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| Longauerová M., Fedorová M., Longauer S., Kadlec J., Bořuta J., Fujda M., Janák G., Vojtko M. |
| HETEROGENEITIES OF CHEMICAL COMPOSITON IN CAST PRODUCTS |
| Keywords: Slabs|surface segregation|structure heterogeneities|centreline noncompactibilities|round blooms|central segregation| |
| No 1 (2007), p. 17-25 |
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| Isayev O., Nosochenko O., Kislitsa V. |
| DEVELOPMENT THE CONTINUOUS CASTING TECHNOLOGY OF Nb-CONTENT STEEL GRADES FOR INTERNAL SLABS AND PLATES QUALITY IMPROVEMENT |
Abstract
A complex technology has been developed at the “Azovstal ” Iron & Steel Works for the production of complex alloying plates made from concast slabs. This technology provides for hot metal and steel desulphuration, silicocalcium wire input, steel band input to the concaster mould melt with the aim of centerline element segregation reduction.
Steel cleanliness in terms of the content of non-metallic inclusions is one of the primary indicators of steel products quality. Presence of non-metallic inclusions in cc steel can be caused by the following:
* washing of refractory lining in steel ladles and tundishes (alumosilicate, magnesite-chromate and spinel solid crystal particles);
* physical and chemical interaction of steel melt during steelmaking, deoxydation and casting processes (alumosilicates, nitrides and sulphides).
To improve steel cleanliness, Azovstal researchers have developed a complex technology of removal of non-metallic inclusions from liquid steel in concaster tundish:
* Partitioning of the tundish space into the inlet part and the distribution chambers using special refractory dams. Special hydromechanical filtering elements having various configurations and channel directions were manufactured and built in on different levels of tundish dams to provide metal flow from the inlet to the distribution chambers.
* Removal of fine inclusions, below 10mm, from steel is possible only by creation of the additional lifting force. It can be implemented by arrangement of gas (argon) shrouding using ceramic channel tuyeres imbedded in the working layer of tundish distribution chambers bottom in the zone of liquid steel flow through filtering elements.
* To modify the inclusions remaining in the melt, the process of calcium-silicide core wire feeding into the tundish has been developed. Steel modification is performed using wire feeder. Calcium silicide introduction into the tundish ensures obtaining uniformly distributed globular calcium oxysulphides in place of earlier existed sulphide and oxide film inclusions located on grain boundaries and simultaneous substantial calcium recovery in liquid steel compared with its introduction into the steel ladle.
Metal contamination with inclusions of various morphology was reduced 2.0 – 3.0 times, plastic properties of the rolled products were improved. Comprehensive metallographic examinations confirmed the efficiency of the applied complex process and high yield of high performance X60 - X70 rolled plates.
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| Keywords: line pipe grades of steel|Nb-content|tundish|inclusions|residual time|refining| |
| No 1 (2007), p. 85-93 |
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