Mechanism of thermal compressive strength evolution of carbon-bearing iron ore pellet without binders during reduction process

Against the background of “carbon peak and carbon neutrality,” it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry. Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property, and the thermal strength of pellet is a crucial metallurgical property that affects its wide application. The carbon-bearing iron ore pellet without binders (CIPWB) was prepared using iron concentrate and anthracite, and the effects of reducing agent addition amount, size of pellet, reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied. Simultaneously, the mechanism of the thermal strength evolution of CIPWB was revealed. The results showed that during the low-temperature reduction process (300–500 °C), the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet, while it gradually decreases with increasing the anthracite ratio. When the CIPWB with 8% anthracite is reduced at 300 °C for 60 min, the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm. Meanwhile, as the temperature is 500 °C, with increasing the anthracite ratio from 2% to 8%, the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N. Furthermore, in the high-temperature reduction process (600–1150 °C), the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature, while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio. With adding 18% anthracite, the thermal compressive strength of pellet reaches the maximum value at 800 °C, namely 35.00 N, and obtains the minimum value at 1050 °C, namely 8.60 N. The thermal compressive strength of CIPWB significantly depends on the temperature, reducing agent dosage, and pellet size.