Influence of Carbon Addition Amount on the Strength and Reduction Performance of Pellet Ore Under Blast Furnace Lump Zone Reaction Conditions

Increasing the proportion of pellets in blast furnace (BF) burdens raises the raw material iron grade and reduces slag volume, thereby lowering fuel consumption. However, due to their dense microstructure, pellets typically exhibit low degrees of reduction. Controlled carbon additions may improve pellet porosity and subsequent reducibility. This study investigates the effects of varying carbon addition ratios on pellet pore structure, compressive strength, and metallurgical properties, including reducibility, reduction swelling, and reduction disintegration after the reduction program. The results show that increasing carbon additions increase porosity in both acidic and basic pellets but reduce compressive strength. For basic pellets, reducibility peaks at 1.5% carbon addition before declining, whereas acidic pellets show progressively lower reducibility with higher carbon ratios, suggesting that excessive carbon adversely impacts reduction kinetics. The reduction swelling index of basic pellets increases with carbon addition, reaching 21.7% at 2% carbon. Conversely, acidic pellets exhibit a maximum swelling index of 14.7% at 1.5% carbon, followed by a decline. These findings provide important theoretical and practical insights for optimizing carbon addition in pellet production.