quenching a sword

Yeah, fresh martensite is brittle. But it's not a one-time thing. Why not reheat it, straighten it, and then re-harden? I do that. My most-warped-ever blade got that way when I was too enthusiastic quenching it, and hit the bottom of the tank. It came out looking like a question mark, but a few minutes later it was straight again, and went on to be a reasonably good blade.

Normalize it thoroughly, and then quench it in such a way that both sides cool uniformly. A single-edged blade can, under some conditions, bend a bit in the plane, because the edge and the spine change phases in different ways, and so change sizes differently.

has a discussion about halfway down.

- ken

The guy should learn a little more about heat treating.

Not only could he have annealed it and straightened it out and rehardened it, but he could have drawn the temper out and then straightened it, if the warps were not too bad. A sword too hard to be bent is of little use, as it would break when it struck anything.

Your "smith" seems to be running on only half the information he needs, maybe less. But he seems to be adept at filling in the gaps with horsesh*t, though.

Sometimes warpage is a result of stresses in the metal, which SHOULD be releived by properly ensuring that the metal heats to or above critical, all the way through, and sometimes from uneven cooling, such as would happen if it were slapped flatside to the cooling liquid, or if it were not smoothly and completely inserted.

Instead the dipsh*t broke the work.

Of course he couldn't straighten it. It was glass friggen hard, just like it was supposed to be. Maroon! So you know what he seems to not, the heat treating process requires that the metal be hardened, then tempered, which takes the metal from the glass hard state, to a softer state that also allows the metal to be flexible while still being harder than the original, untreated state. There are not too many tools that get hardened without a followup temper.

Here's a tidbit that you will know and he might never....

When you overheat a chunk of metal, the grain gets very coarse, and not of much use when hardened, By cycling the heat up past critical, then allowing it to cool in air down to black several times, the grain structure will be reduced to a very fine grain. This will also reduce the stresses in the bar that may cause issues when quenched to harden.

Cheers Trevor Jones

Hi Eric,

Well depending on the material this can be true, however he could have saved the blade, by removing the hardness, normalising, straightening and clamp the blade then re-H&T.

Of course the blade shattered he didn't temper it... no surprises there, it probably would have shattered if he dropped it also.

I know why blades warp, usually due to uneven grinding. A blade that is forged correctly to the right dimensions and then cleaned up lightly doesn't warp. A totally ground blade also wont warp as long as the grinding is even.

Don't know this guy, but that is not right. A sword can be forged without grinding being a manufacturing process at all, and takes a great deal of skill i.e. smooth & no hammer marks, all that is needed is polishing.

What warped the blade wasn't the forging, but the heavy uneven grinding.

Although if he's doing the H&T for the swords himself, then I would suggest not to use the weapon to strike anything harder than custard. I've been making swords for years, for use in a sport, and I don't trust myself to do the H&T evenly. Anyway I've got some professionals to do it for $10-$15 per blade, they do them to a consistent 57 rockwell, and so far the blades have come back the way I sent them (except covered in scale... more polishing).

H&T is an art in itself, and I limit myself to blades under 3 foot. However it's a skill that can be learnt, it just requires practice.

I have to start heat treating larger items, someone asked me to make a

20" draw knife, so it looks like I'll be making that sword forge after all :-(

Regards Charles

snipped-for-privacy@gmail.com wrote:

Lemme guess... he tossed it into a horizontal trough to quench it. Warpage is caused by lots of things, but forging too close to dimension isn't one of them. The most common cause is a lack of dimensional symetry from one side to the other. Long blades will pull off to the side with the most metal. I make swords for a living. I've had my share of warped ones, but none so bad that they couldn't be salvaged. Forge to shape, file to dimension, then heat treat. Do leave the edge bated until after heat treat, as a sharp edge tends to burn and/or crack during quench. Build a vertical quench tank out of large diameter pipe, six to eight inch structural pipe works nicely. Put a little sand in the bottom to prevent the point banging on the bottom of the tank. Bake the sand before you put it in to remove all the miosture; a half hour at three hundred in the oven will do. A couple of inches is plenty. So much for the tank. Fill with a suitable quench oil, leaving a few inches of free space at the top for expansion. Don't want the tank to overflow as the oil heats up.

