Reducing process of sinter in COREX shaft furnace and influence of sinter proportion on reduction properties of composite burden

In order to reduce the materials cost of COREX ironmaking process, sinter has been introduced into the composite burden in China. This work explored the reducing process of sinter in COREX shaft furnace to clarify its reduction properties change and then the effect of sinter proportion on metallurgical performance of composite burden was investigated. The results show that the reducing process of sinter in COREX shaft furnace was basically same with that in blast furnace but sinter seems like breaking faster. Under reducing condition simulated COREX shaft furnace, sinter possessed the worst reduction degradation index (RDI) and undifferentiated reduction index (RI) compared with pellet and iron ore lumps. Macroscopic and microscopic mineralogy changes indicated that sinter presents integral cracking while pellet and lump ore present surface cracking, and no simple congruent relationship exists between cracks of the burden and its ultimate reduction degradation performance. The existence of partial metallurgical performance superposition between composite and single ferrous burden was confirmed. RDI+6.3≥70% and RDI+3.15≥80% were speculated as essential requirements for the composite burden containing sinter in COREX shaft furnace.