Prakt. Met. Sonderband 46 (2014) 253 
DUPLEX STAINLESS STEELS: MICROSTRUCTURAL 
TRANSFORMATIONS INDUCED BY COLD ROLLING 
M. Breda*, L. Pezzato*, |. Mészaros #, I. Calliari* 
* DIl, University of Padova, Italy 
A BME, Budapest University of Technology and Economics, Hungary 
ABSTRACT 
Duplex Stainless Steels (DSS) are austeno-ferritic stainless steels, widely employed in the 
chemical, petrochemical and nuclear industry owing to their favourable combination of 
strength and corrosion resistance properties. However, DSS are affected by phase 
instability during thermal cycles, due to ferrite solid-state phase transformations, which 
s (deformed causes significant decreases in steels features. In addition, the metastable austenitic 
phase can be interested by a strain-induced phase transformation occurring upon cold 
deformation. 
Cold rolling modifies the microstructure by fragmenting and orienting the grains, leading to 
the formation of a heavily banded microstructure. Further, the lattice rearrangement 
caused by plastic deformation may cause the formation of the so-called Strain-Induced 
te of the 102 Martensite (SIM) from austenite, as well known in metastable austenitic stainless steels, 
ion of grain especially when the phase is not well stabilised. 
sion along the The aim of the present work is to study the effects of cold rolling in various DSS grades in 
dation front terms of strain-induced phase transformation and to discuss the associated changes in 
properties, by employing different characterization techniques. 
1. INTRODUCTION 
Duplex stainless steels (DSS) are a category of steels having a biphasic ferritic-austenitic 
microstructure, in which equal volume fractions of the phases provide the best combination 
between mechanical and corrosion-resistance properties. However, due to the instability of 
e Oxidation of the ferritic matrix at the high temperatures, DSS are susceptible to the formation of 
dangerous phases in the temperature range 600-1000°C [1]. These secondary phases 
(2000), 1239- negatively affect the interesting properties of DSS and, therefore, must be avoided [1-2]. 
Thus, all DSS are submitted to a solution-annealing treatment (solubilisation) followed by 
(1981), 115 water quenching, in order to re-dissolve the secondary phases formed during the 
Scientific and manufacturing processes and to obtain a ferrite/austenite ratio of about one. Moreover, 
since austenite is in a metastable condition at room temperature, cold plastic deformation 
2002), 97-109 can cause a diffusionless transformation, especially when the phase is not stabilized by a 
suitable amount of y-promoting elements. This solid-state phase transformation give rise to 
the so-called Strain-induced Martensite (SIM), which is known to occur in metastable 
austenitic stainless steels [3-5] and which has been recently observed in some Lean DSS 
grades [6,7]. 
Cold rolling modifies the microstructure by refining and orienting the grains as the 
thickness reduction increases, causing the formation of a heavily banded microstructure at 
high deformation degrees. The microstructural damage induced by cold working assumes