Phase Investigation of Austempered Ductile Iron

Abstract

In austempering, the microstructural end product of the spheroidal graphite (SG) iron matrix is essentially bainite, a structure formed below the pearlite temperature range but above the martensite range. Ductile cast iron undergoes a remarkable transformation when subjected to the austempering process. Due to isothermal transformation, it produces a microstructure that is stronger and tougher than the structures resulting from conventional heat treatment process. In the present investigation, the SG iron was austempered with three different austempering temperatures (2500C,3000C and 3500C) with varying austempering time. The sample was taken for XRD analysis to study the morphology of the matrix. It was found that both the austenite (111) and ferrite (110) lines are identified nearly in all cases. The maximum intensity of the austenite (111) line is increasing with increasing temperature but ferrite (110) line is increasing with increasing austempering time and decreasing with austempering temoerature. Hence austempering calls for very precise control of process times and temperatures.