I don't see any reason to use something that difficult to form, I mean out of such a large chunk.
I don't know what the carbon content is of railroad rail, but it would be easy to find out. If the carbon is not high enough the blade won't harden enough. Then you did all that work for nothing.
My preference would be to make a few blades out of a truck leaf spring, easy to obtain from any truck shop. Cut to shape with a torch, forge if you wish, and heat treat. Heat treat when you have nothing less of your blade than 1/8" thick for a start.
Heat to cherry red, Check for straightness, reheat again to cherry red if needed and quench in something like old motor oil.
Water would leave cracks in mine.
Then clean up and temper in a household oven, as I recall 350degrees or so for an hour.
The blade if polished bright before you temper will turn straw yellow in color and after cool will just barely be cut with a new good file, like a nickolsen or simmonds.
Now you can install a handle and work a finish edge on it.
Randal Knives of Forida,World famous, used to have instructions about like this.
Good luck.
We did this in the 1970's in our high school shop class. Everybody did it.
Today we would be banned for life.