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The biggest challenge for our society, in order to foster the sustainable circular economy, is the efficient recycling of wastes from industrial, commercial, domestic and other streams. The transition to a circular economy is the goal of the European Commission’s Circular Economy Action, which was first launched in 2015. In 2020 the above action plan announced initiatives along the entire life cycle of the product, with the aim to make sustainable products the norm in the EU. Therefore, it is anticipated that the above action will result in an increase in Europe’s economic competitiveness, sustainability, resource efficiency and resource security. Within this context, the suitability of ferroalumina as a raw material in the blast furnace is investigated. Ferroalumina is the product of the high-pressure filter press dewatering process of the Greek red mud generated during the production of alumina by means of the Bayer cycle. Ferroalumina is a low-cost raw material and its possible charging in the blast furnace and/or steelmaking aggregates is a step towards industrial symbiosis, where the wastes, namely by-products, of an industry or an industrial process, become the raw materials for another. In the present work the effect of ferroalumina addition as a raw material was examined by smelting ferroalumina, blast furnace-slag, lime and scrap at 1550°C in a graphite crucible and a constant slag basicity. The increase of the alumina content in the slag improves the desulfurization capacity. Moreover, the silicon exchange between slag and metal was examined. The results indicate that the alkalis’ capacity of the slag increases with the addition of ferroalumina. The analysis of the finally obtained slag suggests that it could be suitable for utilization in slag-cement production.

A pyrometallurgical process was developed for the recycling of Ni bearing dusts and laterite ore fines by direct reduction smelting in DC (direct current) arc furnace. In the course of the performed industrial trials, besides the Ni-recovery in the liquid bath, slag composition was deliberately adjusted in order to produce a series of metallurgical slags with different chemical and mineralogical composition. The aim of this study was to investigate their suitability as clinker substitute in cement manufacturing. Examined parameters were slag FeOx content, basicity and applied cooling media (air, water cooling). A series of composite Portland and slag cements were manufactured in laboratory scale incorporating 20% and 40% of each slag, respectively, the rest being clinker of OPC (ordinary Portland cement) and 5% gypsum. The extended mineralogical analysis and microstructural properties of the produced slags were examined and correlated with the properties of the produced cements. The physical and mechanical characteristics of all examined cement products were found to meet the requirements of the regulation set for cements. The present research revealed that the most critical parameter in the compressive strength development of the slag cements is the mineralogical composition of the slag. Even in cases where rapid cooling to obtain glassy matrix is not feasible, adjustment of slag analysis to obtain mineralogical phases similar to those met in clinker of OPC, even at higher FeO contents (up to ~21wt.%), can result in production of slag with considerable latent hydraulic properties. These results indicate that there is potentially space for adjustments in conventional EAF (electric arc furnace) steel slags composition to allow for their wider use in cement manufacturing with significant environmental and economic benefits resulting from the reduction of energy requirements, CO2 emissions and natural raw materials consumption.

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.

Purpose – A failed disc that was forged from S355J2 round bar was investigated in order to determine the failure route cause. The purpose of this paper is to determine the defects and route cause analysis regarding their origin. Design/methodology/approach – Macroscopic evaluation, microstructure observation using light optical metallography and scanning electron microscopy with EDX analysis were the techniques used to analyse and characterize the defected areas. Findings – Macro-inclusions (up to 850 µm) that correspond to high melting aluminium rich calcium-aluminate particles were detected. Their formation, possibly due to improper calcium treatment during ladle furnace steel refining process might be associated with clogging problems at casting. SEM-EDX analysis revealed whitish spots containing Zr that could be related to submerged entry nozzle (SEN) erosion/breakage. Characteristic is the large size and unusual shape of the traced particles, as well as the presence of low Si, Na, K. The findings indicated that nozzle clogging and/or breakage at casting was most possibly the root cause of the product’s quality degradation. Originality/value – After extended root cause analysis, specific countermeasures are proposed to avoid clogging phenomena. The suggestions are based on the findings taking into account restrains of the steel-making process. Emphasis was laid in detecting the weaknesses that lead to product quality degradation and consequently in optimizing the steel-making process. Such incidents are often found during steelmaking a useful suggestion to steelmakers is to mark and remove cast parts after SEN problems are encountered. In this way quality issues in intermediate and/or final products will be avoided.

Deoxidized high phosphorus copper (C12200, DHP-Cu) is the principal construction element in piping in water distribution systems and HVAC (Heating Ventilation and Air-Conditioning) installations due to its excellent thermal and electrical conductivity, formability, corrosion resistance and antimicrobial activity. However, design and installation deficiencies or aggressive environmental parameters, such as improper water quality, may lead to unexpected failures causing material losses and many times property damage incurring high costs of repair. A corroded copper water tube caused leakage in a hot water hydraulic installation. The leakage was reported after approximately 6 years in service. Tubes were disconnected from a hydraulic installation and samples were taken for failure investigation. Failure analysis findings suggest strongly that the leakage was caused by tube perforation from the inner waterside due to localized pitting corrosion. The main cause of the accelerated tube pitting corrosion was the improper water chemistry (especially high chlorine content and low pH) inducing chemical attack of copper leading to scale layers of cuprite, chlorides and sulfates.

In the metallurgical plant of LARCO at Larymna, approximately 200000t/y 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.

The tratment of the laterite nickel ferrous ores in Hellas for the production of ferronickel at Larymna is associated with the emission of 200000t/y of fine dust collected in the gas cleaning systems of the rotary kilns (R/Ks), with 1.2-1.5% and 4-5% . Average Ni and C contents respectively . This thesis contributed to the development of a method for the recycling of this dust by means of its direct reduction smelting in a DC-HEP furnace (Direct Current-Hollow Electrode Powder) by its injection through the central hollow graphite electrode. The preliminary theoretical study and the laboratory trials were followed by industrial heat campaigns in the 12st DC-HEP furnace at georgsmarienhutte steelwork in Germany, where around 70t of dust and 2.5t of ore fines were smelted. The Ni-recovery was very high 93-99.9%. Low Nickel alloyed steel grades were produced and various slag types for the investigation of their utilization for the production of composite-portland cements and slag cements. The metallurgical evaluation of the trials was performed and model for the dust reduction smelting process was developed.