Quench Question

[Steve Nuckels]

I recently heard about repeated quenching!

Is there any advantage to double or tripple quenching your blade?

If so, that?


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IN GOD WE TRUST

[Wampus]

You reduce grain size by thermal cycling above critical temp and back down as long as you don't get the blade too hot or keep it above critical for a very long time.  I've read some makers say that quenching on each cycle reduces the grain slightly more because the martensite from the quenches provides more places for small grain structure to start.  Both methods seem to work pretty well from what I've seen, either air cooling each cycle or quenching.  There was some good discussion on grain size reduction in this thread a little while ago:   http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=110;t=001584

[Lin Rhea]

I single quench. The only time I have double quenched is when I am not happy with the first quench for some reason. I will go ahead and come back up to heat and quench again.

A few months ago I made two unofficial mastersmith test knives from damascus. I single quenched one and double quenched the other. I took note of which one was which. I took them to Riverside Machine Shop where we have a knifemaker's meeting every month. I wanted to go through the performance test with them both, just for my own satisfaction.

They both did well through the chopping of 2 X 4's and rope and even the bend, but when I told Jerry Fisk and JR Cook that one of the knives was double quenched, Jerry suggested I bend it again the opposite direction. We choked up on it in the vise a little and it bent 90 degrees just fine. This test is not the final word, because we did not bend the other knife but in one direction. I did the actual bending and I noticed it was a very smooth bend, now cracking at all. I drew the spine on both blades with a torch to soften it much more than I would a practical using knife.
 
      The test does show that, at least, double quenching is not harmful to the steel. Here is a picture of the blade showing the spine. That's JR Cook MS with me in the picture.
 
     I'd like to hear more about what you guys have learned about this. Lin

 

[Steve Nuckels]

Lin, while at the ABS Intro course I double quenched a blade out of necessity because the blade was slightly warped.

A maker on "Virtual Knife Show" described tripple quenching to improve performance!

  http://www.virtualknifeshow.com/  

Just wondering what the consensus sez!

Interesting!

Cool picture too!

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IN GOD WE TRUST

[Wampus]

Cook doesn't still have that ugly multi-colored Ford does he?  Turned all kind of weird green and purple colors when the sunlight hit it.

[Lin Rhea]

Wampus, No he has a new truck now.     Lin

[tippit]

I've tried double & triple quenching and have not found much difference from single quench.  In theory (but don't quote me) when you re-heat to  critical you re-change the grain size that you had quickly quenched from the previous one. The nose cone time /temp cooling cycle seems to be the most important part of quenching.  Multiple times have the risk of screwing that up (just my observation).  Most of the New England blade smiths that I've talked with don't multi quench.  Doc