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Utlenienie wewnętrzne przyczyną uszkodzenia elementów maszyn do przeróbki kamienia

Grygier D., Dudziński W.

Górnictwo Odkrywkowe

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2008

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R. 49/2, nr 4-5

222-225

PL

Przedmiotem badań było koło zębate z odłamanymi trzema zębami, które uległo uszkodzeniu po czterogodzinnej eksploatacji w kruszarce granitu. Element poddany został analizie mającej na celu określenie przyczyn uszkodzenia. Metodyka badań objęła obserwacje makroskopowe oraz mikroskopowe materiału, badania faktograficzne powstałego przełomu oraz pomiary twardości warstwy nawęglonej na powierzchniach roboczych koła oraz we wrębach pomiędzy zębami. Uzyskane wyniki badań wykazały, że bezpośrednią przyczyną uszkodzenia koła zębatego był nieprawidłowo przeprowadzony proces nawęglania oraz niedokładna mechaniczna obróbka powierzchniowa, niedostatecznie usuwająca wady materiałowe powstałe podczas nawęglania.

EN

The tested material was cog-wheel with broken away three teeth, which have been damaged after four-hours of exploitation in impactor of granite. The main purpose of the presented research was finding the causes of this damage. The methodology of investigations contained the macroscopic and microscopic observations of cog-wheels material, formed fracture and also measurements of layer hardness on work surfaces of wheel and in notches among teeth. Analysis of the results has shown that the main reason of damage of cog-wheel was incorrectly process of carburization as well as inaccurate surface mechanical treatment, insufficiently remove material defects, formed during carburisation.

2

The role of Ti, Zr and Ce in shaping of the Cr-Ni-Nb cast steel resistance to carburising

Tęcza G., Zapała R., Kawalec M.

Archives of Foundry Engineering

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2008

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Vol. 8, iss. 3s

144--148

PL

From the centrifugally cast Cr-Ni-Nb steel pipes, specimens were cut out and subjected to carburising for 100 hours in a mixture of charcoal (90%) and Na2CO3 (10%) at the temperatures of 950 and 1150°C. The specimens were cut in direction normal to the pipe axis and were examined by optical and scanning microscopy. As a parameter describing the resistance of the examined alloy to the carburising effect, the thickness of a carburised layer was accepted. It has been observed that additions of Ti and Zr, and of Ti+Zr+Ce introduced jointly, increase the thickness of the carburised layer, while the addition of Ce improves the alloy resistance to carburising. On the alloy surface, a layer composed of oxides, mainly of chromium, silicon and iron, has been formed. Changes in the chemical composition of the surface layer were examined by scanning microscopy.

3

FMR study of nanocarbon materials obtained by carburisation of nanocrystalline iron

Narkiewicz U., Arabczyk W., Pełech I., Guskos N., Typek J., Maryniak M., Woźniak M. J., Matysiak H., Kurzydłowski K. J.

Materials Science Poland

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2006

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Vol. 24, No. 4

1067--1075

EN

Samples of nanocrystalline iron were carburised with ethylene and next reduced with hydrogen. Both carburisation and reduction were monitored by the thermogravimetry. The obtained samples were characterised using X-ray diffraction, high-resolution transmission electron microscopy and ferromagnetic resonance. The samples after carburisation contained cementite (Fe3C) and carbon deposit (nanofibres and nanotubes). As the result of reduction with hydrogen at 450 or 500 °C cementite was reduced to iron. A major part of carbon was also hydrogenated, only thin carbon nanotubes remained. The FMR spectra of the prepared samples were recorded at room temperature. The sample after carburisation has shown a wide FMR line with weak intensity while the resonance field has been shifted to lower magnetic field. This spectrum has been attributed to the presence of cementite. The FMR lines corresponding to samples after reduction are more intense and are connected with the presence of alfa-Fe nanoparticle conglomerates.

4

Carburization of Fe-Ni-Cr alloys at high temperatures

Ul-Hamid A., Tawancy H.M., Al-Jaroudi S.S., Mohammed A.I., Abbas N.M.

