Effect of Micro Constituents on Mechanical Behaviour and Corrosion Characteristics of Heat-Treated Alloyed Ductile Cast Iron

Abstract

The current research is focused on the investigation of response to static and dynamic loading condition and corrosive environment with respect to micro constituents of heat-treated alloyed ductile cast iron (DCI). DCI specimens with carbon equivalent (CE) 4.14 & 4.30 underwent annealing, normalizing, quench & tempering, austempering heat treatments processes by austenitization at 1000°C followed by subsequent cooling/quenching techniques. The dual matrix structure (DMS) heat-treatment process was carried out at austenitizing temperature of 800°C and then quenching into mineral oil maintained at 100°C. The mechanical properties viz. UTS, 0.2% YS, % elongation, Vickers hardness and impact strength was determined following respective ASTM standard and correlated with morphological aspects. To study the response to corrosive environment, respective as-cast and heat-treated specimens of alloys were immersed in sea water for 12 weeks, and at regular interval of 1 week the contaminated water was replaced by fresh sea water. The corrosion rate does not appear to follow a specific pattern, which was due to the replacement of fresh sea water with the contaminated one after every interval. The DMS-treated specimens were found to be more corrosion resistive as compared to other heat treated and as-cast specimens irrespective to the alloy composition. The morphological investigation revealed that graphitic corrosion is the primary phenomena that ultimately resulted in high rate of corrosion in specimens treated with normalizing, quench & tempering and austempering processes yielding to higher nodule count.