Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©2005 by George Langford
Surface Coatings and Heat Resisting Alloys - Lesson 3 - Fifth specimen
Exhaust valve at 100X etched electrolytically
 Here is the exhaust valve from the same Mercury (i.e., Ford Motor Company) engine.

The photomicrograph at left was made at 100X after etching electrolytically in an oxalic acid solution.  The alloy is iron with 16% nickel, 14% chromium, 3% silicon, 0.25% molybdenum, 0.6% manganese, and 1% carbon.  The hardness is Rockwell C27.
Exhaust valve at 500X etched electrolytically
 The second photomicrograph shows the microstructure at 500X magnification.



How was this valve made; and how many different microconstituents can you make out ?
The answers to these questions
are at the bottom of this page.



























Answers:  This is an extremely high quality product made by the shell molding process.  There are primary dendrites (probably FCC austenite) plus a complex multicomponent eutectic ... with at least four additional phases ... maybe even more than one eutectic microconsituent, considering that there are four major elemental components !
Specimen 6 is a molybdenum heating element.