Abstract
The behaviors of impact extrusion of 13Cr and 18-8 stainless steels were investigated using a high energy forming machine Dynapak. The extrusion punch pressure varied with temperature in a similar manner to the flow stress in usual uniaxial deformation. When the extrusion ratio R is smaller than 10, the extrusion punch pressure changes linearly with lnR. However, with R larger than 10, the effect of inertia force becomes an important factor. The initial punch pressure was increased by ρ(Rv)2⁄2g, while the final punch pressure was decreased by ρR2ax⁄g, with R>10, where ρ is the density of material, x is the punch stroke, a is the acceleration of punch, v is the punch velocity, and g is a gravity constant. The punch pressure decreased with extrusion stroke, due to the decrease in punch velocity. The apparent strain rate exponent determined from the dependence of punch pressure on the extrusion velocity was smaller than the values, measured by usual methods, of tension, torsion and compression which was interpreted to be due to the effect of frictional force between a billet and the container.
