In the metallurgical plant of LARCO at Larymna, approximately 200000tly of nickelferrous dust are collected in the gas cleaning systems of the Rotary Kilns (R/Ks) corresponding to an annual production of 100000t FeNi20%. In addition, a stockpile of one million tons of old R/K dust lies close to the plant and the community of Larymna. A "one-stage" environmentally friendly process has been developed for the recycling of this dust by direct reduction smelting in a DC arc furnace. The industrial adaptation of this process was tested in the 125t DC-HEP (Direct Current -Hollow Electrode Powder) furnace at Georgsmarienhutte steelwork (GMH) in Germany. About 70t of dust were directly smelted by injection through the hollow electrode of the furnace. The nickel recovery in the metal bath was 93-99.9%. Final products were low nickel alloyed steel grades and slag suitable for special cement types production. Main cause of the dust generation in the R/Ks is the disintegration of laterite and the ore fines fraction after the ore crushing. Their separation, collection and metallurgical exploitation prior to their feeding in the R/Ks would significantly reduce the amount of the generated dust. Therefore, the smelting of untreated laterite ore fines in the DC-HEP furnace was also indicatively tested. Thus, a zero residues industrial production process was developed for the recycling of nickel bearing dust and ore fines by smelting in a DC-arc furnace, since the finally produced FeNi-alloy and slag are 100% utilized in the steel and cement industry respectively.
Purpose -During steel plate and long-product production, numerous imperfections and defects appear that deteriorate product quality and consequently reduce revenue. The purpose of this paper is to provide a practical overview of typical defects (surface and internal) that occur and their root causes. Design/methodology/approach -The data presented here derive from the quality department and from more than 50 technical reports of ELKEME S.A. on the last decade's production of steel making companies STOMANA S.A. and SIDENOR S.A., with emphasis on the defects occurred in some of the products of the Bulgarian plant. Stereoscopic observations of surface defects, light optical metallography, and scanning electron microscopy with EDS represent the most used techniques to characterize defected macro-/micro-areas and microstructures. Findings -In general, the most commonly encountered defects from semi-finished (billets, blooms, and slabs) and final (round bar and plate) steel products are as follows: network cracks, porosity, gas holes, shrinkage, shell, slivers, casting powder entrapment, ladle slag entrapment, other non-metallic inclusions, low hot ductility, centerline segregation cracking, macro-and micro-segregation, and mechanical defects (scratches, transverse cracks, and seams). Practical implications -External and internal quality improvement can reduce the production cost (Euro/ton). Social implications -Improvement of the quality of industrial plates and long products increases the safety of the further-produced constructions and systems such as bridges, cranes, heavy equipment, automobile parts, etc. Originality/value -Root cause analysis and categorization of the most commonly encountered defects can pave the way to production process improvements that directly affect final product quality and the overall per ton production cost. The benefits of this work obviously affect all steel producers/ processers, and also society through the safety increase achieved by the quality improvement in the steel products used in constructions and automobile parts.
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