The Quantitative Assessment of Retained Austenite in Induction Hardened Ductile Iron

摘要

This study focused on induction hardened ductile iron which has a variability in both the microstructure of the surface hardened case, principally the amount of retained austenite (RA), and the level of residual stress (RS). Retained austenite and residual stress can have a significant effect on mechanical properties. In order to determine what level of retained austenite is acceptable, it will need to be measured by an acceptable metallographic procedure and through the use of X-ray diffraction (XRD), although XRD has proven much more accurate in assessment than optical metallography, However, because of the complexity as well as availability of the XRD equipment, it is not well suited to analysis of camshafts during high volume manufacture or heat treatment of camshafts. Therefore, an acceptable correlation is needed between the two methods of measurement. During this study a correlation has been obtained between the RA values obtained by x-ray diffraction with those obtained by optical metallography. This data for ductile iron expands the database that was available for steels to higher carbon-content ferrous alloys. Finally, a correlation is made between RA content and RS level in order to define a robust process window.