The Figures For 1863-1866 Are Estimates; See The 1894 Report, P. 10. Source: American Iron And Steel Institute, Annual Statistical Report, 1894; 1911, Part Ii, P. 61; 1929, P. 25.
This NBER data series a01208 appears on the NBER website in Chapter 1 at http://www.nber.org/databases/macrohistory/contents/chapter01.html.
NBER Indicator: a01208
Release: NBER Macrohistory Database
National Bureau of Economic Research, Steel Ingots and Castings Production for United States [A01208USA576NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/A01208USA576NNBR/, July 4, 2015.