Posted by TVP on July 10, 2008 at 11:40:59:
In Reply to: Re: grain size of Q&T low alloy steels posted by SMP on July 10, 2008 at 08:59:23:
The oxidation method of ASTM E 112 (section A3.2.1.5) specifies a temperature of 857 +/- 14°C for 1 hour then quench into cold water or brine. It is unlikely that any grain growth occurred. Villela's reagent is a modification of picral, which attacks the interfaces between ferrite & carbide phases. You are most likely observing a decarburized, ferritic microstructure, with the prior austenite grain boundaries being delineated. You can confirm this by sectioning the sample perpendicular to the surface and etching with nital: the decarburized layer will appear light, while the bulk should be dark (as-quenched martensite).