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ARRRRRGHHHHH!


Jesse Fennig

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Okay, so here is the deal. I am mostly a general hobby blacksmith, but a few months ago I decided that I wanted to make knives. I have attempted this three times, each time using a section of a cleaned up (read; annealed, then teeth ground off) Nicholson file that I hot cut to size. I forge a basic shape, then go to the bench grinder, clean it up, spend FOR FREAKING EVER with sandpaper and files to get a nice smooth finish, bring it back up to non-magnetic, then quench it in room temperature water. Every single time it has cracked. The first two were no biggie, because one was just a little chip out of the edge, and I assumed that was because of grooves left in the surface, and the other, I assume for the same reason, was a crack running straight back right below the tip. I just pitched both of them and started over. This time, however, it cracked in the tang, which I literally had not touched with grinder, files, or sandpaper. The steel was brittle enough that I was able to snap the remainder in half with my bare hands, and it was about half an inch wide, by 1/8 or so thick. Am I forging too thin? Should I not start removing metal until after HT? Should I use a slower quench? HELP!!!!

 

If people want pics of the broken blade, I can post them, so that maybe they can see what I did wrong.

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Normalize at least 3 times is what I've heard, heat up to above critical then let air cool, heat up to critical then air cool, heat up little below critical and air cool. This is supposed to reduce the grain size of the steel and relieve stress. Also water is known for cracking blades, it would often kill japanese katanas during the quench. Use some kind of oil.

 

I'm not sure what else you could be doing wrong how ever, I did some files and none of them cracked during the quench, even in freezing cold water in winter, only afterwards when I tried to bend them.

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Dont use water! you can use old motor oil, hydraulic oil, vegitable oil, peanut oil,fish oil, old kitchen fat is a favorite of mine, profecianal quench oil is best ( like parks 50) because of the low flash point but any of those oils will do, Knife blades are too thin for the severe shock of a water quench, thats why your cracking so many. make sure to heat the oil to about 140 degrees F befor you quench, After you quench check your edge with a file to make sure maximum hardness was achieved, then temper back your hardness asap or your blade wont last long in the brittle martenistic condition its in fresh out of the oil. Hope this helps a little ;)

J Anderson R

 

" Fools live to regret there words, wise men to regret there silence"- Will Henry

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I agree with jrassett. When smiths talk about water quench it is actually water,salt,and blue dawn dish soap not just plain water. It must be heated any where from 120 to 170 degree's depending on the smith,steel,quenchant ect. Oil is a much more forgiving quench anything from peanut oil to motor oil can be used a lot of pros use parks 50 oil. If you use oil it needs to be heated as well.

 

Aaron

 

A good analogy is to look at what happens to ice cubes when you pour water on them. Even cold water causes them to fracture.

Edited by A.Young
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Everything I've every tried to quench in water cracked. I have never cracked one in 90 degree vegetable oil. Like the others said, don't waste much time getting it tempered. I had one crack an hour later when I set it down a little rough on a table. It's REALLY brittle right after the quench.

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To summarize,

Don't quench in water, use oil.

Thermal cycling/normalizing treatments after forging are essential.

Use oil! (peanut oil is nice, high flash point, smells good)

 

Concerning brittleness... Yes, you can learn alot from a broken blade, seeing it might hep home in on problems. The first thing to look for is grain appearance at the fracture, judging by what you have said there is a very good chance the grain was coarse, and therefore prone to fracture. Over-heating the steel causes excessive grain growth. This is where thermal cycling/normalizing comes in, it helps refine the grain, making the blade stronger, and removes stresses that could otherwise lead to warping in the quench. It also leaves the steel in a fairly soft state that makes it easier to grind and sand, and may have prevented the hard spot that caused the tang to break when flexed.

 

A couple questions.

What did you use to judge the temperature of the blade during the quench?

Did you quench the entire blade including the tang, the blade, or just the edge?

Are you using coal, gas, or charcoal for forging/heat-treating?

I'm guessing the blade broke before any attempt at tempering?

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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g,day jesse,

mate you have to make sure that there are no sharp edges ,i round off all the sharp edges over the whole blade with 4oo emery no nicks or sharp file lines or anything that can start a crack ,if you use water to h/t use hot tap water with dish washing liquid no bubbles ,and dont get your blade to hot ,use a magnet,and dont rush if your not sure let the blade cool a bit then start with the magnet again,when it dont stick wak it in the water ,count 5 out the water then bak in till it cools .dont rush the magnet thingy practice on a cracked blade its a finite timing,

any way it works for me

john

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Mmmkay, looking over the advice, I think that the overwhelming consensus is that I should never quench in water, hey?

 

My forge is a large steel pot (literally) lined with kaowool, using a single Reil burner. No pyrometer, but the interior of the forge is a pale yellow when burning.

 

The grain structure, when I looked at it with my little 100X hand magnifier, looked remarkably smooth, but probably 100X is not enough to get a good look at hard crystals.

