Two types of direct carbonization methods of BOF slag, and their influencing factors and kinetics mechanism were summarized. The possible rate-limiting step for hotstage carbonation treatment of slag is the diffusion of CO₂ through the product layer to the unreacted zone inside the particle. The increase of temperature can accelerate the diffusion rate of CO₂, and the decrease of particle size of slag can reduce the thickness of product layer that inhibits the diffusion, thus which can contribute to enhancement of CO₂ sequestration and improvement of conversion rate during hot-stage carbonation treatment of slag. The main controlling step for aqueous carbonation treatment is the diffusion of calcium from the inside to the surface of steel slag. Reducing the particle size of steel slag and destroying the product layer by ultrasonic vibration are the most effective ways to accelerate the diffusion leaching of calcium. Due to the high temperature of steel slag from the converter, and both carbonization methods have some limitations, it is considerable to combine the two ways. The slag with high temperature is carbonized by hot-stage carbonation treatment at elevated temperature during cooling. By reducing the particle size of steel slag and increasing the CO₂ pressure, the CO₂ sequestration and calcium conversion rate are improved. Fixing a part of calcium through hot-stage carbonation and then performing aqueous carbonation is beneficial for shortening the aqueous carbonation time. After the steel slag is cooled and continued to be milled, aqueous carbonation treatment is carried out. Combined with size optimization and ultrasonic utilization, the steel slag can be carbonized to the maximum extent, which is more promising for energy save and emission reduction.

The magnesium lance with an evaporation chamber is widely used in the pretreatment process of hot metal desulfurization and graphite spheroidization of cast iron, but the bubble generation mode during the blowing process and its effect on magnesium utilization remain unclear. In this paper, the blowing condition of a certain company was taken as the research condition, and the theoretical calculations showed that the time to reach pressure equilibrium between the inner and outer sides at the outlet of the evaporation chamber during the blowing process was very short (0.005 4 s), and it was considered that bubble generation started at the bottom exit inner diameter of the evaporation chamber. A two-stage bubble generation mode of expansiondetachment for the lance with an evaporation chamber was put forward, with the end of the detachment stage occurring in two scenarios due to instability of the bubble or obstruction on the outer side of the evaporation chamber outlet. On this basis, a mathematical model of bubble generation was established, the effect of bubble refinement on magnesium utilization enhancement was analyzed, and the optimization scheme of opening a curved slot along the bottom of the evaporation chamber was proposed. Field experiments showed that reducing the size of the gas outlet could increase the specific surface area of the bubbles in the melt pool, which effectively improved the utilization rate of magnesium and the life of the lance.

The influence of two slag systems on the type, size and morphology of inclusions in hot work die steel was studied in a 10 t protective atmosphere electroslag remelting furnace. The results show that the mass fraction of T.O in molten steel increases to 0.001 6% and the size of inclusions increases when S2 slag is used for electroslag remelting. The inclusions after S2 slag electroslag remelting are mainly Al₂O₃, while the inclusions after S1 slag are mainly MgO-Al₂O₃. The S1 slag has higher optical basicity and stronger desulfurization ability. The difference in the content of Al_s and Mg in steel is related to the basicity of the two slag. The calculation model of molten slag was established and the activity of Al₂O₃ in slag was calculated. According to the Al-O equilibrium relationship, the content of oxygen in molten steel can be controlled by reducing the activity of Al₂O₃ in slag and increasing the basicity of slag, so as to produce ingots with low oxygen content.

In order to realize the precise control of alloys in the steelmaking process, firstly, the physical and chemical properties of all alloys were analyzed, including the physical form, strength, wear resistance and composition of alloys, and an alloy database was established based on the analytical results to guide the addition of alloys. Secondly, the alloy yield of typical steel grades was analyzed, and a correlation analysis was carried out between the alloy yield and the process parameters using Pearson correlation coefficient, and  the following results was obtained. The Mn element yield increased with the reduction of oxygen content at the end of the converter and the increase of endpoint temperature. T-LSTM neural network and K-means clustering algorithm were used to predict the alloy yield of converter tapping, increasing the temperature of tapping, reducing the end of the oxygen content was conducive to improving the alloy yield. Finally, the intlinprog function based on matlab was used to solve the linear programming for the dosage scheme with the lowest cost, and the intelligent optimization control system of steelmaking alloy was developed to realize the lowest cost of alloy. The alloy intelligent optimization control system was applied in a  120 t converter at a steel mill, the model was operated online  for 8 months and  verified data  from 26 000 furnaces. The average alloy consumption of steel reduced by 0.46 kg/t, and the alloy cost of steel grades reducted by 1.21—6.58 yuan/t,  with an average reduction of  3.71 yuan/t.

