Recrystallization, precipitation and flow behavior of D3 tool steel under hot working condition

Abstract

Hot compression tests were performed on D3 cold-work tool steel at various temperatures of 800–1200°C and strain rates of 0.001–1s−1.The peak stress and strain of flow curves showed uncommon increase within the temperature range of 800–1000°C and strain rates of 0.001–0.1s−1. The dynamic precipitation of fine carbides was found responsible for the observed irregularities. Optical microscopy observations showed the highest rate of precipitation at about 1000°C. At high strain rates (0.1 or 1s−1), the precipitation temperature shifted to around 1100°C. Observations by optical and FESEM microscopes and EBSD measurements implied that dynamic precipitation could retard dynamic recrystallization at low temperatures and strain rates. Partial dynamic recrystallization mainly occurs by “continuous dynamic recrystallization” and partly by “discontinuous dynamic recrystallization” and “particle stimulated nucleation” mechanisms. More dissolution of carbides, less dynamic precipitation and considerable continuous dynamic recrystallization were the major microstructural phenomena at high temperatures (1100°C and 1200°C). The material constants in the hyperbolic sine constitutive equation were determined for low and high temperature regimes. The apparent activation energy for low and high temperature regimes was determined as 566kJ/moland 564kJ/mol, respectively.