Papers by Keyword: Scale

Abstract: The structural-phase compositions of the alloy obtained through reduction melting with oxide waste use from the production of high-alloy steels and alloys with different charge compositions have been studied. It is crucial to determine the technological parameters that ensure the reduction of alloying element losses during the production and use of the alloying material. In the phase composition of the resulting alloy, a solid solution of alloying elements and carbon in the lattice of γ -Fe, Fe3C, as well as FeNi in the case of adding alloyed metal chips to the charge has been found.At the same time, a relative increase in the content of alloying elements in the studied areas of the alloy has been ensured (wt.%): Cr – from 1.84–32.90 to 0.59–43.98; Ni – from 1.41–20.74 to 4.24–45.02; Mo – from 0.35–1.30 to 0.00–11.89; W – from 0.00–0.08 to 0.00–21.37, respectively. This led to the formation of new phase structures containing refractory elements, presumably of carbide and intermetallic nature, which been observed in microstructural images. The proportion of residual carbon in the form of carbide component and residual unreacted reductant is aimed at providing the required reducing capacity during the alloy usage. The studies have identified new technological aspects of processing high-alloy industrial waste, resulting in a resource-efficient alloying material with the potential to partially replace standard ferroalloys in steel production.

Abstract: Calcium sulfate (CaSO₄) scale formation during the phosphoric acid (H₃PO₄) production process presents significant operational challenges. Key variables influencing scale formation include temperature, pressure, stirring speed, and supersaturation. This study aims to evaluate the effect of varying concentrations of ATMP inhibitors on the mass of CaSO₄ scale in a 40% phosphoric acid solution and to analyze the composition of the resulting scale. The experimental procedure involved the addition of ATMP inhibitors at different concentrations, while temperature and stirring speed were varied. The solution was circulated through a sample housing for two hours, after which the mass of the formed scale was measured, and X-Ray Fluorescence (XRF) analysis was performed. The optimal concentration of ATMP inhibitors was found to be 9 ppm at a temperature of 40°C and a stirring speed of 235 rpm. Results indicated that the composition of the CaSO₄ scale produced with ATMP inhibitors was significantly lower than that of samples without inhibitors, with XRF analysis revealing an 8% reduction in CaSO₄ levels

Abstract: The main aspects of effective dephosphorization of steel under conditions of induction melting are presented. Regularities of scale growth on the surface of iron, as well as the conditions of its catastrophic oxidation, are considered. An industrial experiment was conducted to remove phosphorus from steel intended for brake discs.

Abstract: The article presents an alternative method of obtaining aluminium cast iron in the process of self-propagating high-temperature synthesis from disperse waste of machine-building enterprises. The deficiencies of the traditional methods for obtaining structural iron castings with aluminum are established. The analysis of the factors influencing the strength of the SHS aluminium cast iron, the planned experiment for obtaining the maximum strength of SHS aluminium cast iron for two input factors varying at three levels and three parallel observations were carried out. The statistical processing of experimental results is performed. The mathematical model is obtained for the dependence of operational factors on the composition of the charge of the SHS process. The significance of the regression coefficients of the equation is determined. The adequacy of the obtained equation is checked for the results of observations. The analysis of the conditions for the formation of the microstructure of aluminium cast iron in the process of SHS-casting is presented.

Abstract: The high-temperature corrosion behavior of Ni₃Al+2.9 wt% Cr alloy was studied in SO₂-containing environment. Corrosion tests were carried out at 900, 1000, and 1100 °C for 100 h in atmospheric Ar-0.2% SO₂ gas. The alloy corroded relatively slowly due mainly to formation of Al₂O₃ in the scale. Its corrosion kinetics deviated from the parabolic corrosion rate law to a certain extent owing to ensuing scale spallation. This was attributed to (1) stress generated during scaling and the subsequent cooling period, (2) voids that formed due to the Kirkendall effect, and (3) incorporation of sulfur in the scale. The scale that formed after corrosion at 900 °C consisted of the outer NiO scale, middle NiAl₂O₄ scale, and inner Al₂O₃ scale. The increased corrosion rate at 1000 and 1100 °C led to formation of the outer NiO scale, and inner Al₂O₃ scale.

