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INTRODUCTION

THE industrial application of duplex stainless steels (DSS) is increasing, mainly in the chemical, petrochemical, marine, and nuclear industries.[1] Indeed, this family of steels combines good mechanical and corrosion resistance properties due to a d-ferrite/c-austenite phase ratio close to 1. DSS is usually delivered in the annealed two-phase condition after a solution treatment is performed at 1323 K to 1373 K (1050 C to 1100 C). Undesirable phases, such as the r phase, carbides, nitrides, and other intermetallic phases, are known to precipitate in DSS during aging, leading to a dramatic deterioration of the mechanical and corrosion properties.[1,2] In standard and super DSS, the embrittlement nose is caused by the formation of the Cr-Mo-rich r phase and occurs in as few as several minutes of aging at 1173 K (900 C).[3,4] The r phase precipitates mainly in d through an eutectoid transformation of d into r and c2-secondary austenite.[3,5] However, carbides and nitrides precipitate first in this range of temperatures. During aging of 2205 DSS (UNS S32205), Lee et al.[6] observed the migration of the d/c interface boundary into d through the lamellar growth of M23C6 carbides and c2 followed by r-phase precipitation. Chen et al.[7] reported that the r phase preferentially nucleates at the interfaces between preformed M23C6 and d at c/d phase boundaries. When using N as an alloying element in JEAN-YVES MAETZ, Postdoctoral Fellow, SOPHIE CAZOTTES, Assistant Professor, and CATHERINE VERDU and XAVIER KLEBER, Professors, are with the Universite´ de Lyon, INSA Lyon, MATEIS, UMR CNRS 5510, 69621 Villeurbanne, France. Contact e-mail: [email protected] Manuscript submitted March 2, 2015. Article published online November 6, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A

DSS, the precipitation of Cr2N nitrides is likely to occur along d/c and d/d interfaces.[3] Ramirez et al.[8,9] investigated five ferritized DSS reheated at 1173 K to 1473 K (900 C to 1200 C) for a few seconds and proposed a model to describe the migration of the c/d interface due to Cr2N precipitation. Cr2N and c2 grow together in d until the diffusion of the heavy nitride forming elements, such as Cr, Mo, and V, limits the Cr2N growth and allows c2 to grow alone. The Cr2N nitrides remain on the c/c2 interface and dissolve as aging progresses. Since the late 1990s, significant studies have been devoted to the development of lean DSS, a family of stainless steels that combines the good mechanical properties characteristic of DSS with the corrosion resistance of standard austenitic stainless steels.[10,11] The 2101 DSS was mainly designed for light-weight constructions and using this grade instead of the dominating stainless steel grades, typified by the austenitic AISI 304 (EN 1.4301), allows significant weight-saving. As a fact, the 2101 DSS is an economical alternative to these standard austenitic stainless steels. Compared with other DSS, the corrosion resistance and cost-processing of the 2101 DSS are usually weaker, as the Ni and Mo cont