Columbia subject headings:
Harvard subject headings:
Iron industry and trade--Technological innovations.
Iron--Metallurgy--Technological innovations.
Steel industry and trade--Technological innovations.
Steel--Metallurgy--Technological innovations.
Princeton subject headings:
Iron industry and trade--Technological innovations.
Iron--Metallurgy--Technological innovations.
Steel industry and trade--Technological innovations.
Steel--Metallurgy--Technological innovations.