The fracture characteristics and enhancement mechanism of crushing strength for the coke with hot pressing

High-strength coke is essential to the ironmaking and steelmaking industries. The crushing strength of coke could be improved effectively when the hot pressing technique is carried out with proper parameters. The fracture characteristics and enhancement mechanism of crushing strength for the coke with hot pressing were investigated by experiment and finite element method with the brittle cracking model. Results show that the crushing strength of coke is improved greatly when the hot pressing is conducted at 420 ℃∼440 ℃ for the 1/3 coking coal. Coke's crushing strength is mainly affected by porosity and pores' spatial distribution. For the high porosity, the coke has thin pore walls and the cracks could easily penetrate the entire coke. Therefore, the high porosity contributes to the decrease of crushing strength. If the pore distribution is uneven, the cracks expand rapidly in the pores aggregation region and the coke has lower crushing strength. In the initial and middle thermoplastic stages, conducting the hot pressing technique with low stress could enhance the crushing strength of coke. The coke porosity is high when the coal is pressed with high stress at the early thermoplastic stage. The high pressing stress may result in uneven pores distribution if the hot pressing technique is conducted at the middle thermoplastic stage. Therefore, the high pressing stress would impede the enhancement of crushing strength when the coal is pressed at the early and middle thermoplastic stages. When the hot pressing technique is conducted with high stress at the later thermoplastic stage, the coke would have low porosity, even pore distribution, low reactivity and high crushing strength. •Finite element method was used to study the fracture and crushing strength of coke.•Hot pressing operation could effectively enhance coke's crushing strength.•Porosity and pore distribution significantly affect the crushing strength of coke.•The mechanism of enhancing coke's crushing strength by hot pressing was explored.