Measurement of Grain Shape Uniformity

Abstract Cold working is well known to change the properties of metals and alloys. Deformation increases the strength of metals but usually reduces its toughness and leads to anisotropy of properties, that is, directionality. Hot working also produces similar affects; the microstructural results after hot work with low finishing temperatures may appear to be the same as from cold working. Hot rolling of shapes, sheet, plate or bar, for example, elongates the nonmetallic inclusions in the deformation direction, which will reduce the isotropy of mechanical properties. Hot working can also lead to segregation being elongated parallel to the deformation direction, which also reduces isotropy. Reducing the finishing temperature, i. e., the temperature of the steel at the final deformation pass, will promote “banding” – parallel alignment of the constituents into layers, such as alternate bands of ferrite and pearlite. This also promotes anisotropy of mechanical properties, chiefly toughness and ductility. Strength is not usually affected to a significant degree by banding, compared to toughness and ductility. In single phase metals and alloys, the grains will become elongated due to cold working. In hot working, the grain shape may not be equiaxed upon cooling if the finishing temperature is not high enough to promote complete recrystallization upon cooling to ambient temperature.