Evaluation of deformation and recrystallization behavior in oxide dispersion strengthened 18Cr ferritic steel. (August 2020)

• Record Type: Journal Article
• Authors: Dash, Manmath Kumar; Tripathy, Haraprasanna; Saroja, S.; Mythili, R.
• Is Part Of: International journal of pressure vessels and piping. Volume 185(2020)
• Publication Date: 2020-08
• Subjects: Ferritic steel -- EBSD -- Texture -- DSC -- Recrystallization; Pressure vessels -- Periodicals; Pipe -- Periodicals; Récipients sous pression -- Périodiques; Tuyaux -- Périodiques; Pipe; Pressure vessels; Periodicals; 681.76041
• DOI: 10.1016/j.ijpvp.2020.104130
• Languages: English
• ISSNs: 0308-0161

Abstract

Abstract: This paper presents the results of an experimental study aimed to obtain an ultrafine equiaxed grain distribution in 18Cr oxide dispersion strengthened (ODS) ferritic steel through cold working and annealing starting with an initial columnar grain structure with a predominant α-fibre texture in a product consolidated from the alloy powders during extrusion at high temperatures. Deformation along the extruded direction (ED) resulted in the retention of α-fibre texture, while deformation in the transverse direction (TD) showed a shear banded structure with a reduced percentage of α-fibre texture. Differential Scanning Calorimetry (DSC) analysis of the deformed steel established the occurrence of two significant events during heating namely recovery and recrystallization, whose temperatures were influenced by the heating rate. The recovery and recrystallization domains have been distinctly observed at 1350 K and 1420 K respectively at a low heating rate of 7 K min −1 . The resultant microstructure showed very coarse elongated grains interspersed with regions of ultrafine (<1 μm) equiaxed grains, due to the incomplete recovery. The deformed steel was subjected to a two step heat treatment designed based on the above inputs with an aim to reduce the microstructural anisotropy in longitudinal direction. The microstructure of the heat treated steel showed randomization of the initial <1 1 0>//ED α-fibre texture, which improved further with repeated deformation and two step heat treatment cycles. A gradual increase in hardness during the above cycles was observed reflecting the increase in dislocation density which offers the propensity to achieve an ultrafine grained microstructure. Graphical abstract: Image 1 Highlights: This study presents the results of an experimental study aimed to obtain an ultrafine equiaxed grain size distribution in 18Cr ODS steel through series of cold working and annealing steps starting with an initial columnar grain structure and a predominant α-fibre texture in a hot extruded product. The salient features of the study are as follows: Deformation along the extrusion direction (ED) showed retention of α-fibre texture, while deformation in the transverse direction (TD) showed a shear banded structure with a reduced percentage of α-fibre texture. The deformed steel was subjected to a two step heat treatment designed based on the recovery and recrystallization domains identified from DSC analysis to reduce the morphological anisotropy in longitudinal direction, which resulted in the randomization of the initial <1 1 0>//ED α-fibre texture, which improved further with repeated deformation and two step heat treatment cycles. A gradual increase in hardness during the above cycles was observed reflecting the increase in dislocation density which offered the propensity to achieve an ultrafine grained microstructure.