Shu-feng Yang

Influence of FeO and sulfur on solid state reaction between MnO-SiO2-FeO oxides and an Fe-Mn-Si solid alloy during heat treatment at 1473 K

To clarify the influence of FeO and sulfur on solid state reaction between an Fe−Mn−Si alloy and MnO−SiO2−FeO oxides under the restricted oxygen diffusion flux, two diffusion couples with different sulfur contents in the oxides were produced and investigated after heat treatment at 1473 K. The experimental results were also compared with previous work in which the oxides contained higher FeO. It was found that although the FeO content in the oxides decreased from 3wt% to 1wt% which was lower than the content corresponding to the equilibrium with molten steel at 1873 K, excess oxygen still diffused from the oxides to solid steel during heat treatment at 1473 K and formed oxide particles. In addition, increasing the sulfur content in the oxides was observed to suppress the diffusion of oxygen between the alloy and the oxides.

Rational argon stirring for a 150-t ladle furnace

Based on the principle of similarity, water modeling experiments were carried out for a 150-t ladle furnace. The rational parameters of argon stirring were determined as the optimized positions of nozzles, top area of the porous brick, and gas flow rate. The following results are obtained: 1) the optimized positions of two nozzles are at 0.333R (R refers to the radius of the ladle at bottom) with an angle of 135°; 2) the top diameter of the porous brick should be 130 mm; 3) the flow rate of gas should be 25.0-30.6 m^3/h. The plant trial shows that the improved process is effective in enhancing the cleanliness of round billets. The total oxygen content, microinclusions, and macroinclusions in round billets are reduced by 12.5%, 8.2%, and 20%, respectively.

Interfacial reaction mechanism between multi-component oxides and solid alloys deoxidised by Mn and Si during heat treatment

To clarify the interfacial reaction mechanism between multi-component oxides and solid Mn- and Si-deoxidised alloys during heat treatment, five diffusion couples with different compositions of Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO oxide were produced using a confocal scanning laser microscope. The changes in the chemical compositions of the oxide and alloy by heat treatment at 1273 and 1473 K were investigated. The mechanisms of the ‘solid–solid’ and ‘solid–liquid’ interfacial reactions and the diffusion of elements between the alloy and oxide were revealed thermodynamically and are discussed. The results show that counter-diffusion occurring between Mn and Si in the alloy and oxide was the main reaction in the diffusion couples. The MnO content of the oxide and the Si content of the alloy are the driving forces of the interfacial reactions.

Characteristics analysis of inclusion of 60Si2Mn–Cr spring steel via experiments and thermodynamic calculations

A plant trial of the production of 60Si2Mn–Cr spring steel using silicon–manganese combined with aluminium to deoxidise was performed, and the characteristics of inclusions during ladle furnace refining, calcium treatment and in billets were investigated by scanning electron microscope–energy dispersive spectroscopy and thermodynamic calculations. The formation mechanisms of oxide and CaS inclusions are discussed. The experimental observation and thermodynamic analysis showed that calcium treatment cannot entirely modify large-size MgO·Al2O3 spinel inclusions into homogeneous CaO–MgO–Al2O3 inclusions, but formed a liquid xCaO·yAl2O3 layer on its surface. When the Al content was 0.05 mass%, [Mg], [Ca] and [O] in molten steel could be controlled at 2.7∼5 ppm, 2.5∼8 ppm and 4.1∼5.2 ppm, respectively, to achieve inclusions in the low melting point region. A large amount of CaS was generated in the present process due to a higher sulphur concentration in the molten steel and an excessive amount of Ca–Si wire. To avoid/reduce its formation, the sulphur concentration should be controlled to below 70 ppm.