Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
24 Chapter II. STATE OF THE ART
II.1.2.1 Interphase boundary sliding
Sliding involves the translation of a grain with respect to another parallel to a common boundary. Slid-
ing has been identified in hot-worked, as-cast and hot rolled specimens by characterization after de-
formation of polished and marked specimens [12-14].
The SEM picture in Figure II.4 is a good illustration of this phenomenon. It shows that the microgrid
lines are discontinuous along an austenite-ferrite interphase.
δ
γ
10 μm
Figure II.4. A clear example of interphase boundary sliding in a 2205 duplex stainless steel deformed
to 0.15 at 1050°C and 1s -1 [14].
The ability to slide depends on the character of the boundary: coherent and semi-coherent interfaces
being less prone to sliding than incoherent interfaces. This applies also to hot-worked duplex stainless
steels for which the crystallographic nature of the interface is a key parameter controlling the sliding
ability [12]. Indeed, deformation applied to marked, as-cast and wrought specimens showed that slid-
ing at the austenite-ferrite interface is not possible as long as the two phase orientations are related by
a Kurdjumov-Sachs orientation relationship. In a Widmanstätten microstructure, the scratch markers
are slightly deflected at each interphase boundary but do not lose continuity (Figure II.5.a). On the
contrary, in a hot-rolled microstructure, such as the one seen in Figure II.5.b, the scratch markers re-
flect the occurrence of sliding: relative displacements of the markers may reach several micrometers
at the interphase boundaries.