Search

The present work deals with the causes of the damage to the distribution wheel of the main circulation pump of the nuclear power plant. During the solution of the problem, a significant influence of the final machining on the formation of cracks was found. Coarse surface machining can cause strain-induced martensite on the distribution wheel surface. Small pitting, which was observed on the surface of the distribution wheel, can be caused by the presence of martensite with less corrosion resistance. Thermal stress and residual stress after coarse final surface machining caused the growth of the cracks which initiated from the pitting.

Borated austenitic stainless steel is used in nuclear industry due to the high neutron absorption efficiency. The plasma, laser and electron beam welding experiments were used for the study of the weld joints microstructure. The microstructure changes caused by welding process were observed by light optical microscopy and transmission electron microscopy. The microstructural characterization and microchemical analysis showed significant changes of the phase composition in the weld metal mainly. The austenitic dendrites were surrounded by eutectics, which were the mixture of the M2(C,B) and M23(C,B) borocarbides, δ-ferrite and austenite.

A reduction in energy consumption at every stage of the down streaming process is needed to make 3rd generation of biofuels economically viable. In this study, magnetite (Fe3O4) nanoparticles were synthetized by coprecipitation of FeCl2 and FeCl3 in alkaline medium at two different temperatures. The particle sizes were 11.5 ± 4 and 9.5 ± 4 nm for the nanoparticles prepared at 80 °C and 25 °C, respectively. The adsorption of polyethyleneimine (PEI) onto Fe3O4 was studied by equilibrium batch measurements. A mono-layer absorption of PEI was found. The Fe3O4–PEI nanocomposites had a positive zeta potential, which decreased with increasing pH of the solution. The nanocomposites were used for magnetic harvesting of negatively charged Chlorella zofingiensis, Chlorella vulgaris, Chlorella sorokiniana, Chlorella ellipsoidea and Botryococcus braunii microalgae strains. Upon dosage of 200 mg/L of Fe3O4–PEI harvesting efficiencies of 68–97% were achieved at pH 4 within 1 min. The harvesting efficiency decreased with increasing pH of the suspension. The results demonstrate that Fe3O4 nanoparticles synthesized at the lower temperature (25 °C) could be used for an efficient magnetic harvesting of different microalgae strains. The lower synthesis temperature may thereby contribute to the cost reduction of microalgae harvesting.

Paper deals with the welding of AISI 304 thin sheets with the thickness of 1 mm by fiber laser. Statistical software MiniTab was used for planning the experiment. The influence of laser power, welding speed and focal point position on width and depth of weld bead was examined. Output power, welding speed and focus point position were used as variable factors for DOE. Samples were prepared by standard metallography. Weld bead width and depth were evaluated. Statistical results were afterward verified by welding reference samples with material the thickness of 0.25 mm. The difference between real width of weld bead and predicted width obtained from statistical software was 8.26 %. In case of weld depth measurement, the difference was 23 %.

This work is focused on the austenite decomposition in Cr-Mn-N austenitic stainless steels. The experimental steels was solution heat treated (1100°C/30 min. followed by water quenching) and then annealed in the temperature range from 650 to 900°C for holding time 5 min. to 100 hours for the study of precipitation. The precipitation behaviour during isothermal aging was investigated using light optical microscopy, transmission electron microscopy, selected area diffraction and energy-dispersive X-ray spectroscopy. The results show that the phase composition of the precipitates depends on the chemical composition of the experimental steel. The critical temperature of precipitation is 825°C with the corresponding time 100 s.

The time-temperature-precipitation in high-nitrogen austenitic stainless steel was investigated using light optical microscopy, transmission electron microscopy, selected area diffraction and energy-dispersive X-ray spectroscopy. The isothermal precipitation kinetics curves and the corresponding precipitation activation energy were obtained. The diffusion activation energy of M2N precipitation is 129 kJ/mol. The results show that critical temperature for M2N precipitation is about 825°C with the corresponding incubation period 2.5 min.

The paper deals with a detailed analysis of deep drawing DC 01/DIN EN 10130-9 steel sheets of 1 mm in thickness treated by nitro-oxidation in fluid environment. The nitridation at 580°C/45 min and oxidation at 350°C/5 min was used. The surface Fe3O4 and Fe2O3 oxide layer, as well as the presence of Fe2-3N, γ'- Fe4N nitrides and ferritic matrix, was proved by X-ray diffraction. The Fe2-3N nitrides formed a continuous ε-phase of 7,1 μm in thickness with the microhardness 6,5 times higher than the base material. Corrosion resistance test revealed the highest level according to STN EN ISO 10286/C standard in comparison to the non-treated material. Analysis of mechanical properties showed a significant increase of tensile strength. Ductility decreased approximately by 7,5 %. Erichsen cupping test showed a 15 % decrease of Erichsen cupping index. Fukui deep-drawing test of nitro-oxidised steel exhibited 1,5 % increase of "m" deep-drawing coefficient.

This paper analyses the current state of welding duplex stainless steel (DSS). Despite of well-known procedures of welding DSS by standard methods, nowadays modern technologies brings several issues. Electron beam welding showed the problems with achieving the similar phase composition to base metal. By changing the focusing distance and using the post-heating it was possible to bring extra heat input to weld joint what promoted the creation of austenite. Post-heating was performed by additional electron beam pass. By modification of welding procedure it was possible to obtain the phase composition very similar to base metal.

Nitro-oxidized steel specimens welded by a CO2 laser and an electron beam were examined for quality and integrity by visual inspection, microstructure, and microhardness analysis. Visual inspection of the specimens welded by laser revealed the lack of root penetration at maximal welding speed from the selected welding speed range (30 to 60 mm/s) and a neat weld at the welding speed of 40 mm/s. However, in comparison to laser beam welding, the electron beam welding (EBW) process produced the weld joints with a wider heat affected zone, while the weld joints were much more prone to porosity. The microstructure of the weld joints made by both the laser beam welding and EBW methods did not show any abnormalities in phase composition owing to the presence of nitrides in the surface layer of the materials welded after nitro-oxidation.