Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
118 Chapter IV. STRAIN PARTITIONING
IV.4.3.4 Per-phase average strains
In Figure IV.21, two different polygonal lines joining microgrid intersections are drawn and represent
two possible ways of defining the interface between ferrite and austenite, including or not part of the
neighbour phase. The real interface is somewhere in between. Per-phase average deformation can be
computed using the procedure described in section IV.4.3.2 applied to the two different polygonal lines
mentioned previously and defined in Figure IV.21. Different results are obtained if the line “with or
without interface” is used. The average of both values provides a good estimate of the exact values.
20 μm
δ-ferrite
γ-austenite
γ-austenite withinterface
γ-austenite without interface
Figure IV.21. Integration scheme for the average gradient over a phase
IV.4.3.5 Errors on the computation of the strains
There are several elements that induce some errors on the strain calculation. In this section, only a
few of these elements are considered, more details can be found in [98] and [128].
� To estimate the error related to the manual location of the microgrid intersections, the same
region of interest has been analyzed two times and the results given in each case have been
compared. The comparison of the results showed that the error related to the manual location
of the microgrid intersections could be neglected.
� The main source of errors is due to the bad approximation of the interface, as shown by the
difference in the area of the integration domains in each case, which generally is close to 15%
of the area of the characterized area. In fact, the computations “with interface” for the harder
phase (austenite) takes into account this phase plus some domain of the weaker phase (fer-
rite), more strained, and thus gives upper bounds for the average gradient components; it
leads to lower bounds in case of the weaker phase. For a given phase, the error related to the
bad location of the interface can be estimated by the half difference between the result “with
interface” and without interface”. Note that the average of the result “with interface” of a given
phase and the result “without interface” of the other phase, weighted with the corresponding
areas, gives the overall value.