High Carbon Ferrochrome Research Articles

FeCrC, FeW, and NiAl Modified Iron-Based Alloy Coating Deposited by Plasma Transferred Arc Process

The technique of alloying X120Mn12 steel substrate by plasma transferred arc process was used for development of a surface having high wear resistance. High carbon ferrochromium, ferrotungsten, and nickel-aluminum intermetallic powders were combined to form M7C3 carbides inside Fe-based composite surface coating. The phase transformations on these coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM) with energy dispersive spectrometry microanalysis, differential thermal analysis and X-ray diffraction (XRD). The microstructure studies of the superficial layers of the coating revealed a phase mixture of interdendritic austenite (γ) phase structure and fine eutectic M7C3 carbides. The new formed coated surfaces were investigated by change of alloying elements (Cr, W, Ni), size of dendrites, change of eutectic reaction temperatures, hardness, carbide volume ratio of hard phases, and coating thickness as the processing parameters (powder feed rate and heat input). The dry sliding wear tests were performed on a pin on disc machine. The wear rates of the tests were affected by the powder feed rate, powder type, and applied load. Results revealed that processing powder combination used in this study (FeCrC–FeW–NiAl) provided the best option with superior combination of properties on surface of X120Mn12 steel substrate.

<i>In situ</i> Synthesis of Ceramic Phase Reinforced Fe-Based Alloy Surface Coating by PTA

The in-situ ceramic phases reinforced Fe-based surface coating had been produced by prepared high-carbon ferrochromium, ferrovanadium and graphite power on 20g steel through plasma transferred arc weld-surfacing process(PTA). The microstructure and properties were investigated by means of optical microscopy(op), scanning electron microscopy(SEM), X-ray diffraction(XRD) and microhardness meter. The results showed that the substrate and the coating formed good metallurgical bonding.The microstructure of coating consists of primary M7C3 carbide and eutectic structures[M+γ′+M7C3+VC]. The primary hexagonal (Fe,Cr,V)7C3 with larger size evenly distributed in coating and the fine VC particles were globular shape. The microhardness appeared reasonable distribution from substrate to the top ,which ensured that the materials had good abrasive wear resistance.

High Carbon Ferro-chromium Production by Self-reducing Process: Effects of Fe–Si and Fluxing Agent Additions

The technology of self-reducing pellets for ferro-alloys production is becoming an emerging process due to the lower electric energy consumption and the improvement of metal recovery in comparison with the traditional process. This paper presents the effects of reduction temperature, addition of ferro-silicon and addition of slag forming agents for the production of high carbon ferro-chromium by utilization of self-reducing pellets. These pellets were composed of Brazilian chromium ore (chromite) concentrate, petroleum coke, Portland cement, ferro-silicon and slag forming components (silica and hydrated lime). The pellets were processed at 1 773 K, 1 823 K and 1 873 K using an induction furnace. The products obtained, containing slag and metallic phases, were analyzed by scanning electron microscopy and chemical analyses (XEDS). A large effect on the reduction time was observed by increasing the temperature from 1 773 K to 1 823 K for pellets without Fe-Si addition: around 4 times faster at 1 823 K than at 1 773 K for reaction fraction close to one. However, when the temperature was further increased from 1 823 K to 1 873 K the kinetics improved by double. At 1 773 K, the addition of 2% of ferro-silicon in the pellet resulted in an increasing reaction rate of around 6 times, in comparison with agglomerate without it. The addition of fluxing agents (silica and lime), which form initial slag before the reduction is completed, impaired the full reduction. These pellets became less porous after the reduction process.

Iron and chromium sulfates from ferrochromium alloy for tanning

In this study we investigated the production of soluble iron and chromium sulfate complexes from high carbon ferrochromium alloy (Fe–Cr–HC) for utilization as a tanning agent. The temperature, sulfuric acid concentration, and the reaction time between Fe–Cr–HC and sulfuric acid were selected as independent variables for iron and chromium conversion. A quadratic response surface model was adjusted using the Box–Behnken statistical experimental design technique. The results obtained by solving multi-objective optimization problem have shown about 98.6–100% Cr and 86.9–89.1% Fe conversions. Perchloric acid and ammonium sulfate additions were investigated in order to determine the system limitations. The results have showed that an increase of perchloric acid concentration decreased the quantity of soluble chromium and iron compounds, while an ammonium sulfate addition improved the conversion of chromium up to 100%.

