edge quench

It is known as the Modulus of elasticity, or also Young’s Modulus. The “stiffness” of the steel, i.e. the amount of load required to deform a piece of steel elastically, cannot be affected by heat treatment, it is solely a function of the thickness of the cross section. A fully hard piece of steel will deflect exactly the same as a fully annealed piece of steel under the same load, so long as the yield point (the point of permanent deformation) is not reached. Hardening the steel will extend the elastic range higher and thus the yield point will be pushed higher. A soft piece of steel will yield (bend) under much less load than a harder piece of steel which will resist permanent deformation in increasing levels until it breaks.

Tests we have done on knife steels at Ashokan in the past had the soft steel bending at around 52 pounds of pressure, at the yield point no more load is necessary for the steel to continue to bend so the 52 was it for that steel. A hardened piece, from the same bar, took a little over 450 pounds to break. So yes, the fully hardened blade will break, but it could take as much as 9 times more effort to do it, and anywhere less than 400 pounds the blade will simple return to true when the load is removed.

But then impact toughness is another consideration…;)
 
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Thanks Kevin, I suspected Scott and I were discussing two sides of the same coin but I lacked the vocabulary to link the two. By the way, what is Ashokan?
 
So I have two blades 1/2 of each one hardened and tempered. I decided to snap that half in half...follow? They broke just before 45 degrees.

I have two more which are thicker and hardened and tempered the same way. They are very hard and I'm tempering them again (3rd time) at 25 degrees higher. Maybeeeee not necessary in light of what Scott, Chris, and Kevin are talking about? Maybe they don't need too flex beyond that and I should leave them the way they are for good edge retention? But they are very hard to shape with a file.

Luke
 
Well they're out now. They look like they took a nice temper. Straw color. They file easier.
I remember the reason I did this was because I need to straighten them. Since they didn't file easy I thought they weren't tempered right and would break during straightening.
 
I think I can help you out but I need to know a couple of things first. Are you forging you blade or using stock removal? How are you doing your hardening? Are you using a torch, forge or heat treating oven? Also if your blade waited until near 45 degrees to snap and your edge is hard at this point I would consider that a success no matter what technique you used.
 
Thanks Chris, for these four knives I used wood charcoal.

Pertaining to edge geometry and/or heat treat affecting the strength of a blade - not quite sure what I'm dealing with with these two knives in specific. These two knives I like are thicker, I think that's why I was more fortunate with heat treating them, especially with wood charcoal.

I'm glad I didn't try furnace cement right away. I read that it takes a super hot fire to bring the temp up quickly if your're doing it that way. I was pretty clumsy with the knife in the coals, making do without tongs, so they sat in the fire for a long time and heated slow, cooled, heated up again, etc. Then blow on the fire with these two lungs as bellows. Not ideal. in a more controlled forge I'll try furnace cement sometime and full quenches too, - also when I use a known steel. Right know I'm just soaking up experience and knowledge as time and money allow.

I think you're right they're usable knives. In my UNexperienced judgement, I was happy with the grain size. I'm going to finish grind and see how they hold up to actual use. One is thinner than the other. The main area where they'll need strength is going through joints like the neck, hindquarters, and ribs - point first along with rest of an animal or two (or four or five) without sharpening...
 
I am impressed you got the steel hot enough to harden without passing out only using your lungs as a blower. Before I give too much advice on fire and forges are you over 18?
 
I'm good on forges right now - this was an away from home experiment. I'm more set up at home where I'll be able to measure temps, use known steel, etc.
As for now I'd like to figure out the balance between proper heat treat, blade and edge thickness and retention, and the thickness of the point, where it all meets.
My first experiment is just going to be finish grind by intuition.
 
soundmind said:
... It seems the spine has coarse grain and the edge has finer grain.

Does that resonate with anyone? Should I still expect fine grain throughout the whole piece of steel on an edge quench?
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This question was never answered... it could be one of two things... firstly the spine is not martensite and the edge is, so the edge fractures cleanly between the grains, so you can actually sort of see the grainsize... the spine is probably a mix of steel phases or probably carbide segregation, so it does not fracture cleanly, so it looks course.
 
Andre Grobler said:
firstly the spine is not martensite and the edge is, so the edge fractures cleanly between the grains, so you can actually sort of see the grainsize... the spine is probably a mix of steel phases or probably carbide segregation, so it does not fracture cleanly, so it looks course.
Click to expand...

Thanks Andre. Makes sense. Since the time I did this I re-read in my books the chapters on heat treating. What I gathered was the spine must have been banite...but honestly I hadn't really put together yet what you said, that the edge is martensite, the spine is something else. I never thought of one knife being two things but I kind of understand now.

I'm not sure what carbide segregation is or a mix of steel phases...like banite, pearlite, etc altogether - or something. I know I've come across some of that but I can't remember where. It takes me ten reads of the same thing, experience, then read it again before I start to sort of get it.
 
No, the spine would not be bainite unless you could hold it at a temperature above the Mf point for a long period of time. That could be hours depending upon the alloy and the temperature that you hold the steel at. That could happen if you put the blade into the tempering oven before the conversion of austinite to martensite finishes. That is something to avoid.

If you are edge quenching the edge that is quenched converts to untempered martinsite while the steel in the spine that is out of the quenchant will convert to pearlite.

Doug
 
soundmind said:
Thanks Andre. Makes sense. Since the time I did this I re-read in my books the chapters on heat treating. What I gathered was the spine must have been banite...but honestly I hadn't really put together yet what you said, that the edge is martensite, the spine is something else. I never thought of one knife being two things but I kind of understand now.

I'm not sure what carbide segregation is or a mix of steel phases...like banite, pearlite, etc altogether - or something. I know I've come across some of that but I can't remember where. It takes me ten reads of the same thing, experience, then read it again before I start to sort of get it.
Click to expand...
As i understand it, when you cool down slow enough (slower than a simple aircool) from above Critical temp some of the alloying elements will tend to grab the carbon and make and grow large carbides. So you essentially have low carbon steel and carbides. The rest like doug said above
 
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