Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter III. HOT CRACKING RESISTANCE 87
It can be concluded that the origin of the difference between D2_E and D2_W directly comes from to
the work spent for growing voids to final fracture of the specimen.
Figure III.47. Normalization of the force displacement curves for a ligament length of l0 = 22mm for
respectively, the D2_E and D2_W microstructures. The force is normalized by the area of the ligament
that gives a stress and the displacement is divided by the final displacement.
III.6.4 Conclusions
� The EWF concept was applied at high temperature to model microstructures presenting a dif-
ferent austenite morphology (an equiaxed and a Widmanstätten), but with an equal and stable
phase ratio. The results have shown that at 1050°C, an equiaxed morphology (D2_E) was two
times more resistant to crack propagation than a Widmanstätten morphology (D2_W).
� Characterization of the fracture surface and damage match very well with the EWF results. No
differences were pointed out in terms of damage nucleation strain or of crack density.
� Hardness characterizations have shown that there is no difference in term of rheology when
comparing both morphologies.
� The higher hot tearing resistance of the equiaxed morphology compared to the Widmanstätten
morphology is related to the path crack propagation and characteristic length X0.
� Testing DENT specimens with different thicknesses would permit to separate the three contri-
butions and thus estimate the high temperature toughness of the materials.