Abstract
The possibility to modify and to better control the melt composition and the inclusion content by an injection of reactive powder into the liquid steel during RH treatment has been investigated by CRM and SIDMAR. Industrial trials realised in an RH installation equipped for injecting reagent powder during vacuum treatment have been followed up. The specific targets were the reduction of the steel sulphur and nitrogen level and the delivery of a highly clean steel to the continuous caster. Several distinct operating conditions have been tested with modifications in the composition and amount of top slag, the type of injected powder, the flowrate and the injection time, the vacuum level, the deslagging of the ladle after the treatment, etc. A large number of samples and semis have been fully characterised to assess their non-metallic inclusion content. In addition to the conventional optical and electronic image analysis techniques, new procedures have been used based on SEM (scanning electron microscopy) and on PDA OES (pulse distribution analysis optical emission spectrometry). The main conclusions of these measurements are summarised.
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