Repository of Faculty of Metallurgy University of Zagreb
Not a member yet
491 research outputs found
Sort by
Influence of medium and microstructure on corrosion behavior of gray cast iron
Get PDFU ovom radu ispitana je korozijska otpornost sivog lijeva u mediju umjetne kiše i mediju 0,5 M H2SO4 te utjecaj mikostrukture na njegovo korozijsko ponašanje u navedenim medijima. Tafelovom ekstrapolacijom polarizacijskih krivulja je ustanovljeno da ispitani sivi lijev pokazuje izrazito veliku brzinu korozije u kiselom mediju za razliku od ispitivanja u mediju umjetne kiše, gdje brzina korozije poprima znatno manju vrijednost. Međutim, u usporedbi s rezultatima ranijih istraživanja dobivenim za nodularni lijev te su vrijednosti trostruko vede, što upuduje na činjenicu da je nodularni lijev ipak korozijski otporniji u uvjetima atmosferske korozije te stoga i prihvatljiviji za izradu dijelova za poljoprivredne strojeve. Dobiveni rezultati su potvrđeni i metodom elektrokemijske impedancijske spektroskopije, pri čemu je u mediju umjetne kiše za sivi lijev registriran manji otpor prijenosu naboja od nodularnog lijeva. To ukazuje na činjenicu da se na sivom lijevu formirao tanji sloj, koji predstavlja slabu barijeru prema prodiranju agresivnih iona iz otopine. Dobiveno korozijsko ponašanje sivog lijeva u ispitanim medijima može se povezati i s njegovom mikrostrukturom. Naime agresivni ioni iz primijenjenih medija napadaju metalnu osnovu ispitanih materijala, dok grafit zadržava svoj prvobitni oblik. Pri usporedbi s nodularnim lijevom, nodule su se pokazale kao povoljniji oblik izlučenog grafita jer bolje prekrivaju površinu uzorka i slijedom navedenog izoliraju uzorak u procesu elektrokemijske korozije.This paper investigated the corrosion resistance of gray cast iron in the medium of artificial rain and 0.5 M H2SO4 medium and the effect of microstructure on its corrosion behavior in the mentioned media. By Tafel's extrapolation of the polarization curves, it was found that the examined gray cast iron shows an extremely high corrosion rate in the acidic medium, as opposed to the artificial rain test, where the corrosion rate is much lower. However, compared with the results of earlier researches obtained for nodular cast iron these values are three times higher, indicating that the nodular cast iron is more corrosion-resistant to atmospheric corrosion and therefore more acceptable for the manufacture of parts for agricultural machines. The obtained results were confirmed by the method of electrochemical impedance spectroscopy, where in the medium of artificial rain lower value of charge transfer resistance of gray cast iron was registered in opposite to nodular cast iron. These points to the fact that a thin layer formed on the gray cast iron, which represents a weak barrier to penetrating aggressive ions from the solution. The corrosion behavior of the gray cast iron in the tested media can also be related to its microstructure. Namely, aggressive ions from the applied media attack the metal matrix of the examined materials, while the graphite retains its original form. When compared to nodular cast iron, the nodules seems to be a more favorable form of precipitated graphite due to better sample surface covering and therefore the insulation in electrochemical corrosion process
Industrial control measurements of high chromium steel rolls heat treatment
Get PDFIn this paper, industrial control measurements of the heat treatment of high chromium steel (HCS) rolls is presented. Measurements of the gas fired car bottom chamber furnace Bosio PP- KP 70/1150 were carried out in the company Valji d. o. o., Štore, Slovenia. Temperature in the individual heating zones of the furnace, temperatures of the roll surface, furnace external walls, and gas consumption was monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement, and the amount of retained austenite in the heat treated rolls
The effect of heat treatment on the microstructure and mechanical properties of Cu- Al-Mn shape memory alloy
Get PDFThe 8 mm diameter bars of Cu-Al-Mn shape memory alloys were produced by continuous casting technique. The samples were characterised using optical microscopy and scanning electron microscopy along with EDX analysis. The continuous cast alloy revealed some martensitic phase which, after quenching, led to the microstructure that is completely martensite. Quenching of samples had an effect on several mechanical properties and change in morphology of fracture. After ageing at 200 °C and 300 °C the tensile strength increased and elongation is drastically decreased. Morphology of fracture surface was changed from primary ductile to a mixture of intergranular and ductile
Effect of bismuth and rare earth elements on graphite structure in different section thicknesses of spheroidal graphite cast iron castings
