Vacuum Degassing

Technical data sheet and spare parts list

Vacuum Degassing

The concept of employing vacuum conditions to remove dissolved gases from molten steel was first proposed in 1940 by Soviet scientists A. M. Samarin and L. M. Novik. Vacuum degassing has since become an indispensable metallurgical process for achieving high material quality and minimizing defects such as porosity, blistering, and cracking. The process significantly enhances ductility, reduces carbon content, and facilitates the preferential oxidation of dissolved carbon over chromium—an especially critical advantage in stainless steel production. Additionally, vacuum degassing improves the overall economics of premium steel manufacturing by enabling less expensive smelting routes and reducing the consumption of costly alloying and deoxidizing additives.

Vacuum degassing is applied not only to molten metals but also to other liquid materials such as
epoxies and silicones. Consequently, it finds widespread use across diverse industries, including
plastics, beverages, steel, oil and gas, and water treatment. The process is governed by boundary-
layer mass transfer phenomena occurring at the interface between the molten metal and a
reduced-pressure atmosphere. By lowering the ambient pressure, gas solubility in the melt
decreases, allowing dissolved gases to nucleate as bubbles and rise to the surface. This enables
the effective removal of hydrogen (H₂), nitrogen (N₂), and oxygen (O₂), while also supporting
key refining reactions such as desulfurization and decarburization.
In liquid steel vacuum degassing operations, pressures typically range from 0.5 to 10 mbar, with
hydrogen concentrations maintained below 2 ppm. Based on process configuration and
metallurgical objectives, vacuum degassing is broadly classified into three principal techniques:
(i) stream degassing, (ii) circulation degassing, and (iii) ladle or tank degassing.
The pressure within the sealed degassing chamber is reduced using vacuum pumps, whose
selection depends on several process parameters, including the quantity of dissolved gases to be
removed, inert gas flow rate, operating pressure, system volume, target vacuum level, and cycle
time. Commonly used vacuum pump technologies for degassing applications include liquid ring,
claw, and dry screw vacuum pumps.
Vacuum degassing is effective only when the components to be separated possess different
evaporation or solubility characteristics under reduced pressure. The process is carried out after
the molten steel exits the furnace and prior to ingot casting or introduction into a continuous
casting system.
Each vacuum degassing unit is custom-engineered to meet the specific operational and
metallurgical requirements of the process. Our engineering team optimizes all critical parameters
and offers a comprehensive range of standardized vacuum degassing systems tailored for
industrial applications.

Working Principle

Vacuum degassing is performed by placing the liquid-containing ladle inside a sealed chamber
connected to a vacuum pumping system. As the chamber pressure is reduced, the solubility of
dissolved gases decreases in accordance with Henry’s law. To accelerate gas removal, an inert
gas—typically argon—is purged into the molten metal, promoting bubble formation and mass
transfer.
The system consists of vacuum pumps and boosters integrated with the furnace or ladle station.
Once the molten metal is positioned inside the vacuum chamber, a high vacuum is established,
and inert gas is injected from the bottom of the ladle. The resulting gas stirring induces strong
agitation within the melt, continuously exposing fresh metal surfaces to the low-pressure
environment. This enhanced interaction between the molten steel and vacuum facilitates efficient
removal of dissolved gases, leading to improved cleanliness and superior metallurgical quality.