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Jeremy V. Krause




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PostPosted: Fri 21 Jan, 2011 9:08 am    Post subject: Please educate me on these terms         Reply with quote

Given how long I've had this hobby you'd think I would know this but I don't clearly know the difference between shear steel, blister steel, and crucible steel.

Could someone enlighten me about this. I am looking for the "what, when, where, why, and how" of the issue.

I tried wikipedia but didn't get a clear enough handle on this- wikipedia can be like that. . . .
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Timo Nieminen




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PostPosted: Fri 21 Jan, 2011 2:03 pm    Post subject:         Reply with quote

Depending on how you define "crucible steel", blister steel can be a specific type of crucible steel.

A broad definition of crucible steel is that you heat iron and some carbon-contributing material in an enclosed crucible in a furnace.

If you use wrought iron + charcoal (or similar), the carbon will diffuse into the iron. You don't need to melt the iron, but the colder you keep the crucible, the longer it takes. This, non-melting, heating for a week or 2, starting with iron bars in charcoal, produces blister steel.

These blister steel bars aren't very homogeneous, so for practical purposes, one wants to weld, fold, twist, etc., to produce a homogeneous product. This welded and homogenised blister steel is shear steel.

A purist might not want to call blister steel a crucible steel, because the iron bars and charcoal are packed in a big stone pot, rather than a ceramic crucible. It's also much larger.

Less fussy is that crucible steel is sometimes (often? usually?) restricted to processes in which the crucible contents get hot enough to come out in a relatively homogeneous lump (after cooling). Another method of homogenising blister steel, other than welding to make shear steel, was to heat chunks up in a crucible, to melt them this way. This product, crucible steel made from blister steel, was the usual English version of crucible steel. This is slightly funny crucible steel, in that the crucible is fed with a single type of material (as opposed to iron + carbon), and it's removed molten, rather than cooled into a solid chunk in the crucible.

There are two types of classic crucible steel. Iron + charcoal or similar (chunks of wood will do), and iron + cast iron. This last type, iron + cast iron, is the real crucible steel for the strictest of all purists. Low carbon iron, + cast iron at 3-4% carbon, gives a nice high carbon steel when mixed. The usual ratio was about 50/50, which gives carbon contents of about 1-2%, which is high by European standards for use in blades. Carbon content will go down a bit, but the end product is still remarkably high carbon. Thus the reputation of Central Asian/Middle Eastern/Indian blades as hard and sharp, but brittle.

Blister steel and shear steel are well-defined. "Crucible steel" is much fuzzier. "Wootz" is also a fuzzily-defined thing, varying from synonymous with Central Asian or Indian crucible steel, through to following a much narrow recipe/process.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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R D Moore




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PostPosted: Sat 22 Jan, 2011 3:16 pm    Post subject:         Reply with quote

Hey Jeremy
Our own Ric Furrer is an ideal source of information and answers to your questions:
http://doorcountyforgeworks.com/Steel_Making.html
His site has a video of making shear and blister steels I encourage everyone with an interest in seeing. They're well done for these types of presentations (in the smithy and not a studio) and the information is clearly presented. I bet he'd answer an email, too.

"No man is entitled to the blessings of freedom unless he be vigilant in its preservation" ...Gen. Douglas Macarthur
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Jeremy V. Krause




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PostPosted: Sat 22 Jan, 2011 8:10 pm    Post subject:         Reply with quote

Thanks Guys,

So blister steel is a transitional product toward the goal of shear steel?

I had the impression that blister steel and shear steel were different terminal products.
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Timo Nieminen




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PostPosted: Sun 23 Jan, 2011 3:12 pm    Post subject:         Reply with quote

Jeremy V. Krause wrote:
Thanks Guys,

So blister steel is a transitional product toward the goal of shear steel?

I had the impression that blister steel and shear steel were different terminal products.


I know that some blister steel was turned into shear steel. I know that some was turned into (English) crucible steel (mid 1700s and later). AFAIK, most blister steel was converted to shear steel or crucible steel, since it's quite inhomogeneous. Also, "Blister steel is full of fissures and cavities, which render it unfit for forging except for a few rough purposes. It is used for welding to iron for certain parts of machines, for facing hammers and steeling masons' points, etc, but not for edge tools." (Notes on building construction Part 3 Materials, pg 289).

I found some useful/interesting details here:

http://www.topforge.co.uk/Processes.htm

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Jared Smith




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PostPosted: Tue 01 Feb, 2011 2:48 pm    Post subject: Re: Please educate me on these terms         Reply with quote

Jeremy V. Krause wrote:
I don't clearly know the difference between shear steel, blister steel, and crucible steel.

Could someone enlighten me about this. I am looking for the "what, when, where, why, and how" of the issue.

I tried wikipedia but didn't get a clear enough handle on this- wikipedia can be like that. . . .


Jeremy,

Others have already clarified in general what the basic differences are. In case you are interested in the history behind the "shear" term, I will try to explain.

The term "shear" originated from Ambrose Crowley of Newcastle, an 18th century producer that started as a nail maker in the Durham London area, and branched out into a wide range of steel production, and finished steel products targeted towards the navy. He studied the German indirect cake carburizing process that had existed since medieval era, and attempted to duplicate it by cutting blister steel bars and re-heating and welding them using an indirect heat (reverberating) furnace where the blister was segregated from the fuel. This is only a guess, but I suspect that he was trying to imitate the reducing or carburizing aspects of the more successful German producers, and avoid propagating successive layers of blister and slag.. The clean re-heated steel was reforged using water powered hammers. Crowley marketed his steel as "German" steel, and had a stamped emblem of a pair of shears on the bars to indicate that it could be hardened for making tools such as shears. This was recognized as the second highest quality classification of mass produced steel, "shear steel" for about 100 years. However, nothing I have seen indicates that it was suitable for springs, nor indicates that it achieved status equal to the premium "German", "Cologne", or "Swedish" brands of tool grade steel. (These imports and possibly some crucible/ cast iron-blister blends were used to make "coach spring steel", which was the distinguishing term for premium tool grade steel in an English survey of 1858. There was only about 10,000 tons of "coach spring" grade available per year, compared to something like 23,000 tons of shear steel... out of 1.5 million total iron tons per year in England at that time.) Crowley's "German steel" was commonly referred to by others in period literature as "shear steel" due to the stamped logo. (Extensive discussion of the trademark can be found in a law suit near 1833 when an unrelated "Crowley" and Millington marketed a variety of iron types as "Crowley steel" and used markings to indicate different weights.) It is unclear how many grades the original Crowley "shear" brand offered with the shear emblem marking. Some competing brands offered up to 5 grades of quality using variations of reforged blister processes. Successively recarburized after cutting is even thought to have been done during that era. The terms "half shear", "single shear", and "double shear" came into popular use to distinguish bars that were successively cut and re-welded once, twice, or three times. I would guess that these were considered to have successively finer grain, hence better finish polish capability.

Hope that answers the mail on who, what, when, where, and how.

Jared

Absence of evidence is not necessarily evidence of absence!
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Richard Furrer
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Location: Sturgeon Bay, WI
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PostPosted: Mon 21 Mar, 2011 6:54 am    Post subject:         Reply with quote

Jared,
Also:
It is thought the term "shear steel" came to be associated with this material in England in 1760's by William Bertram because a stamp in the shape of a pair of shears was used to mark the bars for sale.
Bertram was German and went to England to find his fortune.

K Barraclough wrote a great set of books on Blister and Crucible steel.

Ric

Ric Furrer
Sturgeon Bay, WI
www.doorcountyforgeworks.com
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