Need help hardening/tempering a few knives

[pathfinder]

Again, awsome answer!  I all of a sudden feel like goon when working in my shop! I'm still distracted by shinny things.

[melsdad]

LRB your explanation is outstanding. I Know a bit about heat treating tools steels, and could not have explained the process better. I even learned a few things in your description.

Hey Moderators, this should become a sticky for future reference. I would hate to see this information get lost!

[scrimman]

Wow.  This site continues to just astound me; the deep knowledge of the old skills by all the members here is incredible!  I'm glad I asked the question; that's much more information than I was expecting and WAY better!  Thanks!

[jmforge]

Good info so far.  Here is some more to cause your cranium to collapse.  Shallow hardening steels like 1095, W1, W2 and real 1084 can be quenched in oil when we are talking about thin pieces like knife blades.  The bad news is that it requires an extremely fast true quenching oil like Parks#50 or the Houghton version, (Q Quench, IIRC) to get the job done properly.  Parks #50 is almost twice as "fast" (7 sec) as Brownells Tough Quench (12-13 sec), which is a "medium/fast" Houghton product.  I suspect that folks on a traditional forum like this might balk at using "modern" low alloy carbon tool or spring steels like O1, 5160, 52100, etc. but the hardening process for those steels is quite a bit easier.  Good mineral oil, etc. will work for them.  HOWEVER, that comes at a price with some of these steels.  You are not going to get the optimum performance out of say O1 or the new Crucible CruForgeV without soaking it prior to quench to get all of the alloying elements back into solution. The same applies to shallow hardening tool steels like W2 that have additional alloying elements like vanadium.  
 The advice most often given to new bladesmiths is to use 5160 or 1075 because they are as foolproof.........or fool resistant as you can get.  1075 or one of the other lower carbon 10xx steels would probably be as close to "authentic' as you could get to the plain carbon steels of yesteryear.

[LRB]

All very true Joe. From what I have read on testing the steels in some old knives, they are closer to .60 in carbon, with some even less. 1075/80, will  make good knives at a minimum risk of a poor outcome. Assuming of course that one uses reasonably proper heat treating methods, and temps.

[jmforge]

Another trick to avoid hard spots when trying to anneal is to shove the heated piece into a bucket of vermiculite and let it cool slowly overnight.  In the old days, folks used sand or ashes from the coal forge, but they don't insulate as well. Another way to solve this problem is to not use steels that tend to air harden which is another really good argument for using something in the range of 1050-1075.  Some stuff, like Crucible's version of L6 will just frustrate you to no end with air hardening from what Kevin Cashen has told me.  O1 can have that problem too, but apparently not as badly. Of couyrse, Kevin uses that combination of steels for damascus, but he is a bit crazy anyway and uses high temp salt pots..lol.  Any steel with a goodly amont of chrome can do that.  The first time that Lin Rhea did his MS performance test, his damascus test blade crack up from the edge too high because the 52100 he had used in the mix had air hardened a little bit in that one spot.
IIRC, Tai Goo makes a number of his primitive knives from plain 10xx steel like 1060 and nobody would ever argue that those blades are inadequate for ANY purpose because of lower carbon content.