Found this info:
HARDENING TEMPERATURES FOR CARBON TOOL STEEL.- The best hardening temperatures for any given tool steel are dependent upon the type of tool and the intended class of service. Wherever possible, the specific recommendations of the tool steel manufacture should be followed. General recommendations for hardening temperatures of carbon tool steel based on carbon contend are as follows: for steel of .65 to .8 per cent content, 1450 to 1550 degrees F; for steel of .8 to .9 percent carbon content, 1410 to 1460 degrees F; for steel to .95 to 1.1 percent carbon content, 1390 to 1430 degrees F and for steels of 1.1 percent and over carbon content, 1380 to 1420 degrees F. For a given hardening temperature range, the higher temperature tend to produce deeper hardness penetration and increased compressional strength while the lower temperatures tend to result in shallower hardness penetration but increased resistance to splitting or bursting stresses.
It seems that one needs to find the sweet spot, ie go just over the hardening temp of the high carbon layer formed on the surface through carburization, and stay below the temp required to harden the low carbon core. That way you will end up with soft pearlite in the core layer, and hard martensite in the case layer.
So to ask the question another way, does anyone know the carbon content of the various steels used to make actions? and what elevated level is typically achieved in the case layer?
It sounds like Brownells may not be far off the mark with their 1400 degree temp.
