Did the First Iron Blacksmiths Learn to Carburize Iron? Part I: Can Iron be Carburized in a Charcoal-Fired Furnace?

Abstract

There is debate in the literature on whether or not iron can be carburized by simply inserting an iron bar into a charcoal fire. Experiments are presented here in which wrought iron bars have been held in a cylindrical enclosure filled with burning charcoal produced by air flowing up from tuyeres at the bottom with the bottom end of the bars held in the 900°C–1050°C range for 30 min. The bars carburized to a remarkable extent. Martensite case depths on a water-quenched bar were measured ranging from 0.75 mm at the hot bottom end and dropping to 0.02 mm at a distance of 295 mm (11.6 inches) up the bar. The surface of the bar was file hard over this length with measured surface hardnesses in the 60–65 Rc range.