Smelting options for carbon ferrochrome based on ore raw materials, middlings and their technological evaluation

The article presents the results of large-scale laboratory tests carried out in the conditions of the Chemical and Metallurgical Institute named after V.I. Zh. Abishev on the use of briquetted mono-charge in the smelting of carbon ferrochrome on a 250 kVA furnace. The purpose of these studies was to determine the technological parameters of the use of briquetted mono-charge containing in its composition chrome ore, wastes from the production of high-carbon ferrochrome, middlings and various carbonaceous reducing agents. The main idea of using these briquettes was to multiply the contact surface of the reductant and ore, which should speed up the technological process. The principal possibility of smelting a standard alloy using briquetted mono-charge is shown. The alloy for individual charge options meets the requirements of the standards. In comparison with the technology without the use of briquettes, the mono-charge technology has shown advantages in all main parameters. The technology with the use of briquettes from the dust of the AktZF gas cleaning system is distinguished by a low yield of non-standard metal and slag, the bulk of the material goes into the gas collection system. Technologies from briquettes from fines pellet production area of Donskoy ore mining and processing plant and flash have very low specific technical and economic indicators and cannot be recommended for industrial use. Improvement of briquetting modes and technology of their smelting is required. The technical and economic indicators were higher than the current one, showed briquettes from ore and coke of the People's Republic of China, briquettes of ore from borlin and shubarkol coals of Kazakhstan.

Optimal System for Improved Internal Model Control of Argon-Oxygen Decarburization Process Based on the Piecewise Linear Model and Time Constant of Filter Optimization

This paper presents an improved internal model control system to raise the efficiency of refining low-carbon ferrochrome. This control system comprises of a piecewise linearized transfer function and an improved internal model controller based on optimized time constant of the filter. The control system is mainly used to control the oxygen supply rate during the argon-oxygen refining for controlling the smelting temperature. The regulatory performance and servo of two closed-loop control schemes are compared between the improved internal model controller based on the optimized filter time 0000-0002-7606-6546and the internal model controller based on the fixed filter time constant. The simulation analysis shows that the piecewise linearized model and the optimization of the time constant of the filter improves the response time, stability, and anti-interference ability of the controller. Then, the proposed improved internal model controller is used to adjust the gas supply flow in 5 ton AOD furnace to control the smelting temperature. Ten production tests performed the effectiveness of the controlling refining optimal system. The analysis of the experimental data shows that the improved internal model control system can shorten the melting time and improve the melting efficiency. Thus, the application of the improved internal model control system in low-carbon ferrochrome refining is an interesting potential direction for future research.

Addition of Chromium and its effect on the microstructure and mechanical properties of laser-coated high carbon ferrochrome alloy on mild steel

Laser cladding is an additive manufacturing technology that can be utilized in surface strengthening, modification, and repair of components that are subjected to adverse working conditions. This can be accomplished by the addition of functionally graded material with a remarkable limit to enhancing an engaged credited property of monolithic material that is superior and better than its monolithic counterparts. Chromium addition to the microstructure of components has been found to increase the electrochemical stability, high-temperature strength and corrosion resistance of laser additive manufactured components. The current study investigates the effect of the extra addition of chromium on the hardness and microstructure of laser coated high carbon ferrochrome FeCrV15 on steel baseplate.

Synthesis and Characterizations of High Carbon Ferrochrome (HCFC) Slag Based Geopolymer

In the present Investigation, Geopolymer (GP) is made using High carbon Ferrochrome (HCFC) slag by synthesizing silicon and aluminum present in it with alkali liquid solution which binds other non-reactive materials present in the slag. The compressive strength of GP is found to be 11 MPa after 7-days of air curing. Increasing air curing time to 28-days, the strength is measured to be 15 MPa. XRD analyses indicate that there is gradual transformation of crystalline phases to non-crystalline glassy phases. SEM images show presence of more amount of glassy phase after air curing for a longer time. This is also corroborated with mechanical properties such as compressive strength. TGA results are also discussed for both uncured and cured GP samples. DSC isotherms indicate oozing out of inbuilt water present in the prepared GP materials which is an indication of condensation polymerization reaction occurring during the formation of Geopolymers.

THEORY AND TECHNOLOGY OF MANUFACTURING A FERROALLOY FROM CARBON FERROCHROME DUSTS

The article contains the research results of obtaining a ferroalloy from a carbon ferrochrome dust containing 30,2% of Сr2O3, 23.4% of SiO2, 32.7% of MgO, 5.0% of FeO, 1.6% of CaO, 4.5%of Al2O3, 2.3%of C, and 0.3 %-others. The studies were carried out by a thermodynamic modeling method using the HSC-5.1 software package (Outokumpy) based on the principle of the Gibbs energy minimum, the Box-Hunter rototable planning technique and electric melting of the dust in an arc furnace. It was found that the interaction of the dust with carbon under equilibrium conditions and in the presence of iron leads to formation of Cr4C(T>10000C),Cr3C2, Cr7C3,Cr (T>11000C), FeSi (T>13000C), SiC (T>14000C), SiOg and Si(T>15000C). In the temperature range of 1745-19000C and in the presence of 18-34% of carbon and 8% of iron of the dust mass, the resulting ferroalloy contained 18.5-25.2% of Si and 46.8-49.4% of Cr (in this case the silicon extraction degree into the alloy was 60.0-64.4%, the chromium one–99.8%). When the electrosmelting the granulated dust together with coke and steel shavings, the chromium extraction degree into the alloy was 98-99%, the silicon one–53-57%; the obtained ferroalloys containing 18.3-21.9% of silicon and 45.6-53.6%of chromium meet the requirements to FeCrSi23-grade ferrosilicochromium.

