Fatigue strength of nitrided 18Ni250 and 18Ni300 grade maraging steels

Abstract

An investigation into the nitriding of maraging steels 18Ni250 and 18Ni300 has been conducted. Preliminary investigations of the nitriding parameters were carried out on 18Ni250 grade steel in an atmosphere of partially dissociated ammonia at temperatures within the range 450 to 520°C and for times from 1 to 24 h. Hardness, depth, and microstructural characteristics of the case were determined. The results of preliminary tests served to facilitate the selection of nitriding process parameters for fatigue test specimens. Specimens were nitrided at 470 and 480°C (grade 18Ni250) and 450 and 470°C (grade 18Ni300). An increase of the bending fatigue limit by 45% was noted in comparison with unnitrided specimens. Within the selected range of nitriding parameters, no effect of nitriding on fatigue strength was observed.