Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
88 Chapter III. HOT CRACKING RESISTANCE
III.7 Influence of the inclusion content
III.7.1 Materials
In order to investigate the influence of the inclusion content on the hot cracking resistance, alloy D1
was considered and compared with alloy D1bis. D1 and D1bis are both 2205-conventional duplex
steels. As a consequence, D1 exhibits the same chemical composition in terms of major elements (Cr,
Ni, Mo, Mn, N…) compared to D1bis, see Table III.11.
%Cr %Ni %Mo %Mn %Si %Cu %C %N
D1 22.90 5.59 3.11 1.75 0.55 0.19 0.02 0.17
D1bis 22.67 5.57 3.21 1.76 0.68 0.20 0.02 0.17
Table III.11. Chemical composition of the D1 and D1bis alloys. Both alloys correspond to a conventional
2205 duplex stainless steel.
From the hot rolled material, model Widmanstätten microstructures of the alloy D1bis were generated
using appropriate heat treatment (HTW.1). Figure III.48.b shows the resulting microstructure: D1bis_W
and the Widmanstätten microstructure of the alloy D1_W is also reported in Figure III.48.a to compare
both microstructures. Microstructure characterizations reveal that both microstructures: D1_W and
D1bis_W were very similar in terms of austenite morphology, average austenite lath thickness, and
volume fraction of phases.
e γ = 49 µm
% γ = 46 ± 3 %
D1_W D1bis_W
γ -Widmanstätten
a) b)
δ
e γ = 49 µm
% γ = 44 ± 3 %
Figure III.48. Widmanstätten model microstructures after HTW.1; a) D1_W and b) D1bis_W.
Several DENT specimens with different ligament lengths were machined from the heat treated blocks
of the alloy D1bis. Then, the specimens were tested under tension at 1050°C and the EWF method
was applied.