Vacuum treated (vacuum degassed) steel is used for  critical applications that require steel with an exceptionally high degree of structural uniformity, internal soundness, and other characteristics which may be impaired by the effects of uncontrolled amounts of dissolved gases. Vacuum degassing treatments, along with various deoxidation practices are specified to control the amounts of dissolved gases in the steel. This post describes 6 benefits of vacuum treatment of steel.

• Reduces Hydrogen content. This reduces the tendency of steel to “flake” or become “embrittled.”
• Reduces Oxygen content. This makes it easier for the steel to conform to restrictive microcleanliness requirements.
• Improves the recovery and uniformity of distribution of alloying elements and other additives.
• Helps control the composition of the steel closer than without vacuum treatment.
• Results in higher and more uniform transverse ductility, improved fatigue resistance, and improved high temperature performance.
• Can be used to achieve exceptionally low carbon content that are otherwise unobtainable by conventional means.

What are some situations where vacuum treatment is employed?

• Large forgings and large cross sections where hydrogen would otherwise remain and contribute to flaking and embrittlement.
• Bearings where uniformity throughout the section is important for critical performance.
• Inverted delta, human critical safety applications where steel toughness and performance place high demands on the steels properties in all directions.

The removal of Oxygen by degassing  is a challenge for the steelmaker, because this element is extremely reactive- it can exist in the steel in many forms, such as free oxygen, dissolved in the melt as a soluble nonmetallic oxide, can combine with carbon to form gaseous oxides, and it can exist as complex oxides in the accompanying slags and refractories in the process.
In post will describe some steel deoxidation  practices and the types of vacuum degassing that are used in the North American steel Industry
Siemens Vacuum Degasser Photo