No full textEffects of additions of 0.00064, 0.001 and 0.0042 wt.% Bi on the graphite structure in the section thicknesses of 3, 12, 25, 38, 50, 75 and 100 mm of spheroidal graphite cast iron castings containing 2.11 wt.% Si and rare earth (RE) elements (Ce + La + Nd + Pr + Sm + Gd) in the range from 0.00297 to 0.00337 wt.% were analyzed in this paper. Addition of Bi was not necessary for obtaining high nodule count and nodularity higher than 80% in section thicknesses of 3, 12 and 25 mm. RE elements showed a beneficial effect on the nodule count and nodularity in these sections. Nodularity was below 80% in section thicknesses of 38 , 50, 75 and 100 mm when Bi was not added. Detrimental effect of RE elements on graphite morphology in these sections was neutral- ized by adequate addition of Bi. Addition of 0.001 wt.% Bi (ratio of RE/Bi = 3.27) was enough to achieve nodularity above 80% in the section thickness of 38 mm. Nodularity was increased above 80% in section thicknesses of 50, 75 and 100 mm by addition of 0.0042 wt.% Bi (ratio of RE/Bi = 0.78). At the same time, Bi significantly increased the nodule count. Nodularity above 80% and the high nodule count in the section thicknesses of 75 and 100 mm were also achieved by using an external metallic chill in the mold. In this case, addition of Bi was not required
Optimization of the circular manhole cover made of ductile cast iron using finite element method
No full textIn this paper, in order to dimension the position and the number of vertical reinforcement, several numerical linear static simulations of bending circular manhole cover of ductile cast iron (grade EN-GJS-500-7) with 600 mm diameter are performed. The analysis of displacement and stress using the finite element method in the software package Autodesk Simulation Mechanical were conducted. Verification of numerical results for the solution of thin circular plate was performed with analytical bending solutions. After checking the numerical procedure on the thin circular plate, two circular vertical reinforcements were added on the underside: internal and external. Numerical simulations investigated the influence of the inner circular reinforcement position on the strength of the circular manhole cover, while equivalent stresses followed by energy theory of strength (von Mises) were monitored. Since maximal equivalent stresses remain on the plate by varying the position of the inner circular reinforcement, simulations with added radial reinforcements are performed. Finally, by optimizing the number of radial reinforcements, the optimum plate design is chosen
Selenium, Sulphur, Trace Metal, and BTEX Levels in Soil, Water, and Lettuce from the Croatian Raša Bay Contaminated by Superhigh-Organic- Sulphur Coal
Get PDFThis paper elaborates soil, water, and lettuce contamination status with respect to selenium, sulphur, trace metals, and BTEX (benzene, toluene, ethylbenzene, and xylenes) in a coal- based area (Raša Bay, Adriatic Sea, Croatia). A local coal-fired power plant polluted soil with S, Se, Cd, and PAHs due to the combustion of domestic superhigh-organic-sulphur coal. The locality is dotted with waste from coal mining/separation, coal combustion, former metal factories, untreated municipal and coal mine effluents, along with various harbour activities, which contribute to environmental contamination. The methodology involved ICP-MS and GC-MS for the measurement of trace elements and BTEX, respectively, while soil sulphur was determined with Eschka’s mixture. The max values of the analysed trace elements in soil (mg/kg) are reported: Hg 1.14, Cd 3.29, V 624, Se 10.3, Pb 872, Cr 1860, Zn 6580, Cu 1850, and U 25.2. According to ecological indices, these values fall into the category of an extremely high level of soil pollution. Elevated total Se values in surface water are ascribed to leaching of seleniferous coal, ash, and coal- polluted soil. Levels of BTEX in water samples were very low (0–0.83 g/L). The data provide basic information on the inorganic and organic contamination status of the Raša Bay area
Hexavalent chromium adsorption capability onto carbon black: kinetic and thermodynamic aspects
Get PDFThe adsorption rate and dynamic behaviour of the system are important factors in the process design and operation control. The aim of this study was to find a suitable kinetic model for the hexavalent chromium removal in a batch reactor. The experimental data were analyzed using four adsorption kinetic models – the pseudo first- and second-order equations, the Elovich equation and intraparticle diffusion equation – so as to determine the best fit equation for the adsorption of Cr(VI) onto the carbon black. The rate constants and related correlation coefficients for each kinetic model were calculated and discussed. Also, the predicted qe, cal values from the kinetic equations were compared with the experimental data. Results showed that the pseudo second- order equation provides the best correlation for the adsorption process, whereas the Elovich equation also good fits with the experimental data. The values of the thermodynamics parameters, including the energy of activation, suggest that physisorption is dominant for the adsorption of Cr(VI) onto the carbon black
Atomistic simulations of deformations in metals
