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Development of a dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86,9Au-9,9Pt-1,5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: α1-phase rich in Au (main phase) and α2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the α1-phase content is about 98,5 wt.% while the content of α2-phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solidus temperature of about 1292 K and a liquidus temperature of about 1412 K. Razvoj dentalne slitine s visokim sadržajem zlata zasnovan je na ternarnom sustavu Au-Pt-Zn s nominalnim sastavom 86,9Au-9,9Pt-1,5Zn i oko 1,5 mas. % mikrolegirajučih elemenata (In, Ir, Rh). Rezultati analize su pokazali da se u slučaju slitine odžarene kod 1223 K u trajanju od 30 minuta i zakaljena u vodi optimalna mehanička svojstva i tvrdoća Au-Pt-Zn slitine mogu postići kombinacijom toplinske obrade na 720 oC u trajanju 20 minuta s naknadnim sporim hlađenjem. Rezultati istraživanja su potvrdili da se mikrostruktura Au-Pt-Zn slitine sastoji od dvije faze: α1-faze bogate sa zlatom (primarna faza) i α2 - faze bogate s platinom (sekundarna faza). Tijekom XRD analize i primjenom Rietveldove metode utvrđeno je da je sadržaj α1-faze oko 98,5 mas. %, dok je sadržaj α2-faze iznosio oko 1,5 mas. %. STA analiza je pokazala da je Au-Pt-Zn slitina imala solidus temperaturu oko 1292 K, a likvidus temperaturu oko 1412 K.

Silver alloys with tellurium, selenium and sulphur fulfil the conditions for the internal oxidation. Microstructure of these alloys consists of matrix (dilute solid solution) and particles of intermetallic compounds. Internal oxidation of ternary alloys is very similar to that of the binary alloys, but there are also distinctions in thermodynamics properties of alloying elements. At the direct oxidation of the particles of the intermetallic compound the phenomena of the selective oxidation was observed. Concentration of more reactive elements is increasing in the oxidized part of the particles of the intermetallic compound (Te in AgTeSe alloys). Therefore the precipitated oxides formed with diffusional internal oxidation are richer with less reactive alloying element (Se in AgTeSe alloy). In the precipitated oxide particles the concentration of selenium is more than twice higher than of tellurium. Legure srebra s telurom, selenom i sumporom ispunjavaju uvjete za unutarnju oksidaciju. Mirkostruktura ovih legura sastoji se od osnove (razrijeđena kruta otopina) i čestica intermetalnih spojeva. Unutarnja oksidacija ternarnih legura veoma je slična onoj za binarne legure, ali postoje i razlike u termodinamičkim svojstvima legirajućih elemenata. Kod izravne oksidacije čestica intermetalnog spoja zapažena je pojava selektivne oksidacije. Koncentracija reaktivnijih elemenata raste u oksidiranom dijelu čestica intermentalnog spoja (Te u AgTeSe leguri). Prema tome precipitirani oksidi nastali difuzijskom unutarnjom oksidacijom su bogati s manje reaktivnim legirajućim elementom (Se u AgTeSe leguri). U percipitiranim oksidnim česticama koncentracija selena je dvostruko veća nego telura.

V prispevku obravnavamo proces notranjega ogljičenja, s katerim lahko izdelamo diskontinuirni kompozit Cu-C. Proces notranjega ogljičenja poteka brez pojava precipitacijske fronte, s sočasnim izločanjem grafitnih delcev po celotnem volumnu, potem ko se v trdni raztopini Cu-matice doseže, na defektih v kristalni mreži pa preseže nasičenost ogljika. Z analizo notranje ogljičenih vzorcev različnih izhodnih mikrostruktur Cu, ki so vsebovale različne vrste in koncentracije defektov (praznine, kristalne meje, dislokacije), smo ugotavljali vpliv izhodne mikrostrukture čistega Cu oz. posameznih vrst defektov na proces notranjega ogljičenja. Na osnovi dobljenih rezultatov in analiz lahko povzamemo, da pri notranjem ogljičenju različnih mikrostruktur čistega bakra precipitirajo iz kristalne mreže submikrometrsko majhni delci grafita. Volumenski delež in velikost grafitnih delcev sta odvisna od izhodne mikrostrukture bakra, temperature in časa notranjega ogljičenja. Največja gostota in najbolj enakomerna razporeditev grafitnih delcev sta doseženi pri gašenih vzorcih, kar kaže, da so klasterji praznin najbolj primerni element kristalne mreže za tvorbo grafitnih delcev. This paper presents the internal carbonisation process involved in the fabrication of a discontinuous Cu-C composite. The precipitation process of carbon particles does not involve the precipitation of the carbonisation front but a simultaneous precipitation of carbon particles throughout the entire volume of the Cu-matrix. The carbon concentration in the matrix reaches its maximum solubility, whereas the carbon super saturation is achieved on the defects in the crystall lattice. With an analysis of internally carbonised samples, containing different types and densities of defects (vacancies, crystall grains, dislocations) we attempted to identify the influence of the initial, pure copper microstructure and the separate types of defects on the internal carbonisation process. On the basis of the results and analyses we concluded that with internal carbonisation of the pure copper microstructure the submicron graphite particles were formed. The volume fraction and the size of the precipitated graphite particles depend on the initial copper microstructure, on the temperature and on the time of internal carbonisation. The highest density and the most uniform distribution were obtained with quenched samples. The results have shown that the clusters of vaccancies are the strongest traps for carbon atoms and the most favorable places for graphite precipitation.