In order to achieve precise control of oxygen content in LF refining process of 1215MS steel，thermodynamic calculations were carried out on the oxygen balance reaction between slag and steel．On the basis of combining production practice in a certain factory，the refining process control techniques such as weak deoxidation of molten steel，the refining slag composition，and modified inclusions in calcium treatment were analyzed and studied．Corresponding improvement measures have been proposed and good results have been achieved．The results showed that by retaining 0.050%-0.060% carbon mass fraction at the end of the converter process，step-by-step weak deoxidation was adopted during the tapping process，controlling the aluminum mass fraction in molten steel to be 0.002 5%-0.004 5%，and the oxygen mass fraction to be 0.003 0%-0.005 0%．LF refining process adjusted the composition of refining slag w(FeO+MnO) to be 5%-7%，w (Al₂O₃) to be 18%-20%，basicity to be 2.0-2.5，Mannesmann index to be 0.10-0.15，and calcium treatment controled the endpoint calcium mass fraction of molten steel to be 0.001 0%-0.002 0% at the end of refining．The mass fraction of dissolved oxygen at the refining endpoint could be precisely controlled to be 0.005 0%-0.006 0%，the total oxygen mass fraction of the casting billet could be controlled to be 0.012%-0.014%，the proportion of sulfide inclusions with a length to width ratio no more than 4  increased from 53.2% to 84.8%.

As a secondary refining apparatus, the ladle furnace(LF) plays a pivotal role in contemporary steelmaking processes. The performance of LF lining refractory materials  is crucial for controlling the composition of molten steel, enhancing production efficiency, and ensuring cost-effectiveness. Magnesia-carbon bricks are frequently utilized as lining materials for their superior high-temperature strength and excellent resistance to erosion. However, under the process model of adding scrap steel to molten steel in LF, the introduction of scrap leads to fluctuations in slag composition, which periodically reduces the slag basicity and consequently accelerates the erosion and degradation of magnesia-carbon bricks. This study focuses on the magnesiacarbon bricks used in the LF at  a steel plant, investigating the impact mechanism of changes in slag basicity on the erosion behavior of these bricks. Research findings indicate that at high basicity (R=4.88), erosion primarily manifests as infiltration; whereas at low basicity (R=1.57), dissolution becomes more prominent, with the rate of dissolution increasing and the thickness of the eroded layer growing as basicity decreases. Furthermore, the analysis of post-service magnesia-carbon bricks from the field corroborates the experimental outcomes, providing theoretical insights for extending the service life of magnesia-carbon bricks.

Based on the prototype, a 380 mm×280 mm bloom mold in a steel plant, the 1∶1 water model was established to study the flow field and phenomena in mold. According to the prediction results, the optimization parameters of casting speed were finally determined. The findings can be summarized as follows. In the mold, an asymmetric flow field was observed. Compared with increasing the casting speed, the increase of the impact depth of jet flow is greater with increasing the immersion depth of SEN. The level fluctuation in mold is larger near the narrow face, the corner and the SEN, while it is smaller near the wide face. With the increase of casting speed, the slag layer fluctuates more violently and the minimum thickness is reduced. With increasing the immersion depth of SEN, the fluctuation of slag layer is weakened and the minimum thickness increases. When the casting speed is set at 0.67 m/min, the recommended immersion depth of SEN is 135－150 mm.

Currently, steel plants mainly use copper-coated steel wire to measure the thickness of the liquid slag layer in the mold, but this method lacks standardized judgment criteria and accurate evaluation. In this study, a high-frequency induction furnace was used to simulate the mold's thermal environment, and copper-coated steel wire was employed to measure slag layer thickness. The post-measurement characteristics of the copper-coated steel wire were analyzed by SEM-EDS. Then, its formation mechanism was analyzed, and the judgment method was optimized. The results show that the powder layer and the upper part of the sintering layer do not reach the copper melting point (1 083 ℃) with no obvious change on the surface of the copper-coated steel wire. The temperature of the lower part of the sintering layer is over 1 083 ℃, after the copper melts, the exposed steel wire oxidizes to black. As the liquid slag layer heats up, the wire gets immersed and turns bright white. This parts not fully covered oxidize slightly, appearing grey. The length of the grey and white sections indicates the slag layer's thickness. This judgment method has been verified in the continuous casting site, but its accuracy is not as good as double-wire wetting method. 