Maximisation of chromium content of ferrochrome in DC arc smelting

DC arc smelting is one of the recent techniques to smelt fine ore particles. First time in the world, Indian chromite ores were smelted in DC arc furnace in Pilot Plant of Mintek, South Africa, to produce high carbon ferrochrome (HCFeCr). Major objective was maximisation of Cr content in HCFeCr. Investigations include factors influencing chromium content, interdependence of C, Si and Cr, and control of reductants for maximising Cr. Screening increased Cr/Fe ratio of feed ore, most important factor, from 2·39 to 2·97, enabling to produce HCFeCr with 65·60%Cr, compared to 64%Cr product from unscreened ore. Product lower in Si, P and S, and 6% higher Cr recovery were achieved compared to conventional AC furnace route. Process holds tremendous potential for low cost HCFeCr production.

Smelting high-carbon ferrochrome with uniform briquetted batch

A method of batch briquetting is proposed to permit the use of fine fractions of ore and carbon reducing agents in ferroalloy production. Briquets are produced in six forms, using four different reducing agents and chrome ore in different ratios. The tests confirm the possibility, in principle, of producing high-carbon ferrochrome from uniform briquetted batch, without the use of ore chunks.

The effect of hydrogen shielding gas on microstructure and abrasive wear behavior in the surface modification process using the tungsten inert gas method

In this study, SAE 1020 steel surfaces were separately alloyed with preplaced high-carbon ferro-chromium (FeCr), ferro-molybdenum (FeMo), and ferro-titanium (FeTi) powders by using a tungsten inert gas (TIG) heat source. By using two different types of shielding gas compositions during the alloying process, the study investigated the effects of modified shielding gas composition on the microstructure, hardness, and abrasive wear resistance of specimens. It was observed that with modifications in shielding gas composition, the microstructure and volume hardness of the specimens changed and no cracks and voids were formed in the interface area. The X-ray examinations of the specimens identified Fe, FeTi, and FeMo phases in their microstructure as the first phase, and Cr7C3, Fe3C, Fe7C3, and TiC phases as the second phase. As a result, it was concluded that changes in shielding gas composition in surface alloying process significantly affect specimens’ microstructure and mechanical properties.

Cr(VI) generation during sample preparation of solid samples – A chromite ore case study

South Africa holds more than 70% of the world’s viable chromite ore reserves and produces ~46.2% of the world’s high carbon ferrochrome. It was recently reported that beneficiated South African chromite ores contained significant amounts of Cr(VI). If this is true, it could have serious consequences for South African chromite mines and the local environment. Currently none of these mines make any provision for Cr(VI) leaching from their mined ores. The data obtained in this study proved that the Cr(VI) content of chromite samples is influenced by the sample preparation technique employed priorto chemical analysis, more specifically, that pulverising of chromite samples in a normal atmospheric environment resulted in Cr(VI) formation. No Cr(VI) was liberated when pulverising was conducted in an inert atmosphere. The presence of Cr(VI) in South African chromite ores therefore seems unlikely. The results also suggest that the perceived threat of Cr(VI) contamination of groundwater and surface water, originating from chromite ore stockpiles, is improbable.Keywords: hexavalent chromium, Cr(VI), sample preparation, pulverising, chromite

