Decarbonized steel is "Bessemer process homogenous wrought iron"
I couldn't cut and paste so you'll need to scroll down to p. 46, but lots of good information here
http://www.davistownmuseum.org/PDFs/GlossaryOfFerrousMetallurgyTerms.pdfFrom
Fire-Arms Manufacture 1880 U.S. Department of Interior, Census Office (I suspect this came from PeteM)
"The earliest use of decarbonized steel or gun-barrels is generally credited to the Remingtons, who made steel barrels for North & Savage, of Middletown, Connecticut, and for the Ames Manufacturing company, of Chicopee, Massachusetts, as early as 1846. It is also stated that some time about 1848 Thomas Warner, a the Whitneyville works, incurred so much loss in the skelp-welding of iron barrels that he voluntarily substituted steel drilled barrels in his contract, making them of decarbonized steel, which was believed by him to be a a novel expedient. The use of soft cast-steel was begun at Harper's Ferry about 1849. After 1873, all small-arms barrels turned out at the national armory at Springfield were made of decarbonized steel(a barrel of which will endure twice as heavy a charge as a wrought-iron barrel), Bessemer steel being used until 1878, and afterward Siemens-Martin steel."
