It appears, depending on the process, that color case hardening can increase steel strength
http://www.sst.net/advantages-case-hardening/

I am however looking for numbers...which are better than 1000 "expert" opinions wink

I should have also mentioned "cold rolling" which was used on decarbonized steel barrels as a means to increase tensile strength. The carbon steel numbers I gave are for cold rolled, not heat treated steel.

AISI 8620 is a chromium, molybdenum, nickel low alloy steel often used for frames today. It is easily carburized and machined when annealed
Carbon - .18 - .23%
Manganese - 0.7 - 0.9%
Chromium - 0.4 - 0.6%
Molybdenum - 0.15 - 0.25%
Nickel - 0.4 - 0.7%
Phosphorus - 0.035% max.
Sulfur - 0.04% max

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