In this paper we present a composite with fine dispersion of nano-sized bubbles, which can be formed by internal oxidation of fine dispersed graphite particles. For this purpose the initial pure Cu ribbons were internally carbonised to obtain very fine, some 100 nm-sized graphite particles homogeneously distributed in the Cu matrix. By the internal oxidation process the reaction of dissolved oxygen with graphite yields the gas products (CO, CO2) which cannot be dissolved in the crystal lattice of the metal. The gas products are meshed in the space previously occupied by graphite and they have a greater specific volume than the solid graphite, thus establishing the compressive stresses in the metalic matrix and consequently causing the strengthening offect. On the other hand, such stress fields can react with sliding dislocation, whereby they impede the dislocation motion and consequently we would expect that the composite mechanical properties would be improved. In this paper we present the composite with the fine dispersion of nano-sized bubbles, which can be formed by the internal oxidation of fine dispersed graphite particles. For this purpose the initial pure Cu ribbons were internally carbonised to obtain very fine some 100 nm sized graphite particles homogeneously distributed in the Cu matrix. By the internal oxidation process the reaction of dissolved oxygen with graphite yields the gas products (CO, CO2), which cannot be dissolved in crystal lattice of the metal. The gas products are meshed in the space previously occupied by graphite and they have a greater specific volume than solid graphite, thus establishing the compressive stresses in the metallic matrix and consequently causing the strengthening effect. On the other hand, such stress field can react with sliding dislocation, whereby they impede the dislocation motion and consequently it would expect that the composite mechanical properties would be improved.

In this article we describe the microstructural changes in the heat affected zone (HAZ) of the tool steel W. Nr. 1.2379, which was surfaced or welded by the submerged arc welding technique (SAW) with different welding parameters. Microstructure of the welds and of the surfacing welds was analysed by optical and scanning electron microscope. In this research, we particularly studied microstructural changes in the area of primary chromium carbides in the HAZ and their effect on the weld crystalization. We came to the conclusion that the temperature in the HAZ is high enough during the welding process that it caused primary carbides to dissolve and concentration of the carbide-forming elements and carbon increased in the surrounding austenite matrix area to eutectic composition, which remelts and solidified as secondary eutectic (ledeburite).

In this work we studied the response of newly developed armored steel plates PROTAC 500 to the ballistic testing with armored piercing bullets with a core of tungsten carbide, charge 7.62 mm. Interactions between the bullets and the steel plate was investigated by standard metallographic and mechanical testing methods. We were interested in the geometric features of interaction, the phenomenon of adiabatic shear bands (ASB), cracks and local failure, local melting and interaction of the components and plate with metal balls fragments in the melt, rate of deformation and the steel hardening.

