Carbide to Graphite Transition Control by Thermal Analysis in Grey Cast Irons

The present work compared the solidification pattern of un-inoculated and inoculated hypoeutectic grey cast irons (3.7-3.8% CE), focused on carbide to graphite formation transition, by the use of an adequate experimental technique, able to measure real stable (Tst) and metastable (Tmst) eutectic temperatures. Have been used three ceramic cups for investigating thermal analysis: (i) for normal solidification; (ii) with addition of Te forTmst measurement; (iii) with more inoculant addition forTst measurement. As a general rule, measured values appear to be lower compared with calculated values (as chemical composition effects), with an average difference at 14.4 degrees C forTst and 8.3 degrees C forTmst. It is found a good relationship between the undercooling degree at the lowest eutectic temperature (Delta T-1) and at the end of solidification (Delta T-3), reported to measuredTmst. The free carbides formation (chill tendency) is in good relationship with the undercooling degree during the eutectic reaction, reported to measuredTmst, especially for thin and medium wall thickness castings. The real measuredTmst instead of calculatedTmst is compulsory for the thin wall castings production, very sensitive to carbides to graphite transition. In the present experimental conditions, no visible relationship appears to be between chill tendency and undercooling at the end of solidification (Delta T-3).