Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter III. HOT CRACKING RESISTANCE 57
Figure III.13 presents typical fracture surfaces of DENT specimens for each grade investigated at dif-
ferent temperatures.
The fracture profile of grade D1 is predominantly flat along the whole ligament at 1050°C (Figure
III.13.a). A classical ductile profile with dimples is observed at the micro-scale. The phenomenon re-
sponsible for cracking initiation is the growth and coalescence of voids ahead the blunted crack tip,
see Figure III.14. The crack propagates under a constant thickness reduction, with a steady-state
geometry of the fracture process zone (FPZ).
The fracture profile of the grade D2 at 1050°C is irregular and shows only a few ductile dimples
(Figure III.13.b). The propagation occurs with varying thickness reduction.
Fracture profiles of both alloys D1 and D2 are flat along the whole ligament at 1200°C (Figure III.13.c
& d). However, the fracture profile of the alloy D1 seems to be a little bit more regular than the fracture
profile of the alloy D2. Examination of the fracture micrographs and profiles match very well with the
EWF results.
1 mm
a) b)
400 μm
1 mm
c) d)
1 mm
1 mm
400 μm
Figure III.13. Fracture micrographs and profiles of the broken DENT specimens (l0 = 37mm); a) D1 at
1050°C; b) D2 at 1050°C; c) D1 at 1200°C. d) D2 at 1200°C. The arrows emphasize the thickness variation
in the profile.