Effect of Heat Retention Time and Pouring Temperature on Graphite Shape and Mechanical Properties of Gray Cast Iron

Abstract

In this study, the ASTM A48 Class 30 gray cast iron was cast in a medium frequency induction furnace. The ultimate tensile strength (UTS), ultimate flexural strength (UFS) and microstructure were determined in accordance with ASTM E8/E 8M-80 and ASTM A438-80 (1997). From the results of this study, the graphite size at overheating temperatures 1350 o C was smaller than that at 1300 o C. Moreover, if the holding time was sufficient, the nested sheet graphite would be completely destroyed. Particularly, in the case of holding time from 5 to 20 minutes, the UTS, UFS are increased and the graphite shape got fine. The smallest graphite size and the highest UTS, UFS values were achieved if 20 minutes holding time is carried out. However, the holding time increased to 30 minutes, the graphite size tended to grow larger, and the UTS, UFS values suffered a decline. In addition, decreasing the average pouring temperature from 1350 o C, 1300 o C to 1260 o C caused the upward trend of the graphite average sizes which were fit with the downward trend in the UTS and UFS values. From the above results, it is possible to determine the casting conditions that can improve the quality of cast iron products in induction furnace are: the optimal average pouring temperature is 1300-1350 o C, while the optimal holding time is 10-30 minutes.