second hardening

R

rlinger

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Mar 29, 2002
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After hardening and tempering, if O1 tool steel needs to be hardened again should it be annealed first (after it had already been hardened and tempered the first time) or will it harden okay just as done the first time? I over ground an area and had to do some reshaping so I lost the temper.

Thanks.
 
Someone may say otherwise but you should be okay to re-HT from where you. I think if it was me I'd normalize; bring to critical and allow to air cool, then HT. But that's probably not necessary.

Dave
 
Thanks Dave,

That's what I went ahead and did. I just re-HT-ed it. Hard as a rock. I'm not really positive what happened the first time. Maybe I over did the tempering. This time I tempered twice at 350 F. for 35 min. each time. The first time I tempered once at 350 F. for 60 min. and again at 325 F. for 60 min. Beats me, but its hard now.
 
I'm not really positive what happened the first time. Maybe I over did the tempering. This time I tempered twice at 350 F. for 35 min. each time. The first time I tempered once at 350 F. for 60 min. and again at 325 F. for 60 min. Beats me, but its hard now.
Click to expand...

If you are willing to release the temperature you austenitized at and hold time, I think I may know why you had the results you did from the tempering sessions. I'm curious.

-Jason
 
Jason, to answer your question: I achieved non-magnetic and soaked for almost a minute.

I think I figured the problem out. For the first HT I had put the blade in the forge blade end first. I have forced air going into the back part of the forge. I did not test the blade for hardness before tempering. The second HT I placed the blade in the forge tang first and did test for hardening before tempering. I think I have a slight anomoly in my forge design. I'll need to force the air into another area for even heating. Regretably, its a little late to be drilling new holes though! The refactory castable doesn't seem to take kindly to that.

Thankfully the O1 seems rather forgiving as far as heat distortion goes so I got away with it this time.
 
Well, 0-1 is easy to heat treat, it was designed to be. So, you are right about it being forgiving in the HT. Hmm, well without actually being there my verdict is one of two things, or both perhaps. The first HT you probably did not get it high enough in temp. Reaching critical means you have just begun to form austenite, you needed more heat or a little longer at that temp you had to get more austenite. I'm going with higher heat though in your case.

The other possibilty is this... If you achieved the temp I think you did (the first HT), a still air quench may be too slow. You may have needed forced air or an oil quench preferrably.

So, what does all this mean? I think that the second time around you obtained suffucient heat, the air quench worked better and ala your success.

You may also have a point about your forge, in the sense that heat is not going where in should be. I would invest in that kiln you have your eye on. Consistancy is a beautiful thing. :cool:

-Jason
 
Jason,

I did not explain myself well enough in my last post. I'm sorry.

My forge (which I poured - don't want to blame it on anyone else) has a design flaw. In the first HT I had the blade at the back part of forge where the forced air enters. The tang was at the front where the real heat is. I tested the TANG with the magnet and pulled the blade out according to that result. I don't believe the blade got warm enough and I got faked out. On the second HT I put the tang in toward the back of forge and the blade pointing towards the forge opening where the real heat is. That did the trick. Actually it took me a full day after the second HT to figure out what the problem was. I need to either build or buy a new forge or figure a better way of forcing the air in. Besides I'm only about a week away from ordering the Even-Heat oven.

I used oil at 140 F. for both HT quenchings.

Thanks Jason.
 
I get it now. Well, you will enjoy using a kiln. Let us know how it works out for you.

-Jason
 
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