Effect of high temperature on macroscopic properties and microstructure of metallurgical coke

Coke produces powder in high-temperature environments, which leads to a decrease in coke strength and affects the smooth operation of blast furnace. To study the effect of high temperature on the macroscopic properties and microstructure, two types of coke were heated to 1100–1400 °C in conditions that simulated a blast-furnace heating regime. The results showed that the weight of the tamping coke (T-coke) and top-charging coke (TC-coke) was reduced by 9.04 g and 8.7 g, respectively, and the coke strength after reaction was reduced by 4.23% and 3.86% with an increase in temperature from 1100 °C to 1400 °C. In addition, the electrical resistance of T-coke and TC-coke decreased from ambient temperature to 1400 °C. The rate of change in electrical resistance had a negative correlation with the coke strength after reaction, which decreased as the change in electrical resistance increased. Comparing the optical texture index, carbon layer spacing, carbon structure parameters, and percentage of large pores in the coke with the heating temperature, it was found that high temperatures led to a decrease in the anisotropic texture of the coke, an increase in the degree of graphitization, partial conversion of amorphous carbon to graphitic carbon, and an increase in the percentage of large pores. Furthermore, the larger the pore area of the coke, the smaller were its pore wall hardness and elastic modulus. These results suggest that a decrease in anisotropic texture and an increase in large pores and the degree of graphitization decrease resistance to temperature, leading to lower strength after reaction.