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The influence of iron impurities on the compression behaviour of Al-2.24Mg-2.09Li alloy
No full textAs a major impurity element in aluminium-lithium (Al-Li) alloys, iron (Fe) reduces formability, fracture toughness, and
fatigue resistance by solidifying into Al6Fe and Al3Fe particles. The research was performed in order to estimate the
influence of Fe impurities on the compression behaviour of Al-2.24Mg-2.09Li alloy. The investigation was performed on
the samples in as cast and solution hardened condition. The solution hardening was applied to improve the mechanical
properties by dissolving intermetallic particles and enriching αAl matrix with Mg. However, the higher strength properties
and temperature increase during the compression testing were observed in as cast condition. Microstructural investigation
revealed significant differences in microstructure changes between the samples in as cast and solution hardened condition.
In as cast sample the barrelling effect led to the unequal deformation and surface texture development. The eutectic Al3Fe
particles located in the αAl interdendritic areas did not significantly impact microstructure changes. Although the solution
hardening led to enrichment of αAl matrix with Mg and Fe, the Al3Fe particles were not dissolved. The coarse morphology
of Al3Fe particles and location at the grain boundaries of αAl grains contributed to low energy intergranular fracture. The
fracture nucleation and propagation across the grain boundaries resulted in lower strength values
Electrochemical investigations of corrosion behavior of gray and nodular cast iron in the medium of artificial seawater
No full textU ovom radu provedena su elektrokemijska ispitivanja sivog i nodularnog lijeva u mediju obične vode i umjetne morske vode u cilju preporuke koji od navedenih materijala je prikladniji za upotrebu u morskoj vodi. Rezultati dobiveni potenciodinamičkom polarizacijom ukazuju na sličnu korozijsku otpornost sivog i nodularnog lijeva u običnoj vodi, za razliku od medija umjetne morske vode, gdje je manju brzinu korozije pokazao nodularni lijev.
Metalografska analiza ispitanih ljevova nakon korozije u umjetnoj morskoj vodi ukazuje na činjenicu da korozja ravnomjerno zahvaća metalnu osnovu (perlit), dok kloridni ioni iz otopine selektivno nagrizaju listiće grafita kod sivog lijeva. Kod nodularnog lijeva kloridni ioni selektivno napadaju metalnu osnovu (perlit).
S obzirom na dobivene rezultate može se zaključiti da je uzorak ispitanog nodularnog lijeva korozijski otporniji u mediju umjetne morske vode od ispitanog uzorka sivog lijeva. Međutim, s obzirom na dobivene iznose brzine korozije, ispitani ljevovi se ne preporučuju za primjenu u morskoj vodi.In this paper, electrochemical investigations of gray and nodular cast irons in the medium of tap water and artificial seawater were carried out in order to recommend which of these materials is more suitable for use in seawater. The results obtained by potentiodynamic polarization indicate a similar corrosion resistance of gray and nodular cast irons in tap water, unlike artificial seawater media, where nodular cast iron showed a lower corrosion rate.
Metallographic analysis of the investigated casts after corrosion in artificial seawater indicates the fact that the corrosion evenly affects the metal base (perlite), while chloride ions from the solution selectively corrode the graphite flakes in gray cast iron. In nodular cast iron, chloride ions selectively attack the metal base (perlite).
Considering the obtained results, it can be concluded that the sample of the tested nodular cast iron is more corrosion resistant in the medium of artificial seawater than the tested sample of gray cast iron. However, given the corrosion rate values obtained, the examined cast irons are not recommended for use in seawater
Influence of cooling rate on microstructure development of AlSi9MgMn alloy
No full textAluminum alloys are widely applied in automotive, aircraft, food, and building industries. Multicomponent technical
AlSi9MgMn alloy is primarily intended for high cooling rate technology. Controlled addition of alloying elements such as
iron and manganese as well as magnesium can improve mechanical and technological properties of the final casting
depending on the cooling conditions during solidification.
