Abstract
The influence of austempering conditions on the microstructure, hardness, tensile strength, and impact toughness of Ce-La inoculated solution-strengthened ferritic ductile irons was analyzed. The austempering was performed at temperatures 280, 320, 420, 520, and 620 °C for periods of 1.5 and 2.5 h. Metallurgical characterization of the samples was determined using scanning electron microscopy, optical microscopy, X-ray diffraction, microhardness, impact, and tensile test. The fracture surfaces of the tensile samples were examined by scanning electron microscopy. Austempering heat treatment significantly enhanced the mechanical characteristics of solution-strengthened ferritic ductile cast iron. This led to the birth of solution-strengthened Ce-La inoculated ferritic cast iron, a new spheroidal graphite cast iron family member with a unique microstructure in an ausferritic matrix. Samples austempered for low temperature exhibited higher impact toughness and tensile strength due to the nano-sized ausferrite phase. Austempering for high temperatures displayed higher elongation.

Key words
austempering, ausferrite, hardness, impact test

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