In order to better understand and develop the technology of integrating dephosphorization and decarburization in a single converter (abbreviated as IDDSC), the relevant thermodynamic issues were discussed by calculation. Based on the thermodynamic calculation, the bridges between the phosphorus distribution ratio, temperature, and slag composition were constructed. Besides, the connections between the dephosphorization behavior and the microstructure of slag were also established by investigating four heats of hot metal smelt using IDDSC technology. As a result, the mechanism of phosphorus enrichment in the dephosphorization slag was revealed. Also, the results show that the dephosphorization efficiency increases gradually with increasing slag basicity. While the dephosphorization efficiency increases first and then decreases with the increase of FeO content in slag. There is a competition relationship between P₂O₅ and FeO in reacting with CaO and SiO₂. When CaO/FeO is relatively high, not enough FeO is provided. Thus P₂O₅ is in priority to react with CaO and SiO₂ through [3n + 2](CaO) + 2SiO₂ + n(P₂O₅) = n(3CaO·P₂O₅)-2CaO·SiO₂(s), generating P₂O₅-rich nC₂S-C₃P solid solution which promotes the removal of [P] from the hot metal. When CaO/FeO is relatively low, FeO competes over P₂O₅ in reacting with CaO and SiO₂ through a(CaO) + b(SiO₂) + c(FeO) = aCaO·bSiO₂·cFeO(s), generating CaFeSiO₄ instead of P₂O₅-rich solid solution. As a consequence, the slag with low CaO/FeO shows a poor dephosphorization ability.

The effect of final electromagnetic stirring parameters, with current intensity increasing from 300 A to 400 A and frequency increasing from 4 Hz to 12 Hz, on the electromagnetic forces and carbon concentration distribution of the central cross section of a 70 steel square billet have been studied. Along the center line of the liquid core zone, current intensity of 400 A and frequency of 8 Hz achieve the maximum electromagnetic force at the position 48 mm away from the billet edge among the 10 groups of stirring parameters. Nevertheless, along diagonal of the liquid core zone, the electromagnetic force near the diagonal center is the greatest and the current intensity of 280 A and frequency of 12 Hz obtain the maximum electromagnetic force. The optimal final electromagnetic stirring (F-EMS) parameter to uniform the central cross-sectional carbon concentration and minimize the center carbon segregation of 70 steel billet was obtained with a current intensity of 280 A and frequency of 12 Hz. Under this stirring parameter, the area ratios of carbon concentrations of 0.66 wt%, 0.70 wt% and 0.74 wt% in the middle of the billet cross section reached 28.5%, 56.9% and 10.9%, respectively. Moreover, the carbon segregation indexes for all sampling points were in the range of 0.92–1.05.

With the extensive use of low-grade Cr-containing ore, the dephosphorisation issue of hot metal containing moderate amounts (0.2%-1%) of chromium is gaining more and more attention. To achieve dephosphorisation and chromium retention, a series of experiments on the dephosphorisation of hot metal containing moderate amounts of chromium were carried out at 1723 K. In the experiments, the crystallisation performance of the slag with various CaO/Fe₂O₃ ratio and Cr₂O₃ content, as well as the transfer of phosphorus and chromium between slag and hot metal at 1723 K were investigated. The results show that the dephosphorisation process goes through four stages: melting and precipitation, dissolution of refractory, continual oxidation, and phase transition. With the increase of CaO/Fe₂O₃ ratio, the chromium loss decreases while the dephosphorisation ratio first increases and then decreases. The addition of Cr₂O₃ promotes the precipitation of Fe(Cr,Al)₂O₄, which inhibits the dephosphorisation and chromium loss.

In this study, a new method is proposed for the plasticization of inclusions by taking advantage of the behavior of alkali metals in lowering the inclusion melting point. A series of experiments with NaF additions to molten steel were carried out using a carbon tube furnace followed by simulated rolling tests using the solidified ingots and characterization of inclusions with the help of automated scanning electron microscopy. Compositional changes of the steel and evolution of gaseous species were evaluated using thermodynamic software FactSage 7.2 (ThermFact Inc., Montreal, QC, Canada). Based on this approach, NaF/steel/inclusion interactions and the effects of NaF addition on the melting point, size and deformability of inclusions were clarified. The modification of MnO-SiO2 inclusions by NaF also promoted the removal of inclusions and improved the cleanliness of steel. The results show that with the addition of NaF, the melting point of inclusions is greatly reduced, the deformability is improved, and the removal of inclusions is enhanced, all of which indicates a good prospect for industrial application.