Optimizing of alloying elements and heat treatment cycle on production of ductile iron casting with subzero impact energy absorption

摘要

Alloy EN-GJL-400-18-LT is the same standard of 60-40-18 of ductile iron, which is required minimum 12J impact energy absorption at -20 °C and Hardness of 130 BHN. This alloy is utilized in manufacturing compressor casing of gas turbine for the first time in Iran. In this research, the effect of elements such as Ni and Si for achieving the impact energy absorption at subzero temperature and the influence of annealing temperature during heat treatment of ductile iron have been investigated. It has been observed that 1 to 1.5% Ni will improve ultimate tensile strength, yield strength and hardness by increasing the pearlite phase however it has inconsiderable effect on impact energy absorption. On the other hand the amount of Si up to 2% has a significant effect on shifting impact transition temperature to subzero temperature by stabilizing ferrite phase. Further study on different heat treatment batch depicts the maximum allowance of pearlite phase for required impact test is 15%. This is obtained by controlling annealing temperature at 910 °C for 4 hours then 750 °C for 3.5 hours and finally cool down to ambient temperature at 100°C/hours.