For painting tracks I use the following procedure:
1- base coat of Model Master Acrylic Gun Metal
2- dry brush Model Master Acrylic Rust to get in the nooks and crannies
3- dry brush Model Master Acrylic Steel to get the highlites
4- burnish the entire track with ground pencil lead (use fingertip, it's the easiest)
5- final weathering with pastel chalks (I do this as the last step on the entire model)
You can do with with Tamiya Acrylics too but you'll have to mix some rust.
Happy Modelling and God Bless
Robert