Found this info:
HARDENING TEMPERATURES FOR CARBON TOOL STEEL: 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.
Lot of apples and oranges in this discussion. Carbon tool steels are not what actions are made of. If we are talking about casehardened receivers (I assume we are) the steel involved is low carbon, about 20 points carbon, and is itself not hardenable by heating above the critical temperature and quenching, regardless of process. That is why it is often casehardened or carburized by one of several processes to give it a hard wear resistant THIN outer layer of high carbon steel to accompany a tough ductile core from which the strength of the structure arises.
That high carbon case is then tempered for several reasons, and this is indeed done at temps of 350-400f. That tempering (or the hardening quench for that matter) has only very minor effects on the low carbon core, and none that need influence this discussion.
It would be well to remember that carburizing of simple low carbon steels is an essentially very low-tech process that is well understood and has been carried on by primitive means for hundreds of years. The matter of whether or not colors are desired as a correlary of this process is another matter: You can have oxide colors without hardening or with it, or none, depending entirely on how the process is managed.
In point of fact, many of the finest London guns of the late nineteenth century, and probably the early twentieth as well, were heat treated and colored in boxes of bone charcoal over hand tended coke fires in the alley behind the workshop - literally.
It would come as a considerable surprise to these skilled artisans that they needed to know or care about decalescence or recalescense.
