The Direct Hot Extrusion of Tubes and Bars from Sponge Iron Powder Billets

Abstract

The hot extrusion of bars and tubes from cold iso-statically pressed billets of NC 100.24 sponge iron powder is described. Extrusion at reduction ratios between 5:1 and 81:1 was performed at two different billet temperatures (1000 and 1150°C) using nominal press speeds from 10 to 250 mm/s. An increase in reduction ratio gave a proportional increase in the extrusion pressures required for similar conditions. Generally, higher extrusion pressures were recorded for the lower billet temperature. Higher peak pressures also resulted from an increase in press speed, although the mean steady-state pressures were not markedly influenced. Product densities for material extruded at 1150°C were >99·5% of a calculated theoretical maximum of 7750 kg/m³. Except for some relatively minor differences in grain size, the general metallurgical condition of the products was not influenced by the various extrusion conditions applied. Tensile tests performed on extruded bar showed that yield strength increased with increase in reduction ratio up to a maximum value. For higher reductions, no further increase in yield strength was apparent, although the ductility was somewhat reduced. Examination of the tensile fracture surfaces revealed the importance of oxide-type inclusions in determining the material properties. Analysis of these oxides gave some indication as to the type of inclusions which have an undesirable influence on the properties of fully dense material manufactured from metal powder by this method.