Influence of Texture on Deformation Mechanism of Hot Extruded Oxide Dispersion Strengthened 18Cr Ferritic Steel
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JMEPEG https://doi.org/10.1007/s11665-020-05155-4
Influence of Texture on Deformation Mechanism of Hot Extruded Oxide Dispersion Strengthened 18Cr Ferritic Steel Manmath Kumar Dash, S. Saroja, R. Mythili, and Arup Dasgupta (Submitted May 30, 2019; in revised form July 27, 2020; Accepted: 14 September 2020) This paper focuses on studying the influence of texture on the deformation mechanism of oxide dispersion strengthened (ODS) 18Cr ferritic steel subjected to high-temperature tensile testing after consolidation by hot extrusion. The initial microstructure of the hot extruded steel showed preferential (1 1 0) planes alignment in perpendicular and parallel direction to extruded (ED) and transverse (TD), respectively. Two types of anisotropy have been highlighted: (1) A strong anisotropy of elongation properties with a transverse ductility is lower as compared to the axial ductility; (2) yield stress anisotropy (mechanical strength anisotropy) which is found to be temperature dependent. The material flow in Æ1 1 1æ direction is observed during the application of load along extruded direction during the tensile test; however, (1 1 0) slip plane normal is parallel to the direction of loading for transverse direction and brings the Schmid factor to a lower level which makes slip activation unlikely. Deformation band is found to be aligned with the loading direction in the ED specimen and covering across a number of neighboring ferrite grains could be noticed irrespective of material flow. However, the areas near the grain boundaries in the microstructure are found to be the strain gradient regions. Further, it shows a preferential accommodation of strain in proximity to the boundary network for TD specimen. High temperature (973 K) tensile test in ED is found to promote grain-subdivision of elongated bands by dynamic recrystallization, and inverse pole figure distribution reveals a preferential increase in the intensity of clustering toward (1 1 1) plane parallel to the loading direction. Keywords
EBSD, hot extrusion, oxide dispersion strengthen (ODS), steel, tensile test, texture
1. Introduction Oxide dispersion strengthened (ODS) alloys are relevant structural materials for both scientific as well as the industrial community owing to their potentially outstanding properties concerning high-temperature stability, strength and creep resistance (Ref 1, 2). In particular, ODS ferritic steels are viewed as candidate core structural materials for cladding application in next generation of sodium-cooled fast breeder reactors (Ref 3) due to their excellent void swelling resistance as compared to austenitic steels which is a crucial property for achieving high burn up in fast reactors (Ref 1, 4). Further, high Cr (> 12%) content in ODS ferritic steel is a prerequisite for enhanced corrosion/oxidation resistance and would be highly desirable from spent fuel reprocessing aspects (Ref 5-7). It is reported that unidirectional processing such as consolidation of these steels by extrusion resulted in a coarse elongated grain structure
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