Revisiting the softening and melting behavior of sinter under simulated blast furnace conditions: Part II – Characteristics of microstructure evolution and grain coarsening

Abstract

Background

To enhance the mechanistic understanding of softening and melting (S&M) behaviors and their role in determining blast furnace (BF) permeability performance, studying macro- and microstructural evolution under high-fidelity yet not oversimplified BF environments is indispensable.

Methods

Building on Part I, this study establishes experimental conditions that faithfully reproduce BF environments. Leveraging these high-fidelity conditions, we investigate the macro- and microstructural evolution and grain size distribution of metallic Fe and FeO at five temperatures: 1150 °C, 1250 °C, 1330 °C, 1430 °C, and 1550 °C.

Significant findings

Key conclusions link microstructural evolution to softening, melting, and dripping behaviors. From 1150 °C to 1550 °C, Fe and FeO grains undergo significant coarsening, with Fe increasing from 0.5–6.0 µm to 3.5–15.0 µm and FeO from 0.7–6.17 µm to 2.1–9.7 µm by 1430 °C. A critical dripping threshold for FeO droplets (>9.5 µm) in sinter ore shows grain coarsening significantly affects dripping timing and behavior. Additionally, the high melting points of slag phases in sinter ore compared to pellets and lump ores limit FeO droplet formation, resulting in less pronounced dripping behavior. These findings emphasize the need to investigate grain coarsening to understand dripping mechanisms across various burden materials and the potential impact of grain size variations on permeability in conventional versus hydrogen-rich blast furnaces.