Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©2005 by George Langford
Low Alloy Steels - Lesson 2 - Fifth specimen
Aircraft landing gear pin at 100X etched
 Here are two pins from an aircraft landing gear. 

The first is shown at left at 100X magnification.

The second pin is shown below at 1000X; Nital etches.
Aircraft landing gear pin at 1000X etched
 Which structure is satisfactory;
and which structure failed in service ?




Pause and think ... then take a look below.



























Answers: The airplane crashed in South America; the pin in the upper image was badly decarburized and is in the annealed condition.  The satisfactory pin shown in the lower image is a quenched and tempered medium carbon steel with a hardness of Rockwell C19.
Move on to Specimen 6.