Secondary metallurgy

Removal of hydrogen from liquid steel in a short time

Fast, reliable and reproducible achievement of lowest carbon contents for the production of thin sheet to produce DDQ and EDDQ (Deep Drawing and Extra Deep Drawing Quality)

To minimize temperature losses of the circulating steel, the vacuum vessel is preheated. The ladle top slag on the liquid steel remains completely closed and insulated against heat losses during the vacuum treatment.

The RH process enables a high throughput of lift gas and thus a high steel circulation rate. The bath surface directly exposed to the vacuum is as large as possible due to an optimized vessel design, thus making optimum use of the reaction space: This results in intensive metallurgical reactions and short treatment times. For this reason, the RH process is particularly suitable for converter steelworks with short cycle times and for long continuous casting sequences with correspondingly short casting times.

A vacuum treatment in which the mass transfer surface is outside the ladle does not require an additional ladle freeboard. This applies in the case that the amount of alloying elements added... and leads to maximum productivity for a given ladle design.

The special feature of the RH process is that the inert lift gas is injected directly into the RH snorkel. This means that no bottom purging plugs are required in the ladle during the RH process. In case of a downstream atmospheric treatment, ladle purging plugs can be switched on. This is done by using purging equipment typically belonging to the plant, which is located upstream of the RH unit.

SMS group's atmospheric ladle treatment processes are used to set the optimum temperature and chemical analysis of the steel as precisely as possible prior to vacuum treatment or casting. In order to increase the steel temperature, heating can be achieved either by an electric arc with electrical energy or by an oxidation reaction with chemical energy. Slag formers and alloying elements can be added under almost inert conditions if required. The most important units in atmospheric processes are ladle furnaces, chemical heating stations and ladle treatment stations.

In the last 20 years two processes have established themselves at the top of secondary metallurgical vacuum processes: the RH process with the variants RH-TOP (Temperature-Oxygen-Powder) and RH-OB (Oxygen Blowing) as well as the VD process (Vacuum Degassing) with the variants VD-OB and VOD (Vacuum Degassing + Oxygen Blowing or Vacuum Oxygen Decarburization). In VD-OB and VOD processes, oxygen blowing lances are additionally used either to optimize the C-O ratio during decarburization or to blow carbon out of the steel as CO with the aid of oxygen.

In the RH process a stream of liquid steel is continuously circulated under vacuum between vacuum vessel and ladle and undesirable elements are removed via the gas phase.

In the VD process, the entire ladle is placed under vacuum in a tank that is vacuum-tightly closed, and steel circulation within the ladle is enabled by bottom stirring through porous plugs in the ladle bottom.

The RH and RH-TOP plants from SMS group are typically installed in steel making plants with batch sizes from 80 to 400 tons. VD and VD-OB plants typically cover batch sizes from 20 to 350 tons, VOD plants from 10 to 180 tons. RH plants and VD plants can be used in both electric and converter steelworks. VOD plants are required in stainless steel production to achieve particularly low carbon contents in an economical way.