Formation of PCDD and PCDF in the thermal treatment of footwear leather wastes

The leather waste generated by the footwear industry is considered dangerous due to the presence of trivalent chromium, derived from the salt utilized to tan hides. In Brazil, the majority of this waste is disposed on landfills and only about 3% are recycled. The thermal treatment is an alternative method for purification of such residues. By using this technique it is possible to generate energy and recover the chromium present in the ash for the production of basic chromium sulfate (tanning industry), high carbon ferrochromium or carbon-free ferrochromium (steel industry). In the last 10 years, the gasification and combustion of footwear leather waste have been intensively studied at the Federal University of Rio Grande do Sul. The research experiment for characterization of the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) were carried out in a semi-pilot unit (350 kW th). From new investments the thermal capacity of the unit will increase to 600 kW th. The unit will produce power from the heat generated in the combustion. The experimental results indicated that during the thermal treatment of footwear leather wastes, the formation mechanism of PCDD/F is the de novo synthesis. Most of PCDD/F were found in the particulate phase (>95%). A kinetic model was used for discussion of the achieved experimental results. The model is based in the carbon gasification, PCDD/F formation, desorption and degradation. From the conclusions obtained in this work will be possible minimize the PCDD/F formation in process of combustion of footwear leather wastes.

Smelting of Iron Ore in Fe–Cr–C–Si Melts

Direct smelting of the South African Sishen hematite ore in Fe–Cr–C–Si melts was studied, where the aim was to increase the Fe/Cr ratio of high carbon ferrochrome melts in order to approach stainless steel compositions. Experiments in the temperature range of 1600°C to 1750°C were conducted in an inductively heated rotating cylinder technique furnace; however, due to the very fast nature of the reactions, the sintered iron ore cylinders were not rotated. The molten alloy contained 50% Cr, 0.25 to 8% C, and 1.5 to 7% Si, balance being Fe. Relevant slag metal equilibrium in the system was determined from literature and Scanning Electron Microscope (SEM) examinations. In Fe–Cr–C melts, the rate increased with increasing temperature and was independent of the carbon concentration while it decreased with decreasing Cr content of the metal. At 1600°C, the formation of a carbide layer surrounding the iron oxide was observed to be a kinetic barrier for reduction. At 1650°C and higher temperatures, a mixed rate control was suggested. When the melt contained Si, the rate again increased with temperature and was independent of Si concentration. The rate limiting factor in Fe–Cr–Si melts was suggested as the diffusion of Si in the formed slag phase. In the presence of both carbon and silicon in the alloy phase the reduction rate was similar to the rates in Fe–Cr–Si melts.

Russian chromium ore in smelting high-carbon ferrochrome at OAO SZF

315 Most Russian chromite ores have a relatively low chromium content. Rich chromium ores are found in small volumes and in poorly studied deposits. Accordingly, the most urgent problem for all Russian producers of chromium ferroalloys is to secure high-grade chromium ore. Large deposits of rich chromite ore are mostly remote from Russian ferroalloy plants. The use of high-quality imported chromium ore is associated with shipping over large distances by sea or by rail and also with import tariffs; this significantly increases rawmaterial costs. In the past decade, OAO Serovskii Zavod Ferrosplavov (SZF) has used chromite ore from Kazakhstan, Albania, Turkey, and India. The high cost and instability of imported ore supplies entails the use of leaner Russian ore. As we know, most industrially useful chromite deposits in Russia are concentrated in the ultrabasic Ural ranges. Originally, these ores were used exclusively in the chemical industry and in refractory production. Given the limited supplies of highquality chromium ore and the consequent revision of the requirements on chromium ore for ferroalloy production, OAO SZF has been using Russian chromite ore for ferrochrome production since 1992. In recent years, industrial tests have been undertaken at the plant with a view to using a mixture of Saranovsk, Verbluzh’egorsk, and Alapaevsk ore with fine ore from Donskoi enrichment facility (Khromtau, Aktyubinsk oblast, Kazakhstan) for the production of high-carbon

The Equilib-ARMAX approach to the dynamic modelling of the melt metallurgy in DC plasma arc smelting operations

A methodology is presented and evaluated to model the metallurgical dynamics of DC plasma arc smelting, using high carbon ferrochrome production as a case study. The model type is called an Equilib-ARMAX model as it integrates fundamental thermodynamic models with dynamic models. The Equilib-ARMAX model takes into account the inherently uncertain nature of smelter plant data, as well as the process dynamics and the moving chemical equilibrium target. The model structure, modelling performance, and model limitations of this model type are presented. The model could predict the metallurgical dynamics well within the inherent uncertainty of the process data.

