EBSD Study on Processing Domain Parameters of Oxide Dispersion Strengthened 18Cr Ferritic Steel

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 $\left(\xi \left(\acute{ϵ}\right)\right)>0$, 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.