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Chemical preparation of tubes before cold drawing
No full textPrior to the technological process of cold drawing of tubes through dies, a very important part is preparation for drawing and pre-treatment of tubes. In the production of cold drawn tubes, pre-treatment involves the chemical removing of impurities and oxides, and subsequently applying the lubricant on to the surface of the tubes. For cleaning, pickling, bath of hydrochloric or sulphuric acid is the most commonly used cleaning agent, which is kept at elevated temperatures. This is a significant problem from an environmental point of view, since it is performed at higher temperatures and with chemically aggressive media. This review paper describes the existing procedures for the chemical preparation of niobium microalloyed steel tubes and the ways of reducing the impact on environment, as well as new approaches that are possible alternatives for surface preparation, without the usage of chemically aggressive media
Analysis of the crack formation in ASIS M2 high- speed tool steel during utilization
No full textTool steels are carbon, alloyed or high-speed steels, produced and processed under the tool steel manufacturing practices to meet special requirements. The advancements in tool steel engineering properties enabled work efficiency improvements in industrial applications. The high-speed tool steels (HSS) are complex iron- based alloys containing carbon, chromium, vanadium, molybdenum, tungsten or substitutional amount of cobalt. The chemical composition of HSS is designed to achieve the highest attainable hardening response, high wear resistance, high resistance to softening effect at elevated temperatures, and good toughness necessary for effective use in industrial cutting operations. The ASIS M2 is a molybdenum- based medium alloyed HSS with good machinability. Favorably designed chemical composition and adequately performed heat treatment assure good combination of toughness, wear resistance and hardness enabling its utilization as twist drills, taps, milling cutters, saws, and knives. It is also commonly used as cold work punches. The research was performed on two samples of ASIS M2 punchers to estimate the cause of the shorter service life. In sample 1 the crack nucleation occurred after 50.000 punched marks, while in sample 2 cracking initiated after 20.000 punched marks. To indicate the cause of sample 2 shorter service life, the results of chemical composition analysis, metallographic analysis, and microhardness measurements were compared. The higher amount of carbide forming elements in sample 2 led to the solidification of higher number of eutectic carbides and precipitation of secondary carbides in intercellular regions. The microstructure analysis indicated significantly higher number of carbide particles in sample 2. The presence of carbide particles led to the texture development and impacted crack propagation direction. Higher amount of carbide particles in sample 2 caused higher crack dissipation and material layering with a decrease in crack propagation depth and shorter service life
The influence of microalloying elements on shape memory alloys properties
No full textLegure s prisjetljivosti oblika (SMA) karakteriziraju specifična i jedinstvena svojstva, efekt prisjetljivosti oblika, pseudoelastičnost te superelastičnost. Efekt prisjetljivosti oblika predstavlja sposobnost legure da se vraća u svoj prvobitni oblik pod utjecajem temperaturnih ili mehaničkih naprezanja. Do efekta dolazi zbog fazne transformacije između austenita i martenzita. Danas postoji velik broj legura s prisjetljivosti oblika, a najvažnije su na bazi nikla, bakra i željeza. U svrhu poboljšanja primarne legure dodavaju joj se mikrolegirajući elementi. Utjecaj mikrolegirajućih elemenata na svojstva legura s prisjetljivosti oblika je različit s obzirom na vrstu legure. Dodatak mikrolegirajućih elemenata ima značajan utjecaj na proizvodnju, morfologiju, strukturu te svojstva metala.Shape memory alloys (SMA) are characterized by specific and unique properties, shape memory effect, pseudoelasticity and superelasticity. The shape memory effect is alloys ability to return to its original shape under the influence of temperature or mechanical stresses. The effect is due to the phase transformation between austenite and martensite. Today, there are a large number of alloys with shape memory effect and the most important are based on nickel, copper, and iron. In order to improve the primary alloy, microalloying elements are added to it. The influence of microalloying elements on the properties of shape memory alloys is different depending on the type of the alloy. The addition of micro alloying elements has a significant impact on the production, morphology, structure and alloys properties
The impact of melt retention time on the strontium modification efficiency
No full textThe modification of eutectic (αAl+βSi) phase is frequently
performed during processing of aluminum-silicone (Al-Si) based foundry
alloys leading to a structural transformation of the eutectic βSi phase from a
course plate to a fine fibrous morphology. The morphological refinement
of the brittle eutectic βSi phase improves ductility, tensile strength, and
elongation. This research was performed to estimate the influence of melt
retention time on strontium (Sr) modification efficiency. For this purpose,
the AlSi12 alloy with eutectic composition was produced and processed by
the addition of AlSr10 master alloy. The samples for chemical, mechanical
and microstructure analysis were taken with melt retention time of 20 min,
40 min and 80 min. The results of chemical composition analysis indicated
the decrease in Sr content with the increase in melt retention time. The poor
Sr recovery was a result of the subsequent addition of chemical degassing
agents led to the gas entrapment in the melt. Consequently, the highest gas
index and most severe porosities were found in sample with retention time
of 20 min. The fully modified eutectic (αAl+βSi) phase morphology was only
obtained in sample with retention time of 20 min. After melt retention time
of 40 min the unmodified plate-like eutectic βSi phase particles were found.
