Strain Hardening Behaviour in Forming of Sintered Iron-0.35% Carbon Powder Metallurgy Preform During Cold Upsetting

A complete experimental investigation on the instantaneous strain-hardening behaviour of powder metallurgy preforms of Fe-0.35%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0.4 and 0.6, respectively, under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (n(i)), strength coefficient (K-i), and the stress as a function of strain and densification were obtained and analyzed. Further, a relation is obtained from a semi-log plot of stress against relative density. This was analyzed to study the hardening behaviour due to the densification as applied stress is a function of induced strain as well as of densification in the powder metallurgy materials.