Soak time HT O1

Stromberg Knives

Stromberg Knives

strombergknives.com
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Jan 3, 2015
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Hi!

I received my Paragon oven a recently and after some reorganizing in my workshop everything is set up and ready for some heat treating.

I mainly use O1 tool steel and I have some question regarding heat treating of it.

Here's a snip from the instructions provided by my steel supplier:

Hardening
Heat slowly and if possible pre-heat at 300/500 degrees centigrade before raising to the hardening temperature of 780/820 degrees centigrade.
Pre-heating is especially desirable for complex sections. Soak thoroughly, allowing 30 minutes per inch of ruling section before quenching.
Light sections should be quenched in oil from the lower end of the hardening range. Long slender sections should always be suspended in the
furnace for heating and quenched by plunging vertically into the oil bath. Tempering is always needed after hardening.
Click to expand...

Most O1 recipes will be similar of this, and they all speak of soak time after the steel has been fully heated through.

In this case it says 30 minutes per inch of ruling section. I interpret that as once the steel is fully heated through I should soak a 1/8 inch blade at 780/820 deg c for like 4 minutes? Would that be correct?

And how do I know that the steel i fully heated before I start the 4 minute timing?

If I understand correctly O1 doesn't hurt to soak for a longer time, but doesn't that increase decarburization and oxidation?

Wouldn't it be best to have as short soak time as necessary while still getting the austenitization done?

Thanks.
 
I take my O1 to 1500 Deg F (815 deg C) and once the oven gets to that temperature, I let it soak for 10 minutes, then quench in 125 deg F (51.5 deg C) canola oil. I get Rc 64.5-65 right out of the quench every time. Now, I could probably drop my temp and hold times down a little, but I like the consistent results I get, so I don't worry about it.


-Adam
 
All hold and soak times start once the oven has reached the set temp. This is part of the programming and will be automatic when you set the parameters. If you are using an oven with no programmed controller, you start the time once the temperature returns to the selected temperature when the blades are inserted, or reaches it if going up to the next step.

In the thickness of a knife blade, the minimum soak time is 10 minutes at any step in the HT. This allows enough time for the heat to get evenly distributed and relieve stress. Within limits, it is far better to soak a little too long than a little too short. Many makers soak every step for 10-15 minutes regardless of whether the HT data calls for it or not.

The soak at the austenitizing step before quench is the most important. It allows all the alloying to get into solution and be ready to convert during the quench. The importance of this soak can't be minimized. 10 minutes is the minimum, and 30 minutes is not a bad idea if you want the top results.

The pre-heat info you posted mentions and the phrase " complex sections", which has to do with machine parts and such. It is to help prevent dimensional distortion. It really doesn't apply to knifemaking, as we will always be dealing with warp, and will also be grinding the blade post-HT. A 5-10 minute pre-soak at 500C won't hurt any steel. More commonly, in knife HT programs you see a 10-30 minute hold (soak) at 650°C/1200°F to equalize the blade before it goes up into the austenite range. This is a requirement for stainless steels, and not a bad idea for carbon steels, too.
 
Thanks! It's evident that the golden rule (which I tend to break too often) also applies here: don't overthink things. ;)

One final question though: since my first heat treat will be a new flat platen with dimensions 300 x 50 x 15 mm, for how long would you soak a more massive piece like that?
 
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