Additional prolongation of melt retention time to 80 min led to the
coarsening of eutectic βSi phase particle. The plate-like eutectic βSi phase
particles were located near the primary αAl dendritic network and
surrounding the primary βSi phase particles. This phase distribution
suggests that the transformation of the primary αAl dendritic network is
followed by solidification of unmodified eutectic βSi phase particles
Ispitivanje korozijske otpornosti alatnih čelika za hladni rad u mediju 3,5 % NaCl
No full textU ovom radu provedeno je ispitivanje korozijske otpornosti različitih uzoraka alatnih čelika za hladni rad u mediju vodovodne vode i otopine 3,5 % NaCl pomoću elektrokemijskih metoda. Tafelovom ekstrapolacijom polarizacijskih krivulja dobivena je manja brzina korozije za alatni čelik oznake K340, što dovodi do činjenice da je ispitani uzorak korozijski otporniji od alatnog čelika oznake K100. O tome svjedoče i rezultati impedancijskih mjerenja pomoću kojih je dobiven veći otpor prijenosa naboja za uzorak oznake K340. To znači da se na uzorku oznake K340 formirao deblji zaštitni sloj koji je imao ulogu barijere prodiranju agresivnog kloridnog medija. Nagrizanjem u nitalu vidljiva je mikrostruktura koja se sastoji od ledeburitne metalne osnove i karbida. Uzorak alatnog čelika oznake K340 ima sitnozrnatu strukturu karbida te je zbog toga i korozijski otporniji od uzorka alatnog čelika oznake K100 čija je struktura karbida krupnozrnata. Svjetlosnim mikroskopom nakon elektrokemijskih ispitivanja u 3,5 % NaCl dobivena je metalografska slika oba uzorka iz koje je vidljivo da je uzorak alatnog čelika oznake K100 više korodirao, dok je uzorak alatnog čelika oznake K340 stvorio znatno manji korozijski sloj i to samo uz rubove uzorka. U skladu s dobivenim rezultatima može se zaključiti da se alatni čelik K340 pokazao korozijski otpornijim i u vodi i u kloridnom mediju.In this paper, the corrosion resistance of different samples of tool steels for cold work in a medium of tap water and 3.5 % NaCl solution was performed using electrochemical methods. Tafel extrapolation of polarization curves resulted in a lower corrosion rate for K340 tool steel, which leads to the fact that the tested sample is more corrosion resistant than K100 tool steel. This is evidenced by the results of impedance measurements, which obtained a higher charge transfer resistance for the sample marked K340. This means that a thicker protective layer was formed on the sample marked K340, which acted as a barrier to the penetration of the aggressive chloride medium. Corrosion in the nital reveals a microstructure consisting of a ledeburite metal base and carbide. The K340 tool steel sample has a fine-grained carbide structure and is therefore more corrosion-resistant than the K100 tool steel sample, whose coarbide structure is coarse-grained. Using a light microscope after electrochemical tests in 3.5 % NaCl, a metallographic image of both samples was obtained, which shows that the K100 tool steel sample corroded more, while the K340 tool steel sample created a significantly smaller corrosion layer and only along the edges of the sample. In accordance with the obtained results, it can be concluded that K340 tool steel proved to be more corrosion resistant in both water and chloride medium
The influence of microstructure on hydrogen diffusion and embrittlement of fine-grained high strength dual-phase steels
No full textThe permeation experiments performed in this study have shown that electrochemical corrosion of dual- phase steels in 2 mol L−1 H2SO4 results in hydrogen evolution and absorption of hydrogen atoms in the material, which leads to degradation known as hydrogen embrittlement (HE). The values of the diffusion coefficient and hydrogen solubility obtained in this study have shown that transport of diffusible hydrogen and high susceptibility to HE depends on different microconstituents acting as hydrogen traps in dual-phase steels. The metallographic and SEM/EDS analyses have revealed elongated inclusions in dual-phase steel marked as DP, acting as irreversible traps in the ferrite- martensite matrix. Room temperature tensile tests of hydrogenated specimens have shown degradation of elongation and contraction compared to those of nonhydrogenated ones. SEM analyses of fracture surfaces have revealed the difference between nonhydrogenated dual-phase steels with ductile fracture and hydrogenated dual-phase steels with brittle fracture