Properties of concrete pavements prepared with ferrochromium slag as concrete aggregate

This paper presents the results of investigation related to both the properties of the ferrochromium slag and the standard physical and mechanical properties of Portland cement concrete pavements (PCCP) made with this slag as aggregate, according to the relevant Croatian standards. Slag is formed as a liquid at 1700 °C in the manufacture of the high-carbon ferrochromium metal and, by slow cooling in the air, the slag crystallizes to give a stable CaO–MgO–Al 2O 3–silicate product with mechanical properties similar to basalt. With a proper selection of slag as an artificial aggregate, concrete pavements with compressive strengths, wear resistance and specific weight higher than in those from natural (limestone) aggregate in commercial Portland cement, type CEM II/B-S 42.5 (EN 197), can be made. The 28-day compressive strength of the concretes made with original unfractioned slag and with standard limestone as aggregates (w/c=0.64 and 350 kg/m 3) reached the values of 57.00 MPa and 36.70 MPa, respectively. Volume stability, high volume mass, good abrasion resistance to wear and crushability make this reinforced slag concrete suitable for wearing courses of concrete pavements for traffic load classes 1 and 2 where carbonate stone material (limestone) mainly does not meet the Standard Technical Requirements for cement concrete slab pavements according to the relevant Croatian standard.

Control of silicon in high carbon ferrochromium produced in submerged arc furnace through redistribution of quartzite in the charge bed

High carbon ferrochromium produced in a submerged arc furnace may contain as much as 4%Si. A high level of silicon in this alloy is not desired. In addition to bringing down the value of the alloy, a high level of silicon increases the specific energy consumption during production of the alloy. Controlling the proportion of silica and coke in the charge can help in bringing down the level of silicon in the hot metal. This strategy is adopted by some ferrochromium manufacturers. However, these practices lead to difficulties in tapping, and to reduced recovery of chromium. A thermochemical analysis of the process showed that silicon in the hot metal was at equilibrium with the slag only at high temperatures, which usually prevailed in regions close to the electrodes. Based on this analysis, a strategy was devised to control silicon in the hot metal by appropriate redistribution of quartzite at the top of the charge bed. Trials were carried out at an industrial plant to control the silicon level using this strategy. Results showed that the silicon level in the hot metal was drastically reduced on redistribution of quartzite. This method can result in a reduction of specific energy and specific coke consumption.

Empleo de cromitas refractarias para la obtención de fundentes aglomerados utilizados en la soldadura automática por arco sumergido (SAW)

In the present work high carbon ferrochrome (load ferrochrome) and slags are obtained, starting frora the metallurgie reductive processing of refractory chromites. The obtaining of alloys and slags is studied using an experiment design based in the relationships among components. The chemical compositions of alloys and slags guarantee their application for the conformation of alloys loads and matrix fluxes amassed for the superficial filling by means of submerged arc welding (SAW). The melting-reduction process is carried out in an electric arc furnace.

Tungsten inert gas surface modification of SAE 4140 steel

In the present study, the surface of SAE 4140 steel was separately arc melted and alloyed with preplaced high carbon ferrochromium powder using a tungsten inert gas (TIG) arc heat source. The effects of specimen thickness and heat input for arc melting and thickness of preplaced high carbon ferrochromium powder layer for surface alloying on the microstructure, hardness and wear properties of the modified surfaces were investigated. Following arc melting and surface alloying, conventional characterisation techniques such as optical microscopy, scanning electron microscopy (SEM), energy dispersive spectrography (EDS) and X-ray diffraction were employed to study the microstructure of the arc melted and alloyed surfaces. Hardness measurements were performed across the modified zones and wear properties of the surfaces were evaluated by a pin-on-disc abrasive wear testing method. The results indicated a significant increase in surface hardness after melting at low heat input (0.7 kJ mm-1) and alloying with a preplaced high carbon ferrochromium powder layer giving a surface composition of 3%C and 25.8%Cr, with higher wear resistance surfaces. This was attributed to the fully martensitic microstructure for surface melting and the high volume friction of Cr7C3 carbides in the matrix of austenite for surface alloying.

