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

The effects of tempering temperature and time on the mechanical properties of ductile cast iron is investigated in the current work. The specimens were austenitized at 900 degrees C for 120 minutes and then quenched in mineral oil at room temperature. Immediately after quenching the specimens were tempered at 400 degrees C and 200 degrees C for 60min, 90min, and 120min. In the tempering temperature range of 200 degrees C-400 degrees C, there is sudden increase in impact strength, ductility and toughness of the materials, as the temperature and time increase. The UTS drops initially, and hardness of materials will depends on amount of phase of martensitic and retained austenitic 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 retained austenitic phase will increase, retained austenitic phase is softer then martensitic so hardness will decrease.