Proceedings book; 19th Internatioal foundrymen conference: Humans - Valuable Resource for Foundry Industry Development
No full textKnowledge is becoming an increasingly important resource for economic development. The Republic of Croatia is facing the challenges of the world economy, with the aim to meet certain requirements in shaping the education system. Ensuring the quality assurance of the education system is just one of the requirements set up as a continuous mission of University of Zagreb Faculty of Metallurgy and other co-organizers from the high-education. As the level of education of the population affects the progress of the economy, it is extremely important for the Republic of Croatia to increase the ratio of highly educated persons. In recent years, the ratio of the highly educated population of the Republic of Croatia has been growing, but in comparison with Europe, Croatia is still lagging behind. In order to increase the share of highly educated persons, it is necessary to invest in the quality of education, both in higher education and in secondary and primary education. This would increase awareness of the importance of education, which would ultimately result in an increase in the ratio of highly educated and competent professionals.
Metal industry as a base branch represents an important factor contributing to the economic potential of each country. Current market development as well as technical and economic objective, the production of high-quality, low-cost and environmentally friendly casting, requires application of recent and advanced materials, as well as production technologies, followed and supported by understanding of production process. The metal industry has been recognized as a “driving subdivision” of economy development.
The motto of the 19th International Foundrymen Conference is focused to the HUMANS as a valuable resource for foundry industry development. Human resources have an unavoidable role in scientific, technological and practical aspects concerning research, development and application of casting technology with the common perspective – increase of competitiveness. Special attention will be focused towards the competitiveness ability of foundries, improvement of materials features and casting technologies, environmental protection as well as subjects connected to the application of castings
Comparison of acetic acid adsorption kinetics on different waste materials
No full textIn this paper, the adsorption properties of two metallurgical wastes (slag and anode dust) and two municipal wastes (eggshells and coffee grounds) were described. Acetic acid was used as the adsorbate Adsorption kinetic was monitored during the adsorption process. The obtained results showed that all tested waste materials can be used as potential cheap adsorbents. Adsorption took place relatively quickly. Equilibrium was reached in 15 minutes, and the adsorption kinetics followed the pseudo-first-order reactions, i.e., can be described by the Lagergren model. All qe values calculated using Ho's model have a negative sign. That indicates that the Ho model is not suitable for describing the kinetics of the tested adsorption systems
Technological and constructional calculation of the cupola furnace
No full textOvaj rad zasniva se na proračunu konstrukcijskih dimenzija i tehnoloških parametra kupolne peći za zadani kemijski sastav taline sivog lijeva u peći zadanog proizvodnog kapaciteta. Za proizvodnju taline sivog lijeva odabrana je kupolna peć zbog jednostavne konstrukcije, manje potrošnje goriva u odnosu na druge agregate, jednostavno je vođenje procesa taljenja kao i održavanja peći, osigurana je kontinuirana proizvodnja taline, a može se mijenjati proizvodni kapacitet peći bez značajne promjene utroška koksa po toni taline. U prvom, teorijskom dijelu, opisana je osnovna funkcija i podjela kupolnih peći, konstrukcijske osobitosti pojedinih njezinih dijelova te procesne zone u radnom prostoru peći. U drugom, proračunskom dijelu rada izračunat je maseni udio pojedinih komponenata zasipa za 100 kg taline da bi se dobio kemijski sastav sivog lijeva oznake EN-GJL-250, a zatim ukupna masa zasipa s