Old catalogs published by United States Steel and Bethlehem Steel used to have all the specifications on railroad tracks, i.e., dimensions, chemical composition, mechanical properties etc. However, I don't know for sure if the new catalogs have that information.
Giovanni S. Crisi
Sao Paulo - Brazil

http://birminghamrail.com/
These people may be able to help with the info you need. I used them for purchasing our crane rails.
John Wright

Hi Chris, I don't know the chemical composition of rail steel, but on some rails that some of the biggest container cranes in the world run back and forth on everyday were welded with 7018M. That was before the Fussion proccess used today. With the Fussion proccess, the ends are square cut with no bevel,with a 1/2" gap. Ceramic molds are set in place and filled, lit with a torch through a hole in the top. The whole proccess to make one weld takes @ 30 min. The welds are X-Ray Quality. I have also used 9018, 11018. depending on what C.W.I was on the job,and what proccedure was on the plans. In any case, rail steel welds with ease, with a little pre heat @250 deg. Once you start the weld don't stop until complete. Try not to get the temp. over 450 deg. during the weld. When complete, wrap the weld with heat blanket. Let cool down slow,@50/70 deg. hr. I've used this proccedure many times and have never had any problems. Have Fun & Happy WELDING