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This paper presents the results of an experimental study aimed to identify hot working domains in oxide dispersion strengthened (ODS) 18Cr ferritic steel over a wide range of temperatures (1323-1473 K) and strain rates (0.01-10 s−1). The experimental data were obtained by uniaxial compression test using the Gleeble-1500D simulator in this range of temperature and strain rate. An inverse relationship with temperature and positive strain rate sensitivity associated with dynamic recovery and recrystallization, which is influenced by temperature and strain rate, was derived from the flow stress. Based on the processing map generated at 0.5 true strain, using rate dynamic material model (DMM) approach and the calculated instability parameter ξϵ´>0, the optimum processing domain has been determined for this steel. The most favorable processing parameters are found in the temperature ranges of 1350-1450 K with a strain rate of 0.01 s−1 and 1473 K with a strain rate 0.1 s−1 with peak efficiency of 30 and 35%, respectively. The material flow behavior was studied using scanning electron microscopy (SEM)-based EBSD microstructural characterization. The steel subjected to 1323 K at high strain rate 10 s−1 in the low-efficiency workability region showed low aspect ratio as compared to the elongated bamboo-like initial microstructure; however, minimum strain rate (0.01 s−1) showing that localized slip/shearing is the key mechanism and fiber texture studied from the intensity distribution of inverse pole figure showed the presence of significant amount of θ-fibers. In contrast, dynamic recrystallization dominated at higher efficiency region in the safe domain of processing map and γ-fiber texture was evident in the specimen deformed at 1373 and 1473 K with strain rate of 0.01 and 0.1 s−1, respectively, which is responsible for the change in the initial 〈1 1 0〉//ED α-fiber texture. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of an experimental study on evolution of the nanocrystalline microstructure in a mechanically alloyed Oxide dispersion strengthened (ODS) 18Cr ferritic steel powder during densification by spark plasma sintering (SPS) in the temperature range of 1273 K (1000 °C) to 1423 K (1150 °C). Systematic Electron Back-Scatter Diffraction analysis has been carried out to study the grain size distribution and texture as a function of consolidation temperatures. Based on the kinetics of the densification process and resultant microstructure/microtexture, a sintering temperature slightly above 1323 K (1050 °C) within a range of 50 K was found to be optimum. The 18Cr-ferritic steel powder consolidated at 1323 K (1050 °C) was also studied to understand the role of dispersoids on microstructure. The dispersoids exerted a profound influence on the strength as well as toughness of the steel by restricting the grain growth at high temperatures. Further, a signature of (1 1 0) grain cluster is observed during consolidation and its preferential growth with increase in sintering temperature is noticed which lead to the alignment of the (1 1 0) plane in the direction of applied pressure. The minimum creep rate of the consolidated steel under a load of 300 MPa was found to be 5E-7 h−1 and 1E-4 h−1 at 873 and 973 K (600 and 700 °C) respectively. The apparent activation energy for creep deformation was estimated as ~ 402 kJ/mol, which is typical of lattice diffusion assisted general climb mechanism of dislocations over the barriers such as present dispersoids. [ABSTRACT FROM AUTHOR]