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A2 hardening problems

Aug 19, 2000
Well, this is going to sound pretty silly to anybody that's worked with A2 before. I bought a length of A2 bar stock 3/4" X 7/8" X 18" and took it to a machine shop to be made into a filing jig. They did a great job with the precision guide pins and and bolt holes and also matching the flats to zero tolerance.

Being a knife maker with plenty of heat treating experience, I decided to heat treat the jig myself. I read the specs in Crucible's handbook and did the best I could at following their advice. The A2 was Crucible steel too. Long story short, the jig is still just as it was from the crucible mill. A file cuts it fairly easily.

At first, I thought all I needed to do was grind off the decarburized area on the flats to get down to the hardened face, but that didn't work out at all. Still soft. Does anyone know any secrets about A2 that might help me?

Here's what I did. I hung the jig halves on a stiff wire to keep them separate and heated them slowly and uniformly until the shadow left them and let them soak for about 10 minutes at that temp. Then, I hung the wire with the jig halves on it on the screen of my 36" shop fan and turned it on and left them till they were room temp. Should have worked shouldn't it?
Sounds like you got some mislabeled steel to me. My experience with A2 is that it is very easy to get the stuff hard. Hell, it air hardens when you grind it and drill it!

Danbo, soul brother of Rambo
I guess that's possible Danbo. I bought the steel at a surplus store, but it was labeled with a sticky lable and inserted into a brown paper tube with the same info on it. It was also precision ground. Sometimes I guess we can get a lemon when we think we're getting a peach
I don't know how you were measuring the soak temp, but, it should be 1750F. I also don't know how thick your parts are, but, A2 requires a rather long soak-about 40 Min for 1/4" thick stock.
My suspicion is you didn't get nearly hot enough or hold long enough.
If you don't protect the steel from Decarb, you're going to produce scrap-A plain atmosphere will decarb the steel severely @ temp.
If you're trying to hold precise tolerances, I'd pay a HT outfit to vaccuum harden it, so you'll have no decarb.

RJ Martin

I work with A2 almost exclusively (my favorite blade steel) and haven't run into your problem. It would be my quess that your soak time is too short. A2 needs to soak about 1 hour per inch of thickness.

For a typical blade (3/16") I soak them for 20 minutes at 1200 then another 20 minutes at 1775. Also you should always use tool wrap unless you have an oven with an inert gas for the chamber.

Let me know if this helps. A2 really isn't difficult to harden.

Well, like they say, when you need a professional service, get a professional. You know how it is when you're trying to pinch pennies and wind up throwing away handfulls of dollars. It's not the first time I've been there and it most probably won't be the last