Process for fabricating steel from ferrous metal particles

Claim 1

A method for conditioning ferrous particles (a) providing as-water-atomized ferrous metal powder whose particles have a martensitic structure, a surface layer of mostly iron oxide thereon, a particle size distribution range which includes no more than traces of about 20 mesh, no more than about 16 weight percent smaller than 230 mesh and the balance between 20 and 230 mesh and a total oxygen content of up to about 1.5 weight percent; (b) placing said powder in a rotatable, substantially horizontally disposed kiln; (c) heating said particles at a temperature between about 900° and 1200° F. for a conditioning period of at least about 10 but no longer than about 30 minutes while simultaneously agitating said particles by rotating said kiln so that the particles are moved around the longitudinal axis of the kiln and continuously flooding them with a controlled reducing atmosphere in sufficient volume to maintain the reducing action throughout said conditioning period to dry the powder particles and to substantially reduce the oxygen content of reducible iron oxides in the surface layer and to reduce the total oxygen content of the powder particles to less than about 0.30 weight percent, thereby obtaining free-flowing, substantially non-agglomerated, un-annealed, conditioned, ferrous powder particles having a tempered martensitic structure and a porous, substantially pure ferrite layer thereon;

Claim 2

A method for conditioning ferrous particles (a) providing as-water-atomized ferrous metal powder whose particles have a martensitic structure, a surface layer of mostly iron oxide thereon, a particle size distribution range which includes no more than traces of about 20 mesh, no more than about 16 weight percent smaller than 230 mesh and the balance between 20 and 230 mesh and a total oxygen content of up to about 1.5 weight percent; (b) placing said powder in a rotatable, substantially horizontally disposed kiln; (c) heating said particles at a temperature between about 900° and 1200° F. for a conditioning period of at least about 10 but no longer than about 30 minutes while simultaneously agitating said particles by rotating said kiln so that the particles are moved around the longitudinal axis of the kiln and continuously flooding them with a controlled reducing atmosphere in sufficient volume to maintain the reducing action throughout said conditioning period to dry the powder particles and to substantially reduce the oxygen content of reducible iron oxides in the surface layer and to reduce the total oxygen content of the powder particles to less than about 0.30 weight percent, thereby obtaining free-flowing, substantially non-agglomerated, un-annealed, conditioned, ferrous powder particles having a tempered martensitic structure and a porous, substantially pure ferrite layer thereon;