The paper contains results of studies on the formation of oxide layers on 13CrMo4-5 steels long-term operated at an elevated temperature. The studied steels were operated at the temperature of 380 °C for 130,000 h (steel 1) and 535 °C for 230,000 h (steel 2). X-ray structural examinations (studying the phase composition and crystallite sizes) were carried out and microscope observations using an optical and scanning microscope were performed. The native material chemical composition was analysed by means of emission spark spectroscopy, while that of oxide layers on a scanning microscope (EDS). The obtained test results showed that the steel exploited at a higher temperature and longer time was significantly degraded.Keywords: Oxide layer, 13CrMo4-5, structure, crystallite sizes, elevated temperature
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