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Studies have been performed on microalloyed steel with three different niobium content: 0, 036%, 0, 048% and 0, 066%. All steels had the same basic chemical composition. Samples for research were taken from different phases of final thermomechanical treatment. The samples were analyzed by transmission electron analysis and X-ray diffraction profile analysis. Precipitation of niobium carbonitrides was observed in all tested samples. In steels with 0, 048% nobium, densely complex carbonitride arrays were observed in the grain and along the boundaries of the crystal grain. The highest degree of interaction between deformation of induced nobium precipitates and dislocations was found in steels with o, o48% Nb. The largest distortion of the crystal lattice was determined on the same samples. In steel with 0, 036% niobium is less pronounced and the crystal lattice distortion is less.

Development of improved equation for better accuracy of calculation of stationary creep rate of creep resisting steels. Effect of acting stress components in particles disjunction matrix. Effect of increase of number of ferrite lattice vacancies.

The fracturing of structural steels in Charpy ductile range is investigated. The dependences load versus deflection and time were recorded and the consumption of energy for different fracturing events, as f.i. plastic deflection and crack propagation was assessed. The micromorphology of the crack surface and lips is examined and the succesions of decohesion mechanims is deduced. The aproximate change of fracturing temperature due to adiabatic dissipation of deformation energy as heat is deduced, also.

The precipitating niobium carbon-nitrides in final thermomechanical treatment of niobium microalloyed steel strip were studied. Transmission electron microscopy was applied to determine the change of niobium precipitation degree, type and share of precipitates , as well as nucleation and growth of precipitates across the phases of the final thermomechanical treatment. The obtained results at the analysis in the every phase of final thermomechanical tretment like precipitation degree, arrangement and interaction of the precipitates and dislocation were showed.

This paper deals the results of investigation the flow stress of several various steel alloys and deformability by torsion test in hot condition int he temperature range 800°C to 1250°C on alloyed structural steels for speciala application and improving : EN 41CrAlMo7, AFNOR, 35NCD16, EN 32CrMo12, En 43CrMo4, En 13CRMo44 and API N80.

Study of microstructural changes in the TiO2 powder induced by high-energy ball milling, performed by hardmetal tools in air and at room temperature, was carried out by applying X-ray diffraction, SEM, Raman and FTIR spectroscopy, and specific surface area (BET) measurements. Observed structural changes followed the phase sequence: anatase Ţ transient (metastable) high-pressure TiO2-II phase Ţ rutile. At the same time specific surface area of powders increased monotonicaly from ~10 m2/g, at beginning, up to ~ 25 m2/g after 3 hours of milling action. In the early stage of milling action the process of particle comminution dominated, and during the later stage the aggregation process was pronounced. The mean crystallite size, evaluated by applying the Scherrer's equation and the estimated half width of the diffraction lines having the highest intensity, and belonging to various phases existing in powder (anatase, TiO2-II, and rutile) varied markedly from beginning of milling action, so that at beginning it was ~30 nm, after 10 minutes of milling it was ~5 nm, and after 3 hours ~10 nm, respectively. These values differed from those regarding the primary particle size, derived from the specific surface area (BET) data, which were (at the same time of milling action) equal to: ~160, ~120 and ~60 nm, respectively. The latter value mentioned indicates that one is capable to prepare successfuly TiO2 "nanocrystalline" powder (with the mean particle size smaller than 100 nm), with different crystallographic forms present in it, if the milling action lasted more than one hour.

Comparative analysis of the structure and properties of the metal of cold-finished extra- thin wall tubes manufactured from billets centrifugally cast in vacuum and from billets obtained by the conventional two-stage process including vacuum induction melting and vacuum refining has been carried out. It is shown that structure and properties of cold-finished tubes made from vacuum-centrifugally cast billets are not inferior to those of tubes from conventional billets ; however, vacuum centrifugal casting of tube billets ensures a lower content of non- metallic inclusions in tube metal along with lower metal and labour consumption.

New deformation anomalies of rheologically complex materials were discovered and demonstrated. It was found out that in the process of axial extention during the decrease of resistance to deformation secondary deformation heterogeneities take place alternated with deformation homogeneities due to changes in resistance to deformation.

On the basis of contemporary ideas on the metal pressure shaping theory and investigation results of the metal stress-stained state during rolling and using variation principles of mechanics, the plastometric classification of metals and alloys, a new rheological model of the high deformation nidus is proposed in this work. The model explains the regularities in the distribution of plastic deformation intensity in the non-contact zones as well as the formation of the feed front end deformation in dependence of the plastometric properties of metals. Experimental data conforming the validity of the model are given also. Na osnovi sodobnih pogledov o teoriji oblikovanja kovin, raziskav napetostnega stanja v kovini med valjanjem z uporabo variacijskih načel mehanike in plastometrične razvrstitve kovin in zlitin se predlaga nov reološki model visoko deformiranega prostora. Ta model razlaga regularnosti v porazdelitvi intenzitete plastične deformacije v coni brez kontakta in nastanek čela deformacijskega prehitevanja v odvisnosti od plastometričnih lastnosti kovin. V članku so priloženi eksperimentalni podatki, ki potrjujejo veljavnost modela.

Lead on the basis of properties is very important in simulation of processes in plastic deformation of metals and alloys. The article deals investigations in processes hot rolling, properties of leads. The results give good correlation and possibility use of lead in investigation of hot rolling.