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

Bearings in the turbopump for the space launchers main engine operate in extremely harsh conditions. The X105CrMo17 (or AIS1 440C) martensitic stainless steel is currently used for manufacturing the rings and balls for these bearings. Nevertheless, certain properties of this steel fall short of those required in future turbopumps. At the present time, there is a wide spread tendency towards partial or total substitution of carbon for nitrogen in stainless steels. Through nitrogen alloying, a fine homogeneous microstructure is obtained which entails an improved combination of mechanical characteristics as well as higher strength and greater corrosion resistance. Consequently bearing materials belonging to the group of High Nitrogen Steels (HNS) have been developed in partnership with steel makers and bearing manufacturers in order to rival X105CrMo17. This paper presents the behavior of XD15NW, a martensitic stainless steel containing 0.2% nitrogen, in a cryogenic environment (liquid nitrogen, 77K) under various working conditions of mechanical tests. This alloy will be compared with the X105CrMo17 steel