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First ever Stress Cracks. YAY


Robert D.

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So today, I was cleaning up a blade that is part of a matched set for a friend of mine and his wife.

They are avid bowhunters, and wanted some hunting knives made.

Did the heat treating and tempering at the same time for each knife, cleaned up the first one yesterday pretty much entirely by hand using just a flat board and sand paper as I wanted to see how long it would take. Thank GOODNESS that is not the blade that broke.

Today I am cleaning up blade #2 and I notice this line in the blade.

 

DSCN0438.JPG

 

Then I notice the much darker thicker line at the spine, which appears MUCH more like a crack then the first one does.

So I stop cleaning up, clamp it in the vice, and give it a couple sharp tugs, nothing, not even a slight " tink " sound. So I grab it with both hands. prop my feat up on the bench, and lay back. after a couple seconds at most, it snaps clean off. ( I weigh 145 lbs, so its not shocking just adding my weight did not break it without trying. ) and low and behold it snapped right at the end of the spine crack, and shows the extent of cracking in the horizontal crack.

 

DSCN0439.JPG

There is the grain and the cracks in all their failed glory, the spine was FOR SURE cracked to heck and there was no fixing it, the horizontal one, had the blade been thicker its possible it could have been ground out, but while the picture is not that great, by my guess my normalization falls into the " 1 - 2 normalization " range on that file normalization pic that has been floating around. I did triple normalize these, however in hindsight I expect that laying red hot metal on a cold concrete floor probably didnt help the cool down process as much, and next time I will be trying to use more space in my forge for the normalization process. I also expect with the relative " ease " I experienced breaking these, that my tempering process is not working to the extent it needs to and needs to be addressed.

DSCN0444.JPG

Here is the grain after I broke the blade at the half way point. I did get my grubby fingers on the grains, so I expect that is why the grain looks a bit larger then it really is close up, that and I dont take good pictures, and my digital camera is the special ed model that takes blurry pics when mounted to a tripod even.

The steel is " Mystery Steel " in a sense, old Leaf Spring, I suspect / treated it as 5160 based on the info I could gather about 1976 Camaro leaf springs, After this testing, I am going to bump my Tempering temps up a bit, from 400 to around 475 - 500 in my crappy toaster oven, and perhaps temper for more then 3x1 hour sessions.

 

But there you have it, my first " Destructive test " of a blade

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Bummer. :( At least it wasn't a sword blade you already had the hilt fittings completed for (that was my first blade lost to post-ht cracking).

 

If it helps any, used leaf springs are known and feared for stress cracks left over from their previous life, especially if they have seen high miles or rough conditions. I'm betting a '76 Camaro has seen both. You are right about the concrete floor being a bad idea, though. 5160 will air-harden in thin sections, so a good uncomfortably warm place to set it down is required.

 

Now for the bad news: That grain is huge. it's not just your grubby fingers, if you can see any grain at all with the naked eye, to say nothing of the blurry camera, it's too big. What's your temperature control method for normalizing?

 

There's nothing wrong with your 400 degree tempering, either. For a small knife I'd go with 375 for 5160. Higher tempering heat will not fix overlarge grain, that happens during the final stages of forging. Do your final few cleanup heats at a low orange heat using gentle hammer blows, turn off the lights, turn your forge way down, and triple normalize by watching for decalescence (the swirling shadows thing I'm always yammering about) rather than using a magnet. When it's time to harden the blade, same thing: forge turned way down, dim light, watch the shadows in the steel until they go away, quench immediately.

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Well, the concrete floor isn't good for softening the metal, but it is great for grain refinement. Slow cooling doesn't help grain refinement; if anything faster cooling does. I'm thinking the blade probably got way too hot during the normalizing heats though (and possibly/probably before).

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at the moment, I have almost no control over the temps, Coal forge and no reliable way to measure temps to see where I am at.

another thing to consider however, is that I did do most of the normalization during the day, outside, in Utah, in the sunlight. I was pulling the blades out of the fire and shifting to the shade to look at the color but perhaps I should start doing my normalization and hardening processes later in the evening, only problem with that is this time of year, the sun is still up at 9:30 at night.

Ohhh to have burned though all this stock so I can buy some new clean fresh stock. I have decided once this stuff is gone, there will be no more leaf springs used for anything, out of the 4-6 hours I spent working on that knife, I would say at least 2 hours of it, was thinning the nearly 1/4 inch of it down to a much more " knife " width.

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At the very least use a piece of pipe or square tubing with one end closed as a muffle in your fire, and rig a shade of some sort. Have a good bed of coke built up, put the pipe in the fire over the center of the pot a few inches above the air blast, and then bury it in coke. All of it except the open end. This will allow you to see the steel as it goes through the transformation. Watch as it comes up to heat and you'll see what appears to be shadows swirling around inside the blade. When those shadows disappear, you have achieved full transformation to austenite. If you pull it out and look at it in full sun, it will appear black. Full sun seriously warps your ability to judge incandescent temperature, on the order of a few hundred degrees worth. Now we know how it got overheated, eh? No worries, we've all done it.

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I forgot to add, if you stick a lump of charcoal or two in the tube with the blade, it creates a reducing atmosphere. This has two advantages: no decarb and no scale formation. Neat, huh?

