Study of Effect of Etching Time and Concentration on Microstructure of SG 400/12 Grade Ductile Cast Iron

Abstract

The study of material microstructure is known as Metallography. This is very critical in estimating the material properties. Metallography can be a very useful quality control tool too. By examining the micrographs one can determine the quality of the product. Micro structural examination is generally done on a sample whose surface has been grinded or polished to a mirror-like finish. SG cast iron is characterized by nodules-like graphite distribution when seen under an optical microscope. The as-polished samples are also etched with various etchants to look at the underlying phases (e.g. ferrite, pearlite, cementite), which also have an effect on the properties of the SG cast-iron. If a casting has predominant ferrite phase, then it would be soft. Ample presence of carbide will lead to a hard material. The study reported here deals with the etching of SG cast iron (400/12 Grade) samples for short etching time (4-10 sec) and also for long etching time (30 sec and 60 sec). For the purpose of observing the microstructure we have used Scanning Electron Microscope (SEM). The optimal solution is taken by the use of regression analysis technique. Etching is the selective corrosion of the surface under consideration to reveal the underlying features. The purpose of etching is to reveal certain features (e.g. grain boundary and phases) which are not visible in the as-polished condition.