A study was made of the weldability of 4-mm-thick aluminium-alloy 5083 plates using friction-stir welding. A plan of experiments was prepared based on the abilities of a universal milling machine, where the tool-rotation speed varied from 200 r/min to 1250 r/min, the welding speed from 71 mm/min to 450 mm/min and the tool tilt angle was held constant at 2. The factors feed per revolution (FPR) and revolution per feed (RPF) were introduced to get a better insight into the friction-stirring process. Samples for microstructure analyses, Vickers micro-hardness measurements and special miniature tensile-testing samples were prepared. The microstructure was prepared for observation on a light microscope under a polarised light source. A set of optimal welding parameters was determined at a FPR of 0.35 mm/r, at which quality welds can be made with a minimal increase in the weld hardness and an up to 15 % drop in the tensile strength. Izdelana je študija varivosti 4 mm debele pločevine iz aluminijeve zlitine 5083 pri varjenju s trenjem in mešanjem. Načrt eksperimentov je bil pripravljen na podlagi sposobnosti univerzalnega frezalnega stroja. Spreminjali smo hitrost vrtenja orodja od 200-1250 r/min, hitrost varjenja 71-450 mm/min, kot nagiba orodja pa je bil konstanten pri 2°. Vpeljana sta bila faktorja podajanje na vrtljaj (FPR) in obratov na podajanje (RPF), s katerima bolj nazorno prikažemo vpliv parametrov procesa. Iz izdelanih varov smo pripravili vzorec za analizo mikrostrukture, vzorec za meritev trdote po Vickersu ter posebne miniaturne epruvete za natezni preizkus. Mikrostruktura je bila pripravljena za opazovanje na svetlobnem mikroskopu v polarizirani svetlobi. Optimalni parametri varjenja so bili ugotovljeni pri FPR 0,35 mm/r, pri čemer dobimo kakovostne zvare, z minimalnim povečanjem trdote vara in do 15-odstotnim padcem natezne trdnosti.

In this work the results of the transformation kinetics of austenite heat resistant stainless steel with 2.27 wt.% silicon were presented. This work concerns the microstructural and fractography analysis during isothermal heat treatment of the steel using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Firstly the steel was solution annealed at 1100 °C for 15 minutes to obtain a homogeneous starting conditions. After that, test samples were isothermal annealed in the temperature range from 600 to 900 °C at different annealing times (from 1 to 956 hours). Microhardness of samples was performed by Vickers method (HV0.3). Results of microstructural and fractography analysis as well as the hardness before and after isothermal heat treatment are shown. Thermodynamic calculation of equilibrium phases using ThermoCalc computer program was performed. It was found that the microstructure of steel after isothermal annealing was consisted of austenite and sigma phase. This phase was observed both at grain boundaries and within the austenite grains. In this case the formation of sigma phase is directly from austenite. Initial precipitation of the sigma phase took place along austenite grain boundaries. Morphology of sigma phase is spherical-oval like. With longer times the sigma phase continued to grow in size to agglomerate and coalesce in the form large angular particles, sometimes clustered at grain boundaries. At temperature of 600 °C the hardness becomes increasing after annealing of 48 hours, while in the temperature range 700-900 °C the hardness increases with annealing times higher from 8 hours.

After the black-oxide coating brown stains were observed forming on the surfaces of grey-cast-iron hot plates made for an electric stove. These stains were metallographically examined using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDXS). For the phase identification we also employed X-ray diffraction (XRD) analyses. The results of the analyses indicated that the stained surfaces of the hot plates were covered with whiskers of hematite (Fe2O3), while on the surfaces of the non-defective hot plates only magnetite (Fe3O4) was present. The thermodynamic calculations confirmed the possibility of the formation of hematite (Fe2O3) as a result of the oxidation of magnetite (Fe3O4) if the partial pressure of oxygen is increased during the black-oxide-coating process.

Results of microstructural and fractographic analysis and hardness testing of heat-resistant stainless steel with 2.27% Si carried out after isothermal annealing at 600°C are presented. Isothermal annealing times were different, from 1 to 702 hours. The microstructural and fractographic analysis were performed with scanning electron microscopy (SEM). The microstructure of investigated steel demonstrated the presence of austenite and little precipitates on grain boundaries. Results of EDX analysis of the precipitates were shown that contents of chromium increasing and nickel decreasing with annealing duration. Also, hardness values were increased (from 163 to 205 HV) with isothermal annealing duration. Fracture surface modes of steel were cleavage transcristalline with inoculation before annealing, and intercristalline and fragile after 702 hours of annealing.

In present work, the hardness, fracture mode and microstructure of heat resistant stainless steel AISI 310S before and after solution heat treatment were investigated. Temperature of solution heat treatment was 1100°C/30 minutes and after solution heat treatment the samples were quenched in water (15°C). Microstructure and fracture surface analysis were carried out with scanning electron microsope (SEM) and energy dispersive X-ray spectrometer (EDX). Microstructure of steel before heat treatment consisted of austenite and delta ferrite. Also, microstructure of steel after solution heat treatment and quenching was heterogeneous and consisted of austenite and delta ferrite. Sigma phase particles were not observed. Solution heat treatment a slight influence on the hardness decreasing (from 203 to 170 HV). Fracture surface before and after solution heat treatment characterized by a ductile fracture mode.

