Dunking hot steel

BD Blades

Well-Known Member
I know there are a few ways folks put their hot blades in the quench oil. One is to quench the edge by putting the blade on a restricter plate and rocking it back and fourth. Another is to stab it in all the way point first, and one more would be to dunk it all the way under edge first. Is one better than the other or are they just different methods?

I started by rocking the edge myself but no longer do that as I had a bit of a quech oil fire one day. I do not have that problem by submeging the blade all at once. Maybe some flash, but a much lower risk for a full on fire in the quench tank.

Your feedback is apprciated.
 
With shallow hardening steels, quenching just the edge will leave just the edge hardened with the back of the blade soft (expect the oil to flare up, and maybe not want to go out without help). This results in what is called a differentially-hardened blade, which is easier to bend, but harder to break. The other two methods are just two different ways to achieve the same thing, which is a through-hardened blade. I generally harden single-edged blades edge first, and double-edged blades point first, but honestly I do not think it matters that much if you go edge first or point first. The shape of your quench tank may be the determining factor...
 
Thanks George,

I guess maybe I didn't ask this question quite right now that I think about it some more and see your reply. I understand about differential hardening and that is usually what I try to do.

If you heat the edge of the blade with a torch and then dunk it completely under edge first instead of rocking it. Would that be good bad or indifferent?
 
Pretty much indifferent. You will get a stronger blade with a full quench, then soften the spine with a torch. In my experience, a point in first quench causes less warpage. You need to experiment and see what works best for you.
 
Here's another wrinkle, with shallow hardening steels, if the spine is thick enough, you will still have differential hardening even if you quench the entire blade. You will also need fine grain for this and the exact alloy will also come in to play as well but then you get down to the thickness of the average blade, 1/4" or less, there is not much difference between the rate of cooling on the surface of the object and the core. The principle rate of difference in the cooling will be caused by the difference in the thickness of the areas of the object. So lets say that you take a piece of 1070 with rather low manganese, just as an example, with fine grain and make a blade that's goes about 3/16" at the spine at the ricasso and tapers to the point and to the edge. Basically I'm just picking a number that I can deal with easily but let's also say that with the grain size and the quenchant used that the depth of hardening is 3/64". Remember that's from each side so the blade will form martensite up to a thickness of 3/32" thick, then there will be a slight transition zone, and thicker than that you will have pearetic steel.

Doug
 
Thanks for the info guys.

I am using 5160 and 52100 which I don't think are shallow hardening steels. I heat the edge and quench the whold blade edge first right now. I am still experimenting and trying to get this HT thing down. Looks like it could take some time before I get what I want, but it is fun experimenting. (more fun when you experiment works)
 
You're right, neither is shallow hardening at all. Some people have had luck with clay coating 5160 real heavy to do a differential hardening but I would think that edge quenching would be the most reliable. Something like 52100 is way too complex for any other method. It's possibly air quenching in thin sections. 52100 is also pretty demanding when it comes to austinizing. It starts growing grain rather quickly with just a little overheating, compared to 5160, and too long of a soak can put too much carbon into solution and increase the amount of retained austinite. I've used it and have had some good luck with it without producing course grain in test blades but I have no way of telling about retained austinite without testing that I cannot afford to have done at this time. So, until I can afford to get a controlled heat source such as a regulated oven or molten salt tank and reduce the luck factor, I'm going to go back to a simpler hypoeutectic steel that does not have as much problem with grain growth or retained austinite formation caused by dissolving too much carbon.

My limited testing has shown, however, that 52100 does show some interesting possibilities with isothermal quenching to form a mixture of martensite and lower bainite.

Doug
 
Thanks Doug

I am also looking into some simpler steels myself. I do a triple edge quench with each of these steels and I will say I have gotten far better performance from the 52100 than the 5160 so far. I have only made about 15 finished knives though.
 
I'm not a triple quench fan, especially with hypereutectic steels but I'm not going there. I agree that 52100 can make a tough as nails blade and if I had the money to invest in a regulated kiln or, better yet, a molten salt bath; both high and low temperature, I would stick with it. I just don't have the coin right now to make that king of investment and probably won't for a while unless I get lucky at the lottery or go out of retirement. Until then I'll stick with an alloy that matches the equipment that I have to heat treat it.

Doug
 
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