Microhardness testers are precision optical instruments and are normally the province of the metallographic laboratory because finished polished microspecimens are required. Readings are best made in the lightly etched condition to aid in locating significant structural areas. Heavy etching could adversely affect the values or obscure the indentations, making them difficult to read. The positive identification of decarburization or untempered martensite, suspected from visual observations, may be verified by using microhardness. Our microhardness tester employs a diamond pyramid indenter having an included angle of 136o between the opposite faces.
Procedure Wash the specimen prepared during the last laboratory period in the ultrasonic cleaner.
Using a microscope, check the specimen for scratches. If the scratches are minimal, proceed to the next step. Otherwise, go back to fine grinding steps for sample preparation. Etch the specimen using appropriate chemical solution. Stop the chemical reaction by immersing the specimen in water or alcohol for 30 seconds.