All you metal guys out there.

[Stringman]

Ok, I think I know the answer here but let's talk about what I did wrong. Following Khalverson build along has generated some pretty nice file knives. However, I got in a discussion with some old blacksmiths the other day and they said if it wasn't tempered then the knife could be harder. In a nutshell, we heated the blade to "nonmetallic" then quenched it. Then heated it to "wheat" color and quenched again. This second step was supposed to soften it up a bit and still keep a hard edge. Using this process I created this knife.



This morning I used my stove in the garage (and some forced air) to temper a few more blades.



Pleased with the results, I cleaned one blade up and mixed some glue to pin some scales on the blade. Everything was together and the pins were in ( but needed set a little deeper) so I clamped the blade in the vise and tapped them with a hammer/punch.



That's right! Good day turned bad... Fortunately I was able to pull the scales apart before the glue setup, but that was small consolation.



My question is: are these blades too brittle if they snap that easy? Or is that what you get with a finely tempered knife?

[Eric Krewson]

Never heard of quenching after the wheat straw color. I have heard of bring the metal to around 400 degrees and holding that temp for 3 or 4 hours to make the metal less brittle.

That said, I know little about heat treating blades just what I have read.

[bubby]

i'm no expert but I know the harder the metal the more brittle, it's got to give a little, I don't know I did my file knifes like khalverson's build and their tough as al get out

[lenador]

All the file knives I've made and to my understanding you are supposed to soften a file up a bit before its knife ready. Because you need softer type metal to keep the edge from chipping. A slightly softer blade will get sharper And last longer. With a hard metal the thin edge could chip and chips force you to remove more metal to retrieve your edge.
 Idk if that makes sense.

[wildman]

I always bring my metal down slow the last time. The 400ish degree thing for the last time is the way to go. Catch the lady of the house gone and put them in the oven for about 3 hrs. I have built several this way as well as hawk heads , which take a beating no troubles. Good luck and nice looking knives!

[Stringman]

So maybe the last quench is unnecessary?!? I'm sure not trying to recreate the wheel, but I'm just concerned that the first softening process was leaving the metal too soft. I'm sensing t hat this is a fine line of brittle vs tough edge that needs to be a personal decision.

[DC]

The first heating is supposed to get it nice and soft, like a nice massage. Quenching seizes it all up, like a charlie horse. The 400 degree soak just relaxes it a bit. 400 is just right, 500 is a bit softer etc.

[Blaflair2]

After u harden it in the gorge u need to bake it in an oven at 400 or so for two hrs about. It was too hard and brittle. Ur looking for 55-60 on the Rockwell scale for hardness. Looks sweet though.

[stickbender]

     I have read in one of the knife making books, about multiple temperings to give the metal a memory to align the molecules better.  Don't know if that would work in your case, or not.  But definitely too hard will cause your result.  Unless you can bond, or forge a softer, steel, or iron to a thin very high carbon piece, you need to bring the temper down, other wise it will give you the results you got.  The super high priced Japanese kitchen knives are made from a hard core, and softer, multiple layers of iron, or steel.  The hard core is tempered to 65-67 RC.  You can get an edge that will literally shave you, and so sharp you can slice a tomato top off, and then invert the tomato, and without holding the tomato, you can slice a very thin slice of tomato off, and keep repeating the move, without having to hold on to the tomato.   It is the utmost in super scary sharp.   The Swedish Mora knives are made with a thin very hard, high carbon piece of steel sandwiched between two softer pieces of steel.  They can flex, and not snap.  They make the ultimate survival knife.  It can take a lot of punishment, and still take a razor edge, and be used for prying, and  hacking, etc.

                                    Wayne

[caveman2533]

I am not a forger but I once made a big bowie from a farriers rasp. I heated it to straw and left it cool for the last temper. don't quench at all for tempering.
steve

[KHalverson]

scott
I believe you have your terminology  mixed up.
the second blade looks like a heat treated i.e quenched blade.
temper removes most of the brittleness imparted by quench and a full hard blade.
a sound temper takes time it requires at least 2- 2 hour soaks @ around 400 f for the files.
if u look at the build along again we tempered the blade then used the torch to draw back the spine while annealing the handle
a properly tempered blade placed in a vice will bend 45 deg no problem and spring back straight and not crack.
the A.B.S performance test requires blades to bend 90 deg and no more than the bottom 1/3 of the blade is allowed to crack.
I would be interested in seeing the grain structure on the broken blade.
is it smooth?
or course grain?

the knife in the first pic looks really good.
im glad ur enjoying building knives it can be a ton of fun

Kevin

[BarredOwl]

What KHalverson said.

 I think it's called a differential heat treat when you temper or draw the blade spine and handle so that is more like spring steel (blue-purple range) or a little softer  and leave the bottom 1/3 from cutting edge up a little harder (straw color), not completely hard like right after the hardening quench.   

For the spine/handle softening I think some blacksmiths heat a block of steel to red hot and lay the blade on it so the entire cutting edge and tip is hanging out in the air and let the heat (color) soak out towards the cutting edge and tip then removing it before it gets too close to the cutting edge and maybe quenching it to stop the heat from soaking out to the cutting edge.  Haven't done that method myself but I'll bet you can probably find some info on the internet maybe even a video or two. 

[HickoryBill]

Yes that blade that broke was to hard/ brittle..Anytime you heat a blade and quench it it hardens it..I usually start out my file knives by annealing them.= Heating them up to nonmatellic and letting them cool down in kitty litter..This cools them slowly.I rough shape my blade blank to desired shape/drill my holes and then harden them..=heat em up to a soft cherry in quench in tranny fluid..then I do my final shaping and polishing..Them they go in the oven at 400 for 3 hours..Letting them cool at room temp..I'm betting it broke at a stress riser..Either in the blade that you couldnt see or one that you created..Files can be finicky tho..and thats just my 2 cents worth...

[Stringman]

Thanks for all the feedback. I have been researching this more and finding that this is a whole new world to me. I'm especially interested in the harden/tempering process that leaves a durable resilient edge. I'm still making and having fun with it, but under no delusions about being any good. Just something fun to play with.



This latest blade is an old Swedish file from my grandpas barn floor. It was hardened and then tempered at @400 for a couple hours. After final sanding and polishing, scales of buckeye burl were added. This is my 4th knife that I've finished.







Again, thanks for the advise!

[KHalverson]

Scott
don't sell your self short.
you are doing very nice work.
I wish my 4th knife had looked half that good.
another thing that comes into play for a resilient edge is edge geometry.
I find an apple seed grind holds an edge much better for heavy work.
your scandi grinds are very nice but may lack a bit of strength under heavy use.
again nice work .
Kevin