EFFECT OF THERMOMECHANICAL PROCESSING ON STRUCTURE AND MECHANICAL PROPERTIES OF DUCTILE IRON

Abstract

Ductile Iron or Nodular Cast Iron is defined as a form of cast iron in which the carbon is present in the form of spherical nodules within ferrite or pearlite matrix or a mixture of both. The carbon content is high compared to steels and also Si is present along with Mg and Ce which aid in making spherical nodules of graphite. The flakes of graphite are however present in other form of cast iron called gray cast iron. Ductile iron is also referred to as nodular or spheroidal graphite cast iron. The Ductile iron is ductile in nature as the name suggests due to the presence of spherical nodules which make its plastic flow easy on application of load. The ductile iron products are finding a phenomenal growth in industrial use because of its high performance to cost ratio. One of the reason for it is the control in its properties during as-cast condition as a result of which high ferrite and pearlite structure can be obtained. Refinement of microstructure is effected by undergoing hot deformation which leads to grain refinement of parent austenite. This is carried out in austenising temperature range. The specimens were reduced to 50% of their sizes and the thermomechanical treatment was done at the strain stain rates of 0.1 s-1, 1 s-1 and 10 s-1 at different hot compression temperatures of 850οC, 950οC and 1050οC using Gleeble 3800 Thermomechanical simulator. The flow curves obtained for each sample that underwent thermomechanical processing were compared and studied. The microstructures were studied with the help of light optical micrographs and SEM micrographs taken for each sample subjected to different processing parameters. Also to know the phases present within the sample XRD was done for each sample and the peaks were studied. Also macro-hardness was determined for each specimen under different test parameters. The macro-hardness of the specimens were determined from Vickers hardness test and ductility of the hot compressed samples was compared to that of as received sample to study the changes in mechanical properties of the ductile iron. Finally the changes in the structure and mechanical properties of the nodular cast iron due to the Thermo-mechanical processing were studied.