Numerical Simulation of Fluid Flow in Bath during Combined Top and Bottom Blowing VOD Refining Process of Stainless Steel

Abstract

The fluid flow in a bath in combined top and bottom blowing vacuum‐oxygen decarburization (VOD) refining process of stainless steel has numerically been simulated. The three‐dimensional mathematical model used is essentially based on that proposed in our previous work for the flow in combined side and top blowing argon‐oxygen decarburization (AOD) process, but considering the influence of reduced ambient pressure. Applying it to the flow in the bath of a 120 t VOD vessel under the refining conditions, the results present that the model can fairly well simulate and estimate the flow phenomena. The flow pattern of molten steel in the bath with the combined blowing is a composite result under the common action of the jets from a three‐hole Laval top lance and gas bottom blowing streams. The jets have a leading role on it; the molten steel in the whole bath is in vigorous stirring and circulatory motion during the blowing process. The streams do not alter the basic features of the gas agitation and liquid flow, but can evidently change the local flow pattern of the liquid and increase its turbulent kinetic energy to a certain extent. The flow field and turbulent kinetic energy distribution in the combined blowing with three tuyeres are more uniform than those in the blowing with double tuyeres. Increasing properly the tuyere eccentricities is of advantage for improving the velocity and turbulent kinetic energy distributions, the stirring and mixing result in the practical VOD refining process.

Study on Mathematical Modeling of Combined Top and Bottom Blowing VOD Refining Process of Stainless Steel

“…The bath is also in vigorous stirring and circulatory motion during the whole refining process . The argon gas blown from the vessel bottom and the formed CO move upward and generate agitation in the bath under the combined action of the inertial force and the buoyancy.…”

“…The bath is also in vigorous stirring and circulatory motion during the whole refining process. [6] The argon gas blown from the vessel bottom and the formed CO move upward and generate agitation in the bath under the combined action of the inertial force and the buoyancy. The supersonic oxygen jets from the multiple-hole top lance impinge and exert a downward action force on the bath, and form a depressed zone at the central location of the bath liquid surface, forcing the molten steel do circulatory motion with the cavity as a center.…”

“…and considering the reduced pressure ambient. From the existing results and the flow and mixing characteristics in a VOD bath with combined top and bottom blowing, the appropriate melting times of the addition agents, i.e. the time lapse values of their cooling effects, were determined according to the respective amounts and bath temperatures at the time of addition.…”

Effects of Ultrasound on the Degassing of Molten Steel in the RH Refining Process

“…and alloy additions are completed during RH treatment. [2][3][4] It is well known that gases such as nitrogen and hydrogen are harmful for steel and their presence is detrimental to the mechanical properties of products. "White spots" occur because hydrogen participates from solution during solidification or the molten steel cannot feed through the interdendritic regions to compensate for the volume shrinkage associated with solidification.…”

“…Progresses of decarburization, removal of nitrogen, hydrogen, inclusions, etc. and alloy additions are completed during RH treatment …”