About the video of Bob Kramer & Anthony Bourdain

PEU

PEU

Gaucho Knifemaker
Joined
Aug 6, 2006
Messages
1,176
No, I'm not posting the video, its in the videos thread, I saw two closed threads already, Im interested in understanding what happens at about minute 6 when Bob removes the blade from the salt bath.
I guess he is talking about the decalescence, and it can be clearly seen, but then the knife is hardened. If the steel goes thru this stage and its not already quenched, how can it be hardened? Or maybe it was just for the camera?

Any metallurgist or someone that plays one on TV :D can help?


Pablo
 
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There is a drop in temperature while going through the critical temperature on the way up and a slight rise in temperature on the way down.

Hoss
 
It's just a matter of video editing.
They left out a few steps in the final cut and didn't show everything - like quenching.
And it's decalescence on the way up and recalescence on the way down.
 
Sorry, recalescence, but if it was on the way down it was too late for quenching right?


Pablo
 
yes it is, unless he would use an air hardening steel (i didn't see the vid)...in that case that would be the quench ;)
 
I think he probably cycled the blade a couple of times before the quench and just for fun he showed the recalescence.

Hoss
 
Maybe its just a normalizing cycle before hardening that was not shown.


Pablo
 
Yep.
Salt pots let you nail the right temp for austenizing, and you go straight from that to the quench NOW to harden.
If you're doing seat of the pants HT, though, without real temp control, the -calescence can tell you a lot about whether you're reading the temp correctly when guessing by color.
 
For those interested, also look up "latent heats". Some schools prefer this term.

Hoss
 
Witnessing decalescence is the only "true" way of knowing your steel is transforming... Right from the horse's mouth, so-to-speak. Bob used recalescence as an example of what the "shadow" looks like.
 
PEU said:
Maybe its just a normalizing cycle before hardening that was not shown.


Pablo
Click to expand...

I'm a little late on seeing this thread, but Devin is right on the money. When they show the phase shift, what they're showing is one of a few thermocycles that most makers do as a way to refine the grain structure before finally quenching. They do actually show the quench, but it's much earlier in the video at time signature 0:52sec. The footage is definitely out of sequence, and the blade isn't hardened at that point. It's just how they decided to tell the story of the process.

Best,
Mareko
 
This might be a good time to mention that learning how to heat treat from a tv show special is probably NOT a good move...


:D
 
Whaaaaaaaat?... You don't harden before you normalize? Matthew, did you not get the memo?
 
Matthew Gregory said:
This might be a good time to mention that learning how to heat treat from a tv show special is probably NOT a good move...


:D
Click to expand...

Ok good to know. I thought I was doing something wrong because it took me longer then 45 minutes to make a knife :)
 
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