Magnacut heat treat fail... what next?

Joseph Bandeko

Joseph Bandeko

Knifemaker / Craftsman / Service Provider
Joined
Dec 9, 2021
Messages
1,356
Hello,
So I just tried to heat treat 3 blades in Magnacut and one in particular came out, well, not hard, and not sure the other two are full hardness either. I think it’s from trying to clamp multiple blades in my aluminum plates at once, taking to long, not enough clamping pressure to hold them down sufficiently, etc.
For the heat treat, I soaked them at 2100F for 15 minutes, attempted to plate quench then straight into dry ice bath (Their in the tempering oven now until I know what to do next 🙄)

So my question is, what do I need to do to them before I can re-heat treat them? Do I need to some sort of normalizing, annealing or can I just start the heat treat over as if nothing happened?
I’m kinda thinking a minimum of a, say 1200F soak/anneal is in order, that would also help considering they came out warped as well.
 
Bunker Hill Blades said:
Hello,
So I just tried to heat treat 3 blades in Magnacut and one in particular came out, well, not hard, and not sure the other two are full hardness either. I think it’s from trying to clamp multiple blades in my aluminum plates at once, taking to long, not enough clamping pressure to hold them down sufficiently, etc.
For the heat treat, I soaked them at 2100F for 15 minutes, attempted to plate quench then straight into dry ice bath (Their in the tempering oven now until I know what to do next 🙄)

So my question is, what do I need to do to them before I can re-heat treat them? Do I need to some sort of normalizing, annealing or can I just start the heat treat over as if nothing happened?
I’m kinda thinking a minimum of a, say 1200F soak/anneal is in order, that would also help considering they came out warped as well.
Click to expand...
Did you do anything to protect against oxidation?

Hoss
 
DevinT said:
Did you do anything to protect against oxidation?

Hoss
Click to expand...
I was getting ready to say:
I figured out what went wrong. When I wrapped them in foil I thought I could get away with only crimping the edges once (🤦) and they got some oxidation, and the soft one got quite a bit of oxidation and when I started grinding into it, there were the telltale signs of heavy oxidation, so unfortunately I will have to start over with that one. Fortunately, the other two seem like it’s light enough to easily grind through with no problems, so those should be just fine.

Moral of the story, DOUBLE CRIMP THE EDGES OF THE FOIL PACKETS!!!!

Thank you for the responses!
Joseph
 
Cushing H. said:
I think i need to get and read through larrins book. I always thought hardness was highest right after quench, and temper always brings the hardness *down* ….
Click to expand...
Yeah, me too. But steel is a strange and wonderful beast. Here's a thread with some more details:

Strange Cryo on AEB-L Anomaly

It just happened again and it's happened on all my AEB-L tests. I'm sure there's an explanation, but heck if I know what. After I remove the AEB-L from the liquid nitrogen the hardness reads 60/61. That's just too low. But if I put it in an oven for just a few minutes at 300-400, the...
www.bladeforums.com www.bladeforums.com
knifesteelnerds.com

What Happens During Tempering of Steel? - Knife Steel Nerds

Thanks to Shawn Houston and Tyler Christian for becoming Knife Steel Nerds Patreon supporters. We have reached our first goal and therefore I will be interviewing Devin Thomas and posting it as an article to the website. In a previous post I wrote about what happens during rapid quenching of...
knifesteelnerds.com knifesteelnerds.com

I've read Larrin's book, but I don't recall this being in there (probably is, I'm just old).

Joseph Bandeko Joseph Bandeko I'm glad you found the trouble and it's only skin deep.
 
I should have said "full hardness". It isn't in all steels, but IIRC some have precipitation hardening or something like that. I believe it is at the high range tempering that it happens (1000°F).
Cryo increasing hardness is an example of a similar effect.

Another important part of waiting to test hardness until after the tempering is that until the structure transformation is complete and the blade is cooled to room temperature it won't read true martensite hardness.

Where I was going in this particular case of these magnacut blades - until they reached -100°F they were still largely austenite. This would test as not hardened properly. Even after the dry ice, until after the temper cycles there would still be some retained austenite that would lower the readings.
 
Yeah I had to grind away enough steel on the one that I couldn’t salvage it to make what I originally planned, but there’s still good hard steel underneath that layer so I was able to grind that off and I will be making something else with it.
Thank you for all the input!
 
I'm never not in awe of the depth and detail of information you knife makers absorb in order to get a good heat treat.

That part of the job, the range of steels and recipes, just seems like pure alchemic wizardry to me.
 
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