Heat Treat Large File Knives?

Andrew Colglazier

Andrew Colglazier

Joined
Sep 14, 2006
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I've been working with large farrier's rasps and making some big knives out of them.

I have been pretty happy with the edges on these large pieces, but find that with peanut oil quenching, the blades tend to be quite tough (springy) but not quite stiff enough for my liking.

My usual technique is to heat the blade to non-magnetic, keep it there for a few minutes, and quench in warmed peanut oil. I do this three times. I usually then differentially temper the blades with a torch.

The edges are normally very good. I would like to get these blades a bit stiffer, however. Shorter blades, it's not an issue.

Any tips?

Thanks!

Andy
 
If you want them more rigid you need to start with thicker stock. If they are breaking or taking a set too easily then you might adjust the heat treat but it will make no difference in the flex, only in the yield and brittle failure points.
 
Justin King said:
If you want them more rigid you need to start with thicker stock. If they are breaking or taking a set too easily then you might adjust the heat treat but it will make no difference in the flex, only in the yield and brittle failure points.
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Hi Justin! I can't start with thicker stock because the files come with a standard thickness. They aren't breaking, they are a bit too flexible.

I could try them without the differential tempering.

Maybe a different quench medium? Water?

Andy
 
If you were able to watch the videos you would see that your heat treat will make no difference in how easily the blade flexes, only at what point it will take a permanent bend or break. As long as you are not exceeding the yield point of the material in it's current state, the flex is virtually the same for wrought iron through all types of steel, regardless of whether they are hardened, annealed, or anywhere in between. If you take two identical pieces of 1095 or whatever, harden one and anneal the other, then begin to load them so that they flex, they will flex to the same degree at the same load, until your load reaches the point where the softer piece takes a permanent bend.
This was a hard concept for me to wrap my mind around but it has been proven by more knowledgeable folks than myself.
 
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I have a lot of Diamond brand rasps and have been told, but need to verify, that they are W2. I have tested some pieces at different thicknesses in oil and water. I found pretty similar results with thinner pieces but the thicker ones worked a little better in water which is the recommended quench for W2. I haven't seen any cracks in either oil or water but the pieces were all 4X1inches and I may have been lucky too. I would think drawing to more flexibility would be good thing in a larger knife. I have very limited experience with rasps but that is my research so far.
 
Justin, I think I understand what you are saying. This would be a cool test to see on slomo video.

These files are very brittle and hard before I work them. It would be interesting to see how much they would flex when struck against another object laterally in slow motion to observe the actual movement of the piece.

In real time, a hard thing to imagine! :thumbup:

Andy
 
byersj79 said:
I have a lot of Diamond brand rasps and have been told, but need to verify, that they are W2. I have tested some pieces at different thicknesses in oil and water. I found pretty similar results with thinner pieces but the thicker ones worked a little better in water which is the recommended quench for W2. I haven't seen any cracks in either oil or water but the pieces were all 4X1inches and I may have been lucky too. I would think drawing to more flexibility would be good thing in a larger knife. I have very limited experience with rasps but that is my research so far.
Click to expand...

It is my understanding that they are W2 also. I haven't tried quenching in water, but using peanut oil, I have never been able to harden them to the same RC as they have when they are new.

I'm interested in more stiffness because, for example when batoning, some energy is lost to blade flex which would go into the wood if the blade were stiffer.

Andy
 
I wouldn't recommend water. Brine will give you a more even quench.

The industry standard fastest brine concentration is 5% - 8% salt solution and may or may not be too fast for thin sections. According to a couple of General Motors metallurgists a higher concentration of salt slows the quench. Take that for what it's worth; I plan on experimenting with this concept in depth, meaning I hope to make brine my main quenchant for 10XX and WX steels.
 
Andrew Colglazier said:
It is my understanding that they are W2 also. I haven't tried quenching in water, but using peanut oil, I have never been able to harden them to the same RC as they have when they are new.
Andy
Click to expand...

ROFL, not surprised you aren't hitting the same RC values quenching in peanut oil :) This is because it is not fast enough, it doesn't cool the steel quick enough to form 100% or close to it hard steel. Read the stickies on hypo and hyper eutectoid steels at the top of this forum, read up on shallow hardening steels VS deep hardening steels also.
 
Sam Salvati said:
ROFL, not surprised you aren't hitting the same RC values quenching in peanut oil :) This is because it is not fast enough, it doesn't cool the steel quick enough to form 100% or close to it hard steel. Read the stickies on hypo and hyper eutectoid steels at the top of this forum, read up on shallow hardening steels VS deep hardening steels also.
Click to expand...

A-reading I will go, a-reading I will go, HI-HO the Derry-O, a-reading I will go!

Thanks for the tips, fellers! :thumbup:

Andy
 
Thanks for the videos, very informative.

I just did some 1095 folder blades and springs with a 7% brine quench, this is the way to go. Very clean and got good hardness.
 
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