Friday, March 20, 2015

Antique objects / Bloom iron ?

On 19/03/15 12:54 AM, Jeff  wrote:

I see that barrel hoops are fairly flexible, but the iron from the bloom that *I* have ... seems to be fairly rigid even in the very thin bits. Is this a steel-vs-bloom-vs-cast-iron thing, or is there a trick to making bloomery iron flex?
Remember that you may certainly be looking at objects made of Bessemer mild steel (possible for anything after 1855) in those 'antique' barrel hoops. Most likely you would be seeing something pretty much like (or actually) a modern mild steel.

Individual iron blooms can vary considerably in actual carbon content, thus potential hardness / rigidity.
Ore type and particle size, layout of the furnace, operating temperature, size of charges - all can effect the potential results.
If we worked with that granular hematite for your smelting course, that stuff tends to the mid carbon ranges for example.
Even a single bloom usually varies across its diameter, typically the top surface having a higher carbon than the base. This difference will often get 'folded in' as the consolidation welding series is undertaken. (And the welding process itself can change the available carbon content.)

Proportion of other trace elements in the ore can also effect the effective hardness / rigidity. Phosphorus for example can certainly make the metal more brittle. This more a problem with natural bog iron ores, some of the rock based types. (One of the advantages of the analog we use here is that we have better control of the elemental content.)

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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