1968 Volume 54 Issue 5 Pages 561-571
respectively. The results are summarized as follows.
1) The maximum extrusion punch pressure pmax changes discontinuously at the temperature of α-γ transformation, and above the temperature, it is related to the temperature T (°K) by the following equation,
pmax=A'In R (B/T)
Where the constant A' decreases with carbon content, while B increases. The estimated punch pressure at the melting temperature Tm, which expresses resistance of viscocity of extrusion at R=2·3, becomes 26kg/mm2, irrespective to the carbon content.
2) The constant B gives the value of the activation energy of deformation ΔH in the relationship B=ΔH/mk, where m is the parameter of stress dependence of the strain rate, and k the Boltzmann constant, respectively. The observed increases of B with the carbon content comes from the dependence of m on the carbon content. The value m changes from 10 to 5 due to the increase of the carbon content from 0.02 to 0.52%, which gives 32-37 kcal/mol as ΔH. This result shows that the activation energy of deformation in the impact extrusion is fairly small compared with the energy of self diffusion of γ-iron, and it is suggested that the deformation mechanism operative in the impact extrusion differs from that for the static deformation.
3) The following empirical relationship in M. K. S. unit for the maximum impact extrusion punch pressure pmax (kg/mm2) versus carbon content C% at different extrusion conditions are proposed, _??_
The second term in the right hand side of the equation represents the inertia resistance associated with the high rate extrusion, where g is the gravity constant and ρ the density of steel.