Iron blooms were carbon-rich steel

Eventually, after a few rounds of steel-making for the cutting edge of the axe, we realised that some of the bog ore blooms in fact incorporated large chunks of carbon-rich steel.

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Pieces from two blooms containing steel. Produced at an iron smelting in 2014 at Thy in Denmark. Photo: Vegard Vike, Museum of Cultural History, UiO.

Good hardening properties

These steel blooms may have been produced in bloomeries with a generous supply of air, evenly distributed across the charcoal (Evenstad 1790:433-437). This would give robust combustion with resultant high temperatures, combined with a strongly reducing atmosphere. This can cause the iron to be in a more melted state, and have a higher level of carbon absorption, particularly on the surface and round the edges. At any rate, the steel in these blooms demonstrated particularly good hardening properties, and we ended up using it for the cutting edge of the Axe.

Literature


Film clip – discovered steel in the bloom (1:50 mins)

An iron bloom was wrought into a thin band to make it ready for the transition from iron to hardenable steel inside a carburising pack. However, thanks to an accidental water quenching, we discovered that the metal was already hardenable. We had the edge steel we needed:


Gallery - blooms of steel

Gallery - blooms of steel
By Vegard Vike
Published July 7, 2016 4:05 PM - Last modified May 5, 2021 12:10 PM