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if you're normalising in bright sunlight, you're almost certainly growing the grain rather than refining it - by the time you see any colour, you're already way too hot...

Jake Cleland - Skye Knives

www.knifemaker.co.uk

"We can't solve problems by using the same kind of thinking we used when we created them."

"Everything should be made as simple as possible, but not simpler."

"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."

 

Albert Einstein

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Sounds like Ill be doing all my heat treating at night from now on if the pipe idea doesnt help out any. Have a nice big pipe I can give this a whirl in to see.

And Ill bet that same process, although would take longer, could also be used for a reducing atmosphere conductive to pattern welding? ( the pipe that is...)

 

now I am going to re normalize everything I have bevels done on and will use that process from now on for everything, I do have a good piece that would work as a shade for my forge. Good ole HP desktop side panel .

Thanks guys, I will give the pointers a try an will let you guys know how it goes.

Edited by Robert D.
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I think Rob Toneguzzo has managed to weld in a pipe in his charcoal forge, but it'll be tricky getting it hot enough if it's a big pipe. Not to mention the risk of welding the billet to the pipe inadvertantly. Not a strong weld, but enough to shift your layers a bit when you try to pry them loose.

 

Good luck! I use 14 inches of two inch pipe that has been squeezed into an oval section, making it about three inches across and 1.5 inches tall. I can get an even heat in about eight to nine inches of that, the open end tends to be much cooler.

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If you are working in bright light and have no direct temp control I would suggest using the magnet method for determining heat. Its not perfect but you should be a lot closer than you are. I use a stainless steel pipe inside my propane forge to keep the heat a bit more even, and a magnet to help with determining temps. Magnet pulls too cold... no pull watch it closely and go slow your looking for the shadows kinda rippling through the steel. once you see it its hard to miss. I'm color blind personally so this is about the only way I can get there. I've got it down to a timing issue at this point but I have done it more than a few times. about 30 seconds past magnetic, and I'm good I just set it on top of my forge to cool slowly or into the cooling media to harden, again not perfect but It works better than no control at all.

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Alan ...... The next time I am out that way and have some time, I am going to head your way and hand deliver a 12 pack of beer as that is the only way I can think of to properly thank you.

Piece on the left, is the blade I just triple hardened it with your pipe trick after triple normalization in the pipe. right side is the piece that broke on me yesterday. Still a bit big, but HOLY COW is there a difference. This is also after 0 tempering cycles ( it is currently in the toaster oven set to 400 ) as I was impatient and wanted to see the grain at the tip after the process, I am going to break it after each temper cycle to see if the grain changes after each cycle.

The girlfriend looked at me kind of funny when I showed her this right before I snapped the picture, she asked me " Why did you spend all that time making that knife just to break it ? "

I cant wait to normalize the other stuff I have sitting " in progress " tomorrow now, I have a couple O1 toolsteel knives I have put off heat treating after the first two I made had some issues including my " backup monosteel puukko " for the KITH that will be my submission should my attempts at " pipe welding " fail this week.

 

DSCN0446.JPG


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Yeah, grain is too crunchy. I suspect the others are dead-on about the heat problem. There's a reason most blacksmith shops are dimly lit!

Don't give up completely on OTS steel. (Old Truck Spring.). I've forged many a blade and found it's incredibly tough with the right HT. You should be able to tell by sight and ear pretty quickly if there's a crack somewhere in the forging process. The problem now is your lighting is just plain off for this work.

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It is funny, I was just today complaining to a blacksmith friend of mine that his shop was too bright. It is very easy to keep hitting the steel longer than you should in daylight, and this very well could be what lead to the cracks. My forge is located outside, and I will only forge on cloudy days or after dark. When I'm heat-treating, it is after dark and preferably with no moon...

George Ezell, bladesmith

" How much useful knowledge is lost by the scattered forms in which it is ushered to the world! How many solitary students spend half their lives in making discoveries which had been perfected a century before their time, for want of a condensed exhibition of what is known."
Buffon


view some of my work

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Well my neighbor on one side ( who is a very abrasive " gent " to say the least ) asked me if I would be so kind as to stop working by 6pm each day.

And by asked, I mean he basically told me I had to, However, noise restrictions in my city dont begin till 10pm, So i just try to do my louder work first and then the quieter stuff after 6. But I dont like the guy and no one on the circle likes him either, I dont know about my neighbor on the other side as they just moved in last week, but I watched them haul a ton of shop type equipment into their garage, so I suspect he is a fellow tinkerer and wont be bothered much by it.

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So I meant to post these this morning, but I had a busy morning.

DSCN0447.JPG

This is after my first normalization.

DSCN0451.JPG

And this is after the second normalization.

Its currently in the oven for its last round, When I attempted to break it the second time around, it was actually so tough it broke one of the screws holding my vice down. If it were not raining right now where I am at I would be outside right now getting ready to heat treat the 5 knives I have waiting to be done.

 

I still think it got a bit warmer then it should have, but its HANDS down better then the last one I did.

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Errrrrr..........

I meant Temper, Not normalization in that last round of pics.....


Tomorrow night, I plan to try my hand at using the pipe and some charcoal to use the pipe trick to forge out some pattern welded steel. If this works, I am going to go to my dads house sunday and grab some 2 inch square pipe so I can work on larger projects that way.

Edited by Robert D.
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