5160 Tricks for the Quench Questions

[Ragnarok Forge]

I am going over to the friend of a friends place to look at a Duncan Ceramic Kiln  It is supposed to be in excellent condition and heats to 2200 degrees F.   It has a shelf for holding materials up off the bottom.  It is priced at $375.  I want to buy a standard knife kiln, but those of us with wives in college have to pinch our pennies. So I am looking at making due with this option for holding set temps for 5160 and 1095 steels.  

Now for the questions.  Once I have the 5160 at the proper temp and soaked long enough to get the carbon fully into solution, do I do a full depth quench with the blade or is an edge quench better?  When using a full quenched blade after the temper, I am thinking I should draw the spine back.  I can use a torch, or I was thinking about using a large flat piece of steel heated in the forge to set the spine on to draw it back.  I am making up four big camp choppers and want get 58 to 60 rockwell on the edge and want to optimize the steel toughness as well.

[bendbig]

just my .02 wouldn't you want to put a piece of heated steel on both sides of your blade to get as even heat as possible. I've had to do this at work on tooling to pull back an edge (spine) I would always use a fire brick to lay the heated steel on then the metal I was drawing back, another piece of heated steel and another brick, to keep everything uniform.

[4est trekker]

My friend is the head blacksmith at the State Historic Park we both work at.  He is also a very good bladesmith.  When doing period work on edged tools, he often does just as you said to draw back the spine; that is, laying it on a piece of hot bar steel and watching carefully as the heat runs toward the edge.  Obviously, your piece has to have a surface smooth and be clean enough to be able to see the color change.  You could also invest in (or make) a set of tempering tongs.  Same basic principal, except that you apply heat to both sides of the blade at once instead of running it up through the edge of the spine.

[Ragnarok Forge]

Bend Big.  I plan to hay the flat of the spine on the steel with the tip of the blade sticking out past the heated plate to allow for the differentiual heating of the tip section being thinner.  

I am trying to find out what the folks who have used this steel a lot do to find the right balance of edge holding while maintaining  toughness. I have been tasked with forging out a couple of cleavers and some kitchen knives for my wife as well.  Tricia decided I have had enough training time and wants a set of kitchen cutlery with my mark on it for her camp kitchen.

[kbaknife]

Lowell, one thing to remember about 5160 is that it is a very deep hardening steel. It has so much chromium in it that just by bringing it up to austenizing temp, as it cools in air, it will harden.
That's something to consider when using an oven for heat treating 5160.
Now I will say, that without a doubt, to get the most out of 5160, it needs to soak at a controlled 1525 degrees for about 8-10 minutes.
Austenizing 5160 in a forge WILL get you some martensite upon quench, but not near what is available.
But, when using a forge, you can sort of control your heat and austenize only the cutting edge, thus leaving the spine and tang martensite free. And those who use forges to harden 5160 are really cutting themselves, their knives and their customers short.
Not so with an oven, as it brings the ENTIRE knife up to temp, and even though you may only quench the lower portion of the blade, everything else will harden to some degree.
This makes it necessary to then soften the tang for any drilling, tapping, threading, etc.  
So keep that in mind when using an oven.
You can also clay portions of your blade to protect it from the quench and minimize hardening, but it'll still harden to some degree.

5160 is a truly GREAT! steel, is readily available and WILL harden to some degree, even with the simplest of equipment - even an A/O torch, which makes it very popular.

But even 5160 takes a while to learn to get the most of.

And we spend a lot of time talking about hardening and tempering, but those are just the last two steps in the heat treating process.
It's all for nought if the steel wasn't prepared correctly up to that point.

[Ragnarok Forge]

KBA Knife,

Thanks for weighing in.  I am just starting with 5160 and have a couple of options for heat treating.  The first is to take it to a local heat treat shop and let them do it.  The other is to pick up the kiln and run the full heat treat myself.  I am working on that last option by looking to purchase a kiln.   I have done the research to understand and work the annealing, and normalizing requirements of the steel.  I am now working to figure out the end of the heat treating and hardening process for 5160.  I have 5 camp choppers and 2 cleavers in the grinding and finishing steps right now.  I want to figure things out before I attempt them and mess up a bunch of work.

[Wampus]

I use a ceramic kiln for a lot of heat treating and there are a couple of things to watch out for.  One is that the direct radiation from the heating elements can heat your steel hotter than what the guage says.  I usually let the kiln stabilize at temp before putting the steel in if that works for what I'm doing.  Mine has a little "bead door" that I can use without having to open the big door.  I also use a little "frog house" of refractory blanket to shield the blade from direct radiated heat, but you need to have it open enough so it gets to the same temp as the rest of the kiln.

The other thing is that there is no fuel like propane burning up the oxygen so there is a lot of it available to oxidize your blade and you will get a lot more scale than with a forge unless you take steps to prevent it.  One thing you can do is put a piece of charcoal in with your blade to burn up some of the oxygen.  A lot of the knife kilns have a system to purge out the oxygen with an inert gas and you could rig up something like that with a ceramic kiln too, but I haven't.  For me the easiest way to prevent scale has been to coat the blade with a very light coat of satanite.  A very thin coat will not slow down the quench at all and actually speeds it up a little because of the surface texture and it helps prevent the scale that you get with bare steel.  Mix it up more watery than paste-like and just paint it on the blade as thin as you can.