Saturday, December 27, 2008

'Steel' - means what?

Without really intending to, I seem to have touched off a big go round on NORSEFOLK. My normal practise it to keep those general discussion pieces pretty general, as the readers on the list can vary a lot in terms of their experience and background knowledge in any given topic area. As I normally do, I try to send back measured responses, even to private e-mails. These take time, and I hate to just 'loose' the writing to a single recipient.

" I beg to differ about archeaologist being less detailed in description then a blacksmith. While I do not know how to forge a blade, I did have to learn different metals there corriosion rates their scientific names, how to preserve them etc. and that there is a difference in the irons and steels. Perhaps some archaeologist are very general but that is old school, not the program I went through."


You may notice in older publication texts that the term 'bronze' is still often used. In more recent publications, the less accurate term 'copper alloy' is often seen. I suspect this is because, with the VA especially, the actual alloy used for jewellery and cauldrons varies so much in terms of proportions of copper, lead, tin, zinc. At some point I be someone got 'nailed' for using the term bronze, when the object had next to no tin in the mix. And so we all suffer a vague language.

I am not referring (mainly) to primary descriptions, but the language used so often in secondary works. Many are the same authors, so the shift to a less accurate, more general language is not understood (by me).

The term 'steel' is used on objects that are made of metals which have an extremely wide, and quite different physical characters. The loose meaning appears to be 'any iron alloyed with some amount of carbon'. I have not noticed any shift towards a more precise definition (but admittedly, I am not an academic or have access to current journals).
If I end up with a bloom with .5 % carbon - it is not the same as if I took a modern commercial alloy at the same carbon content. Or had used a furnace to make a very high carbon metal, then burned out some of the carbon in a forge to lower it to that .5 %. Or taken wrought iron and baked it with carbon dust to get that .5 %. All of these materials would be given the name 'steel', even though their creation method (and most importantly) their working characteristics are quite different.

Yes - this is a 'thing' that gets under my skin. The more experience I accumulate with actually making metal from dirt, much less the more time I spend producing reproductions and replicas using historic tools and methods, the clearer these distinctions become to me. The more it bugs me that the language used is less than accurate.

All the bloomery created iron alloys have a pronounced and extremely significant grain structure. This fibrous texture, caused by slag inclusions is extremely important when it comes to how you actually forge these metals. It also will effect the application of the object.

An example - a Medieval breast plate is made of a billet of wrought iron, which is hammered to a sheet, then the final shape is baked in burned bone. This results in a 'case hardened' piece of metal. The description reads 'made of steel'. Right off the start, the carbon is not equally distributed through the cross section. Second, the initial wrought iron has a grain, and that grain has a line of weakness. An arrow striking along the grain line is sure to penetrate more easily than one running at 90 degrees to this structure. Inclusion of a surface layer of carbon does not change this. One possible solution would be to layer up two individual pieces of wrought iron, welded to each other so that grains crossed each other. However this greatly complicates the task of preparing that initial metal sheet. You can see that there are many implications : speed of production, skill required, cost, status...

Its almost like the difference between pine and oak.

1 comment:

STAG said...

I too once used a phrase that caused great consternation...I referred to chain as "reactive armour", because it turns (reacts) under the blow rather than resisting it in a static fashion like sheet metal. A true tempest in a tea pot.
Good idea for a post though...grin! Thanks.

May Janus's time of celebration leave you without hangover.


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