Particle Stimulated Nucleation in Coarse-Grained Ferritic Stainless Steel
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INTRODUCTION
IT is well known that dispersed non-deformable particles affect both deformed and recrystallized microstructures of several relevant industrial materials such as steels and aluminum alloys.[1–5] The term ‘‘non-deformable’’ means that particles are elastically stiff and much harder than matrix acting as obstacles to dislocation motion. Dislocations are able to bypass these particles and the nature of the dislocation structure developed around non-deformable particles is almost independent of particle mechanical properties.[6] Remarkable changes in the microstructure and crystallographic texture were reported to depend mainly on particle dispersion parameters such as particle volume fraction, size, shape, and interparticle spacing.[7] During large strain deformation of materials containing coarse particles, i.e., with sizes larger than 0.1 lm,[8] non-deformable particles can induce a high degree of local lattice curvature in their vicinity due to the particle-matrix strain incompatibility and, consequently, more complex dislocation structures are formed.[3,8] These regions are in the literature referred to as deformation zones.[9] During subsequent annealing, such particle-related deformation zones are favorable nucleation sites for
RODRIGO PINTO DE SIQUEIRA, PostDoc, and HUGO RICARDO ZSCHOMMLER SANDIM, Associate Professor, are with the Departamento de Engenharia de Materiais, Escola de Engenharia de Lorena, Universidade de Sa˜o Paulo, Lorena SP, 12600-970 Brazil. Contact e-mail: [email protected] DIERK RAABE, Professor, is with the Max-Planck Institut fu¨r Eisenforschung (MPIE), 40237 Du¨sseldorf, Germany. Manuscript submitted September 29, 2011. Article published online September 18, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
primary recrystallization and this mechanism is, hence, referred to as particle-stimulated nucleation (PSN).[3] Most of the literature on the nature of deformation zones is focused on particle-containing face-centered cubic (fcc) materials.[2,10–16] Several works in fcc particle-containing polycrystalline alloys have shown that new grains that nucleated around particles are randomly oriented.[11,17–21] Starting from single-crystal materials, the orientations of the new grains were found to be related to the host orientation of the deformed crystal in which the inhomogeneous deformation zone was formed.[22–24] Recent investigations regarding the effects of non-deformable particles on the nature of the deformation zone were also performed in intermetallic materials such as Fe3Al alloys with B2 ordered structure.[13,25–27] A new approach referred to 3D highresolution EBSD has been used to characterize deformation zones in Ni[24,28] and Fe3Al-based alloys.[29] In spite of the great industrial importance of carbon and ferritic stainless steels (FSS), PSN mechanism is much less investigated in body-centered cubic (bcc) materials. The effect of spherical cementite particles on the nature of the deformation zone has been studied by Gawne and Higgins[30] in a cold-rolled Fe-0.4 pc
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