Effect of Alloying Elements and Technological Parameters of Austempering on the Structure and Mechanical Properties of Ductile Cast Iron (ADI)

The effect of additions of alloying elements (Mo and Ni), austempering time and thickness of the product section on the mechanical properties of industrial ductile iron of grade GGG-70 (EN-GJS-700-2) is studied. Standard keel blocks and crankshafts have been produced by static sand casting from unalloyed, alloyed with 0.2% Mo and 0.2% Mo + 0.6% Ni ductile iron. Austempering is carried out at 350 °C for 90, 120, 150, and 180 min in a salt bath. It is shown that the alloying has a significant effect on the ability of cast iron to austempering and its mechanical properties after heat treatment. Alloyed cast iron has the best combination of ultrahigh yield and tensile strength with high ductility. After austempering, crankshafts alloyed with 0.2% Mo + 0.6% Ni have a typical ductile iron ADI structure even in the thickest sections (58-mm-thick main bearing center) with a uniform hardness distribution.