Get PDFMolekularna dinamika je metoda u kojoj se gibanje svakog pojedinog atoma ili molekule izračunava izravnom primjenom Newtonovih zakona (posebno 2.). Praktičan račun će uključiti veliki broj čestica, od nekoliko desetina do čak nekoliko milijuna. U tako složenim proračunima nužno je koristiti kompjutorsko simuliranje jer je kompleksni izračun nemoguće obaviti analitički za inženjerski relevantne sisteme. Makroskopske veličine se dobivaju statističkom obradom mikroskopskih putanja čestica. To je alat koji možemo koristiti za razumijevanje makroskopske fizike polazeći od atomskih fenomena. Ova metoda posljednjih godina doživljava veliki uzlet i ima široku primjenu za proračun termodinamičkih svojstava plinova, kapljevina i čvrste tvari. U ovom radu ćemo predstaviti simulaciju jednostavnog, ali iznimno važnog eksperimenta jednoosnog istezanja gredice aluminija korištenjem realnog međuatomskog potencijala pri čemu ćemo odrediti krivulju naprezanja-deformacija za sisteme pri različitim temperaturama te ih međusobno usporediti.Molecular dynamics is a method of calculating the motion of each individual atom or molecule utilizing Newton's laws of motion (in particular the 2nd law). The practical approach will include a large number of particles, from several dozens to even a few million. In such a complex calculation, the use of computer simulations is a must because the complex calculation cannot be done analytically for engineering relevant systems. Macroscopic physical quantities are going to be obtained by using statistical analysis of the microscopic particle trajectories. It is a tool for enhancing our understanding of the macroscopic physics starting from atomistic phenomena. This method has received a large boost within the last few years and has found application in the calculation of thermodynamic properties of gases, liquids, and solids. In this work, we shall present a simulation of a simple, but exceptional, uniaxial tensile test of an aluminum bar based on the realistic interatomic potential. We shall determine the stress-strain curve at different temperatures and compare them.
Inorganic ingredients in coal
Get PDFUgljen je heterogeni materijal sastavljen od organskih i anorganskih sastojaka. Anorganski sastojci u obliku minerala i organski vezanih anorganskih elemenata nalaze se u ugljenu kao elementi različitih masenih udjela i elementi u tragovima. Način pojavljivanja i vrste elementa u ugljenu su važan parametar o kojem ovisi ponašanje elemenata za vrijeme pretvorbe ugljena u druge oblike tvari i energije. Anorganski sastojci u ugljenu utječu na tehnološke parametre, okoliš, zdravlje ljudi i postupke recikliranja.
U ovom radu je dan pregled relevantne literature s općenitim informacijama o ugljenu,
pojavnim oblicima, vrsti i sadržaju anorganskih elemenata u ugljenu, načinima njihovog određivanja i utjecaju na okoliš.
Ugljen, kao važan izvor energije i sirovina za proizvodnju drugih ugljičnih materijala i plinova i dalje će se koristiti zbog relativno velikih rezervi. Međutim, postoji sukob između potreba za povećanjem korištenja ugljena s jedne strane i manjeg onečišćenja s druge strane.Coal is a heterogeneous material composed of organic and inorganic constituents. Inorganic ingredients in the form of minerals and organo-bound inorganic elements are found in coal as elements of different weight ratios and trace elements. The appearance and type of elements are an important parameter that depends on the behavior of elements during the conversion of coal to other forms of matter and energy. Inorganic ingredients influence on the technological parameters, environment, human health and recycling processes.
This paper presents a review of relevant literature with general information on coal,
appearance forms, type and content of inorganic elements, methods of their determination and their impact on the environment.
Coal as an important source of energy and raw materials for the production of other carbon materials and gases will continue to be used because of relatively large reserves. However, there is a conflict between the need to increase coal use on the one hand and lower pollution on the other
Corrosion behavior of CuAlNiMn in 0.9% NaCl solution
Get PDFThe corrosion behavior of the CuAlNiMn alloy in 0.9% NaCl solution at pH 7.4, and temperatures of 25, 37 and 50 oC, was investigated by electrochemical methods such as monitoring the open circuit potential, linear and potentiodynamic polarization methods. Investigations were also performed in 0.9% NaCl solution at 37 oC and different pH of solution (pH = 3.4, 5.4 and 7.4). Results of the investigations have shown that increasing the temperature leads to the shift of the open circuit potential values in the negative direction and also leads to increase of the corrosion current density and decrease of the polarization resistance values. Decreasing the pH of solution leads to the increase of the corrosion current density and decrease the values of polarization resistance. After the polarization measurements, corroded electrode surfaces was examined using an optical microscope and SEM. Microscopic images have shown the significant corrosion damages on the CuAlNiMn alloy surface, which manifests itself in the form of a thin leaf, with a larger part of the surface being covered with sheets of corrosion products loosely bonded to the surface which were elevated from the surface of the electrode. SEM surface analysis revealed the existence of two layers on the surface of the alloy: the exterior is extremely damaged, which represent sheets of loosely bonded surface, and an inner layer that also shows significant corrosion damage. The elemental composition of corrosion products on the surface of the samples was determined by EDS analysis