Journal Published Online: 19 April 2017
Volume 6, Issue 3

Strain-Induced Martensite Detection Methods in Cold-Rolled Duplex Stainless Steels



Duplex stainless steels (DSS) are biphasic austeno-ferritic steels, whose favorable combination of mechanical strength and corrosion-resistance properties makes them highly suitable for structural applications in chemical, petrochemical, and nuclear industries. DSS are high-alloyed steels and their interesting features derive from the presence of an almost equal volume fraction of ferrite and austenite, obtained from a suitable balance of the alloying elements and after a proper post-forming heat treatment (solubilization). However, DSS suffer from ferrite instability when heating the material within certain temperature ranges that can cause the precipitation of harmful secondary phases, which consequently limits their utility to below 250°C. Moreover, owing to austenite metastability at room temperature, a diffusionless martensitic transformation can occur after cold deformation, which leads to the formation of the so-called strain-induced martensite (SIM), especially when the phase is not adequately stabilized by a suitable amount of γ-stabilizing elements. In the present work, cold rolling was adopted as a cold deformation process, and four different DSS grades (SAF 2101, 2304, 2205, and 2507) were subjected to thickness reductions from 15 to 85 %. The developed microstructural features were analyzed by means of various characterization techniques (optical and electron metallography, hardness tests, X-ray and neutron time-of-flight diffraction, magnetic measurements, and critical pitting temperature determination), in order to detect and evaluate the amount of transformed austenite and to observe associated changes in properties induced by the occurrence of SIM. The experimental results revealed that the low-alloyed Lean DSS (2101 and 2304) seem to be more prone to SIM formation, whereas 2205 and 2507 grades were found to be more stable, even after large deformations. Nevertheless, the performed analyses pointed out that SIM detection in DSS is not a straightforward process as in austenitic grades, owing to similar crystallographic and magnetic properties of SIM and ferrite.

Author Information

Breda, M.
Industrial Engineering Dept. (DII), Univ. of Padova, Padova PD, IT
Ramous, E.
Industrial Engineering Dept. (DII), Univ. of Padova, Padova PD, IT
Almanza, E.
Metal Mechanics Dept., Instituto Tecnologico de Saltillo, Saltillo, Coah, MX
Calliari, I.
Industrial Engineering Dept. (DII), Univ. of Padova, Padova PD, IT
Pages: 19
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Stock #: MPC20160065
ISSN: 2165-3992
DOI: 10.1520/MPC20160065