Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter IV. STRAIN PARTITIONING 135
� Additional proof
Results about the strain heterogeneity in plane strain compression have been briefly reviewed. Litera-
ture data are completed by the results of this work. For example, the D1_Wiii specimen was macros-
copically deformed to an equivalent strain of 0.391 and two regions located in different areas in the
centre plane of the specimen were analyzed in terms of strain distribution. The overall strain measured
over each region was different: 0.603 in the map 1 and 0.809 in the map 2. This difference can be
attributed to the macroscopic strain heterogeneity. Indeed, as the areas where the strain is mapped
are relatively small (500x500μm), the overall strain depend strongly on the location of the region of
interest in the centre plane of the specimen. Larger areas have to be analyzed so that the overall
strain matches with the applied macroscopic strain.
IV.5.3 Conclusions
� The modified microgrid method was successfully applied to two different duplex stainless
steels providing the strain maps corresponding to both grades.
� The results showed that the D2 alloy is more affected by strain partitioning compared to the al-
loy D1.
� The austenite of the alloy D1 deforms more than the austenite of the alloy D2 whereas the fer-
rite of the alloy D1 strains less than the ferrite of the D2 alloy. This dual effect is a credible ex-
planation of the difference of strain partitioning between the two investigated grades.
� The dispersion of the results, i.e. the differences between the results obtained from one sam-
ple, can be attributed to the macroscopic strain localization.
� The phase rheology depends strongly on the chemical composition, in particular on the streng-
thening effect of element such as Mo.
IV.6 Factors potentially impacting strain localization
As many results were obtained from the D1 grade, it has been decided to focus on this alloy in order to
study the influence of various factors which could potentially impact the strain partitioning in duplex
stainless steel. As some experiments have been carried out successfully at 850°C and 950°C, the
influence of the temperature can be also discussed. In the previous chapter a particular attention has
been paid to generate model microstructures: equiaxed or Widmanstätten. These results are used to
investigate the influence of the phase morphology on the strain partitioning at a given temperature.
IV.6.1 Influence of the temperature
IV.6.1.1 Equiaxed morphology
IV.6.1.1.1 Macroscopic stress strain curves
D1 specimens with an equiaxed morphology (D1_E) were deformed at 1s -1 up to a reduction of 20% at
two different temperatures, 850°C or 950°C.