Oops...440C Heat Treat Mistake

CDHumiston

CDHumiston

Joined
Feb 17, 2009
Messages
1,464
I got sidetracked by the wife with some chores. I was preparing to heat treat a few 440C blades. I threw them in the oven without foil wrapping them!

I didn't even notice until I pulled them out at the end of the cycle. Are they ruined? From what I read it's just going to be hard to finish grind the scale off...
 
The scale really isn't the issue. The problem is the decarb layer that's under the scale. I don't know exactly how deep it's going to be in your case, but I would suspect at least 0.010" deep, probably WELL north of that even. You'll need to grind until you reach hard steel. The decarb layer will be soft and deep. Grind it away until you reach hard steel, especially the edge.
 
samuraistuart said:
The scale really isn't the issue. The problem is the decarb layer that's under the scale. I don't know exactly how deep it's going to be in your case, but I would suspect at least 0.010" deep, probably WELL north of that even. You'll need to grind until you reach hard steel. The decarb layer will be soft and deep. Grind it away until you reach hard steel, especially the edge.
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I have a quality hardness tester. That should help me figure out when I get the decarb off.

Worse case...I lost 3 blades and learned a lesson! FOCUS!
 
samuraistuart said:
The scale really isn't the issue. The problem is the decarb layer that's under the scale. I don't know exactly how deep it's going to be in your case, but I would suspect at least 0.010" deep, probably WELL north of that even. You'll need to grind until you reach hard steel. The decarb layer will be soft and deep. Grind it away until you reach hard steel, especially the edge.
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I would accept twice as much of that decarb so I don’t have to use foil or vacuum .
Interesting situation, I'm waiting to see what will come out of this
 
You didn't give the temperature and time, or blade thickness.
The decarb can be quite deep. Depending on how thick the blades are, you may salvage them as thinner and less wide knives. I would take the edge and spine back a good .030" and then grind the bevels down until you hit hard steel. Dipping in FC will usually show the decarb spots remaining as you get it down to hard steel. My guess is it will be a good .010 per side, maybe more.
 
Stacy E. Apelt - Bladesmith said:
You didn't give the temperature and time, or blade thickness.
The decarb can be quite deep. Depending on how thick the blades are, you may salvage them as thinner and less wide knives. I would take the edge and spine back a good .030" and then grind the bevels down until you hit hard steel. Dipping in FC will usually show the decarb spots remaining as you get it down to hard steel. My guess is it will be a good .010 per side, maybe more.
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Preheated the oven to 1400° and equalize. Ramp to 1850° and hold for 30 minutes.

Plate quenched in aluminum plates and cryo in dry ice and alcohol.

Tempered at 350 for 2 two-hour cycles

The blades don't seem to be that bad to me. I haven't had time to work on them yet.

I'll try and check the smallest one tonight. It's about 6" x 1.5" x 1/8"
 
I think you mentioned the blades are from .130" to .200" thick which leaves plenty to remove any scale or decarb, even if it goes to .010" on each side. The Rc tests should show any decarb so you'll know when it's all removed. A quick dip in FeCl2 should also show when to stop grinding.
 
I just tested the smallest blade and it's a 53HRC I think if I sand a little deeper into the blade it will improve a bit. Definitely not ruined.
 
CDHumiston said:
Being as I'm currently at 53 HRC how much do you think I'll need to remove?
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Nobody can know that , we are all waiting on you . I read something about this a long time ago, but for carbon steel. That the surface layer of decarb. slows down the process, but I wasn't really interested in that then and I didn't read the whole article...
 
Natlek said:
Nobody can know that , we are all waiting on you . I read something about this a long time ago, but for carbon steel. That the surface layer of decarb. slows down the process, but I wasn't really interested in that then and I didn't read the whole article...
Click to expand...

Ha Ha! I'll take it down when I get home from work and let you all know what happens. I have three blades of different sizes and thickness. Hopefully I can salvage them all!
 
Well...I have just learned a huge lesson on what decarb is! It's not some small surface scale that it looks like when you pull the blade from the oven. It goes deep!

Luckily, I think I'll be able to salvage two of the blades. They were pretty thick, and I should be able to get them cleaned up. You can see in the pictures the pitted look even after I ground quite a bit.

The decarb is also hard! I wore out a 36-grit belt getting the three blades fairly clean. The steel is hardened pretty nicely as well. They all test out at 58-59 HRC now. It's just a matter of getting them smoothed out.

So, are they hardened? Yes, they are and fairly well for 440C. Is it really worth keeping them? It is to me. I may sacrifice the small one and snap it in two to see the grain pattern.

My suggestion to everyone, don't forget to wrap your blades!

https://imgur.com/LXn0kwo

https://imgur.com/RC5trr3

https://imgur.com/piIeaqY
 
How much thickness did you lose to get all the decarb off? With 59 Rc I would think you got all the decarb without worry. BUT - I do agree wrap in SS foil for sure. I've used the dry graphite spray on AEB-L up at 1975°F with little enough decarb I wasn't really aware of it. Just light clean up grind on SGA - took off well less than .010" for clean up with Rc in the 60-61Rc range.
 
Ken H> said:
How much thickness did you lose to get all the decarb off? With 59 Rc I would think you got all the decarb without worry. BUT - I do agree wrap in SS foil for sure. I've used the dry graphite spray on AEB-L up at 1975°F with little enough decarb I wasn't really aware of it. Just light clean up grind on SGA - took off well less than .010" for clean up with Rc in the 60-61Rc range.
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Really not sure how much I lost, but it was not too significant. The thin blade is going to be the only one that I'll notice any difference on. The two thicker ones are negligible...
 
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