Hot loading and hot delivery of con-casting billets can significantly reduce rolling costs, save energy, reduce carbon emissions, and improve the economic benefits of enterprises. Good billet quality is the foundation of hot loading and hot delivery, and dent defects in billet are one of the important factors affecting the surface quality of the billet. The influence of mold parameters on billet dents was discussed in the paper. According to the numerical simulation and the shrinkage characteristics of the billet, the mold taper was reasonably designed from the original single-taper to the three-taper, so that the mold taper coincides with the cooling and shrinkage of the liquid steel in the mold, the cooling of the corners and central parts were more uniform, and the defects of dent reduced significantly in billets. The coating and slow cooling strip were added to the mold, weakening the corner cooling, making the cooling of the billet uniform, reducing the occurrence of dents, and improving the hot delivery rate and yield of the billet. After mold parameters optimization, the pass rate for dent in CrMo steel billet increased from 73.73% to 94.80%, the average width of the dent reduced from 45 mm to 15 mm, and the depth reduced from 5 mm to 2 mm.

Aiming at the problem of submerged entry nozzle (SEN) clogging caused by poor fluidity of molten steel during the production of GCr15 bearing steel, an anti-flocculation flow SEN was introduced. The anti-flocculation flow SEN adopts carbon free anti-clogging technology in the inner cavity, which can inhibit the adhesion of inclusions, keep the steel flow channel clean during the casting process, and reduce the mold level fluctuation and flow field structure damage caused by the clogging of the casting channel. Carbon free liner material can also improve the thermal shock resistance of the nozzle and avoid the abnormal phenomenon caused by thermal shock in the nozzle slag line during the casting start. In order to further improve the cleanliness of molten steel and reduce the MgO·Al₂O₃·CaS inclusions in bearing steel, the casting test of calcium-free treatment molten steel was carried out by using the anti-flocculation flow nozzle. The test results showed that there were no significant fluctuations in the mold liquid level during whole casting 8 flows, and the anti-flocculation flow effect of the inner layer material at the nozzle was stable. The nozzle diameter had almost no shrinkage (shrinkage of 0.4-2.0 mm), and the cleanliness of the molten steel was improved while maintaining stable production.

The differentiated effect of adding rare earth CeO₂ and La₂O₃ on the strength and anti-slag erosion capacity was studied. After the addition of rare earth CeO₂, the porosity rate of low carbon magnesia carbon brick was decreased, the volume density and normal temperature compressive strength were increased, and the slag erosion resistance was improved. After the addition of CeO₂, low carbon magnesia carbon bricks were more dense, the volume density increased from 3.00 g/cm³ to 3.04 g/cm³, and the porosity rate decreased from 3.57% to 3.16%. With the addition of rare earth CeO₂, the strength of low carbon magnesia carbon brick also increased, and the compressive strength increased from 34.7 MPa to 41.3 MPa. However, after the addition of La₂O₃, low carbon magnesiacarbon brick self-powdered, the volume density decreased from 3.00 g/cm³ to 2.62 g/cm³, and the porosity rate increased from 3.57% to 8.2%. With the addition of rare earth La₂O₃, the strength of low carbon magnesia carbon brick also decreased, and the compressive strength decreased from 34.7 MPa to 9.6 MPa. The slag erosion resistance of low carbon magnesia carbon bricks was enhanced after adding rare earth CeO₂ and La₂O₃. After 1 600 ℃ for 3 h, the melting loss thickness of low carbon magnesia carbon bricks without the rare earth mixture was 0.83 mm, the  melting loss thickness after adding CeO₂ was 0.40 mm, and the  melting loss thickness after adding La₂O₃ was 0.18 mm.

In order to make the converter vaporizing flue blowing pulverized coal process applied to iron and steel production with low cost and high applicability, and to achieve the purpose of carbon reduction, it is necessary to study the reaction characteristics of pulverized coal gasification-conversion reaction with CO₂ in high temperature flue gas of converter as well as to conduct the exergy. The reaction characteristics of pulverized C-CO₂ under different atmospheric and temperature conditions were investigated by settling furnace experiments, and industrial tests were carried out in a 120 t converter wet flue gas system, the change in exergy loss and exergy efficiency was calculated during the test.The results of the settling furnace experiments showed that the higher the reaction temperature was, the more favorable the reaction of pulverized C-CO₂ was, and it reached the maximum at 1 350 ℃; with the increase of CO₂∶CO ratio in the atmosphere, the conversion of CO₂ in the flue gas showed an increasing trend.The results of the industrial experiments showed that, in the case of pulverized coal blowing amount of 3.76 kg/t, the average volume fraction of CO in the converter gas increased by 5.53 percentage points, the average volume fraction of CO₂ decreased by 3.83 percentage points, and the value of the recovered gas increased by 2 690.95 kJ/m³.And with the increase of coal injection, the exergy efficiency increased by 89.06% which showed that it was feasible to convert CO₂ into CO by blowing pulverized coal in the converter vaporizing flue, and the pulverized coal-CO₂ gasification reaction was well.