The aim of this investigation is the characterization of AlSi9MgMn alloy microstructure and mechanical properties at lower
cooling rates than those for which this alloy was primarily developed. Thermodynamic calculation and thermal analyses
revealed solidification sequence in correlation to the microstructure investigation as follows: development of primary
dendrite network, precipitation of high temperature Al15(Mn,Fe)3Si2 and Al5FeSi phases, main eutectic reaction,
precipitation of intermetallic Al8Mg3FeSi6 phase, and Mg2Si as a final solidifying phase. Influence of microstructure features
investigation and cooling rate reveals significant Al15(Mn,Fe)3Si2 morphology change from Chinese script morphology at
low, irregular broken Chinese script morphology at medium, and globular morphology at high cooling rate. High
manganese content in AlSi9MgMn alloy together with high cooling rate enables the increase of Fe+Mn total amount in the
intermetallic Al15(Mn,Fe)3Si2 phase and encourage favourable morphology development, all resulting in enhanced
mechanical properties in as-cast state
Influence of the magnesite lime on the refractory wall in an electric arc furnace
No full textDanas je elektropećni postupak dobivanja čelika jedan od najzastupljenijih u svijetu stoga je bitno daljnje unapređenje procesa s ciljem što bolje učinkovitosti te sa time i smanjenjem troškova i utjecaja na okoliš. Jedan od velikih faktora u ekološkom i financijskom smislu je remont vatrostalnog dijela peći gdje nastaju velike količine istrošenog vatrostalnog materijala.
Na vatrostalni obzid peći utječu različiti čimbenici a jedan od najvažnijih je troska. Troska se u osnovi dobiva dodatkom vapna u uložak, a sastav vapna uvelike utječe na proces proizvodnje čelika. Koriste se vapna na osnovi kalcija (CaO) i vapna na osnovi magnezija (MgO). U ovom radu će biti istražen utjecaj dodatka magnezitnog vapna u elektrolučnu peć na procese odsumporavanja i odfosforavanjate na trošenje vatrostalnog obzida uz osvrt i na sami remont peći.Today, the electric arc furnace process of steel production is one of the most common in the world, so it is important to further improve the process with the aim of better efficiency and thus reduce costs and environmental impact. One of the major factors in environmental and financial terms is the overhaul of the refractory part of the furnace where large amounts of spent refractory material are generated.
The life of refractory wall of the furnace is affected by various factors and one of the most important is slag. The slag is basically obtained by adding lime to the bucket with cartridge, and the composition of the lime greatly influences the steel production process. Calcium-based lime (CaO) and magnesium-based lime (MgO) are used. In this paper, the influence of the addition of magnesite lime to the electric arc furnace on the processes of desulphurization and phosphorization and on the wear of the refractory wall with a review on the furnace overhaul itself will be investigated
The Interdependence of the Degree of Precipitation and Dislocation Density during the Thermomechanical Treatment of Microalloyed Niobium Steel
No full textIn this paper, thermomechanical processing of niobium microalloyed steel was performed with the purpose of determining the interaction between niobium precipitates and dislocations, as well as determining the influence of the temperature of final deformation on the degree of precipitation and dislocation density. Two variants of thermomechanical processing with dierent final rolling temperatures were carried out. Samples were studied using electrochemical isolation with an atomic absorption spectrometer, transmission electron microscopy, X-ray diraction analysis, and universal tensile testing with a thermographic camera. The results show that the increase in the density of dislocations before the onset of intense precipitation is insignificant because the recrystallization process takes place simultaneously. It increases with the onset of strain-induced precipitation. In this paper, it is shown that niobium precipitates determine the density of dislocations. The appearance of Lüders bands was noticed as a consequence of the interaction between niobium precipitates and dislocations during the subsequent cold deformation. In both variants of the industrial process performed on the cold deformed strip, Lüders bands appeare
Pollution in the marine ecosystem at oil transportation
No full textVoda, more, oceani imaju neprocjenjivo ekološko značenje. Zaštita i očuvanje kvaliteta voda,
mora i oceana važna su ne samo za životinjski i biljni svijet, nego i za samog čovjeka te za
njegov gospodarski i socijalni razvoj. S druge strane, nafta je važan energent industrijske
civilizacije i prijeko potrebna našem društvu, jednostavno bi svakodnevni život čovjeka bio
nezamisliv bez nafte i njenih derivata. Upravo transport nafte pomorskim putem zauzima
važnu gospodarsku granu, koja koristi naftovode i specijalno opremljene tankere za prijevoz
nafte. Nažalost, svjedoci smo da su uz transport nafte neizbježne i tankerske nesreće koje
uzrokuju trajne rizike za onečišćenje mora. Izlijevanje nafte u morski okoliš neželjena je
„katastrofa“ s teškim posljedicama koja narušava opstanak flore i faune te posljedično nanosi
trajnu štetu morskom ekosustavu a time i samom čovjeku. Svako onečišćenje morskog okoliša
naftom uzrokuju ozbiljne posljedice za biljni i životinjski svijet u moru kao i za ljude koji žive
u blizini onečišćenog područja što utječe na njihovu cjelokupnu kvalitetu života.
