| The fracture properties of ductile cast iron (DCI) can be significantly improved by austempering, isothermal transformation in the temperature range from Ar$quot; to Ar` point following austenitization. According to the results of experiment, when a 0.27%Mo-1.08%Ni alloyed DCI was austenitized for 1.5hr at 900 ℃ and austempered for 2hr at temperature range from 280 to 415℃, as the austempering temperature was increased, strength and hardness decreased, while ductility increased. Also, the fracture toughness values K_IC obtained were over about 80 MPa m＾(½) when yield strength, elongation and hardness were the ranges of 750 to 850 MPa, 5 to 8% and 270 to 330 H_B respectively. The homogeneous bainitic microstructure of the austempered ductile iron (ADI) was obtained by the austempering temperature range of 340 to 385 ℃, and its SEM fractography showed a fibrous structure of dimple pattern, and it had the high fracture toughness. |
|
