Influence of Columbium on the 870°C Creep Properties of 18% Chromium Ferritic Stainless Steels

Ferritic stainless steels are commonly used for the structural components in automotive bead-bed catalytic converters. A laboratory investigation was conducted to characterize the elevated temperature creep properties of various ferritic steels. Results show that a significant improvement in 870°C creep strength of 18% chromium steels is achieved with the combination of approximately 0.5% free columbium and a high final annealing temperature. Such steels are shown to have short term 870°C creep properties comparable to type 304 stainless steel. The superior creep strength of columbium-bearing steels appears related to a Laves phase precipitate which forms at elevated temperatures.