The aim of this work is to describe the influence of plasma nitride layers with different case depths which were created in the root of V-notches to notch toughness of 30CrMoV9 steel. The different case depths of nitride layers were achieved by three nitriding processes at temperatures 450 °C, 500 °C and 550 °C. Duration of nitriding process was chosen with regard to the achievement of uniform depth layer on steel surface because determination the final depth of the root of the V-notch is difficult. Chemical composition of steel was verified by GDOES/Bulk method using the LECO SA 2000 device. The experimental works were realized on V-notch samples of size 10x10x55 mm (according to CSN ISO 148-1 standard). The notch toughness tests of steel were carried out using the instrumental Charpy hammer at temperatures -40 °C, +21 °C and + 70 °C. Thickness and microhardness of plasma nitrided layers was evaluated using the automatic microhardness LECO M-400-H device. The metallography was aslo evaluated using a light microscope OLYMPUS GX51. The results of experiments showed that plasma nitriding process has a direct impact on the change of notch toughness parameters. The notch toughness of plasma nitrided steel was decreased. The primary influence on the notch toughness has the case depth of the nitrided layer at the root of the V-notch. The measurements thereinafter showed that the notch toughness values at low temperature (-40 °C) decreased but at higher temperature (+70 °C) decreased too.Keywords: Plasma nitriding, Notch toughness, V-notch, Case depth
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