Influence Mechanism Of Basicity On Consolidation Behavior And Reduction Swelling Mechanism Of Pellets

The blast-furnace burden of iron and steel enterprises in China is mainly sinter.The environmental protection control of sinter production process is much more difficult than that of pellet.Production of high basicity iron ore pellet instead of high basicity sinter,improving the iron grade of blast furnace burden and strengthening blast furnace smelting can effectively reduce the environmental load.At present,there are some problems in the production of basicity pellets,such as low pellet strength and high reduction swelling index rate,which is difficult to meet the requirements of large proportion of pellets in blast furnace.In this paper,the influence mechanism of basicity on pellet consolidation behavior and reduction swelling mechanism was systematically studied with iron powder produced by TISCO as raw material and limestone as flux.By studying the effect of basicity on the strength change,phase transformation and microstructure evolution in the process of preheating,roasting and reduction of basicity pellets,the action mechanism of flux in the process of preheating and roasting of basicity pellets and its effect on the reduction swelling of basicity pellets were revealed.On this basis,the expansion verification test of basicity pellet by grate rotary kiln method was carried out.The main conclusions obtained include:(1)The study on the influence of basicity on the roasting consolidation behavior of pellets shows that when the basicity is lower than0.8,the calcium iron silicate bonding phase increases with the increase of basicity;When the basicity is higher than 1.0,calcium ferrite begins to increase during pellet consolidation,and the compressive strength of pellets is significantly higher than that of lower basicity pellets.When the basicity is 1.0,preheating at 1140 ℃ for 6min and roasting at 1230 ℃ for10 min,the strength of basicity pellets is 3264N/ P.(2)The effect of basicity on t the reduction swelling index rate of pellets showed that with the increase of basicity,the reduction swelling index rate of pellets increased first and then decreased.When the basicity is 0.6-0.8,the reduction swelling index rate is relatively the highest,more than 18%.The formation of calcium iron silicate during pellet consolidation is the main reason for the increase of the reduction swelling.The crystal transformation of calcium iron silicate and hematite is inconsistent in the reduction process,resulting in uneven stress and high the reduction swelling index rate in the reduction process.When the basicity reaches 1.0,the binder phase in the pellet is mainly calcium ferrite.The crystal transformation of calcium ferrite and hematite is the same in the reduction process,the stress is uniform,and the surface cracks of the sphere are significantly reduced.(3)When the basicity is higher than 1.0,it can play its role in reducing the reduction swelling of pellets only under the condition of full consolidation.The expanded verification test of grate rotary kiln was carried out on the pellets with basicity of 1.0.Under the appropriate thermal system,the compressive strength of preheated pellets was greater than 1000 N / P and the AC drum index(-5mm)was less than 5%;The compressive strength of roasted pellets is greater than 3000N/P,and the ISO drum index(+ 6.3mm)is 97.25%,and the reduction swelling index rate is 11.53%.、62 figures,36 tables and 62 references.