Structure and properties of the eutectoid steel u8 after high-temperature deformation: I. Metallographic study and mechanical tests

The phase composition and mechanical properties of the carbon eutectoid steel U8 subjected to hot deformation by torsion in a temperature range of 650-900degreesC have been studied. In the samples deformed above the phase-transformation temperature (at 900-750degreesC), the formation of a mixed pearlitic-martensitic or fully pearlitic structure is shown to be determined by the time of postdeformation isothermal holding at 650degreesC. For the samples deformed in the intercritical temperature range (700-650degreesC), the formation of a mixed pearlitic-martensitic structure is determined by the total time of deformation and subsequent holding at 650degreesC. In two-phase samples, the volume fraction of the pearlitic component increases from the center to the periphery of a sample. It is discovered that, as the preliminary deformation E increases, the mode of fracture of the samples with a fully pearlitic structure changes from ductile at the center, where epsilon = 0, to brittle at the periphery, where epsilon = max.