Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter IV. STRAIN PARTITIONING 125
� More severely strained regions
Finally, it has to be noticed that the more strained zones in the microstructures are almost always si-
tuated in the vicinity of the δ/γ interphase boundaries. Locally, the ratio
� �
� � eq
eq / fluctuates between 2
and 3, and in a few areas, this ratio can reach 5. These results are in agreement with the observa-
tions carried out on the edge part of the hot rolled material or close to the fracture in the DENT speci-
mens showing that damage always nucleates at the δ/γ interphase boundaries, see Figure I.9.b and
Figure III.15.
All these deformation features can be observed in the D1_W microstructure as well as in the D2_W
allowing a better understanding of the mechanisms involved in the high temperature deformation of
duplex stainless steels. Nevertheless, these qualitative comments do not permit to establish accurate
comparisons between both grades. Therefore, additional analysis is needed involving a more quantita-
tive treatment of the strain partitioning in both microstructures.
IV.5.1.2.2 Quantitative analysis
Several options are available to provide quantitative results about the strain partitioning. An overview
of these options is given in this section. The results are presented for each grade keeping in mind that
two different regions were analyzed in the plane strain compression specimen providing two strain
maps: map1 and map2.
� Average deformation per phase.
First of all, the average deformation per phase for both microstructures are computed, the results are
summarized in Table IV.4 for the D1_W microstructure and in Table IV.5 for the D2_W microstructure.
D1_W �� 11 � �� 22 � �� 12 � �� 33 � �� eq �
Overall
Austenite γ
Ferrite δ
Map 1 -0.572 0.452 0.004 0.120 0.603
Map 2 -0.753 0.633 -0.013 0.120 0.809
Map 1 -0.495 ± 0.023 0.398 ± 0.015 0.003 ± 0.006 0.097 ± 0.008 0.525
Map 2 -0.662 ± 0.025 0.589 ± 0.010 -0.001 ± 0.001 0.074 ± 0.016 0.726
Map 1 -0.642 ± 0.001 0.495 ± 0.002 0.004 ± 0.003 0.147 ± 0.001 0.673
Map 2 -0.816 ± 0.002 0.661 ± 0.002 -0.020 ± 0.001 0.154 ± 0.003 0.866
Table IV.4. Average logarithmic deformation per phase in the two strain maps determined in the
D1_W microstructure.
D2_W �� 11 � �� 22 � �� 12 � �� 33 � �� eq �
Overall
Austenite γ
Ferrite δ
Map 1 -0.540 0.463 0.177 0.077 0.619
Map 2 -0.520 0.457 -0.061 0.064 0.572
Map 1 -0.434 ± 0.028 0.364 ± 0.031 0.154 ± 0.009 0.070 ± 0.004 0.499
Map 2 -0.416 ± 0.025 0.347 ± 0.026 -0.031 ± 0.007 0.070 ± 0.001 0.447
Map 1 -0.670 ± 0.010 0.559 ± 0.004 0.198 ± 0.001 0.111 ± 0.006 0.754
Map 2 -0.646 ± 0.004 0.562 ± 0.007 -0.094 ± 0.003 0.084 ± 0.003 0.711
Table IV.5. Average logarithmic deformation per phase in the two strain maps determined in the
D2_W microstructure.