Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter III. HOT CRACKING RESISTANCE 71
Figure III.28 gives an estimation of the Ni-diffusion length in the ferrite for different duration of anneal-
ing at 1050°C.
l δ Ni, T = 1050°C (μm)
100
80
60
40
20
0
�
DNi ( 1050
25.1 μm
12.6 μm
�14
�1
�C) � 4.
39.
10 m².
s
61.6 μm
87.1 μm
0 10 20 30 40 50
t (h)
Figure III.28. Evolution of the Ni-diffusion length in the ferrite as a function of time at T = 1050°C.
III.4.4 Conclusions
Proper control of phase transformation mechanisms has allowed the generation of a variety of micro-
structures with different phase morphologies. By controlling the temperature, the duration of annealing
sequences and the cooling rate, alloys with a desired phase proportion, and desired size and shape of
the microstructure constituents have been produced. Figure III.29 summarizes, for both grades, the
resulting microstructures generated with appropriate heat treatments.
Widmanstätten
(W)
Equiaxed
(E)
e γ = 22 µm
D1 D2
γ δ
e γ = 29 µm
% γ = 45 ± 3 %
% γ = 50 ± 3 %
a) b)
γ
ø γ = 50 µm
δ
% γ = 47 ± 3 %
c) d)
γ
ø γ = 59 µm
% γ = 52 ± 3 %
δ
γ δ
Figure III.29. Summary of the model microstructures obtained with the appropriate heat treatments; a)
D1 Widmanstätten microstructure after HTW.1; b) D2 Widmanstätten microstructure after HTW.1; c) D1
equiaxed microstructure after HTE.2; d) D2 equiaxed microstructure after HTE.2.