Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
130 Chapter IV. STRAIN PARTITIONING
After the normalization step, the purpose is to compare the phase behaviour in both microstructures.
One solution is to calculate the ratios indicated by eq IV-10 and eq IV-11. The results are given in
Table IV.9.
� overall ��� eq � / � eq �D1
_W
� overall ��� eq � / � eq �D2 _W
� overall ��� eq � / � eq �D1
_W
� overall ��� eq � / � eq �D2 _W
� overall ��� eq � / � eq �D1
_W
� overall ��� eq � / � eq �D2 _W
� overall ��� eq � / � eq �D1
_W
� overall ��� eq � / � eq �D2 _W
1.11 0.89
Table IV.9. Comparison between the austenite and the ferrite in both investigated grades.
eq IV-10
eq IV-11
In other words, the values of the ratios calculated with eq IV-10 and eq IV-11 demonstrates that on the
one hand the D1 austenite deforms more than the D2 austenite (about 11% more), and on the other
hand the D1 ferrite strains less than the D2 ferrite (about 11% less).
Two mechanisms can be responsible for the change of rheology of a phase. A phase can be streng-
thened (i) by precipitation or (ii) reinforced by solute strengthening. Through this work, TEM observa-
tions have never shown any precipitates which could explain the strengthening of a phase. In addition,
in the literature, there is not any reference which reports the existence of an hardening precipitation at
high temperature. Figure IV.31 shows illustrations of the solute strengthening effect of various ele-
ments on the ferrite of low-alloyed steels (Figure IV.31.a) and on the austenitic stainless steels (Figure
IV.31) at room temperature. Here, the situation involves high temperatures. As a consequence precau-
tions must be taken when the results of Figure IV.31 are used to analyze high temperature behaviour.
Increase of yield stress Δσy(MPa)
Content of alloying elements (%)
a) b)
Increase of yield stress Δσy(MPa)
Content of alloying elements (%)
Figure IV.31. Influence of alloying content on the yield stress of a) ferrite and b) austenitic stainless
steel at room temperature.