The subject of investigation was the effect of post-weld heat treatment (PWHT) on mechanical properties, hardness distribution across the welded joints, and on the microstructure of AISI 316L austenitic stainless steel weld metal. Steel plates of 15 mm thickness were welded by manual electric arc welding and treated at 600–900°C. The tensile strength increased and impact energy values decreased with the increasing annealing temperature. The hardness test results for the weld metal, which were approximately equal before PWHT and after it, were higher than those for the base metal and the heat-affected zone. The weld metal microstructure was examined by means of an optical microscope and a scanning electron microscope. It demonstrated the presence of austenite, ferrite and microslag inclusions before PWHT, and that of sigma phase after PWHT. Also, the presence of complex Mn-Cr-Si-Ti inclusions in small holes was observed in tensile and impact (Charpy) tested specimens.

U radu su prikazani rezultati ispitivanja metodama bez razaranja, mehaničkih svojstava i mikrostrukture lima iz austenitnog čelika AISI 321 prije i nakon zavarivanja. Lim dimenzija 300x300x10 mm pripremljen je za zavarivanje u obliku sučeljenog V-spoja. Korijen zavara provaren je REL postupkom, a popuna TIG postupkom. Ispitivanja bez razaranja sastojala su se od radiografskih ispitivanja i ispitivanja penetrantima. Mikrostrukturna ispitivanja su obuhvaćala određivanje mikrostrukture zavarenog spoja optičkim mikroskopom. Mjerenje sadržaja delta-ferita provedeno je pomoću feritoskopa. Ispitivanjem bez razaranja utvrđeno je postojanje greške u obliku neprovarenog korijena zavara. Mikrostruktura osnovnog materijala bila je gotovo potpuno austenitna, a zone taljenja austenitno- feritna. Sadržaj delta ferita u osnovnom materijalu iznosio je ispod 1%, dok je u zoni taljenja iznosio oko 8%.

In this paper we present a composite with fine dispersion of nano-sized bubbles, which can be formed by internal oxidation of fine dispersed graphite particles. For this purpose the initial pure Cu ribbons were internally carbonised to obtain very fine, some 100 nm-sized graphite particles homogeneously distributed in the Cu matrix. By the internal oxidation process the reaction of dissolved oxygen with graphite yields the gas products (CO, CO2) which cannot be dissolved in the crystal lattice of the metal. The gas products are meshed in the space previously occupied by graphite and they have a greater specific volume than the solid graphite, thus establishing the compressive stresses in the metalic matrix and consequently causing the strengthening offect. On the other hand, such stress fields can react with sliding dislocation, whereby they impede the dislocation motion and consequently we would expect that the composite mechanical properties would be improved.

Results of mechanical testing and of microstructural analysis of AISI 316L austenitic stainless steel carried out before and after welding and post-weld heat treatment are presented. Steel plates of 15 mm thickness were welded by manual electric arc welding process. Heat treatment consisted of annealing at 600, 700, 800, and 900 °C for two hours, and was followed by cooling in the air. For microstructure examination an optical microscope and a scanning electron microscope were used. The weld metal microstructure demonstrated the presence of austenite, ferrite, and microslag inclusions before annealing, and of sigma phase after annealing. The tensile strength increased and impact energy values decreased with the increasing annealing temperature. Complex Mn-Cr-Si-Ti inclusions in the dimples were observed in the tensile and Charpy tested specimens.

In this study the hardenability, the cooling rates and microstructures of low alloy Cr-Mo and Mn-Mo steels were investigated. The cooling rate determines of amount of martensite structure. Hardenability test was carried out by Jominy method. Microstructure was determined using a scanning electron microscopy (SEM). The cooling rates in the temperature range between 1133 and 973 K at different distances from the quenched end of low alloy Cr-Mo and Mn-Mo steels were found. Also the hardness and microstructures against the distances from quenched end are determined. The economical way of increasing the hardenability of steels (at constant carbon content) is to increase the manganese content.

