Tested a blade today

[kile]

I usually have been making and heat treating blades in batches of 4-5, and taking one of the blades and testing it to see how well I did with the heat treat.(I am still very new at knife making) I did a batch of 3/16" 01 blades, all were the same pattern, a very simple drop point. All were full tang, with thin wooden scale handles, attached with two stainless pins. All were hollow ground on an eight inch wheel. I took one today and tried to ruin it.

Here was my heat treatment for this batch.

To heat treat it, I covered the spine of the blade in some furnace cement, and just left the part of the blade I wanted to harden uncovered. Before I put the furnace cement on I normalized each blade at least twice by heating them up till they reached non magnetic, and letting them cool in air, when the color was gone, I heated them again to non magnetic, and let them cool enough that I could handle them. I heated the blades up with a mapp gas torch in a little firebrick forge, until it wouldn't stick to a magnet. Then I quenched the entire blade in 135 degree Olive oil. I ground off the scale, and put them in my kitchen oven at 375 degrees for an hour. Then I let them cool to room temp, i again heated them to 375 for an hour. Then I hacked at an oak 2"x2" to see if the edge would chip or roll, it had tiny chips when I hit a not, so after I was done grinding, and almost done buffing, I put them in my freezer for about 3 days, then I tempered one more time at 395 for an hour. then I finished the blades and put the handles on. Does everything seem alright so far?

So on to the testing.

I cut up an oak 2x2 with the blade, and noticed that the sharp handle edges started to hurt my hand a little(I will fix that with the next batch) Then I grabbed a stainless roofing nail, and a 3lb hammer, and pounded the blade through the nail. The edge chipped out a small bit, this was at about the center of the blade, I tried again with a concrete nail right at the plunge line, A huge chunk sort of twisted and chipped out, It stayed attached, but was sticking sideways from the rest of the cutting edge, I smashed it with my hammer a couple of times and most of it fell off. This was right at the point where my temper line ran off the bottom of the blade.(I didn't harden quite far enough back on the blade, after heat treat I moved my plunge back)
Then I did the same thing up near the front of the blade near the tip, and I couldn't hurt the blade. It didn't chip, or roll, and it was still semi sharp after going through the nail three times. Then I stabbed the point into some oak boards and pryed it out sideways, no damage. I hammered it into the board over 1/2" and still no damage at all. Then I put the blade in my vise, and tried to bend it with just hand pressure. When the jaws were more toward the front(where about 1/2 the blade was hardened,, I could barely bend it, and it sprung right back to straight. When I clamped the blade in closer to the tang, where only about 1/6 of the blade was hardened, I could bend it easily and it did not spring back at all. I guess this is what I should expect, and it probably means that I should harden a larger portion of the blade, and extend the hardened part back through the tang some. Does that sound right?
So what I am confused about is the pounding through the nails part of my testing. I have done this before and been successful. The front portion of the blade was successful, but the the farther I got to the plunge the more damage the blade suffered. I can see my temper lin, and there appears to be no differences between the front part that went through the nail with no damage, and the middle part which chipped. The part near the plunge where a big chunk blew out was probably because there was such a small peice of hardened blade at that point. So my questions are, what could have caused the middle portion of the blade to chip but not the tip? Are roofing nails, different from concrete nails? Would the difference be significant? How did my blade do compared to others who have tested their 01 blades? The reason I tested this blade was because the temper line showed me that I didn't get enough of the blade hardened, so I didn't want this blade to go to anyone who might want to use it hard. I think the rest of the batch is ok. On smaller blades is there really any advantage to differential hardening? It seems like from my test that if I had hardened the whole blade I wouldn't have been able to bend it at all, with just my body prying on it. So in any type of real application it would be impossible to bend or break the blade if it was fully hard. Does this sound right? Let me know what you experienced guys think about this. Sorry for the long post.
Kyle Fuglesten

 

[Bruce Evans]

Good test Kyle.
First let me say that the stainless nils are on the hard side and the concrete nails are really hard.Most people use regular 16 penny nails or regular bolts not the case hardened ones....
You might be getting the tip a little hotter than the rear of the blade,I used to have this trouble until I was told to warm the back edge of the blade near the plunge lines before putting the whole knife in the fire to bring up to heat,This will let everything heat evenly.This is due to the fact that the blade is thicker at the plunge area than towards the tip.
I still prefer a diferential heat treat on the skinner sized blades myself,This way they won't break at the guard joint when stressed,Yes it should have bent at the plunge as you described due too the fact that less of the blade was hardened.
Great test,But try different nails next time (the concrete nails are hardened so they can penetrate concrete after all,and harder than your blade)
Good luck.
Bruce

 

[peter nap]

Bruce beat me to it. Man do you do a test. I thought I was being rough on them cutting Deputy Dandridge's PVC arms off.
Want to really test it sometime get some old trauma plates at a gunshow and try to thrust through it.

 

[rlinger]

Auh, that's some testing. Reminds me of shock testing a new boat design.

You might try tempering tool steel at 25 degrees F. lower on the second temper (for example: if the first temper is at 375 F., the second would be 350 F.) I wonder, from what I've read, if O1 should be normalized. You might try a blade without normalizing. I think your quench temp. of 135 F. is very close.

On the HT of O-1 in the gas forge: I look for the steel to turn red and wait to see dark spots or shadows to appear on the steel surface. These appear to move slowley and finally disappear. When all are gone and the steel regains a consistent color I quench immediatly. The dark spots or shadowy looking areas (I call the Ghost) is where the steel is austinizing! I have not done enough of it yet to see it with the room lighted - so I make sure all lights are off and the window shades drawn. It does work.

The ghost tip was tought me by Tim Zowada.

RL

 

[LHKnives]

Sounds good! I`m siding with bruce that you got the tip hotter than the rest, I too heat the tang first, then turn it around. It is with my experience that if you were to fully harden an O-1 blade it would be hard to bend, and if it did bend much it surly would snap! go ahead and snap that knife if you can in a few places like the tip, the middle, and at the plung and compare the grain structure. If done right on a differentially h/t blade the grain in the hard edge should be silky smooth, and where it is softer the grain will most likely be a bit coarser. Now compare the broken pieces and see if you can see a difference in grain structure, if the stucture is larger in one hardened part than the other, more than likely it got a bit hotter during H/T.
Wow I`m rambling! but by the sounds of it your doing good! keep testing, and working on it, O-1 is my favoright steel, and it will serve you good!