Naslov
Vodikova krhkost malolegiranih jekel
(Hydrogen embrittlement of low alloyed steels)

Autori
Gojić, Mirko

Vrsta, podvrsta i kategorija rada
Ocjenski radovi, doktorska disertacija

Fakultet
Fakulteta za naravoslovje in tehnologijo Oddelek za montanistiko, Odsek za metalurgijo

Mjesto
Ljubljana

Datum
28.05

Godina
1998

Stranica
92

Mentor
Kosec, Ladislav

Ključne riječi
Cr and Cr-Mo čelici, kaljenje i popuštanje, mikrostruktura, vodikova krhkost, zaštitni film
(Cr and Cr-Mo steels, quenching and tempering, hydrogen embrittlement, protective film)

Sažetak
In this dissertation the investigation of low alloy chromium and chromium-molybdenum steels for production tubing for exploitation of oil are described. The steels are obtained in industry conditions. After tempering at 400oC both steels have shown the presence of orthorhombic cementite (Fe3C) in the ferrite matrix, while after tempering at 700oC the low alloy chromium- molybdenum steel, in addition to the cementite, contains the cubic Mo2C. The orientation relationship between carbides and matrix are: [210]Fe3C‖(120)Fe3C‖(020)Mo2C planes are 7 degree. The susceptibility of steels to hydrogen embrittlement (HE) is determined by means of charge reduction of area after cathodic polarization of tensile loaded specimens in 0.5 mol/l H2SO4 solution with addition of 10 mg/l As2O3 (as „cathodic poison“) and with addition of 5 mmol/l of propargylic alcohol (as inhibitor). The susceptibility of steels to HE, tempered at 700oC, is considerable lower in comparison to the steels tempered at 400oC. Although the low alloy chromium-molybdenum steel has higher mechanical properties, its resistance to HE is better than that of low alloy chromium steel. In spite of all that an important role have finer prior austenite grain and the presence of Mo2C, which is a weak hydrogen trap because of low the interaction energy. The mechanism of HE is based on cracking at the Fe3C/matrix and FeMnS/matrix interfaces. The stress and trapped hydrogen induce interface decohesion with transgranular fracture around hydrogen traps. With addition of propargylic alcohol (PA) to the 0.5 mol/l H2SO4 solution the susceptibility of steels to HE is decreased. The effect of PA is attributed to the formation of the protective film. It is proved that the adsorption of PA on the steel in the sulphuric acid solution is substitutional adsorption process whewre three water molecules are replaced by one molecule of PA. The adsorption of PA corresponds to Flory- Huggins isotherm by free energy adsorption of -15 kJ/mol. The results of electrochemical measurements are confirmed with infrared spectroscopy. The effect of PA on the hydrogen embrittlement of steels can be attributed to the adsorption phenomenon but not to the formation of polymeric film.

Izvorni jezik
Hrvatski

Znanstvena područja
Metalurgija

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