Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
161 Chapter V. CONCLUSIONS and PERSPECTIVES
Chapter V. Conclusions and perspectives
Generally, duplex stainless steels exhibit a poor hot workability which results in the occurrence of
edge-cracks during the hot rolling processing of flat products. The immediate consequence of the poor
hot workability of duplex steels is a dramatic increase of the manufacturing costs because additional
operations like grinding or scraping are often required. Two different duplex grades were investigated:
D1 and D2. The first one, D1, was known to show a reasonable level of hot workability (edge crack
length does not exceed 5mm) whereas D2 is affected by 50mm-long edge-cracks. Both grades consti-
tute good examples to address hot workability issues such as the edge-cracking phenomenon.
Starting from a concrete industrial problem, subjacent scientific issues were identified through this
work. Thus, fundamentals aspects about the origin of the edge-cracking problem were addressed and
industrial recommendations were formulated.
The literature data about the hot working of duplex steels is very rich. In the literature review (Chapter
II), all the factors affecting the hot workability of duplex stainless steels were summarized, and two
missing pieces of the “puzzle” to understand completely the hot workability of duplex steels were iden-
tified.
First of all, the lack of a method that quantifies properly the high temperature resistance to crack prop-
agation was pointed out as a key parameter to better understand the edge-cracking issue. Secondly,
although several authors have suggested the occurrence of strain partitioning between ferrite and
austenite in duplex steels, there was clearly a lack of quantitative data about the high temperature
micro-scale strain distribution. As a consequence, experimental developments were done to provide
quantitative information about high temperature strain partitioning between ferrite and austenite.
These two identified missing pieces of the duplex steels hot workability puzzle were discussed in
depth in chapter III and IV, respectively. After having summarized the chapters describing the results
obtained throughout these investigations, we give a few recommendations in order to design a “better
microstructure”. Finally, as perspectives, several tasks are suggested to complement the work.