Presented are the results of basic research of the formation of non-metallic inclusions in steels for the production of ultra-clean steels were. The thermodynamic conditions of the formation and the kinetic parameters of the precipitation of non-metallic inclusions were studied. The result are clarification of very important mechanisms and modeling of formation of non-metallic inclusions, the kinetics of precipitation, their modifications and also process parameters important for technology for the production of ultra-pure steels.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 1427626In modern practice standard materials do not satisfy anymore the rigorous requirements for applications. Our research was focused on thermodynamic modelling of innovative aluminium alloys with better mechanical properties for high temperature applications. Using different combinations of alloying elements in specific temperature regions the information of which specific phase (solid solution, intermetallic compound) is formed. Alloys systems Al–X–Y (X=Si,Mn, Mg; Y=Zr, Mo) were investigated using thermodynamic equilibrium calculations, thermal analysis, and optical and scanning electron microscopy, in order to analyse the corresponding properties. Determination of chemical composition and types of phases, amount of phase and study of equilibrium and non-equilibrium processes, the characteristic solidification temperatures and mechanical properties for laboratory and potentially industrial aluminium alloys has been conducted.
F.06 Development of a new product
COBISS.SI-ID: 1717599These research activities has been oriented towards study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons. Three castings with different Si and Ni content were prepared. Three positions in casting from the edge to the center, with different cooling rates, were chosen for microstructure investigation. Cerium containing commercial inoculant was used for in-stream inoculation. Chunky graphite area was estimated in micro-and macrostructure. Mechanical properties were determined with tensile test bars taken from the center of the casting. The results showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite. High Si-content is strong chunky graphite promoter, especially in castings with slow cooling rate. Ni addition also promotes chunky graphite formation, but only in thermal center of the casting (where the cooling rate is the lowest). The ductility is severely lowered when chunky graphite appears in the microstructure.
F.09 Development of a new technological process or technology
COBISS.SI-ID: 1767775The contribution describes novel “in situ” measurement of electrical resistivity, dilatometry and thermal analyses of flake and spheroidal graphite cast iron in liquid state, during solidification and in solid state. The shape of graphite formed during solidification influences electrical properties and variations of dimensions of cast irons. The complex “in situ” measurements were performed using in house developed measuring cell. The samples were systematically quantitatively metalographically investigated. It was found that electrical resistivity of lamellar grey cast iron is greater than the electrical resistivity of spheroidal graphite cast iron since the lamellas of graphite interrupt the iron matrix more than the nodules and the conduction electrons are scattered more on interfaces between graphite and metal matrix. The electrical resistivity of the flake graphite cast iron is increasing during solidification and decreasing after solidification. It was demonstrated that using the newly proposed “in situ” method the obtained results of electrical resistivity, dilatations and temperatures the materials properties can be reconstructed.
F.13 Development of new production methods and tools or processes
COBISS.SI-ID: 1717087In this work thermal fatigue resistance of 1.7C, 11.2Cr, 2.0Ni, 1.2Mo steel for hot working rolls was studied using our newly developed test rig with specially prepared test samples. Tests were carried out in temperature range between 500–700 ?C whereas relevant characteristics related to cracks after prescribed cycles were obtained. Average length of all cracks, their density, average length of five longest cracks, and relevant microstructural characteristics of tested specimens were determined. It was found that initiation of cracks is strongly related to the cracking and spalling of carbides at specimen’s surface layer and that cracks growth is related to the characteristics of carbides. For comparison also results for Indefinite Chilled Double Poured roll cast iron researched earlier were given. Based on obtained results, possible improvements of thermal fatigue resistance of these two materials were discussed and proposed.
F.11 Development of a new service
COBISS.SI-ID: 1716575