Study on the Effect of Austempering Temperature and Time on the Corrosion Resistance of Carbidic Austempered Ductile Iron (CADI) Material

Investigation of corrosion resistance and hardness of carbidic austempered ductile iron

Abstract

Carbidic austempered ductile iron (CADI) has emerged as a promising engineering material to replace the ADI for higher wear resistance. It induces interest to study the corrosion behaviour of the material in chloride media, bearing in mind that equipment made from this material may be in constant contact with such media. Corrosion resistance of ductile cast iron is improved by the incorporation of an extra phase in the matrix which typically consisting of some carbides. The objective of the present work is to produce carbides in a ductile cast iron which is subsequently austempered to obtain CADI. Six variants of CADI were produced by heating carbidic ductile iron (CDI) to a austenitization temperature of 975 ºC for the period of 1 hr and quenching it in a salt bath at temperature 325 ºC and at 250 ºC for periods of 1 hr, 2 hr and 3 hr at each temperature. The corrosion resistance was evaluated by using salt spray fog test in accordance with ISO 9227 standards. The mechanical properties- bulk hardness, micro hardness evaluated and microstructure of the CADI were characterized by optical microscope and SEM. CADI sample at Austempering temperature 250 ºC and austempering time 1 hr has given best hardness 58 HRc and lesser corrosion rate 0.2094 mm/year which indicates best corrosion resistance.