Experimental study of the plastic deformation and densification behaviour of some sintered low alloy P/M steels

Elemental powders of atomized iron, graphite, molybdenum, copper and titanium were mixed in suitable proportions using a ball mill, then compacted and sintered in order to yield the alloy compositions such as Fe–0.5% C, Fe–0.5% C–2% Mo, Fe–0.5% C–2% Cu, Fe–0.5% C–2% Mo–2% Cu–2% Ti, Fe–0.5% C–2% Mo–2% Cu–4% Ti. The compacts were prepared in a 1000 kN hydraulic press using suitable cylindrical die-punch combination. Indigenously developed ceramic coated cylindrical preforms were sintered at 1000 ± 10 °C in a muffle furnace for a period of 120 min. In order to study the plastic deformation and densification characteristics of the low alloy powder metallurgy (P/M) preforms under various axial loads, the sintered cylindrical preforms were subjected to cold upsetting, hot upsetting and cold repressing. Further, microstructural analysis was carried out on the cold forged, hot forged and cold repressed alloy samples in order to correlate the plastic deformation and densification characteristics with the metallurgical structure of the sintered and forged alloys. Plain carbon steel preforms were observed to attain the highest levels of densification and axial deformation. Addition of Ti and Mo resulted in reduced levels of deformation as well as densification, irrespective of the mode of forming. The behaviour of the preforms containing Cu and Mo was intermediate between the plain carbon steel and the Ti-based steel. Microstructures of the Mo-containing alloy reveal the presence of fine particulates of Mo, TiC and pearlites, which account for the reduction in densification and deformation levels.