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mfkerr

New To Throwing Knives

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I have discovered through trial and error, unfortunately, that all the torture and testing I have given my other knives, tactical, camp, utility... don't mean a whole lot to the standard a "Throwing" knife needs to be. Ha!!!

Knife makers on this forum, I'm reaching out for your expertise on this subject.

1. Is there anyone here that does or has successfully made throwing knives 11" to 14" long specifically using 5160, AND performs your own heat treating, quenching, normalizing, tempering, ect...?

I would love to hear your process if your willing to share it.

I'm using 5160 obtained from Jantz and stock removal method. Two burner propane forge, and vegetable oil for quenching, and not having much success.

I have been told the heat treating prior to quenching is extremely important. (My method of "a magnet doesn't stick to it do dip it" isn't working for 5160). My blades are breaking even after 450 Deg for 1.5 hrs.

Here are some pics of the grain structure.

5160 Throwing Knives.jpg

Break_Pic-1.jpg

Break_Pic-2.jpg

Break_Pic-3.jpg

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Posted (edited)

All of those grain structures show massive grain growth. 

Are you normalizing a few times prior to quenching? 

Edit: I just realized you said stock removal so the normalizing shouldn't be as big of a deal but I would still normalize a couple times before quenching.

You are probably getting it too hot prior to quenching. It's best, if heat treating without measuring instruments to look for decalescense which appears as shadows moving across the blade as the phase change to austenite happens. When the shadows disappear, you know you've phase changed (more accurate than a magnet). I've never used 5160 so I'm not sure about soak times but I wouldn't think it would need much at all. 

Ideally where those breaks are should be a satin smooth gray without all the "bumps" 

I would use a pipe in your forge to try and keep your heat more even and to allow you to better see the shadows. 

Edited by Cody Killgore

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Posted (edited)

The way I think about it, these are not really knives, they are KSO that are meant to throw at things.  You are not going to chop veggies with them or do any other knifee things.  They only need to look sort of like a knife and stick in a target.  In addition, you are going to lose them, because you are throwing them.  Taking all of that into account, why make them out of hardenable steel?

I make mine out of mild, though the last bunch I made out of T1 because the guy who cuts them for me had some in the shop.  The nice thing about mild is that it won't chip or break under high torque.  It might bend, but then you can hammer them straight again over a stump and be throwing again right away.

As for your HT issue with 5160, it does look like you overheated the steel.  Are you normalizing?   It's hard to tell from your post.  A couple of sub critical heats (heat to around 1500) and cooling in still air should help your grain size.

Just my .02

Geoff

Edited by Geoff Keyes

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If I were going to use 5160 for a thrower, I would just normalize a few times, then overtemper (take it up to around 900 degrees) and leave it at that.  No hardening.  It is a very tough steel as-is.  I agree your grain is massive.  Three normalizations, using a pipe (one end closed) and watching for decalescence is the way to go.  The critical temperature for 5160 is 1525 degrees F, exactly 100 degrees hotter than nonmagnetic.  So lose the magnet, it is not helping you.  

The normalizations will reduce the grain size and the overtemper will combat 5160's tendency to air harden in thin sections.

Oh, and do not soak it at heat.  That just grows the grain.

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Cody, LOL, your right, I never thought about it (using mild steel A36 or whatever I got laying around), Iv'e been looking through my "knife maker paradigm". I'm not planning on selling the throwing "knifes"(KSo), just for some throwing fun with my boys.

...but the anal part of me says, make them indestructible, so I suffer with failure.

Alan, thanks for the degree number. I'll shine my pyrometer on it and see how well I can control the heat.

Definitely going to weld me up the metal tube, that is absolutely genius.

All and all, Thanks for taking the time to comment, everyone. I'll send my experiment results back for those interested.

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13 hours ago, mfkerr said:

... I'll shine my pyrometer on it and see how well I can control the heat.

Unless it is one you paid several thousand dollars for, an infrared pyrometers will lie to you if you point it at something that is glowing.

Watching for the decalescence shadow lines form across the blade is your best option.  

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Good catch, Brian!  

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Thanks for heads up, Brian, It is a relatively inexpensive unit... I haven't tried to use it for this yet. I do have a thermocouple meter, but the heat usually heats up the probe to much and seeps back to the wire.

So I'll have the steel in the 2" pipe I made yesterday, that was suggested in an earlier post.

Not sure if I'll be able to see much of the decalescence  shadows with the 5160 stuffed inside of the pipe. (just youtube'd decalescence, i get it now)

This task is getting more monumental as the hours go by...

I may have to weigh out the factors of everything said so far, against my inexperience with 5160, the trial and errors, and material I'll go through in the process...

Again, thanks to all for your help and advise. This has and is a learning experience.

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Posted (edited)

Many use the pipe to let them see the shadows, but I have a hard time with that.  To my eye, everything looks orange inside the pipe.

What works for me is to keep moving the blade in and out of the forge.  (The pipe still works good for this)  The thin portions will heat up much faster than the thicker ones, so I wait until I see the first hint of a shadow near the edges and tip, then pause outside the forge until they lose the shadow.  The thicker portions will retain the heat longer than the edge/tip, so the shadow will be further up the blade in the next pass.

I keep this process up for both normalizations passes and the quench until I have run the shadow up to include everything I want to be hardened.

I'm always worried about the time effect on grain growth because I don't fully understand all of the factors involved yet.  I try to get through this process as quickly as possible for each heat.  I won't claim to know what I am doing, but the grain in the blades I have broken has always looked pretty good.  Most of my blades are a mix of 1095 and 15N20, and I have always assumed they are at ~0.8% carbon after migration and decarb.  (Someday I need to see if I can verify the carbon content and homogeneity)

Edited by Brian Dougherty
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