"The original quenching and any subsequent "hard fitting" almost always produces stresses in the steel. Recase-hardening without relieving these stresses can lead to serious warpage and improper fitting after the parts are recase-hardened. Furthermore, parts need to be properly polished and sometimes engraving needs to be recut before refinishing takes place. Polishing a case-hardened steel surface is difficult and surface waviness can result due to slight differences of hardness of different regions...... All of these problems can be alleviated by first annealing all of the previously case-hardened parts. Proper annealing relieves the stresses mentioned above as well as diffusing the carbon in the original case deeper into the metal and transforming the phase of the high-carbon steel to a softer more easily worked material."
This was written by the master, Oscar Gaddy in his excellent articles in DGJ, in part II, Spring 1997.
I have a close friend who has done recase-hardening of double gun receivers and other parts in his home workshop for many years. He has never had a problem with warpage of parts, and gives credit for that to the annealing process always done prior to polishing and subsequent work.
Last edited by Stan; 02/06/10 08:34 AM.