STRUCTURE-PROPERTY RELATIONS IN HIGH-MANGANESE-CHROMIUM-COPPER WHITE IRONS

Abstract

The thesis comprises a total of eight chapters. The first chapter introduces cast irons as materials of construction. It deals. with important varities of gray cast irons such as Compacted graphite Silal, Nicrosilal, High Silicon irons and Ni-Resist irons. The second chapter deals with `in depth' information on corrosion, wear, and heat resistant white irons. The usefullness of the Fe-Mn-Cr-Cu alloys, in resisting corrosion and wear, forms the basis of formulating the present problem highlighted in Chapter-III. Chapter IV deals with the experimental techniques and procedures employed with major emphasis on the X-ray diff racto-metry, EPMA, DTA, corrosion testing, compression testing, and quantitative optical metallography. Results and discussion have been divided into three chapters. Chapter V includes the effect of heat treating parameters on the hardness and microstructure characterized qualitatively as well as quantitatively. This has led to the development of a number of models and some new ideas encompassing `quantitative characterization of 2nd phase particles' and `homogeneity/heterogeneity' of the alloy(s)/system. lit Chapter VI deals with the (i) structural investigations by X-ray diffractometry and EPM analysis to carry out a detailed phase analysis and for assessing the partitioning behaviour of Mn, Cr, Si, and Cu into the matrix, massive carbide, dispersed second phase(spherical & plate like) and the hitherto unobserved gray etching phase(formed on heat treating from 1000'C and (ii) study of the transformation behaviour of the alloys by OTA primarily to assess the suitability-of selected microstructures for high temperature applications. Chapter VII is devoted to an assessment of the deformation behaviour of selected microstructures in the as-cast and in the heat treated conditions by compression testing, electro-chemical characterization of selected microstructures by weight loss methods, and a study of the corroded specimens by scanning electron microscopy. A salient feature of the present study has been the development of a number of mathematical models interrelating the (i) heat treating parameters with the.,hardness, (ii) microstructure (especially the effect of second phase corresponding MC & DC) with the corrosion rate, (iii) hardness with the compression strength, (iv) compressive strength with the corrosion behaviour, iv (v) distribution of the massive & dispersed second phase with homogeneity/heterogeneity (vi) size distribution of the dispersed second phase with coarsening Based on the above findings, conclusions have been drawn with regard to the transformation behaviour of the alloys under various heat treating conditions and the suitability of different microstructures from the point of view of corrosion resistance, and mechanical properties finally leading to the optimization of microstructure for obtaining the aforesaid properties. They (conclusions) are enumerated in the, chapter VIII. The key features of the present investigation are (1) the development of corrosion resistant cast iron having corrosion resistance comparable to that obtained in the conventional Ni-Resist cast irons with an additional advantage of improved mechanical properties, (ii) defining a new parameter to represent the homogeneity/heterogeneity of the structure, (iii) development of several `models' very useful for optimizing microstructure & for quantifying structure-property relations, and (iv) extensive use of computational techniques and the development of application software, of immense use for materials development/ characterization, for the IBM compatible PC-AT & PC-486 systems.