Sustainable recycling of ferrous metallic scrap using powder metallurgy process

Powder metallurgy (PM) process can be used for transforming the oxidized ferrous metallic scrap to usable products. The present study establishes an optimized PM-based recycling process to obtain considerably higher physical and mechanical properties of products (cylindrical samples in the present work). To this end, seven parameters including a source of metallic scrap, the quantity of carbothermic reducing agent, and PM process parameters were used to build a Taguchi L18 orthogonal array. In situ reduced and sintered samples made under these 18 conditions were characterized for physical, mechanical, and microstructural characteristics. The gray relational analysis (GRA) approach was used to arrive at the most optimal parametric setting. The grinding sludge as a source of scrap material led to the highest sintered density, hardness, and mechanical strength under these conditions: compaction pressure of 900 MPa, a sintering temperature of 1150 °C, stoichiometrically added graphite (for carbothermic reduction), 90 min of sintering time, and ratio of heating-to-cooling rate of 5/7. This analysis also corroborated with the earlier findings that simultaneous reduction of metal oxides and densification occur in the sintering operation. This newly established PM-based recycling process with GRA-optimized parametric settings improves the product characteristics of interest by approximately 14 % compared to those of the initial optimal setting obtained from L18 outcomes. This was confirmed by analytical prediction as well as confirmatory experiments.