.2.1 Macroscopic stress strain curves
D1 specimens showing a Widmanstätten morphology (D1_W) were deformed at 1s -1 up to a reduction
of 20% at two different temperatures, 850°C or 950°C. The macroscopic equivalent stress strain
curves are presented in Figure IV.39. Typical values of stress are summarized in Table IV.16.
σ eq (MPa)
350
300
250
200
150
100
50
0
1
1 �
�� � s
0 0.05 0.1 0.15 0.2 0.25 0.3
ε eq
850°C
950°C
Figure IV.39. Comparison between the macroscopic equivalent stress strain curves of the Widmanstätten
morphology obtained under plane strain compression at 1s -1 and different temperatures:
T = 850°C and 950°C up to a reduction of 20%.
T (°C) sample �� (s -1 ) 0
� (MPa) � (MPa)
steady state
850°C D1_W ii 1 175 295
950°C D1_W iiii 1 120 205
Table IV.16. Summary of the plane strain compression experimental conditions and typical stress
values for the Widmanstätten morphology at T = 850°C and 950°C.
IV.6.1.2.2 Strain maps
The equivalent strain maps of the Widmanstätten morphology obtained at 850 and 950°C, are shown
in Figure IV.40.a Figure IV.40.b respectively. In the strain map D1_W at 950°C (Figure IV.40.b), it is
difficult to recognize the austenite laths. Indeed, in the region of interest, the laths were cut along their
section and not along their length as in the strain map of D1_W at 850°C (Figure IV.39.a).