Effect of Process Variables on the Dimensional Change of Atomised Ferrous Powder Sintered in Nitrogen Atmosphere

Abstract - Powder metallurgy is a net shape manufacturing approach, which is very attractive because of its ability to form powders directly into finished components. These components are formed in an economical manner having a considerable choice in material properties, mechanical, chemical and microstructure control. The chemical composition of powder blends and their consolidation are characterized producing a full fine pearlitic structure during the sintering process which is important to maintain tensile strength and size control. Changes in dimensions of metal powder compacts do occur during the production process. The ability to control the changes is an important part of the manufacturing process. The outstanding savings achieved through the production of near net shape is the driving force behind this manufacturing process. Size change of the material must be known and it is one of the most important functions when designing compaction dies for new components. In this paper, an overview of the effect of Dimensional change (Growth) during sintering when compared to the two atomized pre alloyed grades of ferrous powders was investigated. Density, spring back, dimensional change were determined in the green and sintered conditions. Densities in the range of 6.0 – 6.6 g/cm3 were achieved by withdrawal die motion and sintering temperature of 1100 °C, 1110 °C and at 1120 °C were utilized. Sintering temperature, green density and % of carbon content were found to be the most significant variable controlling dimensional change.