Effect of Tempering Temperature and Time on Strength and Hardness of Ductile Cast Iron

Abstract

The use of ductile cast iron is as an engineering materials has been increase day by day. it is widely used in manufacturing industry. It have excellent combination of mechanical properties due to same heat treatment process at different time and temperature. It have an excellent combination of tensile strength, wear resistance, good corrosion resistance, good ductility, toughness, impact strength, by using different types of heat treatment process. The effects of tempering temperature and time on the mechanical properties of ductile cast iron is investigated in the current work. The all sample were austenitized at 900°C for 120 minutes and then quenched in mineral oil at room temperature. After quenching the specimens were tempered at 400°C and 200°C for 60min, 90min, and 120min, respectively. In the tempering temperature range of 200°C - 400°C, there is sudden increase in impact strength, ductility and toughness of the materials, as the temperature and time increase. The Ultimate tensile strength drops initially, and hardness of materials will also depends on amount of matrix phase of martensitic and retain- austenitic /ferrite and graphite nodules. In this work alloying elements also effected the microstructure of the specimen. And due to increase tempering time the amount of martensitic phase will decrease and austenitic phase will increase, austenitic phase is softer then martensitic so hardness will decrease. And sample treated to ball on plate wear tester under 20N load at constant speed 10rpm with different times 10min, 20min, 30min for sliding distance 4mm track diameter respectively of same sample. Weight loss was observed in all sample after wear test, the wear resistance was calculated according to the ASTM G 65 standard, and the result showed that in all cases, when the nodules count and nodularity increase the wear resistance decrease and when tempering time and temperature increase the wear resistance will also effected. And by XRD investigate the different matrix and volume fraction, peak analysis.