Maitse P. Sello

Ferritic Stainless Steel Type Aisi 441: the Laves Phase Embrittlement Maitse P. Sello

The topic for this investigation was chosen from an industrial problem experienced by Stainless Steel manufacturer when a hot rolled coil of AISI Type 441 dual-stabilised with Ti and Nb was found to be brittle after hot rolling. AISI Type 441 is being used in the manufacturing of automobile catalytic converter casing, which operates at the temperature region of 900°C and is frequently subjected to temperature variations as the automobile are used intermittently. The respective materials batch was used to evaluate qualitative and quantitatively the Laves phase precipitation during various heat treatment procedures. The time-temperature-precipitation (TTP) determined from the transformation kinetic curves after isothermal annealing at the temperature range of 600-850°C, shows two classical C noses for Laves phase transformation. By applying analytical technique such electron microscopy in combination with computation thermodynamic (CALPHAD approach) to predict precisely any microstructural changes during heat treatment or service life at elevated temperatures and hence, this contributed substantially to any further development of dual stabilised stainless steels.