Materials Science Poland

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2006

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Vol. 24, No. 2/1

319--331

EN

A large number of radiant tubes belonging to an ethylene furnace of a petrochemical plant failed during service. All tubes exhibited severe carburization while some of them lost their structural integrity and sagged. The tube material was based on Fe-Ni- Cr alloy system with three varying compositions. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the microstructure and elemental composition of the tubes material. Microhardness testing was performed to determine their mechanical strength. Experimental results indicated that sagged tubes exhibited higher degree of carburization compared to the other tubes. Microstructure of these tubes also revealed coarser Cr-carbide precipitation and continuous carbide lattice at austenite grain boundaries. It was concluded that exposure to excessive temperature during service was responsible for the degradation of all tube materials. Based upon above results, it was recommended that a better control of furnace temperature should be employed in order to avoid overheating during service.

5

Technology of the nanocarbon materials preparation

Narkiewicz U.

Polish Journal of Chemical Technology

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2005

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Vol. 7, nr 3

87-94

EN

The technology of the nanocarbon materials preparation by the catalytic decomposition of hydrocarbons on nanocrystalline iron is described. Among different methods of nanocarbon materials preparation, this one, based on the catalytical gas-solid reaction can be recommended as a simple, inexpensive, easy to control and easy to process scale up-grading. The use of nanocrystalline iron as a raw material enables carrying out the process in the kinetics area of the reaction, when diffusion is not limiting. There is no need to apply special conditions, as high pressure or vacuum, laser ablation or high temperatures (the process can be carried out with good efficiency in the temperature range from 350 to 550°C). Depending on the process conditions, different forms of nanocarbons can be obtained (amorphous carbon, carbon nanofibers or nanotubes).

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Carburisation of nanocrystalline iron with ethylene

Narkiewicz U., Kucharewicz I., Arabczyk W., Lenart S.

Materials Science Poland

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2005

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Vol. 23, No. 4

939--946

EN

The carburisation of nanocrystalline iron with ethylene has been studied. The carburisation processes were carried out under atmospheric pressure, under the flow of pure ethylene or ethylene-hydrogen mixture at a constant temperature in the range of 310-550 °C. The process was controlled using a spring thermobalance and cathetometer, with the accuracy of 0,1 mg. The phase composition of the samples after carburisation was determined by means of X-ray diffraction (XRD). As a result of the carburisation of nanocrystalline iron with ethylene, the formation of iron carbide Fe3C occurs, followed by the formation of carbon deposits. Under a C2H4/H2 gas mixture, these two reaction steps can be separated, while under pure ethylene the reactions are much faster and the simultaneous formation of iron carbide and carbon deposits is observed. Depending on temperature and on the carburisation degree, various forms of carbon deposits can be observed using TEM: spherical, helicoidal, and nanotubes. The diameter of these carbon forms is below 100 nm.

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Effect of nickel, chromium, silicon and carbon on increased resistance to carburising effect of Ni-Cr cast steel

Chmielewski K., Piekarski B.

Archiwum Odlewnictwa

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2002

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R. 2, nr 4

332--339

EN

The study examines an effect of the basic chemical constituents in austenitic cast steel on an increase in its carburising resistance at a temperature of 900°C and with the carbon potential of atmosphere equal to 0.9%. It has been proved that the increment in sample weight is controlled mainly by the content of nickel, silicon and starting volume of carbon in alloy, while thickness of the carburised layer depends, first of all, on chromium content.

PL

W pracy analizowano wpływ podstawowych składników chemicznych staliwa austenitycznego na wzrost jego odporności na nawęglanie w temperaturze 900°C i przy potencjale węglowym atmosfery 0.9%. Wykazano, że przyrost masy próbek jest kontrolowany głównie zawartością niklu, krzemu i początkową ilością węgla w stopie, a grubość warstwy nawęglonej zależy przede wszystkim od zawartości chromu.