U ovom radu obuhvaćen je pregled najvećih tankerskih nesreća i njihov utjecaj na
okoliš, koje su se dogodile tijekom prošlog i početkom ovog stoljeća. Opisane su najveće
tankerske nesreće čije se posljedice osjećaju i danas. Izdvojena je i Marpol konvencija,
međunarodna konvencija koja uključuje propise sprječavanja onečišćenja morskog okoliša
brodovima iz operativnih ili slučajnih uzroka koju je usvojila i primjenjuje i Republika
Hrvatska.Water, sea, oceans have invaluable ecological significance. The protection and preservation of
the quality of water, sea and ocean are important not only for the flora and fauna, but also for
the humans itself and for our economic and social development. On the other hand, oil is an
important source of energy of industrial civilization and is irreplaceable for our society,
simply daily human life would be unthinkable without oil and its derivatives. The transport of
oil by sea occupies an important economic branch, which uses oil pipelines and specially
equipped tankers to transport oil. Unfortunately, we are witnessing that, in addition to the
transport of oil, tanker accidents are inevitable, which cause permanent risks for marine
pollutions. An oil spill into the marine environment is an unwanted "catastrophe" with severe
consequences that disrupts the survival of flora and fauna and consequently causes permanent
damage to the marine ecosystem and thus to human himself. Any pollution of the marine
environment with oil causes serious consequences for the flora and fauna of the sea as well as
for people who lives near the polluted area, which affects their overall quality of life.
This work includes an overview of the largest tanker accidents and their impact on the
environment, which occurred during the last and the beginning of this century. The biggest
tanker accidents are described and the consequences of which are still felt today. The Marpol
Convention, an international convention that includes regulations for the prevention of
pollution of the marine environment by ships from operational or accidental causes, which has
been adopted and applied by the Republic of Croatia, has also been singled out
Heavy metals in water
No full textZagađenje vode povezano je s geološkim karakteristikama nalazišta vode, ali i industrijskom i ljudskom djelatnošću. Obzirom na važnost vode za živi svijet bitno je vodu što manje zagaditi, a ako je već zagađena adekvatno ju pročistiti. Jedno od značajnih zagađenja vode je zagađenje teškim metalima. Ulaskom u vodeni ekosustav, teški metali u njemu kruže i vrlo često se akumuliraju. Teški metali koji su izrazito toksični su arsen, olovo, živa, kadmij, krom, bakar i nikal. Obzirom na njihov izrazito negativan utjecaj na ljudsko zdravlje u smislu prolaznih smetnji, ali i mutacija i letalnih ishoda neophodno ih je ukloniti iz vode. Uklanjanje se može provesti različitim metodama, poput koagulacije i flokulacije, kemijskog taloženja, flotacije, ionske izmjene, elektrokemijske metode i adsorpcije. Odabir metode ovisi o različitim čimbenicima: vrsti teških metala i njihovoj koncentraciji u vodi, temperaturi i pH vrijednosti vode i sl. U ovom završnom radu dat je pregled najčešćih teških metala, njihove toksičnosti kao i pregled najčešćih metoda za uklanjanje teških metala.Water pollution is related to the geological characteristics of the water site, but also to industrial and human activity. Considering the importance of water for the living world, it is important to pollute the water as little as possible, and if it is already contaminated, adequately purify it. One of the significant water pollution is heavy metal pollution. When they enter the aquatic ecosystem, heavy metals circulate and accumulate very often. Heavy metals that are highly toxic are arsenic, lead, mercury, cadmium, chromium, copper and nickel. Considering their extremely negative impact on human health in terms of transient disturbances, but also of mutations and lethal outcomes, it is necessary to remove them from the water. Removal may be carried out by various methods, such as coagulation and flocculation, chemical precipitation, flotation, ion exchange, electrochemical method and adsorption. The choice of method depends on various factors: the type of heavy metals and their concentration in water, temperature and pH of the water, etc. This final thesis provides an overview of the most common heavy metals, their toxicity, and an overview of the most common heavy metal removal methods
