Microstructures
by George Langford, Sc.D., Massachusetts Institute of Technology, Cambridge, MA, 1966
Copyright©2005 by George Langford
Low Alloy Steels - Lesson 4 - Fifth specimen
Induction hardened steel at 100X etched
 This inductioned hardened cylinder liner was rejected because of the ferrite network seen here at 100X with a Nital etch.

The photomicrograph was taken at the junction between the hardened [brown] case and the spheroidized [blue] pearlitic core.

Why was the cylinder liner spheroidized before the induction hardening step ?

It has something to do with the distribution of the cementite in the spheroidized condition vs. in the ferrite plus pearlite condition.
Here's the complete answer.



























Explanation: The spheroidization was necessary to enable complete austenitization during the very short heating time made possible by the induction heating.  It also improves the toughness of the core.  The ferrite network was already present before the cylinder liner was spheroidized.
Proceed to Specimen 6.