Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
80 Chapter III. HOT CRACKING RESISTANCE
Table III.9 summarizes the results provided in Figure III.40. The plane stress specific work of fracture
at 1050°C is equal to 145 kJ.m - ² and 88 kJ.m - ² for the microstructures D2_E and D2_W, respectively.
It means that at 1050°C, the equiaxed austenite morphology is almost twice more resistant to ductile
tearing than the Widmanstätten austenite morphology.
we (kJ.m - ²) αwp (kJ.m -3 )
D2_E 1050°C 145 ± 16 14.5 ± 0.6
D2_W 1050°C 88 ± 24 13.8 ± 0.8
Table III.9. Results of the EWF method applied at 1050°C to model microstructures: equiaxed (D2_E)
and Widmanstätten (D2_W).
III.6.1.2 Fracture and damage observations
Typical fracture surfaces of DENT specimens are shown in Figure III.41. There is no difference in term
of equivalent strain to fracture, see Table III.10. A classical ductile profile with dimples is observed at
the micro-scale in both cases. However, fracture profiles are significantly different: D2_E exhibits a flat
profile along the whole ligament whereas D2_W exhibits an irregular fracture profile with much coarser
dimples.
1 mm
a) b)
1 mm
Figure III.41. Fracture micrographs and profiles of the broken DENT at 1050°C; a) D2_E (l0=35mm); b)
D2_W (l0=37mm).
eq
� fracture
D2_W 1050°C 1.3 ± 0.1
D2_E 1050°C 1.2 ± 0.1
Table III.10. Estimated values of the equivalent strain to fracture by measuring the thickness of the
specimen at the fracture.
The strain at which damage initiates is not very different when comparing both austenite morpholo-
gies, around 0.5 ± 0.2.