Deformation and temperature aided sintering during hooker extrusion of sintered PM preforms of steel

Abstract

Warm hooker extrusions of sintered powder metallurgical preforms of steel were investigated at different temperatures ranging from room temperature to 773 K in steps of 100 K for strains of 0·87, 1·0, 1·14 and 1·3. The resident densities for extrusion were chosen from the formability limit diagrams generated at different temperatures, which demarcates the safe zone from fail zone. Microstructure characterisations vide pore closure revealed the possibility of deformation and warm working assisted sintering of preforms extruded at warm working temperatures. The rate of force/stroke (dF/dS) and ratio of actual force to theoretical force called correction factor φ for different temperatures were evaluated to substantiate the deformation and warm working assisted sintering. Hardness data of the extruded samples were measured to determine the densification. The extruded samples were analysed for the surface roughness along their length and the optimum temperature for extruding steel preforms for better properties were identified.