Heat the blade to a bright cherry red (1575 to 1600 F) and insert point first into the oil. The oil will flash ignite, but the fire usually goes out when the blade is totally under the surface. The usual safety precautions apply here; gloves, eye protection, leather jacket, plenty of 'jump back' room behind you, the standard stuff when dealing with hot metal and flammable liquids. When the oil stops rolling at the surface, take the blade out and allow to cool to ambient in still air. The blade is now full hard. Clean off the scale with a wire brush, check for straightness, and if it's warped, reheat it to a low orange, (renormalize) allow to cool to black, and file on it until the dimensions are straight. It doesn't take much asymetry to pull off, more than about ten thousandths will start warpage.

Once it comes out of the tank straight, bake it at 375 for two hours and allow to cool to ambient. It's now heat treated. Sharpen the edge with files and/or abrasives and final assemble. Heat treatment does not change the dimension of the blade; if it was X dimension before the quench, it will still be X dimension after, so all the hardware parts you made will still fit.

I cheat; I use machine tools for the shaping of the forged billets, so I have a leg up on keeping the blade symetrical during shaping, but you can get good results with hand tools if you're patient. A good sword has a service life measured in centuries with care, so take your time. Spend a few bucks on good measuring tools, you'll be glad you did. It's not that hard, but like all things, it takes work and lots of patience to get a masterpiece. It's that last thousandth of an inch that matters the most. The closer you get to it, the longer you need to take getting there. Got more questions? I'm here all the time.

Charly

I've read in the $50 dollar knife shop that you can forge down so far that the only stock removal is sharpening the blade.

Stock removal can only go so far, what makes the difference that allows you to forge completely to shape?

I just can't see this, I'm going to have a lot of fun experimenting with small knives. How thick is the edge when you consider it done?

matthew ohio

If the blade was made out of a leaf spring he should have stress relieved the steel before forging it into a blade i.e. forging the curve in the opposite direction and or normalizing (heating above the critical temp for a long time and cooling slowly) in a heat treat furnace if available Maybe he was just showing off! (what I dont know?) Snewt

Well there's leaf spring and there's spring steel.

I buy lengths of spring steel and get about 5 standard sword blades and an odd one out of it.

I've never used a leaf springs, as I don't know what it's been through, and there is a lot of bad press about using old leaf springs.

If he was just showing off he deserves a kick in the nut sack >:-(

Regards Charles

snewt wrote:

Well, if you don't mind hammer marks in the finished piece, you can forge to final shape. I have yet to see anyone that can forge to finished dimension without a big mother press and die set. You can get close, but finished dimension? There's always going to be finishing stock removal to get everything to fit, even if it's only a few thousandths of removal.

Can't see what? Pronoun alert! In fifteen plus years, I have yet to measure a dimension change of more than a half thousandth (0.0005") between the before and after HT on a part. For swords, that's 'close enough' to no change to be no change. This isn't parts for the Shuttle here. As for the edge, I usually leave it between 0.050" and 0.065" until after HT. This gives me enough meat at the edge to withstand the contraction forces and protects the actual 'edge' from pitting, oxidation, and decarburization during the rise to temp. After sharpening, it'll pop hair off my forearm, so that's sharp enough. I figure it gets down into the micron range for final edge radius, but I don't put it under a scanning electron microscope to find out. I go down to 2000 grit carbide paper for the final pass on the edge, which is what's available locally. (I get 2000 grit paper at the auto body supplier. The grit is on the side that doesn't have printing.)

Charly in Ok

re:old leaf springs

Old leaf springs have microfractures in them from all those years of being flexed over billions of potholes, and no amount of heat precesses or forging will remove them. Steel is cheap, why risk a catastrophic failure if you don't have to? OLS is good for machetes, get new stock for blades that matter.

Charly

Hi Ken. Thank you for the informative reply. I checked the swordforum link and it is very useful. I must have missed it when I was searching swordforum. Especially interesting was the paper on HEARTS, the computer simulation of quenching induced deformation.

I am glad to see that it is possible to salvage the blade. The smith took quite a while to forge these. I visited him a few weeks ago, and he was working on one. My hands are full enough with all the other blacksmithing challenges that I am working on now. Currently it is learning how to forge sections that have been forge welded (keep 'em hot).

differently.http://forums.swordforum.com/showthread.php?p=877532has a discussion

Hi snewt. The smith told me that he made it out of a piece of new steel; 1070 as I recall.

