Fuxiang Huang

Inclusion composition control in tyre cord steel by top slag refining

Abstract In order to improve the inclusion type and composition in tyre cord steel, ladle furnace refining has been simulated by laboratory experiments and thermodynamic calculation. It was found that slag metal reaction time and top slag composition have an important influence on the inclusion compositions in the final steel. To produce the desired low melting point ductile inclusions the optimum conditions were: reaction time 60 min, basicity (CaO/SiO2) of top slag in the range of 1·0–1·2 and Al2O3 content of slag in the range of 3–9 mass-%. These were then confirmed in industrial trials.

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Abstract Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr2O3 refractories in a synthesised 50CaO–45Al2O3–5SiO2 liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773 K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr2O3 refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75 mL·min− 1. The slag containing 5 mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.

Investigation on the removal efficiency of inclusions in Al-killed liquid steel in different refining processes

Industry trials were carried out to study the removal efficiency of inclusions in Al-killed liquid steel in the processes of BOF–LF–RH–CC and BOF–RH–CC. It was found that the removal efficiency of inclusions has a high dependence on inclusion types. Solid inclusions are more easily to be removed than liquid inclusions. The removal efficiency of solid Al2O3 inclusions is higher than that of solid CaO–Al2O3–MgO inclusions. As liquid CaO–Al2O3–MgO inclusions coexisted with solid CaO–Al2O3–MgO inclusions in the liquid steel, the low removal efficiency of inclusions in RH degassing process was found in BOF–LF–RH–CC process. However, high removal efficiency and ultra-low total oxygen (T.O) content were obtained in BOF–RH–CC process because the inclusions were mainly composed of solid Al2O3 although initial T.O content before RH degassing was relatively high. This is due to the fact that solid Al2O3 tends to form cluster-shaped inclusions which have both a higher contact angle and a lower work of adhesion with steel than calcium aluminate, resulting in easier removal by RH degassing. Therefore, it is proposed to weaken steel–slag reaction and calcium treatment before RH degassing to retain solid Al2O3 inclusions in the steel.

Desulfurization Behavior and Mechanism of CaO-saturated Slag

To develop a high-efficiency desulfurizer for the production of pipeline steel with the LD-RH-CC process, the desulfurization efficiency and mechanism of CaO-saturated slag were studied using a vacuum-induction furnace and Si-Mo electric resistance furnace. The results show that the desulfurization ability for slag with a small amount of solid CaO was highly enhanced under conditions of satisfied kinetics. The desulfurization reaction of CaO-saturated slag depended on the liquid slag rather than the solid CaO, as sulfur was not detected inside the solid CaO. The desulfurization efficiency of CaO-saturated slag was also influenced by the amount of residual liquid slag and its sulfur absorption ability. The sulfur absorption ability of CaO-CaF2 slag was analyzed to be much higher than that of CaO-Al2O3-CaF2-(SiO2) slag. Moreover, the effect of solid CaO on the desulfurization kinetics was evaluated and the application conditions of CaO-saturated slag were discussed.

Microstructures of Austenitic Stainless Steel Produced by Twin-Roll Strip Caster

The microstructures of austenitic stainless steel strip were studied using color metallographic method and electron probe micro analysis (EPMA). In the cast strips, there are three kinds of solidification structures: fine cellular dendrite in the surface layer, equiaxed grains in the center and fine dendrite between them. The solidification mode in the surface layer is the primary austenite AF mode because of extremely high cooling rate, with the retained ferrite located around the primary cellular austenite. In the fine dendrite zone, the solidification mode of molten stainless steel changes to FA mode and the residual ferrite with fish-bone morphology is located at the core of the dendrite. The retained ferrite of equiaxed grains in the center is located in the center of broken primary ferrite dendrite with vermicular morphology.