 

When I quenched, I had the edge of the blade completely immersed, and about half the tang. I took it out the moment it was no longer glowing; too soon or to late? Next time I think I will drop a magnet into my quench tub (I always hold items to be quenched, so it is plastic). Would it be a bad thing if a magnet were to jump up to a freshly quenched blade?

 

I did not have time to temper; all three literally broke while still underwater.

 

Ummm, it does need to be fully austenitic to quench correctly, right? I check against an old speaker magnet.

 

I annealed it before I did any grinding, filing or sanding, but after forging. I sandwiched it in the middle of a pile of mild steel coupons, and brought the whole thing up to non-magnetic, then shut down my forge. It took about three hours to cool. It went straight from the annealed state to the quench; could that have been an issue?

 

And as a postscript; MAN, these steels are different. Grain and hard spots are so not an issue when you are making decorative candleholders or wall sconces.

Edited by Jesse Fennig
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Mmmkay, looking over the advice, I think that the overwhelming consensus is that I should never quench in water, hey?

 

The grain structure, when I looked at it with my little 100X hand magnifier, looked remarkably smooth, but probably 100X is not enough to get a good look at hard crystals.

 

When I quenched, I had the edge of the blade completely immersed, and about half the tang. I took it out the moment it was no longer glowing; too soon or to late? Next time I think I will drop a magnet into my quench tub (I always hold items to be quenched, so it is plastic). Would it be a bad thing if a magnet were to jump up to a freshly quenched blade?

 

I did not have time to temper; all three literally broke while still underwater.

 

Ummm, it does need to be fully austenitic to quench correctly, right? I check against an old speaker magnet.

 

I annealed it before I did any grinding, filing or sanding, but after forging. I sandwiched it in the middle of a pile of mild steel coupons, and brought the whole thing up to non-magnetic, then shut down my forge. It took about three hours to cool. It went straight from the annealed state to the quench; could that have been an issue?

 

And as a postscript; MAN, these steels are different. Grain and hard spots are so not an issue when you are making decorative candleholders or wall sconces.

I would not go as far as to say -never- quench in water, some people do with good results, but I think part of the key is an interrupted quench. From what I understand, it involves holding the blade in the quenchant for a short period of time, maybe 3 seconds, then removing for a few seconds, then back in the quench for a few more times until the blade is cool. I'm no expert in water quenching (everything I have quenched in water broke too, but that was before I'd read of the interrupted quench technique), I suggest more information can be found searching this forum and the web for 'interrupted quench'. I know there have been threads discussing it in some detail here in the past.

 

If you are like me, though, you've had enough of water quenching at this point...

 

When heating the blade for the quench, I keep a magnet on a long handle close, and occasionally pull the blade from the forge and check it for magnetism, watching for hot spots as I do. Watch the point, they like to get hot alot faster than the rest of the blade, and are easy to overheat. I don't think many bladesmiths quench the tang, even if they harden the entire blade the tang is usually left soft or selectively tempered way back in hardness.

 

I think your blades broke because the quench was too fast, combined with being in an untempered state when flexed. It sounds like coarse grain is not the problem, judging from your description of the fracture.

 

Yes, these steels are fun, very different from mild, I've heard they make good files out of this stuff... ;)

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

RelicForge on facebook
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I have water quenched files successfully. The water needs to be hotter than room temp. I make both my water and oil about the temp of a hot bath. You could be over heating your steel before you quench it; you don't want to be much above non magnetic. You can also quench in brine and I've been told that sea water is a perfect brine and sits about 7% salt naturally. it also needs to be hot. When I oil quench I use veg oil not motor oil especially if it's used because I don't want to breath any vapors that might have heavy metals in them....I tend to be a little paranoid.

Using oil is always a safer bet for the steel. if it doesn't harden you can water quench after that.

Keep plugging away.

Good luck,

JJ

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My thought has come to be that if oil produces good martensite, why risk cracking in water? I'm just simple that way.

 

I know there are some steels that I haven't used (many in fact), but for 10xx and 5160, oil seems to do the trick with low risk.

Edited by jkv
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I agree with jrassett. When smiths talk about water quench it is actually water,salt,and blue dawn dish soap not just plain water. It must be heated any where from 120 to 170 degree's depending on the smith,steel,quenchant ect. Oil is a much more forgiving quench anything from peanut oil to motor oil can be used a lot of pros use parks 50 oil. If you use oil it needs to be heated as well.

 

Aaron

 

A good analogy is to look at what happens to ice cubes when you pour water on them. Even cold water causes them to fracture.

 

 

Your talking about super quench. This is not what smiths are talking about when the say Water Quench. They are talking about quenching in water. However, it is still a risky move if you are not sure of what your doing. Super Quench would crack a carbon steel blade pronto. Its main use is to harden very low carbon steel.

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