Microstructural Refinement and Mechanical Properties of Ferritic Stainless Steel Processed by Equal-Channel Angular Pres

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Microstructural Refinement and Mechanical Properties of Ferritic Stainless Steel Processed by Equal-Channel Angular Pressing Vikas Shivam, Debabrata Bhuyan, N.K. Mukhopadhyay, and R. Manna1 (Submitted May 26, 2020; in revised form August 18, 2020) Ferritic stainless steel (FSS 430) has been deformed by equal-channel angular pressing (ECAP) at room temperature at an equivalent strain (εvm) of 1.2 by adopting the route Bc. Microstructural developments were studied by optical microscopy, transmission electron microscopy, and microtexture by electron backscattered diffraction. Typical ultraﬁne-grains of less 0.2 µm could be identiﬁed. The XRD patterns conﬁrm the presence of a BCC phase alone. An increase in peak broadening is attributed to the reduction of crystallite size and increase of lattice strain arising from deformation during ECAP. The grain reﬁnement takes place through simple shear deformation by elongation of grains, splitting of grains into bands, the subdivision of bands into subgrains by dynamic recovery, and conversion of subgrains into grains by progressive lattice rotation (PLR). Weakly textured rolled ferritic stainless steel is strongly textured at an h for bcc imposed equivalent strain of 0.6 with the development of ideal shear components of D2θ and E materials. On the second pass of ECAP texture is partially randomized and the intensity of components was decreased and new components of D1θ and Fθ are developed due to subdivision of grains into bands, bands into subgrains, and conversion of subgrains into grains of high angle of misorientation by PLR. The yield strength, tensile strength, and hardness are increased almost 1.5 times that of as-received coarse-grained material due to a high degree of grain reﬁnement and an increase in defect density or strain. The yield strength of 687 MPa of as-received material was enhanced to 1093 MPa of ECAPed ferritic stainless steel. However, the material has lost its ductility signiﬁcantly due to high defect density and a signiﬁcant amount of non-equilibrium nature of grain boundaries.

Keywords

EBSD, ECAP, ferritic stainless steel, mechanical properties, microstructure, microtexture

1. Introduction Development of bulk ultraﬁne-grained (UFG) metallic materials is the alluring ﬁeld of metallurgy/materials science because of their potential properties for structural applications (Ref 1-3). The mechanical properties of all polycrystalline materials are governed by several structural parameters; however, the grain size is the most important one and the dominant factor for strengthening (Ref 4). UFG materials are fabricated by assembling individual atoms or consolidating nano-particulate solids (Ref 5). However, these techniques are often limited to the production of a small quantity of samples. On the other hand, UFG structure can be produced by heavy straining or shock loading to reasonably large size components consisting of a coarse-grained phase (Ref 6). Here, a high density of dislocations is incorporated into the mate

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