A Physical Constitutive Equation for Partial Remelting of AISI D2 Tool Steel in Consideration of Geometrical Morphology and Volume Fraction of Solid Particles in Semisolid Slurry

A rolled AISI D2 tool steel was selected as the starting material in this study. Reheating and rapid cooling experiments and microstructural observation of AISI D2 tool steel were conducted. On the basis of the results of microstructural observation and elemental analysis, the microstructural evolution behaviors of AISI D2 tool steel during partial remelting was investigated. The semisolid slurry with homogeneous spherical morphology was obtained when the reheating temperature and isothermal holding time were 1300 °C and 20 s, respectively. In consideration of geometrical morphology and volume fraction of solid particles in semisolid slurry, A physical constitutive equation describing remelting behavior of AISI D2 tool steel during partial remelting was established. In this physical constitutive equation, a truncated octahedron was used as the basic unit. The volume fractions of liquid phase in AISI D2 tool steel reheated to different target temperatures were calculated by used this established physical constitutive equation. The difference between results obtained from high temperature differential scanning calorimetry (HDSC) analysis and physical constitutive equation were caused by the dissolution of residual carbides and the transformation of liquid film to solid phase particles during rapid cooling of AISI D2 tool steel.