ABSTRACT
The effect of austentitizing temperature and quenching medium on ductile cast iron in the as-quenched, cold treated and tempered condition was investigated. The study was based mainly on hardness and impact tests. Ductile cast iron speciemens were first given a normalizing beat treatment before quenching. Normalized specimens were heated to five austentising temperatures (800, 850, 900, 950 and 1000�C), soaked for one hour and quenched in three media (water, brine and ice-water). Some of the specimens were immediately subjected to hardness and impact test in the as-quenched and tempered conditions while others were immediately subjected to cold treatment at 20�C for two weeks in a domestic deep freezer after which hardness and impact tests were conducted in both old and cold treated and tempered conditions. The result shows that, ductile cast iron responded well to hardening in the three media. However, ice-water gave the highest severity of quench for all the austentitizing temperature used. Specimens quenched from 950oC in ice-water, brine and water had the highest hardness values of 511,490 and 480 HB respectively. Optimum hardening temperature for the ductile cast iron was found to be between 900 - 950�C, while optimum tempering temperature for adequate hardness for wear resistance was found to be between 250 - 300�C then for strength and toughness it was found to be between 350 - 400�C.