Influence of material and process parameters on reduction-swelling characteristics of sintered iron pellets

This paper investigates the use of shop-floor ferrous scrap that contains iron ore as a raw material for the purpose of making steel products through an in situ carbothermic reduction. The technique of powder metallurgy (PM) was used for the purpose of studying reduction followed by densification during sintering. Two sources of iron oxide—ferrous grinding-sludge powder and iron ore—and three sources of the carbonaceous material—graphite, charcoal, and carbon black—were considered. The carbonaceous material was added to the iron oxide after calculating the stoichiometric carbon requirement for facilitating both direct reduction and direct–indirect reduction. This involves a simultaneous change in weight and volume. During sintering, an in situ reduction of the iron oxide takes place that often results in severe volumetric changes. The test results revealed the degree of reduction (DOR) and degree of densification (DOD) of the grinding sludge (GS) to be 15% and 45% higher, respectively, than that of iron ore (IO). This is essentially due to the presence of distinct iron-oxide phases coupled with a greater amenability to the occurrence of carbothermic reduction. Indirect reduction also took place and contributed to improving the degree of reduction (DOR) and degree of densification (DOD) of the final products. Overall, the shape stability of the sintered grinding-sludge (GS) powder was found to be optimized when parameter settings of graphite (from 25% in excess to 50% in excess) were added, a compaction pressure of 1050 MPa was applied, and a sintering temperature of 1200 °C was employed. Hence, ferrous scrap can be chosen as direct reduced iron for the manufacture of steel and can also be used for cost-efficient and eco-friendly structural components with a marginal compromise on both the purity and strength of the ferrous products