Redo magnacut hardening

Alex Dron

Alex Dron

Joined
Feb 24, 2007
Messages
328
Performed HT for several Magnacut blades and one did not harden all the way, testing only shows 50-52 RC in multiple spots. The blank was flat ground (thanks to AKS), wrapped in SS foil, and just to be sure I also ground it to 400gr after tempering, before testing.
Still showing 50Rc...
It was pretty thick piece, .22", and I haven't ground bevels - only cut the shape and drilled.
Used "recommended" protocol (2050F x 20 min, quench in plates, LN overnight, 350x2h twice)
All other blades ranged 0.11" to 0.14" turned out as expected 62-63RC.
Just this one failed, probably because cooling rate was not fast enough - plates got very hot and I remember seeing gloving red even after few seconds once I quickly looked under plates to check.
So anyways, it is done what is done.

I want to retry the hardening, and I know I can't just deal with it as with annealed blade. What should I do in order to "normalize" it before second attempt?
NSM has this in datasheet:
Stress Relieving: Hardened Parts: Heat to 25-50°F (15-30°C) below original tempering temperature, hold 2 hours, then furnace cool or cool in still air

Is this my way out? Or should it be rather annealed, which would take me couple days, according to the same datasheet (500F has to be dropped with rate 25F per hour).
Thanks,
Alex
 
Maybe Larrin will ting in with a temper anneal protocol, which would only take 12 hrs or so...
 
Kept pocking the blade with tester and just found couple spots closer to the tip (about 1") with a hardness 62.5RC
Maybe it is not that bad after all... Not sure though how is that possible to have such a big delta
 
It most likely needed a longer soak time.

A subcritical anneal should be good at this point, I would do 1375’f for 8 hours. Wrap in stainless foil.

Larrin will probably chime in.

Hoss
 
I ran the blade through surface grinding to shave about 0.010-0.015 and tested again. 62-63 this time everywhere. Sigh of relief :)
damn that was close to ruin my evening
And happy New Year to everyone!
 
I was going tom suggest taking more off the blade. There was a pinhole or other leak in the foil packet that caused deep decarb in the HT.
 
Alex Dron said:
I ran the blade through surface grinding to shave about 0.010-0.015 and tested again. 62-63 this time everywhere. Sigh of relief :)
damn that was close to ruin my evening
And happy New Year to everyone!
Click to expand...
Well , Happy New Year !
There must be pretty much discoloration on that blade , do you have any picture of knife before you surface grind it ?
 
There was some minor "rainbow" discoloration, but no typical burnt black areas and overall blank was equally grey. I have already ground off the surface, sorry, no pictures.
I'm also frowning at my hardness tester, it is portable AMES Chinese clone, usually pretty accurate but sometimes playing weird tricks when switching between very thin and very thick stock. I wonder if it was one of those moments. It might just went normal after I did a dozen tests on that poor blade. Or combination of both factors, decarb and tester error... can't tell now.
 
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