Image Analysis & Quantitative Metallography

Abstract

The metallographic examination constitutes simply a planar section view of a three dimensional structure. It is not enough to recognize this fact; one must also understand how shape in a three dimensional construction can deg-enerate into traces in random planar section.In fact, one must be able by mental visual skill to recreate from slices of hard boiled egg, the oblate ellipsoid when they came. For example, an inclusion, or porosity can appear to be different when observed in different planer section and the assessment of volume will be qualitative and only quantitative to the extent of visual judgement. Actual quantitative evaluation of inclusion and porosity, their shape and size distribution are very important for predicting the mechanical properties o the metals and alloys. Similarly, the grain size is another important factor in the hardenability of steels, ductility of brass and in the ductile-brittle transition of alloys. The amount of ferrite in stainless steels is a factor in their foregeability. The average flake size of graphite is a control parameter in the strength of gray cast iron. These are only a few instances where numerical limits to metall-ographic parameters arepractical factors in quality or production control. Since we can not obtain large number of specimens to get correct three dimensional picture, quantitative analysis is an appropriate alternative. Two factors must be assumed in all such quantitative studies. The planar section or sections be representative of the whole. In the matter of arriving at average values for dimensions of distributed particles one must have a know-ledge of the actual or approximate shape of the part- icles. Few particles are actually perfectly spherical. but this is a mathematical convenience.