Abstract
The process of vacuum degassing occurs during the secondary refining of special steels. Its main function is to remove undesirable gases. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after the vacuum stage. The results in steel cleanliness were related to a kinetic stirring parameter (βs) of the vacuum station and to the effect of slag viscosity. The removal of inclusions during the vacuum stage reached 64, 75 and 78% in the diameter ranges of 2.5-5, 5-15 and ≥ 15 µm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags' chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion densities for the 2.5-15 µm diameter range and also in the sulfur content in liquid steel. Regarding the effective viscosities of slags, it was concluded that lower values (0.20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0.40 Pa.s) were detrimental to steel cleanliness.
Highlights
In recent decades, the steel industry has been subjected to a large effort aimed at obtaining high quality steels
The resulting chemical compositions of the slag and steel samples taken before and after vacuum degassing are shown in Tables I and II, respectively, including averages and standard deviation for each constituent
The addition of aluminum in the liquid steel for composition adjustment occurs after vacuum degassing treatment, so the total aluminum content is low during the vacuum stage, according Table II, provided during deoxidation[33,34] in tapping stage, before ladle furnace (LF) process
Summary
The steel industry has been subjected to a large effort aimed at obtaining high quality steels. A vacuum degassing station is an important unit process for removal and control of several detrimental impurities[4]. One of these impurities is known as non-metallic inclusions. According to Riyahimalayeri, Ölund and Selleby[2] vacuum degassing should remove the unwanted non-metallic inclusions as much as possible, resulting in a cleaner and more homogeneous steel melt. These unwanted inclusions are related to its destructive effect on the fatigue properties of some steels
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
