Ladle Metallurgy & Continuous Casting
A thermodynamic model was developed and a laboratory vacuum induction furnace was employed to simulate the reoxidation of aluminum-killed calcium-treated steels. A method for representing the size distribution of inclusions using the population density function was applied to study the effect of reoxidation on the inclusion characteristics. A comparison of the size distributions of spinel inclusion populations showed that spinel inclusions produced after reoxidation are larger than those formed prior to reoxidation and calcium treatment.
In the continuous casting of steel, the interaction between the solidified shell surface and mold copper plates has significant effects on the slab surface quality and the casting productivity. Therefore, it is important to clarify the lubrication mechanism between the slab and the mold caused by various factors such as mold oscillation, mold flux properties and casting speed. In this study, friction force was measured with the slab caster equipped with hydraulic oscillators and relationships between the friction force and continuous casting factors were investigated. From these results, states of mold fluxes in the mold were estimated.
In order to simulate the erosion/corrosion phenomena of refractories for continuous casting on calcium-treated steel, the erosion/corrosion experiments of Al2O3-C- and MgO-C-based refractories were conducted by rotating the refractories in the molten steel with slag with CaO/Al2O3 = 1. Additionally, the wettability between this slag and Al2O3 or MgO substrates was determined by the contact angle after 30 minutes holding at 1,550°C. The results of erosion/corrosion test were discussed through the evaluation of wettability and the estimation of the mechanism of interfacial reaction.
Continuously cast slabs with high alloy content are susceptible to centerline segregation defect. Etching techniques are routinely utilized for visual assessment of segregation. This paper introduces a new quantitative technique based on micro x-ray fluorescence analysis that allows rapid generation of chemistry maps from large slab samples.
Nozzle port angle is a critical parameter controlling fluid flow in the continuous casting mold, especially across the top surface. Fluid flow calculations with a three-dimensional (3D) k-e model and die-injection experiments on a one-third-scale water model were performed to quantify the effects of nozzle angle on flow pattern and surface flow. The 15° up-angled nozzle produces more severe jet wobbling for the conditions simulated, resulting in velocity fluctuations at the surface. This could increase surface cracks, powder entrapment and associated downstream problems, especially in advanced high-strength steels.
In the current study, a two-dimensional mathematical model of coupled granular/gas flow is developed to calculate the stress on granular materials in the interior of the blast furnace and on the walls. Comparison to the wall gas pressure distribution of the commercial blast furnace shows that gas temperature is important to get a realistic value of the force due to interphase drag resulting from gas flow through the granular bed. The consequences of operator control actions on the stress distribution are reported. The effects of operator control included are the variation of the gas properties and the properties of the granular column. Also the influence of an increase in belly diameter on the normal stress exerted by the granular materials at the wall is explored.
This study examined the behavior of inclusions in laboratory heats after deoxidation with 0.1 wt.% Al, Ca treatment and reoxidation. Additions of 100 ppm O to reoxidize were examined; effects of 50 ppm S additions and amount of Ca addition were also studied to investigate the role of CaS. Samples were taken at various points after the different additions up to 20 minutes after reoxidation. Automated scanning electron microscopy/energy-dispersive x-ray spectrometry microanalysis was used to analyze the inclusions detected on polished cross-sections. Reoxidation led to formation of predominately spinels after only 5 minutes. CaS was confirmed to have a beneficial effect on reoxidation by delaying the formation of solid spinel inclusions.