Brittle tempering

[NoviceSmith15]

Hey everyone! I have an odd and out of the blue question about tempering, so just humor me for a second. I'm writing a story with a blacksmith protagonist who fails at tempering, so all his products end up brittle. I've heard of this brittleness happening as a result of bad tempering, but I have no clue as to how one does it--and just HOW brittle can the metal get? Thanks!

[Frank Turley]

How brittle can high carbon steel get? The old timers say it gets "Glass hard; dead hard; file hard." You get the hardness by quenching in water or oil at usually a red heat. You have not tempered yet.

 

Glass hard means it will break like glass breaks. Dead hard means it's as hard as it's ever going to get. File hard means that a new file won't cut it; it will just skate on it.

 

Tempering is reheating the metal to a known  temperature below hardening temperature inorder to sacrifice hardness and gain toughness.

 

See my latest post under iforgeiron heading Everything Else. Then, to Choices of metals/materials analogous to fantasy-metals for more explanation.

[Don A]

If you're looking to fail in tempering toward the brittle side, just forget to temper.

 

Like Frank said, I can take a piece of file steel (or any any simple high carbon), heat it to critical and water quench it.

 

If it survives the quench, it will snap/crack/shatter at the least attempt at flexing or even a light blow.

 

Sometimes it will crack just sitting there unless you draw some temper right off.

[781]

It also matters how thin it is on how easily it breaks a 1/16" versus 1" but the above posts are right on

[Richard Furrer]

Brittle:

It can destroy itself when quenched...the dreaded "tink" in the water.

It can be so brittle that it will break just sitting in the corner.

It can be so brittle that it will break when dropped on the floor.

It can be so brittle that it snaps on the swing to cutting something.

it can be so brittle that if it were a blade the tip could fly off when the edge encounters something to cut.

 

An improperly tempered sword can be snapped with bear hands....or even bare hands.

 

An improperly tempered axe can leave its cutting edge in the tree you just tried to fall.

 

Ric

[Frosty]

The problems with bad heat treating have been well covered so I'd like to sidetrack a bit. What's the storyline for the protagonist always producing poorly heat treated items? To do so a smith would either have to have outright BAD training be an imbicile or perhaps under a curse.

 

Seriously, always producing over hard work would require s/he only do half the heat treating process. Like say making a cake and NOT baking it after mixing it. Incredibly unlikely story line, even a nearly completely untrained, inexperienced smith would pick up on tempering first time he saw it done.

 

Frosty the Lucky.

[SoCal Dave]

What about a blacksmith that became colorblind as he got older or was always colorblind?  S/He might not see the true colors in tempering the metal and go to far or not enough in the process.   

[Rich Hale]

Dave, some folks with challenges over come them,,,,most of the folks I know have anyway...I 'spect that smith would know about files and determining hardness.

[Frosty]

.

What about a blacksmith that became colorblind as he got older or was always colorblind?  S/He might not see the true colors in tempering the metal and go to far or not enough in the process.   

 

That's plausible if for some reason he didn't retire or turn tempering over to an apprentice.

 

Frosty the Lucky.

[Frank Turley]

One of my people was color blind and became a working smith. He not only had a "mental alarm" set, but he could tell the heats by how the iron felt under the hammer blow.

[Frosty]

That would be the same thing I do when forging in sunlight, I can't judge forging temps in too bright light. Temper colors are another matter though. Heck, they'd be easier to judge without color, tone and intensity would be enough with practice.

Hmmmmmm.

 

Frosty the Lucky.

[Steve Sells]

What about a blacksmith that became colorblind as he got older or was always colorblind?  S/He might not see the true colors in tempering the metal and go to far or not enough in the process.   