Eric

messagenews: snipped-for-privacy@h3g2000cwc.googlegroups.com...

Hi Charly. Thanks for the reply. The smith was using brine in a vertical tube. He stood on a step stool, so that the blade would go in straight. The quench medium was brine, since he said that he used oil the week before and the blade did not harden.

The tips about regrinding are very helpful. The smith did not mention this at all. He is a professional, who mostly does historical reproduction work. He also teaches for an hourly fee, and three of his students were there. I think that all of them are interested in swords.

Eric

The master smiths at Sheffield in England, would hammer a finished blade that only needed polishing. Don't know anyone that does it this way these days.

Regards Charles

What kind of metal is he using? Even air cooled steel can be quenched in oil.

Okay no one has asked this yet... does he have a website. Is he making true replica dark age swords? Could explain a lot.

Regards Charles

Brine, eh? Must be using 1095 or some other plain carbon alloy for his stock. Most high alloy steels don't like brine, 5160 would tear itself apart in brine. Most likely, his blade was not symetrical when he put it in, or it wasn't evenly heated. I can't figure out why it wouldn't harden in oil; I get good results with plain carbon in oil all the time. Go figurre. It's perfectly understandable why the blade broke, brine would leave it in the high 60s to low 70s Rockwell C, and brittle as cut crystal. Tell his students to drop around here, I teach for free. I love to talk shop.

Charly

1070... geez and he's still getting warping, he must be grinding the sh*t out of the blades.

Some stats about this metal:

1070 is a plain carbon (non-alloy) steel

Carbon: 0.65 to 0.75 Manganese: 0.60 to 0.90 Wear resistance: medium Toughness: high to medium, depending upon carbon content Red hardness: very low Distortion in heat treating: very low Forging: Start at 1,750 to 1,850 F Austenite forging: yes Hardening: 1.450 to 1,550 F Quench: Oil Tempering: 300 to 500 F Rc hardness: 62 to 55, depending upon carbon content.

I suspect he's using a higher carbon content steel and he definitely shouldn't be quenching in brine.

snipped-for-privacy@gmail.com wrote:

I'd guess it didn't harden in oil because the oil was cold. I've had a couple of knife blades not harden or not reach maximum hardness when the oil was only marginally warm.

Whatever the cause it sounds like he shouldn't be teaching and probably he shouldn't be selling his wares.

ron

Hi Ron,

You know I've never had to heat my oil, but I mainly use 5160 or file steel (whatever the hell they used in files 80 years ago). 5160 for swords, although I'm getting ready to do a damascus core with spring and mild steel. Not sure how my H&T guys will handle this, but we'll see how it goes.

Mind you it's never particularly cold here, so I've never really had a problem with the smaller blades.

I don't H&T the swords I make, so the professional H&T guys may indeed heat the oil, I'll have to ask next time I'm there with a batch.

If I was learning from him and later I showed you a bent blade after hardening, and proceeded to snap it I would expect you to kick me in the janglies ;-)

It's funny but many moons ago, when combat ready swords were in their infancy in Oz (yes we are talking more than a 1/4 of a century ago). We had two definite styles of swords those that would spring, and those that would bend, and had to be straightened under foot after combat.

Neither of these would snap under normal conditions, and when a sword dies in combat it's a woeful sound as screams it's death knell. Actually sounds a lot like dropping a lot of loose flat bar... absolutely awful when you recognise it :-(

I been trying to figure out how to use the dimensionally accurate DA swords, common grip size 6-8 cm, without loosing a finger, or getting a cramp. * Note: DA people were the same dimensions as us including hand size... madness.

Regards Charles

r payne wrote:

Yo Charles, did you ever think that maybe the grip length is so short because the swords were made for children? Iron is very recyclable, and we have had a lot of wars since the Ye Olden Dayes. There has been speculation that people weren't shorter back then, but that all the gear got recycled unless it had some historic significance that kept it out of the melting pot. That would tend to sort out all but the 'unusable' gear which survived to modern times. Just a thought, but there might be a kernel of truth in it.

Charly