Abstract
An experimental investigation was carried out to study the effect of graphite nondularity on structure and properties of cast iron with 4-different levels of graphite nodularity and a composition of 3.6%C, 2.2%Si, 0.2%Mn, 1.5%Ni, 0.3%Mo. Microstructural observations and measurements of the retained austenite content, hardness, UTS, 0.2% proof strength, elongation, unnotched Charpy energy and wear rate are reported as functions of austempering time at 440, 370, and 300degreesC after austenitising at 900degreesC. The results of the experimental investigation indicate that graphite nodularity has considerable effect on the microstructure. After 8 min. austempering time at 440 degreesC and 370 degreesC austempering temperatures, the amount of retained austenite (gamma) increases with the graphite nodularity. Most mechanical properties UTS, 0.2% Proof. strength, elongation, unnotched Charpy energy and wear resistance decrease with decreasing graphite nodularity. At an austempering temperature of 370degreesC, the mar rate of 25% graphite nodularity iron is more than 94% graphite nodularity iron by 3.5 and 1.87 times for 30 and 150 minutes respectively. The microstructural investigation and hardness test investigation indicate that the graphite nodularity has a significant effect on the time t(1) corresponding to the end of stage I (process window), whereas decreasing the graphite nodularity delays the end of stage I reaction. The starting time of reaction II, t(2) is determined from the variation of x(y) with austempering time, it is indicated that lower graphite nodularity accelerates the start of stage II reaction.