Plate hardening thin O2 Steel, no oil.

PEU

PEU

Gaucho Knifemaker
Joined
Aug 6, 2006
Messages
1,122
After reading early today the article by @Larrin and subsequently asking him about his opinion on hardening thin O2 steel (Bohler K720) not using oil but quench plates given the long enough time the CCT graphs shows it needs to reach full conversion to martensite, I got the itch to test the theory, and that what I just finished...!

Test conditions:

Prepared 3 sets of samples from my scrap pile, 1.5mm (0.06"), 2mm (0.079") and 2.5mm (0.1") deburred and marked them.
My aluminum quench plates are 20mm thick (0.8") and I put a very heavy weight on top, a piece of train rail.

Heated the oven to 810C (1490C) left it stabilize for 30 minutes
Put all samples at once separated by its thickness
Waited the oven to reach again 810C and set a timer for 10 minutes
Starting by lower thicknesses I plate quenched the samples, it took an average of 50secs to 90sec to reach room temperature, I removed them from the plate with my bare hands.
Grinded the scale off with my belt grinder and measured hardness four times on each billet

1.5mm: 65/66/65/65RC
2mm billet 1: 64/64/64/64
2mm billet 2: 64/64/65/64
2.5mm: 63/64/63/63

I kept untouched samples so I can use a proper surface grinder next week.

IMHO Results speak by themselves, 1.5 and 2mm billets hardened as if they were oil quenched, no significant differences, 2.5mm will have to grind a bit more to see if its scale or they didn't harden properly.

What do you guys think?

Pablo
PS: Larrin post: https://www.bladeforums.com/threads/how-fast-do-you-have-to-quench-hardenability-of-steel.1645480/

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Wow! thats a useful test. I wonder if the scale acts as an insulator and stainless steel foil will give better results.
 
I’ve done this for a while now. I plate quench my O1, up to 2mm thickness. No difference in hardness from an oil quench.

I like it very much , it’s a lot cleaner process with the foil and plates compared to the oil.
 
Looks like this won't work for anything thicker than 2mm. I was hoping I could do 1/8" O1 :p.
 
I was thinking about doing an similar test, you probably just saved me some time. Thank you for sharing your results.
 
I have come across info from the ASM that’s says water cooled copper quench plates can reach the quench of water. The problem is scale build up slows heat transfer. I use gas shielding in my oven so plate quenching carbon steels it easyer. I am planning on building a set of big water cooled copper quench plates. But I’m going to have to cast them as copper that size is rather pricy.
 
Where can one buy water cooled Cooper plates? I used them for my computer but those are not nearly large enough
 
JTknives said:
I use gas shielding in my oven so plate quenching carbon steels it easyer.
Click to expand...

JT do you have a thread where you speak about this gas shielded oven? is it easy to adapt a regular one? Thanks
 
I’d wager that the flatness of the plates and blade would make a difference as well; better surface contact.
 
I appreciate the tests Pablo. Excellent work buddy. But by your very own testing and resulting hardness, anything over 1.5mm, even for O2 which is a very deep hardening steel, the plates are not going to provide the best martensite conversion possible, which we as makers are after (maximum as quenched hardness).

1.5mm was giving a solid 65, and then 66. But......

2mm was giving a solid 64, and then a 65. (Not the maximum as quenched hardness)

What do we learn? O2, which is VERY deep hardening, can be quenched to 65+ with plates, but only in thin cross sections 1.5mm and less. Go beyond 1.5mm-2mm, expect a lower as quenched hardness than is attainable by a faster quench method, as in oil, as O2 was meant to be quenched in.
 
I built my oven so it was tightly sealed. I then sealed every seam with high temp silacon. I used to use nitrogen but was having decarb at the higher temps above 1800°. So I switched to argon which works much better. But it’s 3 times the money. My big bottle 248cf costs me $90+ to fill. And I run at 10cfh and sometimes higher depending. So for me it’s cheeper then foil especially when I account for my time. Blades that need real long soaks still get foiled.

You can’t buy water cooled copper quench plates. Thy uses berialiam copper which is even more expensive.
 
Here’s a thought, and there is probably a reason not to do this that I’m not thinking of, but what if you cooled the liquid cooled quench plates with a flow of alcohol/dry ice. Not so much for the speed of quench, but to have a continuous quick cool to dry ice temps. By the time you make and plumb a water cooled plate set up, replacing the water with dry ice/alcohol would be easy.

I would think you wouldn’t want the hot blade to contact water condensation. But the low temp plates don’t seem like a problem.
 
Alittle condensate on the plates would not hurt a hot blade. It would flash to steam.
 
samuraistuart said:
I appreciate the tests Pablo. Excellent work buddy. But by your very own testing and resulting hardness, anything over 1.5mm, even for O2 which is a very deep hardening steel, the plates are not going to provide the best martensite conversion possible, which we as makers are after (maximum as quenched hardness).

1.5mm was giving a solid 65, and then 66. But......

2mm was giving a solid 64, and then a 65. (Not the maximum as quenched hardness)

What do we learn? O2, which is VERY deep hardening, can be quenched to 65+ with plates, but only in thin cross sections 1.5mm and less. Go beyond 1.5mm-2mm, expect a lower as quenched hardness than is attainable by a faster quench method, as in oil, as O2 was meant to be quenched in.
Click to expand...

True, but I will draw my final conclusions after properly surface grinding the billets and measure again hardness, I want to know how deep it hardened and have a truer surface to properly measure.

Pablo
 
Like other makers, I have successfully plate quenched O1 steel - but only 1/16" thickness. My concern was with warping and de-carb on thin 1/16" steel. I foil wrapped the blades and folder springs that were profiled only..... blades were not ground so they would have full contact with the plates. They were quenched while still in the foil. The hardened blades tested a pt. or two harder than similar 1/16" oil quenched blades. I broke test pieces to examine the grain and under low magnification, they appeared fine and uniform all the way through.

I tested thicker O1 steel by foil wrapping together, face to face, two pieces of 1/16"precision ground O1 to simulate a 1/8" thickness. After plate quenching, the two outside surfaces that were in contact with the plates were fully hardened, but the two inside surfaces were not (I don't recall the Rc of the inside surface)

Saludos

J

JD WARE KNIVES
 
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