Cryogenic rolling element bearings operate in a very hostile environment. Materials used in this environment require a unique combination of characteristics. AISI 440C is the normally selected alloy because of its high chromium content (17%) and resultant corrosion resistance. However, AISI 440C has very poor cryogenic fracture toughness (K_Ic = 11 MPa√m (10 ksi √in.) at - 267°C (- 450°F) and is prone to stress corrosion cracking (SCC). Alternate materials like AISI 9310 or M50NiL can provide the requisite cryogenic fracture toughness (K_Ic = 27.5 MPa√m (25 ksi √in.) at - 267°C (-450°F) and SCC resistance, but neither provide general corrosion resistance due to their low chromium content.

In 1988, MRC Bearings and Pratt and Whitney (P&W) initiated a combined research and development program aimed at developing a cryogenic corrosion resistant, fracture tough bearing steel. The approach was to case harden by carburization a fracture tough class 3 super 12 stainless steel. This paper discusses the successful carburization process developed by MRC and P&W on an experimental carburizing stainless steel bearing alloy developed by Carpenter Technology, designated EX98. Finally, data derived on the resultant material properties will also be discussed.