Papers by Author: Zbigniew Jurasz

Abstract: In this work, the fatigue of P265GH steel acc. to EN 10216-2 has been evaluated by measuring a residual magnetic field (RMF). During experiment the notched-specimen has been loaded with a servo-hydraulic uniaxial MTS test machine and a special magnetic sensor was applied. The measurement distribution of the residual magnetic field was performed in two axes. In the first stage of experiment the specimen was gradually loaded with quasi-static force in range of 0 to 16 kN (~ 0.7 Rm). The increase of strength of residual magnetic field was observed only from 0 to 8 kN, whereas in range 8 to 16 kN this effect was not noticed. In the second stage the controlled tensile fatigue test was performed (R = 0, F_max = 16 kN). Up to 21k load cycles no changes to residual magnetic field were noticed. At 31k cycles the significant increase of amplitude of strength of residual magnetic field change was observed but visual inspection does not show any visible crack, while at 35k cycles crack was visible. It means that applied methodology allow to find the initiation of crack. The performed observation on SEM showed ductile fatigue of fracture.

Abstract: The paper presents an instance of a failure of the casing of a press used to make hexagonal clamps on tubes used in power engineering. The failure occurred during the press operation. The results of microscopic investigations of the cracked area show that the crack was initiated by excessive accumulation of sulfide inclusions with an unfavourable banded structure that formed in the steel. An EDS analysis identified MnS involved in the crack mechanism.Moreover, an FEM simulation of the pressure distribution and an annulus model of axial loading were used to analyse the stress and strain values arising in the press casing under compression. It was found that normal compressive stresses in direction Z were much larger in the region where the crack occurred, which means that the press casing mechanical manufacturing process creates the largest stresses in the fillet radius area. On the other hand, the effect of sulphide inclusions in the material were also considered as a cause of failure.It is concluded that both these factors – equivalent stresses and the high level of sulphide inclusions in the steel structure have an impact on the press casing failure.

Abstract: In this work a failed rotor shaft of φ 7.2 mm diameter manufactured from constructional steel 44SMn28 (1.0762) was examined. Fracture splitting into 2 pieces in the threaded part of the shaft in a direction parallel to the longitudinal axis occurred. The failure was induced by mechanical forces in the threading process. The failed shaft was examined on a metallographic and scanning microscope. It was found that the failure was caused by excessive accumulation of MnS inclusions in an unfavourable banded formation.

Abstract: The influence of yttrium on the corrosion resistance of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil containing 10 wt. % of biocomponents has been studied at 1173 K under thermal shock conditions. These experiments have been carried out by rapid heating of the studied materials up to 1173 K and after two hours cooling down to room temperature. These thermal shocks have been repeated hundreds of times, determining after every shock the mass changes of the corroded samples. It has been found that small amount of yttrium deposited on the steel surface using electrochemical treatment considerably improves the scale adherence and consequently corrosion resistance in the case of X33CrNiMn23-8 steel, containing the highest chromium concentration.

Abstract: The corrosion behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil, containing different bio-component concentrations of (5 and 10 wt. %) has been studied under thermal shock conditions. It has been found that the addition of bio-components to the fuel oil decreases the corrosion resistance of all steels under investigation, this effect being the stronger, the higher was the concentration of bio-component addition. It has been shown, that in spite of bio-component addition, the X33CrNiMn23-8 steel containing the highest chromium concentration, behaved much better than three remaining steels due to the formation of the highly protective chromia scale.

Abstract: Detailed investigations of nonstoichiometry as well as chemical and self-diffusion in nickel oxide have shown that doubly ionised cation vacancies and electron holes are the predominant defects in this material. The present work is an attempt to demonstrate that aliovalent impurities (Cr, Al, Na and Li) may considerably influence the concentration of these defects and, consequently, the oxidation rate of nickel at high temperatures. It has been shown that small amounts of tri-valent impurities (Cr, Al) bring about an increase of the oxidation rate, while mono-valent ones (Li, Na) decrease the rate of oxidation. These phenomena may satisfactorily be explained in terms of a doping effect. All experiments have been carried out as a function of temperature (1373-1673 K) and oxygen pressure (1-105 Pa) and consequently, it was possible to determine the influence of impurities not only on the oxidation rate but also on the activation energy of reaction and its pressure dependence. The results of these investigations could again be elucidated in terms of doping effect.

Abstract: In this paper we give a presentation of the recently developed approaches concerned of the rate of oxidation the Arema steel at high-temperature in first stage of this process. The comparison analysis was performed on the basis of the experimental results of oxidation of cylindrical specimens made of above steel. The experiment was carried out in chamber furnace on series of specimen with dimension Φ = 20 , l=30 mm. The specimens were oxidized at 1000 °C for 10 - 2280 minutes in air and then quenched in silica sand, afterwards were measured and weighed both with and without of scale. The analysis reveals that for longer oxidation time than one hour influence of linear dependence on parabolic growth of scale can be neglected.

Abstract: The results of residual stresses in biocompatible cast Ni-Cr alloys-ceramics joints with an intermediate layer with thickness of about 10μm are discussed. To the experiment were used specimens with dimensions of 45×3×10 mm and 45×4×10 mm made of Cr-Ni alloys-ceramics joint both with and without of application of an intermediate layer. The examinations were carried out by means of metallographical microscope, testing machine and X-ray diffractometer. The measurement of residual macrostresses was carried out by using sin2ψ method. The obtained experimentally values of residual macrostresses are in good agreement with results of numerical simulation performed by means of FEM ANSYS package. The researches have been shown that application of an intermediate ceramics layer influence on increase of strength properties of Ni-Cr alloys-ceramics joints.

Abstract: In this work it will be presented the results of calculation of energy activation Q of selected industrial steels (e.g. grade 55 - carbon steel, LH15 – bearing steel, H10S2M, 4H14N14W2M and 50H21G9N4 valve steels) according to Polish Norm by two methods. In the first method the calculations of Q are based on the dependence of value of parabolic growth rate constants kp in function of reciprocal temperature. The second method is based on the calculated parameters, which allow to determine the value of Q for examined steels by using value of Q for pure iron, taken from literature data, and the particular values of mass concentrations of elements in oxidised steels. The growth kinetics of layers were almost according to parabolic law. The values of parabolic rate constant kp were calculated on the basis of measurements of thickness of oxide layers. To the experiment the cylindrical specimens were used. The isothermal process of oxidation was conducted in chamber furnace at 1100, 1060, 1020, 980 and 940°C in the air. Time of oxidation various from 3 till 1303.5 hrs. The comparison of obtained results of activation energy Q for mentioned methods of each individual examined steels gives a good agreement.