The Use of Byproduct Steel Powder from Ball-Bearing Production in Powder Metallurgy

Abstract

Thousands of tons of valuable steel are obtained at ball-bearing plants in the form of wastes and are not used, although they could be a valuable powder metallurgy raw material. Other authors have demonstrated the possibility of reduction of byproduct steel powder from ball-bearing production; however, the technological process was not investigated sufficiently. The mixture of chips and coolant is dried and then baked in a protective atmosphere. The as-received powder with about 1 % carbon and 5.5–6.5 % oxygen is reduced in hydrogen, dissociated ammonia, or an endothermic atmosphere. It is mixed with carbon and coarse powder. The influence of temperature at recrystallization during reduction, the change of surface area of the powders, and the electrical conductivity were investigated. Compressibility was tested by pressing up to 12 tons/cm², and mechanical strength of the sintered compacts was also tested. The use of this type of steel powder is shown to be advantageous for high-density compacts. The influence of the pressure on the density at first pressing and repressing was investigated. A final density of more than 90% was achieved in different ways. The sintering and resintering temperatures exert a great influence. Heat treatment (after carburizing) of repressed and resintered compacts showed Rockwell hardness of 55–60. The byproduct steel powder from ball-bearing production can be used for structural parts and for other high-density compacts, as well as for other powder metallurgy purposes.