Vacuum Degassed Forging Ingots: Why Vacuum Matters
How vacuum degassing removes hydrogen, oxygen and nitrogen from steel and why it matters for heavy forgings.
The problem: dissolved gases
Liquid steel dissolves hydrogen, nitrogen and oxygen. If hydrogen stays in the solid steel, it can form internal cracks called flakes in heavy forgings after cooling. Oxygen forms oxide inclusions that lower fatigue strength.
How vacuum degassing works
The liquid steel is exposed to a vacuum, typically with argon stirring, in a vacuum degassing unit. Dissolved hydrogen and nitrogen come out of the steel and are pumped away, and oxygen is reduced. Kesari Alloys publishes a vacuum level of 0.25 mbar reached in under five minutes.
Ladle refining first
A ladle refining furnace adjusts the temperature and chemistry, and removes sulphur. Vacuum degassing follows. This sequence gives tighter chemistry control and cleaner steel.
Closed casting
After degassing, the steel is bottom poured under a protective arrangement so it is not exposed to air and does not pick up gas or oxide again.
Vacuum degassing of forging ingots: hydrogen control in forging ingots
For forging ingots, vacuum degassing is the main hydrogen control. A low hydrogen figure at pouring, plus a slow cooling or hydrogen diffusion cycle after forging, is how flakes in heavy sections are avoided.
Who needs it
Any heavy section forging, rotors, shafts, pressure parts and bearing steels, where internal soundness is checked by ultrasonic testing.
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