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The project succeeded in achieving its aim of halving recarburisation levels during the secondary metallurgical treatment and casting of ULC steels at the Dillinger steelworks and Voest Alpine Stahl Linz. At both plants, end carbon levels of greater than and equal to 24ppm were secured on the basis of the following operational measures:

At Dillingen, MgO-C stone with reduced carbon content is used for refractory ladle lining in the slag field, with reduced carbon dolomite C stone being deployed in the steel field. Greater than and equal to 20ppm can be achieved by using carbon-free bonding phases.

Laboratory tests carried out by DIFK GmbH confirm the effectiveness of this measure and show how the capacity of the molten mass to oxygenise upon contact with the fire-resistant material is a decisive factor in carburisation. If the molten mass is able to release extremely high levels of oxygen, this will reduce the propensity for carbon to be dissolved in the steel and create a CO buffer that prevents steel from infiltrating the fire-resistant structure.

Iron oxide (FeO{n}) that has been released in the ladle slag also combines with the carbon-bearing refractory ladle lining to form a CO buffer. At the same time, the increasing viscosity of the slag reduces the capability of the latter to enter the structure. The degree of viscosity can be calculated using the Riboud method.

At both steel plants, casting powder with low levels of soot helps to reduce recarburisation. Optimum results are achieved by avoiding the use of carbon. Although smelting behaviour and slag viscosity can then be controlled by setting the smelting interval, this leads to sensitive operational behaviour.

A combination of soot, the amount of soot, and the type and distribution of particle sizes will determine the smelting behaviour of the casting powder and recarburisation: Preliminary casting powder should form a thin layer of slag as quickly as possible to reduce initially high levels gh levels

Additional information

Authors: BAULIG A, DIFK GmbH, Bonn (DE);OLLIG M, DIFK GmbH, Bonn (DE);POTSCHKE J, DIFK GmbH, Bonn (DE);LACHMUND H, AG der Dillinger Huttenwerke (DE);KOCH E, VASL, Linz (AT);PRESSLINGER H, VASL, Linz (AT)
Bibliographic Reference: EUR 19483 DE (2001), pp.108. Euro: 108
Availability: Available by EUR-OP sales agent
ISBN: ISBN: 92-894-1232-1
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