Hot working of powders : procedure and products

Sammanfattning: This dissertation can be divided into two main parts. The first deals with the hot working conditions of mild steels in powder forging, the second with the deformation behaviour of powder forged products; both monolithic and compound parts are studied. Hot forging of low alloy steel powders makes it possible to produce complicated parts with properties comparable with homogeneous forged parts, whilst reducing the machining operations necessary to a minimum. This powder forging technique is a high production rate method, and can only be applied to mass produced components. It also gives the possibility of complete reconstruction of the shape of the part. Forging of porous preforms however require certain precautions to be made to prevent working faults and to optimize the densification process. These things are therefore studied with some interest. In order to compete with other high production rate methods such as hot forging, the powder forged parts must be economically advantageous. Therefore the most attractive parts to be produced are those in which substantial material is saved, where most machining operations can be excluded and in which material of substantial structure is required. A method to produce compound structural parts of high strength hardened steel and ductile mild steel from alloyed powders is presented. It involves the manufacture of compound preforms by forging and their heat treatment to produce an optimal structure. On examining the deformation behaviour of compound parts produced, a substantial rise in the fracture toughness is seen, which is associated with the interface between hard and ductile material zones.