McQuaid-Ehn test

McQuaid-Ehn test

[mə′kwād ′ān ‚test]
(metallurgy)
A test for determining the grain-size characteristics of a steel in which a sample is carburized for 8 hours at 1700°F (927°C) and cooled slowly; the high-carbon case on slow cooling will reject cementite at the austenite grain boundaries and, by polishing and etching, the grains will clearly be seen under a microscope.