Hardening and Quenching

[ironmonger]

I have no clue about steels and hardening so please excuse my ignorance but...........is there anything to do with the quenching process that would leave the center material less brittle so as to help with a sword not breaking or shattering?

Not so much the process but the material being quenched, Metals like 4140 are engineered to provide deep or through hardening. Strait carbon steels not so much. In theory if you can drop the internal temperature fast enough any carbon steel will harden all the way through. It's just that with thicker cross sections that is pretty hard to do. The differential hardening and quenching results in a lot of internal stress and warping, as seen on the show.

I'm not a metallurgist, but I am a curious blacksmith. One of the best knife makers that I know, Howard Clark, developed into quite a jackleg metallurgist by asking questions that did not have obvious answers.

See paragraph 4
http://arscives.com/mastersofire/8hc.htm

Howard held a workshop at his place in the mid 90's. Aside from the fascinating demonstration of the pattern welded steel that he put on, he also demonstrated his heat treating method that was adapted from industry for use in this patten welded steel business. The salt bath process he used is not well suited to hardening and tempering in the traditional blacksmith method using residual heat to temper the hardened metal.

By heating in a molten salt bath you gain a number of advantages. You are able to control the maximum temperature quite easily. You also are heating in a medium that has a vastly higher specific heat (layman's term possibly) that heats the meal to the hardening temperature very rapidly. The blade was then removed from the high temperature salt bath (1500° or so depending on the steel )and inserted into a low temperature salt bath (perhaps 500° )

After the metal normalizes it is subjected to the same process a number of times. This refines the grain structure but maintains the Rockwell condition. An added benefit is that the metal is coated with a film of salts when it is removed from the baths that prevents oxygen from reacting with the metal.

(further reading about Howard:
http://www.mvforge.com/
http://www.knifepurveyor.com/howard_...nife_3859.aspx
https://www.facebook.com/Morgan-Vall...7129980183355/
one of my favorite knifemakers... lotsa stories.
He dropped out of the knife biz and moved to the Japanese sword world)

As regards the Forged in Fire show (besides the name... you heat in fire and forge on an anvil) and the $10,000 prize, you have to ask your self what the losers are being paid. I know one of the contestants. He had to give up a considerable amount of time to participate in the show. Regardless of outcome, which is a crapshoot given the time frame they have, what professional would give up 2 or 3 weeks of productive shop time just to be on a show. The fella I know gets very serious money for his work and did not make it past the first round.

[TMo]

The slave quenching thing is a wives tale, perpetuated by bad movies. The closest thing there's any historical reference to is the use of cadavers to test a blades ability to chop through flesh and bone. The cadavers of slaves and criminals were used for such, as otherwise it would have been frowned upon as abuse of the dead. There are some legends about Japanese warlords testing new swords by decapitating criminals or captured enemies. Those legends may or may not be true, but no-where is there any reference to quenching a forged blade in a living (or dead) body.

The single heat draw method of hardening and tempering is functional with thin cross sections of material, but isn't terribly consistent as far as results are concerned. Back when I was making knives, I got access to a rockwell tester, and immediately purchased a HT oven, as I discovered that with the interrupted quench method, I was lucky to be within 3 points on the C-scale, with the HT oven, I could hold +/- 1 point from a target easily.

One of the benefits of the interrupted quench is the appearance of a visible 'quench line' in some materials. This is essentially a visible line that results from the change in grain structure with clear boundary formed by the quenching of the edge first, followed by the whole blade after a moment (to draw most of the heat out of the spine without fully quenching) and then a quick edge polish to watch for the residual heat from the spine to bring the edge to the desired temper, and fully quenching once that temper color is seen.

The visible quench line is reminiscent of the Hamon line seen in traditional japanese blades, and as a result is often desirable for collectors. Even after receiving my HT oven and having more consistent results, I would sometimes still use the interrupted quench method for hardening and tempering, because some buyers preferred the visual appeal of the quench line over the technical superiority of the more consistent HT provided by the oven. In the field, the difference was never noticeable in my personal knives, and I never had a complaint about the usability of knives HT'd with either method.

I would accentuate the quench line by polishing (not buffing) the whole blade to a high polish (4,000 grit+) and then etching with a weak acid, grocery store lemon juice would suffice at that level of polish. The hardened edge would become frosted, and the spine would retain the high polish, and the boundary section would take on a nearly lace-like appearance under magnification. The weak acid etch was to bring the line more clearly into view, but looking closely, the three distinct zones where quite visible in the blade to someone looking for it, once a certain level of polish was achieved (usually around 1,000 grit) even without any etch.

[epicfail48]

I have no clue about steels and hardening so please excuse my ignorance but...........is there anything to do with the quenching process that would leave the center material less brittle so as to help with a sword not breaking or shattering?