Atmospheric corrosion of metals and metal alloys
No full textU ovom radu definirana je atmosferska korozija te je dana njezina podjela prema stupnju vlažnosti korodirajuće površine. Pobliže je objašnjen mehanizam atmosferske korozije te su opisani faktori koji utječu na brzinu atmosferske korozije. Sve navedeno je pobliže prikazano primjerima atmosferske korozije metala i metalnih legura te su navedene određene metode njihove zaštite od navedenog tipa korozije.In this paper, atmospheric corrosion is defined and its division according to the degree of humidity of the corroding surface is given. The mechanism of atmospheric corrosion is explained in more detail and the influence of factors on the atmospheric corrosion rate is described. All of the above are presented in detail with examples of atmospheric corrosion of metals and metal alloys, and certain methods of their protection against the specified type of corrosion are listed
Microstructure and properties of silicon alloyed compacted graphite irons (CGI)
No full textThe microstructure, tensile properties and hardness of 25 mm thick compacted graphite iron samples alloyed with 3, 01, 3, 22, 3, 61, 3, 97 and 4, 29 wt. % Si were analyzed in this paper. It was found that Si promotes and strengthens ferrite. Metallic matrix of compacted graphite iron sample alloyed with 3, 01 wt. % Si consisted of 98, 1 % ferrite and 1, 9 % pearlite. Fully ferritic metallic matrix was obtained in compacted graphite iron samples alloyed with 3, 22, 3, 61, 3, 97 and 4, 29 wt. % Si. Nodularity varied from 8 to 13 %. Yield strength increased from 246 to 447 N/mm2, tensile strength increased from 318 to 496 N/mm2, hardness increased from 160 to 227 HBW, and elongation decreased from 3, 6 to 1, 6 % with an increase in Si content from 3, 01 to 4, 29 wt. %. Analyzed Si alloyed compacted graphite iron samples have a very uniform hardness and higher ratio Rp02/Rp02 than conventional ferritic, ferritic-pearlitic and pearlitic compacted graphite iron grades
Phase transformations in Cu-based alloys
No full textLegure s prisjetljivosti oblika (SMA) karakteriziraju dva bitna efekta, psudoelastičnost i efekt prisjetljivosti oblika, koji su posljedica austenitno-martenzitne fazne transformacije. Općenito, efekt prisjetljivosti oblika označava sposobnost materijala da se uslijed djelovanja temperature ili mehaničkog naprezanja vraća u svoj prethodno definirani oblik. Temperatura transformacije SMA legura određuje područje primjene ovih materijala te se variranjem udjela komponenti u leguri može korigirati temperatura transformacije, kao i dizajnirati finalna svojstva materijala za specifična područja primjene. Mikrostrukturna ispitivanja, kojima se prati razvoj martenzita, provode se svjetlosnom mikroskopijom (OM) ili skenirajućom elektronskom mikroskopijom (SEM). Kako bi se ispitala toplinska svojstva SMA legura i odredile temperature transformacije, koriste se metode toplinske analize poput diferencijalne pretražne kalorimetrije (DSC), dilatometrije (DIL) te dinamičko-mehaničke analize (DMA).Shape memory alloys (SMA) show two unique efffects, pseudoelasticity and shape memory effect, which are consequenceof austenitic-martensitic phase transformations. Shape memory effect describes the effect of restoring the original shape under thermal changes or plastic deformation. Martensitic transformation temperatures define application area of SMA alloys, and it is strongly influenced by chemical composition of SMA alloys as well as final properties of material. Microstructure investigations and martensitic formation can be followed by optical microscopy (OM) and scanning electron microscopy (SEM). Thermal properties and transformation temperatures can be determind by thermal analysis techiques, such as differential scanning calorimetry (DSC), dilatometry (DIL) and dynamic-mechanical analysis (DMA)