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 - First specimen
Paper cutting bkade at 100X (greyscale) etched
 This is part of a paper cutter blade that has a high carbon steel cutting edge brazed to it.  It is shown at 100X as a greyscale image.  Note the porosity of the joint; the joining metal is a low melting nonferrous alloy.

From the gradients in the microstructure,
can you tell which piece is the high carbon one ?



Pause a little, formulate  an opinion,
and then look at the answer below.



























Explanation:  The cutting edge is on the right; its carbon has diffused a substantial distance into the substrate steel, even though the joint metal did not penetrate either side nor even wet either side completely.
Paper cutter blade at 100X etched
The cracks visible in the second photomicrograph, shown at left (also at 100X magnification, but in color this time) could have formed due to faulty material, bad grinding practice, or poor heat treatment.
Specimen 2 is a cement mixer shaft.