Yes and no. Japanese swords use a process of applying clay before heat treatment to insulate the spine of the blade from the effects of the quench, so the edge would hardened but the spine wouldn't. To my knowledge it's not a process that hot used much outside of Japan, or on double edged blades

You can get a similar effect on a blade by using an interrupted blade, but it's a lot more random as to if it works or not. A much simpler option if you want to avoid clay is harden the whole blade, then insulate the edge while tempering the spine to blue. Keeping the edge submerged in water while heating the spine with a blowtorch worked pretty well. You won't get the beautiful hamon line, but you will get a blade with a hard edge but a nice springy spine

[HWooldridge]

If you understand the basic physical mechanics, you can also do some interesting things in the home hobby shop...

Another old fable is that thin Persian blades were sometimes "quenched" in a blast of cold air through an arrow slit or narrow window. I read that and thought, 'Hmmm, maybe I can do that with compressed air?' Sure enough, you can make a serviceable tool/blade by starting with high carbon such as 1095, heat it to non-magnetic state and blowing air over the edge. The thin edge cools very quickly and the spine more slowly - so you essentially get a differential quench. Works pretty well on small blades and stuff like scribes or screwdrivers.

I have also made very serviceable springs using plain old A36 steel. In this case, the spring is again heated to non-magnetic but then quenched in a brine solution with a little bit of Dawn soap to act as a surfactant. The steel is quenched but not tempered so whatever martensite is present is not stress relieved. This only works on steels above 20-30 points of carbon but I have made non-critical use springs using this method and they will take about 10-20% memory set then keep their form from that point forward. Works well on both flat springs and coils.

[Juergenwt]

Old trick I learned a long time ago from my master mechanic and still use today. I keep a supply of thin spring steel (1095 etc. dead soft). Anywhere from 0.005 to 0.015 thick. From this I cut and form any type of spring needed like a spring for a snap cover or a spring for holding a part in a fixture etc. etc.. Form spring using the dead soft material until you have exactly the right form.
Heat treat as follows: Usually with a propane torch cherry red. Quench in oil. Do not bent at this time. Spring is glass hard and will break. Now hang the spring by a wire hook (paper clip etc)
and use a SOFT flame - no blue flame, just a yellow soft flame,
from a torch to slowly heat the spring until the remaining oil on the spring starts burning. Let the oil burn off by itself. Dip in oil for a short time (seconds), heat with SOFT flame again until oil burns, dip, heat, dip, heat, four to five times. last dip keep in oil to cool off. You will now have a good looking black spring that will jump back no matter how often you bent it.
Takes very little effort and you will love the result.

[grzdomagala]

Link to Wakter Sorrells "fail" video: https://youtu.be/1zu3BZEOxg4
Find it quite interesting since i wasn't expecting the blade to literally crack...


Wysłane z mojego GT-N7100 przy użyciu Tapatalka

[epicfail48]

Link to Wakter Sorrells "fail" video: https://youtu.be/1zu3BZEOxg4
Find it quite interesting since i wasn't expecting the blade to literally crack...


Wysłane z mojego GT-N7100 przy użyciu Tapatalka

Believe me, neither was he...

It can be bloody random on whether or not a blade cracks. You can do all you want to mitigate the risk, but it never fails that last blade you want to crack will rip itself in freaking half. If you ever wanna see a bladesmith cry/fly into a swearing rage, ask his opinion on water quenches

[JoeLee]

Paul,

The traditional (Roman, I believe) way to harden a long blade is to get it red hot, and then thrust it into the thigh muscle of a slave. This both quenches and nitrides the blade. Everyone but the slave find this to be a very satisfying method.

In the absence of a handy slave, quenching is done in oil or water. Water has a much higher specific heat capacity than oil, so gives a more rapid quench.

The way my metalwork teacher taught me to harden things like chisels was to quench them for a couple of seconds in water, and then quickly polish up a bit of the cutting tip on emery cloth. Heat still inside the chisel reheats the just-quenched surface. When it reaches the right colour (dark straw for a chisel), plunge it back into the water until it goes cold. This hardens and tempers the chisel in one go.

If the knife being hardened has sufficient mass, briefly quenching and then leaving it will probably completely draw the temper, leaving it soft again.

Ian

I don't think they did that. The slave wold be worthless after that, and it would be a total waste of a good slave.

JL....................

[Toolguy]

The Mongolians ( supposedly) quenched their blades by running them through the midsection of enemy POWs. They were going to kill them anyway.

[HWooldridge]

The "run it through a body (any body)" story is a myth. First of all, it would be tough to get consistent results with this method - and blades being heat treated have no hilts/handles so how does one wield the blade? Plus the blade would almost certainly bend as it passes through the torso - after all, it would be around 1500 degrees F or thereabouts.

