Grain boundary characterization and grain size measurement in an ultrafine-grained steel

Abstract

Abstract Ultrafine ferrite grains in a plain C–Mn steel (0.3 mass% C) were produced by large-strain warm compression and subsequent annealing treatment in a temperature range between 773 K and 1003 K. The samples were investigated by means of high-resolution electron back-scatter diffraction. The resulting microstructures showed very fine ferrite grains and homogeneously distributed cementite particles. The majority of the grain boundaries (55–70 %) were classified as high-angle ones (≥ 15° misorientation). When considering only these high-angle grain boundaries, the average grain size changed from 0.9 mm at a deformation temperature of 773 K to 2.2 mm at a deformation temperature of 1003 K. For the same range the average subgrain sizes increased from 0.6 mm to 1.5 mm. The basic result of this study is that the grain size characterization of polycrystalline microstructures with ultrafine grains requires the use of the high-resolution electron back-scatter diffraction method in conjunction with a careful a...