To introduce alloying element additions in a homogeneous form

Die pressing feedstocks generally consist of elemental mixes in order to maintain as high  level of compressibility as possible. Using this approach means that the compressibility is controlled by that of the soft, annealed base iron powder (most commonly iron). Use of a fully pre-alloyed powder would mean that the initial particle hardness and work hardening rate would both be increased by the alloying additions and compressibility therefore reduced.

To incorporate a pressing lubricant

Popular lubricants are stearic acid, stearin, metallic stearates or other organic compound of a waxy nature. The purposes of adding the lubricant are to reduce friction (and therefore even out density variations) during compaction, to reduce ejection forces and to minimise the tendency for ejection cracking in the compact.