Aspects of smelting reduction of chromite ore fines in CaO-FeO-Cr2O3-SiO2-Al2O3 slag system by carbon dissolved in high carbon ferrochromium alloy bath

Chromite reduction by carbon dissolved in a high carbon ferrochromium alloy melt has been investigated in the temperature range 1580-1640°C using a slag system based on CaO2-FeO-Cr2O3-SiO2-Al2O3. Although the reduction is essentially first order with respect to Cr2O3 concentration, it exhibits both zero order and first order reaction kinetics. The zero order period is occupied by the preferential reduction of iron oxide, during which time there is no significant change in the concentration of Cr2O3. The predominance of the divalent chromium oxide in the slag phase is seen to provide further evidence that the reduction of chromite occurs by a stagewise process, involving the thermodynamically stable CrO species. While high basicity slags may be recommended to minimise the generation of CrO, and hence improve reaction kinetics and the extent of Cr2O3 reduction, there is a limitation imposed by chemical erosion of the alumina crucible as the slag basicity is increased above unity, with the dissolving Al2O3 further retarding the reduction kinetics. There is also evidence to suggest the participation of a reductant other than carbon (possibly silicon) in the reduction of chromite.

Kinetics of chromite ore reduction from MgO-CaO-SiO2-FeO-Cr2O3-Al2O3 slag system by carbon dissolved in high carbon ferrochromium alloy bath

Kinetic experiments were performed in an induction furnace to investigate the reduction of chromite ore by carbon dissolved in a high carbon ferrochromium alloy melt under conditions of varying Cr2O3 concentration, slag basicity, and temperature. The results obtained show that chromite reduction by dissolved carbon in slag systems of the type MgO-CaO-SiO2-FeO-Cr2O3- Al2O3 occurs principally by a stagewise process encompassing an intermediate reaction in which the divalent chromium oxide species is involved. During the fast period, Cr2O3 reduction is controlled by the diffusion of oxygen species in the slag for which a mass transfer coefficient of 0·003 cm s-1 was calculated. An activation energy value of 117 kJ mol -1 obtained for the reduction of Cr2O3 implies the rate controlling step is mass transfer of Cr2O3 from the slag to the slag/metal interface, since activation energies for metal phase control are typically <70 kJ mol -1. The second period represents a pseudo-equilibrium condition with respect to Cr2O3 reduction that is probably under thermodynamic control by a step or mechanism involving the reduction of divalent chromium oxide to chromium.

Quaternary Cu-0.7%Cr-0.3%Fe-X alloys

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The aim of the present work was to increase the electrical conductivity and strength of the Cu-0.7wt%Cr-0.3wt%Fe alloy through selective minor additions (≤0.15 wt%) of elements expected to promote precipitation of dissolved Fe: Ti, B, P, Ni & Y. Such quaternary alloys with reduced Fe in solid solution would be expected to have properties equivalent to or better than those of the Cu-1%Cr reference alloy (Alloy Z). The investigation showed that none of the trace element additions significantly improved the size of the age hardening response or the peak aged electrical conductivity of Alloy A, although further work is required on the influence of Ti. Additions of P and B were detrimental. Other trace additions had little or no effect apart from causing some slight changes to the precipitation kinetics. The mechanical properties of the Cu-0.7%Cr-0.3%Fe alloy made with less expensive high carbon ferrochrome were found to be inferior to those of the equivalent alloy made with low carbon ferrochrome.

00/02113 Thermochemical analysis of production of ferrochromium in submerged arc furnace

High carbon ferrochrome is one of the most common ferroalloys produced and is almost exclusively used in the production of stainless steel and high chromium steels. Production takes place primarily in countries with substantial chromite ore supply. Relatively cheap electricity and reductants also contribute to the viability of high carbon ferrochrome. The most common production technology utilized is submerged arc smelting in AC furnaces, although open arc smelting in DC furnaces is becoming increasingly common. A more advanced technology route that includes a prereduction step is only utilized at significant scale by one producer. Production processes have become more energy and metallurgically efficient by utilizing advanced processes such as prereduction, preheating, agglomeration of ore, and CO gas utilization. Recently installed plants display manageable risks in terms of environmental pollution and occupational health.