VOD / VD-OB Processes

VOD / VD-OB Processes

Vacuum Oxygen Decarburizing (VOD) is typically used to produce stainless steels. In comparison to the VD process, VOD treatment involves an additional oxygen blowing step to reduce the steels content of oxidizable compounds as e.g. carbon or phosphor. The oxygen flow can also be used for chemical heating of the melt (VD-OB process), as the chemical reactions of the steel contents with Oxygen are exothermic.

Vacuum Oxygen Decarburizing (VOD) is typically used to produce stainless steels. In comparison to the VD process, VOD treatment involves an additional oxygen blowing step to reduce the steels content of oxidizable compounds as e.g. carbon or phosphor. The oxygen flow can also be used for chemical heating of the melt (VD-OB process), as the chemical reactions of the steel contents with Oxygen are exothermic.

During the decarburization step the vacuum system must be able to operate continuously at a rough pressure in the range of ~50-200 mbar, while simultaneously removing high gas flows of typically 5,000 m³/h to 20,000 m³/h. The decarburation step could last ~10-45 min.

The main challenges of this application are the extreme high amounts of dust particles created during the oxygen blowing phase, next to this gas-flow peaks with high concentrations of unreacted oxygen are possible. 

The decarburization step is always followed by a vacuum degassing (VD) step for which pumping speeds between 50,000 m³/h to 250,000 m³/h at process pressures around 0.67 mbar are necessary.

Dust filtration is required to trap the partly huge amounts of dust created during the process. As the dust particles are often pyrophoric, the filtration system must be designed accordingly. Successfully used filter designs therefore typically use "inert-gas blow-back cleaning" steps to clean the filter surface.

During the long time oxygen blowing operation at rough pressure, the gases leaving the tank degasser do also have a high density, which means that they store a lot of heat energy. To protect the dust-filter from overheating, during the oxygen blowing phase a gas-cooler must be installed in between filter and tank.