Microstructure and mechanical properties of austempered ductile iron with different strength grades

Austempered ductile irons (ADIs) with three strength grades were produced successfully by different two-stage heat treatments. The microstructure and mechanical properties of ADIs such as tensile strength, yield strength, elongation and impact toughness were studied. The results show that the strengths of the three grades ADIs well satisfy the requirement of ASTM standard 897M-06 grade 900/650/09, grade 1050/750/07 and grade 1200/850/04. Meanwhile, the ductile and impact toughness of the ADIs are larger than those required by the ASTM standard. The microstructure has obvious influence on mechanical properties and fracture behavior. With the decrease of austempering temperature, yield strength and tensile strength of the ADIs increase, while both the impact energy and elongation of them decrease.