Still likely a myth but more plausible would be to slaughter enough people for their blood to fill a quench tub then use that for a quench medium - but water would still be more practical.

[danlb]

Since we are being gross...

One of the old tales is that viking blade smiths would quench in the blood of a goat (or other animal) sacrificed to the gods.

One of the reasons that we don't really know exactly how they were made is that sword / knife making was most usually a trade secret of a guild. They did not write down their processes or even their materials. Masters taught apprentices.

Dan

[boslab]

There are absolutely loads of weird and wonderful actual things used in steel, a favourite was "bulls piss", a toung in cheek reference to bull****, as no one would beleive it, we used to add urea aka piss to the melt, in crystallised form of course, a quick cheap way to add nitrogen, well a hell of a lot cheaper than nitrided ferro manganese, low or high carbon depending on what your trying to make, the stink was horrendous, nearly as bad as a sulphur charge. Metallurgy is a complex thing, especially when you get into high strength low alloy and super strength, I reckon there was a new alloy appearing on a weekly basis, (HSLA does some interesting hardening even with carbons of .15, the manganese, chrome etc takes over, (carbon equivalent or CEV), sometimes I wished I could plunge the sample up the bosses arse, hot of course,
Air quench is a common process in steel, Ali, copper, well in fact all metals, sometimes replaced with inert gas quench.
My dad used a handful of lime in the quench bath, stopped it going scummy and such, seemed to help.
Salt or brine quench is as severe as you can get short of going cryogenic.
I remember seeing a Japanese family sword at the V&A in London, the inscription said it cleaved (shoulder to groin) 2 men without damage or bending, apparently prison wasn't a punishment then, it was death, death or death, you got a choice, the curator was a very interesting guy, he described some real horrors, live prisoners were preferred.
Feudal Japan was a scary place to be sure, I would not like to be a sword maker who made a defective weapon, I should imagine you would end up with it in your digestive system,
Mark

[J Tiers]

I have no clue about steels and hardening so please excuse my ignorance but...........is there anything to do with the quenching process that would leave the center material less brittle so as to help with a sword not breaking or shattering?

Kinda.

It has to do with the speed of cooling the metal. You need to quench fast to freeze the metal in the state of maximum hardness. So the surface always cools the fastest, because it is in contact with the quench. Inside will be softer because it is not quenched as fast.... the heat has to pass through all the other metal to get out.

Then also, water is one of the fastest, particularly if it has something in it to raise the boiling temp so less steam is formed to act as a =n insulator. Oil is slower to drw off heat, so it quenches to a lower hardness in the same steel, but may give a deeper effect.

Different steels need different quench. Some need water quench. Some need only oil, and may actually crack if water quenched. Some need only air cooling, and really may crack if water or oil quenched.

The water quench steel (W1 etc) is hard on the outside, but thicker sections may be a lot softer on the inside. Oil quench steel (O1 etc) may harden deeper, but still will be softer on the inside.

Old trick I learned a long time ago from my master mechanic and still use today. I keep a supply of thin spring steel (1095 etc. dead soft). Anywhere from 0.005 to 0.015 thick. From this I cut and form any type of spring needed like a spring for a snap cover or a spring for holding a part in a fixture etc. etc.. Form spring using the dead soft material until you have exactly the right form.
Heat treat as follows: Usually with a propane torch cherry red. Quench in oil. Do not bent at this time. Spring is glass hard and will break. Now hang the spring by a wire hook (paper clip etc)
and use a SOFT flame - no blue flame, just a yellow soft flame,
from a torch to slowly heat the spring until the remaining oil on the spring starts burning. Let the oil burn off by itself. Dip in oil for a short time (seconds), heat with SOFT flame again until oil burns, dip, heat, dip, heat, four to five times. last dip keep in oil to cool off. You will now have a good looking black spring that will jump back no matter how often you bent it.
Takes very little effort and you will love the result.

I found that with generally flat sprngs, it works better and more evenly to lay them on a flat steel plate that you polish first. Watch the plate, and when it gets just a hair past what you want for the spring as far as color, cool the spring down.

If I did not do that, I had trouble with some places not getting tempered as much as others, and the springs might break.

That glass hard deal is no joke. I have accidentally DROPPED a lightweight spring on the concrete before tempering, and had it break in 3 pieces. Just the spring, nothing else dropped, and that was enough to break it Maybe 1/16" wire or so, and about 4" long in a V shape.

And I find that a lot of shapes need a couple annealings before you can finish a sharp bend. bend some, anneal, bend more, etc. Tat was for some Z-shaped springs, they'd break if bent in one go, even from dead soft.

[JoeLee]

The Japs used pine needles to add carbon to the steel when they made swords.

JL................