Actually, traditional color case-hardening whether by carbon pack or cyanide bath is incompatible with the heat treatment of modern through hardening alloys such as 4140. However, the traditional colors can be reproduced on those alloys by heating and quenching from lower temperatures. This is possible because all the temper colors are produced below 700° F. 4140 is typically tempered at about 1000° F after it is hardened to achieve the desired toughness and hardness ( RC 36-40) desired for guns.
Heating and quenching below 1000° have no affect on the original heat treatment yet allows full color(but not "case-hardened") developement. This also explains why Ken Hurst can engrave such pieces without annealing.
OB
Last edited by OB; 11/11/09 03:49 PM.
