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RUHRSTAHL

Technical Reference · Secondary Steelmaking

The Ruhrstahl–Heraeus Process

The Ruhrstahl–Heraeus (RH) process — also called RH degassing — is a major secondary steelmaking and vacuum treatment process used to refine molten steel after primary melting (usually in a BOF or EAF). Developed in the 1950s by the German companies Ruhrstahl and Heraeus, it is one of the most widely used vacuum degassing technologies worldwide.

Industrial vacuum-degassing installation in a modern steelworks
Modern RH vacuum-degassing installation

Main purpose

  • Remove dissolved gases (especially hydrogen and nitrogen)
  • Decarburize the steel to very low carbon levels (down to <10–20 ppm)
  • Improve cleanliness (remove inclusions)
  • Homogenize temperature and composition
  • Allow precise alloying additions under vacuum

Core principle

Vacuum recirculation process. Two snorkels are immersed in the ladle. Argon is injected into the up-leg, creating a gas-lift effect that continuously circulates steel into the vacuum vessel and back down the down-leg. Degassing and refining occur under deep vacuum.

Ruhrstahl–Heraeus vacuum-degassing process diagram
Ruhrstahl–Heraeus vacuum-degassing process

Key operating parameters

Typical industrial values

Heat size
100–400 t
Vacuum level
0.5–5 mbar (often ~0.67 mbar)
Steel circulation rate
85–150 t/min
Treatment / cycle time
15–30 min
Oxygen blowing (RH-OB)
2,000–4,000 Nm³/h
Snorkel diameter
~500–700 mm (e.g. 650 mm common)
Argon lift gas
Continuous injection in up-leg
Vessel preheat
900–1,500 °C
Barometric rise height
~1.45 m under deep vacuum

Main metallurgical functions

  • Ultra-low carbon: routinely < 20 ppm (sometimes < 15 ppm)
  • Hydrogen removal: < 1–2 ppm
  • Nitrogen removal
  • Inclusion flotation and cleanliness improvement
  • Precise alloying under vacuum
  • Chemical heating via oxygen blowing (exothermic C–O and Al–O reactions)
  • Optional powder injection for deep desulphurization (in advanced RH-TOP units)

Where the reactions happen

  • Free surface of the steel bath inside the vacuum vessel
  • Surfaces of rising argon bubbles
  • Splashed / atomized steel droplets in the vessel
  • Bulk steel in the strongly stirred zone of the ladle
  • Interface with the RH slag layer

Process sequence

  1. Vessel preheated → ladle positioned
  2. Snorkels immersed → argon injection starts
  3. Vacuum applied → steel rises and circulates
  4. Oxygen blowing (if RH-OB) for forced decarburization and heating
  5. Alloy additions via vacuum hoppers
  6. Final vacuum hold for gas removal
  7. Snorkels raised → ladle transferred to casting

Advantages vs. other vacuum processes

  • Very high circulation rate → short treatment times even for large heats
  • Excellent mixing independent of ladle size
  • Minimal temperature loss
  • High productivity (long sequences of ultra-low-carbon grades)
  • Flexible (pure degassing, or RH-OB / RH-TOP with oxygen and powder)
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