Abstract: During recent years, several experiences have been executed for interfering in inefficient urban fabrics, all of them had been forced on the basis of centralized intervention approach; determining a territory as the project range, funding sources, ownership, execution, utilization, is a single process , the attribution of which could be found in several cases in the country. The important point in this regards which determines the future strategies is the performance process and method. The global examples and local experiences show that all approaches, plans and executive plans should be developed and materialized on the basis of “people participation” principle. This procedure is executable in various forms; reinforcement of existing buildings, renovation of single parcel and assemblage of small sized parcels are the methods that play important role in this process. The present paper studies different scales of “assemblage” as one of the methods of housing renovation and by using analytic hierarchy model AHP method proves that assemblage in urban block scale by citizenship participation could serve both as a tool for improving land distribution pattern, and, providing new opportunities for the city to develop. The indexes that are used in this survey were selected by literature review and attribution to several executive plan cases.

Abstract: The oxidation behavior of Fe-20Ni alloy under compressive stress in air was studied at 800, 900 °C. The results examined by using scanning electron microscope (SEM) and X-ray diffraction (XRD) indicates that the oxide scales were consisted of an external scale and a subscale which has an intragranular scale (above 5 h at 800 °C and 900 °C) and an intergranular scale. Compared with the unstressed specimen, the growth kinetics of external scale was accelerated by an applied compressive stress. Besides, the compressive stress induced an increase in the growths of intragranular scale and intergranular scale formed on the specimens oxidized at 900 °C. However, the effect of compressive stress on the growth of intergranular scale and intragranular scale was not obvious in the case of 800°C. In addition, cracks developed in the subscale for the specimens oxidized under 2.5 MPa compressive stress when the oxidation time exceeded 20 h.

Abstract: The oxygen permeability of polycrystalline α-alumina wafers, which served as model alumina scales formed on heat-resistant alloys, was evaluated at a temperature of 1873 K. Mass transfer along grain boundaries (GBs) in an alumina wafer exposed to a large oxygen potential gradient (dμ_O), where both oxygen and aluminum mutually diffuse along GBs, was analyzed using ¹⁸O₂ and SIMS. ¹⁸O was concentrated at GB ridges on the high oxygen partial pressure (P_O2(hi)) surface and along the GBs near the P_O2(hi) surface. ¹⁸O adsorbed on the surface diffused almost immediately to surface GBs, resulting in the formation of new alumina by reaction with aluminum diffusing outward along the GBs. Oxygen GB diffusion coefficients in the vicinity of the P_O2(hi) surface were determined from the ¹⁸O depth profile along each GB for the ¹⁸O map of the cross section of the exposed alumina wafer. The oxygen GB diffusion coefficients were comparable to the values calculated from the oxygen permeability constants assuming an electronic conductivity and were obviously lower than those of oxygen GB self-diffusion without an oxygen potential gradient.

Abstract: The application of steel products have been widely used and various research have been developed to find a good and appropriate quality of steel and can be produced in the country without have to be imported, for example alloy steels. One of the alloy steels that have been constantly developed is Ni-Cr-Mo alloy steel with additional nickel, chromium and molybdenum which can increase hardness, tensile strength, ductility and toughness. The effect during the production process is at the heating process that causes the formation of iron oxide layer (scale) and the loss of steel weight. Therefore, the selection of heat treatment methods and techniques are required to increase the mechanical properties of steel, such as hardness, tensile strength, and toughness, with the scale is about <5% of steel weight. In this research, the heat treatment was carried out at austenisation temperature of 800°, 850°, 900°C and at holding time of 20, 40, 60 minutes, then followed by a rapid cooling (quenching) to improve the mechanical properties of hardness. This research also tested the mechanical properties of steel that consist of hardness test and impact test, and metallographic observation that consist of micro structure observation and scale thickness observation. The micro structure from heat treatment process is martensite, it is due to a rapid cooling (quenching) that rapidly change the austenite phase into martensite. The data showed the highest hardness is 588.35 HVN at 850°C of temperature and 60 minutes of holding time, 8.5 Joules of impact energy, and 91.5 μm of scale thickness. While the lowest hardness is 539.34 HVN at 800°C of temperature, 5 Joules of impact energy, and 47.81 μm of scale thickness.

Abstract: SUS 310 stainless steels were corroded at 600, 700 and 800°C for up to 30 h in 1 atm of N₂/H₂O/H₂S-mixed gas. The formed scales consisted primarily of (Fe_0.5Ni_0.5)_0.96S, FeNiS₂, and FeCr₂S₄. They were fragile, porous, and susceptible to spallation. During corrosion, Fe, Ni, and Mn diffused outward, while sulfur and a lesser amount of oxygen diffused inward. The diffusion of Cr and Si was not conspicuous. The formation of sulfide scales and the presence of hydrogen and water vapor in the mixed gases made SUS 310 corrode fast.