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DUPLEX stainless steels usually have a structure composed of equal quantities of austenite and ferrite. These steels have better mechanical properties and corrosion resistance than austenitic stainless steels, particularly regarding crevice and localized corrosion. The presence of stable austenite at room temperature makes duplex stainless steels a very suitable material for the study of the austenite/ferrite transformations. The results obtained on duplex stainless steels have been shown to be applicable to low-carbon steels,[1] in which the data relative to austenite must be calculated from the observations on martensite. The method of correlation with martensite to determine the orientation relationship (OR) between ferrite and austenite has been employed, for example, by Miyamoto et al.,[2] during studies on the crystallography of ferrite particle nucleated intragranularly using (MnS
V(C,N)) complex precipitates as nucleation sites, and by Furuhara et al.,[3] during studies of the crystallography of these same complex precipitates, ferrite and austenite. The nature of the interface between the parent and product phase influences largely the morphology of the precipitates and the mechanical properties of the alloy. Studies performed on copper,[4,5] iron,[6] and iron-chromium-nickel[7,8] alloys show that, although the ORs found on the bcc to fcc reaction are the same as the ones on the opposite reaction, the morphologies encountered tend to be rather different. It is commonly accepted E.F. MONLEVADE, Graduate Student, and I.G.S. FALLEIROS, Professor, are with the Department of Metallurgical and Materials Engineering, Escola Politécnica, University of São Paulo, 05508-900, São Paulo, SP, Brazil. Contact e-mail: [email protected] This article is based on a presentation made in the “Hume-Rothery Symposium on Structure and Diffusional Growth Mechanisms of Irrational Interphase Boundaries,” which occurred during the TMS Winter meeting, March 15–17, 2004, in Charlotte, NC, under the auspices of the TMS Alloy Phases Committee and the co-sponsorship of the TMS-ASM Phase Transformations Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A

that a growing particle nucleated on a grain boundary will have an OR with one adjoining grain and hold an incoherent interface with the other side of the boundary. However, a few studies have shown that there are cases in which the grain boundary particle holds ORs with both adjoining grains simultaneously. King and Bell[9] have reported grain boundary ferrite particles, formed on a coarse-grained sample, holding ORs with both adjoining grains. Fujiwara et al.[10] have shown austenite particles, nucleated on triple line grain boundaries, which had small deviations from exact ORs with two adjoining grains. Hillert[11] has reported grain boundary Widmanstätten austenite growing into both adjoining grains, in a low alloy steel. Recently, the ORs between parent and product phases during formation of pearlite have been studied using the electron backscattered diffraction (E