The paper deals with the steel 41CrAlMo7-10 fatigue characteristics changes following the plasma nitriding process. Two sets of samples were heat-treated identically. Then they were subjected to a plasma nitriding process. The mixture rate of basic gases, hydrogen and nitrogen, forming the atmosphere during the plasma nitriding, was mutually inverted. Process parameters such as the time, applied voltage and pulse length were identical for both sets. Following the heat treatment and surface coating formation of the diffusion layer of nitrides both sets were subject to rotating bending fatigue testing in the machine R.R.Moore L2568 of Instron Co. The fatigue tests were carried out in accordance with the CSN 42 0363 Fatigue Testing of Metals, Methodology of Testing. Then, the tests were evaluated numerically and graphically using Wöhler`s (S-N) curve in a semi-logarithmic form. The testing resulted in either the test sample fracture, or at completion 107 cycles. Evaluated were inclusions in the test bar fractures whereat the stress nucleation and fracture initiation took place. Calculated was the stress intensity factor ΔKImax declared in MPa.m0.5. Thanks to the completed testing, derived and analysed results new knowledge was acquired in the field of plasma nitriding steels.Keywords: Plasma nitriding, 41CrAlMo7-10 steel, fatigue
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