Aiming at the development of increasingly special steels, the industry searches for a constant evolution in the control of its production processes. The demand for these steels has been growing constantly, as well as their requirements. The cleanliness is one of the most important requirements for high-performance steels. Therefore, non-metallic inclusions are one of the most studied associated problems in the steel industry. Non-metallic inclusions can cause exfoliation and cracking, impairing the mechanical properties of the steels and may even interrupt their manufacturing processes. Nonetheless, it is extremely important to carry out a metallic characterization of these inclusions, aiming at reducing or eliminating their deleterious effects. The inclusions of alumina and silica in samples of industrial steels with low (AISI 1020) and high (AISI 1070) carbon content were identified by Scanning Electron Microscope. Low and medium carbon steels showed inclusions that can drastically affect their mechanical properties. This paper presents its characterization, including the minimum in quantity, size, shape and dispersion of steel matrices used in the ASTM 45. It concluded that the market for these steels can be improved due to the characterization of these inclusions and the ways of their reduction.
Keywords:The SAE/AISI 1045 steel is one of the structural steels widely used in the automotive sector to several key components such as connecting shafts, axles etc. It is also used in petrochemicals and power generation units. In material science and engineering; four interdependent parameters are of paramount importance which includes; process structure, properties and performance. Among all factors the structure / microstructure is of utmost importance since it governs the properties at large. For example it depends on the size, shape, and distribution of various micro constituents therein. Therefore, the main aim of this study is to investigate the response of the microstructures (structure-property correlation) upon application of heat treatment processes such as annealing, normalizing, tempering and hardening. This was followed by the characterization such as spectrometry analysis was carried out for chemical composition of the steel. While impact and hardness tests were also conducted. Results suggest an improved toughness and hardness when tempering temperature was reduced. This is attributed to decreased grain sizes of micro constituents upon such treatment. Interestingly one more aspect was noted that the chemical composition changes slightly during heat treatment processes which might be in range of standard. However, it could affect the surface properties of steel during service.
Keywords:Over 140 million tons of copper slag have been accumulated in the Russian Federation and this amount continues to increase. The storage of the copper slag not only requires a large area, but also causes environmental issues. The environmental taxes and landfill maintaining are costly, making it necessary to process the production wastes as completely as possible. At the same time, these slags contain valuable elements, in particular, iron, copper, zinc, selenium, arsenic and some others, which recovery can make the slag utilization profitable. The highest value is represented by iron which content exceeds 40%; it is almost at the level of some iron ores used in the ferrous metallurgy. However, the use of this iron-containing material in the conventional processes of ferrous metallurgy is complicated due to the high content of copper (up to 0.6%) . In addition, the extraction of iron by conventional methods cannot solve the issues with recycling the newly formed slag. Other existing methods of processing of copper-smelting slags are aimed at extraction of certain components, but they cannot solve the issue of their disposal in general.
The purpose of this work was to develop economically feasible methods for the complete utilization of copper-smelting slags and obtain the demanded products.
The object of the study was the dumped slag produced during copper smelting. The slag contains metal particles consisting of copper, iron, antimony and tin. The oxide phase is represented by the iron spinel particles and complex silicates containing iron, zinc and other elements. Spinel contains a relatively high amount of sulfur and the silicate phase contains impurities of non-ferrous metals. According to the XRD analysis, the main iron-containing phases of the sludge are fayalite 2FeO∙SiO2, magnetite Fe3O4, and pyroxene СaFeSiO4.
In this paper, the processing of copper-smelting slags was studied by using solid-phase reduction of iron with carbon from steam coal. At the reduction stage, zinc was extracted into gas phase and during smelting of the reduced semi-finished product the copper-containing cast iron with a high sulfur content and oxide melt were obtained. Afterwards, the grinding media were produced from the obtained cast iron which showed high performance properties, and on the basis of the slag residue proppants were produced that are in demand in the oil and gas industry.
Pipe steel must have high strength, toughness and ductile-brittle transition temperature. To achieve these indicators, the steel has a limited C content, not more than 0.24 wt. %, Mn, no more than 1.4 wt. %, and Si, no more than 0.6 wt. % and this content depends on the strength class of pipe steel. For grain refinement, pipe steel is alloyed with Al, Nb, Ti, V in an amount of not more than 0.15 wt. %. To increase the corrosion resistance, steel may contain a limited amount of Cr, Ni, Mo, Cu. The minimum level should be the content of harmful impurities P, S, N. As a rule, the content of alloying elements and impurities in pipe steel does not exceed 2 wt. %, so this steel can be called a multicomponent low alloyed steel.
