Search Results

Casting technology developmentshave led to a manufacturing process that allows the casting of thin wall (2-3mm) heat resistant ferritic stainless steel exhaust manifolds which can replace stamped and tubular weldments as well as iron castings where temperature requirements are increased. This casting process combines the thin wall and clean metal benefits of the counter gravity, vacuum-assist casting process using thin, light-weight bonded sand molds supported by vacuum-ridgidized sand. This combination is called the LSVAC (Loose Sand Vacuum Assisted Casting) process, a patented process. This process will significantly contribute to the growth of near-net shape steellstainless steel castings for automotive and allied industries. For exhaust manifolds, a modified grade of ferritic stainless steel with good oxidation resistance to 950°C in high dew point synthetic exhaust gas atmospheres was developed.

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.