Addressing the threat of global climate change is an urgent priority for all industries. The Paris Agreement set the global long-term goal of carbon neutral by 2050 for all member countries. As the steel industry occupies approximately 7.2% of the total global greenhouse-gas emissions, innovative technologies that build upon or move beyond the past developments are desired to reach this long-term goal. Various zero carbon technologies have been proposed for the steel industry. This review focuses on the current state of the steel industry from the perspective of long-term targets and pathways for the future. The design of an optimal ironmaking process for low carbon and decarbonization is discussed from a technological perspective, considering comprehensive consistency with sustainability in the steel industry. In particular, perspectives on the hydrogen-based ironmaking process using renewable energy for carbon direct avoidance and smart carbon usage are described.

The preparation of glass microbeads by gas quenching of blast furnace slag is an effective way to achieve efficient recovery and resource utilization of the residual heat from blast furnace slag. However, due to the high viscosity and easy crystallization of blast furnace slag, there are problems such as low bead formation rate, opaque glass microbeads, and poor chemical stability. MnO tempering agent was developed, and the influence of MnO on the crystallization behavior and rheological properties of the tempered slag was analyzed. The evolution law of the crystallization phase of the tempered slag was clarified, and a viscosity-crystallization coupling control method conducive to the bead formation of blast furnace slag was proposed. The results show that during the isothermal process, when the MnO content in the tempered slag is in the range of 0.17–12.24%, with the increase of its content, the initial crystallization temperature and the amount of crystal precipitation gradually decrease, effectively inhibiting the precipitation of crystals. However, when the MnO content exceeds 12.24%, the excessive MnO increases the activity of the easily precipitated phase, and the initial crystallization temperature increases instead. Therefore, when the MnO content in the tempered slag is 12.24%, the crystallization ability is the weakest, and the glass phase content is the highest. In the continuous cooling process, when the MnO content in the tempered slag is 12.24% and the cooling rate exceeds 3°C/s, the tempered slag completely solidifies into a glassy state.

Depending on the operational conditions inside a direct reduction shaft furnace, e.g., ingoing gas temperature, feeding rate of material, and gas composition, the outgoing material will differ. This study investigates how the heating rate affects the reduction during pure hydrogen reduction of commercial iron ore pellets. As expected, the reduction rate increased with increasing heating rate. The heating rate also significantly affected the microstructure evolution inside the pellet. Inside the hydrogen direct reduced pellets, the iron had two appearances: (1) porous iron containing small and numerous intragranular pores, or (2) dense iron with larger but fewer intragranular pores. The pellet reduced with the slowest heating rate consisted of only porous iron, while the faster heating rates comprised porous and dense iron. The amount of dense iron gradually increased with increasing heating rate and was found to start forming at a temperature of around 668°C. The solid iron aggravated the mass transfer through the product layer and decreased the total reaction rate. This led to an expanded spread of the reaction zone as the heating rate increased. Through this work, it was also shown that insignificant reduction took place below a temperature of 450°C. Lastly, the microstructure that evolved during the non-isothermal reduction vastly differs from the microstructure formed during isothermal reduction. Consequently, an effective diffusivity and thermal conductivity that varies with time and temperature must be considered when optimizing the shaft furnace reactor.

The injection of pulverized coal into blast furnaces has alleviated the demand for metallurgical coke, and co-injection technology combining natural gas and pulverized coal with high oxygen enrichment has the potential to further reduce coke use and hence CO₂ emissions. This work presents a steady-state operational model for the co-injection of natural gas and pulverized coal into blast furnaces developed based on mass and energy balance. With the support of industrial data from the commercial blast furnace, the matching relationship between natural gas rate, pulverized coal injection rate, and oxygen enrichment is quantitatively examined under the constraints of raceway adiabatic flame temperature and top gas temperature. The effect of natural gas rate on coke rate and CO₂ emission reduction is investigated. The results show that increasing natural gas injection rate, lower pulverized coal rate and higher oxygen enrichment maintains a constant raceway adiabatic flame temperature and coke rate. Under the optimal operating conditions, the pulverized coal, coke rate, and CO₂ emissions are reduced by 30.2%, 7.3% and 6.2%, respectively. The model and its results are expected to be helpful for a better understanding co-injection of natural gas and pulverized coal into blast furnaces, as well as contribute to reducing coke rate, pulverized coal rate, and CO₂ emissions.

The high temperature oxidation behavior of the electroslag remelting (ESR) process of welded 30CiNiMo8 billets electrode is investigated. High-temperature oxidation experiments are conducted to clarify the scale formation kinetics for the model. The steel is heated at 700–1200°C under a 21% oxygen atmosphere. The oxidation kinetics of the steel follow a parabolic law, with the oxidation rate equilibrium constant lnK = −23.801×1/T+17.866 and apparent activation energy ΔE_a = 197.88 J/mol. The temperature distribution on the electrode surface is obtained by measurement and fitted vertically and horizontally. The temperature increases exponentially with the electrode height, and the temperatures on the surface cross-section are inconsistent. Finally, the oxidation weight gain model is established by applying the isothermal oxidation kinetics model, the Arrhenius equation, and the Simpson formula. The amount of FeO_x carried into the slag under the industry experiment is 58.68 mg/s with the content of FeO as 65 wt%, which is established by the EDS and EBSD of the scale, and 4.77 g of aluminum addition into the slag pool every 5 minutes is suggested to reduce the FeOx potential when using four 160×160 mm welded billets electrode with a descending speed as 1.19×10⁻⁴ m/s.