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

Abstract

Ferritic stainless steel (FSS 430) has been deformed by equal-channel angular pressing (ECAP) at room temperature at an equivalent strain (evm) 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 imposed equivalent strain of 0.6 with the development of ideal shear components of D2θ and $$\bar{E}_{\theta }$$ for bcc 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.