Impact toughness of nitrided steels

The effect of nitriding processes and preliminary heat treatment (quenching + tempering; normalization and high temper) on the impact toughness of structural steels was tested. Charpy specimens were nitrided at 500 - 520°C, 48 - 60 hours in a gaseous media or 6 - 15 hours at ion - nitriding. Nitriding decrease the impact toughness after all heat treatments and in the greatest degree in low alloyed normalized steels. In order to obtain high strength components that can be impact loaded it is necessary to use high alloyed steels quenched and tempered before nitriding. Obtained correlations between the nitriding parameters and the impact toughness were identical after gaseous and ion - nitriding. Conditions of heat treatment must exclude temper embrittlement.