Effects of High Carbon Ferrochrome Additions on the Microstructure and Properties of Fe-C-Cr-Nb Hardfacing Alloys

Fe-Cr-C-Nb hardfacing alloys composed of 1.07-1.33 wt% C, 0.08-2.61 wt% Cr, and 4.55-4.98 wt% Nb were prepared on C45E4 steel surfaces using alloy steel flux-cored wires. The alloy microstructures were studied by optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) and the effects of the alloying elements on the hardfacing properties were determined. The results indicate that these alloys contain martensite, austenite and NbC phases. As the C，Cr and Nb mass fraction in the surfacing material increases, the austenite and NbC contents increase, and the martensite content decreases. The NbC crystallite size in the surface layer affects its hardness and thus its wear resistance. The wear resistance first increases and reaches to its maximum value which is 5.7 times higher than that of the C45E4 steel substrate, while by higher increasing of the mentioned elements, it decreases.

PROSPECTS FOR THE INTEGRATED USE OF SLAG WASTES FROM FERROCHROME PRODUCTION FOR HEAT-RESISTANT MATERIALS

The research results of physicochemical and physicotechnical properties of slag wastes from ferrochrome production as raw materials for heat-resistant materials are presented. Chemical and mineralogical composition of slag from high-carbon ferrochrome production and slag from low-carbon ferrochrome production, as well as their constituent main crystalline phases, represented by magnesium and calcium aluminosilicates of complex composition, have been determined by physicochemical research methods. According to X-ray phase analysis, the slag from the high-carbon ferrochrome production is represented mainly by forsterite Mg2SiO4, spinel MgAl2O4, partially amorphous glass phase and admixture of calcium orthosilicate Ca2SiO4. In the slag from the low-carbon ferrochrome production, the main crystalline phase is calcium orthosilicate γ-Ca2SiO4, as well as magnesium orthosilicate forsterite Mg2SiО4. The research results of specific surface area, average particle size determination and sieve analysis have shown that the slag from the low-carbon ferrochrome production is a finely dispersed gray powder with the following characteristics: the specific surface area – 295 m2 /kg, the average particle size – 6.8 μm, the true density – 3.01 g/cm3 , the bulk density – 739 kg/m3 . The research of the physicochemical and physicotechnical properties has established that in terms of chemical, mineralogical composition and refractoriness indices, the slags from the high-carbon ferrochrome and low-carbon ferrochrome productions can be valuable raw materials for heat-resistant materials.

Recovery of Chromium from Slags Leachates by Electrocoagulation and Solid Product Characterization

Slags produced in the steelmaking industry could be a source of chromium. Slags contain, depending on different types of slags, between 2 to 5 wt.% of Cr. Roasting of slag with NaOH, followed by subsequent leaching can produce leachates which can be efficiently processed using electrocoagulation (EC). This paper provides results from the EC process optimization for Cr(VI) solutions with initial concentration 1000 mg/L of Cr(VI). Influence of pH, current intensity and NaCl concentration on the efficiency of chromium recovery, energy consumption as well as solid product composition is discussed in detail. Optimum of pH = 6 was chosen for EC processing of Cr leachates as well as current intensities of 0.1–0.5 A because of the higher Cr/Fe ratio in solid product compared to higher current intensities. Results of EC processing of four real leachates of electric arc furnace carbon steel slag (EAFC), electric arc furnace stainless steel slag (EAFS), low carbon ferrochrome slag (LC FeCr) and high carbon ferrochrome slag (HC FeCr) were evaluated. Comparison of the results of four real leachate samples is presented. Obtained final solid product was identified as (Fe0.6 Cr0.4)2O3 and with up to 20% of Cr could be used as source of chromium in the ferrochrome production.

PHYSICAL AND CHEMICAL STUDIES OF SLAG OF PRODUCTION OF LOW-CARBON FERROCHROME - COMPONENT OF HEAT-RESISTANT BINDER MATERIAL

The aim of the work is physicochemical studies of chemical and mineralogical composition of the slag from the production of low-carbon ferrochrome proposed to use as a component of heat-resistant binder. As a result of studies, it was found that the main crystal phase in the slag is calcium orthosilicate in the form of γ-Ca2SiO4 modification, which is also partially in the form of α-Ca2SiO4, and magnesian silicates in the form of forsterite Mg2SiО4. The main properties of the slag such as density, specific surface, dispersiveness, refractoriness are determined by the properties of the dominant mineral- calcium orthosilicate. Under conditions of slow cooling of the slag melt, the main mineral in the slag composition, i.e. calcium orthosilicate β-Ca2SiO4 passes into γ-Ca2SiO4 modification with increase in the volume of crystal lattice by ~ 12%, which leads to self-destruction and transition of the slag to a dust state. The results of studies of the specific surface, determination of the average particle size, the results of sieve analysis showed that the slag from the production of low-carbon ferrochrome is a finely dispersed gray powder with the following characteristics: the specific surface is 2955 cm2/g, the average particle size is 6.8 μm, the true density is 3.01 g/cm3, the bulk density is 739 kg/m3. When using the finely dispersed slag from the production of low-carbon ferrochrome as a component of composite binders, the energy-consuming process of its fine grinding can be eliminated. Currently, the slag from the production of low-carbon ferrochrome is practically not used as a secondary mineral raw material. However, the physicochemical properties of the minerals making up the slag allow to recommend it as a component for the manufacture of heat-resistant materials. The results of physical and chemical studies can be used to develop effective technologies for integrated processing of low-carbon ferrochrome slags.