The structure of multicomponent melts has a significant effect on the physical properties of steel [1]. Multicomponent melts have a heterogeneous structure [2], which manifests itself in the features of the temperature dependences of the kinematic viscosity. When the melt is heated above the temperature Th, the heating and cooling curves diverge at T < Th. There is a temperature region near Th, within which the heating and cooling curves form a hysteresis loop [3]. The critical temperature Tk separates regions with different activation energies for viscous flow.
The work investigated the temperature dependences of the kinematic viscosity, surface tension and density in liquid pipe steel. Evaluation of the thermophysical properties of liquid pipe steel was carried out in terms of the cluster size, which are structural components of the melt. The cluster size was calculated using the formula for the kinematic viscosity obtained in the transition state theory [4]. From Arrhenius plots, the activation energy and pre-exponential factor were determined. The relative free volume was found from the Batschinsky relationship [5].
It is shown that the activation energy Ea increases with an increase in the cluster size. This relationship allows one to explain the anomalous behavior of the temperature dependence of the kinematic viscosity. The local change in the viscosity is caused by the decomposition of clusters and the subsequent formation of new clusters of a different size and chemical composition. The viscosity at the cooling stage corresponds to the melt structure formed at the maximum heating temperature. The relationship between the surface tension and the chemical composition in the surface layer of the melt is shown. The melt heating temperature is recommended to obtain the optimal structure of the pipe steel.
The results of laboratory, industrial and calculation researches of physical, chemical and thermophysical processes at the oxidizing roasting (sintering and pelletizing) of the titaniferous raw materials are considered. The estimation of influence of metallurgical properties (reducibility, durability, softening and melting temperatures of roasting ores) on processes heat and mass exchange at the reduction in the blast furnace is executed [1]. Titan-bearing ores with the various TiO2 content are investigated. Tests of ores are provided by ores of the current production in the Gusevogorsky deposit (Russian Federation, average test), and also ores from separate production of ores - is low titanium and is high titanium. Ores of the Kuranakhsky deposit (Russian Federation), the Tebinbulaksky deposit (Republic of Uzbekistan) and high titanium ores of the Medvedevsky deposit and the Yaregsky deposit (both Russian Federation) allowing receive pigmentary titanium dioxide are also considered. Processing of the specified ores assumes so-called schemes «blast furnace - converter» and «metallization - electrosmelting», including oxidizing roasting of ore concentrate with receiving agglomerate and pellets [2, 3]. The micro X-ray diffraction phase analysis and magnetic characteristics of samples is made. The results of industrial tests on change of metallurgical properties of agglomerate and its influence on blast furnace indices are given. Technical and economic indices of blast furnace smelting of agglomerate and pellets (coke consumption and productivity, chemical composition of cast iron and slag), received from a concentrate of the Kachkanarsky deposit, are calculated [4]. As a whole possibility and reasonability of processing of titaniferous ores with the different content of titanium dioxide and receiving vanadium containing cast iron and the slag containing titanium dioxide is shown. Possibility of processing the pigmentary titanium dioxide from titaniferous minerals is introduced [5].
Keywords:ABSTRACT
Processing of ilmenite concentrates into titanium-containing slag, titanium tetrachloride,
and titanium sponge is complicated by the high content of chromium in it. Therefore, the methods
based on preliminary carbon reduction of ilmenite concentrate at 900-1200 °С and following
reduction of reduced iron and chrome by electromagnetic separation are widely used in industry.
Then the non-magnetic titanium-chromium fraction is for hydrochemical treatment to purify it
from chromium and other impurities.
It has been determined that the selective solid-phase reduction of ilmenite chromiumcontaining
concentrate should be performed at 1250 °С and 2 hours’ dwell period. It was found
that the addition of 8% sodium chloride to the charge accelerates the reduction process for iron
from ilmenite. At the same time, the recovery of reduced iron into the magnetic fraction is
76.1%, recovery of chromium is 55.8%, recovery of titanium is 15.3%.
