Development of CSS-421™, A High Performance Carburizing Stainless Steel for High Temperature Aerospace Applications

Today's aerospace engineering challenges demand materials which can operate under conditions of temperature extremes, high loads and harsh, corrosive environments. This paper presents a technical overview of the on-going development of CSS-42L™ (US Patent #5,424,028) [1]. This alloy is a case — carburizable, stainless steel alloy suitable for use in applications up to 427°C (800°F), particularly suited to high performance rolling element bearings, gears, shafts and fasteners. The nominal chemistry of CSS-42L™ includes: (by weight) 0.12% carbon, 14.0% chromium, 0.60% vanadium, 2.0% nickel, 4.75% molybdenum and 12.5% cobalt. Careful balancing of these components combined with VIM-VAR melting produces an alloy that can be carburized and heat treated to achieve a high surface hardness (> 58 HRC at 1mm (0.040 in) depth) with excellent corrosion resistance. The hot hardness of the carburized case is equal to or better than all competitive grades, exceeding 60 HRC at 427°C (800°F). The fracture toughness and impact resistance of the heat treated core material have likewise been evaluated in detail and found to be better than M50-NiL steel. The corrosion resistance has been shown to be equivalent to that of 440C steel in tests performed to date.