I have a friend that is a comercial Photographer out west that is totally colorblind.  He can not tell the difference between the B/W film prints or a color print,  but even grey scale has variances that can be used for tempering,  He just doesnt use the terms yellow/brown/blue.  Same as foriegn languages, just because one does not understand that language does not mean that thay can not comunicate :)

[thingmaker3]

Another possibility might be our fictional smith getting hold of some unexpectedly high alloy steel. Never know what might be in the ore under the next hill! Folk were direct-smelting medium carbon nickel steel from ore in the late bronze age. So if our hero got some stuff smelted from the right (or wrong) carbonates it could make a difference in tempering requirements. (Look up "cobalt siderite.") Might conceivably even be akin to temper embrittlement.

[NoviceSmith15]

Can one forge what he is needing to make, cool it off and leave the tempering process for later, particularly if it is a huge job that needs an entire second day to do?

[Maillemaker]

it's possible, but risky.  Fully hardened steel can crack because of internal stress.  More than one smith as come back to the forge/workshop to find brand new broken blades.

[ThomasPowers]

Cooling from a red heat in air is called normalizing, except for air hardening steels---a modern high alloy category---normalizing makes for a tough steel not extremely hard or brittle.  Cooling slowly usually by being stuck into a heap of wood ash is annealing and makes even high carbon steels soft and easy to work cold, (filing, drilling, etc)  Only by quenching of a steel containing more than 30 points carbon (100 points = 1% C) do you make things HARD and Brittle with the higher the carbon level the harder/more brittle it gets (that can then be moderated by drawing temper on it to trade some of the hardness for toughness)

 

Now steels can be accidentally quenched, a high carbon steel placed in a cold post vise or on a cold metal surface can be "contact quenched" by the cold metal; or of course a piece accidentally flipping out of the tongs and landing in a puddle of water or quench tank---I try not to have any water in my forge when forging blades.

 

In earlier times when what makes iron into steel was not well understood items were often un quenched as higher carbon allows are a bit harder and tougher than low carbon with no extra heat treat.  (However they are much superior in hardness when heat treated!)

 

The legends of taking a broken blade and reforging it into a superior sword I believe were based on the fact that a blade probably broke though uneven carbon content or excessive carbon content for the procedures they used.  Forge welding the pieces back into a billet will both even out the carbon content more and drop it a bit.  (Japanese billets often start at nearly 2% C and through repeated folding and welding often end up at 0.5% C)

 

I claim that the legendary swords were ones where "everything came together perfectly"  The right forging procedures, the perfect heat treatment, the right design---everything was correct for the unknown alloys that the smith used. Famous forgers:  Regin, Waylend, etc; were smiths who paid attention and so "luck" happened m,ore often for them and their blades were a great step BETTER than a run of the mill blade.

 

May I commend to your attention "The Burnished Blade" a fairly old story now that has excellent smithing described in it---even that the smith would be using charcoal and not coal in an medieval setting and has an accidental casehardening described in it.

 

Thomas who will be bringing a Y1K forge burning charcoal to the Albuquerque RenFair Saturday (given no burn ban)

[NoviceSmith15]

I haven't learned how to temper things yet, so all of my finished pieces were quenched in water usually around black heat, at which point I had been banging on it enough to cool it down some. However, none of my pieces seem brittle--certainly not enough to break in water or from just sitting around. The only one I ever was able to break with my hands was one little bar that had rusted pretty bad. That did break, after a nice little jerk, but it still didn't exactly seem brittle.

 

The reason I ask this random question about tempering is because my character is forging prison cell bars (It's set in the medieval time period). He forges the bars one day, and plans to temper them the next day, because it's such a huge job, but before he arrives home from taking a breather, the buyer has already loaded the cart full of bars up and left with them. The buyer came a day early, so the protagonist wasn't expecting him to take the bars yet. He doesn't tell anyone, though, hoping not to get in trouble. Later he is outlawed and eventually imprisoned in one of the many new cells made with his bars. The bars being brittle, rusty and hard, he is able to break enough of them to escape.

[ThomasPowers]

Sorry prison bars in medieval times are low carbon wrought iron; you could quench them in ice water and it would NOT make them a bit harder!