The titanium-chromium fraction was sintered with the calculated amount of soda at 850
°С for 2 hours to separate chromium from titanium compounds and leached with hot water (S:L
= 1:4) at the temperature of 95-100 °С and stirring for 120 minutes. At the same time, the chromium
recovery into the solution was 83.6%. Titanium-beneficiated concentrate contains 6.2%
iron, 36.2% titanium and 0.42% chromium.
The high content of chromium in the ilmenite concentrate makes it difficult to process further into titanium-containing slag, titanium tetrachloride and titanium sponge. The most wide-spread industrial application is obtained by methods based on preliminary carbon-thermal reduction of ilmenite concentrates at 900-1200 °C with the subsequent separation of reduced iron and chromium from them by electromagnetic separation, and the nonmagnetic titanium chromium fraction is sent to hydrochemical treatment for purification from chromium and other impurities.
It has been established that solid-phase selective reduction of chromium-containing ilmenite concentrate should be carried out at a temperature of 1250 °C and an retention time of 2 hours. The addition of 8% in the charge of sodium chloride accelerates the process of reducing iron from ilmenite. In this case, recovery of reduced iron in the magnetic fraction is 76.1%, chromium 55.8%, titanium 15.3%. To separate titanium compounds from chromium, the titanium-chromium fraction is sintered with a calculated amount of soda at 850 °C for 2 hours and leached with hot water (S:L ratio = 1: 4) at a temperature of 95-100 °C and stirred for 120 minutes. The recovery into the chromium solution is 83.6%.
Strength, rigidity and durability of reinforced concrete constructions, with plain round bars of mild steel as rebars, made it the number one medium of construction. Later, ribbed bars of high strength carbon steel were introduced in the hope of making reinforced concrete constructions more economical.
Proponents of ribbed bars overlooked that the provision and presence of ribs make ribbed bars of carbon steel highly susceptible to corrosion. Consequently, constructions with ribbed bars of carbon steel proved to be less sustainable, as such constructions reached states of distress early.
The excessive corrosion destroys or reduces load-carrying capacity of concrete elements, reinforced with ribbed bars. It can also lead to local or total failure of structures during vibratory loadings. Moreover, loose rust on the surface of ribbed bars will prevent any possible passivation of rebars, thereby hastening the process of corrosion in rebars and distress in reinforced concrete constructions.
As claimed solutions, fusion bonded epoxy coated ribbed bars, ribbed stainless steel bars, polymer coated glass fibre and granite reinforced bars, have been used. Besides high cost, these bars do not “bond” with concrete, whereas the availability of competent bond between rebars and the surrounding concrete is an essential requirement for the satisfactory performance of reinforced concrete.
Use of corrosion inhibitors with concrete and provision of surface protection systems in the nature of waterproofing treatment, so as to prevent corrosion in steel elements inside concrete, are accepted practices today.
These alternative solutions cost money, and the performance of concrete elements are dependent upon the performance of the contractor. Moreover, the use of corrosion inhibitors or the provision of surface protection systems cannot solve problems, which may be caused by the lack of bond between rebars and concrete, viz., reduced load-carrying capacities, lack of ductility, and local or total failure of structures during vibratory loadings.
PSWC-BAR, characterized by its plain surface and wave-type configuration, provides a zero-cost solution to all the problems and limitations of ribbed bars and alternative solutions. In due consideration of using steel with high elongation properties, it is recommended to limit the use to steel of yield strength not exceeding 550 MPa. The absence of ribs on the surface of PSWC-BAR makes it free of excessive corrosion, that is associated with conventional ribbed rebars, thereby leading to several-fold enhancement of life span of concrete constructions with PSWC-BAR.
The several-fold enhancement of life span of concrete structures lowers the life-cycle cost of construction to a fraction of what it is today, and it increases very significantly the financial, social, environmental and global sustainability of reinforced concrete constructions than what it is today.
The many benefits of using PSWC-BAR are derived from its physical characteristics of plain surface and wave-type configuration. The use of PSWC-BAR, with its wave-type configuration, leads to enhancement of effective bond between such bars and the surrounding concrete, thereby leading to increased load-carrying capacity, and several-fold increase in ductility and energy-absorbing capacity, making constructions cheaper and safer during earthquake events, adding to the sustainability of reinforced concrete construction.
