Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
54 Chapter III. HOT CRACKING RESISTANCE
III.2.3.4.3 Comparison between both methods
The two methods appear to be very complementary. The main advantages and disadvantages relative
to each technique are summarized in Table III.1.
Manual method � Location of the inclusions
Automatic method
Advantages Disadvantages
� Automatic counting
� Surface analyzed: 20mm² (950
pictures at a magnification of
700x)
� Information about the nature and
size of the particles
� Manual counting
� Surface analyzed: 2mm² (50 pictures
at a magnification of 500x)
� No information about the nature
and size of the particles
� No location of the inclusions
� Impossible to discriminate Mo and
S
Table III.1. Summary of the advantages and disadvantages of both techniques used to determine the
inclusion content.
III.2.3.5 Micro-hardness
Micro-hardness Vickers measurements were carried out on DENT specimens in both phases from the
fracture surface down to the undeformed region. Then, it is possible to plot the evolution of the hard-
ness as a function of the equivalent strain. These measurements provide information concerning the
hardening/softening mechanisms involved in the investigated grades.
III.3 Comparison between as-cast D1 and D2
III.3.1 Results
D1 and D2 differ in chemical composition, especially in terms of nickel and molybdenum content
(Table I.3). These two grades were selected because of a known very different degree of hot worka-
bility (section I.2.1). Comparing these two grades should allow unravelling the key parameters involved
in the hot workability of duplex stainless steels.
The DENT specimens were machined in the as-cast slab of each duplex stainless steel with the liga-
ment located in the columnar zone as shown schematically in Figure III.10.
RD
ND
TD
L
t 0
As-cast slab
Figure III.10. Schematic the as-cast slab showing where the DENT specimens were machined.