Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter III. HOT CRACKING RESISTANCE 93
Damage characterizations carried out on the hot rolled material or on the broken DENT specimens
have demonstrated that the voids always nucleate by decohesion of the δ/γ interfaces and propagate
in the ferrite or along the interphase boundaries. As a consequence, the inclusions located in the aus-
tenite are not so detrimental to the hot tearing resistance. On the contrary, it seems that there is a
relationship between the number of inclusions located in the vicinity of the δ/γ interfaces and the hot
cracking resistance.
The main conclusion of these results is that the lower the inclusion content, the higher the specific
essential work of fracture and the better the hot cracking resistance.
Manual method
Density of inclusions (number of inclusions per mm²), f i
D1_W D1bis_W
γ-austenite 41 477
δ-ferrite 47 504
δ/γ interfaces 23 183
Total 112 1165
Table III.13. Densities of inclusions respectively in ferrite, austenite and interfaces determined with the
optical method in both D1_W and D1bis_W microstructures.
Automatic method
Density of inclusions (number of inclusions per mm²), f i
D1_W D1bis_W
Total 150 1091
Table III.14. Densities of inclusions determined with the SEM method in both D1_W and D1bis_W microstructures.
III.7.3.3 Size of the inclusions
The automatic procedure provides information about the size of the particles. The average diameter of
the particles is about 1.9μm in the D1_W microstructure and about 1.4μm in the D1bis_W microstruc-
ture, see Table III.15. These average values are very close to each other and cannot be invoked to
account for the difference between D1_W and D1bis_W in terms of the hot tearing resistance.
D1_W D1bis_W
Average inclusion equivalent diameter (μm) 1.9 1.4
Table III.15. Average inclusion size in both microstructures D1_W and D1bis_W.