Al₂O₃-rich (>70 wt-%) inclusions generally hard and non-deformable are extremely detrimental for saw wire. In order to explore the source of this type of inclusion and provide solutions, experiments on the interaction between Al-containing MgO–C refractory and high-carbon steel for saw wire was conducted on a laboratorial scale using a cold crucible levitation melting furnace under vacuum conditions. [Al]_S (acid-soluble Al), [C] and [Mg] concentrations in steel, Al₂O₃ concentration in inclusions and microstructure of refractory/steel interface, etc. were analysed to clarify the influence of vacuum pressure, refractory addition amount and interaction time. Based on the experimental results and thermodynamic calculations, a presumable impact mechanism of Al antioxidant in MgO–C refractory on the formation of Al₂O₃-rich inclusions in high-carbon steel for saw wire under vacuum conditions was deduced, which in turn provided a reference for the control of Al₂O₃-rich inclusions in high-carbon steel for saw wire.

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.

Hard inclusions with high melting temperatures such as Al₂O₃ (2054°C) and MgO·Al₂O₃ (2135°C) generate nozzle blockage problems during continuous casting of Al-killed valve spring steel and are very detrimental with respect to fatigue properties. In the present paper, inclusion modification in Al-killed valve spring steel by Na₂CO₃ addition was investigated in the laboratory using a graphite tube resistance furnace. The results show that inclusions with high melting temperature can be successfully modified into Na₂O-containing inclusions with lower melting temperatures by the addition of Na₂CO₃. The effectiveness of inclusion modification can be enhanced by increasing the Na₂CO₃ addition and/or decreasing the amount of Al. This suggests that Na₂CO₃ addition could possibly be a substitute for Ca treatment as a method for preventing nozzle blockage during continuous casting of Al-killed steel.