Completion of the development of a large number of fields in recent years has led to the need to manage the processes occurring at the post-operational stage of the operation of these fields, disrupted by long-term mining operations. One of these processes is the self-discharge of mine water. In 1998, the International Network for Acid Prevention (INAP) was established as an association of leading mining companies (Anglo American, Barrick Gold Corporation, Rio Tinto, etc.). The goal of INAP is to significantly improve the management of sulfide ore materials during and after mining, to reduce the consequences associated with acid drainage by consolidating information and experience in the field of acid drainage, sharing knowledge and research, and developing technologies. However, it has not yet been possible to solve the problem of purifying acidic mine waters from heavy metals and neutralizing them using reagent-free methods on an industrial scale. The increased interest in reagent - free treatment methods of liquid media is explained by the fact that these methods of cleaning and disinfection do not pollute the natural environment with chemicals and do not have a harmful or irritating effect on the human body.
The aim of the work is to develop and scientifically substantiate a set of mathematical models that allow optimizing the technological regime of acid mine water treatment (AMW) by a reagent-free method. To achieve this goal, the following tasks are set and solved:(1)substantiation of a set of models describing the operation processes of mobile technological complexes for the treatment of AMW, (2) development of a methodology for pre-project analysis of the mobile technological complex and (3) development of a mathematical model of the operation process of mine water treatment with the extraction of heavy metals from them. Theoretical and methodological basis of the study was the methods of systems theory, reliability theory, and mathematical modeling. "Event trees" were used as probabilistic models of reliability and safety of EW cleaning systems.A paradigm of minimizing environmental and economic risks caused by the closure of unprofitable copper-zinc-pyrite mines has been developed. The paradigm is formed to prevent an environmental disaster caused by the self-discharge of water from mines that are on " wet " conservation [1]. The resolution of the conflict situation is provided by the introduction of adaptive mobile technological complexes for the treatment of acidic mine waters and the extraction of heavy metals from them. It is shown that mines located on wet conservation are weakly structured objects with unstable functioning and data uncertainty [2,3]. The functioning of the technological complex is represented as a change in the state of its links: water treatment, its treatment in the reactor and separation into target products.
A sustainable steelmaking process is characterized by efficient resource use with minimal energy losses, which in turn may be correlated to process exergy efficiency. This parameter depends on fuel type, secondary energy input such as electricity and steel scrap utilization ability. A high process exergy efficiency is likely to lower carbon footprint of the process through utilization of process fuel gases. RHF is based on dual fuel where it uses coal for reduction and natural gas (a low carbon fuel) for heat generation. RHF also generate rich off gas, with subsequent utilization of this gas to generate power for enhancing energy efficiency. Thus a RHF-EAF (Rotary Hearth Furnace-Electric Arc Furnace) process is expected to emit lower CO2 per ton of crude steel for the dual input fuel mix and given scrap input in steel making. Additionally, RHF-EAF process may also run with higher proportion of steel scrap in addition to DRI produced from virgin source, which has the potential to lower the RHF-EAF emissions further. According to WSA, steel scrap can be recycled infinitely without any loss of quality and recycling of 1 ton of steel scrap saves 1.5 ton of CO2.
Exergy analysis and CO2 emission of dual fuel RHF-EAF process is studied using mathematical models and compared with coal based processes like BF-BOF, COREX-BOF. Two variant of RHF producing iron nugget (ITmk3 process) or DRI (FASTMET process), are considered separately. Although, at lower scrap level BF-BOF always yields lower total exergy loss values as compared to RHF-EAF process, at higher scrap level (50% scrap) RHF-EAF yields lesser total exergy loss which is further lowered on hot charging of the DRI produced. The total exergy loss with hot charging of DRI is lower than BF-Tenova (BOF with Arc facility) process at higher scrap levels (50%). At identical scrap level, RHF-EAF processes are always found to produce higher gas based exergy efficiency. Considering the conversion of product gas exergy to generate electricity, metal based exergy indices of RHF-EAF processes are found to be superior or comparable to coal based BF-BOF and COREX-BOF processes. Net CO2 emission through RHF-EAF processes are (around 1.92-2.01 ton/tcs) found to be comparable to BF-BOF process. Again on consideration of product gas conversion to electricity and carbon credit, CO2 emission from RHF-EAF system is always found to be lower than BF-BOF process.