visinom slojeva pojedinih komponenata zasipa u trupu peći. Za zadani kapacitet peći od 3 t/h proveden je konstrukcijski proračun osnovnih dimenzija peći i sustava za dovod zraka.This paper is based on the calculation of construction dimensions and technological parameters of the cupola furnace for a given chemical composition of gray cast iron melt in a furnace for a given production capacity. The cupola furnace was chosen for the production of gray cast iron melt due to its simple construction, lower fuel consumption compared to other units, the melting process as well as the furnace maintenance is simple, continuous melt production is ensured, and the furnace production capacity can be changed without significant changes in coke consumption per ton of melt. In the first, theoretical part, the basic function and division of the cupola furnaces, the construction features of its individual parts and the process zone in the working space of the furnace are described. In the second, calculation part of the work, the mass fraction of individual charge components per 100 kg of melt was calculated to obtain the chemical composition of gray cast iron marked EN-GJL-250, and then the total charge mass with the height of individual charge components in the furnace. For a given furnace capacity of 3 t / h, the construction calculation of the basic dimensions of the furnace and the air supply system was performed
Melt treatment fading influence on the development of microstructure and mechanical properties of AlSi12 alloy
No full textAluminijske legure zbog povoljnog omjera mehaničkih, fizikalno-kemijskih i
tehnoloških svojstava pronalaze primjenu u gotovo svim industrijskim granama. Na
mehanička svojstva aluminijskih legura utječu parametri poput veličine i oblika zrna, veličine
i raspodjele primarnih i sekundarnih faza, udaljenosti između dendritnih grana te veličine i
raspodjele uključaka. Odabirom adekvatnog kemijskog sastava dodatkom glavnih i sporednih
legirajućih elemenata, elemenata koji utječu na razvoj mikrostrukture te prisutnih nečistoća
postiže se fina sitnozrnata struktura, dok se metalurškom obradom taline utroskivanjem,
cijepljenjem, otplinjavanjem i modifikacijom osigurava učinkovito izlučivanje eutektika (α-Al
+ β-Si) vlaknaste morfologije.
Cilj ovog rada je utvrditi utjecaj vremena zadržavanja taline na slabljenje učinka
cjepiva i modifikatora te razvoj mikrostrukture i mehaničkih svojstava ljevačke AlSi12 legure
za proizvodnju gravitacijski lijevanih zateznih stezaljki tvrtke Dalekovod d.o.o. Vrijeme
zadržavanja taline značajno utječe na učinkovitost tehnološke obrade taline, odnosno na
djelovanje cjepiva i modifikatora. Istraživanje se temelji na hipotezi da će vrijeme
zadržavanja taline utjecati na slabljenje učinka obrade taline, odnosno da će negativno utjecati
na razvoj mikrostrukture i mehaničkih svojstava legureAluminum alloys are used in almost all branches of industry because of their favorable
ratio of mechanical, physico-chemical and technological properties. The mechanical
properties of aluminum alloys are influenced by parameters such as size and shape of the
grain, size and distribution of primary and secondary phases, distance between dendrite
branches, and size and distribution of inclusions. By selection of adequate chemical
compostion by the addition of major and minor alloying elements, elements influencing the
development of microstructure, and present impurities, while metallurgical melt treatment by
fluxing, grain refinement, degassing and modification provides effective solidification of
eutectic (α-Al + β-Si) fibrous morphology.
The aim of this paper is to determine the influence of retention time of the melt on the
fading of the effect of the grain refining elements and modificators, and development of
microstructure and mechanical properties of casting AlSi12 alloy for gravitational casting of
tension clamps from the company Dalekovod d.o.o. Retention time of the melt has significant
influence on the efficiency of metallurgical melt treatment, that is the impact of the grain
refining elements and modificators. The research is based on the hypothesis that the retention
time of the melt will influence the fading of the melt treatment, that is it will negatively affect
the development of microstructure and mechanical properties