William Siemens set up the Sample Steelworks to develop the Siemens-Martin Open Hearth process in 1865, and his steel was in general industrial use by 1875. I've not been able to find any period composition analysis but very much suspect early Seimens steel was low alloy, low carbon; ?1002-1005 and very likely the steel component of Damascus.

P. Webley & Son began using Siemens steel barrels about 1880 and reported excellent results.
John Henry Walsh, The Modern Sportsman's Gun and Rifle: Including Game and Wildfowl Guns, Sporting and Match Rifles, and Revolvers, Volume 1, 1882
Siemens Steel for Gun Barrels
http://books.google.com/books?id=OLwUAAAAYAAJ&pg=PA445&vq
A 13 bore Siemens barrel did not bulge until 19 1/4 Dram Black Powder with a 1 1/4 oz. ball. Siemens then reported a tensile strength of 55,000 - 60,000. That would be similar to AISI 1010.

By one report pre-WWI Siemens may have been similar to AISI 1021 - 1034 Carbon Steels; The Sampling and Chemical Analysis of Iron and Steel, 1915
Oswald Bauer, Eugen Deiss, William Thomas Hall, p. 88.
http://books.google.com/books?id=03w6AAAAMAAJ&dq

Buturlin cited studies conducted at TOZ (Tula Arms Plant) likely immediately before WWI listing Russian Siemens-Martin tensile strength as 85,300 92,400 psi so it is clear that the composition was modified compared to the original process steel.

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