5160 tempering...again

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byersj79

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Nov 17, 2007
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A few weeks ago I ask a few questions about 5160 but I'm still a little confused about the heat treatment. I've read some conflicting data on the internet and a ton of different methods of heat treatment. One way that many have referenced to me is Ed Caffrey's ABS test blade heat treat method which he edge quenches by only heating the edge with a torch. I know many great knife makers heat treat this way but I just can’t see how you can get accurate even heat throughout the edge. He also mentions he triple quenches so does that allow a little less accurate temp and if you triple quench do you not have to soak? I found another website (tellercanyon.com and by the way has beautiful knives) that also edge quenches BUT heats the entire blade to the same temp before edge quenching. They say that the edge is harder than the spine by edge quenching of course but the spine is hardened to a springy state because of the small amount of air hardening that 5160 does. They also harden three times and temper three times but all cycles are 24 hours apart and in between the tempering they soak at -20. Another fella on this site, who I don't remember, said he heats whole blade to temp, soaks for 10min., quenches then as soon as heat treating is done he tempers.

All that being said why is there so many methods to heat treating 5160? Why do you not have to soak if you triple quench? Why wait 24 hours in between each cycle? Does the air hardening of the spine and tang increase the grain structure in that area and can you temper out the brittleness of that less hardened area with the low tempering temp of 5160? I already have the experience of breaking the tang off an unfinished blade because of air hardening. And of course which is the best method of the three mentioned above?

I'm leaning more to the way that Teller Canyon Forge does the heat treating minus the -20 degree soak during temper. Well maybe not the 24hour wait between cycles either. The only concern is the air hardening of the tang and the ability of being able to toughen it up by tempering that area. Ive made a few knives out of 5160 in a different way as mentioned above by hardening the whole blade tempering the whole blade and drawing out the spine and tang with a torch. They seem to have worked out fine and have been used with no complaints but with just my thoughts of Ed Caffrey's method tempering the spine with a torch can't be done with much accuracy. I know this is a long boring post with a lot of questions but I'd appreciate any help you guys might give me.
 
I want to differential heat treat my 5160 hidden tang knives as I do my 10XX ones. As I’ve mentioned when I first started using 5160 I was surprised by the amount of air hardening the steel goes through and I broke the tang off a knife I was working on just by heating an annealed blade to dull red and stamping it. The stamping bent the tang slightly and I tried to bend it back without heat and broke it off. If I edge quench a totally heated blade the spine and tang will be air hardened. Can I temper the brittleness out of that with the 350-375degree tempering of 5160? Or will it temper the harder edge to a workable RC and not touch the softer spine leaving it just as brittle?

I've also found Ed Fowlers heat treat method of 5160 from 2003 http://www.knivesby.com/Ed-Fowlers-heat-treat.html which is very similar to the Teller Canyon Forge methods. It seems like he doesn't soak but I'm wondering if that is the reason for the triple quench and if it is why not soak if you can?

Thanks guys for the replies. I plan on doing some testing this weekend myself but if anyone might know the answers already I'd appreciate your replies.

Jason Byers
 
Providing you have reduced or refined grain size through your forging methods, the finer the grain the lower the temperature it will grow. Grain growth is a function of time and temperature, this is one reason why multiple quench works for us as it reduces time at cirtical.
 
Read the sticky about hypereutectoid steels before HT'ing 52100 !
 
There are two common ways for bladesmiths to approach heat treating in these methods- one which is geared toward the ABS bend test and one which is geared for a general everyday using blade. The ABS bend test is best accomplished with a blade that has low strength with high ductility, this will make for a blade that resists cracking when bent to 90 degrees but it will also make for a blade that will easily bend. Thus the edge quench is the method many prefer for the 90 degree bend. However for general purpose using blades strength can be much more important than bendability and a fully hardened blade with a good temper (tempering is the draw, not the hardening, we need to keep those two separate in our mind) will stand up much better for practical use.

Unless you have done something seriously wrong to bring about retained austenite, there should be no affect or reasonable point in a 24 hour wait before any heat treatments, most of the concepts surrounding this are really just so much snake oil, and I challenge those who propose these quirky rituals to give a detailed explanation as to their reasoning.

5160 does not truly air harden but will form very fine pearlite mixed with harder phases. The phase of steel with the highest strength to toughness ratio is tempered martensite, pearlite will only get you degrees of softness. So heat your 5160 to 1500F -1525F entirely for 5-10 minutes and quench in oil for a through hardening. If you do not have the methods to control the heat for that long you can resort to multiple quenches as many smiths have, the quench locks a percentage of carbon into solution so the next heat can add to it, but a proper soak replaces this improvisation. Then temper the entire blade from 375F-400F (depending on your application). Then use a torch to draw the spine and other areas that you want tougher. Set the edge in a shallow pan of water to protect it from the heat. This will give you a blade that will keep a good strong edge while still gaining impact toughness on the spine. Such a blade, if done correctly, will also pass the ABS test but will spring back considerably instead of folding over like soft lead.

Among bladesmiths you will find as many different ways to heat treat a single steel as there are smiths telling you, I won’t get into the social and psychological reasons as to why this is, but if you look to other industries, that really have to meet serious standards, they all seem to come up with the same heat treatment for these steels. Heat treatments that make for less catchy headlines, but were developed by the people who designed the steels, know them, and know what they are doing.

I have a page based upon the recommendations of ASM, the steel manufacturers, and my own work and study which confirms those same recommendations, perhaps it will be of help:
http://www.cashenblades.com/info/steel/5160.html
 
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I forgot all about this thread and just have to come back to it.

My first suggestion is for those bladesmiths who truly want to know:
Do not take any one's methods for the best way without doing your own testing.
The only way to know is to test a blade to destruction.

If you feel the soft back draw is great, do it - but then etch your blade and see what you have developed. Then compare it to one that was only edge quenched like we do.
You will see a difference. Etching is an excellent method available to any blade smith who wants to improve his hardening methods.

Then flex the blade to destruction and see which method held up the best.

Never let a blade out of your shop that you have not tested for edge flex and cut.
 
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