Well ... this has been interesting. A quick google and Wiki shows me that there are lots of different steels, as Blackbeard says. I guess I expected this, indeed if you google a bit further you can find descriptions of the various grades of spring steel complete with all sorts of data regarding their properties.
But ... there is always a but.... I wonder if we will ever be told which particular steel a particular spring is made from? I did come across a site where you could indeed design your own spring from a particular steel spec/code.
Cheers, Phil