 

His home would be back or above the forge; no way a buyer could load them up without his knowing---remember a smithy had a bunch of people and their families associated with it---have a single person in it is as likely as going to a cardiac operating room today and having only the surgeon there.

 

Medieval ironworking is my area of research interest; if you want brittle bars you could have someone pulling a fast one and substituting bars imported of a low grade wrought iron from a country that's know for brittle iron.  (Books like "Mechanics Exercises" by Moxon list typical irons availability and their properties and what they were good for---it's not medieval being published in 1703 but written in the last half of the 1600's)

 

If you are writing a medieval based story you need to do some more research, (I like the Burnished Blade as it does have quite accurate smithing information in it; I strongly suggest you read it, ILL it from a local library or get a cheap copy at abebooks.com)

[Frosty]

Rather than having an unscrupulous customer stealing the bars from you're smithy, FAR too unlikely as Thomas says, have a freighter switch them enroute for low quality bars so he can sell the good ones.

 

Now, rather than brittle because they're untempered bars, the cells have "muck bar" bars full of impurities and excessive silicate inclusions. While not necessarily brittle they would be far weaker than the specially ordered weapon grade steel bars the king or whoever it was ordered.

 

Muck bar is first run wrought iron, only forged once and has a lot more inclusions than twice wrought or triple wrought. Each forging increases the quality by homogenizing the iron and driving out the slag inclusions.

A few thoughts.

 

Frosty the Lucky.

[thingmaker3]

I haven't learned how to temper things yet, so all of my finished pieces were quenched in water usually around black heat, at which point I had been banging on it enough to cool it down some. However, none of my pieces seem brittle--certainly not enough to break in water or from just sitting around. The only one I ever was able to break with my hands was one little bar that had rusted pretty bad. That did break, after a nice little jerk, but it still didn't exactly seem brittle.

Try hardening from a much higher temperature. Black won't do it. If you are using a low alloy hypoeutectoid steel, it will become nonmagnetic about 50F below the critical temperature. Go read the stickies to learn why "critical" is critical. http://www.iforgeiron.com/topic/25247-heat-treat-information/

[NoviceSmith15]

Well, I didn't mean that the bars got STOLEN--just that the buyer was taking them off. The protagonist is possibly, and admittedly, one of the worst blacksmiths in all of England, and is apprenticed to one of the best. His master's family does live in the house by the smithy, but they are unimportant characters. The master blacksmith is there to help the buyers load the order up in a cart. No stealing involved--just a misunderstanding, because the buyer came a day or two earlier than they should have. The protagonist wasn't able to fix his mistake in time, and considering the extravagent punishment for any kind of sleight towards the buyer (The city's earl), the protagonist decides it's best to keep quiet about it. 

[thingmaker3]

You might want to look into the master-apprentice relationship. No master would ever let this kind of "misunderstanding" occur.

 

Also, if the bars are so bad, why didn't they bust when being loaded?

[Frosty]

Sorry it's too implausible a story line to work. A MASTER smith would be the one selling the work, not an apprentice, even if it was the apprentice's job. He'd be a right poor "master" if he didn't notice unfinished work and loaded it himself. Being as the customer is the local Earl, there's no chance he'd give THAT commission to the apprentice in the first place, too much rides on it being near perfect.

 

The master is mmore likely to be the one imprissoned in this case as well. More likely indentured iin the Earl's smithy rather than thrown in the dungeon. A master blacksmith is just too valuable a person to lock away where his skills go to waste.

 

Your basic premise will work okay but you need to tweek the supporting story line to support it plausibly.

 

Frosty The Lucky.

[NoviceSmith15]

What if the protagonist simply didn't have anything on hand to coat his finished products with rust-resistant qualities (Beeswax)? Then (Considering the damp and leaky conditions of some medieval dungeons) they would rust bad and quick. By the time the protagonist got imprisoned, they would be brittle enough to be split and broken with a nice, strong jerk. Does that sound plausible?

[Maillemaker]

Then how does he become imprisoned?