WORKABILITY STUDIES ON Fe-AI-C ALLOYS

Abstract

Fe-Al alloys have been of interest since the early 1930's as low cost structural alloys because of their excellent oxidation resistance. Iron aluminum alloys offer relatively low material cost, conservation of strategic elements, and a lower density than stainless steels. However, these alloys generally exhibit poor room temperature ductility and low fracture toughness. As yet they are not commercially exploited because they are sensitive to processing. In recent years advanced processing techniques have been used to develop these alloys. Initially Aluminum was not alloyed with iron the reason being lowering of ductility and increase in strength on addition of aluminium to iron. As amount of Aluminum is increased above 18 at% Al ordering reactions take place to give raise to ordered Structures like DO3 and B2. Carbon has a very limited (0.01wt%) solid solubility in Fe-Al alloys. Most of the carbon is present as pervoskite Fe3A1C0.5 precipitates in alloys with low (<37at%) Al-content. Presence of carbon was believed to embrittle Fe3A1 alloys. For these reasons most of the literature is on alloys with very low carbon content. Recently iron aluminides with-carbon are being developed. Addition of carbon results in the precipitation of Fe3AlC0.5 which adds to the strength and properties of the material. It may also affect hydrogen mobility in these alloys which are susceptible to hydrogen induced cracking. A processing route comprising of air induction melting (AIM) with protective cover and electroslag remelting (ESR) for production of iron aluminum alloys containing carbon has been developed. The use of protective cover during AIM results in the minimization of hydrogen gas porosity and a significant reduction in the impurity levels (S, 0 and N). Electroslag remelting of AIM electrode results in ingots free from gas porosity. Workability refers to the relative ease with which a metal can be shaped through plastic deformation. The term workability is often used interchangeably with the term formability. A large number of tests are generally used to evaluate the workability of the material which include tension, torsion, compression and bend. Of these four tests, compression has been the most highly developed as a workability test. iii IPage There are two reasons that Fe- I lwt% Al with 0.5wt% C and 1.1 wt% C alloys are considered for workability studies. ESR processed cast alloys of Fe-1 lwt% Al with 0.5wt% C and 1.1 wt% C have dendritic precipitation of Fe3AlC0.5 at interdendritic regions which gives inhomogeneous structure. Thus the alloys were hot worked to get a more homogeneous microstructure. Workability also depends on the material being processed. Since these alloys are hard they are generally difficult to work. In the present investigation worked alloys of two compositions (Fe-Ilwt% Al with O.Swt% C and 1.lwt% C) are taken and workability tests are conducted on these alloys. The present work includes determination of the workability of these alloys at various temperatures and strain rates. Further it includes the effect of deformation on the microstructure of the alloys. Stain Induced Crack Opening (SICO) was conducted on the samples in Gleeble 3800. The thesis include six chapters in which Chapter 1 gives the introduction of the alloys, processing, workability and the objective of the report. Chapter 2 discusses about different types of Iron Aluminum alloys present, their properties, processing and applications. Chapter 3 gives the general description about workability. Chapter 4 gives the details of Thermo-Mechanical Simulator Gleeble 3800 and SICO test. Chapter 5 gives the experimental procedure of all the experiments conducted for the thesis. Chapter 6 discusses about the results obtained for various tests conducted. Conclusions and suggestions for future work are given at the end of the thesis.