Deformation and Densification of Porous Preforms in Sinterforging. (Part II)

Abstract

Deformation and densification behavior of porous preforms in hot trapped die upsetting and closed die forging (double-cup and doulle-boss) was investigated with Fe-0.5C powder preforms.
For forging processes so far studied including those described in the previous report, no marked difference in deformation behavior was observed between powder preforms and bar stock materials, except cracking tendency of the former. Below 8t/cm² of forging pressure, the mean density of sinterforged specimens increased with increasing material flow during deformation, depending upon the deformation type, but above 8t/cm² the density more than 99.5% of the theoretical value was obtained for any type of forging processes except upsetting. In closed die forging, densification in the specimens proceeded from the zone in initial contact with the punch, through high shear stress zone and then to the free surfaces with some delay.
Residual pore defects were obtained on cracked surfaces, die chilled areas and insufficiently deformed surface layers. Re-sealing of in-process cracks was suggested to occur under suitable forging conditions.