A survey of the solidification structure of austenitic stainless steels is presented. The solidification occurs, depending on the content of the main alloying elements, with the primary formation of delta-ferrite or austenite. In the case of primary solidification of delta-ferrite, this phase reacts with the residual melt producing austenite with a peritectic reaction. The hot workability of the as-solidified microstructure is better in the case of primary solidification of delta-ferrite, since, in this case, the accumulation of impurities in the final melt is prevented. Some impurities, slightly soluble or insoluble in the solid phase at solidification, e.g., lead, decrease the hot workability significantly, which is also lowered in the case of the segregation of soluble impurities at the boundary of austenite and delta-ferrite. The integrity of the continuous cast slab can be improved and the cracking by hot rolling can be prevented by an optimal adiustment of the steel chemical composition and the parameters of continuous casting. Laboratory tests of one-pass rolling of wedge-shaped specimens of industrial steels have confirmed the recommendations and the conclusions in the quoted references. Podan je pregled literature o strjevalni strukturi avstenitnih nerjavnih jekel. Strjevanje se začne v odvisnosti od vsebnosti glavnih legirnih elementov, s primarno kristalizacijo delta-ferita ali avstenita. V primeru primarnega nastanka delta-ferita nastane pri nadaljevanju strjevanja s peritektično reakcijo med trdno fazo in preostalo talino avstenit. Vroča preoblikovalnost jekla s strjevalno mikrostrukturo je boljša pri primarni kristalizaciji delta-ferita, ker ta prepreči koncentracijo nečistoč v jeklu v zadnji meddendritni talini. Nekatere nečistoče, ki so netopne ali malo topne v trdni fazi pri kristalizaciji, npr. svinec, močno zmanjšajo vročo preoblikovalnost jekla s strjevalno strukturo, ki se zmanjša tudi zaradi segregacije topnih nečistoč na meji med avstenitom in delta-feritom. Integriteto kontinuirno litih slabov in obseg razpok pri vročem valjanju je mogoče doseči z uravnoteženjem kemične sestave taline in parametrov kontinuirnega litja. Laboratorijski preizkusi z valjanjem klinastih preizkušancev iz industrijskega jekla s strjevalno strukturo v enem prehodu so potrdili sklepe in priporočila v citiranih referencah.

Poznato je da troska ima veoma važnu ulogu tijekom proizvodnje čelika. U ovom su radu prikazani rezultati karakterizacije skrutnute elektropećne troske nastale tijekom industrijske proizvodnje niskolegiranog krom-molibdenskog čelika (42CrMo4). Karakterizacija troske dobivena je pomoću brojnih komplementarnih metoda (DTA, TGA, DSC, SEM, EDS, PIXE i XRD). Utvrđen je fazni sastav troske i distribucija faza. Nakon 50 minuta upuhivanja kisika troska se primarno sastoji od FeO (wüstite), beta-Ca_2SiO_4 (larnite) i 3CaO×Fe_2O_3×3SiO_2 (andradide). Završna troska uzeta iz lonca prije kontinuiranog lijevanja sadrži: 3CaO×Fe_2O_3×3SiO_2, (Ca, Mn)_2SiO_4 i Mg(Al, Fe)_2O_4 (ferrian-spinel) kao i manji udio K_2Na_4Ca_2Al_6Si_5O_24(CrO_4)_2, FeO i beta- Ca_2SiO_4.

U radu su prikazani rezultati ispitivanja mehaničkih svojstava i mikrostrukture cijevi iz niskolegiranog krom-molibdenskog čelika. Čelik dobiven u industrijskim uvjetima valjan je u toplovaljane bešavne cijevi (promjera 159 mm i debljine stijenke 8 mm). Nakon toga cijevi su se postupkom hladnog pilgerovanja reducirale na vanjski promjer 130 mm i debljinu stijenke 6, 2 mm te su odžarene na 700°C u peći pod zaštitnom atmosferom. Mehanička i mikrostrukturna analiza provedene su na uzorcima nakon žarenja. Mikrostruktura je analizirana pretražnom elektronskom mikroskopijom (SEM) uz primjenu energetsko disperzijske spektralne analize. Utvrđena je bainitna mikrostruktura s izlučenim karbidnim česticama cementitnog tipa. Oko pukotina uz vanjsku stijenku cijevi zapažena je prisutnost kompleksnih oksidnih uključaka.

The effect of post-weld heat treatment on mechanical properties, microstructure and fracture mode of low-alloyed CrMoNb steel was examined using an optical microscope, and a scanning and transmission electron microscopes. Steel plates, 18 mm thick, were welded by means of the submerged arc welding technique and then heat treated in the temperature range from 475 to 700°C. It was found that the tensile strength, hardness and impact energy values decrease with the increasing annealing temperature, except for annealing at 550°C and 625°C. Anomalies were attributed to the precipitation of fine carbides. Complex cementite proved to be beneficial in controlling the fracture mechanism in impact (Charpy V-notch) and tensile tested specimens.