Metallographic Science

Metallography: A Tool for Quality Control

Authored by LECO Corporation and Dr. Lee Dillinger

Metallography is the preparation of specimens for microscopic examination and then the study of the microstructure in relation to the physical and mechanical properties of that particular alloy. This is a text book definition and to one schooled in metallography makes good sense, but in layman’s terms what does itmean? Key words in the definition are "preparation", "microstructure", and "physical and mechanical properties". Preparation involves taking a piece of metal, cutting off a small representative piece, and imbedding it in some molding material because the piece is usually too small to handle conveniently. Next it is ground with several successively finer abrasive grits, polished until all the scratches from the last grind are removed, subjected to a corrosive environment (usually acidic), then viewed on a microscope at magnifications ranging from 50 to 1500 diameters. Microstructure is the microscopic structure of the polished and etched specimen. Physical and mechanical properties deal with hardness, hardenability, ductility, and tensile strength, and all relate to how the material will perform in its designed purpose.