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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 12-26-2020, 04:00 PM
Dan512 Dan512 is offline
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Test heat treats on 3 different steels. Please help me read the results

So today I took a few hours and did a few heat treat tests before moving on with my next knife-making project

To do this, I cut out 2 test pieces each of approx. 20x50mm in size from 3 different steels and hardened them in an electric furnace.

The steels are:
  • 1.2235 / 80 CrV2 / L2
  • 1.2419 / 105WCr2
  • 1.2842 / 90 Mn CrV8 / O2

Each piece was treated with graphite spray to prevent decarburization and slag build-up (I once read this in a US forum, I had the spray there and I thought it couldn't do any harm)

It was quenched within 3-5 seconds in approx. 80 į C rapeseed / canola oil.

I always removed the 1st piece after 5 minutes of oven time (not holding time!), the second after 10 minutes of oven time. I hope that this is sufficient for such small and thin test pieces.

The file test succeeded with every piece, with the 1.2235 with 10 minutes of oven time I noticed that there was a slight decarburization on the edges of the sample, but with the second cut the file slipped.

Then I clamped the samples in the vice and broken them with a pipe wrench or, in the case of the 1.2235, in 3.5mm with a hammer.

Then, using the kiddies' USB microscope, I took a snapshot of each fracture as good as possible, one image each at 50x and 1000x magnification. Please click on the pictures to see a larger view.

It would be great if the specialists her could tell me something about the photos, my "test principle" and the results.

I notice that some pieces have a darker edge and a lighter core. Does that mean the holding time wasn't long enough?

steel 1.2235 (thickness 3.5mm)

Oven running at approx. 840 į C

5 minutes oven time





10 minutes oven time





1.2419 (thickness 2.2mm)

Oven running at approx. 825 į C

5 minutes oven time





10 minutes oven time




Last edited by Dan512; 12-26-2020 at 04:24 PM.
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Old 12-26-2020, 04:02 PM
Dan512 Dan512 is offline
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and the last part

1.2842 (thickness 2.0mm)

Oven running at approx. 810 į C

5 minutes oven time





10 minutes oven time



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  #3  
Old 12-26-2020, 11:29 PM
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cnccutter cnccutter is offline
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Location: Dorena, Oregon
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Good evening Dan.

As you can guess the pictures are not wonderful, but they will work.

If Iím understanding you, you are putting your test strips into a hot kiln for a set time and then quenching. If thatís true, your not getting the metal up to proper temp and most certainly not bringing the partials into solution and allowing full transition. You are also getting huge grain structure and thatís not good. Your also bellow Austenization on the 80crv by 150 degrees. If you hit the Mark, you wouldnít see hardly any grain structure.

Everyone has their methods of heat treating that are slightly different but one common idea is it takes time. Time to gradually bring the steel up to a mid preheat, time to bring the steel up to full austenitize temp, and finally time for the steel to soak and let the structure fully shift. You cant rush this. I always soak my blades for 20 minutes at full temp.

If you look at your pictures, you can clearly see you have very large grain structure. You also clearly have two zones in that grain structure. My guess is your just not making it to temp before your quenching. Both of these issues can be a result of too hot too quick.

You didnít say what the condition of the steel was when you started. New? Annealed? Normalized? Forged scraps? All these can affect your outcome of heat treating.

Someone else will come through and give you their spin in this.
Erik


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Last edited by cnccutter; 12-26-2020 at 11:40 PM.
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Old 12-27-2020, 03:20 AM
Dan512 Dan512 is offline
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Quote:
Originally Posted by cnccutter View Post

You didnít say what the condition of the steel was when you started. New? Annealed? Normalized? Forged scraps? All these can affect your outcome of heat treating.

Erik
Hi Erik,

The steel was new, cut with a band saw from brand new strips that I ordered recently from a specialised shop. They sell it as annealed.
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  #5  
Old 12-29-2020, 09:53 AM
Dan512 Dan512 is offline
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Can anyone else point me in the right direction?
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