Behavior of the nitrogen bearing martensitic stainless steel: XD15NW in cryotechnical environment

Bearings in the turbopump for the space launchers main engine operate in ex tremely harsh conditions. The X105CrMo17 (or AISI 440C) martensitic stainle ss steel is currently used for manufacturing the rings and balls for these bearings. Nevertheless, certain properties of this steel fall short of thos e required in future turbopumps. At the present time, there is a wide sprea d tendency towards partial or total substitution of carbon for nitrogen in stainless steels. Through nitrogen alloying, a fine homogeneous microstruct ure is obtained which entails an improved combination of mechanical charact eristics as well as higher strength and greater corrosion resistance, Conse quently bearing materials belonging to the group of High Nitrogen Steels (H NS) have been developed in partnership with steel makers and bearing manufa cturers in order to rival X105CrMo17. This paper presents the behavior of X D15NW, a martensitic stainless steel containing 0.2% nitrogen, in a cryogen ic environment (liquid nitrogen, 77K) under various working conditions of m echanical tests. This alloy will be compared with the X105CrMo17 steel.